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Register a new userDetectability of Exoplanets in the Beta Pic Moving Group with the Gemini Planet Imager
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We model the detectability of exoplanets around stars in the Beta Pic Moving Group (BPMG) using the Gemini Planet Imager (GPI), a coronagraphic instrument designed to detect companions by imaging. Members of the BPMG are considered promising targets for exoplanet searches because of their youth (~12 MY) and proximity (median distance ~35 pc). We wrote a modeling procedure to generate hypothetical companions of given mass, age, eccentricity, and semi-major axis, and place them around BPMG members that fall within the V-band range of the GPI. We count as possible detections companions lying within the GPIs field of view and H-band fluxes that have a host-companion flux ratio placing them within its sensitivity. The fraction of companions that could be detected depends on their brightness at 12 Myr, and hence formation mechanism, and on their distribution of semi-major axes. We used brightness models for formation by disk instability and core-accretion. We considered the two extreme cases of the semi-major axis distribution - the log-normal distribution of the nearby F and G type stars and a power-law distribution indicated by the exoplanets detected by the radial velocity technique. We find that the GPI could detect exoplanets of all the F and G spectral type stars in the BPMG sample with a probability that depends on the brightness model and semi-major axis distribution. At spectral type K to M1, exoplanet detectability depends on brightness and hence distance of the host star. GPI will be able to detect the companions of M stars later than M1 only if they are closer than 10 pc. Of the four A stars in BPMG sample, only one has V-band brightness in the range of GPI; the others are too bright.
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Aims: We carried out high-resolution spectroscopy and BV(I)_C photometric monitoring of the two fastest late-type rotators in the nearby Beta Pictoris moving group, HD199143 (F7V) and CD-641208 (K7V). The motivation for this work is to investigate the rotation periods and photospheric spot patterns of these very young stars, with a longer term view to probing the evolution of rotation and magnetic activity during the early phases of main-sequence evolution. We also aim to derive information on key physical parameters, such as rotational velocity and rotation period. Methods: We applied maximum entropy (ME) and Tikhonov regularizing (TR) criteria to derive the surface spot map distributions of the optical modulation observed in HD199143 (F7 V) and CD-641208 (K7V). We also used cross-correlation techniques to determine stellar parameters such as radial velocities and rotational velocities. Lomb-Scargle periodograms were used to obtain the rotational periods from differential magnitude time series. Results: We find periods and inclinations of 0.356 days and 21.5deg for HD199143, and 0.355 days and 50.1deg for CD-641208. The spot maps of HD199143 obtained from the ME and TR methods are very similar, although the latter gives a smoother distribution of the filling factor. Maps obtained at two different epochs three weeks apart show a remarkable increase in spot coverage amounting to ~7% of the surface of the photosphere over a time period of only ~20 days. The spot maps of CD-641208 from the two methods show good longitudinal agreement, whereas the latitude range of the spots is extended to cover the whole visible hemisphere in the TR map. The distributions obtained from the first light curve of HD199143 show the presence of an extended and asymmetric active longitude with the maximum filling factor at longitude ~325degree.
We report angular diameters of HIP 560 and 21547, two F spectral type pre-main sequence members of the beta Pic Moving Group. We used the East-West 314-m long baseline of the CHARA Array. The measured limb-darkened angular diameters of HIP 560 and 21547 are 0.492+-0.032 and 0.518+-0.009 mas, respectively. The corresponding stellar radii are 2.1 and 1.6 Rsun for HIP 560 and HIP 21547 respectively. These values indicate that the stars are truly young. Analyses using the evolutionary tracks calculated by Siess, Dufour, and Forestini and the tracks of the Yonsei-Yale group yield consistent results. Analyzing the measurements on an angular diameter vs color diagram we find that the ages of the two stars are indistinguishable; their average value is 13+-2 MY. The masses of HIP 560 and 21547 are 1.65+-0.02 and 1.75+-0.05 Msun, respectively. However, analysis of the stellar parameters on a Hertzsprung-Russell Diagram yields ages at least 5 MY older. Both stars are rapid rotators. The discrepancy between the two types of analyses has a natural explanation in gravitational darkening.
The Gemini Planet (GPI) imager is an extreme adaptive optics system being designed and built for the Gemini Observatory. GPI combines precise and accurate wavefront control, diffraction suppression, and a speckle-suppressing science camera with integral field and polarimetry capabilities. GPIs primary science goal is the direct detection and characterization of young, Jovian-mass exoplanets. For systems younger than 2 Gyr exoplanets more massive than 6 MJ and semimajor axes beyond 10 AU are detected with completeness greater than 50%. GPI will also discover faint debris disks, explore icy moons and minor planets in the solar system, reveal high dynamic range main-sequence binaries, and study mass loss from evolved stars. This white paper explains the role of GPI in exoplanet discovery and characterization and summarizes our recommendations to the NSF-NASA-DOE Astronomy and Astrophysics Advisory Committee ExoPlanet Task Force.
We present on-sky polarimetric observations with the Gemini Planet Imager (GPI) obtained at straight Cassegrain focus on the Gemini South 8-m telescope. Observations of polarimetric calibrator stars, ranging from nearly unpolarized to strongly polarized, enable determination of the combined telescope and instrumental polarization. We find the conversion of Stokes $I$ to linear and circular instrumental polarization in the instrument frame to be $I rightarrow (Q_{rm IP}, U_{rm IP}, P_{rm IP}, V_{rm IP}) = (-0.037 pm 0.010%, +0.4338 pm 0.0075%, 0.4354 pm 0.0075%, -6.64 pm 0.56%)$. Such precise measurement of instrumental polarization enables $sim 0.1%$ absolute accuracy in measurements of linear polarization, which together with GPIs high contrast will allow GPI to explore scattered light from circumstellar disk in unprecedented detail, conduct observations of a range of other astronomical bodies, and potentially even study polarized thermal emission from young exoplanets. Observations of unpolarized standard stars also let us quantify how well GPIs differential polarimetry mode can suppress the stellar PSF halo. We show that GPI polarimetry achieves cancellation of unpolarized starlight by factors of 100-200, reaching the photon noise limit for sensitivity to circumstellar scattered light for all but the smallest separations at which the calibration for instrumental polarization currently sets the limit.
The Gemini Planet Imager (GPI) 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 GPI 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-sigma 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-second exposure with minimal post-processing. Beta Pictoris b is observed at a separation of $434 pm 6$ milli-arcseconds and position angle $211.8 pm 0.5$ deg. Fitting the Keplerian orbit of Beta Pic b using the new position together with previous astrometry gives a factor of three improvement in most parameters over previous solutions. The planet orbits at a semi-major axis of $9.0^{+0.8}_{-0.4}$ AU 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% posterior probability of a transit of the planet in late 2017.
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