Institut de Mécanique Céleste et de Calcul des Éphémérides (IMCCE) Solar System Services (astroquery.imcce or astroquery.solarsystem.imcce)

Overview

IMCCE provides a number of Solar System-related services, two of which are currently implemented here:

• SkyBoT: search for and identify Solar System objects that are present in a given area of the sky at a given time

• Miriade: ephemerides service

Use cases for both services are detailed below.

SkyBot - Solar System Body Identification Service

Cone Search

astroquery.imcce.SkybotClass provides an interface to the cone search offered by SkyBoT.

A simple cone search for Solar System objects in a circular field looks like this:

>>> from astroquery.imcce import Skybot
>>> from astropy.coordinates import SkyCoord
>>> from astropy.time import Time
>>> import astropy.units as u
>>> field = SkyCoord(0*u.deg, 0*u.deg)
>>> epoch = Time('2019-05-29 21:42', format='iso')
>>> results = Skybot.cone_search(field, 5*u.arcmin, epoch)
>>> results["Number", "Name", "RA", "DEC", "Type"]
<QTable length=5>
Number    Name             RA                   DEC             Type
                          deg                   deg
int64    str32          float64               float64          str24
------ ---------- -------------------- --------------------- ---------
    --  2012 BO42 0.019139999999999997              -0.01297 MB>Middle
516566  2007 DH36 0.005300833333333333   0.02301111111111111  MB>Inner
659626  2019 SS82         359.99291625 -0.028969444444444443  MB>Inner
    -- 2019 SH196   359.96022083333327 -0.030131944444444444  MB>Inner
163149 2002 CV106    359.9866720833333  -0.06932138888888889  MB>Inner

cone_search produces a QTable object with the properties of all Solar System bodies that are present in the cone at the given epoch.

The required input arguments for cone_search are the center coordinates of the cone, its radius, as well as the epoch of the observation. Field center coordinates coo should be provided as a SkyCoord object, the radius of the cone rad should be provided as a Quantity object. Note that the maximum cone radius is limited to 10 degrees by the SkyBoT service. The epoch of the observation should be provided as Time object.

The following optional parameters are available:

• location: the location of the observer on Earth using the official list of IAU codes. If no location is provided, the center of the Earth is used as location.

• position_error: the maximum positional uncertainty of each body at the given epoch. This option can be used to improve the reliability of associations with detected sources in the field. If not provided, the maximum positional uncertainty of 120 arcsec is used.

• find_planets, find_asteroids, find_comets: these flags control what types of Solar System objects are identified. By default, each of the flags is True.

For diagnostic purposes, the query payload or raw response from the service can be returned instead of the parsed results using the flags get_query_payload and get_raw_response, respectively.

The resulting QTable contains all available information provided by SkyBoT with corresponding units. The following properties are obtained:

Column Name	Definition
'Number'	Target Number (-1 if none provided, int)
'Name'	Target Name (str)
'RA'	Target RA (J2000, deg, float)
'DEC'	Target declination (J2000, deg, float)
'Type'	Target dynamical/physical type (str)
'V'	Target apparent brightness (V-band, mag, float)
'posunc'	Positional uncertainty (arcsec, float)
'centerdist'	Angular distance of target from cone center (arcsec, float)
'RA_rate'	RA rate of motion (arcsec/hr, float)
'DEC_rate'	Declination rate of motion (arcsec/hr, float)
'geodist'	Geocentric distance of target (au, float)
'heliodist'	Heliocentric distance of target (au, float)
'alpha'	Solar phase angle (deg, float)
'elong'	Solar elongation angle (deg, float)
'x'	Target equatorial vector x (au, float)
'y'	Target equatorial vector y (au, float)
'z'	Target equatorial vector z (au, float)
'vx'	Target velocity vector x (au/d, float)
'vy'	Target velocity vector y (au/d, float)
'vz'	Target velocity vector z (au/d, float)
'epoch'	Ephemerides epoch (JD, float)
'_raj2000'	Astrometric J2000 right ascension
'_decj2000'	Astrometric J2000 declination
'externallink'	External link to the target

