A5002912830- Stellar, planetary, and galactic studies
- Astronomy and Astrophysical Research
- Astrophysics and Star Formation Studies
- Astro and Planetary Science
- Gamma-ray bursts and supernovae
- Astronomical Observations and Instrumentation
- Adaptive optics and wavefront sensing
- Astrophysical Phenomena and Observations
- Space Science and Extraterrestrial Life
- Solar and Space Plasma Dynamics
- Space exploration and regulation
- History and Developments in Astronomy
- Magnetic confinement fusion research
- Geophysics and Gravity Measurements
- Ionosphere and magnetosphere dynamics
- Planetary Science and Exploration
- Calibration and Measurement Techniques
- Indigenous Studies and Ecology
- High-pressure geophysics and materials
- Space Exploration and Technology
- Superconducting Materials and Applications
- Advanced X-ray Imaging Techniques
- Polar Research and Ecology
- Inorganic Fluorides and Related Compounds
- Atmospheric Ozone and Climate
Memorial University of Newfoundland
2023
University of Toronto
2011-2022
East Tennessee State University
2012-2014
University of Bonn
2010-2012
Princeton Plasma Physics Laboratory
2010
National Institute for Fusion Science
2010
Plasma Technology (United States)
2010
University of Illinois Urbana-Champaign
2009
State University of New York at Oswego
2009
Texas A&M University
2009
We used WIRCam on CFHT to observe four transits of the super-Earth GJ 1214b in near-infrared. For each transit we observed two bands nearly-simultaneously by rapidly switching filter wheel back and forth for duration observations. By combining all our J-band (~1.25 microns) observations find a depth this band 1.338\pm0.013% - value consistent with optical reported Charbonneau collaborators. However, best-fit combined Ks-band (~2.15 is deeper: 1.438\pm0.019%. Formally are deeper than...
An analytical derivation is presented for computing mass-loss rates of Cepheids by using the method Castor, Abbott, & Klein (1975) modified to include a term momentum input from pulsation and shocks generated in atmosphere. Using this derivation, are determined as function stellar parameters. When applied set known Cepheids, calculated range 10^{-10} 10^{-7}M_{Sun}/yr, larger than if winds were driven radiation alone. Infrared excesses based on predicted compared observations optical...
Our ability to extract information from the spectra of stars depends on reliable models stellar atmospheres and appropriate techniques for spectral synthesis. Various model codes strategies analysis are available today. We aim compare results deriving parameters using different atmosphere strategies. The focus is set high-resolution spectroscopy cool giant stars. Spectra representing four were made various groups individuals working in area synthesis, asking them derive data provided....
The transit method, employed by MOST, \emph{Kepler}, and various ground-based surveys has enabled the characterization of extrasolar planets to unprecedented precision. These results are precise enough begin measure planet atmosphere composition, planetary oblateness, star spots, other phenomena at level a few hundred parts-per-million. However, these depend on our understanding stellar limb darkening, that is, intensity distribution across disk is sequentially blocked as transits....
In this paper, we have derived Cepheid period–luminosity (P–L) relations for the Large Magellanic Cloud (LMC) fundamental mode Cepheids, based on data released from OGLE-III. We applied an extinction map to correct of these Cepheids. addition VIW-band P–L relations, also include JHK and four Spitzer IRAC-band by matching OGLE-III Cepheids Two Micron All Sky Survey SAGE sets, respectively. test nonlinearity extinction-corrected data. Our results (again) show that LMC are nonlinear in VIJH...
Context. A longstanding challenge for understanding classical Cepheids is the Cepheid mass discrepancy, where theoretical estimates using stellar evolution and pulsation calculations have been found to differ by approximately 10 - 20%. Aims. We study role of pulsation-driven loss during stage as a possible solution this discrepancy. Methods. computed models with mass-loss prescription various amounts convective core overshooting. The contribution towards discrepancy determined these models,...
Two red supergiants of the Per OB1 association, RS and T Per, have been observed in H band using MIRC instrument at CHARA array. The data show clear evidence departure from circular symmetry. We present here new techniques specially developed to analyze such cases, based on state-of-the-art statistical frameworks. stellar surfaces are first modeled as limb-darkened discs SATLAS models that fit both interferometric publicly available spectrophotometric data. Bayesian model selection is then...
Model stellar atmospheres are fundamental tools for understanding observations from interferometry, microlensing, eclipsing binaries and planetary transits. However, the calculations also include assumptions, such as geometry of model. We use intensity profiles computed both plane-parallel spherically symmetric model to determine fitting coefficients in BVRIHK, CoRot Kepler wavebands limb darkening using several different laws, gravity-darkening interferometric angular diameter corrections....
Context. The projection factor p is the key quantity used in Baade-Wesselink (BW) method for distance determination; it converts radial velocities into pulsation velocities. Several methods are to determine , such as geometrical and hydrodynamical models or inverse BW approach when known. Aims. We analyze new HARPS-N spectra of δ Cep measure its cycle-averaged atmospheric velocity gradient order better constrain factor. Methods. first apply derive directly from observations. can be divided...
Abstract From our Secret Lives of Cepheids program, the prototype Classical Cepheid, δ Cep, is found to be an X-ray source with periodic pulsation-modulated variations. This finding complements earlier reported phase-dependent FUV–UV emissions star that increase ∼10–20 times highest fluxes at <?CDATA $\sim 0.90\mbox{--}0.95\phi $?> , just prior maximum brightness. Previously Cep was as potentially variable, using XMM-Newton observations. Additional phase-constrained data were secured Chandra...
