Oscillations in the PMS δ Scuti star V346 Ori
A&A
Astronomy & Astrophysics Oscillations in the PMS δ Scuti star V346 Ori
F. J. G. Pinheiro 2
D. F. M. Folha 2
M. Marconi 1
V. Ripepi 1
F. Palla 0
M. J. P. F. G. Monteiro 2 5
S. Bernabei 3 4
0 INAF-Osservatorio Astrofisico di Arcetri , Largo E. Fermi 5, 50125 Firenze , Italy
1 INAF-Osservatorio Astronomico di Capodimonte , Via Moiariello 16, 80131 Napoli , Italy
2 Centro de Astrof ́ısica da Universidade do Porto , Rua das Estrelas, 4150-762 Porto , Portugal
3 Departamento de Astrof ́ısica, Universidad de La Laguna , Avda. Astrof ́ısico F. Sa ́nchez s/n, Campus de Anchieta, 38206 La Laguna , Spain
4 INAF-Osservatorio Astronomico di Bologna , Via Ranzani 1, 40127 Bologna , Italy
5 Departamento de Matema ́tica Aplicada, Faculdade de Cieˆncias da Universidade do Porto , Portugal
We report the discovery of periodicities in the light curve of the Pre-Main Sequence (PMS) Herbig Ae star V346 Ori. We interpret variations in the light curve of the star as the superposition of at least two periodic signals that result from δ Scuti-type stellar oscillations. The computation of linear non-adiabatic radial pulsation models for PMS stars reproduces these periods for a 1.55 M star with Teff = 7410 K and log L/L = 0.74 pulsating in the fundamental and in the second overtone. If our assumption of radial oscillations is indeed correct, the star's location on the HR diagram places it at a distance significantly smaller than that of the Orion star forming region, hence raising questions regarding the evolutionary status of V346 Ori. Observations with better time sampling and spanning a longer period of time are needed if the latter question is to be addressed fully.
stars; evolution - stars; fundamental parameters - stars; oscillations - stars; pre-main sequence - stars; variables; δ Sct - stars; individual; V346 Ori
1. Introduction
Pre-Main sequence (PMS) evolutionary tracks are of utmost
importance to achieve a complete understanding of the star
formation process. Such tracks allow the determination of both
mass and age of individual young stars
(eg. Hillenbrand 1997)
.
These parameters are fundamental data not only to characterise
the stars themselves but also to investigate how the initial mass
function varies from region to region as a function of cloud
parameters.
PMS evolutionary models are produced by different groups,
each employing different treatments of convection and/or
opacities and also using a different zero-point for the calculated
ages. How is one to assess the accuracy of model
predictions and, possibly, to choose that which better describes the
evolution of stars during their contraction towards the main
sequence?
A powerful test to models is to independently and
accurately derive the mass of PMS objects and compare their
position in the HR diagram with model predictions for the
determined masses. Eclipsing binary systems provide the best
estimates of stellar masses
(Popper 1980; Palla & Stahler
2001)
. Unfortunately, only a few such systems are known that
are sufficiently young to provide a test to the PMS evolutionary
tracks (Covino et al. 2001).
Marconi & Palla (1998)
investigated the pulsational
properties of PMS stars within the mass range 1–4 M , by means
of non-linear calculations of radial modes and derived the
location in the HR diagram of the instability strip for these stars.
The identification of pulsation frequencies in these stars allows
to constrain fundamental stellar parameters such as the mass,
luminosity and effective temperature. This represents a
powerful method to determine the stellar mass for stars that are not
part of the very restricted group of spectroscopic binary
systems. In this way, the number of PMS stars with accurately
determined masses can be increased, allowing more stringent
testing of the PMS evolutionary models.
Several Herbig Ae stars have been identified as pulsators.
Particular attention has been given to HR 5999
(Kurtz &
Marang 1995; Kurtz & Catala 2001)
and V351 Ori
(Marconi
et al. 2000, 2001; Ripepi et al. A&A, submitted)
. The
potential of pulsations for the determination of stellar parameters is
attested by Marconi et al. 2001, 2002). Depending on the
accuracy, number and mode identification of discovered
frequencies, single digit precisions (in percentage) can be achieved
for the stellar mass and radius. Furthermore, for the latter
two parameters, there is the additional advantage that their
determination from oscillations is independent of external
factors, such as reddening.
V346 Ori (HD 287841) is classified as a Herbig Ae star
(The´ et al. 1994)
and given the estimates for its luminosity and
effective temperature
(van den Acker et al. 1998; Valenti et al.
2000)
it is located near or inside the PMS instability strip. It is
therefore a good candidate to display stellar oscillations. With
the aim of increasing the number of known PMS pulsators we
have searched for periodic variability in V346 Ori’s light curve.
In this paper we report o (...truncated)