Stably stratified fluids, such as stellar and planetary atmospheres, can support and propagate gravity waves. On Earth these waves, which can transport energy and momentum over large distances and can trigger convection, contribute to the formation of our weather and global climate. Gravity waves also play a pivotal role in planetary sciences (e.g. Young et al. 1997) and modern stellar physics (Charbonnel & Talon 2007). They have also been proposed as an agent for the heating of stellar atmospheres and coronae (Mihalas & Toomre 1981), the exact mechanism behind which is one of the outstanding puzzles in solar
A space-time analysis of 36 days' worth of full-disk intensity and velocity images, obtained by the Global Oscillation Network Group, is used to produce a high-resolution ഞ-n phase-difference spectrum for the spectral range ( , mHz). This is the first time a phase-difference spectrum has been produced for 4 ≤ ഞ ≤ 2000 0 ≤ n ≤ 8.3 intermediate-ഞ values. The phase differences on the p-mode ridges are found to linearly increase from ∼65Њ at 2 mHz up to ∼95Њ at 4.7 mHz. Only near 3.9 mHz are the differences close to 90Њ, the theoretically expected phase for adiabatic evanescent waves. The phases between the ridges exhibit a steplike behavior in frequency with negative values at low frequency and positive values (greater than 90Њ) at high frequency. The negative phase values are consistent with the extension to low-and moderate-ഞ values of the plateau-interridge regime discovered by Deubner et al. in 1990. However, positive phase values, which represent higher phase for the solar background than for the acoustic modes, were not expected. An understanding of this observed phase-difference behavior will improve our knowledge of the nature of the solar background and its interaction with the acoustic p-modes.
Abstract. An analytical model has been developed to empirically study the effects of stellar spots and faculae on the observed equivalent widths of Li i 6708, Na i 5896 and K i 7699Å lines (and abundances in the case of lithium) in late-type stars, taking into account the changes in the observed magnitudes and colors. Solar spectra corresponding to different active regions are used as input data and a range of filling factors are applied to simulate the surfaces of stars with different levels of activity. Detailed comparisons between predicted and observed photometric colors and equivalent widths are made for late-type stars of the Pleiades and the field. The observed dispersions in K i and Li i equivalent widths for Pleiades stars can be partially accounted by the simultaneous effects of activity on colors and the line formation, indicating that the lithium-rotation connection suggested for ∼0.7−0.9 M Pleiades stars could be due in part to the stellar activity. However, under realistic values for the filling factors, only a small portion of the observed spread could be explained by these effects.
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