Arne A. Wyller

URSIES - An ultravariable resolution single interferometer echelle scanner.

A Fabry-Perot interferometer in a Ramsay mount is used in tandem with an echelle Hilger monochromator with pinholes instead of slits. The instrument, URSIES, is enclosed within a pressure chamber filled with Freon. Photoelectric pulse counting techniques and pressure scanning are used to record the spectrum. This design has four basic advantages: (1) The resolution of the scanner is variable from 5.0 A to 0.005 A, and the effective wavelength range is quite broad, from 3500 A to 13,000 A. (2) A light gain of ten over conventional grating scanners at resolutions of 0.1 A or better is achieved. (3) Very low levels of light from outside the wavelength passband reach the detector; for a resolution of 0.03 A at 6000 A this level is 5%. (4) There are very low levels of scattered light from the pinholes when extended sources are observed. The scattered light from the instrument at the edge of the solar disk is found to be less than 1% from 4000 A to 11,000 A. Measurements demonstrating these advantages are discussed.

OSO-8 observations of CaII H and K, MgII h and k, L? and L? above a sunspot

Observations with the French (L.P.S.P.) experiment on board OSO-8 of a sunspot and nearby plage region are described. The behaviour of the emission cores of the Ca II H and K and Mg II h and k resonance lines is very similar and the correspondence in intensity between the four lines persists in all observed features. In contrast, the Lyman lines show little correlation with the other lines. Their emission regions appear broader in the spectroheliograms than the underlying sunspot structure and must not necessarily possess a counterpart in lower layers. From the central intensity of Lα above the umbra an electron density of 4.3 × 1010 cm-3 ≲ne* ≲2.3 × 1011 cm-3 at 20 000 K is estimated.

Photoelectric line profiles in umbral spectra.

Umbral line profiles of Hα, Na D2 and Hei 10830 have been observed photoelectrically with a pressure scanning spectrometer, URSIES (Ultravariable Resolution Single Interferometer Echelle Scanner). Intermittent pulse counting techniques are applied with integration times as short as 0.8 s which permits selection of moments of good seeing and guiding even in poor climates.The Hα line profile shows in a medium-sized spot (Au = 100 × 10–6 SH) a pronounced weakening in the wings but a persistence of the line core in agreement with the results of Fricke and Elsässer (1965).The profile of the Hei 10830 line shows an unexpected strengthening over the umbra of the two spots which have been observed. The strengthening of the line in the umbral spectrum of a third spot has been confirmed by Dr. Mallia at the Oxford Solar Station (Gornergrat, Switzerland).Na D2 line profile together with continuum observations at λ4260, λ5890, and λ6530 have been accounted for with an empirical (T, τ) relation by one of us (Yun, 1971). The wavelength dependence and the absolute values from 4000 Å to 14000 Å of the intensity curve generated by this relation shows very good agreement with the intensities observed by Wöhl et al. (1970) in a spot of similar diameter.Precision observations of the continuum at λ5890 indicate umbra-to-disk continuum ratios that are higher (0.104) than the Mercury calibrated value by Mattig (0.086) even when a maximal correction for scattered light is applied. Only Zwaans (1965) cool umbral model atmosphere approaches Mattigs continuum value, but this model renders the absorption wings in Na D2 much too deep. It is suggested that future definitive observations should be carried out with coronagraphs under coronal skies or in satellites.

New C13N14 search regions in the solar spectrum

Ten new rotational line positions, due to the (0,0) red C13N14 band, are calculated to fall squarely within continuum regions 1–2 Å wide in the near infrared solar spectrum, λλ, 10 990–11 630. Precision observations of the isotopic line strengths in this spectral region, albeit difficult, should resolve the present ambiguity in the blue-violet observations of whether or not the solar C12/C13 ratio is equal to or larger than the terrestrial ratio.

On D-C electrical conductivity in a partially ionized solar magnetoplasma

A numerical application to the extreme cases of high and low degree of ionization of the binary collision theory of Burgers (1960) and the multiple collision theory of Shkarofsky (1960) shows very good agreement in the values of the magnetic tensor components for solar electrical conductivity. It is pointed out that the inclusion of ion motions in Burgers theory favors its use in the future evaluation of the solar thermal conductivity tensor.

URSIES and the Bartol Coudé Observatory

A polar siderostat with a 36-inch flat Cervit mirror is mounted on top of the fifty foot tall building of the Bartol Research Foundation on the campus of Swarthmore College outside Philadelphia. The beam of parallel light is guided through a hole in the roof down along the optical axis of a 24-inch broken Cassegrain reflector, which is mounted stationarily on the third floor of the building. By the use of a plateglass window in the roof hole the circulation of warm air is eliminated and good to excellent solar and stellar image definition results.