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Introduction

PH15 is the ephemeris of Phoebe. This ephemeris of Phoebe is based on a numerical model fitted to the observations dispatched from 1898 to 2015.
This ephemeris is available for the period from 1875/07/01 to 2022/06/30 and through Chebychev polynomia (ph15.dat) readable with the Fortran subroutines contained in r-ph.f90. This is an update version of PH12 with additional observations from Peng et al. (2015), Gomes-Júnior et al. (2015), Minor Planet Center and NOFS observations.

Files

• README.txt : Explanation file
• ph15.dat : Chebychev polynomia
• r-ph.f90 : Fortran subroutines used to compute ephemeris
• test.f90 : Fortran program to test the computation

The ephemeris can be obtained directly with SPICE Librairy and the bsp file ph15.bsp.

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  =    -0.0565315991521   0.0683541665349   0.0384513619268
y  =     0.0006274528080   0.0005863229898   0.0001848040392

DJ =  2450010.500
x  =    -0.0500077685742   0.0738917050575   0.0401185066835
y  =     0.0006760300996   0.0005207178864   0.0001485809598

DJ =  2450020.500
x  =    -0.0430362381452   0.0787601500517   0.0414224858221
y  =     0.0007170347454   0.0004525975975   0.0001122080648

DJ =  2450030.500
x  =    -0.0356914954854   0.0829370089715   0.0423628543553 
y  =     0.0007507122167   0.0003824804947   0.0000758900642

DJ =  2450040.500
x  =    -0.0280456595218   0.0864045936164   0.0429410513960 
y  =     0.0007772891303   0.0003108114798   0.0000398004898

DJ =  2450050.500
x  =    -0.0201687110819   0.0891493549543   0.0431601262402 
y  =     0.0007969654703   0.0002379757927   0.0000040889789

DJ =  2450060.500
x  =    -0.0121287880118   0.0911613526180   0.0430245339092 
y  =     0.0008099092464   0.0001643119401  -0.0000311119890

DJ =  2450070.500
x  =    -0.0039925210707   0.0924338483511   0.0425399926980 
y  =     0.0008162533798   0.0000901236760  -0.0000656813027

DJ =  2450080.500
x  =     0.0041746055080   0.0929630123083   0.0417133964504  
y  =     0.0008160940137   0.0000156907545  -0.0000995041242

DJ =  2450090.500
x  =     0.0123078794675   0.0927477347517   0.0405527759854 
y  =     0.0008094894147  -0.0000587208587  -0.0001324670901

DJ =  2450100.500
x  =     0.0203429817690   0.0917895403942   0.0390673084757 
y  =     0.0007964600304  -0.0001328486525  -0.0001644536092

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, 553, 36D, 2013, 10p.
ads arXiv

Author

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

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