The timescale of low-mass proto-helium white dwarf evolution

A large number of low-mass (< 0.20 M_sun) helium white dwarfs (He WDs) have recently been discovered. The majority of these are orbiting another WD or a millisecond pulsar (MSP) in a close binary system; a few examples are found to show pulsations or to have a main-sequence star companion. There appear to be discrepancies between the current theoretical modelling of such low-mass He WDs and a number of key observed cases, indicating that their formation scenario remains to be fully understood. Here we investigate the formation of detached proto-He WDs in close-orbit low-mass X-ray binaries (LMXBs). Our prime focus is to examine the thermal evolution and the contraction phase towards the WD cooling track and investigate how this evolution depends on the WD mass. Our calculations are then compared to the most recent observational data. Numerical calculations with a detailed stellar evolution code were used to trace the mass-transfer phase in a large number of close-orbit LMXBs. Subsequently, we followed the evolution of the detached low-mass proto-He WDs, including stages with residual shell hydrogen burning and vigorous flashes caused by unstable CNO burning. We find that the time between Roche-lobe detachment until the low-mass proto-He WD reaches the WD cooling track is typically Delta_t_proto = 0.5 - 2 Gyr, depending systematically on the WD mass and therefore on its luminosity. The lowest WD mass for developing shell flashes is ~0.21 M_sun for progenitor stars of mass M2 <= 1.5 M_sun (and ~0.18 M_sun for M2 = 1.6 M_sun). The long timescale of low-mass proto-He WD evolution can explain a number of recent observations, including some MSP systems hosting He WD companions with very low surface gravities and high effective temperatures. We find no evidence for Delta_t_proto to depend on the occurrence of flashes and thus question the suggested dichotomy in thermal evolution of proto-WDs.Comment: 6 pages, 6 figures, 2 tables, A&A Letters, accepte

Radiative-transfer models for supernovae IIb/Ib/Ic from binary-star progenitors

We present 1-D non-Local-Thermodynamic-Equilibrium time-dependent radiative-transfer simulations for supernovae (SNe) of type IIb, Ib, and Ic that result from the terminal explosion of the mass donor in a close-binary system. Here, we select three ejecta with a total kinetic energy of ~1.2e51erg, but characterised by different ejecta masses (2-5Msun), composition, and chemical mixing. The type IIb/Ib models correspond to the progenitors that have retained their He-rich shell at the time of explosion. The type Ic model arises from a progenitor that has lost its helium shell, but retains 0.32Msun of helium in a CO-rich core of 5.11Msun. We discuss their photometric and spectroscopic properties during the first 2-3 months after explosion, and connect these to their progenitor and ejecta properties including chemical stratification. For these three models, Arnett's rule overestimates the 56Ni mass by ~50% while the procedure of Katz et al., based on an energy argument, yields a more reliable estimate. The presence of strong CI lines around 9000A prior to maximum is an indicator that the pre-SN star was under-abundant in helium. As noted by others, the 1.08micron feature is a complex blend of CI, MgII, and HeI lines, which makes the identification of He uncertain in SNe Ibc unless other HeI lines can be identified. Our models show little scatter in (V-R) colour 10d after R-band maximum. We also address a number of radiative transfer properties of SNe Ibc, including the notion of a photosphere, the inference of a representative ejecta expansion rate, spectrum formation, blackbody fits and "correction factors".Comment: accepted to MNRA

Inferring supernova IIb/Ib/Ic ejecta properties from light curves and spectra: Correlations from radiative-transfer models

We present 1-D non-Local-Thermodynamic-Equilibrium time-dependent radiative-transfer simulations for a large grid of supernovae (SNe) IIb/Ib/Ic that result from the terminal explosion of the mass donor in a close-binary system. Our sample covers ejecta masses $M_{\rm e}$ of 1.7$-$5.2M$_\odot$, kinetic energies $E_{\rm kin}$ of 0.6$-$5.0$\times$10$^{51}$erg, and $^{56}$Ni masses of 0.05$-$0.30M$_\odot$. We find a strong correlation between the $^{56}$Ni mass and the photometric properties at maximum, and between the rise time to bolometric maximum and the post-maximum decline rate. We confirm the small scatter in ($V-R$) at 10d past $R$-band maximum. The quantity $V_{\rm m} \equiv \sqrt{2E_{\rm kin}/M_{\rm e}}$ is comparable to the Doppler velocity measured from HeI 5875\AA\ at maximum in SNe IIb/Ib, although some scatter arises from the uncertain level of chemical mixing. The OI7772\AA\ line may be used for SNe Ic, but the correspondence deteriorates with higher ejecta mass/energy. We identify a temporal reversal of the Doppler velocity at maximum absorption in the $\sim$1.05$\mu$m feature in all models. The reversal is due to HeI alone and could serve as a test for the presence of helium in SNe Ic. Because of variations in composition and ionisation, the ejecta opacity shows substantial variations with both velocity and time. This is in part the origin of the offset between our model light curves and the predictions from the Arnett model.Comment: Accepted for publication in the MNRA

