The subdwarf B star SB 290 - A fast rotator on the extreme horizontal branch

Hot subdwarf B stars (sdBs) are evolved core helium-burning stars with very thin hydrogen envelopes. In order to form an sdB, the progenitor has to lose almost all of its hydrogen envelope right at the tip of the red giant branch. In close binary systems, mass transfer to the companion provides the extraordinary mass loss required for their formation. However, apparently single sdBs exist as well and their formation is unclear since decades. The merger of helium white dwarfs leading to an ignition of core helium-burning or the merger of a helium core and a low mass star during the common envelope phase have been proposed. Here we report the discovery of SB 290 as the first apparently single fast rotating sdB star located on the extreme horizontal branch indicating that those stars may form from mergers.Comment: 5 pages, 4 figures, A&A letters, accepte

Two candidate brown dwarf companions around core helium-burning stars

Hot subdwarf stars of spectral type B (sdBs) are evolved, core helium-burning objects. The formation of those objects is puzzling, because the progenitor star has to lose almost its entire hydrogen envelope in the red-giant phase. Binary interactions have been invoked, but single sdBs exist as well. We report the discovery of two close hot subdwarf binaries with small radial velocity amplitudes. Follow-up photometry revealed reflection effects originating from cool irradiated companions, but no eclipses. The lower mass limits for the companions of CPD-64$^{\circ}$481 ($0.048\,M_{\rm \odot}$) and PHL\,457 ($0.027\,M_{\rm \odot}$) are significantly below the stellar mass limit. Hence they could be brown dwarfs unless the inclination is unfavourable. Two very similar systems have already been reported. The probability that none of them is a brown dwarf is very small, 0.02%. Hence we provide further evidence that substellar companions with masses that low are able to eject a common envelope and form an sdB star. Furthermore, we find that the properties of the observed sample of hot subdwarfs in reflection effect binaries is consistent with a scenario where single sdBs can still be formed via common envelope events, but their low-mass substellar companions do not survive.Comment: accepted to A&

Documentation of the GLAS fourth order general circulation model. Volume 2: Scalar code

Volume 2, of a 3 volume technical memoranda contains a detailed documentation of the GLAS fourth order general circulation model. Volume 2 contains the CYBER 205 scalar and vector codes of the model, list of variables, and cross references. A variable name dictionary for the scalar code, and code listings are outlined

Documentation of the GLAS fourth order general calculation model. Volume 3: Vectorized code for the Cyber 205

Volume 3 of a 3-volume technical memoranda which contains documentation of the GLAS fourth order genera circulation model is presented. The volume contains the CYBER 205 scalar and vector codes of the model, list of variables, and cross references. A dictionary of FORTRAN variables used in the Scalar Version, and listings of the FORTRAN Code compiled with the C-option, are included. Cross reference maps of local variables are included for each subroutine

Documentation of the GLAS fourth order general circulation model. Volume 1: Model documentation

The volume 1, of a 3 volume technical memoranda which contains a documentation of the GLAS Fourth Order General Circulation Model is presented. Volume 1 contains the documentation, description of the stratospheric/tropospheric extension, user's guide, climatological boundary data, and some climate simulation studies

Nuclear shadowing in polarized DIS on ^6LiD at small x and its effect on the extraction of the deuteron spin structure function g_{1}^{d}(x,Q^2)

We consider the effect of nuclear shadowing in polarized deep inelastic scattering (DIS) on ^6LiD at small Bjorken x and its relevance to the extraction of the deuteron spin structure function g_{1}^{d}(x,Q^2). Using models, which describe nuclear shadowing in unpolarized DIS, we demonstrate that the nuclear shadowing correction to g_{1}^{d}(x,Q^2) is significant.Comment: 17 pages, 2 figure

Nuclear effects in g1A(x,Q2)g_{1A}(x,Q^2) at small xx in deep inelastic scattering on 7^7Li and 3^3He

We suggest to use polarized nuclear targets of $^7$Li and $^3$He to study nuclear effects in the spin dependent structure functions $g_{1A}(x,Q^2)$. These effects are expected to be enhanced by a factor of two as compared to the unpolarized targets. We predict a significant $x$ dependence at $10^{-4} \div 10^{-3} \leq x \leq 0.2$ of $g_{1A}(x,Q^2)/g_{1N}(x,Q^2)$ due to nuclear shadowing and nuclear enhancement. The effect of nuclear shadowing at $x \approx 10^{-3}$ is of an order of 16% for $g_{1A=7}^{n.s. 3/2}(x,Q^2)/g_{1N}^{n.s.}(x,Q^2)$ and 10% for $g_{1A=3}^{n.s}(x,Q^2)/g_{1N}^{n.s.}(x,Q^2)$. By imposing the requirement that the Bjorken sum rule is satisfied we model the effect of enhancement. We find the effect of enhancement at $x \approx 0.125 (0.15)$ to be of an order of $20 (55)$ for $g_{1A=7}^{n.s. 3/2}(x,Q^2)/g_{1N}^{n.s.}(x,Q^2)$ and $14 (40)$ for $g_{1A=3}^{n.s}(x,Q^2)/g_{1N}^{n.s.}(x,Q^2)$, if enhancement occupies the region $0.05 \leq x \leq 0.2$ ($0.1 \leq x \leq 0.2$). We predict a 2% effect in the difference of the scattering cross sections of deep inelastic scattering of an unpolarized projectile off $^7$Li with $M_{J}$=3/2 and $M_{J}$=1/2. We also show explicitly that the many-nucleon description of deep inelastic scattering off $^7$Li becomes invalid in the enhancement region $0.05 < x \leq 0.2$.Comment: 29 pages, 5 figures, RevTe

Radiative corrections to deep-inelastic ed−ed- scattering. Case of tensor polarized deuteron

The model-independent radiative corrections to deep-inelastic scattering of unpolarized electron beam off the tensor polarized deuteron target have been considered. The contribution to the radiative corrections due to the hard-photon emission from the elastic electron-deuteron scattering (the so-called elastic radiative tail) is also investigated. The calculation is based on the covariant parametrization of the deuteron quadrupole polarization tensor. The numerical estimates of the radiative corrections to the polarization observables have been done for the kinematical conditions of the current experiment at HERAComment: 21 pages, 5 figure