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1. Spindown of Pulsars Interacting with Companion Winds: The Impact of Magnetospheric Compression

   https://doi.org/10.3847/1538-4357/ad6840  

   Zhong, Yici; Spitkovsky, Anatoly; Mahlmann, Jens_F; Hakobyan, Hayk (September 2024, The Astrophysical Journal)

   Abstract Pulsars in binary systems with strong companion winds can have the magnetopause separating their magnetosphere from the wind located well within their light cylinder. This bow-like enclosure effectively creates a waveguide that confines the pulsar’s electromagnetic fields and can significantly alter its spindown. In this paper, we study the spindown of compressed pulsar magnetospheres in such systems. We parameterize the confinement as the ratio between the equatorial position of the magnetopause (or standoff distance)R_mand the pulsar’s light cylinderR_LC. Using particle-in-cell simulations, we quantify the pulsar spindown for a range of compressions,R_m/R_LC= 1/3–1, and inclination angles,χ= 0°…90°, between magnetic and rotation axes. Our strongly confined models (R_m/R_LC= 1/3) show two distinct limits. Forχ= 0°, the spindown of a compressed pulsar magnetosphere is enhanced by approximately a factor of three compared to an isolated pulsar due to the increased number of open magnetic field lines. Conversely, forχ= 90°, the compressed pulsar spins down at less than 40% of the rate of an isolated reference pulsar due to the mismatch between the pulsar wind stripe wavelength and the waveguide size. We apply our analysis to the 2.77 s oblique rotator (χ= 60°) in the double-pulsar system PSR J0737-3039. With the numerically derived spindown estimate, we constrain its surface magnetic field toB_*≈ (7.3 ± 0.2) × 10¹¹G. We discuss the time modulation of its period derivative, the effects of compression on its braking index, and implications for the radio eclipse in PSR J0737-3039. 

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2. BERM: a Belowground Ecosystem Resiliency Model for estimating Spartina alterniflora belowground biomass

   https://doi.org/10.1111/nph.17607  

   O’Connell, Jessica L.; Mishra, Deepak R.; Alber, Merryl; Byrd, Kristin B. (August 2021, New Phytologist)

   Summary Spatiotemporal patterns ofSpartina alterniflorabelowground biomass (BGB) are important for evaluating salt marsh resiliency. To solve this, we created the BERM (Belowground Ecosystem Resiliency Model), which estimates monthly BGB (30‐m spatial resolution) from freely available data such as Landsat‐8 and Daymet climate summaries.Our modeling framework relied on extreme gradient boosting, and used field observations from four Georgia salt marshes as ground‐truth data. Model predictors included estimated tidal inundation, elevation, leaf area index, foliar nitrogen, chlorophyll, surface temperature, phenology, and climate data. The final model included 33 variables, and the most important variables were elevation, vapor pressure from the previous four months, Normalized Difference Vegetation Index (NDVI) from the previous five months, and inundation.Root mean squared error for BGB from testing data was 313 g m⁻²(11% of the field data range), explained variance (R²) was 0.62–0.77. Testing data results were unbiased across BGB values and were positively correlated with ground‐truth data across all sites and years (r = 0.56–0.82 and 0.45–0.95, respectively).BERM can estimate BGB withinSpartina alterniflorasalt marshes where environmental parameters are within the training data range, and can be readily extended through a reproducible workflow. This provides a powerful approach for evaluating spatiotemporal BGB and associated ecosystem function. 

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3. Ultradiffuse Galaxies (UDGs) with Hyper Suprime-Cam. I. Revised Catalog of Coma Cluster UDGs*

   https://doi.org/10.3847/1538-4365/acd3e7  

   Bautista, Jose Miguel G.; Koda, Jin; Yagi, Masafumi; Komiyama, Yutaka; Yamanoi, Hitomi (July 2023, The Astrophysical Journal Supplement Series)

   Abstract This is the first in a series of papers on the properties of ultradiffuse galaxies (UDGs) in clusters of galaxies. We present an updated catalog of UDGs in the Coma Cluster usingg- andr-band images obtained with Hyper Suprime-Cam (HSC) of the Subaru telescope. We develop a method to find UDGs even in the presence of contaminating objects, such as halos and background galaxies. This study expands upon our previous works that covered about half the area of the Coma Cluster. The HSC observations covered the whole Coma Cluster up to the virial radius and beyond (an area twice as large as the previous studies) and doubled the numbers of UDGs (r_{eff, r}≥ 1.5 kpc) and sub-UDGs (1.0 ≤r_{eff, r}< 1.5 kpc) to 774 and 729, respectively. The new UDGs show internal properties consistent with those of previous studies (e.g., a Sérsic index of approximately 1), and are distributed across the cluster, with a concentration around the cluster center. The whole cluster coverage clearly revealed an excess of their distribution toward the east to southwest direction along the cluster center, where Coma connects to other large-scale structure, and where a known substructure exists (the NGC 4839 subgroup). The alignment of the UDG distribution along the large-scale structure around Coma supports the interpretation that most of them lie at the distance of the Coma Cluster and the NGC 4839 subgroup. 

