Mass Exchange In Binaries Research Articles

Nebular phase properties of supernova Ibc from He-star explosions

Following our recent work on Type II supernovae (SNe), we present a set of 1D nonlocal thermodynamic equilibrium radiative transfer calculations for nebular-phase Type Ibc SNe starting from state-of-the-art explosion models with detailed nucleosynthesis. Our grid of progenitor models is derived from He stars that were subsequently evolved under the influence of wind mass loss. These He stars, which most likely form through binary mass exchange, synthesize less oxygen than their single-star counterparts with the same zero-age main sequence (ZAMS) mass. This reduction is greater in He-star models evolved with an enhanced mass loss rate. We obtain a wide range of spectral properties at 200 d. In models from He stars with an initial mass > 6 M⊙, the [O I] λλ 6300, 6364 is of a comparable or greater strength than [Ca II] λλ 7291, 7323 – the strength of [O I] λλ 6300, 6364 increases with the He-star initial mass. In contrast, models from lower mass He stars exhibit a weak [O I] λλ 6300, 6364, strong [Ca II] λλ 7291, 7323, and also strong N II lines and Fe II emission below 5500 Å. The ejecta density, which is modulated by the ejecta mass, the explosion energy, and clumping, has a critical impact on gas ionization, line cooling, and spectral properties. We note that Fe II dominates the emission below 5500 Å and is stronger at earlier nebular epochs. It ebbs as the SN ages, while the fractional flux in [O I] λλ 6300, 6364 and [Ca II] λλ 7291, 7323 increases with a similar rate as the ejecta recombine. Although the results depend on the adopted wind mass loss rate and pre-SN mass, we find that He-stars of 6–8 M⊙ initially (ZAMS mass of 23–28 M⊙) match the properties of standard SNe Ibc adequately. This finding agrees with the offset in progenitor masses inferred from the environments of SNe Ibc relative to SNe II. Our results for less massive He stars are more perplexing since the predicted spectra are not seen in nature. They may be missed by current surveys or associated with Type Ibn SNe in which interaction power dominates over decay power.

Properties and nature of Be stars

Reliable determination of the basic physical properties of hot emission-line binaries with Roche-lobe filling secondaries is important for developing the theory of mass exchange in binaries. It is not easy, however, due to the presence of circumstellar matter. Here, we report the first detailed investigation of a new representative of this class of binaries, HD 81357, based on the analysis of spectra and photometry from several observatories. HD 81357 was found to be a double-lined spectroscopic binary and an ellipsoidal variable seen under an intermediate orbital inclination of ∼(63 ± 5)°, having an orbital period of 33.d77445(41) and a circular orbit. From an automated comparison of the observed and synthetic spectra, we estimate the component’s effective temperatures to be 12930(540) K and 4260(24) K. The combined light-curve and orbital solutions, also constrained by a very accurate Gaia Data Release 2 parallax, give the following values of the basic physical properties: masses 3.36 ± 0.15 and 0.34 ± 0.04M⊙N, radii 3.9 ± 0.2 and 13.97 ± 0.05R⊙N, and a mass ratio 10.0 ± 0.5. Evolutionary modelling of the system including the phase of mass transfer between the components indicated that HD 81357 is a system observed in the final slow phase of the mass exchange after the mass-ratio reversal. Contrary to what has been seen for similar binaries like AU Mon, no cyclic light variations were found on a time scale an order of magnitude longer than the orbital period.

Properties and nature of Be stars

Reliable determination of the basic physical properties of hot emission-line binaries with Roche-lobe filling secondaries is important for developing the theory of mass exchange in binaries. It is a very hard task, however, which is complicated by the presence of circumstellar matter in these systems. So far, only a small number of systems with accurate values of component masses, radii, and other properties are known. Here, we report the first detailed study of a new representative of this class of binaries, BR CMi, based on the analysis of radial velocities and multichannel photometry from several observatories, and compare its physical properties with those for other well-studied systems. BR CMi is an ellipsoidal variable seen under an intermediate orbital inclination of ∼ 51°, and it has an orbital period of 12919059(15) and a circular orbit. We used the disentangled component spectra to estimate the effective temperatures 9500(200) K and 4655(50) K by comparing them with model spectra. They correspond to spectral types B9.5e and G8III. We also used the disentangled spectra of both binary components as templates for the 2D cross-correlation to obtain accurate radial velocities and a reliable orbital solution. Some evidence of a secular period increase at a rate of (1.1 ± 0.5) s per year was found. This, together with a very low mass ratio of 0.06 and a normal mass and radius of the mass gaining component, indicates that BR CMi is in a slow phase of the mass exchange after the mass-ratio reversal. It thus belongs to a still poorly populated subgroup of Be stars for which the origin of Balmer emission lines is safely explained as a consequence of mass transfer between the binary components.

