Wavelength calibration in physical model based calibration pipelines

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Wavelength calibration in physical model based calibration pipelines. Astronomical Data Analysis III S. Agata

Wavelength calibration in physical model based calibration pipelines. Astronomical Data Analysis III S. Agata sui due Golfi, Naples, April 2004 04/26/04 ADA III - Napoli

Overview • • • IPMG at ST-ECF - Who we are. HST Spectrographs &

Overview • • • IPMG at ST-ECF - Who we are. HST Spectrographs & traditional pipelines. Predictive calibration based on: 1. physical model of the instrument 2. simulated annealing technique for optimization 1. Show we implement this into the science data pipeline. 04/30/04 ADA III - Napoli Fiorentino & Rosa

IPMG at ST-ECF • • • Comprehensive empirical calibration pipeline already exists for the

IPMG at ST-ECF • • • Comprehensive empirical calibration pipeline already exists for the HST STIS Spectrograph We aim to improve those components which benefit from physically motivated corrections Current work includes 1. Wavelength Calibration 2. Calibration lamp line list - measurements at NIST 3. Detector Model repairing the Charge Transfer (CTE) 04/30/04 ADA III - Napoli Fiorentino & Rosa

What is STIS ? • – – – • • STIS is the HST

What is STIS ? • – – – • • STIS is the HST imaging spectrograph. spatially resolved spectroscopy from 1150 Å to 10, 300 Å at low to medium spectral resolution echelle spectroscopy (high resolution) in the ultraviolet. time tagging of photons in the ultraviolet (high time resolution). Since 1997 on board HST Unlikely to be replaced during the remaining HST lifetime 04/30/04 ADA III - Napoli Fiorentino & Rosa

STIS optical layout 04/30/04 ADA III - Napoli Fiorentino & Rosa

STIS optical layout 04/30/04 ADA III - Napoli Fiorentino & Rosa

STIS Pipeline ‘calstis’ • calstis for spectra - series of modules that 1. 2.

STIS Pipeline ‘calstis’ • calstis for spectra - series of modules that 1. 2. 3. 4. Control the data flow through the pipeline Basic 2 -D image reduction (e. g. bias subtraction) Reject cosmic rays from CCD data Process the contemporaneously obtained wavecal data to ascertain zero point shifts in the spectral and spatial directions 5. Extract 1 dimensional spectra – need to know geometry 6. Perform spectroscopic wavelength and flux calibration 7. Sum any CR-SPLIT and REPEATOBS exposures. 04/30/04 ADA III - Napoli Fiorentino & Rosa

Pipeline Flow for Spectroscopic Data 04/30/04 ADA III - Napoli Fiorentino & Rosa

Pipeline Flow for Spectroscopic Data 04/30/04 ADA III - Napoli Fiorentino & Rosa

Where the empirical wavelength calibration is currently used. • Determine MSM offset from wavecal.

Where the empirical wavelength calibration is currently used. • Determine MSM offset from wavecal. • Its purpose is to find the offset of the spectrum from the expected location, owing to non repeatability of the MSM. • Spectroscopic Calibration and Extraction. • 1 -D spectral extraction. A spectrum is extracted along a narrow band, summing over the cross-dispersion direction and subtracting background values to produce a 1 -D array of fluxes for each spectral order. • In order to calculate the offsets and to assign wavelengths the empirical pipeline uses bi-dimensional polynomial dispersion solutions. Therefore it can only apply linear translations (offsets) , but not rotations. 04/30/04 ADA III - Napoli Fiorentino & Rosa

STIS Auto Wavecals A standard wavecal is usually only a few seconds long. •

STIS Auto Wavecals A standard wavecal is usually only a few seconds long. • X and Y displacements based on a few lines. • X and Y are not the same on the whole detector because, the differential rotation (“splaying‘”) of individual echelle orders resulting from the combined effects of the echelle and cross-dispersing elements, cause different orders to be differentially rotated (“splayed”). 04/30/04 ADA III - Napoli Fiorentino & Rosa

Short and Long Wavecal 04/30/04 ADA III - Napoli Fiorentino & Rosa

Short and Long Wavecal 04/30/04 ADA III - Napoli Fiorentino & Rosa

Short and long wavecal (detail) 04/30/04 ADA III - Napoli Fiorentino & Rosa

Short and long wavecal (detail) 04/30/04 ADA III - Napoli Fiorentino & Rosa

Traditional Pipeline’s accuracy vs. Enhanced calibration. • 1)Image shift (-3, +3) pixels due to

