A Search for the Optical/Infrared Counterpart of the Anomalous X-ray Pulsar 1E 1841-045

We have carried out a search for the optical and infrared counterpart of the Anomalous X-ray Pulsar 1E 1841-045, which is located at the center of the supernova remnant Kes73. We present the first deep optical and infrared images of the field of 1E 1841-045, as well as optical spectroscopy results that exclude the brightest objects in the error circle as possible counterparts. A few of the more reddened objects in this region can be considered as particularly interesting candidates, in consideration of the distance and absorption expected from the association with Kes73. The strong interstellar absorption in the direction of the source does not allow to completely exclude the presence of main sequence massive companions.Comment: 8 pages, latex, 6 figures, Submitted to Mon. Not. R. Astron. So

Evolution of isolated neutron stars in globular clusters: number of Accretors

With a simple model from the point of view of population synthesis we try to verify an interesting suggestion made by Pfahl & Rappaport (2001) that dim sources in globular clusters (GCs) can be isolated accreting neutron stars (NSs). Simple estimates show, that we can expect about 0.5-1 accreting isolated NS per typical GC with $M=10^5 M_{\odot}$ in correspondence with observations. Properties of old accreting isolated NSs in GCs are briefly discussed. We suggest that accreting NSs in GCs experienced significant magnetic field decay.Comment: 6 pages, no figures. Submitted to Astronomical and Astrophysical Transactions (style included

Planetesimal collisions in binary systems

We study the collisional evolution of km-sized planetesimals in tight binary star systems to investigate whether accretion towards protoplanets can proceed despite the strong gravitational perturbations from the secondary star. The orbits of planetesimals are numerically integrated in two dimensions under the influence of the two stars and gas drag. The masses and orbits of the planetesimals are allowed to evolve due to collisions with other planetesimals and accretion of collisional debris. In addition, the mass in debris can evolve due to planetesimal-planetesimal collisions and the creation of new planetesimals. We show that it is possible in principle for km-sized planetesimals to grow by two orders of magnitude in size if the efficiency of planetesimal formation is relatively low. We discuss the limitations of our two-dimensional approach.Comment: 5 pages, 5 figures, accepted for publication in MNRA

Spectroscopy across the brown dwarf/planetary mass boundary - I. Near-infrared JHK spectra

With a uniform VLT SINFONI data set of nine targets, we have developed an empirical grid of J,H,K spectra of the atmospheres of objects estimated to have very low substellar masses of \sim5-20 MJup and young ages of \sim1-50 Myr. Most of the targets are companions, objects which are especially valuable for comparison with atmosphere and evolutionary models, as they present rare cases in which the age is accurately known from the primary. Based on the sample youth, all objects are expected to have low surface gravity, and this study investigates the critical early phases of the evolution of substellar objects. The spectra are compared with grids of five different theoretical atmosphere models. This analysis represents the first systematic model comparison with infrared spectra of young brown dwarfs. The fits to the full JHK spectra of each object result in a range of best fit effective temperatures of +/-150-300K whether or not the full model grid or a subset restricted to lower log(g) values is used. This effective temperature range is significantly larger than the uncertainty typically assigned when using a single model grid. Fits to a single wavelength band can vary by up to 1000K using the different models. Since the overall shape of these spectra is governed more by the temperature than surface gravity, unconstrained model fits did not find matches with low surface gravity or a trend in log(g) with age. This suggests that empirical comparison with spectra of unambiguously young objects targets (such as these SINFONI data) may be the most reliable method to search for indications of low surface gravity and youth. For two targets, the SINFONI data are a second epoch and the data show no variations in morphology over time. The analysis of two other targets, AB Pic B and CT Cha B, suggests that these objects may have lower temperatures, and consequently lower masses, than previously estimated.Comment: 15 pages, 13 figure

A Categorization and Parametric Modeling Approach Using Open Geodata Enabling Building Vulnerability Assessment

Due to the increase in the frequency and intensity of natural disasters such as heavy rainfall events, the evaluation of the vulnerability of the built environment is becoming increasingly important. Evaluation techniques for each separate building often require detailed geometric models of the supporting structures and time-consuming simulations. One possibility to overcome this problem is to categorize the buildings in a first step and use representative building models for each category. This paper presents a semi-automated approach for categorizing buildings and creating parametric models for the respective building categories. Using these models, the buildings of a category can be collectively examined for their vulnerability to various impacts. First, this paper introduces open geodata that can be used for this process. For the categorization of the buildings, the collected data is further processed to extract additional information such as building age classes or floor plan geometries of the buildings. This results in a data set, with the help of which the buildings can be categorized. However, information about the load-bearing structure is often missing in the different data sources. By including information on typical construction methods that are associated with the previously determined characteristics (age, floor plan geometry, usage), representative models can be created for individual building categories. In this study, the approach was tested in a selected reference area in Berlin. The results indicate that the presented approach is a promising first step towards deriving geometrical models from open geodata that can be used to evaluate the vulnerability of buildings

