Keyword

Type

Definition

(blank)

none

This keyword is used to enter a blank line into the header, usually to group sections of related information.

ABG-VAL

real

Specifies the value used by the Anti-Blooming Gate (ABG) circuitry of the camera hardware.

AIRMASS

real

Specifies the Airmass for an astronomical image. This is the optical path length through the atmosphere relative to 1.0 units at the zenith.

APERTURE

real

Specifies the aperture of the telescope.

AUTHOR

string

Specifies the name of the author of the image.

BIAS

real

Specifies the electronic offset, or bias, of a CCD detector. This is specified in units of counts, or digital numbers in the image pixel values.

BIASSEC

region

Specifies the column and row region containing the detector bias value. The value is read as a character string and then interpreted as a MIRA region in the form

  [column1:column2,row1:row2]

BITPIX

integer

Specifies number of bits per pixel and the data type are encoded as a single number that is the value of BITPIX. The magnitude (absolute value) ofBITPIX gives the number of bits in each pixel and a negative value signifies floating point pixels. Thus, BITPIX = 8 for byte data, 16 for integer data, 32 for long integer data, and -32 or -64 for real data. A 24 bit RGB image is represented internally to MIRA as BITPIX = 32. For color images, the MIRATYPE keyword distinguishes the data type even though BITPIX = 32 as in a 32 bit integer image. A 24 bit image cannot be saved in FITS format.

BSCALE

real

Specifies a scaling factor used to pack large dynamic range or floating point data into an integer pixel representation. This packing follows the rule:

True value = BZERO + BSCALE x (pixel data value)

BZERO

real

Specifies an offset used in packing large dynamic range or floating point pixel data into an integer representation. The relationship between packed and actual values is given above for the BSCALE keyword.

BUNIT

string

Defines brightness units used by the pixel data. In optical work this is almost always counts but may be Janskys or other units. FITS format files, especially those of raw, unprocessed data, are usually stored in count units if the data originated from a digital detector.

CCDBINn

integer

Specifies the binning value for the axis n, withn=1 referring to the most rapidly changing subscript (the x axis direction).

CCDSEC

region string

Specifies the column and row region containing the unbinned subframe position on the detector. The value is read as a character string and then interpreted as a MIRA region in the form

 [column1:column2,row1:row2]

Compare with binned coordinates in the DATASEC keyword.

CCDSUM

integer

Specifies the number of on-chip summed exposures.

CAMTEMP or

CCD-TEMP

real

Specifies the temperature of the detector, usually a CCD, at the time of the exposure.

CCDTEMP1

real

Specifies the temperature of the detector, usually a CCD, at the time when the exposure started.

CCDTEMP2

real

Specifies the temperature of the detector, usually a CCD, at the time when the exposure finished.

CCD-TREQ

real

This is an antiquated keyword; see SET-TEMP.

CCDBINn or COL_BIN

integer

Specifies the pixel binning for axis n at the time a CCD image was produced. The COL_BIN keyword is antiquated.

COPYRIGH

string

Specifies a copyright statement pertaining to the image.

COMMENT

string

Includes a comment that describes some characteristic of the image or the data. Note thatCOMMENT and HISTORY keyword lines do not use single quotation marks, ' ', to delimit the character string. The lack of quotation marks to delimit the string is unique to the COMMENT and HISTORY keywords.

CLABELn

string

Specifies the text label for the n-th axis.

COPYRIGH

string

Copyright statement for the file.

CRDELTn

real

Specifies the scaling factor in physical coordinate units per pixel for axisn of an image.

CRPIXn

real

Specifies the reference pixel for the physical coordinate system for image axisn. The physical coordinate at image location CRPIXn isCRVALn.

CRTYPEn

string

Specifies the type of physical coordinate system used for axis n.

CRVALn

real

Specifies the zero point of an optional coordinate system for axis n.

CUNITn

string

Specifies the units of measurement on the n-th axis.

DARKTIME

real

Specifies the time in seconds that characterizes the build up of dark count in the sensor that produced the image.

DATAMAX

real

Specifies the maximum pixel value in the image.

DATAMIN

real

Specifies the minimum pixel value in the image.

DATASEC

region string

Specifies the column and row region containing the binned subframe position on the detector. The value is read as a character string and then interpreted as a MIRA region in the form

  [column1:column2,row1:row2]

Compare with unbinned coordinates in the CCDSEC keyword.

