A5088633481- Astronomical Observations and Instrumentation
- Astronomy and Astrophysical Research
- Astrophysical Phenomena and Observations
- Galaxies: Formation, Evolution, Phenomena
- Calibration and Measurement Techniques
- Scientific Research and Discoveries
- Radio Astronomy Observations and Technology
- Gamma-ray bursts and supernovae
- Geophysics and Gravity Measurements
- Stellar, planetary, and galactic studies
- Space exploration and regulation
- Computational Physics and Python Applications
- Planetary Science and Exploration
- Astro and Planetary Science
- Astrophysics and Cosmic Phenomena
- Space Science and Extraterrestrial Life
- Spacecraft Design and Technology
- History and Developments in Astronomy
- Space Exploration and Technology
- Adaptive optics and wavefront sensing
- Advanced X-ray Imaging Techniques
- Cosmology and Gravitation Theories
- Medical Imaging Techniques and Applications
- Sensor Technology and Measurement Systems
- Scientific Measurement and Uncertainty Evaluation
Center for Astrophysics Harvard & Smithsonian
2012-2024
Cornell University
2020
Smithsonian Astrophysical Observatory
1989-2011
Harvard University
2001-2009
CFA Institute
2003
Harvard University Press
1994-2002
University of Ulster
1992-1993
Marshall Space Flight Center
1992
SKA Observatory
1988
University of Cambridge
1983-1987
view Abstract Citations (1626) References (136) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Atlas of Quasar Energy Distributions Elvis, Martin ; Wilkes, Belinda J. McDowell, Jonathan C. Green, Richard F. Bechtold, Jill Willner, S. P. Oey, M. Polomski, Elisha Cutri, Roc We present an atlas the spectral energy distributions (SEDs) normal, nonblazar, quasars over whole available range (radio to 10 keV X-rays) electromagnetic spectrum. The primary (UVSX)...
The CIAO (<i>Chandra</i> Interactive Analysis of Observations) software package was first released in 1999 following the launch <i>Chandra</i> X-ray Observatory and is used by astronomers across world to analyze data as well from other telescopes. From earliest design discussions, planned a general-purpose scientific analysis system optimized for astronomy, consists mainly command line tools (allowing easy pipelining scripting) with parameter-based interface layered on flexible manipulation...
We present the final results of a ROSAT PSPC program to study soft X-ray emission properties complete sample low-z quasars. This includes all 23 quasars from Bright Quasar Survey with z ≤ 0.400 and N<1.9×1020 cm-2. Pointed observations were made for quasars, yielding high signal-to-noise (S/N) spectra most objects, which allowed an accurate determination spectral shape. The following main obtained:
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...
Abstract I discuss the current low Earth orbit artificial satellite population and show that proposed “megaconstellation” of circa 12,000 Starlink Internet satellites would dominate lower part orbit, below 600 km, with a latitude-dependent areal number density between 0.005 0.01 objects per square degree at airmass <2. Such large, low-altitude appear visually bright to ground observers, initial Starlinks are naked-eye objects. model expected illuminated as function latitude, time year,...
The Chandra Source Catalog (CSC) is a general purpose virtual X-ray astrophysics facility that provides access to carefully selected set of generally useful quantities for individual sources, and designed satisfy the needs broad-based group scientists, including those who may be less familiar with astronomical data analysis in regime. first release CSC includes information about 94,676 distinct sources detected subset public ACIS imaging observations from roughly eight years mission. This...
The oxygen abundance gradients among nebular emission line regions in spiral galaxies have been used as important constraints for models of chemical evolution. We present the largest-ever full-wavelength optical spectroscopic sample nebulae a galaxy (M31). collected spectra 253 H ii and 407 planetary (PNe) with Hectospec multi-fiber spectrograph MMT. measure line-of-sight extinction 199 333 PNe; we derive directly, based on electron temperature, 51 use strong-line methods to estimate 192...
The flowing interstellar medium in the central parsec of an active nucleus plays a crucial role determining its observed emission line features. Mass loss from stellar cluster acts as one source material this flow. Since flow is likely to be hypersonic, shock waves will created it. Gas thermal equilibrium with radiation field and at stagnation pressure has ionization parameter corresponding that deduced observations high-ionization broad lines (HIL). obtained shocked gas cools rapidly by...
In this paper I revisit proposed definitions of the boundary between Earth's atmosphere and outer space, considering orbital suborbital trajectories used by space vehicles. particular, investigate inner edge from historical, physical technological viewpoints propose 80 kilometers as a more appropriate than currently popular 100 km Von Kármán line.
view Abstract Citations (143) References (82) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Soft X-Ray Properties of a Complete Sample Optically Selected Quasars. I. First Results Laor, Ari ; Fiore, Fabrizio Elvis, Martin Wilkes, Belinda J. McDowell, Jonathan C. We present the results ROSAT PSPC observations 10 quasars. These objects are part our program to observe complete sample optically selected This includes all 23 quasars from bright quasar survey...
