As soon as now we have recognized an object as a possible planet candidate from the NGTS knowledge, step one is to examine whether or not we additionally see the transit sign in knowledge from the Transiting Survey Exoplanet Satellite tv for pc (TESS). Let’s stroll via an instance of one of many topics that we initially thought was a planet candidate, Topic 69693101. The Planet Hunters NGTS gentle curve for this object seems promising. Additionally the odd/even and secondary eclipse (not proven) gentle curves look effective too and once we analysed the NGTS knowledge we estimated a radius of 1.35 Jupiter radii for the orbiting physique, which is huge however not so huge that we’d instantly rule it out.
Subsequently, we determined to examine the TESS knowledge for this star. Fortunately TESS has noticed this star in two “sectors” which implies now we have roughly 2 months value of knowledge to have a look at (TESS observes a area of the sky, known as a sector, for a month at a time earlier than transferring on, however has is now revisiting areas to assemble extra knowledge). The plot under exhibits the sunshine curves for each sectors with the x-axis exhibiting time in days since a set date. (Astronomers like to make use of a unit known as Julian Days which is the variety of days since January 1st 4713 BC, however this quantity is big so we subtract normal values to make the numbers extra manageable, on this case we’ve subtracted 2457000 days).
At first look, this star seems to be very variable, presumably attributable to some intrinsic stellar variability though periodic indicators like this may be because of it being a binary star system. Step one is to strive part folding the info onto the interval discovered by NGTS. This can be a course of the place we take every part of the lightcurve that corresponds to (what we imagine to be) one orbit of the candidate, centred on the transit, and plot the info on prime of one another. Because of this the transits ought to all be in the course of the plot. The plot under exhibits the info folded onto the two.51 day orbit that NGTS detected, with gray factors exhibiting the uncooked knowledge and pink factors exhibiting the info binned in 10-minute averages.
This seems like a transparent transit sign, though the obvious variability of the star made me cautious when taking a look at this. Subsequently, I attempted folding the info to twice the detected interval and, voila, we are able to clearly see two transits of differing depths which tells us that that is certainly an eclipsing binary system and never a planet candidate. Whereas it’s unlucky that this explicit candidate isn’t a planet, it does imply we are able to focus our time and sources on extra promising candidates which may actually be planets!
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