A5014567632- Stellar, planetary, and galactic studies
- Astronomy and Astrophysical Research
- Astrophysical Phenomena and Observations
- Gamma-ray bursts and supernovae
- Galaxies: Formation, Evolution, Phenomena
- Pulsars and Gravitational Waves Research
- Astronomical Observations and Instrumentation
- Astrophysics and Star Formation Studies
- Astrophysics and Cosmic Phenomena
- Astro and Planetary Science
- High-pressure geophysics and materials
- Adaptive optics and wavefront sensing
- Solar and Space Plasma Dynamics
- Radio Astronomy Observations and Technology
- Nuclear Physics and Applications
- Mechanics and Biomechanics Studies
- Relativity and Gravitational Theory
- History and Developments in Astronomy
- Particle Accelerators and Free-Electron Lasers
- Impact of Light on Environment and Health
- Advanced X-ray Imaging Techniques
- Geophysics and Gravity Measurements
- Cosmology and Gravitation Theories
- Spectroscopy and Laser Applications
- Dark Matter and Cosmic Phenomena
Michigan State University
2016-2025
Time Domain (United States)
2018-2025
International Centre for Radio Astronomy Research
2023
Curtin University
2023
Physical Sciences (United States)
2019-2022
Center for Astrophysics Harvard & Smithsonian
2008-2014
Michigan United
2014
Harvard University Press
2012
Harvard University
2009-2010
Swinburne University of Technology
2003-2010
Globular cluster (GC) systems have now been studied in galaxies ranging from dwarfs to giants and spanning the full Hubble sequence of morphological types. Imaging spectroscopy with Space Telescope large ground-based telescopes together established that most bimodal color distributions reflect two subpopulations old GCs: metal-poor metal-rich. The characteristics both are correlated those their parent galaxies. We argue GCs formed low-mass dark matter halos early universe properties biased...
We describe ongoing searches for intermediate-mass black holes with M BH ≈ 10–10 5 ⊙ . review a range of search mechanisms, both dynamical and those that rely on accretion signatures. find the following conclusions: ▪ Dynamical signatures alike point to high fraction 10 9 –10 galaxies hosting ∼ In contrast, there are no solid detections in globular clusters. There few observational constraints any environment 100–10 4 Considering low-mass hole masses constraining limits, we –σ * relation...
Doppler measurements from Subaru and Keck have revealed radial velocity variations in the V=8.15, G0IV star HD 149026 consistent with a Saturn-Mass planet 2.8766 day orbit. Photometric observations at Fairborn Observatory detected three complete transit events depths of 0.003 mag predicted times conjunction. is now second brightest transiting extrasolar planet. The mass star, based on interpolation stellar evolutionary models, 1.3 +/- 0.1 solar masses; together amplitude, K=43.3 m s^-1, we...
Abstract We present optical and ultraviolet spectra of the first electromagnetic counterpart to a gravitational-wave (GW) source, binary neutron star merger GW170817. Spectra were obtained nightly between 1.5 9.5 days post-merger, using Southern Astrophysical Research Magellan telescopes; UV spectrum was with Hubble Space Telescope at 5.5 days. Our data reveal rapidly fading blue component ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>T</mml:mi>...
The double explosion of SN 2009ip in 2012 raises questions about our understanding the late stages massive star evolution. Here we present a comprehensive study during its remarkable rebrightenings. High-cadence photometric and spectroscopic observations from GeV to radio band obtained variety ground-based space facilities (including Very Large Array, Swift, Fermi, Hubble Space Telescope, XMM) constrain be low energy (E ∼ 1050 erg for an ejecta mass ∼0.5 M☉) asymmetric complex medium shaped...
