A5026653013- Stellar, planetary, and galactic studies
- Gamma-ray bursts and supernovae
- Astronomy and Astrophysical Research
- Astrophysics and Star Formation Studies
- Astrophysics and Cosmic Phenomena
- Pulsars and Gravitational Waves Research
- Astrophysical Phenomena and Observations
- Calibration and Measurement Techniques
- Geophysics and Gravity Measurements
- Adaptive optics and wavefront sensing
- Astronomical Observations and Instrumentation
- Astro and Planetary Science
- Solar and Space Plasma Dynamics
- Geophysics and Sensor Technology
- Electrochemical Analysis and Applications
- Atomic and Molecular Physics
- Ionosphere and magnetosphere dynamics
- High-pressure geophysics and materials
- Electron and X-Ray Spectroscopy Techniques
- Characterization and Applications of Magnetic Nanoparticles
- Particle Accelerators and Free-Electron Lasers
- Geological and Geophysical Studies
- Particle Detector Development and Performance
- Magneto-Optical Properties and Applications
- Statistical and numerical algorithms
Norwich University
2017-2019
Weber State University
2013-2015
University of Denver
2015
East Tennessee State University
2010-2015
University of Wisconsin–Madison
2006-2010
Association of Universities For Research In Astronomy
2009
U.S. National Science Foundation
2009
Kitt Peak National Observatory
2009
Center for Astrophysics Harvard & Smithsonian
2003
Smithsonian Astrophysical Observatory
2000
We present the current results from our ongoing radial-velocity (RV) survey of intermediate-age (2.4 Gyr) open cluster NGC 6819. Using both newly observed and other available photometry astrometry, we define a primary target sample 1454 stars that includes main-sequence, subgiant, giant, blue straggler stars, spanning magnitude range 11 ⩽V⩽ 16.5 an approximate mass 1.1–1.6 M☉. Our covers 23 arcminute (13 pc) square field view centered on cluster. have measured 6571 radial velocities for...
We report on both high-precision photometry from the MOST space telescope and ground-based spectroscopy of triple system delta Ori A consisting a binary O9.5II+early-B (Aa1 Aa2) with P = 5.7d, more distant tertiary (O9 IV > 400 yrs). This data was collected in concert X-ray Chandra Observatory. Thanks to continuous coverage for 3 weeks, light curve reveals clear eclipses between Aa1 Aa2 first time non-phased data. From we have well constrained radial velocity Aa1. While are unable recover...
Polarization has been detected at early times for all types of supernovae (SNe), indicating that such systems result from or quickly develop some form asymmetry. In addition, the detection strong line polarization in SNe is suggestive chemical inhomogeneities ("clumps") layers above photosphere, which may reflect hydrodynamical instabilities during explosion. We have developed a fast, flexible, approximate semi-analytic code modeling polarized radiative transfer within three-dimensional...
We present time-resolved and phase-resolved variability studies of an extensive X-ray high-resolution spectral dataset the $\delta$ Orionis Aa binary system. The four observations, obtained with Chandra ACIS HETGS, have a total exposure time ~479 ks provide nearly complete phase coverage. Variability flux in range 5-25 $\AA$ is confirmed, maximum amplitude about +/-15% within single ~125 observation. Periods 4.76d 2.04d are found flux, as well apparent overall increase level throughout 9-day...
In this paper we present and compare flight results with the latest of ground calibration for HRC-I detector. particular will in data on detector background, effective area, quantum efficiency point spread response function.
We present an overview of four phase-constrained Chandra HETGS X-ray observations Delta Ori A. A is actually a triple system which includes the nearest massive eclipsing spectroscopic binary, Aa, only such object can be observed with little phase-smearing gratings. Since fainter star, Aa2, has much lower luminosity than brighter primary, provides unique to test spatial distribution emitting gas around Aa1 via occultation by photosphere and wind cavity dark secondary. Here we discuss spectrum...
Aims: This paper extends previous studies in modeling time varying linear polarization due to axisymmetric magnetic fields rotating stars. We use the Hanle effect predict variations net line polarization, and geometric arguments generalize these results other mechanisms. Methods: Building on work of Lopez Ariste et al., we simple analytic models stars that are symmetric except for an field lightcurve effect. highlight effects variable as a function viewing inclination axis obliquity....
AH Cep and CW are both early B-type binaries with short orbital periods of 1.8 days 2.7 days, respectively. All four components B0.5V types. The also double-lined spectroscopic eclipsing. Consequently, solutions for stellar parameters make the pair ideal targets a study colliding winds between two B stars. Chandra ACIS-I observations were obtained to determine X-ray luminosities. was detected an unabsorbed luminosity at 90% confidence interval erg s−1, or , relative combined Bolometric...
Observations suggest that stars lose appreciable angular momentum prior to reaching the main sequence. Two principal spin-down mechanisms have been proposed. One is removal of by magnetized winds or jets; other transfer from star its accretion disk through effects magnetic fields. In latter case, spin evolution occurs due both mass along field lines and torques resulting coupling stellar disk. this paper we study in context a varying time. We find variability reduces efficiency with which...
Context. High spectral resolution and long exposure times are providing unprecedented levels of data quality massive stars at X-ray wavelengths. Aims. A key diagnostic the emitting plasma fir lines for He-like triplets. In particular, owing to radiative pumping effects, forbidden-to-intercombination line luminosity ratio, R = f ∕ i , can be used determine proximity hot UV-bright photospheres stars. Moreover, era large observing programs additionally allows investigation variability. Methods....
The Chandra X-ray Observatory (CXO) High Resolution Camera (HRC) is a microchannel plate (MCP) based detector with heritage from similar detectors flown on the Einstein and ROSAT missions. HRC consists of two in common housing. Improvements previous instruments include: fabricating MCP 'low-noise' glass (glass that contains reduced level radioactive isotopes) surrounding housing five sides an active coincidence detector. Both these improvements help to maximize signal background noise ratio....
Context. Line ratios in “fir” triplets of helium-like ions have proven to be a powerful diagnostic conditions X-ray emitting gas surrounding massive stars. Recent observations indicate that these can variable with time.
Polarization is detected at early times for all types of supernovae, indicating that such systems are, or quickly become, asymmetric. Spectropolarimetric observations also show the asymmetry varies in both magnitude and orientation different elements ejecta. One explanation these local chemical inhomogeneities (called clumps) exist ejecta above region where continuum forms. To examine effects clumpiness on observations, I will present results a comparison between fast, flexible, approximate...
Abstract