11/03/2017

Catching up with the astro-ph: 02/01/2017

  • Detection of lithium in nearby young late-M dwarfs (Phan-Bao et al.)  We report here the first clear detections of lithium absorption in four targets and a marginal detection in one target. Our mass estimates indicate that two of them are young brown dwarfs, two are young brown dwarf candidates and one is a young very low-mass star. The closest young field brown dwarf in our sample at only 15 pc is an excellent benchmark for further studying physical properties of brown dwarfs in the range 100150 Myr. We did not detect any debris disks around three late-M dwarfs, and we estimated upper limits to the dust mass of debris disks around them. (at 850 microns, mind you)

Keeping up with the astro-ph: 10/03/2017

  • Constraining proto-planetary disc evolution using accretion rate and disc mass measurements: the usefulness of the dimensionless accretion parameter (Rosotti et al. ) We explore how measurements of protoplanetary disc masses and accretion rates […] can be analysed via the dimensionless accretion parameter, which we define as the product of the accretion rate and stellar age divided by the disc mass. […] we demonstrate that this parameter should be less than or of order unity (e.g. stationary state) for a wide range of evolutionary scenarios, rising above unity only during the final stages of outside in clearing by external photoevaporation. We find that while dust based mass estimates produce results compatible with theoretical expectations assuming canonical dust/gas ratio, the systematically lower CO based estimates yield accretion efficiencies significantly above unity in contrast with the theory. This finding provides additional evidence that CO based disc masses are an under-estimate […]we demonstrate that dust based mass estimates are sufficiently accurate to reveal distinctly higher accretion efficiencies in the Trapezium cluster, where this result is expected given the evident importance of external photoevaporation. We therefore propose the dimensionless accretion parameter as a new diagnostic of external photoevaporation in other star forming regions.

 

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