Search for periodicities of the Solar Irradiance Data from Earth Radiation Budget Satellite (ERBS) using Rayleigh Power Spectrum Analysis

The solar irradiance data plays a very important role for understanding of Solar internal Structure and the solar terrestrial relationships. The Total Solar Irradiance (TSI) is integrated solar energy flux over the entire spectrum which arrives at the top of the atmosphere at the mean sun earth distance. TSI has been monitored from several satellites, e.g. Nimbus 7, Solar Maximum Mission (SMM), The NASA, Earth Radiation Budget Satellite (ERBS), NOAA9, NOAA10, Eureca and the Upper Atmospheric Research Satellite (UARS) etc. From these observations it reveals that the total solar irradiance varies about a small fraction of 0.1 over solar cycle being higher during maximum solar activity condition. In the present paper we have analysed the solar irradiance data from ERBS during the time period from October 15, 1984 to October 15, 2003. First filtering the data by Simple Exponential Smoothing we have applied the Rayleigh Power Spectrum Analysis on the processed data in order to search for its time variation. Study exhibits multi-periodicities on these data around 7, 11, 42, 80, 104, 130, 160, 254, 536, 752, 1142, 1388, 2474 and 4951 days with very high confidence levels (more than 95%). Apart from these strong periods there are some other weak periods around 22, 47, 53, 67, 69, 149, 167, 365, 489 and 683 days. These periods are significantly similar with the periods of other solar activities which may suggest that solar irradiance may be associated with other solar activities.     

On the accuracy of the measurements of low-ℓ solar acoustic oscillations

Using a 1154 d long measurement of solar oscillations, obtained by the Global Oscillation Network Group from 1995 June 10 to 1998 August 6, we study the dependence of the accuracy of radial p-mode parameters on the duration of the observations. It is shown that relatively rare pulses of large power lead to the decrease of the accuracy achievable for a given duration of the observations and it is usually underestimated. The corresponding correction factor to the Libbrecht formula for a frequency accuracy estimation is provided. We have also investigated the influence of the solar activity on the mode parameters soon after the solar activity minimum. There is a clearly visible increase of the radial p-mode power in the beginning of the new solar cycle while the mode frequency variations are within the corresponding error bars.     

Evidence for a long-term variation of the dynamo action responsible for the solar magnetic cycle

By using the sunspot time series as a proxy, we have made a detailed analysis of the mean solar magnetic field over the last two and half centuries, by means of a reconstruction of its phase space. We find evidence of a long-term trend variation of some of the solar physical processes (over a few decades) that might be responsible for the apparent erratic behaviour of the solar magnetic cycle. The analysis is done by means of a careful study of the axisymmetric dynamo model equations, where we show that the temporal counterpart of the magnetic field can be described by a self-regulated two-dimensional dynamic system, usually known as a Van der Pol–Duffing oscillator. Our results suggest that during the last two and half centuries, the velocity of the meridional flow, v _p, and the efficiency of the α mechanism responsible for the conversion of toroidal magnetic field into poloidal magnetic field might have suffered variations that can explain the observed variability in the solar cycle.     

Magneto‐seismology of the solar atmosphere

Magnetohydrodynamic (MHD) waves in solar coronal loops, which were previously only predicted by theory have actually been detected with space‐borne instruments. These observations have given an important and novel tool to measure fundamental parameters in the magnetically embedded solar corona. This paper will illustrate how information about the magnetic and density structure along coronal loops can be determined by measuring the frequency or amplitude profiles of standing fast kink mode oscillations. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Search for relationship between duration of the extended solar cycles and amplitude of sunspot cycle

