arXiv subjects

Jhon Yana Galarza

Publications and source records attributed to Jhon Yana Galarza.

24 records · Page 2Linked to original sources

arXiv2019

The effect of stellar activity on the spectroscopic stellar parameters of the young solar twin HIP 36515

Spectroscopic equilibrium allows us to obtain precise stellar parameters in Sun-like stars. It relies on the assumption of the iron excitation and ionization equilibrium. However, several works suggest that magnetic activity may affect chemical abundances of young active stars, calling into question the validity of this widely-used method. We have tested for the first time variations in stellar parameters and chemical abundances for the young solar twin HIP 36515 ($\sim$0.4 Gyr), along its activity cycle. This star has stellar parameters very well established in the literature and we estimated its activity cycle in $\sim$6 years. Using HARPS spectra with high resolving power (115 000) and signal-to-noise ratio ($\sim$270), the stellar parameters of six different epochs in the cycle were estimated. We found that the stellar activity is strongly correlated with the effective temperature, metallicity, and microturbulence velocity. The possibility of changes in the Li I 6707.8 Åline due to flares and star spots was also investigated. Although the core of the line profile shows some variations with the stellar cycle, it is compensated by changes in the effective temperature, resulting in a non variation of the Li abundance.

astro-ph.SR↗

arXiv2019

Constraining the evolution of stellar rotation using solar twins

The stellar Rotation $vs.$ Age relation is commonly considered as a useful tool to derive reliable ages for Sun-like stars. However, in the light of \kepler\ data, the presence of apparently old and fast rotators that do not obey the usual gyrochronology relations led to the hypothesis of weakened magnetic breaking in some stars. In this letter, we constrain the solar rotation evolutionary track using solar twins. Predicted rotational periods as a function of mass, age, [Fe/H] and given critical Rossby number ($Ro_{\rm crit}$) were estimated for the entire rotational sample. Our analysis favors the smooth rotational evolution scenario and suggests that, if the magnetic weakened breaking scenario takes place at all, it should arise after $Ro_{\rm crit}\gtrsim2.29$ or ages $\gtrsim$5.3 Gyr (at 95$\%$ confidence level).

astro-ph.SR↗

arXiv2016

The Solar Twin Planet Search. V. Close-in, low-mass planet candidates and evidence of planet accretion in the solar twin HIP 68468

[Methods]. We obtained high-precision radial velocities with HARPS on the ESO 3.6 m telescope and determined precise stellar elemental abundances (~0.01 dex) using MIKE spectra on the Magellan 6.5m telescope. [Results]. Our data indicate the presence of a planet with a minimum mass of 26 Earth masses around the solar twin HIP 68468. The planet is a super-Neptune, but unlike the distant Neptune in our solar system (30 AU), HIP 68468c is close-in, with a semi-major axis of 0.66 AU, similar to that of Venus. The data also suggest the presence of a super-Earth with a minimum mass of 2.9 Earth masses at 0.03 AU; if the planet is confirmed, it will be the fifth least massive radial velocity planet discovery to date and the first super-Earth around a solar twin. Both isochrones (5.9 Gyr) and the abundance ratio [Y/Mg] (6.4 Gyr) indicate an age of about 6 billion years. The star is enhanced in refractory elements when compared to the Sun, and the refractory enrichment is even stronger after corrections for Galactic chemical evolution. We determined a NLTE Li abundance of 1.52 dex, which is four times higher than what would be expected for the age of HIP 68468. The older age is also supported by the low log(R'HK) (-5.05) and low jitter. Engulfment of a rocky planet of 6 Earth masses can explain the enhancement in both lithium and the refractory elements. [Conclusions]. The super-Neptune planet candidate is too massive for in situ formation, and therefore its current location is most likely the result of planet migration that could also have driven other planets towards its host star, enhancing thus the abundance of lithium and refractory elements in HIP 68468. The intriguing evidence of planet accretion warrants further observations to verify the existence of the planets that are indicated by our data and to better constrain the nature of the planetary system around this unique star.

