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ORFEUS II FITS Data Format
Contents
4. Format of data
The Echelle images as well as the extracted spectra are available in FITS format. The FITS headers, keywords and formats used are described in the following chapters.A) Images
Echelle images are stored as 1024 x 512 x 16 bit data. This is a sample header of an Echelle image data file:
SIMPLE = T / BITPIX = 16 / NAXIS = 2 / NAXIS1 = 1024 / NAXIS2 = 512 / BUNIT = 'counts/pixel' / unit of pixel values TELESCOP= 'ORFEUS-SPAS II' / mission/satellite name INSTRUME= 'Tuebingen UV Echelle Spectrometer (TUES)' / instrument name DATE = '2000-10-25T11:55:05' / file creation date (YYYY-MM-DDThh:mm:ss UTC) ORIGIN = 'IAAT - Institute for Astronomy and Astrophysics Tuebingen' OBS_CODE= 'TUES2276_2' / observation reference number ORFEUSID= '2276 ' / specific ORFEUS target ID number OBS_NO = '2 ' / Echelle observation number OBJECT = 'HD 93521' / target name RA_OBJ = 162.09750 /[deg] right ascension of object DEC_OBJ = 37.57028 /[deg] declination of object EQUINOX = 2000.0 / equinox of coordinate system DATE-OBS= '1996-11-28T04:56:05' / obs start time (YYY-MM-DDThh:mm:ss UTC) DATE-END= '1996-11-28T05:14:05' / obs stop time (YYY-MM-DDThh:mm:ss UTC) CLOCKCOR= 'NO ' / UTC not guaranteed TIMEREF = 'LOCAL ' / Time frame of satellite TASSIGN = 'SATELLITE' / Times assigned on satellite TIMESYS = 'MJD ' / Modified Julian Date MJDREF = 40000 / [days] MJD of reference date TSTART = 899873765 / [s] from MJDREF TSTOP = 899874845 / [s] from MJDREF TIERRABS= 1 / [s] precision of quoted times EXPTIME = 1080 / [s] exposure time FILENAME= 'tues2276_2.fits' / name of this file COMMENT COMMENT --- Original ORFEUS Header --- COMMENT Description of keywords (not all of them used): COMMENT TARGET: ORFEUS ID / object name COMMENT RA/DEC: epoch 2000 coordinates COMMENT BEOBNR: number of observation COMMENT INTANF: obs.start: day of 1996 / hh:mm:ss COMMENT INTEND: obs. end : day of 1996 / hh:mm:ss COMMENT INTTIM: integration time in seconds COMMENT XTRACT: extraction parameters COMMENT ORBITV: orbital velocity towards object [km/s] COMMENT VHELIO: heliocentric velocity towards object [km/s] COMMENT BLAZEO: blaze correction parameters: offset [mm] COMMENT BLAZEW: blaze correction parameters: width COMMENT CNTRAT: count rates (maximum, actual, image) COMMENT V_KORR: additional radial velocity correction [km/s] COMMENT CORRCT: image processing flags COMMENT FACTOR: scaling factor of image COMMENT UPDATE: last update of ORFEUS Echelle image header COMMENT --- start of ORFEUS header --- HISTORY TARGET: 2276 / HD 93521 HISTORY RA/DEC: 10 48 23.40 / +37 34 13.00 HISTORY BEOBNR: 2 HISTORY INTANF: GMT 333:04:56:05 HISTORY INTEND: GMT 333/05:14:05 HISTORY INTTIM: 1080.00 HISTORY COMMNT: HISTORY XTRACT: 40, 61, 1, 0 HISTORY ORBITV: 0.88, 1.77, 2.63, 3.46, 4.23, 4.93, 5.56, 6.11, 6.56, 6.91, 7.1 HISTORY VHELIO: -26.46 HISTORY BLAZEO: 5.00, 5.10, 5.20, 5.30, 5.40, 5.50, 5.60, 5.70 HISTORY BLAZEW: 0.73, 0.73, 0.73, 0.73, 0.73, 0.73, 0.75, 0.75 HISTORY CNTRAT: 9500.0, 6227.4, 5169.1 HISTORY HISTORY HISTORY HISTORY HISTORY HISTORY HISTORY UPDATE: Thu Mar 5 10:14:25 1998 COMMENT --- end of ORFEUS header --- HISTORY Version of ORFEUS-ECHELLE-FITS routines: HISTORY 1.3, 2000-10-25, Juergen Barnstedt HISTORY For description of ORFEUS II Echelle spectrometer performance see: HISTORY J.Barnstedt, N.Kappelmann, I.Appenzeller, et al., HISTORY Astron. Astrophys. Suppl. Ser. 134, 561-567 (1999) HISTORY (astro-ph/0006295) END
Description of Echelle image keywords:
- SIMPLE, BITPIX, NAXIS, NAXISn, BUNIT, TELESCOP, INSTRUME, DATE, ORIGIN :
- These are standard keywords used in accordance with the
Definition of the Flexible Image Transport System (FITS).
