Variable stars in the bulge globular cluster NGC 6401

Abstract

We present a study of variable stars in globular cluster NGC 6401. The cluster is only 5.3 • away from the Galactic centre and suffers from strong differential reddening. The photometric precision afforded us by difference image analysis resulted in improved sensitivity to variability in formerly inaccessible interior regions of the cluster. We find 23 RRab and 11 RRc stars within one cluster radius (2.4 ), for which we provide coordinates, finder-charts and time-series photometry. Through Fourier decomposition of the RR Lyrae star light curves we derive a mean metallicity of [Fe/H] UVES = −1.13 ± 0.06 ([Fe/H] ZW = −1.25 ± 0.06), and a distance of d ≈ 6.35 ± 0.81 kpc. Using the RR Lyrae population, we also determine that NGC 6401 is an Oosterhoff type I cluster.

The burst observer and optical transient exploring system in the multi-messenger astronomy era

“…Since 1998, ROTSE was devoted to searching optical transients and it operates with a wide FOV (1.85°× 1.85°) camera onto f = 1.9 telescopes without filters (Akerlof et al, 2003). • LCOGT (Las Cumbres Observatory Global Telescope) 4 : It is a network composed of 25 telescopes, including 2 × 2-m, 13 × 1m and 10 × 0.4-m, where the 2-m telescopes were operated by RoboNet (Tsapras et al, 2009) prompt optical emission of GRBs but the discovery of uncataloged objects (Gorbovskoy et al, 2013). • SONG (Stellar Observations Network Group) 6 : It is a Danishled project to design and construct a global network of 1m class robotic telescopes in 8 nodes to undertake longtime monitoring.…”

Zwicky Transient Facility and Globular Clusters: the Period–Luminosity and Period–Luminosity–Color Relations for Late-type Contact Binaries

“…In case of M9, a weighted mean of 7.99 ± 0.16 kpc, measured from using the ab-and c-type RR Lyrae (Arellano Ferro et al 2013), was adopted. For the bulge globular cluster NGC6401, the published distances covered a wide range including ≈ 6.35 ± 0.81 kpc (Tsapras et al 2017, by using RR Lyrae) and ≈ 12.0 ± 1.0 kpc (Barbuy et al 1999, by using horizontal branch on V I-band CMD). Therefore, these two NGC6410 distances were adopted to test their impact on the PL relation.…”

Low-Mass and Sub-stellar Eclipsing Binaries in Stellar Clusters

“…To get a rough estimate of this number, we use five recent publications. In the following, we list the total number of observed stars, the included variable stars (known, new, and suspected), and the eclipsing binaries: 7630/40/1 [148]; 4274/59/0 [149]; 132457/359/30 [150], 31762/47/1 [151]; and 11358/13/1 [152]. The number of detected variables in globular clusters is only a few percent from which only a maximum of 10% are eclipsing binaries.…”