Palomar 12

Palomar 12
Palomar 12 by Hubble Space Telescope, 3.36′ view
Observation data (J2000 epoch)
ClassXII
ConstellationCapricornus
Right ascension21h 46m 38.84s[1]
Declination–21° 15′ 09.4″[1]
Distance63.6 ± 2.9 kly (19.50 ± 0.89 kpc)[2]
Apparent magnitude (V)11.99
Apparent dimensions (V)17.4′
Physical characteristics
Mass1.59×104[3] M☉
Radius162 ± 8 ly[4]
Metallicity = –0.85[3] dex
Estimated age6.5 Gyr[5]
Notable featuresProbably extragalactic
Other designationsGCl 123[6]
See also: Globular cluster, List of globular clusters

Palomar 12 is a globular cluster in the constellation Capricornus, and is a member of the Palomar Globular Clusters group.

First discovered on the National Geographic Society – Palomar Observatory Sky Survey plates by Robert George Harrington and Fritz Zwicky,[7] it was initially catalogued as a globular cluster; however, Zwicky came to believe it was actually a nearby dwarf galaxy in the Local Group. It is a relatively young cluster, being about 30% younger than most of the globular clusters in the Milky Way.[2] It is metal-rich with a metallicity of [Fe/H] ≈ −0.8.[5] It has an average luminosity distribution of Mv = −4.48.[8]

Based on proper motion studies, this cluster was first suspected in 2000 to have been captured from the Sagittarius Dwarf Elliptical Galaxy (SagDEG) about 1.7 Ga ago.[9] It is now generally believed to have originated in that galaxy and is associated with the Sagittarius Stream.[5] It is estimated to be 6.5 Gyr old.[5]

  1. ^ a b Cite error: The named reference aj140_6_1830 was invoked but never defined (see the help page).
  2. ^ a b Cite error: The named reference rosenberg was invoked but never defined (see the help page).
  3. ^ a b Cite error: The named reference apj742_1_51 was invoked but never defined (see the help page).
  4. ^ distance × sin( diameter_angle / 2 ) = 162 ly. radius
  5. ^ a b c d Cite error: The named reference Geisleretal2007 was invoked but never defined (see the help page).
  6. ^ Cite error: The named reference simbad was invoked but never defined (see the help page).
  7. ^ Abell, George O. (1955). "Globular Clusters and Planetary Nebulae Discovered on the National Geographic Society-Palomar Observatory Sky Survey". Publications of the Astronomical Society of the Pacific. 67 (397): 258. Bibcode:1955PASP...67..258A. doi:10.1086/126815.
  8. ^ van den Bergh, Sidney (July 2007). "The Luminosity Distribution of Globular Clusters in Dwarf Galaxies". The Astronomical Journal. 134 (1): 344–345. arXiv:0704.2226. Bibcode:2007AJ....134..344V. doi:10.1086/518868. S2CID 14209616.
  9. ^ D. I. Dinescu; S. R. Majewski; T. M. Girard; K. M. Cudworth (2000). "The Absolute Proper Motion of Palomar 12: A Case for Tidal Capture from the Sagittarius Dwarf Spheroidal Galaxy". The Astronomical Journal. 120 (4): 1892–1905. arXiv:astro-ph/0006314. Bibcode:2000AJ....120.1892D. doi:10.1086/301552. S2CID 118898193.