Object 96: WASP 1
Podcast release date: 17 April 2023
Right ascension: 00:20:40.1
Corresponding Earth location: The outskirts of Ouargla, Algeria
WASP 1 is a star slightly warmer and larger than the Sun located at a distance of 1249 light years (383 pc) in the constellation Andromeda [1, 2]. WASP is an acronym that stands for the Wide Angle Search for Planets, an exoplanet survey where 5.3% of the total research budget went towards developing that clever acronym. As you may or may not have guessed by now, WASP 1 was the first star with an exoplanet found orbiting it by the WASP Project . This actually was quite important as a proof of concept, and it may be what makes this particular astronomical object so important. Before I discuss the object, I'll take some time to discuss the WASP Project. (Just for reference, I also discuss the WASP Project and another exoplanet found by the project in episode 14, so if you like this episode, you might want to listed to that one, although they both cover some of the same scientific material.)
Exoplanets are generally really tough to image directly because they don't produce much electromagnetic radiation and because they are usually located close to much brighter stars. The first exoplanets found orbiting other stars in the 1990s were detected by observing the very small gravitational pull that the exoplanets exerted on the stars that they were orbiting. This caused very small amounts of Doppler shifting in the light from these stars, and through careful measurements of the stars' spectra, it was possible to identify the type of periodic Doppler shifting that would be associated with exoplanets orbiting other stars.
However, these types of observations of stars' spectra are very difficult to do, and by the late 1990s, astronomers developed a new technique for detecting exoplanets. This technique invovled precisely measuring the slight dimming that would occur when exoplanets passed in front of (or, to use the technical term, transited in front of) the stars that they were orbiting. While this technique also involved making insanely precise measurements of these stars changing brightness over time, these measurements are easier to do than the insanely precise measurements of the Doppler shifting of the light from these stars caused by orbiting exoplanets. Moreover, it is easier to make images of lots of stars spread over large areas of sky than it is to make spectral measurements of all of those stars.
The people in the WASP Project realized this and went on to design two rather unusual expolanet-detecting instruments that they named SuperWASP (where the "Super" part of the name "SuperWASP" is not an acronym because the project ran out of the funds allocated for acronym creation when they started building the instrumentation). Many exoplanets up to the year 2000 were detected using standard reflector telescopes in standard multi-purpose observatories, but the limitation in using these telescopes is that they could only look at narrow regions of the sky. The WASP Project people realized that they could actually image really wide areas of the sky using multiple astronomical-grade digital detectors attached to the types of telephoto lenses typically used by by professional sports and wildlife photographers, and they decided that the Canon 200 mm telephoto lenses would work they best for their survey . The WASP Project needed a total of 16 telephoto lenses, so the team sent their instrumentation specialists to their local photography shop to buy up all of the Canon 200 mm telephoto lenses that they could find . After that, they went online and bought up all of the Canon 200 mm telephoto lenses they could find for sale on eBay . (This sounds like a joke, but this is what is actually written in the scientific publication on the WASP Project .) Once the WASP Project had all of their lenses and detectors, they mounted sets of 8 lenses on two separate robotic mounts, one of which was set up on La Palma in the Canary Islands and one of which was installed at the Sutherland Station of the South African Astronomical Observatory . Each set of lenses is able to image the entire sky every 40 minutes if needed, although they usually only do image this once a night .
The SuperWASP instruments started performing astronomical observations in 2004, and in the first year of the survey, they found quite a few stars that might could potentially have had exoplanets orbiting them on the basis that they appeared to vary very slightly in brightness on a regular cycle . However, the people on the WASP Project were very cautious and wanted to confirm that these stars did indeed have exoplanets and were not just varying in brightness for one of half a dozen other reasons. So, they used a spectrometer named SOPHIE (which is another acronym) on the 1.93 m telescope at the Observatoire de Haute-Provence to carefully measure the Doppler shifting of 24 of these stars to see if they moved in such a way that was consistent with exoplanets orbiting them . They were able to confirm that two of the stars did indeed have exoplanets, and, because the WASP project had no budget for creative object names, they designated one of the stars with an exoplanet as WASP-1 and the other as WASP-2 .
So, WASP-1, the object for this podcast episode, was quite important for validating the exoplanet-detection techniques used by the WASP Project. It would have, to use the technical term, sucked if the WASP Project had not found any exoplanets in their first year of operations. So, let's talk a little bit about the exoplanet, which was uncreatively named WASP-1b. This turned out to be what is called a hot Jupiter. The planet is a gas giant located at a distance of 0.039 astronomical units (AU) from its host star . For reference, the distance from the Sun to the Earth is defined as 1 AU, and the distance from the Sun to Mercury is 0.39 AU , so, in comparison, WASP-1b is extremely close to its host star. WASP-1b also orbits its host star really quickly, completing an orbit once every 2 days, 12 hours, and 29 minutes . The planet is 0.85 times the mass of Jupiter but 1.48 times the diameter of Jupiter . This means that WASP-1b is really low in density, probably because it has been heated up a huge amount from being located so close to its host star. While hot gas giants located close to their host stars are actually quite common, WASP-1b is one of the rarer exoplanets that looks abnormally puffy, so it has attracted a lot of extra attention from the exoplanet research community.
The WASP Project has gone on to discover nearly 200 more exoplanets . However, it was the discovery of exoplanets orbiting WASP-1 and WASP-2 that helped to get the project started. Consequently, I am certain that WASP-1 has a special place in the hearts of many of the people who have worked on the WASP Project over the years.
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