B. H. Dunlap

A radio pulsar/x-ray binary link

From X-ray Binary to Pulsar Pulsars with millisecond rotational periods are thought to originate from neutron stars in low-mass x-ray binaries that had their spin frequencies increased by long-lasting mass transfer from their companion stars. Using data from a radio pulsar survey, Archibald et al. (p. 1411, published online 21 May; see the Perspective by Kramer) found a neutron star in a low-mass X-ray binary that is in the process of turning into a radio millisecond pulsar. The system, which consists of a solar-like star and a 1.69-millisecond radio pulsar, has gone through a recent accretion phase, characteristic of low-mass X-ray binaries, but it shows no accretion disk anymore, confirming the evolutionary connection between millisecond radio pulsars and low-mass X-ray binaries. Radio observations reveal a system undergoing the transition from a low-mass x-ray binary star to a millisecond radio pulsar. Radio pulsars with millisecond spin periods are thought to have been spun up by the transfer of matter and angular momentum from a low-mass companion star during an x-ray–emitting phase. The spin periods of the neutron stars in several such low-mass x-ray binary (LMXB) systems have been shown to be in the millisecond regime, but no radio pulsations have been detected. Here we report on detection and follow-up observations of a nearby radio millisecond pulsar (MSP) in a circular binary orbit with an optically identified companion star. Optical observations indicate that an accretion disk was present in this system within the past decade. Our optical data show no evidence that one exists today, suggesting that the radio MSP has turned on after a recent LMXB phase.

A progenitor binary and an ejected mass donor remnant of faint type Ia supernovae

Type Ia supernovae (SN Ia) are the most important standard candles for measuring the expansion history of the universe. The thermonuclear explosion of a white dwarf can explain their observed properties, but neither the progenitor systems nor any stellar remnants have been conclusively identified. Underluminous SN Ia have been proposed to originate from a so-called double-detonation of a white dwarf. After a critical amount of helium is deposited on the surface through accretion from a close companion, the helium is ignited causing a detonation wave that triggers the explosion of the white dwarf itself. We have discovered both shallow transits and eclipses in the tight binary system CD-30 degrees 11223 composed of a carbon/oxygen white dwarf and a hot helium star, allowing us to determine its component masses and fundamental parameters. In the future the system will transfer mass from the helium star to the white dwarf. Modelling this process we find that the detonation in the accreted helium layer is sufficiently strong to trigger the explosion of the core. The helium star will then be ejected at such high velocity that it will escape the Galaxy. The predicted properties of this remnant are an excellent match to the so-called hypervelocity star US 708, a hot, helium-rich star moving at more than 750 km s(-1), sufficient for it to leave the Galaxy. The identification of both progenitor and remnant provides a consistent picture of the formation and evolution of underluminous SNIa.

Evryscope Science: Exploring the Potential of All-Sky Gigapixel-Scale Telescopes

Low-cost mass-produced sensors and optics have recently made it feasible to build telescope arrays which observe the entire accessible sky simultaneously. In this article, we discuss the scientific motivation for these telescopes, including exoplanets, stellar variability, and extragalactic transients. To provide a concrete example we detail the goals and expectations for the Evryscope, an under-construction 780 MPix telescope which covers 8660 sq. deg. in each 2-minute exposure; each night, 18,400 sq. deg. will be continuously observed for an average of ≈6 hr. Despite its small 61 mm aperture, the systems large field of view provides an etendue which is ~10% of LSST. The Evryscope, which places 27 separate individual telescopes into a common mount which tracks the entire accessible sky with only one moving part, will return 1%-precision, many-year-length, high-cadence light curves for every accessible star brighter than ~16th magnitude. The camera readout times are short enough to provide near-continuous observing, with a 97% survey time efficiency. The array telescope will be capable of detecting transiting exoplanets around every solar-type star brighter than mV = 12, providing at least few-millimagnitude photometric precision in long-term light curves. It will be capable of searching for transiting giant planets around the brightest and most nearby stars, where the planets are much easier to characterize; it will also search for small planets nearby M-dwarfs, for planetary occultations of white dwarfs, and will perform comprehensive nearby microlensing and eclipse-timing searches for exoplanets inaccessible to other planet-finding methods. The Evryscope will also provide comprehensive monitoring of outbursting young stars, white dwarf activity, and stellar activity of all types, along with finding a large sample of very-long-period M-dwarf eclipsing binaries. When relatively rare transients events occur, such as gamma-ray bursts (GRBs), nearby supernovae, or even gravitational wave detections from the Advanced LIGO/Virgo network, the array will return minute-by-minute light curves without needing pointing toward the event as it occurs. By coadding images, the system will reach V ~ 19 in 1-hr integrations, enabling the monitoring of faint objects. Finally, by recording all data, the Evryscope will be able to provide pre-event imaging at 2-minute cadence for bright transients and variable objects, enabling the first high-cadence searches for optical variability before, during and after all-sky events.

