A5037692864- Astrophysical Phenomena and Observations
- Stellar, planetary, and galactic studies
- Gamma-ray bursts and supernovae
- Astrophysics and Star Formation Studies
- Astrophysics and Cosmic Phenomena
- Astronomy and Astrophysical Research
- Astronomical Observations and Instrumentation
- Solar and Space Plasma Dynamics
- Astro and Planetary Science
- Pulsars and Gravitational Waves Research
- Galaxies: Formation, Evolution, Phenomena
- Ionosphere and magnetosphere dynamics
- Cosmology and Gravitation Theories
- Geomagnetism and Paleomagnetism Studies
- High-pressure geophysics and materials
- Calibration and Measurement Techniques
- Geophysics and Gravity Measurements
- History and Developments in Astronomy
- Adaptive optics and wavefront sensing
- Radiation Therapy and Dosimetry
- Quantum Chromodynamics and Particle Interactions
- Scientific Research and Discoveries
- Chemical Thermodynamics and Molecular Structure
- Nuclear physics research studies
- Geochemistry and Elemental Analysis
Institute of Astronomy and National Astronomical Observatory
1984-2024
Space Research and Technology Institute
2004-2015
Joint Institute for Laboratory Astrophysics
1999-2012
University of Colorado Boulder
2000-2012
Institute of Solar-Terrestrial Physics
2011
University of Colorado System
2002-2009
Bulgarian Academy of Sciences
1991-2009
Scottsdale Research Institute (United States)
2005
Bulgarian Research and Education Network
1998
Arcetri Astrophysical Observatory
1994
We present results from the first attempts to derive various physical characteristics of dusty Wolf-Rayet star WR 48a based on a multi-wavelength view its observational properties. This is done basis new optical and near-infrared spectral observations data archives in optical, radio X-rays. The spectrum acceptably well represented by sum two spectra: WC8 type WN8h type. strength interstellar absorption features spectra near-by stars D2-3 D2-7 (both members open cluster Danks 2) indicates...
Updated imaging and photometric results from Chandra observations of SN 1987A, covering the last 16 years, are presented. We find that 0.5-2 keV light curve has remained constant at ~8x10^-12 erg s^-1 cm^-2 since 9500 days, with 3-8 continuing to increase until least 10000 days. The expansion rate ring is found be energy dependent, such after day 6000 expands faster in 2-10 band than it does energies <2 keV. Images show a reversal east-west asymmetry between 7000 8000 days explosion. latest...
Abstract Based on our Chandra imaging-spectroscopic observations, we present the latest evolution of X-ray remnant SN 1987A. Recent changes in electron temperatures and volume emission measures suggest that blast wave 1987A is moving out dense inner ring structure, also called equatorial (ER). The 0.5–2.0 keV light curve shows a linearly declining trend (by ∼4.5% yr −1 ) between 2016 2020 as heats hitherto unknown circumstellar medium (CSM) outside ER. While peak 0.3–8.0 image still within...
We analyze four ASCA X-ray observations of the Wolf-Rayet binary system WR 140 obtained between 1993 and 1997 by making use hydrodynamic colliding wind (CW) shock models. The analysis shows that CW models are able to accurately reproduce spectra at different orbital phases using mass-loss parameters within ranges allowed uncertainties. However, some adjustment in currently accepted values semimajor axis time periastron passage may eventually be required. Models allow for electron ion...
We present an extended analysis of the deep Chandra LETG and HETG observations supernova remnant 1987A (SNR 1987A) carried out in 2007. The global fits to grating spectra show that temperature X-ray emitting plasma slower shocks this system has remained stable for last three years, while faster decreased. This evolution is confirmed by first light curves strong emission lines their ratios. On other hand, bulk gas velocities inferred from line profiles are too low account post-shock...
We summarize new X-ray detections of four nitrogen-type Wolf-Rayet (WR) stars obtained in a limited survey aimed at establishing the properties WN across their full range spectral subtypes. None detected is so far known to be close binary. report Chandra WR 2 (WN2), 18 (WN4), and 134 (WN6), an XMM-Newton detection WR79a (WN9ha). These observations clearly demonstrate that both WNE WNL are sources. also discuss archive WN6h 20b, 24, 136 ROSAT non-detections 16 (WN8h) 78 (WN7h). The spectra...
