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The Potential-Density Phase-Shift Method for Determining the Corotation Radii in Spiral and Barred Galaxies
We have developed a new method for determining the corotation radii ofdensity waves in disk galaxies, which makes use of the calculated radialdistribution of an azimuthal phase shift between the potential anddensity wave patterns. The approach originated from improved theoreticalunderstanding of the relation between the morphology and kinematics ofgalaxies and of the dynamical interaction between density waves and thebasic-state disk stars, which results in the secular evolution of diskgalaxies. In this paper we present the rationales behind the method andthe first application of it to several representative barred andgrand-design spiral galaxies, using near-infrared images to trace themass distributions, as well as to calculate the potential distributionsused in the phase-shift calculations. We compare our results with thosefrom other existing methods for locating the corotations and show thatthe new method both confirms the previously established trends ofbar-length dependence on galaxy morphological types and provides newinsights into the possible extent of bars in disk galaxies. The methodalso facilitates the estimation of mass accretion/excretion rates due tobar and spiral density waves, providing an alternative way ofquantifying the importance of these features in disk galaxies. Apreliminary analysis of a larger sample shows that the phase-shiftmethod is likely to be a generally applicable, accurate, and essentiallymodel-independent method for determining the pattern speeds andcorotation radii of single or nested density wave patterns in galaxies.Other implications of the results of this work include that most of thenearby bright disk galaxies appear to possess quasi-stationary spiralmodes; that these density wave modes, as well as the associated basicstates of the galactic disks, slowly transform over the time span of aHubble time due to a collective dissipation process directly related tothe presence of the phase shift between the potential and densitypatterns; and that self-consistent N-particle systems contain physicsnot revealed by the passive orbit analysis approaches.
| Sixth Catalogue of Fundamental Stars (FK6). Part III. Additional fundamental stars with direct solutions
The FK6 is a suitable combination of the results of the HIPPARCOSastrometry satellite with ground-based data, measured over a longinterval of time and summarized mainly in the FK5. Part III of the FK6(abbreviated FK6(III)) contains additional fundamental stars with directsolutions. Such direct solutions are appropriate for single stars or forobjects which can be treated like single stars. Part III of the FK6contains in total 3272 stars. Their ground-based data stem from thebright extension of the FK5 (735 stars), from the catalogue of remainingSup stars (RSup, 732 stars), and from the faint extension of the FK5(1805 stars). From the 3272 stars in Part III, we have selected 1928objects as "astrometrically excellent stars", since their instantaneousproper motions and their mean (time-averaged) ones do not differsignificantly. Hence most of the astrometrically excellent stars arewell-behaving "single-star candidates" with good astrometric data. Thesestars are most suited for high-precision astrometry. On the other hand,354 of the stars in Part III are Δμ binaries in the sense ofWielen et al. (1999). Many of them are newly discovered probablebinaries with no other hitherto known indication of binarity. The FK6gives, besides the classical "single-star mode" solutions (SI mode),other solutions which take into account the fact that hidden astrometricbinaries among "apparently single-stars" introduce sizable "cosmicerrors" into the quasi-instantaneously measured HIPPARCOS proper motionsand positions. The FK6 gives, in addition to the SI mode, the "long-termprediction (LTP) mode" and the "short-term prediction (STP) mode". TheseLTP and STP modes are on average the most precise solutions forapparently single stars, depending on the epoch difference with respectto the HIPPARCOS epoch of about 1991. The typical mean error of anFK6(III) proper motion in the single-star mode is 0.59 mas/year. This isa factor of 1.34 better than the typical HIPPARCOS errors for thesestars of 0.79 mas/year. In the long-term prediction mode, in whichcosmic errors are taken into account, the FK6(III) proper motions have atypical mean error of 0.93 mas/year, which is by a factor of about 2better than the corresponding error for the HIPPARCOS values of 1.83mas/year (cosmic errors included).
| BUDDA: A New Two-dimensional Bulge/Disk Decomposition Code for Detailed Structural Analysis of Galaxies
We present BUDDA (Bulge/Disk Decomposition Analysis), a new code devotedto perform a two-dimensional bulge/disk decomposition directly from theimages of galaxies. The bulge component is fitted with a generalizedSérsic profile, whereas disks have an exponential profile. Noother components are included. Bars and other substructures, likelenses, rings, inner bars, and inner disks, are studied with theresidual images obtained through the subtraction of bulges and disksfrom the original images. This means that a detailed structural analysisof galaxies may be performed with a small number of parameters, andsubstructures may be directly studied with no a priori assumptions. Ashas been already shown by several studies, two-dimensional fitting ismuch more reliable than one-dimensional profile fitting. Moreover, ourcode has been thoroughly tested with artificial data, and we demonstrateit to be an accurate tool for determining structural parameters ofgalaxies. We also show that our code is useful in various kinds ofstudies, including galaxies of, e.g., different morphological types, andinclinations, which also may be observed at different spatialresolutions. Thus, the code has a broader range of potentialapplications than most of the previous codes, which are developed totackle specific problems. To illustrate its usefulness, we present theresults obtained with a sample of 51 mostly early-type galaxies (butcovering the whole Hubble sequence). These results show some of theapplications in which the code may be used: the determination ofparameters for fundamental plane and structural studies, quantitativemorphological classification of galaxies, and the identification andstudy of hidden substructures. We have determined the structuralparameters of the galaxies in our sample and found many examples ofhidden inner disks in ellipticals, secondary bars, nuclear rings anddust lanes in lenticulars and spirals, and also wrong morphologicalclassification cases. We now make BUDDA generally available to theastronomical community.Based on observations made at the Pico dos Dias Observatory(PDO/LNA-CNPq), Brazil.
| The ROSAT all-sky survey catalogue of optically bright OB-type stars.
