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Tom Mazanec
2018-Apr-12, 02:43 PM
Gliese 710 is now expected to miss the solar system by 13,000 AU about the year 1,352,000 AD https://en.wikipedia.org/wiki/Gliese_710
How often does a star come this close to the sun, per billion years?

antoniseb
2018-Apr-12, 02:58 PM
I'm going to guess about once every million years.
If you want a more precise number, tell us what the lower bound for what you'd call a star (15 Jupiter masses?), and do you mean exactly 13,000 AU as the threshold?
Once we have those numbers, the number you ask for should be easy to calculate.

Tom Mazanec
2018-Apr-12, 04:49 PM
Let's cut it at the "classical" red dwarf limit (0.08 solar masses) and have it 13,000 AU or closer.

kzb
2018-Apr-13, 11:29 AM
There was a list of close approaches published just a few years ago. I remember linking to it on here.

However, the closest approaches in that article were in the light-year range, I think there is one due in about 35,000 years or so.

I looked at the Wikipedia link where it says Gliese 710 will approach to 0.2 light years.

But the reference given on that wiki page does not say this as far as I can see. So where has this information come from?

It also says there is a more-than-zero probability of it approaching to 1000 AU !

Anyhow, this GL 710 approach is much closer than in the list I referred to.

I have also linked in the past a paper which gave estimates for close stellar encounter rates in different regions of the galaxy and in globular clusters.

The upshot was that stellar encounters in the central few kpc of the galaxy and in globular clusters are too frequent to allow complex life to evolve in those regions.

kzb
2018-Apr-13, 12:47 PM
Gliese 710 is now expected to miss the solar system by 13,000 AU about the year 1,352,000 AD https://en.wikipedia.org/wiki/Gliese_710
How often does a star come this close to the sun, per billion years?

It's about once every 1 or 2 billion years.

t = 3.3E+07 years * (100 pc^-3/rho) * (mean relative speed of objects km/s) * (1000 AU/r) * (Msun/Mtotal)

rho is the stellar density (0.12/pc^-3 in our locality)

r is the encounter distance, in this case 13000 AU.

The last term is the ratio of the sun's mass to the sum of the masses of the two stars.

The one question I have is the mean relative speed of objects. I have assumed 10 km/s as an order of mag but others may know better.

grant hutchison
2018-Apr-13, 02:11 PM
Twenty years ago, based on Hipparcos data, Sanchez et al (http://adsabs.harvard.edu/abs/1999AJ....117.1042G). set a lower bound of 4.2 * D2.02/Myr, where D is the distance of closest approach in parsecs. Since 13000AU = 0.063pc, that comes to 0.016/Myr = 16 per billion years. They expected more because Hip was incomplete for low mass stars.

Grant Hutchison

George
2018-Apr-13, 03:28 PM
Twenty years ago, based on Hipparcos data, Sanchez et al (http://adsabs.harvard.edu/abs/1999AJ....117.1042G). set a lower bound of 4.2 * D2.02/Myr, where D is the distance of closest approach in parsecs. Since 13000AU = 0.063pc, that comes to 0.016/Myr = 16 per billion years. They expected more because Hip was incomplete for low mass stars.

Nice find, Grant. [That paper shows a slightly different equation (3.5D2.12/Myr).] I assume the extrapolation to a billion years would be fairly speculative, but the best available.

grant hutchison
2018-Apr-13, 04:13 PM
[That paper shows a slightly different equation (3.5D2.12/Myr).]That's interesting. The preprint in my file drawer has the equation I gave. They must have responded to reviewer feedback before publication. The revision takes it down to 10 per billion.

Grant Hutchison

Tom Mazanec
2018-Apr-14, 03:30 PM
This is another star I look forward to seeing in the GAIA release coming up. See if the estimated distance gets any closer.

kzb
2018-Apr-16, 09:43 AM
<deleted post>

kzb
2018-Apr-18, 12:35 PM
Whichever equation you believe, it does seem that encounters similar to this are not uncommon.

Travel between stellar systems that are 0.2 light years apart is less difficult than systems 5 light years apart.

As I've said before on here, this is an argument against that proposed solution to the Fermi paradox, that interstellar travel is just too difficult.

selden
2018-Apr-18, 01:27 PM
FWIW, "Scholz’s star" (WISE J072003.20-084651.2) probably came within 52,000 AU about 70,000 years ago.
See http://www.rochester.edu/newscenter/scholz-star/ and

The Closest Known Flyby of a Star to the Solar System
Eric E. Mamajek, et al.
https://arxiv.org/abs/1502.04655

That paper estimates passages within 0.25 pc happen at a rate of about 0.1/Myr.

George
2018-Apr-19, 01:45 PM
The Closest Known Flyby of a Star to the Solar System
Eric E. Mamajek, et al.
https://arxiv.org/abs/1502.04655

That paper estimates passages within 0.25 pc happen at a rate of about 0.1/Myr. I think that estimate comes from the same folks (Garcia-Sanchez et al) Grant references, but in an updated 2001 paper. [I failed to snag it.]

selden
2018-Apr-19, 01:49 PM
I think that estimate comes from the same folks (Garcia-Sanchez et al) Grant references, but in an updated 2001 paper. [I failed to snag it.]

You're right. Sorry for my sloppy attribution.

George
2018-Apr-19, 04:57 PM
You're right. Sorry for my sloppy attribution.Just a nit.

But it's interesting that there seems to be a significant change in their earlier equation. I'm not that great at finding articles and I had no luck in my novice attempt to find this newer one. Perhaps someone will find this 2001 paper so we can update the equation.

selden
2018-Apr-19, 08:55 PM
The full text of the published paper is behind The American Astronomical Society's paywall, which probably is why you couldn't find it by a Web search.

If you have access to a library which subscribes to the journal, you should be able to get it for free from them.

STELLAR ENCOUNTERS WITH THE OORT CLOUD BASED ON HIPPARCOS DATA
JOAN GARCIA-SANCHEZ, et.al.

(c) 1999. The American Astronomical Society. All rights reserved. Printed in U.S.A.
Received 1998 May 15 ; accepted 1998 September 4

However, its abstract is available for free at http://adsabs.harvard.edu/abs/1999AJ....117.1042G and says


We find that the rate of close approaches by star systems (single or multiple stars) within a distance D (in parsecs) from the Sun is given by N = 3.5D2.12 Myr-1, less than the number predicted by a simple stellar dynamics model.


I also found a couple of copies of the preprint. This one has handwritten figure numbers, so it's probably the oldest: http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.730.5027&rep=rep1&type=pdf

They say

We find that the rate of close approaches by star systems (single or multiple stars) within a distance D (in parsecs) from t h e Sun is given by N = 4.2 D2.02M yr-1, less than the numbers predicted by simple stellar dynamics models.

Note that "numbers" and "models" were changed, too, from plural to singular.

Tom Mazanec
2018-Apr-26, 09:18 PM
When will I find out the refined estimate from GAIA DR2? How long does it take for such data to result in a published prediction?

selden
2018-Apr-26, 10:30 PM
That's entirely up to whoever is interested in doing the research and whatever other priorities they might have. You could try contacting one of the authors of the papers and ask about it.

Tom Mazanec
2018-Apr-28, 11:21 AM
That's entirely up to whoever is interested in doing the research and whatever other priorities they might have. You could try contacting one of the authors of the papers and ask about it.

How would I go about doing that? Should I try to find their email or phone number? And how would I find that information?
What is the best way of doing this?

selden
2018-Apr-28, 12:55 PM
All published scientific articles include the names and institutional affiliations of their authors.

The Web sites of most research and educational institutions include directories of everyone affiliated with them.

Another location method is to do a generic Web search specifying the author's name and the name of the institution.

Jens
2018-Apr-28, 01:10 PM
And just to add, published papers will have at least one ‘corresponding author’ listed, with the email and address.


Sent from my iPhone using Tapatalk

selden
2018-May-08, 05:28 PM
https://arxiv.org/pdf/1805.02644


An independent confirmation of the future flyby of Gliese 710 to the solar system using Gaia DR2

Authors: R. de la Fuente Marcos, C. de la Fuente Marcos

7-May-2018

kzb
2018-May-09, 04:54 PM
https://arxiv.org/pdf/1805.02644


An independent confirmation of the future flyby of Gliese 710 to the solar system using Gaia DR2

Authors: R. de la Fuente Marcos, C. de la Fuente Marcos

7-May-2018


Thanks for posting that!

This paper finds the Gliese 710 approach will be even closer than the 13,000AU in the previous article. The central expectation is 10,721 +/- 2114 AU.

There is a small chance it could be as close as 4303 AU.

