Showing papers by "J. H. J. de Bruijne published in 2003"

High-speed energy-resolved STJ photometry of the eclipsing dwarf nova IY UMa

Abstract: We present high-time-resolution photometry of the dwarf nova IY UMa using the S-Cam2 superconducting tunnel junction device attached to the 4.2-m William Herschel Telescope on La Palma. Exploiting the well-defined white dwarf and hotspot eclipse features, we derive an updated orbital ephemeris for IY UMa and an orbital period of 0.073 908 97(5) d. A white dwarf ingress/egress duration of 31 ± 2 s along with the contact phases of the bright-spot

Radial velocities of early-type stars in the Perseus OB2 association

Abstract: We present radial velocities for 29 B- and A-type stars in the field of the nearby association Perseus OB2. The velocities are derived from spectra obtained with AURELIE, via cross correlation with radial velocity standards matched as closely as possible in spectral type. The resulting accuracy is2-3 km s 1 . We use these measurements, together with published values for a few other early-type stars, to study membership of the association. The mean radial velocity (and measured velocity dispersion) of Per OB2 is 23:5 3: 9k m s 1 , and lies15 km s 1 away from the mean velocity of the local disk field stars. We identify a number of interlopers in the list of possible late-B- and A-type members which was based on Hipparcos parallaxes and proper motions, and discuss the colour-magnitude diagram of the association.

Temperature determination via STJ optical spectroscopy

Abstract: ESA's Superconducting Tunnel Junction (STJ) optical photon-counting camera (S-Cam2) incorporates an array of pixels with intrinsic energy sensitivity. Using the spectral fitting technique common in X-ray astronomy, we fit black bodies to nine stellar spectra, ranging from cool flare stars to hot white dwarfs. The measured temperatures are consistent with literature values at the expected level of accuracy based on the predicted gain stability of the instrument. Having also demonstrated that systematic eects due to count rate are likely to be small, we then proceed to apply the temperature determination method to four cataclysmic variable (CV) binary systems. In three cases we measure the temperature of the accretion stream, while in the fourth we measure the temperature of the white dwarf. The results are discussed in the context of existing CV results. We conclude by outlining the prospects for future versions of S-Cam.

Variability of the accretion stream in the eclipsing polar EP Dra

Abstract: We present the first high time resolution light curves for six eclipses of the magnetic cataclysmic variable EP Dra, taken using the superconducting tunnel junction imager S-Cam2. The system shows a varying eclipse profile between consecutive eclipses over the two nights of observation. We attribute the variable stream eclipse after accretion region ingress to a variation in the amount and location of bright material in the accretion stream. This material creates an accretion curtain as it is threaded by many field lines along the accretion stream trajectory. We identify this as the cause of absorption evident in the light curves when the system is in a high accretion state. We do not see direct evidence in the light curves for an accretion spot on the white dwarf; however, the variation of the stream brightness with the brightness of the rapid decline in flux at eclipse ingress indicates the presence of some form of accretion region. This accretion region is most likely located at high colatitude on the white dwarf surface, forming an arc shape at the foot points of the many field lines channelling the accretion curtain.

12x10 pixels superconducting tunnel junction array based spectro-photometer for optical astronomy

Abstract: Superconducting Tunnel Junctions (STJs) have been extensively investigated as photon detectors covering the range from near-infrared to X-ray energies A 6x6 array of Tantalum junctions has already been used in an optical spectro-photometer With this camera, the European Space Agency has performed multiple astronomical observations of optical sources using the William Herschel 42m telescope at La Palma Following the success of this program, we are now developing a second generation camera The goals of this program are to increase the field of view of the instrument from 4"x4" to 11"x9", to optimize IR rejection filters, possibly extending the 'red' response to ~1μm and to increase the electronics readout speed For these purposes, we are developing a new Superconducting Tunnel Junction Array consisting of 10x12 Tantalum/Aluminium devices as well as an improved readout system In this paper, we review the instrument's architecture and describe the performance of the new detector