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Absolute Magnitude Distributions and Light Curves of Stripped-Envelope Supernovae
The absolute visual magnitudes of three Type IIb, 11 Type Ib, and 13Type Ic supernovae (collectively known as stripped-envelope supernovae)are studied by collecting data on the apparent magnitude, distance, andinterstellar extinction of each event. Weighted and unweighted meanabsolute magnitudes of the combined sample, as well as various subsetsof the sample, are reported. The limited sample size and theconsiderable uncertainties, especially those associated with extinctionin the host galaxies, prevent firm conclusions regarding differencesbetween the absolute magnitudes of supernovae of Types Ib and Ic, andregarding the existence of separate groups of overluminous andnormal-luminosity stripped-envelope supernovae. The spectroscopiccharacteristics of the events of the sample are considered. Three of thefour overluminous events are known to have had unusual spectra. Most butnot all of the normal-luminosity events have had typical spectra. Thelight curves of stripped-envelope supernovae are collected and compared.Because SN 1994I in M51 was very well observed, it often is regarded asthe prototypical Type Ic supernova, but it has the fastest light curvein the sample. Light curves are modeled by means of a simple analyticaltechnique that, combined with a constraint on E/M from spectroscopy,yields internally consistent values of ejected mass, kinetic energy, andnickel mass.

Hydrogen and helium traces in type Ib-c supernovae
Aims.To investigate the spectroscopic properties of a selected opticalphotospheric spectra of core collapse supernovae (CCSNe). Specialattention is devoted to traces of hydrogen at early phases. The impacton the physics and nature of their progenitors is emphasized.Methods: .The CCSNe-sample spectra are analyzed with the parameterizedsupernova synthetic spectrum code "SYNOW" adopting some simplifyingapproximations. Results: .The generated spectra are found to matchthe observed ones reasonably well, including a list of only 23 candidateions. Guided by SN Ib 1990I, the observed trough near 6300 Å isattributed to Hα in almost all type Ib events, although in someobjects it becomes too weak to be discernible, especially at laterphases. Alternative line identifications are discussed. Differences inthe way hydrogen manifests its presence within CCSNe are highlighted. Intype Ib SNe, the Hα contrast velocity (i.e. line velocity minusthe photospheric velocity) seems to increase with time at early epochs,reaching values as high as 8000 km s-1 around 15-20 daysafter maximum and then remains almost constant. The derived photosphericvelocities, indicate a lower velocity for type II SNe 1987A and 1999emas compared to SN Ic 1994I and SN IIb 1993J, while type Ib eventsdisplay a somewhat larger variation. The scatter, around day 20, ismeasured to be ~5000 km s-1. Following two simple approaches,rough estimates of ejecta and hydrogen masses are given. A mass ofhydrogen of approximately 0.02 M_ȯ is obtained for SN 1990I, whileSNe 1983N and 2000H ejected ~0.008 M_ȯ and ~0.08 M_ȯ ofhydrogen, respectively. SN 1993J has a higher hydrogen mass, ~0.7M_ȯ with a large uncertainty. A low mass and thin hydrogen layerwith very high ejection velocities above the helium shell, is thus themost likely scenario for type Ib SNe. Some interesting and curiousissues relating to oxygen lines suggest future investigations.

A search for Low Surface Brightness galaxies in the near-infrared. I. Selection of the sample
A sample of about 3800 Low Surface Brightness (LSB) galaxies wasselected using the all-sky near-infrared (J, H and Ks-band)2MASS survey. The selected objects have a mean central surfacebrightness within a 5'' radius around their centre fainter than 18 magarcsec-2 in the Ks band, making them the lowestsurface brightness galaxies detected by 2MASS. A description is given ofthe relevant properties of the 2MASS survey and the LSB galaxy selectionprocedure, as well as of basic photometric properties of the selectedobjects. The latter properties are compared to those of other samples ofgalaxies, of both LSBs and ``classical'' high surface brightness (HSB)objects, which were selected in the optical. The 2MASS LSBs have aBT_c-KT colour which is on average 0.9 mag bluerthan that of HSBs from the NGC. The 2MASS sample does not appear tocontain a significant population of red objects.All tables and Figs. 2a-c are only available in electronic form athttp://www.edpsciences.org

