Correlating Changes in Spot Filling Factors with Stellar Rotation: The Case of LkCa 4

We present a multi-epoch spectroscopic study of LkCa 4, a heavily spotted non-accreting T Tauri star. Using SpeX at NASA's Infrared Telescope Facility (IRTF), 12 spectra were collected over five consecutive nights, spanning $\approx$ 1.5 stellar rotations. Using the IRTF SpeX Spectral Library, we constructed empirical composite models of spotted stars by combining a warmer (photosphere) standard star spectrum with a cooler (spot) standard weighted by the spot filling factor, $f_{spot}$. The best-fit models spanned two photospheric component temperatures, $T_{phot}$ = 4100 K (K7V) and 4400 K (K5V), and one spot component temperature, $T_{spot}$ = 3060 K (M5V) with an $A_V$ of 0.3. We find values of $f_{spot}$ to vary between 0.77 and 0.94 with an average uncertainty of $\sim$0.04. The variability of $f_{spot}$ is periodic and correlates with its 3.374 day rotational period. Using a mean value for $f^{mean}_{spot}$ to represent the total spot coverage, we calculated spot corrected values for $T_{eff}$ and $L_\star$. Placing these values alongside evolutionary models developed for heavily spotted young stars, we infer mass and age ranges of 0.45-0.6 $M_\odot$ and 0.50-1.25 Myr, respectively. These inferred values represent a twofold increase in the mass and a twofold decrease in the age as compared to standard evolutionary models. Such a result highlights the need for constraining the contributions of cool and warm regions of young stellar atmospheres when estimating $T_{eff}$ and $L_\star$ to infer masses and ages as well as the necessity for models to account for the effects of these regions on the early evolution of low-mass stars.Comment: 21 pages, 9 Figures; Accepted for publication in Ap

GRAVITY K-band spectroscopy of HD 206893 B

Context. Near-infrared interferometry has become a powerful tool for studying the orbital and atmospheric parameters of substellar companions. Aims. We aim to reveal the nature of the reddest known substellar companion HD 206893 B by studying its near-infrared colors and spectral morphology and by investigating its orbital motion. Methods. We fit atmospheric models for giant planets and brown dwarfs and perform spectral retrievals with petitRADTRANS and ATMO on the observed GRAVITY, SPHERE, and GPI spectra of HD 206893 B. To recover its unusual spectral features, first and foremost its extremely red near-infrared color, we include additional extinction by high-altitude dust clouds made of enstatite grains in the atmospheric model fits. However, forsterite, corundum, and iron grains predict similar extinction curves for the grain sizes considered here.We also infer the orbital parameters of HD 206893 B by combining the  100 μas precision astrometry from GRAVITY with data from the literature and constrain the mass and position of HD 206893 C based on the Gaia proper motion anomaly of the system. Results. The extremely red color and the very shallow 1:4 μm water absorption feature of HD 206893 B can be fit well with the adapted atmospheric models and spectral retrievals. By comparison with AMES-Cond evolutionary tracks, we find that only some atmospheric models predict physically plausible objects. Altogether, our analysis suggests an age of  3–300 Myr and a mass of  5–30 MJup for HD 206893 B, which is consistent with previous estimates but extends the parameter space to younger and lower-mass objects. The GRAVITY astrometry points to an eccentric orbit (e = 0:29+0:06 0:11) with a mutual inclination of \u3c34:4 deg with respect to the debris disk of the system. Conclusions. While HD 206893 B could in principle be a planetary-mass companion, this possibility hinges on the unknown influence of the inner companion on the mass estimate of 10+5 4 MJup from radial velocity and Gaia as well as a relatively small but significant Argus moving group membership probability of  61%. However, we find that if the mass of HD 206893 B is \u3c30 MJup, then the inner companion HD 206893 C should have a mass between  8–15 MJup. Finally, further spectroscopic or photometric observations at higher signal-to-noise and longer wavelengths are required to learn more about the composition and dust cloud properties of HD 206893 B