EC 10246−2707: an eclipsing subdwarf B + M dwarf binary

We announce the discovery of a new eclipsing hot subdwarf B + M dwarf binary, EC 10246-2707, and present multi-colour photometric and spectroscopic observations of this system. Similar to other HW Vir-type binaries, the light curve shows both primary and secondary eclipses, along with a strong reflection effect from the M dwarf; no intrinsic light contribution is detected from the cool companion. The orbital period is 0.1185079936 +/- 0.0000000009 days, or about three hours. Analysis of our time-series spectroscopy reveals a velocity semi-amplitude of K_1 = 71.6 +/- 1.7 km/s for the sdB and best-fitting atmospheric parameters of Teff = 28900 +/- 500 K, log g = 5.64 +/- 0.06, and log[N(He)/N(H)] = -2.5 +/- 0.2. Although we cannot claim a unique solution from modeling the light curve, the best-fitting model has an sdB mass of 0.45 Msun and a cool companion mass of 0.12 Msun. These results are roughly consistent with a canonical-mass sdB and M dwarf separated by a ~ 0.84 Rsun. We find no evidence of pulsations in the light curve and limit the amplitude of rapid photometric oscillations to 7.2 x 10^(-12). If EC 10246-2707 evolves into a cataclysmic variable, its period should fall below the famous CV period gap.

A SECOND CASE OF OUTBURSTS IN A PULSATING WHITE DWARF OBSERVED BY KEPLER

We present observations of a new phenomenon in pulsating white dwarf stars: large-amplitude outbursts at timescales much longer than the pulsation periods. The cool (

Two New Variable Hot DQ Stars

{T}_{\mathrm{eff}}

An eclipsing post common-envelope system consisting of a pulsating hot subdwarf B star and a brown dwarf companion

= 11,060 K), hydrogen-atmosphere pulsating white dwarf PG 1149+057 was observed nearly continuously for more than 78.8 day by the extended Kepler mission in K2 Campaign 1. The target showed 10 outburst events, recurring roughly every 8 day and lasting roughly 15 hr, with maximum flux excursions up to 45% in the Kepler bandpass. We demonstrate that the outbursts affect the pulsations and therefore must come from the white dwarf. Additionally, we argue that these events are not magnetic reconnection flares, and are most likely connected to the stellar pulsations and the relatively deep surface convection zone. PG 1149+057 is now the second cool pulsating white dwarf to show this outburst phenomenon, after the first variable white dwarf observed in the Kepler mission, KIC 4552982. Both stars have the same effective temperature, within the uncertainties, and are among the coolest known pulsating white dwarfs of typical mass. These outbursts provide fresh observational insight into the red edge of the DAV instability strip and the eventual cessation of pulsations in cool white dwarfs.

A 1.05?M ? Companion to PSR J2222?0137: The Coolest Known White Dwarf?

We have discovered periodic variations in the light curves of two hot DQ stars from the Sloan Digital Sky Survey, SDSS J220029.08–074121.5 and SDSS J234843.30–094245.3. These are the second and third variables detected among the hot DQs and confirm the existence of a new class of variable white dwarf stars. The amplitudes of the variations are one half as large as those detected in the first discovered variable, SDSS J142625.71+575218.3, and required high signal-to-noise photometry to detect. The pulse shapes of the stars are not like those of known white dwarf pulsators but are similar to the first hot DQ variable, SDSS J142625.71+575218.3.

Radial Velocity Confirmation of a Binary Detected from Pulse Timings

Hot subdwarf B stars (sdBs) are evolved, core helium-burning objects located on the extreme horizontal branch. Their formation history is still puzzling as the sdB progenitors must lose nearly all of their hydrogen envelope during the red-giant phase. About half of the known sdBs are in close binaries with periods from 1.2 h to a few days, a fact that implies they experienced a common-envelope phase. Eclipsing hot subdwarf binaries (also called HW Virginis systems) are rare but important objects for determining fundamental stellar parameters. Even more significant and uncommon are those binaries containing a pulsating sdB, as the mass can be determined independently by asteroseismology. Here we present a first analysis of the eclipsing hot subdwarf binary V2008-1753. The light curve shows a total eclipse, a prominent reflection effect, and low--amplitude pulsations with periods from 150 to 180 s. An analysis of the light-- and radial velocity (RV) curves indicates a mass ratio close to

Fortnightly fluctuations in the O―C diagram of CS 1246

q = 0.146