Photometric Determination of Stellar Radii

Abstract

view Abstract Citations (59) References (43) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Photometric Determination of Stellar Radii Gray, David F. Abstract A simple and accurate method is developed to measure stellar radii. Succinctly stated, one compares the observed absolute energy distribution with an energy distribution predicted from a model-atmosphere computation. The radius is given by the square root of the flux ratio multiplied by the distance to the star. The radius can be determined with an uncertainty of 10 per cent or less provided the distance to the star is well known. The method has the advantages that it uses only the observable region of the spectrum, it does not depend on bolometric corrections, and it is independent of any effective temperature scale The energy distributions of the three visual binary stars 21 Cas A, Boo A, and 70 Oph A were measured with a grating spectrum scanner attached to the Francis C. McMath 24-inch telescope. Line absorption was measured on 8.9 A/mm spectrograms taken with the coud spectrograph on the Kitt Peak 84-inch telescope. Model atmospheres were constructed using a scaled solar temperature distribution. The models include the continuous absorption of the neutral hydrogen atom, the negative hydrogen ion, and the H2 molecule as well as a hydrogenic approximation for the continuous absorption of the heavier elements. The continuous spectra of the models were combined with the observations to give R = 1.11 Ro 1 7 per cent for21 Cas A, R = 1.01 Ro 1 7 per cent for Boo A, and R = 1.21 Ro 1 7 per cent for 70 Oph A. Using the masses derived from the orbital elements, it was possible to obtain accurate values of surface gravity for these stars: g = 2.09 X 10 cm/seci 1 17 per cent for 21 Cas A, 2.20 X 10 cm/sec2 1 17 per cent for Boo A, and 1.82 X 10 cm/sec2 1 15 per cent for 70 Oph A. Photometric radii determined for Vega, Sirius, and the Sun showed close agreement with values obtained from other independent methods. For Sirius g = 1.42 X 10 cm/sec2 1 15 per cent is derived. Using published energy distributions, photometric radii were determined for twenty-nine additional stars. Excellent correlations exist between radius and absolute magnitude, radius and color index, and radius and spectral type. The subgiant stars are clearly separated from the main sequence. The subgiant a C Mi is found to have a surface gravity of 0.99 X 10 cm/sec2 1 14 per cent. Publication: The Astrophysical Journal Pub Date: August 1967 DOI: 10.1086/149256 Bibcode: 1967ApJ...149..317G full text sources ADS | data products SIMBAD (35)