Constraints on smoothness parameter and dark energy using observational H (z) data

With large-scale homogeneity,the universe is locally inhomogeneous,clustering into stars,galaxies and larger structures.Such property is described by the smoothness parameter α which is defined as the proportion of matter in the form of intergalactic medium.If we consider the inhomogeneities over a small scale,there should be modifications of the cosmological distances compared to a homogenous model.Dyer and Roeder developed a second-order ordinary differential equation(D-R equation) that describes the angu...     

Comment on Constraining the smoothness parameter and dark energy using observational H(z) data

We discuss a recent analysis by Yu et al.[RAA 11,125(2011)] about constraints on the smoothness parameter α and dark energy models using observational H(z) data.It is argued here that their procedure is conceptually inconsistent with the basic assumptions underlying the adopted Dyer-Roeder approach.In order to properly quantify the influence of the H(z) data on the smoothness parameter α,a χ2-test involving a sample of type Ia supernovae and H(z) data in the context of a flat ΛCDM model is reanalyzed.This r...     

A constraint on pre-Main-Sequence mass loss

The principal energy source of a pre-Main-Sequence (PMS) star is gravitational contraction. Mass ejection, regardless of its actual mechanism, in effect transfers gravitational potential energy from the entire star to the escaping matter. The virial theorem limits the efficiency of such a process. Theoretical PMS mass-radius relationships limit the total loss to a few tenths of the initial mass. The observed luminosities and estimated mass loss rates of T-Tauri stars are used to estimate the fraction of available energy expended on mass ejection. Actual losses appear to be much smaller than the theoretical limit in most cases. Only stars of emission line intensity classes 4 and 5 may be capable of significant mass loss.Paper presented at the Conference on Protostars and Planets, held at the Planetary Science Institute, University of Arizona, Tucson, Arizona, between January 3 and 7, 1978.     

Detecting non-sinusoidal periodicities in observational data using multiharmonic periodograms

We address the problem of assessing the statistical significance of candidate periodicities found using the so-called 'multiharmonic' periodogram, which is being used for detection of non-sinusoidal signals and is based on the least-squares fitting of truncated Fourier series. The recent author's investigation made for the Lomb–Scargle periodogram is extended to the more general multiharmonic periodogram. As a result, closed and efficient analytic approximations to the false alarm probability, associated with multiharmonic periodogram peaks, are obtained. The resulting analytic approximations are tested under various conditions using Monte Carlo simulations. The simulations showed a nice precision and robustness of these approximations.     

An observational constraint on the existence of proto-superclsuters atz=3.3

The online version of the original article can be found at     

The mass dependence of the overshooting parameter determined from eclipsing binary data

We report the discovery of emission features in the X-ray spectrum of GRO J1655–40 obtained with RXTE during the observation of 1997 February 26. We have fitted the features first by two Gaussian lines which in four spectra analysed have average energies of 5.85±0.08 and 7.32±0.13 keV, strongly suggestive that these are the red- and blueshifted wings of an iron disc line. These energies imply a velocity of ∼0.33 c . The blue wing is less bright than in the calculated profiles of disc lines near a black hole subject to Doppler boosting; however, known Fe absorption lines in GRO J1655–40 at energies between ∼7 and 8 keV can reduce the apparent brightness of the blue wing. Secondly, we have fitted the spectra using the disc line model of Laor based on a full relativistic treatment plus an absorption line, and show that good fits are obtained. This gives a rest-frame energy of the disc line between 6.4 and 6.8 keV, indicating that the line is iron K α emission probably of significantly ionized material. The Laor model shows that the line originates in a region of the accretion disc extending from ∼10 Schwarzschild radii from the black hole outwards. The line is direct evidence for the black hole nature of the compact object, and is the first discovery of a highly red- and blueshifted iron disc line in a Galactic source.     