``Sloshing'' Librations in Lopsided Disk Galaxies
A combined particle-mesh N-body/gridded hydrodynamics/stellar evolutioncode is employed to model the response of a galaxy disk to an impulsiveperturbation. The resulting galaxy is examined for asymmetry inmorphology and dynamics to answer the question of whether free``sloshing'' librations in the plane of the disk can explain therelatively large proportion of asymmetric field spirals. The simulationproduced a perturbed disk containing streamers of gas and stars, gasshocks, and m=1 and m=2 spiral structure. Strong kinematic peculiaritieswere generated as well. However, although the resulting disk reproducedmany of the kinematic features observed in H I synthesis maps, theeffects are relatively short-lived, lasting only on the order of adynamical timescale. The similarities between the model and the tidallydeformed galaxy NGC 5474, however, do leave open the possibility offorced sloshing modes playing a role in galaxies undergoing tidalinteractions.

A Search for Radio Emission from Supernovae with Ages from about 1 Week to More than 80 Years
We report Very Large Array radio observations of 29 supernovae (SNe)with ages ranging from 10 days to about 90 yr past explosion. Theseobservations significantly contribute to the existing data pool on suchobjects. Included are detections of known radio SNe 1950B, 1957D, 1970G,and 1983N, the suspected radio SN 1923A, and the possible radio SN1961V. None of the remaining 23 observations resulted in detections,providing further evidence to support the observed trend that most SNeare not detectable radio emitters. To investigate the apparent lack ofradio emission from the SNe reported here, we have followed standardpractice and used Chevalier's ``standard model'' to derive (upper limitsto) the mass-loss rates for the supernova progenitors. These upperlimits to the fluxes are consistent with a lack of circumstellarmaterial needed to provide detectable radio emission for SNe at theseages and distances. Comparison of the radio luminosities of thesesupernovae as a function of age past explosion to other well-observedradio SNe indicates that the Type II SNe upper limits are moreconsistent with the extrapolated light curves of SN 1980K than of SN1979C, suggesting that SN 1980K may be a more typical radio emitter thanSN 1979C. For completeness, we have included an appendix where theresults of analyses of the non-SN radio sources are presented. Wherepossible, we make (tentative) identifications of these sources usingvarious methods.

Direct Analysis of Spectra of Type Ib Supernovae
Synthetic spectra generated with the parameterized supernovasynthetic-spectrum code SYNOW are compared to photospheric-phase spectraof Type Ib supernovae (SNe Ib). Although the synthetic spectra are basedon simplifying approximations, including spherical symmetry, theyaccount well for the observed spectra. Our sample of SNe Ib obeys atight relation between the velocity at the photosphere, as determinedfrom the Fe II features, and the time relative to that of maximum light.From this we infer that the masses and the kinetic energies of theevents in this sample were similar. After maximum light the minimumvelocity at which the He I features form usually is higher than thevelocity at the photosphere, but the minimum velocity of the ejectedhelium is at least as low as 7000 km s-1. Spectra of SN 2000Hreveal the presence of hydrogen absorption features, and we concludethat hydrogen lines also were present in SNe 1999di and 1954A. Hydrogenappears to be present in SNe Ib in general, although in most events itbecomes too weak to identify soon after maximum light. The hydrogen-lineoptical depths that we use to fit the spectra of SNe 2000H, 1999di, and1954A are not high, so only a mild reduction in the hydrogen opticaldepths would be required to make these events look like typical SNe Ib.Similarly, the He I line optical depths are not very high, so a moderatereduction would make SNe Ib look like SNe Ic.

Bar Galaxies and Their Environments
The prints of the Palomar Sky Survey, luminosity classifications, andradial velocities were used to assign all northern Shapley-Ames galaxiesto either (1) field, (2) group, or (3) cluster environments. Thisinformation for 930 galaxies shows no evidence for a dependence of barfrequency on galaxy environment. This suggests that the formation of abar in a disk galaxy is mainly determined by the properties of theparent galaxy, rather than by the characteristics of its environment.

