Magnetic activity and rotation in latetype stars

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Magnetic activity and rotation in late-type stars
Antonino F. Lanza on behalf of the Group on
Active Stars and Systems INAF- Catania
Astrophysical Observatory, Italy
Catania, December 17 2007
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Main research fields of our group

• Long-term optical studies (flare activity
  activity cycles, stellar differential rotation,
  orbital period modulation in late-type binary
  systems)
• simultaneous multiwavelength observations (3-D
  structure of stellar atmospheres)
• UV, X-ray and radio studies of selected objects
• Modelling of stellar atmospheres
• Dynamo models for single stars and close binary
  systems.

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Activity cycle, preferential longitudes and
orbital period variation in HR1099
(Frasca Lanza 2005 Lanza, Piluso, Rodonò,
Messina, Cutispoto, 2006 based on data mostly
collected at our observing station on Mt. Etna)
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Gravitational quadrupole moment variation in a
magnetically active star
Fg
Q Q0
Fg gt Fg
Q Q1gt Q0
Oblateness changes can be related to the energy
of the internal magnetic field of the active
component (cf. Lanza 2005, 2006), allowing us to
test non-linear dynamo models.
?Q gt 0 ? ?P lt 0 ?Q lt 0 ? ?P gt
0
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Observations and modelling of active stellar
atmospheres
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LINE-DEPTH RATIOS (LDRs) AS TEMPERATURE
DIAGNOSTICS (Gray Johanson 1991 Catalano,
Biazzo, Frasca, Marilli 2002 Biazzo, Frasca,
Catalano, Marilli 2007)
Line depth
, ratio
Very sensitive to Teff s(Teff) 10K!

• Applications of the LDR method
• Starspot temperatures
• RS CVn SB1 systems (Frasca, Biazzo, Catalano,
  Marilli, Messina, Rodonò 2005)
• main sequence stars (Biazzo, Frasca, Henry,
  Catalano, Marilli 2007)
• very young single stars (Biazzo, Frasca, Marilli,
  Covino, Alcalà, Cakirli, in prep.)
• 2) Teff variation of Cepheid stars (Biazzo,
  Frasca, Henry, Catalano, Marilli 2004)
• 3) Teff of Open Cluster stars (Biazzo, Pasquini,
  Girardi, Frasca, da Silva, Setiawan, Marilli,
  Hatzes, Catalano 2007 Pasquini, Biazzo, et al.,
  in prep.)

• LDR-Teff calibrations obtained at
• different spectrograph resolutions
• different gravities
• different rotational velocities
• different metallicities (in progress)

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SPOT/PLAGE MODELLING
Spot model
Grids of light-curve (dots) and temperature-curve
(diamonds) solutions as a function of Tsp/Tph

• Two circular dark spots with the same Tsp
• Spherical limb-darkened stars
• Flux ratio Fsp/Fph
• Black-body energy distribution
• ATLAS9 synthetic spectra (Kurucz 1993)
• PHOENIX NextGen synthetic spectra (Hauschildt
  et al. 1999a, 1999b)
• Interactive simultaneous solutions (chi2
  minimization) of both temperature and light curves

(Tsp, Arel)
Frasca, Biazzo, Catalano, Marilli, Messina,
Rodonò 2005
Frasca, Biazzo, Tas, Evren, Lanzafame 2007
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Semiempirical NLTE modelling of the chromosphere
of the active component of HR 1099
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Activity indicators R_irt and EQW_res
R_irt CDNLTE-vsini-convolved - CDobs EQW_res
EQWNLTE-core EQWobs-core
(Busà et al. 2007)

• EQW_res and R_irt are pure chromospheric
  diagnostics because they are obtained after a
  proper substraction of the photospheric
  contribution
• GAIA will allow us to obtain those diagnostics
  for a sample of several million stars opening the
  possibility of extended statistical studies on
  chromospheric activity.

