Spot-like Structures of Neutron Star Surface Magnetic Fields

There is growing evidence, based on both X-ray and radio observations of isolated neutron stars, that besides the large--scale (dipolar) magnetic field, which determines the pulsar spin--down behaviour, small--scale poloidal field components are present, which have surface strengths one to two orders of magnitude larger than the dipolar component. We argue in this paper that the Hall--effect can be an efficient process in producing such small--scale field structures just above the neutron star surface. It is shown that due to a Hall--drift induced instability, poloidal magnetic field structures can be generated from strong subsurface toroidal fields, which are the result of either a dynamo or a thermoelectric instability acting at early times of a neutron star's life. The geometrical structure of these small--scale surface anomalies of the magnetic field resembles that of some types of ``star--spots''. The magnetic field strength and the length--scales are comparable with values that can be derived from various observations.Comment: 4 pages, 2 figures, accepted by Astronomy & Astrophysics Letters; language improved, 2nd para of Sect. 3 change

The Curious Case of NGC6908

The object NGC6908 was once thought to be simply a surface-brightness enhancement in the eastern spiral arm of the nearby spiral galaxy NGC6907. Based on an examination of near-infrared imaging, the object is shown in fact to be a lenticular S0(6/7) galaxy hidden in the optical glare of the disk and spiral structure of the larger galaxy. New radial velocities of NGC6908 (3,060+/-16 (emission); 3,113+/-73 km/s (absorption)) have been obtained at the Baade 6.5m and the duPont 2.5m telescopes at Las Campanas, Chile placing NGC6908 at the same expansion-velocity distance as NGC6907 (3,190+/-5 km/s), eliminating the possibility of a purely chance line-of-sight coincidence. The once-enigmatic asymmetries in the disk and outer spiral structure of NGC6907 are now explained as being due to an advanced merger event. Newly discovered tails and debris in the outer reaches of this galaxy further support the merger scenario for this system. This pair of galaxies is a rather striking example of two objects discovered over 100 years ago, whose true nature was lost until modern detectors operating at infrared wavelengths gave us a new (high-contrast) look. Other examples of embedded merger remnants may also reveal themselves in the growing samples of near-infrared imaging of nearby galaxies; and a pilot study does reveal several other promising candidates for follow-up observations.Comment: 17 pages, 8 figures, accepted for publication in A

<i>Vibrio rotiferianus</i> sp. nov., isolated from cultures of the rotifer <i>Brachionus plicatilis</i>

Five Gram-negative bacterial strains, oxidase-positive, motile by means of more than one polar flagella, facultative anaerobe, arginine dihydrolase-negative, lysine- and ornithine decarboxylase-positive, sensitive to the vibriostatic agent O/129, were isolated from a flow-through rotifer culture system in Gent, Belgium, and previously characterized by fluorescent amplified fragment length polymorphism. Comparison of the 16S rDNA sequence of strain LMG 21460T indicated close relationships (~99 % similarity) to Vibrio campbellii, Vibrio harveyi, Vibrio alginolyticus and Vibrio parahaemolyticus. However, DNA hybridization experiments revealed similarity values below 70 % with its closest species V. campbellii and V. harveyi. Additionally, the analysed strains differ from related Vibrio species by the utilization of melibiose and production of acid from L-arabinose and amygdalin. Among the strains analysed, differences were observed in some phenotypic characters, particularly susceptibility to ampicillin, polymyxin B and amikacin, and urease activity. The major fatty acids identified were 16:0, 18:1 ?7c, 14:0, 12:0 3-OH and 18:0. Vibrio rotiferianus sp. nov. is proposed, with type strain LMG 21460T (=CAIM 577T); it has a DNA G+C content of 44·5 ± 0·01 mol%

Computation of the modified Bessel function of the third kind of imaginary orders: uniform Airy-type asymptotic expansion

AbstractThe use of a uniform Airy-type asymptotic expansion for the computation of the modified Bessel functions of the third kind of imaginary orders (Kia(x)) near the transition point x=a, is discussed. In A. Gil et al., Evaluation of the modified Bessel functions of the third kind of imaginary orders, J. Comput. Phys. 17 (2002) 398–411, an algorithm for the evaluation of Kia(x) was presented, which made use of series, a continued fraction method and nonoscillating integral representations. The range of validity of the algorithm was limited by the singularity of the steepest descent paths near the transition point. We show how uniform Airy-type asymptotic expansions fill the gap left by the steepest descent method

Convection in protoneutron stars and the structure of surface magnetic fields in pulsars

We consider generation and evolution of small-scale magnetic fields in neutron stars. These fields can be generated by small-scale turbulent dynamo action soon after the collapse when the proto-neutron star is subject to convective and neutron finger instabilities. After instabilities stop, small-scale fields should be frozen into the crust that forms initially at high density about 10^{14} g/cm^{3} and then spreads to the surface. Because of high crustal conductivity, magnetic fields with the lengthscale about 1-3 km can survive in the crust as long as 10-100 Myr and form a sunspot-like structure at the surface of radiopulsars

