Spectroscopy of horizontal branch stars in<i>ω</i> Centauri

Bidin, C. Moni; Villanova, S.; Piotto, G.; Moehler, S.; Cassisi, S.; Momany, Y.

doi:10.1051/0004-6361/201220031

Cited by 33 publications

(45 citation statements)

References 89 publications

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“…The above empirical scenario is further complicated by evidence that ω Cen might also be affected by differential reddening (Dickens & Caldwell 1988;Calamida et al 2005;Majewski et al 2012) at a level of ΔE(B−V) = 0.03-0.04 mag (Moni Bidin et al 2012).…”

Section: Distance Determinationmentioning

confidence: 99%

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On THE RR LYRAE STARS IN GLOBULARS. IV. Ω CENTAURI OPTICAL UBVRI PHOTOMETRY*

Braga

Stetson

Bono

et al. 2016

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New accurate and homogeneous optical UBVRI photometry has been obtained for variable stars in the Galactic globular cluster ω Cen (NGC 5139). We secured 8202 CCD images covering a time interval of 24 years and a sky area of 84×48 arcmin. The current data were complemented with data available in the literature and provided new, homogeneous pulsation parameters (mean magnitudes, luminosity amplitudes, periods) for 187 candidate ω Cen RR Lyrae (RRLs). Among them we have 101RRc (first overtone) and 85RRab (fundamental) variables, and a single candidate RRd (double-mode) variable. Candidate Blazhko RRLs show periods and colors that are intermediate between the RRc and RRab variables, suggesting that they are transitional objects. A comparison of the period distribution and the Bailey diagram indicates that RRLs in ω Cen show a long-period tail not present in typical Oosterhoff II (OoII) globulars. The RRLs in dwarf spheroidals and in ultra-faint dwarfs have properties between Oosterhoff intermediate and OoII clusters. Metallicity plays a key role in shaping the above evidence. These findings do not support the hypothesis that ω Cen is the core remnant of a spoiled dwarf galaxy. Using optical period-Wesenheit relations that are reddening-free and minimally dependent on metallicity we find a mean distance to ω Cen of 13.71±0.08±0.01 mag (semi-empirical and theoretical calibrations). Finally, we invert the I-band period-luminosity-metallicity relation to estimate individual RRLs' metal abundances. The metallicity distribution agrees quite well with spectroscopic and photometric metallicity estimates available in the literature.

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Section: Distance Determinationmentioning

confidence: 99%

“…We adopted, according to Thompson et al (2001) and Lub (2002), a cluster reddening of E(B-V)=0.11 mag. We also took account of the spread in E(B-V ) measured by Moni Bidin et al (2012). According to the reddening law provided by Cardelli et al (1989), we adopted a ratio A I /A V = 0.590.…”

Section: Metallicity Of Rrls Starsmentioning

confidence: 99%

On THE RR LYRAE STARS IN GLOBULARS. IV. Ω CENTAURI OPTICAL UBVRI PHOTOMETRY*

Braga

Stetson

Bono

et al. 2016

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“…Other authors have realized direct measurements of helium enhancement among the stars of ω Centauri. Moehler et al (2011) andMoni Bidin et al (2012) analysed a large group of bHB and eHB stars describing how helium changes with the temperature. The peculiar pattern described by the authors strongly suggest that the bHB and the eHB is populated by second generation stars and that the phenomenon of the late helium flash mixing is involved in shaping the blue end of the HB locus.…”

Section: Spectroscopic Observationsmentioning

confidence: 99%

The mosaic multiple stellar populations in ω Centauri: the horizontal branch and the main sequence

Tailo

Criscienzo

D’Antona

et al. 2016

Mon. Not. R. Astron. Soc.

