The Cluster Ages Experiment (Case). Vii. Analysis of Two Eclipsing Binaries in the Globular Cluster NGC 6362

Abstract

We use photometric and spectroscopic observations of the detached eclipsing binaries V40 and V41 in the globular cluster NGC 6362 to derive masses, radii, and luminosities of the component stars. The orbital periods of these systems are 5.30 and 17.89 d, respectively. The measured masses of the primary and secondary components (M p , M s ) are (0.8337±0.0063, 0.7947±0.0048) M ⊙ for V40 and (0.8215±0.0058, 0.7280±0.0047) M ⊙ for V41. The measured radii (R p , R s ) are (1.3253±0.0075, 0.997±0.013) R ⊙ for V40 and (1.0739±0.0048, 0.7307±0.0046) R ⊙ for V41. Based on the derived luminosities, we find that the distance modulus of the cluster is 14.74±0.04 mag -in good agreement with 14.72 mag obtained from CMD fitting. We compare the absolute parameters of component stars with theoretical isochrones in mass-radius and mass-luminosity diagrams. For assumed abundances [Fe/H] = -1.07, [α/Fe] = 0.4, and Y = 0.25 we find the most probable age of V40 to be 11.7±0.2 Gyr, compatible with the age of the cluster derived from CMD fitting (12.5±0.5 Gyr). V41 seems to be markedly younger than V40. If independently confirmed, this result will suggest that V41 belongs to the younger of the two stellar populations recently discovered in NGC 6362. The orbits of both systems are eccentric. Given the orbital period and age of V40, its orbit should have been tidally circularized some ∼7 Gyr ago. The observed eccentricity is most likely the result of a relatively recent close stellar encounter. : individual (NGC 6362) -stars: individual (V40 NGC 6362, V41 NGC 6362) * This paper includes data gathered with the 6.5-m Magellan Baade and Clay Telescopes, and the 2.5-m du Pont Telescope located at Las Campanas Observatory, Chile.

Constraints on the Distance Moduli, Helium and Metal Abundances, and Ages of Globular Clusters from their RR Lyrae and Non-variable Horizontal-branch Stars. III. M55 and NGC 6362

“…Interestingly, both figures give the impression that V40 and V41 follow somewhat different M-R relations, even on the (log T eff , M V )-plane despite the large error bars attached to the derived temperatures. Kaluzny et al (2015) noticed the same thing, but whereas they tentatively suggested that this was due to a ∼ 1.5 Gyr age difference, the more likely explanation is that V40 has a slightly lower initial helium abundance than V41 (by only ∆Y ∼ 0.007) given that the cluster HB shows unambiguous evidence for a much larger spread in Y .…”

“…The masses and radii of the detached eclipsing binary in M 55 (known as V54) have been derived to within 2.1% and 0.95%, respectively, by Kaluzny et al (2014). The same group (see Kaluzny et al 2015) have been able to measure the masses of the components of two detached eclipsing binaries, V40 and V41, in NGC 6362 to better than 0.71%, as compared with radius uncertainties of < 1.3%. Mean magnitudes and colors of the 15 RR Lyrae variables that have been found in M 55 are provided by Olech et al (1999), who also measured these quantities in the nearly three dozen RR Lyrae that reside in NGC 6362 (Olech et al 2001).…”

The Cluster AgeS Experiment (CASE) – VIII. Age and distance of the Globular Cluster 47 Tuc from the analysis of two detached eclipsing binaries

“…The methods and assumptions we employ follow the ideas of Paczyński (1997) and Thompson et al (2001); more details can be found in Kaluzny et al (2002). Thus far, we have presented results for eight binaries with MS or SG components in four GCs: 47 Tuc (Thompson et al 2010, hereafter TK10), M4 (Kaluzny et al 2013b), M55 ) and NGC 6362 (Kaluzny et al 2015). These are the first and, to the best of our knowledge, the only direct measurements of the fundamental parameters of such stars in GCs.…”

A proper motion study of the globular cluster M12 (NGC 6218)

“…Our PMs are clearly in consistence with those presented by Zl12 up to 20 V mag. Kaluzny et al (2015) and the UV variables found in GUVV2 catalog (ID V (UV ) . ID represents the corresponding star number in our catalog.…”