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Analysis strategy issues for the maintenance of the ICRF axes
In preparation for the evolution of the definition of the VLBI-basedInternational Celestial Reference Frame (ICRF), various elements of theanalysis strategy are investigated, such as reference source selectionand the impact of the status of the terrestrial reference frame in thedata analysis model. We conclude that including the determination ofboth the celestial and the terrestrial reference frames in the analysisdoes not affect the quality of the celestial reference frame. Thedetermination of precession and nutation components is not affected bythe status of the terrestrial reference frame but it is affected by theselection of reference radio sources. Extending an earlier study, threelists of reference sources based on progressively larger tolerances areproposed. They include 181, 225 and 247 objects, respectively.

Construction of a Celestial Coordinate Reference Frame from VLBI Data
A large number (˜2 million) of VLBI observations have been reducedin order to refine the measured coordinates of the observed radiosources. The data reduction was carried out in the OCCAM package usingthe least squares colocation method. Corrections to the coordinates of642 objects were derived. The accuracy of the catalog is no worse than0.2 milliseconds of arc for stable sources.

A new catalogue of ISM content of normal galaxies
We have compiled a catalogue of the gas content for a sample of 1916galaxies, considered to be a fair representation of ``normality''. Thedefinition of a ``normal'' galaxy adopted in this work implies that wehave purposely excluded from the catalogue galaxies having distortedmorphology (such as interaction bridges, tails or lopsidedness) and/orany signature of peculiar kinematics (such as polar rings,counterrotating disks or other decoupled components). In contrast, wehave included systems hosting active galactic nuclei (AGN) in thecatalogue. This catalogue revises previous compendia on the ISM contentof galaxies published by \citet{bregman} and \citet{casoli}, andcompiles data available in the literature from several small samples ofgalaxies. Masses for warm dust, atomic and molecular gas, as well asX-ray luminosities have been converted to a uniform distance scale takenfrom the Catalogue of Principal Galaxies (PGC). We have used twodifferent normalization factors to explore the variation of the gascontent along the Hubble sequence: the blue luminosity (LB)and the square of linear diameter (D225). Ourcatalogue significantly improves the statistics of previous referencecatalogues and can be used in future studies to define a template ISMcontent for ``normal'' galaxies along the Hubble sequence. The cataloguecan be accessed on-line and is also available at the Centre desDonnées Stellaires (CDS).The catalogue is available in electronic form athttp://dipastro.pd.astro.it/galletta/ismcat and at the CDS via anonymousftp to\ cdsarc.u-strasbg.fr ( or via\http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/405/5

Search for point sources of gamma radiation above 15 TeV with the HEGRA AIROBICC array
A search for potential point sources of very high energy gamma rays hasbeen carried out on the data taken simultaneously by the HEGRA AIROBICCand Scintillator arrays from August 1994 to March 2000. The list ofsought sources includes supernova remnants, pulsars, AGNs and binarysystems. The energy threshold is around 15 TeV. For the Crab Nebula, amodest excess of 2.5 standard deviations above the cosmic ray backgroundhas been observed. Flux upper limits (at 90% c.l.) of around 1.3 timesthe flux of the Crab Nebula are obtained, in average, for the candidatesources. A different search procedure has been used for an all-skysearch which yields absolute flux upper limits between 4 and 9 crabsdepending on declination, in the band from delta = 0 to delta =60o. The full versions of Tables 1 and 2, including thecoordinates of the sources, are available in electronic form at the CDSvia anonymous ftp to cdsarc.u-strasbg.fr ( or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/390/39

