Format of FITS files
Each exposure with either arm of the spectrograph generates
2 12k x 6k images, i.e.
140-Mbyte of data.
These are (losslessly) Rice-compressed and stored on the WHT
disk as .fit files with size typically ~ 50 Mbytes.
Each .fit file
includes: the two compressed images from CCD1 and CCD2
(same nomenclature on both arms); the (uncompressed) FITS keywords;
and three FITS tables.
The three FITS tables log respectively
the autoguider residuals, the observing conditions, and
information about the individual fibres.
Typically, exposures are made simultaneously on the blue and red arms,
generating two .fit files, i.e. ~ 100 Mbytes.
During survey observing, a typical night might generate three science exposures
per arm per hour, i.e. ~ 3 Gbytes per night.
The accompanying night-time and day-time calibration exposures
will typically generate much more.
The primary FITS header for an exposure on one arm of the spectrograph
lists ~ 500 keywords and associated values.
Additional headers accompany each of the two CCD images. On both
arms of the spectrograph, the two CCDs
comprising the 2-CCD mosaic are referred to as CCD1 and CCD2.
By way of example, the primary FITS header accompanying
LIFU blue-arm arc exposure
r3070825.fit (taken on the night starting 5 August 2024)
is listed on the two links below:
- Primary FITS header,
keywords ordered as in file
- Primary FITS header, keywords in alphabetic order
Primary-header keywords
likely to be of interest to readers of this page are listed below,
sorted by topic.
Parentheses after a keyword name enclose the
value of the keyword, for r3070825.fit.
- General:
-
OBSERVAT (LAPALMA),
OBSERVER (Lilian Dominguez),
ORIGIN (ING La Palma), TELESCOP (WHT),
- Date, time:
- CONFMJD (60528.022390),
DATE-OBS (2024-08-06), JD (2460528.51202);
ST (20:05:55.56), UT (00:17:19.422), UTOBS
- Target, OB:
- CASUID (2573), CAT-NAME (WV_OB_14278),
CCNAMEn, CHAINED (F),
CHAINID (12857), LNKGROUP (link_2024A2_005), NSALSA (0),
OBCLASS (science), OBID (14278), OBJECT (ARC), OBPRIORI (1.0),
OBSTART (60528.0 days, MJD), OBSGROUP, OBSTEMP (NBCEB),
OBSTYPE (ARC), OBTITLE, SALSA_I (0)
PROGTEMP (61331), TRIMESTE (2024A)
- Sky coordinates, airmass:
- AIRMASS (1.55), AMEND (1.54), AMSTART (1.56),
CAT-RA, CAT-DEC, CAT-EPOC (2000.00), CAT-EQUI (J2000.00),
FLDRA (344.42830 deg), FLDDEC (0.043163 deg),
PM-RA (0.0 sec/year), PM-DEC (0.0 arcsec/year), RA, DEC,
RATRACK (0.0 arcsec/sec),
DECTRACK (0.0 arcsec/sec)
- Telescope and dome:
- ADC1 (-33.65 deg), ADC2 (33.63 deg), ADCINPOS (T), ADCCORR (T),
DAZSTART (116.7 deg), M1PETALS (0.1), MNTPASTA (47.114 deg),
ROTSKYPA (355.748 deg),
ROTTRACK (T), TELSTAT (TRACKING), VIGNETTE (F)
- Focal-plane geometry:
- FLDISTN1 (203.008987), FLDISTN3 (3.031431), FLDISTN5 (-0.080496),
FLDISTN7 (0.0),
PLATESCA (4.930531 deg/m = 17.74 arcsec/mm),
PLATEX0, PLATEY0, PLATER0, SKYCMX (226.3 mm),
SKYCMY (-514.9 mm)
- Focus, and telescope temperature:
-
ACTELFOC (-0.30 mm),
FOCUSALT (0.0 mm), FOCUSFLT (0.0 mm),
