A high resolution mid-infrared image of the Starburst Galaxy M82

We have produced high-resolution images of the nuclear region of M82 with SpectroCam-10, a mid-infrared instrument at the Palomar 5 m telescope. These images were taken at 11.7 m and 9.8 m with a 1m filter bandpass at the diffraction limit of 0.6 arcsec, making them the highest resolution maps yet available of M82. In addition, we have obtained high-resolution (/=2000) maps of the velocity field of the nuclear disk of M82 in the 12.81 m line emission of [NeII]. In these proceedings we present the 11.7 m image, which will appear together with the 9.8 m map and the [Ne II] spectra in a subsequent paper, now in preparation. This image shows very clearly a bridge structure joining the eastern and western clusters.     

Effects of viscous dissipation and free convection currents on the flow of an electrically conducting fluid past an accelerated vertical porous plate

In the present paper, the effects of free convection currents and the viscous dissipation on the unsteady flow of an electrically conducting and viscous incompressible fluid around an uniformly accelerated vertical porous plate subjected to a suction or injection velocity inversely proportional to the square root of time, in presence of a transverse magnetic field, have been investigated. Analytical solutions for the velocity and the temperature distributions, the skin-friction and the rate of heat transfer are obtained for small magnetic parameterM. During the course of discussion the effects of the Grashof number Gr, the Eckert number Ec, the suction/injection parametera have been considered for unit value of the Prandtl number Pr.Nomenclature a suction/injection parameter - C _p specific heat at constant pressure - B ₀ magnetic induction - g acceleration due to gravity - Gr Grashof number (g(T _w –T )/U ₀ ³ ) - K thermal conductivity - M magnetic field parameter (B ₀ ² /U ₀ ² ) - Pr Prandtl number (C _p/K) - T temperature of the fluid near the plate - T _w temperature of the plate - T temperature of the fluid at infinity - t time - t dimensionless time (tU ₀ ² /) - u velocity of the fluid - u non-dimensional velocity (u/U ₀) - U velocity of the plate - U dimensionless velocity of the plate (U/U ₀) - U ₀ reference velocity - v ₀ suction velocity - v ₀ non-dimensional suction velocity (v ₀/U ₀)=at ^–1/2 - Ec Eckert number ((U ₀)^2/3/C _p(T _w –T )) - T dimensionless temperature of the fluid near the plate ((T–T )/(T _w ^–T )) - x, y coordinates along and normal to the plate - x, y dimensionless coordinates (y=yU ₀/) - kinematic viscosity - coefficient of volume expansion - electric conductivity of the fluid - y/2t ^1/2 - density of the fluid - skin-friction - dimensionless skin-friction - q rate of heat transfer - q non-dimensional rate of heat transfer - coefficient of viscosity - _e magnetic permeability On leave of absence from Department of Mathematics, University of Dhaka, Bangladesh     

On transfer equation in a semi-infinite atmosphere with albedo ω>1

In this note we derive an exact solution of transfer equation in a plane-parallel semiinfinite atmosphere with albedo >1, by the method of Laplace transform and Wiener-Hopf technique. The emergent intensityI(0, ) is obtained in terms of theH ⁰-functionH ⁰() (Das Gupta, 1978) for which some good approximations are given. Intensity at any depth is also obtained.I(0, )/I(0, 0) is plotted in graphs against [0,1], and shows a maximum which drops and shifts towards the origin as increases.     

The evaluation of the interplanetary diffusion coefficient for energetic particles employing real magnetic field data

A numerical simulation of energetic particle motion in the interplanetary medium is carried out using HEOS-2 magnetometer data in order to computeD(), the pitch angle diffusion coefficient, where is cosine of pitch angle defined with respect to the local field. WhileD() exceeds that given by quasi-linear theory near 90° pitch angle, it is significantly less at higher values of , leading to a parallel transport coefficient in good accord with that given by experimental studies of solar proton propagation. In particular, =0.031 AU at a particle magnetic rigidity of 455 MV, while experimental results range from 0.05 to 0.07 AU (+100%, –50%) in this rigidity region. Furthermore, observed approximately -dependent solar proton pitch angle distributions are consistent with the computed findingD()/(1 – ²)² ~ constant.The validity of various analytical corrections to quasi-linear theory as 0 are also investigated numerically.     

The velocity correlation function in cosmic-ray diffusion theory

The concept of velocity correlation functions is introduced and applied to the calculation of cosmic ray spatial diffusion coefficients. It is assumed that the pitch angle scattering coefficient is already known from some other theory, and is reasonably well-behaved. Previous results for the coefficient for diffusion parallel to the mean field are recovered when the velocity-changing mechanism is artificially restricted to pitch angle scattering. The velocity correlation method is then applied to the more general case where there are fluctuations in the local mean field. It is found that the parallel diffusion coefficient is reduced in proportion to the amplitude of the field fluctuations, and that the ratio of the perpendicular to parallel diffusion coefficients cannot be greater than B _x ² /B ₀ ² . It is shown in the appendix that the Liouville form of the scattering equation implies that the Fokker-Planck coefficients ²/t=2D and /t=D /, and that all higher-order coefficients are identically zero.     

Extinction and scattering by several types of silicate sphere of radius 0.05–1.0μm,for the wavelength range 0.21–50μm

The exact calculation of scattering and absorption by various sub-micron sized silicate spheres is presented here, using accurately determined optical constants in the wavelength range from 50 m to 0.21 m. The extinction features near 10 m and 20 m for various samples are discussed. It is found that the ratio of peak extinction at 20 m to that at 10 m is constant for small particles up tor=0.4 m, but is less for particles of radius 1 m. The ratio of maximum extinction in the ultraviolet to that at 10 m decreases with increasing particle size.     

On the restrited three-body problem when the mass parameter is small

We study some aspects of the restricted three-body problem when the mass parameter is sufficiently small. First, we describe the global flow of the two-body rotating problem, =0, and we use it for the analysis of the collision and parabolic orbits when 0. Also we show that for any fixed value of the Jacobian constant and for any >0, there exists a ₀>0 such that if the mass parameter [0,₀], then the set of bounded orbits which are not contained in the closure of the set of symmetric periodic orbits has Lebesgue measure less than .Paper presented at the 1981 Oberwolfach Conference on Mathematical Methods in Celestial Mechanics.     

Stability of and motion aboutL 4 at three-to-one commensurability

The stability ofL ₄ and the motion aboutL ₄ in the restricted problem of three bodies is investigated when there is three-to-one commensurability between the long and short periods of motion, that is, when the mass ratio has the value =0.013516.... The two time scale method is used (1) to show thatL ₄ is an unstable equilibrium point when =₃, (2) to determine for what initial conditions periodic orbits occur when ₃, (3) to determine the stability of the periodic orbits, and (4) to investigate the boundedness of the motions aboutL ₄ when ₃.     

Infrared continuum observations of five-minute oscillations

Infrared continuum observations of the Sun at wavelengths between 10 and 30 show a nonisothermal response of the upper photosphere to compression waves associated with the five-minute oscillations. Observations were made with four broad-band filters with effective transmission wavelengths between 10 and 26 and with a 10 aperture. Further observations at submillimeter wavelengths with a 2 aperture did not resolve oscillatory fluctuations of five-minute period.Comparisons with velocity field data of Howard (1976) suggest that the relaxation time of the photosphere exceeds (300/2) seconds at the height of formation of the 26 continuum (_5000Å 10^-2). The photosphere reponds to 3 mHz oscillatory motion with considerably less compression than expected for simple acoustic modes in an adiabatically responsive atmosphere, confirming the evanescent character of the five-minute oscillations.     

On the wavelength dependency of solar limb darkening (λλ303 to 1099 nm)

The limb-darkening data published by Neckel and Labs (1994) (5th-order polynomials P ₅(), = cos ) are used to represent the limb darkening by the functions L _n(), proposed first by Kourganoff (1949a). When plotted against wavelength, the coefficients of these functions show a rather low scatter and appear to be linear functions of either ^–1 or ^#x2212;5.     

