Messier 52 – the NGC 7654 Open Star Cluster

Welcome back to Messier Monday! We continue our tribute to our dear friend, Tammy Plotner, by looking at the open star cluster of Messier 52. Enjoy!

In the 18th century, while searching the night sky for comets, French astronomer Charles Messier kept noting the presence of fixed, diffuse objects in the night sky. In time, he would come to compile a list of approximately 100 of these objects, with the purpose of making sure that astronomers did not mistake them for comets. However, this list – known as the Messier Catalog – would go on to serve a more important function.

One of these objects is Messier 52, an open star cluster that can seen in proximity to the northern constellation Cassiopeia. Located about 5000 light years from Earth, this star cluster is easily spotted in the night sky because of its association with Cassiopeia’s familiar W-shape. It can viewed with binocular and telescopes, and will appears as a hazy, nebulous patch of light.

Description:

Located roughly 5000 light years away, this 35 million year old cluster of stars has around 200 members – one of which is a very peculiar Of star. According to A.K. Pandy (et al), M52 is an interesting cluster in which to study star formation history. As they stated in their 2001 study:

“The colour magnitude diagrams show a large age spread in the ages. Star formation was biased towards relatively higher masses during the early phase of star formation whereas most of the low mass stars of the cluster were formed during the later phase. The star formation seems to have been a gradual process that proceeded sequentially in mass and terminated with the formation of most massive stars.”

The Messier 52 open star cluster. Credit: Wikisky

Indeed, M52 has been very studied for its star structure, including a search for variables. As S.L. Kim (et al), wrote in a 2000 study:

“We have performed a long-term project of CCD photometry of open clusters. Its primary goal is to search for variable stars, in particular short-period (less than a few days) pulsating stars such as Delta Sct, Gamma Dor, and slowly pulsating B-type stars (SPBs). These pulsating stars are recognized as important objects in studying stellar structure and testing evolution theory of intermediate-mass main sequence stars. Thus these clusters are ideal targets to investigate whether Gamma Dor type variability occurs in old open clusters or not.”

And it’s not just the structure they’re looking at – but the time frame in which they formed. As Anil K. Pandey wrote in her 2001 study:

“The distribution of stars in NGC 7654 indicates that the star formation within the cluster is not coeval and has an age spread -50 Myr. We found that star formation took place sequentially in the sense that low mass stars formed first. The star formation history in NGC 7654 supports the conventional picture of star formation in cluster where ‘low mass stars’ form first and star formation continues over a long period of time. The star formation within the cluster terminates with the formation of most massive stars in the cluster.”

History of Observation:

M52 was an original discovery of Charles Messier, captured on the night of September 7th, 1774. As he wrote in his notes at the time:

“Cluster of very small stars, mingled with nebulosity, which can be seen only with an achromatic telescope. It was when he observed the Comet which appeared in this year that M. Messier saw this cluster, which was close to the comet on the 7th of September 1774; it is below the star d Cassiopeiae: that star was used to determine both the cluster of stars and the comet.”

Atlas Image mosaic of Messier 52, as part of the Two Micron All Sky Survey (2MASS). Credit: UMass/UPAC/Caltech/NASA/NSF

Sir William Herschel would also observe M52, but he would keep his notes private. As he wrote on August 29th, 1873:

“All resolved into innumerable small stars without any suspicion of nebulosity. 7 ft., 57. In the sweeper, 30, shews nebulosity, the stars being too obscure to be distinguished with its light tho’ considerable.” and again on December 23, 1805: “Review. Large 10 feet. This is a cluster of pretty condensed stars of different sizes. It is situated in a very rich part of the heavens and can hardly be called insulated, it may only be a very condensed part of the Milky Way which is here much divided and scattered. It is however so far drawn together with some accumulation that it may be called a cluster of the third order.”

Herschel’s son John would also add it to the General Catalog a few years later with less descriptive narrative, but it was Admiral Smyth who described M52’s beauty best when he said:

“An irregular cluster of stars between the head of Cepheus and his daughter’s throne; it lies north-west-by-west of Beta Cassiopeiae, and one third of the way towards Alpha Cephei. This object assumes somewhat of a triangular form, with an orange-tinted 8th-mag star at its vertex, giving it the resemblance of a bird with outspread wings. It is preceded by two stars of 7th and 8th magnitudes, and followed by another of similar brightness; and the field is one of singular beauty under a moderate magnifying power. While these were under examination, one of those bodies called falling stars passed through the outliers. This phenomenon was so unexpected and sudden as to preclude attention to it; but it appeared to be followed by a train of glittering and very minute spangles.”

May it glitter and spangle for you!

The location of Messier 52 in proximity to the constellation Cassiopeia. Credit: IAU and Sky & Telescope magazine (Roger Sinnott & Rick Fienberg)

Locating Messier 52:

In the rich star cluster fields of Cassiopeia, M52 is distinctive for its size and brightness. It’s not hard to find! Begin by identifying the W-shape of Cassiopeia and focus on its two brightest stars – Alpha and Beta. Because this constellation is circumpolar, remembering to look at the side that has the brightest stars or the steepest angle, will help you remember how to find this great open cluster. Now, just draw a mental line between Alpha, the lower star, and Beta, the upper.

Extend that line into space about the same distance and aim your binoculars or finderscope there. In binoculars M52 will show clearly as a beginning to resolve star cloud and a hazy patch in a telescope finderscope. Even the smallest of telescopes can expect resolution from this multi-magnitude beauty and the more aperture you apply, the more stars you will see. M52 is well suited to urban or light polluted skies and stands up well to fairly moonlit conditions and hazy skies.

Object Name: Messier 52
Alternative Designations: M52, NGC 7654
Object Type: Open Galactic Star Cluster
Constellation: Cassiopeia
Right Ascension: 23 : 24.2 (h:m)
Declination: +61 : 35 (deg:m)
Distance: 5.0 (kly)
Visual Brightness: 7.3 (mag)
Apparent Dimension: 13.0 (arc min)

We have written many interesting articles about Messier Objects here at Universe Today. Here’s Tammy Plotner’s Introduction to the Messier ObjectsM1 – The Crab Nebula, and David Dickison’s articles on the 2013 and 2014 Messier Marathons.

Be to sure to check out our complete Messier Catalog. And for more information, check out the SEDS Messier Database.

Sources:

Messier 50 – the NGC 2323 Open Star Cluster

Welcome back to Messier Monday! We continue our tribute to our dear friend, Tammy Plotner, by looking at the open star cluster of Messier 50. Enjoy!

In the 18th century, while searching the night sky for comets, French astronomer Charles Messier kept noting the presence of fixed, diffuse objects in the night sky. In time, he would come to compile a list of approximately 100 of these objects, with the purpose of making sure that astronomers did not mistake them for comets. However, this list – known as the Messier Catalog – would go on to serve a more important function.

One of these objects is the open star cluster known as Messier 50 (aka. NGC 2323). Located at a distance of about 3,200 light-years from Earth, this object sits near the border between the Monoceros and Canis Major constellations. It is described as a ‘heart-shaped’ figure, occupies an area about half the size of the full Moon, and is easy to find because of its proximity to Sirius (the brightest star in the night sky).

Description:

Located about 3,200 light years from our solar system, this stellar gathering could be perhaps as much as 20 light years across, but the central concentration is believed to only span across roughly 10 light years. While that doesn’t seem that large, it’s lit by the candlepower of what could be 200 stars! And picking such a group of stars out of a well-known OB1 association isn’t easy. It requires photometry. As J.J. Claria (et al) remarked in a 1997 study:

“UBV and DDO photoelectric photometry in the field of the open cluster NGC 2323 is presented. The analysis yields 109 probable members; one of them being a red giant, and 3 possible members. The basic cluster parameters are derived. NGC 2323 appears not to be physically connected to the CMa OB1 association.”

Close up of the Messier 50 open star cluster. Credit: Wikisky

In this region of the sky are vast molecular clouds compressing into star forming regions known as OB1 associations. The stars spawned by these vast clouds form into open clusters containing dozens to thousands of members and, over time, disassociate with not only the molecular cloud, but their sibling star clusters as well. Sure, it took 100-120 million years for it to happen, but as the group of stars cut away from the field, each member also aged differently.

By studying open clusters like M50 and its relative M35, we can learn more about the dynamics of star clusters which formed roughly at the same time in the same area. As Jasonjot Kalirai (et al) indicated in their 2003 study:

“The color-magnitude diagrams for the clusters exhibit clear main sequences stretching over 14 mag in the (V, B-V)-plane. Comparing these long main sequences with those of earlier clusters in the survey, as well as with the Hyades, has allowed for accurate distances to be established for each cluster. Analysis of the luminosity and mass functions suggests that, despite their young ages, both clusters are somewhat dynamically relaxed, exhibiting signs of mass segregation. This is especially interesting in the case of NGC 2323, which has an age of only 1.3 times the dynamical relaxation time. The present photometry is also deep enough to detect all of the white dwarfs in both clusters. We discuss some interesting candidates that may be the remnants of quite massive (M>=5Msolar) progenitor stars. The white dwarf cooling age of NGC 2168 is found to be in good agreement with the main-sequence turnoff age. These objects are potentially very important for setting constraints on the white dwarf initial-final mass relationship and the upper mass limit for white dwarf production.”

