Context.
T Tauri has long been the prototypical young pre-main-sequence star. However, with increasing resolution and sensitivity, T Tauri has now been decomposed into a triple system with a complex ...disk and outflow geometry.
Aims.
We aim to measure the brightness of all three components of the T Tauri system (T Tau N, T Tau Sa, and T Tau Sb) in the mid-infrared in order to obtain photometry around the ∼9.7
μ
m silicate feature. This allows us to study their variability and to investigate the distribution of dust and the geometry of circumstellar and circumbinary disks in this complex system.
Methods.
We observe the T Tauri system with the Very Large Telescope (VLT)/VISIR-NEAR instrument, performing diffraction-limited imaging in the mid-infrared. With kernel phase interferometry post-processing of the data, and using the astrometric positions of all three components from VLT/SPHERE, we measure the three components’ individual brightnesses (including the southern binary at an angular separation down to ∼0.2
λ
/
D
) and obtain their photometry. In order to validate our methods, we simulate and recover mock data of the T Tauri system using the observed reference point-spread function of HD 27639.
Results.
We find that T Tau N is rather stable and shows weak silicate emission, while T Tau Sa is highly variable and shows prominent silicate absorption. T Tau Sb became significantly fainter compared to data from 2004 and 2006, suggesting increased extinction by dust. The precision of our photometry is limited by systematic errors in kernel phase interferometry, which is consistent with previous studies using this technique.
Conclusions.
Our results confirm the complex scenario of misaligned disks in the T Tauri system that had been observed previously, and they are in agreement with the recently observed dimming of T Tau Sb in the near-infrared. Our mid-infrared photometry supports the interpretation that T Tau Sb has moved behind the dense region of the Sa-Sb circumbinary disk on its tight orbit around Sa, therefore suffering increased extinction.
Context.
The emission from polycyclic aromatic hydrocarbons (PAHs) arises from the uppermost layers of protoplanetary disks, higher than the optical/near-infrared scattered light and similar to the ...emission from the highly thick
12
CO millimeter lines. The PAH intensity profiles trace the gas distribution and can constrain the penetration depth of UV radiation.
Aims.
We aim to constrain the spatial intensity profiles of the four strongest PAH emission features in the telluric
N
-band spectral region. Thereby, we seek to constrain the dependence of PAH properties on the (radial) location in the disk, such as charge state, the interrelation with the presence and dynamics of small silicate grains, and the correlation of PAH emission with gas or dust.
Methods.
We used the long-slit spectroscopy mode of the VISIR-NEAR experiment to perform diffraction-limited observations of eight nearby Herbig Ae protoplanetary disks. We extracted spectra for various locations along the slit with a spectral resolution of
R
≈ 300 and performed a compositional fit at each spatial location using spectral templates of silicates and the four PAH bands. This yields the intensity versus location profiles of each species.
Results.
We obtained spatially resolved intensity profiles of the PAH emission features in the
N
band for five objects (AB Aurigae, HD 97048, HD 100546, HD 163296, and HD 169142). We observe two kinds of PAH emission geometry in our sample: centrally peaked (HD 97048) and ring-like (AB Aurigae, HD 100546, HD 163296, and potentially HD 169142). Comparing the spatial PAH emission profiles with near-infrared scattered light images, we find a strong correlation in the disk substructure but a difference in radial intensity decay rate. The PAH emission shows a less steep decline with distance from the star. Finally, we find a correlation between the presence of (sub)micron-sized silicate grains and the depletion of PAH emission within the inner regions of the disks.
Conclusions.
In this work we find the following: (1) PAH emission traces the extent of Herbig Ae disks to a considerable radial distance. (2) The correlation between the presence of silicate emission within the inner regions of disks and the depletion of PAH emission can result from dust-mixing and PAH coagulation mechanisms and competition over UV photons. (3) For all objects in our sample, PAHs undergo stochastic heating across the entire spatial extent of the disk and are not saturated. (4) The difference in radial intensity decay rates between the PAHs and scattered-light profiles may be attributed to shadowing and dust-settling effects, which impact the scattering grains more so than the PAHs.
Abstract
Carbon monoxide was recently reported in the atmosphere of the hot Jupiter WASP-39b using the NIRSpec PRISM transit observation of this planet, collected as part of the JWST Transiting ...Exoplanet Community Early Release Science Program. This detection, however, could not be confidently confirmed in the initial analysis of the higher-resolution observations with NIRSpec G395H disperser. Here we confirm the detection of CO in the atmosphere of WASP-39b using the NIRSpec G395H data and cross-correlation techniques. We do this by searching for the CO signal in the unbinned transmission spectrum of the planet between 4.6 and 5.0
μ
m, where the contribution of CO is expected to be higher than that of other anticipated molecules in the planet’s atmosphere. Our search results in a detection of CO with a cross-correlation function (CCF) significance of 6.6
σ
when using a template with only
12
C
16
O lines. The CCF significance of the CO signal increases to 7.5
σ
when including in the template lines from additional CO isotopologues, with the largest contribution being from
13
C
16
O. Our results highlight how cross-correlation techniques can be a powerful tool for unveiling the chemical composition of exoplanetary atmospheres from medium-resolution transmission spectra, including the detection of isotopologues.
Context.
Observations of center-to-limb variations (CLVs) of spectral lines and continua provide a good test for the accuracy of models with a solar and stellar atmospheric structure and spectral ...line formation. They are also widely used to constrain elemental abundances, and are becoming increasingly more important in atmospheric studies of exoplanets. However, only a few such data sets exist for chromospheric lines.
Aims.
