908 research outputs found
Interferometric Observations of the T Tauri Stars in the MBM 12 Cloud
We have carried out a millimeter interferometric continuum survey toward 7
YSOs in the MBM 12 cloud. Thermal emissions associated with 2 YSOs were
detected above the 3- level at 2.1 mm, and one also showed a 1.3 mm
thermal emission. Another object was marginally detected at 2.1 mm. Spectral
energy distributions of the YSOs are well fitted by a simple power-law disk
model. Masses of the circumstellar disks are estimated to be an order of 0.05
M_{\sun}. The circumstellar disks in the MBM 12 cloud have properties in
common with the disks in nearby star-forming regions, in terms of disk
parameters such as a disk mass, as well as an infrared excess.Comment: 9 pages, 3 figures, accepted by ApJ Letter
High Contrast Imaging of the Close Environment of HD 142527 -
Context. It has long been suggested that circumstellar disks surrounding
young stars may be the signposts of planets, and still more since the recent
discoveries of embedded substellar companions. The planet-disk interaction may
create, according to models, large structures, gaps, rings or spirals, in the
disk. In that sense, the Herbig star HD 142527 is particularly compelling as,
its massive disk displays intriguing asymmetries that suggest the existence of
a dynamical peturber of unknown nature. Aims. Our goal was to obtain deep
thermal images of the close circumstellar environment of HD 142527 to re-image
the reported close-in structures (cavity, spiral arms) of the disk and to
search for stellar and substellar companions that could be connected to their
presence. Results. The circumstellar environment of HD 142527 is revealed at an
unprecedented spatial resolution down to the sub arcsecond level for the first
time at 3.8 microns. Our images reveal important radial and azimuthal
asymmetries which invalidate an elliptical shape for the disk as previously
proposed. It rather suggests a bright inhomogeneous spiral arm plus various
fainter spiral arms. We also confirm an inner cavity down to 30 AU and two
important dips at position angles of 0 and 135 deg. The detection performance
in angular differential imaging enables the exploration of the planetary mass
regime for projected physical separations as close as 40 AU. The use of our
detection map together with Monte Carlo simulations sets stringent constraints
on the presence of planetary mass, brown dwarf or stellar companions as a
function of the semi-major axis. They severely constrain the presence of
massive giant planets with semi-major axis beyond 50AU, i.e. probably within
the large disk's cavity that radially extends up to 145 AU or even further
outside.Comment: 8 pages, 7 figures, accepted in A&
Sub-arcsec imaging of the AB Aur molecular disk and envelope at millimeter wavelengths: a non Keplerian disk
We present sub-arcsecond images of AB Auriga obtained with the IRAM Plateau
de Bure interferometer in the isotopologues of CO, and in continuum at 3 and
1.3 mm. Instead of being centrally peaked, the continuum emission is dominated
by a bright, asymmetric (spiral-like) feature at about 140 AU from the central
star. The large scale molecular structure suggests the AB Aur disk is inclined
between 23 and 43 degrees, but the strong asymmetry of the continuum and
molecular emission prevents an accurate determination of the inclination of the
inner parts. We find significant non-Keplerian motion, with a best fit exponent
for the rotation velocity law of 0.41 +/- 0.01, but no evidence for radial
motions. The disk has an inner hole about 70 AU in radius. The disk is warm and
shows no evidence of depletion of CO. The dust properties suggest the dust is
less evolved than in typical T Tauri disks. Both the spiral-like feature and
the departure from purely Keplerian motions indicates the AB Aur disk is not in
quasi-equilibrium. Disk self-gravity is insufficient to create the
perturbation. This behavior may be related either to an early phase of star
formation in which the Keplerian regime is not yet fully established and/or to
a disturbance of yet unknown origin. An alternate, but unproven, possibility is
that of a low mass companion located about 40 AU from AB Aur.Comment: 10 pages, 5 figures, accepted for publication in Astronomy &
Astrophysic
The shadow knows: using shadows to investigate the structure of the pretransitional disk of HD 100453
We present GPI polarized intensity imagery of HD 100453 in Y-, J-, and K1
bands which reveals an inner gap ( au), an outer disk ( au) with
two prominent spiral arms, and two azimuthally-localized dark features also
present in SPHERE total intensity images (Wagner 2015). SED fitting further
suggests the radial gap extends to au. The narrow, wedge-like shape of the
dark features appears similar to predictions of shadows cast by a inner disk
which is misaligned with respect to the outer disk. Using the Monte Carlo
radiative transfer code HOCHUNCK3D (Whitney 2013), we construct a model of the
disk which allows us to determine its physical properties in more detail. From
the angular separation of the features we measure the difference in inclination
between the disks 45, and their major axes, PA = 140 east
of north for the outer disk and 100for the inner disk. We find an
outer disk inclination of from face-on in broad agreement
with the Wagner 2015 measurement of 34. SPHERE data in J- and H-bands
indicate a reddish disk which points to HD 100453 evolving into a young debris
disk
The Case of AB Aurigae's Disk in Polarized Light: Is There Truly a Gap?
Using the NICMOS coronagraph, we have obtained high-contrast 2.0 micron
imaging polarimetry and 1.1 micron imaging of the circumstellar disk around AB
Aurigae on angular scales of 0.3-3 arcsec (40-550 AU). Unlike previous
observations, these data resolve the disk in both total and polarized
intensity, allowing accurate measurement of the spatial variation of
polarization fraction across the disk. Using these observations we investigate
the apparent "gap" in the disk reported by Oppenheimer et al. 2008. In
polarized intensity, the NICMOS data closely reproduces the morphology seen by
Oppenheimer et al., yet in total intensity we find no evidence for a gap in
either our 1.1 or 2.0 micron images. We find instead that region has lower
polarization fraction, without a significant decrease in total scattered light,
consistent with expectations for back-scattered light on the far side of an
inclined disk. Radiative transfer models demonstrate this explanation fits the
observations. Geometrical scattering effects are entirely sufficient to explain
the observed morphology without any need to invoke a gap or protoplanet at that
location.Comment: Accepted to ApJ Letter
Collisional dust avalanches in debris discs
We quantitatively investigate how collisional avalanches may developin debris
discs as the result of the initial break-up of a planetesimal or comet-like
object, triggering a collisional chain reaction due to outward escaping small
dust grains. We use a specifically developed numerical code that follows both
the spatial distribution of the dust grains and the evolution of their
size-frequency distribution due to collisions. We investigate how strongly
avalanche propagation depends on different parameters (e.g., amount of dust
released in the initial break-up, collisional properties of dust grains and
their distribution in the disc). Our simulations show that avalanches evolve on
timescales of ~1000 years, propagating outwards following a spiral-like
pattern, and that their amplitude exponentially depends on the number density
of dust grains in the system. We estimate a probability for witnessing an
avalanche event as a function of disc densities, for a gas-free case around an
A-type star, and find that features created by avalanche propagation can lead
to observable asymmetries for dusty systems with a beta Pictoris-like dust
content or higher. Characteristic observable features include: (i) a brightness
asymmetry of the two sides for a disc viewed edge-on, and (ii) a one-armed open
spiral or a lumpy structure in the case of face-on orientation. A possible
system in which avalanche-induced structures might have been observed is the
edge-on seen debris disc around HD32297, which displays a strong luminosity
difference between its two sides.Comment: 18 pages, 19 figures; has been accepted for publication in Astronomy
and Astrophysics, section 6. Interstellar and circumstellar matter. The
official date of acceptance is 29/08/200
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