So, did age or movement produce the colorful display of stars we can observe in M50 – or was it simply the chemical ingredients responsible? According to a 2005 study conducted by Bragaglia and Monica:

“We describe a long-term project aimed at deriving information on the chemical evolution of the Galactic disk from a large sample of open clusters. The main property of this project is that all clusters are analyzed in a homogeneous way to guarantee the robustness of the ranking in age, distance, and metallicity. Special emphasis is devoted to the evolution of the earliest phases of the Galactic disk evolution, for which clusters have superior reliability with respect to other types of evolution indicators. The project is twofold: on one hand we derive the age, distance, and reddening (and indicative metallicity) by interpreting deep and accurate photometric data with stellar evolution models, and on the other hand, we derive the chemical abundances from high-resolution spectroscopy. The importance of quantifying the theoretical uncertainties by deriving the cluster parameters with various sets of stellar models is emphasized. Stellar evolution models assuming overshooting from convective regions appear to better reproduce the photometric properties of the cluster stars. The examined clusters show a clear metallicity dependence on the galactocentric distance and no dependence on age. The tight relation between cluster age and magnitude difference between the main-sequence turnoff and the red clump is confirmed.”

The M50 open cluster. Credit: Ole Nielsen

History of Observation:

While M50 was possibly discovered by G.D. Cassini 1711, it was independently recovered by Charles Messier on the night of April 5th, 1772. In his notes, he wrote of his discovery:

“Cluster of small stars, more or less brilliant, above the right loins of the Unicorn, above the star Theta of the ear of Canis Major, & near a star of 7th magnitude. It was while observing the Comet of 1772 that M. Messier observed this cluster. He has reported it on the chart of that comet, on which its trace has been drawn.”

It would later be observed by William Hershel, but not until his son John cataloged it before anyone began to notice colors in the stars. However, Admiral Smyth did!

“This is an irregularly round and very rich mass, occupying with its numerous outliers more than the field, and composed of stars from the 8th to the 16th magnitudes; and there are certain spots of splendour which indicate minute masses beyond the power of my telescope. The most decided points are, a red star towards the southern verge, and a pretty little equilateral triangle of 10th sizers, just below, or north of it. The double star here noted was carefully estimated under a full knowledge of the vertical and parallel lines of the field of view: this was made triple by H. [John Herschel], whose 2357 of the Fifth Series it is; but he must be mistaken in calling it Struve 748, which is Theta Orionis. It is sufficiently conspicuous as a double star, and though I perceive an infinitesimal point exactly om the vertical of A, I cannot ascertain whether it is H.’s C. This superb object was discovered by Messier in 1771 [actually 1772], and registered “a mass of small stars more or less brilliant.” It is 9 deg north-north-east of Sirius, and rather more than one-third of the distance between that star and Procyon.”

Locating Messier 50:

Because M50 is such a big and bright open star cluster, it’s relatively easy to find with complicated starhop instructions. Actually, the constellation of Monoceros is more difficult! Begin by identifying the brightest star in northern hemisphere skies – Alpha Canis Major – Sirius. Roughly a handspan to the northeast you’ll see another prominent bright star – Alpha Canis Minor – Procyon.

The location of Messier 50 in the Monoceros constellation. Credit: IAU/Sky & Telescope magazine (Roger Sinnott & Rick Fienberg)

 

Between these two lay the faint and indistinguishable constellation of Monoceros, and slightly southwest of the center point is Messier 50. In small binoculars and a telescope finderscope, you’ll quickly spot a compression in the starfield, and may even be able to see it as a slight contrast change with the unaided eye. In larger binoculars and small telescopes, it blooms into a cloud of stars, well resolved against the grainy backdrop of fainter stars.

In large aperture telescopes, even more stars resolve and colors begin to appear. Because of magnitude and the nature of star clusters, Messier 50 makes an outstanding target for high light pollution areas, moonlit nights and even less than perfect sky conditions.

Enjoy your own “colorful” observations of this rich and beautiful star cluster!

And as always, here are the quick facts on this Messier Object to help you get started:

Object Name: Messier 50
Alternative Designations: M50, NGC 2323
Object Type: Open Galactic Star Cluster
Constellation: Monoceros
Right Ascension: 07 : 03.2 (h:m)
Declination: -08 : 20 (deg:m)
Distance: 3.2 (kly)
Visual Brightness: 5.9 (mag)
Apparent Dimension: 16.0 (arc min)

We have written many interesting articles about Messier Objects here at Universe Today. Here’s Tammy Plotner’s Introduction to the Messier ObjectsM1 – The Crab Nebula, and David Dickison’s articles on the 2013 and 2014 Messier Marathons.

Be to sure to check out our complete Messier Catalog. And for more information, check out the SEDS Messier Database.

Sources:

Messier 47 – the NGC 2422 Open Star Cluster

Welcome back to Messier Monday! In our ongoing tribute to the great Tammy Plotner, we take a look at Orion’s Nebula’s “little brother”, the De Marian’s Nebula!

During the 18th century, famed French astronomer Charles Messier noted the presence of several “nebulous objects” in the night sky. Having originally mistaken them for comets, he began compiling a list of them so that others would not make the same mistake he did. In time, this list (known as the Messier Catalog) would come to include 100 of the most fabulous objects in the night sky.

One of these objects is the open star cluster known as Messier 47 (NGC 2422), which is located in the constellation of Puppis roughly 1,600 light-years from Earth. Located in proximity to Messier 46, this star cluster is estimated to be 78 million years in age. It is also particularly bright, containing about 50 stars and occupying a region that is about the same size as that of the full Moon.

Description:

Spanning across about 12 light years of space, this clump of around 50 stars began their life around 78 million years ago. Now cruising through space some 1600 light years away from Earth, the group continues to distance itself from our solar system at a speed of 9 kilometers per second. For the most part, Messier 47 is a whole lot like the Pleiades star cluster – its brightest member shining just around magnitude 6 and holding a spectral class B2.

But, here you will also find two orange K giants with luminosity of about 200 times that of the Sun. At M47’s center you’ll find binary star, Sigma 1121, with components of magnitude 7.9 both and separated by 7.4 arc seconds. How do we know that M47 is a lot like the Pleiades? Let’s try X-ray sources and the advances of looking at open clusters far more differently than in optical wavelengths. As M. Barbera (et al) said in a 2002 study:

“We present the results of a ROSAT study of NGC 2422, a southern open cluster at a distance of about 470 pc, with an age close to the Pleiades. Source detection was performed on two observations, a 10-ks PSPC and a 40-ks HRI pointing, with a detection algorithm based on wavelet transforms, particularly suited to detecting faint sources in crowded fields. We have detected 78 sources, 13 of which were detected only with the HRI, and 37 detected only with the PSPC. For each source, we have computed the 0.2-2.0 keV X-ray flux. Using optical data from the literature and our own low-dispersion spectroscopic observations, we find candidate optical counterparts for 62 X-ray sources, with more than 80% of these counterparts being late type stars. The number of sources (38 of 62) with high membership probability counterparts is consistent with that expected for Galactic plane observations at our sensitivity. We have computed maximum likelihood X-ray luminosity functions (XLF) for F and early-G type stars with high membership probability. Heavy data censoring due to our limited sensitivity permits determination of only the high-luminosity tails of the XLFs; the distributions are indistinguishable from those of the nearly coeval Pleiades cluster.”

What else might be hiding inside Messier 47? Try new debris disk candidates. As Nadya Gorlova (et al) indicated in a 2004 study:

“Sixty-three members of the 100 Myr old open cluster M47 (NGC 2422) have been detected with the Spitzer Space Telescope. The Be star V 378 Pup shows an excess both in the near-infrared, probably due to free-free emission from the gaseous envelope. Seven other early-type stars show smaller excesses. Among late-type stars, two show large excesses. P1121 is the first known main-sequence star showing an excess comparable to that of Beta Pic, which may indicate the presence of an exceptionally massive debris disk. It is possible that a major planetesimal collision has occurred in this system, consistent with the few hundred Myr timescales estimated for the clearing of the solar system.”

Iof the star cluster Messier 47 taken by the Wide Field Imager camera on the 2.2-metre telescope at ESO’s La Silla Observatory in Chile. Credit: ESO

History of Observation:

Messier 47 was originally discovered before 1654 by Hodierna who described it as:

“[A] Nebulosa between the two dogs”… but it was an observation that wasn’t known about until long after Charles Messier independently recovered it on February 19, 1771. “Cluster of stars, little distant from the preceding; the stars are greater; the middle of the cluster was compared with the same star, 2 Navis. The cluster contains no nebulosity.”

However, it was one of those very rare circumstances when Messier actually made a mistake in his position calculations. Despite this error, the cluster was observed by Caroline Herschel and identified as M47 at least twice in early 1783.

As a consequence of Messier’s position mistake, Sir William Herschel also independently rediscovered it on February 4, 1785, and gave it the number H VIII.38. “A cluster of pretty compressed large [bright] and small [faint] stars. Round. Above [more than] 15′ diameter.” It would be John Herschel, on December 16, 1827, who would be the first to resolve Sigma 1121: “The chief star of a large, pretty rich, straggling cluster. It [the star] is double.”

