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NICMOS STScI Analysis Newsletter 12

NICMOS STScI Analysis Newsletter 12

June 1998


        - NICMOS NEWS
          + New NICMOS Information on the WWW
          + Update on Imaging Polarimetry with NICMOS

	- The Automatic Notification Tool (ANT)


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 newly posted:

 	* NICMOS PlateScale Update, Last Update: 15 June 98 
 	* NICMOS Coronographic Hole Update, Last Update: 15 June 98    
 	* NICMOS Polarimetry Update, Last Update: 15 June 98 
 	* NICMOS Focus Update, Last Update: 18 June 98
	* NICMOS Photometry Update, Last Update: 29 June 98
	* NICMOS Parallel Program, Last Update: 29 June 98 

Since last month, the following ISRs have been published:

	* Imaging Polarimetry with NICMOS 

Update on Imaging Polarimetry with NICMOS

Dean C. Hines
NICMOS Project
Steward Observatory
The University of Arizona

As reported in STAN - NICMOS Number 6 November 1997, NICMOS 
contains optical elements that enable high spatial 
resolution, high sensitivity observations of linearly 
polarized light from 0.8 - 2.1 micron. 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 (standard theory) 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 developed by Hines, Schmidt & Lytle (hereafter 
HSL), and its application to ERO data can be found in Hines, 
D.C., 1998, ``Imaging Polarimetry with NICMOS'' NICMOS/VLT 
Workshop, in press 

HSL UPDATE: The coefficients for the HSL algorithm have been 
refined based on observations an unpolarized (null) standard 
(BD 32 3739: Cycle 7 CAL 7692, 7958: Axon).  Applying these 
new HSL coefficients to the polarized star (CHA-DC-F7) 
yields a measured percentage polarization within 0.3% of
the published value at two different telescope roll angles.  
The new coefficients are listed in Hines (1998) and can 
also be found at 
Observers should use these updated coefficients.

LIMITING POLARIZATION: For observations limited by 
object-noise, uncertainties in percentage polarization of 3%
and 1% per pixel for NIC1 and NIC2 respectively can be 
achieved.  Binning the Stokes parameters before forming the 
percentage polarization (p) and the position angles reduces 
the uncertainties by approximately 1/sqrt(N), where N is the 
number of pixels in the bin.  Uncertainties as low as 0.2% 
should be achievable with bright objects in NIC2.

GHOST IMAGES: Multiple ghost images are seen in images 
obtained through POL0S & POL240S in NIC1, but not through 
POL120S or the NIC 2 polarizers.  The location of ghosts in 
each polarizer appears constant on the detector (i.e.  
independent of telescope or object orientation).  The ghosts 
are offset between POL0S and POL240s, which produces a very 
highly polarized signal in percentage polarization. This 
allows them to be distinguished from real polarized signal.

Details of the HSL algorithm for NICMOS polarimetry and 
examples of the ghost images in the NIC1 polarizers can be 
found at 

The Automatic Notification Tool (ANT)

While one of our goals is to provide an efficient and stable Long Range Plan
(LRP),  we have always recognized that there will be times when the LRP will
need to be modified to react to observatory changes, new planning requirements,
and proposal changes.  Since changes in a visit's plan window can affect your
work schedule, we want to quickly  and consistently alert you when changes
For this purpose we have developed the Automatic Notification Tool.  This tool
detects significant plan window changes and, for any program with at least one
changed visit, automatically generates and e-mails a report to the the PI or
designated contact, PC, and CS.

The ANT will be run weekly starting the week of June 29, 1998.  If you have any
questions or comments you may direct them to your PC or CS.

                         RECENT PREPRINTS
We draw your attention to these papers, based on NICMOS data, that
will appear in the next few months.  This list includes all preprints received
by the STScI Library not yet published in the journals.  Please remember to
include our Library in your preprint distribution list.

PACKHAM, C.  "Evidence for a 20pc Disk at the Nucleus of
Centaurus A"  ApJ 6-2-98


                     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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the Subject: line blank and the following in the body:
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Comments, questions, suggestions, etc. can be e-mailed to
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