Surveyor spacecraft system - Surveyor 6 flight performance Final report

Surveyor 6 spacecraft flight performance characteristics, including data on television equipment, alpha scattering experiment, and powered flight translatio

The X-ray eclipse of the dwarf nova HT CAS observed by the XMM-Newton satellite: spectral and timing analysis

A cataclysmic variable is a binary system consisting of a white dwarf that accretes material from a secondary object via the Roche-lobe mechanism. In the case of long enough observation, a detailed temporal analysis can be performed, allowing the physical properties of the binary system to be determined. We present an XMM-Newton observation of the dwarf nova HT Cas acquired to resolve the binary system eclipses and constrain the origin of the X-rays observed. We also compare our results with previous ROSAT and ASCA data. After the spectral analysis of the three EPIC camera signals, the observed X-ray light curve was studied with well known techniques and the eclipse contact points obtained. The X-ray spectrum can be described by thermal bremsstrahlung of temperature $kT_1=6.89 \pm 0.23$ keV plus a black-body component (upper limit) with temperature $kT_2=30_{-6}^{+8}$ eV. Neglecting the black-body, the bolometric absorption corrected flux is $F^{\rm{Bol}}=(6.5\pm 0.1)\times10^{-12}$ erg s$^{-1}$ cm$^{-2}$, which, for a distance of HT Cas of 131 pc, corresponds to a bolometric luminosity of $(1.33\pm 0.02)\times10^{31}$ erg s$^{-1}$. The study of the eclipse in the EPIC light curve permits us to constrain the size and location of the X-ray emitting region, which turns out to be close to the white dwarf radius. We measure an X-ray eclipse somewhat smaller (but only at a level of $\simeq 1.5 \sigma$) than the corresponding optical one. If this is the case, we have possibly identified the signature of either high latitude emission or a layer of X-ray emitting material partially obscured by an accretion disk.Comment: Accepted for publication on Astronomy and Astrophysics, 200

Mass and Angular Momentum Transfer in the Massive Algol Binary RY Persei

We present an investigation of H-alpha emission line variations observed in the massive Algol binary, RY Per. We give new radial velocity data for the secondary based upon our optical spectra and for the primary based upon high dispersion UV spectra. We present revised orbital elements and an estimate of the primary's projected rotational velocity (which indicates that the primary is rotating 7 times faster than synchronous). We use a Doppler tomography algorithm to reconstruct the individual primary and secondary spectra in the region of H-alpha, and we subtract the latter from each of our observations to obtain profiles of the primary and its disk alone. Our H-alpha observations of RY Per show that the mass gaining primary is surrounded by a persistent but time variable accretion disk. The profile that is observed outside-of-eclipse has weak, double-peaked emission flanking a deep central absorption, and we find that these properties can be reproduced by a disk model that includes the absorption of photospheric light by the band of the disk seen in projection against the face of the star. We developed a new method to reconstruct the disk surface density distribution from the ensemble of H-alpha profiles observed around the orbit, and this method accounts for the effects of disk occultation by the stellar components, the obscuration of the primary by the disk, and flux contributions from optically thick disk elements. The resulting surface density distribution is elongated along the axis joining the stars, in the same way as seen in hydrodynamical simulations of gas flows that strike the mass gainer near trailing edge of the star. This type of gas stream configuration is optimal for the transfer of angular momentum, and we show that rapid rotation is found in other Algols that have passed through a similar stage.Comment: 39 pages, 12 figures, ApJ in press, 2004 June 20 issu

Parallax and Distance Estimates for Fourteen Cataclysmic Variable Stars

I used the 2.4 m Hiltner telescope at MDM Observatory in an attempt to measure trigonometric parallaxes for 14 cataclysmic variable stars. Techniques are described in detail. In the best cases the parallax uncertainties are below 1 mas, and significant parallaxes are found for most of the program stars. A Bayesian method which combines the parallaxes together with proper motions and absolute magnitude constraints is developed and used to derive distance estimates and confidence intervals. The most precise distance derived here is for WZ Sge, for which I find 43.3 (+1.6, -1.5) pc. Six Luyten Half-Second stars with previous precise parallax measurements were re-measured to test the techniques, and good agreement is found.Comment: 33 pages, 3 figures. Astronomical Journal, accepte

An XMM-Newton observation of the nova-like variable UX UMa: spatially and spectrally resolved two-component X-ray emission

In the optical and ultraviolet regions of the electromagnetic spectrum, UX Ursae Majoris is a deeply eclipsing cataclysmic variable. However, no soft X-ray eclipse was detected in ROSAT observations. We have obtained a 38 ksec XMM-Newton observation to further constrain the origin of the X-rays. The combination of spectral and timing information allows us to identify two components in the X-ray emission of the system. The soft component, dominant below photon energies of 2 keV, can be fitted with a multi-temperature plasma model and is uneclipsed. The hard component, dominant above 3 keV, can be fitted with a kT ~ 5 keV plasma model and appears to be deeply eclipsed. We suggest that the most likely source of the hard X-ray emission in UX UMa, and other systems in high mass transfer states, is the boundary layer.Comment: To appear in MNRAS Letter

