NICMOS Status
Roelof de Jong
(STScI)
and the NICMOS team:
Santiago Arribas, Elizabeth Barker,
Eddie Bergeron, Ilana Dashevsky, Anton
Koekemoer, Sangeeta Malhotra,
Bahram Mobasher, Keith Noll, Tom
Wheeler, Tommy Wiklind, Chun Xu
and
Ralph Bohlin, Adam Riess
Overview
•
•
•
•
•
Instrument
Pipeline
Photometry
(Non-)Linearity & Zeropoint
Calibration plans
Instrument
• Very stable due to NICMOS Cryo-cooler
System (NCS)
• Darks, Focus, Flats, Temperature stable
• 2-gyro mode observations successful
• New SPARS MULTIACCUMs added Poster P3-4 Xu
– SPARS4, SPARS16, SPARS32, SPARS128
– SPARS sequences preferred for anything
that has no huge dynamic range
Instrument: dark current
• Dark current
stable
(near day 600
persistence of
Mars
observation)
Instrument: focus
Instrument: 2-gyro mode
PSF nominal
Coronographic rejection identical
(no second roll angle in same orbit)
Poster P3-7 Malhotra
Pipeline/software updates
• MultiDrizzle implemented for NICMOS P3-5 Bergeron
• Routines available for
– SAA cosmic ray persistence removal
– Crosstalk removal (Mr. Stay-puft)
P3-6 Koekemoer
• Improved imaging and new grism
Exposure Time Calculator (July 2004)
– Continues improvements made, always use
the latest version for you proposals
In the pipeline for the Pipeline
• Improved reference files
– Better darks for 77.1K
•
•
•
•
•
SAA clean
Mr. Stay-puft (quadrant crosstalk)
Temperature from bias
Amp glow persistence
Improved treatment of Cosmics removal
– Reduces noise in pixels affected by cosmics
Photometry
• New photometry keywords/zeropoints
– Delivered July 2004
– Main differences with previous values:
•
•
•
•
Separate values Cycles 7/7N and Cycles 11+
Wavelength dependent aperture corrections
Improved (latest) data reduction methods
Better tied to ground-based measurements
Photometry: sensitivity change
• Detector
sensitivity
improved going
from 66 K to
77.1 K after
NCS installation
Photometry: aperture corrections
Aperture radius
NIC1 11.5 pix
NIC2 6.5 pix
NIC3 5.5 pix
• Going from
fixed to infinite
apertures
• Wavelength
dependence
determined
from TinyTim
PSFs
Spectro-photometric calibration
• P330E - Solar Analog
– Spectrum: measurements
+ model
• G191B2B - White Dwarf
– Spectrum: LTE model
• Tied to ground based
through Persson et al.
Standards (2MASS)
(details in forthcoming ISR)
Photometry: count rate standards
• Other HST
spectrophotometric
standards
consistent
Photometry: time evolution
• Some sensitivity
loss in NIC2
• Data in other
two cameras too
noisy
NICMOS non-linearity
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
• Classic well
depth nonlinearity well
understood
• Dependents
on total
counts, not
count rate
• Corrected in
pipeline
Count Rate Non-linearity
• Stellar standards over
a broad magnitude
range were observed
with the grisms
• Comparison with
overlapping STIS
spectra revealed an
unexpected
disagreement between
STIS and NICMOS
• ACS data suggested
NICMOS as the source
of the difference
• Potential for important
consequences to key
NICMOS science
makes this effect
important to
understand
Non-linearity: NICMOS vs ACS
• Similar effect when
comparing NICMOS
grism to ACS
photometry
Non-linearity: wavelength dependence
• Compare observed
NICMOS spectra to
white dwarf
models extended
to IR from STIS
optical
• Effect strongly
reduced at longer
wavelengths
Non-linearity:NICMOS spec vs phot
• Agreement
between observed
NICMOS spectra
and photometry
within errors
• Poor agreement
when spectra are
corrected to STIS
flux expectations
Non-linearity: lamp off/on test
• Increase total
count rate by
adding light
of the flatfield
lamp to the
background
• Count rate
increases as
predicted by
non-linearity
(cycle 7 NIC2 data)
Non-linearity: no trapping signal
• MULTIACCUM
sequences
nearly stable
independent
of count rate
• If nonlinearity
caused by
charge traps,
time scales
have to be
longer than
500 seconds
Non-linearity: The evidence
• NICMOS grism vs
– STIS & ACS spectra
– ACS photometry
• Lamp off/on test
• Supernova models ACS -> NICMOS J&H
• Narrowband vs Broadband filter
throughputs ground vs. inflight
• UDF inconclusive
Non-linearity: UDF vs. ground
• Use color corrections or template fitting
to match F110W to J ground
• Different results depending on reduction
(talk Mobasher & Thompson)
• Effect expected to bottom out at sky
level, ~23 AB-mag F110W for point
sources, earlier extended sources
• Maximum effect ~0.2 mag in F110W, no
effect expected in F160W
Non-linearity: Unknowns
Count Rate  Flux() or Electrons
()
(F110W)~1.02, (F160W)~1.00
•
•
•
•
•
•
•
•
Only incoming photons or add dark current?
Power law correction full count rate range?
Same exponent in all cameras?
Same wavelength dependence in all cameras?
Temperature dependence (cycle 7 vs 11+)
Pixel-to-pixel dependence?
Persistence?
Physical explanation!
Calibration plan
• Usual monitoring: dark, flat, focus, photometry
• Lamp off/on/off test: imaging and grism,
different filters and cameras
• Persistence tests using bright stars and
flatfields, test wavelength and count rate
dependence
• Deeper photometry on faintest standards
• Check consistency between 2MASS and
NICMOS in Orion legacy survey field
• Low frequency flat measurement in Camera 1;
monitoring data show residuals with position
• Non-linearity correction: may be hard to
implement backward compatible with previous
reductions
Poster P3-1 Arribas
Conclusions
• Instrument very stable with NCS
• Photometry:
– Improved aperture corrections
– Possible count rate dependent non-linearity
at <1.6 micron
– Test are scheduled in November to quantify
non-linearity
• For latest news check NICMOS website
• Subscribe to the NICMOS STAN newsletter