WorldWideScience

Sample records for sun type stars

  1. Photometric Variations In The Sun And Solar-Type Stars

    Science.gov (United States)

    Giampapa, Mark

    The rich array of solar magnetic field-related phenomena we see occurs not only on stellar counterparts of our Sun but in stars that represent significant departures in their fundamental parameters from those of the Sun. Though these phenomena appear energetically negligible when compared to the total luminosity of stars, they nevertheless govern the angular momentum evolution and modulate the radiative and particle output of the Sun and late-type stars. The term "The Solar-Stellar Connection" has been coined to describe the solar-stellar synergisms in the investigation of the generation, emergence and coupling of magnetic fields with the outer solar-stellar atmosphere to produce what we broadly refer to as magnetic activity. With the discovery of literally thousands of planets beyond our solar system, the Solar-Stellar-Planet Connection is quickly emerging as a new area of investigation of the impacts of magnetic activity on exoplanet atmospheres. In parallel with this rapid evolution in our perspectives is the advent of transformative facilities for the study of the Sun and the dynamic Universe. The primary focus of this invited talk will be on photometric variations in solar-type stars and the Sun. These brightness variations are associated with thermal homogeneities typically defined by magnetic structures that are also spatially coincident with key radiative proxies. Photometric variability in solar-type stars and the Sun includes transient brightening, rotational modulation by cool spots and cycle-related variability, each with a characteristic signature in time and wavelength. The emphasis of this presentation will be on the relationship between broadband photometric variations and magnetic field-related activity in solar-type stars and the Sun. Facets of this topic will be discussed both retrospectively and prospectively as we enter a revolutionary, new era for astronomy.

  2. Stars resembling the Sun

    Science.gov (United States)

    Cayrel de Strobel, G.

    stars tightly neighbouring the Sun in mass, chemical composition and state of evolution. The surprising result is that the stars occupy in this HR Diagram a rather extended region around the Sun, many of them seem more evolved and older than the Sun, and only 4 of the evolved stars seem younger. The age of some stars in the sample is also discussed in terms of chromospheric activity and Li-content. Our conclusion is much the same as that contained in previous papers we have written on the subject: in spite of a much larger number of stars, we have not been able to nominate a single star of the sample for a ``perfect good solar twin''. Another aim in beginning, 25 years ago, this search for solar analogues, was to have ready a bunch of stars resembling the Sun and analysed spectroscopically in detail, in order that, when planets hunters of solar type stars, finally would have found such a specimen, we would have been able to immediately compare the physical parameters of this star to those of the Sun. We have been lucky enough: one of the good solar analogues we present herewith, is 51 Pegasi (HD 217014) which, according to the very recent observations by Mayor and Queloz (1995), has a planet orbiting around it. And what is more: two other stars possessing planets: 47 Ursae Majoris (HD 95128) and 70 Virginis (HD 117176), have just been discovered by Marcy and Butler (187th Meeting of the AAS, January 1996). One of them, 47 Ursae Majoris, is also included in the list of photometric solar analogues. The other star, 70 Virginis, has only been included after the ``Planets News'', because the colour index (B-V) of this star is slightly higher than the prescribted limit of the selection, (B-V = 0.71, instead, 0.69). It would have been a pity to leave the third '' planet star out of the competition.

  3. Transport Phenomena and Light Element Abundances in the Sun and Solar Type Stars

    CERN Document Server

    Vauclair, S

    2000-01-01

    The observations of light elements in the Sun and Solar type stars givespecial clues for understanding the hydrodynamical processes at work in stellarinteriors. In the Sun 7Li is depleted by 140 while 3He has not increased bymore than 10 0n 3 Gyrs. Meanwhile the inversion of helioseismic modes lead toa precision on the sound velocity of about .1The mixing processes below thesolar convection zone are constrained by these observations. Lithium isdepleted in most Pop I solar type stars. In halo stars however, the lithiumabundance seems constant in the "spite plateau" with no observed dispersion,which is difficult to reconcile with the theory of diffusion processes. In thepresent paper, the various relevant observations will be discussed. It will beshown that the mu-gradients induced by element settling may help solving the"lithium paradox".

  4. The sun, our star

    Science.gov (United States)

    Noyes, R. W.

    Observational data, analytical models, and instrumentation used to study the sun and its evolution are detailed, and attention is given to techniques for converting solar energy to useful power on earth. The star ignited when the mutual gravitational attractions of dust and vapor in a primordial cloud in the Galaxy caused an in-rush of accelerating particles which eventually became dense enough to ignite. The heat grew until inward rushing matter was balanced by outward moving radiative forces. The planets formed from similar debris, and solar radiation is suggested to have triggered the chemical reactions giving rise to life on earth. Visual, spectroscopic, coronagraphic, and UV observations of the sun from the ground and from spacecraft, particularly Skylab, are described, together with features of the solar surface, magnetic field, sunspots, and coronal loops. Models for the processes that occur in the solar interior are explored, as are the causes of solar flares. Attention is given to solar cells, heliostat arrays, wind turbines, and water turbines as means to convert, either directly or indirectly, the earth-bound solar energy to electrical and thermal power. Finally, the life cycle of the sun, about 9 billion yr in duration, is summarized, noting the current status of midlife.

  5. Ionization balance of Ti in the photospheres of the Sun and four late-type stars

    CERN Document Server

    Bergemann, Maria

    2011-01-01

    In this paper we investigate statistical equilibrium of Ti in the atmospheres of late-type stars. The Ti I/Ti II level populations are computed with available experimental atomic data, except for photoionization and collision induced transition rates, for which we have to rely on theoretical approximations. For the Sun, the NLTE line formation with adjusted H I inelastic collision rates and MAFAGS-OS model atmosphere solve the long-standing discrepancy between Ti I and Ti II lines. The NLTE abundances determined from both ionization stages agree within $0.01$ dex with each other and with the Ti abundance in C I meteorites. The Ti NLTE model does not perform similarly well for the metal-poor stars, overestimating NLTE effects in the atmospheres of dwarfs, but underestimating overionization for giants. Investigating different sources of errors, we find that only [Ti/Fe] ratios based on Ti II and Fe II lines can be safely used in studies of Galactic chemical evolution. To avoid spurious abundance trends with met...

  6. The Sun: Our Nearest Star

    Science.gov (United States)

    Adams, M. L.; Six, N. Frank (Technical Monitor)

    2002-01-01

    We have in our celestial backyard, a prime example of a variable star. The Sun, long thought to be "perfect" and unvarying, began to reveal its cycles in the early 1600s as Galileo Galilei and Christoph Scheiner used a telescope to study sunspots. For the past four hundred years, scientists have accumulated data, showing a magnetic cycle that repeats, on average, every eleven (or twenty-two) years. In addition, modern satellites have shown that the energy output at radio and x-ray wavelengths also varies with this cycle. This talk will showcase the Sun as a star and discuss how solar studies may be used to understand other stars.

  7. Basal Chromospheric Flux and Maunder Minimum-type Stars: The quiet-Sun Chromosphere as a Universal Phenomenon

    CERN Document Server

    Schroeder, K -P; Martinez, M I Perez; Cuntz, M; Schmitt, J H M M

    2012-01-01

    Aims: We demonstrate the universal character of the quiet-Sun chromosphere among inactive stars (solar-type and giants). By assessing the main physical processes, we shed new light on some common observational phenomena. Methods: We discuss measurements of the solar Mt. Wilson S-index, obtained by the Hamburg Robotic Telescope around the extreme minimum year 2009, and compare the established chromospheric basal Ca II K line flux to the Mt. Wilson S-index data of inactive ("flat activity") stars, including giants. Results: During the unusually deep and extended activity minimum of 2009, the Sun reached S-index values considerably deeper than in any of its previously observed minima. In several brief periods, the Sun coincided exactly with the S-indices of inactive ("flat", presumed Maunder Minimum-type) solar analogues of the Mt. Wilson sample; at the same time, the solar visible surface was also free of any plages or remaining weak activity regions. The corresponding minimum Ca II K flux of the quiet Sun and ...

  8. High resolution spectroscopy of two young active late type stars within 20 parsecs of the Sun

    Institute of Scientific and Technical Information of China (English)

    Hui-Juan Wang; Jian-Yan Wei

    2009-01-01

    We present high-resolution optical echell spectroscopy of HIP 544 and HIP 46843, two nearby solar like stars. The discovery of these young stars at such a close distance to the Sun is really a surprising phenomenon. It will help us to have a better understanding of the structure and evolutionary history of the Milky Way. The radial ve-locities (RV) of HIP 544 and HIP 46843 are measured to be -6.88±0.13km s-1 and 8.30±0.16km s-1, respectively, which are more accurate than before. The equivalent widths (EW) of the Li I 6707.8 A absorption line of HIP 544 and HIP 46843 are mea-sured to be 110±5mA and 195±5mA respectively. Based on these properties, HIP 544 is estimated to be 100-800Myr old and HIP 46843 30-100Myr old using three relatively creditable methods.

  9. Two sun-like superflare stars rotating as slow as the Sun*

    Science.gov (United States)

    Nogami, Daisaku; Notsu, Yuta; Honda, Satoshi; Maehara, Hiroyuki; Notsu, Shota; Shibayama, Takuya; Shibata, Kazunari

    2014-04-01

    We report on the results of high dispersion spectroscopy of two "superflare stars," KIC 9766237 and KIC 9944137 with Subaru/HDS. Superflare stars are G-type main sequence stars, but show gigantic flares compared to the Sun, which have recently been discovered in the data obtained with the Kepler spacecraft. Though most of these stars are thought to have a rotation period shorter than 10 d on the basis of photometric variabilities, the two targets of the present paper are estimated to have rotation periods of 21.8 d and 25.3 d. Our spectroscopic results clarified that these stars have stellar parameters similar to those of the Sun in terms of the effective temperature, surface gravity, and metallicity. The projected rotational velocities derived by us are consistent with the photometric rotation period, indicating a fairly high inclination angle. The average strength of the magnetic field on the surface of these stars are estimated to be 1-20 G, by using the absorption line of Ca II 8542. We could not detect any hint of binarity in our spectra, although more data are needed to firmly rule out the presence of an unseen low-mass companion. These results claim that the spectroscopic properties of these superflare stars are very close to those of the Sun, and support the hypothesis that the Sun might cause a superflare.

  10. Cartography of the sun and the stars

    CERN Document Server

    Neiner, Coralie

    2016-01-01

    The mapping of the surface of stars requires diverse skills, analysis techniques and advanced modeling, i.e. the collaboration of scientists in various specialties. This volume gives insights into new techniques allowing for the first time to obtain resolved images of stars. It takes stock of what has been achieved so far in Chile, on the ESO VLTI instrument or, in the States, on the CHARA instrument. In recent times interferometry, combined with adaptive optics has allowed to reconstruct images of stars. Besides the Sun (of course) by now five stars have been resolved in detail. In addition to interferometry, this book highlights techniques used for mapping the surfaces of stars using photometry made by space observatories; Zeeman- and Doppler Imaging; mapping the surface element abundances via spectroscopy. This book will also take stock of the best images of the  solar surface, made by connecting the differential rotation to the underlying physical parameters derived from helioseismology. Recent measureme...

  11. Observing the Sun with NuSTAR

    Science.gov (United States)

    Kohler, Susanna

    2016-07-01

    The Nuclear Spectroscopic Telescope Array (NuSTAR) is a space telescope primarily designed to detect high-energy X-rays from faint, distant astrophysical sources. Recently, however, its occasionally been pointing much closer to home, with the goal of solving a few longstanding mysteries about the Sun.Intensity maps from an observation of a quiet-Sun region near the north solar pole and an active region just below the solar limb. The quiet-Sun data will be searched for small flares that could be heating the solar corona, and the high-altitude emission above the limb may provide clues about particle acceleration. [Adapted from Grefenstette et al. 2016]An Unexpected TargetThough we have a small fleet of space telescopes designed to observe the Sun, theres an important gap: until recently, there was no focusing telescope making solar observations in the hard X-ray band (above ~3 keV). Conveniently, there is a tool capable of doing this: NuSTAR.Though NuSTARs primary mission is to observe faint astrophysical X-ray sources, a team of scientists has recently conducted a series of observations in which NuSTAR was temporarily repurposed and turned to focus on the Sun instead.These observations pose an interesting challenge precisely because of NuSTARs extreme sensitivity: pointing at such a nearby, bright source can quickly swamp the detectors. But though the instrument cant be used to observe the bright flares and outbursts from the Sun, its the perfect tool for examining the parts of the Sun weve been unable to explore in hard X-rays before now such as faint flares, or the quiet, inactive solar surface.In a recently published study led by Brian Grefenstette (California Institute of Technology), the team describes the purpose and initial results of NuSTARs first observations of the Sun.Solar MysteriesWhat is NuSTAR hoping to accomplish with its solar observations? There are two main questions that hard X-ray observations may help to answer.How are particles accelerated in

  12. Description of the Sun as a Star: General Physical Characteristics

    Science.gov (United States)

    Kucera, Theresa; Crannell, Carol Jo

    2000-01-01

    Numerical parameters characterizing the size and energy output of the sun are presented. These values are the standard yardstick by which other stars are measured. The large number of significant digits tabulated here serve mainly to illustrate the precision to which these parameters are known. Also listed are parameters characterizing the earth's orbit around the sun and the intensity of the sun's radiation at the mean orbital distance. The appearance of the sun depends critically on how it is observed. Each type of radiation observed carries specific information about the physical processes at work on the sun. Special types of instruments reveal aspects otherwise invisible. Coronagraphs reveal the dimmer outer regions of the sun's atmosphere otherwise visible only during total solar eclipses. Spectroscopy can reveal motions, magnetic field strengths, temperatures and densities. In situ measurements have revealed the characteristics of the solar wind and extended our knowledge of the solar magnetic field both near the earth and beyond the orbits of the planets. As an example, the sun's disk observed almost simultaneously in six different wavelengths of light is shown. In visible light we can see the white disk of the sun with the dark spots known as sunspots. By analyzing the spectral lines produced by the sun we can measure the strength of the sun's magnetic field at its surface, producing a magnetogram. This magnetogram reveals that the sunspots are regions of intense magnetic field. Further images of the sun reveal that the sunspot regions are just the bases of systems of hot loops which emit radio-waves, ultraviolet light and X-rays. The sun imaged in a spectral line of hydrogen known as "H alpha" is shown. In this line we also see the long dark "filaments". These filaments form in long channels between areas of opposing magnetic field. Such channels can be seen in the ultraviolet image. Data concerning the sun are obtained with many different kinds of

  13. Two Sun-like Superflare Stars Rotating as Slow as the Sun

    CERN Document Server

    Nogami, Daisaku; Honda, Satoshi; Maehara, Hiroyuki; Notsu, Shota; Shibayama, Takuya; Shibata, Kazunari

    2014-01-01

    We report on the results of high dispersion spectroscopy of two `superflare stars', KIC 9766237, and KIC 9944137 with Subaru/HDS. Superflare stars are G-type main sequence stars, but show gigantic flares compared to the Sun, which have been recently discovered in the data obtained with the Kepler spacecraft. Though most of these stars are thought to have a rotation period shorter than 10 days on the basis of photometric variabilities, the two targets of the present paper are estimated to have a rotation period of 21.8 d, and 25.3 d. Our spectroscopic results clarified that these stars have stellar parameters similar to those of the Sun in terms of the effective temperature, surface gravity, and metallicity. The projected rotational velocities derived by us are consistent with the photometric rotation period, indicating a fairy high inclination angle. The average strength of the magnetic field on the surface of these stars are estimated to be 1-20 G, by using the absorption line of Ca II 8542. We could not det...

