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Mark Giampapa National Solar Observatory Tucson, Arizona USA 2010 Sagan Summer Workshop 7/26/2010 Stars As Homes for Habitable Planetary Systems the Speaker

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Mark Giampapa National Solar Observatory Tucson, Arizona USA 2010 Sagan Summer Workshop 7/26/2010 Stars As Homes for Habitable Planetary Systems the Speaker SPOTS AND GRANULATION as a Funcon of Mass and Age Mark Giampapa National Solar Observatory Tucson, Arizona USA 2010 Sagan Summer Workshop 7/26/2010 Stars as Homes for Habitable Planetary Systems The Speaker Dr. Mark Giampapa serves as the Deputy Director for the Naonal Solar Observatory (NSO) with specific responsibility for the Tucson/Ki Peak program. A recipient of the George Van Biesbroeck award in recognion of his observaonal and theorecal studies of the stars and Sun, Dr. Giampapa has published over 130 research papers on invesgaons of the origin and nature of stellar magnec acvity. He has supervised in research a number of undergraduate and graduate students who are now leaders in research in stellar astrophysics. Mark received his Bachelors of Science degree in astronomy from USC in 1976 and his PhD in astronomy from the University of Arizona in 1980. He was a Center Fellow at the Harvard‐Smithsonian Center for Astrophysics from 1980‐82 before returning to Tucson to become a permanent scienfic staff member at the Naonal Solar Observatory/NOAO. Mark Giampapa 7/26/2010 2010 Sagan Summer Workshop • First and most apparent non-uniformity observed in the Quiet Sun • Bright cells of irregular polygonal shape separated by dark lanes • Solar granulation ~ 1000 km (1-2 arcsec) and lifetimes of 8 min – 20 min. • High uniformity of brightness and brightness variations across a cell Mark Giampapa 7/26/2010 2010 Sagan Summer Workshop Components of irradiance variaons in the Sun: spots and faculae Why is there not more irradiance variability observed just from mul‐sigma excursions in brightness of some of the millions of convecve granules? Mark Giampapa 7/26/2010 2010 Sagan Summer Workshop Irradiance Variability in the Sun • Magnec features appear to give rise to long‐ and short‐term variaons in the solar irradiance • Random variaons in the number and geometry of turbulent convecve cells should produce global variaons in heat flux • But…. it is the enormous thermal inera of the deeper solar layers that is at the root of solar irradiance variaons. But this same inera tends to damp luminosity variaons we might otherwise expect from structural changes deeper in the sun. Mark Giampapa 7/26/2010 2010 Sagan Summer Workshop Spectroscopic Signatures of Granulaon • The bright regions are correlated with upflows • The darker, cooler regions correspond to downflowing gas Line Bisectors • The effect of granulaon in stellar spectra can be described by the “C‐shape” of the so‐called line bisector • The line bisector is constructed by determining the midpoint of each segment drawn between points at equal depths in the line profile. These midpoints are then connected to yield the “bisector” of the line profile, as illustrated in the next slide Mark Giampapa 7/26/2010 2010 Sagan Summer Workshop C‐shape of line bisectors Mark Giampapa 7/26/2010 2010 Sagan Summer Workshop From Gray (2005) Spectral line asymmetries due to granulaon • Velocity‐brightness correlaon of granulaon leads to natural line asymmetry, i.e., the correlaon between rise and fall velocies and temperature of the granulaon structure • Convecve blueshis can hinder measurement of true radial velocies to accuracies beer than a few hundred m s‐1 Mark Giampapa 7/26/2010 2010 Sagan Summer Workshop Line Bisectors in the Sun Mark Giampapa 7/26/2010 2010 Sagan Summer Workshop Courtesy W. C. Livingston Sun‐as‐a‐star Bisector Variaon Courtesy W. C. Livingston (NSO) Mark Giampapa 7/26/2010 2010 Sagan Summer Workshop Solar bisector data courtesy of W. Livingston (Naonal Solar Observatory) Bisector Span and Color Mark Giampapa 7/26/2010 From Povich et al. (2001) 2010 Sagan Summer Workshop Bisectors and effecve temperature Typical changes in bisector shape with effecve temperature; each panel is for a separate luminosity class. The thin lines show the rms uncertainty in the measurements of the mean bisectors (thick lines). Horizontal placement of the bisectors is arbitrary but ordered by spectral type. From Gray (2005) Bisectors and Luminosity Class Height of the blue‐most point of the mean bisectors, ploed against absolute magnitude. Different luminosity classes are denoted by different symbols. The stars included are restricted in temperature class. Along a vercal line of constant absolute magnitude, hoer stars are higher (Gray 2005; PASP, 117, 711) Granulaon and line strengths Mark Giampapa 7/26/2010 From I. Ramírez, C. Allende Prieto, and 2010 Sagan Summer Workshop D. L. Lambert (2008) Inverse C‐shapes Mark Giampapa Gray & Nagel (1989) 7/26/2010 2010 Sagan Summer