Evolution of black-hole intermediate-mass X-ray binaries: the influence of a circumbinary disc

Justham, Rappaport & Podsiadlowski (2006) recently suggested that black-hole low-mass X-ray binaries (BHLMXBs) with short orbital periods may have evolved from black-hole intermediate-mass X-ray binaries (BHIMXBs). In their model the secondaries in BHIMXBs are assumed to possess anomalously high magnetic fields, so that magnetic braking can lead to substantial loss of angular momentum. In this paper we propose an alternative mechanism for orbital angular momentum loss in BHIMXBs. We assume that a small fraction $\delta$ of the transferred mass from the donor star form a circumbinary disc surrounding the binary system. The tidal torques exerted by the disc can effectively drain orbital angular momentum from the binary. We have numerically calculated the evolutionary sequences of BHIMXBs, to examine the influence of the circumbinary disc on the binary evolution. Our results indicate when \delta\la 0.01-0.1 (depending on the initial orbital periods), the circumbinary disc can cause secular orbital shrinking, leading to the formation of compact BHLMXBs, otherwise the orbits always expand during the evolution. This scenario also suggests the possible existence of luminous, persistent BHLMXBs, but it suffers the same problem as in Justham, Rappaport & Podsiadlowski (2006) that, the predicted effective temperatures of the donor stars are significantly higher than those of the observed donor stars in BHLMXBs.Comment: 7 pages, 5 figures, accepted for publication in MNRA

Developmental regulation of the heat shock response by nuclear transport factor karyopherin-α3

During early stages of Drosophila development the heat-shock response cannot be induced. It is reasoned that the adverse effects on cell cycle and cell growth brought about by Hsp70 induction must outweigh the beneficial aspects of Hsp70 induction in the early embryo. Although the Drosophila heat shock transcription factor (dHSF) is abundant in the early embryo it does not enter the nucleus in response to heat shock. In older embryos and in cultured cells the factor is localized within the nucleus in an apparent trimeric structure that binds DNA with high affinity. The domain responsible for nuclear localization upon stress resides between residues 390 and 420 of the dHSF. Using that domain as bait in a yeast two-hybrid system we now report the identification and cloning of a Drosophila nuclear transport protein karyopherin-α3 (dKap-α3). Biochemical methods demonstrate that the dKap-α3 protein binds specifically to the dHSF’s nuclear localization sequence (NLS). Furthermore, the dKap-α3 protein does not associate with NLSs that contain point mutations, which are not transported in vivo. Nuclear docking studies also demonstrate specific nuclear targeting of the NLS substrate by dKap-α3. Consistant with previous studies demonstrating that early Drosophila embryos are refractory to heat shock as a result of dHSF nuclear exclusion, we demonstrate that the early embryo is deficient in dKap-α3 protein through cycle 12. From cycle 13 onward the transport factor is present and the dHSF is localized within the nucleus thus allowing the embryo to respond to heat shock

Regge-like relation and a universal description of heavy-light systems

Using the Regge-like formula $(M-m_Q)^2=\pi\sigma L$ between hadron mass $M$ and angular momentum $L$ with a heavy quark mass $m_Q$ and a string tension $\sigma$, we analyze all the heavy-light systems, i.e., $D/D_s/B/B_s$ mesons and charmed and bottom baryons.Numerical plots are obtained for all the heavy-light mesons of experimental data whose slope becomes nearly equal to 1/2 of that for light hadrons. Assuming that charmed and bottom baryons consist of one heavy quark and one light cluster of two light quarks (diquark), we apply the formula to all the heavy-light baryons including recently discovered $\Omega_c$'s and find that these baryons experimentally measured satisfy the above formula. We predict the average mass values of $B$, $B_s$, $\Lambda_b$, $\Sigma_c$, $\Xi_c$, and $\Omega_c$ with $L=2$ as 6.01, 6.13, 6.15, 3.05, 3.07, and 3.34 GeV, respectively. Our results on baryons suggest that these baryons can be safely regarded as heavy quark-light cluster configuration. We also find a universal description for all the heavy-light mesons as well as baryons, i.e., one unique line is enough to describe both of charmed and bottom heavy-light systems. Our results suggest that instead of mass itself, gluon flux energy is essential to obtain a linear trajectory.Comment: 10 pages, 8 figures, 5 table