Search

© ESO 2010. We thank Calar Alto Observatory for allocation of director’s discretionary time to this programme. This work was supported by the Spanish Ministerio de Educación y Ciencia (MEC) under grant AYA2005-02750, Ministerio de Ciencia e Innovación (MICINN) under grant AYA2008-06423-C03-03, and the Comunidad de Madrid under PRICIT project S-0505/ESP-0237 (ASTROCAM). M.C.G.O. acknowledges financial support from the European Commission in the form of a Marie Curie Intra European Fellowship (PIEF-GA- 2008-220679). M.H.O. and G.A.E. thank Dr. Chriss Moss, support astronomer at the LT for his help and patience. Also M.H.O. thanks Dr. Santos Pedraz, support astronomer at the Calar Alto Observatory for his help with DDT run. M.H.O. is grateful to Dr. José Antonio Caballero for valuable discussions, and also Dr. Laurence R. Doyle for his suggestions that was the initial inspiration for this work. This research has made use of the SIMBAD database, operated at CDS, Strasbourg, France. The authors gratefully acknowledge the valuable comments and suggestions of an anonymous referee that helped to improve the paper., Context. BD+20 1790 is a young active, metal-rich, late-type K5Ve star. We have undertaken a study of stellar activity and kinematics for this star over the past few years. Previous results show a high level of stellar activity, with the presence of prominence-like structures, spots on the surface, and strong flare events, despite the moderate rotational velocity of the star. In addition, radial velocity variations with a semi-amplitude of up to 1 km s(-1) were detected. Aims. We investigate the nature of these radial velocity variations, in order to determine whether they are due to stellar activity or the reflex motion of the star induced by a companion. Methods. We have analysed high-resolution echelle spectra by measuring stellar activity indicators and computing radial velocity (RV) and bisector velocity spans. Two-band photometry was also obtained to produce the light curve and determine the photometric period. Results. Based upon the analysis of the bisector velocity span, as well as spectroscopic indices of chromospheric indicators, Ca II H & K, H alpha, and taking the photometric analysis into account, we report that the best explanation for the RV variation is the presence of a substellar companion. The Keplerian fit of the RV data yields a solution for a close-in massive planet with an orbital period of 7.78 days. The presence of the close-in massive planet could also be an interpretation for the high level of stellar activity detected. Since the RV data are not part of a planet search programme, we can consider our results as a serendipitous evidence of a planetary companion. To date, this is the youngest main sequence star for which a planetary candidate has been reported., Spanish Ministerio de Educación y Ciencia (MEC), Ministerio de Ciencia e Innovación (MICINN), Comunidad de Madrid under PRICIT, Marie Curie Intra European Fellowship, European Commission, Depto. de Física de la Tierra y Astrofísica, Fac. de Ciencias Físicas, TRUE, pub

© Royal Astronomical Society. Many thanks are due to Dr Andre Maeder, who kindly sent us his unpublished main-sequence interior models. We also are very grateful to Dr Carole Jordan for her careful reading of the manuscript and for many suggestions to clarify and improve its scientific content. The authors are indebted to an anonymous referee for his valuable comments and suggestions on the first version of this paper. This work has been carried out at the Departamento de Astrofísica of the Universidad Complutense (Madrid), and is a part of the project 'Actividad estelar en estrellas de los últimos tipos espectrales' supported by the Spanish Comisión Asesora de Investigación Científica y Tecnológica (CAICYT No. 2254/83). The financial support to one of the authors (BM) with a grant of the Spanish Ministerio de Educación y Ciencia is gratefully acknowledged., In this work we try to establish a connection between the dynamo effect, which operates in the convection zone of late-type stars, and the chromospheric activity observed in these objects. We estímate in a theoretical way, for a sample of main-sequence active stars with spectral types G and K, the magnetic field generated in a region close to the base of the convection zone and the filling factor (fraction of stellar surface covered by strong magnetic fields). The analysis of the behaviour both of the filling factor and the activity indicator R(CaII + MgII) against several stellar parameters ( B-V and the Rossby number) supports the existence of a link between the interior processes and the surface activity., Comisión Asesora de Investigación Científica y Tecnológica (CAICYT), España, Ministerio de Educación y Ciencia (MEC), España, Depto. de Física de la Tierra y Astrofísica, Fac. de Ciencias Físicas, TRUE, pub

© 1997 EDP Sciencies. This research has made use of the Simbad database, operated at CDS, Strasbourg, France. We greatly appreciate the comments and suggestion on this paper by the referee, R. Gratton. DBN acknowledges the support by the Universidad Complutense with a grant and by the Real Colegio Complutense at Harvard University. This work has been partially supported by the Spanish Dirección General de Investigación Científica y Técnica (DGICYT) under projects PB92-0434-c02-01 and PB94-0203., We present an extensive study of lithium abundances in dwarf components of chromospherically active binary stars (CABS). Since most of these binaries have known radii, masses and ages, this kind of data is especially useful for comparisons with theoretical models which try to explain the Li depletion phenomenon. We show that a significant part of these stars have clear Li overabundances with respect to the typical values for stars of the same mass and evolutionary stage. These excesses are evident when comparing our sample of CABS with binary and single stars belonging to open clusters of different ages, namely Pleiades, Hyades, NGC752, M67 and NGC188, which have ages ranging from 7x10^7 to 10^10 yr. The Li excesses are more conspicuous for masses in the range 0.75-0.95 M_⊙., indicating that the rate of Li depletion has been less pronounced in CABS than in single stars. This phenomenon is interpreted in the context of transport of angular momentum from the orbit to the stellar rotation due to tidal effects. This angular momentum transfer would avoid the radial differential rotation and the associated turbulent mixing of material in the stellar interior. Other explanations, however, can not be ruled out. This is the case of transport of material induced by internal gravity waves, which could be inhibited due to the presence of strong magnetic fields associated with the effective dynamo in CABS. The confirmed existence of a relation between Li abundances and the fluxes in Ca II H&K lines can also be accommodated within both scenarios., Universidad Complutense de Madrid (UCM), Real Colegio Complutense at Harvard University, Dirección General de Investigación Científica y Técnica (DGICYT), España, Ministerio de Economía y Competitividad (MINECO), España, Depto. de Física de la Tierra y Astrofísica, Fac. de Ciencias Físicas, TRUE, pub

© European Southern Observatory. © The American Astronomical Society. The INT 2.5 m on the island of La Palma and the 1.23 m and 2.2 m telescopes at Calar Alto Observatory are operated, respectively, by the Royal Greenwich Observatory at the Spanish Roque de los Muchachos Observatory (Instituto de Astrofísica de Canarias), and the Max Plank Institut for Astronomie at the Centro Astronómico Hispano-Alemán of Calar Alto (Almería, Spain). We want to express our gratitude to the staff of both Observatorties for their help during the observational campaigns. This work has been supported by the Spanish Comisión Interministerial de Ciencia y Tecnología under grants PB86-0536-C02 and PB87-0235., A detailed study of the system V772 Her = HD 165590 = ADS 11060 AB is presented. The three identified components are found to be late type stars close to the zero-age main sequence with high rotational velocities. Spectroscopic observations allowed a quantitative determination of stellar activity indicators for the two members of the close binary as well as for the visual companion. An estimation of the most relevant physical parameters has been derived from the colour indices of each of the components and the close system has been found to be an eclipsing binary. This additional source of information combined with published measures of radial velocities, provides the absolute dimensions of the component stars (1.1 and 0.6 solar masses, and 0.9 and 0.6 solar radii) which confirm that the system is very little evolved. Moreover, a distance of 32 +/- 4 parsecs has been found to V772 Her in good agreement with available trigonometric determinations. Finally, we have compared these results with evolutionary models for main sequence stars of solar chemical composition., Comisión Interministerial de Ciencia y Tecnología (CICYT), España, Ministerio de Ciencia e Innovación (MICINN), España, Depto. de Física de la Tierra y Astrofísica, Fac. de Ciencias Físicas, TRUE, pub

