Rotational periods of solar-mass young stars in Orion ^*,**

¹ INAF, Osservatorio Astrofisico di Catania, via S. Sofia, 78, 95123 Catania, Italy e-mail: emarilli@oact.inaf.it
² INAF, Osservatorio Astronomico di Capodimonte, via Moiariello 16, 80131 Napoli, Italy
³ Instituto de Astrofísica de Andalucía, CSIC, Camino Bajo de Huétor 50, 18008 Granada, Spain
⁴ Instituto de Astronomía, Universidad Nacional Autónoma de México, Apdo. Postal 70-264, D.F. CP 04510, México

Received: 27 September 2006
Accepted: 30 November 2006

Abstract

Context.The evolution of the angular momentum in young low-mass stars is still a debated issue. The stars presented here were discovered as X-ray sources in the ROSAT All-Sky Survey (RASS) of the Orion complex and subsequently optically identified thanks to both low and high resolution spectroscopy.

Aims.The determination of the rotational periods in young low-mass stars of different age is fundamental for the understanding of the angular momentum evolution.

Methods.We performed a photometric monitoring program on a sample of 40 solar-mass young stars in the Orion star-forming region, almost all previously identified as weak T Tauri stars (WTTS) candidates. Photometric B and V data were collected from 1999 to 2006 at Catania Astrophysical Observatory (OAC). Data were also acquired in December 1998 at Calar Alto Observatory (CA) and in 1999, 2000, and 2003 at San Pedro Martir (SPM). From the observed rotational modulation, induced by starspots, we derived the rotation periods, using both the Lomb-Scargle periodogram and the CLEAN deconvolution algorithms.

Results.In total, we were able to determine the rotation periods for 39 stars, spanning from about 0.5 to 13 days, showing a rather flat distribution with a peak around 1-2 days. Though some of these stars were found to be spectroscopic binaries, only the systems with shorter orbital periods and circular orbits turned out to be synchronized. In the other cases, the rotational period is shorter than the period of pseudo-synchronization at periastron.

Conclusions.The new data provide further evidence for the spin up of solar-mass stars predicted by models of angular momentum evolution of pre-main sequence (PMS) stars.