Radio-loud active galaxies in the northern ROSAT All-Sky Survey. IV. Properties of sources stronger than 100 mJy at 5 GHz
We present multi-frequency radio data for 741 extragalactic sources witha 5 GHz integrated flux density of > 100 mJy. These sources have beenselected from a cross-correlation of an early ROSAT All-Sky Surveysource list with a list of compact radio sources of the 5 GHz Green Banknorthern sky survey (RGB sample). The majority of sources werequasi-simultaneously observed with the Effelsberg 100-m telescope at 11cm, 6 cm, and 2.8 cm. We have determined the spectrum, size and linearpolarization properties of these sources. We compare the radio data withROSAT measurements and optical data. We find that the X-ray selectedradio sources, when compared with unbiased radio source samples, are onaverage slightly more compact, show a higher fractional polarization, ahigher absolute rotation measure (RM), and have flatter spectra.Absolute RMs are larger for steep spectrum than for flat spectrumsources and for extended than for compact sources. The average redshiftincreases with the radio flux density, which indicates that the X-rayselected radio sources have a larger fraction of beamed radio emission.All source characteristics of the sample are in accordance with presentunification schemes for AGN, where X-ray selected sources are preferablelooked at face on. Tables~1 and 2 are only available in electronic format the CDS via anonymous ftp to cdsarc.u-strasbg.fr ( orvia http://cdsweb.u-strasbg.fr/Abstract.html

Total magnitude, radius, colour indices, colour gradients and photometric type of galaxies
We present a catalogue of aperture photometry of galaxies, in UBVRI,assembled from three different origins: (i) an update of the catalogueof Buta et al. (1995) (ii) published photometric profiles and (iii)aperture photometry performed on CCD images. We explored different setsof growth curves to fit these data: (i) The Sersic law, (ii) The net ofgrowth curves used for the preparation of the RC3 and (iii) A linearinterpolation between the de Vaucouleurs (r(1/4) ) and exponential laws.Finally we adopted the latter solution. Fitting these growth curves, wederive (1) the total magnitude, (2) the effective radius, (3) the colourindices and (4) gradients and (5) the photometric type of 5169 galaxies.The photometric type is defined to statistically match the revisedmorphologic type and parametrizes the shape of the growth curve. It iscoded from -9, for very concentrated galaxies, to +10, for diffusegalaxies. Based in part on observations collected at the Haute-ProvenceObservatory.

Search for an optical counterpart of the COMPTEL source GRO J1753+57.
In November 1992, COMPTEL discovered the unusual and highly variablesource GRO J1753+57. There are no obvious candidates for counterparts inother wavebands, such as a bright radio loud AGN. A thorough search ofradio and NGC sources was undertaken to identify possible counterparts.Two potentially interesting objects were found, NGC 6454 and NGC 6474,but they exhibit only limited optical variability and core emission,contrarily to what would be expected from known extragalacticγ-ray sources. Supportive evidence for the elliptical galaxy NGC6454 comes from previous radio and X-ray measurements.

An image database. II. Catalogue between δ=-30deg and δ=70deg.
A preliminary list of 68.040 galaxies was built from extraction of35.841 digitized images of the Palomar Sky Survey (Paper I). For eachgalaxy, the basic parameters are obtained: coordinates, diameter, axisratio, total magnitude, position angle. On this preliminary list, weapply severe selection rules to get a catalog of 28.000 galaxies, wellidentified and well documented. For each parameter, a comparison is madewith standard measurements. The accuracy of the raw photometricparameters is quite good despite of the simplicity of the method.Without any local correction, the standard error on the total magnitudeis about 0.5 magnitude up to a total magnitude of B_T_=17. Significantsecondary effects are detected concerning the magnitudes: distance toplate center effect and air-mass effect.

The ROSAT AGN content of the 87GB 5 GHz survey: bulk properties of previously optically identified sources.
The cross-correlation of the source list from the ROSAT All-Sky Surveywith the 5 GHz Green Bank survey yields a list of 2127 objects. Abouttwo thirds of them are optically unidentified. The majority of theobjects with known optical counterparts are quasars and radio galaxies,most of them detected in X-rays for the first time. In this paper wepresent a list of the previously optically identified objects with theirmain characteristics and discuss their general (bulk) properties. Wefind strong correlations between luminosities in the radio, optical, andX-ray bands which differ for quasars and radio galaxies. The fraction offlat radio spectrum sources increases with redshift and ~ 95% of allsources above z = 2 are of that type. In the relatively large group ofblazars, radio selected BL Lacs and highly polarized quasars show verysimilar properties while X-ray selected BL Lacs have markedly differentX-ray to radio flux ratios. The sample is large enough and ofsufficiently high quality to reveal clearly various detection biases andselection effects which strongly influence the physical interpretationof the correlations. Radio follow - up observations for thedetermination of the morphological and spectral properties as well asenvironmental conditions are needed for a statistically reliable studyof the sample. The very large group of sources with low radio fluxesremains to be optically identified.

