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

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‘Monster’ Planet Discovery Challenges Formation Theory

Artist’s illustration of a "hot Jupiter". Image Credit: NASA/CXC/M. Weiss A new research presents the discovery of NGTS-1b, a hot-Jupiter transiting an early M-dwarf host in a P~2.6 days orbit discovered as part of the Next Generation Transit Survey (NGTS). The planet has a mass of M~0.8 M(jupiter) making it the most massive planet ever discovered transiting an M-dwarf. NGTS-1b is the third transiting giant planet found around an M-dwarf, reinforcing the notion that close-in gas giants can form and migrate similar to the known population of hot Jupiters around solar type stars. The existence of the 'monster' planet, 'NGTS-1b', challenges theories of planet formation which state that a planet of this size could not be formed around such a small star. According to these theories, small stars can readily form rocky planets but do not gather enough material together to form Jupiter-sized planets. Such massive planets were not thought to exist ar...

ORBITAL PERIODS OF THE PLANETS

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).

CONSTRAINTS ON THE LOCATION OF A POSSIBLE 9TH PLANET

Image: The six most distant known objects in the solar system with orbits exclusively beyond Neptune (magenta) all mysteriously line up in a single direction. Such an orbital alignment can only be maintained by some outside force, Batygin and Brown say. Their paper argues that a planet with 10 times the mass of the earth in a distant eccentric orbit anti-aligned with the other six objects (orange) is required to maintain this configuration. Credit: Caltech The astronomers have noticed some of the dwarf planets and other small, icy objects tend to follow orbits that cluster together. To explain the unusual distribution of these Kuiper Belt objects, several authors have advocated the existence of a superEarth planet in the outer solar system ( planet Nine or planet X ).

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