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Water-Vapor Maser Survey for Active Galactic Nuclei: A Megamaser in NGC 6926
We made a survey of water-vapor maser emission for 93 AGNs with theNobeyama 45-m and Mopra 22-m telescopes from 1999 to 2002. A megamaserwas detected in a Seyfert 2 galaxy, NGC 6926, at a distance of 80Mpc, in2002 June. [Greenhill et al. (2003a) have also reported a detection ofthe megamaser at the close date.] The peak flux density was 110mJy, andthe total isotropic luminosity was 340 Lȯ. The masershows triply peaked spectrum, suggesting an edge-on disk. A narrow-linefeature of the maser components at VLSR = 6001 kms-1 was strongly variable with a time scale of a few tens ofdays, and the variation should be of intrinsic origin. We also showed apossibility of variability of water-vapor maser emission of a megamaserpreviously detected in a Seyfert/ultraluminous FIR galaxy, NGC 6240.
| Radio emission from AGN detected by the VLA FIRST survey
Using the most recent (April 2003) version of the VLA FIRST survey radiocatalog, we have searched for radio emission from >2800 AGN takenfrom the most recent (2001) version of the Veron-Cetty and Veron AGNcatalog. These AGN lie in the 9033 square degrees of sky alreadycovered by the VLA FIRST survey. Our work has resulted in positivedetection of radio emission from 775 AGN of which 214 are new detectionsat radio wavelengths.Tables 3 and 4 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/416/35
| Arcsecond Positions of UGC Galaxies
We present accurate B1950 and J2000 positions for all confirmed galaxiesin the Uppsala General Catalog (UGC). The positions were measuredvisually from Digitized Sky Survey images with rms uncertaintiesσ<=[(1.2")2+(θ/100)2]1/2,where θ is the major-axis diameter. We compared each galaxymeasured with the original UGC description to ensure high reliability.The full position list is available in the electronic version only.
| On the Evolution of Low-Mass X-Ray Binaries under the Influence of a Donor Stellar Wind Induced by X-Rays from the Accretor
In a low-mass X-ray binary (LMXB), an intense stellar wind from the massdonor may be a consequence of the absorption of X-rays from themass-accreting neutron star or black hole, and such a wind could changethe evolution of these binaries dramatically compared with the evolutionof cataclysmic variables (CVs), which are close binaries in which theaccretor is a white dwarf. An analytical study and numerical models showthat, in the closest and brightest LMXBs, a relativistic companion cancapture up to ~10% of the mass lost in the induced stellar wind (ISW)from the main-sequence or subgiant donor, and this is enough to keep theX-ray luminosity of a typical LMXB on the level of LX ~ 5000 Lȯ andto accelerate the rotation of an old neutron star with a low magneticfield into the millisecond-period range. A self-sustained ISW may existeven if the donor does not fill its Roche lobe, but the system can bebright (LX > 100 Lȯ) only if the radius of the donor is asubstantial fraction (>~0.8) of the Roche lobe radius. A lower limiton the Roche lobe filling factor follows from the circumstance that boththe rate E dot _{{wind}} at which work must be done to lift wind matteroff the donor and the rate E dot _{{abs}} at which the donor absorbsX-ray energy are proportional to M dot _{{ISW}} (the ISW mass-loss rate)and from the requirement that E dot _{{wind}} 3hr. In Algol-like LMXBs in the Galactic disk, the timescale for theevaporation (caused by the ISW) of the donor with a low-mass, degeneratehelium core can be smaller than the timescale for the radial expansionof the donor owing to nuclear evolution, and the donor may never fillits Roche lobe. However, if progenitor binaries are initially wideenough, the donor may escape evaporation as a main-sequence star, andsignificant mass transfer may not occur until the secondary evolves intoa giant with a degenerate helium core of large mass and fills its Rochelobe. In globular clusters, as a result of capture and exchangereactions, semidetached Algol-like LMXBs can be formed in which thedonor can fill its Roche lobe even when its degenerate helium core is ofsmall mass, and Roche lobe mediated mass transfer driven by the nuclearevolution of the donor can dominate over capture from the ISW. Thenumerical models formally imply the possible presence in the Galaxy of~104 dim (LX ~ 1--100 Lȯ), long-period LMXBs or radio pulsars withlow-mass (~0.05 Mȯ) companions. Since there are few, if any, knownobservational counterparts of these systems, it is necessary to invoke amechanism or mechanisms to destroy their formal progenitors. Possibledestruction mechanisms include: (1) evaporation driven by the radiationfrom the rapidly rotating pulsar into which the accretor has beentransformed by accretion during the bright LMXB phase, and (2) adynamical instability arising when the donor is almost completelyconvective and fills its Roche lobe. In the case of dynamicaldisruption, the donor may be transformed into the envelope of aThorne-Zytkow (1975) object with a neutron star or black hole core orinto a planet-forming disk around the neutron star or black hole. A fewshort-period (Porb < 3 hr) LMXBs do exist, and, in them, the donormay be a helium white dwarf of mass less than ~0.09 Mȯ. An ISWoperating before the donor fills its Roche lobe may be responsible forreducing the mass of the white dwarf from an initial value of >=0.13Mȯ to a value of <=0.09 Mȯ, thus permitting stable massexchange (at a rate smaller than the Eddington limiting rate) andevolution to longer periods to occur after the donor fills its Rochelobe. Another scenario relies on the collapse of a massive oxygen-neonwhite dwarf, which has accreted from a Roche lobe filling helium whitedwarf. Problems that must be explored further in order to acquire abetter understanding of the evolution of LMXBs include the formation ofa corona around an irradiated low-mass main-sequence or degenerate dwarfstar, accretion of ISW matter by a neutron star or black hole companion,the effect of an ISW on the MSW, formation of millisecond pulsars,complete evaporation of low-mass donors, disruption by tidal forces of alow-mass main-sequence star or a degenerate dwarf companion into a gasdisk around the accretor, and the formation of planetary systems in thedisk around neutron stars and or black holes in post-LMXB systems.
| HI observations of galaxies in nearby Zwicky clusters
The results of a long term project of H I observations of galaxieswithin the boundaries of nearby Zwicky clusters are presented. Thedetection rate is rather low (233 out of 618, i.e., 38 percent) ascompared to other surveys carried out recently. Most of the radialvelocities of the detected galaxies are new determinations. The largespread in radial velocities for many of these clusters is a strongindication for the presence of several foreground and/or backgroundgalaxies.
| Isophotal twisting in isolated elliptical galaxies
Luminosity, ellipticity, and position angle profiles of 43 ellipticalgalaxies selected from the UGC catalog are used to study isophotaltwisting not arising from the intrinsic structure of the object.Isolated galaxies have been chosen to avoid distortions of the isophotesdue to the occurrence of tidal effects of photometric overlapping withclose companions. It is demonstrated that isophotal twisting occurs inisolated galaxies with about the same frequency as for objects inrandomly selected samples. Objects having luminosity profiles close tothe exp 1/4 law show no twist of the isophotes within the errors,whereas any degree of twist is allowed when more complex luminosityprofiles are observed.
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