What does the IMF really tell us about star formation?

Obtaining accurate measurements of the initial mass function (IMF) is often considered to be the key to understanding star formation, and a universal IMF is often assumed to imply a universal star formation process. Here, we illustrate that different modes of star formation can result in the same IMF, and that, in order to truly understand star formation, a deeper understanding of the primordial binary population is necessary. Detailed knowledge on the binary fraction, mass ratio distribution, and other binary parameters, as a function of mass, is a requirement for recovering the star formation process from stellar population measurements

The Long-term Dynamical Evolution of Disk-fragmented Multiple Systems in the Solar Neighborhood

The origin of very low-mass hydrogen-burning stars, brown dwarfs (BDs), and planetary-mass objects (PMOs) at the low-mass end of the initial mass function is not yet fully understood. Gravitational fragmentation of circumstellar disks provides a possible mechanism for the formation of such low-mass objects. The kinematic and binary properties of very low-mass objects formed through disk fragmentation at early times (<10 Myr) were discussed in our previous paper. In this paper we extend the analysis by following the long-term evolution of diskfragmented systems up to an age of 10 Gyr, covering the ages of the stellar and substellar populations in the Galactic field. We find that the systems continue to decay, although the rates at which companions escape or collide with each other are substantially lower than during the first 10 Myr, and that dynamical evolution is limited beyond 1 Gyr. By t = 10 Gyr, about one third of the host stars are single, and more than half have only one companion left. Most of the other systems have two companions left that orbit their host star in widely separated orbits. A small fraction of companions have formed binaries that orbit the host star in a hierarchical triple configuration. The majority of such double-companion systems have internal orbits that are retrograde with respect to their orbits around their host stars. Our simulations allow a comparison between the predicted outcomes of disk fragmentation with the observed low-mass hydrogen-burning stars, BDs, and PMOs in the solar neighborhood. Imaging and radial velocity surveys for faint binary companions among nearby stars are necessary for verification or rejection of the formation mechanism proposed in this paper

Planetary systems in a star cluster I: the Solar system scenario

Stars and planetary system

Stability of multiplanetary systems in star clusters

Most stars form in star clusters and stellar associations. However, only about ˜1 per cent of the presently known exoplanets are found in these environments. To understand the roles of star cluster environments in shaping the dynamical evolution of planetary systems, we carry out direct N-body simulations of four planetary system models in three different star cluster environments with respectively N = 2k, 8k and 32k stars. In each cluster, an ensemble of initially identical planetary systems are assigned to solar-type stars with ˜1 M⊙ and evolved for 50 Myr. We found that following the depletion of protoplanetary discs, external perturbations and planet-planet interactions are two driving mechanisms responsible for the destabilization of planetary systems. The planet survival rate varies from ˜95 per cent in the N = 2k cluster to ˜60 per cent in the N = 32k cluster, which suggests that most planetary systems can indeed survive in low-mass clusters, except in the central regions. We also find that planet ejections through stellar encounters are cumulative processes, as only ˜3 per cent of encounters are strong enough to excite the eccentricity by Δe ≥ 0.5. Short-period planets can be perturbed through orbit crossings with long-period planets. When taking into account planet-planet interactions, the planet ejection rate nearly doubles, and therefore multiplicity contributes to the vulnerability of planetary systems. In each ensemble, ˜0.2 per cent of planetary orbits become retrograde due to random directions of stellar encounters. Our results predict that young low-mass star clusters are promising sites for next-generation planet surveys, yet low planet detection rates are expected in dense globular clusters such as 47 Tuc. Nevertheless, planets in denser stellar environments are likely to have shorter orbital periods, which enhance their detectability.Computational astrophysicsStars and planetary system

