STELLAR SURFACE GRAVITY FROM THE TIME SCALES OF THE BRIGHTNESS VARIATION

Recently, some authors (Kallinger et al. 2016) proposed a new method to derive the stars' surface gravity "g". This parameter is fundamental to derive the mass and radius of the star itself. Mass and radius, in turn, are essential quantity for a correct estimate of the mass and size of extrasolar planets orbiting around it.

So far the measure of "g" was obtained by evaluating the amplitude of the brightness variations. However many stars are too faint to be studied with this approach.
The new method is suggested to analyze the time-scale of these variations due to the surface convection (seen as granulations) and the acoustic oscillations (p-mode pulsation) reaching an error of just 4%.
One of the advantages of this new method (valid for stars with masses between 0.8 and 3 solar masses) is that it is largely independent of the activity level of a star.

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http://advances.sciencemag.org/content/2/1/e1500654.full

► Image Credit:
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For orbital period generally we refer to the sidereal period, that is the temporal cycle that it takes an object to make a full orbit, relative to the stars. This is the orbital period in an inertial (non-rotating) frame of reference (365,25 days for the earth).

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Image: The Kuiper Belt. Credit: NASA . The Kuiper belt is a circumstellar disc in the Solar System beyond the planets, extending from the orbit of Neptune (at 30 AU) to approximately 50 AU from the Sun. It is similar to the asteroid belt (the circumstellar disc located roughly between the orbits of the planets Mars and Jupiter), but it is far larger-20 times as wide and 20 to 200 times as massive.

Fermi Bubbles

Image: A giant gamma-ray structure was discovered in 2010 by processing Fermi all-sky data at energies from 1 to 10 billion electron volts, shown here. The dumbbell-shaped feature (center) emerges from the galactic center and extends 50 degrees north and south from the plane of the Milky Way, spanning the sky from the constellation Virgo to the constellation Grus. Credits: NASA/DOE/Fermi LAT/D. Finkbeiner et al. At a time when our earliest human ancestors mastered walking upright the heart of our Milky Way galaxy underwent a titanic eruption, driving gases and other material outward at 2 million miles per hour.

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