Abstract
epsilon Eridani is one of the nearest solar-type stars. Its proximity and relatively young age allow high-contrast imaging observations to achieve sensitivities to planets at narrow separations down to an inner radius of similar to 5 AU. Previous observational studies of the system report a dust disk with asymmetric morphology as well as a giant planet with large orbital eccentricity, which may require another massive companion to induce the peculiar morphology and to enhance the large orbital eccentricity. In this paper, we report results from deep high-contrast imaging observations to detect the previously reported planet and search for other unseen less massive companions with Subaru/HiCIAO, Gemini-South/NICI, and VLT/NACO. No positive detection was made, but high-contrast measurements with the CH4S narrow-band filter of HiCIAO achieved sensitivities at 14.7 mag differential magnitude level, at an angular separation of 1.0 ''. In terms of planetary mass, as determined by cooling evolutionary models, the highest sensitivities were achieved by the Lp broad-band filter of NACO, resulting in sensitivities corresponding to 1.8, 2.8, and 4.5 M-jup at the projected separation of 3 AU, if 200, 400, and 800 Myr is assumed for the age of the system, respectively. We also discuss origins of the dust disk from the detection sensitivity in the planetary mass and find that a less massive eccentric planet is preferred for disk stirring, which is consistent with the orbital parameters of epsilon Eri b claimed from the previous long-term radial velocity monitoring.
Highlights
Since the discovery of 51 Peg b (Mayor & Queloz 1995), more than 2000 exoplanets have been detected by various complementary methods (Extrasolar Planets Encyclopaedia1), allowing us to recognize the diversity of planetary systems in the Milky Way galaxy, and those discoveries of exoplanet have raised many open questions in understanding their formation and evolution processes
Long-term radial velocity (RV) monitoring has resulted in the discovery of a giant planet, Eri b, around the system (Hatzes et al 2000)
The contrast curve and corresponding planetary mass detection sensitivity are presented in Fig. 2, where we employ the cooling evolutionary model, i.e., the AMES-Cond model (Allard et al 2001; Baraffe et al 2003)
Summary
Since the discovery of 51 Peg b (Mayor & Queloz 1995), more than 2000 exoplanets have been detected by various complementary methods (Extrasolar Planets Encyclopaedia1), allowing us to recognize the diversity of planetary systems in the Milky Way galaxy, and those discoveries of exoplanet have raised many open questions in understanding their formation and evolution processes. Planet, Eri b, has a relatively large orbital eccentricity, which may have resulted from interaction with other companions (e.g., Wu & Murray 2003; Ida et al 2013). The asymmetric disk structure suggests another massive planet at wide orbit, which may be necessary to explain the disk’s morphology and dust replenishment. We report here the results of direct imaging observations for Eri with several ground-based instruments, and achieve the highest contrast measurements for the star obtained so far. 5, we summarize the current constraints for the system with the ground-based high-contrast imagings, and discuss the possible future observational approaches
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