Elements in Aldebaran and instrument response curves.

First I discovered hydrogen in space, then oxygen. Now I've discovered metal!

Ok, "discovered" is perhaps the wrong word because boffins beat me to it some time ago. But if I'd been born 150 years ago, I'd be hailed as a flippin genius, so meet me half way for goodness sake.

And actually I DID make a real discovery last week. I found hydrogen lines in the star Betelgeuse. And I published the results on one of the spectroscopy forums. Unfortunately that turned out to be a mistake, because Betelgeuse is an old cold star which has burned its hydrogen up already...

The guys on the forum were very nice about it and pointed out my error without once mentioning the word "idiot."

Anyway, past failures can't get in the way of future success, so ever onwards:

I managed to get a spectrum of Aldebaran last night. It's the bright orange star in the constellation of Taurus,

and if you've been reading 4AoS over the last few weeks, you will know what the orange colour means. Yes, it means it a cooler star heading towards the end of its life, having burned up its hydrogen (yeah, yeah, much like Betegeuse. I know) and this means it has expanded to a huge diameter; 44X that of the Sun.

(Wikipedia)

What this also means is that it's had time to produce lots of other elements, including metals so it's a great place to look for the heavier elements.

I just searched Google to check what metals I should be looking for, compared to hot stars like Sirius. I seached for "star" Sirius" "Aldebran" and "metal" which took me to these guys:

To those now eternally damned, I was given the charge of relaying to you the licentious proliferation of the cult doom metal entity Aldebaran. As I write this, I feel the strands of myself succumbing to it. It came to my attention in 2003 when a trio of metal fiends first felt the emanations from the dog star, Sirius, home of that which shan't be named.

If you are into the doom metal genre (??) you'll want to go here:

http://www.tvcoast.com/aldebaran/biography.html

Here's the profile from the spectrum photographed last night:

The suspected metal is marked with the blue triangle.

This is the "raw" profile, and the vertical axis represents the strength of light at each wavelength, as recorded by the CCD in the camera. However, the response of the chip to different wavelengths isn't linear. The Nikon D60 loses sensitivity to wavelengths below 5000 and above 6500. Also there's a huge dip between the green and yellow parts of the spectrum (white triangle) which is due to the non-linear response of the camera, and not to any actual feature of the star.

What to do?

Take the spectrum and divide it by a library spectum of a star of the same type to produce an instrument resonse curve for a particular camera:

Instrument response = Raw Spectrum/ Library Spectrum

This sounds difficult but RSpec makes it simple, and even provides the library. It's a K5III star so I just upload it from the supplied database:

The first thing you notice is that it has a much wider range than the Nikon results, especially at the red end. This isn't surprising because the camera has an IR filter which cuts out most of the light above 6500A. You can get this filter removed for about £200 but then the camera is useless for normal photography. And alsomy blue triangle does seem to be associated with a large dip in the library spectrum, suggesting we're onto something.

I'll spare you the next bit so here's my spectrum (red line) after being calibrated for instrument response, and with the library profile above it (blue line). I know there a tendency on 4AoS to overinterpret results but I think we can all agree there is a strong correlation at the marked points, 5184A and 5890A, which confirms the existence in the upper atmosphere of Aldebaran (gulp) TWO elements; Magnesium (Mg) and Sodium (Na)!