M subdwarfs are low-metallicity M dwarfs that typically inhabit the halo population of the Galaxy. Metallicity controls the opacity of stellar atmospheres; in metal-poor stars, hydrostatic ...equilibrium is reached at a smaller radius, leading to smaller radii for a given effective temperature. We compile a sample of 88 stars that span spectral classes K7 to M6 and include stars with metallicity classes from solar-metallicity dwarf stars to the lowest metallicity ultra subdwarfs to test how metallicity changes the stellar radius. We fit models to Palomar Double Spectrograph (DBSP) optical spectra to derive effective temperatures (Teff) and we measure bolometric luminosities (Lbol) by combining broad wavelength-coverage photometry with Gaia parallaxes. Radii are then computed by combining the Teff and Lbol using the Stefan-Boltzman law. We find that for a given temperature, ultra subdwarfs can be as much as five times smaller than their solar-metallicity counterparts. We present color-radius and color-surface brightness relations that extend down to Fe/H of −2.0 dex, in order to aid the radius determination of M subdwarfs, which will be especially important for the WFIRST exoplanetary microlensing survey.
Philip C. Keenan (1908–2000)1 Boeshaar, Patricia C.
Publications of the Astronomical Society of the Pacific,
11/2000, Letnik:
112, Številka:
777
Journal Article
M subdwarfs are low-metallicity M dwarfs that typically inhabit the halo population of the Galaxy. Metallicity controls the opacity of stellar atmospheres; in metal poor stars, hydrostatic ...equilibrium is reached at a smaller radius, leading to smaller radii for a given effective temperature. We compile a sample of 88 stars that span spectral classes K7 to M6 and include stars with metallicity classes from solar-metallicity dwarf stars to the lowest metallicity ultra-subdwarfs to test how metallicity changes the stellar radius. We fit models to Palomar Double Spectrograph (DBSP) optical spectra to derive effective temperatures (\(T_\mathrm{eff}\)) and we measure bolometric luminosities (\(L_\mathrm{bol}\)) by combining broad wavelength-coverage photometry with Gaia parallaxes. Radii are then computed by combining the \(T_\mathrm{eff}\) and \(L_\mathrm{bol}\) using the Stefan-Boltzman law. We find that for a given temperature, ultra-subdwarfs can be as much as five times smaller than their solar-metallicity counterparts. We present color-radius and color-surface brightness relations that extend down to Fe/H of \(-\)2.0 dex, in order to aid the radius determination of M subdwarfs, which will be especially important for the WFIRST exoplanetary microlensing survey.
The B jRI Photometric System Gullixson, Craig A.; Boeshaar, Patricia C.; Tyson, J. Anthony ...
The Astrophysical journal. Supplement series,
07/1995, Letnik:
99
Journal Article
EARLY OPTICAL SPECTROSCOPY OF SUPERNOVA 1987A TYSON, J. ANTHONY; BOESHAAR, PATRICIA C.
Publications of the Astronomical Society of the Pacific,
09/1987, Letnik:
99, Številka:
619
Journal Article
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CCD spectroscopy of SN 1987A from 1987 February 24—28 is presented. Spectra with 10 Å resolution and signal-to-noise ratio in excess of 200, over a range 3900 Å to 9000 Å, are reduced to flux ...relative to the continuum at 8000 Å. Spectra as a function of time and nightly difference spectra are obtained. Strong and broad hydrogen Balmer P-Cygni profiles, increasing in intensity with time, and Hα absorption velocity decreasing from 19,000 km s⁻¹ are seen. Hα velocity components up to 31,000 km s⁻¹ are found on 25 February UT. The He i feature at 5400 Å disappears after 26 February, and Ca ii at 8200 Å appears strongly after 27 February. Spectra as a function of angular distance from SN 1987A are also obtained, showing the adjacent nebular emission ofthe LMC. There is no evidence for a circumstellar shell. These data are most consistent with an unusually low envelope mass progenitor.
We present a list of 103 faint red stars in a 0.7-square-degree area located near NGC 6820/23 on the galactic plane in the constellation Vulpécula. The stars were selected from Near Infrared ...Photographic Sky Survey visual and near-infrared photographic pairs and were chosen for their visual faintness as well as their red colors. Since some of these stars may be intrinsically extremely red they are interesting targets for spectroscopie observation. We note that two of the stars in the list have already been determined to be faint, pure S stars.
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