Palomar globular clusters

The Palomar globular clusters are some of the faintest of all globular clusters in the Milky Way galaxy, and been discovered in the 1950s on the survey plates of the first Palomar Observatory Sky Survey (POSS).[1] In total there are 15 Palomar globular clusters, which include Palomar 1,[2] Palomar 2,[3] Palomar 3,[4] Palomar 4,[5] Palomar 5,[6] Palomar 6,[7] Palomar 7,[8] Palomar 8[9] Palomar 9,[10] Palomar 10,[11] Palomar 11,[12] Palomar 12,[13] Palomar 13,[14] Palomar 14,[15] and Palomar 15.[16] Some Palomar Globulars, like Palomar 6, Palomar 7, Palomar 9, Palomar 10 and Palomar 11 are clusters of average size located nearby, yet obscured in our line of sight by dust. Other Palomar globulars, like Palomar 3, Palomar 4 and Palomar 14 are giants located in the far outer halo of the Milky Way. Observation of different Palomar globulars greatly varies in the degree of difficulty depending on the cluster.

Hale Telescope at Palomar Observatory
Photo of Palomar 6 taken by the Hubble Space Telescope
Palomar 5 located between the two bright stars in the bottom left and top right corners.

History

The Palomar globulars have been discovered fairly late due to them being very faint, heavily obscured, remotely located or having few member stars. For this reason, these were discovered only with the enormous 48-inch Schmidt camera at Palomar. Some of the astronomers who identified these objects as globular clusters include George Abell, Fritz Zwicky, Edwin Hubble, Halton Arp and Walter Baade. All Palomar globulars except two, Palomar 7 (IC1276) and Palomar 9 (NGC6717), have never been seen before. Palomar 9 was observed by William Herschel back on August 7, 1784. Palomar 7 was first discovered by an American astronomer Lewis Swift in 1889, and was independently rediscovered by George Abell as part of the survey in 1952.[17]

Palomar globulars catalogue
Catalogue of Palomar globular clusters[18]
Palomar Constellation RA DEC Size (arcmin) Magnitude Distance from sun (kly) Distance from Galactic Centre (kly)
1 Cepheus 03h 33m 23.0s +79d:34m:50s 2.8 13.18 35.6 55.4
2 Auriga 04h:46m:05.9s +31d:22m:51s 2.2 13.04 90.0 115.5
3 Sextans 10h:05m:31.4s +00d:04m:17s 1.6 14.26 302.3 312.8
4 Ursa Major 11h:29m:16.8s +28d:58m:25s 1.3 14.20 356.2 364.6
5 Serpens 15h:16m:05.3s -00d:06m:41s 8.0 11.75 75.7 60.7
6 Ophiuchus 17h:43m:42.2s -26d:13m:21s 1.2 11.55 19.2 7.2
7 (IC1276) Serpens 18h:10m:44.2s -07d:12m:27s 8.0 10.34 17.6 12.1
8 Sagittarius 18h:41m:29.9s -19d:49m:33s 5.2 11.02 42.1 18.3
9 (NGC6717) Sagittarius 18h:55m:06.2s -22d:42m:03s 5.4 9.28 23.1 7.8
10 Sagitta 19h:18m:02.1s +18d:34m:18s 4.0 13.22 19.2 20.9
11 Aquilla 19h:45m:14.4s -0.8d:00m:26s 10 9.80 42.4 25.8
12 Capricornus 21h:46m:38.8s -21d:15m:03s 2.9 11.99 62.3 51.9
13 Pegasus 23h:06m:44.4s +12d:46m:19s 0.7 13.80 84.1 87.0
14 Hercules 16h:11m:04.9s +14d:57m:29s 2.2 14.74 241.0 225.0
15 Ophiuchus 17h:00m:02.4s -00d:32m:31s 3.0 14.00 145.5 123.6

Visual observation

The Palomar globulars can be observed and identified by amateur astronomers, however dark skies and high power are required. Astronomers have made reports on visual observations using 17.5 inch and larger telescopes.[19][20] Overall, there is great variability in the level of difficulty to observe these objects, yet, for successful observation, skies with no light-pollution and excellent seeing conditions coupled with high power (at least 200 power magnification) are necessary. Many Palomars are small objects and require the observer to know how to navigate the sky precisely, and rely on averted vision when needed. In some Palomars, visual observers can resolve individual stars, while others look hazy. Palomar 9 (NGC 6717) is the easiest object to observe of the Palomar globulars, while Palomar 15 is regarded as the most difficult.

