312 research outputs found
Competences of sustainability professionals, and competence bottlenecks for change towards environmental sustainable behaviour
Systematiek van natuurtypen voor de biotopen heide, moeras, duin, slik en schor: Deel 5: Slik en schor
Constraints on the H2O formation mechanism in the wind of carbon-rich AGB stars
Context. The recent detection of warm HO vapor emission from the outflows
of carbon-rich asymptotic giant branch (AGB) stars challenges the current
understanding of circumstellar chemistry. Two mechanisms have been invoked to
explain warm HO vapor formation. In the first, periodic shocks passing
through the medium immediately above the stellar surface lead to HO
formation. In the second, penetration of ultraviolet interstellar radiation
through a clumpy circumstellar medium leads to the formation of HO
molecules in the intermediate wind.
Aims. We aim to determine the properties of HO emission for a sample of
18 carbon-rich AGB stars and subsequently constrain which of the above
mechanisms provides the most likely warm HO formation pathway.
Methods, Results, and Conclusions. See paper
Ices in the edge-on disk CRBR 2422.8-3423: Spitzer spectroscopy and Monte Carlo radiative transfer modeling
We present 5.2-37.2 micron spectroscopy of the edge-on circumstellar disk
CRBR 2422.8-3423 obtained using the InfraRed Spectrograph (IRS) of the Spitzer
Space Telescope. The IRS spectrum is combined with ground-based 3-5 micron
spectroscopy to obtain a complete inventory of solid state material present
along the line of sight toward the source. We model the object with a 2D
axisymmetric (effectively 3D) Monte Carlo radiative transfer code. It is found
that the model disk, assuming a standard flaring structure, is too warm to
contain the very large observed column density of pure CO ice, but is possibly
responsible for up to 50% of the water, CO2 and minor ice species. In
particular the 6.85 micron band, tentatively due to NH4+, exhibits a prominent
red wing, indicating a significant contribution from warm ice in the disk. It
is argued that the pure CO ice is located in the dense core Oph-F in front of
the source seen in the submillimeter imaging, with the CO gas in the core
highly depleted. The model is used to predict which circumstances are most
favourable for direct observations of ices in edge-on circumstellar disks. Ice
bands will in general be deepest for inclinations similar to the disk opening
angle, i.e. ~70 degrees. Due to the high optical depths of typical disk
mid-planes, ice absorption bands will often probe warmer ice located in the
upper layers of nearly edge-on disks. The ratios between different ice bands
are found to vary by up to an order of magnitude depending on disk inclination
due to radiative transfer effects caused by the 2D structure of the disk.
Ratios between ice bands of the same species can therefore be used to constrain
the location of the ices in a circumstellar disk. [Abstract abridged]Comment: 49 pages, accepted for publication in Ap
Water, hydrogen cyanide, carbon monoxide, and dust production from distant comet 29P/Schwassmann-Wachmann 1
peer reviewedContext. 29P/Schwassmann-Wachmann 1 is a distant Centaur/comet, showing persistent CO-driven activity and frequent outbursts. Aims: We aim to better characterize its gas and dust activity from multiwavelength observations performed during outbursting and quiescent states. Methods: We used the HIFI, PACS and SPIRE instruments of the Herschel space observatory on several dates in 2010, 2011, and 2013 to observe the H2O 557 GHz and NH3 573 GHz lines and to image the dust coma in the far-infrared. Observations with the IRAM 30 m telescope were undertaken in 2007, 2010, 2011, and 2021 to monitor the CO production rate through the 230 GHz line, and to search for HCN at 89 GHz. The 70 and 160 µm PACS images were used to measure the thermal flux from the nucleus and the dust coma. Modeling was performed to constrain the size of the sublimating icy grains and to derive the dust production rate. Results: HCN is detected for the first time in comet 29P (at 5σ in the line area). H2O is detected as well, but not NH3. H2O and HCN line shapes differ strongly from the CO line shape, indicating that these two species are released from icy grains. CO production rates are in the range (2.9-5.6) × 10E28 s−1 (1400-2600 kg s−1). A correlation between the CO production rate and coma brightness is observed, as is a correlation between CO and H2O production. The correlation obtained between the excess of CO production and excess of dust brightness with respect to the quiescent state is similar to that established for the continuous activity of comet Hale-Bopp. The measured Q(H2O)/Q(CO) and Q(HCN)/Q(CO) production rate ratios are 10.0 ± 1.5 % and 0.12 ± 0.03 %, respectively, averaging the April-May 2010 measurements (Q(H2O) = (4.1 ± 0.6) × 10E27 s−1, Q(HCN) = (4.8 ± 1.1) × 10E25 s−1). We derive three independent and similar values of the effective radius of the nucleus, ~31 ± 3 km, suggesting an approximately spherical shape. The inferred dust mass-loss rates during quiescent phases are in the range 30-120 kg s−1, indicating a dust-to-gas mass ratio <0.1 during quiescent activity. We conclude that strong local heterogeneities exist on the surface of 29P, with quenched dust activity from most of the surface, but not in outbursting regions. Conclusions: The volatile composition of the atmosphere of 29P strongly differs from that of comets observed within 3 au from the Sun. The observed correlation between CO, H2O and dust activity may provide important constraints for the outburst-triggering mechanism
The MIRI Medium Resolution Spectrometer calibration pipeline
The Mid-Infrared Instrument (MIRI) Medium Resolution Spectrometer (MRS) is
the only mid-IR Integral Field Spectrometer on board James Webb Space
Telescope. The complexity of the MRS requires a very specialized pipeline, with
some specific steps not present in other pipelines of JWST instruments, such as
fringe corrections and wavelength offsets, with different algorithms for point
source or extended source data. The MRS pipeline has also two different
variants: the baseline pipeline, optimized for most foreseen science cases, and
the optimal pipeline, where extra steps will be needed for specific science
cases. This paper provides a comprehensive description of the MRS Calibration
Pipeline from uncalibrated slope images to final scientific products, with
brief descriptions of its algorithms, input and output data, and the accessory
data and calibration data products necessary to run the pipeline.Comment: 10 pages, 8 figure
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