共查询到20条相似文献，搜索用时 31 毫秒
1.
Beiersdorfer P Boyce KR Brown GV Chen H Kahn SM Kelley RL May M Olson RE Porter FS Stahle CK Tillotson WA 《Science (New York, N.Y.)》2003,300(5625):1558-1559
In laboratory experiments using the engineering spare microcalorimeter detector from the ASTRO-E satellite mission, we recorded the x-ray emission of highly charged ions of carbon, nitrogen, and oxygen, which simulates charge exchange reactions between heavy ions in the solar wind and neutral gases in cometary comae. The spectra are complex and do not readily match predictions. We developed a charge exchange emission model that successfully reproduces the soft x-ray spectrum of comet Linear C/1999 S4, observed with the Chandra X-ray Observatory. 相似文献
2.
High-resolution images of the sun in the soft x-ray to extreme ultraviolet(EUV) regime have been obtained with normal-incidence Cassegrain multilayer telescopes operated from a sounding rocket in space. The inherent energy-selective property of multilayer-coated optics allowed distinct groups of emission lines to be isolated in the solar corona and the transition region. The Cassegrain telescopes provided images in bands centered at 173 and 256 angstroms. The bandpass centered at 173 angstroms is dominated by emission from the ions Fe IX Fe X. This emission is from coronal plasma in the temperature range 0.8 x 10(6) to 1.4 x 10(6)K. The images have angular resolution of about 1.0 to 1.5 arc seconds, and show no degradation because of x-ray scattering. Many features of coronal structure, including magnetically confined loops of hot plasma, coronal plumes, polar coronal holes, faint structures on the size scale of supergranulation and smaller, and features due to overlying cool prominences are visible in the images. The density structure of polar plumes, which are thought to contribute to the solar wind, has been derived from the observations out to 1.7 solar radii. 相似文献
3.
Cravens TE 《Science (New York, N.Y.)》2002,296(5570):1042-1045
The discovery of x-ray emission from comet Hyakutake was surprising given that comets are known to be cold. Observations by x-ray satellites such as the R?ntgen Satellite (ROSAT) indicate that x-rays are produced by almost all comets. Theoretical and observational work has demonstrated that charge-exchange collisions of highly charged solar wind ions with cometary neutral species can explain this emission. X-ray observations of comets and other solar system objects may be used to determine the structure and dynamics of the solar wind. 相似文献
4.
The delta (18)O of minerals from lunar gabbros and basalts are: plgioclases +6.06 to +6.33), pyroxenes (+5.70 to +5.95), and ilmenites (+3.85 to +4.12). The uniformity of these results indicates isotopic equilibrium in the mineral assemblages. Estimated plagioclase-ilmenite temperautres range from 1150 degrees C to 1340 degrees C. The bulk (18)/ (16)O and (30)Si/ (28)Si ratios of these lunar rocks are identical with ratios of terrestrial basalts, but the lunar glass, breccia, and dust are slightly enriched in the heavier isotopes. The lunar hydrogen (formed from solar wind) has a delta D/H of less than-873 per mil and the value may be even lower, as it is probably contaminated with terrestrial hydrogen. The delta (13)C of lunar dust and breccia is unusually high relative to reduced carbon in meteorites or on earth. 相似文献
5.
A three-dimensional x-ray analylsis of a crystallinie solid of Xe(+8) formed by the reaction of XeF(6) with sodium hydroxide solution indicates that it is sodium perxenate octahydrate, Na(4)XeO(6) * 8H(2)O. The perxenate ion, XeO(6)(-4), has approximately a regular octahedral configuration with a mean xenon-oxygen bond length of 1.875 A. 相似文献
6.
Caraveo PA Bignami GF DeLuca A Mereghetti S Pellizzoni A Mignani R Tur A Becker W 《Science (New York, N.Y.)》2003,301(5638):1345-1347
We report the X-ray Multimirror Mission-Newton European Photon Imaging Camera observation of two elongated parallel x-ray tails trailing the pulsar Geminga. They are aligned with the object's supersonic motion, extend for approximately 2', and have a nonthermal spectrum produced by electron-synchrotron emission in the bow shock between the pulsar wind and the surrounding medium. Electron lifetime against synchrotron cooling matches the source transit time over the x-ray features' length. Such an x-ray detection of a pulsar bow shock (with no Halpha emission) allows us to gauge the pulsar electron injection energy and the shock magnetic field while constraining the angle of Geminga's motion and the local matter density. 相似文献
7.
