Astrophysics take the pulse of Delta Scuti stars with TESS

2020-09-01

An artist's impression of a Delta Scuti star. Credit: NASA's Goddard Space Flight Center.


A scientific team led by the Center for Astrobiology (CAB, CSIC-INTA) has used data obtained by several space telescopes, including TESS, to deduce the seismic parameters of a special type of variable stars: the so-called Delta Scuti. The study has revealed that the surface temperature and pulsation frequency of the star are related. These results will help to more accurately determine the ages and distances to this type of stars, as well as their areas of habitability.


Asteroseismology studies the relationship between the physical characteristics of stars and their variations in luminosity due to oscillations (sisms). A scientific team led by researchers from the Center for Astrobiology has used data obtained by the TESS (Transiting Exoplanet Survey Stallite) space telescope, along with previous data obtained by the Kepler and CoRoT space telescopes, to deduce the seismic parameters of 2,400 variable stars of a particular type: the so-called Delta Scuti. 

Delta Scuti variable stars are a type of variable stars that show variations in their luminosity due to pulsations of their surface. They usually have masses between 1.5 and 2.5 solar masses and surface temperatures between 6000 and 9000K. For these stars, asteroseismic relationships remain a source of debate among scientists, unlike better-known stars, such as solar stars.

Thanks to this new analysis, recently published in the journal Astronomy & Astrophysics, researchers have been able to reveal the relationship between surface temperature and gravity with the star's pulsation frequency, as previous theoretical studies predicted. Depending on the ratio discovered, the higher the temperature, the higher the oscillation frequency. In addition, older stars with more gravity have a lower frequency range than young stars and more severe.

For Sebastià Barceló Forteza, a researcher at the CAB who has led the study, "the team's greatest challenge to obtain our results has been to correct the so-called gravity-darkening effect, since these types of stars can rotate extremely quickly. The rapidness of rotation produces a flattening in the stars and a difference in temperatures between the poles and the equator. Our asteroseismic results suggest that we can get its average temperature, regardless of rotation, inclination or other external factors."

Conversely, the results obtained by other methods such as photometry or spectroscopy are greatly affected by rotation and inclination. Thanks to this, we can compare your results and deduce the most likely tilt and rotation. In this way, the gravitational darkening effect not only explains the dispersion in temperature, but also the decrease of the temperature with gravity. Older stars have greater gravity so they are closer to extreme rotation, even if they rotate more slowly.

"This temperature correction will improve the determination of age and distance to the stars themselves and even other galaxies. In addition, it allows greater accuracy in the calculation of the habitable zone for exoplanets around this type of stars", concludes Barceló Forteza.

TESS belongs to a family of space observatories whose mission is to detect planets and their characterization through photometric observations. As David Barrado Navascués, CAB researcher and co-author of the study, points out, "the techniques we are developing with TESS will be applied to the future PLATO space observatory, a medium-class ESA mission that will allow the study of planetary systems similar to ours. The CAB is very involved in the development of this observatory and the experience with TESS will be fundamental to the optimal scientific exploitation of PLATO".

 

Fuente: UCC-CAB

Fecha: 2020-09-01

 

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