Disk Axis Research Articles

The Angstrom Project: a microlensing survey of the structure and composition of the bulge of the Andromeda galaxy

The Andromeda Galaxy Stellar Robotic Microlensing Project (The Angstrom Project) aims to use stellar microlensing events to trace the structure and composition of the inner regions of the Andromeda Galaxy (M31). We present microlensing rate and timescale predictions and spatial distributions for stellar and sub-stellar lens populations in combined disk and barred bulge models of M31. We show that at least half of the stellar microlenses in and around the bulge are expected to have characteristic durations between 1 and 10 days, rising to as much as 80% for brown-dwarf dominated mass functions. These short-duration events are mostly missed by current microlensing surveys that are looking for Macho candidates in the M31 dark matter halo. Our models predict that an intensive monitoring survey programme such as Angstrom, which will be able to detect events of durations upwards of a day, could detect around 30 events per season within ~5 arcminutes of the M31 centre, due to ordinary low-mass stars and remnants. This yield increases to more than 60 events for brown-dwarf dominated mass functions. The overall number of events and their average duration are sensitive diagnostics of the bulge mass, in particular the contribution of low-mass stars and brown dwarfs. The combination of an inclined disk, an offset bar-like bulge, and differences in the bulge and disk luminosity functions results in a four-way asymmetry in the number of events expected in each quadrant defined by the M31 disk axes. The asymmetry is sensitive to the bar prolongation, orientation and mass.

On the source of dense outflows from T Tauri stars - II. Warm disc winds

Recent ultraviolet (UV) observations suggest that there is a hot (T(e)similar or equal to 80 000 K) and dense (Ne similar or equal to 10(10) cm(-3)) wind associated with the large-scale jets observed in classical T Tauri stars (cTTSs). The observations of these rather evolved sources cannot be fitted with the classical cold disc wind solutions. This is not unexpected since the accretion rates are moderate (<= 10(-8) M-circle dot yr(-1)) and the wind lighter than at earlier phases. Henceforth, X-ray radiation from the star and the star-disc interaction region is expected to modify the thermal structure of the inner disc, e.g. the base of the disc wind. Thus, thermal pressure is relevant to load gas on the field lines. In this work, we analyse whether warm disc winds can account for these UV observations. To get a good hint on the physics, we have preferred to focus on analytical work. We have made use of the warm disc wind solution with pressure calculated by Vlahakis et al. The rich complexity of the magnetohydrodynamic (MHD) disc wind kinematics is analysed in detail. We show the following. (i) Warm disc flows departing from the inner disc radius (similar to 0.1 au) reach terminal velocities close to the observed (300 km s(-1)) and that the temperature at the base of the wind is similar to 40 000 K. Thus, the spectral signature of warm disc winds is an enhancement of the chromospheric and transition region spectral indicators by several orders of magnitude, as observed in cTTSs. (ii) Warm disc winds rotate, but their rotation velocity is small since the wind dynamics is based in a transference of angular momentum from the star to the magnetic field. Henceforth, slow rotation plus high temperature (e.g. rotational broadening) show in very broad profiles at the base of the wind. (iii) The kinematics at the base of the wind is dominated by axial expansion; however, above z similar or equal to 5 au, the dominant kinematical component is acceleration along the disc axis. (iv) The most often observed profile is a single-peaked line, slightly blueshifted and asymmetric with a tail to short wavelengths. The full width at half-maximum is clearly suprathermal and depends on the spectral tracer used. Line profiles, fluxes and line ratios are calculated for the C IV[uv1], C II1908, C II](2326), Si III](1892) and [O II](2471) UV lines. In edge-on systems, the profiles range from symmetric lines with suprathermal broadenings for the spectral tracers of the base of the wind (C IV[uv1] and Si II](1892)) to double-peaked profiles for spectral tracers more weighted to higher values of z ([O II] and C II]). In pole-on systems, the profiles are blueshifted (from few to 200 km s(-1)) and asymmetric exhibiting long tails towards the terminal velocity of the wind (V-rad= 300 km s(-1)). To reproduce the observed line fluxes and ratios, winds must be clumpy and extinction by the flaring disc and the wind itself ought to be taken into account.

