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GPI at 2016 SPIE Astronomical Telescopes and Instrumentation

GPI is here at the SPIE Astronomical Telescopes and Instrumentation conference in Edinburgh, Scotland to talk exoplanets and engineering with our colleagues around the world. We have had talks and posters by GPIES team members on topics from AO and instruments to computing and pipelines. This week has also been a great opportunity to meet face-to-face and discuss some of the finer points of GPI technical challenges and plans going forward. Here are some pictures from the week:

Edinburgh, Scotland

Bruce gave a great talk on the GPI instrument and GPIES campaign in the instruments session:

Bruce’s talk about the GPI instrument

Vanessa gave a great talk about GPI’s AO performance in the AO session:

Vanessa’s talk about GPI AO

In her talk, I was especially struck by how well the GPI team has continued to monitor and improve the performance of the instrument, throughout the GPIES campaign.

Franck’s poster was about the GPIES project from a systems level:

Franck’s poster about the GPIES project

Marshall’s poster was about the GPIES pipeline and calibration, critical for extracting accurate exoplanet info from the raw data:

Marshall’s poster about the data pipeline and calibrations

Ben’s poster was about an improved algorithm for finding exoplanets particularly close to the star:

Ben’s poster about detecting exoplanets extremely close to their stars

There were a few more GPIES posters, and I will update the post if I get pictures of more of them soon.

We also took the opportunity to gather 17 of the attending GPIES members for a delicious Indian dinner:

GPIES dinner on Thursday night at the conference

GPIES dinner from Franck’s perspective

I had to add this picture because Dmitry somehow managed to hide in all the dinner pictures

Unfortunately Patrick and Lyra were not able to attend the dinner, and Stephen was only able to stop by to say hi.

After a conference like this, I always leave full of new ideas and a renewed energy for my work. Thanks GPI and SPIE for a great SPIE!

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GPIES May 2016 Observing Run: Women in Astronomy

Hello GPI fans! We are just wrapping up our cloudy, snowy May 2016 GPIES observing run. While the weather wasn’t the best, we accomplished what we could in between the clouds. We also enjoyed the fact that this was the first all-woman run that any of the 5 of us had ever been on. It was a celebration of women in astronomy!

Winter in Chile means snow in the high mountains to the East, as well as a chance of snow at the slightly lower telescope mountains. Here is a wintery view out my window on the plane ride in:

View out the airplane window from Santiago to La Serena

When we arrived at Gemini we were happy to see the cute little zorro that hangs out around the dorms:

Here is a cute little zorro that hangs out by the dorms. Great picture by Kate.

We got a tour of the telescope. It was the first time GPIES student Sarah Blunt had been to Chile, and the rest of us enjoy seeing Gemini again anyway.

Here we are dwarfed by the telescope. From left to right: Katie, Sarah, Jenny, Kim

Gaetano gave us a tour of the telescope. Here we are going up the stairs from the dome floor to the platform.

The observing team for the May 2016 GPIES run. From left: Kate Follette, Kim Ward-Duong, Sarah Blunt, Jenny Patience, and Katie Morzinski

Jenny and Kate led the team and the run, while Kim and Sarah and I were there to help out. We also had assistance on-site from Gemini scientist and GPIES team member Fredrik Rantakyro, as well as other Gemini staff. Remote support was provided by GPIES team members Vanessa Bailey, Rob de Rosa, Jeff Chilcote, and Bruce Macintosh on the Polycom, and others by email and Slack. The reason for such a large complex team is that we optimize the observing campaign to maximize the chance of finding planets.

What does observing for the GPIES campaign involve? Well, 1 person selects targets and directs the night (this was Kate and Jenny), 1 person runs GPI and takes the data (this was Kate and me), 1 person records the log and updates the team (this was Sarah and Kim and me), 1 person runs the pipeline and evaluates the quality of the data (this was Kim and Kate), and 1 person synthesizes and analyzes the progress and makes the big decisions about how best to optimize our time (this was mostly Jenny and a bit Kate).

What are these big decisions about how to best optimize our time? For example, one night the clouds had cleared up a bit but the seeing wasn’t that great, so I took a few data sets while Kim, Kate, and Sarah evaluated the data quality. Then Jenny was comparing our data quality to histograms made by GPIES team members Rob de Rosa and Abhi Rajan to determine whether our data quality was good enough to improve the chances of detecting a planet around the star in question. It was not, so we decided to hand the next hour of observing over to Fredrik to run a GPI queue program. This optimizes use of the telescope for everyone, because we can try to observe that particular star on a different night, while Gemini can get some good science out of its poorer weather by observing targets for a program that doesn’t require the best conditions.

Jenny directs the May 2016 GPIES observing team

The May 2016 GPIES observing team at work

Well, in astronomy as in life, you never know what Mother Earth is going to throw at you. Unfortunately, this run we had a lot of weather, meaning clouds that make for beautiful photos but poor observing:

Sunset

A beautiful backdrop is bad news for astronomers

Virgas* streaming down from the clouds (*A virga is an observable streak or shaft of precipitation, whereas a viga is a wooden beam characteristic of adobe buildings of the southwestern United States and northern Mexico.)

Sunset through the louvers from inside the Gemini dome.

Finally, on the second-to-last day it started snowing, so we had to write off our last night, and chose to head down the mountain a day early to ensure we would catch our flights, since the snow meant the dome would be covered and would not be able to open that night:

Snow on the hillside

Snow at Gemini

The weather was disappointing, but I did have a good time helping out run GPI and discussing the finer points of AO with Vanessa and planet-finding with Jenny, Kate, Kim, and Sarah. The complex GPI instrument and GPIES campaign are made possible by a great collaboration that communicates well to make the best use of our time and observing conditions. Better luck next run, GPIES!

