E. Paunzen et al., ON THE NEW LAMBDA-BOOTIS-TYPE SPECTROSCOPIC BINARY-SYSTEMS HD-84948 AND HD-171948, Astronomy and astrophysics, 329(1), 1998, pp. 155-160
We report the discovery of two new lambda Bootis-type spectroscopic bi
nary systems (HD 84948 and HD 171948). High resolution spectra were an
alyzed in order to derive abundances as well as astrophysical quantiti
es. It resulted in extreme (HD 171948) and moderate (HD 84948) underab
undances of Na, Mg, Si, Ca, Sc, Ti, Cr and Fe with respect to the Sun,
thus establishing all four individual stars as true members of the la
mbda Bootis group. These two systems are therefore the first spectrosc
opic binary systems where both components are lambda Bootis-type stars
. Furthermore, we have discovered delta Scuti type pulsation for one c
omponent of HD 84948 making this star particularly interesting for fur
ther observations. Since many authors have used the rotational velocit
y for discriminating lambda Bootis stars (upsilon sin i > 50 kms(-1)),
we note that both components of HD 171948 are the slowest (upsilon si
n i < 20 kms(-1)) rotating lambda Bootis-type stars known so far. Usin
g the Hipparcos data, we are able to rule out the diffusion/mass-loss
mechanism as origin for these two systems. Pre- as well as Main Sequen
ce evolutionary tracks for the age determination yield consistent resu
lts with the predictions of the diffusion/accretion theory, establishi
ng both systems as being very close to the Main Sequence. A determinat
ion of the orbital elements and/or an asteroseismological investigatio
n of HD 84948 could provide an independent proof of our results.