Posted on by Tammy Plotner

Kepler Drops In On Planetary Nebula

Gemini Observatory image of Kronberger 61 showing the ionized shell of expelled gas resembling a soccer ball. The light of the nebula here is primarily due to emission from twice-ionized oxygen, and its central star can be seen as the slightly bluer star very close to the center of the nebula. Credit: Gemini Observatory/AURA

[/caption]

Discovered by amateur Austrian astronomer, Matthias Kronberger, planetary nebula Kn 61 just happens to be in a relatively small piece of celestial real estate being monitored by NASA’s Kepler planet finding mission. Lucky for us, we’re able to take a look at the photographic results of the new nebula obtained with the Gemini Observatory.

“Kn 61 is among a rather small collection of planetary nebulae that are strategically placed within Kepler’s gaze,” said Orsola De Marco of Macquarie University in Sydney, Australia who is the author of a 2009 paper speculating on how companion stars or even planets may influence and shape the intricate structure seen in many planetary nebulae. “Explaining the puffs left behind when medium sized stars like our Sun expel their last-breaths is a source of heated debate among astronomers, especially the part that companions might play,” says De Marco, “it literally keeps us up at night!”

And visions like this keeps the Kepler Mission continually monitoring a 105 square degree area of sky located in Cygnus looking for changes in stellar brightness which could spell a planetary transit, companion star – or something else. “It is a gamble that possible companions, or even planets, can be found due to these usually small light variations,” says George Jacoby of the Giant Magellan Telescope Organization and the Carnegie Observatories (Pasadena). “However, with enough objects it becomes statistically very likely that we will uncover several where the geometries are favorable – we are playing an odds game and it isn’t yet known if Kn 61 will prove to have a companion.” Jacoby also serves as the Principal Investigator for a program to obtain follow-up observations of Kn 61’s central star with Kepler.

To help sift through the huge amount of data provided by Kepler, professional and amateur astronomers are working as partners to help locate objects such as planetary nebula. So far, six have been found in the digital sky survey – including Kn 61. “Without this close collaboration with amateurs, this discovery would probably not have been made before the end of the Kepler mission. Professionals, using precious telescope time, aren’t as flexible as amateurs who did this using existing data and in their spare time. This was a fantastic pro-am collaboration of discovery,” says Jacoby, who serves as the liaison with the Deep Sky Hunters (DSH) and requested their help to survey the Kepler field. Jacoby published a paper with DSH members in 2010 that describes the techniques used.

“Planetary nebulae present a profound mystery,” says De Marco. “Some recent theories suggest that planetary nebulae form only in close binary or even planetary systems – on the other hand, the conventional textbook explanation is that most stars, even solo stars like our sun, will meet this fate. That might just be too simple.” Jacoby also elucidates that terrestrial observations are unable to detect such phenomena with a high rate of regularity “This is quite likely due to our inability to detect these binaries from the ground and if so then Kepler is likely to push the debate strongly in one direction or the other.”

As for our own galaxy, over 3,000 planetary nebulae have been identified and cataloged. We know they are the end product of a dying star, but not what role companions stars (or even planets) may take in their structure. Of these, only 20% have binary central stars – but this low number may be our inability to resolve them. Hopefully the space-based Kepler telescope can one day reveal their mysteries us!

Original News Source: Gemini Observatory Image Release.

Posted on by Nancy Atkinson

WISE Captures a Glowing Cylinder in Space

NGC 1514, sometimes called the "Crystal Ball" nebula shows a new double ring feature in an image from WISE. Image credit: NASA/JPL-Caltech/UCLA

[/caption]

It’s not like we’ve never seen the planetary nebula NGC 1514 before, but we’ve never seen it though WISE’s infrared eyes, until now. And in a stunning surprise, cylindrical rings appear to be encircling the dying star, like a neon-lit carousel, or perhaps like rolling tire surrounding a glowing blob. “I just happened to look up one of my favorite objects in our WISE catalogue and was shocked to see these odd rings,” said Michael Ressler, a member of the WISE science team at JPL. “This object has been studied for more than 200 years, but WISE shows us it still has surprises.

Space station from the movie 2001: A Space Odyssey.

