TIPS/JIM
July 21, 2011
Agenda:
INS Division News (Danny Lennon)
Improved COS Medium Resolution FUV Line Spread Functions (Jerry Kriss) !
Detection of Line-shaped Tracks in Images with DADD (Peter McCullough) !
Persistence from Cosmic Rays in JWST NIR Detectors (Mike Regan) !
Next TIPS/JIM: August 18, 2011

INS NEWS
HST Instruments: continue to work well and Hubble passed the milestone of its
1,000,000th image with a WFC3/IR Grism observation of HAT-P-7b.
On JWST the main piece of news is that TFI will be descoped. It will now feature interferometric imaging through a non-redundant mask aperture, wide field grism spectroscopy, single object grism spectroscopy for exoplanet transits, and broad band imaging.
Staff changes:
Aparna Maybhate has taken on the role of RIAB Deputy.
Luigi Bedin, Sami Niemi and Brian Ferguson have all left STScI.
Keith Noll will leave in October.
Housing: Bloomberg/Muller moves are almost finished. Our thanks to all concerned. Keswick lease is signed, expect take up occupancy in fall 2012.

TIPS/JIM
July 21, 2011
Agenda:
INS Division News (Danny Lennon)
Improved COS Medium Resolution FUV Line Spread Functions (Jerry Kriss) !
Detection of Line-shaped Tracks in Images with DADD (Peter McCullough) !
Persistence from Cosmic Rays in JWST NIR Detectors (Mike Regan) !
Next TIPS/JIM: August 18, 2011

TIPS
July 21, 2011
Jerry Kriss

n   n   n
The broad wings on the COS Line Spread Function (LSF) were discovered during SMOV (Ghavamian+2009).
The wings are caused by mid-frequency wave-front errors
(MFWFEs) produced by polishing errors on the HST primary and secondary mirrors.
Ghavamian+2009 used WFPC2 measurements of the OTA
MFWFEs (Krist & Burrows 1995) and modeling of the COS optics to derive model LSFs that appeared to be a good match.
6/16/2011 TIPS 2/14

6/16/2011 TIPS
!
3/14

6/16/2011 TIPS
!
4/14

6/16/2011 TIPS 5/14

6/16/2011
Since the deconvolved absorption line isn’t black,
==> The wings on the LSF must
be even broader …
TIPS 6/14

6/16/2011
Geocoronal Ly α in the Mrk 509 observation
TIPS
Light filling the aperture (as scattered light does) extends to ±100 pixels
7/14

n   n   n
In addition to the MFWFEs on the mirrors, there should be scattering from microroughness.
Hasan & Burroughs (1993), using WFPC observations, predict scattering due to microroughness as a power law for the PSF with index − 2.5. (In the far field, diffraction will have a limiting power-law index of − 3.) u
Integrating the PSF over 1 dimension to obtain an LSF for COS will reduce this index by 1: a prediction of − 1.5 for scattering due to microroughness, and a limit of − 2.0 for simple diffraction.
Empirically test a grid of models with two free parameters: u
Core of the new empirical LSF is the same as the current model. u   u
The relative normalization of the power law.
Power-law indices ranging from − 1 to − 2.5.
6/16/2011 TIPS 8/14

n   n   n   n
Best fit index is
− 2.25
Normalization is
1.4% to 2.5% of the peak of the core LSF.
Transition radius is 19 − 23 pixels.
Additional power in the extended wings is ~3%.
6/16/2011 TIPS 9/14

Improvement is slight, but significant
Sk 155/STIS E140H convolved with old and new COS LSFs
6/16/2011 TIPS 10/14

The New LSF Improves Deconvolutions
Sk 155/STIS E140H compared to deconvolved COS spectrum
6/16/2011 TIPS 11/14

Now the ISM lines in Mrk 509 are black
6/16/2011 TIPS 12/14

n   n   n
Adding extended power-law wings to the model COS
LSFs with a power-law index of − 2.25 improves the characterization of the LSF.
LSF wings this steep are even steeper than diffraction alone. This implies that scattering due to microroughness on the HST mirrors is negligible, even in the far UV, and that scattering within COS itself is also negligible.
The additional power in the wings is only ~3%, but this significantly improves modeling of saturated absorption features.
6/16/2011 TIPS 13/14

n   n   n
The ISR is online at: u   http://www.stsci.edu/hst/cos/documents/isrs/
ISR2011_01(v1).pdf
The improved LSFs are online at: u
G130M: http://www.stsci.edu/hst/cos/performance/ spectral_resolution/fuv_130M_lsf_empir.html
u
G160M: http://www.stsci.edu/hst/cos/performance/ spectral_resolution/fuv_160M_lsf_empi.html
Preprint on Mrk 509 results appeared on astro-ph on
July 5: http://arxiv.org/abs/1107.0661
6/16/2011 TIPS 14/14

TIPS/JIM
July 21, 2011
Agenda:
INS Division News (Danny Lennon)
Improved COS Medium Resolution FUV Line Spread Functions (Jerry Kriss) !
Detection of Line-shaped Tracks in Images with DADD (Peter McCullough) !
Persistence from Cosmic Rays in JWST NIR Detectors (Mike Regan) !
Next TIPS/JIM: August 18, 2011

