Discovery of a New Deeply Eclipsing SU UMa-Type Dwarf Nova, IY UMa (= TmzV85)

We discovered a new deeply eclipsing SU UMa-type dwarf nova, IY UMa, which experienced a superoutburst in 2000 January. Our monitoring revealed two distinct outbursts, which suggest a superoutburst interval of ~800 d, or its half, and an outburst amplitude of 5.4 mag. From time-series photometry during the superoutburst, we determined a superhump and orbital period of 0.07588 d and 0.0739132 d, respectively.Comment: 5 pages, 3 figures, accepted by PASJ lette

Superhumps in Cataclysmic Binaries. XXII. 1RXS J232953.9+062814

We report photometry of 1RXS J232953.9+062814, a recently discovered dwarf nova with a remarkably short 64.2-minute orbital period. In quiescence, the star's light curve is that of a double sinusoid, arising from the "ellipsoidal" distortion of the Roche-lobe-filling secondary. During superoutburst, common superhumps develop with a period 3-4% longer than P_orb. This indicates a mass ratio M_2/M_1=0.19+-0.02, a surprisingly large value in so compact a binary. This implies that the secondary star has a density 2-3 times higher than that of other short-period dwarf novae, suggesting a secondary enriched by H-burning prior to the common-envelope phase of evolution. We estimate i=50+-5 deg, M_1=0.63 (+0.12, -0.09) M_sol, M_2=0.12 (+0.03, -0.02) M_sol, R_2=0.121 (+0.010, -0.007) R_sol, and a distance to the binary of 180+-40 pc.Comment: PDF, 17 pages, 3 tables, 5 figures; accepted, in press, to appear June 2002, PASP; more info at http://cba.phys.columbia.edu

STEREO observations of stars and the search for exoplanets

The feasibility of using data from the NASA STEREO mission for variable star and asteroseismology studies has been examined. A data analysis pipeline has been developed that is able to apply selected algorithms to the entire data base of nearly a million stars to search for signs of variability. An analysis limited to stars of magnitude 10.5 has been carried out, which has resulted in the extraction of 263 eclipsing binaries (EBs), of which 122 are not recorded as such in the SIMBAD online data base. The characteristics of the STEREO observations are shown to be extremely well suited to variable star studies with the ability to provide continuous phase coverage for extended periods as well as repeated visits that allow both short- and long-term variability to be observed. This will greatly inform studies of particular stars, such as the pre-cataclysmic variable V471 Tau, as well as the entire classes of stars, including many forms of rotational variability. The high-precision photometry has also revealed a potentially substellar companion to a bright (R= 7.5 mag) nearby star (HD 213597), detected with 5σ significance. This would provide a significant contribution to the exoplanet research if follow-up observations ascertain the mass to be within the planetary domain. Some particularly unusual EBs from the recovered sample are discussed, including a possible reclassification of a well-known star as an EB rather than a rotational variable (HR 7355) and several particularly eccentric systems, including very long period EBs

XO-5b: A Transiting Jupiter-sized Planet With A Four Day Period

The star XO-5 (GSC 02959-00729, V=12.1, G8V) hosts a Jupiter-sized, Rp=1.15+/-0.12 Rjup, transiting extrasolar planet, XO-5b, with an orbital period of P=4.187732+/-0.00002 days. The planet mass (Mp=1.15+/-0.08 Mjup) and surface gravity (gp=22+/-5 m/s^2) are significantly larger than expected by empirical Mp-P and Mp-P-[Fe/H] relationships. However, the deviation from the Mp-P relationship for XO-5b is not large enough to suggest a distinct type of planet as is suggested for GJ 436b, HAT-P-2b, and XO-3b. By coincidence XO-5 overlies the extreme H I plume that emanates from the interacting galaxy pair NGC 2444/NGC 2445 (Arp 143).Comment: 10 pages, 9 Figures, Submitted to Ap

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

We observed the 2002 October-November outburst of the dwarf nova CW Mon. The outburst showed a clear signature of a premaximum halt, and a more rapid decline after reaching the outburst maximum. On two separate occasions, during the premaximum stage and near the outburst maximum, shallow eclipses were recorded. This finding confirms the previously suggested possibility of the grazing eclipsing nature of this system. The separate occurrence of the eclipses and the premaximum halt can be understood as a result of a combination of two-step ignition of an outburst and the inside-out propagation of the heating wave. We detected a coherent short-period (0.02549 d) signal on two subsequent nights around the optical maximum. This signal was likely present during the maximum phase of the 2000 January outburst. We interpret this signal as a signature of the intermediate polar (IP) type pulses. The rather strange outburst properties, strong and hard X-ray emission, and the low luminosity of the outburst maximum might be understood as consequences of the supposed IP nature. The ratio between the suggested spin period and the orbital period, however, is rather unusual for a system having an orbital period of ~0.176 d.Comment: 11 pages, 11 figures, to appear in PAS