OK Ken, and all you other Spectrogurus, here is a spectrum from Eta Carina I captured tonight. It is a stack of 4 still frames, with a single point calibration in VSpec at 11.7 A/pixel. The magenta image on the left is of course the zero order image (synthesized from the spectrum).
I have labelled the peaks. As I don't have a spectrum from Eta to compare it to, can any one confirm the correct wavelengths for the peaks? I just want to check that I haven't done something silly when working out my dispersion from my Betelgeuse image the other night.
Well, you've definitely got a strong Ha line there, but it appears to be slightly redshifted, as they all do (if they're all hydrogen lines, in fact). Since I don't have a calibrated reference spectra on me, it's hard to tell what the other lines are. However, you do have a couple of close lines...the one at 488.3nm is close to the Hb (hydrogen beta) line and the one at 436.6nm is close to the Hg (hydrogen gamma) line.
Just to help you out here....read this (luckily it jogged my memory when I read the equations...simple stuff, really)... Hydrogen Balmer Series
If they're indeed redshifted Hydrogen lines, then it's because of the motions within the Homonculus itself. Most likely from the lobe moving away from us. Or at least from gases (including the lobe) that are in motion away from us.
That's a great spectra! What was the set-up and total exposure??
OK, here's what I see....
Re-calibrate on the bright Ha in the red; this should be 6563A.
If I re-set your wavelengths by 28A ( 6591-6563) then I see:
From the blue to red>
Hgama @4340A
Hbeta @ 4861A
OIII @ 4959/5007A
the double bump @ 5154A; not sure? could be Mg?
This spectra is very typical of a hydrogen emission area. You can see now why the Ha/Hb/OIII filters work so well on this type of object.
For completeness the following are usually also in nebulae spectra:
NeIII @ 3869A
HeII @ 4686A
NII @ 6584A
All this coming from a guy who hasn't seen a star since Xmas!!
5154A....might be one of the Fe lines, although B class stars (which eta probably is...most likely B0 on the assumed temp) don't normally show such strong Fe lines. Fe and Ca II (H and K) lines are usually associated, and normally appear strongly in the cooler classes....namely F, G and K. Usually from about F4 to K5-6, where after they diminish in favour of the strong metal oxide and hydroxyl lines (all molecular lines instead of the monatomic lines). Before then, they lose intensity and the hydrogen lines begin to dominate.
Although, if these spectra are coming from the nebula as well, you'll be getting the other lines mixed in with the pure spectrum from the star.
Hmmmm.
I have the FeI lines at 4956/5270/5328/5455 etc can't see anything close to the 5154A. The first of the Mg triplet is at 5167A.......
Found a spectra in Kaler's book, p243; taken in 1922 it shows many FeII lines around the Hgama region, 4244/4287/4359/4414A
Kaler thinks the original F supergiant has collapsed and become a luminous O supergiant " with an extraordinary absolute bolometric magnitude near -12.5" - maybe on its way to a WR star and/or ready to go "Nova"!!!!!!!
Last edited by Merlin66; 30-01-2009 at 01:26 AM.
Reason: added reference
Well, you've definitely got a strong Ha line there, but it appears to be slightly redshifted, as they all do (if they're all hydrogen lines, in fact). Since I don't have a calibrated reference spectra on me, it's hard to tell what the other lines are. However, you do have a couple of close lines...the one at 488.3nm is close to the Hb (hydrogen beta) line and the one at 436.6nm is close to the Hg (hydrogen gamma) line.
Just to help you out here....read this (luckily it jogged my memory when I read the equations...simple stuff, really)... Hydrogen Balmer Series
If they're indeed redshifted Hydrogen lines, then it's because of the motions within the Homonculus itself. Most likely from the lobe moving away from us. Or at least from gases (including the lobe) that are in motion away from us.