We aim to create a set of standard profiles by means of mosaics made with the CRISP and CHROMIS instruments of the Swedish 1-m Solar Telescope (SST), as well as to explore the robustness of said profiles obtained using this method.
Methods.
For each spectral line, we used a mosaic that ranges from the center to the limb. Each of these mosaics were averaged down to 50 individual spectral profiles and spaced by 0.02 in the
μ
scale. These profiles were corrected for p-mode oscillations, and their line parameters (equivalent width, line shift, full-width at half-maximum, and line depth) were then compared against literature values whenever possible.
Results.
We present a set of 50 average profiles that are spaced equidistantly along the cosine of the heliocentric angle (
μ
) by steps of 0.02 for five continuum points between 4001 and 7772 Å, as well as ten of the most commonly observed spectral lines at the SST (Ca II H & K, Η
β
, Mg I 5173 Å, C I 5380 Å, Fe I 6173 Å, Fe I 6301 Å, Ha, O I 7772 Å, and Ca II 8542 Å).
Conclusions.
The CLV of line profiles and continua are shared in the CDS as machine readable tables, providing a quantitative constraint on theoretical models that aim to model stellar atmospheres.
Molecule mapping of HR8799b using OSIRIS on Keck Petit dit de la Roche, D. J. M.; Hoeijmakers, H. J.; Snellen, I. A. G.
Astronomy and astrophysics (Berlin),
08/2018, Letnik:
616
Journal Article
Recenzirano
Context.
In 2015, Barman et al. (ApJ, 804, 61) presented detections of absorption from water, carbon monoxide, and methane in the atmosphere of the directly imaged exoplanet HR8799b using integral ...field spectroscopy (IFS) with OSIRIS on the Keck II telescope. We recently devised a new method to analyse IFU data, called molecule mapping, searching for high-frequency signatures of particular molecules in an IFU data cube.
Aims.
The aim of this paper is to use the molecule mapping technique to search for the previously detected spectral signatures in HR8799b using the same data, allowing a comparison of molecule mapping with previous methods.
Methods.
The medium-resolution
H
- and
K
-band pipeline-reduced archival data were retrieved from the Keck archive facility. Telluric and stellar lines were removed from each spectrum in the data cube, after which the residuals were cross-correlated with model spectra of carbon monoxide, water, and methane.
Results.
Both carbon monoxide and water are clearly detected at high signal-to-noise, however, methane is not retrieved.
Conclusions.
Molecule mapping works very well on the OSIRIS data of exoplanet HR8799b. However, it is not evident why methane is detected in the original analysis, but not with the molecule mapping technique. Possible causes could be the presence of telluric residuals, different spectral filtering techniques, or the use of different methane models. We do note that in the original analysis methane was only detected in the
K
-band, while the
H
-band methane signal could be expected to be comparably strong. More sensitive observations with the JWST will be capable of confirming or disproving the presence of methane in this planet at high confidence.
Context. In 2015, Barman et al. (ApJ, 804, 61) presented detections of absorption from water, carbon monoxide, and methane in the atmosphere of the directly imaged exoplanet HR8799b using integral ...field spectroscopy (IFS) with OSIRIS on the Keck II telescope. We recently devised a new method to analyse IFU data, called molecule mapping, searching for high-frequency signatures of particular molecules in an IFU data cube. Aims. The aim of this paper is to use the molecule mapping technique to search for the previously detected spectral signatures in HR8799b using the same data, allowing a comparison of molecule mapping with previous methods. Methods. The medium-resolution H- and K-band pipeline-reduced archival data were retrieved from the Keck archive facility. Telluric and stellar lines were removed from each spectrum in the data cube, after which the residuals were cross-correlated with model spectra of carbon monoxide, water, and methane. Results. Both carbon monoxide and water are clearly detected at high signal-to-noise, however, methane is not retrieved. Conclusions. Molecule mapping works very well on the OSIRIS data of exoplanet HR8799b. However, it is not evident why methane is detected in the original analysis, but not with the molecule mapping technique. Possible causes could be the presence of telluric residuals, different spectral filtering techniques, or the use of different methane models. We do note that in the original analysis methane was only detected in the K-band, while the H-band methane signal could be expected to be comparably strong. More sensitive observations with the JWST will be capable of confirming or disproving the presence of methane in this planet at high confidence.
Context.
The direct imaging of rocky exoplanets is one of the major science goals of upcoming large telescopes. The contrast requirement for imaging such planets is challenging. However, the mid-IR ...(infrared) regime provides the optimum contrast to directly detect the thermal signatures of exoplanets in our solar neighbourhood.
Aims.
We aim to exploit novel fast-chopping techniques newly developed for astronomy with the aid of adaptive optics to look for thermal signatures of exoplanets around bright stars in the solar neighbourhood.
Methods.
We used the upgraded Very Large Telescope Imager and Spectrometer for the mid-InfraRed (VISIR) instrument with high-contrast imaging capability optimised for observations at 10 μm to look for exoplanets around five nearby (
d
< 4 pc) stars. The instrument provides an improved signal-to-noise ratio (S/N) by a factor of ~4 in the
N
-band compared to standard VISIR for a given S/N and time.
Results.
In this work, we achieve a detection sensitivity of sub-mJy, which is sufficient to detect a few Jupiter mass planets in nearby systems. Although no detections are made, we achieve most sensitive limits within <2″ for all the observed targets compared to previous campaigns. For
ϵ
Indi A and
ϵ
Eri, we achieve detection limits very close to the giant planets discovered by RV, with the limits on
ϵ
Indi A being the most sensitive to date. Our non-detection therefore supports an older age for
ϵ
Indi A. The results presented here are promising for high-contrast imaging and exoplanet detections in the mid-IR regime.
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