Sufficient Photon Research Articles

ASCA Observations of the Eclipsing IP XY Ari

AbstractWe describe the ASCA observation of the eclipsing intermediate polar (IP) XY Ari (=H0253+19). This system was first discussed by Patterson & Halpern (1990, ApJ, 361, 173) as a possible IP based upon the HEAO-1 data. This system is impossible to study in the optical or ultraviolet because of the 12 mag of optical extinction associated with the molecular cloud Lynds 1457=MBM 12. The system has an orbital period of 0.2526 day and a pulse period of 208 sec. Our preliminary analysis of the ASCA data shows that the eclipse is nearly total (the precision of the background subtraction sets the limit). The eclipse ingress and egress occur very quickly, although we have not yet derived accurate numbers. There are sufficient photons that we can perform crude phase-resolved spectroscopy. The resulting spectra, each covering about 1/4 of the orbit, show that the Fe Kα line is not constant as a function of phase. A sample spectrum is reproduced below. We expect to submit a paper describing the results to the ApJ before the end of 1996.

A fast charge coupled device detector for charge exchange recombination spectroscopy on the DIII-D Tokamak (abstract)

Charge exchange recombination (CER) spectroscopy has become a standard diagnostic for Tokamaks. CER measurements have been used to determine spatially and temporally resolved ion temperature, toroidal and poloidal ion rotation speed, impurity density, and radial electric field. Knowledge of the spatial profile and temporal evolution of the electric field shear in the plasma edge is crucial to understanding the physics of the L to H transition. High speed CER measurements are also valuable for edge localized mode studies. Since the 0.52 ms minimum time resolution of our present system is barely adequate to study the time evolution of these phenomena, we have developed a new charge coupled device (CCD) detector system with about a factor of 2 better time resolution. In addition, our existing system detects sufficient photons to utilize the shortest time resolution only under exceptional conditions. The new CCD detector has a quantum efficiency of about 0.65, which is a factor of 7 better than our previous image intensifier-silicon photodiode detector systems. We have also equipped the new system with spectrometers of lower f/number. This combination should allow more routine operation at the minimum integration time, as well as improving data quality for measurements in the divertor-relevant region outside of the separatrix. Construction details, benchmark data, and initial Tokamak measurements for the new system will be presented.

Imaging Deep Optical Sections with Two-Photon Excitation Fluorescence Microscopy

The technique of optical sectioning allows the visualization of a succession of images of parallel planes within a thick specimen with little or no out-of-focus interference. Ultimately, a limit is reached on the depth to which optical sections can be obtained from a given sample. This limit, up to the working distance of the objective, is largely determined by the degree of light scattering encountered by the incident excitation beam as well as the returning emission signal.Confocal imaging was one of the first optical sectioning techniques applied to fluorescence imaging. Two-photon excitation imaging is a recently developed alternative optical sectioning technique for fluorescence imaging where an excitation wavelength of around twice the excitation peak of the fluorophore is used in a laser-scanning microscope. This excitation wavelength produces very little fluorophore excitation in the bulk of the sample, but when the incident photons are confined in space and time sufficient two-photon absorption events can take place to obtain rapid imaging of fluorophores. With high peak powers—obtained with a sub-picosecond pulsed laser source focused by a lens—sufficient photon density can be obtained for easily detectable two-photon events. Thus fluorophore excitation occurs as two photons are absorbed essentially simultaneously, which act effectively as a single photon of twice the energy (half the wavelength). Two-photon events have a quadratic dependence on intensity, and, therefore, decrease rapidly away from the focal volume of the lens. In a raster scanning system, fluorophore excitation is confined to the optical section being viewed as fluorophore away from the lens focal volume is not excited by the long-wavelength illumination.

