A5063050804- Stellar, planetary, and galactic studies
- Astrophysics and Star Formation Studies
- Astro and Planetary Science
- Astronomy and Astrophysical Research
- Astronomical Observations and Instrumentation
- History and Developments in Astronomy
- Gamma-ray bursts and supernovae
- Adaptive optics and wavefront sensing
- Astrophysical Phenomena and Observations
- Space Science and Extraterrestrial Life
- Molecular Spectroscopy and Structure
- Space Exploration and Technology
- Atmospheric Ozone and Climate
- Geophysics and Gravity Measurements
- Spectroscopy and Laser Applications
- Solar and Space Plasma Dynamics
- Pulsars and Gravitational Waves Research
- Galaxies: Formation, Evolution, Phenomena
- Astrophysics and Cosmic Phenomena
- Calibration and Measurement Techniques
- Radio Astronomy Observations and Technology
- Space exploration and regulation
- Planetary Science and Exploration
- Ionosphere and magnetosphere dynamics
- Optical Polarization and Ellipsometry
Cornell University
2019-2024
Johns Hopkins University
2023-2024
York University
2014-2019
University of Toronto
2006-2015
Arcetri Astrophysical Observatory
2007
European Southern Observatory
2006
University of California, Berkeley
2000-2006
Harvard University Press
2006
University of Michigan–Ann Arbor
2002-2005
Center for Astrophysics Harvard & Smithsonian
1996-2004
We present the initial result of a large spectroscopic survey aimed at measuring timescale mass accretion in young, pre-main-sequence stars spectral type range K0–M5. Using multi-object spectroscopy with VIMOS VLT we identified fraction accreting number young stellar clusters and associations ages between 1–30 Myr. The decreases from ~60% 1.5–2 Myr to ~2% 10 No are found after sensitivity limit 10<sup>-11<sup/> . compared showing ongoing () near-to-mid infrared excess (). In most cases find...
We present UBVRI photometry of 44 Type Ia supernovae (SNe Ia) observed from 1997 to 2001 as part a continuing monitoring campaign at the Fred Lawrence Whipple Observatory Harvard-Smithsonian Center for Astrophysics. The data set comprises 2190 observations and is largest homogeneously reduced sample SNe date, nearly doubling number well-observed, nearby with published multicolor CCD light curves. large U-band unique addition, important connections high redshift. decline rate SN curves...
We present the results of Gemini Deep Planet Survey, a near-infrared adaptive optics search for giant planets and brown dwarfs around 85 nearby young stars. The observations were obtained with Altair system at North telescope, angular differential imaging was used to suppress speckle noise central star. Typically, are sensitive separations beyond 0.5'' 5 σ contrast sensitivities in magnitude difference 1.6 μm 9.5 0.5'', 12.9 1'', 15.0 2'', 16.5 5''. These sufficient detect more massive than...
We present multiple-epoch photometric monitoring in the $J$, $H$, and $K_s$ bands of T1.5 dwarf 2MASS J21392676+0220226 (2M2139), revealing persistent, periodic ($P=7.721\pm$0.005 hr) variability with a peak-to-peak amplitude as high 26% $J$-band. The light curve shape varies on timescale days, suggesting that evolving atmospheric cloud features are responsible. Using interpolations between model atmospheres differing thicknesses to represent heterogeneous surface, we find multi-wavelength...
Most directly imaged giant exoplanets are fainter than brown dwarfs with similar spectra. To explain their relative underluminosity, unusually cloudy atmospheres have been proposed. However, multiple parameters varying between any two objects, it remained difficult to observationally test this idea. We present a new method, sensitive time-resolved Hubble Space Telescope near-infrared spectroscopy, study rotating L/T transition (2M2139 and SIMP0136). The observations provide spatially...
We present a comprehensive analysis of planetary phase variations, including possible light offsets, using eighteen quarters data from the Kepler space telescope. Our found fourteen systems with significant detections in each curve components: planet's function, secondary eclipse, Doppler boosting, and ellipsoidal variations. model full simultaneously, primary transits, derive albedos, day- night-side temperatures planet masses. Most planets manifest low optical geometric albedos (< 0.25),...
