Disentangling Joint Light Curves Using Photocenter Shifts: A Case Study Using NEOWISE Data

The data collected by the Wide-field Infrared Survey Explorer (WISE, Wright et al. 2010) and its follow-up Near Earth Object (NEO) mission (NEOWISE, Mainzer et al. 2011) represent a treasure trove for variability studies. However, the angular resolution imposed by the primary mirror implies that close double stars are often unresolved. Then, variability of one or both stars leads to motion of the image centroid along the connecting line. Knowledge of the angular separation, derived from higher-resolution imaging which resolves both components, allows disentangling of the joint light curve into individual ones. This is illustrated by the case of SPICY 1474 which featured an outburst several years ago. Removal of the contribution of the nearby companion, which led to a dilution of the burst strength, revealed that it was ~0.5 mag brighter than in the joint light curve. A comparison with light curves from unTimely suggests that utilizing the photocenter shift may lead to more reliable results.