The Oceanus Moving Group: A New 500 Myr-Old Host for the Nearest Brown Dwarf

We report the discovery of the Oceanus moving group, a $\approx$ 500 Myr-old group with 50 members and candidate members at distances 2-50 pc from the Sun using an unsupervised clustering analysis of nearby stars with Gaia DR3 data. This new moving group includes the nearest brown dwarf WISE J104915.57-531906.1 AB (Luhman 16 AB) at a distance of 2 pc, which was previously suspected to be young (600-800 Myr) based on a comparison of its dynamical mass measurements with brown dwarf evolutionary models. We use empirical color-magnitude sequences, stellar activity and gyrochronology to determine that this new group is roughly coeval with the Coma Ber open cluster, with an isochronal age of 510 $\pm$ 95 Myr. This newly discovered group will be useful to refine the age and chemical composition of Luhman 16 AB, which is already one of the best substellar benchmarks known to date. Furthermore, the Oceanus moving group is one of the nearest young moving groups identified to date, making it a valuable laboratory for the study of exoplanets and substellar members, with 8 brown dwarf candidate members already identified here.Comment: Submitted to ApJ, first revision. 32 pages, 6 figures, 6 table

Examining the Rotation Period Distribution of the 40 Myr Tucana-Horologium Association with TESS

The Tucana-Horologium Association (Tuc-Hor) is a 40 Myr old moving group in the southern sky. In this work, we measure the rotation periods of 313 Tuc-Hor objects with TESS light curves derived from TESS full frame images and membership lists driven by Gaia EDR3 kinematics and known youth indicators. We recover a period for 81.4% of the sample and report 255 rotaion periods for Tuc-Hor objects. From these objects we identify 11 candidate binaries based on multiple periodic signals or outlier Gaia DR2 and EDR3 re-normalised unit weight error (RUWE) values. We also identify three new complex rotators (rapidly rotating M dwarf objects with intricate light curve morphology) within our sample. Along with the six previously known complex rotators that belong to Tuc-Hor, we compare their light curve morphology between TESS Cycle 1 and Cycle 3 and find they change substantially. Furthermore, we provide context for the entire Tuc-Hor rotation sample by describing the rotation period distributions alongside other youth indicators such as H{\alpha} and Li equivalent width, as well as near ultra-violet and X ray flux. We find that measuring rotation periods with TESS to be a fast and effective means to confirm members in young moving groups.Comment: 27 pages, 12 figure

PERBANDINGAN PENILAIAN SIKLUS HIDUP (LIFE CYCLE ASSESSMENT) PRODUKSI BIODIESEL SECARA KATALIS DARI CRUDE PALM OIL DAN CRUDE JATROPHA CURCAS OIL

Sektor energi memainkan peran penting bagi Indonesia dan bahkan dunia dalam mencapai tujuan pembangunannya. Salah satu isu yang berkaitan dengan negara-negara yang berusaha untuk memanfaatkan bahan bakunya telah muncul secara global dalam pengembangan produksi biodiesel, misalnya USA yang menggunakan kacang kedelai, Eropa menggunakan rapeseed dan Asia khususnya Indonesia menggunakan minyak sawit. Isu global lainnya menempatkan lingkungan sebagai pertimbangan utama, karena produksi biodiesel menghasilkan emisi gas yang meningkatkan risiko pemanasan global dan menyebabkan kerusakan lingkungan. Negara-negara Eropa mengklaim bahwa pengolahan biodiesel yang berasal dari minyak sawit menyebabkan peningkatan emisi karbon yang ditransfer ke atmosfer. Metode yang tepat untuk menganalisis masalah tersebut melalui Penilaian Siklus Hidup (LCA). Produksi biodiesel di Indonesia menggunakan kelapa sawit sebagai bahan bakunya. Selain itu, penggunaan jatropha juga dianjurkan karena merupakan tanaman yang tidak dapat dimakan dan beradaptasi dengan berbagai kondisi tanah kritis yang ada di Indonesia. Studi ini merupakan penilaian komparatif siklus hidup dari produksi biodiesel dari minyak sawit dan jarak yang diproduksi di Indonesia. Analisis dikelompokkan ke dalam tahapan produksi tidak stabil dan tahap produksi stabil untuk mengakomodasi karakteristik pertumbuhan alami dari kedua tanaman ini. Hasil penelitian ini menunjukkan bahwa produksi biodiesel dari kelapa sawit memberikan nilai yang lebih tinggi pada potensi pemanasan global (GWP) daripada jarak pagar. Penggunaan agro-kimia, seperti pupuk, herbisida, insektisida dan pestisida, memberikan kontribusi yang signifikan terhadap total nilai GWP, yaitu masing-masing 68,14% untuk kelapa sawit dan 37,56% untuk jarak pagar. Karakteristik emisi dari kedua tanaman selama periode produktivitas tidak stabil ditemukan berbedaJurnal Teknologi Industri Pertaniandengan produktivitas stabil. Nilai GWP dan konsumsi energi untuk memproduksi biodiesel dari kelapa sawit ditemukan lebih tinggi dari jarak pagar.Kata kunci: penilaian siklus hidup, minyak mentah sawit, minyak mentah jarak pagar, biodiese

Methane Emission From a Cool Brown Dwarf

© 2024, The Author(s). This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY), https://creativecommons.org/licenses/by/4.0/Beyond our solar system, aurorae have been inferred from radio obser- vations of isolated brown dwarfs (e.g. [1]; [2]). Within our solar system, giant planets have auroral emission with signatures across the electromag- netic spectrum including infrared emission of H3+ and methane. Isolated brown dwarfs with auroral signatures in the radio have been searched for corresponding infrared features but have only had null detections (e.g. [3]). CWISEP J193518.59-154620.3. (W1935 for short) is an isolated brown dwarf with a temperature of ∼482 K. Here we report JWST observations of strong methane emission from W1935 at 3.326 microns. Atmospheric mod- eling leads us to conclude that a temperature inversion of ∼300 K centered at 1-10 millibar replicates the feature. This represents an atmospheric tem- perature inversion for a Jupiter-like atmosphere without irradiation from a host star. A plausible explanation for the strong inversion is heating by auroral processes, although other internal and/or external dynamical pro- cesses cannot be ruled out. The best fit model rules out the contribution of H3+ emission which is prominent in solar system gas giants, however this is consistent with rapid destruction of H3+ at the higher pressure where the W1935 emission originates (e.g. [4]).Peer reviewe

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

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 multi-epoch 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; our fastest-moving discovery is WISEA J155349.96+693355.2 (total motion ~2.15"/yr), 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 (~8,700 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.Comment: accepted for publication in The Astrophysical Journa