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1. The Symbiotic X-Ray Binary IGR J16194-2810: A Window on the Future Evolution of Wide Neutron Star Binaries From Gaia

   https://doi.org/10.1088/1538-3873/ad5dfd  

   Nagarajan, Pranav; El-Badry, Kareem; Lam, Casey; Reggiani, Henrique (July 2024, Publications of the Astronomical Society of the Pacific)

   Abstract We present optical follow-up of IGR J16194-2810, a hard X-ray source discovered by the INTEGRAL mission. The optical counterpart is a ∼500L_⊙red giant at a distance of 2.1 kpc. We measured 17 radial velocities (RVs) of the giant over a period of 271 days. Fitting these RVs with a Keplerian model, we find an orbital period ofP_orb= 192.73 ± 0.01 days and a companion mass functionf(M₂) = 0.365 ± 0.003M_⊙. We detect ellipsoidal variability with the same period in optical light curves from the ASAS-SN survey. Joint fitting of the RVs, light curves, and the broadband spectral energy distribution allows us to robustly constrain the masses of both components. We find a giant mass of $M_{\star }={0.99}_{-0.03}^{+0.02}{M}_{\odot }$and a companion mass of $M_2={1.23}_{-0.03}^{+0.05}{M}_{\odot }$, implying that the companion is a neutron star (NS). We recover a 4.06 hr period in the system’s TESS light curve, which we tentatively associate with the NS spin period. The giant does not yet fill its Roche lobe, suggesting that current mass transfer is primarily via winds. Modules for Experiments in Stellar Astrophysics evolutionary models predict that the giant will overflow its Roche lobe in 5–10 Myr, eventually forming a recycled pulsar + white dwarf binary with a ∼900 days period. IGR J16194-2810 provides a window on the future evolution of wide NS + main sequence binaries recently discovered via Gaia astrometry. As with those systems, the binary’s formation history is uncertain. Before the formation of the NS, it likely survived a common envelope episode with a donor-to-accretor mass ratio ≳10 and emerged in a wide orbit. The NS likely formed with a weak kick (v_kick≲ 50 km s⁻¹), as stronger kicks would have disrupted the orbit. 

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2. The X-Ray Luminous Type Ibn SN 2022ablq: Estimates of Preexplosion Mass Loss and Constraints on Precursor Emission

   https://doi.org/10.3847/1538-4357/ad8bc5  

   Pellegrino, C.; Modjaz, M.; Takei, Y.; Tsuna, D.; Newsome, M.; Pritchard, T.; Baer-Way, R.; Bostroem, K_A; Chandra, P.; Charalampopoulos, P.; et al (November 2024, The Astrophysical Journal)

   Abstract Type Ibn supernovae (SNe Ibn) are rare stellar explosions powered primarily by interaction between the SN ejecta and H-poor, He-rich material lost by their progenitor stars. Multiwavelength observations, particularly in the X-rays, of SNe Ibn constrain their poorly understood progenitor channels and mass-loss mechanisms. Here we present Swift X-ray, ultraviolet, and ground-based optical observations of the Type Ibn SN 2022ablq, only the second SN Ibn with X-ray detections to date. While similar to the prototypical Type Ibn SN 2006jc in the optical, SN 2022ablq is roughly an order of magnitude more luminous in the X-rays, reaching unabsorbed luminositiesL_X∼ 4 × 10⁴⁰erg s⁻¹between 0.2–10 keV. From these X-ray observations we infer time-varying mass-loss rates between 0.05 and 0.5M_⊙yr⁻¹peaking 0.5–2 yr before explosion. This complex mass-loss history and circumstellar environment disfavor steady-state winds as the primary progenitor mass-loss mechanism. We also search for precursor emission from alternative mass-loss mechanisms, such as eruptive outbursts, in forced photometry during the 2 yr before explosion. We find no statistically significant detections brighter thanM≈ −14—too shallow to rule out precursor events similar to those observed for other SNe Ibn. Finally, numerical models of the explosion of an ∼15M_⊙helium star that undergoes an eruptive outburst ≈1.8 yr before explosion are consistent with the observed bolometric light curve. We conclude that our observations disfavor a Wolf–Rayet star progenitor losing He-rich material via stellar winds and instead favor lower-mass progenitor models, including Roche-lobe overflow in helium stars with compact binary companions or stars that undergo eruptive outbursts during late-stage nucleosynthesis stages. 