  14. Astrobiologically Interesting Stars within 10 parsecs of the Sun

    CERN Document Server

    De Mello, G F P; Ghezzi, L

    2006-01-01

    The existence of life based on carbon chemistry and water oceans relies upon planetary properties, chiefly climate stability, and stellar properties, such as mass, age, metallicity and Galactic orbits. The latter can be well constrained with present knowledge. We present a detailed, up-to-date compilation of the atmospheric parameters, chemical composition, multiplicity and degree of chromospheric activity for the astrobiologically interesting solar-type stars within 10 parsecs of the Sun. We determine their state of evolution, masses, ages and space velocities, and produce an optimized list of candidates that merit serious scientific consideration by the future space-based interferometry probes aimed at directly detecting Earth-sized extrasolar planets and seeking spectroscopic infrared biomarkers as evidence of photosynthetic life. The initially selected stars number 33 solar-type within the population of 182 stars (excluding late M-dwarfs) closer than 10 pc. A comprehensive and detailed data compilation fo...

  15. A non-LTE study of neutral and singly-ionized iron line spectra in 1D models of the Sun and selected late-type stars

    CERN Document Server

    Mashonkina, L; Shi, J -R; Korn, A J; Grupp, F

    2011-01-01

    A comprehensive model atom for Fe with more than 3000 energy levels is presented. As a test and first application of this model atom, Fe abundances are determined for the Sun and five stars with well determined stellar parameters and high-quality observed spectra. Non-LTE leads to systematically depleted total absorption in the Fe I lines and to positive abundance corrections in agreement with the previous studies, however, the magnitude of non-LTE effect is smaller compared to the earlier results. Non-LTE corrections do not exceed 0.1 dex for the solar metallicity and mildly metal-deficient stars, and they vary within 0.21 dex and 0.35 dex in the very metal-poor stars HD 84937 and HD 122563, respectively, depending on the assumed efficiency of collisions with hydrogen atoms. Based on the analysis of the Fe I/Fe II ionization equilibrium in these two stars, we recommend to apply the Drawin formalism in non-LTE studies of Fe with a scaling factor of 0.1. For the Fe II lines, non-LTE corrections do not exceed 0...

  16. Sun and Other Types of Radiation

    Science.gov (United States)

    ... What Causes Cancer? Sun and Other Types of Radiation Learn about the different types of radiation and ... other diseases. Learn more here. Other Types of Radiation Exposure Not all types of radiation have been ...

  17. AsteroFLAG - from the Sun to the stars

    Energy Technology Data Exchange (ETDEWEB)

    Chaplin, W J; Elsworth, Y [School of Physics and Astronomy, University of Birmingham, Edgbaston, Birmingham, B15 2TT (United Kingdom); Appourchaux, T; Baudin, F [Institut d' Astrophysique Spatiale (IAS), Batiment 121, F-91405, Orsay Cedex (France); Arentoft, T; Christensen-Dalsgaard, J; Kjeldsen, H [Department of Physics and Astronomy, University of Aarhus, DK-8000 Aarhus C (Denmark); Ballot, J [Max-Planck-Institut fuer Astrophysik, Karl-Schwarzschild-Str. 1, Postfach 1317, 85741, Garching (Germany); Bazot, M [Centro de AstrofIsica Universidade do Porto, 4150-762 Porto (Portugal); Bedding, T R [School of Physics, University of Sydney, Sydney, NSW 2006 (Australia); Creevey, O L [High Altitude Observatory, National Center for Atmospheric Research, Boulder, CO 80301 (United States); Duez, V; Garcia, R A [DAPNIA/CEA, CE Saclay, FR-91191 Gif-sur-Yvette Cedex (France); Fletcher, S T [Faculty of Arts, Computing, Engineering and Sciences, Sheffield Hallam University, Sheffield S1 1WB (United Kingdom); Gough, D O; Houdek, G [Institute of Astronomy, University of Cambridge, Cambridge CB3 0HA (United Kingdom); Jimenez, A; Jimenez-Reyes, S J [Instituto de Astrofisica de Canarias, E-38200, La Laguna, Tenerife (Spain); Lazrek, M [LPHEA, Faculte des Sciences Semlalia, Universite Cadi Ayyad, Marrakech (Morocco); Leibacher, J W, E-mail: w.j.chaplin@bham.ac.uk (and others)

    2008-10-15

    We stand on the threshold of a critical expansion of asteroseismology of Sun-like stars, the study of stellar interiors by observation and analysis of their global acoustic modes of oscillation. The Sun-like oscillations give a very rich spectrum allowing the internal structure and dynamics to be probed down into the stellar cores to very high precision. Asteroseismic observations of many stars will allow multiple-point tests of crucial aspects of stellar evolution and dynamo theory. The aims of the asteroFLAG collaboration are to help the community to refine existing, and to develop new, methods for analysis of the asteroseismic data on the Sun-like oscillators.

  18. Grand Challenges in the Physics of the Sun and Sun-like Stars

    CERN Document Server

    Thompson, Michael J

    2014-01-01

    The study of stellar structure and evolution is one of the main building blocks of astrophysics, and the Sun has an importance both as the star that is most amenable to detailed study and as the star that has by far the biggest impact on the Earth and near-Earth environment through its radiative and particulate outputs. Over the past decades, studies of stars and of the Sun have become somewhat separate. But in recent years, the rapid advances in asteroseismology, as well as the quest to better understand solar and stellar dynamos, have emphasized once again the synergy between studies of the stars and the Sun. In this article I have selected two "grand challenges" both for their crucial importance and because I thnk that these two problems are tractable to significant progress in the next decade. They are (i) understanding how solar and stellar dynamos generate magnetic field, and (ii) improving the predictability of geo-effective space weather.

  19. The Sun: A Star at the Center of Our Solar System

    Science.gov (United States)

    Adams, Mitzi L.

    2016-01-01

    There is a star at the center of our solar system! But what is a star? How do stars work? What are the characteristics of our Sun and how are these traits different from other stars? How does the Sun compare to stars such as Betelgeuse and Rigel? "Will the Sun end its life with a bang or a whimper?"

  20. Mass Ejection from Old and Young Stars and the Sun

    Science.gov (United States)

    Jatenco-Pereira, V.; Opher, R.

    1990-11-01

    RESUMEN. Para poder explicar: 1) la enorme cantidad de perdida de masa y la baja velocidad asint5tica de las estrellas gigantes de o, y 2) los flujos de masa observados en protoestrellas, se sugiere un modelo para Ia perdida de masa, en donde se usa un flujo de ondas de Alfvencomo un mecanismo de aceleraci6n para los vientos de estrellas de tipo y vientos en protoestrellas. Se estudian los mecanismos de disipaci5n de las ondas de Alfven: los amortiguamientos no lineal, de superficie reso- nante y turbulento. En nuestro modelo se usa una divergente A(r) = A(R0) (r/r0)5 (donde A(r) es el area a una distancia radial r, y (A(r)/r2)max/(A(ro)/r02 - 10). Tambien se sugiere un modelo para una de hoyo coronal en el Sol. Se muestra que para satisfacer los datos observacionales en el Sol, tomando en cuenta la deposici6n del momento de las ondas de Alfven sobre el viento, se necesita: (a) una divergencia lenta en un hoyo coronal hasta una altura de 0.01 - 0.1 R seguido de (b) una divergencia rap ida de hasta una altura aproximada de 1 R . ABSTRACT: In order to explain (1) a large mass-loss rate and a small asymptotic flow speed of late-type giant stars and (2) the observed protostellar mass outflows, we suggest a model for mass loss, where we use a flux of Alfven waves as a mechanism of acceleration for late-type giant star winds and protostellar winds. We study the Alfven wave dissipation mechanisms: nonlinear damping, resonant surface damping, and turbulent damping. In our model we use a diverging geometry A(r) = A(r0) (r I r )S (where A(r) is the cross sectional area of the geometry at a radial distance r, and(A(r) I r2)max/(A(r0)/r02) = 10). We also suggest a model for a coronal hole geometry in the sun. We show that in order to satisfy the observational data of the sun, taking into account Alfven wave momentum deposition in the wind, we need: (a) a slow divergence in a coronal hole up t6 a height of 0.01 - 0.1 followed by (b) a rapid divergence up to a height of

  1. New Suns in the Cosmos II: Differential rotation in $Kepler$ Sun-like stars

    CERN Document Server

    Chagas, M L Das; Costa, A D; Lopes, C E Ferreira; Sobrinho, R Silva; Paz-Chinchón, F; Leão, I C; Valio, A; de Freitas, D B; Martins, B L Canto; Lanza, A F; De Medeiros, J R

    2016-01-01

    The present study reports the discovery of Sun-like stars, namely main-sequence stars with $T_{\\rm eff}$, $\\log g$ and rotation periods $P_{rot}$ similar to solar values, presenting evidence of surface differential rotation. An autocorrelation of the time series was used to select stars presenting photometric signal stability from a sample of 881 stars with light curves collected by the $Kepler$ space-borne telescope, in which we have identified 17 stars with stable signals. A simple two-spot model together with a Bayesian information criterion were applied to these stars in the search for indications of differential rotation; in addition, for all 17 stars, it was possible to compute the spot rotation period $P$, the mean values of the individual spot rotation periods and their respective colatitudes, and the relative amplitude of the differential rotation.

  2. New Suns in the Cosmos II: differential rotation in Kepler Sun-like stars

    Science.gov (United States)

    Das Chagas, M. L.; Bravo, J. P.; Costa, A. D.; Ferreira Lopes, C. E.; Silva Sobrinho, R.; Paz-Chinchón, F.; Leão, I. C.; Valio, A.; de Freitas, D. B.; Canto Martins, B. L.; Lanza, A. F.; De Medeiros, J. R.

    2016-12-01

    The present study reports the discovery of Sun-like stars, namely main-sequence stars with Teff, log g and rotation periods Prot similar to solar values, presenting evidence of surface differential rotation (DR). An autocorrelation of the time series was used to select stars presenting photometric signal stability from a sample of 881 stars with light curves collected by the Kepler space-borne telescope, in which we have identified 17 stars with stable signals. A simple two-spot model together with a Bayesian information criterion were applied to these stars in the search for indications of DR; in addition, for all 17 stars, it was possible to compute the spot rotation period P, the mean values of the individual spot rotation periods and their respective colatitudes, and the relative amplitude of the DR.

  3. Nearest star the surprising science of our sun

    CERN Document Server

    Golub, Leon

    2014-01-01

    How did the Sun evolve, and what will it become? What is the origin of its light and heat? How does solar activity affect the atmospheric conditions that make life on Earth possible? These are the questions at the heart of solar physics, and at the core of this book. The Sun is the only star near enough to study in sufficient detail to provide rigorous tests of our theories and help us understand the more distant and exotic objects throughout the cosmos. Having observed the Sun using both ground-based and spaceborne instruments, the authors bring their extensive personal experience to this sto

  4. Are the majority of Sun-like stars single?

    CERN Document Server

    Whitworth, A P

    2015-01-01

    It has recently been suggested that, in the field, $\\sim\\!\\!56\\%$ of Sun-like stars ($0.8\\,{\\rm M}_{_\\odot}\\lesssim M_\\star\\lesssim 1.2\\,{\\rm M}_{_\\odot}$) are single. We argue here that this suggestion may be incorrect, since it appears to be based on the multiplicity frequency of systems with Sun-like primaries, and therefore takes no account of Sun-like stars that are secondary (or higher-order) components in multiple systems. When these components are included in the reckoning, it seems likely that only $\\sim\\!46\\%$ of Sun-like stars are single. This estimate is based on a model in which the system mass function has the form proposed by Chabrier, with a power-law Salpeter extension to high masses; there is a flat distribution of mass ratios; and the probability that a system of mass $M$ is a binary is $\\,0.50 + 0.46\\log_{_{10}}\\!\\left(M/{\\rm M}_{_\\odot}\\right)\\,$ for $\\,0.08\\,{\\rm M}_{_\\odot}\\leq M\\leq 12.5\\,{\\rm M}_{_\\odot}$, $\\,0\\,$ for $\\,M12.5\\,{\\rm M}_{_\\odot}$. The constants in this last relation ar...

  5. The Sun. A typical star in the solar neighborhood?

    CERN Document Server

    Melendez, Jorge

    2013-01-01

    The Sun is used as the fundamental standard in chemical abundance studies, thus it is important to know whether the solar abundance pattern is representative of the solar neighborhood. Albeit at low precision (0.05 - 0.10 dex) the Sun seems to be a typical solar-metallicity disk star, at high precision (0.01 dex) its abundance pattern seems abnormal when compared to solar twins. The Sun shows a deficiency of refractory elements that could be due to the formation of terrestrial planets. The formation of giant planets may also introduce a signature in the chemical composition of stars. We discuss both planet signatures and also the enhancement of neutron-capture elements in the solar twin 18 Sco.

  6. Asteroseismology from multi-month Kepler photometry: the evolved Sun-like stars KIC 10273246 and KIC 10920273

    NARCIS (Netherlands)

    T.L. Campante; R. Handberg; S. Mathur; T. Appourchaux; T.R. Bedding; W.J. Chaplin; B. Mosser; O. Benomar; A. Bonanno; E. Corsaro; S.T. Fletcher; P. Gaulme; S. Hekker; C. Karoff; D. Salabert; G.A. Verner; T.R. White; G. Houdek; I.M. Brandao; O.L. Creevey; G. Dogan; M. Bazot; J. Christensen-Dalsgaard; M.S. Cunha; Y. Elsworth; D. Huber; H. Kjeldsen; M. Lundkvist; J. Molenda-Zakowicz; M.J.P.F.G. Monteiro; D. Stello; B.D. Clarke; F.R. Girouard; J.R. Hall; R.A. Garcia; C. Regulo

    2011-01-01

    Context. The evolved main-sequence Sun-like stars KIC 10273246 (F-type) and KIC 10920273 (G-type) were observed with the NASA Kepler satellite for approximately ten months with a duty cycle in excess of 90%. Such continuous and long observations are unprecedented for solar-type stars other than the

  7. Spectrometer for Sky-Scanning Sun-Tracking Atmospheric Research (4STAR: Instrument Technology

    Directory of Open Access Journals (Sweden)

    Yohei Shinozuka

    2013-08-01

    Full Text Available The Spectrometer for Sky-Scanning, Sun-Tracking Atmospheric Research (4STAR combines airborne sun tracking and sky scanning with diffraction spectroscopy to improve knowledge of atmospheric constituents and their links to air-pollution/climate. Direct beam hyper-spectral measurement of optical depth improves retrievals of gas constituents and determination of aerosol properties. Sky scanning enhances retrievals of aerosol type and size distribution. 4STAR measurements will tighten the closure between satellite and ground-based measurements. 4STAR incorporates a modular sun-tracking/ sky-scanning optical head with fiber optic signal transmission to rack mounted spectrometers, permitting miniaturization of the external optical head, and future detector evolution. Technical challenges include compact optical collector design, radiometric dynamic range and stability, and broad spectral coverage. Test results establishing the performance of the instrument against the full range of operational requirements are presented, along with calibration, engineering flight test, and scientific field campaign data and results.

  8. The Colorful Demise of a Sun-like Star

    Science.gov (United States)

    2007-01-01

    This image, taken by NASA's Hubble Space Telescope, shows the colorful 'last hurrah' of a star like our Sun. The star is ending its life by casting off its outer layers of gas, which formed a cocoon around the star's remaining core. Ultraviolet light from the dying star makes the material glow. The burned-out star, called a white dwarf, is the white dot in the center. Our Sun will eventually burn out and shroud itself with stellar debris, but not for another 5 billion years. Our Milky Way Galaxy is littered with these stellar relics, called planetary nebulae. The objects have nothing to do with planets. Eighteenth- and nineteenth-century astronomers named them planetary nebulae because through small telescopes they resembled the disks of the distant planets Uranus and Neptune. The planetary nebula in this image is called NGC 2440. The white dwarf at the center of NGC 2440 is one of the hottest known, with a surface temperature of nearly 400,000 degrees Fahrenheit (200,000 degrees Celsius). The nebula's chaotic structure suggests that the star shed its mass episodically. During each outburst, the star expelled material in a different direction. This can be seen in the two bow tie-shaped lobes. The nebula also is rich in clouds of dust, some of which form long, dark streaks pointing away from the star. NGC 2440 lies about 4,000 light-years from Earth in the direction of the constellation Puppis. The image was taken Feb. 6, 2007 with Hubble's Wide Field Planetary Camera 2. The colors correspond to material expelled by the star. Blue corresponds to helium; blue-green to oxygen; and red to nitrogen and hydrogen.

  9. Photometric Variability in Kepler Target Stars: The Sun Among Stars -- A First Look

    CERN Document Server

    Basri, Gibor; Batalha, Natalie; Gilliland, Ronald L; Jenkins, Jon; Borucki, William J; Koch, David; Caldwell, Doug; Dupree, Andrea K; Latham, David W; Meibom, Soeren; Howell, Steve; Brown, Tim

    2010-01-01

    The Kepler mission provides an exciting opportunity to study the lightcurves of stars with unprecedented precision and continuity of coverage. This is the first look at a large sample of stars with photometric data of a quality that has heretofore been only available for our Sun. It provides the first opportunity to compare the irradiance variations of our Sun to a large cohort of stars ranging from vary similar to rather different stellar properties, at a wide variety of ages. Although Kepler data is in an early phase of maturity, and we only analyze the first month of coverage, it is sufficient to garner the first meaningful measurements of our Sun's variability in the context of a large cohort of main sequence stars in the solar neighborhood. We find that nearly half of the full sample is more active than the active Sun, although most of them are not more than twice as active. The active fraction is closer to a third for the stars most similar to the Sun, and rises to well more than half for stars cooler t...

  10. HARPS-N observes the Sun as a star

    CERN Document Server

    Dumusque, Xavier; Phillips, David F; Buchschacher, Nicolas; Cameron, Andrew Collier; Cecconi, Massimo; Charbonneau, David; Cosentino, Rosario; Ghedina, Adriano; Latham, David W; Li, Chih-Hao; Lodi, Marcello; Lovis, Christophe; Molinari, Emilio; Pepe, Francesco; Udry, Stephane; Sasselov, Dimitar; Szentgyorgyi, Andrew; Walsworth, Ronald

    2015-01-01

    Radial velocity perturbations induced by stellar surface inhomogeneities including spots, plages and granules currently limit the detection of Earth-twins using Doppler spectroscopy. Such stellar noise is poorly understood for stars other than the Sun because their surface is unresolved. In particular, the effects of stellar surface inhomogeneities on observed stellar radial velocities are extremely difficult to characterize, and thus developing optimal correction techniques to extract true stellar radial velocities is extremely challenging. In this paper, we present preliminary results of a solar telescope built to feed full-disk sunlight into the HARPS-N spectrograph, which is in turn calibrated with an astro-comb. This setup enables long-term observation of the Sun as a star with state-of-the-art sensitivity to radial velocity changes. Over seven days of observing in 2014, we show an average 50\\cms radial velocity rms over a few hours of observation. After correcting observed radial velocities for spot and...

  11. Magnetic cycles of Sun-like stars with different levels of coronal and chromospheric activity — comparison with the Sun

    Science.gov (United States)

    Shimanovskaya, Elena; Bruevich, Vasiliy; Bruevich, Elena

    2016-09-01

    The atmospheric activity of the Sun and Sun-like stars is analyzed involving observations from the HK-project at the Mount Wilson Observatory, the California and Carnegie Planet Search Program at the Keck and Lick Observatories and the Magellan Planet Search Program at the Las Campanas Observatory. We show that for stars of F, G and K spectral classes, the cyclic activity, similar to the 11-yr solar cycle, is different: it becomes more prominent in K-stars. Comparative study of Sun-like stars with different levels of chromospheric and coronal activity confirms that the Sun belongs to stars with a low level of chromospheric activity and stands apart among these stars by its minimum level of coronal radiation and minimum level of variations in photospheric flux.

  12. Magnetic cycles of Sun-like stars with different levels of coronal and chromospheric activity -- comparison with the Sun

    CERN Document Server

    Bruevich, E A; Shimanovskaya, E V

    2016-01-01

    The atmospheric activity of the Sun and Sun-like stars is analyzed involving observations from HK-project at the Mount Wilson Observatory, the California and Carnegie Planet Search Program at the Keck and Lick Observatories and the Magellan Planet Search Program at the Las Campanas Observatory. We show that for stars of F, G and K spectral classes, the cyclic activity, similar to the 11-yr solar cycles, is different: it becomes more prominent in K-stars. Comparative study of Sun-like stars with different levels of the chromospheric and coronal activity confirms that the Sun belongs to stars with the low level of the chromospheric activity and stands apart among these stars by the minimum level of its coronal radiation and the minimum level of its variations of the photospheric flux.

  13. Challenges for asteroseismic analysis of Sun-like stars

    CERN Document Server

    Chaplin, W J; Appourchaux, T; Elsworth, Y; New, R; Toutain, T

    2008-01-01

    Asteroseismology of Sun-like stars is undergoing rapid expansion with, for example, new data from the CoRoT mission and continuation of ground-based campaigns. There is also the exciting upcoming prospect of NASA's Kepler mission, which will allow the asteroseismic study of several hundred Sun-like targets, in some cases for periods lasting up to a few years. The seismic mode parameters are the input data needed for making inference on stars and their internal structures. In this paper we discuss the ease with which it will be possible to extract estimates of individual mode parameters, dependent on the mass, age, and visual brightness of the star. Our results are generally applicable; however, we look at mode detectability in the context of the upcoming Kepler observations. To inform our discussions we make predictions of various seismic parameters. To do this we use simple empirical scaling relations and detailed pulsation computations of the stochastic excitation and damping characteristics of the Sun-like...

  14. A Solar cycle correlation of coronal element abundances in Sun-as-a-star observations

    Science.gov (United States)

    Brooks, David H.; Baker, Deborah; van Driel-Gesztelyi, Lidia; Warren, Harry P.

    2017-08-01

    The elemental composition in the coronae of low-activity solar-like stars appears to be related to fundamental stellar properties such as rotation, surface gravity, and spectral type. Here we use full-Sun observations from the Solar Dynamics Observatory, to show that when the Sun is observed as a star, the variation of coronal composition is highly correlated with a proxy for solar activity, the F10.7 cm radio flux, and therefore with the solar cycle phase. Similar cyclic variations should therefore be detectable spectroscopically in X-ray observations of solar analogs. The plasma composition in full-disk observations of the Sun is related to the evolution of coronal magnetic field activity. Our observations therefore introduce an uncertainty into the nature of any relationship between coronal composition and fixed stellar properties. The results highlight the importance of systematic full-cycle observations for understanding the elemental composition of solar-like stellar coronae.

  15. HARPS-N OBSERVES THE SUN AS A STAR

    Energy Technology Data Exchange (ETDEWEB)

    Dumusque, Xavier; Glenday, Alex; Phillips, David F.; Charbonneau, David; Latham, David W.; Li, Chih-Hao; Sasselov, Dimitar; Szentgyorgyi, Andrew; Walsworth, Ronald [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Buchschacher, Nicolas; Lovis, Christophe; Pepe, Francesco; Udry, Stéphane [Observatoire Astronomique de l’Université de Genève, 51 Chemin des Maillettes, 1290 Sauverny (Switzerland); Cameron, Andrew Collier [SUPA, School of Physics and Astronomy, University of St. Andrews, North Haugh, St. Andrews, Fife, KY16 9SS (United Kingdom); Cecconi, Massimo; Cosentino, Rosario; Ghedina, Adriano; Lodi, Marcello; Molinari, Emilio, E-mail: xdumusque@cfa.harvard.edu [INAF—Fundación Galileo Galilei, Rambla José Ana Fernández Pérez 7, E-38712 Breña Baja (Spain)

    2015-12-01

    Radial velocity (RV) perturbations induced by stellar surface inhomogeneities including spots, plages and granules currently limit the detection of Earth-twins using Doppler spectroscopy. Such stellar noise is poorly understood for stars other than the Sun because their surface is unresolved. In particular, the effects of stellar surface inhomogeneities on observed stellar radial velocities are extremely difficult to characterize, and thus developing optimal correction techniques to extract true stellar radial velocities is extremely challenging. In this paper, we present preliminary results of a solar telescope built to feed full-disk sunlight into the HARPS-N spectrograph, which is in turn calibrated with an astro-comb. This setup enables long-term observation of the Sun as a star with state-of-the-art sensitivity to RV changes. Over seven days of observing in 2014, we show an average 50 cm s{sup −1} RV rms over a few hours of observation. After correcting observed radial velocities for spot and plage perturbations using full-disk photometry of the Sun, we lower by a factor of two the weekly RV rms to 60 cm s{sup −1}. The solar telescope is now entering routine operation, and will observe the Sun every clear day for several hours. We will use these radial velocities combined with data from solar satellites to improve our understanding of stellar noise and develop optimal correction methods. If successful, these new methods should enable the detection of Venus over the next two to three years, thus demonstrating the possibility of detecting Earth-twins around other solar-like stars using the RV technique.

  16. Superflares on solar-type stars.

    Science.gov (United States)

    Maehara, Hiroyuki; Shibayama, Takuya; Notsu, Shota; Notsu, Yuta; Nagao, Takashi; Kusaba, Satoshi; Honda, Satoshi; Nogami, Daisaku; Shibata, Kazunari

    2012-05-16

    Solar flares are caused by the sudden release of magnetic energy stored near sunspots. They release 10(29) to 10(32) ergs of energy on a timescale of hours. Similar flares have been observed on many stars, with larger 'superflares' seen on a variety of stars, some of which are rapidly rotating and some of which are of ordinary solar type. The small number of superflares observed on solar-type stars has hitherto precluded a detailed study of them. Here we report observations of 365 superflares, including some from slowly rotating solar-type stars, from about 83,000 stars observed over 120 days. Quasi-periodic brightness modulations observed in the solar-type stars suggest that they have much larger starspots than does the Sun. The maximum energy of the flare is not correlated with the stellar rotation period, but the data suggest that superflares occur more frequently on rapidly rotating stars. It has been proposed that hot Jupiters may be important in the generation of superflares on solar-type stars, but none have been discovered around the stars that we have studied, indicating that hot Jupiters associated with superflares are rare.

  17. Catastrophic rotational braking among Sun-like stars. A model of the Sun's rotation evolution

    Science.gov (United States)

    Gondoin, P.

    2017-03-01

    Context. Observations of young open clusters show a bimodal distribution of stellar rotation. In those clusters, Sun-like stars group into two main populations of fast and slow rotators. Beyond an age of approximately 600 Myr, the two populations converge towards a single sequence of slow rotators. Aims: The present study addresses the origin of this bimodal distribution and the cause of its observed evolution. Methods: New prescriptions of mass-loss rate and Alfven radius dependences on Rossby number suggested by observations are implemented in a phenomenological model of angular-momentum loss and redistribution. The obtained model is used to calculate the time evolution of a rotation-period distribution of solar-mass stars similar to that observed in the 5 Myr-old NGC 2362 open cluster. The simulated distributions at subsequent ages are compared with those of h Per, the Pleiades, M 50, M 35, and M 37. Results: The model is able to reproduce the appearance and disappearance of a bimodal rotation-period distribution in open clusters providing that a brief episode of large-angular-momentum loss is included in the early evolution of Sun-like stars. Conclusions: I argue that a transitory episode of large-angular-momentum loss occurs on Sun-like stars with Rossby numbers between 0.13 and 0.3. This phenomenon of enhanced magnetic braking by stellar wind would be mainly driven by a rapid increase of mass loss at a critical rotation rate. This scenario accounts for the bimodal distribution of stellar rotation in open clusters with ages between 20-30 Myr and approximately 600 Myr. The mass-loss rate increase could account for a significant fraction of the X-ray luminosity decay of Sun-like stars in the 0.13-0.3 Rossby number range where a transition from the saturated to the non-saturated regime of X-ray emission is observed. Observed correlations between Li abundance and rotation sequences in the Pleiades and M 34 clusters support this scenario.

  18. Detection of Planetary Transits Across a Sun-like Star

    CERN Document Server

    Charbonneau, D; Latham, D W; Mayor, M; Charbonneau, David; Brown, Timothy M.; Latham, David W.; Mayor, Michel

    1999-01-01

    We report high precision, high cadence photometric measurements of the star HD 209458, which is known from radial velocity measurements to have a planetary mass companion in a close orbit. We detect two separate transit events at times that are consistent with the radial velocity measurements. In both cases, the detailed shape of the transit curve due to both the limb darkening of the star and the finite size of the planet is clearly evident. Assuming stellar parameters of 1.1 R_Sun and 1.1 M_Sun, we find that the data are best interpreted as a gas giant with a radius of 1.27 +/- 0.02 R_Jup in an orbit with an inclination of 87.1 +/- 0.2 degrees. We present values for the planetary surface gravity, escape velocity, and average density, and discuss the numerous observations that are warranted now that a planet is known to transit the disk of its parent star.

