With a focus on off-the-shelf components, Twinkle is the first in a series of cost competitive small satellites managed and financed by Blue Skies Space Ltd. The satellite is based on a high-heritage Airbus platform that will carry a 0.45 m telescope and a spectrometer which will provide simultaneous wavelength coverage from 0.5–4.5 μm. The spacecraft prime is Airbus Stevenage while the telescope is being developed by Airbus Toulouse and the spectrometer by ABB Canada. Scheduled to begin scientific operations in 2025, Twinkle will sit in a thermally-stable, sun-synchronous, low-Earth orbit. The mission has a designed operation lifetime of at least seven years and, during the first three years of operation, will conduct two large-scale survey programmes: one focused on Solar System objects and the other dedicated to extrasolar targets. Here we present an overview of the architecture of the mission, refinements in the design approach, and some of the key science themes of the extrasolar survey.
The latest generation of infrared long-baseline interferometric instruments combines high spatial resolution with spectroscopic
capabilities, enabling fascinating new studies of the AU-scale circumstellar environment around young stellar
objects. Here, we present recent investigations, which we conducted using the VLTI instruments AMBER and MIDI and
which demonstrate these new observational possibilities.
In one study, we combine near- and mid-infrared interferometry
(H-/K-/N-band) to constrain the geometry and radial
temperature profile of the circumstellar accretion disk around the Herbig Be star MWC147. Using detailed radiative
transfer modeling, we find strong evidence for the presence of an optically-thick inner gaseous disk. In another investigation,
we used AMBER's medium spectral resolution mode (R = 1500) to study the spatial origin of the hydrogen Brγ
line for five Herbig Ae/Be stars, associating the line emission with different physical mechanisms, such as disk winds and
magnetospheric accretion. Finally, we present AMBER H- and K-band observations of the close binary star θ1OrionisC and illustrate the benefits of fitting wavelength-differential visibilities and closure phases. Besides yielding a high observing
efficiency, this approach is also insensitive to calibration errors, induced, for instance, by fast changing atmospheric
conditions.
We present the results of N-band spectro-interferometric observations of the silicate carbon star Hen 38 (IRAS08002-3803) with the MID-infrared Interferometric instrument (MIDI) at the Very Large Telescope Interferometer (VLTI) of the European Southern Observatory (ESO). Our observations of IRAS08002-3803 with baseline lengths of 39-47 m have spatially resolved the dusty environment of a silicate carbon star for the first time and revealed an unexpected wavelength dependence of the angular size in the N band: the uniform-disk diameter is found to be constant and ~36 mas (72 R*) between 8 and 10 μm, while it steeply increases longward of 10 μm to reach ~53 mas (106 R*) at 13 μm. Neither spherical shell models nor axisymmetric disk models consisting of silicate grains alone can simultaneously explain the observed wavelength dependence of the visibility and the spectral energy distribution (SED). We propose that the circumstellar environment of IRAS08002-3803 may consist of two grain species coexisting in the disk: silicate and a second grain species, for which we consider amorphous carbon, large silicate grains, and metallic iron grains. Comparison of the observed visibilities and SED with our models shows that such disk models can fairly - though not entirely satisfactorily - reproduce the observed SED and N-band visibilities. Our MIDI observations and the radiative transfer calculations lend support to the picture where oxygen-rich material around IRAS08002-3803 is stored in a circumbinary disk surrounding the carbon-rich primary star and its putative low-luminosity companion.
We report on observations of circumstellar disks around young stars that have been obtained with the MIDI instrument, which is mounted on the VLT Interferometer and operates in the 10 μm atmospheric window. The maximum spatial resolution of 5 milli-arcsec corresponds to sub-AU scales at the distance to nearby star formation regions. Thus, we can study the disks on the spatial scales at which important processes occur, such as accretion, dust processing, and planet formation. The main results obtained so far can be summarized as follows: 1. The measured interferometric visibilities are in good qualitative agreement with those predicted by models of circumstellar disks. In particular, a predicted correlation between the strength of the far-infrared excess and the spatial structure of the disk is confirmed by direct measurements; 2. In several objects strong evidence for deviations from circular symmetry is present, indicating that an inclined disk is indeed the dominant component seen in the mid-infrared; 3. The dust properties are not uniform over the disk, but are instead a strong function of distance to the central star. The dust in the innermost disk regions is observed to be more "processed" than the dust further out, both in Herbig Ae star disks and in those around T Tauri stars.
We present bispectrum speckle interferometric observations of the deeply embedded protostellar outflow source S140 IRS1. Using the SAO 6 m telescope, we obtained a K-band image with diffraction-limited resolution of 76 mas, which is the highest resolution image of a young outflow source ever obtained in the infrared. Our image shows the circumstellar environment of S140 IRS1 in unprecedented detail
and suggests that the central source is marginally resolved with a FWHM diameter of approximately 20 mas (approx 20 AU). The dominant feature is a bright extended and very clumpy structure pointing away from the central source in exactly the same direction as the blue-shifted CO outflow lobe. We interprete this feature as the clumpy inner surface of a partially evacuated cavity in the circumstellar envelope around IRS1, which has been excavated by the strong outflow from IRS1. In addition, we find several arc-like structures north-east of IRS 1, extended diffuse emission south of IRS 1, and four new point sources. The diffuse and fragmentary structures close to IRS 1 appear to trace circumstellar material swept up by energetic outflows. In combination with molecular line emission maps from the literature, our image provides direct confirmation that two distinct bipolar outflow systems continue to be driven from IRS 1 on scales between 3" and 100". Our speckle observations provide important complementary information for future long-baseline interferometric observations, for example with the LBT.
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