astro-ph.EP↗

arXiv2016

High precision analysis of the solar twin HIP 100963

Methods. We used the HIRES spectrograph on the Keck I telescope to acquire high-resolution (R $\approx$ 70000) spectra with a high signal-to-noise ratio (S/N $\approx$ 400 - 650 per pixel) of HIP 100963 and the Sun for a differential abundance analysis. We measured the equivalent widths (EWs) of iron lines to determine the stellar parameters by employing the differential spectroscopic equilibrium. We determined the composition of volatile, refractory, and neutron-capture elements through a differential abundance analysis with respect to the Sun. Results. The stellar parameters we found are $T_{\rm{eff}}=5818 \pm 4$ K, log $g = 4.49 \pm 0.01$ dex, $v_{t} = 1.03 \pm 0.01 $ $\rm{km\ {s}}^{-1}$ , and [Fe/H] $ = -\ 0.003 \pm 0.004$ dex. These low errors allow us to compute a precise mass ($1.03^{+0.02}_{-0.01}$ M$_{\odot}$) and age (2.0 $\pm$ 0.4 Gyr), obtained using Yonsei-Yale isochrones. Using our [Y/Mg] ratio, we have determined an age of $2.1 \pm 0.4$ Gyr, in agreement with the age computed using isochrones. Our isochronal age also agrees with the age determined from stellar activity (2.4 $\pm$ 0.3 Gyr). We study the abundance pattern with condensation temperature ($\rm{T_{cond}}$) taking corrections by the GCE into account. We show that the enhancements of neutron-capture elements are explained by contributions from both the $s$- and $r$-process. The lithium abundance follows the tight Li-age correlation seen in other solar twins. Conclusions. We confirm that HIP 100963 is a solar twin and demonstrate that its abundance pattern is about solar after corrections for GCE. The star also shows enrichment in $s-$ and $r$-process elements, as well as depletion in lithium that is caused by stellar evolution.

astro-ph.SR↗

arXiv2016

Serendipitous discovery of the faint solar twin Inti 1

Methods. We determine the atmospheric parameters and differential abundances using high-resolution ($R \approx 50 000$), high signal-to-noise (S/N $\approx$ 110 - 240 per pixel) Keck HIRES spectra for our solar twin candidate, the previously known solar twin HD 45184, and the Sun. Results. For the bright solar twin HD 45184, we found $T_{\rm{eff}} = 5864 \pm 9$ K, log $g = 4.45 \pm 0.03$ dex, $v_{t} = 1.11 \pm 0.02$ $\rm{km\ {s}}^{-1}$, and [Fe/H]$ = 0.04 \pm 0.01$ dex, which are in good agreement with previous works. The star Inti 1 has atmospheric parameters $T_{\rm{eff}} = 5837 \pm 11$ K, log $g = 4.42 \pm 0.03$ dex, $v_{t} = 1.04 \pm 0.02$ $\rm{km\ {s}}^{-1}$, and [Fe/H]$ = 0.07 \pm 0.01$ dex that are higher than solar. The age and mass of the solar twin HD 45184 (3 Gyr and 1.05 $\rm{M_{\odot}}$) and the faint solar twin Inti 1 (4 Gyr and 1.04 $\rm{M_{\odot}}$) were estimated using isochrones. The differential analysis shows that HD 45184 presents an abundance pattern that is similar to typical nearby solar twins; this means this star has an enhanced refractory relative to volatile elements, while Inti 1 has an abundance pattern closer to solar, albeit somewhat enhanced in refractories. The abundance pattern of HD 45184 and Inti 1 could be reproduced by adding $\approx 3.5\ \rm{M_{\oplus}}$ and $\approx 1.5\ \rm{M_{\oplus}}$ of Earth-like material to the convective zone of the Sun. Conclusions. The star Inti 1 is a faint solar twin, therefore, it could be used to calibrate the zero points of different photometric systems. The distant solar twin Inti 1 has an abundance pattern similar to the Sun with only a minor enhancement in the refractory elements. It would be important to analyze other distant solar twins to verify whether they share the Sun's abundance pattern or if they are enhanced in refractories, as is the case in the majority of nearby solar twins.

astro-ph.SR↗

arXiv2013

Number Counts and Non-Gaussianity

We describe a general procedure for using number counts of any object to constrain the probability distribution of the primordial fluctuations, allowing for generic weak non-Gaussianity. We apply this procedure to use limits on the abundance of primordial black holes and dark matter ultracompact minihalos (UCMHs) to characterize the allowed statistics of primordial fluctuations on very small scales. We present constraints on the power spectrum and the amplitude of the skewness for two different families of non-Gaussian distributions, distinguished by the relative importance of higher moments. Although primordial black holes probe the smallest scales, ultracompact minihalos provide significantly stronger constraints on the power spectrum and so are more likely to eventually provide small-scale constraints on non-Gaussianity.

astro-ph.CO↗