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Astron. Astrophys. 341, 527-538 (1999)

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6. The Li I photospheric line

BD+[FORMULA] has strong Li I [FORMULA]6708 Å absorption, which, along with other considerations, caused J94 to argue for a youthful evolutionary status. J94 found line profile and EW variations in their data and we have also observed significant changes both between and during the two nights of observation (see Figs. 6 and 7). Fig. 6 shows average line profiles at several epochs. On August 4 (left panel ) the line depth was smaller with a raised core at phases 0.0, 0.5 and 0.6. On August 5 (right panel ) there are more noticeable changes in the line asymmetry - the position of maximum absorption appears towards the red at [FORMULA] and drifts back to the blue at [FORMULA]. The changes in the Li I [FORMULA] 6708 profiles are followed closely by the nearby Ca I [FORMULA] 6717 line.

[FIGURE] Fig. 6. Sequence of Li I ([FORMULA]6707 Å) line profiles on August 4 (left ) and August 5 (right ). Each profile is an average of four consecutive spectra taken near the phase indicated above it in the plot. Phases were computed according to the period of 10.17 hrs (J94) fixing zero phase at the time of the first exposure on the first night, as in Sect. 4.1

[FIGURE] Fig. 7. Time series of the Li I EW on August 4 (open circles ) and August 5 (filled circles . Measurements are very scattered in both nights but it can be seen that the Li I EW is systematically lower on August 4

Fig. 7 shows the total EW of the Li [FORMULA] 6708 feature on August 4 (open circles ) and 5 (filled circles ). The error on a single EW measurement is approximately 20 m Å. The EWs show no sign of variation on each night, but there is a significant increase in the mean EW from 142 m Å on August 4 to 215 m Å on August 5. Possibly some of this variation is in the sytematic placement of the continuum, but this could not explain the majority of the difference. The nearby blend of two iron lines at 6704 Å shows an increase in its mean EW from 120 m Å to 145 m Å. Problems with blending of the 6708 Å feature itself are also unlikely to play a part at this spectral resoltuion. The nearby Fe I [FORMULA] Å and Sm II [FORMULA] 6707.50 Å lines are too weak [FORMULA]20 m Å to have much effect. Another possibility is that the largely unknown contribution from molecular opacity might vary in a phase dependent way. There is little overlap in the phase coverage of our observations, although what there is, suggests no phase dependent behaviour. In this situation it is difficult to say whether the EW enhancement on August 5 is a long term effect or perhaps some transient phenomenenon associated with the chromospheric flare activity we observed. Further discussion of the Li variations are given in Sect. 8.4.

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© European Southern Observatory (ESO) 1999

Online publication: December 4, 1998
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