Pulsating Stars & Spectrocopy Denis GILLET Directeur de - - PowerPoint PPT Presentation

Pulsating Stars & Spectrocopy

Denis GILLET

Directeur de recherche au CNRS Observatoire de Haute Provence denis.gillet@oamp.fr

An outstanding laboratory

Our Galaxy: 100 billion stars about a star

• n 100,000

is pulsating

The Sun

Stellar pulsation

Stable (ordinary star) & Unstable (pulsating star)

limit cycle limit cycle

deadening

Initially pushing below the equilibrium radius value

R* = 40 000 000 km 70% H 29.9% He 0.1% other

RR Lyrae star

Iben 1971 PASP 83, 697

photosphere 40,000 K 10,000 K

The he κ- me mecha hanism

energy kinetic with *

H H : ion recombinat body

• three

e e e + → + +

+

Chapter 6

• hydrogen ionization zone (H H+ and He He+)

T = 10,000 – 15,000 K

• helium II ionization zone (He+ He++)

T = 40,000 K

• If the star is too hot, the ionization

zones will be too near the surface to drive the oscillations.

• This accounts for the “blue edge”
• f the instability strip.
• The “red edge” is probably due to

the onset of convection.

 

1 s t

• v

e r t

• n

e f u n d a m e n t a l n

• p

u l s a t I

• n

The insta instability ility strip strip

Atmospheric dynamics

• f

pulsating stars

RR Lyr

T

eff = 7175 K

M = 0.6 Msun L = 62 Lsun 90 layers

• pacity with Fe

Fokin & Gillet 1997 A&A 325, 1013

RR Lyr

Fokin & Gillet 1997 A&A 325, 1013

RR Lyr

Fokin & Gillet 1997 A&A 325, 1013

the density decreases

• f one million times!

Fokin & Gillet 1997 A&A 325, 1013

5 shock waves in RR Lyr – their velocity

Mach number =20

Comparaison de la dynamique atmosphérique dans le cas d'une pulsation classique (small amplitudes) et dans le cas d'une pulsation de fortes amplitudes (atmosphere with shock waves). From Ernst A. Dorfi Universität Wien.

Dynamique extrême de l'atmosphère d'une supergéante pulsante subissant des chocs de très forte intensité conduisant à des phénomènes de perte de masse sporadiques. From Ernst A. Dorfi Universität Wien.

Types of Waves

www.astro.uwo.ca/~jlandstr/planets/webfigs/earth/slide1.html

Longitudinal Waves

In a longitudinal wave the particle displacement is parallel to the direction of wave propagation.

Transverse Waves

In a transverse wave the particle displacement is perpendicular to the direction of wave propagation.

Water Waves or in Solids

Water waves are an example of waves that involve a combination of both longitudinal and transverse motions.

Standing wave

In the pipe, the particles oscillate back and forth, right and left, though they are not all moving in the same direction at the same time; some are moving to the right while others are moving to the left.

Here is an animation of a theoretical model of a protostellar jet like the one from HH47. The material in the jet cools rapidly, causing it to break up into clumps and "bullets". (From Jim Stone, http://www.astro.princeton.edu/~jstone/pjets.html)

Shocks in a protostellar jet

The weak shock: viscous shock front

unperturbed gas

ρ1

shock wake

ρ2

1

~ mean free path

ρ ρ γ p p h h u h u + − ≡ + = + 1 1 2 2

2 2 2 1 2 1

∞ → − + → − + + = ≡

1 2 1 2 1 1

if 1 1 ) 1 ( 2 ) 1 ( 2 M M M γ γ η γ γ ρ ρ η

ρ ρ



Maxwellian velocity distribution

T2 T1

T2 T1

Compression rate

The strong shock: Hypersonic/Radiative shock wave

Hydrodynamic and radiative shocks

Précurseur radiatif

T ρ

excitation ionization translational

The compression in the shock wake

Fadeyev & Gillet 2001 A&A 368, 901

From Alpher & Greyber 1958

Radiative and full-radiative shocks

Fr ≠ 0, Pr ≅ 0, Er ≅ 0 Fr ≠ 0, Pr ≠ 0, Er ≠ 0

• r

From R.A. Gross 1968

From where did emission lines come?

What does happen when the radiative flux photoionize the preshock region ?

M1 = 6.5

∞ → − + → − + + = ≡

if 1 1 ) 1 ( 2 ) 1 ( 2 M M M γ γ η γ γ ρ ρ η

Fadeyev & Gillet 2001 A&A 368, 901

Final compression ratio ρN/ρ1 at the postshock outer boundary XN of shock

Fadeyev & Gillet 2001 A&A 368, 901

3D simulation of shock wave with turbulence using detailed chemistry. M = 4.156 Mt = 0.25.

Master of science in aerospace engineering by H.Narayanan Nagarajan 2009 University of Texas at Arlington.

KVA

Spectrum behaviors

Emission lines Absorption lines Continuum

Origin of stellar photons ?