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EQW_res vs. RHK
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A H-alpha lighthouse on II Peg
(Lanzafame et al., in progress)
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Observations and modelling of outer atmospheres

• Plasma dynamics in the transition region as
  revealed by line Doppler shifts and non-thermal
  broadening helps to constrain models of coronal
  structure and heating (e.g., Spadaro, Lanza,
  Karpen Antiochos, 2006)

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TR velocity fields from line redshifts
Alpha Centauri A (Pagano et al. 2004)
Some examples of solar-like and non-solar-like
behaviour
AU Microscopi (Pagano et al. 2000 Redfield et
al. 2002)
Csi Bootis (Pagano et al. 2006)
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Partecipation to CoRoT

• Microvariability simulations to compare different
  techniques of planetary transit detection (Moutou
  et al. 2005, Lanza et al. 2006)
• Methods for analysis of optical wide-band light
  curves to measure
• rotation period
• surface distribution of active regions
• surface differential rotation (Lanza, Rodonò,
  Pagano 2004 Lanza, Bonomo, Rodonò 2007)
• Filtering stellar microvariability for planetary
  transit detection (Bonomo Lanza 2007, AA
  submitted).

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Modelling the Sun-as-a-star irradiance variations

• A testbed for methods to analyse CoRoT time
  series
• Accuracy of VIRGO/SoHo TSI hourly measurements
  about 20 ppm
• Time extension of VIRGO series 11 years (solar
  cycle 23)

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Spot modelling
For stars having a vsini lt 20-25 km/s Doppler
imaging techniques cannot be applied to map their
surface We have developed techniques of spot
modelling for TSI that can be applied to CoRoT
data.
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(Lanza, Rodonò, Pagano 2004, AA 425, 707)
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Model ME distributions vs. observed sunspot group
area distributions at different epochs along
solar cycle 23
The area ratio between facular and spotted area
is fixed at Q 9 (see Lanza et al. 2007, AA
464, 741)
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RACE-OC project Rotation and ACtivity Evolution
in Open Clusters

• Objectives
• Evolution of angular momentum of late-type (G-M)
  stars from the study of members of open clusters
  of different age and initial chemical composition

• Evolution of properties of magnetic activity
  manifestations starspot temperature and area,
  longitude distribution, permanent active
  longitudes, flip-flop phenomena, activity cycles,
  surface differential rotation,
• Evolution of the connection between rotational
  properties and magnetic activity dynamos,
  star-disk locking, magnetic braking, .

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NGC 2099 (M37) 500 Myr
Rotation period (d)
(Messina et al., in progress)
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Angular momentum evolution in solar-like stars
theory

• Lanza (2006, 2007) developed models for the
  torsional oscillations in the Sun and solar-like
  stars, linking the angular velocity variation to
  the geometry and intensity of internal magnetic
  fields
• We are applying those modelling tools to study
  angular momentum evolution in late-type stars.

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Future perspectives

• Stellar activity and solar-stellar connection
  with CoRoT light curves
• Magnetic activity in stars with planets
• new modelling approaches to reduce its impact for
  planet detection and characterization
• star-planet magnetic interaction
• Angular momentum evolution in single late-type
  stars and close binary systems
• Long-term studies to understand stellar dynamo
  action
• Active region properties vs. stellar parameters
  across the H-R diagram
• Multiwavelength studies to understand
  non-radiative heating of stellar atmospheres in
  late-type stars
• Partecipation to the ESA cornerstone mission
  GAIA
• Partecipation to the future ESA mission PLATO.

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Thank you for your attention
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Additional material
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Orbital period modulation in late-type close
binaries
RS CVn
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Testing spot modelling techniques with solar data

• In the case of the Sun, we can apply spot models
  to TSI data and check whether the models
  reproduce the observed sunspot group
  configurations
• Since latitude information in the rotational
  modulation of the TSI is very small (i 90o),
  only total area variations and longitude
  distributions of active regions can be compared.

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SDR from ME models for Eps Eri
(Preliminary results with Ppole fixed, i30o)
(Lanza et al., in progress)