Context.
Directly imaged planets and substellar companions are key targets for the characterization of self-luminous atmospheres. Their photometric appearance at 4–5
μ
m is sensitive to the chemical ...composition and cloud content of their atmosphere.
Aims.
We aim to systematically characterize the atmospheres of directly imaged low-mass companions at 4–5
μ
m. We want to homogeneously process the data, provide robust flux measurements, and compile a photometric library at thermal wavelengths of these mostly young, low-gravity objects. In this way, we want to find trends related to their spectral type and surface gravity by comparing with isolated brown dwarfs and predictions from atmospheric models.
Methods.
We used the high-resolution, high-contrast capabilities of NACO at the Very Large Telescope (VLT) to directly image the companions of HIP 65426, PZ Tel, and HD 206893 in the NB4.05 and/or
M
′ filters. For the same targets, and additionally
β
Pic, we also analyzed six archival VLT/NACO datasets which were taken with the NB3.74,
L
′, NB4.05, and
M
′ filters. The data processing and photometric extraction of the companions was done with
PynPoint
while the
species
toolkit was used to further analyze and interpret the fluxes and colors.
Results.
We detect for the first time HIP 65426 b, PZ Tel B, and HD 206893 B in the NB4.05 filter, PZ Tel B and HD 206893 B in the
M
′ filter, and
β
Pic b in the NB3.74 filter. We provide calibrated magnitudes and fluxes with a careful analysis of the error budget, both for the new and archival datasets. The
L
′–NB4.05 and
L
′–
M
′ colors of the studied sample are all red while the NB4.05–
M
′ color is blue for
β
Pic b, gray for PZ Tel B, and red for HIP 65426 b and HD 206893 B (although typically with low significance). The absolute NB4.05 and
M
′ fluxes of our sample are all larger than those of field dwarfs with similar spectral types. Finally, the surface gravity of
β
Pic b has been constrained to log
g
= 4.17
−0.13
+0.10
dex from its photometry and dynamical mass.
Conclusions.
A red color at 3–4
μ
m and a blue color at 4–5
μ
m might be (partially) caused by H
2
O and CO absorption, respectively, which are expected to be the most dominant gaseous opacities in hot (
T
eff
≳ 1300 K) atmospheres. The red characteristics of
β
Pic b, HIP 65426 b, and HD 206893 B at 3–5
μ
m, as well as their higher fluxes in NB4.05 and
M
′ compared to field dwarfs, indicate that cloud densities are enhanced close to the photosphere as a result of their low surface gravity.
Context. MWC 758 is a young star surrounded by a transitional disk. The disk shows an inner cavity and spiral arms that could be caused by the presence of protoplanets. Recently, a protoplanet ...candidate has been detected around MWC 758 through high-resolution L′-band observations. The candidate is located inside the disk cavity at a separation of ~111 mas from the central star, and at an average position angle of ~165.5°. Aims. We aim at detecting accreting protoplanet candidates within the disk of MWC 758 through angular spectral differential imaging (ASDI) observations in the optical regime. In particular, we explore the emission at the position of the detected planet candidate. Methods. We have performed simultaneous adaptive optics observations in the Hα line and the adjacent continuum using SPHERE/ZIMPOL at the Very Large Telescope (VLT). Results. The data analysis does not reveal any Hα signal around the target. The derived contrast curve in the B_Ha filter allows us to derive a 5σ upper limit of ~7.6 mag at 111 mas, the separation of the previously detected planet candidate. This contrast translates into a Hα line luminosity of LHα ≲ 5×10−5 L⊙ at 111 mas. Assuming that LHα scales with Lacc as in classical T Tauri stars (CTTSs) as a first approximation, we can estimate an accretion luminosity of Lacc < 3.7 × 10−4 L⊙ for the protoplanet candidate. For the predicted mass range of MWC 758b, 0.5–5 MJup, this implies accretion rates smaller than Ṁ < 3.4 × (10−8−10−9)M⊙ yr−1, for an average planet radius of 1.1 RJup. Therefore, our estimates are consistent with the predictions of accreting circumplanetary accretion models for Rin = 1RJup. The ZIMPOL line luminosity is consistent with the Hα upper limit predicted by these models for truncation radii ≲3.2 RJup. Conclusions. The non-detection of any Hα emitting source in the ZIMPOL images does not allow us to unveil the nature of the L′ detected source. Either it is a protoplanet candidate or a disk asymmetry.
FU Orionis: The MIDI VLTI Perspective Quanz, S. P; Henning, Th; Bouwman, J ...