For the detailed statistical analysis of the X-ray emission of hot starswe selected all stars of spectral type O and B listed in the Yale BrightStar Catalogue and searched for them in the ROSAT All-Sky Survey. Inthis paper we describe the selection and preparation of the data andpresent a compilation of the derived X-ray data for a complete sample ofbright OB stars.
| Astrophysics in 2003
Five coherent sections appear this year, addressing solar physics,cosmology (with WMAP highlights), gamma-ray bursters (and theirassociation with Type Ia supernovae), extra-solar-system planets, andthe formation and evolution of galaxies (from reionization to assemblageof Local Group galaxies). There are also eight incoherent sections thatdeal with other topics in stellar, galactic, and planetary astronomy andthe people who study them.
| Vitesses radiales. Catalogue WEB: Wilson Evans Batten. Subtittle: Radial velocities: The Wilson-Evans-Batten catalogue.
We give a common version of the two catalogues of Mean Radial Velocitiesby Wilson (1963) and Evans (1978) to which we have added the catalogueof spectroscopic binary systems (Batten et al. 1989). For each star,when possible, we give: 1) an acronym to enter SIMBAD (Set ofIdentifications Measurements and Bibliography for Astronomical Data) ofthe CDS (Centre de Donnees Astronomiques de Strasbourg). 2) the numberHIC of the HIPPARCOS catalogue (Turon 1992). 3) the CCDM number(Catalogue des Composantes des etoiles Doubles et Multiples) byDommanget & Nys (1994). For the cluster stars, a precise study hasbeen done, on the identificator numbers. Numerous remarks point out theproblems we have had to deal with.
| Control of star formation by supersonic turbulence
Understanding the formation of stars in galaxies is central to much ofmodern astrophysics. However, a quantitative prediction of the starformation rate and the initial distribution of stellar masses remainselusive. For several decades it has been thought that the star formationprocess is primarily controlled by the interplay between gravity andmagnetostatic support, modulated by neutral-ion drift (known asambipolar diffusion in astrophysics). Recently, however, bothobservational and numerical work has begun to suggest that supersonicturbulent flows rather than static magnetic fields control starformation. To some extent, this represents a return to ideas popularbefore the importance of magnetic fields to the interstellar gas wasfully appreciated. This review gives a historical overview of thesuccesses and problems of both the classical dynamical theory and thestandard theory of magnetostatic support, from both observational andtheoretical perspectives. The outline of a new theory relying on controlby driven supersonic turbulence is then presented. Numerical modelsdemonstrate that, although supersonic turbulence can provide globalsupport, it nevertheless produces density enhancements that allow localcollapse. Inefficient, isolated star formation is a hallmark ofturbulent support, while efficient, clustered star formation occurs inits absence. The consequences of this theory are then explored for bothlocal star formation and galactic-scale star formation. It suggests thatindividual star-forming cores are likely not quasistatic objects, butdynamically collapsing. Accretion onto these objects varies depending onthe properties of the surrounding turbulent flow; numerical models agreewith observations showing decreasing rates. The initial massdistribution of stars may also be determined by the turbulent flow.Molecular clouds appear to be transient objects forming and dissolvingin the larger-scale turbulent flow, or else quickly collapsing intoregions of violent star formation. Global star formation in galaxiesappears to be controlled by the same balance between gravity andturbulence as small-scale star formation, although modulated by coolingand differential rotation. The dominant driving mechanism instar-forming regions of galaxies appears to be supernovae, whileelsewhere coupling of rotation to the gas through magnetic fields orgravity may be important.
| An IUE survey of interstellar H I LY alpha absorption. 1: Column densities
We measure Galactic interstellar neutral hydrogen column densities byanalyzing archival interstellar Ly alpha absorption line data toward 554B2 and hotter stars observed at high resolution with the IUE satellite.This study more than doubles the number of lines of sight with measuresof N(H I) based on Ly alpha. We have included the scattered lightbackground correction algorithm of Bianchi and Bohlin in our datareduction. We use the correlation between the Balmer discontinuity(c1) index and the stellar Ly alpha absorption in order toassess the effects of stellar Ly alpha contamination. Approximately 40%of the B stars with measured (c1) index, exhibit seriousstellar Ly alpha contamination. One table contains the derived values ofthe interstellar N(H I) for 393 stars with at most small amounts ofstellar contamination. Another lists the observed values of total N(H I)for 161 stars with suspected stellar Ly alpha contamination and/oruncertain stellar parameters.
| Fifth fundamental catalogue. Part 2: The FK5 extension - new fundamental stars
The mean positions and proper motions for 3117 new fundamental starsessentially in the magnitude range about 4.5 to 9.5 are given in thisFK5 extension. Mean apparent visual magnitude is 7.2 and is on average2.5 magnitudes fainter then the basic FK5 which has a mean magnitude of4.7. (The basic FK5 gives the mean positions and proper motions for theclassical 1535 fundamental stars). The following are discussed: theobservational material, reduction of observations, star selection, andthe system for the FK5 extension. An explanation and description of thecatalog are given. The catalog of 3117 fundamental stars for the equinoxand epoch J2000.0 and B1950.0 is presented. The parallaxes and radialvelocities for 22 extension stars with large forecasting effects aregiven. Catalogs used in the compilation of the FK5 fundamental catalogare listed.