  19. High-energy irradiances of Sun-like stars

    Science.gov (United States)

    Sanz-Forcada, Jorge; Ribas, Ignasi

    2015-07-01

    Research on exoplanetary atmospheres has developed an increasing interest. Astrobiology has put its eyes on the effects that stellar irradiance may have on the atmosphere of planets, and on the early development of life. The high energy (XUV and UV) part of the spectrum is of special interest for this purpose. Part of this spectral range, the EUV is of no access to current telescopes, hampering the studies that intend to model planetary atmospheres. A program was developed to to circumvent this problem, and to provide with spectral energy distributions of stars hosting exoplanets (X-exoplanets) in the XUV range. We present here a work in which we develop further this program to create a semiempirical grid of models of emission of Sun-like stars, based on real data and coronal models, covering the XUV and UV ranges. These models will represent a great improvement with respect to currently used models of the solar irradiance at different ages, and intend to be the reference for the years to come. These models will be of special interest to reproduce the conditions of the Earth and solar system planets during different stages of the evolution, and can be safely exported to exoplanets orbiting Sun-like stars.

  20. Understanding Space Weather: The Sun as a Variable Star

    Science.gov (United States)

    Strong, Keith; Saba, Julia; Kucera, Therese

    2012-01-01

    The Sun is a complex system of systems and until recently, less than half of its surface was observable at any given time and then only from afar. New observational techniques and modeling capabilities are giving us a fresh perspective of the solar interior and how our Sun works as a variable star. This revolution in solar observations and modeling provides us with the exciting prospect of being able to use a vastly increased stream of solar data taken simultaneously from several different vantage points to produce more reliable and prompt space weather forecasts. Solar variations that cause identifiable space weather effects do not happen only on solar-cycle timescales from decades to centuries; there are also many shorter-term events that have their own unique space weather effects and a different set of challenges to understand and predict, such as flares, coronal mass ejections, and solar wind variations.

  1. Hysteresis Effect in the Activity Indices of the Atmospheres of the Sun and Solar-Type Stars During the Rising and Falling Phases of Cycles

    Science.gov (United States)

    Bruevich, E. A.; Yakunina, G. V.

    2016-09-01

    The hysteresis effect that shows up as a nonunique relationship among the emissions from the photosphere, chromosphere, and corona during the rising and falling phases of solar and stellar activity is analyzed. The following solar indices are analyzed and compared in different phases of the cycle: the radiative flux in the hydrogen Lyman alpha line FLα, radio emission at 10.7 cm F10.7, the sunspot number SSN, the radiative flux in the 530.0 nm green coronal line F530.3, the solar constant TSI, and the relative flux ratio c/w (ratio of the fluxes in the center and in the wings) for the 280 nm Mg II line. In stars with cycles, a hysteresis effect is observed between the CaII chromospheric S-activity index for stars in the Mount Wilson HK project and the photospheric flux Fph for these stars.

  2. The pulsations of the Sun and the stars

    CERN Document Server

    Rozelot, Jean-Pierre

    2011-01-01

    This volume of lecture notes brings together the knowledge on pulsations of the Sun and the stars, with a particular emphasis on recent observations and modelling, and on the influence of pulsations of other physical processes. The book begins with an extensive introduction to helioseismology. The solar cycle and gravity modes are discussed before the focus is widened from helioseismology to asteroseismology which is detailed in a series of specific chapters. Based on courses given at a graduate school, these tutorial lecture notes will be of interest and useful to a rather broad audience of scientists and students.

  3. A Spatially Resolved X-ray Image of a Star Like the Sun.

    Science.gov (United States)

    Schmitt, J H; Kürster, M

    1993-10-08

    Observations made with the x-ray satellite ROSAT (Roentgen Satellite) have produced the first spatially resolved x-ray image of a corona around a star like our sun. The star is the secondary in the eclipsing binary system alpha Coronae Borealis (CrB), which consists of one star of spectral type A0V and one of type G5V. The x-ray light curve of alpha CrB shows a total x-ray eclipse during secondary optical minimum, with the G star behind the A star. The totality of the eclipse demonstrates that the A-type component in alpha CrB is x-ray dark and that the x-ray flux arises exclusively from the later-type companion. The x-ray eclipse ingress and egress are highly asymmetric compared with the optical eclipse, indicating a highly asymmetric x-ray intensity distribution on the surface of the G star. From a detailed modeling of the ingress and egress of the x-ray light curve, an eclipse map of the G star was constructed by a method based on an optimization by simulated annealing.

  4. Astrometric jitter of the sun as a star

    CERN Document Server

    Makarov, V V; Ulrich, R K

    2010-01-01

    The daily variation of the solar photocenter over some 11 years is derived from the Mount Wilson data reprocessed by Ulrich et al. 2010 to closely match the surface distribution of solar irradiance. The standard deviations of astrometric jitter are 0.52 $\\mu$AU and 0.39 $\\mu$AU in the equatorial and the axial dimensions, respectively. The overall dispersion is strongly correlated with the solar cycle, reaching $0.91 \\mu$AU at the maximum activity in 2000. The largest short-term deviations from the running average (up to 2.6 $\\mu$AU) occur when a group of large spots happen to lie on one side with respect to the center of the disk. The amplitude spectrum of the photocenter variations never exceeds 0.033 $\\mu$AU for the range of periods 0.6--1.4 yr, corresponding to the orbital periods of planets in the habitable zone. Astrometric detection of Earth-like planets around stars as quiet as the Sun is not affected by star spot noise, but the prospects for more active stars may be limited to giant planets.

  5. Spectrometer for Sky-Scanning, Sun-Tracking Atmospheric Research (4STAR) Instrument Improvements

    Science.gov (United States)

    Dunagan, Stephen E.; Redemann, Jens; Chang, Cecilia; Dahlgren, Robert; Fahey, Lauren; Flynn, Connor; Johnson, Roy; Kacenelenbogen, Meloe; Leblanc, Samuel; Liss, Jordan; text-decoration: none; " href="javascript:void(0); " onClick="displayelement('author_20170005591'); toggleEditAbsImage('author_20170005591_show'); toggleEditAbsImage('author_20170005591_hide'); "> hide

    2017-01-01

    The Spectrometer for Sky-Scanning, Sun-Tracking Atmospheric Research (4STAR) combines airborne sun tracking and sky scanning with grating spectroscopy to improve knowledge of atmospheric constituents and their links to air-pollution and climate. Hyper-spectral measurements of direct-beam solar irradiance provide retrievals of gas constituents, aerosol optical depth, and aerosol and thin cloud optical properties. Sky radiance measurements in the principal and almucantar planes enhance retrievals of aerosol absorption, aerosol type, and size mode distribution. Zenith radiance measurements are used to retrieve cloud properties and phase, which in turn are used to quantify the radiative transfer below cloud layers. These airborne measurements tighten the closure between satellite and ground-based measurements. In contrast to the Ames Airborne Tracking Sunphotometer (AATS-14) predecessor instrument, new technologies for each subsystem have been incorporated into 4STAR. In particular, 4STAR utilizes a modular sun-trackingsky-scanning optical head with fiber optic signal transmission to rack mounted spectrometers, permitting miniaturization of the external optical head, and spectrometerdetector configurations that may be tailored for specific scientific objectives. This paper discusses technical challenges relating to compact optical collector design, radiometric dynamic range and stability, and broad spectral coverage at high resolution. Test results benchmarking the performance of the instrument against the AATS-14 standard and emerging science requirements are presented.

  6. No Sun-like dynamo on the active star ζ Andromedae from starspot asymmetry.

    Science.gov (United States)

    Roettenbacher, R M; Monnier, J D; Korhonen, H; Aarnio, A N; Baron, F; Che, X; Harmon, R O; Kővári, Zs; Kraus, S; Schaefer, G H; Torres, G; Zhao, M; ten Brummelaar, T A; Sturmann, J; Sturmann, L

    2016-05-12

    Sunspots are cool areas caused by strong surface magnetic fields that inhibit convection. Moreover, strong magnetic fields can alter the average atmospheric structure, degrading our ability to measure stellar masses and ages. Stars that are more active than the Sun have more and stronger dark spots than does the Sun, including on the rotational pole. Doppler imaging, which has so far produced the most detailed images of surface structures on other stars, cannot always distinguish the hemisphere in which the starspots are located, especially in the equatorial region and if the data quality is not optimal. This leads to problems in investigating the north-south distribution of starspot active latitudes (those latitudes with more starspot activity); this distribution is a crucial constraint of dynamo theory. Polar spots, whose existence is inferred from Doppler tomography, could plausibly be observational artefacts. Here we report imaging of the old, magnetically active star ζ Andromedae using long-baseline infrared interferometry. In our data, a dark polar spot is seen in each of two observation epochs, whereas lower-latitude spot structures in both hemispheres do not persist between observations, revealing global starspot asymmetries. The north-south symmetry of active latitudes observed on the Sun is absent on ζ And, which hosts global spot patterns that cannot be produced by solar-type dynamos.

  7. Superflares on Sun-Like Stars: Bane of Habitability?

    Science.gov (United States)

    Ayres, T.

    2014-04-01

    A key aspect of planetary habitability is the existence of rare, but catastrophic events. One Earthly example is the attribution of several geological mass extinctions to asteroid collisions. Indeed, the Late Heavy Bombardment, during which the 600 Myr old Earth was pummeled persistently by impactors over a period of perhaps a hundred Myr, likely significantly delayed the permanent foothold of life on our planet. Another, less well known, example is the proposed existence of "superflares" on Sun-like stars. Although the quantity of energy in a superflare is negligible compared with the time-integrated X-ray dose from the quiescent multi-MK corona, the quality of the radiation (i.e., composition dominated by gamma rays) released from the transient, but extreme, outburst is what could be of concern to the survival of primitive lifeforms struggling for existence on a semi-habitable world. However, existing reports of superflares mainly involve interpretations of historical materials, such as long-term astronomical plate collections; there are very few concrete examples of such events observed by modern techniques at the most relevant wavelengths, namely ultraviolet or X-rays. The lack of good examples is mostly because these rare events are, well, rare. However, a recent HST Cosmic Origins Spectrograph program to record the ultraviolet spectrum of young (~50 Myr) solar analog EK Draconis, fortuitously captured a giant, hour-long FUV transient, in hot lines like the C IV 155 nm doublet (T~100,000 K), and very toasty Fe XXI 124 nm coronal forbidden line (~10 MK). If translated into the equivalent GOES 0.1-0.8 nm X-ray fluence, the event would correspond to an X25000-class flare (most extreme observed on the Sun might reach as high as a mere X50). The EK Dra giant flare, as viewed with the excellent wavelength resolution, broad coverage, and high sensitivity of COS, provides the opportunity to deduce properties of such events to help inform possible impacts on planetary

  8. Lithium Abundance Of The Solar-Type Superflare Stars

    Science.gov (United States)

    Honda, Satoshi; Notsu, Yuta; Maehara, Hiroyuki; Notsu, Shota; Shibayama, Takuya; Nogami, Daisaku; Shibata, Kazunari

    2016-07-01

    We performed the high dispersion spectroscopy of solar-type superflare stars by Subaru/HDS, and estimate the stellar parameters and lithium abundance of the stars to compare with the Sun. Our spectroscopic analysis of superflare stars show more than half of targets have no evidence of binary system and the stellar parameters are in the range of solar-type stars (Notsu et al. 2015a&b). We also investigate the correlations of Lithium abundance with stellar atmospheric parameters, rotational velocity, and superflare activities to understand the nature of superflare stars and the possibility of the nucleosynthesis of lithium by superflares. The derived lithium abundance in superflare stars do not show the correlation with stellar parameters. As compared with the lithium abundance in Hyades cluster which is younger than the sun, it is suggested that half of observed stars are young. However, there are some objects which show the low lithium and slowly rotate from the estimated v sin(i) and period of brightness variation. These results indicate that the superflare stars are not only young stars but also old stars like our sun. In our observations, we could not find the any evidence of lithium productions by superflare.

  9. From the sun to the Galactic Center: dust, stars and black hole(s)

    Science.gov (United States)

    Fritz, Tobias

    2013-07-01

    The centers of galaxies are their own ultimate gravitational sinks. Massive black holes and star clusters as well as gas are especially likely to fall into the centers of galaxies by dynamical friction or dissipation. Many galactic centers harbor supermassive black holes (SMBH) and dense nuclear (star) clusters which possibly arrived there by these processes. Nuclear clusters can be formed in situ from gas, or from smaller star clusters which fall to the center. Since the Milky Way harbors both an SMBH and a nuclear cluster, both can be studied best in the Galactic Center (GC), which is the closest galactic nucleus to us. In Chapter 1, I introduce the different components of the Milky Way, and put these into the context of the GC. I then give an overview of relevant properties (e.g. star content and distribution) of the GC. Afterwards, I report the results of four different studies about the GC. In Chapter 2, I analyze the limitations of astrometry, one of the most useful methods for the study of the GC. Thanks to the high density of stars and its relatively small distance from us it is possible to measure the motions of thousands of stars in the GC with images, separated by few years only. I find two main limitations to this method: (1) for bright stars the not perfectly correctable distortion of the camera limits the accuracy, and (2) for the majority of the fainter stars, the main limitation is crowding from the other stars in the GC. The position uncertainty of faint stars is mainly caused by the seeing halos of bright stars. In the very center faint unresolvable stars are also important for the position uncertainty. In Chapter 3, I evaluate the evidence for an intermediate mass black hole in the small candidate cluster IRS13E within the GC. Intermediate mass black holes (IMBHs) have a mass between the two types of confirmed black hole: the stellar remnants and the supermassive black holes in the centers of galaxies. One possibility for! their formation is the

  10. Magnetic fields on young, moderately rotating Sun-like stars II. EK Draconis (HD 129333)

    CERN Document Server

    Waite, Ian; Carter, Brad; Petit, Pascal; Jeffers, Sandra; Morin, Julien; Vidotto, Aline; Donati, Jean-Francois

    2016-01-01

    The magnetic fields, activity and dynamos of young solar-type stars can be empirically studied using time-series of spectropolarimetric observations and tomographic imaging techniques such as Doppler imaging and Zeeman Doppler imaging. In this paper we use these techniques to study the young Sun-like star EK Draconis (Sp-Type: G1.5V, HD 129333) using ESPaDOnS at the Canada-France-Hawaii Telescope and NARVAL at the T\\`elescope Bernard Lyot. This multi-epoch study runs from late 2006 until early 2012. We measure high levels of chromospheric activity indicating an active, and varying, chromosphere. Surface brightness features were constructed for all available epochs. The 2006/7 and 2008 data show large spot features appearing at intermediate-latitudes. However, the 2012 data indicate a distinctive polar spot. We observe a strong, almost unipolar, azimuthal field during all epochs that is similar to that observed on other Sun-like stars. Using magnetic features, we determined an average equatorial rotational vel...