Brane-world Cosmologies with non-local bulk effects

It is very common to ignore the non-local bulk effects in the study of brane-world cosmologies using the brane-world approach. However, we shall illustrate through the use of three different scenarios, that the non-local bulk-effect ${\cal P}_{\mu\nu}$ does indeed have significant impact on both the initial and future behaviour of brane-world cosmologies.Comment: 17 pages, no figures, iopart.cls, submitted to CQ

The component masses of the cataclysmic variable V347 Puppis

We present time-resolved spectroscopy and photometry of the double-lined eclipsing cataclysmic variable V347 Pup (=LB 1800). There is evidence of irradiation on the inner hemisphere of the secondary star, which we correct for using a model to give a secondary-star radial velocity of KR= 198 ± 5 km s−1. The rotational velocity of the secondary star in V347 Pup is found to be v sin i= 131 ± 5 km s−1 and the system inclination is i= 840 ± 23. From these parameters we obtain masses of M1= 0.63 ± 0.04 M⊙ for the white dwarf primary and M2= 0.52 ± 0.06 M⊙ for the M0.5V secondary star, giving a mass ratio of q= 0.83 ± 0.05. On the basis of the component masses, and the spectral type and radius of the secondary star in V347 Pup, we find tentative evidence for an evolved companion. V347 Pup shows many of the characteristics of the SW Sex stars, exhibiting single-peaked emission lines, high-velocity S-wave components and phase-offsets in the radial velocity curve. We find spiral arms in the accretion disc of V347 Pup and measure the disc radius to be close to the maximum allowed in a pressureless disc

The rapid rotation and complex magnetic field geometry of Vega

The recent discovery of a weak surface magnetic field on the normal intermediate-mass star Vega raises the question of the origin of this magnetism in a class of stars that was not known to host magnetic fields. We aim to confirm the field detection and provide additional observational constraints about the field characteristics, by modelling the magnetic geometry of the star and by investigating the seasonal variability of the reconstructed field. We analyse a total of 799 circularly-polarized spectra collected with the NARVAL and ESPaDOnS spectropolarimeters during 2008 and 2009. We employ a cross-correlation procedure to compute, from each spectrum, a mean polarized line profile with a signal-to-noise ratio of about 20,000. The technique of Zeeman-Doppler Imaging is then used to determine the rotation period of the star and reconstruct the large-scale magnetic geometry of Vega at two different epochs. We confirm the detection of circularly polarized signatures in the mean line profiles. The amplitude of the signatures is larger when spectral lines of higher magnetic sensitivity are selected for the analysis, as expected for a signal of magnetic origin. The short-term evolution of polarized signatures is consistent with a rotational period of 0.732 \pm 0.008 d. The reconstructed magnetic topology unveils a magnetic region of radial field orientation, closely concentrated around the rotation pole. This polar feature is accompanied by a small number of magnetic patches at lower latitudes. No significant variability in the field structure is observed over a time span of one year. The repeated observation of a weak photospheric magnetic field on Vega suggests that a previously unknown type of magnetic stars exists in the intermediate-mass domain. Vega may well be the first confirmed member of a much larger, as yet unexplored, class of weakly-magnetic stars.Comment: Accepted by Astronomy & Astrophysics. Abstract shortened to respect the arXiv limit of 1920 character

Variable Stars in the Cetus dSph Galaxy: Population Gradients and Connections with the Star Formation History

We investigate the variable star content of the isolated, Local Group, dwarf spheroidal galaxy (dSph) Cetus. Multi-epoch, wide-field images collected with the VLT/VIMOS camera allowed us to detect 638 variable stars (630 RR Lyrae stars and 8 Anomalous Cepheids), 475 of which are new detections. We present a full catalogue of periods, amplitudes, and mean magnitudes. Motivated by the recent discovery that the pulsational properties of the RR Lyrae stars in the Tucana dSph revealed the presence of a metallicity gradient within the oldest (>10 Gyr old) stellar populations, we investigated the possibility of an analogous effect in Cetus. We found that, despite the obvious radial gradient in the Horizontal Branch (HB) and Red Giant Branch (RGB) morphologies, both becoming bluer on average for increasing distance from the center of Cetus, the properties of the RR Lyrae stars are homogeneous within the investigated area (out to r~15'), with no significant evidence of a radial gradient. We discuss this in connection with the star formation history (SFH) previously derived for the two galaxies. The observed differences between these two systems show that even systems this small show a variety of early evolutionary histories. These differences could be due to different merger or accretion histories.Comment: Accepted for publication on MNRAS. The complete set of light curves and finding charts, together with the full table of the pulsational properties of all variable stars will be available in the on-line edition of the pape

Algebraic renormalization of twisted N=2 supersymmetry with Z=2 central extension

We study the renormalizability of (massive) topological QCD based on the algebraic BRST technique by adopting a non-covariant Landau type gauge and making use of the full topological superalgebra. The most general local counter terms are determined and it is shown that in the presence of central charges the BRST cohomology remains trivial. By imposing an additional set of stability constraints it is proven that the matter action of topological QCD is perturbatively finite.Comment: 37 pages, AMSTE