Long‐Term Optical and X‐Ray Observations of the Old Novae DI Lacertae and V841 Ophiuchi1

Abstract

ABSTRACT. We present an analysis of ground-based optical photometry and spectroscopy and Rossi X-Ray T iming Explorer X-ray observations of the old novae DI Lacertae and V841 Ophiuchi. Our optical photometry data (obtained with the automated photometry telescope RoboScope) comprise an almost decade-long light curve for each star, while the contemporaneous spectroscopy and X-ray observations repeatedly sampled each nova during separate intervals of B45È55 days in length. The long-term optical light curves of both novae reveal quasi-periodic variability on typical timescales of D30È50 days with amplitudes of *V D 0.4È0.8 mag. V841 Oph also displays a long-term, sinusoidal modulation of its optical light on a timescale of 3.5È5 yr. The optical spectra of these novae display quite di †erent characteristics from each other, with DI Lac showing narrow Balmer emission cores situated in broad absorption troughs while V841 Oph exhibits strong single-peaked Balmer, He I, and He II emission lines. We Ðnd little change between spectra obtained during di †erent optical brightness states. The X-ray count rates for both novae were very low counts s~1), and there was no reliable correlation between X-ray and optical brightness. The ([1.5 combined X-ray spectrum of DI Lac is best Ðt by a bremsstrahlung emission model (with kT D 4 keV and cm~3) ; the X-ray spectrum of V841 Oph is too weak to allow model Ðtting. We discuss the N H \ 1.8 ] 1022 possible origin of variability in these old novae in terms of magnetic activity on the secondary star, dwarf nova type disk instabilities, and the "" hibernation ÏÏ scenario for cataclysmic variable stars.

The fight for accretion: discovery of intermittent mass transfer in BB Doradus in the low state

“…Similar quasi‐periodic brightenings have been observed in other nova‐like CVs in the high state with similar recurrence times (see e.g. Honeycutt, Robertson & Turner 1998; Hoard et al 2000). The cause that produces this variability is still unknown, but mass transfer oscillations due to migration of starspots under the L1 point (Livio & Pringle 1994) and stunted dwarf nova outbursts (Honeycutt et al 1998) are among the proposed mechanisms.…”

Long-term photometric behavior of the eclipsing Z Cam-type dwarf nova AY Psc

“…These events are best characterized as the small amplitude outbursts, which have properties very similar to the stunted outbursts seen in some NLs (e.g. Honeycutt et al 1995Honeycutt et al , 1998Honeycutt et al , 2001Honeycutt et al , 2014Warner 1995;Hoard et al 2000;Ramsay et al 2016). Table 2 summarizes the properties of stunted outbursts in AY Psc.…”

The 1991-2012 Light Curve of the Old Nova Hr Lyrae

“…Such variations have been studied in connection with possible chromospheric activity cycles on the secondary star in the range 3-15 yr (e.g., Warner 1988;Bianchini 1990). However, shorter variations in the range 30-50 days have also been reported for some old novae (e.g., Della Valle & Rosino 1987;Hoard et al 2000). In HR Lyr the quasi-periodic variations occur mostly in the range 60-300 days, and mostly take the form of sawtoothedlike ramps in the light curve.…”