Oral Presentation
Early results from HAWC+/SOFIA: far-IR polarization mapping of Rho Oph A at 89 and 155 microns
Presenter: Giles Novak (Northwestern University)
Kilo-pixel polarimetric cameras for far-IR/submm telescopes are now yielding extremely detailed molecular cloud polarization maps. But we know that not all cloud regions exhibit grain alignment, and our inability to confidently model variations in grain alignment efficiency is severely limiting the extent to which we can use polarization maps to constrain theories of star/planet formation. Observations of the variation in fractional polarization p as a function of wavelength, a.k.a. “polarization spectra”, provide a promising way to overcome this problem by constraining grain alignment prescriptions such as those based on the radiative torques (RATs) alignment mechanism. We used the HAWC+ polarimeter for SOFIA to obtain detailed polarization maps of the nearby (d ~ 150 pc) star forming core Rho Oph A, at both 89 and 155 microns. Our maps cover both the dense star forming core and the warmer, more tenuous region lying eastward of the core, where a young early-type star in a champagne-type HII region is found. This star, called S1, is the main heat source for Rho Oph A. We present preliminary maps of the quantity p(155)/p(89), which shows strong spatial variations that are strongly correlated with column density, in the sense that sharply falling p(lambda) is seen for high density sightlines while flatter or rising p(lambda) predominates near S1. We show that this observation is qualitatively consistent with the prediction of RATs theory, and we suggest that the observation can be used to determine which wavelengths of radiation are responsible for magnetic grain alignment in Rho Oph A.
asiaa.sinica.edu.tw