In this paper, we review the impact of small sample statistics on detection thresholds and corresponding confidence levels (CLs) in high contrast imaging at small angles. When looking close to the star, the number of resolution elements decreases rapidly towards small angles. This reduction of the number of degrees of freedom dramatically affects CLs and false alarm probabilities. Naively using the same ideal hypothesis and methods as for larger separations, which are well understood and commonly assume Gaussian noise, can yield up to one order of magnitude error in contrast estimations at fixed CL. The statistical penalty exponentially increases towards very small inner working angles. Even at 5-10 resolution elements from the star, false alarm probabilities can be significantly higher than expected. Here we present a rigorous statistical analysis which ensures robustness of the CL, but also imposes a substantial limitation on corresponding achievable detection limits (thus contrast) at small angles. This unavoidable fundamental statistical effect has a significant impact on current coronagraphic and future high contrast imagers. Finally, the paper concludes with practical recommendations to account for small number statistics when computing the sensitivity to companions at small angles and when exploiting the results of direct imaging planet surveys.

We present intermediate resolution (R ∼ 8,000 -12,000) high signal-to-noise H− and K−band spectroscopy of a sample of 37 optically visible stars, ranging in spectral type from O3 to B3 and representing most luminosity classes. Spectra of this quality can be used to constrain the temperature, luminosity and general wind properties of OB stars, when used in conjunction with sophisticated atmospheric model codes. Most important is the need for moderately high resolutions (R ≥ 5000) and very high signal-to-noise (S/N ≥ 150) spectra for a meaningful profile analysis. When using near-infrared spectra for a classification system, moderately high signalto-noise (S/N ∼ 100) is still required, though the resolution can be relaxed to just a thousand or two. In the appendix we provide a set of very high quality near-infrared spectra of Brackett lines in six early-A dwarfs. These can be used to aid in the modeling and removal of such lines when early-A dwarfs are used for telluric spectroscopic standards.

We present high-contrast observations of the circumstellar environment of the Herbig Ae/Be star HD100546. The final 3.8 µm image reveals an emission source at a projected separation of 0.48 ′′ ±0.04 ′′ (corresponding to ∼47±4 AU) at a position angle of 8.9• ±0.9• . The emission appears slightly extended with a point source component with an apparent magnitude of 13.2 ± 0.4 mag. The position of the source coincides with a local deficit in polarization fraction in near-infrared polarimetric imaging data, which probes the surface of the well-studied circumstellar disk of HD100546. This suggests a possible physical link between the emission source and the disk. Assuming a disk inclination of ∼47• the de-projected separation of the object is ∼68 AU. Assessing the likelihood of various scenarios we favor an interpretation of the available high-contrast data with a planet in the process of forming. Followup observations in the coming years can easily distinguish between the different possible scenarios empirically. If confirmed, HD100546 "b" would be a unique laboratory to study the formation process of a new planetary system, with one giant planet currently forming in the disk and a second planet possibly orbiting in the disk gap at smaller separations.

Context. Ground-based high-dispersion (R ∼ 100 000) spectroscopy (HDS) is proving to be a powerful technique with which to characterize extrasolar planets. The planet signal is distilled from the bright starlight, combining ral and time-differential filtering techniques. In parallel, high-contrast imaging (HCI) is developing rapidly, aimed at spatially separating the planet from the star. While HDS is limited by the overwhelming noise from the host star, HCI is limited by residual quasi-static speckles. Both techniques currently reach planet-star contrast limits down to ∼10 −5 , albeit for very different types of planetary systems. Aims. In this work, we discuss a way to combine HDS and HCI (HDS+HCI). For a planet located at a resolvable angular distance from its host star, the starlight can be reduced up to several orders of magnitude using adaptive optics and/or coronography. In addition, the remaining starlight can be filtered out using high-dispersion spectroscopy, utilizing the significantly different (or Doppler shifted) high-dispersion spectra of the planet and star. In this way, HDS+HCI can in principle reach contrast limits of ∼10 −5 ×10 −5 , although in practice this will be limited by photon noise and/or sky-background. In contrast to current direct imaging techniques, such as Angular Differential Imaging and Spectral Differential Imaging, it will work well at small working angles and is much less sensitive to speckle noise. For the discovery of previously unknown planets HDS+HCI requires a high-contrast adaptive optics system combined with a high-dispersion R ∼ 100 000 integral field spectrograph (IFS). This combination currently does not exist, but is planned for the European Extremely Large Telescope. Methods. We present simulations of HDS+HCI observations with the E-ELT, both probing thermal emission from a planet at infrared wavelengths, and starlight reflected off a planet atmosphere at optical wavelengths. For the infrared simulations we use the baseline parameters of the E-ELT and METIS instrument, with the latter combining extreme adaptive optics with an R = 100 000 IFS. We include realistic models of the adaptive optics performance and atmospheric transmission and emission. For the optical simulation we also assume R = 100 000 IFS with adaptive optics capabilities at the E-ELT. Results. One night of HDS+HCI observations with the E-ELT at 4.8 μm (Δλ = 0.07 μm) can detect a planet orbiting α Cen A with a radius of R = 1.5 R earth and a twin-Earth thermal spectrum of T eq = 300 K at a signal-to-noise (S/N) of 5. In the optical, with a Strehl ratio performance of 0.3, reflected light from an Earth-size planet in the habitable zone of Proxima Centauri can be detected at a S/N of 10 in the same time frame. Recently, first HDS+HCI observations have shown the potential of this technique by determining the spin-rotation of the young massive exoplanet β Pictoris b. Conclusions. The exploration of the planetary systems of our neighbor stars is of great scientific and philosophical value. The HD...

