arXiv subjects

Jonathan Kemp

Publications and source records attributed to Jonathan Kemp.

21 records · Page 2Linked to original sources

arXiv2002

1RXS J232953.9+062814: A Dwarf Nova with a 64-minute Orbital Period and a Conspicuous Secondary Star

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. 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 around the orbit. The orbital period is shorter than any other cataclysmic variable save for a handful of helium-star systems and V485 Centauri (59 minutes). The secondary is much hotter than main sequence stars of similar mass, but is well-matched by helium-enriched models, indicating that the secondary evolved from a more massive progenitor. A preliminary calculation in which a 1.2 solar-mass star begins mass transfer near the end of H burning matches this system's characteristics remarkably well.

astro-ph↗

arXiv2000

Outbursts of EX Hydrae: mass-transfer events or disc instabilities?

We present the 45-yr record of EX Hya's lightcurve and discuss the characteristics of its 15 observed outbursts. We then concentrate on the 1998 outburst, reporting the first outburst X-ray observations. We discover an X-ray beat-cycle modulation, indicating that an enhanced accretion stream couples directly with the magnetosphere in outburst, confirming our previous prediction. Optical eclipse profiles late in outburst show that the visible light is dominated by an enhanced mass-transfer stream overflowing the accretion disc. We are uncertain whether the enhanced mass transfer is triggered by a disc instability, or by some other cause. While in outburst, EX Hya shows some of the characteristics of SW Sex stars.

astro-ph↗

arXiv1999

XTE J2123-058: A New Neutron Star X-Ray Transient

We report on optical and RXTE observations of a new high-latitude bursting X-ray transient, XTE J2123-058. We identified the optical counterpart, measured the 5.9573 hr orbital period and constrained the binary inclination and the source distance. The distance lower limit indicates that the source is at least 2.6 kpc from the Galactic plane, which is unusual for an LMXB. RXTE observations were made between June and August 1998 during the first detected outburst from this source. We describe correlations between X-ray timing and spectral properties and discuss the possibility that the propeller mechanism turned on during the decay of the outburst. During one of the RXTE observations, we detect a pair of high frequency QPOs at 847.1 +/- 5.5 Hz and 1102 +/- 13 Hz simultaneously. According to the beat frequency model, the QPO separation implies a neutron star spin period near 3.9 ms. As the X-ray flux decreases at the end of the outburst, the amplitude of the optical modulation increases significantly. This behavior can be explained if the size of the accretion disk decreases during the decay of the outburst.

astro-ph↗