History of the solar rotation
History of the stellar rotation
Helioseismology
Stellar Rotation
Rhita-Maria Ouazzani
SAC - Aarhus University
August the 13th 2014
R-M. Ouazzani (SAC - Aarhus University)
SAC summerschool
August the 13th 2014
1 / 19
History of the solar rotation
History of the stellar rotation
Helioseismology
Outlines
1
History of the solar rotation
2
History of the stellar rotation
3
Helioseismology
R-M. Ouazzani (SAC - Aarhus University)
SAC summerschool
August the 13th 2014
2 / 19
History of the solar rotation
History of the stellar rotation
Helioseismology
The Sun’s surface rotates !
One instrument : the refracting telescope and three astronomers :
Johannes Fabricius
(1587-1617)
Christoph Scheiner
(1575-1650)
Galileo Galilei
(1564-1642)
1611 Fabricius first recorded westward motion of spots
on the solar disk in about two weeks.
Scheiner suggested that they were due to small planets
revolving around an immaculate non-rotating Sun.
Beginning of the long standing Spots vs Planet War !
1612 Galileo confirmed Fabricius’ discovery relying on
the foreshortenning of spots close to the limbs.
→ The Sun rotates in 26 days !
R-M. Ouazzani (SAC - Aarhus University)
SAC summerschool
August the 13th 2014
3 / 19
History of the solar rotation
History of the stellar rotation
Helioseismology
The Sun’s surface rotates !
What is a sunspot ?
Temporary phenomena on the photosphere
of the Sun that appear visibly as dark spots.
They are caused by intense magnetic
activity inhibiting convection
→ areas of reduced surface temperature
They usually appear as pairs of
spots of opposite magnetic poles.
R-M. Ouazzani (SAC - Aarhus University)
SAC summerschool
August the 13th 2014
4 / 19
History of the solar rotation
History of the stellar rotation
Helioseismology
The Sun’s surface rotates differentially !
Scheiner
(1575-1650)
Carrington
(1826-1875)
Spörer
(1822-1895)
Faye
(1814-1902)
1630 Scheiner : spots closer to the equator rotate faster
1850s Carrington and Spörer and independently Faye
proposed :
Ω = 14◦ 37 − 3◦ 10sin2 φ
deg/day
→ The Sun’s surface rotates differentially !
spots cover only a limited surface of the solar disk ±30◦
R-M. Ouazzani (SAC - Aarhus University)
SAC summerschool
August the 13th 2014
5 / 19
History of the solar rotation
History of the stellar rotation
Helioseismology
The Sun rotates differentially !
First use of spectroscopy for astronomical purposes
Doppler shift : Hermann Vogel (1841-1907)
Light at frequency fs by a source moving at velocity v
received frequency from a standing observer :
fobs = fs /(1 − v /c) where c is the speed of light
Doppler shift of lines at opposite edges of the solar disk
gives the solar surface rotation at latitude a given latitude
→ Access all the latitudes !
R-M. Ouazzani (SAC - Aarhus University)
SAC summerschool
August the 13th 2014
6 / 19
History of the solar rotation
History of the stellar rotation
Helioseismology
The Sun rotates differentially !
One instrument : the spectrograph and three major contributors :
Nils Dunér
(1839-1914)
Jakob Halm
(1839-1914)
Walter Adams
(1876-1956)
1900s Dunér and Halm confirmed Faye’s rotation
law with coverage of latitude up to the poles
→ Velocity field for the solar surface
Soon after Adams shows that spectral lines emitted
at different heights give different rotation velocities
Mount Wilson Observatory, George Hale’s world’s greatest telescope (1908)
→ The Sun rotates differentially in depth !
R-M. Ouazzani (SAC - Aarhus University)
SAC summerschool
August the 13th 2014
7 / 19
History of the solar rotation
History of the stellar rotation
Helioseismology
The Sun rotates differentially !