Additional resources

References
  1. Abell, G. 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): 258–261. Bibcode:1955PASP...67..258A. doi:10.1086/126815. ISSN 0004-6280. JSTOR 40676260. S2CID 208869169.
  2. Rosenberg, A., Saviane, I., Piotto, G., Aparicio, A., & Zaggia, S. R. (1998). Palomar 1: Another Young Galactic Halo Globular Cluster?. The Astronomical Journal, 115(2), 648.
  3. Bonatto, Charles; Chies-Santos, Ana L (2020-04-01). "Lifting the dust veil from the globular cluster Palomar 2". Monthly Notices of the Royal Astronomical Society. 493 (2): 2688–2693. doi:10.1093/mnras/staa510. hdl:10183/212352. ISSN 0035-8711.
  4. Catelan, M.; Ferraro, F. R.; Rood, R. T. (2001-10-20). "Horizontal‐Branch Models and the Second‐Parameter Effect. IV. The Case of M3 and Palomar 3". The Astrophysical Journal. 560 (2): 970–985. arXiv:astro-ph/0106554. Bibcode:2001ApJ...560..970C. doi:10.1086/323049. ISSN 0004-637X. S2CID 17178717.
  5. Zonoozi, Akram Hasani; Haghi, Hosein; Küpper, Andreas H. W.; Baumgardt, Holger; Frank, Matthias J.; Kroupa, Pavel (2014-06-01). "Direct N-body simulations of globular clusters – II. Palomar 4". Monthly Notices of the Royal Astronomical Society. 440 (4): 3172–3183. doi:10.1093/mnras/stu526. ISSN 1365-2966.
  6. Bonaca, Ana; Pearson, Sarah; Price-Whelan, Adrian M.; Dey, Arjun; Geha, Marla; Kallivayalil, Nitya; Moustakas, John; Muñoz, Ricardo; Myers, Adam D.; Schlegel, David J.; Valdes, Francisco (2020-01-27). "Variations in the Width, Density, and Direction of the Palomar 5 Tidal Tails". The Astrophysical Journal. 889 (1): 70. arXiv:1910.00592. Bibcode:2020ApJ...889...70B. doi:10.3847/1538-4357/ab5afe. ISSN 1538-4357. S2CID 203626938.
  7. Lee, J. W., & Carney, B. W. (2002). Near-Infrared Photometry of the Globular Cluster Palomar 6. The Astronomical Journal, 123(6), 3305.
  8. Barbuy, B., Ortolani, S., & Bica, E. (1998). Terzan 3 and IC 1276 (Palomar 7): Two metal-rich bulge globular clusters uncovered. Astronomy and Astrophysics Supplement Series, 132(3), 333-340.
  9. Astronomy and Astrophysics Supplement Series, Vol. 45, p. 53-60 (1981)
  10. Ortolani, S., Barbuy, B., & Bica, E. (1999). Colour-magnitude diagrams of the post-core collapse globular clusters NGC 6256 and NGC 6717 (Palomar 9). Astronomy and Astrophysics Supplement Series, 136(2), 237-243.
  11. Kaisler, D., Harris, W. E., & McLaughlin, D. E. (1997). Palomar 10 and NGC 6749: A Study in Contrasts. Publications of the Astronomical Society of the Pacific, 109(738), 920.
  12. Brian, Lewis, M. S. Liu, W. M. Paust, N. E. Q. Chaboyer (2006-01-13). A New Color-Magnitude Diagram for Palomar 11. OCLC 691210799.{{cite book}}: CS1 maint: multiple names: authors list (link)
  13. Cohen, J. (2003). Pal 12 As A Part of the Sgr Stream; the Evidence From Abundance Ratios. arXiv preprint astro-ph/0311187.
  14. M. H. Siegel et al 2001 AJ 121 935
  15. Sollima, A.; Martínez-Delgado, D.; Valls-Gabaud, D.; Peñarrubia, J. (2010-12-14). "Discovery of Tidal Tails Around the Distant Globular Cluster Palomar 14". The Astrophysical Journal. 726 (1): 47. doi:10.1088/0004-637x/726/1/47. ISSN 0004-637X. S2CID 118471604.
  16. Myeong, G. C.; Jerjen, Helmut; Mackey, Dougal; Da Costa, Gary S. (2017-05-11). "Tidal Tails around the Outer Halo Globular Clusters Eridanus and Palomar 15". The Astrophysical Journal. 840 (2): L25. arXiv:1704.07690. Bibcode:2017ApJ...840L..25M. doi:10.3847/2041-8213/aa6fb4. ISSN 2041-8213. S2CID 118856686.
  17. "Palling Around With Palomar Globular Clusters". Sky & Telescope. 2016-08-17. Retrieved 2022-06-04.
  18. Harris, W. E. (1996). A Catalog of Parameters for Globular Clusters in the Milky Way. AJ 112, 1487.
  19. "The Palomar Globulars". www.astronomy-mall.com. Retrieved 2022-06-03.
  20. "The Palomar Globular Clusters". www.deep-sky.co.uk. Retrieved 2022-06-03.
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