Block time step storage scheme for astrophysical N-body simulations

Astrophysical research in recent decades has made significant progress thanks to the availability of various N-body simulation techniques. With the rapid development of high-performance computing technologies, modern simulations have been able to use the computing power of massively parallel clusters with more than 105 GPU cores. While unprecedented accuracy and dynamical scales have been achieved, the enormous amount of data being generated continuously poses great challenges for the subsequent procedures of data analysis and archiving. In this paper, we propose an adaptive storage scheme for simulation data, inspired by the block time step (BTS) integration scheme found in a number of direct N-body integrators available nowadays, as an urgent response to these challenges. The proposed scheme, namely, the BTS storage scheme, works by minimizing the data redundancy by assigning individual output frequencies to the data as required by the researcher. As demonstrated by benchmarks, the proposed scheme is applicable to a wide variety of simulations. Despite the main focus of developing a solution for direct N-body simulation data, the methodology is transferable for grid-based or tree-based simulations where hierarchical time stepping is used.FWN – Publicaties zonder aanstelling Universiteit Leide

Loneliness is associated with smoking and alcohol consumption in older adults: Findings from the Chinese Longitudinal Healthy Longevity Survey

Introduction Despite the well-known health risks associated with tobacco smoking and alcohol consumption, this study explores the association between loneliness and these behaviors specifically among the elderly in the Chinese context. It examines the relationship between loneliness and the tendency to smoke and drink among this demographic. Additionally, the research investigates how these associations vary between genders among the elderly, identifying distinct patterns in the relationship between loneliness and smoking and alcohol consumption among elderly men and women. Method This secondary cross-sectional analysis used data from the 2017–2018 Chinese Longitudinal Healthy Longevity Survey. We employed multivariate multinomial logistic regression to analyze these relationships, including sex-specific associations, and reported adjusted odds ratios (AOR), confidence intervals (CI), and p-values. The analysis was conducted using STATA version 18, with significant p-values set at 0.05. Result Our analysis included 15,874 participants, of which 6.4% (95% CI: 6.0 – 6.8; N=1015) were categorized as Always Lonely, indicating frequent loneliness, and 17.0% (95% CI: 16.4 – 17.6; N=2702) as Sometimes Lonely, indicating occasional loneliness, with 76.6% (95% CI: 75.9 – 77.2; N=12,157) not experiencing loneliness. The mean age was 85.5 years with a standard deviation of 11.7. Gender distribution showed that 43.6% (n=6925) were male and 56.4% (n=8949) were female. Frequently lonely participants had increased odds of current smoking (AOR = 1.26; 95% CI: 1.01–1.57; p = 0.040), while those occasionally lonely were less inclined towards current drinking (AOR = 0.81; 95% CI: 0.70–0.94; p = 0.005). Gender-specific outcomes indicated that often lonely men were more likely to smoke (AOR = 1.43; 95% CI: 1.10–1.87; p = 0.008) and were also less likely to be current drinkers (AOR = 0.74; 95% CI: 0.55–0.98; p = 0.038). No significant associations were found for women in smoking or drinking behaviors relative to loneliness levels. Conclusion Our study identified a significant relationship between loneliness and a higher likelihood of smoking in elderly Chinese men, not women, and observed gender-specific differences in alcohol use, with men showing a lower likelihood of drinking when occasionally lonely, a pattern absent in women. Future prospective studies are required to confirm these findings

On the survival of resonant and non-resonant planetary systems in star clusters

Stars and planetary system

The long-term survival chances of young massive star clusters

We review the long-term survival chances of young massive star clusters (YMCs), hallmarks of intense starburst episodes often associated with violent galaxy interactions. We address the key question as to whether at least some of these YMCs can be considered proto-globular clusters (GCs), in which case these would be expected to evolve into counterparts of the ubiquitous old GCs believed to be among the oldest galactic building blocks. In the absence of significant external perturbations, the key factor determining a cluster's long-term survival chances is the shape of its stellar initial mass function (IMF). It is, however, not straightforward to assess the IMF shape in unresolved extragalactic YMCs. We discuss in detail the promise of using high-resolution spectroscopy to make progress towards this goal, as well as the numerous pitfalls associated with this approach. We also discuss the latest progress in worldwide efforts to better understand the evolution of entire cluster systems, the disruption processes they are affected by, and whether we can use recently gained insights to determine the nature of at least some of the YMCs observed in extragalactic starbursts as proto-GCs. We conclude that there is an increasing body of evidence that GC formation appears to be continuing until today; their long-term evolution crucially depends on their environmental conditions, however.Comment: invited refereed review article; ChJA&A, in press; 33 pages LaTeX (2 postscript figures); requires chjaa.cls style fil