WFC3 SMOV Science Report
04 August 2009
4 August 2009
1
WFC3 Science Report For 04 Aug 2009
1) 11552, Characterization of the WFC3 IR Grisms, Visit 01
preliminary results
2) 11447, WFC3 IR Background
3) 11426, WFC3 UVIS Contamination Monitor
4 August 2009
2
11552, Characterization of the
WFC3 IR Grisms
• Activity - Visit 01 (of 4).
• Objective – Measure image displacement, spectral trace
and dispersion, and throughput of the IR G102 and G141
grisms.
• Status – Visit 01: Successfully obtained G102 spectra of flux
standard GD-153 at 3 different IR field points (center and
two corners).
• Results
» Quick look shows GD-153 well exposed, at expected levels, and at
expected locations within the field
4 August 2009
3
11552 Image
Embargoed figure - Do not distribute
0th
order
1st order
2nd order
other stars
Flux standard GD-153 with the WFC3/IR G102 grism
4 August 2009
4
11447, WFC3 IR Background
•
Activity - Visit 34 (of 22). Proposal measures readnoise, dark current
and diffuse background in IR channel.
•
Objective – Measure diffuse background light in the IR channel through
observations of low stellar density fields
•
Status – 3 external orbits in Visit 34, aimed at the HST orbit pole
obtained on 2009/july/19 analysis ongoing,
•
Preliminary Results
» definite illumination pattern in the frame, near bright earth limb, appears in
each of five exposures during Visit 34, shape is the same but brightness
changes.
» Up to factor of 2 difference in brightness between “dark” and “bright” sides of
image.
» Background light, as measured for each W&M filter from external images of
a single field of medium zodiacal light level, are compared to those
anticipated from known sources (e.g. Zodiacal light) and WFC3 throughput
(cf. Table 7.12 of Instrument Handbook), but this is still ongoing analysis.
4 August 2009
5
11447 IR Background @Orbit Pole
Aug 3, 2009
Stray light at left side of the IR
sensor (quads 1 and 2) evident
in ~75 deg of 360 deg of HST
orbital phase, of Visit 34 of
Program 11447 of the orbit
pole. Sky is as much as twice as
bright in columns 5-204 as in
columns 512-711. Morphology
of stray light is the same in
each of the five exposures in
which it appears; only its
brightness changes. From
individual samples up the ramp,
we estimate that the blurred
edge of the stray light (near
column 200) is not due to
image motion evident in stars.*
*Due to gyro guiding snafu, the coordinates of
_raw.fits ((298,-21) = incorrect) differ from _jif.fits
4((162,+61)
August 2009
= correct, they match the star field) !
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11447 IR Background @Orbit Pole
Columns
5:204
512:711
Earth Shine
Earth Shine
Aug 3, 2009
4 August 2009
7
11447: Total ETC Background
4 August 2009
8
11426 –
UVIS Contamination Monitor
•
•
Activity - monitor UV photometric throughput over time & wavelength
Objectives - Measure relative throughput as a function of time and
wavelength. Assess internals for any changes in readnoise, dark current,
or flatfield.
– Observe one white dwarf standard star (grw+70) with 512x512 subarrays one
per chip (C512A, C512C) once per week during SMOV
– Two exposures obtained in all UV filters plus F606W, F814W and also 2
biases, 2 darks, 3 tungsten flats (f336w, f438w, f606w)
•
•
Status - Six visits completed, over period of 33 days, including before and
after the second anneal in July.
Results:
 No significant changes in relative throughput as function of time;
 Readnoise of science pixels stable, amp B shows lowest scatter (stdev 0.01)
compared to other amps (0.02-0.03).
 Dark current is stable
 Lamp output decreased by ~1% over the ~35days.
4 August 2009
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11426 Co-adding bluest filters
UVIS1, C512A
UVIS2, C512C
anneal
Relative flux
Relative flux
anneal
Co-added f218w, f225w, f275w, f280n
4 August 2009
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Readnoise
- Readnoise in e-/s/pix
in the different quadrants
- Based on science pixels only
- Measured from bias pairs,
assuming gain=1.5e-/DN
- No trend with time
- Statistics as a set:
Amp
A
B
C
D
mean
2.90
2.98
2.89
3.00
stdev
0.03
0.01
0.02
0.02
A
C
B
D
median
2.91
2.98
2.89
3.01
-Outliers under investigation
4 August 2009
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Dark current over time
Discussed in more detail elsewhere but included here for completeness.
Median dark levels, in e-/s/pix, for chip 2 as function of MJD; anneals marked with dashed lines.
Three highest darks still under investigation; so far, no correlation with time since pinning
(bowtie) exposure, window temperature, bright earth, time since SAA passage, or hot pixels.
4 August 2009
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Contam.monitor intflats - levels
1.02
F336W
visit2/1
visit6/1
0.98
F438W
visit2/1
visit6/1
F606W
visit2/1
visit6/1
4 August 2009
- Average line plots through chip1 in Visit2/Visit1 ratio and
Visit 6/Visit 1 ratio, with 33 days between Visit 6 & 1
- F336W flats are noisier: tungsten lamp is relatively red so
that despite long exptime (2000sec) they have only ~20%
flux level of F438W, F606W
- Ratios are flat except for expected filter features
- Lamp seems to be dimming slightly: ~1% decrease in flux
seen in all three filters. Similar trend seen in bowtie monitor.
F336W
mean stdev
1.003 0.015
1.002 0.017
0.996 0.017
0.996 0.015
0.995 0.017
0.995 0.015
0.990 0.017
0.990 0.015
0.988 0.017
0.988 0.015
IMAGE RATIO STATISTICS, CHIP 1
F438W
F606W
median mean stdev median
mean stdev median
1.002
1.003 0.007 1.003
1.007 0.007 1.007
1.002
1.003 0.007 1.002
1.007 0.007 1.007
0.996
1.001 0.007 1.001
0.999 0.007 0.999
0.996
1.000 0.007 1.000
0.999 0.007 0.999
0.994
1.000 0.007 1.000
1.000 0.007 1.000
0.994
1.000 0.007 1.000
1.000 0.007 1.000
0.989
0.990 0.007 0.990
0.991 0.007 0.991
0.989
0.991 0.007 0.991
0.991 0.007 0.991
0.988
0.989 0.007 0.989
0.991 0.007 0.990
0.988
0.989 0.007 0.989
0.991 0.007 0.991
Filter features appearing in ratio due to first intflat of the
set being shifted relative to others
13