© ESO 2015. Artículo firmado por 20 autores. Based on observations collected at the German-Spanish Astronomical Center, Calar Alto, jointly operated by the Max-Planck-Institut fur Astronomie Heidelberg and the Instituto de Astrofísica de Andalucía (CSIC). Based on observations made with the Italian Telescopio Nazionale Galileo (TNG) operated on the island of La Palma by the Fundacion Galileo Galilei of the INAF (Instituto Nazionale di Astrofisica); and with he Nordic Optical Telescope, operated on the island of La Palma jointly by Denmark, Finland, Iceland, Norway, and Sweden; and with the Mercator Telescope, operated on the island of La Palma by the Flemish Community (obtained with the HERMES spectrograph, which is supported by the Fund for Scientific Research of Flanders (FWO), Belgium, the Research Council of K. U. Leuven, Belgium, the Fonds National Recherches Scientific (FNRS), Belgium, the Royal Observatory of Belgium, the Observatoire de Geneve, Switzerland and the Thuringer Landessternwarte Tautenburg, Germany), all operated at the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias. This work was supported by the Spanish Ministerio de Educación y Ciencia (MEC) under grant AYA2005-02750, Ministerio de Ciencia e Innovación (MICINN) under grant AYA2008-06423-C03-03, AstroMadrid S2009/ESP-1496. M. Hernán Obispo wants to especially thanks to P. Figueira and M. Marmier for their availability to help and for providing us with the CORALIE data used in the activity study and the information requested. M. C. Gálvez Ortiz acknowledges financial support by the Spanish MICINN under the Consolider-Ingenio 2010 Program grant CSD2006-00070: first Science with the GTC (http://www.iac.es/consolider-ingenio-gtc). She also acknowledges the support of a JAE-Doc CSIC fellowship co-funded with the European Social Fund under the program "Junta para la Ampliación de Estudios". Financial support was also provided by the Spanish Ministerio de C, Context. In a previous paper we reported a planetary companion to the young and very active K5Ve star BD+20 1790. We found that this star has a high level of stellar activity (log R'_HK = -3.7) that manifests in a plethora of phenomena (starspots, prominences, plages, large flares). Based on a careful study of these activity features and a deep discussion and analysis of the effects of the stellar activity on the radial velocity measurements, we demonstrated that the presence of a planet provided the best explanation for the radial velocity variations and all the peculiarities of this star. The orbital solution resulted in a close-in massive planet with a period of 7.78 days. However, a paper by Figueira et al. (2010, A&A, 513, L8) questioned the evidence for the planetary companion. Aims. This paper aims to more rigorously assess the nature of the radial velocity measurements with an expanded data set and new methods of analysis. Methods. We have employed Bayesian methods to simultaneously analyse the radial velocity and activity measurements based on a combined data set that includes new and previously published observations. Results. We conclude that the Bayesian analysis and the new activity study support the presence of a planetary companion to BD+20 1790. A new orbital solution is presented, after removing the two main contributions of stellar jitter, one that varies with the photometric period (2.8 days) and another that varies with the synodic period of the star-planet system (4.36 days). We present a new method to determine these jitter components, considering them as second and third signals in the system. A discussion on possible star-planet interaction is included, based on the Bayesian analysis of the activity indices, which indicates that they modulate with the synodic period. We propose two different sources for flare events in this system: one related to the geometry of the system and the relative movement of the star and planet, and a second one pur, Ministerio de Ciencia e Innovacion (MICINN), Ministerio de Economía y Competitividad (MINECO), Comunidad de Madrid, Fund for Scientific Research of Flanders (FWO), Belgium, Research Council of K. U. Leuven, Belgium, Fonds National Recherches Scientific (FNRS), Belgium, Royal Observatory of Belgium, Observatoire de Geneve, Switzerland, Thuringer Landessternwarte Tautenburg, Germany, Ministerio de Educacion y Ciencia (MEC), España, Unión Europea (UE), JAE-Doc CSIC fellowship, Fondo Social Europeo (FSE), UE, CENTRO DE EXCELENCIA EN ASTROFÍSICA Y TECNOLOGÍAS AFINES (CATA), Chile, Comisión Nacional de Investigación Científica y Tecnológica (CONICYT), Chile, Depto. de Física de la Tierra y Astrofísica, Fac. de Ciencias Físicas, TRUE, pub

© European Southern Observatory. © EDP Sciences. The INT 2.5m on the island of La Palma and the 2.2m telescope at Calar Alto Observatory are operated respectively, by the Royal Greenwich Observatory at the Spanish Observatorio del Roque de Los Muchachos (Instituto de Astrofísica de Canarias), and the Max Planck lnstitut für Astronomie at the Centro Astronómico Hispano-Alemán of Calar Alto (Almería, Spain). We want to express our gratitude to the staff of both Observatories for their help during the observations. This work has been supported by the Universidad Com­plutense de Madrid and the Spanish Dirección General de Investigación Científica y Técnica (DGICYT) under grant PB91-0348., We present measurements of the emission core width W_0 and the wavelength separation of the K_1 dips, W_1, of the Ca II H and K emission lines observed on high-dispersion spectra of 28 chromospherically active binary systems (RS CVn and BY Dra stars) and 18 single active stars. We test the width-luminosity correlations (the Wilson-Bappu (WB) effect, and (W_1, M_V) in these very active stars and analyse the influence of the activity level (I_K3) and the rotational broadening (Vsin i) in these correlations. We have found that for very active stars the emission widths, both W_0 and W_1, are larger than expected from previously accepted width-luminosity relations. The stars with strong emission intensities, I_K3 and large values of Vsin i seem to present larger values of W_0 than resulted from WB relation, the effect of the rotational velocity being the most remarkable. On the contrary, W_1 is strongly influenced by I_K3 but the effect of the rotational broadening is lesser. We also analyse the behaviour of the Ca II H and K line parameters in these very active stars in relation with less active stars and we found that the increase of W_1 and I_K1 With I_K3 presents a flattening for the most active stars which is different for each value of W_0. Finally we also find a Hepsilon width-luminosity correlation in the stars of the sample in which this emission line is present., Universidad Complutense de Madrid (UCM), Dirección General de Investigación Científica y Técnica (DGICYT), España, Ministerio de Economía y Competitividad (MINECO), España, Depto. de Física de la Tierra y Astrofísica, Fac. de Ciencias Físicas, TRUE, pub

© ESO, 2016. This work was supported by the Spanish Ministerio de Economía y Competitividad under grant AYA2011-29754-C03-03., Context. Runaway O- and early B-type stars passing through the interstellar medium at supersonic velocities and characterized by strong stellar winds may produce bow shocks that can serve as particle acceleration sites. Previous theoretical models predict the production of high-energy photons by nonthermal radiative processes, but their efficiency is still debated. Aims. We aim to test and explain the possibility of emission from the bow shocks formed by runaway stars traveling through the interstellar medium by using previous theoretical models. Methods. We applied our model to AE Aurigae, the first reported star with an X-ray detected bow shock, to BD+43 3654, in which the observations failed in detecting high-energy emission, and to the transition phase of a supergiant star in the late stages of its life. Results. From our analysis, we confirm that the X-ray emission from the bow shock produced by AE Aurigae can be explained by inverse Compton processes involving the infrared photons of the heated dust. We also predict low high-energy flux emission from the bow shock produced by BD+43 3654, and the possibility of high-energy emission from the bow shock formed by a supergiant star during the transition phase from blue to red supergiant. Conclusions. Bow shocks formed by different types of runaway stars are revealed as a new possible source of high-energy photons in our neighborhood., Ministerio de Economía y Competitividad (MINECO), Depto. de Física de la Tierra y Astrofísica, Fac. de Ciencias Físicas, TRUE, pub

