Spectroscopic and asteroseismic analysis of the remarkable main-sequence A star KIC 11145123

Abstract

A spectroscopic analysis was carried out to clarify the properties of KIC 11145123 -the first main-sequence star with a determination of core-to-surface rotation -based on spectra observed with the High Dispersion Spectrograph (HDS) of the Subaru telescope. The atmospheric parameters (T eff = 7600 K, log g = 4.2, ξ = 3.1 km s −1 and [Fe/H] = −0.71 dex), the radial and rotation velocities, and elemental abundances were obtained by analysing line strengths and fitting line profiles, which were calculated with a 1D LTE model atmosphere. The main properties of KIC 11145123 are: (1) A low [Fe/H] = −0.71 ± 0.11 dex and a high radial velocity of −135.4 ± 0.2 km s −1 . These are remarkable among late-A stars. Our best asteroseismic models with this low [Fe/H] have slightly high helium abundance and low masses of 1.4 M ⊙ . All of these results strongly suggest that KIC 11145123 is a Population II blue straggler; (2) The projected rotation velocity confirms the asteroseismically predicted slow rotation of the star; (3) Comparisons of abundance patterns between KIC 11145123 and Am, Ap, and blue stragglers show that KIC 11145123 is neither an Am star nor an Ap star, but has abundances consistent with a blue straggler. We conclude that the remarkably long 100-d rotation period of this star is a consequence of it being a blue straggler, but both pathways for the formation of blue stragglers -merger and mass loss in a binary system -pose difficulties for our understanding of the exceedingly slow rotation. In particular, we show that there is no evidence of any secondary companion star, and we put stringent limits on the possible mass of any such purported companion through the phase modulation (PM) technique.

Asteroseismic Modeling of Gravity Modes in Slowly Rotating A/F Stars with Radiative Levitation

“…Such a slow rotation period is quite rare compared to observations from the study by Li et al (2019b), who show that the rotation period distribution-based on 611 γDor stars-is Gaussian-like and peaks at ∼1 day, although some excess around slow rotation is seen in the distribution. A spectroscopic follow-up of KIC 11145123 by Takada-Hidai et al (2017) shows that the star has a low surface metallicity ([Fe/H]=- 0.71 0.11 dex) and its low lithium abundance is compatible with those of the blue stragglers (Glaspey et al 1994). Moreover, these authors did not find any presence of a companion.…”

“…The period spacing in the corotating frame DP co is in this case roughly equal to the period spacing in the inertial frame. The coverages in metallicity for the two stars are based on spectroscopic measurements from Takada-Hidai et al (2017) and Van Reeth et al (2016) for KIC 11145123 and KIC 9751996, respectively, where the measured value and the upper and lower values of the uncertainty intervals listed in these studies are used. Besides the mass, the method by Mombarg et al (2019) also provides us with an estimate for the hydrogen mass fraction inside the convective core (X c ).…”

“…The initial helium content is then set by Asplund et al (2009). We have chosen this approach to set the initial composition, as Takada-Hidai et al (2017) Verma et al (2019). In a second approach, we use this enrichment rate by Verma et al (2019), despite its large uncertainties, to set the initial composition for both stars.…”

Reliability of stellar inclination estimated from asteroseismology: analytical criteria, mock simulations and Kepler data analysis

“…We would like to point that "the roundest A-type star" KIC 11145123 (Kurtz et al 2014;Gizon et al 2016) presents an interesting example in this context. (Takada-Hidai et al 2017) found that the spectroscopically measured value of v sin i ⋆ ≃ 5km/s suffers from systematic overestimate, and asteroseismically derived equatorial rotation velocity of v sin i ⋆ ≃ 1km/s proved to be more reliable. This suggests that the spectroscopic measurement of v sin i ⋆ for slowly rotating stars needs to be interpreted with caution, which is in good agreement with our conclusions from Figure 8.…”

On the first δ Sct–roAp hybrid pulsator and the stability of p and g modes in chemically peculiar A/F stars

“…We measured the rotational line broadening, vsin i, using the same procedure applied to the extremely slowly rotating A star KIC 11145123 (Takada-Hidai et al 2017), namely that of Takeda et al (2008), in which vsin i is obtained as the intercept of a leastsquares fit of the line broadening, v rm , as a function of W λ . For this, we used 55 Fe I lines that we considered to be unblended, to be consistent with the Fe abundance of 7.5 ± 0.3 dex, and to be symmetric.…”