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Observing planet formation at close range: Gemini Planet Imager’s view of the TW Hya disk

Investigations of star and planet formation have long focused on the rich stellar nurseries of Taurus, Ophiuchus, Chamaeleon, and a handful of similarly nearby (but lower mass) molecular clouds. These regions, which lie just beyond 100 pc, are collectively host to hundreds of low-mass, pre-main sequence (T Tauri) stars with ages of a few million years and less. They hence provide large samples of stars with orbiting circumstellar disks that span a wide range of evolutionary stages.

Examples of protoplanetary disks that lie closer than ~100 pc to Earth are far fewer and farther between. However — because their proximity affords the maximum possible linear spatial resolution — these nearby disks provide unique opportunities to test theories describing the planet formation process (see http://cosmicdiary.org/geminiplanetimager/2015/09/16/what-do-we-know-about-planet-formation/). Furthermore, the T Tauri star-disk systems within 100 pc of the Sun tend to be older, on average, than the large numbers of star-disk systems that are still found in or near their natal dark clouds. Hence, circumstellar disks orbiting the nearest known young stars are particularly informative about the late stages of planet formation, as disks disperse and any planets born therein are reaching their final masses (for a brief overview of the study of nearby young stars, see 2015arXiv151000741K).

TW Hydrae was the first of these nearby T Tauri stars to be identified, and remains the best-studied such system. At just 54 pc from Earth and a ripe young age of roughly 8 million years, this nearly solar-mass star and its orbiting, circumstellar disk of dust and gas has become a “go-to” target for new imaging facilities seeking to demonstrate their capabilities. For example, TW Hya has already been the subject of a significant number of ALMA First Light and Early Science programs aimed at investigating the chemistry and structure of its 200-AU-diameter disk.

Hence, when Gemini Planet Imager (GPI) became available for Early Science observations last year, TW Hya beckoned. Given GPI’s potential to perform diffraction-limited, coronagraphic near-infrared imaging on the 8-meter Gemini South telescope, GPI imaging of TW Hya offered the chance to image a protoplanetary disk in its giant planet and Kuiper Belt formation (~10-50 AU) regions at a jaw-dropping ~1.5 AU resolution. In combination with GPI’s polarimetric capability, such observations can tease out the faint signature of starlight scattered off circumstellar dust, potentially yielding an unprecedently detailed view of the surface of the nearly face-on disk.

Our team’s observations of TW Hya were challenging for GPI; the star lies at the faint end of the useful range of its adaptive optics (AO) unit. But our team had successfully imaged the circumbinary disk orbiting the close binary T Tauri system V4046 Sgr with GPI (Rapson et al. 2015ApJ…803L..10R), a system very similar to TW Hya in many respects (including its I magnitude). So we had hope for TW Hya as well.

TWHya_GPIpubImage

The GPI observations of TW Hya did not disappoint. These new GPI coronagraphic/polarimetric AO images confirm the presence of a dark gap in the TW Hya disk at 23 AU that was previously tentatively identified via near-infrared imaging with the Subaru telescope (Akiyama et al. 2015ApJ…802L..17A). The GPI imaging furthermore clearly resolve the disk gap, allowing us to measure its width (~5 AU) and depth (~50%) and thereby facilitating direct comparison with detailed numerical simulations of planets forming in circumstellar disks. The comparisons we have carried out thus far (see above) indicate that the 5-AU-wide gap’s observed structure could be generated by a sub-Jupiter-mass planet orbiting within the disk at a position roughly equivalent to that of Uranus in our solar system. For the gory details, see Rapson et al. (2015ApJ…815L..26).

Further scrutiny of the TW Hya disk with GPI and SPHERE in their differential coronagraphic imaging modes may yield direct detection of the planet(s) that appears to be actively carving a gap in the TW Hya disk — especially if the putative planet is still actively accreting gas from the disk. There are other possible explanations for the formation of gaps and rings in disks, however. In particular, dust grain fragmentation and ice condensation rates may change rapidly with disk radius, yielding sharp variations in small grain surface densities and/or reflective properties that can produce the appearance of disk gaps when imaged in scattered starlight. Or the inner regions of the disk may be partially shadowing exterior regions. ALMA imaging of the TW Hya disk should provide definitive tests of these alternative scenarios for the gap at 23 AU seen in our GPI imaging.

-Joel Kastner (Center for Imaging Science and School of Physics & Astronomy, Rochester Institute of Technology)

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Extreme Solar Systems Featured in Online Press Conference

Announcement from the AAS

The American Astronomical Society (AAS) will convene an online press conference on Tuesday, 1 December, featuring exciting new results on exoplanets from Extreme Solar Systems III, a conference taking place from 29 November through 4 December 2015 at the Waikoloa Beach Marriott Resort & Spa on Hawaii Island.

ExSS III is the third in a series of conferences that began with Extreme Solar Systems in 2007 in Santorini, Greece, and was followed by Extreme Solar Systems II in 2011 in Jackson Hole, Wyoming. Next week’s conference, like the previous two, will cover all aspects of research on exoplanets. Some 350 researchers from all over the world are registered for the meeting.

ExSS III isn’t set up for the types of press conferences held during regular AAS meetings, but because there are so many potentially newsworthy presentations, the organizers and the AAS Press Office have come up with a plan for an online briefing to be held beginning at 7 am HAST on Tuesday, 1 December. That’s 9 am PST on the US West Coast, 12 pm EST on the East Coast, 17:00 UTC/GMT, and 6:00 pm CET in Central Europe. The briefing will last no more than one hour and will be conducted as a Google+ Hangout On Air; viewers without Google+ accounts may participate via YouTube.