- OBS_CODE :
- This keyword is used as a unique reference to this specific observation.
It is composed of the instrument name (TUES = Tuebingen Ultraviolet Echelle
Spectrometer), the ORFEUS target ID (4 digits), underline character ("_"),
and the observation number for this target.
- ORFEUSID :
- The ORFEUS target ID, see List of all ORFEUS Echelle targets.
- OBS_NO :
- The ORFEUS Echelle observation number for this target. Usually a single number,
but in some cases composed from two numbers, separated by an underline character.
The second number is the number of the pointing during this observation:
Several pointings during a single observation were carried out sometimes
to improve the alignment of the telescope ("grid search"). This resulted
partially in very short integrations.
- OBJECT :
- The name of the target.
- RA_OBJ, DEC_OBJ, EQUINOX :
- Right ascension and declination of the object in decimal degrees,
and equinox (2000.0) of the coordinates.
- DATE-OBS, DATE-END :
- Start date and time and stop date and time of the observation
(format yyy-mm-ddThh:mm:ss), Universal Time.
- CLOCKCOR :
- NO = UTC not guaranteed.
- TIMEREF :
- LOCAL = Time frame of satellite.
- TASSIGN :
- SATELLITE = Times assigned on satellite.
- MJDREF, TSTART, TSTOP :
- MJD (Modified Julian Date) of reference date (40000 days),
start and stop time of observation in seconds from MJD.
- TIERRABS :
- Precision of quoted times (1 s).
- EXPTIME :
- Exposure time in seconds.
- FILENAME :
- Name of this file.
The "COMMENT" lines following these keywords describe the original ORFEUS keywords used with the data supplied to the guest observers. The original ORFEUS header follows as "HISTORY" entries. The original ORFEUS keywords are described here in detail:
- TARGET:
- ORFEUS ID / name of the target.
- RA/DEC:
- Equinox 2000 coordinates, right ascension and declination.
Format: hh mm ss.ss / dd mm ss.ss
- BEOBNR:
- Number of observation (see OBS_NO).
- INTANF:
- Start of observation: day of 1996 / hh:mm:ss
- INTEND:
- End of observation: day of 1996 / hh:mm:ss
- INTTIM:
- Integration time in seconds (see EXPTIME).
- XTRACT:
- Extraction parameters: first and last extracted Echelle order
(in most cases all orders: 40 to 61),
flag for automatic centering of Echelle orders (im most cases 1),
flag for 45 degree tilted extraction (in most cases 0).
- ORBITV:
- Orbital radial velocity component of the satellite towards the object
in km/s: 11 equidistant values for the given observation period.
- VHELIO:
- Heliocentric radial velocity component towards object in km/s.
- BLAZEO:
- Offset of blaze function from center of detector [mm], given
for the Echelle orders 40, 43, 46, 49, 52, 55, 58 and 61.
The values for the orders in between are linearly interpolated.
- BLAZEW:
- Relative width of blaze function, given for the same Echelle
orders as the BLAZEO values.
- CNTRAT:
- Three count rate values in counts/s:
- Maximum count rate of lower electronic threshold, taken from this or any other observation of this object.
- Actual average count rate of lower electronic threshold.
- Registered count rate in this Echelle image.
- V_KORR:
- Additional radial velocity correction in km/s (in most cases 0.0).
- CORRCT:
- Used only in rebinned images, not available in orignal
Echelle observations.
5 flags indicating the corrections applied to this image
for rebinning:
- Averaging of pixel 511/512.
- Observing block wavelength correction.
- Orbital radial velocity correction.
- Heliocentric radial velocity correction.
- Additional radial velocity correction.
- FACTOR:
- Used only in rebinned images, not available in orignal
Echelle observations.
Scaling factor of image, needed to minimize rounding errors
during rebinning of the image.
- UPDATE:
- Time and date of last update of ORFEUS Echelle image header.
B) Extracted data of individual echelle orders
The Echelle spectra are extracted order by order, there are overlap regions between adjacent orders. The extracted orders are stored in FITS format as binary table extensions. The spectra are available as each order in one file or as all orders contained in one file. The primary header contains all information concerning this certain observation or this file, the binary table extension header contains all information concerning the extracted data of the respective order.
