WUPPE Data

WUPPE Data FITS Files

Description of the Instrument

The Wisconsin Ultraviolet Photo-Polarimeter Experiment (WUPPE) was one of three ultraviolet (UV) telescopes on the Astro-1 payload which flew aboard the space shuttle Columbia during a nine day mission in December 1990. It was reflown for 16 days in March 1995 on board Endeavour during the Astro-2 mission. WUPPE is a 0.5m f/10 Cassegrain telescope and spectropolarimeter. It obtained simultaneous spectra and polarization measurements, with a spectral resolution of about 16A, from 1450 to 3200A. A set of halfwave plates at 6 different angles provide spectropolarimetric modulation with 16A resolution on point sources through apertures from 6 to 40 arcsec. Calibrations of instrumental polarimetric efficiency, residual polarization, position angle registration, and flux sensitivity were performed by a combination of preflight laboratory measures and in-flight standard star observations. The data are corrected for telemetry errors, thermal background, cosmic ray hits, second order contamination, pointing errors, and instrumental polarization, which is roughly 0.05%. A detailed description of the instrument is given in Nordsieck et al 1994, SPIE, 2010, 2. See also the WUPPE web site for more information: http://www.sal.wisc.edu/WUPPE

WUPPE Data Set

Astro 1 & 2 WUPPE reduced data products include calibrated spectra and polarizations. During the Astro-2 mission WUPPE took 369 observations of 254 objects; some objects have multiple pointings. 112 pointings of 79 targets were taken of WUPPE prime targets. WUPPE also observed the prime targets of the other two UV instruments which yielded good spectra in many cases but generally did not have sufficient signal-to-noise for useful polarization measurements. The WUPPE prime target polarization results represent the majority of the useful polarimetry obtained by WUPPE during the Astro-2 mission. There were 149 pointings of 90 objects of Hopkins Ultraviolet Telescope (HUT) prime interest and 108 pointings of 85 objects of Ultraviolet Imaging Telescope (UIT) interest. The data set given here is for the WUPPE prime pointings only. The HUT & UIT results will be submitted at a later date.

The data have been processed using methods developed for the ground- based spectropolarimetric data from the Pine Bluff Observatory (PBO) of the University of Wisconsin. This involves summation of equivalent readouts on a particular object, subtraction of background scans, division by the flat field calibration spectra, flux calibration using spectra of known bright stars, polarimetric calibration using data obtained during pre-launch and in-flight observations. For halfwave mode data, the filters are differenced and a Fourier analysis, pixel-by-pixel as a function of filter angle, is done to give Stokes parameters %Q and %U spectra along with an Error spectrum, all consisting of 1024 32-bit data points for each array from about 1450 to 3200A.

WUPPE data analysis and software development takes place at the Univer- sity of Wisconsin Space Astronomy Laboratory (SAL). Much of the WUPPE reduction software is based on a FORTRAN language generalized Reticon detector/spectropolarimeter package (REDUCE) developed at SAL to support ground-based (PBO) and rocket UV spectropolarimetric data. This software package was operating on UNIX based microVAXes for several years and is currently running on Silicon Graphics Indy machines running IRIX 6.3.

The Stokes %Q and %U, and %Error spectra and flux calibrated (Flambda- ergs/cm**2/sec/A) data along with pertinent housekeeping data and data reduction information for each of the Astro-2 WUPPE prime target halfwave mode pointings (112 pointings of 79 targets, about 2.6 Mbytes of data) have been written to FITS files and are described in this document.

FITS File Naming Convention

The file name consists of the following:

WUPPE2_ObjectID_PointingID_HW.fits (e.g. WUPPE2_PHI-PER_220311_HW.fits)

where

ObjectID = The Mission Target List name. The names are common to the HUT, UIT and WUPPE instruments. The number of characters in ObjectID can vary from 3 to 8 characters and may be a mix of numbers and/or alphabetic information and may contain embedded '-'s.

PointingID = a 6 digit number representing the object identification number which was assigned during the mission. Each Astro-2 shuttle pointing had a unique PointingID number. (However, the PointingID number may not be unique for both Astro missions. A small number of PointingIDs used in the Astro-1 mission were also used in Astro-2.)

HW is the Halfwave polarimeter mode.

Example files and Description of the WUPPE2 Halfwave FITS files

Example FITS files for the Halfwave mode data:
WUPPE2_PHI-PER_220311_HW.fits
WUPPE2_GAM2VEL_220410_HW.fits (flux-only data)

The FITSIO package, version 4.14, written by William Pence at the Goddard Spaceflight Center, was used to generate the FITS files. They were written on a Silicon Graphics Indy running IRIX 6.3.