Large-scale asymmetry of rotation curves in lopsided spiral galaxies
Many spiral galaxies show a large-scale asymmetry with a cos phidependence in their rotation curves as well as in their morphology, suchas M 101 and NGC 628. We show that both these features can be explainedby the response of a galactic disk to an imposed lopsided halopotential. A perturbation potential of 5% is deduced for themorphologically lopsided galaxies in the Rix & Zaritsky(\cite{Rix95}) sample. This is shown to result in a difference of 10 %or >=20-30 km s-1 in the rotation velocity on the twosides of the major axis. Interestingly, the observed isophotal asymmetryin a typical spiral galaxy is not much smaller and it results in avelocity asymmetry of 7 % or ~ 14-21 km s-1. Hence, wepredict that most spiral galaxies show a fairly significant rotationalasymmetry. The rotation velocity is shown to be maximum along theelongated isophote - in agreement with the observations along the SW inM 101, while it is minimum along the opposite direction. This resultleads to the distinctive asymmetric shape of the rotation curve whichrises more steeply in one half of the galaxy than the other, as observedby Swaters et al. (\cite{Swae99}). This shape is shown to be a robustfeature and would result for any centrally concentrated disk. The netdisk lopsidedness and hence the asymmetry in the rotation curve ispredicted to increase with radius and hence can be best studied using HIgas as the tracer.

Supernovae in isolated galaxies, in pairs and in groups of galaxies
In order to investigate the influence of environment on supernova (SN)production, we have performed a statistical investigation of the SNediscovered in isolated galaxies, in pairs and in groups of galaxies. 22SNe in 18 isolated galaxies, 48 SNe in 40 galaxy members of 37 pairs and211 SNe in 170 galaxy members of 116 groups have been selected andstudied. We found that the radial distributions of core-collapse SNe ingalaxies located in different environments are similar, and consistentwith those reported by Bartunov, Makarova & Tsvetkov. SNe discoveredin pairs do not favour a particular direction with respect to thecompanion galaxy. Also, the azimuthal distributions inside the hostmembers of galaxy groups are consistent with being isotropics. The factthat SNe are more frequent in the brighter components of the pairs andgroups is expected from the dependence of the SN rates on the galaxyluminosity. There is an indication that the SN rate is higher in galaxypairs compared with that in groups. This can be related to the enhancedstar formation rate in strongly interacting systems. It is concludedthat, with the possible exception of strongly interacting systems, theparent galaxy environment has no direct influence on SN production.

Supernovae in the nuclear regions of starburst galaxies
The feasibility of using near-infrared observations to discoversupernovae in the nuclear and circumnuclear regions of nearby starburstgalaxies is investigated. We provide updated estimates of the intrinsiccore-collapse supernova rates in these regions. We discuss the problemof extinction, and present new estimates of the extinction towards 33supernova remnants in the starburst galaxy M 82. This is done using Hiand H2 column density measurements. We estimate the molecularto atomic hydrogen mass ratio to be 7.4+/-1.0 in M 82. We have assemblednear-infrared photometric data for a total of 13 core-collapsesupernovae, some unpublished hitherto. This constitutes the largestdatabase of infrared light curves for such events. We show that theinfrared light curves fall into two classes, `ordinary' and `slowlydeclining'. Template JHKL light curves are derived for both classes. Forordinary core-collapse supernovae, the average peak JHKL absolutemagnitudes are -18.4, -18.6, -18.6 and -19.0 respectively. The slowlydeclining core-collapse supernovae are found to be significantly moreluminous than the ordinary events, even at early times, having averagepeak JHKL absolute magnitudes of -19.9, -20.0, -20.0 and -20.4respectively. We investigate the efficiency of a computerized imagesubtraction method in supernova detection. We then carry out a MonteCarlo simulation of a supernova search using K-band images of NGC 5962.The effects of extinction and observing strategy are discussed. Weconclude that a modest observational programme will be able to discovera number of nuclear supernovae.

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.

Departures From Axisymmetric Morphology and Dynamics in Spiral Galaxies
New H I synthesis data have been obtained for six face-on galaxies withthe Very Large Array. These data and reanalyses of three additional datasets make up a sample of nine face-on galaxies analyzed for deviationsfrom axisymmetry in morphology and dynamics. This sample represents asubsample of galaxies already analyzed for morphological symmetryproperties in the R band. Four quantitative measures of dynamicalnonaxisymmetry are compared with one another and to the quantitativemeasures of morphological asymmetry in H I and the R band to investigatethe relationships between nonaxisymmetric morphology and dynamics. Wefind no significant relationship between asymmetric morphology and mostof the dynamical measures in our sample. A possible relationship isfound, however, between morphology and dynamical position angledifferences between approaching and receding sides of the galaxy.

