The VLT-FLAMES Tarantula Survey

Abstract

Aims. We estimate physical parameters for the late-type massive stars observed as part of the VLT-FLAMES Tarantula Survey (VFTS) in the 30 Doradus region of the Large Magellanic Cloud (LMC). Methods. The observational sample comprises 20 candidate red supergiants (RSGs) which are the reddest ((B − V) > 1 mag) and brightest (V < 16 mag) objects in the VFTS. We use optical and near-infrared (near-IR) photometry to estimate their temperatures and luminosities, and introduce the luminosity–age diagram to estimate their ages. Results. We derive physical parameters for our targets, including temperatures from a new calibration of (J − Ks)0 colour for luminous cool stars in the LMC, luminosities from their J-band magnitudes (thence radii), and ages from comparisons with current evolutionary models. We show that interstellar extinction is a significant factor for our targets, highlighting the need to take it into account in the analysis of the physical parameters of RSGs. We find that some of the candidate RSGs could be massive AGB stars. The apparent ages of the RSGs in the Hodge 301 and SL 639 clusters show a significant spread (12–24 Myr). We also apply our approach to the RSG population of the relatively nearby NGC 2100 cluster, finding a similarly large spread. Conclusions. We argue that the effects of mass transfer in binaries may lead to more massive and luminous RSGs (which we call “red stragglers”) than expected from single-star evolution, and that the true cluster ages correspond to the upper limit of the estimated RSG ages. In this way, the RSGs can serve as a new and potentially reliable age tracer in young star clusters. The corresponding analysis yields ages of 24−3+5 Myr for Hodge 301, 22−5+6 Myr for SL 639, and 23−2+4 Myr for NGC 2100.

Effects of Close Binary Evolution on the Main-sequence Morphology of Young Star Clusters

“…As shown in Fig. 5, our result is compatible with the recent observational estimates by Beasor et al (2019) and Britavskiy et al (2019). Our analytic result also agrees with corresponding estimates for clusters up to 1000 Myr (see Figure 2 of Niederhofer et al 2015).…”

Multiplicity of the red supergiant population in the young massive cluster NGC 330

“…We note that the suggestion of Milone et al (2018), that the main-sequence population of NGC 330 consists of 32 Myr and 40 Myr populations, cannot explain the spread in luminosities that is observed in the RSG population. Using the luminosity distribution, we estimate a red straggler fraction of 50%, in excellent agreement with Britavskiy et al (2019).…”

“…Table 2 compiles the physical properties of NGC 330 and summarises the main results of this study. Britavskiy et al (2019) suggested to use an arbitrary cutoff of log(L/L ) = 4.3 to distinguish between RSGs and lower-A&A proofs: manuscript no. 36741corr Notes.…”

“…Patrick et al 2016). Following the arguments in Britavskiy et al (2019), we assumed that the relative luminosity range of a single RSG in a coeval cluster is ∼5% and therefore considered all RSGs with luminosities above logL/L = 4.2 to be red stragglers. This resulte in a red-straggler fraction in NGC 330 of 50%, in excellent agreement with the results of Britavskiy et al (2019).…”

“…Following the arguments in Britavskiy et al (2019), we assumed that the relative luminosity range of a single RSG in a coeval cluster is ∼5% and therefore considered all RSGs with luminosities above logL/L = 4.2 to be red stragglers. This resulte in a red-straggler fraction in NGC 330 of 50%, in excellent agreement with the results of Britavskiy et al (2019). A more quantitative comparison is beyond the scope of this study, but if the spread of luminosities of RSGs can be attributed to binary post-interaction products, this would suggest similar binary fractions within young massive clusters.…”