Thanks for the link. I'll be honest... at this stage of my spectroscopic experience sometimes it all looks a bit daunting... so I'm not confident at identifying when to expect Balmer lines, and Fraunhofer lines, etc but I can see it simple when it's pointed out!
Quote:
Originally Posted by Merlin66
That's a great spectra! What was the set-up and total exposure??
All this coming from a guy who hasn't seen a star since Xmas!!
Each image was about (from memory) 0.6s, 0 brightness, moderate gain with the DMK, SA, C8 combo unguided. Images were stacked in Registax, so they are averaged, not added.
Quote:
Originally Posted by renormalised
Although, if these spectra are coming from the nebula as well, you'll be getting the other lines mixed in with the pure spectrum from the star.
That could be true. The homunculus was starting to appear in the zero order image.
Quote:
Originally Posted by Merlin66
Hmmmm.
I have the FeI lines at 4956/5270/5328/5455 etc can't see anything close to the 5154A. The first of the Mg triplet is at 5167A.......
Found a spectra in Kaler's book, p243; taken in 1922 it shows many FeII lines around the Hgama region, 4244/4287/4359/4414A
Kaler thinks the original F supergiant has collapsed and become a luminous O supergiant " with an extraordinary absolute bolometric magnitude near -12.5" - maybe on its way to a WR star and/or ready to go "Nova"!!!!!!!
The fact that EtaCar isn't stable is what has me interested.
Quote:
Originally Posted by renormalised
You're most likely right....as I said it might be a Fe line. It was only a guess as I don't have any calibrated references to look at.
Very good spectra, though
Thanks for your encouragement, guys! So much to learn... I love it! I'll fire up the lappy and have another play with it... maybe calibrate off the Ha and Hb lines and see how things look then. But in answer to my original question 11.7A/pixel doesn't seem to be way off the mark, so I guess the lack of blue response is real.
Al,
that's where I find the response + dispersion calibration against a A or B class star is effective. You can work off the zero order and the H alpha line. Provided you keep the optical system the same, it can then be used over multiple sessions, with only minor adjustments to get the dispersion fine tuned.
Found a spectra in Kaler's book, p243; taken in 1922 it shows many FeII lines around the Hgama region, 4244/4287/4359/4414A
Kaler thinks the original F supergiant has collapsed and become a luminous O supergiant " with an extraordinary absolute bolometric magnitude near -12.5" - maybe on its way to a WR star and/or ready to go "Nova"!!!!!!!
That's what I would expect.....FeII being the doubly ionised form, occurs at much higher temps than FeI and in the bluer/UV region of the spectrum. How strong are the lines??
LBV's, especially one as massive as Eta, wouldn't normally stay an F class Hypergiant for very long...too unstable hydrostatically. I'd say most of it's existence in the post MS was as an O or B class Hypergiant. I'd even push that bolometric mag up a notch or two (although, -12.5 is close enough). Also stars that massive don't normally become WR stars...too much mass to lose. They never expose their cores like that before they go pop. Most of the stars that become WR sit around the 30-50 solar mass area. At the most massive up to around 70, but many stars in the 60-70 solar mass area also go pop before reaching the WR stage.
Last edited by renormalised; 30-01-2009 at 10:35 AM.
Al,
that's where I find the response + dispersion calibration against a A or B class star is effective. You can work off the zero order and the H alpha line. Provided you keep the optical system the same, it can then be used over multiple sessions, with only minor adjustments to get the dispersion fine tuned.
cheers
Mark
Understood. Not that I've had any success at that yet... I've attached an example: a spectrum of Rigel I captured the other night. B8Ia star but not much evidence of a Ha line in my spectrum. As you can see, the blue response is also down on the DMK (it was also down on the ToUcam which makes me wonder it it isn't something else other than the camera?).
I've just done this exercise to try and get my head around the camera response. At the moment I'm not getting a consistent camera response curve from different spectra (so I have more learning to do) though I expect to get a handle on that as I learn.
