zyntrax

The Sun is short on refractory (rocky) elements next to nearby Sun-like stars, by about 0.01 dex. Refractories condense first out of a cooling disk, so the Sun having rocky planets is one explanation. The abundance gradient against condensation temperature, the Tc slope, became a planet-formation tracer.

A new paper gives a duller cause: star spots. Refractory elements tend to have low first-ionization potentials and strong lines, which makes them the most sensitive to the cool, magnetized air inside a spot. So a spotted star looks refractory-poor in a way that tracks Tc, with no planet involved.

Casey, Bedell and co-authors (Flatiron) show it three ways. More active stars show steeper Tc slopes, the least active near zero, across 79 Sun-like stars with activity re-measured from their own HARPS spectra. A simulated spotted Sun reproduces the reported slopes. And a sunspot umbra lifts many elements by up to a factor of three over the quiet Sun.

Caveats: preprint (Oct 13), not peer reviewed; the authors call their own fit physically unmotivated and warn against causal claims drawn from it; the simulations skip non-LTE, magnetic fields and molecular lines; and the umbra is an extreme, not a whole star.

This does not kill planet formation. It asks that any Tc-slope claim show a quiet star first.