Astrophysique gamma nucléaire, Toulouse 19-21 avril 2004Novae – M. Hernanz 1 Nucléosynthèse...

Astrophysique gamma nucléaire, Toulouse 19-21 avril 2004 Novae – M. Hernanz 1

Nucléosynthèse dans les novae

Margarita Hernanz Institut d’Estudis Espacials de Catalunya, IEEC-CSIC,

Barcelona• Modèles de novae classiques:

introduction; principales propriétés observationnelles scénario: combustion explosive de l´H et “thermonuclear runaway” modèles de novae; incertitudes nucléosynthèse génerale

• Modèles d’emission :nucleosynthèse noyaux radioactifs spectres et courbes de lumièrerevue des observationsprespectives futures de détection avec INTEGRAL et d’autres instruments


Observation d’une nova

Nova Cygni 1975


Observations avec le Telescope Spatial Hubble (HST)

Nova Cygni 1992


Qu’est-ce que sait une nova?

Une explosion d’une naine blanche dans un système stellaire double


Observation des novae: courbe de lumière optiqueL

umin

osit

é

temps


Observation des novae: courbe de lumière optique

La luminosité augmente par des facteurs 104

Lum

inos

ité

temps


Observation des novae: courbe de lumière optique: relation luminosité maximum-taux tombée luminosité

Lum

inos

ité

temps tombée L

t2 L/10

t2=10 jours: nova rapide

t2=250 jours: nova très lente

Determination de distances20j 200j


Observation des novae: courbes de lumière

Satellite IUE (UV): Lbol(LV+LUV)=ct.

FH Ser 1970

Nova Cyg 1978

Lbol(LV+LUV+ LIR) =ct.


Observation des novae: spectres, determination d’abondances

Vitesses d’expansion ~ 102-103 km/s

Enrichissements en C, N, O, Ne

Metallicités >> Solaires


Exemple: détermination d’abondances

à partir d’observations

dans l’IR


Distribution des novae dans notre galaxie

~35 novae/an dans notre galaxie (mais seulement 3-5 sont découvertes)


Qu’est-ce que sait une nova? ScénarioTransfer de matière de l’étoile

compagnone vers la naine blanche (variable

cataclismique )

Combustion hydrogène conditions dégénerescence à

la surface de la naine blanque

“avalanche termique”

Combustion explosive H

Décroissance noyaux radioactifs de courte vie dans l’enveloppe (transport

par convection)

Expansion enveloppe, augmentation L et expulsion matière


Modèles de nova: Combustion termonucléaire de l’Hydrogène

Echelles de temps plus relevantes

accrétion ~ Macc/M ~ 104 - 105 yr

nucléaire ~ CpT/nuc ; au max. nuc: abondances solaires 1-10s; abondances >sol. <<1s

dynamique ~ Hp/cs ~ (1/g)(P/)1/2 ; quand P et maximum: ~ 1s

Phases évolutives plus importantes

• Accrétion: accrétion < nucléaire : accumulation matière P critique (T<TFermi degener.)

• TNR (avalanche termique): dégénérescence empêche exp. enveloppe

MAIS: T T> TFermi (~108K per MNB =1M)

CNO solaire: nuc ~ dyn ; CNO >sol.: nuc << dyn T & nuc avant expan.


Modèles de nova: combustion termonu-cléaire de l’Hydrogène. Cycle CNO

13N

15O 16O

14N

12C 13C

15N

17O

17F

AX

(p,)

(p,)(+)

14O

18Ne

18F 19F

18O102s 176s

93s

862s

158min

• Au début: + < (p,)

Cycle CNO “opère” en equ.• T ~108 K: + > (p,)

Cycle CNO +-limité (goulot de bouteille)

• Convection: incorporation matière “fraîche” à la couche de combustionconv < +: transport noyaux +-instables aux régions externes froides où ils ne sont pas détruits Sa décroissance postérieure à la surface provoque l’expansion et l’augmentation de luminosité

