Rotating models of young solar-type stars : Exploring braking laws and angular momentum transport processes

We study the predicted rotational evolution of solar-type stars from the pre-main sequence to the solar age with 1D rotating evolutionary models including physical ingredients. We computed rotating evolution models of solar-type stars including an external stellar wind torque and internal transport of angular momentum following the method of Maeder and Zahn with the code STAREVOL. We explored different formalisms and prescriptions available from the literature. We tested the predictions of the models against recent rotational period data from extensive photometric surveys, lithium abundances of solar-mass stars in young clusters, and the helioseismic rotation profile of the Sun. We find a best-matching combination of prescriptions for both internal transport and surface extraction of angular momentum. This combination provides a very good fit to the observed evolution of rotational periods for solar-type stars from early evolution to the age of the Sun. Additionally, we show that fast rotators experience a stronger coupling between their radiative region and the convective envelope. Regardless of the set of prescriptions, however, we cannot simultaneously reproduce surface angular velocity and the internal profile of the Sun or the evolution of lithium abundance. We confirm the idea that additional transport mechanisms must occur in solar-type stars until they reach the age of the Sun. Whether these processes are the same as those needed to explain recent asteroseismic data in more advanced evolutionary phases is still an open question.Comment: 16 pages, 16 figures, accepted for publication in A&

Impact of internal gravity waves on the rotation profile inside pre-main sequence low-mass stars

We study the impact of internal gravity waves (IGW), meridional circulation, shear turbulence, and stellar contraction on the internal rotation profile and surface velocity evolution of solar metallicity low-mass pre-main sequence stars. We compute a grid of rotating stellar evolution models with masses between 0.6 and 2.0Msun taking these processes into account for the transport of angular momentum, as soon as the radiative core appears and assuming no more disk-locking from that moment on.IGW generation along the PMS is computed taking Reynolds-stress and buoyancy into account in the bulk of the stellar convective envelope and convective core (when present). Redistribution of angular momentum within the radiative layers accounts for damping of prograde and retrograde IGW by thermal diffusivity and viscosity in corotation resonance. Over the whole mass range considered, IGW are found to be efficiently generated by the convective envelope and to slow down the stellar core early on the PMS. In stars more massive than ~ 1.6Msun, IGW produced by the convective core also contribute to angular momentum redistribution close to the ZAMS. Overall, IGW are found to significantly change the internal rotation profile of PMS low-mass stars.Comment: Accepted for publication in A&A (15 pages

Tidal dissipation in rotating low-mass stars and implications for the orbital evolution of close-in planets I. From the PMS to the RGB at solar metallicity

Star-planet interactions must be taken into account in stellar models to understand the dynamical evolution of close-in planets. The dependence of the tidal interactions on the structural and rotational evolution of the star is of peculiar importance and should be correctly treated. We quantify how tidal dissipation in the convective envelope of rotating low-mass stars evolves from the pre-main sequence up to the red-giant branch depending on the initial stellar mass. We investigate the consequences of this evolution on planetary orbital evolution. We couple the tidal dissipation formalism described in Mathis (2015) to the stellar evolution code STAREVOL and apply it to rotating stars with masses between 0.3 and 1.4 M$_\odot$. In addition, we generalize the work of Bolmont & Mathis (2016) by following the orbital evolution of close-in planets using the new tidal dissipation predictions for advanced phases of stellar evolution. On the PMS the evolution of tidal dissipation is controlled by the evolution of the internal structure of the contracting star. On the MS it is strongly driven by the variation of surface rotation that is impacted by magnetized stellar winds braking. The main effect of taking into account the rotational evolution of the stars is to lower the tidal dissipation strength by about four orders of magnitude on the main-sequence, compared to a normalized dissipation rate that only takes into account structural changes. The evolution of the dissipation strongly depends on the evolution of the internal structure and rotation of the star. From the pre-main sequence up to the tip of the red-giant branch, it varies by several orders of magnitude, with strong consequences for the orbital evolution of close-in massive planets. These effects are the strongest during the pre-main sequence, implying that the planets are mainly sensitive to the star's early history.Comment: 13 pages, 7 figures, accepted for publication in A&

