J/AJ/99/1831 M 68 BVRI photometry (Alcaino+ 1990)
BVRI CCD photometry of the metal-poor globular cluster M68 (NGC 4590)
Alcaino G., Liller W., Alvarado F., Wenderoth E.
<Astron. J. 99, 1831 (1990)>
=1990AJ.....99.1831A 1990AJ.....99.1831A
ADC_Keywords: Clusters, globular ; Photometry, CCD
Abstract:
We present BVRI photometry of the low metallicity globular cluster M68
(NGC 4590) observed with a CCD camera and the 2.2m telescope at ESO/La
Silla, and have compared our BV color-magnitude diagrams with the
observational results of a previous research. At magnitudes V<22, our
BV results, obtained using the INVENTORY code, are in very close
agreement with those of the other authors who used DAOPHOT in their
reductions. At fainter levels, selection effects appear to affect
INVENTORY more than DAOPHOT. We find that VTO-HB=3.42±0.10, in
accord with values found for other clusters. The comparison between
our four-color observations and the theoretical isochrones
consistently yield a cluster age of 13Gyr with a likely external
uncertainty of 2 or 3Gyr. Our derived values for the interstellar
reddening at longer wavelengths are generally in agreement
(±0.02mag) with what would be expected assuming E(B-V)=0.07mag and
(m-M)V=15.25.
Objects:
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RA (2000) DE Designation(s)
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12 39 27.9 -26 44 35 M 68 = NGC 4590
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table6.dat 52 685 CCD magnitudes and colors for 685 stars in NGC 4590
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Byte-by-byte Description of file: table6.dat
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Bytes Format Units Label Explanations
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1- 3 I3 -- Star Star number
5- 6 A2 --- Saw Sawyer Hogg name (1973PDDO....3....6S 1973PDDO....3....6S)
8- 10 I3 pix Xpos X position (2)
12- 14 I3 pix Ypos Y position (2)
16- 21 F6.3 mag Vmag V magnitude
23- 27 F5.3 mag B-V ? B-V colour index
29- 33 F5.3 mag V-R ? V-R colour index
35- 39 F5.3 mag R-I ? R-I colour index
41- 45 F5.3 mag V-I ? V-I colour index
47- 51 F5.3 mag B-I ? B-I colour index
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Note (2): 1 pix = 0.36 arcsec. The origin of (X, Y) coordinates is located at
the bottom right.
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History: Prepared via OCR at CDS.
(End) Marie-Jose Wagner, Patricia Bauer [CDS] 16-May-1997