View Full Version here: : Eta Car Spectrum
31-03-2011, 10:31 PM
I have not been able to use my L200 spectrograph due to a mechanical failure along with very crappy weather.
I have now fixed the spectrograph and installed the neon reference lamp. This makes measurement of the lines much easier.
I took 2 sets of exposures of eta Car a few nights ago. I calibrated the spectrum using about 10 lines of neon emission lines.
The result is interesting with very obvious emission lines.
I processed the 2 different areas of the spectrum and joined them together to create the spectrum below.
The very strong H alpha line is obvious but I'm not sure what the other 2 strong lines are.
If you look at the raw spectrum there are lots of fainit lines above and below the star spectrum. These are from the surrounding nebula.
If I ever get a clear night again I will have another go and use longer exposures. The total for this spectrum was 4x5 mins for the green end and 5x1 min for the red end.
01-04-2011, 12:09 AM
I can't add any knowledge, but I will say it's very interesting to see the spectra with h-alpha so obvious like that.
I am so excited you are doing this on E.Carinae!!!
I regularly search the web for updates on this star, and just so exciting that someone here on the forum is keeping track of it.
Keep up the good work, it is appreciated. :)
01-04-2011, 05:47 AM
I'm glad you're back in action!
is the 3A red shift a reasonable figure for eta car???
Will be interesting to compare your data gong forward.
01-04-2011, 12:04 PM
I'm not sure about the redshift. I searched for other spectra of eta car but only found UV and IR areas. I will have to read some more papers.
01-04-2011, 01:55 PM
Hi Terry, thanks for posting the Spectrum,:thanx:
From another Eta Carina fan:thumbsup:
01-04-2011, 04:08 PM
I hope to make some more progress this weekend.
01-04-2011, 04:45 PM
I'm assuming the section of the spctrum image is around the 5869 region? Interesting that you've recorded some of the nebula spectrum with such a short exposure and long slit.
If we can identify some of these lines -maybe they can be used for calibration??
01-04-2011, 05:51 PM
Some hits that may be useful.
This one references some of the older harvard spectra - interesting read.
01-04-2011, 05:56 PM
I used the join function in vspec to blend the 2 images.
The calibration for both image sets was 5 sec exposures x 5 stacked of the neon spectrum so I don't need to use any star lines for calibration. I used all the neon lines to calibrate but it is pretty linear anyway.
The only problem is that the silt seems to be tilted. The zero order slit is vertical but it becomes progressively more tilted as you get into the IR. It has a 6deg tilt in the IR range. The tilt in the spectrum however is the oposite way of only about 1 deg. I opted not to correct the tilt and just used the same crop of the calibration lines and the image lines.
I was also amazed that there were lines from the nebula. I thought that they might be ghost images left over from the neon lines but they don't line up at all with the neon lines. I will try again when the cloud goes away.
01-04-2011, 06:06 PM
The Littrow spectroscope has two "distortions" - Slant and tilt.
The spectrum should always be set up horizontal.
When this is done the lines will appear tilted in the spectrum by about 4 degrees (caused by the pick off mirror positioning in the Littrow) and is very constant.
The slant of the spectrum band across the CCD chip does change with increasing wavelength.
When the 600 l/mm grating is used in the 2nd order, for instance, the spectrum may appear well down in the CCD frame.
The testing I'm doing with the 1800 l/mm grating show it will be difficult to get the zero order and the far IR on small chips! (without changing the tilt of the grating holder!!) IRIS can correct for both.
(I'm assuming the image you published was just the 5000A section...)
01-04-2011, 08:04 PM
Yes. I only published the green end. This is the red end attached.
03-04-2011, 03:11 PM
I took this spectrum last night between the clouds from ~2300hrs. The clouds rolled in after I had taken exposures of 2 regions of the spectrum so I could not take any images of a known star to calibrate the instrument response.
The exposures were 300 sec x 5 combined with Iris using the composit command.
the 2 regions were then joined in Vspec after calibrating using about 20 neon lines.