FITS files including the polarimetry are generally 25920 bytes in length; the size can be larger with more FITS header records. The flux-only FITS files are generally 11520 bytes.

A WUPPE2 Halfwave Level 1 FITS file looks like the following:

            +-------------------+
            |                   |
            |    Header         |
            |                   |
            +-------------------+

            +-------------------+
            |                   |
            | Data (1024 x 4)   |
            |  Flambda          |
            |  %Q               |
            |  %U               |
            |  %Error           |
            |                   |
            +-------------------+

The set of basic header information includes the primary array keywords and keywords describing the data arrays, target information, telescope engineering data relative to the observation, and calibration information. A set of comments giving the data reduction history is also included along with a "Special Comments" section. The exact headers of the 2 example files are given below. The primary array data (1024 x 4 32 bits per data point) consists of the Flux array in units of ergs/cm**2/sec/A (Flambda), the Stokes parameters %Q, %U, and %Error. For the fluxes, bad data have been zeroed out. For the polarization data, the bad data are when the %Error data have been zeroed out. The %Q and %U data remain (allowing inspection of those data) but should not be used.

FITS File Header

FITS File header(flux & polarimetric data): WUPPE2_PHI-PER_220311_HW.fits

 SIMPLE  =                    T / file does conform to FITS standard             
 BITPIX  =                  -32 / number of bits per data pixel                  
 NAXIS   =                    2 / number of data axes                            
 NAXIS1  =                 1024 / length of data axis   1                        
 NAXIS2  =                    4 / length of data axis   2                        
 COMMENT   FITS (Flexible Image Transport System) format defined in Astronomy and
 COMMENT   Astrophysics Supplement Series v44/p363, v44/p371, v73/p359, v73/p365.
 COMMENT   Contact the NASA Science Office of Standards and Technology for the   
 COMMENT   FITS Definition document #100 and other FITS information.             
 COMMENT   FITSIO package v4.14 used                                             
 CRVAL1  =              1354.00 / Wavelength in Angstroms of first pixel         
 CDELT1  =                 2.00 / Number of Angstroms/pixel                      
 CRPIX1  =                 1.00 / Starting pixel number                          
 CTYPE1  = 'WAVELENGTH'         / Wavelength in Angstroms                        
 CTYPE2  = 'FLAMBDA '           / Flux (ERGS/CM**2/SEC/A)                        
 CTYPE3  = '%Q      '           / Linear Stokes %Q                               
 CTYPE4  = '%U      '           / Linear Stokes %U                               
 CTYPE5  = '%Error  '           / Error in %Polarization                         
 COMMENT   The errors given in the error array are the statistical errors        
 COMMENT   based on the residuals of the least squared fit to the 3              
 COMMENT   filter-pair polarimetric data (see section 2.3 of Wolff,              
 COMMENT   Nordsieck & Nook 1996 AJ 111, 856).                                   
 COMMENT   The instrumental polarization stability of WUPPE is +/- 0.04%         
 COMMENT   and the polarization efficiency is Pol/20.                            
 COMMENT   ***IMPORTANT NOTE***                                                  
 COMMENT   **The ERROR array is also being used as a QUALITY array.              
 COMMENT   **For bad/contaminated data, the errors have been set to zero         
 COMMENT   **but the %Q & %U arrays for those wavelengths remain unchanged       
 COMMENT   **to allow inspection of the bad data.                                
 ORIGIN  = 'UW-Space Astronomy Lab' / Creator of FITS file                       
 DATE    = ' 5/02/98'           / FITS file creation date                        
 COMMENT = 'Thu Feb  5 15:32:52 1998' / Date FITS file was created               
 COMMENT = 'Silicon Graphics Indy - Irix 6.3' / Computer used to write FITS files
 DATE-OBS= '05/03/95'           / Date of Observation (GMT) dd/mm/yy             
 OBSERVAT= 'ASTRO-2 '           / Observatory                                    
 TELESCOP= 'WUPPE   '           / Telescope                                      
 INSTRUME= 'SPECTROPOLARIMETER' / Instrument Used                                