Discovery and Validation of a High-Density sub-Neptune from the K2 Mission

We report the discovery of BD+20594b, a high density sub-Neptune exoplanet, made using photometry from Campaign 4 of the two-wheeled Kepler (K2) mission, ground-based radial velocity follow-up from HARPS and high resolution lucky and adaptive optics imaging obtained using AstraLux and MagAO, respectively. The host star is a bright ($V=11.04$, $K_s = 9.37$), slightly metal poor ([Fe/H]$=-0.15\pm 0.05$ dex) solar analogue located at $152.1^{+9.7}_{-7.4}$ pc from Earth, for which we find a radius of $R_*=0.928^{+0.055}_{-0.040}R_\odot$ and a mass of $M_* = 0.961^{+0.032}_{-0.029}M_\odot$. A joint analysis of the K2 photometry and HARPS radial velocities reveal that the planet is in a $\approx 42$ day orbit around its host star, has a radius of $2.23^{+0.14}_{-0.11}R_\oplus$, and a mass of $16.3^{+6.0}_{-6.1}M_\oplus$. Although the data at hand puts the planet in the region of the mass-radius diagram where we could expect planets with a pure rock (i.e. magnesium silicate) composition using two-layer models (i.e., between rock/iron and rock/ice compositions), we discuss more realistic three-layer composition models which can explain the high density of the discovered exoplanet. The fact that the planet lies in the boundary between "possibly rocky" and "non-rocky" exoplanets, makes it an interesting planet for future RV follow-up.Comment: 12 pages, 11 figures. Accepted for publication in Ap

Does the Debris Disk around HD 32297 Contain Cometary Grains?

We present an adaptive optics imaging detection of the HD 32297 debris disk at L' (3.8 \microns) obtained with the LBTI/LMIRcam infrared instrument at the LBT. The disk is detected at signal-to-noise per resolution element ~ 3-7.5 from ~ 0.3-1.1" (30-120 AU). The disk at L' is bowed, as was seen at shorter wavelengths. This likely indicates the disk is not perfectly edge-on and contains highly forward scattering grains. Interior to ~ 50 AU, the surface brightness at L' rises sharply on both sides of the disk, which was also previously seen at Ks band. This evidence together points to the disk containing a second inner component located at $\lesssim$ 50 AU. Comparing the color of the outer (50 $< r$/AU $< 120$) portion of the disk at L' with archival HST/NICMOS images of the disk at 1-2 \microns allows us to test the recently proposed cometary grains model of Donaldson et al. 2013. We find that the model fails to match the disk's surface brightness and spectrum simultaneously (reduced chi-square = 17.9). When we modify the density distribution of the model disk, we obtain a better overall fit (reduced chi-square = 2.9). The best fit to all of the data is a pure water ice model (reduced chi-square = 1.06), but additional resolved imaging at 3.1 \microns is necessary to constrain how much (if any) water ice exists in the disk, which can then help refine the originally proposed cometary grains model.Comment: Accepted to ApJ January 13, 2014. 12 pages (emulateapj style), 9 figures, 1 tabl

ALMA Discovery of a Disk around the Planetary-Mass Companion Sr 12 C

We report an Atacama Large Millimeter/submillimeter Array 0.88 mm (Band 7) continuum detection of the accretion disk around SR 12 c, an ∼11 M Jup planetary-mass companion (PMC) orbiting its host binary at 980 au. This is the first submillimeter detection of a circumplanetary disk around a wide PMC. The disk has a flux density of 127 ± 14 μJy and is not resolved by the ∼0.″1 beam, so the dust disk radius is likely less than 5 au and can be much smaller if the dust continuum is optically thick. If, however, the dust emission is optically thin, then the SR 12 c disk has a comparable dust mass to the circumplanetary disk around PDS 70 c but is about five times lower than that of the ∼12 M Jup free-floating OTS 44. This suggests that disks around bound and unbound planetary-mass objects can span a wide range of masses. The gas mass estimated with an accretion rate of 10-11 M ⊙ yr-1 implies a gas-to-dust ratio higher than 100. If cloud absorption is not significant, a nondetection of 12CO(3-2) implies a compact gas disk around SR 12 c. Future sensitive observations may detect more PMC disks at 0.88 mm flux densities of ≲ 100 μJy

Spatially Resolved Imaging of the Inner Fomalhaut Disk Using JWST/MIRI

Planetary debris disks around other stars are analogous to the asteroid and Kuiper belts in the Solar System. Their structure reveals the configuration of small bodies and provides hints for the presence of planets. The nearby star Fomalhaut hosts one of the most prominent debris disks, resolved by the Hubble Space Telescope, Spitzer, Herschel and the Atacama Large Millimeter Array. Images of this system at mid-infrared wavelengths using JWST/MIRI not only show the narrow Kuiper belt-analogue outer ring, but also that (1) what was thought from indirect evidence to be an asteroid-analogue structure is instead broad, extending outward into the outer system, and (2) there is an intermediate belt, probably shepherded by an unseen planet. The newly discovered belt is demarcated by an inner gap, located at ~78 au, and it is misaligned relative to the outer belt. The previously known collisionally generated dust cloud, Fomalhaut b, could have originated from this belt, suggesting increased dynamical stirring and collision rates there. We also discovered a large dust cloud within the outer ring, possible evidence of another dust-creating collision. Taken together with previous observations, Fomalhaut appears to be the site of a complex and possibly dynamically active planetary system

