Date: September 17, 2011

Title: Planet Host Stars

Podcaster:

Organization: National Optical Astronomy Observatory (NOAO)

Links:
Website(s) you want to have a link to: http://www.noao.edu
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Description: A discussion of planet host stars.

Bio: Rob Sparks is a science education specialist in the EPO group at NOAO and works on the Galileoscope project (www.galileoscope.org), providing design, dissemination and professional development. He also blogs at halfastro.wordpress.com.

Sponsors: This episode of “365 Days Of Astronomy” has been brought to you by the National Optical Astronomy Observatory. NOAO is a US national research and development center for ground-based nighttime astronomy. We provide astronomers access to world-class observing facilities on a peer-reviewed basis. Our mission is to engage in programs to develop the next generation of telescopes, instruments, and software tools necessary to enable exploration and investigation through the observable Universe. For information on observing proposals or our public programs, please visit www.noao.edu for more information.

Transcript:

Rob: Hi, this is Rob Sparks of the National Optical Astronomy Observatory and I would like to welcome you to this edition of the 365 Days of Astronomy podcast. I am sitting here with Simon Schuler of NOAO. Good morning, Simon.

Simon: Good morning.

Rob: How are you doing, today?

Simon: Just great, thank you very much.

Rob: Today we are here to talk about extrasolar planet hosts, but first could you tell me a little bit about your position here at NOAO.

Simon: Sure, like you said, my name is Simon Schuler. I am a Leo Goldberg Fellow here at NOAO. The Leo Goldberg Fellowship is a five year fellowship given to a new post-doc every year here at NOAO and I am coming to the end of my fellowship actually. I have been here for five years and enjoyed it very much and been doing a lot of research.

Rob: You do a lot of work looking at the host stars of extra solar planets. So the first question is what makes a good host star?

Simon: That’s a good question and it can have many different answers. It depends what you are interested in. I think what most people would find interesting is host stars that are like our Sun. This is one of the main reasons we look for extrasolar planets, aside from just understanding how planets form and knowing that there are other planets out there. We are interested in finding systems like our own, in finding systems that are conducive to hosting life and the only place we know now that life exists is around our Sun so a good starting point is looking for stars like our Sun.

Rob: Stars have different compositions which may aid in the formation of planets and I understand you do a lot of work looking at the compositions of stars.

Simon: That’s correct. That’s basically what I do. I derive the abundances of stars, meaning I determine the compositions of different stars. In extrasolar planets, I look at stars we know to host planets and stars we don’t know to host planets to see if there are any differences in the compositions of those stars and to see if those compositions may tell us something about planet formation.

Rob: You recently received a grant from NASA to work with the Kepler Science Group. Tell me what that work will entail and what you hope to learn about planet hosts.

Simon: Kepler is a very successful mission of NASA right now looking for planets around over 100,000 stars, staring at once piece of the sky looking for planetary transits which are planets moving in front of the stars and Kepler is measuring the slight dimming of the star as the planet moves in front, and of the 100,000 plus stars that Kepler is looking at, they so far have found over 1200 planetary candidates. That’s about a factor of three or four more than we have known so far. What’s interesting about the Kepler planets is they are mostly small. They are much smaller than the planets we have known about so far found by other methods, we’re talking about Jupiter sized planets. The planets Kepler’s finding are Neptune sized and smaller, even down to Earth sized. What I will be doing with the Kepler group is deriving the compositions of some of these host stars and comparing the differences in the compositions of those stars with small planets and large planets because there is some indication they might be different.

Rob: The big question is what would make a good host star for Earth type planets?

Simon: Well, that kind of goes back to the previous question about what makes a good host star. Again, if we are interested in finding planets that are suitable for hosting life, as far as what we know is life, then it would be stars like the Sun. And these are stars that may be a little bit bigger than the Sun or a little bit smaller than the Sun but the sweet spot is right around there, solar mass stars.

Rob: You talked about the compositions of stars. What types of metals and ratios are we looking for for things like our Sun

Simon: It seems that the most interesting elements to look at are what we would call the refractor elements. These elements are rocky elements or hard elements, something like iron or nickel and things like magnesium, zinc and things like this. These are interesting to look at because these are what planets are made of. Terrestrial type planets. Obviously terrestrial type planets are rocky so you need rocky material and these kinds of elements make up that rocky material. Looking for different patterns in these refractory elements may tell us something about planet formation.

Rob: I know that as time has gone on the composition of the interstellar gas stars form from changes as supernova seeds them with elements. How old are the stars we are looking at. A billion years ago? Five billion years ago? Ten billion years ago?

Simon: Overall people are looking at a mix of different ages. Our Sun of course is about five billion years.

Rob: So we know that five billion years is good.

Simon: That’s exactly right. So some of the stars that people are looking at are older than the Sun, maybe seven or eight billion years. But then also people are looking at very young stars where they may still have the discs forming around the stars, where the planets could be forming in these discs so they are looking at quite a range. So far most of the planets we are finding are around stars that have a composition like the Sun, so metal rich. Planets really haven’t been found around metal poor stars and metal poor stars tend to be older stars so we are not really finding a lot of planets around really old stars, maybe about 10 billion years which is quite interesting. Solar age, maybe five billion years is still good, but 10 billion years is too old.

Rob: Obviously you are going to be doing this work in the future so what new instruments would you like to see developed for you to continue your research. If you had a blank check to design your own ideal instrument, what would it be?

Simon: Oh my goodness! Wouldn’t that be fun! To do my work I use high resolution spectrographs. These are what we call workhorse instruments. Most observatories have them, they gather the light from a star and spread it out to high dispersion so I can look at absorption lines from the atmospheres of the stars. Now going back to Kepler, most of the planets that Kepler is finding, most of these small planets are around faint stars. To observe faint stars, you need big telescopes. To do high resolution spectroscopy, you need a lot of photons. So you need a large telescope with an efficient spectrograph to do the kind of work that I do. To do the faint stars that Kepler is finding, even the largest telescope in the world now, the 10 meter Keck telescope, doesn’t quite cut it. You need several Keck nights to observe one star to get the data I would need to do what I like to do. So the next generation of telescopes, the 30 meter telescopes, a very efficient high resolution spectrograph will be essential to continue this kind of work on fainter and fainter stars that Kepler is finding and future missions will no doubt find.

Rob: Thank you very much for joining me today, Simon.

Simon: Thank you very much. It’s been my pleasure.

Rob: This is Rob Sparks for the 365 Days of Astronomy podcast and I hope you will join us again next month.

End of podcast:

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