The evolution from visible to infrared variable AGB stars

Results of the Vassiliadis and Wood (1993) model for the evolution on the AGB are used to study how DENIS can complement an optical and IRAS based study of Long Period Variable AGB stars in a field towards the galactic bulge.     

Stellar sources in the isogal inner galactic bulge field (l=0°,b= − 1°)

ISOGAL is a survey at 7 and 15 μm with ISOCAM of the inner galactic disk and bulge of our Galaxy. The survey covers ∼ 22 deg² in selected areas of the centrall = ±30 degree of the inner Galaxy. In this paper, we report the study of a small ISOGAL field in the inner galactic bulge (l = 0°,b = −1°, area = 0.033deg²). Using the multicolor nearinfrared data (IJK_s) of DENIS (DEep Near Infrared Southern Sky Survey) and mid-infrared ISOGAL data, we discuss the nature of the ISOGAL sources. The various color-color and color-magnitude diagrams are discussed in the paper. While most of the detected sources are red giants (RGB tip stars), a few of them show an excess in J-K_s and K_s-[15] colors with respect to the red giant sequence. Most of them are probably AGB stars with large mass-loss rates.     

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.     

Reconstruction of the direction of the true anisotropy of galactic cosmic rays

A method of reconstructing the declination of galactic cosmic ray anisotropy is described, and its results are presented. The method is based on analysis of delay distributions in symmetrically arranged detectors of an air shower array, and it represents a modification of the crossed telescopes method. It is shown that the declination of the true anisotropy vector is close to 60° (i.e., this vector lies approximately within the galactic plane). Because of this, the true degree of anisotropy of galactic cosmic rays is severalfold higher than the first harmonic of intensity in the sidereal time (the quantity measured directly), and it equals about 0.2%.     

Carbon stars in infrared surveys

In order to prepare the analysis of the forthcoming near-IR surveys (DENIS, 2MASS) and to interpret them in terms of galactic structure and AGB evolution, we present model predictions of AGB distributions in K, in 12m and in (J-K, [12–25]) space, as they will be obtained from these surveys, cross-correlated with IRAS Catalog. The simulations have been made by adding the AGB to the Besançon model.     

Galaxy candidates in the Zone of Avoidance

Motivated by recent discoveries of nearby galaxies in the Zone of Avoidance (ZOA), we conducted a pilot study of galaxy candidates at low galactic latitude, near galactic longitude l  ∼ 135°, where the Supergalactic plane is crossed by the Galactic plane. We observed with the 1-m Wise Observatory in the l band 17 of the 'promising' candidates identified by visual examination of Palomar red plates by Hau et al. A few candidates were also observed in R or B bands, or had spectroscopic observations performed at the Isaac Newton Telescope and at the Wise Observatory. Our study suggests that there are probably 10 galaxies in this sample. We also identify a probable planetary nebula. The final confirmation of the nature of these sources must await the availability of full spectroscopic information. The success rate of ∼ 50 per cent in identifying galaxies at galactic latitude | b | < 5° indicates that the ZOA is a promising region to discover new galaxies.     

ME／EXOSAT银道扫描数据的直接解调成像

利用对象重建的直接解调方法，我们对EXOSAT卫星ME探测器银道扫描观测数据进行了重新分析，研究了在以往的分析中难以分辨的几个天区中的分立X射线源．利用Bootstrap方法，我们对成像结果进行了统计误差分析，给出了点源位置和流强的误差．     

A systematic cross-search for radio/infrared counterparts of XMM-<Emphasis Type="Italic">Newton</Emphasis> sources

We present a catalog of cross-correlated radio, infrared and X-ray sources using a very restrictive selection criteria with an IDL-based code developed by us. The significance of the observed coincidences was evaluated through Monte Carlo simulations of synthetic sources following a well-tested protocol. We found 3320 coincident radio/X-ray sources with a high statistical significance characterized by the sum of error-weighted coordinate differences. For 997 of them, 2MASS counterparts were found. The percentage of chance coincidences is less than 1%. X-ray hardness ratios of well-known populations of objects were used to provide a crude representation of their X-ray spectrum and to make a preliminary diagnosis of the possible nature of unidentified X-ray sources. The results support the fact that the X-ray sky is largely dominated by Active Galactic Nuclei at high galactic latitudes (|b|≥10°). At low galactic latitudes (|b|≤10°) most of unidentified X-ray sources (∼94%) lie at |b|≤2°. This result suggests that most of the unidentified sources found toward the Milky Way plane are galactic objects. Well-known and unidentified sources were classified in different tables with their corresponding radio/infrared and X-ray properties. These tables are intended as a useful tool for researchers interested in particular identifications.     

