3. Stars with negative binary detection
The stars for which we could not detect a companion are listed in Table 4. To facilitate a comparison with previous reports of a companion, we list the true PA of our observation in Column (3); this includes the limb slope measured from the fringe speed, listed in Column (2). The SNR of the data, listed in Column (4), gives an indication of the minimum magnitude difference of a companion that would have been consistent with our data. In Column (5), we list the possible reason for non-detection by us. The case of SAO 93950 has already been discussed in Sect. 2.10.
Table 4. Summary of negative detection results
3.1. SAO 96810
SAO 96810 is a spectroscopic binary, with a period of 7.25 years (Pédoussault et al. 1988). A companion was detected from our earlier observation (Paper III), but we do not detect it from the data reported here. Insufficient SNR is a good explanation, the companion being about 2 mag fainter than the primary in the K band. The companion was resolved earlier also by Edwards et al. (1980), while other LO (Africano et al. 1977; Eitter & Beavers 1979) and speckle observations (Mason 1996) in the visual failed to detect it.
3.2. SAO 93961
SAO 93961 belongs to the Hyades cluster, and is a well studied sub-arcsecond binary with an orbital period of 40.4 yrs. A long list of LO observations of this source in the visual are listed in Evans (1984), who infers the spectral type of the secondary to be F9V. This source has been observed repeatedly also by speckle in the visual (see for instance Hartkopf et al. 1997), and more recently in the near-IR (Patience et al. 1998). Our negative detection is most likely due to the fact that our lightcurve partially fell in a gap between two blocks of data (see Paper I).
3.3. SAO 93975
SAO 93975 is a LO binary with a projected angular separation of 10 mas at PA=284o and 5 mas at PA=86o (Peterson et al. 1981). These authors suggest a G0V spectral type for the companion. Also Radick & Lien (1980) have reported this star to be double, however the companion was not detected in several other LO (White 1979; Evans & Edward 1981; Fekel et al. 1980; Radick & Lien 1982; Radick et al. 1982), as well as speckle observations (Mason et al. 1993; Mason 1996), all in the visual. We could not detect the companion either. As for SAO 93961 above, our lightcurve partially fell between two data blocks and hence our negative result is not conclusive.
3.4. SAO 93981
This star is a suspected LO binary with = along PA=292o (Radick & Lien 1982). It is unlikely that we could fail to detect such a wide companion in our observation, unless it had a much higher brightness ratio in the near-IR than the 1 mag reported in the visual. However, we also note that many other observers have failed to detect it both by LO in the visual (Radick et al. 1982; Evans & Edwards 1981; Peterson et al. 1981), as well as by speckle in the visual and near-IR (Mason et al. 1993; Mason 1996; Patience et al. 1998).
© European Southern Observatory (ESO) 1999
Online publication: October 4, 1999