Point source

About: Point source is a research topic. Over the lifetime, 5077 publications have been published within this topic receiving 94091 citations.

Optics of photoretinoscopy: results from ray tracing

Abstract: Recent photographic studies have generated renewed interest in the optics of the retinoscopic (skiascopic) image. In photoretinoscopy the subject's eye is illuminated by a point source of light and the fundal image of this light at the plane of the subject's pupil is observed or photographed from a position near the source. The image so obtained is a function of the dioptric defocus of the eye relative to the camera, D, the distance of the source and camera from the eye, A, the radius of the subject's pupil, R, and the distance of the point source from the edge of the camera aperture, E. The fraction of the subject's pupil which is not filled with light is termed the "Dark Fraction" (DF) and may be computed from a simple ray tracing model of the eye. It is given in terms of the above parameters by the equation DF = E/(2ARD). The validity of this equation was tested with a photoretinoscope and artificial eye. The photoretinoscope, which is a novel modification of an isotropic photorefractor, is also described.

Final SAS-2 gamma-ray results on sources in the galactic anticenter region

Abstract: Analysis of SAS-2 high energy Gamma ray data from the direction of the galactic anticenter shows that this region is characterized by: a diffuse emission from the galactic plane which has a maximum along b=0 deg and an enhancement toward negative latitudes associated with Gould's Belt, a strong point source in the direction of the Crab nebula, and a second intense localized source near galactic coordinates 195 deg, +5 deg. Gamma ray emission from the Crab source is dominated by a pulsed flux from PSR 0531+21. The total flux above 100MeV is 3.7 + or - 0.8 million/sq cm s. The source near 195 deg, + 5 deg has a flux above 100 MeV of 4.3 + or - 0.9 million/sq cm s. Its spectrum appears flatter than that of the Crab. The diffuse galactic plane emission at negative lattitudes shows a general correlation with the local matter distribution associated with Gould's Belt. The calculated Gamma ray intensity agrees well with the SAS-2 observations.

Molecular outflows associated with a flux-limited sample of bright far-infrared sources

Abstract: Results of a systematic search for high-velocity CO emission from a sample of bright FIR sources from the IRAS Point Source Catalog are presented. This extends the original survey to a complete flux-limited sample. Results of CO mapping toward 22 FIR sources are given, showing that all of the sources are associated with strong CO emission that is peaked close to the FIR sources. Based on their IR colors and positional coincidence with strong CO emission, it is suggested that the sample is composed entirely of luminous, young stellar objects. New detections of molecular outflows were made toward six of the FIR sources. These outflows are relatively energetic, with typical mechanical energies of 10 to the 45th ergs. 30 refs.

Quantitative point source photoacoustic inversion formulas for scattering and absorbing media.

Abstract: We present here an expression for the photoacoustic contribution of an optical point source in a diffusive and absorbing medium. By using this measurement as a reference, we present a direct inversion formula that recovers the absorption map quantitatively, at the same time accounting for instrumental factors such as the source strength, the shape of the optical pulse, and the impulse response and finite size of the transducers. We further validate this expression through accurate numerical simulations showing that the absorption map is recovered quantitatively in the presence of a rotating geometry. We finally discuss how the presented solutions for point sources within the photoacoustic problem enable the use of concurrent fluorescence and ultrasound measurements as appropriate for a hybrid tomographic system. The proposed system could retrieve absorption information using photoacoustic measurements, and use these data to more accurately describe the fluorescence problem and improve reconstruction fidelity.

Will point sources spoil 21-cm tomography?

Abstract: 21-cm tomography is emerging as a promising probe of the cosmological dark ages and the epoch of reionization, as well as a tool for observational cosmology in general. However, serious sources of foreground contamination must be subtracted for experimental efforts to be viable. In this paper, we focus on the removal of unresolved extragalactic point sources with smooth spectra, and evaluate how the residual foreground contamination after cleaning depends on instrumental and algorithmic parameters. A crucial but often ignored complication is that the synthesized beam of an interferometer array shrinks towards higher frequency, causing complicated frequency structure in each sky pixel as ‘frizz’ far from the beam centre contracts across unresolved radio sources. We find that current-generation experiments should none the less be able to clean out this point source contamination adequately, and quantify the instrumental and algorithmic design specifications required to meet this foreground challenge.