DATE-MID

date+time

Specifies the UT date and time at mid exposure. This keyword is added or updated by the Combine Images command. It gives the weighted average time of mid exposure based on the exposures of the images combined, as well as the combining method and the normalization method. See the DATE-OBS keyword for a description of the format.

DATE-OBS

date+time

Specifies the Universal Time ("UT") date and tiem at the beginning of the exposure.

Before 1999, the FITS standard expressed this in the format dd/mm/yy and did not specify whether the date and time applied to the beginning, middle, or end of the exposure. Beginning in 1999, the FITS standard revised the format to solve the Year 2000 (Y2k) problem and specified that the time shall apply to the beginning of the exposure. The new format uses a 4 digit year and it includes the time value from theTIME-OBS keyword. The letter T is used to separate the date and time information. The format of the new DATE-OBS keyword is

yyyy-mm-ddThh:mm:ss.sss

DATEFITS

date+time

Specifies the date and time when the image was most recently written to FITS format. See the DATE-OBS keyword for a description of the format.

DEC

degrees, or DMS string (non standard)

Specifies the declination at the center of the image specified in units of decimal degrees (FITS standard). Another common implementation is to use a string formatted with degrees, minutes, and seconds (DMS format).

DETECTOR

string

Specifies an identification string for the sensor used to acquire the image.

DWELL

real

Specifies the dark integration time. Also used sometimes to specify the lag time between beginning to flush the CCD and the actual beginning of the exposure.

END

none

This keyword is required to signify the end of the header. This tells the FITS reading program that the pixel data begins at the next 2880 byte offset from the beginning of the file.

EPOCH

real

Specifies the decimal year of observation of the image. The positions of moving objects are strictly correct only at the epoch of the image.

EQUINOX

real

Specifies the coordinate reference time for the system of right ascension and declination used by the image. Modern catalogs use the J2000 equinox.

EXPTIME

real

Specifies the exposure time in seconds.

FFT-COMP

string

Specifies the type of components of an image that is a Fourier Transform.

FFT-TYPE

string

Specifies the status of an FFT image. If the value of this keyword is FFT, the image is in the Fourier transform domain. If the value is Inverse FFT, the image has been inverse transformed from an FFT'd image.

FILE

string

Specifies the name of a disk file that was turned into a FITS file. The time this was done may be reflected in the value of the DATEFITS keyword.

FILTER

string

Specifies the name of the filter used in the observation.

FOCALLEN

real

Specifies the focal length of the telescope.

GAIN

real

Specifies the detector gain, often referred to as the inverse gain in units of electrons per count.

HISTORY

string

Includes a comment that describes how the data have been changed by image processing operations. MIRA makes profuse use of HISTORY keywords. Note thatHISTORY and COMMENT keyword lines do not use single quotation marks, ' ', to delimit the character string. The lack of quotation marks to delimit the string is unique to the HISTORY and COMMENT keywords.

IMAGETYP

string

Describes the type of observation in the image. This is intended for automated data reduction operations. The typical options are

OBSTYPE=

'normal '

'flat '

'dark '

'zero ' or 'bias '

INSTRUME

string

Specifies a name or description of the instrument (telescope, spectrograph, etc.) used in obtaining the image.

MIRAPROC

string

A string of codes used to monitor image processing steps. Used internally by Mira.

MIRATYPE

string

Specifies the data type of the image as a character string.

NAXIS

integer

Specifies number of coordinate dimensions. MIRA supports 1 and 2 dimensional image data.

NAXIS1

integer

Specifies number of pixels along the image axis whose subscript changes most rapidly from pixel to pixel. This corresponds to column number in a 2-d image.

NAXIS2

integer

Specifies number of pixels along the image axis whose subscript changes next most rapidly afterNAXIS1 . This corresponds to row number in a 2-d image. In a 1 dimensional image, the NAXIS2 keyword has either a value of 1 or is not present in the image header.

NAXISn

integer

Specifies the number of pixels along the n-th axis.

NPHOTSTD

integer

Specifies the number of objects used to calculate the photometric quantities inZERO-PT value and ZERPTERR

NSKYPIX

real

Specifies number of pixels used to estimate the background.

N-COADDS

integer

Specifies the number of image frames that were summed to produce the image. Antiquated, replaced by theCCDSUM keyword.

OBJECT

string

Specifies the name of 7 other descriptive information about the image.

OBSSTATE

string

Specifies a state flag that describes the operating mode of the detector at the time of the observation.

ORIGIN

string

Specifies the software that created the original image.