At first glance the rings look like the double-ringed space station in the movie 2001: A Space Odyssey. (Too bad the Bad Astronomer beat me to that likeness. He also compared it to a tuna can.)

Other people see different things in this image.

“I am reminded of the jellyfish exhibition at the Monterey Bay Aquarium — beautiful things floating in water, except this one is in space,” said Edward (Ned) Wright, the principal investigator of the WISE mission at UCLA, and a co-author of a paper on the findings, reported in the Astronomical Journal.

WISE was able to spot the rings for the first time because their dust is being heated and glows with the infrared light that WISE can detect. In visible-light images, the rings are hidden from view, overwhelmed by the brightly fluorescing clouds of gas.

Here’s what NGC 1514 looks like in visible light from a ground observatory:

NGC1514 in visible light. Image credit: Digitized Sky Survey/STScI

The object is actually a pair of stars, seen as a single dot at the center of the blue orb. One star is a dying giant somewhat heavier and hotter than our sun, and the other was an even larger star that has now contracted into a dense body called a white dwarf. As the giant star ages, it sheds some its outer layers of material. An inner shell of ejected material is seen in bright, light blues. An outer shell can also be seen in more translucent shades of blue.

This planetary nebula is also called the “Crystal Ball” nebula, and Ressler said although NGC 1514’s structure looks unique, is probably similar in overall geometry to other hour-glass nebulae, such as the Engraved Hourglass Nebula.

Planetary Nebula MyCn18: An Hourglass Pattern Around a Dying Star. Credit: Raghvendra Sahai and John Trauger (JPL), the WFPC2 science team, and NASA.

The structure looks different in WISE’s view because the rings are detectable only by their heat; they do not fluoresce at visible wavelengths, as do the rings in the other objects.

The WISE science team says that more oddballs like NGC 1514 are sure to turn up in the plethora of WISE data — the first batch of which will be released to the astronomical community in spring 2011.

Source: JPL

Posted on by Nancy Atkinson

Chinese Dragon in Space!

NGC 5189. Credit: ESO

[/caption]
This new image from the ESO telescope in Chile shows what looks like a Chinese dragon in the sky. But really, it is NGC 5189 an S-shaped planetary nebula adorned with red and green cosmic fireworks. This dragon isn’t breathing fire – the colorful “smoke” is a signal that a star is dying.

At the end of its life, a star with a mass less than eight times that of the Sun will blow its outer layers away, giving rise to a planetary nebula. Some of these stellar puffballs are almost round, resembling huge soap bubbles or giant planets (hence the name), but others, such as NGC 5189 are more intricate.

In particular, this planetary nebula exhibits a curious “S”-shaped profile, with a central bar that is most likely the projection of an inner ring of gas discharged by the star, seen edge on. The details of the physical processes producing such a complex symmetry from a simple, spherical star are still the object of astronomical controversy. One possibility is that the star has a very close (but unseen) companion. Over time the orbits drift due to precession and this could result in the complex curves on the opposite sides of the star visible in this image.

This image has been taken with the New Technology Telescope at ESO’s La Silla Observatory in Chile, using the now decommissioned EMMI instrument. It is a combination of exposures taken through different narrowband filters, each designed to catch only the light coming from the glow of a given chemical element, namely hydrogen, oxygen and nitrogen.

Source: ESO

Posted on by Jean Tate

Planetary Nebulae

No, planetary nebulae are not nebulae found around planets; nor are they nebulae produced by planets … rather, they got stuck with this name because the first ones to be observed (and written about) look like planets (well, they did through the eyepieces of the telescopes of the time … somewhat).

Charles Messier – yep, the comet hunting guy – listed M27 in his famous catalog; that’s the Dumbbell Nebula, and the first planetary nebula recorded (1764). It was Herschel – the guy who discovered Uranus – who dreamed up the name ‘planetary nebula’; and why? Because, to him, they looked a bit like the gas giants Jupiter, Saturn, and Uranus (Neptune wasn’t discovered then). There are four planetary nebulae in Messier’s list; in addition to M27, there’s M57 (the Ring Nebula), M76 (Little Dumbbell Nebula), and M97 (Owl Nebula). So why did Herschel say planetary nebulae looked like giant planets, including Saturn? Because, in 1781, he discovered one – NGC 7009 – that looked like Saturn! Guess what it’s called? The Saturn Nebula.

