A5024184752- Stellar, planetary, and galactic studies
- Gamma-ray bursts and supernovae
- Astronomy and Astrophysical Research
- Astrophysical Phenomena and Observations
- Astrophysics and Star Formation Studies
- Pulsars and Gravitational Waves Research
- Galaxies: Formation, Evolution, Phenomena
- Astronomical Observations and Instrumentation
- Astro and Planetary Science
- Adaptive optics and wavefront sensing
- Geophysics and Gravity Measurements
- Scientific Research and Discoveries
- Astrophysics and Cosmic Phenomena
- History and Developments in Astronomy
- Calibration and Measurement Techniques
- Solar and Space Plasma Dynamics
- Dark Matter and Cosmic Phenomena
- Nuclear Physics and Applications
- Nuclear Materials and Properties
- Radio Astronomy Observations and Technology
- Particle physics theoretical and experimental studies
- Cosmology and Gravitation Theories
- Space Exploration and Technology
- Risk and Safety Analysis
- Radiation Therapy and Dosimetry
Center for Astrophysics Harvard & Smithsonian
2013-2024
Smithsonian Astrophysical Observatory
2014-2023
Harvard University
1999-2014
Harvard University Press
2004-2006
Association of Universities For Research In Astronomy
2001-2003
U.S. National Science Foundation
2001-2003
Kitt Peak National Observatory
2001-2003
University of Maryland, College Park
1998
National Museum of Natural History
1988
Smithsonian Institution
1988
We present early observations of the afterglow GRB 030329 and spectroscopic discovery its associated supernova SN 2003dh. obtained spectra each night from March 30.12 (0.6 days after burst) to April 8.13 (UT) (9.6 burst). The cover a wavelength range 350-850 nm. consist power-law continuum (Fν ∝ ν-0.9) with narrow emission lines originating H II regions in host galaxy, indicating low redshift z = 0.1687. However, our taken 2003 5 show broad peaks flux characteristic supernova. Correcting for...
We report the detection of a planet whose orbit surrounds pair low-mass stars. Data from Kepler spacecraft reveal transits across both stars, in addition to mutual eclipses giving precise constraints on absolute dimensions all three bodies. The is comparable Saturn mass and size, nearly circular 229-day around its two parent eclipsing stars are 20% 69% as massive sun, have an eccentric 41-day orbit. motions bodies confined within 0.5 degree single plane, suggesting that formed circumbinary disk.
We present 1210 Johnson/Cousins B, V, R, and I photometric observations of 22 recent Type Ia supernovae (SNe Ia): SNe 1993ac, 1993ae, 1994M, 1994S, 1994T, 1994Q, 1994ae, 1995D, 1995E, 1995al, 1995ac, 1995ak, 1995bd, 1996C, 1996X, 1996Z, 1996ab, 1996ai, 1996bk, 1996bl, 1996bo, 1996bv. Most the photometry was obtained at Fred Lawrence Whipple Observatory Harvard-Smithsonian Center for Astrophysics in a cooperative observing plan aimed improving database Ia. The redshifts sample range from cz =...
We present multiband photometry of 185 type-Ia supernovae (SNe Ia), with over 11,500 observations. These were acquired between 2001 and 2008 at the F. L. Whipple Observatory Harvard-Smithsonian Center for Astrophysics (CfA). This sample contains largest number homogeneously observed reduced nearby SNe Ia (z ≲ 0.08) published to date. It more than doubles sample, bringing SN cosmology point where systematic uncertainties dominate. Our natural system has a precision ≲0.02 mag in BVRIr'i' ≲0.04...
The Hectospec is a 300 optical fiber fed spectrograph commissioned at the MMT in spring of 2004. In configuration pioneered by Autofib instrument Anglo‐Australian Telescope, Hectospec's probes are arranged radial "fisherman on pond" geometry and held position with small magnets. A pair high‐speed, six‐axis robots move buttons between observing configurations within ∼300 s, to an accuracy ∼25 μm. fibers run for 26 m MMT's focal surface bench spectrograph, operating R∼1000–2000. Hectochelle,...
