Astron. Astrophys. 363, L25-L28 (2000)

5. Discussion and conclusions

The presence of a normal late-type companion could not explain the ultraviolet excess, or the EUVE and ROSAT detections of HD 199143. However, the presence of an accretion disk around our hypothetical companion, such as that found in LMXB or T Tauri systems, might easily explain those properties, as well as the infrared excess, the presence of emission lines and the variability. In such a scenario, the high rotational velocity of HD 199143 could be due to a spin-up in its past by accretion from the companion.

At first glance, a scenario in which a nearby main-sequence star like HD 199143 would have a T Tauri-like companion would seem far-fetched. However, Mathioudakis et al. (1995) report the presence a strongly flaring K7e-M0e dwarf with a high Li abundance only 5 arcminutes from HD 199143. The optical spectrum of this star, BD-17^o6128, is identical to that of many T Tauri stars. From Digital Sky Survey images we identify BD-17^o6128 with HD 358623. An inspection of the Tycho-2 Catalogue (Hog et al. 2000) shows that this star has a proper motion of 59 3 and -63 3 mas yr^-1 in and , identical to that of HD 199143. From the fact that HD 358623 is the only star within a 5 degree radius for which this is the case, we exclude the possibility that this could be a coincidence and conclude that the two stars form a genuine proper motion pair. Using the data by Mathioudakis et al. (1995), and the newly determined distance, we compute the absolute luminosity of BD-17^o6128 to be 0.34 0.06 , employing a similar procedure to that followed for HD 199143. Comparison with the pre-main sequence evolutionary tracks by D'Antona & Mazzitelli (1997) yields an age of 10⁷ years for BD-17^o6128, consistent with a T Tauri nature of this star.

Using the radial velocity of HD 199143 determined in Sect. 2, and the parallax and proper motions listed in the Hipparcos catalogue, we compute the galactic space velocity components of HD 199143 to be km s^-1. This space motion is similar to that of many stars in the vicinity of the Tucanae and TW Hydra associations (Zuckerman & Webb 2000), suggesting that these stars might have formed from the same cloud complex. We conclude that HD 199143 and BD-17^o6128 could very well be the first two members of a region of recent star formation similar to the TW Hydrae Association and the newly identified Tucanae Association (Kastner et al. 1997; Zuckerman & Webb 2000). If confirmed, a further study of these two enigmatic stars could lead to a better understanding of the star formation history in the solar neighbourhood.

© European Southern Observatory (ESO) 2000

Online publication: December 11, 2000
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