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NICMOS STScI Analysis Newsletter 6

NICMOS STScI Analysis Newsletter 6

November 1997


	 - The HST Data Handbook, Version 3.0.
         - NICMOS NEWS
           + New NICMOS Information on the WWW
         - HST DATA HANDBOOK: The NICMOS section
         - Progress of the NICMOS Pure Parallel Program
	 - Imaging Polarimetry with NICMOS
 The HST Data Handbook, Version 3.0

 The latest version (V 3.0) of the HST Data Handbook is now in print, and
 copies of the handbook will be automatically mailed to all Cycle 6 and 7 
 PIs. Others may request a paper copy by sending a request, with the
 correct mailing address, to 
 New NICMOS Information on the WWW
 Similar to all Space Telescope Instruments, the NICMOS home page on
 the World Wide Web is updated with all instrument developments. The
 NICMOS home page can be found by visiting the STScI WWW page
 ( and following Observing links to the NICMOS
 Web pages.
 Since last month, the following items have been new POSTS in the
 ADVISORIES and other pages:

    * The Frequestly Asked Question PAGE has been updated.
    * 1997 HST Calibration Workshop -- NICMOS PAPERS page has been updated.
    * The Focus Update page including the coronograph has been updated.
    * NICMOS Reference Files List PAGE has been updated (19 November 1997)
    * A REVISED Cycle 7 Calibration Plan link is available from the advisories
      or the calibration page.
    * New Software Tools links are available from the NICMOS Software page.
      NICMOS Look and CALNICC are NICMOS Software tools developed at the
      Space Telescope - European Coordinating Facility. 
    * A memo describing the "bars" phenomenon has been posted to the NICMOS 
      "advisories" web site. The memo also describes how to avoid "bars" 
      in your images, and how to detect and get rid of them if they are

 Since last month, the following Instrument Science Reports have been made
 available on the NICMOS documentation Web Page:
    * NICMOS Pointed Thermal Background: Results from On-Orbit data.
    * Characteristics of NICMOS Detector Dark Observations. 
    * Camera 3 Performance.
    * The STScI NICMOS Pipeline: CALNICA, Single Image Reduction (Rev. A)
    * The STScI NICMOS Pipeline: CALNICB, Reduction of Image Associations 

 The Data Handbook contains important information on the HST data GOs
 and GTOs receive, including explanations on the data format, on the
 data reduction steps performed by the automatic pipelines, on sources
 of uncertainties in the data, and on available tools for data
 The 1997 HST Data Handbook has been released in October 1997 (editor: 
 Mark Voit) and contains sections on the NICMOS data reduction and analysis 
 which will help GOs and GTOs with their observations. 
 The new edition of the Data Handbook can be found at:
 or can be accessed from the NICMOS WWW Documentation page.

 The NICMOS section of the HST Data Handbook was written by Daniela
 Calzetti and Howard Bushouse, with contributions from Chris Skinner,
 Eddie Bergeron, Luis Colina and Anatoli Suchkov. 

 Progress of the NICMOS Pure Parallel Program
 As discussed in the May 1997 NICMOS STAN, the combination of the Second
 Generation HST Science Instruments and the Solid State Recorder has
 enabled an expanded parallel science program. As recommended by the
 Cycle 7 TAC, the STScI has taken on the task of managing large,
 archival pure-parallel programs as a community service. A Parallel
 Working Group (PWG) has also be established to advise on this effort.
 While a more elaborate parallel program for NICMOS, STIS, and WFPC2 is
 in development by STScI and the PWG and is expected to go into
 operation this winter with the availability of the POM proposal
 crafting software, we have been obtaining as much parallel NICMOS data
 as possible.

 Starting in June 1997, NICMOS "One Orbit Parallel" program observations
 have been obtained (mainly with Cameras 1 and 2 in focus) in the F110W,
 F160W, and F222M filters. These observations are designed to fit into a
 single long (~40 minutes) or short (~20 minutes) scheduling
 opportunity. Multiple orbit opportunities merely execute the same
 sequence of NICMOS exposures repetitively. These data have been
 obtained under program ID  7676, 7726, 7729, 7701, 7779, and 7780 (the
 latter two proposals use the Camera 3 focus position -- which places
 Camera 3 ~4 mm from optimal focus). Data obtained by these proposals
 may be obtained from the STARVIEW system and further information from:

 Following analysis of some of these data and discussions with the PWG, 
 we have defined a "NICMOS Modified One Orbit Parallel" program (Ids:
 7811, 7812) to improve the usefulness of these observations. These
 programs begin execution the second week of November 1997.

