EDP Sciences
Free access
Issue
A&A
Volume 452, Number 1, June II 2006
Page(s) 245 - 252
Section Interstellar and circumstellar matter
DOI http://dx.doi.org/10.1051/0004-6361:20054706


A&A 452, 245-252 (2006)
DOI: 10.1051/0004-6361:20054706

Accretion in the $\mathsf{\rho}$-Ophiuchi pre-main sequence stars

A. Natta, L. Testi and S. Randich

Osservatorio Astrofisico di Arcetri, INAF, Largo E. Fermi 5, 50125 Firenze, Italy
    e-mail: natta@arcetri.astro.it

(Received 16 December 2005 / Accepted 20 February 2006)

Abstract
Aims.The aim of this paper is to provide a measurement of the mass accretion rate in a large, complete sample of objects in the core of the star forming region $\rho$ Oph.
Methods.The sample includes most of the objects (104 out of 111) with evidence of a circumstellar disk from mid-infrared photometry; it covers a stellar mass range from about 0.03 to 3 $M_\odot$ and it is complete to a limiting mass of ~0.05 $M_\odot$. We used J and K-band spectra to derive the mass accretion rate of each object from the intensity of the hydrogen recombination lines, Pa$\beta$ or Br$\gamma$. For comparison, we also obtained similar spectra of 35 diskless objects.
Results.The results show that emission in these lines is only seen in stars with disks, and can be used as an indicator of accretion. However, the converse does not hold, as about 50% of our disk objects do not have detectable line emission. The measured accretion rates show a strong correlation with the mass of the central object ( $\dot M_{\rm acc}$  $\propto M_\star^{1.8\pm0.2}$) and a large spread, of two orders of magnitude at least, for any interval of $M_\star$. A comparison with existing data for Taurus shows that the objects in the two regions have similar behaviour, at least for objects more massive than $\sim $0.1 $M_\odot$. The implications of these results are briefly discussed.


Key words: stars: formation -- accretion, accretion disks -- stars: activity

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© ESO 2006

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