Multisite multitechnique monitoring of a large sample of  Doradus candidates
P. Mathias1, E. Chapellier1, J.-M. Le Contel1, J.-P. Sareyan1,
Garrido2, E. Rodriguez2, E. Poretti3, A. Arellano Ferro4, L. Alvarez 4, L. Parrao4
L. Eyer5, C. Aerts6, W. Weiss7, A. Zhou8
1 Observatoire de la Côte d'Azur, Département Fresnel,
UMR 6528, F-06304 Nice Cedex 4, France
2 Instituto de Astrofisica de Andalucia, Apt. 3044, E-18080 Granada,
Spain
3 Osservatorio Astronomico di Brera, Via Bianchi 46, 23807 Merate, Italy
4 Instituto de Astronomia, Universidad Nacional Autonoma de Mexico,
Apdo. Postal 70-264, Mexico D.F., 04510
5 Princeton University Observatory, Princeton, NJ 08544, USA
6 Katholieke Universiteit Leuven, Departement Natuurkunde en Sterrenkunde,
Celestijnenlaan 200 B, B - 3001 Leuven, Belgium
7 Institute for Astronomy, University of Vienna, Tuerkenschanzstrasse 17,
1180 Vienna, Austria
8 National Astronomical Observatories, Chinese Academy of Sciences,
Beijing 100012, PR China
Asterosismology requires intensive monitoring as well as a
large precision in the measures.
These objectives will be fulfilled by the COROT mission
(http://www.astrsp-mrs.fr/projets/corot/) which will
observe Scuti and Sun-like stars during runs of 150 days.
However, up to now, the modes detected in these stars are
p-modes, propagating preferentially in the outer layers.
It should be valuable to monitor also stars presenting g-modes
which propagate deeper.
These modes have been detected in a few stars (DA and DB
white dwarfs, SPB and Doradus stars essentially).
Among them, Doradus stars match very well the scientific aspects
investigated by COROT, i.e. pulsation in solar-like and classical
Scuti stars.
The Doradus stars, laying in the HRD in between the Sun and
the Scuti stars, constitute a new class of pulsating
variables discovered only recently.
These objects are thought to exhibit multiperiodic high-order low degree
g-mode
oscillations with periods in the range of 0.5 - 3 days (see e.g. Kaye et al.
1999, PASP 111, 840).
One proposed destabilization mechanism is explained by the
modulation of the radiative
flux by convection at the base of a deep envelope convection zone
(Guzik et al. 2000, ApJ 542, L57).
Much effort is currently made to find new members of this group,
to constrain their pulsation characteristics and their position in the HRD.
On one side, where is the Doradus stars red border, on the
other side where stands the blue border as some Scuti stars
have also been classified as Doradus stars?
Indeed, the number of bona fide members is still low, and show quite a
large variety in their observational behaviour (see e.g.
http://sirius.saao.ac.za/~gerald/gdorlist.html).
For instance, their observational instability strip partly covers that
of Scuti stars, and at least one Doradus variable
also pulsates in Scuti p-modes (Handler et al., in press).
In this case, these "hybrids" are particularly important for
asterosismology since both
the upper and deeper layers are probed by respectively p- and g-waves.
A few stars with surface abundances peculiarities have also been observed
to exhibit Doradus variations, e.g. Bootis stars
(Gray & Kaye 1999, AJ 118, 2993) or Am stars (Gray & Kaye, in
preparation).
We will present here the first results of an international multisite
multitechnique campaign concerning a large sample of Doradus
candidates. In particular, we derived the upper v sin i value, and
the variability. This work is at half track, the final objectives being
to identifiy at least the main pulsation modes for the maximum
number of stars and to select at least one star for a COROT Additional
Program.
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