HIP 10725: The first solar twin/analogue field blue straggler

Abstract

Context. Blue stragglers are easy to identify in globular clusters, but are much harder to identify in the field. Here we present the serendipitous discovery of one field blue straggler, HIP 10725, that closely matches the Sun in mass and age, but with a metallicity slightly lower than solar. Aims. We characterise the solar twin/analogue HIP 10725 to assess whether this star is a blue straggler. Methods. We employed spectra with high resolution (R ∼ 10 5 ) and high signal-to-noise ratio (330) obtained with UVES at the VLT to perform a differential abundance analysis of the solar analogue HIP 10725. Radial velocities obtained by other instruments were also used to check for binarity. We also studied its chromospheric activity, age, and rotational velocity. Results. HIP 10725 is severely depleted in beryllium ([Be/H] ≤ −1.2 dex) for its stellar parameters and age. The abundances relative to solar of the elements with Z ≤ 30 show a correlation with condensation temperature, and the neutron capture elements produced by the s-process are greatly enhanced, while the r-process elements seem normal. We found its projected rotational velocity (v sin i = 3.3 ± 0.1 km s −1 ) to be significantly higher than solar and incompatible with its isochrone-derived age. Radial velocity monitoring shows that the star has a binary companion. Conclusions. Based on the high s-process element enhancements and low beryllium abundance, we suggest that HIP 10725 has been polluted by mass transfer from an AGB star that probably had an initial mass of about 2 M . The radial velocity variations suggest the presence of an unseen binary companion, probably the remnant of a former AGB star. Isochrones predict a solar-age star, but this disagrees with the high projected rotational velocity and high chromospheric activity. We conclude that HIP 10725 is a field blue straggler, rejuvenated by the mass-transfer process of its former AGB companion.

Signatures of rocky planet engulfment in HAT-P-4

“…However, in our system the ages of the two stars agree within the errors (2.7 ± 1.3 Gyr and 2.9 ± 1.8 Gyr), also when they are derived with the PARSEC isochrones (Bressan et al 2012). BS stars present significant rotational velocities, intense activity, and very low Li content (e.g., Fuhrmann & Bernkopf 1999;Schirbel et al 2015;Ryan et al 2001). None of these characteristics are seen in star A or star B.…”

The Li–age correlation: the Sun is unusually Li deficient for its age

“…In addition, Figure 2 presents more than 10 new solar twins in the age interval 0.0 ≤ Age (Gyr) 2.0, where it is possible to notice the sharp decrease of Li abundances with age. This behaviour might be explained by the fastrotator nature of young solar type stars (Pace & Pasquini 2004;Barnes 2007;do Nascimento et al 2014;dos Santos et al 2016), which may influence on internal stellar structures (Ballot et al 2007;Brown et al 2008) and enhance internal transport mechanisms (e.g., Schirbel et al 2015), then affecting how fast Li is burnt in young solar twins. It is interesting noting that at this age interval the data is more well represented by the non-standard evolution solar model of Do Nascimento et al (2009), which takes in consideration rotation induced mixing and diffusion.…”

Chemical evolution of the Galactic bulge as traced by microlensed dwarf and subgiant stars

“…If these two stars indeed were to be considered as blue straggler stars, their stellar age estimates could be too young. However, in the case of the solar analogue HIP 10725, which has several signatures of blue stragglers, such as non-detectable lithium, non-detectable beryllium, and large excess of neutron capture elements, just a small amount of mass transferred (less than 0.01 M ) was enough to introduce the observed excess of n-capture elements; as a consequence of the extra-mixing because of the transfer of angular momentum, lithium and beryllium were depleted (Schirbel et al 2015 Fig. 3.…”