Models of late-type stellar photospheres

Gustafsson, B.; Jørgensen, U. G.

doi:10.1007/bf01208251

Cited by 41 publications

(15 citation statements)

References 150 publications

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“…The problem largely stems from the fact that any molecule found in a stellar atmosphere-even that of an M-type star-must be considered ''high temperature,'' while most laboratory data have been obtained at much lower temperatures and do not include high-excitation transitions. The situation has decidedly improved in the past years, in large part due to the great efforts by a few groups to compute ab initio line lists (e.g., Partridge & Schwenke 1997;Harris et al 2002), and it now seems quite satisfactory regarding oxygen-rich mixtures, such as TiO (see reviews by Jorgensen 1994 andTsuji 1986).…”

Section: Introductionmentioning

confidence: 99%

The Effective Temperature Scale of Galactic Red Supergiants: Cool, but Not as Cool as We Thought

Levesque¹,

Massey²,

Olsen³

et al. 2005

ApJ

462

652

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We use moderate-resolution optical spectrophotometry and the new MARCS stellar atmosphere models to determine the effective temperatures of 74 Galactic red supergiants (RSGs). The stars are mostly members of OB associations or clusters with known distances, allowing a critical comparison with modern stellar evolutionary tracks. We find we can achieve excellent matches between the observations and the reddened model fluxes and molecular transitions, although the atomic lines Ca i k4226 and Ca ii H and K are found to be unrealistically strong in the models. Our new effective temperature scale is significantly warmer than those in the literature, with the differences amounting to 400 K for the latest type M supergiants (i.e., M5 I). We show that the newly derived temperatures and bolometric corrections give much better agreement with stellar evolutionary tracks. This agreement provides a completely independent verification of our new temperature scale. The combination of effective temperature and bolometric luminosities allows us to calculate stellar radii; the coolest and most luminous stars (KW Sgr, Case 75, KY Cyg, HD 206936 = Cep) have radii of roughly 1500 R (7 AU), in excellent accordance with the largest stellar radii predicted from current evolutionary theory, although smaller than that found by others for the binary VV Cep and for the peculiar star VY CMa. We find that similar results are obtained for the effective temperatures and bolometric luminosities using only the dereddened V À K colors, providing a powerful demonstration of the self-consistency of the MARCS models.

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Section: Introductionmentioning

confidence: 99%

The Effective Temperature Scale of Galactic Red Supergiants: Cool, but Not as Cool as We Thought

Levesque¹,

Massey²,

Olsen³

et al. 2005

ApJ

462

652

View full text Add to dashboard Cite

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“…Rood 1973;Sweigart, Mengel, & Demarque 1974;Sweigart 1987;Castellani & Tornambé 1991; On the other hand, theoretical spectral libraries suffer from insufficient atomic data and physical understanding. Even the most recent models may be inadequate, especially for cool stars (Buser & Kurucz 1992;Morossi et al 1993;Kirkpatrick et al 1993;Gustafsson & Jørgensen 1994). These theoretical libraries have to be validated by acquiring as much empirical data as possible.…”

Section: Introductionmentioning

confidence: 99%

On the Origin of the UV Upturn in Elliptical Galaxies. I. Sensitivity of UV Population Synthesis to Various Input Parameters

