Fred F. Forbes

A Polarizer for the Vacuum Ultraviolet

The construction and optical properties of a MgF(2) double Rochon prism are described. The prism is useful as a polarizer or analyzer in the vacuum uv wavelengths longer than 1300 A. Measurements of MgF(2) transmission and of polarizer angular beam deviation from 1150 AS to 2900 A are presented.

Large Aperture Aluminum Alloy Telescope Mirrors

Large aperture Al alloy telescope mirrors consisting of Tenzalloy Al coated with Ni alloy, presenting performance data

A high-resolution Fourier-transform infrared spectrometer.

We have developed a Fourier-transform infrared spectrometer having a resolution of 0.5 cm- over the range of wavelength from I to 5.5 microns. It has been used to observe the sun over this wavelength range from a Lear Jet flying at an altitude of 14 km, and to observe a number of stars from the ground, using the 229-cm telescope of the Steward Observatory and the 152-cm aluminum-mirror telescope at the Observatorio Astron6mico Nacional in the Sierra de San Pedro Martir, Baja California, Mexico. The solar spectrum is given here, while the ground-based spectra are being published separately. Key words: instrumentation - spectrometer - solar spectrum

Stability of Tenzaloy Aluminum Mirrors

We have tested several cast Tenzaloy aluminum mirrors, using standard optical test procedures. Although our tests are not extensive, we have established that Tenzaloy mirrors stable within one or two waves (5000 A), or less, can and have been made. This result is in contrast to that which has been obtained for mirrors cast from 356-T6 alloy, which are not satisfactorily stable.

A 40-cm Welded-Segment Lightweight Aluminum Alloy Telescope Mirror

A 40-cm aluminum alloy, nickel plated, mirror has been made by welding together six individually cast segments. The mirror is shown to be stable to within one wave over a temperature of 58 degrees C primarily due to the use of the aluminum alloy Tenzaloy. The weldment as well as the alloy itself are now known to be capable of essentially complete stress relief by annealing. The possibilities of extending the welding technique to considerably larger telescope systems is also discussed.

ANDERSON MESA, ARIZONA, AS A SITE FOR AN OPTICAL ARRAY

From measurements of cloud cover, seeing profiles, and microthermal properties, Anderson Mesa, near Flagstaff, Arizona, has been evaluated as a potential site for an optical interferometric array. From satellite cloud measurements, northern Arizona was found to have experimental clearer skies than those of southern Arizona and New Mexico during 1984-87, with an expected lower frequency and extent of monsoon-related activity. Using a simple and inexpensive system for measuring instantaneous FWHM of stellar images, the seeing at Anderson Mesa was determined to be well represented by the statistics at the nearby USNO flagstaff Station from which a median seeing of 1.2 arcsec FWHM has been reported. Limited microthermal measurements indicate that Anderson Mesa is rather similar to Mount Graham where tree cover plays a significant role. Anderson Mesa is concluded to be a highly suitable site for an optical array.

THE INFRARED SPECTRUM OF ALPHA HERCULIS FROM 4000 TO 4800 CM-1

We have put intO operation a rapid-scanning Michelson interferometer (Fourier-transform spectrometer) and have used it on the Steward Observatory 229-cm reflector to observe infrared spectra of a dozen stars at 0.5 cm-1 resolution. In this paper, we present the portion of the a Her spectrum from 4000 to 4800 cm-1. A number of atomic and molecular absorption features have been identified. Most prominent are the CO AV = 2 bands of 12C16O; a feature which may be identified with has been pointed out. Key words: infrared spectra - a Herculis - interferometry

THE INFRARED SPECTRUM OF TWO CARBON STARS FROM 4000 TO 6700 CM-1

The infrared spectra of Y CVn and U Hya from 4000 to 6700 cm-1 are presented. Preliminary identffications of molecular and atomic features have been made. The bearing of these observations on observed C12lC13 ratios is discussed. The spectra are corrected for atmospheric extinction to a reference altitude of 14 km. Key words: infrared spectra - interferometry

STELLAR AND PLANETARY SPECTRA IN THE INFRARED FROM 1.35 TO 4.10 MICRONS.

Stellar and planetary IR spectra from spectrometer with rotating circular variable thickness interference filter

Stellar photometric data for various photocathode materials.

There presently exists in the literature sufficiently accurate narrow band filter photometric stellar data for approximately 1000 of the brightest stars to allow the computation of the radiant energy of these stars per square cnetimeter incident to the earths atmosphere. In addition to the photometric measurements obtained using an RCA 1P21, S-4 photosensitive surface, recent narrow band photometry using an RCA 7102, S-l photosensitive surface has allowed the energy computations to be extended to the new ir wavelengths. We have computed the radiant energy falling on the earth from outside the earths atmosphere in terms of amperes per square centimeter of telescope aperture for the S-l, 4, 11, 17, and 20 (Ref. 3) and Bialkali photomultiplier tubes and for the silicon detector. The computations are based directly upon precise narrow band filter photometer measurements of individual stars; therefore, the usual assumptions involving bolometric corrections or star temperature are advantageously disregarded. The compilation of results for nearly 1000 stars has been condensed in Table I to include the fifty-seven navigational stars. In addition to the navigational star number, Table I lists the Bright Star catalog number (BS) (Ref. 9) common constellation name, V magnitude, Sidereal Hour Angle (S.H.A.), declination (DEC),