A new, Gaia-based, catalogue of blue straggler stars in open clusters

Abstract

Context. Blue straggler stars are exotic objects present in all stellar environments whose nature and formation channels are still partially unclear. They seem to be particularly abundant in open clusters (OCs), thus offering a unique chance to tackle these problems statistically. Aims. We aim to build up a new and homogeneous catalogue of blue straggler stars (BSS) in Galactic OCs using Gaia to provide a more solid assessment of the membership of these stars. We also aim to explore possible relationships of the straggler abundance with the parent cluster's structural and dynamical parameters. As a by-product, we also search for possible yellow straggler stars (YSS), which are believed to be stragglers in a more advanced evolution stage. Methods. We employed photometry, proper motions, and parallaxes extracted from Gaia DR2 for 408 Galactic star clusters and searched for stragglers within them after performing a careful membership analysis. Results. The number of BBS emerging from our more stringent, selection criteria turns out to be significantly smaller than in previous versions of this catalogue. OCs are therefore not a preferable environment for these kinds of stars anymore. In addition, we found that BSS start to appear in clusters with ages larger than log(t) ∼ 8.7 and are therefore absent in very young star clusters. Conclusions. The present catalogue supersedes the previous ones in several ways: membership assessment, number of stragglers found, and so forth. The new list includes 897 BSS and 77 YSS candidates in 408 OCs. We expect this catalogue to be the basis for a new round of studies of BSS and YSS.

UOCS VII. Blue Straggler Populations of Open Cluster NGC 7789 with UVIT/AstroSat

“…Upon comparing our 16 BSS candidates with the BSS candidates identified by Rain, Ahumada, & Carraro (2021), we find 9 BSS to be common. 4 BSS candidates identified by Nine et al (2020) and 3 BSS candidates identified by Rao et al (2021) are missing in Rain, Ahumada, & Carraro (2021). Most of their remaining 7 BSS candidates are located beyond 28 from the cluster center, the radius of the cluster as per Rao et al (2021).…”

“…Blue straggler stars (BSS) are one of the exotic stellar populations whose evolution differs from normal single stars. They are commonly found in diverse stellar environments such as globular clusters (Sandage 1953;Fusi Pecci et al 1992;Sarajedini 1993), open clusters (Johnson & Sandage 1955;Burbidge & Sandage 1958;Sandage 1962;Rain, Ahumada, & Carraro 2021), dwarf galaxies (Momany et al 2007;Mapelli et al 2009), and galactic fields (Preston & Snedon 2000). There are three fundamental mechanisms that explain the formation of BSS: (a) direct stellar collisions in dynamical interactions in dense stellar environments (Hills & Day 1976), (b) mass transfer in close binary systems (McCrea 1964), and (c) merger or mass transfer of an inner binary in a triple system through Kozai mechanism (Perets & Fabrycky 2009).…”

“…Cantat-Gaudin et al (2018) estimated the distance of the cluster to be 2075 pc based on the Gaia DR2 membership analysis. Using the cluster members identified by Cantat-Gaudin et al (2018) and Cantat-Gaudin & Anders (2020), a BSS catalogue of 408 open clusters was presented by Rain, Ahumada, & Carraro (2021). They reported 16 BSS candidates in NGC 7789.…”

Highlights of Discoveries for δ Scuti Variable Stars From the Kepler Era

“…The A-F main-sequence stars occupy a small region in the center of the H-R diagram, but have been differentiated into not only δ Sct and γ Doradus (abbreviated as γ Dor) variables (Pollard, 2009;Balona et al, 2011a), but also metallic-line A (Am) (Smalley et al, 2017), peculiar abundance A (Ap) (Mathys et al, 2020), rapidly-oscillating Ap (roAp) (Holdsworth, 2021) stars, α 2 CVn variables (Sikora et al, 2019), λ Boo stars (Murphy and Paunzen, 2017), the High Amplitude δ Sct (HADS) (McNamara, 2000) and SX Phe (Nemec et al, 2017) stars, blue stragglers (Rain et al, 2021), and the maybe "mythical" 1 Maia variables (Breger, 1980;Cox, 1983;Daszyńska-Daszkiewicz et al, 2017;White et al, 2017;Balona, 2018). Kepler observations have revealed overlap and commonalities among these types, pointing the way to a more fundamental understanding of the origins of the diverse phenomena seen in these stars.…”

Clean catalogues of blue horizontal-branch stars using Gaia EDR3

“…Those with an effective temperature of T eff ≥ 10 000 K have spectra that are similar to the much younger population I Btype main-sequence stars but with weaker Helium lines, which can be distinguished spectroscopically (see Figure 1). The main challenge in producing a catalogue of low contamination is differentiating between blue horizontal-branch stars and younger, population I main-sequence A-type and B-type stars as well as blue stragglers, which are older, population II main-sequence stars that have been rejuvenated through acquisition of additional mass (Rain et al 2021) and that display A-type spectra. The additional mass may be gained by Roche Lobe overflow in a close binary system (McCrea 1964), through stellar merger (Hills & Day 1976;Davies et al 1994), or both.…”