26 September 2015 at 11:25 pm #573478
I`m hoping to see if I can detect some doppler shift in the spectrum of Mizar over a period of time as its a spectroscopic binary and while taking some spectra last night (25/09/15) I was struck by the similarity with the spectrum of eps Auriga (also taken last night) a star I`ve not tried before.
Hopefully the resolution of my Alpy will show some doppler shift??
The O2 lines in the red were very clear also!.
Attachments:27 September 2015 at 5:27 pm #577071
Those are both nice spectra with clear atmospheric O2 absorption and stellar hydrogen absorption lines.
That is an interesting project to look for a change in the doppler shift. I do not know the velocity of the various components so can’t comment further on feasibility, but a great idea.
Andy27 September 2015 at 6:29 pm #577072
Cheers Andy!. I`m also wondering if eclipsing binaries the likes of Algol would show any doppler shift too?.
Steve27 September 2015 at 9:41 pm #577073
I’ve done some very rough back of the envelope calculations. Assuming the separation is 0.062 AU and the period is 2.867 days. Then I get an orbital speed of 235 km/s, which in direct line of sight would equate to about 5 Angstroms around H-Alpha. However the shift would be twice this since at one stage it would be moving towards us, then half an orbit later away from us. So an overall 10 Angstrom shift, requiring a minimum resolution of about 600.
It is possible I’ve made a slip somewhere in my calculation, but if not then it could be an interesting challenge.
Andy27 September 2015 at 11:56 pm #577074
Thanks for that Andy, I`m pretty sure I could detect a 10 Angstrom shift …just!! with my setup… I think!!
Steve28 September 2015 at 2:36 pm #577078Robin LeadbeaterParticipant
Hi Steve, Andy,
Provided you have good lines to work with it is fairly straightforward to measure radial velocities to a precision 1/10 of the resolution or better. (As I plan to show at the workshop in a couple of weeks) so an ALPY with say 10A resolution could measure a 1A shift or 50km/s at 6000A as a reasonable target.
You can go much, much more precise than this though if you use an off telescope fibre fed spectrograph and correlation techniques as is done for exoplanets. eg Buil measured to 50m/s (yes metres!) using a 0.6A resolution echelle spectrograph which I think works out at ~1/500 of the resolution
Robin28 September 2015 at 7:57 pm #577083
Wow, 50m/s! That is impressive. I’m looking forward to your talk.
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