J/AJ/114/2381 UBVI photometry of NGC 7252 (Miller+, 1997)
The star cluster system of the merger remnant NGC 7252.
Miller B.W., Whitmore B.C., Schweizer F., Fall S.M.
<Astron. J. 114, 2381 (1997)>
=1997AJ....114.2381M 1997AJ....114.2381M
ADC_Keywords: Galaxies, photometry ; Photometry, UBVRI ; Clusters, globular
Abstract:
We present new U, B, V, and I images of the prototypical merger
remnant NGC 7252 obtained with the WFPC2 instrument of the Hubble
Space Telescope. The photometry reaches about 3 mag deeper than the
previous observations with WF/PCI and we detect 499 cluster
candidates, most of them previously undiscovered. We can distinguish
three populations of star clusters. We confirm the existence of a very
luminous, blue population of clusters with a narrow range in color.
Comparisons with Bruzual & Charlot (1996, in preparation) models
incorporating a Salpeter stellar IMF show that the mean ages of these
clusters are 650Myr for [Fe/H]=0.0 and 750 Myr if [Fe/H]=-0.3.
Therefore, these are the clusters that formed during the merger event.
The upper limit to the effective radii of these objects is 4.8±0.4pc
(for D=64.4Mpc, H0=75), suggesting that they have physical
properties like Galactic globular clusters. The second population of
clusters is associated with the inner disk. Their (U-B) colors and
reddening-free Q values indicate that their light is dominated by O
stars and that they have ages less than 10Myr. However, with
<Reff≥8.3±0.6pc, these objects may be more like stellar
associations and they may not survive for a significant time. Finally,
there is also evidence for the presence of the most luminous of the
old, metal-poor globular clusters that belonged to the progenitor
galaxies. The cluster luminosity function is a single power law with
slope α~-1.8 down to a limiting magnitude of V=26. The current
specific cluster frequency is SN=0.6±0.3 for old clusters and
young clusters with M>105M☉, but after the remnant has faded
for about 15Gyr SN will have increased to about 2.5. The central
disk is now resolved into much finer detail than in earlier WF/PCI
observations and the light profile of the nuclear region is consistent
with a single power law with slope γ=-1.26±0.03. After both
the main body and the cluster system of NGC 7252 have aged, for
several Gyr it may have the properties of a field elliptical.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tables.dat 84 80 Cluster candidates in NGC 7252
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Byte-by-byte Description of file: tables.dat
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Bytes Format Units Label Explanations
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1- 2 I2 --- MWS97 Sequential number ([MWS97] NN in simbad)
4- 10 F7.3 arcsec oRA Offset from right ascension (1)
12- 18 F7.3 arcsec oDE Offset from declination (1)
20- 24 F5.2 arcsec rproj Projected radius
26- 30 F5.2 mag Vmag V magnitude corrected for foreground extinction
32- 35 F4.2 mag e_Vmag rms uncertainty on Cmag
37- 41 F5.2 mag U-B ? U-B colour index corrected for foreground
extinction
43- 46 F4.2 mag e_U-B ? rms uncertainty on U-B
48- 52 F5.2 mag B-V ? B-V colour index corrected for foreground
extinction
54- 57 F4.2 mag e_B-V ? rms uncertainty on B-V
59- 63 F5.2 mag V-I ? V-I colour index corrected for foreground
extinction
65- 68 F4.2 mag e_V-I ? rms uncertainty on V-I
70- 74 F5.2 mag Q ? Reddening-free index Q=(U-B)-0.72(B-V)
76- 79 F4.2 mag e_Q ? rms uncertainty on Q
81- 84 F4.1 pc Reff ? Effective radius
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Note (1): Coordinates are with respect to the nuclear position:
RA=22:20:44.775, DE=-24:40:41.831, J2000.
A positive offset indicates that the object is east or north of
the nucleus.
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History: Prepared via OCR at CDS.
(End) Marie-Jose Wagner, Patricia Bauer [CDS] 22-Mar-1999