~


Modèles de novae: nécessité de mélange coeur-enveloppe

• Z observée >> solaire mélange CO ou ONe - enveloppe solaire accretée

• Explosion elle-même surabondance initiale de CNO mélange

Many classical nova ejecta are enriched in CNO and Ne. Rosner and coworkers recently suggested that

the enrichment might originate in the resonant interaction between large-scale shear flows in the accreted H/He envelope and gravity waves at the interface between the envelope and the underlying C/O white dwarf (WD). The shear flow amplifies the waves, which eventually form cusps and break. This wave breaking injects a spray of C/O into the superincumbent H/He. In the absence of enrichment prior to ignition, the base of the convective zone, does not reach the C/O interface. As a result, there is no additional mixing, and the runaway is slow. In contrast, the formation of a mixed layer during the accretion of H/He, prior to ignition, causes a more violent runaway. The envelope can be enriched by 25% of C/O by mass (consistent with that observed in some ejecta) for shear velocities, over the surface, with Mach numbers 0.4.

Alexakis et al., 2004, ApJ


HYDRODYNAMICAL CODE

Lagrangian, one-dimensional, implicit

Convection included

Hydrostatic accretion phase also modelled

Profiles of , T, v ... along the envelope for each time

&Detailed nucleosynthesis, including

radioactive nuclei

Modèles de novae: calcul théorique


Modèles de novae: proprietés générales


Modèles de novae: reactions nucléaires importantes


Nucleosynthèse dans les novae et evolution chimique de la Galaxie

Mejec(theor.) ~ 2x10-5 M/nova

R(novae) ~ 35 novae/an

Age Galaxie ~ 1010 années

Mejec,total(novae) ~ 7x106 M = (7x10-4 M/an) 1/3000 Mgal(gaz+pous.)

Novae peuvent être responsables des abondances galactiques des isotopes surproduits (par rap. Sol.) par des facteurs 3000


Nucleosynthèse dans les novae: surproductions vs. solaires



ONe

1.35M


Other signatures of radioactivities in novae: presolar grains

Amari et al. 2001, ApJ

five SiC and one graphite grain from the Murchison meteorite show isotopic compositions indicating a nova origin


Why novae emit gamma-rays? Explosive H-burning: synthesis of +-unstable nuclei

13N 14O 15O 17F 18F

862s 102s 176s 93s 158min.

crucial for enve-lope expansion

crucial for -ray emission(through e--e+ annihilation)

Other radioactive nuclei synthesized

7Be 22Na 26Al

77days 3.75yrs 106yrs

line 478keV 1275keV 1809keV

e-capture e+-emission


Main radioactive isotopes synthesized in classical novae

Nucleus Type of emission Nova type

13N 862 s511 keV line

continuum (E<511 keV)CO and ONe

18F 158 min511 keV line

continuum (E<511 keV)CO and ONe

7Be 77 days 478 keV line CO mainly

22Na 3.75 yr 1275 keV line ONe

26Al 1.0X106 yr 1809 keV line ONe


Radioactivities in novae ejecta: some examples

Nova type MWD(M ) MTOTejected

(M )<KE>

(erg·g-1)

13N (M )*

( =862 s)

18F (M )*

( =158 min)

7Be (M )

( =77 days)

22Na (M )

( =3.75 yr)

CO 0.8 6.2 x 10-5 8 x 1015 1.5 (-7) 1.8 (-9) 6.0 (-11) 7.4 (-11)

CO 1.15 1.3 x 10-5 4 x 1016 2.3 (-8) 2.6 (-9) 1.1 (-10) 1.1 (-11)

ONe 1.15 2.6 x 10-5 3 x 1016 2.9 (-8) 5.9 (-9) 1.6 (-11) 6.4 (-9)

ONe 1.25 1.8 x 10-5 4 x 1016 3.8 (-8) 4.5 (-9) 1.2 (-11) 5.9 (-9)

* 1 h after Tpeak Rates for 18F+p reactions from Utku et al. (1998)