ROSAT PSPC Observations of the Intermediate Polar TV Columbae

view Abstract Citations (7) References (35) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS ROSAT PSPC Observations of the Intermediate Polar TV Columbae Vrtilek, S. D. ; Silber, A. ; Primini, F. ; Raymond, J. C. Abstract The intermediate polar TV Columbae was observed for 8640s with the ROSAT PSPC. The best-fitting model to the 0.1-2.0 keV spectrum combines a power law with photon index α = 0.82 and a 54 eV blackbody, both observed through a column density of 4.6 x 1020 cm-2. No evidence is seen for line emission from the Fe L-shell complex. We observe an X-ray/optical flux ratio of 0.2: our measured X-ray photon flux is not sufficient to produce the He II λ1640 recombination line flux found by lUE. Some of the missing X-ray flux can be attributed to absorption in an accretion curtain. An additional very soft EUV component (e.g., a 20 eV blackbody) could provide sufficient photons in the 55-100 eV band to account for most of the He ii luminosity while remaining hidden to the PSPC and lUE. A second possibility is that the X-ray flux is indeed small and collisional excitation accounts for 80% of the He II λ1640 flux. Because of instrumental difficulties, we are unable to confirm the 32 minute period observed with EXOSAT and attributed to rotation of the white dwarf. Publication: The Astrophysical Journal Pub Date: July 1996 DOI: 10.1086/177479 Bibcode: 1996ApJ...465..951V Keywords: STARS: NOVAE; CATACLYSMIC VARIABLES; STARS: INDIVIDUAL CONSTELLATION NAME: TV COLUMBAE; ULTRAVIOLET: STARS; X-RAYS: STARS full text sources ADS | data products SIMBAD (4) MAST (1) INES (1) HEASARC (1)

Kirkpatrick-Baez optics for a sub-μm synchrotron X-ray microbeam and its applications to X-ray analysis

A synchrotron X-ray microprobe system based on Kirkpatrick-Baez optics has been developed using X-rays from a multipole wiggler at the Photon Factory to achieve a beam size of less than 1 μm with a sufficient photon flux. Either a double-crystal or a synthetic multilayer monochromator was used for the monochromatization of incident X-rays. The characteristics of the X-ray microprobe were experimentally examined. Though the beam size could be changed from 2 μm to sub-μm, the minimum beam size obtained was about 0.7 × 0.9 μm 2 with a photon flux of 2 × 10 8 ph/ s/300 mA for 9 keV X-rays by a multilayer monochromator. The capabilities of the X-ray microbeam system have been demonstrated for X-ray fluorescence trace element analysis. The sensitivity was three orders of magnitude higher compared to a similar type of X-ray microbeam system previously developed for X-rays from a bending magnet. An X-ray micro-diffraction experiment has also been performed for the characterization of local layer defects observed in surface stabilized ferroelectric liquid crystals.

A compact radiation source for digital subtractive angiography

Beam requirements for 33 keV radiation used in digital subtraction angiography have been established through extended experimentation first at Stanford and later at the National Synchrotron Light Source in Brookhaven. So far research and development of this medical procedure to image coronary blood vessels have been undertaken on large high energy electron storage rings. With progress in this diagnostic procedure, it is interesting to look for an optimum concept for providing a 33 keV radiation source which would fit into the environment of a hospital. A variety of competing effects and technologies to produce 33 keV radiation are available, but none of these processes provides the combination of sufficient photon flux and monochromaticity except for synchrotron radiation from an electron storage ring. The conceptual design of a compact storage ring optimized to fit into a hospital environment and producing sufficient 33 keV radiation for digital subtraction radiography will be discussed.

