69 research outputs found
ALMA observations of the "fresh" carbon-rich AGB star TX Piscium. The discovery of an elliptical detached shell
Aims. The carbon-rich asymptotic giant branch (AGB) star TX Piscium (TX Psc)
has been observed multiple times during multiple epochs and at different
wavelengths and resolutions, showing a complex molecular CO line profile and a
ring-like structure in thermal dust emission. We investigate the molecular
counterpart in high resolution, aiming to resolve the ring-like structure and
identify its origin. Methods. Atacama Large Millimeter/submillimeter Array
(ALMA) observations have been carried out to map the circumstellar envelope
(CSE) of TX Psc in CO(2-1) emission and investigate the counterpart to the
ring-like dust structure. Results. We report the detection of a thin,
irregular, and elliptical detached molecular shell around TX Psc, which
coincides with the dust emission. This is the first discovery of a
non-spherically symmetric detached shell, raising questions about the shaping
of detached shells. Conclusions. We investigate possible shaping mechanisms for
elliptical detached shells and find that in the case of TX Psc, stellar
rotation of 2 km/s can lead to a non-uniform mass-loss rate and velocity
distribution from stellar pole to equator, recreating the elliptical CSE. We
discuss the possible scenarios for increased stellar momentum, enabling the
rotation rates needed to reproduce the ellipticity of our observations, and
come to the conclusion that momentum transfer of an orbiting object with the
mass of a brown dwarf would be sufficient
Molecular line study of the S-type AGB star W Aquilae. ALMA observations of CS, SiS, SiO and HCN
Context. With the outstanding spatial resolution and sensitivity of the
Atacama Large Millimeter/sub-millimeter Array (ALMA), molecular gas other than
the abundant CO can be observed and resolved in circumstellar envelopes (CSEs)
around evolved stars, such as the binary S-type Asymptotic Giant Branch (AGB)
star W Aquilae. Aims. We aim to constrain the chemical composition of the CSE
and determine the radial abundance distribution, the photospheric peak
abundance, and isotopic ratios of a selection of chemically important molecular
species in the innermost CSE of W Aql. The derived parameters are put into the
context of the chemical evolution of AGB stars and are compared with
theoretical models. Methods. We employ one-dimensional radiative transfer
modeling - with the accelerated lambda iteration (ALI) radiative transfer code
- of the radial abundance distribution of a total of five molecular species
(CS, SiS, 30SiS, 29SiO and H13CN) and determine the best fitting model
parameters based on high-resolution ALMA observations as well as archival
single-dish observations. The additional advantage of the spatially resolved
ALMA observations is that we can directly constrain the radial profile of the
observed line transitions from the observations. Results. We derive abundances
and e-folding radii for CS, SiS, 30SiS, 29SiO and H13CN and compare them to
previous studies, which are based only on unresolved single-dish spectra. Our
results are in line with previous results and are more accurate due to
resolution of the emission regions
A chemical survey of exoplanets with ARIEL
Thousands of exoplanets have now been discovered with a huge range of masses, sizes and orbits: from rocky Earth-like planets to large gas giants grazing the surface of their host star. However, the essential nature of these exoplanets remains largely mysterious: there is no known, discernible pattern linking the presence, size, or orbital parameters of a planet to the nature of its parent star. We have little idea whether the chemistry of a planet is linked to its formation environment, or whether the type of host star drives the physics and chemistry of the planetâs birth, and evolution. ARIEL was conceived to observe a large number (~1000) of transiting planets for statistical understanding, including gas giants, Neptunes, super-Earths and Earth-size planets around a range of host star types using transit spectroscopy in the 1.25â7.8 ÎŒm spectral range and multiple narrow-band photometry in the optical. ARIEL will focus on warm and hot planets to take advantage of their well-mixed atmospheres which should show minimal condensation and sequestration of high-Z materials compared to their colder