Diagnosing The Nature Of H2 Emission In Young Circumstellar Disks

Details Diagnosing The Nature Of H2 Emission In Young Circumstellar Disks Diagnosing The Nature Of H2 Emission In Young Circumstellar Disks

Jan 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011aas...21734020j&link_type=abstract

American Astronomical Society, AAS Meeting #217, #340.20; Bulletin of the American Astronomical Society, Vol. 43, 2011

Astronomy and Astrophysics

Astronomy

Scientific paper

Young circumstellar disks are important for the understanding of the early evolution of stellar systems. While molecular hydrogen has been detected from the regions surrounding many young stellar objects (YSOs), the excitation mechanism for the abundant H2 within the circumstellar disk is unclear [Bary et al., 2003; Bitner et al., 2008]. Three excitation mechanisms have been proposed: shocks within the disk, UV-induced fluorescence at its surface, or X-ray excitation [Beck et al., 2008]. We analyzed H2 emission from the central regions around YSOs to understand the physical processes of and conditions around young circumstellar disks.
Beck et al. [2008] studied a set of bright YSOs in the Taurus-Auriga cloud complex and concluded, on the basis of K-band spectroscopy, that much of the observable H2 emission around these objects was due to shocked gas, likely as part of the associated Herbig-Haro outflows. However, their data lacks the H-band (higher-excitation) H2 lines that can better probe the effects of UV-fluorescence at the surface of circumstellar disks. (UV fluorescence excites the H & K-band transitions, whereas warm (1,800K) shocked gas will have significant flux only in the K-band lines).
We used the TripleSpec instrument (J, H, K-band spectroscopy) on the Apache Point Observatory 3.5-m telescope to detect H2 emission in the inner regions around YSOs in the Taurus-Auriga cloud complex and the Orion Molecular Cloud. TripleSpec is uniquely suited to observing the full suite of ro-vibrational transitions of H2, from which we can extract excitation temperatures and infer (possibly multiple) excitation mechanisms. We have observed all six objects from Beck et al and a larger catalogue at high signal to noise. Our data analysis confirms their conclusions that shock heating is responsible for the bulk of the H2 emission.
We acknowledge the APS department at the University of Colorado for their support.

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