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Scientific paper
May 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992aas...180.3708a&link_type=abstract
American Astronomical Society, 180th AAS Meeting, #37.08; Bulletin of the American Astronomical Society, Vol. 24, p.788
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2
Scientific paper
We have obtained IUE observations of the peculiar red giants HD 191589 (M0S) and pi (1) Gru (S5,7e) and have derived distances to them based on the fluxes of their companions. LWP and SWP observations of HD 191589 indicate that an F0-F2 companion dominates the light in the UV region. Based on the line spectrum, the companion is less luminous than a giant. Matching the fluxes with F-type standards, we derive m_v = 11.0 for the secondary, and a distance modulus m-M = 8.8 +/- 0.4 to the system, with the largest part of the uncertainty due to the luminosity assumed for the secondary. The companion to pi (1) Gru is reported to be a G0 V star (Feast, MNRAS, 113, 510, 1953) 2" away from the primary and m_v = 10.9. The IUE LWP region spectrum is consistent with the dG0 classification, except for the presence of emission lines of Mg II lambda 2800 and C II lambda 2325 arising from the S star. Unless the red giant has unusually weak chromospheric emission, a composite fit to the spectrum cannot be matched by using other gM or S stars and a G0 companion this faint. We find a better fit when m_v= 10.4 +/- 0.1 for the secondary, resulting in m-M = 6.0 for the system. HD 191589 needs infrared photometry, but based on its UBV colors and a B.C. = -1.2 as for an M0 giant, we find Mbol = -2.7, which is less luminous than current asymptotic branch models predict for thermal pulsing to occur. For pi (1) Gru, we obtain Mbol = -4.8 at maximum light using photometry from Feast et al, MNRAS, 174, 81p, 1976, which is fainter than other determinations due to the increase in the measured apparent brightness for the secondary. (1) Guest Observer, International Ultraviolet Explorer (2) Member of the GHRS Science Team
Ake Thomas B.
Johnson Hollis R.
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