Are There Rings Around the Sun?

The Theory of Alfven drag (Drell et al. in J Geophys Res 70: 3131–3145 1965; Anselmo and Farinella in Icarus, 58, 182–185 1983) is applied here to show that the existence of a possible solar ring structure at a radial distance of 0.02 AU (~4R _⊙ , R _⊙  = radius of the sun) predicted by earlier authors (Brecher et al. in Nature 282, 50–52 1979; Rawal in Bull. Astr. Soc. India 6, 92–95 1978, Moon Planets 24, 407–414 1981, Moon Planets 31, 175–182 1984, J Astrophys Astr 10, 257–259 1989) may not survive Alfven drag produced during even moderate solar magnetic storms which take place from time to time through the age of the sun, but a possible solar ring structure at a radial distance of 0.13 AU (~27R _⊙ ) (Brecher et al. in Nature 282, 50–52 1979; Rawal in Bull. Astr. Soc. India 6, 92–95 1978, Moon Planets 24, 407–414 1981, Moon Planets 31, 175–182 1984, J Astrophys Astr 10, 257–259 1989) may survive intense Alfven drag produced during even strong magnetic storms of magnetic field value up to 1,000 G.     

On Mid-Term Periodicities in Cosmic Rays

The contributions of quasi-periodic variations of cosmic rays for T>27 days at the primary energies to which neutron monitors are sensitive have a rather complicated character. They were reported in several papers (e.g. Valdés-Galicia, Perez-Enriquez, and Otaola, 1996; Mavromichalaki et al., 2003; Kudela et al., 2002; Caballero and Valdés-Galicia, 2001) from individual stations and for various time intervals covered. The data archive of several neutron monitor stations developed within the NMDB project () now involves long time series of measurements at neutron monitors situated at different geomagnetic cut-off rigidity positions and at different altitudes. It is updated continuously. Using the daily averages of cosmic-ray intensity at three selected stations within NMDB: i) the temporal evolution of the selected quasi-periodicities, especially those of approximately 1.7 yr, 150 days and 26 – 32 days respectively, until 2008 are reviewed, ii) the similarities of the spectra are checked and iii) the occurrence of quasi-periodicities with those observed in solar, interplanetary and geomagnetic activities (Moussas et al., 2005; Richardson and Cane, 2005) as well as in energetic particles below the atmospheric threshold are discussed (Laurenza et al., 2009).     

Exact solutions: neutral and charged static perfect fluids with pressure

We show in this article that charged fluid with pressure derived by Bijalwan (Astrophys. Space. Sci. doi:, 2011a) can be used to model classical electron, quark, neutron stars and pulsar with charge matter, quasi black hole, white dwarf, super-dense star etc. Recent analysis by Bijalwan (Astrophys. Space. Sci., 2011d) that all charged fluid solutions in terms of pressure mimic the classical electron model are partially correct because solutions by Bijalwan (Astrophys. Space. Sci. doi:, 2011a) may possess a neutral counterpart. In this paper we characterized solutions in terms of pressure for charged fluids that have and do not have a well behaved neutral counter part considering same spatial component of metric e ^λ for neutral and charged fluids. We discussed solution by Gupta and Maurya (Astrophys. Space Sci. 331(1):135–144, 2010a) and solutions by Bijalwan (Astrophys. Space Sci. doi:, 2011b; Astrophys. Space Sci. doi:, 2011c; Astrophys. Space Sci., 2011d) such that charged fluids possess and do not possess a neutral counterpart as special cases, respectively. For brevity, we only present some analytical results in this paper.     

Realization of Einstein’s Machian Program: the Pioneers and fly-by anomalies Part I

In a previous paper (Berman, in Astrophys. Space Sci., 2011), we showed how to prove the two Pioneers Anomalies, and now we add the fly-bys, by means of a rotating Universe. We discuss Einstein’s Machian program, which we find as being fullfilled. Godlowski et al. (Los Alamos Archives, 2003) idea for a rotating General Relativistic Universe, led us to the adopted model. Updated evidence on rotation is cited (Godlowski, in Los Alamos Archives, 2011; Ni in Phys. Rev. Lett. 107(5):051103, 2011). We conclude that a rotating and expanding Universe may be the unique solution to the apparent divergences between Einstein and Mach. This is cosmologically important.     

Axially symmetric non-static domain walls in scalar–tensor theories of gravitation

An axially symmetric non-static space-time is considered in the presence of thick domain walls in the scalar–tensor theories formulated by Brans and Dicke (Phys. Rev. 124:925, 1961) and Saez and Ballester (Phys. Lett. A 113:467, 1985). Exact cosmological models, in both the theories, are presented with the help of special law of variation proposed by Berman (Nuovo Cim. B 74:182, 1983), for Hubble’s parameter. Some physical and kinematical properties of the models are discussed.      