 MODE    = 'HW      '           / Halfwave Polarimeter Mode                      
 OBJECT  = 'PHI-PER '           / Object Observed                                
 NAME2   = 'HD10516 '           / Alternate Target Name                          
 ID      = '2203-11 '           / Target ID                                      
 PRIME   = 'WUPPE   '           / Prime Instrument                               
 EQUINOX =              1950.00 / Equinox for coordinates                        
 RA      =                25.13 / Right ascension in degrees                     
 DEC     =                50.44 / Declination in degrees                         
 GMTSTART= '64/20:54'           / GMT start time of observation (dd/hh:mm)       
 METSTART= '03/14:16'           / Mission Elapsed Time start time (dd/hh:mm)     
 EXPOSURE=                997.0 / Useful Exposure Time (seconds)                 
 FRAMETIM=                  0.2 / Frametime for each scan (seconds)              
 SEQ-NUM =                  106 / WUPPE Sequence Number                          
 HVPS    =                 3.70 / High Voltage Power Supply (volts)              
 GAIN    = 'High    '           / Spectrometer Gain (High or Low)                
 THERM   =               -33.10 / Instrument temperature (Centigrade)            
 POSANGLE=               197.20 / Observatory Position Angle                     
 IMCSTATU= '-1      '           / Image Motion Compensation System status        
 COMMENT   IMCS:-1=man disab;0=auto disab;1=enab;2=out of limits                 
 DAYNIGHT= 'Day     '           / Day-Night Status                               
 COMMENT   Day-Night designations: "Night", "Day" (All Night or All Day)         
 COMMENT   "MostN", "MostD" (Mostly Night or Mostly Day), "N/D" or "D/N"         
 COMMENT   (Night into Day, Day into Night, roughly half the time in each).      
 APERTURE=                    8 / Aperture Used                                  
 COMMENT   Ap 8=6"x12";Ap 1=40" diam;Ap 2=4.2" diam                              
 FILTER  =                    6 / Starting Filter Number                         
 CALIBRAT= ' wuppe2i'           / Instrumental polarization calibration used     
 AVE-POL =                0.436 / Mean %Pol over entire wavelength region        
 AVE-ERRO=                0.004 / Mean %Error in %Pol                            
 AVE-PA  =                 49.4 / Mean Position Angle (degrees)                  
 COMMENT   Useful data generally are from 1450A-3200A with a spectral            
 COMMENT   resolution of 16A.                                                    
 HISTORY   Data Reduction History                                                
 HISTORY   Wavelength calibration using Aluminum lines (created 4/25/95)         
 HISTORY   Filter mixing fixed for 0.2 sec frametime scans                       
 HISTORY   Remove cosmic ray hits & telemetry errors & deviant scans             
 HISTORY   Remove offsets & thermal background & correct for thermal drift       
 HISTORY   Remove detector background (Astro-2 dtr bkg: created 5/22/95)         
 HISTORY   Apply noise reduction & 2nd order correction(created 3/13/96)         
 HISTORY   For each scan, correct for image motion in pitch & yaw                
 HISTORY   Apply flat field for Astro-2 point source (created 3/21/96)           
 HISTORY   Apply flux calibration: used HST standards & ptg correction           
 HISTORY   (created 4/1/97)                                                      
 HISTORY   Apply Astro-2 high gain instrumental polarization calibration:        
 HISTORY   wuppe2i (created 5/16/96)                                             
 COMMENT   WUPPE Astro-2 flux calibration has a relative flux accuracy           
 COMMENT   of 5% between 1700A and 3000A and 10% outside this range.             
 COMMENT   Due to pointing instabilities, fluxes are not absolute.               
 COMMENT   WUPPE Astro-2 instrumental polarization is Q=-0.04% and               
 COMMENT   U=-0.08% (which has been removed).                                    
 COMMENT   Special Comments                                                      
 COMMENT   *2400A "Glitch"*                                                      
 COMMENT   The data between about 2380A and 2420A are bad (& therefore the       
 COMMENT   error array has been set to zero) due to a detector flaw in           
 COMMENT   the "A" polarimetric array.                                           
=========================================================================================

