A reexamination of the Gum nebula

A detailed analysis of interstellar measurements in the direction of the Gum nebula is carried out. The ionized region is shown to have an angular radius of 18° and appears to be bounded by a shell of neutral gas. The mean electron temperature deduced from radio-frequency absorption measurements is found to be 8500K. These parameters suggest that the nebula is the normal and possibly evolved Hii region of Pup and ² Vel, rather than the fossil Strömgren sphere of the Vela supernova as suggested by Brandtet al. (1971).     

Пульсар в краБе: замагниченные трещины в коре как ключ к механизмам истечения вещества, радио- и высокочастотного излучений

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A coronal loop model for the production of X-ray and radio flares in the RS CVn binary HR 1099

The RS CVn binary stellar system HR 1099 is a source of both X-ray and radio flares. We present here a model of the system in which the two types of flare are produced by the same population of mildly-relativistic ( 10) electrons, injected into a coronal loop. After reviewing possible radiation mechanisms we conclude that, given the probable conditions in the flaring region, the radio emission is gyrosynchrotron radiation and the X-ray emission is thermal bremsstrahlung. The thermal X-ray source must lie in the stellar chromosphere, but the apparent absence of plasma absorption at radio frequencies indicates that the radio source is located high in the coronal loop. Using the relationships given by Dulk and Marsh (1982) for the radio emission from a power-law electron energy spectrum,N() ( - 1)^–, we conclude that 3 7, with 30% of the electron population trapped in the radio source. Some implications of these results for one particular version of the model are discussed.     

Sub-arcsec 10 μm imaging of β pictoris and other star disk candidates

We have used the ESO 10 m camera, TIMMI, to image with a very high angular resolution (PFoV: 0.3; FWHM:0.9) several main-sequence star disk candidates. Information on the -Pictoris dust disk has been obtained in a region largely inaccessible to previous observations: 0–80 AU, with a resolution of about 5 AU after deconvolution. Another promising target for 10 m imaging, 51 Ophiuchi, appears point-like.based on data collected at the European Southern Observatory (ESO), La Silla, Chile     

Optical Identification of IRAS Point Sources. Galaxies. X

The tenth list of objects from the BIG (Byurakan-IRAS Galaxies) sample, containing 104 galaxies identified with 60 point sources from the IRAS PSC catalog, is introduced. The identifications have been made in the region +69°+73° and 09^h50^m15^h20^m with an area of 107 sq.deg. The identified objects include 13 Sy candidates, 5 compact star-formation galaxies, 11 interacting pairs (including 5 merger candidates) and 1 interacting triple system, 5 LSB galaxies, and 5 groups. 21 objects are also identified with radio sources. The optical coordinates, their deviations from the IR coordinates, V stellar magnitudes, morphological types, angular sizes of the central regions, and position angles have been determined. The identified galaxies are of Sa-Sc, SB, and Irr morphological types, the optical stellar magnitudes lie in the range 15^m.0-21^m.5, and the angular sizes of the central regions lie in the range 3-32. Finding charts from the DSS2 are included for these objects.     

A theory for gamma ray and X-ray burst sources

A common mechanism for both X-ray and-ray bursters is proposed on the basis that a window can be created transiently in the polar cap of a degenerate star, a white dwarf for X-ray bursts and a neutron star for-ray bursts. The window exposes transiently a hot degenerate sub-layer of the star at shallow depth, from which escapes blackbody flux for a source at temperature 3 kev with window radius 10 km in the case of X-ray bursts and for a source at temperature 300 kev with window radius 0.5 km in the case of-ray bursts.     

Diffuse galactic FUV radiation and interstellar dust grains

A re-analysis of the diffuse far UV radiation ( 1350–1480 Å) observed in the sky region ofl ^II180° and 0°b ^II40° is presented, as a revised version of a paper by Hayakawaet al. (1969). In comparison with the previous one, the value of the half optical depth of the Galazxy in our wavelength region is reduced, and the values of the albedo coefficient and the forward phase functiong are not well determined. If, however, we combine our results with the theoretical model of interstellar grains by Gilra, the value of is given by 0.13(5)0.18(5).     

