A5100460379- Stellar, planetary, and galactic studies
- Astronomy and Astrophysical Research
- Adaptive optics and wavefront sensing
- Astrophysical Phenomena and Observations
- Astrophysics and Star Formation Studies
- Gamma-ray bursts and supernovae
- Astronomical Observations and Instrumentation
- Pulsars and Gravitational Waves Research
- Galaxies: Formation, Evolution, Phenomena
- Astro and Planetary Science
- Optical Systems and Laser Technology
- Calibration and Measurement Techniques
- Advanced optical system design
- Relativity and Gravitational Theory
- History and Developments in Astronomy
- Astrophysics and Cosmic Phenomena
- Dark Matter and Cosmic Phenomena
- Cosmology and Gravitation Theories
- Scientific Research and Discoveries
- Mechanics and Biomechanics Studies
- Heat Transfer Mechanisms
- Particle Accelerators and Free-Electron Lasers
- Optical measurement and interference techniques
- Advanced Measurement and Metrology Techniques
- Solar and Space Plasma Dynamics
University of California, Berkeley
2016-2025
Chongqing Public Health Medical Center
2025
Chongqing Medical University
2025
University of Southern Queensland
2024
University of Oxford
2024
Leibniz Institute for Astrophysics Potsdam
2024
NASA Exoplanet Science Institute
2024
California Institute of Technology
2009-2024
University of Chicago
2024
University of Southern California
2024
We report new precision measurements of the properties our Galaxy's supermassive black hole. Based on astrometric (1995-2007) and radial velocity (2000-2007) from W. M. Keck 10-meter telescopes, a fully unconstrained Keplerian orbit for short period star S0-2 provides values Ro 8.0+-0.6 kpc, M_bh 4.1+-0.6x10^6 Mo, hole's velocity, which is consistent with zero 30 km/s uncertainty. If hole assumed to be at rest respect Galaxy, we can further constrain fit obtain = 8.4+-0.4 kpc 4.5+-0.4x10^6...
We present new proper motion measurements and simultaneous orbital solutions for three newly identified (S0-16, S0-19, S0-20) four previously known (S0-1, S0-2, S0-4, S0-5) stars at the Galactic Center. This analysis pinpoints Galaxy's central dark mass to within +-1 milli-arcsec and, first time from dynamics, limits its 1.5+-0.5 mas/y, which is consistent with our derivation of position Sgr A* in infrared reference frame (+-10 mas). The estimated motions 3.7 (+-0.2) x 10^6 (Ro/8kpc)^3 Mo;...
We present new, more precise measurements of the mass and distance our Galaxy's central supermassive black hole, Sgr A*. These results stem from a new analysis that than doubles time baseline for astrometry faint stars orbiting A*, combining two decades speckle imaging adaptive optics data. Specifically, we improve images by using information about star's orbit deep data (2005 - 2013) to inform search star in years (1995 2005). When this technique is combined with first complete re-reduction...
The supermassive black hole at the center of Milky Way plays host to a massive, young cluster that may have formed in one most inhospitable environments Galaxy. We present new measurements global properties this cluster, including initial mass function (IMF), age, and mass. These results are based on Keck laser-guide-star adaptive optics observations used identify stars measure their Kp-band luminosity as presented Do et al. A Bayesian inference methodology is developed simultaneously fit...
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...
Abstract We present the analysis of five black hole candidates identified from gravitational microlensing surveys. Hubble Space Telescope astrometric data and densely sampled light curves ground-based surveys are fit with a single-source, single-lens model in order to measure mass luminosity each lens determine if it is hole. One targets (OGLE-2011-BLG-0462/MOA-2011-BLG-191 or OB110462 for short) shows significant >1 mas coherent shift, little no flux, has an inferred 1.6–4.4 M ⊙ . This...
Observations of the millimeter sky contain valuable information on a number signals, including blackbody cosmic microwave background (CMB), Galactic emissions, and Compton-y distortion due to thermal Sunyaev-Zel'dovich (tSZ) effect. Extracting new insight into cosmological astrophysical questions often requires combining multiwavelength observations spectrally isolate one component. In this work, we present arc-minute-resolution map, which traces out line-of-sight-integrated electron...
Abstract Gravitational microlensing provides a unique opportunity to probe the mass distribution of stars, black holes, and other objects in Milky Way. Population simulations are necessary interpret results from surveys. The contribution binary is often neglected or minimized analysis observations despite high percentage systems microlensing's ability binaries. To simulate population effects, we added multiple Stellar Interface for Evolution Atmospheres ( SPISEA ), which simulates stellar...
We present new proper motions from the 10 m Keck telescopes for a puzzling population of massive, young stars located within 3.5" (0.14 pc) supermassive black hole at Galactic Center. Our motion measurements have uncertainties only 0.07 mas/yr (3 km/s), which is ~7 times better than previous these stars, and enables us to measure accelerations as low 0.2 mas/yr^2 (7 km/s/yr). Using measurements, line-of-sight velocities literature, 3D additional in central parsec, we constrain true orbit...
We present significantly improved proper motion measurements of the Milky Way's central stellar cluster. These improvements are made possible by refining our astrometric reference frame with a new geometric optical distortion model for W. M. Keck II 10 m telescope's Adaptive Optics camera (NIRC2) in its narrow field mode. For first time, this is constructed from on-sky measurements, and available to public. When applied widely dithered images, it produces residuals separations stars that...
