NICMOS Status Roelof de Jong (STScI) and the NICMOS team: - - PowerPoint PPT Presentation

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

– SPARS4, SPARS16, SPARS32, SPARS128 – SPARS sequences preferred for anything that has no huge dynamic range

Poster P3-4 Xu

Instrument: dark current

• Dark current

stable

(near day 600 persistence of Mars

• bservation)

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
• Routines available for

– SAA cosmic ray persistence removal – Crosstalk removal (Mr. Stay-puft)

• Improved imaging and new grism

Exposure Time Calculator (July 2004)

– Continues improvements made, always use the latest version for you proposals

P3-6 Koekemoer P3-5 Bergeron

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

• Going from

fixed to infinite apertures

• Wavelength

dependence determined from TinyTim PSFs

Aperture radius NIC1 11.5 pix NIC2 6.5 pix NIC3 5.5 pix

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

spectro- photometric standards consistent

Photometry: time evolution

• Some sensitivity

loss in NIC2

• Data in other

two cameras too noisy

NICMOS non-linearity

• Classic well

depth non- linearity well understood

• Dependents
• n total

counts, not count rate

• Corrected in

pipeline

QuickTime™ and a TIFF (LZW) decompressor are needed to see this picture.

Count Rate Non-linearity

• Stellar standards over

a broad magnitude range were observed with the grisms

• Comparison with
• verlapping STIS

spectra revealed an unexpected disagreement between STIS and NICMOS

• ACS data suggested

NICMOS as the source

• f 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

• ptical
• 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

• f 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

• f count rate
• If non-

linearity 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 ∝ Fluxα(λ) or Electrons α(λ)

α(F110W)~ 1.02, α(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 λ< 1.6 micron – Test are scheduled in November to quantify non-linearity

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