Tubingen, September, Optical spectroscopy of the born- again Sakurai's object in 1996 Igor Savanov Simon Jeffery Don Pollacco Denis Shulyak and others

Tubingen, September, The rapid evolution: The extraordinarily rapid evolution of the born-again giant Sakurai’s object following discovery in 1996 has been investigated in papers by Duerbeck et al., Shetrone & Keane, Asplund et al, Jeffery, Pollacco, Kipper & Klochkova, Pavlenko and others. The evolution was traced both in a continued cooling of the stellar surface and dramatic changes in chemical composition on a timescale of a mere few months. The abundance alterations are the results of the mixing and nuclear reactions which have ensued due to the final He-shell flash which occurred during the descent along the white dwarf cooling track. The observed changes in the H and Li abundances can be explained by ingestion and burning of the H-rich envelope and Li-production through the Cameron-Fowler mechanism. The rapidly increasing abundances of the light s-elements are consistent with current s-processing by neutrons released from the concomitantly produced 13C.

Tubingen, September, What we want to know: Photospheric diagnostic from high and medium resolution spectrograms Tracing of the evolution on timescales months/weeks Circumstellar diagnostic

Tubingen, September, New grid of models: Line-by-line opacity stellar model atmospheres D. Shulyak, V. Tsymbal T. Ryabchikova et al;A&A 428, 993–1000 (2004) T eff = 6000 (500) 8500 Log g=0.0 (0.5) 1.0 N(H)= 0.01,0.03,0.1,0.3 N(C)=0.003, 0.01,0.03,0.1

Tubingen, September, |DATASET: |DATASET: R=5000 JD= R= R= R= R= R= R= R= R= R= aat aat R= wht R= wht R= R= R= R= R= R= R= R= R= R= R=

Tubingen, September, |DATASET: |DATASET: MCDONALD *RAO R= MCDONALD mentioned by Asplund MCDONALD mentioned by Asplund R= MCDONALD *RAO CTIO Shetrone,Keane R= S/N= CTIO Wallerstein R= WHT Pollacco R= S/N= low PFES 6 meter SAO Klochkova V Lynx Lynx 269

Tubingen, September, Optical spectroscopy in 1996:

Tubingen, September, H line profiles : T=8000 K log g =0.5, Vt=7.5, H=0.01, C/He=0.1 AAT

Tubingen, September, H line profiles : T=8000 K log g =0.5, Vt=7.5, H=0.01, C/He=0.1 log ε(O)=9.3; log ε(N)=9.0

Tubingen, September, Zr II lines: New and improved experimental oscillator strengths in Zr II and the solar abundance of zirconium, Ljung, G.; Nilsson, H.; Asplund, M.; Johansson, S. AA, 456, 2006, pp Ljung, G.Nilsson, H.Asplund, M.Johansson, S. Ljung, G.Nilsson, H.Asplund, M.Johansson, S.

Tubingen, September, Y II, Ba II. La II lines:

Tubingen, September, Abundances:

Tubingen, September, Ca II lines:

Tubingen, September, Rapid evolution ?

Tubingen, September, Our plans: We are compiling a library of optical spectra obtained during 1996 in order: - to ensure that the observed record of this extremely rare phenomenon remains accessible to future researchers and - to re-visit the question of its early evolution. This is particularly important for understanding the precise timing and magnitude of the dredge-up of material to the surface of the star following a late thermal pulse. We present preliminary results of a new analysis of some of these data. These include possibly the first direct evidence of dynamical behaviour in the expanding stellar envelope.