Evolved massive stars at low-metallicity

Abstract

We present a clean, magnitude-limited (IRAC1 or WISE1 ≤ 15.0 mag) multiwavelength source catalog for the Large Magellanic Cloud (LMC). The catalog was built by crossmatching (1″) and deblending (3″) between the source list of Spitzer Enhanced Imaging Products and Gaia Data Release 2, with strict constraints on the Gaia astrometric solution in order to remove the foreground contamination. It is estimated that about 99.5% of the targets in our catalog are most likely genuine members of the LMC. The catalog contains 197 004 targets in 52 different bands, including two ultraviolet, 21 optical, and 29 infrared bands. Additional information about radial velocities and spectral and photometric classifications were collected from the literature. We compare our sample with the sample from Gaia Collaboration (2018, A&A, 616, A12), indicating that the bright end of our sample is mostly comprised of blue helium-burning stars (BHeBs) and red HeBs with inevitable contamination of main sequence stars at the blue end. After applying modified magnitude and color cuts based on previous studies, we identified and ranked 2974 red supergiant, 508 yellow supergiant, and 4786 blue supergiant candidates in the LMC in six color-magnitude diagrams (CMDs). The comparison between the CMDs from the two catalogs of the LMC and Small Magellanic Cloud (SMC) indicates that the most distinct difference appears at the bright red end of the optical and near-infrared CMDs, where the cool evolved stars (e.g., red supergiant stars (RSGs), asymptotic giant branch stars, and red giant stars) are located, which is likely due to the effect of metallicity and star formation history. A further quantitative comparison of colors of massive star candidates in equal absolute magnitude bins suggests that there is essentially no difference for the BSG candidates, but a large discrepancy for the RSG candidates since LMC targets are redder than the SMC ones, which may be due to the combined effect of metallicity on both spectral type and mass-loss rate as well as the age effect. The effective temperatures (Teff) of massive star populations are also derived from reddening-free color of (J − KS)0. The Teff ranges are 3500 < Teff < 5000 K for an RSG population, 5000 < Teff < 8000 K for a YSG population, and Teff > 8000 K for a BSG population, with larger uncertainties toward the hotter stars.

The Sample of Red Supergiants in Twelve Low-Mass Galaxies of the Local Group

“…For LMC (SMC, the following numbers in the brackets refers to SMC), 2,286 (for SMC 921) out of 4,823 (for SMC 2,138) RSGs in our sample can be matched with Yang et al (2021a) and Yang et al (2020) and 2,537 (for SMC 1,217) are new in this work. On the other hand, 688 (for SMC 318) out of 2,974 (for SMC 2,138) RSGs in Yang et al (2021a) are not included in our sample.…”

“…For LMC (SMC, the following numbers in the brackets refers to SMC), 2,286 (for SMC 921) out of 4,823 (for SMC 2,138) RSGs in our sample can be matched with Yang et al (2021a) and Yang et al (2020) and 2,537 (for SMC 1,217) are new in this work. On the other hand, 688 (for SMC 318) out of 2,974 (for SMC 2,138) RSGs in Yang et al (2021a) are not included in our sample. These 688 (for SMC 318) RSGs are distributed on both sides of the common sample in the (J − K) 0 vs. K 0 diagram, which can be caused by the slightly different selection of the red and blue boundaries of the RSGs in the two works.…”

“…This work identifies 4,823 and 2,138 RSGs in LMC and SMC respectively, an apparently much larger sample than the 2,974 and 1,239 RSGs by Yang et al (2021a) and Yang et al (2020).…”

“…In details, the sample galaxies include: the dwarf elliptical (dE) galaxy NGC 147 and NGC 185; dwarf spheroidal (dSph) galaxy Pegasus Dwarf (DDO 216), Sextans A and B; dwarf irregular (dIrr) galaxy IC 10, IC 1613, WLM (DDO 221) and Leo A (DDO 69). In addition, SMC (Irr), LMC (SBm) and NGC 6822 (dIrr) that are well studied by Yang et al (2019Yang et al ( , 2020Yang et al ( , 2021a are also included because the present sample of RSGs can still be improved. The fundamental information about these 12 galaxies is listed in Table 1, including the position, type, diameter, Galactic foreground extinction, and distance modulus (µ) from references.…”

“…Quite some efforts are devoted to distinguish member stars from foreground stars. Yang et al (2019Yang et al ( , 2020 and Yang et al (2021a) separated efficiently the SMC and LMC members from foreground stars by using astrometric solution from Gaia/DR2 and combined a variety of color-magnitude diagrams (CMDs) to identify 1,239 and 2,974 RSGs in SMC and LMC, which is a drastic increase from previous studies (Feast et al 1980;Catchpole & Feast 1981;Wood et al 1983;Pierce et al 2000;Massey 2002;Massey & Olsen 2003;Neugent et al 2012;González-Fernández et al 2015;Yang & Jiang 2011, 2012. This revolutionary progress comes from both more data and the effective method to identify the member stars of the Magellanic Clouds (MCs) since the MC members concentrate on the proper motions expected from the motion of MCs relative to the Galaxy.…”