I was tracking these runaway stars for a SF story i had in mind, but this is the closest one i have heard of yet, and the ArXiv paper describes one that also passed thru 2.5 mya.
Gliese 710 will pass the Sun even closer
Close approach parameters recalculated based on the first Gaia data release
http://www.aanda.org/articles/aa/abs/2016/11/aa29835-16/aa29835-16.html
Close encounters of the stellar kind
https://arxiv.org/abs/1412.3648
tl:dr article
http://www.businessinsider.com/star-hurting-towards-solar-system-2016-12\
"Gliese 710 is about half the size of our sun, and it is set to reach Earth in 1.35 million years, according to a paper published in the journal Astronomy & Astrophysics in November.
And when it arrives, the star could end up a mere 77 light-days away from Earth — one light-day being the equivalent of how far light travels in one day, which is about 26 billion kilometers, the researchers worked out.
As far as we know, Gliese 710 isn't set to collide directly with Earth, but it wil be passing through the Oort Cloud, a shell of trillions of icy objects at the furthest reaches of our solar system. "
Seems like a great opportunity to send out some interstellar probes. The star will be trailing lots of ISM, free gas that would help bring a ramjet up to speed, and track till you could curve towards another destination. Likewise, a solar sail probe launched out in front of it by laser could "hitchhike" , and get some deep space ISM , and EM measurements.
Can we think of some other opportunities that this might present ? If we are past the filter by then, then we will already prob have samples of the Oort objects, but looks like they will be delivering then...
This article points to a paper that shows destabilized comets coming in at 160 kp/s, that is way beyond anything we have seen before,...
"The team’s spectrographic analysis, using Hubble data collected from two observing runs separated by six days, detected carbon gas and silicon in the light of HD 172555 moving across the face of the star at a speed of 160 kilometers per second."
This is a young star, and disk, but still surprising pertubations.
A New Look at ‘Exocomets’
http://www.centauri-dreams.org/?p=36939
You can't have an oort cloud comet hit the Earth at 160 km/s. The absolute fastest that anything falling from an orbit bound to our sun (oort cloud comets being very lightly bound) in the outer solar system can hit the Earth is about (((1+ square root of 2)* the Earth's orbital velocity)^2 + Earth's escape velocity^2)^0.5, or about 73 kilometers per second. This is if it falls from basically infinity (oort cloud distances) to the Earth's distance from the sun, reaching solar escape velocity at our altitude (square root of two times our orbital velocity) ... (read more)