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Stellar Rotation Helioseismology

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Stellar Rotation Helioseismology 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 Christoph Scheiner Galileo Galilei (1587-1617) (1575-1650) (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 Carrington Spörer Faye (1575-1650) (1826-1875) (1822-1895) (1814-1902) 1630 Scheiner : spots closer to the equator rotate faster 1850s Carrington and Spörer and independently Faye proposed : 2 ­ 14±37 3±10sin Á deg/day Æ ¡ 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 : f fs /(1 v/c) where c is the speed of light obs Æ ¡ 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 Jakob Halm Walter Adams (1839-1914) (1839-1914) (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 Jakob Halm Walter Adams (1839-1914) (1839-1914) (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 vsini Limits only projected equatorial velocities! !needs the stellar radius and the inclination angle ) - Periodic variation in strength of spectral lines P ! rot 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 Pol Swings (1897-1963) (1906-1983) 1929-1934 Otto Struve First used the spectral line rotational broadening to obtain projected velocities The values of vsini fell into the range 0-250 km/s The Sun is a slow rotator (2 km/s) ! Correlation vsini - 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 1949 : Statistical studies of stellar rotation in spectroscopy (1925-1999) - Limited resolution only rapid to moderate rotators (M 1.5M ) ! È ¯ - Lack of correlation between vsini and galactic coordinate v )Ç È Mean rotation velocity v Ç È Rotation increases from very low values for F-type to maximum values for B-type stars B large radius effect : v ­R 2¼R/P Æ Æ rot Sp. M R v ­ Prot 5 1 M R km/s 10¡ s¡ days O5 39.5¯ 17.2¯ 190 1.5 4.85 B5 7.0 4.0 210 7.6 0.96 A5 2.2 1.7 160 13.0 0.56 Luminosity class : F5 1.4 1.2 25 3.0 2.42 V main sequence stars ! G0 1.05 1.04 12 1.6 4.55 II - IV subgiants and giants (McNally 1965) ! R-M. Ouazzani (SAC - Aarhus University) 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 Robert Kraft (1909-1994) (1927-) From the Sun : Ca II H and K emission lines tracers of chromospheric activity in late type stars Wilson 1966, Kraft 1967 vsini 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 Evry Schatzman (1920-2010) Angular Momentum : measures the rotational momentum of a system J I­ , I R ½r2dV : moment of inertia, ­ 2¼/P : angular velocity Æ Æ Æ rot Conservation law : d J T , external torques T due to binarity, disk, magnetic field... dt Æ Mass ejection at the equator Schatzman 1952 : Magnetic braking d d I­ R2­ M dt Æ dt (R­2) · M ¸p then, f f 2 (R­ )i Æ Mi where p 16 for a solar model on the MS ' J J /100 ¢M/M 25% f Æ i ) Æ 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 Evry Schatzman (1920-2010) Angular Momentum : measures the rotational momentum of a system J I­ , I R ½r2dV : moment of inertia, ­ 2¼/P : angular velocity Æ Æ Æ rot Conservation law : d J T , external torques T due to binarity, disk, magnetic field... dt Æ Schatzman 1952 : Magnetic braking d d I­ D2­ M dt Æ dt (R­2) · M ¸p then, f f 2 (R­ )i Æ Mi where D is the Alfven radius D 15R here p 3800 for a solar model on' the¯ MS ' J J /100 ¢M/M 0.12% f Æ i ) Æ 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) 1/2 empirical law : ­ t¡ ! / Loss of angular momentum ­3 compatible with Schatzman’s/¡ magnetic braking formalism Li abundance follows v decay (until the Hyades) Ç rot È Improved gyrochronology : Barnes 2003, Barnes 2007, Karoff et al.
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