Double detonations in double white dwarf (WD) binaries undergoing unstable mass transfer have emerged recent years as one of the most promising Type Ia supernova (SN Ia) progenitor scenarios. One potential outcome this "dynamically driven double-degenerate double-detonation" (D^6) scenario is that companion WD survives explosion and flung away with a velocity equal to its > 1000 km/s pre-SN orbital velocity. We perform search for these hypervelocity runaway WDs using Gaia's second data...
We analyze pre-explosion near- and mid-infrared (IR) imaging of the site SN 2023ixf in nearby spiral galaxy M101 characterize candidate progenitor star. The star displays compelling evidence variability with a possible period $\approx$1000 days an amplitude $\Delta m \approx 0.6$ mag extensive monitoring Spitzer Space Telescope since 2004, likely indicative radial pulsations. Variability consistent this is also seen near-IR $J$ $K_{s}$ bands between 2010 2023, up to just 10 before explosion....
We have created specialized target lists for radial velocity surveys that are biased toward stars (1) possess planets and (2) easiest to observe with current detection techniques. use a procedure uniformly estimates fundamental stellar properties of Tycho 2 stars, errors, using spline functions broadband photometry proper motion found in Hipparcos/Tycho 2MASS. provide Teff distance 2.4 × 106 lack trigonometric distances. For appear be FGK dwarfs, we also derive [Fe/H] identify unresolved...
A growing number of low luminosity and surface brightness astronomical objects challenge traditional notions both galaxies star clusters. To address this challenge, we propose a definition galaxy that does not depend on cold dark matter model the universe: is gravitationally bound collection stars whose properties cannot be explained by combination baryons Newton's laws gravity. After exploring several possible observational diagnostics definition, critically examine classification...
We use a combined imaging and spectroscopic survey of the nearby central cluster galaxy, M87, to assemble sample 34 confirmed ultra compact dwarfs (UCDs) with half-light radii >~ 10 pc measured from Hubble Space Telescope images. This doubles existing in making it largest such for any while extending detection UCDs unprecedentedly low luminosities (MV = -9). With this expanded sample, we find no correlation between size luminosity, contrast previous suggestions, general galactocentric...
We introduce and provide the scientific motivation for a wide-field photometric spectroscopic chemodynamical survey of nearby early-type galaxies (ETGs) their globular cluster (GC) systems. The SAGES Legacy Unifying Globulars GalaxieS (SLUGGS) is being carried out primarily with Subaru/Suprime-Cam Keck/DEIMOS. former provides deep gri imaging over 900 arcmin2 field-of-view to characterize GC host galaxy colors spatial distributions, identify targets. NIR Ca ii triplet line-of-sight...
We present Keck/DEIMOS spectroscopy of Segue 1, an ultra-low luminosity (M_V = -1.5) Milky Way satellite companion. While the combined size and 1 are consistent with either a globular cluster or dwarf galaxy, we spectroscopic evidence that this object is dark matter-dominated galaxy. identify 24 stars as members mean heliocentric recession velocity 206 +/- 1.3 kms. measure internal dispersion 4.3+/-1.2 Under assumption these in dynamical equilibrium, infer total mass 4.5^{+4.7}_{-2.5} x 10^5...
We present the most extensive combined photometric and spectroscopic study to date of enormous globular cluster (GC) system around M87, central giant elliptical galaxy in nearby Virgo cluster. Using observations from DEIMOS LRIS at Keck, Hectospec on MMT, we derive new, precise radial velocities for 451 GCs with projected radii ~ 5 185 kpc. combine these measurements literature data a total sample 737 objects, which use re-examination kinematics GC M87. The are analyzed context archival...
We present a spectro-photometric survey of 2522 extragalactic globular clusters (GCs) around twelve early-type galaxies, nine which have not been published previously. Combining space-based and multi-colour wide field ground-based imaging, with spectra from the Keck DEIMOS instrument, we obtain an average 160 GC radial velocities per galaxy, high velocity precision 15 km/s GC. After studying photometric properties systems, such as their spatial colour distributions, focus on kinematics...