Tom Mazanec
2018-May-11, 02:27 AM
Will future data Releases refine this further?

selden
2018-May-11, 03:09 AM
Yes: future Gaia data releases are intended to have better accuracy in their measurements. Unfortunately, though, the next one (DR3) won't be published for another two years.

Roger E. Moore
2018-Aug-02, 01:00 PM
The most recent paper on stellar flybys of the Solar System is below. It will be interesting to see a large-scale map of objects in the Oort Cloud (if we are ever so lucky) to see if "damage" to it from past flybys can be discerned.

Also, it occurs to me that there should be a lot of material from other stars' Oort Clouds out there in our own, a sort of interstellar mixing of materials. Perhaps we've had exocomets in the past made from different materials than our usual ones--heavier in metals, lighter in metals, different rock compositions, etc.

More to come, a likeable topic. Papers are dated from most recent to further past.

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http://adsabs.harvard.edu/abs/2018arXiv180702960P

Outer solar system possibly shaped by a stellar fly-by

Pfalzner, Susanne; Bhandare, Asmita; Vincke, Kirsten; Lacerda, Pedro
07/2018

The planets of our solar system formed from a gas-dust disk. However, there are some properties of the solar system that are peculiar in this context. First, the cumulative mass of all objects beyond Neptune (TNOs) is only a fraction of what one would expect. Second, unlike the planets themselves, the TNOs do not orbit on coplanar, circular orbits around the Sun, but move mostly on inclined, eccentric orbits and are distributed in a complex way. This implies that some process restructured the outer solar system after its formation. However, some of TNOs, referred to as Sednoids, move outside the zone of influence of the planets. Thus external forces must have played an important part in the restructuring of the outer solar system. The study presented here shows that a close fly-by of a neighbouring star can simultaneously lead to the observed lower mass density outside 30 AU and excite the TNOs onto eccentric, inclined orbits, including the family of Sednoids. In the past it was estimated that such close fly-bys are rare during the relevant development stage. However, our numerical simulations show that such a scenario is much more likely than previously anticipated. A fly-by also naturally explains the puzzling fact that Neptune has a higher mass than Uranus. Our simulations suggest that many additional Sednoids at high inclinations still await discovery, perhaps including bodies like the postulated planet X.

Roger E. Moore
2018-Aug-02, 01:39 PM
Gliese 710 gets the lion's share of reporting on flyby stars. The reporting comes in spikes, starting around 1997, with smaller spikes in academic output since.

==================================

http://adsabs.harvard.edu/abs/2018RNAAS...2b..30D

An Independent Confirmation of the Future Flyby of Gliese 710 to the Solar System Using Gaia DR2

de la Fuente Marcos, Raúl; de la Fuente Marcos, Carlos
05/2018

Gliese 710 is a K7V star located 19 pc from the Sun in the constellation of Serpens Cauda, which is headed straight for the solar system. Berski & Dybczynski (2016) used data from Gaia DR1 to show that this star will be 13366 AU from the Sun in 1.35 Myr from now. Here, we present an independent confirmation of this remarkable result using Gaia DR2. Our approach is first validated using as test case that of the closest known stellar flyby, by the binary WISE J072003.20-084651.2 or Scholz's star. Our results confirm, within errors, those in Berski & Dybczynski (2016), but suggest a somewhat closer, both in terms of distance and time, flyby of Gliese 710 to the solar system. Such an interaction might not significantly affect the region inside 40 au as the gravitational coupling among the known planets against external perturbation can absorb efficiently such a perturbation, but it may trigger a major comet shower that will affect the inner solar system.

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http://adsabs.harvard.edu/abs/2017MNRAS.472.4634K

Oort spike comets with large perihelion distances

Królikowska, Malgorzata; Dybczynski, Piotr A.
12/2017

The complete sample of large-perihelion nearly-parabolic comets discovered during the period 1901-2010 is studied, starting with their orbit determination. Next, an orbital evolution that includes three perihelion passages (previous-observed-next) is investigated in which a full model of Galactic perturbations and perturbations from passing stars is incorporated. We show that the distribution of planetary perturbations suffered by actual large-perihelion comets during their passage through the Solar system has a deep, unexpected minimum around zero, which indicates a lack of 'almost unperturbed' comets. Using a series of simulations we show that this deep well is moderately resistant to some diffusion of the orbital elements of the analysed comets. It seems reasonable to assert that the observed stream of these large-perihelion comets experienced a series of specific planetary configurations when passing through the planetary zone. An analysis of the past dynamics of these comets clearly shows that dynamically new comets can appear only when their original semimajor axes are greater than 20 000 au. On the other hand, dynamically old comets are completely absent for semimajor axes longer than 40 000 au. We demonstrate that the observed 1/aori-distribution exhibits a local minimum separating dynamically new from dynamically old comets. Long-term dynamical studies reveal a wide variety of orbital behaviour. Several interesting examples of the action of passing stars are also described, in particular the impact of Gliese 710, which will pass close to the Sun in the future. However, none of the obtained stellar perturbations is sufficient to change the dynamical status of the analysed comets.

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http://adsabs.harvard.edu/abs/2016A%26A...595L..10B

Gliese 710 will pass the Sun even closer. Close approach parameters recalculated based on the first Gaia data release

Berski, Filip; Dybczynski, Piotr A.
11/2016

Context. First results based on Gaia data show that the well-known star Gliese 710 will be the closest flyby star in the next several Myrs and its minimum distance from the Sun will be almost five times smaller than that suggested by pre-Gaia solution.
Aims: The aim of this work is to investigate the proximity parameters and the influence of the close approach of Gliese 710 on the basis of Gaia DR1. Furthermore, we compare new results with previous works based on HIP2 and Tycho 2 catalogues to demonstrate how Gaia improves the accuracy of determination of such phenomena.
Methods: Using a numerical integration in an axisymmetric Galactic model, we determine new parameters of the close encounter for Gliese 710. Adding ten thousand clones drawn with the use of a covariance matrix, we estimate the most probable position and velocity of this star at the minimum distance from the Sun.
Results: Our calculations show that Gliese 710 will pass 13365 AU from the Sun in 1.35 Myr from now. At this proximity it will have the brightness of -2.7 mag and a total proper motion of 52.28 arcsec per year. After the passage of Gliese 710 we will observe a large flux of new long-period comets. Thanks to the Gaia mission, the uncertainties of the minimum distance and time of the close approach are several times smaller than suggested by previous works based on data from earlier observations.

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http://adsabs.harvard.edu/abs/2015MNRAS.454.3267F

Finding the imprints of stellar encounters in long-period comets

Feng, Fabo; Bailer-Jones, C. A. L.
12/2015

The Solar system's Oort cloud can be perturbed by the Galactic tide and by individual passing stars. These perturbations can inject Oort cloud objects into the inner parts of the Solar system, where they may be observed as the long-period comets (periods longer than 200 yr). Using dynamical simulations of the Oort cloud under the perturbing effects of the tide and 61 known stellar encounters, we investigate the link between long-period comets and encounters. We find that past encounters were responsible for injecting at least 5 per cent of the currently known long-period comets. This is a lower limit due to the incompleteness of known encounters. Although the Galactic tide seems to play the dominant role in producing the observed long-period comets, the non-uniform longitude distribution of the cometary perihelia suggests the existence of strong - but as yet unidentified - stellar encounters or other impulses. The strongest individual future and past encounters are probably HIP 89825 (Gliese 710) and HIP 14473, which contribute at most 8 and 6 per cent to the total flux of long-period comets, respectively. Our results show that the strength of an encounter can be approximated well by a simple proxy, which will be convenient for quickly identifying significant encounters in large data sets. Our analysis also indicates a smaller population of the Oort cloud than is usually assumed, which would bring the mass of the solar nebula into line with planet formation theories.

