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Binary systems are important probes of the origin of stars with peculiar chemical features through the interactions between two stars. We have studied the evolution of a metal-free massive binary after the collision of the supernova ejecta with a low-mass companion. Theoretical models are developed using simulations of binaries after core-collapse supernovae using stellar evolution models, supernova ejecta models, and hydrodynamic simulations of the system consisting of supernova ejecta and companion stars. We find that these first star survivors will be observed as metal-rich halo stars in our Galaxy. In combination with the theoretical research, we looked for observational counterparts in the Galactic halo using the observational database where elemental abundances and kinematic data are available. We have also searched for the progenitor binary systems based on radial velocity monitoring. We report the current status of the search for massive binaries in the solar vicinity. The proposed scenario demands a new channel of star formation in the early universe and is a supplementary scenario for the origin of the known metal-poor stars.

We have performed the near-infrared photometric monitoring observations of two TeV gamma-ray binaries with O-stars (LS 5039 and 1FGL J1018.6−5856), using IRSF/SIRIUS at SAAO, in order to study the stellar parameters and their perturbations caused by the binary interactions. The whole orbital phase was observed multiple times and no significant variabilities including orbital modulations were detected for both targets. Assuming that the two systems are colliding wind binaries, we estimate the amplitude of flux variation caused by the difference in the optical depth of O-star wind at inferior conjunction, where the star is seen through the cavity created by pulsar wind, and other orbital phases without pulsar-wind intervention. The derived amplitude is <0.001 mag, which is about two orders of magnitude smaller than the observed upper limit. Also using the upper limits of the near-infrared variability, we for the first time obtain the upper limit of the dust formation rate resulting from wind–wind collision in O-star gamma-ray binaries. [ABSTRACT FROM AUTHOR]

γ Cas analog sources are a subset of Be stars that emit intense and hard X-ray emission. Two competing ideas for their X-ray production mechanism are (a) the magnetic activities of the Be star and its disk and (b) the accretion from the Be star to an unidentified compact object. Among such sources, π Aqr plays a pivotal role as it is one of the only two spectroscopic binaries observed for many orbital cycles and one of the three sources with X-ray brightness sufficient for detailed X-ray spectroscopy. Bjorkman et al. (2002, ApJ, 573, 812) estimated the secondary mass >2.0  M ⊙ with optical spectroscopy, which would argue against the compact object being a white dwarf (WD). However, their dynamical mass solution is inconsistent with an evolutionary solution and their radial velocity measurement is inconsistent with later work by Nazé et al. (2019, A&A, 632, A23). We revisit this issue by adding a new data set with the NuSTAR X-ray observatory and the HIDES échelle spectrograph. We found that the radial velocity amplitude is consistent with Nazé et al. (2019, A&A, 632, A23), which is only half of that claimed by Bjorkman et al. (2002, ApJ, 573, 812). Fixing the radial velocity amplitude of the primary, the secondary mass is estimated as <1.4  M ⊙ over an assumed range of the primary mass and the inclination angle. We further constrained the inclination angle and the secondary mass independently by fitting the X-ray spectra with a non-magnetic or magnetic accreting WD model under the assumption that the secondary is indeed a WD. The two results match well. We thus argue that the possibility of the secondary being a WD should not be excluded for π Aqr. [ABSTRACT FROM AUTHOR]

The binary of the pulsar PSR B1259−63 and the Be star LS 2883 has been observed at the 2010 and 2014 periastron passages in the near-infrared (NIR) bands using the IRSF/SIRIUS and SIRPOL. The light curves in the J -, H -, and K s-bands are almost identical in these periastron passages. A flare starts no later than 10 days before periastron and the maximum brightening of about 0.1 mag is observed 12–17 days after periastron. The rising part of the light curve is steeper and reaches a peak slightly earlier in the K s-band than in the other bands, thus a characteristic track appears on the NIR color–magnitude diagram. The time lag between the NIR light curves indicates that the variation in the Be circumstellar disk first occurs in an outer region. We propose that the initial rapid contraction followed by the gradual expansion of the disk is evoked by the rapidly changing tidal torque around periastron and the resultant change of the optically thick area causes the observed NIR light curves. [ABSTRACT FROM AUTHOR]

