Abstract
We derive relative proper motions of stars in the fields of the globular clusters M12, NGC 6362, M4, M55, M22, NGC 6752, NGC 3201, M30, M10, NGC 362, M5 and 47 Tucanae based on data ...collected between 1997 and 2015 with the 1-m Swope telescope of Las Campanas Observatory. We determine membership class and membership probability for over 446 000 objects, and show that these are efficient methods for separating field stars from members of the cluster. In particular, membership probabilities of variable stars and blue/yellow/red stragglers are determined. Finally, we find absolute proper motions for six globular clusters from our sample: M55, NGC 3201, M10, NGC 362, M5 and 47 Tuc. An electronic catalogue of the derived proper motions is publicly available via the internet.
ABSTRACT
We use photometric and spectroscopic observations of the eclipsing binary E32 in the globular cluster 47 Tuc to derive the masses, radii, and luminosities of the component stars. The system ...has an orbital period of 40.9 d, a markedly eccentric orbit with e = 0.24, and is shown to be a member of or a recent escaper from the cluster. We obtain $M_{\rm p} = 0.862\pm 0.005 \, \mathrm{M}_\odot$, $R_{\rm p} = 1.183\pm 0.003 \, \mathrm{R}_\odot$, $L_{\rm p} = 1.65\pm 0.05 \, \mathrm{L}_\odot$ for the primary and $M_{\rm s} = 0.827\pm 0.005 \, \mathrm{M}_\odot$, $R_{\rm s} = 1.004\pm 0.004 \, \mathrm{R}_\odot$, $L_{\rm s} = 1.14\pm 0.04\, \mathrm{L}_\odot$ for the secondary. Based on these data and on an earlier analysis of the binary V69 in 47 Tuc, we measure the distance to the cluster from the distance moduli of the component stars, and, independently, from a colour – surface brightness calibration. We obtain 4.55 ± 0.03 and 4.50 ± 0.07 kpc, respectively – values compatible within 1$\, \sigma$ with recent estimates based on Gaia DR2 parallaxes. By comparing the M–R diagram of the two binaries and the colour–magnitude diagram of 47 Tuc to Dartmouth model isochrones we estimate the age of the cluster to be 12.0 ± 0.5 Gyr, and the helium abundance of the cluster to be Y ≈ 0.25.
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 days, respectively. The measured masses of the primary and secondary components (M sub(p), M sub(s)) are (0.8337 + or - 0.0063, 0.7947 + or - 0.0048) M sub(middot in circle) for V40 and (0.8215 + or - 0.0058, 0.7280 + or - 0.0047) M sub(+ or -) for V41. The measured radii (R sub(p), R sub(s)) are (1.3253 + or - 0.0075, 0.997 + or - 0.013) R sub(middot in circle) for V40 and (1.0739 + or - 0.0048, 0.7307 + or - 0.0046) R sub(middot in circle) for V41. Based on the derived luminosities, we find that the distance modulus of the cluster is 14.74 + or - 0.04 mag-in good agreement with 14.72 mag obtained from color-magnitude diagram (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, alpha /Fe = 0.4, and Y = 0.25 we find the most probable age of V40 to be 11.7 + or - 0.2 Gyr, compatible with the age of the cluster derived from CMD fitting (12.5 + or - 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.
Context. Origin and evolution of blue stragglers in globular clusters is still a matter of debate. Aims. The aim of the present investigation is to reproduce the evolutionary history of four binary ...blue stragglers in four different clusters, for which precise values of global parameters are known. Methods. Using the model for cool close binary evolution that we developed, progenitors of all investigated binaries were found and their parameters evolved into the presently observed values. Results. The results show that the progenitors of the binary blue stragglers are cool close binaries with period of a few days, which transform into stragglers by rejuvenation of the initially less massive component as a result of mass transfer from its more massive companion overflowing the inner critical Roche surface. The parameters of V209 from omega Cen indicate that the binary is substantially enriched in helium. This is an independent and strong evidence of the existence of the helium rich subpopulation in this cluster.
ABSTRACT
We use photometric and spectroscopic observations of four detached eclipsing binaries in the globular cluster NGC 3201 to derive masses, radii, and luminosities of the component stars. ...Spanning across almost three magnitudes in the colour–magnitude diagram, the components offer a unique possibility to test the theory of stellar evolution. Their masses, radii, and luminosities range from 0.66 to 0.84 M⊙, 0.68 to 2.46 R⊙, and 0.38 to 5.56 L⊙, respectively. The distance to the cluster measured from the distance moduli of the component stars amounts to 4.54$^{+0.11}_{-0.14}$ kpc and agrees with the recent estimate based on Gaia parallaxes. By comparing the M − R and M − L diagrams of the component stars and the colour–magnitude diagram of NGC 3201 to Dartmouth model isochrones, we estimate the most probable age of the cluster to be 11.5 ± 0.5 Gyr. This estimate is based on three binaries only, as the fourth one seems to evolve along a different path, probably due to non-standard chemical composition and/or history. We confirm the tendency, observed in earlier CASE papers, for the age indicated by the M − R diagram to be younger than that implied by the colour–magnitude diagram.
