Validation of Exoplanets Exhibiting Dynamical Interaction

Abstract

The Transiting Exoplanet Survey Satellite (TESS) uses transit photometry to detect exoplanets. To confirm if it is a planet, a second detection method is used to determine the planet's mass. But with the number of candidates waiting for confirmation, statistical tools have been developed to validate exoplanets so that false positives could be ruled out quickly. One such tool is the Tool for Rating Interesting Candidate Exoplanets and Reliability Analysis of Transits Originating from Proximate Stars (TRICERATOPS) [Giacalone et al., 2021].

TRICERATOPS works well for systems with strict periodicity but I investigated its performance in validate systems exhibiting dynamical interactions or Transit Timing Variations (TTVs). For a system to be deemed as validated, it needs a false positive probability (FPP) below 0.015. An FPP between 0.015 and 0.5 indicates a likely planet while an FPP above 0.5 indicates a false positive. By varying the TTV amplitude, TTV period, and impact parameter of the transit of a mock system, I tested how well TRICERATOPS worked.

I discovered that TRICERATOPS struggles to validate a planet with a relative TTV amplitude of 5.38% of the transit duration and it increases until a relative TTV amplitude of 17.9% where the FPP reaches 1. Varying the TTV period at an amplitude below this limit does not seem to have an effect on the FPP. There is no reliable interpretation of the FPP when above this limit. The impact parameter caused the FPP to increase at about b=0.5-0.6 as it increased.

The conclusion of this test is that TRICERATOPS is not a viable tool for systems with TTVs unless the TTVs have been carefully corrected. Otherwise, the system may be classified as a false positive.

Popular Abstract

When people think about space they may think about something practical like the satellites that orbit the Earth and help us in our day-to-day lives. Or they think about something more fantastical like aliens on another world, like from Star Trek. This project leans toward the fantastical side of the spectrum but is not quite the same. It is about validating exoplanets around distant stars. These planets have been detected using the transit method. This means we measure the light coming from a star and when that light dims, it means an object has eclipsed it. If this happens at regular intervals, we know there is the possibility of there being an exoplanet and we can find its size from how much light is blocked. The problem is then, how do we know if it is a planet we are seeing and not maybe a binary system where two stars orbit each other? We cannot see the planet, so we use another detection method like radial velocity, which detects massive planets close to the star by seeing how much the gravitational forces from the planets affect the star. This is perfect because transits are easier to detect for massive planets close to the Sun! That means these planets are likely to be gas giants like Jupiter where a year on the planet takes on average 5 days. Hence, it is very unlikely there is any alien life on these planets.

Scientists discover many candidates, so they created tools to determine which of these candidates are the most interesting to focus on. One of these tools is the Tool for Rating Interesting Candidate Exoplanets and Reliability Analysis of Transits Originating from Proximate Stars or TRICERATOPS like the dinosaur. This tool analyzes data from a transit and calculates the probability of the object being a false positive. It allows scientists to determine what object to do follow-up studies on.

But what about the dynamical interaction? This could mean that the star has more than one planet orbiting around it, just like our own solar system. These planets will affect each other with their gravity, slowly varying their orbital period. They are no longer at regular intervals, which means that the length of a year on the planets is going to vary. Now the question this project seeks to answer is if TRICERATOPS can be used to accurately validate planets that have these irregular orbits. This is important to further help scientists not waste time doing follow-up observations on objects that cannot be exoplanets so that they can focus on discovering new worlds in this galaxy. And perhaps discover some aliens along the way.

• author: Mohamed Ali, Warsame
• supervisor: Judith Korth; Alexander Mustill
• organization: Department of Physics; Astrophysics
• course: FYSK04 20241
• year: 2024
• type: M2 - Bachelor Degree
• subject: Physics and Astronomy
• keywords: TESS, TRICERATOPS, Exoplanets, Transit photometry, Validation, Hot Jupiter, Transit Timing Variation
• report number: 2024–EXA232
• language: English
• id: 9169874
• date added to LUP: 2024-08-12 08:45:44
• date last changed: 2024-08-12 08:45:44