© 1998 EDP Sciencies. This research has made use of the Simbad database, operated at CDS, Strasbourg, France. We greatly appreciate the comments and suggestions on this paper by the referee, Dr. Sofia Randich, which helped to improve the presentation and discussion of the results. DBN acknowledges the support by the Universidad Complutense, the Real Colegio Complutense at Harvard University, and the MEC/Fulbright commission. This work has been partially supported by the Spanish Dirección General de Educación Superior (DGES) under projects PB92-0434-C02-01, PB94-0203, and PB95-1132-C02-01., We present a study of the lithium abundances of a sample of evolved components of Chromospherically Active Binary Systems. We show that a significant part of them have lithium excesses, independently of their mass and evolutionary stage. Therefore, it can be concluded that Li abundance does not depend on age for giant components of CABS. These overabundances appear to be closely related to the stellar rotation, and we interpret them as a consequence of the transfer of angular momentum from the orbit to the rotation as the stars evolve: in and off the Main Sequence, in a similar way as it happens in the dwarf components of the same systems and in the Tidally Locked Binaries belonging to the Hyades and M67., Universidad Complutense de Madrid (UCM), Real Colegio Complutense at Harvard University, Ministerio de Educación y Ciencia (MEC), España, Spanish Dirección General de Educación Superior (DGES), Comisión Fulbright, España, Depto. de Física de la Tierra y Astrofísica, Fac. de Ciencias Físicas, TRUE, pub

© 1988 American Astronomical Society. The JKT on the island of La Palma and the l.5 m Tele­scope at Calar Alto are operated, respectively, by the Royal Greenwich Observatory at the Spanish Roque de los Mucha­chos Observatory (Instituto de Astrofísica de Canarias), and Observatorio Astronómico Nacional at the Spanish Ca­lar Alto Observatory (Almería). We want to express our gratitude to the staffs of the observatories for their help dur­ing the observational campaigns. This work has been sup­ported by the Spanish Comisión Asesora de Investigación Cientifica y Técnica (CAICYT No. 2254/83 and No. 3455/ 83)., From 1984 to 1986, we made several observational campaigns at Calar Alto and La Palma Observator­ies using the uvby and ß photometric systems to monitor a selected sample of late-type variable stars. In this paper we present the ß values for 38 uvby standard stars to contribute to the uvby-ß calibration works on late-type stars. In the final discussion, the ß computed values are plotted against the Ström­gren b - y, m_1, and c_1 indices., Comisión Asesora de Investigación Cientifica y Técnica (CAICYT), España, Depto. de Física de la Tierra y Astrofísica, Fac. de Ciencias Físicas, TRUE, pub

© ESO 2013. We are grateful to the referee for her/his valuable suggestions and comments, which helped us to improve the paper. The authors acknowledge support by DGI of the Spanish Ministerio de Educación y Ciencia under grants AYA2010-21782-C03-03, FEDER funds, Plan Andaluz de Investigación Desarrollo e Innovación (PAIDI) of Junta de Andalucía as research group FQM-322, and the excellence fund FQM-5418. J.A.C. and J.F.A.C. are researchers of CONICET. J.F.A.C. was supported by grant PIP 2011-0100285 (CONICET). J.A.C. by grant PICT 2008-0627, from ANPCyT and PIP 20100078 (CONICET). J.L.S. acknowledges support by the Spanish Ministerio de Innovación y Tecnología under grant AYA2008-06423-C03-03. F. B. acknowledges partial support of the ASI-INAF agreement n. I/009/10/0., Aims. We aim to study the spatial distribution of the physical and chemical properties of the X-ray emitting plasma of the supernova remnant G272.2-3.2 in order to obtain important constraints on its ionization stage, the progenitor supernova explosion, and the age of the remnant. Methods. We report on combined XMM-Newton and Chandra images, median photon energy maps, silicon and sulfur equivalent width maps, and a spatially resolved spectral analysis for a set of regions of the remnant. Complementary radio and Ha observations, available in the literature, are also used to study the multi-wavelength connection of all detected emissions. Results. The X-ray morphology of the remnant displays an overall structure with an almost circular appearance and a centrally brightened hard region with a peculiar elongated hard structure oriented along the northwest-southeast direction of the central part. The X-ray spectral study of the regions shows distinct K alpha emission-line features of metal elements, confirming the thermal origin of the emission. The X-ray spectra are well represented by an absorbed variable abundance non-equilibrium ionization thermal plasma model, which produces elevated abundances of Si, S, and Fe in the circular central region, typical of ejecta material. The values of abundances found in the central region of the supernova remnant favor a Type Ia progenitor for this remnant. The outer region shows abundances below the solar value, to be expected if the emission arises from the shocked interstellar medium. The relatively low ionization timescales suggest non-equilibrium ionization. We identify the location of the contact discontinuity. Its distance to the outer shock is higher than expected for expansion in a uniform media, which suggests that the remnant spent most of its time in more dense medium., DGI of the Spanish Ministerio de Educación y Ciencia, FEDER funds, Plan Andaluz de Investigación Desarrollo e Innovación (PAIDI) of Junta de Andalucía, Excellence fund, CONICET, ANPCyT, Spanish Ministerio de Innovación y Tecnología, ASI-INAF, Depto. de Física de la Tierra y Astrofísica, Fac. de Ciencias Físicas, TRUE, pub

© 2001 RAS. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved. This research has made use the of the SIMBAD data base, operated at CDS, Strasbourg, France, and the ARI Database for Nearby Stars, Astronomisches Rechen-Institut, Heidelberg. We thank Dr D. Barrado y Navascués for providing us with some additional candidates to our initial sample of late-type stars. We also thank the anonymous referee for suggesting several improvements and helpful comments. This work was supported by the Universidad Complutense de Madrid and the Spanish Dirección General de Enseñanza Superior e Investigación Científica (DGESIC) under grant PB97-0259., This is the first paper of a series aimed at studying the properties of late-type members of young stellar kinematic groups. We concentrate our study on classical young moving groups such as the Local Association (Pleiades moving group, 20-150 Myr), IC 2391 supercluster (35 Myr), Ursa Major group (Sirius supercluster, 300 Myr), and Hyades supercluster (600 Myr), as well as on recently identified groups such as the Castor moving group (200 Myr). In this paper we compile a preliminary list of single late-type possible members of some of these young stellar kinematic groups. Stars are selected from previously established members of stellar kinematic groups based on photometric and kinematic properties as well as from candidates based on other criteria such as their level of chromospheric activity, rotation rate and lithium abundance. Precise measurements of proper motions and parallaxes taken from the Hipparcos Catalogue, as well as from the Tycho-2 Catalogue, and published radial velocity measurements are used to calculate the Galactic space motions (U, V W) and to apply Eggen's kinematic criteria in order to determine the membership of the selected stars to the different groups. Additional criteria using age-dating methods for late-type stars will be applied in forthcoming papers of this series. A further study of the list of stars compiled here could lead to a better understanding of the chromospheric activity and their age evolution, as well as of the star formation history in the solar neighbourhood. In addition, these stars are also potential search targets for direct imaging detection of substellar companions., Universidad Complutense de Madrid (UCM), Dirección General de Enseñanza Superior e Investigación Científica (DGESIC), España, Ministerio de Educación, Cultura y Deporte (MECD), España, Depto. de Física de la Tierra y Astrofísica, Fac. de Ciencias Físicas, TRUE, pub

