227 research outputs found
ALMA observations of the protostellar disk around the VeLLO IRAS 16253-2429
We present ALMA long-baseline observations toward the Class 0 protostar IRAS
16253-2429 (hereafter IRAS 16253) with a resolution down to 0.12" (~15 au). The
1.3 mm dust continuum emission has a deconvolved Gaussian size of 0.16" x 0.
07" (20 au x 8.8 au), likely tracing an inclined dusty disk. Interestingly, the
position of the 1.38 mm emission is offset from that of the 0.87 mm emission
along the disk minor axis. Such an offset may come from a torus-like disk with
very different optical depths between these two wavelengths. Furthermore,
through CO (2 - 1) and C18O (2 - 1) observations, we study rotation and infall
motions in this disk-envelope system and infer the presence of a Keplerian disk
with a radius of 8 - 32 au. This result suggests that the disk could have
formed by directly evolving from a first core, because IRAS16253 is too young
to gradually grow a disk to such a size considering the low rotation rate of
its envelope. In addition, we find a quadruple pattern in the CO emission at
low velocity, which may originate from CO freeze out at the disk/envelope
midplane. This suggests that the "cold disk" may appear in the early stage,
implying a chemical evolution for the disk around this proto-brown dwarf (or
very low-mass protostar) different from that of low-mass stars.Comment: accepted for publication in ApJ, 11 pages, 6 figure
Detection of 40-48 GHz dust continuum linear polarization towards the Class 0 young stellar object IRAS 16293-2422
We performed the new JVLA full polarization observations at 40-48 GHz
(6.3-7.5 mm) towards the nearby ( 1473.4 pc) Class 0 YSO IRAS
16293-2422, and compare with the previous SMA observations reported by Rao et
al. (2009; 2014). We observed the quasar J1407+2827 which is weakly polarized
and can be used as a leakage term calibrator for 9 GHz observations, to
gauge the potential residual polarization leakage after calibration. We did not
detect Stokes Q, U, and V intensities from the observations of J1407+2827, and
constrain (3-) the residual polarization leakage after calibration to
be 0.3\%. We detect linear polarization from one of the two binary
components of our target source, IRAS\,16293-2422\,B. The derived polarization
position angles from our observations are in excellent agreement with those
detected from the previous observations of the SMA, implying that on the
spatial scale we are probing (50-1000 au), the physical mechanisms for
polarizing the continuum emission do not vary significantly over the wavelength
range of 0.88-7.5 mm. We hypothesize that the observed polarization
position angles trace the magnetic field which converges from large scale to an
approximately face-on rotating accretion flow. In this scenario, magnetic field
is predominantly poloidal on 100 au scales, and becomes toroidal on smaller
scales. However, this interpretation remains uncertain due to the high dust
optical depths at the central region of IRAS\,16293-2422\,B and the uncertain
temperature profile. We suggest that dust polarization at wavelengths
comparable or longer than 7\,mm may still trace interstellar magnetic field.
Future sensitive observations of dust polarization in the fully optically thin
regime will have paramount importance for unambiguously resolving the magnetic
field configuration.Comment: 14 pages, 7 figures, accepted to A&A. Comments are welcom
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