298 research outputs found
The Herschel view of GAS in Protoplanetary Systems (GASPS): First comparisons with a large grid of models
The Herschel GASPS key program is a survey of the gas phase of protoplanetary discs, targeting 240 objects which cover a large range of ages, spectral types, and disc properties. To interpret this large quantity of data and initiate self-consistent analyses of the gas and dust properties of protoplanetary discs, we have combined the capabilities of the radiative transfer code MCFOST with the gas thermal balance and chemistry code ProDiMo to compute a grid of ≈300 000 disc models (DENT). We present a comparison of the first Herschel/GASPS line and continuum data with the predictions from the DENT grid of models. Our objective is to test some of the main trends already identified in the DENT grid, as well as to define better empirical diagnostics to estimate the total gas mass of protoplanetary discs. Photospheric UV radiation appears to be the dominant gas-heating mechanism for Herbig stars, whereas UV excess and/or X-rays emission dominates for T Tauri stars. The DENT grid reveals the complexity in the analysis of far-IR lines and the difficulty to invert these observations into physical quantities. The combination of Herschel line observations with continuum data and/or with rotational lines in the (sub-)millimetre regime, in particular CO lines, is required for a detailed characterisation of the physical and chemical properties of circumstellar discs
Evidence for a circumplanetary disk around protoplanet PDS 70 b
We present the first observational evidence for a circumplanetary disk around
the protoplanet PDS~70~b, based on a new spectrum in the band acquired with
VLT/SINFONI. We tested three hypotheses to explain the spectrum: Atmospheric
emission from the planet with either (1) a single value of extinction or (2)
variable extinction, and (3) a combined atmospheric and circumplanetary disk
model. Goodness-of-fit indicators favour the third option, suggesting
circumplanetary material contributing excess thermal emission --- most
prominent at m. Inferred accretion rates (-- yr) are compatible with observational
constraints based on the H and Br lines. For the planet, we
derive an effective temperature of 1500--1600 K, surface gravity , radius , mass , and possible thick clouds.
Models with variable extinction lead to slightly worse fits. However, the
amplitude (mag) and timescale of variation
(~years) required for the extinction would also suggest
circumplanetary material.Comment: 8 pages, 2 figures, 1 table. This is a pre-copyedited,
author-produced PDF of an article accepted for publication in ApJL on 2019
May 1
A library of near-infrared integral field spectra of young M-L dwarfs
We present a library of near-infrared (1.1-2.45 microns) medium-resolution
(R~1500-2000) integral field spectra of 15 young M6-L0 dwarfs, composed of
companions with known ages and of isolated objects. We use it to (re)derive the
NIR spectral types, luminosities and physical parameters of the targets, and to
test (BT-SETTL, DRIFT-PHOENIX) atmospheric models. We derive infrared spectral
types L0+-1, L0+-1, M9.5+-0.5, M9.5+-0.5, M9.25+-0.25, M8+0.5-0.75, and
M8.5+-0.5 for AB Pic b, Cha J110913-773444, USco CTIO 108B, GSC 08047-00232 B,
DH Tau B, CT Cha b, and HR7329B, respectively. BT-SETTL and DRIFT-PHOENIX
models yield close Teff and log g estimates for each sources. The models seem
to evidence a 600-300+600 K drop of the effective temperature at the M-L
transition. Assuming the former temperatures are correct, we derive new mass
estimates which confirm that DH Tau B, USco CTIO 108B, AB Pic b, KPNO Tau 4,
OTS 44, and Cha1109 lay inside or at the boundary of the planetary mass range.
We combine the empirical luminosities of the M9.5-L0 sources to the Teff to
derive semi-empirical radii estimates that do not match "hot-start"
evolutionary models predictions at 1-3 Myr. We use complementary data to
demonstrate that atmospheric models are able to reproduce the combined optical
and infrared spectral energy distribution, together with the near-infrared
spectra of these sources simultaneously. But the models still fail to represent
the dominant features in the optical. This issue casts doubts on the ability of
these models to predict correct effective temperatures from near-infrared
spectra alone. We advocate the use of photometric and spectroscopic data
covering a broad range of wavelengths to study the properties of very low mass
young companions to be detected with the planet imagers (Subaru/SCExAO,
LBT/LMIRCam, Gemini/GPI, VLT/SPHERE).Comment: 27 pages, 14 tables, 19 figures, accepted for publication in
Astronomy & Astrophysic
The large-scale disk fraction of brown dwarfs in the Taurus cloud as measured with Spitzer
Aims. The brown dwarf (BD) formation process has not yet been completely
understood. To shed more light on the differences and similarities between star
and BD formation processes, we study and compare the disk fraction among both
kinds of objects over a large angular region in the Taurus cloud. In addition,
we examine the spatial distribution of stars and BD relative to the underlying
molecular gas Methods. In this paper, we present new and updated photometry
data from the Infrared Array Camera (IRAC) aboard the Spitzer Space Telescope
on 43 BDs in the Taurus cloud, and recalculate of the BD disk fraction in this
region. We also useed recently available CO mm data to study the spatial
distribution of stars and BDs relative to the cloud's molecular gas. Results.
