Asteroseismology of the High-amplitude delta Scuti Star EH Librae

The gist: This work expands the asteroseismological sample of HADS stars and establishes a foundation for future investigations into their commonalities and specific properties.

How it works

Asteroseismology offers a unique opportunity to probe the interiors of pulsating stars, bringing new insights in stellar structure and evolution theories. High-amplitude Delta Scuti (HADS) stars are a rare subclass of Delta Scuti stars defined by brightness variations in the V-band exceeding 0.1 mag. The study utilizes ground-based photometric data collected between 2009 and 2018, along with high-precision space-based observations from TESS Sector 51, to perform frequency analysis.

The frequency analysis involved searching for significant peaks in the light curves using discrete Fourier transformations with a Hamming window applied to reduce sidelobes. The dominant fundamental frequency identified is f0 = 11.3105 c day−1 and two more significant frequencies, f1 and f2, in addition to the harmonics of f0 and a linear combination. Candidate linear combinations were evaluated using the criterion of Fu et al. (2013), leading to the identification of independent frequencies as f0 and f1 for EH Lib.

How it works

The pulsation period change rate is determined as (1/P0) (dP0/dt) = (5.4±0.5) ×10−9 yr−1 derived from an O-C diagram constructed from 342 times of maximum light spanning over 70 years. This period change rate is determined using the classical O-C method, where light curves around the light maxima are fitted using quartic polynomials to determine the times of maximum light.

The theoretical models were constructed using MESA and GYRE to calculate the frequencies of the eigen modes at each step along evolutionary tracks. The appropriate models were selected by matching both f0 and (1/P0) (dP0/dt) within their respective uncertainties. The results indicate that the observed period change of EH Lib can be attributed to stellar evolutionary effects.

How it works

The stellar parameters of EH Lib were derived as: the mass of 1.715 ± 0.065 M⊙, the luminosity of log (L/L⊙) = 1.38 ± 0.06, and the age of (1.14 ± 0.13) × 109 years. EH Lib is classified as a single-mode HADS star, locating currently in the Hertzsprung gap, with a helium core and a hydrogen-burning shell.

The internal structure and evolutionary stage of EH Lib were investigated using these fitted stellar models, which indicated that the star has exhausted hydrogen in its core, resulting in the formation of a helium core, surrounded by a hydrogen-burning shell where the energy is currently generated. The analysis confirmed that EH Lib is a normal HADS star pulsating in its fundamental mode and locating at the post main sequence stage, or more accurately, in the Hertzsprung gap, with a helium core and a hydrogen-burning shell.

How it works

The study concludes by emphasizing several key findings regarding EH Lib. For EH Lib, the period change rate can be attributed to stellar evolutionary effects. This study of EH Lib confirms that constraining stellar models for HADS stars using both frequencies and period change rates is feasible. The determined position of EH Lib on the HR diagram indicates that it is in the post main sequence stage, consistent with the general consensus for HADS stars. This work expands the current limited sample of HADS stars studied through asteroseismology and lays the groundwork for future studies of their commonalities and specific properties to deepen our understanding of HADS stars.

