The HERMES RAP A feasibility study

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The HERMES RAP- A feasibility study -

• Elizabeth Wylie de Boer
• Ken Freeman

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Overview

• Automated reduction and analysis pipeline for
  HERMES data
• Capable of outputting
• Atmospheric Parameters - General metallicity -
  Specific element abundances
• Basic reduction
• Atmospheric parameters
• Teff, log g, M/H
• Detailed abundances
• Potential traps, uncertainties

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Basic Reduction

• Based on AAOmega program - 2dfdr
• Produces sky-subtracted, wavelength-calibrated
  spectra

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Atmospheric Parameters

• Two stage process
• 1. First pass for approximate estimates
• Gives smaller range for model grid
• Second pass to refine parameters

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First pass - Skymapper

• Can obtain Teff, log g, M/H from Skymapper
  photometry (Keller et al. 2007)
• Uses UVGRIZ filters, Kurucz model grid
• For ?0.05mag gives parameters
• ?Teff 100K, ?log g 0.5, ?M/H 0.5
• (See Stefan Kellers Talk at 1130)

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Second Pass

• Get Teff, log g, M/H, Vrot, Vrad
• Grid of synthetic spectra (Munari et al. 2005)
• Range of T, log g, M/H, Vrot, alpha-enhancement
  and microturbulence
• Adapt chi-squared minimisation technique
  comparing observed spectrum over smaller grid

M/H
log g
Teff
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Second Pass

• Munari et al. 2005 - Test applications
• Eclipsing binaries, Chi-squared vs orbital
  solution
• ?T 42K, ?log g 0.03 dex, ?Vrot 4 km/s,
  ?M/H 0.06 dex
• RAVE spectra, Chi-squared vs spectral
  classification
• ?T 3, ?log g 0.25 dex
• Larger errors due to range in classification
  scheme

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Atmospheric Parameters - Summary -

• Firstly through Skymapper photometry
• Secondly through chi-squared fit
• Accuracy of 12
• Provides parameters to adopt for model
• Model gets passed to next stage..

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Detailed Abundances

• Pipeline for individual abundances
• (HERES - Barklem et al. 2005)
• Use spectrum synthesis
• MOOG (Sneden 1973)
• Atmospheric Model
• Line list
• Observed Spectrum

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Detailed Abundances

• Take atmospheric model - fix hereafter
• Synthesize spectra for region
• Derive Fe, Ti abundances - M/H
• Set Fe and Ti and then derive element abundances
  from individual lines
• Assume scaled solar value for all initially

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Synthesis Example
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Synthesis Example
X/H - 0.50 - 0.25
0.00 0.25 0.50
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Fe and Ti
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Light elements (non alpha)
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Alpha elements
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Light and Heavy s-process
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Abundance Error Analysis

• Main uncertainty due to spread in abundance
  derived from individual lines - std dev, ?
• Abundances depend on Teff, log g and ?
• Solve abundances again for ? Teff, ? log g, ??
• Gives estimate of uncertainty due to model, BUT
  increases computing time by 3x

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Practicalities

• 1 x Reduction through 2dfdr minutes
• 1 x Skymapper model seconds
• 1 x Chi-sqaured fitting for model minutes
• 1 x Synthesis of spectral region seconds
• N x Chi-squared fitting for abundances minutes
• Telescope -- Results minutes per star

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Potential Traps

• Continuum fitting - 2dfdr
• Marked effect on abundances - care required
• Fitting correct line for analysis
• Set conditions for small wavelength shifts
• Setup initial line lists to avoid blended lines

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Initial Set-up

• Choose region of spectra for maximum abundances
  in minimum coverage
• Initial Line list
• Correct log gf values
• List of lines to be measured
• Avoid blends, molecular bandheads
• Line list set up correctly only once

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Summary

• Reduction pipeline based on AAO 2dfdr
• Approximate atmospheric model from Skymapper
  photometry
• Refine atmospheric model from chi-squared
  minimisation
• Automated procedure for individual abundances
• Fit Fe, Ti first then set for remaining analysis
• Each line solved individually
• Error analysis from std dev of individual lines

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Reduced Spectra
Telescope
2drdf
Skymapper Photometry
Model Grid Chi-sqaured fit
Initial Teff, log g, M/H
Final Teff, log g, M/H ()
N
Element abundance
Synthetic spectra Chi-squared fit
Teff, log g, M/H () Abundances for X elements