‘Nomadic’ nuclei of galaxies

In this paper we discuss observational and theoretical arguments in favour of hypothesis on nomad life of active nuclei inside and outside galaxies as well as its consequences. It may be the anisotropic collapse of a supermassive star, or the disruption of a supermassive binary system after the collapse of one companion that would give birth to such nuclei. We predict the existence of veritable quasi-stellar active objects without any ghost gagalies.     

‘Prominences’ of RY Tauri

High-resolution spectroscopic monitoring of the Nai D lines in the T Tau-type star RY Tau results in the discovery of relatively cool gas clouds ascending and descending inside the stellar wind on a time-scale of few days and co-rotating with the star. Radial velocity of the clouds varies from –100 to +100 km s^–1, which is twice as large as thev sini of the star.Paper presented at the 11th European Regional Astronomical Meetings of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain.     

Pitch angle scattering of solar particles: Comparison of ‘particle’ and ‘field’ approach

In the quasi-linear theory of pitch angle scattering the power spectrum of magnetic field fluctuations is related to the shape of the pitch angle diffusion coefficient D(), the absolute value of the mean free path , and the rigidity dependence of the mean free path (R). We discuss these relations in detail during the solar particle event of 11 April, 1978 which was observed on HELIOS-2 at a distance of 0.49 AU from the Sun. Magnetic field measurements obtained during the time of the event are used as a basis for the layer model in which the method of particle trajectories in an actually measured field is used to simulate pitch angle diffusion. The values of D() and based on the trajectory simulation for 100 MeV protons (field approach) are compared with results obtained from solar proton data (particle approach) and with predictions from quasi-linear theory based on the additional assumption of the slab model for magnetic field fluctuations (QLT approach). The time of the event is characterized by a high level of field fluctuations, the observed mean free path of about 0.03 AU for 100 MeV protons is smaller than the average value near 1 AU. Results from the field and particle approaches agree surprisingly well. The remaining difference in the mean free path of about a factor of 2 could be due to tangential discontinuities which are measured by the magnetometer, but not seen by the real particles traveling along the average field. The results from the field and QLT approaches based on the same set of magnetic field measurements differ by about a factor of 4. One of the reasons for this discrepancy is that the conditions for resonance scattering are only marginally valid. In addition, the wave vectors representing Alfvén-type fluctuations may not be totally field aligned. This deviation from the slab model would cause an increase of the theoretically predicted mean free path and lead to better agreement with the other two approaches.     

An apparent ‘even-odd’ cycle distribution in Mt. Wilson ‘numbers of spots’ data

Mt. Wilson numbers of spots data (as defined in Howard et al., 1984) appear to be distributed according to even-odd cycle numbering. Linear fits of annual numbers of spots versus annual sunspot number for even- and odd-numbered cycles have slopes which are statistically different at the 5% level of significance. The existence of an even-odd split in Mt. Wilson numbers of spots data may be due either to a real difference in even- and odd-numbered cycles on the Sun or to a difference in weather at Mt. Wilson (perhaps, related to the 22-yr rhythm of drought in the western United States) during even- and odd-numbered cycles, or both. For cycle 22, an even-numbered cycle, the peak numbers of spots is estimated to be near 2600.     

75th Anniversary of ‘Existence of Electromagnetic–Hydrodynamic Waves’

We have recently passed the 75th anniversary of one of the most important results in solar and space physics: Hannes Alfvén’s discovery of Alfvén waves and the Alfvén speed. To celebrate the anniversary, this article recounts some major episodes in the history of magnetohydrodynamic (MHD) waves. Following an initially cool reception, Alfvén’s ideas were propelled into the spotlight by Fermi’s work on cosmic rays, the new mystery of coronal heating, and, as scientific perception of interplanetary space shifted dramatically and the space race started, detection of Alfvén waves in the solar wind. From then on, interest in MHD waves boomed, laying the foundations for modern remote observations of MHD waves in the Sun, coronal seismology, and some of today’s leading theories of coronal heating and solar wind acceleration. In 1970, Alfvén received the Nobel Prize for his work in MHD, including these discoveries. The article concludes with some reflection about what the history implies about the way we do science, especially the advantages and pitfalls of idealised mathematical models.     