The detection of an unidentified variable gamma-ray source by COMPTEL.
We report the detection of an unidentified, high galactic latitude,γ-ray source (GRO J1753+57) by the COMPTEL instrument onboard theCompton Gamma-ray Observatory. The source was clearly detected duringobservations in November 1992 and had a flux in the 1-3MeV band ofapproximately half that of the Crab. All other observations of thisregion by COMPTEL only yield upper limits, or marginal detections,showing that this source is highly variable on a timescale of weeks.Possible counterparts are discussed.

An X-ray catalog and atlas of galaxies
An X-ray catalog and atlas of galaxies observed with the EinsteinObservatory imaging instruments (IPC and HRI) are presented. The catalogcomprises 493 galaxies, including targets of pointed observations, andRSA or RC2 galaxies serendipitously included in Einstein fields. A totalof 450 of these galaxies were imaged well within the instrumentalfields, resulting in 238 detections and 2123 sigma upper limits. Theother galaxies were either at the edge of the visible field of view orconfused with other X-ray sources. For these a rough measure of theirX-ray emission is also given. The atlas shows X-ray contour maps ofdetected galaxies superposed on optical photographs and givesazimuthally averaged surface brightness profiles of galaxies detectedwith a high signal-to-noise ratio.

H I absorption in radio elliptical galaxies - Evidence for infall
A complete sample of 29 radio galaxies with compact cores has beenobserved by the VLA in the H I line to an almost uniform optical-depthsensitivity of about 0.01 at a velocity resolution of 40 km/s. Thesegalaxies were selected using continuum observations of an almostcomplete sample of 49 radio galaxies; 21-cm core flux densities aregiven for these galaxies. H I absorption was detected in four galaxies,NGC 3894, NGC 5363, 3C 236, and 4C 31.06, bringing to eight the numberof radio ellipticals in which H I absorption has been detected. In allcases, absorption is seen redshifted wiht respect to the galaxy'ssystemic velocity, or close to the systemic velocity, or both. Noblueshifted absorption components are seen. These observationsdemonstrate the infall of H I to the inner regions of radio ellipticalgalaxies. The estimated infall rates (a few hundredths of a solar massper year) are more than adequate to fuel the nuclear activity.

IRAS observations of radio galaxies
IRAS measurements at 25, 60, and 100 microns have been used to analyzethe far-infrared properties of radio galaxies. Fifty-eight of the 131objects surveyed were detected at the level of better than 300 mJy at 60microns. The most powerful radio galaxies are strong emitters in the farinfrared. Large infrared emission is shown to be correlated with thepresence of strong emission lines in the optical spectra. The infraredcolors of the strong radio galaxies are similar to those of MarkarianSeyferts. The results are shown to be consistent with recent resultsimplying that the host galaxies of radio sources are not normal giantellipticals and that galaxy-galaxy interactions may power luminous radiosources. Finally, some similarities between powerful radio galaxies andpowerful infrared galaxies are noted and briefly discussed.

Infrared studies of elliptical galaxies. I - an optically selected sample
The nuclei of 65 elliptical galaxies have been observed in the infrared,including the first large set of sensitive measurements of ellipticalsat 10 microns. About 30 percent of the sample shows a significant excessover photospheric emission at 10 microns, and the galaxies with strong10 micron emission are not distinctive in terms of their opticalproperties. The infrared excess in ellipticals is steep, with anequivalent color temperature of 700 K and below. The 1-10 micronemission probably comes from late-type giants with the same luminosityfunction as observed in the Galactic nuclear bulge. Most of the excess10 micron emission over photospheric emission may come from stars withan excess due to dust from mass loss on the AGB.

