Seminar report:
Understanding the evolution of
star-exoplanet systems

Contents:

• Understanding the evolution of star-exoplanet systemsby Katja Poppenhäger
• Seminar scheduleSeminar schedule

How to cure a boring day:

In the 1990s when I studied astrophysics exoplanets was something new. Only one exoplanet was known at that time. I found it very interesting and did complement to my astrophysics with biology evolution studies and bio physics studies, there where no astrobiology invented in that time.

All these make todays seminar very interesting for me, something has happened since my own studies.

Some useful links:

Exoplanet:

• https://en.wikipedia.org/ wiki/ Exoplanet (Exoplanet, Wikipedia)

Understanding the evolution of star-exoplanet systems:

By Prof. Dr. Katja Poppenhäger

You can read her abstract here:
"Stars and their exoplanets evolve together over billions of years, just like our own solar system. Many known exoplanetary systems have planets orbiting their host stars at much closer distances than we observe in the solar system, with orbital periods of only a few days. In such systems one expects the star and its close-in planet to interact through tidal and magnetic forces, tying their evolution together. These interactions can give us insights into fundamental properties of star-planet systems which are hard to constrain otherwise: the time scale over which close-in planets spiral into the star, the evolution of stellar activity, and the amount of atmospheric evaporation and the habitability for all planets in a system with a close-in planet. Gaia and other telescopes have now opened up new pathways to measure how stars and planets interact with each other. I will present new approaches to test for planet-induced influences on stars through wide binary systems, motivate a new look at stellar magnetic activity measurements, and discuss how planetary atmospheres can evaporate over the lifetime of exoplanets."

Katja is Prof. Dr. at Potsdam University, the seminar was held at Stockholm University 2019.

Nowadays we have statistics over many thousands of exoplanets. Katja shows how the exoplanets divide up in different groups. The fourth quadrant is empty because of limitations in todays instrument. Katja has the second quadrant as her specialist area in her science work. Exoplanets that are closer then 0.1 AU and masses from 0.1 to 10 Earth masses.

Katja tells:
Exoplanets close to its host star interact through tidal and magnetic forces.

Katja tells:
The tidal force can speed up a star rotation's speed by gravitational force. Normally the orbit of the exoplanet is faster than the star's rotation and then it cause the star rotation to speed up. When a star's rotation is fast its surface activity is higher, it can be measured in X-ray wavelenght.

Lars comment:
Compare this with how our  Earth - Moon system, in this case Moon slow down Earth's rotation because Moon orbits with a slower speed than Earth's rotation. Energy is transferred from Earth to Moon and the distance increase, the opposite to Star - Exoplanet system above.

Katja tells:
When exoplanets orbit close to the star they orbit in the stars' strong magnetic field.

Katja tells:
Very hot exoplanets could not have clouds because the gas does not condense.

Katja tells:
With todays high resolution instruments it could be seen a gap between the group of Super-Earths and Mini-Neptunes. There is a theory that exoplanets from the top half migrate down to the lower half.

Katja tells:
If the spectra is analyzed at others wavelengths then visual it's possible to see absorption outside the exoplanet's radie, its atmosphere. We use this to get information how fast a close exoplanet outgases. These spectra at IR and UV can not be taken from ground level because of Earth's atmosphere absorption, satellites and balloons needed.

Katja gives a summary:

- Tidal interaction: possible spin-up of star, still not fully understood

- Magnetic interaction: possible flare triggering

- Planetary evaporation: high-energy emission caused by stellar activity

After there was a couple of questions. Katja explain that radiation from stellar surface don't follow todays theory, it drops of faster than it should when star ages.

Katja shows a typical intensity drop when an exoplanet pass behind the star, it's the exoplanet's emission, ultrahot gas-planet. The time scale of X-axis is hour.

If you want to know more about Katja's research I have found a couple of links:

• http://katjapoppenhaeger.com/ (Katja Poppenhäger)
• https://www.youtube.com/watch?v=MFegyFv9WqY (Is there a new Earth out there? Katja Poppenhäger TED talks at Youtube)

Take your time, the download looks to be slow.

She is a very active astronomer and I wish here the best luck and progress in her research of exoplanets !

These seminars are a good cure to my boring days. Do you have boring days too? Join me next time!

• https://www.nordita.org/ events/ seminars/ schedule/ (Theory seminar schedule, Nordita)

If you don't live in Stockholm in Sweden as I do I'm sure that you can find something similar to visit at your place. Or you do as all other do, search the internet, TED Talks is good.

• https://www.ted.com/ (TED Talks)

No more boring days!