Spectral distribution line sources

The fundamental quantity for interferometry is the source s visibility function. The spatial coherence properties of the source is connected with the two-dimensional Fourier transform of the spatial intensity distribution on the ce-setial sphere by virtue of the van Cittert - Zemike theorem. The measured fringe contrast is given by the source s visibility at a spatial frequency B/X, measured in units line pairs per radian. The temporal coherence properties is determined by the spectral distribution of the detected radiation. The measured fringe contrast therefore also depends on the spectral properties of the source and the instrument. 

Figure 2.4. Spectral power distribution of a typical line source, a mercury arc lamp (IES, 1981 Billmeyer and Saltzman, 1981).

Relation of such empirical calibration to quantitative spectroscopic theory was pursued with two of the different source lamps by determining their spectral distributions from high resolution spectro-graphic plates made by repeated flashes, combined with numerical evaluation of Tji via equation (2.3) using the band transition probability factor or /-number, and the pressure broadening factor, as well as the absorber temperature, as selectable parameters. Uncertainty concerning the presence of continuum radiation between the OH lines in the source spectrum ultimately limited the definiteness of this calibration procedure. 

As has been previously demonstrated in Eqs. (3.6) and (3.7), the sensitivity of the instrument for the analyte line is proportional to the intensity of the excitation source and is also a function of the spectral distribution of the source. Anything that changes the intensity or spectral distribution of the excitation source will cause a change in the analyte sensitivity. If the changes are uncontrolled or unpredictable, then analytical errors due to drift are encountered. Some of the sources of drift are inherent to the instrument design and cannot be controlled by the operator. On the other hand, there are techniques that can minimize the importance of the drifts inherent in the instrument. 

The slit function can be observed well in the imaging of line sources when the inlet and outlet slits (and the middle slit if present) are moved synchronously. If the slit is too wide the line of a mercury lamp does not appear as the expected Gaussian-shaped curve intensity distribution, but as a triangle. If the inlet and exit slits are different, a trapezoid is obtained. Triangular shapes in the spectrum indicate defective adjustment of slit widths in the equipment. These effects are observed mainly in spectrometers in which only a small number of preset slit widths can be selected. Distortion of a spectral band is negligible only if... 

The spectral distribution for M 82 is shown in Figure 3. The 2.2, 3.5, 11.6, and 19y observations were made with 60-75" beams on the KPNO 1.3-m and Mt. Hopkins Observatory 1.5-m reflectors. The letter "A" denotes the lly and 20y fluxes for the 3 x 10 beam of the AFCRL rocket-borne infrared sky survey (Walker and Price 1975) note that M 82 is the only identified extragalactic source in the catalog of that survey. The 8-13y spectrum was obtained by Gillett, Kleinmann, Wright and Capps (1975) using a 7" beam, and the "silicate" absorption and Nell line emission are clearly evident. The 69u data was obtained by Kleinmann, Wright, 5 Fazio (1969) with the... 

In contrast to a line source (LS) the term continuum source (CS) describes a radiation source, which generates a spectrum with a continuous spectral distribution over a broad wavelength range. Nevertheless a CS can be operated continuously or discontinuously, i.e. in a continuous or in a pulsed mode. An instructive review of CS for common spectroscopic applications has been published by Ingle and Crouch [71]. 

X-ray spectroscopy has also been applied to the interpretation of solar spectra, which are emitted by solar flares. Now stellar objects are under investigation by X-ray satellites such as Chandra and XMM. Whereas the present X-ray telescopes are medium resolution devices, the next generation (Constellation-X, XEUS) will provide sufficient spectral resolution for detailed analysis. The spectra from distant object usually suffer from low statistics solar flares have low emission time and the observation time of stellar objects is limited. In addition, the electron distribution is not Maxwellian, in general, and some of the spectral lines may be polarized. Therefore, verified theoretical data are of great importance to interpret solar and stellar spectra, where they provide the only source of information on the plasma state. 

A study of local environment of Fe ions in FeIn2S4 structure was carried out by the Mossbauer spectroscopy in a transmission geometry at the room temperature using a MS2000 spectrometer and Fe/Rh (40 mCi) source. MOSMOD software modified for distribution of quadrupole splitting (AE) was used to process the spectra. All isomer shifts (8) are presented with respect to the a-Fe standard sample. The FWHM of spectral lines has been fixed to be 0.15 mm/s. 

Figure 2. Left Signal from the direction of the galactic center as measured by H.E.S.S.. The solid line marks the expectation for a point source. Right Spectral energy distribution for the galactic center as derived by H.E.S.S. in comparison with measurements by CANGAROO (Tsuchiya et al., 2004) and Whipple (Kosack et al., 2004).

Apart from the atomic and ion lines of the species present in a plasma source an emission spectrum has a continuum on which the emission lines are superimposed. This extends over the whole spectrum. It is due to the interactions between free electrons ( Bremsstrahlung ) and to the interaction of free and bound electrons ( recombination continuum ). The former is particularly important in the UV spectral region, whereas the latter is important at longer wavelengths. The spectral intensity distribution for the continuum radiation is given by ... 

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