131 research outputs found
CCS Imaging of the Starless Core L1544: An Envelope with Infall and Rotation
We have carried out observations of the starless core L1544 in the CCS
(J_N=3_2-2_1) line at 9 millimeters wavelength using the BIMA array. The maps
show an elongated condensation, 0.15 x 0.045 pc in size, with stronger emission
at the edges. The appearance is consistent with a flattened, ringlike structure
viewed at high inclination to the line of sight. The CCS molecule is likely
heavily depleted in the inner part of the core. The position velocity diagram
along the major axis shows a remarkable pattern, a "tilted ellipse", that can
be reproduced by a simple model ring with motions of both infall and rotation.
The models suggest comparable velocities for infall and rotation, ~0.1 km/s, in
the outermost envelope, at radius 15000 AU.Comment: 14 pages, 4 figures, AAS-LaTex v4.0, will be published in ApJ
The circumstellar disk of AB Aurigae: evidence for envelope accretion at late stages of star formation?
The circumstellar disk of AB Aurigae has garnered strong attention owing to
the apparent existence of spirals at a relatively young stage and also the
asymmetric disk traced in thermal dust emission. However, the physical
conditions of the spirals are still not well understood. The origin of the
asymmetric thermal emission is unclear.
We observed the disk at 230 GHz (1.3 mm) in both the continuum and the
spectral line ^12CO J=2-1 with IRAM 30-m, the Plateau de Bure interferometer,
and the Submillimeter Array to sample all spatial scales from 0.37" to about
50". To combine the data obtained from these telescopes, several methods and
calibration issues were checked and discussed.
The 1.3 mm continuum (dust) emission is resolved into inner disk and outer
ring. Molecular gas at high velocities traced by the CO line is detected next
to the stellar location. The inclination angle of the disk is found to decrease
toward the center. On a larger scale, based on the intensity weighted
dispersion and the integrated intensity map of ^12CO J=2-1, four spirals are
identified, where two of them are also detected in the near infrared. The total
gas mass of the 4 spirals (M_spiral) is 10^-7 < M_spiral < 10^-5 M_sun, which
is 3 orders of magnitude smaller than the mass of the gas ring. Surprisingly,
the CO gas inside the spiral is apparently counter-rotating with respect to the
CO disk, and it only exhibits small radial motion.
The wide gap, the warped disk, and the asymmetric dust ring suggest that
there is an undetected companion with a mass of 0.03 M_sun at a radius of 45
AU. Although an hypothetical fly-by cannot be ruled out, the most likely
explanation of the AB Aurigae system may be inhomogeneous accretion well above
or below the main disk plane from the remnant envelope, which can explain both
the rotation and large-scale motions detected with the 30-m image.Comment: 17 pages, 13 figures, accepted for publication in A&A journal. Typos
are correcte
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