Traditional Pipeline’s accuracy vs. Enhanced calibration. • 1)Image shift (-3, +3) pixels due to the MSM. • 2)Thermal effects cause the spectrum to drift by about 0. 1 pixels up to 0. 35 pixels per orbit. • 3)Shift not always precisely determined due to, for instance, a short wavecal. 04/30/04 1)The Absolute Wavelength zero points shifts are not predicted with the traditional calibration (errors in E 140 H up to 1. 3 km/s 0. 5 -1. 0 Pixel). We aim to reach 0. 1 pixel precision. 2)We will have an homogenous calibration for each mode and overall the lifetime of STIS. ADA III - Napoli Fiorentino & Rosa

The alternative: predictive calibration “The calibration of astronomical data can be significantly improved by

The alternative: predictive calibration “The calibration of astronomical data can be significantly improved by constructing instrument models which incorporate as fully as possible a knowledge of optical and detector physics” A typical example is the wavelength calibration – empirical dispersion relations should be replaced by a physical model (simple ray trace) of the spectrograph This usually yields better than 0. 1 % accuracy (1 pix in 1000) straight away Distortions may be added to go to sub-pixel accuracy • • 04/30/04 ADA III - Napoli Fiorentino & Rosa

Predictive Calibration: Echelle model & Simulated Annealing. • Mathematical model with about 35 parameters

Predictive Calibration: Echelle model & Simulated Annealing. • Mathematical model with about 35 parameters which need to be optimized. Derivatives cannot be easily formulated analytical inversion is impossible. • Simulated Annealing (SA) is one of the technique which cope with such a problem. • Although easy in principle, its implementation may not be trivial. 04/30/04 ADA III - Napoli Fiorentino & Rosa

Simulated Annealing. • SA exploits an analogy between the way in which a metal

Simulated Annealing. • SA exploits an analogy between the way in which a metal cools and freezes into a minimum energy crystalline structure and the search for a minimum in a more general system. • SA don’t get trapped at local minima. • The algorithm accepts also changes that increase objective function f with a probability following the Boltzmann probability distribution. • Not all sets of parameters which minimize the cost function are physically acceptable therefore our SA algorithm will make those configurations extremely costly. • 04/30/04 ADA III - Napoli Fiorentino & Rosa

SA Data Flow Start Randomize according to the T Better than the current solution

SA Data Flow Start Randomize according to the T Better than the current solution ? Decrease Temperature Yes Store it. NO No Yes Accept or reject based on Boltzmann Probability Distribution. No Min Temperature reached ? Random tries > Max_Iteration ? Exit Yes ADA III - Napoli

Fitlines Mode, Slit, Central wavelength, Catalog lines Wavecal (FITS Image) Center a box around

Fitlines Mode, Slit, Central wavelength, Catalog lines Wavecal (FITS Image) Center a box around the predicted lines positions and estimate the exact observed positions by fitting the line shape with a Gaussoid. Calculates the predicted X, Y lines positions on the detector. Output: observed X, Y lines positions on the detector. 04/30/04 ADA III - Napoli Fiorentino & Rosa

STIS Anneal One or more configuration file each with 35 parameters One or more

STIS Anneal One or more configuration file each with 35 parameters One or more sets of lines positions from Fitlines. Annealing Algorithm to optimize the set of parameters for each configuration. If config file is good store it If not good repeat the anneling process. 04/30/04 ADA III - Napoli Fiorentino & Rosa

Reference Files Data Flow Master Catalog Extract. Sub. Catalog Wavecal exposure Mode, Cen. Wave,

Reference Files Data Flow Master Catalog Extract. Sub. Catalog Wavecal exposure Mode, Cen. Wave, Slit. Pos, Config File What else? Fitlines (X, Y)measured STISAnneal Not possible to anneal all parameters at the same time therefore needs to identify set of them to be annealed. New Cfg File Store it or not Store it ? If good store it If not good New Master ? Reject Bad lines, Change Weights, Intensity thresholds ADAgood III -? Napoli Not Yet Learning curve for a new instrument.

SA into the Science pipeline • Once all the reference files have been determined

SA into the Science pipeline • Once all the reference files have been determined we will be able to predict, for a given configuration and for each order and lambda, the position on of the corresponding line on the detector. • However, in order to cope with the non repeatibility of the MSM, another SA need to be run each time a science exposure is taken. 04/30/04 ADA III - Napoli Fiorentino & Rosa

SA into the Science Pipeline User selects a mode, Central wavelength … Run Fitlines

SA into the Science Pipeline User selects a mode, Central wavelength … Run Fitlines + Fast-Anneal in order to calculate the actual MSM position Final set of config files for each mode, Central wavelength, slit, Epoch. Run Calstis Config File extracted but MSM positions may no longer be accurate. 04/30/04 ADA III - Napoli Fiorentino & Rosa

