NICMOS STScI Analysis Newsletter 6
November 1997
CONTENTS:
- 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
- APPENDIX: NICMOS CONTACTS
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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 help@stsci.edu.
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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
(http://www.stsci.edu/) 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
there.
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
HST DATA HANDBOOK : the NICMOS section
--------------------------------------
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
analysis.
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:
http://www.stsci.edu/documents/data-handbook.html
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:
http://archive.stsci.edu/pure_parallels.html
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
(http://www.stsci.edu/ftp/instrument_news/NICMOS/nicmos_doc_handb.html).
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
(http://www.stsci.edu/ftp/instrument_news/NICMOS/NICMOS_CAL97/hinesd.ps).
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.
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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
http://www.stsci.edu/public/propinfo.html.
Analysis, STSDAS or any other HST-related questions can also be
addressed to help@stsci.edu.
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