2025MNRAS.539.3830K

2025MNRAS.539.3830K - Mon. Not. R. Astron. Soc., 539, 3830-3841 (2025/June-1)

The new compact triple system: discovery of bright third star around contact binary using LAMOST-MRS spectra and photometry.

We present a study of the third star orbiting around known contact eclipsing binary J04+25 using spectra from the LAMOST medium-resolution survey (MRS) and publicly available photometry. This is a rare case of a hierarchical triple, where the third star is significantly brighter than the inner contact subsystem. We successfully extracted radial velocities for all three components, using the binary spectral model in two steps. Third star radial velocities have high precision and allow direct fitting of the orbit. The low precision of radial velocity measurements in the contact system is compensated by large number statistics. We employed a template matching technique for light curves to find periodic variation due to the light time travel effect (LTTE) using several photometric data sets. Joint fit of third star radial velocities and LTTE allowed us to get a consistent orbital solution with $P_3=941.40\pm 0.03$ d and $e_3=0.059\pm 0.007$ . We made estimations of the masses $M_{\rm 12,~3}\sin ^3{i_3}=1.05\pm 0.02,~0.90\pm 0.02~\mathrm{M}_\odot$ in a wide system and discussed possible determination of an astrometric orbit in the future data release of Gaia. Additionally, we propose an empirical method for measuring a period and minimal mass of contact systems, based on variation of the projected rotational velocity ( $V \sin {i}$ ) from the spectra.

Journal keyword(s): binaries: eclipsing - binaries: spectroscopic - stars: fundamental parameters - stars individual: T-Tau0-03027

Status at CDS : Large table(s) will be appraised for possible ingestion in VizieR.

N	Identifier	Otype	ICRS (J2000) RA	ICRS (J2000) DEC	Mag U	Mag B	Mag V	Mag R	Mag I	Sp type	#ref 1850 - 2026	#notes
1	[DCO2008] T-Tau0-03027	EB*	04 29 01.0926384024	+25 41 44.257319124		14.815		12.860		~	9	0

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`UCAC2 40811218`	`2MASS J04290108+2541443`	`[DCO2008] T-Tau0-03027`
`AP J04290108+2541443`	`TIC 268143030`	`Gaia DR2 151001777293928576`
`ATO J067.2545+25.6956`	`ZTF J042901.09+254144.1`	`Gaia DR3 151001777293928576`