On the apparent absence of WR+NS systems: the curious case of WR124. (arXiv:1811.10691v1 [astro-ph.HE])

On the apparent absence of WR+NS systems: the curious case of WR124. (arXiv:1811.10691v1 [astro-ph.HE])
<a href="http://arxiv.org/find/astro-ph/1/au:+Toala_J/0/1/0/all/0/1">J.A. Toala</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Oskinova_L/0/1/0/all/0/1">L.M. Oskinova</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Hamann_W/0/1/0/all/0/1">W.-R. Hamann</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ignace_R/0/1/0/all/0/1">R. Ignace</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Sander_A/0/1/0/all/0/1">A.A.C. Sander</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Shenar_T/0/1/0/all/0/1">T. Shenar</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Todt_H/0/1/0/all/0/1">H. Todt</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Chu_Y/0/1/0/all/0/1">Y.-H. Chu</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Guerrero_M/0/1/0/all/0/1">M.A. Guerrero</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Hainich_R/0/1/0/all/0/1">R. Hainich</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Torrejon_J/0/1/0/all/0/1">J.M. Torrejon</a>

Among different types of massive stars in advanced evolutionary stages is the
enigmatic WN8h type. There are only a few Wolf-Rayet (WR) stars with this
spectral type in our Galaxy. It has long been suggested that WN8h-type stars
are the products of binary evolution that may harbor neutron stars (NS). One of
the most intriguing WN8h stars is the runaway WR124 surrounded by its
magnificent nebula M1-67. We test the presence of an accreting NS companion in
WR124 using 100 ks long observations by the Chandra X-ray observatory. The hard
X-ray emission from WR124 with a luminosity of $L_mathrm{X}$= 10$^{31}$ erg
s$^{-1}$ is marginally detected. We use the non-LTE stellar atmosphere code
PoWR to estimate the WR wind opacity to the X-rays. The wind of a WN8-type star
is effectively opaque for X-rays, hence the low X-ray luminosity of WR124 does
not rule out the presence of an embedded compact object. We suggest that, in
general, high opacity WR winds could prevent X-ray detections of embedded NS,
and be an explanation for the apparent lack of WR+NS systems.

Among different types of massive stars in advanced evolutionary stages is the
enigmatic WN8h type. There are only a few Wolf-Rayet (WR) stars with this
spectral type in our Galaxy. It has long been suggested that WN8h-type stars
are the products of binary evolution that may harbor neutron stars (NS). One of
the most intriguing WN8h stars is the runaway WR124 surrounded by its
magnificent nebula M1-67. We test the presence of an accreting NS companion in
WR124 using 100 ks long observations by the Chandra X-ray observatory. The hard
X-ray emission from WR124 with a luminosity of $L_mathrm{X}$= 10$^{31}$ erg
s$^{-1}$ is marginally detected. We use the non-LTE stellar atmosphere code
PoWR to estimate the WR wind opacity to the X-rays. The wind of a WN8-type star
is effectively opaque for X-rays, hence the low X-ray luminosity of WR124 does
not rule out the presence of an embedded compact object. We suggest that, in
general, high opacity WR winds could prevent X-ray detections of embedded NS,
and be an explanation for the apparent lack of WR+NS systems.

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