S. V. Berdyugina

Evolution and rotation of large-scale photospheric magnetic fields of the sun during cycles 21-23 : Periodicities, north-south asymmetries and r-mode signatures

We present the results of an extensive time series analysis of longitudinally-averaged synoptic maps, recorded at the National Solar Observatory (NSO/Kitt Peak) from 1975 to 2003, and provide evidence for a multitude of quasi-periodic oscillations in the photospheric magnetic field of the Sun. In the low frequency range, we have located the sources of the 3.6 yr, 1.8 yr, and 1.5 yr periodicities that were previously detected in the north-south asymmetry of the unsigned photospheric flux (Knaack et al. 2004, A&A, 418, L17). In addition, quasi-periodicities around 2.6 yr and 1.3 yr have been found. The 1.3 yr period is most likely related to large-scale magnetic surges toward the poles and appeared in both hemispheres at intermediate latitudes ∼30°-55° during the maxima of all three cycles 21-23, being particularly pronounced during cycle 22. Periods near 1.3 yr have recently been reported in the rotation rate at the base of the convection zone (Howe et al. 2000, Science, 287, 2456), in the interplanetary magnetic field and geomagnetic activity (Lockwood 2001, J. Geophys. Res., 106, 16021) and in sunspot data (Krivova & Solanki 2002, A&A, 394, 701). In the intermediate frequency range, we have found a series of quasi-periodicities of 349-307 d, 282 ± 4 d, 249-232 d, 222-209 d, 177 ± 2 d, 158-151 d, 129-124 d and 103-100 d, which are in good agreement with period estimates for Rossby-type waves and occurred predominantly in the southern hemisphere. We provide evidence that the best known of these periodicities, the Rieger period around 155 d, appeared in the magnetic flux not only during cycle 21 but also during cycle 22, likely even during cycle 23. The high frequency range, which covers the solar rotation periods, shows a dominant (synodic) 28.1 ± 0.1 d periodicity in the southern hemisphere during cycles 21 and 22. A periodicity around 25.0-25.5 d occurred in the south during all three cycles. The large-scale magnetic field of the northern hemisphere showed dominant rotation periods at 26.9 ± 0.1 d during cycle 21, at 28.3-29.0 d during cycle 22 and at 26.4 ± 0.1 d during cycle 23.

Periodic oscillations in the north-south asymmetry of the solar magnetic field

. We report on significant periodic variations of the magnetic activity between the north and south hemisphere of the Sun. For this purpose, we have investigated the north-south asymmetry of two solar data sets, namely the Kitt Peak synoptic Carrington rotation maps of the photospheric magnetic field (1975-2003) and monthly averaged sunspot areas (1874-2003). Using Fourier and wavelet analysis, we have found a regular pattern of pronounced oscillations with periods of 1.50 ± 0.04 yr, 1.79 ± 0.06 yr and 3.6 ± 0.3 yr in the magnetic flux asymmetry. The former two periods are related to a process which leads to a gradual shift in the excess magnetic flux from north to south or vice versa. Additional periods of 43.4 ± 7.1 yr (twice the magnetic cycle) and 320-329 days were detected in the sunspot asymmetry.

G-band spectral synthesis and diagnostics of simulated solar magneto-convection

Realistic simulations of radiative magneto-convection in the solar (sub)photosphere are used for a spectral synthesis of Fraunhofers G band, which is dominated by spectral lines from the CH molecule. It is found that the spatial pattern of integrated G-band brightness closely matches the spatial structure of magnetic flux concentrations in the convective downflow regions. The brightness contrast is mainly caused by the weakening of CH lines due to the reduced CH abundance and the resulting shift of the optical depth scale in the hot and tenuous magnetic flux concentrations. Various properties of the synthetic brightness images agree well with G-band observations. These results lends credit to the observational usage of G-band bright features as proxies for magnetic flux concentrations in the solar photosphere. However, the converse is only correct in a limited sense: only a fraction of the magnetic flux concentrations turn out to be bright in the G band.

