A5070080305- Stellar, planetary, and galactic studies
- Astrophysical Phenomena and Observations
- Calibration and Measurement Techniques
- Atomic and Molecular Physics
- Astronomy and Astrophysical Research
- Solar and Space Plasma Dynamics
- Adaptive optics and wavefront sensing
- Astro and Planetary Science
- X-ray Spectroscopy and Fluorescence Analysis
- Astronomical Observations and Instrumentation
- Astrophysics and Star Formation Studies
- Mass Spectrometry Techniques and Applications
- Particle Detector Development and Performance
- Gamma-ray bursts and supernovae
- CCD and CMOS Imaging Sensors
- Ionosphere and magnetosphere dynamics
- Nuclear Physics and Applications
- Laser-induced spectroscopy and plasma
- Astrophysics and Cosmic Phenomena
- Galaxies: Formation, Evolution, Phenomena
- Planetary Science and Exploration
- Atmospheric Ozone and Climate
- History and Developments in Astronomy
- Advanced X-ray and CT Imaging
- High-pressure geophysics and materials
Center for Astrophysics Harvard & Smithsonian
2005-2024
Smithsonian Astrophysical Observatory
1995-2020
Harvard University
2000-2014
Lawrence Livermore National Laboratory
1991-2008
University of California, Berkeley
1993-1998
A commonly used measure to summarize the nature of a photon spectrum is so-called hardness ratio, which compares numbers counts observed in different passbands. The ratio especially useful distinguish between and categorize weak sources as proxy for detailed spectral fitting. However, this regime classical methods error propagation fail, estimates become unreliable. Here we develop rigorous statistical treatment ratios that properly deals with detected photons independent Poisson random...
Deep Chandra Low Energy Transmission Grating and High Resolution Camera spectroscopic observations of the isolated neutron star candidate RX J1856.5-3754 have been analyzed to search for metallic resonance cyclotron spectral features pulsation behavior. As found from earlier observations, X-ray spectrum is well represented by an ~60 eV (7 × 105 K) blackbody. No unequivocal evidence line or edge has found, arguing against metal-dominated models. The data contain no pulsation, we place a 99%...
Stars of stellar type later than about M3.5 are believed to be fully convective and therefore unable support magnetic dynamos like the one that produces 11-year solar cycle. Because their intrinsic faintness, very few late M stars have undergone long-term monitoring test this prediction, which is critical our understanding field generation in such stars. Magnetic activity also interest as driver UV X-ray radiation, well energetic particles winds, affect atmospheres close-in planets lie...
We present the first X-ray spectrum obtained by Low-Energy Transmission Grating Spectrometer (LETGS) aboard Chandra X-Ray Observatory. The is of Capella and covers a wavelength range 5-175 Å (2.5-0.07 keV). measured resolution, which in good agreement with ground calibration, Deltalambda approximately 0.06 (FWHM). Although in-flight calibration LETGS progress, high spectral resolution unique coverage are well demonstrated results from Capella, coronal source rich emission lines. While...
We present an exploratory Chandra ACIS-S3 study of the diffuse component Cosmic X-ray Background in 0.3-7 keV band for four directions at high Galactic latitudes, with emphasis on details ACIS instrumental background modeling. Observations dark Moon are used to model detector background. A comparison data and obtained stowed outside focal area showed that does not emit significantly our band. Point sources down 3 10^-16 erg/s/cm2 0.5-2 excluded two deepest observations. estimate contribution...
We have analyzed data from two sets of calibration observations the Moon made by Chandra X-ray Observatory. In addition to obtaining a spectrum bright side that shows several distinct fluorescence lines, we also clearly detect time-variable soft emission, primarily O VII Ka and VIII Lya, when viewing optically dark side. The apparent dark-side brightness varied at least an order magnitude, up 2x10^-6 phot/s/arcmin^2/cm^2 between 500 900 eV, which is comparable typical 3/4-keV-band background...