But I think I'm missing something... I think I should be able to save the camera response curve and use it on other spectra, shouldn't I? How do I do that? Each Time I try I get another copy of the raw spectrum, not the camera response curve...
Understood. Not that I've had any success at that yet... I've attached an example: a spectrum of Rigel I captured the other night. B8Ia star but not much evidence of a Ha line in my spectrum. As you can see, the blue response is also down on the DMK (it was also down on the ToUcam which makes me wonder it it isn't something else other than the camera?).
I've just done this exercise to try and get my head around the camera response. At the moment I'm not getting a consistent camera response curve from different spectra (so I have more learning to do) though I expect to get a handle on that as I learn.
But I think I'm missing something... I think I should be able to save the camera response curve and use it on other spectra, shouldn't I? How do I do that? Each Time I try I get another copy of the raw spectrum, not the camera response curve...
Al.
I had the same problem with saving the response curve. The .spc files will only save 4 graphs.
I display the camera response curve that you want to save and then rename it as the 2nd reference graph. There is a way to do this in the "edit" menu. (I will look up the correct button when I get home as I don't have the program here at work.)
The other option is to save the response curve as a .dat file.
You can then open up the file you want to calibrate as well as the response curve and using the "divide" function correct the unknown graph.
Terry / Al,
the attached pdf, (hope you can read it OK) were instructions given to me by Robin Leadbetter on how to process spectra, and get a camera response curve. It may be going over old ground, but I thought it may help. Certainly helped me!
Another comment from Robin was on the use of a focal reducer to improve the image. The aim was to get the smallest size zero order image, (basically increase FOV) and prevent significant focus shift and also smearing across the spectra. I've been using a 120mm f8 refractor and I get far better spectra when I use a 0.6x reducer and drop it to f5.
The exposure times are virtually unaffected.
Terry / Al,
the attached pdf, (hope you can read it OK) were instructions given to me by Robin Leadbetter on how to process spectra, and get a camera response curve. It may be going over old ground, but I thought it may help. Certainly helped me!
Another comment from Robin was on the use of a focal reducer to improve the image. The aim was to get the smallest size zero order image, (basically increase FOV) and prevent significant focus shift and also smearing across the spectra. I've been using a 120mm f8 refractor and I get far better spectra when I use a 0.6x reducer and drop it to f5.
The exposure times are virtually unaffected.
cheers
Mark
Thanks Mark
This is what I have been doing also. My hassle was the saving of the instrument response graph to use on other spectra that I hadn't identified.
At present I'm using my VC200L at f8 and find that the focus seems to be best on the spectrum when the zero order image of the star is also at it's sharpest. I use my home made bahinov(?sp) mask. (It gives an interesting effect on the spectrum also).
With the scope at f8 my ST9E gives ~40A/pixel. I don't want to make it any smaller with a focal reducer. I have ordered a spacer that will extend the camera further from the grating and this should give me about 25A/pixel. I will experiment with the focal reducer when this arrives.
I had the same problem with saving the response curve. The .spc files will only save 4 graphs.
I display the camera response curve that you want to save and then rename it as the 2nd reference graph. There is a way to do this in the "edit" menu. (I will look up the correct button when I get home as I don't have the program here at work.)
The other option is to save the response curve as a .dat file.
You can then open up the file you want to calibrate as well as the response curve and using the "divide" function correct the unknown graph.
Thanks, Mark! Sounds exactly like what I've been missing. I'll have a play.
Quote:
Originally Posted by Heian
Terry / Al,
the attached pdf, (hope you can read it OK) were instructions given to me by Robin Leadbetter on how to process spectra, and get a camera response curve. It may be going over old ground, but I thought it may help. Certainly helped me!
Another comment from Robin was on the use of a focal reducer to improve the image. The aim was to get the smallest size zero order image, (basically increase FOV) and prevent significant focus shift and also smearing across the spectra. I've been using a 120mm f8 refractor and I get far better spectra when I use a 0.6x reducer and drop it to f5.
