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TESS: A ‘Hot Saturn’ & Asteroseismology

It’s good to see TESS, the Transiting Exoplanet Survey Satellite, producing early results. We’re coming up on the one year anniversary of its launch last April 18, with the spacecraft’s four cameras doing month-long stares at 26 vertical strips of sky, beginning with the southern hemisphere. Two years of such scanning will produce coverage of 85 percent of the sky.

The focus on bright, nearby stars is a shift from the Kepler strategy. While both missions have dealt with planetary transits across the face of their star as seen from the spacecraft, TESS is going to be producing plenty of data for follow-ups, planets close enough that we can consider studying their atmospheres with future missions beginning with the James Webb Space Telescope. Kepler’s long stare was of distant stars in a specific region, the idea being to gain a statistical understanding of the prevalence of planets. TESS gets us closer to home.

Now we have TOI-197 (TOI stands for ‘TESS Object of Interest’), a planet close to the size of Saturn in a tight orbit of its star (about 14 days). Asteroseismology comes into play here, with astronomers from the TESS Asteroseismic Science Consortium (TASC) using stellar oscillations to make a call on the star’s age, about 5 billion years. The star turns out to be slightly larger than the Sun, a late subgiant / early red giant, while the candidate planet shows a radius 9 times that of Earth. It masses 60 Earths, and its density is 1/13th that of our own planet.

Image: A “hot Saturn” passes in front of its host star in this illustration. Astronomers who study stars used “starquakes” to characterize the star, which provided critical information about the planet. Credit: Gabriel Perez Diaz, Instituto de Astrofísica de Canarias.

Asteroseismologists examine seismic waves in stars (think of them as ‘starquakes’) that show up as changes in brightness, and offer useful clues about about radius, mass and age. TOI-197 turns out to be the first TESS planet for which the oscillations of the host star can be measured. It’s interesting to see, then, that in addition to the paper on TOI-197, we also have a new paper that will prove useful for TESS characterizations going forward. It’s a target list, prepared by TASC, that identifies some 25,000 stars that are both Sun-like and oscillating.

So the asteroseismology work with TESS data gets underway. Steve Kawaler (Iowa State University) notes the scope of the work:

“The thing that’s exciting is that TESS is the only game in town for awhile and the data are so good that we’re planning to try to do science we hadn’t thought about. Maybe we can also look at the very faint stars – the white dwarfs – that are my first love and represent the future of our sun and solar system.”

An interesting thought given shape by the TOI-197 findings that reveal TESS’ potential for asteroseismology. From the discovery paper:

TOI-197 provides a first glimpse at the strong potential of TESS to characterize exoplanets using asteroseismology. TOI-197.01 has one the most precisely characterized densities of known Saturn-sized planets to date, with an uncertainty of ∼ 15%. Thanks to asteroseismology the planet density uncertainty is dominated by measurements of the transit depth and the radial velocity amplitude, and thus can be expected to further decrease with continued transit observations and radial velocity follow-up, which is readily performed given the brightness (V=8) of the star. Ensemble studies of such precisely characterized planets orbiting oscillating subgiants can be expected to yield significant new insights on the effects of stellar evolution on exoplanets, complementing current intensive efforts to characterize planets orbiting dwarfs.

We also have in TOI-197 an addition to the list of close-in transiting worlds around evolved stars; i.e., stars that have begun their transition to red giant status. Worlds like this undergo what the paper calls ‘radius reinflation’ as the host star evolves up the red giant branch. According to the paper, TESS is expected to “detect oscillations in thousands of main-sequence, subgiant and early red-giant stars… and simulations predict that at least 100 of these will host transiting or non-transiting exoplanets.”

The papers are Schofield et al., “The Asteroseismic Target List for Solar-like Oscillators Observed in 2 minute Cadence with the Transiting Exoplanet Survey Satellite,” Astrophysical Journal Supplement Series Vol. 241, No. 1 (14 March 2019). Abstract; and Huber et al., “A Hot Saturn Orbiting an Oscillating Late Subgiant Discovered by TESS,” accepted at the Astronomical Journal (preprint).


Comments on this entry are closed.

