Mysterious delta Scuti stars start to surrender secrets

The key to unlocking the secrets of a large group of pulsating stars has been discovered by an international team of astrophysicists. Pulsations are a common feature of stars. They are natural resonances, formed by trapped waves like those in musical instrument, and provide a unique way to look inside stars. Studies that use pulsations - the field of asteroseismology - allow us to test models of stellar evolution, and have been extremely successful on a range of different classes of stars. In one class of stars, however, scientists have been frustrated in their attempts to use astroseismology. The so-called delta (d) Scuti stars present seemingly random spectra of pulsation overtones, making it very hard to interpret the pulsations to glean clues about their internal structures. In a new study, by a team including researchers at the University of Birmingham, UK, and the University of Sydney, Australia, a subset of this class has been found that shows much simpler, ordered and understandable pulsation spectra. The discovery was made using data from the NASA Transiting Exoplanet Survey Satellite (TESS), and the NASA Kepler Mission. The ordered spectra offer the potential to unlock a treasure trove of information on this important group of stars. The study is published in Nature. "Asteroseismology is the method we use to reveal the usually hidden interiors of stars," explains co-author Dr Tanda Li of the School of Physics and Astronomy at Birmingham. "Asteroseismology has yielded a wealth of fascinating insights on many types of stars, including the Sun, but until now the random spectra of delta-Scutis has limited our ability to use pulsations to tell us about these stars."

The new subset of stars tend to be younger than their seemingly random cousins. Birmingham co-author Dr Warrick Ball says: "This fits the picture in which we know pulsation spectra tend to get more complicated as stars age. The youngest stars therefore give us our best shot at finding ordered spectra".

Professor Bill Chaplin, who leads the research group working on asteroseismology at Birmingham, added: "We are now in a position to start to probe these stars, and to use them as benchmarks to help us interpret the huge numbers of other stars in the group that present more complicated pulsation spectra."

Astronomy student discovers 17 new planets, including Earth-sized world

University of British Columbia astronomy student Michelle Kunimoto has discovered 17 new planets, including a potentially habitable, Earth-sized world, by combing through data gathered by NASA's Kepler mission. Over its original four-year mission, the Kepler satellite looked for planets, especially those that lie in the "Habitable Zones" of their stars, where liquid water could exist on a rocky planet's surface. The new findings, published in The Astronomical Journal, include one such particularly rare planet. Officially named KIC-7340288 b, the planet discovered by Kunimoto is just 1 0.5 times the size of Earth - small enough to be considered rocky, instead of gaseous like the giant planets of the Solar System - and in the habitable zone of its star. "This planet is about a thousand light years away, so we're not getting there anytime soon!" said Kunimoto, a PhD candidate in the department of physics and astronomy. "But this is a really exciting find, since there have only been 15 small, confirmed planets in the Habitable Zone found in Kepler data so far." The planet has a year that is 142 0.5 days long, orbiting its star at 0.444 Astronomical Units (AU, the distance between Earth and our Sun) - just bigger than Mercury's orbit in our Solar System, and gets about a third of the light Earth gets from the Sun. Of the other 16 new planets discovered, the smallest is only two-thirds the size of Earth - one of the smallest planets to be found with Kepler so far. The rest range in size up to eight times the size of Earth.

Kunimoto is no stranger to discovering planets: she previously discovered four during her undergraduate degree at UBC. Now working on her PhD at UBC, she used what is known as the "transit method" to look for the planets among the roughly 200,000 stars observed by the Kepler mission.

"Every time a planet passes in front of a star, it blocks a portion of that star's light and causes a temporary decrease in the star's brightness," Kunimoto said. "By finding these dips, known as transits, you can start to piece together information about the planet, such as its size and how long it takes to orbit."

Kunimoto also collaborated with UBC alumnus Henry Ngo to obtain razor-sharp follow-up images of some of her planet-hosting stars with the Near InfraRed Imager and Spectrometer (NIRI) on the Gemini North 8-metre Telescope in Hawaii.

"I took images of the stars as if from space, using adaptive optics," she said. "I was able to tell if there was a star nearby that could have affected Kepler's measurements, such as being the cause of the dip itself."

In addition to the new planets, Kunimoto was able to observe thousands of known Kepler planets using the transit-method, and will be reanalysing the exoplanet census as a whole.

"We'll be estimating how many planets are expected for stars with different temperatures," said Kunimoto's PhD supervisor and UBC professor Jaymie Matthews. "A particularly important result will be finding a terrestrial Habitable Zone planet occurrence rate. How many Earth-like planets are there? Stay tuned."