Stars with short orbital periods at the center of our galaxy offer a powerful and unique probe supermassive black hole. Over past 17 years, W. M. Keck Observatory has been used to image Galactic highest angular resolution possible today. By adding this data set advancing methodologies, we have detected S0-102, star orbiting galaxy's hole period just 11.5 years. S0-102 doubles number stars full phase coverage less than 20 It thereby provides opportunity future measurements resolve...
We present progenitor-star detections, light curves, and optical spectra of SN2009ip the 2009 transient in UGC2773 (U2773-OT), which were not genuine SNe. Precursor variability decade before outburst indicates that both progenitor stars LBVs. Their pre-outburst curves resemble S Doradus phases preceded giant eruptions eta Carinae SN1954J (V12 NGC2403), with intermediate luminosities. HST detections a discovery indicate U2773-OT progenitors supergiants likely initial masses 50-80 Msun $\ga$20...
Energetic flares are observed in the Galactic supermassive black hole Sagittarius A* from radio to X-ray wavelengths. On a few occasions, simultaneous have been detected IR and observations, but clear counterparts at longer wavelengths not seen. We present flare over several hours on 2006 July 17 with Chandra X-Ray Observatory, Keck II telescope, Caltech Submillimeter Array. All telescopes strong events, submillimeter peak is found occur nearly 100 minutes after peak. polarization data show...
During 5 years of Chandra observations, we have identified seven X-ray transients located within 23 pc Sgr A*. These sources each vary in luminosity by more than a factor 10 and peak luminosities greater × 1033 ergs s-1, which strongly suggests that they are accreting black holes or neutron stars. The the intermediate between those typically considered outburst quiescence for binaries. Remarkably, four these lie only 1 This implies that, compared to numbers similar systems pc, overabundant...
We present a new geometric distortion model for the narrow-field mode of near-infrared camera (NIRC2) fed by adaptive optics system on W. M. Keck II telescope. The and NIRC2 were realigned 2015 April 13. Observations crowded globular cluster, M53, obtained before after realignment to characterize field distortion. distorted positions M53 stars compared with precise astrometry this cluster from Hubble Space Telescope observations. resulting map constructed just is consistent previous solution...
We report on the structure of nuclear star cluster in innermost 0.16 pc Galaxy as measured by number density profile late-type giants. Using laser guide adaptive optics conjunction with integral field spectrograph, OSIRIS, at Keck II telescope, we are able to differentiate between older, (∼ 1 Gyr) stars, which presumed be dynamically relaxed, and unrelaxed young 6 Myr) population. This distinction is crucial for testing models stellar cusp formation vicinity a black hole, assume that stars...
We present new high angular resolution near-infrared spectroscopic observations of the nuclear star cluster surrounding Milky Way's central supermassive black hole. Using integral-field spectrograph OSIRIS on Keck II behind laser-guide-star adaptive optics system, this survey enables us to separate early-type (young, 4-6 Myr) and late-type (old, >1 Gyr) stars with a completeness 50% down K' = 15.5 mag, which corresponds ~10 \msun for stars. This work increases radial extent reported...
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 present new kinematic measurements and modeling of a sample 116 young stars in the central parsec Galaxy order to investigate properties stellar disk. The were derived from combination speckle laser guide star adaptive optics imaging integral field spectroscopy Keck telescopes. Compared earlier disk studies, most important measurement improvement is precision accelerations plane sky, which have factor six smaller uncertainties (~10 uas/yr/yr). also added first radial velocity for 8 stars,...
As a young massive cluster in the Central Molecular Zone, Arches is valuable probe of stellar Initial Mass Function (IMF) extreme Galactic Center environment. We use multi-epoch Hubble Space Telescope observations to obtain high-precision proper motion and photometric measurements cluster, calculating membership probabilities for stars down 1.8 M$_{\odot}$ between radii 0.25 pc -- 3.0 pc. achieve sample with just ~8% field contamination, significant improvement over photometrically-selected...
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...
A three-dimensional conductive nanocomposite with an ordered network and low percolation threshold has been successfully prepared by blending graphite nanosheets (GNs) polyethylene on a two-roll mill. The orient intensively in the composite, leading to highly anisotropic properties. fraction of closest possesses sharp positive pressure coefficient resistivity, which abrupt transition can be attributed compressive-stress-induced deformation network. Such piezoresistive effects depend strongly...
We report the first time series of broadband infrared color measurements Sgr A Ã , variable emission source associated with supermassive black hole at Galactic center.Using laser and natural guide star adaptive optics systems on Keck II Telescope, we imaged in multiple near-infrared filters a typical cycle $3 minutes during four observing runs (2005Y2006), two which were simultaneous Chandra X-ray measurements.In spite large range dereddened flux densities for (2Y30 mJy), all our...
We present the results of near-infrared (2 and 3 microns) monitoring Sgr A*-IR with 1 min time sampling using natural laser guide star adaptive optics (LGS AO) system at Keck II telescope. was observed continuously for up to three hours on each seven nights, between 2005 July 2007 August. is detected all times variable, a median 2 micron flux density 0.192 mJy, corresponding 16.3 magnitude K'. These observations allow us investigate Nyquist sampled periods ranging from about minutes an hour....