The Effective Temperatures and Physical Properties of Magellanic Cloud Red Supergiants: The Effects of Metallicity

By Emily M. Levesque, Philip Massey, Kirsty Olsen, B. Plez, G. Meynet, Andre Maeder. 2006

160 citations recorded by the source corpus.

We present moderate-resolution spectrophotometry of 36 red supergiants (RSGs) in the LMC and 37 RSGs in the SMC. Using the MARCS atmosphere models to fit this spectrophotometry, we determine the stars' physical properties and compare the results to evolutionary models. The (V - R)0 broadband colors agree with those from fitting the optical spectrophotometry, but (V - K)0 results show metallicity-dependent systematic differences in the physical properties. We conclude that this is likely due to the limitations of static 1D models, and accept that there is still some uncertainty in the effective temperature scale. We find that the temperature scales for Milky Way, LMC, and SMC K-type supergiants agree with each other, while for M-type supergiants the LMC and SMC scales are cooler than the Galactic scale by 50 and 150 K, respectively. Since spectral classification of RSGs is based on TiO line strengths, it follows that stars with lower abundances of these elements must be cooler in order to have the line strengths associated with a given spectral type. However, this effect is not sufficient to explain the shift in average spectral type between the three galaxies. Instead, metallicity's effect on the coolest extent of stellar evolution is primarily responsible. Our results bring RSGs into much better agreement with stellar evolutionary theory, although the SMC RSGs show a considerably larger spread in effective temperatures at a given luminosity than the LMC stars. This is expected due to the larger effects of rotational mixing in lower metallicity stars. We also find that the reddening distribution of RSGs in the Clouds is skewed significantly toward higher values, consistent with our recent finding that Galactic RSGs show extra extinction due to circumstellar dust.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/815409c5d2188b2387a05cb5a8fcd9734d88d905

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Citations in the corpus

Unifying Type II Supernova Light Curves with Dense Circumstellar Material (2016, result): “For example, SN 2009kr was a IIL inferred to have a reasonably normal progenitor radius of ∼ 400 − 800R , which is consistent with the radii of standard RSGs (Levesque et al. 2005, 2006).”
Progenitors of Core-Collapse Supernovae (2009, methodology): “The effective temperatures and bolometric luminosities of Galactic and Magellanic Cloud RSGs have been revised with new model atmospheres(Levesque et al. 2005, 2006).”
Observational Constraints on the Progenitors of Core-Collapse Supernovae: The Case for Missing High-Mass Stars (2015, background): “Detections of red supergiants in JHK-bands are quite PASA, 32, e016 (2015) doi:10.1017/pasa.2015.17 powerful indicators of the bolometric flux, since extinction uncertainties are lower and the bolometric corrections are less uncertain (Levesque et al. 2006).”
MESA ISOCHRONES AND STELLAR TRACKS (MIST). I. SOLAR-SCALED MODELS (2016, background): “Shortly after, Levesque et al. (2006) utilized these new models to analyze a sample of RSGs in the Magellanic Clouds and confirmed previous results from Elias et al. (1985) that these RSGs belong to earlier spectral subtypes compared to their galactic counterparts.”
Scaled solar tracks and isochrones in a large region of the Z-Y plane. II. From 2.5 to 20 solar masses (2009, methodology): “Levesque et al. (2006) extended their study to Magellanic Cloud red supergiants to test the effects of metallicity and found evidence of significant visual extinction because of circumstellar dust.”
THEORETICAL EVOLUTION OF OPTICAL STRONG LINES ACROSS COSMIC TIME (2013, background): “(2) The Hayashi track shifts to hotter effective temperatures at low metallicities, enabling metal-rich massive stars to maintain a higher effective temperature compared with metal-poor stars of similar spectral types (Elias et al. 1985; Levesque et al. 2006).”
Measuring the Progenitor Masses and Dense Circumstellar Material of Type II Supernovae (2017, methodology): “This is significantly lower than the expected limit of ∼25Me, obtained from the comparison of the observed properties of RSGs with their possible evolutionary tracks (Levesque et al. 2005, 2006).”
Production of dust by massive stars at high redshift (2011, background): “However, RSGs up to 25 M⊙ have been detected in the Local Group (e.g., Levesque et al, 2005, 2006).”
Luminosities and mass-loss rates of SMC and LMC AGB stars and red supergiants (2009, background): “Most of the RSGs are consistent with the 10–20 M⊙ tracks (cf. the discussion on the revised spectral type eff ctive temperature calibration in Levesque et al. 2005, 2006).”