3 General results

3.1 HAeBe candidates detected as spectroscopic binaries

Table 2 presents the 13 binary systems detected among our main sample, i.e. the HAeBe candidates from Table 1 of the catalogue of Thé et al. (1994).

  

Table 2: HAeBe candidates detected as spectroscopic binaries

$^{\mathrm{a}}$ Bouvier et al. 1998; $^{\mathrm{b}}$ Leinert et al. 1997b; $^{\mathrm{c}}$ Pirzkal et al. 1997; $^{\mathrm{d}}$ Bernacca et al. 1993; $^{\mathrm{e}}$ Böhm & Catala 1995; $^{\mathrm{f}}$ Finkenzeller 1985.

A first group of 6 stars in Table 2 were identified as spectroscopic binaries thanks to the detection of the Li I 6708Å absorption line. This indicates the presence of a T Tauri companion. Their spectra are shown in Fig. 1.

  

Figure 1: HAeBe candidates identified as binaries thanks to the detection of Li I 6708Å line, attributed to a cooler companion. Laboratory positions of He I 6678.154, Li I 6707.800 and Ca I 6717.681Å lines are shown with doted lines

Based on stellar models obtained with ATLAS9 (Kurucz 1993) and with solar metallicity, we computed synthetic spectra with SYNSPEC (Hubeny et al. 1994) for various spectral type (B0, B5, A0, A5, F0, F5, G5 and K5). The spectra are shown in Fig. 2 in the Li I 6708Å line region (the rotational velocity for each spectrum is $V_\mathrm{rot}=50\,$$\mathrm{km\,s}^{-1}$). The Li I 6708Å line, very weak, is not seen in these models (see Gerbaldi et al. 1995; King et al. 1997 for a detailed analysis of the synthetic spectrum of the Li I line in normal in A, F and solar type stars).

  

Figure 2: Kurucz models for solar metallicity stars of various spectral types ($V_\mathrm{rot}=50\,$$\mathrm{km\,s}^{-1}$) in the Li I 6708Å region

Note: even if such synthetic spectra are only valid for Main Sequence stars, they help us identifying some interesting features in our HAeBe spectra. Indeed, in addition to the Li I 6708Å line, other absorption lines were found to be indicator of a T Tauri companion. Noticeably, we see in Fig. 2 that the absorption feature at 6678Å is firstly identified as the Fe I 6677.989Å line in late-type stars, and then as the He I 6678.154Å line when the stellar temperature increases towards earlier-type stars. The Ca I 6717.681Å line is seen in late-type stars but not in hotter stars. Thus, the presence in a HAeBe spectrum of the Fe I 6678 and Ca I 6718Å lines, even if harder to detect that the Li I line, are other features that sign the existence of a cooler companion (see the typical case of HK Ori in Fig. 1).

Figure 3 shows the Li I 6103.65Å line region for the HAeBe stars with positive Li I 6708Å line detection.

  

Figure 3: Ca I lines of HAeBe candidates identified as binaries with positive Li I detection (laboratory positions are shown with doted lines)

No evidence of Li I 6104Å absorption is seen, due to a blend with stronger Fe I and Ca I lines (see also Dunkin et al. 1997). The metallic lines Ca I 6102.723 and 6122.217Å are absent in spectra of A/B type stars (as shown is the synthetic spectra in Fig. 4), but their presence in our HAeBe spectra (Fig. 3) are also an evidence for a second lower-mass component.

  

Figure 4: Kurucz models for solar metallicity stars of various spectral types ($V_\mathrm{rot}=50\,$$\mathrm{km\,s}^{-1}$) in the Ca I 6103Å region

The second group in Table 2 is composed of 7 stars for which strong evidences of radial velocity variations have been recorded. If a radial velocity curve and an orbital period could be proposed from our observations, the star is indicated as SB1 for single-lined spectroscopic binary. Figures 5 to 13 show the spectra of stars with radial velocity variations; velocity measurements are gathered in Table 3. For two stars (HD 53367 and AS 442), tentative radial velocity curves and orbital solutions have been obtained using a modified version of the program from Corporon et al. (1996).