Roger E. Moore
2018-Aug-02, 01:40 PM
http://adsabs.harvard.edu/abs/2015MNRAS.448..588D

Near-parabolic comets observed in 2006-2010 - II. Their past and future motion under the influence of the Galaxy field and known nearby stars

Dybczynski, Piotr A.; Królikowska, Malgorzata
03/2015

In the first part of this research we extensively investigated and carefully determined osculating, original (when entering Solar system) and future (when leaving it), orbits of 22 near-parabolic comets with small perihelion distance (qosc < 3.1 au), discovered in years 2006-2010. Here, we continue this research with a detailed study of their past and future motion during previous and next orbital periods under the perturbing action of our Galactic environment. At all stages of our dynamical study, we precisely propagate in time the observational uncertainties of cometary orbits. For the first time in our calculations, we fully take into account individual perturbations from all known stars or stellar systems that closely (less than 3.5 pc) approach the Sun during the cometary motion in the investigated time interval of several million years. This is done by means of a direct numerical integration of the N-body system comprising of a comet, the Sun and 90 potential stellar perturbers. We show a full review of various examples of individual stellar action on cometary motion. We conclude that perturbations from all known stars or stellar systems do not change the overall picture of the past orbit evolution of long-period comets. Their future motion might be seriously perturbed during the predicted close approach of Gliese 710 star but we do not observe significant energy changes. The importance of stellar perturbations is tested on the whole sample of 108 comets investigated by us so far and our previous results, obtained with only Galactic perturbations included, are fully confirmed. We present how our results can be used to discriminate between dynamically new and old near-parabolic comets and discuss the relevance of the so-called Jupiter-Saturn barrier phenomenon. Finally, we show how the Oort spike in the 1/a-distribution of near-parabolic comets is built from both dynamically new and old comets. We also point out that C/2007 W1 seems to be the first serious candidate for interstellar provenance.

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http://adsabs.harvard.edu/abs/2015A%26A...575A..35B

Close encounters of the stellar kind

Bailer-Jones, C. A. L.
03/2015

Stars which pass close to the Sun can perturb the Oort cloud, injecting comets into the inner solar system where they may collide with the Earth. Using van Leeuwen's re-reduction of the Hipparcos data complemented by the original Hipparcos and Tycho-2 catalogues, along with recent radial velocity surveys, I integrate the orbits of over 50 000 stars through the Galaxy to look for close encounters. The search uses a Monte Carlo sampling of the covariance of the data in order to properly characterize the uncertainties in the times, distances, and speeds of the encounters. I show that modelling stellar encounters by assuming instead a linear relative motion produces, for many encounters, inaccurate and biased results. I find 42, 14, and 4 stars which have encounter distances below 2, 1, and 0.5 pc respectively, although some of these stars have questionable data. Of the 14 stars coming within 1 pc, 5 were found by at least one of three previous studies (which found a total of 7 coming within 1 pc). The closest encounter appears to be Hip 85605, a K or M star, which has a 90% probability of coming between 0.04 and 0.20 pc between 240 and 470 kyr from now (90% Bayesian confidence interval). However, its astrometry may be incorrect, in which case the closest encounter found is the K7 dwarf GL 710, which has a 90% probability of coming within 0.10-0.44 pc in about 1.3 Myr. A larger perturbation may have been caused by gamma Microscopii, a G6 giant with a mass of about 2.5 M&sun;, which came within 0.35-1.34 pc (90% confidence interval) around 3.8 Myr ago.

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http://adsabs.harvard.edu/abs/2011MNRAS.418.1272J

Effect of different stellar galactic environments on planetary discs - I. The solar neighbourhood and the birth cloud of the Sun

Jiménez-Torres, Juan J.; Pichardo, Barbara; Lake, George; Throop, Henry
12/2011

We have computed trajectories, distances and times of closest approaches to the Sun by stars in the solar neighbourhood with known position, radial velocity and proper motions. For this purpose, we have used a full potential model of the Galaxy that reproduces the local z-force, the Oort constants, the local escape velocity and the rotation curve of the Galaxy. From our sample, we constructed initial conditions, within observational uncertainties, with a Monte Carlo scheme for the 12 most suspicious candidates because of their small tangential motion. We find that the star Gliese 710 will have the closest approach to the Sun, with a distance of approximately 0.34 pc in 1.36 Myr in the future. We show that the effect of a flyby with the characteristics of Gliese 710 on a 100 au test particle disc representing the Solar system is negligible. However, since there is a lack of 6D data for a large percentage of stars in the solar neighbourhood, closer approaches may exist. We calculate parameters of passing stars that would cause notable effects on the solar disc. Regarding the birth cloud of the Sun, we performed experiments to reproduce roughly the observed orbital parameters such as eccentricities and inclinations of the Kuiper belt. It is now known that in Galactic environments, such as stellar formation regions, the stellar densities of new born stars are high enough to produce close encounters within 200 au. Moreover, in these Galactic environments, the velocity dispersion is relatively low, typically sigma˜ 1-3 km s-1. We find that with a velocity dispersion of ˜1 km s-1 and an approach distance of about 150 au, typical of these regions, we obtain approximately the eccentricities and inclinations seen in the current Solar system. Simple analytical calculations of stellar encounters effects on the Oort Cloud are presented.

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http://adsabs.harvard.edu/abs/2011AN....332..831S

The error ellipsoid in phase space of stellar encounters and its evolution in time

Serafin, R. A.; Birkenbach, B.
10/2011

We systematically investigate stellar encounters in their six-dimensional phase space, including also the error ellipsoid and its evolution in time. It allows to give not only a mathematical model of stellar encounters but also an error model for this process. On that occasion we derive fundamental formulae for the positional error in {R}n: the probability of a position X falling into the error ellipsoid, the standard deviation in an arbitrary direction, and we briefly discuss the mean positional error in {R}n. The case of the close encounter of the star GL 710 (HIP 89825) is an illuminating example of applying the derived results. Moreover, we show that the error ellipsoid can also be successfully applied to approximate the confidence region.

Roger E. Moore
2018-Aug-02, 01:41 PM
http://adsabs.harvard.edu/abs/2010AstL...36..220B

Searching for stars closely encountering with the solar system

Bobylev, V. V.
03/2010

Based on a new version of the Hipparcos catalog and currently available radial velocity data, we have searched for stars that either have encountered or will encounter the solar neighborhood within less than 3 pc in the time interval from -2 Myr to +2 Myr. Nine new candidates within 30 pc of the Sun have been found. To construct the stellar orbits relative to the solar orbit, we have used the epicyclic approximation. We show that, given the errors in the observational data, the probability that the well-known star HIP 89 825 (GL 710) encountering with the Sun most closely falls into the Oort cloud is 0.86 in the time interval 1.45 ± 0.06 Myr. This star also has a nonzero probability, 1 × 10-4, of falling into the region d < 1000 AU, where its influence on Kuiper Belt objects becomes possible.

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http://adsabs.harvard.edu/abs/2002Icar..157..228M

Characteristics and Frequency of Weak Stellar Impulses of the Oort Cloud

Matese, John J.; Lissauer, Jack J.
05/2002

We have developed a model of the response of the outer Oort cloud of comets to simultaneous tidal perturbations of the adiabatic galactic force and a stellar impulse. The six-dimensional phase space of near-parabolic comet orbital elements has been subdivided into cells. A mapping of the evolution of these elements from beyond the loss cylinder boundary into the inner planetary region over the course of a single orbit is possible. This is done by treating each perturbation separately, and in combination, during a time interval of 5 Myr. We then obtain the time dependence of a wide range of observable comet flux characteristics, which provides a fingerprint of the dynamics. These include the flux distributions of energy, perihelion distance, major axis orientation, and angular momentum orientation. Correlations between these variables are also determined. We show that substantive errors occur if one superposes the separately obtained flux results of the galactic tide and the stellar impulse rather than superposing the tidal and impulsive perturbations in a single analysis. Detailed illustrations are given for an example case where the stellar mass and relative velocity have the ratio M*/ Vrel=0.043 M&sun;/km s -1 and the solar impact parameter is 45,000 AU. This case has features similar to the impending Gliese 710 impulse with the impact parameter selected to be close to the low end of the predicted range. We find that the peak in the observable comet flux exceeds that due to the galactic tide alone by ≈41%. We also present results for the time dependence of the flux enhancements and for the mean encounter frequency of weak stellar impulse events as functions of M*/ Vrel and solar impact parameter.

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http://adsabs.harvard.edu/abs/1999AJ....117.1042G

Stellar Encounters with the Oort Cloud Based on HIPPARCOS Data [ Erratum: 1999AJ....118..600G ]

García-Sánchez, Joan; Preston, Robert A.; Jones, Dayton L.; Weissman, Paul R.; Lestrade, Jean-François; Latham, David W.; Stefanik, Robert P.
02/1999

We have combined Hipparcos proper-motion and parallax data for nearby stars with ground-based radial velocity measurements to find stars that may have passed (or will pass) close enough to the Sun to perturb the Oort cloud. Close stellar encounters could deflect large numbers of comets into the inner solar system, which would increase the impact hazard at Earth. We find that the rate of close approaches by star systems (single or multiple stars) within a distance D (in parsecs) from the Sun is given by N= 3.5D^2.12 Myr^-1, less than the number predicted by a simple stellar dynamics model. However, this value is clearly a lower limit because of observational incompleteness in the Hipparcos data set. One star, Gliese 710, is estimated to have a closest approach of less than 0.4 pc 1.4 Myr in the future, and several stars come within 1 pc during a +/-10 Myr interval. We have performed dynamical simulations that show that none of the passing stars perturb the Oort cloud sufficiently to create a substantial increase in the long-period comet flux at Earth's orbit.

