Magnetic clouds are thought to be large flux ropes propagating through the heliosphere. Their twisted magnetic fields are mostly modeled by a constant-alpha force-free field in a circular cylindrical flux rope (the Lundquist solution). However, the interplanetary flux ropes are three dimensional objects. In reality they possibly have a curved shape and an oblate cross section. Recently we have found two force-free models of flux ropes which takes into account the mentioned features. These are (i) a constant-alpha force-free configuration in an elliptic flux rope (Vandas & Romashets 2003, A&A, 398, 801), and (ii) a non-constant-alpha force-free field in a toroid with arbitrary aspect ratio (Romashets & Vandas 2003, AIP Conf Ser. 679, 180). Two magnetic cloud observations were analyzed. The magnetic cloud of October 18-19, 1995 has been fitted by Lepping et al. (1997, JGR, 102, 14049) with use of the Lundquist solution. The cloud has a very flat magnetic field magnitude profile. We fitted it by the elliptic solution (i). The magnetic cloud of November 17-18, 1975 has been fitted by Marubashi (1997) with use of a toroidally adjusted Lundquist solution. The cloud has a large magnetic field vector rotation and a large magnetic field magnitude increase over the background level. We fitted it by the toroidal solution (ii). The both fits match the rotation of the magnetic field vector in a comparable quality to the former fits, but the description of the magnetic field magnitude profiles is remarkable better. It is possible to incorporate temporal effects (expansion) of magnetic clouds into the new solutions through a time-dependent alpha parameter as in Shimazu & Vandas (2002, EP&S, 54, 783).

Text below is an extended abstract of the poster, presented on JD03 session during 25th GA IAU in Sydney.

Using Mees Solar Observatory active-region vector magnetograms and Mt. Wilson Observatory full-disk longitudinal magnetograms, we measure both the twist and tilt of the magnetic fields of 368 active regions. This dataset clearly shows two well-known phenomena, Joy’s law and the hemispheric helicity rule, as well as a lesser-known twist-tilt relationship, which is the point of this work. Those regions that closely follow Joy’s law show no twist-tilt relationship, which is a predicted consequence of convective buffeting of initially untwisted and unwrithed flux tubes through the Σ effect. Those regions that strongly depart from Joy’s law show significantly larger than average twist and a very strong twist-tilt relationship. These properties suggest that the twist-tilt relationship in these regions is due to kinking of flux tubes that are highly twisted but not strongly writhed.

We illustrate that helicity is not a necessary ingredient for fast dynamo action; we use the stagger-grid method of Galsgaard, Nordlund and others (e.g. Galsgaard & Nordlund 1997, and applied to dynamos by e.g. Dorch 2000): we solve the full MHD equations including a forcing term that keeps the kinetic energy at an approximately constant level. A 3-d flow with no mean helicity (an ABC-like flow without cosines, cf. Galloway & Proctor 1992) is implemented and it turns out that apart from the high growth rate in the linear regime (compared to kinematic dynamo action, cf. Archontis & Dorch 2003a), the dynamo saturates at a level significantly higher that the intermittent turbulent dynamos (cf. Archontis & Dorch 2003b); namely at exact energy equipartition. During the linear regime, several kinematic modes are present, e.g. a sheet/vortex-mode and a mode that resembles the ABC ”double cigar” mode (e.g. Dorch 2000). In the non-linear regime, the magnetic topology is not symmetric, but the initial structure of the velocity field is retained. The presence of helicity is not a requirement for dynamo action but it is rather the stretching ability of the flow that amplifies the magnetic energy in an exponential manner (Archontis & Dorch, in preparation).

We have discovered unusual inversion of circular polarization in both components of an active region. We have observed the region for six consecutive days in May 96 using the RATAN-600 radio telescope with high polarization accuracy up to 0.5 %. The observations were taken in the range of 1.7 to 30 cm. At short wavelengths the circular polarization scans revealed a bipolar structure, expected since the magnetic field is bipolar. However, for all six days and while the region was moving from the center of the disk to the west limb, the circular polarization dropped practically to zero at 14.5 cm and at longer wavelengths the sense of the polarization was reversed.

We examined the evolution of active regions and found that rotational motions of the neutral line in the δ-type magnetic configuration are common in the flare-productive active regions.

Over the wavelength interval of 150 mÅ redward of line center of the FeI λ5324.19 Å to 150 mÅ to the blue, in steps of 10 mÅ, observations of a simple sunspot were obtained with the Video Vector Magnetograph at Huairou Solar Observing Station (HSOS) of National Astronomical Observatories. In this paper, we present results of the inversion of stokes polarization profiles of this sunspot to recover the vector magnetic field parameters of the spectral line forming region using the FeI λ5324.19 Å using a nonlinear least-squares fitting. At the same time, curves of the observed variation of azimuth with wavelength were compared with model calculations for the azimuth at each wavelength as derived the inverse Zeeman effect modified by Faraday rotation. Hagyard, et al. (2000, Solar Phys. 191, 309) find it is difficult to separate two effects of Faraday rotation and π —σ rotation. However, π —σ rotation relates to the Landé factor of a spectral line. For the spectral line FeI λ5324.19 Å, its Landé factor g = 1.5. In the solar magnetic field atmosphere, its Zeeman split is less than that of line FeI 5250.22 Å which has larger Landé factor g = 3. The correlations in Figure 1 show that the azimuth rotation increases as the field strength increases and inclination angle decreases. The results show that rotation of the azimuth is less significant in observation taken near the center of the FeI λ5324.19 A than that of FeI λ5252.22 Â line.

