Steve Bruce Howell

Kepler-63b: A Giant Planet in a Polar Orbit around a Young Sun-like Star

We present the discovery and characterization of a giant planet orbiting the young Sun-like star Kepler-63 (KOI-63, m_(Kp) = 11.6, T_(eff) = 5576 K, M_★ = 0.98 M_☉). The planet transits every 9.43 days, with apparent depth variations and brightening anomalies caused by large starspots. The planets radius is 6.1 ± 0.2 R_⊕, based on the transit light curve and the estimated stellar parameters. The planets mass could not be measured with the existing radial-velocity data, due to the high level of stellar activity, but if we assume a circular orbit, then we can place a rough upper bound of 120 M_⊕ (3σ). The host star has a high obliquity (ψ = 104°), based on the Rossiter-McLaughlin effect and an analysis of starspot-crossing events. This result is valuable because almost all previous obliquity measurements are for stars with more massive planets and shorter-period orbits. In addition, the polar orbit of the planet combined with an analysis of spot-crossing events reveals a large and persistent polar starspot. Such spots have previously been inferred using Doppler tomography, and predicted in simulations of magnetic activity of young Sun-like stars.

SPECTROSCOPY OF NEW AND POORLY KNOWN CATACLYSMIC VARIABLES IN THE KEPLER FIELD

The NASA Kepler mission has been in science operation since 2009 May and is providing high precision, high cadence light curves of over 150,000 targets. Prior to launch, nine cataclysmic variables were known to lie within Keplers field of view. We present spectroscopy for seven systems, four of which were newly discovered since launch. All of the stars presented herein have been observed by, or are currently being observed by, the Kepler space telescope. Three historic systems and one new candidate could not be detected at their sky position and two candidates are called into question as to their true identity.

A Photometric and Spectroscopic Study of the Cataclysmic Variable ST LMi during 2005-2006* **

We present orbit-resolved spectroscopic and photometric observations of the polar ST LMi during its recent low and high states. In the low-state spectra, we report the presence of blue and red satellites in the Hα emission line; the velocities and visibility of the satellites vary with phase. This behavior is similar to emission-line profile variations recently reported in the low state of AM Her, which were interpreted as being due to magnetically confined gas motions in large loops near the secondary. Our low-state spectroscopy of ST LMi is discussed in terms of extreme chromospheric activity on the secondary star. Concurrent photometry indicates that occasional low-level accretion may be present, as well as cool regions on the secondary near the inner Lagrangian point, L1. Furthermore, we report a new extreme low state of the system at V ~ 18.5 mag. Our orbital high-state spectroscopy reveals changes in the emission-line profiles with orbital phases that are similar to those reported by earlier high-state studies. The complicated emission-line profiles generally consist of two main components. The first has radial velocity variations identical to that of the major emission Hα component seen in the low state. The second is an additional redshifted component appearing at the phases of maximum visibility of the accreting column of the white dwarf; it is interpreted as being due to infall velocities on the accreting magnetic pole of the white dwarf. At the opposite phases, an extended blue emission wing appears on the emission-line profiles. We confirm the presence of a broad absorption feature near 6275 A, which has been previously identified as a Zeeman σ- absorption component of Hα. This feature appears at just those phases when the accretion pole region is most directly visible and most nearly face-on to the observer.

Discovery of Nonradial Pulsations in PQ Andromedae

We have detected pulsations in time‐series photometry of the WZ Sge dwarf nova PQ Andromedae. The strongest peak in the power spectrum occurs at a period of 10.5 minutes. Similar periods have been observed in other WZ Sge systems and are attributed to ZZ Ceti–type nonradial pulsations. There is no indication in the photometry of an approximately 1.7 hr orbital period, as reported in previous spectroscopic observations.

Lifting the Iron Curtain: Toward an Understanding of the Iron Stars XX Oph and AS 325

We present new optical, near-infrared, and archival ultraviolet observations of XX Ophiuchi and AS 325, two proposed iron stars. These unusual stars have optical spectra dominated by emission lines arising from hydrogen, as well as ionized metals such as iron, chromium, and titanium. Both stars have been classified as iron stars, and a number of exotic models have been presented for their origin. Using 2 years of moderately high resolution optical spectroscopy, the first high signal-to-noise ratio K-band spectroscopy of these sources (which reveals stellar photospheric absorption lines), and new near-infrared interferometric observations, we confirm that both systems are composed of two stars, likely binaries, containing a hot Be star with an evolved late-type secondary. The hydrogen emission features arise in the hot wind from the Be star, while the corresponding P-Cygni absorption lines are produced from dense material in the expanding, radiation-driven wind around each system. The optical Fe ii emission lines are pumped by ultraviolet Fe ii absorption lines through fluorescence. Contrary to some claims in the literature, the spectral features of XX Oph and AS 325 are quite similar, evidence that they are comparable systems. We examine the variability of the spectral morphology and radial velocity motions of both sources. We also study the variability of XX Oph during a major photometric event and find that the spectral nature of the system varies during the event. A comparison of the velocity of the absorption- line components in our new spectra with those in the literature show that the structure of the stellar wind from XX Oph has changed since the system was observed in 1951.