We report the discovery of a planetary-mass companion, HD 106906 b, with the new Magellan Adaptive Optics (MagAO) + Clio2 system. The companion is detected with Clio2 in three bands: J, K S , and L , and lies at a projected separation of 7. 1 (650 AU). It is confirmed to be comoving with its 13±2 Myr-old F5 host using Hubble Space Telescope/Advanced Camera for Surveys astrometry over a time baseline of 8.3 yr. DUSTY and COND evolutionary models predict the companion's luminosity corresponds to a mass of 11 ± 2 M Jup , making it one of the most widely separated planetary-mass companions known. We classify its Magellan/Folded-Port InfraRed Echellette J/H/K spectrum as L2.5 ± 1; the triangular H-band morphology suggests an intermediate surface gravity. HD 106906 A, a pre-main-sequence Lower Centaurus Crux member, was initially targeted because it hosts a massive debris disk detected via infrared excess emission in unresolved Spitzer imaging and spectroscopy. The disk emission is best fit by a single component at 95 K, corresponding to an inner edge of 15-20 AU and an outer edge of up to 120 AU. If the companion is on an eccentric (e > 0.65) orbit, it could be interacting with the outer edge of the disk. Close-in, planet-like formation followed by scattering to the current location would likely disrupt the disk and is disfavored. Furthermore, we find no additional companions, though we could detect similar-mass objects at projected separations > 35 AU. In situ formation in a binary-star-like process is more probable, although the companion-to-primary mass ratio, at < 1%, is unusually small. Subject headings: instrumentation: adaptive optics -open clusters and associations: individual (Lower Centaurus Crux) -planet-disk interactions -planetary systems -stars: individual (HD 106906)

We present the results of a survey of 45 young (P250 Myr), close (P50 pc) stars with the Simultaneous Differential Imager (SDI) implemented at the VLT and the MMT for the direct detection of extrasolar planets. As part of the survey, we observed 54 objects, consisting of 45 close, young stars; two more distant (<150 pc), extremely young (10 Myr) stars; three stars with known radial velocity planets; and four older, very nearby (20 pc) solar analogs. Our SDI devices use a double Wollaston prism and a quad filter to take images simultaneously at three wavelengths surrounding the 1.62 m methane absorption bandhead found in the spectrum of cool brown dwarfs and gas giant planets. By differencing adaptive opticsYcorrected images in these filters, speckle noise from the primary star is significantly attenuated, resulting in photon (and flat-field)YnoiseYlimited data. In our VLT data, we achieved H-band contrasts k10 mag (5) at a separation of 0.5 00 from the primary star on 45% of our targets and H-band contrasts k 9 mag at a separation of 0.5 00 on 80% of our targets. With these contrasts, we can image (5 detection) a 7 M J planet 15 AU from a 70 Myr K1 star at 15 pc or a 7.8 M J planet at 2 AU from a 12 Myr M star at 10 pc. We detected no candidates with S/N > 2 which behaved consistently like a real object. From our survey null result, we can rule out (with 93% confidence) a model planet population where N (a) / constant out to a distance of 45 AU.

We present direct imaging observations at wavelengths of 3.3, 3.8 (L ′ band), and 4.8 (M band) µm, for the planetary system surrounding HR 8799. All three planets are detected at L ′ . The c and d component are detected at 3.3 µm, and upper limits are derived from the M band observations. These observations provide useful constraints on warm giant planet atmospheres. We discuss the current age constraints on the HR 8799 system, and show that several potential co-eval objects can be excluded from being co-moving with the star. Comparison of the photometry is made to models for giant planet atmospheres. Models which include non-equilibrium chemistry provide a reasonable match to the colors of c and d. From the observed colors in the thermal infrared we estimate T eff < 960 K for b, and T eff =1300 and 1170 K for c and d, respectively. This provides an independent check on the effective temperatures and thus masses of the objects from the Marois et al. (2008) results.

We present the first multi-wavelength, high-contrast imaging study confirming the protoplanet embedded in the disk around the Herbig Ae/Be star HD100546. The object is detected at L (∼ 3.8 µm) and M (∼ 4.8 µm), but not at K s (∼ 2.1 µm), and the emission consists of a point source component surrounded by spatially resolved emission. For the point source component we derive apparent magnitudes of L = 13.92 ± 0.10 mag, M = 13.33 ± 0.16 mag, and K s > 15.43 ± 0.11 mag (3σ limit), and a separation and position angle of (0.457 ± 0.014) and (8.4 ± 1.4) • , and (0.472 ± 0.014) and (9.2 ± 1.4) • in L and M , respectively. We demonstrate that the object is co-moving with HD100546 and can reject any (sub-)stellar fore-/background object. Fitting a single temperature blackbody to the observed fluxes of the point source component yields an effective temperature of T ef f = 932 +193−202 K and a radius for the emitting area of R = 6.9 +2.7 −2.9 R Jupiter . The best-fit luminosity is L = (2.3 +0.6 −0.4 ) · 10 −4 L . We quantitatively compare our findings with predictions from evolutionary and atmospheric models for young, gas giant planets, discuss the possible existence of a warm, circumplanetary disk, and note that the de-projected physical separation from the host star of (53 ± 2) au poses a challenge standard planet formation theories. Considering the suspected existence of an additional planet orbiting at ∼13-14 au, HD100546 appears to be an unprecedented laboratory to study the formation of multiple gas giant planets empirically. Subject headings: planets and satellites: detection -planets and satellites: formation -planets and satellites: gaseous planets -protoplanetary disks -planet-disk interactions -stars: pre-main sequence Electronic address: sascha.quanz@astro.phys.ethz.ch 1 Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere, Chile, under program number 091.C-0818(A).