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johnb

With spectroscopy we can ?

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So after some reading it seems with spectroscopy we can

A – Tell the temperature of the Star ( or nebula I assume )

B – Tell the chemical composition of the Star (or object we are studying)

C – Calculate velocity (I think)

Am I on the right lines ?, did I miss anything ?

Regards

John B

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So after some reading it seems with spectroscopy we can

A – Tell the temperature of the Star ( or nebula I assume )

B – Tell the chemical composition of the Star (or object we are studying)

C – Calculate velocity (I think)

Am I on the right lines ?, did I miss anything ?

Regards

John B

Also pressure(density) from the pressure broadening of the line eg the difference between main sequence and giant star spectra and from the fact that forbidden lines only appear at the very low pressures in nebulae)

Magnetic fields from theline splitting due to the Zeeman effect.

This is a graphic I use in my presentations on spectroscopy when explaining why it it such an important tool.

Cheers

Robin

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Nice slide Robin. There is also an awful lot of other important information that astronomers have derived using spectra of stars - some of it pretty mind-blowing for instance:

- if star is in a binary (or a multiple) star system you can potentially get a spectra with the combined spectra of the two stars in it - and using the way the lines move in the spectra as they go round each other you can work out the orbital parameters of the stars in the system

- if the star has exoplanets going round it you can determine the number and orbital parameters of the exoplanets going round it

- even better if you capture the spectra when an exoplanet is in front of the star you can extract the spectra of the exoplanet by subtracting the spectra from the star when the exoplanet was not in front of it!

- if you know the type of star you are looking at you can use deviations of expected intensity in some of the Calcium lines (and others) to work out the sort of material that is between us and the star!

- the shapes of the lines can be used to determine details of the stellar winds in some stars - wind momentum, terminal wind velocity

- the wind momentum is directly related to the luminosity of the star - from this believe it or not we can now work out the distance to the star

- also the shapes of the lines will tell you if there is an inflow of material going into the star and if the star has a disk of material going round it.

- high precision spectroscopy allows you to do something called astroseismology - all stars pulsate as detailed in Robins diagram - the lines in the spectra of the star move as the stars pulsate - capturing this data allows you to study the structure of the star potentially deep below the stellar atmosphere.

and there is lots more...

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Tell us more please!

TheThing

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Wow! That's more than I would have thought. Other than a spectroscopy filter what else you need to get started?

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Some more then that astronomers have done:

- you can use spectra to detect mass exchange between stars in a binary system (if the stars are close enough to each other that the mass flow from one star to another)

- for stars with disks of material going round them such as Be stars the shape of some of the spectral lines allow you to calculate the inclination of the disk to you

- you can use spectra to determine the inclination of the star to you. For instance for vega it has been shown that one of its poles is facing us

- as we see the sun as a disk you can take spectra of different parts of the disk of the sun and observe the structure of the sun at different depths in its atmosphere. The nearer you take spectra to the limb of the sun the higher up in the sun's atmosphere you observe

- a number of spectra of standard stars have been taken by the hubble and other space telescopes. If you then take spectra from earth you can compare the difference between that spectra and the space one to determine the elements and the amount of extinction that light has as it goes through our atmosphere

- detection of starspots in some stars using molecular Titanium Oxide bands formed in them

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That's why I'm keen to give it another try. I didn't realise there was so much to it.

TheThing

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Dipper,

Not all of these things can be done with a spectroscopy filter such as a star analyser.

The star analyser (with a camera attached) and a reasonable amateur telescope will allow you to:

- measure the temperature of a star

- identify some of the absorption lines in the atmosphere

- measure redshifts of distant quasars fairly accurately

- identify the type of a supernova (if its bright enough)

The others require a high resolution spectroscope and for some of the items eg examining atmospheres on exoplanets require a really big telescope eg the keck in Hawaii or ideally the James Webb Telescope when it comes online :0)

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Oh, I see, thanks. When the finances allow I'll read more about it. It looks like an interesting field of astronomy to indulge in.

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Hi

Do amateur astronomers do this for their own interest or is this part of a astronomical research project where data is sent to a central point? I'm asking as this looks like an interesting activity to get involved in.

Thanks in advance for any replies.

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At present I'm still learning how to use mine properly, so am just adding my data to exist ant data at the NLO and with other members. In the end I would like to progress to being part of a pro-am task, but will probably need to move from the star analyser to something like a Lisa or a Lihres

Kate

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I'm learning as well and if all goes well will overtime upgrade to hires (well as much as the pocket will allow) I may then use spectroscopy in my PHD, that is however a few years away.

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Also the Convento group runs Pro-Am campaigns (Thre next is WR134,5,7 next year)

http://www.stsci.de/convento/

and Ernst Pollmann's website, though there is some overlap with the ARAS group there

http://www.astrospectroscopy.de/

There are also occasional ad hoc requests from pros via AAVSO for example which amateur spectroscopists can contibute usefully to eg

http://www.astrosurf.com/aras/surveys/chcyg/index.html and others on the ARAS website

but Pro-Am work in spectroscopy is relatively new and we and the pros are still exploring what is possible. (Generally much more than was originally though feasible so there is likely for plenty of opportunities for those interested in working in this challenging area)

Cheers

Robin

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Diffraction spikes also produce spectra. This is because light is made up of many wavelengths, and each wavelength is diffracted by a different amount. Hence the diffraction grating.

You must have noticed the bright spotlights on TV sometime when the diffraction spikes are noticeable in the extreme. Next time you see these spikes, take a look at the colours in them as they progress outwards.. Diffraction is here being used to give this effect.

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Diffraction spikes also produce spectra. This is because light is made up of many wavelengths, and each wavelength is diffracted by a different amount. Hence the diffraction grating. You must have noticed the bright spotlights on TV sometime when the diffraction spikes are noticeable in the extreme. Next time you see these spikes, take a look at the colours in them as they progress outwards.. Diffraction is here being used to give this effect.

Valid point - my vid demos spectra from a very coarse grating eg kitchen sieve at
:rolleyes:

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