| 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 (130.79.128.5) or via\http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/405/5
| The Ringed Spiral Galaxy NGC 4622. I. Photometry, Kinematics, and the Case for Two Strong Leading Outer Spiral Arms
The intriguing nearly face-on southern ringed spiral galaxy NGC 4622,the first galaxy definitively shown to have leading spiral structure, isrevisited in this paper with new images from the Hubble SpaceTelescope's (HST) WFPC2, together with ground-based optical and near-IRimaging, and a Fabry-Perot Hα velocity field. The data provide newinformation on the disk/bulge/halo mix, rotation curve, star formationin the galaxy, and the sense of winding of its prominent spiral arms.Previously, we suggested that the weaker, inner single arm most likelyhas the leading sense, based on a numerical simulation. Now, takingadvantage of HST resolution and using de Vaucouleurs' standardextinction and reddening technique to determine the near side of thegalaxy's slightly tilted disk, we come to the more surprising conclusionthat the two strong outer arms have the leading sense. We suggest thatthis highly unusual configuration may be the result of a past minormerger or mild tidal encounter. Possible evidence for a minor merger isfound in a short, central dust lane, although this is purelycircumstantial and an unrelated interaction with a different companioncould also be relevant. The leading arms may be allowed to persistbecause NGC 4622 is dark halo dominated (i.e., not ``maximum disk'' inthe inner regions) and displays a significantly rising rotation curve.The new HST observations also reveal a rich globular cluster system inthe galaxy. The mean color of these clusters is (V-I)0=1.04,and the specific frequency is 3.4+/-0.6. The luminosity function ofthese clusters confirms the membership of NGC 4622 in the CentaurusCluster.Based on observations with the NASA/ESA Hubble Space Telescope, obtainedat the Space Telescope Science Institute, which is operated by theAssociation of Universities for Research in Astronomy, Inc., undercontract NAS 5-26555.
| Walraven photometry of nearby southern OB associations
Homogeneous Walraven (VBLUW) photometry is presented for 5260 stars inthe regions of five nearby southern OB associations: Scorpio Centaurus(Sco OB2), Orion OB1, Canis Major OB1, Monoceros OB1, and Scutum OB2.Derived V and (B - V) in the Johnson system are included.
| Empirical temperature calibrations for early-type stars
Three temperature calibrations of suitable photometric quantities havebeen derived for O and B stars. A sample of 120 stars with reliableT(eff.) determinations has been used for establishing each calibration.The different calibrations have been critically discussed and compared.Temperature determinations for 1009 program stars have been obtainedwith an accuracy of the order of 10 percent.
| Leading Pairs and Trailing Single Spiral Arms: Observations and Simulations of NGC4622
NGC4622 has a most unusual spiral arm pattern. Besides a pair of outerarms which wind outward clockwise (CW), Byrd et al. (1989) pointed out aweaker, single, inner arm winding outward counterclockwise. Byrd et al.suspected the single arm must lead, a rare configuration. Buta, Crocker,and Byrd's (1992) BVI photometry showed the inner arm is a real stellardisk feature. Assuming a flat rotation curve, Byrd, Freeman, and Howard(1993) simulated a single leading and outer trailing pair of arms forNGC4622 via a plunging low-mass perturber along the plane of a disk in amassive halo. However, new HST data (Byrd, Buta, and Freeman 2001)indicate via dust cloud silhouettes that the east edge of the galaxy isnearer. Additional Hα spectra indicate that the north edge alongthe disk line of nodes is receding relative to the center. The diskmaterial thus orbits CW and the arm pair leads, winding out in thedirection of disk orbital motion ``counter" to common theoreticalexpectations. Conversely, the inner single arm trails. The spectraindicate that the rotation curve is rising and getting steeper withincreasing radius in the outer disk where the pair of arms is found.There is some indication that it is flat in the single arm region(although there is little ionized gas there). This unusual curve appearsto be a key to understanding the NGC4622 arm pattern. An encounter muchlike our previous work but with the new rotation curve successfullyproduces an inner single trailing, outer pair leading spiral armpattern. See http://bama.ua.edu/ ~rbuta/ngc4622. We find support for theencounter in the lack of a systematic BVI azimuthal color displacementin the outer pair, indicating a young impulsive perturbation which iswinding up. We find evidence in the HST images that the inner patterncontains a one-sided periodic orbit ring whose pattern speed results ina clear angular displacement between the B, V, and I maximum radialdistances. Grant support: NASA/STScI GO 8707 and NSF AST-0206177.
| A catalog of ultraviolet interstellar extinction excesses for 1415 stars
Ultraviolet interstellar extinction excesses are presented for 1415stars with spectral types B7 and earlier. The excesses with respect to Vare derived from Astronomical Netherlands Satellite (ANS) 5-channel UVphotometry at central wavelengths of approximately 1550, 1800, 2500, and3300 A. A measure of the excess extinction in the 2200-A extinction bumpis also given. The data are valuable for investigating the systematicsof peculiar interstellar extinction and for studying the character of UVinterstellar extinction in the general direction of stars for which theextinction-curve shape is unknown.
| Supernova 2001jx in NGC 4622
IAUC 7833 available at Central Bureau for Astronomical Telegrams.
| The life cycle of galaxies.
