Absolute Parameters of the Southern Detached Eclipsing Binary DG Mic

TL;DR

This study delivers a precise dynamical and spectroscopic analysis of the near‑twin detached eclipsing binary DG Mic, combining new mid‑resolution spectroscopy with TESS, ASAS, and WASP photometry. Using a WD+Monte Carlo approach constrained by a spectroscopically determined $T_{\rm eff,1}$ and a fixed $q$ from radial velocities, the authors derive nearly identical masses ($M_1\approx M_2\approx1.65\,M_\odot$) and well‑constrained radii ($R_1\approx1.63\,R_\odot$, $R_2\approx1.91\,R_\odot$) for a detached configuration, with $P_{orb}=2.69592$ days. The SED fitting shows negligible reddening and a distance of $d\approx224$ pc, consistent with Gaia, while evolutionary analysis with Geneva models places the system at an age of about $713$ Myr with both components on the main sequence; a radius anomaly in the secondary hints at past mass transfer and near‑term evolutionary changes. Overall, DG Mic emerges as a robust benchmark detached A‑type binary for testing stellar evolution and binary interaction models, and highlights the value of combining spectroscopy, multi‑band photometry, and SED analyses in binary studies.

Abstract

As part of an ongoing programme of observing detached eclipsing binary stars in the southern sky, we present the first analysis of spectroscopic observations of the Algol-type binary system DG Mic. A spectroscopic analysis of mid-resolution spectra allowed us to constrain the effective temperature of the primary component and to test the consistency of the system parameters with its spectral energy distribution (SED). Combined solutions of mid-resolution spectra and TESS, ASAS and WASP light curves imply a system of two almost identical components ($q$ = 0.99) in circular orbits. Our final model shows that the system is a detached binary star. The masses and radii of the primary and secondary components of DG Mic were derived to be 1.65($\pm$0.12) M$_\odot$, 1.64($\pm$0.18) M$_\odot$ and 1.63($\pm$0.10) R$_\odot$, 1.91($\pm$0.13) R$_\odot$, respectively. According to Geneva evolution models, both components of the system are main-sequence stars and their age is approximately 713 Myr.

Figures (7)

• Figure 1: Sample spectrum of DG Mic for orbital phase 0.5. The hydrogen Balmer lines, Mg II (4481) line, and many metallic lines are visible in the spectrum.
• Figure 2: Radial velocities of DG Mic obtained using the cross-correlation method (open and filled circles) and the best theoretical fit (solid line).
• Figure 3: Observed spectrum of the primary component at orbital phase 0.5 (blue solid line) together with the best-fitting synthetic spectrum (red dashed line) generated from the Atlas9 models Castelli2003. The best-fit parameters are $T_{\rm eff} = 7300 \pm 150$ K, $v \sin i = 110 \pm 10$ km s$^{-1}$, and [m/H] $= 0.0 \pm 0.15$ dex. The comparison was performed in the wavelength range 4750--5200 Å, covering H$_\beta$ and strong metallic lines.
• Figure 4: Synthetic spectrum models for spectra taken at phase 0.25. Left: Model with relatively lower temperature components fits better to metallic lines. Right: Model with relatively higher temperatures fits better to $H\beta$ line.
• Figure 5: Upper panel: TESS, ASAS and WASP light curves of DG Mic and the best theoretical fits; Lower panel: Roche geometry of the DG Mic system.