We use photometric and spectroscopic observations of the eclipsing binaries V65, V66, and V69 in the field of the globular cluster M4 to derive masses, radii, and luminosities of their components. ...The orbital periods of these systems are 2.29, 8.11, and 48.19 days, respectively. Based on systemic velocities and relative proper motions, we show that all three systems are members of the cluster. We find that the distance to M4 is 1.82 + or - 0.04 kpc-in good agreement with recent estimates based on entirely different methods. We compare the absolute parameters of V66 and V69 with two sets of theoretical isochrones in mass-radius and mass-luminosity diagrams, and for assumed Fe/H = -1.20, alpha /Fe = 0.4, and Y = 0.25 we find the most probable age of M4 to be between 11.2 and 11.3 Gyr. Age and distance determinations can be further improved when infrared eclipse photometry is obtained.
We present photometric and spectroscopic analysis of AE For - a detached eclipsing binary composed of two late K dwarfs. The masses of the components are found to be 0.6314 ± 0.0035 and 0.6197 ± ...0.0034 M and the radii to be 0.67 ± 0.03 and 0.63 ± 0.03 R for primary and secondary component, respectively. Both components are significantly oversized compared to theoretical models, which we attribute to their high activity. They show Hα, Hβ, Hγ, Ca H and Ca K in emission, and are heavily spotted, causing large variations of the light curve.
RR Lyrae stars in NGC 6362 Smolec, R; Moskalik, P; Kałużny, J ...
Monthly notices of the Royal Astronomical Society,
05/2017, Volume:
467, Issue:
2
Journal Article
Peer reviewed
Open access
Abstract
We present the analysis of the top-quality photometry of RR Lyrae stars in the globular cluster NGC 6362, gathered over 11 observing seasons by the Cluster AgeS Experiment (CASE) project. 16 ...stars are fundamental mode pulsators (RRab stars) and 16 are first overtone pulsators (RRc stars). In two stars, previously identified as RRab, V3 and V34, we detect additional periodicity identified as radial first overtone mode. Lower than usual period ratios (0.730 and 0.728), dominant pulsation in the radial fundamental mode and presence of a long-period modulation indicate that these two variables are not classical RRd stars, but are new members of the recently identified class of anomalous RRd variables. In a significant fraction of RRc stars, 63 per cent, we detect additional shorter period variability in the (0.60, 0.65)P1 range. This form of double-periodic pulsation must be common in first overtone RR Lyr stars, as space observations indicate. The incidence rate we find in NGC 6362 is the highest in ground-based observations reported so far. We study the properties of these stars in detail; in particular, we confirm that in the colour–magnitude diagram, this group is adjacent to the interface between RRab and RRc stars, as first reported in the analysis of M3 observations by Jurcsik et al. The incidence rate of the Blazhko effect is also very high: we observe it in 69 per cent of RRab stars and in 19 per cent of RRc stars. Rare, double-periodic modulation is reported in one RRab and in one RRc star. Finally, we discuss V37 – a peculiar variable in which we detect two close high-amplitude periodicities and modulation. Its previous classification as RRc must be treated as tentative.
We report a spectroscopic study of 19 photometric variables and 55 blue, yellow, and red straggler candidates in the field of ω Centauri. We confirm the cluster membership of 18 variables and ...54 straggler candidates. Velocity variations are detected in 22 objects, and another 17 objects are suspected to be velocity-variable. The velocities of 11 objects vary consistently with their photometric periods, allowing their mass functions to be calculated. Among them, we find no indication of the presence of a massive degenerate component. On the basis of both photometric and spectroscopic data, we estimate that the fraction of binaries among blue stragglers may be as high as 69 per cent.
A SECOND NEUTRON STAR IN M4? Kaluzny, J; Rozanska, A; ROZYCZKA, M ...
Astrophysical journal. Letters,
05/2012, Volume:
750, Issue:
1
Journal Article
Peer reviewed
Open access
We show that the optical counterpart of the X-ray source CX 1 in M4 is a ~20th magnitude star, located in the color-magnitude diagram on (or very close to) the main sequence of the cluster, and ...exhibiting sinusoidal variations of the flux. We find the X-ray flux to be also periodically variable, with X-ray and optical minima coinciding. Stability of the optical light curve, lack of UV-excess, and unrealistic mean density resulting from period-density relation for semidetached systems speak against the original identification of CX 1 as a cataclysmic variable. We argue that the X-ray active component of this system is a neutron star (probably a millisecond pulsar).
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