Astronomy and Astrophysics – Astronomy
Scientific paper
Oct 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997pasp..109.1170c&link_type=abstract
Publications of the Astronomical Society of the Pacific, v.109, p.1170-1180
Astronomy and Astrophysics
Astronomy
5
Methods: Data Analysis, Occultations
Scientific paper
We present a method for speeding up numerical calculations of a light curve for a stellar occultation by a planetary atmospheric model that has spherical symmetry. This improved speed makes least squares fitting for model parameters practical. Our method takes as input several sets of values for the first two radial derivatives of the refractivity at different values of model parameters, and interpolates to obtain the light curve at intermediate values of one or more model parameters. It was developed for small occulting bodies such as Pluto and Triton, but is applicable to planets of all sizes. We also present the results of a series of tests showing that our method calculates light curves that are correct to an accuracy of 10(-4) of the unocculted stellar flux. The test benchmarks are (i) an atmosphere with a 1/r dependence of temperature, which yields an analytic solution for the light curve, (ii) an atmosphere that produces an exponential refraction angle, and (iii) a small-planet isothermal mode. With our method, least-squares fits to noiseless data also converge to values of parameters with fractional errors consistent with the level of synthetic noise added to the light curve. We conclude: (i) one should interpolate refractivity derivatives and then form light curves from the interpolated values, rather than interpolating the light curves themselves; (ii) for best accuracy, one must specify the atmospheric model for radii many scale heights above half light; and (iii) for atmospheres with smoothly varying refractivity with altitude, light curves can be sampled as coarsely as two points per scale height. (SECTION: Computing and Data Analysis)
Chamberlain D.
Elliot Jim
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