Sakurai's Object

Discovered by Sakurai

First modern case of a Very Late Thermal Pulse

He reignition event on the white dwarf cooling track

Common but rarely observed

After its discovery, an old PN was found

Expectations

'Born again' PN

Slow evolution back to AGB (centuries)

Ejection of H-poor nebula

Return to white dwarf

Occurs in our Galaxy once a decade

Born again PN

A78

A30

A58/V605 Aql

A few more

Observed VLTP's

CK Vul (1672: Hevelius)

V605 Aql (1918)

Related

R CrB stars

[WC] stars

Light curve

Between April

and Oct 96:

-H disappeared

-C2 bands appeared

Evolution

Very fast evolution not predicted by old VLTP models

Solved by Lawlor & MacDonald: low convection efficiency leads to double evolution

Prediction: fast reheating of Sakurai's Object

Ionization:
a star reheats

Evidence for ionization found in 2002 (Kerber et al)

Confirmed by a VLA 6cm detection in Feb. 2004

Possibly resolved central source, with flux of 0.1 mJy

Background: VLT OIII image

Photo-ionization model

Cloudy model. Constraints are:

Asplund abundances

Kerber line ratios

VLA radio flux

Radio flux due to free-free emission from ionized carbon

Ionized mass is 10-3 solar masses

(lower if gas is highly clumpy)

Stellar temperatureof 15kK may be a bit too high

Stellar model with strongly reduced mixing efficiency

VLTP: 1991.9

Brightening in

1994 is a temperature

effect

Slow return

2021-2250: related

to the [WC] stars?

Implications

Ionization suggests reheating has started

Supports reduced convective mixing

Ionized mass of 10-3 solar masses

High yield of primary carbon

Dominant source of cosmic 13C

5-10% of PNe may show H-poor clumps

[WC] stars may be on return loop

Dust

Light curve traces sudden and initially episodic dust formation

Gas-to-dust ratio of 10-50

New source of galactic carbonaceous dust

Yield of 10-5 to 10-6 solar masses per year

Important in regions without carbon stars

Inner Galactic disk

Main source of 13C-rich dust

Firsts!

First observation of reheating after a VLTP

First time the formation of a PN has been followed from its ejection to its ionization

First detection of radio emission from H-poor gas

Hajduk et al., Science, 308, 21 (2005)

Bipolarity

VLTP ejecta are often bipolar:

A30

V605 Aql

A78?

CK Vul

Sakurai?

Bipolarity in single star evolution

Rotation?

Magnetic fields?

CK Vul IPHAS image

Spitzer spectra
(Evans et al)

Strong dust continuum

Hydrocarbons

No minerals,

e.g TiC, MgS

Model spectra

HCN

C2H2

C2H2+C2H

UV-driven chemistry

H points at pre-1996

ejection event

Molecules

Hydrocarbons require H-rich ejecta

Ejection event prior to Oct 196

H deficiency in 1996 may be caused by ejection rather than ingestion

Summary

Ionization suggests fast reheating in Sakurai's Object

Models suggest a second cooling event to come

Ejecta mass suggests VLTP events are important for Galactic chemical evolution

13C, carbonaceous dust

Hydrocarbons suggest an early mass ejection

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To become born again later this year

2005-06-24T11:15:28