Variability of the HeIλ5876 Å line in early type chemically peculiar stars. II

To try to understand the behavior of helium variability in Chemically Peculiar stars, we continued our on‐going observational campaign started by Catanzaro, Leone & Catalano (1999). In this paper we present a new set of time resolved spectroscopic observations of the HeI5876 Å line for a sample of 10 stars in the spectral range B3 ‐ A2 and characterized by different overabundances. This line does not show variability in two stars: HD77350 and HD175156. It shows instead an equivalent width variation in phase with the Hipparcos light curve for two stars: HD79158 and HD196502. Antiphase variations have been found in 4 stars of our sample, namely: HD35502, HD124224, HD129174 and HD142990. Nothing we can say about HD115735 because of the constancy of Hipparcos photometric data, while no phase relation has been observed for HD90044. In the text we discuss the case of HD175156, according to photometric calibration and our spectroscopic observations we rule out the membership of this star to the main sequence chemically peculiar stars. We confirm the results obtained in the previous paper for which phase relations between light, spectral and magnetic variations are not dependent on stellar spectral type or peculiarity subclass.     

Triviality of λϕ4 theory in 3+1-dimensional spatially flat Robertson-Walker space in Gaussian approximation

We investigate λϕ⁴ theory within the Gaussian approximation in spatially flat Robertson-Walker space in 3+1 dimensions. After having performed an adiabatic expansion for one of the ansatz functions we find that the renormalization of the energy-momentum tensor provides two additional constraints which have to be satisfied by bare couplings. These conditions force the theory to be trivial after renormalization.     

Iron abundance and microturbulence in Arcturus,Canopus, α Cen A,and Sun from FeI and FeII lines

The iron abundance and microturbulent velocities in Arcturus, Canopus, and α CenA have been determined from Fel and Fell lines relative to the Sun. α CenA is found to have an enhanced iron abundance, while Canopus and Arcturus are found to have a deficiency of iron. The behaviour of the determined microturbulent velocities is discussed.     

Formation of the FeI 5324.19 line in the sun and theoretical calibration of solar magnetic telescope

Using the Unno-Beckers equations and the Rnnge-Kutta method with variable steplength, we calculated the formation in a magnetic field of the FeI λ 5324.19 line in the solar photosphere, sunspot penumbra and umbra, and determined various theoretical calibration parameters for the magnetic and radial velocity fields. These parameters for the transverse and velocity fields have good linearity and stability and adequate sensitivity, making the line very suitable for the study of solar active regions. When observing the transverse field, the filter should best be placed 0.10 – 0.11 A away from the line centre. The calibration is rather complicated when magneto-optical effects are considered. Temperature sensitivity effects of this line should not be serious.     

The Diffuse λ 2200 Å Interstellar Absorption Band and the Abundances of Neutral Interstellar Hydrogen and Sodium

The equivalent width of the diffuse interstellar absorption band W₂₂₀₀ and the abundances of neutral interstellar hydrogen and sodium derived from the interstellar absorption lines in the spectra of hot stars are well correlated each other.     

Abundance analysis of the γ Doradus–δ Scuti hybrid metallic line (Am) star HD 8801

Low frequency oscillation, typical for γ Doradus g‐mode type stellar core sensitive pulsation, as well as higher frequency δ Scuti type pulsation typical for p ‐modes, sensitive to the envelope, make HD 8801 a remarkable hybrid pulsator with the potential to probe a stellar structure over a wide range of radius. In addition HD 8801 is a rare pulsating metallic line (Am) star. We determined the astro‐physical fundamental parameters to locate HD 8801 in the H‐R diagram. We analyzed the element abundances, paying close attention to the errors involved, and confirm the nature of HD 8801 as a metallic line (Am) star. We also determined an upper limit on the magnetic field strength. Our abundance analysis is based on classical techniques, but uses for the final step a model atmosphere calculated with the abundances determined by us. We also discuss spectropolarimetric observations obtained for HD 8801. This object is remarkable in several respects. It is a nonmagnetic metallic line (Am) star, pulsating simultaneously in p‐ and g‐modes, but also shows oscillations with periods in between these two domains, whose excitation requires explanation. Overall, the pulsational incidence in unevolved classical Am stars is believed to be quite low; HD 8801 does not conform to this picture. Finally, about 75 % of Am stars are located in short‐period binaries, but there is no evidence that HD 8801 has a companion. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The ever challenging emission‐line binary β Lyrae

