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Sbordone L.,Landessternwarte Heidelberg | Sbordone L.,University Paris Diderot | Bonifacio P.,University Paris Diderot | Caffau E.,Landessternwarte Heidelberg | Caffau E.,University Paris Diderot
Memorie della Societa Astronomica Italiana, Supplementi - Journal of the Italian Astronomical Society, Supplement | Year: 2012

We discuss the current status of the sample of Lithium abundances in extremely metal poor (EMP) turn-off (TO) stars collected by our group, and compare it with the available literature results. In the last years, evidences have accumulated of a progressive disruption of the Spite plateau in stars of extremely low metallicity. What appears to be a flat, thin plateau above [Fe/H]∼-2.8 turns, at lower metallicities, into a broader distribution for which the plateau level constitutes the upper limit, but more and more stars show lower Li abundances. The sample we have collected currently counts abundances or upper limits for 44 EMP TO stars between [Fe/H]=-2.5 and -3.5, plus the ultra-metal poor star SDSS J102915+172927 at [Fe/H]=-4.9. The "meltdown" of the Spite plateau is quite evident and, at the current status of the sample, does not appear to be restricted to the cool end of the effective temperature distribution. SDSS J102915+172927 displays an extreme Li depletion that contrasts with its otherwise quite ordinary set of [X/Fe] ratios. © SAIt 2012.


Grellmann R.,Ludwig Maximilians University of Munich | Grellmann R.,European Southern Observatory | Ratzka T.,Ludwig Maximilians University of Munich | Ratzka T.,University of Graz | And 4 more authors.
Astronomy and Astrophysics | Year: 2015

Context: Observations and simulations have clearly established that most stars form in multiple systems. Characterizing their properties is thus important for our understanding of the star formation process. Aims: To provide statistics about the number of companions per star over the full range of angular distances, infrared long-baseline interferometric studies can be employed to fill the gap between spectroscopic and adaptive optics searches. The Upper Scorpius OB association is a good target for such observations, because its stellar content is very well known from both spectroscopic and adaptive optics searches. Methods: We used the ESO Very Large Telescope Interferometer to perform long-baseline interferometric observations of a sample of seven B stars. Furthermore, we used ROSAT X-ray data to search for indications of low-mass companions. Results: With the interferometric observations, we find previously known companions around σ Sco and HR 6027. For the other targets we determine the parameter space in which the presence of companions can be excluded from our data. For two of the B stars in our sample, π Sco and HR 6026, the detection of X-ray emission provides indirect evidence of previously unknown low-mass companions. Conclusions: In total we find two previously unknown companions. We can exclude the presence of other unknown companions within the separation range of ∼2 to ∼100 mas and for a brightness ratio ≥0.1.


Bicknell G.V.,Australian National University | Wagner S.J.,Landessternwarte Heidelberg
Astronomy and Astrophysics | Year: 2011

Context. Recently observed rapid time variability in the gamma ray emission from the blazar PKS 2155-304 indicates that either the site of gamma ray emission is close to the black hole or the jet has a very high Lorentz factor. Consideration of the opacity of gamma rays close to the black hole provides additional information related to these two possibilities. Aims. We investigate the TeV gamma ray opacity resulting from pair production on soft photons radiated by the black hole accretion disk, considering situations where the radiation produced by the disk is close to that predicted by the Shakura-Sunyaev model and situations where the disk radiation is much less. Methods. We utilise expressions for the pair opacity of very high energy gamma rays developed by Gould and Schréder and Donea and Protheroe and use expressions for the disk radiation field produced by an accretion disk external to a Poynting flux dominated jet. A lower level of disk emission is modelled by using the spectrum corresponding to a lower accretion rate. We also consider changes in the shape of the gamma ray sepctrum as a flare emerges from the optically thick region. Results. If the gravitational power resulting from accretion is dissipated by radiation in the region of the disk external to the jet, then TeV gamma rays are opaque out to of order 40 gravitational radii â‰̂ 6 × 10 15 cm from the black hole. However, the opacity is considerably reduced if the disk radiates a negligible amount of gravitational power as would be the case if there is a significant disk wind external to the jet. In either case the absence of spectral changes during observed flares excludes scenarios in which the TeV gamma rays are emitted even in regions of modest pair opacity. © 2010 ESO.


