HL Tauri is a young
protostar (star which is still gaining mass by accretion from a
surrounding disk, the accretion disk, and is emitting ionized
material in jets from its poles) 140 parsecs (457 light years) from
our Solar System in the constellation of Taurus. It's disk has been
known and observed for a number of years, however recent observations
by the Atacama Large Millimeter/submillimeter Array (ALMA) revealed
this disk to be divided into a series of light and dark bands. This
is surprising, as such banding is usually associated with planet
formation in a more developed disk (a protoplanetary disk) with
darker zones forming where (invisible) planets have formed and either
accreted or tidally pushed away the (visible) dust in a the dark
bands.
In a paper published on the arXiv database at Cornell University Library on 11 March
2016, a team of astronomers led by Carlos Carrasco-González
of the Instituto de Radioastronomíay Astrofísica discuss a
series of new observations of HL Tauri made with the Very Large Array
(VLA) of the National Radio Astronomy Observatory at wavelengths of
6.7, 7.0 and 7.3 mm (observations of remote objects at different wavelengths tend to
reveal different features, as different molecules reflect light at
different wavelengths) between December 2014 and September
2015.
The Keplerian Disk of Class I Protostar L1489 IRS. Recent studies of the Keplerian Disks around other Protostars with the Submillimeter Array
(SMA) have suggested that in the early Class 0 Protostar stage little
rotation occurs within the Keplerian Disk and the rate of infalling
(i.e. the rate at which material falls from...
Protoplanetary disks around Class I Protostars in the ρ Ophiuchi Star Forming Region. Stars are thought to form from the aggregation of material from vast
clouds of molecules known as Stellar Nurseries or Star Forming...
Water and Hydroxides in the Circumstellar Disk around HD 163296. HD 163296 is a young Herbig Ae star (a star producing heat by
gravitational collapse, which is expected will fuse Hydrogen in the
future, but which has not reached this stage yet) slightly under 400
light years from Earth. It is surrounded by a fairly well documented
circumstellar disk, which reaches slightly over 900 AU from the star
(i.e. over 900 times as far from the star as Earth is from the...
Atacama Large
Millimeter/submillimeter Array of HL Tauri at a wavelength of 1.3 mm.
The positions of the reported dark
(D1-D7; dotted lines) and bright rings (B1-B7; dashed lines) are shown. Carrasco-González et al. (2016).
Carrasco-González
et al. were able to observe
many of the features seen in the ALMA images of HL Tauri, including the
innermost dark and light bands. However the much longer wavelengths
used by the enabled a much more detailed study of the inner part of
the disk, an area essentially opaque in the ALMA images. This enabled
Carrasco-González
et al. to make
estimations of the density of particles and average grain sizes
within different parts of the disk.
Left:
VLA image at 7.0 mm with an angular resolution of ~20 au (0.”15;
tapered image). Right: Close-up to the center of the disk. VLA image
at 7.0 mm with an angular resolution of ~10 au (~0.”7;
natural weighting). The positions of the reported dark (D1-D7; dotted
lines) and bright rings
(B1-B7; dashed lines) from the ALMA images are shown. The inner disk
and the first pair of dark (D1) and bright (B1) rings are clearly
seen in the 7.0 mm images. Carrasco-González et al. (2016).
The
VLA observations showed showed structure within the dust distribution
in the innermost bright ring of HL Tauri. Here the dust was found to
form clumps or knots, most of which were of a temporary nature, but
with one particularly dense clump on the northeastern part of the
limb being more permanent in nature. Carrasco-González
et al. suggest that this is possibly a protoplanet in the
earliest stages of formation, and that therefore planet formation
around of HL Tauri is beginning in the brighter areas of the disk, not
the lighter, with the bright areas representing parts of the disk
with higher densities due to early stage planetary accretion rather
than areas from which dust has been cleared by later stage planetary
formation.
(a)
Superposition of the VLA 7.0 mm image (contours; naturally weighted
image; beam size ≈0:”067)
over the ALMA 1.3 mm image (colour scale). Contour levels are -4, 4,
6, 8, 10, 15, 20, 25, 30, 40, 50, 100, and 150 times the rms of the
7.0 mm map, 3.5 μJy
beam-1. The two arrows mark the direction of the
collimated jet at a P.A. of ~45º.
(b) A close-up to the center of the disk. Colour scale is the ALMA
1.3 mm image and contours are from the high angular resolution VLA
7.0 mm image (robust 0 weighted image; beam size ≈0:”04).
Contour levels are 3, 4, 5, 6, 7, 8, 12, 16, 20, 24, 28, 32, 40, 48,
and 56 times 7 μJy
beam-1. (c) and (d): Comparison between sub-bands contour
images at 7.3 mm and 6.7 mm (robust 0.4 weighting; beam sizes ≈0:”053)
over the 7.0 mm colour scale image. Contours in both panels are 8, 9,
10, 11, 12, 13, 14, 15, and 16 times 6 μJy
beam-1.
See also...
The Keplerian Disk of Class I Protostar L1489 IRS. Recent studies of the Keplerian Disks around other Protostars with the Submillimeter Array
(SMA) have suggested that in the early Class 0 Protostar stage little
rotation occurs within the Keplerian Disk and the rate of infalling
(i.e. the rate at which material falls from...Protoplanetary disks around Class I Protostars in the ρ Ophiuchi Star Forming Region. Stars are thought to form from the aggregation of material from vast
clouds of molecules known as Stellar Nurseries or Star Forming...Water and Hydroxides in the Circumstellar Disk around HD 163296. HD 163296 is a young Herbig Ae star (a star producing heat by
gravitational collapse, which is expected will fuse Hydrogen in the
future, but which has not reached this stage yet) slightly under 400
light years from Earth. It is surrounded by a fairly well documented
circumstellar disk, which reaches slightly over 900 AU from the star
(i.e. over 900 times as far from the star as Earth is from the...
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