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.
We adapt the friends of friends algorithm to the analysis of light curves, and show that it can be succesfully applied to searches for transient phenomena in large photometric databases. As a test ...case we search OGLE-III light curves for known dwarf novae. A single combination of control parameters allows us to narrow the search to 1% of the data while reaching a ≈90% detection efficiency. A search involving ≈2% of the data and three combinations of control parameters can be significantly more effective - in our case a 100% efficiency is reached. The method can also quite efficiently detect semi-regular variability. In particular, 28 new semi-regular variables have been found in the field of the globular cluster M22, which was examined earlier with the help of periodicity-searching algorithms.
Based on over 3000 BV images of M4 collected in years 1995-2009 we obtain light curves of 22 variables, 10 of which are newly detected objects. We identify four detached eclipsing binaries and eight ...contact binaries. Accurate periods are found for all but two variables. Nineteen variables are proper-motion members of the cluster, and the remaining three are field stars. Five variables are optical counterparts of X-ray sources. For one of the variables unassociated with Xray sources we report a flare lasting for about 90 min and reaching an amplitude of Delta V=0.11 mag. One of the new contact binaries has a record-low mass ratio q=0.06. Another four such systems show season-to-season luminosity variations probably related to magnetic activity cycles, whose lengths are surprisingly similar to that of the solar cycle despite a huge difference in rotational periods. The location of contact binaries on the color-magnitude diagram of M4 strongly suggests that at least in globular clusters the principal factor enabling EW systems to form from close but detached binaries is stellar evolution. We identify 46 blue and yellow stragglers in M4 and discuss their properties. We also derive a map of the differential extinction in the central part of M4, and determine the reddening of a selected reference region, E (B-V)=0.392 mag.
The field of the globular cluster M22 (NGC 6656) was monitored between 2000 and 2008 in a search for variable stars. BV light curves were obtained for 359 periodic, likely periodic, and long-term ...variables, 238 of which are new detections. 39 newly detected variables, and 63 previously known ones are members or likely members of the cluster, including 20 SX Phe, 10 RRab and 16 RRc type pulsators, one BL Her type pulsator, 21 contact binaries, and 9 detached or semi-detached eclipsing binaries. The most interesting among the identified objects are V112 - a bright multimode SX Phe pulsator, V125 - a β Lyr type binary on the blue horizontal branch, V129 - a blue/yellow straggler with a W UMa-like light curve, located halfway between the extreme horizontal branch and red giant branch, and V134 - an extreme horizontal branch object with P=2.33 d and a nearly sinusoidal light curve. All four of them are proper motion members of the cluster. Among nonmembers, a P=2.83 d detached eclipsing binary hosting a δ Sct type pulsator was found, and a peculiar P=0.93 d binary with ellipsoidal modulation and narrow minimum in the middle of one of the descending shoulders of the sinusoid. We also collected substantial new data for previously known variables. In particular we revise the statistics of the occurrence of the Blazhko effect in RR Lyr type variables of M22.
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