Non-circular Orbits Research Articles

OASIS integral-field spectroscopy of the central kpc in 11 Seyfert 2 galaxies

We map narrow-line regions (NLRs) of 11 nearby Seyfert 2 galaxies with the optical integral-field spectrograph OASIS mounted at CFHT. We model emission-line profiles of 5 forbidden-line doublets and 2 Balmer lines, correcting for the underlying stellar absorption by reconstructing stellar spectra with synthetic evolutionary stellar population models. For each of the 11 targets, we present 2D maps of surface brightness in the observed emission lines, diagnostic line intensity ratios, gas kinematics (mean line-of-sight velocity and velocity dispersion), electron density, and interstellar reddening, and we plot spatially resolved spectral-diagnostic diagrams. The stellar data are represented by maps of mean line-of-sight (LOS) velocities and of the relative mass fractions of the young stellar populations. The gas velocity fields in 80% of the sample exhibit twisted S-shaped isovelocity contours, which are signatures of non-circular orbits and indicate non-axisymmetric gravitational potentials, gas motions out of the galactic plane, or possible outflows and inflows. Based on the kinematic measurements, we identified a possible nuclear ring or radial gas flow in NGC 262 (Mrk 348), not reported before. Eight of the eleven observed objects exhibit strongly asymmetric or multi-component emission-line profiles, in most cases confined to an elongated region passing through the galactic centre, perpendicular to the major axis of emission.

Motion of dust in mean motion resonances with planets

Effect of stellar electromagnetic radiation on motion of spherical dust particle in mean-motion orbital resonances with a planet is investigated. Planar circular restricted three-body problem with the Poynting-Robertson (P-R) effect yields monotonous secular evolution of eccentricity when the particle is trapped in the resonance. Elliptically restricted three-body problem with the P-R effect enables nonmonotonous secular evolution of eccentricity and the evolution of eccentricity is qualitatively consistent with the published results for the complicated case of interaction of electromagnetic radiation with nonspherical dust grain. Thus, it is sufficient to allow either nonzero eccentricity of the planet or nonsphericity of the grain and the orbital evolutions in the resonances are qualitatively equal for the two cases. This holds both for exterior and interior mean-motion orbital resonances. Evolutions of longitude of pericenter in the planar circular and elliptical restricted three-body problems are shown. Our numerical integrations suggest that any analytic expression for secular time derivative of the particle's longitude of pericenter does not exist, if a dependence on semi-major axis, eccentricity and longitude of pericenter is considered (the P-R effect and mean-motion resonance with the planet in circular orbit is taken into account). Change of optical properties of the spherical grain with the heliocentric distance is also considered. The change of the optical properties: i) does not have any significant influence on secular evolution of eccentricity, ii) causes that the shift of pericenter is mainly in the same direction/orientation as the particle motion around the Sun. The statements hold both for circular and noncircular planetary orbits.

Unstable Disk Galaxies. II. The Origin of Growing and Stationary Modes

I decompose the unstable growing modes of stellar disks to their Fourier components and present the physical mechanism of instabilities in the context of resonances. When the equilibrium distribution function is a nonuniform function of the orbital angular momentum, the capture of stars into the corotation resonance imbalances the disk angular momentum and triggers growing bar and spiral modes. The stellar disk can then recover its angular momentum balance through the response of nonresonant stars. I carry out a complete analysis of orbital structure corresponding to each Fourier component in the radial angle and present a mathematical condition for the occurrence of van Kampen modes, which constitute a continuous family. I discuss the discreteness and allowable pattern speeds of unstable modes and argue that the mode growth is saturated due to the resonance overlapping mechanism. An individual growing mode can also be suppressed if the corotation and inner Lindblad resonances coexist and compete to capture a group of stars. Based on this mechanism, I show that self-consistent scale-free disks with a sufficient distribution of noncircular orbits should be stable under perturbations of angular wavenumber m > 1. I also derive a criterion for the stability of stellar disks against nonaxisymmetric excitations.

