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Kepler Mission
Greg Hullender
post Sep 7 2009, 03:43 PM
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Sure. Let me know if you can't download this -- it's my first try at using skydrive.

http://cid-6f25d46a94c04426.skydrive.live....ht%20Curves.pdf

This is a bit rough, since I just threw it together on Saturday, but I'm pretty confident it's correct. If you see something wrong, don't hesitate to let me know.

The derivations don't require anything beyond 10th-grade algebra and trigonometry. There is a faster way to get there using multi-variable calculus (and you have to do it that way to get limb-darkening) but I didn't put that into this document.

--Greg
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Hungry4info
post Sep 9 2009, 03:54 AM
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Thank-you so much for that, works great biggrin.gif


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Holder of the Tw...
post Sep 9 2009, 02:57 PM
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A minor mission update has been posted, as usual the link is here.

Basicly everything is routine right now, and they are making some headway in understanding the safing events.
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Greg Hullender
post Sep 9 2009, 04:34 PM
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QUOTE (JGodbaz @ Sep 2 2009, 05:52 AM) *
If stars like this exist, then different regions of the star's equator would be at different temperatures

Perhaps the bigger question is whether stars exist which are significantly brighter on one side than the other -- for whatever reason.

--Greg
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centsworth_II
post Sep 9 2009, 06:59 PM
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I thought maybe Kepler data would lend itself to studying surface phenomena like flares and star spots, but was surprised to see that the BIG thing is going to be using the data to study star interiors!

The Kepler team will use seismic techniques to probe the cores of a large number of stars.
"The quality of the Kepler data and the large number of stars observed are expected to lead to a huge step
forward in understanding of stellar evolution. During the first nine months in space Kepler will survey more
than 5000 stars for oscillations. Based on those measurements around 1100 stars will be followed for
detailed studies throughout the full mission. The accuracy with which Kepler will be able to measure stellar
oscillations is so high that the science team expects to watch directly the change in stars as they age."


There is an international group formed specifically to do these studies, the Kepler Asteroseismic Science Consortium.

One of the members, the Danish Asteroseismology Centre has an informative website with lots of pretty graphics which gives some basic background.
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Greg Hullender
post Sep 23 2009, 05:31 PM
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Another Mission Manager update:

http://www.kepler.arc.nasa.gov/about/manager.html

The second quarterly roll went well. Also, some of the data are now publicly available!

http://archive.stsci.edu/kepler/

Be interesting to see what's in there.

--Greg
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Syrinx
post Sep 25 2009, 02:13 AM
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QUOTE (Greg Hullender @ Sep 23 2009, 10:31 AM) *
Be interesting to see what's in there.

An SQL query with Availability_Flag = 2 returns 165831 results.

QUOTE
Availability Flag
Source availability flag. Non-zero values indicate the target has been observed. A "1" means the target has been observed but is not restricted to Science Team members. A "2" means the target was observed by the Kepler Science Team (and therefore unavailable to GO proposer's). The Kepler Science Team has exclusive rights to all targets on the exoplanet survey list (as described in Policy 4 of the Science Utilization Policy; KKPO-16104).

I guess that means the science team is interested in ~166k targets, at least so far.
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Greg Hullender
post Sep 25 2009, 03:47 AM
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Yeah, it looks like they won't make the first quarter's raw data available for another twelve months. Then they'll release more of it annually. Oh well. At least they DO plan to make it all available eventually.

--Greg
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Holder of the Tw...
post Sep 25 2009, 02:25 PM
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QUOTE (Syrinx @ Sep 24 2009, 09:13 PM) *
~166k targets, at least so far.

That would be every star currently being watched for transits. All the giant stars they can identify are already off the list. The number will fall as more and more dwarf stars are eliminated as being too active to be good candidates. In a few months time it should be down to about 100K.
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Greg Hullender
post Sep 25 2009, 04:27 PM
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What was the reason for excluding giant stars? Are they all too variable? Or simply too bright to be able to measure the effect of a transit of even a giant planet?

--Greg
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Holder of the Tw...
post Sep 25 2009, 06:37 PM
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To tell the truth, I'm not really sure. I just know that they are being excluded. The fact that they are much more luminous does make it harder to detect planets, I'm certain. Other factors might be that the transit time will be much longer, allowing stellar variablity to play a larger noise factor. Also, they are concentrating on looking for solar system analogs with possible earth like worlds. Any that avoided being swallowed and still existed would be fried. Anything made habitable would have an orbital period too long for confirmation.

I saw some indications on internet search engines that guest observers were inquiring about the possibility of seaching for transits around sub-giants and giants, so there might be some kind of side program going on for these. But the web pages for those were pulled.
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Byran
post Sep 26 2009, 01:10 PM
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Holder of the Two Leashes when approximately report about discovery of the first planets? On conferences DPS 2009 the new discovery Kepler are expected?


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Hungry4info
post Sep 26 2009, 07:31 PM
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QUOTE (Greg Hullender @ Sep 25 2009, 11:27 AM) *
What was the reason for excluding giant stars? Are they all too variable? Or simply too bright to be able to measure the effect of a transit of even a giant planet?


As I understand it, all else held constant, brighter transits are easier to detect due to a higher S/N.
Giant stars have much larger angular surface areas, so when the planet transits across, the planet blocks a significantly lower fraction of light, producing much fainter transit signals.


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Holder of the Tw...
post Sep 26 2009, 08:20 PM
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Yes, you're right. Perhaps I didn't state that as well as we could. The surface brightness doesn't matter, the planet will be blocking the same fraction of light no matter what. Giants are more luminous due to a much larger surface as well as a much greater total energy output. The fraction of blocked light for any given planet size is less for larger stars. And the signal will be stronger depending on the apparent magnitude, as seen by Kepler and not how bright the star actually is. The fact that there are so many giants showing up and being ignored is simply due to the fact you can see them from further away.

QUOTE (Byran @ Sep 26 2009, 07:10 AM) *
...when approximately report about discovery of the first planets?


Sorry, all I know is from public sources, so it's what I'm told and what I can infer. smile.gif
They have stated that by the end of the year they will be ready to announce a lot of short period planets, those that have orbits measured in days.

If you want insider information, you're going to have to track down ustrax. Either that or maybe crack the code on one of his frickin anagrams rolleyes.gif .
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nprev
post Sep 27 2009, 01:18 AM
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If I'm not mistaken, Kepler's focus on finding Earth-sized planets seems to also lean a bit towards the serendipitous possibility of finding worlds around suitable stars in "Goldilocks zones", which would be one reason to exclude giant stars.

Another would be that smaller worlds probably aren't likely to be found around giants. Massive luminous stars often die too young to form mature planetary systems (or blow all the excess gas & dust away before one has the chance to form), and old red giants would tend to swallow up inner planets. At the other extreme, red dwarfs are thought to have extensive starspotting which would complicate detection confirmations considerably.

All in all, it's probably more statistically productive to focus on middle main-sequence dwarfs given Kepler's strategy & capabilities.


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A few will take this knowledge and use this power of a dream realized as a force for change, an impetus for further discovery to make less ancient dreams real.
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