october 4 5 2012 n.
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ASPCAP Review Progress report and schedule now and ahead

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October 4-5, 2012. ASPCAP Review Progress report and schedule now and ahead. Performance.

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Overall, good performance for high metallicity ([Fe/H]>-1) stars with good S/N (>70) spectra: Teff to about 3%, logg to about 0.2 dex, and [Fe/H] to better than 0.1 dex. Small systematic offsets (0.1-0.3 dex) in surface gravity.

Significantly poorer performance at low metallicity, with a systematic offset in gravity of up to ~ 1 dex.


Systematic offsets in gravity

Degeneracies for metal-poor stars



  • Raw mean (and std. deviation) for abundances in M13, M5 and M67 members (apstar results)
  • M67 M5 M13
  • ________________________________
  • <[Fe/H]> +0.01 (0.04) -1.26 (0.11) -1.51 (0.13)
  • <[C/Fe]> -0.06 (0.08) -0.23 (0.19) -0.02 (0.36)
  • <[N/Fe]> +0.20 (0.11) +0.50 (0.32) +0.58 (0.29)
  • <[α/Fe]> +0.02 (0.03) +0.11 (0.10) +0.20 (0.08)
  • Three types of sources
  • Random errors
  • Atmospheric/Instrumental distortions
  • Systematic errors
  • Model approximations

Random and systematic due to instrumental distortions may look random

Random can be studied by adding purely random noise

Instrumental distortions can be studied by looking at plate repeatability


Systematic errors in models identified looking at accurate reference values

and trends

fe h dispersion
[Fe/H] dispersion

Includes three discussed sources

of error

σ ~ 0.04 dex for M67

σ ~ 0.12 dex for M5 and M13

Random noise should not be

dominant source except for

M13 at S/N<100

purely random noise
Purely random noise

Random errors are VERY small

σ ~ 0.03 for S/N≥ 20 at [Fe/H]=0

σ ~ 0.1 at S/N=40 for M13

Need S/N≥80 for σ~0.04 in this cluster

purely random noise1
Purely random noise

Random errors important for C, and especially N in metal-poor stars

Small for α/Fe

purely random noise2
Purely random noise

Random errors important

for Teff at all [Fe/H]

M13: 300, 150, 100 and 50K

at S/N=10, 20, 40 and 80

M67: 300, 50, 35 and 30 K

at S/N=10, 20, 40 and 80

for logg at low [Fe/H]

M13: 1.3,0.5,0.2,0.1 dex

at S/N=10, 20, 40 and 80



ferre random errors
Ferre random errors

Random errors from inverting curvature

matrix within a factor ~ 2




model systematic errors
Model systematic errors

0.1 dex /1000 K for M67

<0.01 dex/1000 K for M5/M13

0.04 dex errors at [Fe/H]~0

but negligible in globulars

(where random dominate)

Note better results than those

Shown by Szabolcs (apstar vs.



Scatter, noding, and

systematics get worse

at low S/N

At high S/N, repeatability

to better than 0.1 dex

in [Fe/H], but still seems

to be dominant source of

Error at S/N>100

error summary
Error summary
  • We effectively have a S/N limited by systematics in the observations, probably around S/N~100.
  • Performance for metal-rich stars is currently limited by systematics in the models at about 0.04 dex, since required S/N is not as high for main parameters.
  • Performance at the metal-poor end is limited by random noise (dominated by systematics due to instrument/atmospheric distortion), since high S/N is required to reduce errors. Large model systematics for logg.
error summary1
Error summary
  • Currently random errors of about 100 K (100 K systematic) in Teff, 0.1 dex (0.2-1.0 dex systematic, depending on metallicity) in logg, and 0.1 dex (0.1 dex systematic) in [Fe/H].
  • C and N require in general higher S/N, especially N and especially in metal-poor stars. [α/Fe] easier in terms of S/N.
  • ASPCAP does well within x2 estimated purely random errors, but need to consider two more contributions: systematics in the models for metal-rich stars (which limits, e.g. σ[Fe/H] to ~ 0.05 dex), and repeatability when photon noise is < 1% (which limits actual S/N<100-150).

Currently using the original Kurucz & Castelli (2004) models.

Newer, more consistent, better MARCS and Kurucz models in hand (Meszaros+ 2012).


Hotter Tlusty models in hand.

Plans to provide cooler models by Garcia Hernandez & Zamora.

Main issue now to figure out how to fill the holes for synthesis.


Long evolution that culminated early this year.

A paper is in preparation (Shetrone+ 2012).

Only limited evolution expected in the future (somenonetheless): solar f-values consistent with models, Arcturus/solar f-values.

  • Teff,logg,[Fe/H] solid for start doing science now, with the caveat that systematic errors in logg need to be corrected.
  • C and N require higher S/N than Teff,logg,[Fe/H] and have therefore larger error bars, especially for metal-poor stars, and exhibit (unless S/N is fairly high) noding issues. [α/Fe] easier.
  • Our proposal for DR10 is to release Teff,logg,[Fe/H], and possibly [α/Fe], with error bars from internal FERRE calculated random errors (capping S/N~100 in the input error bars), inflated to account for known systematics as a function of parameters.