Studying planetary nebulae with the TESS Space Telescope

2020-03-24

Image of the Helix Nebula as seen by the Hubble Space Telescope. Credit: NASA, ESA, C.R. O'Dell (Vanderbilt University), and M. Meixner, P. McCullough and G. Bacon (Space Science Telescope Institute).


A scientific team led by the Centro de Astrobiología (CAB, CSIC-INTA) has used the TESS space telescope to study the nucleus of several planetary nebulae. The data analysed have shown clear signs of variability, which would be compatible, in most cases, with the presence of a companion star. This binariity could explain the complex morphologies presented by these enigmatic objects. 


Our Sun, at an age of approximately 4.5 billion years, is currently in the middle of its life. In another 5 billion years, its size will increase to almost reach the orbit of Mars, expelling the outer layers of its atmosphere and forming what is known as a planetary nebula. This final phase in the life of the stars occurs in a very short period of time in astronomical terms (about thirty thousand to seventy thousand years), until the nebula is dispelled in the interstellar environment. About 99% of the stars in the Universe will end their lives this way.

We currently know more than 3000 planetary nebulae in our galaxy. 80% of them have complex morphologies, very difficult to explain with the basic model of planetary nebulae formation, which would lead to rather spherical nebulae. The fascinating morphologies observed seem to indicate asymmetries during the star's mass loss process, something that could be the result of binary interactions, that is, of the central star with another companion star. However, this binariity hypothesis does not yet have clear observational evidence as, to date, only about 60 central binary stars of planetary nebulae have been detected. Therefore, the detection of more binary stars is essential for the in-depth study of this phase of the life of stars like the Sun.

This study, led by Alba Aller Egea, a researcher at the Centro de Astrobiología, and recently published in the journal Astronomy & Astrophysics, has used data from the TESS Space Telescope (Transiting Exoplanet Survey Satellite) to detect binary stars in the nucleus of several planetary nebulae. "Of the eight central stars of planetary nebulae analyzed, seven show clear signs of variability, compatible in most cases with the presence of a companion star. The octave, which does not appear to have variability in at least the 27 days in which the data have been taken, is the only seemingly spherical planetary nebula in the sample, something that would corroborate the theory of binariity," Aller notes. Of particular interest are the results obtained for the Helix Nebula (pictured). This nebula is one of the most studied and also one of the closest to Earth (about 650 light-years away). As Aller points out, "thanks to TESS data we detect, for the first time, a clear variability in light that comes to us from its central star (what we call the light curve, see image). This variability could be consistent with the presence of a low-mass companion star or sub-sea object (such as a brown dwarf or exoplanet), which might be reflecting the light of the primary star, much hotter. The period of such a signal is 2.8 days, which would be, if confirmed by that companion star, the time when both stars would orbit around each other."

"TESS data have also allowed us to analyze other intrinsic characteristics of the stars themselves, such as the frequencies of their pulsations or rotation, something that we have seen in two of the stars of the sample (NGC 246 and RWT 152)", says Sebastià Barceló Forteza, CAB researcher and co-author of the study.

An important aspect to note is that "although this satellite was born with the main goal of detecting earth-sized planets, its capabilities provide a unique opportunity to investigate in many other fields of astrophysics, as we have seen. By looking at the whole sky, TESS gives us access to a lot of scientific cases to exploit. And by doing so with a cadence of 2 minutes it allows us to see phenomena with a very fast and very precise variability, since it allows us to detect variations in the light of the stars of up to 100 parts per million (100 windows turned off in a skyscraper of 1 million windows on). In this case, we have used the data of this satellite for a different field of the main purpose of the telescope, which will allow us to better understand the death of stars like the Sun", says Jorge Lillo-Box, researcher at cab and co-author of the study.


 

Fuente: UCC-CAB

Fecha: 2020-03-24

 

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