Surface-effect corrections for solar-like oscillations using 3D hydrodynamical simulations

The space-borne missions have provided us with a wealth of high-quality observational data that allows for seismic inferences of stellar interiors. This requires the computation of precise and accurate theoretical frequencies, but imperfect modeling of the uppermost stellar layers introduces systematic errors. To overcome this problem, an empirical correction has been introduced by Kjeldsen et al. (2008, ApJ, 683, L175) and is now commonly used for seismic inferences. Nevertheless, we still lack a physical justification allowing for the quantification of the surface-effect corrections. We used a grid of these simulations computed with the CO$^5$BOLD code to model the outer layers of solar-like stars. Upper layers of the corresponding 1D standard models were then replaced by the layers obtained from the horizontally averaged 3D models. The frequency differences between these patched models and the 1D standard models were then calculated using the adiabatic approximation and allowed us to constrain the Kjeldsen et al. power law, as well as a Lorentzian formulation. We find that the surface effects on modal frequencies depend significantly on both the effective temperature and the surface gravity. We further provide the variation in the parameters related to the surface-effect corrections using their power law as well as a Lorentzian formulation. Scaling relations between these parameters and the elevation (related to the Mach number) is also provided. The Lorentzian formulation is shown to be more robust for the whole frequency spectrum, while the power law is not suitable for the frequency shifts in the frequency range above $\nu_{\rm max}$.Comment: 11 pages, 14 figures, 4 tables; accepted for publication in Astronomy & Astrophysic

On a generalization of Jacobi's elliptic functions and the Double Sine-Gordon kink chain

A generalization of Jacobi's elliptic functions is introduced as inversions of hyperelliptic integrals. We discuss the special properties of these functions, present addition theorems and give a list of indefinite integrals. As a physical application we show that periodic kink solutions (kink chains) of the double sine-Gordon model can be described in a canonical form in terms of generalized Jacobi functions.Comment: 18 pages, 9 figures, 3 table

3D molecular line formation in dwarf carbon-enhanced metal-poor stars

We present a detailed analysis of the carbon and nitrogen abundances of two dwarf carbon-enhanced metal-poor (CEMP) stars: SDSS J1349-0229 and SDSS J0912+0216. We also report the oxygen abundance of SDSS J1349-0229. These stars are metal-poor, with [Fe/H] < -2.5, and were selected from our ongoing survey of extremely metal-poor dwarf candidates from the Sloan Digital SkySurvey (SDSS). The carbon, nitrogen and oxygen abundances rely on molecular lines which form in the outer layers of the stellar atmosphere. It is known that convection in metal-poor stars induces very low temperatures which are not predicted by `classical' 1D stellar atmospheres. To obtain the correct temperature structure, one needs full 3D hydrodynamical models. Using CO5BOLD 3D hydrodynamical model atmospheres and the Linfor3D line formation code, molecular lines of CH, NH, OH and C2 were computed, and 3D carbon, nitrogen and oxygen abundances were determined. The resulting carbon abundances were compared to abundances derived using atomic CI lines in 1D LTE and NLTE. There is not a good agreement between the carbon abundances determined from C2 bands and from the CH band, and molecular lines do not agree with the atomic CI lines. Although this may be partly due to uncertainties in the transition probabilities of the molecular bands it certainly has to do with the temperature structure of the outer layers of the adopted model atmosphere. We explore the influence of the 3D model properties on the molecular abundance determination. In particular, the choice of the number of opacity bins used in the model calculations and its subsequent effects on the temperature structure and molecular line formation is discussed. (Abridged)Comment: Poster presented at IAU JD 10, Rio de Janeiro, 10-11 August 2009, published in Memorie della Societa' Astronomica Italiana, Vol. 80 n.3 P.735. One reference corrected, matches the published versio

Three carbon-enhanced metal-poor dwarf stars from the SDSS - Chemical abundances from CO^5BOLD 3D hydrodynamical model atmospheres

The origin of carbon-enhanced metal-poor stars enriched with both s and r elements is highly debated. Detailed abundances of these types of stars are crucial to understand the nature of their progenitors. The aim of this investigation is to study in detail the abundances of SDSS J1349-0229, SDSS J0912+0216 and SDSS J1036+1212, three dwarf CEMP stars, selected from the Sloan Digital Sky Survey. Using high resolution VLT/UVES spectra (R ~ 30 000) we determine abundances for Li, C, N, O, Na, Mg, Al, Ca, Sc, Ti, Cr, Mn, Fe, Co, Ni and 21 neutron-capture elements. We made use of CO^5BOLD 3D hydrodynamical model atmospheres in the analysis of the carbon, nitrogen and oxygen abundances. NLTE corrections for C I and O I lines were computed using the Kiel code. We classify SDSS J1349-0229 and SDSS J0912+0216 as CEMP-r+s stars. SDSS J1036+1212 belongs to the class CEMP-no/s, with enhanced Ba, but deficient Sr, of which it is the third member discovered to date. Radial-velocity variations have been observed in SDSS J1349-0229, providing evidence that it is a member of a binary system. The chemical composition of the three stars is generally compatible with mass transfer from an AGB companion. However, many details remain difficult to explain. Most notably of those are the abundance of Li at the level of the Spite plateau in SDSS J1036+1212 and the large over-abundance of the pure r-process element Eu in all three stars.Comment: 12 pages, 15 figures. Accepted for publication in A&

