Radiative accelerations on Ne in the atmospheres of late B stars

Radiative accelerations on Ne are calculated for the atmospheres of main sequence stars with 11000 < Teff < 15000 K, corresponding to the range of the HgMn stars. The calculations take into account neon fine structure as well as shadowing of neon lines using the entire Kurucz line list, bound-bound, bound-free, and free-free opacity of H, He, and C as well as some NLTE effects. NLTE effects modify the radiative acceleration by a factor of order 100 in the outer atmosphere. The dependence of the radiative acelerations on the Ne abundance, Teff, and gravity is studied. Radiative accelerations are well below gravity in the entire range of Teff and it is predicted that in stable atmospheres Ne should sink and be observed as underabundant. This agrees with recent observations of low Ne abundances in HgMn stars.Comment: Accepted by Monthly Notices of the Royal Astronomical Society, 2002 August 21. 10 pages, 9 Postscript figures (needed new version due to error in the listed originally-received date; corrected typo in author line)

Neon abundances in mercury-manganese stars: Radiative accelerators and non-LTE calculations

We make new non-local thermodynamic equilibrium calculations to deduce the abundances of neon from visible-region echelle spectra of selected Ne i lines in seven normal stars and 20 HgMn stars. We find that the best strong blend-free Ne line that can be used at the lower end of the effective temperature Teff range is λ6402, although several other potentially useful Ne i lines are found in the red region of the spectra of these stars. The mean neon abundance in the normal stars (log A=8.10) is in excellent agreement with the standard abundance of neon (8.08). However, in HgMn stars neon is almost universally underabundant, ranging from marginal deficits of 0.1–0.3 dex to underabundances of an order of magnitude or more. In many cases, the lines are so weak that only upper limits can be established. The most extreme example found is υ Her with an underabundance of at least 1.5 dex. These underabundances are qualitatively expected from radiative acceleration calculations, which show that Ne has a very small radiative acceleration in the photosphere, and that it is expected to undergo gravitational settling if the mixing processes are sufficiently weak and there is no strong stellar wind. According to theoretical predictions, the low Ne abundances place an important constraint on the intensity of such stellar winds, which must be less than 10−14 M⊙ yr−1 if they are non-turbulent

Neon abundances in normal late-B and mercury-manganese stars

We make new Non-LTE calculations to deduce abundances of neon from visible-region echelle spectra of selected Ne I lines in 7 normal stars and 20 HgMn stars. We find that the best strong blend-free Ne line which can be used at the lower end of the Teff range is 6402 A, although several other potentially useful Ne I lines are found in the red region of the spectra of these stars. The mean neon abundance in the normal stars (log A =8.10) is in excellent agreement with the standard abundance of neon (8.08). However, in HgMn stars, neon is almost universally underabundant, ranging from marginal deficits of 0.1-0.3 dex to underabundances of an order of magnitude or more. In many cases, the lines are so weak that only upper limits can be established. The most extreme example found is upsilon Her with an underabundance of at least 1.5 dex. These underabundances are qualitatively expected from radiative acceleration calculations, which show that Ne has a very small radiative acceleration in the photosphere and is expected to undergo gravitational settling if mixing processes are sufficiently weak, and there is no strong stellar wind. According to the theoretical predictions of Landstreet et al. (1998), the low Ne abundances place an important constraint on the intensity of such stellar winds, which must be less than $10^-14 M_sun per yr if they are non-turbulent.Comment: 10 pages, 1 figure, received 23 June 2000, accepted 4 August 2000, by Monthly Notices of the Royal Astronomical Societ

Synthetic Spectra and Light Curves of Interacting Binaries and Exoplanets with Circumstellar Material: SHELLSPEC

Program SHELLSPEC is designed to calculate light-curves, spectra and images of interacting binaries and extrasolar planets immersed in a moving circumstellar environment which is optically thin. It solves simple radiative transfer along the line of sight in moving media. The assumptions include LTE and optional known state quantities and velocity fields in 3D. Optional (non)transparent objects such as a spot, disc, stream, jet, ufo, shell or stars may be defined (embedded) in 3D and their composite synthetic spectrum calculated. Roche model can be used as a boundary condition for the radiative transfer. Recently a new model of the reflection effect, dust and Mie scattering were incorporated into the code. $\epsilon$ Aurigae is one of the most mysterious objects on the sky. Prior modeling of its light-curve assumed dark, inclined, disk of dust with the central hole to explain the light-curve with a sharp mid-eclipse brightening. Our model consists of two geometrically thick flared disks. Internal optically thick disk and external optically thin disk which absorbs and scatters radiation. Shallow mid-eclipse brightening may result from eclipses by nearly edge-on flared (dusty or gaseous) disks. Mid-eclipse brightening may also be due to strong forward scattering and optical properties of the dust which can have an important effect on the light-curves. There are many similarities between interacting binary stars and transiting extrasolar planets. Reflection effect which is briefly reviewed is one of them. The exact Roche shape and temperature distributions over the surface of all currently known transiting extrasolar planets have been determined. In some cases (HAT-P-32b, WASP-12b, WASP-19b) departures from the spherical shape can reach 7-15%.Comment: 6 pages, 2 figures, to appear in the Proceedings: From Interacting Binaries to Exoplanets: Essential Modeling Tools, IAU Symposium 282, held in Tatranska Lomnica, July 201

Search for star-planet interaction

We analyse the chromospherical activity of stars with extrasolar planets and search for a possible correlation between the equivalent width of the core of Ca II K line and orbital parameters of the planet. We found a statistically significant evidence that the equivalent width of the Ca II K line reversal, which originates in the stellar chromosphere depends on the orbital period P_orb of the exoplanet. Planets orbiting stars with T_eff < 5500 K and with P_orb < 20 days generally have much stronger emission than planets at similar temperatures but at longer orbital periods. P_orb=20 days marks a sudden change in behaviour, which might be associated with a qualitative change in the star-planet interaction.Comment: 2 pages, 2 figures, to appear in the proceedings of IAU Symposium 282: "From Interacting Binaries to Exoplanets:Essential Modeling Tools