CW5 Berlin, December 11 th 2003 ABOUT SOME TRAPS 1 About some traps in fundamental parameter determination of target stars Friedrich Kupka Max-Planck-Institute for Astrophysics Hydrodynamics Group

CW5 Berlin, December 11 th 2003 ABOUT SOME TRAPS 2 SOME POPULAR TRAPS hidden use of model physics (circular argument) neglection of systematic errors: ∆ scatter  ∆ error hidden systematic errors silent break down of model physics usage of calibrations outside their validity range and for sure many more of them...

CW5 Berlin, December 11 th 2003 ABOUT SOME TRAPS 3 Hidden use of model physics The determination of log(g) for Vega – Fundamental value unknown inspite of this: primary calibration point for synthetic photometry – Moon & Dworetsky 1985: empirically corrected ATLAS6 grids for Strömgren colours based on a mixture of true fundamental values and further calibrations (either log(g) or T eff unknown) Vega's log(g): Balmer lines, Balmer jump fits from ATLAS6 models  calibration point in MD ! Castelli & Kurucz A&A 281, 817 (1994): values derived in this way depend on unknown He abundance – ATLAS9 based FeI / FeII as "supporting results”

CW5 Berlin, December 11 th 2003 ABOUT SOME TRAPS 4 Model atmosphere grids I Current grids: why not trust them ? – ATLAS9 (  BaSeL, etc.), New MARCS, and PHOENIX: based on Kurucz atomic data – none fits Strömgren m 0 metallicity index (A-G type stars) – none correctly predicts the Balmer jump for F stars (surface gravity, luminosity,...) – outdated grids still widely used as black boxes (ATLAS9 C93 distribution)

CW5 Berlin, December 11 th 2003 ABOUT SOME TRAPS 5 Model atmosphere grids II Current grids – are as poor in convection modelling as in 1970 – usually lack numerical resolution (computational costs, non-uniform over HRD) – incorrectly predict Balmer line profiles over the HRD for A-G stars (except for calibration star!) – are in disagreement with observational input from mid A stars (temperature gradients, microturbulence)

CW5 Berlin, December 11 th 2003 ABOUT SOME TRAPS 6 Neglection of systematic errors Accuracy of T eff of fundamental stars – for many “fundamental stars” visual fluxes have not been measured (=L, M, R known without use of stellar models) – A0 – G2 MS: ~6: < 200 K, ~15: < 400 K  Why ? poor (post-Hipparcos!) parallaxes, spectrophotometry – between 8000 K and 9500 K: no pairs with known M – even with these data:  some models excluded Balmer line profiles for the Sun & other stars – confusing results [ cf. Barklem et al. A&A 385, 951 (2002)] – resolved (perhaps ?) by improving convection physics

CW5 Berlin, December 11 th 2003 ABOUT SOME TRAPS 7 Hidden systematic errors Spectral line ratios and absolute T eff – Line depth ratios of selected pairs correlate with photometric temperature indicators (D. Gray) – Use colour index vs. T eff relation  line ratios f(T eff ) – Problem: relative scale ! The T eff (line ratio) scale inherits systematic errors from the T eff (colour) scale – IRFM also not free from systematics ( binaries, IR fluxes ) – Solar T eff : calibration errors, solar cycle, etc.  ∆ T eff ~10 K. – A&A 411, 559 (2003): ∆ T eff (sun)=0, ∆ T eff (stars)~5-10 K ?!?

CW5 Berlin, December 11 th 2003 ABOUT SOME TRAPS 8 Breakdown of model physics Abundance determinations – oscillator strengths: a few 1000 accurately measured – Wiese's law: the lower the accuracy, the more optimistic the error estimate (factor >2 in dex !) – successful “fits“ can be very deceiving (example Li) – 1D LTE/NLTE  3D LTE  3D NLTE: example: the Li determination of extreme Pop. II/Pop. III stars  internal, statistical accuracy estimates for abundances can be completely knocked over by (unexpected) systematic errors...

CW5 Berlin, December 11 th 2003 ABOUT SOME TRAPS 9 Calibration of parameters Tuning convection in low mass stars – lack of alternatives  adjustments to fit the sun – but: an evolution model which fits the sun does not have to be good for anything else – one which does not is even more questionable ! – uncertainty of lower RGB (1M solar ): ±100 K – uncertainty of PMS (D-burning phase): ±175 K – both due to convection alone... – different models/parameters in interior and atmosphere increase uncertainty

CW5 Berlin, December 11 th 2003 ABOUT SOME TRAPS 10 Conclusions I General comments – a good direct measurement can never be substituted by clever, arbitrarily (?) accurate calibrations – systematic errors  intrinsic ones Fundamental parameters – ASTRA project (S.J. Adelman, A. Gulliver, B. Smalley)  new spectrophotometric fluxes (near UV – near IR), recalibration of stellar flux standards (50 cm robotic telescope, first light in spring 2004) – the long wait for the GAIA mission (too long for COROT)

CW5 Berlin, December 11 th 2003 ABOUT SOME TRAPS 11 Conclusions II New model atmosphere grids – require adequate resolution in grid parameters – more cross-checking with fundamental stellar data – a better treatment of convection; diffusion, opacities,... – taking black boxes from the shelf remains dangerous Convection – “non-local models” and numerical simulations – solar calibration approach insufficient  observations (including particularly MOST & COROT...)

CW5 Berlin, December 11 th 2003 ABOUT SOME TRAPS 12 Extra slides and literature I Figures shown – Smalley B., Kupka F., A&A 328, 349 (1997): Fig. 6 (m 0 -index) inability of models to match A-stars and the sun simultaneously – same paper: Fig. 5 (c 1 -index): systematics, “feature” for F-stars – Smalley et al., A&A 395, 601 (2002): Fig. 2 (H  -profiles) small mixing length/flux overshooting – Stein R.F., Nordlund Å., ApJ 499, 914 (1998): Fig. 14, 15 inhomogeneity of solar surface convection – Nordlund Å., Stein R.F., ASP Conf. Ser. 203, 362 (2000) photospheric levitation (1D / 3D, turbulent pressure) Tables shown – Smalley et al., A&A 395, 601 (2002): Tables 2 and 5 fundamental parameters: error sources; mid A-star problem – Asplund et al., A&A 399, L31 (2003): Table 1(electronic version) the Li problem (3D NLTE – 3D LTE – 1D LTE/NLTE)

CW5 Berlin, December 11 th 2003 ABOUT SOME TRAPS 13 Extra slides and literature II Useful literature – Asplund M., Carlsson M., Botnen A.V., A&A 399, L31 (2003) – Barklem P.S. et al., A&A 385, 951 (2002) – Gray D.F., Johanson H.L., PASP 103, 439 (1991) – Moon T.T., Dworetsky M.M., MNRAS 217, 305 (1985) – Kurucz R.L., Astrophys. and Space Sci. Library, Vol. 274, Dordrecht: Kluwer Academic Publishers, ISBN , 2002, p. 3 – 14 (  PUERTOVALLARTA:2001) – Nordlund Å., Stein R.F., ASP Conf. Ser. 203, 362 (2000) – Smalley B., MNRAS 265, 1035 (1993) – Smalley B., Kupka F., A&A 328, 349 (1997) – Smalley B., Gardiner R.B., Kupka, F., Bessell M.S., A&A 395, 601 (2002) – Stein R.F., Nordlund Å., ApJ 499, 914 (1998)