On a possible mechanism of low surface magnetic field structure of quark stars

Following some of the recent articles on hole super-conductivity and related phenomena by Hirsch (Phys. Lett. A 134:451, 1989; Phys. Rev. B 68:184502, 2003a; Phys. Rev. B 71:184521, 2005a and Phys. Lett. A 345:453, 2005b) a simple model is proposed to explain the observed low surface magnetic field of the expected quark stars. It is argued that the diamagnetic moments of the electrons circulating in the electro-sphere induce a magnetic field, which forces the existing quark star magnetic flux density to become dilute. For the sake of completeness, we have also included the analyses of instability at the normal-super-conducting interface due to excess accumulation of magnetic flux lines. The instability at the interface has also been studied numerically.      

Theoretical overview on high-energy emission in microquasars

Microquasar (MQ) jets are sites of particle acceleration and synchrotron emission. Such synchrotron radiation has been detected coming from jet regions of different spatial scales, which for the instruments at work nowadays appear as compact radio cores, slightly resolvedradio jets, or (very) extended structures (e.g. Mirabel and Rodríguez, 1999; Fender, 2001; Corbel et al., 2002). Because of the presence of relativistic particles and dense photon, magnetic and matter fields, these outflows are also the best candidates to generate the very high-energy (VHE) gamma-rays detected coming from two of these objects, LS 5039 and LS I +61 303 (Aharonian, 2005; Aharonian et al., 2006a; and Albert, 2006, respectively), and may be contributing significantly to the X-rays emitted from the MQ core (e.g. Markoff et al., 2001; Bosch-Ramon et al., 2005a). In addition, beside electromagnetic radiation, jets at different scales are producing some amount of leptonic and hadronic cosmic rays (CR), and evidences of neutrino production in these objects may be eventually found. In this work, we review on the different physical processes that may be at work in or related to MQ jets. The jet regions capable to produce significant amounts of emission at different wavelengths have been reduced to the jet base, the jet at scales of the order of the size of the system orbital semi-major axis, the jet middle scales (the resolved radio jets), and the jet termination point. The surroundings of the jet could be sites of multiwavelength emission as well, deserving also an insight. We focus on those scenarios, either hadronic or leptonic, in which it seems more plausible to generate both photons from radio to VHE and high-energy neutrinos. We briefly comment as well on the relevance of MQ as possible contributors to the galactic CR in the GeV–PeV range.     

Neutrino radiation of the AGN black holes

In the framework of ‘microscopic’ theory of black holes (J. Phys. Soc. Jpn. Suppl. B 70, 84, 2001; Astrophys. USSR 4, 659, 1996; 35, 335, 1991, 33, 143, 1990, 31, 345, 1989a; Astrophys. Space Sci. 1, 1992; Dokl. Akad. Nauk USSR 309, 97, 1989b), and references therein, we address the ‘pre-radiation time’ (PRT) of neutrinos from black holes, which implies the lapse of time from black hole’s birth till radiation of an extremely high energy neutrinos. For post-PRT lifetime, the black hole no longer holds as a region of spacetime that cannot communicate with the external universe. We study main features of spherical accretion onto central BH and infer a mass accretion rate onto it, and, further, calculate the resulting PRT versus bolometric luminosity due to accretion onto black hole. We estimate the PRTs of AGN black holes, with the well-determined masses and bolometric luminosities, collected from the literature by Woo Jong-Hak and Urry (Astrophys. J. 579, 530, 2002) on which this paper is partially based. The simulations for the black holes of masses M _BH ≃(1.1⋅10⁶ ÷4.2⋅10⁹) M _⊙ give the values of PRTs varying in the range of about T _BH ≃(4.3⋅10⁵ ÷5.6⋅10¹¹) yr. The derived PRTs for the 60 AGN black holes are longer than the age of the universe (∼13.7 Gyr) favored today. At present, some of remaining 174 BHs may radiate neutrinos. However, these results would be underestimated if the reservoir of gas for accretion in the galaxy center is quite modest, and no obvious way to feed the BHs with substantial accretion.     

