Sapaki: Galactic O3If* star possibly born in isolation

Abstract

Context: The study of high-mass stars found to be isolated in the field of the Milky Way may help to probe the feasibility of the core-accretion mechanism in the case of massive star formation. The existence of truly isolated stars may efficiently probe the possibility that individual massive stars can be born in isolation. Aims: We observed WR67a (hereafter Sapaki), an O3If* star that appears to be isolated close to the center of a well-developed giant cavity that is aptly traced by 8.0 $\mu$m hot dust emission. Methods: We acquired medium-resolution ($R=4100$) and moderate signal-to-noise ($S/N=95$ at 4500 Å) spectra for Sapaki in the range of 3800-10500 Å with the Magellan Echellette (MagE) at Las Campanas Observatory. We computed the line-of-sight total extinctions. Additionally, we restricted its heliocentric distance by using a range of different estimators. Moreover, we measured its radial velocity from several lines in its spectrum. Finally, we analyzed its proper motions from Gaia to examine its possible runaway status. Results: The star has been classified as having the spectral type O3If* given its resemblance to standard examples of the class. In addition, we found that Sapaki is highly obscured, reaching a line-of-sight extinction value of $A_V=7.87$. We estimated the heliocentric distance to be in the range of $d=4-7$ kpc. We also estimated its radial velocity to be $V_r=-34.2\pm 15.6$ km/s. We may also discard its runaway status solely based on its 2D kinematics. Furthermore, by analyzing proper motions and parallaxes provided by Gaia, we found only one other star with compatible measurements. Conclusions: Given its apparent non-runaway status and the absence of clustering, Sapaki appears to be a solid candidate for isolated high-mass star formation in the Milky Way.

7 pages, 3 figures, 2 tables

References in corpus (18)

• Gaia Data Release 3: Summary of the content and survey properties
• Theory of Star Formation
• Estimating distances from parallaxes. V: Geometric and photogeometric distances to 1.47 billion stars in Gaia Early Data Release 3
• Gaia Early Data Release 3: The astrometric solution
• Gaia Early Data Release 3: Parallax bias versus magnitude, colour, and position
• UBVJHK synthetic photometry of Galactic O stars
• Photo-astrometric distances, extinctions, and astrophysical parameters for Gaia EDR3 stars brighter than G=18.5
• Stellar clusterings around "Isolated" Massive YSOs in the LMC
• Runaway OB Stars in the Small Magellanic Cloud: Dynamical Versus Supernova Ejections
• A close encounter of the massive kind
• The VLT-FLAMES Tarantula Survey: Observational evidence for two distinct populations of massive runaway stars in 30 Doradus
• TESS Input Catalog versions 8.1 and 8.2: Phantoms in the 8.0 Catalog and How to Handle Them
• The Discovery of a Very Massive Star in W49
• Two O2 If*/WN6 stars possibly ejected from the massive young Galactic cluster Westerlund 2
• Escape from the Bermuda cluster: orphanization by multiple stellar ejections
• A Search for In-Situ Field OB Star Formation in the Small Magellanic Cloud
• On the origin of very massive stars around NGC 3603
• Discovery of two Galactic Wolf-Rayet stars in Circinus

Cited by in corpus (1)

• Isolated massive star candidates in NGC 4242 with GULP