AGES OF YOUNG STAR CLUSTERS, MASSIVE BLUE STRAGGLERS, AND THE UPPER MASS LIMIT OF STARS: ANALYZING AGE-DEPENDENT STELLAR MASS FUNCTIONS

Massive stars rapidly change their masses through strong stellar winds and mass transfer in binary systems. We show that such mass changes leave characteristic signatures in stellar mass functions of young star clusters which can be used to infer their ages and to identify products of binary evolution. We model the observed present day mass functions of the young Galactic Arches and Quintuplet star clusters using our rapid binary evolution code. We find that shaping of the mass function by stellar wind mass loss allows us to determine the cluster ages to 3.5$\pm$0.7 Myr and 4.8$\pm$1.1 Myr, respectively. Exploiting the effects of binary mass exchange on the cluster mass function, we find that the most massive stars in both clusters are rejuvenated products of binary mass transfer, i.e. the massive counterpart of classical blue straggler stars. This resolves the problem of an apparent age spread among the most luminous stars exceeding the expected duration of star formation in these clusters. We perform Monte Carlo simulations to probe stochastic sampling, which support the idea of the most massive stars being rejuvenated binary products. We find that the most massive star is expected to be a binary product after 1.0$\pm$0.7 Myr in Arches and after 1.7$\pm$1.0 Myr in Quintuplet. Today, the most massive 9$\pm$3 stars in Arches and 8$\pm$3 in Quintuplet are expected to be such objects. Our findings have strong implications for the stellar upper mass limit and solve the discrepancy between the claimed 150 $\mathrm{M}_\odot$ limit and observations of fours stars with initial masses of 165-320 $\mathrm{M}_\odot$ in R136 and of SN 2007bi, which is thought to be a pair-instability supernova from an initial 250 $\mathrm{M}_\odot$ star. Using the stellar population of R136, we revise the upper mass limit to values in the range 200-500 $\mathrm{M}_\odot$.

New findings supporting the presence of a thick disc and bipolar jets in the $\mathsf{\beta}$ Lyrae system

Context. Understanding large-scale mass exchange in binaries also requires studies of complicated objects in the rapid phases of the process. β Lyr is one such object. Aims. Our goals were to analyse 52 photographic and 651 electronic spectra of β Lyr to obtain additional information about circumstellar matter and to investigate spectrophotometric information for the first time. Methods. Improved quadratic ephemeris was derived via orbital solution with the FOTEL program. The spectra were disentangled using the KOREL program. Spectrophotometric quantities of 15 stronger absorption lines of the primary were measured and corrected for the orbital continuum variations using the fluxes calculated from a fit of the light curves with the BINSYN program. Central intensities of the V and R peaks of the Hα emission line were measured and corrected for the orbital light changes using the R-band light curve numerically modelled with the program PERIOD04. Results. Disentangling of photographic and electronic spectra led to the detection of weak absorption lines originating from the pseudophotosphere of the accretion disc. This way, a rich line spectrum of the accretion disc, not limited to only two previously known Si ii 6347 and Si ii 6371 lines, was obtained. A projected rotational velocity of 180 km s −1 was estimated for the disc spectrum. Such a value agrees well with the assumption of the Keplerian rotation of the outer layers of the accretion disc. After the correction, a pronounced increase of the strength of all absorption lines around phases of the primary eclipse was found. We argue that this is due to additional absorption of the light of the primary in one of the jets and/or scattering envelope above the accretion disc of the gainer. The net intensity of the V peak of Hα shows no orbital variation, but a possible 271-d periodicity. The net intensity of the R peak shows mild orbital changes and a slow change over a cycle of about 2780 days. These results seem to support the earlier conclusion that the Hα emission originates in the jet-like structures. Conclusions. All new findings support the current picture that the circumstellar structures of β Lyr consist of a thick accretion disc, bipolar jets, and a scattering envelope above the disc.

The physics of type Ia supernovae

The basic recipe for SN Ia explosions is simple. A white dwarf in a binary system, growing towards the limiting Chandrasekhar mass, contracts and ignites under degenerate (electron gas) conditions, causing a thermonuclear runaway. Burning 1.4 M ⊙ of 12C and 16O in equal proportions to 1.398776 M ⊙ of 56Ni releases the mass difference in nuclear binding energy, i.e., a thermonuclear explosion of about about 2.19×10 51 erg, which disrupts the original white dwarf completely. The subtraction of the gravitational binding energy of the white dwarf of (≈(5–6)×10 50 erg), plus the observed fact that not all material is burned to Fe/Ni (rather to intermediate elements like Mg, Si, S, Ca), leads to the observed explosion energies (≈1.3×10 51 erg). The decay chain 56Ni → 56Co → 56Fe can explain the lightcurve. The remaining questions are: how can cool and stable white dwarfs be turned into exploding objects via binary mass exchange; what variety of original white dwarf sizes, metallicities and accretion scenarios is expected; how does the ignition occur and does the burning front propagate; how does this relate to burning conditions, energy generation, nucleosynthesis results, 56Ni masses and the small observed variety in explosive events; how can observed spectra (and their Doppler broadening) act as diagnostics for explosion models and nucleosynthesis predictions? We will address these issues within existing 1D spherically symmetric models with parameterized burning front prescriptions and attempt to discuss the relation to multi-D models.