© ESO, 2016. This work was supported by the Spanish Ministerio de Economía y Competitividad under grant AYA2011-29754-C03-03., Context. Runaway O- and early B-type stars passing through the interstellar medium at supersonic velocities and characterized by strong stellar winds may produce bow shocks that can serve as particle acceleration sites. Previous theoretical models predict the production of high-energy photons by nonthermal radiative processes, but their efficiency is still debated. Aims. We aim to test and explain the possibility of emission from the bow shocks formed by runaway stars traveling through the interstellar medium by using previous theoretical models. Methods. We applied our model to AE Aurigae, the first reported star with an X-ray detected bow shock, to BD+43 3654, in which the observations failed in detecting high-energy emission, and to the transition phase of a supergiant star in the late stages of its life. Results. From our analysis, we confirm that the X-ray emission from the bow shock produced by AE Aurigae can be explained by inverse Compton processes involving the infrared photons of the heated dust. We also predict low high-energy flux emission from the bow shock produced by BD+43 3654, and the possibility of high-energy emission from the bow shock formed by a supergiant star during the transition phase from blue to red supergiant. Conclusions. Bow shocks formed by different types of runaway stars are revealed as a new possible source of high-energy photons in our neighborhood., Ministerio de Economía y Competitividad (MINECO), España, Depto. de Física de la Tierra y Astrofísica, Fac. de Ciencias Físicas, TRUE, pub

© 2012. The American Astronomical Society. All rights reserved. Printed in the U.S.A.This work was supported by the Spanish Government (AYA2011-30147-C03-02 and AYA2011-29754-C03-03). J.L.-S. thanks project AstroMadrid (S2009/ESP-1496) for partial support. G.E.R. and M.V.dV. were supported by PIP 0078 (CONICET) and PICT 2007-00848, Préstamo BID (ANPCyT). G.E.R. received additional support from the Spanish Ministerio de Innovación y Tecnología (AYA 2010-21782-C03-01). We thank the referee for useful comments and suggestions., Runaway stars produce shocks when passing through interstellar medium at supersonic velocities. Bow shocks have been detected in the mid-infrared for several high-mass runaway stars and in radio waves for one star. Theoretical models predict the production of high-energy photons by non-thermal radiative processes in a number sufficiently large to be detected in X-rays. To date, no stellar bow shock has been detected at such energies. We present the first detection of X-ray emission from a bow shock produced by a runaway star. The star is AE Aur, which was likely expelled from its birthplace due to the encounter of two massive binary systems and now is passing through the dense nebula IC 405. The X-ray emission from the bow shock is detected at 30" northeast of the star, coinciding with an enhancement in the density of the nebula. From the analysis of the observed X-ray spectrum of the source and our theoretical emission model, we confirm that the X-ray emission is produced mainly by inverse Compton upscattering of infrared photons from dust in the shock front., Comunidad de Madrid, Spanish Government, Ministerio de Innovación y Tecnología, CONICET, Préstamo BID (ANPCyT), Depto. de Física de la Tierra y Astrofísica, Fac. de Ciencias Físicas, TRUE, pub

© European Southern Observatory, Far ultraviolet emission lines in a sample of seven stars of spectral type later than F5 and different luminosity class have been analyzed to calculate the electron density and pressure in the formation region of the lines. Three different methods were used. We obtain electron pressures larger than solar for all dwarf stars of the sample. The low resolution observations were made with the IUE satellite., Depto. de Física de la Tierra y Astrofísica, Fac. de Ciencias Físicas, TRUE, pub

This article has been accepted for publication in Monthly notices of the Royal Astronomical Society © 2013 MNRAS. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved. MAL-G and JL-S acknowledge support by the Spanish Ministerio de Ciencía e Innovación under grant AYA2008-06423-C03-03. JFA-C is a researcher of the CONICET and acknowledges support by grant PICT 2007-02177 (SecyT). PGP-G acknowledges support from the Spanish Programa Nacional de Astronomía y Astrofísica under grants AYA2009-10368 and AYA2009-07723-E. We would like to acknowledge the anonymous referee for a fruitful discussion about the results of this work. His/her comments on the text content have allowed us to notoriously improve this manuscript., Nearby star-forming regions are ideal laboratories to study high-energy emission of different stellar populations, from very massive stars to brown dwarfs. NGC 2023 is a reflection nebula situated to the south of the Flame Nebula (NGC 2024) and at the edge of the H II region IC 434, which also contains the Horsehead Nebula (Barnard 33). NGC 2023, NGC 2024, Barnard 33 and the surroundings of the O-type supergiant star zeta Ori constitute the south part of the Orion B molecular complex. In this work, we present a comprehensive study of X-ray emitters in the region of NGC 2023 and its surroundings. We combine optical and infrared data to determine physical properties (mass, temperature, luminosity and the presence of accretion discs) of the stars detected in an XMM-Newton observation. This study has allowed us to analyse spectral energy distribution of these stars for the first time and determine their evolutionary stage. Properties of the X-ray emitting plasma of these stars are compared to those found in other nearby star-forming regions. The results indicate that the stars that are being formed in this region have characteristics, in terms of physical properties and luminosity function, similar to those found in the Taurus-Auriga molecular complex., Spanish Ministerio de Ciencía e Innovación, SecyT, Spanish Programa Nacional de Astronomía y Astrofísica, Depto. de Física de la Tierra y Astrofísica, Fac. de Ciencias Físicas, TRUE, pub

© 2015. The American Astronomical Society. The software used in this work was developed in part by the DOE-supported ASC/Alliance Center for Astrophysical Thermonuclear Flashes at the University of Chicago. HST data presented in this paper were obtained from MAST. STScI is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. Support for MAST for non-HST data is provided by the NASA Office of Space Science via grant NNX13AC07G and by other grants and contracts. This work was supported by the Spanish Government under research projects AYA2011-29754-C03-01 and AYA2011-29754-C03-03. M.O. and J.F.A-C. acknowledge support by the Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET, Argentina). Finally, we thank the referee for useful comments and suggestions., We investigate the plausibility of detecting X-ray emission from a stellar jet that impacts a dense molecular cloud, a scenario that may be typical for classical T Tauri stars with jets in dense star-forming complexes. We first model the impact of a jet against a dense cloud using two-dimensional axisymmetric hydrodynamic simulations, exploring different configurations of the ambient environment. Then, we compare our results with XMM-Newton observations of the Herbig-Haro object HH 248, where extended X-ray emission aligned with the optical knots is detected at the edge of the nearby IC 434 cloud. Our simulations show that a jet can produce plasma with temperatures up to 10^7 K, consistent with production of X-ray emission, after impacting a dense cloud. We find that jets denser than the ambient medium but less dense than the cloud produce detectable X-ray emission only at impact with the cloud. From an exploration of the model parameter space, we constrain the physical conditions (jet density and velocity and cloud density) that reproduce the intrinsic luminosity and emission measure of the X-ray source possibly associated with HH 248 well. Thus, we suggest that the extended X-ray source close to HH 248 corresponds to a jet impacting a dense cloud., National Aeronautics and Spacial Agency (NASA), EE.UU, Gobierno de España, Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET, Argentina), DOE-supported ASC/Alliance Center for Astrophysical Thermonuclear Flashes, University of Chicago (EE.UU), Depto. de Física de la Tierra y Astrofísica, Fac. de Ciencias Físicas, TRUE, pub

