Third-dredge-up oxygen in planetary nebulae

The planetary nebulae He 2-436 and Wray 16-423 in the Sagittarius dwarf galaxy appear to result from nearly twin stars, except that third-dredge-up carbon is more abundant in He 2-436. A thorough photoionization-model analysis implies that ratios Ne/O, S/O and Ar/O are significantly smaller in He 2-436, indicative of third-dredge-up oxygen enrichment. The enrichment of oxygen with respect to carbon is (7 +/- 4)%. Excess nitrogen in Wray 16-423 suggests third dredge-up of late CN-cycle products even in these low-mass, intermediate-metallicity stars.Comment: To appear in Astron. Astrophys. Lett. (Latex, 5 pages, 1 postscript figure

Detection of the Central Star of the Planetary Nebula NGC 6302

NGC 6302 is one of the highest ionization planetary nebulae known and shows emission from species with ionization potential >300eV. The temperature of the central star must be >200,000K to photoionize the nebula, and has been suggested to be up to ~ 400,000K. On account of the dense dust and molecular disc, the central star has not convincingly been directly imaged until now. NGC 6302 was imaged in six narrow band filters by Wide Field Camera 3 on HST as part of the Servicing Mission 4 Early Release Observations. The central star is directly detected for the first time, and is situated at the nebula centre on the foreground side of the tilted equatorial disc. The magnitudes of the central star have been reliably measured in two filters(F469N and F673N). Assuming a hot black body, the reddening has been measured from the (4688-6766\AA) colour and a value of c=3.1, A_v=6.6 mag determined. A G-K main sequence binary companion can be excluded. The position of the star on the HR diagram suggests a fairly massive PN central star of about 0.64,M_sun close to the white dwarf cooling track. A fit to the evolutionary tracks for (T,L,t)=(200,000K, 2000L_sun, 2200yr), where t is the nebular age, is obtained; however the luminosity and temperature remain uncertain. The model tracks predict that the star is rapidly evolving, and fading at a rate of almost 1 % per year. Future observations could test this prediction.Comment: 13 pages, 5 figures, submitted to ApJ Letters on 25.09.2009 accepted on 19.10.200

Ведущая роль Национальной академии наук Украины в системе подготовки научных кадров высшей квалификации

В статье представлены результаты исследования современной системы подготовки научных и научно-педагогических кадров высшей квалификации в Украине, дана оценка качественного уровня развития аспирантур и докторантур в разных секторах науки, сформулированы системные проблемы, обусловленные сложной социальной и экономической ситуацией в научно-технологической сфере страны, отражена ведущая роль Национальной академии наук Украины в национальной системе подготовки научных и научно-педагогических кадров.У статті наведено результати дослідження сучасної системи підготовки наукових і науково-педагогічних кадрів вищої кваліфікації в Україні, дано оцінку якісного рівня розвитку аспірантур і докторантур у різних секторах науки, сформульовано системні проблеми, зумовлені складною соціальною і економічною ситуацією в науково-технологічній сфері країни, відображено провідну роль Національної академії наук України в національній системі підготовки наукових і науково-педагогічних кадрів.Results of studies of the contemporary system for training of research and lecturing personnel with higher qualification in Ukraine are given, the quality of post-graduate and post-doctorate courses in various sectors of science is judged, systemic problems are outlined, originating from difficult social and economic situation in the Ukrainian science & technology sector, the leading role of the National Academy of Sciences in the system for training research and lecturing personnel is highlighted

Spiky density of states in large complex Al-Mn phases

First-principle electronic structure calculations have been performed in crystalline complex phases mu-Al4Mn and lambda-Al4Mn using the TB-LMTO method. These atomic structures, related to quasicrystalline structures, contain about 560 atoms in a large hexagonal unit cell. One of the main characteristic of their density of states is the presence of fine peaks the so-called "spiky structure". From multiple-scattering calculations in real space, we show that these fine peaks are not artifacts in ab-initio calculations, since they result from a specific localization of electrons by atomic clusters of different length scales

The low wind expansion velocity of metal-poor carbon stars in the Halo and the Sagittarius stream

We report the detection, from observations using the James Clerk Maxwell Telescope, of CO J $=$ 3$\to$ 2 transition lines in six carbon stars, selected as members of the Galactic Halo and having similar infrared colors. Just one Halo star had been detected in CO before this work. Infrared observations show that these stars are red (J-K $>$3), due to the presence of large dusty circumstellar envelopes. Radiative transfer models indicates that these stars are losing mass with rather large dust mass-loss rates in the range 1--3.3 $\times$$10^{-8}$M$_{\odot}$yr$^{-1}$, similar to what can be observed in the Galactic disc. We show that two of these stars are effectively in the Halo, one is likely linked to the stream of the Sagittarius Dwarf Spheroidal galaxy (Sgr dSph), and the other three stars certainly belong to the thick disc. The wind expansion velocities of the observed stars are low compared to carbon stars in the thin disc and are lower for the stars in the Halo and the Sgr dSph stream than in the thick disc. We discuss the possibility that the low expansion velocities result from the low metallicity of the Halo carbon stars. This implies that metal-poor carbon stars lose mass at a rate similar to metal-rich carbon stars, but with lower expansion velocities, as predicted by recent theoretical models. This result implies that the current estimates of mass-loss rates from carbon stars in Local Group galaxies will have to be reconsidered.Comment: 10 pages, 7 figures, accepted for publication in MNRA

Scale Dependence of Polarized DIS Asymmetries

We compare the $Q^{2}$ dependence of the polarized deep inelastic scattering proton asymmetry, driven by the leading order Altarelli Parisi evolution equations, to those arising from fixed order $\alpha_{s}$ and $\alpha_{s}^{2}$ approximations. It is shown that the evolution effects associated with gluons, which are not properly taken into account by the leading order approximation, cannot be neglected in the analysis of the most recent experimental data.Comment: Latex file, (9 figures in postcript available from [email protected]

Subarcsecond Submillimeter Imaging of the Ultracompact HII Region G5.89-0.39

We present the first subarcsecond submillimeter images of the enigmatic ultracompact HII region (UCHII) G5.89-0.39. Observed with the SMA, the 875 micron continuum emission exhibits a shell-like morphology similar to longer wavelengths. By using images with comparable angular resolution at five frequencies obtained from the VLA archive and CARMA, we have removed the free-free component from the 875 micron image. We find five sources of dust emission: two compact warm objects (SMA1 and SMA2) along the periphery of the shell, and three additional regions further out. There is no dust emission inside the shell, supporting the picture of a dust-free cavity surrounded by high density gas. At subarcsecond resolution, most of the molecular gas tracers encircle the UCHII region and appear to constrain its expansion. We also find G5.89-0.39 to be almost completely lacking in organic molecular line emission. The dust cores SMA1 and SMA2 exhibit compact spatial peaks in optically-thin gas tracers (e.g. 34SO2), while SMA1 also coincides with 11.9 micron emission. In CO(3-2), we find a high-velocity north/south bipolar outflow centered on SMA1, aligned with infrared H2 knots, and responsible for much of the maser activity. We conclude that SMA1 is an embedded intermediate mass protostar with an estimated luminosity of 3000 Lsun and a circumstellar mass of ~1 Msun. Finally, we have discovered an NH3 (3,3) maser 12 arcsec northwest of the UCHII region, coincident with a 44 GHz CH3OH maser, and possibly associated with the Br gamma outflow source identified by Puga et al. (2006).Comment: 41 pages, 11 figures, published in The Astrophysical Journal (2008) Volume 680, Issue 2, pp. 1271-1288. An error in the registration of the marker positions in Figure 11 has been corrected in this versio