The Astrophysical journal,
09/2006, Letnik:
648, Številka:
1
Journal Article
Recenzirano
Odprti dostop
We present the first mid-infrared interferometric measurements of FU Orionis. We clearly resolve structures that are best explained with an optically thick accretion disk. A simple accretion disk ...model fits the observed SED and visibilities reasonably well and does not require the presence of any additional structure such as a dusty envelope. The inclination and also the position angle of the disk can be constrained from the multibaseline interferometric observations. Our disk model is in general agreement with most published near-infrared interferometric measurements. From the shape and strength of the 8-13 km spectrum, the dust composition of the accretion disk is derived for the first time. We conclude that most dust particles are amorphous and already much larger than those typically observed in the ISM. Although the high accretion rate of the system provides both high temperatures out to large radii and an effective transport mechanism to distribute crystalline grains, we do not see any evidence for crystalline silicates in either the total spectrum or the correlated flux spectra from the inner disk regions. Possible reasons for this nondetection are mentioned. All results are discussed in context with other high spatial resolution observations of FU Ori and other FU Ori objects. We also address the question whether FU Ori is in a younger evolutionary stage than a classical T Tauri star.
The system of fourplanets discovered around the intermediate-mass star HR8799 offers a unique opportunity to test planet formation theories at large orbital radii and to probe the physics and ...chemistry at play in the atmospheres of self-luminous young (~30 Myr) planets. In this paper (Paper IV), we aim to use these spectra and available photometry to determine how they compare to known objects, what the planet physical properties are, and how their atmospheres work. We compare the available spectra, photometry, and spectral energy distribution (SED) of the planets to field dwarfs and young companions. Our empirical analysis and atmospheric modelling show that an enhanced content in dust and decreased CIA of H2 is certainly responsible for the deviation of the properties of the planet with respect to field dwarfs. The analysis suggests in addition that HR8799c and b have later spectral types than the two other planets, and therefore could both have lower masses.
The circumstellar disk of PDS 70 hosts two forming planets, which are actively accreting gas from their environment. The physical and chemical characteristics of these planets remain ambiguous due to ...their unusual spectral appearance compared to more evolved objects. In this work, we report the first detection of PDS 70 b in the Br
α
and
M
′ filters with VLT/NACO, a tentative detection of PDS 70 c in Br
α
, and a reanalysis of archival NACO
L
′ and SPHERE
H
23 and
K
12 imaging data. The near side of the disk is also resolved with the Br
α
and
M
′ filters, indicating that scattered light is non-negligible at these wavelengths. The spectral energy distribution (SED) of PDS 70 b is well described by blackbody emission, for which we constrain the photospheric temperature and photospheric radius to
T
eff
= 1193 ± 20 K and
R
= 3.0 ± 0.2
R
J
. The relatively low bolometric luminosity, log(
L
∕
L
⊙
) = −3.79 ± 0.02, in combination with the large radius, is not compatible with standard structure models of fully convective objects. With predictions from such models, and adopting a recent estimate of the accretion rate, we derive a planetary mass and radius in the range of
M
p
≈ 0.5–1.5
M
J
and
R
p
≈ 1–2.5
R
J
, independently of the age and post-formation entropy of the planet. The blackbody emission, large photospheric radius, and the discrepancy between the photospheric and planetary radius suggests that infrared observations probe an extended, dusty environment around the planet, which obscures the view on its molecular composition. Therefore, the SED is expected to trace the reprocessed radiation from the interior of the planet and/or partially from the accretion shock. The photospheric radius lies deep within the Hill sphere of the planet, which implies that PDS 70 b not only accretes gas but is also continuously replenished by dust. Finally, we derive a rough upper limit on the temperature and radius of potential excess emission from a circumplanetary disk,
T
eff
≲ 256 K and
R
≲ 245
R
J
, but we do find weak evidence that the current data favors a model with a single blackbody component.
Context.
The Medium Resolution Spectrometer (MRS) of the Mid-Infrared Instrument (MIRI) on board the
James Webb
Space Telescope (JWST) will give access to mid-infrared (mid-IR) spectra (5–28 microns) ...while retaining spatial information. With the unparalleled sensitivity of JWST and the MIRI detectors, the MRS has the potential to revolutionise our understanding of giant exoplanet atmospheres.
Aims.
Molecular mapping is a promising detection and characterisation technique used to study the spectra of directly imaged exoplanets. We aim to examine the feasibility and application of this technique to MRS observations.
Methods.
