Travis Metcalfe (SSI) Magnetic Activity Cycles and the Solar-Stellar Connection

Population as context Böhm-Vitense (2007)

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)

Stellar activity cycles Mount Wilson survey found magnetic activity cycles in many stars Mean activity level and cycle period scale with Rossby number (P rot /  c ) Survey ended in 2000’s after more than 30 years of Ca HK observations Baliunas et al. (1995)

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)

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)

Scaling for other stars Metcalfe et al. (2007) Parameterize shifts with  ~ A 0 (R / M) Q j (D c ) and fit the MDI p-mode data A 0 ~ activity level, while the depth of the source D c ~ H p ~ L 1/4 R 3/2 / M Normalizing shifts by this parametrization removes most of the dependencies

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)

Predictions for Kepler Metcalfe et al. (2007) Chaplin et al. (2007) Karoff, Metcalfe, Chaplin et al. (2009)

Garcia et al. (2010) Salabert et al. (2011) Solar pattern of frequency and amplitude changes observed in HD 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

Short cycles with Kepler Mathur et al. (in preparation)

Southern HK project Metcalfe et al. (2009, arXiv: ) 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

HD (  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)

 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)

Ca HK observations Metcalfe et al. (2013)

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)

 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)

Short cycle grand minimum? Metcalfe et al. (2013)

Activity sequences revisited Böhm-Vitense (2007)  Eri

Rotational history Bouvier (2008)

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 (collaborations welcome). More good news: Las Cumbres Observatory Global Telescope (LCOGT) network will have medium-res spectrographs with Ca HK in 2015.