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We interpret the stellar population of ω Centauri by means of a population synthesis analysis, following the most recent observational guidelines for input metallicities, helium and [(C+N+O)/Fe] contents. We deal at the same time with the main sequences, sub-giant and horizontal branch data. The reproduction of the observed color magnitude features is very satisfying and bears interesting hints concerning the evolutionary history of this peculiar stellar ensemble. Our main results are: 1) no significant spread in age is required to fit the colour-magnitude diagram. Indeed we can use coeval isochrones for the synthetic populations, and we estimate that the ages fall within a ∼ 0.5 Gyr time interval; in particular the most metal rich population can be coeval (in the above meaning) with the others, if its stars are very helium-rich (Y∼0.37) and with the observed CNO enhancement ([(C+N+O)/Fe] = + 0.7); 2) a satisfactory fit of the whole HB is obtained, consistent with the choice of the populations providing a good reproduction of the main sequence and sub giant data. 3) the split in magnitude observed in the red HB is well reproduced assuming the presence of two stellar populations in the two different sequences observed: a metal poor population made of stars evolving from the blue side (luminous branch) and a metal richer one whose stars are in a stage closer to the zero age HB (dimmer branch). This modelization also fits satisfactorily the period and the [Fe/H] distribution of the RR Lyrae stars.

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“…The properties of these subpopulations have been deeply investigated over the past 20 years using both photometry (Lee & Carney 1999;Pancino et al 2000;Ferraro et al 2004;Sollima et al 2005;Calamida et al 2009;Bellini et al 2010) and spectroscopy (Origlia et al 2003;Johnson & Pilachowski 2010;Pancino et al 2011aPancino et al , 2011bMoni Bidin et al 2012;Simpson & Cottrell 2013;Villanova et al 2014). Such peculiar characteristics locate ω Cen in between the properties of GCs and the more luminous dwarf galaxies (Tolstoy et al 2009).…”

Section: Theory Versus Observations: the Case Of ω Cenmentioning

confidence: 99%

Blue Straggler Masses From Pulsation Properties. Ii. Topology of the Instability Strip

Fiorentino

Marconi

Bono

et al. 2015

ApJ

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We present a new set of nonlinear, convective radial pulsation models for main-sequence stars computed assuming three metallicities: Z = 0.0001, 0.001, and 0.008. These chemical compositions bracket the metallicity of stellar systems hosting SX Phoenicis stars (SXPs, or pulsating Blue Stragglers), namely, Galactic globular clusters and nearby dwarf spheroidals. Stellar masses and luminosities of the pulsation models are based on alpha-enhanced evolutionary tracks from the BASTI website. We are able to define the topology of the instability strip (IS)and in turn the pulsation relations for the first four pulsation modes. We found that third overtones approach a stable nonlinear limit cycle. Predicted and empirical ISs agree quite well in the case of 49 SXPs belonging to ω Cen. We used theoretical period-luminosity (PL) relations in Band V bands to identify their pulsation mode. We assumed Z = 0.001 and Z = 0.008 as mean metallicities of SXPs in ω Cen. We found respectively 13-15 fundamental, 22-6 first-overtone, and 9-4 second-overtone modes. Five are unstable in the third-overtone mode only for Z = 0.001. Using the above mode identification and applying the proper mass-dependent PL relations, we found masses ranging from ∼1.0 to 1.for Z = 0.001 and 0.008, respectively. Our investigation supports the use of evolutionary tracks to estimate SXP masses. We will extend our analysis to higher helium content, which may have an impact on our understanding of the blue stragglerstars formation scenario.

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Spectroscopy of horizontal branch stars inω Centauri

Cited by 33 publications

References 89 publications

On THE RR LYRAE STARS IN GLOBULARS. IV. Ω CENTAURI OPTICAL UBVRI PHOTOMETRY*

On THE RR LYRAE STARS IN GLOBULARS. IV. Ω CENTAURI OPTICAL UBVRI PHOTOMETRY*

The mosaic multiple stellar populations in ω Centauri: the horizontal branch and the main sequence

Blue Straggler Masses From Pulsation Properties. Ii. Topology of the Instability Strip

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