Kepler News and Results

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Re: Kepler News and Results

Post by tommi59 on 16th March 2013, 5:51 pm

The Markov Chain Monte Carlo analysis of the
RV data yields a mass estimate for the d planet of 9.50+6.23
−8.17M⊕
(Geoff Marcy 2012, private communication
http://authors.library.caltech.edu/36783/1/0004-637X_762_2_129.pdf
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Re: Kepler News and Results

Post by Lazarus on 18th March 2013, 3:16 pm

Another study of the radius distribution of the Kepler planets...

The Radius Distribution of Small Planets Around Cool Stars
http://arxiv.org/abs/1303.3013

For stars with Teff<4000 K, the most common planet size appears to be 1 – 1.5 R. There also appears to be an excess of planets at 2 – 2.5 R, perhaps indicating a population of planets with low-density (H/He) atmospheres.
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Re: Kepler News and Results

Post by tommi59 on 19th March 2013, 7:34 am

What density is low density?? up to 2.0 g/cm3 ? Intermediate density 2.0-4.0 g/cm3 ? high over 4 ?
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Re: Kepler News and Results

Post by Lazarus on 19th March 2013, 12:50 pm

It's a qualitative description not a quantitative one.
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Re: Kepler News and Results

Post by Sirius_Alpha on 3rd April 2013, 9:02 am

Mission Update
http://www.spaceref.com/news/viewsr.rss.spacewire.html?pid=43725

The wheel rest period of January 17-January 27 appears to have had no beneficial impact on alleviating the elevated friction in reaction wheel #4.
At this point, all mitigation steps to preserve wheel life have been implemented, and no additional steps are planned at this time. We will continue to monitor wheel performance and respond accordingly if conditions warrant.

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Re: Kepler News and Results

Post by Lazarus on 5th April 2013, 12:54 pm

Gravitational lensing in a WD+dM binary

http://spaceref.com/astronomy/gravity-bending-find-leads-to-kepler-meeting-einstein.html
http://arxiv.org/abs/1304.1165
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Re: Kepler News and Results

Post by Stalker on 7th April 2013, 2:18 am

I have a question.

Is Kepler-37 a cold subdwarf? Look at Groombridge 1830 and μ Cas A, both are sdG type stars, and compare them to Kepler-37:

Groombridge 1830
Mass: 0.661 Ms
Radius: 0.681 Rs
Temperature: 4759 K
Metallicity: -1.33

μ Cas A
Mass: 0.74 Ms
Radius: 0.791 Rs
Temperature: 5332 K
Metallicity: -0.84

Kepler-37
Mass: 0.803 Ms
Radius: 0.770 Rs
Temperature: 5417 K
Metallicity: -0.32


Last edited by Stalker on 8th April 2013, 1:34 am; edited 1 time in total

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Re: Kepler News and Results

Post by Shellface on 7th April 2013, 6:58 pm

In short, no. I believe the upper cutoff for subdwarfs is at between Fe/H -0.6 and -0.7 or so, and a M/H of -0.3 is typical for a field star (particularly a thick disk star).

If you're looking for a better-studied analogue, HD 4208 is similar but a bit hotter:

M: 0.827
Teff (K): 5599 ± 19 K
[Fe/H] (dex): -0.28 ± 0.01 dex

While HD 63765 has a similar effective temperature, but is less metal-poor:

M: 0.828
Teff (K): 5432 ± 19
[Fe/H] (dex): -0.16 ± 0.01

(Data from Sousa et al. 2008)

I'd wager that the discrepancies is due to the stellar models used.

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Re: Kepler News and Results

Post by Stalker on 8th April 2013, 1:34 am

Thanks you!

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Re: Kepler News and Results

Post by ThinkerX on 8th April 2013, 2:14 am

Worth pointing out here: Fe/H ratings for stars vary widely. In different catalogs I have seen differences of 50% or more for the same star.

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Re: Kepler News and Results

Post by Lazarus on 8th April 2013, 2:13 pm

Isn't subdwarf status more about location on the H-R diagram than the metallicity?

I.e. low metallicity is what causes a star to be a subdwarf, but subdwarf status itself is determined by the low luminosity?
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Re: Kepler News and Results

Post by Stalker on 8th April 2013, 3:58 pm

Lazarus wrote:Isn't subdwarf status more about location on the H-R diagram than the metallicity?

I.e. low metallicity is what causes a star to be a subdwarf, but subdwarf status itself is determined by the low luminosity?

Yes, but Kepler Kepler-37 is (in my eyes) smaller than a normal GV (this is why i compare it to other known subwarves). In the HR diagram, this star would be a little "under" the cuvre of V stars, but may be not enough to be called a subdwarf.

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Re: Kepler News and Results

Post by Shellface on 8th April 2013, 4:32 pm

ThinkerX wrote:Worth pointing out here: Fe/H ratings for stars vary widely. In different catalogs I have seen differences of 50% or more for the same star.
What catalogues are you looking at? Photometric metallicities tend to be… weird, but spectroscopic metallicities are generally accurate to their errors (generally less than ± 0.05 dex for high S/N spectra). Spectroscopic values earlier than the 90s or so are also generally inaccurate, because most spectrometers… sucked back then.