Using the largest high-resolution spectroscopic sample to date of young, very low mass stars (VLMS) and brown dwarfs (BDs), we investigate disk accretion in objects ranging from just above hydrogen-burning limit all way nearly planetary masses. Our 82 targets span spectral types M5 M9.5, or masses 0.15 Msun down ~15 Jupiters. They are confirmed members rho Oph, Taurus, Cha I, IC 348, R CrA, Upper Sco TW Hydrae regions, with ages <1 ~10 Myr. The contains 41 BDs (spectral >= M6.5). We...
We have obtained intermediate-resolution optical spectroscopy of 44 candidate very low mass members the nearby young open cluster IC2391. Of these, 26 spectra are totally new, 14 were already analyzed in a previous paper and another four common. These spectra, taken at Cerro Tololo 4-meter Magellan I II telescopes, allow us to confirm 33 them as likely members, based on their spectral types, presence Li, Halpha emission. Among these new is CTIO-160 (M7), first IC2391 satisfy all criteria for...
We present Gemini near-infrared adaptive optics imaging and spectroscopy of a planetary-mass candidate companion to 1RXS J160929.1–210524, roughly solar-mass member the 5 Myr old Upper Scorpius association. The object, separated by 2.22'' or 330 AU at ~150 pc, has infrared colors spectra suggesting temperature 1800−100+200 K, spectral type L4−2+1. H- K-band provide clear evidence low surface gravity, thus youth. Based on widely used DUSTY models, we infer mass 8−2+4 MJup. If gravitationally...
We have carried out sensitive 1.3 mm observations of 20 young brown dwarfs in the Taurus star-forming region, representing largest sample substellar objects targeted a deep millimeter-continuum survey to date. Under standard assumptions, masses dwarf disks range from ≲0.4 several Jupiter masses. Their relative disk are comparable those derived for coeval low-mass stars; most them ≲1%-5% range, and there is no clear change mass with object 0.015 3 M☉. Specifically, we do not find evidence...
We have conducted a comprehensive search for optical phase variations of all planet candidates with tight orbits in fifteen quarters data from the Kepler space telescope. After correcting systematics, we found eight systems that appear to show secondary eclipses as well variations. Of these, five (Kepler-5, Kepler-6, Kepler-8, KOI-64 and KOI-2133) are new three (TrES-2, HAT-P-7 KOI-13) previously published curves, albeit many fewer observations. model full curve each candidate, including...
This paper describes a James Clerk Maxwell Telescope (JCMT) legacy survey that has been awarded roughly 500 hr of observing time to be carried out from 2007 2009. In this survey, we will map with SCUBA‐2 (Submillimetre Common‐User Bolometer Array 2) almost all the well‐known low‐mass and intermediate‐mass star‐forming regions within 0.5 kpc are accessible JCMT. Most these locations associated Gould Belt. From observations, produce flux‐limited snapshot star formation near Sun, providing...
We present J-band imaging and H+K-band low-resolution spectroscopy of 2MASS1207-3932 AB, obtained with VLT NACO. For the putative planetary mass secondary, we find J = 20.0+/-0.2 mag. The HK spectra both components imply low gravity, a dusty atmosphere for secondary. Comparisons to synthetic yield Teff_A ~ 2550+/-150K, Teff_B 1600+/-100K, consistent their late-M mid-to-late L types. these Teff, an age 5-10 Myrs, evolutionary models M_A 24+/-6 M_Jup M_B 8+/-2 M_Jup. Independent comparisons...
We present the results of a multiplicity survey 212 T Tauri stars in Chamaeleon I and Taurus-Auriga star-forming regions, based on high-resolution spectra from Magellan Clay 6.5 m telescope. From these data, we achieved typical radial velocity precision ~80 m/s with slower rotators yielding better precision, general. For 174 stars, obtained multi-epoch data sufficient time baselines to identify binaries variations. identified eight close four triples, which three two, respectively, are new...
We estimate cluster ages from lithium depletion in five pre-main-sequence groups found within 100 pc of the Sun: TW Hydrae association, η Chamaeleontis cluster, β Pictoris moving group, Tucanae-Horologium and AB Doradus group. determine surface gravities, effective temperatures, abundances for over 900 spectra through least-squares fitting to model-atmosphere spectra. For each we compare dependence abundance on temperature with isochrones evolutionary tracks obtain model-dependent ages. find...
