Constraining Binary Evolution with Gravitational Wave Measurements of Chirp Masses

Using the StarTrack binary population synthesis code we investigate the properties of population of compact object binaries. Taking into account the selection effects we calculate the expected properties of the observed binaries.We analyze possible constraints on the stellar evolution models and find that an observed sample of about one hundred mergers will yield strong constraints on the binary evolution scenarios.Comment: Invited talk at "The Astrophysics of Gravitational Wave Sources" Workshop; April 24-26, 2003, U. Maryland; 10 page

Evolving R Coronae Borealis Stars with MESA

The R Coronae Borealis (RCB) stars are rare hydrogen--deficient, carbon--rich supergiants. They undergo extreme, irregular declines in brightness of many magnitudes due to the formation of thick clouds of carbon dust. It is thought that RCB stars result from the mergers of CO/He white dwarf (WD) binaries. We constructed post--merger spherically asymmetric models computed with the MESA code, and then followed the evolution into the region of the HR diagram where the RCB stars are located. We also investigated nucleosynthesis in the dynamically accreting material of CO/He WD mergers which may provide a suitable environment for significant production of 18O and the very low 16O/18O values observed. We have also discovered that the N abundance depends sensitively on the peak temperature in the He--burning shell. Our MESA modeling consists of engineering the star by adding He--WD material to an initial CO--WD model, and then following the post--merger evolution using a nuclear--reaction network to match the observed RCB abundances as it expands and cools to become an RCB star. These new models are more physical because they include rotation, mixing, mass-loss, and nucleosynthesis within MESA. We follow the later evolution beyond the RCB phase to determine the stars' likely lifetimes. The relative numbers of known RCB and Extreme Helium (EHe) stars correspond well to the lifetimes predicted from the MESA models. In addition, most of computed abundances agree very well with the observed range of abundances for the RCB class.Comment: 14 pages, 7 figures, MNRAS in pres

Using the Values-Practice Framework to adopt lifetime optimising behaviours: the case of maintenance

The influence that consumers have on the lifespan of products has attracted increased attention in recent years. Studies have provided an overall understanding of the factors that influence consumer attitudes and behaviours towards product longevity, categorised around the physical properties of a product, and individual and societal characteristics. However, such studies do not yet adequately explain how people could adopt product lifetime optimising behaviours. To fill this gap, the paper analyses a range of studies on what influences product lifetimes, focusing on maintenance activities. It proposes the use of the Values-Practice framework derived from two theoretical positions, social psychology and social practice theory, to consider how to facilitate the adoption of lifetime optimising behaviours. To build this framework, it analyses studies that classify factors influencing attitudes and behaviours towards product lifetimes and then links these to the ‘meaning’, ‘competence’ and ‘material’ elements of practice. The framework could be used as a tool to aid designers under stand the different elements and factors that engage people in maintenance activities. The paper concludes by considering the research requirements for the future application of the framework

Potential Models and Lattice Gauge Current-Current Correlators

We compare current-current correlators in lattice gauge calculations with correlators in different potential models, for a pseudoscalar charmonium in the quark-gluon plasma. An important ingredient in the evaluation of the current-current correlator in the potential model is the basic principle that out of the set of continuum states, only resonance states and Gamow states with lifetimes of sufficient magnitudes can propagate as composite objects and can contribute to the current-current correlator. When the contributions from the bound states and continuum states are properly treated, the potential model current-current correlators obtained with the potential proposed in Ref. [11] are consistent with the lattice gauge correlators. The proposed potential model thus gains support to be a useful tool to complement lattice gauge calculations for the study of $Q\bar Q$ states at high temperatures.Comment: 18 pages, 4 figures, to be published in Physcial Review