We present images from five observations of the quasar 3C 273 with Chandra X-Ray Observatory. The jet has at least four distinct features that are not resolved in previous observations. first knot (A1) is very bright X-rays. Its X-ray spectrum well fitted a power law α = 0.60 ± 0.05 (where Sν ∝ ν-α). Combining this measurement lower frequency data shows pure synchrotron model can fit 1.647 GHz to 5 keV (over nine decades energy) 0.76 0.02, similar spectral slope. Thus, we place limit on...
Abstract An α Ω dynamo, combining shear and cyclonic convection in the tachocline, is believed to generate solar cycle. However, this model cannot explain cycles fast rotators (with minimal shear) or fully convective stars (no tachocline); an analysis of these could therefore provide key insights into how work. We reexamine ASAS data for 15 M dwarfs, 11 which are presumed convective; addition newer ASAS-SN confirms roughly 12 them, while presenting new revised rotation periods 5 stars. The...
We have analyzed data from two Chandra imaging observations of Proxima Centauri, searching for an X-ray halo arising charge exchange between highly charged ions in its stellar wind and neutral gas the surrounding interstellar medium. Based upon our model Cen's emission, absence any detectable signal places a statistical 3 σ upper limit ~3 × 10-13 M☉ yr-1 (14☉) on mass-loss rate (9☉ 2 4☉ 1 σ), with uncertainty roughly factor 3. This is orders magnitude smaller than limits that been placed...
We have analyzed Chandra High-Energy Transmission Grating spectra of the active RS CVn-type binary V711 Tauri (HR 1099; HD 22468) in order to examine chemical composition its coronae. Observed fluxes and flux upper limits for spectral lines from a range charge states iron, covering species Fe XVI-Fe XXV, been used determine emission measure distribution as function temperature, while observed line-to-continuum ratio has absolute iron abundance, Fe/H. Abundances elements O, Ne, Mg, Si, S, Ar...
Despite the fact that overwhelming majority of stars are late spectral type (F-M) and lie on main sequence, we know nothing about their stellar winds. Existing measurements winds only apply to high-mass O B stars, red giants, supergiants extend down a few times 10-10 M☉ yr-1, as compared solar rate ~2 × 10-14 yr-1. Attempts detect from late-type dwarf have date resulted in loose upper limits order 10-12 10-11 We propose novel method studying through observation charge exchange-induced X-ray...
A flat-crystal spectrometer for analyzing ultrasoft x rays in the wavelength region 10–25 Å was constructed use on an electron beam ion trap. The employs a position-sensitive proportional counter detection and affords nominal resolving power of 2000 at Bragg angle 45°. Measurements L-shell spectra Ne-like Fe16+ 3s1/2–3p3/2 transitions near Na-like Pb71+, which fall into from 13.5 to 17.5 Å, are presented demonstrating high throughput excellent signal-to-noise characteristics. actual achieved...
We report a technique for measuring the lifetimes of long-lived excited levels in highly charged ions that fall into range from ${10}^{\mathrm{\ensuremath{-}}2}$ to ${10}^{\mathrm{\ensuremath{-}}7}$ sec, inaccessible existing methods. Employing fast-switching electron beam produce and excite electrostatically trapped ions, are determined by observing fluorescent decay metastable levels. A value 90.5\ifmmode\pm\else\textpm\fi{}1.5 \ensuremath{\mu}sec is obtained 1s2s...
We report the first observation of magnetic octupole decay in x-ray spectrum a highly charged ion. Detailed analyses low-energy region n=3\ensuremath{\rightarrow}4 spectra nickel-like ${\mathrm{Th}}^{62+}$ and ${\mathrm{U}}^{64+}$ show an intense line at 2558.7\ifmmode\pm\else\textpm\fi{}0.2 2689.3\ifmmode\pm\else\textpm\fi{}0.2 eV, respectively, that is attributed to transition (3${\mathit{d}}^{9}$4s${)}_{\mathit{J}=3}$\ensuremath{\rightarrow}(3${\mathit{d}}^{10}$${)}_{\mathit{J}=0}$....