When spectroscopes were used to observe planetary nebulae, they caused excitement; unlike stars and (what we today call) galaxies – which have dark absorption lines in their spectra – planetary nebula have bright emission lines (and essentially nothing else, i.e. no continuum emission). Further, the brightest of the lines (actually two, close together), in most planetary nebulae, corresponded to nothing ever seen in any laboratory spectrum … so they were thought to be caused by an as yet undiscovered element, called nebulium.

Today we understand planetary nebulae to be a short-lived phase of (most) stars … after the red giant phase, when the star’s fuel has been exhausted, it shrinks to become a white dwarf. The gas expelled during the red giant phase become heated and ionized by the intense UV radiation of the new white dwarf (these central objects, in most planetary nebulae, are among the hottest stars). The plasma has an extremely low density, which means that certain excited, meta-stable states of ions such as O2+ can jump to a lower energy state by emission of ‘forbidden’ radiation (rather than by collision).

Such spectacular objects … no surprise that Universe Today has many stories and articles on planetary nebulae! Here are just a few Found: Planetary Nebula Around Heavy Stars, Planets May Actually Shape Planetary Nebulae, Will We Look Like This in 5 Billion Years?, and Penetrating New View Into The Helix Nebula.

Astronomy Cast’s Nebulae has more on planetary nebulae; the following episodes put planetary nebulae into a broader astronomical context: The End of the Universe Part 1: The End of the Solar System, The Life of the Sun, and The Life of Other Stars.

Source: SEDS

Posted on by Nicholos Wethington

Very First Image of a Very Hot Star

No, this article is not about Johnny Depp or Angelina Jolie. They may be hot stars, but in comparison to the star at the center of the Bug Nebula, pictured left, they’ve got nothin’. The first image of the star at the center of the Bug Nebula (NGC 6302) has been taken by a team of astronomers at the Jodrell Bank Centre for Astrophysics, using the newly refurbished Hubble Space Telescope. This star, one of the hottest in the galaxy, has a temperature of about 200,000 Kelvin – 33 times hotter than the Sun – and is at the center of one of the most beautiful planetary nebula in the galaxy.

The star at the heart of the Bug Nebula, which lies about 3500 light-years away from Earth in the constellation Scorpius, is what gives the two lobes of the formation their glow. Its extreme temperature of at least 200,000 K (and possibly up to 400,000 K) ionizes the gas in the nebula, which is itself composed of ejecta from the star as it shed its corona during the later stages of its life. The star has gone through its red giant phase and is now a late-stage white dwarf.

As a comparison to how hot the star powering the luminosity of the Bug Nebula is, our Sun’s hottest temperature is 5,800 Kelvin which is about 5,500 degrees Celsius and almost 10,000 degrees Fahrenheit. The mass of the star is calculated to be 0.64 solar masses, though it was many times heavier than the Sun before it ejected much of its matter into the nebula.

The astronomers were lucky to have been able to image the star at this point in its life, as the light it is emitting is fading at about 1% a year. Professor Albert Zijlstra of the University of Manchester said in an email interview, “The star seems to be in a phase where nuclear burning has ceased very recently (within the past 100-1000 yr). It is radiating its left-over surface heat away, and that goes quickly. At some time heat from interior will take over, and as that is a much larger heat reservoir, the star will fade much more slowly from that point.”

This does not mean, however, that the ionized gas in the nebula will fade out quite as quickly, Zijlstra said. ‘The nebula is ionized by ultra-violet photons from the star. The ionized elements recombine with electrons, before being re-ionized. Normally, there is a good balance between ionizations and recombinations. In NGC 6302, if the star is fading rapidly, it is possible that the time scale for recombinations is longer than the time over which the star fades. The nebula would ‘remember’ a more luminous star, and be ionized to a higher degree than the star could currently support. It is like living off your savings.”The Bug Nebula, as imaged by the Hubble Space Telescope's Wide-Field Camera 3. Image Credit: Anthony Holloway, JBCA

There have been many attempts at imaging this star, but the brightness of the nebula combined with the dust obscuring the star made imaging difficult. Only with the new Wide-Field Camera 3, installed on the Hubble earlier this year, were the astronomers able to make out the star buried in the heart of the Bug Nebula.

