High-contrast imaging in the Hyades with snapshot LOCI

To image faint substellar companions obscured by the stellar halo and speckles, scattered light from the bright primary star must be removed in hardware or software. We apply the "locally-optimized combination of images" (LOCI) algorithm to 1-minute Keck Observatory snapshots of GKM dwarfs in the Hyades using source diversity to determine the most likely PSF. We obtain a mean contrast of 10^{-2} at 0.01", 10^{-4} at <1", and 10^{-5} at 5". New brown dwarf and low-mass stellar companions to Hyades primaries are found in a third of the 84 targeted systems. This campaign shows the efficacy of LOCI on snapshot imaging as well as on bright wide binaries with off-axis LOCI, reaching contrasts sufficient for imaging 625-Myr late-L/early-T dwarfs purely in post-processing.Comment: 12 pages, 12 figures, to appear in SPIE Astronomy 2012, paper 8447-16

Testing the universality of star formation - I. Multiplicity in nearby star-forming regions

We have collated multiplicity data for five clusters (Taurus, Chamaeleon I, Ophiuchus, IC 348 and the Orion Nebula Cluster). We have applied the same mass ratio (flux ratios of ΔK≤ 2.5) and primary mass cuts (∼0.1-3.0 M⊙) to each cluster and therefore have directly comparable binary statistics for all five clusters in the separation range 62-620 au, and for Taurus, Chamaeleon I and Ophiuchus in the range 18-830 au. We find that the trend of decreasing binary fraction with cluster density is solely due to the high binary fraction of Taurus; the other clusters show no obvious trend over a factor of nearly 20 in density. With N-body simulations, we attempt to find a set of initial conditions that are able to reproduce the density, morphology and binary fractions of all five clusters. Only an initially clumpy (fractal) distribution with an initial total binary fraction of 73 per cent (17 per cent in the range 62-620 au) is able to reproduce all of the observations (albeit not very satisfactorily). Therefore, if star formation is universal, then the initial conditions must be clumpy and with a high (but not 100 per cent) binary fraction. This could suggest that most stars, including M dwarfs, form in binarie

CO(J = 1-0) Imaging of M51 with CARMA and the Nobeyama 45 m Telescope

We report the CO(J = 1-0) observations of the Whirlpool Galaxy M51 using both the Combined Array for Research in Millimeter Astronomy (CARMA) and the Nobeyama 45 m telescope (NRO45). We describe a procedure for the combination of interferometer and single-dish data. In particular, we discuss (1) the joint imaging and deconvolution of heterogeneous data, (2) the weighting scheme based on the root-mean-square (rms) noise in the maps, (3) the sensitivity and uv coverage requirements, and (4) the flux recovery of a combined map. We generate visibilities from the single-dish map and calculate the noise of each visibility based on the rms noise. Our weighting scheme, though it is applied to discrete visibilities in this paper, should be applicable to grids in uv space, and this scheme may advance in future software development. For a realistic amount of observing time, the sensitivities of the NRO45 and CARMA visibility data sets are best matched by using the single-dish baselines only up to 4-6 kλ (about 1/4-1/3 of the dish diameter). The synthesized beam size is determined to conserve the flux between the synthesized beam and convolution beam. The superior uv coverage provided by the combination of CARMA long baseline data with 15 antennas and NRO45 short spacing data results in the high image fidelity, which is evidenced by the excellent overlap between even the faint CO emission and dust lanes in an optical Hubble Space Telescope image and polycyclicaromatichydrocarbon emission in a Spitzer 8 μm image. The total molecular gas masses of NGC 5194 and 5195 (d = 8.2 Mpc) are 4.9 × 10^9 M_⊙ and 7.8 × 10^7 M_⊙, respectively, assuming the CO-to-H_2 conversion factor of X _(CO) = 1.8 × 10^(20) cm-2(K km s^(–1))^(–1). The presented images are an indication of the millimeter-wave images that will become standard in the next decade with CARMA and NRO45, and the Atacama Large Millimeter/Submillimeter Array