Solar System siblings. Said warm and hot atmospheres are expected to be more representative of the planetary bulk composition. Observations of these warm/hot exoplanets, and in particular of their elemental composition (especially C, O, N, S, Si), will allow the understanding of the early stages of planetary and atmospheric formation during the nebular phase and the following few million years. ARIEL will thus provide a representative picture of the chemical nature of the exoplanets and relate this directly to the type and chemical environment of the host star. ARIEL is designed as a dedicated survey mission for combined-light spectroscopy, capable of observing a large and well-defined planet sample within its 4-year mission lifetime. Transit, eclipse and phase-curve spectroscopy methods, whereby the signal from the star and planet are differentiated using knowledge of the planetary ephemerides, allow us to measure atmospheric signals from the planet at levels of 10â100 part per million (ppm) relative to the star and, given the bright nature of targets, also allows more sophisticated techniques, such as eclipse mapping, to give a deeper insight into the nature of the atmosphere. These types of observations require a stable payload and satellite platform with broad, instantaneous wavelength coverage to detect many molecular species, probe the thermal structure, identify clouds and monitor the stellar activity. The wavelength range proposed covers all the expected major atmospheric gases from e.g. H2O, CO2, CH4 NH3, HCN, H2S through to the more exotic metallic compounds, such as TiO, VO, and condensed species. Simulations of ARIEL performance in conducting exoplanet surveys have been performed â using conservative estimates of mission performance and a full model of all significant noise sources in the measurement â using a list of potential ARIEL targets that incorporates the latest available exoplanet statistics. The conclusion at the end of the Phase A study, is that ARIEL â in line with the stated mission objectives â will be able to observe about 1000 exoplanets depending on the details of the adopted survey strategy, thus confirming the feasibility of the main science objectives.Peer reviewedFinal Published versio
The instrument control unit of the PLATO payload: design consolidation following the preliminary design review by ESA
PLATO is an M-class mission (M3) of the European Space Agency (ESA) whose launch is scheduled in 2026. The main aim of the mission is the detection and characterization of terrestrial exoplanets orbiting around bright solar-type star. The payload consists of 26 small telescopes: 24 "normal" cameras and 2 "fast" cameras. The huge amount of data produced by the PLATO telescopes is acquired and processed on-board by the Data Processing System (DPS) made up by various processing electronic units. The DPS of the PLATO instrument comprises the Normal and Fast DPUs (Data Processing Units) and a single ICU (Instrument Control Unit), are data routed through a SpaceWire network. The topic of this paper is the description of the architecture of the ICU and its role within the DPS, the status of the Avionic Validation Model (AVM) testing at the end of the Unit Preliminary Design Review (UPDR) performed by ESA and the results of the test of the first engineering model
Die UniversitĂ€tssternwarte Wien: Die groĂe Kuppel
Detailaufnahme der UniversitĂ€tssternwarte Wien. Die groĂe 14m Kuppel ist dr zentrale Blickfang. Das Foto wurde von Prof. Franz Kerschbaum aufgenommen. Blickwinkel vom Weinhauser Kirchturm
Teilansicht der UniversitÀtssternwarte Wien: Die Wiener Sternwarte
Die Detailansicht zeigt den Eingangsbereich mit seinem groĂen Glasdach. SĂŒden ist rechts. Unter dm Glasdach befindet sich die groĂe Treppe, ĂŒber die man in die eigentliche Sternwarte gelangt. Das Foto wurde vom weinhauser Kirchturm aufgenommen. Fotograf: Prof. Franz Kerschbau
Die UniversitÀtssternwarte Wien: Dtailansicht der Sternwarte
Das Institut fĂŒr Astrophysik aufgenommen vom Weinhauser Kirchturm. Fotograf: Prof. Franz Kerschbaum
Die UniversitĂ€tssternwarte Wien: Die groĂe Kuppel
Ausschnittsvergröserung der groĂen Kuppel der UniversitĂ€tssternwarte. In der Kuppel befindet sich der groĂe 68 cm Refraktor der Sternwarte. Aufgenommen vom Weinhauser Kirchturm. Fotograf: Prof. Franz Kerschbau
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