Raul Michel Murillo | Searcharxiv

arXiv2026

Extremely Low Mass Ratio Contact Binaries. III. Photometric and Spectroscopic Investigations of Eleven Systems

We present photometric and spectroscopic investigations of 11 totally eclipsing contact binaries with mass ratios below 0.15, classifying them as extremely low mass ratio contact binaries. The ground-based multiband light curves were modeled with PHysics Of Eclipsing BinariEs to derive the photometric parameters of these systems. The TESS light curves of J011323 and J002747 show pronounced asymmetries and continuous variations. Markov Chain Monte Carlo modeling suggests that these variations are related to longitudinal migration of spots on the primary components. Spectral subtraction of the LAMOST spectra reveals excess chromospheric emission in six systems, while no detectable excess emission is found in the other five. The O$-$C analysis indicates secular period increases in six systems and secular decreases in five systems. We estimated their orbital angular momenta and performed a dynamical analysis. {Within our adopted semi-analytical framework without energy transfer, the formation of these observed systems requires additional angular momentum loss beyond saturated magnetic braking and gravitational radiation, but this requirement could be modified by different assumptions on mass transfer or radius evolution.

astro-ph.SR↗

arXiv2026

CCD () photometry of the open cluster NGC 6793 and its dynamical evolution

We present new astrophysical parameters for the open cluster NGC~6793 based on new CCD $UBV(RI)_{KC}$ photometry. We derived a reddening of $E(B-V) = 0.24 \pm 0.02$~mag and a heavy element abundance of $Z = 0.024$ ($[Fe/H] = +0.20$~dex). Padova isochrone fitting to the $V \times (B-V)$ colour-magnitude diagram yields an intermediate age of $525 \pm 51$~Myr and a distance modulus of $μ= 8.80 \pm 0.05$~mag, corresponding to a distance of $d = 575 \pm 58$~pc from the Sun. The core radius of NGC~6793 appears to be shrinking due to advanced dynamical evolution ($\logτ_{2} = 1.13$), driven by mass segregation and the evaporation of low-mass stars from the central region. The ratios of core to half-mass radius ($R_{c}/R_{h}$) and half-mass to Jacobi radius ($R_{h}/R_{J}$) indicate that the cluster's evolution is governed by the combined effects of internal two-body relaxation, mass segregation, and external tidal perturbations. The ratio $R_{t}/R_{J} = 0.99$ suggests that the cluster is currently in a tidally filling state. The parameter pairs ($t_{diss}/t_{rlx_{1}} = 40$, $\log R_{J}/R_{c} = 0.72$) and ($R_{h}/R_{J} = 0.38$, $\logρ_{amb} = -0.88$) place NGC~6793 among the relatively compact clusters within $R_{GC} < 7.9$~kpc. This implies a compact internal structure that is stable against the combined effects of two-body encounters and tidal heating. Given its current state, NGC~6793 will likely dissolve and disperse before entering the final contraction phase ($R_{4}$ regime).

astro-ph.GA↗