Publications of the Astronomical Society of the Pacific

Clayton, Donald D.

doi: 10.1086/133686pmid: N/A

The scientific career of W. A. Fowler enduringly enriched astronomy by providing us with a systematic treatment of nuclear reaction rates in stars. I clarify how and why this achievement earned him both the 1979 Bruce Medal of the Astronomical Society of the Pacific and the 1983 Nobel Prize in physics (jointly with S. Chandrasekhar). I attempt to share my understanding and experience of this great man, what he was like personally, and the larger context of his life.

Trimble, Virginia; Leonard, Peter J. T.

doi: 10.1086/133687pmid: N/A

Ap95 differs from Ap91 to Ap94 primarily in Ap number. That is, it once again attempts to highlight some areas of our mutual science where a major event has occurred during the year (a possible solution of the Type II supernova problem, the faintness of quasar host galaxies, and the collision of Shoemaker-Levy 9 with Jupiter), but also to focus on some topics where dogged determination is producing more gradual advances (dense star clusters, the second parameter problem, inventories of nearby objects and dark matter candidates). In moderate departure from the rules of Ap92-94, there has been some deliberate up-dating of topics discussed previously. The topics are only partly ordered from nearby to far away.

Mould, Jeremy

doi: 10.1086/133688pmid: N/A

Recent results are collected on the luminosity function in the halo of the Galaxy. Several lines of evidence are converging on the conclusion that there is a turnover in the halo main sequence luminosity function and its associated initial mass function. These include: the luminoisty function in globular clusters, the luminosity function of high proper motion stars in the solar neighborhood, the luminosity function at large distances from the Galactic plane, and the mass distribution function of microlensing objects.

Osaki, Yoji

doi: 10.1086/133689pmid: N/A

Outburst mechanisms of dwarf novae are discussed. There is a rich variety in outburst behaviors of non-magnetic cataclysmic variable stars, starting from non-outbursting nova-like stars to various sub-classes of dwarf novae (i.e., U Gem-type, Z Cam-type, and SU UMa-type). A unification model for dwarf nova outbursts is proposed within the basic framework of the disk instability model in which two different intrinsic instabilities (i.e., the thermal instability and the tidal instability) within accretion disks play an essential role. Non-magnetic cataclysmic variables are classified into four regions in the orbital-period versus mass-transfer-rate diagram, showing different combinations of stability behavior for the two intrinsic instabilities in accretion disks, and their different outburst behaviors are basically understood in this diagram. We discuss several problems concerning the thermal limit-cycle instability model for dwarf novae above the period gap. We then discuss the thermal-tidal instability model for SU UMa stars, dwarf novae below the period gap, in which the coupling of the two intrinsic instabilities in the accretion disk plays a unique role. In particular, a rich variety of outburst behaviors of cataclysmic variables below the period gap (i.e., starting from "permanent superhumpers", to Z Cam-like SU UMa stars, "ER UMa stars", to ordinary SU UMa stars, and finally to WZ Sge stars) is understood by the thermal-tidal instability model.

Reed, B. Cameron

doi: 10.1086/133690pmid: N/A

H-beta photometry for 116 stars listed in Stephenson and Sanduleak's (1971) catalog of Luminous Stars in the Southern Milky Way_ is reported. The vast majority of these objects are O and B-type stars; a few are A, F, or Wolf-Rayet stars. A systematic difference of on the order of 30 mmag between the present results and those of other investigators is noted.

Upgren, A. R.; Harlow, J. J. B.

doi: 10.1086/133691pmid: N/A

Radial velocities are presented for 53 dwarf K and M stars, eight of which are radial velocity standards. This is the second list in a program to determine space motions for all of the stars in the McCormick lists of dwarf stars. The observations reported here differ from those of the first list in that they were made using the 1.88m David Dunlap reflector. One of the stars varies in radial velocity, consistent with a spectroscopic binary with a period of about 48 days.

