travis metcalfe (ssi)
DESCRIPTION
Magnetic Activity Cycles and the Solar-Stellar Connection. Travis Metcalfe (SSI). Population as context. B ö hm-Vitense (2007). Magnetic regions on the Sun are bright in Mg II (UV) and Ca II (optical) Measure ratio of total emission in line cores to flux in the wings - PowerPoint PPT PresentationTRANSCRIPT
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Travis Metcalfe (SSI)
Magnetic Activity Cycles and the Solar-Stellar Connection
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Population as context
Böhm-Vitense (2007)
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Solar activity
• Magnetic regions on the Sun are bright in Mg II (UV) and Ca II (optical)
• Measure ratio of total emission in line cores to flux in the wings
• Use disk-integrated time series measurements to track magnetic cycles
Frohlich & Lean (2004)
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Stellar activity cycles
• Mount Wilson survey found magnetic activity cycles in many stars
• Mean activity level and cycle period scale with Rossby number (Prot / c )
• Survey ended in 2000’s after more than 30 years of Ca HK observations
Baliunas et al. (1995)
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• Solar p-mode shifts first detected in 1990, depend on frequency and degree
• Even the lowest degree solar p-modes are shifted by the magnetic cycle
• Unique constraints on the mechanism could come from asteroseismology
Frequency shifts
Libbrecht & Woodard (1990)
Salabert et al. (2004)
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• Magnetic perturbations modify the near-surface propagation speed
• Also leads to decreased convective velocity and change in temperature
• Distinct behavior for solar f-modes and p-modes confirms these sources
Theoretical interpretation
Goldreich et al. (1991)
Dziembowski & Goode (2005)
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Scaling for other stars
Metcalfe et al. (2007)
• Parameterize shifts with ~ A0 (R / M) Qj(Dc) and fit the MDI p-mode data
• A0 ~ activity level, while the depth of the source Dc ~ Hp ~ L1/4 R3/2 / M
• Normalizing shifts by this parametrization removes most of the dependencies
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HD 2151 ( Hydri)
MODEL
OBSERVATIONS
• Reanalysis of archival IUE data, including more recent observations
• Asteroseismic data from 2000 (just past maximum) and 2005 (near minimum)
• Mean shift: 0.1 ± 0.4 Hz, individual n=18 frequency shift: 0.17 ± 0.62 Hz
Metcalfe et al. (2007)
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Predictions for Kepler
Metcalfe et al. (2007)
Chaplin et al. (2007)
Karoff, Metcalfe, Chaplin et al. (2009)
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Garcia et al. (2010)
Salabert et al. (2011)
• Solar pattern of frequency and amplitude changes observed in HD 49933
• Frequency dependence of shifts also similar to (but larger than) solar
• Larger shifts for an F star supports Dziembowski scaling for other stars
CoRoT: HD 49933
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Short cycles with Kepler
Mathur et al. (in preparation)
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Southern HK project
Metcalfe et al. (2009, arXiv:0909.5464)
• Small telescopes at CTIO run by SMARTS partners: Yale, GSU, STScI, et al.
• Service observing 2-3x per month using RC Spec with R ~ 2500 at Ca HK
• Monitor bright southern asteroseismic targets for stellar activity variations
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HD 17051 ( Hor)
• Shortest measured stellar activity cycle in a solar-type star: 1.6 years
• Sampling permits some indication of the rotation rate: ~3x solar (8.5 days)
• Coronal activity cycle found from XMM x-ray measurements
Metcalfe et al. (2010)Sanz Forcada et al. (2013)
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Eri: exoplanet host
• Jovian-mass exoplanet in ~7 year orbit from radial velocity observations
• Magnetic activity ruled out as the source of RV signal using Ca HK data
• Exoplanet confirmed from astrometric orbit with HST fine guidance sensors
Hatzes et al. (2000)
Benedict et al. (2006)
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Ca HK observations
Metcalfe et al. (2013)
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Interacting dynamos?
• Helioseismic signature of the 11-year activity cycle shows shorter variations
• Residuals reveal ~2 year signal with high amplitude during 11-year maxima
• Second solar dynamo in near surface shear layer, pumped up by rising flux?
Fletcher et al. (2010)
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Eri: dual magnetic cycles
• Recent data since 1994 show coherent cycle with short period ~3 years
• Archival data from Mount Wilson also reveal long period cycle ~13 years
• Artificial data with two periods: remaining peaks are artifacts of sampling
Metcalfe et al. (2013)
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Short cycle grand minimum?
Metcalfe et al. (2013)
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Activity sequences revisited
Böhm-Vitense (2007)
Eri
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Rotational history
Bouvier (2008)
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Future prospects
• Bad news: the SMARTS low-res spectrograph was decommissioned last month, bringing the southern HK project to an unexpected end.
• Good news: an archive of the time-series Ca HK measurements since 2007 is publicly available at http://solar-stellar.org (collaborations welcome).
• More good news: Las Cumbres Observatory Global Telescope (LCOGT) network will have medium-res spectrographs with Ca HK in 2015.