5 Tertiary components

 

On some object frames there were one or several faint stars located close to the main pair. To make our information on the environment of our doubles more comprehensive we tried to detect all the stars lying closer than $\approx 15-20\hbox{$^{\prime\prime}$}$ to the primary. Also some relatively bright stars were sometimes measured at larger separations. Too faint, tertiary components were not measured in the ultraviolet.

Some fifty tertiaries were found, with a V -magnitude difference with the primary up to $7^{\rm m}$. At the level of $\Delta {\it V}\approx 5^{\rm m}-6^{\rm m}$ the scope is apparently complete. This detection was followed by an immediate ("on-fly") estimation of the V - and B -magnitude differences with the primary component, obviously a rather rough estimate because normally the magnitude difference is too large: errors are about $0.2^{\rm m}$ in $\Delta {\it V}$ and $0.3^{\rm m}$ in $\Delta ({\it B}-{\it V})$. Relative positions of detected stars have an uncertainty of about 1-2 pixels ($0\hbox{$.\!\!^{\prime\prime}$}5-1\hbox{$^{\prime\prime}$}$).

The parameters of all surrounding stars are collected in Table 5. Columns give the WDS identifier, a companion identifier, differential photometry data $\Delta {\it V}$ and $\Delta ({\it B}-{\it V})$and position parameters $\rho$ and $\theta$ relative to the primary. The last column denotes the reference to the method with which these parameters were obtained. Original "on-fly" data are signed as "F", while other cases are described below.

  

Table 5: Faint stars in the vicinity of the objects. Low-case identifiers ID are arbitrary ones. See more description in text

For some "tertiaries" we made an attempt to improve the quality of our data.

The results from full-aperture ($\approx 34\hbox{$^{\prime\prime}$}$) photometry of sufficiently distant and not very faint star are presented with a reference "P". They were obtained by exactly the same technique as the total object photometry. The astrometry quality remains the same as for "F"-cases, while errors of V and $({\it B}-{\it V})$ are less, about $\pm0.1^{\rm m}$ and $\pm0.15^{\rm m}$, respectively.

Some multiple stars with up to 5 visual companions were measured with the help of DAOPHOT. These results are added to Table 5 with a remark "D" or "d", depending upon the choice of stars for the point spread function model. The first case corresponds to the usage of a bright enough and well separated star in the field. The "d"-method corresponds to the use of an artificial PSF star with Moffat shape determined from the binary star fit (see Sect. 2). The estimated precision of the DAOPHOT technique is $\pm0.05^{\rm m}$ in photometry and $\pm0.1\hbox{$^{\prime\prime}$}$ in astrometry.

All the errors of photometry given above correspond to magnitude difference $<5^{\rm m}$; they are about 1.5 times larger for $\Delta {\it V}$ between $5^{\rm m}$ and $6^{\rm m}$ and 2 times larger for fainter stars.

To make sure that we have not assigned the wrong identifier to a previously known tertiary component, we extracted the existing information on them from WDS (1996). The tertiaries were identified using their $\rho$ and $\theta$. WDS gave four identifications of our tertiaries, their identifiers in Table 5 are given in upper-case; all the rest are in lower-case letters.

Evidently, most stars are field ones. The comparison of their photometric parallaxes to spectroscopic ones of primaries (or to those from Hipparcos when available) is the subject of further study in order to decide about the physicity of some companions to the main pairs A+B. An interesting case is a non-WDS bright and close tertiary companion "c" of WDS 17357-4731 = CP-47 11654. According to its photometry, it has a higher probability to be a physical one than the B-component.