Correlated type III burst emission from distant sources on the Sun

We report the observation and interpretation of a correlated type III burst emitted from distant sources on the Sun. The angular separation between the distant sources is as large as 26 or 10⁶ km. There was an active region 30° behind the limb, and it is believed that the type III burst emission originated from activity in this region. The implications of the locations of the correlated sources with regard to the geometry of the magnetic structures involved in the flare process are discussed.On leave from Indian Institute of Astrophysics, Kodaikanal, India.     

A high resolution mid-infrared image of the Starburst Galaxy M82

We have produced high-resolution images of the nuclear region of M82 with SpectroCam-10, a mid-infrared instrument at the Palomar 5 m telescope. These images were taken at 11.7 m and 9.8 m with a 1m filter bandpass at the diffraction limit of 0.6 arcsec, making them the highest resolution maps yet available of M82. In addition, we have obtained high-resolution (/=2000) maps of the velocity field of the nuclear disk of M82 in the 12.81 m line emission of [NeII]. In these proceedings we present the 11.7 m image, which will appear together with the 9.8 m map and the [Ne II] spectra in a subsequent paper, now in preparation. This image shows very clearly a bridge structure joining the eastern and western clusters.     

Eclipse Observations of Compact Sources in the Outer Solar Corona

We report here on high angular resolution observations of solar noise storm sources at a frequency of 75 MHz. The data for the study were obtained at the Gauribidanur Radio Observatory (long.: 77°2612 E, lat.: 13°3612 N) about 100 km north of Bangalore, India, during the solar eclipse of 24 October 1995. Our main conclusion is that there are structures of angular size 2.5 arc min in the outer solar corona.     

Models for optical and infrared polarization from CW1103+254

Multiband observations of the AM Herculis-type binary CW1103+254 show significant circular polarization (13%) in the J band. Recently, a model with high temperature (kT20 keV) and small dimensionless plasma parameter (10⁴) was suggested for the emitting region. However, it gives negligible polarization in the J band. In this paper, a method, in which the J band polarization and the peak frequency of the spectrum are taken into account, is used to determine T and . For the viewing angle =80° and the magnetic field B=30MG, we find that kT=5.0 keV and =10⁶. The temperature of the emitting region is close to the value (kT=8.7 keV) derived for the region emitting cyclotron lines in VV Puppis. If these radiations arise from the post-shock regions, then these temperatures are significantly lower than those predicted by standard accretion models or the shock structure is inhomogenous and more complex than previously assumed.Paper presented at the IAU Colloquium No. 93 on Cataclysmic Variables. Recent Multi-Frequency Observations and Theoretical Developments, held at Dr. Remeis-Sternwarte Bamberg, F.R.G., 16–19 June, 1986.     

A deeply embedded companion to LKHα198

The region around the Herbig Ae/Be star LkH198 was imaged at 10m with the CAMIRAS camera at the Canada-France-Hawaii Telescope and the Nordic Optical Telescope. We discovered a deeply embedded companion 6 north of LkH198, which may be responsible for most of the far-infrared emission in the region and for driving the molecular flow. LkH198 appears point-like at our resolution (FWHM 1.3), excluding an extended envelope of transiently heated small grains as the dominant origin of the mid-infrared excess in that star.     

Linearized limb-darkening coefficients for use in analysis of eclipsing binary light curves

Linear limb-darkening coefficientsu required in the analysis of eclipsing binary curves, are tabulated for a wide range of effective temperature (50 000° to 4000°), wavelength (0.2 2.2 ), and gravitiesg (2.0logg5.0). The computation is based on the comprehensive range of model atmospheres of Carbon and Gingerich (1969).The results are compared with the theoretical values of Hosokawa (1957), Kopal (1959) and Grygaret al. (1972), and examined in relation to empirically determined values ofu from analyses of eclipsing binary light curves. An improved agreement between theory and observation for the calculated limb-darkening coefficients of the present work is noted.     

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.     

