Magnetic activity and rotation in late-type stars. Antonino F. Lanza on behalf of the G roup on A ctive S tars and S ystems INAF- Catania Astrophysical Observatory, Italy. Catania, December 17 2007. Main research fields of our group.
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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 F’g > Fg Q = Q1>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 > 0 P < 0 Q < 0 P > 0
LINE-DEPTH RATIOS (LDRs) AS TEMPERATURE DIAGNOSTICS (Gray & Johanson 1991; Catalano, Biazzo, Frasca, Marilli 2002; Biazzo, Frasca, Catalano, Marilli 2007) , ratio Line depth Very sensitive to Teff : σ(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: • differentspectrograph resolutions • differentgravities • differentrotational velocities • differentmetallicities (in progress…)
SPOT/PLAGE MODELLING d(dy)=0.04 mag d<Teff>=39 K dEWHalpha=0.033 Å dEWHe=0.030 Å Very active star dV=0.65 mag d<Teff>=127 K dEWHalpha=2.69 Å dEWHe=0.10 Å Moderately active star Biazzo, Frasca, Henry, Catalano, Marilli 2007 Plage model • Two circular plages • Flux ratio Fplage/Fchrom • Interactive solutions of the Halpha curve 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, Taş, Evren, Lanzafame 2007
Semiempirical NLTE modelling of the chromosphere of the active component of HR 1099
R_IRT 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.
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 lineredshifts 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.
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 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, ….
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.
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)