We find that the disk fraction among BDs in the Taurus cloud is 41 \pm 12%, a
value statistically consistent with the one among TTS (58 \pm 9%). We find that
BDs in transition from a state where they have a disk to a diskless state are
rare, and we study one isolated example of a transitional disk with an inner
radius of \approx 0.1 AU (CFHT BD Tau 12, found via its relatively small mid-IR
excess compared to most members of Taurus that have disks. We find that BDs are
statistically found in regions of similar molecular gas surface density to
those associated with stars. Furthermore, we find that the gas column density
distribution is almost identical for stellar and substellar objects with and
without disks.Comment: 8 page, 6 figures, Accepted in Astronomy & Astrophysics
HST Scattered Light Imaging and Modeling of the Edge-on Protoplanetary Disk ESO-H 569
We present new HST ACS observations and detailed models for a recently
discovered edge-on protoplanetary disk around ESO H 569 (a low-mass T
Tauri star in the Cha I star forming region). Using radiative transfer models
we probe the distribution of the grains and overall shape of the disk
(inclination, scale height, dust mass, flaring exponent and surface/volume
density exponent) by model fitting to multiwavelength (F606W and F814W) HST
observations together with a literature compiled spectral energy distribution.
A new tool set was developed for finding optimal fits of MCFOST radiative
transfer models using the MCMC code emcee to efficiently explore the high
dimensional parameter space. It is able to self-consistently and simultaneously
fit a wide variety of observables in order to place constraints on the physical
properties of a given disk, while also rigorously assessing the uncertainties
in those derived properties. We confirm that ESO H 569 is an optically
thick nearly edge-on protoplanetary disk. The shape of the disk is well
described by a flared disk model with an exponentially tapered outer edge,
consistent with models previously advocated on theoretical grounds and
supported by millimeter interferometry. The scattered light images and spectral
energy distribution are best fit by an unusually high total disk mass (gas+dust
assuming a ratio of 100:1) with a disk-to-star mass ratio of 0.16.Comment: Accepted for publication in Ap
Long-lived Dust Rings around HD 169142
Recent Atacama Large Millimeter/submillimeter Array (ALMA) observations of the protoplanetary disk around HD 169142 reveal a peculiar structure made of concentric dusty rings: a main ring at similar to 20 au, a triple system of rings at similar to 55-75 au in millimetric continuum emission, and a perturbed gas surface density from the (CO)-C-12,(CO)-C-13, and (CO)-O-18 (J = 2-1) surface brightness profile. In this Letter, we perform 3D numerical simulations and radiative transfer modeling exploring the possibility that two giant planets interacting with the disk and orbiting in resonant locking can be responsible for the origin of the observed dust inner rings structure. We find that in this configuration the dust structure is actually long lived while the gas mass of the disk is accreted onto the star and the giant planets, emptying the inner region. In addition, we also find that the innermost planet is located at the inner edge of the dust ring, and can accrete mass from the disk, generating a signature in the dust ring shape that can be observed in mm ALMA observations
Gas and dust in the Beta Pictoris Moving Group as seen by the Herschel Space Observatory
Context. Debris discs are thought to be formed through the collisional
grinding of planetesimals, and can be considered as the outcome of planet
formation. Understanding the properties of gas and dust in debris discs can
help us to comprehend the architecture of extrasolar planetary systems.
Herschel Space Observatory far-infrared (IR) photometry and spectroscopy have
provided a valuable dataset for the study of debris discs gas and dust
composition. This paper is part of a series of papers devoted to the study of
Herschel PACS observations of young stellar associations.
Aims. This work aims at studying the properties of discs in the Beta Pictoris
Moving Group (BPMG) through far-IR PACS observations of dust and gas.
Methods. We obtained Herschel-PACS far-IR photometric observations at 70, 100
and 160 microns of 19 BPMG members, together with spectroscopic observations of
four of them. Spectroscopic observations were centred at 63.18 microns and 157
microns, aiming to detect [OI] and [CII] emission. We incorporated the new
far-IR observations in the SED of BPMG members and fitted modified blackbody
models to better characterise the dust content.
