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Determining the precise ages of young (tens to a few hundred Myr) kinematic (‘moving’) groups is important for placing star, protoplanetary disc, and planet observations on an evolutionary timeline. The nearby ∼25 Myr-old β Pictoris Moving Group (BPMG) is an important benchmark for studying stars and planetary systems at the end of the primordial disc phase. Gaia DR3 astrometry and photometry, combined with ground-based observations and more sophisticated stellar models, permit a systematic re-evaluation of BPMG membership and age. We combined Gaia astrometry with previously published radial velocities to evaluate moving group membership in a Bayesian framework. To minimize the effect of unresolved stellar multiplicity on age estimates, we identified and excluded multistar systems using Gaia astrometry, ground-based adaptive optics imaging, and multi-epoch radial velocities, as well as literature identifications. We estimated age using isochrone and lithium-depletion-boundary fitting with models that account for the effect of magnetic activity and spots on young, rapidly rotating stars. We find that age estimates are highly model-dependent; Dartmouth magnetic models with ages of 23 ± 8 and 33$^{+9}_{-11}$ Myr provide best fits to the lithium depletion boundary and Gaia MG versus BP–RP colour–magnitude diagram, respectively, whereas a Dartmouth standard model with an age of 11$^{+4}_{-3}$ Myr provides a best fit to the 2-Micron All-Sky Survey-Gaia$M_{K_S}$ versus BP–RP colour–magnitude diagram.

 

Y dwarfs, the coolest known spectral class of brown dwarfs, overlap in mass and temperature with giant exoplanets, providing unique laboratories for studying low-temperature atmospheres. However, only a fraction of Y dwarf candidates have been spectroscopically confirmed. We present Keck/NIRES near-infrared spectroscopy of the nearby (d≈ 6–8 pc) brown dwarf CWISE J105512.11+544328.3. Although its near-infrared spectrum aligns best with the Y0 standard in theJband, no standard matches well across the fullYJHKwavelength range. The CWISE J105512.11+544328.3 NH₃-H= 0.427 ± 0.0012 and CH₄-J= 0.0385 ± 0.0007 absorption indices and absolute Spitzer [4.5] magnitude of 15.18 ± 0.22 are also indicative of an early-Y dwarf rather than a late-T dwarf. CWISE J105512.11+544328.3 additionally exhibits the bluest Spitzer [3.6]−[4.5] color among all spectroscopically confirmed Y dwarfs. Despite this anomalously blue Spitzer color given its low luminosity, CWISE J105512.11+544328.3 does not show other clear kinematic or spectral indications of low metallicity. Atmospheric model comparisons yield a log(g) ≤ 4.5 andT_eff≈ 500 ± 150 K for this source. We classify CWISE J105512.11+544328.3 as a Y0 (pec) dwarf, adding to the remarkable diversity of the Y-type population. JWST spectroscopy would be crucial to understanding the origin of this Y dwarf’s unusual preference for low-gravity models and blue 3–5μm color.

 

We present the analysis of two unusually red L dwarfs, CWISE J075554.14−325956.3 (W0755−3259) and CWISE J165909.91−351108.5 (W1659−3511), confirmed by their newly obtained near-infrared spectra collected with the TripleSpec4 spectrograph on the Southern Astrophysical Research Telescope. We classify W0755−3259 as an L7 very low-gravity dwarf, exhibiting extreme redness with a characteristic peakedH-band and spectral indices typical of low-gravity late-type L dwarfs. We classify W1659-3511 as a red L7 field-gravity dwarf, with a more roundedH-band peak and spectral indices that support a normal gravity designation. W1659−3511 is noticeably fainter than W0755−3259, and the roundedH-band of W1659−3511 may be evidence of CH₄absorption.

 

Precise radial velocity (PRV) surveys are important for the search for Earth analogs around nearby bright stars, which induce a small stellar reflex motion with an RV amplitude of ∼10 cm s⁻¹. Detecting such a small RV signal poses challenges to instrumentation, data analysis, and the precision of astrophysical models to mitigate stellar jitter. In this work, we investigate an important component in the PRV error budget—the spectral contamination from the Earth’s atmosphere (tellurics). We characterize the effects of telluric absorption on the RV precision and quantify its contribution to the RV error budget over time and across a wavelength range of 350 nm–2.5μm. We use simulated solar spectra with telluric contamination injected, and we extract the RVs using two commonly adopted algorithms: dividing out a telluric model before performing cross-correlation or forward modeling the observed spectrum incorporating a telluric model. We assume various degrees of cleanness in removing the tellurics. We conclude that the RV errors caused by telluric absorption can be suppressed to close to or even below 1–10 cm s⁻¹in the blue optical region. At red through near-infrared wavelengths, however, the residuals of tellurics can induce an RV error on the meter-per-second level even under the most favorable assumptions for telluric removal, leading to significant systematic noise in the RV time series and periodograms. If the red-optical or near-infrared becomes critical in the mitigation of stellar activity, systematic errors from tellurics can be eliminated with a space mission such as EarthFinder.

