D. S. Evans

The occultation of Epsilon Geminorum by Mars - Analysis of McDonald data

An analysis of observations of the occultation of Epsilon Gem by Mars on April 8, 1976, is presented. The data were obtained by three neighboring telescopes at McDonald Observatory. Intensity fluctuations on time scales of the order of 100 ms were observed simultaneously at the three telescopes. As the observations compare well with predictions of turbulent scintillation theory, it is concluded that such fluctuations were probably largely the effect of stellar scintillations in the Martian atmosphere. The stellar diameter is included as a parameter in the theory but in a way which differs from previously published interpretations of occultations of extended sources by planetary atmospheres. Scintillations govern the experimental uncertainty in the deduction of the scale height of the high Martian atmosphere. A density scale height of 9.9 + or - 2.5 km is obtained at an altitude of 74 + or - 8 km above the mean surface. For CO 2 gas, this result corresponds to a temperature of 190 + or - 50 K.

The angular diameter of X Cancri.

Analysis of an occultation reappearance of the semiregular variable X Cancri observed with the 107-inch telescope of McDonald Observatory on 9 November 1971 by the laser group using slightly modified laser equipment. The problem of the effective temperature of this carbon star is discussed, and estimates near 2500 K are derived both from the occultation data and from an integration based on the multicolor photometry reported by Mendoza (1967). This figure is 300-400 K higher than Mendozas calibration, and it is clear that unsolved problems remain in many areas connected with these stars.