→ Widely unknown Exoplanet Astronomer

The last couple of days I have spent learning Autodesk Maya which is a 3D computer graphics software. The motivation behind it was to be able to illustrate and animate exoplanet science. Below are a few of my initial results.

I learned a lot of Maya from the Maya videos by Stu. I would recommend you have a look at them.

The James Webb Space Telescope (JWSP) is a large space telescope, scheduled for launch in 2014. It has frequently been referred to as the successor of the Hubble Space Telescope. One major difference to be aware of between this space telescope and Hubble is that the James Webb Space Telescope will be observing mainly at infrared wavelengths. The JWST will amongst other things study the first galaxies formed, peer through dusty clouds to view stars forming planetary systems and survey the distant universe at IR-wavelengths, but what exactly is it expected to do for exoplanet research?

The James Webb Space Telescope

According to the NASA JWST website:

” The James Webb Space Telescope will study the physical and chemical properties of solar systems (including our own) and where the building blocks of life may be present. “

After doing some research on the web I found that the James Webb Space Telescope  is expected to be able to:

• Image / characterize planets with a wide range of masses and separations
• Identify atmospheric gasses not yet discovered such as water vapour, carbon dioxide and methane (using the transit method) in Hot Jupiters (and possibly characterize the atmospheres of Super Earths).
• Detect planet features by studying only a single transit event
• Detect thermal emission from super-Earths in the habitable zone which transit M stars by studing a few transits

This is a question of great interest to exoplanet astronomers who wish to measure the properties of exoplanets. Exoplanets have been found to orbit stars which are more than a 1000 times more active than our own sun. It is essential that astronomers know how the host star activity affects the exoplanet orbiting around it as a slight inaccurate measurement leads to wrong estimations of the exoplanet properties. Apart from our own sun, it is very hard to study the surface details on stars as they are so incredibly far away. We cannot simpy look directly at the surfaces of stars. Instead astronomers study the surface details on stars using indirect methods such as long time photometry and doppler imaging.

Shown are the sunpots(black) and faculae (bright yellow). Credit: NASA

Starspots (like sunspots on our own Sun) are darker areas on the surface of the star which are caused by magnetic fields. They are cooler than the surrounding area on the star and thus appear black when compared to the rest of the star. The brighter patches on the sun are known as the faculae. They usually occur at the same time as sun spots occur. Solar variability is very wavelength dependant. The irradiance (power incident on a surface) from the sun changes very little at visible wavelengths but it changes an order of magnitude more at shorter wavelengths (UV).

Understanding the host star’s change in flux as a function of activity is important when doing transit photometry. If for instance a big sunspot crosses the surface at the same time which the exoplanet is crossing, the exoplanet will seem as though it is bigger and that it is blocking out more light. This will lead to incorrect measurements of the size of the exoplanet. To be able to more accurately determine the size of exoplanets it is essential that one also knows something about the activity of the host star. Understanding the how the host star affects the measured properties of exoplanets is a active area of research at the moment.

To be able to find the radius of an exoplanet, astronomers study the lighcurve. The lightcurve is made by plotting the flux form the host star as a function of time. Here is an example of a light curve:

The depth of the light curve will depend on a number of things such as the radius of the exoplanet and the distance of the exoplanet  from the host star. However, it is not only the properties of the exoplanet which matter. Imagine a star-planet system where we now double the radius of the host star whilst keeping the radius of the planet the same. In this case the exoplanet will block out the same amount of light, but the dip in the light curve will be smaller, since the host star has a greater flux.

Thus, from the transit method astronomers are only able to derive the radius of the exoplanet relative to the radius of the host star.  The unit used is the radius of the planet over the radius of the host star, Rp/R*.