Novel modelling of ultra-compact X-ray binary evolution - stable mass transfer from white dwarfs to neutron stars

Tight binaries of helium white dwarfs (He WDs) orbiting millisecond pulsars (MSPs) will eventually "merge" due to gravitational damping of the orbit. The outcome has been predicted to be the production of long-lived ultra-compact X-ray binaries (UCXBs), in which the WD transfers material to the accreting neutron star (NS). Here we present complete numerical computations, for the first time, of such stable mass transfer from a He WD to a NS. We have calculated a number of complete binary stellar evolution tracks, starting from pre-LMXB systems, and evolved these to detached MSP+WD systems and further on to UCXBs. The minimum orbital period is found to be as short as 5.6 minutes. We followed the subsequent widening of the systems until the donor stars become planets with a mass of ~0.005 Msun after roughly a Hubble time. Our models are able to explain the properties of observed UCXBs with high helium abundances and we can identify these sources on the ascending or descending branch in a diagram displaying mass-transfer rate vs. orbital period.Comment: 6 pages, 4 figures, MNRAS Letters, in pres

Evolution towards and beyond accretion-induced collapse of massive white dwarfs and formation of millisecond pulsars

Millisecond pulsars (MSPs) are generally believed to be old neutron stars (NSs), formed via type Ib/c core-collapse supernovae (SNe), which have been spun up to high rotation rates via accretion from a companion star in a low-mass X-ray binary (LMXB). In an alternative formation channel, NSs are produced via the accretion-induced collapse (AIC) of a massive white dwarf (WD) in a close binary. Here we investigate binary evolution leading to AIC and examine if NSs formed in this way can subsequently be recycled to form MSPs and, if so, how they can observationally be distinguished from pulsars formed via the standard core-collapse SN channel in terms of their masses, spins, orbital periods and space velocities. Numerical calculations with a detailed stellar evolution code were used for the first time to study the combined pre- and post-AIC evolution of close binaries. We investigated the mass transfer onto a massive WD in 240 systems with three different types of non-degenerate donor stars: main-sequence stars, red giants, and helium stars. When the WD is able to accrete sufficient mass (depending on the mass-transfer rate and the duration of the accretion phase) we assumed it collapses to form a NS and we studied the dynamical effects of this implosion on the binary orbit. Subsequently, we followed the mass-transfer epoch which resumes once the donor star refills its Roche lobe and calculated the continued LMXB evolution until the end. We demonstrate that the final properties of these MSPs are, in general, remarkably similar to those of MSPs formed via the standard core-collapse SN channel. However, the resultant MSPs created via the AIC channel preferentially form in certain orbital period intervals. Finally, we discuss the link between AIC and young NSs in globular clusters. Our calculations are also applicable to progenitor binaries of SNe Ia under certain conditions. [Abridged]Comment: 26 pages, 20 figures, 2 tables. A few references added. A&A in pres

Nuclear timescale mass transfer in models of supergiant and ultra-luminous X-ray binaries

We investigate how the proximity of supergiant donor stars to the Eddington-limit, and their advanced evolutionary stage, may influence the evolution of massive and ultra-luminous X-ray binaries with supergiant donor stars (SGXBs and ULXs). We construct models of massive stars with different internal hydrogen/helium gradients and different hydrogen-rich envelope masses, and expose them to slow mass loss to probe the response of the stellar radius. In addition, we compute the corresponding Roche-lobe overflow mass-transfer evolution with our detailed binary stellar evolution code, approximating the compact objects as point masses. We find that a hydrogen/helium gradient in the layers beneath the surface, as it is likely present in the well-studied donor stars of observed SGBXs, can enable nuclear timescale mass-transfer in SGXBs with a BH or a NS accretor, even for mass ratios in excess of 20. In our binary evolution models, the donor stars rapidly decrease their thermal equilibrium radius and can therefore cope with the inevitably strong orbital contraction imposed by the high mass ratio. Our results open a new perspective for understanding the large number of Galactic SGXBs, and their almost complete absence in the SMC. They may also offer a way to obtain more ULX systems, to find nuclear timescale mass-transfer in ULX systems even with neutron star accretors, and shed new light on the origin of the strong B-field in these neutron stars.Comment: 23 pages, 21 figures, we are thankful for any comments an this draf

Ultra-luminous X-ray sources and neutron-star-black-hole mergers from very massive close binaries at low metallicity

