We present the first VLTI/MIDI observations of the Be star alpha Ara (HD 158 427), showing a nearly unresolved circumstellar disk in the N band. The interferometric measurements made use of the UT1 ...and UT3 telescopes. The projected baselines were 102 and 74 meters with position angles of 7° and 55°, respectively. These measurements put an upper limit on the envelope size in the N band under the uniform disk approximation of $\phi_{\rm max}= 4\pm1.5$ mas, corresponding to 14 $R_{\star}$, assuming $R_{\star}=4.8~R_\odot$ and the Hipparcos distance of 74 pc. On the other hand the disk density must be large enough to produce the observed strong Balmer line emission. In order to estimate the possible circumstellar and stellar parameters we have used the SIMECA code developed by Stee et al. (1995, A&A, 300, 219) and Stee & Bittar (2001, A&A, 367, 532). Optical spectra taken with the échelle instrument Heros and the ESO-50 cm telescope, as well as infrared ones from the 1.6m Brazilian telescope were used together with the MIDI spectra and visibilities. These observations place complementary constraints on the density and geometry of the alpha Ara circumstellar disk. We discuss the potential truncation of the disk by a companion and we present spectroscopic indications of a periodic perturbation of some Balmer lines.
Aims.
We studied the accretion disk of the archetypal eruptive young star FU Orionis with the use of mid-infrared interferometry, which enabled us to resolve the innermost regions of the disk down to ...a spatial resolution of 3 milliarcseconds (mas) in the
L
band, that is, within 1 au of the protostar.
Methods.
We used the interferometric instrument MATISSE/VLTI to obtain observations of FU Ori’s disk in the
L
,
M
, and
N
bands with multiple baseline configurations. We also obtained contemporaneous photometry in the optical
(UBVRIr
′
i
′
;
SAAO and Konkoly Observatory) and near-infrared
(JHK
s
;
NOT). Our results were compared with radiative transfer simulations modeled by
RADMC
-3
D
.
Results.
The disk of FU Orionis is marginally resolved with MATISSE, suggesting that the region emitting in the thermal infrared is rather compact. An upper limit of ~1.3 ± 0.1 mas (in
L
) can be given for the diameter of the disk region probed in the
L
band, corresponding to 0.5 au at the adopted
Gaia
EDR3 distance. This represents the hot, gaseous region of the accretion disk. The
N
-band data indicate that the dusty passive disk is silicate-rich. Only the innermost region of said dusty disk is found to emit strongly in the
N
band, and it is resolved at an angular size of ~5 mas, which translates to a diameter of about 2 au. The observations therefore place stringent constraints for the outer radius of the inner accretion disk. Dust radiative transfer simulations with
RADMC
-3
D
provide adequate fits to the spectral energy distribution from the optical to the submillimeter and to the interferometric observables when opting for an accretion rate
M ~
2 × 10
−5
M
⊙
yr
−1
and assuming
M
*
= 0.6
M
⊙
, Most importantly, the hot inner accretion disk’s outer radius can be fixed at 0.3 au. The outer radius of the dusty disk is placed at 100 au, based on constraints from scattered-light images in the literature. The dust mass contained in the disk is 2.4 × 10
−4
M
⊙
, and for a typical gas-to-dust ratio of 100, the total mass in the disk is approximately 0.02
M
⊙
. We did not find any evidence for a nearby companion in the current interferometric data, and we tentatively explored the case of disk misalignment. For the latter, our modeling results suggest that the disk orientation is similar to that found in previous imaging studies by ALMA. Should there be an asymmetry in the very compact, inner accretion disk, this might be resolved at even smaller spatial scales (≤1 mas).
Context. VX Sgr is a cool, evolved, and luminous red star whose stellar parameters are difficult to determine, which affects its classification.
Aims. We aim to spatially resolve the photospheric ...extent as well as the circumstellar environment.
Methods. We used interferometric observations obtained with the MATISSE instrument in the L (3-4 mu m), M (4.5-5 mu m), and N (8-13 mu m) bands. We reconstructed monochromatic images using the MIRA software. We used 3D radiation-hydrodynamics simulations carried out with (COBOLD)-B-5 and a uniform disc model to estimate the apparent diameter and interpret the stellar surface structures. Moreover, we employed the radiative transfer codes OPTIM3D and RADMC3D to compute the spectral energy distribution for the L, M, and N bands, respectively.
