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Variable Stars
Hi all, first time post in this NG.
I was watching a documentary about the search for planets orbiting other solar systems last night.The program explained how astronomers searching for alien planets look for stars which show a varience in the light they give out, which would indicate orbiting planets which block the light reaching our telescopes. It suddenly dawned on me that what they were talking about is a charactistic of so-called "variable stars", which have been known about for years. Am I thinking along the right lines? Larry |
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Variable Stars
"LazzaH" wrote in message om... Hi all, first time post in this NG. I was watching a documentary about the search for planets orbiting other solar systems last night.The program explained how astronomers searching for alien planets look for stars which show a varience in the light they give out, which would indicate orbiting planets which block the light reaching our telescopes. It suddenly dawned on me that what they were talking about is a charactistic of so-called "variable stars", which have been known about for years. Am I thinking along the right lines? Larry Same principle as eclipsing binaries, but the effect expected is far smaller than what is usually seen in typical stellar binaries. The best known example of a planet that transits a star results in drops in brightness of the order of 2%. Detecting a terrestrial planet would require reliable detection of drops of order 0.01%. This is difficult, but not impossible. The main use would be to get statistical information on the likely number of stars with planets. Of course, it only gives you the stars with planets that happen to have orbits with "nodes" in the plane of the line of sight. All the other possible planets remain undetected. The main advantage of the method is that precise photometry is easier to implement than ultraprecise positional measurements. -- Mike Dworetsky (Remove "pants" spamblock to send e-mail) |
#3
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Variable Stars
Wasn't it LazzaH who wrote:
Hi all, first time post in this NG. I was watching a documentary about the search for planets orbiting other solar systems last night.The program explained how astronomers searching for alien planets look for stars which show a varience in the light they give out, which would indicate orbiting planets which block the light reaching our telescopes. It suddenly dawned on me that what they were talking about is a charactistic of so-called "variable stars", which have been known about for years. Am I thinking along the right lines? Not really. What happens is that the light gets very slightly Doppler shifted due to the wobble imparted by planets going round the star. Now that we have ways of measuring the spectral lines we can see these shifts. A planet doesn't cause the star's brightness to change. The term "variable star" refers to a star which changes in brightness by a noticeable amount. The one thing that we did know about before 1995 was "spectroscopic binary stars". These are caused by the same sort of Doppler effect, but in this case there are two stars which orbit each other, causing significantly greater Doppler shifts which could be detected with pre- 1995 technology. We could tell that there were two stars even though they were too close together to be resolved by direct observation. The light from one of the starts would be red shifted when it was in a part of it's orbit moving away from us, and the other would be blue shifted. -- Mike Williams Gentleman of Leisure |
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Variable Stars
In message , Mike Williams
writes Wasn't it LazzaH who wrote: Hi all, first time post in this NG. I was watching a documentary about the search for planets orbiting other solar systems last night.The program explained how astronomers searching for alien planets look for stars which show a varience in the light they give out, which would indicate orbiting planets which block the light reaching our telescopes. It suddenly dawned on me that what they were talking about is a charactistic of so-called "variable stars", which have been known about for years. Am I thinking along the right lines? Not really. What happens is that the light gets very slightly Doppler shifted due to the wobble imparted by planets going round the star. Now that we have ways of measuring the spectral lines we can see these shifts. A planet doesn't cause the star's brightness to change. All true, but as Mike Dworetsky has pointed out, the variation in light as a planet transits the star is also being used to look for them. It's even being used by amateurs, which is definitely not the case for the Doppler technique. -- Rabbit arithmetic - 1 plus 1 equals 10 Remove spam and invalid from address to reply. |
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Variable Stars
Jonathan Silverlight
wrote: It's even being used by amateurs, which is definitely not the case for the Doppler technique. Not so. See the magnificent achievements of Tome Kaye and his collaborators at: http://www.spectrashift.com/ Best, Stephen Remove footfrommouth to reply -- + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + Stephen Tonkin | ATM Resources; Astro-Tutorials; Astro Books + + (N51.162 E0.995) | http://www.astunit.com + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + |
#6
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Variable Stars
In message , Stephen Tonkin
writes Jonathan Silverlight wrote: It's even being used by amateurs, which is definitely not the case for the Doppler technique. Not so. See the magnificent achievements of Tome Kaye and his collaborators at: http://www.spectrashift.com/ That was quick! As Samuel Johnson noted "you will find it a very good practice always to verify your references!" and when I don't, I usually regret it. I'm very impressed. It seems there's very little well-equipped amateurs can't do. It wasn't long before Jack Newton imaged the Hubble Deep Field, for instance. Which brings me to something I saw recently. How faint is Io in eclipse, as imaged by Galileo and shown on the last "Sky at Night"? Could an interference filter be used to isolate aurora light, for instance? -- Rabbit arithmetic - 1 plus 1 equals 10 Remove spam and invalid from address to reply. |
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