Ming Zhao

Imaging the Surface of Altair

Spatially resolving the surfaces of nearby stars promises to advance our knowledge of stellar physics. Using optical long-baseline interferometry, we constructed a near-infrared image of the rapidly rotating hot star Altair with a resolution of <1 milliarcsecond. The image clearly reveals the strong effect of gravity darkening on the highly distorted stellar photosphere. Standard models for a uniformly rotating star cannot explain our findings, which appear to result from differential rotation, alternative gravity-darkening laws, or both.

The antidepressant sertraline improves the phenotype, promotes neurogenesis and increases BDNF levels in the R6/2 Huntington's disease mouse model

Huntingtons disease (HD) is an inherited progressive neurodegenerative disorder characterized by progressive movement, psychiatric and cognitive disturbances. Previous studies have indicated that HD pathogenesis may be mediated in part by loss of brain derived neurotrophic factor (BDNF). Antidepressants selectively blocking serotonin reuptake can increase BDNF levels, and also may increase neurogenesis. Here we report that an SSRI antidepressant, sertraline, prolongs survival, improves motor performance, and ameliorates brain atrophy in the R6/2 HD mouse model. Six-week-old R6/2 mice and nontransgenic control mice were administered either sertraline or vehicle daily. Motor function was assessed in an accelerating rotarod test and evaluated at 10 weeks. R6/2 mice exhibited reduced time on the rod. Sertraline treatment improved the motor performance in R6/2 mice, but did not affect nontransgenic mice. R6/2 mice showed significant striatal atrophy which was reduced by sertraline treatment. These beneficial effects of sertraline are associated with enhanced neurogenesis and increased BDNF levels in brain treated with sertraline. The effective serum and brain levels of sertraline are comparable to the levels achieved in human antidepressant treatment. Our findings provide evidence that sertraline is neuroprotective in this HD model. Successful treatment with sertraline in depressed HD patients has been reported; moreover, sertraline is safe and well-tolerated for long-term administration, including in HD patients. Our findings suggest that a clinical trial of SSRI treatment in order to retard disease progression in human HD may be warranted.

Exoplanet Orbit Database. II. Updates to Exoplanets.org

The Exoplanet Orbit Database (EOD) compiles orbital, transit, host star, and other parameters of robustly-detected exoplanets reported in the peer-reviewed literature. The EOD can be navigated through the Exoplanet Data Explorer (EDE) plotter and table, available on the World Wide Web at exoplanets.org. The EOD contains data for 1492 confirmed exoplanets as of 2014 July. The EOD descends from a table provided by Butler and coworkers in 2002 and the Catalog of Nearby Exoplanets (Butler and coworkers in 2006), and the first complete documentation for the EOD and the EDE was presented by Wright and coworkers in 2011. In this work, we describe our work since then. We have expanded the scope of the EOD to include secondary eclipse parameters and asymmetric uncertainties and expanded the EDE to include the sample of over 3000 Kepler Objects of Interest (KOIs) and other real planets without good orbital parameters (such as many of those detected by microlensing and imaging). Users can download the latest version of the entire EOD as a single comma separated value file from the front page of exoplanets.org.

Sertraline slows disease progression and increases neurogenesis in N171-82Q mouse model of Huntington's disease

Huntingtons disease (HD) is an inherited progressive neurodegenerative disorder resulting from CAG repeat expansion in the gene that encodes for the protein huntingtin. To identify neuroprotective compound (s) that can slow down disease progression and can be administered long term with few side effects in Huntingtons disease, we investigated the effect of sertraline, a selective serotonin reuptake inhibitor (SSRI) which has been shown to upregulate BDNF levels in rodent brains. We report here that in HD mice sertraline increased BDNF levels, preserved chaperone protein HSP70 and Bcl-2 levels in brains, attenuated the progression of brain atrophy and behavioral abnormalities and thereby increased survival. Sertraline also enhanced neurogenesis, which appeared to be responsible for mediating the beneficial effects of sertraline in HD mice. Additionally, the effective levels of sertraline are comparable to the safe levels achievable in humans. The findings suggest that sertraline is a potential candidate for treatment of HD patients.

Imaging and Modeling Rapidly Rotating Stars: α Cephei and α Ophiuchi

We present submilliarcsecond resolution imaging and modeling of two nearby rapid rotators α Cephei and α Ophiuchi, obtained with the CHARA array—the largest optical/IR interferometer in the world. Incorporating a gravity-darkening model, we are able to determine the inclination, the polar and equatorial radius and temperature, as well as the fractional rotation speed of the two stars with unprecedented precision. The polar and equatorial regions of the two stars have ∼2000 K temperature gradient, causing their apparent temperatures and luminosities to be dependent on their viewing angles. Our modeling allow us to determine the true effective temperatures and luminosities of α Cep and α Oph, permitting us to investigate their true locations on the H-R diagram. These properties in turn give us estimates of the masses and ages of the two stars within a few percent of error using stellar evolution models. Also, based on our gravity-darkening modeling, we propose a new method to estimate the masses of single stars in a more direct way through V sin i measurements and precise geometrical constraint. Lastly, we investigate the degeneracy between the inclination and the gravity-darkening coefficient, which especially affects the modeling of α Oph. Although incorporating V sin i has lifted the degeneracy to some extent, higher-resolution observations are still needed to further constrain the parameters independently.

