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Astron. Astrophys. 325, 383-390 (1997)

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4. Results

[FORMULA] 3.6 cm

Fig. 1 shows that at [FORMULA] 3.6 cm the inner part of the jet in 1038+528 A seems to curve more towards the NE in 1983.4 than in 1981.2. In the 1990.5 map this part of the jet appears oriented nearer to the North. The maps of 1038+528 B at epochs 1981.2 and 1983.4 do not reveal any significant changes in the structure of the source at the resolution of our maps. However, for 1990.5 both the map and the parameters listed in Table 1, show changes in the structure compared to those for the two previous epochs: the distance between the two components has increased by [FORMULA] as, whereas the flux density of the eastmost component has decreased by [FORMULA] since 1981.2.

The astrometric analysis of the 1981.2 and 1983.4 VLBI observations of this pair of radio sources is presented elsewhere (MES 1994). We present here the analysis of the June 1990 observations. Fig. 3 shows the evolution of the angular separation over a decade, expressed as the change in position of the reference point in quasar A with respect to that in B, and taking as the origin of coordinates the relative position in 1981.2. The position in 1983.4, with respect to that in 1981.2, corresponds to a vector of magnitude [FORMULA] µas, in the NW direction (P.A. [FORMULA]), and the corresponding relative position in 1990.5 to a vector of magnitude [FORMULA] [FORMULA] as in the NW direction (P.A. [FORMULA]). Table 2 lists the separations between A and B for all three epochs. The error bars in Fig. 3 and Table 2 follow from the error analysis in Sect. 5.


Table 2. Top: Relative separations between quasars A and B, in 1981.2, 1983.4, and 1990.5 at [FORMULA] 3.6 cm derived from the astrometric analysis using VLBI3. The standard errors, [FORMULA], follow from the error analysis described in Sect. 5. Bottom: fixed J2000.0 source coordinates used for quasar A in the astrometric analysis (these coordinates correspond to GSFC global solution GLB831 (Chopo Ma, priv. comm.)).

[FIGURE] Fig. 3. Decadal evolution of the separation between quasars 1038+528 A and B at [FORMULA] 3.6 cm and [FORMULA] 13 cm. The lower figure is a "blow up" of the [FORMULA] 3.6 cm part of the upper figure. This evolution is expressed as a change in the position of the reference point in quasar A with respect to that in B, starting from their relative positions in 1981.2. Error bars represent our estimated standard errors (see text). Opacity effects in the core of the quasars 1038+528 A are inferred to be responsible for the dependence of the relative position on the observing wavelength, as suggested by Marcaide and Shapiro (1983) (see text).

[FORMULA] 13 cm

Comparing the results from the [FORMULA] 13 cm data for the three epochs we find no significant changes of the brightness distributions of the quasars A and B. We also find no evidence for any significant change in position of the reference point. However, there does exist a systematic difference between the angular separations measured at [FORMULA] 3.6 cm and [FORMULA] 13 cm; we find the difference in separation for 1981.2, 1983.4 and 1990.5 to be [FORMULA], [FORMULA] and [FORMULA] µas, respectively, in the NE direction (P.A. [FORMULA] and [FORMULA], respectively). Thus, within our estimated standard errors, the magnitude of this difference remained constant.

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© European Southern Observatory (ESO) 1997

Online publication: May 5, 1998