L. Mosoni

THE 2008 OUTBURST OF EX Lup—SILICATE CRYSTALS IN MOTION

EX Lup is the prototype of the EXor class of eruptive young stars. These objects show optical outbursts which are thought to be related to runaway accretion onto the star. In a previous study we observed in situ crystal formation in the disk of EX Lup during its latest outburst in 2008, making the object an ideal laboratory to investigate circumstellar crystal formation and transport. This outburst was monitored by a campaign of ground-based and Spitzer Space Telescope observations. Here we modeled the spectral energy distribution (SED) of EX Lup in the outburst from optical to millimeter wavelengths with a two-dimensional radiative transfer code. Our results showed that the shape of the SED at optical wavelengths was more consistent with a single-temperature blackbody than a temperature distribution. We also found that this single-temperature component emitted 80%-100% of the total accretion luminosity. We concluded that a thermal instability, the most widely accepted model of EXor outbursts, was likely not the triggering mechanism of the 2008 outburst of EX Lup. Our mid-infrared Spitzer spectra revealed that the strength of all crystalline bands between 8 and 30 μm increased right after the end of the outburst. Six months later, however, the crystallinity in the 10 μm silicate feature complex decreased. Our modeling of the mid-infrared spectral evolution of EX Lup showed that, although vertical mixing should be stronger during the outburst than in the quiescent phase, fast radial transport of crystals (e.g., by stellar/disk wind) was required to reproduce the observed mid-infrared spectra.

First AU-scale observations of V1647 Orionis with VLTI/MIDI

The young eruptive star V16470ri was observed with MIDI, the mid-infrared interferometric instrument at the Very Large Telescope Interferometer (VLTI), on March 2, 2005. We present the first spectrally resolved interferometric visibility points for this object. Our results show that (1) the mid-infrared emitting region is extended, having a size of ≈7 AU at 10μm; (2) no signatures of a close companion can be seen; (3) the 8-13μm spectrum exhibits no obvious spectral features. Comparison with similar observations of Herbig Ae stars suggests that V1647 Ori probably possesses a disk of moderate flaring. A simple disk model with T ∼ r -0.53 , Σ ∼ r -1.5 , M d = 0.05 M ⊙ is able to fit both the spectral energy distribution and the observed visibility values simultaneously.

Deep Extragalactic VLBI-Optical Survey (DEVOS) - I. Pilot MERLIN and VLBI observations

We present the results of the pilot observations of the Deep Extragalactic VLBI-Optical Survey (DEVOS). Our ultimate aim is to collect information on compact structures in a large sample of cxtragalaclic radio sources (∼10 4 objects) up to two orders of magnitude fainter than those studied in typical imaging Very Long Baseline Interferometry (VLBI) surveys up until now. This would lead to an unprecedented data base for various astrophysical, astrometric and cosmological studies. The first global VLBI observations of the DEVOS programme were successfully conducted in May 2002. We selected sources without any spectral criterion from the Very Large Array (VLA) Faint Images of the Radio Sky at Twenty-centimeters (FIRST) catalogue. that are also detected with the Multi-Element Radio Linked Interferometer Network (MERLIN). The DEVOS pilot sample sources are in the area of the sky that is covered hy the Sloan Digital Sky Survey (SDSS). We describe the sample selection and present high resolution 5-GHz radio images of the sources. Based on the results of this pilot study, we estimate the outcome of and the resources needed for a full-scale DEVOS project.

MATISSE a four beams combiner in the mid-infrared for the VLTI

A first generation of VLTI (Very Large Telescopes Interferometer) focal instruments, AMBER in the near-infrared and MIDI in the mid-infrared, has been already integrated and tested. New and important science results have been obtained. These instruments combine two (for MIDI) or three (for AMBER) beams coming from the eight telescopes installed at Cerro Paranal (four 8-meters and four 1.8-meters telescopes). In order to improve the capabilities of the interferometer and to engage a new scientific prospective, the second generation of VLTI instruments is currently under study. MATISSE belongs to this second generation. MATISSE objective is the image reconstruction. It will extend the astrophysical potential of the VLTI by overcoming the ambiguities existing in the interpretation of simple visibility measurements. It is a spectro-interferometer combining up to four beams with a large spectral coverage ranging from 3 to 25 μm (L, M, N and Q bands). Different spectral resolutions (between 30 and 1500) are foreseen. MATISSE will measure closure phase relations thus offering an efficient capability for image reconstruction. The concept of MATISSE is presented in this paper. The recombination mode of MATISSE is similar to the AMBER beam combination, but has been adapted to the constraints specific to the mid-infrared domain.