Presenters and onsite reporters will gather in the Paniolo room at the Marriott — though, strictly speaking, this isn’t necessary, as all participants will be using their own computers to connect to the briefing. Here’s the lineup:

Rick Fienberg (American Astronomical Society)
Host & Moderator

Paul Kalas (Univ. of California, Berkeley) & Abhijith Rajan (Arizona State Univ.)
Resolving the HD 106906 Disk with the Gemini Planet Imager

Thayne Currie (National Astronomical Observatory of Japan)
Extreme Exoplanet Direct Imaging: New Results and the Path to Imaging Another Earth

Jason Steffen (University of Nevada, Las Vegas)
Dynamical Considerations for Life in Multihabitable Planetary Systems

Lisa Kaltenegger (Cornell University)
Independent Commentary

The briefing will last no more than one hour and will be conducted as a Google+ Hangout On Air, with journalists and the public invited to participate via the associated YouTube or Google+ pages:

YouTube: https://www.youtube.com/watch?v=HXfbVxbqWKU

Google+: https://plus.google.com/events/cq682ju6jeetqmsosst1t0vk3eg

Those watching on YouTube should be able to ask questions via text chat, while those on Google+ should be able to ask questions via the built-in Q&A app. In case either or both of those features don’t work, as a backup journalists may send questions by email to press@aas.org.

Links to the briefing will be provided in a subsequent advisory, on Monday, 30 November.

Contact:

Rick Fienberg
AAS Press Officer
+1 202-328-2010 x116
rick.fienberg@aas.org

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What do we know about planet formation?

Understanding how planets form in the Universe is one of the main motivations for GPI. Thanks to its advanced design, GPI specializes in finding and studying giant planets that are similar to Jupiter in our solar system. These are the kind of planets whose origin we hope to understand much better after our survey is complete.

Fig1

This artist’s impression shows the formation of a gas giant planet around a young star. Credit: ESO/L. Calçada

We know that planets form within protoplanetary disks that orbit young stars, and gas giants need to be fully formed within 3-10 million years of the formation of their parent star as the gaseous nebula dissipates past this point. This very important time constraint is based on statistics of observed protoplanetary disks in nearby young stellar associations such as Taurus. At present there are two main rival theories of giant planet formation — core accretion and gravitational instability, which effectively represent the “bottom up” and “top down” routes to planetary genesis.

Core accretion relies on the formation of a planetary core — a compact, massive object composed of refractory elements, similar to a terrestrial planet like Earth but typically more massive. Cores form by assembly of a large number of planetesimals — smaller asteroid-like bodies composed of rock and ice that collide with each other, merge and grow in size. This process is thought to be rather slow, especially if it happens far from the star, where the characteristic timescales, which are determined by the local orbital period, become very long. As protoplanetary cores increase their mass, their gravitational pull attracts gas from the surrounding nebula, forming atmospheres around them. Atmospheric mass increases quite rapidly, and at some point the whole gaseous envelope becomes self-gravitating. In theoretical models, this transition typically occurs when the core mass exceeds 10-20 Earth masses. Beyond this point rapid gas accretion ensues, turning the core into a giant planet in a relatively short period of time. This process is accompanied by a brief phase of high luminosity as the gravitational energy of accreted gas is radiated away. The final mass of the planet is likely to be set by how much nebular gas is available for accretion, which may be limited by the formation of a gap around the planetary orbit, or by the dispersal of the protoplanetary disk.

Gravitational instability may operate in cold, massive disks in which random gas overdensities start growing under their own self-gravity, which neither pressure nor rotational support can initially resist. If this collapse of dense regions can continue deeply into the nonlinear regime, and their density come to far exceed the nebula’s, such clumps become self-gravitating objects — and, over time, contract, cool, and look like giant planets. Theoretical arguments and numerical simulations suggest that this is possible only when the collapsing gas is able to cool rapidly. Otherwise, pressure inside the contracting clump would increase so fast that it could stall collapse. Detailed analysis shows that in gravitationally unstable disks, conditions for such rapid cooling are realized only far from the star, beyond approximately 50 AU, which is in the range of separations probed by GPI.

Fig2

A schematic illustration of the two main theoretical channels of the giant planet formation: core accretion (on the left) and gravitational instability (on the right). Credit: NASA and A. Feild (STScI)

Both theories have their own virtues and problems. Core accretion is natural in the sense that it represents a culminating step in the formation of terrestrial planets (or massive cores). It nicely explains the overabundance of refractory elements and the presence of cores for giant planets in the solar system (although the latter is not so obvious in the case of Jupiter). It also naturally accounts for the so-called metallicity correlation — the tendency of more metal-rich stars to host a giant planet: higher abundance of metals in the nebula increases the availability of solids and speeds up core growth, facilitating core accretion. However, formation of the core is the Achilles’ heel of core accretion because it typically takes a long time. Standard theory predicts that far from the star, the core buildup by planetesimal coagulation should take much longer than the lifespan of a protoplanetary disk, which is several million years. This makes it problematic to explain the origin of directly imaged planets by core accretion at tens of AU from their stars. That’s why a number of ideas have been proposed recently for speeding up core formation, by efficient accretion of either cm- or mm-sized “pebbles” early on, or small fragments and debris resulting from planetesimal collisions at later stages.

Gravitational instability nicely bypasses the nebula-lifetime constraint as it should operate on a relatively short dynamical timescale, which is about thousands of years at 100 AU distances. However, as mentioned above, conditions for this formation channel can exist only far from the star. It also requires very massive protoplanetary disks, typically tens of percent of the stellar mass, which may not be unusual early on but is not very common in later stages. High disk mass raises a number of important issues for gravitational instability. Bound objects produced by gravitational instability are expected to have rather high initial masses (of order 10 Jupiter masses), and can easily grow from planetary mass into the brown dwarf regime by accreting from the surrounding dense nebula. Tidal coupling to a massive disk may also lead to fast migration of forming protoplanets towards the star, where they can be efficiently destroyed.

Fig3

A series of snapshots from a simulation of a gravitationally unstable protoplanetary disk. Bright objects seen at late stages are the self-gravitating clumps forming as a result of gravitational instability that may subsequently turn into giant planets. Credit: G. Lufkin et al (University of Washington)

Discoveries of planets such as 51 Eri b are very important for understanding the efficiency of each of these two channels (their “branching ratios”) in producing the planets we have observed. With its small projected separation of only 13 AU and relatively low mass (possibly as low as two Jupiter masses) this object would have little problem forming by core accretion even at its current location, which is close to the orbit of Saturn in our solar system. At this stage, gravitational instability appears a more unlikely scenario for 51 Eri b. GPI and similar surveys will provide better statistics for directly imaged planets at different separations, and give us a much better understanding of how the majority of giant planets form in the Universe.

Roman Rafikov (IAS)

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What Self-Luminous Planets are Like

The planets that we are familiar with in our own solar system have evolved, aged, and cooled, for over 4.5 billion years since the Sun and planets formed. What do planets look like at younger ages? Can we use the light that a planet emits to understand its past history?

When we look at a planet like Jupiter with our eyes, the light that we see is Sunlight that is reflected back to us at Earth, scattered by clouds and gasses in the planet’s atmosphere. But what would Jupiter look like if we instead could see only its thermal “heat” emission, far beyond the visible spectrum? We can use infrared light detectors on telescopes to see this thermal emission, which comes from the deep interior below the visible clouds. We can use this light to precisely “take Jupiter’s temperature” in a way that you can’t do with reflected Sunlight. It turns out that our 4.5 billion-year-old planets are cold enough that their thermal “heat” radiation is quite small. We can only detect it because we are so close by.

[left] Jupiter as it appears to our eyes, in reflected sunlight. [right] Jupiter as it appears at a wavelength of 5 microns.  These long wavelengths are far beyond visible light, in the thermal infrared.

[left] Jupiter as it appears to our eyes, in reflected sunlight. [right] Jupiter as it appears at a wavelength of 5 microns. These long wavelengths are far beyond visible light, in the thermal infrared.

But that wasn’t always the case. Planets start their lives hot. In our current understanding of planet formation, making a planet is a tremendously energetic event. For Jupiter-like giant planets, hundreds of Earth masses of hydrogen dominated gas is pulled via gravity from large distances within the planet-forming nebula, down onto a large “seed core” of ice and rock. The kinetic energy of this moving gas becomes trapped in the opaque planet interior and is converted into thermal (heat) energy within the planet. A young Jupiter, right after formation, might be 10 times hotter in temperature, and over 10,000 times brighter in infrared radiation. These young planets are hot, bright, and much easier to see.

But like an ember that cools after being ejected from the fire, so do planets cool off over time. Trying to understand the specifics of how fast this cooling occurs, and how that impacts the planetary properties that we see, is one of the main reasons that GPI was built.   The interior energy that slowly flows through the planet’s atmosphere, out into space as infrared light, wanes over time, so the atmosphere we see cools and changes.

The atoms and molecules we expect to see in these atmospheres depend strongly on temperature. Three of the most abundant molecules are water vapor (H2O), carbon monoxide (CO), and methane (CH4). These molecules all absorb light at infrared wavelengths, so they are easy for GPI to see. When atmospheres cool, they also form clouds. Earth’s clouds are made of water and Jupiter’s clouds are made of ammonia (NH3). But warmer gas giant planets can have much stranger clouds. The hottest planets will have clouds made of iron droplets and rock dust. Cooler planets, like a middle-aged Jupiter, should have clouds of salt (KCl) and sodium sulfide (Na2S). What we don’t yet know is how thick these clouds are, and if they form all over the visible atmosphere.

This rendering shows a possible view of a young Jupiter-like planet, 51 Eri b.  It is glowing in thermal emission and shown as being partly cloudy.

This rendering shows a possible view of a young Jupiter-like planet, 51 Eri b. It is glowing in thermal emission and shown as being partly cloudy.

 

We expect to see significant differences between very young planets, and those that are cooler and more middle-aged. As mentioned above, their temperatures and atmospheres change over time, but even the sizes of the planets changes. When their interiors cool off, the hydrogen gas contracts and the planets shrink. We’re using GPI to understand how this planetary cooling and shrinking process works, for planets at different ages.

Could we detect a young, hot rocky planet, like a young Earth? That will be possible in the future, but is beyond the reach of GPI. Such planets are much harder to see than young gas giants because of their much smaller sizes. They just don’t put out as much infrared light. It also might be difficult to recognize such a planet if we saw it, because we have little intuition for what such a planet might look like. Its atmosphere might be made of a mix of water vapor, CO2, and some gaseous components from vaporized rocks. Work for the future!

Jonathan Fortney

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How GPI Works to See Planets

I sometimes compare the challenge of directly detecting a Jupiter orbiting a nearby star to finding a glowing needle in a haystack.  Oh, and by the way, the haystack is on fire.

It’s about as hard as seeing a candle a foot away from a spotlight (1 million candlepower) at a distance of 100 miles.

Why is doing this so difficult?  There are three primary reasons:

1.  We observe through atmospheric turbulence, which blurs our view of the star-planet system and scatters starlight, obscuring the faint planet beneath.

2.  Light obeys a wave property called diffraction, which scatters light from a planet’s host star throughout the image, obscuring the planet.  This effect occurs even in near-perfect optical systems above the atmosphere, like the Hubble Space Telescope.

3.  The optics within telescopes and instruments are imperfect, which further distorts the optical wavefront and introduces speckles, or tiny images of the star that look like false planets, into the image.

The Gemini Planet Imager was designed to control and suppress these effects.  The four components of GPI that do this are:  an Adaptive Optics system, a coronagraph, a sensor that spectroscopically differentiates planets from starlight, and data post-processing techniques.

The Adaptive Optics (AO) system is the component of GPI that corrects for the effects of atmospheric turbulence and optical imperfections, allowing the telescope to observe stars as though the atmosphere were not present.  AO systems use flexible deformable mirrors to cancel the distortion induced by the atmosphere.  In GPI, a wavefront sensor updates 1000 times per second to measure the distortion at high precision.  A real-time control computer uses these measurements to estimate the deformable mirror shape needed to exactly cancel this turbulence.

GPI’s deformable mirror is a 2 cm-square MEMS, or Micro-Electrical Mechanical System, with 4096 microactuators.  Manufactured by Boston Micromachines, MEMS devices are etched from silicon wafers lithographically in a method similar to semiconductor fabrication.  Once nothing more than a glint in an engineer’s eyes, MEMS deformable mirrors have now been demonstrated on multiple astronomical AO systems and have proven reliable.

GPI-MEMS3Courtesy Daren Dillon / UCSC.

coronagraph is an optical device used to block starlight and physically suppress the effects of diffraction.  GPI uses a Lyot coronagraph design, named after Bernard Lyot, who first used a coronagraph to block out the sun’s glare and reveal its corona.  GPI’s Lyot coronagraph introduces a hard edged stop where the star comes to focus, blocking most of its light, as well as an apodized optic in the Lyot plane, where the remaining diffracted light from the star is isolated and blocked.  Light from other objects in the field passes through the coronagraph unimpeded.

The Integral Field Spectrograph (IFS) in GPI breaks light into its constituent wavelengths, or a spectrum, just as a prism does.  The magic of the IFS is that it performs this task at every location in the image, so that the spectrum of a potential planet can be measured simultaneously with the starlight spectrum.  Since light emitted from the planet has different spectral features from the starlight (induced by chemical components in its atmosphere such as methane), this information can be used to differentiate a planet candidate from residual star speckles.  In addition, since star speckles are produced by diffraction, they appear to change position at different wavelengths, while true planets stay fixed at all wavelengths.

The post-processing analysis takes advantage of this differentiation to find fainter planets than would be visible otherwise in a process known as Spectral Differential Imaging (SDI).  A further step is Angular Differential Imaging (ADI), which takes advantage of the natural rotation of the sky, and thus the star-planet orientation, with respect to the telescope’s azimuth.   ADI algorithms essentially look for planets that rotate with the sky rather than with the starlight speckle pattern.

AOoffon_corona_GPI_arrows

GPI’s view of the Beta Pictoris star/planet system as each component is turned on.  Image credit:  GPIES team; Beta Pictoris:  C. Marois/NRC Canada, Gemini Observatory.

It is only the combination of these four approaches in tandem – and not any one of them – that allows GPI to detect planets successfully.  For example, the coronagraph, IFS, and post-processing components all rely critically on the AO system to remove the effects of the atmosphere first.  Similarly, if no post-processing were used, GPI’s performance would not be sufficient to detect planets as faint as it does.

So, quite literally, GPI is more than the sum of its parts.


The Gemini Planet Imager instrument and scientific data reduction pipeline were built by many scientists at the American Museum of Natural History, ASU, Univ. Toronto, Gemini Observatory, HIA, JPL, LLNL, Lowell Observatory, NASA Ames, SETI, STSci, Univ. Montreal, Berkeley, UCLA, UCSC, and UGA.  

 

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Debris Disks: Searching for Dust to Find Planets

GPI_BP1_1

A star system where gas and dust have formed into a disk around a newly formed star. The leftover disk will most likely form planets, comets and asteroids. Credit: NASA

No one is ever excited when the topic of “dust” is brought up. Usually dust is a hindrance – something you sweep away during spring-cleaning, or an annoyance because your allergies can’t handle it. But for astronomers, finding dust around another star – i.e., circumstellar dust – is like finding the next piece of an interstellar puzzle. That’s because circumstellar dust holds clues to understanding not only the origins of planets outside of our solar system, but also gives us a leg up in figuring out our place in the Universe.

Before we can uncover the secret of how dust and exoplanets are linked, we need to understand what happens after a planetary system forms. Once a star is created, it leaves behind a large disk of gas and dust. The gas and dust start sticking together and coalescing into larger objects such as planets, asteroids and comets. The central star removes the remaining gas and dust either by accreting it, or by throwing it out of the system with its stellar wind and radiation pressure. About 10 million years or so after the star forms, all of the leftover dust and gas have either been ejected out of the system, eaten up by the star, or used to form planets, asteroids and comets. But here’s a mystery: astronomers have found stars much older than 10 million years with circumstellar dust.

So then where does all this dust come from if we know it shouldn’t be there?

One word – collisions.

GPI_BP1_Collisions_2

Large planets will gravitationally tug on smaller bodies such as asteroids and comets as they pass by. And if these asteroids and comets are pulled hard enough, they will eventually collide with one another! This can be catastrophic and destructive, breaking the original asteroid into smaller chunks. These chunks can then collide and become still smaller and smaller andGPI_BP1_signposts_3 smaller – grinding down the original body into dust. The dust then forms a disk around the star — what astronomers call a “debris disk.”