An Infrared Search for Extinguished Supernovae in Starburst Galaxies
IR and radio-band observations of heavily extinguished regions instarburst galaxies suggest a high supernova (SN) rate associated withsuch regions. Optically measured SN rates may therefore underestimatethe total SN rate by factors of up to 10, as a result of the very highextinction (A_B~10-20 mag) to core-collapse SNe in starburst regions.The IR/radio SN rates come from a variety of indirect means, however,which suffer from model dependence and other problems. We describe adirect measurement of the SN rate from a regular patrol of starburstgalaxies done with K'-band imaging to minimize the effects ofextinction. A collection of K'-band measurements of core-collapse SNenear maximum light is presented. Such measurements (excluding 1987A) arenot well reported in the literature. Results of a preliminary K'-bandsearch, using the MIRC camera at the Wyoming Infrared Observatory and animproved search strategy using the new ORCA optics, are described. Amonthly patrol of a sample of IRAS bright (mostly starburst) galaxieswithin 25 Mpc should yield 1-6 SNe yr^-1, corresponding to the range ofestimated SN rates. Our initial MIRC search with low resolution (2.2"pixels) failed to find extinguished SNe in the IRAS galaxies, limitingthe SN rate outside the nucleus (at greater than 15" radius) to lessthan 3.8 far-IR SN rate units (SNe per century per 10^10 L_solarmeasured at 60 and 100 mum, or FIRSRU) at 90% confidence. The MIRCcamera had insufficient resolution to search nuclear starburst regions,where starburst and SN activity is concentrated; therefore, we wereunable to rigorously test the hypothesis of high SN rates in heavilyobscured star-forming regions. We conclude that high-resolution nuclearSN searches in starburst galaxies with small fields are more productivethan low-resolution, large-field searches, even for our sample of large(often several arcminutes) galaxies. With our ORCA high-resolutionoptics, we could limit the total SN rate to less than 1.3 FIRSRU at 90%confidence in 3 years of observations, lower than most estimates.

Radio Supernovae as Distance Indicators
Long-term monitoring of the radio emission from supernovae with the VeryLarge Array (VLA) shows that the radio "light curves" evolve in asystematic fashion with a distinct peak flux density (and thus, incombination with a distance, a peak spectral luminosity) at eachfrequency and with a well-defined time from explosion to that peak.Studying these two quantities at 6 cm wavelength, peak spectralluminosity (L6 cm peak), and time after explosion date(t0) to reach that peak (t6 cm peak - t0), we find thatthey appear related. In particular, based on two objects, Type Ibsupernovae may be approximate radio "standard candles" with a 6 cm peakluminosity of L6 cm peak ~ 19.9 x 1026 ergs s-1 Hz-1;also, based on two objects, Type Ic supernovae may be approximate radiostandard candles with a 6 cm peak luminosity of L6 cm peak~ 6.5 x 1026 ergs s-1 Hz-1; and, based on 12 objects, Type II supernovaeappear to obey a relation L6 cm peak ~= 5.5 x1023(t6 cm peak - t0)1.4 ergs s-1 Hz-1, with time measuredin days. If these relations are supported by further observations, theyprovide a means for determining distances to supernovae, and thus totheir parent galaxies, from purely radio continuum observations. Withcurrently available sensitivity of the VLA, it is possible to employthese relations for objects further than the Virgo Cluster out to ~100Mpc. With planned improvements to the VLA and the possible constructionof more sensitive radio telescopes, these techniques could be extendedto z ~ 1 for some classes of bright radio supernovae.

A Photometric Method for Quantifying Asymmetries in Disk Galaxies
A photometric method for quantifying deviations from axisymmetry inoptical images of disk galaxies is applied to a sample of 32 face-on andnearly face-on spirals. The method involves comparing the relativefluxes contained within trapezoidal sectors arranged symmetrically aboutthe galaxy center of light, excluding the bulge and/or barred regions.Such a method has several advantages over others, especially whenquantifying asymmetry in flocculent galaxies. Specifically, theaveraging of large regions improves the signal-to-noise in themeasurements; the method is not strongly affected by the presence ofspiral arms; and it identifies the kinds of asymmetry that are likely tobe dynamically important. Application of this ``method of sectors'' toR-band images of 32 disk galaxies indicates that about 30% of spiralsshow deviations from axisymmetry at the 5 sigma level.

