arXiv subjects

Jaqueline K. Faherty

Publications and source records attributed to Jaqueline K. Faherty.

3 recordsLinked to original sources

arXiv2026

Benchmark Brown Dwarf Systems I: Chemical Abundance Analysis of FGK Stars with Wide-Separation Brown Dwarf Companions Using PEPSI

We present results from a spectroscopic survey of 32 FGK stars hosting brown dwarfs, using high-resolution optical spectra (R = 130,000 and 50,000) obtained with the PEPSI spectrograph on the Large Binocular Telescope. The primary goal of this survey is to determine precise stellar parameters and abundances for 11 elements (C, O, Mg, Si, Ca, Al, Ti, Fe, Y, S, and N) in these systems. We employ spectral synthesis within the BACCHUS framework to derive precise stellar properties and elemental abundance ratios. For our average S/N $>$ 200 data, we achieve a typical error of 42 K in T$_\mathrm{eff}$ and $\sim$0.03 dex for [Fe/H]. We observe a significant dispersion from a solar C/O ratio among the sample of brown dwarf host stars that host primarily wide-orbit brown dwarfs. Using established theoretical chemical frameworks, we discuss the implications of the observed Mg/Si and Ca/Al ratios for cloud properties in the brown dwarf companions. Finally, we evaluate the applicability of the [Y/Mg] stellar clock for our sample and discuss the broader implications of our results. This work provides a timely and uniform abundance analysis of host stars, supporting extended wavelength brown dwarf observations in the era of JWST.

astro-ph.SR↗

arXiv2019

A 3 Gyr White Dwarf with Warm Dust Discovered via the Backyard Worlds: Planet 9 Citizen Science Project

Infrared excesses due to dusty disks have been observed orbiting white dwarfs with effective temperatures between 7200 K and 25000 K, suggesting that the rate of tidal disruption of minor bodies massive enough to create a coherent disk declines sharply beyond 1~Gyr after white dwarf formation. We report the discovery that the candidate white dwarf LSPM J0207+3331, via the Backyard Worlds: Planet 9 citizen science project and Keck Observatory follow-up spectroscopy, is hydrogen-dominated with a luminous compact disk (L$_{\rm IR}$/L$_{\star}$=14%) and an effective temperature nearly 1000K cooler than any known white dwarf with an infrared excess. The discovery of this object places the latest time for large scale tidal disruption events to occur at $\sim$3 Gyr past the formation of the host white dwarf, making new demands of dynamical models for planetesimal perturbation and disruption around post main sequence planetary systems. Curiously, the mid-IR photometry of the disk cannot be fully explained by a geometrically thin, optically thick dust disk as seen for other dusty white dwarfs, but requires a second ring of dust near the white dwarf's Roche radius. In the process of confirming this discovery, we found that careful measurements of WISE source positions can reveal when infrared excesses for white dwarfs are co-moving with their hosts, helping distinguish them from confusion noise.

astro-ph.SR↗

arXiv2015

The Brown Dwarf Kinematics Project (BDKP). IV. Radial Velocities of 85 Late-M and L dwarfs with MagE

Radial velocity measurements are presented for 85 late M- and L-type very low mass stars and brown dwarfs obtained with the Magellan Echellette (MagE) spectrograph. Targets primarily have distances within 20 pc of the Sun, with more distant sources selected for their unusual spectral energy distributions. We achieved precisions of 2--3 km/s, and combined these with astrometric and spectrophotometric data to calculate $UVW$ velocities. Most are members of the thin disk of the Galaxy, and velocity dispersions indicate a mean age of 5.2$\pm$0.2 Gyr for sources within 20 pc. We find significantly different kinematic ages between late-M dwarfs (4.0$\pm$0.2 Gyr) and L dwarfs (6.5$\pm$0.4 Gyr) in our sample that are contrary to predictions from prior simulations. This difference appears to be driven by a dispersed population of unusually blue L dwarfs which may be more prevalent in our local volume-limited sample than in deeper magnitude-limited surveys. The L dwarfs exhibit an asymmetric $U$ velocity distribution with a net inward flow, similar to gradients recently detected in local stellar samples. Simulations incorporating brown dwarf evolution and Galactic orbital dynamics are unable to reproduce the velocity asymmetry, suggesting non-axisymmetric perturbations or two distinct L dwarf populations. We also find the L dwarfs to have a kinematic age-activity correlation similar to more massive stars. We identify several sources with low surface gravities, and two new substellar candidate members of nearby young moving groups: the astrometric binary DENIS J08230313$-$4912012AB, a low-probability member of the $β$ Pictoris Moving Group; and 2MASS J15104786-2818174, a moderate-probability member of the 30-50 Myr Argus Association.

astro-ph.SR↗