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1. ARMADA. II. Further Detections of Inner Companions to Intermediate-mass Binaries with Microarcsecond Astrometry at CHARA and VLTI

   https://doi.org/10.3847/1538-3881/ac8eae  

   Gardner, Tyler ; Monnier, John D. ; Fekel, Francis C. ; Le Bouquin, Jean-Baptiste ; Scovera, Adam ; Schaefer, Gail ; Kraus, Stefan ; Adams, Fred C. ; Anugu, Narsireddy ; Berger, Jean-Philippe ; et al ( October 2022 , The Astronomical Journal)

   Abstract We started a survey with CHARA/MIRC-X and VLTI/GRAVITY to search for low-mass companions orbiting individual components of intermediate-mass binary systems. With the incredible precision of these instruments, we can detect astrometric “wobbles” from companions down to a few tens of microarcseconds. This allows us to detect any previously unseen triple systems in our list of binaries. We present the orbits of 12 companions around early F- to B-type binaries, 9 of which are new detections and 3 of which are first astrometric detections of known radial velocity (RV) companions. The masses of these newly detected components range from 0.45 to 1.3 M ⊙ . Our orbits constrain these systems to a high astrometric precision, with median residuals to the orbital fit of 20–50 μ as in most cases. For seven of these systems we include newly obtained RV data, which help us to identify the system configuration and to solve for masses of individual components in some cases. Although additional RV measurements are needed to break degeneracy in the mutual inclination, we find that the majority of these inner triples are not well aligned with the wide binary orbit. This hints that higher-mass triples are more misaligned compared tomore »solar and lower-mass triples, though a thorough study of survey biases is needed. We show that the ARMADA survey is extremely successful at uncovering previously unseen companions in binaries. This method will be used in upcoming papers to constrain companion demographics in intermediate-mass binary systems down to the planetary-mass regime.« less
2. The MOSDEF survey: direct-method metallicities and ISM conditions at z ∼ 1.5–3.5

   https://doi.org/10.1093/mnras/stz3032  

   Sanders, Ryan L. ; Shapley, Alice E. ; Reddy, Naveen A. ; Kriek, Mariska ; Siana, Brian ; Coil, Alison L. ; Mobasher, Bahram ; Shivaei, Irene ; Freeman, William R. ; Azadi, Mojegan ; et al ( November 2019 , Monthly Notices of the Royal Astronomical Society)

   We present detections of [O iii] λ4363 and direct-method metallicities for star-forming galaxies at z = 1.7–3.6. We combine new measurements from the MOSFIRE Deep Evolution Field (MOSDEF) survey with literature sources to construct a sample of 18 galaxies with direct-method metallicities at z > 1, spanning 7.5 < 12+log(O/H) < 8.2 and log(M*/M⊙) = 7–10. We find that strong-line calibrations based on local analogues of high-redshift galaxies reliably reproduce the metallicity of the z > 1 sample on average. We construct the first mass–metallicity relation at z > 1 based purely on direct-method O/H, finding a slope that is consistent with strong-line results. Direct-method O/H evolves by ≲0.1 dex at fixed M* and star formation rate from z ∼ 0 to 2.2. We employ photoionization models to constrain the ionization parameter and ionizing spectrum in the high-redshift sample. Stellar models with supersolar O/Fe and binary evolution of massive stars are required to reproduce the observed strong-line ratios. We find that the z > 1 sample falls on the z ∼ 0 relation between ionization parameter and O/H, suggesting no evolution of this relation from z ∼ 0 to z ∼ 2. These results suggest that the offset of the strong-line ratios of this sample from local excitation sequences is driven primarilymore »by a harder ionizing spectrum at fixed nebular metallicity compared to what is typical at z ∼ 0, naturally explained by supersolar O/Fe at high redshift caused by rapid formation time-scales. Given the extreme nature of our z > 1 sample, the implications for representative z ∼ 2 galaxy samples at ∼1010 M⊙ are unclear, but similarities to z > 6 galaxies suggest that these conclusions can be extended to galaxies in the epoch of reionization.

