The evolved circumbinary disk of AC Her: a radiative transfer, interferometric and mineralogical study

We aim to constrain the structure of the circumstellar material around the post-AGB binary and RV Tauri pulsator AC Her. We want to constrain the spatial distribution of the amorphous as well as of the crystalline dust. We present very high-quality mid-IR interferometric data that were obtained with MIDI/VLTI. We analyse the MIDI data and the full SED, using the MCMax radiative transfer code, to find a good structure model of AC Her's circumbinary disk. We include a grain size distribution and midplane settling of dust self-consistently. The spatial distribution of crystalline forsterite in the disk is investigated with the mid-IR features, the 69~$\mu$m band and the 11.3~$\mu$m signatures in the interferometric data. All the data are well fitted. The inclination and position angle of the disk are well determined at i=50+-8 and PA=305+-10. We firmly establish that the inner disk radius is about an order of magnitude larger than the dust sublimation radius. Significant grain growth has occurred, with mm-sized grains being settled to the midplane of the disk. A large dust mass is needed to fit the sub-mm fluxes. By assuming {\alpha}=0.01, a good fit is obtained with a small grain size power law index of 3.25, combined with a small gas/dust ratio <10. The resulting gas mass is compatible with recent estimates employing direct gas diagnostics. The spatial distribution of the forsterite is different from the amorphous dust, as more warm forsterite is needed in the surface layers of the inner disk. The disk in AC Her is very evolved, with its small gas/dust ratio and large inner hole. Mid-IR interferometry offers unique constraints, complementary to mid-IR features, for studying the mineralogy in disks. A better uv coverage is needed to constrain in detail the distribution of the crystalline forsterite in AC Her, but we find strong similarities with the protoplanetary disk HD100546.Comment: update with final version published in A&

Roche-lobe filling factor of mass-transferring red giants - the PIONIER view

Using the PIONIER visitor instrument that combines the light of the four Auxiliary Telescopes of ESO's Very Large Telescope Interferometer, we measure precisely the diameters of several symbiotic and related stars: HD 352, HD 190658, V1261 Ori, ER Del, FG Ser, and AG Peg. These diameters - in the range of 0.6 to 2.3 milli-arcseconds - are used to assess the filling factor of the Roche lobe of the mass-losing giants and provide indications on the nature of the ongoing mass transfer. We also provide the first spectroscopic orbit of ER Del, based on CORAVEL and HERMES/Mercator observations. The system is found to have an eccentric orbit with a period of 5.7 years. In the case of the symbiotic star FG Ser, we find that the diameter is changing by 13% over the course of 41 days, while the observations of HD 352 are indicative of an elongation. Both these stars are found to have a Roche filling factor close to 1, as is most likely the case for HD 190658 as well, while the three other stars have factors below 0.5-0.6. Our observations reveal the power of interferometry for the study of interacting binary stars - the main limitation in our conclusions being the poorly known distances of the objects.Comment: A&A, in pres

Imaging the dust sublimation front of a circumbinary disk

We present the first near-IR milli-arcsecond-scale image of a post-AGB binary that is surrounded by hot circumbinary dust. A very rich interferometric data set in six spectral channels was acquired of IRAS08544-4431 with the new RAPID camera on the PIONIER beam combiner at the Very Large Telescope Interferometer (VLTI). A broadband image in the \textit{H} band was reconstructed by combining the data of all spectral channels using the SPARCO method. We spatially separate all the building blocks of the IRAS08544-4431 system in our milliarcsecond-resolution image. Our dissection reveals a dust sublimation front that is strikingly similar to that expected in early-stage protoplanetary disks, as well as an unexpected flux signal of $\sim$4\% from the secondary star. The energy output from this companion indicates the presence of a compact circum-companion accretion disk, which is likely the origin of the fast outflow detected in H$\alpha$. Our image provides the most detailed view into the heart of a dusty circumstellar disk to date. Our results demonstrate that binary evolution processes and circumstellar disk evolution can be studied in detail in space and over time.Comment: PR @ http://www.eso.org/public/news/eso1608

Untersuchung von Methoden zur Unterdrückung des Spektrometeruntergrunds beim KATRIN-Experiment

Das KATRIN Experiment wird die Neutrinomassse bis auf 0,2eV (90% C.L.) bestimmen. Um die geforderte Auflösung zu erreichen, muss der Untergrund im niedrigen mHz Bereich liegen. Dazu muss der natürliche Untergrund an verschiedenen Stellen im Experiment reduziert werden. Im Rahmen dieser Arbeit wurden Untersuchungen zur Reduktion des Untergrundes an zwei wichtigen Komponenten des Experiments durchgeführt. Erstens wird der im Hauptspektrometer durch kosmische Strahlung induzierte Untergrund durch eine elektrostatische Abschirmung unterdrückt. Zweitens wird die Charakteristik der intrinsischen Penningfalle zwischen Vor- und Hauptspektrometer untersucht. Mit dem genauen Verständnis der Falle war es möglich diese mittels dreier verschiedener Methoden in regelmäßigen Abständen zu entleeren

A call to safeguard sexual and reproductive health information and services during Ebola outbreaks

The recent Ebola virus disease (EVD) outbreaks in 2021 exemplify how sexual and reproductive health services are too often considered unessential during health emergencies. Bleeding for reasons other than EVD, such as pregnancy complications or rape, can be construed as EVD symptoms, reinforcing fear and stigmatisation, and delaying timely access to adequate care. In this commentary, we urgently call on all humanitarian actors to integrate the Minimum Initial Services Package for Sexual and Reproductive Health in Crisis Situations into current and future EVD preparedness and response efforts

