A5060770170- Stellar, planetary, and galactic studies
- Astrophysics and Star Formation Studies
- Astronomy and Astrophysical Research
- Astro and Planetary Science
- Astronomical Observations and Instrumentation
- Gamma-ray bursts and supernovae
- Astrophysical Phenomena and Observations
- Space Exploration and Technology
- Solar and Space Plasma Dynamics
- Adaptive optics and wavefront sensing
- Molecular Spectroscopy and Structure
- History and Developments in Astronomy
- Calibration and Measurement Techniques
- Astronomical and nuclear sciences
- Astrophysics and Cosmic Phenomena
- Planetary Science and Exploration
- Spectroscopy and Laser Applications
- Geomagnetism and Paleomagnetism Studies
- Nuclear physics research studies
- Technology Assessment and Management
- Scientific Measurement and Uncertainty Evaluation
- Historical Astronomy and Related Studies
- Quantum Chromodynamics and Particle Interactions
- Spacecraft Design and Technology
- Particle accelerators and beam dynamics
University of Rochester
2016-2025
Jet Propulsion Laboratory
2016-2025
The Aerospace Corporation
2022
Space Telescope Science Institute
2009-2021
California Institute of Technology
2020-2021
Goddard Space Flight Center
2018-2021
Ames Research Center
2021
Cornell University
2020
University of Exeter
2016
Union astronomique internationale
2015
While the strong anticorrelation between chromospheric activity and age has led to common use of Ca II H K emission index (R'HK = LHK/Lbol) as an empirical estimator for solar-type dwarfs, existing activity-age relations produce implausible ages at both high low levels. We have compiled R'HK data from literature young stellar clusters, richly populating first time end relation. Combining cluster with modern estimates analyzing color dependence index, we derive improved calibration F7-K2...
We present an analysis of the intrinsic colors and temperatures 5–30 Myr old pre-main-sequence (pre-MS) stars using F0- through M9-type members nearby, negligibly reddened groups: η Cha cluster, TW Hydra Association, β Pic Moving Group, Tucana-Horologium Association. To check consistency spectral types from literature, we estimate new for 52 nearby pre-MS with F3 M4 optical spectra taken SMARTS 1.5 m telescope. Combining these published photometry literature (Johnson–Cousins BVIC, 2MASS JHKS...
We present a sample of 824 solar and late-type stars with X-ray luminosities rotation periods. This is used to study the relationship between stellar activity derive new estimate convective turnover time. From an unbiased subset this power law slope unsaturated regime, L_X / L_bol = Ro^β, fit as β= -2.70 +/- 0.13. inconsistent canonical β=-2 confidence 5 sigma, argues for additional term in dynamo number equation. simple scaling analysis implies ΔΩ/ Ω= Ω^0.7, i.e. differential solar-type...
Abstract BANYAN Σ is a new Bayesian algorithm to identify members of young stellar associations within 150 pc the Sun. It includes 27 with ages in range ∼1–800 Myr, modeled multivariate Gaussians six-dimensional (6D) XYZUVW space. first such multi-association classification tool include nearest sub-groups Sco-Cen OB star-forming region, IC 2602, 2391, Pleiades and Platais 8 clusters, ρ Ophiuchi, Corona Australis, Taurus star formation regions. A model field stars built from mixture based on...
We present a self-consistent, absolute isochronal age scale for young (< 200 Myr), nearby 100 pc) moving groups in the solar neighbourhood based on homogeneous fitting of semi-empirical pre-main-sequence model isochrones using tau^2 maximum-likelihood statistic Naylor & Jeffries M_V, V-J colour-magnitude diagram. The final adopted ages are: 149+51-19 Myr AB Dor group, 24+/-3 {\beta} Pic group (BPMG), 45+11-7 Carina association, 42+6-4 Columba 11+/-3 {\eta} Cha cluster, 45+/-4...