  • Michael C. Fidler April 2, 2019, 17:44

    One problem TESS has is in the reports that could be fixed is the use of designaters for stars. These stars are nearby and bright enough to be found in most astronomy charts and software planetarium program’s. Yet the public outreach has not caught on that putting the common designated name and coordinates plus the distance in light years that would have a large public relations effect. The idea that the public could go out in the night with a pair of binoculars and see the stars that have exoplanets should be used to develop support and funding for projects like TESS and WFIRST. Give them something they can relate to and you will have a large support for such endevours

    • Paul Gilster April 2, 2019, 19:49

      Good point, and one I hadn’t even thought about! Thanks.

    • Bruce D. Mayfield April 3, 2019, 10:05

      That is a very good suggestion Michael. For example, what is and where is TOI-197?

      • Michael C. Fidler April 3, 2019, 19:21

        That’s a good point, and starting with TOI-197 does not get you very far. TOI stands for TESS Objects of Interest, which is not on any current charts or planetarium programs. They do give you a clue in the abstract for the Astronomical Journal paper on arXiv, TOI-197 (HIP116158). HIP is from the Hipparcos catalogue which is from https://en.wikipedia.org/wiki/Hipparcos, which you can then accessed via http://simbad.u-strasbg.fr/simbad/sim-id?Ident=HIP116158&submit=submit+id. The simplest and oldest and most common designator for this star is the HD 221416, it is from The Henry Draper Catalogue (HD) and is an astronomical star catalogue published between 1918 and 1924, giving spectroscopic classifications for 225,300 stars. https://en.wikipedia.org/wiki/Henry_Draper_Catalogue
        This is what is used in most of the planetarium programs and charts and is a totally American Catalogue! The programs SkyChart/Cartes du Ciel and Stellarium will give you information on the star HD 221416/TOI-197 and an interesting Russian site gives more details about the star and its planet: http://www.allplanets.ru/star.php?star=HD%20221416

        • Bruce D. Mayfield April 5, 2019, 17:21

          Thanks for sharing all that Michael. Can’t read Russian, but the simbad data shows the star’s previous claim to fame as a high proper motion star. That would make it either relatively close, which I doubt, since it isn’t well known, or a star with an intrinsically high velocity. If it’s high velocity, it held onto its planet during whatever turmoil accelerated it. Interesting …

          • Michael C. Fidler April 5, 2019, 22:51

            Well, I can’t read Russian either, but use google’s Chrome browser that has an extension available: Google Translate, that can be added. This does automatic translation of web pages and is very convenient! The Russian site list it’s distance as 96 parsecs and Stellarium gives a distant of 317 light years. Possible a fast moving halo star from a past merger.

  • Michael C. Fidler April 5, 2019, 23:58

    Scientists Discover Exotic New Patterns of Synchronization.

    In a world seemingly filled with chaos, physicists have discovered new forms of synchronization and are learning how to predict and control them.


    “Objects with rhythms naturally synchronize. Yet the phenomenon went entirely undocumented until 1665, when the Dutch physicist and inventor Christiaan Huygens spent a few days sick in bed. A pair of new pendulum clocks — a kind of timekeeping device that Huygens invented — hung side by side on the wall. Huygens noticed that the pendulums swung exactly in unison, always lurching toward each other and then away. Perhaps pressure from the air was synchronizing their swings? He conducted various experiments. Standing a table upright between the clocks had no effect on their synchronization, for instance. But when he rehung the clocks far apart or at right angles to each other, they soon fell out of phase. Huygens eventually inferred that the clocks’ “sympathy,” as he called it, resulted from the kicks that their swings gave each other through the wall.”

    This has more to it, then it seems, read the complete article then ponder the different aspects of it. Synchronization and Asteroseismology are directly related along with exoplanet orbits, tides, rotation and tidal locking. At first it seems we may be reading to much into the idea but when you realize this affects everything from quantum entanglement to the neurons in your brain to computer networks to the rotation of galaxies to mini big bangs, ETC…

    What is interesting is its relation to AC power generating systems and Nikola Tesla’s earthquake oscillator, this could foreshadow new forms of interstellar propulsion, Breakthrough Starshot probes, LENR power.

    My favorite scene in “2001 A Space Odyssey” is when he is transported thru the stargate and you see these beautiful time crystals changing in Synchronization… ;-})