  11. Dust discs around intermediate mass and Sun-like stars in the 16 Myr old NGC 1960 open cluster

    CERN Document Server

    Smith, R

    2011-01-01

    We present an analysis of Spitzer IRAC (3.6--8um) and MIPS (24um) imaging of members of the 16(+10/-5)Myr old open cluster NGC 1960 (M36). Models of terrestrial planet formation indicate that rocky planets are likely to achieve their final masses at around 10-30Myr, and thus this cluster is at an interesting epoch for planet formation. We find 21 B-F5 type stars and 14 F6-K9 type stars which have 24um excess emission, and thus determine that >30% of B-F5 type stars and >23% of F6-K9 type stars in this cluster have 24um excess emission. These excess frequencies are similar to those observed in other clusters of similar age. Three early type stars have excesses at near-infrared wavelengths. Analysis of their SEDs confirms that these are true debris discs and not remnant primordial or transitional discs. None of the 61 sun-like stars have confirmed near-infrared excess, and we can place a limit on the frequency of 8um excess emission around sun-like stars of <7%. All of the detected excesses are consistent wi...

  12. Understanding Activity Cycles of Solar Type Stars with Kepler

    Science.gov (United States)

    Tovar, Guadalupe; Montet, Benjamin; Johnson, John A.

    2017-01-01

    As the era of exploring new worlds and systems advances we seek to answer the question: How common is our Sun? There is considerable evidence about the recurring activity cycles of our Sun but very little is known about the activity cycles of other stars. By calibrating the full frame images from the original Kepler mission that were taken once a month over the course of four years, we are able to do relative photometry on roughly 5 million stars. By building a model of the pixel response function we were able to achieve 0.8% precision photometry. We identify 50,000 solar type stars based on magnitude, surface gravity, and temperature cuts. We observe the relative increase and decrease in brightness of the stars indicating signs of activity cycles similar to our Sun. We continue to explore how a data driven pixel response function model could improve our precision to 0.1% photometry measurements.

  13. Magnetic fields in early-type stars

    CERN Document Server

    Grunhut, Jason H

    2015-01-01

    For several decades we have been cognizant of the presence of magnetic fields in early-type stars, but our understanding of their magnetic properties has recently (over the last decade) expanded due to the new generation of high-resolution spectropolarimeters (ESPaDOnS at CFHT, Narval at TBL, HARPSpol at ESO). The most detailed surface magnetic field maps of intermediate-mass stars have been obtained through Doppler imaging techniques, allowing us to probe the small-scale structure of these stars. Thanks to the effort of large programmes (e.g. the MiMeS project), we have, for the first time, addressed key issues regarding our understanding of the magnetic properties of massive (M > 8 M_sun) stars, whose magnetic fields were only first detected about fifteen years ago. In this proceedings article we review the spectropolarimetric observations and statistics derived in recent years that have formed our general understanding of stellar magnetism in early-type stars. We also discuss how these observations have fu...

  14. Spectroscopy of late type giant stars

    Science.gov (United States)

    Spaenhauer, A.; Thevenin, F.

    1984-06-01

    An attempt to calibrate broadband RGU colors of late type giant stars in terms of the physical parameters of the objects is reported. The parameters comprise the effective temperature, surface gravity and global metal abundance with respect to the sun. A selection of 21 giant star candidates in the Basel fields Plaut 1, Centaurus III and near HD 95540 were examined to obtain a two color plot. Attention is focused on the G-R color range 1.5-2.15 mag, i.e., spectral types K0-K5. A relationship between R and the metallicity is quantified and shown to have a correlation coefficient of 0.93. No correlation is found between metallicity and gravity or R and the effective temperature.

  15. Spectral magnetohydrodynamic simulations of the sun and stars

    Science.gov (United States)

    Brun, A. S.

    The purpose of this lecture is two fold: first, to describe a powerful numerical technic, namely the spectral method, to solve the compressible (anelastic) magnetohydrodynamic (MHD) equations in spherical geometry and then to discuss some recent numerical applications to study stellar dynamics and magnetism. We thus start by describing the semi-implicit, anelastic spherical harmonic (ASH) code. In this code, the main field variables are projected into spherical harmonics for their horizontal dimensions and into Chebyshev polynomials for their radial direction. We then present, high resolution 3 D MHD simulations of the convective region of A- and G-type stars in spherical shells. We have chosen to model A and G-type stars because they represent good proxies to study and understand stellar dynamics and magnetism given their strikingly different internal “up-side-down” structure and magnetic activity level. In particular, we discuss the nonlinear interactions between turbulent convection, rotation and magnetic fields and the possibility for such flows and fields to lead to dynamo action. We find that both core and envelope turbulent convective zones are efficient at inducing strong mostly non-axisymmetric fields near equipartition but at the expense of damping the differential rotation present in the purely hydrodynamic progenitor solutions.

  16. Toroidal vs. poloidal magnetic fields in Sun-like stars: a rotation threshold

    CERN Document Server

    Petit, P; Solanki, SK; Donati, J-F; Aurière, M; Lignières, F; Morin, J; Paletou, F; Ramírez, J; Catala, C; Fares, R

    2008-01-01

    From a set of stellar spectropolarimetric observations, we report the detection of surface magnetic fields in a sample of four solar-type stars, namely HD 73350, HD 76151, HD 146233 and HD 190771. Assuming that the observed variability of polarimetric signal is controlled by stellar rotation, we establish the rotation periods of our targets, with values ranging from 8.8 d (for HD 190771) to 22.7 d (for HD 146233). Apart from rotation, fundamental parameters of the selected objects are very close to the Sun's, making this sample a practical basis to investigate the specific impact of rotation on magnetic properties of Sun-like stars. We reconstruct the large-scale magnetic geometry of the targets as a low-order (l<10) spherical harmonics expansion of the surface magnetic field. From the set of magnetic maps, we draw two main conclusions. (a) The magnetic energy of the large-scale field increases with rotation rate. The increase of chromospheric emission with the mean magnetic field is flatter than observed ...

  17. Dynamical systems for modeling evolution of the magnetic field of the Sun, stars and planets

    Science.gov (United States)

    Popova, E.

    2016-12-01

    The magnetic activity of the Sun, stars and planets are connected with a dynamo process based on the combined action of the differential rotation and the alpha-effect. Application of this concept allows us to get different types of solutions which can describe the magnetic activity of celestial bodies. We investigated the dynamo model with the meridional circulation by the low-mode approach. This approach is based on an assumption that the magnetic field can be described by non-linear dynamical systems with a relatively small number of parameters. Such non-linear dynamical systems are based on the equations of dynamo models. With this method dynamical systems have been built for media which contains the meridional flow and thickness of the spherical shell where dynamo process operates. It was shown the possibility of coexistence of quiasi-biennial oscillations, 22-year cycle, and grand minima of magnetic activity which is consistent with the observational data for the solar activity. We obtained different regimes (oscillations, vacillations, dynamo-bursts) depending on a value of the dynamo-number, the meridional circulation, and thickness of the spherical shell. We discuss features of these regimes and compare them with the observed features of the magnetic fields of the Sun, stars and Earth. We built theoretical paleomagnetic time scale and butterfly-diagrams for the helicity and toroidal magnetic field for different regimes.

  18. ADVANCED BURNING STAGES AND FATE OF 8-10 M{sub Sun} STARS

    Energy Technology Data Exchange (ETDEWEB)

    Jones, S.; Hirschi, R. [Astrophysics Group, Lennard Jones Building, Keele University, Staffordshire ST5 5BG (United Kingdom); Nomoto, K. [Kavli Institute for the Physics and Mathematics of the Universe (WPI), University of Tokyo, Kashiwa, Chiba 277-8583 (Japan); Fischer, T.; Martinez-Pinedo, G. [GSI Helmholtzzentrum fuer Schwerionenforschung GmbH, Planckstrasse 1, D-64291 Darmstadt (Germany); Timmes, F. X. [School of Earth and Space Exploration, University of Arizona, Tempe, AZ 85287 (United States); Herwig, F. [Joint Institute for Nuclear Astrophysics, University of Notre Dame, IN 46556 (United States); Paxton, B. [KITP and Department of Physics, University of California, Santa Barbara, CA 93106 (United States); Toki, H. [Research Center for Nuclear Physics (RCNP), Osaka University, Osaka 567-0047 (Japan); Suzuki, T. [Department of Physics, College of Humanities and Sciences, Nihon University Sakurajosui 3-25-40, Setagaya-ku, Tokyo 156-8550 (Japan); Lam, Y. H. [Institut fuer Kernphysik, Technische Universitaet Darmstadt, Schlossgartenstrasse 2, D-64289 Darmstadt (Germany); Bertolli, M. G., E-mail: s.w.jones@keele.ac.uk [Theoretical Division, Los Alamos National Laboratory, Los Alamos, NM 87545 (United States)

    2013-08-01

    The stellar mass range 8 {approx}< M/M{sub Sun} {approx}< 12 corresponds to the most massive asymptotic giant branch (AGB) stars and the most numerous massive stars. It is host to a variety of supernova (SN) progenitors and is therefore very important for galactic chemical evolution and stellar population studies. In this paper, we study the transition from super-AGB (SAGB) star to massive star and find that a propagating neon-oxygen-burning shell is common to both the most massive electron capture supernova (EC-SN) progenitors and the lowest mass iron-core-collapse supernova (FeCCSN) progenitors. Of the models that ignite neon-burning off-center, the 9.5 M{sub Sun} star would evolve to an FeCCSN after the neon-burning shell propagates to the center, as in previous studies. The neon-burning shell in the 8.8 M{sub Sun} model, however, fails to reach the center as the URCA process and an extended (0.6 M{sub Sun }) region of low Y{sub e} (0.48) in the outer part of the core begin to dominate the late evolution; the model evolves to an EC-SN. This is the first study to follow the most massive EC-SN progenitors to collapse, representing an evolutionary path to EC-SN in addition to that from SAGB stars undergoing thermal pulses (TPs). We also present models of an 8.75 M{sub Sun} SAGB star through its entire TP phase until electron captures on {sup 20}Ne begin at its center and of a 12 M{sub Sun} star up to the iron core collapse. We discuss key uncertainties and how the different pathways to collapse affect the pre-SN structure. Finally, we compare our results to the observed neutron star mass distribution.

  19. The First Focused Hard X-Ray Images of the Sun With NuSTAR

    DEFF Research Database (Denmark)

    Grefenstette, Brian W.; Glesener, Lindsay; Krucker, Sam

    2016-01-01

    We present results from the the first campaign of dedicated solar observations undertaken by the Nuclear Spectroscopic Telescope ARray (NuSTAR) hard X-ray (HXR) telescope. Designed as an astrophysics mission, NuSTAR nonetheless has the capability of directly imaging the Sun at HXR energies (>3 ke......V) with an increase in sensitivity of at least two magnitude compared to current non-focusing telescopes. In this paper we describe the scientific areas where NuSTAR will make major improvements on existing solar measurements. We report on the techniques used to observe the Sun with NuSTAR, their limitations......, and full-disk HXR images of the Sun....

  20. The Sun as a star: empirical estimates of stellar coronal mass ejection rates and properties

    Science.gov (United States)

    Aarnio, Alicia

    2017-05-01

    Our nearest star provides exquisite, up-close views of the physical processes driving energetic phenomena we observe on stars and cannot yet spatially resolve. Stars provide a statistical ensemble of solar analogs spanning a range of ages representing snapshots along our Sun's full life cycle. In this talk, I will share a project bringing the astronomer's large scale statistical approach to bear on solar data. Combining a decades' worth of solar flare and CME data, we characterize for the first time a relationship between flare and CME properties in order to extend analogy to readily observable stellar flares. We aim to better understand the properties and evolution of magnetic activity on Sun-like stars and exoweather on planets about distant Suns.

  1. The First Focused Hard X-Ray Images of the Sun With NuSTAR

    DEFF Research Database (Denmark)

    Grefenstette, Brian W.; Glesener, Lindsay; Krucker, Sam

    2016-01-01

    We present results from the the first campaign of dedicated solar observations undertaken by the Nuclear Spectroscopic Telescope ARray (NuSTAR) hard X-ray (HXR) telescope. Designed as an astrophysics mission, NuSTAR nonetheless has the capability of directly imaging the Sun at HXR energies (>3 ke......V) with an increase in sensitivity of at least two magnitude compared to current non-focusing telescopes. In this paper we describe the scientific areas where NuSTAR will make major improvements on existing solar measurements. We report on the techniques used to observe the Sun with NuSTAR, their limitations......, and full-disk HXR images of the Sun....

  2. The variability of Sun-like stars: reproducing observed photometric trends

    CERN Document Server

    Shapiro, A I; Krivova, N A; Schmutz, W K; Ball, W T; Knaack, R; Rozanov, E V; Unruh, Y C

    2014-01-01

    The Sun and stars with low magnetic activity levels, become photometrically brighter when their activity increases. Magnetically more active stars display the opposite behaviour and get fainter when their activity increases. We reproduce the observed photometric trends in stellar variations with a model that treats stars as hypothetical Suns with coverage by magnetic features different from that of the Sun. The presented model attributes the variability of stellar spectra to the imbalance between the contributions from different components of the solar atmosphere, such as dark starspots and bright faculae. A stellar spectrum is calculated from spectra of the individual components, by weighting them with corresponding disc area coverages. The latter are obtained by extrapolating the solar dependences of spot and facular disc area coverages on chromospheric activity to stars with different levels of mean chromospheric activity. We have found that the contribution by starspots to the variability increases faster...

  3. Spectrometers for Sky-Scanning, Sun-Tracking Atmospheric Research (4STAR) Upgrade to Full Sun-Sky-Cloud-Trace Gas Spectrometry Capability for Airborne Science

    Science.gov (United States)

    Dunagan, S. E.; Flynn, C. J.; Johnson, R. R.; Kacenelenbogen, M. S.; Knobelspiesse, K. D.; LeBlanc, S. E.; Livingston, J. M.; Redemann, J.; Russell, P. B.; Schmid, B.; Segal-Rosenhaimer, M.; Shinozuka, Y.

    2014-12-01

    The Spectrometers for Sky-Scanning, Sun-Tracking Atmospheric Research (4STAR) instrument has been developed at NASA Ames in collaboration with Pacific Northwest National Laboratory (PNNL) and NASA Goddard, supported substantially since 2009 by NASA's Radiation Science Program and Earth Science Technology Office. It combines grating spectrometers with fiber optic links to a tracking, scanning head to enable sun tracking, sky scanning, and zenith viewing. 4STAR builds on the long and productive heritage of the NASA Ames Airborne Tracking Sunphotometers (AATS-6 and -14), which have yielded more than 100 peer-reviewed publications and extensive archived data sets in many NASA Airborne Science campaigns from 1986 to the present. The baseline 4STAR instrument has provided extensive data supporting the TCAP (Two Column Aerosol Project, July 2012 & Feb. 2013), SEAC4RS (Studies of Emissions, Atmospheric Composition, Clouds and Climate Coupling by Regional Surveys, 2013), and ARISE (Arctic Radiation - IceBridge Sea and Ice Experiment, 2014), field campaigns.This poster presents plans and progress for an upgrade to the 4STAR instrument to achieve full science capability, including (1) direct-beam sun tracking measurements to derive aerosol optical depth spectra, (2) sky radiance measurements to retrieve aerosol absorption and type (via complex refractive index and mode-resolved size distribution), (3) cloud properties via zenith radiance, and (4) trace gas spectrometry. Technical progress in context with the governing physics is reported on several upgrades directed at improved light collection and usage, particularly as related to spectrally and radiometrically stable propagation through the collection light path. In addition, improvements to field calibration and verification, and flight operability and reliability are addressed.