POLARIZED REFLECTED LIGHT FROM THE EXOPLANET HD189733b: FIRST MULTICOLOR OBSERVATIONS AND CONFIRMATION OF DETECTION

We report the first multicolor polarimetric measurements (UBV bands) for the hot Jupiter HD189733b and confirm our previously reported detection of polarization in the B band. The wavelength dependence of polarization indicates the dominance of Rayleigh scattering with a peak in the blue B and U bands of ~10–4 ± 10–5 and at least a factor of two lower signal in the V band. The Rayleigh-like wavelength dependence, also detected in the transmitted light during transits, implies a rapid decrease of the polarization signal toward longer wavelengths. Therefore, the nondetection by Wiktorowicz, based on a measurement integrated within a broad passband covering the V band and partly covering the B and R bands, is inconclusive and consistent with our detection in B. We discuss possible sources of the polarization and demonstrate that effects of incomplete cancellation of stellar limb polarization due to starspots or tidal perturbations are negligible as compared with scattering polarization in the planetary atmosphere. We compare the observations with a Rayleigh-Lambert model and determine effective radii and geometrical albedos for different wavelengths. We find a close similarity of the wavelength-dependent geometrical albedo with that of the Neptune atmosphere, which is known to be strongly influenced by Rayleigh and Raman scattering. Our result establishes polarimetry as a reliable means for directly studying exoplanetary atmospheres.

The molecular Zeeman effect and diagnostics of solar and stellar magnetic fields - II. Synthetic Stokes profiles in the Zeeman regime

Recent advances in the computation of the Zeeman splitting of molecular lines have paved the way for their use as diagnostics of solar and stellar magnetic fields. A systematic study of their diagnostic capabilities had not been carried out so far, however. Here we investigate how molecular lines can be used to deduce the magnetic and thermal structure of sunspots, starspots and cool stars. First, we briefly describe the Stokes radiative transfer of Zeeman-split molecular lines. Then, we compute Stokes spectra of TiO, OH, CH and FeH lines and investigate their diagnostic capabilities. We also compare the synthetic profiles with observations. Spectra of TiO, OH and FeH are found to be interesting diagnostics of sunspot magnetic fields. This is also true for cool stars, where, however, the OH Stokes V profiles may require very high S/ N data to be reliably employed. Finally we investigate the potential of various molecular bands for high-contrast imaging of the solar surface. The violet CN and CH bands turn out to be most promising for imaging the photosphere, the TiO bands are excellent for imaging sunspot umbrae, while the UV OH band can be used for imaging both the photosphere and sunspots.

First Detection of Polarized Scattered Light from an Exoplanetary Atmosphere

We report the first direct detection of an exoplanet in the visible polarized light. The transiting planet HD 189733b is one of the very hot Jupiters with shortest periods and, thus, smallest orbits, which makes them ideal candidates for polarimetric detections. We obtained polarimetric measurements of HD 189733 in the B band well distributed over the orbital period and detected two polarization maxima near planetary elongations with a peak amplitude of ∼2 # 10 . Assuming Rayleigh scattering, we estimated the effective size of the scattering atmo4 sphere (Lambert sphere) to be 1.5 0.2 , which is 30% larger than the radius of the opaque body previously RJ inferred from transits. If the scattering matter fills the planetary Roche lobe, the lower limit of the geometrical albedo can be estimated as 0.14. The phase dependence of polarization indicates that the planetary orbit is oriented almost in a north-south direction with a longitude of ascending node Q p (16 or 196) 8. We obtain independent estimates of the orbit inclination i p 98 8 and eccentricity e p 0.0 (with an uncertainty of 0.05), which are in excellent agreement with values determined previously from transits and radial velocities. Our findings clearly demonstrate the power of polarimetry and open a new dimension in exploring exoplanetary atmospheres even for systems without transits. Subject headings: planetary systems — stars: individual (HD 189733)techniques: polarimetric Online material: color figures

