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Astron. Astrophys. 357, 548-552 (2000)

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3. 36 Lyn

Shore et al. (1990) discovered magnetically controlled circumstellar matter around the helium-weak star 36 Lyncis (= HD 79158 = HR 3652), for which no previous period was available. Magnetic field measurements indicated a period of 3.834 days. Their ephemeris is

JD (phase = 0.0) = 2443000.0 + 3.834 E

for which positive crossover is at phase 0.50 [FORMULA] 0.03. The C IV line in the ultraviolet is strongest at magnetic null values.

Twenty-three and 38 sets of good Strömgren differential observations were made with the FCAPT during the 1997-98 and 1998-99 observing seasons, respectively (Table 3). The photometry period algorithms yield a period of 3.831 days. But the light curves indicate that a period of 3.834 days gives the best agreement between the u , v , b , and y values for the two observing seasons. Thus the ephemeris of Shore et al. (1990) is adopted. However, as there is not a previous set of at least fair quality photometry and as the phenomena are complex, it is not possible to improve the period at this time.

Fig. 2 shows the light curves for u , v , b , and y whose amplitudes are, respectively, 0.035, 0.025, 0.015, and 0.010, mag. The light curves appear to be in phase. But for y with its small amplitude it is difficult to tell. u , v , and b each show a maximum near phase 0.05 with a minimum near 0.35. Another minimum may be near phase 0.80 which is most clearly seen in v and b . In comparison the magnetic field has a maximum near phase 0.50 and a minimum near phase 0.0 while the C IV line maxima are at phases 0.35 and 0.80 which are those of the minima if both sets of data are correctly phased together.

[FIGURE] Fig. 2. Differential FCAPT uvby photometry of 36 Lyn (filled squares) is displayed using the ephemeris JD (phase = 0.0) = 2443000.0 + 3.834 E.

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© European Southern Observatory (ESO) 2000

Online publication: June 5, 2000