Showing papers by "Chang-Hwan Lee published in 2001"
TL;DR: In this paper, it was shown that the result of helium core burning in a massive star is independent of whether the core is covered by a hydrogen envelope, or not, while it burns.
85 citations
TL;DR: In this article, the authors show that the standard scenario for evolving neutron stars that are recycled in common envelope evolution is not sufficient for the observation of 50 carbon-oxygen white dwarf binaries, since their formation rate is roughly equal to that of the eccentric binaries and the time over which they can be observed is 2 orders of magnitude longer.
Abstract: At least one, but more likely two or more, eccentric neutron star, carbon-oxygen white dwarf binaries with an unrecycled pulsar have been observed. According to the standard scenario for evolving neutron stars that are recycled in common envelope evolution, we expect to observe 50 such circular neutron star, carbon-oxygen white dwarf binaries, since their formation rate is roughly equal to that of the eccentric binaries and the time over which they can be observed is 2 orders of magnitude longer, as we shall outline. We observe at most one or two such circular binaries, and from that we conclude that the standard scenario must be revised. Introducing hypercritical accretion into common envelope evolution removes the discrepancy by converting the neutron star into a black hole which does not emit radio waves, and therefore would not be observed.
24 citations
TL;DR: In this paper, it was shown that the result of a helium core burning in a massive star is independent of whether the core is covered by a hydrogen envelope, or "naked" while it burns.
Abstract: The discrepancy in the past years of many more black-hole soft X-ray transients (SXTs), of which a dozen have now been identified, had challenged accepted wisdom in black hole evolution. The sheer number of inferred SXTs requires that many, if not most, stars of ZAMS masses $20-35\msun$ end up as black holes (Portegies Zwart et al. 1997; Ergma & van den Heuvel 1998). In this paper we show that this can be understood by challenging the accepted wisdom that the result of helium core burning in a massive star is independent of whether the core is covered by a hydrogen envelope, or "naked" while it burns. The latter case occurs in binaries when the envelope of the more massive star is transferred to the companion by Roche Lobe overflow while in either main sequence or red giant stage. For solar metallicity, whereas the helium cores which burn while naked essentially never go into high-mass black holes, those that burn while clothed do so, beginning at ZAMS mass $\sim 20\msun$, the precise mass depending on the $^{12}C(\alpha,\gamma)^{16}$O rate as we outline. In this way the SXTs can be evolved, provided that the H envelope of the massive star is removed only following the He core burning. We also show that in order to evolve a black hole of mass $\gsim 10\msun$ such as observed in Cyg X-1, even employing extremely massive progenitors of ZAMS mass $\gsim 60\msun$ for the black hole, the core must be covered by hydrogen during a substantial fraction of the core burning. In other words, the progenitor must be a WNL star. We evolve Cyg X-1 in an analogous way to which the SXTs are evolved, the difference being that the companion in Cyg X-1 is more massive than those in the SXTs, so that Cyg X-1 shines continuously.
11 citations
TL;DR: In this paper, the formation of low-mass black hole X-ray binaries with main sequence companions that have formed through case C mass transfer (mass transfer following the helium core burning phase of the black hole progenitor) was studied.
10 citations
TL;DR: In this article, the formation of low-mass black hole X-ray binaries with main sequence companions that have formed through case C mass transfer (mass transfer following the helium core burning phase of the black hole progenitor) was studied.
Abstract: We study the formation of low-mass black hole X-ray binaries with main sequence companions that have formed through case C mass transfer (mass transfer following the helium core burning phase of the black hole progenitor). We identify these objects with the observed soft X-ray transients. Although this scenario requires a set of fine tuned conditions, we are able to produce a current Galactic population of about 2000 objects, in agreement with estimates based on observations.
The narrow interval in initial separations leading to case C mass transfer, combined with the allowed narrow range of separations after the common envelope evolution, constrains the common envelope efficiency in this scenario: $\lambda \alpha_{ce} \approx 0.2-0.5$.
8 citations
01 Jan 2001
TL;DR: In this article, the authors repeat Woosley's argument that at some ZAMS mass stars will skip convective carbon burning, with extremely important consequences that have been detailed in Papers 13, 14, 15, 16, 17, 20 and 21.
Abstract: In Sec . 3 of this article we repeat Woosley 's argument that at some ZAMS mass stars will skip convective carbon burning , with extremely important consequences that have been detailed in Papers 13 , 14, 15 , 16, 17 , 20 and 21 . Until Paper 21, some of our arguments were based on conjecture , especially in the case of "naked " helium stars , those that have lost their hydrogen envelopes , because evolutions of these in the previous literature had used 2-3 times too large He wind losses . The history of how Stephen Wellstein with Norbert Langer burned naked He stars down to CO cores , and then Alexander Heger evolved these, using the Woosley & Weaver KEPLER computer program , down to Fe cores is outlined in the present paper with appropriate references . These more or less definite results show the earlier conjectured ones to be correct . Appreciable corrections would only occur for wind losses lower by a factor of 4 or more from the ones previously used , and such a factor seems excessive. It is essential for the evolution of a star whether the reaction C+C occurs or is "skipped". This reaction is referred to in the literature as "convective carbon burning". We don't think this is a good designation , because its important consequences do not depend on its convectivity , nor is it clear that the alternative destruction of carbon , by the reaction 12C(a, -y)160 , is radiative . The important difference is that the C + a reaction takes place at T^_, 20 keV , while the C + C reaction requires a temperature of about 80 keV. There is a striking difference between naked and clothed He cores . Clothed He cores have a protective layer of hydrogen around them . This diminishes the loss of mass by wind from the surface . Moreover, in the surface layer the H+H reaction proceeds , creating additional He. In naked He stars , the amount of He is limited and can only diminish by wind. Once it is used up, the remaining C can only be used up by the reaction 12C+12C-+24Mg (or 20Ne+a ), at the much higher temperature.
19 Apr 2001
TL;DR: In this paper, a gamma ray burst was used to power a Type Ib supernova (SN) and showed that there is evidence both that the black hole was spun up by accretion and that there was a supernova explosion.
Abstract: We suggest Nova Sco 1994 (GRO 1655-40) as a possible relic of a Gamma Ray Burster (GRB) and Type Ib supernova (SN) explosion, showing that there is evidence both that the black hole was spun up by accretion and that there was a supernova explosion. We use the disc energy delivered from the rotational energy of the black hole to power the SN, and give arguments that roughly equal energy goes into the GRB and into the accretion disc to power the supernova.
TL;DR: In this paper, the authors investigated the soft X-ray transients with black hole primaries which may have been the sources of gamma-ray bursts and hypernovae earlier in their evolution.
Abstract: We investigate the soft X-ray transients with black hole primaries which may have been the sources of gamma-ray bursts and hypernovae earlier in their evolution. We find that the black-hole mass increases with the orbital period of the binary, both for systems with main-sequence donors and for those with evolved donors. This correlation can be understood in terms of angular-momentum support in the helium star progenitor of the black hole, if the systems with shorter periods had more rapidly rotating primaries prior to their explosion: centrifugal support will then prevent more of its mass from collapsing into the black hole. This trend of more rapidly rotating stars in closer binaries is very generally seen, and in the present case can be understood in terms of spin-up during spiral in and subsequent tidal coupling. We investigate the relation quantitatively and obtain reasonable agreement with the observed mass-period correlation. A natural consequence of this observation is that black holes formed in soft X-ray transients acquire significant Kerr parameters. This makes them good sources of power for gamma-ray bursts and hypernovae, via the Blandford-Znajek mechanism, and thus supports our model for the origin of gamma-ray bursts in soft X-ray transients.