Updated version of the ‘homogeneous catalog of open cluster parameters’

We report a new version of the “Homogeneous catalog of open cluster parameters” maintained by our team over the last decades. The catalog is based on redetermination of the main parameters of clusters (color excesses, heliocentric distances, and ages) based on published photometric measurements, in particular, those provided by the 2MASS point-source catalog. Currently, our catalog provides the parameters for 959 clusters. It also gives the estimates of cluster radial velocities for 496 clusters partly based on the data fromRAVE catalog. Estimates of proper-motion components are provided for all clusters included into the catalog. We analyze the distributions of the errors of the main cluster parameters and compare the distribution of cluster positions projected onto the Galactic plane with the distribution of cosmic masers thereby validating the distance scale of open clusters.     

The three-dimensional structure of ‘loop-like’ coronal mass ejections

We have measured the brightness and latitudinal extent of the depleted (cavity) region behind the leading edge of three coronal mass ejection (CME) events from the Skylab epoch. The events chosen are among those believed to be typical of non-impulsive, loop-like CMEs (Sime, MacQueen, and Hundhausen, 1984). The pre-event coronal brightness has been matched by a model corona, assuming both a background contribution and a contribution from a range of hypothetical streamer models, distinguished by differing longitudinal extent. Then, assuming that the cavities are voided regions in which the local electron density is negligible, we estimate their minimum line-of-sight extent and find them to be comparable to, or greater than, their measured latitudinal extent. As a result, we suggest this unambiguously demonstrates the three-dimensional nature of these — and likely, this class of — events.     

A distinctive type of ascending prominence — ‘fountain’

Cinematographic observations of solar prominences made at Mauna Loa during the past couple of years suggest that there is a well-defined sub-class of ascending prominences characterized by closed-system transference of chromospheric material along an arch or loop (up one leg and down the other); meanwhile the entire prominence envelope steadily rises upward and expands through the corona. We denote these prominences as fountains. Several examples are described. Fountains appear to be well contained by coronal magnetic fields. Their total kinetic energy is in the order of 10³⁰ erg but dissipation is typically quite slow (over time periods like 100 min) so that the correlative disturbances (radio bursts, coronal transients, chromopsheric brightenings, etc.) are generally unspectacular or non-existent.This research was started when E. T.-H. was still on the staff of the High Altitude Observatory.The National Center for Atmospheric Research is sponsored by the National Science Foundation.     

The existence of a ‘gap’ in the evolutionary sequence of pulsars

A replot of period derivative against period is done for about 300 pulsars, and the main features of the plot are discussed. The significance of a gap in this plot is reexamined and the existence of pulsars with nulling and subpulse drifting behaviour below this gap is pointed out. The implications of this for pulsar evolution are also discussed.     

Variations of ‘wavelengths’ and ‘bisector indices’ of 70 solar spectral lines between 3300 and 3960 Å in Kitt Peak FTS spectra

Wavelengths and bisector indices (a special measure for the asymmetry of a line near its bottom) are determined for 70 lines in each of 47 high-dispersion spectra. The spectra were obtained with the Fourier Transform Spectrograph connected to the McMath Telescope at Kitt Peak National Observatory; they all cover the same spectral range from 3200 to 4000 Å and concern either the full disk (19 disk spectra), or the disk center (9 center spectra), or two areas at sin = 0.85 on the west- and east-side of the disk (19 limb spectra). The main observing seasons were June 1986, June 1987, April and June/July 1988. The - relative - position of an individual line in one spectrum can be established with a precision of about 4 m s^-1, the precision of one bisector index is 1–2 m s^-1.Wavelengths and bisector indices show of course the typical characteristics which result from the familiar effects known as blueshift, limb effect and line asymmetry. However, concerning their variations in time, unexpected results are obtained:(1) Even in disk spectra the time-scales of the wavelength variations are often in the order of one hour or less. (2) For all 3 types of spectra (disk, center, limb) the variations depend not only on the known parameters such as line depth and - occasionally - excitation potential, but also - often even primarily - on wavelength. (3) In center spectra, the wavelength differences between strong and faint lines can vary by as much as 500 m s^-1, in disk spectra short-time variations of wavelength differences can amount to more than 50 m s^-1. (4) For most spectra there is not only a very pronounced and narrow correlation between line shift and line temperature (a special measure for the line depth), but also a significant correlation between line shift and variation of the bisector index.Clearly, the observed effects must be attributed to variations of the velocity fields in the upper photosphere/lower chromosphere (super-granulation cells, overshooting, oscillations), which either influence the line wavelengths directly via the Doppler-effect, or indirectly by changing the contrast between the blue-shifted granules and the red-shifted intergranular lanes. Because of the snapshot character of the observations, no reliable conclusions can be drawn on the actual time-dependency.     