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3. Hubble Space Telescope Observations of GW170817: Complete Light Curves and the Properties of the Galaxy Merger of NGC 4993

   https://doi.org/10.3847/1538-4357/ac3e59  

   Kilpatrick, Charles D. ; Fong, Wen-fai ; Blanchard, Peter K. ; Leja, Joel ; Nugent, Anya E. ; Palmese, Antonella ; Paterson, Kerry ; Starkenburg, Tjitske ; Alexander, Kate D. ; Berger, Edo ; et al ( February 2022 , The Astrophysical Journal)

   Abstract We present the complete set of Hubble Space Telescope imaging of the binary neutron star merger GW170817 and its optical counterpart AT 2017gfo. Including deep template imaging in F814W, F110W, F140W, and F160W at 3.4 yr post-merger, we reanalyze the full light curve of AT 2017gfo across 12 bands from 5 to 1273 rest-frame days after merger. We obtain four new detections of the short γ -ray burst 170817A afterglow from 109 to 170 rest-frame days post-merger. These detections are consistent with the previously observed β = −0.6 spectral index in the afterglow light curve with no evidence for spectral evolution. We also analyze our limits in the context of kilonova afterglow or IR dust echo emission but find that our limits are not constraining for these models. We use the new data to construct deep optical and IR stacks, reaching limits of M = −6.3 to −4.6 mag, to analyze the local environment around AT 2017gfo and low surface brightness features in its host galaxy NGC 4993. We rule out the presence of any globular cluster at the position of AT 2017gfo to 2.3 × 10 4 L ⊙ , including those with the reddest V − Hmore »colors. Finally, we analyze the substructure of NGC 4993 in deep residual imaging and find shell features that extend up to 71.″8 (14.2 kpc) from NGC 4993. The shells have a cumulative stellar mass of 6.3 × 10 8 M ⊙ , roughly 2% of NGC 4993, and mass-weighted ages of >3 Gyr. We conclude that it was unlikely that the GW170817 progenitor system formed in the galaxy merger.« less
4. Bridging the Gap: Categorizing Gravitational-wave Events at the Transition between Neutron Stars and Black Holes

   https://doi.org/10.3847/1538-4357/ac5f03  

   Farah, Amanda ; Fishbach, Maya ; Essick, Reed ; Holz, Daniel E. ; Galaudage, Shanika ( May 2022 , The Astrophysical Journal)

   Abstract We search for features in the mass distribution of detected compact binary coalescences which signify the transition between neutron stars (NSs) and black holes (BHs). We analyze all gravitational-wave (GW) detections by the LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration (LVK) made through the end of the first half of the third observing run, and find clear evidence for two different populations of compact objects based solely on GW data. We confidently (99.3%) find a steepening relative to a single power law describing NSs and low-mass BHs below 2.4 − 0.5 + 0.5 M ⊙ , which is consistent with many predictions for the maximum NS mass. We find suggestions of the purported lower mass gap between the most massive NSs and the least massive BHs, but are unable to conclusively resolve it with current data. If it exists, we find the lower mass gap’s edges to lie at 2.2 − 0.5 + 0.7 M ⊙ and 6.0 − 1.4 + 2.4 M ⊙ . We reexamine events that have been deemed “exceptional” by the LVK collaborations in the context of these features. We analyze GW190814 self-consistently in the context of the full population of compactmore »binaries, finding support for its secondary to be either a NS or a lower mass gap object, consistent with previous claims. Our models are the first to accommodate this event, which is an outlier with respect to the binary BH population. We find that GW200105 and GW200115 probe the edges of, and may have components within, the lower mass gap. As future data improve global population models, the classification of these events will also improve.« less
5. BEBOP III. Observations and an independent mass measurement of Kepler-16 (AB) b – the first circumbinary planet detected with radial velocities

   https://doi.org/10.1093/mnras/stab3712  

   Triaud, Amaury H. M. J. ; Standing, Matthew R. ; Heidari, Neda ; Martin, David V. ; Boisse, Isabelle ; Santerne, Alexandre ; Correia, Alexandre C. M. ; Acuña, Lorena ; Battley, Matthew ; Bonfils, Xavier ; et al ( February 2022 , Monthly Notices of the Royal Astronomical Society)

   The radial velocity method is amongst the most robust and most established means of detecting exoplanets. Yet, it has so far failed to detect circumbinary planets despite their relatively high occurrence rates. Here, we report velocimetric measurements of Kepler-16A, obtained with the SOPHIE spectrograph, at the Observatoire de Haute-Provence’s 193cm telescope, collected during the BEBOP survey for circumbinary planets. Our measurements mark the first radial velocity detection of a circumbinary planet, independently determining the mass of Kepler-16 (AB) b to be $0.313 \pm 0.039\, {\rm M}_{\rm Jup}$, a value in agreement with eclipse timing variations. Our observations demonstrate the capability to achieve photon-noise precision and accuracy on single-lined binaries, with our final precision reaching $\rm 1.5~m\, s^{-1}$ on the binary and planetary signals. Our analysis paves the way for more circumbinary planet detections using radial velocities which will increase the relatively small sample of currently known systems to statistically relevant numbers, using a method that also provides weaker detection biases. Our data also contain a long-term radial velocity signal, which we associate with the magnetic cycle of the primary star.