Examinando por Autor "Crowther, P. A."

Mostrando 1 - 4 de 4

Restringido
2D kinematics of massive stars near the Galactic Centre
(Oxford Academics: Oxford University Press, 2021-01-14) Libralato, M.; Lennon, D. J.; Bellini, A.; Van der Marel, R.; Clark, S. J.; Najarro, F.; Patrick, Lee R.; Anderson, J.; Bedin, L. R.; Crowther, P. A.; Mink, S. E.; Evans, C. J.; Platais, I.; Sabbi, E.; Sohn, S. T.; Agencia Estatal de Investigación (AEI); Agencia Canaria de Investigación, Innovación y Sociedad de la Información (ACIISI); Generalitat Valenciana; Ministero dell'Istruzione, dell'Università e della Ricerca (MIUR); Bedin, L. [0000-0003-4080-6466]; Patrick, L. [0000-0002-9015-0269]; Libralato, M. [0000-0001-9673-7397]
The presence of massive stars (MSs) in the region close to the Galactic Centre (GC) poses several questions about their origin. The harsh environment of the GC favours specific formation scenarios, each of which should imprint characteristic kinematic features on the MSs. We present a 2D kinematic analysis of MSs in a GC region surrounding Sgr A* based on high-precision proper motions obtained with the Hubble Space Telescope. Thanks to a careful data reduction, well-measured bright stars in our proper-motion catalogues have errors better than 0.5 mas yr−1. We discuss the absolute motion of the MSs in the field and their motion relative to Sgr A*, the Arches, and the Quintuplet. For the majority of the MSs, we rule out any distance further than 3–4 kpc from Sgr A* using only kinematic arguments. If their membership to the GC is confirmed, most of the isolated MSs are likely not associated with either the Arches or Quintuplet clusters or Sgr A*. Only a few MSs have proper motions, suggesting that they are likely members of the Arches cluster, in agreement with previous spectroscopic results. Line-of-sight radial velocities and distances are required to shed further light on the origin of most of these massive objects. We also present an analysis of other fast-moving objects in the GC region, finding no clear excess of high-velocity escaping stars. We make our astro-photometric catalogues publicly available.
Acceso Abierto
Mapping the core of the Tarantula Nebula with VLT-MUSE II. The spectroscopic Hertzsprung-Russell diagram of OB stars in NGC 2070
(EDP Sciences, 2021-04-13) Castro, N.; Crowther, P. A.; Evans, C. J.; Vink, J. S.; Puls, J.; Herrero, A.; García, M.; Selman, F. J.; Roth, M. M.; Simón Díaz, S.; Deutsche Forschungsgemeinschaft (DFG); Agencia Canaria de Investigación, Innovación y Sociedad de la Información (ACIISI); Agencia Estatal de Investigación (AEI); Castro, N. [0000-0003-0521-473X]; Vink, J. S. [0000-0002-8445-4397]
We present the spectroscopic analysis of 333 OB-type stars extracted from VLT-MUSE observations of the central 30 × 30 pc of NGC 2070 in the Tarantula Nebula on the Large Magellanic Cloud, the majority of which are analysed for the first time. The distribution of stars in the spectroscopic Hertzsprung-Russell diagram (sHRD) shows 281 stars in the main sequence. We find two groups in the main sequence, with estimated ages of 2.1 ± 0.8 and 6.2 ± 2 Myr. A subgroup of 52 stars is apparently beyond the main sequence phase, which we consider to be due to emission-type objects and/or significant nebular contamination affecting the analysis. As in previous studies, stellar masses derived from the sHRD are systematically larger than those obtained from the conventional HRD, with the differences being largest for the most massive stars. Additionally, we do not find any trend between the estimated projected rotational velocity and evolution in the sHRD. The projected rotational velocity distribution presents a tail of fast rotators that resembles findings in the wider population of 30 Doradus. We use published spectral types to calibrate the He Iλ4921/He IIλ5411 equivalent-width ratio as a classification diagnostic for early-type main sequence stars when the classical blue-visible region is not observed. Our model-atmosphere analyses demonstrate that the resulting calibration is well correlated with effective temperature.
Restringido
The R136 star cluster dissected with Hubble Space Telescope/STIS – II. Physical properties of the most massive stars in R136
(Oxford Academics: Oxford University Press, 2020-09-14) Bestenlehner, J. M.; Crowther, P. A.; Caballero Nieves, S. M.; Schneider, F. R. N.; Simón Díaz, S.; Brands, S. A.; De Koter, A.; Gräfener, G.; Herrero, A.; Langer, N.; Lennon, D. J.; Maíz Apellániz, J.; Puls, J.; Vink, Jorick S.; Agencia Canaria de Investigación, Innovación y Sociedad de la Información (ACIISI); Agencia Estatal de Investigación (AEI); Schneider, F. [0000-0002-5965-1022]; Bestenlehner, J. [0000-0002-0859-5139]; Caballero Nieves, S. [0000-0002-8348-5191]; Maíz Apellániz, J. [0000-0003-0825-3443]; Unidad de Excelencia Científica María de Maeztu Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737; Centros de Excelencia Severo Ochoa, INSTITUTO DE ASTROFÍSICA DE CANARIAS (IAC), SEV-2015-0548
We present an optical analysis of 55 members of R136, the central cluster in the Tarantula Nebula of the Large Magellanic Cloud. Our sample was observed with STIS aboard the Hubble Space Telescope, is complete down to about 40M(circle dot), and includes seven very massive stars with masses over 100M(circle dot). We performed a spectroscopic analysis to derive their physical properties. Using evolutionary models, we find that the initial mass function of massive stars in R136 is suggestive of being top-heavy with a power-law exponent gamma approximate to 2 +/- 0.3, but steeper exponents cannot be excluded. The age of R136 lies between 1 and 2Myr with a median age of around 1.6Myr. Stars more luminous than log L/L-circle dot = 6.3 are helium enriched and their evolution is dominated by mass-loss, but rotational mixing or some other form of mixing could be still required to explain the helium composition at the surface. Stars more massive than 40 M-circle dot have larger spectroscopic than evolutionary masses. The slope of the wind-luminosity relation assuming unclumped stellar winds is 2.41 +/- 0.13 which is steeper than usually obtained (similar to 1.8). The ionizing (log Q(0) [ph/s] = 51.4) and mechanical (logL(SW) [erg/s] = 39.1) output of R136 is dominated by the most massive stars (> 100M(circle dot)). R136 contributes around a quarter of the ionizing flux and around a fifth of the mechanical feedback to the overall budget of the Tarantula Nebula. For a census of massive stars of the Tarantula Nebula region, we combined our results with the VLT-FLAMES Tarantula Survey plus other spectroscopic studies. We observe a lack of evolved Wolf-Rayet stars and luminous blue and red supergiants.
Acceso Abierto
The VLT-FLAMES Tarantula Survey
(Astronomical Science, 2020-09-01) Evans, C. J.; Lennon, D.; Langer, N.; Almeida, L.; Bartlett, E.; Bastian, N.; Bestenlehner, J. M.; Britavskiy, N.; Castro, N.; Clark, S.; Crowther, P. A.; De Koter, A.; De Mink, S.; Dufton, P. L.; Fossati, L.; García, M.; Gieles, M.; Gräfener, G.; Grin, N.; Hénault Brunet, V.; Herrero, A.; Howarth, I.; Izzard, R.; Kalari, V.; Maíz Apellániz, J.; Markova, N.; Najarro, F.; Patrick, Lee R.; Puls, J.; Ramírez Agudelo, O.; Renzo, M.; Sabín Sanjulián, C.; Sana, H.; Schneider, F.; Schootemeijer, A.; Simón Díaz, S.; Smartt, S.; Taylor, W.; Tramper, F.; Van Loon, J.; Villaseñor, J.; Vink, J. S.; Walborn, N.
The VLT-FLAMES Tarantula Survey (VFTS) was an ESO Large Programme that has provided a rich, legacy dataset for studies of both resolved and integrated populations of massive stars. Initiated in 2008 (ESO Period 82), we used the Fibre Large Array Multi Element Spectrograph (FLAMES) to observe more than 800 massive stars in the dramatic 30 Doradus star-forming region in the Large Magellanic Cloud. At the start of the survey the importance of multiplicity among high-mass stars was becoming evident, so a key feature was multi-epoch spectroscopy to detect radial-velocity shifts arising from binary motion. Here we summarise some of the highlights from the survey and look ahead to the future of the field.