A&A 405, 149-163 (2003)
DOI: 10.1051/0004-6361:20030644

Further identification of ROSAT all-sky survey sources in Orion

A. Frasca¹, J. M. Alcalá², E. Covino², S. Catalano¹, E. Marilli¹ and R. Paladino<sup>2

1</sup>  INAF, Osservatorio Astrofisico di Catania, via S. Sofia 78, 95123 Catania, Italy
²  INAF, Osservatorio Astronomico di Capodimonte, via Moiariello 16, 80131 Napoli, Italy

(Received 17 February 2003 / Accepted 24 April 2003 )

Abstract
We report on the identification of 22 ROSAT All-Sky Survey (RASS) X-ray sources distributed in the general direction of the Orion star-forming region. The X-ray sample contains sources from the ROSAT bright source catalogue and from previous detections. The optical identifications are based on intermediate-resolution spectroscopy and  UBV Johnson photometry using a 1m-class telescope. The strengths of the H , D ₂ and lithium lines for the stellar counterparts are evaluated applying the spectral subtraction technique, using templates of the same spectral type. Radial velocities of the optical counterparts are also reported. Thirteen of the optical counterparts show the lithium absorption line in their spectra and have radial velocities consistent with the Orion star forming region. Four of these objects can be classified as new bona-fide T Tauri stars.

Key words: X-ray: stars -- stars: pre-main-sequence -- stars: low-mass, brown dwarfs -- stars: activity -- ISM: individual objects: Orion -- stars: formation

Offprint request: A. Frasca, afr@sunct.ct.astro.it

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