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J/AJ/109/650                                          Arp 2 ( Buonanno+ 1995)
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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
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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. AJ, 100, 1811 (1990), AJ, 105, 184
  (1993)].  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, Delta (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
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(End)                                                         [CDS]  11-Jul-1995