gaia: algorithms for the external...
TRANSCRIPT
Gaia: algorithms for the external calibration
Montegriffo P., Cacciari C., Ragaini S.
Thursday, February 18, 16
Roma & Teramo(Obs., ASDC)
Edinburgh (Royal Observatory)
Cambridge (Institute of Astronomy)(CU5 leadership)
Leiden (Observatory)
Bologna (INAF-OABO)
Barcelona(Universitat de Barcelona)
Bologna
Thursday, February 18, 16
Photometry Measurement Concept
Figures courtesy Anthony Brown
RP spectrum of M dwarf (V = 17.3 mag)Red box: data sent to ground
White contour: sky-background levelColour coding: signal intensity
During 5 years of mission each source is observed on average 80 times all over the
focal plane
Thursday, February 18, 16
Star motion in 10 s
Astrometric Field CCDs
Blue Photom
eter CC
Ds
Sky Mapper CCDs
Red Photom
eter CC
Ds
Radial-Velocity Spectrometer CCDs
Basic Angle
Monitor
Wave Front Sensor
Basic Angle
Monitor
Wave Front Sensor
Focal PlaneFigure courtesy Alex Short
Thursday, February 18, 16
Star motion in 10 s
Astrometric Field CCDs
Blue Photom
eter CC
Ds
Sky Mapper CCDs
Red Photom
eter CC
Ds
Radial-Velocity Spectrometer CCDs
Basic Angle
Monitor
Wave Front Sensor
Basic Angle
Monitor
Wave Front Sensor
Focal PlaneFigure courtesy Alex Short
• PSF/LSF variation
BP - FoV Preceding - ROW7
-15 .0 -12 .5 -10 .0 - 7 . 5 - 5 . 0 - 2 . 5 0.0 2.5 5.0 7.5 10.0 12.5 15.0Sample position
0.001
0.01
0.1
LSF
BP - FoV Preceding - ROW1
-15 .0 -12 .5 -10 .0 - 7 . 5 - 5 . 0 - 2 . 5 0.0 2.5 5.0 7.5 10.0 12.5 15.0Sample position
0.001
0.01
0.1
LSF
Thursday, February 18, 16
Star motion in 10 s
Astrometric Field CCDs
Blue Photom
eter CC
Ds
Sky Mapper CCDs
Red Photom
eter CC
Ds
Radial-Velocity Spectrometer CCDs
Basic Angle
Monitor
Wave Front Sensor
Basic Angle
Monitor
Wave Front Sensor
Focal Plane
• PSF/LSF variation• Dispersion & geometry
Thursday, February 18, 16
Star motion in 10 s
Astrometric Field CCDs
Blue Photom
eter CC
Ds
Sky Mapper CCDs
Red Photom
eter CC
Ds
Radial-Velocity Spectrometer CCDs
Basic Angle
Monitor
Wave Front Sensor
Basic Angle
Monitor
Wave Front Sensor
Focal Plane
• PSF/LSF variation• Dispersion & geometry• Small scale (flat fields...)
Thursday, February 18, 16
Star motion in 10 s
Astrometric Field CCDs
Blue Photom
eter CC
Ds
Sky Mapper CCDs
Red Photom
eter CC
Ds
Radial-Velocity Spectrometer CCDs
Basic Angle
Monitor
Wave Front Sensor
Basic Angle
Monitor
Wave Front Sensor
Focal Plane
• PSF/LSF variation• Dispersion & geometry• Small scale (flat fields...)• Background (stray-light)
Thursday, February 18, 16
Star motion in 10 s
Astrometric Field CCDs
Blue Photom
eter CC
Ds
Sky Mapper CCDs
Red Photom
eter CC
Ds
Radial-Velocity Spectrometer CCDs
Basic Angle
Monitor
Wave Front Sensor
Basic Angle
Monitor
Wave Front Sensor
Focal Plane
• PSF/LSF variation• Dispersion & geometry• Small scale (flat fields...)• Background (stray-light)
Figure courtesy Giorgia Busso
Thursday, February 18, 16
Star motion in 10 s
Astrometric Field CCDs
Blue Photom
eter CC
Ds
Sky Mapper CCDs
Red Photom
eter CC
Ds
Radial-Velocity Spectrometer CCDs
Basic Angle
Monitor
Wave Front Sensor
Basic Angle
Monitor
Wave Front Sensor
Focal Plane
• PSF/LSF variation• Dispersion & geometry• Small scale (flat fields...)• Background (stray-light)• Large scale response (QEs, FoVs, filter coating...)