Photometry and spectroscopy of the object Cha Halpha 1, located in the Chamaeleon I star-forming cloud, show that it is a approximately 10(6)-year-old brown dwarf with spectral type M7.5 to M8 and 0.04 +/- 0.01 solar masses. Quiescent x-ray emission was detected in a 36-kilosecond observation with 31.4 +/- 7.7 x-ray photons, obtained with the Rontgen Satellite (ROSAT), with 9final sigma detection significance. This corresponds to an x-ray luminosity of 2.57 x 10(28) ergs per second and an x-ray to bolometric luminosity ratio of 10(-3.44). These are typical values for late M-type stars. Because the interior of brown dwarfs may be similar to that of convective late-type stars, which are well-known x-ray sources, x-ray emission from brown dwarfs may indicate magnetic activity. 相似文献
8.
Fourteen profiles of electron density in the ionosphere of Venus were obtainecd by the dual-frequency radio occulation method with the Pioneer Venus orbiter between 5 and 30 December 1978. The solar zenith angles for these measurements were between about 85 degrees and 92 degrees , and the latitudes ranged from about 81 degrees to 88 degrees (ecliptic north). In addition to the expected decreasein peak electron density from about 1.5 x 10(3) to 0.5 x 10(3) per cubic centimeter with increasing solar zenith angle, a region of almost constant electron density above about 250 kilometers was observed. The ionopause height varies from about 300 to 700 kilometers and seems to be influenced by diurnal changes in solar wind conditions. The structures of the profiles are consistent with models in which O(2)(+) dominates near the ionization peak and is replaced by O(+) at higher altitudes. 相似文献
9.
Drescher M Hentschel M Kienberger R Tempea G Spielmann C Reider GA Corkum PB Krausz F 《Science (New York, N.Y.)》2001,291(5510):1923-1927
Single soft-x-ray pulses of approximately 90-electron volt (eV) photon energy are produced by high-order harmonic generation with 7-femtosecond (fs), 770-nanometer (1.6 eV) laser pulses and are characterized by photoionizing krypton in the presence of the driver laser pulse. By detecting photoelectrons ejected perpendicularly to the laser polarization, broadening of the photoelectron spectrum due to absorption and emission of laser photons is suppressed, permitting the observation of a laser-induced downshift of the energy spectrum with sub-laser-cycle resolution in a cross correlation measurement. We measure isolated x-ray pulses of 1.8 (+0.7/-1.2) fs in duration, which are shorter than the oscillation cycle of the driving laser light (2.6 fs). Our techniques for generation and measurement offer sub-femtosecond resolution over a wide range of x-ray wavelengths, paving the way to experimental attosecond science. Tracing atomic processes evolving faster than the exciting light field is within reach. 相似文献
10.
A brilliant new comet (1979 XI: Howard-Koomen-Michels) was discovered in data from the Naval Research Laboratory's orbiting SOLWIND coronagraph. An extensive sequence of pictures, telemetered from the P78-1 satellite, shows the coma, accompanied by a bright and well-developed tail, passing through the coronagraph's field of view at afew million kilometers from the sun. Preliminary orbital calculations based on the observed motion of the comet's head and morphology of the tail indicate that this previously unreported object is a sungrazing comet and may be one of the group of Kreutz sungrazers. It appears from the data that the perihelion distance was less than 1 solar radius, so that the cometary nucleus encountered dense regions of the sun's atmosphere, was completely vaporized, and did not reappear after the time of closest approach to the sun. After this time, however, cometary debris, scattered into the ambient solar wind, caused a brightening of the corona over one solar hemisphere and to heliocentric distances of 5 to 10 solar radii. 相似文献
11.
