A5067120075- Stellar, planetary, and galactic studies
- Astronomy and Astrophysical Research
- Astrophysics and Star Formation Studies
- Astronomical Observations and Instrumentation
- Astro and Planetary Science
- Astrophysical Phenomena and Observations
- Gamma-ray bursts and supernovae
- Conservation Techniques and Studies
- Spectroscopy and Laser Applications
- Adaptive optics and wavefront sensing
- History and Developments in Astronomy
- Library Science and Information Systems
- Solar and Space Plasma Dynamics
- Galaxies: Formation, Evolution, Phenomena
- Optics and Image Analysis
- Atmospheric Ozone and Climate
- Space Exploration and Technology
- Cultural Heritage Materials Analysis
- Inertial Sensor and Navigation
- Geophysics and Gravity Measurements
- Pulsars and Gravitational Waves Research
- Color Science and Applications
- Astrophysics and Cosmic Phenomena
- Historical Astronomy and Related Studies
- Calibration and Measurement Techniques
University of Delaware
2015-2024
University of Colorado Boulder
2022
Laboratory for Atmospheric and Space Physics
2022
Western University
2014
Massachusetts Institute of Technology
2011
University of California, San Diego
2011
Association of Universities For Research In Astronomy
2000-2007
U.S. National Science Foundation
2000-2007
Cerro Tololo Inter-American Observatory
2007
University of Massachusetts Amherst
1998-2006
Between 1997 June and 2001 February the Two Micron All Sky Survey (2MASS) collected 25.4 Tbytes of raw imaging data covering 99.998% celestial sphere in near-infrared J (1.25 μm), H (1.65 Ks (2.16 μm) bandpasses. Observations were conducted from two dedicated 1.3 m diameter telescopes located at Mount Hopkins, Arizona, Cerro Tololo, Chile. The 7.8 s integration time accumulated for each point on sky strict quality control yielded a 10 σ point-source detection level better than 15.8, 15.1,...
Before the 2-Micron All-Sky Survey (2MASS) began, only six objects were known with spectral types later than M9.5 V. In first 371 deg2 of actual 2MASS survey data, we have identified another 20 such spectroscopically confirmed using Low Resolution Imaging Spectrograph (LRIS) at W. M. Keck Observatory. Because TiO and VO bands, which dominate far-optical portions late-M spectra, disappear in these cooler dwarfs, define a new class "L" metallic oxides are replaced by hydrides neutral alkali...
The Third Catalogue of Nearby Stars (Gliese & Jahreiss Preliminary Version the third Stars, 1991) includes over 1850 stars which lie north δ 30° and are either identified as spectral type M, or unclassified but with an absolute visual magnitude estimate M<SUB>V</SUB>>+8.O. Although there is no uniformity in selection criteria, many lack basic data (radial velocities, types, accurate photometry), observational properties these underlie most estimates fundamental characteristics...
Trigonometric parallax determinations are presented for 28 late type dwarfs and brown dwarfs, including eight M with spectral types between M7 M9.5, 17 L L0 L8, three T dwarfs. Broadband photometry at CCD wavelengths (VRIz) and/or near-IR (JHK) these objects 24 additional late-type Supplemented astrometry from the literature, ten two parallaxes established by association bright, usually HIPPARCOS primaries, this material forms basis studying various color-color color-absolute magnitude...
We present JHKs photometry, far red spectra, and spectral classifications for an additional 67 L dwarfs discovered by the Two Micron All Sky Survey. One of goals this new search was to locate more examples latest dwarfs. Of discoveries, 17 have types L6 or later. Analysis these discoveries shows that Hα emission has yet be convincingly detected in any dwarf later than type L4.5, indicating a decline absence chromospheric activity Further analysis 16 (and possibly four more) are lithium brown...
Spectroscopic data for the southern stars (δ<-30) in PMSU survey are presented. The were combined with from Paper I [Reid, Hawley & Gizis, AJ, 110, 1838 (1995)] to obtain a list of all magnetically active dMe survey. incidence activity increases monotonically toward later spectral type, reaching level 60% at types >M5. This is not selection effect, since chromospheric (L<SUB>Hα</SUB>/L<SUB>bol</SUB>) remains high throughout type range where increasing. At very late types, there...
