This article describes the operation of the near-infrared wavefront sensing based Adaptive Optics (AO) system CIAO. The Coudé Infrared Adaptive Optics (CIAO) system is a central auxiliary component ...of the Very Large Telescope (VLT) interferometer (VLTI). It enables in particular the observations of the Galactic Center (GC) using the GRAVITY instrument. GRAVITY is a highly specialized beam combiner, a device that coherently combines the light of the four 8-m telescopes and finally records interferometric measurements in the K-band on 6 baselines simultaneously. CIAO compensates for phase disturbances caused by atmospheric turbulence, which all four 8 m Unit Telescopes (UT) experience during observation. Each of the four CIAO units generates an almost diffraction-limited image quality at its UT, which ensures that maximum flux of the observed stellar object enters the fibers of the GRAVITY beam combiner. We present CIAO performance data obtained in the first 3 years of operation as a function of weather conditions. We describe how CIAO is configured and used for observations with GRAVITY. In addition, we focus on the outstanding features of the near-infrared sensitive Saphira detector, which is used for the first time on Paranal, and show how it works as a wavefront sensor detector.
Stars form by accreting material from their surrounding disks. There is a consensus that matter flowing through the disk is channelled onto the stellar surface by the stellar magnetic field. This is ...thought to be strong enough to truncate the disk close to the corotation radius, at which the disk rotates at the same rate as the star. Spectro-interferometric studies in young stellar objects show that hydrogen emission (a well known tracer of accretion activity) mostly comes from a region a few milliarcseconds across, usually located within the dust sublimation radius.sup.1-3. The origin of the hydrogen emission could be the stellar magnetosphere, a rotating wind or a disk. In the case of intermediate-mass Herbig AeBe stars, the fact that Brackett gamma (Brgamma) emission is spatially resolved rules out the possibility that most of the emission comes from the magnetosphere.sup.4-6 because the weak magnetic fields (some tenths of a gauss) detected in these sources.sup.7,8 result in very compact magnetospheres. In the case of T Tauri sources, their larger magnetospheres should make them easier to resolve. The small angular size of the magnetosphere (a few tenths of a milliarcsecond), however, along with the presence of winds.sup.9,10 make the interpretation of the observations challenging. Here we report optical long-baseline interferometric observations that spatially resolve the inner disk of the T Tauri star TW Hydrae. We find that the near-infrared hydrogen emission comes from a region approximately 3.5 stellar radii across. This region is within the continuum dusty disk emitting region (7 stellar radii across) and also within the corotation radius, which is twice as big. This indicates that the hydrogen emission originates in the accretion columns (funnel flows of matter accreting onto the star), as expected in magnetospheric accretion models, rather than in a wind emitted at much larger distance (more than one astronomical unit).
In this article, we describe the Mid-Infrared Imager Module (MIRIM), which provides broadband imaging in the 5-27 μm wavelength range for the James Webb Space Telescope. The imager has a pixel scale ...and a total unobstructed view of 74″ × 113″. The remainder of its nominal 113″ × 113″ field is occupied by the coronagraphs and the low-resolution spectrometer. We present the instrument optical and mechanical design. We show that the test data, as measured during the test campaigns undertaken at CEA-Saclay, at the Rutherford Appleton Laboratory, and at the NASA Goddard Space Flight Center, indicate that the instrument complies with its design requirements and goals. We also discuss the operational requirements (multiple dithers and exposures) needed for optimal scientific utilization of the MIRIM.