We present maps made with MERLIN and the VLA of compact steep-spectrum radio sources at wavelengths 18, 6 2 em subarcsecond resolution. The were selected from 3C Peacock & Wall surveys. Study angular structures found shows that high-frequency survey preferentially selects sizes < 0.1 arcsec, even though their spectra are still steep. resolved quasars in this study have predominantly complex or distorted structures, whereas galaxies tend to simpler 'double' type structures.
The near-term search for life beyond the solar system currently focuses on transiting planets orbiting small M dwarfs, and challenges of detecting signs in their atmospheres. However, white dwarfs (WDs) would provide a unique opportunity to characterize rocky worlds. discovery first giant planet dwarf, WD 1856+534b, showed that planetary-mass objects can survive close-in orbits around WDs. large radius ratio between host renders them exceptional targets transmission spectroscopy. Here, we...
Abstract The solar system object 2005 VL1 passed close to Earth in late 1965. It has been suggested that it is actually the space probe Venera-2. However, a comparison of orbits presented this note demonstrates proposed association incorrect.
view Abstract Citations (125) References (90) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Absorption in X-Ray Spectra of High-Redshift Quasars Elvis, Martin ; Fiore, Fabrizio Wilkes, Belinda McDowell, Jonathan Bechtold, Jill We present evidence that X-ray absorption is common high-redshift quasars. have studied six (z~3) quasars with the ROSAT PSPC which four are directions low Galactic N_H_. Three out these show excess absorption, while only three ~50 z...
view Abstract Citations (40) References (67) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Testing Models for the Quasar Big Blue Bump via Color-Color Diagrams Siemiginowska, Aneta ; Kuhn, Olga Elvis, Martin Fiore, Fabrizio McDowell, Jonathan Wilkes, Belinda J. We discuss several models of quasar big blue bump emission in color-color and color-luminosity diagrams. define broad passbands: IR (0.8-1.6 μm), VIS (4000-8000 Å), UV (1000-2000 UV1 (1400-2000 Å)...
In May 2019 SpaceX launched its first batch of 60 Starlink communication satellites, which surprised astronomers and laypeople with their appearance in the night sky. Astronomers have only now, a little over year later, accumulated enough observations constellation satellites like those being by OneWeb, run computer simulations likely impact when fully deployed, to thoroughly understand magnitude complexity problem. This research informed discussion at Satellite Constellations 1 (SATCON1)...
[Abridged] We present ISO far-infrared (IR) observations of 21 hard X-ray selected AGN from the HEAO-1 A2 sample. compare far-IR to spectral energy distributions (SEDs) this sample with various radio and optically samples. The hard-X-ray shows a wider range optical/UV shapes extending redder near-IR colors. bluer objects are Seyfert 1s, while mostly intermediate or type 2 Seyferts. This is consistent modified unification model in which amount obscuring material increases viewing angle may be...
view Abstract Citations (59) References (30) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Unusual Quasar PG 1407+265 McDowell, Jonathan C. ; Canizares, Claude Elvis, Martin Lawrence, Andrew Markoff, Sera Mathur, Smita Wilkes, Belinda J. 1407+265, discovered in the Palomar-Green Survey (Schmidt & Green 1983), was identified as a z ∼ 1 radio-quiet quasar on basis of single weak line. Further observations over wide wavelength range confirm identification...
Chandra observations of the supermassive black hole in nucleus IC 1459 show a weak (LX = 8 × 1040 ergs s-1, 0.3-8 keV), unabsorbed nuclear X-ray source, with slope Γ 1.88 ± 0.09, and no strong Fe K line at 6.4 keV (EW < 382 eV). This describes normal active galactic (AGN) spectrum but lies 3 10-7 below Eddington limit. The spectral energy distribution is extremely radio-loud compared to quasars. surrounded by hot interstellar medium (kT ~ 0.5-0.6 keV) an average density 0.3 cm-3, within...
We resolve the extended X-ray emission from prototypical ultraluminous infrared galaxy Arp 220. Extended, faint, edge-brightened, soft lobes outside optical are observed to a distance of 10-15 kpc on each side nuclear region. Bright plumes inside isophotes coincide with line and extend 11 end across nucleus. The data for cannot be fitted by single-temperature plasma display range temperatures 0.2 1 keV. emerge bright, diffuse circumnuclear in inner 3 centered Hα peak, which is displaced...
We present the first results from 60ks of observations Arp 220 using ACIS-S instrument on Chandra. report detection several sources near galaxy's nucleus, including a point source with hard spectrum that is coincident western radio nucleus B. This mildly absorbed (N_H ~ 3 x 10^22 cm^-2) and has an estimated luminosity 4 10^40 erg/s. In addition, fainter may coincide eastern A. Extended X-ray emission in vicinity raises total nuclear 2-10 keV to 1.2 10^41 erg/s, but we cannot rule out hidden...
Emission from discrete point sources dominates the X-ray luminosity in spiral galaxies. We present results a survey of 11 nearby, nearly face-on galaxies with Chandra Observatory. These span Hubble sequence for spirals, allowing insights into source population many diverse systems. In this paper, we lists along fluxes, luminosities, colors, and variability properties. briefly discuss functions how they relate to star formation host also colors what these can tell us about composition population.