Keywords

The study reports photometric and spectroscopic observations of two recently recognized contact binary systems. Both systems show total eclipses and analysis of the light curves indicates both have very low mass ratios of less than 0.3. We derive absolute parameters from color and distance based calibrations and show that, although both have low mass ratios, they are likely to be in a stable orbit and unlikely to merge. In other respects, both systems have characteristics similar to other contact binaries with the secondary larger and brighter than their main sequence counterparts and we also find that the secondary is considerably denser than the primary in both systems.

I present the effervescent zone model to account for the compact dense circumstellar material (CSM) around the progenitor of the core collapse supernova (CCSN) SN 2023ixf. The effervescent zone is composed of bound dense clumps that are lifted by stellar pulsation and envelope convection to distances of ≈tens × au, and then fall back. The dense clumps provide most of the compact CSM mass and exist alongside the regular (escaping) wind. I crudely estimate that for a compact CSM within R_CSM ≈ 30 au that contains M_CSM ≈ 0.01 M_⊙, the density of each clump is k_b ≳ 3000 times the density of the regular wind at the same radius and that the total volume filling factor of the clumps is several percent. The clumps might cover only a small fraction of the CCSN photosphere in the first days post-explosion, accounting for the lack of strong narrow absorption lines. The long-lived effervescent zone is compatible with no evidence for outbursts in the years prior to the SN 2023ixf explosion and the large-amplitude pulsations of its progenitor, and it is an alternative to the CSM scenario of several-years-long high mass loss rate wind.

We conduct one-dimensional stellar evolution simulations of red supergiant (RSG) stars that mimic common envelope evolution (CEE) and find that the inner boundary of the envelope convective zone moves into the initial envelope radiative zone. The envelope convection practically disappears only when the RSG radius decreases by about an order of magnitude or more. The implication is that one cannot split the CEE into one stage during which the companion spirals-in inside the envelope convective zone and removes it, and a second slower phase when the companion orbits the initial envelope radiative zone and a stable mass transfer takes place. At best, this might take place when the orbital separation is about several solar radii. However, by that time other processes become important. We conclude that as of yet, the commonly used alpha-formalism that is based on energy considerations is the best phenomenological formalism.

In this study, we determined the physical parameters of W UMa type contact binaries and their stability of mass transfer with different stellar mass ranges over a broad space by applying the basic dynamical evolution equations of the W UMa type contact binaries using accretor and donor masses between 0.079 and 2.79 M_⊙. In these systems, we have studied the three subclasses of W UMa systems of A-, B- and W-type contact binaries using the initial and final mass ranges and we investigated different stellar and orbital parameters for the subclasses of W UMa systems. We examined the stability of the W UMa type contact binaries using the orbital parameters such as critical mass ratio, Roche lobe radius of the donor star and mass ratio of these systems. Thus, we computed the observed and calculated physical parameters of A-, B- and W-type W UMa systems. Moreover, we determined the combined and color temperatures to classify the three subclasses of the systems. Also, we presented the result of the internal stellar structure and evolution of W UMa type contact binaries by using the polytropic model.

In this paper, we investigate the orbital and stellar parameters of low- and intermediate-mass close binary systems. We use models, presented in the catalog of Han et al. and calculate parameters of accretors. We also construct distributions of systems along luminosity, semimajor axis and angular momentum, and make some conclusions on their evolution with time. We compare the results with observational data and it shows a good agreement. The set of theoretical models published quite adequately describes the observational data and, consequently, can be used to determine the evolutionary path of specific close binary systems, their initial parameter values and final stages.

We present detailed observations of ZTF18abukavn (SN2018gep), discovered in high-cadence data from the Zwicky Transient Facility as a rapidly rising (1.4 ± 0.1 mag hr⁻¹) and luminous (${M}_{g,\mathrm{peak}}=-20$ mag) transient. It is spectroscopically classified as a broad-lined stripped-envelope supernova (Ic-BL SN). The high peak luminosity (${L}_{\mathrm{bol}}\gtrsim 3\times {10}^{44}\,\mathrm{erg}\,{{\rm{s}}}^{-1}$), the short rise time (${t}_{\mathrm{rise}}=3\,\mathrm{days}$ in g band), and the blue colors at peak ($g\mbox{--}r\sim -0.4$) all resemble the high-redshift Ic-BL iPTF16asu, as well as several other unclassified fast transients. The early discovery of SN2018gep (within an hour of shock breakout) enabled an intensive spectroscopic campaign, including the highest-temperature (${T}_{\mathrm{eff}}\gtrsim {\rm{40,000}}\,{\rm{K}}$) spectra of a stripped-envelope SN. A retrospective search revealed luminous (${M}_{g}\sim {M}_{r}\approx -14$ mag) emission in the days to weeks before explosion, the first definitive detection of precursor emission for a Ic-BL. We find a limit on the isotropic gamma-ray energy release ${E}_{\gamma ,\mathrm{iso}}\lt 4.9\times {10}^{48}\,\mathrm{erg}$, a limit on X-ray emission ${L}_{{\rm{X}}}\lt {10}^{40}\,\mathrm{erg}\,{{\rm{s}}}^{-1}$, and a limit on radio emission $\nu {L}_{\nu }\lesssim {10}^{37}\,\mathrm{erg}\,{{\rm{s}}}^{-1}$. Taken together, we find that the early ($\lt 10\,\mathrm{days}$) data are best explained by shock breakout in a massive shell of dense circumstellar material (0.02 ${M}_{\odot }$) at large radii ($3\times {10}^{14}\,\mathrm{cm}$) that was ejected in eruptive pre-explosion mass-loss episodes. The late-time ($\gt 10\,\mathrm{days}$) light curve requires an additional energy source, which could be the radioactive decay of Ni-56.