Inspiralling compact binaries in quasi-elliptical orbits: The complete third post-Newtonian energy flux

The instantaneous contributions to the third post-Newtonian (3PN) gravitational wave luminosity from the inspiral phase of a binary system of compact objects moving in a quasi-elliptical orbit is computed using the multipolar post-Minkowskian wave generation formalism. The necessary inputs for this calculation include the 3PN accurate mass quadrupole moment for general orbits and the mass octupole and current quadrupole moments at 2PN. Using the recently obtained 3PN quasi-Keplerian representation of elliptical orbits, the flux is averaged over the binary's orbit. Supplementing this by the important hereditary contributions arising from tails, tails of tails, and tails-squared terms calculated in a previous paper, the complete 3PN energy flux is obtained. The final result presented in this paper would be needed for the construction of ready-to-use templates for binaries moving on noncircular orbits, a plausible class of sources not only for the space-based detectors like LISA but also for the ground-based ones.

Easy Method of Patient Positioning for Convergent-Beam Cardiac SPECT

The use of convergent-beam SPECT can increase detection sensitivity; however, the projection data are likely to be truncated if the patient is not properly positioned. This article describes a patient-positioning method that has been adopted in our hospital for cardiac SPECT scans when convergent-beam collimators are used. The system that we use has 3 detector heads and a patient table (i.e., bed) with 3 locking positions: left, center, and right. When convergent-beam collimators are used in a cardiac SPECT scan, the patient table is locked in the left position, and a noncircular contour orbit is set up. We were able to acquire truncation-free cardiac projections for all of our patients. Patient positioning in convergent-beam SPECT is important. If the patient is not positioned properly, then the heart may be truncated in some projection views. The use of the left locking position of the patient table positions the heart at the center of rotation, and the heart is not truncated in the projection data.

Gyroscopic precession in non-circular orbits: a phase-locked tetrad approach

We deduce the explicit form of a phase-locked (PL) tetrad, adapted to a small spinning particle (a test gyroscope) following an arbitrary geodesic orbit in the Schwarzschild geometry of a gravitational source. We subsequently obtain the analytic expression of the gyroscopic precessional velocity Ω in a non-circular orbit, by means of the Fermi rotation coefficients related to the tetrad’s transport law. As an application, we compute the orbital shift in the spin vector, considering a spinning test particle (the gyroscope) in a slightly non-circular orbital motion in the weak gravitational field limit. We compare our results with those of other previous works.

The M Dwarf GJ 436 and its Neptune‐Mass Planet

ABSTRACTWe determine stellar parameters for the M dwarf GJ 436, which hosts a Neptune‐mass planet. We employ primarily spectral modeling at low and high resolution, examining the agreement between model and observed optical spectra of five comparison stars of type M0–M3. The modeling of high‐resolution optical spectra suffers from uncertainties in TiO transitions, affecting the predicted strengths of both atomic and molecular lines in M dwarfs. The determination of Teff, gravity, and metallicity from optical spectra remains at ∼10%. As molecules provide opacity both in lines and as an effective continuum, determining molecular transition parameters remains a challenge facing models such as the PHOENIX series, best verified with high resolution and spectrophotometric spectra. Our analysis of GJ 436 yields an effective temperature of Teff = 3350 ± 300 K and a mass of 0.44 M⊙. New Doppler measurements of GJ 436 with a precision of 3 m s−1 taken during 6 years improve the Keplerian model of the planet, giving it a minimum mass Msin i = 0.0713 MJup = 22.6 M⊕, period P = 2.6439 days, and eccentricity e = 0.16 ± 0.02. The noncircular orbit contrasts with the tidally circularized orbits of all close‐in exoplanets, implying either ongoing pumping of eccentricity by a more distant companion, or a higher Q value for this low‐mass planet. The velocities indeed reveal a long‐term trend, indicating a possible distant companion.

