Color Variability of HBC 722 in the Post-Outburst Phases

TL;DR

This study monitored HBC 722's post-outburst phases through multi-band photometry, revealing color changes, periodic signals, and flickering activity indicative of evolving physical conditions in the star's emitting regions.

Contribution

It provides detailed photometric analysis of HBC 722's post-outburst behavior, identifying periodicities and flickering, which enhances understanding of the star's physical changes after outburst.

Findings

Detected three periodic signals around 1, 6, and 10 days.

Observed day-scale variability and possible intra-day flickering.

Classified post-outburst phases based on brightness and color variations.

Abstract

We carried out photometric observations for HBC 722 in SDSS r, i and z bands from 2011 April to 2013 May with a Camera for Quasars in Early uNiverse attached to the 2.1m Otto Struve telescope at McDonald Observatory. The post-outburst phenomena were classified into five phases according to not only brightness but also color variations, which might be caused by physical changes in the emitting regions of optical and near-infrared bands. A series of spectral energy distribution (SED) is presented to support color variations and track the time evolution of SED in optical/near-infrared bands after the outburst. Given two years of data, possible periodicities of r, i and z bands were checked. We found out three families of signals around ~6, ~10 and ~1 days in three bands, which is broadly consistent with Green et al. (2013). We also examined short term variability (intra-day and day scales) to search for evidences of flickering by using the micro-variability method. We found clear signs of day scale variability and weak indications of intra-day scale fluctuations, which implies that the flickering event occurs in HBC 722 after outburst.