Radial Velocity Evidence for a Post-mass-transfer Massive Binary System NaSt1
11 affiliations
- 1Suranaree University of Technology
- 2National Astronomical Research Institute of Thailand
- 3California Institute of Technology
- 4University of California
- 5Carnegie Institution for Science
- 6Columbia University
- 7Flatiron Institute
- 8Michigan State University
- 9University of California at Santa Cruz
- 10University of Arizona
- 11The Thacher School
Abstract
We present multiepoch high-resolution optical spectroscopy ( R ≃ 80,000) of the emission-line object NaSt1 to test its proposed binary nature, along with long-term multiband photometry, mid-infrared spectroscopy, and spatially resolved integral field unit (IFU) spectroscopy to probe the circumstellar kinematics of the system. We detect two groups of 36 emission lines showing radial velocity (RV) variation with a mean period of 311 ± 5 days, but varying in opposite phase. We associate these two groups with the optically thick wind of the stripped primary star and the wind–wind collision region with the companion star, providing strong evidence for binarity. The RV and light curve (LC) periods are consistent within the uncertainties, ruling out ellipsoidal modulation, which would require an orbital period of about 620 days. The RV–LC phase relationship and high-ionization lines favor binary interaction over pulsations. We model the 1–5 μ m spectrum of NaSt1 and find two optically thin dust components: hot: T h ≃ 1230 K and M h ≃ 2 × 10 ⁻¹⁰ M ⊙ , and warm: T c ≃ 660 K and M c ≃ 3 × 10 ⁻⁸ M ⊙ . IFU spectroscopy spatially resolves the circumstellar medium in the [N ii ] λ 6548 and λ 6584 emission lines, showing a deprojected expansion velocity of ∼31 km s ⁻¹ , implying a dynamical age of ∼40 yr. This short timescale suggests that the nebula was produced by recent mass loss. The system may represent a Galactic analog of a massive binary undergoing a mass-loss process to become a stripped-envelope supernova progenitor.
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BibTeX
@article{wangnok2026radial,
title = {{Radial Velocity Evidence for a Post-mass-transfer Massive Binary System NaSt1}},
author = {Kittipong Wangnok and Samaporn Tinyanont and Ryan M. Lau and Ryan J. Foley and R. Paul Butler and Poemwai Chainakun and Kyle W. Davis and Kishalay De and Jared A. Goldberg and Bradford Holden and Adriana Kuehnel and Nathan Smith and Jonathan J. Swift and Steven S. Vogt},
journal = {The Astrophysical Journal},
year = {2026},
month = oct,
doi = {10.3847/1538-4357/aea4a0},
url = {https://iopscience.iop.org/article/10.3847/1538-4357/aea4a0},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Radial Velocity Evidence for a Post-mass-transfer Massive Binary System NaSt1
AU - Kittipong Wangnok
AU - Samaporn Tinyanont
AU - Ryan M. Lau
AU - Ryan J. Foley
AU - R. Paul Butler
AU - Poemwai Chainakun
AU - Kyle W. Davis
AU - Kishalay De
AU - Jared A. Goldberg
AU - Bradford Holden
AU - Adriana Kuehnel
AU - Nathan Smith
AU - Jonathan J. Swift
AU - Steven S. Vogt
PY - 2026
DA - 2026/10/07
JO - The Astrophysical Journal
DO - 10.3847/1538-4357/aea4a0
UR - https://iopscience.iop.org/article/10.3847/1538-4357/aea4a0
AB - We present multiepoch high-resolution optical spectroscopy ( R ≃ 80,000) of the emission-line object NaSt1 to test its proposed binary nature, along with long-term multiband photometry, mid-infrared spectroscopy, and spatially resolved integral field unit (IFU) spectroscopy to probe the circumstellar kinematics of the system. We detect two groups of 36 emission lines showing radial velocity (RV) variation with a mean period of 311 ± 5 days, but varying in opposite phase. We associate these two groups with the optically thick wind of the stripped primary star and the wind–wind collision region with the companion star, providing strong evidence for binarity. The RV and light curve (LC) periods are consistent within the uncertainties, ruling out ellipsoidal modulation, which would require an orbital period of about 620 days. The RV–LC phase relationship and high-ionization lines favor binary interaction over pulsations. We model the 1–5 μ m spectrum of NaSt1 and find two optically thin dust components: hot: T h ≃ 1230 K and M h ≃ 2 × 10 ⁻¹⁰ M ⊙ , and warm: T c ≃ 660 K and M c ≃ 3 × 10 ⁻⁸ M ⊙ . IFU spectroscopy spatially resolves the circumstellar medium in the [N ii ] λ 6548 and λ 6584 emission lines, showing a deprojected expansion velocity of ∼31 km s ⁻¹ , implying a dynamical age of ∼40 yr. This short timescale suggests that the nebula was produced by recent mass loss. The system may represent a Galactic analog of a massive binary undergoing a mass-loss process to become a stripped-envelope supernova progenitor.
SN - 0004-637X
SN - 1538-4357
ER -