4. Optical follow-up observations

Medium-resolution spectra for the objects of our sample were obtained with the Intermediate Dispersion Spectrograph at the Cassegrain focus of the Isaac Newton Telescope in La Palma. The 500 mm camera, equipped with a TEK TK1024A CCD, was used in conjunction with the gratings R600R and R1200Y, giving a resolution of about 4200 and 8400, respectively. The observations were performed in October 1994, when both gratings were used, and in November 1995, when only the R1200Y was used. Exposure times ranged from 200 to 1200 seconds. Close to each stellar frame a wavelength calibration CuNe lamp was exposed; tungsten flat field exposure were taken both at the beginning and at the end of the night.

The CCD frames were reduced with the IRAF package. Each image was de-biased and flat fielded. The spectra were extracted with the IRAF task apall, which allows optimum extraction, cleaning from cosmic ray events, and background subtraction. Wavelength calibration was performed using the dispersion solution determined on the CuNe spectra by fitting an order two polynomial, with a rms of 0.03 Å for the R600R grating and 0.01 Å for the R1200Y grating.

Low-resolution spectra of additional objects were obtained at the European Southern Observatory (ESO) using the 1.52m telescope equipped with a Boller & Chivens spectrograph, in November 1995. A 900 grooves/mm (ESO # 5) grating and the CCD FORD 2048L of pixels were used. With this set-up a mean resolution of about 2.5 Å (FWHM) in the spectral range was achieved. The reduction of these spectra was carried out using the MIDAS package. Bias and dark subtraction was first performed on each frame. The 2-D frames were then divided by a mean flat-field and then calibrated in wavelength. The sky subtraction, the extraction of one dimensional spectra and the flux calibration using a mean response function, were finally performed.

Spectral types have been assigned using the library of stellar spectra by Jacoby et al. (1984), available in digital form. For each of our stars a first guess of the spectral type was given by visual comparison. Then, we performed an iterative comparison in the following way: each spectrum was first normalized to the continuum; the spectral type standard spectrum was then normalized and rebinned to the same resolution and spectral range as the problem star; an overplot of the two spectra allowed us to compare directly different spectral features and reject or accept the guessed spectral type. Finally, we assigned the spectral type of the standard which follows most closely the features of the problem star. Particular attention was given to features like CaI 6718 Å, Fe I blend 6495 Å and TiO bands. The line, in emission in most of our stars, was not used for the spectral classification. Except for the spectra obtained at ESO (which cover the 4700 to 6800 Å spectral range), all of our spectra cover a short spectral range (from 6300 to 6800 Å). Bearing this in mind, we estimate that our classification can be uncertain to about one or two sub-classes and 3 sub-classes for the stars earlier than about G5.

 

