Interstellar H2O masers. a tracer of galactic spiral structure?

The large-scale distribution of interstellar H₂O masers is given in this paper. Present results show that H₂O masers can trace galactic spiral structure, and we also briefly discuss how to obtain a more accurate distribution of H₂O masers from future observations.     

Interstellar chemistry recorded by nitrogen isotopes in Solar System organic matter

The relationship between the organic and D/H ratios in small Solar System bodies (meteorites, interplanetary dust and comets) suggests that isotopic exchange reactions taking place at various temperatures are at the origin of the observed variations. These relationships are used to determine the exothermicity (ΔE) of ion-molecule reactions that fractionated the nitrogen isotopic ratio in the presolar molecular cloud; that is ΔE=43±10 K. Comparison with current models of interstellar chemistry suggests that such a value could be achieved by condensation of ¹⁵N-rich gas-phase precursors onto grain surfaces and their further isolation from the gas by incorporation into large macromolecular structures.     

Diffuse Interstellar Band at 862 nm as a Reddening Tracer for GAIA

We investigate the plausibility of using diffuse interstellar band at862 nm for tracing interstellar extinction with the ESA's astrometric space mission GAIA. For this purpose we perform numerical tests to simulate the conditions of real observations, covering a wide range of stellar parameters and different amounts of interstellar extinction. Our simulations indicate that with the present Radial Velocity Spectrometer setup the uncertainty in color excess of σ_E(B-V)≤ 0.05 can be achieved only for the interstellar reddening tracers brighter than V ∼ 13. None of the plausible tracers can provide accurate color excesses (σ _E(B-V) ≤ 0.05) at the distances beyond 2 kpc. We therefore conclude that with the currently planned instrumentation onboard GAIA this method can not be used as a stand-alone approach for probing interstellar extinction on the Galactic distance scales within the framework of the GAIA mission. This revised version was published online in July 2006 with corrections to the Cover Date.     

Interstellar Grains as Amino Acid Factories and the Origin of Life

Some two decades ago, Hoyle and Wickramasinghe (1976) proposed that the physical conditions inside dense molecular clouds favour the formation of amino acids and complex organic polymers. There now exists both astronomical and laboratory evidence supporting this idea. Recent millimeter array observations have discovered the amino acid glycine (NH₂CH₂COOH) in the gas phase of the dense star-forming cloud Sagittarius B2. These observations would pose serious problems for present-day theories of molecule formation in space because it is unlikely that glycline can form by the gas-phase reaction schemes normally considered for dense cloud chemistry. Several laboratory experiments suggest a new paradigm in which amino acids and other large organic molecules are chemically manufactured inside the bulk interior of icy grain mantles photoprocessed by direct and scattered ultraviolet starlight. Frequent chemical explosions of the processed mantles would eject large fragments of organic dust into the ambient cloud. Large dust fragments break up into smaller ones by sputtering and ultimately by photodissociation of individual molecules. Hence, a sizeable column density (N≈ 10¹⁰−10¹⁵ cm^-2) of amino acids would be present in the gaseous medium as a consequence of balancing the rate of supply from exploding mantles with the rate of molecule destruction. Exploding mantles can therefore solve the longstanding molecule desorption problem for interstellar dense cloud chemistry. A sizeable fraction of the organic dust population can survive destruction and seed primitive planetary systems throughout our galaxy with prebiological organic molecules needed for proteins and nucleic acids in living organisms. This possibility provides fresh grounds for a new version of the old panspermia hypothesis first introduced by Anaxagoras. It is shown that panspermia is more important than asteroid and cometary organic depositions onto primitive Earth. Furthermore, no appeal to Miller-Urey synthesis in a nonoxidizing atmosphere of primitive Earth is then needed to seed terrestrial life. This revised version was published online in July 2006 with corrections to the Cover Date.     

Interstellar polarization in a molecular cloud in serpens

Observations of the polarization of stars in the direction of a molecular cloud in Serpens are presented. A dependence of the degree of linear polarization on total absorption A_v is found in their direction, different for stars in the cloud and in its vicinity. On this basis, it is concluded that the polarizing efficiency of particles in the cloud is reduced. Translated from Astrofizika, Vol. 43, No. 3, pp. 397-403, July–September, 2000.     

Ultraviolet Photoprocessing of Interstellar Dust Mantles as a Source of Polycyclic Aromatic Hydrocarbons and Other Conjugated Molecules

By co-depositing a gas mixture of simple carbon- and nitrogen-containing molecules with water on a 10 K surface and exposing it to ultraviolet radiation, we were able to form a residue. This residue was then placed aboard the EURECA satellite behind a magnesium fluoride window and exposed to solar radiation for 4 months before it was returned and analyzed. The resulting residue is believed to simulate the photoprocessing of organic dust mantles in the interstellar medium. Mass spectrometry indicated that the photoprocessing created a rich mixture of polycyclic aromatic hydrocarbons (PAHs) and other conjugated organic molecules, which may explain how PAHs are replenished in space.     

