present accuracies in spectroscopic chemical abundances
DESCRIPTION
” These things … were not discovered by philosophy or the arts of reason , but by chance . …. There are still many things of excellent use , stored up in the lap of nature , … lying quite out of the path of imagination .” - PowerPoint PPT PresentationTRANSCRIPT
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”These things … were not discovered by philosophy or the arts of reason, but by chance. …. There are still many things of excellent use, stored up in the lap of nature, … lying quite out of the path of imagination.”
Francis Bacon, Novum Organum (1620)
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Present accuracies in spectroscopic chemical abundances
• Rarely better than 0.1 dex (even relatively)• Some ~0.01 dex. What do we learn from
those?
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Solar composition not normal
for solar-type stars
Meléndez et al. (2009)
≈0.08 dex≈20%
Birth environment? Effects of planets? Not full mixing?
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Present accuracies in spectroscopic chemical abundances
• Rarely better than 0.1 dex (even relatively)• ~0.01 dex in special cases only.What are the problems?• Obs. data: Blends, continua• Fundamental parameters: Teff, log g, mass, radius, distance,
extinction, …• Modelling: Atomic data, non-LTE, convection, …• Interpretation: What do atmospheric abundances represent?Solution: Fit realistic and physically consistent 3D NLTE, MHD models to adequate observables. (Any other decent ways??)
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The multi-D world of stars
And there are more: , B, d/dt of all of the above.
Stars contain a wealth of information about themselves, their planetary systems and their birth environments
Gilm
ore
et a
l. (2
012)
, The
Mes
seng
er
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The many Ds of hi-res instrumentation
• Wavelength coverage• Resolving power• Achievable signal-to-noise ratio• Various calibrational needs• Stability• Multiplexing• Polarimetry• ... Can we have it all
in one instrument?
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Wavelength coverage: Spectral lines and continua
GJ 849 (M 3.5 V) Heiter et al. (2012)
YCVn (C 5,4) UUAur (C 5 II) Lambert et al. (1986)
J-band K-band ”Quasi continua”for C stars CO 1st overtone offers diagnostics on
structure and dynamicsNote: unidentified lines!
Near IR useful for cool stars… but many unidentified lines
as yet.
J-bandSatisfactory continua for M stars
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Spectral resolution:Line profiles for convection, rotation, magnetic fields, …
Ramírez et al. (2010): HD 122563
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Line profiles for convection, rotation,
magnetic fields, …
Gray & Brown (2006):Arcturus
Resolve the spectra fully!
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NG
C 63
97 @
[Fe/
H]=-
2.1
Korn
et a
l. (2
006,
200
7)N
ordl
ande
r et a
l. (2
012)
Achievable S/N
NGC 6752 @ [Fe/H]=-1.6: Ca, Sc, Ti and Fe
TOP stars: 30 h with FLAMES-UVESS/N 35 per rebinned pixel
Gruyters et al. (2012)
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Blaze correction reliability
More generally: why accept calibrations that are ”astronomical” rather than physical?
cf. Korn (2002)
amplitude ≥5%!
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Physical calibration of spectrometer
See Stubbs & Tonry (2012): arXiv1206.6695:Addressing the Photometric Calibration Challenge: Explicit determination of the Instrumental Response and Atmospheric Response Functions, and Trying it All Together.
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(Spectro)photometry
Teff to 50K => B-V to 0.01 or V-K to 0.03 mag.or corresponding accuracy in spectrophotometric gradients.
Problem: Variable stars! Simultaneous data needed.
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Polarization
With a 1‰ accuray in polarizationmean fields of about 100 Gauss should be measurable => 0.03 dex in abundance(better with IR lines observed!)
See Fabbian et al. (2010)
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Our CODEX: No SIMPLE compromises!
E-ELT instrumentation: second to none
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So: Do new things!
• Look deeper!• Go for higher resolution and S/N!• Explore new wavelength regions!• Take control of calibrations!• Invest into extra dimensions like polarization …
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Time resolution
Cieslinski et al. (2010): Polar (AM Her star) RBS 0324
15 min intervals.Much higher frequency requires special measures.
Hd HeII Hb
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Achievable S/N
• S/N per unit timetime domain ever more importantability to study ever shorter phenomena limited by the light collecting power and the read-out time
Barclay et al. (2011)