Exoplanet detections have revolutionized astronomy, offering new insights into solar system architecture and planet demographics. While nearly 1,900 exoplanets have now been discovered and confirmed, ...none are still in the process of formation. Transition disks, protoplanetary disks with inner clearings best explained by the influence of accreting planets, are natural laboratories for the study of planet formation. Some transition disks show evidence for the presence of young planets in the form of disk asymmetries or infrared sources detected within their clearings, as in the case of LkCa 15 (refs 8, 9). Attempts to observe directly signatures of accretion onto protoplanets have hitherto proven unsuccessful. Here we report adaptive optics observations of LkCa 15 that probe within the disk clearing. With accurate source positions over multiple epochs spanning 2009-2015, we infer the presence of multiple companions on Keplerian orbits. We directly detect Hα emission from the innermost companion, LkCa 15 b, evincing hot (about 10,000 kelvin) gas falling deep into the potential well of an accreting protoplanet.
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DOBA, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, SBMB, SIK, UILJ, UKNU, UL, UM, UPUK
The origin of extragalactic magnetic fields is still poorly understood. Based on a dedicated suite of cosmological magneto-hydrodynamical simulations with the ENZO code we have performed a survey of ...different models that may have caused present-day magnetic fields in galaxies and galaxy clusters. The outcomes of these models differ in cluster outskirts, filaments, sheets and voids and we use these simulations to find observational signatures of magnetogenesis. With these simulations, we predict the signal of extragalactic magnetic fields in radio observations of synchrotron emission from the cosmic web, in Faraday rotation, in the propagation of ultra high energy cosmic rays, in the polarized signal from fast radio bursts at cosmological distance and in spectra of distant blazars. In general, primordial scenarios in which present-day magnetic fields originate from the amplification of weak ( nG) uniform seed fields result in more homogeneous and relatively easier to observe magnetic fields than astrophysical scenarios, in which present-day fields are the product of feedback processes triggered by stars and active galaxies. In the near future the best evidence for the origin of cosmic magnetic fields will most likely come from a combination of synchrotron emission and Faraday rotation observed at the periphery of large-scale structures.
ABSTRACT The Large Binocular Telescope Interferometer (LBTI) is a versatile instrument designed for high angular resolution and high-contrast infrared imaging (1.5-13 m). In this paper, we focus on ...the mid-infrared (8-13 m) nulling mode and present its theory of operation, data reduction, and on-sky performance as of the end of the commissioning phase in 2015 March. With an interferometric baseline of 14.4 m, the LBTI nuller is specifically tuned to resolve the habitable zone of nearby main-sequence stars, where warm exozodiacal dust emission peaks. Measuring the exozodi luminosity function of nearby main-sequence stars is a key milestone to prepare for future exo-Earth direct imaging instruments. Thanks to recent progress in wavefront control and phase stabilization, as well as in data reduction techniques, the LBTI demonstrated in 2015 February a calibrated null accuracy of 0.05% over a 3 hr long observing sequence on the bright nearby A3V star β Leo. This is equivalent to an exozodiacal disk density of 15-30 zodi for a Sun-like star located at 10 pc, depending on the adopted disk model. This result sets a new record for high-contrast mid-infrared interferometric imaging and opens a new window on the study of planetary systems.
Abstract
We present near-infrared Large Binocular Telescope LMIRCam imagery of the disk around the Herbig Ae/Be star AB Aurigae. A comparison of the surface brightness at
K
s
(2.16
μ
m), H
2
O ...narrowband (3.08
μ
m), and
L
′
(3.7
μ
m) allows us to probe the presence of icy grains in this (pre)transitional disk environment. By applying reference differential imaging point-spread function subtraction, we detect the disk at high signal-to-noise ratios in all three bands. We find strong morphological differences between the bands, including asymmetries consistent with the observed spiral arms within 100 au in
L
′
. An apparent deficit of scattered light at 3.08
μ
m relative to the bracketing wavelengths (
K
s
and
L
′
) is evocative of ice absorption at the disk surface layer. However, the Δ(
K
s
− H
2
O) color is consistent with grains with little to no ice (0%–5% by mass). The
Δ
(
H
2
O
−
L
′
)
color, conversely, suggests grains with a much higher ice mass fraction (∼0.68), and the two colors cannot be reconciled under a single grain population model. Additionally, we find that the extremely red
Δ
(
K
s
−
L
′
)
disk color cannot be reproduced under conventional scattered light modeling with any combination of grain parameters or reasonable local extinction values. We hypothesize that the scattering surfaces at the three wavelengths are not colocated, and that the optical depth effects in each wavelength result from probing the grain population at different disk surface depths. The morphological similarity between
K
s
and H
2
O suggests that their scattering surfaces are near one another, lending credence to the Δ(
K
s
− H
2
O) disk color constraint of <5% ice mass fraction for the outermost scattering disk layer.
