Globular Cluster Photometry with the {ital Hubble} {ital Space} {ital T}{ital elescope}. VII. Color Gradients and Blue Stragglers in the Central Region of M30 from Wide Field Planetary Camera 2 Observations
- UCO/Lick Observatory, Department of Astronomy and Astrophysics, University of California at Santa Cruz, 1156 High Street, Santa Cruz, CA 95064 (United States)
- Fermi National Accelerator Laboratory, Box 500, Batavia, IL 60510 (United States)
- Department of Astronomy and Astrophysics, Pennsylvania State University, University Park, PA 16802 (United States)
- Institute for Advanced Study, School of Natural Sciences, Princeton, NJ 08540 (United States)
We present F555W ({ital V}), F439W ({ital B}), and F336W ({ital U}) photometry of 9507 stars in the central 2{prime} of the dense, post{endash}core-collapse cluster M30 (NGC 7099) derived from {ital Hubble} {ital Space} {ital T}{ital elescope} 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, {ital F}{sub BSS} {equivalent_to} {ital N}(BSS)/{ital N}({ital V} {lt} {ital V}{sub HB} + 2), is 0.25 {plus_minus} 0.05 in the inner region of M30 ({ital r} {lt} 20{double_prime}), significantly higher than the frequency found in other clusters: {ital F}{sub BSS} = 0.05{endash}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. An unusually blue star ({ital B} = 18.6, {ital B}{minus}{ital V} = {minus}0.97), possibly a cataclysmic variable based on its color, is found about 1&arcsec;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 ({ital B} {lt} 16.6) appear to be depleted by a factor of 2{endash}3 in the inner {ital r} {lt} 10{double_prime} relative to fainter giants, subgiants, and main-sequence turnoff stars (95{percent} significance). We confirm that there is a radial gradient in the color of the overall cluster light, going from {ital B}{minus}{ital V} {approximately} 0.82 at {ital r} {approximately} 1{prime} to {ital B}{minus}{ital V} {approximately} 0.45 in the central 10{double_prime}. 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{percent} higher than predicted by the model (3.8 {sigma} effect), roughly independent of red giant brightness over the range {ital M}{sub {ital V}} = {minus}2 to +2. {copyright} {ital {copyright} 1998.} {ital The American Astronomical Society}
- OSTI ID:
- 303409
- Journal Information:
- Astronomical Journal, Vol. 116, Issue 4; Other Information: PBD: Oct 1998
- Country of Publication:
- United States
- Language:
- English
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