1,721,006 research outputs found
Prospects for a global heterogeneous telescope network (HTN)
No full textThe goal of this meeting is to make real progress towards the creation of a global, heterogeneous network of telescopes (HTN). The purpose of this introductory talk is to set the stage for several days of discussion about how we might create such a network. I describe the generic structure of an HTN, the roles of the necessary components, describe the interfaces needed, and discuss the management problems, and the need for a market model. (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
RTML: remote telescope markup language and you
No full textIn order to coordinate the use of robotic and remotely operated telescopes in networks-like Gottingen's MOnitoring NEtwork of Telescopes (MONET)-a standard format for the exchange of observing requests and reports is needed. I describe the benefits of Remote Telescope Markup Language (RTML), an XML-based protocol originally developed by the Hands-On Universe Project, which is being used and further developed by several robotic telescope projects and firms
Remote telescope markup language (RTML)
No full textRemote Telescope Markup Language (RTML) is an XML-based document format for the generic description of astronomical observation requests. The latest versions (3.x) constitute a substantial modification of the previous published standard (RTML 2.1), incorporating a highly restructured syntax and many new features necessary in order to permit the use of RTML to organize and operate heterogeneous networks of telescopes with complex instruments and to assist both the users and the servers in the preparation, modification, and execution of remote observing requests. (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
RTML: remote telescope markup language and you
No full textIn order to coordinate the use of robotic and remotely operated telescopes in networks-like Gottingen's MOnitoring NEtwork of Telescopes (MONET)-a standard format for the exchange of observing requests and reports is needed. I describe the benefits of Remote Telescope Markup Language (RTML), an XML-based protocol originally developed by the Hands-On Universe Project, which is being used and further developed by several robotic telescope projects and firms
The symptoms and causes of CV low-states
No full textI present recent results on the symptoms and causes of extended photometric low-states seen in a large fraction of cataclysmic variables and particularly well in AM Her stars. The most likely cause of low-states - stellar starspots on the secondary stars appearing at the L-1-point - implies that the light curves of AM Her stars can be used to constrain the spottedness of the secondaries. Using the AAVSO light and a flux-dependent bolometric correction, a statistical model for the spots near the L-1-point of AM Her itself is derived. The implied density of spots can only be explained if the spottedness of the L-1-point is unusual, for instance if the observed prominences are forced to wandering down the Roche potential towards the L-1-point. The polar results can be easily applied to VY Sd low-states if the latter stars contain hot whits dwarfs: the irradiated discs can be rapidly drained of material, preventing the occurrence of dwarf nova eruptions during near total cessations of mass-transfer. (C) 2000 Elsevier Science B.V. All rights reserved
The MONET project and beyond
No full textThe "MOnitoring NEtwork of Telescopes" (MONET) consists of two 1.2-m imaging telescopes funded by the Alfried Krupp von Bohlen und Halbach Foundation and the Georg-August-Universitat Gottingen and will be operated by the McDonald Observatory in West Texas and the South African Astronomical Observatory at Sutherland. Scheduled to go into full operation in 2005, it will be used to perform a variety of monitoring and survey observations over the whole sky, to aid observations by satellites and 10m-class telescopes like the VLT, HET and SALT telescopes, and will be available to participating school classes all over the world. Through our development and use of Remote Telescope Markup Language (RTML), MONET should be one of the kernels of a growing international network of heterogeneous telescopes
Estimating the baryonic masses of face-on spiral galaxies from stellar kinematics
No full textThe kinematic dispersions of disc stars can be used to measure the dynamic contributions of baryons to the rotation curves of spiral galaxies and hence to trace the amount and distribution of the remaining dark matter. However, the simple single-component infinite disc model traditionally used to convert stellar dispersions to mass densities is no longer adequate. The dark matter halo has a significant effect upon the stellar dispersions for any non-maximal disc. The correction for cuspy dark matter haloes is particularly large, suggesting that such models are not consistent with the observed stellar dispersions. When a more realistic model for the vertical gravity of the disc is used, the derived stellar surface densities are generally larger (smaller) for disc radii smaller (larger) than 2.3 times the radial scalelength. When the vertical gravity correction is applied to the radially resolved stellar mass-to-light ratios derived by the DiskMass consortium, the true values are not constant but decrease with radius, as expected from photometric colour gradients, and the true mass scalelengths are about 80 per cent of the photometric scalelengths. The effects of a thin gaseous disc are larger than expected, especially when an allowance is made for optically thick or CO-dark gas. The presence of a thick-disc stellar component has severe consequences, particularly if its radial scalelength is smaller than that of the thin disc, as it appears to be in the Milky Way
The difficulty of measuring the local dark matter density
