Abstract
Directly imaging exoplanets is challenging because quasi-static phase aberrations in the pupil plane (speckles) can mimic the signal of a companion at small angular separations. Kernel ...phase, which is a generalization of closure phase (known from sparse aperture masking), is independent of pupil plane phase noise to second order and allows for a robust calibration of full pupil, extreme adaptive optics observations. We applied kernel phase combined with a principal component based calibration process to a suitable but not optimal, high cadence, pupil stabilized L’-band ($3.8\, {\mu \rm m}$) data set from the ESO archive. We detect eight low-mass companions, five of which were previously unknown, and two have angular separations of ∼0.8–1.2 λ/D (i.e. ∼80–$110\, \text{mas}$), demonstrating that kernel phase achieves a resolution below the classical diffraction limit of a telescope. While we reach a 5σ contrast limit of ∼1/100 at such angular separations, we demonstrate that an optimized observing strategy with more diversity of PSF references (e.g. star-hopping sequences) would have led to a better calibration and even better performance. As such, kernel phase is a promising technique for achieving the best possible resolution with future space-based telescopes (e.g. James Webb Space Telescope), which are limited by the mirror size rather than atmospheric turbulence, and with a dedicated calibration process also for extreme adaptive optics facilities from the ground.
We present high-contrast observations of the circumstellar environment of the Herbig Ae/Be star HD 100546. The final 3.8 mu m image reveals an emission source at a projected separation of 0".48 + or ...- 0".04 (corresponding to ~47 + or - 4 AU) at a position angle of 8degrees.9 + or - 0degrees.9. The emission appears slightly extended with a point source component with an apparent magnitude of 13.2 + or - 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 HD 100546. This suggests a possible physical link between the emission source and the disk. Assuming a disk inclination of ~47degrees, the de-projected separation of the object is degrees68 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. Follow-up observations in the coming years can easily distinguish between the different possible scenarios empirically. If confirmed, HD 100546 "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.
We present the first multi-wavelength, high-contrast imaging study confirming the protoplanet embedded in the disk around the Herbig Ae/Be star HD 100546. The object is detected at L' (~3.8 mu m) and ...M' (~4.8 mu m), but not at Ks (~2.1 mu m), 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 + or - 0.10 mag, M' = 13.33 + or - 0.16 mag, and Ks > 15.43 + or - 0.06 mag (3sigma limit), and a separation and position angle of (0.457 + or - 0.014)" and (8.4 + or -1.4)degrees, and (0.472 + or - 0.014)" and (9.2 + or - 1.4)degrees in L' and M', respectively. We demonstrate that the object is co-moving with HD 100546 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 sub(eff) = 932 super(+193) sub(-202) K and a radius for the emitting area of R = 6.9 super(+2.7) sub(-2.9)R sub(Jupiter). The best-fit luminosity is L = (2.3 super(+0.6) sub(-0.4)) times 10 super(-4) L sub(middot in circle). 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 deprojected physical separation from the host star of (53 + or - 2) AU poses a challenge to standard planet formation theories. Considering the suspected existence of an additional planet orbiting at ~13-14 AU, HD 100546 appears to be an unprecedented laboratory to study the formation of multiple gas giant planets empirically.
Brown dwarfs exhibit patchy or spatially varying banded cloud structures that are inferred through photometric and spectroscopic variability modeling techniques. However, these methods are ...insensitive to rotationally invariant structures, such as the bands seen in Jupiter. Here, we present H-band Very Large Telescope/NaCo linear polarization measurements of the nearby Luhman 16 L/T transition binary, which suggest that Luhman 16A exhibits constant longitudinal cloud bands. The instrument was operated in pupil tracking mode, allowing us to unambiguously distinguish between a small astrophysical polarization and the ∼2% instrumental linear polarization. We measure the degree and angle of linear polarization of Luhman 16A and B to be pA = 0.031% 0.004% and A = −32° 4°, and pB = 0.010% 0.004% and , respectively. Using known physical parameters of the system, we demonstrate that an oblate homogeneous atmosphere cannot account for the polarization measured in Luhman 16A, but could be responsible for that of the B component. Through a nonexhaustive search of banded cloud morphologies, we demonstrate a two-banded scenario that can achieve a degree of linear polarization of p = 0.03% and conclude that the measured polarization of the A component must be predominantly due to cloud banding. For Luhman 16B, either oblateness or cloud banding could be the dominant source of the measured polarization. The misaligned polarization angles of the two binary components tentatively suggest spin-orbit misalignment. These measurements provide new evidence for the prevalence of cloud banding in brown dwarfs while at the same time demonstrating a new method-complementary to photometric and spectroscopic variability methods-for characterizing the cloud morphologies of substellar objects without signs of variability.
