SEARCH · Search NASA
Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
WN6 crystallizes in the orthorhombic Cmmm space group. The structure is zero-dimensional and consists of four ammonia molecules and two WN4 clusters. In each WN4 cluster, W6+ is bonded in a square co-planar geometry to four equivalent N1- atoms. All W–N bond lengths are 2.19 Å. N1- is bonded in a 2-coordinate geometry to one W6+ and one N1- atom. The N–N bond length is 1.17 Å.
Results are presented of a study of 77 high-resolution IUE spectra of the WN6 star HD 192163, for which new IUE observations obtained over 48 hrs in 1987 were combined with data drawn from the IUE archive, covering various epochs over the 1978-1987 period. The 1987 series of 48 spectra were found to exhibit significant variability over a period of 24 hrs in the N IV 1718-A, C IV 1550-A, and He II 1640-A P Cygni profiles. The possible causes of these variabilities are considered in terms of binary-induced changes due to a compact companion and intrinsic stellar wind variations.
W43N38 crystallizes in the monoclinic Cm space group. The structure is two-dimensional and consists of one W43N38 sheet oriented in the (2, 0, -1) direction. there are forty-three inequivalent W sites. In the first W site, W is bonded to six N atoms to form edge-sharing WN6 octahedra. There are a spread of W–N bond distances ranging from 2.07–2.29 Å. In the second W site, W is bonded to six N atoms to form edge-sharing WN6 octahedra. There are a spread of W–N bond distances ranging from 2.15–2.22 Å. In the third W site, W is bonded in a 3-coordinate geometry to three N atoms. There are one shorter (2.05 Å) and two longer (2.18 Å) W–N bond lengths. In the fourth W site, W is bonded to six N atoms to form distorted edge-sharing WN6 octahedra. There are a spread of W–N bond distances ranging from 2.00–2.37 Å. In the fifth W site, W is bonded in a 3-coordinate geometry to three N atoms. There are two shorter (2.16 Å) and one longer (2.18 Å) W–N bond lengths. In the sixth W site, W is bonded to six N atoms to form distorted edge-sharing WN6 octahedra. There are a spread of W–N bond distances ranging from 1.98–2.38 Å. In the seventh W site, W is bonded in a 3-coordinate geometry to three N atoms. There are two shorter (2.12 Å) and one longer (2.16 Å) W–N bond lengths. In the eighth W site, W is bonded to six N atoms to form edge-sharing WN6 octahedra. There are a spread of W–N bond distances ranging from 2.03–2.31 Å. In the ninth W site, W is bonded in a 3-coordinate geometry to three N atoms. All W–N bond lengths are 2.14 Å. In the tenth W site, W is bonded in a 3-coordinate geometry to three N atoms. There are two shorter (2.13 Å) and one longer (2.15 Å) W–N bond lengths. In the eleventh W site, W is bonded to six N atoms to form edge-sharing WN6 octahedra. There are a spread of W–N bond distances ranging from 2.02–2.30 Å. In the twelfth W site, W is bonded to six N atoms to form edge-sharing WN6 octahedra. There are a spread of W–N bond distances ranging from 1.99–2.33 Å. In the thirteenth W site, W is bonded in a 3-coordinate geometry to three N atoms. All W–N bond lengths are 2.14 Å. In the fourteenth W site, W is bonded in a 3-coordinate geometry to three N atoms. All W–N bond lengths are 2.14 Å. In the fifteenth W site, W is bonded to six N atoms to form edge-sharing WN6 octahedra. There are a spread of W–N bond distances ranging from 2.00–2.32 Å. In the sixteenth W site, W is bonded to six N atoms to form edge-sharing WN6 octahedra. There are a spread of W–N bond distances ranging from 2.00–2.32 Å. In the seventeenth W site, W is bonded in a 3-coordinate geometry to three N atoms. All W–N bond lengths are 2.14 Å. In the eighteenth W site, W is bonded in a 3-coordinate geometry to three N atoms. All W–N bond lengths are 2.14 Å. In the nineteenth W site, W is bonded to six N atoms to form edge-sharing WN6 octahedra. There are a