Bulge-Disk Decomposition of 659 Spiral and Lenticular Galaxy Brightness Profiles
We present one of the largest homogeneous sets of spiral and lenticulargalaxy brightness profile decompositions completed to date. The 659galaxies in our sample have been fitted with a de Vaucouleurs law forthe bulge component and an inner-truncated exponential for the diskcomponent. Of the 659 galaxies in the sample, 620 were successfullyfitted with the chosen fitting functions. The fits are generally welldefined, with more than 90% having rms deviations from the observedprofile of less than 0.35 mag. We find no correlations of fittingquality, as measured by these rms residuals, with either morphologicaltype or inclination. Similarly, the estimated errors of the fittedcoefficients show no significant trends with type or inclination. Thesedecompositions form a useful basis for the study of the lightdistributions of spiral and lenticular galaxies. The object base issufficiently large that well-defined samples of galaxies can be selectedfrom it.

The Southern Sky Redshift Survey
We report redshifts, magnitudes, and morphological classifications for5369 galaxies with m_B <= 15.5 and for 57 galaxies fainter than thislimit, in two regions covering a total of 1.70 sr in the southerncelestial hemisphere. The galaxy catalog is drawn primarily from thelist of nonstellar objects identified in the Hubble Space TelescopeGuide Star Catalog (GSC). The galaxies have positions accurate to ~1"and magnitudes with an rms scatter of ~0.3 mag. We compute magnitudes(m_SSRS2) from the relation between instrumental GSC magnitudes and thephotometry by Lauberts & Valentijn. From a comparison with CCDphotometry, we find that our system is homogeneous across the sky andcorresponds to magnitudes measured at the isophotal level ~26 magarcsec^-2. The precision of the radial velocities is ~40 km s^-1, andthe redshift survey is more than 99% complete to the m_SSRS2 = 15.5 maglimit. This sample is in the direction opposite that of the CfA2; incombination the two surveys provide an important database for studies ofthe properties of galaxies and their large-scale distribution in thenearby universe. Based on observations obtained at Cerro TololoInter-American Observatory, National Optical Astronomy Observatories,operated by the Association of Universities for Research in Astronomy,Inc., under cooperative agreement with the National Science Foundation;Complejo Astronomico El Leoncito, operated under agreement between theConsejo Nacional de Investigaciones Científicas de laRepública Argentina and the National Universities of La Plata,Córdoba, and San Juan; the European Southern Observatory, LaSilla, Chile, partially under the bilateral ESO-ObservatórioNacional agreement; Fred Lawrence Whipple Observatory;Laboratório Nacional de Astrofísica, Brazil; and the SouthAfrican Astronomical Observatory.

Optical Spectra of Supernovae
The temporal evolution of the optical spectra of various types ofsupernovae (SNe) is illustrated, in part to aid observers classifyingsupernova candidates. Type II SNe are defined by the presence ofhydrogen, and they exhibit a very wide variety of photometric andspectroscopic properties. Among hydrogen-deficient SNe (Type I), threesubclasses are now known: those whose early-time spectra show strong SiII (Ia), prominent He I (Ib), or neither Si II nor He I (Ic). Thelate-time spectra of SNe Ia consist of a multitude of blended emissionlines of iron-group elements; in sharp contrast, those of SNe Ib and SNeIc (which are similar to each other) are dominated by several relativelyunblended lines of intermediate-mass elements. Although SNe Ia, whichresult from the thermonuclear runaway of white dwarfs, constitute arather homogeneous subclass, important variations in their photometricand spectroscopic properties are undeniably present. SNe Ib/Ic probablyresult from core collapse in massive stars largely stripped of theirhydrogen (Ib) and helium (Ic) envelopes, and hence they are physicallyrelated to SNe II. Indeed, the progenitors of some SNe II seem to haveonly a low-mass skin of hydrogen; their spectra gradually evolve toresemble those of SNe Ib. In addition to the two well-known photometricsubclasses (linear and plateau) of SNe II, which may exhibit minorspectroscopic differences, there is a new subclass (SNe IIn)distinguished by relatively narrow emission lines with little or no PCygni absorption component and slowly declining light curves. Theseobjects probably have unusually dense circumstellar gas with which theejecta interact.