We describe the structural and kinematic properties of first compact stellar systems discovered by AIMSS project. These spectroscopically confirmed objects have sizes ($\sim$6 $<$ R$_{\rm e}$ [pc] 500) masses ($\sim$2$\times$10$^{6}$ M$_*$/M$_\odot$ 6$\times$10$^{9}$) spanning range massive globular clusters (GCs), ultra dwarfs (UCDs) elliptical galaxies (cEs), completely filling gap between star galaxies. Several are close analogues to prototypical cE, M32. objects, which more than...
We investigate the kinematic properties and stellar population of Galactic satellite Willman 1 (Wil 1) by combining Keck/DEIMOS spectroscopy with Kitt Peak National Observatory mosaic camera imaging. Wil 1, also known as SDSS J1049+5103, is a nearby, ultra-low luminosity Milky Way companion. This object lies in region size–luminosity space (MV ∼ −2 mag, d 38 kpc, rhalf 20 pc) occupied satellites Boötes II Segue 2, but no other old system. use color–magnitude criteria to identify 45 stars...
We report the discovery of a candidate stellar-mass black hole in Milky Way globular cluster M62. detected candidate, which we term M62-VLA1, core using deep radio continuum imaging from Karl G. Jansky Very Large Array. M62-VLA1 is faint source, with flux density 18.7 +/- 1.9 microJy at 6.2 GHz and flat spectrum (alpha=-0.24 0.42, for S_nu = nu^alpha). M62 second hole; unlike two holes previously found M22, associated Chandra X-ray supporting its identification as binary. Measurements...
Although the colour distribution of globular clusters in massive galaxies is well known to be bimodal, spectroscopic metallicity has been measured only a few galaxies. After redefining calcium triplet index–metallicity relation, we use our relation derive 903 11 early-type This largest sample cluster metallicities yet assembled. We compare these with those derived from Lick indices finding good agreement. In six eight sufficient numbers high-quality spectra find bimodality distribution. Our...
We present the widest-field resolved stellar map to date of closest ($D\sim3.8$ Mpc) massive elliptical galaxy NGC 5128 (Centaurus A; Cen A), extending out a projected galactocentric radius $\sim150$ kpc. The dataset is part our ongoing Panoramic Imaging Survey Centaurus and Sculptor (PISCeS) utilizing Magellan/Megacam imager. resolve population old red giant branch stars down $\sim1.5$ mag below tip branch, reaching surface brightness limits as low $\mu_{V,0}\sim32$ arcsec$^{-2}$. resulting...
We report the detection of steady radio emission from known X-ray source X9 in globular cluster 47 Tuc. With a double-peaked C IV line its ultraviolet spectrum providing clear signature accretion, this had been previously classified as cataclysmic variable. In deep ATCA imaging 2010 and 2013, we identified at both 5.5 9.0 GHz, with spectral index (defined $S_{\nu}\propto\nu^{\alpha}$) $\alpha=-0.4\pm0.4$. Our measured flux density $42\pm4$ microJy/beam GHz implies luminosity ($\nu L_{\nu}$)...
Our current understanding of galaxy evolution still has many uncertainties associated with the details accretion, processing, and removal gas across cosmic time. The next generation radio telescopes will image neutral hydrogen (HI) in galaxies over large volumes at high redshifts, which provide key insights into these processes. We are conducting COSMOS HI Large Extragalactic Survey (CHILES) Karl G. Jansky Very Array, is first survey to simultaneously observe from z=0 z~0.5. Here, we report...
ABSTRACT Searches for circumstellar material around Type Ia supernovae (SNe Ia) are some of the most powerful tests nature SN progenitors, and radio observations provide a particularly sensitive probe this material. Here, we report SNe their lower-luminosity thermonuclear cousins. We present largest, sensitive, spectroscopically diverse study prompt ( <?CDATA ${\rm{\Delta }}t\lesssim 1$?> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi...