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We have obtained Hubble Space Telescope (HST) coronagraphic observations of the circumstellar disk around M star TWA 7 using the Space Telescope Imaging Spectrograph (STIS) instrument in visible light. Together with archival observations, including HST/NICMOS using the F160W filter and Very Large Telescope/SPHERE at the H-band in polarized light, we investigate the system in scattered light. By studying this nearly face-on system using geometric disk models and Henyey–Greenstein phase functions, we report a new discovery of a tertiary ring and a clump. We identify a layered architecture: three rings, a spiral, and an ≈150 au2 elliptical clump. The most extended ring peaks at 28 au, and the other components are on its outskirts. Our point-source detection-limit calculations demonstrate the necessity of disk modeling in imaging fainter planets. Morphologically, we witness a clockwise spiral motion, and the motion pattern is consistent with both solid body motion and local Keplerian motion; we also observe underdensity regions for the secondary ring that might result from mean-motion resonance or moving shadows: both call for re-observations to determine their nature. Comparing multi-instrument observations, we obtain blue STIS-NICMOS color, a STIS-SPHERE radial distribution peak difference for the tertiary ring, and a high SPHERE-NICMOS polarization fraction; these aspects indicate that TWA 7 could retain small dust particles. By viewing the debris disk around M star TWA 7 at a nearly face-on vantage point, our study allows for the understanding of such disks in scattered light in both system architecture and dust property. [ABSTRACT FROM AUTHOR]

The Advanced Technology Large-Aperture Space Telescope (ATLAST) is a concept for an 8- to 16-m ultraviolet optical near infrared space observatory for launch in the 2025 to 2030 era. ATLAST will allow astronomers to answer fundamental questions at the forefront of modern astrophysics, including: Is there life elsewhere in the Galaxy? We present a range of science drivers and the resulting performance requirements for ATLAST (8- to 16-marcsec angular resolution, diffraction limited imaging at 0.5-μm wavelength, minimum collecting area of 45 m2, high sensitivity to light wavelengths from 0.1 to 2.4 μm, high stability in wavefront sensing and control). We also discuss the priorities for technology development needed to enable the construction of ATLAST for a cost that is comparable to that of current generation observatory-class space missions. [ABSTRACT FROM AUTHOR]

HR 8799 is currently the only multiple-planet system that has been detected with direct imaging, with four giant planets of masses 7-10 Mjup orbiting at large separations (15-68 AU) from this young late A star. Orbital motion provides insight into the stability and possible formation mechanisms of this planetary system. Dynamical studies can also provide constraints on the planets' masses, which help calibrate evolutionary models, yet measuring the orbital motion is a very difficult task because the long-period orbits (50-500 yr) require long time baselines and high-precision astrometry. This paper studies the three planets HR 8799 b, c, and d in the archival data set of HR 8799 obtained with the Hubble Space Telescope (HST) NICMOS coronagraph in 1998. The detection of all three planets is made possible by a careful optimization of the Locally Optimized Combination of Images algorithm, and we used a statistical analysis of a large number of reduced images. This work confirms previous astrometry for planet b and presents new detections and astrometry for planets c and d. These HST images provide a ten-year baseline with the discovery images from 2008, and therefore offer a unique opportunity to constrain their orbital motion now. Recent dynamical studies of this system show the existence of a few possible stable solutions involving mean motion resonances (MMRs), where the interaction between c and d plays a major role. We study the compatibility of a few of these stable scenarios (1d:lc, 1d:2c, or 1d:2c:4d) with the new astrometric data from HST. In the hypothesis of a 1d:2c:4b MMR our best orbit fit is close to the stable solution previously identified for a three-planet system and involves low eccentricity for planet d (ed = 0.10) and moderate inclination of the system (i = 28.0 deg), assuming a coplanar system, circular orbits for b and c, and exact resonance with integer period ratios. Under these assumptions, we can place strong constraints on the inclination of the system (27.3-31.4 deg) and on the eccentricity for d ed < 0.46. Our results are robust to small departures from exact integer period ratios and consistent with previously published results based on dynamical studies for a three-planet system prior to the discovery of the fourth planet. [ABSTRACT FROM AUTHOR]

This paper summarizes the general theory and properties for Apodized Pupil Lyot Coronagraphs which consist of a classical hard-edged Lyot coronagraph with an upstream pupil apodization. The ideal apodization function can be determined from an integral eigenvalue problem which solutions are prolate spheroidal functions. Solutions exist for any geometrty, including rectangular, circular, or elliptical. Formal solutions can be extended to the case of arbitrary apertures, using generalized prolate spheroidal functions for centrally obstructed apertures, spiders, or segmented telescopes. The properties of these coronagraphs enable the possibility of multiple stage coronagraphy and achromatization. The new instrument Gemini Planet Imager (GPI) will include such a coronagraph. [ABSTRACT FROM PUBLISHER]