The C/CO ratio in B335 and the decaying dark matter neutrino hypothesis

C¹⁸O J  = 2–1, C¹⁷O J  = 2–1 and [C  I ] ³P₁–³P₀ emission from the dense cold cloud B335 has been observed and modelled in order to determine the C/CO ratio. The observed ratio is compared with a prediction by Tarafdar who assumes a mechanism in which the CO dissociation is caused by photons of energy ∼ 13.8 eV. These were postulated by Sciama to result from the decay of dark matter neutrinos. Our value for the C/CO ratio sets an upper limit to the strength of the neutrino decay dissociation process, thus providing a significant datum for interstellar chemistry theory.     

Evolution of Magnetic fields in Bok Globules?

We study the influence and structure of the magnetic field in the early phases of low-mass star formation using polarization maps of Bok globules at a wavelength of 850 μm, obtained with the Submillimeter Common-User Bolometer Array (SCUBA) at the James Clerk Maxwell Telescope (JCMT). We discuss observations of the following sources: CB 26—a small globule with a nearly dispersed dense core and a young and large circumstellar disk, CB 54—a large globule with a massive dense core and a deeply embedded young stellar cluster, and B 335, CB 230, and CB 244—three nearby, relatively isolated small globules with low-mass protostellar cores. We find strongly aligned polarization vectors in the case of CB 26, B 335, and CB 230, whereas the vector orientations in the case of CB 54 and CB 244 are more or less randomly distributed. The degree of polarization, amounting to several percent, was found to decrease toward the center in each source. Assuming dichroic emission by aligned non-spherical grains as the polarization mechanism, where the magnetic field plays a role in the alignment process, we derive magnetic field strengths and structures from the observed polarization patterns. We compare the magnetic field topology with the morphology and outflow directions of the globules. In the Class 0 sources B 335, CB 230, and CB 244, the magnetic field is oriented almost perpendicular to the ouflow direction. In contrast, the inclination between outflow axis and magnetic field direction is much more moderate (36°) in the more evolved Class I source CB26.     

Structure and dynamics of cool flare loops

MSDP observations of the 16 May, 1981 two-ribbon flare are used to study the physical structure and the dynamical behaviour of cool flare loops. The loops have been detected in the H line just after the flare maximum and they appeared in absorption against the disk. Using the first-order differential cloud model (DCM1) technique, we derive empirically some basic plasma parameters at 15 points along one loop leg. The flow velocities and the true heights have been reconstructed with respect to a geometrical projection. Subsequently, detailed non-LTE models of cool loops have been constructed in order to fit H source function values previously derived from DCM1 analysis. It is demonstrated that this source function is rather sensitive to the radial component of the flow velocity (the so-called Doppler brightening) and to enhanced irradiation of the loops from the underlying flare ribbons. In this way, we have been able to estimate quantitatively all plasma parameters which determine the physical structure of cool loops (i.e., the temperature, pressure, density), as well as the momentum-balance condition within the loops. For these dark loops we have arrived at relatively low gas pressures of the order of 0.1–0.5 dyne cm^-2 with corresponding electron densities around 10¹¹ cm^-3. Pressure-gradient forces have been found to be of small importance in the momentum-balance equation, and thus they cannot explain departures from a free-fall motion found in our MSDP data analysis. We propose three possible solutions to this problem.     

Structure and dynamics of two-dimensional oval configurations

Preliminary results are presented of 100 000-body simulations of gravitational plasmas. Results are illustrated by diagrams showing for an individual computer experiment, the excitation of an oscillatory mode of the oval equilibrium configuration. Results are further illustrated by a diagram showing ellipticity as a function of angular momentum for a sequence of configurations of given particle number, illustrating the transition from rotationally symmetric to oval equilibrium configurations.Paper presented at the 11th European Regional Astronomical Meeting of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain.     