We report the result of a study of magnetic helicity in solar active regions during 1980-2000. Using the vector magnetograms from four instruments (Haleakala Stokes Polarimeter, Marshall Space Flight Center, Mitaka Solar Flare Telescope and Okayama Observatory Solar Telescope) we calculated the force-free parameter α and computed a slope dα/dφ as the linear fit of α vs. latitude φ, using annual subsets of data. The hemispheric helicity rule can be expressed in terms of this slope as dα/dφ < 0. We find that each instrument exhibits change in sign of dα/dφ for some years. However, we do not see consistency between different instruments in regards to years disobeying the rule. We show that this inconsistency can be attributed to insufficient numbers of active regions in annual subsets of data. We conclude that the present data sets do not allow to make statistically significant inference about possible cyclic variation of the hemispheric helicity rule.

For further discussion see Hagyard et al., 2003, ApJ, submitted.

We present first attempts to compare the Birmingham Solar-Oscillations Network (BiSON) high precision solar mean magnetic field (SMMF) data of four years with the occurrence of CMEs (coronal mass ejections) as recorded by LASCO on board SOHO. The BiSON magnetic measurement technique is given in Chaplin et al. (2003). Particularly interesting results of recent SMMF high-cadence observations have come from studies of correlation between the SMMF determined by MDI and the occurrence of CMEs (Boberg and Lundstedt 2000 and Boberg et al 2002). Two frequency ranges, centered on 13 and 90 minutes, have been identified as possibly correlating with CME occurrence.

We have used BiSON SMMF data from two sites to investigate CME related SMMF signals to try to confirm the MDI results. To search methodically through our data set we have developed two correlation techniques suited to short (up to 32 minutes) and long (up to 3 hours) period wavelets, respectively. For short periods we analyzed SMMF data in the vicinity of CMEs, and for long periods we compared SMMF results for days with and without recorded CMEs. In neither period range have we yet clearly identified correlations between SMMF power excesses and CME onsets. For the details of the techniques and the results see Chaplin et al. (2004).

An eruptive process of a quiescent filament on Feb. 18, 2003 that initiated a CME was recorded by the full disk Hα telescope in HSOS (Huairou Solar Observing Station) and by the Solar and Heliospheric Observatory (SOHO). The eruption revealed a typical process of energy release and dense plasma ejection caused by magnetic instability. Filament eruptions, flares and CMEs are believed to be the same magnetic eruption and reconnection event in three different stages. This feature was shown more clearly during eruption of the quiescent filament because of the simple and regular magnetic line-of-sight field in photosphere compared to active regions with complex magnetic configurations. The filament was located near the solar northwest limb (N 30-40, W 40-80) on Feb. 18, 2003 with height about 11000 km. It began to erupt at 02:00 UT. Bright ribbons appeared at the magnetic feet of the filament in EIT/195 at 02:30 UT. The post-eruption loops formed at 04:00 UT and lasted about 6 hours. The CME appeared on EIT/C2 images at 02:30UT with an Ω shape, just the same as the filament erupted. The speed of mass ejected of the filament was about 250km/s. We also notice that the height of the filament increased and the magnetic fields with opposite polarity moved towards each other before the filament erupted. The filament eruption reveals that the filament may be held in the corona by the twisted magnetic fields which also keep the cool plasma from escaping the solar surface. If the twisted field was broken by some magnetic instabilities, the filament would erupt. The presence of post-eruption loops implies a transition process from non-potential (twisted) to potential field magnetic configuration in the filament.

Observations have indicated that the net helicity sign of active regions is predominantly negative in the northern hemisphere and positive in the southern (see Table 1). From Table 1, we find that the hemispheric sign rule of helicity parameter αbest does not change with another solar cycle; but the helicity parameter Hc seems to show a weak opposite hemispheric preference for Huairou data in the solar cycle 23 and no preference for Mees data. How to explain such a phenomenon? We think one reason may be from the action of Faraday rotation. Faraday rotation will cause a counterclockwise rotation of the azimuth for a positive polarity field and vice versa. During the cycle 22, the polarity of leading sunspots is dominantly negative in the northern hemisphere and positive in the southern. The effect of Faraday rotation, which is determined mostly by a leading polarity sunspot, has a positive contribution to the percentage of current helicity signs in active regions and leads to the increase of the strength of the hemispheric sign rule. In the cycle 23, the polarity of most leading sunspots is positive in the northern hemisphere and Faraday rotation will decrease the percentage of current helicity signs. Consequently, the strength of the hemispheric rule should be weakened. On the other hand, Hc is more susceptible to Faraday rotation than αbest because it is mainly related to the areas where the line-of-sight field is strong. Therefore, if the effect of Faraday rotation is not completely removed in our observations, the hemispheric sign rule showed is weak in the cycle 23 than in the cycle 22 (for αbest), even opposite (for Hc).