Buschkamp P.,Max Planck Institute for Extraterrestrial Physics | Seifert W.,Landessternwarte Heidelberg | Polsterer K.,Ruhr University Bochum | Hofmann R.,Max Planck Institute for Extraterrestrial Physics | And 10 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2012

LUCI (former LUCIFER) is the full cryogenic near-infrared multi-object spectrograph and imager at the LBT. It presently allows for seeing limited imaging and multi-object spectroscopy at R∼2000-4000 in a 4x4arcmin 2 FOV from 0.9 to 2.5 micron. We report on the instrument performance and the lessons learned during the first two years on sky from a technical and operational point of view. We present the upcoming detector upgrade to Hawaii-2 RG arrays and the operating modes to utilize the binocular mode, the LBT facility AO system for diffraction limited imaging as well as to use the wide-field AO correction afforded by the multi-laser GLAO System ARGOS in multi-object spectroscopy. © 2012 SPIE.


Jankowsky F.,Landessternwarte Heidelberg | Wagner S.,Landessternwarte Heidelberg
EPJ Web of Conferences | Year: 2015

The Automatic Telescope for Optical Monitoring (ATOM) for H.E.S.S. is an 75? cm optical telescope which operates fully automated. As there is no observer present during observation, an auxiliary all-sky camera serves as weather monitoring system. This device takes an all-sky image of the whole sky every three minutes. The gathered data then undergoes live-analysis by performing astrometric comparison with a theoretical night sky model, interpreting the absence of stars as cloud coverage. The sky monitor also serves as tool for a meteorological analysis of the observation site of the the upcoming Cherenkov Telescope Array. This overview covers design and benefits of the all-sky camera and additionally gives an introduction into current efforts to integrate the device into the atmosphere analysis programme of H.E.S.S. © Owned by the authors, published by EDP Sciences, 2015.


Jutte M.,Ruhr University Bochum | Knierim V.,Ruhr University Bochum | Polsterer K.,Ruhr University Bochum | Lehmitz M.,Max Planck Institute for Astronomy | And 3 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2010

The successful roll-out of the control software for a complex NIR imager/spectrograph with MOS calls for flexible development strategies due to changing requirements during different phases of the project. A waterfall strategy used in the beginning has to change to a more iterative and agile process in the later stages. The choice of an appropriate program language as well as suitable software layout is crucial. For example the software has to accomplish multiple demands of different user groups, including a high level of flexibility for later changes and extensions. Different access levels to the instrument are mandatory to afford direct control mechanisms for lab operations and inspections of the instrument as well as tools to accomplish efficient science observations. Our hierarchical software structure with four layers of increasing abstract levels and the use of an object oriented language ideally supports these requirements. Here we describe our software architecture, the software development process, the different access levels and our commissioning experiences with LUCIFER 1. © 2010 SPIE.


Reipurth B.,University of Hawaii at Manoa | Bally J.,University of Colorado at Boulder | Aspin C.,University of Hawaii at Manoa | Connelley M.S.,University of Hawaii at Manoa | And 4 more authors.
Astronomical Journal | Year: 2013

HH 222 is a giant shocked region in the L1641 cloud, and is popularly known as the Orion Streamers or "the waterfall" on account of its unusual structure. At the center of these streamers are two infrared sources coincident with a nonthermal radio jet aligned along the principal streamer. The unique morphology of HH 222 has long been associated with this radio jet. However, new infrared images show that the two sources are distant elliptical galaxies, indicating that the radio jet is merely an improbable line-of-sight coincidence. Accurate proper motion measurements of HH 222 reveal that the shock structure is a giant bow shock moving directly away from the well-known, very young, Herbig Be star V380 Ori. The already known Herbig-Haro object HH 35 forms part of this flow. A new Herbig-Haro object, HH 1041, is found precisely in the opposite direction of HH 222 and is likely to form part of a counterflow. The total projected extent of this HH complex is 5.3 pc, making it among the largest HH flows known. A second outflow episode from V380 Ori is identified as a pair of HH objects, HH 1031 to the northwest and the already known HH 130 to the southeast, along an axis that deviates from that of HH 222/HH 1041 by only 3.°7. V380 Ori is a hierarchical quadruple system, including a faint companion of spectral type M5 or M6, which at an age of ∼1 Myr corresponds to an object straddling the stellar-to-brown dwarf boundary. We suggest that the HH 222 giant bow shock is a direct result of the dynamical interactions that led to the conversion from an initial non-hierarchical multiple system into a hierarchical configuration. This event occurred no more than 28,000 yr ago, as derived from the proper motions of the HH 222 giant bow shock. © 2013. The American Astronomical Society. All rights reserved.