Hampton, Melissa; Henry, Gregory W.; Eaton, Joel A.; Nolthenius, Richard A.; Hall, Douglas S.

doi: 10.1086/133692pmid: N/A

We have solved two sets of light curves of HD 12545 at its epoch of extreme spottedness in 1990-91, one of which coincides with an independent set analyzed recently by Strassmeier and Olah. Even for the huge amplitudes observed, these light-curve solutions did not give reliable determinations of several important spot properties. Specifically, we find that we could obtain acceptable solutions for a wide range of inclination; that spot temperature depends on inclination assumed, falling in the range Delta-T = Tstar - Tspot = 650-1200 K for inclinations of 70-30 deg; that spot latitudes derived from the light curves are unreliable; and that our independent spot solutions disagree with Strassmeier and Olah's. On a more positive note, changes in the light curve over the past five years seem to have been caused primarily by rearrangement of persisting spot groups, and we note that the high level of activity implied by its H-alpha emission, makes HD 12545 a prime candidate for a white-light flare star.

Thorstensen, John R.; Patterson, Joseph O.; Shambrook, Anouk; Thomas, Gino

doi: 10.1086/133693pmid: N/A

We obtained time-resolved spectroscopy of seven SU UMa-type dwarf novae and determined orbital periods from velocities of their H-alpha emission lines. The stars and their periods are FO And (0.07161 d=103.1 min), FS Aur (0.0595 d=87.7 min), WX Cet (0.05826 d=82.9 min), AQ Eri (0.06093 d=87.7 min), TY Psc (0.06833 d=98.4 min), CY UMa (0.06957 d=100.2 min), and SS UMi (0.06778 d=97.6 min). This substantially increases the number of well-determined orbital periods Porb for SU UMa stars. The period uncertainties are all < 0.3 percent, sufficent to confront theories accounting for the superhumps observed photometrically during superoutbursts. Combining these periods with others from the literature we show that the correlation between superhump period excess delta-P/Porb and Porb is described by delta-P/Porb = -0.0344+(0.0382 hr-1) X Porb. The correlation is clear, but the scatter is greater than the measurement uncertainties. We also obtained contemporaneous timeseries photometry in the low state for TY Psc, AZ Eri, SS UMi, and CY UMa. TY Psc shows a ~0.2 mag modulation at the orbital period. While the others all show considerable variation, none of them appeared to vary periodically, and none eclipse. The white dwarf photosphere in TY Psc is noticable in the optical spectrum at minimum light.

Hoard, D. W.; Wallerstein, George; Willson, L. A.

doi: 10.1086/133694pmid: N/A

ROSAT PSPC pointed observations of PU Vulpeculae on 1992 November 10-12 UT give a count rate of 4.00 ± 0.75 X 10-3 cts/s in the energy range from 0.1 to 1.8 keV. The count rate outside this energy range is approximately zero. An analysis of the energy spectrum, with the requirement that the result be consistent with the observed reddening of about 0.50 mag, yields T=0.25 (+0.19, -0.13) keV and log(NH) = 21.40 (+0.28, -0.35) for a bremsstrahlung emission model. FG Serpentis was not detected during an 8467 s ROSAT PSPC pointed exposure on 1992 March 8-23 UT. Serendipitous X-ray sources detected nearby give an upper limit of ~9.3 X 10-4 ct/s for the X-ray emission from FG Ser. The post-outburst X-ray fluxes of FG Ser and PU Vul are compared to those of three other symbiotic novae, HM Sagittae, V1016 Cygni and RR Telescopii. The eclipsing nova-like variable V Sagittae was serendipitously observed during the ROSAT exposure of PU Vul and found to have a count rate of 0.013 ± 0.003 cts/s, which is about the same as it showed during Einstein IPC observations in 1979-80. A period of 6.0 hr is detected in the X-ray data; this period is roughly half the length of the observed orbital period of V Sge.

Fabregat, Juan; Reig, Pablo

doi: 10.1086/133695pmid: N/A

We present the absolute flux calibration for the uvby photometric system passbands, derived from homogeneous spectroscopic and photometric standard star lists, and referred to the Vega absolute flux calibration of Hayes (1985).