We present an analysis of the ages and star formation history F-type stars in Upper Scorpius (US), Centaurus–Lupus (UCL), Lower Centaurus–Crux (LCC) subgroups Scorpius–Centaurus (Sco-Cen), nearest OB association. Our parent sample is kinematically selected Hipparcos de Zeeuw et al., restricted to 138 members. have obtained classification-resolution optical spectra also determined spectroscopic accretion disk fraction. With 2MASS photometry, we estimate reddening extinction for each place...
We present results of a spectroscopic survey for new K- and M-type members Scorpius-Centaurus (Sco-Cen), the nearest OB Association (~100-200 pc). Using an X-ray, proper motion color-magnitude selected sample, we obtained spectra 361 stars, which report spectral classifications Li Halpha equivalent widths. identified 156 Sco-Cen, recovered 51 previously published members. have combined these with known to form sample 493 solar-mass (~0.7-1.3 Msun) Sco-Cen. investigated star-formation history...
Early Origin of Earth's Magnetic Field magnetic field protects us from stellar winds and radiation the Sun. Understanding when, during formation, large-scale was established is important because it impacts understanding young atmosphere exosphere. By analyzing ancient silicate crystals, Tarduno et al. (p. 1238 ; see Perspective by Jardine ) demonstrate that existed 3.4 to 3.45 billion years ago, pushing back oldest record geomagnetic strength 200 million years. This result combined with...
Jeffries & Binks (2014) and Malo et al. have recently reported Li depletion boundary (LDB) ages for the {\beta} Pictoris moving group (BPMG) which are twice as old oft-cited kinematic age of $\sim$12 Myr. In this study we present (1) a new evaluation internal kinematics BPMG using revised Hipparcos astrometry best available published radial velocities, assess whether useful can be derived, (2) derive an isochronal based on placement A-, F- G-type stars in colour-magnitude diagram (CMD). We...
We present the results of a precise near-infrared (NIR) radial velocity (RV) survey 32 low-mass stars with spectral types K2-M4 using CSHELL at NASA IRTF in $K$-band an isotopologue methane gas cell to achieve wavelength calibration and novel iterative RV extraction method. surveyed 14 members young ($\approx$ 25-150 Myr) moving groups, field star $\varepsilon$ Eridani as well 18 nearby ($<$ 25 pc) achieved typical single-measurement precisions 8-15 m s$^{-1}$ long-term stability 15-50...
Abstract A complete accounting of nearby objects—from the highest-mass white dwarf progenitors down to low-mass brown dwarfs—is now possible, thanks an almost set trigonometric parallax determinations from Gaia, ground-based surveys, and Spitzer follow-up. We create a census objects within Sun-centered sphere 20 pc radius check published literature decompose each binary or higher-order system into its separate components. The result is volume-limited ∼3600 individual star formation products...
We present 4.5, 8, and 16 μm photometry from the Spitzer Space Telescope for 204 stars in Upper Scorpius OB association. The data are used to investigate frequency properties of circumstellar disks around with masses between ~0.1 20 M☉ at an age ~5 Myr. identify 35 that have emission 8 or excess stellar photosphere. lower mass (~0.1-1.2 M☉) appear surrounded by primordial optically thick based on characteristics. Stars more massive than ~1.8 fractional luminosities suggesting inner ~10 AU...
We present results of a spectroscopic survey X-ray– and proper-motion–selected samples late-type stars in the Lower Centaurus–Crux (LCC) Upper Centaurus–Lupus (UCL) subgroups nearest OB association: Scorpius-Centaurus. The primary goals are to determine star formation history assess frequency accreting sample dominated by "post–T Tauri" pre–main-sequence (PMS) stars. investigate two samples: (1) proper-motion candidates from ACT Catalog Tycho Reference (TRC) with X-ray counterparts ROSAT...
We examine thermal infrared images of η Car at wavelengths from 4.8 to 25 μm obtained with the MIRAC3 camera system Magellan Observatory, and we conclude that Car's circumstellar Homunculus Nebula contains much more mass (12 M⊙) kinetic energy (1049.6–1050 ergs) than had previously been recognized. Excess far-infrared emission a large cold dust discovered recently by Morris et al., which they attributed 110 K in compact equatorial torus. Our suggest, however, roughly 10 M⊙ or resides instead...