The prolate Bok globules evidence for the existence of dark matter sub-halo

Although the existence of dark matter is generally accepted by the mainstream scientific community, there is no generally agreed direct detection of it. Also, observations show that some Bok globules are prolate in some regions without suitable explanation for its cause. In this paper, we investigate the effect of dark matter sub-halo in transformation of the Bok globules from spherical to the prolate shape. We limit the investigation to a particular case that the magnetic field and turbulent effects are negligible through the Bok globule. We consider the gravitational effect of dark matter sub-halo on the isothermal Bok globule that is exposed to suitable distance of it. The results show that the dark matter sub-halo can justify the transformation of Bok globules in some regions. In this paper, we introduce a new method for proving the existence of dark matter sub halo.     

Optical and submillimetre observations of Bok globules – tracing the magnetic field from low to high density

Although the stellar initial mass function (IMF) has only been directly determined in star clusters, it has been manifoldly applied on galaxy-wide scales. But taking the clustered nature of star formation into account the galaxy-wide IMF is constructed by adding all IMFs of all young star clusters leading to an integrated galactic initial mass function (IGIMF). The IGIMF is top-light compared to the canonical IMF in star clusters and steepens with decreasing total star formation rate (SFR). This discrepancy is marginal for large disc galaxies but becomes significant for Small Magellanic Cloud type galaxies and less massive ones. We here construct IGIMF-based relations between the total far- and near-ultraviolet luminosities of galaxies and the underlying SFR. We make the prediction that the Hα luminosity of star-forming dwarf galaxies decreases faster with decreasing SFR than the ultraviolet (UV) luminosity. This turn-down of the Hα/UV-flux ratio should be evident below total SFRs of  10⁻² M_⊙ yr⁻¹  .     

SO and SiO emission around the young cluster in the CB 34 globule

The globule CB 34, which harbours a cluster of class 0 young stellar object (YSO) protostars, has been investigated through a multiline SO and SiO survey at millimetre wavelengths. The SO data reveal that the globule consists of three quiescent high-density (∼10⁵ cm⁻³) clumps, labelled A, B and C, with sizes of ∼  0.2–0.3 pc  . The SiO data provide evidence for high-velocity gas across the globule. Most likely, the high-velocity gas is distributed in three distinct high-velocity outflows associated with the YSOs in each of the three clumps. High-velocity SO features have been detected only towards the two brightest SiO outflows. These broad SO components exhibit spatial and spectral distributions which are consistent with those of the SiO emission, so they can also be used as tracers of the outflows.
The comparison between the spatial and spectral properties of the SO and SiO emissions in the three clumps suggests different evolutionary stages for the embedded YSOs. In particular, the YSO associated with clump C exhibits some peculiarities, namely smaller SiO linewidths, lower SiO column densities, a lack of extended SiO structure and of SO wings, and the presence of a SO spatial distribution which is displaced with respect to the location of the YSO. This behaviour is well explained if the SiO and SO molecules which were produced at high velocities in the shocked region have been destroyed or slowed down because of the interaction with the ambient medium, and the chemistry is dominated again by low-temperature reactions. Thus our observations strongly suggest that the YSO in clump C is in a more evolved phase than the other members of the cluster.     

X-ray variability of the Seyfert 1 Markarian 335: power spectrum and time lags

To investigate further the comparison between active galactic nuclei (AGN) and black hole X-ray binaries, we have studied the main X-ray variability properties of the Seyfert 1 galaxy Mrk 335. We put particular emphasis on the X-ray time lags, which is a potentially important diagnostic of physical models. From a 100 ks observation by XMM–Newton , we show that the power spectrum of this source is well fitted by a bending power-law model, and the bend time-scale T _b is precisely at the value predicted by the T _b versus Hβ linewidth relation of McHardy et al. Variations in different energy bands show time-scale-dependent time lags, where higher energy bands lag lower ones. The lag, τ, varies as a function of the Fourier frequency, f , of the variability component in the light curves as  τ∝ f ⁻¹  at low frequencies, but there is a sharp cut-off in the lags at a frequency close to the bend frequency in the power spectrum. Similar behaviour is seen in black hole X-ray binary systems. The length of the time lags increases continuously with energy separation, in an almost loglinear relation. We show that the lag spectra can be produced by fluctuations propagating through the accretion flow as long as the energy spectrum of the X-ray emitting region hardens towards the centre.     