Zijlstra said of the Hubble’s capabilities, “It is a combination of sensitivity and available filters. The nebula is very bright, and it is difficult to detect the faint star against the very bright nebular background. To get the best sensitivity, you need high resolution (which dilutes the nebulae light while concentrating the stellar light – this requires HST), good sensitivity and ideally, a filter which excludes the brightest emission lines (H alpha, [O III]). We detected the star with two different filters which select fainter emission lines, which reduces the glare from the nebula. The extinction through the dust in the nebula is also very high, which makes the star even fainter especially in the blue.”

Further observations of the star are definitely in order, including molecular and dust spectroscopy, but Zijlstra said his team does not have any observations of the star planned as of now. The results of the imaging and calculations detailing the properties of the star will be published in The Astrophysical Journal, but a pre-print article is available on Arxiv.

A zoom animation of some of the images put together is also available on the Jodrell Bank Centre for Astrophysics site right here.

Source: Jodrell Bank press release, email interview with Albert Zijlstra

Posted on by Nancy Atkinson

Found: Planetary Nebula Around Heavy Stars

An optical image from the 0.6-m University of Michigan/CTIO Curtis Schmidt telescope of the brightest Radio Planetary Nebula in the Small Magellanic Cloud, JD 04. The inset box shows a portion of this image overlaid with radio contours from the Australia Telescope Compact Array. The planetary nebula is a glowing record of the final death throes of the star. (Optical images are courtesy of the Magellanic Cloud Emission Line Survey (MCELS) team).

[/caption]
Planetary nebula – the glowing gaseous shells thrown off by stars during the latter stages of their evolution – were thought to only form around stars the size of our Sun or smaller. Although astronomers had predicted these shells should form around “heavier” stars, none had ever been detected. Until now. An international team of scientists have discovered a new class of object which they call “Super Planetary Nebulae,” found around stars up to 8 times the mass of the Sun.  

“This came as a shock to us,” said Miroslav Filipovic from the University of Western Sydney “as no one expected to detect these object at radio wavelengths and with the present generation of radio telescopes. We have been holding up our findings for some 3 years until we were 100% sure that they are indeed Planetary Nebulae”.

 The team surveyed the Magellanic Clouds, the two companion galaxies to the Milky Way, with radio telescopes of the Commonwealth Scientific and Industrial Research Organisation (CSIRO) Australia Telescope National Facility. They noticed that 15 radio objects in the Clouds match with well known planetary nebulae observed by optical telescopes.
 
The new class of objects are unusually strong radio sources and are associated with larger original stars (progenitors), up to 8 times the mass of the Sun. The nebular material around each star may have as much as 2.6 times the mass of the Sun.

Filipovic’s team argues that the detections of these new objects may help to solve the so called “missing mass problem” – the absence of planetary nebulae around central stars that were originally 1 to 8 times the mass of the Sun. Up to now most known planetary nebulae have central stars and surrounding nebulae with respectively only about 0.6 and 0.3 times the mass of the Sun but none have been detected around more massive stars.

Some of the 15 newly discovered planetary nebulae in the Magellanic Clouds are 3 times more luminous than any of their Milky Way cousins. But to see them in greater detail astronomers will need the power of a coming radio telescope – the Square Kilometre Array planned for the deserts of Western Australia.

The scientist’s paper appears in the journal Monthly Notices of the Royal Astronomical Society.

Lead image caption: An optical image from the 0.6-m University of Michigan/CTIO Curtis Schmidt telescope of the brightest Radio Planetary Nebula in the Small Magellanic Cloud, JD 04. The inset box shows a portion of this image overlaid with radio contours from the Australia Telescope Compact Array. The planetary nebula is a glowing record of the final death throes of the star. (Optical images are courtesy of the Magellanic Cloud Emission Line Survey (MCELS) team).

Source: RAS