COLDER AND HOTTER: INTERFEROMETRIC IMAGING OF β CASSIOPEIAE AND α LEONIS

Near-infrared interferometers have recently imaged a number of rapidly rotating A-type stars, finding levels of gravity darkening inconsistent with theoretical expectations. Here, we present new imaging of both a cooler star ??Cas (F2IV) and a hotter one ? Leo (B7V) using the CHARA array and the MIRC instrument at the H band. Adopting a solid-body rotation model with a simple gravity darkening prescription, we modeled the stellar geometric properties and surface temperature distributions, confirming that both stars are rapidly rotating and show gravity darkening anomalies. We estimate the masses and ages of these rapid rotators on L-R pol and H-R diagrams constructed for non-rotating stars by tracking their non-rotating equivalents. The unexpected fast rotation of the evolved sub-giant ??Cas offers a unique test of the stellar core-envelope coupling, revealing quite efficient coupling over the past ~0.5?Gyr. Lastly, we summarize all our interferometric determinations of the gravity darkening coefficient for rapid rotators, finding that none match the expectations from the widely used von Zeipel gravity darkening laws. Since the conditions of the von Zeipel law are known to be violated for rapidly rotating stars, we recommend using the empirically derived ??= 0.19 for such stars with radiation-dominated envelopes. Furthermore, we note that no paradigm exists for self-consistently modeling heavily gravity-darkened stars that show hot radiative poles with cool convective equators.

FIRST RESOLVED IMAGES OF THE ECLIPSING AND INTERACTING BINARY β LYRAE

We present the first resolved images of the eclipsing binary β Lyrae, obtained with the CHARA Array interferometer and the MIRC combiner in the H band. The images clearly show the mass donor and the thick disk surrounding the mass gainer at all six epochs of observation. The donor is brighter and generally appears elongated in the images, the first direct detection of photospheric tidal distortion due to Roche lobe filling. We also confirm expectations that the disk component is more elongated than the donor and is relatively fainter at this wavelength. Image analysis and model fitting for each epoch were used for calculating the first astrometric orbital solution for β Lyrae, yielding precise values for the orbital inclination and position angle. The derived semimajor axis also allows us to estimate the distance of β Lyrae; however, systematic differences between the models and the images limit the accuracy of our distance estimate to about 15%. To address these issues, we will need a more physical, self-consistent model to account for all epochs as well as the multiwavelength information from the eclipsing light curves.

Resolving Vega and the inclination controversy with CHARA/MIRC

Optical and infrared interferometers definitively established that the photometric standard Vega (={alpha} Lyrae) is a rapidly rotating star viewed nearly pole-on. Recent independent spectroscopic analyses could not reconcile the inferred inclination angle with the observed line profiles, preferring a larger inclination. In order to resolve this controversy, we observed Vega using the six-beam Michigan Infrared Combiner on the Center for High Angular Resolution Astronomy Array. With our greater angular resolution and dense (u, v)-coverage, we find that Vega is rotating less rapidly and with a smaller gravity darkening coefficient than previous interferometric results. Our models are compatible with low photospheric macroturbulence and are also consistent with the possible rotational period of {approx}0.71 days recently reported based on magnetic field observations. Our updated evolutionary analysis explicitly incorporates rapid rotation, finding Vega to have a mass of 2.15{sup +0.10}{sub -0.15} M{sub Sun} and an age 700{sup -75}{sub +150} Myr, substantially older than previous estimates with errors dominated by lingering metallicity uncertainties (Z = 0.006{sup +0.003}{sub -0.002}).

In the Shadow of the Transiting Disk: Imaging epsilon Aurigae in Eclipse

Epsilon Aurigae (ε Aur) is a visually bright, eclipsing binary star system with a period of 27.1 years. The cause of each 18-month-long eclipse has been a subject of controversy for nearly 190 years because the companion has hitherto been undetectable. The orbital elements imply that the opaque object has roughly the same mass as the visible component, which for much of the last century was thought to be an F-type supergiant star with a mass of ∼15M⊙ (M⊙, mass of the Sun). The high mass-to-luminosity ratio of the hidden object was originally explained by supposing it to be a hyperextended infrared star or, later, a black hole with an accretion disk, although the preferred interpretation was as a disk of opaque material at a temperature of ∼500 K, tilted to the line of sight and with a central opening. Recent work implies that the system consists of a low-mass (2.2M⊙–3.3M⊙) visible F-type star, with a disk at 550 K that enshrouds a single B5V-type star. Here we report interferometric images that show the eclipsing body moving in front of the F star. The body is an opaque disk and appears tilted as predicted. Adopting a mass of 5.9M⊙ for the B star, we derive a mass of ∼(3.6 ± 0.7)M⊙ for the F star. The disk mass is dynamically negligible; we estimate it to contain ∼0.07M⊕ (M⊕, mass of the Earth) if it consists purely of dust.directly detected the eclipsing body, allowing us to measure theproperties of the companion. We used the MIRC four-telescopebeam combiner at the CHARA Array to obtain images of epsilonAurigae during ingress into eclipse during autumn 2009. Theseimages show the intrusion of a dark, elongated structure that re-sembles the large disk as rst discussed by Ludendor

An interferometry imaging beauty contest

We present a formal comparison of the performance of algorithms used for synthesis imaging with optical/infrared long-baseline interferometers. Five different algorithms are evaluated based on their performance with simulated test data. Each set of test data is formatted in the OI-FITS format. The data are calibrated power spectra and bispectra measured with an array intended to be typical of existing imaging interferometers. The strengths and limitations of each algorithm are discussed.