Stabilization of the motion of a disk rolling on a horizontal plane by using a translational moving rod along its axis

This work deals with the stabilization and control of a system which is composed of a disk rolling on a plane, a translational joint attached along the disk's axis, and a controlled rod that moves along the translational joint (see Figures 1 and 2). The disk's motion is controlled by the moving rod, a “directional control” moment, and a pedalling moment. It is shown here that by applying a kind of inverse dynamics control, the motion of the disk is stabilized, while simultaneously controlling its speed and direction in such a manner that the point of contact between the disk and the horizontal plane will be able asymptotically to track any given smooth ground trajectory.

Properties of SS433 and ultraluminous X-ray sources in external galaxies

We suggest that the ultraluminous X-ray sources located in external galaxies (ULXs) are supercritical accretion disks like that in SS433, observed close to the disk axis. We estimate parameters of the SS433 funnel, where the relativistic jets are formed. Emergent X-ray spectrum in the proposed model of the multicolor funnel (MCF) is calculated. The spectrum can be compared with those of ULXs. We predict a complex absorption-line spectrum with broad and shallow K$\alpha$/Kc blends of the most abundant heavy elements and particular temporal variability. Another critical idea comes from observations of nebulae around the ULXs. We present results of 3D-spectroscopy of nebulae of two ULXs located in Holmberg II and NGC6946. In both cases the nebula is found to be powered by the central black hole. The nebulae are compared with SS433 nebula (W50).

Internal Alignment of the Halos of Disk Galaxies in Cosmological Hydrodynamic Simulations

Seven cosmological hydrodynamic simulations of disk galaxy formation are analyzed to determine the alignment of the disk within the dark matter halo and the internal structure of the halo. We find that the orientation of the outer halo, beyond ~0.1rvir, is unaffected by the presence of the disk. In contrast, the inner halo is aligned such that the halo minor axis aligns with the disk axis. The relative orientations of these two regions of the halo are uncorrelated. The alignment of the disk and inner halo appears to take place simultaneously through their joint evolution. The lack of connection between these two regions of the halo should be taken into account when modeling tidal streams in the halos of disk galaxies and when calculating intrinsic alignments of disk galaxies based on the properties of dark matter halos.

Outflows in the Orion Nebula: HH 540 from the Beehive Proplyd

We present Hubble Space Telescope Advanced Camera for Surveys images of the giant proplyd 181-826 in the southern Orion Nebula. This object exhibits a variety of known proplyd properties—an optically visible central star, a silhouette disk, a bright proplyd ionization front, and a bipolar microjet emerging along the disk axis that powers a larger Herbig-Haro flow. The proplyd ionization front is remarkable because of its large size (a radius of about 800 AU) and because of its corrugated structure consisting of a set of coaxial rings with the same orientation as the embedded silhouette disk. The rings are centered on the disk/jet axis, and we discuss possible mechanisms for their formation. The silhouette disk has an outer radius of about 160 AU, and its axis is inclined by an angle of about 60° with respect to our line of sight. A prominent reflection nebula protrudes along the disk axis toward the south, marking the base of the approaching outflow, and a faint knot on the north side of the disk indicates that the nebula is bipolar. Fabry-Pérot images reveal a high-velocity blueshifted jet with a mass-loss rate of about 10-8 M⊙ yr-1 emerging along the disk axis. It has a velocity (corrected for the outflow inclination angle) of about 160 km s-1 and can be traced for about 1' toward the south. A chain of three lower velocity blueshifted bow shocks, collectively known as HH 540, extend several arcminutes south of 181-826 along the same axis, tracing a large-scale outflow powered by this jet.

