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1. The Seoul National University AGN Monitoring Project. IV. Hα Reverberation Mapping of Six AGNs and the Hα Size–Luminosity Relation

   https://doi.org/10.3847/1538-4357/ace1e5  

   Cho, Hojin ; Woo, Jong-Hak ; Wang, Shu ; Son, Donghoon ; Shin, Jaejin ; Rakshit, Suvendu ; Barth, Aaron J. ; Bennert, Vardha N. ; Gallo, Elena ; Hodges-Kluck, Edmund ; et al ( August 2023 , The Astrophysical Journal)

   The broad-line region (BLR) size–luminosity relation has paramount importance for estimating the mass of black holes in active galactic nuclei (AGNs). Traditionally, the size of the HβBLR is often estimated from the optical continuum luminosity at 5100 Å, while the size of the HαBLR and its correlation with the luminosity is much less constrained. As a part of the Seoul National University AGN Monitoring Project, which provides 6 yr photometric and spectroscopic monitoring data, we present our measurements of the Hαlags of high-luminosity AGNs. Combined with the measurements for 42 AGNs from the literature, we derive the size–luminosity relations of the HαBLR against the broad Hαand 5100 Å continuum luminosities. We find the slope of the relations to be 0.61 ± 0.04 and 0.59 ± 0.04, respectively, which are consistent with the Hβsize–luminosity relation. Moreover, we find a linear relation between the 5100 Å continuum luminosity and the broad Hαluminosity across 7 orders of magnitude. Using these results, we propose a new virial mass estimator based on the Hαbroad emission line, finding that the previous mass estimates based on scaling relations in the literature are overestimated by up to 0.7 dex at masses lower than 10⁷M_⊙.

    

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2. The Panchromatic Hubble Andromeda Treasury: Triangulum Extended Region (PHATTER). III. The Mass Function of Young Stellar Clusters in M33

   https://doi.org/10.3847/1538-4357/ac51cf  

   Wainer, Tobin M. ; Johnson, L. Clifton ; Seth, Anil C. ; TorresVillanueva, Estephani E. ; Dalcanton, Julianne J. ; Durbin, Meredith J. ; Dolphin, Andrew ; Weisz, Daniel R. ; Williams, Benjamin F. ( March 2022 , The Astrophysical Journal)

   We measure the star cluster mass function (CMF) for the Local Group galaxy M33. We use the catalog of stellar clusters selected from the Panchromatic Hubble Andromeda Treasury: Triangulum Extended Region survey. We analyze 711 clusters in M33 with$7.0<\log (\mathrm{Age}/\mathrm{yr})<8.5$, and log(M/M_⊙) > 3.0 as determined from color–magnitude diagram fits to individual stars. The M33 CMF is best described by a Schechter function with power-law slopeα= −${2.06}_{-0.13}^{+0.14}$, and truncation mass log(M_c/M_⊙)$={4.24}_{-0.13}^{+0.16}$. The data show strong evidence for a high-mass truncation, thus strongly favoring a Schechter function fit over a pure power law. M33's truncation mass is consistent with the previously identified linear trend betweenM_c, and star formation rate surface density, Σ_SFR. We also explore the effect that individual cluster mass uncertainties have on derived mass function parameters, and find evidence to suggest that large cluster mass uncertainties have the potential to bias the truncation mass of fitted mass functions at the 1σlevel.

    

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3. A Linear Relation between the Color Stretch s BV and the Rising Color Slope s0*(B−V) of Type Ia Supernovae

   https://doi.org/10.3847/1538-4357/acc404  

   Chen, Ping ; Dong, Subo ; Ashall, Chris ; Benetti, S. ; Bersier, D. ; Bose, S. ; Brimacombe, Joseph ; Brink, Thomas G. ; Buckley, David A. H. ; Cappellaro, Enrico ; et al ( April 2023 , The Astrophysical Journal)

   Using data from the Complete Nearby (redshiftz_host< 0.02) sample of Type Ia Supernovae (CNIa0.02), we find a linear relation between two parameters derived from theB−Vcolor curves of Type Ia supernovae: thecolor stretchs_BVand the rising color slope$s_0^{*}(B-V)$after the peak, and this relation applies to the full range ofs_BV. Thes_BVparameter is known to be tightly correlated with the peak luminosity, especially forfast decliners(dim Type Ia supernovae), and the luminosity correlation withs_BVis markedly better than with the classic light-curve width parameters such as Δm₁₅(B). Thus, our new linear relation can be used to infer peak luminosity from$s_0^{*}$. Unlikes_BV(or Δm₁₅(B)), the measurement of$s_0^{*}(B-V)$does not rely on a well-determined time of light-curve peak or color maximum, making it less demanding on the light-curve coverage than past approaches.

    

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4. Using the Gaia Excess Uncertainty as a Proxy for Stellar Variability and Age

   https://doi.org/10.3847/1538-4357/ace044  

   Barber, Madyson G. ; Mann, Andrew W. ( August 2023 , The Astrophysical Journal)

   Stars are known to be more active when they are young, resulting in a strong correlation between age and photometric variability. The amplitude variation between stars of a given age is large, but the age–variability relation becomes strong over large groups of stars. We explore this relation using the excess photometric uncertainty in Gaia photometry (Var_G,Var_BP, andVar_RP) as a proxy for variability. The metrics follow a Skumanich-like relation, scaling as ≃t^−0.4. By calibrating against a set of associations with known ages, we show how theVar of population members can predict group ages within 10%–20% for associations younger than ≃2.5 Gyr. In practice, age uncertainties are larger, primarily due to the finite group size. The index is most useful at the youngest ages (<100 Myr), where the uncertainties are comparable to or better than those derived from a color–magnitude diagram (CMD). The index is also widely available, easy to calculate, and can be used at intermediate ages where there are few or no pre- or post-main-sequence stars. We further show howVar can be used to find new associations and test if a group of comoving stars is a real coeval population. We apply our methods to Theia groups within 350 pc and find ≳90% are inconsistent with drawing stars from the field and ≃80% have variability ages consistent with those derived from the CMD. Our findings suggest the great majority of these groups contain real populations.

    

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5. Surf Zone Waves at the Onset of Breaking: 2. Predicting Breaking and Breaker Type

   https://doi.org/10.1029/2020JC016935  

   Carini, Roxanne J. ; Chickadel, C. Chris ; Jessup, Andrew T. ( April 2021 , Journal of Geophysical Research: Oceans)

   This is the second of a two‐part series concerning remote observation and wave‐by‐wave analysis of the onset of breaking for spilling and plunging waves in the surf zone. Nearshore phase‐averaged and phase‐resolving wave models parameterize and directly simulate wave breaking and require realistic critical values of key wave parameters, such as the depth‐limited breaking indexγ, steepness, or phase speed to initialize wave breaking. Using LIDAR line‐scans and infrared imagery, we observe over 1,600 breaking waves at the US Army Corps of Engineers Field Research Facility (FRF) in Duck, NC, and examine these parameters on a wave‐by‐wave basis at the onset of breaking for 413 spilling and 111 plunging waves. We find thatγis maximum near the onset of breaking at values consistent with those previously observed at the FRF, but thatγfor plunging waves (0.73 ≤ γ_P ≤ 0.81) is greater thanγfor spilling waves (0.63 ≤ γ_S ≤ 0.71). Direct estimates of wave face slope are maximum at the onset of breaking, approximately 22° for spilling and 30° for plunging waves. Using the relationship betweenγand wave face slope, we develop a threshold for the onset of breaking that is a linear function of the two parameters. Wave face slope andγare further used together to quantify whether a spilling‐ or plunging‐type breaker is more likely. We test the Miche steepness limit on our depth‐limited breaking data and find it correctly predicts only 10% of the plunging breakers and none of the spilling breakers in the surf zone.

    

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