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Discovery of a runaway star likely ejected by a Type Iax Supernova

A. Bhat, M. Hollands, M. Dorsch, S. Geier, U. Heber, D. Koester, R. Pakmor, Ken J. Shen

Abstract

Over the past decade, runaway stars have been identified, believed to originate either as surviving donors of Type Ia supernovae or as partially deflagrated accretors producing Type Iax supernovae. While the former have been extensively studied recently, the origins of the latter (also called LP 40-365 type stars) remain under-explored and therefore less well understood. So far seven such objects are known. In this paper, we report the discovery of a new LP 40-365 type runaway star, notably hotter than previously studied members of this class. Spectral analysis confirms that its atmosphere is neon- and oxygen-dominated, consistent with earlier analyses of other LP 40-365 type stars. Kinematic analysis indicates that the star has a high probability of being unbound from the Galaxy and was most likely ejected from the Galactic disk approximately 2.8 Myr ago with an ejection velocity exceeding 600 km/s. This result further emphasizes the discrepancy between the abundance yields and kick velocities predicted by white dwarf deflagration models and those observed in stars of LP 40-365 type, underscoring the need for a reassessment of such systems.

Discovery of a runaway star likely ejected by a Type Iax Supernova

Abstract

Over the past decade, runaway stars have been identified, believed to originate either as surviving donors of Type Ia supernovae or as partially deflagrated accretors producing Type Iax supernovae. While the former have been extensively studied recently, the origins of the latter (also called LP 40-365 type stars) remain under-explored and therefore less well understood. So far seven such objects are known. In this paper, we report the discovery of a new LP 40-365 type runaway star, notably hotter than previously studied members of this class. Spectral analysis confirms that its atmosphere is neon- and oxygen-dominated, consistent with earlier analyses of other LP 40-365 type stars. Kinematic analysis indicates that the star has a high probability of being unbound from the Galaxy and was most likely ejected from the Galactic disk approximately 2.8 Myr ago with an ejection velocity exceeding 600 km/s. This result further emphasizes the discrepancy between the abundance yields and kick velocities predicted by white dwarf deflagration models and those observed in stars of LP 40-365 type, underscoring the need for a reassessment of such systems.
Paper Structure (13 sections, 5 equations, 13 figures, 6 tables)

This paper contains 13 sections, 5 equations, 13 figures, 6 tables.

Table of Contents

  1. Introduction
  2. Target Selection and data acquisition
  3. Spectroscopy
  4. Photometry
  5. Kinematic analysis
  6. The lower limit of distance
  7. Distance sampling with flat magnitude prior
  8. Kinematic age
  9. Evolutionary status and the problem with Type Iax survivors
  10. Discussion
  11. Distance prior
  12. Priors on mass and their influence on kinematics
  13. Standard O/Ne-core models

Figures (13)

  • Figure 1: A comparison between the normalized observed spectrum of J1022-3414 and two known LP 40$-$365 type stars from raddi2019 retrieved from the ESO archive. The two known LP 40$-$365 type stars have been smoothed to the same resolution as J1022-3414 and wavelengths are at rest. Lines of magnesium, neon, and oxygen are marked. J1022-3414 shows broader lines than the other two.
  • Figure 2: The best-fit spectrum in the rest-frame (red) overlaid on top of the co-added FORS2 spectrum (grey). Prominent lines of oxygen (blue), neon (orange), and magnesium (green) are marked.
  • Figure 3: Comparison of the best-fit model (red) and the models that have $T_\mathrm{eff}$ of $21300$ K and $18900$ K (in purple and cyan respectively), for a strong magnesium absorption line.
  • Figure 4: The SED of J1022-3414 . Photometry was queried from DELVE DR2 2022ApJS..261...38D, SPLUS DR4 2024AA...689A.249H, Gaia DR3 Gaia3, SkyMapper skymapper, and GALEX 2005ApJ...619L...1M. The model spectrum (in gray) is smoothed for visual clarity. The flux is multiplied with $\lambda^2$ to reduce the flux steepness.
  • Figure 5: Posterior distributions of the distance, absolute magnitude, mass, radius, ejection velocity, and midplane-crossing time. Vertical dashed lines represent $16-84\%$ confidence intervals.
  • ...and 8 more figures