arXiv subjects

Ahmad Sarostad

Publications and source records attributed to Ahmad Sarostad.

4 recordsLinked to original sources

arXiv2026

Detailed TESS-Based Light Curve Modeling and Fundamental Parameter Estimation of 27 W UMa-Type Contact Binaries

We performed a comprehensive analysis of 27 short period contact binary systems for which no light curve analysis had previously been reported. Photometric time-series data from the TESS mission were used in this analysis. The observational results were validated using additional TESS sectors, along with complementary photometric observations from the ASAS-SN survey. The photometric light curves of the 27 contact binary systems were analyzed with the BSN application. Model solutions were obtained through iterative fitting followed by MCMC-based refinement to derive reliable system parameters, and starspot configurations were incorporated for seven targets exhibiting O'Connell effect asymmetries. The absolute parameters of the target systems were derived using the empirical parameter relationship between orbital period and semi-major axis. Based on the results of the light curve solutions and the estimated absolute parameters, five of the analyzed systems are identified as A-subtype, while the remaining targets belong to the W-subtype. We analyzed a sample of 484 W UMa contact binaries to identify the physical and orbital parameters that most effectively distinguish A-subtype from W-subtype systems using t-statistics. Three targets exhibited extremely low mass ratios, and their orbital analysis confirmed that they are dynamically stable. The evolutionary states of the systems were examined, showing that lower-mass companions are generally more evolved, while more massive components remain less evolved. The positions of the systems and their stellar components were compared across four diagrams derived from empirical parameter relationship studies, showing good agreement with the linear fits.

astro-ph.SR↗

arXiv2025

The First In-depth Photometric Study of the Four Delta Scuti Stars Using TESS Data

The first in-depth photometric study of four Delta Scuti stars was performed. We used time series data from the Transiting Exoplanet Survey Satellite (TESS) that is available in different sectors. According to the extracted maxima from TESS space-based observations, we calculated an ephemeris for each star. We estimated the physical parameters of the target stars based on the Gaia Data Release 3 (DR3) parallax method. The results obtained for the surface gravity of the stars are consistent with the reports of the TESS Input Catalog and Gaia DR3. We estimated the pulsating constant based on the physical parameters and period of the stars. Therefore, we found that the stars 2MASS 15515693-7759002 and 2MASS 07513202+0526526 belong to the fundamental, while 2MASS 00044615+4936439 and 2MASS 10215638-3326137 relate to the first overtone. The Fourier analysis using the Period04 program was done for each star. As we showed in the Hertzsprung-Russell (H-R) diagram, the stars are located in the instability strip of the Delta Scuti stars region. Four target stars were found to be of the low-amplitude Delta Scuti star type.

astro-ph.SR↗

arXiv2024

First Light Curve Analysis of NSVS 8294044, V1023 Her, and V1397 Her Contact Binary Systems

The first photometric light curve investigation of the NSVS 8294044, V1023 Her, and V1397 Her binary systems is presented. We used ground-based observations for the NSVS 8294044 system and Transiting Exoplanet Survey Satellite (TESS) data for V1023 Her and V1397 Her. The primary and secondary times of minima were extracted from all the data, and by collecting the literature, a new ephemeris was computed for each system. Linear fits for the O-C diagrams were conducted using the Markov chain Monte Carlo (MCMC) method. Light curve solutions were performed using the PHysics Of Eclipsing BinariEs (PHOEBE) Python code and the MCMC approach. The systems were found to be contact binary stars based on the fillout factor and mass ratio. V1023 Her showed the O'Connell effect, and a cold starspot on the secondary component was required for the light curve solution. The absolute parameters of the system were estimated based on an empirical relationship between orbital period and mass. We presented a new T-M equation based on a sample of 428 contact binary systems and found that our three target systems were in good agreement with the fit. The positions of the systems were also depicted on the M-L, M-R, q-L_{ratio}, and M_{tot}-J_0 diagrams in the logarithmic scales.

astro-ph.SR↗

arXiv2024

Period-Luminosity Relationship for $δ$ Scuti Stars Revisited

The Gaia DR3 parallax approach was used to estimate the absolute parameters of 2375 Delta Scuti stars from the ASAS catalog. The selected stars have a variety of observational characteristics, with a higher than 80% probability of being Delta Scuti stars. We have displayed all the stars in the Hertzsprung-Russell (H-R) diagram along with the Delta Scuti instability strip, the Zero Age Main Sequence (ZAMS), and the Terminal-Age Main Sequence (TAMS). Then, we determined which fundamental and overtone modes each star belongs to using pulsation constant (Q) calculations. In addition, we evaluated the parameters in the Q calculation equation using three machine learning methods, which showed that surface gravity and temperature have the greatest effect on its calculation. The Period-Luminosity (P-L) relationship of the Delta Scuti stars was also revisited. Eventually, using least squares linear regression, we made four linear fits for fundamental and overtone modes and updated their relationships.

astro-ph.SR↗