260 research outputs found
Resolved images of the protoplanetary disk around HD 100546 with ALMA
The disk around the Herbig Ae/Be star HD 100546 has been extensively studied
and it is one of the systems for which there are observational indications of
ongoing and/or recent planet formation. However, up until now no resolved image
of the millimeter dust emission or the gas has been published. We present the
first resolved images of the disk around HD 100546 obtained in Band 7 with the
ALMA observatory. The CO (3-2) image reveals a gas disk that extends out to 350
au radius at the 3-sigma level. Surprisingly, the 870um dust continuum emission
is compact (radius <60 au) and asymmetric. The dust emission is well matched by
a truncated disk with outer radius of 50 au. The lack of
millimeter-sized particles outside the 60 au is consistent with radial drift of
particles of this size. The protoplanet candidate, identified in previous
high-contrast NACO/VLT L' observations, could be related to the sharp outer
edge of the millimeter-sized particles. Future higher angular resolution ALMA
observations are needed to determine the detailed properties of the millimeter
emission and the gas kinematics in the inner region (<2arcsec). Such
observations could also reveal the presence of a planet through the detection
of circumplanetary disk material.Comment: 6 pages, 4 figures. Accepted in ApJ
Direct imaging constraints on planet populations detected by microlensing
Results from gravitational microlensing suggested the existence of a large
population of free-floating planetary mass objects. The main conclusion from
this work was partly based on constraints from a direct imaging survey. This
survey determined upper limits for the frequency of stars that harbor giant
exoplanets at large orbital separations. Aims. We want to verify to what extent
upper limits from direct imaging do indeed constrain the microlensing results.
We examine the current derivation of the upper limits used in the microlensing
study and re-analyze the data from the corresponding imaging survey. We focus
on the mass and semi-major axis ranges that are most relevant in context of the
microlensing results. We also consider new results from a recent M-dwarf
imaging survey as these objects are typically the host stars for planets
detected by microlensing. We find that the upper limits currently applied in
context of the microlensing results are probably underestimated. This means
that a larger fraction of stars than assumed may harbor gas giant planets at
larger orbital separations. Also, the way the upper limit is currently used to
estimate the fraction of free-floating objects is not strictly correct. If the
planetary surface density of giant planets around M-dwarfs is described as
df_Planet ~ a^beta da, we find that beta ~ 0.5 - 0.6 is consistent with results
from different observational studies probing semi-major axes between ~0.03 - 30
AU. Having a higher upper limit on the fraction of stars that may have gas
giant planets at orbital separations probed by the microlensing data implies
that more of the planets detected in the microlensing study are potentially
bound to stars rather than free-floating. The current observational data are
consistent with a rising planetary surface density for giant exoplanets around
M-dwarfs out to ~30 AU.Comment: Accepted for publication in A&A as Research Note, 3 page
Dust rings and filaments around the isolated young star V1331 Cygni
We characterize the small and large scale environment of the young star V1331
Cygni with high resolution HST/WFPC2 and Digitized Sky Survey images. In
addition to a previously known outer dust ring (~30'' in diameter), the
HST/WFPC2 scattered light image reveals an inner dust ring for the first time.
