High-resolution spectroscopy and broad-band imaging of the young planetary nebula K 3-35

We present high-resolution echelle and long-slit spectra and broad-band ( R , I ) images of the very young planetary nebula K 3-35. Several emission lines are identified, including the He  ii  4686 line and strong [N  ii ]6548, 6583 and [O  iii ]4959, 5007 emissions [ I ([N  ii ])/ I (H α )≃5.5, I ([O  iii ])/ I (H β )≃30]. A systemic velocity V _LSR≃10±2 km s⁻¹ for K 3-35 is obtained from the optical emission lines. Two different kinematic components are identified in the nebula. One of them is probably related to the elliptical envelope previously observed. The second component exhibits systematic changes of the radial velocity with position, and a relatively small velocity width. This component may be attributed to the precessing jet-like outflows previously identified. The R and I images and the deduced R − I colour map strongly support the existence of a dense, partially neutral disc-like region in the equatorial plane of the nebula, which probably represents an equatorial density enhancement in a previously ejected slow wind. Diagnostic diagrams for line intensity ratios in K 3-35 and collimated components of other planetary nebulae suggest that the emission spectrum of this kind of structure is a combination of radiative and shock excitation, in agreement with recent models of shocks in a strongly photoionized medium.     

An asteroseismic study of the β Cephei star θ Ophiuchi: spectroscopic results

The central stars of highly evolved planetary nebulae (PNe) are expected to have closely similar absolute visual magnitudes M_V . This enables us to determine approximate distances to these sources where one knows their central star visual magnitudes, and levels of extinction. We find that such an analysis implies values of D which are similar to those determined by Phillips; Cahn, Kaler & Stanghellin; Acker, and Daub. However, our distances are very much smaller than those of Zhang; Bensby & Lundstrom, and van de Steene & Zijlstra. The reasons for these differences are discussed, and can be traced to errors in the assumed relation between brightness temperature and radius.
Finally, we determine that the binary companions of such stars can be no brighter than   M_V ∼ 6 mag  , implying a spectral type of K0 or later in the case of main-sequence stars.     

85 Peg A: what age for a low-metallicity solar-like star?

We explore the possible evolutionary status of the primary component of the binary 85 Pegasi, listed as a target for asteroseismic observations by the MOST satellite. In spite of the assessed 'subdwarf' status, and of the accurate distance determination from the Hipparcos data, the uncertainties in the metallicity and age, coupled with the uncertainty in the theoretical models, lead to a range of predictions on the oscillation frequency spectrum. Nevertheless, the determination of the ratio between the small separation in frequency modes, and the large separation as suggested by Roxburgh, provides a very good measure of the star age, quite independent of the metallicity in the assumed uncertainty range. In this range, the constraint on the dynamical mass and the further constraint provided by the assumption that the maximum age is 14 Gyr limits the mass of 85 Peg A to the range from 0.75 to  0.82 M_⊙  . This difference of a few hundredths of a solar mass leads to well detectable differences both in the evolutionary stage (age) and in the asteroseismic properties. We show that the age determination which will be possible through the asteroseismic measurements for this star is independent either of the convection model adopted or the microscopic metal diffusion. The latter conclusion is strengthened by the fact that, although metal diffusion is still described in an approximate way, recent observations suggest that real stars suffer a smaller metal sedimentation compared with the models.     

3D numerical simulations of a radiative Herbig–Haro jet in a supersonic side wind

We have performed 3D numerical simulations of an over-pressurized Herbig–Haro-type jet which propagates into a sidestreaming environment. The interaction between the jet and the sidewind results in a perpendicular acceleration of the jet material, and a consequent curvature of the jet as it moves into the anisotropic medium. We find that an approximately steady configuration is achieved both for a sidewind that is perpendicular to the jet and for a sidewind inclined at 45° towards the jet source. The curvature obtained in both these models is consistent with analytic models of the jet/sidewind problem.   We have also calculated Hα maps, which show an emitting sheath around the upwind (with respect to the sidewind) side of the jet beam. This emitting sheath may explain part of the observed emission from curved stellar jets.     

