Absolute Magnitudes and Colors of A-F Supergiants from Near-Infrared Features. II. The Galactic Sample

Abstract

view Abstract Citations (13) References (53) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Absolute Magnitudes and Colors of A-F Supergiants from Near-Infrared Features. II. The Galactic Sample Slowik, Donald J. ; Peterson, Deane M. Abstract In this paper we extend the calibration of the infrared oxygen triplet at λ7774 Å as a luminosity indicator in A and F supergiants. We add five members of southern Galactic clusters to the nine northern objects previously considered, and find them completely consistent with the earlier relations. The result is a substantially improved fit between equivalent width and absolute visual magnitude. We reconsider the error estimates of the colors, and particularly, reduce our estimates of the errors in the colors of the northern objects. An increase in the estimated intrinsic dispersion in absolute magnitude of these objects about the mean relation, to about 0.50 mag, follows directly from the decrease in the estimated uncertainty in the reddening corrections. We also reconsider the problem of estimating intrinsic color using our measure of the infrared Ca II triplet strength. Again, the added data increase the quality of the calibration. Several techniques developed in the literature for estimating colors are compared with the Ca II indicator, and found to be less accurate, or, if comparable, costly in observing time. Further, we have looked at the issue of contamination by undetected companions. Use of IUE archives provided only one example among our sample, an object whose duplicity had been previously reported. We argue that crowding is infrequent and easily detected in the majority of cases. Toward an understanding of the nature of this equivalent width- absolute magnitude relation, we show that LTE model atmospheres adequately predict the ultraviolet, visible and near-infrared colors and H features of our sample. This is an important check against significant departures from the thin ("plane-parallel") approximation for the atmospheres of these high luminosity objects, and from LTE in the hydrogen atom. However, this test does not include the most luminous of these objects, which may still require more sophisticated treatment. Publication: The Astronomical Journal Pub Date: May 1995 DOI: 10.1086/117445 Bibcode: 1995AJ....109.2193S Keywords: STARS: GIANTS; STARS: FUNDAMENTAL PARAMETERS full text sources ADS | data products SIMBAD (28) MAST (1)