Messier 79

Messier 79 (also known as M79 or NGC 1904) is a globular cluster in the southern constellation Lepus. It was discovered by Pierre Méchain in 1780 and is about 42,000 light years away from Earth and 60,000 light years from the Galactic Center.

Messier 79
Observation data (J2000 epoch)
ClassV[1]
ConstellationLepus
Right ascension05h 24m 10.59s[2]
Declination−24° 31′ 27.3″[2]
Distance12.9 kpc (42 kly)[3]
Apparent magnitude (V)+8.56[2]
Apparent dimensions (V)8.7'
Physical characteristics
Metallicity = –1.55[4] dex
Estimated age11.7 Gyr[4]
Other designationsM79, NGC 1904, GCl 10, Melotte 34[2]

Like Messier 54 (the other extragalactic globular on Messier's list), it is thought that it is not native to the Milky Way galaxy at all, but instead to the putative Canis Major Dwarf Galaxy, which is currently experiencing a very close encounter with our galaxy. This is, however, a contentious subject as astronomers are still debating the nature of the Canis Major dwarf galaxy itself.[5]

Color-magnitude diagram
An infrared color-magnitude diagram of Messier 79.

This color-magnitude diagram was made using near-infrared images of the cluster in J and K bands. J-band magnitude is plotted along the y-axis and J to K dominant color is plotted along the x-axis. Such a diagram is made rapidly with specialized code for crowded-field photometry.[6]

From this, it is evident that most of the bright stars in this cluster are red giants. The elongated branch is the red giant branch. Some of the stars in the diagram, including those extending outward from the red giant branch toward the upper left, are actually foreground stars that are not members of the cluster.

Altogether three regions of the Hertzsprung-Russell diagram are present here: the low-mass end of the main sequence, the complete red giant branch and the horizontal branch. Compared to optical bands, in infrared bands the lower main sequence is shallower and the horizontal branch is steeper (the blue end is fainter and the red end is brighter).

References
  1. Shapley, Harlow; Sawyer, Helen B. (August 1927), "A Classification of Globular Clusters", Harvard College Observatory Bulletin, 849 (849): 11–14, Bibcode:1927BHarO.849...11S
  2. "M 79". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 17 November 2006.
  3. Harris, William E. (December 2010), A New Catalog of Globular Clusters in the Milky Way, arXiv:1012.3224, Bibcode:2010arXiv1012.3224H
  4. Koleva, M.; et al. (April 2008), "Spectroscopic ages and metallicities of stellar populations: validation of full spectrum fitting", Monthly Notices of the Royal Astronomical Society, 385 (4): 1998–2010, arXiv:0801.0871, Bibcode:2008MNRAS.385.1998K, doi:10.1111/j.1365-2966.2008.12908.x
  5. López-Corredoira, M.; Momany, Y.; Zaggia, S.; Cabrera-Lavers, A. (2007). "Re-affirming the connection between the Galactic stellar warp and the Canis Major over-density". Astronomy and Astrophysics. 472 (3): l47. arXiv:0707.4440. Bibcode:2007A&A...472L..47L. doi:10.1051/0004-6361:20077813.
  6. This diagram was made by Astromundus students attending lectures and a workshop by Peter Stetson, the writer of DAOPHOT, standard code for crowded-field photometry. Date: June 2011, University of Rome Tor Vergata

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