THE GEMINI NICI PLANET-FINDING CAMPAIGN: DISCOVERY OF A CLOSE SUBSTELLAR COMPANION TO THE YOUNG DEBRIS DISK STAR PZ Tel

Abstract

We report the discovery of a tight substellar companion to the young solar\nanalog PZ Tel, a member of the Beta Pictoris moving group observed with high\ncontrast adaptive optics imaging as part of the Gemini NICI Planet-Finding\nCampaign. The companion was detected at a projected separation of 16.4 +/- 1.0\nAU (0.33 +/- 0.01") in April 2009. Second-epoch observations in May 2010\ndemonstrate that the companion is physically associated and shows significant\norbital motion. Monte Carlo modeling constrains the orbit of PZ Tel B to\neccentricities > 0.6. The near-IR colors of PZ Tel B indicate a spectral type\nof M7+/-2 and thus this object will be a new benchmark companion for studies of\nultracool, low-gravity photospheres. Adopting an age of 12 +8 -4 Myr for the\nsystem, we estimate a mass of 36 +/- 6 Mjup based on the Lyon/DUSTY\nevolutionary models. PZ Tel B is one of few young substellar companions\ndirectly imaged at orbital separations similar to those of giant planets in our\nown solar system. Additionally, the primary star PZ Tel A shows a 70 um\nemission excess, evidence for a significant quantity of circumstellar dust that\nhas not been disrupted by the orbital motion of the companion.\n