A5006073929- Astrophysical Phenomena and Observations
- Stellar, planetary, and galactic studies
- Astronomy and Astrophysical Research
- Pulsars and Gravitational Waves Research
- Planetary Science and Exploration
- Astro and Planetary Science
- Seismic Imaging and Inversion Techniques
- Gamma-ray bursts and supernovae
- Adaptive optics and wavefront sensing
- Astrophysics and Star Formation Studies
- Astronomical Observations and Instrumentation
- Hydraulic Fracturing and Reservoir Analysis
- Reservoir Engineering and Simulation Methods
- Galaxies: Formation, Evolution, Phenomena
- Relativity and Gravitational Theory
- Atmospheric Ozone and Climate
- Cosmology and Gravitation Theories
- Seismic Waves and Analysis
- Mechanics and Biomechanics Studies
- Radioactive contamination and transfer
- History and Developments in Astronomy
- Black Holes and Theoretical Physics
- Heat Transfer Mechanisms
- Astronomical and nuclear sciences
- Statistical and numerical algorithms
University of California, Los Angeles
2015-2024
ExxonMobil (United States)
2002-2022
ExxonMobil (Germany)
2012-2019
UCLA Health
2019
Dartmouth College
2014
In this Letter, we demonstrate that short-period stars orbiting around the supermassive black hole in our Galactic Center can successfully be used to probe gravitational theory a strong regime. We use 19 years of observations two best measured constrain hypothetical fifth force arises various scenarios motivated by development unification or some models dark matter and energy. No deviation from General Relativity is reported strength restricted an upper 95% confidence limit...
Gravitational redshift in the Galactic Center General relativity predicts that light emitted by an object a strong gravitational field—for example, close to black hole—should be shifted longer wavelengths. This does not exist Newtonian theory of gravity. Do et al. monitored position and spectrum star S0-2 as it passed Sagittarius A*, supermassive hole at center Milky Way. Around closest part S0-2's 16-year orbit, they detected effect on its spectrum. These results are more consistent with...
We report the first star formation history study of Milky Way's nuclear cluster (NSC) that includes observational constraints from a large sample stellar metallicity measurements. These measurements were obtained recent surveys Gemini and VLT 770 late-type stars within central 1.5 pc. measurements, along with photometry spectroscopically derived temperatures, are forward modeled Bayesian inference approach. Including improves overall fit quality, as low-temperature red giants previously...
Abstract We present the first estimate of intrinsic binary fraction young stars across central ≈0.4 pc surrounding supermassive black hole (SMBH) at Milky Way Galactic center (GC). This experiment searched for photometric variability in 102 spectroscopically confirmed stars, using 119 nights 10″ wide adaptive optics imaging observations taken W. M. Keck Observatory over 16 yr <?CDATA $K^{\prime} $?> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">...
Abstract The star S0-2, which orbits the supermassive black hole (SMBH) in our Galaxy with a period of 16 years, provides strongest constraint on both mass SMBH and distance to Galactic center. S0-2 will soon provide first measurement relativistic effects near SMBH. We report limits binarity from radial velocity (RV) monitoring, has implications for understanding its origin robustness as probe central gravitational field. With 87 RV measurements, include 12 new observations that we present,...
Abstract We present the results of first systematic search for spectroscopic binaries within central 2 × 3 arcsec around supermassive black hole at center Milky Way galaxy. This survey is based primarily on over a decade adaptive optics-fed integral-field spectroscopy ( R ∼ 4000), obtained as part Galactic Center Orbits Initiative Keck Observatory, and it has limiting K ’-band magnitude 15.8, which least 4 mag deeper than previous searches larger radii nuclear star cluster. From this primary...
Abstract Stars often reside in binary configurations. The nuclear star cluster surrounding the supermassive black hole (SMBH) Galactic Center (GC) is expected to include a population. In this dense environment, frequently encounters and interacts with neighboring stars. These interactions vary from small perturbations violent collisions. former case, weak gravitational unbind soft over evaporation timescale, which depends on properties as well density of objects velocity dispersion....
We measure the 3D kinematic structures of young stars within central 0.5 parsec our Galactic Center using 10 m telescopes W.~M.~Keck Observatory over a time span 25 years. Using high-precision measurements positions on sky, and proper motions radial velocities from new observations literature, we constrain orbital parameters for each star. Our results show two statistically significant sub-structures: clockwise stellar disk with 18 candidate stars, as has been proposed before, but an...
We present two decades of new high-angular-resolution near-infrared data from the W. M. Keck Observatory that reveal extreme evolution in X7, an elongated dust and gas feature, presently located half arcsecond Galactic Center supermassive black hole. With both spectro-imaging observations Br-{\gamma} line-emission Lp (3.8 {\mu}m) imaging data, we provide first estimate its orbital parameters quantitative characterization morphology mass. find leading edge X7 appears to be on a mildly...
OSIRIS is a near-infrared (1.0--2.4 $\mu$m) integral field spectrograph operating behind the adaptive optics system at Keck Observatory, and one of first lenslet-based spectrographs. Since its commissioning in 2005, it has been productive instrument, producing nearly half laser guide star (LGS AO) papers on Keck. The complexity raw data format necessitated custom reduction pipeline (DRP) delivered with instrument order to iteratively assign flux overlapping spectra proper spatial spectral...
