Eta Car - Spectra????

[Merlin66]

Anyone managing to get clear skies in Oz?????
I'd love to see some spectra of Eta... I think it would be a good subject for regular monitoring.

Ken

[sheeny]

I haven't Ken. Eta is one of the projects I've been trying to do, but between weather and family I've had a poor run at it this year. Will keep trying when opportunities arise though.

Betelgeuse is the another bright one worth watching I think too, given it has been shrinking in size but not changing brightness:shrug:.

Al.

[sheeny]

Clear sky tonight Ken so I made a point of getting out there and getting a spectrum or 2.:)

This was my first real go with a new arrangement:
C11, SA100 Grism (EO 2° wedge), 0.5FR and ST8i camera.

I captured a spectrum of GamCru first so I could extract a camera response curve, and then took one of EtaCar. I got a bit of a tadpole tale to the star image but I captured the spectra anyway, then afterwards removed the SA and ST8i to check collimation which all looked pretty good... I need to track that down...:(

What I need help with though is handling the fits files in VSpec.

My old procedure was I captured on the DMK, processed in R5 and saved as a fits. Opened it in IRIS and subtract sky background and save again, then open that in VSpec and all is hunky dory.

With the ST8i I saved directly as a fits file, opened in IRIS to subtract the sky background and saved again, but VSpec will not open the files... it says the file format is not correct.:eyepop: So I tried opening the fits file in R5 just to save it, then IRIS, then VSpec but R5 introduces a heap of noise, though VSpec will open it.

Is there something I'm missing?

Al.

[sheeny]

I just found an old document you sent me Ken... I'll try K3 instead of R5 when I get a chance... time for sleep now.:)

Al.

[ericwbenson]

What software are you using to save the ST8 FITS file? VSpec is particular about the data type used in the FITS file. The latest VSpec (v3.7.2) I can get it to read 32bit float or 16 bit integers saved in MaxIm (with compression turned off). Previous versions had trouble with one or the other (can't recall which)

EB

[Terry B]

If you save the file in Iris as a .pic file then VSpec is happy to open it.

[robin_astro]

Hi Al,

The tadpole in the zero order is probably an effect of the wedge prism. (Instead of a nice round zero order image you get a little very low dispersion spectrum with a bit of comma as well thrown in) With careful focussing, the spectrum itself should be (a little bit) sharper though, particularly at the red end.

Re Vspec and fits, I have just posted some ideas on Ken's Yahoo group

Robin
(In a wet and miserable NW England :( )

[sheeny]

CCDOps (?) v5 I think it is:P. I'll have to fire up the lappy to make sure.


Thanks Terry I'll try that! Sounds simple... no extra step in the work flow.:thumbsup:

Aaaahhhh... thanks Robin! You've saved me much frustration trying to solve something I needn't!:thumbsup:

I did manage to process a raw spectrum of Eta Carina enough to find my dispersion was 10A/pixel, but I can extend it out further (up into the baffle tube of the C11 so it doesn't affect focus):).

Al.

[sheeny]

It works like a dream when you know what your doing...:P Thanks for the help guys!

Here's my first attempt at a spectrum of Eta Carina with the C11, SA100 grism and ST8i.

Its very noisy - the result of too little exposure I feel. This is one shot, and as my camera is ABG I didn't push it too hard to try to keep it linear (more work to do there to find the limit:)).

This 16 bit processing business is pretty new to me so, its baby steps ATM. Any tips gratefully accepted!:lol:

This spectrum is a different shape to what I'm used to with the DMK. I think this is more realistic. The Ha line is so strong the DMK can't handle it linearly I think and still get any other detail.

Al.

[Alchemy]

Ok, what does it all mean.... I'm not being funny, the spectrum you have taken , what does it tell us, I'm in tested to know more.

[sheeny]

Wow! What a question! Its hard to know where to start or now much to say... and I don't mean that in a way to offend or put down:).

There are basically 3 types of spectra: a continuum (produced by hot black bodies and hot gas under high pressure), emission spectra (produced by hot gas) and absorption spectra (produced by cold gas when a continuum shines through it). The spectrum from Eta Carina is an emission spectrum so it has bright lines at specific frequencies/wavelengths (colours) that correspond to the gases and temperature of the gases in the cloud.

Eta Carina is a very large star (I think there's about 6 stars in the system) and its very unstable. It went through a false supernova event in the 1800s (1841?:shrug:) and has always varied in brightness. Eta Carina is surrounded by a gas cloud that was probably ejected from the main star during the 1841 false supernova event called the Homunculus. The radiation from the star is heating the gas in the surrounding gas cloud which in turn causes it to emit spectral lines.

Eta Carina could go supernova at any time, so it is an interesting object to study because if we track its behaviour right up to a SN then we might learn some signals that indicate when a SN is about to happen.