Performance of Near-Infrared High-Contrast Imaging Methods with JWST from Commissioning

The James Webb Space Telescope (JWST) will revolutionize the field of high-contrast imaging and enable both the direct detection of Saturn-mass planets and the characterization of substellar companions in the mid-infrared. While JWST will feature unprecedented sensitivity, angular resolution will be the key factor when competing with ground-based telescopes. Here, we aim to characterize the performance of several extreme angular resolution imaging techniques available with JWST in the 3-5 µm regime based on data taken during the instrument commissioning. Firstly, we introduce custom tools to simulate, reduce, and analyze JWST NIRCam and MIRI coronagraphy data and use these tools to extract companion detection limits from on-sky NIRCam round and bar mask coronagraphy observations. Secondly, we present on-sky JWST NIRISS aperture masking interferometry (AMI) and kernel phase imaging (KPI) observations from which we extract companion detection limits using the publicly available fouriever tool. Scaled to a total integration time of one hour and a target of the brightness of AB Dor (W1 ≈ 4.4 mag, W2 ≈ 3.9 mag), we find that NIRISS AMI and KPI reach contrasts of ∼ 7-8 mag at ∼ 70 mas and ∼ 9 mag at ∼ 200 mas. Beyond ∼ 250 mas, NIRCam coronagraphy reaches deeper contrasts of ∼ 13 mag at ∼ 500 mas and ∼ 15 mag at ∼ 2 arcsec. While the bar mask performs ∼ 1 mag better than the round mask at small angular separations ≲ 0.75 arcsec, it is the other way around at large angular separations ≳ 1.5 arcsec. Moreover, the round mask gives access to the full 360 deg field-of-view which is beneficial for the search of new companions. We conclude that already during the instrument commissioning, JWST high-contrast imaging in the L- and M-bands performs close to its predicted limits and is a factor of ∼ 10 times better at large separations than the best ground-based instruments operating at similar wavelengths despite its \u3e 2 times smaller collecting area

Improved Orbital Constraints and Hα\alpha Photometric Monitoring of the Directly Imaged Protoplanet Analog HD 142527 B

Companions embedded in the cavities of transitional circumstellar disks have been observed to exhibit excess luminosity at H$\alpha$, an indication that they are actively accreting. We report 5 years (2013-2018) of monitoring of the position and H$\alpha$ excess luminosity of the embedded, accreting low-mass stellar companion HD 142527 B from the MagAO/VisAO instrument. We use pyklip, a python implementation of the Karhounen-Loeve Image Processing algorithm, to detect the companion. Using pyklip forward modeling, we constrain the relative astrometry to $1-2 \mathrm{mas}$ precision and achieve sufficient photometric precision ($\pm0.2 \mathrm{mag}, 3\%$ error) to detect changes in the H$\alpha$ contrast of the companion over time. In order to accurately determine the relative astrometry of the companion, we conduct an astrometric calibration of the MagAO/VisAO camera against 20 years of Keck/NIRC2 images of the Trapezium cluster. We demonstrate agreement of our VisAO astrometry with other published positions for HD 142527 B, and use orbitize! to generate a posterior distribution of orbits fit to the relative astrometry of HD 142527 B. Our data suggest that the companion is close to periastron passage, on an orbit significantly misinclined with respect to both the wide circumbinary disk and the recently observed inner disk encircling HD 142527 A. We translate observed H-alpha contrasts for HD 142527 B into mass accretion rate estimates on the order of $4-9\times10^{-10} \mathrm{M_\odot}\mathrm{yr}^{-1}$. Photometric variation in the H-alpha excess of the companion suggests that the accretion rate onto the companion is variable. This work represents a significant step towards observing accretion-driven variability onto protoplanets, such as PDS 70 b\&c.Comment: Accepted to the Astronomical Journal. 32 pages, 16 figures, 8 tables, 4 appendice

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