A model of rapid burster MXB 1730-335

A model of rapid burster MXB 1730-335, the source of type II X-ray burst is proposed, based on the Rayleigh-Taylor instability due to interaction of relativistic electrons produced by the rapid rotation of a highly magnetized neutron star, and the infalling accreted matter through the magnetic funnel at the poles. Conclusions are made that type II X-ray burster may be a constant source of cosmic rays and such a mechanism may be the progenitor of some forms of nebulae.Permanent address: Imphal College, Imphal, Manipur.     

The first CO(1-0) mapping of the globule IC 1396 W

Near-infrared observations indicate that three H₂ outflows and their driving sources are present in the globule IC 1396 W, where the existence of molecular outflows has also been suggested by some authors. We made the first CO(1-0) map of IC 1396 W, and found that its CO molecular cloud may consist of three physically distinct components with different velocities. We detected neither molecular outflows nor the dense cores associated with candidate driving sources. One possible reason is that CO(1-0) and its isotopes cannot trace high density gas, and another is that the beam of our observation is too large to observe them. The CO cloud may be one part of the natal molecular cloud of IC 1396 W, in the process of disrupting and blowing away. The CO cloud seems to be in the foreground of the H₂ outflows.     

Huygens Probe descent dynamics inferred from Channel B signal level measurements

The signal strength of the Huygens Probe Channel B transmission to the Cassini Orbiter was monitored during the Probe descent through Titan's atmosphere on 14 January 2005. A model of the Probe motion during the mission was constructed to include Probe spin, coning motion and tilt caused by varying wind speeds. This simple model is sufficient to reproduce the most prominent features seen in the signal level measurements. It provides estimates of the coning and tilt angles as well as the direction of the Huygens coordinate axes over extended time intervals in the mission.     

Study of grain alignment efficiency and a distance estimate for small globule CB4

We study the polarization efficiency(defined as the ratio of polarization to extinction) of stars in the background of the small, nearly spherical and isolated Bok globule CB4 to understand the grain alignment process. A decrease in polarization efficiency with an increase in visual extinction is noticed. This suggests that the observed polarization in lines of sight which intercept a Bok globule tends to show dominance of dust grains in the outer layers of the globule. This finding is consistent with the results obtained for other clouds in the past. We determined the distance to the cloud CB4 using near-infrared photometry(2MASS J H KScolors) of moderately obscured stars located at the periphery of the cloud. From the extinction-distance plot,the distance to this cloud is estimated to be(459 ± 85) pc.     

Suzaku observations of Markarian 335: evidence for a distributed reflector

We report on a 151-ks net exposure Suzaku observation of the narrow-line Seyfert 1 galaxy Mrk 335. The 0.5–40 keV spectrum contains a broad Fe line, a strong soft excess below about 2 keV and a Compton hump around 20–30 keV. We find that a model consisting of a power law and two reflectors provides the best fit to the time-averaged spectrum. In this model, an ionized, heavily blurred, inner reflector produces most of the soft excess, while an almost neutral outer reflector (outside ∼ 40 r _g) produces most of the Fe line emission. The spectral variability of the observation is characterized by spectral hardening at very low count rates. In terms of our power-law + two-reflector model it seems like this hardening is mainly caused by pivoting of the power law. The rms spectrum of the entire observation has the curved shape commonly observed in active galactic nuclei, although the shape is significantly flatter when an interval which does not contain any deep dip in the light curve is considered. We also examine a previous 133-ks XMM–Newton observation of Mrk 335. We find that the XMM–Newton spectrum can be fitted with a similar two-reflector model as the Suzaku data and we confirm that the rms spectrum of the observation is flat. The flat rms spectra, as well as the high-energy data from the Suzaku PIN detector, disfavour an absorption origin for the soft excess in Mrk 335.