This page presents the description of the parameters and ephemeris in the DynAstVO database. This service provides orbital elements of Near-Earth objects. The database is available on the VESPA datacenter.
The database provides for each asteroid, orbital elements and their uncertainty, the state-vector, information about the observations, Minimum Orbital Intersection distance (MOID), and the covariance matrix of the system, as well as general information on their magnitude. Osculating orbital elements are given as elliptic and cartesian coordinates, in the ecliptic J2000 reference frame. A link gives also the ephemeris file (in bsp format) usable with the SPICE library (NASA/JPL).
The database is daily updated in an automatic process for objects with new observations. The observations comes from the Minor Planet Center.
The orbital elements are computed based on a fit to the astrometric data available at IAU/MPC, with outlier rejection and weighting according to Farnocchia et al. (2015). Osculating orbital elements are given as elliptic and cartesian coordinates, in ecliptic J2000 reference frame. Computation are done by considering 8 perturbing planets, and 4 biggest asteroids (Ceres, Vespa, Pallas, Hygiea), relativistic effects, and TDB time scale, with masses and positions taken from the INPOP13c solution. Numerical integration is performed with an Radau adaptive-step integrator.
The magnitude is given with two parameters: absolute magnitude H and the slope parameter G. H is determined by fitting to observations whereas G is fixed and taken from MPC.
For every object, the orbital elements (semi major axis, eccentricity, inclination, longitude of ascending node, argument of perihelion and mean anomaly) are provided for two different epochs: one is specific to the object and corresponds approximately to the middle of the observational period, the other one (with the suffix 'standard') is common to every object and corresponds to the 1st of July of the current year.
A short description of DynAstVO is also given in Desmars et al. (2017)
| column index | type | unit | description |
| target_name | char | Name of object (number or designation) | |
| creation_date | char | Date of first entry of this granule | |
| modification_date | char | Date of last modification | |
| release_date | char | Start of public access period | |
| access_url | char | URL of the ephemeris bsp file | |
| publisher | char | A short string identifying the entity running the data service used. | |
| bib_reference | char | Bibliographic reference of the service | |
| semi_major_axis | double | au | Semi major axis at epoch |
| eccentricity | double | Eccentricity at epoch | |
| inclination | float | deg | Inclination at epoch, referred to Ecliptic J2000 |
| long_asc | float | deg | Longitude of ascending node at epoch, J2000.0 |
| arg_perihel | float | deg | Argument of Perihelion at epoch, J2000.0 |
| mean_anomaly | float | deg | Mean anomaly at epoch |
| epoch | double | Epoch of the osculating elements | |
| semi_major_axis_error | float | au | Semimajor axis error |
| eccentricity_error | float | Eccentricity error | |
| inclination_error | float | deg | Inclination error |
| long_asc_error | float | deg | Longitude of ascending node error |
| arg_perihel_error | float | deg | Argument of Perihelion error |
| mean_anomaly_error | float | deg | Mean anomaly error |
| moid | float | au | Minimum Orbital Intersection Distance with Earth orbit |
| spu | float | arcsec | Sky-plane uncertainty at epoch |
| magnitude | float | Absolute magnitude of the object from HG magnitude system | |
| slope | float | G slope parameter from HG magnitude system | |
| id_mpc | int | MPC number of the object (if object is numbered) | |
| id_spk | int | NAIF integer ID code (used for bsp file) | |
| id_gaia | long | Gaia integer ID code | |
| alt_target_name | char | Alternative target name (number, name, designations) | |
| covar_mat | char | Coefficient of covariance matrix in json format (Note that only the triangular matrix is provided with 21 coefficients c1,1,c1,2,...,c1,6, c2,2, ..., c2,6, ...,c6,6). | |
| cartesian_x | double | au | State-vector x position component |
| cartesian_y | double | au | State-vector y position component |
| cartesian_z | double | au | State-vector z position component |
| cartesian_vx | double | au/d | State-vector vx velocity component |
| cartesian_vy | double | au/d | State-vector vy velocity component |
| cartesian_vz | double | au/d | State-vector vz velocity component |
| pha | char | Potentially hazardous asteroid | |
| dynamical_class | char | Dynamic class of object (Apollo, Aten, Amor, Atira) | |
| dynamical_type | char | Class of the object | |
| fit_nb_obs_used | int | Number of observations used in the fit | |
| fit_nb_obs_rejected | int | Number of observations rejected in the fit | |
| fit_nb_obs_ranging | int | Number of radar ranging measurement | |
| fit_nb_obs_doppler | int | Number of radar doppler measurement | |
| fit_jd_initial | double | Julian date of first observation used in the fit | |
| fit_jd_final | double | Julian date of last observation used in the fit | |
| lastdou | char | Last Daily Orbit Update used for orbit determination | |
| rms_obs | double | arcsec | Root mean square of observations |
| semi_major_axis_standard | double | au | Semi major axis at standard epoch |
| eccentricity_standard | double | Eccentricity at standard epoch | |
| inclination_standard | float | deg | Inclination at standard epoch |
| long_asc_standard | float | deg | Longitude of ascending node (J2000.0) at standard epoch |
| arg_perihel_standard | float | deg | Argument of perihelion (J2000.0) at standard epoch |
| mean_anomaly_standard | float | deg | Mean anomaly at standard epoch |
| epoch_standard | double | Standard epoch of orbital elements (identical for every object, first of July of the current year) | |
| cartesian_x_standard | double | au | State-vector x position component at standard epoch |
| cartesian_y_standard | double | au | State-vector y position component at standard epoch |
| cartesian_z_standard | double | au | State-vector z position component at standard epoch |
| cartesian_vx_standard | double | au/d | State-vector vx velocity component at standard epoch |
| cartesian_vy_standard | double | au/d | State-vector vy velocity component at standard epoch |
| cartesian_vz_standard | double | au/d | State-vector vz velocity component at standard epoch |
Other parameters visible on VESPA and not listed above are used for VESPA purpose only.
Credits:
Creators: J. Desmars
Contributors: J. Desmars, W. Thuillot, D. Hestroffer, P. David, P. Le Sidaner, PADC
Publisher: Paris Astronomical Data Centre - IMCCE
Last update: 2019.02.19