J/AJ/109/650 Arp 2 (Buonanno+ 1995)
Young Globular Clusters in the Milky Way: Arp 2
Buonanno R., Corsi C.E., Fusi Pecci F., Richer H.B., Fahlman G.G.
<Astron. J. 109, 650 (1995)>
=1995AJ....109..650B 1995AJ....109..650B
ADC_Keywords: Clusters, globular ; Photometry, CCD
Abstract:
We have obtained the first B,V CCD color-magnitude diagram (CMD) of
the galactic globular cluster Arp 2. About 1600 stars have been
measured between the tip of the red giant branch at V ∼ 15.5 and
V ∼ 23.5, about two magnitudes below the main sequence turnoff. A
centrally concentrated population of blue stragglers has been
detected. The slope of the red giant branch and the overall CMD
morphology are consistent with that of a metal-poor cluster, with
[Fe/H] = 18.4±0.25. A preliminary spectroscopic measurement based
on the Ca II triplet yields [Fe/H] = -1.73±0.05. The comparison of
the CMD of Arp 2 with that of other clusters favors a value more
metal-poor than that indicated by the Ca II triplet. In this respect,
Arp 2 is similar to Ruprecht 106 [Buonanno et al. =1990AJ....100.1811B 1990AJ....100.1811B
and =1993AJ....105..184B 1993AJ....105..184B]. Differential ages between Arp 2 and a
number of reference clusters are obtained from the vertical age
parameter Delta V^TO_HB, and the horizontal age parameter,
Δ(B-V)^TO_RGB. By requiring both age estimators to give
consistent results, we find that Arp 2 is ∼ 3 Gyr younger than the
group of the metal-poor clusters and slightly older than Ruprecht 106.
The detection of young metal-poor clusters ([Fe/H] ≤ -1.8) implies a
complex scenario for the origin of the galactic halo, possibly
involving interactions with satellite galaxies and their cluster
systems.
Objects:
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RA (2000) DE Designation(s)
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19 28 44 -30 21.5 Arp 2 = C 1925-304
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 28 1586 Magnitudes, colors, and positions of stars in
the central field of Arp 2
table2.tex 100 965 TeX version of Table 2
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 4 I4 --- Star Star number
5-12 F8.3 mag Vmag V magnitude
13-19 F7.3 mag B-V (B-V) color
20-24 I5 arcsec Xpos *X coordinate in local system
25-28 I4 arcsec Ypos *Y coordinate in local system
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Note on Xpos, Ypos:
X and Y coordinates in local system (hence, useful just for
identification purposes) and are expressed in arcseconds relative
to an arbitrary "center" adopted for the cluster.
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Origin: AAS CD-ROM series, Volume 4, 1995 Lee Brotzman [ADS] 26-Apr-1995
(End) [CDS] 11-Jul-1995