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Introduction

PH12 is the ephemeris of Phoebe. This ephemeris of Phoebe is based on a numerical model fitted to the observations dispatched from 1898 to 2012.
This ephemeris is available for the period from 1875/07/01 to 2022/06/30 and through Chebychev polynomia (ph12.dat) readable with the Fortran subroutines contained in r-ph12.f90.

Files

• README.txt : Explanation file
• ph12.dat : Chebychev polynomia
• r-ph12.f90 : Fortran subroutines used to compute ephemeris
• test.f90 : Fortran program to test the computation
• ph12.tar.gz : Tar file of previous files

Fortran subroutines

• header: Read the header of ph12.dat to load information such as degree of polynomia or period of validity
  • Out
    • nc : degree of polynomia
    • ni : number of intervals
    • a : first date of validity
    • b : last date of validity
• load: Load the coefficients of Chebychev polynomia
  • In
    • nc : degree of polynomia (given by header)
    • ni : number of intervals (given by header)
  • Out
    • cf : coefficients
    • dat : limit period of intervals
• pos_ph12: Compute the position and velocity for a specific date (in TDB)
  • In
    • a : first date of validity (given by header)
    • b : last date of validity (given by header)
    • nc : degree of polynomia (given by header)
    • ni : number of intervals (given by header)
    • cf : coefficients (given by load)
    • dat : period of intervals (given by load)
    • t : time in Julian Day(TDB) (given by user)
  • Out
    • x : 6-dimension vector position-velocity

Units

Positions and velocities are delivered in au and au/day.

Example

Computation of test program should provide:

DJ =  2450000.500
x  =     -0.0565331612828     0.0683539886662     0.0384516012357
v  =      0.0006274381157     0.0005863244731     0.0001848068219
  
DJ =  2450010.500
x  =     -0.0500094770787     0.0738915516615     0.0401187775865
v  =      0.0006760155712     0.0005207212932     0.0001485844868
  
DJ =  2450020.500
x  =     -0.0430380897546     0.0787600402881     0.0414227955219
v  =      0.0007170207018     0.0004526029081     0.0001122122879
  
DJ =  2450030.500
x  =     -0.0356934838269     0.0829369615563     0.0423632094735
v  =      0.0007506989597     0.0003824876405     0.0000758949141
  
DJ =  2450040.500
x  =     -0.0280477753291     0.0864046264541     0.0429414578429
v  =      0.0007772769397     0.0003108203647     0.0000398058905
  
DJ =  2450050.500
x  =     -0.0201709424078     0.0891494848086     0.0431605890901
v  =      0.0007969545986     0.0002379862858     0.0000040948415
  
DJ =  2450060.500
x  =     -0.0121311204687     0.0911615948338     0.0430250573146
v  =      0.0008098999282     0.0001643238889    -0.0000311057595
  
DJ =  2450070.500
x  =     -0.0039949380689     0.0924342165894     0.0425405797986
v  =      0.0008162458227     0.0000901369008    -0.0000656748103
  
DJ =  2450080.500
x  =      0.0041721225095     0.0929635183165     0.0417140493061
v  =      0.0008160884008     0.0000157050494    -0.0000994974835
  
DJ =  2450090.500
x  =      0.0123053506931     0.0927483881427     0.0405534955108
v  =      0.0008094858976    -0.0000587057170    -0.0001324604177
  
DJ =  2450100.500
x  =      0.0203404288541     0.0917903484568     0.0390680943969
v  =      0.0007964587389    -0.0001328329038    -0.0001644470244

Reference

Desmars J, Li S.N., Tajeddine R., Peng Q.Y., Tang Z.H.
Phoebe's Orbit from ground-based and space-based observations
A&A xxx, pp xxx-xxx, 2013

Author

J. Desmars, SHAO/IMCCE, desmars@imcce.fr.

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