Treatment of star catalog biases in asteroid astrometric observations

In this paper, we discuss the detection of systematic biases in star positions of the USNO A1.0, A2.0, and B1.0 catalogs, as deduced from the residuals of numbered asteroid observations. We present a technique for the removal of these biases, and validate this technique by illustrating the resulting improvements in numbered asteroid residuals, and by establishing that debiased orbits predict omitted observations more accurately than do orbits derived from non-debiased observations. We also illustrate the benefits of debiasing to high-precision astrometric applications such as asteroid mass determination and collision analysis, including a refined prediction of the impact probability of 99942 Apophis. Specifically, we find the IP of Apophis to be lowered by nearly an order of magnitude to 4.5 × 10⁻⁶ for the 2036 close approach.     

Anisotropy of the space orientation of radio sources. I: The catalog

A catalog of extended extragalactic radio sources consisting of 10461 objects is compiled based on the list of radio sources of the FIRST survey. A total of 1801 objects are identified with galaxies and quasars of the SDSS survey and the Veron-Veron catalog. The distribution of position angles of the axes of radio sources from the catalog is determined, and the probability that this distribution is equiprobable is shown to be less than 10⁻⁷. This result implies that at Z equal to or smaller than 0.5, the spatial orientation of the axes of radio sources is anisotropic at a statistically significant level.     

Analysis of A0–A2 star counts based on the SAO catalog

Rostov Pedagogical Institute. Translated from Astrofizika, Vol. 30, No. 3, pp. 495–508, May–June, 1989.     

A compiled catalog of rotation measures of radio point sources

We compiled a catalog of Faraday rotation measures(RMs) for 4553 extragalactic radio point sources published in literature. These RMs were derived from multi-frequency polarization observations. The RM data are compared to those in the NRAO VLA Sky Survey(NVSS) RM catalog. We reveal a systematic uncertainty of about 10.0 ± 1.5 rad m-2in the NVSS RM catalog. The Galactic foreground RM is calculated through a weighted averaging method by using the compiled RM catalog together with the NVSS RM catalog,with careful consideration of uncertainties in the RM data. The data from the catalog and the interface for the Galactic foreground RM calculations are publicly available on the webpage: http://zmtt.bao.ac.cn/RM/.     

The new helium-weak star HR 446

The CP star HR 446 (HD 9531, B8p V,m=5.69) is one of the CP stars with no definitely assigned peculiarity type. In this contribution it is shown by application of the synthetic spectra, that the star is a helium-weak type of the titanium-strontium subgroup. Photometric observations confirmed the rotational period of 0.6684 d discovered earlier. Our photometric observations do not permit to find rapid variability exceeding 0.005 mag within the limits of 5–300 min.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.     

Dense star clusters as the sources of gamma-ray-burst progenitors

Two independent sets of arguments lead us to conclude that the progenitors of superintense bursts (with an energy yield larger than that for ordinary supernovae by one or two orders of magnitude) are born in massive dense star clusters, but generally flare up only after they have left the cluster; these are the same objects that are the progenitors of gamma-ray bursts (GRBs). Each of the giant stellar arcs which are grouped into multiple systems of stellar complexes in the LMC and NGC 6946 could only be produced by a single powerful energy release near its center. The progenitors of these systems of arc-shaped stellar complexes must have had a common source nearby, and it could only be a massive star cluster. Such clusters are actually known near both systems. On the other hand, calculations of the dynamical evolution of star clusters show that close binary systems of compact objects are formed in the dense central parts of the clusters and are then ejected from them during triple encounters. Mergers of the components of such systems are believed to be responsible for GRBs. Since their progenitors are ejected from the cluster before merging, the arc-shaped stellar complexes produced by GRBs are observed near (but not around) the parent clusters. If a considerable fraction of the GRB progenitors are formed as a result star encounters in massive star clusters, and if the GRBs themselves trigger star formation near the parent clusters, then observations of GRBs in star-forming regions are consistent with their origin during mergers of pairs of compact objects.     

Hard X-ray survey of the Galactic plane region in Crux: A catalog of sources

This paper belongs to a series of papers devoted to a hard X-ray survey of the sky. We analyze a large set of observations of the Galactic plane region in Crux with the IBIS telescope onboard the INTEGRAL observatory. We have detected 47 sources. There are 12 active galactic nuclei and 11 and 6 galactic binary systems with high-mass and low-mass optical companions, respectively, among the identified objects. Thirteen objects remain unidentified.     

Investigating statistical and spectral characteristics of the radio sources from the RadioAstron catalog at millimetric wavelengths

We consider some statistical characteristics of radio sources at 22 GHz in the framework of the preparatory works on the RadioAstron space mission. The expected density of radio sources with inverted spectra is estimated. Based on the observations of the radio sources from the preliminary RadioAstron sample, we compare the expected and measured angular densities of the radio sources with inverted spectra. The optical characteristics of the objects with inverted spectra and of the sources from the complete sample are compared as well. We present some spectral parameters of the radio sources observed at two different frequencies. Some conclusions about the completeness and reliability of the preliminary RadioAstron catalog are made.     

