J/AJ/116/1757 M30 UBV photometry (Guhathakurta+, 1998)
Globular cluster photometry with the Hubble Space Telescope.
VII. Color gradients and blue stragglers in the central region of M30 from
Wide Field Planetary Camera 2 observations.
Guhathakurta P., Webster Z.T., Yanny B., Schneider D.P., Bahcall J.N.
<Astron. J. 116, 1757 (1998)>
=1998AJ....116.1757G 1998AJ....116.1757G
ADC_Keywords: Clusters, globular ; Stars, blue ; Photometry, UBV
Mission_Name: HST
Keywords: blue stragglers - color-magnitude diagrams -
globular clusters: individual: M 30, NGC 7099 - stars: evolution -
stars: luminosity function, mass function
Abstract:
We present F555W (V), F439W (B), and F336W (U) photometry of 9507
stars in the central 2' of the dense, post-core-collapse cluster M30
(NGC 7099) derived from Hubble Space Telescope Wide Field Planetary
Camera 2 images. These data are used to study the mix of stellar
populations in the central region of the cluster. Forty-eight blue
straggler stars are identified; they are found to be strongly
concentrated toward the cluster center. The specific frequency of blue
stragglers, FBSS=N(BSS)/N(V<VHB+2), is 0.25±0.05 in the inner
region of M30 (r<20"), significantly higher than the frequency found
in other clusters: FBSS=0.05-0.15. The shape of M30's blue straggler
luminosity function resembles the prediction of the collisional
formation model, and is inconsistent with the binary merger model of
Bailyn & Pinsonneault (1995ApJ...439..705B 1995ApJ...439..705B). An unusually blue star
(B=18.6, B-V=-0.97), possibly a cataclysmic variable based on its
color, is found about 1.2" from the crowded cluster center; the
photometric uncertainty for this star is large, however, because of
the presence of a very close neighbor. Bright red giant stars (B<16.6)
appear to be depleted by a factor of 2-3 in the inner r<10" relative
to fainter giants, subgiants, and main-sequence turnoff stars (95%
significance). We confirm that there is a radial gradient in the color
of the overall cluster light, going from B-V∼0.82 at r∼1' to B-V∼0.45
in the central 10". The central depletion of the bright red giants is
responsible for about half of the observed color gradient; the rest of
the gradient is caused by the relative underabundance of faint red
main-sequence stars near the cluster center (presumably a result of
mass segregation). The luminosity function of M30's evolved stars does
not match the luminosity function shape derived from standard stellar
evolutionary models: the ratio of the number of bright giants to the
number of turnoff stars in the cluster is 30% higher than predicted by
the model (3.8σ effect), roughly independent of red giant
brightness over the range MV=-2 to +2.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 44 9940 M 30 stellar photometry and astrometry
--------------------------------------------------------------------------------
See also:
J/AJ/107/1745 : HST UVI photometry of M15. II. (Yanny+, 1994)
J/AJ/108/1786 : Blue stragglers + variable stars in M3 (Guhathakurta+, 1994)
J/AJ/113/669 : Stars in M13 core (Cohen+ 1997)
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 I4 --- GWY Identification number (1)
6- 11 F6.2 arcsec oRA Relative right ascension to star 3611 (J2000) (2)
13- 18 F6.2 arcsec oDE Relative declination to star 3611 (J2000) (2)
20- 25 F6.2 arcsec r Projected distance from the cluster centroid (3)
27- 31 F5.2 mag Vmag V magnitude
33- 37 F5.2 mag B-V B-V colour index
39- 43 F5.2 mag U-V ? U-V colour index
--------------------------------------------------------------------------------
Note (1): Cl* NGC 7099 GWY NNNN in Simbad
Note (2): Star 3611 position: RA=21h40min22.402s, DE=-23°10'42.42" (J2000.0)
Note (3): Cluster centroid position:
RA=21h40min22.24s, DE=-23°10'50.0" (J2000.0)
--------------------------------------------------------------------------------
History: Copied from ftp ku.sns.ias.edu
References:
Guhathakurta et al., Paper I. 1992AJ....104.1790G 1992AJ....104.1790G
Yanny et al., Paper II. 1994AJ....107.1745Y 1994AJ....107.1745Y, Cat. J/AJ/107/1745
Guhathakurta et al., Paper III. 1994AJ....108.1786G 1994AJ....108.1786G, Cat. J/AJ/108/1786
Yanny et al., Paper IV. 1994ApJ...435L..59Y 1994ApJ...435L..59Y
Guhathakurta et al., Paper V. 1996AJ....111..267G 1996AJ....111..267G
Cohen et al., Paper VI. 1997AJ....113..669C 1997AJ....113..669C, Cat. J/AJ/113/669
(End) Patricia Bauer [CDS] 09-Nov-1998