The exposure times are virtually unaffected.
cheers
Mark
Thanks for the document, I've had a read - just the right mix of stuff I knew and stuff I didn't.Thanks!
Some interesting stuff in there about losing detail in the blue... maybe I'll have to play about with my FR again, etc (I haven't been using it, but the seeing might be destroying all detail in the short wavelengths.
Al.
Last edited by sheeny; 30-01-2009 at 03:35 PM.
Reason: I had a read
Al,
On the Rigel graph/ curve, all the "data" below 400nm is suspect... I would dump it and ignore, I lay a bet it's not real. The atmosphere cuts out most of everything below 350nm and there's effectively zero response from the DMK at 300nm.......
Robin's note is great. VSpec, Tutorial 5, (http://astrosurf.com/Vdesnoux/tutorial5.html)
gives the VSpec method in detail ( just remember, see page 7, to "Edit-Replace")
re Camera response: I occasionally use the Canon 350D with Canon and Zuiko lenses with the Baader grating mounted infront of the lens.
I find the response curve can change dramatically depending on the lenses being used!!
Terry, A little surprised to get best spectra focus when the zero order is focussed... I usually have to tweek the focus to get best results ( 12" LX200, 200mm Littrow, 1200lpm grating). The reducer also reduces the scale of the spectra ( ie shorter focal length). The distance from the grating to the CCD chip I find is more imprortant for dispersion and resolution.
Great stuff... we seem to be generating some interest looking at the number of hits on the thread!!!
Al,
On the Rigel graph/ curve, all the "data" below 400nm is suspect... I would dump it and ignore, I lay a bet it's not real. The atmosphere cuts out most of everything below 350nm and there's effectively zero response from the DMK at 300nm.......
Robin's note is great. VSpec, Tutorial 5, (http://astrosurf.com/Vdesnoux/tutorial5.html)
gives the VSpec method in detail ( just remember, see page 7, to "Edit-Replace")
re Camera response: I occasionally use the Canon 350D with Canon and Zuiko lenses with the Baader grating mounted infront of the lens.
I find the response curve can change dramatically depending on the lenses being used!!
Terry, A little surprised to get best spectra focus when the zero order is focussed... I usually have to tweek the focus to get best results ( 12" LX200, 200mm Littrow, 1200lpm grating). The reducer also reduces the scale of the spectra ( ie shorter focal length). The distance from the grating to the CCD chip I find is more imprortant for dispersion and resolution.
Great stuff... we seem to be generating some interest looking at the number of hits on the thread!!!
OK Ken. So you're saying the drop off of the spectra below 400nm is to be expected, so I shouldn't be expecting to capture a spectrum similar to the library spectrum in this range... so I probably shouldn't be so concerned about my apparent lack of blue response.
I must say I'm loving this thread! I'm learning heaps! Thanks guys!
Another Attempt.
The attached images is a spectrum of OY Car. This is an eclipsing dwarf nova that is currently in outburst. I have done some short time series over a few nights of this star and the series from the same night as the spectrum is attached.
I can't really identify any of the lines. Any suggestions. A summed spectrum form MNRAS is here but this seems different.
You may have a H(gamma), H(beta), HeI and maybe a H(epsilon). You may even have a H(delta) line...but they're all pretty broad. I don't think the resolution of the spectra is high enough to say for certain, though. I can't see any Ha line there...unless you have a redshifted Ha line at 6720A??!!.
... so I'm not confident at identifying when to expect Balmer lines, and Fraunhofer lines, etc but I can see it simple when it's pointed out!
I'll fire up the lappy and have another play with it... maybe calibrate off the Ha and Hb lines and see how things look then. But in answer to my original question 11.7A/pixel doesn't seem to be way off the mark, so I guess the lack of blue response is real.
. As you can see, the blue response is also down on the DMK (it was also down on the ToUcam which makes me wonder it it isn't something else
other than the camera?).
