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INWARD MOTIONS IN STARLESS CORES TRACED WITH CS (3-2) AND (2-1) LINES
CHANG WON LEE,PHILIP C. MYERS,RENE? PLUME 한국천문학회 2004 Journal of The Korean Astronomical Society Vol.37 No.5
We compare the results of the surveys of starless cores performed with CS (2-1) and (3-2) lines tostudy inward motions in the cores. The velocity shifts of the CS(3-2) and (2-1) lines with respect toN2H+ are found to correlate well with each other and to have similar number distributions, implyingthat, in many cores, systematic inward motions of gaseous material may occur over a range of density ofat least a factor 4. Fits of the CS spectra to a 2-layer radiative transfer model in ten infall candidatessuggest that the median eective line-of-sight speed of the inward-moving gas is 0:07 km s1 forCS (3-2) and 0:04 km s1 for CS(2-1). Considering that the optical depth obtained from the ts isusually smaller in CS(3-2) than in (2-1) line, this may indicate that CS(3-2) usually traces inner, densergas with greater inward motions than CS(2-1) implying that many of the infall candidates have fasterinfall toward the center. However, this conclusion may not be representative of all starless core infallcandidates, due to the statistically small number analyzed here. Further line observations will be usefulto test this conclusion.
Dust Polarization toward Embedded Protostars in Ophiuchus with ALMA. I. VLA 1623
Sadavoy, Sarah I.,Myers, Philip C.,Stephens, Ian W.,Tobin, John,Commerç,on, Benoî,t,Henning, Thomas,Looney, Leslie,Kwon, Woojin,Segura-Cox, Dominique,Harris, Robert American Astronomical Society 2018 The Astrophysical journal Vol.859 No.2
<P>We present high-resolution (similar to 30 au) ALMA Band 6 dust polarization observations of VLA 1623. The VLA 1623 data resolve compact similar to 40 au inner disks around the two protobinary sources, VLA 1623-A and VLA 1623-B, and also an extended similar to 180 au ring of dust around VLA 1623-A. This dust ring was previously identified as a large disk in lower-resolution observations. We detect highly structured dust polarization toward the inner disks and the extended ring with typical polarization fractions similar to 1.7% and similar to 2.4%, respectively. The two components also show distinct polarization morphologies. The inner disks have uniform polarization angles aligned with their minor axes. This morphology is consistent with expectations from dust scattering. By contrast, the extended dust ring has an azimuthal polarization morphology not previously seen in lower-resolution observations. We find that our observations are well-fit by a static, oblate spheroid model with a flux-frozen, poloidal magnetic field. We propose that the polarization traces magnetic grain alignment likely from flux freezing on large scales and magnetic diffusion on small scales. Alternatively, the azimuthal polarization may be attributed to grain alignment by the anisotropic radiation field. If the grains are radiatively aligned, then our observations indicate that large (similar to 100 mu m) dust grains grow quickly at large angular extents. Finally, we identify significant proper motion of VLA 1623 using our observations and those in the literature. This result indicates that the proper motion of nearby systems must be corrected for when combining ALMA data from different epochs.</P>
INTERNAL MOTIONS IN STARLESS DENSE CORES
Lee, Chang Won,Myers, Philip C. IOP Publishing 2011 The Astrophysical journal Vol.734 No.1
<P>This paper discusses the statistics of internal motions in starless dense cores and the relation of these motions to core density and evolution. Four spectral lines from three molecular species are analyzed from single-pointing and mapped observations of several tens of starless cores. Blue asymmetric profiles are dominant, indicating that inward motions are prevalent in sufficiently dense starless cores. These blue profiles are found to be more abundant, and their asymmetry is bluer, at core positions with stronger N2H+ line emission or higher column density. Thirty-three starless cores are classified into four different types according to the blueshift and redshift of the lines in their molecular line maps. Among these cores, contracting motions dominate: 19 are classified as contracting, 3 as oscillating, 3 as expanding, and 8 as static. Contracting cores have inward motions all over the core with those motions predominating near the region of peak density. Cores with the bluest asymmetry tend to have greater column density than other cores and all five cores with peak column density > 6 x 10(21) cm(-2) are found to be contracting. This suggests that starless cores are likely to have contracting motions if they are sufficiently condensed. Our classification of the starless cores may indicate a sequence of core evolution in the sense that column density increases from static to contracting cores: the static cores in the earliest stage, the expanding and/or the oscillating cores in the next, and the contracting cores in the latest stage.</P>
Dust Polarization toward Embedded Protostars in Ophiuchus with ALMA. II. IRAS 16293-2422
Sadavoy, Sarah I.,Myers, Philip C.,Stephens, Ian W.,Tobin, John,Kwon, Woojin,Segura-Cox, Dominique,Henning, Thomas,Commerç,on, Benoî,t,Looney, Leslie American Astronomical Society 2018 The Astrophysical journal Vol.869 No.2