THE HORIZONTAL BRANCH OF NGC 1851: CONSTRAINTS FROM ITS RR LYRAE VARIABLES

Journal Article · Tue Jan 01 04:00:00 EST 2013 · Astronomical Journal (New York, N.Y. Online)

DOI:https://doi.org/10.1088/0004-6256/145/1/25· OSTI ID:22089727

Kunder, Andrea; De Propris, Roberto; Walker, Alistair ^[1]; Salaris, Maurizio ^[2]; Cassisi, Santi ^[3]; Stetson, Peter B. ^[4]; Catelan, Marcio; Amigo, Pia ^[5]

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1. NOAO-Cerro Tololo Inter-American Observatory, Casilla 603, La Serena (Chile)
2. Astrophysics Research Institute, Liverpool John Moores University, Twelve Quays House, Egerton Wharf, Birkenhead CH41 1LD (United Kingdom)
3. INAF-Osservatorio Astronomico di Collurania, Via M. Maggini, I-64100 Teramo (Italy)
4. Dominion Astrophysical Observatory, Herzberg Institute of Astrophysics, National Research Council, Victoria, BC (Canada)
5. Departamento de Astronomia y Astrofisica, Pontificia Universidad Catolica de Chile, Av. Vicuna Mackenna 4860, 782-0436 Macul, Santiago (Chile)

We use the pulsational properties of the RR Lyrae variables in the globular cluster NGC 1851 to obtain detailed constraints of the various sub-stellar populations present along its horizontal branch. On the basis of detailed synthetic horizontal branch modeling, we find that minor helium variations (Y {approx} 0.248-0.280) are able to reproduce the observed periods and amplitudes of the RR Lyrae variables, as well as the frequency of fundamental and first-overtone RR Lyrae stars. Comparison of number ratios among the blue and red horizontal branch components and the two observed subgiant branches also suggest that the RR Lyrae variables originated from the progeny of the bright subgiant branch. The RR Lyrae variables with slightly enhanced helium (Y {approx} 0.270-0.280) have longer periods at a given amplitude, as is seen with Oosterhoff II (OoII) RR Lyrae variables, whereas the RR Lyrae variables with Y {approx} 0.248-0.270 have shorter periods, exhibiting properties of Oosterhoff I (OoI) variables. This correlation does suggest that the pulsational properties of RR Lyrae stars can be very useful for tracing the various subpopulations and can provide suitable constraints on the multiple population phenomenon. It appears to be of great interest to explore whether this conclusion can be generalized to other globular clusters hosting multiple populations.

• OSTI ID: 22089727
• Journal Information: Astronomical Journal (New York, N.Y. Online), Journal Name: Astronomical Journal (New York, N.Y. Online) Journal Issue: 1 Vol. 145; ISSN 1538-3881
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
AMPLITUDES
ASTRONOMY
ASTROPHYSICS
COMPARATIVE EVALUATIONS
CORRELATIONS
GALAXIES
HELIUM
STAR CLUSTERS
VARIABLE STARS