  FITS File header (flux only data):  WUPPE2_GAM2VEL_220410_HW.fits 

 SIMPLE  =                    T / file does conform to FITS standard             
 BITPIX  =                  -32 / number of bits per data pixel                  
 NAXIS   =                    2 / number of data axes                            
 NAXIS1  =                 1024 / length of data axis   1                        
 NAXIS2  =                    1 / length of data axis   2                        
 COMMENT   FITS (Flexible Image Transport System) format defined in Astronomy and
 COMMENT   Astrophysics Supplement Series v44/p363, v44/p371, v73/p359, v73/p365.
 COMMENT   Contact the NASA Science Office of Standards and Technology for the   
 COMMENT   FITS Definition document #100 and other FITS information.             
 COMMENT   FITSIO package v4.14 used                                             
 CRVAL1  =              1364.00 / Wavelength in Angstroms of first pixel         
 CDELT1  =                 2.00 / Number of Angstroms/pixel                      
 CRPIX1  =                 1.00 / Starting pixel number                          
 CTYPE1  = 'WAVELENGTH'         / Wavelength in Angstroms                        
 CTYPE2  = 'FLAMBDA '           / Flux (ERGS/CM**2/SEC/A)                        
 ORIGIN  = 'UW-Space Astronomy Lab' / Creator of FITS file                       
 DATE    = ' 5/02/98'           / FITS file creation date                        
 COMMENT = 'Thu Feb  5 17:45:06 1998' / Date FITS file was created               
 COMMENT = 'Silicon Graphics Indy - Irix 6.3' / Computer used to write FITS files
 DATE-OBS= '17/03/95'           / Date of Observation (GMT) dd/mm/yy             
 OBSERVAT= 'ASTRO-2 '           / Observatory                                    
 TELESCOP= 'WUPPE   '           / Telescope                                      
 INSTRUME= 'SPECTROPOLARIMETER' / Instrument Used                                
 MODE    = 'HW      '           / Halfwave Polarimeter Mode                      
 OBJECT  = 'GAM2VEL '           / Object Observed                                
 NAME2   = 'HD68273 '           / Alternate Target Name                          
 ID      = '2204-10 '           / Target ID                                      
 PRIME   = 'WUPPE   '           / Prime Instrument                               
 EQUINOX =              1950.00 / Equinox for coordinates                        
 RA      =               122.01 / Right ascension in degrees                     
 DEC     =               -47.20 / Declination in degrees                         
 GMTSTART= '76/01:42'           / GMT start time of observation (dd/hh:mm)       
 METSTART= '14/19:30'           / Mission Elapsed Time start time (dd/hh:mm)     
 EXPOSURE=                214.0 / Useful Exposure Time (seconds)                 
 FRAMETIM=                  0.2 / Frametime for each scan (seconds)              
 SEQ-NUM =                  433 / WUPPE Sequence Number                          
 HVPS    =                 3.10 / High Voltage Power Supply (volts)              
 GAIN    = 'Low     '           / Spectrometer Gain (High or Low)                
 THERM   =               -33.10 / Instrument temperature (Centigrade)            
 POSANGLE=               161.70 / Observatory Position Angle                     
 IMCSTATU= '1       '           / Image Motion Compensation System status        
 COMMENT   IMCS:-1=man disab;0=auto disab;1=enab;2=out of limits                 
 DAYNIGHT= 'Night   '           / Day-Night Status                               
 COMMENT   Day-Night designations: "Night", "Day" (All Night or All Day)         
 COMMENT   "MostN", "MostD" (Mostly Night or Mostly Day), "N/D" or "D/N"         
 COMMENT   (Night into Day, Day into Night, roughly half the time in each).      
 APERTURE=                    8 / Aperture Used                                  
 COMMENT   Ap 8=6"x12";Ap 1=40" diam;Ap 2=4.2" diam                              
 FILTER  =                    6 / Starting Filter Number                         
 COMMENT   Useful data generally are from 1450A-3175A with a spectral            
 COMMENT   resolution of 16A.                                                    
 HISTORY   Data Reduction History                                                
 HISTORY   Wavelength calibration using Aluminum lines (created 4/25/95)         
 HISTORY   Filter mixing fixed for 0.2 sec frametime scans                       
 HISTORY   Remove cosmic ray hits & telemetry errors & deviant scans             
 HISTORY   Remove offsets & thermal background & correct for thermal drift       
 HISTORY   Remove detector background (Astro-2 dtr bkg: created 5/22/95)         
 HISTORY   Apply noise reduction & 2nd order correction(created 3/13/96)         
 HISTORY   NO correction for image motion in pitch & yaw                         
 HISTORY   Apply flat field for Astro-2 diffuse source (created 3/28/96)         
 HISTORY   Apply flux calibration: used HST standards & NO ptg correction        
 HISTORY   (created 4/1/97)                                                      
 COMMENT   WUPPE Astro-2 flux calibration has a relative flux accuracy           
 COMMENT   of 5% between 1700A and 3000A and 10% outside this range.             
 COMMENT   Due to pointing instabilities, fluxes are not absolute.               
 COMMENT   Special Comments                                                      
 COMMENT   Very bright object;Defocussed Image                                   

The programs wfitsread.f and wfluxfitsread.f were written to verify the contents of the Astro-2 WUPPE Level1 FITS files. They also use the FITSIO v4.14 software package. These programs create ASCII dump files.

Further Information

WUPPE Reference List
see www.sal.wisc.edu/WUPPE/pubswuppe.html for the latest list of WUPPE references.

To request copies of relevant WUPPE documents, preprints/reprints, bibliography, or general questions, please email Marilyn Meade at the UW Space Astronomy Laboratory. See also the WUPPE Web site: http://www.sal.wisc.edu/WUPPE