Periodic behavior of the HeI6678 emission in δ Sco

vendredi 8 janvier 2010 par Ernst Pollmann

The spectral range 6500-6700 Å includes both Halpha and the HeI line at 6678 Å, and this report covers our observations made of those two lines. This permits a study of the correlation between their equivalent widths (EWs) and line profiles. A signal-to- noise ratio (as a rule > 400) is necessary to obtain simultaneous information about the strength and line profile behaviour of Halpha and the double-peak emission line of HeI 6678 Å.

Following the generally accepted assumption that the disc of this binary system is being fed essentially in a kind of outbursts of the helium zone near the photosphere of the primary component, a comparison of the contemporaneous equivalent widths of Hα and HeI6678 Å permits the study of the correlation between them (Fig. 1). Such a correlation should give an impression about the quantities, how the matter of the disk depends of them.

Since April 2005, during every observing season, the observed correlation impressively supports the existence of this disc-feeding process, in which the slope of the linear fit shown in Fig. 1 reflects the quantitative correlation.

Beside the simultaneous analysis of the EWs, the variability of the HeI 6678 Å double-peaked line profile offered excellent possibilities to monitor the V/R ratio. During 2009, it was possible for the first time, with satisfying results, to monitor the increasing phase, the maximum and the descent phase of the V/R ratio (Fig. 2). In preceding seasons, merely the descent could be measured. On this occasion I would like to emphasize particularly that, amongst others, members of the French group, ARAS, have strongly contributed to this high measuring density.

The V/R measurements of the present 5 cycles permitted an analysis of its possible periodicity (Fig.2). Independently of each other Thom Gandet, Thomas Rivinius and E. Pollmann, calculated with the same data set, the following periods :

Gandet : 533 d (± 41 d) Rivinius : 536 d (± 4 d) Pollmann : 544 d (± 15 d)

The ephemeris of this V/R variability is the following : JD 2453462 + 538 * E. How long the periodicity of the V/R ratio is preserved remains to be seen. It is possible that the coming periastron passage in 2010/2011 will have a decisive influence in triggering a new photospheric outburst.

Independently of the discovery of the HeI 6678 Å V/R periodicity, we found during certain phase intervals in 2006 and 2009 that a third component (triple-peaked-structure) was observable. A check of all present spectra did show that this triple-peaked-structure is obviously limited only to the phase intervals 0.75-1.1 (see the following spectra 2006/04/02 – 2009/08/04 in the attached file.).

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