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Appendix A: Previous measurements

HD 142666, that is also known as V 1026 Sco, was classified as Herbig Ae/Be-star by Gregorio-Hetem et al. (1992). It has a spectral type of A 7 III (e.g., Blondel et al. 2006). The source belongs to the star formation region R 1 in Scorpius (Vieira et al. 2003). According to Meeus et al. (2001), HD 142666 is a group-II object whose disk is flat. The object is a photometrically variable UX Ori star (Natta et al. 1997), i.e., dust clouds with a size in the range of the stellar diameter move into the line of sight of the observer from time to time. The extinction then increases and the stellar light can be reddened depending on the absorbing material. Considering polarimetric measurements (Hales et al. 2006) and the high variability of the flux in the NIR and visual wavelength range (ΔV = 1.2; Meeus et al. 1998), the disk is assumed to be inclined. The approximate age of the object is 10  million years (Natta et al. 1997). Millimeter measurements indicate this age, as well. The low decrease in the millimeter flux towards longer wavelengths could be a hint of cm-sized dust grains (Natta et al. 2004). Brγ measurements showed that the circumstellar disk around HD 142666 is still active with an accretion rate of Ṁ = 1 × 10^-8   M_⊙   yr^-1 (Garcia-Lopez et al. 2006).

AS 205, also known as V866 Scorpii, is a member of the Upper Scorpius association, West from the ρ Ophiuc star forming region (Reipurth & Zinnecker 1993). As formerly observed by Herbig & Rao (1974), AS 205 has an infrared companion at a position angle of PA = 211° and at an angular distance of 1.32″, i.e., at a projected distance of 210   AU (Prato et al. 2003).

Observations in the I and NIR bands could spatially resolve both components with the northern component as the brighter source (Reipurth & Zinnecker 1993; Liu et al. 1996). Visual and NIR Speckle-interferometric observations (Koresko 2002) as well as spectrally highly resolving measurements (Eisner et al. 2005), have shown that the southern component is a close binary system (angular distance 8.5″, position angle PA = 101° ± 1°), as well. Both components of this system have similar brightnesses in the R and I bands and similar stellar properties (L_⋆ = 0.44   L_⊙ and 0.44   L_⊙; M_⋆ = 0.74   M_⊙ and 0.54   M_⊙; A_V = 3.9   mag and 3.4   mag, respectively; Eisner et al. 2005). Although the age of the entire system is still discussed, it is assumed that all the components have simultaneously formed by fragmentation from the same region of the molecular cloud. The northern and southern components show hints of accretion (Cohen & Kuhi 1979; Prato et al. 1997; Eisner et al. 2005). Johns-Krull et al. (2000) have derived an accretion rate of Ṁ = 6.7 × 10^-7   M_⊙   yr^-1 from the profile of the C IV line of the northern component. Considering the high activity and variability of the source which has been known for 30 years already, Welin (1976) assumed that AS 205 is a good candidate for future FU Ori variability outbursts.

© ESO, 2013