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A new simulation ASL software for VLBI observations is presented. The software is part of the ASL for Windows project. It implements a new class of mathematical algorithms that allow a user to completely simulate any VLBI observation on the MS Windows platform. In particular, simulations of the interferometer structure and its configuration, and simulations of a radio source structure, and noises of the observations are considered. The possibility of introducing new radio telescopes (including space radio telescopes) is also explored and presented in the software. The software is extremely user friendly.
We (Polcaro \& Viotti, 1997) proposed at the VII ADASS Conference a simple slitless spectroscopy method that was effectively employed in the search of very high mass stars, as well as in the identification of optical conterpart of galactic X-Ray sources (se, e.g. Bernabei \& Polcaro, 2002; Israel et al., 1999). However, despite of the great progress made in the last decade, the study of the very high mass stars remains hampered by the lack of statistics and only a few hundred stars with M{, where the most significant features of WR stars and LBV's are directly evident. We tested the method on the well studied galaxy M 101 and we was able to immediately identify all the previously known HII regions with WR star signature. Furthermore, the peculiarity of the spectrum of the M101 active nucleus was also clear. We thus suggest that the new procedure can also be employed for the identification of AGN's in galaxy clusters.
Model Based Corrections to Data from Radiation Damaged Detectors.
Space based CCDs suffer continual bombardment from the hostile radiation environment which gradually degrades their performance and potentially limits their operational lifetime. As part of our effort to enhance the calibration of STIS (a spectrograph onboard the Hubble Space Telescope), we have developed a model of the readout process for CCD detectors suffering from degraded charge transfer efficiency. The model enables us to make predictive corrections to data obtained with such detectors. We present examples of the corrections possible using this technique and compare them to what can be achieved using a more conventional empirical approach. In addition we discuss some of the difficulties of providing users with automated implementations of this this kind of data analysis software.
The Dust InfraRed ToolBox (DIRT - a part of the Web Infrared ToolShed, or WITS, located at http://dustem.astro.umd.edu) is a Java applet for modeling astrophysical processes in circumstellar shells around young and evolved stars. DIRT has been used by the astrophysics community for about 5 years. Users can automatically and efficiently search grids of pre-calculated models to fit their data. A large set of physical parameters and dust types are included in the model database, which contains over 500,000 models.
We are adding new functionality to DIRT to support IR/submm missions such as SIRTF, SOFIA, and Herschel. A new Instrument module allows for plotting of the model points convolved with the spatial and spectral responses of the selected instrument. This lets users better fit data from specific instruments. Currently, we have implemented modules for the Infrared Array Camera (IRAC) and Multiband Imaging Photometer (MIPS) on board SIRTF.
The ESA satellite Planck, scheduled for launch in 2007, is the 3rd generation of CMB space missions (after COBE and WMAP) designed to produce measurements of temperature anisotropy over full sky. The Low Frequency Instrument onboard Planck will cover the frequency range 30 - 70 GHz. Ground Tests are a fundamental milestone within the development of LFI, since they allow both the validation of the instrument and the collection of relevant information about its electronics which will increase the value of the data collected during the flight, allowing a better calibration and a more powerful diagnostic. For this reason it is important that not only the final reports, but all the information generated by the ground tests is collected and stored within the Instrument Ground Segment, in order to allow its retrieval and analysis along the mission and the proprietary phase for instrument calibration and diagnostic. More over Data Handling is fundamental during the tests themselves since many organization and sites (industry, instrument consortium and the ground segment) will be involved in this activity generating an amount of information equivalent to several percent of the whole information produced by the mission.
The Space Interferometry Mission (SIM) will provide unprecedented precision of micro-arcsecond (Î?as) for searching extra-solar planets and possible life in the universe. SIM will also revolutionize our understanding of the dynamics and evolutions of the local universe by hundred-fold improvements of astrometry measurements. SIM has two guide interferometers to provide stable orientations of the baseline, and a science interferometer to measure stellar fringes. All of SIM measurements are based on the fringes on the CCD detector. In order to do fringe tracking on interferometers it is necessary to develop new algorithms to calculate fringe parameters fast and accurately. For the high-speed fringe tracking systems with photon starve measurements phasor algorithms of fringe tracking are compared with other techniques. Wide wavelength coverage in applying phasor algorithms is demonstrated. The results of MAM testbed on fringe tracking are analyzed. The new phasor algorithms for compressing data rate of flight system are studied.
This work is supported under contract with the National Aeronautics and Space Administration.
As part of our effort to support the calibration of the Chandra X-ray Observatory's High Resolution Mirror Assembly (HRMA), we often have to run many computationally intensive simulation programs. In order to maximize our efficiency we have written a suite of programs to distribute batch jobs by exploiting idle workstations during non-work hours. We will discuss the system architecture of the Scheduler programs which were written to facilitate the tedious task of submitting a large number of batch jobs. As a demonstration of the capabilities of the Scheduler program, we will describe its use in the analysis of flight calibration data. We will also compare the efficiency of the Scheduler to the Sun's Grid Engine.
During early flight operation, the Chandra X-ray Observatory's Advanced CCD Imaging Spectrometer (ACIS) suffered degradation of charge transfer inefficiency (CTI) due to radiation induced charge trapping. The ACIS front-illuminated detector CTI has significantly degraded in time with respect to the intrinsic energy resolution of the chips. In this presentation we use the degradation of CTI in the ACIS camera as an example of how software was adapted to fix a significant and unforeseen post-launch problem in on-board hardware. We will discuss the impact of CTI on events, rmf and gain files. Then, we will discuss the software updates necessary to alleviate the degradation effects and to improve spectral resolution. Finally, we will highlight other ACIS hardware problems and their corresponding software solutions. This work was supported by NASA contract NAS8-39073.