Atlas Image mosaic obtained of Messier 47 as part of the Two Micron All Sky Survey (2MASS). Credit: UMass/IPAC/Caltech/NASA/NSF

The “Messy” mistake would haunt star catalogs – including both Herschel’s and Dreyer’s for years, until the whole clerical error was cleared up by Owen Gingerich in 1960:

“More explicit reasons for this identification [of M47 with NGC 2422] were given independently in 1959 by T.F. Morris, a member of the Messier Club of the Royal Astronomical Society of Canada’s Montreal Centre. Dr. Morris suggested that an error in signs in the difference between M47 and the comparison star could account for the position. Messier determined the declination of a nebula or cluster by measuring the difference between the object and a comparison star of known declination. The right ascension could be found by recording the times at which the object and the star drifted across a central wire in his telescope’s field; the time interval gives the difference in right ascension. The differences between Messier’s 1770 [actually 1771] position for M47 and his stated comparison star, 2 Navis (now 2 Puppis), if applied with opposite signs, leads to NGC 2422. Clearly, Messier made a mistake in computation!”

May you have Caroline Herschel’s luck finding it!

Locating Messier 47:

There is no simple way of finding Messier 47 in the finderscope of a telescope, but it’s not too hard with binoculars. Begin your hunt a little more than a fist width east/northeast of bright Sirius (Alpha Canis Majoris)… or about 5 degrees (3 finger widths) south of Alpha Monoceros. (It can sometimes by seen with the unaided eye under good conditions as a dim nebulosity.)  There you will find two open clusters that will usually appear in the same average binocular field of view.

Messier 47 location. Image: IAU and Sky & Telescope magazine (Roger Sinnott & Rick Fienberg)

M47 is the westernmost of the pair. It will appear slightly brighter and the stars will be more fewer and more clearly visible. In the finderscope it will appear as if it is resolving, while neighboring eastern M46 will just look like a foggy patch. Because M47’s stars are brighter, it is better suited to less than perfect sky conditions, showing as a compression that begins to resolve in binoculars and will resolves almost fully even a small telescope.

And here are the quick facts on this Messier Object to help you get started:

Object Name: Messier 47
Alternative Designations: M47, NGC 2422
Object Type: Open Galactic Star Cluster
Constellation: Puppis
Right Ascension: 07 : 36.6 (h:m)
Declination: -14 : 30 (deg:m)
Distance: 1.6 (kly)
Visual Brightness: 5.2 (mag)
Apparent Dimension: 30.0 (arc min)

We have written many interesting articles about Messier Objects here at Universe Today. Here’s Tammy Plotner’s Introduction to the Messier Objects, , M1 – The Crab Nebula, M8 – The Lagoon Nebula, and David Dickison’s articles on the 2013 and 2014 Messier Marathons.

Be to sure to check out our complete Messier Catalog. And for more information, check out the SEDS Messier Database.

Sources:

Messier 46 – the NGC 2437 Open Star Cluster

Welcome back to Messier Monday! In our ongoing tribute to the great Tammy Plotner, we take a look at Orion’s Nebula’s “little brother”, the De Marian’s Nebula!

During the 18th century, famed French astronomer Charles Messier noted the presence of several “nebulous objects” in the night sky. Having originally mistaken them for comets, he began compiling a list of them so that others would not make the same mistake he did. In time, this list (known as the Messier Catalog) would come to include 100 of the most fabulous objects in the night sky.

One of these objects is the open star cluster known as Messier 46, which is located about 5,500 light years away in the southern Puppis constellation. Located in close proximity to another open cluster (Messier 47), this bright, rich cluster is about 300 million years old and is home to many stars – an estimated 500 – and some impressive nebulae too.

Description:

Crammed into about 30 light years of space, around 150 resolvable stars and up to 500 possible stellar members all took off together on a journey through space some 300 million years ago. At this point in time, they are about 5,400 light years away from our solar system, but they aren’t standing still. They’re pulling away from us at a speed of 41.4 kilometers per second.

The Messier 46 open star cluster. Credit: Jose Luis Martinez

If you notice something just a bit different about one of the stars along the northern edge – then you’ve caught on to one of the most famous features of Messier 46 – its resident planetary nebula. While radial velocities show it probably isn’t a true member of the cluster, it’s still a cool feature!

But, is there more to this cluster than that? You bet. Messier 46 has also been highly studied for its core properties. As Saurabh Sharma (et al) indicated in a 2006 study:

“The study of Galactic open clusters is of great interest in several astrophysical aspects. Young open clusters provide information about current star formation processes and are key objects for clarifying questions of Galactic structure, while observations of old and intermediate-age open clusters play an important role in studying the theories of stellar and Galactic evolution. A detailed analysis of the structure of coronae of open clusters is needed to understand the effects of external environments, like the Galactic tidal field and impulsive encounters with interstellar clouds, etc., on dynamical evolution of open clusters. Extensive studies of the coronal regions of clusters have not been carried out so far mainly because of unavailability of photometry in a large field around open star clusters. The ability to obtain improved photometry of thousands of stars means that large-scale studies of open clusters can be conducted to study the spatial structure and stability of Galactic open clusters. With the addition of photometry of a nearby field region it is possible to construct luminosity functions (LFs) and MFs, which are useful for understanding cluster-formation processes and the theory of star formation in open clusters.”

History of Observation:

Messier 46 is an original discovery of Charles Messier, caught on February 19, 1771, just after he released his first catalog of entries. In his journal, he wrote:

“A cluster of very small stars, between the head of the Great Dog and the two hind feet of the Unicorn, [its position] determined by comparing this cluster with the star 2 Navis, of 6th-magnitude, according to Flamsteed; one cannot see these stars but with a good refractor; the cluster contains a bit of nebulosity.”

Messier 46 and NGC 2437. Credit: NASA

At the time of its discovery, Messier had not published his findings quite as immediately as we do today, so another astronomer also independently discovered this cluster as well… Caroline Herschel. “March 4th, [17]83. 1 deg S following the nebula near the 2nd Navis… a Nebula the figure is done by memory. My Brother observed it with 227 and found it to be, an astonishing number of stars. it is not in Mess. catalogue.”

It would be John Herschel in 1833 who would discover the planetary nebula while cataloging it: “The brightest part of a very fine rich cluster; stars of 10th magnitude; which fills the field. Within the cluster at its northern edge is a fine planetary nebula.”

But, as always, Admiral Symth has a way with words and observations. As he wrote of the object:

“A very delicate double star in a fine cluster, outlying the Galaxy, over Argo’s poop. A 8 1/2 [mag], and B 11, both pale white.A noble though rather loose assemblage of stars from the 8th to the 13th magnitude, more than filling the field, especially in length, with power 93; the most compressed part trending sf [south following, SE] and np [north preceding, NW]. Among the larger [brighter] stars on the northern verge is an extremely faint planetary nebula, which is 39 H. IV. [NGC 2438], and 464 of his son’s Catalogue. This was discovered by Messier in 1769, who considered it as being “rather enveloped in nebulous matter;” this opinion, however, must have arisen from the splendid glow of mass, for judging from his own remark, it is not likely that he perceived the planetary nebula on the north. WH [William Herschel], who observed it in 1786, expressly says, “no connexion with the cluster, which is free from nebulosity.” Such is my own view of attentively gazing; but the impression left on the senses, is that of awful vastness and bewildering distance, – yet including the opinion, that those bodies bespangled the vastness of space, may differ in magnitude and other attributes.”

Pretty amazing considering these gentlemen did all of their observations visually and knew nothing about today’s parallaxes, radial velocities or any other type of thing. May your own observations be as talented…

Locating Messier 46:

There is no simple way of finding Messier 46 in the finderscope of a telescope, but it’s not too hard with binoculars. Begin your hunt a little more than a fistwidth east/northeast of bright Sirius (Alpha Canis Majoris)… or about 5 degrees (3 finger widths) south of Alpha Monoceros. There you will find two open clusters that will usually appear in the same average binocular field of view. M46 is the easternmost of the pair.

Messier 46 location. Credit: IAU/Sky & Telescope magazine (Roger Sinnott & Rick Fienberg)

It will appear slightly dimmer and the stars will be more concentrated. In the finderscope it will appear as a slightly foggy patch, while neighboring western M47 will try to begin resolution. Because M46’s stars are fainter, it is better suited to darker sky conditions, showing as a compression in binoculars and will resolve fairly well with even a small telescope. However, you will need at least a 6″ telescope to perceive the planetary nebula.

And here are the quick facts on this Messier Object to help you get started:

Object Name: Messier 46
Alternative Designations: M46, NGC 2437
Object Type: Open Galactic Star Cluster
Constellation: Puppis
Right Ascension: 07 : 41.8 (h:m)
Declination: -14 : 49 (deg:m)
Distance: 5.4 (kly)
Visual Brightness: 6.0 (mag)
Apparent Dimension: 27.0 (arc min)

We have written many interesting articles about Messier Objects here at Universe Today. Here’s Tammy Plotner’s Introduction to the Messier Objects, , M1 – The Crab Nebula, M8 – The Lagoon Nebula, and David Dickison’s articles on the 2013 and 2014 Messier Marathons.

Be to sure to check out our complete Messier Catalog. And for more information, check out the SEDS Messier Database.

Sources:

Messier 39 – The NGC 7092 Open Star Cluster

Welcome back to Messier Monday! In our ongoing tribute to the great Tammy Plotner, we take a look at the open galactic star cluster known as Messier 39. Enjoy!

During the 18th century, famed French astronomer Charles Messier noted the presence of several “nebulous objects” in the night sky. Having originally mistaken them for comets, he began compiling a list of them so that others would not make the same mistake he did. In time, this list (known as the Messier Catalog) would come to include 100 of the most fabulous objects in the night sky.

