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Register a new userMagellan Adaptive Optics first-light observations of the exoplanet beta Pic b. II. 3-5 micron direct imaging with MagAO+Clio, and the empirical bolometric luminosity of a self-luminous giant planet
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Young giant exoplanets are a unique laboratory for understanding cool, low-gravity atmospheres. A quintessential example is the massive extrasolar planet $beta$ Pic b, which is 9 AU from and embedded in the debris disk of the young nearby A6V star $beta$ Pictoris. We observed the system with first light of the Magellan Adaptive Optics (MagAO) system. In Paper I we presented the first CCD detection of this planet with MagAO+VisAO. Here we present four MagAO+Clio images of $beta$ Pic b at 3.1 $mu$m, 3.3 $mu$m, $L^prime$, and $M^prime$, including the first observation in the fundamental CH$_4$ band. To remove systematic errors from the spectral energy distribution (SED), we re-calibrate the literature photometry and combine it with our own data, for a total of 22 independent measurements at 16 passbands from 0.99--4.8 $mu$m. Atmosphere models demonstrate the planet is cloudy but are degenerate in effective temperature and radius. The measured SED now covers $>$80% of the planets energy, so we approach the bolometric luminosity empirically. We calculate the luminosity by extending the measured SED with a blackbody and integrating to find log($L_{bol}$/$L_{Sun}$) $= -3.78pm0.03$. From our bolometric luminosity and an age of 23$pm$3 Myr, hot-start evolutionary tracks give a mass of 12.7$pm$0.3 $M_{Jup}$, radius of 1.45$pm$0.02 $R_{Jup}$, and $T_{eff}$ of 1708$pm$23 K (model-dependent errors not included). Our empirically-determined luminosity is in agreement with values from atmospheric models (typically $-3.8$ dex), but brighter than values from the field-dwarf bolometric correction (typically $-3.9$ dex), illustrating the limitations in comparing young exoplanets to old brown dwarfs.
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Methods used to detect giant exoplanets can be broadly divided into two categories: indirect and direct. Indirect methods are more sensitive to planets with a small orbital period, whereas direct detection is more sensitive to planets orbiting at a large distance from their host star. %, and thus on long orbital period. This dichotomy makes it difficult to combine the two techniques on a single target at once. Simultaneous measurements made by direct and indirect techniques offer the possibility of determining the mass and luminosity of planets and a method of testing formation models. Here, we aim to show how long-baseline interferometric observations guided by radial-velocity can be used in such a way. We observed the recently-discovered giant planet $beta$ Pictoris c with GRAVITY, mounted on the Very Large Telescope Interferometer (VLTI). This study constitutes the first direct confirmation of a planet discovered through radial velocity. We find that the planet has a temperature of $T = 1250pm50$,K and a dynamical mass of $M = 8.2pm0.8,M_{rm Jup}$. At $18.5pm2.5$,Myr, this puts $beta$ Pic c close to a hot start track, which is usually associated with formation via disk instability. Conversely, the planet orbits at a distance of 2.7,au, which is too close for disk instability to occur. The low apparent magnitude ($M_{rm K} = 14.3 pm 0.1$) favours a core accretion scenario. We suggest that this apparent contradiction is a sign of hot core accretion, for example, due to the mass of the planetary core or the existence of a high-temperature accretion shock during formation.
Clio is an adaptive-optics camera mounted on the 6.5 meter MMT optimized for diffraction-limited L and M-band imaging over a ~15 field. The instrument was designed from the ground up with a large well-depth, fast readout thermal infrared (~3-5 micron) 320 by 256 pixel InSb detector, cooled optics, and associated focal plane and pupil masks (with the option for a coronograph) to minimize the thermal background and maximize throughput. When coupled with the MMTs adaptive secondary AO (two warm reflections) systems low thermal background, this instrument is in a unique position to image nearby warm planets, which are the brightest in the L and M-band atmospheric windows. We present the current status of this recently commissioned instrument that performed exceptionally during first light. Our instrument sensitivities are impressive and are sky background limited: for an hour of integration, we obtain an L-band 5 sigma detection limit of of 17.0 magnitudes (Strehl ~80%) and an M-band limit of 14.5 (Strehl ~90%). Our M-band sensitivity is lower due to the increase in thermal sky background. These sensitivities translate to finding relatively young planets five times Jupiter mass at 10 pc within a few AU of a star. Presently, a large Clio survey of nearby stellar systems is underway including a search for planets around solar-type stars, M dwarfs, and white dwarfs. Even with a null result, we can place strong constraints on planet distribution models.