Photoevaporation of disks around massive stars and application to ultracompact H II regions

Young massive stars produce sufficient Lyman continuum photon luminosity Phi(sub i) to significantly affect the structure and evolution of the accretion disks surrounding them. A nearly static, ionized, isothermal 10(exp 4) K atmosphere forms above the neutral disk for disk radii r less than r(sub g) = 10(exp 15) M(sub 1) cm, where M(sub *) = 10 solar mass M(sub 1) is the stellar mass. For r approximately greater than r(sub g) the diffuse field created by hydrogen recombinations to the ground state in the photoionized gas above the disk produces a steady evaporation at the surface of the disk, and this H II gas flows freely out to the ISM (the 'disk wind'). The detailed structure depends on the mass-loss rate dot-M(sub w) of the fast, approximately greater than 1000 km/sec, stellar wind from the massive star. A critical mass-loss rate dot-M(sub cr) is defined such that the ram pressure of the stellar wind equals the thermal pressure of the H II atmosphere at r(sub g). In the weak stellar wind solution, dot-M(sub w) less than dot-M(sub cr), the diffuse photons from the atmosphere above r(sub g) produce a photoevaporative mass-loss rate from the disk at r approximately greater than r(sub g) of order 1 x 10(exp -5)(Phi(sub 49))(exp 1/2)(M(sub 1))(exp 1/2) solar mass/year, where Phi(sub i) = 10(exp 49) Phi(sub 49)/sec. The resulting slow (10 to 50 km/sec) ionized outflow, which persists for approximately greater than 10(exp 5) year for disk masses M(sub d) approximately 0.3 M(sub *), may explain the observational characteri stics of unresolved, ultracompact H II regions. In the strong stellar wind solution, dot-M(sub w) greater than dot-M(sub cr), the ram pressure of the stellar wind blows down the atmosphere for r less than r(sub g) and allows the stellar photons to penetrate to greater radii and smaller heights. A slow, ionized outflow produced mainly by diffuse photons is again created for r less than r(sub g); however, it is now dominated by the flow at r(sub w)(greater than r(sub g)), the radius at which the stellar wind ram pressure equals the thermal pressure in the evaporating flow. The mass-loss rate from the disk is of order 6 x 10(exp -5)dot-M(sub w-6) v(sub w8)(Phi (sub 49))(exp -1/2) solar mass/year, where dot-M(sub w-6) = M(sub w)/10(exp -6) solar mass/year and v(sub w8) = v(sub w)/1000 km/sec is the stellar wind velocity. The resulting outflow, which also persists for approximately greater than 10(exp 5) year may explain many of the more extended (r approximately greater than 10(exp 16) cm) ultracompact H II regions. Both the weak-wind and the strong-wind models depend entirely on stellar parameters Phi(sub i), M(sub *), dot-M(sub w)) and are independent of disk parameters as long as an extended r much greater than (r(sub g)), neutral disk exists. We compare both weak-wind and strong-wind model results to the observed radio free-free spectra and luminosities of ultracompact H II regions and to the interesting source MWC 349.

ROSAT observations of cataclysmic variables: A search for the boundary layer emission

Many cataclysmic variables (CVs) and low-mass X-ray binaries show He II line emission at wavelength 1640 and wavelength 4686. As recombination lines of an ion requiring 55 eV for ionization, these lines cannot be attributed to gravitational heating in the disk but could be due to reprocessed 55-280 eV X-rays which may be produced in a boundary layer at the disk/star surface. We undertook a search for this soft component using the Positon Sensitve Proportional Counter (PSPC) on ROSAT. The photon fluxes we observe are not sufficient to produce the He II wavelength 1640 fluxes observed by IUE. If we assume that the X-ray luminosity is due to emission from a boundary layer, then the observed quiescent luminosity is one-quarter of the total accretion luminosity as determined by optical and ultraviolet observations rather than the one-half that is predicted by some theories. An additional very soft component (e.g. an approximately equal 10-20 eV blackbody) could provide sufficient photons in the 0.055-0.100 keV band to produce the observed He II fluxes and contribute the additional luminosity from the boundary layer while remaining hidden to the PSPC and IUE. Alternatively, the high He II line fluxes could be evidence for high-temperature collisionally ionized material. We also find evidence for line emission at approximately equal 0.9 keV consistent with L-shell emission from highly ionized iron.