The Chandra spacecraft has been launched successfully on July 23, 1999. payload consists of a high resolution X- ray telescope, two imaging detector systems in the focal plane and transmission gratings. Each one gratings can be put beam behind telescope grating spectrometers are optimized for low energy, respectively. Low Energy Transmission Grating Spectrometer three parts: high-resolution array detector, to read-out spectral image.
Chandra observations toward the nearby molecular cloud MBM 12 show unexpectedly strong and nearly equal foreground O VIII VII emission. As observed portion of is optically thick at these energies, emission lines must be formed nearby, coming from either Local Bubble (LB) or charge exchange with ions Sun. Equilibrium models for LB predict stronger than VIII, so results suggest that far equilibrium a substantial another source, such as within solar system. Despite likely contamination, we can...
The past decade has seen a surge of interest in astrophysical charge exchange (CX). impetus was the discovery X-ray emission from comets 1996, soon followed by observation CX planetary atmospheres and throughout heliosphere. Geocoronal heliospheric are now recognized as contributing considerable fraction soft background, stellar-wind is expected to occur astrospheres surrounding many stars. may also contribute line supernova remnants, Galactic Center, Ridge. This article summarizes key...
We present results from two Chandra imaging observations of Ross 154, a nearby flaring M dwarf star. During 61-ks ACIS-S exposure, very large flare occurred (the equivalent solar X3400 event, with L_X = 1.8x10^30 ergs/s) in which the count rate increased by factor over 100. The early phase shows evidence for Neupert effect, followed further rise and then two-component exponential decay. A was also observed at end later 48-ks HRC-I observation. Emission non-flaring phases both analyzed low...
Solar wind charge exchange (SWCX) X-rays are emitted when highly charged solar ions such as O7 + collide with neutral gas, including the Earth's tenuous outer atmosphere (exosphere or geocorona) and hydrogen helium from local interstellar medium drifting through heliosphere. This geocoronal heliospheric emission comprises a significant varying fraction of soft X-ray background (SXRB) is seen in every observation, intensity dependent on conditions observation geometry. Under right conditions,...
Observations of Fe XVIII and XIX X-ray, extreme-UV, far-UV line emission, formed at the peak Capella's (α Aurigae's) emission measure distribution ubiquitous in spectra many cool stars galaxies, provide a unique opportunity to test robustness spectral models. The Astrophysical Plasma Emission Code (APEC) is used identify over 35 lines from these two ions alone, compare model predictions with obtained Chandra Low Energy Transmission Grating High Spectrometers, Far Ultraviolet Spectroscopic...
Extensive X-ray and extreme ultraviolet (EUV) photometric observations of the eclipsing RS CVn system AR Lac were obtained over years 1997 to 2013 with Chandra Observatory Extreme Ultraviolet Explorer. During primary eclipse, HRC count rates decrease by ~40%. A similar minimum is seen during one eclipse observed EUVE but not in others owing intrinsic source variability. Little evidence for secondary eclipses present either or EUV data, reminiscent earlier observations. Primary allow us...
The diffuse soft X-ray background comes from distant galaxies, hot Galactic gas, and within the solar system. latter emission arises charge exchange between highly charged wind ions neutral gas. This so-called (SWCX) is spatially temporally variable interferes with our measurements of more cosmic while also providing important information on nature wind–interstellar medium interaction. We present results analysis eight Chandra observations Deep Field North (CDFN) goal measuring SWCX...
The spectra of highly ionized iron species between 7 and 9 Å have been studied using data obtained at the Princeton Large Torus tokamak under plasma conditions similar to those present in solar stellar flares. wavelengths many lines are measured with very high accuracy (λ/Δλ up 4 × 104), along several other such as He-like Al XII Mg XI. Theoretical that predict both wavelength intensity Fe emission compared observed used make accurate line identifications. Virtually all found arise from n =...