arXiv subjects

William M. Best

Publications and source records attributed to William M. Best.

3 recordsLinked to original sources

arXiv2026

The Companions to B and A Stars Snapshot (C-BASS) Survey: I. Discovery of a Young Brown Dwarf Companion to HIP 17453

We report the detection of a new brown dwarf companion to HIP 17453 A, a chemically peculiar A0V star located at a distance of 81 pc. HIP 17453 A was observed with high-resolution adaptive optics imaging using the Near-Infrared Camera 2 on the Keck II telescope as part of the Companions to B and A Stars Snapshot (C-BASS) survey over a ten-year baseline, revealing the presence of a companion with proper motion consistent with the primary. We estimate the age of the HIP 17453 system as 280 $\pm$ 125 Myr, and with follow-up intermediate resolution (R~1800) spectroscopic observations with the Gemini Near Infra-Red Spectrograph (GNIRS) on the Gemini-North telescope, we found the spectrum of HIP 17453 B to be consistent with a spectral type of L2 $\pm$ 1. Through interpolation of Sonora Diamondback evolutionary models, we calculate an effective temperature of $1953^{+84}_{-78}$ K and mass of $53^{+10}_{-8}$ $M_{Jup}$ for HIP 17453 B, which corresponds to a mass ratio of $q = 0.024 \pm 0.004$ for the HIP 17453 system. With its intermediate mass and young age, HIP 17453 B joins a small set of benchmark brown dwarf companions around early-type stars that are suitable for follow-up atmospheric and evolutionary studies.

astro-ph.SR↗

arXiv2024

Estimating Photometric Distances to Ultracool Dwarfs in Next Generation Space-based Infrared Surveys: Synthetic Photometry and New Absolute Magnitude Versus Spectral Type Relations for JWST, Euclid, and Roman Filters

We synthesize JWST NIRCam photometry for the F164N, F187N, F212N narrow filters, F140M, F162M, F182M, F210M medium filters, and F115W, F150W, F200W wide filters, Euclid Near Infrared Spectrometer and Photometer (NISP) photometry for the $Y_E J_E H_E$ filters, and Roman Wide Field Instrument (WFI) photometry for the F106, F129, F146, F158, F184 and F213 filters using SpeX prism spectra and parallaxes of 688 field-age and 151 young ($\lesssim$ 200 Myr) ultracool dwarfs (spectral types M6-T9). We derive absolute magnitude-spectral type polynomial relations that enable the calculation of photometric distances for ultracool dwarfs observed with JWST, and to be observed with Euclid and Roman, in the absence of parallax measurements. Additionally, using the synthesized photometry to generate color-color figures can help distinguish high-redshift galaxies from brown dwarf interlopers in survey datasets. In particular, anticipating the upcoming Euclid Early Release Observations, we provide synthetic Euclid colors for ultracool dwarfs in our sample.

astro-ph.SR↗

arXiv2023

The Hawaii Infrared Parallax Program. VI. The Fundamental Properties of 1000+ Ultracool Dwarfs and Planetary-mass Objects Using Optical to Mid-IR SEDs and Comparison to BT-Settl and ATMO 2020 Model Atmospheres

We derive the bolometric luminosities ($L_{\mathrm{bol}}$) of 865 field-age and 189 young ultracool dwarfs (spectral types M6-T9, including 40 new discoveries presented here) by directly integrating flux-calibrated optical to mid-IR spectral energy distributions (SEDs). The SEDs consist of low-resolution ($R\sim$ 150) near-IR (0.8-2.5 $μ$m) spectra (including new spectra for 97 objects), optical photometry from the Pan-STARRS1 survey, and mid-IR photometry from the CatWISE2020 survey and Spitzer/IRAC. Our $L_{\mathrm{bol}}$ calculations benefit from recent advances in parallaxes from Gaia, Spitzer, and UKIRT, as well as new parallaxes for 19 objects from CFHT and Pan-STARRS1 presented here. Coupling our $L_{\mathrm{bol}}$ measurements with a new uniform age analysis for all objects, we estimate substellar masses, radii, surface gravities, and effective temperatures ($T_{\mathrm{eff}}$) using evolutionary models. We construct empirical relationships for $L_{\mathrm{bol}}$ and $T_{\mathrm{eff}}$ as functions of spectral type and absolute magnitude, determine bolometric corrections in optical and infrared bandpasses, and study the correlation between evolutionary model-derived surface gravities and near-IR gravity classes. Our sample enables a detailed characterization of BT-Settl and ATMO 2020 atmospheric model systematics as a function of spectral type and position in the near-IR color-magnitude diagram. We find the greatest discrepancies between atmospheric and evolutionary model-derived $T_{\mathrm{eff}}$ (up to 800 K) and radii (up to 2.0 $R_{\mathrm{Jup}}$) at the M/L transition boundary. With 1054 objects, this work constitutes the largest sample to date of ultracool dwarfs with determinations of their fundamental parameters.

astro-ph.SR↗