TIPS/JIM
June 19, 2008
Agenda:
INS Division News (Stefano Casertano)
HST Pointing: Some Recent Statistics (Matt Lallo)
Updated CTE correction formulae for ACS (Marco Chiaberge)
NIRCam: Status Update (Kailash Sahu)
Next TIPS/JIM: July 17, 2008
1
HST News:
Preparation for the servicing mission continues smoothly; the last HST MSR
(Tuesday June 17) was dedicated to a review of the status of STScI work for SM4
and SMOV.
STScI will conduct a Readiness Review September 9-10.
JWST News:
Following the successful PDR and NAR earlier this year, JWST has now passed the
Science Mission Directorate review at NASA Headquarters.
Division news:
We plan to add new staff in preparation for the upcoming HST and JWST work.
o Interviews for several open RIA positions are ongoing. The first new hire,
Tyler Desjardins, will arrive Monday June 23.
o Derck Massa, a Visiting Scientist, will join the COS/STIS Team on
August 4. Other members of the research staff will arrive in the next three
months (dates TBD).
HR is implementing a mechanism to provide input on supervisors’ performance as
part of the Performance Appraisal process. All INS staff will receive an email
inviting them to fill in an evaluation of their supervisors. The evaluation form
will be short, but will provide an opportunity to include free-form comments if
desired. The input will be collected anonymously and collated by HR for use by
the supervisor’s manager. Participation is voluntary but strongly encouraged. Of
course, we continue to have an open door policy and strongly encourage anyone
with comments, praise, or concerns for managers’ performances to talk to us
directly; this new mechanism is meant to provide an additional, confidential
channel to convey such information.
The work of the Diversity, Culture, and Respect Working Group has received
numerous accolades from external groups that have reviewed the Institute’s
performance and status in these areas. After a very successful year of activity, we
are looking for up to three new members to provide a fresh perspective and help
with he tasks ahead. Please send nominations (including self-nominations) to
Kevin Lindsay or Stefano Casertano.
In the spirit of the DCRWG’s recommendation to hold more social events, we
continue to look for sponsors for luncheons and afternoon gatherings. To
accommodate the sponsors’ constraints, this month’s afternoon gathering will take
place June 26 at 4:30pm in the CafeCon.
We want to remind all Division staff of the availability of Beth Spotts, the
Institute’s Ombudsperson. She will be at the Institute on July 23, and after that
every month on the third Wednesday. She can be found in S216C. We encourage
you to please use Beth as a confidential resource for any workplace (or personal)
issues you might have. Confidentiality is strictly protected in all cases (with limits
in cases involving physical abuse or endangerment). Talk to Beth if you have any
questions.
TIPS/JIM
June 19, 2008
Agenda:
INS Division News (Stefano Casertano)
HST Pointing: Some Recent Statistics (Matt Lallo)
Updated CTE correction formulae for ACS (Marco Chiaberge)
NIRCam: Status Update (Kailash Sahu)
Next TIPS/JIM: July 17, 2008
1
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HST Pointing Improvements
Why Improve HST Pointing & Astrometry?
1. Absolute astrometry increasingly important:
-
multi-mission archives, multi-wavelength campaigns, coordinated observations
“Fundamentally important property of HST data” – STUC, 2002
2. Improved pointing supports the most efficient COS acquisition scenarios.
3. Well-calibrated FOV entering SM4 simplifies SMOV calibrations & operations.
What Comprised the Initiative?
1. Use of GSC2 in operations since mid-2006 (Cycle 15)
-
Reduces catalog error to 0.25˝ (1! absolute) and 0.18˝ (1! relative across FOV)
2. Retroactive improvements in HLA astrometry
-
Updated astrometry keywords by identifying GSC2 objects in images. Other methods for archive astrometry
improvements being assessed.
3. SI & FGS alignment calibrations (“focal plane alignment”)
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Focal Plane Alignment
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Basic Process
!
!
!
!
1. update FGS magnifications (this linear distortion term continues to trend significantly for many years on-orbit)
2. with ~20mas astrometry stars, use guidestars and astrometer FGS to obtain zero point and rotation of the three FGSs
3. with the resulting current FGS calibrations, determine accurate relative locations of SIs
4. make operational updates to SIAF, FGS matrices, FGS magnifications and related products.
CAL-OTA 11021 and the routine FGS calibration program obtained such data.
! New FGS calibrations were made operational on 2008.014 (matrices & magnifications)
! SI updates were not made due to the loss of ACS, and small deltas for WFPC2 & NICMOS
Assessing the Improvement
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Compare guidestar pairs’ angular separation based on their GSC coordinates against their
separation based on their FGS-observed locations and operational transformation to V2V3.
