E. Nielsen
A5025971439- Stellar, planetary, and galactic studies
- Astro and Planetary Science
- Ionosphere and magnetosphere dynamics
- Astronomy and Astrophysical Research
- Earthquake Detection and Analysis
- Solar and Space Plasma Dynamics
- Astrophysics and Star Formation Studies
- Planetary Science and Exploration
- Geomagnetism and Paleomagnetism Studies
- GNSS positioning and interference
- Space Exploration and Technology
- Gamma-ray bursts and supernovae
- Astronomical Observations and Instrumentation
- Adaptive optics and wavefront sensing
- Space Science and Extraterrestrial Life
- Geophysics and Gravity Measurements
- Spacecraft Design and Technology
- Magnetic confinement fusion research
- Seismic Waves and Analysis
- Calibration and Measurement Techniques
- Space Satellite Systems and Control
- Spacecraft and Cryogenic Technologies
- Scientific Research and Discoveries
- Computational Fluid Dynamics and Aerodynamics
- Space exploration and regulation
New Mexico State University
2020-2025
University of Washington
2004-2024
Stanford University
2015-2023
Kavli Institute for Particle Astrophysics and Cosmology
2015-2023
University of California, San Diego
2023
University of Victoria
2020-2023
University of Notre Dame
2020-2022
Search for Extraterrestrial Intelligence
2015-2020
University of Hawaii System
2012-2015
Max Planck Society
2001-2014
Abstract We present a statistical analysis of the first 300 stars observed by Gemini Planet Imager Exoplanet Survey. This subsample includes six detected planets and three brown dwarfs; from these detections our contrast curves we infer underlying distributions substellar companions with respect to their mass, semimajor axis, host stellar mass. uncover strong correlation between planet occurrence rate star M * > 1.5 ⊙ more likely masses 2 13 Jup axes 3–100 au at 99.92% confidence. fit...
An exoplanet extracted from the bright Direct imaging of Jupiter-like exoplanets around young stars provides a glimpse into how our solar system formed. The brightness requires use next-generation devices such as Gemini Planet Imager (GPI). Using GPI, Macintosh et al. discovered planet orbiting star, 51 Eridani (see Perspective by Mawet). planet, Eri b, has methane signature and is probably smallest that been directly imaged. These findings open door to understanding origins herald dawn new...
As part of the ground‐based program for International Magnetospheric Study (IMS), a new two‐station VHF radar auroral experiment, STARE, has been constructed in northern Scandinavia. Each these stations can provide good spatial and temporal resolution measurements intensity Doppler velocity irregularities within 300,000 km 2 scattering region. Approximately 230,000 regions are common to both radars this area it is possible compare backscattered signals observed by two combine data derive...
We report results of a direct imaging survey for giant planets around 80 members the Beta Pic, TW Hya, Tucana-Horologium, AB Dor, and Hercules-Lyra moving groups, observed as part Gemini NICI Planet-Finding Campaign. For this sample, we obtained median contrasts \Delta H=13.9 mag at 1" in combined CH4 narrowband ADI+SDI mode H=15.1 2" H-band ADI mode. found numerous (>70) candidate companions our images. Some these candidates were rejected common-proper motion using archival data; reobserved...
The orbital eccentricities of directly imaged exoplanets and brown dwarf companions provide clues about their formation dynamical histories. We combine new high-contrast imaging observations substellar obtained primarily with Keck/NIRC2 together astrometry from the literature to test for differences in population-level eccentricity distributions 27 long-period giant planets between 5-100 AU using hierarchical Bayesian modeling. Orbit fits are performed a uniform manner short arcs; this...
Abstract M dwarfs are common host stars to exoplanets but often lack atmospheric abundance measurements. Late-M also good analogs the youngest substellar companions, which share similar T eff ∼ 2300–2800 K. We present analyses for M7.5 companion HIP 55507 B and its K6V primary star with Keck/KPIC high-resolution ( R 35,000) K -band spectroscopy. First, by including KPIC relative radial velocities between secondary in orbit fit, we improve dynamical mass precision 60% find <?CDATA...
Since patients with chronic obstructive pulmonary disease (COPD) infrequently discuss treatment preferences about end-of-life care physicians, the goal of present study was to identify which specific areas communication occur between severe COPD and their how rate quality this communication. A total 115 oxygen-dependent COPD, identified in clinics three hospitals through an oxygen delivery company, were enrolled study. 17‐item questionnaire (QOC) administered patients, along other measures,...
We report the first radar soundings of ionosphere Mars with MARSIS (Mars Advanced Radar for Subsurface and Ionosphere Sounding) instrument on board orbiting Express spacecraft. Several types ionospheric echoes are observed, ranging from vertical caused by specular reflection horizontally stratified to a wide variety oblique diffuse echoes. The believed arise mainly structures associated complex crustal magnetic fields Mars. Echoes at electron plasma frequency cyclotron period also provide...
We have examined the relationship between radial mean Doppler velocities observed with coherent radars, such as in STARE (Scandinavian Twin Auroral Radar Experiment) system, and electron drift an incoherent scatter facility. The two sets of measurements were made simultaneously can high accuracy be related to a common magnetic flux tube. find that density irregularities produced by two‐stream instability E region are limited value near ion acoustic velocity. Moreover, we this is strong...