Thermal-magnetic relation in a sunspot and a map of its Wilson depression

We present relations between thermal and magnetic quantities in a simple, isolated sunspot, as deduced from the inversion of 1.56 µm spectropolarimetric data. We used a combination of two infrared Fe I lines at 15 648.5 A and 15 652.8 A in the inversions. Due to the high Zeeman sensitivity of these lines, we can study this relationship in the entire sunspot. The relevant parameters were derived both as a function of location within the sunspot and of height in the atmosphere using an inversion technique based on response functions. In this paper we relate the magnetic vector with temperature. We find a non- linear relationship between the various components of the magnetic vector and temperature, which confirm the results from earlier investigations. We also computed the Wilson depression and the plasma β for the observed sunspot and compare our results with earlier findings.

The Observation of Sunspot Light-Bridge Structure and Dynamics

We present very high resolution multiwavelength images of a sunspot light bridge in NOAA Active Region 10132 taken at the Swedish 1 m Solar Telescope on La Palma on 2002 September 25. The adaptive optics-corrected images resolve 100 km scale bright grains on either side of an approximately 380 km dark lane in the center of the bridge. Movies of the data show the grains in a steady unidirectional flow with an average speed of 900 m s-1 along the entire length of the bridge. Overturning motions are seen in the larger grains, suggesting a convective origin for these structures. Simultaneous 160 nm ultraviolet images from the Transition Region and Coronal Explorer (TRACE) satellite show a constant brightness enhancement over the light bridge, implying a steady chromospheric heat source. TRACE 160 nm movies do not resolve the unidirectional flow; instead, they suggest that a horizontal oscillatory motion exists in the chromosphere of the light bridge. A C2.0 flare at 16:00 UT, one ribbon of which occurs directly along the light bridge, indicates a high level of magnetic stress and impulsive dissipation associated with the observed light-bridge dynamics.

BUTTERFLY DIAGRAM AND ACTIVITY CYCLES IN HR 1099

We analyze photometric data of the active RS CVn–type star HR 1099 for the years 1975–2006 with an inversion technique and reveal the nature of two activity cycles of 15–16 yr and yr duration. The 16 yr cycle is 5.3 0.1 related to variations of the total spot area and is coupled with the differential rotation, while the 5.3 yr cycle is caused by the symmetric redistribution of the spotted area between the opposite stellar hemispheres (flip-flop cycle). We recover long-lived active regions comprising two active longitudes that migrate in the orbital reference frame with a variable rate because of the differential rotation along with changes in the mean spot latitudes. The migration pattern is periodic with the 16 yr cycle. Combining the longitudinal migration of the active regions with a previously measured differential rotation law, we recover the first stellar butterfly diagram without an assumption about spot shapes. We find that mean latitudes of active regions at opposite longitudes change antisymmetrically in the course of the 16 yr cycle: while one active region migrates to the pole, the other approaches the equator. This suggests a precession of the global magnetic field with respect to the stellar rotational axis. Subject headings: binaries: spectroscopic — stars: activity — stars: individual (HR 1099) — stars: rotation — stars: spots — techniques: photometric

The molecular Zeeman effect and diagnostics of solar and stellar magnetic fields. III. Theoretical spectral patterns in the Paschen-Back regime

An overview of the theory of the Zeeman eect in diatomic molecules for the limiting Hunds cases (a) and (b) is given and a numerical approach for the intermediate coupling case (a{b) is developed. In contrast to earlier derivations, which were limited to doublets, this approach is valid for terms of any multiplicity. General properties of the Zeeman eect for the various cases are deduced. Finally, calculated Land e factors for prominent molecular bands in sunspot and cool-star spectra are employed to predict the general behaviour of these bands in the presence of a magnetic eld below the Paschen-Back limit. The limiting eld strength is calculated and listed.