研究目的
Understanding the formation and evolution of planetary systems requires a detailed census of the galactic planet population. Surveys sensitive to planets orbiting at a wide range of semimajor axes about stars with a variety of spectral types and ages are required to measure the planet mass and semimajor axis distributions as a function of host mass, age, metallicity, and environment.
研究成果
We presented the results of the LEECH direct imaging survey for wide-orbit gas-giant planets. LEECH was performed at 3.8 μm where colder planets emit more of their ?ux. This allowed us to emphasize proximity over youth in our target selection, resulting in increased sensitivity interior to 20 au compared to previous surveys. We reached deeper average contrast around our targets than Rameau et al. (2013), who also reported the results of a large L′ survey. We are typically ?1 mag more sensitive as a function of angular separation due to the performance of the LBT deformable secondary AO system and the thermal–infrared sensitivity of LBTI/LMIRcam. We are even more sensitive as a function of orbital radius in astronomical units after accounting for the different average distance of our targets, 25 pc for LEECH and 40 pc for Rameau et al. (2013).
研究不足
The accuracy of all the evolutionary models we use is limited by the incomplete treatment of the relevant physics—including the initial entropy, the behavior and appearance of clouds, and the treatment of atmospheric dynamics and disequilibrium chemistry—and all of these issues tend to become more severe at lower masses and effective temperatures.
1：Experimental Design and Method Selection:
The LEECH survey was conducted using the LBTI instrument at the LBT on Mt. Graham in southern Arizona. Observations were performed in direct imaging mode with LBTI and are not interferometric. The survey was designed with two facets: a statistical survey to better inform our understanding of the wide-orbit giant-planet distribution and characterization of known low-mass systems and directly imaged planets.
2：Sample Selection and Data Sources:
We compiled a master target list comprising four sublists for use during the LEECH survey. Each sublist carried a slightly different emphasis, though the guiding principles for each were relative proximity and age ?1 Gyr.
3：List of Experimental Equipment and Materials:
The LBTI instrument, LMIRcam module of LBTI, and the HAWAII-2RG detector were used.
4：Experimental Procedures and Operational Workflow:
Our standard observing procedure aligned both images of a target star in the upper section of the detector keeping each image 3″ from the edge of the detector and leaving 5″ between the images. We collected data using an up–down nod pattern to track low spatial frequency variations in the sky background level, and high and low spatial frequency detector drifts.
5：Data Analysis Methods:
We use a bad-pixel mask to identify pixels with persistent problems and correct them using the median of the nearest eight good pixels. LMIRcam images exhibit low-level time-variable offsets in each 64?×?1024 pixel readout channel. We remove these offsets by subtracting the median pixel value from each channel after excluding all 3σ outliers.
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