We present new observations of the planet beta Pictoris b from 2018 with GPI, the first GPI observations following conjunction. Based on these new measurements, we perform a joint orbit fit to the available relative astrometry from ground-based imaging, the Hipparcos Intermediate Astrometric Data (IAD), and the Gaia DR2 position, and demonstrate how to incorporate the IAD into direct imaging orbit fits. We find a mass consistent with predictions of hot-start evolutionary models and previous works following similar methods, though with larger uncertainties: 12.8 [+5.3, -3.2] M_Jup. Our eccentricity determination of 0.12 [+0.04, -0.03] disfavors circular orbits. We consider orbit fits to several different imaging datasets, and find generally similar posteriors on the mass for each combination of imaging data. Our analysis underscores the importance of performing joint fits to the absolute and relative astrometry simultaneously, given the strong covariance between orbital elements. Time of conjunction is well constrained within 2.8 days of 2017 September 13, with the star behind the planets Hill sphere between 2017 April 11 and 2018 February 16 (+/- 18 days). Following the recent radial velocity detection of a second planet in the system, beta Pic c, we perform additional two-planet fits combining relative astrometry, absolute astrometry, and stellar radial velocities. These joint fits find a significantly smaller mass for the imaged planet beta Pic b, of 8.0 +/- 2.6 M_Jup, in a somewhat more circular orbit. We expect future ground-based observations to further constrain the visual orbit and mass of the planet in advance of the release of Gaia DR4.
We present high resolution adaptive optics (AO) corrected images of the silhouette disk Orion 218-354 taken with Magellan AO (MagAO) and its visible light camera, VisAO, in simultaneous differential imaging (SDI) mode at H-alpha. This is the first image of a circumstellar disk seen in silhouette with adaptive optics and is among the first visible light adaptive optics results in the literature. We derive the disk extent, geometry, intensity and extinction profiles and find, in contrast with previous work, that the disk is likely optically-thin at H-alpha. Our data provide an estimate of the column density in primitive, ISM-like grains as a function of radius in the disk. We estimate that only ~10% of the total sub-mm derived disk mass lies in primitive, unprocessed grains. We use our data, Monte Carlo radiative transfer modeling and previous results from the literature to make the first self-consistent multiwavelength model of Orion 218-354. We find that we are able to reproduce the 1-1000micron SED with a ~2-540AU disk of the size, geometry, small vs. large grain proportion and radial mass profile indicated by our data. This inner radius is a factor of ~15 larger than the sublimation radius of the disk, suggesting that it is likely cleared in the very interior.
MagAO is the new adaptive optics system with visible-light and infrared science cameras, located on the 6.5-m Magellan Clay telescope at Las Campanas Observatory, Chile. The instrument locks on natural guide stars (NGS) from 0$^mathrm{th}$ to 16$^mathrm{th}$ $R$-band magnitude, measures turbulence with a modulating pyramid wavefront sensor binnable from 28x28 to 7x7 subapertures, and uses a 585-actuator adaptive secondary mirror (ASM) to provide flat wavefronts to the two science cameras. MagAO is a mutated clone of the similar AO systems at the Large Binocular Telescope (LBT) at Mt. Graham, Arizona. The high-level AO loop controls up to 378 modes and operates at frame rates up to 1000 Hz. The instrument has two science cameras: VisAO operating from 0.5-1 $mu$m and Clio2 operating from 1-5 $mu$m. MagAO was installed in 2012 and successfully completed two commissioning runs in 2012-2013. In April 2014 we had our first science run that was open to the general Magellan community. Observers from Arizona, Carnegie, Australia, Harvard, MIT, Michigan, and Chile took observations in collaboration with the MagAO instrument team. Here we describe the MagAO instrument, describe our on-sky performance, and report our status as of summer 2014.
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