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In this case study, we describe the design and implementation of the Backyard Worlds: Cool Neighbors citizen science project, which combines image-level deep learning with Zooniverse-hosted online crowdsourcing to mine large astronomical sky maps for rare celestial objects called \"brown dwarfs.\" Specifically, Cool Neighbors uses machine learning to pre-select the sky images shown to volunteers. Cool Neighbors represents an excellent opportunity to interrogate the effects of incorporating artificial intelligence into a citizen science project; its sibling project, Backyard Worlds: Planet 9, uses no artificial intelligence, providing a natural point of comparison for participant engagement metrics. Through analysis of more than 10 million total Zooniverse classifications from the combination of Cool Neighbors and Backyard Worlds: Planet 9, among other results, we find (1) Cool Neighbors volunteers perform ~3x more classifications per unit of time invested than Backyard Worlds: Planet 9 volunteers, and (2) each registered Cool Neighbors participant performs ~2-5x more classifications than each registered Backyard Worlds: Planet 9 participant. We also discuss our measured approach to presenting the complementarity of machine learning and citizen science in volunteer-facing Cool Neighbors materials. Finally, we present a survey of advanced Backyard Worlds participants, which indicates that these citizen scientists are by and large not dissuaded from participating in Cool Neighbors because of its usage of artificial intelligence.

Beyond our Solar System, aurorae have been inferred from radio observations of isolated brown dwarfs 1 , 2 . Within our Solar System, giant planets have auroral emission with signatures across the electromagnetic spectrum including infrared emission of H 3 + and methane. Isolated brown dwarfs with auroral signatures in the radio have been searched for corresponding infrared features, but only null detections have been reported 3 . CWISEP J193518.59-154620.3. (W1935 for short) is an isolated brown dwarf with a temperature of approximately 482 K. Here we report James Webb Space Telescope observations of strong methane emission from W1935 at 3.326 μm. Atmospheric modelling leads us to conclude that a temperature inversion of approximately 300 K centred at 1–10 mbar replicates the feature. This represents an atmospheric temperature 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 external dynamical processes cannot be ruled out. The best-fitting model rules out the contribution of H 3 + emission, which is prominent in Solar System gas giants. However, this is consistent with rapid destruction of H 3 + at the higher pressure where the W1935 emission originates 4 . Methane emission from a very cool brown dwarf, perhaps arising from an aurora, has been detected in James Webb Space Telescope observations.

We introduce the Wide-field Retrieval of Astrodata Program (WRAP), a tool created to aid astronomers in gathering photometric and astrometric data for point sources that may confuse simple cross-matching algorithms because of their faintness or motion. WRAP allows astronomers to correctly cross-identify objects with proper motion across multiple surveys by wedding the catalog data with its underlying images, thus providing visual confirmation of cross-associations in real time. Developed within the Backyard Worlds: Planet 9 citizen science project, WRAP aims to aid in the characterization of faint, high motion sources by this collaboration (and others).

Beyond our solar system, aurorae have been inferred from radio observations of isolated brown dwarfs (e.g. Hallinan et al. 2006; Kao et al. 2023). Within our solar system, giant planets have auroral emission with signatures across the electromagnetic 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. Gibbs et al. 2022). 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 modeling leads us to conclude that a temperature inversion of ~300 K centered at 1-10 millibar replicates the feature. This represents an atmospheric temperature 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 processes 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. Helling et al. 2019).

We present the discovery of CWISE J203546.35-493611.0, a peculiar M8 companion to the M4.5 star APMPM J2036-4936 discovered through the citizen science project Backyard Worlds: Planet 9. Given CWISE J203546.35-493611.0's proper motion (\\(\\mu_{\\alpha}\\), \\(\\mu_{\\delta}\\)) = (\\(-\\)126\\(\\pm\\)22, \\(-\\)478\\(\\pm\\)23) and angular separation of 34.2\\(''\\) from APMPM 2036-4936, we calculate a chance alignment probability of \\(1.15 \\times 10^{-6}\\). Both stars in this system appear to be underluminous, and the spectrum obtained for CWISE J203546.35-493611.0 shows a triangular H band. Further study of this system is warranted to understand these peculiarities.

We present the discovery of CWISE J052306.42\\(-\\)015355.4, which was found as a faint, significant proper motion object (0.52 \\(\\pm\\) 0.08 arcsec yr\\(^{-1}\\)) using machine learning tools on the unWISE re-processing on time series images from the Wide-field Infrared Survey Explorer. Using the CatWISE2020 W1 and W2 magnitudes along with a \\(J-\\)band detection from the VISTA Hemisphere Survey, the location of CWISE J052306.42\\(-\\)015355.4 on the W1\\(-\\)W2 vs. \\(J-\\)W2 diagram best matches that of other known, or suspected, extreme T subdwarfs. As there is currently very little knowledge concerning extreme T subdwarfs we estimate a rough distance of \\(\\le\\) 68 pc, which results in a tangential velocity of \\(\\le\\) 167 km s\\(^{-1}\\), both of which are tentative. A measured parallax is greatly needed to test these values. We also estimate a metallicity of \\(-1.5 <\\) [M/H] \\(< -0.5\\) using theoretical predictions.

We have used data from the UKIRT Hemisphere Survey (UHS) to search for substellar members of the Hyades cluster. Our search recovered several known substellar Hyades members, and two known brown dwarfs that we suggest may be members based on a new kinematic analysis. We uncovered thirteen new substellar Hyades candidates, and obtained near-infrared follow-up spectroscopy of each with IRTF/SpeX. Six candidates with spectral types between M7 and L0 are ruled out as potential members based on their photometric distances (\\(\\gtrsim\\)100 pc). The remaining seven candidates, with spectral types between L5 and T4, are all potential Hyades members, with five showing strong membership probabilities based on BANYAN \\(\\Sigma\\) and a convergent point analysis. Distances and radial velocities are still needed to confirm Hyades membership. If confirmed, these would be some of the lowest mass free-floating members of the Hyades yet known, with masses as low as \\(\\sim\\)30 \\(M_{\\rm Jup}\\). An analysis of all known substellar Hyades candidates shows evidence that the full extent of the Hyades has yet to be probed for low-mass members, and more would likely be recovered with deeper photometric and astrometric investigations.

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 \\(\\sim\\)40 pc, CWISE J0146\\(-\\)0508AB has a projected separation of \\(\\sim\\)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 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)_{\\rm MKO}\\) color of 2.97\\(\\pm\\)0.03 mag and a \\(J_{\\rm MKO}-\\)W2 color of 4.93\\(\\pm\\)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 CH\\(_4\\) absorption 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 L8\\(\\gamma\\)-T0\\(\\gamma\\). We tentatively find that CWISE J0506\\(+\\)0738 is variable at 3-5 \\(\\mu\\)m based on multi-epoch 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 the \\(\\beta\\) Pic moving group. A future parallax measurement will help to establish a more definitive moving group membership for this unusual object.

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 two 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.