scholarly journals The completeness-corrected rate of stellar encounters with the Sun from the first Gaia data release

2017 ◽  
Vol 609 ◽  
pp. A8 ◽  
Author(s):  
C. A. L. Bailer-Jones
Keyword(s):  
Oort Cloud ◽  
Selection Function ◽  
The Sun ◽  
Accurate Analysis ◽  
The Past ◽  
Gravitational Perturbations ◽  
Galactic Potential ◽  
Data Release ◽  
Spatial Velocity ◽  
To Come

I report on close encounters of stars to the Sun found in the first Gaia data release (GDR1). Combining Gaia astrometry with radial velocities of around 320 000 stars drawn from various catalogues, I integrate orbits in a Galactic potential to identify those stars which pass within a few parsecs. Such encounters could influence the solar system, for example through gravitational perturbations of the Oort cloud. 16 stars are found to come within 2 pc (although a few of these have dubious data). This is fewer than were found in a similar study based on Hipparcos data, even though the present study has many more candidates. This is partly because I reject stars with large radial velocity uncertainties (>10 km s-1), and partly because of missing stars in GDR1 (especially at the bright end). The closest encounter found is Gl 710, a K dwarf long-known to come close to the Sun in about 1.3 Myr. The Gaia astrometry predict a much closer passage than pre-Gaia estimates, however: just 16 000 AU (90% confidence interval: 10 000–21 000 AU), which will bring this star well within the Oort cloud. Using a simple model for the spatial, velocity, and luminosity distributions of stars, together with an approximation of the observational selection function, I model the incompleteness of this Gaia-based search as a function of the time and distance of closest approach. Applying this to a subset of the observed encounters (excluding duplicates and stars with implausibly large velocities), I estimate the rate of stellar encounters within 5 pc averaged over the past and future 5 Myr to be 545 ± 59 Myr-1. Assuming a quadratic scaling of the rate within some encounter distance (which my model predicts), this corresponds to 87 ± 9 Myr-1 within 2 pc. A more accurate analysis and assessment will be possible with future Gaia data releases.

scholarly journals New stellar encounters discovered in the second Gaia data release

2018 ◽  
Vol 616 ◽  
pp. A37 ◽  
Author(s):  
C. A. L. Bailer-Jones ◽  
J. Rybizki ◽  
R. Andrae ◽  
M. Fouesneau
Keyword(s):  
Monte Carlo ◽  
Oort Cloud ◽  
The Sun ◽  
Dimensional Phase Space ◽  
Cool Stars ◽  
Galactic Potential ◽  
Data Release ◽  
Present Rate ◽  
Galaxy Model ◽  
Space Data

Passing stars may play an important role in the evolution of our solar system. We search for close stellar encounters to the Sun among all 7.2 million stars in Gaia DR2 that have six-dimensional phase space data. We characterize encounters by integrating their orbits through a Galactic potential and propagating the correlated uncertainties via a Monte Carlo resampling. After filtering to remove spurious data, we find 694 stars that have median (over uncertainties) closest encounter distances within 5 pc, all occurring within 15 Myr from now. 26 of these have at least a 50% chance of coming closer than 1 pc (and 7 within 0.5 pc), all but one of which are newly discovered here. We confirm some and refute several other previously-identified encounters, confirming suspicions about their data. The closest encounter in the sample is Gl 710, which has a 95% probability of coming closer than 0.08 pc (17 000 AU). Taking mass estimates obtained from Gaia astrometry and multiband photometry for essentially all encounters, we find that Gl 710 also has the largest impulse on the Oort cloud. Using a Galaxy model, we compute the completeness of the Gaia DR2 encountering sample as a function of perihelion time and distance. Only 15% of encounters within 5 pc occurring within ±5 Myr of now have been identified, mostly due to the lack of radial velocities for faint and/or cool stars. Accounting for the incompleteness, we infer the present rate of encounters within 1 pc to be 19.7 ± 2.2 per Myr, a quantity expected to scale quadratically with the encounter distance out to at least several pc. Spuriously large parallaxes in our sample from imperfect filtering would tend to inflate both the number of encounters found and this inferred rate. The magnitude of this effect is hard to quantify.

scholarly journals Comet C/2018 V1 (Machholz–Fujikawa–Iwamoto): dislodged from the Oort Cloud or coming from interstellar space?

