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Title: THE CARINA PROJECT. VI. THE HELIUM-BURNING VARIABLE STARS

Abstract

We present new optical (BVI) time-series data for the evolved variable stars in the Carina dwarf spheroidal galaxy. The quality of the data and the observing strategy allowed us to identify 14 new variable stars. Eight out of the 14 are RR Lyrae (RRL) stars, 4 are Anomalous Cepheids (ACs), and 2 are geometrical variables. Comparison of the period distribution for the entire sample of RRLs with similar distributions in nearby dwarf spheroidal galaxies and in the Large Magellanic Cloud indicates that the old stellar populations in these systems share similar properties. This finding is also supported by the RRL distribution in the Bailey diagram. On the other hand, the period distribution and the Bailey diagram of ACs display significant differences among the above stellar systems. This evidence suggests that the properties of intermediate-age stellar populations might be affected both by environmental effects and structural parameters. We use the BV Period-Wesenheit (PW) relation of RRLs together with evolutionary prescriptions and find a true distance modulus of 20.09 {+-} 0.07 (intrinsic) {+-} 0.1 (statistical) mag that agrees quite well with similar estimates available in the literature. We identified four peculiar variables. Taking into account their position in the Bailey diagram andmore » in the BV PW relation, two of them (V14 and V149) appear to be candidate ACs, while two (V158 and V182) might be peculiar RRLs. In particular, the variable V158 has a period and a V-band amplitude very similar to the low-mass RRL-RRLR-02792-recently identified by Pietrzynski et al. in the Galactic bulge.« less

Authors:
; ; ; ;  [1];  [2]; ;  [3];  [4]; ; ;  [5];  [6];  [7];  [8];  [9];  [10]
  1. INAF-Osservatorio Astronomico di Capodimonte, Via Moiariello 16, I-80131 Napoli (Italy)
  2. Dominion Astrophysical Observatory, NRC-Herzberg, 5071 West Saanich Road, Victoria, BC V9E 2E7 (Canada)
  3. Dipartimento di Fisica-Universita di Roma Tor Vergata, Via della Ricerca Scientifica 1, I-00133 Roma (Italy)
  4. INAF-Osservatorio Astronomico di Collurania, via M. Maggini, I-64100 Teramo (Italy)
  5. INAF-Osservatorio Astronomico di Roma, Via Frascati 33, I-00040 Monte Porzio Catone (Italy)
  6. INAF-Osservatorio Astronomico di Bologna, via Ranzani 1, I-40127 Bologna (Italy)
  7. Instituto de Astrofisica de Canarias, Calle Via Lactea s/n, E-38205 La Laguna, Tenerife (Spain)
  8. INAF-Osservatorio Astronomico di Trieste, via G. B. Tiepolo 11, I-40131 Trieste (Italy)
  9. Universite de Nice-Sophia Antipolis, Lab. Lagrange, UMR 7293, Observatoire de la Cote dAzur, BP 4229, F-06304 Nice (France)
  10. Cerro Tololo Inter-American Observatory, National Optical Astronomy Observatory, Casilla 603, La Serena (Chile)
Publication Date:
OSTI Identifier:
22133842
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 775; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; AMPLITUDES; CEPHEIDS; DISTANCE; ENVIRONMENTAL EFFECTS; HELIUM BURNING; MAGELLANIC CLOUDS; MASS