Infrared studies of X-ray sources

A detailed study of the infrared radiation from galactic X-ray sources indicates that the galactic bulge sources and X-ray binary sources have different infrared emission characteristics. The galactic bulge sources seem to show a power law dependence between the X-ray flux and the infrared flux emitted by the X-ray source. The results presented suggests that the infrared radiation in the galactic bulge sources is dominated by free-free radiation and, in the case of eclipsing binary sources, the black-body emission from the early-type companion star contributes significantly to the infrared radiation.     

Sweeping-out of dust from spiral galaxy as a result of “magnetic sling” effect

A new mechanism of sweeping out of dust grains beyond galactic disks both in the radial direction along the galactic plane and in the vertical, cross-disk direction is proposed. The mechanism is driven by the interaction of dust grains with the bisymmetric nonstationary magnetic field of the galaxy, whose lines are curved and corotate with the stellar spiral density wave responsible for the arms. We attribute the radial transfer of interstellar dust grains in the plane of galactic disks to the fact that charged dust grains are “glued” to magnetic field lines and are therefore pushed outward because of the rotation of magnetic field lines and their tilt with respect to the radial direction parallel to the disk plane. In addition, dust is swept out vertically in the cross-disk direction because of the drift motion in crossed magnetic and gravitational fields (both are parallel to the galactic plane). Numerical computations of the motion of dust grains in real magneto-gravitational fields with the allowance for the drag force from interstellar gas show that the time scale of dust grain transport beyond galactic disks is on the order of 1 Gyr or shorter.     

The distribution of infrared sources in the galactic plane

A study of the galactic structure has been made by deriving the brightness distribution of the galactic plane at 2.2 m and 4.2 m near infrared region using infrared objects detected by ground-based sky surveys. The infrared brightness distribution shows distinct peaks at every 8–12° galactic longitude and indicates a periodic structure. The one-to-one positional correlation observed between the periodic structure in 2.2 m infrared brightness and the 2.6 mm CO emission line suggests that the near-infrared sources are strongly associated with dense clouds of molecular hydrogen distributed in the galactic plane.     

WSRT observations of radio sources in the galactic plane near l =54°

A radio continuum map of a 1°5 X 1°5 region in the galactic plane nearl = 54° is presented at 49 cm with a resolution of 100 arcsec X 200 arcsec. The shell source G 54.4 - 0.3 has the characteristics of a supernova remnant while the second large ring structure G 53.9 + 0.3 is a Hn ring consisting of W 52 and several small-diameter thermal sources. One of the twelve small-diameter sources (G 54.73 + 0.61) has a spectral index⇏ -1.6.     

The inner Galaxy resolved at IJK using DENIS data

We present the analysis of three-colour optical/near-infrared images, in IJK , taken for the DEep Near Infrared Southern Sky Survey (DENIS) project. The region considered covers 17.4 deg² and lies within <5°, b <1.°5. The adopted methods for deriving photometry and astrometry in these crowded images, together with an analysis of the deficiencies nevertheless remaining, are presented. The numbers of objects extracted in I , J and K are 748 000, 851 000 and 659 000 respectively, to magnitude limits of 17, 15 and 13. Eighty per cent completeness levels typically fall at magnitudes 16, 13 and 10 respectively, fainter by about 2 mag than the usual DENIS limits as a result of the crowded nature of these fields. A simple model to describe the disc contribution to the number counts is constructed, and parameters for the dust layer are derived. We find that a formal fit of parameters for the dust plane, from these data in limited directions, gives a scalelength and scaleheight of 3.4±1.0 kpc and 40±5 pc respectively, and a solar position 14.0±2.5 pc below the plane. This latter value is likely to be affected by localized dust asymmetries. We convolve a detailed model of the systematic and random errors in the photometry with a simple model of the Galactic disc and dust distribution to simulate expected colourmagnitude diagrams. These are in good agreement with the observed diagrams, allowing us to isolate those stars from the inner disc and bulge. After correcting for local dust-induced asymmetries, we find evidence for longitude-dependent asymmetries in the distant J and K sources, consistent with the general predictions of some Galactic bar models. We consider complementary L -band observations in the companion paper.     