The birth of a planetary nebula around the carbon star IRC+10216

Our current understanding of the evolution of solar-type stars suggests that after a period as a red giant star, during which mass loss occurs continuously in the form of a stellar wind, a period of intense mass loss known as a superwind occurs, during which a significant fraction of the envelope of the star is ejected into space, forming the material from which a planetary nebula (PN) will be constructed. It has been suggested that this superwind ejects material from the star in a toroidal or disc-like fashion, rather than isotropically. Here we present Hubble Space Telescope optical images of a toroidal superwind caught in the act: our images of the carbon star IRC+10216, which is believed to be in the final stages of red giant evolution, show that most of its optical emission is a bipolar reflection nebula. We show that the full spectral energy distribution and these images can be modelled as an equatorially enhanced dusty superwind, providing the first direct observational support for the toroidal superwind model, and supporting the 'interacting winds' model of PN formation.     

Spectroscopic study of the supergiant star 6 Cassiopeiae

Twenty-five coudé spectrograms (22 with dispersion 12 Å mm^–1 and three 7 Å mm^–1) of 6 Cassiopeiae (A3 Ia) have been studied. The observations were made at the Haute Provence Observatory. The results of the analysis suggest a correlation between the variations of the equivalent widths, the microturbulence and the radial velocity. The radial velocity and turbulent velocity present a rapid variation with time, even in intervals as short as about an hour. The hydrogen lines are slightly asymmetric but the strongest Feii lines are clearly asymmetric. We found that the amount of asymmetry of the strongest Feii lines (I>6) correlates with the loggf value, with the estimated laboratory intensityI, and with the equivalent widthW .The observations have been made at the Astronomical Observatory of Haute Provence (CNRS). This work has been supported by TUBITAK (Scientific and Technical Research Council of Turkey), and partially by CNR (Consiglio Nazionale delle Ricerche) of Italy.     

The exceptional Herbig Ae star HD 101412: The first detection of resolved magnetically split lines and the presence of chemical spots in a Herbig star

In our previous search for magnetic fields in Herbig Ae stars, we pointed out that HD 101412 possesses the strongest magnetic field among the Herbig Ae stars and hence is of special interest for follow‐up studies of magnetism among young pre‐main‐sequence stars. We obtained high‐resolution, high signal‐to‐noise UVES and a few lower quality HARPS spectra revealing the presence of resolved magnetically split lines. HD 101412 is the first Herbig Ae star for which the rotational Doppler effect was found to be small in comparison to the magnetic splitting and several spectral lines observed in unpolarized light at high dispersion are resolved into magnetically split components. The measured mean magnetic field modulus varies from 2.5 to 3.5kG, while the mean quadratic field was found to vary in the range of 3.5 to 4.8 kG. To determine the period of variations, we used radial velocity, equivalent width, line width, and line asymmetry measurements of variable spectral lines of several elements, as well as magnetic field measurements. The period determination was done using the Lomb‐Scargle method. The most pronounced variability was detected for spectral lines of He I and the iron peak elements, whereas the spectral lines of CNO elements are only slightly variable. From spectral variations and magnetic field measurements we derived a potential rotation period P_rot = 13.86 d, which has to be proven in future studies with a larger number of observations. It is the first time that the presence of element spots is detected on the surface of a Herbig Ae/Be star. Our previous study of Herbig Ae stars revealed a trend towards stronger magnetic fields for younger Herbig Ae stars, confirmed by statistical tests. This is in contrast to a few other (non‐statistical) studies claiming that magnetic Herbig Ae stars are progenitors of the magnetic Ap stars. New developments in MHD theory show that the measured magnetic field strengths are compatible with a current‐driven instability of toroidal fields generated by differential rotation in the stellar interior. This explanation for magnetic intermediate‐mass stars could be an alternative to a frozen‐in fossil field (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Magnetic field and chemical composition of the peculiar star HD 10221

We analyzed the chemical composition of the chemically peculiar (CP) star HD 0221=43 Cas using spectra taken with the NES spectrograph of the 6-m telescope with a spectral resolution of 45 000. The Hβ line profile corresponds most closely to T_eff = 11 900 K and log g = 3.9. The rotational velocity is v_e sin i = 27 ± 2 km s^?1, and the microturbulence is ξ_t = 1 km s^?1. The results of our abundance determination by the method of synthetic spectra show that the star has chemical anomalies typical of SrCrEu stars, although its effective magnetic field is weak, B_e < 100 G. For silicon, we obtained an abundance distribution in atmospheric depth with a sharp jump of 1.5 dex at an optical depth of log τ₅₀₀₀ = ?0.3 and with silicon concentration in deep atmospheric layers. Similar distributions were found in the atmospheres of cooler stars with strong and weak magnetic fields. A comparison of the chemical peculiarities in HD 10221 with known CP stars with magnetic fields of various strengths leads us to conclude that a low rotational velocity rather than amagnetic field is the determining factor in the formation mechanism of chemical anomalies in the atmospheres of CP stars.     

The FORS Deep Field: the photometric catalog

The FORS Deep Field project is a multi-colour, multi-object spectroscopical investigation of a ∼ 7′ × ′' region near the south galactic pole based mostly on observations carried out with the FORS instruments attached to the VLT telescopes. It includes the QSO Q 0103-260 (z = 3.36). The goal of this study is to improve our understanding of the formation and evolution of galaxies in the young Universe. In this contribution, the photometric observations are presented. In particular, a combined B and I selected UBgRIJKs photometric catalog of 8753 objects in the FDF is presented and its content is briefly described. The formal 50% completeness limits for point sources, derived from the coadded images, are 25.64, 27.69, 26.86, 26.68, 26.37, 23.60 and 21.57in U, B, g, R, I, J and Ks, respectively. This revised version was published online in August 2006 with corrections to the Cover Date.