  4. Spectral variability of photospheric radiation due to faculae. I. The Sun and Sun-like stars

    Science.gov (United States)

    Norris, Charlotte M.; Beeck, Benjamin; Unruh, Yvonne C.; Solanki, Sami K.; Krivova, Natalie A.; Yeo, Kok Leng

    2017-09-01

    Context. Stellar spectral variability on timescales of a day and longer, arising from magnetic surface features such as dark spots and bright faculae, is an important noise source when characterising extra-solar planets. Current 1D models of faculae do not capture the geometric properties and fail to reproduce observed solar facular contrasts. Magnetoconvection simulations provide facular contrasts accounting for geometry. Aims: We calculate facular contrast spectra from magnetoconvection models of the solar photosphere with a view to improve (a) future parameter determinations for planets with early G type host stars and (b) reconstructions of solar spectral variability. Methods: Regions of a solar twin (G2, log g = 4.44) atmosphere with a range of initial average vertical magnetic fields (100 to 500 G) were simulated using a 3D radiation-magnetohydrodynamics code, MURaM, and synthetic intensity spectra were calculated from the ultraviolet (149.5 nm) to the far infrared (160 000 nm) with the ATLAS9 radiative transfer code. Nine viewing angles were investigated to account for facular positions across most of the stellar disc. Results: Contrasts of the radiation from simulation boxes with different levels of magnetic flux relative to an atmosphere with no magnetic field are a complicated function of position, wavelength and magnetic field strength that is not reproduced by 1D facular models. Generally, contrasts increase towards the limb, but at UV wavelengths a saturation and decrease are observed close to the limb. Contrasts also increase strongly from the visible to the UV; there is a rich spectral dependence, with marked peaks in molecular bands and strong spectral lines. At disc centre, a complex relationship with magnetic field was found and areas of strong magnetic field can appear either dark or bright, depending on wavelength. Spectra calculated for a wide variety of magnetic fluxes will also serve to improve total and spectral solar irradiance

  5. Capture of the Sun's Oort cloud from stars in its birth cluster.

    Science.gov (United States)

    Levison, Harold F; Duncan, Martin J; Brasser, Ramon; Kaufmann, David E

    2010-07-09

    Oort cloud comets are currently believed to have formed in the Sun's protoplanetary disk and to have been ejected to large heliocentric orbits by the giant planets. Detailed models of this process fail to reproduce all of the available observational constraints, however. In particular, the Oort cloud appears to be substantially more populous than the models predict. Here we present numerical simulations that show that the Sun captured comets from other stars while it was in its birth cluster. Our results imply that a substantial fraction of the Oort cloud comets, perhaps exceeding 90%, are from the protoplanetary disks of other stars.

  6. Seismic constraints on rotation of Sun-like star and mass of exoplanet.

    Science.gov (United States)

    Gizon, Laurent; Ballot, Jérome; Michel, Eric; Stahn, Thorsten; Vauclair, Gérard; Bruntt, Hans; Quirion, Pierre-Olivier; Benomar, Othman; Vauclair, Sylvie; Appourchaux, Thierry; Auvergne, Michel; Baglin, Annie; Barban, Caroline; Baudin, Fréderic; Bazot, Michaël; Campante, Tiago; Catala, Claude; Chaplin, William; Creevey, Orlagh; Deheuvels, Sébastien; Dolez, Noël; Elsworth, Yvonne; García, Rafael; Gaulme, Patrick; Mathis, Stéphane; Mathur, Savita; Mosser, Benoît; Régulo, Clara; Roxburgh, Ian; Salabert, David; Samadi, Réza; Sato, Kumiko; Verner, Graham; Hanasoge, Shravan; Sreenivasan, Katepalli R

    2013-08-13

    Rotation is thought to drive cyclic magnetic activity in the Sun and Sun-like stars. Stellar dynamos, however, are poorly understood owing to the scarcity of observations of rotation and magnetic fields in stars. Here, inferences are drawn on the internal rotation of a distant Sun-like star by studying its global modes of oscillation. We report asteroseismic constraints imposed on the rotation rate and the inclination of the spin axis of the Sun-like star HD 52265, a principal target observed by the CoRoT satellite that is known to host a planetary companion. These seismic inferences are remarkably consistent with an independent spectroscopic observation (rotational line broadening) and with the observed rotation period of star spots. Furthermore, asteroseismology constrains the mass of exoplanet HD 52265b. Under the standard assumption that the stellar spin axis and the axis of the planetary orbit coincide, the minimum spectroscopic mass of the planet can be converted into a true mass of 1.85(-0.42)(+0.52)M(Jupiter), which implies that it is a planet, not a brown dwarf.

  7. Seismic constraints on rotation of Sun-like star and mass of exoplanet

    CERN Document Server

    Gizon, Laurent; Michel, Eric; Stahn, Thorsten; Vauclair, Gérard; Bruntt, Hans; Quirion, Pierre-Olivier; Benomar, Othman; Vauclair, Sylvie; Appourchaux, Thierry; Auvergne, Michel; Baglin, Annie; Barban, Caroline; Baudin, Fréderic; Bazot, Michaël; Campante, Tiago; Catala, Claude; Chaplin, William; Creevey, Orlagh; Deheuvels, Sébastien; Dolez, Noël; Elsworth, Yvonne; García, Rafael; Gaulme, Patrick; Mathis, Stéphane; Mathur, Savita; Mosser, Benoît; Régulo, Clara; Roxburgh, Ian; Salabert, David; Samadi, Réza; Sato, Kumiko; Verner, Graham; Hanasoge, Shravan; Sreenivasan, Katepalli R

    2013-01-01

    Rotation is thought to drive cyclic magnetic activity in the Sun and Sun-like stars. Stellar dynamos, however, are poorly understood owing to the scarcity of observations of rotation and magnetic fields in stars. Here, inferences are drawn on the internal rotation of a distant Sun-like star by studying its global modes of oscillation. We report asteroseismic constraints imposed on the rotation rate and the inclination of the spin axis of the Sun-like star HD 52265, a principal target observed by the CoRoT satellite that is known to host a planetary companion. These seismic inferences are remarkably consistent with an independent spectroscopic observation (rotational line broadening) and with the observed rotation period of star spots. Furthermore, asteroseismology constrains the mass of exoplanet HD 52265b. Under the standard assumption that the stellar spin axis and the axis of the planetary orbit coincide, the minimum spectroscopic mass of the planet can be converted into a true mass of 1.85 (+0.52,-0.42) M...

  8. A super-Earth-sized planet orbiting in or near the habitable zone around Sun-like star

    CERN Document Server

    Barclay, Thomas; Howell, Steve B; Rowe, Jason F; Huber, Daniel; Isaacson, Howard; Jenkins, Jon M; Kolbl, Rea; Marcy, Geoffrey W; Quintana, Elisa V; Still, Martin; Twicken, Joseph D; Bryson, Stephen T; Borucki, William J; Caldwell, Douglas A; Ciardi, David; Clarke, Bruce D; Christiansen, Jessie L; Coughlin, Jeffrey L; Fischer, Debra A; Li, Jie; Haas, Michael R; Hunter, Roger; Lissauer, Jack J; Mullally, Fergal; Sabale, Anima; Seader, Shawn E; Smith, Jeffrey C; Tenenbaum, Peter; Uddin, AKM Kamal; Thompson, Susan E

    2013-01-01

    We present the discovery of a super-earth-sized planet in or near the habitable zone of a sun-like star. The host is Kepler-69, a 13.7 mag G4V-type star. We detect two periodic sets of transit signals in the three-year flux time series of Kepler-69, obtained with the Kepler spacecraft. Using the very high precision Kepler photometry, and follow-up observations, our confidence that these signals represent planetary transits is >99.1%. The inner planet, Kepler-69b, has a radius of 2.24+/-0.4 Rearth and orbits the host star every 13.7 days. The outer planet, Kepler-69c, is a super-Earth-size object with a radius of 1.7+/-0.3 Rearth and an orbital period of 242.5 days. Assuming an Earth-like Bond albedo, Kepler-69c has an equilibrium temperature of 299 +/- 19 K, which places the planet close to the habitable zone around the host star. This is the smallest planet found by Kepler to be orbiting in or near habitable zone of a Sun-like star and represents an important step on the path to finding the first true Earth ...

  9. Metallicity of Sun-like G-stars that have Exoplanets

    Indian Academy of Sciences (India)

    Shashanka R. Gurumath; K. M. Hiremath; V. Ramasubramanian

    2017-06-01

    By considering the physical and orbital characteristics of G type stars and their exoplanets, we examine the association between stellar mass and its metallicity that follows a power law. Similar relationship is also obtained in case of single and multiplanetary stellar systems suggesting that, Sun′s present mass is about 1% higher than the estimated value for its metallicity. Further, for all the stellar systems with exoplanets, association between the planetary mass and the stellar metallicity is investigated, that suggests planetary mass is independent of stellar metallicity. Interestingly, in case of multiplanetary systems, planetary mass is linearly dependent on the stellar absolute metallicity, that suggests, metal rich stars produce massive (≥1 Jupiter mass) planets compared to metal poor stars. This study also suggests that there is a solar system planetary missing mass of ∼0.8 Jupiter mass. It is argued that probably 80% of missing mass is accreted onto the Sun and about 20% of missing mass might have been blown off to the outer solar system (beyond the present Kuiper belt) during early history of solar system formation. We find that, in case of single planetary systems, planetary mass is independent of stellar metallicity with an implication of their non-origin in the host star’s protoplanetary disk and probably are captured from the space. Final investigation of dependency of the orbital distances of planets on the host stars metallicity reveals that inward migration of planets is dominant in case of single planetary systems supporting the result that most of the planets in single planetary systems are captured from the space.

  10. Evolution of the cycles of magnetic activity of the Sun and Sun-like stars in time

    CERN Document Server

    Bruevich, E A; Artamonov, B P

    2016-01-01

    We applied the method of continuous wavelet-transform to the time-frequency analysis to the sets of observations of relative sunspot numbers, sunspot areas and to 6 Mount Wilson HK-project stars with well-defined magnetic cycles. Wavelet analysis of these data reveals the following pattern: at the same time there are several activity cycles whose periods vary widely from the quasi-biennial up to the centennial period for the Sun and vary significant during observations time of the HK-project stars. These relatively low-frequency periodic variations of the solar and stellar activity gradually change the values of periods of different cycles in time. This phenomenon can be observed in every cycles of activity

  11. Sun

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    @@ Sun Microsystems, Inc. is committed to open standards,a standardization system, and sharing within the information tech nology field, focusing not only on technical innovation, but also on new ideas, practices and future development.

  12. Spectrometers for Sky-Scanning, Sun-Tracking Atmospheric Research (4STAR): Airborne Concepts and Ground Prototype Measurements

    Science.gov (United States)

    Russell, P. B.; Schmid, B.; Flynn, C.; Dunagan, S. E.; Johnson, R. R.; Redemann, J.; Livingston, J.

    2007-12-01

    A collaboration between NASA Ames Research Center and Battelle Pacific Northwest Division is exploring new instrument concepts that combine sky scanning and spectroscopy with the direct sun transmission measurement capabilities of previous instruments like the NASA Ames Airborne Tracking Sunphotometers (AATS). Additional technical goals are to reduce instrument size, weight, and power requirements while increasing autonomy, so as to permit operation on a wider range of aircraft, including unmanned aerial vehicles (UAVs). The overall science goal for the new instruments is to improve knowledge of atmospheric constituents and their links to climate using a variety of airborne measurement approaches including satellite validation. The sky scanning capability will enable retrievals of aerosol type (via complex refractive index and shape) and aerosol size distribution extending to larger sizes than attainable by direct-beam sunphotometry alone. The spectroscopic capability will improve measurements of gas constituents (e.g., H2O, O3, NO2, SO2) . Concepts explored to date for an airborne Spectrometer for Sky-Scanning, Sun-Tracking Atmospheric Research (4STAR-Air) include using fiber optics to link a spectrometer inside the aircraft to optical entrance ports in a relatively small tracking/scanning head outside the aircraft. 4STAR feasibility depends on overcoming three technological hurdles: 1. Maintaining calibration to 1% stability over a period of months. 2. Demonstrating stray light rejection to permit measuring skylight within a few degrees of the sun. 3. Devising a fiber optic coupling that maintains 1% calibration stability with as many as possible of the following desirable characteristics: detachable during assembly before calibration; detachable between calibration and scientific measurements; rotatable during measurements. To investigate ways to overcome these hurdles we have developed a ground-based prototype, 4STAR-Ground. To date 4STAR-Ground has been

  13. Planet signatures in the chemical composition of Sun-like stars

    CERN Document Server

    Melendez, Jorge

    2016-01-01

    There are two possible mechanisms to imprint planet signatures in the chemical composition of Sun-like stars: i) dust condensation at the early stages of planet formation, causing a depletion of refractory elements in the gas accreted by the star in the late stages of its formation; ii) planet engulfment, enriching the host star in lithium and refractory elements. We discuss both planet signatures, the influence of galactic chemical evolution, and the importance of binaries composed of stellar twins as laboratories to verify abundance anomalies imprinted by planets.

  14. Gravitational Waves from Stellar Black Hole Binaries and the Impact on Nearby Sun-like Stars

    Science.gov (United States)

    Lopes, Ilídio; Silk, Joseph

    2017-07-01

    We investigate the impact of resonant gravitational waves on quadrupole acoustic modes of Sun-like stars located nearby stellar black hole binary systems (such as GW150914 and GW151226). We find that the stimulation of the low-overtone modes by gravitational radiation can lead to sizeable photometric amplitude variations, much larger than the predictions for amplitudes driven by turbulent convection, which in turn are consistent with the photometric amplitudes observed in most Sun-like stars. For accurate stellar evolution models, using up-to-date stellar physics, we predict photometric amplitude variations of 1-103 ppm for a solar mass star located at a distance between 1 au and 10 au from the black hole binary and belonging to the same multi-star system. The observation of such a phenomenon will be within the reach of the Plato mission because the telescope will observe several portions of the Milky Way, many of which are regions of high stellar density with a substantial mixed population of Sun-like stars and black hole binaries.