Gravitational waves from the binary black hole (BH) merger GW150914 may enlighten our understanding of ultra-luminous X-ray sources (ULXs), as BHs>30Msun can reach luminosities>4x10^39 erg s^-1 without exceeding their Eddington limit. It is then important to study variations of evolutionary channels for merging BHs, which might instead form accreting BHs and become ULXs. It was recently shown that massive binaries with mass ratios close to unity and tight orbits can undergo efficient rotational mixing and evolve chemically homogeneously, resulting in a compact BH binary. We study similar systems by computing ~120000 detailed binary models with the MESA code covering a wide range of initial parameters. For initial mass ratios M2/M1~0.1-0.4, primaries >40Msun can evolve chemically homogeneously, remaining compact and forming a BH without undergoing Roche-lobe overflow. The secondary then expands and transfers mass to the BH, initiating a ULX phase. We predict that ~1 out of 10^4 massive stars evolves this way, and that in the local universe 0.13 ULXs per Msun yr^-1 of star-formation rate are observable, with a strong preference for low-metallicities. At metallicities log Z>-3, BH masses in ULXs are limited to 60Msun due to the occurrence of pair-instability supernovae which leave no remnant, resulting in an X-ray luminosity cut-off. At lower metallicities, very massive stars can avoid exploding as pair-instability supernovae and instead form BHs with masses above 130Msun, producing a gap in the ULX luminosity distribution. After the ULX phase, neutron-star-BH binaries that merge in less than a Hubble time are produced with a formation rate <0.2 Gpc^-3 yr^-1. We expect that upcoming X-ray observatories will test these predictions, which together with additional gravitational wave detections will provide strict constraints on the origin of the most massive BHs that can be produced by stars.Comment: Accepted for publication in A&A. 19 Pages plus 16 pages of appendices. Abstract abridge

Correlation of Matrix Metalloproteinases and Tissue Inhibitors of Matrix Metalloproteinase Expression in Ileal Carcinoids, Lymph Nodes and Liver Metastasis with Prognosis and Survival

Purpose: Ileal carcinoids are gut epithelial tumors originating from serotonin-containing enterochromaffin (EC) cells. Therapeutic options for effectively inhibiting the growth and spread of metastatic carcinoids are still limited. We aimed to identify the role of matrix metalloproteinases (MMPs) and their endogenous tissue inhibitors (TIMPs) during tumor development and metastasis. Patients and Methods: Tissue samples were obtained from surgically treated patients. Expression of the EC-cell marker, vesicular monoamine transporter-1 (VMAT-1), was used to verify ileal carcinoids. We investigated the differential expression of MMP-2, 7, 9, 11, and 13 and their endogenous inhibitors (TIMP-1, 2, and 3) by quantitative real-time RT-PCR in 25 primary tumors, their corresponding lymph node metastases and/or liver metastases and matched normal mucosa. Results: Significantly increased expression of VMAT-1, MMP-2, MMP-11, TIMP-1 and TIMP-3 was determined by quantitative RT-PCR in EC-cell carcinoids compared to normal intestinal mucosa (p < 0.05). In contrast, MMP-2 and MMP-9 as well as TIMP-1, TIMP-2, and TIMP-3 expression in primary tumors of patients with liver metastases (M1) was significantly lower than in patients lacking liver metastases (M0). EC-cell tumors were significantly larger in the M1 group of tumors, while VMAT-1 expression was significantly decreased. We found an inverse correlation between tumor size and prognosis. Univariate analysis further revealed that decreased expression of VMAT-1, MMP-2 and TIMP-3 in primary tumors was significantly associated with a reduced survival time of the patients. Conclusion: Our data reveal that MMP-2 and TIMP-3 expression together with VMAT-1 expression are of potential prognostic and clinical value in ileal carcinoids. Copyright (C) 2008 S. Karger AG, Base

The Role of State Health Departments in Supporting Community-based Obesity Prevention

Background: Recent national attention to obesity prevention has highlighted the importance of community-based initiatives. State health departments are in a unique position to offer resources and support for local obesity prevention efforts. Community Context: In North Carolina, one-third of children are overweight or obese. North Carolina's Division of Public Health supports community-based obesity prevention by awarding annual grants to local health departments, providing ongoing training and technical assistance, and engaging state-level partners and resources to support local efforts. Methods: The North Carolina Division of Public Health administered grants to 5 counties to implement the Childhood Obesity Prevention Demonstration Project; counties simultaneously carried out interventions in the community, health care organizations, worksites, schools, child care centers, and faith communities. Outcome: The North Carolina Division of Public Health worked with 5 local health departments to implement community-wide policy and environmental changes that support healthful eating and physical activity. The state health department supported this effort by working with state partners to provide technical assistance, additional funding, and evaluation. Interpretation: State health departments are well positioned to coordinate technical assistance and leverage additional support to increase the strength of community-based obesity prevention efforts