Thursday, February 18, 16
Star motion in 10 s
Astrometric Field CCDs
Blue Photom
eter CC
Ds
Sky Mapper CCDs
Red Photom
eter CC
Ds
Radial-Velocity Spectrometer CCDs
Basic Angle
Monitor
Wave Front Sensor
Basic Angle
Monitor
Wave Front Sensor
Focal Plane
• PSF/LSF variation• Dispersion & geometry• Small scale (flat fields...)• Background (stray-light)• Large scale response (QEs, FoVs, filter coating...)• Linearity (gates)• Flux loss• CTI mitigation• Decontamination• Deblending
Thursday, February 18, 16
Bologna, 18,19 February 2016 P. Montegriffo
Calibration strategy
• Internal calibrationThe goal is to provide an internally consistent flux scale all through the mission, across the focal plane, and for bright and faint sources. This is achieved by calibrating the relative variations of the instrument through the comparison of observations at different positions of the focal plane and different epochs for a set of reference sources.
Thursday, February 18, 16
Bologna, 18,19 February 2016 P. Montegriffo
Calibration strategy
• Internal calibrationThe goal is to provide an internally consistent flux scale all through the mission, across the focal plane, and for bright and faint sources. This is achieved by calibrating the relative variations of the instrument through the comparison of observations at different positions of the focal plane and different epochs for a set of reference sources.
• External calibrationThe aim of the external calibration is to determine the characteristics of the mean instrument by using a suitable number of spectro-photometric standard stars (SPSS) whose absolute spectral energy distributions (SEDs) are known with great accuracy from ground observations
Thursday, February 18, 16
Bologna, 18,19 February 2016 P. Montegriffo
Calibration strategy
• Internal calibrationThe goal is to provide an internally consistent flux scale all through the mission, across the focal plane, and for bright and faint sources. This is achieved by calibrating the relative variations of the instrument through the comparison of observations at different positions of the focal plane and different epochs for a set of reference sources.
• External calibrationThe aim of the external calibration is to determine the characteristics of the mean instrument by using a suitable number of spectro-photometric standard stars (SPSS) whose absolute spectral energy distributions (SEDs) are known with great accuracy from ground observations
•Purpose: - provide calibrated spectra in ‘physical units’
Thursday, February 18, 16
Bologna, 18,19 February 2016 P. Montegriffo
Calibration strategy
• Internal calibrationThe goal is to provide an internally consistent flux scale all through the mission, across the focal plane, and for bright and faint sources. This is achieved by calibrating the relative variations of the instrument through the comparison of observations at different positions of the focal plane and different epochs for a set of reference sources.
• External calibrationThe aim of the external calibration is to determine the characteristics of the mean instrument by using a suitable number of spectro-photometric standard stars (SPSS) whose absolute spectral energy distributions (SEDs) are known with great accuracy from ground observations
•Purpose: - provide calibrated spectra in ‘physical units’- give feedback to CU8 for AP classification
Thursday, February 18, 16
Bologna, 18,19 February 2016 P. Montegriffo
Calibration strategy
• Internal calibrationThe goal is to provide an internally consistent flux scale all through the mission, across the focal plane, and for bright and faint sources. This is achieved by calibrating the relative variations of the instrument through the comparison of observations at different positions of the focal plane and different epochs for a set of reference sources.