  15. Global helioseismology (WP4.1): From the Sun to the stars & solar analogs

    CERN Document Server

    Garcia, Rafael A

    2016-01-01

    Sun-as-a star observations put our star as a reference for stellar observations. Here, I review the activities in which the SPACEINN global seismology team (Working Package WP4.1) has worked during the past 3 years. In particular, we will explain the new deliverables available on the SPACEINN seismic+ portal. Moreover, special attention will be given to surface dynamics (rotation and magnetic fields). After characterizing the rotation and the magnetic properties of around 300 solar-like stars and defining proper metrics for that, we use their seismic properties to characterize 18 solar analogues for which we study their surface magnetic and seismic properties. This allows us to put the Sun into context compared to its siblings.

  16. The First Focused Hard X-ray Images of the Sun with NuSTAR

    CERN Document Server

    Grefenstette, Brian W; Krucker, Säm; Hudson, Hugh; Hannah, Iain G; Smith, David M; Vogel, Julia K; White, Stephen M; Madsen, Kristin K; Marsh, Andrew J; Caspi, Amir; Chen, Bin; Shih, Albert; Kuhar, Matej; Boggs, Steven E; Christensen, Finn E; Craig, William W; Forster, Karl; Hailey, Charles J; Harrison, Fiona A; Miyasaka, Hiromasa; Stern, Daniel; Zhang, William W

    2016-01-01

    We present results from the the first campaign of dedicated solar observations undertaken by the \\textit{Nuclear Spectroscopic Telescope ARray} ({\\em NuSTAR}) hard X-ray telescope. Designed as an astrophysics mission, {\\em NuSTAR} nonetheless has the capability of directly imaging the Sun at hard X-ray energies ($>$3~keV) with an increase in sensitivity of at least two magnitude compared to current non-focusing telescopes. In this paper we describe the scientific areas where \\textit{NuSTAR} will make major improvements on existing solar measurements. We report on the techniques used to observe the Sun with \\textit{NuSTAR}, their limitations and complications, and the procedures developed to optimize solar data quality derived from our experience with the initial solar observations. These first observations are briefly described, including the measurement of the Fe K-shell lines in a decaying X-class flare, hard X-ray emission from high in the solar corona, and full-disk hard X-ray images of the Sun.

  17. Observations of non-solar-type dynamo processes in stars with shallow convective zones

    NARCIS (Netherlands)

    Jeffers, S.V.; Donati, J.F.; Alecian, E.; Marsden, S.C.

    2010-01-01

    The magnetic field topology and differential rotation are fundamental signatures of the dynamo processes that generate the magnetic activity observed in the Sun and solar-type stars. To investigate how these dynamo processes evolve in stars with shallow convective zones, we present high-resolution s

  18. Rotation period distribution of CoRoT and Kepler Sun-like stars

    Science.gov (United States)

    Leão, I. C.; Pasquini, L.; Ferreira Lopes, C. E.; Neves, V.; Valcarce, A. A. R.; de Oliveira, L. L. A.; Freire da Silva, D.; de Freitas, D. B.; Canto Martins, B. L.; Janot-Pacheco, E.; Baglin, A.; De Medeiros, J. R.

    2015-10-01

    Aims: We study the distribution of the photometric rotation period (Prot), which is a direct measurement of the surface rotation at active latitudes, for three subsamples of Sun-like stars: one from CoRoT data and two from Kepler data. For this purpose, we identify the main populations of these samples and interpret their main biases specifically for a comparison with the solar Prot. Methods: Prot and variability amplitude (A) measurements were obtained from public CoRoT and Kepler catalogs, which were combined with public data of physical parameters. Because these samples are subject to selection effects, we computed synthetic samples with simulated biases to compare with observations, particularly around the location of the Sun in the Hertzsprung-Russel (HR) diagram. Publicly available theoretical grids and empirical relations were used to combine physical parameters with Prot and A. Biases were simulated by performing cutoffs on the physical and rotational parameters in the same way as in each observed sample. A crucial cutoff is related with the detectability of the rotational modulation, which strongly depends on A. Results: The synthetic samples explain the observed Prot distributions of Sun-like stars as having two main populations: one of young objects (group I, with ages younger than ~1 Gyr) and another of main-sequence and evolved stars (group II, with ages older than ~1 Gyr). The proportions of groups I and II in relation to the total number of stars range within 64-84% and 16-36%, respectively. Hence, young objects abound in the distributions, producing the effect of observing a high number of short periods around the location of the Sun in the HR diagram. Differences in the Prot distributions between the CoRoT and Kepler Sun-like samples may be associated with different Galactic populations. Overall, the synthetic distribution around the solar period agrees with observations, which suggests that the solar rotation is normal with respect to Sun

  19. OBSERVATIONS OF INTENSITY FLUCTUATIONS ATTRIBUTED TO GRANULATION AND FACULAE ON SUN-LIKE STARS FROM THE KEPLER MISSION

    Energy Technology Data Exchange (ETDEWEB)

    Karoff, C. [Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, DK-8000 Aarhus C (Denmark); Campante, T. L. [Centro de Astrofisica and Faculdade de Ciencias, Universidade do Porto, Rua das Estrelas, 4150-762 Porto (Portugal); Ballot, J. [CNRS, Institut de Recherche en Astrophysique et Planetologie, 14 avenue Edouard Belin, F-31400, Toulouse (France); Kallinger, T. [Instituut voor Sterrenkunde, K. U. Leuven, Celestijnenlaan 200D, B-3001 Leuven (Belgium); Gruberbauer, M. [Institute for Computational Astrophysics, Department of Astronomy and Physics, Saint Mary' s University, B3H 3C3 Halifax (Canada); Garcia, R. A. [Laboratoire AIM, CEA/DSM-CNRS-Universit Paris Diderot, IRFU/SAp, Centre de Saclay, F-91191 Gif-sur-Yvette Cedex (France); Caldwell, D. A.; Christiansen, J. L. [SETI Institute/NASA Ames Research Center, Moffett Field, CA 94035 (United States); Kinemuchi, K., E-mail: karoff@phys.au.dk [Bay Area Environmental Research Inst./NASA Ames Research Center, Moffett Field, CA 94035 (United States)

    2013-04-10

    Sun-like stars show intensity fluctuations on a number of timescales due to various physical phenomena on their surfaces. These phenomena can convincingly be studied in the frequency spectra of these stars-while the strongest signatures usually originate from spots, granulation, and p-mode oscillations, it has also been suggested that the frequency spectrum of the Sun contains a signature of faculae. We have analyzed three stars observed for 13 months in short cadence (58.84 s sampling) by the Kepler mission. The frequency spectra of all three stars, as for the Sun, contain signatures that we can attribute to granulation, faculae, and p-mode oscillations. The temporal variability of the signatures attributed to granulation, faculae, and p-mode oscillations was analyzed and the analysis indicates a periodic variability in the granulation and faculae signatures-comparable to what is seen in the Sun.

  20. Contributions to Proceedings from the NATO Advanced Research Workshop on the Seismology of the Sun and the Distant Stars

    Science.gov (United States)

    1985-01-01

    Advanced research results on the seismology of the Sun and distant stars is presented. Topics presented include: (1) detection of global convective wave flows; (2) observation of low degree p-mode oscillations; and (3) techniques for spectral deconvolution.

  1. Prevalence of Earth-size planets orbiting Sun-like stars.

    Science.gov (United States)

    Petigura, Erik A; Howard, Andrew W; Marcy, Geoffrey W

    2013-11-26

    Determining whether Earth-like planets are common or rare looms as a touchstone in the question of life in the universe. We searched for Earth-size planets that cross in front of their host stars by examining the brightness measurements of 42,000 stars from National Aeronautics and Space Administration's Kepler mission. We found 603 planets, including 10 that are Earth size ( ) and receive comparable levels of stellar energy to that of Earth (1 - 2 R[Symbol: see text] ). We account for Kepler's imperfect detectability of such planets by injecting synthetic planet-caused dimmings into the Kepler brightness measurements and recording the fraction detected. We find that 11 ± 4% of Sun-like stars harbor an Earth-size planet receiving between one and four times the stellar intensity as Earth. We also find that the occurrence of Earth-size planets is constant with increasing orbital period (P), within equal intervals of logP up to ~200 d. Extrapolating, one finds 5.7(-2.2)(+1.7)% of Sun-like stars harbor an Earth-size planet with orbital periods of 200-400 d.

  2. Upgrade of the NASA 4STAR (Spectrometer for Sky-Scanning, Sun-Tracking Atmospheric Research) to its Full Science Capability of Sun-Sky-Cloud-Trace Gas Spectrometry in Airborne Science Deployments

    Science.gov (United States)

    Johnson, Roy R.; Russell, P.; Dunagan, S.; Redemann, J.; Shinozuka, Y.; Segal-Rosenheimer, M.; LeBlanc, S.; Flynn, C.; Schmid, B.; Livingston, J.

    2014-01-01

    The objectives of this task in the AITT (Airborne Instrument Technology Transition) Program are to (1) upgrade the NASA 4STAR (Spectrometer for Sky-Scanning, Sun-Tracking Atmospheric Research) instrument to its full science capability of measuring (a) direct-beam sun transmission to derive aerosol optical depth spectra, (b) sky radiance vs scattering angle to retrieve aerosol absorption and type (via complex refractive index spectra, shape, and mode-resolved size distribution), (c) zenith radiance for cloud properties, and (d) hyperspectral signals for trace gas retrievals, and (2) demonstrate its suitability for deployment in challenging NASA airborne multiinstrument campaigns. 4STAR combines airborne sun tracking, sky scanning, and zenith pointing with diffraction spectroscopy to improve knowledge of atmospheric constituents and their links to air pollution, radiant energy budgets (hence climate), and remote measurements of Earth's surfaces. Direct beam hyperspectral measurement of optical depth improves retrievals of gas constituents and determination of aerosol properties. Sky scanning enhances retrievals of aerosol type and size distribution. 4STAR measurements are intended to tighten the closure between satellite and ground-based measurements. 4STAR incorporates a modular sun-tracking/sky-scanning optical head with fiber optic signal transmission to rack mounted spectrometers, permitting miniaturization of the external optical head, and future detector evolution. 4STAR test flights, as well as science flights in the 2012-13 TCAP (Two-Column Aerosol Project) and 2013 SEAC4RS (Studies of Emissions and Atmospheric Composition, Clouds and Climate Coupling by Regional Surveys) have demonstrated that the following are essential for 4STAR to achieve its full science potential: (1) Calibration stability for both direct-beam irradiance and sky radiance, (2) Improved light collection and usage, and (3) Improved flight operability and reliability. A particular challenge

  3. Prevalence of Earth-size Planets Orbiting Sun-like Stars

    Science.gov (United States)

    Petigura, Erik Ardeshir

    2015-04-01

    In this thesis, I explore two topics in exoplanet science. The first is the prevalence of Earth-size planets in the Milky Way Galaxy. To determine the occurrence of planets having different sizes, orbital periods, and other properties, I conducted a survey of extrasolar planets using data collected by NASA's Kepler Space Telescope. This project involved writing new algorithms to analyze Kepler data, finding planets, and conducting follow-up work using ground-based telescopes. I found that most stars have at least one planet at or within Earth's orbit and that 26% of Sun-like stars have an Earth-size planet with an orbital period of 100 days or less. The second topic is the connection between the properties of planets and their host stars. The precise characterization of exoplanet hosts helps to bring planet properties like mass, size, and equilibrium temperature into sharper focus and probes the physical processes that form planets. I studied the abundance of carbon and oxygen in over 1000 nearby stars using optical spectra taken by the California Planet Search. I found a large range in the relative abundance of carbon and oxygen in this sample, including a handful of carbon-rich stars. I also developed a new technique called SpecMatch for extracting fundamental stellar parameters from optical spectra. SpecMatch is particularly applicable to the relatively faint planet-hosting stars discovered by Kepler.

  4. A New Association of Post-T Tauri Stars Near The Sun

    CERN Document Server

    Torres, C A O; Quast, G R; De la Reza, R; Jilinski, E; Torres, Carlos A. O.; Silva, Licio da; Quast, Germano R.; Reza, Ramiro de la; Jilinski, Evgueni

    2000-01-01

    Observing ROSAT sources in 20 x 25 deg centered at the high latitude active star ER Eri, we found evidences for a new young nearby association (~30Myr at~60pc), the Horologium Association (HorA), formed by at least 10 probable and 6 possible members, some being Post-T Tauri stars. We examine several requirements that characterize a young association and they, together, create a strong evidence for the reality of the HorA. In fact, the Li line intensities are between those of the oldest classical T Tauri stars and the ones of the Local Association stars. The space velocities of the HorA relative to the Sun, U= -9.5+/-1.0, V = -20.9 +/- 1.1, W = -2.1 +/- 1.9, are not far from those of the Local Association. We suggest that some hotter and non-X-ray active stars, with similar space velocities, could be massive members of the HorA, among them, the nearby Be star Achernar. The maximum of the mass distribution function of the HorA is around 0.8 solar masses. At its distance, the projected size of the HorA, ~50 pc, ...

  5. The Solar Twin Planet Search: IV. The Sun as a typical rotator and evidence for a new rotational braking law for Sun-like stars

    CERN Document Server

    Santos, Leonardo A dos; Nascimento, José-Dias do; Bedell, Megan; Ramírez, Iván; Bean, Jacob L; Asplund, Martin; Spina, Lorenzo; Dreizler, Stefan; Alves-Brito, Alan; Casagrande, Luca

    2016-01-01

    It is still unclear how common the Sun is when compared to other similar stars in regards to some of its physical properties, such as rotation. Considering that gyrochronology relations are widely used today to estimate ages of stars in the main sequence, and that the Sun is used to calibrate it, it is crucial to assess if these procedures are acceptable. We analyze the rotational velocities -- limited by the unknown rotation axis inclination angle -- of an unprecedented large sample of solar twins in order to study the rotational evolution of Sun-like stars, and assess if the Sun is a typical rotator. We use high-resolution ($R = 115000$) spectra obtained with the HARPS spectrograph and ESO's 3.6 m telescope at La Silla Observatory. The projected rotational velocities for 82 solar twins are estimated by line profile fitting with synthetic spectra. Macroturbulence velocities are inferred from a prescription that accurately reflects their dependence with effective temperature and luminosity of the stars. Our s...

  6. Long-term radial-velocity variations of the Sun as a star: the HARPS view

    CERN Document Server

    Lanza, A F; Monaco, L; Haywood, R D

    2016-01-01

    Stellar radial velocities play a fundamental role in the discovery of extrasolar planets and the measurement of their physical parameters as well as in the study of stellar physical properties. We investigate the impact of the solar activity on the radial velocity of the Sun using the HARPS spectrograph to obtain measurements that can be directly compared with those acquired in the extrasolar planet search programs. We use the Moon, the Galilean satellites, and several asteroids as reflectors to measure the radial velocity of the Sun as a star and correlate it with disc-integrated chromospheric and magnetic indexes of solar activity that are similar to stellar activity indexes. We discuss in detail the systematic effects that affect our measurements and the methods to account for them. We find that the radial velocity of the Sun as a star is positively correlated with the level of its chromospheric activity at about 95 percent significance level. The amplitude of the long-term variation measured in the 2006-2...

