Protostars and Planets VI, Heidelberg, July 15-20, 2013

Poster 2S012

X-Shooter monitoring of the accretion rate in Herbig Ae/Be stars

Mendigutía, Ignacio (Clemson University, Department of Physics and Astronomy)
Brittain, Sean (Clemson University, Department of Physics and Astronomy)
Mora, Alcione (GAIA Science Operations Centre, ESA/ESAC)
Muzerolle, James (Space Telescope Science Institute)
Meeus, Gwendolyn (Universidad Autónoma de Madrid, Departamento de Física Teórica)
Oudmaijer, Rene (University of Leeds, School of Physics & Astronomy)
Montesinos, Benjamín (Centro de Astrobiología, INTA/CSIC)
Rigliaco, Elisabetta (University of Arizona, Department of Planetary Science)
Eiroa, Carlos (Universidad Autónoma de Madrid, Departamento de Física Teórica)

The mass accretion rate is a fundamental parameter necessary to understand the evolution of pre-main sequence stars. However, the accretion properties of the Herbig Ae/Be (HAeBe) stars are much less known than for their less-massive counterparts. We have observed 14 HAeBe stars over five epochs separated by timescales ranging from days to months, using the X-Shooter spectrograph on the VLT. Its wide wavelength coverage (310–2475 nm) allows us to monitor the continuum excess in the Balmer region of the spectra, and several UV, optical, and near-IR lines that are commonly used as accretion tracers for lower mass pre-main sequence stars. The underlying aim that motivates these observations is twofold. First, to determine the accuracy of the accretion tracers by comparing their variability with that of the accretion rate, which can be directly measured from the Balmer discontinuity excess. Second, to compare the variability behavior of intermediate-mass T-Tauri, HerbigAe (HAe) and Herbig Be (HBe) stars, which can be crucial to understand whether magnetospheric accretion could cease at some point within the HAeBe regime. This poster presents results for two prototypical, isolated HAe stars included in the sample, HD 31648 and HD 163296, for which a comprehensive analysis has been carried out (paper submitted to ApJ). We show evidence that all accretion-line luminosity empirical correlations for low-mass stars can be extended to HAe stars with properties similar to the ones analyzed, and discuss their accretion variability. In addition, this poster presents several preliminary results for the HBes in the sample, whose properties will be compared with those previously obtained for the HAes. The validity of magnetospheric accretion will be discussed, versus the alternative, boundary layer paradigm. The X-Shooter dataset that we are analyzing represents a promising tool to better understand the accretion properties of the most massive pre-main sequence stars able to form planets in their disks, the HAeBes.

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