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Your search keyword '"Kee, N. D."' showing total 13 results
Start Over Author "Kee, N. D." Publisher edp sciences
13 results on '"Kee, N. D."'

1. X-Shooting ULLYSES: Massive stars at low metallicity. I. Project description

Author

Vink, Jorick S., primary, Mehner, A., additional, Crowther, P. A., additional, Fullerton, A., additional, Garcia, M., additional, Martins, F., additional, Morrell, N., additional, Oskinova, L. M., additional, St-Louis, N., additional, ud-Doula, A., additional, Sander, A. A. C., additional, Sana, H., additional, Bouret, J.-C., additional, Kubátová, B., additional, Marchant, P., additional, Martins, L. P., additional, Wofford, A., additional, van Loon, J. Th., additional, Grace Telford, O., additional, Götberg, Y., additional, Bowman, D. M., additional, Erba, C., additional, Kalari, V. M., additional, Abdul-Masih, M., additional, Alkousa, T., additional, Backs, F., additional, Barbosa, C. L., additional, Berlanas, S. R., additional, Bernini-Peron, M., additional, Bestenlehner, J. M., additional, Blomme, R., additional, Bodensteiner, J., additional, Brands, S. A., additional, Evans, C. J., additional, David-Uraz, A., additional, Driessen, F. A., additional, Dsilva, K., additional, Geen, S., additional, Gómez-González, V. M. A., additional, Grassitelli, L., additional, Hamann, W.-R., additional, Hawcroft, C., additional, Herrero, A., additional, Higgins, E. R., additional, John Hillier, D., additional, Ignace, R., additional, Istrate, A. G., additional, Kaper, L., additional, Kee, N. D., additional, Kehrig, C., additional, Keszthelyi, Z., additional, Klencki, J., additional, de Koter, A., additional, Kuiper, R., additional, Laplace, E., additional, Larkin, C. J. K., additional, Lefever, R. R., additional, Leitherer, C., additional, Lennon, D. J., additional, Mahy, L., additional, Maíz Apellániz, J., additional, Maravelias, G., additional, Marcolino, W., additional, McLeod, A. F., additional, de Mink, S. E., additional, Najarro, F., additional, Oey, M. S., additional, Parsons, T. N., additional, Pauli, D., additional, Pedersen, M. G., additional, Prinja, R. K., additional, Ramachandran, V., additional, Ramírez-Tannus, M. C., additional, Sabhahit, G. N., additional, Schootemeijer, A., additional, Reyero Serantes, S., additional, Shenar, T., additional, Stringfellow, G. S., additional, Sudnik, N., additional, Tramper, F., additional, and Wang, L., additional

Published
2023
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2. X-Shooting ULLYSES: Massive stars at low metallicity. III. Terminal wind speeds of ULLYSES massive stars

Author

Hawcroft, C., Sana, H., Mahy, L., Sundqvist, J. O., de Koter, A., Crowther, P. A., Bestenlehner, J. M., Brands, S. A., David-Uraz, A., Decin, L., Erba, C., Garcia, M., Hamann, W. -R., Herrero, A., Ignace, R., Kee, N. D., Kubátová, B., Lefever, R., Moffat, A., Najarro, F., Oskinova, L., Pauli, D., Prinja, R., Puls, J., Sander, A. A. C., Shenar, T., St-Louis, N., ud-Doula, A., and Vink, J. S.

Subjects
Astrophysics - Solar and Stellar Astrophysics, Space and Planetary Science, Astrophysics of Galaxies (astro-ph.GA), FOS: Physical sciences, Astronomy and Astrophysics, Astrophysics - Astrophysics of Galaxies, Solar and Stellar Astrophysics (astro-ph.SR)
Abstract

The winds of massive stars have an impact on stellar evolution and on the surrounding medium. The maximum speed reached by these outflows, the terminal wind speed, is a global wind parameter and an essential input for models of stellar atmospheres and feedback. With the arrival of the ULLYSES programme, a legacy UV spectroscopic survey with HST, we have the opportunity to quantify the wind speeds of massive stars at sub-solar metallicity (in the Large and Small Magellanic Clouds, 0.5Z and 0.2Z) at an unprecedented scale. We empirically quantify the wind speeds of a large sample of OB stars, including supergiants, giants, and dwarfs at sub-solar metallicity. Using these measurements, we investigate trends of terminal wind speed with a number of fundamental stellar parameters, namely effective temperature, metallicity, and surface escape velocity. We empirically determined the terminal wind speed for a sample of 149 OB stars in the Magellanic Clouds either by directly measuring the maximum velocity shift of the absorption component of the Civ 1548-1550 line profile, or by fitting synthetic spectra produced using the Sobolev with exact integration method. Stellar parameters were either collected from the literature, obtained using spectral-type calibrations, or predicted from evolutionary models. We find strong trends of terminal wind speed with effective temperature and surface escape speed when the wind is strong enough to cause a saturated P Cygni profile in Civ 1548-1550. We find evidence for a metallicity dependence on the terminal wind speed proportional to Z^0.22+-0.03 when we compared our results to previous Galactic studies. Our results suggest that effective temperature rather than surface escape speed should be used as a straightforward empirical prediction of terminal wind speed and that the observed metallicity dependence is steeper than suggested by earlier works., Comment: 21 pages, 16 figures, 8 tables. Accepted in A&A

Published
2023
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10. Spiral arms and instability within the AFGL 4176 mm1 disc

Author

Johnston, K. G., Hoare, M. G., Beuther, H., Kuiper, R., Kee, N. D., Linz, H., Boley, P., Maud, L. T., Ahmadi, A., Robitaille, T. P., Johnston, K. G., Hoare, M. G., Beuther, H., Kuiper, R., Kee, N. D., Linz, H., Boley, P., Maud, L. T., Ahmadi, A., and Robitaille, T. P.

Abstract

We present high-resolution (30 mas or 130 au at 4.2 kpc) Atacama Large Millimeter/submillimeter Array observations at 1.2 mm of the disc around the forming O-type star AFGL 4176 mm1. The disc (AFGL 4176 mm1-main) has a radius of ∼1000 au and contains significant structure, most notably a spiral arm on its redshifted side. We fitted the observed spiral with logarithmic and Archimedean spiral models. We find that both models can describe its structure, but the Archimedean spiral with a varying pitch angle fits its morphology marginally better. As well as signatures of rotation across the disc, we observe gas arcs in CH3CN that connect to other millimetre continuum sources in the field, supporting the picture of interactions within a small cluster around AFGL 4176 mm1-main. Using local thermodynamic equilibrium modelling of the CH3CN K-ladder, we determine the temperature and velocity field across the disc, and thus produce a map of the Toomre stability parameter. Our results indicate that the outer disc is gravitationally unstable and has already fragmented or is likely to fragment in the future, possibly producing further companions. These observations provide evidence that disc fragmentation is one possible pathway towards explaining the high fraction of multiple systems around high-mass stars. © ESO 2020.

Published
2020

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