Evolved massive stars at low-metallicity

Abstract

We present a clean, magnitude-limited (IRAC1 or WISE1 ≤ 15.0 mag) multiwavelength source catalog for the Small Magellanic Cloud (SMC) with 45 466 targets in total, with the purpose of building an anchor for future studies, especially for the massive star populations at low-metallicity. The catalog contains data in 50 different bands including 21 optical and 29 infrared bands, retrieved from SEIP, VMC, IRSF, AKARI, HERITAGE, Gaia, SkyMapper, NSC, Massey (2002, ApJS, 141, 81), and GALEX, ranging from the ultraviolet to the far-infrared. Additionally, radial velocities and spectral classifications were collected from the literature, and infrared and optical variability statistics were retrieved from WISE, SAGE-Var, VMC, IRSF, Gaia, NSC, and OGLE. The catalog was essentially built upon a 1″ crossmatching and a 3″ deblending between the Spitzer Enhanced Imaging Products (SEIP) source list and Gaia Data Release 2 (DR2) photometric data. Further constraints on the proper motions and parallaxes from Gaia DR2 allowed us to remove the foreground contamination. We estimate that about 99.5% of the targets in our catalog are most likely genuine members of the SMC. Using the evolutionary tracks and synthetic photometry from MESA Isochrones & Stellar Tracks and the theoretical J − KS color cuts, we identified 1405 red supergiant (RSG), 217 yellow supergiant, and 1369 blue supergiant candidates in the SMC in five different color-magnitude diagrams (CMDs), where attention should also be paid to the incompleteness of our sample. We ranked the candidates based on the intersection of different CMDs. A comparison between the models and observational data shows that the lower limit of initial mass for the RSG population may be as low as 7 or even 6 M⊙ and that the RSG is well separated from the asymptotic giant branch (AGB) population even at faint magnitude, making RSGs a unique population connecting the evolved massive and intermediate stars, since stars with initial mass around 6 to 8 M⊙ are thought to go through a second dredge-up to become AGB stars. We encourage the interested reader to further exploit the potential of our catalog.

Evolved massive stars at low-metallicity

“…The comparison between our sample and Gaia Collaboration et al (2018b) indicates that 99.98% of our targets are consistent with their results. This suggests that our results are highly reliable without sophisticated correction (see more details and discussion in Section 2 of Yang et al 2019). Figure 4 shows PM R.A. versus PM Decl.…”

“…The procedure we used for data reduction is the same as in Yang et al (2019), hence we briefly describe the procedure here. More details can be found in the original paper.…”

“…Green contours show the number density in each digram. After selecting the fiducial sample of 197,004 targets, we retrieved the following additional data (deblended with a search radius of 3 ) by using a search radius of 1 from different dataset ranging from the ultraviolet (UV) to far-infrared (FIR) as shown below (more details about each dataset can be found in Yang et al 2019): 44,524 matches (∼23%) from the VISTA survey of the Magellanic Clouds system (VMC) DR4 (Cioni et al 2011)); 136,935 matches (∼70%) from the IRSF Magellanic Clouds point source catalog (MCPS) (Kato et al 2007); 37,116 matches (∼19%) from AKARI LMC point source catalog (Onaka et al 2007;Murakami et al 2007;Kato et al 2012); 49 matches from HERschel Inventory of the Agents of Galaxy Evolution (HER-ITAGE) band-merged source catalog (units are in flux [mJy] instead of magnitude; Pilbratt et al 2010;Meixner et al 2013;Seale et al 2014); 162,462 matches (∼82%) from SkyMapper DR1.1 (Keller et al 2007;Bessell et al 2011;Wolf et al 2018); 151,476 matches (∼77%) from the NOAO source catalog (NSC) DR1 (Nidever et al 2018)); 20,379 matches (∼10%) from a UBVR CCD survey of the MCs by Massey (2002) (M2002); 74,104 matches (∼38%) from Optical Gravitational Lensing Experiment (OGLE; Udalski et al 1992;Szymanski 2005;Udalski et al 2008Udalski et al , 2015 Shallow Survey in the LMC (Ulaczyk et al 2012); 215 matches from revised GALEX source catalog for the All-Sky Imaging Survey (GUVcat_AIS) (Morrissey et al 2007;Bianchi et al 2017).…”

“…The massive star candidates, for example, blue supergiant stars (BSGs), yellow supergiant stars (YSGs), and red supergiant stars (RSGs), were identified by utilizing evolutionary tracks and synthetic photometry. This also showed that there was a relatively clear separation between RSGs and asymptotic giant branch stars (AGBs) down to the tip of the red giant branch (TRGB) after the astrometric constraints (see Figure 15 of Yang et al 2019), even though the following study of Yang et al (2020) also indicates that the boundary between RSGs and AGBs is still blurred in all aspects.…”

“…We already built a source catalog for the SMC (Yang et al 2019), by applying strict constraints on the Gaia astrometric so-lution and collecting a large amount of multiwavelength photometry and time-series data, as well as auxiliary spectroscopic and/or photometric classifications from the literature. The massive star candidates, for example, blue supergiant stars (BSGs), yellow supergiant stars (YSGs), and red supergiant stars (RSGs), were identified by utilizing evolutionary tracks and synthetic photometry.…”