Proper motions and membership probabilities of stars in the region of globular cluster NGC 6366

Abstract

Context. NGC 6366 is a metal-rich globular cluster that is relatively unstudied. It is a kinematically interesting cluster, reported as belonging to the slowly rotating halo system, which is unusual given its metallicity and spatial location in the Galaxy. Aims. The purpose of this research is to determine the relative proper motion and membership probability of the stars in the region of globular cluster NGC 6366. To target cluster members reliably during spectroscopic surveys without including field stars, a good proper motion and membership probability catalogue of NGC 6366 is needed. Methods. To derive relative proper motions, the archival data from the Wide Field Imager mounted on the ESO 2.2 m telescope have been reduced using a high precision astrometric software. The images used are in the B, V, and I photometric bands with an epoch gap of ∼3.2 yr. The calibrated BV I magnitudes have been determined using recent data for secondary standard stars. Results. We determined relative proper motions and cluster membership probabilities for 2530 stars in the field of globular cluster NGC 6366. The median proper motion rms errors for stars brighter than V ∼ 18 mag is ∼2 mas yr −1 , which gradually increases to ∼5 mas yr −1 for stars having magnitudes V ∼ 20 mag. Based on the membership catalogue, we checked the membership status of the X-ray sources and variable stars of NGC 6366 mentioned in the literature. We also provide the astronomical community with an electronic catalogue that includes B, V, and I magnitudes; relative proper motions; and membership probabilities of the stars in the region of NGC 6366.

Chemical analysis of eight giant stars of the globular cluster NGC 6366

“…11 the global abundance pattern for NGC 6366, with star 05 highlighted. As previously discussed in Section 4.1, Sariya & Yadav (2015) gave zero membership probability to star 05 based on its proper motion, while our radial velocity measurements suggest a value compatible with NGC 6366 kinematics. Chemically, this star follows the general abundance pattern of the GC.…”

“…Using the cross-correlation method, Johnson et al (2016) found a mean heliocentric RV of −122.3 km s −1 (σ = 1.5 km s −1 ) for NGC 6366. The proper motion analysis of Sariya & Yadav (2015) gave zero membership probability for star 05 and membership probability > 0.95 for stars 03, 07, 08 and 11. Stars 01, 06 and 11 were not present in their study.…”

Photometric and kinematic study of the three intermediate age open clusters NGC 381, NGC 2360, and Berkeley 68

“…The kinematic study of a cluster is important in determining membership of the cluster stars as determination of the membership is essential in the accurate estimation of cluster parameters (e.g., Chen et al 2011;Sariya & Yadav 2015). The major difficulty in determination of the cluster parameters using isochrone fitting is contamination by the field stars.…”

Proper motions of stars in the globular clusters using WFI@2.2 m telescope

“…Our research group derived proper motions and membership probabilities for the stars in the area of globular clusters NGC 6809, NGC 6366 and NGC 3201 (Sariya et al 2012(Sariya et al , 2015(Sariya et al , 2017. Number of the studied stars is ∼12600, 2530 and 8322 for NGC 6809, NGC 6366 and NGC 3201 consecutively.…”

“…Devesh P. Sariya, Ing-Guey Jiang & R. K. S. Yadav Reference stars to calculate proper motions were selected using the position of stars in the color-magnitude diagrams (CMD) and then, the program was iterated to include good proper motion. The detailed procedures to obtain the proper motion has been discussed by A06; Bellini et al (2009); Yadav et al (2008Yadav et al ( , 2013; Sariya et al (2012Sariya et al ( , 2015Sariya et al ( , 2017. A centroid around the cluster proper motion center in the vector point diagrams gives the cluster members.…”