We have undertaken a spectroscopic survey at high dispersion of
some known Bootis stars with a view to testing the hypothesis of
Venn & Lambert (1990), who suggested a depleted gas accretion
model. In a first paper we found (Hauck et al. 1995, hereafter
Paper I) circumstellar shell (CS) features in the CaII-K line of two stars
(HD 16955 and HD 204965) and a possible such feature for HD 220061.
New observations were made at the Haute-Provence Observatory in
1994 and 1995 and we present here evidence for the presence of
circumstellar components around some other
Bootis stars.
Since publication of Paper I, many papers on the Bootis stars
have been published, among which we may mention those from
Holweger & Rentzsch-Holm (1995) and Andrillat et al.
(1995). Holweger and Rentzsch-Holm report on high-resolution
observations of the CaII-K line in two samples of A stars,
Bootis
and dusty normal A stars, finding CS components for five out of eleven
Bootis stars. Their conclusion is that the presence of detectable
amounts of circumstellar gas in A stars is rare among chemically normal A
stars. However the
Bootis stars are metal-deficient and nearly half of their sample are surrounded by circumstellar gas. A similar conclusion is
reached by Andrillat et al. (1995), who observed a sample of 20
Bootis stars in three wavelength regions in the near infrared. Seven
stars of this sample exhibit evidence of shells. It is also important to
pay attention to temporal variations of
for both the stellar and
circumstellar lines. Many authors have reported lately on the
pulsation and variability of some
Bootis stars (Weiss et al.
1994; Kuschnig et al. 1994a,b; Paunzen et al.
1995a,b; Paunzen 1995; Bohlender et al.
1996) and Holweger & Rentzsch-Holm (1995) have
mentioned a
variation of the CS component of HD 111786 between
1990 and 1994. At the earlier date the CS component is slightly blue
shifted, while at the second date it is red shifted. Faraggiana
et al. (1997) consider this star to be a spectroscopic binary whose
Bootis primary has a high rotation speed, while the secondary has
an F type and a slow rotation; one of the two components pulsates.