compute_va_effects

stcal.velocity_aberration.compute_va_effects(velocity_x, velocity_y, velocity_z, ra, dec)

Compute velocity aberration effects.

Computes constant scale factor due to velocity aberration as well as corrected RA and DEC values.

Parameters:

• velocity_x (float) – The components of the velocity of JWST, in km / s with respect to the Sun. These are celestial coordinates, with x toward the vernal equinox, y toward right ascension 90 degrees and declination 0, z toward the north celestial pole.

• velocity_y (float) – The components of the velocity of JWST, in km / s with respect to the Sun. These are celestial coordinates, with x toward the vernal equinox, y toward right ascension 90 degrees and declination 0, z toward the north celestial pole.

• velocity_z (float) – The components of the velocity of JWST, in km / s with respect to the Sun. These are celestial coordinates, with x toward the vernal equinox, y toward right ascension 90 degrees and declination 0, z toward the north celestial pole.

• ra (float) – The right ascension and declination of the target (or some other point, such as the center of a detector) in the barycentric coordinate system. The equator and equinox should be the same as the coordinate system for the velocity.

• dec (float) – The right ascension and declination of the target (or some other point, such as the center of a detector) in the barycentric coordinate system. The equator and equinox should be the same as the coordinate system for the velocity.

Returns:

• scale_factor (float) – Multiply the nominal image scale (e.g., in degrees per pixel) by this value to obtain the image scale corrected for the “aberration of starlight” due to the velocity of JWST with respect to the Sun.

• apparent_ra (float) – Apparent star position in the moving telescope frame.

• apparent_dec (float) – Apparent star position in the moving telescope frame.