Two periods during which the convection boundary was in Scandinavian Twin Auroral Radar Experiment field of view a few hours before and after magnetic noon are analyzed. We find that sporadic spatially isolated flow across occurs on time scales minutes regions ionosphere range size from 50 km to 300 km. suggest antisunward immediately north maps into low‐latitude layer. Our observations then indicate flux layer is transported outward. estimate typical transfer rate 2.5×10 4 Wb s −1 for one...
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...
The Mars Advanced Radar for Subsurface and Ionospheric Sounding aboard Express has been in operation over 2 years. Between 14 August 2005 31 July 2007, we obtain 34,492 ionospheric traces, of which 14,060 yield electron density profiles 12,291 acceptable fits to the Chapman model. These results are used study Martian ionosphere under changing conditions: presence or absence solar energetic particles, EUV flux, season, zenith angle, latitude. 2‐year average subsolar maximum n 0 is 1.62 × 10 5...
We report the discovery of a tight substellar companion to young solar analog PZ Tel, member Beta Pictoris moving group observed with high contrast adaptive optics imaging as part Gemini NICI Planet-Finding Campaign. The was detected at projected separation 16.4 +/- 1.0 AU (0.33 0.01") in April 2009. Second-epoch observations May 2010 demonstrate that is physically associated and shows significant orbital motion. Monte Carlo modeling constrains orbit Tel B eccentricities > 0.6. near-IR...
We present the discovery of a wide (67 AU) substellar companion to nearby (21 pc) young solar-metallicity M1 dwarf CD−35 2722, member ≈100 Myr AB Doradus association. Two epochs astrometry from NICI Planet-Finding Campaign confirm that 2722 B is physically associated with primary star. Near-IR spectra indicate spectral type L4±1 moderately low surface gravity, making it one coolest companions found date. The absorption lines and near-IR continuum shape agree especially well dusty field L4.5...
We present spectro-photometry spanning 1-5 $\mu$m of 51 Eridani b, a 2-10 M$_\text{Jup}$ planet discovered by the Gemini Planet Imager Exoplanet Survey. In this study, we new $K1$ (1.90-2.19 $\mu$m) and $K2$ (2.10-2.40 spectra taken with as well an updated $L_P$ (3.76 $M_S$ (4.67 photometry from NIRC2 Narrow camera. The data were combined $J$ (1.13-1.35 $H$ (1.50-1.80 discovery epoch goal better characterizing properties. Eri b is redder than field brown dwarfs known young T-dwarfs similar...
We expand on the results of Nielsen et al. (2008), using null result for giant extrasolar planets around 118 target stars from VLT NACO H and Ks band planet search (Masciadri 2005), MMT Simultaneous Differential Imaging (SDI) survey (Biller 2007), Gemini Deep Planet Survey (Lafreniere 2007) to set constraints population planets. Our analysis is extended include luminosity models Fortney as well correlation between stellar mass frequency found by Johnson (2007). Doubling sample size FGKM...
We present a new matched filter algorithm for direct detection of point sources in the immediate vicinity bright stars. The stellar Point Spread Function (PSF) is first subtracted using Karhunen-Lo\'eve Image Processing (KLIP) with Angular and Spectral Differential Imaging (ADI SDI). KLIP-induced distortion astrophysical signal included template by computing forward model PSF at every position image. To optimize performance algorithm, we conduct extensive planet injection recovery tests tune...
Abstract orbitize! is an open-source, object-oriented software package for fitting the orbits of directly imaged objects. It packages Orbits Impatient (OFTI) algorithm and a parallel-tempered Markov Chain Monte Carlo (MCMC) into consistent intuitive Python API. makes it easy to run standard astrometric orbit fits; in less than 10 lines code, users can read data, perform one fit using OFTI another MCMC, make two publication-ready figures. Extensive pedagogical tutorials, intended be navigable...
We have carried out high contrast imaging of 70 young, nearby B and A stars to search for brown dwarf planetary companions as part the Gemini NICI Planet-Finding Campaign. Our survey represents largest, deepest planets around high-mass (~1.5-2.5 M_sun) conducted date includes planet hosts beta Pic Fomalhaut. obtained follow-up astrometry all candidate within 400 AU projected separation in uncrowded fields identified new low-mass HD 1160 HIP 79797. found that previously known young companion...
We have completed a high-contrast direct imaging survey for giant planets around 57 debris disk stars as part of the Gemini NICI Planet-Finding Campaign. achieved median H-band contrasts 12.4 mag at 0.5" and 14.1 1" separation. Follow-up observations 66 candidates with projected separation < 500 AU show that all them are background objects. To establish statistical constraints on underlying planet population based our data, we developed new Bayesian formalism incorporates (1) non-detections,...
We present optical and near-infrared high contrast images of the transitional disk HD 100546 taken with Magellan Adaptive Optics system (MagAO) Gemini Planet Imager (GPI). GPI data include both polarized intensity total imagery, MagAO are in Simultaneous Differential Imaging mode at H{\alpha}. The new H -band represent a significant enhancement sensitivity field rotation compared to previous sets enable detailed exploration substructure disk. processed variety differential imaging techniques...
Abstract Using the Gemini Planet Imager located at South, we measured near-infrared (1.0–2.4 μ m) spectrum of planetary companion to nearby, young star β Pictoris. We compare obtained with currently published model grids and known substellar objects present best matching models as well observed objects. Comparing empirical measurement bolometric luminosity evolutionary models, find a mass 12.9 ± 0.2 <?CDATA ${{ \mathcal M }}_{\mathrm{Jup}}$?> , an effective temperature 1724 15 K, radius 1.46...