Magnetic White Dwarfs in the Two Micron All Sky Survey: A Search for Candidate Binary Systems

Our understanding of the formation and evolution of magnetic cataclysmic variables from initially detached, post-common-envelope binary stars containing a magnetic white dwarf and a main-sequence star is currently poorly constrained, due to the lack of observational identification of the progenitor systems. Very few potential pre-cataclysmic variables containing a magnetic white dwarf are known, compared with ≈25% of the cataclysmic variable population that contain magnetic white dwarfs. We present the results of a search for candidate binary systems containing a magnetic white dwarf, which utilized photometric data from the Two Micron All Sky Survey (2MASS; as well as Hubble Space Telescope and WIYN Observatory follow-up data for several objects). Our target sample was drawn primarily from the comprehensive list of magnetic white dwarfs by Wickramasinghe & Ferrario, plus several recently identified objects selected from the literature. Out of 51 2MASS detections, no convincing binary candidates were found. However, six objects merit additional observation to determine the origin of a small near-infrared excess that could be attributed to a very low mass stellar or substellar companion. An additional four white dwarfs are possibly at the centers of previously unknown, and likely unresolved, planetary nebulae.

A decade of extrasolar planets around normal stars: The Kepler Mission: Design, expected science results, opportunities to participate

Kepler is a Discovery-class mission designed to determine the frequency of Earth-size and smaller planets in and near the habitable zone (HZ) of spectral type F through M dwarf stars. The instrument consists of a 0.95 m aperture photometer to do high precision photometry of 100,000 solar-like stars to search for patterns of transits. The depth and repetition time of transits provide the size of the planet relative to the star and its orbital period. Multi-band ground-based observation of these stars is currently underway to estimate the stellar parameters and to choose appropriate targets. With these parameters, the true planet radius and orbit scale, hence the relation to the HZ can be determined. These spectra are also used to discover the relationships between the characteristics of planets and the stars they orbit. In particular, the association of planet size and occurrence frequency with stellar mass and metallicity will be investigated. At the end of the four year mission, several hundred terrestrial planets should be discovered with periods between 1 day and 400 days if such planets are common. A null result would imply that terrestrial planets are rare. Based on the results of the recent Doppler-velocity discoveries, over a thousand giant planets will also be found. Information on the albedos and densities of those giants showing transits will be obtained. The mission is now in Phase C/D development and is scheduled for launch in 2008 into a 372-day heliocentric orbit.

Periodic Variables and Gyrochronology in the Open Cluster NGC 2301

We present the results of a search for periodic variables within 4078 time-series light curves and an analysis of the period-color plane for stars in the field of the open cluster NGC 2301. One hundred thirty-eight periodic variables were discovered, of which five are eclipsing binary candidates with unequal minima. The remaining 133 periodic variables appear to consist mainly of late-type stars whose variation is due to rotation modulated by star spot activity. The determined periods range from less than a day to over 14 days and have nearly unreddened B - R colors in the range of 0.8 to 2.8. The Barnes (2003) interpretation of the period-color plane of late type stars is tested with our data. Our data did not show distinct I and C sequences, likely due to nonmember field stars contaminating in the background, as we estimate the total contamination to be 43%. Using different assumptions, the gyrochronological age of the cluster is calculated to be 210 ± 25 Myr, which falls in the range of age values (164-250 Myr) determined by previous studies. Finally, we present evidence which nullifies the earlier suggestion that two of the variable stars in NGC 2301 might be white dwarfs.

Behind the Iron Curtain: The Environments of the Iron Stars AS 325 and XX Oph

ABSTRACT.We present new photometric and spectroscopic observations of the Iron stars AS 325 and XX Oph. Both stars are binaries composed of a Be star primary plus a luminous red star. Long-term optical photometry of AS 325 reveals it to be a 513-day period eclipsing binary with highly variable eclipses. The primary eclipse is that of the Be star with no secondary eclipse observed. This is not surprising given the small comparative size of the more massive companion. The red star in AS 325 is observed to be a variable star ranging from K2.5 to a M5 in spectral type and shown to be a supergiant of luminosity class II. The red secondary star is the major cause of the variable eclipses. A simple model is advanced to explain the complex behavior observed for Balmer hydrogen emission and Caxa0II H and K absorption lines as a function of eclipse phase. Spatially resolved near-IR spectroscopy of XX Oph shows the binary to be sitting in a large cavity-like region of space surrounded by reflective dust. AS 325 and XX...

ORBIT-RESOLVED PHOTOMETRY AND ECHELLE SPECTROSCOPY OF THE CATACLYSMIC VARIABLE ST LMi DURING A 2007 HIGH STATE

We present high-resolution echelle spectra and contemporaneous photometry of the polar ST LMi during a high state in 2007 March. Emission lines at Hα, He I λ5876, and He I λ7065 show similar line profiles over orbital phase and have narrow and broad components. These profile changes with phase are very similar to those reported in earlier high-state studies of ST LMi. The radial velocity curves from double Gaussian fits to the line profiles are interpreted as two crossing curves, neither of which is coincident with the orbital motion of the secondary star. We attribute one component to infall motions near the white dwarf and the other to a gas streaming along magnetic field lines connecting the two stars.