A brief history of investigations of Lyr, an emission‐line binary and one of the first ever discovered Be stars is presented. A rather fast progress in the understanding of this enigmatic object during the past fifteen years is then discussed in some detail. The current picture of β Lyr is that it is an eclipsing binary in a stage of mass transfer between the components. The mass‐losing star is a B6‐8II object, with a mass of about 3 M_⊙, which is filling the Roche lobe and sending material towards its more massive companion at a rate of about 2 × 10^—5 M_⊙ yr^—1. This leads to the observed rapid increase of the orbital period at a rate of 19 s per year. The mass‐gaining star is as early B star with a mass of about 13 M_⊙. It is completely hidden inside an opaque accretion disk, jet‐like structures, perpendicular to the orbital plane and a light‐scattering halo above the poles of the star. The observed radiation of the disk corresponds to an effective temperature which is much lower than what would correspond to an early B star. The disk shields the radiation of the central star in the directions along the orbital plane and redistributes it in the directions perpendicular to it. That is why the mass‐losing star appears brighter of the two in the optical region of the spectrum. At present, rather reliable estimates of all basic properties of the binary and its components are available. However, in spite of great progress in understanding the system in recent years, some disagreement between the existing models and observed phase variations still remains, both for continuum and line spectrum, which deserves further effort.     

Altitude profiles of the photoelectron induced OD(λ6300Å) predawn enhancement by observation and theory

Emission profiles of the 6300Åline are determined from OGO 4 data in the dark ionosphere during conjugate sunrise. From Saint-Santin electron density profile measurements, it is shown that, for the two cases studied in December 1967, the recombination cannot account for the measured O¹D emission profiles. However, direct photoelectron-oxygen excitation can reproduce the data: if the photoelectron escape flux in the sunlit ionosphere, computed from standard photoelectron production, is transmitted through the field tube with an additional attenuation of 0.6 due to angular diffusion through photoelectron-electron and photoelectron-ion Coulomb collisions, the Hinteregger (1965) solar flux data must be increased by a factor 2, which agrees with previous results.     

A model of magnetically induced disc–corona for black hole binaries

We propose a model of magnetic connection (MC) of a black hole with its surrounding accretion disc based on large-scale magnetic field. The MC gives rise to transport of energy and angular momentum between the black hole and the disc, and the closed field lines pipe the hot matter evaporated from the disc, and shape it in the corona above the disc to form a magnetically induced disc–corona system, in which the corona has the same configuration as the large-scale magnetic field. We numerically solve the dynamic equations in the context of the Kerr metric, in which the large-scale magnetic field is determined by dynamo process and equipartition between magnetic pressure and gas pressure. Thus we can obtain a global solution rather than assuming the distribution of large-scale magnetic field beforehand. The main MC effects lie in three aspects. (1) The rotational energy of a fast-spinning black hole can be extracted, enhancing the dissipation in the accretion disc, (2) the closed field lines provide a natural channel for corona matter escaping from disc and finally falling into black hole and (3) the scope of the corona can be bounded by the conservation of magnetic flux. We simulate the high-energy spectra of this system by using Monte Carlo method, and find that the relative hardness of the spectra decreases as accretion rate or black hole spin a _* increases. We fit the typical X-ray spectra of three black hole binaries  (GRO J1655−40, XTE 1118+480 and GX 339−4)  in the low/hard or very high state.     

High‐pressure phase transitions of α‐quartz under nonhydrostatic dynamic conditions: A reconnaissance study at PETRA III

Hypervelocity collisions of solid bodies occur frequently in the solar system and affect rocks by shock waves and dynamic loading. A range of shock metamorphic effects and high‐pressure polymorphs in rock‐forming minerals are known from meteorites and terrestrial impact craters. Here, we investigate the formation of high‐pressure polymorphs of α‐quartz under dynamic and nonhydrostatic conditions and compare these disequilibrium states with those predicted by phase diagrams derived from static experiments under equilibrium conditions. We create highly dynamic conditions utilizing a mDAC and study the phase transformations in α‐quartz in situ by synchrotron powder X‐ray diffraction. Phase transitions of α‐quartz are studied at pressures up to 66.1 and different loading rates. At compression rates between 0.14 and 1.96 GPa s^?1, experiments reveal that α‐quartz is amorphized and partially converted to stishovite between 20.7 GPa and 28.0 GPa. Therefore, coesite is not formed as would be expected from equilibrium conditions. With the increasing compression rate, a slight increase in the transition pressure occurs. The experiments show that dynamic compression causes an instantaneous formation of structures consisting only of SiO₆ octahedra rather than the rearrangement of the SiO₄ tetrahedra to form a coesite. Although shock compression rates are orders of magnitude faster, a similar mechanism could operate in impact events.     

