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 (Prot / 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 ~ 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

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 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

Short cycles with Kepler

Mathur et al. (in preparation)

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

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)

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 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.