=================================================

http://adsabs.harvard.edu/abs/1997AAS...191.6906M

Close Approaches of Stars to the Oort Cloud: Algol and Gliese 710

Molnar, L. A.; Mutel, R. L.
12/1997

The gravitational impulse of close approaches of stars to the Oort comet cloud are thought to be responsible for randomizing the orientations and eccentricities of their orbits. Particularly close encounters or combinations of more distant encounters can affect the distribution of comets observed at Earth. We present calculations of the recent encounter with Algol and the future encounter with Gliese 710. The Algol computation uses a new measurement of the proper motion made with Very Long Baseline Interferometry, which has uncertainties six times less than the Hipparcos measurements. We discuss in detail the various sources of uncertainty. We find that including the galactic rotation and oscillation about the midplane is essential to accurately compute not only the distance of closest encounter, but also which side of the Sun the stars will pass. Finally, we discuss the impact of the Algol passage on the observed distribution of comet orbits.

Roger E. Moore
2018-Aug-02, 01:41 PM
http://adsabs.harvard.edu/abs/1997ESASP.402..617G

A Search for Stars Passing Close to the Sun

Garcia-Sanchez, J.; Preston, R. A.; Jones, D. L.; Weissman, P. R.; Lestrade, J.-F.; Latham, D. W.; Stefanik, R. P.
08/1997

We have combined Hipparcos proper motion and parallax data for nearby stars with ground-based radial velocity measurements to find stars which may have passed (or will pass) close enough to the Sun to perturb the Oort cloud. Close stellar encounters could deflect large numbers of comets into the inner solar system, with possibly serious consequences for the impact hazard on the Earth. Only one star (Gliese 710) is found with a predicted closest approach of less than 0.5 parsec, although several stars come within about 1 parsec during a +/- 8.5 Myr interval. In most cases the uncertainty in closest approach distance is dominated either by uncertainties in published radial velocity measurements or by uncertainties in the barycentric motion of binary systems. We have begun a program to obtain new radial velocities for stars in our sample with no previously published values.

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http://adsabs.harvard.edu/abs/1997DPS....29.2501W

Close Approaches of Stars to the Solar System

Weissman, P. R.; Garcia-Sanchez, J.; Preston, R. A.; Jones, D. L.; Lestrade, J.-F.; Latham, D. W.
07/1997

We have combined Hipparcos proper motion and parallax data for nearby stars with ground-based radial velocity measurements to find stars which may have passed (or will pass) close enough to the Sun to perturb the Oort cloud. Close stellar encounters could deflect large numbers of comets into the planetary region and raise impact rates on the planets and their satellites, with possible consequences for biological evolution on Earth. From the data analyzed to date, we find that the number N of close stellar approaches within a distance D from the Sun (measured in parsecs) is given by N ~ 5 D(2) Myr(-1) , in agreement with previously predicted values (Weissman, 1980 Nature 288, 242). Only one star, Gliese 710, is found with a predicted closest approach distance < 10(5) AU (0.5 parsecs), although several stars come within about 1 parsec during a +/-8.5 Myr interval. The predicted minimum distance for Gliese 710 is 53,000 to 71,000 AU, approximately 1.0 to 1.4 Myr in the future. Gliese 710 is a late-type dwarf star (dM1 or K7 V) with an estimated mass of 0.42 M{_sun}, and is currently about 19 parsecs from the Sun. The star may be a binary. The absence of close stellar approaches in the recent past is consistent with analyses of the orbital element distributions of long-period comets by Weissman (1993 BAAS 25, 1063) which determined that we are not currently in a cometary shower. The expected dynamical effects of the closest encounters on the Oort cloud will be discussed. In most cases the uncertainty in closest approach distance is dominated either by uncertainties in published radial velocity measurements or by uncertainties in the barycentric motion of binary systems. We have begun a program to obtain radial velocities for stars in our sample with no previously published values.

================================================== ==

http://adsabs.harvard.edu/abs/1997xmm..pres...14.

The impact of Hipparcos star-fixing extends to life's evolution

05/1997

"ESA's Hipparcos brings the greatest step forward in star measurements since Tycho Brahe," Bonnet says. "When the Danish astronomer died in 1601, the German astronomer Johannes Kepler inherited his careful observations. Kepler used them to discover the laws of the motions of planets, and paved the way for Isaac Newton's gravitational theory. Now we have another multinational success story from European astronomy".

"Hipparcos began as an imaginative French concept to chart the stars by satellite," Bonnet continues. "ESA adopted the idea and many astronomers in our member states collaborated in the mission. A hundred-fold improvement in the accuracy of star positions may already alter the size of the Universe and the ages of stars. So don't be surprised if the results from Hipparcos are as revolutionary as Tycho Brahe's, in their impact on our knowledge of the cosmos."

The study of the Earth itself will benefit from the new star data. Wobbles of the Earth and variations in its rate of rotation can now be measured far more accurately. The ozone layer will be monitored by ESA's Envisat environmental mission, by looking for chemical alterations in the light from 1000 Hipparcos stars, when seen on lines of sight slanting through the atmosphere.

Even the erratic evolution of life on Earth may make more sense, as Hipparcos picks out stars that passed close enough to cause trouble here. Reliable identifications of stars heading towards or away from our vicinity were impossible before Hipparcos. The satellite measured shifts in the directions of stars in the sky with such high precision that astronomers can now pick out those few stars that scarcely change their bearings. Such stars are probably moving almost directly towards or away from us. A US-European team, led by Robert Preston at the Jet Propulsion Laboratory in California, used Hipparcos to search for nearby stars with very small shifts in position. They were, or will be, passers-by.

Gliese 710, an inconspicuous star in the constellation Ophiuchus, is currently 63 light-years away and approaching at about 14 kilometres per second. From the Hipparcos data, it will pass within about one light-year, one million years from now. Joan Garcia-Sanchez, a doctoral student in Preston's team, identifies Gliese 710 in one of the scientific posters that display Hipparcos results in Venice. Garcia-Sanchez has found evidence that Gliese 710 is today moving more slowly towards the Sun than it was several decades ago. That may mean it is orbiting around another star, so far unidentified. If so, the closest distance to which Gliese 710 will approach may be nearer or farther than in the team's initial estimate.

The stars of the Alpha Centauri system, at 4 light-years, are the nearest at present. Several stars investigated by Preston and his colleagues will come within 3 light-years during the next 8,500,000 years. Others have already passed by during a similar time-span and are now travelling away from us.

"A star coming too near could put the Earth at risk," Bob Preston explains. "It might dislodge comets from a swarm that surrounds the Sun in the Oort Cloud, and send them into the inner Solar System. Some comets could then collide with our planet. The fossils tell us of past disasters, in extinctions of many species, and we hope to identify culprits among stars now hurrying away from the scene. The theory isn't new, but only now can we check it, thanks to the amazing precision of Hipparcos."

Uncertainty about the timing of the stellar visits arises from inadequate information about the speed of approach or recession. That is measured from ground-based observatories, by shifts in the wavelengths of light (blueshifts and redshifts). A team led by Dave Latham at the Center for Astrophysics in Cambridge, Massachusetts, is busy making fresh observations to improve the ground-based data on the visitors, past and future.


================================================== ==

http://adsabs.harvard.edu/abs/1997IAUJD..14E..51G

A Search for Stars Passing Close to the Sun

Garcia-Sanchez, J.; Preston, R. A.; Jones, D. L.; Lestrade, J.-F.; Weissman, P. R.; Latham, D. W.
00/1997

We have combined HIPPARCOS proper motion and parallax data for nearby stars with ground-based radial velocity measurements to find stars which may have passed (or will pass) close enough to the Sun to disrupt the Oort cloud. Such close encounters could deflect large numbers of comets into the inner solar system, with possibly serious consequences for biological evolution. From the data analyzed to date, we find the number N of close stellar approaches within a distance D from the Sun (in pc) is given by N ~5 {D^2} {{Myr}^{-1}}, in good agreement with previously predicted values. Only one star (Gliese 710) is found with a predicted closest distance of less than 0.5 parsec, although several stars come within about 1 parsec during a +/- 8.5 Myr interval. In most cases the uncertainty in closest approach distance is dominated either by uncertainties in published radial velocity measurements or by uncertainties in the barycentric motion of binary systems. We have started a program to obtain new radial velocities for stars in our sample with no previously published values.

