Extended Deep Minimum and Subsequent Brightening of RX And in 1996-1997

Abstract

We discovered that RX And, one of prototypical Z Camtype dwarf novae, underwent a deep, extended faint state in 1996-1997. Time-resolved photometry at the bottom of the fading revealed the presence of strong flickering, and the absence of detectable orbital modulation. This finding indicates that the mass-transfer remained even at the deepest minimum of the fading, contrary to what was observed in a deep minimum of a VY Scl-type star, MV Lyr. RX And subsequently underwent a brightening (outburst) during its recovery stage. The photometric and spectroscopic characteristics of the brightening significantly differed from those of ordinary outbursts of RX And, and are considered to resemble an inside-out type outburst of a long-period dwarf nova. An examination of historical visual observations revealed the possible presence of ∼10-yr periodicity, which is close to what has been proposed for MV Lyr. The common observed features between RX And and VY Scl-type stars may suggest a common underlying mechanism for producing temporary deep fadings. The departure from the disk instability model, as observed in VY Scl-type stars, was not apparent in the present fading of RX And. In conjunction with the recently published Hubble Space Telescope observation during the same fading, we can conclude that the phenomenological difference from the VY Scl-type fading is understood as a smaller effect of irradiation on the accretion disk in RX And.

Detection of Short Fading Episodes in Two Dwarf Novae from VSNET Observations

“…The phenomenon in RX And seems to be more easily understandable with a temporary reduction in masstransfer rate, since RX And has already shown a much longer episode of reduced mass-transfer (Sion et al 2001;Kato et al 2002d;Schreiber et al 2002). Although the exact cause of reduced mass-transfer in VY Scl-type stars is not yet clarified, the starspot hypothesis (Livio, Pringle 1994) would be a promising explanation.…”

“…Schreiber et al (2002) even suggested that RX And is a transitional object between Z Cam-type dwarf novae and VY Scl-type stars (cf. Warner, van Citters 1974;Warner 1995;Greiner 1998), although Kato et al (2002d) reported difference between fadings in RX And and in VY Scl-type stars. Schreiber et al (2002) examined the historical light curve of RX And and reported that typical fadings of RX And lasted for ∼100 d. 2 Here we report on the detection of an unusually short fading episode in 2002.…”

“…Oppenheimer et al 1998). Most recently, RX And has been shown to be an unique Z Cam-type dwarf nova which also exhibits occasional "low states" (Sion et al 2001;Kato et al 2002d;Schreiber et al 2002). Schreiber et al (2002) even suggested that RX And is a transitional object between Z Cam-type dwarf novae and VY Scl-type stars (cf.…”

Grazing Eclipsing Dwarf Nova CW Monocerotis: Dwarf Nova-Type Outburst in a Possible Intermediate Polar?

“…In many short-period dwarf novae with rather high mass-transfer rates, such a condition is difficult to achieve. Nevertheless, the same system is shown to undergo unusual outbursts, resembling those of GK Per, when the mass-transfer rate is temporarily reduced (RX And: Kato et al 2002c). Many of the well-observed long outbursts of CW Mon (cf.…”

UBVRI observations of the flickering of the dwarf nova RX And

“…Following the AAVSO light curve generator, during the last years RX And varies in the range 10.9 ≤ V ≤ 14.9 and 9.5 ≤ B ≤ 15.0. There was an extended faint state of RX And in 1996, when the brightness remained about 15 mag in V band for ≈ 100 days (Kato et al 2002).…”