This ring has a maximum radius of 6.5'' and is possibly related to a molecular
envelope. Large-scale optical images show that V1331 Cyg is located at the tip
of a long dust filament linking it to the dark cloud LDN 981. We discuss the
origin of the observed dust morphology and analyze the object's relation to its
parent dark cloud LDN 981. Finally, based on recent results from the
literature, we investigate the properties of V1331 Cyg and conclude that in its
current state the object does not show suffcient evidence to be characterized
as an FU Ori object.Comment: 15 pages ApJ preprint style including 3 figures, accepted for
publication in ApJ (Feb. 2007
A Hubble View of Star Forming Regions in the Magellanic Clouds
The Magellanic Clouds (MCs) offer an outstanding variety of young stellar
associations, in which large samples of low-mass stars (with masses less than 1
solar mass) currently in the act of formation can be resolved and explored
sufficiently with the Hubble Space Telescope. These pre-main sequence (PMS)
stars provide a unique snapshot of the star formation process, as it is being
recorded for the last 20 Myr, and they give important information on the
low-mass Initial Mass Function (IMF) of their host environments. We present the
latest results from observations with the Advanced Camera for Surveys (ACS) of
such star-forming regions in the MCs, and discuss the importance of Hubble}for
a comprehensive collection of substantial information on the most recent
low-mass star formation and the low-mass IMF in the MCs.Comment: To appear in the proceedings of the 41st ESLAB Symposium: The Impact
of HST on European Astronomy, 4 pages, LaTeX ESA Publications style, 5
Figure
Atmospheric Retrieval of L Dwarfs: Benchmarking Results and Characterizing the Young Planetary Mass Companion HD 106906 b in the Near-infrared
© 2023. The Author(s). Published by the American Astronomical Society. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY), https://creativecommons.org/licenses/by/4.0We present model constraints on the atmospheric structure of HD 106906 b, a planetary-mass companion orbiting at a ∼700 au projected separation around a 15 Myr old stellar binary, using the APOLLO retrieval code on spectral data spanning 1.1–2.5 μm. C/O ratios can provide evidence for companion formation pathways, as such pathways are ambiguous both at wide separations and at star-to-companion mass ratios in the overlap between the distributions of planets and brown dwarfs. We benchmark our code against an existing retrieval of the field L dwarf 2MASSW J2224–0158, returning a C/O ratio consistent with previous fits to the same JHK s data, but disagreeing in the thermal structure, cloud properties, and atmospheric scale height. For HD 106906 b, we retrieve C/O =0.53−0.25+0.15 , consistent with the C/O ratios expected for HD 106906's stellar association and therefore consistent with a stellar-like formation for the companion. We find abundances of H2O and CO near chemical equilibrium values for a solar metallicity but a surface gravity lower than expected, as well as a thermal profile with sharp transitions in the temperature gradient. Despite high signal-to-noise ratio and spectral resolution, more accurate constraints necessitate data across a broader wavelength range. This work serves as preparation for subsequent retrievals in the era of JWST, as JWST's spectral range provides a promising opportunity to resolve difficulties in fitting low-gravity L dwarfs and also underscores the need for simultaneous comparative retrievals on L-dwarf companions with multiple retrieval codes.Peer reviewe
V1647 Orionis: One Year into Quiescence
We present new optical, near-IR, and mid-IR observations of the young
eruptive variable star V1647 Orionis that went into outburst in late 2004 for
approximately two years. Our observations were taken one year after the star
had faded to its pre-outburst optical brightness and show that V1647Ori is
still actively accreting circumstellar material. We compare and contrast these
data with existing observations of the source from both pre-outburst and
outburst phases. From near-IR spectroscopy we identify photospheric absorption
features for the first time that allow us to constrain the classification of
the young star itself. Our best fit spectral type is M0+-2 sub-classes with a
visual extinction of 19+-2 magnitudes and a K-band veiling of rK~1.5+-0.2. We
estimate that V1647Ori has a quiescent bolometric luminosity of ~9.5Lsun and a
mass accretion rate of ~1.10^-6Msun yr^-1. Our derived mass and age, from
comparison with evolutionary models, are 0.8+-0.2 Msun and ~0.5Myrs,
respectively. The presence towards the star of shock excited optical [S II] and