Sample spectrum primary header:
SIMPLE = T / Written by IDL: Wed Oct 25 10:21:15 2000 BITPIX = 8 NAXIS = 0 EXTEND = T FILENAME= 'tues2276_2_ord61.fits'/ name of this file ORD_FRST= 61 / first echelle order in this file ORD_LAST= 61 / last echelle order in this file WVL_FRST= 904.673 / [A] first wavelength in this file WVL_LAST= 926.478 / [A] last wavelength in this file TELESCOP= 'ORFEUS-SPAS II' / mission/satellite name INSTRUME= 'Tuebingen UV Echelle Spectrometer (TUES)' / instrument name DATE = '2000-10-25T09:21:14' / file creation date (YYYY-MM-DDThh:mm:ss UTC) ORIGIN = 'IAAT - Institute for Astronomy and Astrophysics Tuebingen' OBS_CODE= 'TUES2276_2' / observation reference number ORFEUSID= '2276 ' / specific ORFEUS target ID number OBS_NO = '2 ' / Echelle observation number OBJECT = 'HD 93521' / target name RA_OBJ = 162.09750 /[deg] right ascension of object DEC_OBJ = 37.57028 /[deg] declination of object EQUINOX = 2000.0 / equinox of coordinate system DATE-OBS= '1996-11-28T04:56:05' / obs start time (YYY-MM-DDThh:mm:ss UTC) DATE-END= '1996-11-28T05:14:05' / obs stop time (YYY-MM-DDThh:mm:ss UTC) CLOCKCOR= 'NO ' / UTC not guaranteed TIMEREF = 'LOCAL ' / Time frame of satellite TASSIGN = 'SATELLITE' / Times assigned on satellite TIMESYS = 'MJD ' / Modified Julian Date MJDREF = 40000 / [days] MJD of reference date TSTART = 899873765 / [s] from MJDREF TSTOP = 899874845 / [s] from MJDREF TIERRABS= 1 / [s] precision of quoted times EXPTIME = 1080 / [s] exposure time COMMENT ********************* COMMENT The following data are displayed in the COMMENT original ORFEUS header format. COMMENT --- ORFEUS header --- COMMENT COMMENT RA / DEC (2000) [hh mm ss.ss / +dd mm ss.ss] : RA_DEC = '10 48 23.40 / +37 34 13.00' COMMENT integration start time [UT, day of 1996 /hh:mm:ss] : INTSTART= 'GMT 333:04:56:05' COMMENT integration stop time [UT, day of 1996 /hh:mm:ss] : INTSTOP = 'GMT 333/05:14:05' COMMENT original image file : IMGFILE = '/users_12/ORFII/BILDER/E2276/2276_2.bil' TILTEDEX= 'no' / tilted extraction (yes/no) COMMENT ORFEUS comment : ORFCOMM = '' CORBLAZE= 'yes' / blaze correction (yes/no) COMMENT blaze offset values [mm]: OFSBLAZE= ' 5.00, 5.10, 5.20, 5.30, 5.40, 5.50, 5.60, 5.70' COMMENT blaze width values : WIDBLAZE= ' 0.73, 0.73, 0.73, 0.73, 0.73, 0.73, 0.75, 0.75' COREFFAR= 'yes' / effective area correction (yes/no) COMMENT count rates (maximum, actual, image) [counts/sec]: CNTRATES= '9500.0, 6227.4, 5169.1' CORBACKG= 'yes' / background subtraction (yes/no) AVERG512= 'yes' / averaging of pixels 511/512 (yes/no) EDGECORR= 'yes' / edge correction (yes/no) OBSBLKCO= 'yes' / observation block correction (yes/no) BLKCORR = 1.0000321 / observation block wavelength correction factor ORBRVCOR= 'yes' / orbital relative velocity correction (yes/no) ORBITRV = 4.6 / [km/s] average orbital relative velocity VHELCORR= 'yes' / heliocentric correction (yes/no) VHELIOCE= -26.5 / [km/s] heliocentric velocity AVELCORR= 'yes' / additional radial velocity correction (yes/no) ADDRADV = 0.0 / [km/s] additional radial velocity COMMENT wavelength calibration parameters : WLCALPAR= '41.5990, 475.945, 3.52602, -0.480310, -0.335360, -0.0108750, 1.06074' COMMENT --- end of ORFEUS header --- COMMENT ********************* HISTORY Version of ORFEUS-ECHELLE-FITS routines: HISTORY 1.2, 2000-10-13, Juergen Barnstedt HISTORY For description of ORFEUS II Echelle spectrometer performance see: HISTORY J.Barnstedt, N.Kappelmann, I.Appenzeller, et al., HISTORY Astron. Astrophys. Suppl. Ser. 134, 561-567 (1999) END
Description of spectrum primary header keywords:
- SIMPLE, BITPIX, NAXIS, EXTEND, FILENAME :
- These are standard keywords used in accordance with the
Definition of the Flexible Image Transport System (FITS).