The Chandra X-Ray Observatory was launched in July 1999, and is thus in its fifth year on-orbit. The Monitoring and Trends team at the Chandra X-Ray Center (CXC) is charged with tracking observatory performance parameters to optimize the mission's science return. We have built from scratch an IDL-based system, called 'dtrend' (derivative trending), for visualizing and quantifying long-term trends. Data are input from our databases of over 600 engineering mnemonics, averaged on 5 minute intervals over the course of the entire mission. Dtrend computes the mean, standard deviation, first derivative and second derivative for each parameter. The derivatives are then used to predict the next 6 month cycle. Output is presented via web pages with statistical summary tables and graphics color-coded to highlight threat level or potential problems. This paper will discuss the algorithms and metrics used to predict future behavior based on previous trends and how the CXC can efficiently identify, track, and possibly curtail problems to extend the length and quality of the Chandra science mission. This work is supported by NASA contract NAS8-39073.
Instrument physical models are now being employed to enhance the calibration 2D echelle data on the ground (VLT UVES) and in orbit (HST STIS).
In order to make full use of the predictive power inherent in such models it is vital that the models are validated against reference calibration data frames with adequate methods.
In the present poster we describe results obtained by a study on the intrinsic precision and shortcomings of line-centering algorithms used to locate the monochromatic slit images in 2D echelle wavelengths calibration frames from HST STIS spectrograph. We started with a 2D Gaussian profile fitting implementing the Lavengerg Marquardt (LM) method, improved the line shape model to reflect better the actual elongated slit images, and investigated other methods to enhance robustness under conditions of extremely low signal.
We discuss problems and possible solutions for the extreme low signal-to-noise domain.
The calculation of flux upper limits in the source-free (background) regions of photon-limited images is complicated by instrumental and statistical modelling and requires non-trivial computational effort. We propose a scheme where the properties of source-free image regions are pre-calculated and catalogued in a compact form to allow rapid estimation of flux limits and statistical properties of the background. We examine the expected speed-up in massive all-sky queries resulting from such a system to pre-screen coordinate requests before running a full analysis.
To enhance the ability of astronomers to perform simulations of deep galaxy fields, we are developing a web simulator with this express purpose. Because our simulator uses real galaxy templates extracted from deep multicolor HST observations (the recently released GOODS fields), it represents a distinct improvement over the relatively rudimentary simulation tools currently available (artdata or skymaker) or standardly available exposure time calculators, both for the purposes of visualization and for making comparisons against real observations. Objects on these images are generated by a pixel-by-pixel resampling of objects, paying special attention to the best-fit pixel spectral energy distributions. Users can specify simulations with up to five different filters, with different pixel sizes, point spread functions, and zero points depending upon the passband. For our engine, we use the BUCS software already used in a variety of faint galaxy work. To facilitate these complex simulations we have begun to develop a simple web-base interface to the BUCS engine. While the site has only recently begun construction, long term plans may include adding galaxy templates from a variety of different surveys as well as the ability to perform no-evolution simulations based upon local, intermediate-redshift, and high-redshift surveys. Cameras from a number of well-known telescopes (HST, Keck, VLT) should also be a welcome addition. We see this as being an extremely useful tool come proposal time.
The reduction of raw echelle data is a straightforward, although quite complicated task, where the reliability of the final result strongly depends on precise accomplishment of each step. Therefore the choice of reduction package best suited for the particular instrument is very important.
We have tested several software packages commonly used for reduction of data from fiber-fed echelle spectrographs. We used them for processing of raw CCD echellegram of several early-type stars secured with HEROS fiber echelle spectrograph currently installed at Cassegrain focus of Ondrejov observatory 2m telescope.
The main interest was focused on the methods and algorithms of determination of dispersion relation. The spectra were reduced until the individual one-dimensional lambda-calibrated orders were obtained. The precision of wavelength calibration was then checked by measurement of radial velocity of telluric lines.
The Advanced Technology Solar Telescope (ATST) is intended to be the premier solar observatory for experimental physics. Unlike its night-time counterparts which operate with relatively fixed instrument sets, ATST's science goals and requirements are best met by a laboratory style instrument configuration, where scientific requirements often require that instrumentation be assembled by scientists to meet the unique demands of each experiment's goals. In order to maximize observing efficiency the ATST software and control systems must be designed to operate smoothly in this environment.
In order to meet the requirement of providing flexibility in a laboratory style operations environment, the control system uses a Virtual Instrument Model. This report introduces this model and briefly outlines its salient characteristics. The aim it to provide some insight into the approach being proposed as part of the overall software and controls design and to provide a foundation for discussions on the advantages and disadvantages of using a virtual instrument model.
In the recent years, type Ia supernovae studies took considerable importance in cosmology, owing to the fact that they are probably standard candles. To get rid of this probably, it is necessary to study a large sample of nearby supernovae in an homogeneous way. This led a Franco-American consortium to build the Supernova Integral Field Spectrograph (SNIFS), which will aim at observing more than 400 supernovae during the next 2-3 years. To be able to help the instrument definition, to predict the instrument performances and to allow for an early development of the data reduction software, we have developed a numerical simulator of this instrument as realistic as possible. This implies to account for all physical phenomena that, one way or another, disturb the incident object wave front. We will describe the strategy adopted to treat all the disturbances and the different steps of the wave-front propagation through the instrument. The model we used is based mainly on Fourier optics and use Zernike polynomials phase masks to handle the effects of the atmosphere and the optical aberrations of the instrument.
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