Out of the 206 X-ray sources, 89 have one or several nearby (
arcsec) potential
optical counterparts (brighter than V=16 mag) in Simbad and/or GSC, including four
previously known PMS stars (namely CrAPMS 1, 2, 3, and TY CrA)
and four previously known older stars. In addition, there is one optically faint neutron
star (V=25.7 mag, see footnote 2) and three extra-galactic sources (see Table 3).
To identify a large fraction of the remaining 81 unidentified X-ray sources,
we performed low-resolution spectroscopy of 148 stars,
which are potential optical counterparts to 56 of those 81 X-ray sources.
No. | Optical position | ![]() |
V | ![]() |
ID | Remarks | |
Table 2 |
![]() |
![]() |
![]() |
mag |
![]() |
||
1 | 18:35:06.2 | -34:04:02.8 | 28 | 13.9 | -1.15 | ||
3 | 18:35:46.6 | -32:59:31.2 | 12 | 9.8 | -1.24 | p | globular cluster NGC 6652 |
8 | 18:36:39.5 | -34:51:25.0 | 16 | 13.0 | -1.45 | y | |
9 | 18:37:17.6 | -34:42:42.2 | 8 | 11.3 | -2.31 | n | |
11 | 18:38:20.2 | -35:23:37.2 | 5 | 12.2 | -2.26 | d | dKe star |
12 | 18:39:04.9 | -37:05:27.8 | 22 | 13.1 | -1.30 | n | |
13 | 18:39:05.3 | -37:26:21.8 | 16 | 10.9 | -2.35 | y | |
17 | 18:40:37.6 | -37:28:18.1 | 28 | 11.2 | -2.27 | d | dKe star |
19 | 18:40:53.3 | -35:46:44.6 | 22 | 14.5: | -0.84 | y | |
23 | 18:41:48.6 | -35:25:43.6 | 14 | 9.7 | -2.44 | y | |
27 | 18:42:58.0 | -35:32:42.9 | 10 | 12.2 | -1.73 | y | |
30 | 18:44:21.9 | -35:41:43.6 | 29 | 11.3 | -1.81 | y | |
31 | 18:44:31.1 | -37:23:34.3 | 26 | 13.1 | -1.13 | y | |
35 | 18:45:09.3 | -33:24:03.9 | 26 | 12.3 | -2.18 | n | |
36 | 18:45:34.8 | -37:50:19.6 | 7 | 9.2 | -2.45 | y | HD 173148, G5 V, PM=[4.7,-32.0] |
38 | 18:46:43.9 | -36:04:52.2 | 13 | 12.0 | -2.14 | IRAS 18433-3608 | |
39 | 18:46:45.6 | -36:36:18.1 | 8 | 10.3 | -2.45 | y | |
42 | 18:47:14.0 | -37:09:48.3 | 6 | 12.1 | -2.09 | ||
45 | 18:47:44.6 | -40:24:22.2 | 34 | 5.2 | -4.18 | n | ![]() |
48 | 18:48:35.8 | -34:58:20.4 | 38 | 13.3 | -1.73 | ||
53 | 18:52:17.3 | -37:00:12.0 | 14 | 13.9 | -0.98 | y | IRAS 18489-3703 |
54 | 18:52:24.8 | -37:30:35.6 | 10 | 12.5 | -1.57 | d | dMe star |
55 | 18:53:06.0 | -36:10:22.8 | 28 | 9.6 | -2.47 | y | HD 174656, G6 IV, PM=[-1.2,-34.0] |
59 | 18:54:29.0 | -37:39:04.5 | 26 | 11.8 | -2.23 | ||
63 | 18:56:37.3 | -37:54:26.9 | 26 | 25.7 | +4.77 | p | neutron star RXJ1856.5-3754 |
64 | 18:56:44.0 | -35:45:31.9 | 10 | 13.0 | -2.08 | y | |
65 | 18:56:49.2 | -40:21:07.0 | 34 | 14.9 | -0.92 | ||
