Showing papers by "Edwin A. Valentijn published in 2007"

The Future of Photometric, Spectrophotometric and Polarimetric Standardization

Abstract: The OmegaCAM wide-field imager will start operations at the ESO VLT Survey Telescope at Paranal in 2007. The photometric calibration of OmegaCAM data depends on standard-star measurements that cover the complete 1 × 1 FoV of OmegeaCAM. A catalog fullfilling this requirement for 8 Landolt equatorial fields, denoted the OmegaCAM Secondary Standards Catalog, will be constructed from OmegaCAM observations during the first year of operations. Here we present the ‘Preliminary Catalog’ which will be used to bootstrap the construction of the OmegaCAM Secondary Standards Catalog. Thus the Preliminary Catalog will be used to assess the performance of OmegaCAM+VST early-on. The catalog is based on WFC data from the INT.

HST/ACS observations of shell galaxies : inner shells, shell colours and dust

Abstract: Context. Shells in Elliptical Galaxies are faint, sharp-edged features, believed to provide evidence for a merger event. Accurate photometry at high spatial resolution is needed to learn on presence of inner shells, population properties of shells, and dust in shell galaxies. Aims. Learn more about the origin of shells and dust in early type galaxies. Methods. V −I colours of shells and underlying galaxies are derived, using HST Advanced Camera for Surveys (ACS) data. A galaxy model is made locally in wedges and subtracted to determine shell profiles and colours. We applied Voronoi binning to our data to get smoothed colour maps of the galaxies. Comparison with N-body simulations from the literature gives more insight to the origin of the shell features. Shell positions and dust characteristics are inferred from model galaxy subtracted images. Results. The ACS images reveal shells well within the effective radius in some galaxies (at 0.24re = 1.7 kpc in the case of NGC 5982). In some cases, strong nuclear dust patches prevent detection of inner shells. Most shells have colours which are similar to the underlying galaxy. Some inner shells are redder than the galaxy. All six shell galaxies show out of dynamical equilibrium dust features, like lanes or patches, in their central regions. Our detection rate for dust in the shell ellipticals is greater than that found from HST archive data for a sample of normal early-type galaxies, at the 95% confidence level. Conclusions. The merger model describes better the shell distributions and morphologies than the interaction model. Red shell colours are most likely due to the presence of dust and/or older stellar populations. The high prevalence and out of dynamical equilibrium morphologies of the central dust features point towards external influences being responsible for visible dust features in early type shell galaxies. Inner shells are able to manifest themselves in relatively old shell systems.

Astro-WISE: Chaining to the Universe

Abstract: The recent explosion of recorded digital data and its processed derivatives threatens to overwhelm researchers when analysing their experimental data or when looking up data items in archives and file systems. While current hardware developments allow to acquire, process and store 100s of terabytes of data at the cost of a modern sports car, the software systems to handle these data are lagging behind. This general problem is recognized and addressed by various scientific communities, e.g., DATAGRID/EGEE federates compute and storage power over the high-energy physical community, while the astronomical community is building an Internet geared Virtual Observatory, connecting archival data. These large projects either focus on a specific distribution aspect or aim to connect many sub-communities and have a relatively long trajectory for setting standards and a common layer. Here, we report "first light" of a very different solution to the problem initiated by a smaller astronomical IT community. It provides the abstract "scientific information layer" which integrates distributed scientific analysis with distributed processing and federated archiving and publishing. By designing new abstractions and mixing in old ones, a Science Information System with fully scalable cornerstones has been achieved, transforming data systems into knowledge systems. This break-through is facilitated by the full end-to-end linking of all dependent data items, which allows full backward chaining from the observer/researcher to the experiment. Key is the notion that information is intrinsic in nature and thus is the data acquired by a scientific experiment. The new abstraction is that software systems guide the user to that intrinsic information by forcing full backward and forward chaining in the data modelling.

