EDP Sciences
Free access
Volume 424, Number 2, September III 2004
Page(s) 603 - 612
Section Interstellar and circumstellar matter
DOI http://dx.doi.org/10.1051/0004-6361:20040356

A&A 424, 603-612 (2004)
DOI: 10.1051/0004-6361:20040356

Accretion in brown dwarfs: An infrared view

A. Natta1, L. Testi1, J. Muzerolle2, S. Randich1, F. Comerón3 and P. Persi4

1  Osservatorio Astrofisico di Arcetri, INAF, Largo E. Fermi 5, 50125 Firenze, Italy
    e-mail: natta@arcetri.astro.it
2  Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721, USA
3  European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching, Germany
4  Istituto Astrofisica Spaziale e Fisica Cosmica, CNR, via del Fosso del Cavaliere, 00133 Roma, Italy

(Received 27 February 2004 / Accepted 26 May 2004)

This paper presents a study of the accretion properties of 19 very low mass objects ( $M_\star$~ 0.01-0.1  $M_\odot$) in the regions Chamaeleon I and $\rho$ Oph. For 8 objects we obtained high resolution H $\alpha$ profiles and determined mass accretion rate  $\dot M_{\rm ac}$ and accretion luminosity $L_{\rm ac}$. Pa $\beta$ is detected in emission in 7 of the 10 $\rho$ Oph objects, but only in one in Cha I. Using objects for which we have both a determination of $L_{\rm ac}$ from H $\alpha$ and a Pa $\beta$ detection, we show that the correlation between the Pa $\beta$ luminosity and luminosity $L_{\rm ac}$, found by Muzerolle et al. (1998) for T Tauri stars in Taurus, extends to objects with mass ~0.03  $M_\odot$; L(Pa $\beta$) can be used to measure $L_{\rm ac}$ also in the substellar regime. The results were less conclusive for Br $\gamma$, which was detected only in 2 objects, neither of which had an H $\alpha$ estimate of $\dot M_{\rm ac}$. Using the relation between L(Pa $\beta$) and $L_{\rm ac}$ we determined the accretion rate for all the objects in our sample (including those with no H $\alpha$ spectrum), more than doubling the number of substellar objects with known $\dot M_{\rm ac}$. When plotted as a function of the mass of the central object together with data from the literature, our results confirm the trend of lower $\dot M_{\rm ac}$ for lower $M_\star$, although with a large spread. Some of the spread is probably due to an age effect; our very young objects in $\rho$ Oph have on average an accretion rate at least one order of magnitude higher than objects of similar mass in older regions. As a side product, we found that the width of H $\alpha$ measured at 10% peak intensity is not only a qualitative indicator of the accreting nature of very low mass objects, but can be used to obtain a quantitative, although not very accurate, estimate of $\dot M_{\rm ac}$ over a large mass range, from T Tauri stars to brown dwarfs. Finally, we found that some of our objects show evidence of mass-loss in their optical spectra.

Key words: stars: low-mass, brown dwarfs -- stars: formation -- stars: activity -- line: profiles -- accretion, accretion disks

SIMBAD Objects

© ESO 2004

What is OpenURL?

The OpenURL standard is a protocol for transmission of metadata describing the resource that you wish to access.

An OpenURL link contains article metadata and directs it to the OpenURL server of your choice. The OpenURL server can provide access to the resource and also offer complementary services (specific search engine, export of references...). The OpenURL link can be generated by different means.

  • If your librarian has set up your subscription with an OpenURL resolver, OpenURL links appear automatically on the abstract pages.
  • You can define your own OpenURL resolver with your EDPS Account.
    In this case your choice will be given priority over that of your library.
  • You can use an add-on for your browser (Firefox or I.E.) to display OpenURL links on a page (see http://www.openly.com/openurlref/). You should disable this module if you wish to use the OpenURL server that you or your library have defined.