We used the instrument simulator
MIRISIM
to create mock observations of resolved star and exoplanet systems. As an input for the simulator, we used stellar and planet parameters from literature, with the planet spectrum being modelled with the radiative transfer code
petitRADTRANS
. After processing the raw data with the JWST pipeline, we high pass filter the data to account for the stellar point spread function, and used a forward modelling approach to detect the companions and constrain the chemical composition of their atmospheres through their molecular signatures.
Results.
We identified limiting factors in spectroscopic characterisation of directly imaged exoplanets with the MRS and simulated observations of two representative systems, HR8799 and GJ504. In both systems, we could detect the presence of multiple molecules that were present in the input model of their atmospheres. We used two different approaches with single molecule forward models, used in literature, that are sensitive to detecting mainly H2O, CO, CH4, and NH3, and a log-likelihood ratio test that uses full atmosphere forward models and is sensitive to a larger number of less dominant molecular species.
Conclusions.
We show that the MIRI MRS can be used to characterise widely separated giant exoplanets in the mid-IR using molecular mapping. Such observations would provide invaluable information for the chemical composition of the atmosphere, complementing other JWST observing modes, as well as ground-based observations.
Accurate measurements of the physical structure of protoplanetary discs are critical inputs for planet formation models. These constraints are traditionally established via complex modelling of ...continuum and line observations. Instead, we present an empirical framework to locate the CO isotopologue emitting surfaces from high spectral and spatial resolution ALMA observations. We apply this framework to the disc surrounding IM Lupi, where we report the first direct, i.e. model independent, measurements of the radial and vertical gradients of temperature and velocity in a protoplanetary disc. The measured disc structure is consistent with an irradiated self-similar disc structure, where the temperature increases and the velocity decreases towards the disc surface. We also directly map the vertical CO snow line, which is located at about one gas scale height at radii between 150 and 300 au, with a CO freeze-out temperature of 21 ± 2 K. In the outer disc (>300 au), where the gas surface density transitions from a power law to an exponential taper, the velocity rotation field becomes significantly sub-Keplerian, in agreement with the expected steeper pressure gradient. The sub-Keplerian velocities should result in a very efficient inward migration of large dust grains, explaining the lack of millimetre continuum emission outside of 300 au. The sub-Keplerian motions may also be the signature of the base of an externally irradiated photo-evaporative wind. In the same outer region, the measured CO temperature above the snow line decreases to ≈15 K because of the reduced gas density, which can result in a lower CO freeze-out temperature, photo-desorption, or deviations from local thermodynamic equilibrium.
Context. R Aqr is a symbiotic binary system consisting of a mira variable, a hot companion with a spectacular jet outflow, and an extended emission line nebula. Because of its proximity to the Sun, ...this object has been studied in much detail with many types of high resolution imaging and interferometric techniques. We have used R Aqr as test target for the visual camera subsystem ZIMPOL, which is part of the new extreme adaptive optics (AO) instrument SPHERE at the Very Large Telescope (VLT). Aims. We describe SPHERE/ZIMPOL test observations of the R Aqr system taken in Hα and other filters in order to demonstrate the exceptional performance of this high resolution instrument. We compare our observations with data from the Hubble Space Telescope (HST) and illustrate the complementarity of the two instruments. We use our data for a detailed characterization of the inner jet region of R Aqr. Methods. We analyze the high resolution ≈ 25 mas images from SPHERE/ZIMPOL and determine from the Hα emission the position, size, geometric structure, and line fluxes of the jet source and the clouds in the innermost region <2′′ (<400 AU) of R Aqr. The data are compared to simultaneous HST line filter observations. The Hα fluxes and the measured sizes of the clouds yield Hα emissivities for many clouds from which one can derive the mean density, mass, recombination time scale, and other cloud parameters. Results. Our Hα data resolve for the first time the R Aqr binary and we measure for the jet source a relative position 45 mas West (position angle −89.5°) of the mira. The central jet source is the strongest Hα component with a flux of about 2.5 × 10-12 erg cm-2 s-1. North east and south west from the central source there are many clouds with very diverse structures. Within 0.5′′ (100 AU) we see in the SW a string of bright clouds arranged in a zig-zag pattern and, further out, at 1′′−2′′, fainter and more extended bubbles. In the N and NE we see a bright, very elongated filamentary structure between 0.2′′−0.7′′ and faint perpendicular “wisps” further out. Some jet clouds are also detected in the ZIMPOL O I and He I filters, as well as in the HST-WFC3 line filters for Hα, O III, N II, and O I. We determine jet cloud parameters and find a very well defined correlation Ne ∝ r-1.3 between cloud density and distance to the central binary. Densities are very high with typical values of Ne ≈ 3 × 105 cm-3 for the “outer” clouds around 300 AU, Ne ≈ 3 × 106 cm-3 for the “inner” clouds around 50 AU, and even higher for the central jet source. The high Ne of the clouds implies short recombination or variability timescales of a year or shorter. Conclusions. Hα high resolution data provide a lot of diagnostic information for the ionized jet gas in R Aqr. Future Hα observations will provide the orientation of the orbital plane of the binary and allow detailed hydrodynamical investigations of this jet outflow and its interaction with the wind of the red giant companion.
