J/AJ/114/189 M 4 CCD photometry (Alcaino+, 1997)
The main sequence of the globular cluster M4=NGC 6121 from CCD NTT photometry.
Alcaino G., Liller W., Alvarado F., Kravtsov V., Ipatov A., Samus N.,
Smirnov O.
<Astron. J. 114, 189 (1997)>
=1997AJ....114..189A 1997AJ....114..189A
ADC_Keywords: Clusters, globular ; Photometry, CCD ; Photometry, UBVRI
Abstract:
With the ESO NTT, we have obtained accurate CCD UBVI photometry of
1649 stars in an extended field in the globular cluster M 4 = NGC
6121. The position of the main-sequence turnoff is found to be at
VTO=17.0±0.1mag, (B-V)=0.863±0.007, (V-I)=1.224±0.010,
(B-I)=2.084±0.010. Our turnoff point is redder and fainter than
those found for M 4 in the majority of recent studies, probably
because of our field being located in the western, most reddened part
of the cluster. The spread of stars around the main-sequence locus has
an unusual shape (broadening near the turnoff point and close to the
photometric limit), earlier noticed by Richer et al.
(1995ApJ...451L..17R 1995ApJ...451L..17R) and attributed by them to photometric effects.
We have analyzed the possible reasons for this effect and concluded
that, at least in our case, it is most probably due to differential
absorption. We confirm the deviation of theoretical isochrones from
the fainter parts of the M 4 main-sequence locus found by Alcaino et
al. (1988ApJ...330..569A 1988ApJ...330..569A). Several curious structural details (a
depression and an excess of stars) have been revealed in the brighter
parts of the main-sequence luminosity function of M 4.
Objects:
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RA (2000) DE Designation(s)
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16 23 35.4 -26 31 32 M 4 = NGC 6121
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table3.dat 48 1649 CCD photometry in M4
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 4 I4 --- ALAK Running number (1)
6- 13 F8.3 pix xpos x coordinate (along RA, increases to the east)
15- 22 F8.3 pix ypos y coordinate (along DEC, increases to the south)
24- 29 F6.3 mag Vmag V magnitude
31- 36 F6.3 mag U-B ? U-B color (blank if not available)
38- 42 F5.3 mag B-V B-V color
44- 48 F5.3 mag V-I ? V-I color (blank if not available)
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Note (1): Cl* NGC 6121 ALAK NNNN in Simbad
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Acknowledgements: Nicolai N. Samus
(End) Patricia Bauer [CDS] 18-May-1999