CoRoT 102699796, the first metal-poor Herbig Ae pulsator: a hybrid δ Sct-γ Dor variable?

Abstract

We present the analysis of the time series observations of CoRoT 102699796 obtained by the Convection, Rotation and planetary Transits (CoRoT) satellite that show the presence of five independent oscillation frequencies in the range 3.6-5 c d^-1. Using spectra acquired with FLAMES@VLT, we derive the following stellar parameters: spectral type F1V, T_eff= 7000 ± 200 K, log (g) = 3.8 ± 0.4, [M/H]=-1.1 ± 0.2, v sin i= 50 ± 5 km s^-1, L/L_⊙= 21⁺²¹_{- 11}. Thus, for the first time we report the existence of a metal-poor, intermediate-mass pre-main-sequence (PMS) pulsating star. Ground-based and satellite data are used to derive the spectral energy distribution (SED) of CoRoT 102699796 extending from the optical to mid-infrared wavelengths. The SED shows a significant IR excess at wavelengths greater than ∼5 μm. We conclude that CoRoT 102699796 is a young Herbig Ae (F1Ve) star with a transitional disc likely associated with the H II region [FT96]213.1-2.2.

The pulsation frequencies have been interpreted in the light of the non-radial pulsation theory, using the LOSC code in conjunction with static and rotational evolutionary tracks. A minimization algorithm was used to find the best-fitting model with M= 1.84 M_⊙, T_eff= 6900 K which imply an isochronal age of t∼ 2.5 Myr. This result is based on the interpretation of the detected frequencies as g modes of low-moderate n-value. To our knowledge, this is the first time that such modes are identified in a intermediate-mass PMS pulsating star. Since CoRoT 102699796 lies in the region of the Hertzsprung-Russell (HR) diagram where the δ Sct and γ Dor instability strips intersect, we argue that the observed pulsation characteristics are intermediate between these classes of variables, i.e. CoRoT 102699796 is likely the first PMS hybrid γ Dor-δ Sct pulsator ever studied.