The International Deep Planet Survey II: The frequency of directly imaged giant exoplanets with stellar mass

Radial velocity and transit methods are effective for the study of short orbital period exoplanets but they hardly probe objects at large separations for which direct imaging can be used. We carried out the international deep planet survey of 292 young nearby stars to search for giant exoplanets and determine their frequency. We developed a pipeline for a uniform processing of all the data that we have recorded with NIRC2/Keck II, NIRI/Gemini North, NICI/Gemini South, and NACO/VLT for 14 years. The pipeline first applies cosmetic corrections and then reduces the speckle intensity to enhance the contrast in the images. The main result of the international deep planet survey is the discovery of the HR 8799 exoplanets. We also detected 59 visual multiple systems including 16 new binary stars and 2 new triple stellar systems, as well as 2,279 point-like sources. We used Monte Carlo simulations and the Bayesian theorem to determine that 1.05[+2.80-0.70]% of stars harbor at least one giant planet between 0.5 and 14M_J and between 20 and 300 AU. This result is obtained assuming uniform distributions of planet masses and semi-major axes. If we consider power law distributions as measured for close-in planets instead, the derived frequency is 2.30[+5.95-1.55]%, recalling the strong impact of assumptions on Monte Carlo output distributions. We also find no evidence that the derived frequency depends on the mass of the hosting star, whereas it does for close-in planets. The international deep planet survey provides a database of confirmed background sources that may be useful for other exoplanet direct imaging surveys. It also puts new constraints on the number of stars with at least one giant planet reducing by a factor of two the frequencies derived by almost all previous works.Comment: 83 pages, 13 figures, 15 Tables, accepted in A&

Testing the universality of star formation - II. Comparing separation distributions of nearby star-forming regions and the field

We have measured the multiplicity fractions and separation distributions of seven young star-forming regions using a uniform sample of young binaries. Both the multiplicity fractions and separation distributions are similar in the different regions. A tentative decline in the multiplicity fraction with increasing stellar density is apparent, even for binary systems with separations too close (19-100au) to have been dynamically processed. The separation distributions in the different regions are statistically indistinguishable over most separation ranges, and the regions with higher densities do not exhibit a lower proportion of wide (300-620au) relative to close (62-300au) binaries as might be expected from the preferential destruction of wider pairs. Only the closest (19-100au) separation range, which would be unaffected by dynamical processing, shows a possible difference in separation distributions between different regions. The combined set of young binaries, however, shows a distinct difference when compared to field binaries, with a significant excess of close (19-100au) systems among the younger binaries. Based on both the similarities and differences between individual regions, and between all seven young regions and the field, especially over separation ranges too close to be modified by dynamical processing, we conclude that multiple star formation is not universal and, by extension, the star formation process is not universal.Comment: accepted for publication in MNRA

Dynamically Driven Evolution of the Interstellar Medium in M51

Massive star formation occurs in giant molecular clouds (GMCs); an understanding of the evolution of GMCs is a prerequisite to develop theories of star formation and galaxy evolution. We report the highest-fidelity observations of the grand-design spiral galaxy M51 in carbon monoxide (CO) emission, revealing the evolution of GMCs vis-a-vis the large-scale galactic structure and dynamics. The most massive GMCs (giant molecular associations (GMAs)) are first assembled and then broken up as the gas flow through the spiral arms. The GMAs and their H_2 molecules are not fully dissociated into atomic gas as predicted in stellar feedback scenarios, but are fragmented into smaller GMCs upon leaving the spiral arms. The remnants of GMAs are detected as the chains of GMCs that emerge from the spiral arms into interarm regions. The kinematic shear within the spiral arms is sufficient to unbind the GMAs against self-gravity. We conclude that the evolution of GMCs is driven by large-scale galactic dynamics—their coagulation into GMAs is due to spiral arm streaming motions upon entering the arms, followed by fragmentation due to shear as they leave the arms on the downstream side. In M51, the majority of the gas remains molecular from arm entry through the interarm region and into the next spiral arm passage

Detecting Exoplanets Closer to Stars with Moderate Spectral Resolution Integral-Field Spectroscopy