Astro-WISE: Chaining to the Universe

Abstract: The recent explosion of recorded digital data and its processed derivatives threatens to overwhelm researchers when analysing their experimental data or looking up data items in archives and file systems. While current hardware developments allow the acquisition, processing and storage of hundreds of terabytes of data at the cost of a modern sports car, the software systems to handle these data are lagging behind. This problem is very general and is well recognized by various scientific communities; several large projects have been initiated, e.g., DATAGRID/EGEE {http://www.eu-egee.org/} federates compute and storage power over the high-energy physical community, while the international astronomical community is building an Internet geared Virtual Observatory {http://www.euro-vo.org/pub/} (Padovani 2006) connecting archival data. These large projects either focus on a specific distribution aspect or aim to connect many sub-communities and have a relatively long trajectory for setting standards and a common layer. Here, we report first light of a very different solution (Valentijn & Kuijken 2004) to the problem initiated by a smaller astronomical IT community. It provides an abstract scientific information layer which integrates distributed scientific analysis with distributed processing and federated archiving and publishing. By designing new abstractions and mixing in old ones, a Science Information System with fully scalable cornerstones has been achieved, transforming data systems into knowledge systems. This break-through is facilitated by the full end-to-end linking of all dependent data items, which allows full backward chaining from the observer/researcher to the experiment. Key is the notion that information is intrinsic in nature and thus is the data acquired by a scientific experiment. The new abstraction is that software systems guide the user to that intrinsic information by forcing full backward and forward chaining in the data modelling.

The Secondary Standards Programme for OmegaCAM

Abstract: The OmegaCAM wide-field imager will start operations at the ESO VLT Survey Telescope at Paranal in 2007. The photometric calibration of OmegaCAM data depends on standard-star measurements that cover the complete 1°×1° FOV. A catalog fullfilling this requirement for 8 Landolt equatorial fields, denoted the OmegaCAM Secondary Standards Catalog, will be constructed from OmegaCAM observations during the first year of operations. We present the `Preliminary Catalog' which will be used to bootstrap the construction of the OmegaCAM Secondary Standards Catalog. Thus the Preliminary Catalog will be used to assess the performance of OmegaCAM+VST early-on. The catalog is based on WFC data from the INT.

Searching for known asteroids in the WFI archive using Astro-WISE

Abstract: This study is aimed at deriving new and/or improved photometry for known asteroids using Wide Field Imager (WFI) archival images. We present studies on a set of 354 asteroid occurrences of 144 dierent asteroids found on WFI images using the Astro-WISE system. The set is likely to be polluted with 3% non-asteroids. The set was found using a set of 798 asteroid predictions obtained with the Skybot web service. So for 44% of the predictions, the asteroids were found on the WFI frames. Identifying the asteroids on the frames was done by comparing sizes and phase angles of found sources within 15 arcsec of the predicted position with predicted values. Of the found asteroids, 88% were found within 3 arcsec from their predicted positions. The most plausible cause for not finding 56% of the asteroids is the big uncertainty in their orbital elements. Nevertheless, 56% of the found asteroids were unnumbered asteroids, asteroids of which their orbital elements are not yet known with high precision.

HST/ACS observations of shell galaxies: inner shells, shell colours and dust

Abstract: AIM:Learn more about the origin of shells and dust in early type galaxies. METHOD: V-I colours of shells and underlying galaxies are derived, using HST Advanced Camera for Surveys (ACS) data. A galaxy model is made locally in wedges and subtracted to determine shell profiles and colours. We applied Voronoi binning to our data to get smoothed colour maps of the galaxies. Comparison with N-body simulations from the literature gives more insight to the origin of the shell features. Shell positions and dust characteristics are inferred from model galaxy subtracted images. RESULT: The ACS images reveal shells well within the effective radius in some galaxies (at 1.7 kpc in the case of NGC 5982). In some cases, strong nuclear dust patches prevent detection of inner shells. Most shells have colours which are similar to the underlying galaxy. Some inner shells are redder than the galaxy. All six shell galaxies show out of dynamical equilibrium dust features, like lanes or patches, in their central regions. Our detection rate for dust in the shell ellipticals is greater than that found from HST archive data for a sample of normal early-type galaxies, at the 95% confidence level. CONCLUSIONS: The merger model describes better the shell distributions and morphologies than the interaction model. Red shell colours are most likely due to the presence of dust and/or older stellar populations. The high prevalence and out of dynamical equilibrium morphologies of the central dust features point towards external influences being responsible for visible dust features in early type shell galaxies. Inner shells are able to manifest themselves in relatively old shell systems.