Paul A. Mason

AR Ursae Majoris Discovered to Be a Persistent Radio Polar: Results from a VLA Survey of Magnetic Cataclysmic Variables

We conducted a VLA survey of nine magnetic cataclysmic variable stars (MCVs) at 8.436 GHz in 2003 October, to constrain models of radio emission. A follow-up study was conducted in 2004 September. We obtained the first radio detections of AR UMa, the MCV with the highest known magnetic field (230 MG), at flux densities of 0.422 ± 0.060 mJy (2003 October 16) and 0.734 ± 0.095 mJy (2004 September 4). We have completed the sample of radio observations of MCVs out to 100 pc. Surprisingly, the only radio-selected CV, FIRST J1023+0038, was not detected. An upper limit of 0.20 mJy (4 σ) was obtained. The original radio MCV, AM Her, was detected with a flux density of 0.586 ± 0.074 mJy (2003 October 17), consistent with previous observations. Typical (4 σ) upper limits of 0.12 mJy were obtained for other targets. The lack of radio emission from isolated magnetic white dwarfs, as well as from nonmagnetic CVs (outside of outburst), places constraints on radio emission mechanisms for CVs. We suggest that accretion disks may preclude radio emission. Also, since we detect radio emission from AM Her in a low state and the pre-CV V471 Tau is a persistent radio source, accretion is not a necessary condition. A secondary with a kilogauss magnetic field might be necessary. We argue that the emission from AR UMa originates near the secondary. AR UMa joins AM Her and AE Aqr as the only confirmed persistent radio MCVs, and we suggest avenues of further study.

Rotational Synchronization May Enhance Habitability for Circumbinary Planets: Kepler Binary Case Studies

We report a mechanism capable of reducing (or increasing) stellar activity in binary stars, thereby potentially enhancing (or destroying) circumbinary habitability. In single stars, stellar aggression towards planetary atmospheres causes mass-loss, which is especially detrimental for late-type stars, because habitable zones are very close and activity is long lasting. In binaries, tidal rotational breaking reduces magnetic activity, thus reducing harmful levels of XUV radiation and stellar mass-loss that are able to erode planetary atmospheres. We study this mechanism for all confirmed circumbinary (p-type) planets. We find that main sequence twins provide minimal flux variation and in some cases improved environments, if the stars rotationally synchronize within the first Gyr. Solar-like twins, like Kepler 34 and Kepler 35, provide low habitable zone XUV fluxes and stellar wind pressures. These wide, moist, habitable zones may potentially support multiple habitable planets. Solar-type stars with lower mass companions, like Kepler 47, allow for protected planets over a wide range of secondary masses and binary periods. Kepler 38 and related binaries are marginal cases. Kepler 64 and analogues have dramatically reduced stellar aggression due to synchronization of the primary, but are limited by the short lifetime. Kepler 16 appears to be inhospitable to planets due to extreme XUV flux. These results have important implications for estimates of the number of stellar systems containing habitable planets in the Galaxy and allow for the selection of binaries suitable for follow-up searches for habitable planets.

The Optical Orbital Light Curve Of The Low-Mass X-Ray Binary V1408 Aquilae (=4U 1957+115)

V1408 Aql (= 4U 1957+115) is a low-mass X-ray binary with an orbital period of nearly 9.3 hr, whose compact star is a black hole candidate. The system shows a large-amplitude orbital photometric modulation at optical wavelengths. We have obtained new optical photometry of V1408 Aql from which we derive the orbital light curve and an improved orbital ephemeris. We show that the orbital light curve can be reproduced by a model in which the accretion disk around the compact star is thin, axisymmetric, and uneclipsed. The secondary star is heated by X-rays from the compact star and the accretion disk. The orbital modulation is produced entirely by the changing aspect of the irradiated secondary star with orbital phase. Because the system does not eclipse, the fits of the model light curves are insensitive to the orbital parameters, allowing a wide range of orbital inclinations and mass ratios.

CONSTRAINING THE RADIATION AND PLASMA ENVIRONMENT OF THE KEPLER CIRCUMBINARY HABITABLE-ZONE PLANETS

The discovery of many planets using the Kepler telescope includes ten planets orbiting eight binary stars. Three binaries, Kepler-16, Kepler-47, and Kepler-453, have at least one planet in the circumbinary habitable-zone (BHZ). We constrain the level of high-energy radiation and the plasma environment in the BHZ of these systems. With this aim, BHZ limits in these Kepler binaries are calculated as a function of time, and the habitability lifetimes are estimated for hypothetical terrestrial planets and/or moons within the BHZ. With the time-dependent BHZ limits established, a self-consistent model is developed describing the evolution of stellar activity and radiation properties as proxies for stellar aggression toward planetary atmospheres. Modeling binary stellar rotation evolution, including the effect of tidal interaction between stars in binaries is key to establishing the environment around these systems. We find that Kepler-16 and its binary analogs provide a plasma environment favorable for the survival of atmospheres of putative Mars-sized planets and exomoons. Tides have modified the rotation of the stars in Kepler-47 making its radiation environment less harsh in comparison to the solar system. This is a good example of the mechanism first proposed by Mason et al. Kepler-453 has an environment similar to that of the solar system with slightly better than Earth radiation conditions at the inner edge of the BHZ. These results can be reproduced and even reparametrized as stellar evolution and binary tidal models progress, using our online tool this http URL

THE CASE FOR A LOW MASS BLACK HOLE IN THE LOW MASS X-RAY BINARY V1408 AQUILAE (= 4U 1957+115)

There are very few confirmed black holes with a mass that could be

Comparison of the BATSE LAD & SD light curves of Sco X-1: 1991–1996

\sim\! 4\, M_\odot

A Jansky VLA Survey of Magnetic Cataclysmic Variable Stars. I. The Data

and no neutron stars with masses greater than

The Habitability of Circumbinary Planets: Stellar and Planetary Interaction

\sim\! 2\, M_\odot

High-energy transient events from Scorpius X-1 and Cygnus X-1

, creating a gap in the observed distribution of compact star masses. Some black holes with masses between 2 and

Long-term Optical Observations of Two LMXBS: UW CrB (=MS 1603+260) and V1408 Aql (=4U 1957+115)

4\, M_\odot