We report the detection of a faint stellar companion to famous nearby A5V star Alcor (80 UMa). The has M-band ($\lambda$ = 4.8 $\mu$m) magnitude 8.8 and projected separation 1".11 (28 AU) from Alcor. is most likely low-mass ($\sim$0.3 \msun) active which responsible for Alcor's X-ray emission detected by ROSAT (L$_{\rm X}$ $\simeq$ 10$^{28.3}$ erg/s). nuclear member Ursa Major cluster (UMa; d 25 pc, age 0.5 Gyr), been occasionally mentioned as possible distant (709") quadruple Mizar ($\zeta$...
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...
A candidate extrasolar planet companion to the young brown dwarf 2MASSW J1207334-393254 (2M1207) was recently discovered by Chauvin et al. They find that 2M1207 B's temperature and luminosity are consistent with being a young, \~5 M_Jupiter planet. The system is purported be member of TW Hya association (TWA), situated ~70 pc away. Using revised space motion vector for TWA, improved proper 2M1207, I use moving cluster method estimate distance other TWA members. derived (53+-6 pc) forces half...
We present Spitzer photometric (IRAC and MIPS) spectroscopic (IRS low resolution) observations for 314 stars in the Formation Evolution of Planetary Systems Legacy program. These data are used to investigate properties evolution circumstellar dust around solar-type spanning ages from approximately 3 Myr–3 Gyr. identify 46 sources that exhibit excess infrared emission above stellar photosphere at 24 μm, 21 with excesses 70 μm. Five an have characteristics optically thick primordial disks,...
We report the discovery of a planetary-mass companion, HD 106906 b, with new Magellan Adaptive Optics (MagAO) + Clio2 system. The companion is detected in three bands: J, KS, and L', lies at projected separation 71 (650 AU). It confirmed to be comoving its 13 ± 2 Myr F5 host using Hubble Space Telescope Advanced Camera for Surveys astrometry over time baseline 8.3 yr. DUSTY COND evolutionary models predict that companion's luminosity corresponds mass 11 MJup, making it one most widely...
The statistical properties of circumstellar disks around young stars are important for constraining theoretical models the formation and early evolution planetary systems. In this brief review, I survey literature related to ground-based Spitzer-based infrared (IR) studies stellar clusters, with particular emphasis on tracing primordial (``protoplanetary'') through spectroscopic photometric diagnostics. available data demonstrate that fraction optically thick and/or those which show evidence...
We present the results of a survey 45 young (≲250 Myr), close (≲50 pc) stars with Simultaneous Differential Imager (SDI) implemented at VLT and MMT for direct detection extrasolar planets. As part survey, we observed 54 objects, consisting close, stars; two more distant (<150 pc), extremely (≤10 Myr) three known radial velocity planets; four older, very nearby (≤20 solar analogs. Our SDI devices use double Wollaston prism quad filter to take images simultaneously wavelengths surrounding 1.62...
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 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,...
ABSTRACT In this brief communication we provide the rationale for and outcome of International Astronomical Union (IAU) resolution vote at XXIXth General Assembly in Honolulu, Hawaii, 2015, on recommended nominal conversion constants selected solar planetary properties. The problem addressed by is a lack established between values SI units: missing standard has caused proliferation (e.g., radius, irradiance, luminosity, effective temperature, mass parameter) literature, with cited typically...
<abridged> The large relative sizes of circumstellar and circumplanetary disks imply that they might be seen in eclipse stellar light curves. We estimate a survey ~10^4 young (~10 Myr old) post-accretion pre-MS stars monitored for ~10 years should yield at least few deep eclipses from surrounding low mass companion stars. present photometric spectroscopic data K5 star (1SWASP J140747.93-394542.6), newly discovered ~0.9 Msun member the ~16 Myr-old Upper Cen-Lup subgroup Sco-Cen kinematic...