arXiv subjects

Michael Weber

Publications and source records attributed to Michael Weber.

At least 37 records · Page 2Linked to original sources

arXiv2020

HIRES, the high-resolution spectrograph for the ELT

HIRES will be the high-resolution spectrograph of the European Extremely Large Telescope at optical and near-infrared wavelengths. It consists of three fibre-fed spectrographs providing a wavelength coverage of 0.4-1.8 mic (goal 0.35-1.8 mic) at a spectral resolution of ~100,000. The fibre-feeding allows HIRES to have several, interchangeable observing modes including a SCAO module and a small diffraction-limited IFU in the NIR. Therefore, it will be able to operate both in seeing and diffraction-limited modes. ELT-HIRES has a wide range of science cases spanning nearly all areas of research in astrophysics and even fundamental physics. Some of the top science cases will be the detection of bio signatures from exoplanet atmospheres, finding the fingerprints of the first generation of stars (PopIII), tests on the stability of Nature's fundamental couplings, and the direct detection of the cosmic acceleration. The HIRES consortium is composed of more than 30 institutes from 14 countries, forming a team of more than 200 scientists and engineers.

astro-ph.IM↗

arXiv2020

Spatially Resolved Ultraviolet Spectroscopy of the Great Dimming of Betelgeuse

The bright supergiant, Betelgeuse (Alpha Orionis, HD 39801) experienced a visual dimming during 2019 December and the first quarter of 2020 reaching an historic minimum 2020 February 7$-$13. During 2019 September-November, prior to the optical dimming event, the photosphere was expanding. At the same time, spatially resolved ultraviolet spectra using the Hubble Space Telescope/Space Telescope Imaging Spectrograph revealed a substantial increase in the ultraviolet spectrum and Mg II line emission from the chromosphere over the southern hemisphere of the star. Moreover, the temperature and electron density inferred from the spectrum and C II diagnostics also increased in this hemisphere. These changes happened prior to the Great Dimming Event. Variations in the Mg II k-line profiles suggest material moved outwards in response to the passage of a pulse or acoustic shock from 2019 September through 2019 November. It appears that this extraordinary outflow of material from the star, likely initiated by convective photospheric elements, was enhanced by the coincidence with the outward motions in this phase of the $\sim$400 day pulsation cycle. These ultraviolet observations appear to provide the connecting link between the known large convective cells in the photosphere and the mass ejection event that cooled to form the dust cloud in the southern hemisphere imaged in 2019 December, and led to the exceptional optical dimming of Betelgeuse in 2020 February.

astro-ph.SR↗

arXiv2019

Automated Focal Loss for Image based Object Detection

Current state-of-the-art object detection algorithms still suffer the problem of imbalanced distribution of training data over object classes and background. Recent work introduced a new loss function called focal loss to mitigate this problem, but at the cost of an additional hyperparameter. Manually tuning this hyperparameter for each training task is highly time-consuming. With automated focal loss we introduce a new loss function which substitutes this hyperparameter by a parameter that is automatically adapted during the training progress and controls the amount of focusing on hard training examples. We show on the COCO benchmark that this leads to an up to 30% faster training convergence. We further introduced a focal regression loss which on the more challenging task of 3D vehicle detection outperforms other loss functions by up to 1.8 AOS and can be used as a value range independent metric for regression.

cs.CV↗

arXiv2019

Spectangular: Disentangling variable spectra

Spectangular is a GUI based software package written in C++ designed for spectral disentangling on the wavelength scale. The code disentangles spectra of SB1 and SB2 systems and can now also be used also for spectra showing variability. In this work, effects of variability caused by telluric lines, line profile, and continuum flux are being investigated. Also shown is the disentangling on spectra from an artificial eclipsing binary. It is now possible to optimize on the flux ratios of each spectrum, making the disentangling a technique for extracting photometric information from spectroscopic observations usually provided by additional photometry. Furthermore, we make some comments about changes to the code since it was first published.

astro-ph.IM↗

arXiv2018

MultiNet: Real-time Joint Semantic Reasoning for Autonomous Driving

While most approaches to semantic reasoning have focused on improving performance, in this paper we argue that computational times are very important in order to enable real time applications such as autonomous driving. Towards this goal, we present an approach to joint classification, detection and semantic segmentation via a unified architecture where the encoder is shared amongst the three tasks. Our approach is very simple, can be trained end-to-end and performs extremely well in the challenging KITTI dataset, outperforming the state-of-the-art in the road segmentation task. Our approach is also very efficient, taking less than 100 ms to perform all tasks.

cs.CV↗

arXiv2017

Contemporaneous Imaging Comparisons of the Spotted Giant $σ$ Geminorum Using Interferometric, Spectroscopic, and Photometric Data

Nearby, active stars with relatively rapid rotation and large starspot structures offer the opportunity to compare interferometric, spectroscopic, and photometric imaging techniques. In this paper, we image a spotted star with three different methods for the first time. The giant primary star of the RS Canum Venaticorum binary $σ$ Geminorum ($σ$ Gem) was imaged for two epochs of interferometric, high-resolution spectroscopic, and photometric observations. The light curves from the reconstructions show good agreement with the observed light curves, supported by the longitudinally-consistent spot features on the different maps. However, there is strong disagreement in the spot latitudes across the methods.