Brace LH Theis RF Krehbiel JP Nagy AF Donahue TM McElroy MB Pedersen A 《Science (New York, N.Y.)》1979,203(4382):763-765
Altitude profiles of electron temperature and density in the ionosphere of Venus have been obtained by the Pioneer Venus orbiter electron temperatutre probe. Elevated temperatutres observed at times of low solar wind flux exhibit height profiles that are consistent with a model in which less than 5 percent of the solar wind energy is deposited at the ionopause and is conducted downward through an unmagnetized ionosphere to the region below 200 kilomneters where electron cooling to the neutral atmosphere proceeds rapidly. When solar wind fluxes are higher, the electron temperatures and densities are highly structured and the ionopause moves to lower altitudes. The ionopause height in the late afternoon sector observed thus far varies so widely from day to (day that any height variation with solar zenith angle is not apparent in the observations. In the neighborhood of the ionopause, measuremnents of plasma temperatures and densities and magnetic field strength indicate that an induced magnetic barrier plays an important role in the pressure transfer between the solar wind and the ionosphere. The bow, shock is marked by a distinct increase in electron current collected by the instrument, a featutre that provides a convenient identification of the bow shock location. 相似文献
12.
McCracken KG 《Science (New York, N.Y.)》1966,154(3752):1000-1002
The emission of 20 to 60 kev x-rays by an astronomical object in the constellation of Cygnus has been observed with a balloon-borne x-ray telescope flown from Hyderabad, India. The balloon data, used in conjunction with data pertaining to the flux in the wavelength range from 2 to 10 A can be fitted by a power law in photon energy varying as (h(v))-(1.7). The Cygnus object is the brightest object in the sky in the hard x-ray wavelength range and has the hardest spectrum of all observed objects that emit x-rays. The astronomical object should be capable of accelerating protons up to energies of the order of 10(18) electron volts. Upper limits to the hard x-ray fluxes from Sco XR-1, Cyg XR-2, Oph XR-1, and Ser XR-1 are established; it is shown that the Sco XR-1 spectrum is very soft. 相似文献
13.
Conrath B Flasar FM Hanel R Kunde V Maguire W Pearl J Pirraglia J Samuelson R Gierasch P Weir A Bezard B Gautier D Cruikshank D Horn L Springer R Shaffer W 《Science (New York, N.Y.)》1989,246(4936):1454-1459
The infrared interferometer spectrometer on Voyager 2 obtained thermal emission spectra of Neptune with a spectral resolution of 4.3 cm(-1). Measurements of reflected solar radiation were also obtained with a broadband radiometer sensitive in the visible and near infrared. Analysis of the strong C(2)H(2) emission feature at 729 cm(-1) suggests an acetylene mole fraction in the range between 9 x 10(-8) and 9 x 10(-7). Vertical temperature profiles were derived between 30 and 1000 millibars at 70 degrees and 42 degrees S and 30 degrees N. Temperature maps of the planet between 80 degrees S and 30 degrees N were obtained for two atmospheric layers, one in the lower stratosphere between 30 and 120 millibars and the other in the troposphere between 300 and 1000 millibars. Zonal mean temperatures obtained from these maps and from latitude scans indicate a relatively warm pole and equator with cooler mid-latitudes. This is qualitatively similar to the behavior found on Uranus even though the obliquities and internal heat fluxes of the two planets are markedly different. Comparison of winds derived from images with the vertical wind shear calculated from the temperature field indicates a general decay of wind speed with height, a phenomenon also observed on the other three giant planets. Strong, wavelike longitudinal thermal structure is found, some of which appears to be associated with the Great Dark Spot. An intense, localizd cold region is seen in the lower stratosphere, which does not appear to be correlated with any visible feature. A preliminary estimate of the effective temperature of the planet yields a value of 59.3 +/- 1.0 kelvins. Measurements of Triton provide an estimate of the daytime surface temperature of 38(+3)(-4) kelvins. 相似文献
14.
McKeegan KD Kallio AP Heber VS Jarzebinski G Mao PH Coath CD Kunihiro T Wiens RC Nordholt JE Moses RW Reisenfeld DB Jurewicz AJ Burnett DS 《Science (New York, N.Y.)》2011,332(6037):1528-1532
All planetary materials sampled thus far vary in their relative abundance of the major isotope of oxygen, (16)O, such that it has not been possible to define a primordial solar system composition. We measured the oxygen isotopic composition of solar wind captured and returned to Earth by NASA's Genesis mission. Our results demonstrate that the Sun is highly enriched in (16)O relative to the Earth, Moon, Mars, and bulk meteorites. Because the solar photosphere preserves the average isotopic composition of the solar system for elements heavier than lithium, we conclude that essentially all rocky materials in the inner solar system were enriched in (17)O and (18)O, relative to (16)O, by ~7%, probably via non-mass-dependent chemistry before accretion of the first planetesimals. 相似文献
15.
