Max Planck Institute for Extraterestrische Physik

Garching bei München, Germany

Max Planck Institute for Extraterestrische Physik

Garching bei München, Germany
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Nisini B.,National institute for astrophysics | Tafalla M.,Observatorio Astronomico Nacional IGN | Benedettini M.,National institute for astrophysics | Dionatos O.,Copenhagen University | And 4 more authors.
Astronomy and Astrophysics | Year: 2011

Context. The emission from Herbig-Haro objects and supersonic molecular outflows is understood as cooling radiation behind shocks, which are initiated by a (proto-)stellar wind or jet. Within a given object, one often observes both dissociative (J-type) and non-dissociative (C-type) shocks, owing to the collective effects of internally varying shock velocities. Aims. We aim at the observational estimation of the relative contribution to the cooling by CO and H2O, as this provides decisive information for understanding the oxygen chemistry behind interstellar shock waves. Methods. The high sensitivity of HIFI, in combination with its high spectral resolution capability, allowed us to trace the H2O outflow wings at an unprecedented signal-to-noise ratio. From the observation of spectrally resolved H2O and CO lines in the HH52-54 system, both from space and from the ground, we arrived at the spatial and velocity distribution of the molecular outflow gas. Solving the statistical equilibrium and non-LTE radiative transfer equations provides us with estimates of the physical parameters of this gas, including the cooling rate ratios of the species. The radiative transfer is based on an accelerated lambda iteration code, where we use the fact that variable shock strengths, distributed along the front, are naturally implied by a curved surface. Results. Based on observations of CO and H2O spectral lines, we conclude that the emission is confined to the HH54 region. The quantitative analysis of our observations favours a ratio of the CO-to-H2O-cooling-rate â‰" 1. Formally, we derived the ratio Λ(CO)/Λ(o- H2O) = 10, which is in good agreement with earlier determination of 7 based on ISO-LWS observations. From the best-fit model to the CO emission, we arrive at an H2O abundance close to 1 × 10-5. The line profiles exhibit two components, one that is triangular and another that is a superposed, additional feature. This additional feature is likely to find its origin in a region that is smaller than the beam where the ortho-water abundance is smaller than in the quiescent gas. Conclusions. Comparison with recent shock models indicate that a planar shock cannot easily explain the observed line strengths and triangular line profiles. We conclude that the geometry can play an important role. Although abundances support a scenario where J-type shocks are present, higher cooling rate ratios are derived than predicted by these types of shocks. © 2011 ESO.


Wyrowski F.,Max Planck Institute for Radio Astronomy | Van Der Tak F.,SRON Netherlands Institute for Space Research | Van Der Tak F.,University of Groningen | Herpin F.,University of Bordeaux 1 | And 72 more authors.
Astronomy and Astrophysics | Year: 2010

Early results from the Herschel Space Observatory revealed the water cation H2O+ to be an abundant ingredient of the interstellar medium. Here we present new observations of the H2O and H 2O+ lines at 1113.3 and 1115.2 GHz using the Herschel Space Observatory toward a sample of high-mass star-forming regions to observationally study the relation between H2O and H 2O+. Nine out of ten sources show absorption from H 2O+ in a range of environments: the molecular clumps surrounding the forming and newly formed massive stars, bright high-velocity outflows associated with the massive protostars, and unrelated low-density clouds along the line of sight. Column densities per velocity component of H2O+ are found in the range of 1012 to a few 1013 cm-2. The highest N(H2O+) column densities are found in the outflows of the sources. The ratios of H 2O+/H2O are determined in a range from 0.01 to a few and are found to differ strongly between the observed environments with much lower ratios in the massive (proto)cluster envelopes (0.01-0.1) than in outflows and diffuse clouds. Remarkably, even for source components detected in H2O in emission, H2O+ is still seen in absorption. © 2010 ESO.


Nisini B.,National institute for astrophysics | Benedettini M.,University of Rome Tor Vergata | Codella C.,National institute for astrophysics | Giannini T.,National institute for astrophysics | And 71 more authors.
Astronomy and Astrophysics | Year: 2010

Context. The far-IR/sub-mm spectral mapping facility provided by the Herschel-PACS and HIFI instruments has made it possible to obtain, for the first time, images of H2O emission with a spatial resolution comparable to ground based mm/sub-mm observations. Aims. In the framework of the Water In Star-forming regions with Herschel (WISH) key program, maps in water lines of several outflows from young stars are being obtained, to study the water production in shocks and its role in the outflow cooling. This paper reports the first results of this program, presenting a PACS map of the o-H2O 179 μm transition obtained toward the young outflow L1157. Methods. The 179 μm map is compared with those of other important shock tracers, and with previous single-pointing ISO, SWAS, and Odin water observations of the same source that allow us to constrain the H2O abundance and total cooling. Results. Strong H2O peaks are localized on both shocked emission knots and the central source position. The H2O 179 μm emission is spatially correlated with emission from H2 rotational lines, excited in shocks leading to a significant enhancement of the water abundance. Water emission peaks along the outflow also correlate with peaks of other shock-produced molecular species, such as SiO and NH3. A strong H2O peak is also observed at the location of the proto-star, where none of the other molecules have significant emission. The absolute 179 μm intensity and its intensity ratio to the H2O 557 GHz line previously observed with Odin/SWAS indicate that the water emission originates in warm compact clumps, spatially unresolved by PACS, having a H2O abundance of the order of 10-4. This testifies that the clumps have been heated for a time long enough to allow the conversion of almost all the available gas-phase oxygen into water. The total H2O cooling is ∼10 -1 $L-\odot$, about 40% of the cooling due to H 2 and 23% of the total energy released in shocks along the L1157 outflow. © 2010 ESO.