Abstract
Recent atmospheric models for brown dwarfs suggest that the existence of clouds in substellar objects is not needed to reproduce their spectra, nor their rotationally induced photometric ...variability, believed to be due to the heterogeneous cloud coverage of brown dwarf atmospheres. Cloud-free atmospheric models also predict that their flux should not be polarized, as polarization is produced by the light scattering of particles in the inhomogeneous cloud layers of brown dwarf atmospheres. To shed light on this dichotomy, we monitored the linear polarization and photometric variability of the most variable brown dwarf, 2MASS J21392676+0220226. We used FORS2 at the UT1 telescope to monitor the object in the
z
band for six hours, split on two consecutive nights, covering one-third of its rotation period. We obtained the Stokes parameters, and we derived its time-resolved linear polarization, for which we did not find significant linear polarization (
P
= 0.14% ± 0.07%). We modeled the linear polarimetric signal expected assuming a map with one or two spot-like features and two bands using a polarization-enabled radiative transfer code. We obtained values compatible with the time-resolved polarimetry obtained for 2MASS J21392676+0220226. The lack of significant polarization might be due to photometric variability produced mostly by banded structures or small-scale vortices, which cancel out the polarimetric signal from different regions of the dwarf’s disk. Alternatively, the lack of clouds in 2MASS J21392676+0220226 would also explain the lack of polarization. Further linear polarimetric monitoring of 2MASS J21392676+0220226, during at least one full rotational period, would help to confirm or discard the existence of clouds in its atmosphere.
Abstract We present JWST MIRI Medium Resolution Spectrograph (MRS) observations of the β Pictoris system. We detect an infrared excess from the central unresolved point source from 5 to 7.5 μ m which ...is indicative of dust within the inner ∼7 au of the system. We perform point-spread function (PSF) subtraction on the MRS data cubes and detect a spatially resolved dust population emitting at 5 μ m. This spatially resolved hot dust population is best explained if the dust grains are in the small grain limit (2 π a ≪ λ ). The combination of unresolved and resolved dust at 5 μ m could suggest that dust grains are being produced in the inner few astronomical units of the system and are then radiatively driven outwards, where the particles could accrete onto the known planets in the system, β Pictoris b and c. We also report the detection of an emission line at 6.986 μ m that we attribute to Ar ii . We find that the Ar ii emission is spatially resolved with JWST and appears to be aligned with the dust disk. Through PSF-subtraction techniques, we detect β Pictoris b at the 5 σ level in our MRS data cubes and present the first mid-infrared spectrum of the planet from 5 to 7 μ m. The planet’s spectrum is consistent with having absorption from water vapor between 5 and 6.5 μ m. We perform atmosphere model grid fitting of the spectra and photometry of β Pictoris b and find that the planet’s atmosphere likely has a substellar C/O ratio.
We present L'- and J-band high-contrast observations of HD 169142, obtained with the Very Large Telescope/NACO AGPM vector vortex coronagraph and the Gemini Planet Imager, respectively. A source ...located at 0".156 + or - 0".032 north of the host star (P.A. = 7degrees.4 + or - 11degrees.3) appears in the final reduced L' image. At the distance of the star (~ 145 pc), this angular separation corresponds to a physical separation of 22.7 + or - 4.7 AU, locating the source within the recently resolved inner cavity of the transition disk. The source has a brightness of L' = 12.2 + or - 0.5 mag, whereas it is not detected in the J band (J >13.8 mag). If its L' brightness arose solely from the photosphere of a companion and given the J -L' color constraints, it would correspond to a 28-32 M sub(Jupiter) object at the age of the star, according to the COND models. Ongoing accretion activity of the star suggests, however, that gas is left in the inner disk cavity from which the companion could also be accreting. In this case, the object could be lower in mass and its luminosity enhanced by the accretion process and by a circumplanetary disk. A lower-mass object is more consistent with the observed cavity width. Finally, the observations enable us to place an upper limit on the L'-band flux of a second companion candidate orbiting in the disk annular gap at ~50 AU, as suggested by millimeter observations. If the second companion is also confirmed, HD 169142 might be forming a planetary system, with at least two companions opening gaps and possibly interacting with each other.
In the 1980s, excess infrared emission was discovered around main-sequence stars; subsequent direct-imaging observations revealed orbiting disks of cold dust to be the source. These 'debris disks' ...were thought to be by-products of planet formation because they often exhibited morphological and brightness asymmetries that may result from gravitational perturbation by planets. This was proved to be true for the β Pictoris system, in which the known planet generates an observable warp in the disk. The nearby, young, unusually active late-type star AU Microscopii hosts a well-studied edge-on debris disk; earlier observations in the visible and near-infrared found asymmetric localized structures in the form of intensity variations along the midplane of the disk beyond a distance of 20 astronomical units. Here we report high-contrast imaging that reveals a series of five large-scale features in the southeast side of the disk, at projected separations of 10-60 astronomical units, persisting over intervals of 1-4 years. All these features appear to move away from the star at projected speeds of 4-10 kilometres per second, suggesting highly eccentric or unbound trajectories if they are associated with physical entities. The origin, localization, morphology and rapid evolution of these features are difficult to reconcile with current theories.
PDF