Second species solutions with an 0(μν), 1/3<ν<1, near-moon passage

This paper uses Guillaume's extension of the Breakwell-Perko matching theory for the restricted three-body problem with small mass ratio >0 to establish the existence and asymptotic approximation of one-parameter families of second species periodic solutions with one near-moon passage of , during a half-period. The deflection angle at such a near moon passage, 0(^1–v), approaches zero as the mass ratio approaches zero.This work was supported by the National Science Foundation under Grant GP42739.     

Mid- and far-infrared extinction coefficients of hydrous silicate minerals

Extinction coefficients were measured for three kind of hydrous silicate minerals, montmorillonite, chlorite and serpentine, from 7 to 140 m. The infrared extinction coefficients of these minerals show (1) a few broad bands in the mid-infrared region and (2) a less steep wavelength-dependence in the far-infrared region, in contrast to those of high-temperature magnesium silicates. In the far-infrared region, montmorillonite shows a ^–0.8±0.1 dependence (, the wavelength) without any band structure, chlorite has a double maxima structure around 80 m, and serpentine shows a rather steep dependence with a small peak at 77 m.The changes of mid-infrared spectra by heating were measured. Change in chlorite spectrum is the most significant. Many fine features appear by heating and then they disappear. Above 900°C one broad feature remains around 10 m. Fine features of the montmorillonite spectrum disappear by heating. For serpentine, many new peaks appear and the spectrum resembles the spectrum of olivin. In near-infrared a band around 2.72 m disappears by heating.Extinction coefficients at very low temperatures were measured in the far-infrared region. For montmorillonite and serpentine, the spectrum is the same as that at room temperature. The double peaks of chlorite around 80 m become higher.     

Polyoxymethylene co-polymers on grains

Conditions prevalent in dense molecular clouds are shown to favour the polymerization of H₂CO molecules and the deposition of formaldehyde co-polymer mantles, with typical radii 10^–5 cm, on smaller refractory grains. If a significant fraction of such co-polymer coated grains are expelled with systematic gas flows into the general interstellar medium, these moderately refractory grains may be responsible for the bulk of interstellar extinction and polarization at optical wavelengths. Mie calculations for a mixture consisting of iron, graphite and POM particles are presented as an example where POM grains of radii 0.15 dominate the extinction at optical wavelengths, providing a satisfactory overall fit to a range of extinction data. A size distribution of POM needles with a mean radius 0.15 also provides good agreement with data on interstellar linear as well as circular polarization. Suitably end-capped and stabilized co-polymer-coated grains, with either silicate or graphite cores, may survive at temperatures 450 K under interstellar ambient conditions and be responsible for the 10 emission feature in many sources. Theoretically computed band profiles of the 10 -feature in POM coated grains, in general, provide better agreement with observations than most types of silicate grains considered so far. We also note that an unexplained dip at 10 in the 8–12 feature of the infrared source OH 231.8+4.2 may be a signature of POM grains; likewise, a persistent 3.3 emission feature in many different types of infrared source could be attributed to the CH stretching mode in formaldehyde co-polymer grains.     

Arome,a balloon-borne instrument for astronomical near-infrared spectrophotometry

We present here the French balloon-borne experiment named AROME. This astronomical instrument is specifically designed for the detection of near infrared emission bands (=3–12m) from extended sources of low surface brightness with an angular resolution of 0.5°. The rms sensitivity achieved is of the order of 10^-8 Wm^-2sr^-1, in terms of the power radiated in the 3.3m band. We recall that this program led to the first detection of the 3.3m feature in the spectrum of the diffuse galactic emission. The scientific results were presented and interpreted in Paper I, Giard et al., 1989. Future work will include both the observation of fainter objects at 3.3m and the detection of other emission bands at 6.2 and 11.3m.     