Citation Formats

Coppola, G., Marconi, M., Ripepi, V., Dall'Ora, M., Musella, I., Stetson, P. B., Bono, G., Buonanno, R., Fabrizio, M., Ferraro, I., Iannicola, G., Pulone, L., Fiorentino, G., Monelli, M., Nonino, M., Thevenin, F., and Walker, A. R., E-mail: coppola@na.astro.it. THE CARINA PROJECT. VI. THE HELIUM-BURNING VARIABLE STARS. United States: N. p., 2013. Web. doi:10.1088/0004-637X/775/1/6.
Coppola, G., Marconi, M., Ripepi, V., Dall'Ora, M., Musella, I., Stetson, P. B., Bono, G., Buonanno, R., Fabrizio, M., Ferraro, I., Iannicola, G., Pulone, L., Fiorentino, G., Monelli, M., Nonino, M., Thevenin, F., & Walker, A. R., E-mail: coppola@na.astro.it. THE CARINA PROJECT. VI. THE HELIUM-BURNING VARIABLE STARS. United States. doi:10.1088/0004-637X/775/1/6.
Coppola, G., Marconi, M., Ripepi, V., Dall'Ora, M., Musella, I., Stetson, P. B., Bono, G., Buonanno, R., Fabrizio, M., Ferraro, I., Iannicola, G., Pulone, L., Fiorentino, G., Monelli, M., Nonino, M., Thevenin, F., and Walker, A. R., E-mail: coppola@na.astro.it. Fri . "THE CARINA PROJECT. VI. THE HELIUM-BURNING VARIABLE STARS". United States. doi:10.1088/0004-637X/775/1/6.
@article{osti_22133842,
title = {THE CARINA PROJECT. VI. THE HELIUM-BURNING VARIABLE STARS},
author = {Coppola, G. and Marconi, M. and Ripepi, V. and Dall'Ora, M. and Musella, I. and Stetson, P. B. and Bono, G. and Buonanno, R. and Fabrizio, M. and Ferraro, I. and Iannicola, G. and Pulone, L. and Fiorentino, G. and Monelli, M. and Nonino, M. and Thevenin, F. and Walker, A. R., E-mail: coppola@na.astro.it},
abstractNote = {We present new optical (BVI) time-series data for the evolved variable stars in the Carina dwarf spheroidal galaxy. The quality of the data and the observing strategy allowed us to identify 14 new variable stars. Eight out of the 14 are RR Lyrae (RRL) stars, 4 are Anomalous Cepheids (ACs), and 2 are geometrical variables. Comparison of the period distribution for the entire sample of RRLs with similar distributions in nearby dwarf spheroidal galaxies and in the Large Magellanic Cloud indicates that the old stellar populations in these systems share similar properties. This finding is also supported by the RRL distribution in the Bailey diagram. On the other hand, the period distribution and the Bailey diagram of ACs display significant differences among the above stellar systems. This evidence suggests that the properties of intermediate-age stellar populations might be affected both by environmental effects and structural parameters. We use the BV Period-Wesenheit (PW) relation of RRLs together with evolutionary prescriptions and find a true distance modulus of 20.09 {+-} 0.07 (intrinsic) {+-} 0.1 (statistical) mag that agrees quite well with similar estimates available in the literature. We identified four peculiar variables. Taking into account their position in the Bailey diagram and in the BV PW relation, two of them (V14 and V149) appear to be candidate ACs, while two (V158 and V182) might be peculiar RRLs. In particular, the variable V158 has a period and a V-band amplitude very similar to the low-mass RRL-RRLR-02792-recently identified by Pietrzynski et al. in the Galactic bulge.},
doi = {10.1088/0004-637X/775/1/6},
journal = {Astrophysical Journal},
number = 1,
volume = 775,
place = {United States},
year = {Fri Sep 20 00:00:00 EDT 2013},
month = {Fri Sep 20 00:00:00 EDT 2013}
}
  • We present an analysis of photometric and spectroscopic data of the Carina dSph galaxy, testing a new approach similar to that used to disentangle multiple populations in Galactic globular clusters (GCs). We show that a proper color combination is able to separate a significant fraction of the red giant branch (RGB) of the two main Carina populations (the old one, ∼12 Gyr, and the intermediate-age one, 4-8 Gyr). In particular, the c {sub U,} {sub B,} {sub I} = (U – B) – (B – I) pseudo-color allows us to follow the RGB of both populations along a relevant portionmore » of the RGB. We find that the oldest stars have a more negative c {sub U,} {sub B,} {sub I} pseudo-color than intermediate-age ones. We correlate the pseudo-color of RGB stars with their chemical properties, finding a significant trend between the iron content and the c {sub U,} {sub B,} {sub I}. Stars belonging to the old population are systematically more metal-poor ([Fe/H] =–2.32 ± 0.08 dex) than the intermediate-age ones ([Fe/H] =–1.82 ± 0.03 dex). This gives solid evidence of the chemical evolution history of this galaxy, and we have a new diagnostic that can allow us to break the age-metallicity degeneracy of H-burning advanced evolutionary phases. We compared the distribution of stars in the c {sub U,} {sub B,} {sub I} plane with theoretical isochrones, finding that no satisfactory agreement can be reached with models developed in a theoretical framework based on standard heavy element distributions. Finally, we discuss possible systematic differences when compared with multiple populations in GCs.« less
  • We obtained single-phase near-infrared (NIR) magnitudes in the J- and K-band for a sample of 33 RR Lyrae (RRL) stars in the Carina dSph galaxy. Applying different theoretical and empirical calibrations of the NIR period–luminosity–metallicity relation for RRL stars, we find consistent results and obtain a true, reddening-corrected distance modulus of 20.118 ± 0.017 (statistical) ± 0.11 (systematic) mag. This value is in excellent agreement with the results obtained in the context of the Araucaria Project from NIR photometry of red clump stars (20.165 ± 0.015) and the tip of red giant branch (20.09 ± 0.03 ± 0.12 mag inmore » the J band, 20.14 ± 0.04 ± 0.14 mag in the K band), as well as with most independent distance determinations to this galaxy. The NIR RRL method proved to be a reliable tool for accurate distance determination at the 5% level or better, particularly for galaxies and globular clusters that lack young standard candles, like Cepheids.« less
  • Models are constructed for helium-burning stars which possess a hydrogen- rich envelope in radiative equilibrium. These inhomogeneous models are obtained from the models constructed for homogeneous, pure helium-burning stars by use of an approximation method. This method is applicable only if the fractions of the total mass and total energy production contained in the envelope are small. The bolometric luminosity is assumed to be the same as that of a homogeneous, pure helium star of the same mass M. If the hydrogen abundance X' (by weight) in the envelope is near unity, then the presence of a hydrogen-rich envelope containingmore » a mass fraction Q' of only 0.1 is found to increase the radius of the star by a factor of about 10. The factor by which the radius is increased is independent of mass M but increases rapidly with both X' and Q'. The present approximate models are in good agreement with more accurate ones constructed for larger values of Q'. Assuming the 0-type subdwarf HZ 44 to be represented by a model of this type, its mass and absolute bolometric magnitude can be estimated. It is found that M approx equal 0.5 M/sub sun/, M/sub bol/ approx equal +0.8, and Q' approx equal 0.05. The possible evolutionary significance of the present models and their relation to the observed properties of the nuclei of planetary nebulae and of the hot subwarfs are discussed. The approximation method is described in general form and is applied to pure helium star models to show that inclusion of the free-free contribution to the opacity in the outer layers of the pure helium models would increase their radii by no more than 2 or 3 per cent. (auth)« less
  • It is shown that the luminosity of a helium core is nearly independent of the birning rates; a change of ten orders of magnitude in the burning rates changes the luminosity by only about 3%. Changes in the chemical composition (helium into carbon and oxygen), on the other hand, have large effects. Also, models with two burning regions react strongly on changes in the burning rates; for such models, triple solutions may occur. One of the solutions is argued to be secularly unstable. (auth)