THE RR LYRAE VARIABLES AND HORIZONTAL BRANCH OF NGC 6656 (M22)<sup>,</sup>

Kunder, Andrea; Stetson, P. B.; Cassisi, S.; Layden, Andrew C.; Bono, G.; Catelan, M.; Walker, A. R.; Paredes, Leonardo A.; Clem, James L.; Matsunaga, Noriyuki; Salaris, Maurizio; Lee, Jae Woo; Chaboyer, Brian

doi:10.1088/0004-6256/146/5/119

Cited by 86 publications

(112 citation statements)

References 143 publications

(192 reference statements)

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“…We notice that this simulation reproduces (i) the ratios between stars within the RR Lyrae instability strip, blueward of it with M V < 16, and in the blue tail, i.e. M V > 16 measured by Kunder et al (2013), within Poisson errors; (ii) the number ratio between metal-poor and metal-rich stars within the region considered in this paper; (iii) roughly, the segregation of the stars of different groups in the T eff − M V plane observed in this paper; (iv) the average He abundance of metal-rich stars in the range of effective temperature observed in this paper (the actual value of Y = 0.29 is at the lower limit of the range admitted by our data); and the number ratio of metal poor/metal rich stars measured on the SGB by Marino et al (2009). The scatter in the observed diagram of Fig.…”

Section: Discussionsupporting

confidence: 60%

“…-In addition, there should also be more He-rich stars in M 22, not observed by us because hotter than 10 700 K. They should make up about 28% of the cluster. Using photometry by Kunder et al (2013), we found that half of them are hotter than 14 000 K, that is, less massive than ∼0.54 M . These stars should be very rich in He (Y > 0.33).…”

Section: Discussionmentioning

confidence: 96%

“…We then finally assumed the following recipe for the different populations of M 22: We assumed for both the metal-poor and metal-rich HB stellar components an RGB progenitor whose age at the RGB tip is equal to 12 Gyr. Finally, a differential reddening of 0.05 mag (see Kunder et al 2013) was added to the synthetic data. We had to assume values of Y that are actually lower than determined from our spectroscopic data for the He-rich populations.…”

Section: Discussionmentioning

confidence: 99%

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The Na-O anticorrelation in horizontal branch stars

Gratton

Lucatello

Sollima

et al. 2014

A&A

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We obtained high-resolution spectra for 94 candidate stars belonging to the HB of M 22 with FLAMES. Previous works have indicated that this cluster has split subgiant (SGB) and red giant branches (RGB) and hosts two different stellar populations, differing in overall metal abundance and both exhibiting a Na-O anti-correlation. The HB stars we observed span a restricted temperature range (7800 < T eff < 11 000 K), where about 60% of the HB stars of M 22 are. Within our sample, we can distinguish three groups of stars segregated (though contiguous) in colours: Group 1 (49 stars) is metal-poor, N-normal, Na-poor, and O-rich: our abundances for this (cooler) group match those determined for the primordial group of RGB stars (a third of the total) from previous studies very well. Group 2 (23 stars) is still metal-poor, but it is N-and Na-rich, though only very mildly depleted in O. We can identify this intermediate group as the progeny of the metal-poor RGB stars that occupy an intermediate location along the Na-O anti-correlation and include about 10% of the RGB stars. The third group (20 stars) is metal-rich, Na-rich, and O-rich. This hotter group most likely corresponds to the most O-rich component of the previously found metal-rich RGB population (a quarter of the total). We did not observe any severely O-depleted stars and we think that the progeny of these stars falls on the hotter part of the HB. Furthermore, we found that the metal-rich population is also over-abundant in Sr, in agreement with results for corresponding RGB and SGB stars. However, we do not find any significant variation in the ratio between the sum of N and O abundances to Fe. We do not have C abundances for our stars. There is some evidence of an enhancement of He content for Groups 2 and 3 stars (Y = 0.338 ± 0.014 ± 0.05); the error bar due to systematics is large, but a consistent analysis of data for several GCs confirms that stars in these groups within M 22 are probably overabundant in He. We conclude that on the whole, our results agree with the proposition that chemical composition drives the location of stars along the HB of a GC. Furthermore, we found a number of fast rotators. They are concentrated in a restricted temperature range along the HB of M 22. Fast rotating stars might be slightly less massive and bluer than slowly rotating ones, but other interpretations are possible.

