We derive new empirical calibrations for strong-line diagnostics of gas-phase metallicity in local star-forming galaxies by uniformly applying the T_e method over the full metallicity range probed by the Sloan Digital Sky Survey (SDSS). To measure electron temperatures at high metallicity, where the auroral lines needed are not detected in single galaxies, we stacked spectra of more than 110 000 galaxies from the SDSS in bins of log[O ii]/Hβ and log[O iii]/Hβ. This stacking scheme does not assume any dependence of metallicity on mass or star formation rate, but only that galaxies with the same line ratios have the same oxygen abundance. We provide calibrations which span more than 1 dex in metallicity and are entirely defined on a consistent absolute T_e metallicity scale for galaxies. We apply our calibrations to the SDSS sample and find that they provide consistent metallicity estimates to within 0.05 dex.

As the only directly imaged multiple planet system, HR 8799 provides a unique opportunity to study the physical properties of several planets in parallel. In this paper, we image all four of the HR 8799 planets at H band and 3.3 μm with the new Large Binocular Telescope adaptive optics system, PISCES, and LBTI/LMIRCam. Our images offer an unprecedented view of the system, allowing us to obtain H and 3.3 μm photometry of the innermost planet (for the first time) and put strong upper limits on the presence of a hypothetical fifth companion. We find that all four planets are unexpectedly bright at 3.3 μm compared to the equilibrium chemistry models used for field brown dwarfs, which predict that planets should be faint at 3.3 μm due to CH₄ opacity. We attempt to model the planets with thick-cloudy, non-equilibrium chemistry atmospheres but find that removing CH₄ to fit the 3.3 μm photometry increases the predicted L' (3.8 μm) flux enough that it is inconsistent with observations. In an effort to fit the spectral energy distribution of the HR 8799 planets, we construct mixtures of cloudy atmospheres, which are intended to represent planets covered by clouds of varying opacity. In this scenario, regions with low opacity look hot and bright, while regions with high opacity look faint, similar to the patchy cloud structures on Jupiter and L/T transition brown dwarfs. Our mixed-cloud models reproduce all of the available data, but self-consistent models are still necessary to demonstrate their viability.

In this paper we present the laboratory characterization and performance evaluation of the First Light Adaptive Optics (FLAO) the Natural Guide Star adaptive optics system for the Large Binocular Telescope (LBT). The system uses an adaptive secondary mirror with 672 actuators and a pyramid wavefront sensor with adjustable sampling of the telescope pupil from 30×30 down to 4×4 subapertures. The system was fully assembled in the Arcetri Observatory laboratories, passing the acceptance test in December 2009. The performance measured during the test were closed to goal specifications for all star magnitudes. In particular FLAO obtained 83% Strehl Ratio (SR) in the bright end (8.5 magnitudes star in R band) using H band filter and correcting 495 modes with 30×30 subapertures sampling. In the faint end (16.4 magnitude) a 5.0% SR correcting 36 modes with 7×7 subapertures was measured. The seeing conditions for these tests were 0.8" (r0 = 0.14m @ 550 nm) and an average wind speed of 15m/s. The results at other seeing conditions up to 1.5" are also presented. The system has been shipped to the LBT site, and the commissioning is taking place since March to December 2010. A few on sky results are presented.

Astronomy & Astrophysics (A&A) is an international journal which publishes papers on all aspects of astronomy and astrophysics

We utilized the new high-order (250-378 mode) Magellan Adaptive Optics system (MagAO) to obtain very high spatial resolution observations in "visible light" with MagAO's VisAO CCD camera. In the good-median seeing conditions of Magellan (05-07), we find MagAO delivers individual short exposure images as good as 19 mas optical resolution. Due to telescope vibrations, long exposure (60 s) r' (0.63 μm) images are slightly coarser at FWHM = 23-29 mas (Strehl ~28%) with bright (R < 9 mag) guide stars. These are the highest resolution filled-aperture images published to date. Images of the young (~1 Myr) Orion Trapezium θ¹ Ori A, B, and C cluster members were obtained with VisAO. In particular, the 32 mas binary θ¹ Ori C ₁ C ₂ was easily resolved in non-interferometric images for the first time. The relative positions of the bright trapezium binary stars were measured with ~0.6-5 mas accuracy. We are now sensitive to relative proper motions of just ~0.2 mas yr^–1 (~0.4 km s^–1 at 414 pc)—this is a ~2-10 × improvement in orbital velocity accuracy compared to previous efforts. For the first time, we see clear motion of the barycenter of θ¹ Ori B ₂ B ₃ about θ¹ Ori B ₁. All five members of the θ¹ Ori B system appear likely to be a gravitationally bound "mini cluster," but we find that not all the orbits can be both circular and co-planar. The lowest mass member of the θ¹ Ori B system (B ₄; mass ~0.2 M _☉) has a very clearly detected motion (at 4.1 ± 1.3 km s^–1; correlation = 99.9%) w.r.t. B ₁. Previous work has suggested that B ₄ and B ₃ are on long-term unstable orbits and will be ejected from this "mini cluster." However, our new "baseline" model of the θ¹ Ori B system suggests a more hierarchical system than previously thought, and so the ejection of B ₄ may not occur for many orbits, and B ₃ may be stable against ejection in the long-term. This "ejection" process of the lowest mass member of a "mini cluster" could play a major role in the formation of low-mass stars and brown dwarfs.