Timescale of mass accretion in pre-main-sequence stars

Abstract

We present the initial result of a large spectroscopic survey aimed at measuring the timescale of mass accretion in young, pre-mainsequence stars in the spectral type range K0-M5. Using multi-object spectroscopy with VIMOS at the VLT we identified the fraction of accreting stars in a number of young stellar clusters and associations of the ages of between 1-30 Myr. The fraction of accreting stars decreases from ∼60% at 1.5-2 Myr to ∼2% at 10 Myr. No accreting stars are found after 10 Myr at a sensitivity limit of 10 −11 M yr −1 . We compared the fraction of stars showing ongoing accretion ( f acc ) to the fraction of stars with near-to-mid infrared excess ( f IRAC ). In most cases we find f acc < f IRAC , i.e., mass accretion appears to cease (or drop below detectable level) earlier than the dust is dissipated in the inner disk. At 5 Myr, 95% of the stellar population has stopped accreting material at a rate of > ∼ 10 −11 M yr −1 , while ∼20% of the stars show near-infrared excess emission. Assuming an exponential decay, we measure a mass accretion timescale (τ acc ) of 2.3 Myr, compared to a near-to-mid infrared excess timescale (τ IRAC ) of 3 Myr. Planet formation and/or migration, in the inner disk might be a viable mechanism to halt further accretion onto the central star on such a short timescale.

Disk Dispersal: Theoretical Understanding and Observational Constraints

“…In the inner disk (∼ 1AU), however, there appears to be clearer evidence of simultaneous dispersal. The fraction of accreting disks (withṀ acc > 10 −11 M ⊙ yr −1 ) in stellar groups declines on timescales similar to those of NIR excesses (Fedele et al 2010), with some non-accreting sources (withṀ acc < 10 −11 M ⊙ yr −1 ) still showing IR excesses (also Ingleby et al 2013, Hardy et al 2015. This may indicate that gas in the inner disk is removed first, consistent with dispersal scenarios (see Alexander et al 2014).…”

Resolved Co Gas Interior to the Dust Rings of the Hd 141569 Disk

“…Far-infrared gas emission lines have also been detected by Herschel around HD172555 (Riviere-Marichalar et al 2012) and HD 32297 (Donaldson et al 2013). The gas revealed by these observations may be left over from the primordial disk, which is expected to dissipate after a few million years (Fedele et al 2010), or created in a second generation process, such as the evaporation of infalling comets (Beust & Valiron 2007), or the collisional release of gas through sublimation (Zuckerman & Song 2012) or vaporization (Czechowski & Mann 2007).…”

Circumstellar disks and planets

“…Over the last three decades, this approach has been used to determine the typical ∼ 5 Myr time scale for disk survival (Fedele et al, 2010), hence planet formation, as well as to assess the presence of dust grains 1 mm in size or larger in the majority of protoplanetary disks . Similarly, recent…”