Pro: large number statistics
Con: doesn’t tell you what’s happening at the SI
Target coordinates obtained from science data
For centroidable astrometric targets, determine from the science data headers the RA & Dec
and compare against their astrometric coordinates
Pro: measures exactly what you want to check
Con: more labor intensive and not possible/feasible in most cases
Guidestar Separations
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Guidestar Separations
Guide Star Pair Fit Error during 2005 GSC1 Ops
2
1.8
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2005 2005.1 2005.2 2005.3 2005.4 2005.5 2005.6 2005.7 2005.8 2005.9
2006
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Guidestar Separations
Guide Star Pair Fit Error during 2007 GSC2 Ops
2
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1.4
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2007 2007.1 2007.2 2007.3 2007.4 2007.5 2007.6 2007.7 2007.8 2007.9
2008
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Guide Star Pair Fit Error since 2008.014 realignment
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2008.15
2008.2
2008.25
2008.3
2008.35
Guidestar Separations
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GSC1- 2005
2000
1000
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1
2
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GSC2 Operations - 2007
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GSC2 & New Calibrations, 2008 days 14 - present
2000
1000
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arcseconds
1
2
Target Coordinates Spot Check
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1.0
0.8
0.6
Observations of Upgren 69 with WFPC2/PC:
0.4
RA & Dec for centroided pixel position using DS9
compared against Tycho position with proper motions
applied.
0.2
-1.0
-0.8
-0.6
-0.4
-0.2
0.0
0.0
-0.2
-0.4
-0.6
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0.2
0.4
0.6
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1.0
Cycle 17 Onward
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Maintain pointing and astrometry close to the GSC2-catalog
limited value of ~0.2 arcseconds
Align new SIs & FGSs
Newly flown instruments trend the most. Keep new FGS from acting as dominant guider
during Cycle 17.
Only use dedicated HST time when necessary
-
Track COS & STIS missed distances. From the stored slew amount to center a target with
the on-board acq, we will obtain a large number of “missed distances” indicating pointing
performance. These data were amassed with STIS for a number of years in early 2000 and
facilitated FGS alignment in 2002.
-
Guidestar pair statistics, sorted by FGS, gives information to facilitate alignment.
All-sky UCAC3 (early 2009) can allow accurate SI alignment to be accomplished without
dedicated observations.
TIPS/JIM
June 19, 2008
Agenda:
INS Division News (Stefano Casertano)
HST Pointing: Some Recent Statistics (Matt Lallo)
Updated CTE correction formulae for ACS (Marco Chiaberge)
NIRCam: Status Update (Kailash Sahu)
Next TIPS/JIM: July 17, 2008
1
UPDATED CTE CORRECTION
FORMULAE FOR ACS
Marco Chiaberge
Pey Lian Lim, Vera Kozhurina-Platais, Marco Sirianni
Ron Gilliland, Jennifer Mack
CHARGE TRANFER EFFICIENCY (CTE) per pixel
Defined as CTE = 1 - ΔQ/Q = 1 - CTI
For an ideal CCD CTE = 1.0
For real CCDs CTE < 1
manufacturing imperfections in the crystalline lattice
radiation damage (increasing with time)
The total CTE is CTEN
significant effect for large CCDs
CTE depends on flux, sky level, # of transfers
The effect of CTE on stellar photometry
is to reduce the measured flux
(up to ~20% or more)
A fraction of the “lost” flux goes into the “tail”
But significant flux is just lost and cannot be recovered
Photometric test
Allows to measure the total flux lost and
provides correction formulae for photometry.
Stars are positioned at different distance from the readout
amplifier thus changing the number of transfers and therefore
the impact of CTE.