2019 ◽  
Vol 489 (1) ◽  
pp. 951-961 ◽  
Author(s):  
C de la Fuente Marcos ◽  
R de la Fuente Marcos
Keyword(s):  
Solar System ◽  
Dynamical Evolution ◽  
Oort Cloud ◽  
Interstellar Space ◽  
The Sun ◽  
The Past ◽  
Using Data ◽  
To Receive ◽  
Practical Feasibility

ABSTRACT The chance discovery of the first interstellar minor body, 1I/2017 U1 (‘Oumuamua), indicates that we may have been visited by such objects in the past and that these events may repeat in the future. Unfortunately, minor bodies following nearly parabolic or hyperbolic paths tend to receive little attention: over 3/4 of those known have data-arcs shorter than 30 d and, consistently, rather uncertain orbit determinations. This fact suggests that we may have observed interstellar interlopers in the past, but failed to recognize them as such due to insufficient data. Early identification of promising candidates by using N-body simulations may help in improving this situation, triggering follow-up observations before they leave the Solar system. Here, we use this technique to investigate the pre- and post-perihelion dynamical evolution of the slightly hyperbolic comet C/2018 V1 (Machholz–Fujikawa–Iwamoto) to understand its origin and relevance within the context of known parabolic and hyperbolic minor bodies. Based on the available data, our calculations suggest that although C/2018 V1 may be a former member of the Oort Cloud, an origin beyond the Solar system cannot be excluded. If extrasolar, it might have entered the Solar system from interstellar space at low relative velocity with respect to the Sun. The practical feasibility of this alternative scenario has been assessed within the kinematic context of the stellar neighbourhood of the Sun, using data from Gaia second data release, and two robust solar sibling candidates have been identified. Our results suggest that comets coming from interstellar space at low heliocentric velocities may not be rare.

Approaches of stars to the Sun

1999 ◽  
Vol 173 ◽  
pp. 345-352 ◽  
Author(s):  
P.A. Dybczyński ◽  
P. Kankiewicz
Keyword(s):  
Minimum Distance ◽  
Galactic Disk ◽  
Equations Of Motion ◽  
Oort Cloud ◽  
The Sun ◽  
The Past ◽  
Straight Line ◽  
The Galaxy ◽  
Hipparcos Catalogue ◽  
Nearby Stars

AbstractClose approaches of stars to the Solar System perturb comets from the Oort cloud so that they pass into the planetary system − the gravitational impulse changes the distribution of observable comets. This paper presents the results of calculations of the motion of stars in the solar neighbourhood in the past and future. The main results for each star are: the time of the encounter and the minimum distance between the Sun and the star. They are calculated using three different methods: a straight line motion model, a model with a Sun − star Keplerian interaction, and the numerical integration of the equations of motion with galactic perturbations included. In the last case, two models of the Galactic potential are used: a simplified potential of the Galactic disk and the more complex potential of the Galaxy by Dauphole and Colin. Coordinates and velocities of nearby stars are taken from several different catalogues: the Gliese catalogue, the Hipparcos catalogue, and the Barbier-Brossat catalogue of Radial Velocities.

Suicidal Behavior in Black South Africans

Crisis ◽  
2003 ◽  
Vol 24 (1) ◽  
pp. 24-28 ◽  
Author(s):  
Lourens Schlebusch ◽  
Naseema B.M. Vawda ◽  
Brenda A. Bosch
Keyword(s):  
South African ◽  
Suicidal Behavior ◽  
Health Care Facilities ◽  
South African Society ◽  
South Africans ◽  
The Past ◽  
The People ◽  
Care Facilities ◽  
Black South Africans ◽  
To Come

Summary: In the past suicidal behavior among Black South Africans has been largely underresearched. Earlier studies among the other main ethnic groups in the country showed suicidal behavior in those groups to be a serious problem. This article briefly reviews some of the more recent research on suicidal behavior in Black South Africans. The results indicate an apparent increase in suicidal behavior in this group. Several explanations are offered for the change in suicidal behavior in the reported clinical populations. This includes past difficulties for all South Africans to access health care facilities in the Apartheid (legal racial separation) era, and present difficulties of post-Apartheid transformation the South African society is undergoing, as the people struggle to come to terms with the deleterious effects of the former South African racial policies, related socio-cultural, socio-economic, and other pressures.

