hot dq white dwarf stars : a new challenge to stellar evolution

Hot DQ White Dwarf Stars : A New Challenge to Stellar Evolution

Patrick Dufour,University of Arizona

James Liebert, University of Arizona

Gilles Fontaine, Université de Montréal

Natalie Behara, Observatoire Paris-Meudon

Outline

-A Brief Introduction to White Dwarfs

-Spectral Evolution

-DQ White Dwarfs

-Hot DQ

-H1504+65 and Evolutionary Scenario

Jordan & Rauch 1994

Werner & Herwig 2006

“Born-Again scenario”

DODZ

DC

DQ

DADB

PG1159

Evolution

DC

Teff~150,000 K

Helium-richHydrogen-rich

~4000 K

??

DB gap

RCrB?

EHe?

CE?

???

Outline

-A Brief Introduction to White Dwarfs

-Spectral Evolution

-DQ White Dwarfs

-Hot DQ

-H1504+65 and Evolutionary Scenario

Dufour et al. 2005

Dufour et al. 2005

Log q(He) = MHe/M*

log q(He)=-4.0

log q(He)=-3.0

log q(He)=-2.0

FRD

Brassard et al. 2006

G 35-26

11,000 K < Teff < 14,000 K

8.8 < log g < 9.0

C/He ~ 3x10-2

G 227-5

12,000 K < Teff < 13,000 K

log g fixed at 8.0

C/He ~ 3x10-3

Thejll et al. 1990Wegner & Koester 1985

G 227-5

Outline

-A Brief Introduction to White Dwarfs

-Spectral Evolution

-DQ White Dwarfs

-Hot DQ

-H1504+65 and Evolutionary Scenario

G 227-5

Dufour et al 2005

Naive expectation

1- Calculate hotter DQ models

2- Make fits

3- Write paper

4- Move on to the next project

Pure Helium

Log C/He = 0

Log C/He= 1

Pure Carbon

24,000 K, log g = 8.0, 8.5 and 9.0

∫HdTeff4 /4

Outline

-A Brief Introduction to White Dwarfs

-Spectral Evolution

-DQ White Dwarfs

-Hot DQ

-H1504+65 and Evolutionary Scenario

Werner & Herwig 2006

Typical PG 1159 abundances:

33% He

50% C

15% O

2% Ne

H1504+65

• Teff ~ 175,000 K – 200,000 K• Log g = 8• C ~ 48 %• O ~ 48 %• He < 1 %• Extreme PG1159 ?• Burned carbon ?• O/Ne/Mg core ?

Pure carbon, Teff = 30,000 K

DO

DCDZDQ

DA

DB

PG1159

Evolution

DC

150,000 K

Helium-richHydrogen-rich

~4000 K DQ (2nd sequence ?)

H1504+65

Hot DQ

H and He poor

?

Conclusions

-Discovery of a new type of star : white dwarfs with pure carbon atmospheres

-cool down version of H1504+65?

-High mass stars on MS around 8-10 Msun?

-O/Ne/Mg core ?

-Higher S/N observations (MMT) coming soon

-more theoretical calculations/other evolutionary scenario?

Thank you