Abstract
Herbig Ae/Be stars represent the early outcomes of star formation and the initial stages of planet formation at intermediate stellar masses. Understanding both of these processes requires ...detailed characterization of their disk structures and companion frequencies. We present new 3.7 μm imaging of the Herbig Be star MWC 297 from nonredundant masking observations on the phase-controlled, 23 m Large Binocular Telescope Interferometer. The images reveal complex disk structure on the scales of several au, as well as a companion candidate. We discuss physical interpretations for these features and demonstrate that the imaging results are independent of choices such as priors, regularization hyperparameters, and error-bar estimates. With an angular resolution of ∼17 mas, these data provide the first robust Extremely Large Telescope–resolution view of a distant young star.
The Hunt for Observable Signatures of Terrestrial Systems survey searches for dust near the habitable zones (HZs) around nearby, bright main-sequence stars. We use nulling interferometry in the N ...band to suppress the bright stellar light and to probe for low levels of HZ dust around the 30 stars observed so far. Our overall detection rate is 18%, including four new detections, among which are the first three around Sun-like stars and the first two around stars without any previously known circumstellar dust. The inferred occurrence rates are comparable for early-type and Sun-like stars, but decrease from % for stars with previously detected cold dust to % for stars without such excess, confirming earlier results at higher sensitivity. For completed observations on individual stars, our sensitivity is five to ten times better than previous results. Assuming a lognormal excess luminosity function, we put upper limits on the median HZ dust level of 13 zodis (95% confidence) for a sample of stars without cold dust and of 26 zodis when focusing on Sun-like stars without cold dust. However, our data suggest that a more complex luminosity function may be more appropriate. For stars without detectable Large Binocular Telescope Interferometer (LBTI) excess, our upper limits are almost reduced by a factor of two, demonstrating the strength of LBTI target vetting for future exo-Earth imaging missions. Our statistics are limited so far, and extending the survey is critical to informing the design of future exo-Earth imaging surveys.
Abstract
The Large Binocular Telescope (LBT) has two 8.4 m primary mirrors that produce beams that can be combined coherently in a “Fizeau” interferometric mode. In principle, the Fizeau point-spread ...function (PSF) enables the probing of structure at a resolution up to three times better than that of the adaptive-optics-corrected PSF of a single 8.4 m telescope. In this work, we examined the nearby star Altair (5.13 pc, type A7V, hundreds of Myr to ≈1.4 Gyr) in the Fizeau mode with the LBT at Br
α
(4.05
μ
m) and carried out angular differential imaging to search for companions. This work presents the first filled-aperture LBT Fizeau science data set to benefit from a correcting mirror that provides active phase control. In the analysis of the
λ
/
D
angular regime, the sensitivity of the data set is down to ≈0.5
M
⊙
at 1″ for a 1.0 Gyr system. This sensitivity remains limited by the small amount of integration time, which is in turn limited by the instability of the Fizeau PSF. However, in the Fizeau fringe regime we attain sensitivities of Δ
m
≈ 5 at 0.″2 and put constraints on companions of 1.3
M
⊙
down to an inner angle of ≈0.″15, closer than any previously published direct imaging of Altair. This analysis is a pathfinder for future data sets of this type, and represents some of the first steps to unlocking the potential of the first Extremely Large Telescope. Fizeau observations will be able to reach dimmer targets with upgrades to the instrument, in particular the phase detector.
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 (0".5-0".7), 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 mu m) 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 theta super(1) Ori A, B, and C cluster members were obtained with VisAO. In particular, the 32 mas binary theta super(1) Ori C sub(1)C sub(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 super(-1) (~0.4 km s super(-1) at 414 pc)-this is a ~2-10 x improvement in orbital velocity accuracy compared to previous efforts. For the first time, we see clear motion of the barycenter of theta super(1) Ori B sub(2)B sub(3) about theta super(1) Ori B sub(1). All five members of the theta super(1) 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 theta super(1) Ori B system (B sub(4); mass ~0.2 M sub(middot in circle)) has a very clearly detected motion (at 4.1 + or - 1.3 km s super(-1); correlation = 99.9%) w.r.t. B sub(1). Previous work has suggested that B sub(4) and B sub(3) are on long-term unstable orbits and will be ejected from this "mini cluster." However, our new "baseline" model of the theta super(1) Ori B system suggests a more hierarchical system than previously thought, and so the ejection of B sub(4) may not occur for many orbits, and B sub(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.
Forty-seven nearby main-sequence stars were surveyed with the Keck Interferometer mid-infrared Nulling instrument (KIN) between 2008 and 2011, searching for faint resolved emission from exozodiacal ...dust. Observations of a subset of the sample have already been reported, focusing essentially on stars with no previously known dust. Here we extend this previous analysis to the whole KIN sample, including 22 more stars with known near- and/or far-infrared excesses. In addition to an analysis similar to that of the first paper of this series, which was restricted to the 8-9 mu m spectral region, we present measurements obtained in all 10 spectral channels covering the 8-13 mu m instrumental bandwidth. For solar-type stars with no known infrared excess, likely to be the most relevant targets for a future exo-Earth direct imaging mission, we find that their median zodi level is 12+ or -24 zodis and lower than 60 zodis with 95% confidence, if a lognormal zodi luminosity distribution is assumed.
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