NGC 7468: A galaxy with an inner polar disk

We present our spectroscopic observations of the galaxy NGC 7468 performed at the 6-m Special Astrophysical Observatory telescope using the UAGS long-slit spectrograph, the MPFS multi-pupil fiber spectrograph, and the IFP scanning Fabry-Perot interferometer. We found no significant deviations from the circular rotation of the galactic disk in the velocity field in the regions of brightness excess along the major axis of the galaxy (the putative polar ring). Thus, these features are either tidal structures or weakly developed spiral arms. However, we detected a gaseous disk at the center of the galaxy whose rotation plane is almost perpendicular to the plane of the galactic disk. The central collision of NGC 7468 with a gas-rich dwarf galaxy and their subsequent merging seem to be responsible for the formation of this disk.     

On the change of the inner boundary of an optically thick accretion disk around white dwarfs using the dwarf nova SS Cyg as an example

We present the results of our studies of the aperiodic optical flux variability for SS Cyg, an accreting binary systemwith a white dwarf. The main set of observational data presented here was obtained with the ANDOR/iXon DU-888 photometer mounted on the RTT-150 telescope, which allowed a record (for CCD photometers) time resolution up to 8 ms to be achieved. The power spectra of the source’s flux variability have revealed that the aperiodic variability contains information about the inner boundary of the optically thick flow in the binary system. We show that the inner boundary of the optically thick accretion disk comes close to the white dwarf surface at the maximum of the source’s bolometric light curve, i.e., at the peak of the instantaneous accretion rate onto the white dwarf, while the optically thick accretion disk is truncated at distances 8.5 × 10⁹ cm ∼10R _WD in the low state. We suggest that the location of the inner boundary of the accretion disk in the binary can be traced by studying the parameters of the power spectra for accreting white dwarfs. In particular, this allows the mass of the accreting object to be estimated.     

LOLAS: an optical turbulence profiler in the atmospheric boundary layer with extreme altitude resolution

We report the development and first results of an instrument called Low Layer SCIDAR (Scintillation Detection and Ranging) (LOLAS) which is aimed at the measurement of optical-turbulence profiles in the atmospheric boundary layer with high altitude resolution. The method is based on the Generalized SCIDAR (GS) concept, but unlike the GS instruments which need a 1-m or larger telescope, LOLAS is implemented on a dedicated 40-cm telescope, making it an independent instrument. The system is designed for widely separated double-star targets, which enables the high altitude resolution. Using a 200-arcsec-separation double star, we have obtained turbulence profiles with unprecedented 12-m resolution. The system incorporates necessary novel algorithms for autoguiding, autofocus and image stabilization. The results presented here were obtained at Mauna Kea Observatory. They show LOLAS capabilities but cannot be considered as representative of the site. A forthcoming paper will be devoted to the site characterization. The instrument was built as part of the Ground Layer Turbulence Monitoring Campaign on Mauna Kea for Gemini Observatory.     

Hill stability of a triple system with an inner binary of large mass ratio

We determine the maximum dimensionless pericentre distance a third body can have to the barycentre of an extreme mass ratio binary, beyond which no exchange or ejection of any of the binary components can occur. We calculate this maximum distance, q '/ a , where q ' is the pericentre of the third mass to the binary barycentre and a is the semimajor axis of the binary, as a function of the critical value of   L ²  E   of the system, where L is the magnitude of the angular momentum vector and E is the total energy of the system. The critical value is obtained by calculating   L ²  E   for the central configuration of the system at the collinear Lagrangian points. In our case we can make approximations for the system when one of the masses is small. We compare the calculated values of the pericentre distance with numerical scattering experiments as a function of the eccentricity of the inner orbit, e , the mutual inclination i and the eccentricity of the outer orbit, e '. These show that the maximum observed value of   q '/ a   is indeed the critical q '/ a , as expected. However, when   e '→1  , the maximum observed value of q '/ a is equal to the critical value calculated when   e '=0  , which is contrary to the theory, which predicts exchange distances several orders of magnitude larger for nearly parabolic orbits. This does not occur because changes in the binding energy of the binary are exponentially small for distant, nearly parabolic encounters.     

Luminous infrared galaxies with the submillimeter array: probing the extremes of star formation

Luminous and Ultraluminous infrared galaxies (ULIRGs) contain the most intense regions of star formation in the local universe. Because molecular gas is the fuel for current and future star formation, the physical properties and distribution of the warm, dense molecular gas are key components for understanding the processes and timescales controlling star formation in these merger and merger remnant galaxies. We present new results from a legacy project on the Submillimeter Array which is producing high resolution images of a representative sample of galaxies with log L _FIR >11.4 and D<200 Mpc.     

Tidal effects of a massive spheroidal halo on an inner spheroidal contracting visible body: Application to an evolutionary disk-galaxy model

The effects of the tidal interactions between two coaxial, homogeneous spheroids, one (the “Brigt Component”: B) completely embedded in the other (the “Dark Halo”: D), along a quasi-static contraction, are considered. The aim is to look how the dynamical properties and the final morphology of the B subsystem may be affected by the presence of the D component. Three initial configurations are considered: the quasi-spherical “Dark Halo” D coincides with the “Visible Component” B (case C); D is flatter than B but the two spheroids have the same semiminor axis (case N); no D component is assumed; the “visible” spheroid is single (case S). The application to an evolutionary disk-galaxy model is considered under some simple assumptions: i) in cases C and N the spheroidal halo is massive (mass ratio “dark”/“bright” about ten) and dissipationless. For a mass ratio like this, the tidal interaction of the B component over D turns to be negligible in the course of the contraction; adding to that the lack of dissipation, it appears plausible to take the D component as frozen along the evolution; ii) the degree of anisotropy and the angular momentum of B, J_B, are conserved. The conservation of J_B provides us the time-independent relationship among the key physical quantities and gives the possibility to draw the evolutionary tracks on the plane (axis ratio σ_B, semimajor axis a_B) without any explicit time-scale; iii) the global “star formation rate” is parametrized according to a simple “Schmidt power law” proportional to the square of gas density. At every step of the quasi-static contraction, the structure is determined by the tensor virial theorem extended to a double configuration. The model is very idealized, particularly because there are no available tidal gravitational terms other than for the case of two homogeneous. Nevertheless, the method based on the tensor virial appears powerful to gain insight into the correlations among the physical quantities involved and into their trend along the evolution. One of the main result is a clear indication of a leading role played by the axis ratio of the “Dark-Halo” component which might be, to the extent that this simple picture can be compared with a real galactic system, a possible new physical parameter to be added to mass and angular momentum for separating spirals from S0 galaxies.     

Kelvin-Helmholtz instability of the magnetopause boundary: Comparison with observed fluctuations

We present a numerical investigation of the Kelvin-Helmholtz instability problem, in MHD approximation, for transitions involving continuous variations of both magnetic field and plasma parameters. The variations have been chosen in such a way as to reproduce general features of possible magnetopause transitions. The study, which leads to prediction of a wavelength of maximum instability, has been confronted with recent observational results of surface fluctuations of the magnetopause.     

Attitude stability of a spacecraft with two flexible solar arrays on a stationary orbit around an asteroid subjected to gravity gradient torque

In the gravity field of an asteroid with the second order and degree harmonics C ₂₀ and C ₂₂, the attitude stability of a spacecraft with two flexible solar arrays on a stationary orbit subjected to the fourth-order gravity gradient torque is investigated in this paper. The sufficient conditions of attitude stability of the spacecraft are obtained, the effect of the direction of the flexible solar arrays and some special cases are discussed. Taking the asteroids 4769 Castalia, 25143 Itokawa and the imaginary asteroids as examples, the attitude stability domains, determined by the sufficient conditions, of the spacecrafts moving on stationary orbits around them are presented. It is found that the attitude stability domains of the spacecraft with two flexible solar arrays are evidently different when the solar arrays are installed in different directions; the effect of the harmonics C ₂₀ and C ₂₂ of the asteroids has the significant influence on the attitude stability domains of the spacecrafts with flexible appendages moving on stationary orbits; in the certain case, the effect of the harmonics C ₂₀ and C ₂₂ of the asteroids has no influence on the attitude stability domains of the rigid spacecrafts moving on stationary orbits, but in the other cases, the effect of the harmonics C ₂₀ and C ₂₂ of the asteroids has also the significant influence on the attitude stability domains of the rigid spacecrafts moving on stationary orbits; whether the harmonics C ₂₀ and C ₂₂ of the asteroids are considered or not, the effect of flexible appendages decreases the attitude stability domains.     