Workshop Mark Giampapa Gray & Nagel (1989) 7/26/2010 2010 Sagan Summer Workshop Gray, Carney & Yong (2008) Summary: Granulaon • The tops of convecon cells produce the patchwork known as granulaon on the Sun and late‐type stars. Granulaon in giant stars appears to be characterized by larger spaal scales than in dwarfs, i.e., larger convecve elements. • Line bisectors reveal the asymmetries in line profiles as a result of convecon and the ensuing granulaon paern. Bisectors in solar‐ type stars have a characterisc “C‐shape” with a blueward amplitude due to the velocity‐brightness correlaon of granulaon. • Bisector amplitudes decrease toward later dwarf spectral types. • In bright giants the largest upward velocies due to the convecve granulaon paern occur near the line cores; the blue‐most point moves out into the wings toward subgiants and dwarfs. Mark Giampapa 7/26/2010 2010 Sagan Summer Workshop Granulaon (cont’d.) • Short and long‐term variability in bisector amplitudes have been observed in stars and the Sun‐as‐a‐star. The variaons may or may not be periodic. • In the Sun, average photospheric bisector amplitudes are an‐ correlated with the solar cycle, i.e., lower amplitudes at solar maximum and higher amplitudes at solar minimum. • A “granulaon boundary” exists in the H‐R diagram where on the “hot” side the late‐type stars exhibit an inverse C‐shape while on the “cool” side the normal C‐shape is observed. However, red giant branch and red horizontal branch giants cooler than 4100 K show an inverse C‐shape. The origin of the inverse C‐shape is not known. • In red giant branch stars, small variaons in radial velocity at the 500 – 150 m/sec level are seen in objects that have either regular or inverse C‐shapes. This is thought to be a manifestaon of upward moving and downward flowing large convecon cells. Mark Giampapa 7/26/2010 2010 Sagan Summer Workshop Spots • Most prominent manifestaon of magnec acvity on the Sun • Modulates the luminous output in the Sun and late‐type stars as seen in photometric bands • Direct detecon in molecular lines • Can produce spectral line distorons • Can affect interpretaon of astrometric and transit measurements Mark Giampapa 7/26/2010 2010 Sagan Summer Workshop Modulates the irradiance of the Sun and the brightness of late‐type stars in photometric bands 7/26/2010 Spot color signatures Mark Giampapa 7/26/2010 2010 Sagan Summer Workshop Astrometric signature of spots • Star spots can shi photocenter of the star by 0.1% ‐ 0.2% • Earth‐Sun astrometric amplitude at 10 pc is 0.3 μas or 0.03% of the stellar diameter • Spots can shi photocenter 3 – 6 mes the size of the astrometric signature Mark Giampapa 7/26/2010 2010 Sagan Summer Workshop Zeeman‐Doppler Imaging • Doppler Imaging • Zeeman‐Doppler Imaging Atomic lines Molecular lines Observaonal evidence for (P. Pet) magnec fields across the HR diagram, IAUS 259, Nov 5, 2008, Tenerife Berdyugina Mark Giampapa 2010 Sagan Summer Workshop Observaonal evidence for magnec fields across the HR Mark Giampapa diagram, IAUS 259, Nov 5, 2008, 7/26/2010 2010 Sagan Summer Workshop Tenerife Berdyugina Spot modulaon of stellar light curves Hyades member VB 73 (G1 V)—from Radick et al. (1995) Mark Giampapa 7/26/2010 2010 Sagan Summer Workshop 0.15 IC 2391 0.1 Pleiades 0.05 IC 2602 NGC 3532 Hyades Sun 0 Data sources: Messina et al. 0 1000 2000 3000 4000 5000 (2001); Radick et al. (1995); Saar, AGE (Myr) Barnes & Meibom (2010—NGC 3532—private communicaon) -0.5 -1 IC 2391 Pleiades IC 2602 -1.5 NGC 3532 -2 Hyades -2.5 Sun -3 Data sources: Messina et al. 0 1 2 3 4 (2001); Radick et al. (1995); Saar, 7/26/2010 LOG (AGE) (Myr) Barnes & Meibom (2010—NGC 3532—private communicaon) -0.5 -1 IC 2391 Pleiades IC 2602 -1.5 NGC 3532 -2 Hyades -2.5 Sun -3 7/26/2010 0 1 2 3 4 LOG (AGE) (Myr) 0 IC 2391 Pleiades 0.5 IC 2602 NGC 3532 Hyades 1 Sun 1.5 Data sources: Messina et al. 0 1 2 3 4 (2001); Radick et al. (1995); Saar, LOG (AGE) (Myr) Barnes & Meibom (2010—NGC 3532—private communicaon) -0.5 0 -1 IC 2391 Pleiades IC 2391 Pleiades IC 2602 0.5 -1.5 IC 2602 NGC 3532 NGC 3532 -2 Hyades Hyades 1 -2.5 Sun Sun -3 1.5 0 1 2 3 4 0 1 2 3 4 LOG (AGE) (Myr) LOG (AGE) (Myr) Data sources: Messina et al. Mark Giampapa (2001); Radick et al. (1995); Saar, 7/26/2010 2010 Sagan Summer Workshop Barnes & Meibom (2010—NGC 3532—private communicaon) Messina et al. (2001) Fekel & Henry (1998) Mark Giampapa 7/26/2010 2010 Sagan Summer Workshop Summary: Spots • Sunspots and starspots are characterized by lower temperatures and stronger magnec fields than their surrounding respecve photospheres. Spots can produce distorons in line profiles, unique spectral line features, polarimetric signals, and color signatures. Spots also can contribute “astrometric noise.” • Irradiance and brightness variaons in the Sun and stars are due to spaal inhomogeneies defined by magnec structures combined with the large thermal inera of the outer convecon zone.
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