68 | 18:57:34.1 | -37:32:32.3 | 25 | 15.0: | -1.02 | y | |
73 | 18:58:43.4 | -37:06:26.5 | 7 | 4.9 | -4.86 | p | ![]() |
77 | 19:00:49.5 | -34:52:49.2 | 33 | 8.4 | -3.61 | HD 176247, G1 V, PM=[23.4,-24.0] | |
80 | 19:01:09.5 | -36:47:51.7 | 11 | 12.7 | -1.97 | y | VSS VIII-27 |
81 | 19:01:26.7 | -40:22:34.0 | 24 | 13.6 | -1.37 | n | |
82 | 19:01:28.7 | -34:22:35.5 | 25 | 8.2 | -3.29 | y | HD 176383, F5 V, PM=[9.9,-46.8] |
83 | 19:01:34.9 | -37:00:55.8 | 7 | 11.3 | -2.03 | p | CrAPMS 1, K1 IV, wTTS |
84 | 19:01:40.8 | -36:52:34.2 | 30 | 9.5 | -2.79 | p | TY CrA, Herbig Ae/Be PMS star |
85 | 19:01:40.5 | -36:44:31.9 | 27 | 13.0: | -1.56 | y | VSS VIII-26 |
87 | 19:02:01.9 | -37:07:43.2 | 14 | 10.4 | -2.57 | p | CrAPMS 2, G5 IV, wTTS, PM=[0.0,-33.0] |
89 | 19:02:22.1 | -36:55:40.8 | 2 | 13.8 | -1.60 | p | CrAPMS 3, K2 IV, wTTS |
90 | 19:02:22.7 | -39:22:21.9 | 11 | 14.2 | -1.46 | ||
91 | 19:02:25.9 | -36:17:39.0 | 32 | e | galaxy CGMW 4-4634 | ||
93 | 19:02:43.6 | -34:19:00.4 | 35 | 13.7 | -1.75 | ||
95 | 19:03:00.6 | -40:09:16.8 | 33 | 13.4 | -1.35 | n | |
97 | 19:03:58.4 | -38:04:01.0 | 70 | 13.1 | -2.04 | z | |
102 | 19:04:38.8 | -40:48:15.4 | 29 | 11.4 | -2.39 | ||
108 | 19:06:24.8 | -37:03:41.7 | 7 | 5.0 | -5.37 | n | ![]() |
110 | 19:06:52.5 | -37:48:37.6 | 16 | 6.2 | -5.26 | n | HR 7232, G5 IV, d=17 pc |
111 | 19:07:50.4 | -39:23:32.2 | 9 | 14.2 | -0.84 | z |
No. | Optical position | ![]() |
V | ![]() |
ID | Remarks | |
![]() |
![]() |
![]() |
mag |
![]() |
|||
112 | 19:09:39.8 | -39:49:38.4 | 16 | 6.5 | -4.19 | n | HR 7255, K1 III, PM=[-4.9,-21.7], d=107 pc |
114 | 19:10:47.8 | -38:54:34.7 | 19 | 7.6 | -3.92 | n | HD 178558, F5 V, PM=[26.7,-33.5], d=61 pc |
115 | 19:11:34.7 | -34:35:09.1 | 10 | 10.7 | -2.37 | d | dKe star |
116 | 19:11:47.1 | -36:41:42.9 | 7 | 13.5 | -2.09 | d | dMe star |
117 | 19:12:35.8 | -34:31:31.8 | 14 | 11.4 | -2.38 | n | |
119 | 19:13:10.5 | -36:21:46.0 | 20 | 12.9 | -1.98 | ||
122 | 19:13:44.8 | -33:04:06.6 | 20 | 14.1 | -1.23 | ||
123 | 19:13:51.8 | -33:48:21.4 | 38 | 14.6 | -1.13 | ||
127 | 19:15:32.5 | -35:28:49.2 | 23 | 14.4 | -1.23 | ||
128 | 19:15:46.7 | -33:22:06.3 | 7 | 12.3 | -2.17 | z | see (1) |
130 | 19:16:13.8 | -35:48:11.7 | 11 | 14.0 | -1.28 | d | dKe star |
135 | 19:17:23.8 | -37:56:50.4 | 8 | 9.9 | -2.37 | y | SAO 211129, K2, PM=[3.5,-31.0] |
138 | 19:18:12.4 | -38:23:04.2 | 5 | 8.6 | -2.28 | n | HD 180445, G8 V, PM=[99.5,-93.0], d=42 pc |