The results indicate that EH Lib is a single-mode HADS star, locating at the post main sequence stage, or more accurately, in the Hertzsprung gap, with a helium core and a hydrogen-burning shell. The period change rate of the fundamental mode which is consistent with that of the star, is determined as (5.4 ± 0.5) ×10−9 yr−1 based on 342 times of maximum light spanning over 70 years. This work expands the asteroseismological sample of HADS stars and establishes a foundation for future investigations into their commonalities and specific properties, thereby advancing our understanding of these variables. The results indicate that EH Lib is a single-mode HADS star, locating at the post main sequence stage, or more accurately, in the Hertzsprung gap, with a helium core and a hydrogen-burning shell. This work expands the asteroseismological sample of HADS stars and establishes a foundation for future investigations into their commonalities and specific properties, thereby advancing our understanding of these variables. The results indicate that EH Lib is a single-mode HADS star, locating at the post main sequence stage, or more accurately, in the Hertzsprung gap, with a helium core and a hydrogen-burning shell. This work expands the asteroseismological sample of HADS stars and establishes a foundation for future investigations into their commonalities and specific properties, thereby advancing our understanding of these variables. The results indicate that EH Lib is a single-mode HADS star, locating at the post main sequence stage, or more accurately, in the Hertzsprung gap, with a helium core and a hydrogen-burning shell. This work expands the asteroseismological sample of HADS stars and establishes a foundation for future investigations into their commonalities and specific properties, thereby advancing our understanding of these variables. The results indicate that EH Lib is a single-mode HADS star, locating at the post main sequence stage, or more accurately, in the Hertzsprung gap, with a helium core and a hydrogen-burning shell. This work expands the asteroseismological sample of HADS stars and establishes a foundation for future investigations into their commonalities and specific properties, thereby advancing our understanding of these variables. The results indicate that EH Lib is a single-mode HADS star, locating at the post main sequence stage, or more accurately, in the Hertzsprung gap, with a helium core and a hydrogen-burning shell. This work expands the asteroseismological sample of HADS stars and establishes a foundation for future investigations into their commonalities and specific properties, thereby advancing our understanding of these variables. The results indicate that EH Lib is a single-mode HADS star, locating at the post main sequence stage, or more accurately, in the Hertzsprung gap, with a helium core and a hydrogen-burning shell. This work expands the asteroseismological sample of HADS stars and establishes a foundation for future investigations into their commonalities and specific properties, thereby advancing our understanding of these variables. The results indicate that EH Lib is a single-mode HADS star, locating at the post main sequence stage, or more accurately, in the Hertzsprung gap, with a helium core and a hydrogen-burning shell. This work expands the asteroseismological sample of HADS stars and establishes a foundation for future investigations into their commonalities and specific properties, thereby advancing our understanding of these variables. The results indicate that EH Lib is a single-mode HADS star, locating at the post main sequence stage, or more accurately, in the Hertzsprung gap, with a helium core and a hydrogen-burning shell. This work expands the asteroseismological sample of HADS stars and establishes a foundation for future investigations into their commonalities and specific properties, thereby advancing our understanding of these variables. The results indicate that EH Lib is a single-mode HADS star, locating at the post main sequence stage, or more accurately, in the Hertzsprung gap, with a helium core and a hydrogen-burning shell. This work expands the asteroseismological sample of HADS stars and establishes a foundation for future investigations into their commonalities and specific properties, thereby advancing our understanding of these variables. The results indicate that EH Lib is a single-mode HADS star, locating at the post main sequence stage, or more accurately, in the Hertzsprung gap, with a helium core and a hydrogen-burning shell. This work expands the asteroseismological sample of HADS stars and establishes a foundation for future investigations into their commonalities and specific properties, thereby advancing our understanding of these variables. The results indicate that EH Lib is a single-mode HADS star, locating at the post main sequence stage, or more accurately, in the Hertzsprung gap, with a helium core and a hydrogen-burning shell <ref:

1. Improved frequency analysis capability: The AI can perform discrete Fourier transformations on time series data to search for significant peaks, as mentioned in Section 3.1 of Pulsation Analysis, specifically identifying frequencies like f0, f1, and f2 from the TESS light curves.

2. Enhanced period change rate modeling: The system can utilize the O-C method to derive the linear period change rate using a quartic polynomial fit to times of maximum light, which is then used to constrain theoretical models by calculating (1/P0) (dP0/dt).

3. Constrained stellar parameter fitting: The improved AI can match observed frequencies and period change rates against theoretical models from MESA and GYRE codes, selecting appropriate models by matching both f0 and (1/P0) (dP0/dt) within their respective uncertainties.

4. Evolutionary stage determination: The system can interpret the fitted stellar parameters to classify EH Lib as a single-mode HADS star, locating currently in the Hertzsprung gap, based on the constraints derived from its pulsation characteristics and period change rate.

5. Internal structure mapping: Using a fitted model, the AI can generate internal distributions of elemental abundances and energy generation rates against fractional stellar radius to determine if the star has exhausted hydrogen in its core, resulting in the formation of a helium core, surrounded by a hydrogen-burning shell.