Had there not been large planets around these stars, there might not have been any destructive collisions, which in turn would not produce any dust for us to find. In other words, finding dust around a star is like seeing a large signpost saying “PLANETS! Come and get ‘em’!” Of course, initially we don’t actually see the planets. But knowing a debris disk exists around these stars tells us there is a good chance we’ll find them.

Detecting Dust

GPI_BP1_excess_4

Emission spectrum seen from a star that does and does not have dust around it. A star with dust will have excess infrared radiation compared to the emission from the star. Credit: NASA

Now, astronomers typically look for debris disks by measuring the infrared light coming from a star. Dust around a star will warm as it soaks up the light from the central star. As it heats up, it will start emitting its own light in the infrared – just like a stove-top coil will begin to feel hot before you see it glow red. The amount of infrared light the dust gives off, combined with what the star produces, will be more than the amount of infrared light produced only by the star. This excess light is what betrays the presence of dust in the system. This dust is usually 10 to 100 microns in size, or roughly the thickness of a human hair.

Astronomers have found infrared excess emission – most likely caused by debris disks – in over 1,000 star systems, all of which have the potential to host planetary systems.

But what about planets? How can we confirm that planets are responsible for the creation of the dust we’re seeing?

combinedimage

Left: Hubble image of the Fomalhaut dust ring. Credit: Kalas et al. 2012. Center: Beta pic debris disk by Smith and Terrile. Right: Beta pic b planet over plotted on image of the beta pic debris disk. The stars in each image are blocked out by a coronagraph.

In some cases, taking an image of a system that has a known debris disk reveals much more than one can discern from just measuring the amount of infrared light produced by a star. In 2005, GPIES’ own Dr. Paul Kalas and his team used the Hubble Space Telescope to image the debris belt of Fomalhaut – a star roughly 16 times brighter and almost four billion years younger than our sun. These images show a sharp, eccentrically misaligned ring, which hints that a large planet might be orbiting inside the ring. Follow-up observations inspired by this suspicion revealed a planet, Fomalhaut b, though not the one thought responsible for the shape of the debris disk.

Another star system whose imaged disk betrays the existence of a planet is “beta Pictoris” – or beta Pic for short. Beta Pic’s debris disc was the first to be imaged. In 1984, Dr. Brad Smith and Dr. Rich Terrile took an image of the beta Pic disk by blocking out the star’s light using a coronagraph, which revealed an edge-on disk. The disk of this 20-million- year-old star – much younger than our sun – is full of warps and substructures. Such structures in the disk led astronomers to believe that a large planet may be influencing its shape.

And then..

In 2008, astronomers finally discovered the faint signal of a planet eight times the mass of Jupiter, captured in images taken by the Very Large Telescope in 2003. These two systems are only the tip of the iceberg, as many more such stars have been studied, all of which show a wide variety of disk structures and hint at the presence of planets hidden behind the dust.

How does this all link back to us here on Earth?

Although the puzzle of each exosolar system becomes clearer when we study its debris disk, information gleaned from every system can be used to deduce whether a planetary system like ours can form elsewhere in the Universe. This is mainly because the interaction of our solar system’s planets and debris disk – which is made up of the asteroid belt between Mars and Jupiter, and the Kuiper belt way past Neptune – have heavily influenced the current structure of our solar system.GPI_BP1_LHB_8

Roughly 3.7 billion years ago, Jupiter and Saturn began a gravitational dance in which the orbital periods of the titans lined up, and for every orbit around the Sun Jupiter made, Saturn made two. This enhanced gravitational interaction forced Saturn to migrate slowly away from the Sun, pushing Uranus and Neptune further out in the solar system as well. Neptune fatefully crashed into the outer Kuiper belt, sending large ice and rock bodies hurling all over the solar system, and turning its inner region– and Earth – into an interplanetary shooting range. A large amount of dust would have been created during this time period, one quite noticeable to any alien observing our system.

Although this event made the primordial Earth a hellish place to live, there is some good news. Some scientists have theorized that a large portion of Earth’s oceans were fed by the transport of these water-rich comets and asteroids from the Kuiper belt during the “Late Heavy Bombardment.”. And so had it not been for the relationship between our planets and debris belts, Earth would probably not exist as we know it.

We have seen evidence of similar catastrophic events around the young “eta Corvi” system. Using spectroscopic data obtained in 2010 from the Spitzer Space Telescope, Dr. Carey Lisse’s team discovered that for some reason, large numbers of cometary bodies from the outer regions of this system were colliding with a planetary sized body in the inner regions, and releasing water ice dust whose total mass was about 0.1% of all the water in Earth’s oceans!

The similarity between eta Corvi and our early solar system is uncanny. Additionally, it’s exciting to think that the events that may have allowed for life to arise on Earth are currently going on around other stars – events that require a symbiotic relationship between planets and the remnant asteroid and comet population.

Events that we can witness by studying debris disks.

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Hello from AAS!

Happy new year, Internet! I’m starting off the year at the 225th meeting of the American Astronomical Society. It’s an annual conference where all the professional astronomers in the United States get together and talk about space! There’s been some really cool presentations, including the discovery of Earth-sized planets in possibly habitable orbits around other stars by Kepler. Sounds pretty cool right?

A subset of the GPI team was here for the AAS. We gave an update on the GPI Exoplanet Survey, presented posters on debris disks and exoplanets imaged by GPI, and even had a press conference on recent GPI results!