Not Available
| The local system of early type stars - Spatial extent and kinematics
Published uvby and H-beta photometric data and proper motions arecompiled and analyzed to characterize the structure and kinematics ofthe bright early-type O-A0 stars in the solar vicinity, with a focus onthe Gould belt. The selection and calibration techniques are explained,and the data are presented in extensive tables and graphs and discussedin detail. The Gould belt stars of age less than 20 Myr are shown togive belt inclination 19 deg to the Galactic plane and node-lineorientation in the direction of Galactic rotation, while the symmetricaldistribution about the Galactic plane and kinematic properties (purecircular differential rotation) of the belt stars over 60 Myr oldresemble those of fainter nonbelt stars of all ages. The unresolveddiscrepancy between the expansion observed in the youngest nearby starsand the predictions of simple models of expansion from a point isattributed to the inhomogeneous distribution of interstellar matter.
| Search for Beta Cephei stars south of declination -20 deg. II - Photometric and spectrographic observations of early B giants and subgiants - Winter objects
Results of the second part of a program begun in 1975 (Jerzykiewicz andSterken, 1977) are presented. Out of 39 Beta Cephei candidates observedphotometrically, seven turned out to vary with the b ranges exceeding0.020 m, while 21 have been found constant to within 0.010 m or better.For the 56 comparison stars these numbers are 6 and 25, respectively.From spectrographic observations one of the candidates, HD 129557 = HR5488 (B2 III), iis found to be a Beta Cephei variable with a period of0.135 d and the 2 K amplitude of 18.4 km/s. A comparison of the resultsof this program with other recent photometric searches for Beta Cepheivariables shows good agreement in most cases. There are severaldiscrepant stars, however. These are discussed in some detail. Aconclusion emerges that in the low temperature extension of the BetaCephei region, if such an extension exists at all, on-and-off typepulsations occur.
| Dust-penetrated morphology in the high-redshift universe: Clues from NGC 922
Results from the Hubble Deep Field (HDF) North and South show a largepercentage of high-redshift galaxies whose appearance falls outsidetraditional classification systems. The nature of these objects ispoorly understood, but sub-mm observations indicate that at least someof these systems are heavily obscured (Sanders \cite{sanders00}). Thisraises the intriguing possibility that a physically meaningfulclassification system for high-redshift galaxies might be more easilydevised at rest-frame infrared wavelengths, rather than in the opticalregime. Practical realization of this idea will become possible with theadvent of the Next Generation Space Telescope (NGST). In order toexplore the capability of NGST for undertaking such science, we presentNASA-IRTF and SCUBA observations of NGC 922, achaotic system in our local Universe which bears a striking resemblanceto objects such as HDF 2-86 (z=0.749) in the HDF North. If objects suchas NGC 922 are common at high-redshifts, then thisgalaxy may serve as a local morphological ``Rosetta stone'' bridging lowand high-redshift populations. In this paper we demonstrate thatquantitative measures of galactic structure are recoverable in therest-frame infrared for NGC 922 seen at highredshifts using NGST, by simulating the appearance of this galaxy atredshifts z=0.7 and z=1.2 in rest-frame K'. While this object cannot beclassified within any optical Hubble bin, simulated NGST images at theseredshifts can be readily classified using the dust penetrated z ~ 0template of Block & Puerari (\cite{blockpuerari99}) and Buta &Block (\cite{butablock01}). The near-infrared disk of NGC 922 is notpeculiar at all; rather, it is remarkably regular, even presentingspiral arm modulation, a characteristic signature of several granddesign galaxies. Our results suggest that the capability of efficientlyexploring the rest-wavelength IR morphology of high-z galaxies shouldprobably be a key factor in deciding the final choice of instruments forthe NGST.
| A Dust-penetrated Classification Scheme for Bars as Inferred from Their Gravitational Force Fields
The division of galaxies into ``barred'' (SB) and ``normal'' (S) spiralsis a fundamental aspect of the Hubble galaxy classification system. This``tuning fork'' view was revised by de Vaucouleurs, whose classificationvolume recognized apparent ``bar strength'' (SA, SAB, SB) as acontinuous property of galaxies called the ``family.'' However, the SA,SAB, and SB families are purely visual judgments that can have littlebearing on the actual bar strength in a given galaxy. Until veryrecently, published bar judgments were based exclusively on blue lightimages, where internal extinction or star formation can either mask abar completely or give the false impression of a bar in a nonbarredgalaxy. Near-infrared camera arrays, which principally trace the oldstellar population in both normal and barred galaxies, now facilitate aquantification of bar strength in terms of their gravitationalpotentials and force fields. In this paper, we show that the maximumvalue, Qb, of the ratio of the tangential force to the meanaxisymmetric radial force in a barred disk galaxy is a quantitativemeasure of the strength of a bar. Qb does not measure barellipticity or bar shape but rather depends on the actual forcing due tothe bar embedded in its disk. We show that a wide range of true barstrengths characterizes the category ``SB,'' while the de Vaucouleurscategory ``SAB'' corresponds to a narrower range of bar strengths. Wepresent Qb values for 36 galaxies, and we incorporate our barclasses into a dust-penetrated classification system for spiralgalaxies.
| The interstellar 2200 A band - A catalogue of equivalent widths
Not Available
| Space velocities and ages of nearby early-type stars
Photometric distances and space velocities have been calculated for 458B0-A0 stars with apparent magnitudes not exceeding 6.5. UsingStromgren's ubvy-beta photometry the effective temperature and theposition in bolometric magnitude over the zero-age main sequence of thestars were derived. These quantities were used to obtain age and massfor 423 of the stars by interpolation in the models of stellar evolutionfor the chemical composition (X Z) = (0.7, 0.03). A relation forderiving interstellar reddening for normal stars in the intermediategroup is given.