© ESO 2010. Part of this work was co-supported by the Spanish MICINN, Ministerio de Ciencia e Innovación project numbers: AYA2008- 00695 and AYA2008-06423-C03-03. J. López Santiago is a postdoctoral fellow of the ASTROCAM (Red de Astrofísica en la CAM) with project number S-0505/ESP/000237 of the IV PRICIT Plan Regional de Investigación Científica e Innovación Tecnológica de la Comunidad de Madrid. The authors would like to thank the referee for useful comments and suggestions that allowed us to improve our work., Aims. We present a compilation of spectroscopic data from a survey of 144 chromospherically active young stars in the solar neighborhood, which may be used to investigate different aspects of its formation and evolution in terms of kinematics and stellar formation history. The data have already been used by us in several studies. With this paper, we make all these data accessible to the scientific community for future studies on different topics. Methods. We performed spectroscopic observations with echelle spectrographs to cover the entirety of the optical spectral range simultaneously. Standard data reduction was performed with the IRAF echelle package. We applied the spectral subtraction technique to reveal chromospheric emission in the stars of the sample. The equivalent width of chromospheric emission lines was measured in the subtracted spectra and then converted to fluxes using equivalent width-flux relationships. Radial and rotational velocities were determined by the cross-correlation technique. Kinematics, equivalent widths of the lithium line lambda 6707.8 angstrom and spectral types were also determined. Results. A catalog of spectroscopic data is compiled: radial and rotational velocities, space motion, equivalent widths of optical chromospheric activity indicators from Ca II H & K to the calcium infrared triplet and the lithium line in lambda 6708 angstrom. Fluxes in the chromospheric emission lines and R(HK)' are also determined for each observation of a star in the sample. We used these data to investigate the emission levels of our stars. The study of the Ha emission line revealed two different populations of chromospheric emitters in the sample, clearly separated in the log F(H alpha)/F(bol) - (V - J) diagram. The dichotomy may be associated with the age of the stars., Spanish MICINN, Ministerio de Ciencia e Innovación, Depto. de Física de la Tierra y Astrofísica, Fac. de Ciencias Físicas, TRUE, pub

© 2009. The American Astronomical Society. All rights reserved. We are grateful to the anonymous referee, J. F. Albacete Colombo, and J. Sánz Forcada for helpful discussion and advice. Financial support was provided by the Universidad Complutense de Madrid, the Comunidad Autónoma de Madrid, the Spanish Ministerio Educación y Ciencia, and the European Social Fund under grants: AyA200502750, AyA2005-04286, AyA2005-24102-E, AyA2008-06423C03-03, AyA2008-00695, PRICITS-0505/ESP-0237, and CSD2006-0070. This research has made use of the SIMBAD, operated at Centre de Données astronomiques de Strasbourg, France, and the NASA's Astrophysics Data System., We used the Aladin Virtual Observatory tool and High Resolution Imager ROSAT archival data to search for X-ray variability in scale of days in 23 young stars in the sigma Orionis cluster and a background galaxy. Five stars displayed unambiguous flares and had probabilities p(var) >> 99% of being actual variables. Two of the detected flares were violent and long lasting, with maximum duration of six days and amplitude of eight times above the quiescent level. We classified another four stars as possible X-ray variables, including the binary system formed by the B2Vp star sigma Ori E and its close late-type companion. This makes a minimum frequency of high-amplitude X-ray variability in excess of a day of 39% among sigma Orionis stars. The incidence of this kind of X-ray variability seems to be lower among classical T Tauri stars with mid-infrared flux excesses than among fast-rotating, disk-less young stars., Universidad Complutense de Madrid, Comunidad Autónoma de Madrid, Spanish Ministerio Educación y Ciencia, European Social Fund, Depto. de Física de la Tierra y Astrofísica, Fac. de Ciencias Físicas, TRUE, pub

© European Southern Observatory. © 1993 EDP Sciencies. The authors acknowlege valuable discussion with and suggestion from Roberto Pallavicini. The Calar Alto Observatory is operated jointly by the Max-Planck-Institut für Astronomie (Heidelberg) and the Spanish Comisión Nacional de Astronomía. We thank the Calar Alto staff for their help during the observations. This work has been supported in part by the Universidad Complutense de Madrid., Observations of the Li i doublet at 6707.8 angstrom for a sample of active binary systems RS CVn and By Dra have been carried out at the Calar Alto Observatory with the 2.2 m telescope. In addition, some single stars with different chromospheric activity levels have also been observed mainly for comparison purposes. Gaussian fits have been performed in order to separate the Fe I line at 6707.4 angstrom which is usually blended with the Li I doublet. Once the fit was achieved, the equivalent width was measured for each separated line. The contributions due to the continuum from both components have been taken into account to correct the equivalent width measurements. A curve-of-growth method has been used to derive lithium abundances. We have obtained a Li excess in the binary systems, in particular the K type stars. A correlation of the Li abundance with the activity levels is confirmed, as it was found by other authors, but RS CVn and BY Dra systems are 0.5 dex more active than single stars for the same Li abundance., Universidad Complutense de Madrid (UCM), Depto. de Física de la Tierra y Astrofísica, Fac. de Ciencias Físicas, TRUE, pub

© 2015. The American Astronomical Society. All rights reserved. This research was partially supported by grant AYA2011-29754-C03-01 from the Government of Spain., In this work, we identify 63 bona fide new candidates to T Tauri stars (TTSs) in the Taurus-Auriga region, using its ultraviolet excess as our baseline. The initial data set was defined from the GALEX all sky survey (AIS). The GALEX satellite obtained images in the near-ultraviolet (NUV) and far-ultraviolet (FUV) bands where TTSs show a prominent excess compared with main-sequence or giants stars. GALEX AIS surveyed the Taurus-Auriga molecular complex, as well as a fraction of the California Nebula and the Perseus complex; bright sources and dark clouds were avoided. The properties of TTSs in the ultraviolet (GALEX), optical (UCAC4), and infrared (2MASS) have been defined using the TTSs observed with the International Ultraviolet Explorer reference sample. The candidates were identified by means of a mixed ultraviolet-optical-infrared excess set of colors; we found that the FUV-NUV versus J-K color-color diagram is ideally suited for this purpose. From an initial sample of 163,313 bona fide NUV sources, a final list of 63 new candidates to TTSs in the region was produced. The search procedure has been validated by its ability to detect all known TTSs in the area surveyed: 31 TTSs. Also, we show that the weak-lined TTSs are located in a well-defined stripe in the FUV-NUV versus J-K diagram. Moreover, in this work, we provide a list of TTSs photometric standards for future GALEX-based studies of the young stellar population in star forming regions., Government of Spain, Depto. de Física de la Tierra y Astrofísica, Fac. de Ciencias Físicas, TRUE, pub

