Understanding Compact Object Formation and Natal Kicks. IV. The case of IC 10 X-1

The extragalactic X-ray binary IC 10 X-1 has attracted attention as it is possibly the host of the most massive stellar-mass black-hole (BH) known to date. Here we consider all available observational constraints and construct its evolutionary history up to the instant just before the formation of the BH. Our analysis accounts for the simplest possible history that includes three evolutionary phases: binary orbital dynamics at core collapse, common envelope (CE) evolution, and evolution of the BH--helium star binary progenitor of the observed system. We derive the complete set of constraints on the progenitor system at various evolutionary stages. Specifically: right before the core collapse event, we find the mass of the BH immediate progenitor to be > 31 Msun (at 95% of confidence, same hereafter). The magnitude of the natal kick imparted to the BH is constrained to be < 130 km/s. Furthermore, we find that the "enthalpy" formalism recently suggested by Ivanova & Chaichenets is able to explain the existence of IC 10 X-1 without the need of invoking unreasonably high CE efficiencies. With this physically motivated formalism, we find that the CE efficiency required to explain the system is in the range of 0.6--1.Comment: 15 pages, 9 figures, submitted to Ap

Constraints on Natal Kicks in Galactic Double Neutron Star Systems

Since the discovery of the first double neutron star (DNS) system in 1975 by Hulse and Taylor, there are currently 8 confirmed DNS in our galaxy. For every system, the masses of both neutron stars, the orbital semi- major axis and eccentricity are measured, and proper motion is known for half of the systems. Using the orbital parameters and kinematic information, if available, as constraints for all system, we investigate the immediate progenitor mass of the second-born neutron star and the magnitude of the supernova kick it received at birth, with the primary goal to understand the core collapse mechanism leading to neutron star formation. Compared to earlier studies, we use a novel method to address the uncertainty related to the unknown radial velocity of the observed systems. For PSR B1534+12 and PSR B1913+16, the kick magnitudes are 150 - 270 km/s and 190 - 450 km/s (with 95% confidence) respectively, and the progenitor masses of the 2nd born neutron stars are 1.3 - 3.4 Msun and 1.4 - 5.0 Msun (95%), respectively. These suggest that the 2nd born neutron star was formed by an iron core collapse supernova in both systems. For PSR J0737-3039, on the other hand, the kick magnitude is only 5 - 120 km/s (95%), and the progenitor mass of the 2nd born neutron star is 1.3 - 1.9 Msun (95%). Because of the relatively low progenitor mass and kick magnitude, the formation of the 2nd born neutron star in PSR J0737-3039 is potentially connected to an electron capture supernova of a massive O - Ne - Mg white dwarf. For the remaining 5 Galactic DNS, the kick magnitude ranges from several tens to several hundreds of km/s, and the progenitor mass of the 2nd formed neutron star can be as low as ~1.5 Msun, or as high as ~8 Msun. Therefore in these systems, it is not clear which type of supernova is more likely to form the 2nd neutron star.Comment: 13 pages, 16 figures, accepted for publication in Ap

Risks and Mitigating Factors in Psychosocial Adjustment of Spousal Caregivers of People with Dementia

By applying the Stress Process Model to examine the characteristics of people with dementia and their spousal caregivers, this study aims to identify the potential risk and mitigating factors of psychosocial adjustment among the spousal caregivers. We recruited 80 care recipient-caregiver couples in Hong Kong and examined the relationships of socio-economic, care recipient’s, and caregiver’s factors with spousal caregivers’ psychosocial adjustment. It was found that care recipients’ cognitive functions were associated with caregivers’ reported frequencies of their behavioral and psychological symptoms of dementia (BPSD) (r = .30, p = .008), and caregivers’ perceived burden of caregiving (r = -.54, p = .008). Caregivers’ quality of life was associated with their perceived caregiving burden (r = -.82, p = .001) and self-efficacy (r = .32, p = .001). Upon further examining the caregiving model with these parameters, a significant multivariate general linear model was found with (F (1, 12) = 13.06, p = .001, partial eta square = .70, observed power = .99). Moreover, female caregivers reported higher sense of caregiving stress and poorer quality of life than male caregivers. This study found that the cognitive functions and BPSD of care recipients with dementia and perceived level of caregiving burden are strongly associated with degrees of psychosocial adjustment among their spousal caregivers. The self-perceived caregiving role in a family is also a possible confounding factor contributing to the perceived caregiving burden. To support in-home caregiving of people with dementia, strategies to empower spousal caregivers to execute their caregiving roles are recommended