While radial velocity surveys have demonstrated that the population of gas giants peaks around $3~\text{au}$, the most recent high-contrast imaging surveys have only been sensitive to planets beyond $\sim~10~\text{au}$. Sensitivity at small angular separations from stars is currently limited by the variability of the point spread function. We demonstrate how moderate-resolution integral field spectrographs can detect planets at smaller separations ($\lesssim~0.3$ arcseconds) by detecting the distinct spectral signature of planets compared to the host star. Using OSIRIS ($R$ $\approx$ 4000) at the W. M. Keck Observatory, we present the results of a planet search via this methodology around 20 young targets in the Ophiuchus and Taurus star-forming regions. We show that OSIRIS can outperform high-contrast coronagraphic instruments equipped with extreme adaptive optics and non-redundant masking in the $0.05-0.3$ arcsecond regime. As a proof of concept, we present the $34\sigma$ detection of a high-contrast M dwarf companion at $\approx0.1$" with a flux ratio of $\approx0.92\%$ around the field F2 star HD 148352. We developed an open-source Python package, breads, for the analysis of moderate-resolution integral field spectroscopy data in which the planet and the host star signal are jointly modeled. The diffracted starlight continuum is forward-modeled using a spline model, which removes the need for prior high-pass filtering or continuum normalization. The code allows for analytic marginalization of linear hyperparameters, simplifying posterior sampling of other parameters (e.g., radial velocity, effective temperature). This technique could prove very powerful when applied to integral field spectrographs like NIRSpec on the JWST and other upcoming first-light instruments on the future Extremely Large Telescopes.Comment: Accepted for publication in the Astronomical Journal on May 12, 202

High contrast imaging at the LBT: the LEECH exoplanet imaging survey

In Spring 2013, the LEECH (LBTI Exozodi Exoplanet Common Hunt) survey began its $\sim$130-night campaign from the Large Binocular Telescope (LBT) atop Mt Graham, Arizona. This survey benefits from the many technological achievements of the LBT, including two 8.4-meter mirrors on a single fixed mount, dual adaptive secondary mirrors for high Strehl performance, and a cold beam combiner to dramatically reduce the telescope's overall background emissivity. LEECH neatly complements other high-contrast planet imaging efforts by observing stars at L' (3.8 $\mu$m), as opposed to the shorter wavelength near-infrared bands (1-2.4 $\mu$m) of other surveys. This portion of the spectrum offers deep mass sensitivity, especially around nearby adolescent ($\sim$0.1-1 Gyr) stars. LEECH's contrast is competitive with other extreme adaptive optics systems, while providing an alternative survey strategy. Additionally, LEECH is characterizing known exoplanetary systems with observations from 3-5$\mu$m in preparation for JWST.Comment: 12 pages, 5 figures. Proceedings of the SPIE, 9148-2

Constraints on the architecture of the HD 95086 planetary system with the Gemini Planet Imager

We present astrometric monitoring of the young exoplanet HD 95086 b obtained with the Gemini Planet Imager between 2013 and 2016. A small but significant position angle change is detected at constant separation; the orbital motion is confirmed with literature measurements. Efficient Monte Carlo techniques place preliminary constraints on the orbital parameters of HD 95086 b. With 68% confidence, a semimajor axis of 61.7^{+20.7}_{-8.4} au and an inclination of 153.0^{+9.7}_{-13.5} deg are favored, with eccentricity less than 0.21. Under the assumption of a co-planar planet-disk system, the periastron of HD 95086 b is beyond 51 au with 68% confidence. Therefore HD 95086 b cannot carve the entire gap inferred from the measured infrared excess in the SED of HD 95086. We use our sensitivity to additional planets to discuss specific scenarios presented in the literature to explain the geometry of the debris belts. We suggest that either two planets on moderately eccentric orbits or three to four planets with inhomogeneous masses and orbital properties are possible. The sensitivity to additional planetary companions within the observations presented in this study can be used to help further constrain future dynamical simulations of the planet-disk system.Comment: Accepted for publication in ApJ