The New Horizons spacecraft will encounter Pluto in 2015 July. As this fast flyby yield a picture of frozen time, ground-based observations are key to understanding dwarf ice planet, especially with regard the seasonal transport surface volatiles. This paper reports on changes Pluto's rotational light curve as evidence for transport. Historical consistent stable frost pattern, but since 2002, began appear both curves and Hubble Space Telescope maps. Our BVR at Table Mountain Observatory from...
Abstract The Hamburg (H4) meteorite fell on 17 January 2018 at 01:08 UT approximately 10 km north of Ann Arbor, Michigan. More than two dozen fragments totaling under 1 kg were recovered, primarily from frozen lake surfaces. fireball initial velocity was 15.83 ± 0.05 s −1 , based four independent records showing the above 50 altitude. radiant had a zenith angle 66.14 0.29° and an azimuth 121.56 1.2°. resulting low inclination (<1°) Apollo‐type orbit has large aphelion distance Tisserand...
We propose a new approach to Bayesian prior probability distributions (priors) that can improve orbital solutions for low-phase-coverage orbits, where data cover less than approximately 40% of an orbit. In instances low phase coverage such as with stellar orbits in the Galactic center or directly-imaged exoplanets, have constraining power and thus priors bias parameter estimates produce under-estimated confidence intervals. Uniform priors, which are commonly assumed orbit fitting, notorious...
As the closest example of a galactic nucleus, Galactic center (GC) presents an exquisite laboratory for learning about supermassive black holes (SMBH) and their environment. We describe several exciting new research directions that, over next 10 years, hold potential to answer some biggest scientific questions raised in recent decades: Is General Relativity (GR) correct description holes? What is nature star formation extreme environments? How do stars compact objects dynamically interact...
We investigate the star formation rate and its location in major merger cluster Abell 2465 at $z$ = 0.245. Optical properties of are described Paper I. Measurements H$\alpha$ infrared dust emission galaxies were made with an interference filter centred on redshifted line a wavelength 817 nm utilized data from WISE satellite 12 $\mu$m band. Imaging Johnson $U$ $B$ bands was obtained, along SDSS $u$ $r$ used to study blue fraction, which appears enhanced, as further signatures cluster. Star...
While the Milky Way Nuclear star cluster has been studied extensively, how it formed is uncertain. Studies have shown contains a solar and supersolar metallicity population that may in-situ, along with subsolar via mergers of globular clusters dwarf galaxies. Stellar abundance measurements are critical to differentiate between formation scenarios. We present new [$M/H$] $\alpha$-element abundances [$\alpha/Fe$] two subsolar-metallicity stars in Galactic Center. These observations were taken...
Abstract We present the first observational constraint on Brackett- γ (Br ) recombination line emission associated with supermassive black hole at center of our Galaxy, known as Sgr A*. By combining 13 yr data adaptive optics fed integral field spectrograph OSIRIS W. M. Keck Observatory obtained part Galactic Center Orbits Initiative, we extract near-infrared spectrum within ∼0.2″ and derive an upper limit Br flux. The aperture was set to match size disk-like structure that recently reported...
Motion of short-period stars orbiting the supermassive black hole in our Galactic Center has been monitored for more than 20 years. These observations are currently offering a new way to test gravitational theory an unexplored regime: strong field, around hole. In this proceeding, we present three results: (i) constraint on hypothetical fifth force obtained by using 19 years two best measured S0-2 and S0-38 ; (ii) upper limit secular advance argument periastron star (iii) sensitivity...
We present the status and plans for Keck All sky Precision Adaptive optics (KAPA) program. KAPA includes (1) an upgrade to I laser guide star adaptive (AO) facility improve image quality coverage, (2) inclusion of AO telemetry-based point spread function estimates with all science exposures, (3) four key programs, (4) educational component focused on broadening participation women underrepresented groups in instrumentation. For this conference we focus upgrades since 2020 SPIE proceedings1...
Summary One of the critical components for a successful 4D seismic project is to maximize imaging repeatability between different vintages in processing by use same flows and parameters, including migration velocity model. There are examples that significant changes shallow reservoirs occur surveys, leading degradation consequently uncertainties interpretation underlying reservoirs. A recent West Africa such an example where increases gas saturation reservoir due production resulted up 10%...
Summary Pre-Salt seismic data typically suffers from significant challenges due to illumination, non-primary mode noises (converted waves, multiples) arising hard contrast. The cumulative effect leads loss of signal quality and frequency in the data. Elastic FWI provides a path forward addressing many these by directly inverting raw shots produce elastic properties such as impedance, Vp/Vs P-wave velocity. Using field example we will demonstrate efficacy eFWI approach.
We present the first estimate of intrinsic binary fraction young stars across central $\approx$ 0.4 pc surrounding supermassive black hole (SMBH) at Milky Way Galactic center (GC). This experiment searched for photometric variability in 102 stars, using 119 nights 10"-wide adaptive optics imaging observations taken Keck Observatory over 16 years K'- and H-bands. photometrically detected three all which are situated more than 1" (0.04 pc) from SMBH one which, S2-36, is newly reported here...