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4. The Factory and the Beehive. V. Chromospheric and Coronal Activity and Its Dependence on Rotation in Praesepe and the Hyades

   https://doi.org/10.3847/1538-4357/ad117e  

   Núñez, Alejandro; Agüeros, Marcel_A; Curtis, Jason_L; Covey, Kevin_R; Douglas, Stephanie_T; Chu, Sabine_R; DeLaurentiis, Stanislav; Wang, Minzhi_Luna; Drake, Jeremy_J (February 2024, The Astrophysical Journal)

   Abstract Low-mass (≲1.2M_⊙) main-sequence stars lose angular momentum over time, leading to a decrease in their magnetic activity. The details of this rotation–activity relation remain poorly understood, however. Using observations of members of the ≈700 Myr old Praesepe and Hyades open clusters, we aim to characterize the rotation–activity relation for different tracers of activity at this age. To complement published data, we obtained new optical spectra for 250 Praesepe stars, new X-ray detections for 10, and new rotation periods for 28. These numbers for Hyads are 131, 23, and 137, respectively. The latter increases the number of Hyads with periods by 50%. We used these data to measure the fractional Hαand X-ray luminosities,L_Hα/L_bolandL_X/L_bol, and to calculate Rossby numbersR_o. We found that at ≈700 Myr almost all M dwarfs exhibit Hαemission, with binaries having the same overall color–Hαequivalent width distribution as single stars. In theR_o–L_Hα/L_bolplane, unsaturated single stars follow a power law with indexβ= −5.9 ± 0.8 forR_o> 0.3. In theR_o–L_X/L_bolplane, we see evidence for supersaturation for single stars withR_o≲ 0.01, following a power law with index ${\beta }_{\sup }={0.5}_{-0.1}^{+0.2}$, supporting the hypothesis that the coronae of these stars are being centrifugally stripped. We found that the criticalR_ovalue at which activity saturates is smaller forL_X/L_bolthan forL_Hα/L_bol. Finally, we observed an almost 1:1 relation betweenL_Hα/L_bolandL_X/L_bol, suggesting that both the corona and the chromosphere experience similar magnetic heating. 

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5. Spectral Indices of Vegetation Condition and Soil Water Content Reflect Controls on CH ₄ and CO ₂ Exchange in Sphagnum ‐Dominated Northern Peatlands

   https://doi.org/10.1029/2021JG006486  

   Tucker, Colin; O’Neill, Ally; Meingast, Karl; Bourgeau‐Chavez, Laura; Lilleskov, Erik; Kane, Evan S. (June 2022, Journal of Geophysical Research: Biogeosciences)

   Abstract Northern peatlands play an important role in the global C cycle due to their large C stocks and high potential methane (CH₄) emissions. The CH₄and CO₂cycles of these systems are closely linked to hydrology, with water table level regulating the balance of oxic and anoxic conditions and the water content ofSphagnummosses that dominate primary production. Previous work has demonstrated that hyperspectral indices well‐suited to the detection of altered hydrology inSphagnumpeatlands are also highly correlated with GPP. However, little work has been done to extend these findings to CH₄effluxes. In this study, we evaluate the utility of four hyperspectral indices, two reflecting vegetation photosynthetic function (chlorophyll index (CI); normalized difference vegetation index) and two reflecting water content (wetness index (WI); floating water band index), for detecting effects of altered water table, precipitation, and vegetation community on CH₄and CO₂exchange in two peatland mesocosm studies. We found that CI is a good predictor of net CO₂exchange, and that it captured both drought and vegetation effects consistently across a broad range of vegetation treatments. Further, we demonstrate for the first time that WI combined with CI explained a significant percentage of CH₄efflux (R² = 0.32–0.57). Our results indicate that CI and WI together may be effective tools for detecting effects of altered hydrology and vegetation on northernSphagnum‐peatland CH₄and CO₂emissions, with implications for detecting and modeling changes in emissions of greenhouse gases at scales ranging from the ecosystem to the Earth system. 

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