| Nearby Optical Galaxies: Selection of the Sample and Identification of Groups
In this paper we describe the Nearby Optical Galaxy (NOG) sample, whichis a complete, distance-limited (cz<=6000 km s-1) andmagnitude-limited (B<=14) sample of ~7000 optical galaxies. Thesample covers 2/3 (8.27 sr) of the sky (|b|>20deg) andappears to have a good completeness in redshift (97%). We select thesample on the basis of homogenized corrected total blue magnitudes inorder to minimize systematic effects in galaxy sampling. We identify thegroups in this sample by means of both the hierarchical and thepercolation ``friends-of-friends'' methods. The resulting catalogs ofloose groups appear to be similar and are among the largest catalogs ofgroups currently available. Most of the NOG galaxies (~60%) are found tobe members of galaxy pairs (~580 pairs for a total of ~15% of objects)or groups with at least three members (~500 groups for a total of ~45%of objects). About 40% of galaxies are left ungrouped (field galaxies).We illustrate the main features of the NOG galaxy distribution. Comparedto previous optical and IRAS galaxy samples, the NOG provides a densersampling of the galaxy distribution in the nearby universe. Given itslarge sky coverage, the identification of groups, and its high-densitysampling, the NOG is suited to the analysis of the galaxy density fieldof the nearby universe, especially on small scales.
| Search for Beta Cephei stars south of declination -20 deg. I - Incidence of light variability among early B giants and subgiants: Summer objects
Not Available
| Galaxy coordinates. II. Accurate equatorial coordinates for 17298 galaxies
Using images of the Digitized Sky Survey we measured coodinates for17298 galaxies having poorly defined coordinates. As a control, wemeasured with the same method 1522 galaxies having accurate coordinates.The comparison with our own measurements shows that the accuracy of themethod is about 6 arcsec on each axis (RA and DEC).
| Spiral patterns with straight arm segments
The phenomenon of `rows', which are straight geometrical segments in thespiral arms of galaxies, is studied. The Whirlpool nebula, Messier 51(NGC 5194) in Canes Venatici, is considered to be an example of a giantgrand design galaxy. Optical photographs, Hα, ultraviolet andfar-ultraviolet images, CO, 21-cm and synchrotron emission maps, and aK_s-band mosaic of M51 are studied. With this observational material,multiple rows can be recognized in the spiral arms of the galaxy. Therows comprise a major part of the arms. The lengths of the rows increasealmost linearly with distance from the centre. They intersect oneanother at an (average) angle ~2π/3. A possible physical explanationof the phenomenon of rows is discussed on the basis of the assumptionthat the formation of straight arm segments might be due to thegas-dynamical effect of stability of flat shock fronts, and the tendencyof a slightly curved shock front to become flat. A quantitativeflattening criterion enables an explanation of the geometricalproperties of the arm patterns found in M51 and also in M101. A brieflist of spirals with rows is given.
| UBV photometry of southern early-type stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1974MNRAS.168..451H&db_key=AST
| New kinematical data for bright southern OB-stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1972A&AS....5..129L&db_key=AST
| Bogus dust screens from well-mixed exponential discs in galaxies
The V-K colours along the minor axes of spiral galaxies typically changefrom red to blue with increasing distance, giving the impression thatthe near side is systematically screened by dust. Such a preferredorientation for dust screens is unlikely. Here we show that commonextinction from the embedded dust layer in an exponential disc has thesame effect, making the near side systematically redder as theinclination increases. The galaxy NGC 2841 is modelled as an example,where the V-K profile is profoundly asymmetric and actually step-likeacross the centre. We predict that the minor-axis emission profile ofthe same dust in the far-infrared, at wavelength lambda ~ 200 mu m, willbe much more symmetric than the optical profiles, implying nearly equalcolumn densities of dust on both sides of the minor axis.
| Four-color and H-beta photometry for bright B-type stars in the southern hemisphere.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1971AJ.....76..621C&db_key=AST
| Toward a dust penetrated classification of the evolved stellar Population II disks of galaxies
To derive a coherent physical framework for the excitation of spiralstructure in galaxies, one must consider the co-existence of twodifferent dynamical components: a gas-dominated Population I disk (OBassociations, HII regions, cold interstellar HI gas) and an evolvedstellar Population II component. The Hubble classification scheme has asits focus, the morphology of the Population I component only. In thenear-infrared, the morphology of evolved stellar disks indicates asimple classification scheme: the dominant Fourier m-mode in the dustpenetrated regime, and the associated pitch angle. On the basis ofdeprojected K' (2.1microns ) images, we propose that the evolved stellardisks may be grouped into three principal dust penetrated archetypes:those with tightly wound stellar arms characterised by pitch angles atK' of ~ 10(deg) (the alpha class), an intermediate group with pitchangles of ~ 25(deg) (the beta class) and thirdly, those with openspirals demarcated by pitch angles at K' of ~ 40(deg) (the gamma bin).There is no correlation between our dust penetrated classes and opticalHubble binning; the Hubble tuning fork does not constrain the morphologyof the old stellar Population II disks. Any specific dust penetratedarchetype may be the resident disk of both an early or late type galaxy.The number of arms and the pitch angle of the arms at K' of theearly-type `a' spiral NGC 718 are almost identical to those for thelate-type `c' spiral NGC 309. We demonstrate that galaxies on oppositeends of the tuning fork can display remarkably similar evolved diskmorphologies and belong to the same dust penetrated class. Furthermore,a prototypically flocculent galaxy such as NGC 5055 (Elmegreen arm class3) can have an evolved disk morphology almost identical to that of NGC5861, characterised in the optical as having one of the most regularspiral patterns known and of Elmegreen class 12. Both opticallyflocculent or grand design galaxies can reside within the same dustpenetrated morphological bin. As was suggested by Block et al.(\cite{block94a}), it is the gas dominated Population I component whichdetermines the optical types (a, b, c), decoupled from the PopulationII. Those L=lopsided galaxies (where m=1 is a dominant mode) aredesignated Lalpha , Lbeta and Lgamma according to the dust penetratedpitch angle; E=evensided galaxies (where m=2 is the dominant Fouriermode) are classified into classes Ealpha , Ebeta and Egamma , accordingto our three principal dust penetrated archetypes. The L and E modes arethe most common morphologies in our sample, which spans a range ofHubble types from early (a) to late (irregular). Having formulated ourdust penetrated classification scheme here, we have tested it on anindependent sample of 45 face-on galaxies observed in the near-infraredby Seigar and James (\cite{seigar98a}, b).