Properties and Formation of the Multiple Protostellar System L1551 IRS 5

We present an observation of L1551 IRS 5 at 7 mm with an angular resolution as high as ~004 (5 AU). Apart from the two main components oriented north-south with a projected separation of 47 AU, we discover a third component lying 13 AU to the southeast of the northern component, thereby making L1551 IRS 5 a triple protostellar system. The two main components comprise circumstellar dust disks with dimensions of ~17 AU, together with bipolar ionized jets collimated within a radial distance of 3 AU from their central protostars. The third component likely has an even smaller circumstellar dust disk with a dimension of ~9 AU. The relative proper motion of the two main components is consistent with a circular coplanar orbit with an orbital separation of ~50 AU, orbital period of ~380 yr, and total mass of ~0.9 M☉. Their measured disk sizes are smaller than the predicted gravitationally truncated sizes of ~26 AU. Together with the predicted minimum size for a circumbinary gap, noncircular coplanar orbits are constrained to an eccentricity 0.3. The disks of the two main components are accurately aligned with each other, as well as with a surrounding molecular pseudodisk. Furthermore, the clockwise orbital motion of these components coincides with the clockwise rotational motion of the pseudodisk. These attributes constitute a smoking gun for the formation of the two main components as a result of fragmentation within the inner regions of their parent pseudodisk. By contrast, the disk of the third component is significantly misaligned; measurements of its relative proper motion are required in order to help deduce its origin.

Infrared Spectroscopy of Symbiotic Stars. V. First Orbits for Three S-Type Systems: Henize 2-173, CL Scorpii, and AS 270

Infrared radial velocities have been used to compute first orbits of the M giants in three southern S-type symbiotic systems. Of the three, Hen 2-173 has the longest orbital period, 911 days, and also has a noncircular orbit with an eccentricity of 0.21. The large value of its mass function suggests that Hen 2-173 may be an eclipsing system. For CL Sco our spectroscopic orbital period of 626 days is essentially identical to the previously determined light variability period of 625 days, and we have adopted the latter. AS 270 has an orbital period of similar length, 671 days, and both CL Sco and AS 270 have circular orbits. Only CL Sco has been extensively investigated previously, and we compare our results with the conclusions of Kenyon & Webbink. We also have examined the period-eccentricity relation for 30 S-type symbiotics. Circular orbits are found for 81% of the systems with orbital periods up to 800 days, while they occur for only 22% with periods greater than 800 days. This distribution is quite unlike that for G and K giants; rather, it is similar to that for barium stars, another type of mass-transfer binary, which also consists of a late-type giant and a white dwarf companion.

Bright Be-shell stars

Echelle observations are presented and discussed for 23 of the 27 known shell stars brighter than about 6.5 mag. In addition to those typical cases, three stars with known transitions between emission & shell and pure emission line appearance, and three rapidly rotating B stars without records of line emission (Bn stars) are added to the sample. Long-term V/R emission-line variability and central quasi emission bumps (CQEs) in photospheric lines were found in 75% of all normal shell stars. This strongly suggests that the velocity law in most, if not all, disks of Be stars is roughly Keplerian. Both phenomena may occur in the same star but not at the same time. This is in agreement with the previous conclusion that CQEs only form in the presence of negligible line-of-sight velocities while long-term V/R variations are due to non-circular gas particle orbits caused by global disk oscillations. V/R variations associated with binary orbits are much less pronounced. Similarly, phase lags between different lines were detected in long-term V/R variable stars only. A binary fraction of only one-third is too low to support binary hypotheses as an explanation of the Be phenomenon. CQEs detected in 3 out of 19 Bn stars reveal the presence of disk-like equatorial concentrations of matter in B stars without emission lines. Accordingly, there seem to be intermediate cases between disk-free B stars and Be stars. Previous claims of the existence of shell stars with low v sin i could not be confirmed. Shell stars are Be stars viewed equator-on, and their observed rotational velocities are indistinguishable from the equatorial ones which are the same as in Be stars. The mean fraction of the critical rotation velocity is 81 ± 12%. The standard deviation is comparable to, or even less than, the observational uncertainties. Since this would require star-to-star differences to be negligible, which is unrealistic, the correlation between the widths of strong spectral lines and the stellar rotation velocities may be truncated or severely distorted at its extreme end. A number of not previously known facts about individual stars is also reported.