We present UBVRI photometry of 44 Type Ia supernovae (SNe Ia) observed from 1997 to 2001 as part a continuing monitoring campaign at the Fred Lawrence Whipple Observatory Harvard-Smithsonian Center for Astrophysics. The data set comprises 2190 observations and is largest homogeneously reduced sample SNe date, nearly doubling number well-observed, nearby with published multicolor CCD light curves. large U-band unique addition, important connections high redshift. decline rate SN curves...
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>...
We have discovered a star, SDSS J090745.0+024507, leaving the Galaxy with heliocentric radial velocity of 853 ± 12 km s-1, largest ever observed in Milky Way halo. The star is either hot blue horizontal-branch or B9 main-sequence distance 39 71 kpc, respectively. Corrected for solar reflex motion and to local standard rest, Galactic rest-frame 709 s-1. suggest that this first example hypervelocity ejected from center, as predicted by Hills later discussed Yu & Tremaine. star's vector points...
We present extensive optical and infrared photometry of the afterglow gamma-ray burst (GRB) 030329 its associated supernova (SN) 2003dh over first two months after detection (2003 March 30-May 29 UT). Optical spectroscopy from a variety telescopes is shown and, when combined with photometry, allows an unambiguous separation between SN contributions. The GRB initially power-law continuum but shows significant color variations during week that are unrelated to presence SN. early light curve...
We present extensive early photometric (ultraviolet through near-infrared) and spectroscopic (optical data on supernova (SN) 2008D as well X-ray analysis the associated Swift transient (XRT) 080109. Our span a time range of 5 hr before detection to 150 days after its detection, detailed allowed us derive constraints nature SN progenitor; throughout we draw comparisons with results presented in literature find several key aspects that differ. show spectrum XRT 080109 can be fit equally by an...
We present multi-band optical photometry of 94 spectroscopically confirmed Type Ia supernovae (SNe Ia) in the redshift range 0.0055–0.073, obtained between 2006 and 2011. There are a total 5522 light-curve points. show that our natural-system SN has precision ≲ 0.03 mag BVr'i', 0.06 u', 0.07 U for points brighter than 17.5 estimate it systematic uncertainty 0.014, 0.010, 0.012, 0.046, 0.073 BVr'i'u'U, respectively. Comparisons standard-system with published light curves comparison stars...
Hypervelocity stars (HVSs) travel with such extreme velocities that dynamical ejection via gravitational interaction a massive black hole (MBH) is their most likely origin. Observers have discovered dozens of unbound main-sequence since the first in 2005, and velocities, stellar nature, spatial distribution, overall numbers B Milky Way halo all fit an MBH Theorists proposed various mechanisms for ejecting stars, these can be tested larger more complete samples. HVSs' properties are linked to...
The Hypervelocity Star survey presents the currently largest sample of radial velocity measurements halo stars out to 80 kpc. We apply spherical Jeans modeling these data in order derive mass profile Galaxy. restrict analysis distances larger than 25 kpc from Galactic center, where density is well approximated by a single power law with logarithmic slope between -3.5 and -4.5. With this restriction, we also avoid complication flattened disk. In range < r kpc, dispersion declines remarkably...
We have discovered a detached pair of white dwarfs (WDs) with 12.75 min orbital period and 1,315 km/s radial velocity amplitude. measure the full parameters system using its light curve, which shows ellipsoidal variations, Doppler boosting, primary secondary eclipses. The is 0.25 Msun tidally distorted helium WD, only second WD known. unseen 0.55 carbon-oxygen WD. two WDs will come into contact in 0.9 Myr due to loss energy angular momentum via gravitational wave radiation. Upon systems may...
We analyze radial velocity observations of the 12 extremely low-mass <0.25 Msol white dwarfs (WDs) in MMT Hypervelocity Star Survey. Eleven WDs are binaries with orbital periods shorter than 14 hours; one non-variable WD is possibly a pole-on system among our non-kinematically selected targets. Our sample unique: it complete well-defined range apparent magnitude and color. The mass functions imply that unseen companions most likely other WDs, although neutron star cannot be excluded. Six 11...
