High-resolution stellar vidicon spectrophotometry. I - Variable mass loss from Arcturus and the hypothesis of giant convective elements

Abstract

High-resolution spectrophotometry of the variable Ca n K-line in the K2 IIIp star a Boo was performed on five occasions over the period 1974 April-1976 February with the McMath Solar Telescope at Kitt Peak National Observatory and an experimental SEC vidicon camera. The results are compared with Copernicus observations of the Mg n h and k lines (1973 May 19; 1974 May 20) and with earlier Ca n data of Griffin, and it is found that either of two states may typically occur in the Arcturus chromosphere. From comparison with the results of model calculations for expanding chromospheres, it is concluded that these correspond respectively to a "normal" state in which the mass loss dMjdt < 10~9 M Q yr~1 and an "abnormal" state in which dMjdt # 8 x 10-9 M© yr-1. In the latter case, the expansion velocity is ~13 km s" 1 at optical depth unity in the K-line, which exceeds the local sound speed. It is suggested that the abnormal state represents the rise to the photosphere of a very large convective element {d r*j r*) as hypothesized for red giants by Schwarzschild.

Stellar chromospheres - H-alpha and CA II K profiles

“…Stars hotter than B-V -1.4 (dwarfs, early G and K giants) show the reverse blue asymmetry. Mullan (1978) We conclude from this behaviour that for a mass conservative gas flow (Chiu et al, 1977) Athay (1976) and Ulmschneider (1979).…”

On the Binary Nature of 1RXS J162848.1−415241

“…The temporal variability of the Caii peak asymmetries is well documented for Arcturus (α Boo; K2III). Arcturus has shown transitions from V /R > 1 to V /R < 1 in the Ca ii K emission core ratio (Chiu et al 1977, Gray 1980. Temporal variations of the Ca ii emission cores have been observed in other latetype stars and are described in Rebolo et al (1989), García López et al (1992) and references therein.…”

First detection of winds in red giants by microwave continuum techniques

“…Ayres, Simon, and Linsky (1982) have made two independent estimates for the mass loss rate of a Boo of 3 X 10 " 10 and 2 X 10 -9 M 0 yr _ \ based on two different ultraviolet spectroscopic diagnostics. Line profile modeling of the asymmetric Mg n resonance fines in a Boo by Chiu et al (1977) implied M = 8 X 10 -9 M q yr _1 , but their unrealistic assumptions of complete frequency redistribution of scattering photons and plane-parallel geometry make this estimate uncertain. In a more recent calculation of the a Boo Mg n fine profiles that does not make these simplifications, Linsky (1982, 1984) derived a total mass loss rate of ~ 1 X 10 ~1 0 Mq yr Since this value is similar to the ionized mass loss rate derived in the present study, we believe that the wind from a Boo is largely ionized.…”