HST NICMOS Polarization Observations of Massive YSOs

Details HST NICMOS Polarization Observations of Massive YSOs HST NICMOS Polarization Observations of Massive YSOs

Dec 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006aas...20910504s&link_type=abstract

2007 AAS/AAPT Joint Meeting, American Astronomical Society Meeting 209, #105.04; Bulletin of the American Astronomical Society,

Astronomy and Astrophysics

Astronomy

Scientific paper

Massive Young Stellar Objects (YSOs), like low-mass YSOs, appear to be surrounded by optically thick envelopes or disks and have regions, often bipolar, that are seen in polarized scattered light at NIR wavelengths. Whereas a low-mass YSO has a relatively simple accretion disk and bi-polar cones of scattered light, the massive YSO's morphology is confused by the presence of multiple stars, other YSOs, and obscuring dense molecular clouds within the same cluster core. Unlike low-mass YSOs, it has been suggested that massive YSOs form, not by accretion from their surrounding disks, but instead by coalescence of low-mass stars in the cores of dense stellar clusters.
We are using the high spatial resolution of NICMOS on Hubble Space Telescope to examine the disks and outflow regions of massive YSOs in star-forming regions within a few kpc of the Sun to identify YSOs that perhaps might have been formed by coalescence instead of disk accretion. Here we report on 2 micron polarimetry of S255-IRS1 and NGC6334-V. S255-IRS1 consists of two YSOs (luminosities corresponding to early B stars) with overlapping scattered light cones; neither YSO is aligned with the local magnetic field. NGC6334-V consists of a double-lobed bright reflection nebula seen against a dark region, probably an optically thick molecular cloud. Our polarization measurements show that the illuminating star lies 2'' south of the line connecting the two lobes; this star is not detected at 2 micron, but there are a small radio source and a MIR source at this location. We discuss the asymmetric appearance of all three YSOs.
Support for this work was provided by NASA through grant number GO-10519 from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555.

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