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The AMIGA sample of isolated galaxies. II. Morphological refinement
We present a refinement of the optical morphologies for galaxies in theCatalog of Isolated Galaxies that forms the basis of the AMIGA (Analysisof the interstellar Medium of Isolated GAlaxies) project. Uniformreclassification using the digitized POSS II data benefited from thehigh resolution and dynamic range of that sky survey. Comparison withindependent classifications made for an SDSS overlap sample of more than200 galaxies confirms the reliability of the early vs. late-typediscrimination and the accuracy of spiral subtypes within Δ T =1-2. CCD images taken at the Observatorio de Sierra Nevada were alsoused to solve ambiguities in early versus late-type classifications. Aconsiderable number of galaxies in the catalog (n = 193) are flagged forthe presence of nearby companions or signs of distortion likely due tointeraction. This most isolated sample of galaxies in the local Universeis dominated by two populations: 1) 82% are spirals (Sa-Sd) with thebulk being luminous systems with small bulges (63% between types Sb-Sc)and 2) a significant population of early-type E-S0 galaxies (14%). Mostof the types later than Sd are low luminosity galaxies concentrated inthe local supercluster where isolation is difficult to evaluate. Thelate-type spiral majority of the sample spans a luminosity rangeMB-corr = -18 to -22 mag. Few of the E/S0 population are moreluminous than -21.0 marking the absence of the often-sought superL* merger (e.g. fossil elliptical) population. The rarity ofhigh luminosity systems results in a fainter derived M* forthis population compared to the spiral optical luminosity function(OLF). The E-S0 population is from 0.2 to 0.6 mag fainter depending onhow the sample is defined. This marks the AMIGA sample as unique amongsamples that compare early and late-type OLFs separately. In othersamples, which always involve galaxies in higher density environments,M^*_E/S0 is almost always 0.3-0.5 mag brighter than M^*_S, presumablyreflecting a stronger correlation between M* andenvironmental density for early-type galaxies.

Kinematics of the local universe . XII. 21-cm line measurements of 586 galaxies with the new Nançay receiver
This paper presents 586 new 21-cm neutral hydrogen line measurementscarried out with the FORT receiver of the meridian transit Nançayradiotelescope in the period July 2000-March 2003. This observationalprogramme is part of a larger project aiming at collecting an exhaustiveand magnitude-complete HI extragalactic catalogue for Tully-Fisherapplications. It is associated with the building of the MIGALEspectroscopic archive and database.Tables 2, 3 and HI-profiles and corresponding comments are onlyavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr ( or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/430/373, or directly atour web site http://klun.obs-nancay.fr

Revised positions for CIG galaxies
We present revised positions for the 1051 galaxies belonging to theKarachentseva Catalog of Isolated Galaxies (CIG). New positions werecalculated by applying SExtractor to the Digitized Sky Survey CIG fieldswith a spatial resolution of 1 arcsper 2. We visually checked theresults and for 118 galaxies had to recompute the assigned positions dueto complex morphologies (e.g. distorted isophotes, undefined nuclei,knotty galaxies) or the presence of bright stars. We found differencesbetween older and newer positions of up to 38 arcsec with a mean valueof 2 arcsper 96 relative to SIMBAD and up to 38 arcsec and 2 arcsper 42respectively relative to UZC. Based on star positions from the APMcatalog we determined that the DSS astrometry of five CIG fields has amean offset in (alpha , delta ) of (-0 arcsper 90, 0 arcsper 93) with adispersion of 0 arcsper 4. These results have been confirmed using the2MASS All-Sky Catalog of Point Sources. The intrinsic errors of ourmethod combined with the astrometric ones are of the order of 0 arcsper5.Full Table 1 is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr ( or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/411/391

Small-amplitude density waves in galactic discs with radial gradients
Stellar discs of highly flattened giant galaxies, including that of theMilky Way, are studied by linear theory to determine the stability ofsuch discs against small-amplitude gravity perturbations. In order tounderstand the physics of the problem better, the simplest theoreticalmodel is applied. That is, the local disc is studied by employing themethod of particle orbit theory. In this purely Lagrangian method, anapproximate solution of the Newtonian equations of the motion of starsis obtained using a general technique based upon the perturbationmethod. In the second order of Lindblad's epicyclic theory, expressionsare found for the unperturbed motions of stars in a stationary systemwith an axially symmetric mass distribution. Then, expressions are foundfor the perturbed motions of stars when the small non-axisymmetricgravity perturbation is additionally taken into account. The perturbedterms are obtained as second-order oscillations. To describe the orderedbehaviour of a medium near its quasi-equilibrium state, these equationsfor the trajectories of stars are used to obtain the dispersion relationthat connects the frequency of excited collective oscillations with thewavenumber throughout the disc, including resonant regions. Using thedispersion relation, a new class of gradient microinstabilities of anon-uniformly rotating disc inherent in an inhomogeneous system isdiscussed. The Landau mechanism of excitation of spiral density wavesworks at the corotation resonance between stars and hydrodynamically(Jeans) stable perturbations (e.g. those produced by a bar-likestructure, a spontaneous perturbation and/or a companion galaxy). Aphysical aetiology of the gradient microinstabilities of collisionlessstellar discs is explained. Such instabilities can develop only if theinhomogeneous and non-uniformly rotating disc of stars is Jeans-stable.Certain astronomical implications of the theory for actual galaxies areexplored as well. In particular, the development of these instabilitiesof a stellar disc can result directly in the formation of differentobservable structural features, e.g. spiral arms and collisionlessdynamical relaxation of the system on the Hubble time-scale.

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Observation and Astrometry data

Right ascension:21h32m25.10s
Aparent dimensions:1′ × 0.389′

Catalogs and designations:
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NGC 2000.0NGC 7085

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