This time there are some obvious He lines as well as the Ha line.
I'm still not sure what the lines are at 5753A and 5873A.
03-04-2011, 09:28 PM
I found a paper with a list of the identified lines. The paper is from 1953 but is still valid.
I have annotated the lines I can identify.
03-04-2011, 09:54 PM
Can you PM details of the paper you found.
04-04-2011, 05:58 AM
Looking really good Terry.
(Still working on conecting the L200 to my scope)
04-04-2011, 06:59 AM
Well done Terry!
08-04-2011, 11:14 AM
I've just seen this thread and can confirm the [NeII] and HeI lines at the left of your spectra. I've been monitoring both these lines for the last few months (at around R=18,000) as part of an RV study of the eta Car ejecta "cloud". The Sodium D1 and D2 ISM lines are also present, just to the right of the HeI line, but don't really show up at your resolution.
08-04-2011, 12:01 PM
Thanks Bernard. Good to see I found the correct lines.
How are you monitoring the star?
My spectrum was only taken with a 200mm scope so getting a good S/N isn't very easy.
09-04-2011, 10:27 AM
I monitor that particular window with my Lhires III+ST-8XE+C8 using a 2400 l/mm grating and a 19um slit.
Getting a decent SNR on a bright object should not be a real problem if (a) you make a long exposure and (b) you guide/autoguide well. Attached is an image of a fairly recent spectra made with my 200mm (C8) scope with a total exposure time of 50 min. I'm not allowed to show a spectra of that same region made with a +3m professional telescope but I can assure you the pro resolution and SNR was not that much better.
09-04-2011, 10:56 AM
I should add that since last week I've switched from the C8 to C11 and may start using my C14, but that size is not needed for bright objects and is also counter productive, due to the star's larger Airey disc.
Thanks for this thread Terry - fascinating reading. Do you have data below and above the range you've shown? I was interested to see what sort of peaks existed around the 510ish and 680ish OIII and SII bands that narrowband imagers use.
09-04-2011, 03:52 PM
My image is a stack of 5x300sec exposures in each region using a VC200L, 600l/mm grating with the minimum width slit that the L200 has and a ST9E with 20um pixels. Clearly more exposure time is the key here.
I am using a guide scope and seem to be able to keep the star on the slit reasonably well with this.
I would like to keep monitoring eta Car. How often do you think is reasonable to take exposures to potentially show any change?
It clearly takes time to do so with limited clear weather and other objects that I monitor.
I haven't tried other areas of the spectrum due to the crappy weather. I will see what I can do.
09-04-2011, 10:27 PM
The only emissions of any 'consequence' near those two ares are a whole bunch of FeII lines betweenH beta (4861) and 5500, and HeI at 7065.
09-04-2011, 10:36 PM
Given that you have a 20um pixel (the ST-9 isn't the bast match for higher res work) and that you need a two pixel coverage to meet the Nyquist criteria, you won't gain any resolution by using a slit narrower than 40um ... which will also give better throughput.
Normally you don't need to monitor eta Car more than once a month.
09-04-2011, 10:45 PM
Have you measured the 'minimum' slit width you are using? If it is less than 40um, as mentioned earlier, you are wasting light without gaining any resolution and that may be the reason your SNR isn't as good as it could be.
09-04-2011, 10:50 PM
No I haven't measured the slit. How do you do it?
I know the ST9E isn't the best for this use but it's what I have. I could attach my ST10XME with 6.4um pixels but I use it for photometry and would have to take the filter wheel off and on to swap the roles --Too much hassle.
10-04-2011, 02:15 AM
A quick method the check the slit is to measure the FWHM width of a "good" exposure of a zero slit image.
I recommend setting the gap to 3 -4 pixel FWHM (this is not as rigorous as it should be, but seems to work pretty well for novices)
This will then at least match your pixel size better than working out the linear star size on the slit and setting to that.
You can see the impact when using a neon reference - the FWHM doesn't change much when the slit is adjusted when you have larger CCD pixels.
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