D
C
A
C
B
A
WFC
HRC
D
Observations
Programs: CAL/ACS 9648, 10043, 10368 (PI:A. Riess),
10730 (PI: Chiab)
FILTERS:
F606W, F775W, F502N
EXP TIMES: 30s, 360s for HRC; 30s and 400s for WFC
(for HRC/F502N, 360s only)
Post-flash used to achieve higher background levels
F606W, LOW-FLASH, MED-FLASH, HIGH-FLASH
Exp times: 30s, 360s
No CR-REJECTION, no dithering
2 Observations/year (Cycle 11-13)
Cycle 14 only 1 epoch (March 2006), no post-flash
Cycle 15 1 test visit (Jul- Sept 2006) to test CR-SPLIT + dithering
POTENTIAL PROBLEMS
Background levels
Cycle 13, August 2005, HRC
FLASH=0.5s
FLASH=1s
FLASH=3s
HOT PIXELS
HRC, F606W, 30s
25”x25”
COSMIC RAYS
WFC F606W, 400s
30”x30”
CR are not uniformly distributed
CRs and hot pixels may affect CTE estimates
More important for low CTI, they increase the error
Published results before our new analysis
WFC
time dependent formula based on 3 epochs
March 2003 – Feb 2004
Riess & Mack ISR 2004-006
HRC
time dependent formula based on 1 epoch
March 2003
Riess ISR 2003 – 009
ANALYSIS PROCEDURE
• IRAF, SM, some IDL
• Generate “clean”, deep, drz image using all data
• Identify cosmic rays, hot pixels and saturated pixels and mark
them on DQ extension of FLT files
• Mask out area around the saturated stars
• Measure flux of “good” stars only on the single_sci files
• Reject outliers (sigma clipping, 3 itearations)
• Fit delta mag vs # of transfers for different bins of flux
HRC – F606W 360sec
WFC F775W – 400s
Photometry
Aperture photometry with “phot” (iraf. noao)
R = 3 pixels
Larger aperture radii return too few stars
Background is measured in an annulus around
each star (r = 15 d = 3)
WFC F775W - 30s
March 2006
A linear fit is performed
for each bin of flux
(blue lines)
Errors on the slope
are estimated
(yellow lines)
Δmag = ax + b
a = (7.9 ± 0.6) e-5
At y = 2000 this means
a loss of 0.158 ± 0.015 mag
WFC F606W – 30s
March 2003
HRC F502N 360s
Mar 2006
Results (Δmagy=2000) are collected for all bins of stellar flux and
sky background at each epoch
We assume a linear dependence with flux, sky, and # of transfers
in agreement with other instruments and with internal CTE tests
Δmagy=2000 = 10A’ x SKY B x FLUX C
For each epoch, the coefficients A’, B, C of the formula are
determined by performing a multi-linear regression fit
A’ IS TIME DEPENDENT
We assume linear dependence on time and Δmag ~ 0 at t = 0 (launch)
We use Δmagy=0 = 0
Δmag = 10A x SKYB x FLUXC x Y/2000 x (MJD-52333)/365
The coefficients A, B, C are not time dependent and can
be averaged between epochs
Weighted means are calculated using 4 epochs
(March 2003, March 2005, Aug 2005, March 2006)
Typical errors on the coefficients (single epoch) ≤ 0.1
B is the coefficient with the largest spread among epochs
(σ = 0.06 WFC, σ = 0.04 for HRC)
A
B
C
WFC
HRC
-0.15 ± 0.04
-0.44 ± 0.05
(0.14 ± 0.14)
(-0.89 ± 0.26)
-0.25 ± 0.01
-0.15 ± 0.02
(-0.31 ± 0.02)
(-0.24 ± 0.13)
-0.44 ± 0.01
-0.36 ± 0.01
(-0.64 ± 0.05)
(-0.21 ± 0.07)
TESTING THE FORMULAE
Apply the correction to data from different epochs, for different
sky levels using the same data that were used to derive the formula
Apply the correction to photometry performed with ePSF
(both aperture photometry and PSF fitting)
Compare prediction of the formula with measured mag losses
at different epochs
F502N - 30s
March 2005
F775W – 30s
March 2005
HRC F606W 30s - March 2003
March 2006
ePSF photometry
WFC F606W
Aperture photometry
30s vs 400s - March 2006
PSF fitting
COMPARISON WITH PREVIOUS FORMULA
ACS fail.
SM4
Sky = 2e
Flux = 650
Sky = 2e
Flux = 2500e
Sky = 2e
Flux = 650
RESULTS and FUTURE WORK
• Data from 4 epochs (March 2003 through March 2006) were analyzed
using a new data analysis strategy aimed at obtaining “cleaner” results
• We derived time-dependent correction formulae for both
HRC and WFC that are accurate at the level of a few percent
• New observations after SM4 using CR-REJ and possibly dithering
• Procedures should be made automatic (or semi-automatic)
• Formula for different aperture radii
• Better data might lead to a better characterization
Different form of the formula?
Cycle 11 observations, from ISR ACS 2003 009
TIPS/JIM
June 19, 2008
Agenda:
INS Division News (Stefano Casertano)
HST Pointing: Some Recent Statistics (Matt Lallo)
Updated CTE correction formulae for ACS (Marco Chiaberge)
NIRCam: Status Update (Kailash Sahu)
Next TIPS/JIM: July 17, 2008
1
NIRCam: Status Update
Optical Telescope Element
(OTE)
Primary
Mirror
1m
Cold, spacefacing side
Integrate
d
Science
Instrume
nt
Module
(ISIM)
Spacecraft Bus
Sunshield
Warm, Sun-facing side
Kailash C. Sahu
NIRCam’s Role in JWST’s
Science Themes
NIRCam
NIRCAM_X000
Modern Universe
Clusters
Clusters&&
Morphology
Reionoization
First
FirstGalaxies
Galaxies
Recombination
Forming Atomic Nuclei
Inflation
Quark Soup
First Light in the Universe:
NIRCam will execute deep surveys to find and
categorize first galaxies.