ORIGIN-C

integer

Specifies the column number origin of a sub-image.

ORIGIN-R

integer

Specifies the row number origin of a sub-image in its parent image.

OBSERVER

string

Specifies the name or a description of the observer who obtained the image.

OBSRVTRY

string

Specifies the name of the observatory where the data were taken.

OBSTYPE

string

Describes the type of observation in the image. This is intended for automated data reduction operations and is software specific. This is antiquated and has been replaced by IMAGETYP.

PALETTEn

string

Identifies the n-th line of the saved palette and display information. The value of n is in the range 0 to 3.

PSF-FWHM

real

Specifies the FWHM of the point spread function for the image. MIRA saves this value to the header when the FWHM is computed as consequence of a Radial Profile Plot.

PROCESS

string

Specifies a series of flags that describe the processing done to the image. This is implementation dependent.

RA

degrees, or HMS string (non standard)

Specifies the right ascension at the center of the image in units of decimal degrees (FITS standard). Another common implementation is to use a string formatted with hours, minutes, and seconds (HMS Format)

REFBIAS

string

Specifies the reference bias value for a CCD frame that was obtained at or shortly after the time of exposure.

ROW_BIN

integer

Specifies the row direction binning of physical pixels into image pixels at the time a CCD image was produced. Use CCDBIN2, as the ROW_BIN keyword is antiquated.

RDNOISE

real

Specifies the detector readout noise in units of electrons per pixel.

REFERENC

string

A bibliographic reference.

SKYCOUNT

real

Specifies the zero point term in the polynomial fit to the background of an image. If a polynomial of order higher than 1 is used for the background, this is the value of the lowest order (constant) term.

SKYSIGMA

real

Specifies the standard deviation of the fit to the background in units of counts.

SIMPLE

boolean

Specifies whether the pixel data adhere to standard FITS format, with values T or F. The value T (true) means that every aspect of the data is FITS standard. The value F (false) indicates that the image is nonstandard in some way, and that your software must how to handle it.

SITEELEV

real

Specifies the elevation of the observing site in units of meters.

SITELAT

degrees or DMS string

Specifies the latitude of the observing site. This is supposed to be specified in degrees but a common implementation is to use a string formatted with degrees, minutes, and seconds (DMS Format).

SITELONG

degrees or DMS string

Specifies the longitude of the observing site. This is supposed to be specified in degrees but a common implementation is to use a string formatted with degrees, minutes, and seconds (DMS Format). In most common usage for astronomical images, longitude west of Greenwich, England is specified as positive; namely, all locations in the Americas have positive longitude.

SITESYS

string

Specifies the coordiante system used for the SITExxxx keywords. The standard value is NAD83, referring to the geodetic coordinate system definition of 1983.

TELESCOP

string

Specifies the name or a description of the telescope used for the observation.

TIME-MID

time

Specifies the mid exposure time for a combined image (one made by combining the pixel intensities of more than 1 image). See the DATE-MID keyword for details.

TIME-OBS

time

Specifies the Universal Time at the beginning of the exposure. This is specified using the format hh:mm:ss.ssss.

Beginning in 1999, the FITS standard merged the TIME-OBS value with theDATE-OBS value as part of a solution to the Year 2000 problem. See the description under theDATE-OBS keyword.

TIMEFITS

time

Specifies the time when the image was most recently written to FITS format. This is specified in Universal Time in the format hh:mm:ss.ssss.

TRIMSEC

region

Specifies the region of a CCD image which should remain after trimming away the under-scan and/or over-scan bias region. The value is read as a character string and then interpreted as a MIRA region in the form

  [column1:column2,row1:row2]

WCOEFTYP

string

Specifies the wavelength solution type for which the WVCOEFn keyword values pertain. The most common value is polynomial.

WCOEFORD

integer

Specifies the numerical order of the wavelength solution contained in the WVCOEFn keywords.

WVCOEFn

string

Identifies the n-th line of wavelength calibration coefficients. The value of n is in the range 0 to 9.

X-OFFSET

integer

Specifies the column offset of the subimage on the detector. This is obsolete, replaced byCCDSEC keyword.

Y-OFFSET

integer

Specifies the column offset of the subimage on the detector. This is obsolete, replaced byCCDSEC keyword.

XTENSION

boolean

Specifies that the file contains FITS extensions, T or F.

ZERO-PT

real

Specifies the photometric zero point of the image expressed as a magnitude.

ZERPTERR

real

Specifies the uncertainty in the value of ZERO-PT.