Asteroids are small rocky bodies that are left over from the time of the formation of the Solar System. They range in sizes from small rocks that you could see on the side of a lake to hundreds of kilometers across. There are as many as hundreds of millions of these within our own Solar System, so it comes as no surprise that we often see them in the TESS light curves, manifesting themselves as spikes or dips or anything in between.
The above figure shows the light curves of six bright stars observed by TESS, sorted by their distance with reference to the top object (the red light curve). As you can see, almost all of them show a ‘strange’ signal, which is very likely caused by an object such as an asteroid passing through the field of view.
This next figure shows an approximation of a possible path of the asteroid, which was determined by matching the times of the events with the locations of the target stars. The target stars are highlighted with circles of the same colours as the light curves in the first image, and the times are the times in hours since the first event (in the orange light curve). Based on a very simple estimations of the times and projected distances, we can approximate the projected speed of the asteroid to be around 0.6 arcseconds per hour.
Asteroids are fascinating objects that allow us to probe the conditions of the Solar System during the time of its formation (4.5 billion years ago!). If you’re interested in making your own light curves, such as those in the top figure, you can download a program called LATTE to have a go.
The pattern seen in this light curve could be due to the variability of a young stellar object (YSO), which is often related to a disc obscuring some of the stars light and/or material accreting onto the star. Studies of the symmetries in the LCs of YSOs can help us understand the environment around the star.
Some stars are quiet,
Some stars pulsate,
Some stars are single,
Some have a mate.
This is a pulsating star in a binary system. Thank you to the citizen scientists who brought this fun system to our attention and suggested it as a lightcurve of the week. https://www.zooniverse.org/projects/nora-dot-eisner/planet-hunters-tess/talk/2112/1030293?comment=2048847&page=1
This week we have an EB where the two stars get so close to one another that their gravitational pull distorts their shapes, changing it from a sphere to a rugby-ball type shape. The increase in surface area from this results in an increase in observed flux after the primary eclipse. If you look carefully you can also see a small secondary eclipse!
The light curve of TIC 394177355 was already flagged by the Kepler team (KOI-3156) when it was observed back in 2015. It shows a multi-eclipsing quintuple system of pulsating stars with orbital periods of 94.2, 8.65, 1.52 and 1.43 days. TESS saw this target 5 years later in Sector 15, and observed it during a triple eclipse. Check out the paper by Hełminiak et al. (2017) to find out more about this very interesting and rare system.
This week we have a beautiful Delta Scuti variable that shows both primary and secondary eclipses caused by a second star. The beat-like pattern that we can see in the light curve is due to the star pulsating at two very similar, but slightly different, frequencies. Have you seen any more of these on Planet Hunters TESS?
This is a light curve of an eclipsing binary with some strange out-of-transit-variability. The transit depths suggest that there is one large and hot star and one small and cold star in this system.
In addition to planets, there are many other interesting and unexplained systems to be found within the TESS data. Professor Matthew Kenworthy from the University of Leiden, for example, is searching for circumplanetary disks of dust and rings by looking for the shadows they cast as they pass between us and their parent stars.
Searching for Disks
by Professor Matthew Kenworthy
We’re looking for stars that have single eclipses that last from a few days to a few weeks but that have no other apparent eclipses outside of this period of time.
During the eclipse, which can be anything from a 5% dip to a 90% dip, the brightness of the star can change in a matter of hours – as shown in the image below. Essentially we are looking for any kind of saw tooth pattern in the light curve.
What we think we are seeing is a large disk of dust around an unseen planet or star, and that this disk has rings in it that block out light from the host star. The sawtooth light curve is what you get when the edges of the rings cross in front of the star.
If you spot a light curve that has these characteristics it would be great if you could tag it on talk with #disk. Any stars you can identify will help tremendously in finding and understanding these curious objects!
This beautiful dwarf nova has so far been observed by TESS in all of the northern hemisphere observational sectors released to date (sectors 14 to 18).