astro-ph.SR↗

arXiv2017

Fully Convolutional Neural Networks for Dynamic Object Detection in Grid Maps

Grid maps are widely used in robotics to represent obstacles in the environment and differentiating dynamic objects from static infrastructure is essential for many practical applications. In this work, we present a methods that uses a deep convolutional neural network (CNN) to infer whether grid cells are covering a moving object or not. Compared to tracking approaches, that use e.g. a particle filter to estimate grid cell velocities and then make a decision for individual grid cells based on this estimate, our approach uses the entire grid map as input image for a CNN that inspects a larger area around each cell and thus takes the structural appearance in the grid map into account to make a decision. Compared to our reference method, our concept yields a performance increase from 83.9% to 97.2%. A runtime optimized version of our approach yields similar improvements with an execution time of just 10 milliseconds.

cs.CV↗

arXiv2016

Spectral disentangling with Spectangular

The paper introduces the software Spectangular for spectral disentangling via singular value decomposition with global optimisation of the orbital parameters of the stellar system or radial velocities of the individual observations. We will describe the procedure and the different options implemented in our program. Furthermore, we will demonstrate the performance and the applicability using tests on artificial data. Additionally, we use high-resolution spectra of Capella to demonstrate the performance of our code on real-world data. The novelty of this package is the implemented global optimisation algorithm and the graphical user interface (GUI) for ease of use. We have implemented the code to tackle SB1 and SB2 systems with the option of also dealing with telluric (static) lines.

astro-ph.IM↗

arXiv2015

The LEECH Exoplanet Imaging Survey: Orbit and Component Masses of the Intermediate Age, Late-Type Binary NO UMa

We present high-resolution Large Binocular Telescope LBTI/LMIRcam images of the spectroscopic and astrometric binary NO UMa obtained as part of the LBTI Exozodi Exoplanet Common Hunt (LEECH) exoplanet imaging survey. Our H, K$_s$, and L'-band observations resolve the system at angular separations <0.09". The components exhibit significant orbital motion over a span of ~7 months. We combine our imaging data with archival images, published speckle interferometry measurements, and existing spectroscopic velocity data to solve the full orbital solution and estimate component masses. The masses of the K2.0$\pm$0.5 primary and K6.5$\pm$0.5 secondary are 0.83$\pm$0.02 M$_{\odot}$ and 0.64$\pm$0.02 M$_{\odot}$, respectively. We also derive a system distance of d = 25.87$\pm$0.02 pc and revise the Galactic kinematics of NO UMa. Our revised Galactic kinematics confirm NO UMa as a nuclear member of the ~500 Myr old Ursa Major moving group and it is thus a mass and age benchmark. We compare the masses of the NO UMa binary components to those predicted by five sets of stellar evolution models at the age of the Ursa Major group. We find excellent agreement between our measured masses and model predictions with little systematic scatter between the models. NO UMa joins the short list of nearby, bright, late-type binaries having known ages and fully characterized orbits.

astro-ph.SR↗

arXiv2015

Stellar rotation, binarity, and lithium in the open cluster IC4756

An important aspect in the evolutionary scenario of cool stars is their rotation and the rotationally induced magnetic activity and interior mixing. Stars in open clusters are particularly useful tracers for these aspects because of their known ages. We aim to characterize the open cluster IC4756 and measure stellar rotation periods and surface differential rotation for a sample of its member stars. Thirty-seven cluster stars were observed continuously with the CoRoT satellite for 78 days in 2010. Follow-up high-resolution spectroscopy of the CoRoT targets and deep Strömgren $uvbyβ$ and H$α$ photometry of the entire cluster were obtained with our robotic STELLA facility and its echelle spectrograph and wide-field imager, respectively. We determined high-precision photometric periods for 27 of the 37 CoRoT targets and found values between 0.155 and 11.4 days. Twenty of these are rotation periods. Twelve targets are spectroscopic binaries of which 11 were previously unknown; orbits are given for six of them. Six targets were found that show evidence of differential rotation with $ΔΩ/Ω$ in the range 0.04-0.15. Five stars are non-radially pulsating stars with fundamental periods of below 1d, two stars are semi-contact binaries, and one target is a micro-flaring star that also shows rotational modulation. Nine stars in total were not considered members because of much redder color(s) and deviant radial velocities with respect to the cluster mean. H$α$ photometry indicates that the cluster ensemble does not contain magnetically over-active stars. The cluster average metallicity is -0.08$\pm$0.06 (rms) and its logarithmic lithium abundance for 12 G-dwarf stars is 2.39$\pm$0.17 (rms). [...]

astro-ph.SR↗

arXiv2013

Surface differential rotation of IL Hya from time-series Doppler images

We present a time-series Doppler imaging study of the K-subgiant component in the RS CVn-type binary system IL Hya (P orb=12.905 d). From re-processing the unique long-term spectroscopic dataset of 70 days taken in 1996/97, we perform a thorough cross-correlation analysis to derive surface differential rotation. As a result we get solar-type differential rotation with a shear value alpha of 0.05, in agreement with preliminary suggestions from previous attempts. A possible surface pattern of meridional circulation is also detected.

