LissajousDither

class marxs.missions.chandra.LissajousDither(**kwargs)

Bases: FixedPointing

Lissajous dither pattern with adjustable parameters.

Parameters:

DitherAmpastropy.units.Quantity

(pitch, yaw, roll) dither amplitude

DitherPeriodastropy.units.Quantity

(pitch, yaw, roll) dither Period in sec

DitherPhaseastropy.units.Quantity

(pitch, yaw, roll) dither phase at time = 0 in radian

Define a new MARXS element.

Methods Summary

dither(time)	Calculate the dither offset relative to pointing direction.
photons_dir(coos, time)	Calculate direction on photons in homogeneous coordinates.
pointing(time)	Calculate the pointing direction for a set of times There are the steps to convert the dither (which are offsets) to the total pointing direction with the roll properly taken care of.
write_asol(photons, asolfile[, timestep])	Write an aspect solution (asol) file

Methods Documentation

dither(time)

Calculate the dither offset relative to pointing direction.

Parameters:

timenp.array

Time when the dither motion should be calculated

Returns:

deltanp.array of shape (N, 3)

dither motion offset in pitch, yaw, roll for N times in rad

photons_dir(coos, time)

Calculate direction on photons in homogeneous coordinates.

Parameters:

coosastropy.coordiantes.SkyCoord

Origin of each photon on the sky

timenp.array

Time for each photons in sec

Returns:

photons_dirnp.array of shape (n, 4)

Homogeneous direction vector for each photon

pointing(time)

Calculate the pointing direction for a set of times There are the steps to convert the dither (which are offsets) to the total pointing direction with the roll properly taken care of. (See marxasp.c in the marx code for more details.) 1. Convert ra/dec offsets to absolute pointing. 2. Roll resulting vector about nominal pointing 3. Convert result to ra/dec.

Parameters:

timenp.array

Array of times

Returns:

pointing(n, 3) np.array

Ra, Dec, roll values in radian for the pointing direction at time t.

write_asol(photons, asolfile, timestep=0.256)

Write an aspect solution (asol) file

Chandra analysis scripts often require an aspect solution, which is essientially a list of pointing directions in the dither pattern vs. time. This method write such a list to a file.

Parameters:

photonsastropy.table.Table or astropy.table.Row

Table with photon properties. Some meta data from the header of this table is required (e.g. the length of the observation).

asolfilestring

Path and file name where the asol file is saved.

timestampfloat

Time step between entries in the asol file in seconds.