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3. The Early Ultraviolet Light Curves of Type II Supernovae and the Radii of Their Progenitor Stars

   https://doi.org/10.3847/1538-4357/ad3de8  

   Irani, Ido; Morag, Jonathan; Gal-Yam, Avishay; Waxman, Eli; Schulze, Steve; Sollerman, Jesper; Hinds, K-Ryan; Perley, Daniel A; Chen, Ping; Strotjohann, Nora L; et al (July 2024, The Astrophysical Journal)

   Abstract We present a sample of 34 normal Type II supernovae (SNe II) detected with the Zwicky Transient Facility, with multiband UV light curves starting att≤ 4 days after explosion, and X-ray observations. We characterize the early UV-optical color, provide empirical host-extinction corrections, and show that thet> 2 day UV-optical colors and the blackbody evolution of the sample are consistent with shock cooling (SC) regardless of the presence of “flash ionization” features. We present a framework for fitting SC models that can reproduce the parameters of a set of multigroup simulations up to 20% in radius and velocity. Observations of 15 SNe II are well fit by models with breakout radii <10¹⁴cm. Eighteen SNe are typically more luminous, with observations att≥ 1 day that are better fit by a model with a large >10¹⁴cm breakout radius. However, these fits predict an early rise during the first day that is too slow. We suggest that these large-breakout events are explosions of stars with an inflated envelope or with confined circumstellar material (CSM). Using the X-ray data, we derive constraints on the extended (∼10¹⁵cm) CSM density independent of spectral modeling and find that most SN II progenitors lose $\dot{M}<{10}^{-4}{M}_{\odot }{\mathrm{yr}}^{-1}$up to a few years before explosion. We show that the overall observed breakout radius distribution is skewed to higher radii due to a luminosity bias. We argue that the ${66}_{-22}^{+11}\%$of red supergiants (RSGs) explode as SNe II with breakout radii consistent with the observed distribution of RSGs, with a tail extending to large radii, likely due to the presence of CSM. 

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4. Extreme Mass Loss in Low-mass Type Ib/c Supernova Progenitors

   https://doi.org/10.3847/2041-8213/ac9b3d  

   Wu, Samantha_C; Fuller, Jim (November 2022, The Astrophysical Journal Letters)

   Abstract Many core-collapse supernovae (SNe) with hydrogen-poor and low-mass ejecta, such as ultra-stripped SNe and type Ibn SNe, are observed to interact with dense circumstellar material (CSM). These events likely arise from the core collapse of helium stars that have been heavily stripped by a binary companion and have ejected significant mass during the last weeks to years of their lives. In helium star models run to days before core collapse we identify a range of helium core masses ≈2.5–3M_⊙whose envelopes expand substantially due to the helium shell burning while the core undergoes neon and oxygen burning. When modeled in binary systems, the rapid expansion of these helium stars induces extremely high rates of late-stage mass transfer ( $\dot{M}\gtrsim {10}^{-2}{M}_{\odot }{\mathrm{yr}}^{-1}$) beginning weeks to decades before core collapse. We consider two scenarios for producing CSM in these systems: either mass transfer remains stable and mass loss is driven from the system in the vicinity of the accreting companion, or mass transfer becomes unstable and causes a common envelope event (CEE) through which the helium envelope is unbound. The ensuing CSM properties are consistent with the CSM masses (∼10⁻²–1M_⊙) and radii (∼10¹³–10¹⁶cm) inferred for ultra-stripped SNe and several type Ibn SNe. Furthermore, systems that undergo a CEE could produce short-period neutron star binaries that merge in less than 100 Myr. 

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5. 1RXH J082623.6–505741: A New Long-period Cataclysmic Variable with an Evolved Donor and a Low Mass-transfer Rate

   https://doi.org/10.3847/1538-4357/ac7b25  

   Sokolovsky, Kirill V.; Strader, Jay; Swihart, Samuel J.; Aydi, Elias; Bahramian, Arash; Chomiuk, Laura; Heinke, Craig O.; Hughes, Allison K.; Li, Kwan-Lok; de Oliveira, Raimundo Lopes; et al (August 2022, The Astrophysical Journal)

   Abstract We report the discovery of 1RXH J082623.6−505741, a 10.4 hr orbital period compact binary. Modeling extensive optical photometry and spectroscopy reveals a ∼0.4M_⊙K-type secondary transferring mass through a low-state accretion disk to a nonmagnetic ∼0.8M_⊙white dwarf. The secondary is overluminous for its mass and dominates the optical spectra at all epochs and must be evolved to fill its Roche Lobe at this orbital period. The X-ray luminosityL_X∼ 1–2 × 10³²erg s⁻¹derived from both new XMM-Newton and archival observations, although high compared to most CVs, still only requires a modest accretion rate onto the white dwarf of $\dot{M}$∼ 3 × 10⁻¹¹to 3 × 10⁻¹⁰M_⊙yr⁻¹, lower than expected for a cataclysmic variable with an evolved secondary. No dwarf nova outbursts have yet been observed from the system, consistent with the low derived mass-transfer rate. Several other cataclysmic variables with similar orbital periods also show unexpectedly low mass-transfer rates, even though selection effects disfavor the discovery of binaries with these properties. This suggests the abundance and evolutionary state of long-period, low mass-transfer rate cataclysmic variables are worthy of additional attention. 

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