- 4430 - AGES OF STARS? - The upcoming Roman Space Telescope will gather data from hundreds of millions of stars through its “Galactic Bulge Time Domain Survey”, one of three core community surveys it will conduct. Roman will look toward our galaxy's center—a region crowded with stars—to measure how many of these stars change in brightness over time. These measurements will enable multiple science investigations, from searching for distant exoplanets to determining the stars' rotation rates.
------------------------- 4430 - AGES OF STARS?
- An image of our sun was taken in August
2012 by NASA’s “Solar Dynamics Observatory” shows a number of sunspots. Other
stars also experience starspots, which cause the star’s observed brightness to
vary as the spots rotate in and out of view. By measuring those changes in
brightness, astronomers can infer the star’s rotation period.
-
- NASA’s “Nancy Grace Roman Space Telescope”
will collect brightness measurements for hundreds of thousands of stars located
in the direction of the center of our Milky Way galaxy, yielding information
about their rotation rates.
-
- It's a real challenge to determine the ages
of stars. Once a star like our sun has settled into steady nuclear fusion, or
the mature phase of its life, it changes little for billions of years. One
exception to that rule is the star's rotation period—how quickly it spins. By
measuring the rotation periods of hundreds of thousands of stars, the Nancy Grace Roman Space Telescope
promises to bring new understandings of stellar populations in our Milky Way
galaxy after it launches by May 2027.
-
- Stars are born spinning rapidly. However,
stars of our sun's mass or smaller will gradually slow down over billions of
years. That slowdown is caused by interactions between a stream of charged
particles known as the stellar wind and the star's own magnetic field. The
interactions remove angular momentum, causing the star to spin more slowly,
much like an ice skater will slow down when they extend their arms.
-
- This effect, called magnetic braking,
varies depending on the strength of the star's magnetic field. Faster-spinning
stars have stronger magnetic fields, which causes them to slow down more
rapidly. Due to the influence of these magnetic fields, after about one billion
years stars of the same mass and age will spin at the same rate.
-
- Therefore, if you know a star's mass and
rotation rate, you potentially can estimate its age. By knowing the ages of a
large population of stars, we can study how our galaxy formed and evolved over
time.
-
- Astronomers measure the rotation rate of a
distant star by lookong for changes in the star's brightness due to
starspots. Starspots, like sunspots on
our sun, are cooler, darker patches on a star's surface. When a starspot is in
view, the star will be slightly dimmer than when the spot is on the far side of
the star.
-
- If a star has a single, large spot on it,
it would experience a regular pattern of dimming and brightening as the spot rotated
in and out of view. (This dimming can be differentiated from a similar effect
caused by a transiting exoplanet.) But a star can have dozens of spots
scattered across its surface at any one time, and those spots vary over time,
making it much more difficult to tease out periodic signals of dimming from the
star's rotation.
-
- Astronomers at the University of Florida
are developing new techniques to extract a rotation period from measurements of
a star's brightness over time. They are
using a type of artificial intelligence known as a convolutional neural network
to analyze light curves, or plots of a star's brightness, over time. To do
this, the neural network first must be trained on simulated light curves.
-
- This program lets the user set a number of
variables, like the star's rotation rate, the number of spots, and spot
lifetimes. Then it will calculate how spots emerge, evolve, and decay as the
star rotates and convert that spot evolution to a light curve—what we would
measure from a distance.
-
- The team has already applied their trained
neural network to data from NASA's TESS (Transiting Exoplanet Survey
Satellite). Systematic effects make it more challenging to accurately measure
longer stellar rotation periods, yet the team's trained neural network was able
to accurately measure these longer rotation periods using the TESS data.
-
- A star can have dozens of spots scattered
across its surface at any one time, causing irregular brightness fluctuations
that make it difficult to tease out periodic signals of dimming due to the
star’s rotation.
-
-
April 11, 2023 AGES
OF STARS? 4430
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------ “Jim Detrick” -----------
--------------------- --- Saturday, April 13,
2024
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