A significant fraction of massive stars are moving supersonically through the interstellar medium (ISM), either due to disruption a binary system or ejection from their parent star cluster. The interaction wind with ISM produces bow shock. In late evolutionary stages these may undergo rapid transitions red blue and vice versa on Hertzsprung–Russell diagram, accompanying changes stellar winds shocks. Recent three-dimensional simulations shock produced by nearby runaway supergiant (RSG)...
Polaris is one of the most observed stars in night sky, with recorded observations spanning more than 200 years. From these observations, can study real-time evolution via secular rate change pulsation period. However, measurements period do not agree predictions from state-of-the-art stellar models. We show that this may imply currently losing mass at a yr−1 based on difference between modeled and rates change, consistent pulsation-enhanced Cepheid loss. A relation loss has important...
We present results from a study of the eclipsing, colliding-wind binary V444 Cyg that uses combination X-ray and optical spectropolarimetric methods to describe 3-D nature shock wind structure within system. have created most complete light curve date using 40 ksec new data Swift, 200 archived XMM-Newton observations. In addition, we characterized intrinsic, polarimetric phase-dependent behavior strongest emission lines obtained with University Wisconsin's Half-Wave Spectropolarimeter....
Over the past decade, Secret Lives of Cepheids (SLiC) program has been carried out at Villanova University to study aspects and behaviors classical that are still not well understood. In this, first several planned papers on Cepheids, we report current results for δ Cep, Cepheid prototype. Ongoing photometry obtained search changes in pulsation period, light-curve morphology, amplitude. Combining our with times maximum light compilation by Berdnikov et al. returns a small period change dP/dt...
Limb darkening is a fundamental ingredient for interpreting observations of planetary transits, eclipsing binaries, optical/infrared interferometry and microlensing events. However, this modeling traditionally represents limb by simple law having one or two coefficients that have been derived from plane-parallel model stellar atmospheres, which has done many researchers. More recently, researchers gone beyond models considered other geometries. We previously studied the limb-darkening...
Context. The projection factor (p), which converts the radial velocity to pulsational velocity, is an important parameter in Baade-Wesselink (BW) type analysis and distance scale work. p-factor either adopted as a constant or linearly depending on logarithmic of pulsating periods.
Context. One challenge for measuring the Hubble constant using Classical Cepheids is calibration of Leavitt Law or period-luminosity relationship. The Baade-Wesselink method distance determination to relies on ratio measured radial velocity and pulsation velocity, so-called projection factor ability measure stellar angular diameters. Aims. We use spherically-symmetric model atmospheres explore dependence p-factor diameter corrections as a function period. Methods. Intensity profiles are...
Measurements of rates period change Classical Cepheids probe stellar physics and evolution. Additionally, better understanding Cepheid structure evolution provides greater insight into their use as standard candles tools for measuring the Hubble constant. Our recent study nearest Cepheid, Polaris, suggested that it is undergoing enhanced mass loss when compared to canonical model predictions. In this work, we expand analysis measured about 200 Galactic compare them population synthesis...
The classical Cepheid $l$ Carinae is an essential calibrator of the Leavitt Law as a rare long-period Galactic Cepheid. Understanding properties this star will also constrain physics and evolution massive ($M \ge 8$ $M_\odot$) Cepheids. challenge, however, precisely measuring star's pulsation period its rate change. former important for calibrating latter stellar modeling. In work, we combine previous time-series observations spanning more than century with new to remeasure compute We...
With a focus on off-the-shelf components, Twinkle is the first in series of cost competitive small satellites managed and financed by Blue Skies Space Ltd. The satellite based high-heritage Airbus platform that will carry 0.45 m telescope spectrometer which provide simultaneous wavelength coverage from 0.5-4.5 $\rm{μm}$. spacecraft prime Stevenage while being developed Toulouse ABB Canada. Scheduled to begin scientific operations 2025, sit thermally-stable, sun-synchronous, low-Earth orbit....
In this article, we test the hypothesis that Cepheids have infrared excesses due to mass loss. We fit a model using mass-loss rate and stellar radius as free parameters optical observations from OGLE-III survey 2MASS SAGE data sets. The sample of predicted minimum rates ranging zero $10^{-8}M_\odot$ $yr^{-1}$, where depend on chosen dust properties. use radii compute Period-Radius relation for LMC Cepheids, estimate uncertainty caused by presence excess determining angular diameters with...
It has been claimed that period-luminosity (P–L) relations derived from infrared observations of Large Magellanic Cloud (LMC) Cepheids are less dependent on the metallicity Cepheids. In this work, LMC SAGE survey combined with OGLE II optical to model and predict mass-loss rates. The rates fit data predicted range about 10−12 10−7 M☉/yr; however, depend assumed value dust-to-gas ratio. By comparing stellar luminosities model, it is shown mass loss affects structure scatter P–L relation. Mass...
Analyses of recent observations the sole classical Cepheid in Kepler field, V1154 Cygni, found random changes about 30 minutes pulsation period.These period challenge standard theories and evolution because change is non-secular, explaining this jitter necessary for understanding stellar role Cepheids as precise candles.We suggest that convection convective hot spots can explain observed jitter.Convective alter timing flux maximum minimum light curve, hence measured period.We present a model...