Many stars are not alone, but instead form part of a multi-stellar system of two or more stars that are gravitationally bound together. Even though the prime science goal of TESS is to find exoplanets, it also observes a plethora of eclipsing binaries that allow us to study these systems in more detail.

The light curve of TIC 8153514, observed in Sector 21, shows a sharp eclipse superimposed on top of the signal of a variable star.

If you see eclipsing binaries on PHT you can tag it with #EB or #eclipsingbinary to let others known what you have found!

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!

TIC 219107776 as seen on Planet Hunters TESS in Sector 18.