Redundant variables for ‘global’ regularization of the three-body problem

It has been shown (Heggie, 1974) that the equations of motion for the three-body problem may be cast into a form which is regular for collisions betweenany pair of bodies. The method proceeds by two stages, namely

Short-term periodicities of the sun's ‘mean’ and differential rotation

We have looked for periodicities in solar differential rotation on time scales shorter than the 11-year solar cycle through the power- spectrum analysis of the differential rotation parameters determined from Mt. Wilson velocity data (1969–1994) and Greenwich sunspot group data (1879–1976). We represent the differential rotation by a set of Gegenbauer polynomials (()= + (5sin₂–1)+ (21sin₄–14sin₂+1)). For the Mt. Wilson data, we focus on observations obtained after 1981 due to the reduced instrumental noise and have binned the data into intervals of 19 days. We calculated annual averages for the sunspot data to reduce the uncertainty and corrected for outliers occuring during solar cycle minima. The power spectrum of the photospheric mean rotation , determined from the velocity data during 1982–1994, shows peaks at the periods of 6.7–4.4 yr, 2.2 ± 0.4 yr, 1.2 ± 0.2 yr, and 243 ± 10 day with 99.9% confidence level, which are similar to periods found in other indicators of solar activity suggesting that they are of solar origin. However, this result has to be confirmed with other techniques and longer data sets. The 11-yr periodicity is insignificant or absent in . The power spectra of the differential rotation parameters and , determined from the same subset, show only the solar cycle period with a 99.9% confidence level.The time series of determined from the yearly sunspot group data obtained during 1879–1976 is very similar to the corresponding time series of . After correcting for data with large error bars (occurring during cycle minima), we find periods, which are most likely harmonics of the solar cycle, such as 18.3 ± 3.0 yr and 7.5 ± 0.5 yr in and confirmed these and the 3.0 ± 0.1 yr period in . The original time series show in addition some shorter periods, absent in the corrected data, representing temporal variations during cycle minimum. Given their large error bars, it is uncertain whether they represent a solar variation or not. The results presented here show considerable differences in the periodicities of and determined from the velocity data and the spot group data. These differences may be explained by assuming that the rotation rates determined from velocity and sunspot data represent the rotation rates of the Sun's surface layers and of somewhat deeper layers.     

On ‘bimodality of the solar cycle’ and the duration of cycle 21

The period-growth dichotomy of the solar cycle predicts that cycle 21, the present solar cycle, will be of long duration (>133 mo), ending after July 1987. Bimodality of the solar cycle (i.e., cycles being distributed into two groups according to cycle length, based on a comparison to the mean cycle period) is clearly seen in a scatter diagram of descent versus ascent durations. Based on the well-observed cycles 8–20, a linear fit for long-period cycles (being a relatively strong inverse relationship that is significant at the 5% level and having a coefficient of determination r ² 0.66) suggests that cycle 21, having an ascent of 42 mo, will have a descent near 99 mo; thus, cycle duration of about 141 mo is expected. Like cycle 11, cycle 21 occurs on the downward envelope of the sunspot number curve, yet is associated with an upward first difference in amplitude. A comparison of individual cycle, smoothed sunspot number curves for cycles 21 and 11 reveals striking similarity, which suggests that if, indeed, cycle 21 is a long-period cycle, then it too may have an extended tail of sustained, low, smoothed sunspot number, with cycle 22 minimum occurring either in late 1987 or early 1988.     

Rapid changes in the fine structure of a coronal ‘bright point’ and a small coronal ‘active region’

A coronal bright point is resolved into a pattern of emission which, at any given time, consists of 2 or 3 miniature loops (each 2500 km in diameter and 12 000 km long). During the half-day lifetime of the bright point individual loops evolved on a time scale 6 min. A small ctive region seemed to evolve in this way, but the occasional blurring together of several loops made it difficult to follow individual changes.     