Weak nuclei of powerful radio sources - Spectra and polarizations
Observations are presented of the spectra and polarizations of the weakcores of extended extragalactic radio sources. These cores typicallyshow peaked spectra, and, below a luminosity of about 10 to the 26thW/Hz, are unpolarized with 90 percent confidence upper limits of about0.6 percent. In both of these properties the cores distinguishthemselves as a class from strong, active compact sources, such as thosethat show superluminal motion. The relation between these weak cores andother classes of compact sources and the implications for 'unified'models based on relativistic beaming are briefly discussed. It isconcluded that there is a distinct class of compact objects, differentfrom relativistic jets, which appear in the form of separate weak ordominant cores, or as the base component in superluminal jets.

Photoelectric Observations of Interacting and Compact Galaxies
Not Available

A correlation between ellipticity and core-strength in extended radio galaxies
It is shown that in the case of extended radio sources a correlationexists between the fraction of the radio flux retained in the corecomponent and the ellipticity of the underlying galaxy. The correlationis in the sense that stronger cores occur in flatter galaxies. It wouldseem that there exists a class of intrinsically rounder, redder, massiveellipticals with larger velocity dispersions and metallicities, that canform extended radio sources more efficiently. Thus the occurrence of aradio source appears to be related to the dynamical and chemicalevolution of the Galaxy.

An infrared and optical investigation of galactic nuclei with compact radio sources
Infrared multicolor (JHKLN) photometry and optical spectrophotometry ofa sample of bright (mv less than or = 18) galaxies with powerful compactnuclear radio sources (S greater than or = 200 mJy at 5 GHz) arepresented. Nearly all of the objects (85 percent or more) have anonstellar optical-infrared nuclear continuum whose strength is roughlyproportional to that of the compact radio source. Except for their lowerluminosities, the nuclei in these galaxies probably resemble radio-loudquasars. Compact nuclear radio sources with associated large-scaledouble radio lobes probably have enhanced nonstellar optical-infraredcontinua compared to the objects without such extended radio emission.The sample is diverse in its emission-line properties. Generally, theradio-loud objects have much stronger emission lines than do the nucleiof normal (radio-quiet) early-type galaxies.

X-ray observations of peculiar galaxies with the Einstein Observatory
The results of X-ray observations with the Einstein Observatory of 33galaxies are presented. Almost all of these galaxies, some of which liein groups and in interactive pairs, display disturbed morphologies. Nouniform, well-defined selection criterion can describe the samplegalaxies, but almost all lie in a region of the optical color/colordiagram that suggests that they are experiencing bursts of starformation. This region is compatible with the locus of Markariangalaxies. The observed sample and the X-ray data are presented, and theX-ray data are discussed and compared with the optical and radioproperties of the galaxies. It is concluded that nuclear activity is notthe predominant source of X-rays in late-type peculiar galaxies and thatthe X-ray emission is likely to originate from the Population I galacticcomponent, in particular binary sources and possible young SNR's.

Westerbork observations of flat spectrum galaxies in the 5 GHz 'S4' survey
Observations made with the Westerbork Synthesis Radio Telescope at 6 cmand 21 cm are reported for a complete sample of sources from theNRAO-Bonn 'S4' survey at 5 GHz that have flat high frequency spectra andare identified with galaxies. Most of the brighter galaxies in thesurvey appear to be related to BL Lac objects. The BL Lac galaxy 1101 +38 has been found to have an extended radio component of about 3 arcminassociated with it. An extended component located only on one side ofthe nucleus has been found in the case of 0309 + 41, which is identifiedwith an 18m galaxy.

The 5 GHz strong source surveys. IV - Survey of the area between declination 35 and 70 degrees and summary of source counts, spectra and optical identifications
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1978AJ.....83..451P&db_key=AST

A pencil-beam survey of radio sources at 178 MHz
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1969MNRAS.145..181C&db_key=AST

Identifications of radio sources with bright galaxies
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1967MNRAS.135..231C&db_key=AST

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Observation and Astrometry data

Right ascension:17h44m56.50s
Aparent dimensions:1.38′ × 1.047′

Catalogs and designations:
Proper Names   (Edit)
NGC 2000.0NGC 6454

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