We describe our completed spectroscopic survey for unbound hypervelocity stars (HVSs) ejected from the Milky Way. Three new discoveries bring total number of HVSs to 21. place constraints on nature and their distances using moderate resolution MMT spectroscopy. Half are fast rotators; they certain 2.5-4 Msun main sequence at 50 - 120 kpc distances. Correcting stellar lifetime, implies that Way a rate 1.5e-6 /yr. The observed likely continuously over past 200 Myr do not share common flight...
We present follow-up spectroscopy of 711 white dwarfs within 100 pc, and a detailed model atmosphere analysis the pc dwarf sample in SDSS footprint. Our spectroscopic is complete for 83% hotter than 6000 K, where atmospheric composition can be constrained reliably. identify 1508 DA with pure hydrogen atmospheres. The mass distribution has an extremely narrow peak at $0.59~M_{\odot}$, reveals shoulder from relatively massive $M=0.7$-$0.9~M_{\odot}$. Comparing this binary population synthesis...
We present new radial velocity and X-ray observations of extremely low mass (ELM, ∼0.2 M☉) white dwarf (WD) candidates in the Sloan Digital Sky Survey Data Release 7 area. identify seven binary systems with 1–18 hr orbital periods. Five will merge due to gravitational wave radiation within 10 Gyr, bringing total number merger found ELM 24. The has now quintupled known WD population. It also discovered eight shortest period detached currently known. discuss characteristics non-merger observed...
We present the discovery of 17 low-mass white dwarfs (WDs) in short-period (P ⩽ 1 day) binaries. Our sample includes four objects with remarkable log g ≃ 5 surface gravities and orbital solutions that require them to be double degenerate All lowest gravity WDs have metal lines their spectra implying long gravitational settling times or ongoing accretion. Notably, six our binary merger <10 Gyr. Four ≳0.9 M☉ companions. If companions are massive WDs, these binaries will evolve into stable mass...
ABSTRACT We report evidence for excess blue light from the Type Ia supernova (Sn Ia) SN 2012cg at 15 and 16 days before maximum B -band brightness. The emission is consistent with predictions impact of on a non-degenerate binary companion. This first companion to normal Ia. Sixteen light, <?CDATA $B-V$?> <?MML <mml:math> <mml:mi>B</mml:mi> <mml:mo>−</mml:mo> <mml:mi>V</mml:mi> </mml:math>?> color 0.2 mag bluer than other At later times, this has typical curve, extinction-corrected...
We present the final sample of 98 detached double white dwarf (WD) binaries found in Extremely Low Mass (ELM) Survey, a spectroscopic survey targeting <0.3 Msun He-core WDs completed Sloan Digital Sky Survey footprint. Over course we observed ancillary low mass WD candidates like GD278, which show is P=0.19 d binary, as well that turn out to be field blue straggler/subdwarf A-type stars with luminosities too large given their Gaia parallaxes. Here, define clean ELM complete within our target...
We present early photometric and spectroscopic data on the afterglow of GRB 060218 report evolution underlying supernova SN 2006aj. Our span a time range 4-23 days after clearly establish that 2006aj is fast-evolving broad-lined Type Ic with an extremely short rise (~10 days) large optical peak luminosity (MV = -18.7 mag). The properties are deduced well since gamma-ray burst (GRB) does not contribute significant amount to total light output. spectra show broad lines indicative expansion...
The disruption of binary stars by the tidal field black hole in Galactic Center can produce hypervelocity observed halo. We use numerical models to simulate full spectrum observable velocities ejected into halo this process. Our model includes a range parameters for binaries with 3-4 M_Solar primaries, consideration radial orbits through an approximate mass distribution Galaxy, and impact stellar lifetimes. calculate ejection reproduce previous results mean velocity at center. predicts that...
We describe new radial velocity and X-ray observations of extremely low-mass white dwarfs (ELM WDs, ∼0.2 M☉) in the Sloan Digital Sky Survey Data Release 4 MMT Hypervelocity Star survey. identify four short period binaries, including two merger systems. These bring total number binary systems identified our survey to 20. No main-sequence or neutron star companions are visible available optical photometry, radio, data. Thus, most likely WDs. Twelve these will merge within a Hubble time due...