In addition to all the GPI results, the GPI team also had a team lunch to talk about starlight subtraction. Even with the star masked out, starlight still diffracts around the coronagraph and hides the faint exoplanets and debris disks that we are trying to see. As you might guess, starlight subtraction is a really important for GPI, especially with the kickoff of the GPI Exoplanet Survey just a couple of months ago. The content of meeting was a bit technical so I’ll spare you the summary here. It was a productive lunch though, and overall it’s been a great conference!

The only good picture is the one in which my eyes are closed.

The GPI Team in Seattle. Photo credit: Marshall Perrin

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The Gemini Planet Imager Produces Stunning Observations In Its First Year

Fig1_HR8799_image_Ingraham2014

GPI imaging of the planetary system HR 8799 in K band, showing 3 of the 4 planets. (Planet b is outside the field of view shown here, off to the left.) These data were obtained on November 17, 2013 during the first week of operation of GPI and in relatively challenging weather conditions, but with GPI’s advanced adaptive optics system and coronagraph the planets can still be clearly seen and their spectra measured (see Figure 2). Image Credit: Christian Marois (NRC Canada), Patrick Ingraham (Stanford University) and the GPI Team.

Gemini Observatory
Media Advisory

For release at the American Astronomical Society meeting press confer-ence January 6, 2015, 10:15am (PST)

Publication-quality images available at:
www.gemini.edu/node/12314

THE GEMINI PLANET IMAGER PRODUCES STUNNING OBSERVATIONS IN ITS FIRST YEAR

Stunning exoplanet images and spectra from the first year of science operations with the Gemini Planet Imager (GPI) were featured today in a press conference at the 225th meeting of the American Astronomical Society (AAS) in Seattle, Washington. The Gemini Planet Imager GPI is an advanced instrument designed to observe the environments close to bright stars to detect and study Jupiter-like exoplanets (planets around other stars) and see proto-stellar material (disk, rings) that might be lurking next to the star.

Marshall Perrin (Space Telescope Science Institute), one of the instru-ment’s team leaders, presented a pair of recent and promising results at the press conference. He revealed some of the most detailed images and spectra ever of the multiple planet system HR 8799. His presentation also included never-seen details in the dusty ring of the young star HR 4796A. “GPI’s advanced imaging capabilities have delivered exquisite images and data,” said Perrin. “These improved views are helping us piece together what’s going on around these stars, yet also posing many new questions.”

Fig2_HR8799_spectra_Ingraham2014_v2

GPI spectroscopy of planets c and d in the HR 8799 system. While earlier work showed that the planets have similar overall brightness and colors, these newly-measured spectra show surprisingly large differences. The spectrum of planet d increases smoothly from 1.9-2.2 microns while planet c’s spectrum shows a sharper kink upwards just beyond 2 microns. These new GPI results indicate that these similar-mass and equal-age planets nonetheless have significant differences in atmospheric properties, for in-stance more open spaces between patchy cloud cover on planet c versus uniform cloud cover on planet d, or perhaps differences in atmospheric chemistry. These data are helping refine and improve a new generation of atmospheric models to explain these effects. Image Credit: Adapted from Ingraham et al. 2014. Patrick Ingraham (Stan-ford University), Mark Marley (NASA Ames), Didier Saumon (Los Alamos Na-tional Laboratory) and the GPI Team.



The GPI spectra obtained for two of the planetary members of the HR 8799 system presents a challenge for astronomers. GPI team member Patrick Ingraham (Stanford University), lead the paper on HR 8799. In-graham reports that the shape of the spectra for the two planets differ more profoundly than expected based on their similar colors, indicating significant differences between the companions. “Current atmospheric models of exoplanets cannot fully explain the subtle differences in color that GPI has revealed. We infer that it may be differences in the cover-age of the clouds or their composition.” Ingraham adds, “The fact that GPI was able to extract new knowledge from these planets on the first commissioning run in such a short amount of time, and in conditions that it was not even designed to work, is a real testament to how revolu-tionary GPI will be to the field of exoplanets.”

Fig3_HR4796A_images_Perrin2015

GPI imaging polarimetry of the circumstellar disk around HR 4796A, a ring of dust and planetesimals similar in some ways to a scaled up version of the solar system’s Kuiper Belt. These GPI observations reveal a complex pattern of variations in brightness and polarization around the HR 4796A disk. The western side (tilted closer to the Earth) appears brighter in polarized light, while in total intensity the eastern side appears slightly brighter, particu-larly just to the east of the widest apparent separation points of the disk. Reconciling this complex and apparently-contradictory pattern of brighter and darker regions required a major overhaul of our understanding of this circumstellar disk. Image Credit: Marshall Perrin (Space Telescope Science Institute), Gaspard Duchene (UC Berkeley), Max Millar-Blanchaer (University of Toronto), and the GPI Team.

Perrin, who is working to understand the dusty ring around the young star HR 4796A, said that the new GPI data present an unprecedented level of detail in studies of the ring’s polarized light. “GPI not only sees the disk more clearly than previous instruments, it can also measure how polarized its light appears, which has proven crucial in understand-ing its physical properties.” Specifically, the GPI measurements of the ring show it must be partially opaque, implying it is far denser and more tightly compressed than similar dust found in the outskirts of our own Solar System, which is more diffuse. The ring circling HR 4796A is about twice the diameter of the planetary orbits in our Solar System and its star about twice our Sun’s mass. “These data taken during GPI commis-sioning show how exquisitely well its polarization mode works for studying disks. Such observations are critical in advancing our under-standing of all types and sizes of planetary systems — and ultimately how unique our own solar system might be,” said Perrin.

