H-R Diagram Challenge

[John Murrell]

Following my lecture last night here is the challenge.

 

Assemble your own H-R diagram and plot images and or spectra of the stars on it showing the true colour or the shape of the spectrum.

 

No cheating with the star colours - you must use the same image settings and processing for all the images - you can't just take an image of Betelgeuse or Deneb and 'adjust' the colours in an image manipulation programme or using the camera settings to get the colours 'right'

 

Extra marks for getting a double with both stars showing the correct colours.

 

Hint - try imaging the stars with them out of focus and maybe let them trail - it works with film - see David Malin's book

 

Suggest you start with the bright stars first - there are a fair selection about.

 

For a copy of the H-R Diagram showing some of the target stars try here: http://www.helsinki.fi/~ajliljes/UniverseNow/hrdiagram.jpg

 

Perhaps Paul will buy us a Diffraction Grating and a Mono CCD Camera or even a proper spectrograph and camera ! (Thinks perhaps I should make my donation to the society this year conditional on it being spent on a Spectrograph ??)

 

Regards

 

John Murrell

Meteorologist & Webmaster

Croydon Astronomical Society

England, UK

Web: www.croydonastro.org.uk

 

 

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[John Murrell]

I have just thought of a way of measuring Star colours so you can obtain it's temperature using nothing more than a digital camera. Digital cameras have filters over each Pixel to record the colour information. It should in theory at least be possible to use the brightness of a star in each of the filter bands - usually Red Green & Blue to obtain the brightness and from this obtain a colour index that relates to the temperature. One will have to use the camera in RAW mode to ensure the electronics do not play about with the values and also probably take some dark frames with similar exposures.

 

It is important that the star image covers several pixels due to the different colour filters. Also the image should not saturate in any of the bands. I would suggest that the best way to do this is to de-focus the star image slightly so it is a spot rather than a point.

 

Go out and give it a try and let us know how you get on !

 

For those stuck under cloud or behind their computer go and do a search on the internet to find out if anyone has done this before and if you find some good pages send us the links.

 

John Murrell

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[John Murrell]

Hi everyone,

 

Just following my own instruction I have been out and taken some RAW images of Vega and Deneb. I have attached two images of the de-focused stars. These are JPGs from part of the RAW image - heavily compressed but they show some interesting artefacts including the outer red ring, the dimmer mottled interior and the brighter blue shell.

 

Anyone got any good ideas about why this is so ?

 

I may have gone a bit to excess with this de-focusing. The near focus image of a wider field shows the stars around Deneb with an exposure of 8s at f4 at 1250ASA shows stars to at least mag 6 without any dark frames. The colours in that show quite well but Deneb is clearly saturated. However it shows some other O&B stars and a lot of K stars quite well. Also some cooler M stars but they are buried in the noise / light pollution.

 

Anyone else tried it yet ?

 

John

[John Murrell]

Has anyone made any progress yet on the CAS H-R diagram ? If you have some colour calibrated images, colour measurements or spectra let me know and we can put them on the CAS H-R diagram. In terms of distance & luminosity I am quite happy to accept the values from one of the Astronomical Databases such as SINBAD.

 

The correct colour is sufficient challenge for the present.

 

John

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[Roy Easto]

From the short talk on Friday can anyone remember the names of the
webcams that were recommended for astrophotography. I remember the
Philips Toucam camera but was more interested in the larger cameras
better suited to dark conditions and higher resolution.

My particular interest is that I want to create some time lapse movies
of the sky (but on a budget).

Thanks,

Roy

[John Murrell]

Hi Roy,

Have a look at
http://www.theimagingsource.com/en/topics/firewire-cameras-at-the-imaging-so
urce/ also the Atik cameras at
http://www.telescope-service.com/atik/start/atikstart.html

The Atik cameras are cooled and therefore cost more but have lower noise.

Most of the cameras use the Sony chips as do the Starlite Xpress cameras.
The major difference over the Toucam is the ability to take longer
exposures.

The other option is something like a second hand Canon 10D if you want
colour - the sensors have more Pixels but you need a mains power supply.

All of them need a laptop to record the data.

John

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[Graeme Coates]

The Toucams can all be modified to perform long exposures (the
"SC" (Steve Chambers) mod) and there are loads of guides on the net to
do this. The reason why these webcams are so good is the Sony CCD that
is used - these are excellent. However, if you are really handy with a
soldering iron/making circuit boards, then you can take it much
further than this and replace the CCD sensor with the icx414/icx424
like the Atiks). Greg Beeke details the mod here:

http://cosmicshed.blogspot.com/2007/11/icx414-sc4-webcam-modifications.html

And the icx424 replacement is on Steve's website at http://www.pmdo.com

Another alternative is to replace the colour chip with a more
sensitive b/w chip (the ICX098BL) which doesn't gain you any chip
size, but gives you a better response. You could also design a cooling
system for the toucams too - again several guides out there.

There's also the Meade DSI range - the DSI III has a large chip - but
the price takes it into the realms of "proper" ccd cameras.

The Imaging Source cameras are good (I have one) - though they are
touted more as planetary cameras since they have quite small pixels,
the "AS" versions do long-exposures, and the more expensive ones do
have reasonably sized chips.

The Atik range have some good cameras and give very good results
(though are less like webcams, since they even come with cooling and
an ST4 guider socket :) The Atik-16ic really is a very good camera
for the money.

Other options include something like an integrating video camera like
the Watec - though to record the results you'll need a video capture
card (or some way of converting the video out signal to a PC friendly
one).


Cheers,

GC