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  Low Resolution spectra of Be  Star   V831 Cas   (Vmag 11.3)   20-24 Sept 2008


The only spectra of V831 Cas currently in the ARAS BeAm database dates from December 1996, so an update is overdue. Three low resolution spectra were measured  on 20th,22nd and 24th September 2008 using the Star Analyser grating. While not showing the detailed line profile, it should be possible to estimate if  the strength of the H alpha emission line has changed significantly.

 

The risk of interference from background stars and spectra increases as the technique is extended  to fainter stars.  Before imaging, the Digitized Sky Survey image of the area was examined to determine the best orientation of the camera to minimise such problems. After imaging, the actual spectrum position was overlaid on the DSS image to check for interfering stars.  One was identified  at approximately  the 5600A position and has been removed from the plot of the spectrum taken 24th Sept. There are no stars visible in the DSS image at the H alpha position)



The Star Analyser spectra were reduced in the usual way and finally normalised using a fit to the continuum.  The 1996 spectrum from the OHP ELODIE database was normalised in the same way and gaussian filtered to match the Star Analyser resolution for comparison.

The 1996 filtered ELODIE spectrum  suggests that the H alpha emission should be clearly visible, peaking at about 12% above the continuum in a Star Analyser spectrum provided a sufficiently low signal/noise ratio could be achieved. 
Three spectra of successively increasing total exposure were taken on different nights. The spectrum on 24th September taken under improved sky conditions clearly shows the H alpha emission peaking approximately 7% above the continuum. The measured level is lower than that measured in 1996 but the difference may not be statistically significant.

A high resolution plot of the H alpha region from the 1996 spectrum in the ELODIE Archive

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