Roger E. Moore
2018-Aug-02, 01:57 PM
Several papers have recently focused on Scholz's Star, WISE J072003.20-084651.2, which apparently made a close flyby within human existence, though not within human history. Again, papers are listed most recent first, then on back in time. The last paper is the actual discovery paper for Scholz's Star.

==========================================

http://adsabs.harvard.edu/abs/2018MNRAS.476L...1D

Where the Solar system meets the solar neighbourhood: patterns in the distribution of radiants of observed hyperbolic minor bodies

de la Fuente Marcos, Carlos; de la Fuente Marcos, Raúl; Aarseth, Sverre J.
05/2018

Observed hyperbolic minor bodies might have an interstellar origin, but they can be natives of the Solar system as well. Fly-bys with the known planets or the Sun may result in the hyperbolic ejection of an originally bound minor body; in addition, members of the Oort cloud could be forced to follow inbound hyperbolic paths as a result of secular perturbations induced by the Galactic disc or, less frequently, due to impulsive interactions with passing stars. These four processes must leave distinctive signatures in the distribution of radiants of observed hyperbolic objects, both in terms of coordinates and velocity. Here, we perform a systematic numerical exploration of the past orbital evolution of known hyperbolic minor bodies using a full N-body approach and statistical analyses to study their radiants. Our results confirm the theoretical expectations that strong anisotropies are present in the data. We also identify a statistically significant overdensity of high-speed radiants towards the constellation of Gemini that could be due to the closest and most recent known fly-by of a star to the Solar system, that of the so-called Scholz's star. In addition to and besides 1I/2017 U1 (`Oumuamua), we single out eight candidate interstellar comets based on their radiants' velocities.

==========================================

http://adsabs.harvard.edu/abs/2015AJ....149..104B

WISE J072003.20-084651.2: an Old and Active M9.5 + T5 Spectral Binary 6 pc from the Sun

Burgasser, Adam J.; Gillon, Michaël; Melis, Carl; Bowler, Brendan P.; Michelsen, Eric L.; Bardalez Gagliuffi, Daniella; Gelino, Christopher R.; Jehin, E.; Delrez, L.; Manfroid, J.; Blake, Cullen H.
03/2015

We report observations of the recently discovered, nearby late-M dwarf WISE J072003.20-084651.2. New astrometric measurements obtained with the TRAPPIST telescope improve the distance measurement to 6.0 ± 1.0 pc and confirm the low tangential velocity (3.5 ± 0.6 km s-1) reported by Scholz. Low-resolution optical spectroscopy indicates a spectral type of M9.5 and prominent Halpha emission (< {{log }10}{{L}Halpha }/{{L}bol}> = -4.68 ± 0.06), but no evidence of subsolar metallicity or Li i absorption. Near-infrared spectroscopy reveals subtle peculiarities that can be explained by the presence of a T5 binary companion, and high-resolution laser guide star adaptive optics imaging reveals a faint (DeltaH = 4.1) candidate source 0\buildrel{\prime\prime}\over{.} 14 (0.8 AU) from the primary. With high-resolution optical and near-infrared spectroscopy, we measure a stable radial velocity of +83.8 ± 0.3 km s-1, indicative of old disk kinematics and consistent with the angular separation of the possible companion. We measure a projected rotational velocity of v sin i = 8.0 ± 0.5 km s-1 and find evidence of low-level variabilty (˜1.5%) in a 13 day TRAPPIST light curve, but cannot robustly constrain the rotational period. We also observe episodic changes in brightness (1%-2%) and occasional flare bursts (4%-8%) with a 0.8% duty cycle, and order-of-magnitude variations in Halpha line strength. Combined, these observations reveal WISE J0720-0846 to be an old, very low-mass binary whose components straddle the hydrogen burning minimum mass, and whose primary is a relatively rapid rotator and magnetically active. It is one of only two known binaries among late M dwarfs within 10 pc of the Sun, both of which harbor a mid T-type brown dwarf companion. We show that while this specific configuration is rare (≲1.6% probability), roughly 25% of binary companions to late-type M dwarfs in the local population are likely low-temperature T or Y brown dwarfs.

==========================================

http://adsabs.harvard.edu/abs/2014A%26A...561A.113S

Neighbours hiding in the Galactic plane, a new M/L dwarf candidate for the 8 pc sample

Scholz, R.-D.
01/2014

Aims: Using Wide-field Infrared Survey Explorer (WISE) data and previous optical and near-infrared sky surveys, we try to identify still missing stellar and substellar neighbours of the Sun.
Methods: When checking the brightest red WISE sources for proper motions and colours expected for nearby M and L dwarfs, we also approached the thin Galactic plane. Astrometry (proper motion and parallax measurements) and the available photometry were used to obtain first estimates of the distance and type of nearby candidates.
Results: We have discovered WISE J072003.20-084651.2, an object with moderately high proper motion (mu ≈ 120 mas/yr) that lies at low Galactic latitude (b = +2.3°), with similar brightness (J ≈ 10.6, w2 ≈ 8.9) and colours (I - J ≈ 3.2, J - Ks ≈ 1.2, w1 - w2 ≈ 0.3) as the nearest known M-type brown dwarf LP 944-20. With a photometric classification as an M9 ± 1 dwarf, its photometric distance lies in the range between about 5 and 7 pc, based on comparison with absolute magnitudes of LP 944-20 alone or of a sample of M8-L0 dwarfs. The slightly larger distance derived from our preliminary trigonometric parallax (7.0 ± 1.9 pc) may indicate a close binary nature. The new neighbour is an excellent target for planet search and low-mass star/brown dwarf studies.

Roger E. Moore
2018-Aug-02, 02:13 PM
Possibly the paper that started it all.

==============================================

http://adsabs.harvard.edu/abs/1996EM%26P...72...19M

Encounters of the Sun with Nearby Stars in the Past and Future

Mülläri, A. A.; Orlov, V. V.
02/1996

The relative space motions of the Sun and nearby stars are considered. The coordinates and velocities of the stars are taken from the Catalogue of Nearby Stars by Gliese and Jahreiss (1991). The minimum space separation between the Sun and every star as well as the corresponding moment of time are calculated by two ways. Firstly, the straight line motions are considered. Secondly, the effect of the Galaxy potential is taken into account. The Galaxy model proposed by Kutuzov and Ossipkov (1989) is used. Twenty five stars approaching the Sun closer than two parsecs are selected. The effects of the uncertainties in the observational data are studied. The influence of the encounters to the Oort cloud is discussed.

Roger E. Moore
2018-Aug-02, 02:16 PM
And notes about a star I have trouble finding information on in arvix

https://en.wikipedia.org/wiki/Gamma_Microscopii

selden
2018-Aug-03, 12:37 PM
And notes about a star I have trouble finding information on in arvix

https://en.wikipedia.org/wiki/Gamma_Microscopii

Did you try searching with its HIP catalog number? The Google search string
"HIP 103738" site:arxiv.org
returned links to five papers, all discussing close-encounters. I haven't compared these results with papers you've already mentioned, though.

Note: I've edited the list below, sorting it into order of increasing publication date, and adding the title of one of them.



[PDF]Close encounters of the stellar kind
https://arxiv.org/pdf/1412.3648
by CAL Bailer-Jones - ‎2014 - ‎Cited by 24 - ‎Related articles
Dec 11, 2014 - The nominal orbit of Hip 103738 (gamma Microscopii) rela- tive to the Sun in Galactic cylindrical coordinates (r, z,φ) over the past. 7.8Myr.

[PDF]On the accuracy of close stellar approaches determination
https://arxiv.org/pdf/1502.05518
by PA Dybczyński - ‎2015 - ‎Cited by 20 - ‎Related articles
Feb 19, 2015 - Distribution of clones of HIP 103738. Figure 9. Distribution of clones HIP 87052 nominal proximity points obtained on the basis of different astro ...

[PDF]Finding the imprints of stellar encounters in long period comets
https://arxiv.org/pdf/1509.07222
by F Feng - ‎2015 - ‎Cited by 17 - ‎Related articles
Oct 3, 2015 - encounters are HIP 103738 (gamma Microscopii) and HIP 14576. (Algol), both of which are massive and relatively slow. The radial velocity of ...

[PDF]arXiv:1707.05277v4 [astro-ph.SR] 21 Dec 2017 [A CATALOGUE OF CLOSE ENCOUNTER PAIRS]
https://arxiv.org/pdf/1707.05277
by F Feng - ‎2017 - ‎Cited by 2 - ‎Related articles
Dec 21, 2017 - HIP 103738 xh. 0.929 0.919 0.442 1.528. -3.85. -3.86. -4.18. -3.57. 17.97. 17.94. 16.67. 19.20. HIP 71683 xh. 0.976 0.976 0.947 1.007. 0.03.

