Context. GQ Lup A is a classical T Tauri star that shows clear signs of accretion
through the presence of inverse P Cygni profiles in its main emission
lines.
Recently, Neuhäuser et al. (2005, A&A, 435, L13) found a co-moving sub-stellar
companion of GQ Lup A, raising the importance of determining precise stellar
parameters, system age, and distance to GQ Lup.
Aims. Our main objective is to use spectrophotometric time series to determine GQ Lup A
stellar parameters and predict its photospheric spectral distribution.
The excess spectral luminosity can then be measured and employed to test predictions of
magnetospheric accretion models of classical T Tauri stars.
Methods. We present the analysis of 18 spectrophotometric observations of the
T Tauri star GQ Lup A (K7) obtained with the Boller & Chivens
spectrograph at the 1.52 m ESO telescope in La Silla. We also revisited archival
photometric data of this star, comparing previous light curve
variability with our more recent data.
Results. We determined the photospheric flux of GQ Lup A on each observing
night and obtained the stellar radius (R⋆ = 1.8 ± 0.3 R⊙), adopting a
mean distance of 150 ± 20 pc to the Lupus 1 cloud.
Assuming a K7 V temperature of 4060 K, the luminosity of GQ Lup A
is L⋆ = 0.8 ± 0.3 L⊙. Standard evolutionary models
indicate a stellar mass of M⋆ = 0.8 ± 0.2 M⊙ and an age of 3 ± 2 Myr.
GQ Lup A spectral lines are consistent with a projected rotational velocity of
vsini = 6.5 ± 2.0 km s-1. We measured the excess emission – veiling – and used
the resulting photospheric spectral distribution to calculate a stellar extinction (AV)
of 0.5 ± 0.1. The veiling was found to be variable and periodic at 10.7 ± 1.6 days,
which is consistent with the period of GQ Lup A obtained from archival B band
photometric data (10.43 ± 0.12 days). The star exhibits strong emission lines with
substantial variability in flux. The emission line fluxes are
strongly correlated with one another but not
with veiling