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Astron. Astrophys. 334, 558-570 (1998)

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2. Observational data used

Since I have had no chance to observe [FORMULA]  CMa myself, this study is based solely on the observational data either published or kindly provided in advance of publication by several colleagues.

2.1. RV data

Basic information about the data is summarized in Table 1. I used either the mean RV or the mean He I triplet RV to be able to employ all available observations. It is necessary to warn, however, that the Lick velocities from Chile are based on the H [FORMULA] emission. Yerkes early RVs are based on absorption lines but the emission RV is also given for the first two spectra. In all cases I derived heliocentric Julian Dates (HJDs hereafter) if they were not given in the original source. Since neither the exact number of lines measured for RV nor the S/N ratio are known for some of the data sets, I only assigned all RVs by weights inversely proportional to the dispersion of the original spectra (cf., e.g., Horn et al. 1996). The only exception is the last data set, based on high-dispersion Reticon spectra, for which I somewhat arbitrarily adopted weight 1 (instead of 7.7 which would come out from a straightforward calculation) since these RVs rest on a single line and since putting such a large weight on two localized data sets could overweight them in the combined fits. Note that the weights only played a role in least-square fits to the data. They are given explicitly in Table 1.


Table 1. Journal of RV data sets of [FORMULA]  CMa .
Sources in column "S": A... Frost et al. (1926); B... Campbell & Moore (1928); C... van Hoof (1975) remeasured by Baade (1982a); D... Abt & Levy (1978); E... Baade (1982a); F... Baade (1982b); G... Baade (1984);

2.2. Photometry

Stoy (1959) reported that [FORMULA]  CMa is a light variable. Since then, a large number of photometric observations of [FORMULA]  CMa has been accumulated. I collected and homogenized a representative set of photometric observations which were - or could be - calibrated to the standard UBV or uvby systems. An interested reader can find the details on the individual data sets and their homogenization in the Appendix.

It is useful to consider the true noise level of the existing photometric data. To this end I extracted the observations of all four comparison stars used by various observers from the Hipparcos catalogue. A time plot of these observations immediately shows that HR 2733 varies with a cycle of (353 [FORMULA] 6) d and a full amplitude of 0 [FORMULA] 029. Individual observations of the remaining three comparisons scatter within 0 [FORMULA] 03. I calculated Fourier periodograms for all four comparisons for periods from 0 [FORMULA] 4 to 2 [FORMULA] 0 and the results for the highest peaks found are summarized in Table 2. For HR 2733, I analyzed the O-C deviations from the 353-d cycle. They define the amplitude limits of the periodic signals over that range of possible periods.


Table 2. Periodic signals with largest amplitude found in the Hipparcos [FORMULA] photometry of the four stars used as comparisons for [FORMULA]  CMa. Errors of the last decimal digit of the period and semi-amplitude (in brackets) and the rms error of a single observation calculated from a sinusoidal fit for the respective period are given

2.3. Balmer line profiles

I also compiled the equivalent widths and peak intensities of the H [FORMULA] and H [FORMULA]   emission lines of [FORMULA]  CMa from more recent spectral observations. These are listed in Table 3. Additionally, Dr. T. Rivinius very kindly put at my disposal the H [FORMULA] peak intensities derived from the unpublished measurements in the Heros spectra. These measurements will later be published in detail by their authors.


Table 3. Equivalent widths and peak intensities of the H [FORMULA] and H [FORMULA]   emission lines compiled from various sources.
Notes: Data sources are identified in column "S" as follows: 1... Dachs et al. (1981); 2... Baade (1984); 3... Dachs et al. (1986); 4... Hanuschik et al. (1988); 5... Dachs et al. (1992); 6... Hanuschik et al. (1996); 7... Zboril et al. (1997). In cases when the equivalent widths and peak intensities were not tabulated in the original papers, I measured the peak intensities in the published line profiles

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© European Southern Observatory (ESO) 1998

Online publication: May 15, 1998