Spectrophotometric Flux Calibration
F-flux, C-count rate, S-sensitivity
F(l )= C(l)/S(l)
or
S = C/Fstd
Details: Net Count Rate, C
1.
2.
3.
4.
5.
6.
7.
8.
9.
Background
Flat Field, P and L
Stray Light
Noise and Artifacts, eg Dust and Fringing
Operational Changes, eg G140L +3" ‡ -3"
Wavelength Calibration
Temperature
Time
Non-linearities, eg CTE losses
Details: Standard Star Flux, Fstd
1.
2.
3.
4.
5.
Teff & G from Balmer lines Finley
V band normalization of Landolt
LTE Koester = Hubeny
LTE ‡ non-LTE
WD agrees w/ Solar Analog in IR
MAJOR CONTRIBUTORS TO THE UNCERTAINTY OF A FLUX
DISTRIBUTION OF A SINGLE OBSERVATION
- RELATIVE TO THE V BAND
- IN ADDITION TO COUNTING STATISTICS OF THE OBSERVATION
I. UNCERTAINTIES IN THE COUNT RATES
A. REPEATABILITY IN BROAD BANDS
MODE
Bandpass (A)
one sigma (%)
G140L
350
50
0.54
0.46-.79*
G230L
1000
100
0.18
0.19-.59*
G230LB
1000
100
0.27
0.27-.39*
G430L
2000
200
0.32
0.20-.56*
G750L
2800
400
0.15
0.13-.91*
* Small correction for counting statistics
B. UNCERTAINTY (%) IN CTE CORRECTION
TIME
100e-
1 YEAR
5 YEARS
0.6
3
1000e0.3
1.5
10000e~0
~0
II. UNCERTAINTIES IN THE MODELS
A. STELLAR TEMPERATURE uncertainties, eg formal uncertainty of +/- 1000K for
G191B2B at 61200K makes <<1% flux differences.
B. INDEPENDENT HUBENY, KOESTER LTE CODES now agree in the continuum to
a worst case of 1% at 3microns.
C. RELATIVE STIS FLUXES agree w/ models to 1% at 2000A and below.
D. NICMOS SOLAR ANALOG AND G191B2B AGREE TO ~1% at 1.5microns and beyond
E. COMPOSITE MODEL ERROR BUDGET is 1% to 2000A, deceasing linearly to
zero at 5500A, and increasing linearly to 1% in the 1.5-3micron range.