arXiv subjects

Anastasiia Plotnikova

Publications and source records attributed to Anastasiia Plotnikova.

4 recordsLinked to original sources

arXiv2026

Photometric Identification of Unresolved Binary Stars in Nearby Open Star Clusters

This paper introduces a new method to search for unresolved binary stars in open star clusters. The work aims at improving the approach introduced previously, which employs the (H-W2)-W1 versus W2-(BP-K) photometric diagram. This diagram, in tandem with the Gaia Color Magnitude Diagram (CMD) and using theoretical isochrones as reference sequences, is used to estimate the binary star fraction and the distribution of the component mass ratio $q$ in eight nearby open star clusters, including Pleiades, Alpha Per, and Praesepe, which we investigated in previous studies. In this study, to alleviate the uncertainties associated with the use of theoretical isochrones, we propose an empirical isochrones approach. We show that this is an effective approach to exploring a wider primary-mass interval, in particular for the region of low-mass sources. Box-and-whisker plots are used to present the distribution of the component mass ratio $q$. The mode of distribution turns out to be in the range $0.43-0.83$ and $0.38-0.63$ for Gaia and infrared-visible photometry, respectively. In addition, we update the algorithm to obtain the binary fraction, whose estimate lies in the range $0.16 - 0.36$ and $0.21 - 0.44$, depending on the adopted method, and show that in previous studies the binary fraction was overestimated. We do not find evidence that the variable spatial resolution of the employed catalogs (Gaia, 2MASS, and WISE) affects the precision of the binary fraction estimate.

astro-ph.GA↗

arXiv2024

The chemical evolution of the Milky Way thin disk using solar twins

In this study we address whether the age--metallicity relation (AMR) deviates from the expected trend of metallicity increasing smoothly with age. We also show the presence (or absence) of two populations, as recently claimed using a relatively small dataset. Moreover, we studied the Milky Way thin disk's chemical evolution using solar twins, including the effect of radial migration and accretion events. In particular, we exploited high-resolution spectroscopy of a large sample of solar twins in tandem with an accurate age determination to investigate the Milky Way thin disk age--metallicity relationship. Additionally, we derived the stars' birth radius and studied the chemical evolution of the thin disk. We discovered that statistical and selection biases can lead to a misinterpretation of the observational data. An accurate accounting of all the uncertainties led us to detect no separation in the AMR into different populations for solar twins around the Sun (-0.3 < [Fe/H] < 0.3 dex). This lead us to the conclusion that the thin disk was formed relatively smoothly. For the main scenario of the Milky Way thin disk formation, we suggest that the main mechanism for reaching today's chemical composition around the Sun is radial migration with the possible contribution of well-known accretion events such as Gaia-Enceladus/Sausage (GES) and Sagittarius (Sgr).

astro-ph.GA↗

arXiv2023

Very metal-poor stars in the solar vicinity: kinematics and abundance analysis

Very metal-poor stars contain crucial information on the Milky Way's infancy. In our previous study \citep{Plotnikova_2022} we derived a mean age of $\sim$ 13.7 Gyr for a sample of these stars in the Sun's vicinity. In this work, we investigate the chemical and kinematics properties of these stars with the goal of obtaining some insights on their origin and their parent population. We did not find any Al-Mg anti-correlation, which lead us to the conclusion that these stars did not form in globular clusters, while the detailed analysis of their orbital parameters reveals that these stars are most probably associated with the pristine Bulge of the Milky Way. We then sketch a scenario for the formation of the Milky Way in which the first structure to form was the Bulge through rapid collapse. The other components have grown later on, with a significant contribution of accreted structures.

astro-ph.GA↗

arXiv2022

Very metal-poor stars in the solar vicinity: age determination

The ages of the oldest and most metal-poor stars in the Milky Way bear important information on the age of the Universe and its standard model. We analyze a sample of 28 extremely metal-poor field stars in the solar vicinity culled from the literature and carefully determine their ages. To this aim, we critically make use of Gaia data to derive their distances and associated uncertainties. Particular attention has been paid to the estimate of the reddening and its effect on the derivation of stellar ages. We employed different reddenings and super-impose isochrones from different sources in the stars color-magnitude diagram built up with different photometric systems. We highlight subtle metallicity effects when using the Johnson photometry for low metallicity stars and finally adopt Gaia photometry. An automatic fitting method is devised to assign ages to each individual star taking into account the uncertainties in the input parameters. The mean age of the sample turns out to be $13.9 \pm 0.5$ Gyr using Padova isochrones, and $13.7 \pm 0.4$ Gyr using BASTI isochrones. We found also a group of very metal-poor stars ($\left[\frac{Fe}{H}\right]$: -2.7 -2.0 dex) with relatively young ages, in the range 8 --10 Gyr.

astro-ph.SR↗