150 research outputs found
Shadows and cavities in protoplanetary disks: HD163296, HD141569A, and HD150193A in polarized light
The morphological evolution of dusty disks around young (few Myr-old) stars
is pivotal to better understand planet formation. Since both dust grains and
the global disk geometry evolve on short timescale, high-resolution imaging of
a sample of objects may provide important hints towards such an evolution. We
enlarge the sample of protoplanetary disks imaged in polarized light with
high-resolution by observing the Herbig Ae/Be stars HD163296, HD141569A, and
HD150193A. We integrate our data with previous datasets to paint a larger
picture of their morphology. We report a weak detection of the disk around
HD163296 in both H and Ks band. The disk is resolved as a broken ring structure
with a significan surface brightness drop inward of 0.6 arcsec. No sign of
extended polarized emission is detected from the disk around HD141569A and
HD150193A. We propose that the absence of scattered light in the inner 0.6
arcsec around HD163296 and the non-detection of the disk around HD150193A may
be due to similar geometric factors. Since these disks are known to be flat or
only moderately flared, self-shadowing by the disk inner wall is the favored
explanation. We show that the polarized brightness of a number of disks is
indeed related to their flaring angle. Other scenarios (such as dust grain
growth or interaction with icy molecules) are also discussed. On the other
hand, the non-detection of HD141569A is consistent with previous datasets
revealing the presence of a huge cavity in the dusty disk.Comment: 10 pages, 5 figures; accepted by Astronomy & Astrophysic
Can a planet explain different cavity sizes for small & large dust grains in transition disks?
Dissimilarities in the spatial distribution of small (μm-size) and large (mm-size) dust grains at the cavity edge of transition disks have been recently pointed out and are now under debate. We obtained VLT/NACO near-IR polarimetric observations of SAO 206462 (HD 135344B). The disk around the star shows very complex structures, such as dips and spirals. We also find an inner cavity much smaller than what is inferred from sub-mm images. The interaction between disk and orbiting companion(s) may explain this discrepanc
The protoplanetary disk of FT Tauri: multi-wavelength data analysis and modeling
Investigating the evolution of protoplanetary disks is crucial for our
understanding of star and planet formation. Several theoretical and
observational studies have been performed in the last decades to advance this
knowledge. FT Tauri is a young star in the Taurus star forming region that was
included in a number of spectroscopic and photometric surveys. We investigate
the properties of the star, the circumstellar disk, and the accretion and
ejection processes and propose a consistent gas and dust model also as a
reference for future observational studies. We performed a multi-wavelength
data analysis to derive the basic stellar and disk properties, as well as mass
accretion/outflow rate from TNG-Dolores, WHT-Liris, NOT-Notcam, Keck-Nirspec,
and Herschel-Pacs spectra. From the literature, we compiled a complete Spectral
Energy Distribution. We then performed detailed disk modeling using the MCFOST
and ProDiMo codes. Multi-wavelengths spectroscopic and photometric measurements
were compared with the reddened predictions of the codes in order to constrain
the disk properties. This object can serve as a benchmark for primordial disks
with significant mass accretion rate, high gas content and typical size.Comment: 16 pages, 9 figures, accepted for publication in A&
Small vs large dust grains in transitional disks: do different cavity sizes indicate a planet?
Transitional disks represent a short stage of the evolution of circumstellar
material. Studies of dust grains in these objects can provide pivotal
information on the mechanisms of planet formation. Dissimilarities in the
spatial distribution of small (micron-size) and large (millimeter-size) dust
grains have recently been pointed out. Constraints on the small dust grains can
be obtained by imaging the distribution of scattered light at near-infrared
wavelengths. We aim at resolving structures in the surface layer of
transitional disks (with particular emphasis on the inner 10 - 50 AU), thus
increasing the scarce sample of high resolution images of these objects. We
obtained VLT/NACO near-IR high-resolution polarimetric differential imaging
observations of SAO 206462 (HD135344B). This technique allows one to image the
polarized scattered light from the disk without any occulting mask and to reach
an inner working angle of 0.1''. A face-on disk is detected in H and Ks bands
between 0.1'' and 0.9''. No significant differences are seen between the H and
Ks images. In addition to the spiral arms, these new data allow us to resolve
for the first time an inner cavity for small dust grains. The cavity size
(about 28 AU) is much smaller than what is inferred for large dust grains from
(sub)mm observations (39 to 50 AU). The interaction between the disk and
potential orbiting companion(s) can explain both the spiral arm structure and
the discrepant cavity sizes for small and large dust grains. One planet may be
carving out the gas (and, thus, the small grains) at 28 AU, and generating a
pressure bump at larger radii (39 AU), which holds back the large grains. We
analytically estimate that, in this scenario, a single giant planet (with a
mass between 5 and 15 Jupiter masses) at 17 to 20 AU from the star is
consistent with the observed cavity sizes.Comment: 11 pages, 6 figures; accepted for publication in A&
Detection of Sharp Symmetric Features in the Circumbinary Disk Around AK Sco
The Search for Planets Orbiting Two Stars (SPOTS) survey aims to study the
formation and distribution of planets in binary systems by detecting and
characterizing circumbinary planets and their formation environments through
direct imaging. With the SPHERE Extreme Adaptive Optics instrument, a good
contrast can be achieved even at small (<300 mas) separations from bright
stars, which enables studies of planets and disks in a separation range that
