Question about Eta Car spectrum, 02 Aug 2014

[Rob_K]

Clear night tonight with moonlight not a huge influence. I took another low-res spectrum of Eta Car using Canon 650D, 200mm lens and SA100 grating, stacking 27 exposures.

There is something that seems quite unusual with it - the camera seems to be picking up a response in the 350-400nm range where nothing is visible in the four other spectra I've taken, using the same settings & exposures. In fact, I can't find any spectra taken with this set-up that show any significant response in this wavelength region.

Got me perplexed. The hi-res spectra campaign for this object is concentrated on the 460nm upwards region. Any ideas or suggestions?

I've attached a reduced-size image but the full size is at the following link - click to enlarge if necessary. My spectrum from tonight is the lower one, with the spectrum from 28 July at top.
http://i727.photobucket.com/albums/w...l.jpg~original

Cheers -

[malclocke (Malc)]

Hi Rob,

My guess is contamination from a field star. In your top image I can see a spectrum just below eta car. In the lower image I can't see it, and the field looks slightly rotated compared to the top image.

[Rob_K]

Thanks Malc - that was my thought too and tonight I think I tracked down the culprit. While the star is considerably dimmer than EC and at its brightness there would be little at the red end with a DSLR, I think I'll have to bin these dammit. Really annoying with the star at a very interesting phase and clear skies as rare as hens' teeth.

Ah well, if it's fine tomorrow night I'll try a radically different orientation just for peace of mind. Thanks again!

Cheers -