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Section: Discussionsupporting

confidence: 60%

Section: Discussionmentioning

confidence: 96%

Section: Discussionmentioning

confidence: 99%

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The Na-O anticorrelation in horizontal branch stars

Gratton

Lucatello

Sollima

et al. 2014

A&A

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“…Despite being located in relatively close proximity to the Sun, R = 3.2 kpc, studies of this cluster are hampered by its location toward the crowded and heavily extincted Galactic bulge, making it difficult to disentangle cluster parameters, due to e.g., contamination from field stars and differential reddening (Monaco et al 2004;Kunder et al 2013).…”

Section: Ngc 6656 -M22mentioning

confidence: 99%

Spectroscopic signatures of extratidal stars around the globular clusters NGC 6656 (M 22), NGC 3201, and NGC 1851 from RAVE

Kunder

Bono

Piffl³

et al. 2014

A&A

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Context. Stellar population studies of globular clusters have suggested that the brightest clusters in the Galaxy might actually be the remnant nuclei of dwarf spheroidal galaxies. If the present Galactic globular clusters formed within larger stellar systems, they are likely surrounded by extra-tidal halos and/or tails made up of stars that were tidally stripped from their parent systems. Aims. The stellar surroundings around globular clusters are therefore one of the best places to look for the remnants of an ancient dwarf galaxy. Here an attempt is made to search for tidal debris around the supernovae (SNe) enriched globular clusters M22 and NGC 1851 as well as the kinematically unique cluster NGC 3201. Methods. The stellar parameters from the Radial Velocity Experiment (RAVE) are used to identify stars with RAVE metallicities, radial velocities and elemental-abundances consistent with the abundance patterns and properties of the stars in M22, NGC 1851 and NGC 3201. Results. The discovery of RAVE stars that may be associated with M22 and NGC 1851 are reported, some of which are at projected distances of ∼10 degrees away from the core of these clusters. Numerous RAVE stars associated with NGC 3201 suggest that either the tidal radius of this cluster is underestimated, or that there are some unbound stars extending a few arc minutes from the edge of the cluster's radius. No further extra-tidal stars associated with NGC 3201 could be identified. The bright magnitudes of the RAVE stars make them easy targets for high resolution follow-up observations, allowing an eventual further chemical tagging to solidify (or exclude) stars outside the tidal radius of the cluster as tidal debris. In both our radial velocity histograms of the regions surrounding NGC 1851 and NGC 3201, a peak of stars at ∼230 km s −1 is seen, consistent with extended tidal debris from ω Centauri.

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“…Indeed, observing campaigns that monitor globular clusters are still going on both from the ground (e.g. Kains et al 2015Kains et al , 2013Arellano Ferro et al 2015;Carretta et al 2014;Kunder et al 2013;Amigo et al 2013;Figuera Jaimes et al 2013) and from space (e.g. Neeley et al 2015;Contreras Ramos et al 2013;Montiel & Mighell 2010).…”

Section: Introductionmentioning

confidence: 99%

RR Lyrae mode switching in globular cluster M 68 (NGC 4590)

Kains

Bramich

Ferro

et al. 2015

A&A

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We build on our detailed analysis of time-series observations of the globular cluster M 68 to investigate the irregular pulsational behaviour of four of the RR Lyrae stars in this cluster. M 68 is one of only two globular clusters in which mode switching of RR Lyrae stars has previously been reported. We discuss one additional case, as well as a case of irregular behaviour, and we briefly revisit the two previously reported cases with a homogeneous analysis. We find that in 2013, V45 was pulsating in the first-overtone mode alone, despite being previously reported as a double-mode (fundamental and first overtone) pulsator in 1994, and that the amplitude of the fundamental mode in V7 is increasing with time. We also suggest that V21 might not have switched pulsation modes as previously reported, although the first overtone seems to be becoming less dominant. Finally, our analysis of available archival data confirms that V33 lost a pulsation mode between 1950 and 1986.

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THE RR LYRAE VARIABLES AND HORIZONTAL BRANCH OF NGC 6656 (M22)^,

Cited by 86 publications

References 143 publications

The Na-O anticorrelation in horizontal branch stars

The Na-O anticorrelation in horizontal branch stars

Spectroscopic signatures of extratidal stars around the globular clusters NGC 6656 (M 22), NGC 3201, and NGC 1851 from RAVE

RR Lyrae mode switching in globular cluster M 68 (NGC 4590)

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THE RR LYRAE VARIABLES AND HORIZONTAL BRANCH OF NGC 6656 (M22),

Cited by 86 publications

References 143 publications

The Na-O anticorrelation in horizontal branch stars

The Na-O anticorrelation in horizontal branch stars

Spectroscopic signatures of extratidal stars around the globular clusters NGC 6656 (M 22), NGC 3201, and NGC 1851 from RAVE

RR Lyrae mode switching in globular cluster M 68 (NGC 4590)

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THE RR LYRAE VARIABLES AND HORIZONTAL BRANCH OF NGC 6656 (M22)^,