We present spectroscopy and time-series photometry of the newly discovered dwarf nova 1RXS J232953.9+062814. Photometry in superoutburst reveals a superhump with a period of 66.06(6) minutes. The low state spectrum shows Balmer and HeI emission on a blue continuum, and in addition shows a rich absorption spectrum of type K4 ± 2. The absorption velocity is modulated sinusoidally at P orb = 64.176(5) min, with semi-amplitude K = 348(4) km s −1 . The low-state light curve is double-humped at this period, and phased as expected for ellipsoidal variations. The absorption strength does not vary appreciably

Stellar evolution models which include the effect of helium and heavy element diffusion have been calculated for initial iron abundances of [Fe/H] = −2.3, −2.1, −1.9 and −1.7. These models were calculated for a large variety of masses and three separate mixing lengths, α = 1.50, 1.75 and 2.00 (with α = 1.75 being the solar calibrated mixing length). The change in the surface iron abundance for stars of different masses was determined for the ages 11, 13 and 15 Gyr. Iron settles out of the surface convection zone on the main sequence; this iron is dredged back up when the convection zone deepens on the giant branch. In all cases, the surface [Fe/H] abundance in the turn-off stars was at least 0.28 dex lower than the surface [Fe/H] abundance in giant-branch stars of the same age. However, recent high dispersion spectra of stars in the globular cluster NGC 6397 found that the turn-off and giant branch stars had identical (within a few percent) iron abundances of [Fe/H] = −2.03 (Gratton et al. 2001). These observations prove that heavy element diffusion must be inhibited in the surface layers of metal-poor stars. When diffusion is inhibited in the outer layers of a stellar model, the predicted temperatures of the models are similar to models evolved without diffusion, while the predicted lifetimes are similar to stars in which diffusion is not inhibited. Isochrones constructed from the models in which diffusion is inhibited fall half-way between isochrones without diffusion, and isochrones with full diffusion. As a result, absolute globular cluster ages which are based upon the absolute magnitude of the turn-off are 4% larger than ages inferred from full diffusion isochrones, and 4% smaller than ages inferred from no diffusion isochrones.

We report the results of long observing campaigns on two novalike variables: V442 Ophiuchi and RX J1643.7+3402. These stars have high-excitation spectra, complex line profiles signifying mass loss at particular orbital phases, and similar orbital periods (respectively 0.12433 and 0.12056 d). They are well-credentialed members of the SW Sex class of cataclysmic variables. Their light curves are also quite complex. V442 Oph shows periodic signals with periods of 0.12090(8) and 4.37(15) days, and RX J1643.7+3402 shows similar signals at 0.11696(8) d and 4.05(12) d. We interpret these short and long periods respectively as a "negative superhump" and the wobble period of the accretion disk. The superhump could then possibly arise from the heating of the secondary (and structures fixed in the orbital frame) by inner-disk radiation, which reaches the secondary relatively unimpeded since the disk is not coplanar.At higher frequencies, both stars show another type of variability: quasi-periodic oscillations (QPOs) with a period near 1000 seconds. Underlying these strong signals of low stability may be weak signals of higher stability. Similar QPOs, and negative superhumps, are quite common features in SW Sex stars. Both can in principle be explained by ascribing strong magnetism to the white dwarf member of the binary; and we suggest that SW Sex stars are borderline AM Herculis binaries, usually drowned by a high accretion rate. This would provide an ancestor channel for AM Hers, whose origin is still mysterious.

We present spectroscopy and time-series photometry of the dwarf nova QZ Ser. The spectrum shows a rich absorption line spectrum of type K4±2. K-type secondary stars are generally seen in dwarf novae with orbital periods P orb ∼ 6 h, but in QZ Ser the absorption radial velocities show an obvious modulation (semi-amplitude 207(5) km s −1 ) at P orb = 119.752(2) min, much shorter than typical for such a relatively warm and prominent secondary spectrum. The Hα emission-line velocity is modulated at the same period and roughly opposite phase. Time-series photometry shows flickering superposed on a modulation with two humps per orbit, consistent with ellipsoidal variation of the secondary's light. QZ Ser is a second example of a relatively short-period dwarf nova with a surprisingly warm secondary. Model calculations suggest that the secondary is strongly enhanced in helium, and had already undergone significant nuclear evolution when mass transfer began. Several sodium absorption features in the secondary spectrum are unusually strong, which may indicate that the present-day surface was the site of CNO-cycle hydrogen burning in the past.

ABSTRACT. We present spectroscopy of seven cataclysmic variable stars with orbital periods greater than P orb 5 hr, all but one of which are known to be dwarf novae. Using radial velocity measurements we improve on previous orbital period determinations, or derive periods for the first time. The stars and their periods are TT Crt, 0.2683522(5) days; EZ Del, 0.2234(5) days; LL Lyr, 0.249069(4) days; UY Pup, 0.479269(7) days; RY Ser, 0.3009(4) days; CH UMa, 0.3431843(6) days; and SDSS J081321ϩ452809, 0.2890(4) days. For each of the systems, we detect the spectrum of the secondary star, estimate its spectral type, and derive a distance based on the surface brightness and Roche lobe constraints. In five systems we also measure the radial velocity curve of the secondary star, estimate orbital inclinations, and, where possible, estimate distances based on the -M (max) V relation found by Warner. In concordance with previous studies, we find that all the secondary stars have, P orb to varying degrees, cooler spectral types than would be expected if they were on the main sequence at the measured orbital period.