Issue |
A&A
Volume 392, Number 2, September III 2002
|
|
---|---|---|
Page(s) | 515 - 528 | |
Section | Interstellar and circumstellar matter | |
DOI | https://doi.org/10.1051/0004-6361:20020854 | |
Published online | 30 August 2002 |
On the Period-Luminosity-Colour-Metallicity relation and the pulsational characteristics of λ Bootis type stars*
1
Institut für Astronomie der Universität Wien, Türkenschanzstr. 17, 1180 Wien, Austria
2
Zentraler Informatikdienst der Universität Wien, Universitätsstr. 7, 1010 Wien, Austria
3
South African Astronomical Observatory, PO Box 9, Observatory 7935, South Africa
4
Department of Physics, University of Cape Town, Private Bag, Rondebosch 7701, South Africa
5
Max-Planck-Institut für Astronomie, Königsstuhl 17, 69117 Heidelberg, Germany
6
Department of Physics, University of the North-West, Private Bag X2046, Mmabatho 2735, South Africa
7
Research School of Astronomy and Astrophysics, Australian National University, Canberra, ACT 0200, Australia
Corresponding author: E. Paunzen, ernst.paunzen@univie.ac.at
Received:
12
April
2002
Accepted:
6
June
2002
Generally, chemical peculiarity found for stars on the upper main
sequence excludes δ Scuti type pulsation (e.g. Ap and Am stars), but
for the group of λ Bootis stars it is just the opposite. This makes them very
interesting for asteroseismological investigations. The group of λ Bootis type
stars comprises late B- to early F-type, Population I objects which
are basically metal weak, in particular the Fe group elements, but
with the clear exception of C, N, O and S.
The present work is a continuation of the studies by Paunzen et al. ([CITE],
[CITE]), who presented first results on the pulsational characteristics of
the λ Bootis stars. Since then, we have observed 22 additional objects; we
found eight new pulsators and confirmed another one. Furthermore, new
spectroscopic data (Paunzen [CITE]) allowed us to sort out misidentified
candidates and to add true members to the group. From 67 members
of this group, only two are not photometrically investigated yet which
makes our analysis highly representative.
We have compared our results on the pulsational behaviour of the λ Bootis stars
with those of a sample of δ Scuti type objects. We find that at
least 70% of all λ Bootis type stars inside the classical instability strip
pulsate, and they do so with high overtone modes (Q
< 0.020 d). Only
a few stars, if any, pulsate in the fundamental mode. Our photometric
results are in excellent agreement with the spectroscopic work on
high-degree nonradial pulsations by Bohlender et al. ([CITE]). Compared to
the δ Scuti stars, the cool and hot borders of the instability
strip of the λ Bootis stars are shifted by about 25 mmag,
towards smaller .
Using published abundances and the metallicity sensitive indices of the
Geneva 7-colour and Strömgren
systems, we have derived [ Z]
values which describe the surface abundance of the heavier elements for
the group members. We find that the
Period-Luminosity-Colour relation for the group of λ Bootis stars is within the errors
identical with that of the normal δ Scuti stars. No clear evidence
for a statistically significant metallicity term was detected.
Key words: stars / λ Bootis ; stars / chemically peculiar; stars / early type
© ESO, 2002
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