README_oclc_ey92

These routines implement the model of Elliot, J. L. and L. A. Young 1992.
Analysis of stellar occultation data for planetary atmospheres. I - Model
fitting, with application to Pluto. Astronomical Journal 103, 991-1015.

The routines are called oclc_ey92_*.  oclc stands for OCcultation
LightCurve.  EY92 refers to the Elliot and Young 1992 paper cited above.
Other occultation lightcurves can be implemented, and will be prefixed
oclc_<other>_.pro.

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VARIABLES
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a
exponent for non-constant mean moleculr weight mu(r) = mu0 * (r/r0)^-a
Unitless

b
Exponent for non-constant temperature, T(r) = T * (r/r0)^b
Unitless.

aser       A(a, b, delta) in EY92
Series in delta for use in calculating theta
Unitless.

bser       B(a,b,delta) in EY92
Series in delta for use in calculating dtheta
Unitless.

cser       C(delta_tau) in EY92
Series in delta_tau for use in calculating optical depth
Unitless.

dist       D in EY92
Distance between target and observer
cm

dtheta     d theta/d r in EY92
Derivative of the bending angle with respect to planet radius,
positive for an isothermal atmosphere.
radian/cm

htau1
scale height of absorbtion coefficient
cm

kappa
linear absorption coefficient
kappa = kappa1 exp( - (r-r1)/(htau1 * (r/r1) ) )     EY92 3.23
1/cm (or cm^2/cm^3, cross section per particle * particle/volume)

kappa1
linear absorption coefficient at r1 (top of haze)
1/cm (or cm^2/cm^3, cross section per particle * particle/volume)

lam        lambda in EY92
Ratio of radius (r) to scale height (H).  Since H = kT r^2/(mu m_adu M G),
this is the same as the ratio of kinetic energy (kT) to potential
energy (mu m_adu M G/r).
unitless

lam0        lambda0 in EY92
Reference energy ratio. Energy ratio, lambda, evaluated at the
reference radius, r0.
unitless

nu
Refractivity. 
Unitless

nu0 
Reference refractivity. Refractivity at r0
Unitless

phi
normalized stellar flux.
unitless.

r
planet radius (distance from planet center).
cm

r0
reference planet radius (distance from planet center).
cm

rh
half-light planet radius
cm

r1
planet radius of top of haze layer
cm

r2
planet radius where line-of-sight optical depth = 1
cm

rtau_ref
planet radius for reference tauobs, tauobs_ref
(normally tauobs_ref = 1, whence rtau_ref = r2)

rsurf
planet radius of surface.
flux is cut off (no diffraction) at r < rsurf
cm

rho
shadow radius (distance from shadow center), negative for
far-limb contribution.
cm.

rho_h
half-light shadow radius
cm

rho_min
minimum observer shadow radius
cm

t
temperature
K

t0
temperature at reference radius, r0
K

theta
bending angle, negative for an isothermal atmosphere.
radians.

tauobs
line-of-sight optical depth
unitless.

tauobs_ref
value of tauobs at planet radius rtau_ref

v
shadow velocity
cm/s

vperph
perpendicular shadow velocity
cm/s


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LOW-LEVEL FUNCTIONS
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aser   = oclc_ey92_aseries(a, b, delta)
bser   = oclc_ey92_bseries(a, b, delta)
cser   = oclc_ey92_cseries(delta_tau)
dtheta = oclc_ey92_dtheta(r0, theta0,lam0,a,b, r)
phi    = oclc_ey92_phi_of_r(r0,nu0,lam0,a,b,r1,kappa1,htau1,dist,rsurf, r)
lam    = oclc_ey92_lam(r0, lam0, a, b, r)
nu     = oclc_ey92_nu(r0, nu0,lam0,a,b, r)
rho    = oclc_ey92_r_of_rho(r0, nu0,lam0,a,b, dist, r)
rho    = oclc_ey92_rho_of_r(r0, nu0,lam0,a,b, dist, r)
tauobs = oclc_ey92_tauobs(r1, r2, htau1, r)
theta  = oclc_ey92_theta(r0,nu0,lam0,a,b, r)