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Transcript
Dynamite Diameters Observations of main sequence stars with long baseline optical/infrared interferometry Tabetha Boyajian (Georgia State University / CHARA) Hubble Fellow Symposium March 8-11, 2010 3 Big Picture: Empirically determined H-R diagram from interferometric measurements Spica An interferometer measure the angular diameter (θ) of a star. (yields the effective temperature and L with distance and flux) Important issues at hand: Calibration of temperature scales established through less direct methods Discrepancies between theory and observations Hyades Giants Regulus Vega Procyon Altair Sun 4 α Cen A,B 61 Cyg A,B Interferometers today Direct methods to Current and Future Optical / Infrared Interferometers measure stellar sizes: Long baseline optical interferometry Eclipsing binaries Occultation (Planetary and Lunar) Speckle interferometry 5 a) Closed 2006, b) closed 2009, c) under construction The CHARA Array Six 1 meter telescopes with maximum baseline of 330 meters Longest optical interferometer in the world Five beam combiners available (2,3, and 4 telescope modes) Accommodates remote and parallel observing modes 6 7 The First Diameters 1921 Michelson and Pease measure the diameter of Betelgeuse 20-foot interferometer mounted on the 100inch Hooker telescope 1950-1972 Narrabri Stellar Intensity Interferometer 32 diameters of stars measured in the visible Empirical temperature scale for stars hotter than our Sun is based upon this data 8 Code et al. 1976 Progress Total # of stars with angular diameter measurement Stars with σθ < 5% Stars with σθ < 5% and on main-sequence 9 1997 2004 145 458 (~3) 45 242 (~5.5) 6 24 Source: Davis 1997 (4) Source: Richichi et al. 2005 (CHARM2 Catalogue) Census 2009 10 *Measurements outlined in black are from the CHARA Array. Does not include new results presented here on K-M dwarfs. How do direct measurements compare to semi-empirical values? APL99=Allende Prieto and Lambert 1999; GCS07=Holmberg 2007; Tak07=Takeda 2007 11 Boyajian et al. 2009, 2010, in Inconsistencies and their implications Y2 isochrones fit to empirically determined T and L to determine M and age Results agree well will eclipsing binaries If temperature is over-estimated: Gravity (log g) is over-estimated e.g.: if you use spectroscopic log g and interferometric radius to derive a mass, then the star appears too massive Radius is under-estimated Age is under-estimated 12 Boyajian et al. 2009, 2010, in prep Metallicity effects on temperature A0 K0 A0 K0 Effective temperature calibrations Calibrations used for transforming observed colors and metallicity to temperatures Solution finds coefficients to polynomial where θ=5040/T, X is color index and [Fe/H] is metallicity of object (Alonso et al. 1996) Spread in temperatures of different scales is up to 300K At [Fe/H]=-1.5, the empirical scale is ~200K cooler for all stars in other relations compared here 13 EFF a0 a1 X a2 X 2 a3 X[Fe/H] a4 [Fe/H] a5[Fe/H]2 Observations of late-type dwarfs K-M stars with diameters measured to better than 5% 14 Theory versus observation: I Masses for single stars are derived from the K-band mass-luminosity relationship from Delfosse et al. 2000, and assume a 10% error. (TOP) The solid black line is a 5 Gyr isochrone from the BCAH98 models (Baraffe et al. 1998) for Lmix=Hp, the dotted and dashed lines are Lmix=1.5 and 1.9 Hp, respectively. (BOTTOM) dotted line 15 signifies zero deviation between observation and model. Theory versus observation: II López-Morales 2007 More data makes these plots look a little different A new explanation is needed to explain offset in single stars Demory et al. 2009 (Includes Mass<.9 M) Berger et al. 2006 16 Theory versus observation: III ll The KINK and The GAP 17 Interferometry allows us to empirically determine fundamental properties of stars in order to provide the foundation for calibrating the effective temperature scales and testing model atmosphere and evolution calculations For main sequence stars, the temperature is often overestimated while the radius is underestimated compared to observations Thank you for your interference! 18