(Conformal) Killing vectors and their associated bivectors

Fayos and Sopuerta have recently set up a formalism for studying vacuum spacetimes with an isometry, a formalism that is centred around the bivector corresponding to the Killing vector and that adapts the tetrad to the bivector. Steele has generalized their approach to include the homothetic case. Here, we generalize this formalism to arbitrary spacetimes and to homothetic and conformal Killing vectors but do not insist on aligning the tetrad with the bivector. The most efficient way to use the formalism to find conformal Killing vectors (proper or not) of a given spacetime is to combine it with the notion of a preferred tetrad. A metric by Kimura is used as an illustrative example

Cellular immune response in infected mice to NSP protein encoded by the negative strand NS RNA of influenza A virus

Influenza A virus belongs to a family of enveloped viruses with an RNA genome of negative polarity consisting of 8 RNA segments. The transcription of this RNA genome results in the synthesis of positive-sense mRNAs that translate up to 16 unique viral proteins with the help of splicing and translational shift mechanisms. The 8th NS segment encodes the NS1 protein (27 kDa), which is an active interferon antagonist, and the nuclear export protein NEP (14 kDa) through the standard negative polarity pathway. In addition, an alternative open reading frame for the synthesis of a third viral protein (NSP, negative-strand protein) by means of a direct translation of genome polarity RNA (the so-called positive polarity genome strategy) was identified in the NS segment. Since it is unknown as to whether the NSP protein can be synthesized in the infected organism post viral infection, the generation of spleen leucocytes specific to this protein was studied in mice after two sequential infections with influenza A viruses of H1N1 and H3N2 subtypes. It was found that leucocyte clones specifically recognizing a peptide domain in the central region of the NSP protein (amino acid positions 82-119) were generated in mice infected with influenza A viruses. In silico prediction has shown strong major histocompatibility complex-1 (MHC-I) and MHC-II specific epitopes in this central domain of the NSP. Comparative analysis of the influenza H3N2 viruses circulating in humans during 1968-2018 has shown high NSP variability, which was similar to that shown for the hemagglutinin (HA) and neuraminidase (NA) proteins. The highest variability was found to be in the N- and C-terminal parts of the NSP. These observations suggest that synthesis of the NSP protein occurs in infected animals and further support a bipolar (ambisense) strategy of the RNA genome of human influenza A virus.Influenza A virus belongs to a family of enveloped viruses with an RNA genome of negative polarity consisting of 8 RNA segments. The transcription of this RNA genome results in the synthesis of positive-sense mRNAs that translate up to 16 unique viral proteins with the help of splicing and translational shift mechanisms. The 8th NS segment encodes the NS1 protein (27 kDa), which is an active interferon antagonist, and the nuclear export protein NEP (14 kDa) through the standard negative polarity pathway. In addition, an alternative open reading frame for the synthesis of a third viral protein (NSP, negative-strand protein) by means of a direct translation of genome polarity RNA (the so-called positive polarity genome strategy) was identified in the NS segment. Since it is unknown as to whether the NSP protein can be synthesized in the infected organism post viral infection, the generation of spleen leucocytes specific to this protein was studied in mice after two sequential infections with influenza A viruses of H1N1 and H3N2 subtypes. It was found that leucocyte clones specifically recognizing a peptide domain in the central region of the NSP protein (amino acid positions 82-119) were generated in mice infected with influenza A viruses. In silico prediction has shown strong major histocompatibility complex-1 (MHC-I) and MHC-II specific epitopes in this central domain of the NSP. Comparative analysis of the influenza H3N2 viruses circulating in humans during 1968-2018 has shown high NSP variability, which was similar to that shown for the hemagglutinin (HA) and neuraminidase (NA) proteins. The highest variability was found to be in the N- and C-terminal parts of the NSP. These observations suggest that synthesis of the NSP protein occurs in infected animals and further support a bipolar (ambisense) strategy of the RNA genome of human influenza A virus

Extremely metal-poor stars from the SDSS

We give a progress report about the activities within the CIFIST Team related to the search for extremely metal-poor stars in the Sloan Digital Sky Survey's spectroscopic catalog. So far the search has provided 25 candidates with metallicities around or smaller -3. For 15 candidates high resolution spectroscopy with UVES at the VLT has confirmed their extremely metal-poor status. Work is under way to extend the search to the SDSS's photometric catalog by augmenting the SDSS photometry, and by gauging the capabilities of X-shooter when going to significantly fainter targets.Comment: 6 pages, 6 figures, Proceedings paper of the conference "A stellar journey: A symposium in celebration of Bengt Gustafsson's 65th birthday