R. F. Stiening

The pulsation index, effective temperature, and thickness of the hydrogen layer in the pulsating DA white dwarf G117-B15A

We have measured the amplitude of the 215 s pulsation of the pulsating DA white dwarf, or ZZ Ceti star, G117-B15A in six passbands with effective wavelengths from 1570 to 6730 A. We find that the index of the pulsation is l = 1 with a high degree of confidence, the first unambiguous determination of l for a pulsation of a ZZ Ceti star. We also find that log g and T(sub eff) are tightly correlated for model atmospheres that fit the data, such that at log g = 7.5 the temperature is 11,750 K and at log g = 8.0 the temperature is 12,375 K. Adopting log g = 7.97 +/- 0.06 from published observations of the optical spectrum of G117-B15A, the correlation yields T(sub eff) = 12,375 +/- 125 K. This temperature is free of flux calibration errors and should be substantially more reliable than temperatures derived for IUE spectra. Since G117-B15A is thought to lie close to the blue edge of the ZZ Ceti instability strip, this low temperature also implies a low temperature for the blue edge. Using pulsation models calculated by Fontaine et al. (1992) and Bradley (1994), we find that the mass of the hydrogen layer in G117-B15A lies between 1.0 x 10(exp -6) solar mass (for k = 1) and 8 x 10(exp -5) solar mass (for k = 2). This range of masses is (barely) consistent with the masses predicted by recent models for the ejection of planetary nebulae, (8-13) x 10(exp -5) solar mass. The mass is too large to be consistent with models invoking thin hydrogen layers to explain the spectral evolution of white dwarfs.

Eclipse studies of the dwarf nova HT Cassiopeiae. I, Observations and system parameters

Optical eclipses are used to investigate the structure of the dwarf nova HT Cas. We present high-speed multicolor light curves covering four eclipses at UBR in 1982 September and 12 eclipses at UBVR in 1983 November-December. From the latter we derive high-quality mean light curves that cleanly separate the white dwarf and accretion disk eclipses. The bright spot is weak or absent during our observations, but a 0.3 mag orbital modulation, centered on mid-eclipse, is seen in the U-band. We define a purely photometric model of the system using contact timings of the white dwarf from the data presented here and measurements of the bright spot eclipses in other data (published by Patterson in 1981).

On the mass of the compact object in the black hole binary A0620-00

Multicolor orbital light curves of the black hole candidate binary A0620-00 are presented. The light curves exhibit ellipsoidal variations and a grazing eclipse of the mass donor companion star by the accretion disk. Synthetic light curves were generated using realistic mass donor star fluxes and an isothermal blackbody disk. For mass ratios of q = M1/M sub 2 = 5.0, 10.6, and 15.0 systematic searches were executed in parameter space for synthetic light curves that fit the observations. For each mass ratio, acceptable fits were found only for a small range of orbital inclinations. It is argued that the mass ratio is unlikely to exceed q = 10.6, and an upper limit of 0.8 solar masses is placed on the mass of the companion star. These constraints imply 4.16 +/- 0.1 to 5.55 +/- 0.15 solar masses. The lower limit on M1 is more than 4-sigma above the mass of a maximally rotating neutron star, and constitutes further strong evidence in favor of a black hole primary in this system.

High Resolution Beam Profile Monitors in the SLC

In the SLC linac, low emittance beams with typical transverse dimensions less than 0.2 mm must be accelerated without effective emittance growth. In order to monitor this we have installed a high resolution beam profile monitor system which consists of an aluminum target covered with a fine-grained phosphor, a magnifying optical system, a television camera and video signal recording electronics. The image formed when the beam strikes the phosphor screen is viewed on a CRT monitor at the console and selected horizontal and vertical slices of the beam spot intensity are recorded. A 20 MHz transient waveform recorder is used to sample and digitize the raw video signal along the selected slice. The beam width is determined by fitting the background subtracted data to a Gaussian. Beam spots less than 6 × 3 mm can be viewed. Beam spot sizes ¿x,y < 80¿m have been measured.

V795 Herculis (=PG 1711+336), a peculiar intermediate polar without strong X-ray emission

The peculiar cataclysmic variable V795 Her (PG 1711+336) has been classified as an intermediate polar because it displays two different and incommensurate periods, a photometric period of 0.1164865 d and a spectroscopic period of 0.1082648. The photometric period has been interpreted as the beat period between orbital period and the rotation period of the white dwarf. Doubts remain about the intermediate polar model for V795 Her because the predicted rotation period of the white dwarf has not been found in any data and because EXOSAT did not detect any X-ray emission from the system. Also, there is evidence that V795 Her is related to systems with precessing accretion disks.

RF Beam Deflection Measurements and Corrections in the SLC Linac

The requirements of RF acceleration in the SLC Linac to produce high energy beams are complicated by the presence of small transverse RF beam deflections which arise from several sources. These RF deflections place stringent tolerances on the phase and amplitude stability of the klystrons. They also force the use of special magnetic bumps to correct the trajectories of oppositely charged beams that will pass down the linac. If left unabated, RF deflections can limit the performance of the SLC. There are several methods to reduce the deflections. Many measurements of RF deflections have been made in the low energy part of the linac where the beams are most sensitive.

Mathematical Models for the Control Program of the SLAC Linear Collider

The operation of the SLAC two-mile linear accelerator in the single pass collider mode will be computer controlled. Mathematical models will be used in the control program to set up and restore the beam optics and to correct orbits. Some of the requirements imposed upon the on-line model calculations and the ways to satisfy these requirements will be described in this paper.

Accelerator Physics Measurements at the Damping Ring

Besides the optics measurements described elsewhere, machine experiments were done at the SLC damping ring to determine some of its parameters. The synchrotron radiation energy loss which gives the damping rates was measured by observing the RF-voltage dependence of the synchronous phase angle. The emittance was obtained from the synchrotron light monitor, scraper measurements and by extracting the beam through a doublet and measuring its size for different quadrupole settings. Current dependent effects such as parasitic mode losses, head tail instabilities, synchrotron and betatron frequency shifts were measured to estimate the impedance. RF-cavity beam loading and its compensation were also studied and ion collection was investigated. All results agree reasonably well with expectations and indicate no limitations to the design performance.

Generation and Acceleration of High Intensity Beams in the SLC Injector

A new gun pulser and substantially increased focusing have been added to the first 100 m of the SLAC linac in order to provide a pair of intense electron bunches to the SLC damping ring. Each bunch from this injector must have 5 x 1010 electrons, an invariant emittance ¿¿ ¿ 1.8 x 10-3 m-rad and the pair must have an energy spread of less than 2% . Wakefield instabilities present in earlier versions of this injector 1 have been controlled by reducing the transverse beam dimension by a factor of 3.

The slac linear collider - a status report☆

This report presents progress made at the Stanford Linear Collider (SLC). Design goals of the various components are compared to measurements made on the equipment. 8 figs., 2 tabs. (JDH)