No full textThe analysis of the vertical velocity dispersion of disc stars in the local Milky Way is the most direct astronomical means of estimating the local dark matter density, ρDM. Current estimates for ρDM based on the mid-plane dynamic density use a local baryonic correction that ignores the non-local effects of spiral structure and significantly underestimates the amount of dynamically relevant gas now known to be present in the ISM; the additional gas plus the remaining uncertainties make it practically impossible to measure ρDM from mid-plane kinematics alone. The sampling of inhomogeneous tracer populations with different scale-heights and scale-lengths results in a systematic increase in the observed dispersion gradients and changes in the nominal density distributions that, if not properly considered, can be misinterpreted as a sign of more dark matter. If the disc gravity is modelled locally using an infinite disc, the local variation in the vertical gravity due to the globally exponential disc components results in an underestimation of the baryonic contribution by as much as ~40%. Given only the assumptions of stationarity, an axially and vertically symmetric disc, doubly exponential tracer and mass-component density profiles, a phenomenologically justified model for the cross-dispersion component σRz, and a realistic model for gz(z), it is possible to solve the full vertical Jeans equation analytically for the vertical dispersion σz(z) and hence test the robustness of previous attempts at measuring ρDM. When the model parameters for σRz are estimated from SEGUE G dwarf star data, it is still not possible to explain the difference in behaviour seen in the simple thick- and thin-disc datasets reported by Buedenbender et al. (2014, MNRAS, submitted). Rather than being a fundamental problem with the kinematical model, this effect appears to be a further sign of the difficulty of defining and handling kinematically homogeneous tracer populations
Optimising optimal image subtraction
No full textDifference imaging is a technique for obtaining precise relative photometry of variable sources in crowded stellar fields and, as such, constitutes a crucial part of the data reduction pipeline in surveys for microlensing events or transiting extra-solar planets. The Optimal Image Subtraction (OIS) algorithm of Alard & Lupton (1998) permits the accurate differencing of images by determining convolution kernels which, when applied to reference images with particularly good seeing and signal-to-noise (SIN), provide excellent matches to the point-spread functions (PSF) in other images of the time series to be analysed. The convolution kernels are built as linear combinations of a set of basis functions, conventionally bivariate Gaussians modulated by polynomials. The kernel parameters, mainly the widths and maximal degrees of the basis function model, must be supplied by the user. Ideally, the parameters should be matched to the PSF, pixel-sampling, and SIN of the data set or individual images to be analysed. We have studied the dependence of the reduction outcome as a function of the kernel parameters using our new implementation of OIS within the IDL-based TRIPP package. From the analysis of noise-free PSF simulations of both single objects and crowded fields, as well as the test images in the ISIS OIS software package, we derive qualitative and quantitative relations between the kernel parameters and the success of the subtraction as a function of the PSF widths and sampling in reference and data images and compare the results to those of other implementations found in the literature. On the basis of these simulations, we provide recommended parameters for data sets with different SIN and sampling. (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinhei
Substantial stream-disc overflow found in three-dimensional SPH simulations of cataclysmic variables
No full textWe study numerically the interaction of the infalling gas stream and the rim of the accretion disc in cataclysmic variables. The simulations were performed with a smoothed particle hydrodynamics scheme with high spatial resolution. Parameters of the systems AM CVn, OY Car, DQ Her, U Gem and IP Peg were used for the simulations. The simulations cover a wide range of orbital periods, mass ratios and mass transfer rates, as well as different thermal states of the accretion disc. The main result of this study is that the accretion stream is not stopped at the impact region (the bright spot at the outer rim of the disc). In fact, after undergoing the shock interaction, most of the matter is deflected vertically and flows in a more or less diffuse stream to inner parts of the disc, hitting the disc surface close to the circularization radius at orbital phase 0.5. This is a common feature in all systems for all simulated parameters. This stream overflow can cause the X-ray absorption dips observed in cataclysmic variables (CVs) and low-mass X-ray binaries (LMXBs) around orbital phase 0.7, if the inclination is at least 65 degrees. Under certain circumstances, namely a sudden increase of the mass transfer rate from the secondary or a rather small disc, parts of the overflowing stream bounce off the disc surface after hitting it at orbital phase approximate to0.5. Another absorption region can be expected around orbital phase 0.2. In our simulations most of the infalling matter reaches the inner disc very quickly. This must alter the evolution of the quiescent disc and the outburst behaviour considerably compared with purely Viscous transport of the material through the disc from the outer rim, and therefore should be taken into account in dwarf nova outburst cycle calculations. To our knowledge, the consequences of such a massive stream overflow for the dwarf nova outburst cycle have not been considered yet
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