[PDF]New stellar encounters discovered in the second Gaia data release
https://arxiv.org/pdf/1805.07581
by CAL Bailer-Jones - ‎2018 - ‎Related articles
May 19, 2018 - Hip 103738 (gamma Microscopii). This G6 giant was the potentially most massive encounter coming within 1pc in pa- per 1, found to have ...

Roger E. Moore
2018-Aug-03, 01:48 PM
Oh! Outstanding! Thank you! :)

I think arvix keeps interpreting "Microscopii" as "microscope", because of the papers I get back from a search string.

selden
2018-Aug-03, 02:10 PM
Oh! Outstanding! Thank you! :)

You're very welcome.


I think arvix keeps interpreting "Microscopii" as "microscope", because of the papers I get back from a search string.

I also tried a search using the star's formal IAU TLA "GAM Mic", but that didn't find anything. I wonder if there might be some older papers (pre-Hipparcos). Hmm. They'd probably use its Draper catalog number "HD 199951".

[... searching ...]

That search returns the following (again sorted by increasing date), although they don't actually predate Hipparcos:



[PDF]XID: Cross-Association of ROSAT/Bright Source Catalog X-ray ...
https://arxiv.org/pdf/astro-ph/0004053
by RE Rutledge - ‎2000 - ‎Cited by 78 - ‎Related articles
210117.46−321528.0. HD 199951. **. G4III. 5.543 : 4.677 ... ... ... ... 210117.46−321528.0. IRAS 20582−3227. IR ./. : 1RXSJ210139.7+680936. 0.0514 (0.0089).

[PDF]Elemental Abundances of Solar Sibling Candidates
https://arxiv.org/pdf/1405.1723
by I Ramirez - ‎2014 - ‎Cited by 22 - ‎Related articles
May 7, 2014 - at most ∼ 6300 K. HD 199951, on the other hand, appears to be a giant star of younger age than solar. All of our other targets have stellar ...

[PDF]On the accuracy of close stellar approaches determination
https://arxiv.org/pdf/1502.05518
by PA Dybczyński - ‎2015 - ‎Cited by 20 - ‎Related articles
Feb 19, 2015 - HD 199951. A. 1.18. -3.86. 2.36. -3.90 c, f. 110893. HD 239960. A. 1.92. 0.09. 1.92. 0.09 a, b, c, e, f a - Jiménez-Torres et al. (2011), b - Bobylev ...




ETA1: That last was included in the previous list of papers.
ETA2: Another source of references to papers about particular stars is Simbad, which claims that HD 199951 (or one of its 38 synonyms) is referenced in at least 71 papers since 1850. Scroll down to the bottom of
http://simbad.u-strasbg.fr/simbad/sim-id?Ident=HD+199951&NbIdent=1&Radius=2&Radius.unit=arcmin&submit=submit+id

Roger E. Moore
2018-Aug-03, 02:31 PM
Thank you again!

And a relevant recent paper...

https://arxiv.org/abs/1808.00053

Habitability in the Omega Centauri Cluster

Stephen R. Kane, Sarah J. Deveny
(Submitted on 31 Jul 2018)

The search for exoplanets has encompassed a broad range of stellar environments, from single stars in the solar neighborhood to multiple stars and various open clusters. The stellar environment has a profound effect on planet formation and stability evolution and is thus a key component of exoplanetary studies. Dense stellar environments, such as those found in globular clusters, provide particularly strong constraints on sustainability of habitable planetary conditions. Here, we use Hubble Space Telescope observations of the core of the Omega Centauri cluster to derive fundamental parameters for the core stars. These parameters are used to calculate the extent of the Habitable Zone of the observed stars. We describe the distribution of Habitable Zones in the cluster and compare them with the stellar density and expected stellar encounter rate and cluster dynamics. We thus determine the effect of the stellar environment within the Omega Centauri core on the habitability of planets that reside within the cluster. Our results show that the distribution of Habitable Zone outer boundaries generally lie within 0.5 AU of the host stars, but that this small cross-sectional area is counter-balanced by a relatively high rate of stellar close encounters that would disrupt planetary orbits within the Habitable Zone of typical Omega Centauri stars.

publiusr
2018-Aug-03, 08:54 PM
Gliese 710 is now expected to miss the solar system by 13,000 AU about the year 1,352,000 AD https://en.wikipedia.org/wiki/Gliese_710


From that link:
"There is even a 1/10,000 chance of the star penetrating into the region (d < 1,000 AU) where the influence of the passing star on Kuiper belt objects is significant."

Eesh!

I wonder if Gliese 710 was what was called DM61 366 in THE STARFLIGHT HANDBOOK.

Roger E. Moore
2018-Aug-10, 12:42 PM
https://phys.org/news/2018-08-impact-stellar-intruder-solar.html

More news on stellar flybys

Roger E. Moore
2018-Aug-14, 11:13 PM
https://arxiv.org/abs/1707.05277

A catalogue of close encounter pairs

Fabo Feng, Hugh R. A. Jones, Tabassum S. Tanvir
(Submitted on 17 Jul 2017 (v1), last revised 21 Dec 2017 (this version, v4))

We provide a catalogue of pairs of stars whose periapses are less than 1pc within the past or future 100 Myr. We use astrometric data from TGAS, Hipparcos and radial velocity data from RAVE and XHIP to find the space motions and hence the initial conditions of 229, 441 stars in Galactic coordinates. We simulate the orbits of these stars and focus on the time, distance and velocity at periastron for 8149 pairs using the k-d tree algorithm to find nearest neighbors. We find an anisotropy in the directions of encounter pairs caused by the solar apex motion, indicating a role of peculiar motion imposing an anisotropic tidal force on planetary systems. We call this effect "kinematic tide". Among the encounter pairs there are 4 encounters with the Solar System with periapses less than 1 pc and 96 pairs with periapses less than 0.1 pc. We also find 577 close encounters of stars which host planetary systems and/or debris disks. We discuss a range of uses for an encounter catalogue and present an example of how the time-varying network of stellar motions will be crucial for efficient interstellar travel between planetary systems.

Roger E. Moore
2018-Aug-17, 12:56 PM
Seems to be closely related to this topic.........


https://arxiv.org/abs/1808.05531

Photo-evaporation of proto-planetary gas discs due to flybys of external single stars in different orbits

Yuan-Zhe Dai, Hui-Gen Liu, Wen-bo Wu, Ji-Wei Xie, Ming Yang, Hui Zhang
(Submitted on 16 Aug 2018)

During the evolution of proto-planetary disc, photo-evaporations of both central and external stars play important roles. Considering the complicated radiation surroundings in the clusters, where the star formed, the proto-planetary discs survive in different lifetimes due to flyby events. In this paper, we mainly focus on the disc around a T Tauri star, which encounters with another main-sequence star with different temperatures in hyperbolic orbits with different peri-center distances, eccentricities and inclinations. We find the criterion for gap-opening due to photo-evaporation of central star after the flyby event. A gap is opened in the late stage of gas disc, and induce that the gap only influence the planet formation and migration limitedly. If the flyby orbit has a moderate value of peri-center distance, which weakly depends on the eccentricity and inclination, the external photo-evaporation lead to a maximum mass loss during the flyby event. Flyby stars in orbits with smaller eccentricities or larger inclinations induce larger mass loss. Adopting a simple multiple flyby models, we conclude that in open clusters, gas discs usually survive in typical lifetimes between 1 and 10 Myr, except there are many massive stars in dense open clusters. In globular clusters, discs disperse very quickly and hardly produce the gas giant planets. The fast-depleted discs are probably responsible for the null detection of giant planets in globular clusters.

Roger E. Moore
2018-Aug-23, 10:19 PM
An assortment of papers, newly discovered, many under the old "Nemesis" header for this topic.


https://arxiv.org/abs/1302.3827

Nemesis encounters of nearby Hipparcos stars

Igor Yu. Potemine
(Submitted on 15 Feb 2013)

Very close encounters of stars might lead to significant perturbations of their Oort-type clouds, planetesimal belts and planetary systems. We have calculated encounter parameters of Hipparcos stars using HIP2, Pulkovo and CRVAD2 catalogs of radial velocities. It turns out that some stars have encounters within 0.1 pc from each other and might be on an essential collision course up to few thousands AU. We present here examples with accurate astrometric data and stable with respect to errors of radial velocities within ± 0.3 km/s. They include β vs. γ Virginis, 61 Cygni vs. χ1 Orionis as well as close encounters involving η Bootis, AB Doradus, 61 Ursa Majoris and others.