With the advent of JWST, we are acquiring unprecedented insights into the physical and chemical structure of the inner regions of planet-forming disks where terrestrial planet formation occurs. Very ...low-mass stars (VLMSs) are known to have a high occurrence of the terrestrial planets orbiting them. Exploring the chemical composition of the gas in these inner disk regions can help us better understand the connection between planet-forming disks and planets. sun We used the dust-fitting tool DuCK to determine the dust continuum and to place constraints on the dust composition and grain sizes. We used 0D slab models to identify and fit the molecular spectral features, which yielded estimates on the temperature, column density, and emitting area. To test our understanding of the chemistry in the disks around VLMSs, we employed the thermo-chemical disk model P RO D I M O and investigated the reservoirs of the detected hydrocarbons. We explored how the C/O ratio affects the inner disk chemistry. JWST reveals a plethora of hydrocarbons, including CH3 CH4 C2H2 CCH2 C2H6 C3H4 C4H2 and C6H6 which suggests a disk with a gaseous C/O\,>\,1. Additionally, we detect CO2 CO2 HCN and HC3N H2O and OH are absent from the spectrum. We do not detect polycyclic aromatic hydrocarbons. Photospheric stellar absorption lines of H2O and CO are identified. Notably, our radiation thermo-chemical disk models are able to produce these detected hydrocarbons in the surface layers of the disk when C/O\,>\,1. The presence of C C+ H, and H2 is crucial for the formation of hydrocarbons in the surface layers, and a C/O ratio larger than 1 ensures the surplus of C needed to drive this chemistry. Based on this, we predict a list of additional hydrocarbons that should also be detectable. Both amorphous and crystalline silicates (enstatite and forsterite) are present in the disk and we find grain sizes of 2 and 5\,mu m. The disk around Sz28 is rich in hydrocarbons, and its inner regions have a high gaseous C/O ratio. In contrast, it is the first VLMS disk in the MINDS sample to show both distinctive dust features and a rich hydrocarbon chemistry. The presence of large grains indicates dust growth and evolution. Thermo-chemical disk models that employ an extended hydrocarbon chemical network together with C/O\,>1 are able to explain the hydrocarbon species detected in the spectrum.
The low-resolution spectrometer of the MIRI, which forms part of the imager module, will provide R ∼ 100 long-slit and slitless spectroscopy from 5 to 12 μm. The design is optimized for observations ...of compact sources, such as exoplanet host stars. We provide here an overview of the design of the LRS, and its performance as measured during extensive test campaigns, examining in particular the delivered image quality, dispersion, and resolving power, as well as spectrophotometric performance, flatfield accuracy, and the effects of fringing. We describe the operational concept of the slitless mode, which is optimally suited to transit spectroscopy of exoplanet atmospheres. The LRS mode of the MIRI was found to perform consistently with its requirements and goals.
MINDS: The DR Tau disk Temmink, Milou; van Dishoeck, Ewine F.; Grant, Sierra L. ...
Astronomy and astrophysics (Berlin),
6/2024, Letnik:
686
Journal Article
Recenzirano
Odprti dostop
Context . The MRS mode of the JWST-MIRI instrument has been shown to be a powerful tool to characterise the molecular gas emission of the inner region of planet-forming disks. Investigating their ...spectra allows us to infer the composition of the gas in these regions and, subsequently, the potential atmospheric composition of the forming planets. We present the JWST-MIRI observations of the compact T-Tauri disk, DR Tau, which are complemented by ground-based, high spectral resolution ( R ~ 60 000–90 000) CO ro-vibrational observations. Aims . The aim of this work is to investigate the power of extending the JWST-MIRI CO observations with complementary, high-resolution, ground-based observations acquired through the SpExoDisks database, as JWST-MIRI’s spectral resolution ( R ~ 1500– 3500) is not sufficient to resolve complex CO line profiles. In addition, we aim to infer the excitation conditions of other molecular features present in the JWST-MIRI spectrum of DR Tau and link those with CO. Methods . The archival complementary, high-resolution CO ro-vibrational observations were analysed with rotational diagrams. We extended these diagrams to the JWST-MIRI observations by binning and convolution with JWST-MIRI’s pseudo-Voigt line profile. In parallel, local thermal equilibrium (LTE) 0D slab models were used to infer the excitation conditions of the detected molecular species. Results . Various molecular species, including CO, CO 2 , HCN, and C 2 H 2 , are detected in the JWST-MIRI spectrum of DR Tau, with H 2 O being discussed in a subsequent paper. The high-resolution observations show evidence for two 12 CO components: a broad component (full width at half maximum of FWHM ~33.5 km s −1 ) tracing the Keplerian disk and a narrow component ( FWHM ~ 11.6 km s −1 ) tracing a slow disk wind. The rotational diagrams yield CO excitation temperatures of T ≥ 725 K. Consistently lower excitation temperatures are found for the narrow component, suggesting that the slow disk wind is launched from a larger radial distance. In contrast to the ground-based observations, much higher excitation temperatures are found if only the high- J transitions probed by JWST-MIRI are considered in the rotational diagrams. Additional analysis of the 12 CO line wings suggests a larger emitting area than inferred from the slab models, hinting at a misalignment between the inner ( i ~ 20°) and the outer disk ( i ~ 5°). Compared to CO, we retrieved lower excitation temperatures of T ~ 325-900 K for 12 CO 2 , HCN, and C 2 H 2 . Conclusions . We show that complementary, high-resolution CO ro-vibrational observations are necessary to properly investigate the excitation conditions of the gas in the inner disk and they are required to interpret the spectrally unresolved JWST-MIRI CO observations. These additional observations, covering the lower- J transitions, are needed to put better constraints on the gas physical conditions and they allow for a proper treatment of the complex line profiles. A comparison with JWST-MIRI requires the use of pseudo-Voigt line profiles in the convolution rather than simple binning. The combined high-resolution CO and JWST-MIRI observations can then be used to characterise the emission, in addition to the physical and chemical conditions of the other molecules with respect to CO. The inferred excitation temperatures suggest that CO originates from the highest atmospheric layers close to the host star, followed by HCN and C 2 H 2 which emit, together with 13 CO, from slightly deeper layers, whereas the CO 2 emission originates from even deeper inside or further out of the disk.