Results. We have detected far-IR excess emission toward nine BPMG members,
including the first detection of an IR excess toward HD 29391.The star HD
172555, shows [OI] emission, while HD 181296, shows [CII] emission, expanding
the short list of debris discs with a gas detection. No debris disc in BPMG is
detected in both [OI] and [CII]. The discs show dust temperatures in the range
55 to 264 K, with low dust masses (6.6*10^{-5} MEarth to 0.2 MEarth) and radii
from blackbody models in the range 3 to 82 AU. All the objects with a gas
detection are early spectral type stars with a hot dust component.Comment: 12 pages, 7 figures, 6 table
Panchromatic observations and modeling of the HV Tau C edge-on disk
We present new high spatial resolution (<~ 0.1") 1-5 micron adaptive optics
images, interferometric 1.3 mm continuum and 12CO 2-1 maps, and 350 micron, 2.8
and 3.3 mm fluxes measurements of the HV Tau system. Our adaptive optics images
reveal an unusually slow orbital motion within the tight HV Tau AB pair that
suggests a highly eccentric orbit and/or a large deprojected physical
separation. Scattered light images of the HV Tau C edge-on protoplanetary disk
suggest that the anisotropy of the dust scattering phase function is almost
independent of wavelength from 0.8 to 5 micron, whereas the dust opacity
decreases significantly over the same range. The images further reveal a marked
lateral asymmetry in the disk that does not vary over a timescale of 2 years.
We further detect a radial velocity gradient in the disk in our 12CO map that
lies along the same position angle as the elongation of the continuum emission,
which is consistent with Keplerian rotation around an 0.5-1 Msun central star,
suggesting that it could be the most massive component in the triple system. We
use a powerful radiative transfer model to compute synthetic disk observations
and use a Bayesian inference method to extract constraints on the disk
properties. Each individual image, as well as the spectral energy distribution,
of HV Tau C can be well reproduced by our models with fully mixed dust provided
grain growth has already produced larger-than-interstellar dust grains.
However, no single model can satisfactorily simultaneously account for all
observations. We suggest that future attempts to model this source include more
complex dust properties and possibly vertical stratification. (Abridged)Comment: 26 pages, 11 figures, editorially accepted for publication in Ap
Multiwavelength studies of the gas and dust disc of IRAS 04158+2805
We present a study of the circumstellar environment of IRAS 04158+2805 based
on multi-wavelength observations and models. Images in the optical and
near-infrared, a polarisation map in the optical, and mid-infrared spectra were
obtained with VLT-FORS1, CFHT-IR, and Spitzer-IRS. Additionally we used an
X-ray spectrum observed with Chandra. We interpret the observations in terms of
a central star surrounded by an axisymmetric circumstellar disc, but without an
envelope, to test the validity of this simple geometry. We estimate the
structural properties of the disc and its gas and dust content. We modelled the
dust disc with a 3D continuum radiative transfer code, MCFOST, based on a
Monte-Carlo method that provides synthetic scattered light images and
polarisation maps, as well as spectral energy distributions. We find that the
disc images and spectral energy distribution narrowly constrain many of the
disc model parameters, such as a total dust mass of 1.0-1.75x10^-4 sollar
masses and an inclination of 62-63 degrees. The maximum grain size required to
fit all available data is of the order of 1.6-2.8 microns although the upper
end of this range is loosely constrained. The observed optical polarisation map
is reproduced well by the same disc model, suggesting that the geometry we find
is adequate and the optical properties are representative of the visible dust
content. We compare the inferred dust column density to the gas column density
derived from the X-ray spectrum and find a gas-to-dust ratio along the line of
sight that is consistent with the ISM value. To our knowledge, this measurement
is the first to directly compare dust and gas column densities in a
protoplanetary disc.Comment: 8 figures, 11 pages, accepted by A&
JWST imaging of edge-on protoplanetary disks. I. Fully vertically mixed 10m grains in the outer regions of a 1000 au disk
Scattered light imaging of protoplanetary disks provides key insights on the
geometry and dust properties in the disk surface. Here we present JWST
2--21\,m images of a 1000\,au-radius edge-on protoplanetary disk
surrounding an 0.4\, young star in Taurus, 2MASS\,J04202144+2813491.
These observations represent the longest wavelengths at which a protoplanetary
disk is spatially resolved in scattered light. We combine these observations
with HST optical images and ALMA continuum and CO mapping. We find that the
changes in the scattered light disk morphology are remarkably small across a
factor of 30 in wavelength, indicating that dust in the disk surface layers is
characterized by an almost gray opacity law. Using radiative transfer models,
we conclude that grains up to m in size are fully coupled to
the gas in this system, whereas grains m are strongly settled
towards the midplane. Further analyses of these observations, and similar ones
of other edge-on disks, will provide strong empirical constraints on disk
dynamics and evolution and grain growth models. In addition, the 7.7 and
12.\,m JWST images reveal an X-shaped feature located above the warm
molecular layer traced by CO line emission. The highest elevations at which
this feature is detectable roughly match the maximal extent of the disk in
visible wavelength scattered light as well as of an unusual kinematic signature
in CO. We propose that these phenomena could be related to a disk wind
entraining small dust grains.Comment: Accepted for publication in the Astronomical Journa
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