Infrared Absolute Calibration. I. Comparison of Sirius with Fainter Calibration Stars

A challenge in absolute calibration is to relate very bright stars with physical flux measurements to faint ones within range of modern instruments, e.g., those on large ground-based telescopes or the James Webb Space Telescope (JWST). We propose Sirius as the fiducial color standard. It is an A0V star that is slowly rotating and does not have infrared excesses due to either hot dust or a planetary debris disk; it also has a number of accurate (∼1%–2%) absolute flux measurements. We accurately transfer the near-infrared flux from Sirius to BD +60 1753, an unobscured early A-type star (A1V, V ≈ 9.6, E(B – V) ≈ 0.009) that is faint enough to serve as a primary absolute flux calibrator for JWST. Its near-infrared spectral energy distribution and that of Sirius should be virtually identical. We have determined its output relative to that of Sirius in a number of different ways, all of which give consistent results within ∼1%. We also transfer the calibration to GSPC P330-E, a well-calibrated close solar analog (G2V). We have emphasized the 2MASS K S band, since it represents a large number and long history of measurements, but the theoretical spectra (i.e., from CALSPEC) of these stars can be used to extend this result throughout the near- and mid-infrared.

Co-accretion + Giant Impact Origin of the Uranus System: Post-impact Evolution

We investigate aspects of the co-accretion + giant impact scenario proposed by Morbidelli et al. (2012) for the origin of the Uranian satellites. In this model, a regular satellite system formed during gas accretion is impulsively destabilized by a Uranus-tipping impact, producing debris that ultimately re-orients to the planet’s new equatorial plane and re-accumulates into Uranus’ current large moons. We first investigate the nodal randomization of a disk of debris resulting from disruptive collisions between the hypothesized prior satellites. Consistent with Morbidelli et al., we find that an impact-generated interior c-disk with mass ≥10−2 Uranus masses is needed to cause sufficient nodal randomization to appropriately realign the outer debris disk. We then simulate the reaccumulation of the outer debris disk into satellites and find that disks with larger initial radii are needed to produce an outer debris disk that extends to Oberon’s distance, and that Uranus’ obliquity prior to the giant impact must have been substantial, ≥40°, if its original co-accreted satellite system was broadly similar in radial scale to those at Jupiter and Saturn today. Finally, we explore the subsequent evolution of a massive, water-dominated inner c-disk as it condenses, collisionally spreads, and spawns new moons beyond the Roche limit. We find that intense tidal dissipation in Uranus (i.e., ( Q / k 2 ) U ≤ 10 2 ) is needed to prevent large icy moons spawned from the inner disk from expanding beyond the synchronous orbit, where they would be long lived and inconsistent with the lack of massive inner moons at Uranus today. We conclude that while a co-accretion + giant impact is viable it requires rather specific conditions.

EXPRES. III. Revealing the Stellar Activity Radial Velocity Signature of ϵ Eridani with Photometry and Interferometry

The distortions of absorption line profiles caused by photospheric brightness variations on the surfaces of cool, main-sequence stars can mimic or overwhelm radial velocity (RV) shifts due to the presence of exoplanets. The latest generation of precision RV spectrographs aims to detect velocity amplitudes ≲ 10 cm s−1, but requires mitigation of stellar signals. Statistical techniques are being developed to differentiate between Keplerian and activity-related velocity perturbations. Two important challenges, however, are the interpretability of the stellar activity component as RV models become more sophisticated, and ensuring the lowest-amplitude Keplerian signatures are not inadvertently accounted for in flexible models of stellar activity. For the K2V exoplanet host ϵ Eridani, we separately used ground-based photometry to constrain Gaussian processes for modeling RVs and TESS photometry with a light-curve inversion algorithm to reconstruct the stellar surface. From the reconstructions of TESS photometry, we produced an activity model that reduced the rms scatter in RVs obtained with EXPRES from 4.72 to 1.98 m s−1. We present a pilot study using the CHARA Array and MIRC-X beam combiner to directly image the starspots seen in the TESS photometry. With the limited phase coverage, our spot detections are marginal with current data but a future dedicated observing campaign should allow for imaging, as well as allow the stellar inclination and orientation with respect to the debris disk to be definitively determined. This work shows that stellar surface maps obtained with high-cadence, time-series photometric and interferometric data can provide the constraints needed to accurately reduce RV scatter.

Multiband Imaging of the HD 36546 Debris Disk: A Refined View from SCExAO/CHARIS*

We present the first multiwavelength (near-infrared; 1.1–2.4 μm) imaging of HD 36546's debris disk, using the Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) system coupled with the Coronagraphic High Angular Resolution Imaging Spectrograph (CHARIS). As a 3–10 Myr old star, HD 36546 presents a rare opportunity to study a debris disk at very early stages. SCExAO/CHARIS imagery resolves the disk over angular separations of ρ ∼ 0.″25–1.″0 (projected separations of rproj ∼ 25–101 au) and enables the first spectrophotometric analysis of the disk. The disk’s brightness appears symmetric between its eastern and western extents, and it exhibits slightly blue near-infrared colors on average (e.g., J−K = −0.4 ± 0.1)—suggesting copious submicron-sized or highly porous grains. Through detailed modeling adopting a Hong scattering phase function (SPF), instead of the more common Henyey–Greenstein function, and using the differential evolution optimization algorithm, we provide an updated schematic of HD 36546's disk. The disk has a shallow radial dust density profile (α in ≈ 1.0 and α out ≈ −1.5), a fiducial radius of r 0 ≈ 82.7 au, an inclination of i ≈ 79.°1, and a position angle of PA ≈ 80.°1. Through spine tracing, we find a spine that is consistent with our modeling, but also with a “swept-back wing” geometry. Finally, we provide constraints on companions, including limiting a companion responsible for a marginal Hipparcos–Gaia acceleration to a projected separation of ≲0.″2 and to a minimum mass of ≲11 M Jup.

An Unbiased Mineral Compositional Analysis Technique for Circumstellar Disks

A circumstellar disk that surrounds a star is composed of gas, dust, and rocky objects that are in orbit around it. Around infant stars, this disk can act as a source of material that can be used to form planetesimals, which can then accrete more material and form into planets. Studying the mineral composition of these disks can provide insight into the processes that created our solar system. The purpose of this paper is to analyze the mineral composition of these disks by using a newly created python package, Min-CaLM. This package determines the relative mineral abundance within a disk by using a linear regression technique called non-negative least square minimization. The circumstellar disks that are capable of undergoing compositional analysis must have a spectrum with both a detectable mid-infrared excess and prominent silicate features. From our sample, there are only eight debris disks that qualify to be candidates for the Min-CaLM program. The mineral compositions calculated by Min-CaLM are then compared to the Tholen asteroid classification scheme. HD 23514, HD 105234, HD 15407A, BD+20 307, HD 69830, and HD 172555 are found to have a compositions similar to that expected for C-type asteroids, TYC 9410-532-1 resembles the composition of S-type asteroids, and HD 100546 resembles D-type asteroids. Min-CaLM also calculates the mineral compositions of the comets Tempel 1 and Hale-Bopp, and they are used as a comparison between the material in our early solar system and the debris disk compositions. KEYWORDS: Debris disk; Mineral; Composition; Analysis; Asteroid; Circumstellar; Spectroscopy; Python