Coupling the dynamics and the molecular chemistry in the Galactic center

The physical conditions of the Galactic center (GC) clouds moving with non-circular velocities are not well-known. We have studied the physical conditions of these clouds with the aim of better understanding the origin of the outstanding physical conditions of the GC molecular gas and the possible effect of the large scale dynamics on these physical conditions.Using published CO(1-0) data, we have selected a set of clouds belonging to all the kinematical components seen in the longitude-velocity diagram of the GC. We have done a survey of dense gas in all the components using the J=2-1 lines of CS and SiO as tracers of high density gas and shock chemistry. We have detected CS and SiO emission in all the kinematical components. The gas density and the SiO abundance of the clouds in non-circular orbits are similar those in the nuclear ring (GCR). Therefore, in all the kinematical components there are dense clouds that can withstand the tidal shear. However, there is no evidence of star formation outside the GCR. The high relative velocity and shear expected in the dust-lanes along the bar major axis could inhibit the star formation process, as observed in other galaxies. The high SiO abundances derived in the non-circular velocity clouds are likely due to the large-scale shocks that created the dust lanes

Volume fusion for two-circular-orbit cone-beam tomography

By using the Feldkamp-Davis-Kress (FDK) algorithm, we can efficiently produce a digital volume, called the FDK volume, from cone-beam data acquired along a circular scan orbit. Due to the insufficiency of the cone-beam data set, the FDK volume suffers from nonuniform reproduction exactness. Specifically, the midplane (on the scan-orbit plane) can be exactly reproduced, and the reproduction exactness of off-midplanes decreases as the distance from the midplane increases. We describe the longitudinal falling-off degradation by a hatlike function and the spatial distribution over the object domain by an exactness volume. With two orthogonal circular scan orbits, we can reconstruct two FDK volumes and generate two exactness volumes. We propose a volume fusion scheme to combine the two FDK volumes into a single volume. Let Va and Vb denote the two FDK volumes, let Ea and Eb denote the exactness volumes for orbits Gamma(a) and Gamma(b), respectively, then the volume fusion is defined by Vab=VaWa+VbWb, with Wa=Ea/(Ea+Eb) and Wb=1-Wa. In the result, the overall reproduction exactness of Vab is expected to outperform that of Va, or Vb, or (Va+Vb)/2. In principle, this volume-fusion scheme is applicable for general cone-beam tomography with multiple nonorthogonal and noncircular orbits.

Automatic estimation of detector radial position for contoured SPECT acquisition using CT images on a SPECT/CT system

An algorithm was developed to estimate noncircular orbit (NCO) single-photon emission computed tomography (SPECT) detector radius on a SPECT/CT imaging system using the CT images, for incorporation into collimator resolution modeling for iterative SPECT reconstruction. Simulated male abdominal (arms up), male head and neck (arms down) and female chest (arms down) anthropomorphic phantom, and ten patient, medium-energy SPECT/CT scans were acquired on a hybrid imaging system. The algorithm simulated inward SPECT detector radial motion and object contour detection at each projection angle, employing the calculated average CT image and a fixed Hounsfield unit (HU) threshold. Calculated radii were compared to the observed true radii, and optimal CT threshold values, corresponding to patient bed and clothing surfaces, were found to be between -970 and -950 HU. The algorithm was constrained by the 45 cm CT field-of-view (FOV), which limited the detected radii to < or = 22.5 cm and led to occasional radius underestimation in the case of object truncation by CT. Two methods incorporating the algorithm were implemented: physical model (PM) and best fit (BF). The PM method computed an offset that produced maximum overlap of calculated and true radii for the phantom scans, and applied that offset as a calculated-to-true radius transformation. For the BF method, the calculated-to-true radius transformation was based upon a linear regression between calculated and true radii. For the PM method, a fixed offset of +2.75 cm provided maximum calculated-to-true radius overlap for the phantom study, which accounted for the camera system's object contour detect sensor surface-to-detector face distance. For the BF method, a linear regression of true versus calculated radius from a reference patient scan was used as a calculated-to-true radius transform. Both methods were applied to ten patient scans. For -970 and -950 HU thresholds, the combined overall average root-mean-square (rms) error in radial position for eight patient scans without truncation were 3.37 cm (12.9%) for PM and 1.99 cm (8.6%) for BF, indicating BF is superior to PM in the absence of truncation. For two patient scans with truncation, the rms error was 3.24 cm (12.2%) for PM and 4.10 cm (18.2%) for BF. The slightly better performance of PM in the case of truncation is anomalous, due to FOV edge truncation artifacts in the CT reconstruction, and thus is suspect. The calculated NCO contour for a patient SPECT/CT scan was used with an iterative reconstruction algorithm that incorporated compensation for system resolution. The resulting image was qualitatively superior to the image obtained by reconstructing the data using the fixed radius stored by the scanner. The result was also superior to the image reconstructed using the iterative algorithm provided with the system, which does not incorporate resolution modeling. These results suggest that, under conditions of no or only mild lateral truncation of the CT scan, the algorithm is capable of providing radius estimates suitable for iterative SPECT reconstruction collimator geometric resolution modeling.

