Header Regulation

(1) Needed Part

$\bullet$ The keywords for standard FITS

The keywords below must appear in all FITS files and have a fixed format.

SIMPLE	: ' T' if the file subjects to the FITS regulation
BITPIX	: number of bits and type of the data
NAXIS	: number of dimensions of the data
NAXIS1	: number of pixels in x-axis
NAXIS2	: number of pixels in y-axis

$\bullet$ Basic information for NoRH data

The keywords bellow should appear in all FITS files related to NoRH data.

$\circ$ Information on observation time

STARTFRM	: the first IDs of used frames
ENDFRM	: the last IDs of used frames
JST-STRT	: the start time (JST) of integration for STARTFRM
JST-END	: the end time (JST) of integration for ENDFRM
JST-TIME	: exact middle time (JST) between the JST-STRT and JST-END
JST-DATE	: the date (JST) for JST-STRT. The format is yyyy-mm-dd
STRT-OBS	: UT for JST-STRT
END-OBS	: UT for JST-END
TIME-OBS	: UT for JST-TIME
DATE-OBS	: UT for JST-DATE

$\circ$ Information of data contents

OBJECT	: fixed to sun
TELESCOP	: fixed to radioheliograph
ORIGIN	: fixed to nobeyama radio obs
POLARIZ	: choose from rcp, lcp, r+l, r-l, l-r, r|l, (r-l)/(r+l), unknown
ATT-10DB	: choose from 00dB, 10dB
OBS-MODE	: choose from fix, alt
OBS-FREQ	: choose from 17GHz, 34GHz
FRM-STAT	: choose from 1-sec obs, event, calib
DATA-TYP	: brief description of data type, e.g. cleaned_map

$\circ$ Information of FITS header version

FITS header version. Now the newest is ver 2.0

HDRIDENT

: 'HeliogFITS 2.0'

(2) Ephemeris

The keywords bellow should appear in NoRH image files. These are necessary for obtaining the heliographic coordinates or the beam patterns. They are not only the parameters determined from the date and time, but also those local to the Nobeyama site.

SOLR	: apparent radius of the solar disk
SOLP	: polar angle of the sun
SOLB	: the heliographic latitude of the solar disk center
DEC	: declination of the Sun at Nobeyama
HOURA	: hour angle of the Sun at Nobeyama
AZIMUTH	: azimuthal angle of the Sun at Nobeyama
ALTITUDE	: altitude of the Sun at Nobeyama
ZANGLE	: zenith angle of the Sun at Nobeyama
PMAT1/2/3/4	: transformation matrics between the antenna coordinates (on the geosphere:
	antenna north is up) and the solar-disk coordinates (on the celestial sphere:
	solar-north is up)

(3) Image coordinates

The keywords bellow should appear in NoRH image files in order to co-align them with images obtained at other frequencies. They are basically regulated by the FITS standard.

CTYPE1 / CTYPE2:

type of coordinate axis. Usually ' solar-west' and ' solar-north', respectively. The origin is at the solar disk center.

CDELT1 / CDELT2: size of pixel in arcsec

CRVAL1/CRVAL2/CRPIX1/CRPIX2:

The coordinate value of center of the CPIX1th pixel equals to the CRVAL1 in coordinate CTYPE1. That's same for '...2'. The NoRH standard is

CRVAL1 = 0.00 (fixed)
CRVAL2 = 0.00 (fixed)
CRPIX1 = 'x' of the pixel for the solar disk center in the image
CRPIX1 = 'y' of the pixel for the solar disk center in the image

In case of partial images (ipx), CRVAL1 and CRVAL2 may be larger than the size of the image or may have negative values.

Note that, in the FITS regulation, the center of the pixel is the origin of the position. Be careful when you try to coalign with the image described with a coordinate which has its origin at the edge of the pixel. The distance (in arcsec) of the image center from the Solar disk center is given as
x-offset = ( NAXIS1/2+0.5- CRPIX1)* CDELT1+ CRVAL1
y-offset = ( NAXIS2/2+0.5- CRPIX2)* CDELT2+ CRVAL2

(4) Parameters for each synthesis program

Parameters for synthesis should be given in order to make it possible to re-synthesize with these. Although they may be diffferent from one program to another, some keywords are common. They may be input parameters for synthesis
$\circ$ what program is used for synthesis,
$\circ$ parameters for calibration (e.g. used frame ID),
$\circ$ parameters for synthesis itself, (CLEAN parameters etc.)
and output on synthesis
$\circ$ value of an indicator variable for CLEAN results.
The following keywords are recommended to be included at least.

PROGNAME	: The format is arbitrary
NFRCAL	: number of frames used for calibration
CRITER	: CLEAN criterion
SOLR-FAC	: ratio of the radio to optical solar disk radius
MBEAMC	: main beam correction
NCOMPO	: number of CLEAN conponents
DDOFF1	: x-offset of the center of the dirty solar disk
DDOFF2	: y-offset of the center of the dirty solar disk
DSKBR	: brightness of the dirty solar disk
BUNIT	: unit of the intensity of the image, usually brightness temperature in Kelvin (K).

(5) Others

Other keywords could be added.