One instrument : the spectrograph and three major contributors :
Nils Dunér
(1839-1914)
Jakob Halm
(1839-1914)
Walter Adams
(1876-1956)
1900s Dunér and Halm confirmed Faye’s rotation
law with coverage of latitude up to the poles
→ Velocity field for the solar surface
Soon after Adams shows that spectral lines emitted
at different heights give different rotation velocities
Mount Wilson Observatory, George Hale’s world’s greatest telescope (1908)
→ The Sun rotates differentially in depth !
R-M. Ouazzani (SAC - Aarhus University)
SAC summerschool
August the 13th 2014
8 / 19
History of the solar rotation
History of the stellar rotation
Helioseismology
Outlines
1
History of the solar rotation
2
History of the stellar rotation
3
Helioseismology
R-M. Ouazzani (SAC - Aarhus University)
SAC summerschool
August the 13th 2014
9 / 19
History of the solar rotation
History of the stellar rotation
Helioseismology
The modern era of Stellar Physics
A step forward, one astronomer : George Ellery Hale (1868-1938),
and the first large telescopes :
Mount Wilson : 1.5 m telescope (first light 1908), and 2.5 m (1917)
Mount Palomar : 5 m telescope (first light 1949)
Stellar rotation with two techniques :
Photometry :
- Detection of tracers such as spots or bright areas → Prot
Limits → work only for spotted stars
Spectroscopy :
- Doppler broadening of spectral lines → v sin i
Limits → only projected equatorial velocities
⇒ needs the stellar radius and the inclination angle
- Periodic variation in strength of spectral lines → Prot
R-M. Ouazzani (SAC - Aarhus University)
SAC summerschool
August the 13th 2014
10 / 19
History of the solar rotation
History of the stellar rotation
Helioseismology
The Rotation to Spectral type correlation
Otto Struve
(1897-1963)
Pol Swings
(1906-1983)
1929-1934 Otto Struve
First used the spectral line rotational broadening to obtain projected velocities
The values of v sin i fell into the range 0-250 km/s
→ The Sun is a slow rotator (2 km/s)
→ Correlation v sin i - stars spectral types
The early O B A and early F-type stars have large rotation velocities
whereas in late F-type and later types, rapid rotation is found only in binaries
1936 Pol Swings :
In close short period binaries axial rotation tends to synchronize with the orbital motion
⇒ F and later-types single stars are naturally slow rotators
R-M. Ouazzani (SAC - Aarhus University)
SAC summerschool
August the 13th 2014
11 / 19
History of the solar rotation
History of the stellar rotation
Helioseismology
The Rotation to Spectral type correlation
Arne Slettebak
(1925-1999)
1949 : Statistical studies of stellar rotation in spectroscopy
- Limited resolution → only rapid to moderate rotators (M > 1.5M¯ )
- Lack of correlation between v sin i and galactic coordinate ⇒ < v >
Mean rotation velocity < v >
Rotation increases from very low values for F-type
to maximum values for B-type stars
B large radius effect : v = ΩR = 2πR/Prot
Sp.
Luminosity class :
V → main sequence stars
II - IV → subgiants and giants
R-M. Ouazzani (SAC - Aarhus University)
O5
B5
A5
F5
G0
M
M¯
39.5
7.0
2.2
1.4
1.05
R
R¯
17.2
4.0
1.7
1.2
1.04
v
km/s
190
210
160
25
12
Ω
10−5 s−1
1.5
7.6
13.0
3.0
1.6
Prot
days
4.85
0.96
0.56
2.42
4.55
(McNally 1965)
SAC summerschool
August the 13th 2014
12 / 19
History of the solar rotation
History of the stellar rotation
Helioseismology
The Rotation and Activity relation
A step forward, the 40-years Ca HK project at Mount Wilson Observatory
Olin Wilson
(1909-1994)
Robert Kraft
(1927-)
From the Sun : Ca II H and K emission lines tracers
of chromospheric activity in late type stars
Wilson 1966, Kraft 1967
v sin i and Ca II measurements on 100 stars :
Rotation velocities are higher among stars with Ca II
emission than among those without
Stars with Ca II emission are on average younger
than stars without
⇒ Rotation declines with age due to a braking
mechanism related to magnetic activity
R-M. Ouazzani (SAC - Aarhus University)
SAC summerschool
August the 13th 2014
13 / 19
History of the solar rotation
History of the stellar rotation
Helioseismology
Why are low mass stars braked along MS evolution ?