One of these objects is known as Messier 39, an open star cluster located in the direction of the Cygnus constellation. Because of its proximity to Deneb and its size – it is actually larger in the night sky than a full Moon – it is easily observed using binoculars and small, low magnification telescopes.

Description:

Positioned only about 800 light years away from our solar system, this 300 million year old group of about 30 stars may look like they are spread fairly far apart in the sky. But as clusters go, they are close, really close! This group is gathered in space in only a 7 light year neighborhood! All of its stars are main sequence and the very brightest of them are just about to evolve into the red giant star phase.

In a study done by Jean Claude Mermilliod (et al), they conducted a long-term monitoring of solar-type dwarfs with CORAVEL – a study which took 19 years. While most individual radial velocities were never published – apart from a small number of spectroscopic binaries – the stars themselves and their properties were well documented in the works of B. Uyaniker and T. L. Landecker of the National Research Council, Herzberg Institute of Astrophysics.

Low-magnification image of Messier 39. Credit: Christian van Endern

As Uyaniker and Landecker claimed in their 2002 study, “A Highly Ordered Faraday-Rotation Structure in the Interstellar Medium“:

“We describe a Faraday rotation structure in the interstellar medium detected through polarimetric imaging at 1420 MHz from the Canadian Galactic Plane Survey (CGPS). The structure, at l = 918,b = -25, has an extent of ~2°, within which polarization angle varies smoothly over a range of ~100°. Polarized intensity also varies smoothly, showing a central peak within an outer shell. This region is in sharp contrast to its surroundings, where low-level chaotic polarization structure occurs on arcminute scales. The Faraday rotation structure has no counterpart in radio total intensity and is unrelated to known objects along the line of sight, which include a Lynds Bright Nebula, LBN 416, and the star cluster M39 (NGC 7092). It is interpreted as a smooth enhancement of electron density. The absence of a counterpart, in either optical emission or total intensity, establishes a lower limit to its distance. An upper limit is determined by the strong beam depolarization in this direction. At a probable distance of 350 ± 50 pc, the size of the object is 10 pc, the enhancement of electron density is 1.7 cm-3, and the mass of ionized gas is 23 M. It has a very smooth internal magnetic field of strength 3 UG, slightly enhanced above the ambient field. G91.8-2.5 is the second such object to be discovered in the CGPS, and it seems likely that such structures are common in the magneto-ionic medium.”

So where do these gases come from? Perhaps they are there all along. As Yu N. Efremov and T.G. Sitnik wrote in their 1988 study:

“It is found that about 90% of young clusters o-b2 and OB-associations situated within 3 kpc from the Sun are united into complexes with diameters from 150 to 700 pc. Almost all complexes contain giant molecular clouds with masses. A number of complexes (mostly large ones)-are connected with giant H I clouds; a few of small complexes are situated in the H I-caverns. Older (>b2) cluster avoid the regions occupied by young star groups. Complexes often have an hierarchic structure; some neighbouring complexes may be united into supercomplexes with diameters about 1.5 kpc.”

Does this mean it’s possible that M39 could be more than one cluster combined? As H. Schneider wrote in his 1987 study:

“Early-type stars up to 12.0 mag and spectral type F2 in two young northern clusters were investigated by means of Stromgren and H-beta photometry. The distance and reddening of the clusters were estimated, and the membership of the stars discussed. In the case of NGC 7039 a distance of 675 pc and a color excess of E(b-y) = 0.056 were found; the respective values for NGC 7063 were 635 pc and E(b-y) = 0.062. The reality of NGC 7039 is somewhat puzzling: it seems that there exists a loose star aggregate called NGC 7039, containing about six to nine stars, and in the background another cluster at a distance of about 1500 pc. Besides this, variable reddening across the cluster area is probable.”

Atlas Image mosaic of Messier 39, obtained as part of the Two Micron All Sky Survey (2MASS). Credit: NASA/NSF/IPAC/Caltech/Univ. of Mass.

History of Observation:

While it is possible this bright star cluster was remarked upon by Aristotle as a cometary appearing object about 325 BC, and it is also possible that it may have been discovered by Le Gentil in 1750, the fact remains M39 is most frequently attributed to be an original discovery of Charles Messier. As he recorded in his notes:

“In the night of October 24 to 25, 1764, I observed a cluster of stars near the tail of Cygnus: One distinguishes them with an ordinary (nonachromatic) refractor of 3 and a half feet; they don’t contain any nebulosity; its extension can occupy a degree of arc. I have compared it with the star Alpha Cygni, and I have found its position in right ascension of 320d 57′ 10″, and its declination of 47d 25′ 0″ north.”

Because Sir William Herschel did not publish his findings on Messier’s works, very few have read his observations of the object -“Consists of such large and straggling stars that I could not tell where it began nor where it ended. It cannot be called a cluster.” However, it would later go on to receive a New General Catalog (NGC) designation by Sir John Herschel who would describe it as “A star of 7th mag [position taken], one of a large loose cluster of stars of 7th to 10th magnitude; very coarsely scattered, and filling many fields.”

Even as accomplished as historic observers were, they sometimes didn’t always do the right thing. In the case of Messier 39, it is so close to us that it appears large dimensionally in the sky – and therefore needs less magnification instead of more to be properly studied as a whole. However, don’t always put away the magnfication, because as Admiral Smyth reports:

“A loose cluster, or rather splashy galaxy field of stars, in a very rich visinity between the Swan’s tail and the Lizard, due south of Beta Cephei, and east-north-east of Deneb [Alpha Cygni]. This was picked up by Messier in 1764, with his 3 1/2 foot telescope, and registered as being a degree in diameter. Among them there are several pairs, of which a couple were slightly estimated; the first being the brightest star (7m) and its comes, and the second a pretty pair of 10th-magnitudes.”

The location of Messier 39 in the Cygnus constellation. Credit: IAU/Sky & Telescope magazine/Roger Sinnott & Rick Fienberg)

Locating Messier 39:

This coarse open star cluster is easily found in small optics. Start first by identifying the very large constellation of Cygnus and pinpointing its brightest, northernmost star. Aim you binoculars there. You’ll find M39 about 9 degrees east and a bit north of Deneb (Alpha Cygni). If at first you don’t succeed, try looking at Deneb from a dark sky location and see if you can spot a small, hazy patch about a fist width away to the east. There’s your star cluster!

It will also show easily in the telescope finderscope as a hazy patch and even begin resolution with larger aperture finders. M39 is very well suited to light polluted skies and moonlit observing and will even hold up well to less than ideal sky conditions. Small instruments will easily see a bright handful of stars while larger telescopes will resolve many more faint members and pairs. Because of its large apparent size, you’ll enjoy viewing M39 far more if you use the least amount of magnification possible.

Enjoy this star-studded cluster and the great Milky Way field that frames it!

And here are the quick facts on this Messier Object to help get you started:

Object Name: Messier 39
Alternative Designations: M39, NGC 7092
Object Type: Galactic Open Star Cluster
Constellation: Cygnus
Right Ascension: 21 : 32.2 (h:m)
Declination: +48 : 26 (deg:m)
Distance: 0.825 (kly)
Visual Brightness: 4.6 (mag)
Apparent Dimension: 32.0 (arc min)

We have written many interesting articles about Messier Objects here at Universe Today. Here’s Tammy Plotner’s Introduction to the Messier Objects, , M1 – The Crab Nebula, M8 – The Lagoon Nebula, and David Dickison’s articles on the 2013 and 2014 Messier Marathons.

Be to sure to check out our complete Messier Catalog. And for more information, check out the SEDS Messier Database.

Sources:

Messier 38 – The Starfish Cluster

Welcome back to Messier Monday! In our ongoing tribute to the great Tammy Plotner, we take a look at the Starfish Cluster, otherwise known as Messier 38. Enjoy!

During the 18th century, famed French astronomer Charles Messier noted the presence of several “nebulous objects” in the night sky. Having originally mistaken them for comets, he began compiling a list of them so that others would not make the same mistake he did. In time, this list (known as the Messier Catalog) would come to include 100 of the most fabulous objects in the night sky.

One of these objects it the Starfish Cluster, also known as Messier 38 (or M38). This open star cluster is located in the direction of the northern Auriga constellation, along with the open star clusters M36 and M37. While not the brightest of the three, the location of the Starfish within the polygon formed by the brightest stars of Auriga makes it very easy to find.

Description:

Cruising around our Milky Way some 4200 light years from our solar system, this 220 million year old group of stars spreads itself across about 25 light years of space. If you’re using a telescope, you may have noticed its not alone… Messier 38 might very well be a binary star cluster! As Anil K. Pandey (et al) explained in a 2006 study:

“We present CCD photometry in a wide field around two open clusters, NGC 1912 and NGC 1907. The stellar surface density profiles indicate that the radii of the clusters NGC 1912 and NGC 1907 are 14′ and 6′ respectively. The core of the cluster NGC 1907 is found to be 1′.6±0′.3, whereas the core of the cluster NGC 1912 could not be defined due to its significant variation with the limiting magnitude. The clusters are situated at distances of 1400±100 pc (NGC 1912) and 1760±100 pc (NGC 1907), indicating that in spite of their close locations on the sky they may be formed in different parts of the Galaxy.”