Emission mechanisms:

• Positron annihilation

• e+ - e- two 511 keV photons (10 %)

positronium formation• (90 %)

two 511 keV s three <511 keV s

(25 %) (75 %)

Positron-unstable nuclei included:

13N = 862 s18F = 158 min22Na = 3.75 yrs

Modèles de novae: calcul théorique des spectres

Monte Carlo code for -ray production and transport (Ambwani & Sutherland 1988)


• Nuclear decay

7B (-) 7Li 478 keV( = 77 days)

22Na (+) 22Ne 1275 keV( = 3.75 yrs)

• Inverse Compton scattering

Absorption mechanisms:

• Photo-electric absorption (E < 100 keV)

• e- - e+ production (E > 1022 keV)

• Compton scattering (100 keV<E<5 MeV)

Emission mechanisms (cont.)

Modèles de novae: calcul théorique des spectres


Spectra of CO novaeMWD = 1.15 M

• e+ annihilation and Comptonization continuum and 511 keV line; e+ from 13N and 18F

predicted theoretically by Clayton & Hoyle 1974; Leising & Clayton 1987

• photoelectric absorption cutoff at 20 keV• 478 keV line from 7Be decay • transparent at 48 h

d=1 kpc

Gómez-Gomar, Hernanz, José, Isern,1998, MNRAS


Spectra of CO novae

MWD = 0.8 M

• lower fluxes

• longer duration: at 48 h there is still continuum and 511 keV line emission

• larger opacities of the expanding shells than in 1.15 M

d=1 kpc



Spectra of ONe novae

MWD = 1.15 M (solid)

1.25 M (dotted)

• photoelectric absorption cutoff at 30 keV• continuum and 511 keV as in CO novae• 1275 keV line from 22Na decay • similar behaviour for the 2 models, because of similar KE and yields

d=1 kpc



Light curves: 478 keV (7Be) line

Only in CO novae

tmax: 13 days (0.8M)

5 days (1.15 M)

duration: some weeks

Flux (1-2)x10-6 ph/cm2/s

d=1 kpc


Observations: 478 keV line (7Be)

Harris et al. 1991 and 2001

SMM

TGRS

Theory: F<2.5x10-6/dkpc2

predicted theoretically by Clayton 1981


Radioactivities in novae ejecta: some examples

Nova type MWD(M ) MTOTejected

(M )<KE>

(erg·g-1)

13N (M )*

( =862 s)

18F (M )*

( =158 min)

7Be (M )

( =77 days)

22Na (M )

( =3.75 yr)

CO 0.8 6.2 x 10-5 8 x 1015 1.5 (-7) 1.8 (-9) 6.0 (-11) 7.4 (-11)

CO 1.15 1.3 x 10-5 4 x 1016 2.3 (-8) 2.6 (-9) 1.1 (-10) 1.1 (-11)

ONe 1.15 2.6 x 10-5 3 x 1016 2.9 (-8) 5.9 (-9) 1.6 (-11) 6.4 (-9)

ONe 1.25 1.8 x 10-5 4 x 1016 3.8 (-8) 4.5 (-9) 1.2 (-11) 5.9 (-9)

* 1 h after Tpeak Rates for 18F+p reactions from Utku et al. (1998)


Light curves: 1275 keV (22Na) line

Rise phase

Exponential decline

tmax: 20 days (1.15M), 12 days (1.25 M)

duration: some months Flux 2x10-5 ph/cm2/s

Only in ONe

novae

d=1 kpc


Observations: 1275 keV line (22Na)

Iyudin et al. 1995, A&A

CGRO/COMPTEL: no detection; upper limits

predicted theoretically by Clayton & Hoyle, 1974


Observations : 1275 keV line (22Na)

Iyudin et al. 1995, A&A

Upper limits in agreement with current theoretical

predictions


Light curves: 511 keV line

• 511 keV line in ONe novae remains after 2 days until 1 week because of e+ from 22Na• Very early appearence, before visual maximum (i.e, before discovery)