| MK Spectral Types for Bright Southern OB Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1969ApJ...157..313H&db_key=AST
| Galaxy collisions.
Theories of how galaxies, the fundamental constituents of large-scalestructure, form and evolve have undergone a dramatic paradigm shift inthe last few decades. Earlier views were of rapid, early collapse andformation of basic structures, followed by slow evolution of the stellarpopulations and steady buildup of the chemical elements. Currenttheories emphasize hierarchical buildup via recurrent collisions andmergers, separated by long periods of relaxation and secularrestructuring. Thus, collisions between galaxies are now seen as aprimary process in their evolution. This article begins with a briefhistory; we then tour parts of the vast array of collisional forms thathave been discovered to date. Many examples are provided to illustratehow detailed numerical models and multiwaveband observations haveallowed the general chronological sequence of collisional morphologiesto be deciphered, and how these forms are produced by the processes oftidal kinematics, hypersonic gas dynamics, collective dynamical frictionand violent relaxation. Galaxy collisions may trigger the formation of alarge fraction of all the stars ever formed, and play a key role infueling active galactic nuclei. Current understanding of the processesinvolved is reviewed. The last decade has seen exciting new discoveriesabout how collisions are orchestrated by their environment, howcollisional processes depend on environment, and how these environmentsdepend on redshift or cosmological time.
| A Photometric Investigation of the SCORPlO-CENTAURUS Association
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1968ApJS...15..459G&db_key=AST
| Resonance Rings and Galaxy Morphology
Rings of star formation are a common phenomenon of early to intermediateHubble type disk galaxies. Most rings form by gas accumulation atresonances, usually under the continuous action of gravity torques froma bar pattern, but sometimes in response to a mild tidal interactionwith a nearby companion. In either case, a resonance is a very specialplace in any galaxy where star formation can be enhanced and may proceedeither as a starburst or continuously over a long time period. Thisarticle describes the characteristic morphologies of bar-driven andtidally-driven resonance rings.
| Cosmic Masks Still Dance
The Hubble classification scheme of galaxies is based on their opticalappearance or `masks'. As one goes from early to late type spirals, bothbarred and unbarred, the optical appearance will be dominated more andmore by the young Population I, i.e., blue stars and dust. Atlasesreveal the rich variety of responses of the Population I component ofgas and dust (the mask) to the underlying, older, stellar population.However, the gaseous Population I component, may only constitute 5percent of the dynamical mass of the galaxy. Masks of negligible massmay conceal the human face - and that of galaxy. In the near-infrared,the morphology of older star-dominated disk indicates a simpleclassification scheme: the dominant Fourier m-mode in the dustpenetrated regime, and the associated pitch angle. A ubiquity of low m=1and m=2 modes is confirmed. On the basis of deprojected H (1.65 μm)and K' (2.1μm) images, we propose that the evolved stellar disks maybe grouped into three principal dust penetrated archetypes: those withtightly wound stellar arms characterised by pitch angles at K' of ~10^° (the α class), an intermediate group with pitch angles of~ 25^° (the β class) and thirdly, those with open spiralsdemarcated by pitch angles at K' of ~ 40^° (the γ bin). Flator falling rotation curves give rise to the tightly wound α class;rising rotation curves are associated with the open γ class. Theobserved dust penetrated classes are inextricably related to the rate ofshear in the stellar disk, as determined by A/ω. Here A is thefirst Oort constant andω denotes the angular velocity. There is nocorrelation between our dust penetrated classes and optical Hubblebinning; the Hubble tuning fork does not constrain the morphology of theold stellar Population II disks. NGC 3223 and NGC 7083 (both SbI-II andalmost the same absolute blue magnitude) have identical Hubble types andidentical luminosity classes; the dust penetrated disk of NGC 3223 hastightly wrapped arms of class α, whereas the near-infrared disk ofNGC 7083 has open arms of class γ. This is in turn associated withtheir very different rotation curve shapes yielding different rates ofshear A/ω in their stellar disks. Any specific dust penetratedarchetype may be the resident disk of both an early or late type galaxy.The number of arms and the pitch angle of the arms at K' of theearly-type `a' spiral NGC 718 are almost identical to those for thelate-type `c' spiral NGC 309. We demonstrate that galaxies on oppositeends of the tuning fork can display remarkably similar evolved diskmorphologies and belong to the same dust penetrated class. In thissense, there is no differentiation between an early and late typegalaxy: the Hubble tuning fork becomes a circle. Furthermore, aprototypically flocculent galaxy such as NGC 5055 (Elmegreen arm class3) can have an evolved disk morphology almost identical to that of NGC5861, characterised in the optical as having one of the most regularspiral patterns known and of Elmegreen class 12. Both opticallyflocculent or grand design galaxies can reside within the same dustpenetrated morphological bin. As was suggested by Block et al. (1994a),it is the gas dominated Population I component which determines theoptical types (a, b, c). This may be partially or even fully decoupledfrom the Population II disk. Those L=lopsided galaxies (where m=1 is adominant mode) are designated Lα, Lβ and Lγ accordingto the dust penetrated pitch angle; E=evensided galaxies (where m=2 isthe dominant Fourier mode) are classified into classes Eα, Eβand Eγ, according to our three principal dust penetratedarchetypes. The L and E modes are the most common morphologies in oursample, which spans a range of Hubble types from early (a) to late(irregular).