Mid-infrared interferometric variability of DG Tauri : Implications for the inner-disk structure

Context. DG Tau is a low-mass pre-main sequence star, whose strongly accreting protoplanetary disk exhibits a so-far enigmatic behavior: its mid-infrared thermal emission is strongly time-variable, even turning the 10 μ m silicate feature from emission to absorption temporarily. Aims. We look for the reason for the spectral variability at high spatial resolution and at multiple epochs. Methods. Infrared interferometry can spatially resolve the thermal emission of the circumstellar disk, also giving information about dust processing. We study the temporal variability of the mid-infrared interferometric signal, observed with the VLTI/MIDI instrument at six epochs between 2011 and 2014. We fit a geometric disk model to the observed interferometric signal to obtain spatial information about the disk. We also model the mid-infrared spectra by template fitting to characterize the profile and time dependence of the silicate emission. We use physically motivated radiative transfer modeling to interpret the mid-infrared interferometric spectra. Results. The inner disk ( r μ m absorption feature related to amorphous silicate grains. The outer disk ( r > 1−3 au) spectra show a crystalline silicate feature in emission, similar to the spectra of comet Hale-Bopp. The striking difference between the inner and outer disk spectral feature is highly unusual among T Tauri stars. The mid-infrared variability is dominated by the outer disk. The strength of the silicate feature changed by more than a factor of two. Between 2011 and 2014 the half-light radius of the mid-infrared-emitting region decreased from 1.15 to 0.7 au. Conclusions. For the origin of the absorption we discuss four possible explanations: a cold obscuring envelope, an accretion heated inner disk, a temperature inversion on the disk surface and a misaligned inner geometry. The silicate emission in the outer disk can be explained by dusty material high above the disk plane, whose mass can change with time, possibly due to turbulence in the disk.

VLTI/MIDI atlas of disks around low- and intermediate-mass young stellar objects

Context. Protoplanetary disks show large diversity regarding their morphology and dust composition. With mid-infrared interferometry the thermal emission of disks can be spatially resolved, and the distribution and properties of the dust within can be studied. Aims. Our aim is to perform a statistical analysis on a large sample of 82 disks around low- and intermediate-mass young stars, based on mid-infrared interferometric observations. We intend to study the distribution of disk sizes, variability, and the silicate dust mineralogy. Methods. Archival mid-infrared interferometric data from the MIDI instrument on the VLTI are homogeneously reduced and calibrated. Geometric disk models are used to fit the observations to get spatial information about the disks. An automatic spectral decomposition pipeline is applied to analyze the shape of the silicate feature. Results. We present the resulting data products in the form of an atlas, containing N band correlated and total spectra, visibilities, and differential phases. The majority of our data can be well fitted with a continuous disk model, except for a few objects, where a gapped model gives a better match. From the mid-infrared size--luminosity relation we find that disks around T Tauri stars are generally colder and more extended with respect to the stellar luminosity than disks around Herbig Ae stars. We find that in the innermost part of the disks (

MATISSE Science Cases

r \lesssim 1

CHARA and e-VLBI observations of Algol

~au) the silicate feature is generally weaker than in the outer parts, suggesting that in the inner parts the dust is substantially more processed. We analyze stellar multiplicity and find that in two systems (AB Aur and HD 72106) data suggest a new companion or asymmetric inner disk structure. We make predictions for the observability of our objects with the upcoming MATISSE instrument, supporting the practical preparations of future MATISSE observations of T Tauri stars.

High-resolution radio imaging of the most distant radio quasar SDSS J0836+0054

MATISSE is foreseen as a mid-infrared spectro-interferometric instrument combining the beams of up to four UTs/ATs of the Very Large Telescope Interferometer (VLTI). MATISSE will measure closure phase relations and thus offer an efficient capability for image reconstruction. In addition to this, MATISSE will open 2 new observing windows at the VLTI: the L and M band in addition to the N band. Furthermore, the instrument will offer the possibility to perform simultaneous observations in separate bands. MATISSE will also provide several spectroscopic modes. In summary, MATISSE can be seen as a successor of MIDI by providing imaging capabilities in the mid-infrared domain (for a more detailed description of MATISSE see Lopez et al., these proceedings).

Rapid e-EVN studies of newly discovered gamma-ray blazars

The CHARA Array is funded by the National Science Foundation through NSF grants AST-0307562 and AST06006958 and by Georgia State University through the College of Arts and Sciences and the Office of the Vice President for Research. e-VLBI developments in Europe are supported by the EC DG-INFSO funded Communication Network Developments project ’EXPReS’, Contract No. 02662 (http://www.expres-eu.org/). The European VLBI Network (http://www.evlbi.org/) is a joint facility of European, Chinese, South African and other radio astronomy institutes funded by their national research councils.