We have combined 2MASS and POSS II data in a search for nearby ultracool (later than M6.5) dwarfs with K_s<12. Spectroscopic follow-up observations identify 53 M7 to M9.5 seven L dwarfs. The observed space density is 0.0045 +- 0.0008 M8-M9.5 per cubic parsec, without accounting biases, consistent mass function that smooth across the stellar/substellar limit. show frequency of H alpha emission peaks at ~100% then decreases cooler In absolute terms, however, as measured by ratio bolometric...
We present the discovery of two T dwarf binaries, 2MASS 1225-2739AB and 1534-2952AB, identified in a sample 10 dwarfs imaged with Hubble Space Telescope (HST) Wide Field Planetary Camera 2. Companionship is established by uniquely red F814W-F1042M colors binary components, caused heavily pressure-broadened K I absorption centered at 7665 7699 Å. The separations systems are 0282 ± 0005 0065 0007, implying projected 3.17 0.14 1.0 0.3 AU, respectively. These close similar to those found...
Abstract Carbon dioxide (CO 2 ) is a key chemical species that found in wide range of planetary atmospheres. In the context exoplanets, CO an indicator metal enrichment (that is, elements heavier than helium, also called ‘metallicity’) 1–3 , and thus formation processes primary atmospheres hot gas giants 4–6 . It one most promising to detect secondary terrestrial exoplanets 7–9 Previous photometric measurements transiting planets with Spitzer Space Telescope have given hints presence but not...
Abstract Measuring the metallicity and carbon-to-oxygen (C/O) ratio in exoplanet atmospheres is a fundamental step towards constraining dominant chemical processes at work and, if equilibrium, revealing planet formation histories. Transmission spectroscopy (for example, refs. 1,2 ) provides necessary means by abundances of oxygen- carbon-bearing species; however, this requires broad wavelength coverage, moderate spectral resolution high precision, which, together, are not achievable with...
We present astrometric and spectroscopic observations confirming that two nearby G dwarf systems (Gliese 417 = BD+36 2162 Gliese 584AB eta CrB AB) have a widely separated, L dwarf, substellar companion. Using age estimates of the primaries, we estimate masses for these dwarfs from theoretical evolutionary tracks. For L4.5 Gl 417B an 0.08-0.3 Gyr mass 0.035+/-0.015 M_sun. L8 584C 1.0-2.5 0.060+/-0.015 This latter object also shows evidence spectrum variability, which may be due to surface...
We present high-resolution echelle spectroscopy of 676 nearby M dwarfs. Our measurements include radial velocities, equivalent widths important chromospheric emission lines, and rotational velocities for rapidly rotating stars. identify several distinct groups by their Hα properties investigate variations in activity among early (M0–M2.5) mid (M3–M6) Using a volume-limited sample together with relationship between age activity, we show that the rate star formation immediate solar...
We present near-infrared spectra for a sample of T dwarfs, including 11 new discoveries made using the 2 Micron All Sky Survey. These objects are distinguished from warmer (L-type) brown dwarfs by presence methane absorption bands in 1-2.5 μm spectral region. A first attempt at classification scheme is made, based on strengths CH4 and H2O shapes 1.25, 1.6, 2.1 flux peaks. Subtypes T1 V-T8 V defined, indices useful presented. The subclasses appear to follow decreasing Teff scale, evolution...
We have used new astrometric and spectroscopic observations to refine the volume-complete sample of M dwarfs defined in previous papers this series. With addition Hipparcos astrometry, our revised VC2 includes 558 main-sequence stars 448 systems. Analysis that data set shows no evidence any systematic kinematic bias. Combining those with a Hipparcos-based AFGK within 25 pc Sun, we derived solar neighborhood luminosity function, Φ(MV), for absolute magnitudes between -1 +17. Using empirical...
We present a spectroscopic classification system for M-dwarfs and M-subdwarfs based on quantitative measures of TiO CaH features in the region lambda 6200 - 7400 Angstroms. Our sample cool stars covers range from solar metallicity to most extreme subdwarfs known. Using synthetic spectra computed by Allard Hauschildt (1995), we derive metallicities stars. Stars are classified as dwarfs (M V), (sdM), or (esdM). These classifications correspond [m/H] ~ 0.0, -1.2, -2.0 respectively. scale agrees...
