KITP: Z and M

Debra Fischer talking about correlations between metallicity and mass of stars and planets

Two samples: Coralie data from Santos et al and Lick/Keck data

need to get uniform sampled subsets, looking at giant mass planets

known (cf Santos et al 2004, Fischer & Valenti 2005, Udry & Santos 2007)
trend to N ~ Z2
for short orbital period giant planets over -0.5 < Z < +0.5

everyone is redoing their analysis, remeasuring Z and making use of bigger samples, longer observing stretches and higher velocity sensitivity (and hence lower mass planets)

surface gravity, g, confounds Teff and Z estimates

she also sees much flatter distribution for M_planet < 90 Earth masses

Israelian claims lithium depletion in sunlike stars with known orbiting planets
lithium in photosphere destroyed by presence of planet? opposite of usual concern that planet bombardment enhances lithium
hypothesis that this is due enhanced mixing of surface layer – hmm

implies ~ 50% of stars have no planets (like that…)

or, the stars with no known planets did eat their planets, and are actually enhanced over the baseline?! [nah, Debra says that doesn't work when you look at how it ties in with the F stars and xA subgiants]

Pinsonneault et al 2001 – hotter stars with thin convection zones can have large Δ Z from planetary pollution if planets to plop onto stars a lot

don’t see super metal rich stars for hot stars and refractory metal
planets could still be plopping into stars, but mixing below the surface convection zone

see planet vs Z correlation in sub-giants, which have deepened convection zones, implies no autocorrelation due to planets messing up Z

need Kepler astroseismology to get metallicity gradients inside star

BUT… Pasquini et al 2007: giant stars with planets have metallicity average offset from comparable main sequence stars… hmm

of course with the giants, they are seeing more massive stars and planets in longer period orbits

JJ has a substantial paper in prep looking at Z and M correlations from -1 to +0.5 and from M to A stars

Argument that total amount of metals, or conversely surface density of disk midplanes is what matters

this is not trivial – since, eg, ice line shifts with mass and specific angular momentum ought to have some spread as well as ratio of disk mass to stellar mass

still, there is spread at all Z and M values, so really median over all these that matters

needs work from the modeling side, interesting

Dave reminds us that M dwarf metallicity estimates are from photometry,
spectroscopic metallicity determinations for M stars is dodgy, no nice Fe proxy
too many molecules


  1. #1 Craig Heinke
    April 2, 2010

    Quick note on the metallicity of hot stars angle; planets will fill their Roche lobes as they approach the star, and dump their matter directly into the stars’ outermost layers. (Some papers have pointed this out.) This relates to the Pinsonneault paper, in that they won’t deposit their metals in deeper convection zones.
    Unless, of course, the planet is bumped into a high-eccentricity orbit that sends it straight into the star.

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