J/AJ/113/264 Photometry of young globular clusters (Sarajedini+ 1997)
Reddenings, Metallicities, and Possible Abundance Anomalies
in Young Globular Clusters
Sarajedini A., Layden A.
<Astron. J. 113, 264 (1997)>
=1997AJ....113..264S 1997AJ....113..264S
ADC_Keywords: Clusters, globular ; Photometry, CCD
Abstract:
We present new photometry in the VI passbands for the ``young''
globular clusters Rup 106, Ter 7, and Arp 2. After formulating the
simultaneous reddening and metallicity (SRM) method of Sarajedini [AJ,
107, 618 (1994)] in the BV passbands, we apply it, along with the SRM
method in VI, to the red giant branches (RGBs) of these clusters using
B-V photometry from the literature and the V-I data presented herein.
We find [Fe/H]=-1.90±0.10, E(B-V)=0.18±0.02 for Rup 106,
[Fe/H]=-0.82±0.15, E(B-V)=0.07±0.03 for Ter 7, and
[Fe/H]=-1.84±0.09, E(B-V)=0.10±0.02 for Arp 2. Furthermore, in
light of this new abundance for Ter 7 and recent work on the
luminosity of the red horizontal branch, we rederive the age of Ter 7
finding it to be some 6 Gyr younger than 47 Tuc. We show that the SRM
method is insensitive to age for clusters with purely red HBs and ages
as young as ∼5 Gyr; for clusters with bluer HBs, the SRM method is
only mildly sensitive to age differences between such clusters and the
calibrating (standard) clusters. From these metallicity estimates, we
conclude that the photometric abundances of the program clusters based
on the properties of the RGB are systematically lower
({DELTA}[Fe/H]=0.1-0.4dex) than those derived using other indicators,
in particular the Ca II triplet method. We note that the young
globular cluster Palomar 12 also exhibits this behavior. We suggest
that this discrepancy is due to systematic differences in the
[α/Fe] ratios between the young clusters and the ``normal''
Galactic globulars used to calibrate the abundance determination
methods. However, we are unable to completely reconcile all the
observations of Rup 106 using this approach. Systematic differences in
[α/Fe] between the young clusters and the rest of the Galactic
globulars may indicate differences in their chemical enrichment
histories, perhaps due to differing environments at the times of their
formation. Interestingly, both Ter 7 and Arp 2 are believed to be
members of the Sagittarius dwarf galaxy.
(Copyright) 1997 American Astronomical Society.
Objects:
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RA (2000) DE Designation(s)
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12 38 40 -51 09.1 Ruprecht 106
19 17 42 -34 39.4 Terzan 7
19 28 44 -30 21.5 Arp 2
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 51 3123 CCD photometry for Ruprecht 106
table3.dat 51 699 CCD photometry for Terzan 7
table4.dat 51 896 CCD photometry for Arp 2
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Byte-by-byte Description of file: table2.dat table3.dat table4.dat
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Bytes Format Units Label Explanations
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1- 4 I4 --- Star Star number
6- 12 F7.2 pix Xpos X CCD coordinate (1)
14- 20 F7.2 pix Ypos Y CCD coordinate (1)
22- 27 F6.2 mag Vmag V magnitude
29- 34 F6.3 mag e_Vmag Error in Vmag
36- 41 F6.2 mag V-I V-I color
43- 48 F6.3 mag e_V-I Error in V-I
50- 51 I2 --- N Number of detections
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Note (1): North is the the left, East is down.
1 pix = 0.44 arcsec for table2.dat (Rup 106)
1 pix = 0.40 arcsec for table3.dat and table4.dat (Ter 7 and Arp 2)
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Origi n:AAS CD-ROM series, Volume 8, 1997 Lee Brotzman [ADS] 30-Mar-1997
(End) [CDS] 03-Jul-1997