Jankowsky F.,Landessternwarte Heidelberg | Wagner S.,Landessternwarte Heidelberg
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2014

The High Energy Stereoscopic System (H.E.S.S.) in Namibia measures gamma-ray emission via the detection of Cherenkov light in the optical waveband and is therefore highly sensitive to changes in the transparency of the atmosphere. This is especially true for aerosols, small dust particles covering the sky at the H.E.S.S. site and severely reducing the atmospheric transparency for blue Cherenkov light for several days each year. To quantify this effect, the Cherenkov Transparency Coefficient has been introduced as a hardware-independent parameter, which enables a correction of measured gamma-ray brightnesses. Neighbouring the Cherenkov array, the Automated Telescope for Optical Monitoring (ATOM) operates an all-sky cloud camera as secondary instrument. Due to its high exposure frequency, the cloud camera may act as a detection system, if image parameters indicating low Cherenkov transparency are identified. However, the current instrument - originally conceived as a weather warning system - only produces white-light frames in low resolution. This study examines all frames taken with the current instrument since 2008 which coincide with H.E.S.S. observations in order to characterise relations with the measured Cherenkov transparency. As a result of this preliminary study, trivial relations between the examined sky monitor observations and gamma-ray brightness can be excluded. However, it is planned to expand the scope of this activity with an upgraded device by introducing colour dependency and more advanced photometry with a larger number of objects in the near future. © 2014 SPIE.


Jankowsky F.,Landessternwarte Heidelberg | Wagner S.,Landessternwarte Heidelberg
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2014

The Automatic Telescope for Optical Monitoring (ATOM) is a 75 cm Ritchey-Chrétien telescope situated in Göllschau, Namibia, which forms part of the High Energy Stereoscopic System (H.E.S.S.). This paper presents ANDAQ, which allows to step from robotic to fully automatic observation by eliminating the need for daily human interaction. The main module responsible for the telescope operation forms a newly developed observer program, which also includes control of the telescope enclosure and offers various other tasks, like automated flat-fielding with live-analysis. ANDAQ features its own TCP server for outside communication, making it possible to insert commands during the night. It possesses various means of monitoring internal and environmental parameters, and adjusts observation if necessary. This paper includes an description of the all-sky camera serving as cloud detector, supplemented by an additional rain detection device, and shows how operation is stopped as soon as weather parameters are below a defined standard, and automatically restarted once conditions recover. ANDAQ possesses a modular design based on a management core which starts and stops components as needed. This eases introduction of further functionality considerably and current development efforts include closer links to the main H.E.S.S. operation as well as live-analysis of exposures, allowing repeated observation in case of increased activity of a source. ANDAQ has undergone extensive testing and has not seen any major problems so far. It may thus well serve as base for a future automated monitoring programme for the Cherenkov Telescope Array. © 2014 SPIE.


Buschkamp P.,Max Planck Institute for Extraterrestrial Physics | Hofmann R.,Max Planck Institute for Extraterrestrial Physics | Gemperlein H.,Max Planck Institute for Extraterrestrial Physics | Polsterer K.,Ruhr University Bochum | And 8 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2010

The LUCIFER-MOS unit is the full cryogenic mask-exchange unit for the near-infrared multi-object spectrograph LUCIFER at the Large Binocular Telescope. We present the design and functionality of this unique device. In LUCIFER the masks are stored, handled, and placed in the focal plane under cryogenic conditions at all times, resulting in very low thermal background emission from the masks during observations. All mask manipulations are done by a novel cryogenic mask handling robot that can individually address up to 33 fixed and user-provided masks and place them in the focal plane with high accuracy. A complete mask exchange cycle is done in less than five minutes and can be run in every instrument position and state reducing instrument setup time during science observations to a minimum. Exchange of old and new MOS masks is likewise done under cryogenic conditions using a unique exchange drive mechanism and two auxiliary cryostats that attach to the main instrument cryostat. © 2010 Copyright SPIE - The International Society for Optical Engineering.

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