Anisotropic hydraulic permeability in compressed articular cartilage

The extent to which articular cartilage hydraulic permeability is anisotropic is largely unknown, despite its importance for understanding mechanisms of joint lubrication, load bearing, transport phenomena, and mechanotransduction. We developed and applied new techniques for the direct measurement of hydraulic permeability within statically compressed adult bovine cartilage explant disks, dissected such that disk axes were perpendicular to the articular surface. Applied pressure gradients were kept small to minimize flow-induced matrix compaction, and fluid outflows were measured by observation of a meniscus in a glass capillary under a microscope. Explant disk geometry under radially unconfined axial compression was measured by direct microscopic observation. Pressure, flow, and geometry data were input to a finite element model where hydraulic permeabilities in the disk axial and radial directions were determined. At less than 10% static compression, near free-swelling conditions, hydraulic permeability was nearly isotropic, with values corresponding to those of previous studies. With increasing static compression, hydraulic permeability decreased, but the radially directed permeability decreased more dramatically than the axially directed permeability such that strong anisotropy (a 10-fold difference between axial and radial directions) in the hydraulic permeability tensor was evident for static compression of 20–40%. Results correspond well with predictions of a previous microstructurally-based model for effects of tissue mechanical deformations on glycosaminoglycan architecture and cartilage hydraulic permeability. Findings inform understanding of structure-function relationships in cartilage matrix, and suggest several biomechanical roles for compression-induced anisotropic hydraulic permeability in articular cartilage.

High-resolution imaging polarimetry of HL Tau and magnetic field structure

We present high quality near infrared imaging polarimetry of HL Tau at 0.4 to 0.6 arcsec resolution, obtained with Subaru/CIAO and UKIRT/IRCAM. 3-D Monte Carlo modelling with aligned oblate grains is used to probe the structure of the circumstellar envelope and the magnetic field, as well as the dust properties. At J band the source shows a centrosymmetric pattern dominated by scattered light. In the H and K bands the central source becomes visible and its polarisation appears to be dominated by dichroic extinction, with a position angle inclined by � 40 ◦ to the disc axis. The polarisation pattern of the environs on scales up to 200 AU is consistent with the same dichroic extinction signature superimposed on the centrosymmetric scattering pattern. These data can be modelled with a magnetic field which is twisted on scales from tens to hundreds of AU, or alternatively by a field which is globally misaligned with the disc axis. A unique solution to the field structure will require spatially resolved circular polarisation data. The best fit Monte Carlo model indicates a shallow near infrared extinction law. When combined with the observed high polarisation and non-negligible albedo these constraints can be fitted with a grain model involving dirty water ice mantles in which the largest particles have radii slightly in excess of 1 µm. The best fit model has an envelope structure which is slightly flattened on scales up to several hundred AU. Both lobes of the bipolar outflow cavity contain a substantial optical depth of dust (not just within the cavity walls). Curved, approximately parabolic, cavity walls fit the data better than a conical cavity. The small inner accretion disc observed at millimetre wavelengths is not seen at this spatial resolution.

Do bulges of early- and late-type spirals have different morphology?

We study HST/NICMOS H-band images of bulges of two equal-sized samples of early- (T R C 3 ≤ 3) and late-type spiral (mainly Sbc-Sc) galaxies matched in outer disk axis ratio. We find that bulges of late-type spirals are more elongated than their counterparts in early-type spirals. Using a KS-test we find that the two distributions are different at the 98.4% confidence level We conclude that the two data sets are different, i.e. late-type galaxies have a broader ellipticity distribution and contain more elongated features in the inner regions. We discuss the possibility that these would correspond to bars at a later evolutionary stage, i.e. secularly evolved bars. Consequent implications are raised, and we discuss relevant questions regarding the formation and structure of bulges. Are bulges of early-type and late-type spirals different? Are their formation scenarios different? Can we talk about bulges in the same way for different types of galaxies?

Mechanics of Disk-Type False Twisting

A triple-stack multiple-disk spindle unit is used widely in actual draw texturing processes. In this kind of friction false twisting process, the angle of inclination (angle between yarn path and disk axis) is an important factor that determines yarn tension and twisting torque over the disk surface. This paper proposes a new theory that will give a more precise angle of inclination using differential geometry. The basic assumptions are that the disk profile is represented as an outer surface of a torus, and the yarn path over the disk surface forms a geodesic line. The angle of inclination is calculated by this theory in the actual range of the disk diameter, the radius of the disk edge, and the distance between two neighboring disk axes. The inclination angle obtained by this theory gives smaller values than the angles obtained by previous studies, but the experimental data agree best with the value calculated by this theory. We also explain how to calculate the entry angle (the angle of wrap) and the limiting value of the angle of wrap to guarantee smooth contact of the yarn with the disk periphery. The effect of the profile represented by the radius of the disk on the angle of inclination, and the angle of wrap is also investigated.

