The stellar population of the Rosat North Ecliptic Pole survey

¹ INAF – Osservatorio Astronomico di Palermo, Piazza del Parlamento 1, 90134, Palermo, Italy e-mail: giusi@astropa.inaf.it
² Dipartimento di Scienze Fisiche e Astronomiche – Università di Palermo, Piazza del Parlamento 1, 90134 Palermo, Italy
³ Astrophysics Mission Division, RSSD of ESA/ESTEC, Postbus 299, 2200 AG Noordwjik, The Netherlands
⁴ Institute for Astronomy, University of Hawai'i, 2680 Woodlawn Drive, Honolulu, HI 96822, USA
⁵ INAF – Istituto di Radioastronomia INAF-CNR, via Gobetti 101, 40129, Bologna, Italy
⁶ Department of Astronomy, University of Michigan, 918 Dennison Building, Ann Arbor, MI 48109-1042, USA
⁷ LAEFF, European Space Astronomy Center, Apartado 50727, 28080 Madrid, Spain

Received: 31 July 2006
Accepted: 10 October 2006

Abstract

Context.X-ray surveys are a very efficient mean of detecting young stars and therefore allow us to study the young stellar population in the solar neighborhood and the local star formation history in the last billion of years.

Aims.We want to study the young stellar population in the solar neighborhood, to constrain its spatial density and scale height as well as the recent local star formation history.

Methods.We analyze the stellar content of the ROSAT North Ecliptic Pole survey, and compare the observations with the predictions derived from stellar galactic model. Since the ROSAT NEP survey is sensitive at intermediate fluxes is able to sample both the youngest stars and the intermediate age stars (younger than 10⁹ years), linking the shallow and deep flux surveys already published in the literature.

Results.We confirm the existence of an excess of yellow stars in our neighborhood previously seen in shallow survey, which is likely due to a young star population not accounted for in the model. However the excellent agreement between observations and predictions of dM stars casts some doubt on the real nature of this active population.