The diffusion-induced nova scenario: CK Vul and PB8 as possible observational counterparts

M. M. MILLER BERTOLAMI; ALTHAUS, L. G.; OLANO, C.; JIMÉNEZ, N.

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY

WILEY-BLACKWELL PUBLISHING, INC

Lugar: Londres; Año: 2011 vol. 415 p. 1396 - 1408

0035-8711

We propose a scenario for the formation of DA white dwarfs with very thin helium buffers. Forthese stars we explore the possible occurrence of diffusion-induced CNO-flashes during theirearly cooling stage. In order to obtain very thin helium buffers, we simulate the formationof low-mass remnants through an asymptotic giant branch (AGB) final/late thermal pulse(AFTP/LTP scenario). Then we calculate the consequent white dwarf cooling evolution bymeans of a consistent treatment of element diffusion and nuclear burning.   Based on physically sound white dwarf models, we find that the range of helium buffermasses for these diffusion-induced novae to occur is significantly smaller than that predictedby the only previous study of this scenario. As a matter of fact, we find that these flashes dooccur only in some low-mass (M 0.6 M ) and low-metallicity (Z ZAMS 0.001) remnantsabout 106 ­107 yr after departing from the AGB. For these objects, we expect the luminosityto increase by about 4 orders of magnitude in less than a decade. We also show that diffusion-induced novae should display a very typical eruption light curve, with an increase of about afew magnitudes per year before reaching a maximum of MV  -5 to -6. Our simulations showthat surface abundances after the outburst are characterized by log N H /N He  -0.15 . . . 0.6and N > C O by mass fractions. Contrary to previous speculations we show that these eventsare not recurrent and do not change substantially the final H-content of the cool (DA) whitedwarf.   Finally, with the aid of model predictions we discuss the possibility that Nova Vul 1670(CK Vul) and the recently proposed [WN/WC]-central stars of planetary nebulae could beobservational counterparts of this diffusion-induced nova scenario. We conclude that, despitediscrepancies with observations, the scenario offers one of the best available explanations forCK Vul and, with minor modifications, explains the observed properties of [WN/WC]-centralstars of planetary nebulae.