Kinematics of the Central Stars Powering Bowshock Nebulae and the Large Multiplicity Fraction of Runaway OB Stars
| Autor: | Kobulnicky, Henry A., Chick, William T. |
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| Rok vydání: | 2022 |
| Předmět: | |
| Druh dokumentu: | Working Paper |
| DOI: | 10.3847/1538-3881/ac7f2b |
| Popis: | OB stars powering stellar bowshock nebulae (SBNe) have been presumed to have large peculiar velocities. We measured peculiar velocities of SBN central stars to assess their kinematics relative to the general O star population using $Gaia$ EDR3 data for 267 SBN central stars and a sample of 455 Galactic O stars to derive projected velocities $v_{\rm 2D}$. For a subset of each sample we obtained new optical spectroscopy to measure radial velocities and identify multiple-star systems. We find a minimum multiplicity fraction of 36$\pm$6% among SBN central stars, consistent with $>$28% among runaway Galactic O stars. The large multiplicity fraction among runaways implicates very efficient dynamical ejection rather than binary-supernova origins. The median $v_{\rm 2D}$ of SBN central stars is $v_{\rm 2D}$=14.6 km s$^{-1}$, larger than the median $v_{\rm 2D}$=11.4 km s$^{-1}$ for non-bowshock O stars. Central stars of SBNe have a runaway ($v_{\rm 2D}$$>$25 km s$^{-1}$) fraction of 24$^{+9}_{-7}$%, consistent with the 22$^{+3}_{-3}$% for control-sample O stars. Most (76%) of SBNe central stars are not runaways. Our analysis of alignment ($\Delta_{\rm PA}$) between the nebular morphological and $v_{\rm 2D}$ kinematic position angles reveals two populations: a highly aligned ($\sigma_{PA}$=25$^\circ$) population that includes stars with the largest $v_{\rm 2D}$ (31% of the sample) and a random (non-aligned) population (69% of the sample). SBNe that lie within or near HII regions comprise a larger fraction of this latter component than SBNe in isolated environments, implicating localized ISM flows as a factor shaping their orientations and morphologies. We outline a new conceptual approach to computing the Solar LSR motion, yielding [U$_\odot$, V$_\odot$, W$_\odot$]= [5.5, 7.5, 4.5] km s$^{-1}$. Comment: Accepted for publication in AAS journals |
| Databáze: | arXiv |
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