• External calibrationThe aim of the external calibration is to determine the characteristics of the mean instrument by using a suitable number of spectro-photometric standard stars (SPSS) whose absolute spectral energy distributions (SEDs) are known with great accuracy from ground observations
•Purpose: - provide calibrated spectra in ‘physical units’- give feedback to CU8 for AP classification
Predictions
0 5 1 0 1 5 2 0 2 5 3 0 3 5 4 0 4 5 5 0 5 5 6 0Sample position
0
10,000
20,000
30,000
40,000
50,000
60,000
70,000
80,000
90,000
100,000
110,000
120,000
130,000
140,000
flux
[pho
tons
/s/n
m]
Predictions
0 5 1 0 1 5 2 0 2 5 3 0 3 5 4 0 4 5 5 0 5 5 6 0Sample position
0
10,000
20,000
30,000
40,000
50,000
60,000
70,000
80,000
90,000
100,000
110,000
120,000
130,000
140,000
flux
[pho
tons
/s/n
m]
Thursday, February 18, 16
Bologna, 18,19 February 2016 P. Montegriffo
f(u) =Z 1
0L�(u + �(1/�, ⇣), ⇣) · R(�, ⇣) · s(�) d�
XP spectra formation
General formulation of the XP instrument:2
4u � samples� � wavelengths⇣ � ACfieldangle
3
5
Thursday, February 18, 16
Bologna, 18,19 February 2016 P. Montegriffo
f(u) =Z 1
0L�(u + �(1/�, ⇣), ⇣) · R(�, ⇣) · s(�) d�
XP spectra formation
General formulation of the XP instrument:2
4u � samples� � wavelengths⇣ � ACfieldangle
3
5
Observation LSF Response SEDDispersion
Thursday, February 18, 16
Bologna, 18,19 February 2016 P. Montegriffo
BP - FoV Preceding - ROW4
-20 .0 -17 .5 -15 .0 -12 .5 -10 .0 - 7 . 5 - 5 . 0 - 2 . 5 0.0 2.5 5.0 7.5 10.0 12.5 15.0 17.5 20.0Sample position
0.001
0.01
0.1
LSF
f(u) =Z 1
0L�(u + �(1/�, ⇣), ⇣) · R(�, ⇣) · s(�) d�
XP spectra formation
General formulation of the XP instrument:2
4u � samples� � wavelengths⇣ � ACfieldangle
3
5
Observation LSF Response SEDDispersion
Thursday, February 18, 16
Bologna, 18,19 February 2016 P. Montegriffo
BP - FoV Preceding - ROW4
-20 .0 -17 .5 -15 .0 -12 .5 -10 .0 - 7 . 5 - 5 . 0 - 2 . 5 0.0 2.5 5.0 7.5 10.0 12.5 15.0 17.5 20.0Sample position
0.001
0.01
0.1
LSF
f(u) =Z 1
0L�(u + �(1/�, ⇣), ⇣) · R(�, ⇣) · s(�) d�
XP spectra formation
General formulation of the XP instrument:2
4u � samples� � wavelengths⇣ � ACfieldangle
3
5
Observation LSF Response SEDDispersion
BP - FoV Preceding - ROW4
-20 .0 -17 .5 -15 .0 -12 .5 -10 .0 - 7 . 5 - 5 . 0 - 2 . 5 0.0 2.5 5.0 7.5 10.0 12.5 15.0 17.5 20.0Sample position
0.001
0.01
0.1
LSF
Thursday, February 18, 16
Bologna, 18,19 February 2016 P. Montegriffo
BP - FoV Preceding - ROW4
-20 .0 -17 .5 -15 .0 -12 .5 -10 .0 - 7 . 5 - 5 . 0 - 2 . 5 0.0 2.5 5.0 7.5 10.0 12.5 15.0 17.5 20.0Sample position
0.001
0.01
0.1
LSF
f(u) =Z 1
0L�(u + �(1/�, ⇣), ⇣) · R(�, ⇣) · s(�) d�
XP spectra formation
General formulation of the XP instrument:2
4u � samples� � wavelengths⇣ � ACfieldangle
3
5
Observation LSF Response SEDDispersion
BP - FoV Preceding - ROW4
-20 .0 -17 .5 -15 .0 -12 .5 -10 .0 - 7 . 5 - 5 . 0 - 2 . 5 0.0 2.5 5.0 7.5 10.0 12.5 15.0 17.5 20.0Sample position
0.001
0.01
0.1
LSF
!1 !2 !3
Thursday, February 18, 16
Bologna, 18,19 February 2016 P. Montegriffo
BP - FoV Preceding - ROW4
-20 .0 -17 .5 -15 .0 -12 .5 -10 .0 - 7 . 5 - 5 . 0 - 2 . 5 0.0 2.5 5.0 7.5 10.0 12.5 15.0 17.5 20.0Sample position
0.001
0.01
0.1
LSF
f(u) =Z 1
0L�(u + �(1/�, ⇣), ⇣) · R(�, ⇣) · s(�) d�
XP spectra formation
General formulation of the XP instrument:2
4u � samples� � wavelengths⇣ � ACfieldangle
3
5
Observation LSF Response SEDDispersion
