Computer Science
Scientific paper
Jan 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996phdt.........5p&link_type=abstract
Thesis (PH.D.)--BRIGHAM YOUNG UNIVERSITY, 1996.Source: Dissertation Abstracts International, Volume: 57-04, Section: B, page: 26
Computer Science
1
Scientific paper
New uvby-beta-hk photometric observations of over 500 F- and G-type supergiant stars are reported. Special care to obtain accurate reductions of c_1, the luminosity indicator for these stars, and m_1, a metallicity indicator, are described. Whereas photometric reductions of y_{rm mag}=V_ {rm mag}, b-y, hk, and beta for yellow supergiants can usually be merged with non-supergiants without significant error, m_1 and especially c_1 require special treatment. A new reddening calibration for yellow supergiants is reported using (m_1) corrected for metallicity as the temperature indicator. Using b -y, c_1, and hk, values for temperature, surface gravity, and metallicity have been estimated from the new Kurucz model atmospheres. The inferred temperatures appear to be reasonable but the surface gravities needed to be corrected and the metallicities need further improvement. Since the Kurucz models predict values of log g which imply absolute magnitudes which are too faint for these stars based upon observations of supergiants of known absolute magnitude in our galaxy as well as in the Large and Small Magellanic Clouds, a correction in terms of log g has been applied to the derived values of MV. The metallicity values derived here imply a difference in (Fe/H) between the Small Magellanic Cloud and the Large Magellanic Cloud of about 0.3 dex, in rough agreement with spectroscopic studies. However, to our surprise the results do not indicate the expected difference in (Fe/H) between the Large Magellanic Cloud and the Milky Way Galaxy (found spectroscopically to be about 0.3 dex). This may be due to microturbulence differences between supergiant stars in our galaxy as compared to those in the Magellanic clouds. Yellow supergiant stars in this study do not clearly delineate galactic spiral arm structure as one would expect. Errors in their distances is probably the dominant cause, but random motions will also cause them to leave their spiral arm birthplaces. An attempt to derive an improved galactic metallicity gradient for yellow supergiant stars was unsuccessful due in part to the wide variation in metallicity among the program stars.
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