We present new astrometry for the young (12-21 Myr) exoplanet beta Pictoris b taken with the Gemini/NICI and Magellan/MagAO instruments between 2009 and 2012. The high dynamic range of our ...observations allows us to measure the relative position of beta Pic b with respect to its primary star with greater accuracy than previous observations. Based on a Markov Chain Monte Carlo analysis, we find the planet has an orbital semi-major axis of 9.1 super(+5.1) sub(-0.5) AU and orbital eccentricity <0.15 at 68% confidence (with 95% confidence intervals of 8.2-48 AU and 0.00-0.82 for semi-major axis and eccentricity, respectively, due to a long narrow degenerate tail between the two). We find that the planet has reached its maximum projected elongation, enabling higher precision determination of the orbital parameters than previously possible, and that the planet's projected separation is currently decreasing. With unsaturated data of the entire beta Pic system (primary star, planet, and disk) obtained thanks to NICI's semi-transparent focal plane mask, we are able to tightly constrain the relative orientation of the circumstellar components. We find the orbital plane of the planet lies between the inner and outer disks: the position angle (P.A.) of nodes for the planet's orbit (211.8 + or - 0degrees3) is 7.4sigma greater than the P.A. of the spine of the outer disk and 3.2sigma less than the warped inner disk P.A., indicating the disk is not collisionally relaxed. Finally, for the first time we are able to dynamically constrain the mass of the primary star beta Pic to 1.76 super(+0.18) sub(-0.17)M sub(middot in circle).
We present optical and near-infrared adaptive optics (AO) imaging and spectroscopy of 13 ultracool (>M6) companions to late-type stars (K7-M4.5), most of which have recently been identified as ...candidate members of nearby young moving groups (YMGs; 8-120 Myr) in the literature. Three of these are new companions identified in our AO imaging survey, and two others are confirmed to be comoving with their host stars for the first time. The inferred masses of the companions (~10-100 M sub(Jup)) are highly sensitive to the ages of the primary stars; therefore we critically examine the kinematic and spectroscopic properties of each system to distinguish bona fide YMG members from old field interlopers. The new M7 substellar companion 2MASS J02155892-0929121 C (40-60 M sub(Jup)) shows clear spectroscopic signs of low gravity and, hence, youth. The primary, possibly a member of the ~40Myr Tuc-Hor moving group, is visually resolved into three components, making it a young low-mass quadruple system in a compact (<, ~100AU) configuration. In addition, Li sub(I) lambda6708 absorption in the intermediate-gravity M7.5 companion 2MASS J15594729+4403595 B provides unambiguous evidence that it is young (<, ~200Myr) and resides below the hydrogen-burning limit. Three new close-separation (<1") companions (2MASS J06475229-2523304 B, PYC J11519+0731 B, and GJ4378 Ab) orbit stars previously reported as candidate YMG members, but instead are likely old (> ~1 Gyr) tidally locked spectroscopic binaries without convincing kinematic associations with any known moving group. The high rate of false positives in the form of old active stars with YMG-like kinematics underscores the importance of radial velocity and parallax measurements to validate candidate young stars identified via proper motion and activity selection alone. Finally, we spectroscopically confirm the cool temperature and substellar nature of HD 23514 B, a recently discovered M8 benchmark brown dwarf orbiting the dustiest-known member of the Pleiades.
Young M-type binaries are particularly useful for precise isochronal dating by taking advantage of their extended pre-main sequence evolution. Orbital monitoring of these low-mass objects becomes ...essential in constraining their fundamental properties, as dynamical masses can be extracted from their Keplerian motion. Here, we present the combined efforts of the AstraLux Large Multiplicity Survey, together with a filler sub-programme from the SpHere INfrared Exoplanet (SHINE) project and previously unpublished data from the FastCam lucky imaging camera at the Nordical Optical Telescope (NOT) and the NaCo instrument at the Very Large Telescope (VLT). Building on previous work, we use archival and new astrometric data to constrain orbital parameters for 20 M-type binaries. We identify that eight of the binaries have strong Bayesian probabilities and belong to known young moving groups (YMGs). We provide a first attempt at constraining orbital parameters for 14 of the binaries in our sample, with the remaining six having previously fitted orbits for which we provide additional astrometric data and updated Gaia parallaxes. The substantial orbital information built up here for four of the binaries allows for direct comparison between individual dynamical masses and theoretical masses from stellar evolutionary model isochrones, with an additional three binary systems with tentative individual dynamical mass estimates likely to be improved in the near future. We attained an overall agreement between the dynamical masses and the theoretical masses from the isochrones based on the assumed YMG age of the respective binary pair. The two systems with the best orbital constrains for which we obtained individual dynamical masses, J0728 and J2317, display higher dynamical masses than predicted by evolutionary models.
One of the central goals of the Spitzer Legacy Project "From Cores to Disks" (c2d) is to determine the frequency of circumstellar disks around weak-line T Tauri stars (WTTSs) and to study the ...properties and evolutionary status of these disks. Here we present a census of disks for a sample of over 230 WTTSs located in the c2d IRAC and MIPS maps of the Ophiuchus, Lupus, and Perseus Molecular Clouds. We find that similar to 20% of the WTTSs in a magnitude-limited subsample have IR excesses at IRAC wavelengths. These disks frequencies are similar to 3-6 times larger than that recently found for a sample of relatively isolated WTTSs located outside the highest extinction regions covered by the c2d maps. The disk fractions we find are more consistent with those obtained in recent Spitzer studies of WTTSs in young clusters such as IC 348 and Tr 37. According to their location in the H-R diagram, the WTTSs with excesses in our sample are among the younger part of the age distribution. Still, up to similar to 50% of the apparently youngest stars in the sample show no evidence of IR excess, suggesting that the circumstellar disks of a sizable fraction of pre-main-sequence stars dissipate in a timescale of similar to 1 Myr. We also find that none of the stars in our sample apparently older than similar to 10 Myr have detectable circumstellar disks at wavelengths <24 mu m. The WTTS disks in our sample exhibit a wide range of properties (SED morphology, inner radius, L sub(disk)/L sub(o), etc.) that bridge the gaps observed between the CTTSs and the debris disk regimes.