Giant planets are usually thought to form within a few tens of AU their host stars, and hence it came as surprise when we found what appeared be planetary mass (∼ 0.008 M ⊙ ) companion around the 5 Myr-old solar star 1RXS J160929.1-210524 in Upper Scorpius association.At time, took object's membership -established from near-infrared, H-and K-band spectroscopy-and its proximity (2.2 ′′ , or 330 AU) primary strong evidence for companionship, but could not verify common proper motion.Here,...
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...
The Fine Guidance Sensor (FGS) is one of the four science instruments on board James Webb Space Telescope (JWST). FGS features two modules: an infrared camera dedicated to fine guiding observatory and a module, Near-Infrared Imager Slitless Spectrograph (NIRISS) covering wavelength range between 0.7 5.0 μm with field view 2.2' X 2.2'. NIRISS has observing modes: 1) broadband imaging featuring seven eight NIRCam filters, 2) wide-field slitless spectroscopy at resolving power rv150 1 2.5 μm,...
We analyze new/archival VLT/NaCo and Gemini/NICI high-contrast imaging of the young, self-luminous planet β Pictoris b in seven near-to-mid IR photometric filters, using advanced image processing methods to achieve high signal-to-noise, precision measurements. While Pic b's near-IR colors mimic those a standard, cloudy early-to-mid L dwarf, it is overluminous mid-infrared compared field L/T dwarf sequence. Few substellar/planet-mass objects—i.e., κ And 1RXJ 1609B—match JHKsL' photometry its...
We report the results of a J-band search for cloud-related variability in atmospheres 62 L4–T9 dwarfs using Du Pont 2.5 m telescope at Las Campanas Observatory and Canada–France–Hawaii Telescope on Mauna Kea. find 9 57 objects included our final analysis to be significantly variable with >99% confidence, 5 which are new discoveries. In study, strong signals (peak-to-peak amplitudes >2%) confined L/T transition (4/16 L9–T3.5 spectral types 0/41 all other types). The probability that observed...
We present the analysis of high-resolution optical spectra four transits 55Cnc e, a low-density, super-Earth that orbits nearby Sun-like star in under 18 hours. The inferred bulk density planet implies substantial envelope, which, according to mass-radius relationships, could be either low-mass extended or high-mass compact atmosphere. Our observations investigate latter scenario, with water as dominant species. take advantage Doppler cross-correlation technique, high-spectral resolution and...
Abstract We present the wide field slitless spectroscopy mode of NIRISS instrument on James Webb Space Telescope. This employs two orthogonal low-resolution (resolving power ≈150) grisms in combination with a set six blocking filters wavelength range 0.8–2.3 μ m to provide spectrum almost every source across field-of-view. When combined low background, high sensitivity and spatial resolution afforded by telescope, this will enable unprecedented studies structure evolution distant galaxies....
Abstract The Near-Infrared Imager and Slitless Spectrograph (NIRISS) is the science module of Canadian-built Fine Guidance Sensor onboard James Webb Space Telescope (JWST). NIRISS has four observing modes: (1) broadband imaging featuring seven eight NIRCam filters, (2) wide-field slitless spectroscopy at a resolving power ∼150 between 0.8 2.2 μ m, (3) single-object cross-dispersed (SOSS) enabling simultaneous wavelength coverage 0.6 2.8 m R ∼ 700, mode optimized for exoplanet relatively...
Abstract We present the first analysis of JWST near-infrared spectroscopy stellar flares from TRAPPIST-1 during transits rocky exoplanets. Four were observed 0.6–2.8 μ m with Near Infrared Imager and Slitless Spectrograph 0.6–3.5 TRAPPIST-1b, f, g. discover P α Br β line emission characterize flare continuum at wavelengths 1–3.5 for time. Observed lines include H , –P ϵ He i λ 0.7062 m, two Ca ii infrared triplet (IRT) lines, IRT. observe a reversed Paschen decrement γ alongside changes in...