Dwarf novae are stellar binaries where one companion is a main sequence star and the other a white dwarf. In these systems material is transferred from the main sequence star to the white dwarf, forming an accretion disk and resulting in quasi-periodic outbursts, as seen in the lightcurve above. See https://blog.planethunters.org/2012/04/07/dwarf-novae/ for more details on these fun systems!
Dr. Annaleise Depper (Evaluation Officer, Public Engagement with Research) at the University of Oxford shares the results and findings from an evaluation of Planet Hunters conducted in 2019.
Read the full report here: http://bit.ly/Planet-Hunters-evaluation
Exploring the Impact of Planet Hunters TESS
by Dr. Annaleise Depper
To date, over 15,000 citizen scientist volunteers from over 98 different countries worldwide have contributed their time to classify millions of light curves through Planet Hunters TESS.
Still, questions remain as to why people engage in project like Planet Hunters; what, if anything, do people learn; what factors limit people’s participation; and what can researchers at the University of Oxford learn from people’s experiences in order to enhance the project?
In 2019, I carried out an evaluation of Planet Hunters TESS, which allowed me to explore these questions by engaging with the volunteers through an online survey. A total of 577 volunteers completed this survey, thereby sharing their views and experiences. While the findings are not necessarily representative of all of the volunteers, the results have provided important information about the value and barriers to taking part in Planet Hunters, and the ways in which the project could be enhanced.
Thank you to all the 577 citizen scientist volunteers who took the time to complete this survey, and shared their open and honest reflections, thoughts and recommendations.
Here’s a brief summary of what we found out:
Planet Hunters has resulted the following outcomes and impacts on volunteers:
- 74% learned about Astronomy
- 66% enjoyed learning about Astronomy through Planet Hunters
- 21% felt inspired to learn more about Astronomy beyond the project
- 19% experienced a feeling of pride and satisfaction in being a citizen scientist
- 8% experienced positive benefits to their individual wellbeing
Hearing from the volunteers:
“I learned about the actual research medium taking place and how it really works instead of viewing a graphic or reading an article.”
“I am making 3 beginners telescopes and planning to start a small Astronomy club to inspire more people in Astronomy. Planet Hunters opened my mind in many ways””
“I love what I’ve done and knowing that I am participating in a project that search for new planets makes me feel excited”
“My student really got into the project. They thought it was really neat that they would get an acknowledgement if they helped find a planet, and were excited by the fact it was really data. I asked them to do a minimum of 20 classifications and no student did less than twice that (and some completed as many as 150 classifications)”
Benefits and challenges of Planet Hunters
A key strength of Planet Hunters is its ability to bring together groups of people, including those without a background in science, to become citizen scientists and actively engaged in the exoplanet search.
At the same time, 49% of Planet Hunters volunteers highlighted a reason that limited their participation in the project, including:
- Personal circumstances
- Issues with the platform, interface and accessibility
- Limited understanding
- Tedious, fatigue and repetition
- Lack of individual feedback and recognition
- Classification anxieties
- Commitment to other Zooniverse projects
How can Planet Hunters become more inclusive of its growing, diverse community?
There is still work to be done to ensure that Planet Hunters remains rewarding, motivating and inclusive of all volunteers. Around 50% of volunteers provided a recommendation that could support the development of Planet Hunters; including:
- Providing additional information and support to volunteers
- Improving accessibility and interface usability
- Providing more feedback
Next steps for the PHT team
The Planet Hunters TESS team are currently thinking of ways to implement some of the recommended changes – here’s some of the areas they are exploring:
- Translating the project into multiple languages
- Launching a mobile app
- Offering more training and support e.g. video tutorials
- A ‘meet the researcher’ or ‘meet the volunteer’ blog
- Improving and supporting use of Planet Hunters in the classroom for educational purposes
- More regular updates e.g. to the results page; Twitter
Read the full evaluation report here: http://bit.ly/Planet-Hunters-evaluation