Antonino F. Lanza on behalf of the Group on

Active Stars and Systems

INAF- Catania Astrophysical Observatory, Italy

Magnetic activity and rotation in late-type stars

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)

Q = Q0

Q = Q1> Q0

Q > 0 P < 0

Q < 0 P > 0

Fg

F’g > Fg

Gravitational quadrupole moment variation in a magnetically active star

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.

Observations and modelling of active stellar

atmospheres

LLINE-INE-DDEPTH EPTH RRATIOS (LDRs) AS ATIOS (LDRs) AS TTEMPERATURE EMPERATURE

DDIAGNOSTICSIAGNOSTICS(Gray & Johanson 1991; Catalano, Biazzo, Frasca, Marilli 2002; Biazzo, Frasca, Catalano, Marilli 2007)

c

λc

F

FFd

2

1

d

dLDR Line depth

Applications of the LDR method:1) 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:

1) different spectrograph resolutions

2) different gravities

3) different rotational velocities

4) different metallicities (in progress…)

, ratio

Very sensitive to Teff : σ(Teff) ≤10K!

K10d

d0.01

K4800GIA

LDR

T

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

Spot model

Plage model Two circular plages

Flux ratio Fplage/Fchrom

Interactive solutions of the Halpha curve

SSPOT/POT/PPLAGE LAGE MMODELLINGODELLING

(Tsp, Arel)

Frasca

, Bia

zzo, C

ata

lano, M

arilli, M

essin

a, R

od

onò 2

00

5

Frasca, Biazzo, Taş, Evren, Lanzafame 2007

Grids of light-curve (dots) and temperature-curve (diamonds) solutions as a function of Tsp/Tph

d(dy)=0.04 mag

d<Teff>=39 K

dEWHalpha=0.033 Å

dEWHe=0.030 Å

Bia

zzo,

Fra

sca,

Henry

, C

ata

lano,

Mari

lli 2

00

7

Moderately active star

dV=0.65 magd<Teff>=127 K

dEWHalpha=2.69 Å

dEWHe=0.10 Å

Very active star

Semiempirical NLTE modelling of the chromosphere of the active component of HR

1099

Activity indicators: R_irt and EQW_res

• 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.

R_IRT

R_irt = CDR_irt = CDNLTE-vsini-convolved NLTE-vsini-convolved - CD- CDobsobs

EQW_resEQW_res =EQWEQWNLTE-core NLTE-core – EQW– EQWobs-coreobs-core

(Busà et al. 2007)

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 non-thermal broadening helps to constrain models of coronal structure and heating (e.g., Spadaro, Lanza, Karpen & Antiochos, 2006);

TR velocity fields from line redshifts

Some examples of solar-like and non-solar-like behaviour

Alpha Centauri A (Pagano et al. 2004)

Csi Bootis (Pagano et al. 2006)

AU Microscopi (Pagano et al. 2000; Redfield et al. 2002)

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 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, A&A 464, 741)

RACE-OC project: Rotation and ACtivity Evolution in Open

Clusters

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, ….

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;

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)