Examinando por Autor "Lennon, Daniel J."

Mostrando 1 - 9 de 9

Restringido
2D kinematics of massive stars near the Galactic Centre
(Oxford Academics: Oxford University Press, 2021-01-14) Libralato, M.; Lennon, Daniel 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
A detailed non-LTE analysis of LB-1: Revised parameters and surface abundances
(EDP Sciences, 2020-01-31) Simón Díaz, S.; Maíz Apellániz, J.; Lennon, Daniel J.; González Hernández, J. I.; Allende Prieto, C.; Castro, N.; De Burgos, A.; Dufton, P. L.; Herrero, A.; Toledo Padrón, B.; Smartt, S. J.; Agencia Estatal de Investigación (AEI); Ministerio de Economía y Competitividad (MINECO); Science and Technology Facilities Council (STFC); Simón Díaz, S. [0000-0003-1168-3524]; Maíz Apellániz, J. [0000-0003-0825-3443]; Lennon, D. J. [0000-0003-3063-4867]; González Hernández, J. I. [0000-0002-0264-7356]; Castro, N. [0000-0003-0521-473X]; De Burgos, A. [0000-0003-4729-0722]; Herrero, A. [0000-0001-8768-2179]; Toledo Padrón, B. [0000-0002-8194-215X]; Smartt, S. J. [0000-0002-8229-1731]; Unidad de Excelencia Científica María de Maeztu Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737
Context. It has recently been proposed that LB-1 is a binary system at 4 kpc consisting of a B-type star of 8 M-circle dot and a massive stellar black hole (BH) of 70 M-circle dot. This finding challenges our current theories of massive star evolution and formation of BHs at solar metallicity. Aims. Our objective is to derive the effective temperature, surface gravity, and chemical composition of the B-type component in order to determine its nature and evolutionary status and, indirectly, to constrain the mass of the BH. Methods. We use the non-LTE stellar atmosphere code FASTWIND to analyze new and archival high-resolution data. Results. We determine (T-eff, log g) values of (14& x2006;000 +/- 500 K, 3.50 +/- 0.15 dex) that, combined with the Gaia parallax, imply a spectroscopic mass, from log g, of 3.2(-1.9)(+2.1) M(circle dot)3.2-1.9+2.1M circle dot$ 3.2<^>{+2.1}_{-1.9}\,M_\odot $ and an evolutionary mass, assuming single star evolution, of 5.2(-0.6)(+0.3) M(circle dot)5.2-0.6+0.3M circle dot$ 5.2<^>{+0.3}_{-0.6}\,M_\odot $. We determine an upper limit of 8 km s(-1) for the projected rotational velocity and derive the surface abundances; we find the star to have a silicon abundance below solar, and to be significantly enhanced in nitrogen and iron and depleted in carbon and magnesium. Complementary evidence derived from a photometric extinction analysis and Gaia yields similar results for T-eff and log g and a consistent distance around 2 kpc. Conclusions. We propose that the B-type star is a slightly evolved main sequence star of 3-5 M-circle dot with surface abundances reminiscent of diffusion in late B/A chemically peculiar stars with low rotational velocities. There is also evidence for CN-processed material in its atmosphere. These conclusions rely critically on the distance inferred from the Gaia parallax. The goodness of fit of the Gaia astrometry also favors a high-inclination orbit. If the orbit is edge-on and the B-type star has a mass of 3-5 M-circle dot, the mass of the dark companion would be 4-5 M-circle dot, which would be easier to explain with our current stellar evolutionary models.
Acceso Abierto
Deriving stellar parameters from GALANTE photometry: bias and precision
(Oxford Academics: Oxford University Press, 2020-04-09) Lorenzo Gutiérrez, A.; Alfaro, Emilio J.; Maíz Apellániz, J.; Barbá, R. H.; Marín Franch, A.; Ederoclite, A.; Cristóbal Hornillos, D.; Varela, J.; Vázquez Ramió, H.; Cenarro, A. J.; Lennon, Daniel J.; García Lario, P.; Daflon, S.; Borges Fernandes, M.; Agencia Estatal de Investigación (AEI); Maíz Apellániz, J. [0000-0003-0825-3443]; Marín Franch, A. [0000-0002-9026-3933]; Centros de Excelencia Severo Ochoa, INSTITUTO DE ASTROFISICA DE ANDALUCIA (IAA), SEV-2017-0709; Unidad de Excelencia Científica María de Maeztu Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737
In this paper, we analyse how to extract the physical properties from the GALANTE photometry of a stellar sample. We propose a direct comparison between the observational colours (photometric bands normalized to the 515 nm central wavelength) and the synthetic colours derived from different stellar libraries. We use the reduced χ2 as the figure of merit for selecting the best fitting between both colour sets. The synthetic colours of the Next Generation Spectral Library (NGSL) provide a valuable sample for testing the uncertainty and precision of the stellar parameters derived from observational data. Reddening, as an extrinsic stellar physical parameter becomes a crucial variable for accounting for the errors and bias in the derived estimates: the higher the reddenings, the larger the errors and uncertainties in the derived parameters. NGSL colours also enable us to compare different theoretical stellar libraries for the same set of physical parameters, where we see how different catalogues of models can provide very different solutions in a, sometimes, non-linear way. This peculiar behaviour makes us to be cautious with the derived physical parameters obtained from GALANTE photometry without previous detailed knowledge of the theoretical libraries used to this end. In addition, we carry out the experiment of deriving physical stellar parameters from some theoretical libraries, using some other libraries as observational data. In particular, we use the Kurucz and Coelho libraries, as input observational data, to derive stellar parameters from Coelho + TLUSTY and Kurucz + TLUSTY stellar libraries, respectively, for different photometric errors and colour excesses.© 2020 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society
Acceso Abierto
Hubble spectroscopy of LB-1: Comparison with B+black-hole and Be+stripped-star models
(EDP Sciences, 2021-05-14) Lennon, Daniel J.; Maíz Apellániz, J.; Irrgang, A.; Bohlin, R. C.; Deustua, S.; Dufton, P. L.; Simón Díaz, S.; Herrero, A.; Casares, J.; Muñoz Darias, T.; Smartt, S. J.; González Hernández, J. I.; De Burgos, A.; Agencia Estatal de Investigación (AEI); Agencia Canaria de Investigación, Innovación y Sociedad de la Información (ACIISI); Ministerio de Economía y Competitividad (MINECO); Deutsche Forschungsgemeinschaft (DFG); National Aeronautics and Space Administration (NASA); Lennon, D. J. [0000-0003-3063-4867]
Context. LB-1 (alias ALS 8775) has been proposed as either an X-ray dim B-type star plus black hole (B+BH) binary or a Be star plus an inflated stripped star (Be+Bstr) binary. The latter hypothesis contingent upon the detection and characterization of the hidden broad-lined star in a composite optical spectrum. Aims. Our study is aimed at testing the published B+BH (single star) and Be+Bstr (binary star) models using a flux-calibrated UV-optical-IR spectrum. Methods. The Space Telescope Imaging Spectrograph (STIS) on board the Hubble Space Telescope (HST) was used to obtain a flux-calibrated spectrum with an accuracy of ∼1%. We compared these data with non-local thermal equilibrium (non-LTE) spectral energy distributions (SED) and line profiles for the proposed models. The Hubble data, together with the Gaia EDR3 parallax and a well-determined extinction, were used to provide tight constraints on the properties and stellar luminosities of the LB-1 system. In the case of the Be+Bstr model we adopted the published flux ratio for the Be and Bstr stars, re-determined the Teff of the Bstr using the silicon ionization balance, and inferred Teff for the Be star from the fit to the SED. Results. The UV data strongly constrain the microturbulence velocity to ≲2 km s−1 for the stellar components of both models. We also find stellar parameters consistent with previous results, but with greater precision enabled by the Hubble SED. For the B+BH single-star model, we find the parameters (Teff, log(L/L⊙), Mspec/M⊙) of the B-type star to be (15 300 ± 300 K, 3.23−0.10+0.09, 5.2−1.4+1.8). For the Bstr star we obtain (12 500 ± 100 K, 2.70−0.09+0.09, 0.8−0.3+0.5), and for the Be star (18 900 ± 200 K, 3.04−0.09+0.09, 3.4−1.8+3.5). While the Be+Bstr model is a better fit to the He I lines and cores of the Balmer lines in the optical, the B+BH model provides a better fit to the Si IV resonance lines in the UV. The analysis also implies that the Bstr star has roughly twice the solar silicon abundance, which is difficult to reconcile with a stripped star origin. The Be star, on the other hand, has a rather low luminosity and a spectroscopic mass that is inconsistent with its possible dynamical mass. Conclusions. We provide tight constraints on the stellar luminosities of the Be+Bstr and B+BH models. For the former, the Bstr star appears to be silicon-rich, while the notional Be star appears to be sub-luminous for a classical Be star of its temperature and the predicted UV spectrum is inconsistent with the data. This latter issue can be significantly improved by reducing the Teff and radius of the Be star, at the cost, however, of a different mass ratio as a result. In the B+BH model, the single B-type spectrum is a good match to the UV spectrum. Adopting a mass ratio of 5.1 ± 0.1, from the literature, implies a BH mass of ∼21−8+9 M⊙.
Acceso Abierto
Search for Galactic runaway stars using Gaia Data Release 1 and HIPPARCOS proper motions (Corrigendum)
(EDP Sciences, 2019-09-04) Maíz Apellániz, J.; Pantaleoni González, M.; Barbá, R. H.; Simón Díaz, S.; Negueruela, I.; Lennon, Daniel J.; Sota, A.; Trigueros Páez, E.; Maíz Apellániz, J. [0000-0003-0825-3443]; Pantaleoni González, M. [0000-0001-9933-1229]; Barbá, R. [0000-0003-1086-1579]; Simón Díaz, S. [0000-0003-1168-3524]; Trigueros Páez, E. [0000-0001-6770-1977]
Erratum for: A&A, 616, A149 (2018), https://doi.org/10.1051/0004-6361/201832787
Acceso Abierto
Spectroscopic characterization of the known O-star population in Cygnus OB2: Evidence of multiple star-forming bursts
(EDP Sciences, 2020-10-15) Berlanas, S. R.; Herrero, A.; Comerón, F.; Simón Díaz, S.; Lennon, Daniel J.; Pasquali, A.; Maíz Apellániz, J.; Sota, A.; Pellerín, A.; Agencia Estatal de Investigación (AEI); Ministerio de Economía y Competitividad (MINECO); Pasquali, L. [0000-0003-2423-1826]; Centros de Excelencia Severo Ochoa, INSTITUTO DE ASTROFÍSICA DE CANARIAS (IAC), SEV-2015-0548; Unidad de Excelencia Científica María de Maeztu Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737
Context. Cygnus OB2 provides a unique insight into the high-mass stellar content in one of the largest groups of young massive stars in our Galaxy. Although several studies of its massive population have been carried out over the last decades, an extensive spectroscopic study of the whole known O-star population in the association is still lacking. Aims. We aim to carry out a spectroscopic characterization of all the currently known O stars in Cygnus OB2, determining the distribution of rotational velocities and accurate stellar parameters to obtain an improved view of the evolutionary status of the region. Methods. Based on existing and new optical spectroscopy, we performed a detailed quantitative spectroscopic analysis of all the known O-type stars identified in the association. For this purpose, we used the user-friendly iacob-broad and iacob-gbat automatized tools, FASTWIND stellar models, and astrometry provided by the Gaia second data release. Results. We created the most complete spectroscopic census of O stars carried out so far in Cygnus OB2 using already existing and new spectroscopy. We present the spectra for 78 O-type stars, from which we identify new binary systems, obtain the distribution of rotational velocities, and determine the main stellar parameters for all the stars in the region that have not been detected as double-line spectroscopic binaries. We also derive radii, luminosities, and masses for those stars with reliable Gaia astrometry, in addition to creating the Hertzsprung-Russell Diagram to interpret the evolutionary status of the association. Finally, we inspect the dynamical state of the population and identify runaway candidates. Conclusions. Our spectroscopic analysis of the O-star population in Cygnus OB2 has led to the discovery of two new binary systems and the determination of the main stellar parameters, including rotational velocities, luminosities, masses, and radii for all identified stars. This work has shown the improvement reached when using accurate spectroscopic parameters and astrometry for the interpretation of the evolutionary status of a population, revealing, in the case of Cygnus OB2, at least two star-forming bursts at ~3 and ~5 Myr. We find an apparent deficit of very fast rotators in the distribution of rotational velocities. The inspection of the dynamical distribution of the sample has allowed us to identify nine O stars with peculiar proper motions and discuss a possible dynamical ejection scenario or past supernova explosions in the region.
Acceso Abierto
The IACOB project VI. On the elusive detection of massive O-type stars close to the ZAMS
(EDP Sciences, 2020-06-30) Holgado, G.; Simón Díaz, S.; Haemmerlé, L.; Lennon, Daniel J.; Barbá, R. H.; Cerviño, M.; Castro, N.; Herrero, A.; Meynet, G.; Arias, J. I.; Agencia Estatal de Investigación (AEI); Agencia Canaria de Investigación, Innovación y Sociedad de la Información (ACIISI); Swiss National Science Foundation (SNSF); European Research Council (ERC); Holgado, G. [0000-0002-9296-8259]; Unidad de Excelencia Científica María de Maeztu Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737
Context. The apparent lack of massive O-type stars near the zero-age main sequence, or ZAMS (at ages <2 Myr), is a topic that has been widely discussed in the past 40 yr. Different explanations for the elusive detection of these young massive stars have been proposed from the observational and theoretical side, but no firm conclusions have been reached yet. Aims. We reassess this empirical result here, benefiting from the high-quality spectroscopic observations of (more than 400) Galactic O-type stars gathered by the IACOB and OWN surveys. Methods. We used effective temperatures and surface gravities resulting from a homogeneous semi-automatized IACOB-GBAT/FASTWIND spectroscopic analysis to locate our sample of stars in the Kiel and spectroscopic Hertzsprung-Russell (sHR) diagrams. We evaluated the completeness of our magnitude-limited sample of stars as well as potential observational biases affecting the compiled sample using information from the Galactic O star catalog. We discuss limitations and possible systematics of our analysis method, and compare our results with other recent studies using smaller samples of Galactic O-type stars. We mainly base our discussion on the distribution of stars in the sHR diagram in order to avoid the use of still uncertain distances to most of the stars in our sample. However, we also performed a more detailed study of the young cluster Trumpler-14 as an illustrative example of how Gaia cluster distances can help to construct the associated classical HR diagram. Results. We find that the apparent lack of massive O-type stars near the ZAMS with initial evolutionary masses in the range between ≈30 and 70 M⊙ still persist even when spectroscopic results from a large non-biased sample of stars are used. We do not find any correlation between the dearth of stars close to the ZAMS and obvious observational biases, limitations of our analysis method, and/or the use of one example spectroscopic HR diagram instead of the classical HR diagram. Finally, by investigating the effect of the efficiency of mass accretion during the formation process of massive stars, we conclude that an adjustment of the mass accretion rate towards lower values than canonically assumed might reconcile the hotter boundary of the empirical distribution of optically detected O-type stars in the spectroscopic HR diagram and the theoretical birthline for stars with masses above ≈30 M⊙. Last, we also discuss how the presence of a small sample of O2-O3.5 stars found much closer to the ZAMS than the main distribution of Galactic O-type star might be explained in the context of this scenario when the effect of nonstandard star evolution (e.g. binary interaction, mergers, and/or homogeneous evolution) is taken into account.
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, Daniel 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, Daniel J.; 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.