Perspectives on effectively constraining the location of a massive trans-Plutonian object with the New Horizons spacecraft: a sensitivity analysis

The radio tracking apparatus of the New Horizons spacecraft, currently traveling to the Pluto system where its arrival is scheduled for July 2015, should be able to reach an accuracy of 10 m (range) and 0.1  $\text{ mm } \text{ s }^{-1}$ mm s ? 1 (range-rate) over distances up to 50 au. This should allow to effectively constrain the location of a putative trans-Plutonian massive object, dubbed Planet X (PX) hereafter, whose existence has recently been postulated for a variety of reasons connected with, e.g., the architecture of the Kuiper belt and the cometary flux from the Oort cloud. Traditional scenarios involve a rock-ice planetoid with $m_\mathrm{X}\approx 0.7\,m_{\oplus }$ m X ≈ 0.7 m ⊕ at some 100–200 au, or a Jovian body with $m_\mathrm{X}\lesssim 5\,m_\mathrm{J}$ m X ? 5 m J at about 10,000–20,000 au; as a result of our preliminary sensitivity analysis, they should be detectable by New Horizons since they would impact its range at a km level or so over a time span 6 years long. Conversely, range residuals statistically compatible with zero having an amplitude of 10 m would imply that PX, if it exists, could not be located at less than about 4,500 au ( $m_\mathrm{X}=0.7\,m_{\oplus }$ m X = 0.7 m ⊕ ) or 60,000 au ( $m_\mathrm{X}=5\,m_\mathrm{J}$ m X = 5 m J ), thus making a direct detection quite demanding with the present-day technologies. As a consequence, it would be appropriate to rename such a remote body as Thelisto. Also fundamental physics would benefit from this analysis since certain subtle effects predicted by MOND for the deep Newtonian regions of our Solar System are just equivalent to those of a distant pointlike mass.     

Star and planet-formation with ALMA: an overview

Submillimeter observations with ALMA will be the essential next step in our understanding of how stars and planets form. Key projects range from detailed imaging of the collapse of pre-stellar cores and measuring the accretion rate of matter onto deeply embedded protostars, to unravelling the chemistry and dynamics of high-mass star-forming clusters and high-spatial resolution studies of protoplanetary disks down to the 1 AU scale.     

Chemical and physical properties of gas jets in comets: I. Monte Carlo model of an inner cometary coma

We describe a 3-dimensional, time-dependent Monte Carlo model developed to analyze the chemical and physical nature of a cometary gas coma. Our model includes the necessary physics and chemistry to recreate the conditions applicable to Comet Hale-Bopp when the comet was near 1 AU from the Sun. Two base models were designed and are described here. The first is an isotropic model that emits particles (parents of the observed gases) from the entire nucleus; the second is a jet model that ejects parent particles solely from discrete active areas on the surface of the comet nucleus, resulting in coma jets. The two models are combined to produce the final model, which is compared with observations. The physical processes incorporated in both base models include: (1) isotropic ejection of daughter molecules (the observed gases) in the parent's frame of reference, (2) solar radiation pressure, (3) solar insolation effects, (4) collisions of daughter products with other molecules in the coma, and (5) acceleration of the gas in the coma. The observed daughter molecules are produced when a parent decays, which is represented by either an exponential decay distribution (photodissociation of the parent gas) or a triangular distribution (production from a grain extended source). Application of this model to the analysis the OH, C₂ and CN gas jets observed in the coma of Comet Hale-Bopp is the focus of the accompanying paper [Lederer, S.M., Campins, H., Osip, D.J., 2008. Icarus, in press (this issue)].     

A method for using a fully coupled climate system model to generate detailed surface boundary conditions for paleoclimate modeling investigations: an early Paleogene example

Although fully coupled models of the earth system are now common, simpler model architectures maintain significant utility, and scientific investigations aimed at understanding paleoclimates are frequently conducted with fixed sea surface temperature (SST) or slab ocean modeling experiments. One of the challenges facing the paleoclimate community is that the proxy data used to generate SST boundary conditions exist at a finer resolution and with very limited spatial coverage when compared to a climate model. In addition, SST proxy estimates often represent a single season or annual average conditions. This mismatch in coverage and resolution frequently results in paleoclimate modelers using SST distributions that have very limited spatial and temporal variability. In many regions, a spatially and temporally detailed SST distribution may be necessary for the accurate reproduction of paleoclimatic conditions. Here we borrow from the concept of flux correction and, using available proxy estimates of SST as our guide, force a fully coupled earth system model to produce a spatially and temporally detailed SST distribution for the paleoclimate of the early Paleogene (45–65 Ma). The SST values we produce represent a conservative estimate of early Paleogene high latitude SSTs and match tropical temperatures for this time period well. In addition to matching proxy estimates, our model-derived SST distribution has spatial and temporal variability that meshes well with global climate model resolution. This detailed SST distribution is now available to us as we investigate the causes and sensitivities of early Paleogene climate in fixed SST and slab ocean modeling experiments. The method we used to generate this spatially and temporally detailed SST distribution may prove useful for those investigating other time periods in the past, or the future, for which detailed model boundary conditions are unavailable.     