Screen Wonders of the Past: And to Come?

1957 ◽  
Vol 11 (4) ◽  
pp. 381-393
Author(s):  
Kenneth MacGowan
Keyword(s):  
The Past ◽  
To Come

Music and Memory: The Tlatelolco Refrain

2015 ◽  
Vol 2 (1) ◽  
Author(s):  
Josh Kun
Keyword(s):  
State Violence ◽  
First Century ◽  
Student Movements ◽  
Octavio Paz ◽  
Mexican History ◽  
The Past ◽  
Rock Bands ◽  
To Come ◽  
Musical Memory ◽  
A Current

Ever since the 1968 student movements and the events surrounding the Tlatelolco massacre, Mexico City rock bands have openly engaged with the intersection of music and memory. Their songs offer audiences a medium through which to come to terms with the events of the past as a means of praising a broken world, to borrow the poet Adam Zagajewski’s phrase. Contemporary songs such as Saúl Hernández’s “Fuerte” are a twenty-first-century voicing of the ceaseless revolutionary spirit that John Gibler has called “Mexico unconquered,” a current of rebellion and social hunger for justice that runs in the veins of Mexican history. They are the latest additions to what we might think about as “the Mexico unconquered songbook”: musical critiques of impunity and state violence that are rooted in the weaponry of memory, refusing to focus solely on the present and instead making connections with the political past. What Octavio Paz described as a “swash of blood” that swept across “the international subculture of the young” during the events in Tlatelolco Plaza on October 2, 1968, now becomes a refrain of musical memory and political consciousness that extends across eras and generations. That famous phrase of Paz’s is a reminder that these most recent Mexican musical interventions, these most recent formations of a Mexican subculture of the young, maintain a historically tested relationship to blood, death, loss, and violence.

Corporate Reorganization Law and Forces of Change

2020 ◽  
Author(s):  
Sarah Paterson
Keyword(s):  
Financial Crisis ◽  
Conceptual Framework ◽  
Conceptual Frameworks ◽  
Corporate Reorganization ◽  
Process Of Change ◽  
The Past ◽  
To Come ◽  
The Way

This book is concerned with the way in which forces of change, from the fields of finance and non-financial corporates, cause participants in the corporate reorganization process to adapt the ways in which they mobilize corporate reorganization law. It argues that scholars, practitioners, judges, and the legislature must all take care to connect their conceptual frameworks to the specific adaptations which emerge from this process of change. It further argues that this need to connect theoretical and policy concepts with practical adaptations has posed particular challenges when US corporate reorganization law has been under examination in the decade since the financial crisis. At the same time, the book suggests that English scholars, practitioners, judges, and the legislature have been more successful, over the course of the past ten years, in choosing concepts to frame their analysis which are sensitive to the ways in which corporate reorganization law is currently used. Nonetheless, it suggests that new problems may be on the horizon for English corporate reorganization lawyers in adapting their conceptual framework in the decades to come.

scholarly journals A Sense of Presence: Mediating an American Apocalypse

Religions ◽  
2021 ◽  
Vol 12 (1) ◽  
pp. 59
Author(s):  
Rachel Wagner
Keyword(s):  
Religious Practice ◽  
Religious Institutions ◽  
The Past ◽  
Sense Of Presence ◽  
The World ◽  
The Future ◽  
To Come

Here I build upon Robert Orsi’s work by arguing that we can see presence—and the longing for it—at work beyond the obvious spaces of religious practice. Presence, I propose, is alive and well in mediated apocalypticism, in the intense imagination of the future that preoccupies those who consume its narratives in film, games, and role plays. Presence is a way of bringing worlds beyond into tangible form, of touching them and letting them touch you. It is, in this sense, that Michael Hoelzl and Graham Ward observe the “re-emergence” of religion with a “new visibility” that is much more than “simple re-emergence of something that has been in decline in the past but is now manifesting itself once more.” I propose that the “new awareness of religion” they posit includes the mediated worlds that enchant and empower us via deeply immersive fandoms. Whereas religious institutions today may be suspicious of presence, it lives on in the thick of media fandoms and their material manifestations, especially those forms that make ultimate promises about the world to come.