© The Royal Astronomical Society. This work has been partially funded by the Ministry of Science and Innovation of Spain through grant: AYA2011-29754-C03-C01 and AYA2011-29754-C03-C03. This paper is based on data obtained by the NASA mission GALEX., The Taurus-Aurigamolecular complex (TMC) is the main laboratory for the study of low-mass star formation. The density and properties of interstellar dust are expected to vary across the TMC. These variations trace important processes such as dust nucleation or the magnetic field coupling with the cloud. In this paper, we show how the combination of near ultraviolet (NUV) and infrared (IR) photometry can be used to derive the strength of the 2175 Å bump and thus any enhancement in the abundance of small dust grains and polycyclic aromatic hydrocarbons in the dust grains size distribution. This technique is applied to the envelope of the TMC, mapped by the GALEXAll Sky Survey (AIS). Ultraviolet and IR photometric data have been retrieved from the GALEX-AIS and the 2MASS catalogues. NUV and K-band star counts have been used to identify the areas in the cloud envelope where the 2175 Å bump is weaker than in the diffuse interstellar medium namely, the low column density extensions of L1495, L1498 and L1524 in Taurus, L1545, L1548, L1519, L1513 in Auriga and L1482-83 in the California region. This finding agrees with previous results on dust evolution derived from Spitzer data and suggests that dust grains begin to decouple from the environmental Galactic magnetic field already in the envelope., Ministerio de Ciencia e Innovación (MCINN), España, Depto. de Física de la Tierra y Astrofísica, Fac. de Ciencias Físicas, TRUE, pub

The Gould Belt is the local superassociation of star formation. The age of the Belt is some few 10(7) yr, henceforth, its population is dominated by luminous young OB associations and low mass pre-main sequence stars. Attempts to unveil the low mass population have been run making use of the ROSAT all-sky survey. The all sky ultraviolet survey run by the GALaxy Evolution eXplorer (GALEX) maps several regions in the Belt. In this contribution, we present the preliminary analysis of the UV stellar population towards the Taurus region, one of the nearest and best studied regions of star formation., Ministerio de Ciencia e Innovación, Unidad Deptal. de Astronomía y Geodesia, Fac. de Ciencias Matemáticas, TRUE, pub

© European Southern Observatory. © EDP Sciencies The Isaac Newton Telescope, on the island of La Palma, is operated by the Royal Greenwich Observatory at the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias. We are grateful to the VILSPA staff for the use of their facil­ities. We thank Dr. R. González Riestra and Dr. J. Zamorano for help with IHAP use. The authors are indebted to an anonymous referee for his critical reading of the manuscript and valuable comments. This work has been supported by the Spanish Comisión Asesora de Investigación Científica y Técnica (CAICYT No. 2254/83)., We report here new Ca II H and K emission line fluxes and equivalent widths for seven RSCVn binary systems, observed at several orbital phases. All the stars show enhanced chromospheric activity. With information from available spectra, an in­ dividual study for each star has been done. Double emission has been found for some systems in which perhaps the hotter compo­nent could be the more active. We have tested spectroscopically the model of localized active regions for the prototype RSCVn., Comisión Asesora de Investigación Científica y Técnica (CAICYT), España, Comisión Interministerial de Ciencia y Tecnología (CICYT), España, Depto. de Física de la Tierra y Astrofísica, Fac. de Ciencias Físicas, TRUE, pub

© European Southern Observatory. The authors are very grateful to Dr. F.M. Walter for many valuable comments and suggestions., We have studied a sample of ten RS CVn systems by means of IUE high resolution long wavelength spectra. A general trend toward decreasing chromospheric activity (R_hk) for slower rotating stars has been found. Considering the R_hk values and their relation with structural parameters (T_eff, logg, log P_rot) we suggest that there are two pos­sible different activity levels. The less active systems have Rhk chromospheric activity levels similar to the single cool stars showing the same general trend. A relation between R_hk and the inverse Rossby number has been obtained, in which the RS CVn stars fill the gap found by Rucinski between W UMa and the main-sequence stars., Depto. de Física de la Tierra y Astrofísica, Fac. de Ciencias Físicas, TRUE, pub

© 2013. The American Astronomical Society. This work was supported by the Spanish Government (AYA2011-29754-C03-01 and AYA2011-29754-C03-03). C. S. P. was supported by the COSPAR Capacity Building Workshop Fellowship Program and the Universidad Nacional de La Plata to develop this work at the Universidad Complutense de Madrid. M. M. is supported through the ASI-INAF contract I/009/10/0. JFAC is a staff researcher of the CONICET and acknowledges support by grant PIP 2011 0100285. J.L.-S. would like to thank Drs. F. J. Carrera, P. G. Pérez González and S. Mateos for fruitful discussion on the spectral X-ray emission properties of AGN. We also acknowledges the referee of this manuscript for their suggestions and comments. Facilities: XMM-Newton (EPIC), Chandra (ACIS), Spitzer (IRAC, MIPS)., Protostellar jets appear at all stages of star formation when the accretion process is still at work. Jets travel at velocities of hundreds of km s^-1, creating strong shocks when interacting with the interstellar medium. Several cases of jets have been detected in X-rays, typically showing soft emission. For the first time, we report evidence of hard X-ray emission possibly related to non-thermal processes not explained by previous models of the post-shock emission predicted in the jet/ambient interaction scenario. HH 80 is located at the south head of the jet associated with the massive protostar IRAS 18162-2048. It shows soft and hard X-ray emission in regions that are spatially separated, with the soft X-ray emission region situated behind the region of hard X-ray emission. We propose a scenario for HH 80 where soft X-ray emission is associated with thermal processes from the interaction of the jet with denser ambient matter and hard X-ray emission is produced by synchrotron radiation at the front shock., Ministerio de Ciencia e Innovación (MCINN), España, Agenzia Spaziale Italiana (ASI), Istituto Nazionale di Astrofisica (INAF), Universidad Nacional de La Plata, Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Argentina, Depto. de Física de la Tierra y Astrofísica, Fac. de Ciencias Físicas, TRUE, pub

El objetivo principal del proyecto de innovación docente es reforzar las habilidades técnicas (soft skills) de los alumnos de astrofísica del Grado en Física y Matemáticas y del Máster en Astrofísica de la Facultad. De cara a los Trabajos Fin de Grado y a las asignaturas prácticas del Máster, consideramos necesario que los alumnos adquieran un dominio previo de ciertas herramientas para un mejor aprovechamiento de los contenidos y un desarrollo fructífero de los TFG y TFM. En particular, consideramos fundamental la familiarización con entornos UNIX, la capacidad de realizar programas básicos en Python para el tratamiento de datos astronómicos, el manejo de grandes bases de datos y la utilización de software libre para astronomía.