Effects on Breathing of Agonists to μ-opioid or GABA\u3csub\u3eA\u3c/sub\u3e Receptors Dialyzed into the Ventral Respiratory Column of Awake and Sleeping Goats

Pulmonary ventilation (V̇I) in awake and sleeping goats does not change when antagonists to several excitatory G protein-coupled receptors are dialyzed unilaterally into the ventral respiratory column (VRC). Concomitant changes in excitatory neuromodulators in the effluent mock cerebral spinal fluid (mCSF) suggest neuromodulatory compensation. Herein, we studied neuromodulatory compensation during dialysis of agonists to inhibitory G protein-coupled or ionotropic receptors into the VRC. Microtubules were implanted into the VRC of goats for dialysis of mCSF mixed with agonists to either μ-opioid (DAMGO) or GABAA (muscimol) receptors. We found: (1) V̇I decreased during unilateral but increased during bilateral dialysis of DAMGO, (2) dialyses of DAMGO destabilized breathing, (3) unilateral dialysis of muscimol increased V̇I, and (4) dialysis of DAMGO decreased GABA in the effluent mCSF. We conclude: (1) neuromodulatory compensation can occur during altered inhibitory neuromodulator receptor activity, and (2) the mechanism of compensation differs between G protein-coupled excitatory and inhibitory receptors and between G protein-coupled and inotropic inhibitory receptors

State-Dependent and -Independent Effects of Dialyzing Excitatory Neuromodulator Receptor Antagonists into the Ventral Respiratory Column

Unilateral dialysis of the broad-spectrum muscarinic receptor antagonist atropine (50 mM) into the ventral respiratory column [(VRC) including the pre-Bötzinger complex region] of awake goats increased pulmonary ventilation (V̇i) and breathing frequency (f), conceivably due to local compensatory increases in serotonin (5-HT) and substance P (SP) measured in effluent mock cerebral spinal fluid (mCSF). In contrast, unilateral dialysis of a triple cocktail of antagonists to muscarinic (atropine; 5 mM), neurokinin-1, and 5-HT receptors does not alter V̇i or f, but increases local SP. Herein, we tested hypotheses that 1) local compensatory 5-HT and SP responses to 50 mM atropine dialyzed into the VRC of goats will not differ between anesthetized and awake states; and 2) bilateral dialysis of the triple cocktail of antagonists into the VRC of awake goats will not alter V̇i or f, but will increase local excitatory neuromodulators. Through microtubules implanted into the VRC of goats, probes were inserted to dialyze mCSF alone (time control), 50 mM atropine, or the triple cocktail of antagonists. We found 1) equivalent increases in local 5-HT and SP with 50 mM atropine dialysis during wakefulness compared with isoflurane anesthesia, but V̇i and f only increased while awake; and 2) dialyses of the triple cocktail of antagonists increased V̇i, f, 5-HT, and SP

Progenitors of gravitational wave mergers: Binary evolution with the stellar grid-based code ComBinE

The first gravitational wave detections of mergers between black holes and neutron stars represent a remarkable new regime of high-energy transient astrophysics. The signals observed with LIGO-Virgo detectors come from mergers of extreme physical objects which are the end products of stellar evolution in close binary systems. To better understand their origin and merger rates, we have performed binary population syntheses at different metallicities using the new grid-based binary population synthesis code ComBinE. Starting from newborn pairs of stars, we follow their evolution including mass loss, mass transfer and accretion, common envelopes and supernova explosions. We apply the binding energies of common envelopes based on dense grids of detailed stellar structure models, make use of improved investigations of the subsequent Case BB Roche-lobe overflow and scale supernova kicks according to the stripping of the exploding stars. We demonstrate that all the double black hole mergers, GW150914, LVT151012, GW151226, GW170104, GW170608 and GW170814, as well as the double neutron star merger GW170817, are accounted for in our models in the appropriate metallicity regime. Our binary interaction parameters are calibrated to match the accurately determined properties of Galactic double neutron star systems, and we discuss their masses and types of supernova origin. Using our default values for the input physics parameters, we find a double neutron star merger rate of about 3.0 Myr-1 for Milky-Way equivalent galaxies. Our upper limit to the merger-rate density of double neutron stars is R≃400 yr-1 Gpc-3 in the local Universe (z=0)