Structure of energy quantum levels in a quantum dot shaped as an oblate body of revolution

It was shown that the electron energy spectrum in a disk-shaped potential well is characterized by two types of levels. One is characterized by a quantum number corresponding to carrier motion mainly along the disk axis. Energy intervals between such levels are large. As a rule, only a single electron level of this type can fit into the InAs quantum dot with GaAs surroundings. The second-type levels form a substructure with quantum numbers corresponding to carrier rotation about the polar axis and motion along the major disk axis. The distances between such levels are rather short. The theory makes it possible to determine the number of such levels as a function of the disk thickness and diameter and the conditions of the quantum dot transition into the quantum well with a large number of substructure levels.

A numerical study of the rotational behavior of the white dwarf in DQ Herculis, II: the turn-over scenario

The optical pulsations in DQ Her are universally believed to be due to emission from the magnetic poles of the white dwarf. However, there is no way for a pulsation to be seen if the magnetic axis and the spin axis are aligned; whether the optical pulsation is seen directly from the magnetic poles or as a result of re-processing this beam from sides in an accretion disc, the magnetic and spin axes must be offset. This fact explains why the `oblique rotator' model has been adopted as a standard model for the DQ Her primary. In a recent paper, we have computed several axisymmetric models simulating the DQ Her white dwarf before its `turn-over' (where the term `turn-over' describes the process by which the magnetic axis gets inclining relative to the spin axis at a gradually increasing angle, the so-called `turn-over angle'). For such models, we have found that the moment of inertia along the rotation axis, I33, is less than the moment(s) of inertia along the two other principal axes, I11=I22. The situation I11>I33 is known as `dynamical asymmetry', and can cause a spontaneous turn-over of the magnetic axis with respect to the rotation axis . Consequently, the DQ Her white dwarf is either an oblique rotator undergoing its turn-over phase, or it is already qalmostequal a `perpendicular rotator', i.e., its turn-over angle is almost equal to 90°. Assuming the first case, we study numerically the so-called `turn-over scenario', that is, a scenario on rotational evolution in which the turn-over phase is taken into account. We give emphasis on computations concerning the spin-down time rate of the DQ Her white dwarf due to turn-over (not to be confused with its spin-uptime rate due to accretion) for several possible values of the magnetic field.

The Euler machine

In order to illustrate Euler's equations for rotation, we haveconstructed an apparatus in which a circular disc is attached tohorizontal axle, such that the disc axis and axle are at a45° angle. The total angular momentum L⃗and constant angular velocity ω⃗ vectors aretherefore not collinear. The first experiment measured thetorque necessary to maintain a fixed axis of rotation. Afterthe constraining torque is removed, the resulting oscillationmakes an interesting demonstration of the thrust produced by an off-axis wheel. The amplitude of the axle's oscillation around avertical axis has been measured and analysed using angularmomentum vectors in a rotating system.

Magnetic fields in discs: what can be learned from infrared and mm polarimetry?

Polarimetric imaging in the infrared and submm offers the possibility of identifying magnetic field configurations in astronomical objects. To test this conjecture a set of field geometries within internally heated discs has been modelled and polarization transfer followed for a range of view angles with respect to the disc axis. The wavelength range considered is from the mid-infrared to submm, the dominant polarization processes then being only dichroic emission and absorption by aligned grains. A sample of the resulting polarization images is presented and their salient features discussed. There are obvious, and some not so obvious, associations of polarization structure with the parent model field and, while these are not always unique, they will usually lead to strong constraints on the field configuration. For star formation regions the polarization structure is likely to be on a small spatial scale and then the full potential of this technique must await the advent of millimetre synthesis systems.

