## 4. Application and results## 4.1. Per (HD 24912)
In the periodogram (see Fig. 4) the most significant power outside the
contaminated frequency range is found at
= 6.96(4) c d We investigated whether the relatively low power on the blue side at could be due to wind contamination. Simultaneously taken UV spectra (Kaper et al. 1999) show that a new DAC developed at low velocity around BJD 2447818.9. Similar simultaneous observations from another campaign on this star (see Henrichs et al. 1998a) showed that the new development of a DAC is accompanied by enhanced blue-shifted absorption in H. The HeI line presently studied is probably also partly formed in the wind and therefore should in principle display similar kind of extra absorption, which would disturb the period analysis. We therefore excluded the 24 spectra between BJD 2447818.975 and BJD 2447819.1 in our further period analysis. These spectra showed extra blue-shifted absorption which was not present in other spectra, and which we attribute to wind effects. This procedure indeed decreased somewhat the asymmetry in amplitude, although not completely. Some wind absorption is undoubtedly still present in a number of spectra, but a thorough elimination is beyond hope. A second cause might be a blending effect by the partly overlapping (unidentified) weak lines in the alleged blue continuum which may have distorted the normalization. We consider this as less important. We furthermore folded the spectra with
(right panel in Fig. 2). This shows
a clear NRP pattern in the range from -100 to
160 km s Considerable power is also found at
= 9.14(7) c d From the phase diagram belonging to
we can derive the azimuthal degree,
, according to Telting &
Schrijvers (1997, hereafter TS) by measuring the difference in phase
at 230 km s Table 2 of TS lists coefficients of empirical linear fits to
input and output values of synthetic
data generated by Monte Carlo calculations for various pulsation
parameters. We show below that in our case the ratio of horizontal to
vertical motions, We can determine the direction of the pulsation mode if the stellar
rotation rate is known. Periodicities in stellar wind features suggest
that the rotation period, , is 2 or 4
days (Kaper et al. 1999). We obtain in both cases that the mode must
be prograde. The value of ## 4.2. Cep (HD 210839)
Outside the contaminated frequency range we find significant power at
two different frequencies: at =
1.96(8) c d
Although is nearly twice , it cannot be its first harmonic since the ratio = 1.86(10) deviates more than 1 from the exact value of 2. In addition, in all velocity bins the power at lies systematically below the power at (see Fig. 6). This makes the probability of being a harmonic of less than . We could also exclude being a harmonic by considering the consistency check for the amplitude ratio and the phase relation of the main frequency and its first harmonic as given by TS. They find that = 2 = 1.50(6), where the phase at line center of the main frequency is denoted by and of the first harmonic by . For Cep we obtain = 1.6(3). This would give fair confidence that the higher frequency could indeed be the first harmonic of the lower, except that in all model calculations by TS the ratio of the amplitudes of the first harmonic to the main frequency is considerably smaller than we observe, which makes as a first harmonic very unlikely, which we therefore consider as a second NRP mode. For the second mode we find =
22.4(3). From this value we derive
= 5.2(7) using a
0.3 fit with
86 confidence, which implies
= 5 as the most probable value for
this second NRP mode and Adopting an upper limit to the rotation period of 4.5 days, using a
radius of 19 R, a mass of 59
M (Puls et al. 1996) and an
inclination angle of 90 © European Southern Observatory (ESO) 1999 Online publication: April 12, 1999 |