Context. Debris disks or belts are important signposts for the presence of colliding planetesimals and, therefore, for ongoing planet formation and evolution processes in young planetary systems. ...Imaging of debris material at small separations from the star is very challenging but provides valuable insights into the spatial distribution of the so-called hot dust produced by solid bodies located in or near the habitable zone. We report the first detection of scattered light from the hot dust around the nearby (d = 28.33 pc) A star HD 172555. Aims. We want to constrain the geometric structure of the detected debris disk using polarimetric differential imaging (PDI) with a spatial resolution of 25 mas and an inner working angle of about 0.1″. Methods. We measured the polarized light of HD 172555, with SPHERE/ZIMPOL, in the very broadband (VBB) or RI filter (λc = 735 nm, Δλ = 290 nm) for the projected separations between 0.08″ (2.3 au) and 0.77″ (22 au). We constrained the disk parameters by fitting models for scattering of an optically thin dust disk taking the limited spatial resolution and coronagraphic attenuation of our data into account. Results. The geometric structure of the disk in polarized light shows roughly the same orientation and outer extent as obtained from thermal emission at 18 μm. Our image indicates the presence of a strongly inclined (i ≈ 103.5°), roughly axisymmetric dust belt with an outer radius in the range between 0.3″ (8.5 au) and 0.4″ (11.3 au). An inner disk edge is not detected in the data. We derive a lower limit for the polarized flux contrast ratio for the disk of (Fpol)disk/F∗ > (6.2 ± 0.6) × 10−5 $(F_{\rm{pol}})_{\rm{disk}}/F_{\ast}> (6.2 \pm 0.6)\times 10^{-5}$(Fpol)disk/F∗>(6.2±0.6)×10−5 in the VBB filter. This ratio is small, only ~9%, when compared to the fractional infrared flux excess (≈ 7.2 × 10−4). The model simulations show that more polarized light could be produced by the dust located inside ≈2 au, which cannot be detected with the instrument configuration used. Conclusions. Our data confirm previous infrared imaging and provide a higher resolution map of the system, which could be further improved with future observations.
Aims. We investigate the nature of the innermost regions with radii of several AUs of seven circumstellar disks around pre-main-sequence stars, T Tauri stars in particular. Our object sample contains ...disks apparently at various stages of their evolution. Both single stars and spatially resolved binaries are considered. In particular, we search for inner disk gaps as proposed for several young stellar objects (YSOs). When analyzing the underlying dust population in the atmosphere of circumstellar disks, the shape of the 10 μm feature should additionally be investigated. Methods. We performed interferometric observations in N band (8-13 μm) with the Mid-Infrared Interferometric Instrument (MIDI) at the Very Large Telescope Interferometer (VLTI) using baseline lengths of between 54 m and 127 m. The data analysis is based on radiative-transfer simulations using the Monte Carlo code MC3D by modeling simultaneously the spectral energy distribution (SED), N band spectra, and interferometric visibilities. Correlated and uncorrelated N band spectra are compared to investigate the radial distribution of the dust composition of the disk atmosphere. Results. Spatially resolved mid-infrared (MIR) emission was detected in all objects. For four objects (DR Tau, RU Lup, S CrA N, and S CrA S), the observed N band visibilities and corresponding SEDs could be simultaneously simulated using a parameterized active disk-model. For the more evolved objects of our sample, HD 72106 and HBC 639, a purely passive disk-model provides the closest fit. The visibilities inferred for the source RU Lup allow the presence of an inner disk gap. For the YSO GW Ori, one of two visibility measurements could not be simulated by our modeling approach. All uncorrelated spectra reveal the 10 μm silicate emission feature. In contrast to this, some correlated spectra of the observations of the more evolved objects do not show this feature, indicating a lack of small silicates in the inner versus the outer regions of these disks. We conclude from this observational result that more evolved dust grains can be found in the more central disk regions.
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