STIS SMOV Science Report
June 9, 2009
This presentation contains material that is embargoed until after the SM4
ERO press conference. Images/spectra of external (astronomical) objects
may not be altered, distributed, reproduced, published, displayed, or used in
any other way without the consent of the STScI Director or the HST Project.
STIS CTE Determinations
• Internal spot check (11400)
– Limited subset of normal sparse field internal CTE
measurements
– Designed to check reliability of existing formula
• External Spectra from 11386 Focus Check
– Large aperture spectra included to allow effect of
CTE on small aperture throughput measurement
to be checked
– Much higher signal level than 11400
CHARGE TRANSFER
CTInefficiency = 1 - ChargeTransferEfficiency
CTE ~ 0.999….
Charge ‘left’ after N pixels = CTEN
(e.g. 0.999500 ~ 0.6)
N
1024-N
D
B
Sparse Field Internal CTE Measurement
SB/SD = CTE(2N-1024)
925
D
Program 11400:
•
•
•
•
B
4xAmpD and 4xAmpB tungsten spectra at row 925
5xAmpD and 5xAmpB tunsten spectra at row 530
Low s/n due to high CTI makes single frames problematic
Images combined to improve S/N before extracting spectra
Measured CTI for case of low signal and background, GAIN=1
CTI
Year since 2000.6
Correct to zero background before estimating time dependence:
CTI0 = CTI . exp(2.97(B/G)0.21) where
B=Background
G=Gross signal
STIS CCD CTI for Low Signal limit and GAIN=1
CTI at zero background
[Caveat: Assume background dominated by spurious charge]
Time Constant (pre SM4) = 0.218
Time Constant (post SM4) = 0.211
Year since 2000.6
Program 11386
• External focus check
• Measured throughput of STIS 0.1x0.09 aperture with
G230LB grating
• Also took deep and shallow 52X2 comparison
spectra to calibrate other effects on count rate
– CTE effects
– Non-PSF related throughput changes
• Can also use these to verify current pipeline CTE
calibration
• Should redo verification after including new dark and
bias files
e- per pixel per read, integrated perpendicular to
dispersion direction, in the shortest of the 11386
exposures (2.4 s per subexposure)
“Embargoed figure - Do not distribute”
Standard calstis flux calibration, CTE
correction omitted (4 X 2.4 s expo).
Solid line gives reference spectrum.
“Embargoed figure - Do not distribute”
Standard calstis flux calibration, CTE
correction included (4 X 2.4 s expo).
Solid line gives reference spectrum.
“Embargoed figure - Do not distribute”
Standard calstis flux calibration, CTE
correction omitted (4 X 38.4 s expo).
Solid line gives reference spectrum.
“Embargoed figure - Do not distribute”
Standard calstis flux calibration, CTE
correction included (4 X 38.4 s expo).
Solid line gives reference spectrum.
“Embargoed figure - Do not distribute”
STIS CTE
• Results appear consistent with our prerepair CTE estimates
• Full recalibration will require additional
observations, currently included as part
of cycle 17 calibration plan
Upcoming Observations
•
FUV Dark Check 11390
– Watch how dark rate increases as function of time since HV on.
•
NUV MAMA Recovery
–
–
–
–
•
•
Visit 1 June 8, 19:55 UT
Visit 2 June 9, 21:40 UT
Visit 3 June 11, 17:22 UT
Visit 4 June 13, 17:15 UT
+ ongoing CCD Darks and Biases
Next week, much of remaining STIS SMOV will be completed,
including internal and external spectra with MAMAs, and
standard sensitivity monitor observations for all detectors.