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La Silla Observatory (Iztok Boncina/ESO)
It seems like every month a new kind of member is added to the ever growing exoplanet family: bigger, more massive, closer, brighter, hotter, rockier. The latest one, discovered by colleagues at my new institute, the Max Planck Institute for Astronomy in Heidelberg, is kind of special: it’s thought to have formed in another galaxy.
The discovery of planet Gliese 581 g, an exoplanet just 3 times the mass of our Earth and located in its host star’s Habitable Zone, was one of the biggest science headlines of the year. The news broke, typically, somewhere between my observing proposal deadline and box number 15: “all the crap that didn’t fit into boxes 1-14″, and by the time I’d read the story the internets was awash with all the details already.
As it turns out, I’m glad I haven’t written about it yet, as the story just got a little bit more interesting. With the headline still hot on the media’s most-read lists, astronomers from the Geneva exoplanet group have this week cast doubt on the discovery. Using data of GJ581 from the HARPS spectrograph at the ESO 3.6-m telescope at La Silla, the instrument par excellence for planet hunting by radial velocities, they haven’t been able to confirm or reject the Californians’ findings, obtained with the HIRES spectrograph on Keck.
Fig. 1: An image of Beta Pic's companion taken with the apodising phase plate on VLT/NaCo, after processing. The light from the central star was blocked out (in processing). Credit: ESO
Astronomers have many ways of spotting exoplanets round far away stars – but getting a direct look at them, especially with ground-based telescopes, remains a difficult job. With a planet emitting very little light of its own, and appearing to us essentially on top of the host star, its radiation is completely drowned in the image of the star. Catching those few photons and separating them from the flood of light from the star requires some clever observational tricks. To do this with ground-based telescopes, we at the very least need adaptive optics, to prevent the atmosphere from creating a blurry mess and keep the image nice and sharp, and often some sort of mask that will block out as much as possible of the stellar light. But an upgrade to one of ESO’s near-infrared workhorse imager NaCo on VLT’s 4th Unit Telescope has just made it a whole lot easier.
Top: Image of star HR8799 and its exoplanet HR8799c (ESO/M.Janson). Bottom: The spectrum as recorded by the NACO detector, prior to extraction ; the vertical direction is spatial, horizontal is spectral (M. Janson et al, 2010)
Astronomers collaborating from both sides of the Atlantic have obtained the first direct spectrum of an exoplanet. The news here is mainly that they managed to record the spectrum and separate it reliably from that of the host star. Their short letter in ApJ, posted to astro-ph yesterday, doesn’t delve deeply into the implications of what they found but focuses more on the way they obtained, processed and analysed their data to separate the planet’s signature from that of the star.
At a conference last week, a team of astronomers announced the discovery of 32 new exoplanets. This confirms what many already suspected: they’re everywhere! The disoveries were made by European astronomers based around Prof. Michel Mayor‘s group at the Observatory of Geneva, who continue to increase their exoplanet tally since they spotted the first one around a regular star, back in 1995. Their secret? A small telescope with a damn fine instrument, that they themselves built specifically for the job.
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