The search for the first stars formed from metal-free gas in the universe is one of the key issues in astronomy because it relates to many fields, such as the formation of stars and galaxies, the evolution of the universe, and the origin of elements. It is not still clear if metal-free first stars can be found in the present universe. These first stars are thought to exist among extremely metal-poor stars in the halo of our Galaxy. Here we propose a new scenario for the formation of low-mass first stars that have survived until today and observational counterparts in our Galaxy. The first stars in binary systems, consisting of massive- and low-mass stars, are examined using stellar evolution models, simulations of supernova ejecta colliding with low-mass companions, and comparisons with observed data. These first star survivors will be observed as metal-rich halo stars in our Galaxy. We may have identified a candidate star in the observational database where elemental abundances and kinematic data are available. Our models also account for the existence in the literature of several solar-metallicity stars that have space velocities equivalent to the halo population. The proposed scenario demands a new channel of star formation in the early universe and is a supplementary scenario for the origin of the known metal-poor stars. [ABSTRACT FROM AUTHOR]

We consider a confined space molecular communication system, where molecules or information carrying particles are used to transfer information on a microfluidic chip. Considering that information-carrying particles can follow two main propagation schemes: passive transport, and active transport, it is not clear which achieves a better information transmission rate. Motivated by this problem, we compare and analyze both propagation schemes by deriving a set of analytical and mathematical tools to measure the achievable information rates of the on-chip molecular communication systems employing passive to active transport. We also use this toolbox to optimize design parameters such as the shape of the transmission area, to increase the information rate. Furthermore, the effect of separation distance between the transmitter and the receiver on information rate is examined under both propagation schemes, and a guidepost to design an optimal molecular communication setup and protocol is presented. [ABSTRACT FROM PUBLISHER]

Molecular communication is a novel communication paradigm inspired by information processing in biological systems using molecules as information medium. In this study, we achieved the selective propagation of transport vesicles which is an essential technique to establish a molecular communication system using artificial cells. The hybridisation of DNA was employed to conduct a signal-induced delivery of transport vesicles from a sender to a receiver vesicle formed with phospholipids. Oligonucleotide lipids each with a different single-stranded DNA, which acts as recognition tags, were embedded in the sender, receiver and transport vesicles. The addition of a DNA signal with a complementary sequence to connect two oligonucleotide lipids induced the assembly of two types of large unilamellar vesicles as well as recombination of the vesicles. In addition, the selective delivery of transport vesicles between sender and receiver giant vesicles is discussed, based on the results of fluorescence microscopic observations. [ABSTRACT FROM AUTHOR]

We aimed to create an autonomous on-chip system that performs targeted delivery of lipid vesicles (liposomes) as nano- or microscale reactors using machinery from biological systems. Reactor-liposomes would be ideal model cargoes to realize biomolecular-motor-based biochemical analysis chips; however, there are no existing systems that enable targeted delivery of cargo-liposomes in an autonomous manner. By exploiting biomolecular-motor-based motility and DNA hybridization, we demonstrate that single-stranded DNA (ssDNA)-labeled microtubules (MTs), gliding on kinesin-coated surfaces, acted as cargo transporters and that ssDNA-labeled cargo-liposomes were loaded/unloaded onto/from gliding MTs without bursting at loading reservoirs/micropatterned unloading sites specified by DNA base sequences. Our results contribute to the development of an alternative strategy to pressure-driven or electrokinetic flow-based microfluidic devices. [ABSTRACT FROM AUTHOR]

