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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
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) 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). 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: ---------------------------------------------------------- RA (2000) DE Designation(s) ---------------------------------------------------------- 16 23 35.4 -26 31 32 M 4 = NGC 6121 ---------------------------------------------------------- File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table3.dat 48 1649 CCD photometry in M4
Byte-by-byte Description of file: table3.dat
Bytes Format Units Label Explanations
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)
Note (1): Cl* NGC 6121 ALAK NNNN in Simbad
Acknowledgements: Nicolai N. Samus
(End) Patricia Bauer [CDS] 18-May-1999
The document above follows the rules of the Standard Description for Astronomical Catalogues.From this documentation it is possible to generate f77 program to load files into arrays or line by line

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