C. D. McKeith

Interferometer-grating spectrograph for high resolution astronomical spectroscopy in the middle uv

A high resolution spectrograph is described, which is to be used for a program of uv astronomical spectroscopy from a moderately stabilized, star pointing balloon-borne platform. A spectral resolving power >10(5) is achieved using an optically contacted Fabry-Perot interferometer in crossed dispersion with a grating order sorter.

High resolution interferometric studies of the solar magnesium ii doublet spectral region

The resonance lines of M gn (A = 279.55 and 280.27 nm) are just beyond the extinction limit of the Earth’s atmosphere. Because of the high cosmic abundance of magnesium, these lines are particularly important in ultraviolet astronomy and with the extension of interference spectroscopy into the far ultraviolet (Bradley 1968), sophisticated optical techniques can now be employed at these wavelengths. On the Sun, the M gn resonance lines consist of a broad absorption with a pronounced emission core similar to the H and K lines of Ca 11, but with more prominent emission and absorption features, so that the Mg 11H and K lines are much more sensitive indicators of chromospheric phenomena. The discovery (Kachalov & Yakovleva, 1962) of structure in the emission core, giving a doubly reversed profile, confirmed the similarity with CAII. The structure of the emission core was well resolved in high resolution {ca. 3 pm) echelle spectrograms obtained with a Sun-pointed rocket (Purcell, Garrett & Tousey 1963). These echelle line profiles were, however, composite ones averaged over one third of the solar disk, so that it was not possible to distinguish between profiles from quiet and active regions, or to determine centre-to-limb variations.

A stable, high finesse scanning Fabry-Perot interferometer with piezoelectric transducers

A Fabry-Perot interferometer is described which employs different piezoelectric ceramics for plate parallelism adjustment and spectral scanning. A high finesse is maintained over periods of several days and the wavelength scale is approximately a linear function of the applied scan voltage.

A Discussion on astronomy in the ultraviolet - Interstellar gas studies in the balloon ultraviolet

Spectral observations at a resolution of 0.1 A covering the region 2870—2740 A have been made of several stars with an objective grating spectrograph mounted on a balloon-borne star-stabilized platform. We report our measurements of the interstellar lines of Mg II at 2795.53 A and 2802.70 A and Mg i at 2852.13 A. There are two important astrophysical reasons for observing these interstellar lines. First, in the general (H i) interstellar medium, Mg is predominantly in the Mg”** state, so its interstellar abundance can be determined directly from the Mg ii lines if the position on the curve of growth is known. Second, observation of both Mg+ and Mg° gives information on the ionization balance and leads to a value for the interstellar electron density. Values for the interstellar Mg abundance and electron density are derived for the gas in the directions of the stars observed. The results indicate that the predominant ionizing mechanism in cool clouds is photoionization by starlight

A mechanically scanned interferometer-echelle spectrometer for the middle ultraviolet

A high spectral resolution, photoelectric spectrometer is described which employs a Fabry-Perot interferometer in tandem with an echelle grating monochromator. Spectral recording is achieved by simultaneous mechanical scanning of the interferometer and the grating premonochromator. The spectrometer is intended for use in a programme of astronomical spectroscopy in the middle ultraviolet. Design considerations and some details of the performance of a prototype instrument in the ultraviolet are presented.

Stellar Studies in the Balloon Ultraviolet

Observations with a spectral resolution of 0.01 nm have been made for several stars in the balloon ultraviolet. For the two coolest stars studied ((3 Ori and a Lyr) wavelengths of all observed spectral features in the range 273-288 nm are given with an accuracy of approximately ± 0.004 nm. Using these results the velocity field in the atmosphere of (3 Ori has been investigated and evidence is found for an outward motion in the higher layers and a pulsation-type motion in the deepest layers. The strength of the Mg+ resonance and subordinate lines near 280 nm for all the stars observed is compared with non-l.t.e. calculations. Good agreement between observation and theory is found for main sequence stars but the stronger lines in the supergiants imply microturbulent velocities >10 km s_1.