Winds from asymptotic giant branch (AGB) stars not only provide mass and energy return, but also produce dust grains in massive elliptical galaxies. Due to the fast stellar velocity, the wind is thought to form a comet-like tail, similar to Mira in the Local Bubble. Many massive elliptical galaxies and cluster centrals host extended dusty cold filaments. We carry out both analytical and numerical studies of the interaction between an AGB wind and the surrounding hot gas. We find that the cooling time of the tail is inversely proportional to the ambient pressure. In the absence of cooling, or in low-pressure environments (e.g., the outskirts of elliptical galaxies), AGB winds are quickly mixed into the hot gas, and all the AGB winds have a similar appearance and head-to-tail ratio. In high-pressure environments, such as the Local Bubble and the central regions of massive elliptical galaxies, some of the gas in the mixing layer between the stellar wind and the surrounding hot gas can cool efficiently and cause the tail to become longer. Our simulated tail of Mira itself has a similar length and velocity to that observed, and appears similar to the simulated AGB tail in the central regions of massive galaxies. While confirmation awaits future studies, we speculate that instead of thermal instability, the induced condensation at the mixing layer of AGB winds may be the origin of cold filaments in massive galaxies and galaxy clusters. This naturally explains the existence of dust and polycyclic aromatic hydrocarbon in the filaments.

Recent high-cadence transient surveys and rapid follow-up observations indicate that some massive stars may dynamically lose their own mass within decades before supernovae (SNe). Such a mass-loss forms "confined" circumstellar medium (CSM); a high-density material distributed only within a small radius (≲10¹⁵ cm with the mass-loss rate of 0.01 ∼ 10⁻⁴ M_⊙ yr⁻¹). While the SN shock should trigger particle acceleration and magnetic field amplification in the "confined" CSM, synchrotron emission may be masked in centimeter wavelengths due to free–free absorption; the millimeter range can, however, be a potential new window. We investigate the time evolution of synchrotron radiation from the system of a red supergiant surrounded by the "confined" CSM, relevant to typical Type II-P SNe. We show that synchrotron millimeter emission is generally detectable, and that the signal can be used as a sensitive tracer of the nature of the "confined" CSM; it traces different CSM density parameter space than in the optical. Furthermore, our simulations show that the "confined" CSM efficiently produces secondary electrons and positrons through proton inelastic collisions, which can become main contributors to the synchrotron emission in several ten days since the SN. We predict that the synchrotron emission is detectable by ALMA, and suggest that it will provide a robust evidence of the existence of the "confined" CSM.

Aluminium-26 is a short-lived radionuclide with a half-life of 0.72 Myr, which is observed today in the Galaxy via γ-ray spectroscopy and is inferred to have been present in the early solar system via analysis of meteorites. Massive stars are considered the main contributors of ²⁶Al. Although most massive stars are found in binary systems, the effect, however, of binary interactions on the ²⁶Al yields has not been investigated since Braun & Langer. Here we aim to fill this gap. We have used the MESA stellar evolution code to compute massive (10 M_⊙ ≤ M ≤ 80 M_⊙) nonrotating single and binary stars of solar metallicity (Z = 0.014). We computed the wind yields for the single stars and for the binary systems where mass transfer plays a major role. Depending on the initial mass of the primary star and orbital period, the ²⁶Al yield can either increase or decrease in a binary system. For binary systems with primary masses up to ∼35–40 M_⊙, the yield can increase significantly, especially at the lower mass end, while above ∼45 M_⊙ the yield becomes similar to the single-star yield or even decreases. Our preliminary results show that compared to supernova explosions, the contribution of mass loss in binary systems to the total ²⁶Al abundance produced by a stellar population is minor. On the other hand, if massive star mass loss is the origin of ²⁶Al in the early solar system, our results will have significant implications for the identification of the potential stellar, or stellar population, source.

We report our observations of HSC16aayt (SN 2016jiu), which was discovered by the Subaru/Hyper Suprime-Cam (HSC) transient survey conducted as part of the Subaru Strategic Program. It shows very slow photometric evolution and its rise time is more than 100 days. The optical magnitude change in 400 days remains within 0.6 mag. Spectra of HSC16aayt show a strong narrow emission line and we classify it as a Type IIn supernova. The redshift of HSC16aayt is 0.6814 ± 0.0002 from the spectra. Its host galaxy center is at 5 kpc from the supernova location and HSC16aayt might be another example of isolated Type IIn supernovae, although the possible existence of underlying star-forming activity of the host galaxy at the supernova location is not excluded.