Rotating ‘star-in-a-box’ experiments

Using the radiation hydrodynamics code CO⁵BOLD in its ‘star-in-a-box’ setup, we have performed exploratory simulations of global convection in a rotating reference frame. The goal is to study the interaction of convection and rotation by direct numerical simulation. For these first experiments, we chose an idealized configuration (a scaled-down, fast rotating Sun) whose properties resemble those of red supergiants in some respect. We describe the setup and time evolution of these models, and discuss the particular problems we have encountered. Finally, we derive the resulting differential rotation pattern and meridional flow field by temporal and azimuthal averaging of the simulation data. We find anti-solar differential rotation for all cases studied so far. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

On two different types of sunsports-‘vortices’ and ‘sources’-within A U(1)-symmetric Yang-Mills-Higgs system

An intimate link between the structure of the sunspot's magnetic field contiguration and the behaviour of the Higgs field phase at large distances from spot's center is discussed within a U(1)-symmetric Yang-Mills-Higgs gauge theory. It is shown, in particular, that the total magnetic flux of standard sunspots can acquirediscrete values only. A conclusion is also arrived at that, in addition to standard sunspots (magneticvortices), a new sort of sunspots (magneticsources (sinks)), whose total magnetic flux iszero, could principally be observed on the Sun; the two sorts of spots are shown to stand in adual orcomplementary relation to each other. In this connection, finally, a question about the possible role of the divergence of electromagnetic potential — the field violating a gauge invariance of the theory — in physics of two-dimensional solar phenomena is briefly touched.     

The investigations of ‘zodiacal light’ of isolated AE-Herbig stars with non-periodic Algol-type minima

High linear polarization (up to 5–8%) discovered by our group in the deep minima of isolated AE-Herbig stars is discussed in the framework of the model of zodiacal light produced by scattering matter in a circumstellar dust envelope (probably in protoplanetary discs). The numerical simulations of polarizational and colourimetrical properties of the scattered light based on the Mie theory permit to obtain from the observations some important parameters of circumstellar dust: the size distribution of grains, their rough chemical composition (silicate/graphite), the flatness of the dust envelope.Moreover, the position angle of polarization in deep minima may be used for determination of the symmetry axis projection of circumstellar disc on the sky relative to the direction of local interstellar magnetic field. The latest is important in order to understand the role of the magnetic field at the initial phase of gravitational collapse of protostellar clouds.Finally, the component of linear polarization which is due to the alignment of nonspherical circumstellar grains may be separate from the observed polarization under certain conditions.Paper presented at the 12th European Regional Astronomical Meetings of the IAU European Astronomers Look to the Future, held 8–11 October, 1990 in Davos, Switzerland.     

Response of the Solar Atmosphere to the Emergence of ‘Serpentine’ Magnetic Field

Active region magnetic flux that emerges to the photosphere from below will show complexity in the structure, with many small-scale fragmented features appearing in between the main bipole and then disappearing. Some fragments seen will be absorbed into the main polarities and others seem to cancel with opposite magnetic field. In this paper we investigate the response of the corona to the behaviour of these small fragments and whether energy through reconnection will be transported into the corona. In order to investigate this we analyse data from the Hinode space mission during flux emergence on 1?–?2 December 2006. At the initial stages of flux emergence several small-scale enhancements (of only a few pixels size) are seen in the coronal line widths and diffuse coronal emission exists. The magnetic flux emerges as a fragmented structure, and coronal loops appear above these structures or close to them. These loops are large-scale structures – most small-scale features predominantly stay within the chromosphere or at the edges of the flux emergence. The most distinctive feature in the Doppler velocity is a strong ring of coronal outflows around the edge of the emerging flux region on the eastern side which is either due to reconnection or compression of the structure. This feature lasts for many hours and is seen in many wavelengths. We discuss the implications of this feature in terms of the onset of persistent outflows from an active region that could contribute to the slow solar wind.     

Guide and examples for users of the ‘SPACEKAP’ style file

Guide and examples for users of the SPACEKAP style fileBasic instructions