A5087561231- Stellar, planetary, and galactic studies
- Astrophysics and Star Formation Studies
- Astro and Planetary Science
- Astronomy and Astrophysical Research
- Astronomical Observations and Instrumentation
- Molecular Spectroscopy and Structure
- Astrophysical Phenomena and Observations
- Gamma-ray bursts and supernovae
- History and Developments in Astronomy
- Adaptive optics and wavefront sensing
- Advanced Combustion Engine Technologies
- Scientific Research and Discoveries
- Atmospheric Ozone and Climate
- Space Exploration and Technology
- Historical Astronomy and Related Studies
- Spatial and Panel Data Analysis
- Spacecraft and Cryogenic Technologies
- Calibration and Measurement Techniques
- Statistical Methods and Applications
- Regional Economic and Spatial Analysis
- Spectroscopy and Laser Applications
- Meteorological Phenomena and Simulations
- Pulsars and Gravitational Waves Research
- CCD and CMOS Imaging Sensors
- Tribology and Lubrication Engineering
Pennsylvania State University
2015-2024
Celanese (United States)
2023
University of Hawaii System
2009-2010
National Aeronautics and Space Administration
2005-2008
Center for Astrophysics Harvard & Smithsonian
1999-2007
Harvard University Press
2006
Harvard University
2000-2005
University of Arizona
1997-2004
European Southern Observatory
2004
Smithsonian Astrophysical Observatory
1999-2002
We present a new census of the stellar and substellar members young cluster IC 348. have obtained images at I Z for 42'x28' field encompassing combined these measurements with previous optical near-infrared photometry. From spectroscopy candidate appearing in data, we identified 122 members, 15 which spectral types M6.5-M9, corresponding to masses 0.08-0.015 M_sun by recent evolutionary models. The latest 348 now contains total 288 23 are later than M6 thus likely be brown dwarfs. an...
We present multiband photometry of 185 type-Ia supernovae (SNe Ia), with over 11,500 observations. These were acquired between 2001 and 2008 at the F. L. Whipple Observatory Harvard-Smithsonian Center for Astrophysics (CfA). This sample contains largest number homogeneously observed reduced nearby SNe Ia (z ≲ 0.08) published to date. It more than doubles sample, bringing SN cosmology point where systematic uncertainties dominate. Our natural system has a precision ≲0.02 mag in BVRIr'i' ≲0.04...
We present near- and mid-infrared photometry obtained with the Spitzer Space Telescope of ∼300 known members IC 348 cluster. merge this existing ground-based optical near-infrared in order to construct optical-infrared spectral energy distributions (SEDs) for all cluster a complete atlas these SEDs. employ observations investigate both frequency nature circumstellar disk population The span wavelength range between 3.6 24 μm, corresponding radii ∼0.1-5 AU from central star. are sufficiently...
We have analyzed nearly all images of the Taurus star-forming region at 3.6-24um that were obtained during cryogenic mission Spitzer Space Telescope (46 deg^2) and measured photometry for known members are within these data, corresponding to 348 sources. classified according whether they show evidence disks envelopes (classes I, II, III). The disk fraction in is 75% solar-mass stars declines 45% low-mass brown dwarfs (0.01-0.3 M_sun). This dependence on stellar mass similar Cha although...
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...
By combining a deep optical imaging (I, z') survey of 8 deg2 in the Taurus star-forming region with data from Two-Micron All-Sky Survey (2MASS) and follow-up spectroscopy, we have performed search for low-mass members that is complete to 0.02 M☉ reddenings AV ≲ 4. We report discovery nine new spectral types M5.75-M9.5, corresponding masses 0.1-0.015 by recent evolutionary models. The M9.5 member least massive brown dwarf found date region. derive an initial mass function (IMF) fields...
We have obtained moderate-resolution (R = 800-1200) K-band spectra for ~100 stars within and surrounding the cloud core of ρ Oph. measured spectral types continuum veilings combined this information with results from new deep imaging. Using latest evolutionary tracks D'Antona & Mazzitelli to interpret H-R diagram Oph, we infer ages ranging between 0.1 1 Myr class II III sources (i.e., those that emerged their natal cocoons). A few may be slightly older. The initial mass function (IMF) peaks...