Miriade - Ephemeris Service

The Miriade service enable the query of Solar System object ephemerides. The most minimalistic get_ephemerides query looks like this:

>>> from astroquery.imcce import Miriade
>>> Miriade.get_ephemerides('Ceres')
<Table length=1>
    epoch           RA             DEC         ...   DEC_rate       rv
      d            deg             deg         ... arcsec / min   km / s
   float64       float64         float64       ...   float64     float64
-------------- ------------ ------------------ ... ------------ ----------
2461053.384583 11.912435375 -3.715397138888889 ...       0.3874   22.45706

This query will return ephemerides for asteroid Ceres, for the current epoch, and for a geocentric location. The query output is formatted as a Table.

Ephemerides Queries

Miriade queries are highly customizable.

Epochs and Location

get_ephemerides is able to query a range of epochs starting at epoch epoch in steps of epoch_step for a total of epoch_nsteps. epoch has to be provided as a Time object, a float (interpreted as Julian Date), or a string (interpreted as iso date YYYY-MM-DD HH-MM-SS). Time steps epoch_step are provided as string that consist of a floating point number followed by a single character: d refers to days, h to hours, m to minutes, s to seconds; e.g., '1.23d' defines a time step of 1.23 days. epoch_nsteps defines the number of steps between the individual ephemerides. By default, epoch_nsteps = 1, which means that only a single epoch epoch will be queried.

Consider the following example, which queries ephemerides for asteroid Pallas over an entire year with a time step of 1 day:

>>> from astroquery.imcce import Miriade
>>> Miriade.get_ephemerides('Pallas', epoch='2019-01-01',
...                         epoch_step='1d', epoch_nsteps=365)
<Table length=365>
  epoch           RA                 DEC         ...   DEC_rate       rv
    d            deg                 deg         ... arcsec / min   km / s
float64       float64             float64       ...   float64     float64
--------- ------------------ ------------------- ... ------------ ----------
2458484.5 200.58658462499997  -5.998279138888889 ...       0.1585  -19.36784
2458485.5 200.92701474999998  -5.933115777777778 ...       0.1673  -19.41378
2458486.5 201.26418570833332  -5.864435027777778 ...       0.1761  -19.45526
2458487.5       201.59803025 -5.7921869444444445 ...       0.1851  -19.49211
2458488.5 201.92848124999998  -5.716322083333334 ...       0.1942  -19.52419
      ...                ...                 ... ...          ...        ...
2458844.5  261.5084273333333   3.596639722222222 ...       0.0295   -2.51070
2458845.5      261.885360875  3.6093634722222223 ...       0.0341   -2.72909
2458846.5         262.261614  3.6239013055555556 ...       0.0386   -2.94674
2458847.5 262.63715837499996           3.6402525 ...       0.0431   -3.16358
2458848.5  263.0119662916667   3.658415888888889 ...       0.0477   -3.37956

The observer location is defined through the location keyword, expecting a string containing the official IAU observatory code, a spacecraft name, or a set of coordinates (see the Miriade manual for details).

Coordinate Types

The Miriade system offers a range of different coordinate types - sets of coordinates and properties that can be queried. In agreement with the Miriade webform query, the coordinate type in get_ephemerides is defined through an integer value. For a full discussion of the different coordinate types we refer to this section of the Miriade website. The keyword coordtype controls which set of coordinates and properties are queried.