Isotope identification in NO as a chemical tracer in the middle atmosphere

The nitrogen isotope ratio of middle atmosphere nitrogen oxide is predicted as a function of altitude. Nitrogen oxides originate photochemically either from stratospheric nitrous oxide reacting with O(¹D) or in the mesosphere and thermosphere from direct dissociation of N₂ and ionization-initiated reactions involving O₂ and N₂. During its formation process, N₂O acquires a nitrogen isotopic composition of N isotopes different than N₂. Photodissociation within the stratosphere also modifies the proportion of isotopes. Reaction of stratospheric NO with O₃ produces NO₂, which when photodissociated yields NO depleted in ¹⁵N relative to NO₂ in laboratory air. The value of δ¹⁵NO in the stratosphere is −100‰. In the altitude region between 50 and 65 km, NO is transformed into NO₂ and then returned to NO by reaction of NO₂ with O and by NO₂ photodissociation. These reactions determine the isotopic makeup of NO. Above 65 km, nitric oxide is produced by local ionization processes and gas phase photochemical reactions involving N₂ and excited O₂. These processes determine the isotopic composition of NO in the upper mesosphere and thermosphere. Here δ¹⁵NO is 0‰. Air transported into the mesosphere above 65 km will reflect the NO isotopic values of the region below, while mesospheric NO transported below 65 km will not be distinguishable from NO originating in the stratosphere.     

Interstellar reddening in a high-latitude field around omega bootis

Photoelectric UBV observations of stars show the existence of an interstellar dust cloud of 0.2 mag. visual extinction and 1.5 pc diameter at 60°.5 galactic latitude. Properties of the cloud and the interstellar polarization in the region are being discussed.     

Interstellar Scintillation Studies of Pulsars and Distribution of Scattering Plasma in the Local Interstellar Medium

Pulsar scintillation measurements from the Ooty Radio Telescope (ORT) are used to investigate the distribution of scattering in the Local Interstellar Medium (LISM; region of ≲ 1 kpc of the Sun), specifically the region in and around the Local Bubble. A 3-componentmodel, where the Solar neighborhood is surrounded by a shell of enhanced plasma turbulence, is proposed for the LISM. Further, the Ooty data, along with those from Parkes and other telescopes are used for investigating thedistribution of scattering towards the nearby Loop I Superbubble. This revised version was published online in July 2006 with corrections to the Cover Date.     

Mass-Stripping Analysis of an Interstellar Cloud by a Supernova Shock

The interaction of supernova shocks and interstellar clouds is an important astrophysical phenomenon since it can result in stellar and planetary formation. Our experiments attempt to simulate this mass-loading as it occurs when a shock passes through interstellar clouds. We drive a strong shock using the Omega laser (∼5kJ)into a foam-filled cylinder with an embedded Al sphere(diameterD=120 μm) simulating an interstellar cloud. The density ratio between Al and foamis∼9. We have previously reported on the interaction between shock and cloud, the ensuing Kelvin-Helmholtz and Widnall instabilities, and the rapid stripping of all mass from the cloud. We now present a theory that explains the rapid mass-stripping. The theory combines (1) the integral momentum equations for a viscous boundary layer, (2) the equations for a potential flow past a sphere, (3) Spalding's law of the wall for turbulent boundary layers, and (4) the skin friction coefficient for a turbulent boundary layer on a flat plate. The theory gives as its final result the mass stripped from a sphere in a turbulent high Reynolds number flow, and it agrees very well with our experimental observations.     

The Spectroscopic Idebtification of Interstellar Grains

It is shown that the condition of matching the 3.3–3.9 μm spectrum of the galactic infrared source GC-IRS 7 leads to a remarkably tight convergence on the transmittance curve measured in the laboratory for the dessicated bacterium E. coli.Other materials, including certain biochemicals and postulated prebiologic compounds, are shown to be deficient with regard to meeting this condition. This revised version was published online in July 2006 with corrections to the Cover Date.     

X-ray emission as a tracer of circumstellar matter around herbig ae/be stars

We have detected X-ray emission (1 keV) from young intermediate-mass stars (Herbig Ae/Be stars). Since these stars are not supposed to produce intrinsic X-ray emission (no convection, no coronae), we believe that our results suggest that the X-ray emission actually traces the shock interaction of the Ae/Be star stellar winds with remnant circumstellar matter left over from the star formation process, the presence of which is also indicated by far-infrared (IRAS) and submm/mm continuum data.     