RXJ 0209.1-1536 2 09 06.70 -15 35 43.0 -3.6 0.7 13.0 -1.32 0.81

RXJ 0210.4-1308NE 2 10 25.84 -13 07 57.0 3.0 4.9 10.5 -2.29 0.76

RXJ 0212.3-1330 2 12 18.72 -13 30 42.1 17.6 -17.3 11.4 -2.01 0.65

RXJ 0215.0-1402 2 15 00.45 -14 01 31.9 13.8 31.9 15.1 -0.77 0.54

RXJ 0218.6-1004 2 18 39.54 -10 04 05.0 -12.3 6.3 11.8 -1.79 0.81

RXJ 0219.4-1321B 2 19 25.30 -13 21 06.6 9.6 -12.0 14.8 -0.81 0.65

RXJ 0219.7-1026 2 19 47.38 -10 25 39.9 -9.3 6.9 11.6 -1.50 0.70

RXJ 0220.4-1305 2 20 28.34 -13 05 23.9 0.5 -18.8 14.6 -0.75 0.27

RXJ 0223.3-1615NE 2 23 21.41 -16 14 20.9 -5.3 12.8 13.4 -1.51 0.86

RXJ 0229.5-1224 2 29 35.05 -12 24 08.8 13.0 -13.6 9.9: -2.74 0.54 HD 15526

RXJ 0237.3-0527 2 37 19.85 -05 26 54.1 4.6 7.6 13.3 -1.24 0.54

RXJ 0239.1-1028 2 39 08.72 -10 27 44.1 -0.6 2.7 13.2 -1.50 0.65

RXJ 0243.9-0850 2 43 52.29 -08 49 30.3 18.3 14.2 12.9 -1.53 0.59

RXJ 0248.3-1117 2 48 22.16 -11 17 12.3 25.8 6.4 12.0 -2.00 0.65

RXJ 0251.8-0203 2 51 48.47 -02 03 38.1 11.1 -8.9 12.7 -1.58 0.76

RXJ 0254.8-0709SE 2 54 52.43 -07 09 24.2 4.7 5.8 14.5 -0.78 0.59

RXJ 0255.8-0750S 2 55 52.63 -07 50 39.0 -3.4 -15.3 14.0 -1.06 0.81

RXJ 0309.1+0324N 3 09 09.86 03 23 44.4 25.7 5.6 10.2 -2.33 0.59

RXJ 0312.8-0414NW 3 12 50.43 -04 14 08.1 20.8 -18.4 9.9 -2.22 0.76

RXJ 0314.8-0406 3 14 50.70 -04 05 56.4 -14.6 -5.5 14.4 -1.16 0.70

RXJ 0317.9+0231 3 17 59.18 02 30 12.9 11.6 32.9 11.0 -2.26 0.70

RXJ 0319.3+0003 3 19 22.53 00 02 32.4 -0.2 17.6 9.2: -3.24 0.27 SAO 130417, (1)

RXJ 0324.4+0231 3 24 25.22 02 31 01.2 3.6 -7.7 12.4 -1.45 0.65

RXJ 0329.1+0118 3 29 08.01 01 18 05.3 -15.0 11.4 10.7 -2.52 0.65

RXJ 0330.7+0306N 3 30 43.45 03 05 47.9 12.4 2.6 10.9 -1.86 0.81

RXJ 0333.0+0354 3 33 01.54 03 53 38.4 3.0 14.9 13.3 -1.55 0.70

RXJ 0333.1+1036 3 33 11.62 10 35 56.3 -9.6 9.8 11.7 -1.84 0.65

RXJ 0336.0+0846 3 36 00.32 08 45 35.7 15.4 0.6 12.4 -1.94 0.76

RXJ 0338.1+1224 3 38 09.04 12 23 53.1 16.6 0.6 10.9 -2.55 0.65

RXJ 0338.3+1020 3 38 18.21 10 20 17.1 21.6 -6.2 11.0 -2.30 0.70

RXJ 0339.6+0624 3 39 40.57 06 24 43.1 13.5 -17.3 11.3 -2.38 0.70

RXJ 0340.3+1220 3 40 19.26 12 20 18.0 -1.4 -0.3 12.5 -1.36 0.76

RXJ 0340.5+0639 3 40 31.48 06 39 00.3 -15.4 11.8 13.2 -1.79 0.81

RXJ 0341.2+0453 3 41 14.30 04 53 25.4 3.2 -11.0 15.2 -0.17 0.70

RXJ 0341.2+0759 3 41 14.36 07 59 33.1 7.1 -3.7 10.7 -2.65 0.70

RXJ 0343.6+1039 3 43 40.51 10 39 14.0 -1.9 -9.3 10.2 -2.50 0.65

RXJ 0344.8+0359 3 44 53.15 03 59 30.9 9.0 5.6 12.3 -1.50 0.81

RXJ 0347.2+0933SW 3 47 14.25 09 32 53.0 21.5 -1.4 13.4 -1.24 0.65

RXJ 0347.9+0616 3 47 56.81 06 16 07.0 19.1 -4.8 11.0 -2.40 0.70

RXJ 0348.2+1109 3 48 16.50 11 08 41.0 -4.6 -0.8 10.1: -2.34 0.70 HD 23793 B, (2)

RXJ 0348.5+0832 3 48 31.42 08 31 37.5 15.9 -7.5 10.9 -2.04 0.76

RXJ 0349.4+1255N 3 49 27.85 12 54 41.4 -6.5 6.1 9.1: -2.83 0.65 BD+12 511

RXJ 0350.2+0849 3 50 12.91 08 49 34.0 -4.5 -6.1 12.1 -2.09 0.81

RXJ 0350.6+0454 3 50 41.72 04 53 44.7 -28.8 -3.4 15.2 -0.82 0.76

RXJ 0350.6+1033 3 50 40.80 10 32 51.1 -9.3 19.9 10.1 -2.70 0.59

RXJ 0351.4+0953W 3 51 26.30 09 53 37.0 2.6 -16.5 12.6 -1.23 0.65

RXJ 0351.8+0413 3 51 49.40 04 13 30.7 -16.5 -12.3 13.5 -1.51 0.81

RXJ 0352.4+1223 3 52 24.68 12 22 44.2 -4.2 -6.9 9.5: -2.93 0.59 BD+11 533

 

 