1959 Theoretical explanation for low mass stars braking on the MS
Angular Momentum : measures the rotational momentum of a system
R
J = IΩ , I = ρr2 dV : moment of inertia, Ω = 2π/Prot : angular velocity
Evry Schatzman
(1920-2010)
Conservation law :
d
J = T , external torques T due to binarity, disk, magnetic field...
dt
Mass ejection at the equator
Schatzman 1952 : Magnetic braking
d
d
IΩ = R2 Ω M
dt
dt
·
¸
(RΩ2 )f
Mf p
then,
=
(RΩ2 )i
Mi
where p'16 for a solar model on the MS
Jf = Ji /100 ⇒ ∆M/M = 25%
Incompatible with observations
R-M. Ouazzani (SAC - Aarhus University)
SAC summerschool
August the 13th 2014
14 / 19
History of the solar rotation
History of the stellar rotation
Helioseismology
Magnetic braking along the MS for low mass stars
1959 Theoretical explanation for low mass stars braking on the MS
Angular Momentum : measures the rotational momentum of a system
R
J = IΩ , I = ρr2 dV : moment of inertia, Ω = 2π/Prot : angular velocity
Evry Schatzman
(1920-2010)
Conservation law :
d
J = T , external torques T due to binarity, disk, magnetic field...
dt
Schatzman 1952 : Magnetic braking
d
d
IΩ = D2 Ω M
dt
dt
·
¸
(RΩ2 )f
Mf p
then,
=
(RΩ2 )i
Mi
where D is the Alfven radius D' 15R¯
here p' 3800 for a solar model on the MS
Jf = Ji /100 ⇒ ∆M/M = 0.12%
R-M. Ouazzani (SAC - Aarhus University)
SAC summerschool
August the 13th 2014
15 / 19
History of the solar rotation
History of the stellar rotation
Helioseismology
Gyrochronology
A. Skumanich
1972 Observational evidence for Schatzman’s magnetic braking
MWO’s observations of Hyades and Pleiades, and solar observations
Comparing rotation velocities of MS low mass stars :
Pleiades (40 Myrs) Hyades (400 Myrs) Sun (4.5 Gyrs)
→ empirical law : Ω ∝ t −1/2
Loss of angular momentum ∝ −Ω3
compatible with Schatzman’s magnetic braking formalism
Li abundance follows < vrot > decay (until the Hyades)
Improved gyrochronology : Barnes 2003, Barnes 2007, Karoff et al. 2013
Age of exoplanetary systems with no other data than the photometric ones :
spots’ rotation → Prot ⇒ age !
R-M. Ouazzani (SAC - Aarhus University)
SAC summerschool
August the 13th 2014
16 / 19
History of the solar rotation
History of the stellar rotation
Helioseismology
Outlines
1
2
History of the solar rotation
History of the stellar rotation
→
Surface Rotation
——————————————————
3
Helioseismology
R-M. Ouazzani (SAC - Aarhus University)
→
Internal Rotation !
SAC summerschool
August the 13th 2014
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History of the solar rotation
History of the stellar rotation
Helioseismology
To be continued...
R-M. Ouazzani (SAC - Aarhus University)
SAC summerschool
August the 13th 2014
18 / 19
History of the solar rotation
History of the stellar rotation
Helioseismology
Bibliography
Stellar Rotation, Jean-Louis Tassoul 2009
Physics, Formation and Evolution of Rotating Stars, André Maeder 2009
The Rotation of Sun and Stars, ed. J.P Rozelot, C. Neiner, LNP 765, 2009
The Rotation of Sun and Stars, ed. M.J. Goupil, K. Belkacem, F. Lignières,
J.J. Green, LNP 865, 2013
R-M. Ouazzani (SAC - Aarhus University)
SAC summerschool
August the 13th 2014
19 / 19