First light of the Gemini Planet imager

Abstract

The Gemini Planet Imager is a dedicated facility for directly imaging and spectroscopically characterizing extrasolar planets. It combines a very high-order adaptive optics system, a diffraction-suppressing coronagraph, and an integral field spectrograph with low spectral resolution but high spatial resolution. Every aspect of the Gemini Planet Imager has been tuned for maximum sensitivity to faint planets near bright stars. During first-light observations, we achieved an estimated H band Strehl ratio of 0.89 and a 5-σ contrast of 10(6) at 0.75 arcseconds and 10(5) at 0.35 arcseconds. Observations of Beta Pictoris clearly detect the planet, Beta Pictoris b, in a single 60-s exposure with minimal postprocessing. Beta Pictoris b is observed at a separation of 434 ± 6 milliarcseconds (mas) and position angle 211.8 ± 0.5°. Fitting the Keplerian orbit of Beta Pic b using the new position together with previous astrometry gives a factor of 3 improvement in most parameters over previous solutions. The planet orbits at a semimajor axis of [Formula: see text] near the 3:2 resonance with the previously known 6-AU asteroidal belt and is aligned with the inner warped disk. The observations give a 4% probability of a transit of the planet in late 2017.

Keywords: debris disks; extreme adaptive optics; high-contrast imaging.

Fig. 1.

RGB color composite of a single 60-s H band (1.5–1.8 μm) GPI image of Beta Pictoris. The short, medium, and long segments of H band are mapped to RGB. The image has been high-pass filtered to remove diffuse background light, but no PSF subtraction has been applied. The four sharp spots at 1:00, 4:00, 7:00, and 10:00 are diffracted images of the star generated by a reference grid inside GPI.

Fig. 2.

Combined 30-min GPI image of Beta Pictoris. The spectral data have been median-collapsed into a synthetic broadband 1.5–1.8 μm channel. The image has been PSF subtracted using angular and spectral differential techniques. Beta Pictoris b is detected at a signal-to-noise of $\sim 100$.

Fig. 3.

Contrast vs. angular separation at H (1.6 μm) for a PSF-subtracted 30-min GPI exposure. Contrast is shown for PSF subtraction based on either a flat spectrum similar to a L dwarf or a methane-dominated spectrum (which allows more effective multiwavelength PSF subtraction.) For comparison, a 45-min 2.1-μm Keck sequence is also shown. (Other high-contrast AO imaging setups such as Subaru HiCIAO, Gemini NICI, and VLT NACO have similar performance to that of Keck.)

Fig. 4.

The projected separation of β Pic b relative to β Pic in celestial coordinates. Data before the GPI point in late 2013 are from ref. . The GPI measurement shows that β Pic b has passed quadrature and allows a prediction of conjunction in September–December 2017. The red and blue trajectories show 100 solutions drawn from the posterior distribution of likely orbital solutions determined from our Monte Carlo Markov chain analysis of these data.

Fig. 5.

Posterior distribution of the orbital elements of β Pic b: semimajor axis, a; epoch of periapse, τ (in units of the orbital period); argument of periapse, ω; argument of the ascending node, Ω; inclination, i; and eccentricity, e. The plot shows the joint distributions as contours (0.1, 0.5, and 0.9) and marginalized probability density functions as histograms. The well-represented degeneracy in ω, e.g., see ω versus a, is good evidence of reliable sampling of the posterior distribution. Vertical dotted lines in the histograms denote the 68% confidence interval.