Planet found orbiting small, cool star

Date:
August 4, 2020
Source:
National Radio Astronomy Observatory
Summary:
Precision measurements made with the VLBA have revealed that
a small, cool star 35 light-years from Earth is orbited by a
Saturn-sized planet once every 221 days.



FULL STORY ========================================================================== Using the supersharp radio "vision" of the National Science Foundation's continent-wide Very Long Baseline Array (VLBA), astronomers have
discovered a Saturn-sized planet closely orbiting a small, cool star
35 light-years from Earth. This is the first discovery of an extrasolar
planet with a radio telescope using a technique that requires extremely
precise measurements of a star's position in the sky, and only the second planet discovery for that technique and for radio telescopes.


==========================================================================
The technique has long been known, but has proven difficult to use. It
involves tracking the star's actual motion in space, then detecting a
minuscule "wobble" in that motion caused by the gravitational effect
of the planet. The star and the planet orbit a location that represents
the center of mass for both combined. The planet is revealed indirectly
if that location, called the barycenter, is far enough from the star's
center to cause a wobble detectable by a telescope.

This technique, called the astrometric technique, is expected to be particularly good for detecting Jupiter-like planets in orbits distant
from the star. This is because when a massive planet orbits a star,
the wobble produced in the star increases with a larger separation
between the planet and the star, and at a given distance from the star,
the more massive the planet, the larger the wobble produced.

Starting in June of 2018 and continuing for a year and a half, the
astronomers tracked a star called TVLM 513-46546, a cool dwarf with less
than a tenth the mass of our Sun. In addition, they used data from nine previous VLBA observations of the star between March 2010 and August 2011.

Extensive analysis of the data from those time periods revealed a telltale wobble in the star's motion indicating the presence of a planet comparable
in mass to Saturn, orbiting the star once every 221 days. This planet
is closer to the star than Mercury is to the Sun.

Small, cool stars like TVLM 513-46546 are the most numerous stellar
type in our Milky Way Galaxy, and many of them have been found to have
smaller planets, comparable to Earth and Mars.



========================================================================== "Giant planets, like Jupiter and Saturn, are expected to be rare around
small stars like this one, and the astrometric technique is best at
finding Jupiter- like planets in wide orbits, so we were surprised to
find a lower mass, Saturn- like planet in a relatively compact orbit. We expected to find a more massive planet, similar to Jupiter, in a wider
orbit," said Salvador Curiel, of the National Autonomous University of
Mexico. "Detecting the orbital motions of this sub-Jupiter mass planetary companion in such a compact orbit was a great challenge," he added.

More than 4,200 planets have been discovered orbiting stars other than
the Sun, but the planet around TVLM 513-46546 is only the second to be
found using the astrometric technique. Another, very successful method,
called the radial velocity technique, also relies on the gravitational
effect of the planet upon the star. That technique detects the slight acceleration of the star, either toward or away from Earth, caused by
the star's motion around the barycenter.

"Our method complements the radial velocity method which is more
sensitive to planets orbiting in close orbits, while ours is more
sensitive to massive planets in orbits further away from the star," said
Gisela Ortiz-Leon of the Max Planck Institute for Radio Astronomy in
Germany. "Indeed, these other techniques have found only a few planets
with characteristics such as planet mass, orbital size, and host star
mass, similar to the planet we found. We believe that the VLBA, and the astrometry technique in general, could reveal many more similar planets."
A third technique, called the transit method, also very successful,
detects the slight dimming of the star's light when a planet passes in
front of it, as seen from Earth.

The astrometric method has been successful for detecting nearby binary
star systems, and was recognized as early as the 19th Century as a
potential means of discovering extrasolar planets. Over the years, a
number of such discoveries were announced, then failed to survive further scrutiny. The difficulty has been that the stellar wobble produced by a
planet is so small when seen from Earth that it requires extraordinary precision in the positional measurements.

"The VLBA, with antennas separated by as much as 5,000 miles, provided us
with the great resolving power and extremely high precision needed for
this discovery," said Amy Mioduszewski, of the National Radio Astronomy Observatory.

"In addition, improvements that have been made to the VLBA's sensitivity
gave us the data quality that made it possible to do this work now,"
she added.

The National Radio Astronomy Observatory is a facility of the National
Science Foundation, operated under cooperative agreement by Associated Universities, Inc.


========================================================================== Story Source: Materials provided by
National_Radio_Astronomy_Observatory. Note: Content may be edited for
style and length.


========================================================================== Journal Reference:
1. Salvador Curiel, Gisela N. Ortiz-Leo'n, Amy J. Mioduszewski, Rosa M.

Torres. An Astrometric Planetary Companion Candidate to the M9
Dwarf TVLM 513-46546. The Astronomical Journal, 2020; 160 (3):
97 DOI: 10.3847/1538- 3881/ab9e6e ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/08/200804122220.htm

--- up 2 weeks, 6 days, 1 hour, 55 minutes
* Origin: -=> Castle Rock BBS <=- Now Husky HPT Powered! (1337:3/111)