Velocity effects on the profiles of Hα and two FeI lines

Profiles are computed for Ha and two Fei lines for a differentially moving atmosphere. The results show that the profiles are asymmetric and that velocity measurements made in the Doppler cores will often lead to erroneous results when the velocity gradient is significant in the regions of the atmosphere where the core forms.The National Center for Atmospheric Research is sponsored by the National Science Foundation.     

The iron emission line complex of MCG‐5‐23‐16: the long XMMNewton look

We present the results of the simultaneous XMM‐Newton and Chandra observations of the bright Seyfert 1.9 galaxy MCG–5‐23‐16, which is one of the best known examples of a relativistically broadened iron Kα line. We find that: a) the soft X‐ray emission is likely to be dominated by photoionized gas, b) the complex iron emission line is best modelled with a narrow and a broad component with a FWHM ∼44000 km/s. This latter component has an EW ∼50 eV and its profile is well described with an emission line mainly originating from the accretion disk a few tens of gravitational radii from the central black hole and viewed with an inclination angle ∼40°. We found evidence of a possible sporadic absorption line at ∼7.7 keV which, if associated with Fe XXVI Kα resonance absorption, is indicative of a possible high velocity (v ∼ 0.1c) outflow. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

1–100 μm energy spectra and 2.3–4 μm spectrophotometry of MSC stars

The JHKL' photometry and 2.3–4 μm spectrophotometry of some M giants, S type stars and carbon stars are presented in this paper. It is found that in combination with IRAS data, the energy spectra in 1–100 μm of S type stars are intermediate between those of M giants and carbon stars, which are obviously different. The spectrophotometry in the near infrared shows that, besides carbon stars, which have HCN and C₂H₂ strong absorptions at 3.1 μm, some S type stars have the similar but weaker absorption in the same spectral region. However, no trace of any absorption at 3.1 μm can be seen in M giants. These results probably provide more evidence for the M-S-C sequence in the late stage of stellar evolution.     

CORA — emission line fitting with Maximum Likelihood

The advent of pipeline‐processed data both from space‐ and ground‐based observatories often disposes of the need of full‐fledged data reduction software with its associated steep learning curve. In many cases, a simple tool doing just one task, and doing it right, is all one wishes. In this spirit we introduce CORA, a line fitting tool based on the maximum likelihood technique, which has been developed for the analysis of emission line spectra with low count numbers and has successfully been used in several publications. CORA uses a rigorous application of Poisson statistics. From the assumption of Poissonian noise we derive the probability for a model of the emission line spectrum to represent the measured spectrum. The likelihood function is used as a criterion for optimizing the parameters of the theoretical spectrum and a fixed point equation is derived allowing an efficient way to obtain line fluxes. As an example we demonstrate the functionality of the program with an X‐ray spectrum of Capella obtained with the Low Energy Transmission Grating Spectrometer (LETGS) on board the Chandra observatory and choose the analysis of the Ne IX triplet around 13.5 Å.     

A near‐infrared/optical/X‐ray survey in the centre of σ Orionis

Because of the intense brightness of the OB‐type multiple star system σ Ori, the low‐mass stellar and substellar populations close to the centre of the very young σ Orionis cluster is poorly know. I present an IJHK_s survey in the cluster centre, able to detect from the massive early‐type stars down to cluster members below the deuterium burning mass limit. The near‐infrared and optical data have been complemented with X‐ray imaging. Ten objects have been found for the first time to display high‐energy emission. Previously known stars with clear spectroscopic youth indicators and/or X‐ray emission define a clear sequence in the I vs. I – K_s diagram. I have found six new candidate cluster members that follow this sequence. One of them, in the magnitude interval of the brown dwarfs in the cluster, displays X‐ray emission and a very red J – K_s colour, indicative of a disc. Other three low‐mass stars have excesses in the K_s band as well. The frequency of X‐ray emitters in the area is 80±20 %. The spatial density of stars is very high, of up to 1.6±0.1 arcmin^–2. There is no indication of lower abundance of substellar objects in the cluster centre. Finally, I also report two cluster stars with X‐ray emission located at only 8000–11000 AU to σ Ori AB, two sources with peculiar colours and an object with X‐ray emission and near‐infrared magnitudes similar to those of previously‐known substellar objects in the cluster. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Elemental abundance analyses with DAO spectrograms: XXXIII. β UMa (A0mA1 IV‐V), α Dra (A0 III), π Dra (A2 IIIs), and κ Cep (B9 III)