=====================================

NEMESIS: Near Encounters with M-dwarfs from an Enormous Sample and Integrated Simulations

Bochanski, John J.; Sanderson, R. E.; West, A. A.; Burgasser, A. J.
01/2011

The latest spectroscopic catalog of M dwarfs identified in the Sloan Digital Sky Survey provides radial velocities, proper motions and distances for nearly 40,000 low-mass stars. Using the full 6D phase space coverage and a realistic Galactic potential, we calculated orbits for each star in the sample. The sample consists of stars from both the thin and thick disks, and the orbital properties between the two groups are compared. We also examine trends in orbital properties with spectroscopic features, such as Balmer emission and molecular bands, that should correlate with age. In addition, we have identified a number of stars that will pass very close to the Sun within the next 1000 Myrs. These stars form the "Nemesis" family of orbits. Potential encounters with these stars could have a significant impact on orbits of Oort Cloud and Kuiper Belt members as well as the planets. We comment on the probability of a catastrophic encounter within the next 1000 Myrs.

================================

https://arxiv.org/abs/1007.0437

Nemesis Reconsidered

Adrian L. Melott (University of Kansas), Richard K. Bambach (Smithsonian Institution Museum of Natural History)
(Submitted on 2 Jul 2010)

The hypothesis of a companion object (Nemesis) orbiting the Sun was motivated by the claim of a terrestrial extinction periodicity, thought to be mediated by comet showers. The orbit of a distant companion to the Sun is expected to be perturbed by the Galactic tidal field and encounters with passing stars, which will induce variation in the period. We examine the evidence for the previously proposed periodicity, using two modern, greatly improved paleontological datasets of fossil biodiversity. We find that there is a narrow peak at 27 My in the cross-spectrum of extinction intensity time series between these independent datasets. This periodicity extends over a time period nearly twice that for which it was originally noted. An excess of extinction events are associated with this periodicity at 99% confidence. In this sense we confirm the originally noted feature in the time series for extinction. However, we find that it displays extremely regular timing for about 0.5 Gy. The regularity of the timing compared with earlier calculations of orbital perturbation would seem to exclude the Nemesis hypothesis as a causal factor.

=======================================

https://arxiv.org/abs/1003.5308

Giant Nemesis candidate HD 107914 / HIP 60503 for the perforation of Oort cloud

Igor Yu. Potemine
(Submitted on 27 Mar 2010)

So far, GJ 710 is the only known star supposed to pass through outskirts of the solar system within 1 ly. We have reexamined the SIMBAD database for additional stellar candidates (from highest ratios of squared parallax to total proper motion) and compared them with new HIP2 parallaxes and known radial velocities. At the moment, the best nominee is double star HD 107914 in the constellation Centaurus at ≈ 78.3 pc from the Sun whose principal component is a white (A-type) giant. It does not seem to appear neither in general catalogues of radial velocities available at SIMBAD nor in authoritative Garcia-Sanchez et al. papers on stellar encounters with the solar system. Awaiting for the value vr of its radial velocity, uknown to the author, we have calculated limits of |vr| necessary to this star to pass within 1 ly and 1 pc from the Sun in linear approximation. A very accurate value of its total proper motion is also extremely important. In the case of vr = −100 km/s and most "advantageous" HIP2 data, HD 107914 could pass as near as 8380 AU from the Sun in an almost direct collision course with the inner part of the solar system! Inversely, if vr had a great positive value, then HIP 60503 could be the creator of peculiar trajectories of detached trans-Neptunian objects like Sedna.

====================================

https://arxiv.org/abs/1509.07222

Finding the imprints of stellar encounters in long period comets

Fabo Feng, C. A. L. Bailer-Jones
(Submitted on 24 Sep 2015 (v1), last revised 3 Oct 2015 (this version, v2))

The solar system's Oort cloud can be perturbed by the Galactic tide and by individual passing stars. These perturbations can inject Oort cloud objects into the inner parts of the solar system, where they may be observed as the long-period comets (periods longer than 200 years). Using dynamical simulations of the Oort cloud under the perturbing effects of the tide and 61 known stellar encounters, we investigate the link between long-period comets and encounters. We find that past encounters were responsible for injecting at least 5% of the currently known long-period comets. This is a lower limit due to the incompleteness of known encounters. Although the Galactic tide seems to play the dominant role in producing the observed long-period comets, the non-uniform longitude distribution of the cometary perihelia suggests the existence of strong -- but as yet unidentified -- stellar encounters or other impulses. The strongest individual future and past encounters are probably HIP 89825 (Gliese 710) and HIP 14473, which contribute at most 8% and 6% to the total flux of long-period comets, respectively. Our results show that the strength of an encounter can be approximated well by a simple proxy, which will be convenient for quickly identifying significant encounters in large data sets. Our analysis also indicates a smaller population of the Oort cloud than is usually assumed, which would bring the mass of the solar nebula into line with planet formation theories.

===================================

https://arxiv.org/abs/1403.6633

The secular evolution of the Kuiper belt after a close stellar encounter

D. Punzo, R. Capuzzo-Dolcetta, S. Portegies Zwart
(Submitted on 26 Mar 2014 (v1), last revised 27 Aug 2014 (this version, v3))

We show the effects of the perturbation caused by a passing by star on the Kuiper belt objects (KBOs) of our Solar System. The dynamics of the Kuiper belt (KB) is followed by direct N-body simulations. The sampling of the KB has been done with N up to 131,062, setting the KBOs on initially nearly circular orbits distributed in a ring of surface density Σ∼r^−2. This modelization allowed us to investigate the secular evolution of the KB upon the encounter with the perturbing star. Actually, the encounter itself usually leads toward eccentricity and inclination distributions similar to observed ones, but tends also to excite the low-eccentricity population (e<0.1 around a ∼40 AU from the Sun), depleting this region of low eccentricities. The following long-term evolution shows a "cooling" of the eccentricities repopulating the low-eccentricity area. In dependence on the assumed KBO mass spectrum and sampled number of bodies, this repopulation takes place in a time that goes from 0.5 Myr to 100 Myr. Due to the unavoidable limitation in the number of objects in our long-term simulations (N ≤ 16384), we could not consider a detailed KBO mass spectrum, accounting for low mass objects, thus our present simulations are not reliable in constraining correlations among inclination distribution of the KBOs and other properties, such as their size distribution. However, our high precision long term simulations are a starting point for future larger studies on massively parallel computational platforms which will provide a deeper investigation of the secular evolution (∼100 Myr) of the KB over its whole mass spectrum.

Roger E. Moore
2018-Aug-23, 10:24 PM
https://arxiv.org/abs/1004.1557

Transit of Luyten 726-8 within 1 ly from Epsilon Eridani

Igor Yu. Potemine
(Submitted on 9 Apr 2010)

This is one of results from our program of massive simulations of close encounters for all nearby stars. Epsilon Eridani is an extremely interesting star having one confirmed planet and multiple asteroid and debris belts. It should have a quite massive Oort cloud as well. Deltorn et al. searched for past Nemesis encounters of ε Eri. In this paper we show that, according to current astrometric data, an other famous nearby star Luyten 726-8AB (=BL/UV Ceti) will pass at ≲ 0.93 ly from Epsilon Eridani in ≈ 31.5 kyr. So, it will probably pierce through the outer part of the hypothetical Oort cloud of ϵ Eri. BL/UV Ceti has only about 20 percent of the solar mass. Nevertheless, it could influence directly some long-period comets of Epsilon Eridani. The duration of mutual transit of two star systems within 1 ly from each other is ≳ 4.6 kyr. Our simulations show that stellar encounters within 1 ly might be more frequent than previously thought. It could explain Proxima's peculiar trajectory with respect to α Cen AB or even Sedna's trajectory in the solar system.

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https://arxiv.org/abs/astro-ph/0105284

Search for Nemesis Encounters with Vega, epsilon Eridani, and Fomalhaut

J.-M. Deltorn (Space Telescope Science Institute), P. Kalas (University of California, Berkeley)
(Submitted on 16 May 2001)

We calculate the space motions of 21,497 stars to search for close stellar encounters with Vega, epsilon Eridani and Fomalhaut during the past 1 Myr. We discover that epsilon Eridani experienced three <2 pc encounters over the past 100,000 yr. Within the uncertainties, epsilon Eridani is having a close encounter with Kapteyn's star near the present epoch, with a 42.2 percent probability that the closest approach distance is <1 pc. Vega and Fomalhaut experienced four and six <2 pc encounters, respectively, over the past 1 Myr. Each had one encounter with a roughly 2 percent probability that the closest approach distance is less than 0.5 pc. These encounters will not directly influence the debris disks observed around Vega, epsilon Eridani and Fomalhaut, but they may pass through hypothetical Oort clouds surrounding these stars. We find that two other Vega-like stars, HD 17848 and HD 20010, experienced rare, <0.1 pc stellar encounters that are more likely to directly perturb their circumstellar disks.

