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Object Name: Messier 93
Alternative Designations: M93, NGC 2447
Object Type: Type g Open Star Cluster
Right Ascension: 07 : 44.6 (h:m)
Declination: -23 : 52 (deg:m)
Distance: 3.6 (kly)
Visual Brightness: 6.0 (mag)
Apparent Dimension: 22.0 (arc min)
Locating Messier 93: Thanks to what seems like the brighter stars of the winter constellations, M93 isn’t too hard to find… All you need to do is get Sirius! Slightly less than a fistwidth southeast of one of the brightest stars in the night sky, you’ll spy fainter north/south pairing of Omicron 1 and Omicron 2 Canis Majoris. M93 is located along the identical parallel (declination). Now continue your starhop another fistwidth (10 degrees) to Xi Puppis and you’ll catch it to the north. Very bright and resolvable, M93 works well witn any size optics (binoculars or telescopes) and makes a splendid urban target and holds up very well to “moon pollution”!
What You Are Looking At: Hanging out in space some 3,600 light years away and covering an expanse of nearly 25 light years, M93′s brightest stars are type B9 blue giants of type B9 with a estimated age of roughly 100 million years. But blue giant stars aren’t the only type you’ll find here. There are at least 3 red giant stars as well.
“Chemical abundances of about fifteen elements from oxygen to europium are measured in seven red giants of the two open clusters NGC 2360 and NGC 2447. The effective temperatures of the giants are determined spectroscopically by taking advantage of their known masses (~2 Mo in NGC 2360 and ~3 Mo in NGC 2447) and bolometric magnitudes. The average iron abundances we obtain for the two clusters are [Fe/H]=0.07 for NGC 2360 and [Fe/H]=0.03 for NGC 2447. Evolutionary stellar model calculations are performed in the mass range 1-4 Mo in order to analyze the surface Na and O abundances predicted after the first dredge-up. The sodium abundance shows a well defined correlation with stellar mass in the 2-3 Mo range.
The agreement between our Na abundance determinations in NGC 2360 and our model predictions at 2 Mo is very good. In contrast, the overabundance in one of the three stars in NGC 2447 exceeds that predicted at 3 Mo by ~0.08 dex, which is significant compared to the observational error bars.” says S. Hamdan (et al). “The effects of core overshooting, convection prescription, metallicity and nuclear reaction rates on the Na surface predictions of our models are investigated. An oxygen deficiency relative to iron by 0.2 dex is measured in our stars, in disagreement with our model predictions. Assuming that the Sun is 0.1-0.3 dex enriched in oxygen relative to neighbor stars could explain the discrepancy.”
So why are studies like the 2MASS project so important when it comes to something like a open star cluster? “We use Two Micron All-Sky Survey (2MASS) to study open clusters in the solar neighborhood. Dias (2003) compiles a catalogue of optical open clusters from literature. The error and consistency are difficult to estimate due to different observational systems and resources. In order to study the effect of dynamical evolution and galactic location on open clusters, we use radial density profile from 2MASS point source catalogue to reestimate the size of clusters. We also discuss the difference between different methods.” says H.C. Lee. ” We find that the sizes of old open clusters are larger, and the number densities of them are smaller. Old open clusters are distributed higher from the disk. We work out the main sequence luminosity function and main sequence mass function of 17 open clusters. We do not find the relation between age and luminosity function and mass function. We conclude that in the contest of main sequence luminosity function and mass function, 2MASS data is suitable for clusters within 2 kpc from the sun and age less than 3×10 8 yr only. Moreover, we find that an interesting result, the power index of field-star luminosity functions on different locations are very similar, the average value is 0.336±0.01″
History: Discovered on March 20, 1781 by Charles Messier and logged as: “Cluster of small stars, without nebulosity, between the Greater Dog [Canis Major] and the prow of the ship [Puppis of Argo Navis].”, M93 would begin the astronomy career of one very special lady – Caroline Herschel.
On February 26, 1783, Caroline Herschel did something no other woman had done before her… used her own telescope to located a deep space object and begin her own catalog of observations. In her notes she writes: “Nebula, about 1 1/4 deg north preceding the bright star in the Ship [or more exactly] preceding the 1st Navis [Puppis] towards 23 Canis majoris. My Brother examined it with [magnification] 460 and found not less than 20 stars, with 227 above 40. with a compound eyepiece perhaps 100 and 150 very beautiful, nothing nebulous among them. Messier has it not.”
Although Charles Messier gets the full credit for discovery and logging M93, enjoy this bright and beautiful cluster of stars as the “Opening Night” of the first lady of astronomy!
Top M93 image credit, Palomar Observatory courtesy of Caltech, M923 HR Diagram (AANDA), M93 2MASS image and M93 image courtesy of NOAO/AURA/NSF.