STScI
Peter R. McCullough
Jul 21, 2011
1

How fast we are progressing… n   n   n
2007, First Map of an Alien World, SST press release for Nature article of Knutson et al.
2009, Alien Maps of an Ocean-bearing World,
ApJ title of Cowan et al.
2011, Observational Evidence of Sentient Life on an Earth-like Planet, TIPS alternative title of McCullough
2/11

How fast we are progressing… n   n   n
2007, First Map of an Alien World, SST press release for Nature article of Knutson et al.
2009, Alien Maps of an Ocean-bearing World,
ApJ title of Cowan et al.
2011, Observational Evidence of Sentient Life on an Earth-like Planet, McCullough (this work)
3/11

DADD
= Doubling Accumulation Drift Detection
DADD brought to you by … n   n   n   n
Jill Tarter, JHU seminar 2004-2005
Richard Stauduhar (1940-2010), mathematician for the SETI Institute and U.C. Berkeley Space
Sciences Lab, private communication 2005.
Cullers & Deans 1992, unpublished*, cited by
Backus, P. R. 1993, The NASA SETI Microwave Observing project Targeted Search, in Third Decennial US-USSR
Conference on SETI, ASP Conference Series, Vo. 47, p. 323.
SetiQuest.org, sonata-1.0.16.zip
* thanks to Jill Lagerstrom (and the authors) for obtaining a scanned copy of this unpublished report.
4/11

Line-shaped streaks (from bright lights on Earth) appear in ~30% of HST WFC3 observations of the dark-side of Earth, (taken for flat fields, to be described in a future TIPS). DADD automates flagging of pixels within streaks.
5/11

DADD = Doubling Accumulation Drift Detection
M spectra, each with N channels
Requirement of slow drift: |slope| > 1
Mathematical operations:
Brute force: ~2NM 2
DADD: ~2 NM log
2
M
DADD accumulates pairwise like the FFT ;
DADD reuses sums of pixels common to multiple lines across the 2-D array.
To apply DADD to 2-D imagery, we analyze the image successively four times with rotations of 0º, 90º, 180º, and 270º in order to detect trails of arbitrary slope and origin.
N Frequencies
6/11

DADD = Doubling Accumulation Drift Detection
0 0
0 1
00 00 0001
00 11 0111
01 12
01 23
0000 0000
0000 1111
0011 1122
0011 2233
0112 2334
0112 3445
0123 3456
0123 4567
continuous functions:
all steps = 0 or 1 channel
constant derivatives
N Frequencies
7/11

DADD is sensitive
8/11

DADD is sensitive, quick,
Execution time per track identified
= 0.7 seconds per megapixel
= 2.8 s for 2048x2048
9/11

DADD is sensitive, quick, and stands alone
Execution time per track identified
= 0.7 seconds per megapixel
= 2.8 s for 2048x2048
C code operating on 16-bit FITS 2-D images, with an IDL wrapper to facilitate preprocessing and post-processing analysis.
(WFC3 ISR coming soon)
10/11

Summary: DADD can be used for detection of …
1.
SETI signals, e.g. weak, drifting narrowband CW signal in time series of RF spectra
2.
Streaks across dark-Earth flat-fields (as illustrated)
3.
Cosmic ray trails*
4.
Asteroid or satellite trails*
5.
Bleeding (overexposed PSF) trails* ^
6.
Slitless grism spectra* ^
* DADD is less sensitive to shorter line segments.
^ DADD is probably overkill where orientation of trails is fixed and known a priori.
11/11

TIPS/JIM
July 21, 2011
Agenda:
INS Division News (Danny Lennon)
Improved COS Medium Resolution FUV Line Spread Functions (Jerry Kriss) !
Detection of Line-shaped Tracks in Images with DADD (Peter McCullough) !
Persistence from Cosmic Rays in JWST NIR Detectors (Mike Regan) !
Next TIPS/JIM: August 18, 2011

Mike Regan

Cosmic rays on JWST will be much more common than on HST
•   Around 20% of pixels will be affected in a 1000 sec exposure.
•   If there is long lasting persistence
–   Could lead to a noise floor
•   Experiment
–   Use existing ground test dark cubes
•   20 ~1 hour NIRSpec Darks
•   20 ~25 min NIRCAM Darks
–   Look at effect of CRs in subsequent darks

Example dark measurement for NIRSpec shows low dark current.

!

Results extend to the lowest fluence events.

There is still persistence in the 2 nd and 3 rd exposures after the CR.
!

There is still persistence in the 2 nd and 3 rd exposures after the CR.
!

•   The total observed persistence depends on both the magnitude of the CR and the amount of time before reset.
•   CRs during idle should not affect the total noise.
•   The persistence signal should be able to be modeled since we will have all the information.
•   Bright sources in long science exposures will be the major sources of persistence.
•   Sets of long dark exposures are very useful.