We present a new investigation of the influence unresolved binaries on form deduced for stellar luminosity function from photometric parallax surveys. have compiled catalogue photometry and binary statistics stars known to be north -30° declination within 8 parsecs Sun, used these as reference sample our multiplicity analysis. M-dwarfs comprise almost eighty percent sample. The overall fraction amongst 106 systems (and 151 stars) in this is only 35%. Transforming local mass function, we find...
Analysis of initial observations sky surveys has shown that the resulting photometric catalogs, combined with far-red optical data, provide an extremely effective method finding isolated, very low-temperature objects in general field. Follow-up have already identified more than 25 sources temperatures cooler latest M dwarfs. A comparison detailed model predictions (Burrows & Sharp 1999) indicates these L dwarfs between ≈2000 ± 100 K and 1500 K, while available trigonometric parallax data...
We report the discovery of a widely separated (258&farcs;3+/-0&farcs;4) T dwarf companion to Gl 570ABC system. This new component, 570D, was initially identified from Two Micron All-Sky Survey. Its near-infrared spectrum shows 1.6 and 2.2 µm CH4 absorption bands characteristic dwarfs, while its common proper motion with system confirms companionship. 570D (MJ=16.47+/-0.07) is nearly full magnitude dimmer than only other known companion, 229B, estimates L=&parl0;2.8+/-0.3&parr0;x10-6 L middle...
We present the results from a spectroscopic study of 1080 nearby active M dwarfs, selected by correlating Two Micron All Sky Survey and ROSAT catalogs. have derived spectral types estimated distances for all our stars. The range between K5 M6. Nearly half stars lie within 50 pc. measured equivalent width Hα emission line. Our targets show an increase in chromospheric activity early to midspectral types, with peak around M5. Using count rate hardness ratios obtained catalog, we X-ray...
We present analysis of HST Planetary Camera images twenty L dwarfs identified in the course Two Micron All-Sky Survey. Four targets have faint, red companions at separations between 0.07 and 0.29 arcseconds (1.6 to 7.6 AU). In three cases, bolometric magnitudes components differ by less than 0.3 magnitudes. Since cooling rate for brown is a strong function mass, similarity luminosities implies comparable masses. The faint component 2M0850 system, however, over 1.3 fainter primary I-band,...
As part of our on-going investigation into the magnetic field properties ultracool dwarfs, we present simultaneous radio, X-ray, and Hα observations three M9.5-L2.5 dwarfs (BRI 0021-0214, LSR 060230.4+391059,and 2MASS J052338.2-140302).We do not detect X-ray or radio emission from any sources, despite previous detections BRI 0021 2M0523-14.Steady variable are detected 2M0523-14 0021, respectively, while no is 0602+39.Overall, survey nine M8-L5 doubles number observed in X-rays, triples L...
Multiplicity is a key statistic for understanding the formation of very low mass (VLM) stars and brown dwarfs. Currently, separation distribution VLM binaries remains poorly constrained at small separations ($\leq$ 1 AU), leading to uncertainty in overall binary fraction. We approach this problem by searching late-M/early-L plus T dwarf spectral whose combined light spectra exhibit distinct peculiarities, allowing separation-independent identification. define set indices designed identify...
We present the results of a near-infrared (NIR) spectroscopic follow-up survey 182 M4-L7 low-mass stars and brown dwarfs (BDs) from BANYAN All-Sky Survey (BASS) for candidate members nearby, young moving groups (YMGs).We confirm signs low-gravity 42 new BD discoveries with estimated masses between 8-75 M Jup identify previously unrecognized low gravity 24 known BDs.This allows us to refine fraction in high-probability BASS sample ∼ 82%.We use this unique 66 BDs, supplemented 22 BDs...
The James Webb Space Telescope (JWST) presents the opportunity to transform our understanding of planets and origins life by revealing atmospheric compositions, structures, dynamics transiting exoplanets in unprecedented detail. However, high-precision, timeseries observations required for such investigations have unique technical challenges, prior experience with Hubble, Spitzer, other facilities indicates that there will be a steep learning curve when JWST becomes operational. In this...