Lopsided Spiral Galaxies and a Limit on the Galaxy Accretion Rate
We present a measurement of lopsidedness for the stellar disks of 60field spiral galaxies in terms of the azimuthal m = 1 Fourier amplitude,A1, of the stellar light. We confirm the previous result (Rix &Zaritsky) that ~30% of field spiral galaxies in a magnitude-limitedsample exhibit significant lopsidedness ( >= 0.2) atlarge radii (R > 1.5 disk scalelengths). We conjecture that thislopsidedness is caused by tidal interactions and calculate an upperlimit on the accretion rate of small galaxies. We exploit thecorrelation between lopsidedness and photometric measures of recent starformation (Zaritsky) to obtain two independent estimates of the lifetimeof these m = 1 distortions. First, we show that lopsided galaxies havean excess of blue luminosity relative to that of symmetric galaxies withthe same H I linewidth, which we attribute to a recent star formationepisode that was triggered by an interaction between the galaxy and acompanion. We use stellar population models (Bruzual & Charlot) toestimate the time since that interaction. Second, we use the N-bodysimulation of an infalling satellite by Walker, Mihos, & Hernquistto estimate how fast tidally induced m = 1 distortions are erasedthrough phase mixing. Both approaches indicate that the observations areconsistent with a hypothesized tidal interaction that occurred about 1Gyr ago for galaxies that are lopsided at the 20% level. By combiningthis lifetime estimate for lopsidedness, the observed frequency of suchdistortions, and a correction to the survey volume that depends on theincrease in luminosity during an interaction, we derive an upper limiton the current companion accretion rate of field spiral galaxies (forcompanion masses ~10% parent galaxy mass) that lies in the range0.07--0.25 Gyr-1. The principal uncertainty in this limit arises fromambiguities in the interpretation of the correlation betweenlopsidedness and MB.

Galaxies with a UV excess in which supernovae have been observed.
Not Available

The statistics analysis of recent supernovae.
Not Available

Supernovae and Massive Star Formation Regions
We have extended the work of Van Dyk [AJ, 103, 1788 (1992)] on theassociation of supernovae with massive star formation regions, as tracedby giant H II regions, in late-type galaxies. In this paper, weconcentrate only on supernovae arising from massive progenitors, TypeIb/c and Type II, using ground-based CCD Hα images. We improveupon earlier studies by increasing the supernova sample, by includingonly spectroscopically classified supernovae, and by obtaining moreaccurate astrometry of the supernovae and their environments. We findthat the degree of association of both supernova types with H II regionsin their parent galaxies is not significantly different, implying thatboth types arise from essentially the same range of stellar masses. Fromconsideration of the statistics in this paper, including the Hαluminosities of the H II regions with which supernovae are associated,we can exclude the Wolf-Rayet star progenitor model for most Type Ib/csupernovae. Instead, the progenitors of Type Ib/c supernovae areprobably in relatively close binary systems, rather than single stars orstars in wide binaries (possible progenitor systems for Type Ilsupernovae); interaction with a companion star can severely deplete thehydrogen envelope prior to explosion.

Redshift periodicity in the Local Supercluster.
Persistent claims have been made over the last ~15yr that extragalacticredshifts, when corrected for the Sun's motion around the Galacticcentre, occur in multiples of ~24 or ~36km/s. A recent investigation byus of 40 spiral galaxies out to 1000km/s, with accurately measuredredshifts, gave evidence of a periodicity ~37.2-37.7km/s. Here we extendour enquiry out to the edge of the Local Supercluster (~2600km/s),applying a simple and robust procedure to a total of 97 accuratelydetermined redshifts. We find that, when corrected for related vectorsclose to recent estimates of the Sun's galactocentric motion, theredshifts of spirals are strongly periodic (P~37.6km/s). The formalconfidence level of the result is extremely high, and the signal is seenindependently with different radio telescopes. We also examine a furthersample of 117 spirals observed with the 300-foot Green Bank telescopealone. The periodicity phenomenon appears strongest for the galaxieslinked by group membership, but phase coherence probably holds overlarge regions of the Local Supercluster.

X-ray emission from supernovae: a review of the observations
Supernovae have been expected to be X-ray sources for many years. Thispaper reviews the observations that have detected or placed upper limitson the emission of X-rays from supernovae. A firm upper limit exists onX-ray emission from Type Ia supernovae based upon an observation of SN1992A (parent galaxy: NGC 1380) made with ROSAT. The type II supernovaedetected include SN 1978K (NGC 1313), SN 1980K (NGC 6946), SN 1986J (NGC891), SN 1987A (Large Magellanic Cloud), and, most recently, SN 1993J(NGC 3031). These supernovae emit X-rays by at least two differentprocesses. The author briefly reviews the proposed emission mechanisms.

