000001998 001__ 1998
000001998 005__ 20160701171657.0
000001998 0247_ $$2DOI$$a10.1051/0004-6361:20077932
000001998 037__ $$aASTROimport-155
000001998 100__ $$avan Hoof, P. A. M.
000001998 245__ $$aThe onset of photoionization in Sakurai's Object (V4334 Sagittarii)
000001998 260__ $$c2007
000001998 520__ $$aWe investigate the reheating of the very late thermal pulse (VLTP) object V4334 Sgr (Sakurai's Object) using radio observations from the Very Large Array, and optical spectra obtained with the Very Large Telescope. We find a sudden rise of the radio flux at 5 and 8 GHz - from ≤90 μJy and 80 ± 30 μJy in February 2005 to 320~μJy and 280~μJy in June 2006. Optical line emission is also evolving, but the emission lines are fading. The optical line emission and early radio flux are attributed to a fast shock (and not photoionization as was reported earlier) which occurred around 1998. The fading is due to post-shock cooling and recombination. The recent rapid increase in radio flux is evidence for the onset of photoionization of carbon starting around 2005. The current results indicate an increase in the stellar temperature to 12 kK in 2006. The mass ejected in the VLTP eruption is M_ej ≥ 10-4 M_⊙, but could be as high as 10-2 M_⊙, depending mainly on the distance and the clumping factor of the outflow. We derive a distance between 1.8 and 5 kpc. A high mass loss could expose the helium layer and yield abundances compatible with those of [WC] and PG1159 stars. Based on observations collected at the European Southern Observatory, Chile (programmes 71.D-0396, 75.D-0471, 77.D-0394). 
000001998 700__ $$a Hajduk, M.
000001998 700__ $$a Zijlstra, A. A.
000001998 700__ $$a Herwig, F.
000001998 700__ $$a Evans, A.
000001998 700__ $$a van de Steene, G. C.
000001998 700__ $$a Kimeswenger, S.
000001998 700__ $$a Kerber, F.
000001998 700__ $$a Eyres, S. P. S.
000001998 773__ $$cL9-L12$$i1$$pAstronomy and Astrophysics$$v471$$y2007
000001998 85642 $$ahttp://esoads.eso.org/abs/2007A%26A...471L...9V
000001998 905__ $$apublished in
000001998 980__ $$aREFERD