Further evidence of the link between activity and metallicity using the flaring properties of stars in the Kepler field

The magnetic activity level of low-mass stars is known to vary as a function of the physical properties of the star. Many studies have shown that the stellar mass and rotation are both important parameters that determine magnetic activity levels. In contrast, the impact of a star's chemical composition on magnetic activity has received comparatively little attention. Data sets for traditional activity proxies, e.g. X-ray emission or calcium emission, are not large enough to search for metallicity trends in a statistically meaningful way. Recently, studies have used the photometric variability amplitude as a proxy for magnetic activity to investigate the role of metallicity because it can be relatively easily measured for large samples of stars. These studies find that magnetic activity and metallicity are positively correlated. In this work, we investigate the link between activity and metallicity further by studying the flaring properties of stars in the Kepler field. Similar to the photometric variability, we find that flaring activity is stronger in more metal-rich stars for a fixed mass and rotation period. This result adds to a growing body of evidence that magnetic field generation is correlated with metallicity.Comment: 6 pages, 5 figures, accepted for publication in MNRA

User-centricity and Public Values in eGovernment: Friend or Foe?

In their delivery of services, public administrations seek to develop a ‘citizen-centric’ approach. Concomitantly, user-centricity is emerging as a widely accepted construct for Web 3.0 applications supporting the digital interaction between service providers and recipients. The digitalization of public services can positively impact important public values, such as efficiency and transparency. However, the digital divide highlights that information and communication technologies can simultaneously neglect public needs. This begs the question of whether user-centricity reflects or conflicts with public values. To answer this question, we present a systematic review of existing literature on user-centricity and public values. The contribution of this paper is an extended taxonomy of public values for user- centricity, as well as recommendations for public policy to address conflicts between public values and user-centricity

User-centricity and Public Values in eGovernment: Friend or Foe?

In their delivery of services, public administrations seek to develop a ‘citizen-centric’ approach. Concomitantly, user-centricity is emerging as a widely accepted construct for Web 3.0 applications supporting the digital interaction between service providers and recipients. The digitalization of public services can positively impact important public values, such as efficiency and transparency. However, the digital divide highlights that information and communication technologies can simultaneously neglect public needs. This begs the question of whether user-centricity reflects or conflicts with public values. To answer this question, we present a systematic review of existing literature on user-centricity and public values. The contribution of this paper is an extended taxonomy of public values for user-centricity, as well as recommendations for public policy to address conflicts between public values and user-centricity

The impact of metallicity on the evolution of the rotation and magnetic activity of Sun-like stars

This is the author accepted articleThe rotation rates and magnetic activity of Sun-like and low-mass (.1.4M) main-sequence stars are knownto decline with time, and there now exist several models for the evolution of rotation and activity. However,the role that chemical composition plays during stellar spin-down has not yet been explored. In this work,we use a structural evolution code to compute the rotational evolution of stars with three different masses (0.7, 1.0, and 1.3M) and six different metallicities, ranging from [Fe/H]=−1.0 to [Fe/H]= +0.5. We also implement three different wind-braking formulations from the literature (two modern and one classical) and compare their predictions for rotational evolution. The effect that metallicity has on stellar structural properties,and in particular the convective turnover timescale, leads the two modern wind-braking formulations to predict a strong dependence of the torque on metallicity. Consequently, they predict that metal rich stars spin-down more effectively at late ages (>1 Gyr) than metal poor stars, and the effect is large enough to be detectable with current observing facilities. For example, the formulations predict that a Sun-like (solar-mass and solar-aged) star with [Fe/H]=−0.3 will have a rotation period of less than 20 days. Even though old, metal poor stars are predicted to rotate more rapidly at a given age, they have larger Rossby numbers and are thus expected to have lower magnetic activity levels. Finally, the different wind-braking formulations predict quantitative differences in the metallicity-dependence of stellar rotation, which may be used to test themER