Letter to the Editor

Discovery of a very cool object with extraordinarily strong H emission ^*

¹ Laboratorio de Astrofísica Espacial y Física Fundamental, INTA, PO Box 50727, 28080 Madrid, Spain
² Institute of Astronomy, University of Hawaii at Manoa. 2680 Woodlawn Drive, Honolulu, HI 96822, USA
³ Instituto de Astrofísica de Canarias, 38205 La Laguna, Tenerife, Spain
⁴ Consejo Superior de Investigaciones Científicas, CSIC, Spain
⁵ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany

Corresponding author: D. Barrado y Navascués, barrado@laeff.esa.es

Received: 22 July 2002
Accepted: 27 August 2002

Abstract

We report on the finding of the strongest Hα emission – pseudoequivalent width of 705 Å – known so far in a young, late type dwarf. This object, named as S Ori 71, is a substellar candidate member of the 1–8 Myr star cluster σ Orionis. Due to its overluminous location in color-magnitude diagrams, S Ori 71 might be younger than other cluster members, or a binary of similar components. Its mass is in the range 0.021–0.012 , depending on evolutionary models and possible binarity. The broad Hα line of S Ori 71 appears asymmetric, indicative of high velocity mass motions in the Hα forming region. The origin of this emission is unclear at the present time. We discuss three possible scenarios: accretion from a disk, mass exchange between the components of a binary system, and emission from a chromosphere.