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Rocket Experiment by Electronic Camera for Studying the Metallic Discontinuities in the Ultraviolet Spectrum of ‘A’ Stars

Published online by Cambridge University Press:  14 August 2015

M. Combes
M. Combes*
Affiliation:
Observatoire de Paris, Meudon, France

Abstract

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  1. 1. Ultraviolet spectra (1400–1800 Å) of Ap, Am and normal A stars are needed by F. Praderie, R. Bonnet and R. Cayrel.

    The spectral resolution has to be nearly 1 Å. Accurate relative photometry (5%) and absolute calibration (30–50%) are required.

    A rocket experiment, proposed to ESRO by M. Combes and P. Felenbok is planned for launch in 1972.

  2. 2. As neutral silicon and magnesium are very efficient ultra-violet absorbents, A stars ultraviolet fluxes are very faint (Praderie, 1968).

    Then a very luminous optical set-up and a high efficiency receiver have to be used. A 30 cm in diameter concave objective grating is associated with a Lallemand electronic camera. The grating (2000 //mm; //l) is holographically made (Labeyrie, 1969). The electronic camera is electrostatically focussed. A semi-transparent solar-blind CsL photocathode is used (Carruthers, 1966).

  3. 3. A little mirror, placed against the grating and forming a direct view of the sky, permits to establish an absolute wavelength scale.

    During the fly, before and after stellar observations, a little concave mirror mounted into the opening side-door is used to form on the photocathode a spectrum of a Deuterium calibrated lamp. Two photomultipliers, one on each side of the electronic camera, control the lamp stability.

    The complete mounting is calibrated in the laboratory using a thermopile as reference, before the launch and after the recovery of the waterproof payload.

  4. 4. The chosen stars are the brightest Ap and Am stars: α Dra (Ap; mv = 3.64; equivalent type A 0) and α2 Lib (Am; mv = 2.75; equivalent type A3-A7).

    It seems to be possible to obtain spectra (1400-1800 Å) of the Ap star with a spectral resolution of 1 Å and a signal to noise ratio better than 40. But at a pinch one may accept a resolution of 2 Å and a signal to noise ratio of 15 for the shortest range of the Ap star spectrum.

Type
Part III: UV Astronomy
Information
Symposium - International Astronomical Union , Volume 41: New Technique in Space Astronomy , 1971 , pp. 361 - 362
Copyright
Copyright © Reidel 1971 

References

Carruthers, M. M.: 1966, Report of N.R.L. Progress, p. 7.Google Scholar
Labeyrie, J., Cordelle, J., Flamand, J., and Pieuchard, G.: 1969, ‘Aberration Corrected Concave Gratings Made Holographically’, submitted to the ICO 8 meeting, Reading, July 1969.Google Scholar
Praderie, F.: 1968, ‘Theoretical Ultra-violet Flux in Am and Normal A Stars’, in Proceedings of the Third Harvard Smithsonian Conference on Stellar Atmospheres, April 1968.Google Scholar