Context. Since 1995 and the first discovery of an exoplanet orbiting a main-sequence star, 4000 exoplanets have been discovered using several techniques. However, only a few of these exoplanets were ...detected through direct imaging. Indeed, the imaging of circumstellar environments requires high-contrast imaging facilities and accurate control of wavefront aberrations. Ground-based planet imagers such as VLT/SPHERE or Gemini/GPI have already demonstrated great performance. However, their limit of detection is hampered by suboptimal correction of aberrations unseen by adaptive optics (AO). Aims. Instead of focusing on the phase minimization of the pupil plane as in standard AO, we aim to directly minimize the stellar residual light in the SPHERE science camera behind the coronagraph to improve the contrast as close as possible to the inner working angle. Methods. We propose a dark hole (DH) strategy optimized for SPHERE. We used a numerical simulation to predict the global improvement of such a strategy on the overall performance of the instrument for different AO capabilities and particularly in the context of a SPHERE upgrade. Then, we tested our algorithm on the internal source with the AO in closed loop. Results. We demonstrate that our DH strategy can correct for aberrations of phase and amplitude. Moreover, this approach has the ability to strongly reduce the diffraction pattern induced by the telescope pupil and the coronagraph, unlike methods operating at the pupil plane. Our strategy enables us to reach a contrast of 5e-7 at 150 mas from the optical axis in a few minutes using the SPHERE internal source. This experiment establishes the grounds for implementing the algorithm on sky in the near future.
We present the first resolved image of the debris disk around the 16+ or -8 Myr old star, HD 114082. The observation was made in the H-band using the SPHERE instrument. The star is at a distance of ...92 + or - 6 pc in the Lower Centaurus Crux association. Using a Markov chain Monte Carlo analysis, we determined that the debris is likely in the form of a dust ring with an inner edge of 27.7 super(+2.8) sub(-3.5) au, position angle -74.3degrees super(+0.5) sub(-1.5), and an inclination with respect to the line of sight of 6.7degrees super(+3.8) sub(-0.4). The disk imaged in scattered light has a surface density that is declining with radius of ~r super(-4), which is steeper than expected for grain blowout by radiation pressure. We find only marginal evidence (2sigma) of eccentricity and rule out planets more massive than 1.0 M sub(Jup) orbiting within 1 au of the inner edge of the ring, since such a planet would have disrupted the disk. The disk has roughly the same fractional disk luminosity (L sub(disk)/Ll ow *= 3.3 x 10 super(-3)) as HR 4796 A and beta Pictoris, however it was not detected by previous instrument facilities most likely because of its small angular size (radius ~0.4"), low albedo (~0.2), and low scattering efficiency far from the star due to high scattering anisotropy. With the arrival of extreme adaptive optics systems, such as SPHERE and GPI, the morphology of smaller, fainter, and more distant debris disks are being revealed, providing clues to planet-disk interactions in young protoplanetary systems.
We describe a joint high-contrast imaging survey for planets at the Keck and Very Large Telescope of the last large sample of debris disks identified by the Spitzer Space Telescope. No new substellar ...companions were discovered in our survey of 30 Spitzer-selected targets. We combine our observations with data from four published surveys to place constraints on the frequency of planets around 130 debris disk single stars, the largest sample to date. For a control sample, we assembled contrast curves from several published surveys targeting 277 stars that do not show infrared excesses. We assumed a double power-law distribution in mass and semimajor axis (SMA) of the form , where we adopted power-law values and logarithmically flat values for the mass and SMA of planets. We find that the frequency of giant planets with masses 5-20 MJup and separations 10-1000 au around stars with debris disks is 6.27% (68% confidence interval 3.68%-9.76%), compared to 0.73% (68% confidence interval 0.20%-1.80%) for the control sample of stars without disks. These distributions differ at the 88% confidence level, tentatively suggesting distinctness of these samples.
We report the discovery of a tight substellar companion to the young solar analog PZ Tel, a member of the {beta} Pic moving group observed with high-contrast adaptive optics imaging as part of the ...Gemini Near-Infrared Coronagraphic Imager Planet-Finding Campaign. The companion was detected at a projected separation of 16.4 {+-} 1.0 AU (0.''33 {+-} 0.''01) in 2009 April. Second-epoch observations in 2010 May demonstrate that the companion is physically associated and shows significant orbital motion. Monte Carlo modeling constrains the orbit of PZ Tel B to eccentricities >0.6. The near-IR colors of PZ Tel B indicate a spectral type of M7 {+-} 2 and thus this object will be a new benchmark companion for studies of ultracool, low-gravity photospheres. Adopting an age of 12{sup +8} {sub -4} Myr for the system, we estimate a mass of 36 {+-} 6 M {sub Jup} based on the Lyon/DUSTY evolutionary models. PZ Tel B is one of the few young substellar companions directly imaged at orbital separations similar to those of giant planets in our own solar system. Additionally, the primary star PZ Tel A shows a 70 {mu}m emission excess, evidence for a significant quantity of circumstellar dust that has not been disrupted by the orbital motion of the companion.
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