Thought I would take the opportunity to provide some notes of my experiences in

astronomical spectroscopy to date with current projects carried out and others I would like to do in the hope it may help/motivate other people.

My simple aim when I started out on astronomical spectroscopy was to take

spectra and to understand how the spectral lines in stars are formed. So thats

two objectives the practical side of doing spectroscopy and the theoretical side

of finding out why things are

the way they are.

Sounds simple enough but when you start delving into the subject

there is a lot to learn - however taking the spectra is far easier

than understanding why the lines are formed.

So I started with a couple of projects:

- before going near the sky calibrate the spectroscope using the internal

calibration lamp on my L200 and also some external

calibration bulbs - I used the ones from Habitat detailed on Buils website at

http://astrosurf.com/buil/calibration/lamp1.htm

- take spectra of a bright star across its continuum and the sun/moon and learn

a spectra data reduction process to process the spectra

- take spectra of a spectroscopic binary to see the radial motion of

the stars - my results are here for this task:

http://f1.grp.yahoofs.com/v1/QHP_TEwOlSOe0oy6uHI3PfjBV0-yD2UBS3dWed50Kqlz8CIAbID\

3q6UT9y4lCnNvjP3LxcdcPxtdwnEi7phTlstrhkgGiw/John_s/mizargrouporiginal.jpg

- take spectra of epsilon aurigae and submit to the current campaign

that Robin is coordinating

What I can say about the projects is that I have managed to complete

them all. However there is room for improvement for what I have done:

increasing the resolution of the spectra I have taken by going to

second order on my L200 or using a higher resolution grating - would get me to R

~ 15000 and would give me more a chance to get reasonably accurate measurements

of periods of binaries and give me more accurate wavelength measurements for

taking high resolution spectra of bright stars suchas epsilon aurigae. These are

projects for me next year.

As well as improving on the above there are other projects which

I have been thinking about:

Project A

- measure continua of stars using ultra-low resolution spectroscopy

from say 2 to 50 Angstroms resolution. Key stellar paramaters can

be calculated from these type of measurements - temperature, gravity

and metallicity. Two significant surveys have been carried out which

provide reference field stars and data for doing these surveys: the LICK survey

and more recently the MILES survey.

Under 1000 stars has been carried out in each of these

surveys and it would be interesting to carry out a similar analysis on

stars that were not covered and which are in the range of amateurs

such as myself

Project B

- using data from above to practice classifying star spectral

types would also be interesting and perhaps looking at rules for

classifying stars where our cameras have highest quantum efficiency

as currently most of the classification rules are at the blue end

(3800-4500A)for historical reasons or up at infra-red or beyond.

So plenty of projects to carry out then even at low resolution :0)

Lets talk about the second objective - the theory behind how spectra

are formed. Basically what I want to do is before I go out in the

field to take detailed spectra of a star I want to know what I

should expect to see and why so that if I do see something

unexpected I can talk about it to other amateurs.

Finding out what I should expect to see is easier than understanding

why its that way so I will cover that first.

There are several ways of doing this but I use VOSPEC which is

a great tool and it can be found at

http://www.sciops.esa.int/index.php?project=ESAVO&page=vospec

along with some great flash videos showing you how to use the tool.

Benefit of this tool is it accesses loads of archives for stars and

you can also look at spectra of synthetic stars built out of stellar models as

well.

So thats great as long as the star is there but if you want to know

things like what elements are for what lines. You can look at a

library of elements such as you do in VSPEC but then you normally

have options as several elements have absorption lines around a

specific wavelength.

So this is where stellar modelling comes in.

There is available on the net free software which will allow you to produce your

own stellar models :0)

There are several available out there but I use Kurucz stellar

modelling software called ATLAS which has been updated by Castelli to

run on linux. This models the main sequence stars which are not too

hot eg O stars or the ones that are too cool).

Before you go - oh no not linux I need another PC and how much is

this going to cost I will say that -to use Atlas you can run it on your own PC

and all the software is free providing you have an internet connection and

enough spare disk space on your PC)

How you do it is you download Virtual PC (if you have good old XP like me or you

can use the Windows 7 equivalent which is also free)and install it on your

machine.

You then install linux on your machine - I use fedora - you can

download the software from their site.

Next you install two compilers a free c one the GNU version and the intel

fortran compiler details of how to do this are on the intel web site.

Next you follow the instructions linked to the Atlas cookbook and you

download the atlas code and data and compile it.

Link to Atlas cookbook is here:

http://wwwuser.oat.ts.astro.it/atmos/atlas_cookbook/Atlas_Cookbook.html

There are two versions of Atlas - Atlas9 and Atlas12. Atlas9 is what

I have used up to now and it appears to work - The main atlas program

generates the stellar model then you have two other programs in the Atlas9 sweet

called Width and Synthe which let you specify the resolution and then generate

the spectra. The data file which has the spectra in it has the great advantage

of telling you what elements are contributing to the spectra :0)

Although as input into Atlas you need to have a starting model for

your star - you can access grids at kurucz web site

http://kurucz.harvard.edu/

However to choose a grid you need to know the temperature, gravity

and metallicity of the star you are studying. So how do you know that?

Well you can get the data from simbad at

http://simbad.u-strasbg.fr/simbad/

But if you can't find the data online you'll have to work it out for

yourself - that means probably doing Project A which I mentioned

above.

Thats enough on Atlas.

If you want to look at hot stars and stars with accretion disks then

you could try TLUSTY which can be found at http://nova.astro.umd.edu/

although I have not tried to get that program working on linux yet.

Ok so we are now in a position to produce synthetic spectra for a

star and compare it against the spectra we see.

Now for the tricky question why does the spectra appear in the way

it does.

I'll now list a set of books which will help you on your way to

answering this question...and will comment on them

Non-technical books:

- Keith Robinsons books appear to be an excellent non-technical

introduction to the theory behind spectroscopy and starlight. I have

only flicked through them myself but only some vey basic school

algebra is all you require - his books are called Starlight and

Spectroscopy: Key to the stars and can be found on amazon.

- Obviously there will be ken's book when it comes out but I believe

it focusses on the practical aspects of spectroscopy and not the

theory behind why stars have the spectra they have

Technical books:

To get the most out of the following books you will need to understand

quite a bit of calculus - Schaums outline in calculus and advanced

calculus should suffice for these.

Here are two undergraduate books on astronomy:

An Introduction to stellar Astrophysics - Francis Le blanc - this is

an excellent introduction and the chapter on stellar atmospheres

is excellent

An introduction to Modern Astrophysics - Carroll/Ostle - also called

the big orange book is excellent in its encyclopaedic coverage of

astrophysics although in my opinion some bits could be more simply

explained

Now onto the postgraduate level stuff

Stellar Photospheres - David Gray - I have only just bought this and

in my opinion this is THE book on stellar spectroscopy if you want

to see how the professionals do it - it covers a lot of ground and is

quite readable and has plenty references out to the professional

literature. I am ploughing through it and this book represents

about how far my undertanding has got to in why spectra are the way

they are.

Now for the advanced stuff:

Gray covers only slightly more than Local Thermodynamic Equilibrium models so

where the non-local thermodynamic equilibrium models are described have to head

to

Rutten: Radiative Transfer in Stellar Atmospheres - this is freely

available on the web and will be the next book I want to study after

completing Gray

And finally the book we have all been waiting for which is the new

edition of Stellar Atmospheres which is written by Mihalas and Hubeny

which is due out on amazon any month now....this one is not for the

light hearted...

I think thats enough for now any comments from people out there

welcome I am interested to see who out there is trying to climb

this slippery pole of finding out what the spectra of stars is all

about

John