Gemini Planet Imager discovers its first new planet

Hi MagAO fans… this planet discovery did not actually use MagAO (too bad!), but it includes MagAO team members Kate Follette and Katie Morzinski, and MagAO user/operator/blogger Kim Ward-Duong, and MagAO users Jenny Patience and Abhi Rajan, as well as involving our favorite technique of Extreme Exoplanet AO… so we thought you might be interested to hear about the first new planet discovered by the Gemini Planet Imager (GPI)!

Gemini is our neighboring telescope to the South on Cerro Pachon, and the Gemini Planet Imager has been mentioned on the MagAO blog before. The GPI Exoplanet Survey is a large program to look for new planets around young stars. It uses an extreme AO system with a MEMS deformable mirror to correct high-order turbulence, a specialized coronagraph to block out the light of the central star, and an integral field spectrograph to break the light into a rainbow of colors at each point in the image plane, in the 1-2 micron regime. See this blog post for more on how GPI works to see planets.

Today the Science article came out announcing the discovery of GPI’s first new planet, 51 Eri b, by Bruce Macintosh, James Graham, and the rest of the GPI/GPIES team. (ArXiv version.) Please see the press release for the full story! Here is a brief taste in pictures:

The 51 Eridani system consists of a ~20-Myr-old F-type star with a ~2000-AU-away distant pair of M dwarfs at ~6 AU from each other.
Here is a picture of the star in the sky, by Franck Marchis and Sarah Blunt — it is about 30 pc (almost 100 light years) away:

Location of 51 Eri in the constellation of Eridanus (The River). With a brightness of 5 magnitude in visible and a declination of -2 degrees, the star is visible with naked eyes in the Northern and Southern hemispheres. Click here to generate this figure, credit: Aladin Sky Atlas & F. Marchis, SETI Institute; Astrostudio.com & Sarah Blunt, SETI Institute.


And a fly-by simulation of the system by Jenny Patience and James Cornelison:

Simulated fly-by of the 51 Eridani star and planet system from Franck Marchis on Vimeo.

Closer in to the star GPI found a planet at 13 AU — which would be a little bit outside the orbit of Saturn in our Solar System. Here is the discovery image, by Julien Rameau and Christian Marois:

Discovery image of the planet 51 Eridani b with the Gemini Planet Imager taken in the near-infrared light on December 18 2014. The bright central star has been mostly removed to enable the detection of the exoplanet one million times fainter. Credit: Julien Rameau (UdeM) and Christian Marois (NRC Herzberg)

Here is an artist’s conception of the system, as seen from near the planet, by Danielle Futselaar and Franck Marchis:

An artistic conception of the Jupiter-like exoplanet, 51 Eri b, seen in the near-infrared light that shows the hot layers deep in its atmosphere glowing through clouds. Because of its young age, this young cousin of our own Jupiter is still hot and carries information on the way it was formed 20 million years ago. Credit: Danielle Futselaar & Franck Marchis, SETI Institute

An integral part of GPI (haha…) is the Integral Field Spectrograph that takes a little spectrum of every point in the image. This way, we can discover the planet, as well as measure its properties like its temperature, at the same time. Check this movie out which shows the brightness of the planet at each wavelength, in two different ways of looking at it, by Robert De Rosa and Christian Marois: (It’s an animated gif… I hope it works on your browser/device.)

The Gemini Planet Imager utilizes an integral field spectrograph, an instrument capable of taking images at multiple wavelengths‚or colors‚ of infrared light simultaneously, in order to search for young self-luminous planets around nearby stars. The left side of the animation shows the GPI images of the nearby star 51 Eridani in order of increasing wavelength from 1.5 to 1.8 microns. The images have been processed to suppress the light from 51 Eridani, revealing the exoplanet 51 Eridani b (indicated) which is approximately a million times fainter than the parent star. The bright regions to the left and right of the masked star are artifacts from the image processing algorithm, and can be distinguished from real astrophysical signals based on their brightness and position as a function of wavelength. The spectrum of 51 Eridani b, on the right side of the animation, shows how the brightness of the planet varies as a function of wavelength. If the atmosphere was entirely transmissive, the brightness would be approximately constant as a function of wavelength. This is not the case for 51 Eridani b, the atmosphere of which contains both water (H20) and methane (CH4). Over the spectral range of this GPI dataset, water absorbs photons between 1.5 and 1.6 microns, and methane absorbs between 1.6 and 1.8 microns. This leads to a strong peak in the brightness of the exoplanet at 1.6 microns, the wavelength at which absorption by both water and methane is weakest. Credit: Robert De Rosa (UC Berkeley), Christian Marois (NRC Herzberg, University of Victoria)

Well, as I said above, please see the paper (ArXiv version) and the press release for the full story. Thanks for reading. We’re so excited for GPI’s first planet, and we can’t wait to look at it with MagAO!

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