Task SSB-43: Added the definition for the central beamlets.

CAL/CalibrationCommon/doc/Holography_Data_Set.md

@@ -39,6 +39,7 @@ Below is the list of defined attributes in this version of HDS:
 - **SAS_ids**:  An array that contains the SAS ids that were created for all observation runs of the holography observation.  *Unit:  [n.a.]*
 - **Target_station_name**:  Name of the LOFAR target station.  *Unit:  [n.a.]*
 - **Target_station_position**:  Position in cartesian coordinates.  *Unit:  [m, m, m]*
+- **Central_beamlets**:  An array that contains the central beamlet number for each frequency.  *Unit:  [n.a.]* 
 - **Source_name**:  Name of the source observed during the holography observation.  *Unit:  [n.a.]*
 - **Source_position**:  Celestial coordinates (RA, DEC, EPOCH) of the source.  *Unit:  [rad, rad, n.a.]*
 - **Observation_time**:  Planned start and end time-stamps of the entire holography observation in MJD.  *Unit:  [s]*
@@ -116,7 +117,7 @@ As described before each cross-correlation table can be accessed by indices, mea
         /Source_position (compound(double, double, string), RA, DEC and Epoch of the source in the sky
         /Target_station_name (string), name of the target station
         /Target_station_position (double[3]), position of the centre of the station in cartesian coordinates
-
+        /Central_beamlets (1-d array, int), beamlet number of the central beamlet, index is the frequency
         /Specified_reference_station (1-d array, string), entries are reference station names [optional]
         /Specified_frequency (1-d array, double), entries are the frequencies of all observations that were specified [optional]
         /Specified_RA_DEC (2-d array, compound[double, double, string[10]]), indices are frequency index, beamlet# [optional]