antonino f. lanza on behalf of the group on active stars and systems inaf- catania astrophysical...
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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.
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
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)
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.
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;
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.
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.