The sense of rotation of subhaloes in cosmological dark matter haloes

We present a detailed analysis of the velocity distribution and orientation of orbits of subhaloes in high resolution cosmological simulations of dark matter haloes. We find a trend for substructure to preferentially revolve in the same direction as the sense of rotation of the host halo: there is an excess of prograde satellite haloes. Throughout our suite of nine host haloes (eight cluster sized objects and one galactic halo) there are on average 59% of the satellites corotating with the host. Even when including satellites out to five virial radii of the host, the signal still remains pointing out the relation of the signal with the infall pattern of subhaloes. However, the fraction of prograde satellites weakens to about 53% when observing the data along a (random) line-of-sight and deriving the distributions in a way an observer would infer them. This decrease in the observed prograde fraction has its origin in the technique used by the observer to determine the sense of rotation, which results in a possible misclassification of non-circular orbits. We conclude that the existence of satellites on corotating orbits is another prediction of the cold dark matter structure formation scenario, although there will be difficulties to verify it observationally. Since the galactic halo simulation gave the same result as the cluster-sized simulations, we assume that the fraction of prograde orbits is independent of the scale of the system, though more galactic simulations would be necessary to confirm this.

Signatures of rapid movement of electrons in valence band region: Interdependence of position, time and temperature

Position, time and temperature are the fundamental variables that describe the local energy state of electrons. In general, ionization defined only in terms of the average behavior of the electrons over an atom. The velocity, acceleration and path type of the electron will be different for electrons at different position, time and temperature in the atom since electrons are known to occupy different orbits depending on shell-type that would vary from atom to atom. These variations when summed for millions and billions of electrons can be significant in situations where the assumed qualitative character of physical events will affect the quantitative outcome, particularly when the results are brought up to the engineering scale. The accuracy required for identifying the initiation mechanism of aging of metals in contrast to that of stress corrosion may be quite different, not to mention the added effects of the environment involving high temperature and/or irradiation. The activities of the electrons near the peripheral region of the atom have known to dominate the engineering properties of matter. They, however, are least known in quantum physics because past interest has been centered on releasing energy from the atomic nucleus. The advent of nanotechnology has given hopes to the engineers that they may soon find the answers to their problems at the subatomic scale level with the assistance of high resolution electron microscopes where the detail observation of electron behavior may be made possible in the not too distant future. It is with this spirit that an initial effort is made to find the interdependence relation for the position r, time t and temperature T of an electron traveling at constant velocity and constant acceleration. The difference is explored by keeping in mind that the long journey cannot start without taking the first step. In this respect, the behavior of electrons in a hydrogen atom will be taken as the model to show that electrons move rapidly in the atom at 2.188 × 10 8 cm/s. The approach applies to other atoms with valence bands. The electron velocity can change by one order of magnitude even without accounting for deformities due to vibrations and non-circular orbits. These details can be accounted for and are dictated by the activated energy state of the atoms and the ways with which masses and/or energies are converted from one form to another. The present objective is to determine the combined effects of r, t and T on the electron behavior. To reiterate, the method used to obtain the results or the hydrogen atom can be extended to other atoms having valence bands. With attention focused on the electrons, a r– t– T relation is found for the hydrogen similar to that of the Heisenberg uncertainty principle involving the momentum and position of a particle. For electrons traveling at constant velocity, the relation rtT = ( h / 2 π k ) r b ( n ) has been found with h and k being, respectively, the Planck’s and Boltzmann’s constant. The Bohr radius is r b ( n ) with n = 1, 2, … being the quantum number. The relation changes to r 3 T / t = ( h 3 / 8 π 2 k 2 m 2 ) ( 1 / r b ( n ) ) for electrons moving with constant acceleration. The mass of the electron is m. By holding one of the three variables r, t and T constant, uncertainty in the remaining two variables would still prevail with the same interpretation as the Heisenberg principle. To reiterate, different rtT relations can be found for different atoms. However, it suffices to use the hydrogen model to show that the movements of the atoms are highly active near the outer rim of the atoms. Those in the valence band region are of particular interest to the engineers because they dominate the mechanical strength of solids in addition to the macroscopic electrical and optical properties. Even with the current power resolution of TEM and SEM, the chemical decomposition for the alloy damaged at the nanometer scale, say caused by stress corrosion, has revealed the need to examine the detail behavior of the electrons. The available data has already provided useful quantitative information that will lead to the next step of investigation. As the calculations at the subatomic scale gain accuracy and better physical understanding, they can extend the results to larger scales at the atomic and molecular scale and hopefully will connect with results to the multiscale models and take them to the engineering scale.