Fig4_HR4796A_diagram_Perrin2015

Diagram depicting the GPI team’s revised model for the orientation and composition of the HR 4796A ring. To explain the observed polarization levels, the disk must consist of relatively large (> 5 µm) silicate dust parti-cles, which scatter light most strongly and polarize it more for forward scat-tering. To explain the relative faintness of the east side in total intensity, the disk must be dense enough to be slightly opaque, comparable to Sat-urn’s optically thick rings, such that on the near side of the disk our view of its brightly illuminated inner portion is partially obscured. This revised model requires the disk to be much narrower and flatter than expected, and poses a new challenge for theories of disk dynamics to explain. GPI’s high contrast imaging and polarimetry capabilities together were essential for this new synthesis. Image Credit: Marshall Perrin (Space Telescope Science Institute).

During the commissioning phase, the GPI team observed a variety of targets, ranging from asteroids in our solar system, to an old star near its death. Other teams of scientists have been using GPI as well and al-ready astronomers around the world have published eight papers in peer-reviewed journals using GPI data. “This might be the most produc-tive new instrument Gemini has ever had,” said Professor James Graham of the University of California, who leads the GPI science team and who will describe the GPI exoplanet survey (see below) in a talk scheduled at the AAS meeting on Thursday, January 8th.

The Gemini Observatory staff integrated the complex instrument into the telescope’s software and helped to characterize GPI’s performance. “Even though it’s so complicated, GPI now operates almost automati-cally,” said Gemini’s instrument scientist for GPI Fredrik Rantakyro. “This allows us to start routine science operations.” The instrument is now available to astronomers and their proposals are scheduled to start observing in early 2015. In addition, “shared risk” observations are al-ready underway, starting in November 2014.
The one thing GPI hasn’t done yet is discovered a new planet. “For the early tests, we concentrated on known planets or disks” said GPI PI Bruce Macintosh. Now that GPI is fully operational, the search for new planets has begun. In addition to observations by astronomers world-wide, the Gemini Planet Imager Exoplanet Survey (GPIES) will look at 600 carefully selected stars over the next few years. GPI ‘sees’ planets through the infrared light they emit when they’re young, so the GPIES team has assembled a list of the youngest and closest stars. So far the team has observed 50 stars, and analysis of the data is ongoing. Discov-ering a planet requires confirmation observations to distinguish a true planet orbiting the target star from a distant star that happens to sneak into GPI’s field of view – a process that could take years with previous instruments. The GPIES team found one such object in their first survey run, but GPI observations were sensitive enough to almost immediately rule it out. Macintosh said, “With GPI, we can tell almost instantly that something isn’t a planet — rather than months of uncertainty, we can get over our disappointment almost immediately. Now it’s time to find some real planets!”
Science Contacts:

Marshall Perrin
Space Telescope Science Institute
Phone: (410) 507-5483
e-mail: mperrin@stsci.edu

James Graham
University of California Berkeley
Phone: (510) 926-9820
e-mail: jrg@berkeley.edu
Media Contact:

Peter Michaud
Gemini Observatory
Phone: (808) 936-6643
e-mail: pmichaud@gemini.edu

The Gemini Planet Imager (GPI) instrument was constructed by an international col-laboration led by Lawrence Livermore National Laboratory under Gemini’s supervi-sion. The GPI Exoplanet Survey (GPIES) is the core science program to be carried out with it. GPIES is led by Bruce Macintosh, now a professor at Stanford University and James Graham, professor at the University of California at Berkeley and is de-signed to find young, Jupiter-like exoplanets. They survey will observe 600 young nearby stars in 890 hours over three years. Targets have been carefully selected by team members at Arizona State University, the University of Georgia, and UCLA. The core of the data processing architecture is led by Marshall Perrin of the Space Tele-scope Science Institute, with the core software originally written by University of Montreal, data management infrastructure from UC Berkeley and Cornell University, and contributions from all the other team institutions. The SETI institute located in California manages GPIES’s communications and public outreach. Several teams lo-cated at the Dunlap Institute, the University of Western Ontario, the University of Chicago, the Lowell Observatory, NASA Ames, the American Museum of Natural His-tory, University of Arizona and the University of California at San Diego and at Santa Cruz also contribute to the survey. The GPI Exoplanet Survey is supported by the NASA Origins Program NNX14AG80, the NSF AAG program, and grants from other institutions including the University of California Office of the President. Dropbox Inc. has generously provided storage space for the entire survey’s archive.

About Gemini Observatory:
The Gemini Observatory is an international collaboration with two identical 8-meter telescopes. The Frederick C. Gillett Gemini Telescope is located on Mauna Kea, Ha-wai’i (Gemini North) and the other telescope on Cerro Pachón in central Chile (Gem-ini South); together the twin telescopes provide full coverage over both hemi-spheres of the sky. The telescopes incorporate technologies that allow large, rela-tively thin mirrors, under active control, to collect and focus both visible and infra-red radiation from space.

The Gemini Observatory provides the astronomical communities in six partner countries with state-of-the-art astronomical facilities that allocate observing time in proportion to each country’s contribution. In addition to financial support, each country also contributes significant scientific and technical resources. The national research agencies that form the Gemini partnership include: the U.S. National Sci-ence Foundation (NSF); the Canadian National Research Council (NRC); the Brazil-ian Ministério da Ciência, Tecnologia e Inovação (MCTI); the Australian Research Council (ARC); the Argentinean Ministerio de Ciencia, Tecnología e Innovación Pro-ductiva; and the Chilean Comisión Nacional de Investigación Cientifica y Tecnológica (CONICYT). The Observatory is managed by the Association of Universities for Re-search in Astronomy, Inc. (AURA) under a cooperative agreement with the NSF. The NSF also serves as the executive agency for the international partnership.

 

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