Orbital Periods for the Unusual Dwarf Novae ER Ursae Majoris and V1159 Orionis

Abstract

ER UMa (PG 0943+521), VI159 Ori, and RZ LMi constitute a small recently recognized group of dwarf novae, called the RZ LMi stars or the ER UMa stars. They share many features of the SU UMa-type, but have shorter outburst cycles than had been known previously. Here we establish orbital periods, based on emission-line radial velocities, for ER UMa (0.06366±0.00003 d = 91.67±0.04 min) and VI159 Ori (0.06217801 ± 1.3X 10" 7 d = 89.5363± 0.0002 min). The precise orbital period for VI159 Ori depends on an extrapolation of cycle count from 1991 to 1994, which is slightly uncertain, but the daily cycle count is reasonably secure. These orbital periods are similar to those of the more common, less frequently outbursting SU UMa stars. As is generally the case, the orbital periods derived here are slightly shorter than the periods of photometric superhumps which appear in superoutburst. The superhump period excesses found here are compatible with, but marginally larger than, those seen in other SU UMa stars of similar period. While the empirical link between ER UMa stars and SU UMa stars is generally strengthened by these results, the trend toward slightly larger period excesses (if true) can be interpreted as a tendency for systems with larger mass ratios to develop larger mass-transfer rates at a given orbital period.

SPH simulations of negative (nodal) superhumps: a parametric study

“…Patterson et al (1995) show evidence of a 82.7‐min periodicity in V1159 Ori which occurred on two separate nights, and they identify this as a negative superhump signal. Using the spectroscopically determined P orb = 89.5363 min (Thorstensen et al 1997), this yields a period deficit of −7.6 per cent, where we had expect a value closer to ɛ − ∼−1.6 per cent based on our results. Similarly, Gao et al (1999) and Zhao et al (2006) report finding negative superhumps in ER UMa also with a very large period deficit of ɛ − =−7.5 per cent.…”

Finding the most variable stars in the Orion Belt with the All Sky Automated Survey

“…V1159 Ori was discovered by Wolf & Wolf (1906), who gave it the name "Var.,Orionis 36.1906", and first investigated by Kippenhahn (1953) and Jablonski & Cieslinski (1992). Afterwards, its very short outburst cycle, superhumps, orbital periods, and high energy (X-ray, ultraviolet) emission have been studied by a number of authors (Nogami et al 1995;Robertson et al 1995;Patterson et al 1995;Thorstensen et al 1997;Szkody et al 1999). We can add little to the knowledge on V1159 Ori except for its supercycle period.…”

FUSE and IUE Spectroscopy of the Prototype Dwarf Nova ER Ursa Majoris During Quiescence

“…Having the Gaia distance removes one free parameter. Optical spectroscopic observations (Szkody et al 1996;Thorstensen et al 1997) reveal narrow line widths and low radial velocities in ER UMa (K 1 ∼ 50km/s), which may be indicating the system orbital inclination may be low. Therefore, we first restricted the range of disk inclination angles in our disk modeling to be 18 degrees.…”

“…Szkody et al(1996) cite the line widths, small equivalent widths and low radial velocity amplitude of ER UMa as indicating a low inclination. On the other hand, Thorstensen et al (1997) double convolution method, that the separation of the Gaussian peaks is 1260 km/s and the radial velocity of the WD is 48 km/sec. If one assumes 1M ⊙ for the WD and 0.1M ⊙ for the secondary star and applies Kepler's 3rd Law, the corresponding inclination is i ∼ 50 • .…”