A catalog of intracluster gas temperatures

We have searched the Einstein Monitor Proportional Counter (MPC) data base for observations of clusters of galaxies. By coadding the MPC spectra obtained during all pointed observations of clusters with IPC count rates greater than 0.1 counts/s, we have obtained sufficient photon statistics to estimate the X-ray temperature of 84 clusters. Combining the MPC results with EXOSAT and Ginga results reported in the literature yields a combined sample of 104 clusters with known X-ray temperatures. One of the best studied X-ray correlations between clusters is that between their X-ray luminosity and gas temperature. We show that the best-fit power-law relation for our combined cluster sample can be explained by the observed increase in the gas-to-stellar mass ratio between low- and high-temperature clusters. The statistical significance of any evolution in our combined X-ray sample has been examined and compared with the statistical properties of clusters culled from optical catalogs. We find that there is strong evidence for a decrease in the X-ray luminosity of optically rich clusters beyond z approximately about 0.06. This result is used to estimate the normalization of the primordial power spectrum of density fluctuations.

Synthesis of a highly luminescent terbium chelate and its application to actin

We synthesized a highly luminescent terbium chelate which consists of DTPA as a chelating group, phalloin as an actin-binding ligand and an aromatic ring as a sensitizer of Tb emission. The synthesis was based on the property of DTPA dianhydride that has the capacity to react with two amines, while retaining its ability to chelate Tb 3+ (the resulting DTPA possesses three car☐yl groups). We screened 17 kinds of aromatic compounds for their ability to sensitize Tb emission with near UV excitation. All of the compounds tested had both a 6-membered ring and one or two amino group(s). Among them, cytosine was the best sensitizer. From the peak-peak ratio, the fluorescence intensity of a solution of Tb-DTPA-cytosine-phalloin-labeled actin was about one-fourth of an equimolar solution of tetramethylrhodamine. The excitation peak was about 302 nm. Emission from a single muscle fiber stained with this new Tb chelate was so intense that we could accumulate sufficient photon counts in a short time. Also, actin bundles stained with the Tb chelate were able to be visualized under a fluorescence microscope. The stability constant of the chelator was 10 22.46 M −1 for Tb 3+. This value was very similar to that of DTPA, which possessed five car☐yl groups. The new Tb chelate had additional expediencies. It was electrically neutral, which made it quite suitable for studying electrostatic circumstances around the terbium site on actin. We present data on this issue. Tb 3+ itself is optically isotropic. However, cytosine of the Tb chelate has a polarized absorption transition dipole moment. Therefore, in conjunction with the long-lived excited state, the synthesized Tb chelate has potential of serving to probe the slow rotational relaxation of actin filaments. We can simply replace phalloin with other agents to label not only actin but also various proteins. Such Tb chelates will be a quite useful tool for a variety of biological studies.

X-ray diagnostic for current density profiling relativistic electron beams in vacuum and gas

An x-ray imaging technique has been studied for the purpose of observing the current density profile in a high-current relativistic electron beam (50 MeV, 10 kA). Calculations and measurements of energy spectra and intensities are in good agreement. Results indicate sufficient photon yield for pinhole imaging when the beam deposits a small part of its energy in high-Z gas or a thin high-Z foil. Characteristic L and K x-ray emission is not found not be a reliable technique due to strong L and K shell fluorescence in the presence of intense bremsstrahlung radiation. It is also found that at pressures on the order of one atmosphere, the density of energy deposition in a gas cell is too small to generate sufficient photon yield for time-resolved measurements.

