Download Magnetic Activity Cycles and the Solar

Magnetic Activity Cycles and the
Solar-Stellar Connection
Travis Metcalfe (SSI)
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
Frohlich & Lean (2004)
• Use disk-integrated time
series measurements to
track magnetic cycles
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)
Frequency shifts
Salabert et al. (2004)
• 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
Libbrecht & Woodard (1990)
Theoretical interpretation
• Magnetic perturbations
modify the near-surface
propagation speed
Goldreich et al. (1991)
Dziembowski & Goode (2005)
• Also leads to decreased
convective velocity and
change in temperature
• Distinct behavior for solar
f-modes and p-modes
confirms these sources
Scaling for other stars
• 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
Metcalfe et al. (2007)
HD 2151 ( Hydri)
Metcalfe et al. (2007)
• Reanalysis of archival
IUE data, including more
recent observations
• Asteroseismic data from
2000 (just past maximum)
and 2005 (near minimum)
MODEL
OBSERVATIONS
• Mean shift: 0.1 ± 0.4
Hz, individual n=18
frequency shift: 0.17 ±
0.62 Hz
Predictions for Kepler
Chaplin et al. (2007)
Metcalfe et al. (2007)
Karoff, Metcalfe, Chaplin et al. (2009)
CoRoT: HD 49933
Garcia et al. (2010)
• Solar pattern of frequency
and amplitude changes
observed in HD 49933
• Frequency dependence
of shifts also similar to
(but larger than) solar
Salabert et al. (2011)
• Larger shifts for an F star
supports Dziembowski
scaling for other stars
Short cycles with Kepler
Mathur et al. (in preparation)
Southern HK project
• 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
Metcalfe et al. (2009, arXiv:0909.5464)
HD 17051 ( Hor)
• Shortest measured stellar
activity cycle in a solartype 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
Sanz Forcada
et al. (2013)
Metcalfe
et al. (2010)
 Eri: exoplanet host
• Jovian-mass exoplanet in
~7 year orbit from radial
velocity observations
Hatzes et al. (2000)
• Magnetic activity ruled
out as the source of RV
signal using Ca HK data
• Exoplanet confirmed from
astrometric orbit with HST
fine guidance sensors
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
 Eri
Böhm-Vitense (2007)
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.