THA 15-31: Discovery with VLT/X-Shooter and Swift/UVOT of a new symbiotic star of the accreting-only variety

Abstract

We report the discovery and characterization of a new symbiotic star of the accreting-only variety, which we observed in the optical/near-infrared (NIR) with VLT/X-Shooter and in the X-rays/ultraviolet with Swift/UVOT+XRT. The new symbiotic star, THA 15-31, was previously described as a pre-main sequence star belonging to the Lupus~3 association. Our observations, ancillary data, and Gaia EDR3 parallax indicate that THA 15-31 is a symbiotic star composed of an M6III red giant and an accreting companion, is subject to E(B-V)=0.38 reddening, and is located at a distance of ~12 kpc and at 1.8 kpc above the Galactic plane in the outskirts of the Bulge. The luminosity of the accreting companion is ~100 Lsun, placing THA 15-31 among the symbiotic stars accreting at a high rate (2.5e-08 Msun/yr if the accretion is occurring on a white dwarf of 1 Msun). The observed emission lines originate primarily from HI, HeI, and FeII, with no HeII or other high-excitation lines observed; a sharp central absorption superimposed on the Balmer emission lines is observed, while all other lines have a simple Gaussian-like profile. The emission from the companion dominates over the M6III red giant at $U$ and $B$-band wavelengths, and is consistent with an origin primarily in an optically thick accretion disk. No significant photometric variability is observed at optical or NIR wavelengths, suggesting either a face-on orbital orientation and/or that the red giant is far from Roche-lobe filling conditions. The profile of emission lines supports a low orbital inclination if they form primarily in the accretion disk. An excess emission is present in AllWISE W3 (12 micron) and W4 (22 micron) data, radiating a luminosity ~35 Lsun, consistent with thermal emission from optically thin circumstellar dust.

12 pages, 7 figures: accepted for publication in Astronomy & Astrophysics

References in corpus (21)

• The Zwicky Transient Facility: System Overview, Performance, and First Results
• The Zwicky Transient Facility: Data Processing, Products, and Archive
• The All-Sky Automated Survey for Supernovae (ASAS-SN) Light Curve Server v1.0
• The GALAH Survey: Scientific Motivation
• Initial Performance of the NEOWISE Reactivation Mission
• The GALAH+ Survey: Third Data Release
• X-Shooter spectroscopy of young stellar objects in Lupus: Accretion properties of class II and transitional objects
• Three-dimensional mapping of the local interstellar medium with composite data
• A 3D extinction map of the Northern Galactic Plane based on IPHAS photometry
• A census of symbiotic stars in the 2MASS, WISE and Gaia surveys
• IGR J16194-2810: a new symbiotic X-ray binary
• Optical emission from massive donors in ULX binary systems
• A machine learning approach for identification and classification of symbiotic stars using 2MASS and WISE
• Reduction of the maximum mass-loss rate of OH/IR stars due to unnoticed binary interaction
• Substellar Objects in Nearby Young Clusters (SONYC) VIII: Substellar population in Lupus 3
• X-ray broad-band study of the symbiotic X-ray binary 4U 1954+31
• Increasing activity in T CrB suggests nova eruption is impending
• The GALAH Survey and Symbiotic Stars. I. Discovery and follow-up of 33 candidate accreting-only systems
• Detection of X-rays from the jet-driving Symbiotic Star MWC 560
• Very Long Baseline Interferometry imaging of the advancing ejecta in the first gamma-ray nova V407 Cyg
• Wind mass transfer in S-type symbiotic binaries III. Confirmation of a wind focusing in EG Andromedae from the nebular [OIII]λ5007 line

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