Constraining Coronal Heating: Employing Bayesian Analysis Techniques to Improve the Determination of Solar Atmospheric Plasma Parameters

One way of revealing the nature of the coronal heating mechanism is by comparing simple theoretical one-dimensional hydrostatic loop models with observations at the temperature and/or density structure along these features. The most well-known method for dealing with comparisons like that is the χ ² approach. In this paper we consider the restrictions imposed by this approach and present an alternative way for making model comparisons using Bayesian statistics. In order to quantify our beliefs we use Bayes factors and information criteria such as AIC and BIC. Two datasets (Ugarte-Urra et al. 2005; Priest et al. 2000) are reanalyzed using the method described above. For the dataset of Ugarte-Urra et al. (2005), we conclude to apex dominant heating as the likely heating candidate, whereas the dataset of Priest et al. (2000) implies basal heating. Note that these new results are different from those obtained using the chi-squared statistic. For this we suggest that proper usage of Classical and Bayesian statistics should be applied in order to make safe assumptions about the nature of the coronal heating mechanisms.     

Variable equation of state for Bianchi type-VI<Subscript>0</Subscript> dark energy models

We present dark energy models in an anisotropic Bianchi type-VI₀ (B-VI₀) space-time with a variable equation of state (EoS). The EoS for dark energy ω is found to be time dependent and its existing range for derived models is in good agreement with the recent observations of SNe Ia data (Knop et al. in Astrophys. J. 598:102 2003), SNe Ia data with CMBR anisotropy and galaxy clustering statistics (Tegmark et al. in Astrophys. J. 606:702, 2004b) and latest a combination of cosmological datasets coming from CMB anisotropies, luminosity distances of high redshift type Ia supernovae and galaxy clustering (Hinshaw et al. in Astrophys. J. Suppl. 180:225, 2009; Komatsu et al. in Astrophys. J. Suppl. 180:330, 2009). The cosmological constant Λ is found to be a positive decreasing function of time and it approaches a small positive value at late time (i.e. the present epoch) which is corroborated by results from recent supernovae Ia observations. The physical and geometric aspects of the models are also discussed in detail.     

String cosmological models in five dimensional bimetric theory of gravitation

Five-dimensional spherically symmetric space-time is considered in bimetric theory of gravitation formulated by Rosen (Gen. Rel. Grav. 4, 435, 1973) in the presence of cosmic string dust cloud. Exact cosmological models which represent geometric (Nambu) string, p-string (Takabayasi string) and Reddy string (Astrophys. Space Sci. 301, 2006) are obtained in the static and non-static cases. Some physical properties of the models are also discussed.     

On Signatures of Twisted Magnetic Flux Tube Emergence

Recent studies of NOAA active region 10953, by Okamoto et al. (Astrophys. J. Lett. 673, 215, 2008; Astrophys. J. 697, 913, 2009), have interpreted photospheric observations of changing widths of the polarities and reversal of the horizontal magnetic field component as signatures of the emergence of a twisted flux tube within the active region and along its internal polarity inversion line (PIL). A filament is observed along the PIL and the active region is assumed to have an arcade structure. To investigate this scenario, MacTaggart and Hood (Astrophys. J. Lett. 716, 219, 2010) constructed a dynamic flux emergence model of a twisted cylinder emerging into an overlying arcade. The photospheric signatures observed by Okamoto et al. (2008, 2009) are present in the model although their underlying physical mechanisms differ. The model also produces two additional signatures that can be verified by the observations. The first is an increase in the unsigned magnetic flux in the photosphere at either side of the PIL. The second is the behaviour of characteristic photospheric flow profiles associated with twisted flux tube emergence. We look for these two signatures in AR 10953 and find negative results for the emergence of a twisted flux tube along the PIL. Instead, we interpret the photospheric behaviour along the PIL to be indicative of photospheric magnetic cancellation driven by flows from the dominant sunspot. Although we argue against flux emergence within this particular region, the work demonstrates the important relationship between theory and observations for the successful discovery and interpretation of signatures of flux emergence.     

Kaluza-Klein radiating model in a general scalar-tensor theory

A five dimensional Kaluza-Klein space-time is considered in the presence of prefect fluid source in the general scalar-tensor theory of gravitation proposed by Nordtvedt (Astrophys. J. 161:1069, 1970) with the help of special law of variation for Hubble’s parameter given by Bermann (Nuovo Cimento 74B:182, 1983). A cosmological model with a negative constant deceleration parameter is obtained in this theory. Some physical properties of the model are also discussed.     

