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4 Results of the spectroscopy

Stars which fullfill all the following conditions (according to their high-resolution spectra, if available, otherwise we use the low-resolution spectra) are classified as new PMS stars, i.e. appear as such in Table 4:

All these stars are classified as young stars (letter y in Col. ID in Table 3).

Table 4 lists for all newly discovered TTS their official designation, PMS type (i.e. whether wTTS or cTTS), the spectral type, thje H$\alpha $and lithium equivalent widths, the projected rotational velocity, the radial velocity, the X-ray luminosity, and some remarks, e.g. on binarity.

All stars with a detected lithium line, which is weaker than 0.1 Å, and all F-, G-, and K-type stars with a detected lithium line, which is weaker than the Ca 6718 Å line, are classified as ZAMS stars (letter z in Col. ID in Table 3). Stars without detectable lithium, but H$\alpha $ emission are classified as dKe or dMe stars (letter d in Col. ID in Table 3).


 \begin{figure}
\par\includegraphics[angle=-90,width=15cm,clip]{ds1875_f5.ps}
\end{figure} Figure 5: Low-resolution optical spectra of previously suspected young stars. Spectra obtained at the ESO-3.5 m-NTT of stars suspected to be young prior to the ROSAT mission, namely CrAPMS 3/c (new wTTS), MR81 H$\alpha $ 2 (new cTTS), Kn anon 2, MR81 H$\alpha $ 10 (no lithium, i.e. both non-TTS), and for comparison we also show CrAPMS 3 (wTTS). The dotted line shows the location of the lithium 6708 Å line

In Table 3, we list the nature of the newly identified X-ray sources. Among the 56 X-ray sources for which we performed low-resolution spectroscopy of potential optical counterparts, we identified 19 new pre-main sequence stars, nine new zero-age main-sequence stars, and seven new dKe/dMe stars. Two of the new PMS stars have $W_{\lambda}({\rm H\alpha})~\ge~10$ Å, i.e. are classical TTS, and 17 are weak-line TTS, four of which form two visual pairs, which are spatially unresolved with ROSAT, i.e. one pair corresponds to one X-ray source each.

The spatial distribution of the CrA RASS sources and TTS is shown in Fig. 1. While all the previously known TTS in CrA including those found by EO cluster on the main dark cloud, the new ROSAT TTS are more widely distributed. In particular, they are almost all located west of the cloud. The two new cTTS appear to be situated in two small cloud-lets, where they most certainly have formed. The new wTTS may have also formed in such small cloud-lets outside the current borders of the CrA cloud, and those small cloud-lets may well have dispersed since they formed stars, similar to some seemingly off-cloud wTTS near Cha I (Alcalá et al. 1995; Mizuno et al. 1998), see below.

Finding charts for the new PMS stars can be found in Fig. 2, the optical spectra for our new TTS are shown in Fig. 3 (high-resolution spectra from CTIO, if available) and Fig. 4 (low-resolution spectra from ESO-1.52 m for the other new TTS). In Fig. 5, we also show the four spectra of previously suspected young stars obtained at the ESO-3.5 m-NTT.

As seen in Fig. 6, all new TTS show more lithium than ZAMS stars of the same spectral type, i.e. are younger than ZAMS; hence, they are pre-MS stars. There are some new M-type TTS in CrA, which have depleted more than half of their primordial lithium (lower right of Fig. 6). As for similar M-type TTS in Taurus, these objects could be classified as post-TTS.


   
Table 4: New T Tauri stars in CrA. We list object number and ROSAT designation as in Tables 2 and 3, pre-main sequence type, spectral type, H$\alpha $ and lithium equivalent widths (negative when in emission) from high-resolution spectra (unless given with colons), rotational velocity, helio-centric radial velocity, X-ray luminosity (in 130 pc distance, calculated from counts, exposure and ECF listed in Table 2, 65 pc for TTS No. 82), and some remarks
No. Object PMS Spec $W_{\lambda }$(H$\alpha $) $W_{\lambda }$(Li) $v \cdot \sin i$ RadVel $\log~L_{\rm X}$ Remarks
Table 2 designation type type [Å] [Å] $[{\rm km~s^{-1}}]$ $[{\rm km~s^{-1}}]$ $[{\rm erg~s^{-1}}]$  
8 RXJ1836.6-3451 wTTS M0 -2.4 0.54 34.1 -1.6 30.27  
13 RXJ1839.0-3726 wTTS K1 +0.1 0.34 17.8 -4.8 30.24 (1)
19 RXJ1840.8-3547 wTTS M4 -6.9: 0.36:     29.82  
23 RXJ1841.8-3525 wTTS G7 +1.0 0.25 30.0 -3.1 30.62 (2)
27 RXJ1842.9-3532 cTTS K2 -30.7 0.38 23.7 -1.2 30.34 (3)
30 RXJ1844.3-3541 wTTS K5 -0.4 0.41 38.8 -4.9 30.60  
31 RXJ1844.5-3723 wTTS M0 -5.3: 0.52:     30.59  
36 RXJ1845.5-3750 wTTS G8 +0.8 0.24 54.6 -1.3 30.81 HD 173148 (1)
39 RXJ1846.7-3636 NE wTTS K6 -0.6 0.47 30.8 -2.5 30.38 8'' pair (4)
39 RXJ1846.7-3636 SW wTTS K7 -0.2 0.43 17.5 -2.6 30.38 8'' pair (4)
53 RXJ1852.3-3700 cTTS K3 -33.8 0.51 21.8 0.0 30.41 IRAS 18489-3703 (5)
55 RXJ1853.1-3609 wTTS K2 +1.4: 0.39:     30.60 HD 174656
64 RXJ1856.6-3545 wTTS M2 -1.6: 0.25:     29.78  
68 RXJ1857.5-3732 E wTTS M5 -3.4 0.23 28.7 -3.1 29.93 close binary (4)
68 RXJ1857.5-3732 W wTTS M6 -4.7 0.42 11.9 -2.9 29.93 close binary (4)
80 RXJ1901.1-3648 wTTS K4 +0.1: 0.44:     29.88 VSS VIII-27
82 RXJ1901.4-3422 wTTS F7 +2.2 0.09 57.6 -3.3 29.77 HD 176383 (2)
85 RXJ1901.6-3644 wTTS M0 -2.3: 0.54:     30.18 VSS VIII-26
135 RXJ1917.4-3756 wTTS K2 -0.9: 0.48:     30.61 SAO 211129

Notes: (1) Complex H$\alpha $ profile. (2) Given the relatively early spectral type and relatively small lithium strength, this star could be either pre- or zero-age MS stars (see also Sect. 6.3). Its Hipparcos distance is 65 pc, $L_{\rm X}$ given for 65 pc. (3) Also observed with low resolution in 1995 and twice in 1996, when $W_{\lambda}({\rm H\alpha})$ varied from -53.6 Å to -88.7 Å from night to night. Double-peaked ${\rm H \alpha}$ emission, also HeI and [OII] emission. (4) Visual pair; position given in Table 3 is for the primary, i.e. the slightly brighter star; not resolved spatially with ROSAT (the combined $L_{\rm X}$ is given). (5) Observed once in 1995 with low resolution and about the same H$\alpha $ as given above for high-resolution spectrum, and five times with low resolution in 1996 with $W_{\lambda}({\rm H\alpha})$ from -5.22 Å to -8.97 Å.



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