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Astron. Astrophys. 322, 835-840 (1997)

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2. Observations

The data come from three sources: Wilson's (1978) observations of the Moon from 1966 - 1971 and 1974 - 1977 at Mount Wilson Observatory, plus two independent measurements of the disk-averaged K-line flux. Observations have been made at Kitt Peak National Observatory (KPNO) by White & Livingston (1978, 1981) since late 1974, and at Sacramento Peak Observatory (SPO) since 1976 (Keil & Worden 1984; Keil 1992). Donahue & Keil (1995) analyzed the solar SDR using the SPO data alone.

The SPO and KPNO K-line index has been converted to the Mount Wilson S index using the solar 10.7 cm flux as an intermediary (Baliunas et al. 1995). This is necessary because the K-line observations and Mount Wilson S observations do not overlap sufficiently to permit a direct calibration. The time series is shown in Fig. 1. Nearly the entire time series is plotted by Baliunas et al. (1995) in their Fig. 1d.

[FIGURE] Fig. 1. The time series of solar disk-integrated Ca II K-line emission. Symbols are: [FORMULA] - Mount Wilson lunar measurements ( Wilson 1978); [FORMULA] - KPNO disk-integrated K-line flux (White & Livingston 1978, 1981); [FORMULA] - SPO disk-integrated K-line flux (Keil & Worden 1984; Keil 1992). The SPO and KPNO fluxes have been converted to the Mount Wilson S index (see text).

In a first step the time-series was cleaned from long-term trends having its origin in the solar 11 y cycle. Fig. 2 shows a 400-day subsample of the cleaned data to demonstrate the rotational modulation. ARGD is clearly apparent in Fig. 2, and that all of the parameters related to rotational modulation are strongly variable on time-scales spanning only a few rotational cycles.

[FIGURE] Fig. 2. A 400 d subsample during mid-1989 demonstrating strong variability of amplitude and phase of rotational modulation.

In a second step we have placed the data into daily bins and further, the observational gaps in the time series were filled with zeroes because our wavelet code is written for equally spaced data.

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© European Southern Observatory (ESO) 1997

Online publication: June 5, 1998