3D RECONSTRUCTION OF BREAST CANCER FROM MAMMOGRAMS USING VOLUME RENDERING TECHNIQUES

2015 ◽  
Vol 75 (2) ◽  
Author(s):  
Ho Wei Yong ◽  
Abdullah Bade ◽  
Rajesh Kumar Muniandy
Keyword(s):  
Breast Cancer ◽  
3D Reconstruction ◽  
Computational Cost ◽  
Reconstruction Method ◽  
Cancer Model ◽  
Volume Reconstruction ◽  
The Past ◽  
Breast Cancer Model ◽  
Reconstruction Software ◽  
To Come

Over the past thirty years, a number of researchers have investigated on 3D organ reconstruction from medical images and there are a few 3D reconstruction software available on the market. However, not many researcheshave focused on3D reconstruction of breast cancer’s tumours. Due to the method complexity, most 3D breast cancer’s tumours reconstruction were done based on MRI slices dataeven though mammogram is the current clinical practice for breast cancer screening. Therefore, this research will investigate the process of creating a method that will be able to reconstruct 3D breast cancer’s tumours from mammograms effectively.  Several steps were proposed for this research which includes data acquisition, volume reconstruction, andvolume rendering. The expected output from this research is the 3D breast cancer’s tumours model that is generated from correctly registered mammograms. The main purpose of this research is to come up with a 3D reconstruction method that can produce good breast cancer model from mammograms while using minimal computational cost.

scholarly journals Galactic tide and local stellar perturbations on the Oort cloud: creation of interstellar comets

2019 ◽  
Vol 629 ◽  
pp. A139 ◽  
Author(s):  
S. Torres ◽  
M. X. Cai ◽  
A. G. A. Brown ◽  
S. P. Zwart
Keyword(s):  
Dynamical Evolution ◽  
Cumulative Effect ◽  
Oort Cloud ◽  
Radial Velocities ◽  
Current Status ◽  
Interstellar Space ◽  
The Sun ◽  
Semi Major Axis ◽  
Software Environment ◽  
External Perturbations

Comets in the Oort cloud evolve under the influence of internal and external perturbations, such as giant planets, stellar passages, and the Galactic gravitational tidal field. We aim to study the dynamical evolution of the comets in the Oort cloud, accounting for the perturbation of the Galactic tidal field and passing stars. We base our study on three main approaches; analytic, observational, and numerical. We first construct an analytical model of stellar encounters. We find that individual perturbations do not modify the dynamics of the comets in the cloud unless very close (<0.5 pc) encounters occur. Using proper motions, parallaxes, and radial velocities from Gaia DR2 and combining them with the radial velocities from other surveys, we then construct an astrometric catalogue of the 14 659 stars that are within 50 pc of the Sun. For all these stars we calculate the time and distance of closest approach to the Sun. We find that the cumulative effect of relatively distant (≤1 pc) passing stars can perturb the comets in the Oort cloud. Finally, we study the dynamical evolution of the comets in the Oort cloud under the influence of multiple stellar encounters from stars that pass within 2.5 pc of the Sun and the Galactic tidal field over ±10 Myr. We use the Astrophysical Multipurpose Software Environment (AMUSE), and the GPU-accelerated direct N-body code ABIE. We considered two models for the Oort cloud, compact (a ≤ 0.25 pc) and extended (a ≤ 0.5 pc). We find that the cumulative effect of stellar encounters is the major perturber of the Oort cloud for a compact configuration while for the extended configuration the Galactic tidal field is the major perturber. In both cases the cumulative effect of distant stellar encounters together with the Galactic tidal field raises the semi-major axis of ~1.1% of the comets at the edge of the Oort cloud up to interstellar regions (a > 0.5 pc) over the 20 Myr period considered. This leads to the creation of transitional interstellar comets (TICs), which might become interstellar objects due to external perturbations. This raises the question of the formation, evolution, and current status of the Oort cloud as well as the existence of a “cloud” of objects in the interstellar space that might overlap with our Oort cloud, when considering that other planetary systems should undergo similar processes leading to the ejection of comets.

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