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https://arxiv.org/abs/astro-ph/0011279

Close stellar encounters with planetesimal discs: The dynamics of asymmetry in the Beta Pictoris system

J.D. Larwood (Univ. of London), P.G. Kalas (UC Berkeley)
(Submitted on 14 Nov 2000)

We numerically investigate the dynamics of how a close stellar fly-by encounter of a symmetrical circumstellar planetesimal disc can give rise to the many kinds of asymmetries and substructures attributed to the edge-on dusty disc of Beta Pic. In addition we present new optical coronagraphic observations of the outer parts of Beta Pic's disc, and report that the radial extent is significantly greater than was found in previous measurements. The northeasterly extension of the disc's midplane is now measured out to 1835au from the star; the southwesterly component is measured out to 1450au. Hence we use the length asymmetry induced in a distribution of simulation test particles as the principal diagnostic feature when modelling the disc response, in order to constrain fly-by parameters. In particular we favour a low inclination prograde and near-parabolic orbit perturber of mass approximately 0.5 Solar masses. These initial conditions suggest that the perturber could have been physically associated with Beta Pic prior to the encounter. Thus we also consider the possibility that the perturber could be bound to Beta Pic: a consideration also of general interest where dust discs are known to exist in binary star systems. In some of our models, we can relate groupings of perturbed particles to the large-scale structure of the Beta Pic disc. The groupings correspond to: high eccentricity and inclination particles that reach apocentre and maximum height in the southwest, moderately eccentric and low inclination particles that reach apocentre in the northeast, and relatively unperturbed particles inside approximately 200au radius.

Roger E. Moore
2018-Nov-09, 02:43 AM
Discovery of yet another lone nearby brown dwarf -- and a fly-by!


https://arxiv.org/abs/1811.03477

WISE J064336.71-022315.4: A Thick Disk L8 Gaia DR2-Discovered Brown Dwarf at 13.9 Parsecs

E. E. Mamajek, et al. (Submitted on 8 Nov 2018)

While spectroscopically characterizing nearby ultracool dwarfs discovered in the Gaia Second Data Release with the TripleSpec spectrograph on the Palomar 200" telescope, we encountered a particularly cool, nearby, new member of the solar neighborhood: Gaia DR2 3106548406384807680 = WISE J064336.71-022315.4 = 2MASS J06433670-0223130. The Gaia parallax corresponds to a distance of 13.9 ± 0.3 pc. Using our TripleSpec spectrum we classify W0643 as spectral type L8, and measured a heliocentric radial velocity of 142 ± 12 km s-1. When combined with Gaia astrometry, we determine a Galactic velocity (heliocentric; U towards Galactic center) of U,V,W = -109, -91, -12 (±10, 5, 3) km s−1. We estimate that W0643 passed within ∼1.4 pc away from the Sun ∼100,000 years ago.

Roger E. Moore
2018-Nov-23, 01:00 AM
Close passages are more likely in clusters, which can ruin planetary systems all over.

https://arxiv.org/abs/1811.08598

Survival Rates of Planets in Open Clusters: the Pleiades, Hyades, and Praesepe clusters

M. S. Fujii, Y. Hori (Submitted on 21 Nov 2018)

In clustered environments, stellar encounters can liberate planets from their host stars via close encounters. Although the detection probability of planets suggests that the planet population in open clusters resembles that in the field, only dozens of planet-hosting stars have been discovered in open clusters. We explore the survival rates of planets against stellar encounters in open clusters similar to the Pleiades, Hyades, and Praesepe and embedded clusters. We perform a series of N-body simulations of high-density and low-density open clusters, open clusters that grow via mergers of subclusters, and embedded clusters. We semi-analytically calculate the survival rate of planets in star clusters up to ~1 Gyr using relative velocities, masses, and impact parameters of intruding stars. Less than 1.5% of close-in planets within 1 AU and at most 7% of planets with 1--10 AU are ejected by stellar encounters in clustered environments after the dynamical evolution of star clusters. If a planet population from 001-100 AU in an open cluster initially follows the probability distribution function of exoplanets discovered in the field by RV surveys with semi-major axis (ap) between 0.03--3 AU (∝ a −0.6 p), the PDF of surviving planets beyond ~10 AU in open clusters follows ∝ a −0.76 p, which is consistent with the result of direct-imaging surveys. The production rate of free-floating planets (FFPs) per star is 0.0096--0.18, where we assume that all the stars initially have one giant planet with a mass of 1--13 M-Jup in a circular orbit. The expected frequency of FFPs is compatible with the upper limit on that of FFPs indicated by recent microlensing surveys.

publiusr
2018-Dec-10, 11:55 PM
if Gliese 710 has a distant planet--it's hill sphere will have to be taken into account--in that the orbit that systems potential planets describe widen the threat zone...

Roger E. Moore
2019-Feb-28, 02:05 PM
A close shave, just 15 million years ago. Could have happened to us.

https://arxiv.org/abs/1902.10220

A Near-coplanar Stellar Flyby of the Planet Host Star HD 106906

Robert J. De Rosa, Paul Kalas (Submitted on 26 Feb 2019)

We present an investigation into the kinematics of HD 106906 using the newly released Gaia DR2 catalog to search for close encounters with other members of the Scorpius-Centaurus (Sco-Cen) association. HD 106906 is an eccentric spectroscopic binary that hosts both a large asymmetric debris disk extending out to at least 500 au and a directly imaged planetary-mass companion at a projected separation of 738 au. The cause of the asymmetry in the debris disk and the unusually wide separation of the planet is not currently known. Using a combination of Gaia DR2 astrometry and ground-based radial velocities, we explore the hypothesis that a close encounter with another cluster member within the last 15 Myr is responsible for the present configuration of the system. Out of 461 stars analyzed, we identified two candidate perturbers that had a median closest approach (CA) distance within 1 pc of HD 106906: HIP 59716 at D CA =0.65 +0.93 −0.40 pc (t CA =−3.49 +0.90 −1.76 Myr) and HIP 59721 at D CA =0.71 +0.18 −0.11 pc (t CA =−2.18 +0.54 −1.04 Myr), with the two stars likely forming a wide physical binary. The trajectories of both stars relative to HD 106906 are almost coplanar with the inner disk (Δθ=5.4±1.7 deg and 4.2 +0.9 −1.1 deg). These two stars are the best candidates of the currently known members of Sco-Cen for having a dynamically important close encounter with HD 106906, which may have stabilized the orbit of HD 106906 b in the scenario where the planet formed in the inner system and attained high eccentricity by interaction with the central binary.

Roger E. Moore
2019-Jun-28, 01:34 AM
It might be that rogue planets are pretty common. Shades of When Worlds Collide!

https://arxiv.org/abs/1902.09804

Fly-by encounters between two planetary systems I: solar system analogues

Daohai Li, Alexander J. Mustill, Melvyn B. Davies

(Submitted on 26 Feb 2019 (v1), last revised 27 Jun 2019 (this version, v2))

Stars formed in clusters can encounter other stars at close distances. In typical open clusters in the Solar neighbourhood containing hundreds or thousands of member stars, ten to twenty per cent of Solar-mass member stars are expected to encounter another star at distances closer than 100 au. These close encounters strongly perturb the planetary systems, directly causing ejection of planets or their capture by the intruding star, as well as exciting the orbits. Using extensive N-body simulations, we study such fly-by encounters between two Solar System analogues, each with four giant planets from Jupiter to Neptune. We quantify the rates of loss and capture immediately after the encounter, e.g., the Neptune analogue is lost in one in four encounters within 100 au, and captured by the flying-by star in one in twelve encounters. We then perform long-term (up to 1 Gyr) simulations investigating the ensuing post-encounter evolution. We show that large numbers of planets are removed from systems due to planet--planet interactions and that captured planets further enhance the system instability. While encounters can initially leave a planetary system containing more planets by inserting additional ones, the long-term instability causes a net reduction in planet number. A captured planet ends up on a retrograde orbit in half of the runs in which it survives for 1 Gyr; also, a planet bound to its original host star but flipped during the encounter may survive. Thus, encounters between planetary systems are a channel to create counter-rotating planets, This would happen in around 1% of systems, and such planets are potentially detectable through astrometry or direct imaging.