The 2001-2003 Low State of Nova Lacertae 1950 (DK Lac)

TL;DR

This study presents extensive photometric observations of DK Lac over 19 years, revealing a low state, increased variability during the low state, and long-term brightness decline, with implications for nova hibernation theories.

Contribution

It provides the first detailed long-term photometric analysis of DK Lac's low state, including spectral data, and discusses the implications for nova hibernation scenarios.

Findings

No periodicities detected in the data.

Variability in the low state is about twice that in the high state.

Brightness declined by 0.2 mag over 19 years.

Abstract

We report on extensive photometry of DK Lac obtained during the interval 1990-2009, which includes a 2 mag low state during 2001-2003. Much of the photometry consists of exposures obtained with a typical spacing of several days, but also includes 26 sequences of continuous photometry each lasting 2 to 7 hours. We find no evidence for periodicities in our data. We do find that the random variations in the low state are ~2x those in the high state, when expressed in magnitudes. The lack of orbital-time-scale variations is attributed to the nearly face-on presentation of the disk. There is a 0.2 mag decline in the high state brightness of the system over 19 years, which is consistent with the behavior of other old novae in the decades following outburst. High-state spectra are also presented and discussed. We find that the equivalent width of H$\alpha$ falls by ~2x from 1991 to 2008. The photometric properties are discussed in the context of the hibernation scenario for the behavior of novae between outbursts, in which we conclude that low states in old novae are probably unrelated to their possible entrance into hibernation.