HI Bright Galaxies in the Southern Zone of Avoidance

A blind survey for HI bright galaxies in the southern Zone of Avoidance, (212 deg < l < 36 deg; |b| < 5 deg), has been made with the 21 cm multibeam receiver on the Parkes 64 m radiotelescope. The survey, sensitive to normal spiral galaxies to a distance of about 40 Mpc and more nearby dwarfs, detected 110 galaxies. Of these, 67 have no counterparts in the NASA/IPAC Extragalactic Database. In general, the uncataloged galaxies lie behind thicker obscuration than do the cataloged objects. All of the newly-discovered galaxies have HI flux integrals more than an order of magnitude lower than the Circinus galaxy. The survey recovers the Puppis cluster and foreground group (Kraan-Korteweg & Huchtmeier 1992), and the Local Void remains empty. The HI mass function derived for the sample is satisfactorily fit by a Schechter function with parameters alpha = 1.51 +- 0.12, Phi* = 0.006 +- 0.003, and log M* = 9.7 +- 0.10.Comment: To appear in The Astronomical Journa

Anomalous wave reflection from the interface of two strongly nonlinear granular media

Granular materials exhibit a strongly nonlinear behaviour affecting the propagation of information in the medium. Dynamically self-organized strongly nonlinear solitary waves are the main information carriers in granular chains. Here we report the first experimental observation of the dramatic change of reflectivity from the interface of two granular media triggered by a noncontact magnetically induced initial precompression. It may be appropriate to name this phenomenon the "acoustic diode" effect. Based on numerical simulations, we explain this effect by the high gradient of particle velocity near the interface.Comment: 14 pages, 3 figure

Vector-soliton collision dynamics in nonlinear optical fibers

We consider the interactions of two identical, orthogonally polarized vector solitons in a nonlinear optical fiber with two polarization directions, described by a coupled pair of nonlinear Schroedinger equations. We study a low-dimensional model system of Hamiltonian ODE derived by Ueda and Kath and also studied by Tan and Yang. We derive a further simplified model which has similar dynamics but is more amenable to analysis. Sufficiently fast solitons move by each other without much interaction, but below a critical velocity the solitons may be captured. In certain bands of initial velocities the solitons are initially captured, but separate after passing each other twice, a phenomenon known as the two-bounce or two-pass resonance. We derive an analytic formula for the critical velocity. Using matched asymptotic expansions for separatrix crossing, we determine the location of these "resonance windows." Numerical simulations of the ODE models show they compare quite well with the asymptotic theory.Comment: 32 pages, submitted to Physical Review

New HI-detected Galaxies in the Zone of Avoidance

We present the first results of a blind HI survey for galaxies in the southern Zone of Avoidance with a multibeam receiver on the Parkes telescope. This survey is eventually expected to catalog several thousand galaxies within Galactic latitude |b|<5 degrees, mostly unrecognised before due to Galactic extinction and confusion. We present here results of the first three detections to have been imaged with the Australia Telescope Compact Array (ATCA). The galaxies all lie near Galactic longitude 325 degrees and were selected because of their large angular sizes, up to 1.3 degrees. Linear sizes range from 53 to 108 kpc. The first galaxy is a massive 5.7x10^11 solar mass disk galaxy with a faint optical counterpart, SGC 1511.1--5249. The second is probably an interacting group of galaxies straddling the Galactic equator. No optical identification is possible. The third object appears to be an interacting pair of low column density galaxies, possibly belonging to an extended Circinus or Centaurus A galaxy group. No optical counterpart has been seen despite the predicted extinction (A(B) = 2.7 - 4.4 mag) not being excessive. We discuss the implications of the results, in particular the low HI column densities (~10^19 atoms/sq.cm) found for two of the three galaxies.Comment: 17 pages, 8 figures (Fig.1 in three parts, Fig.5 in two parts). To appear in Astronomical Journal (Dec 1998). See http://www.atnf.csiro.au/research/multibea

Differential reductions of the Kadomtsev-Petviashvili equation and associated higher dimensional nonlinear PDEs

We represent an algorithm allowing one to construct new classes of partially integrable multidimensional nonlinear partial differential equations (PDEs) starting with the special type of solutions to the (1+1)-dimensional hierarchy of nonlinear PDEs linearizable by the matrix Hopf-Cole substitution (the B\"urgers hierarchy). We derive examples of four-dimensional nonlinear matrix PDEs together with they scalar and three-dimensional reductions. Variants of the Kadomtsev-Petviashvili type and Korteweg-de Vries type equations are represented among them. Our algorithm is based on the combination of two Frobenius type reductions and special differential reduction imposed on the matrix fields of integrable PDEs. It is shown that the derived four-dimensional nonlinear PDEs admit arbitrary functions of two variables in their solution spaces which clarifies the integrability degree of these PDEs.Comment: 20 pages, 1 fugur

Free Energy Minimizers for a Two--Species Model with Segregation and Liquid-Vapor Transition

We study the coexistence of phases in a two--species model whose free energy is given by the scaling limit of a system with long range interactions (Kac potentials) which are attractive between particles of the same species and repulsive between different species.Comment: 32 pages, 1 fig, plain tex, typeset twic

SN 1986J VLBI. The Evolution and Deceleration of the Complex Source and a Search for a Pulsar Nebula