Model tmax* (h) Fmax (ph/cm2/s)

**

CO, 0.8 M - - - 2.6 x 10-5

CO, 1.15 M 6.5 5.3 x 10-4

ONe, 1.15 M 6 1.0 x 10-3

ONe, 1.25 M 5 1.9 x 10-3

In CO and ONe novae

d=1 kpc


The continuum and the 511 keV line, e--e+

annihilation, are the most intense emissions, but their duration is very short and they appear before visual discovery

detection requires “a posteriori” analyses with wide FOV instruments (BATSE, TGRS, RHESSI)

future hard X/soft -ray surveys like EXIST can provide unique information about the Galactic nova distribution


Gamma-ray and visual light curves

Visual maximum later than 511 keV and continuum maxima


Observations of the 511 keV line

Harris et al. 1999, ApJ

• Observation of 5 known Galactic novae in the broad TGRS FOV in the period 1995 Jan - 1997 June

• High E-resolution Ge detector: ability to detect 511 keV line blueshifted w.r.t. background line

WIND/TGRS: no detection; upper limits


Line profiles: 511 keV lineCO nova

MWD = 1.15 M

d=1 kpc

The line is blueshifted, until the envelope reaches transparency:

518 keV (1h) 512 keV (24h)

FWHM (12h)= 7 keV


Observations of the 511 keV line

Harris et al. 2000, ApJ

WIND/TGRS: “constraining” the Galactic nova rate from a survey of the Southern Sky during 1995-1997

From the non detection, an upper limit of the Galactic nova rate was extracted:

< 123 yr-1 (CO novae; rdetect.: 0.9 kpc )

< 238 yr-1 (ONe novae; rdetect.: 0.7 kpc )

Promising for future wide FOV instruments sensitive in the soft -ray range (20-511) keV


Observations: 511 keV line

Hernanz, Smith, Fishman, et al., 2000, Proc. 5th CGRO Symp.

Pup91 Sgr92#1 Cyg92 Sco92 Cas93 Aql95 Cir95 Vel99

Date ofdiscovery

Dec 27 Feb 13 Feb 19 May 26 Dec 8 Feb 7 Jan 27 May 22

mv (max.) 6.4 7.3 4.2 7.3 5.3 8.1 7.2 2.8

t2 (d) 15 4-14 16 73 33 11 20 6

d (kpc) 2.9 3.6 1.7 0.8 2.8 1.9 4 2

List of nearby novae (d < 3-4 kpc) since CGRO launch

Refs.: IAU circulars and Shafter 1997, Ap. J. 487, 226

Other candidate novae: Cru96, Sco97, Sgr98, Oph98, Sco98, Mus98

CGRO/BATSE


Light curves: 511 keV line and continuum

CO Nova, 1.15 M ONe Nova, 1.15 M

d=1 kpc


Summary of BATSE observations: 3- upper limits to the fluxes (ph/cm2/s)

F(obs) F(model)

(250-511) keV 5.2·10-3 2.3·10-3

511 keV line (*) 1.0·10-3 4.8·10-4

511 keV line (**) 2.4·10-3 4.8·10-4

Nova Sco 1992 (model: 1.15M CO nova at d=0.8 kpc)

Nova Cyg 1992 (model: 1.25M ONe nova at d=1.7 kpc)

F(obs) F(model)

(250-511) keV 3.6·10-3 5.3·10-3

511 keV line (*) 7.1·10-4 1.0·10-3

511 keV line (**) 2.3·10-3 1.0·10-3

Nova Vel 1999 (model: 1.25 M ONe nova at d=2 kpc)

F(obs) F(model)

(250-511) keV 5.3·10-3 1.7·10-3

511 keV line (*) 1.0·10-3 3.5·10-4

511 keV line (**) 1.6·10-3 3.5·10-4

* using 250-511 keV data with assumed Comptonization; ** using 511 keV data only


Light curves: 511 keV line. Influence of Mejected

F when Mej

F when Mej

d=1 kpc

e+: 13N and 18F e+: 13N, 18F and 22Na


Light curves: 511 keV line. Influence of vejec.

