Planet Discovered Using Telephoto Camera Lenses

[rvr] writes "The Space Telescope Science Institute (STScI) reports the discovery of an extra-solar planet called XO-1b, which orbits a dim star in Corona Borealis every 4 days. To find it, the brightness of several thousand stars were regularly scanned using two mini-telescopes in Hawaii. This equipment was built using commercial hardware: two digital cameras, attached to telephoto camera lenses on a robotic equatorial mount. A team of amateur astronomers helped with their own equipment to discard or confirm dozens of suspected transits."

Correct Link

[timgoh0]

The second link in the article appears to be pointing to the wrong place. The correct link should be this [hawaii.edu]

Re:Good news everyone!

[cnettel]

Note that we don't see the planet. We see that we see less of the light from the star. If the planet would be Earth-like (or a reasonably dense gas giant), we wouldn't get any absorption spectra clues for the chemical composition, as all wavelengths would be absorbed in the "eclipsed" region of the star's disc.

Re:Uranus jokes are LAME!

[Tony Hoyle]

http://dictionary.reference.com/search?q=uranus [reference.com]

You'll find both are valid, depending on your regional accent.

I personally have never heard your version.

Abstract...

[ajpr]

http://www.spaceref.com/news/viewsr.html?pid=20665 [spaceref.com]

Re:Real ingenuity

[TapeCutter]

Amature astronomers often contribute to science but are not always interested in the formalities of academia, just the fact that a technique _seems_ to work is enough for post grads to take notice and give it a try. The two groups have a long history of complementing each other.

Most "amatures" seem to use the technology to "smell the roses", making images that rival the hubble in beauty. [arcor-online.de] There is nothing really scientific about the images themselves, but then again the "blue marble" wasn't really all that scientific either.

Not That Easy

[Rob Carr]

f that's what we can do now with such modest optics, I imagine it won't take much more than a decade or two before we're able to detect the signature of life in some extra-solar planet out there.

There's an upper limit [newscientistspace.com] on what can be seen from Earth's surface. Alas, we will need space-based telescopes to find other Earths. I suppose we could find Jupiter-sized planets with lifesigns on them. Given that terrestrial life might have needed a solid surface to evolve on, I'm not sure how likely that is. Then again, it's a big galaxy, and even the weird and unlikely has to happen someplace.

Re:Tight Orbit

[hde226868]

There is no danger in the planet impacting on the star. For this you would have to invoke some mechanism that is able to get rid of the planet's orbital angular momentum, which is very difficult to acheive. So, while the planet is close to its star, it is in no danger of falling in - only very much in the future once the star leaves the main sequence and becomes a red giant. But that's some billion years in the future... (as an aside, a similar misconception is that if a star suddenly turns supernova and becomes a black hole, many people believe that planets surrounding that star would get "sucked in". For the same reason, that's not a problem either). Note that Mercury in our solar system has an 88d orbit, and has happily lived there for 4.5 billion years.

What is more worrisome is that the planet gets heated up due to its proximity to the star and is evaporated. But again, planets have an awful amount of mass, so this shouldn't be too much of a problem either. For example, there is a 4.4 jupiter masses planet around Tau Bootis, in a 3.3d orbit (http://www.exoplaneten.de/tauboo/english.html [exoplaneten.de]), but the general estimate for objects of this kind (dubbed "hot jupiters") is that they will survive for billions of years. The reason for this is that the mass loss rate caused by the proximity of the star is still negligible compared to the mass of the planet. Take a look at the article by Ferlet et al., on p. 226 of a recent conference on explanets, the proceedings of which are at http://www.obs-hp.fr/www/pubs/Coll51Peg/proceeding s.html [obs-hp.fr].

Re:Tight Orbit

[hde226868]

First of all, sunspots are more or less static in location on the surface of the star. For typical late type stars the rotation period is similar to that of our Sun, about a month, so you wouldn't see this type of variations on a timescale of 4d (we can measure the rotation speed of stars spectroscopically using standard techniques). Furthermore, even if the star rotates with a 4d period, since sunspots change in shape, each time you see the sunspot pass the surface of the star you'd see a slightly different lightcurve. Planets don't change in shape and are very symmetric objects, so the lightcurves will look very different. Finally, sunspots don't last for a very long time, so if you see a planet now and you still see it one year later, you've excluded the sunspot theory, even if you couldn't exclude it using my previous arguments.

Let's hope this doesn't turn into Nikon vs. Canon!

[Glytch]

Very cool project. I've heard of amateur astrophotographers using fast lenses, but this takes it to a whole new level. The lenses used in this telescope (Canon's 200mm f/1.8 L lens) not only collect an enormous amount of light, but are also among the highest quality lenses ever made.

