Search for: All records

Clouds and other features in exoplanet and brown dwarf atmospheres cause variations in brightness as they rotate in and out of view. Ground-based instruments reach the high contrasts and small inner working angles needed to monitor these faint companions, but their small fields of view lack simultaneous photometric references to correct for non-astrophysical variations. We present a novel approach for making ground-based light curves of directly imaged companions using high-cadence differential spectrophotometric monitoring, where the simultaneous reference is provided by a double-grating 360○ vector Apodizing Phase Plate (dgvAPP360) coronagraph. The dgvAPP360 enables high-contrast companion detections without blocking the host star, allowing it to be used as a simultaneous reference. To further reduce systematic noise, we emulate exoplanet transmission spectroscopy, where the light is spectrally dispersed and then recombined into white-light flux. We do this by combining the dgvAPP360 with the infrared Arizona Lenslets for Exoplanet Spectroscopy integral field spectrograph on the Large Binocular Telescope Interferometer. To demonstrate, we observed the red companion HD 1160 B (separation ∼780 mas) for one night, and detect $8.8{{\ \rm per\ cent}}$ semi-amplitude sinusoidal variability with an ∼3.24 h period in its detrended white-light curve. We achieve the greatest precision in ground-based high-contrast imaging light curves of sub-arcsecond companions to date, reaching $3.7{{\ \rm per\ cent}}$ precision per 18-min bin. Individual wavelength channels spanning 3.59–3.99 μm further show tentative evidence of increasing variability with wavelength. We find no evidence yet of a systematic noise floor; hence, additional observations can further improve the precision. This is therefore a promising avenue for future work aiming to map storms or find transiting exomoons around giant exoplanets.

 

We use observations with the infrared-optimized Magellan Adaptive Optics (MagAO) system and Clio camera in 3.9μm light to place stringent mass constraints on possible undetected companions to Sirius A. We suppress the light from Sirius A by imaging it through a grating vector-apodizing phase plate coronagraph with a 180° dark region (gvAPP-180). To remove residual starlight in postprocessing, we apply a time-domain principal-components-analysis-based algorithm we call PCA-Temporal, which uses eigen time series rather than eigenimages to subtract starlight. By casting the problem in terms of eigen time series, we reduce the computational cost of postprocessing the data, enabling the use of the fully sampled data set for improved contrast at small separations. We also discuss the impact of retaining fine temporal sampling of the data on final contrast limits. We achieve postprocessed contrast limits of 1.5 × 10⁻⁶–9.8 × 10⁻⁶outside of 0.″75, which correspond to planet masses of 2.6–8.0M_J. These are combined with values from the recent literature of high-contrast imaging observations of Sirius to synthesize an overall completeness fraction as a function of mass and separation. After synthesizing these recent studies and our results, the final completeness analysis rules out 99% of ≥9M_Jplanets from 2.5 to 7 au.

 

Understanding the physical processes sculpting the appearance of young gas-giant planets is complicated by degeneracies confounding effective temperature, surface gravity, cloudiness, and chemistry. To enable more detailed studies, spectroscopic observations covering a wide range of wavelengths are required. Here we present the first L-band spectroscopic observations of HR 8799 d and e and the first low-resolution wide-bandwidth L-band spectroscopic measurements of HR 8799 c. These measurements were facilitated by an upgraded LMIRCam/ALES instrument at the Large Binocular Telescope, together with a new apodizing phase plate coronagraph. Our data are generally consistent with previous photometric observations covering similar wavelengths, yet there exists some tension with narrowband photometry for HR 8799 c. With the addition of our spectra, each of the three innermost observed planets in the HR 8799 system has had its spectral energy distribution measured with integral field spectroscopy covering ∼0.9–4.1μm. We combine these spectra with measurements from the literature and fit synthetic model atmospheres. We demonstrate that the bolometric luminosity of the planets is not sensitive to the choice of model atmosphere used to interpolate between measurements and extrapolate beyond them. Combining luminosity with age and mass constraints, we show that the predictions of evolutionary models are narrowly peaked for effective temperature, surface gravity, and planetary radius. By holding these parameters at their predicted values, we show that more flexible cloud models can provide good fits to the data while being consistent with the expectations of evolutionary models.

 

We report the results of polarimetric observations of the total solar eclipse of 21 August 2017 from Rexburg, Idaho (USA).We use three synchronized DSLR cameras with polarization filters oriented at 0, 60, and 120 to provide high-dynamic-range RGB polarization images of the corona and surrounding sky.We measure tangential coronal polarization and vertical sky polarization, both as expected. These observations provide detailed detections of polarization neutral points above and below the eclipsed Sun where the coronal polarization is canceled by the sky polarization.We name these special polarization neutral points afterMinnaert and Van de Hulst. 

The sky polarization pattern during solar eclipse totality shifts from the usual daytime clear-sky pattern, with maximum polarization in an arc located 90° from the Sun, to one with maximum polarization slightly above the horizon in a ring nominally concentric about the zenith. A sequence of 9 visible-wavelength all-sky images are shown throughout totality for the 21 August 2017 solar eclipse from a site near Rexburg, ID USA (43.8294°N, 111.8849°W). A neutral region appeared in the southwest quadrant of the all-sky images, directly opposite the eclipsed Sun, and evolved in size and radial position throughout the 2 min 17 s of totality. 

Determining whether a cloud is composed of spherical water droplets of polyhedral ice crystals (i.e., the thermodynamic phase) from a passive remote sensing instrument is very difficult because of the immense variety of clouds and their highly variable microphysical properties. To improve upon the popular method of radiance ratios, we enhance the classification ability by adding polarimetric sensitivity to an instrument that measures radiance in three short-wave infrared bands. Clouds typically induce a polarization signature on the order of a percent, and so sensitive optics are required for accurate classification. In this paper, we present the combination of spectral and polarimetric sensitivity for cloud thermodynamic phase classification using data from a ground-based, 3-band, short-wave infrared polarimeter and cloud-phase validation from a dual-polarization lidar. We then analyze the classification quality of various methods using surface-fitting techniques to show that the addition of polarimetry is advantageous for cloud classification.