Nisini B.,National institute for astrophysics | Benedettini M.,University of Rome Tor Vergata | Codella C.,National institute for astrophysics | Giannini T.,National institute for astrophysics | And 76 more authors.
Astronomy and Astrophysics | Year: 2010

Context. The far-IR/sub-mm spectral mapping facility provided by the Herschel-PACS and HIFI instruments has made it possible to obtain, for the first time, images of H2O emission with a spatial resolution comparable to ground based mm/sub-mm observations. Aims. In the framework of the Water In Star-forming regions with Herschel (WISH) key program, maps in water lines of several outflows from young stars are being obtained, to study the water production in shocks and its role in the outflow cooling. This paper reports the first results of this program, presenting a PACS map of the o-H2O 179 μm transition obtained toward the young outflow L1157. Methods. The 179 μm map is compared with those of other important shock tracers, and with previous single-pointing ISO, SWAS, and Odin water observations of the same source that allow us to constrain the H2O abundance and total cooling. Results. Strong H2O peaks are localized on both shocked emission knots and the central source position. The H2O 179 μm emission is spatially correlated with emission from H2 rotational lines, excited in shocks leading to a significant enhancement of the water abundance. Water emission peaks along the outflow also correlate with peaks of other shock-produced molecular species, such as SiO and NH3. A strong H2O peak is also observed at the location of the proto-star, where none of the other molecules have significant emission. The absolute 179 μm intensity and its intensity ratio to the H2O 557 GHz line previously observed with Odin/SWAS indicate that the water emission originates in warm compact clumps, spatially unresolved by PACS, having a H2O abundance of the order of 10-4. This testifies that the clumps have been heated for a time long enough to allow the conversion of almost all the available gas-phase oxygen into water. The total H2O cooling is ∼10 -1 L⊙, about 40% of the cooling due to H2 and 23% of the total energy released in shocks along the L1157 outflow. © 2010 ESO.


Vokrouhlicky D.,Charles University | Farnocchia D.,Jet Propulsion Laboratory | Capek D.,Academy of Sciences of the Czech Republic | Chesley S.R.,Jet Propulsion Laboratory | And 3 more authors.
Icarus | Year: 2015

We use the recently determined rotation state, shape, size and thermophysical model of Apophis to predict the strength of the Yarkovsky effect in its orbit. Apophis does not rotate about the shortest principal axis of the inertia tensor, rather its rotational angular momentum vector wobbles at an average angle of 37° from the body axis. Therefore, we pay special attention to the modeling of the Yarkovsky effect for a body in such a tumbling state, a feature that has not been described in detail so far. Our results confirm that the Yarkovsky effect is not significantly weakened by the tumbling state. The previously stated rule that the Yarkovsky effect for tumbling kilometer-size asteroids is well represented by a simple model assuming rotation about the shortest body axis in the direction of the rotational angular momentum and with rotation period close to the precession period is confirmed. Taking into account uncertainties of the model parameters, as well as the expected density distribution for Apophis' spectral class, we predict the secular change in the semimajor axis is (-12.8±3.6)×10-4au/Myr (formal 1σ uncertainty). The currently available astrometric data for Apophis do not allow an unambiguous direct detection of the Yarkovsky effect. However, the fitted secular change in semimajor axis of (-23±13)×10-4au/Myr is compatible with the model prediction. We revise the Apophis' impact probability information in the second half of this century by extending the orbital uncertainty derived from the current astrometric data and by taking into account the uncertainty in the dynamical model due to the thermal recoil accelerations. This is done by mapping the combined uncertainty to the close encounter in 2029 and by determining the statistical weight of the known keyholes leading to resonant impact orbits. Whereas collision with the Earth before 2060 is ruled out, impacts are still possible from 2060 with probabilities up to a few parts in a million. More definitive analysis will be available after the Apophis apparition in 2020-2021. © 2015 Elsevier Inc.


Haeuser M.,Universitats Sternwarte Munich | Lang-Bardl F.,Universitats Sternwarte Munich | Richter J.,Universitats Sternwarte Munich | Hess H.-J.,Universitats Sternwarte Munich | And 7 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2014

We present a Θ - Φ-style fiber-positioner prototype, which will be controlled via the EMI-robust CAN-Bus. Our positioner points without iterations or a metrology system. Due to the overlapping patrol disc of 17.3 mm diameter, we reach a filling factor of 100 %. The positioners diameter is 14.6 mm, containing the control electronics on a contemporary PCB of 13.5 mm width. While moving, the power consumption does not lead to a significant rise in temperature. Given a mechanical reference point measured by stall detection, the absolute accuracy is 27 μm (1σ = 14 μm) and pointings are repeatable with 7 μm (1σ = 4 μm). Better positioning may be reachable with upcoming calibration. © 2014 SPIE.

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