| A Survey of Southern Be Stars
Not Available
| Vorontsov-Vel'yaminov's rows in giant spiral galaxies: geometrical properties and physical interpretation.
Not Available
| The Scorpio-Centaurus Association, IV. Interstellar absorption lines in the Southern Milky Way
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1962MNRAS.124..195B&db_key=AST
| 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.
| The Scorpio-Centaurus association: I. Radial velocities of 120 bright stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1960MNRAS.121..263B&db_key=AST
| An Einstein X-Ray Survey of Optically Selected Galaxies. I. Data
We present the results of a complete Einstein imaging proportionalcounter X-ray survey of optically selected galaxies from theShapley-Ames Catalog, the Uppsala General Catalogue, and the EuropeanSouthern Observatory Catalog. Well-defined optical criteria are used toselect the galaxies, and X-ray fluxes are measured at the opticallydefined positions. The result is a comprehensive list of X-ray detectionand upper limit measurements for 1018 galaxies. Of these, 827 haveeither independent distance estimates or radial velocities. Associatedoptical, redshift, and distance data have been assembled for thesegalaxies, and their distances come from a combination of directlypredicted distances and those predicted from the Faber-Burstein GreatAttractor/Virgocentric infall model. The accuracy of the X-ray fluxeshas been checked in three different ways; all are consistent with thederived X-ray fluxes being of <=0.1 dex accuracy. In particular,there is agreement with previously published X-ray fluxes for galaxiesin common with a 1991 study by Roberts et al. and a 1992 study byFabbiano et al. The data presented here will be used in further studiesto characterize the X-ray output of galaxies of various morphologicaltypes and thus to enable the determination of the major sourcescontributing to the X-ray emission from galaxies.
| Ansolute Magnitudes of Stars in the Scorpo-Centaurus Association.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1958ApJ...128..533B&db_key=AST
| Spectral types and luminosities of B, A and F southern stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1957MNRAS.117..449D&db_key=AST
| Metallicity Indices for Multi-Population Models.II.Bulges of Galaxies
We report metallicity indices in the Lick system (Hβ, Fe52, Fe53,NaD, Mg_2_) for a sample of 45 spiral bulges in the southern hemisphere.The velocity dispersion σ was also derived for each object. Spiralbulges and elliptical galaxies show a continuity in diagrams like theplane Mg_2_- or σ-Mg_2_. Using calibrations derived fromchemical evolutionary models, we estimated metallicities and abundanceratios for those bulges. The sample mean metallicity is [Fe/H]= -0.19+/- 0.27(rmsd), and the mean abundance ratios are [Mg/Fe] = 0.46 +/-0.11 (rmsd) and [Na/Fe] = 0.45 +/- 0.19(rmsd). These abundances suggestthat spiral bulges (like E's) were chemically enriched by type IIsupernovae, and that the main star formation era occurred in a timescale of the order of 1-2 Gyr.
| Galactic Rings
About one fifth of all spiral disk galaxies include a ring-shapedpattern in the light distribution, and an additional one third appear tohave broken or partial rings made up of spiral arms (pseudorings). Theserings are a special problem in galaxy morphology with a direct bearingon the internal dynamics and evolution of disk galaxies. Morphologicaldata have shown that rings are most often associated with bars or othercommon nonaxisymmetric perturbations, such as ovals. Kinematic andmetric data have provided considerable evidence for intrinsic ovalshapes and preferred alignments between ring major axes and bars.Photometric data have demonstrated that most rings are sites of currentactive star formation, and in some galaxies a ring is the only placewhere recent star formation is found. A few rings are sites of the mostspectacular "starbursts" known in non-violently interacting galaxies.Though a small fraction of observed rings may be due to collisions ormergers of galaxies, or to accretion of intergalactic gas, the vastmajority of rings are probably simple resonance phenomena, caused by theactions of a rotating bar or other nonaxisymmetic disturbance on themotions of gas clouds in the disk. The evidence in support of this ideahas accumulated steadily during the past 15 years, and our goal in thisreview is to bring together a large body of theoretical andobservational results in one place. We shall see that rings are anatural consequence of barred galaxy dynamics, and that they are moreeasily understood than the bars and ovals which undoubtedly create them.However, there are interesting problems, such as the lack of any ringsin some barred galaxies, the less common but by no means rare cases ofrings in nonbarred galaxies, the role of mild tidal interactions, wherethe gas that fuels star formation in rings actually comes from, theexistence of different ring types of very different time-scales in thesame galaxy. We will discuss these problems in some detail here, andindicated where the solutions may lie.
| On the individual parallaxes of the brighter galactic helium stars in the southern hemisphere, together with considerations on the parallax of stars in general.
