TESS launched this week. Not many minutes after lift-off on a SpaceX Falcon 9, it was in space. It will find tens of thousands of new planets, but will need help from the ground. PEST has been gearing up for this support role since March last year.
It started with an email from Karen Collins (Harvard-Smithsonian Center for Astrophysics, CfA). Would I like to be on the TESS Follow-up Observing Program Working Group? Of course I said yes!
Since then I’ve developed further software tools, received access to the TESS web portal, made test observations and reports, and very important – agreed standard filenames for data submissions.
So how is this different from how PEST operates now? I currently observe candidate stars to catch planet transits, measuring the minute dimming of the star. PEST is pretty good for an earth-bound small telescope, with one planet co-discovery having a transit of just 0.3%. But being in space, TESS can detect transits that are at least ten times shallower. PEST is immersed in our atmosphere, limiting what I can see to about 0.2%.
If I will not actually be able to detect the small Earth-like planets that TESS is after, what role can I have? It turns out that, figuratively, TESS will look at whole forests and may not see individual trees. The four TESS cameras take in vast sweeps of the sky at a time – 96° by 24°. Imagine if your phone camera could snap a scene that stretches from the horizon to directly above you, and 48 full moons across. TESS aims to survey almost the entire sky in its 2 year primary mission, hence the super wide field. But this mean each TESS pixel covers a relatively large patch of sky, in which there may be several stars. If a transit signal is seen in this pixel, how do we know it hasn’t come from a star other than the actual target? An eclipsing binary star could mimic an exoplanet transit signal.
This is where the follow-up program and observatories like PEST come in. PEST’s vision is nearly 20 times finer than TESS’s. Each of my pixels covers just 1.2″ of sky (that’s a 5mm mosquito viewed from 860m away). PEST will be a candidate killer – separating out the impostors, with the survivors being passed to bigger telescopes to confirm.
I’ve had to work on the PEST photometry programs to be able to do this efficiently – i.e. not just measure the target star, but also everything near it as well, and to automatically flag any misbehaving star. This work continues.
There will now be a 60 day commissioning period for the spacecraft before TESS observes its first field – in the southern hemisphere (which suits me!). The first batch of candidates should be released early in 2019. PEST, now topped with a new roof, and a fresh coat of paint, will be ready!