Protein–lipid interactions in reconstituted high density lipoproteins: apolipoprotein and cholesterol influence

Two fluorescent probes— cis- and trans-parinaric acids were used to study the dimensions, lipid dynamics and apolipoprotein location in the reconstituted discoidal high density lipoproteins (rHDL). The rHDL particles made from apolipoprotein A-I (apoA-I), dipalmitoylphosphatidylcholine (DPPC), with or without cholesterol (Chol) were compared with the analogous particles with two other apolipoproteins-apoE and apoA-II. The data obtained for apoA-I-containing rHDL were as follows: (1) the inclusion of 8 mol.% of cholesterol did not significantly change the particle dimensions (13±1 nm) or the mean distance between apoA-I and the disc axis; (2) the phospholipid domains—boundary lipid region in the close vicinity to apoA-I molecule and the remaining part of the bilayer—existed at temperatures both lower and above DPPC transition temperature T t; (3) at T< T t Chol molecules preferentially accumulated in the central area with a radius of 2.8 nm that conserved partially after DPPC phase transition; (4) inhomogeneous cholesterol distribution was assumed to exist within these domains. A hydrophobic matching concept was used to compare protein–lipid interactions in rHDL particles. For complexes with all three apolipoproteins studied, at T< T t the probe mobility in the lipid phase of rHDL was significantly higher compared to pure DPPC bilayer. After temperature-induced transition, mobility increased significantly still being lower in rHDL. The comparative study of lipid dynamics in apoA-I-, apoE- and apoA-II-containing complexes revealed the presence of boundary lipid in all three complexes without cholesterol. The degree of cholesterol exclusion from the boundary lipid region seems to increase in the order A-I<E<A-II for Chol-containing complexes, the exclusion being an inherent property of the particular apolipoprotein molecule.

CO Survey of Nearby Spiral Galaxies with the Nobeyama 45-m Telescope: I. The Data

Abstract We mapped the 12CO($J = 1 -0$) emission along the major and minor axes of disks or bars of 25 nearby galaxies using the Nobeyama 45-m telescope with a spatial resolution of $0.01$–$0.12 D_{25}$ ($D_{25}$: de Vaucouleurs’ diameter), and detected the CO emission at 8–42 positions along each axis. The galaxy sample includes morphological type Sab and Scd as well as barred and nonbarred. These data are useful to statistically study the internal distribution and dynamics of molecular gas in galaxies and to deduce common characteristic properties. In this paper, we describe the sample and observations, present all spectra and measured line parameters, and examine the relations between the global molecular gas mass and the Hubble type, the total mass of the galaxies, and the star-formation rate.

Host Galaxies, Obscuration, and Nuclear Structure of Three Nearby Compact Symmetric Objects

We present three-band Hubble Space Telescope imaging of three nearby (z „ 0.1) compact symmetric objects: 4C 31.04, 1946]708, and 1146]596. These objects were chosen on the basis of proximity to Earth as well as H I 21 cm line absorption. The inner H-band isophotes of these galaxies are well —tted by Nuker models, typical of nearby elliptical galaxies. Each shows a signi—cant —attening in the isophotal pro—le at radii as well as signi—cant variations in ellipticity and P.A. However, as previous D0A.5, authors have noted, neither is uncommon for elliptical galaxies. All three objects show modest departures from Nuker law models at radii of 1¨5 kpc. Each galaxy shows large well-distributed dust h 60 features, which are somewhat concentrated in the nuclear regions in features that resemble disks or tori. We —nd that the amount of dust in these galaxies is about 10 times higher than normal for elliptical galaxies and radio galaxy hosts. The major axes of the nuclear dust disks tend to be oriented roughly perpendicular to the radio axis. One galaxy, 4C 31.04, exhibits bright nuclear regions well aligned with the radio axis, while another, 1146]596, shows a signi—cant near-IR excess resembling a stellar bar along its dust disk. The combination of outwardly normal isophotal pro—les with signi—cant variations in P.A. and ellipticity is consistent with the host galaxies being relatively recent merger remnants and the mergers having occurred yr ago. Such a merger could have ii triggered ˇˇ the onset of the current Z108 active phase seen in these objects, but our data require a signi—cant time delay between the merger event and the onset of nuclear activity. However, these data are also consistent with the hypothesis that the onset of nuclear activity in radio galaxies is due to relatively minor ii feeding ˇˇ events and/or the formation of ii bars within bars,ˇˇ events which would disturb the internal kinematics only slightly.

