Examinando por Autor "Oudmaijer, R. D."

Mostrando 1 - 4 de 4

Acceso Abierto
Catalogue of new Herbig Ae/Be and classical Be stars. A machine learning approach to Gaia DR2
(EDP Sciences, 2020-06-04) Vioque, M.; Oudmaijer, R. D.; Schreiner, M.; Mendigutía, I.; Baines, D.; Mowlavi, N.; Pérez Martínez, R.; European Research Council (ERC); Comunidad de Madrid; National Aeronautics and Space Administration (NASA); Unidad de Excelencia Científica María de Maeztu Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737
Context. The intermediate-mass pre-main sequence Herbig Ae/Be stars are key to understanding the differences in formation mechanisms between low- and high-mass stars. The study of the general properties of these objects is hampered by the lack of a well-defined, homogeneous sample, and because few and mostly serendipitously discovered sources are known. Aims. Our goal is to identify new Herbig Ae/Be candidates to create a homogeneous and well defined catalogue of these objects. Methods. We have applied machine learning techniques to 4 150 983 sources with data from Gaia DR2, 2MASS, WISE, and IPHAS or VPHAS+. Several observables were chosen to identify new Herbig Ae/Be candidates based on our current knowledge of this class, which is characterised by infrared excesses, photometric variabilities, and Hα emission lines. Classical techniques are not efficient for identifying new Herbig Ae/Be stars mainly because of their similarity with classical Be stars, with which they share many characteristics. By focusing on disentangling these two types of objects, our algorithm has also identified new classical Be stars. Results. We have obtained a large catalogue of 8470 new pre-main sequence candidates and another catalogue of 693 new classical Be candidates with a completeness of 78.8 ± 1.4% and 85.5 ± 1.2%, respectively. Of the catalogue of pre-main sequence candidates, at least 1361 sources are potentially new Herbig Ae/Be candidates according to their position in the Hertzsprung-Russell diagram. In this study we present the methodology used, evaluate the quality of the catalogues, and perform an analysis of their flaws and biases. For this assessment, we make use of observables that have not been accounted for by the algorithm and hence are selection-independent, such as coordinates and parallax based distances. The catalogue of new Herbig Ae/Be stars that we present here increases the number of known objects of the class by an order of magnitude.
Acceso Abierto
Discovery of a jet from the single HAe/Be star HD 100546
(EDP Sciences, 2020-06-10) Schneider, P. C.; Dougados, C.; Whelan, E. T.; Eislöffel, J.; Günther, M. N.; Huélamo, N.; Mendigutía, I.; Oudmaijer, R. D.; Beck, T. L.; Agencia Estatal de Investigación (AEI); National Aeronautics and Space Administration (NASA); Deutsches Zentrum für Luft- und Raumfahrt (DLR); 0000-0002-5094-2245; 0000-0001-6496-0252; 0000-0003-4243-2840; 0000-0002-2711-8143; 0000-0002-0233-5328; Unidad de Excelencia Científica María de Maeztu Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737
Young accreting stars drive outflows that collimate into jets, which can be seen hundreds of au from their driving sources. Accretion and outflow activity cease with system age, and it is believed that magneto-centrifugally launched disk winds are critical agents in regulating accretion through the protoplanetary disk. Protostellar jets are well studied in classical T Tauri stars (M-star less than or similar to 2M(circle dot)), while few nearby (d less than or similar to 150pc) intermediate-mass stars (M-star=2-10 M-circle dot), known as Herbig Ae/Be stars, have detected jets. We report VLT/MUSE observations of the Herbig Ae/Be star HD 100546 and the discovery of a protostellar jet. The jet is similar in appearance to jets driven by low-mass stars and compares well with the jet of HD 163296, the only other known optical jet from a nearby Herbig Ae/Be star. We derive a (one-sided) mass-loss rate in the jet of log (M) over dot(jet) similar to -9.5 (in M-circle dot yr(-1)) and a ratio of outflow to accretion of roughly 3 x 10(-3), which is lower than that of CTTS jets. The discovery of the HD 100546 jet is particularly interesting because the protoplanetary disk around HD 100546 shows a large radial gap, spiral structure, and might host a protoplanetary system. A bar-like structure previously seen in H alpha with VLT/SPHERE shares the jet position angle, likely represents the base of the jet, and suggests a jet-launching region within about 2 au. We conclude that the evolution of the disk at radii beyond a few au does not affect the ability of the system to launch jets.
Acceso Abierto
K-band GRAVITY/VLTI interferometry of “extreme” Herbig Be stars. The size–luminosity relation revisited
(EDP Sciences, 2021-08-11) Marcos Arenal, P.; Mendigutía, I.; Koumpia, E.; Oudmaijer, R. D.; Vioque, M.; Guzmán Díaz, J.; Wichittanakom, C.; De Wit, W. J.; Montesinos, B.; Ilee, J. D.; Agencia Estatal de Investigación (AEI), European Research Council; Comunidad de Madrid; Science and Technology Facilities Council (STFC); European Research Council (ERC); Marcos Arenal, P. [0000-0003-1549-9396]
Context. It has been hypothesized that the location of Herbig Ae/Be stars (HAeBes) within the empirical relation between the inner disk radius (rin), inferred from K-band interferometry, and the stellar luminosity (L*), is related to the presence of the innermost gas, the disk-to-star accretion mechanism, the dust disk properties inferred from the spectral energy distributions (SEDs), or a combination of these effects. However, no general observational confirmation has been provided to date. Aims. This work aims to test whether the previously proposed hypotheses do, in fact, serve as a general explanation for the distribution of HAeBes in the size–luminosity diagram. Methods. GRAVITY/VLTI spectro-interferometric observations at ~2.2 μm have been obtained for five HBes representing two extreme cases concerning the presence of innermost gas and accretion modes. V590 Mon, PDS 281, and HD 94509 show no excess in the near-ultraviolet, Balmer region of the spectra (ΔDB), indicative of a negligible amount of inner gas and disk-to-star accretion, whereas DG Cir and HD 141926 show such strong ΔDB values that cannot be reproduced from magnetospheric accretion, but probably come from the alternative boundary layer mechanism. In turn, the sample includes three Group I and two Group II stars based on the Meeus et al. SED classification scheme. Additional data for these and all HAeBes resolved through K-band interferometry have been compiled from the literature and updated using Gaia EDR3 distances, almost doubling previous samples used to analyze the size–luminosity relation. Results. We find no general trend linking the presence of gas inside the dust destruction radius or the accretion mechanism with the location of HAeBes in the size–luminosity diagram. Similarly, our data do not support the more recent hypothesis linking such a location and the SED groups. Underlying trends are present and must be taken into account when interpreting the size–luminosity correlation. In particular, it cannot be statistically ruled out that this correlation is affected by dependencies of both L* and rin on the wide range of distances to the sources. Still, it is argued that the size–luminosity correlation is most likely to be physically relevant in spite of the previous statistical warning concerning dependencies on distance. Conclusions. Different observational approaches have been used to test the main scenarios proposed to explain the scatter of locations of HAeBes in the size–luminosity diagram. However, none of these scenarios have been confirmed as a fitting general explanation and this issue remains an open question.
Acceso Abierto
The accretion rates and mechanisms of Herbig Ae/Be stars
(Oxford Academics: Oxford University Press, 2020-01-20) Wichittanakom, C.; Oudmaijer, R. D.; Fairlamb, J. R.; Mendigutía, I.; Vioque, M.; Ababakr, K. M.; Comunidad de Madrid; European Research Council (ERC); National Science Foundation (NSF); Mendigutía, I. [0000-0002-0233-5328]; Farlamb, J. [0000-0002-2833-2344]; Unidad de Excelencia Científica María de Maeztu Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737
This work presents a spectroscopic study of 163 Herbig Ac/Be stars. Amongst these, we present new data for 30 objects. Stellar parameters such as temperature, reddening, mass, luminosity, and age are homogeneously determined. Mass accretion rates are determined from Ha emission line measurements. Our data is complemented with the X-Shooter sample from previous studies and we update results using Gain DR2 parallaxes giving a total of 78 objects with homogeneously determined stellar parameters and mass accretion rates. In addition, mass accretion rates of an additional 85 HAeBes are determined. We confirm previous findings that the mass accretion rate increases as a function of stellar mass, and the existence of a different slope for lower and higher mass stars, respectively. The mass where the slope changes is determined to be 3.98(-0.94)(+1.37) M-circle dot. We discuss this break in the context of different modes of disc accretion for low- and high-mass stars. Because of their similarities with T Tauri stars, we identify the accretion mechanism for the late-type Herbig stars with the Magnetospheric Accretion. The possibilities for the earlier-type stars are still open, we suggest the Boundary Layer accretion model may be a viable alternative. Finally, we investigated the mass accretion age relationship. Even using the superior Gaia based data, it proved hard to select a large enough sub-sample to remove the mass dependence in this relationship, Yet, it would appear that the mass accretion does decline with age as expected from basic theoretical considerations.