In this contribution we give summaries of the oral and poster papers presented in Joint Discussion Session 4, Astrophysical Impact of Abundances in Globular Cluster Stars, at the XXVth IAU General Assembly. The full text of the papers can be found in Volume 75, issue 2, of the MEMORIE della Società Astronomica Italiana (Journal of the Italian Astronomical Society; see the web address: <sait.oat.ts.astro.it>).

Globular cluster systems are often thought to be associated with violent formation events such as galaxy mergers or the formation of large bulges. However, formation in relatively ordered regions such as thin disks may also be an important process which has been overlooked.

Recent high-quality spectroscopic studies of the M31 globulars show that a significant number of the clusters projected on its disk belong to a rapidly rotating thin disk. This contrasts strongly with the Milky Way system, which is composed of a halo and thick disk system and has no known thin disk globulars. It is also likely that M31 has experienced no minor mergers since the globular cluster formation epoch, as such a merger would have heated the globulars into a thick disk system. The metallicity distributions of the disk and non-disk clusters are quite similar.

As the nearest giant elliptical galaxy, NGC 5128 (Centaurus A) is an excellent place to use globular clusters (GCs) and host galaxy field stars to study galaxy evolution. We have performed a detailed investigation of this galaxy, comparing field star kinematics with the metallicities, ages, and kinematics of GCs. We used our sample of 780 planetary nebulae (PNe) to trace the kinematics of the field star population. Our survey for GCs bring the total number of confirmed GCs to 215. Using spectra of the brightest GCs to determine ages, we find that the metal-rich GCs have a mean age of approximately 4-5 Gyr, and that their kinematics are similar to those of the PNe. The metal-poor GCs have old ages similar to the Galactic GCs, and show a weaker kinematic correlation with the field stars. It is possible that NGC 5128 was formed by the merger of two or more disk galaxies at the time that the metal-rich clusters were formed.

We have measured the dynamical mass of the highly luminous star cluster W3 in the young merger remnant galaxy NGC 7252. The value is Mdyn = (8 ± 2) × 107M⊙, and represents the highest dynamically-confirmed mass for an extra-galactic star cluster so far. The dynamical mass is in excellent agreement with the luminous mass (Maraston et al. 2001). This results from the use of stellar population models that include correctly the brightest AGB stellar phase, dominant in young stellar populations. To classify W3, we employ the fundamental plane of stellar systems (Bender, Burstein & Faber 1992), for the first time in these kinds of studies. We find that W3 lies far from typical Milky Way globular clusters, but it is also far from the heavyweights ωCen in the Milky Way and G1 in M31, because it is too extended for its mass, and from dwarf elliptical galaxies because it is much more compact for its mass. Instead W3 lies close to the ultra-compact Fornax objects (Drinkwater et al. 2003) and to the compact elliptical M32, possibly shedding light on the still mysterious nature of these objects. A previously deserted region of the fundamental plane starts to be populated.

The superior resolution and large format of the Advanced Camera for Surveys (ACS) on the Hubble Space Telescope (HST) make it a powerful new tool in the study of extra-galactic globular cluster (GC) systems. We summarize some early results on GC populations from the ACS GTO program, concentrating on the extreme cases of the isolated dwarf NGC 2915 and the core of the massive lensing cluster Abell 1689.

We present recent results from our long-term Gemini/GMOS study of globular clusters (GCs) in early-type galaxies. To date, we have obtained photometry and spectroscopy for GCs in NGCs 3379, 4649, 524, 7332, and IC 1459. We find a clear bimodality in the NGC 4649 GC color distribution, with the fraction of blue/red clusters increasing with galacto-centric radius. We derive ages and metallicities for 22 GCs in NGC 3379, finding that most of the clusters appear old (10–15 Gyr); however, there is a group of 4 metal-rich, younger clusters with ages of 2–6 Gyr. The NGC 3379 GC velocity dispersion decreases with radius, as does the inferred (local) mass-to-light ratio: there is no evidence for a dark matter halo in NGC 3379 based on our GC data.

We confirm and extend our previous detection of a population of intergalactic globular clusters in Abell 1185, and report the first discovery of an intergalactic globular cluster in the nearby Virgo cluster of galaxies. The numbers, colors and luminosities of these objects can place constraints on their origin, which in turn may yield new insights to the evolution of galaxies in dense environments.

Cold Dark Matter simulations predict 10-100 x more dwarf satellite galaxies than are observed. Some of these ‘missing satellites’ may have been accreted, along with their globular clusters (GCs), by giant galaxies (Cote et al. 1998). But examples of dwarfs in the early stages of disruption have remained elusive.