Classification of Power Density Spectrum Features and Estimation of the δ-invariant Value for the Z Source GX 340+0

We present a theoretical analysis of Rossi X-Ray Timing Explorer data of Z source GX 340+0 obtained by Jonker et al. In the frameworks of the recently formulated transition layer model, the δ-angle is an angle between the neutron star (NS) magnetospheric axis and the disk (presumably NS rotational) axis. We determine the angle δ = 63 ± 03, which is a combination of the simultaneously observed kilohertz quasi-periodic and horizontal-branch oscillation frequencies. While these three frequencies change by a factor of 3 or more, their δ-combination stays almost constant. GX 340+0 is the fourth source (in addition to 4U 0614+09, Scorpius X-1, and 4U 1702-42) for which δ has been determined. With one (constrained) parameter, at most, we make a complete classification of six observed power spectral features, including the two kilohertz frequencies, the first and second harmonics of the horizontal-branch oscillation frequency, the low-frequency noise component, and the break frequencies. We demonstrate that a new component discovered by Jonker et al. in the GX 340+0 power spectrum is related to the viscous-frequency branch that has in fact been reported earlier in 4U 1728-34 by Ford & van der Klis. Finally, we reclassify several previously misidentified features in the power spectrum.

Constraining the Black Hole Mass and Accretion Rate in the Narrow‐Line Seyfert 1 Galaxy RE J1034+396

We present a comprehensive study of the spectrum of the narrow-line Seyfert 1 (NLS1) galaxy RE J1034+396, summarizing the information obtained from the optical to X-rays with observations from the William Herschel 4.2 m Telescope, the Hubble Space Telescope, the Extreme Ultraviolet Explorer, ROSAT, ASCA, and BeppoSAX. The BeppoSAX spectra reveal a soft component which is well represented by two blackbodies with kTeff = 60 and 160 eV, mimicking that expected from a hot, optically thick accretion disk around a low-mass black hole. This is borne out by our modeling of the optical-to-X-ray nuclear continuum, which constrains the physical parameters of a NLS1 for the first time. The models demonstrate that RE J1034+396 is likely to be a system with a nearly edge-on accretion disk (60°-75° from the disk axis), accreting at nearly Eddington rates (0.3-0.7LEdd) onto a low-mass black hole (Mbh ~ 2-10 × 106 M☉). This is consistent with the hypothesis that NLS1s are Seyfert-scale analogies of galactic black hole candidates. The unusually high temperature of the big blue bump reveals a flat power-law-like continuum in the optical/UV which is consistent with an extrapolation to the hard X-ray power law, and which we speculate may be similar to the continuum component observed in BL Lac objects in their quiescent periods. From the BeppoSAX and ASCA data, we find that the slope of the hard X-ray power law depends very much on the form of the soft component which is assumed. For our best-fitting models, it lies somewhere between α = 0.7 and 1.3 and thus may not be significantly softer than active galactic nuclei in general.

Testing the Unified Model with an Infrared‐selected Sample of Seyfert Galaxies

We present a series of statistical tests done to a sample of 29 Seyfert 1 and 59 Seyfert 2 galaxies selected from mostly isotropic properties, their far infrared fluxes and warm infrared colors. Such selection criteria provide a profound advantage over the criteria used by most investigators in the past, such as ultraviolet excess. These tests were done using ground based high resolution VLA A-configuration 3.6 cm radio and optical B and I imaging data. From the relative number of Seyfert 1's and Seyfert 2's we calculate that the torus half opening angle is 48deg. We show that, as seen in previous papers, there is a lack of edge-on Seyfert 1 galaxies, suggesting dust and gas along the host galaxy disk probably play an important role in hiding some nuclei from direct view. We find that there is no statistically significant difference in the distribution of host galaxy morphological types and radio luminosities of Seyfert 1's and Seyfert 2's, suggesting that previous results showing the opposite may have been due to selection effects. The average extension of the radio emission of Seyfert 1's is smaller than that of Seyfert 2's by a factor of ~2-3, as predicted by the Unified Model. A search for galaxies around our Seyferts allows us to put a lower and an upper limit on the possible number of companions around these galaxies of 19% and 28%, respectively, with no significant difference in the number of companion galaxies between Seyfert 1's and Seyfert 2's. We also show that there is no preference for the radio jets to be aligned closer to the host galaxy disk axis in late type Seyferts, unlike results claimed by previous papers. These results, taken together, provide strong support for a Unified Model in which type 2 Seyferts contain a torus seen more edge-on than the torus in type 1 Seyferts.