Stimulated comption effect in very compact radio sources

Expressions for the stimulated Compton effect are derived that are complete to order /ge/, where is the photon energy in the laboratory system, and =m ₀ C ² is the electron energy. Explicit formulas are given for the energy flow between a relativistic electron and a radiation field that obeys a power law so that the number of photons is proportional to ^–m–1. The amount of energy gained by an electron per second is then numerically calculated for conditions suggested by very compact radio sources as a function of the width of the spectrum, the spectral index, and the electron energy.The National Center for Atmospheric Research is sponsored by the National Science Foundation.     

On periodic flybys of the moon

This paper considers the plane circular restricted three-body problem for small . Symmetric periodic solutions of the second species (passing near the body of mass ) and their distance from the center of the body of mass are studied by constructing perturbations of arc-solutions (solutions with consecutive collisions) existing for =0. Orbits which also pass near the body of mass 1- are studied in detail. The results are applied to finding periodic orbits in the Earth-Moon system and in the Sun-Jupiter system.Russian version: Preprint No. 91 (1978) of Inst. Appl. Math.; present English translation was made by L. M. Perko and W. C. Schulz (February 1979).     

Near-infrared observations of the peculiar binary system epsilon Aurigae

Near-infrared photometric and low-resolution spectroscopic observations of Aurigae at two phases during the current eclipse are presented. The eclipse depths are found to be wavelength-independent in the infrared right up to 2.5 m. There is no infrared excess at wavelengths shorter than 2.5 m. The light absorbing particles in the eclipsing body must be larger than 10 m in size.     

Three-dimensional,periodic, ‘halo’ orbits

A largely numerical study was made of families of three-dimensional, periodic, halo orbits near the collinear libration points in the restricted three-body problem. Families extend from each of the libration points to the nearest primary. They appear to exist for all values of the mass ratio , from 0 to 1. More importantly, most of the families contain a range of stable orbits. Only near L₁, the libration point between the two primaries, are there no stable orbits for certain values of . In that case the stable range decreases with increasing , until it disappears at =0.0573. Near the other libration points, stable orbits exist for all mass ratios investigated between 0 and 1. In addition, the orbits increase in size with increasing .     

A search for carbon stars in the AFGL Catalogue

A comparison between theGeneral Catalogue of Cool Carbon Stars (CCS) and theAFGL Catalogue has been performed.Eighty-five stars have been found in common between the two lists. Eighty-four stars which were present in Baumert's comparison between CCS and the 2 Sky Survey have no counterpart in the AFGL. Four new tentative identifications are given. The analysis of the two colours diagrams K-[4.2 ] vs. I-K and I-[4.2 ] vs. [4.2 ]-[11 ] led to the conclusion that all the infrared emission from the sources seems to come from a single circumstellar shell.     

A photometric study of faculae and sunspots between 1.2 and 1.6 μm

We investigate further the interpretation of dark magnetic faculae observed in previous imaging of the solar photosphere at 1.63 m. We show that their contrast at 1.63 m increases with magnetic flux beyond a threshold value of 2 × 10¹⁸ Mx and blends smoothly with the contrast vs flux relation measured at this wavelength for larger structures of sunspot size. Not all facular structures that are bright in Ca K are dark at 1.63 m, apparently because their magnetic flux is not large enough. After correction for blurring, the contrast of the dark faculae observed near the disc center at 1.63 m is approximately 4%. But our observations at 1.23 m, which probe slightly higher photospheric levels, do not show these dark faculae. These results indicate that magnetic flux tubes of diameter as small as 500 km significantly inhibit convective heat flow to the photosphere, much as do sunspot flux tubes of much larger diameter. They also suggest that, in even smaller flux tubes, the inhibition becomes rapidly less significant. Finally, we show that the sunspot-size dependence of umbral infrared contrast versus wavelength that we observe can probably be explained in terms of instrumental blurring. Observations with lower scattered light will be required to determine whether a real decrease of contrast with diameter also plays a role.