Month: February 2014

Directly Imaged L-T Transition Exoplanets in the Mid-Infrared

2M1207 b (pronounced two-mass-twelve-oh-seven-bee) is often considered the first directly imaged extrasolar planet. Though its primary star, 2M1207 A, is actually a brown dwarf, b shares many properties with the HR 8799 planets. Andy Skemer analyzed images taken with MagAO+Clio2 and compared the results with images of the HR 8799 planets taken with the LBT. The interesting thing about 2M1207 b is that it doesn’t seem to have methane in its atmosphere — otherwise we wouldn’t have been able to see it since methane should absorb all the light at the wavelength we used.

Imaging 2M1207 b is extremely challenging from a technical standpoint. 2M1207 A is a faint brown dwarf, which doesn’t emit enough visible photons for our wavefront sensor. Instead, we locked on an off-axis (and still faint) star 40″ away from the science target. The result demonstrates that MagAO can produce reasonable Strehl ratio images on targets that are too faint to serve as their own guide-star.

2M1207 A, and its planetary-mass companion, 2M1207 b, the first directly-imaged exoplanet (Chauvin et al. 2004). When 2M1207 b was first discovered, it was noted to have unusually red colors, and to be extremely faint compared to other red (L-type) brown dwarfs. This image, taken by MagAO/Clio at 3.3 micron, would show a dark planet if 2M1207 b had properties similar to “normal” objects. Instead, we find the 2M1207 b is bright at 3.3 microns, suggesting an almost complete lack of methane gas.

Abstract: Gas-giant planets emit a large fraction of their light in the mid-infrared (≳3μm), where photometry and spectroscopy are critical to our understanding of the bulk properties of extrasolar planets. Of particular importance are the L and M-band atmospheric windows (3-5μm), which are the longest wavelengths currently accessible to ground-based, high-contrast imagers. We present binocular LBT AO images of the HR 8799 planetary system in six narrow-band filters from 3-4μm, and a Magellan AO image of the 2M1207 planetary system in a broader 3.3μm band. These systems encompass the five known exoplanets with luminosities consistent with L→T transition brown dwarfs. Our results show that the exoplanets are brighter and have shallower spectral slopes than equivalent temperature brown dwarfs in a wavelength range that contains the methane fundamental absorption feature. For 2M1207 b, we find that thick clouds and non-equilibrium chemistry caused by vertical mixing can explain the object’s appearance. For the HR 8799 planets, we find that the atmospheres must have patchy clouds, along with non-equilibrium chemistry. Together, the presence of a heterogeneous surface and vertical mixing presents a picture of dynamic planetary atmospheres in which both horizontal and vertical motions influence the chemical and condensate profiles.

You can download the pre-print at astro-ph.

Exoclimes III

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I just got back to sunny, 80-degree Tucson, Arizona from a snowy, 30-degree exotic climate, at the Exoclimes III conference in Davos, Switzerland.
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This conference was a meeting of solar and extrasolar planetary scientists to discuss the latest research on planetary interiors, atmospheres, weather, climates, energy budgets, variability, etc. Of course, for bodies like Earth and Venus the talks were more on the weather and climate side, whereas for bodies like HD 189733 b and Luhman-16 B, the talks were more on the energy budget and variability side [links are to PDFs of some example talks]. But it was really impressive to see these fields coming together, and to think about linking what we know about the Solar System planets and moons to extrasolar worlds.

On Thursday, Andy Skemer (LBTI Instrument Scientist and MagAO Officemate Extraordinaire) gave a talk about the mid-infrared properties of directly-imaged exoplanets:
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Because a lot of the talks earlier in the week had been about transit spectroscopy of close-in hot jupiters and neptunes, Andy did a little compare-and-contrast for transiting planets vs directly imaged planets:
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He noted that most of the transit-spectroscopy talks concluded with “Needs more telescope time,” whereas for direct imaging, we “need more capable instruments”. That is, direct imaging is still very much technology-limited, and it is the next generation of AO instruments that are finally enabling us to image these challenging planets. (Direct imaging is also physics-limited, in a way, because if there were earths and jupiters all over the place, then at least some of them would be easier to observe!)

This is where MagAO comes in. It is the first adaptive-secondary AO system in the southern hemisphere, and has an extremely functional pyramid wavefront sensor than enables us to get down to ~130 nm rms WFE. We can image from 600 nm to 5 microns with our two science cameras, VisAO and Clio2. Andy works with MagAO’s older sister, the LBT adaptive optics system, and to emphasize the state-of-the-art AO systems we have, he showed Simone Esposito’s classic PSF from SPIE 2010 San Diego:
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And here are Runa Briguglio and Armando Riccardi with one of the LBT adaptive secondary mirrors:
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Andy talked about the work he’s done imaging extrasolar planets HR 8799 bcde and 2MASS 1207 b with LBTAO and MagAO — here are some of his images from LBT and MagAO:
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While we are as-yet still at the handful-of-planets level, direct imaging is rapidly advancing, and MagAO has a unique role to play. It was exciting to see all the work being done by Solar System planetary scientists and transit-spectroscopists, and to see how important high-contrast AO systems like MagAO are to complete the picture we have of extrasolar worlds.

I had a poster presentation showing MagAO first-light images of the exoplanet Beta Pictoris b. Jared submitted his paper and mine will be coming soon, and there are figures here from both papers:
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What we’re finding is that Beta Pic b fits in very well with the brown dwarf sequence for early L’s, whereas the other directly imaged planets HR 8799 bcde and 2MASS 1207 b seem to be an extension of the L sequence. The flux is depressed at 3.3um at L’ according to my MagAO/Clio2 data, and I have the smallest M’ error bars yet. Trying a range of models, we can fit the NIR okay, but are having difficulties with the 3-4um region. The conference was a great showcase for this type of work, because as we are obtaining more data, we are also modeling more complexity in atmospheres, including low-gravity objects like Beta Pic b that has different cloud properties than those previously modeled in field brown dwarfs.

The conference had long lunches (and picked up again in the evening), and towards the end of the week, we direct imagers (Andy, Mike Liu, and I) went on a ski outing during one of these. Here is the ski lift on the bunny hill, and a tram we took later to see the top of the Alps (the serious skiing is up there).
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Since we live in Tucson where it’s 80 degrees in February, Andy and I were wearing a lot of borrowed gear:
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We stuck to the bunny hill:
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Quote of the day: “It’s like there’s no friction!” –Andy
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Mike snowboarded from the rope tow.

Our conference center was the same place where they have the World Economic Forum, and we were wondering if the world economic leaders get ski breaks too. (We thought they have the World Economic Forum in Davos because you think about the economy a lot there, like when you’re paying 5 Francs for tap water at a restaurant.)
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Anyway, it was a great conference, and I look forward to the next one!