Discover Dependencies Select a mode and fetch all the wavecals. Relation T, Focal Length

Discover Dependencies Select a mode and fetch all the wavecals. Relation T, Focal Length ? N Wavecals extracted. Run Fitlines +Anneal Enhance the model N Config files Analyze config files against environmental conditions. 04/30/04 Number of config files reduced. ADA III - Napoli Fiorentino & Rosa

Modeling Echelle Spectrographs At the ST-ECF we are currently implementing a STIS model based

Modeling Echelle Spectrographs At the ST-ECF we are currently implementing a STIS model based on first optical principles. It incorporates off-plane grating equations and 3 D rotations in order to account for line tilt and order curvature. Similar formalism had already been partially implemented and applied for FOS(HST), UVES, CASPEC pipelines with significant science improvement. See Ballester and Rosa A&AS 126, 563 -571 (1997). www. stecf. org/poa/pcrel/scicase. html www. eso. org/observing/dfo/quality/Messenger/UVES_Messenger_101. html 04/30/04 ADA III - Napoli Fiorentino & Rosa

Good only for HST spectrographs ? • Predictive calibration can be applied to any

Good only for HST spectrographs ? • Predictive calibration can be applied to any spectrograph. • We aim to implement the STIS pipeline such that can be easily re-used for other spectrograph (i. e. Object oriented code). • Although this is just a part of a pipeline… 04/26/04 ADA III - Napoli Fiorentino & Rosa

Status of the STIS implementation • • • Prototype implementation finished (C++). Wavelength calibration

Status of the STIS implementation • • • Prototype implementation finished (C++). Wavelength calibration translated into C in order to import into the existing IRAF/C STIS pipeline. Reference files production is in C++ and does not need to be translated since it is an offline tools. Future items: Analyze science cases in order to test the CE_CALSTIS. Enhance the model (MSM model). 04/30/04 ADA III - Napoli Fiorentino & Rosa

Referenced articles & URL links • • Ballester and Rosa Astron. & Astrophysic. Suppl.

Referenced articles & URL links • • Ballester and Rosa Astron. & Astrophysic. Suppl. Ser 126, 563 -571 (1997). Ballester & Rosa ADASS XIII, Instrument Modeling in Observational Astronomy. Kirkpatrick, S. , C. D. Gelatt Jr. , M. P. Vecchi, "Optimization by Simulated Annealing", Science, 220, 4598, 671 -680, 1983. Metropolis, N. , A. Rosenbluth, M. Rosenbluth, A. Teller, E. Teller, "Equation of State Calculations by Fast Computing Machines", J. Chem. Phys. , 21, 6, 1087 -1092, 1953. URL links: • www. stecf. org/poa/pcrel/scicase. html • www. stecf. org/poa/index 2. html • www. eso. org/observing/dfo/quality/Messenger/UVES_Messenger_101. html • 04/30/04 ADA III - Napoli Fiorentino & Rosa

Science Improved: FOS case. • • Effect of the improved dispersion relation. We looked

Science Improved: FOS case. • • Effect of the improved dispersion relation. We looked at the interstellar absorption lines imprinted on the spectrum of a low red-shift quasar (PG 1115+407, PI B. Wills). There were two separate FOS observations red and black dots. All measurements have been reduced to barycentric velocities. The solid line is the weighted average of HI 21 cm line observations with the dashed lines indicating the range of velocities found in the line of sight. 04/30/04 ADA III - Napoli Fiorentino & Rosa

Standard Calfos dispersion solution 04/30/04 ADA III - Napoli Fiorentino & Rosa

Standard Calfos dispersion solution 04/30/04 ADA III - Napoli Fiorentino & Rosa

Improved dispersion solution. 04/30/04 ADA III - Napoli Fiorentino & Rosa

Improved dispersion solution. 04/30/04 ADA III - Napoli Fiorentino & Rosa

STIS Spectroscopic Capabilities • 04/30/04 ADA III - Napoli Fiorentino & Rosa

STIS Spectroscopic Capabilities • 04/30/04 ADA III - Napoli Fiorentino & Rosa

Traditional Pipeline’s accuracy vs. enhanced calibration. • Image shift (-3, +3) pixels due to

Traditional Pipeline’s accuracy vs. enhanced calibration. • Image shift (-3, +3) pixels due to the MSM. • Thermal effects cause the spectrum to drift of about 0. 1 pixels up to 0. 35 pixels per orbit. • Shift not always precisely determined due to, for instance, a short wavecal. 04/30/04 ADA III - Napoli Fiorentino & Rosa