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What are Faculae?

What are Faculae?. Tom Berger, Alan Title, Ted Tarbell Lockheed Martin Solar and Astrophysics Lab Luc Rouppe van der Voort Institute for Theoretical Astrophysics, Oslo Norway Mats L ö fdahl, G ö ran Scharmer Institute for Solar Physics, Royal Swedish Academy of Sciences. Introduction.

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What are Faculae?

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  1. What are Faculae? Tom Berger, Alan Title, Ted Tarbell Lockheed Martin Solar and Astrophysics Lab Luc Rouppe van der Voort Institute for Theoretical Astrophysics, Oslo Norway Mats Löfdahl, Göran Scharmer Institute for Solar Physics, Royal Swedish Academy of Sciences

  2. Introduction • Why study faculae? 90% (or 100%?) of the variation of total solar irradiance is accounted for by the “competition” between dark sunspots and bright facular and network areas. Sunspot contrast is independent of disk position but facular contrast depends sensitively on disk position and wavelength: faculae are brightest near the limb and (sometimes) dark at disk center. Accurate knowledge of the center-to-limb variation (CLV) of facular contrast is a key input to solar irradiance models. • What do we know about faculae to date? They are associated with magnetic fields and have been theorized (and modeled) to be the hot walls of thin flux tubes in the photosphere. Measurements of facular contrast CLV as a function of magnetic flux density have not been conclusive – spatial resolution has been a challenge.

  3. Swedish 1-meter Solar Telescope: 2002

  4. SST G-band AR 10377 06-June-2003 m = 0.6 q= 53° Tickmarks = 1 Mm

  5. SST 630.25nm AR 10377 06-June-2003 m = 0.6 q= 53° Tickmarks = 1 Mm

  6. SST G-band AR 10377 06-June-2003 m = 0.6 q =53° 0.81Rs 0.80Rs 0.79Rs 0.78Rs

  7. 2 1 5 4 3

  8. Cut 1 Cut 2 Cut 4 Cut 3

  9. Cut 5

  10. Facular brightening ~ 400 km

  11. Topka et al., ApJ 1997 Previous Analysis: Image Contrast vs. Magnetic Flux Density

  12. 430.5 nm G-band Facular Contrast vs. Magnetic Flux Density

  13. 436.4 nm continuum Facular Contrast vs. Magnetic Flux Density

  14. Facular Contrast vs. Line-of-sight Angle

  15. 16-June-2003 G-band faculae: = 0.65 q = 49º

  16. 16-June-2003 G-band faculae:  = 0.65 q = 49º

  17. 16-June-2003 G-band faculae:  = 0.65 q = 49º

  18. 3D compressible MHD models • Carlsson, Stein, et al., ApJL 2004 July • Keller, Schussler, et al., ApJL 2004 May

  19. From Keller, Schussler, et al., ApJL 2004 May

  20. Conclusions • Facular contrast as a function of magnetic flux density is constant down to 200 G levels. Previous measurements had insufficient spatial resolution and binned on magnetogram signal thus blending micropores with the bright faculae. • Magnetic element contrast is a strong function of flux density: magnetic elements are dark below ~900 G. Beck, Schmidt, et al., A&A 2005. • Faculae are not magnetic elementbright-points seen near the limb – they arenot the hot walls of “flux tubes” Faculae are granules seen through the magnetic field. • This explains why faculae appear so much “deeper” than flux tube hot walls and are much wider than any magnetic element bright points seen near disk center. • Richard Muller was right after all to call them “facular granules” way back in 1982.

  21. Solar-B Contributions • Continual observations of uniform quality allows • Statistical studies of center-to-limb facular irradiance function. • “Irradiance” history of active regions from emergence to decay. • Joint observations of facular dynamics with bolometric instruments in space (e.g. EVE on SDO) • Duration of mission from solar minimum to solar maximum allows • Accurate study of the phase of irradiance cycle relative to sunspot cycle. • Settlement of the irradiance vs. luminosity argument – are there other contributions to TSI besides sunspots and faculae/network fields?

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