Para conocer la población estelar de las regiones de formación estelar, los estudios en infrarrojo son la herramienta perfecta para caracterizar el estado evolutivo de los objetos encontrados. Sin embargo, en estas longitudes de onda se encuentra que se pierde parte de la población, ya sea por estar muy absorbida o por que dejen de mostrar propiedades infrarrojas. Por ello, es necesario buscar un método complementario para revelar la población al completo. Los rayos X duros (> 1 ke V) atraviesan las nubes de gas y el polvo sin casi interaccionar con la materia debida a la pequea sección eficaz de estos últimos. Esto sumado a que los objetos estelares jóvenes muestran una intensa emisión en rayos X permite a los estudios combinados de IR y rayos X caracterizar las regiones de formación estelar en su totalidad. Un estudio combinando observaciones en rayos X, fotometría infrarroja y optica, se llevará a cabo para estudiar la población de NGC 2023 y de la Nube Molecular de Orión B. Los objetivos de este trabajo son: l. Realizar un estudio de la población estelar de NGC 2023, obteniendo las propiedades infrarrojas y de rayos X, así como sus parámetros estelares. 2. Realizar un estudio global de la población que compone la Nebulosa Molecular de Orión B. 3. Obtener la población estelar joven menos masiva, estudiando si exiten diferencias en el mecanismo de formación estelar, tanto a nivel individual dentro de la nebulosa de Orión B como en relación con los complejos vecinos. 4. Estudiar las propiedades infrarrojas y las propiedades coronales de las miembros de la Nube Molecular de Orión B. 5. Y estudiar la influencia de los distintos frentes de ionización que actúan en la nebulosa de Orión B y su influencia en la juventud de las fuentes que circundan..., To know the stellar population of star forming regions, IR studies are the perfect tool to characterize the evolutionary stage of the objects found. However, it is found that at these wavelengths part of the population is lost, because they are very absorbed or because they cease to show infrared properties. Therefore, it is necessary to look for a complementary method to relieve the entire population. As with radio-waves, hard X-rays (> 1 keV) pass through clouds of gas and dust without interacting with matter due to the effective section of the latter. This, coupled with the fact that young stellar objects show intense X-ray emission, allows combined IR and X-ray studies to characterize stellar regions revealing the entire population of the cloud. A study of this type, combining observations in X-rays, infrared and optical photometry will be carried out to study the population of NGC 2023 and Orion B. The main aims of this work are: 1. Perform a study of the stellar population of NGC 2023. Obtaining the infrared and X-ray properties, as well as their stellar parameters. 2. Perform a global study of the population that makes up the Orion B Molecular Cloud. 3. Reveal the less massive young stellar population, studying whether differences exist in the stellar formation mechanism, both individually within the Orion B nebula and in relation to neighboring complexes. 4. Study the infrared properties and coronal properties of the members of the cloud. 5. And to study the influence of the different ionizing fronts acting on the Orion B nebula and its influx in the youth of the surrounding fountains...

El objetivo de este trabajo es el estudio de los procesos de emisión no térmica que tienen lugar en los choques formados por diferentes objetos estelares. Para ello, partiendo de modelos anteriores, hemos elaborado un modelo no térmico capaz de explicar y reproducir dicha emisión. En primer lugar, se han estudiado las observaciones en rayos-X, infrarrojo y radio disponibles para diferentes choques producidos por la interacción del viento de estrellas masivas con el medio interestelar, y los datos observacionales se han comparado con los resultados de las simulaciones obtenidas a partir de nuestro modelo teórico, lo que ha permitido calcular el valor de los diferentes parámetros que intervienen en los choques. El modelo presentado en este trabajo tiene un carácter genérico. Por ello, hemos podido extender su uso a choques producidos por otros objetos estelares, como es el caso de la transición de supergigante azul a supergigante roja en las últimas fases evolutivas de algunas estrellas, en las que el choque es formado por la interacción de los vientos estelares expulsados en las fases posteriores a la secuencia principal. Para ello, hemos usado como referencia la estrella Betelgeuse y las simulaciones hidrodinámicas que sobre ella se han desarrollado. Posteriormente, hemos extendido el estudio de la emisión no térmica a los choques formados por las explosiones de supernova. Particularmente, hemos aplicado nuestro modelo al remanente de la supernova SN 1006 para intentar explicar los datos observacionales en altas energías (tanto rayos-X como rayos-gamma) que se tienen de ese objeto. Para ello hemos acoplado nuestro modelo a simulaciones MHD en 3D que describen la evolución de la supernova, para predecir la emisión no térmica y la compararla con los datos observacionales. Resultados y Conclusiones En esta tesis doctoral se ha podido confirmar, a partir del desarrollo de un modelo teórico, que la emisión en altas energías detectada en algunos choques formados por estre

Para conocer la población estelar de las regiones de formación estelar, los estudios en infrarrojo son la herramienta perfecta para caracterizar el estado evolutivo de los objetos encontrados. Sin embargo, en estas longitudes de onda se encuentra que se pierde parte de la población, ya sea por estar muy absorbida o por que dejen de mostrar propiedades infrarrojas. Por ello, es necesario buscar un método complementario para revelar la población al completo. Los rayos X duros (> 1 ke V) atraviesan las nubes de gas y el polvo sin casi interaccionar con la materia debida a la pequea sección eficaz de estos últimos. Esto sumado a que los objetos estelares jóvenes muestran una intensa emisión en rayos X permite a los estudios combinados de IR y rayos X caracterizar las regiones de formación estelar en su totalidad. Un estudio combinando observaciones en rayos X, fotometría infrarroja y optica, se llevará a cabo para estudiar la población de NGC 2023 y de la Nube Molecular de Orión B. Los objetivos de este trabajo son: l. Realizar un estudio de la población estelar de NGC 2023, obteniendo las propiedades infrarrojas y de rayos X, así como sus parámetros estelares. 2. Realizar un estudio global de la población que compone la Nebulosa Molecular de Orión B. 3. Obtener la población estelar joven menos masiva, estudiando si exiten diferencias en el mecanismo de formación estelar, tanto a nivel individual dentro de la nebulosa de Orión B como en relación con los complejos vecinos. 4. Estudiar las propiedades infrarrojas y las propiedades coronales de las miembros de la Nube Molecular de Orión B. 5. Y estudiar la influencia de los distintos frentes de ionización que actúan en la nebulosa de Orión B y su influencia en la juventud de las fuentes que circundan...

El objetivo de este trabajo es el estudio de los procesos de emisión no térmica que tienen lugar en los choques formados por diferentes objetos estelares. Para ello, partiendo de modelos anteriores, hemos elaborado un modelo no térmico capaz de explicar y reproducir dicha emisión. En primer lugar, se han estudiado las observaciones en rayos-X, infrarrojo y radio disponibles para diferentes choques producidos por la interacción del viento de estrellas masivas con el medio interestelar, y los datos observacionales se han comparado con los resultados de las simulaciones obtenidas a partir de nuestro modelo teórico, lo que ha permitido calcular el valor de los diferentes parámetros que intervienen en los choques. El modelo presentado en este trabajo tiene un carácter genérico. Por ello, hemos podido extender su uso a choques producidos por otros objetos estelares, como es el caso de la transición de supergigante azul a supergigante roja en las últimas fases evolutivas de algunas estrellas, en las que el choque es formado por la interacción de los vientos estelares expulsados en las fases posteriores a la secuencia principal. Para ello, hemos usado como referencia la estrella Betelgeuse y las simulaciones hidrodinámicas que sobre ella se han desarrollado. Posteriormente, hemos extendido el estudio de la emisión no térmica a los choques formados por las explosiones de supernova. Particularmente, hemos aplicado nuestro modelo al remanente de la supernova SN 1006 para intentar explicar los datos observacionales en altas energías (tanto rayos-X como rayos-gamma) que se tienen de ese objeto. Para ello hemos acoplado nuestro modelo a simulaciones MHD en 3D que describen la evolución de la supernova, para predecir la emisión no térmica y la compararla con los datos observacionales. Resultados y Conclusiones En esta tesis doctoral se ha podido confirmar, a partir del desarrollo de un modelo teórico, que la emisión en altas energías detectada en algunos choques formados por estre, The emission from shocks originated from the interaction of massive stars and supernova remnants with the interstellar medium shows that great amounts of energy are released in these processes and that a signi cant part of it is radiated as high-energy photons. In these shocks, protons and electrons are accelerated and emit photons when they cool down. If particle acceleration is e cient enough, the radiated photons can reach very high energies and be detected in X- and -rays. Objectives and methodology: The main objective of this work is to study the nonthermal emission processes that take place in shocks formed by di erent stellar objects. To do so, we have started from previous models to elaborate a nonthermal theoretical model able to explain and predict such emission. First, X-ray, infrared and radio observations have been studied for di erent shocks produced by the interaction of the stellar wind of massive stars with the interstellar medium, and the data have been compared to the results of our simulations, which permits to determine the physical parameters of the particles accelerated at the shock front. The model presented in this Thesis has a general approach. Thus, we also extended its application to the shocks produced by other stellar objects, as is the case of supergiant stars during the transition from blue to red supergiant at the late stages of some evolved stars, during which the shock is formed by the interaction of the stellar winds ejected in the post main-sequence stages. We used hydrodynamic simulations of Betelgeuse as a reference for our study...