Here, we list the different coordinates and properties as returned by get_ephemerides for the different coordinate types available (the item numbers refer to the integer code to be provided to the keyword coordtype to use these sets) :

1. Spherical coordinates (default):

Column Name	Definition
epoch	Ephemerides epoch (JD, float)
RA	Target RA at ephtype (deg, float)
DEC	Target declination at ephtype (deg, float)
delta	Distance from observer (au, float)
V	Apparent visual magnitude (mag, float)
alpha	Solar phase angle (deg)
elong	Solar elongation angle (deg)
RAcosD_rate	Rate of motion in RA * cos(DEC) (arcsec/min, float)
DEC_rate	Rate of motion in DEC (arcsec/min, float)

2. Rectangular coordinates:

Column Name	Definition
epoch	Ephemerides epoch (JD, float)
px	X position state vector (au, float)
py	Y position state vector (au, float)
pz	Z position state vector (au, float)
delta	Distance from observer (au, float)
heldist	Target heliocentric distance (au, float)
alpha	Solar phase angle (deg)
elong	Solar elongation angle (deg)
V	Apparent visual magnitude (mag, float)
vx	X velocity state vector (au/d, float)
vy	Y velocity state vector (au/d, float)
vz	Z velocity state vector (au/d, float)

3. Local coordinates:

Column Name	Definition
epoch	Ephemerides epoch (JD, float)
siderealtime	Local sidereal time (h min s, float)
AZ	Target azimuth (deg, float)
EL	Target elevation (deg, float)
delta	Distance from observer (au, float)
V	Apparent visual magnitude (mag, float)
alpha	Solar phase angle (deg)
elong	Solar elongation angle (deg)
refrac	Refraction (arcsec)

4. Hour angle coordinates:

Column Name	Definition
epoch	Ephemerides epoch (JD, float)
siderealtime	Local sidereal time (h min s, float)
hourangle	Target hour angle (deg, float)
dec	Target declination at ephtype (deg)
delta	Distance from observer (au, float)
V	Apparent visual magnitude (mag, float)
alpha	Solar phase angle (deg)
elong	Solar elongation angle (deg)
airmass	Target airmass (float)

5. Dedicated to observations:

Column Name	Definition
epoch	Ephemerides epoch (JD, float)
siderealtime	Local sidereal time (h min s, float)
RA	Target RA at ephtype (deg, float)
DEC	Target declination at ephtype (deg, float)
hourangle	Target hour angle (deg, float)
AZ	Target azimuth (deg, float)
EL	Target elevation (deg, float)
delta	Distance from observer (au, float)
V	Apparent visual magnitude (mag, float)
alpha	Solar phase angle (deg)
elong	Solar elongation angle (deg)
airmass	Target airmass (float)
RAcosD_rate	Rate of motion in RA * cos(DEC) (arcsec/min, float)
DEC_rate	Rate of motion in DEC (arcsec/min, float)

Other parameters

A range of additional parameters is available in get_ephemerides to modify the query results:

• timescale: switch between UTC (default) and TT

• planetary_theory: use planetary ephemerides other than INPOP

• ephtype: switch between J2000 ephemerides (default) and other coordinates

• refplane: switch from equatorial coordinates (default) to ecliptical coordinates

• elements: switch to MPCORB ephemerides instead of ASTORB

• radial_velocity: provides additional information on target’s radial velocity

See the Miridae documentation for details.

Acknowledgements

This submodule makes use of IMCCE’s SkyBoT VO tool and the IMCCE Miriade service. Additional information on SkyBoT can be obtained from Berthier et al. 2006.

Please consider the following notes from IMCCE:

• If SkyBoT was helpful for your research work, the following acknowledgment would be appreciated: “This research has made use of IMCCE’s SkyBoT VO tool”, or cite the following article 2006ASPC..351..367B.

• If Miriade was helpful for your research work, the following acknowledgment would be appreciated: “This research has made use of IMCCE’s Miriade VO tool”

The development of this submodule was funded through NASA PDART Grant No. 80NSSC18K0987 to the sbpy project.

Reference/API

astroquery.imcce Package

IMCCE

author:

Michael Mommert (mommermiscience@gmail.com)

Classes

MiriadeClass()	A class for querying the IMCCE/Miriade service.
SkybotClass()	A class for querying the IMCCE SkyBoT service.
Conf()	Configuration parameters for astroquery.imcce.