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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
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.
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)
Gravitational quadrupole moment variation
in a magnetically active star
Fg
Q = Q0
Q = Q1> Q0
F’g > Fg
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
Q > 0 
P < 0
non-linear dynamo models.
Q < 0

P > 0
Observations and modelling of
active stellar atmospheres
LINE-DEPTH RATIOS (LDRs) AS TEMPERATURE DIAGNOSTICS
(Gray & Johanson 1991; Catalano, Biazzo, Frasca, Marilli 2002; Biazzo, Frasca, Catalano, Marilli 2007)
Fc  Fλ , ratio LDR  d1
d2
Fc
Very sensitive to Teff : σ(Teff ) ≤10K!
Line depth
d
0.01
1) different spectrograph resolutions
2) different gravities
3) different rotational velocities
4) different metallicities (in progress…)
 10 K
4800 K
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.)

1)
 LDR-Teff calibrations obtained at:
dT
dLDRGIA
SPOT/PLAGE MODELLING
dV=0.65 mag
d<Teff>=127 K
dEWHalpha=2.69 Å
dEWHe=0.10 Å
Spot model
Grids
of light-curve
(dots) and temperature-curve
Very
active
star
(diamonds) solutions as a function of Tsp/Tph
 Spherical limb-darkened stars
(Tsp, Arel)
 Flux ratio Fsp/Fph
 Black-body energy distribution

ATLAS9 synthetic spectra (Kurucz 1993)
PHOENIX NextGen synthetic spectra
(Hauschildt et al. 1999a, 1999b)
Biazzo, Frasca, Henry, Catalano, Marilli 2007

Interactive simultaneous solutions (chi2 minimization)
of both temperature and light curves

Plage model
 Two circular plages
 Flux ratio Fplage/Fchrom
 Interactive solutions of the Halpha curve
d(dy)=0.04 mag
d<Teff>=39 K
dEWHalpha=0.033 Å
dEWHe=0.030 Å
Frasca, Biazzo, Taş, Evren, Lanzafame 2007
Frasca, Biazzo, Catalano, Marilli, Messina, Rodonò 2005

Two circular
Moderately
activedark
star spots with the same Tsp
Semiempirical NLTE modelling of the chromosphere
of the active component of HR 1099
Activity indicators: R_irt and EQW_res
R_IRT
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.
EQW_res vs. RHK
A H-alpha lighthouse on II Peg
(Lanzafame et al., in progress)
Observations and modelling of
outer atmospheres
• Plasma dynamics in the transition region as
revealed by line Doppler shifts and nonthermal broadening helps to constrain models
of coronal structure and heating (e.g.,
Spadaro, Lanza, Karpen & Antiochos, 2006);
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)
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, A&A submitted).
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);
Spot modelling
For stars having a vsini < 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.
(Lanza, Rodonò, Pagano 2004, A&A 425, 707)
Model ME distributions vs. observed sunspot
distributions at different epochs along solar cycle 23:
group
area
The area ratio between facular and spotted area is fixed at Q = 9 (see Lanza et al. 2007, A&A 464, 741)
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, flipflop phenomena, activity cycles, surface differential rotation, …
 Evolution of the connection between rotational properties and magnetic
activity: dynamos, star-disk locking, magnetic braking, ….
NGC 2099 (M37) [500 Myr]
Rotation period (d)
(Messina et al., in progress)
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.
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.
Thank you for your attention
Additional material
Orbital period modulation in
late-type close binaries
RS CVn
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.
SDR from ME models for Eps Eri
(Preliminary results with Ppole fixed, i=30o)
(Lanza et al., in progress)