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Astron. Astrophys. 355, 256-260 (2000)

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2. Observations and reduction

We observed three outburst objects, CI Cam, Nova Sgr 1998, and U Sco, using the low resolution spectropolarimeter, HBS (see Kawabata et al. 1999), mounted on the 36 inch reflector at the Dodaira observatory. As for the observations and subsequent reduction procedures, we followed the standard method introduced by Kawabata et al. (1999). In observations, we used the D1 diaphragm (17" [FORMULA], projected on the sky), resulting in the spectral resolution of about 100 Å which is limited by the seeing size. In reduction, we binned the Stokes parameter spectra ([FORMULA] and [FORMULA]) to reduce the photon noise as far as possible. The resultant data quality is [FORMULA] typically. However, we cannot attain such qualities for some objects or in some wavelength regions due to the low S/N: [FORMULA] on Apr.10 and [FORMULA] on Apr.11 for the blue region ([FORMULA] Å) of CI Cam, respectively, non significant detection for Nova Sgr 1998, and [FORMULA] for U Sco on Feb.27. The polarization spectra are displayed in Fig. 1a-c.

[FIGURE] Fig. 1. The polarization spectra of a CI Cam, b Nova Sgr 1998, and c U Sco. Top panels (I) show the flux uncorrected for air-mass, middle panels (p) show the polarization degree, and bottom panels ([FORMULA]) show the position angle. In the middle panel of Fig. 1a, the solid curve represents the best fitted solution with the Serkowski law (see text), while the dashed curve is the solution with the Wilking law for the interstellar polarization.

The journal of observations is shown in Table 1.


Table 1. The journal of observations: The third column shows the exposure time per a frame times the number of frames.

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© European Southern Observatory (ESO) 2000

Online publication: March 17, 2000