Duration of the extended solar cycles is taken into the consideration. The beginning of cycles is counted from the moment of polarity reversal of large-scale magnetic field in high latitudes, occurring in the sunspot cycle n till the minimum of the cycle n + 2. The connection between cycle duration and its amplitude is established. Duration of the “latent” period of evolution of extended cycle between reversals and a minimum of the current sunspot cycle is entered. It is shown, that the latent period of cycles evolution is connected with the next sunspot cycle amplitude and can be used for the prognosis of a level and time of a sunspot maximum. The 24th activity cycle prognosis is made. The found dependences correspond to transport dynamo model of generation of solar cyclicity, it is possible with various speed of meridional circulation. Long-term behavior of extended cycle's lengths and connection with change of a climate of the Earth is considered. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Characteristics of the Radiation from Blazars

We have collected short-timescale variability data of 47 blazars, estimated the masses of their central black holes and the sizes of their radiation regions at different wavebands, and made a statistical analysis on the calculated results. It is found that the central black hole mass of blazars falls in the range 10⁷M to 10¹⁰M, and that the BL Lac objects and the flat-spectrum radio quasars have very different central black hole masses (the latter being generally greater), while they have very similar sizes of radiation regions in the infrared and γ-ray wavebands. Also, using the collected bolometric luminosity data, we have analyzed the relationship between the bolometric luminosity of blazars and their short-timescale variability, and it is concluded that the radiations from the radio-selected BL Lac objects (RBLs) and flat-spectrum radio quasars (FSRQs) are strongly beam-confined, while the effect of relativistic beaming is relatively small for the X-ray-selected BL Lac objects (XBLs).     

Rotation of the solar core from BiSON and LOWL frequency observations

Determination of the rotation of the solar core requires very accurate data on splittings for the low-degree modes which penetrate to the core, as well as for modes of higher degree to suppress the contributions from the rest of the Sun to the splittings of the low-degree modes. Here we combine low-degree data based on 32 months of observations with the BiSON network and data from the LOWL instrument. The data are analysed with a technique that specifically aims at obtaining an inference of rotation that is localized to the core. Our analysis provides what we believe is the most stringent constraint to date on the rotation of the deep solar interior.     

The Holmberg effect of Luminous Red Galaxy (LRG) pairs of the SDSS Data Release 4 (SDSS4)

We investigate the Holmberg effect of Luminous Red Galaxy (LRG) pairs of the SDSS Data Release 4 (SDSS4). It is found that the Holmberg effect of LRG pairs has no statistical significance. According to types of the two components in each pair, we divide the isolated LRG pair sample into three subsamples: the early+early subsample, the late+late subsample and the early+late subsample. Further analyses show that all LRG pair subsamples do not exhibit statistically significant Holmberg effect. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Colour change measurements of gravitational microlensing events by using the difference image analysis method

Detecting colour changes of a gravitational microlensing event induced by the limb-darkened extended source effect is important for obtaining useful information about both the lens and the source star. However, precise measurements of the colour changes are hampered by blending, which also causes colour changes of the event. In this paper, we show that although the colour change measured from the subtracted image by using the recently developed photometric method of the 'difference image analysis' (DIA) differs from the colour change measured by using the conventional method based on the extraction of the individual source stars' point spread functions, the curve of the colour changes (colour curve) constructed by using the DIA method enables one to obtain the same information about the lens and source star, but with significantly reduced uncertainties due to the absence of blending. We investigate the patterns of the DIA colour curves for both single lens and binary lens events by constructing colour change maps.     

Confirmation and characterization of neglected WDS systems using Gaia data release 3 and the virtual observatory

The aim of this article is making use of the Gaia DR3 catalogue and virtual observatory tools, to confirm and characterize 428 binary and multiple stellar systems classified as neglected (only one observation) in the Washington Double Star Catalogue (WDS). The components of the stellar systems have the same parallax and proper motion (within the errors) and are separated by less than 50,000 AU, which minimizes the number of by-chance counterparts. Effective temperatures calculated using VOSA were used to estimate stellar masses. Binding energies were calculated for 42 binary systems confirming they are physical pairs. Also we found 75 pairs with F/G- M spectral types, which are very interesting to improve the determination of the metallicity of the M star from the higher mass component.     

