Probing hypergiant mass loss with adaptive optics imaging and polarimetry in the infrareD: MMT-Pol and LMIRCam observations of IRC +10420 and VY Canis Majoris

Journal Article · Wed Jul 01 04:00:00 EDT 2015 · The Astronomical Journal (Online)

DOI:https://doi.org/10.1088/0004-6256/150/1/15· OSTI ID:22879469

Shenoy, Dinesh P.; Jones, Terry J. ^[1]; Packham, Chris; Lopez-Rodriguez, Enrique ^[2]

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1. Minnesota Institute for Astrophysics, University of Minnesota, 116 Church St. SE, Minneapolis, MN 55455 (United States)
2. Department of Physics and Astronomy, University of Texas—San Antonio, One UTSA Circle, San Antonio TX 78249 (United States)

We present 2–5 μm adaptive optics (AO) imaging and polarimetry of the famous hypergiant stars IRC +10420 and VY Canis Majoris. The imaging polarimetry of IRC +10420 with MMT-Pol at 2.2 μm resolves nebular emission with intrinsic polarization of 30%, with a high surface brightness indicating optically thick scattering. The relatively uniform distribution of this polarized emission both radially and azimuthally around the star confirms previous studies that place the scattering dust largely in the plane of the sky. Using constraints on scattered light consistent with the polarimetry at 2.2 μm, extrapolation to wavelengths in the 3–5 μm band predicts a scattered light component significantly below the nebular flux that is observed in our Large Binocular Telescope/LMIRCam 3–5 μm AO imaging. Under the assumption this excess emission is thermal, we find a color temperature of ∼500 K is required, well in excess of the emissivity-modified equilibrium temperature for typical astrophysical dust. The nebular features of VY CMa are found to be highly polarized (up to 60%) at 1.3 μm, again with optically thick scattering required to reproduce the observed surface brightness. This star’s peculiar nebular feature dubbed the “Southwest Clump” is clearly detected in the 3.1 μm polarimetry as well, which, unlike IRC +10420, is consistent with scattered light alone. The high intrinsic polarizations of both hypergiants’ nebulae are compatible with optically thick scattering for typical dust around evolved dusty stars, where the depolarizing effect of multiple scatters is mitigated by the grains’ low albedos.

• OSTI ID: 22879469
• Journal Information: The Astronomical Journal (Online), Journal Name: The Astronomical Journal (Online) Journal Issue: 1 Vol. 150; ISSN 1538-3881
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ASTROPHYSICS
BRIGHTNESS
COLOR
COSMIC DUST
EMISSIVITY
LIGHT SCATTERING
LIMITING VALUES
MASS TRANSFER
NEBULAE
POLARIMETRY
POLARIZATION
SKY
STELLAR WINDS
SUPERGIANT STARS
TELESCOPES
WAVELENGTHS