- ORD_FRST, ORD_LAST :
- First and last extracted echelle order in this file (range 40 - 61).
- WVL_FRST, WVL_LAST :
- First and last wavelength in this file (in Å).
- TELESCOP, INSTRUME, DATE, ORIGIN, OBS_CODE, ORFEUSID, OBS_NO, OBJECT, RA_OBJ, DEC_OBJ, EQUINOX, DATE-OBS, DATE-END, CLOCKCOR, TIMEREF, TASSIGN, TIMESYS, MJDREF, TSTART, TSTOP, TIERRABS, EXPTIME :
- See description of image header keywords.
The following keywords show the original ORFEUS header data used with the files supplied to the guest observers. The keywords are described here in detail:
- RA_DEC :
- Equinox 2000 coordinates, right ascension and declination.
Format: hh mm ss.ss / dd mm ss.ss
- INTSTART :
- Start of observation: day of 1996 / hh:mm:ss
- INTSTOP :
- End of observation: day of 1996 / hh:mm:ss
- IMGFILE :
- Original image file at IAAT.
- TILTEDEX :
- Extraction flag: tilted extraction (yes/no).
- ORFCOMM :
- Comment on this observation.
- CORBLAZE :
- Extraction flag: blaze correction (yes/no).
- OFSBLAZE :
- Offset of blaze function from center of detector [mm], given
for the Echelle orders 40, 43, 46, 49, 52, 55, 58 and 61.
The values for the orders in between are linearly interpolated.
- WIDBLAZE :
- Relative width of blaze function, given for the same Echelle
orders as the OFSBLAZE values.
- COREFFAR :
- Extraction flag: effective area correction (yes/no).
- CNTRATES :
- Three count rate values in counts/s:
- Maximum count rate of lower electronic threshold, taken from this or any other observation of this object.
- Actual average count rate of lower electronic threshold.
- Registered count rate in this Echelle image.
- CORBACKG :
- Extraction flag: background subtraction (yes/no).
- AVERG512 :
- Extraction flag: averaging of pixels 511/512 (yes/no).
- EDGECORR :
- Extraction flag: edge correction (yes/no).
- OBSBLKCO :
- Extraction flag: observation block correction (yes/no)
- BLKCORR :
- Observation block wavelength correction factor.
- ORBRVCOR :
- Extraction flag: orbital relative velocity correction (yes/no).
- ORBITRV :
- Average orbital relative velocity in km/s.
- VHELCORR :
- Extraction flag: heliocentric correction (yes/no).
- VHELIOCE :
- Heliocentric velocity in km/s.
- AVELCORR :
- Extraction flag: additional radial velocity correction (yes/no).
- ADDRADV :
- Additional radial velocity in km/s.
- WLCALPAR :
- Seven wavelength calibration parameters (for internal documentation only).
Sample spectrum binary table extension header:
XTENSION= 'BINTABLE' /Binary table written by MWRFITS BITPIX = 8 /Required value NAXIS = 2 /Required value NAXIS1 = 42 /Number of bytes per row NAXIS2 = 837 /Number of rows PCOUNT = 0 /Normally 0 (no varying arrays) GCOUNT = 1 /Required value TFIELDS = 11 /Number of columns in table INHERIT = T / primary header applies to this extension EXTNAME = 'ORDER_61' / name of this binary table extension ECHORDER= 61 / echelle order (range 40 - 61) WVLSTART= 904.673 / [A] start wavelength in this extension WVLEND = 926.478 / [A] end wavelength in this extension CUTWIDTH= 9 / [pixel] extraction cut width Y_SHIFT = -3 / [pixel] extraction y-position shift TFORM1 = 'E ' / TFORM2 = 'I ' / TFORM3 = 'E ' / TFORM4 = 'E ' / TFORM5 = 'E ' / TFORM6 = 'E ' / TFORM7 = 'E ' / TFORM8 = 'E ' / TFORM9 = 'E ' / TFORM10 = 'E ' / TFORM11 = 'E ' / COMMENT / TTYPE1 = 'WAVELENGTH' / TUNIT1 = 'ANGSTROM' / TDISP1 = 'F9.3 ' / COMMENT / TTYPE2 = 'PIXEL ' / TUNIT2 = 'PIXEL