apply_proper_motion

giant.catalogues.utilities:

giant.catalogues.utilities.apply_proper_motion(star_records, new_time, copy=True)

This function adjusts the right ascension and declination of stars to a new time.

The right ascension and declination are updated using the corresponding proper motion of the stars. The formulation used here assumes constant linear velocity as described in section 1.2.8 of “The Hipparcos and Tycho2 Catalogues”. The bearing measurement is converted to a unit vector, which is then updated using vector addition with the delta applied along the vectors of increasing right ascension and increasing declination. This model also allows for consideration of a radial velocity, but that is currently not implemented.

The stars input into this method should be a pandas dataframe with the GIANT format. Specifically, this function requires the dataframe to have columns of ['ra', 'dec', 'ra_proper_motion', 'dec_proper_motion', 'epoch'] with units of degrees, degrees/year, and SI years (since January 1, 1) respectively. The updated bearing can be stored either in a copy of the dataframe, or in-place, depending on the copy key word argument. Either way the resulting dataframe is returned.

The new_time parameter should either be a datetime object, or a float of the modified julian years for the desired time. The copy flag states whether to return a copy of the dataframe with the updates applied (recommended), or to make the updates in place.

Parameters:

• star_records (DataFrame) – a pandas dataframe containing the bearing and proper motion of star records to be updated

• new_time (Real | datetime) – the new epoch to calculate the star positions at expressed as a mjy float or python datetime object

• copy (bool) – An option flag indicating whether to make a copy of star_records before applying proper motion

Returns:

a pandas dataframe containing the star records with bearing values updated to the new epoch

Return type:

DataFrame