The Starfish Cluster also known as Messier 38. Credit: Wikisky

So what’s happening here? Chances are, when you’re looking at M38, you’re looking at a star cluster that’s currently undergoing a real close encounter! Said M.R. de Oliveira (et al) said in their 2002 study:

“The possible physical relation between the closely projected open clusters NGC 1912 (M 38) and NGC 1907 is investigated. Previous studies suggested a physical pair based on similar distances, and the present study explores in more detail the possible interaction. Spatial velocities are derived from available radial velocities and proper motions, and the past orbital motions of the clusters are retrieved in a Galactic potential model. Detailed N-body simulations of their approach suggest that the clusters were born in different regions of the Galaxy and presently experience a fly-by.”

However, it was Sang Hyun Lee and See-Woo Lee who gave us the estimates of M38’s distance and age. As they wrote in their 1996 study, “UBV CCD Photometry of Open Cluster NGC 1907 and NGC 1912“: The distance difference of the two clusters is 300pc and the age difference is 150 Myr. These results imply that the two clusters are not physically connected.”

So, how do we know they are two clusters passing in the night? The credit for that goes to de Oliveira and colleagues, who also asserted in their 2002 study:

“These simulations also shows that the faster the clusters approach the weaker the tidal debris in the bridge region, which explain why there is, apparently, no evidence of a material link between the clusters and why it should not be expected. It would be necessary to analyse deep wide field CCD photometry for a more conclusive result about the apparent absence of tidal link between the clusters.”

Atlas image mosaic of the Starfish Cluster (Messier 38), obtained as part of the Two Micron All Sky Survey (2MASS). Credit: NASA/NSF/Caltech/UofMass/IPAC

History of Observation:

This wonderful star cluster was originally discovered by Giovanni Batista Hodierna before 1654 and independently rediscovered by Le Gentil in 1749. However, it was Charles Messier’s catalog which brought it to attention:

“In the night of September 25 to 26, 1764, I have discovered a cluster of small stars in Auriga, near the star Sigma of that constellation, little distant from the two preceding clusters: this one is of square shape, and doesn’t contain any nebulosity, if one examines it with a good instrument: its extension may be 15 minutes of arc. I have determined its position: its right ascension was 78d 10′ 12″, and its declination 36d 11′ 51″ north.”

By correcting cataloging its position, M38 could later be studied by other astronomers who would also add their own notes. Caroline, then William Herschel would observe it, where the good Sir William would add to his private notes: “A cluster of scattered, pretty large [bright] stars of various magnitudes, of an irregular figure. It is in the Milky Way.”

Messier Object 38 would then later be added to the New General Catalog by John Herschel, who wasn’t particularly descriptive, either. However, there was an historic astronomer who was determined to examine this star cluster and it was Admiral Symth:

“A rich cluster of minute stars, on the Waggoner’s left thigh, of which a remarkable pair in the following are here estimated. A [mag] 7, yellow; and B 9, pale yellow; having a little companion about 25″ off in the sf [south following, SE] quarter. Messier discovered this in 1764, and described it as ‘a mass of stars of a square form without any nebulosity, extending to about 15′ of a degree;’ but it is singular that the palpable cruciform shape of the most clustering part did not attract his notice. It is an oblique cross, with a pair of large [bright] stars in each arm, and a conspicuous single one at the centre; the whole followed by a bright individual of the 7th magnitude. The very unusual shape of this cluster, recalls the sagacity of Sir William Herschel’s speculations upon the subject, and very much favours the idea of an attractive power lodged in the brightest part. For although the form be not globular, it is plainly to be seen that there is a tendency toward sphericity, by the swell of the dimensions as they draw near the most luminous place, denoting, as it were, a stream, or tide, of stars, setting toward the centre. As the stars in the same nebula must be very merely all at the same relative distance from us, and they appear to be about the same size [brightness], Sir William infers that their real magnitudes must be nearly equal. Granting, therefore, that these nebulae and clusters of stars are formed by their mutual attraction, he concludes that we may judge of their relative age, by the disposition of their component parts, those being the oldest which are the most compressed.”

Open Cluster M38, photographed on Feb 19, 2015. Credit: Wikipedia Commons/Miguel Garcia

Perhaps by taking his time and really observing, Smyth gained some insight into the true nature of M38! Observe it yourself, and see if you can also locate NGC 1907. It’s quite a pair!

Locating Messier 38:

Locating Messier 38 is relatively easy once you understand the constellation of Auriga. Looking roughly like a pentagon in shape, start by identifying the brightest of these stars – Capella. Due south of it is the second brightest star which shares its border with Beta Tauri, El Nath. By aiming binoculars at El Nath, go north about 1/3 the distance between the two and enjoy all the stars!

You will note two very conspicuous clusters of stars in this area, and so did Le Gentil in 1749. Binoculars will reveal the pair in the same field, as will telescopes using lowest power. The dimmest of these is the M38, and will appear vaguely cruciform in shape. At roughly 4200 light years away, larger aperture will be needed to resolve the 100 or so fainter members. About 2 1/2 degrees to the southeast (about a finger width) you will see the much brighter M36.

More easily resolved in binoculars and small scopes, this “jewel box” galactic cluster is quite young and about 100 light years closer. If you continue roughly on the same trajectory about another 4 degrees southeast you will find open cluster M37. This galactic cluster will appear almost nebula-like to binoculars and very small telescopes – but comes to perfect resolution with larger instruments.

The location of Messier 38 open star cluster in the Auriga constellation. Credit: IAU and Sky & Telescope magazine (Roger Sinnott & Rick Fienberg)

While all three open star clusters make fine choices for moonlit or light polluted skies, remember that high sky light means less faint stars which can be resolved – robbing each cluster of some of its beauty. Messier 38 is faintest and northernmost of the trio and located almost in the center of the Auriga pentagon. Binoculars and small telescopes will easily spot its cross-shaped pattern.

And here are the quick facts on the Starfish Nebula to help you get started:

Object Name: Messier 38
Alternative Designations: M38, NGC 1912
Object Type: Galactic Open Star Cluster
Constellation: Auriga
Right Ascension: 05 : 28.4 (h:m)
Declination: +35 : 50 (deg:m)
Distance: 4.2 (kly)
Visual Brightness: 7.4 (mag)
Apparent Dimension: 21.0 (arc min)

We have written many interesting articles about Messier Objects here at Universe Today. Here’s Tammy Plotner’s Introduction to the Messier Objects, , M1 – The Crab Nebula, M8 – The Lagoon Nebula, and David Dickison’s articles on the 2013 and 2014 Messier Marathons.

Be to sure to check out our complete Messier Catalog. And for more information, check out the SEDS Messier Database.

Sources:

Messier 37 – the NGC 2099 Open Star Cluster

Welcome back to Messier Monday! In our ongoing tribute to the great Tammy Plotner, we take a look at the open star cluster known as Messier 37. Enjoy!

During the 18th century, famed French astronomer Charles Messier noted the presence of several “nebulous objects” in the night sky. Having originally mistaken them for comets, he began compiling a list of them so that others would not make the same mistake he did. In time, this list (known as the Messier Catalog) would come to include 100 of the most fabulous objects in the night sky.

One of these objects is the open star cluster known as Messier 37 (aka M37 and NGC 2099). Located in the direction of the Auriga constellation, Messier 37 is one of three open star clusters (including Messier 36 and Messier 38) in this portion of the night sky – and also the brightest.

Description:

Of the trio of Messier star clusters in this area, M37 is by far the most stellar populated. It contains at least 150 stars that are around magnitude 12 and easily resolved by even small telescopes – and science is still counting actual members! At around 347 – 550 million years old, you’ll find at least a dozen red giants living here about 4,500 light years away from Earth… and they do it in a neighborhood that spans anywhere from 20 to 25 light years across!

The open star cluster Messier 37. Credit: Wikisky

Just how many stars might be inside this intermediate-aged cluster? As R. Sagar and Nilakshi of the Indian Institute for Astrophysics said in their 2002 study:

“The CCD observations of the rich open star cluster NGC 2099 and its surrounding field region have been carried out up to a limiting magnitude of V ~ 22 mag in B, V and I passbands for the first time. A total of ~ 12 000 stars have been observed in the area of about 24 arcmin x 34 arcmin in the cluster region, as well as ~ 2180 stars in the ~ 12arcmin x 12arcmin area of the field region located ~ 45arcmin away from the cluster center.”

Out of this huge number of stars, astronomers have been able to observe white dwarfs, too. This helps us to understand how they develop and what affects their helium or hydrogen content. Jasonjot Singh Kalirai et al. had the following to say in a 2004 study:

“Spectra have been obtained of 21 white dwarfs (WDs) in the direction of the young, rich open star cluster NGC 2099. This represents an appreciable fraction (>30%) of the cluster’s total WD population. The mean derived mass of the sample is 0.8 M—about 0.2 M larger than the mean seen among field WDs. A surprising result is that all of the NGC 2099 WDs have hydrogen-rich atmospheres (DAs); none exhibit helium-rich ones (DBs) or any other spectral class. We explore possible reasons for the lack of DBs in these clusters and conclude that the most promising scenario for the DA/DB number ratio discrepancy in young clusters is that hot, high-mass WDs do not develop large enough helium convection zones to allow helium to be brought to the surface and turn a hydrogen-rich WD into a helium-rich one.”