Environmental dependence of stellar mass,SFR, and SSFR for the Luminous Red Galaxy (LRG) sample of the SDSS DR7

Using the Luminous Red Galaxy (LRG) sample of the Sloan Digital Sky Survey Data Release 7 (SDSS DR7), we investigate the environmental dependence of stellar mass, star formation rate (SFR) and specific star formation rate (SSFR) of LRGs. It is found that stellar mass of LRGs nearly is independent of local environments, and that the environmental dependence of SFR and SSFR in the LRG sample is much weaker than the one in the Main galaxy sample. One possible explanation is that galaxy color and morphology are a pair of galaxy properties most predictive of local environments, while LRGs are a group of galaxies that are likely to be luminous, red and of early types (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The main sequence from F to K stars of the solar neighbourhood in SDSS colours

For an understanding of Galactic stellar populations in the SDSS filter system well defined stellar samples are needed. The nearby stars provide a complete stellar sample representative for the thin disc population. We compare the filter transformations of different authors applied to the main sequence stars from F to K dwarfs to SDSS filter system and discuss the properties of the main sequence. The location of the mean main sequence in colour‐magnitude diagrams is very sensitive to systematic differences in the filter transformation. A comparison with fiducial sequences of star clusters observed in g ′, r ′, and i ′ show good agreement. Theoretical isochrones from Padua and from Dartmouth have still some problems, especially in the (r – i) colours. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Structure of a simple sunspot from the inversion of IR spectral data

Analysis of spectral data of two neighboring infrared lines, Fe I 15648.5 Å (g = 3) and FeI 15652.9 Å (g_eff = 1.53) are carried out for a simple sunspot when it was near the solar disk center (μ = 0.92), to understand the basic structure of sunspot magnetic field. Inversions of Stokes profiles are carried out to derive different atmospheric parameters both as a function of location within the sunspot and height in the atmosphere. As a result of the inversion we have obtained maps of magnetic field strength, temperature, line‐of‐sight velocity, field inclination and azimuth for different optical depth layers between log(τ₅) = 0 and log(τ₅) = –2.0. In this paper we present few results from our inversion for a layer averaged between log(τ5) from 0.0 to –0.5.     

Search for nonpotential features in the magnetic field of the solar active region SD 135 on 1984 June 4

Wir untersuchten die Struktur des Magnetfeldes in der relativ kleinen und einfachen solaren aktiven Region SD 135/1984 in der frühen, relativ ruhigen Phase am 24. Juni. Für diese Arbeit nutzten wir die Daten des Vektormagnetografen des SibIZMIR und Resultate von Modellrechnungen in der stromfreien Näherung. Wir haben das gemessene Magnetfeld mit dem Transversal-Feld der Modellrechnung verglichen. Wir konnten keinen signifikanten Nonpotential-Effekt größer als im Niveau der Sensitivität des Transversal-Magnetfeldes B_T 200 G finden. Wir schluß-folgern daher, daß die globale Magnetfeldstruktur in der untersuchten solaren aktiven Region nahezu eine Potentialstruktur besaß. Die Effekte der Entwicklung der aktiven Region auf die Magnetfeldstruktur scheinen vernachlässigbar zu sein.     

Objective classification of galaxy spectra using the information bottleneck method

A new method for classification of galaxy spectra is presented, based on a recently introduced information theoretical principle, the information bottleneck . For any desired number of classes, galaxies are classified such that the information content about the spectra is maximally preserved. The result is classes of galaxies with similar spectra, where the similarity is determined via a measure of information. We apply our method to ∼6000 galaxy spectra from the ongoing 2dF redshift survey, and a mock-2dF catalogue produced by a cold dark matter (CDM) based semi-analytic model of galaxy formation. We find a good match between the mean spectra of the classes found in the data and in the models. For the mock catalogue, we find that the classes produced by our algorithm form an intuitively sensible sequence in terms of physical properties such as colour, star formation activity, morphology, and internal velocity dispersion. We also show the correlation of the classes with the projections resulting from a principal component analysis.