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Дата изменения: Fri Jan 10 22:40:40 2003
Дата индексирования: Sat Dec 22 09:04:48 2007
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XMM-Newton Science Analysis System


esky2det (esky2det-1.5.1) [xmmsas_20030110_1802-5.4.1]

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Task requirements.

The task clearly needs to know the direction in space of the focal axis of the relevant instrument at the time of the observation of interest. The SAS provides a confusing variety of routes to obtain this and the SAS developer who wants to provide the user with an interface which combines simplicity with flexibility has something of an uphill job. In esky2det I have chosen to break the necessary information up into 3 pieces: the name of the instrument, the date-time of the observation and the spacecraft pointing direction (attitude) at this time. The task processes this as follows: the instrument identification and the observation date-time are used together to calculate (from values stored in the CCF) the instrument boresight correction at the time of the observation; this correction is then applied to the spacecraft pointing.

There are three ways to pass the instrument and date-time to esky2det, governed by the parameter calinfostyle:

1. calinfostyle = `srcset': the information is sought from INSTRUME and DATE-OBS keywords in the header of the source list specified by inset. These should be found in the primary headers of all XMM PPS (Pipeline Product Set) data sets. Note that this style only works if datastyle = `set'; if datastyle = `user', the user presumably has no source list dataset to provide.

2. calinfostyle = `otherset': the information is sought from INSTRUME and DATE-OBS keywords in the header of the data set specified by calinfoset.

3. calinfostyle = `user': the information must be provided by the user via the parameters instrument and datetime.

The situation as regards the spacecraft attitude information is very similar: this trio of angles may be found in the headers of PPS product datasets as the keywords RA_PNT, DEC_PNT and PA_PNT. The style is controlled via the parameter attinfostyle and if this equals `user' the angles can be supplied by the user via the parameters attra, attdec and attapos.

A fourth way exists to pass the spacecraft attitude to the task. If attinfostyle is set to `atthkset' then the task looks for the name of the attitude history file output by the task atthkgen. This file is normally part of the XMM PPS. There are numerous keywords in the header of this file recording either means or medians of attitude history values obtained from a variety of sources. Facility is provided in esky2det via the parameter attstyle to access either the AAHF* set of keywords (attstyle = `mean') or the MAHF* set (attstyle = `median').

In order to be able to apply the correct boresight correction, as well as to have access to the instrument specifications, the task requires access to the CCF components relevant to the dates of observation and analysis. This is achieved in the usual way by constructing a cif file with cifbuild and pointing to it with the environment variable SAS_CCF.