Astron. Astrophys. 349, 475-484 (1999)

3. The EC95/Ser-X3 region

The region around SVS4 contains a number of interesting radio sources. [For a detailed discussion see for example Curiel, 1995 or Rodríguez et al. 1989]. Our low-resolution D-array map is shown in Fig. 1. The positions of a number of IR sources from Eiroa & Casali (1992) have been labelled. The position of Ser X3 is also shown.

Fig. 1. D-array map of the SVS4 cluster, including EC92 and EC95. The positions of the IR sources (triangles) are taken from Eiroa & Casali (1992). These sources have been labelled with the numbers from Table 1 of Eiroa & Casali (1992). The position of the X-ray source Ser-X3 is marked by a cross, with size 10" corresponding to the positional error given by P98. The position of EC95 is marked with a star (close to the position of the cross centre). The triangle just above this is EC92. Two other possible radio counterparts are seen, corresponding to EC117 and EC90.

A close-up view of S68-2 is provided by the A array 4.9GHz map from the 20th July 1995 (Fig. 2). The correspondence between Ser-X3 and S68-2 is clear. A clear identification can also be made between the S68-2 and the IR object EC95. Ser-X3 also correlates well with the position of EC95, as noted by P98. The coincidence of the radio source, X-ray source and IR source provides a strong case that all three detections originate for the same system. We henceforth refer to this object as EC95. We note here as an aside that a set of positions given in an earlier paper by Eiroa & Casali (1989) place the nearby IR source EC92 at a position coincident with the radio source. An earlier paper by Gómez de Castro et al. (1988), from which Eiroa & Casali (1989) obtained their positions, gives a position of EC95 and EC92 consistent with the later Eiroa & Casali (1992) paper. We conclude that the Eiroa & Casali (1992) positions as shown in Fig. 1 are correct, and that the earlier Eiroa & Casali (1989) positions are discrepant, probably because the positions of the sources can depend on the wavelength of the obserations (Gómez de Castro et al. observed in the I band, whilst Eiroa & Casali (1989) observed in the J, H and K bands).

Fig. 2. A-array map of the immediate neighbourhood of S68-2 (contours). Contour levels are 3, 6, 10, 15, 20 and 30 times the RMS background (5Jy). The position of the X-ray source Ser-X3 is marked by the cross. The cross is 10" from one side to the other, representing the quoted positional error of P98. The positions of infrared sources from Eiroa & Casali (1992) are also shown as circles whose diameters are 2".

3.1. Properties of the radio source associated with EC95

The radio fluxes for EC95 measured from our maps are shown in Table 1. Also shown are the derived radio luminosities, for a distance of 310 pc (de Lara et al. 1991). From the simultaneous 4.9 and 8.4 GHz data taken on 20/07/95, we can deduce that the radio emission has a falling spectrum, with spectral index . The source is detected at all three dates, suggesting that the radio emission is stable, and if associated with a corona, quiescent. No significant variation is seen between the radio brightness measured on the 1st May 1995 and that measured on the 20th July, a period of approximately two-and-a-half months. The 8.4 GHz flux has varied by about 20% between 1993 and 1995, but again this is not significant. We searched for short time scale activity of S68-2 by subtracting the other sources in the field from the visibility data, and then examining the source flux as a function of time. We found no evidence of variability on time scales of minutes to hours for any of the data sets. No evidence of circular polarisation was found. We place an upper limit on the percentage circular polarisation of based on the measured RMS of 0.03 mJy.

© European Southern Observatory (ESO) 1999

Online publication: September 2, 1999
helpdesk.link@springer.de