spread of W–N bond distances ranging from 2.00–2.32 Å. In the twentieth W site, W is bonded in a 3-coordinate geometry to three N atoms. All W–N bond lengths are 2.14 Å. In the twenty-first W site, W is bonded to six N atoms to form edge-sharing WN6 octahedra. There are a spread of W–N bond distances ranging from 2.00–2.32 Å. In the twenty-second W site, W is bonded in a 3-coordinate geometry to three N atoms. There are two shorter (2.13 Å) and one longer (2.14 Å) W–N bond lengths. In the twenty-third W site, W is bonded to six N atoms to form edge-sharing WN6 octahedra. There are a spread of W–N bond distances ranging from 2.02–2.31 Å. In the twenty-fourth W site, W is bonded to six N atoms to form edge-sharing WN6 octahedra. There are a spread of W–N bond distances ranging from 1.98–2.34 Å. In the twenty-fifth W site, W is bonded in a 3-coordinate geometry to three N atoms. There are two shorter (2.13 Å) and one longer (2.14 Å) W–N bond lengths. In the twenty-sixth W site, W is bonded in a 3-coordinate geometry to three N atoms. There are one shorter (2.09 Å) and two longer (2.15 Å) W–N bond lengths. In the twenty-seventh W site, W is bonded in a 3-coordinate geometry to three N atoms. There are two shorter (2.13 Å) and one longer (2.14 Å) W–N bond lengths. In the twenty-eighth W site, W is bonded in a 3-coordinate geometry to three N atoms. There are two shorter (2.17 Å) and one longer (2.18 Å) W–N bond lengths. In the twenty-ninth W site, W is bonded to six N atoms to form edge-sharing WN6 octahedra. There are a spread of W–N bond distances ranging from 2.13–2.23 Å. In the thirtieth W site, W is bonded to six N atoms to form edge-sharing WN6 octahedra. There are a spread of W–N bond distances ranging from 2.07–2.30 Å. In the thirty-first W site, W is bonded to six N atoms to form edge-sharing WN6 octahedra. There are a spread of W–N bond distances ranging from 2.15–2.22 Å. In the thirty-second W site, W is bonded in a 3-coordinate geometry to three N atoms. There are one shorter (2.09 Å) and two longer (2.18 Å) W–N bond lengths. In the thirty-third W site, W is bonded in a 3-coordinate geometry to three N atoms. There are two shorter (2.13 Å) and one longer (2.16 Å) W–N bond lengths. In the thirty-fourth W site, W is bonded to six N atoms to form edge-sharing WN6 octahedra. There are a spread of W–N bond distances ranging from 2.07–2.29 Å. In the thirty-fifth W site, W is bonded in a 3-coordinate geometry to three N atoms. There are two shorter (2.16 Å) and one longer (2.18 Å) W–N bond lengths. In the thirty-sixth W site, W is bonded in a 3-coordinate geometry to three N atoms. All W–N bond lengths are 2.16 Å. In the thirty-seventh W site, W is bonded in a 3-coordinate geometry to three N atoms. There are one shorter (2.16 Å) and two longer (2.17 Å) W–N bond lengths. In the thirty-eighth W site, W is bonded to six N atoms to form edge-sharing WN6 octahedra. There are a spread of W–N bond distances ranging from 2.16–2.21 Å. In the thirty-ninth W site, W is bonded in a 3-coordinate geometry to three N atoms. There are one shorter (2.10 Å) and two longer (2.14 Å) W–N bond lengths. In the fortieth W site, W is bonded in a 3-coordinate geometry to three N atoms. There are two shorter (2.15 Å) and one longer (2.17 Å) W–N bond lengths. In the forty-first W site, W is bonded to six N atoms to form edge-sharing WN6 octahedra. There are a spread of W–N bond distances ranging from 2.13–2.20 Å. In the forty-second W site, W is bonded in a 3-coordinate geometry to three N atoms. All W–N bond lengths are 2.17 Å. In the forty-third W site, W is bonded in a 3-coordinate geometry to three N atoms. There are two shorter (2.12 Å) and one longer (2.17 Å) W–N bond lengths. There are thirty-eight inequivalent N sites. In the first N site, N is bonded to six W atoms to form distorted NW6 pentagonal pyramids that share a cornercorner with one NW4 trigonal pyramid, edges with six NW6 pentagonal pyramids, and edges with two equivalent NW5 trigonal bipyramids. In the second N site, N is bonded to six W atoms to form distorted NW6 pentagonal pyramids that share corners with two equivalent NW5 trigonal bipyramids, edges with six NW6 pentagonal pyramids, an edgeedge with one NW5 trigonal bipyramid, and edges with two equivalent NW4 trigonal pyramids. In the third N site, N is bonded to five W atoms to form distorted NW5 trigonal bipyramids that share corners with three NW6 pentagonal pyramids, edges with three NW6 pentagonal pyramids, edges with two equivalent NW5 trigonal bipyramids, and edges with two equivalent NW4 trigonal pyramids. In the fourth N site, N is bonded to six W atoms to form distorted NW6 pentagonal pyramids that share corners with two equivalent NW4 trigonal pyramids, edges with six NW6 pentagonal pyramids, and an edgeedge with one NW4 trigonal pyramid. In the fifth N site, N is bonded to four W atoms to form NW4 trigonal pyramids that share corners with three NW6 pentagonal pyramids, corners with two equivalent NW4 trigonal pyramids, edges with three NW6 pentagonal pyramids, and edges with two equivalent NW5 trigonal bipyramids. In the sixth N site, N is bonded to six W atoms to form distorted edge-sharing NW6 pentagonal pyramids. In the seventh N site, N is bonded in a distorted T-shaped geometry to three W atoms. In the eighth N site, N is bonded to six W atoms to form distorted edge-sharing NW6 pentagonal pyramids. In the ninth N site, N is bonded in a distorted T-shaped geometry to three W atoms. In the tenth N site, N is bonded to six W atoms to form distorted edge-sharing NW6 pentagonal pyramids. In the eleventh N site, N is bonded in a distorted T-shaped geometry to three W atoms. In the twelfth N site, N is bonded to six W atoms to form distorted edge-sharing NW6 pentagonal pyramids. In the thirteenth N site, N is bonded in a distorted T-shaped geometry to three W atoms. In the fourteenth N site, N is bonded to six W atoms to form distorted edge-sharing NW6 pentagonal pyramids. In the fifteenth N site, N is bonded in a distorted T-shaped geometry to three W atoms. In the sixteenth N site, N is bonded to six W atoms to form distorted edge-sharing NW6 pentagonal pyramids. In the seventeenth N site, N is bonded in a distorted T-shaped geometry to three W atoms. In the eighteenth N site, N is bonded to six W atoms to form distorted edge-sharing NW6 pentagonal pyramids. In the nineteenth N site, N is bonded in a distorted T-shaped geometry to three W atoms. In the twentieth N site, N is bonded to six W atoms to form distorted edge-sharing NW6 pentagonal pyramids. In the twenty-first N site, N is bonded in a distorted T-shaped geometry to three W atoms. In the twenty-second N site, N is bonded to six W atoms to form distorted NW6 pentagonal pyramids that share a cornercorner with one NW5 trigonal bipyramid and edges with six NW6 pentagonal pyramids. In the twenty-third N site, N is bonded in a distorted T-shaped geometry to three W atoms. In the twenty-fourth N site, N is bonded to six W atoms to form distorted NW6 pentagonal pyramids that share edges with six NW6 pentagonal pyramids and edges with two equivalent NW5 trigonal bipyramids. In the twenty-fifth N site, N is bonded in a distorted T-shaped geometry to three W atoms. In the twenty-sixth N site, N is bonded to six W atoms to form distorted NW6 pentagonal pyramids that share corners with three NW5 trigonal bipyramids, edges with six NW6 pentagonal pyramids, and an edgeedge with one NW5 trigonal bipyramid. In the twenty-seventh N site, N is bonded to five W atoms to form distorted NW5 trigonal bipyramids that share corners with three NW6 pentagonal pyramids, edges with three NW6 pentagonal pyramids, and edges with two equivalent NW5 trigonal bipyramids. In the twenty-eighth N site, N is bonded to six W atoms to form distorted NW6 pentagonal pyramids that share edges with six NW6 pentagonal pyramids and edges with two equivalent NW5 trigonal bipyramids. In the twenty-ninth N site, N is bonded in a rectangular see-saw-like geometry to four W atoms. In the thirtieth N site, N is bonded to six W atoms to form distorted NW6 pentagonal pyramids that share corners with three NW5 trigonal bipyramids, edges with six NW6 pentagonal pyramids, and an edgeedge with one NW5 trigonal bipyramid. In the thirty-first N site, N is bonded to five W atoms to form distorted NW5 trigonal bipyramids that share corners with three NW6 pentagonal pyramids, edges with three NW6 pentagonal pyramids, and edges with two equivalent NW5 trigonal bipyramids. In the thirty-second N site, N is bonded to six W atoms to form distorted NW6 pentagonal pyramids that share a cornercorner with one NW6 pentagonal pyramid, edges with six NW6 pentagonal pyramids, and edges with two equivalent NW5 trigonal bipyramids. In the thirty-third N site, N is bonded in a rectangular see-saw-like geometry to four W atoms. In the thirty-fourth N site, N is bonded to six W atoms to form distorted NW6 pentagonal pyramids that share corners with two equivalent NW5 trigonal bipyramids, edges with eight NW6 pentagonal pyramids, and an edgeedge wit
W5Fe3N8 is Caswellsilverite-like structured and crystallizes in the hexagonal P-6m2 space group. The structure is three-dimensional. there are three inequivalent W3+ sites. In the first W3+ site, W3+ is bonded to six N3- atoms to form WN6 octahedra that share corners with six equivalent WN6 pentagonal pyramids, corners with six equivalent FeN6 pentagonal pyramids, edges with six equivalent WN6 octahedra, a faceface with one WN6 pentagonal pyramid, and a faceface with one FeN6 pentagonal pyramid. There are three shorter (2.13 Å) and three longer (2.27 Å) W–N bond lengths. In the second W3+ site, W3+ is bonded to six N3- atoms to form WN6 octahedra that share corners with twelve FeN6 pentagonal pyramids, edges with six equivalent WN6 octahedra, and faces with two FeN6 pentagonal pyramids. All W–N bond lengths are 2.14 Å. In the third W3+ site, W3+ is bonded to six equivalent N3- atoms to form a mixture of distorted edge, face, and corner-sharing WN6 pentagonal pyramids. The corner-sharing octahedral tilt angles are 44°. All W–N bond lengths are 2.15 Å. There are two inequivalent Fe3+ sites. In the first Fe3+ site, Fe3+ is bonded to six equivalent N3- atoms to form distorted FeN6 pentagonal pyramids that share corners with twelve equivalent WN6 octahedra, edges with six equivalent FeN6 pentagonal pyramids, and faces with two equivalent WN6 octahedra. The corner-sharing octahedral tilt angles are 45°. All Fe–N bond lengths are 2.20 Å. In the second Fe3+ site, Fe3+ is bonded to six N3- atoms to form distorted FeN6 pentagonal pyramids that share corners with twelve WN6 octahedra, edges with six equivalent FeN6 pentagonal pyramids, and faces with two WN6 octahedra. The corner-sharing octahedral tilt angles are 45°. There are three shorter (2.18 Å) and three longer (2.21 Å) Fe–N bond lengths. There are four inequivalent N3- sites. In the first N3- site, N3- is bonded to six W3+ atoms to form a mixture of distorted edge, face, and corner-sharing NW6 pentagonal pyramids. In the second N3- site, N3- is bonded to three equivalent W3+ and three equivalent Fe3+ atoms to form a mixture of distorted edge, face, and corner-sharing NFe3W3 pentagonal pyramids. In the third N3- site, N3- is bonded to three equivalent W3+ and three equivalent Fe3+ atoms to form distorted NFe3W3 pentagonal pyramids that share corners with nine NW6 pentagonal pyramids, edges with nine NW6 pentagonal pyramids, and a faceface with one NFe3W3 pentagonal pyramid. In the fourth N3- site, N3- is bonded to three equivalent W3+ and three equivalent Fe3+ atoms to form a mixture of distorted edge, face, and corner-sharing NFe3W3 pentagonal pyramids.
WN2 is Brookite-like structured and crystallizes in the triclinic P1 space group. The structure is three-dimensional. there are eight inequivalent W6+ sites. In the first W6+ site, W6+ is bonded to six N3- atoms to form a mixture of distorted edge and corner-sharing WN6 octahedra. The corner-sharing octahedra tilt angles range from 29–63°. There are a spread of W–N bond distances ranging from 1.84–2.36 Å. In the second W6+ site, W6+ is bonded to six N3- atoms to form a mixture of distorted edge and corner-sharing WN6 octahedra. The corner-sharing octahedra tilt angles range from 29–63°. There are a spread of W–N bond distances ranging from 1.84–2.37 Å. In the third W6+ site, W6+ is bonded to six N3- atoms to form a mixture of distorted edge and corner-sharing WN6 octahedra. The corner-sharing octahedra tilt angles range from 29–63°. There are a spread of W–N bond distances ranging from 1.84–2.37 Å. In the fourth W6+ site, W6+ is bonded to six N3- atoms to form a mixture of distorted edge and corner-sharing WN6 octahedra. The corner-sharing octahedra tilt angles range from 29–63°. There are a spread of W–N bond distances ranging from 1.84–2.37 Å. In the fifth W6+ site, W6+ is bonded to six N3- atoms to form a mixture of distorted edge and corner-sharing WN6 octahedra. The corner-sharing octahedra tilt angles range from 29–63°. There are a spread of W–N bond distances ranging from 1.84–2.37 Å. In the sixth W6+ site, W6+ is bonded to six N3- atoms to form a mixture of distorted edge and corner-sharing WN6 octahedra. The corner-sharing octahedra tilt angles range from 29–63°. There are a spread of W–N bond distances ranging from 1.84–2.37 Å. In the seventh W6+ site, W6+ is bonded to six N3- atoms to form a mixture of distorted edge and corner-sharing WN6 octahedra. The corner-sharing octahedra tilt angles range from 29–63°. There are a spread of W–N bond distances ranging from 1.84–2.35 Å. In the eighth W6+ site, W6+ is bonded to six N3- atoms to form a mixture of distorted edge and corner-sharing WN6 octahedra. The corner-sharing octahedra tilt angles range from 29–63°. There are a spread of W–N bond distances ranging from 1.84–2.36 Å. There are sixteen inequivalent N3- sites. In the first N3- site, N3- is bonded in a 3-coordinate geometry to three W6+ atoms. In the second N3- site, N3- is bonded in a 3-coordinate geometry to three W6+ atoms. In the third N3- site, N3- is bonded in a 3-coordinate geometry to three W6+ atoms. In the fourth N3- site, N3- is bonded in a 3-coordinate geometry to three W6+ atoms. In the fifth N3- site, N3- is bonded in a 3-coordinate geometry to three W6+ atoms. In the sixth N3- site, N3- is bonded in a 3-coordinate geometry to three W6+ atoms. In the seventh N3- site, N3- is bonded in a 3-coordinate geometry to three W6+ atoms. In the eighth N3- site, N3- is bonded in a 3-coordinate geometry to three W6+ atoms. In the ninth N3- site, N3- is bonded in a 3-coordinate geometry to three W6+ atoms. In the tenth N3- site, N3- is bonded in a 3-coordinate geometry to three W6+ atoms. In the eleventh N3- site, N3- is bonded in a 3-coordinate geometry to three W6+ atoms. In the twelfth N3- site, N3- is bonded in a 3-coordinate geometry to three W6+ atoms. In the thirteenth N3- site, N3- is bonded in a 3-coordinate geometry to three W6+ atoms. In the fourteenth N3- site, N3- is bonded in a 3-coordinate geometry to three W6+ atoms. In the fifteenth N3- site, N3- is bonded in a 3-coordinate geometry to three W6+ atoms. In the sixteenth N3- site, N3- is bonded in a 3-coordinate geometry to three W6+ atoms.
Fe3(WN2)4 crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. there are two inequivalent W4+ sites. In the first W4+ site, W4+ is bonded to six N3- atoms to form distorted WN6 pentagonal pyramids that share corners with eight FeN6 octahedra, edges with six WN6 pentagonal pyramids, and faces with two FeN6 octahedra. The corner-sharing octahedra tilt angles range from 43–47°. There are a spread of W–N bond distances ranging from 2.06–2.12 Å. In the second W4+ site, W4+ is bonded to six N3- atoms to form distorted WN6 pentagonal pyramids that share corners with ten FeN6 octahedra, edges with six WN6 pentagonal pyramids, and a faceface with one FeN6 octahedra. The corner-sharing octahedra tilt angles range from 45–47°. There are a spread of W–N bond distances ranging from 2.06–2.18 Å. There are two inequivalent Fe+2.67+ sites. In the first Fe+2.67+ site, Fe+2.67+ is bonded to six N3- atoms to form FeN6 octahedra that share corners with twelve WN6 pentagonal pyramids, edges with two equivalent FeN6 octahedra, and faces with two equivalent WN6 pentagonal pyramids. There are two shorter (1.96 Å) and four longer (2.08 Å) Fe–N bond lengths. In the second Fe+2.67+ site, Fe+2.67+ is bonded to six N3- atoms to form FeN6 octahedra that share corners with twelve WN6 pentagonal pyramids, edges with six equivalent FeN6 octahedra, and faces with two WN6 pentagonal pyramids. There are a spread of Fe–N bond distances ranging from 2.07–2.37 Å. There are four inequivalent N3- sites. In the first N3- site, N3- is bonded in a 6-coordinate geometry to three W4+ and three equivalent Fe+2.67+ atoms. In the second N3- site, N3- is bonded in a 6-coordinate geometry to three W4+ and three equivalent Fe+2.67+ atoms. In the third N3- site, N3- is bonded in a rectangular see-saw-like geometry to three W4+ and one Fe+2.67+ atom. In the fourth N3- site, N3- is bonded in a 5-coordinate geometry to three W4+ and two equivalent Fe+2.67+ atoms.
CrWN2 is Caswellsilverite-like structured and crystallizes in the trigonal R3m space group. The structure is three-dimensional. W3+ is bonded to six N3- atoms to form distorted WN6 pentagonal pyramids that share corners with nine equivalent CrN6 octahedra, edges with three equivalent CrN6 octahedra, edges with six equivalent WN6 pentagonal pyramids, and a faceface with one CrN6 octahedra. The corner-sharing octahedra tilt angles range from 1–46°. There are three shorter (2.13 Å) and three longer (2.14 Å) W–N bond lengths. Cr3+ is bonded to six N3- atoms to form CrN6 octahedra that share corners with nine equivalent WN6 pentagonal pyramids, edges with six equivalent CrN6 octahedra, edges with three equivalent WN6 pentagonal pyramids, and a faceface with one WN6 pentagonal pyramid. All Cr–N bond lengths are 2.11 Å. There are two inequivalent N3- sites. In the first N3- site, N3- is bonded to three equivalent W3+ and three equivalent Cr3+ atoms to form edge-sharing NCr3W3 octahedra. In the second N3- site, N3- is bonded in a 6-coordinate geometry to three equivalent W3+ and three equivalent Cr3+ atoms.
LiWN2 is Caswellsilverite-like structured and crystallizes in the trigonal R3m space group. The structure is three-dimensional. Li1+ is bonded to six N3- atoms to form distorted LiN6 pentagonal pyramids that share corners with nine equivalent WN6 octahedra, edges with three equivalent WN6 octahedra, edges with six equivalent LiN6 pentagonal pyramids, and a faceface with one WN6 octahedra. The corner-sharing octahedra tilt angles range from 3–46°. There are three shorter (2.19 Å) and three longer (2.36 Å) Li–N bond lengths. W5+ is bonded to six N3- atoms to form WN6 octahedra that share corners with nine equivalent LiN6 pentagonal pyramids, edges with six equivalent WN6 octahedra, edges with three equivalent LiN6 pentagonal pyramids, and a faceface with one LiN6 pentagonal pyramid. There are three shorter (2.09 Å) and three longer (2.10 Å) W–N bond lengths. There are two inequivalent N3- sites. In the first N3- site, N3- is bonded to three equivalent Li1+ and three equivalent W5+ atoms to form a mixture of distorted face, edge, and corner-sharing NLi3W3 pentagonal pyramids. The corner-sharing octahedra tilt angles range from 0–45°. In the second N3- site, N3- is bonded to three equivalent Li1+ and three equivalent W5+ atoms to form a mixture of face, edge, and corner-sharing NLi3W3 octahedra.
MnWN2 crystallizes in the hexagonal P6_3mc space group. The structure is three-dimensional. W4+ is bonded to six N3- atoms to form WN6 octahedra that share corners with six equivalent MnN4 tetrahedra, edges with six equivalent WN6 octahedra, and edges with three equivalent MnN4 tetrahedra. There are three shorter (2.10 Å) and three longer (2.34 Å) W–N bond lengths. Mn2+ is bonded to four N3- atoms to form MnN4 tetrahedra that share corners with six equivalent WN6 octahedra, corners with six equivalent MnN4 tetrahedra, and edges with three equivalent WN6 octahedra. The corner-sharing octahedra tilt angles range from 27–57°. There is three shorter (1.81 Å) and one longer (2.01 Å) Mn–N bond length. There are two inequivalent N3- sites. In the first N3- site, N3- is bonded in a distorted trigonal non-coplanar geometry to three equivalent W4+ and three equivalent Mn2+ atoms. In the second N3- site, N3- is bonded in a distorted rectangular see-saw-like geometry to three equivalent W4+ and one Mn2+ atom.
FeWN2 is Caswellsilverite-like structured and crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. W3+ is bonded to six equivalent N3- atoms to form distorted WN6 pentagonal pyramids that share corners with twelve equivalent FeN6 octahedra, edges with six equivalent WN6 pentagonal pyramids, and faces with two equivalent FeN6 octahedra. The corner-sharing octahedral tilt angles are 45°. All W–N bond lengths are 2.12 Å. Fe3+ is bonded to six equivalent N3- atoms to form FeN6 octahedra that share corners with twelve equivalent WN6 pentagonal pyramids, edges with six equivalent FeN6 octahedra, and faces with two equivalent WN6 pentagonal pyramids. All Fe–N bond lengths are 2.21 Å. N3- is bonded to three equivalent W3+ and three equivalent Fe3+ atoms to form a mixture of distorted edge, face, and corner-sharing NFe3W3 pentagonal pyramids.
W2N3 is Corundum-like structured and crystallizes in the monoclinic Cm space group. The structure is three-dimensional. there are three inequivalent W+4.50+ sites. In the first W+4.50+ site, W+4.50+ is bonded to six N3- atoms to form a mixture of distorted edge and corner-sharing WN6 pentagonal pyramids. The corner-sharing octahedra tilt angles range from 4–45°. There are a spread of W–N bond distances ranging from 2.10–2.13 Å. In the second W+4.50+ site, W+4.50+ is bonded to six N3- atoms to form a mixture of distorted edge, face, and corner-sharing WN6 pentagonal pyramids. The corner-sharing octahedral tilt angles are 0°. There are a spread of W–N bond distances ranging from 2.07–2.10 Å. In the third W+4.50+ site, W+4.50+ is bonded to six N3- atoms to form a mixture of edge, face, and corner-sharing WN6 octahedra. There are a spread of W–N bond distances ranging from 1.99–2.13 Å. There are four inequivalent N3- sites. In the first N3- site, N3- is bonded in a rectangular see-saw-like geometry to four W+4.50+ atoms. In the second N3- site, N3- is bonded in a rectangular see-saw-like geometry to four W+4.50+ atoms. In the third N3- site, N3- is bonded in a rectangular see-saw-like geometry to four W+4.50+ atoms. In the fourth N3- site, N3- is bonded in a rectangular see-saw-like geometry to four W+4.50+ atoms.
In this paper we report the remarkable changes which occured in the Small Magellanic Cloud W-R system HD5980 = AB5 between 1978 and 1991. Within this timescale, there has been a systematic enhancement (by factors of 2-10 depending on the line) in the equivalent widths of all emission lines, and a change in the relative strengths of N III, N IV, and N V lines. Currently, the W-R spectrum is more typical of a WN6 star than a WN3 or WN4, as it was originally classified. The terminal speed of the wind has diminished by approximately 600 km/s, while the system has brightened in the visual by 0.45 mag. The UV (1850 A) continuum changed by less than 0.13 mag. The change from WN3 or WN4 to WN6 is unprecedented. The system appears to be composed at least three stars: two WNs in mutual 19.266 day orbit and an O-type supergiant. We propose that the changes observed in HD 5980 are related to an increase in wind density of one (or both?) of the W-R components, where the brighter WN6 component will dominate the W-R spectrum after the change, and we speculate that this modification of the wind structure is driven by tidal interaction induced by a possible current periastron passage of the third component in the system.
The short-period (1.64 d) near-contact eclipsing WN6+O9 binary system CQ Cep provides an ideal laboratory for testing the predictions of X-ray colliding wind shock theory at close separation where the winds may not have reached terminal speeds before colliding. We present results of a Chandra X-ray observation of CQ Cep spanning ∼1 day during which a simultaneous Chandra optical light curve was acquired. Our primary objective was to compare the observed X-ray properties with colliding wind shock theory, which predicts that the hottest shock plasma (T ≳ 20 MK) will form on or near the line-of-centers between the stars. The X-ray spectrum is strikingly similar to apparently single WN6 stars such as WR 134 and spectral lines reveal plasma over a broad range of temperatures T ∼ 4-40 MK. A deep optical eclipse was seen as the O star passed in front of the Wolf-Rayet star and we determine an orbital period P {sub orb} = 1.6412400 d. Somewhat surprisingly, no significant X-ray variability was detected. This implies that the hottest X-ray plasma is not confined to the region between the stars, at odds with the colliding wind picture and suggesting that other X-ray production mechanisms may be at work. Hydrodynamic simulations that account for such effects as radiative cooling and orbital motion will be needed to determine if the new Chandra results can be reconciled with the colliding wind picture.
Available spectrometric and photometric observations of Wolf-Rayet stars by the OAO 2 spacecraft in the UV range are discussed along with radio astronomical observations of W stars with symmetrical nebulae around them. The scanned spectrum of the WN5 star HD 50896 between 1200 and 1900 A is illustrated together with the photometered spectrum of the WN6 star HD 192163 from 1330 to 3320 A. RF observations of NGC 6888 around HD 192163 are examined relative to interpretation of the properties of a WN6 star ejecting mass into a nebular shell.
Previous studies have demonstrated that putatively single nitrogen-type Wolf-Rayet stars (WN stars) without known companions are X-ray sources. However, almost all WN star X-ray detections so far have been of earlier WN2-WN6 spectral subtypes. Later WN7-WN9 subtypes (also known as WNL stars) have proved more difficult to detect, an important exception being WR 79a (WN9ha). We present here new X-ray detections of the WNL stars WR 16 (WN8h) and WR 78 (WN7h). These new results, when combined with previous detections, demonstrate that X-ray emission is present in WN stars across the full range of spectral types, including later WNL stars. The two WN8 stars observed to date (WR 16 and WR 40) show unusually low X-ray luminosities (L{sub x} ) compared to other WN stars, and it is noteworthy that they also have the lowest terminal wind speeds (v{sub {infinity}}). Existing X-ray detections of about a dozen WN stars reveal a trend of increasing L{sub x} with wind luminosity L{sub wind} = (1/2)M-dot v{sup 2}{sub {infinity}}, suggesting that wind kinetic energy may play a key role in establishing X-ray luminosity levels in WN stars.
We report the serendipitous discovery of a heavily reddened Wolf-Rayet star that we name WR 142b. While photometrically monitoring a cataclysmic variable, we detected weak variability in a nearby field star. Low-resolution spectroscopy revealed a strong emission line at 7100 A, suggesting an unusual object and prompting further study. A spectrum taken with the Hobby-Eberly Telescope confirms strong He II emission and an N IV 7112 A line consistent with a nitrogen-rich Wolf-Rayet star of spectral class WN6. Analysis of the He II line strengths reveals no detectable hydrogen in WR 142b. A blue-sensitive spectrum obtained with the Large Binocular Telescope shows no evidence for a hot companion star. The continuum shape and emission line ratios imply a reddening of E(B - V) = 2.2-2.6 mag. We estimate that the distance to WR 142b is 1.4 {+-} 0.3 kpc.
We present new results on the chemical composition of the Galactic ring nebula NGC 6888 surrounding the WN6(h) star WR136. The data are based on deep spectroscopical observations taken with the High Dispersion Spectrograph at the 8.2 m Subaru Telescope. The spectra cover the optical range from 3700 to 7400 Å. The effect of the CNO cycle is well-identified in the abundances of He, N, and O, while elements not involved in the synthesis such as Ar, S, and Fe present values consistent with the solar vicinity and the ambient gas. The major achievement of this work is the first detection of the faint C II λ4267 recombination line in a Wolf-Rayet nebula. This allows us to estimate the C abundance in NGC 6888 and therefore investigate for the first time the trace of the CNO cycle in a ring nebula around a Wolf-Rayet star. Although the detection of the C II line has a low signal-to-noise ratio, the C abundance seems to be higher than the predictions of recent stellar evolution models of massive stars. The Ne abundance also shows a puzzling pattern with an abundance of about 0.5 dex lower than the solar vicinity, which may be related to the action of the NeNa cycle. Attending to the constraints imposed by the dynamical timescale and the He/H and N/O ratios of the nebula, the comparison with stellar evolution models indicates that the initial mass of the stellar progenitor of NGC 6888 is between 25 M {sub ☉} and 40 M {sub ☉}.
In order to assess the long-term star formation history, we performed an infrared spectroscopic search for massive stars, detecting for the first time 14 early-type stars, including one WN6 star and four O4–7 stars.