We present our survey for optically faint variable objects using multi-epoch (8−10 epochs over 2−4 years) i′-band imaging data obtained with Subaru Suprime-Cam over 0.918 deg2 in the Subaru/XMMNewton Deep Field (SXDF). We found 1040 optically variable objects by image subtraction for all the combinations of images at different epochs. This is the first statistical sample of variable objects at depths achieved with 8-10m class telescopes or HST. The detection limit for variable components is i′ vari 25.5 mag. These variable objects were classified into variable stars, supernovae (SNe), and active galactic nuclei (AGN), based on the optical morphologies, magnitudes, colors, and opticalmid- infrared colors of the host objects, spatial offsets of variable components from the host objects, and light curves. Detection completeness was examined by simulating light curves for periodic and irregular variability. We detected optical variability for 36 ± 2% (51 ± 3% for a bright sample with i′ < 24.4 mag) of X-ray sources in the field. Number densities of variable obejcts as functions of time intervals t and variable component magnitudes i′ vari are obtained. Number densities of variable stars, SNe, and AGN are 120, 489, and 579 objects deg−2, respectively. Bimodal distributions of variable stars in the color-magnitude diagrams indicate that the variable star sample consists of bright (V 22 mag) blue variable stars of the halo population and faint (V 23.5 mag) red variable stars of the disk population. There are a few candidates of RR Lyrae providing a possible number density of 10−2 kpc−3 at a distance of > 150 kpc from the Galactic center.

Publication Date



This is the pre-print of an article published by the American Astronomical Society. The final, published version is available here: https://doi.org/10.1086/527467

© 2008 The American Astronomical Society

Also archived in: arXiv:0712.3108 v1 Dev 19 2007

Note: imported from RIT’s Digital Media Library running on DSpace to RIT Scholar Works in February 2014.

Document Type


Department, Program, or Center

School of Physics and Astronomy (COS)


RIT – Main Campus