A mid-IR interferometric survey with MIDI/VLTI: resolving the second-generation protoplanetary disks around post-AGB binaries

We present a mid-IR interferometric survey of the circumstellar environment of a specific class of post-Asymptotic Giant Branch (post-AGB) binaries. For this class the presence of a compact dusty disk has been postulated on the basis of various spatially unresolved measurements. Our interferometric survey was performed with the MIDI instrument on the VLTI. In total 19 different systems were observed using variable baseline configurations. Combining all the visibilities at a single wavelength at 10.7 micron, we fitted two parametric models to the data: a uniform disk (UD) and a ring model mimicking a temperature gradient. We compared our observables of the whole sample, with synthetic data computed from a grid of radiative transfer models of passively irradiated disks in hydrostatic equilibrium. These models are computed with a Monte Carlo code that has been widely applied to describe the structure of protoplanetary disks around young stellar objects (YSO). The spatially resolved observations show that the majority of our targets cluster closely together in the distance-independent size-colour diagram, and have extremely compact N-band emission regions. The typical uniform disk diameter of the N-band emission region is about 40 mass which corresponds to a typical brightness temperature of 400-600~K. The resolved objects display very similar characteristics in the interferometric observables and in the spectral energy distributions. Therefore, the physical properties of the disks around our targets must be similar. The grid of protoplanetary disk models covers very well the observed objects. Much like for young stars, the spatially resolved N-band emission region is determined by the hot inner rim of the disk. Continued comparisons between post-AGB and protoplanetary disks will help to understand grain growth and disk evolution processes,Comment: 30 pages, 21 figures, in press in Astronomy and Astrophysic

Kinetic hierarchy and propagation of chaos in biological swarm models

We consider two models of biological swarm behavior. In these models, pairs of particles interact to adjust their velocities one to each other. In the first process, called 'BDG', they join their average velocity up to some noise. In the second process, called 'CL', one of the two particles tries to join the other one's velocity. This paper establishes the master equations and BBGKY hierarchies of these two processes. It investigates the infinite particle limit of the hierarchies at large time-scale. It shows that the resulting kinetic hierarchy for the CL process does not satisfy propagation of chaos. Numerical simulations indicate that the BDG process has similar behavior to the CL process

Mathematical description of bacterial traveling pulses

The Keller-Segel system has been widely proposed as a model for bacterial waves driven by chemotactic processes. Current experiments on {\em E. coli} have shown precise structure of traveling pulses. We present here an alternative mathematical description of traveling pulses at a macroscopic scale. This modeling task is complemented with numerical simulations in accordance with the experimental observations. Our model is derived from an accurate kinetic description of the mesoscopic run-and-tumble process performed by bacteria. This model can account for recent experimental observations with {\em E. coli}. Qualitative agreements include the asymmetry of the pulse and transition in the collective behaviour (clustered motion versus dispersion). In addition we can capture quantitatively the main characteristics of the pulse such as the speed and the relative size of tails. This work opens several experimental and theoretical perspectives. Coefficients at the macroscopic level are derived from considerations at the cellular scale. For instance the stiffness of the signal integration process turns out to have a strong effect on collective motion. Furthermore the bottom-up scaling allows to perform preliminary mathematical analysis and write efficient numerical schemes. This model is intended as a predictive tool for the investigation of bacterial collective motion

How linear features alter predator movement and the functional response

In areas of oil and gas exploration, seismic lines have been reported to alter the movement patterns of wolves (Canis lupus). We developed a mechanistic first passage time model, based on an anisotropic elliptic partial differential equation, and used this to explore how wolf movement responses to seismic lines influence the encounter rate of the wolves with their prey. The model was parametrized using 5 min GPS location data. These data showed that wolves travelled faster on seismic lines and had a higher probability of staying on a seismic line once they were on it. We simulated wolf movement on a range of seismic line densities and drew implications for the rate of predator–prey interactions as described by the functional response. The functional response exhibited a more than linear increase with respect to prey density (type III) as well as interactions with seismic line density. Encounter rates were significantly higher in landscapes with high seismic line density and were most pronounced at low prey densities. This suggests that prey at low population densities are at higher risk in environments with a high seismic line density unless they learn to avoid them

The dynamic atmospheres of Mira stars: comparing the CODEX models to PTI time series of TU And

Our comprehension of stellar evolution on the AGB still faces many difficulties. To improve on this, a quantified understanding of large-amplitude pulsator atmospheres and interpretation in terms of their fundamental stellar parameters are essential. We wish to evaluate the effectiveness of the recently released CODEX dynamical model atmospheres in representing M-type Mira variables through a confrontation with the time-resolved spectro-photometric and interferometric PTI data set of TU And. We calibrated the interferometric K-band time series to high precision. This results in 50 nights of observations, covering 8 subsequent pulsation cycles. At each phase, the flux at 2.2$\mu$m is obtained, along with the spectral shape and visibility points in 5 channels across the K-band. We compared the data set to the relevant dynamical, self-excited CODEX models. Both spectrum and visibilities are consistently reproduced at visual minimum phases. Near maximum, our observations show that the current models predict a photosphere that is too compact and hot, and we find that the extended atmosphere lacks H2O opacity. Since coverage in model parameter space is currently poor, more models are needed to make firm conclusions on the cause of the discrepancies. We argue that for TU And, the discrepancy could be lifted by adopting a lower value of the mixing length parameter combined with an increase in the stellar mass and/or a decrease in metallicity, but this requires the release of an extended model grid.Comment: 5 pages, 5 figures, accepted for publication in A&A Letter