Desde que en 1995 se descubriera el primer exoplaneta, la búsqueda de planetas alrededor de otras estrellas se ha convertido en uno de los campos con mayor productividad en Astrofísica, una auténtica cacería que ha dado como fruto cerca de 2000 nuevos mundos. La fauna planetaria descubierta presenta una diversidad nunca antes imaginada, tan amplia que ha llevado a replantear las teorías de formación de planetas, para poder explicar su existencia. La búsqueda de exoplanetas se ha centrado tradicionalmente en estrellas con niveles muy bajos de actividad. Los surveys de búsqueda de planetas descartaban de manera sistemática las estrellas activas y jóvenes, en favor de estrellas más viejas y menos activas. Esto introduce un importante sesgo observacional en los resultados, dejando sin explorar un importante régimen en el espacio de parámetros, imprescindible para ayudar a reconstruir los escenarios de formación y describir las etapas más tempranas de la evolución de los sistemas planetarios. Detectar planetas en estrellas jóvenes puede proporcionar una información muy valiosa de los mecanismos de formación y su escala temporal. Sin embargo, hay muy pocos planetas detectados en estrellas con edades menores de 100 millones de años. Esta Tesis doctoral se centra en el estudio de la estrella BD+ 20 1790, de tipo espectral K5Ve, excepcionalmente activa (log R′ HK=-3.7) y joven, con una edad estimada de 35-80 millones de años. En comparación con objetos del mismo tipo espectral, velocidad de rotación y rango de edad, BD+20 1790 presenta un nivel de actividad muy elevado, que se manifiesta en una plétora de fenómenos en todas las capas de la atmósfera. Mediante espectroscopía multilongitud de onda con alta resolución espectral y datos fotométricos de varias épocas, se ha podido determinar qué fenómenos ocurren en las distintas capas de la atmósfera de la estrella, su escala temporal y su intensidad. En la cromosfera se detectaron estructuras tipo protuberancia co-rotando con l, Since the first exoplanet was discovered in 1995, the search of planets around other stars has become one of the more productive fields in Astrophysics, a real "hunt" that has provided about 2000 new worlds. The planetary "zoo" found until now presents a diversity that could not be imagined before and that has led to reconsider planetary formation theories in order to explain their existence. The exoplanet searches have been centered traditionally in stars with low activity levels. Planet search surveys avoid systematically active and young stars, favoring older and less active ones. This introduces an important observational bias in the results, leaving unexplored an important parameter space, essential to aid in the formation scenario reconstruction and to describe the earliest stages of planetary systems evolution. Detecting planets in young stars can provide a valuable information about the migration processes or their atmosphere evolution. There is an important dearth of planets around stars with ages under 100 Million years. This PhDwork is focused in the study of BD+ 20 1790, a KV5e young star, exceptionally active (log R′ HK=-3.7), with an estimated age of 35-80 million years. In comparison with stars of similar spectral type, rotational velocity and age, BD+ 20 1790 presents a high activity level, that manifests in a plethora of phenomena in all atmospheric layers. Through an spectroscopic multiwavelength coverture of high resolution echelle spectra, and the analysis of photometric data obtained in several epochs, the different phenomena that occur in different layers of the star atmosphere could be determined, as well as their temporal scale and intensity. In the chromosphere, protuberance-like structures that co-rotate with the star have been detected, located in unstable latitudes far from the equatorial plane. Also plage emissions are found. From the photometric analysis, photospheric spots are detected with a spot filling factor of the stellar disc ran

In this work, we identify 63 bona fide new candidates to T Tauri stars (TTSs) in the Taurus-Auriga region using as baseline its ultraviolet excess. The initial data set has been defined from the GALEX all sky survey (AIS). The GALEX satellite obtained images in the near ultraviolet (NUV) and far ultraviolet (FUV) bands where the TTSs show a prominent excess, compared with main sequence or giants stars. GALEX AIS surveyed the Taurus-Auriga molecular complex, as well as, a fraction of the California Nebula and the Perseus complex; bright sources and the dark clouds themselves are avoided. The properties of the TTSs in the ultraviolet (GALEX), optical (UCAC4) and infrared (2MASS) have been defined using as qualification sample the TTSs observed with the International Ultraviolet Explorer. The candidates have been identified by means of a mixed ultraviolet-optical-infrared excess set of colors; it is found that the color-color diagram FUV-NUV versus J-K is ideally suited for this purpose. From an initial sample of 163,313 bona-fide NUV sources, a final list with 63 new candidates to TTSs in the region has been produced. The search procedure has been validated by its ability to detect all known TTSs in the area surveyed: 31 TTSs. Also, it is shown that the weak-lined TTSs are located in a well defined stripe in the FUV-NUV versus J-K diagram. Moreover, we provide in this work a list of TTSs photometric standards for future GALEX-based studies of the young stellar population in star forming regions., Gobierno de España, Depto. de Estadística e Investigación Operativa, Unidad Deptal. de Astronomía y Geodesia, Fac. de Ciencias Matemáticas, TRUE, pub

Desde que en 1995 se descubriera el primer exoplaneta, la búsqueda de planetas alrededor de otras estrellas se ha convertido en uno de los campos con mayor productividad en Astrofísica, una auténtica cacería que ha dado como fruto cerca de 2000 nuevos mundos. La fauna planetaria descubierta presenta una diversidad nunca antes imaginada, tan amplia que ha llevado a replantear las teorías de formación de planetas, para poder explicar su existencia. La búsqueda de exoplanetas se ha centrado tradicionalmente en estrellas con niveles muy bajos de actividad. Los surveys de búsqueda de planetas descartaban de manera sistemática las estrellas activas y jóvenes, en favor de estrellas más viejas y menos activas. Esto introduce un importante sesgo observacional en los resultados, dejando sin explorar un importante régimen en el espacio de parámetros, imprescindible para ayudar a reconstruir los escenarios de formación y describir las etapas más tempranas de la evolución de los sistemas planetarios. Detectar planetas en estrellas jóvenes puede proporcionar una información muy valiosa de los mecanismos de formación y su escala temporal. Sin embargo, hay muy pocos planetas detectados en estrellas con edades menores de 100 millones de años. Esta Tesis doctoral se centra en el estudio de la estrella BD+ 20 1790, de tipo espectral K5Ve, excepcionalmente activa (log R′ HK=-3.7) y joven, con una edad estimada de 35-80 millones de años. En comparación con objetos del mismo tipo espectral, velocidad de rotación y rango de edad, BD+20 1790 presenta un nivel de actividad muy elevado, que se manifiesta en una plétora de fenómenos en todas las capas de la atmósfera. Mediante espectroscopía multilongitud de onda con alta resolución espectral y datos fotométricos de varias épocas, se ha podido determinar qué fenómenos ocurren en las distintas capas de la atmósfera de la estrella, su escala temporal y su intensidad. En la cromosfera se detectaron estructuras tipo protuberancia co-rotando con l