These are most likely not telephoto lenses

[Flying pig]

Sorry to be a lens Nazi, but these are hardly telephoto lenses. "Telephoto" does not just mean "Long focal length", it has a specific meaning. A telephoto lens has its optical centre OUTSIDE the front element; it is how it is possible to produce (say) a 600mm lens that is only 300-400mm long. These are 200mm f/1.8 and I suspect the optical centre of being inside of the front element. 200mm wide aperture lenses (which are hardly routine amateur stuff) usually work with matched telephoto adaptors at which point they DO usually become telephoto lenses in combination.

Telephotos are always an optical tradeoff where the compact dimensions are at the expense of various kinds of optical goodness. Reverse telephotos, used to give enough room in the shutter box between the film and the rear element of, say, a 21mm lens, are a different matter; they can be well designed because the greater distance to the rear element means the maximum angle of the exit rays is lower. Leitz were always able to get the best optical quality for their M series rangefinders, though, because the absence of the mirror box give fewer constraints in rear element placement.

Interestingly, if you are a lens geek, telephotos were originally developed because early news photographer cameras did not have enough extension on their baseboard bellows to focus long lenses. bellows to

Re:Real ingenuity

[Shigeru]

I don't mean to diminish the cleverness of those involved in this project at all, but the article summary is a little misleading. While the discovery was made with very small-scale telescopes, the confirmation that this was actually a planet came from two large telescopes, the Harlan J. Smith Telescope (2.7 meter aperture) and the Hobby-Eberly Telescope (9.2 meter effective aperture), as the linked article mentions.

Finding extrasolar planets by the transit method, where you moniter large fields of stars and look for brightness variations as a planet passes in front of one of your targets and blocks some light, is pretty straight-forward. You tend to only need somewhere between 0.1% and 1% precision in your photometry, which requires some work to achieve, but is by no means prohibitive. So it's a good technique for amateurs to get involved with, especially when you consider that smaller telescopes tend to have larger fields of view, so you can moniter more stars at once. But the main stumbling block transit-searchers have run into is the false positive rate. The biggest surveys have found a huge false-positive rate (90-95%) among the planet candidates. It turns out there are lots of things that can make a star dim at fixed intervals, from grazing binaries to starspots.

As a result, transit planet candidates are only considered confirmed when there are measurements of a radial-velocity wobble consistent with the orbital period found by the transit. To get the radial velocity precision you need (for the Hot Jupiters transits detect, precision of tens of meters per second is sufficient), it takes a precise, high resolution spectrograph (very expensive), mounted on a large telescope (at least a couple meters).

I should also point out that transit searches are sensitive mainly to close-in planets. The sensitivity function drops very quickly as the planet moves further out (both because you need a longer sustained campaign, and because the chances of the planet's orbit crossing the star decreases). All the transit detections thus far have been from planets with several-day orbits. While this is interesting science, there's a lot of work to be done with planets in other regimes. The straight-up radial velocity technique gets you planets at seperations between 0 and 5 AU or so (over 150 planets found this way so far), the microlensing method can also detect planets at much larger orbital separations (2 or 3 planets up until now), and direct imaging is ideally suited for large-seperation planets (only the 1 good planet at this point). My point is that you can't cover this whole range of parameter space with small telescopes alone. Radial velocity and direct imaging require large investments in hardware, both in the large telescope itself and the instrumentation (disclaimer: I work on direct imaging, that's why I keep bringing it up). It's also important to note that one of the reasons people find transiting planets so interesting is the possibility of getting spectral information out of the planets. NASA's Spitzer space telescope recently detected the secondary eclipse (the loss of light when the planet is hidden behind the star) of two transiting extrasolar planets. This is pretty exciting science, since you can really compare data to models this way, but it requires some extensive telescope set-ups to get it done.

So again, this is certainly a great project for getting amateurs involved in the planet-finding game, and I"m very impressed with this result. But don't close down Keck and the VLT and Hubble just yet; there's a lot of work to be done in extrasolar planet research, and much of it requires large telescopes with new (read: expensive) instruments.

Re:Why two lenses/cameras?

[suitti]

You are looking for a slight dimming. The atmosphere of the Earth can provide slight dimming. Two cameras looking through different bits to of the Earth's atmosphere can provide extra confidence that the dimming you detect is not here at home.

Re:Real ingenuity

[graemecoates]

A lot of "amateurs" actually do work that is too much of a hassle for current science. E.g. mineralogy is mainly done by amateurs these days.

In astronomy, main areas of "amateur" research work are: supernova hunting, comet hunting, variable star monitoring (probably the biggest I reckon), minor planet (asteroid) hunting and tracking including occulation timing and rotation rate determination and now work on exoplanet discovery, and even trying to find afterglows for gamma ray bursters.

In many ways, the term "amateur" almost undermines the level and quality of the work performed - in lots of cases, the data is very good indeed (and often have inspirational ways of performing the measurements) - it's just they don't get paid for it and often have a day job as well. The "pros" don't do this grunt work as it costs too much, but they will pick up the work if anything interesting is found.

Having said this, there are now dedicated survey instruments (eg WASP, NEAT to name a couple) that the pros have setup that are starting to beat amateurs to some of the observations, but often use no more advanced technology than a dedicated amateur would.