Fluorescence and Excitation of Molecular Hydrogen in the Circumstellar Environment of PMS Stars
Abstract
TW Hya will likely have the richest and best exposed far-UV spectrum of any member of the important class of classical T Tauri stars (CTTS) because of its uniquely low extinction (A_v approx. 0.0), the face-on geometry of its disk that minimizes local extinction, absence of a local molecular cloud, and 50 pc distance (the closest for a CTTS). We request a deep exposure of TW Hya to improve the model for H_2 fluorescence (primarily by Lyman-alpha) as demonstrated by our analysis of the very rich H_2 emission line spectrum in the 1170-1600 A range seen in HSTSTIS echelle data. Since the FUSE band includes H_2 emission lines pumped from different rovibrational states in the ground electronic system, including much lower energy states than are sampled by STIS, we can study the population of rovibrational states within the ground electronic state, search for other fluorescent channels, infer the shape of the stellar Lyman-alpha line, study possible excitation mechanisms, and derive a lower limit for the amount of H_2 that is located in the stellar disk. In a short (2.1 ks) test spectrum of TW Hya the probable detection of the two H_2 emission lines demonstrates the feasibility of our program. The requested spectrum will also provide excellent profiles of the OVI emission lines that are needed to set upper limits on the amount of H_2 present in accretion columns andor outflows and to compare with models of line formation in accretion flows along magnetic flux tubes connecting the disk to polar magnetic starspots.
- Publication:
-
FUSE Proposal
- Pub Date:
- 2003
- Bibcode:
- 2003fuse.prop.C067L
- Keywords:
-
- FUSE Proposal ID #C067