A higher-dimensional string cosmological model in Brans–Dicke theory of gravitation

Field equations in the presence of cosmic string source are obtained in a scalar tensor theory of gravitation proposed by Brans and Dicke (Phys. Rev. 124, 925 (1961)) with the aid of a five-dimensional Kaluza–Klein metric. An exact string cosmological model is presented which represents a five-dimensional Reddy string (Astrophys. Space Sci. 286, 2003b) in Brans–Dicke theory. Some physical properties of the model are also discussed     

LRS Bianchi type-II dark energy model in a scalar–tensor theory of gravitation

A locally rotationally symmetric Bianchi type-II (LRS B-II) space-time with variable equation of state (EoS) parameter and constant deceleration parameter have been investigated in the scalar-tensor theory proposed by Saez and Ballester (Phys. Lett. A 113:467, 1986). The scalar-tensor field equations have been solved by applying variation law for generalized Hubble’s parameter given by Bermann (Nuovo Cimento 74:182, 1983). The physical and kinematical properties of the model are also discussed.     

Comments on “Effects of Strong Regular Refraction in the Solar Radio Pulse Structure in Spike Events” by Afanasiev and Altyntsev and “Mathematical Modeling of the Formation of Type IIId Solar Decameter Radio Bursts with Echo Components” by Afanasiev

Presented are some comments on the papers by Afanasiev and Altyntsev (Solar Phys. 234, 151, 2006) and by Afanasiev (Solar Phys. 238, 87, 2006) devoted to the study of the influence of solar corona inhomogeneities on the form of radio bursts. It is pointed out that in these papers incorrect use is made of methods used previously in investigations into radio wave propagation through a randomly inhomogeneous ionosphere.     

A new class of LRS Bianchi type-II dark energy models with variable EoS parameter

A new class of dark energy models in a Locally Rotationally Symmetric Bianchi type-II (LRS B-II) space-time with variable equation of state (EoS) parameter and constant deceleration parameter have been investigated in the present paper. The Einstein’s field equations have been solved by applying a variation law for generalized Hubble’s parameter given by Berman: Nuovo Cimento 74:182 (1983) which generates two types of solutions for the average scale factor, one is of power-law type and other is of the exponential-law form. Using these two forms, Einstein’s field equations are solved separately that correspond to expanding singular and non-singular models of the universe respectively. The dark energy EoS parameter ω is found to be time dependent and its existing range for both models is in good agreement with the three recent observations of (i) SNe Ia data (Knop et al.: Astrophys. J. 598:102 (2003)), (ii) SNe Ia data collaborated with CMBR anisotropy and galaxy clustering statistics (Tegmark et al.: Astrophys. J. 606:702 (2004)) and latest (iii) a combination of cosmological datasets coming from CMB anisotropies, luminosity distances of high redshift type Ia supernovae and galaxy clustering (Hinshaw et al.: Astrophys. J. Suppl. 180:225 (2009); Komatsu et al. Astrophys. J. Suppl. 180:330 (2009)). The cosmological constant Λ is found to be a positive decreasing function of time and it approaches a small positive value at late time (i.e. the present epoch) which is corroborated by results from recent supernovae Ia observations. The physical and geometric behaviour of the universe have also been discussed in detail.     

Revisiting the classical electron model in general relativity

Motivated by earlier studies (Tiwari et al. in Astrophys. Space Sci. 182:105, 1984; Herrera and Varela in Phys. Lett. 189:11, 1994), we model electron as a spherically symmetric charged perfect fluid distribution of matter. The existing model is extended assuming a matter source that is characterized by quadratic equation of state in the context of general theory of relativity. For the suitable choices of the parameters, our charged fluid models almost satisfy the physical properties of electron.     

Pursuing Local Group blue massive stars with WSO-ISSIS

The Local Group galaxies enable us to study the impact of metallicity on the structure and evolution of massive stars through spectroscopic analyses. However, color-based target selection for spectroscopy (in absence of known spectral types), though relatively successful, usually produces lists dominated by B-type modest-mass stars. We have developed a friends of friends code to find OB associations in Local Group galaxies (Garcia et al. in Astron. Astrophys. 502:1015, 2009; Bull. Soc. R. Sci. Liege 80:381, 2011a). The interpretation of the association’s color-magnitude diagrams (CMDs) and the automatic determination of evolutionary masses for the members, allow a more insightful choice of candidates for spectroscopy and to spot out potential advanced evolutionary stages (Garcia et al. in Astron. Astrophys. 523:A23, 2010). We show our results on the dwarf irregular IC 1613 as illustration of the potential of the method.     

A dark energy model in a scalar tensor theory of gravitation

LRS Bianchi type-I dark energy model with variable equation of state (EoS) parameter is presented in the scalar-tensor theory of gravitation proposed by Saez and Ballester (Phys. Lett. A 113:467, 1986). To get a determinate solution of the field equations we take the help of special law of variation for Hubble’s parameter presented by Bermann (Nuovo Cimento B 74:182, 1983) which yields a cosmological model with negative constant deceleration parameter. Some physical and kinematical properties of the model are also discussed.