So, we’re setting the stage with number of stars and types. We have white dwarfs – but what about variables? Y.B. Kang (et al), put it this way in a 2007 study:

“Time-series CCD photometric observations of the intermediate-age open cluster NGC 2099 were performed to search for variable stars. We also carried out BV photometry to study physical properties of variables in the cluster. Using V-band time-series data, we carefully examined light variations of about 12,000 stars in the range of 10 < V < 22 mag. A total of 24 variable stars have been identified; seven stars are previously known variables and 17 stars are newly identified. On the basis of observational properties such as light curve shape, period, and amplitude, we classified the new variable stars as nine delta Scuti-type pulsating stars, seven eclipsing binaries, and one peculiar variable star. Judging from the position of delta Scuti-type stars in the color-magnitude diagram, only two stars are likely to have the cluster membership. One new variable KV10 shows peculiar light variations with a delta Scuti-type short period of about 0.044 day as well as a long period of 0.417 day.”

M37 (NGC 2099) open cluster. Credit: Wikipedia Commons

So what does knowing about these two types of stars help with our understanding of stellar evolution? That’s one of the goals of the RACE-OC project. As S. Messina (et al) said in 2008:

“Rotation and solar-type magnetic activity are closely related to each other in main-sequence stars of G or later spectral types. The presence and level of magnetic activity depend on star’s rotation, and rotation itself is strongly influenced by strength and topology of the magnetic fields. Open clusters represent especially useful targets to investigate the connection between rotation and activity. The open cluster NGC 2099 has been studied as a part of the RACE-OC project (Rotation and ACtivity Evolution in Open Clusters), which is aimed at exploring the evolution of rotation and magnetic activity in the late-type members of open clusters of different ages. We collected time series CCD photometric observations of this cluster in January 2004, and we determined the presence of periodicities in the flux variation related to the stellar rotation by Fourier analysis. We investigate the relations between activity manifestations, such as the light curve amplitude, and global stellar parameters. Results: We have discovered 135 periodic variables, 122 of which are candidate cluster members. Determination of rotation periods of G- and K-type stars has allowed us to better explore the evolution of angular momentum at an age of about 500 Myr. In our analysis, we have also identified 3 new detached eclipsing binary candidates among cluster members. A comparison with the older Hyades cluster (~625 Myr) shows that the newly-determined distribution of rotation periods is consistent with the scenario of rotational braking of main-sequence spotted stars as they age. However, a comparison with the younger M 34 cluster (~200 Myr) shows that the G8-K5 members of these clusters have the same rotation period distribution. That is, G8-K5 members in NGC 2099 seem to have experienced no significant braking in the age range from ~200 to ~500 Myr. Finally, NGC 2099 members have a smaller level of photospheric magnetic activity, as measured by light curve amplitude, than in younger stars of the same mass and rotation, suggesting that the activity level also depends on some other age-dependent parameters.”

History of Observation:

Although this great star cluster was originally recorded Giovanni Batista Hodierna before 1654, it would be 230 years before his records would be uncovered, so when Charles Messier first logged as Messier 37, it was believed to be an independent discovery.

“In the same night [September 2 to 3, 1764], I have observed a second cluster of small stars which were not very distant from the preceding, near the right leg of Auriga and on the parallel of the star Chi of that constellaiton: the stars there are smaller than that of the preceding cluster: they are also closer to each other, and contain a nebulosity. With an ordinary refractor of 3 feet and a half, one has difficulty to see these stars; but one distinguishes them with an instrument of greater effectivity. I have determined the position fo this cluster, which may have an extension of 8 to 9 minutes of arc: its right ascension was 84d 15′ 12″, and its declination 32d 11′ 51″ north.”

While William Herschel would return in later years to study Messier’s object, he did not publish his notes – but gives some great observing advice:

“A useful, coarse step; it will serve to learn to see nebulae, because it contains many small stars mixed with others in various magnitudes, many of which are not to be seen without great and long attention.” Messier 37 would be later given its NGC catalog designation by John Herschel who was the first to make a guess at its true stellar population: “Very fine large cluster, all resolved into stars of 10th to 13th magnitude. It fills 1 1/2 field, but the straggling stars extend very far. There may be 500 stars.”

As always, Admiral Smyth was the most poetical about his observing, and of M37 he writes:

“A magnificent object, the whole field being strewed as it were with sparkling gold-dust; and the group is resolvable into about 500 stars, from the 10th to the 14th magnitudes, besides the outliers. It was found and fixed by Messier in 1764, who described it as “a mass of small stars, much enveloped in nebulous matter.” This nebulous matter, however, yields to my telescope, and resolves into infinitely minute points of lucid light, among the distinct little individuals.”

The location of Messier 37 in the constellation Auriga. Credit: IAU and Sky & Telescope magazine (Roger Sinnott & Rick Fienberg)

Locating Messier 37:

Locating Messier 37 is relatively easy once you understand the constellation of Auriga. Looking roughly like a pentagon in shape, start by identifying the brightest of these stars – Capella. Due south of it is the second brightest star which shares its border with Beta Tauri, El Nath. By aiming binoculars at El Nath, go north about 1/3 the distance between the two and enjoy all the stars! You will note two very conspicuous clusters of stars in this area, and so did Le Gentil in 1749.

Binoculars will reveal the pair in the same field, as will telescopes using lowest power. The dimmest of these is the M38, and will appear vaguely cruciform in shape. At roughly 4200 light years away, larger aperture will be needed to resolve the 100 or so fainter members. About 2 1/2 degrees to the southeast (about a finger width) you will see the much brighter M36.

More easily resolved in binoculars and small scopes, this “jewel box” galactic cluster is quite young and about 100 light years closer. If you continue roughly on the same trajectory about another 4 degrees southeast you will find open cluster M37. This galactic cluster will appear almost nebula-like to binoculars and very small telescopes – but comes to perfect resolution with larger instruments.

While all three open star clusters make fine choices for moonlit or light polluted skies, remember that high sky light means less faint stars which can be resolved – robbing each cluster of some of its beauty. Messier 37 is the brightest and easternmost of the trio and you’ll very much notice its density.

When you view this cluster with binoculars, you’ll be seeing it much as Messier did… But use the power of a telescope if you can. Because this cloud of stars is quite worth your time and attention!

Object Name: Messier 37
Alternative Designations: M37, NGC 2099
Object Type: Galactic Open Star Cluster
Constellation: Auriga
Right Ascension: 05 : 52.4 (h:m)
Declination: +32 : 33 (deg:m)
Distance: 4.4 (kly)
Visual Brightness: 6.2 (mag)
Apparent Dimension: 24.0 (arc min)

We have written many interesting articles about Messier Objects here at Universe Today. Here’s Tammy Plotner’s Introduction to the Messier Objects, , M1 – The Crab Nebula, M8 – The Lagoon Nebula, and David Dickison’s articles on the 2013 and 2014 Messier Marathons.

Be to sure to check out our complete Messier Catalog. And for more information, check out the SEDS Messier Database.

Sources:

Messier 36 – The Pinwheel Cluster

Welcome back to Messier Monday! In our ongoing tribute to the great Tammy Plotner, we take a look at the Pinweel Cluster, otherwise known as Messier 36. Enjoy!

During the 18th century, famed French astronomer Charles Messier noted the presence of several “nebulous objects” in the night sky. Having originally mistaken them for comets, he began compiling a list of them so that others would not make the same mistake he did. In time, this list (known as the Messier Catalog) would come to include 100 of the most fabulous objects in the night sky.

Included in this list is the open star cluster Messier 36, also known as the Pinwheel Cluster. This cluster is so-named because of its association with the Auriga constellation (aka. “the Charioteer”). Though similar in size and make-up to the Pleiades Cluster (Messier 45), the Pinwheel Cluster is actually ten times farther away from Earth – and one of the most distant of any clusters catalogued by Messier.

What You Are Looking At:

Located a little more than 4000 light years from our solar system, this group of about 60 stars spans across about 14 light years of space. As you are studying it, you’ll notice one star which seems brighter than the rest… With good reason! Its a spectral type B2 and about 360 more luminous than our Sun. Many of the cluster members here are also B-type stars and rapid rotators.

Close-up of the central region of Messier 36. Credit: Wikisky

This means that 25 million year old Messier 36 shares a lot in common with another nearby star cluster, the Pleiades. By taking a deep look at young clusters with stars of varying ages, astronomers are able to how long circumstellar disks may last – giving us a clue as to whether or not planet-forming stars may lay within them.

As Karl E. Haisch, Jr. (et al), wrote in a 2001 study “Disk Frequencies and Lifetimes in Young Clusters“:

“We have completed the first systematic and homogeneous survey for circumstellar disks in a sample of young clusters that both span a significant range in age and contain statistically significant numbers of stars whose masses span nearly the entire stellar mass spectrum. Analysis of the combined survey indicates that the cluster disk fraction is initially very high and rapidly decreases with increasing cluster age, such that one-half the stars within the clusters lose their disks in 3 million years. Moreover, these observations yield an overall disk lifetime of ~6 million years in the surveyed cluster sample. This is the timescale for essentially all the stars in a cluster to lose their disks. This should set a meaningful constraint for the planet-building timescale in stellar clusters.”

ut, can M36 hold surprises? You betcha’. As Bo Reipurth stated in a 2008 study titled “Star Formation and Molecular Clouds towards the Galactic Anti-Center“:

“The open cluster M36 (NGC 1960), which apparently forms the center of the Aur OB1 association, has been the subject of numerous analyses, and of these the earliest studies are today of historical interest only. NGC 1960 has recently attracted attention as the most likely origin of a massive OB star that exploded about 40,000 yr ago, creating the supernova remnant Simeis 147, an old supernova remnant listed in the catalog compiled at Simeiz by Gaze & Shajn (1952). A pulsar, PSR J0538+2817, has been found near the center of Simeis 147.”

