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Astron. Astrophys. 328, L37-L39 (1997)

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1. Introduction

Sirius-like systems, i.e. binaries consisting of an early type star and a white dwarf, are quite interesting because of their evolutionary history, probably involving mass exchange. There are not many Sirius-like systems known.

[FORMULA] Crt (HD 97277 = HR 4343) is a bright ([FORMULA]) star of type A2 III (Levato 1972, Smalley et al. 1997). Its radial velocity (RV) has been measured sporadically during the beginning of this century and the measurements were reported by Campbell & Moore (1928). Although the star was found to have variable RV (between -3 and +16 km s-1), and although it is bright with "good lines", surprisingly no one seems to have observed it since then, until recently.

In 1991, a white dwarf was detected at the position of [FORMULA] Crt by the ROSAT X-ray and EUV surveys (Fleming et al. 1991). From this and the earlier reported variable RV it was suspected that [FORMULA] Crt is a Sirius-like system with an orbital period of [FORMULA] days (the estimate by Fleming et al. 1991, as corrected by Smalley et al. 1997). However, Smalley et al. (1997) report on spectra taken for the purpose of elemental abundance analyses, from which they also measured the RV of [FORMULA] Crt: they find it stable at 10-12 km s-1, where the difference between individual RVs is not significant, because their error ranges from 2 to 5 km s-1. From this, they conclude that the older measurements reported by Campbell & Moore (1928) are erroneous (because they are from different sources) and that [FORMULA] Crt and the white dwarf form a wide long-period system or are not physically connected.

We found that this deserved further investigation. First, as Smalley et al. already remark, there is the possibility that their sampling was unlucky, and that [FORMULA] Crt is in a highly elliptical orbit, so that the RV is nearly stable most of the time and only in short time intervals changes strongly. Second, to us it seems unlikely that an amplitude of almost 20 km s-1 could have been caused by systematic errors in the old measurements. After all, Campbell & Moore report about the careful corrections for possible systematic errors in the different observations. Furthermore, on three occasions two RVs are given for the same date, indicating independent measurements of the same plate. Their differences can serve as a measure for the RV error; they never exceed 2.2 km s-1.

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© European Southern Observatory (ESO) 1997

Online publication: March 26, 1998