Radial velocities and kinematic ages of nearby T dwarfs from Keck/NIRSPEC high-resolution spectroscopy

Stars and planetary system

Unveiling the Inhibitory Potentials of Peptidomimetic Azanitriles and Pyridyl Esters towards SARS-CoV-2Main Protease: A MolecularModelling Investigation

The severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) is responsible for COVID-19, which was declared a global pandemic in March 2020 by the World Health Organization (WHO). Since SARS-CoV-2 main protease plays an essential role in the virus’s life cycle, the design of small drug molecules with lower molecular weight has been a promising development targeting its inhibition. Herein, we evaluated the novel peptidomimetic azatripeptide and azatetrapeptide nitriles against SARS-CoV-2 main protease. We employed molecular dynamics (MD) simulations to elucidate the selected compounds’ binding free energy profiles against SARS-CoV-2 and further unveil the residues responsible for the drug-binding properties. Compound 8 exhibited the highest binding free energy of 49.37 0.15 kcal/mol, followed by compound 7 (39.83 0.19 kcal/mol), while compound 17 showed the lowest binding free energy (23.54 0.19 kcal/mol). In addition, the absorption, distribution, metabolism, and excretion (ADME) assessment was performed and revealed that only compound 17 met the drug-likeness parameters and exhibited high pharmacokinetics to inhibit CYP1A2, CYP2C19, and CYP2C9 with better absorption potential and blood-brain barrier permeability (BBB) index. The additional intermolecular evaluations suggested compound 8 as a promising drug candidate for inhibiting SARS-CoV-2 Mpro. The substitution of isopropane in compound 7 with an aromatic benzene ring in compound 8 significantly enhanced the drug’s ability to bind better at the active site of the SARS-CoV-2 Mpro

A Self-consistent Model for Brown Dwarf Populations

We present a self-consistent model of the Milky Way to reproduce the observed distributions (spectral type, absolute J-band magnitude, effective temperature) and total velocity dispersion of brown dwarfs. For our model, we adopt parametric forms for the star formation history and initial-mass function, published evolutionary models, and theoretical age–velocity relations. Using standard Markov Chain Monte Carlo methods, we derive a power-law index of the initial-mass function of α = −0.71 ± 0.11, which is an improvement over previous studies. We consider a gamma-function form for the star formation history, though we find that this complex model is only slightly favored over a declining exponential. We find that a velocity variance that linearly increases with age and has an initial value of km s−1 best reproduces the total velocity dispersions. Given the similarities to main-sequence stars, this suggests brown dwarfs likely form via similar processes, but we recognize that the sizable uncertainties on σ0 preclude firm conclusions. To further refine these conclusions, we suggest that wide-field infrared imaging or low-resolution spectroscopic surveys, such as with the Nancy Grace Roman Space Telescope or Euclid, could provide large samples of brown dwarfs with robust spectral types that could probe the thickness of the thin disk. In this way, the number counts and population demographics could probe the same physical processes as with the kinematic measurements, however may provide larger samples and be subject to different selection biases

Beyond the Local Volume. II. Population Scaleheights and Ages of Ultracool Dwarfs in Deep HST/WFC3 Parallel Fields

Ultracool dwarfs (UCDs) represent a significant proportion of stars in the Milky Way, and deep samples of these sources have the potential to constrain the formation history and evolution of low-mass objects in the Galaxy. Until recently, spectral samples have been limited to the local volume (d \u3c 100 pc). Here, we analyze a sample of 164 spectroscopically characterized UCDs identified by Aganze et al. in the Hubble Space Telescope (HST) WFC3 Infrared Spectroscopic Parallel Survey (WISPS) and 3D-HST. We model the observed luminosity function using population simulations to place constraints on scaleheights, vertical velocity dispersions, and population ages as a function of spectral type. Our star counts are consistent with a power-law mass function and constant star formation history for UCDs, with vertical scaleheights of 249 pc for late-M dwarfs, 153 pc for L dwarfs, and 175 pc for T dwarfs. Using spatial and velocity dispersion relations, these scaleheights correspond to disk population ages of 3.6 Gyr for late-M dwarfs, 2.1 Gyr for L dwarfs, and 2.4 Gyr for T dwarfs, which are consistent with prior simulations that predict that L-type dwarfs are on average a younger and less dispersed population. There is an additional 1–2 Gyr systematic uncertainty on these ages due to variances in age-velocity relations. We use our population simulations to predict the UCD yield in the James Webb Space Telescope PASSAGES survey, a similar and deeper survey to WISPS and 3D-HST, and find that it will produce a comparably sized UCD sample, albeit dominated by thick disk and halo sources

Kinematics, rotation, and multiplicity of ultracool dwarfs with high-resolution near-infrared spectroscopy

Stars and planetary system

Beyond the Local Volume. I. Surface Densities of Ultracool Dwarfs in Deep HST/WFC3 Parallel Fields

