✍ Scribed by Roger W. Day
No coin nor oath required. For personal study only.
Grevesse and Swings (1968) and, independently, Lambert et al. (1969) identified the [Ca HI 4s z S1/2-3d z D3/2 line at 7323.90/~ in the Sun. Unfortunately, this line usually appears as an asymmetry in a much stronger telluric water line at 7323.97 • and is difficult to resolve, as evidenced by the disparity in the equivalent widths reported in the previous papers (Wz= 6.0 and 15_ 5 mA respectively). High resolution scans taken at high altitude on two very dry days enabled Lambert and Mallia (1969) to partially resolve the [Ca u] line and measure its equivalent width at several points on the solar disk. Their east limb scans achieved the greatest separation; however, they still mentioned blending difficulties associated with the red wing of the HzO line, with a terrestrial line in the blue wing of the forbidden line, and with a suspected very weak (Wz ~ 1 m,~) terrestrial line within the [Ca ll] profile itself.
These telluric blending problems could be avoided if scans of a planet such as Mars were taken at a time when that planet's geocentric radial velocity shifted the forbidden Ca H line into a spectral region free of terrestrial lines. ]'his should lead to a more accurate value for the equivalent width. The purpose of this note is to report such observations. First, though, it should be mentioned that this method has been used before in a number of planetary observations; for instance, in the discovery of water vapor on Mars by Spinrad et al. (1963) and in later investigations like that of Tull and Barker (1972), the latter also reporting several solar lines previously undetected due to telluric blending. Application of this technique to the [Ca II] line was suggested independently by Young and Schorn (1970).
On January 12, 1972, the McDonald Observatory's 107-in. (2.7 m) telescope, the Tull echelle coude scanner (Tull, 1972) and an RCA gallium-arsenide phototube were used to observe Mars. On that date the planet shifted the [Ca II] line about 0.44/~ to the red, into a region free of any known terrestrial lines. Two scans, covering an interval of 2 ~, were obtained at a resolution of 66 rnA; the co-added scans totaled approximately 32000 counts per channel in the continuum. The data were processed by a fast Fourier transform smoothing program based on the techniques discussed by Brault and White (1971). Identifications were made using the lists of Moore et al. (1966) and Davis and Phillips (1963). The scale (/~/channel) was determined from the least-blended lines. In order to check the continuum level, all known solar lines within the scan were inserted into a spectral synthesis program; the resulting synthesized scan showed the continuum to be well-defined even after the telluric
📜 SIMILAR VOLUMES
Observations of solar X-ray line emission using crystal spectrometers during a large chromospheric flare have provided a list of wavelengths with a precision of 0.003 A\_ in first order of diffraction and correspondingly better in higher orders. In addition to the resonance, intersystem (1 1S0-2 zP1