We report on VLBI observations of supernova 1986J in the spiral galaxy NGC 891 at two new epochs, 1990 July and 1999 February, t=7.4 and 15.9 yr after the explosion, and on a comprehensive analysis of these and earlier observations from t~4 yr after the explosion date, which we estimate to be 1983.2 +/- 1.1. The source is a shell or composite, and continues to show a complex morphology with large brightness modulations along the ridge and with protrusions. The supernova is moderately to strongly decelerated. The average outer radius expands as t^(0.71 +/- 0.11), and the expansion velocity has slowed to 6000 km/s at t=15.9 yr from an extrapolated 20,000 km/s at t=0.25 yr. The structure changes significantly with time, showing that the evolution is not self-similar. The shell structure is best visible at the latest epoch, when the protrusions have diminished somewhat in prominence and a new, compact component has appeared. The radio spectrum shows a clear inversion above 10 GHz. This might be related to a pulsar nebula becoming visible through the debris of the explosion. The radio flux density between 1.5 and 23 GHz decreases strongly with time, with the flux density proportional to t^(-2.94 +/- 0.24) between t~15 to 19 yr. This decrease is much more rapid than that found in earlier measurements up to t~6 yr.Comment: 24 pages, 9 Figures, LaTeX Accepted for Publication in the Astrophysical Journa

Supernova type Ia luminosities, their dependence on second parameters, and the value of H_0

A sample of 35 SNe Ia with good to excellent photometry in B and V, minimum internal absorption, and 1200 < v < \approx 30000 km/s is compiled from the literature. As far as their spectra are known they are all Branch-normal. For 29 of the SNe Ia also peak magnitudes in I are known. The SNe Ia have uniform colors at maximum, i.e. =-0.012 mag (sigma=0.051) and =-0.276 mag (sigma=0.078). In the Hubble diagram they define a Hubble line with a scatter of $\sigma_M$=0.21-0.16 mag, decreasing with wavelength. The scatter is further reduced if the SNe Ia are corrected for differences in decline rate Delta_m_15 or color (B-V). A combined correction reduces the scatter to sigma<=0.13 mag. After the correction no significant dependence remains on Hubble type or galactocentric distance. The Hubble line suggests some curvature which can be differently interpreted. A consistent solution is obtained for a cosmological model with Omega_M=0.3, Omega_Lambda=0.7, which is indicated also by much more distant SNe Ia. Absolute magnitudes are available for eight equally blue (Branch-normal) SNe Ia in spirals, whose Cepheid distances are known. If their well defined mean values of M_B, M_V, and M_I are used to fit the Hubble line to the above sample of SNe Ia one obtains H_0=58.3 km/s/Mpc, or, after adjusting all SNe Ia to the average values of Delta_m_15 and (B-V), H_0=60.9 km/s/Mpc. Various systematic errors are discussed whose elimination tends to decrease H_0. The finally adopted value at the 90-percent level, including random and systematic errors, is H_0=58.5 +/- 6.3 km/s/Mpc. Several higher values of H_0 from SNe Ia, as suggested in the literature, are found to depend on large corrections for variations of the light curve parameter and/or on an unwarranted reduction of the Cepheid distances of the calibrating SNe Ia.Comment: 42 pages, including 9 figures; submitted to Ap

Cepheid Calibration of the Peak Brightness of SNe Ia -- IX. SN 1989B in NGC 3627

(Abridged) Repeated imaging observations have been made of NGC 3627 with the HST in 1997/98, over an interval of 58 days. Images were obtained on 12 epochs in the F555W band and on five epochs in the F814W band. The galaxy hosted the prototypical, `Branch normal', type Ia supernova SN 1989B. A total of 83 variables have been found, of which 68 are definite Cepheid variables with periods ranging from 75 days to 3.85 days. The de-reddened distance modulus is determined to be (m-M)_0= 30.22+/-0.12 (internal uncertainty) using a subset of the Cepheid data whose reddening and error parameters are secure. The photometric data of Wells et al. (1994), combined with the Cepheid data for NGC 3627 give M_B(max)= -19.36+/-0.18 and M_V(max)= -19.34+/-0.16 for SN 1989B. Combined with the previous six calibrations in this program, plus two additional calibrations determined by others gives the mean absolute magnitudes at maximum of = -19.48+/-0.07 and = -19.48 +/-0.07 for `Branch normal' SNe Ia at this interim stage in the calibration program. The second parameter correlations of M(max) of blue SNe Ia with decay rate, color at maximum, and Hubble type are re-investigated. The dependence of on decay rate is non-linear, showing a minimum for decay rates between 1.0< Delta m_15 <1.6. Magnitudes corrected for decay rate show no dependence on Hubble type, but a dependence on color remains. Correcting both the fiducial sample of 34 SNe Ia with decay-rate data and the current 8 calibrating SNe Ia for the correlation with decay rate as well as color gives H_0= 60+/-2 (internal) km/s/Mpc, in both B and V. The same value to within 4% is obtained if only the SNe Ia in spirals (without second parameter corrections) are considered.Comment: 32 pages (with 7 tables and 14 figures) LaTeX, uses emulateapj.sty; a full-resolution version with complete figs. 4 and 5 is available at http://www.astro.unibas.ch/cosmology/papers.html ; accepted for publication in Ap