was previously inaccessible. Here, we report the discovery of resolved
scattered light emission from the circumbinary disk around the well-studied
young double star AK Sco, at projected separations in the ~13--40 AU range. The
sharp morphology of the imaged feature is surprising, given the smooth
appearance of the disk in its spectral energy distribution. We show that the
observed morphology can be represented either as a highly eccentric ring around
AK Sco, or as two separate spiral arms in the disk, wound in opposite
directions. The relative merits of these interpretations are discussed, as well
as whether these features may have been caused by one or several circumbinary
planets interacting with the disk.Comment: 10 pages, 3 figures, accepted for publication in ApJ Letters. Minor
(proof-level) corrections implemented in this versio
Evolution of protoplanetary disks from their taxonomy in scattered light: Group I vs. Group II
High-resolution imaging reveals a large morphological variety of
protoplanetary disks. To date, no constraints on their global evolution have
been found from this census. An evolutionary classification of disks was
proposed based on their IR spectral energy distribution, with the Group I
sources showing a prominent cold component ascribed to an earlier stage of
evolution than Group II. Disk evolution can be constrained from the comparison
of disks with different properties. A first attempt of disk taxonomy is now
possible thanks to the increasing number of high-resolution images of Herbig
Ae/Be stars becoming available. Near-IR images of six Group II disks in
scattered light were obtained with VLT/NACO in Polarimetric Differential
Imaging, which is the most efficient technique to image the light scattered by
the disk material close to the stars. We compare the stellar/disk properties of
this sample with those of well-studied Group I sources available from the
literature. Three Group II disks are detected. The brightness distribution in
the disk of HD163296 indicates the presence of a persistent ring-like structure
with a possible connection with the CO snowline. A rather compact (less than
100 AU) disk is detected around HD142666 and AK Sco. A taxonomic analysis of 17
Herbig Ae/Be sources reveals that the difference between Group I and Group II
is due to the presence or absence of a large disk cavity (larger than 5 AU).
There is no evidence supporting the evolution from Group I to Group II. Group
II are not evolved version of the Group I. Within the Group II disks, very
different geometries (both self-shadowed and compact) exist. HD163296 could be
the primordial version of a typical Group I. Other Group II, like AK Sco and
HD142666, could be smaller counterpart of Group I unable to open cavities as
large as those of Group I.Comment: 16 pages, 7 figures, published by A&
Near-IR observations of the young star [BHB2007]-1: A sub-stellar companion opening the gap in the disk
The presence of planets or sub-stellar objects still embedded in their native
protoplanetary disks is indirectly suggested by disk sub-structures like gaps,
cavities, and spirals. However, these companions are rarely detected. We
present VLT/NACO high-contrast images in , , , and band
of the young star [BHB2007]-1 probing the inclined disk in scattered light and
revealing the probable presence of a companion. The point source is detected in
the band in spatial correspondence with complementary VLA
observations. This object is constrained to have a mass in the range of 37-47
M and is located at 50 au from the central star, inside the 70 au-large
disk cavity recently imaged by ALMA, that is absent from our NACO data (down to
20 au). This mass range is compatible with the upper end derived from the size
of the ALMA cavity. The NIR disk brightness is highly asymmetric around the
minor axis, with the southern side 5.5 times brighter than the northern side.
The constant amount of asymmetry across all wavelengths suggests that it is due
to a shadow cast by a misaligned inner disk. The massive companion that we
detect could, in principle, explain the possible disk misalignment, as well as
the different cavity sizes inferred by the NACO and ALMA observations. The
confirmation and characterization of the companion is entrusted to future
observations.Comment: 9 pages, 5 figures, 3 tables. Accepted for publication on Ap
Detection rate for significant cancer at confirmatory biopsy in men enrolled in Active Surveillance protocol: 20 cores vs 30 cores vs MRI/TRUS fusion prostate biopsy
Introduction: The detection rate for significant prostate cancer of extended vs saturation vs mMRI/TRUS fusion biopsy was prospectively evaluated in men enrolled in active surveillance (AS) protocol. Mterials and methods: From May 2013 to September 2016 75 men aged 66 years (median) with very low risk PCa were enrolled in an AS protocol and elegible criteria were: life expectancy greater than 10 years, cT1C, PSA below 10 ng/ml, PSA density < 0.20, 2 < unilateral positive biopsy cores, Gleason score (GS) equal to 6, greatest percentage of cancer (GPC) in a core < 50%. All patients underwent 3.0 Tesla pelvic mpMRI before confirmatory transperineal extended (20 cores) or saturation biopsy (SPBx; 30 cores) combined with mpMRI/TRUS fusion targeted biopsy (4 cores) of suspicious lesions (PI-RADS 3-5). Results: 21/75 (28%) patients were reclassified by SPBx based on upgraded GS ≥ 7; mpMRI lesions PI-RADS 4-5 vs PI-RADS 3-5 diagnosed 9/21 (42.8%) vs 16/21 (76.2%) significant PCa with 2 false positives (6.5%). The detection rate for significant PCa was equal to 76.2% (mpMRI/TRUS fusion biopsy) vs 81% (extended) vs 100% (SPBx) (p = 0.001); mpMRI/TRUS targeted biopsy and extended biopsy missed 5/21 (23.8%) and 4/21 (19%) significant PCa which were found by SPBx (p = 0.001) being characterised by the presence of a single positive core of GS ≥ 7 with GPC < 10%. Conclusions: Although mpMRI improve the diagnosis of clinically significant PCa, SPBx is provided of the best detection rate for PCa in men enrolled in AS protocols who underwent confirmatory biopsy
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