- ID:
- ivo://CDS.VizieR/J/MNRAS/403/1213
- Title:
- Tracers of stellar mass-loss. I.
- Short Name:
- J/MNRAS/403/1213
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present optical and IR integrated colours and SBF magnitudes, computed from stellar population synthesis models that include emission from the dusty envelopes surrounding TP-AGB stars undergoing mass-loss. We explore the effects of varying the mass-loss rate by one order of magnitude around the fiducial value, modifying accordingly both the stellar parameters and the output spectra of the TP-AGB stars plus their dusty envelopes. The models are single burst, and range in age from a few Myr to 14Gyr, and in metallicity between Z=0.0001 and Z=0.07; they combine new calculations for the evolution of stars in the TP-AGB phase, with star plus envelope SEDs produced with the radiative transfer code DUSTY. We compare these models to optical and near-IR data of single AGB stars and Magellanic star clusters. This comparison validates the current understanding of the role of mass-loss in determining stellar parameters and spectra in the TP-AGB. However, neither broad-band colours nor SBF measurements in the optical or the near-IR can discern global changes in the mass-loss rate of a stellar population. We predict that mid-IR SBF measurements can pick out such changes, and actually resolve whether a relation between metallicity and mass-loss exists.
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- ID:
- ivo://CDS.VizieR/J/A+A/647/A167
- Title:
- Using H-bump to identify RSGs in NGC6822
- Short Name:
- J/A+A/647/A167
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a case study in which we used a novel method to identify red supergiant (RSG) candidates in NGC 6822 based on their 1.6um H-bump. We collected 32 bands of photometric data for NGC 6822 ranging from the optical to the mid-infrared (MIR), derived from Gaia, PS1, LGGS, VHS, UKIRT, IRSF, HAWK-I, Spitzer, and WISE. Using the theoretical spectra from MARCS, we demonstrate that there is a prominent difference around 1.6um (H-bump) between targets with high and low surface gravity (HSG and LSG). Taking advantage of this feature, we identify efficient color-color diagrams of rzH (r-z versus z-H) and rzK (r-z versus z-K) to separate HSG (mostly foreground dwarfs) and LSG targets (mainly background red giant stars, asymptotic giant branch stars, and RSGs) from crossmatching of optical and near-infrared (NIR) data. Moreover, synthetic photometry from ATLAS9 gives similar results. We further separated RSG candidates from the remaining LSG candidates as determined by the H-bump method by using semi-empirical criteria on NIR color-magnitude diagrams, where both the theoretic cuts and morphology of the RSG population are considered. This separation produced 323 RSG candidates. The simulation of foreground stars with Besancon models also indicates that our selection criteria are largely free from the contamination of Galactic giants. In addition to the H-bump method, we used the traditional BVR method (B-V versus V-R) as a comparison and/or supplement by applying a slightly aggressive cut to select as many RSG candidates as possible (358 targets). Furthermore, the Gaia astrometric solution was used to constrain the sample, where 181 and 193 targets were selected with the H-bump and BVR method, respectively. The percentages of selected targets in the two methods are similar at ~60%, indicating a comparable accuracy of the two methods. In total, there are 234 RSG candidates after combining targets from the two methods, and 140 (~60%) of them are in common. The final RSG candidates are in the expected locations on the mid-infrared color-magnitude diagram with [3.6]-[4.5]<~0 and J-[8.0]~1.0. The spatial distribution is also coincident with the far-ultraviolet-selected star formation regions, suggesting that the selection is reasonable and reliable. We indicate that our method can also be used to identify other LSG targets, such as red giants and asymptotic giant branch stars, and it can also be applied to most of the nearby galaxies by using recent large-scale ground-based surveys. Future ground- and space-based facilities may promote its application beyond the Local Group.