139 | 19:18:27.0 | -39:13:01.4 | 37 | 13.8 | -1.64 | ||
141 | 19:19:31.0 | -36:39:30.7 | 12 | 7.2 | -4.80 | n | HD 180802, F7 V, PM=[36.4,-95.4], d=49 pc |
142 | 19:19:54.7 | -39:25:10.1 | 13 | 9.2 | -3.34 | n | HD 180863, G8/K0 III, PM=[10.4,-126.0] |
145 | 19:21:01.0 | -33:20:28.7 | 34 | 14.1 | -1.38 | ||
147 | 19:21:29.7 | -34:59:00.6 | 11 | 6.5 | -3.32 | z | HR 7330, G1.5 V, d=21 pc, see (2) |
151 | 19:23:20.0 | -36:58:31.0 | 16 | 11.0 | -2.83 | ||
154 | 19:23:53.0 | -40:36:56.5 | 10 | 4.0 | -5.05 | p | ![]() |
155 | 19:24:07.5 | -33:33:30.0 | 36 | 15.6 | -0.81 | ||
158 | 19:24:34.9 | -34:42:37.9 | 11 | 15.3 | -0.97 | d | dMe star |
165 | 19:27:26.7 | -38:46:39.4 | 32 | 15.6 | -0.51 | n | |
166 | 19:27:56.6 | -39:54:39.4 | 30 | 13.1 | -2.66 | ||
167 | 19:28:05.5 | -40:50:04.1 | 7 | 8.2 | -3.31 | p | HD 182776, K2.5 III, RS CVn-type, d=240 pc |
169 | 19:28:12.4 | -39:14:56.5 | 20 | 15.3 | -1.24 | ||
171 | 19:28:31.9 | -35:07:58.8 | 3 | 8.7 | -2.60 | z | HD 182928, G5 V, PM=[-16.3,-14.4], d=234 pc, see (1) |
172 | 19:28:48.7 | -36:46:19.5 | 35 | 12.5 | -2.01 | n | |
174 | 19:29:13.1 | -40:55:15.0 | 34 | 13.7 | -2.47 | n | |
175 | 19:29:35.0 | -40:18:39.2 | 22 | 12.9 | -1.48 | z | IRAS 19261-4024, see (1) |
176 | 19:29:51.1 | -37:02:16.7 | 21 | 9.1 | -3.74 | n | HD 183198, G6 V, PM=[-22.2,-14.7], d=46 pc |
177 | 19:29:57.8 | -33:38:16.6 | 5 | 13.1 | -1.76 | ||
178 | 19:30:01.6 | -33:02:43.1 | 22 | 12.6 | -2.73 | ||
179 | 19:30:38.3 | -35:26:21.8 | 36 | 13.4 | -1.54 | n | |
181 | 19:31:22.9 | -40:08:19.8 | 37 | 12.2 | -2.40 | n | |
183 | 19:31:38.7 | -33:54:43.2 | 16 | 17.0 | +0.56 | e | galaxy PKS 1928-340 |
187 | 19:32:43.8 | -34:32:14.4 | 10 | 14.1 | -1.52 | n | |
189 | 19:32:54.1 | -35:54:33.7 | 25 | 14.9 | -1.28 | ||
190 | 19:33:17.8 | -33:37:43.0 | 14 | 15.4 | -0.93 | n | |
191 | 19:33:19.6 | -38:12:13.6 | 19 | 12.0: | -2.26 | z | |
193 | 19:33:40.4 | -34:53:32.0 | 15 | 12.5 | -1.92 | ||
195 | 19:34:32.6 | -36:21:11.6 | 31 | 13.4 | -1.80 | z | |
197 | 19:34:46.6 | -38:05:15.2 | 9 | 8.9 | -3.03 | n | HD 184189, M2 III, 19
![]() |
199 | 19:36:01.5 | -33:25:42.9 | 31 | 14.8 | -1.38 | ||
200 | 19:36:04.3 | -40:02:58.6 | 37 | 12.6 | -2.27 | z | |
202 | 19:37:16.3 | -39:58:01.4 | 56 | 19.0 | 0.80 | e | quasar PKS 1933-400 |
Notes:
(1) Maybe weak lithium (or noise), complex H,
maybe double-lined,
could be ZAMS, RS CVn-type, dKe/dMe, or a cool Algol.