Dynamics of the Interstellar Gas in the Vicinity of a Bar

A numerical simulation of the disk dynamics of a flat stellar-gaseous galaxy is presented. This simulation is based on N-body modelling for a stellar disk, together with integration of the two-dimensional hydrodynamic equations for a gaseous disk. The existence of a quasi-periodic regime of disk evolution found earlier in a purely hydrodynamic simulation is confirmed. Intense gas flows in the central area of the disk due to the saddle point of the bar potential can support the active galactic nuclei in Seyfert galaxies and form double nuclei.     

On The Nature of Interstellar Grains

Data on interstellar extinction are interpreted to imply an identification of interstellar grains with naturally freeze-dried bacteria and algae. The total mass of such bacterial and algal cells in the galaxy is enormous, ～ 10⁴⁰ g. The identification is based on Mie scattering calculations for an experimentally determined size distribution of bacteria. Agreement between our model calculations and astronomical data is remarkably precise over the wavelength intervals 1 μ^-1 < λ^-1 < 1.94 μ^-1and 2.5 μ^-1 < λ^-1 < 3.0 μ^-1. Over the more restricted waveband 4000–5000 Å an excess interstellar absorption is found which is in uncannily close agreement with the absorption properties of phytoplankton pigments. The strongest of the diffuse interstellar bands are provisionally assigned to carotenoid-chlorophyll pigment complexes such as exist in algae and pigmented bacteria. The λ2200 Å interstellar absorption feature could be due to `degraded' cellulose strands which form spherical graphitic particles, but could equally well be due to protein-lipid-nucleic acid complexes in bacteria and viruses. Interstellar extinction at wavelengths λ < 1800 Å could be due to scattering by virus particles.     

Low Frequency Cosmic Background for a Cloudy Interstellar Medium Model

The first interpretation of the cosmic noise background spectrum over a broad frequency band from 0.25 - 200 MHz using a cloudy interstellar medium model is given.     

Discovery of the First Interstellar Comet and the Spatial Density of Interstellar Objects in the Solar Neighborhood

Solar System Research - The discovery of the first interstellar comet 2I/Borisov confirmed the astronomers’ speculation that the passage through the solar system of relatively large objects...     

Interstellar scintillation of compact extragalactic radio sources

The recent discovery of radio variability of a quasar on short time-scales (hours) prompts us to examine what is expected in respect of the interstellar scintillation of very compact, extragalactic radio sources. We find that large-amplitude, rapid, variability is predicted at commonly observed radio frequencies (1–20 GHz) over the vast majority of the extragalactic sky. As a guide to assist observers in understanding their data, we demonstrate simple techniques for predicting the effects of interstellar scintillation on any extragalactic source.     

Interstellar clouds and the formation of stars

Part I gives a survey of the drastic revision of cosmic plasma physics which is precipitated by the exploration of the magnetosphere throughin situ measurements. The pseudo-plasma formalism, which until now has almost completely dominated theoretical astrophysics, must be replaced by an experimentally based approach involving the introduction of a number of neglected plasma phenomena, such as electric double layers, critical velocity, and pinch effect. The general belief that star light is the main ionizer is shown to be doubtful; hydromagnetic conversion of gravitational and kinetic energy may often be much more important.In Part II the revised plasma physics is applied to dark clouds and star formation. Magnetic fields do not necessarily counteract the contraction of a cloud; they may just as well pinch the cloud. Magnetic compression may be the main mechanism for forming interstellar clouds and keeping them together.Part III treats the formation of stars in a dusty cosmic plasma cloud. Star formation is due to an instability, but it is very unlikely that it has anything to do with the Jeans instability. A reasonable mechanism is that the sedimentation of dust (including solid bodies of different size) is triggering off a gravitationally assisted accretion. A stellesimal accretion analogous to the planetesimal accretion leads to the formation of a star surrounded by a very low density hollow in the cloud. Matter falling in from the cloud towards the star is the raw material for the formation of planets and satellites.The study of the evolution of a dark cloud leads to a scenario of planet formation which is reconcilable with the results obtained from studies based on solar system data. This means that the new approach to cosmical plasma physics discussed in Part I logically leads to a consistent picture of the evolution of dark clouds and the formation of solar systems.     

Interstellar Scintillations of Polarization of Compact Sources

We present analysis of a high spatial resolution ( approximately 1&farcs;5) O vi lambda1032 spectroheliogram taken with the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) spectrometer on the Solar and Heliospheric Observatory. This image shows numerous narrow, looplike structures. The widths of the narrowest resolved features are at the spatial resolution of the SUMER spectrometer. In contrast to earlier Skylab observations, however, comparisons with a Michelson Doppler Imager magnetogram reveals that the majority of these looplike structures do not connect network magnetic fields. Instead, they extend from the supergranulation network into the cell-center regions where no magnetic fields are detected in these data. We conjecture that these fine structures are related to spicules and are highly dynamic.