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Register a new userA proper motion study of the globular cluster M10
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L. Chen
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We present the first proper motion study of M10 (NGC6254). Absolute proper motions of about 532 stars in the field of the globular cluster M10 were determined with respect to Hipparcos and ACT reference stars. In addition to photographic plates of Bonn and Shanghai also wide field CCD observations as second epoch plates were used. The wide field CCD observations show an accuracy comparable to that of the photographic plates. A good coincidence of the solutions based on reference stars from Hipparcos and from ACT was found. Our final proper motions allow a sufficient separation of cluster and field stars. Two population II Cepheids were confirmed to be members of M10. The absolute proper motion of M10 was determined and combined with its distance from the Sun and its radial velocity. The space motion and metallicity of M10 indicates the characteristics of a halo object with an orbit reaching to a maximal z-distance of less than 3kpc.
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We have derived the absolute proper motion (PM) of the globular cluster M55 using a large set of CCD images collected with the du Pont telescope between 1997 and 2008. We find (PM_RA*cos(DEC), PM_DEC) = (-3.31 +/- 0.10, -9.14 +/- 0.15) mas/yr relative to background galaxies. Membership status was determined for 16 945 stars with 14<V<21 from the central part of the cluster. The PM catalogue includes 52 variables of which 43 are probable members of M55. This sample is dominated by pulsating blue straggler stars but also includes 5 eclipsing binaries, three of which are main sequence objects. The survey also identified several candidate blue, yellow and red straggler stars belonging to the cluster. We detected 15 likely members of the Sgr dSph galaxy located behind M55. The average PM for these stars was measured to be (PM_RA*cos(DEC), PM_DEC)=(-2.23 +/- 0.14, -1.83 +/- 0.24) mas/yr.
With a high value of heliocentric radial velocity, a retrograde orbit, and being suspected to have an extragalactic origin, NGC 3201 is an interesting globular cluster for kinematical studies. Our purpose is to calculate the relative proper motions (PMs) and membership probability for the stars in the wide region of globular cluster NGC 3201. Proper motion based membership probabilities are used to isolate the cluster sample from the field stars. The membership catalogue will help address the question of chemical inhomogeneity in the cluster. Archive CCD data taken with a wide-field imager (WFI) mounted on the ESO 2.2m telescope are reduced using the high-precision astrometric software developed by Anderson et al. for the WFI images. The epoch gap between the two observational runs is $sim$14.3 years. To standardize the $BVI$ photometry, Stetsons secondary standard stars are used. The CCD data with an epoch gap of $sim$14.3 years enables us to decontaminate the cluster stars from field stars efficiently. The median precision of PMs is better than $sim$0.8 mas~yr$^{-1}$ for stars having $V<$18 mag that increases up to $sim$1.5 mas~yr$^{-1}$ for stars with $18<V<20$ mag. Kinematic membership probabilities are calculated using proper motions for stars brighter than $Vsim$20 mag. An electronic catalogue of positions, relative PMs, $BVI$ magnitudes and membership probabilities in $sim$19.7$times$17 arcmin$^2$ region of NGC 3201 is presented. We use our membership catalogue to identify probable cluster members among the known variables and $X$-ray sources in the direction of NGC 3201.
Using astrometric techniques developed by Anderson et al., we determine proper motions (PMs) in 14.60 arcmin X 16.53 arcmin area of the kinematically thick-disk globular cluster M12. The clusters proximity and sparse nature makes it a suitable target for ground-based telescopes. Archive images with time gap of 11.1 years were observed with wide-field imager (WFI) mosaic camera mounted on ESO 2.2 m telescope. The median value of PM error in both components is 0.7 mas/yr for the stars having V less than or equal to 20 mag. PMs are used to determine membership probabilities and to separate field stars from the cluster sample. In electronic form, a membership catalog of 3725 stars with precise coordinates, PMs, BVRI photometry is being provided. One of the possible applications of the catalog was shown by gathering the membership information of the variable stars, blue stragglers and X-ray sources reported earlier in the clusters region.
The field of the globular cluster M10 (NGC 6254) was monitored between 1998 and 2015 in a search for variable stars. V -light curves were derived for 40 variables or likely variables, most of which are new detections. Proper motions obtained within the CASE project indicate that 18 newly detected variables and 14 previously known ones are members or likely members of the cluster, including one RRc-type, three type II Cepheids, and 14 SX Phe-type pulsators, one contact binary, and six semi-regular red giants. As a byproduct of the search we discovered a candidate binary comprised of main sequence stars with the record-short orbital period of 0.042 d. We also confirmed the photometric variability of the red straggler M10-VLA1 hinted at by Shishkovsky et al. (2018), who discovered this object spectroscopically. In Appendix 1 we show that CASE proper motion measurements are in a good agreement with those retrieved from the Gaia archive, while Appendix 2 presents evidence for low frequency {gamma} Doradus-type oscillations in SX Phe stars belonging to M10.
We derive relative proper motions of stars in the fields of globular clusters M4, M12, M22, NGC 3201, NGC 6362 and NGC 6752 based on a uniform data set collected between 1997 and 2008. We assign a membership class for each star with a measured proper motion, and show that these membership classes can be successfully used to eliminate field stars from color-magnitude diagrams of the clusters. They also allow for the efficient selection of rare objects such as blue/yellow/red stragglers and stars from the asymptotic giant branch. Tables with proper motions and photometry of over 87000 stars are made publicly available via the Internet.
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