The IDL programme package PARALLEL has been written to investigate the capability of time-parallel observations in main direction during Bragg observations.

The problem is that during Bragg observations one SODART telescope looks in a different direction (hereafter called Bragg direction) as the second telescope and the other instruments (called main direction). The question is whether during the long Bragg observations any useful observation in main direction can be done.

Two main programmes exist:

1) MAIN_P_BRAGG:

The Bragg source is given. Which sources can be observed in main direction time-parallel to Bragg observations ?

The Bragg source will be observed with a certain energy (the central energy during a Bragg panel scan). This energy determines (through the Bragg reflection condition) the Bragg angle, which is allowed to vary between 22 and 75 deg. The angular distance between the sources in Bragg and main directions is just the double Bragg angle.

The vector in main direction can be rotated about the vector in Bragg direction, and gives a circle on the sky. This circle together with the field of view (FOV) of a certain instrument gives a stripe on the sky, where sources are observable by this instrument, in principle.

Since the field of view of the main instruments differ substantially, a given source close to main direction may be observable by one instrument and not by another one. For example, the probability to find a suitable source for the wide-field instruments MART (FOV = 6x6 deg^2) or FUVITA (FOV = 72 arcmin diameter) is much higher than for JET-X (FOV = 20 arcmin diameter). For the second SODART telescope the wide-field detectors HEPC (FOV = 60 arcmin) or KFRD (FOV = 50 arcmin) should be used rather than LEPC (FOV = 30 arcmin) or SIXA (FOV = 25 arcmin). The polarimeter SXRP is coupled with the same SODART telescope as the Bragg spectrometer, and can not be active during Bragg observations.

Additionally, the Sun position must be taken into account. The conditions when an observations is allowed are given in the procedure PARAMETERS. These conditions reduce the accepted region to a relatively small partition of the stripe. Vice versa, a given position in the stripe can be observed only in a certain time period of the year.

This programme investigates for a given Bragg source position the possibility of parallel observations in main direction. Constraints by Sun positions are taken into account. It calculates for a given day in the year the allowed region on the sky or, vice versa, for a given source in main direction the allowed time period in the year and tells you which instruments can observe this source.

2) BRAGG_P_MAIN:

Here, a main source is given. Is any of the 11 preferred Bragg sources observable time-parallel to main observations?

The programme checks whether the main source direction is compatible with the coordinates and line energies of a number of bright X-ray sources (see file brsrcF.txt) with X-ray lines observed by ASCA. Constraints by Sun positions are NOT taken into account. If you find a positive result, the observability of these sources must be cross-checked by programme MAIN_P_BRAGG.

The structure of calls and data fluxes is shown in the figure: struct_par.gif.

written by Hans Wiebicke, October 2000