  

Figure 5: Spectra of T Ori in the region of He I 5875.621, Na I 5889.951 and 5895.924Å (doted lines show their laboratory position) at three different JDs (Julian Day). Radial velocity variations are present in the broad photospheric He I lines and Na I lines, as well as in the He I emission feature. Note the strong interstellar Na I absorption lines indicated (IS)

  

Table 3: HAeBe candidates detected as spectroscopic binaries, through radial velocity variability. Errors are 5$\mathrm{km\,s}^{-1}$ for HD 53367, MWC 300, AS 442, MWC 361, and 10$\mathrm{km\,s}^{-1}$ for T Ori, MWC 1080. A symbol "$^{\star}$'' indicates a line with emission

 

Table 3: continued

 

Table 3: continued

  

Figure 6: He I 6678Å line of HD 53367 at various JDs with radial velocity variations

  

Figure 7: Heliocentric radial velocity versus Julian Day for HD 53367 showing the temporal spread of our observations. Error bars on the individual points are 5$\mathrm{km\,s}^{-1}$

  

Figure 8: Velocity curve for HD 53367. Error bars on the individual points are 5$\mathrm{km\,s}^{-1}$, parameters for the proposed solution are overplotted

  

Figure 9: Spectra of MWC 300 in the region of He I 5875.621, Na I 5889.951 and 5895.924Å (doted lines show their laboratory position) at six different JDs. Radial velocity variations are present in the broad photospheric He I and Na I lines

  

Figure 10: Si II 6347.109 and 6371.37Å doublet lines in AS 442 at two different JDs. The division of both spectra figures the radial velocity variation of the doublet lines due to orbital motion

  

Figure 11: Same as Fig. 8 for AS 442

  

Figure 12: Radial velocity variations of the MWC 361 He I 6678Å line

  

Figure 13: Spectra of MWC 1080 in the region of He I 5875.621Å (doted lines show its laboratory position) at four different JDs. Radial velocity variations are present in the very broad photospheric He I lines. Strong interstellar Na I absorption lines are indicated (IS)

For those stars known to be members of visual binary systems, we give in the last column of Table 2 their separation $\rho_\mathrm{vis}$. For the visual pairs showing radial velocity variations, this separation $\rho_\mathrm{vis}$ is probably not related to the spectroscopic binary separation $\rho_\mathrm{spec}\,<\,\rho_\mathrm{vis}$: a third component is likely involved in those systems, making them hierarchical multiple systems. Each star is discussed in details in Sect. 4.

3.2 Detected binaries among T2-T5 sample

Table 4 gives the binary systems spectroscopically detected among HAeBe candidates from Tables 2 to 5 of the catalogue of Thé et al. (1994). Note that MWC 623 spectrum in the Li I 6708Å region, already published in Zickgraf & Stahl (1989), is not presented here.

  

Table 4: Detected spectroscopic binaries among T2-T5 sample

Figures 14 to 16 present the spectra for the spectroscopic binaries V361 Ori and HD 199603 and a preliminary velocity curve for the spectroscopic binary V361 Ori.

  

Figure 14: Same as Fig. 12 for V361 Ori

  

Figure 15: Same as Fig. 8 for V361 Ori. Star symbols represent overplotted data from Abt et al. (1991)

  

Figure 16: H$\alpha$ 6563Å line of HD 199603 at various JDs. Variations in radial velocity are seen. Narrow absorption lines are due to atmospheric H2O

3.3 HAeBe candidates undetected as spectroscopic binaries

Table 5 reports all the negative results for Li I line or radial velocity variations. Some stars with insufficient data to detect orbital motion are marked with "-" in the corresponding column.

  

Figure 17: HAeBe without Li I 6708Å line detection

  

Table 5: HAeBe candidates undetected as spectroscopic binary. ($v\!\sin \!i\,$references in Table 2)

Figures 17 and 18 show the Li I 6708 and Ca I 6103Å regions for some HAeBe candidates (to be compared with Figs. 1 and 3 which show binary stars). Figure 19 shows the He I 6678Å line of GU CMa with strong variability.

  

Figure 18: HAeBe (without Li I 6708Å line) around Ca I 6103 and 6122Å

  

Figure 19: He I 6678Å line of GU CMa at various JDs. Variations in radial velocity and intensity are observed

3.4 Undetected spectroscopic binaries among T2-T5 sample

Table 6 reports all the negative results for Li I search or radial velocity variations searches for the T2-T5 sample.

  

Table 6: Undetected spectroscopic binaries in the T2-T5 sample

$^{\mathrm{a}}$ This object (= HER 4636) is a visual binary (Chelli et al. 1995) with separation $\rho_\mathrm{vis}=4\hbox{$^{\prime\prime}$}$;individual components were observed spectroscopically and remarks apply for each star.

3.5 Some stars misclassified as HAeBe candidates or doubtful cases

Table 7 presents some stars that, according to the presently available spectra, are very unlikely to be HAeBe candidates.

  

Table 7: Stars rejected as HAeBe or doubtful case