The neutral carbon distribution in a bipolar outflow/molecular disc source configuration: G35.2−0.74N

Maps are presented of ³ P ₁→³ P ₀[C  i ] and J =2→1 C¹⁸O line emission from the interstellar molecular cloud G35.2−0.74N. The maps are interpreted with reference to a previous model for the structure of the cloud in which opposing jets from a central object, embedded in a rotating interstellar disc, precess and drive a bipolar molecular outflow. The C¹⁸O emission traces the rotating interstellar disc, but the [C  i ] emission shows several features. An unresolved component is observed which probably results from dissociation of CO in the centre of the disc by UV radiation from the central source. Background [C  i ] emission is also observed which shares the rotation of the disc on larger scales. The C  i /CO ratio in these components is typically a few per cent. High-velocity [C  i ] emission, where C  i /CO is high (>0.1–0.4), is observed between the CO molecular outflow and the cavity exacavated by the jet. This material has probably been accelerated by the jet but dissociated by far-UV radiation propagating through the cavity. The C  i /CO ratio falls as the shocked outflow later sweeps up CO.     

Scaling for the intensity of radiation in spherical and aspherical planetary nebulae

Planetary nebulae are imaged using three different physical processes. The first process is the expansion of the shell, which can be modelled by the canonical laws of motion in the spherical case and by momentum conservation when gradients of density are present in the interstellar medium. The second process is the diffusion of particles that radiate from the advancing layer. Three-dimensional diffusion from a sphere and one-dimensional diffusion with drift are analysed. The third process is the composition of an image through an integral operation along the line of sight. The framework developed is applied to A39, the Ring nebula and the etched hourglass nebula MyCn 18.     

Precessing collimated outflows in the planetary nebula IC 4846

We present [N  ii ] and H α images and high-resolution long-slit spectra of the planetary nebula IC 4846, which reveal, for the first time, its complex structure and the existence of collimated outflows. The object consists of a moderately elongated shell, two (and probably three) pairs of collimated bipolar outflows at different orientations, and an attached circular shell. One of the collimated pairs is constituted by two curved, extended filaments the properties of which indicate a high-velocity, bipolar precessing jet. A difference of ≃10 km s⁻¹ is found between the systemic velocity of the precessing jets and the centroid velocity of the nebula, as recently reported for Hu 2-1. We propose that this difference is as a result of orbital motion of the ejection source in a binary central star. The orbital separation of 30 au and period 100 yr estimated for the binary are similar to those in Hu 2-1, linking the central stars of both planetary nebulae to interacting binaries. Extraordinary similarities also exist between IC 4846 and the bewildering planetary nebula NGC 6543, suggesting a similar formation history for both objects.     

A radio-emitting outflow in the quiescent state of A0620−00: implications for modelling low-luminosity black hole binaries

Deep observations with the Very Large Array of A0620–00, performed in 2005 August, resulted in the first detection of radio emission from a black hole binary at X-ray luminosities as low as 10^−8.5 times the Eddington limit. The measured radio flux density, of  51 ± 7 μJy  at 8.5 GHz, is the lowest reported for an X-ray binary system so far, and is interpreted in terms of partially self-absorbed synchrotron emission from outflowing plasma. Making use of the estimated outer accretion rate of A0620−00 in quiescence, we demonstrate that the outflow kinetic power must be energetically comparable to the total accretion power associated with such rate, if it was to reach the black hole with the standard radiative efficiency of 10 per cent. This favours a model for quiescence in which a radiatively inefficient outflow accounts for a sizable fraction of the missing energy, and, in turn, substantially affects the overall dynamics of the accretion flow. Simultaneous observations in the X-ray band, with Chandra , confirm the validity of a non-linear radio/X-ray correlation for hard state black hole binaries down to low quiescent luminosities, thereby contradicting some theoretical expectations. Taking the mass term into account, the A0620−00 data lie on the extrapolation of the so-called Fundamental Plane of black hole activity, which has thus been extended by more than two orders of magnitude in radio and X-ray luminosity. With the addition of the A0620−00 point, the plane relation provides an empirical proof for the scale invariance of the jet-accretion coupling in accreting black holes over the entire parameter space observable with current instrumentation.     

The emission and kinematic structures of the bipolar planetary nebula M 1-8

We have undertaken echelle spectroscopy and narrow-band line imaging of the bipolar planetary nebula M 1-8. This has permitted us to map the outflow in [N  ii ]λλ 6548+6583 Å, Hα, and in the v = 1–0 S(1) transition of H₂ at λ 2.122 μm. It has also permitted us to acquire high-resolution spectra for [N  ii ]λ 6583 Å, Hα and He  ii λ 6560 Å. Our observations support the results of a previous 2MASS analysis by two of the authors (J. P. Phillips and G. Ramos-Larios), and confirm that there is strong H₂ emission outside of the ionized zone, as well as along the major axis of the outflow. Finally, we have investigated the spatial structure of the outflow in low and high excitation lines, and noted evidence for strong ionization stratification within the envelope of the source. We also note that major axis spectra show asymmetries attributable to outflow along the lobes, oriented at an angle i ∼ 35°–40° to the line of sight. Asymmetries along the minor axis, by contrast, appear to be associated with the central collimating disc, and may be interpretable in terms of asymmetries in disc structure, or rotation at an angular velocity of Ω∼ 1.4 10⁻¹² rad s⁻¹. If the disc arises due to common-envelope evolution, then it seems that angular momentum constraints must be relatively tight, and can only be satisfied given fairly extreme physical assumptions (such as low disc mass, high primary star mass, a low distance to the source and so forth).     

Does the plasma composition affect the long-term evolution of relativistic jets?

We study the influence of the matter content of extragalactic jets on their morphology, dynamics and emission properties. For this purpose we consider jets of extremely different compositions, including pure leptonic and baryonic plasmas. Our work is based on two-dimensional relativistic hydrodynamic simulations of the long-term evolution of powerful extragalactic jets propagating into a homogeneous environment. The equation of state used in the simulations accounts for an arbitrary mixture of electrons, protons and electron–positron pairs. Using the hydrodynamic models, we have also computed synthetic radio maps and the thermal bremsstrahlung X-ray emission from their cavities.
Although there is a difference of about three orders of magnitude in the temperatures of the cavities inflated by the simulated jets, we find that both the morphology and the dynamic behaviour are almost independent of the assumed composition of the jets. Their evolution proceeds in two distinct epochs. During the first one, multidimensional effects are unimportant and the jets propagate ballistically. The second epoch starts when the first larger vortices are produced near the jet head, causing the beam cross-section to increase and the jet to decelerate. The evolution of the cocoon and cavity is in agreement with a simple theoretical model. The beam velocities are relativistic  ( Γ ≃4)  at kiloparsec scales, supporting the idea that the X-ray emission of several extragalactic jets may be due to relativistically boosted CMB photons. The radio emission of all models is dominated by the contribution of the hotspots. All models exhibit a depression in the X-rays surface brightness of the cavity interior, in agreement with recent observations.     

A pilot study of the radio‐continuum emission from MASH planetary nebulae

We report an Australia Telescope Compact Array (ATCA) radio‐continuum observations of 26 planetary nebulae (PNe) at wavelengths of 3 and 6 cm. This sample of 26 PNe were taken from the Macquarie/AAO/Strasbourg Hα PNe (MASH) catalogue and previous lists. We investigate radio detection quality including measured and derived parameters for all detected or marginally detected PNe from this combined sample. Some 11 objects from the observed sample have been successfully detected and parametrized. Except for one, all detected PNe have very low radio surface brightnesses. We use a statistical distance scale method to calculate distances and ionised masses of the detected objects. Nebulae from this sample are found tobe large (>0.2 pc in diameter) and highly diluted which indicates old age. For 21 PNe from this sample we list integrated Hα fluxes and interstellar extinction coefficients, either taken from the literature or derived here from the Balmer decrement and radio to Hα ratio methods. Finally, our detected fraction of the MASH pilot sample is relatively low compared to the non‐MASH sub‐sample. We conclude that future radio surveys of the MASH sample must involve deeper observations with better uv coverage in order to increase the fraction of detected objects and improve the quality of the derived parameters (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Three-dimensional hydrodynamical simulations of the large-scale structure of W50−SS433

We present 3D hydrodynamical simulations of a precessing jet propagating inside a supernova remnant (SNR) shell, particularly applied to the W50−SS433 system in a search for the origin of its peculiar elongated morphology. Several runs were carried out with different values for the mass-loss rate of the jet, the initial radius of the SNR, and the opening angle of the precession cone. We found that our models successfully reproduce the scale and morphology of W50 when the opening angle of the jets is set to 10° or if this angle linearly varies with time. For these models, more realistic runs were made considering that the remnant is expanding into an interstellar medium with an exponential density profile (as H  i observations suggest). Taking into account all these ingredients, the large-scale morphology of the W50−SS433 system, including the asymmetry between the lobes (formed by the jet–SNR interaction), is well reproduced.