Nonaxisymmetric Structures in the Stellar Disks of Galaxies
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJ...447...82R&db_key=AST

A Preliminary Classification Scheme for the Central Regions of Late-Type Galaxies
The large-scale prints in The Carnegie Atlas of Galaxies have been usedto formulate a classification scheme for the central regions oflate-type galaxies. Systems that exhibit small bright central bulges ordisks (type CB) are found to be of earlier Hubble type and of higherluminosity than galaxies that do not contain nuclei (type NN). Galaxiescontaining nuclear bars, or exhibiting central regions that are resolvedinto individual stars and knots, and galaxies with semistellar nuclei,are seen to have characteristics that are intermediate between those oftypes CB and NN. The presence or absence of a nucleus appears to be auseful criterion for distinguishing between spiral galaxies andmagellanic irregulars.

Quantitative Morphology of Bars in Spiral Galaxies
As suggested by numerical simulations, the axis ratio of the bar is afundamental parameter to describe the dynamical evolution of a barredgalaxy. In a first-order approximation considering bars as ellipticalfeatures, visual measurements of bar axis ratios and lengths of 136spiral galaxies were performed on photographs of good linear scale.Despite the limitations affecting such measurements, morphologicalproperties of bars in spirals along the Hubble sequence as well as therelationship between the bar axis ratio and nuclear star formationactivity are studied. It is found that the relative length of bars inearly-type galaxies is, on average, about a factor of 3 larger than thelength observed in late-type spirals. Also, a relation between barlengths and bulge diameters is observed for both early-type andlate-type spirals, confirming results from previous works. Furthermore,although the number of objects is small, there is an apparentcorrelation between the presence of nuclear star formation activity andthe bar axis ratio: about 71% of the starburst galaxies included in thesample have a strong bar (b/a < 0.6). The introduction of thesequantitative parameters in galaxy classification schemes is discussed.

Distribution of supernovae relative to spiral arms and H II regions
We have studied the association of supernovae in spiral galaxies withsites of recent stars formation -- sprial arms and H II regions. It isshown that supernovae (SNe) of Types Ia, Ib, and II exhibitconcentration to spiral arms and their distributions over the distanceto the nearest spiral arm do not differ significantly. This result isconfirmed by a Kolmogorov-Smirnov test comparison with the distancedistributions, expected if SNe are distributed randomly inside the modelgalaxy. SNe of types Ib and II show a strong concentration towards H IIregions, while distribution of SNe Ia can be explained by chancesuperposition. All studied distributions of SNe Ib and II show strikingsimilarity, which suggests that their progenitors are massive stars withsimilar ages and initial masses. The association of SNe Ia with spiralarms suggests that their progenitors in spiral galaxies are likely to beintermediate mass stars.

On the size and formation mechanism of the largest star-forming complexes in spiral and irregular galaxies
The average diameters of the largest star complexes in most of thespiral and irregular galaxies in the Sandage and Bedke Atlas of Galaxieswere measured from the Atlas photographs. The complex diametersDc correlate with galaxy magnitude as Dc = 0.18 -0.14MB, which has about the same slope as the correlation forthe largest H II regions studied by Kennicutt. There is no obviouscorrelation between Dc and either Hubble type or spiral armclass at a given magnitude. The variation of Dc withMB closely matches the expected variation in thecharacteristic length of the gaseous gravitational instabilityconsidering that the rotation curve varies with MB and thatthe stability parameter Q is about 1 in the outer regions of the disk.This match corresponds to an effective velocity dispersion of 6.1 km/sthat is about the same for all spiral and irregular galaxies.

UBVRI photometry of SN 1993J in M81: The first 120 days
We present photometry of SN 1993J in M81 (NGC 3031) in theJohnson-Cousins UBVRI system, starting within three days of the probabletime of explosion and ending 120 days later. The reddening along theline of sight to this supernova is uncertain--there is evidence forsmall (E(B-V) approximately equals 0.08 mag) and moderate (E(B-V)approximately equals 0.32 mag) values. For each value, we correct theobserved fluxes for extinction and calculate the evolution of the sum ofall optical flux, which contains roughly half of the supernova's totalflux during the period of observation. We also fit the colors to aPlanck function, and determine the temperature and total luminosity ofthe supernova for each value of reddening. A peculiar Type II supernova,SN 1993J gradually evolved spectroscopically to resemble a Type Ib insome respects. We compare its boloometric evolution with that of theprototypical Type Ib SN 1983N, and find the two to be similar.

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Right ascension:02h35m32.60s
Aparent dimensions:1.778′ × 1.585′

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