Molecular communication is a bio-inspired communication paradigm using molecules as information carriers. The molecular communication system includes propagation of information carrier molecules between a molecular sender and a molecular receiver and followed by amplification of the information at the receiver. In this article, we built an example molecular communication system using a gemini peptide lipid as a molecular switch. The molecular switch embedded in the lipid bilayer membranes exhibited photoresponsive recognition behaviour towards metal ions, such as Cu2+ and Zn2+, to control propagation of molecular capsules formed by small liposomes to a giant liposomal receiver. In addition, the molecular switch acted as an artificial receptor in the receiver, receiving a photonic signal to communicate with an enzyme as a signal amplifier by using Cu2+ ion as a mediator between the receptor and the amplifier. [ABSTRACT FROM AUTHOR]

We report results from X-ray and optical observations of the Galactic black hole candidate MAXI J1828−249 performed with Suzaku and the Kanata telescope around the X-ray flux peak in the 2013 outburst. The time-averaged X-ray spectrum covering 0.6–168 keV was approximately characterized by a strong multi-color disk blackbody component with an inner disk temperature of ∼0.6 keV, and a power-law tail with a photon index of ∼2.0. We detected an additional structure at 5–10 keV, which can be modeled neither with X-ray reflection on the disk nor relativistic broadening of the disk emission. Instead, it was successfully reproduced with a Comptonization of disk photons by thermal electrons with a relatively low temperature (≲10 keV). We infer that the source was in the intermediate state, considering its long-term trend in the hardness intensity diagram, the strength of the spectral power-law tail, and its variability properties. The low-temperature Comptonization component could be produced in a boundary region between the truncated standard disk and the hot inner flow, or a Comptonizing region that somehow developed above the disk surface. The multi-wavelength spectral energy distribution suggests that the optical and ultraviolet fluxes were dominated by irradiated outer disk emission. [ABSTRACT FROM AUTHOR]

We present optical and near-infrared observations of the nearby Type Iax supernova (SN) 2014dt from 14 to 410 d after the maximum light. The velocities of the iron absorption lines in the early phase indicated that SN 2014dt showed slower expansion than the well-observed Type Iax SNe 2002cx, 2005hk, and 2012Z. In the late phase, the evolution of the light curve and that of the spectra were considerably slower. The spectral energy distribution kept roughly the same shape after ∼100 d, and the bolometric light curve flattened during the same period. These observations suggest the existence of an optically thick component that almost fully trapped the γ-ray energy from 56Co decay. These findings are consistent with the predictions of the weak deflagration model, leaving a bound white dwarf remnant after the explosion. [ABSTRACT FROM AUTHOR]

We present results of optical polarimetric and multi-band photometric observations for γ-ray loud, narrow-line Seyfert 1 galaxy 1H 0323+342. This object has been monitored by the 1.5-m Kanata telescope since 2012 September, but following a γ-ray flux enhancement detected by Fermi Large Area Telescope (Fermi-LAT) on MJD 56483 (2013 July 10), dense follow-up was performed by 10 0.5–2.0-m telescopes in Japan over one week. The 2-yr RC-band light curve showed clear brightening corresponding to the γ-ray flux increase, and then decayed gradually. The high state as a whole lasted for ∼ 20 d, during which we clearly detected optical polarization from this object. The polarization degree (PD) of the source increased from 0%–1% in quiescence to ∼ 3% at maximum and then declined to the quiescent level, with the duration of the enhancement being less than 10 d. The moderate PD around the peak allowed us to precisely measure the daily polarization angle (PA). As a result, we found that the daily PAs were almost constant and aligned to the jet axis, suggesting that the magnetic field direction at the emission region is transverse to the jet. This implies either a presence of helical/toroidal magnetic field or transverse magnetic field compressed by shock(s). We also found small-amplitude intra-night variability during the 2-hr continuous exposure on a single night. We discuss these findings based on the turbulent multi-zone model recently advocated by Marscher (2014, ApJ, 780, 87). Optical to ultraviolet (UV) spectrum showed a rising shape in the higher frequency and the UV magnitude measured by Swift/UVOT (UV and Optical Telescope) was steady even during the flaring state, suggesting that thermal emission from accretion disk is dominant in that band. [ABSTRACT FROM AUTHOR]