High resolution spectroscopy of bright subdwarf B stars

Radial velocity curves for 15 bright subdwarf B binary systems have been measured using high precision radial velocity measurements from high S/N optical high-resolution spectra. In addition, two bright sdB stars are discovered to be radial velocity variable but the period could not yet be determined. The companions for all systems are unseen. The periods range from about 0.18 days up to more than ten days. The radial velocity semi amplitudes are found to lie between 15 and 130 . Using the mass functions, the masses of the unseen companions have been constrained to lower limits of 0.03 up to 0.55 , and most probable values of 0.03 up to 0.81 . The invisible companions for three of our program stars are undoubtedly white dwarfs. In the other cases they could be either white dwarfs or main sequence stars. For two stars the secondaries could possibly be brown dwarfs. As expected, the orbits are circular for most of the systems. However, for one third of the program stars we find slightly eccentric orbits with small eccentricities of –0.06. This is the first time that non-circular orbits have been found in sdB binaries. No correlation with the orbital period can be found.

Five New Multicomponent Planetary Systems

We report Doppler measurements for six nearby G- and K-type main-sequence stars that show multiple low-mass companions, at least one of which has planetary mass. One system has three planets, the fourth triple-planet system known around a normal star, and another has an extremely low minimum mass of 18 M_⊕. HD 128311 (K0 V) has two planets (one previously known) with minimum masses (M sin i) of 2.18M_J and 3.21M_J and orbital periods of 1.26 and 2.54 yr, suggesting a possible 2 : 1 resonance. For HD 108874 (G5 V), the velocities reveal two planets (one previously known) having minimum masses and periods of (M sin i_b = 1.36M_J, P_b = 1.08 yr) and (M sin i_c = 1.02M_J, P_c = 4.4 yr). HD 50499 (G1 V) has a planet with P = 6.8 yr and M sin i = 1.7M_J, and the velocity residuals exhibit a trend of -4.8 m s^(-1) yr^(-1), indicating a more distant companion with P > 10 yr and minimum mass of 2M_J. HD 37124 (G4 IV-V) has three planets, one having M sin i = 0.61M_J and P = 154.5 days, as previously known. We find two plausible triple-planet models that fit the data, both having a second planet near P = 840 days, with the more likely model having its third planet in a 6 yr orbit and the other one in a 29 day orbit. For HD 190360, we confirm the planet having P = 7.9 yr and M sin i = 1.5M_J as found by the Geneva team, but we find a distinctly noncircular orbit with e = 0.36 ± 0.03, rendering this not an analog of as had been reported. Our velocities also reveal a second planet with P = 17.1 days and M sin i = 18.1 M_⊕. HD 217107 (G8 IV) has a previously known hot Jupiter with M sin i = 1.4M_J and P = 7.13 days, and we confirm its high eccentricity, e = 0.13. The velocity residuals reveal an outer companion in an eccentric orbit, having minimum mass of M sin i > 2M_J, eccentricity e ~ 0.5, and a period P > 8 yr, implying a semimajor axis α > 4 AU and providing an opportunity for direct detection. We have obtained high-precision photometry of five of the six planetary host stars with three of the automated telescopes at Fairborn Observatory. We can rule out significant brightness variations in phase with the radial velocities in most cases, thus supporting planetary reflex motion as the cause of the velocity variations. Transits are ruled out to very shallow limits for HD 217107 and are also shown to be unlikely for the prospective inner planets of the HD 37124 and HD 108874 systems. HD 128311 is photometrically variable with an amplitude of 0.03 mag and a period of 11.53 days, which is much shorter than the orbital periods of its two planetary companions. This rotation period explains the origin of periodic velocity residuals to the two-planet model of this star. All of the planetary systems here would be further constrained with astrometry by the Space Interferometry Mission.

