An eyepiece interferometer for double star measurement.

Abstract

view Abstract Citations (1) References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS An eyepiece interferometer for double star measurement. Wilson, Raymond H., Jr. ; Moore, Walter Lee Abstract The desirability and feasibility of an eyepiece interferometer was called to our attention early in 1951 by a private communication from W. S. Finsen of Union Observatory, Johannesburg, and later by his publication.1 The Anderson-type interferometer, in use by Wilson at Flower Observatory since 1934, would not be readily adaptable for testing and use on other telescopes. On the other hand, an eyepiece interferometer made to fit in a standard eyepiece tube could, with relatively minor adjustments and calibrations, be used on any telescope having a focal ratio between limits for which the interferometer was designed. Following the general plan suggested by Fin- sen, light from the objective enters the present interferometer through a collimating lens 16 mm diameter, 38 mm focal length, focussed in the telescope so as to produce parallel rays from a star. The slits for dividing the beam, cut out of thin brass shim stock, are located at the Ramsden disc (image of the objective) of the collimator. The outer boundary of the slits is a circle having a diameter of 1.9 mm, which would, therefore, be entirely within the Ramsden disc for any objective with focal ratio shorter than f/20, provided all centers are coaxial. The slit mechanism was designed by Dr. Moore, who did the machine work involved on all parts of the interferometer. It consists of 3 plates of thin brass shim stock, in one of which is a fixed punch hole, centered on the optical axis, which always forms the outer boundary of the slits. The inner boundaries are formed by edges of the other two plates, mounted in contact with the first, and each attached separately to two opposite screw nuts which are both engaged to the same screw bolt having opposite threads on each end. Readings of the screw head can thus be calibrated to give the variable separations of the slits, whose inner boundary may be straight or circular, depending on which edge of the movable sheets marks it. Slits so situated are optically equivalent to similar slits having the full diameter of the objective and located near its plane. They can be freely rotated for proper orientation on a double star, and their position angle is indicated by a vernier pointer on a ~-inch aluminum circle. After passing the slits, the light from a star is next received by a miniature telescope, through the eyepiece of which the interference pattern may be viewed. Except that its objective must enclose the light cone from the slits, there are no requirements on its construction aside from convenience of size, optical feasibility and sufficient magnification to show clearly the interference fringes. The present instrument has an objective 21 mm in diameter, and slightly over 2 inches focal length. The eye end is a tube capable of delicate focussing adjustment, which holds snugly a standard i14-inch tube commercial eyepiece of about -21-inch effective focal length. All optical surfaces of the eyepiece interferometer are coated. The total length of the instrument is about 6 inches. Tests on several telescopes over ten inches in diameter, including both refractors and reflectors, have shown clear interference fringe patterns suitable for measurement of double stars. For precise work with any telescope it would be necessary only to calibrate the orientation on a wide fixed double, with slits very narrow so as to elongate and line up the diffraction images. Linear and hence angular scale can be determined from measuring-screw determinations of the slit dimensions combined with the focal lengths of the objective and collimator, which result directly from a measured diameter of the Ramsden disc. Approximate test measures of close doubles with the i8-inch Flower refractor during this past summer have indicated the feasibility of such development of the instrument to its expected precision. Publication: The Astronomical Journal Pub Date: June 1954 DOI: 10.1086/106994 Bibcode: 1954AJ.....59..195W full text sources ADS |