RUB: Presumed Young Star Turns Out to be a Galactic Senior Citizen

[bystander]

Presumed Young Star Turns Out to be a Galactic Senior Citizen
Ruhr-Universität Bochum | 2017 Jan 16

It was considered a teenager among the stars. But now one thing has become clear: this celestial object was formed when our galaxy was born. Why did researchers get it wrong for many decades?

49 Lib, a relatively bright star in the southern sky, is twelve billion years old rather than just 2.3 billion. For many decades, researchers were stumped by conflicting data pertaining to this celestial body, because they had estimated it as much younger than it really is. Determining its age anew, astronomers at Ruhr-Universität Bochum (RUB) have now successfully resolved all inconsistencies. Dr Klaus Fuhrmann and Prof Dr Rolf Chini published their results in the “Astrophysical Journal”.

“It had previously been assumed that the star was only half as old as our sun,” says Chini. “However, our data have shown that it had been formed at the time that our galaxy was born.” The reason for the error: the celestial object is a dual star system, as was proved by another research group in 2016. Chini’s team has now demonstrated the mechanism used by the star partner of 49 Lib to fake its age. ...

Bright Times for an Ancient Star - Klaus Fuhrmann, Rolf Chini

• Astrophysical Journal 834(2):114 (2017 Jan 10) DOI: 10.3847/1538-4357/834/2/114

[Ann]

Ruhr Universität Bochum wrote:
The partner of 49 Lib is an almost extinguished star that is as good as invisible. At the end of its life, it had transferred a part of its matter to 49 Lib – this is what had made the estimation of age so confusing.

So 49 Lib is a blue straggler.

At first, both stars had similar mass properties as the sun. When 49 Lib took over a part of the matter of its extinguishing partner, it gained a weight of approximately 0.55 solar masses.

So both stars would originally have been sunlike. The now invisible previously primary star might have been a bit more massive than the Sun, and the companion would have been less massive - maybe they were a pair similar to the two bright components of Alpha Centauri. The bright G2V component of Alpha Centauri has 1.10 solar masses, versus 0.92 solar masses for the secondary, K1V, component, according to Jim Kaler.

If a 0.92 star were to gain 0.55 solar masses, its mass would be 1.43 solar. The mass of well-known nearby and therefore bright F-type star Procyon is 1.42 solar, according to Jim Kaler. So the bright component of 49 Lib might be an F-type star like Procyon.

Normally I would check the color indexes of 49 Lib and Procyon with my software, but it is currently broken. But if I read Simbad correctly, the B-V of 49 Lib is 0.52. That's a bit red for an F-type star, but acceptable. Procyon appears to be bluer, about 0.42.

Ann