An empirical model for protostellar collapse

We propose a new analytic model for the initial conditions of protostellar collapse in relatively isolated regions of star formation. The model is non-magnetic, and is based on a Plummer-like radial density profile as its initial condition. It fits: the observed density profiles of pre-stellar cores and Class 0 protostars; recent observations in pre-stellar cores of roughly constant contraction velocities over a wide range of radii; and the lifetimes and accretion rates derived for Class 0 and Class I protostars. However, the model is very simple, having in effect only 2 free parameters, and so should provide a useful framework for interpreting observations of pre-stellar cores and protostars, and for calculations of radiation transport and time-dependent chemistry. As an example, we model the pre-stellar core L1544.Comment: To appear in Astrophysical Journal, Jan 20th, 2001. 18 pages incl. 3 fig

A Physical Model for the Origin of Quasar Lifetimes

We propose a model of quasar lifetimes in which observational quasar lifetimes and an intrinsic lifetime of rapid accretion are strongly distinguished by the physics of obscuration by surrounding gas and dust. Quasars are powered by gas funneled to galaxy centers, but for a large part of the accretion lifetime are heavily obscured by the large gas densities powering accretion. In this phase, starbursts and black hole growth are fueled but the quasar is buried. Eventually, feedback from accretion energy disperses surrounding gas, creating a window in which the black hole is observable optically as a quasar, until accretion rates drop below those required to maintain a quasar luminosity. We model this process and measure the unobscured and intrinsic quasar lifetimes in a hydrodynamical simulation of a major galaxy merger. The source luminosity is determined from the black hole accretion rate, calculated from local gas properties. We calculate the column density of hydrogen to the source along multiple lines of sight and use these column densities and gas metallicities to determine B-band attenuation of the source. Defining the observable quasar lifetime as the total time with an observed B-band luminosity above some limit L_B,min, we find lifetimes ~10-20 Myr for L_B,min=10^11 L_sun (M_B=-23), in good agreement with observationally determined quasar lifetimes. This is significantly smaller than the intrinsic lifetime ~100 Myr obtained if attenuation is neglected. The ratio of observed to intrinsic lifetime is also strong function of both the limiting luminosity and the observed frequency.Comment: 5 pages, 4 figures, submitted to ApJ Letter

Lifetime of the embedded phase of low-mass star formation and the envelope depletion rates

Motivated by a considerable scatter in the observationally inferred lifetimes of the embedded phase of star formation, we study the duration of the Class 0 and Class I phases in upper-mass brown dwarfs and low-mass stars using numerical hydrodynamics simulations of the gravitational collapse of a large sample of cloud cores. We resolve the formation of a star/disk/envelope system and extend our numerical simulations to the late accretion phase when the envelope is nearly totally depleted of matter. We adopted a classification scheme of Andre et al. and calculate the lifetimes of the Class 0 and Class I phases (\tau_C0 and \tau_CI, respectively) based on the mass remaining in the envelope. When cloud cores with various rotation rates, masses, and sizes (but identical otherwise) are considered, our modeling reveals a sub-linear correlation between the Class 0 lifetimes and stellar masses in the Class 0 phase with the least-squares fit exponent m=0.8 \pm 0.05. The corresponding correlation between the Class I lifetimes and stellar masses in the Class I is super-linear with m=1.2 \pm 0.05. If a wider sample of cloud cores is considered, which includes possible variations in the initial gas temperature, cloud core truncation radii, density enhancement amplitudes, initial gas density and angular velocity profiles, and magnetic fields, then the corresponding exponents may decrease by as much as 0.3. The duration of the Class I phase is found to be longer than that of the Class~0 phase in most models, with a mean ratio \tau_CI / \tau_C0 \approx 1.5--2. A notable exception are YSOs that form from cloud cores with large initial density enhancements, in which case \tau_C0 may be greater than \tau_CI. Moreover, the upper-mass (>= 1.0 Msun) cloud cores with frozen-in magnetic fields and high cloud core rotation rates may have the \tau_CI / \tau_C0 ratios as large as 3.0--4.0. (Abdridged).Comment: Accepted for publication by The Astrophysical Journa