A new technique has made it possible to measure the velocity of portions of the solar wind during its flow outward from the sun. This analysis utilizes spacecraft (ISEE-3) observations of radio emission generated in regions of the solar wind associated with solar active regions. By tracking the source of these radio waves over periods of days, it is possible to measure the motion of the emission regions. Evidence of solar wind acceleration during this outward flow, consistent with theoretical models, has also been obtained. 相似文献
16.
Tu CY Zhou C Marsch E Xia LD Zhao L Wang JX Wilhelm K 《Science (New York, N.Y.)》2005,308(5721):519-523
The origin of the solar wind in solar coronal holes has long been unclear. We establish that the solar wind starts flowing out of the corona at heights above the photosphere between 5 megameters and 20 megameters in magnetic funnels. This result is obtained by a correlation of the Doppler-velocity and radiance maps of spectral lines emitted by various ions with the force-free magnetic field as extrapolated from photospheric magnetograms to different altitudes. Specifically, we find that Ne7+ ions mostly radiate around 20 megameters, where they have outflow speeds of about 10 kilometers per second, whereas C3+ ions with no average flow speed mainly radiate around 5 megameters. Based on these results, a model for understanding the solar wind origin is suggested. 相似文献
17.
Gibson EA Paul A Wagner N Tobey R Gaudiosi D Backus S Christov IP Aquila A Gullikson EM Attwood DT Murnane MM Kapteyn HC 《Science (New York, N.Y.)》2003,302(5642):95-98
We demonstrate enhanced generation of coherent light in the "water window" region of the soft x-ray spectrum at 4.4 nanometers, using quasi-phase-matched frequency conversion of ultrafast laser pulses. By periodically modulating the diameter of a gas-filled hollow waveguide, the phase mismatch normally present between the laser light and the generated soft x-ray light can be partially compensated. This makes it possible to use neon gas as the nonlinear medium to coherently convert light up to the water window, illustrating that techniques of nonlinear optics can be applied effectively in the soft x-ray region of the spectrum. These results advance the prospects for compact coherent soft x-ray sources for applications in biomicroscopy and in chemical spectroscopy. 相似文献
18.
Observations of the Trapezium region in the Orion Nebula obtained with the high-resolution x-ray imaging instrument on board the Einstein Observatory reveal at least 58 sources of x-ray emission. All but two of the sources can be identified with visible stars. The strongest x-ray source is the star Theta(1)C, which excites the emission nebula. Its x-ray luminosity is 6 x 10(32) ergs per second. The rest of the x-ray sources may be identified with stars of all spectral types. Strong x-ray emission is not observed from members of the infrared cluster embedded within the Orion molecular cloud. 相似文献
19.
Gorenstein P Harris B Gursky H Giacconi R Novick R Bout PV 《Science (New York, N.Y.)》1971,172(3981):369-372
X-ray emission from the Cygnus Loop was observed in the energy region around 0.2 to 1 kiloelectronvolt with a collector that focused x-rays along one dimension while scanning across the nebula. The total integrated intensity is 1.3x 10(-8) erg per square centimeter per second. The one-dimensional x-ray structure has the same angular size-about 3 degrees-as the outermost boundaries of the optical filaments. There is no increase in x-ray emission at the center of the nebula nor at the strong feature that is seen in certain radio maps. The x-ray spectrum is consistent with thermal radiation from a hot plasma at a temperature of about 4 x 10(6) degrees K with evidence for a line at 19 angstroms corresponding to the 2p-->1s transition of O VIII. 相似文献
20.
Vaiana GS Reidy WP Zehnpfennig T Vanspeybroeck L Giacconi R 《Science (New York, N.Y.)》1968,161(3841):564-567
High-resolution solar x-ray images were obtained with a rocket-borne grazing incidence telescope. The x-ray flare is large in extent, has fine strulctuire, and follows a neutral magnetic line. X-ray emitting coronal links interconnect active regions. The general coronal emission at the limb and several faint regions on the disc are observed. 相似文献