Indicators of Mass in Spherical Stellar Atmospheres

Lester

2013

A&A

Model stellar atmospheres are fundamental tools for understanding stellar observations from interferometry, microlensing, eclipsing binaries and planetary transits. However, the calculations also include assumptions, such as the geometry of the model. We use intensity profiles computed for both plane-parallel and spherically symmetric model atmospheres to determine fitting coefficients in the BVRIHK, CoRot and Kepler wavebands for limb darkening using several different fitting laws, for gravity-darkening and for interferometric angular diameter corrections. Comparing predicted variables for each geometry, we find that the spherically symmetric model geometry leads to different predictions for surface gravities log g < 3. In particular, the most commonly used limb-darkening laws produce poor fits to the intensity profiles of spherically symmetric model atmospheres, which indicates the need for more sophisticated laws. Angular diameter corrections for spherically symmetric models range from 0.67 to 1, compared to the much smaller range from 0.95 to 1 for plane-parallel models.

Section: Angular Diameter Correctionssupporting

confidence: 92%

Spherically-symmetric model stellar atmospheres and limb darkening

Lester

2013

A&A

“…When combined with model stellar atmospheres, it is possible to determine the angular diameter where the intensity approaches zero and the optical depth approaches zero (θ τ →0 ) which is designated θ LD (e.g. Lester et al 2013).…”

Section: Indexmentioning

confidence: 99%

“…found that the best-fit limbdarkening angular diameter from interferometric observations do not yield unique measurements of stellar properties. Lester et al (2013) presented a study of CLIV and spectra as a function of stellar mass. If one knows precisely the stellar radius and effective temperature, then the stellar mass can be, at best, measured to a precision of a factor of a few.…”

Section: Indexmentioning

confidence: 99%

“…However, this value is also sensitive to turbulence and convective velocities (Gray & Pugh 2012), increasing the uncertainty of the final estimated mass. and Lester et al (2013) showed it is possible to infer a star's mass from the extension of the atmosphere by using measurements of the star's CLIV and stellar atmospheric models. measured a mass for Betelgeuse to be about 12 -16 M ⊙ , much smaller than found using stellar evolution models.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Stellar Atmospheres, Atmospheric Extension, and Fundamental Parameters: Weighing Stars Using the Stellar Mass Index

Baron

Norris

et al. 2016

ApJ

Self Cite

One of the great challenges in understanding stars is measuring their masses. The best methods for measuring stellar masses include binary interaction, asteroseismology and stellar evolution models, but these methods are not ideal for red giant and supergiant stars. In this work, we propose a novel method for inferring stellar masses of evolved red giant and supergiant stars using interferometric and spectrophotometric observations combined with spherical model stellar atmospheres to measure what we call the stellar mass index, defined as the ratio between the stellar radius and mass. The method is based on the correlation between different measurements of angular diameter, used as a proxy for atmospheric extension, and fundamental stellar parameters. For a given star, spectrophotometry measures the Rosseland angular diameter while interferometric observations generally probe a larger limb-darkened angular diameter. The ratio of these two angular diameters is proportional to the relative extension of the stellar atmosphere, which is strongly correlated to the star's effective temperature, radius and mass. We show that these correlations are strong and can lead to precise measurements of stellar masses.

“…In a previous paper, Lester et al (2013) used the SATLAS (Lester & Neilson 2008) suite of programs to compute spherical stellar atmospheres and synthetic spectra of red giants and red supergiants, which were then searched for indicators of mass. That search concentrated on the visible spectral region, 300-1000nm, because optical interferometry in this region yields the highest angular resolution and also because it has been the traditional range of high-resolution stellar spectroscopy.…”

Section: Introductionmentioning

confidence: 99%

Indicators of Stellar Mass in the PhotometricH-band

Lester

Khatu

2017

PASP

Self Cite

Extensive infrared spectral surveys, such as the APOGEE survey in the H-band, are now being conducted, many targeting the Galactic Bulge and recording observations of primarily red giant stars. However, because stars of different masses converge to the red giant region, the masses of single red giant stars are poorly constrained. These surveys are now using spectral resolving powers that are high enough to measure the equivalent widths of individual spectral lines, which are mostly from molecular species. Because other observations can constrain or determine the star's luminosity and radius, we have computed spherical stellar atmospheres for a fixed luminosity and radius but for a range of masses. We then computed the H-band flux spectrum for each model and searched for spectral lines that are sensitive to mass. Our synthetic spectra reveal many lines of CO that become weaker with increasing stellar mass. To explore this, we created a ratio of equivalent widths using a representative, unblended CO line and an unblended OH line that did not vary with mass. We found that this ratio varied about 30% over the mass range from. We repeated the spectral analysis using spherical model stellar atmospheres computed with a composition »1 3 solar and found that the ratio displayed a very similar dependence on mass. The presence in the H-band of spectral features sensitive to the masses of red giant stars opens up the potential of constraining more tightly the physical properties of the stars making up the galactic bulge and globular clusters.