1 / 18

Present accuracies in spectroscopic chemical abundances

” 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 .”

mikasi
Download Presentation

Present accuracies in spectroscopic chemical abundances

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. ”Thesethings … were not discovered by philosophy or the arts ofreason, but by chance. …. Thereare still manythingsof excellent use, storedup in the lapofnature, … lyingquiteoutof the pathofimagination.” Francis Bacon, NovumOrganum (1620)

  2. Present accuracies in spectroscopicchemicalabundances • Rarelybetterthan 0.1 dex (evenrelatively) • Some ~0.01 dex. What do welearnfrom those?

  3. Solar composition not normal for solar-type stars Meléndez et al. (2009) ≈0.08 dex≈20% Birth environment? Effects of planets? Not full mixing?

  4. Present accuracies in spectroscopicchemicalabundances • Rarelybetterthan 0.1 dex (evenrelatively) • ~0.01 dex in special casesonly. Whatare the problems? • Obs. data: Blends, continua • Fundamental parameters: Teff, log g, mass, radius, distance, extinction, … • Modelling: Atomic data, non-LTE, convection, … • Interpretation: What do atmosphericabundancesrepresent? Solution: Fit realistic and physicallyconsistent 3D NLTE, MHD modelstoadequateobservables. (Anyotherdecentways??)

  5. 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 Gilmore et al. (2012), The Messenger

  6. The many Ds of hi-res instrumentation • Wavelengthcoverage • Resolving power • Achievable signal-to-noise ratio • Various calibrational needs • Stability • Multiplexing • Polarimetry • ... Can we have it all in one instrument?

  7. Wavelengthcoverage: Spectrallines and continua GJ 849 (M 3.5 V) Heiteret al. (2012) YCVn (C 5,4) UUAur(C 5 II) Lambert et al. (1986) J-band Satisfactorycontinua for M stars J-band K-band ”Quasicontinua”for C stars CO 1st overtone offers diagnostics on structure and dynamics Note: unidentifiedlines! Near IR useful for cool stars … butmanyunidentifiedlines as yet.

  8. Spectral resolution:Line profilesfor convection, rotation, magneticfields, … Ramírez et al. (2010): HD 122563

  9. Line profilesfor convection, rotation, magneticfields, … Gray & Brown (2006): Arcturus Resolve the spectrafully!

  10. Achievable S/N NGC 6752 @ [Fe/H]=-1.6: Ca, Sc, Ti and Fe NGC 6397 @ [Fe/H]=-2.1 Korn et al. (2006, 2007) Nordlander et al. (2012) TOP stars: 30 h with FLAMES-UVES S/N  35 per rebinned pixel Gruyters et al. (2012)

  11. Blaze correction reliability cf. Korn (2002) More generally: why accept calibrations thatare ”astronomical” rather thanphysical? amplitude ≥5%!

  12. Physicalcalibrationofspectrometer See Stubbs & Tonry (2012): arXiv1206.6695: Addressing the PhotometricCalibrationChallenge: Explicit determination of the Instrumental Response and AtmosphericResponseFunctions, and Trying it All Together.

  13. (Spectro)photometry Teffto 50K => B-V to 0.01 or V-K to 0.03 mag. or correspondingaccuracy in spectrophotometric gradients. Problem: Variable stars! Simultaneous data needed.

  14. Polarization With a 1‰ accuray in polarization meanfieldsofabout 100 Gauss shouldbe measurable => 0.03 dexin abundance (betterwith IR linesobserved!) SeeFabbian et al. (2010)

  15. Our CODEX: No SIMPLE compromises! E-ELT instrumentation: second to none

  16. So: Do new things! • Look deeper! • Go for higher resolution and S/N! • Explore new wavelength regions! • Takecontrolofcalibrations! • Investinto extra dimensions like polarization …

  17. Time resolution Cieslinski et al. (2010): Polar (AM Her star) RBS 0324 15 min intervals. Muchhigherfrequencyrequires special measures. HdHeII Hb

  18. Achievable S/N • S/N per unit time time domain ever more important ability to study ever shorter phenomena limited by the light collecting power and the read-out time Barclay et al. (2011)

More Related