Identification of red high proper-motion objects in Tycho-2 and 2MASS catalogues using Virtual Observatory tools

¹ Centro de Astrobiología (INTA-CSIC), Departamento de Astrofísica, PO Box 78, 28691 Villanueva de la Cañada, Madrid, Spain
e-mail: fran.jimenez-esteban@cab.inta-csic.es
² Spanish Virtual Observatory, Spain
³ Saint Louis University, Madrid Campus, Division of Science and Engineering, Avenida del Valle 34, 28003 Madrid, Spain
⁴ Departamento de Astrofísica y Ciencias de la Atmósfera, Facultad de Ciencias Físicas, Avenida Complutense s/n, 28040 Madrid, Spain
⁵ Departamento de Física, Ingeniería de Sistemas y Teoría de la Señal, Escuela Politécnica Superior, University of Alicante, Apdo. 99, 03080 Alicante, Spain
⁶ Instituto de Astrofísica de Canarias, 38200 La Laguna, Tenerife, Spain

Received: 1 November 2011
Accepted: 16 January 2012

Abstract

Aims. With available Virtual Observatory tools, we looked for new M dwarfs in the solar neighbourhood and M giants with high tangential velocities.

Methods. From an all-sky cross-match between the optical Tycho-2 and the near-infrared 2MASS catalogues, we selected objects with proper motions μ  >  50 mas yr^-1 and very red V_T − K_s colours. For the most interesting targets, we collected multi-wavelength photometry, constructed spectral energy distributions, estimated effective temperatures and surface gravities from fits to atmospheric models, performed time-series analysis of ASAS V-band light curves, and assigned spectral types from low-resolution spectroscopy obtained with CAFOS at the 2.2 m Calar Alto telescope.

Results. We got a sample of 59 bright red high proper-motion objects, including fifty red giants, four red dwarfs, and five objects reported in this work for the first time. The five new stars have magnitudes V_T  ≈  10.8–11.3 mag, reduced proper motions midway between known dwarfs and giants, near-infrared colours typical of giants, and effective temperatures T_eff  ≈  2900–3400 K. From our time-series analysis, we discovered a long secondary period in Ruber 4 and an extremely long primary period in Ruber 6. With the CAFOS spectra, we confirmed the red giant nature of Ruber 7 and 8, the last of which seems to be one of the brightest metal-poor M giants ever identified.