Poster Abstracts

Name/Affiliation:  Simone Antoniucci (INAF - Osservatorio Astronomico di Roma (Italy))

Title:  HI lines in Young Stellar Objects: a probe of accretion and circumstellar properties

HI recombination lines at optical/near-IR wavelengths are a powerful diagnostic tool for the study of accreting Young Stellar Objects (YSOs). On the one hand these lines are commonly used as a tracer of the mass accretion process, on the other hand they can also be employed to probe the physical properties of the gas in the circumstellar structures. A first example of the possible use of HI lines is given by the POISSON project (Protostellar Optical-Infrared Spectral Survey On NTT), a large low-resolution spectral survey of 150 YSOs from five different star-forming regions. In this work we used the near-IR HI lines as a proxy for the mass accretion rate (using empirical relationships connecting line flux to the accretion luminosity), thus obtaining a large database of values, which allowed us to study the temporal evolution of the accretion rate. A different application of results from HI lines involves the analysis HI decrements (i.e. the flux ratio of the lines of a series relative to one used as reference). VLT/X-Shooter with its broad wavelength coverage and moderate spectral resolution is the perfect instrument to study the HI decrements of the Balmer, Paschen, and Brackett series. Based on X-Shooter spectra of a sample of YSOs in Lupus, I will discuss the potential and limitations of the decrement analysis. In particular, I will focus on the correlations between the decrement shape, the observed line profiles, and the (stellar and accretion) properties of the objects.