I present new results from a continuing program to identify and characterize the low-mass stellar substellar populations in young cluster IC 348 (0.5-10 Myr). Optical spectroscopy has revealed objects with spectral types as late M8.25. The intrinsic J-H H-K colors of these sources are dwarflike, whereas R-I I-J appear intermediate between dwarfs giants. Furthermore, spectra 6500 9500 Å reproduced well averages standard dwarf giant spectra, suggesting that such should be used classification...
We have obtained images of the Trapezium Cluster (140'' × 140''; 0.3 pc pc) with Hubble Space Telescope Near-Infrared Camera and Multi-Object Spectrometer (NICMOS). Combining these data new ground-based K-band spectra (R = 800) existing spectral types photometry, we constructed an H-R diagram used it other arguments to infer masses ages. To allow comparison results our previous studies IC 348 ρ Oph, first use models D'Antona & Mazzitelli. With models, distributions ages comparable samples...
We present infrared photometry obtained with the IRAC camera on Spitzer Space Telescope of a sample 82 pre-main-sequence stars and brown dwarfs in Taurus star-forming region. find clear separation some color-color diagrams between objects without disks. A few "transition" are noted, which correspond to systems inner disk has been evacuated small dust. Separating pure from remnant protostellar envelopes is more difficult at wavelengths, especially for infall low rates large angular momenta....
We report the discovery of T dwarf companions to nearby stars HN Peg (G0V, 18.4 pc, ~0.3 Gyr) and HD 3651 (K0V, 11.1 ~7 Gyr). During an ongoing survey 5'x5' fields surrounding in solar neighborhood with IRAC aboard Spitzer Space Telescope, we identified these as candidate dwarfs based on their mid-IR colors. Using near-IR spectra obtained SpeX at NASA IRTF, confirm presence methane absorption that characterizes measure spectral types T2.5+/-0.5 T7.5+/-0.5 for B B, respectively. By comparing...
We present photometry at 3-24um for all known members of the Upper Scorpius association (~11 Myr) based on images these objects obtained with Spitzer Space Telescope and Wide-field Infrared Survey Explorer. have used data to identify that exhibit excess emission from circumstellar disks estimate evolutionary stages disks. Through this analysis, we found ~50 new candidates transitional, evolved, debris The fraction harboring inner primordial is <10% B--G stars (M>1.2 Msun) increases later...
We present extensive optical and infrared photometry of the afterglow gamma-ray burst (GRB) 030329 its associated supernova (SN) 2003dh over first two months after detection (2003 March 30-May 29 UT). Optical spectroscopy from a variety telescopes is shown and, when combined with photometry, allows an unambiguous separation between SN contributions. The GRB initially power-law continuum but shows significant color variations during week that are unrelated to presence SN. early light curve...
We present observations of Halpha emission line profiles taken at Magellan Observatory for a sample 39 young low-mass stars and brown dwarfs in the Taurus Chamaeleon I star forming regions. have identified 11 new substellar accretors, more than tripling number known with measurable accretion activity. These include lowest-mass objects yet seen accretion, masses down to ~0.015 Msun. Using models produced magnetospheric flows, most widely applicable primary calibrator now available, we...
We present the results of a program to acquire photometry for eighty-six late-M, L, and T dwarfs using Infrared Array Camera (IRAC) on Spitzer Space Telescope. examine behavior these cool in various color-color color-magnitude diagrams composed near-IR IRAC data. The exhibit most distinctive positions diagrams. In M_5.8 versus [5.8]-[8.0], data are not monotonic either magnitude or color, giving clearest indication yet that one parameter family Teff. Because metallicity does vary enough...
