RR Lyrae stars in the globular cluster Palomar 2

A CCD VI imaging time-series over 11-year is employed to explore the light curves of stars in the field of Palomar 2. We discovered 20 RRab and 1 RRc variables. A revision of Gaia-DR3 data enabled us to identify 10 more variables and confirm the RRab nature of 6 of them and one RGB. The cluster membership is discussed and 18 variables are most likely cluster members. The Fourier light curve decomposition for the 11 best quality light curves of cluster member stars leads to independent estimates of the cluster distance 27.2 +- 1.8 kpc and [Fe/H]ZW=-1.39 +- 0.55. We confirm the cluster as of the Oo I type.Comment: 10 pages, 6 figures, 1 table. Submitted to Revista Mexicana de Astronom\'ia y Astrof\'isic

The variable stars in the field of NGC 6139: A critical approach to their reddening and membership

We present a CCD $VI$ time-series analysis of the globular cluster NGC 6139 and its variable star population. Using the astrometric data available in $Gaia$-DR3 we performed a membership analysis that enabled the construction of a clean Colour-Magnitude Diagram (CMD). Variable stars in the field of the cluster reported by $Gaia$-DR3 and newly discovered ones in this paper are classified and their membership is critically evaluated. We report two cluster member RRc (V12, V15) and four SR (V13, V14, V17, V18) not previously detected and assign variable names to V11 and V16 detected by $Gaia$ as they proof to be cluster members. Light curves and periods for non-member $Gaia$ eclipsing binaries, semi regular variables and newly detected RR Lyrae stars are provided. Fourier decomposition of the light curves of the cluster member RRab and RRc stars leads to the values [Fe/H]=$-1.63$ dex, and distance of 9.63$\pm$0.68 kpc. The Oosterhoff type II nature of the cluster is confirmed. We adopted the mean reddening $E(B-V)$=0.786 mag and performed a differential reddening analysis based on the dispersion of the red giant branch. The differential map allowed a mild correction of the CMD.Comment: 12 pages, 10 figures, 5 table

Variable stars in the field of the Galactic bulge globular cluster NGC 6522

We present a comprehensive analysis of the variable stars projected on the field of the Galactic bulge globular cluster NGC 6522, offering valuable insights into their characteristics. Using proper motions from Gaia DR3, we aim to distinguish between field stars and true cluster members. For an accurate color-magnitude diagram of the member stars, we produced a differential reddening map. We detect and discuss the peculiarities of variable stars of the types RR Lyrae, type II Cepheids, Long Period Variables (LPV) and eclipsing binaries, whose light curves are available through the OGLE III and IV databases. Notably, we explore the variable V24, which shows a prominent phase modulation resulting from period changes in a time scale of ~1100 days. The variable stars among the cluster members serve as indicators of the cluster metallicity and distance; these determinations are based on their light curves. With the Fourier light curve decomposition of three RRc stars, we have derived the following cluster parameters: the metallicity in the spectroscopic scale [Fe/H]$_{\rm UVES}$=--1.16 $\pm$0.09; and the mean distance $D=8.77 \pm 0.16$ kpc.Comment: 15 pages, 10 Figures, 3 table

A revisit to the region of Collinder 132 using Carte du Ciel and Astrographic Catalogue plates

Aims. Based on stellar positions and proper motions, we aim to re-analyse the region of the controversial open cluster Collinder 132. Methods. We have developed a model which analyses the proper motion distribution and the stellar density to find moving groups. The astrometric data were obtained from four Carte du Ciel (CdC) and one Astrogaphic Catalogue (AC) plates of the Córdoba Astronomical Observatory collection (Argentina). Results. We detected an open cluster from the field stars and calculated the mean proper motion and the membership probabilities of the region's stars. We report new coordinates of its centre αc = 108\fdg347, δc = -31\fdg011, the components of mean proper motion μ αcosδ = -2.62±0.44 mas/yr, μδ = 4.79±0.88 mas/yr. Thirteen stars are astrometric members giving a value of 20' for the cluster angular diameter. Six stars fulfil the astrometric and photometric criteria for being cluster members and locate the cluster at 360 pc from the Sun. We propose a simple model for the analysis of the proper motion distribution of an association. We report the components of the association mean proper motion μαcosδ = -1.38±0.14 mas/yr, μδ = 2.26±0.16 mas/yr. We found 149 astrometric members, 11 of which have reliable photometric data that locate them betweeen 417 and 660 pc from the Sun.Este documento tiene una corrección (ver documento relacionado).Instituto de Astrofísica de La PlataFacultad de Ciencias Astronómicas y Geofísica

A revisit to the regions of some van den Bergh open clusters using photometric and astrometric parameters

We present results of a study that combines photometry and astrometry for the open clusters vdB80, vdB85 and vdB130. We apply a model which analyses the proper motion distribution and the stellar density to find the kinematic parameters and stellar membership in the region of the mentioned open clusters. The astrometric data are obtained from UCAC4 catalogue. For each cluster, we report the centre coordinates, the components of mean proper motion, the angular diameter and the astrometric members. They are: α=97°.73938±0°.00846,δ=-9°.66953±0°.01177,μαcosδ=-2.13±0.47mas/yr,μδ=-0.95±0.47mas/yr,12′ , 15 members; vdB85: α=101°.71670±0°.00808,δ=1°.34392±0°.01253,μαcosδ=0.89±0.43mas/yr,μδ=3.24±0.43mas/yr,8′ members; vdB130: α=304°.44001±0°.01407,δ=39°.32745±0°.00726,μαcosδ=-4.14±0.25mas/yr,μδ=-5.15±0.25mas/yr,9′ 9 members. We analyse the incidence of the proper motion errors in the determination of the cluster parameters and of the stellar membership and find that they are not significantly changed. We finally compare the astrometric members with the photometric ones given in the literature.Instituto de Astrofísica de La PlataFacultad de Ciencias Astronómicas y Geofísica