Photometric study of new southern SU UMa-type dwarf novae and candidates: V877 Ara, KK Tel and PU CMa

Abstract

We photometrically observed the three dwarf novae V877 Ara, KK Tel and PU CMa. We discovered the undisputed presence of superhumps in V877 Ara and KK Tel, with mean periods of 0.084 11(2) and 0.088 08(3) d, respectively. Both V877 Ara and KK Tel are confirmed to belong to long‐period SU UMa‐type dwarf novae. In V877 Ara, we found a large decrease of the superhump period . There is evidence that the period of KK Tel decreased at a similar or a more exceptional rate. Coupled with the past studies of superhump period changes, these findings suggest that a previously neglected diversity of phenomena is present in long‐period SU UMa‐type dwarf novae. The present discovery of a diversity in long‐period SU UMa‐type systems would become an additional step towards a full understanding of the dwarf nova phenomenon. PU CMa is shown to be an excellent candidate for an SU UMa‐type dwarf nova. We examined the outburst properties of these dwarf novae, and derived characteristic outburst recurrence times. Combined with the recently published measurement of the orbital period of PU CMa, we propose that PU CMa is the first object filling the gap between the extreme WZ Sge‐type and ER UMa‐type stars.

Photometric study of new southern SU UMa-type dwarf novae and candidates - III. NSV 10934, MM Sco, AB Nor and CAL 86

“…Although the supercycle length of NSV 10934 has not yet been established, the intervals between normal outbursts (40–60 d) are typical values for an SU UMa‐type dwarf nova in the intermediate activity class (Vogt 1993). The apparent lack of terminal brightening during the superoutburst plateau also fits the general properties of an SU UMa‐type dwarf nova with this superhump period (Kato et al 2003b). However, the presence of terminal rapid declines during normal outbursts (Kato et al 2002a) is rather unusual, because the contribution from quiescent luminosity usually works to slow down the decline rate near the terminal stage of such outbursts (e.g.…”

“…The superhumps and superoutbursts are now widely believed to be a result of the combination of two types of disc instabilities (thermal and tidal instabilities), which have provided a laboratory to understand the basic astrophysical processes, such as the origin of viscosity and resonant actions on a fluid disc in close binaries; see a review by Osaki (1996), and see also Ogilvie (2002) for recent theoretical development. We, the VSNET Collaboration (Kato et al 2003d), 1 have been studying the properties of (mostly new) southern SU UMa‐type dwarf novae, candidates, and related systems with a perspective described in Kato et al (2003b). In this paper, we report on the detection of superhumps in three systems, and we also report on photometric observations of an SU UMa‐type candidate which underwent a likely normal outburst.…”

In-the-gap SU UMa-type dwarf nova, Var73 Dra with a supercycle of about 60 days

“…Kato et al (2001a) and Kato et al (2003c) proposed a possibility thatṖ SH /P SH is related to the mass transfer rate: SU UMa stars with largerṖ SH /P SH tend to have larger mass transfer rates, and those withṖ SH /P SH close to and smaller than zero have smallṀ. The quite short supercycle length of about 60 d suggests a highṀ in the present object (discussed later), which may support this possiblity.…”

“…The quadratic term measures the superhump period decrease to be a rate ofṖ SH /P SH = −1.7(2) × 10 −3 , which is one order of magnitude larger than the largest values known (see Kato et al 2003c). …”

“…Following this discovery, similar behavior has been found in several SU UMa stars: V485 Cen (Olech 1997), EG Cnc , SW UMa (Semeniuk et al 1997;Nogami et al 1998a), V1028 Cyg (Baba et al 2000), WX Cet (Kato et al 2001a), and HV Vir (Kato et al 2001b). These stars are, however, concentrated around the period minimum in the P orb distribution, and SU UMa stars with relatively long P orb have been confirmed to show P SH decrease with a similar rate ofṖ SH /P SH ∼−5 × 10 −5 (see Kato et al 2003c). Very recently, Kato et al (2003c) reported large negative derivatives of P SH in V877 Ara (Ṗ SH /P SH = −1.5(±0.2) × 10 −4 , P SH = 0.08411(2) d) and KK Tel (Ṗ SH /P SH = −3.7(±0.4) × 10 −4 , P SH = 0.08808 d), and pointed out a diversity ofṖ SH /P SH in long-period SU UMa-type dwarf novae.…”