In the past few years, several disks with inner holes that are empty of small dust grains have been detected and known as transitional disks. Recently, Spitzer has identified a new class "pre-transitional disks" gaps; these objects an optically thick disk separated from outer by thin gap. A near-infrared spectrum provided first confirmation gap in pre-transitional LkCa 15 verifying excess emission this object was due to disk. Here we investigate difference between nature regions using same...
We present near-infrared (1.0-2.4 μm) spectra confirming the youth and cool temperatures of six brown dwarfs low-mass stars with circumstellar disks toward Chamaeleon II Ophiuchus star-forming regions. The spectrum one our objects indicates a spectral type ~L1, making it latest young identified to date. Comparing dwarfs, field giant stars, we define 1.49-1.56 μm H2O index capable determining ±1 subtype, independent gravity. have also defined an based on 1.14 sodium feature that is sensitive...
I am using multi-epoch astrometry from the Wide-field Infrared Survey Explorer (WISE) to search for new members of solar neighborhood via their high proper motions. Through this work, have identified WISE J104915.57-531906.1 as a motion object and found additional detections in images Digitized Sky Survey, Two Micron All-Sky Deep Near-Infrared Southern Sky. measured parallax 0.496+/-0.037" (2.0+/-0.15 pc) these surveys, making third closest system Sun. During spectroscopic observations with...
Planet formation is profoundly impacted by the properties of protoplanetary disks and their central star. However, how disk vary with stellar parameters remains poorly known. Here, we present first comprehensive, comparative Spitzer/IRS study dust gas around young Sun-like stars (K1–M5) cool stars/brown dwarfs (M5–M9). The comparison these two large samples over 60 sources reveal major differences in evolution both components. We report detection organic molecules brown dwarfs. rate...
We present a census of circumstellar disks in the Chamaeleon I star-forming region. Using Infrared Array Camera and Multiband Imaging Photometer on board Spitzer Space Telescope, we have obtained images at 3.6, 4.5, 5.8, 8.0, 24 μm. To search for new disk-bearing members cluster, performed spectroscopy objects that red colors these data. Through this work, discovered four with spectral types M4, M6, M7.5, L0. The first three are highly embedded (AJ ∼ 5) reside near known protostars,...
The discovery of large numbers young low-mass stars and brown dwarfs over the past decade has made it possible to investigate star formation early evolution in a previously unexplored mass regime. In this review, we begin by describing surveys for members nearby associations, open clusters, star-forming regions, methods used characterize their stellar properties. We then use observations these populations test theories at low masses. For comparison models, consider initial function,...
We present 161 Spitzer Infrared Spectrograph (IRS) spectra of T Tauri stars and young brown dwarfs in the Taurus star-forming region. All targets were selected based on their infrared excess are therefore surrounded by protoplanetary disks; they form complete sample all available IRS with excesses Taurus. also seven Class 0/I objects to protostars use spectral indices that not significantly affected extinction distinguish between envelope- disk-dominated objects. Together data from...
We present the results of a search for new members Taurus star-forming region using data from Spitzer Space Telescope and XMM-Newton Observatory. have obtained optical near-infrared spectra 44 sources that exhibit red colors are indicative stars with circumstellar disks 51 candidate young were identified by Scelsi coworkers XMM-Newton. also performed spectroscopy on four possible companions to reported Kraus Hillenbrand. Through these spectra, we demonstrated youth membership 41 sources, 10...
The clusters of young stars in massive star-forming regions show a wide range sizes, morphologies, and numbers stars. Their highly subclustered structures are revealed by the MYStIX project's sample 31,754 nearby sites star formation (regions at distances <3.6 kpc that contain least one O-type star.) In 17 surveyed MYStIX, we identify subclusters using finite mixture models—collections isothermal ellipsoids model individual subclusters. Maximum likelihood estimation is used to estimate...
The high-precision astrometry from the second data release of Gaia mission has made it possible to greatly improve census members nearby clusters and associations. I have applied Taurus star-forming region, refining sample known identifying candidates for undiscovered members. resulting samples provide best constraints date on distribution ages initial mass function (IMF) in Taurus. Several studies over last 30 years proposed existence a population older stars (>=10 Myr) that is associated...