 

We present the discovery of CWISE J050626.96+073842.4 (CWISE J0506+0738), an L/T transition dwarf with extremely red near-infrared colors discovered through the Backyard Worlds: Planet 9 citizen science project. Photometry from UKIRT and CatWISE give a (J−K)_MKOcolor of 2.97 ± 0.03 mag and aJ_MKO− W2 color of 4.93 ± 0.02 mag, making CWISE J0506+0738 the reddest known free-floating L/T dwarf in both colors. We confirm the extremely red nature of CWISE J0506+0738 using Keck/NIRES near-infrared spectroscopy and establish that it is a low-gravity, late-type L/T transition dwarf. The spectrum of CWISE J0506+0738 shows possible signatures of CH₄absorption in its atmosphere, suggesting a colder effective temperature than other known, young, red L dwarfs. We assign a preliminary spectral type for this source of L8γ–T0γ. We tentatively find that CWISE J0506+0738 is variable at 3–5μm based on multiepoch WISE photometry. Proper motions derived from follow-up UKIRT observations combined with a radial velocity from our Keck/NIRES spectrum and a photometric distance estimate indicate a strong membership probability in theβPic moving group. A future parallax measurement will help to establish a more definitive moving group membership for this unusual object.

 

We present a survey for photometric variability in young, low-mass brown dwarfs with the Spitzer Space Telescope. The 23 objects in our sample show robust signatures of youth and share properties with directly imaged exoplanets. We present three new young objects: 2MASS J03492367+0635078, 2MASS J09512690−8023553, and 2MASS J07180871−6415310. We detect variability in 13 young objects, and find that young brown dwarfs are highly likely to display variability across the L2–T4 spectral type range. In contrast, the field dwarf variability occurrence rate drops for spectral types >L9. We examine the variability amplitudes of young objects and find an enhancement in maximum amplitudes compared to field dwarfs. We speculate that the observed range of amplitudes within a spectral type may be influenced by secondary effects such as viewing inclination and/or rotation period. We combine our new rotation periods with the literature to investigate the effects of mass on angular momentum evolution. While high-mass brown dwarfs (>30M_Jup) spin up over time, the same trend is not apparent for lower-mass objects (<30M_Jup), likely due to the small number of measured periods for old, low-mass objects. The rotation periods of companion brown dwarfs and planetary-mass objects are consistent with those of isolated objects with similar ages and masses, suggesting similar angular momentum histories. Within the AB Doradus group, we find a high-variability occurrence rate and evidence for common angular momentum evolution. The results are encouraging for future variability searches in directly imaged exoplanets with facilities such as the James Webb Space Telescope and 30 m telescopes.

 

Abstract In an effort to identify nearby and unusual cold objects in the solar neighborhood, we searched for previously unidentified moving objects using CatWISE2020 proper motion data combined with machine learning methods. We paired the motion candidates with their counterparts in 2MASS, UHS, and VHS. Then we searched for white dwarf, brown dwarf, and subdwarf outliers on the resulting color–color diagrams. This resulted in the discovery of 16 new dwarfs, including 2 nearby M dwarfs (<30 pc), a possible young L dwarf, a high-motion early-T dwarf, and 3 later-T dwarfs. This research represents a step forward in completing the census of the Sun’s neighbors. 

Abstract While stars are often found in binary systems, brown dwarf binaries are much rarer. Brown dwarf–brown dwarf pairs are typically difficult to resolve because they often have very small separations. Using brown dwarfs discovered with data from the Wide-field Infrared Survey Explorer (WISE) via the Backyard Worlds: Planet 9 citizen science project, we inspected other, higher-resolution, sky surveys for overlooked cold companions. During this process, we discovered the brown dwarf binary system CWISE J0146−0508AB, which we find has a very small chance alignment probability based on the similar proper motions of the components of the system. Using follow-up near-infrared spectroscopy with Keck/NIRES, we determined component spectral types of L4 and L8 (blue), making CWISE J0146−0508AB one of only a few benchmark systems with a blue L dwarf. At an estimated distance of ∼40 pc, CWISE J0146−0508AB has a projected separation of ∼129 au, making it the widest-separation brown dwarf pair found to date. We find that such a wide separation for a brown dwarf binary may imply formation in a low-density star-forming region. 

We present the largest and most homogeneous collection of near-infrared (NIR) spectra of Type Ia supernovae (SNe Ia): 339 spectra of 98 individual SNe obtained as part of the Carnegie Supernova Project-II. These spectra, obtained with the FIRE spectrograph on the 6.5 m Magellan Baade telescope, have a spectral range of 0.8–2.5μm. Using this sample, we explore the NIR spectral diversity of SNe Ia and construct a template of spectral time series as a function of the light-curve-shape parameter, color stretchs_BV. Principal component analysis is applied to characterize the diversity of the spectral features and reduce data dimensionality to a smaller subspace. Gaussian process regression is then used to model the subspace dependence on phase and light-curve shape and the associated uncertainty. Our template is able to predict spectral variations that are correlated withs_BV, such as the hallmark NIR features: Mgiiat early times and theH-band break after peak. Using this template reduces the systematic uncertainties inK-corrections by ∼90% compared to those from the Hsiao template. These uncertainties, defined as the meanK-correction differences computed with the color-matched template and observed spectra, are on the level of 4 × 10⁻⁴mag on average. This template can serve as the baseline spectral energy distribution for light-curve fitters and can identify peculiar spectral features that might point to compelling physics. The results presented here will substantially improve future SN Ia cosmological experiments, for both nearby and distant samples.