Mid- and far-infrared extinction coefficients of hydrous silicate minerals

Extinction coefficients were measured for three kind of hydrous silicate minerals, montmorillonite, chlorite and serpentine, from 7 to 140 m. The infrared extinction coefficients of these minerals show (1) a few broad bands in the mid-infrared region and (2) a less steep wavelength-dependence in the far-infrared region, in contrast to those of high-temperature magnesium silicates. In the far-infrared region, montmorillonite shows a ^–0.8±0.1 dependence (, the wavelength) without any band structure, chlorite has a double maxima structure around 80 m, and serpentine shows a rather steep dependence with a small peak at 77 m.The changes of mid-infrared spectra by heating were measured. Change in chlorite spectrum is the most significant. Many fine features appear by heating and then they disappear. Above 900°C one broad feature remains around 10 m. Fine features of the montmorillonite spectrum disappear by heating. For serpentine, many new peaks appear and the spectrum resembles the spectrum of olivin. In near-infrared a band around 2.72 m disappears by heating.Extinction coefficients at very low temperatures were measured in the far-infrared region. For montmorillonite and serpentine, the spectrum is the same as that at room temperature. The double peaks of chlorite around 80 m become higher.     

The Hard X-ray Imaging Spectrometer (HXIS)

The HXIS, a joint instrument of the Space Research Laboratory at Utrecht, The Netherlands, and the Department of Space Research of the University of Birmingham, U.K., images the Sun in hard X-rays: Six energy bands in energy range 3.5–30 keV, spatial resolution 8 over Ø 240 and 32 over Ø 624 field of view, and time resolution of 0.5–7 s depending on the mode of operation. By means of a flare flag it alerts all the other SMM instruments when a flare sets in and informs them about the location of the X-ray emission. The experiment should yield information about the position, extension and spectrum of the hard X-ray bursts in flares, their relation to the magnetic field structure and to the quasi-thermal soft X-rays, and about the characteristics and development of type IV electron clouds above flare regions.     

Relativistic Beaming and Orientation Effects in Lobe-Dominated Quasars

We examine a simple statistical consequence of relativistic beaming model using the core-to-lobe flux density ratio (R) and projected linear size (D) as orientation indicators. It is shown that the observed R-D intercept for the 3CRR source sample provides values of the bulk Lorentz factor () which are consistent with the beaming scenario. The result also shows that if the lobe-dominated quasars are to be unified with the core-dominated quasars, they should be oriented at a median angle, _{_med} 40° with respect to the line of sight, but if with powerful radio galaxies, then _{_med} 24°. Application of this result to the quasar-galaxy unification scheme using the observed angular size-redshift relation shows that the scheme is consistent with the observed data.     

B,V surface photometry of the UV continuum galaxy NGC 838

Surface photometry of the UV continuum galaxy NGC 838 has been carried out in theB, V system using photographic plates obtained with the 74 Kottamia telescope, Egypt. Isophotes, luminosity profiles, integrated photographic magnitudes, effective diameters and other photometric parameters are derived.The photoelectrically calibrated total apparent magnitudes areB _T =13.57 with maximum diameters 1.57×1.34 (at threshold _m =27.7 mag.//) andV _T =12.91 with maximum diameters 1.54×1.32 (at threshold _m =27.7 mag./). The integrated colour index(B–V) _T =0.66 and the effective surface brightness _e (B=19.0 mag./) and _e (V=19.7 mag./. The major axis is at position angle =85°±1°.The nucleus of NGC 838 is quite blue (integrated colour(B–V)=0.41 forr ^*<0.1) compared to normal galaxies while the colour becomes redder from the nucleus outwards. The UV excess, H emission and radio continuum emission previously observed from this galaxy by other investigators may be attributed to a recent burst of star formation in the nucleus of the galaxy of duration slightly greater than 2×10⁷ yr.     

Взаимооействие Излучения Рентгеновскооо Истооника с АтмосФерой Нормальной Звезды в Тесных Двойных Системах

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Optical Identifications of IRAS Point Sources. Galaxies. VII

A seventh list of objects from the BIG (Byurakan-IRAS galaxies) sample is given: 95 galaxies identified with 63 point sources from the IRAS Point Source Catalog. The identifications were based on the Digital Sky Survey (DSS), the First Byurakan Survey, blue and red maps from the Palomar Observatory Sky Survey, and infrared fluxes at 12, 25, 60, and 100 m in the region of +65° 69° and 14^h00^m 18^h05^m with an area of 96 deg². For the identified galaxies the optical coordinates, their departures from the IR coordinates, the stellar V magnitudes, morphological types, angular sizes, and position angles were determined. The objects have optical magnitudes in the range of 13 ^m .8-21 ^m .5 and angular sizes in the range of 4-38. Finder charts from the DSS are given for these objects.