CSI 2264: Accretion process in classical T Tauri stars in the young cluster NGC 2264^⋆

¹ Departmento de Física-Icex-UFMG Antônio Carlos, 6627, 31270-90 Belo Horizonte MG Brazil
e-mail: alana@fisica.ufmg.br
² Univ. Grenoble Alpes, IPAG, 38000 Grenoble, France
³ CNRS, IPAG, 38000 Grenoble, France
⁴ Spitzer Science Center, California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91125, USA
⁵ Astronomy Department, California Institute of Technology, Pasadena, CA 91125, USA
⁶ NASA Ames Research Center, Kepler Science Office, Mountain View, CA 94035, USA
⁷ Universität Wien, Institut für Astrophysik, Türkenschanzstrasse 17, 1180 Vienna, Austria
⁸ Departmento de Física, Universidade Federal de Sergipe, SE 49100-000 Aracaju, Brazil
⁹ INAF–Osservatorio Astronomico di Palermo, Piazza del Parlamento 1, 90134 Palermo, Italy
¹⁰ MIT Kavli Institute for Astrophysics and Space Research, 77 Mass Ave 37-582f, Cambridge, MA 02139, USA
¹¹ Instituto de Astrofísica e Ciências Espaciais and Faculdade de Ciências Universidade do Porto, CAUP, Rua da Estrelas, 4150-762 Porto, Portugal

Received: 25 May 2015
Accepted: 4 September 2015

Abstract

Context. NGC 2264 is a young stellar cluster (~3 Myr) with hundreds of low-mass accreting stars that allow a detailed analysis of the accretion process taking place in the pre-main sequence.

Aims. Our goal is to relate the photometric and spectroscopic variability of classical T Tauri stars to the physical processes acting in the stellar and circumstellar environment, within a few stellar radii from the star.

Methods. NGC 2264 was the target of a multiwavelength observational campaign with CoRoT, MOST, Spitzer, and Chandra satellites and photometric and spectroscopic observations from the ground. We classified the CoRoT light curves of accreting systems according to their morphology and compared our classification to several accretion diagnostics and disk parameters.

Results. The morphology of the CoRoT light curve reflects the evolution of the accretion process and of the inner disk region. Accretion burst stars present high mass-accretion rates and optically thick inner disks. AA Tau-like systems, whose light curves are dominated by circumstellar dust obscuration, show intermediate mass-accretion rates and are located in the transition of thick to anemic disks. Classical T Tauri stars with spot-like light curves correspond mostly to systems with a low mass-accretion rate and low mid-IR excess. About 30% of the classical T Tauri stars observed in the 2008 and 2011 CoRoT runs changed their light-curve morphology. Transitions from AA Tau-like and spot-like to aperiodic light curves and vice versa were common. The analysis of the Hα emission line variability of 58 accreting stars showed that 8 presented a periodicity that in a few cases was coincident with the photometric period. The blue and red wings of the Hα line profiles often do not correlate with each other, indicating that they are strongly influenced by different physical processes. Classical T Tauri stars have a dynamic stellar and circumstellar environment that can be explained by magnetospheric accretion and outflow models, including variations from stable to unstable accretion regimes on timescales of a few years.