Optical depth τ and spectral line formation

τ increasing

Stellar Atmosphere

λ λ ξ c × ∆ = + =

2 2 th

V width line

5 1

2 2

= ≈

th th turb

V E E ξ

Type spectral : B8 V ~ 3 masses solaires Type spectral : A7 V ~ 2 masses solaires

H H He I H H He I

The behaviour of the line strength

A star hosting a surface dark spot close to the equator, spectral line profiles are affected throughout their whole width as the spot is carried around the star by rotation. If the spot is located close to the pole, spectral lines are only affected in their core regions.

Stellar tomography Jean-Francois Donati - 25/10/2006 - http://www.ast.obs-mip.fr/article.php3?id_article=457

RR Lyrae @ R = 27,000 and 2.5 m

• 2.5 m telescope

Las Campanas Observatory

• R = 27,000
• Time resolution: 3-10 min
• S/N = 20
• 3500-9000 A

Hα

George W. Preston

The evolution of Hα profiles during pulsation cycles for WY Ant and XZ Aps, as well as for RV Oct based on many more observations, can be viewed as GIF animations in slides 83–86 of the PowerPoint file HNRLecture2009 at ftp: //ftp.obs.carnegiescience.edu/pub/gwp/HNRLecture.

RV Oct in April 2007

λ5876 (HeI) max max

I(Hα)/I(He) = 1.75/1.20 = 1.46

Preston 2011 AJ 141:6, 1

jump shift

Helium-Sodium show !

weak strong |300 km/s|  |300 km/s|

RV Oct AS Vir LOOK!

IS-NaI IS NaI

D3

Preston 2011 AJ 141:6, 1

• 3.6 m telescope

CFHT Observatory

• R = 65,000
• Time resolution: 7 min
• S/N = 180 - 210
• 3000-10100 A

RR Lyr @ R = 65,000 and 3.6 m

Observations by Gillet, Fabas, Lèbre, 2013, A&A

The Schwarzschild mechanism

in RR Lyr

RR Lyr - R = 65,000 - 3.6 m CFHT - Time resolution: 7 min - S/N = 200

The Schwarzschild mechanism

in RR Lyr

RR Lyr Hα

Gillet, Fabas, Lèbre, 2013, A&A in press

The Schwarzschild mechanism

RR Lyr: R = 27,000 and 2.5 m

• 2.5 m telescope

Las Campanas Observatory

• R = 27,000
• Time resolution: 3-10 min
• S/N = 20
• 3500-9000 A

Hα

George W. P t Preston, G.W. 2011 AJ 141 1

⇒ A line doubling phenomenon

The Schwarzschild mechanism

1953, Trans. IAU, 8, 811

The line doubling ⇒ presence of a shock wave in the atmosphere

Emission lines:

Produced by the shock

0.911

RR Lyr HeI 5875

Gillet, Fabas, Lèbre, 2013, A&A

0.911

RR Lyr HeI 5875

Gillet, Fabas, Lèbre, 2013, A&A

0.911

RR Lyr HeII 4686

Gillet, Fabas, Lèbre, 2013, A&A

0.911

RR Lyr HeII 4686

Gillet, Fabas, Lèbre, 2013, A&A

4680 4685 4690

wavelength (A)

5870 5875 5880 5885

6550 6560 6570 6580

0.870 0.896 0.909 0.917 0.925 0.934 0.942 0.950 0.978

HeII HeI Hα

AS Vir : inset boxes surround HeII and HeI emission lines in 3 successive spectra

Preston 2011 AJ 141:6, 1

Detection of helium emissions was confirmed in June and November 2012 by Thierry Garrel with its 35 cm and a spectro to R = 11,000!

LES RÉSULTATS DE THIERRY GARREL :

• Les 15/6, 24/6, 6/11/2012, HeI est en émission (pour seulement quelques minutes) quand Hα est à son intensité maximale.
• Le 24/6 montre HeI 5876 et HeI 6678 simultanément en émission; seul HeI 5876 est observé en émission les 15/6 et 6/11.
• Le 24/6, l’intensité de Hα est plus forte que les 15/6 et 6/11.

Le résultat le plus intéressant trouvé par Thierry GARREL est qu'il y a presque un quart (0.23) de période Blazhko entre les

• bservations des 15/6 et 24/6. DONC l‘émission de l'hélium est présente très longtemps (peut-être pendant la moitié la période

Blazhko). Il sera donc facile de la détecter lorsqu'elle est là. Un autre résultat intéressant : il y a au moins 1,5 année de visibilité de l’HeI (CFHT observation July 4, 2011). Animation of spectra of RR Lyr during maximum by Thierry Garrel for HeI 5875 and neutral sodium NaD on 2012-06-16 and 2012-06-24

High resolution spectrum of Procyon - F5 IV

High resolution spectrum of Sun - G2 V

High resolution spectrum of Arcturus - K1 III