Not Available
| The Catalog of Southern Ringed Galaxies
The Catalog of Southern Ringed Galaxies (CSRG) is a comprehensivecompilation of diameters, axis ratios, relative bar position angles, andmorphologies of inner and outer rings, pseudorings, and lenses in 3692galaxies south of declination -17 deg. The purpose of the catalog is toevaluate the idea that these ring phenomena are related to orbitalresonances with a bar or oval in galaxy potentials. The catalog is basedon visual inspection of most of the 606 fields of the Science ResearchCouncil (SRC) IIIa-J southern sky survey, with the ESO-B, ESO-R, andPalomar Sky surveys used as auxiliaries when needed for overexposed coreregions. The catalog is most complete for SRC fields 1-303 (mostly southof declination -42 deg). In addition to ringed galaxies, a list of 859mostly nonringed galaxies intended for comparison with other catalogs isprovided. Other findings from the CSRG that are not based on statisticsare the identification of intrinsic bar/ring misalignment; bars whichunderfill inner rings; dimpling of R'1pseudorings; pointy, rectangular, or hexagonal inner or outer ringshapes; a peculiar polar-ring-related system; and other extreme examplesof spiral structure and ring morphology.
| NGC 4378's one-armed spiral pattern: Leading or trailing?
Observations and simulations of the galaxy NGC 4622 indicate that it hasa true leading arm winding outward opposite the sense of disk spin. Thearm is apparently a long-lived density wave leading out to a resonancering. Simulations of a plunging retrograde passage of a small companioncreates this pattern. A proper match to the observations does not resultunless self gravity is unimportant in the disk. We now investigatewhether or not NGC 4378, another single-armed disk galaxy, also has aleading density wave arm. We find via simulations that NGC 4378'spattern is not a leading density wave but is instead an impulsivetrailing arm created by a grazing passage of a small companion. Thisimpulsive arm has a short lifetime in the simulations. Nevertheless,like in NGC 4622, a nongravitating (halo dominated) disk is necessary tocreate the observed pattern in NGC 4378.
| Evolution of spiral structure in an interacting triple galactic system I. M 31-type systems
We investigate the effect of two small companion galaxies in thecreation and evolution of spiral arms in a disk galaxy. Both companionsmove in circular orbits around the main galaxy. Using a two dimensionalself-consistent computer simulation code we find that, when there isonly one companion, one leading or two trailing spiral arms are formed,depending on the rotation of the companion (retrograde or directrespectively). In the case of two companion galaxies, when thecompanions move in opposite directions, three spiral arms are formed,one leading and two trailing. The appearance of the above structuresuggests that each companion acts independently on the main disk galaxy.The created spiral arms may intersect each other, resulting in thedisappearance of the weaker arm.
| 2.1 μm images of the evolved stellar disk and the morphological classification of spiral galaxies
Near-infrared images confirm that the Hubble classification of spiralgalaxies does not constrain the morphology of their stellar PopulationII disk, since galaxies on opposite ends of the spiral sequence candisplay remarkably similar evolved disk morphologies. Thus, the gasdominated Population I component determines the types (a, b, c),decoupled from the Population II. The underlying mass distributionsobserved in the infrared are exceptionally regular, suggesting thatlarge scale spiral structure is principally intrinsic, as argued by themodal theory. Moreover, single arms, bisymmetric arms, lopsidednessand/or bars dominate the old stellar disk. The absence of infraredmultiple-armed structure is attributed to the efficiency of InnerLindblad Resonance absorption in the evolved Population II disk. Theseobservations support a coherent framework for galaxy classificationbased on three parameters: stellar disk "temperature", gas content andactive disk mass.
| Formation of a retrograde spiral arm induced by a Ram pressure
The response of a galactic disk to a ram pressure due to anintergalactic gas is studied; it is found that the ram pressure excitesa spiral structure in the disk. Development of a prominent spiralstructure is demonstrated by a simple numerical simulation of a gas disksubjected to a ram pressure. The spiral structure induced by a rampressure is a wave phenomenon, and, in contrast to the normal spiralwaves, it is single-armed and slowly rotates in a retrograde direction.The sense of the spiral is trailing with respect to the patternrotation; thus the spiral is apparently leading with respect to thegalatic rotation. The spiral pattern slowly winds up in a retrogradedirection.
| Astrophysics in 1993
After the astronomical excitements of 1991 and 1992, 1993 was frankly abit of a letdown. More papers by more people were submitted andpublished than ever before (and this review has twice as many authors asthe previous ones). Nevertheless, there seem to have been fewer large,definitive steps. As a result, we have focused on a handful of broadterrains for which the maps have improved, including stellar rotationand mass loss, dynamics of globular clusters, and quasar absorptionlines, but have also highlighted many more of the small steps by whichastonomy advances toward inventorying and and understanding theuniverse. As a consequence, the ordering of topics is less obviouslyfrom near to far than in 1991 and 1992. And the potential formisattributions and unjustifiable neglect is probably somewhat larger.
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הכנס מאמר חדש
לינקים קשורים
הכנס לינק חדש
משמש של הקבוצה הבאה
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תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | מזבח |
| התרוממות ימנית: | 17h24m01.10s |
| סירוב: | -62°51'51.0" |
| גודל גלוי: | 5.7 |
| מרחק: | 502.513 פארסק |
| תנועה נכונה: | -0.1 |
| תנועה נכונה: | -9.3 |
| B-T magnitude: | 5.485 |
| V-T magnitude: | 5.651 |
קטלוגים וכינוים:
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INHABITED SKY