This paper presents extended analyses of β UMa (A0mA1 IV‐V), α Dra (A0 III), π Dra (A2 IIIs), and κ Cep (B9 III) which have previously been studied in this series. α Dra is a metal‐poor star while κ Cep has solar abundances. Both β UMa and π Dra are Am stars. Whenever possible, more accurate and precise gf values replace older values. High S/N (200+) and high dispersion Dominion Astrophysical Observatory spectrograms to the red of previously obtained spectra supplement the observations. The derived rotational velocities are 45, 25, 26, and 23 km s^–1, respectively. These LTE fine analyses use the ATLAS9 and the WIDTH9 programs of R. L. Kurucz. The results of the extended and the previous analyses are in good agreement. Thus in the past decade a significant improvement in the system of gf values has not been achieved although for many lines there have been changes. The use of additional regions has increased the quality of some results (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

A new γ-ray pulsar: PSR 0740-28

We made a period folding analysis on two sets of COS-B observations and obtained a clearly pulsed phase structure in the γ-ray photons from the direction of PSR 0740-28. The phase diagrams from the two different data sets have a similar structure and the period and period rate are close to radio expectations. The probability of the two phase structures arising by chance is less than 2×10⁻⁵. Hence we believe PSR 0740-28 is a new γ-ray pulsar.     

A propensity for n‐ω‐amino acids in thermally altered Antarctic meteorites

Abstract– Asteroids and their fragments have impacted the Earth for the last 4.5 Gyr. Carbonaceous meteorites are known to contain a wealth of indigenous organic molecules, including amino acids, which suggests that these meteorites could have been an important source of prebiotic organic material during the origins of life on Earth and possibly elsewhere. We report the detection of extraterrestrial amino acids in thermally altered type 3 CV and CO carbonaceous chondrites and ureilites recovered from Antarctica. The amino acid concentrations of the thirteen Antarctic meteorites ranged from 300 to 3200 parts‐per‐billion (ppb), generally much less abundant than in amino acid‐rich CI, CM, and CR carbonaceous chondrites that experienced much lower temperature aqueous alteration on their parent bodies. In contrast to low‐temperature aqueously altered meteorites that show complete structural diversity in amino acids formed predominantly by Strecker–cyanohydrin synthesis, the thermally altered meteorites studied here are dominated by small, straight‐chain, amine terminal (n‐ω‐amino) amino acids that are not consistent with Strecker formation. The carbon isotopic ratios of two extraterrestrial n‐ω‐amino acids measured in one of the CV chondrites (δ¹³C approximately ?25‰) are consistent with ¹³C‐depletions observed previously in hydrocarbons produced by Fischer‐Tropsch type reactions. The predominance of n‐ω‐amino acid isomers in thermally altered meteorites hints at cosmochemical mechanisms for the preferential formation and preservation of a small subset of the possible amino acids.     

Measuring ΩM and ΩΛ with long‐duration gamma‐ray bursts

Gamma‐ray bursts (GRBs) are one of the most luminous events in the Universe. In addition, the Universe itself is almost transparent to γ ‐rays, making GRBs detectable up to very high redshifts. As a result, GRBs are very suitable to probe the cosmological parameters. This work shows the potential of long‐duration GRBs for measuring the cosmological parameters Ω_M and Ω_Λ by comparing the observed log N ‐log P distribution with the theoretical one. Provided that the GRBs rate and luminosity function are well determined, the best values and 1σ confidence intervals obtained are Ω_M = 0.22^+0.05_–0.03 and Ω_Λ = 1.06^+0.05_–0.10. Finally, a set of simulations show the ability of the method to measure Ω_M and Ω_Λ (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)