We report on the present stage of SN 1987A as observed by Chandra X-ray Observatory. reanalyze published observations and add three more epochs data to get a consistent picture evolution fluxes in several energy bands. discuss implications calibration issues for data. Using most recent files, we find that 0.5-2.0 keV band have increased ~6 x 10 ^-13 erg s^-1 cm^-2 per year since 2009. This is contrast with our previous result light curve showed sudden flattening Based new analysis, conclude...
We report and interpret Hubble Space Telescope (HST) Imaging Spectrograph (STIS) long-slit observations of the optical ultraviolet (1150-10270 Å) emission line spectra rapidly brightening spot 1 on equatorial ring SN 1987A between 1997 September 1999 October (days 3869-4606 after outburst). The is caused by radiative shocks created where supernova blast wave strikes dense gas protruding inward from ring. measure tabulate identifications, fluxes, and, in some cases, widths shifts. compute...
Chandra grating spectra of a sample 15 massive OB stars were analysed under the basic assumption that X-ray emission is produced in an ensemble shocks formed winds driven by these objects. Shocks develop either as result radiation-driven instabilities or due to confinement wind relatively strong magnetic field, and since they are radiative, simple model their was developed allows direct comparison with observations. According our model, shock structures (clumps, complete fractional shells)...
We present the evolution of radial expansion SNR 1987A as measured using Chandra X-ray observations taken over last 10 years. To characterize complex structure remnant and isolate measurement, we fit images to several empirical models including: a simple circular torus, torus with bilateral lobes, four tangentially extended lobes. discuss results this measure in context overall supernova remnant, for which believe have end free phase its transition adiabatic (at least along equatorial ring)....
Previous studies have demonstrated that putatively single nitrogen-type Wolf-Rayet stars (WN stars) without known companions are X-ray sources. However, almost all WN star detections so far been of earlier WN2 - WN6 spectral subtypes. Later WN7 WN9 subtypes (also as WNL proved more difficult to detect, an important exception being WR 79a (WN9ha). We present here new the 16 (WN8h) and 78 (WN7h). These results, when combined with previous detections, demonstrate emission is in across full...
Two-dimensional calculations of colliding stellar winds are performed for the case a WR + O binary system. The effects energy losses by free-free emission and Comptonization as well those wind acceleration considered. results show that interaction region must be powerful X-ray source. main dimensional parameters determining spectrum luminosity system mass losses, velocities, separation between stars their chemical composition (the characteristics WN WC systems very different). An...
We report on the results of our monitoring program remnant SN 1987A with Advanced CCD Imaging Spectrometer (ACIS) board {\it Chandra X-ray Observatory}. Two new observations have been performed in AO2, bringing total to four over past two years. Over this time period, techniques for correction ``Charge Transfer Inefficiency (CTI)'' and use charge spreading provide angular resolution somewhat better than pixel size detector become available at Penn State. processed all using sub-pixel obtain...
We discuss the X-ray emission observed from supernova remnant 1987A with Chandra X-Ray Observatory. analyze a high-resolution spectrum obtained in 1999 October high-energy transmission grating (HETG). From this we measure strengths and an average profile of lines. also high signal-to-noise ratio CCD 2000 December. The good statistics (≈9250 counts) spatial resolution provided by telescope allow us to perform spectroscopic analyses different regions remnant. relevant shock physics that can...
We report an upturn in the soft X-ray light curve of SNR 1987A late 2003 (~6200 days after explosion), as observed with Chandra X-Ray Observatory. Since early 2004, rapid increase 0.5-2 keV band can no longer be described by exponential density distribution model which we successfully fitted data between 1990 and 2003. Around day 6200, also find that fractional contribution to flux from decelerated shock begins exceed fast brightening becomes "global" rather than "spotty." interpret these...
We present an update on the results of our monitoring observations X-ray remnant supernova (SN) 1987A with Chandra. As 2002 December, we have performed a total seven SN 1987A, which allows us to monitor details earliest stage evolution in X-rays. The high angular resolution images from latest data reveal developments new X-ray-bright spots northwestern and southwestern portions remnant, as well changes eastern side. observed soft flux is increasing more rapidly than ever, 0.5-2 keV band (fX...
