Photometric observations of selected, optically bright quasars for Space Interferometry Mission and other future celestial reference frames

TL;DR

This study presents photometric data for 235 extragalactic objects, aiding the selection of celestial reference frame targets for the Space Interferometry Mission and future astrometric applications.

Contribution

It provides the first extensive photometric dataset for potential SIM targets, highlighting variability and discrepancies with existing catalogs to support mission planning.

Findings

36% of sources differ by over 1 mag from catalog values

10 sources differ by over 3 mag, indicating significant variability

The dataset supports long-term variability studies of reference frame sources

Abstract

Photometric observations of 235 extragalactic objects that are potential targets for the Space Interferometry Mission (SIM) are presented. Mean B, V, R, I magnitudes at the 5% level are obtained at 1 - 4 epochs between 2005 and 2007 using the 1-m telescopes at Cerro Tololo Inter-American Observatory and Naval Observatory Flagstaff Station. Of the 134 sources which have V magnitudes in the Veron & Veron-Cetty catalog a difference of over 1.0 mag is found for the observed-catalog magnitudes for about 36% of the common sources, and 10 sources show over 3 mag difference. Our first set of observations presented here form the basis of a long-term photometric variability study of the selected reference frame sources to assist in mission target selection and to support in general QSO multi-color photometric variability studies.