BP - FoV Preceding - ROW4
-20 .0 -17 .5 -15 .0 -12 .5 -10 .0 - 7 . 5 - 5 . 0 - 2 . 5 0.0 2.5 5.0 7.5 10.0 12.5 15.0 17.5 20.0Sample position
0.001
0.01
0.1
LSF
!1 !2 !3
Sample
Thursday, February 18, 16
Bologna, 18,19 February 2016 P. Montegriffo
XP instrument model
f(u) =Z 1
0L�(u + �(1/�)) · R(�) · s(�) d�
Thursday, February 18, 16
Bologna, 18,19 February 2016 P. Montegriffo
XP instrument model
f(u) =Z 1
0L�(u + �(1/�)) · R(�) · s(�) d�
...discretize
f(uj) =X
i
L�(uj + �(1/�i)) · R(�i) · s(�i) ��i
Thursday, February 18, 16
Bologna, 18,19 February 2016 P. Montegriffo
XP instrument model
�!f = I⇥�!s
f(u) =Z 1
0L�(u + �(1/�)) · R(�) · s(�) d�
...discretize
f(uj) =X
i
L�(uj + �(1/�i)) · R(�i) · s(�i) ��i
Thursday, February 18, 16
Bologna, 18,19 February 2016 P. Montegriffo
XP instrument model
�!f = I⇥�!s
f(u) =Z 1
0L�(u + �(1/�)) · R(�) · s(�) d�
...discretize
f(uj) =X
i
L�(uj + �(1/�i)) · R(�i) · s(�i) ��i
Thursday, February 18, 16
Bologna, 18,19 February 2016 P. Montegriffo
XP instrument model
�!f = I⇥�!s
f(u) =Z 1
0L�(u + �(1/�)) · R(�) · s(�) d�
...discretize
f(uj) =X
i
L�(uj + �(1/�i)) · R(�i) · s(�i) ��i
Calibrate s by solving a linear system of equations
Thursday, February 18, 16
Bologna, 18,19 February 2016 P. Montegriffo
�!s = B⇥�!b
Source SED model
s(�) =X
i
biBi(�)
•Express source SEDs as a linear combination of a suitable set of basis functions:
.... or in matrix notation
�!f = (I⇥B)⇥
�!b
External calibration means solve for SED shape parameters
Thursday, February 18, 16
Bologna, 18,19 February 2016 P. Montegriffo
Instrument update process
•Use SPSS to constraint instrument model I
�!f = I⇥�!s
•Each model component depends on a (small) number of adjustable parameters
f(u) =Z 1
0L�(u + �(1/�)) · R(�) · s(�) d�
L�(u) = H0(u, �) +nLX
i=1
hi Hi(u, �)
R(�) =nRX
j=0
rj Rj(�)
•Constrained solution: response and the effective LSFs as linear combinations of ad hoc basis functions
�(1/�) = d0 + d1 �0(1/�)
Thursday, February 18, 16
Bologna, 18,19 February 2016 P. Montegriffo
f 'Z 1
0f(u) du =
Z 1
0
Z 1
0L�(u + �(1/�)) du · R(�) · s(�) d�
Integrated photometry calibration
Thursday, February 18, 16
Bologna, 18,19 February 2016 P. Montegriffo
f 'Z 1
0f(u) du =
Z 1
0
Z 1
0L�(u + �(1/�)) du · R(�) · s(�) d�
Integrated photometry calibration
Thursday, February 18, 16
Bologna, 18,19 February 2016 P. Montegriffo
f 'Z 1
0f(u) du =
Z 1
0
Z 1
0L�(u + �(1/�)) du · R(�) · s(�) d�
Integrated photometry calibration
f 'Z 1
0R(�) · s(�) d�
Thursday, February 18, 16
Bologna, 18,19 February 2016 P. Montegriffo
f 'Z 1
0f(u) du =
Z 1
0
Z 1
0L�(u + �(1/�)) du · R(�) · s(�) d�
Integrated photometry calibration
•External calibration of integrated G, GBP, GRP photometry achieved by fitting the actual shape of the passband through SPSS usage
•Only a zeropoint is needed (no color terms) to link to the absolute flux scale
f 'Z 1
0R(�) · s(�) d�
Thursday, February 18, 16
Schedule
ProposalConcept & Technology Study
Mission Selection
Re-Assessment StudyPhase B1
Scientific operation
Launch December 2013
Final
Studies
Data Processing
Implementation
Data Processing
Definition
Operation
Mission ProductsIntermediate
Selection of Prime Contractor (EADS Astrium SAS)
Phase B2Phase C/D
Software Development (DPAC)
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2021
TodayFigure courtesy Michael Perryman and François Mignard
2022
Thursday, February 18, 16