Optical spectra of selected Chamaeleon I young stellar objects

We present optical spectra of eight candidate brown dwarfs and a previously known T Tauri star (Sz 33) of the Chamaeleon I dark cloud. We derived spectral types based on the strength of the TiO or VO absorption bands present in the spectra of these objects as well as on the PC3 index of Martin et al. (1999). Photometric data from the literature are used to estimate the bolometric luminosities for these sources. We apply D'Antona & Mazzitelli (1997) pre-main sequence evolutionary tracks and isochrones to derive masses and ages. Based on the presence of Halpha in emission, we confirm that most of the candidates are young objects. Our sample however includes two sources for which we can only provide upper limits for the emission in Halpha; whereas these two objects are most likely foreground/background stars, higher resolution spectra are required to confirm their true nature. Among the likely cloud members, we detect one new sub-stellar object and three transition stellar/sub-stellar sources.Comment: 22 pages - manuscript forma

The Magnificent Seven in the dusty prairie -- The role of interstellar absorption on the observed neutron star population

The Magnificent Seven have all been discovered by their exceptional soft X-ray spectra and high ratios of X-ray to optical flux. They all are considered to be nearby sources. Searching for similar neutron stars with larger distances, one expects larger interstellar absorption resulting in harder X-ray counterparts. Current interstellar absorption treatment depends on chosen abundances and scattering cross-sections of the elements as well as on the 3D distribution of the interstellar medium. After a discussion of these factors we use the comprehensive 3D measurements of the Local Bubble by Lallement et al. 2003 to construct two simple models of the 3D distribution of the hydrogen column density. We test these models by using a set of soft X-ray sources with known distances. Finally, we discuss possible applications for distance estimations and population synthesis studies

Transit observations at the observatory in Grossschwabhausen: XO-1b and TrES-1

We report on observations of transit events of the transiting planets XO-1b and TrES-1 with the AIU Jena telescope in Grossschwabhausen. Based on our IR photometry (in March 2007) and available transit timings (SuperWASP, XO and TLC-project-data) we improved the orbital period of XO-1b (P = 3.941497$\pm$0.000006) and TrES-1 (P = 3.0300737$\pm$0.000006), respectively. The new ephemeris for the both systems are presented.Comment: 4 pages, 2 figure

Edge-on disk around the T Tauri star [MR81] Halpha 17 NE in CrA

Using the speckle camera SHARP at the 3.5m ESO NTT, K\"ohler and collaborators found an object ~3.5 mag fainter in K only 1.3" north-east of the T Tauri star [MR81] Ha 17 in the Corona Australis (CrA) star-forming region, which could be either a brown dwarf or a T Tauri star with an edge-on disk. We attempt to study this faint object in detail. We acquired deep VLT NACO near-infrared images at three epochs to determine, whether [MR81] Ha 17 and the nearby faint object are co-moving and to measure the infrared colors of both objects. We obtained optical and infrared spectra of both objects with the VLT using FORS and ISAAC, respectively, to determine spectral types and temperatures as well as ages and masses. The T Tauri star [MR81] Ha 17 and the faint nearby object have a projected separation of 1369.58 mas, i.e. 178 AU at 130 pc. They share the same proper motion (~5 sigma), so that they most certainly form a bound binary pair. The apparently fainter component [MR81] Ha 17 NE has a spectral type of M2e, while the apparently brighter component [MR81] Ha 17 SW, the previously known T Tauri star, has a spectral type of M4-5e. We can identify a nearly edge-on disk around [MR81] Ha 17 NE by visual inspection, which has a diameter of at least 30 to 50 AU. We are able to detect strong emission lines in [MR81] Ha 17 NE, which are almost certainly due to ongoing accretion. The NE object is detectable only by means of its scattered light. If both objects are coeval (2-3 Myr) and located at the same distance (~130 pc as CrA), then the apparently fainter [MR81] Ha 17 NE is more massive (primary) component with a nearly edge-on disk and the apparently brighter component [MR81] Ha 17 SW is less massive (com- panion). Both are low-mass T Tauri stars with masses of ~0.5 and 0.23 \pm 0.05 solar masses, respectively.Comment: A&A in pres