 The NICMOS Modified One Orbit Parallel program obtains F110W and F160W
 imaging and G096,G141 spectroscopy. Improved MULTIACCUM sequences and
 two dither positions are obtained for each filter. The Field Offset
 Mirror has been positioned to greatly reduce the vignetting in Camera 3
 and a pair of dithered images separated by 2 arcseconds are obtained
 for each filter or grism observation. While the short opportunity
 observations are exclusively imaging, two thirds of the  longer
 opportunities include G096 or G141 grism observations (with appropriate
 F110W and F160W images in a 4:1 exposure time ratio). Camera 2 long
 wavelength (F222M) observations are also obtained (rather out of focus)
 to measure the thermal background.
 Imaging Polarimetry with NICMOS
 NICMOS contains optical elements which enable high spatial 
 resolution, high sensitivity observations of linearly 
 polarized light from 0.8 - 2.1 micron.  The filter wheels 
 for NIC1 and NIC2 each contain three polarizing elements 
 sandwiched with band-pass filters.  The overall design of 
 NICMOS and relevant band-passes are given in the NICMOS 
 Instrument Handbook Version 2.0 
 Preflight Thermal Vacuum tests revealed that each polarizer 
 has a unique polarizing efficiency, and that the position 
 angle offsets differ from the nominal positions of 0, 120 & 
 240 degrees.  Therefore a reduction algorithm different from 
 the ideal case treated in the NICMOS Instrument Handbook 
 Version 2.0 is required for proper reduction of astronomical 
 polarimetry data.  A full description of the Thermal Vacuum 
 test results, the new algorithm (hereafter HSL), and its 
 application to ERO data can be found in Hines, D.C., 
 Schmidt, G.D. & Lytle, D., 1997, HST Calibration Workshop 
 In addition to testing the polarizing optics, the Thermal 
 Vacuum tests also revealed the following properties of the 
 NICMOS system:
 1) The polarization induced by the mirrors in the NICMOS 
 optical train appears to be small (<= 1%).
 2) The Grisms are slightly sensitive to the orientation of 
 incoming polarized light, with G206 showing the largest 
 variation in intensity (approximately 5%) for completely 
 polarized light.  This effect scales with percentage 
 polarization and will be negligible for the majority of 
 astronomical situations.
 Item (1) suggests that the instrumental polarization will be 
 small and will not be a function of instrument orientation.  
 Item (2) suggests that Grism observations of very highly 
 polarized objects (e.g.  reflection nebulae), may have 
 relative flux uncertainties = +/- 0.05*flux.
 Polarimetry data were obtained for IRC +10216 and CRL 2688 
 in NIC1 and NIC2 respectively as part of the Early Release 
 Observations program.  The descriptions of the observations 
 can be obtained on the STScI website via the Cycle 7 
 proposal number or PI name (ERO 7120: Skinner; ERO 7115: 
 Hines).  Overall, the NICMOS and ground-based polarimetry 
 agree remarkably well, once the NICMOS polarimetric images 
 are binned to match the spatial resolution of the 
 ground-based images.
 Variations of the percentage polarization in relatively 
 uniform regions of the HSL-reduced IRC +10216 and CRL 2688 
 data suggest uncertainties of order 3-5% (in percentage 
 polarization per pixel), and comparison with the 
 ground-based data suggests an uncertainty in the position 
 angles of order 2 degrees in 5x5 pixel bins.
 Binning the data BEFORE converting from Stokes parameters to 
 percentage polarization and position angle should allow 
 uncertainties as low as 1% per bin.  We emphasis that, while 
 the Instrumental Polarization is expected to be low (<= 1%), 
 it is still uncertain and should be treated as an unknown.
 The Cycle 7 calibration program is under way (CAL/NIC 7692: 
 Axon) and is observing several polarized and unpolarized 
 objects in both cameras to measure the instrumental 
 polarization and verify the absolute position angle 
 calibration.  Redundant sets of observations separated in 
 time (and thus with different space craft orientations) will 
 provide strong constraints on the stability and 
 uncertainties of the system.
                           APPENDIX: NICMOS Contacts
 Any questions about the scheduling of your observations should be
 addressed to your Program Coordinator. Post-Observation questions can
 be addressed to your Contact Scientist. If you do not know who these
 persons are, you can find the information on the WWW at
 Analysis, STSDAS or any other HST-related questions can also be
 addressed to
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