(2) Our detection of weak lithium with
(Li)
(Ca)
confirms the classification of HR 7330 as member of the
200 Myr
old nearby Castor moving group by Barrado y Navascues (1998).
Low-dispersion spectra were taken with the Boller & Chivens spectrograph of the
ESO 1.5 m telescope on La Silla in twelve nights, namely 1995 July 16/17 to 21/22
and 1996 July 20/21 to 25/26. The wavelength range is 4500 to 6850 Å and
the spectral resolution is Å. For technical details and data
reduction, we refer to the relevant part of Sect. 2.2 in Walter et al. (1997).
In addition to those potential RASS source counterparts, we also observed
a number of previously known or suspected young stars in CrA, because their lithium
line strength was not known, see Table 1 for those data;
most of these spectra were taken with the Boller & Chivens spectrograph.
However, the stars HBC 673, 675, 677, and CrAPMS 3/c were observed with
the ESO-3.5 m-NTT.
Here, we observed in the red medium-dispersion mode (EMMI red arm,
CCD # 36, grating 6) at a resolution of 5500 in the wavelength range
from 6160 to 7740 Å. While we could not detect lithium in HBC 673 and 675,
we confirmed HBC 677 to be a cTTS and CrAPMS 3/c to be a wTTS (see Table 1).
![]() |
Figure 1:
Spatial distribution of RASS sources in CrA.
We show all 206 RASS sources as dots superimposed on
three contour levels of the IRAS 100
![]() ![]() |
For most of the RASS counterparts with detected lithium (in low-resolution spectra),
we then took high-resolution spectra to confirm their youth.
The high dispersion spectra were obtained with the CTIO 4m telescope and
echelle spectrograph on 14 to 17 July 1998.
We used the 226-3 cross disperser and the 31.6 l/mm
echelle with the red optics. We used the SITe 2K #6 CCD detector, at a gain
of 5, corresponding to about 1 e- per ADU and a read noise of about
3 e-. We used the GG385 filter for order sorting. We used a 150 m
(1 arcsec) slit and decker #9 (3.3 arcsec) for the stellar observations.
The seeing was generally 1 to 1.5 arcsec, and there were some clouds on 3 of the
4 nights. The spectra cover the range from roughly 4400 Å through 7500 Å at
a resolution of 25000.
We obtained projector flat images to flatten the spectra. A Th-Ar
comparison source was observed before and after each telescope slew.
Each stellar observation was made in three parts to facilitate cosmic ray
removal. Initial reductions were undertaken at CTIO, using the IRAF DOECSLIT
package. We corrected for bias, extracted the orders, divided by the flats,
and solved for the
dispersion. The data were rebinned to a linear wavelength scale in each order.
We removed the global background (the scattered light
correction) but did not attempt to subtract the local background.
The data were further reduced using IDL.
We flattened the spectra in each order to remove any residual curvature
left from the original flat division. We trimmed the ends
of the orders.
We then filtered the three individual spectra of each object
to remove cosmic rays, and coadded the spectra.
We determine radial velocities by cross-correlating the spectra against
the sky spectra. We expect an internal precision of about 1 km s-1, except
for the targets with poorer S/N.
Copyright The European Southern Observatory (ESO)