An observational constraint on the existence of proto-superclusters at z =3.3

Observations have been conducted using the Ooty Radio Telescope in order to place constraints on the evolutionary scenario leading to the formation of the present day superclusters. The experiment attempted to detect 21 cm emission from massive neutral hydrogen condensates at a redshift ofz = 3.3. In an Einstein de-Sitter universe with baryon density Ω = 0.05, about ten condensates were expected in the volume surveyed if superclusters, having H I masses ≃5 × 10₁₅ M _⊙, were the first objects to separate out of the Hubble expansion. The sensitivity of our experiment rules out the existence of these condensates atz = 3.3 unless their lifetimes are less than one-tenth the dispersion in their epoch of formation or the proto-superclusters subtend angles greater than 6 arcmin. The result indicates that superclusters form at z > 3.3 if indeed they were the first objects to condense out of the Hubble flow. An erratum to this article is available at .     

A possible observational constraint on the production of lithium by galactic novae

Recent computations (D'Antona and Mazzitelli, 1982), together with the general scheme of evolution of cataclysmic binaries (CBs), lead to conclude that the secondaries in those CBs having periods shorter than 4.5 hr have a large³He content in the envelope, ranging from 10^–4 (P=4.5 hr) to >2×10^–3 (P=3 hr) in mass fraction, if the nova systems have an age of some billion years. The consequence on the frequency of novae outbursts is shortly examined. If lithium is produced by galactic novae, the⁷Li content of old disk stars should be very close to the Population II content.Presented at the 5th European Workshop on White Dwarfs, Kiel, 1984.     

Testing X-ray measurements of galaxy cluster gas mass fraction using the cosmic distance-duality relation

We propose a consistency test for some recent X-ray gas mass fraction(fgas) measurements in galaxy clusters, using the cosmic distance-duality relation, ηtheory = DL(1 + z) 2/DA, with luminosity distance(DL) data from the Union2 compilation of type Ia supernovae. We set ηtheory ≡1, instead of assigning any redshift parameterizations to it, and constrain the cosmological information preferred by fgasdata along with supernova observations. We adopt a new binning method in the reduction of the Union2 data, in order to minimize the statistical errors. Four data sets of X-ray gas mass fraction, which are reported by Allen et al.(two samples), LaRoque et al. and Ettori et al., are analyzed in detail in the context of two theoretical models of fgas. The results from the analysis of Allen et al.’s samples demonstrate the feasibility of our method. It is found that the preferred cosmology by LaRoque et al.’s sample is consistent with its reference cosmology within the 1σ confidence level. However, for Ettori et al.’s fgas sample, the inconsistency can reach more than a 3σ confidence level and this dataset shows special preference to an Λ = 0 cosmology.     

Study of the primary cosmic radiation mass composition near the “knee” from EAS data

A string-decay cascade phenomenological model that conservatively extrapolates accelerator data has been adapted to cosmic ray-air collisions. Monte Carlo simulations of extensive air showers (EAS) initiated by primary protons and nuclei have been performed. The best agreement between the predictions of this model and experimental data on spectra of electron sizes (N_e) for vertical incidence at different altitudes is found for a heavy mass composition of the cosmic rays (above the “knee” energy).     

Anisotropic universe and observational constraint on the dark energy models with the cosmological redshift drift

This study set out to examine the effect of anisotropy on the various dark energy models by using the observational data, including the Sandage-Loeb test, Strongly gravitationally lensing, observational Hubble data, and Baryon Acoustic Oscillations data. In particular, we consider three cases of dark energy models: the cosmological constant model, which is most favored by current observations, the wCDM model where dark energy is introduced with constant w equation of state parameter and in Chevalier-Polarski-Linder parametrization where ω is allowed to evolve with redshift. With an anisotropy framework, a maximum likelihood method to constrain the cosmological parameters was implemented. With an anisotropic universe, we also study the behavior of different cosmological parameters such as Hubble parameter, EoS parameter, and deceleration parameter of dark energy models mentioned. The results indicate that the Bianchi type I model for the dark energy models are consistent with the combined observational data.