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Feasibility of detecting Be star outbursts using Star Analyser grating (2)

Magnitude  9.3   Be  Star IL Cep (HD 216629)   Sept 2008

There are several hundred Be stars in the ARAS Beam database between mag 9 and 12 (the estimated lower limit for obtaining high S/N spectra with the Star Analyser at Three Hills Observatory). Most have either no data or only old data from over 5 years ago. This could prove a fertile area for amateurs interested in checking the current status of these stars.

The latest spectrum of HD216629 in the ARAS Beam database is dated1997 so an update is overdue. At Mag 9.3 however it is outside the range of most amateur medium resulution spectrographs. A low resolution spectrum can easily  be obtained however using the Star Analyser grating. While not showing the detailed line profile, it should be possible to make an estimate of the strength of any emission line to flag any needing follow up measurements.

 

HD216629 is a multiple star system. By rotating the grating, it was possible to separate out the spectrum from the just resolveable nearby companion. The H alpha emission is clearly visible in the spectrum image (The bright spot just discernable further into the red  is caused by a faint background star. It is important to always check the spectrum image for interefering background stars when using a slitless setup)






The Star Analyser spectrum was reduced in the usual way and finally normalised using a fit to the continuum so that the  lines strengths relative to the continuum could be compared. Spectra taken from the OHP ELODIE database from 1994-1997 are shown normalised in the same way for comparison.
(Note, the ELODIE spectra are at much higher resolution than the Star Analyser (~40000 compared with ~100)  A Gaussian filter was applied to the ELODIE results to simulate the Star Analyser resolution.

There is good agreement between the features in the current spectrum taken with the Star Analyser and  those taken 1994-1997 using ELODIE. In particular, the H alpha emission line is of similar strength with a perhaps 20% weakening curently compared with the earlier spectra, though this may be within the error of the technique. (The slight fine scale ripple in the Star Analyser spectrum is though to have been produced by the algorithm used to rotate the image prior to extracting the spectral data)



For completeness here is a high resolution plot of the H alpha region from the 1997 spectrum in the ELODIE Archive

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