Yi¹,

Demarque²,

Oemler³

1997

ApJ

113

137

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We present models of the late stages of stellar evolution intended to explain the "UV upturn" phenomenon in elliptical galaxies. Such models are sensitive to values of a number of poorly-constrained physical parameters, including metallicity, age, stellar mass loss, helium enrichment, and the distribution of stars on the zero age horizontal branch (HB). We explore the sensitivity of the results to values of these parameters, and reach the following conclusions.Old, metal rich galaxies, such as giant ellipticals, naturally develop a UV upturn within a reasonable time scale -less than a Hubble time -without the presence of young stars. The most likely stars to dominate the UV flux of such populations are low mass, core helium burning (HB and evolved HB) stars. Metal-poor populations produce a higher ratio of UV-to-V flux, due to opacity effects, but only metal-rich stars develop a UV upturn, in which the flux increases towards shorter UV wavelengths.Model color-magnitude diagrams and corresponding integrated spectra (for various values of age, metallicity, helium enrichment, mass loss efficiency, initial mass function, and the HB mass dispersion factor) are available on S.Y.'s world wide web site http://shemesh.gsfc.nasa.gov/model.html. them are mainly aiming at solving the "UV upturn problem", where the UV upturn is defined as the increasing flux in the UV (1,000 -2,500Å) with decreasing wavelength, as found in giant elliptical galaxies (Code & Welch 1979;Faber 1983;Burstein et al. 1988).The most serious concern about such elaborate population studies is that the effects of input parameters on the resulting UV flux are very poorly understood. Unlike population synthesis in the optical band, UV population synthesis for old stellar systems, such as elliptical galaxies, is very sensitive to various detailed physical assumptions. This is because most candidates for UV sources are highly evolved stars whose properties are governed by several input parameters that have not yet been determined very well. Among such parameters are mass loss and its distribution, galactic helium enrichment (∆Y /∆Z ), and initial mass function. In particular, as we will show later, the assumptions about mass loss and its distribution influence the magnitude of the resulting UV flux significantly. Many recent population synthesis studies have been presented to the readers without addressing the sensitivity of their results and conclusions to alterations in the adopted input parameters.The main goals of this paper are to illustrate the sensitivity of the model UV spectrum to various input parameters, and to investigate the plausibility of UV-bright core helium-burning stars as the major UV sources in giant elliptical galaxies. This paper complements previous works in the literature. Greggio & Renzini (1990) explored the sensitivity of the UV modeling to ∆Y /∆Z and to the metallicity-dependence of mass loss. The effects of age and metallicity have been investigated by several groups, among which the works of Bressan et al. (1994), Dorman et al...

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“…Other, more detailed discussions can be found in e.g. Gustafsson & J0rgensen (1994). Atomic and molecular data are the main ingredient of any realistic models.…”

Section: Ingredients For a Good Model Atmospherementioning

confidence: 99%

Model Atmospheres for Normal and Peculiar Red Giant Stars

Plez

2000

Symp. - Int. Astron. Union

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Abstract. I review the current status of model atmospheres for red giants, with special emphasis on recent progress and newer grids. I draw attention to some specific problems regarding opacity sources and present current and forthcoming efforts in cool-star atmospheric modeling. BackgroundThis paper follows up the excellent review articles of Johnson (1986), Gustafsson h J0rgensen (1994), andGustafsson (1995). I will emphasize specific problems, recent achievements in producing and using newer grids, and upcoming models.I shall review models for all types of red giants, the O-rich Κ and M stars, the C-rich R, N, and J-type stars, the intermediate MS, S and SC stars, as well as hydrogen-deficient (HdC) carbon stars and R CrB stars. At this point it is useful to recall that the chemistry in the atmosphere of these stars is dominated mostly by the C/O ratio. In O-rich objects, with C/O < 1, most C goes into CO, the most stable molecule, and the remaining Ο binds into oxides like TiO, VO, and H2O. In a C-rich mixture, most Ο is bound in CO, and the remaining C forms CN, C2, CH, HCN, C2H2, etc. When C/O ~ 1, most C and Ο is in CO, most Ν in N2, and metals with lower abundances start building compounds in significant amounts: ZrO, LaO, YO, and so on. This effect is often enhanced in S stars by the overabundance of s-elements dredged up on the AGB. Note also that at lower metallicity, molecules like CH are privileged over species such as C2, the abundance of which drops faster with decreasing C abundance. This explains the dominant spectral features of CH stars.

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Models of late-type stellar photospheres

Cited by 41 publications

References 150 publications

The Effective Temperature Scale of Galactic Red Supergiants: Cool, but Not as Cool as We Thought

The Effective Temperature Scale of Galactic Red Supergiants: Cool, but Not as Cool as We Thought

On the Origin of the UV Upturn in Elliptical Galaxies. I. Sensitivity of UV Population Synthesis to Various Input Parameters

Model Atmospheres for Normal and Peculiar Red Giant Stars

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