HiDistribution and Kinematics of UGCA 86

We present 21 cm H I line and 408 MHz and 1.4 GHz continuum observations of the Magellanic dwarf galaxy UGCA 86, made with the Dominion Radio Astrophysical Observatory (DRAO) Synthesis Telescope. UGCA 86 is detected in the continuum at both frequencies, with 408 MHz flux density S408 = 120 ± 30 mJy and 1.4 GHz flux density S1400 = 79 ± 3 mJy. The H I structure of UGCA 86 is complex, with two separate components: a rotating disk and a highly elongated spur that is kinematically disjunct from the disk. The H I disk is centered on the optical galaxy with similar axial ratio and orientation of the major axis. An area of the disk with a peculiar velocity of ~25 km s-1 relative to the regular rotation of the disk is found on the southern side, where most of the star formation is concentrated. The spur is seen along the minor axis of UGCA 86 and overlaps in part with the disk. Toward the optical center of UGCA 86, the velocity difference between the spur and the disk is 40 km s-1, about one-third of the rotation velocity of the H I disk at 6 kpc from the center. This implies a large radial component of the orbital velocity of the spur and therefore a significantly noncircular orbit. The median H I velocity dispersion of the disk is 8.8 km s-1, similar to other (dwarf) galaxies. The H I velocity dispersion of the spur varies from 10 to 30 km s-1. A possible tidal origin of the spur is considered in view of the proximity of the large Scd galaxy IC 342. However, the orientation of the spur along the minor axis and its spatial overlap with the disk suggest that the spur is located far outside the plane of the H I disk. No evidence is found that the outer H I disk is warped, which poses a problem for the interpretation of the spur as a tidal tail induced by IC 342. Detailed modeling of the IC 342/UGCA 86 system will be required before a tidal origin of the spur can be dismissed conclusively. The possibility that the spur is part of the nascent cloud of UGCA 86 or the remains of a small dwarf galaxy is presented as an alternative interpretation.

Analytical attitude prediction of spin stabilized spacecrafts perturbed by magnetic residual torque

Abstract An analytical approach for spin-stabilized spacecraft attitude prediction is presented for the influence of the residual magnetic torques. Assuming an inclined dipole model for the Earth’s magnetic field, an analytical averaging method is applied to obtain the mean residual torque every orbital period. The orbit mean anomaly is utilized to compute the average components of residual torque in the spacecraft body frame reference system. The theory is developed for time variations in the orbital elements, and non-circular orbits, giving rise to many curvature integrals. It is observed that the residual magnetic torque does not have component along the spin axis. The inclusion of this torque on the rotational motion differential equations of a spin stabilized spacecraft yields conditions to derive an analytical solution. The solution shows that residual torque does not affect the spin velocity magnitude, contributing only for the precession and the drift of the spin axis of the spacecraft.

An algorithm for the retrieval of the earth's atmospheric parameters from occultation data of GPS/LEO satellites with non-circular orbits

A more direct iterative algorithm of the atmospheric bending angle in the retrieval of the earth's atmospheric parameters from radio occultation data of GPS/LEO satellites on non-circular orbits is presented. The convergence of this iterative method is mathematically proved. By using the simulative software package SHAOOS for the earth atmosphere retrieval from the GPS occultation observations, the effects of the circular orbit assumption on the retrieved atmospheric profiles are estimated quantitatively, and under the condition of non-circular orbits, the consistency of different iterative processes is verified. In addition, the shortage of a kind of iterative algorithm by means of series expansion is indicated.