Accretion-driven magnetic field decay in neutron stars

There are many arguments which imply that the evolution of the magnetic field may be substantially different for isolated neutron stars than it is for neutron stars entering close binary systems. It is likely that various processes accompanying mass exchange in binaries can influence the evolution of the magnetic field. The present paper considers the decay of the field which, before the mass-exchange stage, was confined to the neutron star crust. We concentrate on effects produced by additional heating due to accretion. The internal temperature of accreting neutron stars is rather high at high accretion rates, and, therefore, the crustal conductivity should be lower than for non-accreting stars. Besides, the temperature distribution may be strongly non- uniform for rapidly cooling neutron stars (such cooling is typical, for example, for stars with exotic matter in the core). This non-uniformity may be responsible for effective thermomagnetic processes in the crust. Both of these phenomena are taken into account in our study. Computations indicate a much more rapid field decay for accreting neutron stars. For binaries with high accretion rates (⁠|$M\ge3\times 10^{-10}\enspace\text M_\odot\enspace\text {yr}^{-1}$|⁠) and long mass-exchange stages (⁠|$\ge10^6- 10^7\enspace \text yr$|⁠), the field of the neutron star can be a factor |$\sim 10^3-10^4$| lower than that of isolated neutron stars. The suggested mechanism can provide an explanation of the low magnetic fields of many pulsars entering binaries.

The Blue Straggler Stars of Galactic Clusters

AbstractThe origin and evolution of blue straggler stars (BS) in clusters is still an unsolved problem for our understanding of stellar evolution. Several rivalling theories exist, of which that of Saio & Wheeler (1980) is the most interesting one since it assumes additional mixing of fuel in the interior of BS. This theory predicts larger luminosity-to-mass ratios for a given position in the HR diagram compared to the standard evolution theory. This theory has been taylored for the old galactic cluster NGC 7789 which contains many bona fide BS, but it can also be used for other clusters of similar ages. The other theories rely on the standard theory of stellar evolution and assume (1) binary mass exchange or even merging, or (2) delayed star formation. In either case follows a “normal” luminosity-to-mass ratio. We report here on a careful spectroscopic investigation in order to discrimate between these rivalling theories.

Red Supergiants and Neutrino Emission. II

view Abstract Citations (28) References (112) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Red Supergiants and Neutrino Emission. II Stothers, Richard Abstract The variation with stellar mass of the ratio of the numbers of blue and red supergiants is investigated. Statistical data for supergiants in young open clusters and subgroups of associations are collected to supplement a more restricted list in Paper I. Improved methods are used to identify hydrogen-burning supergiants, as well as faint supergiant remnants of binary mass exchange, and to arrange the bright evolved supergiants in order of their masses Neither of these two operations requires knowledge of stellar distances or luminosities. Relevant published woth on stellar evolution, rotation, mass loss, and duplicity is used to predict upper and lower limits on the blue-to-red ratio. It is concluded that (1) the observed paucity of very massive red supergiants (and of caibon stars) confirms and extends the trend observed in Paper I, and thereby supports the idea of neutrino-induced acceleration of the carbonburning and later phases of evolution; (2) the h and Persei association shows the same dependence of the blue-to-red ratio on stellar mass as do other clusters and associations; and (3) a moderate decrease of the blue-to-red ratio is observed with increasing galactocentric distance in the Galaxy (as in M33) and seems to be due to a relative scarcity of extremely young stars in distant galactic regions. Publication: The Astrophysical Journal Pub Date: August 1972 DOI: 10.1086/151593 Bibcode: 1972ApJ...175..717S full text sources ADS | data products SIMBAD (30)

Red Supergiants and Neutrino Emission

Investigation of the variation with stellar mass of the ratio of the numbers of blue and red supergiants. Statistical data for supergiants in young open clusters and subgroups of associations are collected to supplement a more restricted list presented earlier. Improved methods are used to identify hydrogen-burning supergiants, as well as faint supergiant remnants of binary mass exchange, and to arrange the bright evolved supergiants in order of their masses. Neither of these two operations requires knowledge of stellar distances or luminosities. Relevant published work on stellar evolution, rotation, mass loss, and duplicity is used to predict upper and lower limits on the blue-to-red ratio. It is concluded that the observed paucity of very massive red supergiants (and of carbon stars) confirms and extends the trend previously observed, and thereby supports the idea of neutrino-induced acceleration of the carbon burning and later phases of evolution; the h and chi Persei association shows the same dependence of the blue-to-red-ratio on stellar mass as do other clusters and associations; and a moderate decrease of the blue-to-red ratio is observed with increasing galactocentric distance in the Galaxy (as in M33) and seems to be due to a relative scarcity of extremely young stars in distant galactic regions.