2MASS Atlas Image Mosaic of the open star cluster Messier 36. Credit: NASA/IPAC/Caltech/University of Massachusetts

And the search for planet-building stars within M36 hasn’t stopped yet. The Spitzer Space telescope will also be investigating it, thanks to a proposal made by George Rieke:

“We propose a deep IRAC/MIPS survey of NGC 1960, a ~20 Myr-old massive cluster unexplored in the mid infrared. This cluster is at a key stage in terrestrial planet formation. Our survey will likely detect infrared excess emission from debris disks and transition disks from ~ 100 intermediate-mass (1-3 solar mass) stars. Together with ground-based photometry/spectroscopy of this cluster, proposed observations of 10 Myr-old NGC 6871, scheduled cycle 4 observations of the massive 13 Myr old clusters h and chi Persei, and existing data on NGC 2547 at 30 Myr, this survey will yield robust constraints on the frequency of debris/transition disks as a function of spectral type, age, and cluster environment at a critical age range for planet formation. This survey will provide a benchmark study of the observable signatures of terrestrial planet formation that will inform James Webb Space Telescope observations of planet-forming disks a decade from now.”

History of Observation:

The presence of this awesome star cluster was first recorded by Giovanni Batista Hodierna before 1654 and re-discovered by Le Gentil in 1749. However, it was Charles Messier who took the time to carefully record its position for future generations:

“In the night of September 2 to 3, 1764, I have determined the position of a star cluster in Auriga, near the star Phi of that constellation. With an ordinary refractor of 3 feet and a half, one has difficulty to distinguish these small stars; but when employing a stronger instrument, one sees them very well; they don’t contain between them any nebulosity: their extension is about 9 minutes of arc. I have compared the middle of this cluster with the star Phi Aurigae, and I have determined its position; its right ascension was 80d 11′ 42″, and its declination 34d 8′ 6″ north.”

M36 Open Cluster. Credit: NOAO/AURA/NSF

It would be observed again by Caroline, William and John Herschel who would be the first to note the double star in M36’s center. Although none of their notes are particularly glowing on this awesome star cluster, Admiral Symth does come to the historic rescue!

“A neat double star in a splendid cluster, on the robe below the Waggoner’s left thigh, and near the centre of the Galaxy stream. A [mag] 8 and B 9, both white; in a rich though open splash of stars from the 8th to the 14th magnitudes, with numerous outliers, like the device of a star whose rays are formed by very small stars. This object was registered by M. [Messier] in 1764; and the double star, as H. [John Herschel] remarks, is admirably placed, for future astronomers to ascertain whether there be internal motion in clusters. A line carried from the central star in Orion’s belt, through Zeta Tauri, and continued about 13deg beyond, will reach the cluster, following Phi Aurigae by about two degrees.”

Locating Messier 36:

Locating Messier 36 is relatively easy once you understand the constellation of Auriga. Looking roughly like a pentagon in shape, start by identifying the brightest of these stars – Capella. Due south of it is the second brightest star which shares its border with Beta Tauri, El Nath. By aiming binoculars at El Nath, go north about 1/3 the distance between the two and enjoy all the stars!

You will note two very conspicuous clusters of stars in this area, and so did Le Gentil in 1749. Binoculars will reveal the pair in the same field, as will telescopes using lowest power. The dimmest of these is the M38, and will appear vaguely cruciform in shape. At roughly 4200 light years away, larger aperture will be needed to resolve the 100 or so fainter members. About 2 1/2 degrees to the southeast (about a finger width) you will see the much brighter M36.

The location of M36 in the Auriga constellation. Credit: IAU and Sky and Telescope Magazine (Roger Sinnott & Rick Fienberg)

More easily resolved in binoculars and small scopes, this “jewel box” galactic cluster is quite young and about 100 light years closer. If you continue roughly on the same trajectory about another 4 degrees southeast you will find open cluster M37. This galactic cluster will appear almost nebula-like to binoculars and very small telescopes – but comes to perfect resolution with larger instruments.

While all three open star clusters make fine choices for moonlit or light polluted skies, remember that high sky light means less faint stars which can be resolved – robbing each cluster of some of its beauty. Messier 36 is intermediate brightness of the trio and you’ll quite enjoy its “X” shape and many pairings of stars!

Has the central double changed with time? Why not observe for yourself and see!

Object Name: Messier 36
Alternative Designations: M36, NGC 1960, Pinwheel Cluster
Object Type: Galactic Open Star Cluster
Constellation: Auriga
Right Ascension: 05 : 36.1 (h:m)
Declination: +34 : 08 (deg:m)
Distance: 4.1 (kly)
Visual Brightness: 6.3 (mag)
Apparent Dimension: 12.0 (arc min)

We have written many interesting articles about Messier Objects here at Universe Today. Here’s Tammy Plotner’s Introduction to the Messier Objects, , M1 – The Crab Nebula, M8 – The Lagoon Nebula, and David Dickison’s articles on the 2013 and 2014 Messier Marathons.

Be to sure to check out our complete Messier Catalog. And for more information, check out the SEDS Messier Database.

Sources:

Messier 35 – the NGC 2168 Open Star Cluster

Welcome back to Messier Monday! In our ongoing tribute to the great Tammy Plotner, we take a look at the open star cluster known as Messier 35. Enjoy!

During the 18th century, famed French astronomer Charles Messier noted the presence of several “nebulous objects” in the night sky. Having originally mistaken them for comets, he began compiling a list of them so that others would not make the same mistake he did. In time, this list (known as the Messier Catalog) would come to include 100 of the most fabulous objects in the night sky.

One of these objects is known as Messier 35, a large open star cluster located in the northern constellation Gemini. M35 is the only Messier Object located in Gemini, and lies near the border with the adjacent constellations of  Taurus, Auriga and Orion. It consists several hundred stars that are scattered over an area that is about the same size as a Full Moon.

What You Are Looking At:

Messier 35 is 2,800 light years away from Earth and is relatively young as star clusters go, having formed only about 100 million years ago. The cluster occupies a region of space that is roughly 24 light years in diameter, and an area of 28 arc minutes on the sky – which is roughly equal to the size of the full Moon.

Image of Messier 35 obtained by the Two Micron All Sky Survey (2MASS). Credit: NASA/2MASS

M35 has a central mass that spans 11.4 light years (3.75 parsecs), with an estimated mass of 1600 to 3200 solar masses. While most of the molecule cloud from which it formed has been blown away, some of the material resides in the immediate vicinity of its stars. This can be seen in the way that light from its particularly bright blue stars is scattered to create a diffuse glow.

These are the hottest main sequence stars in the cluster, which correspond to a spectral classification of B3. M35 also contains more evolved stars, including several orange and yellow giants, which have longer lifespans than the more-massive blue stars (only a few tense of millions of years).

As a result, these stars will likely die out in the near future while the smaller stars continue to evolve, drastically affecting the cluster’s luminosity and appearance. In short, it will become redder and dimmer over time.

History of Observation:

This wonderful star cluster was discovered by Philippe Loys de Chéseaux 1745-46 and recovered again by John Bevis before 1750. However, we know and love it best as Messier Object 35, when it was penned into being by Charles Messier. As he wrote of the cluster upon observing it for the first time:

“In the night of August 30 to 31, 1764, I have observed a cluster of very small stars, near the left foot of Castor, little distant from the stars Mu and Eta of that constellation [Gemini]. When examining this star cluster with an ordinary refractor of 3 feet, it seemed to contain nebulosity; but having examined it with a good Gregorian telescope which magnified 104 times, I have noticed that it is nothing but a cluster of small stars, among which there are some which are of more light; its extension may be 20 minutes of arc. I have compared the middle of this cluster with the star Eta of Castor; its right ascension has been concluded at 88d 40′ 9″, and its declination at 24d 33′ 30″ north.”

Close-up of the Messier 35 open star cluster, showing its blue stars. Credit: Wikisky

How long would it be before the companion cluster was observed as well? My guess is Sir William Herschel’s time. Although Herschel would not publish his notes on Messier objects, they do state while observing M35 that “There is no central condensation to denote a globular form.”

And what of Admiral Smyth? He observed the cluster in September of 1836, though he appeared to have missed its companion cluster. As he recorded of M35 at the time:

“A cluster, near Castor’s right foot, in the Galaxy, discovered and registered by Messier in 1764. It presents a gorgeous field of stars from the 9th to the 16th magnitudes, but with the center of mass less rich than the rest. From the small stars being inclined to form curves of three, four, and often with a large [bright] one at the root of the curve, it somewhat reminds one of the bursting of a sky-rocket.”

A nice description, but if you see the companion cluster, you’ll know it!

Locating Messier 35:

Locating M35 in binoculars is fairly easy once you recognize the constellation of Gemini. You’ll find it just a little more than the average field of view north of Eta – the center most of the three “foot” stars on the northernmost twin. In the finderscope of a telescope, begin with Eta and starhop north until you spot a faint fuzzy in the finderscope.

The location of Messier 35 in the norther n Gemini constellation. Credit: IAU/Sky & Telescope magazine/Roger Sinnott & Rick Fienberg

Because Messier 35 is large, you’ll need low magnification to appreciate the size of this cluster in a telecope. It stands up well to moonlight and light polluted skies – as well as less than perfect sky conditions, but you will need around a 10″ or larger telescope to really begin to notice its companion cluster, NGC 2158. In smaller telescopes with good conditions, it will appear as a faint nebulous patch.