MINDS: The DR Tau disk Temmink, Milou; van Dishoeck, Ewine F; Grant, Sierra L ...
Astronomy and astrophysics (Berlin),
06/2024, Letnik:
686
Journal Article
Recenzirano
Context. The MRS mode of the JWST-MIRI instrument has been shown to be a powerful tool to characterise the molecular gas emission of the inner region of planet-forming disks. Investigating their ...spectra allows us to infer the composition of the gas in these regions and, subsequently, the potential atmospheric composition of the forming planets. We present the JWST-MIRI observations of the compact T-Tauri disk, DR Tau, which are complemented by ground-based, high spectral resolution (R ~ 60 000–90 000) CO ro-vibrational observations. Aims. The aim of this work is to investigate the power of extending the JWST-MIRI CO observations with complementary, high-resolution, ground-based observations acquired through the SpExoDisks database, as JWST-MIRI’s spectral resolution (R ~ 1500– 3500) is not sufficient to resolve complex CO line profiles. In addition, we aim to infer the excitation conditions of other molecular features present in the JWST-MIRI spectrum of DR Tau and link those with CO. Methods. The archival complementary, high-resolution CO ro-vibrational observations were analysed with rotational diagrams. We extended these diagrams to the JWST-MIRI observations by binning and convolution with JWST-MIRI’s pseudo-Voigt line profile. In parallel, local thermal equilibrium (LTE) 0D slab models were used to infer the excitation conditions of the detected molecular species. Results. Various molecular species, including CO, CO2, HCN, and C2H2, are detected in the JWST-MIRI spectrum of DR Tau, with H2O being discussed in a subsequent paper. The high-resolution observations show evidence for two 12CO components: a broad component (full width at half maximum of FWHM ~33.5 km s−1) tracing the Keplerian disk and a narrow component (FWHM ~ 11.6 km s−1) tracing a slow disk wind. The rotational diagrams yield CO excitation temperatures of T ≥ 725 K. Consistently lower excitation temperatures are found for the narrow component, suggesting that the slow disk wind is launched from a larger radial distance. In contrast to the ground-based observations, much higher excitation temperatures are found if only the high-J transitions probed by JWST-MIRI are considered in the rotational diagrams. Additional analysis of the 12CO line wings suggests a larger emitting area than inferred from the slab models, hinting at a misalignment between the inner (i ~ 20°) and the outer disk (i ~ 5°). Compared to CO, we retrieved lower excitation temperatures of T ~ 325-900 K for 12CO2, HCN, and C2H2. Conclusions. We show that complementary, high-resolution CO ro-vibrational observations are necessary to properly investigate the excitation conditions of the gas in the inner disk and they are required to interpret the spectrally unresolved JWST-MIRI CO observations. These additional observations, covering the lower-J transitions, are needed to put better constraints on the gas physical conditions and they allow for a proper treatment of the complex line profiles. A comparison with JWST-MIRI requires the use of pseudo-Voigt line profiles in the convolution rather than simple binning. The combined high-resolution CO and JWST-MIRI observations can then be used to characterise the emission, in addition to the physical and chemical conditions of the other molecules with respect to CO. The inferred excitation temperatures suggest that CO originates from the highest atmospheric layers close to the host star, followed by HCN and C2H2 which emit, together with 13CO, from slightly deeper layers, whereas the CO2 emission originates from even deeper inside or further out of the disk.
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