System Requirements for Polarization Capability

The purpose of this paper is to point out that1) proper treatment of polarization by a telescope is not only important for polarimetry, but also for other observations requiring high signal-to-noise ratio, and2) this does put a constraint on telescope design, which, however, is not unduly restrictive.Polarimetry is the observational technique which can detect anisotropics in point sources, their environment, or the medium between them and us. Modern optical polarimetry can be linear or circular, and is making progress towards spectropolarimetry and imaging polarimetry using panoramic detectors (e.g. McLean, 1984). Given sufficient photons, the precision obtained is as high as 1 part in 50 000 (see Odell, 1981 for a project requiring this precision), but more often a precision between 1 part in 1 000 to 10 000 is sufficient. (Spectro)polarimetry has been applied to planets, the Sun and other stars, stellar systems and galaxy nuclei; for a few modern investigations, see Baur, 1981; Jones et al, 1981; Schmidt and Miller, 1980. Experience in radio-astronomy has shown that when facilities for polarimetry are offered, many applications emerge from the astronomical community, yielding data that cannot be obtained by other techniques. It is essential that at least some of the large optical telescopes are capable of ob-serving polarization cleanly.

The Solar Tracking Pattern in a Closed Alfalfa Canopy1

The average cosine of the solar incidence angle for all leaflets within a closed alfalfa canopy [leaf area index (LAI) = 4 to 5] was relatively high during the morning hours, decreased to a minimum level during the early afternoon, and increased again during late afternoon hours. High values for cosine of the solar incidence angle indicate the leaflets were exposed near normal to the sun's rays. This resulted from diaheliotropic leaflet movements. The lower, midday values were associated with leaf cupping movements. Leaf cupping began about 3 h after the beginning of the midday decline in xylem water potential but the recovery from cupping, as evidenced by the return of diaheliotropic movements, occurred in the absence of the recovery of xylem water potential. An evaluation of tracking ability revealed an increasing average cosine of incidence angle with increasing leaflet age resulting in a canopy architecture which would enhance light interception by the lower strata. Light flux density measurements indicated that most leaflets in the upper canopy were exposed to sufficient photosynthetic photon flux density (PPFD) to saturate nearly saturate the photosynthetic process. However, PPFD available to leaflets in the lower canopy ranged from 45% required for saturation of photosynthesis for the average nontracking leaflet to about 85% for leaflets with a cosine of incidence of 1.0. Since most leaflets in the lower strata maintained relatively high cosine of incidence angle values, the results suggest that the observed tracking gradient (increasing ability with leaflet age) may provide the alfalfa plant with a mechanism for maintaining photosynthetic productivity in lower leaves. The data are discussed in terms of the potential carbon gain benefit to the alfalfa plant resulting from the tracking gradient within the canopy.

Photoelectric spectrophotometry of radio galaxies

The absolute energy distributions from 3200 to 10,000 A of 26 3CR radio galaxies are determined on the basis of spectrophotometric observations with the multichannel spectrometer of the Hale 5-m telescope. It is found that there is a continuous range of emission-line characteristics and UV excess in the sample and that a strong correlation exists between the nonthermal component luminosity and hydrogen emission, which favors the hypothesis that direct photoionization by the nuclear radiation is responsible for the emission lines observed. Calculations are performed which show that in almost all cases the power-law component model provides sufficient UV photons to produce the observed H-beta line. Indications are obtained that the optical nuclear component is related to the radio emission in some complex manner and that strong radio galaxies tend to be accompanied by UV excess and emission lines.

Noninvasive, Infrared Monitoring of Cerebral and Myocardial Oxygen Sufficiency and Circulatory Parameters

The relatively good transparency of biological materials in the near infrared region of the spectrum permits sufficient photon transmission through organs in situ for the monitoring of cellular events. Observations by infrared transillumination in the exposed heart and in the brain in cephalo without surgical intervention show that oxygen sufficiency for cytochrome a,a3, function, changes in tissue blood volume, and the average hemoglobin-oxyhemoglobin equilibrium can be recorded effectively and in continuous fashion for research and clinical purposes. The copper atom associated with heme a3 did not respond to anoxia and may be reduced under normoxic conditions, whereas the heme-a copper was at least partially reducible.