RXJ 0354.3+0535 3 54 21.28 05 35 40.9 -0.5 -14.2 10.1 -2.51 0.54

RXJ 0354.4+1204 3 54 25.15 12 04 07.9 -3.3 -14.9 11.2 -2.36 0.70

RXJ 0354.8+1232 3 54 50.70 12 32 06.4 4.9 10.7 12.9 -1.40 0.81

RXJ 0356.7+0943 3 56 45.51 09 43 39.4 -4.0 -13.2 13.3 -1.44 0.70

RXJ 0357.3+1258 3 57 21.34 12 58 17.3 3.8 3.6 10.9 -2.16 0.70

RXJ 0358.1+0932 3 58 12.62 09 32 21.6 -13.5 -2.1 12.2 -1.42 0.70

RXJ 0400.0+0730 4 00 01.14 07 30 10.4 -0.7 4.0 12.2 -1.86 0.65

RXJ 0400.1+0818N 4 00 09.37 08 18 19.3 6.6 4.0 9.9: -1.54 0.65 BD+07 582B, (3)

RXJ 0400.8+1116 4 00 53.92 11 15 27.8 -25.2 21.9 13.8 -1.07 0.70

RXJ 0402.5+0552 4 02 35.68 05 51 36.0 -18.0 14.5 10.9 -2.08 0.70

RXJ 0403.5+0837 4 03 29.69 08 37 14.2 35.6 4.7 12.6 -1.42 0.76

RXJ 0404.4+0519 4 04 28.48 05 18 43.7 -5.1 4.0 10.9 -2.02 0.81

RXJ 0405.5+0324 4 05 30.24 03 23 50.4 -2.1 6.5 11.5 -1.61 0.81

RXJ 0407.2+0113N 4 07 16.49 01 13 14.5 15.2 -4.3 10.5 -2.50 0.54

RXJ 0407.6+0638 4 07 37.26 06 38 45.2 9.5 -23.1 14.8 -0.56 0.54

RXJ 0408.6+1017 4 08 39.90 10 17 32.6 -13.5 -26.8 12.6 -1.84 0.65

RXJ 0408.8+1028 4 08 49.57 10 27 50.0 -3.8 -4.3 8.9: -2.08 0.70 HD 26172

RXJ 0409.8+1209 4 09 51.54 12 09 02.3 22.0 -7.6 12.0 -1.81 0.65 HD 286556

RXJ 0410.6+0608 4 10 39.66 06 08 38.9 -22.2 -19.8 12.9 -1.56 0.86

RXJ 0413.2+1028 4 13 14.66 10 28 01.1 -10.7 -14.7 14.9 -0.56 0.65

RXJ 0418.6+0143 4 18 39.27 01 42 10.5 13.5 29.9 12.3 -1.83 0.59

RXJ 0419.8+0214 4 19 49.92 02 13 43.5 -13.8 -11.3 14.6 -0.61 0.76

RXJ 0419.9+0231 4 19 59.60 02 30 30.6 -11.5 24.1 13.6 -0.54 0.76

RXJ 0422.9+0141 4 22 54.61 01 41 32.1 22.5 -17.7 12.3 -1.63 0.70

RXJ 0423.5+0955 4 23 30.28 09 54 30.0 10.6 13.8 11.6 -1.66 0.49

RXJ 0425.5+1210 4 25 35.30 12 10 00.0 -6.3 -0.5 10.4 -2.40 0.65 HD 286753

RXJ 0426.4+0957W 4 26 26.77 09 56 59.7 11.6 -3.4 12.0 -1.91 0.81

RXJ 0427.4+1039 4 27 30.29 10 38 48.9 -11.1 1.7 11.3 -2.05 0.65

RXJ 0427.5+0616 4 27 32.07 06 15 52.1 0.4 1.8 10.6 -1.80 0.76

RXJ 0427.8+0049 4 27 52.84 00 49 25.9 -5.5 3.3 9.0: -2.92 0.22 BD+00 760, (4)

