Time-Domain Astrophysics in crowded star fields. Globular clusters and variable star searches.
R. Figuera Jaimes
University of Saint Andrews
D. M. Bramich, Jesper Skottfelt, N. Kains, K. Horne
The study of 17 globular clusters is presented. The sample was analyzed by using Electron-Multiplying CCDs (EMCCDs) with the aim to obtain a better resolution of the very crowded central regions of those stellar systems. Due to the amplification of the signal in the extended readout register of the EMCCD and by taking images with very short exposures times the effect of the turbulence in the atmosphere was effectively frozen and minimized. The resulting images were shifted and added to produce images with normal exposures times which were used to explore the central region of the clusters for previously unknown variable stars.

Using these techniques the resolution of the images approached those obtained using space telescopes, the blending between stars was avoided or minimized and there were not saturated stars in the field. So that, a more complete analysis of the images was done as well as a better census of the variable stars in those stellar systems.

The analyzes of 5 cluster was already published with a discovery of 64 previously unknown variables from which most of them are variables in the red giant branch (RGB), ~10 are RR Lyrae and 4 are W Virginis type.

There are 12 clusters more in preparation with ~250 candidates to be previously unknown variables where ~200 belong to the RGB and ~50 belong to the horizontal branch (HB).

A survey using CCDs is also been done to have a wider covering of the stars in the field of the clusters.