Protoneutron star dynamos and pulsar magnetism

We have investigated the turbulent mean-field dynamo action in protoneutron stars that are subject to convective and neutron finger instabilities during the early evolutionary phase. While the first one develops mostly in the inner regions of the star, the second one is favored in the outer regions, where the Rossby number is much smaller and a mean-field dynamo action is more efficient. By solving the mean-field induction equation we have computed the critical spin period below which no dynamo action is possible and found it to be $\sim 1$ s for a wide range of stellar models and for both axisymmetric and non-axisymmetric magnetic fields. Because this critical period is substantially longer than the characteristic spin period of very young pulsars, we expect that a mean-field dynamo will be effective for most protoneutron stars. The saturation dipole field estimated by making use of the model of ``global'' quenching fits well the pulsar magnetic fields inferred from the spin-down data. Apart from the large scale magnetic field, our model predicts also a generation of small scale fields which are typically stronger than the poloidal field and can survive during the lifetime of pulsars. Extremely rapidly rotating protoneutron stars ($P \sim 1$ ms) may have the dipole field $\sim (3-6) \times 10^{14}$ G.Comment: 7 pages, 6 figures, to appear on A&

Infrared spectroscopy of the largest known trans-neptunian object 2001 KX76

We report complete near-infrared (0.9-2.4 $\mu$m) spectral observations of the largest know trans-neptunian objects (TNO) 28976 = 2001 KX$_{76}$ taken in two different nights using the new Near Infrared Camera Spectrometer (NICS) attached to the 3.56m Telescopio Nazionale Galileo (TNG). The spectra are featureless and correspond to a neutral colored object. Our observations indicate that the surface of 2001 KX$_{76}$ is probably highly evolved due to long term irradiation, and that collisional resurfacing processes have not played an important role in its evolution.Comment: 1 Latex file, 2 postscript files. A&A in pres

Ascending Higher: The Story of Aviation at Western

Western Michigan University College of Aviation celebrates 75 years of aviation education. From modest beginnings in 1939, our curriculum has expanded to offer degrees in aviation flight science, aviation management and operations, and aviation maintenance technology. We currently have a fleet of advanced training aircraft, modern facilities in Battle Creek and more than 740 undergraduate students in the program. With this book, we take a look back. We celebrate the visionaries of the past who helped us realize our current successes. We commemorate the events and advancements in our storied aviation program. And we look to the bright future that lies before us.https://scholarworks.wmich.edu/books/1778/thumbnail.jp

<i>Vibrio kanaloae</i> sp. nov., <i>Vibrio pomeroyi</i> sp. nov. and <i>Vibrio chagasii</i> sp. nov., from sea water and marine animals

The taxonomic position of the fluorescent amplified fragment length polymorphism fingerprinting groups A46 (five isolates), A51 (six isolates), A52 (five isolates) and A53 (seven isolates) obtained in a previous study were further analysed through a polyphasic approach. The 23 isolates were phylogenetically related to Vibrio splendidus, but DNA-DNA hybridization experiments proved that they belong to three novel species. Chemotaxonomic and phenotypic analyses further disclosed several features that differentiate between the 23 isolates and known Vibrio species. The names Vibrio kanaloae sp. nov. (type strain LMG 20539T=CAIM 485T; EMBL accession no. AJ316193; G+C content 44·7 mol%), Vibrio pomeroyi sp. nov. (type strain LMG 20537T=CAIM 578T; EMBL accession no. AJ491290; G+C content 44·1 mol%) and Vibrio chagasii sp. nov. (type strain LMG 21353T=CAIM 431T; EMBL accession no. AJ316199; G+C content 44·6 mol%) are respectively proposed to encompass the five isolates of A46, the six isolates of A51 and the 12 isolates of A52/A53. The three novel species can be distinguished from known Vibrio species by several phenotypic features, including utilization and fermentation of various carbon sources, -galactosidase activity and fatty acid content (particularly of 12 : 0, 14 : 0, 14 : 0 iso and 16 : 0 iso)

The Occurrence of the Hall--Instability in Crusts of Isolated Neutron Stars

In former papers we showed that during the decay of a neutron star's magnetic field under the influence of the Hall--drift, an unstable rise of small--scale field structures at the expense of the large--scale background field may happen. This linear stability analysis was based on the assumption of a uniform density throughout the neutron star crust, whereas in reality the density and all transport coefficients vary by many orders of magnitude. Here, we extend the investigation of the Hall--drift induced instability by considering realistic profiles of density and chemical composition, as well as background fields with more justified radial profiles. Two neutron star models are considered differing primarily in the assumption on the core matter equation of state. For their cooling history and radial profiles of density and composition we use known results to infer the conductivity profiles. These were fed into linear calculations of a dipolar field decay starting from various initial configurations. At different stages of the decay, snapshots of the magnetic fields at the equator were taken to yield background field profiles for the stability analysis. The main result is that the Hall instability may really occur in neutron star crusts. Characteristic growth times are in the order of \lesssim 10^4 ... 10^6 yrs depending on cooling age and background field strength. The influence of the equation of state and of the initial field configuration is discussed.Comment: 16 pages, 16 figures, PS, submitted to A&A. Justification/discussion slightly changed/extended in replying to the referee. Changes on p. 3, 11, 13, framed by XXX mark