FOCUS (0.0m), FOCUSTMP (-0.995 mm),
FTSINPOS (T), FTSTILT (-0.031 degC),
TELFOCUS (0.69 mm), TEMPTUBE (18.48 degC),
TILTCORR (T)
- Configuration:
- FPMODE (LIFU), FLORIENT (-4.252 deg), IFUPAn (-9999),
INFILE, OBSMODE (LIFU),
OBSTEMPB, OBSTEMPE, OUTFILE, PLATE (LIFU),
- Autoguiding:
-
AGACQT (7 sec), AGBUNDLE (LIFU),
AGDRXBn, AGDRYBn, AGDRXEn, AGDRYEn,
AGEXPMGn, AGGUIT (1 sec),
AGMAGNIn, AGMAGOFF (28.75), AGMRMSn,
AGSIGBn, AGSIGEn,
AGSNRTH (3.0), AGSTAT (0),
AGTRANn, AGTRMSn,
AGXn, AGYn,
AGXSEEn, AGYSEEn, AGXSRMSn, AGYSRMSn,
AUTOMODE (UNLOCKED), AUTOX, AUTOY (0.0, 0.0),
LFUGS* (~ 20 keywords), LFUGSCLS (STAR), LFUGSMGG (g = 17.01), LFUGSRA/DEC
- Spectrograph:
- CAMERA (WEAVEBLUE),
CAMTEMP (138.0 degC), CENWAVE (0 nm), DISPERSI (0.0 nm/mm),
FOCUSMTA (7065 micron), FOCUSMTB (7265 micron),
FSTATION (WEAVE), HART (BOTH_OPEN),
INSTRUME (WEAVEBLUE), LINEMM (3056 /mm),
MAITSLIT (F), MODE (HIGHRES),
SLITEX (LIFU), SLITIL (LIFU),
TILT (0), TIP (-9999), VPH (HighRes2)
- Detector:
- BIASSECn, BUNIT (adu),
CCDCHIP (CCDWEAVEBLUE1),
CCDNAME (CCDWEAVEBLUE1),
CCDTYPE (E2VCCD231-C6),
CCDXPIXE and CCDYPIXE (15 mic), CCDSPEED (FAST), CCDXBIN (1), CCDYBIN (1),
CHIPNAME (CCDWEAVEBLUE1),
DETECTOR (WVBLUE), EXPOSED = EXPTIME (180.000), GAIN (1.3),
READNOIS (3.0 e-), TRIMSECn, ZNAXIS1 (6276), ZNAXIS2 (6192)
- Calibration:
- ARCSRC (ThArCr), CALFILTA (WCALU_clear1), CALFILTB (EMPTY),
FLATSRC (NONE), FLILUn (0)
- Data:
- BSCALE (1.0), BUNIT (adu), BZERO (32768),
CHECKSUM, DASCHAN 1), RUN (3070825), RUNSET (1:1:3070825),
WINNO (1), ZCMPTYPE (RICE_1)
- Comments:
- Observing conditions:
-
AGTRAN (0.39),
AGXSEE (0.9 arcsec), AGYSEE (0.7 arcsec),
GHRILTMB (1097723060 degC),
GHRILTME (1097723060 degC),
LOCHUMB (19%), LOCHUME (18%),
LOCPRESB 776 (mbar), LOCPRESE (776 mbar),
LOCTEMPB (18.6 degC), LOCTEMPE (18.7 degC),
MIRTEMPB (19 degC), MIRTEMPE (20 degC),
SEEINGB (0.5 arcsec), SEEINGE (0.8 arcsec),
SKYBRTEL (20.0), SKBRTELB (20.0), SKBRTELE (20.0),
SKYBRZEN (21.4), SKBRZENB (21.4), SKBRZENE (21.4),
TELHUMB (17%), TELHUME (17%),
TELTEMPB (19 degC), TELTEMPE (19 degC),
WINDSPB (18 km/h), WINDSPE (11 km/h),
WINDDIRB (8 deg), WINDDIRE (7 deg)
-
Software version numbers:
- CVER (3.4.5),
DATAMVER (8.00), DITHVER
For readability, a few of the numbers have been converted (above) to
more convenient units,
and numbers given to many decimal places may have been rounded.
Some of the parameters listed above will not be relevant to LIFU observations.
For some parameters (e.g. dome azimuth) there exist keywords for both
start-of-exposure (suffix START or B)
and end-of-exposure (suffix END or E) values, and for some (e.g. airmass)
for values representative of the whole exposure as well.
'n' at the end of a keyword name quoted above
indicates that there are several similar keywords
with n varying 1, 2, 3 etc. (e.g. over the 4 quadrants of the CCD, or over
the 8 guide stars used in MOS mode).
Chris Benn, Lilian Domínguez, Cecilia Fariña
Back to LIFU home page
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