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A Novel SIM- -BASED Technique for the BASED Technique for the A - - PowerPoint PPT Presentation

Mar 18, 2023 12 likes •112 views

A Novel SIM- -BASED Technique for the BASED Technique for the A Novel SIM Precise Determination of Absolute Stellar Fluxes Precise Determination of Absolute Stellar Fluxes Jay B. Holberg LPL, University of Arizona Absolute Stellar Fluxes

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SLIDE 1

A Novel SIM A Novel SIM-

  • BASED Technique for the

BASED Technique for the Precise Determination of Absolute Stellar Fluxes Precise Determination of Absolute Stellar Fluxes

Jay B. Holberg LPL, University of Arizona

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SLIDE 2

Absolute Stellar Fluxes

How Absolute Fluxes are Traditionally Measured

  • 1. Pick a Bright Flux Standard - say Vega
  • 2. Com pare the Observed Flux of Vega with a Calibrated

Laboratory Standard – say a Black Body – using the Sam e Telescope.

  • 3. Account for and Correct all System atic Errors

Current Status

  • 1. On an absolute physical scale stellar fluxes are uncertain

at the level of 1% at optical wavelengths.

  • 2. In the UV and the Near IR uncertainties are considerably

higher.

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SLIDE 3

Absolute Fluxes – DA White Dwarfs - SIM

The basic idea:

  • 1. Use White Dwarf Physics to Determine the Relative

Fluxes of DA White Dwarfs.

  • 2. Use Highly Accurate SIM Parallaxes to Convert These

Relative Fluxes to Absolute Fluxes.

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SLIDE 4

DA White Dwarfs

  • Pure-Hydrogen Photospheres
  • Fully Radiative Atm ospheres
  • Sim ple, Continuum -Dom inated Spectra
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SLIDE 5

Spectral Fitting for Teff and log g Sirius B

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SLIDE 6

Teff = 25,193 (±37) K Log g = 8.556 (±0.010)

Sirius B Barstow et al. (2005) Synthetic Photometry

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SLIDE 7

Stellar Photom etry

( )

2 2 /

) log , ( 4 D R g T H f

eff λ λ

π =

fλ = Observed flux at the top of the Earth’s Atmosphere Hλ(Teff, log g) = Eddington Flux at the Stellar Surface R = Stellar Radius D = Stellar Distance Hλ

  • Radiative Transfer – Physics of Hydrogen Atom

R - White Dwarf Interior Physics – Mass-Radius Relation and White Dwarf Cooling

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SLIDE 8

Correlation of Photometric Parallaxes with Trigonometric Parallaxes

  • Fig. 2 Holberg et al. 2008
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SLIDE 9

DA White Dwarfs can be used as absolute flux standards – if accurate parallaxes can be determined.

Remaining Questions

How accurately can we compute white dwarf synthetic fluxes? What residual uncertainties are associated with emergent fluxes? How well can we determine white dwarf radii?

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SLIDE 10

Holberg et al. 2006