Ideology and the limits of self-interest: System justification motivation and conservative advantages in mass politics

It is commonly assumed that political attitudes are driven by self-interest and that poor people heavily favor policies aimed at redistributing wealth. This assumption fails to explain the popularity of economic conservatism and the degree of support for the capitalist system. Such outcomes are typically explained by the suggestion that most poor people believe they will become rich one day. In a representative sample of low-income Americans, we observed that less than one-fourth were optimistic about their economic prospects. Those respondents who believed that they would become rich one day were no more likely to endorse the legitimacy of the system and no more supportive of conservative ideology or the Republican Party, compared to those who did not believe they would become rich. From a system justification perspective, we propose that people are motivated to defend the social systems on which they depend, and this confers a psychological advantage to conservative ideology. Providing ideological support for the status quo serves epistemic motives to reduce uncertainty, existential motives to reduce threat, and relational motives to share reality with members of mainstream society. We summarize evidence from the United States, Argentina, Lebanon, and other countries bearing on these propositions—including a survey administered shortly before the 2016 U.S. Presidential election—and discuss political implications of system justification motivation.Fil: Jost, John T.. University of New York; Estados UnidosFil: Langer, Melanie. University of New York; Estados UnidosFil: Badaan, Vivienne. University of New York; Estados UnidosFil: Azevedo, Flávio. Universitat Zu Köln; AlemaniaFil: Etchezahar, Edgardo Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Saavedra 15. Centro Interdisciplinario de Investigaciones en Psicología Matemática y Experimental Dr. Horacio J. A. Rimoldi; ArgentinaFil: Ungaretti, Joaquín. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Saavedra 15. Centro Interdisciplinario de Investigaciones en Psicología Matemática y Experimental Dr. Horacio J. A. Rimoldi; ArgentinaFil: Hennes, Erin P.. Purdue University; Estados Unido

Are the Models for Type Ia Supernova Progenitors Consistent with the Properties of Supernova Remnants?

We explore the relationship between the models for progenitor systems of Type Ia supernovae and the properties of the supernova remnants that evolve after the explosion. Most models for Type Ia progenitors in the single degenerate scenario predict substantial outflows during the presupernova evolution. Expanding on previous work, we estimate the imprint of these outflows on the structure of the circumstellar medium at the time of the supernova explosion, and the effect that this modified circumstellar medium has on the evolution of the ensuing supernova remnant. We compare our simulations with the observational properties of known Type Ia supernova remnants in the Galaxy (Kepler, Tycho, SN 1006), the Large Magellanic Cloud (0509-67.5, 0519-69.0, N103B), and M31 (SN 1885). We find that optically thick outflows from the white dwarf surface (sometimes known as accretion winds) with velocities above 200 km/s excavate large low-density cavities around the progenitors. Such large cavities are incompatible with the dynamics of the forward shock and the X-ray emission from the shocked ejecta in all the Type Ia remnants that we have examined.Comment: To appear in ApJ. 17 pages, 10 figures, emulateap

The HD5980 multiple system: Masses and evolutionary status

New spectroscopic observations of the LBV/WR multiple system HD5980 in the Small Magellanic Cloud are used to address the question of the masses and evolutionary status of the two very luminous stars in the 19.3d eclipsing binary system. Two distinct components of the N V 4944 A line are detected in emission and their radial velocity variations are used to derive masses of 61 and 66 Mo, under the assumption that binary interaction effects on this atomic transition are negligible. We propose that this binary system is the product of quasi-chemically homogeneous evolution with little or no mass transfer. Thus, both of these binary stars may be candidates for gamma-ray burst progenitors or even pair instability supernovae. Analysis of the photospheric absorption lines belonging to the third-light object in the system confirm that it consists of an O-type star in a 96.56d eccentric orbit (e=0.82) around an unseen companion. The 5:1 period ratio and high eccentricities of the two binaries suggest that they may constitute a hierarchical quadruple system.Comment: 27 pages, 8 tables, 15 figures; accepted A

Diverse N-heterocyclic ring systems via aza-Heck cyclizations of <i>N</i>-(pentafluorobenzoyloxy)sulfonamides

Aza-Heck cyclizations initiated by oxidative addition of Pd(0)-catalysts into the N-O bond of N-(pentafluoro-benzoyloxy)sulfonamides are described. These studies, which encompass only the second class of aza-Heck reaction developed to date, provide direct access to diverse N-heterocyclic ring systems