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
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:
FileName Lrecl Records Explanations
ReadMe 80 . This file tables.dat 84 80 Cluster candidates in NGC 7252
Byte-by-byte Description of file: tables.dat
Bytes Format Units Label Explanations
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
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.
History: Prepared via OCR at CDS.
(End) Marie-Jose Wagner, Patricia Bauer [CDS] 22-Mar-1999
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