Results. MATISSE observations unveil, for the first time, the morphology of VX Sgr across the L, M, and N bands. The reconstructed images show a complex morphology with brighter areas whose characteristics depend on the wavelength probed. We measured the angular diameter as a function of the wavelength and showed that the photospheric extent in the L and M bands depends on the opacity through the atmosphere. In addition to this, we also concluded that the observed photospheric inhomogeneities can be interpreted as convection-related surface structures. The comparison in the N band yielded a qualitative agreement between the N-band spectrum and simple dust radiative transfer simulations. However, it is not possible to firmly conclude on the interpretation of the current data because of the difficulty in constraing the model parameters using the limited accuracy of our absolute flux calibration.
Conclusions. MATISSE observations and the derived reconstructed images unveil the appearance of VX Sgr's stellar surface and circumstellar environment across a very large spectral domain for the first time.
Context.
Carbon is one of the most abundant components in the Universe. While silicates have been the main focus of solid phase studies in protoplanetary discs (PPDs), little is known about the solid ...carbon content especially in the planet-forming regions (~0.1–10 au). Fortunately, several refractory carbonaceous species present C-H bonds (such as hydrogenated nano-diamond and amorphous carbon as well as polycyclic aromatic hydrocarbons), which generate infrared (IR) features that can be used to trace the solid carbon reservoirs. The new mid-IR instrument MATISSE, installed at the Very Large Telescope Interferometer (VLTI), can spatially resolve the inner regions (~1–10 au) of PPDs and locate, down to the au-scale, the emission coming from carbon grains.
Aims.
Our aim is to provide a consistent view on the radial structure, down to the au-scale, as well as basic physical properties and the nature of the material responsible for the IR continuum emission in the inner disk region around HD 179218.
Methods.
We implemented a temperature-gradient model to interpret the disk IR continuum emission, based on a multiwavelength dataset comprising a broadband spectral energy distribution and VLTI
H
-,
L
-, and
N
-bands interferometric data obtained in low spectral resolution. Then, we added a ring-like component, representing the carbonaceous
L
-band features-emitting region, to assess its detectability in future higher spectral resolution observations employing mid-IR interferometry.
Results.
Our temperature-gradient model can consistently reproduce our dataset. We confirmed a spatially extended inner 10 au emission in
H
- and
L
-bands, with a homogeneously high temperature (~1700 K), which we associate with the presence of stochastically heated nano-grains. On the other hand, the
N
-band emitting region presents a ring-like geometry that starts at about 10 au with a temperature of 400 K. Moreover, the existing low resolution MATISSE data exclude the presence of aromatic carbon grains (i.e., producing the 3.3 μm feature) in close proximity tothe star (≲1 au). Future medium spectral resolution MATISSE data will confirm their presence at larger distances.
Conclusions.
Our best-fit model demonstrates the presence of two separated dust populations: nano-grains that dominate the near- to mid-IR emission in the inner 10 au region and larger grains that dominate the emission outward. The presence of such nano-grains in the highly irradiated inner 10 au region of HD 179218 requires a replenishment process. Considering the expected lifetime of carbon nano-grains from The Heterogeneous dust Evolution Model for Interstellar Solids (THEMIS model), the estimated disk accretion inflow of HD 179218 could significantly contribute to feed the inner 10 au region in nano-grains.Moreover, we also expect a local regeneration of those nano-grains by the photo-fragmentation of larger aggregates.
Context.
Eta Carinae is a highly eccentric, massive binary system (semimajor axis ~15.5 au) with powerful stellar winds and a phase-dependent wind-wind collision (WWC) zone. The primary star,
η
Car ...A, is a luminous blue variable (LBV); the secondary,
η
Car B, is a Wolf-Rayet or O star with a faster but less dense wind. Aperture-synthesis imaging allows us to study the mass loss from the enigmatic LBV
η
Car. Understanding LBVs is a crucial step toward improving our knowledge about massive stars and their evolution.
Aims.
Our aim is to study the intensity distribution and kinematics of
η
Car’s WWC zone.
Methods.
Using the VLTI-MATISSE mid-infrared interferometry instrument, we perform Br
α
imaging of
η
Car’s distorted wind.
Results.
We present the first VLTI-MATISSE aperture-synthesis images of
η
Car A’s stellar windin several spectral channels distributed across the Br
α
4.052 μm line (spectral resolving power
R
~ 960). Our observations were performed close to periastron passage in February 2020 (orbital phase ~ 14.0022). The reconstructed iso-velocity images show the dependence of the primary stellar wind on wavelength or line-of-sight (LOS) velocity with a spatial resolution of 6 mas (~14 au). The radius of the faintest outer wind regions is ~26 mas (~60 au). At several negative LOS velocities, the primary stellar wind is less extended to the northwest than in other directions. This asymmetry is most likely caused by the WWC. Therefore, we see both the velocity field of the undisturbed primary wind and the WWC cavity. In continuum spectral channels, the primary star wind is more compact than in line channels. A fit of the observed continuum visibilities with the visibilities of a stellar wind CMFGEN model (CMFGEN is an atmosphere code developed to model the spectra of a variety of objects) provides a full width at half maximum fit diameter of the primary stellar wind of 2.84 ± 0.06 mas (6.54 ± 0.14 au). We comparethe derived intensity distributions with the CMFGEN stellar wind model and hydrodynamic WWC models.
