Red supergiants in the LMC — II. Spectrophotometry and model atmospheres

Oestreicher, M. O.; Schmidt-Kaler, Th.

doi:10.1046/j.1365-8711.1998.01501.x

Cited by 13 publications

(7 citation statements)

References 7 publications

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“…Improved stellar atmospheres applicable to RSGs are under construction (Gustafsson et al 2003, Plez 2003 but until these are generally available we turn to the "Atlas 9" model atmospheres of Kurucz (1992) to help answer this question 4 . Although Oestreicher & Schmidt-Kaler (1998) find that the Atlas 9 models significantly underestimate the amount of molecular absorption for some lines in late-type stars, we show that there is pretty good agreement in Fig. 3, where we compare the coolest of Kurucz (1992) models to the spectra of three of our spectral standards.…”

Section: Physical Parameters and Stellar Evolutionmentioning

confidence: 54%

The Evolution of Massive Stars. I. Red Supergiants in the Magellanic Clouds

Massey¹,

Olsen²

2003

Astron J

179

264

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We investigate the red supergiant (RSG) content of the SMC and LMC using multi-object spectroscopy on a sample of red stars previously identified by BVR CCD photometry. We obtained high accuracy (< 1 km s −1 ) radial velocities for 118 red stars seen towards the SMC and 167 red stars seen towards the LMC, confirming most of these (89% and 95%, respectively) as red supergiants (RSGs).Spectral types were also determined for most of these RSGs. We find that the distribution of spectral types is skewed towards earlier type at lower metallicities: the average (median) spectral type is K5-7 I in the SMC, M1 I in the LMC, and M2 I in the Milky Way. Our examination of the Kurucz Atlas 9 model atmospheres suggests that the effect that metallicity has on the appearance on the TiO lines is probably sufficient to account for this effect, and we argue that RSGs in the Magellanic Clouds are 100 • K (LMC) and 300 • K (SMC) cooler than Galactic stars of the same spectral types. The colors of the Kurucz models are not consistent with this interpretation for the SMC, although other models (e.g., Bessel et al.) show good agreement. A finer grid of higher-resolution synthetic spectra appropriate to cool supergiants is needed to better determine the effective temperature scale. We compare the distribution of RSGs in the H-R diagram to that of various stellar evolutionary models; we find that none of the models produce RSGs as cool and luminous as what is actually observed. This result is much larger than any uncertainty in the effective temperature scale. We note that were we to simply adopt the uncorrected Galactic effective scale for RSGs and apply this to our sample, then the SMC's RSGs would be under luminous compared to the LMC's, contrary to what we expect from stellar evolution considerations.In all of our H-R diagrams, however, there is an elegant sequence of decreasing effective temperatures with increasing luminosities; explaining this will be an -3important test of future stellar evolutionary models. Finally, we compute the blue-to-red supergiant ratio in the SMC and LMC, finding that the values are indistinguishable (∼ 15) for the two Clouds. We emphasize that "observed" B/R values must be carefully determined if a comparison to that predicted by stellar models is to be meaningful. The non-rotation Geneva models overestimate the number of blue-to-red supergiants for the SMC, but underestimate it for the LMC; however, given the inability to produce high luminosity RSGs in the models that match what is observed in the H-R diagram, such a disagreement is not surprising.

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Section: Physical Parameters and Stellar Evolutionmentioning

confidence: 54%

The Evolution of Massive Stars. I. Red Supergiants in the Magellanic Clouds

Massey¹,

Olsen²

2003

Astron J

179

264

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“…(1) Oestreicher & Schmidt-Kaler (1998). and so it is possible to define a threshold to attain a given completeness. This selection scheme has an important caveat: most late giants will fall within the same range as SGs, and while this is not a problem for other galaxies where simple cuts in magnitude can weed out these stars, in the MW this strategy is not feasible.…”

Section: Completeness Of the Samplementioning

confidence: 99%

A new survey of cool supergiants in the Magellanic Clouds

González-Fernández

Dorda

Negueruela

et al. 2015

A&A

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Aims. In this study we conduct a pilot program aimed at the red supergiant population of the Magellanic Clouds. We intend to extend the current known sample to the unexplored low end of the brightness distribution of these stars, building a more representative dataset with which to extrapolate their behaviour to other Galactic and extra-galactic environments. Methods. We select candidates using only near infrared photometry, and with medium resolution multi-object spectroscopy, we perform spectral classification and derive their line-of-sight velocities, confirming the nature of the candidates and their membership in the clouds. Results. Around two hundred new red supergiants have been detected, hinting at a yet to be observed large population. Using nearand mid-infrared photometry we study the brightness distribution of these stars, the onset of mass-loss, and the effect of dust in their atmospheres. Based on this sample, new a priori classification criteria are investigated, combining mid-and near-infrared photometry to improve the observational efficiency of similar programs to this.

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“…Finally, the MCs represent a relatively "clean" environment, with minimal and uniform reddenings, which avoid some of the difficulties inherent in studying RSGs in the Milky Way (Paper I). Oestreicher & Schmidt-Kaler (1998, 1999 used an earlier version of the MARCS models (Bessell et al 1998) with their own spectrophotometry and CCD photometry to analyze a large sample of LMC stars. They conclude that the MARCS models did the best of the thenavailable models at fitting the data, and derived physical properties using these fits.…”

Section: Introductionmentioning

confidence: 99%

“…Also, our sample consists of stars whose radial velocities have been shown to be consistent with membership in the Magellanic Clouds by Massey & Olsen (2003). This list extends to stars which have cooler effective temperatures than do any of the Oestreicher & Schmidt-Kaler (1998, 1999 LMC stars. In addition, our sample includes SMC RSGs, providing important tests at even lower metallicities.…”

Section: Introductionmentioning

confidence: 99%

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

Levesque

Massey

Olsen

et al. 2006

ApJ

206

382

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International audienceWe 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

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Red supergiants in the LMC — II. Spectrophotometry and model atmospheres

Cited by 13 publications

References 7 publications

The Evolution of Massive Stars. I. Red Supergiants in the Magellanic Clouds

The Evolution of Massive Stars. I. Red Supergiants in the Magellanic Clouds

A new survey of cool supergiants in the Magellanic Clouds

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

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