ON THE PERIOD DISTRIBUTION OF CLUSTER RR LYRAE STARS TO CONSTRAIN THEIR HELIUM CONTENT: THE CASE OF {omega} CENTAURI

Journal Article · Thu Sep 01 04:00:00 EDT 2011 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/738/1/111· OSTI ID:21582865

Marconi, M ^[1]; Bono, G ^[2]; Caputo, F ^[3]; Piersimoni, A M; Pietrinferni, A ^[4]

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1. INAF-Osservatorio Astronomico di Capodimonte, Via Moiariello 16, 80131 Napoli (Italy)
2. Dipartimento di Fisica, Universita di Roma Tor Vergata, Via della Ricerca Scientifica 1, 00133 Roma (Italy)
3. INAF-Osservatorio Astronomico di Roma, Via Frascati 33, 00040 Monte Porzio Catone (Italy)
4. INAF-Osservatorio Astronomico di Collurania, Via M. Maggini, Teramo (Italy)

We present new sets of nonlinear, time-dependent convective hydrodynamical models of RR Lyrae stars assuming two metal (Z = 0.0005, Z = 0.001) and three helium abundances (Y = 0.24, 0.30, 0.38). For each chemical composition, we constructed a grid of fundamental and first overtone models covering a broad range of stellar masses and luminosities. To constrain the impact of the helium content on RR Lyrae properties, we adopted two observables-period distribution and luminosity amplitudes-that are independent of distance and reddening. The current predictions confirm that the helium content has a marginal effect on the pulsation properties. The key parameter causing the difference between canonical and He-enhanced observables is the luminosity. We compared current predictions with the sample of 189 RR Lyrae stars in {omega} Cen and found that the period range of He-enhanced models is systematically longer than observed. These findings apply to metal-poor and metal-intermediate He-enhanced models. To further constrain the impact of He-enhanced structures on the period distribution, we also computed a series of synthetic horizontal branch (HB) models and found that the predicted period distribution, based on a Gaussian sampling in mass, agrees quite well with observations. This applies not only to the minimum fundamentalized period of RR Lyrae stars (0.39 versus 0.34 days) but also to the fraction of Type II Cepheids (2% versus 3%). We also computed a series of synthetic HB models assuming a mixed HB population in which the 80% is made of canonical HB structures, while the 20% is made of He-enhanced (Y = 0.30) HB structures. We found that the fraction of Type II Cepheids predicted by these models is almost a factor of two larger than observed (5% versus 3%). This indicates that the fraction of He-enhanced structures in {omega} Cen cannot be larger than 20%.

• OSTI ID: 21582865
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 738; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
CEPHEIDS
CHEMICAL COMPOSITION
DISTRIBUTION
ELECTRODES
ELEMENTS
EVOLUTION
FLUID MECHANICS
FLUIDS
GASES
GRIDS
HELIUM
HYDRODYNAMICS
LUMINOSITY
MECHANICS
NONMETALS
OPTICAL PROPERTIES
OSCILLATIONS
PHYSICAL PROPERTIES
PULSATING VARIABLE STARS
PULSATIONS
RARE GASES
SIMULATION
STAR EVOLUTION
STARS
TIME DEPENDENCE
VARIABLE STARS