We discuss the results from deep Chandra LETG observations of supernova remnant 1987A (SNR 1987A). find that a distribution shocks, spanning same range velocities (from ~300 to 1700 km s-1) as deduced in first part our analysis, can account for entire X-ray spectrum this object. The postshock temperature is bimodal, peaking at kT ~ 0.5 and ~3 keV. Abundances inferred have values similar those inner circumstellar ring, except abundances nitrogen oxygen are approximately factor 2 lower than...
We have undertaken deep, high-resolution observations of SN 1987A at ≈20 years after its explosion with the Chandra HETG and LETG spectrometers. Here we present X-ray spectra having unprecedented spectral resolution signal-to-noise ratios in 6-20 Å bandpass, which includes H-like He-like lines Si, Mg, Ne, as well O VIII bright Fe XVII lines. In joint analysis data, find that there has been a significant decrease from 2004 to 2007 average temperature highest component shocked-plasma emission....
We have analysed the X-ray emission from a sample of close WR+O binaries using data public Chandra and XMM-Newton archives. Global spectral fits show that two-temperature plasma is needed to match these objects as hot component (kT > 2 keV) an important ingredient models. In binaries, X-rays likely originate in colliding stellar wind (CSW) shocks driven by massive winds binary components. CSW are expected be radiative due high density interaction region. Opposite this, our analysis shows...
$\sim$18 yr after the supernova explosion, blast wave of SNR 1987A is entering main body equatorial circumstellar material, which causing a dramatic brightening remnant. We recently reported observational evidence for this event from our {\it Chandra} data (Park et al. 2005b; P05 hereafter). present here temporal evolution X-ray emitting shock parameters and detailed description spectral image analysis 1987A, on was based. While remnant becomes brighter, softening overall spectrum continues...
The effects of nonequilibrium ionization are explicitly taken into account in a numerical model which describes colliding stellar winds (CSW) massive binary sytems. This new is used to analyze the most recent X-ray spectra WR+OB system WR 147. basic result that it can adequately reproduce observed emission (spectral shape, flux) but some adjustment wind parameters required. Namely, (i) velocities must be higher by factor 1.4 - 1.6; (ii) mass loss reduced ~ 2. reduction for well within...
We continue to explore the validity of reflected-shock structure (RSS) picture in SNR 1987A that was proposed our previous analyses X-ray emission from this object. used an improved version RSS model a global analysis 14 CCD spectra monitoring program with Chandra. In framework picture, we are able match both expansion velocity curve deduced images and light curve. Using simplified analysis, also show X-rays non-thermal radio may originate same shock (the blast wave). believe using grating...
We have used the excellent sensitivity of XMM-Newton to obtain first high-quality X-ray spectrum a Wolf-Rayet (W-R) star that is not known be member binary system. Our target, nitrogen-type WR 110 (HD 165688), was also observed and detected with Very Large Array at four different frequencies. The radio flux density increases frequency according power law Sν ∝ ν+0.64±0.10, in very good agreement behavior expected for free-free wind emission. data give an ionized mass-loss rate = 4.9 × 10-5 M☉...
Recent optical and infrared studies have revealed that the heavily reddened starburst cluster Westerlund 1 (Wd 1) contains at least 22 Wolf-Rayet (W-R) stars, constituting richest W-R population of any Galactic cluster. We present results a sensitive Chandra X-ray observation Wd detected 12 known stars mysterious emission-line star W9. The fraction WN is nearly identical to WC stars. WR-A WR-B, as well W9, are exceptionally luminous in X-rays similar hard, absorbed spectra with strong Si...
We report the first results from deep X-ray observations of supernova remnant SNR 1987A with Chandra LETG. Temperatures inferred line ratios range ~0.1 to 2 keV and increase ionization potential. Expansion velocities profiles ~300 1700 km s-1, much less than radial expansion radio images. can account for these a scenario in which X-rays are emitted by shocks produced where blast wave strikes dense protrusions inner circumstellar ring, also responsible optical hot spots.