Assembly of Galaxies:
NIRCam will provide details on shapes and
colors of galaxies.
Birth of Stars and Protoplanetary Systems:
NIRCam will be ideal to study disks and protoplanetary systems.
young solar system
Kuiper Belt
Planets
Planetary Systems and Origins of Life:
NIRCam and its coronagraph will image and
characterize disks and planets, and study
extrasolar planets with high S/N observations.
What’s NIRCam?
•NIRCam is the near-infrared camera (0.6-5
microns) for JWST
–Dichroic used to split range into short (0.62.3µm) and long (2.4-5µ) sections
–Nyquist sampling at 2 and 4µm
–Coronagraphic capability for both short and
long wavelengths
–Low-resolution spectroscopic capability in
the LW channel.
•NIRCam is the wavefront sensor
–Must be fully redundant
2 Channels Per Module
– 7 wide band filters (4 SW,
3 LW) for deep surveys
– Survey efficiency is
increased by observing the
same field at long and
short wavelength
simultaneously
• Pixel scale:
SW: 0.032”/pix
LW: 0.064”/pix
Module B
• Each module has two
channels (0.6 to 2.3 µm
and 2.4 to 5 µm)
Module A
Short wavelength channel
2.2’
Long wavelength channel
NIRCam Optical Layout*
*there are 2 identical modules
Pupil Imaging Lens Assembly
Shortwave Focal
Plane Housing Fold
Mirror
Shortwave Fold
Mirror
Longwave Focal
Plane Housing Fold
Mirror
Shortwave Triplet
Subassembly
Shortwave Filter
Wheel Assembly
Elements
Longwave Triplet
Subassembly
Dichroic
Beamsplitter
Longwave Filter
Wheel Assembly
Elements
Collimator Triplet
Subassembly
Coronagraph
Elements
First Fold Mirror
Subassembly
Starlight from
OTE
Pick off Mirror
Subassembly
JWST-Spitzer Image Comparison
1’x1’ region in the UDF – 3.5 to 5.8 µm
Spitzer, 25 hour per band
JWST, 1000s per band (simulated)
(GOODS collaboration)
Courtesy: Stefano Casertano
Precision Transit Light Curves
• Large collecting area
– 45 × Spitzer, Kepler
– 350 × CoRoT
• Increased SNR (∝D), faster
observations (∝D2)
• Very precise light curves for
primary eclipses
– Smaller planets
– Rings, moons, etc.
– Ingress & egress curves for
temp map (Rauscher et al)
• Thermal mapping (secondary
transit light curves).
E. Rauscher et al. (2007)
Transits With NIRCAM
• Lenses introduce 4,8,12 λ of defocus to spread light over many hundreds of
pixels
– Reduce flat-field errors for bright stars 5<K<10 mag
– Ultra-high precision data for bright transits
• Diffused images (weak lenses) or spectrally dispersed images (grism)
reduce brightness/pixel by >5 mag. K=3-5 mag stars not saturated.
PSF with F212N & Weak Lenses
Courtesy John Krist
In Focus F210M
8λ Defocus x10
4λ Defocus
12λ Defocus x10
SW #1 Flight detector
Illuminated
Dark
• RN and QE better than spec requirements. But minor problems remain…
• First-frame effect (RN is larger in the first few ms after reset, which effects
first 2 rows).
• RN level is unstable, which may require active temperature control.
Current Status
• FPA has been thoroughly tested at UofA.
• It has gone to Lockheed Martin for checkout of the focal plane
electronics.
• FSW script development is in progress at STScI. Script testing
will be done in GSFC/LMATC in 2008/2009.
• Calibration, DMS, PPS and ETC development in progress.
Project is moving along!
NIRCam qualification focal plane.
NIRCam ETU bench.
1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017
Concept Development
mission formulation
authorized
science operations
mission implementation
NIRCam delivery
launch
Summary
• NIRCam will be a versatile instrument capable of
detecting “First Light” galaxies
• Recent additions to NIRCam such as long
wavelength slitless grisms and use of weak lenses
make it also capable of definitive exoplanet studies
• Both NIRCam and the entire JWST Project are
making great progress towards a 2013 launch.