Today I presented the latest Planet Hunters NGTS results at the UK National Astronomy Conference held at the University of Warwick. Good news everyone! I’m very happy to announce that the Planet Hunters NGTS has discovered four new planet candidates. What’s more, we’ve been able to observe three of these new potential planet candidates with the Gemini South Telescope in Chile!
Over the past few months, I’ve been developing a software pipeline that combines all of your assessments for the various workflows that make up the website. It sifts through the candidates output by the NGTS algorithm, looking for new potential planets. After a preliminary search of the available classifications, I picked the best candidates, classified by secondary eclipse checks and odd/even transit checks, and shared the results with the rest of the NGTS team. Four of these candidates appear to be potential transiting planets, and are shown in Figure 1.
The four objects still remain planetary candidates, as there is a lot of work to go from a potential planet to a real planet. To confirm a possible transit event, additional detection methods must be used to obtain the mass of the orbiting object to ensure that it is less massive than the star, or additional observations must be made to help statistically rule out astrophysical false positives (such as eclipsing binaries) that could mimic a planetary transit. Validating these planets will be a difficult process, as these candidates are around faint stars.
Over the past month, three candidate planets have been observed to perform follow-up observations. Working with collaborators in the US, we have applied for observing time at the Gemini South Telescope. This involves justifying why the candidate planets are interesting (there is a lot of really interesting scientific research that people want to do and that we have to compete for), justifying why the Gemini telescope and the Zorro instrument (see next paragraph) are the best tools for the job (in this case, Zorro is one of the few instruments in the world that can perform the kind of observations we need; the other is Alopeke at the Gemini North Telescope in Hawaii), and calculating the time we need to use the telescope.
The instrument we use is the “Zorro Speckle Imager”. Zorro takes image after image of the star, which allows us to “freeze” the effects of the Earth’s atmosphere that distort the light from the star (this effect is known as atmospheric seeing, see Figure 2). This allows us to identify if there are other stars close enough to the target that the NGTS telescopes cannot distinguish them. These background stars contaminate the measured light of the main target star and dilute the light curve of the eclipsing binary star making secondary transits observable, mimicking what would be observed for a real transiting planet. This is not a design flaw of the NGTS, but a reality that different telescopes are built for different purposes. For example, Zorro was not designed to study a target for long periods of time like the NGTS to find these transits in the first place. Using different telescopes to track and confirm exoplanets is a lot like having a football team. If the defender doesn’t take the ball from the other team (NGTS observes the pass), he can’t pass it to the midfielder to advance up the pitch (Zorro checking the other star).
Our observations were conducted several weeks ago by Gemini and a talented team of astronomers and support staff from NASA, and we hope to receive full final results soon.
What about the impactors in our analogy? Even if we find that these targets are single stars, that is not the final step in confirming exoplanets (again, that is a big “if”). Ideally, we would make “radial velocity” measurements that would allow us to measure the mass of the exoplanet. This technique works by detecting how much the star is “wobbling”. This wobble is caused by the exoplanet orbiting the star, and the amount of wobble is related to the mass of the exoplanet. When we say that a planet orbits the Sun, we actually mean that the planet and the Sun orbit the center of common mass of the entire solar system. This point just happens to be very close to the Sun because the Sun is very large. The same can be said for exoplanets and their stars. Radial velocity measurements play the role of the striker in this analogy, but it is important to state that this is not the end and there is still a lot of testing and data that must be collected to confirm if any of these candidates are actual exoplanets. If radial velocity measurements are not available, “multicolor photometry” can be used to help validate the candidates. This involves checking if the depth of the transit is the same when observing the star with different filters in a telescope. These filters only let certain colors of light through, just like Elton John’s famous tinted glasses make it appear mostly pink. If there is a difference in depth, it suggests that there is a background eclipsing binary star system that is mimicking an exoplanet transit. The difference in depth is because stars have different colors depending on how hot they are. So if you see a shallower or deeper transit using a different filter, it’s because the background star is not as bright in that filter. These four stars are difficult to observe for radial velocity because they are very faint and would take a lot of time even with the world’s largest telescopes, but the first step is to confirm the Zoro observations. Once the Zoro data has been analyzed and interpreted, we will determine the next steps.
We’re very happy to have found the candidates. Even if we can’t confirm these candidates as official planets, just discovering them is an important step. We can use these planet candidates to estimate the proportion of exoplanets around stars observed by NGTS. Thanks to everyone who has contributed to the project so far, whether it be classifying light curves or discussing potential candidates and strange themes on the talk board. Without you, this project would not have been possible. We also thank the very helpful team of Gemini instrument scientists who helped us prepare the observations, and the team at NASA who processed the data.
Also, in the exoplanet transit search, there is still a lot to sift through with the secondary eclipses and odd/even transits checks. Now that I’ve run my first search, I plan to do a lot more work on analyzing the classification data over the coming months. I expect to find many more candidates. Stay tuned! I’ll keep you posted on the blog.