F when vej

F 0 before when vejd=1 kpc


Nuclear uncertainties related with 18F synthesis (511 keV & continuum emission)

Coc, Hernanz, José, Thibaud, 2000, A&A

Rates obtained including the latest experimental data up to the end of 1999


Recent experimental

determination of the 18F(p,)15O reaction

rate de Séreville, Coc, Angulo et al. 2003,Phys. Rev. C:reduction of the uncertainty and nominal rate similar

Good news!

Nuclear uncertainties related with 18F synthesis (511 keV & continuum emission)


Model MWD(M ) 511 keV line* 478 keV line 1275 keV line continuum*

(170-470 keV)

CO 0.8 0.7 0.13 - - - 0.4

CO 1.15 2.4 0.16 - - - 2.0

ONe 1.15 3.7 - - - 0.5 3.0

ONe 1.25 4.3 - - - 0.5 3.0

* 10 h integration time starting 5 h after Tpeak

Observations with INTEGRAL/SPI

Width of the lines fully taken into account

3 detectability distances (kpc): lines and continuum


Spectra binned with E=E/2 and continuum sensitivity of IBIS/ISGRI (E=E/2; tobs=10h)

1.25 ONe mixing with core new 18F+p & 17O+p nuclear reaction rates (affecting 18F synthesis and thus 511 keV line and continuum)Nucleosynthesis from this model: published in José, Hernanz et al. ApJLett., 2003; -ray spectra: unpublished

Observations with INTEGRAL/IBIS


M

C

A

Continuum detectability distances with IBIS-ISGRI (at 100 keV):

•tobs=time if time<10h

•tobs=10h if time>10h

time: since explosion (Tpeak))

M: model shown in previous page

A&C: other models

But chance nova in FOV very small

Observations with INTEGRAL/IBIS


Novae distances observed

Distances from Shafter 1997,ApJ

1275 keV: d<0.5kpc 1/5 yr

511 keV & cont.: d<(3-4)kpc (6-9)/(5 yr)


Galactic distribution of -ray emission from novae

Observations (upper limits): Leising et al. 1988, Harris et al 1991, 1996

Theoretical predictions:Jean, Hernanz, Gómez-Gomar, José, 2000, MNRAS


26Al ejected masses by ONe novaeNuclear uncertainties

WD mass Minimum Best Maximum

1.15 8.6·10-9 2.1·10-8 3.1·10-8

1.25 3.6·10-9 1.2·10-8 1.6·10-8

1.35 6.6·10-10 3.2·10-9 4.8·10-9

Max/Min

3.6

4.4

7.3

(all in M) José, Coc and Hernanz 1999, ApJ

Contribution of novae to Galactic 26Al:

M(26Al) 2.0 M * Mej(26Al)/(10-7 M) * RN/(35 yr-1) * fONe/0.5 0.4 M

< M(26Al) from CGRO/COMPTEL 1809 keV map


Summary (-ray emission)• Classical novae produce gamma-rays:

CO novae: lines at 478 and 511 keV; continuum 20E 511 keV

ONe novae: lines at 511 keV and 1275 keV; continuum 20E 511 keV

•Detectability distances with INTEGRAL/SPI typically are 0.2 kpc during weeks (478 keV line), 0.5 kpc during months (1275 keV line) and 3 kpc during hours (511 keV and continuum)

• Future 1275 keV emission map will provide direct and unique information about the distribution of ONe novae in the Galaxy.

•The continuum and the 511 keV line are the most intense emissions, but their duration is very short and they appear before visual discovery

detection requires “a posteriori” analyses with wide FOV instruments (BATSE, TGRS)

future gamma-ray surveys (EXIST?) can provide unique information about the Galactic nova distribution

Astrophysique gamma nucléaire, Toulouse 19-21 avril 2004Novae – M. Hernanz 1 Nucléosynthèse...

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