NO.' / TDISP2 = 'I6 ' / COMMENT / TTYPE3 = 'COUNTS_RAW' / TUNIT3 = 'COUNTS/PIXEL' / TDISP3 = 'F10.1 ' / COMMENT / TTYPE4 = 'COUNTS_BLAZE_CORRECTED' / TUNIT4 = 'COUNTS/PIXEL' / TDISP4 = 'F10.1 ' / COMMENT / TTYPE5 = 'BACKGROUND_RAW' / TUNIT5 = 'COUNTS/PIXEL' / TDISP5 = 'F10.1 ' / COMMENT / TTYPE6 = 'BACKGROUND_SMOOTHED' / TUNIT6 = 'COUNTS/PIXEL' / TDISP6 = 'F10.1 ' / COMMENT / TTYPE7 = 'PHOTON_FLUX' / TUNIT7 = 'PHOTONS/CM^2/SEC/ANGSTROM' / TDISP7 = 'G15.5E3 ' / COMMENT / TTYPE8 = 'ENERGY_FLUX' / TUNIT8 = 'ERG/CM^2/SEC/ANGSTROM' / TDISP8 = 'G15.5 ' / COMMENT / TTYPE9 = 'RELATIVE_ERROR' / TUNIT9 = ' ' / TDISP9 = 'F8.3 ' / COMMENT / TTYPE10 = 'EDGE_CORR' / TUNIT10 = 'SCALING FACTOR' / TDISP10 = 'F8.3 ' / COMMENT / TTYPE11 = 'BLAZE_CORR' / TUNIT11 = 'SCALING FACTOR' / TDISP11 = 'F8.4 ' / COMMENT / END
Description of spectrum binary table extension header keywords:
- XTENSION, BITPIX, NAXIS, NAXISn, PCOUNT, GCOUNT, TFIELDS :
- These are standard binary extension keywords used in accordance with the
Definition of the Flexible Image Transport System (FITS): Binary Table Extension.
- INHERIT :
- Always = 'T' : Primary header applies to this extension.
- EXTNAME :
- Name of this binary table extension ('ORDER_' + number of Echelle order).
- ECHORDER :
- Number of this Echelle order (range 40 - 61).
- WVLSTART, WVLEND :
- Start wavlength and end wavelength (in Å) in this binary extension table.
- CUTWIDTH :
- Vertical width of extraction strip (in pixels).
- Y_SHIFT :
- Y-position shift of extraction strip with respect to default position (in pixels).
- TFORMn, TTYPEn, TUNITn, TDISP :
- These are standard binary extension keywords used in accordance with the
Definition of the Flexible Image Transport System (FITS): Binary Table Extension.
Description of the 11 data columns within one binary table extension:
- 1: WAVELENGTH (Single Precision Floating Point)
- Wavelength in Å.
- 2: PIXEL (16-Bit Integer)
- X-pixel number within Echelle image
- 3: COUNTS_RAW (Single Precision Floating Point)
- Number of counts after extraction, only averaging of pixel 511/512
applied (in counts/pixel).
- 4: COUNTS_BLAZE_CORRECTED (Single Precision Floating Point)
- Number of counts after all processing steps (in counts/pixel).
- 5: BACKGROUND_RAW (Single Precision Floating Point)
- Background before smoothing, scaled with the extraction widths of background
and Echelle order (in counts/pixel).
- 6: BACKGROUND_SMOOTHED (Single Precision Floating Point)
- Background smoothed, as used for subtraction (in counts/pixel).
- 7: PHOTON_FLUX (Single Precision Floating Point)
- Flux in Photons/cm2/s/Å.
- 8: ENERGY_FLUX (Single Precision Floating Point)
- Flux in Ergs/cm2/s/Å.
- 9: RELATIVE_ERROR (Single Precision Floating Point)
- Relative error (poisson statistics of COUNTS_RAW and BACKGROUND_SMOOTHED).
- 10: EDGE_CORR (Single Precision Floating Point)
- Factor for correction of sensitivity loss at the detector edges.
- 11: BLAZE_CORR (Single Precision Floating Point)
- Correction factor of blaze function.
Formula of calculation:
COUNTS_BLAZE_CORRECTED =(COUNTS_RAW - BACKGROUND_SMOOTHED) / BLAZE_CORR / EDGE_CORR
RELATIVE_ERROR =
SQRT(COUNTS_RAW + BACKGROUND_SMOOTHED*width_factor) /
(COUNTS_RAW - BACKGROUND_SMOOTHED)
The above page was written by Jürgen Barnstedt from the
ORFEUS Group at Tübingen and is reproduced here for the
MAST archive with his permission.
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