Theories of gamma-ray burst sources

A review of recent theoretical work on gamma-ray bursts is given. The emphasis is put on the localization of sources. It is concluded that sources of gamma-ray bursts must be either old Population I or Population II objects with a mechanism implying that the sources are not too far from the galactic plane. According to this conclusion the more relevant models are probably flare stars or accretion on old neutron stars, radiation of the gravitational energy of the accretion, or thermonuclear explosions.Paper presented at the Symposium on Cosmic Gamma-Ray Bursts, held at Toulouse, France, 26–29 November, 1979.     

The warping of the galactic plane and changes of ellipticity

Observational evidence on the widespread occurrence of warping of the outer part of the galactic plane in many galaxies is presented and various hypotheses for its explanation are reviewed. None is found to be able to account for all the cases reported. Other phenomena considered are: (1) deviations from the galactic plane in the innermost nuclear region; (2) differences in orientation of the nucleus and disk in spiral galaxies; (3) changing ellipticity with distance from the center.After discussing the observations available, a theory has been developed which explains the phenomena mentioned as natural consequences of the non-steady nature of galactic systems due to time-dependent metric. This manifests itself in the appearance of tangential acceleration which leads necessarily to variability of the orbital plane and orbital eccentricity in dependence on the radius vector of the orbits.     

Further observations of radio sources from the BG survey. II. Mainly extragalactic

New observations of six fields from the low galactic latitude BG survey are presented. The radio sources within each of these fields appear to be of a predominantly extragalactic nature. However, one object is in close positional proximity to the pulsar 1922 + 20 and the possibility of their association is considered. The extended source BGE 0323 + 65 is shown to be unlikely to exist.     

Young Close-By Neutron Stars: The Gould Belt Vs. The Galactic Disc

We present new population synthesis calculations of close young neutron stars. In comparison with our previous investigation we use a different neutron star mass spectrum and different initial spatial and velocity distributions. The results confirm that most of ROSAT dim radioquiet isolated neutron stars had their origin in the Gould Belt. We predict that about several tens of young neutron stars can be identified in ROSAT All Sky Survey data at low galactic latitudes. Some of these sources also can have counterparts among EGRET unidentified sources.     

X-ray sources and the diffuse background

Possible numbers of X-ray sources at various flux levels are considered and their contribution to the background evaluated. Our conclusions are: The mean spectrum of Quasi-Stellar Objects and the nuclei of Seyfert galaxies between optical and X-ray wavelengths is characterized by a spectral index well in excess of 1.0. These objects may make an important contribution to the soft X-ray background. Observations of Q.S.O. may allow a decisive test for the cosmological interpretation of the redshifts of the Q.S.O. With regard to galactic sources we find that few undetected sources of the Sgr-Sco type exist, that these sources are located in the immediate neighborhood of the galactic center and that they account for at least 80% of the total galactic source luminosity. However, many intrinsically much fainter galactic sources may exist.     

The efficiency of gravitational diffusion for the separation of elements in the prestellar gas

The gravitational separation of iron atoms with respect to hydrogen is evaluated by simple models of globular clusters and spherical galaxies before star formation, as well as in a column of gas perpendicular to the galactic plane in the solar neighborhood. The changes of the iron abundance are small, but qualitatively consistent with the observed facts: (1) there is a positive correlation between the mass number of the element and the steepness of its abundance gradient; (2) there is a connection between the mass and the density concentration of the globular clusters and their chemical composition; (3) the changes of the chemical content in the galactic plane are very small during the life of the galactic disk, but are increasingly significant in the upper layers.     

The luminosity function of low-mass X-ray binaries in galaxies

The X-ray luminosity function of low-mass binaries constructed from the observations of point like X-ray sources in galactic bulges can be explained in terms of the main evolutionary relations for the rate of mass transfer onto a compact object. The observed scatter of luminosities for individual low-mass X-ray sources in our Galaxy is shown to be satisfactorily described by a symmetric quasi-Lorentz curve with a dispersion proportional to the mean luminosity. Such a form of the mean luminosity function for individual sources does not affect the power-law pattern of the luminosity function for the entire population of sources that is expected for a power-law dependence of the mass transfer rate in a close binary on the mass of the Roche lobe—filling optical component.