Ultracool dwarf stars and brown dwarfs provide a unique probe of large-scale Galactic structure and evolution; however, until recently spectroscopic samples of sufficient size, depth, and fidelity have been unavailable. Here, we present the identification of 164 M7-T9 ultracool dwarfs in 0.6 deg2 of deep, low-resolution, near-infrared spectroscopic data obtained with the Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) instrument as part of the WFC3 Infrared Spectroscopic Parallel Survey and the 3D-HST survey. We describe the methodology by which we isolate ultracool dwarf candidates from over 200,000 spectra, and show that selection by machine-learning classification is superior to spectral index-based methods in terms of completeness and contamination. We use the spectra to accurately determine classifications and spectrophotometric distances, the latter reaching to ∼2 kpc for L dwarfs and ∼400 pc for T dwarfs

Beyond the Local Volume II: Population Scaleheights and Ages of Ultracool Dwarfs in Deep HST/WFC3 Parallel Fields

Ultracool dwarfs represent a significant proportion of stars in the Milky Way,and deep samples of these sources have the potential to constrain the formation history and evolution of low-mass objects in the Galaxy. Until recently, spectral samples have been limited to the local volume (d<100 pc). Here, we analyze a sample of 164 spectroscopically-characterized ultracool dwarfs identified by Aganze et al. (2022) in the Hubble Space Telescope WFC3 Infrared Spectroscopic Parallel (WISP) Survey and 3D-HST. We model the observed luminosity function using population simulations to place constraints on scaleheights, vertical velocity dispersions and population ages as a function of spectral type. Our star counts are consistent with a power-law mass function and constant star formation history for ultracool dwarfs, with vertical scaleheights 249$_{-61}^{+48}$ pc for late M dwarfs, 153$_{-30}^{+56}$ pc for L dwarfs, and 175$_{-56}^{+149}$ pc for T dwarfs. Using spatial and velocity dispersion relations, these scaleheights correspond to disk population ages of 3.6$_{-1.0}^{+0.8}$ for late M dwarfs, 2.1$_{-0.5}^{+0.9}$ Gyr for L dwarfs, and 2.4$_{-0.8}^{+2.4}$ Gyr for T dwarfs, which are consistent with prior simulations that predict that L-type dwarfs are on average a younger and less dispersed population. There is an additional 1-2 Gyr systematic uncertainty on these ages due to variances in age-velocity relations. We use our population simulations to predict the UCD yield in the JWST PASSAGES survey, a similar and deeper survey to WISPS and 3D-HST, and find that it will produce a comparably-sized UCD sample, albeit dominated by thick disk and halo sources.Comment: submitted to Ap

The Brown Dwarf Kinematics Project (BDKP): V. Radial and rotational velocities of T Dwarfs from Keck/NIRSPEC high-resolution spectroscopy

Stars and planetary system

Primeval very low-mass stars and brown dwarfs. I. Six new L subdwarfs, classification and atmospheric properties

This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society. ©: 2016 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reservedWe have conducted a search for L subdwarf candidates within the photometric catalogues of the UKIRT Infrared Deep Sky Survey and Sloan Digital Sky Survey. Six of our candidates are confirmed as L subdwarfs spectroscopically at optical and/or near infrared wavelengths. We also present new optical spectra of three previously known L subdwarfs (WISEA J001450.17-083823.4, 2MASS J00412179+3547133, ULAS J124425.75+102439.3). We examined the spectral types and metallicity subclasses classification of known L subdwarfs. We summarised the spectroscopic properties of L subdwarfs with different spectral types and subclasses. We classify these new L subdwarfs by comparing their spectra to known L subdwarfs and L dwarf standards. We estimate temperatures and metallicities of 22 late type M and L subdwarfs by comparing their spectra to BT-Settl models. We find that L subdwarfs have temperatures between 1500 K and 2700 K, which are higher than similarly-typed L dwarfs by around 100-400 K depending on different subclasses and subtypes. We constrained the metallicity ranges of subclasses of M, L and T subdwarfs. We also discussed the spectral type and absolute magnitude relationships for L and T subdwarfs.Peer reviewedFinal Published versio

Spitzer Follow-up of Extremely Cold Brown Dwarfs Discovered by the Backyard Worlds: Planet 9 Citizen Science Project

We present Spitzer follow-up imaging of 95 candidate extremely cold brown dwarfs discovered by the Backyard Worlds: Planet 9 citizen science project, which uses visually perceived motion in multiepoch Wide-field Infrared Survey Explorer (WISE) images to identify previously unrecognized substellar neighbors to the Sun. We measure Spitzer [3.6]–[4.5] color to phototype our brown dwarf candidates, with an emphasis on pinpointing the coldest and closest Y dwarfs within our sample. The combination of WISE and Spitzer astrometry provides quantitative confirmation of the transverse motion of 75 of our discoveries. Nine of our motion-confirmed objects have best-fit linear motions larger than 1'' yr⁻¹; our fastest-moving discovery is WISEA J155349.96+693355.2 (μ ≈ 2.”15 yr⁻¹), a possible T-type subdwarf. We also report a newly discovered wide-separation (~400 au) T8 comoving companion to the white dwarf LSPM J0055+5948 (the fourth such system to be found), plus a candidate late T companion to the white dwarf LSR J0002+6357 at 5 5 projected separation (~8700 au if associated). Among our motion-confirmed targets, five have Spitzer colors most consistent with spectral type Y. Four of these five have exceptionally red Spitzer colors suggesting types of Y1 or later, adding considerably to the small sample of known objects in this especially valuable low-temperature regime. Our Y dwarf candidates begin bridging the gap between the bulk of the Y dwarf population and the coldest known brown dwarf