Low‐temperature primordial gas in merging halos

The thermal regime of the baryons behind shock waves arising in the process of virialization of dark matter halos is governed at certain conditions by radiation of HD lines. A small fraction of the shocked gas can cool down to the temperature of the cosmic microwave background (CMB). We estimate an upper limit for this fraction: at z = 10 it increases sharply from about q_T ∼ 10^–3 for dark halos of M = 5 × 10⁷ M_⊙ to ∼ 0.1 for halos with M = 10⁸ M_⊙. Further increase of the halo mass does not lead however to a significant growth of q_T – the asymptotic value for M ≫ 10⁸ M_⊙ is 0.3. We estimate the star formation rate associated with such shock waves, and show that they can provide a small but not negligible fraction of the star formation. We argue that extremely metal‐poor low‐mass stars in the Milky Way may have been formed from primordial gas behind such shocks. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Star Forming Regions and Galactic structure

The main kinematic characteristics of our Galaxy are analyzed using a catalog of about 2700 Galactic star-forming regions. The terminal velocities of the star-forming regions confirm that the rotation curve for the inner Galaxy is flat from |l| 23°. Bends in the rotation curve are probably due to motions in spiral arms. The Galaxy rotates with a circular velocity of 200 ± 10 km s-1. Evidence for an expanding ring-like structure at 3 kpc is presented. An l - v diagram for the catalog sources in the first and fourth Galactic quadrants is constructed. Density wave theory is used to show that a two-spiral model with a pitch angle of -9° and large-amplitude velocity perturbations in the region of 3 kpc can satisfactory describe the main features of the l - v diagram to Galactocentric radii of 6-7 kpc.     

Observations of High Resolution Spectra of Comet Hale-Bopp (C/1995 O1) at the SAO of the RAS

We present the results of the preliminary study of the comet Hale-Bopp spectrum obtained April 17, 1997 by K. Churyumov and F. Mussayev with the help of the 1-meter Zeiss reflector and the echelle spectrometer (spectral resolutionλ/Δ λ ≈ 50000), CCD and the long slit, oriented along the radius-vector(“Sun-comet direction”). Energy distributions for three selected regions including the C₃, C₂ (0-0) and CN(Δ ν = 0) molecules emissions of the comet Hale-Bopp spectrum were built. The rotational lines of the CN(Δ ν = 0) band were identified. The nature of the high emission peak near λ 4020 Å in the C₃ band is discussed. The presence of the cometary continuum of the nonsolar origin is assumed.     

CAN WE OBSERVE THE TEMPERATURE INHOMOGENEITIES AND MAGNETIC FLUX TUBES AS THE FINE STRUCTURE ON THE EXTREME LIMB OF THE SUN?

Fine structure of brightness inhomogeneities with I r.m.s. = 2.9% was discovered on the extreme limb of the Sun on the best quality white-light photographs obtained at the Soviet Stratospheric Solar Observatory. The concept is that temperature inhomogeneities are responsible for the limb structure. The real value T r.m.s. = 109K is required to explain our observations. Another possible explanation is that small-scale magnetic flux tubes with the realistic filling factor f* = 1% are the source of the limb brightness fluctuations.     

The Relationship Between Kinematics and Spatial Structure of the Large-Scale Solar Magnetic Field

The rotation of large-scale solar magnetic fields has been investigated by analysing a 20-yr series of synoptic maps of the radial magnetic field. For this purpose, a specially adapted method of spectral analysis was used. We calculated rotation spectra of the magnetic field as functions of the rotation period, heliographic latitude, and longitudinal wave number, k. These spectra reveal the existence of a number of discrete, rigidly rotating components (modes) of the magnetic field, whose rotation periods lie in the wide range from 26.5 to 30.5 days. The significant spectral maxima lie in the (rotation period–latitude) plane close to the curve that represents the differential rotation of small-scale magnetic features. For the first harmonic of the magnetic field (k=1) the properties of the rotation spectra are consistent with those reported by Antonucci, Hoeksema, and Scherrer (1990). However, the distribution of the rigidly rotating modes over rotation period and their latitudinal structure change systematically with the harmonic number k. As k increases, the mean distance P in rotation period between the modes decreases, from 1.2 days for k=1 to 0.3–0.5 days for k=4. This decreasing period separation is accompanied by a decrease of the characteristic latitude separation between the mode maxima. The latitudinal and longitudinal discrete spatial scales of the non-axisymmetric magnetic field appear to be connected with each other, as well as with the temporal scale P.     