astro-ph.SR↗

arXiv2013

OpenSPIM - an open access platform for light sheet microscopy

Light sheet microscopy promises to revolutionize developmental biology by enabling live in toto imaging of entire embryos with minimal phototoxicity. We present detailed instructions for building a compact and customizable Selective Plane Illumination Microscopy (SPIM) system. The integrated OpenSPIM hardware and software platform is shared with the scientific community through a public website, thereby making light sheet microscopy accessible for widespread use and optimization to various applications.

q-bio.QM↗

arXiv2012

Net-charge fluctuations and balance functions at the LHC

The measurement of event-by-event fluctuations and charge-dependent particle correlations are used to study properties of nuclear matter at high temperatures as produced in ultrarelativistic heavy-ion collisions. We present results for event-by-event net-charge fluctuations and charge balance functions in Δη and Δϕ in Pb-Pb collisions at sqrt(s_NN)= 2.76 TeV.

nucl-ex↗

arXiv2012

Correlations and fluctuations studied with ALICE

The measurement of particle correlations and event-by-event fluctuations of physical observables allows to study a large variety of properties of the matter produced in ultra relativistic heavy-ion collisions. We will present results for two-particle correlations, mean transverse momentum fluctuations, and net charge fluctuations in Pb-Pb collisions at 2.76 TeV.

nucl-ex↗

arXiv2011

Parallel Recursive State Compression for Free

This paper focuses on reducing memory usage in enumerative model checking, while maintaining the multi-core scalability obtained in earlier work. We present a tree-based multi-core compression method, which works by leveraging sharing among sub-vectors of state vectors. An algorithmic analysis of both worst-case and optimal compression ratios shows the potential to compress even large states to a small constant on average (8 bytes). Our experiments demonstrate that this holds up in practice: the median compression ratio of 279 measured experiments is within 17% of the optimum for tree compression, and five times better than the median compression ratio of SPIN's COLLAPSE compression. Our algorithms are implemented in the LTSmin tool, and our experiments show that for model checking, multi-core tree compression pays its own way: it comes virtually without overhead compared to the fastest hash table-based methods.

cs.DS↗

arXiv2011

The spectroscopic orbit of Capella revisited

Context. Capella is among the few binary stars with two evolved giant components. The hotter component is a chromospherically active star within the Hertzsprung gap, while the cooler star is possibly helium-core burning. Aims. The known inclination of the orbital plane from astrometry in combination with precise radial velocities will allow very accurate masses to be determined for the individual Capella stars. This will constrain their evolutionary stage and possibly the role of the active star's magnetic field on the dynamical evolution of the binary system. Methods. We obtained a total of 438 high-resolution échelle spectra during the years 2007-2010 and used the measured velocities to recompute the orbital elements. Our double-lined orbital solution yields average residuals of 64 m/s for the cool component and 297 m/s for the more rapidly rotating hotter component. Results. The semi-amplitude of the cool component is smaller by 0.045 km/s than the orbit determination of Torres et al. from data taken during 1996-1999 but more precise by a factor of 5.5, while for the hotter component it is larger by 0.580 km/s and more precise by a factor of 3.6. This corresponds to masses of 2.573\pm0.009 M_sun and 2.488\pm0.008 M_sun for the cool and hot component, respectively. Their relative errors of 0.34% and 0.30% are about half of the values given in Torres et al. for a combined literature- data solution but with absolute values different by 4% and 2% for the two components, respectively. The mass ratio of the system is therefore q = M_A/M_B = 0.9673 \pm 0.0020. Conclusions. Our orbit is the most precise and also likely to be the most accurate ever obtained for Capella.

astro-ph.SR↗

arXiv2011

Generic Programming of Reusable, High Performance Container Types using Automatic Type Hierarchy Inference and Bidirectional Antichain Typing

We introduce a new compile-time notion of type subsumption based on type simulation. We show how to apply this static subsumption relation to support a more intuitive, object oriented approach to generic programming of reusable, high performance container types. As a first step towards an efficient implementation of the resulting type system in a compiler we present a novel algorithm for bidirectional type inference over arbitrary syntax graphs. The algorithm uses the new static type subsumption relation to compress the data that has to be stored for each node in the typeflow graph. During typeflow analysis this means that the set of types for a given node can be symbolically represented using antichains instead of using bitvectors or some other explicit set representation. This results in a typing algorithm that is both flexible and precise and shows good performance on representative instances.

cs.PL↗

arXiv2010

Three years of experience with the STELLA robotic observatory

Since May 2006, the two STELLA robotic telescopes at the Izana observatory in Tenerife, Spain, delivered an almost uninterrupted stream of scientific data. To achieve such a high level of autonomous operation, the replacement of all troubleshooting skills of a regular observer in software was required. Care must be taken on error handling issues and on robustness of the algorithms used. In the current paper, we summarize the approaches we followed in the STELLA observatory.

astro-ph.IM↗