The weak-line T Tauri star V410 Tau

I. A multi-wavelength study of variability

¹ Osservatorio Astronomico di Palermo, Piazza del Parlamento 1, 90134 Palermo, Italy
² Instituto de Astrofísica de Andalucía, CSIC, Camino Bajo de Huétor 24, 18008 Granada, Spain
³ Centre for Astrophysics, University of Porto, Rua das Estrelas, 4150 Porto, Portugal
⁴ Departamento de Matemática, Instituto Superior de Engenharia do Porto, 4150 Porto, Portugal
⁵ Departamento de Matemática Aplicada, Faculdade de Cíencas da Universidade do Porto, 4169 Porto, Portugal
⁶ Ulug Beg Astronomical Institute, Astronomicheskaya 33, 700052 Tashkent, Uzbekistan
⁷ USRA/USNO Flagstaff Station, PO Box 1149, Flagstaff, AZ 86002-1149, USA
⁸ Thüringer Landessternwarte, Karl-Schwarzschild-Observatorium, Sternwarte 5, 07778 Tautenburg, Germany
⁹ Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
¹⁰ Max-Planck Institut für extraterrestrische Physik, Postfach 1312, 85741 Garching, Germany
¹¹ University of Michigan, 953 Dennison Building, Ann Arbor, MI 48109, USA
¹² Indiana University, 727 E. 3rd Street, Bloomington, IN 47405-7105, USA

Corresponding author: B. Stelzer, stelzer@astropa.unipa.it

Received: 16 June 2003
Accepted: 4 September 2003

Abstract

We present the results of an intensive coordinated monitoring campaign in the optical and X-ray wavelength ranges of the low-mass, pre-main sequence star V410 Tau carried out in November 2001. The aim of this project was to study the relation between various indicators for magnetic activity that probe different emitting regions and would allow us to obtain clues on the interplay of the different atmospheric layers: optical photometric star spot (rotation) cycle, chromospheric Hα emission, and coronal X-rays. Our optical photometric monitoring has allowed us to measure the time of the minimum of the lightcurve with high precision. Joining the result with previous data we provide a new estimate for the dominant periodicity of V410 Tau ( d). This updated value removes systematic offsets of the time of minimum observed in data taken over the last decade. The recurrence of the minimum in the optical lightcurve over such a long timescale emphasizes the extraordinary stability of the largest spot. This is confirmed by radial velocity measurements: data from 1993 and 2001 fit almost exactly onto each other when folded with the new period. The combination of the new data from November 2001 with published measurements taken during the last decade allows us to examine long-term changes in the mean light level of the photometry of V410 Tau. A variation on the timescale of 5.4 yr is suggested. Assuming that this behavior is truly cyclic V410 Tau is the first pre-main sequence star on which an activity cycle is detected. Two X-ray pointings were carried out with the Chandra satellite simultaneously with the optical observations, and centered near the maximum and minimum levels of the optical lightcurve. A relation of their different count levels to the rotation period of the dominating spot is not confirmed by a third Chandra observation carried out some months later, during another minimum of the 1.87 d cycle. Similarly we find no indications for a correlation of the Hα emission with the spots' rotational phase. The lack of detected rotational modulation in two important activity diagnostics seems to argue against a direct association of chromospheric and coronal emission with the spot distribution.