RXJ 0429.9+0155 4 29 56.94 01 54 48.9 0.8 12.0 11.1 -2.19 0.70

RXJ 0433.7+0522 4 33 46.09 05 22 09.1 18.8 -16.6 15.3 -0.71 0.81

RXJ 0434.3+0226 4 34 19.51 02 26 26.1 5.8 2.1 13.3 -1.12 0.86

RXJ 0435.5+0455 4 35 31.56 04 55 32.3 -8.9 -12.6 9.7 -2.78 0.49

RXJ 0441.9+0537 4 41 57.64 05 36 34.3 0.3 7.3 10.2: -1.78 0.70 BD+05 706

RXJ 0442.3+0118 4 42 18.61 01 17 39.9 8.9 3.5 11.2 -2.03 0.70

RXJ 0442.5+0906 4 42 31.94 09 06 01.7 -16.5 10.1 10.6: -1.94 0.76 BD+08 742

RXJ 0442.6+1018 4 42 40.81 10 17 44.8 -3.6 3.3 8.2 -2.59 0.65

RXJ 0442.9+0400 4 42 54.69 04 00 11.7 9.6 1.7 10.9 -2.21 0.70

RXJ 0444.3+0941 4 44 20.21 09 41 06.8 1.5 0.3 8.6: -2.60 0.65 HD 287017

RXJ 0444.4+0725 4 44 27.16 07 24 59.8 -9.3 8.7 13.7 -1.22 0.65

RXJ 0444.7+0814 4 44 45.44 08 13 47.6 -20.1 4.5 11.8 -1.86 0.70

RXJ 0445.2+0729 4 45 13.18 07 29 17.7 -9.9 10.4 12.2 -1.97 0.81

RXJ 0445.3+0914 4 45 23.81 09 13 47.8 -4.9 -13.0 11.8 -2.15 0.65

RXJ 0445.5+1207 4 45 36.49 12 07 51.1 -7.4 -22.4 12.9 -1.74 0.76

RXJ 0448.0+0738 4 48 00.86 07 37 56.9 -5.6 -7.0 11.2 -1.40 0.70

RXJ 0450.0+0151 4 50 04.68 01 50 43.1 17.0 13.2 12.2 -1.63 0.86

RXJ 0451.6+0619 4 51 41.51 06 19 20.6 -12.4 -18.1 12.8 -1.73 0.86

RXJ 0459.9+1017 4 59 54.95 10 17 18.2 -12.6 0.9 14.4 -0.62 0.76

RXJ 0511.2+1031 5 11 15.98 10 30 36.0 -1.2 8.9 14.0 -1.02 0.86

RXJ 0511.9+1112 5 12 00.30 11 12 19.8 -9.5 -14.1 11.4 -2.21 0.65

RXJ 0512.0+1020 5 12 03.21 10 20 06.8 -7.5 5.3 11.3 -1.99 0.76

RXJ 0513.6+0955 5 13 40.44 09 54 50.7 -13.5 2.3 12.0 -2.08 0.65

 

RXJ 0516.3+1148 5 16 21.52 11 47 47.3 5.3 -3.2 12.4 -1.53 0.86

RXJ 0523.0+0934 5 23 04.65 09 34 01.0 -25.2 5.0 10.4 -2.64 0.76

RXJ 0523.5+1005 5 23 33.72 10 04 29.8 -1.5 -11.1 11.2 -1.81 0.76

RXJ 0523.9+1101 5 23 57.04 11 00 57.5 -26.4 15.9 10.8 -2.62 0.70

RXJ 0525.7+1205SE 5 25 47.21 12 04 10.2 0.6 36.3 14.1 -1.17 0.65

RXJ 0528.4+1213 5 28 25.74 12 12 36.1 -4.9 5.9 11.5 -1.77 0.81

RXJ 0528.5+1219 5 28 35.19 12 19 04.0 1.8 10.1 12.7 -1.77 0.70

RXJ 0528.9+1046 5 28 58.50 10 45 37.9 -7.9 -0.1 12.7 -1.71 0.76

RXJ 0529.3+1210 5 29 18.97 12 09 29.7 -4.6 3.6 12.9 -1.36 0.54

RXJ 0530.9+1227 5 30 57.23 12 27 26.8 27.3 0.4 10.7 -2.19 0.70

RXJ 0531.8+1218 5 31 47.77 12 18 08.1 16.4 12.8 12.1 -2.06 0.81

Remarks: (1) Not listed in the GSC; (2) HD 23793 B (F5V) and the early-type star HR 1174 (B3) are an optical pair with separation (Lindroos 1986); the later type star is more likely to be the true optical counterpart of the X-ray source (e.g. Schmitt et al. 1993); (3) Companion N is an unresolved binary itself; (4) Not listed in the GSC.

In Table 4 (click here), we present the results of our spectroscopic observations. We list all the counterparts observed (with names from Tables 2 (click here) and 3 (click here)), identify the telescope, i.e. the resolution and wavelength range used, give equivalent widths of the and LiI lines, and list the spectral types. In the lithium column, "no'' means that no lithium line has been detected above the noise. Where possible, upper limits have been estimated (but not reported here), resulting always lower than 0.1 Å. The typical error in the Li equivalent width is mÅ, mainly due to uncertainties in the location of the continuum.