And as always, here are the quick facts on M35 to get you started!

Object Name: Messier 35
Alternative Designations: M35, NGC 2168
Object Type: Galactic Open Star Cluster
Constellation: Gemini
Right Ascension: 06 : 08.9 (h:m)
Declination: +24 : 20 (deg:m)
Distance: 2.8 (kly)
Visual Brightness: 5.3 (mag)
Apparent Dimension: 28.0 (arc min)

We have written many interesting articles about Messier Objects here at Universe Today. Here’s Tammy Plotner’s Introduction to the Messier Objects, , M1 – The Crab Nebula, M8 – The Lagoon Nebula, and David Dickison’s articles on the 2013 and 2014 Messier Marathons.

Be to sure to check out our complete Messier Catalog. And for more information, check out the SEDS Messier Database.

Sources:

Messier 34 – the NGC 1039 Open Star Cluster

Welcome back to Messier Monday! In our ongoing tribute to the great Tammy Plotner, we take a look at the Triangulum Galaxy, also known as Messier 33. Enjoy!

During the 18th century, famed French astronomer Charles Messier noted the presence of several “nebulous objects” in the night sky. Having originally mistaken them for comets, he began compiling a list of them so that others would not make the same mistake he did. In time, this list (known as the Messier Catalog) would come to include 100 of the most fabulous objects in the night sky.

One of these objects is known as Messier 34, an open star cluster located in the northern Perseus constellation. Located at a distance of about 1,500 light years from Earth, it is one of the closest Messier objects to Earth, and is home to an estimated 400 stars. It is also bright enough to be seen with the naked eye or binoculars, where light conditions permit.

What You Are Looking At:

This cluster of stars started its journey off together through our galaxy some 180 million years ago as part of the “Local Association”… groups of stars like the Pleiades, Alpha Persei Cluster and the Delta Lyrae Cluster that share a common origin, but have become gravitationally unbound and are still moving together through space. We know the stars are related by their common movement and ages, but what else do we know about them?

The core region of the Messier 34 open star cluster. Credit: Wikisky

Well, one thing we do know is that out of the 354 stars in the region survey, 89 of them are actual cluster members and that all six of the visual binaries and three of the four known Ap stars are members of the cluster. There’s even a giant among them! But like almost all stars out there, we know they usually aren’t singles and actually have companions. As Theodore Simon wrote in his 2000 study regarding NGC 1039 and NGC 3532:

“Roughly half the sources detected in both images have likely optical counterparts from earlier ground-based surveys. The remainder are either prospective cluster members or foreground/background stars, which can be decided only through additional photometry, spectroscopy, and proper-motion studies. There is some indication (at the 98% confidence level) that solar-type stars may lack the extreme rotation and activity levels shown by those in the much younger Pleiades and alpha Persei clusters, but a detailed assessment of the coronal X-ray properties of these clusters must await more sensitive observations in the future. If confirmed, this finding could help to rule out the possibility that stellar dynamo activity and rotational braking are controlled by a rapidly spinning central core as stars pass through this phase of evolution from the Pleiades stage to that represented by the Hyades.”

If there’s companion stars to be discovered, what else might be in the field that we just can quite “see”? Try white dwarfs. As Kate Rubin (et al.) published in the May 2008 issue of the Astronomical Journal:

“We present the first detailed photometric and spectroscopic study of the white dwarfs (WDs) in the field of the ~225 Myr old (log ?cl = 8.35) open cluster NGC 1039 (M34) as part of the ongoing Lick-Arizona White Dwarf Survey. Using wide-field UBV imaging, we photometrically select 44 WD candidates in this field. We spectroscopically identify 19 of these objects as WDs; 17 are hydrogen-atmosphere DA WDs, one is a helium-atmosphere DB WD, and one is a cool DC WD that exhibits no detectable absorption lines. Of the 17 DAs, five are at the approximate distance modulus of the cluster. Another WD with a distance modulus 0.45 mag brighter than that of the cluster could be a double-degenerate binary cluster member, but is more likely to be a field WD. We place the five single cluster member WDs in the empirical initial-final mass relation and find that three of them lie very close to the previously derived linear relation; two have WD masses significantly below the relation. These outliers may have experienced some sort of enhanced mass loss or binary evolution; however, it is quite possible that these WDs are simply interlopers from the field WD population.”

Close-up image of M34 showing its white dwarf population, taken by the Sloan Digital Sky Survey. Credit: SDSS

While it sounds a little confusing, it’s all about how star clusters evolve. As David Soderblom wrote in a 2001 study:

“We analyze Keck Hires observations of rotation in F, G, and K dwarf members of the open cluster M34 (NGC 1039), which is 250 Myr old, and we compare them to the Pleiades, Hyades, and NGC 6475. The upper bound to rotation seen in M34 is about a factor of two lower than for the 100 Myr-old Pleiades, but most M34 stars are well below this upper bound, and it is the overall convergence in rotation rates that is most striking. A few K dwarfs in M34 are still rapid rotators, suggesting that they have undergone core-envelope decoupling, followed by replenishment of surface angular momentum from an internal reservoir. Our comparison of rotation in these clusters indicates that the time scale for the coupling of the envelope to the core must be close to 100 Myr if decoupling does, in fact, occur.”

History of Observation:

M34 was probably first found by Giovanni Batista Hodierna before 1654, and independently rediscovered by Charles Messier in on August 25, 1764. As he described it in his notes:

“I have determined the position of a cluster of small stars between the head of the Medusa and the left foot of Andromeda almost on the parallel of the star Gamma of that letter constellation. With an ordinary refractor of 3 feet, one distinguishes these stars; the cluster may have 15 minutes in extension. I have determined its position with regard to the star Beta in the head of the Medusa; its right ascension has been concluded at 36d 51′ 37″, and its declination as 41d 39′ 32″ north.”

Image of Messier 34 taken by the Two Micron All-Sky Survey (2MASS) of Messier 34 (also known as M34 or NGC 1039). Credit: 2MASS/UMass/IPAC-Caltech/NASA/NSF

Over the years, a great many historic observers would turn a telescope its way to examine it – also looking for more. Said Sir William Herschel: “A cluster of stars; with 120, I think it is accompanied with mottled light, like stars at a distance.” Yet very little more can be seen except for the fact that most of the stars seem to be arranged in pairs – the most notable being optical double in the center – h 1123 – which was cataloged by Sir John Herschel on December 23rd, 1831.

Charles Messier discovered it independently on August 25th, 1764, and included it in the Messier Catalog. As he wrote in the first edition of the catalog:

“In the same night of [August] 25 to 26, I have determined the position of a cluster of small stars between the head of the Medusa [Algol] & the left foot of Andromeda almost on the parallel of the star Gamma of that letter constellation. With an ordinary [non-achromatic] refractor of 3 feet [FL], one distinguishes these stars; the cluster may have 15 minutes in extension. I have determined its position with regard to the star Beta in the head of the Medusa; its right ascension has been concluded at 36d 51? 37?, & its declination as 41d 39? 32? north.”

But as always, it was Admiral William Henry Smyth who described the object with the most florid prose. As he wrote in his notes when observing the cluster in October 1837, he noted the following:

“A double star in a cluster, between the right foot of Andromeda and the head of Medusa; where a line from Polaris between Epsilon Cassiopeiae and Alpha Persei to within 2deg of the parallel of Algol, will meet it. A and B, 8th magnitudes, and both white. It is in a scattered but elegant group of stars from the 8th to the 13th degree of brightness, on a dark ground, and several of them form into coarse pairs. This was first seen and registered by Messier, in 1764, as a “mass of small stars;” and in 1783 was resolved by Sir W. Herschel with a seven-foot reflector: with the 20-foot he made it “a coarse cluster of large stars of different sizes.” By the method he applied to fathom the galaxy, he concluded the profundity of this object not to exceed the 144th order.”

The location of Messier 34 in the northern Perseus constellation. Credit: IAU and Sky & Telescope magazine (Roger Sinnott & Rick Fienberg)

Locating Messier 34:

M34 is easily found in binoculars about two fields of view northwest of Algol(Beta Persei). You will know when you have found this distinctive star cluster because “X” marks the spot! In a telescope finderscope, it will appear as a faint, hazy spot and will fully resolve to most average telescopes. Messier 34 makes an excellent target for moonlit nights or light polluted areas and will stand up well to less than perfect sky conditions.

It can even be seen unaided from ideal locations! Enjoy your observations!

And as always, we’ve included the quick facts on this Messier Object to help you get started:

Object Name: Messier 34
Alternative Designations: M34, NGC 1039
Object Type: Galactic Open Star Cluster
Constellation: Perseus
Right Ascension: 02 : 42.0 (h:m)
Declination: +42 : 47 (deg:m)
Distance: 1.4 (kly)
Visual Brightness: 5.5 (mag)
Apparent Dimension: 35.0 (arc min)

We have written many interesting articles about Messier Objects here at Universe Today. Here’s Tammy Plotner’s Introduction to the Messier Objects, , M1 – The Crab Nebula, M8 – The Lagoon Nebula, and David Dickison’s articles on the 2013 and 2014 Messier Marathons.

Be to sure to check out our complete Messier Catalog. And for more information, check out the SEDS Messier Database.

Sources: