Examinando por Autor "Schneider, P. C."

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Acceso Abierto
An X-ray activity cycle on the young solar-like star ɛ Eridani
(EDP Sciences, 2020-04-15) Coffaro, M.; Stelzer, B.; Orlando, S.; Hall., J.; Metcalfe, T. S.; Wolter, U.; Mittag, M.; Sanz Forcada, J.; Schneider, P. C.; Ducci, L.; Deutsches Zentrum für Luft- und Raumfahrt (DLR); European Research Council (ERC); National Science Foundation (NSF); Agencia Estatal de Investigación (AEI); Metcalfe, T. S. https://orcid.org/0000-0003-4034-0416; Unidad de Excelencia Científica María de Maeztu Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737
Chromospheric Ca II activity cycles are frequently found in late-type stars, but no systematic programs have been created to search for their coronal X-ray counterparts. The typical time scale of Ca II activity cycles ranges from years to decades. Therefore, long-lasting missions are needed to detect the coronal counterparts. The XMM-Newton satellite has so far detected X-ray cycles in five stars. A particularly intriguing question is at what age (and at what activity level) X-ray cycles set in. To this end, in 2015 we started the X-ray monitoring of the young solar-like star ɛ Eridani, previously observed on two occasions: in 2003 and in early 2015, both by XMM-Newton. With an age of 440 Myr, it is one of the youngest solar-like stars with a known chromospheric Ca II cycle. We collected the most recent Mount Wilson S-index data available for ɛ Eridani, starting from 2002, including previously unpublished data. We found that the Ca II cycle lasts 2.92 ± 0.02 yr, in agreement with past results. From the long-term XMM-Newton lightcurve, we find clear and systematic X-ray variability of our target, consistent with the chromospheric Ca II cycle. The average X-ray luminosity is 2 × 1028erg s−1, with an amplitude that is only a factor of 2 throughout the cycle. We apply a new method to describe the evolution of the coronal emission measure distribution of ɛ Eridani in terms of solar magnetic structures: active regions, cores of active regions, and flares covering the stellar surface at varying filling fractions. Combinations of these three types of magnetic structures can only describe the observed X-ray emission measure of ɛ Eridani if the solar flare emission measure distribution is restricted to events in the decay phase. The interpretation is that flares in the corona of ɛ Eridani last longer than their solar counterparts. We ascribe this to the lower metallicity of ɛ Eridani. Our analysis also revealed that the X-ray cycle of ɛ Eridani is strongly dominated by cores of active regions. The coverage fraction of cores throughout the cycle changes by the same factor as the X-ray luminosity. The maxima of the cycle are characterized by a high percentage of covering fraction of the flares, consistent with the fact that flaring events are seen in the corresponding short-term X-ray lightcurves predominately at the cycle maxima. The high X-ray emission throughout the cycle of ɛ Eridani is thus explained by the high percentage of magnetic structures on its surface.
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.