Searching for secondary photometric standards for wide FOV and fast transients observations

Author: Alexei Pozanenko

Abstract: We discuss an approach to the automatic selection of secondary photometric standards. In particular the problem of photometric standards arises in a large FOV and real-time photometric observations such as Gamma-ray burst (GRB). Quality of the selected standards influences the photometric light curve of the values obtained by different observatories. It is particularly important, since for the most of the afterglows the following cross-calibration is not performed, and the photometric light curve data are collected from the GCN original publications network. Some of parameters of cross identified sources of various catalogs which to be identified as candidates in the photometric standards are point-like objects, non-variable stars, non-extreme color stars etc.

For the selection of appropriate secondary photometric standards a conceptual approach to solving the problem has been applied. The main distinguishing feature of the approach consists in formulation of the problem in terms of the application domain, independently of particular resources (catalogs, services, photometric systems). Classes of application objects and functions expressing data transformations required for solving the problem are specified declaratively at the mediator layer that is provided for virtual integration of heterogeneous information resources hiding them from the application. Specifically the conceptual problem solving approach is implemented in the hybrid architecture combining mediation support facilities with the AstroGrid. Mapping of the resource schemas into the mediator metadata is performed in accordance with the global/local-as-view data integration approach.

For the secondary standards search problem two subject mediators have been specified. One of them actually performs the solution of the standards selection, and another, auxiliary one provides for elimination of the variable stars during the selection process. While solving the problem, a set of real catalogs to be used can be changed without changing the specifications of the mediators and supporting tools. Currently, a set of catalogs used includes: SDSS, 2MASS, USNO-A2.0, USNO-B1.0, ASAS, GSC, UCAC, GCVS, VSX, NVSS, NED. The secondary standards search is organized in real time as a follow-up to a GRB event notification and using in GRB follow-up networks.