I S L A An Astronomical World Space Observatory for The First Century of the 3 rd Millenium

ISLA will be an astronomical observatory, operating at the upper limit of our planet Earth atmosphere, offering space like observing conditions in most aspects. ISLA can be maintained easily, modified easily if necessary, always kept at the state of the art and operated for very extended periods without polluting the stratosphere. ISLA is ideally suited to become the first world space observatory as the observing conditions are very much space-like – diffraction limited angular resolution, very low ambient temperature, remote control – however ISLA is easily accessible, telescopes and instruments can be continuously improved and ISLA's costs corresponds only to those of ground-based modern astronomical installations like the ESO-VLT-, KECK- and GEMINI-observatories. The cost of observing and experimenting on ISLA will be orders of magnitudes lower than those of building and operating any space telescope, allowing the astronomers of developing nations to participate in the ISLA observatory within their limited financial possibilities as competent and full partners. ISLA's 4-m and 2-m telescopes will operate diffraction limited from 0.3 μm in the optical, over the infrared, far-infrared to the sub-mm spectral range. ISLA's individual telescopes will permit imaging with 20 milli-arcsec spatial resolution in the optical, 5 times better than the Hubble Space Telescope. ISLA's telescopes can be combined to form an interferometer with a maximum baseline of 250 m with nearly complete coverage of the u,v plane. Interferometric resolution will be of the order of 20 micro-arcsec for the optical. ISLA will thus offer spatial resolution comparable or better than the intercontinental VLBI radio interferometers. ISLA's telescope efficiency will be many orders of magnitude better than comparable ground-based telescopes. The light collecting power of ISLA's interferometric telescopes will be orders of magnitudes greater than the future space interferometers under discussion. ISLA, being an aviation project and not a space project, can be realised in the typical time scale for the development of aviation: about 5 years. ISLA's cost for the whole observatory, including its movable ground station etc. will be of the order of a typical medium size ESA space mission. ISLA's lifetime will be in excess of many decades, as it can easily be maintained, modernised, repaired and improved. ISLA will become the origin of a new astronomical international organisation with worldwide participation. ISLA's telescopes will be of the greatest importance to all astronomical fields, as it will permit to study much fainter, much more distant objects with microscopic spatial resolution in wavelength regions inaccessible from ground. ISLA's many telescopes permit easily simultaneous observations at many wavelengths for rapidly varying objects, from continuously monitoring the surfaces of the planets in our solar system, surfaces of close-by stars, nuclei of galaxies to QSO's. This revised version was published online in July 2006 with corrections to the Cover Date.     

The Sinistral–Dextral Regularity: An Independent Test

Leroy, Bommier, and Sahal-Bréchot (1984) determined the vector magnetic field in a large sample of quiescent prominences. The direction of the axial component is in general subject to a 180 deg uncertainty. We have selected those prominences in the sample whose field direction is unambiguous. For 95 such prominences, only 3 do not obey the hemispheric preferences of sinistral or dextral filaments, discovered by Martin, Tracadas, and Billamoria (1994). No explanation for the exceptional cases was found.A search of the Ottawa River Solar Observatory archives was made to check on the structural signatures of sinistral and dextral filaments. Of 32 filaments in common with the Leroy data set, 12 were classifiable as sinistral or dextral from their H fine structure and of these, 3 were exceptions to the hemispheric rule.Thus only a small percentage of quiescent filaments disobeys the hemispheric rule.     

Effects of Interference and Oxidation on the UV/Visible Rejection Properties of Filters for Soft X-ray Detectors

We report on UV/Visible transmission measurements of aluminum coated Lexan filters designed as UV blocking filters for soft x-ray detectors. Transmission of the filters in the 2300-8000 Å wavelength range is significantly higher than expected. It cannot be accounted for applying a simple slab model of the transmission and adopting material properties reported in the literature. We show that this is due to interference effects which are strongly dependent on the filter geometry, and to oxidation of exposed aluminum surfaces and/or chemical interaction with the plastic support. The results of this work have led to the redesign of the Advanced X-ray Astrophysics Facility High Resolution Camera UV blocking filters.     

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.