ABSTRACT
From Nov. 2019 to May 2020, the red supergiant star Betelgeuse experienced an unprecedented drop of brightness in the visible domain called the Great Dimming event (GDE). Large atmospheric ...dust clouds and large photospheric convective features are suspected to be responsible for it. To better understand the dimming event, we used mid-infrared long-baseline spectro-interferometric measurements of Betelgeuse taken with the Very Large Telescope Interferometer/Multi AperTure mid-Infrared SpectroScopic Experiment (VLTI/MATISSE) instrument before (Dec. 2018), during (Feb. 2020), and after (Dec. 2020) the GDE. We present data in the 3.98–4.15 µm range to cover SiO spectral features molecules as well as adjacent continuum. We have employed geometrical models, image reconstruction, as well as radiative transfer models to monitor the spatial distribution of SiO over the stellar surface. We find a strongly inhomogeneous spatial distribution of SiO that appears to be looking very different between our observing epochs, indicative of a vigorous activity in the stellar atmosphere. The contrast of our images is small in the pseudo-continuum for all epochs, implying that our MATISSE observations support both cold spot and dust cloud model.
SPHERE (which stands for Spectro-Polarimetric High-contrast Exoplanet REsearch) is a second-generation Very Large Telescope (VLT) instrument dedicated to high-contrast direct imaging of exoplanets ...whose first-light is scheduled for 2011. Within this complex instrument one of the central components is the apodized Lyot coronagraph (ALC). The principal aim of this paper is to report the first laboratory experiment of the ALC designed for the SPHERE instrument. The performance and sensitivity of the optical configuration was first numerically studied with an end-to-end approach (see the results in paper I subtitled “Detailed numerical study”). Made confident by the results, we then tested a prototype on an infrared coronagraphic bench. We measured the transmission profiles of the apodizer prototype and the coronagraphic performance of the apodized Lyot coronagraph in Y, J, and H bands. The coronagraph sensitivity to lateral and longitudinal misalignments of its three main components (apodizer, coronagraphic mask and Lyot stop) was finally studied in H band. We can conclude that the prototype meets the SPHERE technical requirements for coronagraphy.
Context.
Asymptotic giant branch (AGB) stars are one of the main sources of dust production in the Galaxy. However, it is not yet clear what this process looks like and where the dust happens to be ...condensing in the circumstellar environment.
Aims.
By characterizing the location of the dust and the molecules in the close environment of an AGB star, we aim to achieve a better understanding the history of the dust formation process.
Methods.
We observed the carbon star R Scl with the thermal-infrared VLTI/MATISSE instrument in
L
- and
N
-bands. The high angular resolution of the VLTI observations (as small as 4.4 mas in the
L
-band and 15 mas in the
N
-band with ATs), combined with a large
uv
-plane coverage allowed us to use image reconstruction methods. To constrain the dust and molecules’ location, we used two different methods: one using MIRA image reconstruction algorithm and the second using the 1D code RHAPSODY.
Results.
We found evidence of C
2
H
2
and HCN molecules between 1 and 3.4
R
*
which is much closer to the star than the location of the dust (between 3.8 and 17.0
R
*
). We also estimated a mass-loss rate of 1.2 ± 0.4 × 10
−6
M
⊙
yr
−1
. In the meantime, we confirmed the previously published characteristics of a thin dust shell, composed of amorphous carbon (amC) and silicon carbide (SiC). However, no clear SiC feature has been detected in the MATISSE visibilities. This might be caused by molecular absorption that can affect the shape of the SiC band at 11.3 µm.
Conclusions.
The appearance of the molecular shells is in good agreement with predictions from dynamical atmosphere models. For the first time, we co-located dust and molecules in the environment of an AGB star. We confirm that the molecules are located closer to the star than the dust. The MIRA images unveil the presence of a clumpy environment in the fuzzy emission region beyond 4.0
R
*
. Furthermore, with the available dynamic range and angular resolution, we did not detect the presence of a binary companion. To solve this problem, additional observations combining MATISSE and SAM-VISIR instrument should enable this detection in future studies.
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