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We present the results of an observational campaign for the long-period variable subdwarf B star PG 1338+ 481. Seven continuous weeks of observing time at the Steward Observatory 1.55 m Kuiper telescope on Mount Bigelow, Arizona, and the 1.3 m MDM telescope at Kitt Peak rendered $250 hr of simultaneous U/R time series photometry, as well as an extra $70 hr of R-band-only data. The analysis of the combined light curves resulted in the extraction of 13 convincing periodicities in the 2100-7200 s range, with amplitudes up to $0.3% and $0.2% in the U and R, respectively. Comparing the ratios of amplitudes in the two wave bands to those predicted from theory suggests the presence of dipole modes, a notion that is further supported by the period spacing between the highest amplitude peaks. If confirmed, this poses a challenge to current nonadiabatic theory. At the quantitative level, we find that the distribution of the observed period spectrum is highly nonuniform and much sparser than that predicted from a representative model. We provide a possible interpretation in the text. The asteroseismological analysis attempted for PG 1338+481 on the basis of six observed periodicities believed to constitute consecutive dipole modes renders encouraging results. Fixing the effective temperature and surface gravity to the spectroscopic estimates, we successfully isolate just one family of optimal models that can reproduce the measured periods to better than 1% . While the stellar parameters thus inferred must be regarded as preliminary, the achieved fit bodes well for future asteroseismic analyses of long-period variable subdwarf B stars.

Context. The origin of solar transition region redshifts is not completely understood. Current research is addressing this issue by investigating three-dimensional magneto-hydrodynamic models that extend from the photosphere to the corona. Aims. By studying the average properties of emission line profiles synthesized from the simulation runs and comparing them to observations with present-day instrumentation, we investigate the origin of mass flows in the solar transition region and corona. Methods. Doppler shifts were determined from the emission line profiles of various extreme-ultraviolet emission lines formed in the range of T = 10 4 −10 6 K. Plasma velocities and mass flows were investigated for their contribution to the observed Doppler shifts in the model. In particular, the temporal evolution of plasma flows along the magnetic field lines was analyzed.Results. Comparing observed vs. modeled Doppler shifts shows a good correlation in the temperature range log(T /[K]) = 4.5−5.7, which is the basis of our search for the origin of the line shifts. The vertical velocity obtained when weighting the velocity by the density squared is shown to be almost identical to the corresponding Doppler shift. Therefore, a direct comparison between Doppler shifts and the model parameters is allowed. A simple interpretation of Doppler shifts in terms of mass flux leads to overestimating the mass flux. Upflows in the model appear in the form of cool pockets of gas that heat up slowly as they rise. Their low temperature means that these pockets are not observed as blueshifts in the transition region and coronal lines. For a set of magnetic field lines, two different flow phases could be identified. The coronal part of the field line is intermittently connected to subjacent layers of either strong or weak heating, leading either to mass flows into the loop (observed as a blueshift) or to the draining of the loop (observed as a redshift).