University of Minnesota
School of Physics & Astronomy

Physics and Astronomy Calendar

Friday, January 22nd 2016
2:30 pm:
Thesis Defense in Nicholson 155
Speaker: Dinesh Shenoy, MN Institute for Astrophysics
Subject: A Study of Hypergiant Mass Loss in the Near-To-Mid Infrared: VY CMa, IRC +10420, mu Cep and rho Cas
This is the public portion of Mr. Shenoy's thesis defense. His adviser is Terry Jones.

Stars of initial mass greater than 9 M_sun become red supergiants (RSGs), a short-lived stage during which they experience mass-loss that strongly influences their post-RSG evolution and end state. The highest luminosity RSGs, referred to here as hypergiants, experience episodic mass-loss whose mechanism remains poorly understood and motivates observations to help constrain it. This thesis studies mass loss from hypergiant stars with near-to-mid infrared imaging over a range of angular scales. The recent mass-loss history of the extreme red supergiant VY Canis Majoris and the warm hypergiant star IRC +10420 are studied at the sub-arcsecond scale with adaptive optics imaging and imaging polarimetry from 1 - 5 micron using LMIRCam on the Large Binocular Telescope (LBT) and MMT-Pol at the MMT Observatory. The nebular features of both VY CMa and IRC +10420 are found to be highly polarized from 1 - 3 micron, with optically thick scattering required to reproduce the observed surface brightness. The polarimetry of their nebula is contrasted, with VY CMa’s consistent with scattered light alone, while IRC +10420’s nebular emission is mostly thermal with a color temperature well above that for typical astrophysical dust. To probe further into hypergiants' history of mass-loss, mid-IR imaging with MMT/MIRAC and SOFIA/FORCAST is used to study VY CMa, IRC +10420 and two additional hypergiants: the RSG mu Cep and the warm hypergiant rho Cas. Average mass-loss rates are computed using DUSTY 1-D radiative transfer models. Two distinct periods are found in the mass-loss history of IRC +10420, with an order of magnitude decrease in the recent past, with the change indicating its evolution beyond the RSG stage.

The weekly calendar is also available via subscription to the physics-announce mailing list, and by RSS feed.