PICsar: A 2.5D axisymmetric,relativistic, electromagnetic,Particle in Cell code with a radiation absorbing boundary

We present PICsar – a new Particle in Cell code geared towards efficiently simulating the magnetosphere of the aligned rotator. PICsar is a special relativistic, electromagnetic, charge conservative code that can be used to simulate arbitrary electromagnetics problems in axisymmetry. It features stretchable body-fitted coordinates that follow the surface of a sphere, simplifying the application of boundary conditions in the case of the aligned rotator; a radiation absorbing outer boundary, which allows a steady state to be set up dynamically and maintained indefinitely from transient initial conditions; and algorithms for injection of charged particles into the simulation domain. The code is parallelized using MPI and scales well to a large number of processors. We discuss the numerical methods used in PICsar and present tests of the code. In particular, we show that PICsar can accurately and efficiently simulate the magnetosphere of the aligned monopole rotator in the force-free limit. We present simulations of the aligned dipole rotator in a forthcoming paper.     

TZ Lyrae： an Algol-type Eclipsing Binary with Mass Transfer

We present a detailed investigation of the Algol-type binary TZ Lyrae, based on 55 light minimum timings spanning 90 years. It is found that the orbital period shows a long-term increase with a cyclic variation superimposed. The rate of the secular increase is dP/dt = 7.18 × 10?8d yr?1, indicating that a mass transfer from the less massive component to the more massive one at a rate of dm = 2.21 × 10-8M⊙yr-1. The cyclic component, with a period of P3 = 45.5 yr and an amplitude of A = 0d.0040, may be interpreted as either the light-time effect in the presence of a third body or magnetic activity cycles in the components. Using the latest version Wilson-Devinney code, a revised photometric solution was deduced from B and V observations. The results show that TZ Lyr is an Algol-type eclipsing binary with a mass ratio of q = 0.297(±0.003). The semidetached configuration with a lobe-filling secondary suggests a mass transfer from the secondary to the primary, which is in agreement with the long-term period increase of the binary system.     

1580 Betulia: An unusual asteroid with an extraordinary lightcurve

Results of UBV photometry and polarimetry of 1580 Betulia during its 1976 apparition are presented. The synodic period of rotation is found to be 6.130 hr. The linear phase coefficient and absolute magnitude of the primary maximum in V are 0.032 mag/deg and 14.88, respectively. No color variations with rotation or solar phase angle detected, the mean colors being B?V = 0.66 and U?B = 0.24. Betulia's lightcurve is unique among asteroids studied to date in that it displays three maxima and three minima within one rotational cycle, indicative of a region of greater roughness and/or a dark spot on one of its broad faces. Polarization results indicate a low albedo and a mean diameter of about 7 km, establishing Betulia as the first C type asteroid to be found among the Mars crossers. A model accounting for most features of Betulia's lightcurve is given by a prolate spheroid rotating about one of its shorter axes having an axis ratio of 1:1.21 with a major topographic feature on one of its broad faces.     

iShocks: X-ray binary jets with an internal shocks model

In the following paper, we present an internal shocks model, iShocks, for simulating a variety of relativistic jet scenarios; these scenarios can range from a single ejection event to an almost continuous jet, and are highly user configurable. Although the primary focus in the following paper is black hole X-ray binary jets, the model is scale and source independent and could be used for supermassive black holes in active galactic nuclei or other flows such as jets from neutron stars. Discrete packets of plasma (or 'shells') are used to simulate the jet volume. A two-shell collision gives rise to an internal shock, which acts as an electron re-energization mechanism. Using a pseudo-random distribution of the shell properties, the results show how for the first time it is possible to reproduce a flat/inverted spectrum (associated with compact radio jets) in a conical jet whilst taking the adiabatic energy losses into account. Previous models have shown that electron re-acceleration is essential in order to obtain a flat spectrum from an adiabatic conical jet: multiple internal shocks prove to be efficient in providing this re-energization. We also show how the high-frequency turnover/break in the spectrum is correlated with the jet power,  ν _b ∝ L ^∼0.6_W  , and the flat-spectrum synchrotron flux is correlated with the total jet power,   F _ν∝ L ^∼1.4_W  . Both the correlations are in agreement with previous analytical predictions.