Kepler News and Results

Led_Zep wrote:http://arxiv.org/abs/1303.0227

All Six Planets Known to Orbit Kepler-11 Have Low Densities

That's gross, planets c, e, f are more sort of mini-Saturn that mini-Neptune. Maybe the system had very little metals available during planets formation - but the host star, though old, seems to be of solar-like metallicity.

Some studies indicate that fluffy super earths are likely H2O free, just surrounded by an atmosphere of H/He:
http://arxiv.org/abs/1210.7810

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

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 T_eff<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.

What density is low density?? up to 2.0 g/cm3 ? Intermediate density 2.0-4.0 g/cm3 ? high over 4 ?

It's a qualitative description not a quantitative one.

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.

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

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

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.

Thanks you!

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.

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?

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.

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.