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.

► Read more>>
http://advances.sciencemag.org/content/2/1/e1500654.full

► Image Credit:
Wikimedia Common

Comments

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).

RADIATIVE CLEARING OF PROTOPLANETARY DISCS

Image: protoplanetary disc surrounding the young star HL Tauri, a very young T Tauri star in the constellation Taurus, approximately 450 light-years (140 pc) from Earth in the Taurus Molecular Cloud. These new ALMA observations reveal substructures within the disc that have never been seen before and even show the possible positions of planets forming in the dark patches within the system. Credit: ALMA (ESO/NAOJ/NRAO) T Tauri stars are pre-main-sequence stars in the process of contracting to the main sequence. Their central temperatures are too low for hydrogen fusion. Instead, they are powered by gravitational energy released as the stars contract, while moving towards the main sequence, which they reach after about 100 million years. Roughly half of T Tauri stars have circumstellar disks, which in this case are called protoplanetary discs because they are probably the progenitors of planetary systems like the Solar System.

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 ).

SpaceTime

Search This Blog