The Solar Twin Planet Search

Abstract

Context. It is still unclear how common the Sun is when compared to other similar stars in regards to some of its physical properties, such as rotation. Considering that gyrochronology relations are widely used today to estimate ages of stars in the main sequence, and that the Sun is used to calibrate it, it is crucial to assess whether these procedures are acceptable. Aims. We analyze the rotational velocities, limited by the unknown rotation axis inclination angle, of an unprecedented large sample of solar twins to study the rotational evolution of Sun-like stars, and assess whether the Sun is a typical rotator. Methods. We used high-resolution (R = 115 000) spectra obtained with the HARPS spectrograph and the 3.6 m telescope at La Silla Observatory. The projected rotational velocities for 81 solar twins were estimated by line profile fitting with synthetic spectra. Macroturbulence velocities were inferred from a prescription that accurately reflects their dependence with effective temperature and luminosity of the stars. Results. Our sample of solar twins include some spectroscopic binaries with enhanced rotational velocities, and we do not find any nonspectroscopic binaries with unusually high rotation velocities. We verified that the Sun does not have a peculiar rotation, but the solar twins exhibit rotational velocities that depart from the Skumanich relation. Conclusions. The Sun is a regular rotator when compared to solar twins with a similar age. Additionally, we obtain a rotational braking law that better describes the stars in our sample (v ∝ t −0.6 ) in contrast to previous, often-used scalings.

A revised gyro-age for M67 fromKepler/K2-Campaign-5light curves

“…They report a vsini value of 4.0 ± 0.5 km s −1 for the other one, S1452; this is about twice the typical value of the other stars they measured. While they didn't have any evidence for binarity in the case of S1452, Geller et al (2015) do list it as a spectroscopic binary. Still, these observations demonstrate that some sun-like stars in M 67 are fast rotators.…”

“…dos Santos et al (2016) determined vsini values for 82 nearby single and binary solar twins. Amongst the single twins near the solar age, vsini ranges from about 0.7 to 2.0 km s −1 .…”

The Solar Twin Planet Search

“…The projected rotational velocity of HIP 68468 was estimated through spectral synthesis by dos Santos et al (2016), taking into account both the instrumental (∆λ = λ/R) and macroturbulent broadening (using a radial-tangential macroturbulence profile; Gray 2005).…”

“…dos Santos et al (2016) provided a new macroturbulence calibration that takes the T eff and log g dependence into account. This gives a projected rotation velocity for HIP 68468 of v sin i = 1.92 ± 0.13 km s −1 (dos Santos et al 2016), which agrees within the errors with the rotation velocity predicted by the v rot -age relation by dos Santos et al (2016) at HIP 68468's age (5.9 Gyr), v rot = 1.86 km s −1 .…”

“…Our HARPS data have previously been used to obtain stringent constraints on planets around two important solar twins, 18 Sco, which is the brightest solar twin and is younger than the Sun (Meléndez et al 2014a), and HIP 102152, an old solar twin with a low lithium content (Monroe et al 2013). Our HARPS data were also used to study the rotation-age relation, showing that our Sun is a regular rotator (dos Santos et al 2016).…”