On the spectrum the wavelength of the light is the independent variable across the X axis and the intensity is the dependent variable on the Y axis. The dominant line in this spectrum is the Ha (H alpha) line at 6563A. That corresponds to electrons dropping from energy level 3 to 2 in Hydrogen atoms. The next most significant line at about 4800A is the Hb (H beta) which is electrons dropping from level 4 to 2, and the next one to the left of that is probably the H gamma line (level 5 to 2).

At each end of the spectrum is quite a bit of noise, because I only took one image, and the camera response at those wavelengths is weak, and I probably didn't expose it enough anyway.

About every 6 years or so Eta Carina goes through a variation where the strength of the lines for different elements changes. This happened in January this year. Other typical spectral lines commonly found in Eta Carina spectra are those of He (Helium) and Fe (Iron). They might be there now but they are probably lost in the noise on my spectrum:(.

Not sure how much of your question I've answered so ask again if there's something I've missed.:)

Al.

[sheeny]

Here's anoher spectrum from tonight. It's still got a bad S/N ratio but it is a little better than my last one. This was my first image for the evening. I then setup for a better exposure when I saw how this was... then computer problems struck.:rolleyes: After having to start the PC again, I had a series of captures running in CCDSoft when I got a virtual memory warning, and the thing slowed right down. I didn't think that when you pressed abort, CCDSoft would erase the images it had captured so far:rolleyes:... By then Eta was very low in the sky and the clouds started.

Oh well...

I have added the lines for H in green. This spectrum was catured at 8A/pixel.

I think I can see the potential of the ST8i now...:D

Al.

[Alchemy]

Thanks for taking the time to reply, I was somewhat vague with my question, although you covered it well, i downloaded a sprectum app for the iPad ..... Crikeys trying to work out what line pertains to what element..... Got your work cutout there. It would be interesting to know if any particular change, indicates a SN potential, although having listened to one of the Astros omy 162 lectures, it just goes without any visual warning, but more research will no doubt clarify that.

I have noted, during my reading, of spectroscopic binaries, have you been able to image a spectrum and clarify the difference, or are we going to a whole different level with that kind of detail?

Edit, whilst My curiosity has been pricked, is it possible for amateur measurements to check for star velocity..... I suspect that's a tough one requiring serious detail in the spectrum, but I thought I'd ask anyway

Thanks
Clive

[sheeny]

Oh I know what you mean, Clive. It's all very daunting at first. However, it gets better with a bit of experience.:) You soon get to know what lines to expect in what type of star, and VSpec (the freeware I use to process spectra) has some cool tools to help identify lines etc.:thumbsup:



Generally, you have a fair idea what spectral class a star is before capturing a spectrum, so for spectroscopic binaries it would be possible to subtract the spectrum from one of the stars (using a library spectrum of the correct type) to reveal the spectrum of the other.

Amateurs can certainly make doppler shift measurements of stars, galaxies and quasars. To do it justice requires a higher resolution (slit type) spectrograph rather than the Staranalyser (SA100) which I currently have.:)

I think I remember a post on the Staranalyser Yahoo group about some doppler shift measurments made with an SA! It can be done, but you need a big doppler shift.

Al.

[Alchemy]

:thumbsup:

[robin_astro]

http://www.threehillsobservatory.co.uk/astro/spectra_3.htm
http://www.threehillsobservatory.co.uk/astro/spectra_22.htm
http://www.threehillsobservatory.co.uk/astro/spectra_6.htm

:)

redshifts of stars in our galaxy and binary orbit redshifts are smaller though and need high resolution spectrographs. It can be done by amateurs though eg here is a paper published on a pro am collaboration I was involved in recently measuring the orbital parameters of WR140
http://www.stsci.de/pdf/liege_wr140.pdf
and of course Tom Kaye's and Christian Buil's remarkable exoplanet detections
http://www.spectrashift.com/
http://www.astrosurf.com/~buil/extrasolar/obs.htm

Robin
www.threehillsobservatory.co.uk (http://www.threehillsobservatory.co.uk)

[Merlin66]

John S has managed to get some interesting spectra of capella showing the doppler shift of the Ha lines using the Spectra-L200.
All these things can be done...just needs a good spectroscope (:D) and the rigor to do it.
Ken

[Merlin66]

Guys,
I assume the weather is going to improve now the footy finals are over...Collingwood :eyepop:- see what happens when I leave the country - a new prime minister, the dollar gets stronger....and Collingwood win!

Eta car is rising in the evenings - any chance of starting a campaign to gather regular spectral data??? I'd hate to miss this one pop!!

[higginsdj]

Hmmmm - My 14" won't swing between my forks with the ST-8E and I set a limit of -65 Dec for safety. Not sure how much more of the southern sky I will lose with the L200 and ST-8E attached but I think it will be a sizable amount....

Cheers

[Merlin66]

Just a reminder...eta is a southern hemisphere target.... if you can now is the time to start collecting the pre-eruption spectral data....

[sheeny]

:thumbsup: Its just cloud stopping me ATM. I've been away for 4 days and I believe we've had cloud here the whole time... that's bad!:lol:

Al.