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Re: Kepler News and Results

Post by ThinkerX on 8th April 2013, 11:55 pm

What catalogues are you looking at? Photometric metallicities tend to be… weird, but spectroscopic metallicities are generally accurate to their errors (generally less than ± 0.05 dex for high S/N spectra). Spectroscopic values earlier than the 90s or so are also generally inaccurate, because most spectrometers… sucked back then

Don't remember all of them right off - this was about six years ago. The Geneva-Copenhagen survey was one. Also Edvardson 'Chemical Evolution of the Galactic Disk', and Strobels 'A Catalog of Fe/H Determinations'. There were at least two others, one brand new at the time (though maddeningly, the names escape me and I can't find the relevant notes). One of these was the averaged results of four or five catalogs - it was one I came to rely on. I do remember, though, that all of them, regardless of how new they were or how accurate they claimed to be often put forth a wide range of Fe/H measurements. Exact matches, or even agreements within the range you cited were rare. Maybe a couple of them did date from the 1990's or a bit earlier.

For what its worth I see this elsewhere as well. Magnitudes, for example, differ from one catalog to another, as do spectral types, proper motions, and even exact positions.


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Re: Kepler News and Results

Post by Stalker on 9th April 2013, 2:20 am

Do we know a planet orbiting an actual (not yet evolved) cold subdwarf?

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Re: Kepler News and Results

Post by Lazarus on 9th April 2013, 1:20 pm

I don't think there are any known planets around subdwarfs. Maybe HIP 13044 is a "retired" subdwarf?

Also, has the Kepler-37 paper been made available without having to go through the Nature paywall?
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Re: Kepler News and Results

Post by Sirius_Alpha on 9th April 2013, 4:07 pm

Lazarus wrote:Also, has the Kepler-37 paper been made available without having to go through the Nature paywall?
AFAIK: No.

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Re: Kepler News and Results

Post by Led_Zep on 15th April 2013, 4:50 pm

http://www.spacedaily.com/reports/prnewswire-space-news.html?doc=201304151432PR_NEWS_USPR_____DC94898&showRelease=1&dir=0&categories=AEROSPACE-AND-SPACE-EXPLORATION&andorquestion=OR&&passDir=0,1,2,3,4,5,6,15,17,34

NASA will host a news briefing at 2 p.m. EDT, Thursday, April 18, to announce new discoveries from the agency's Kepler mission.
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Re: Kepler News and Results

Post by Sirius_Alpha on 15th April 2013, 7:00 pm

Lazarus wrote:I don't think there are any known planets around subdwarfs.
KOI-55 comes to mind. And of course circumbinary planetary systems often host subdwarfs.

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Re: Kepler News and Results

Post by Lazarus on 16th April 2013, 12:55 am

Yes but those are hot subdwarfs (mainly sdB), unlike the cool subdwarfs we were discussing in regards to Kepler-37.

There are two very different categories of objects termed "subdwarfs": cool subdwarfs which are metal-poor main sequence stars, and hot subdwarfs (sdO/sdB/sdA?) which seem to be the result of enhanced mass loss during the evolution of a giant star.
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Re: Kepler News and Results

Post by Led_Zep on 21st April 2013, 6:21 am

I like it :

http://www.nytimes.com/interactive/science/space/keplers-tally-of-planets.html?ref=space&_r=0

Surprise : did Kepler-71b annonced ?
(put on « sort by order of discovery », it‘s the last system)
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Re: Kepler News and Results

Post by Edasich on 21st April 2013, 10:57 am

Sirius_Alpha wrote:
Lazarus wrote:I don't think there are any known planets around subdwarfs.
KOI-55 comes to mind. And of course circumbinary planetary systems often host subdwarfs.

I also think of V391 Pegasi and recently detected DW Lyncis' substellar companion... Rolling Eyes

I like it :

http://www.nytimes.com/interactive/science/space/keplers-tally-of-planets.html?ref=space&_r=0

Surprise : did Kepler-71b annonced ?
(put on « sort by order of discovery », it‘s the last system)

Surprise for real. It looks like an inflated hot Jupiter around a G or K dwarf.
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Re: Kepler News and Results

Post by Lazarus on 21st April 2013, 11:11 am

Edasich wrote:
Sirius_Alpha wrote:
Lazarus wrote:I don't think there are any known planets around subdwarfs.
KOI-55 comes to mind. And of course circumbinary planetary systems often host subdwarfs.

I also think of V391 Pegasi and recently detected DW Lyncis' substellar companion... Rolling Eyes
I'll say this again, sdB/sdO stars (extreme horizontal branch stars) are not related to the low-metallicity main sequence subdwarfs that we were discussing. Rolling Eyes
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Re: Kepler News and Results

Post by Edasich on 22nd April 2013, 12:46 pm

Glad to see at least these latest Kepler planets listed at EPE, though there are 27 extrasolar planet candidates left to be listed (notably Kepler-37 b, c &d, HAT-P-42 & 43 b and WASP-71 b).
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Re: Kepler News and Results

Post by Lazarus on 23rd April 2013, 2:02 am

KOI-200b and KOI-889b: two transiting exoplanets detected and characterized with Kepler, SOPHIE and HARPS-N
http://arxiv.org/abs/1304.6002

A couple of jovian-size planets in close-in orbits.
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Re: Kepler News and Results

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