[Fe II] emission as well as near-IR H2 and [Fe II] emission perhaps suggests
that a new Herbig-Haro flow is becoming visible close to the star.Comment: 22 pages, 19 Figures, accepted AJ 13 October 200
Dissecting the Moth: Discovery of an off-centered ring in the HD 61005 debris disk with high-resolution imaging
The debris disk known as "The Moth" is named after its unusually asymmetric
surface brightness distribution. It is located around the ~90 Myr old G8V star
HD 61005 at 34.5 pc and has previously been imaged by the HST at 1.1 and 0.6
microns. Polarimetric observations suggested that the circumstellar material
consists of two distinct components, a nearly edge-on disk or ring, and a
swept-back feature, the result of interaction with the interstellar medium. We
resolve both components at unprecedented resolution with VLT/NACO H-band
imaging. Using optimized angular differential imaging techniques to remove the
light of the star, we reveal the disk component as a distinct narrow ring at
inclination i=84.3 \pm 1.0{\deg}. We determine a semi-major axis of a=61.25 \pm
0.85 AU and an eccentricity of e=0.045 \pm 0.015, assuming that periastron is
located along the apparent disk major axis. Therefore, the ring center is
offset from the star by at least 2.75 \pm 0.85 AU. The offset, together with a
relatively steep inner rim, could indicate a planetary companion that perturbs
the remnant planetesimal belt. From our imaging data we set upper mass limits
for companions that exclude any object above the deuterium-burning limit for
separations down to 0.3". The ring shows a strong brightness asymmetry along
both the major and minor axis. A brighter front side could indicate
forward-scattering grains, while the brightness difference between the NE and
SW components can be only partly explained by the ring center offset,
suggesting additional density enhancements on one side of the ring. The
swept-back component appears as two streamers originating near the NE and SW
edges of the debris ring.Comment: 6 pages, 6 figures. Accepted to Astronomy and Astrophysics letter
High-resolution polarimetry of Parsamian 21: revealing the structure of an edge-on FU Ori disc
We present the first high spatial resolution near-infrared direct and
polarimetric observations of Parsamian 21, obtained with the VLT/NACO
instrument. We complemented these measurements with archival infrared
observations, such as HST/WFPC2 imaging, HST/NICMOS polarimetry, Spitzer IRAC
and MIPS photometry, Spitzer IRS spectroscopy as well as ISO photometry. Our
main conclusions are the following: (1) we argue that Parsamian 21 is probably
an FU Orionis-type object; (2) Parsamian 21 is not associated with any rich
cluster of young stars; (3) our measurements reveal a circumstellar envelope, a
polar cavity and an edge-on disc; the disc seems to be geometrically flat and
extends from approximately 48 to 360 AU from the star; (4) the SED can be
reproduced with a simple model of a circumstellar disc and an envelope; (5)
within the framework of an evolutionary sequence of FUors proposed by Green et
al. (2006) and Quanz et al. (2007), Parsamian 21 can be classified as an
intermediate-aged object.Comment: Accepted for publication in the MNRAS. 16 pages, 18 figures and 5
table
Exploring dust around HD142527 down to 0.025" / 4au using SPHERE/ZIMPOL
We have observed the protoplanetary disk of the well-known young Herbig star
HD 142527 using ZIMPOL Polarimetric Differential Imaging with the VBB (Very
Broad Band, ~600-900nm) filter. We obtained two datasets in May 2015 and March
2016. Our data allow us to explore dust scattering around the star down to a
radius of ~0.025" (~4au). The well-known outer disk is clearly detected, at
higher resolution than before, and shows previously unknown sub-structures,
including spirals going inwards into the cavity. Close to the star, dust
scattering is detected at high signal-to-noise ratio, but it is unclear whether
the signal represents the inner disk, which has been linked to the two
prominent local minima in the scattering of the outer disk, interpreted as
shadows. An interpretation of an inclined inner disk combined with a dust halo
is compatible with both our and previous observations, but other arrangements
of the dust cannot be ruled out. Dust scattering is also present within the
large gap between ~30 and ~140au. The comparison of the two datasets suggests
rapid evolution of the inner regions of the disk, potentially driven by the
interaction with the close-in M-dwarf companion, around which no polarimetric
signal is detected.Comment: 11 pages, 7 figures, accepted for publication in A
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