  7. High dispersion spectroscopy of solar-type superflare stars with Subaru/HDS

    CERN Document Server

    Notsu, Yuta; Maehara, Hiroyuki; Notsu, Shota; Shibayama, Takuya; Nogami, Daisaku; Shibata, Kazunari

    2015-01-01

    We carried out spectroscopic observations with Subaru/HDS of 50 solar-type superflare stars found from Kepler data. More than half (34 stars) of the target stars show no evidence of the binary system, and we confirmed atmospheric parameters of these stars are roughly in the range of solar-type stars. We then conducted the detailed analyses for these 34 stars. First, the value of the "$v\\sin i$" (projected rotational velocity) measured from spectroscopic results is consistent with the rotational velocity estimated from the brightness variation. Second, there is a correlation between the amplitude of the brightness variation and the intensity of Ca II IR triplet line. All the targets expected to have large starspots because of their large amplitude of the brightness variation show high chromospheric activities compared with the Sun. These results support that the brightness variation of superflare stars is explained by the rotation of a star with large starspots.

  8. {High dispersion spectroscopy of solar-type superflare stars with Subaru/HDS†

    Science.gov (United States)

    Notsu, Yuta; Honda, Satoshi; Maehara, Hiroyuki; Notsu, Shota; Shibayama, Takuya; Nogami, Daisaku; Shibata, Kazunari

    We carried out spectroscopic observations with Subaru/HDS of 50 solar-type superflare stars found from Kepler data. More than half (34 stars) of the target stars show no evidence of the binary system, and we confirmed atmospheric parameters of these stars are roughly in the range of solar-type stars. We then conducted the detailed analyses for these 34 stars. First, the value of the ``v sin i'' (projected rotational velocity) measured from spectroscopic results is consistent with the rotational velocity estimated from the brightness variation. Second, there is a correlation between the amplitude of the brightness variation and the intensity of Ca II IR triplet line. All the targets expected to have large starspots because of their large amplitude of the brightness variation show high chromospheric activities compared with the Sun. These results support that the brightness variation of superflare stars is explained by the rotation of a star with large starspots.

  9. Prevalence of Earth-size planets orbiting Sun-like stars

    CERN Document Server

    Petigura, Erik A; Marcy, Geoffrey W

    2013-01-01

    Determining whether Earth-like planets are common or rare looms as a touchstone in the question of life in the universe. We searched for Earth-size planets that cross in front of their host stars by examining the brightness measurements of 42,000 stars from National Aeronautics and Space Administration's Kepler mission. We found 603 planets, including 10 that are Earth size (1-2 Earth-radii) and receive comparable levels of stellar energy to that of Earth (within a factor of four). We account for Kepler's imperfect detectability of such planets by injecting synthetic planet-caused dimmings into the Kepler brightness measurements and recording the fraction detected. We find that $11\\pm4%$ of Sun-like stars harbor an Earth-size planet receiving between one and four times the stellar intensity as Earth. We also find that the occurrence of Earth-size planets is constant with increasing orbital period (P), within equal intervals of logP up to $\\sim200$ d. Extrapolating, one finds $5.7^{+1.7}_{-2.2}%$ of Sun-like s...

  10. Young Stars and Planets Near the Sun in 2015: Five Takeaways and Five Predictions

    CERN Document Server

    Liu, Michael C

    2016-01-01

    I present a highly biased and skewed summary of IAU Symposium 314, "Young Stars and Planets Near the Sun," held in Atlanta. This summary includes takeaway thoughts about the rapidly evolving state of the field, as well as crowd-sourced predictions for progress over the next ~10 years. We predict the elimination of 1-2 of the currently recognized young moving groups, the addition of 3 or more new moving groups within 100 pc, the continued lack of a predictive theory of stellar mass, robust measurements of the gas and dust content of circumstellar disks, and an ongoing struggle to achieve a consensus definition for a planet.

  11. Many skies alternative histories of the Sun, Moon, planets, and stars

    CERN Document Server

    Upgren, Arthur

    2005-01-01

    Many Skies: Alternative Histories of the Sun, Moon, Planets, and Stars examines the changes in science that  alternative solar, stellar, and galactic arrangements would have brought, and explores the different theologies, astrologies, and methods of tracking time that would have developed to reflect them. Our perception of our surroundings, the number of gods we worship, the symbols we use in art and literature, even the way we form nations and empires are all closely tied to our particular (and accidental) placement in the universe.  Upgren also explores the actual ways tha

  12. A photometric and spectroscopic survey of solar twin stars within 50 parsecs of the Sun: I. Atmospheric parameters and color similarity to the Sun

    CERN Document Server

    de Mello, G F Porto; da Silva, L; de Nader, R V

    2013-01-01

    Solar twins and analogs are fundamental in the characterization of the Sun's place in the context of stellar measurements, as they are in understanding how typical the solar properties are in its neighborhood. They are also important for representing sunlight observable in the night sky for diverse photometric and spectroscopic tasks, besides being natural candidates for harboring planetary systems similar to ours and possibly even life-bearing environments. We report a photometric and spectroscopic survey of solar twin stars within 50 pc of the Sun. Hipparcos absolute magnitudes and (B-V)_Tycho colors were used to define a 2 sigma box around the solar values, where 133 stars were considered. Additional stars resembling the solar UBV colors in a broad sense, plus stars present in the lists of Hardorp, were also selected. All objects were ranked by a color-similarity index with respect to the Sun, defined by uvby and BV photometry. Moderately high-resolution, high-S/N spectra were used for a subsample of equat...

  13. Prevalence of Earth-size Planets Orbiting Sun-like Stars

    CERN Document Server

    Petigura, Erik Ardeshir

    2015-01-01

    In this thesis, I explore two topics in exoplanet science. The first is the prevalence of Earth-size planets in the Milky Way Galaxy. To determine the occurrence of planets having different sizes, orbital periods, and other properties, I conducted a survey of extrasolar planets using data collected by NASA's Kepler Space Telescope. This project involved writing new algorithms to analyze Kepler data, finding planets, and conducting follow-up work using ground-based telescopes. I found that most stars have at least one planet at or within Earth's orbit and that 26% of Sun-like stars have an Earth-size planet with an orbital period of 100 days or less. The second topic is the connection between the properties of planets and their host stars. The precise characterization of exoplanet hosts helps to bring planet properties like mass, size, and equilibrium temperature into sharper focus and probes the physical processes that form planets. I studied the abundance of carbon and oxygen in over 1000 nearby stars using ...

  14. Rotating models of young solar-type stars : Exploring braking laws and angular momentum transport processes

    CERN Document Server

    Amard, Louis; Charbonnel, Corinne; Gallet, Florian; Bouvier, Jérôme

    2016-01-01

    We study the predicted rotational evolution of solar-type stars from the pre-main sequence to the solar age with 1D rotating evolutionary models including physical ingredients. We computed rotating evolution models of solar-type stars including an external stellar wind torque and internal transport of angular momentum following the method of Maeder and Zahn with the code STAREVOL. We explored different formalisms and prescriptions available from the literature. We tested the predictions of the models against recent rotational period data from extensive photometric surveys, lithium abundances of solar-mass stars in young clusters, and the helioseismic rotation profile of the Sun. We find a best-matching combination of prescriptions for both internal transport and surface extraction of angular momentum. This combination provides a very good fit to the observed evolution of rotational periods for solar-type stars from early evolution to the age of the Sun. Additionally, we show that fast rotators experience a st...

  15. Brightness Variations of Sun-like Stars: The Mystery Deepens - Astronomers facing Socratic "ignorance"

    Science.gov (United States)

    2009-12-01

    An extensive study made with ESO's Very Large Telescope deepens a long-standing mystery in the study of stars similar to the Sun. Unusual year-long variations in the brightness of about one third of all Sun-like stars during the latter stages of their lives still remain unexplained. Over the past few decades, astronomers have offered many possible explanations, but the new, painstaking observations contradict them all and only deepen the mystery. The search for a suitable interpretation is on. "Astronomers are left in the dark, and for once, we do not enjoy it," says Christine Nicholls from Mount Stromlo Observatory, Australia, lead author of a paper reporting the study. "We have obtained the most comprehensive set of observations to date for this class of Sun-like stars, and they clearly show that all the possible explanations for their unusual behaviour just fail." The mystery investigated by the team dates back to the 1930s and affects about a third of Sun-like stars in our Milky Way and other galaxies. All stars with masses similar to our Sun become, towards the end of their lives, red, cool and extremely large, just before retiring as white dwarfs. Also known as red giants, these elderly stars exhibit very strong periodic variations in their luminosity over timescales up to a couple of years. "Such variations are thought to be caused by what we call 'stellar pulsations'," says Nicholls. "Roughly speaking, the giant star swells and shrinks, becoming brighter and dimmer in a regular pattern. However, one third of these stars show an unexplained additional periodic variation, on even longer timescales - up to five years." In order to find out the origin of this secondary feature, the astronomers monitored 58 stars in our galactic neighbour, the Large Magellanic Cloud, over two and a half years. They acquired spectra using the high resolution FLAMES/GIRAFFE spectrograph on ESO's Very Large Telescope and combined them with images from other telescopes [1

  16. Interactions between brown-dwarf binaries and Sun-like stars

    CERN Document Server

    Kaplan, M; Whitworth, A P

    2012-01-01

    Several mechanisms have been proposed for the formation of brown dwarfs, but there is as yet no consensus as to which -- if any -- are operative in nature. Any theory of brown dwarf formation must explain the observed statistics of brown dwarfs. These statistics are limited by selection effects, but they are becoming increasingly discriminating. In particular, it appears (a) that brown dwarfs that are secondaries to Sun-like stars tend to be on wide orbits, $a\\ga 100\\,{\\rm AU}$ (the Brown Dwarf Desert), and (b) that these brown dwarfs have a significantly higher chance of being in a close ($a\\la 10\\,{\\rm AU}$) binary system with another brown dwarf than do brown dwarfs in the field. This then raises the issue of whether these brown dwarfs have formed {\\it in situ}, i.e. by fragmentation of a circumstellar disc; or have formed elsewhere and subsequently been captured. We present numerical simulations of the purely gravitational interaction between a close brown-dwarf binary and a Sun-like star. These simulatio...

  17. High Precision Full Stokes Spectropolarimetry of the Sun as a star-Instrument design aspects

    CERN Document Server

    Bose, Souvik

    2016-01-01

    The magnetic field plays a major role in governing the dynamics of the sun. Many interesting features like sunspots, flares, prominences, and Coronal Mass Ejections (CMEs) occur on its surface due to the dynamics associated with the magnetic fields. The magnetic activity exhibits spatial scales ranging from very fine scale (below the resolution limit of the current largest telescope) to large scale such as sunspots, active regions and the spatial scales as large as the sun itself. While the major efforts in building large telescopes is going on towards the goal of resolving smallest structure possible we propose here to measure the magnetic field on the global scale. For this purpose we propose an instrument to carryout high precision and high accurate spectropolarimetry of sun-as-a-star. In this thesis, we explore various instrumental design aspects that are necessary to make such observations. As part of the design consideration we have analysed a major noise source i.e. seeing induced cross-talk through si...

  18. Ancient Black Hole Speeds Through Sun's Galactic Neighborhood, Devouring Companion Star

    Science.gov (United States)

    2001-09-01

    Astronomers using the National Science Foundation's Very Long Baseline Array (VLBA) radio telescope have found an ancient black hole speeding through the Sun's Galactic neighborhood, devouring a small companion star as the pair travels in an eccentric orbit looping to the outer reaches of our Milky Way Galaxy. The scientists believe the black hole is the remnant of a massive star that lived out its brief life billions of years ago and later was gravitationally kicked from its home star cluster to wander the Galaxy with its companion. "This discovery is the first step toward filling in a missing chapter in the history of our Galaxy," said Felix Mirabel, an astrophysicist at the Institute for Astronomy and Space Physics of Argentina and French Atomic Energy Commission. "We believe that hundreds of thousands of very massive stars formed early in the history of our Galaxy, but this is the first black hole remnant of one of those huge primeval stars that we've found." "This also is the first time that a black hole's motion through space has been measured," Mirabel added. A black hole is a dense concentration of mass with a gravitational pull so strong that not even light can escape it. The research is reported in the Sept. 13 issue of the scientific journal Nature. XTE J1118+480 The object is called XTE J1118+480 and was discovered by the Rossi X-Ray satellite on March 29, 2000. Later observations with optical and radio telescopes showed that it is about 6,000 light-years from Earth and that it is a "microquasar" in which material sucked by the black hole from its companion star forms a hot, spinning disk that spits out "jets" of subatomic particles that emit radio waves. Most of the stars in our Milky Way Galaxy are within a thin disk, called the plane of the Galaxy. However, there also are globular clusters, each containing hundreds of thousands of the oldest stars in the Galaxy which orbit the Galaxy's center in paths that take them far from the Galaxy's plane. XTE J

  19. Asteroseismic Inference for Solar-Type Stars

    CERN Document Server

    Monteiro, M J P F G; Thompson, M J

    2001-01-01

    The oscillation spectra of solar-type stars may in the not-too- distant future be used to constrain certain properties of the stars. The CD diagram of large versus small frequency separations is one of the powerful tools available to infer the properties - including perhaps masses and ages - of stars which display a detectable spectrum of oscillation. Also, the border of a convective region in a solar-type star gives rise to a characteristic periodic signal in the star's low-degree p-mode frequencies. Such a signature contains information about the location and nature of the transition between convective and non-convective regions in the star. In this work we address some of the uncertainties associated with the direct use of the CD diagram to evaluate the mass and age of the star due to the unknown contributions that make the stars different from the evolutionary models used to construct our reference grid. We also explore the possibility of combining an amplitude versus period diagram with the CD diagram to...

  20. WASP-26b: A 1-Jupiter-mass planet around an early-G-type star

    CERN Document Server

    Smalley, B; Cameron, A Collier; Gillon, M; Hellier, C; Lister, T A; Maxted, P F L; Queloz, D; Triaud, A H M J; West, R G; Bentley, S J; Enoch, B; Pepe, F; Pollacco, D L; Segransan, D; Smith, A M S; Southworth, J; Udry, S; Wheatley, P J; Wood, P L; Bento, J

    2010-01-01

    We report the discovery of WASP-26b, a moderately over-sized Jupiter-mass exoplanet transiting its 11.3-magnitude early-G-type host star (1SWASP J001824.70-151602.3; TYC 5839-876-1) every 2.7566 days. A simultaneous fit to transit photometry and radial-velocity measurements yields a planetary mass of 1.02 +/- 0.03 M_Jup and radius of 1.32 +/- 0.08 R_Jup. The host star, WASP-26, has a mass of 1.12 +/- 0.03 M_sun and a radius of 1.34 +/- 0.06 R_sun and is in a visual double with a fainter K-type star. The two stars are at least a common-proper motion pair with a common distance of around 250 +/- 15 pc and an age of 6 +/- 2 Gy.

  1. Variability of stellar granulation and convective blueshift with spectral type and magnetic activity. I. K and G main sequence stars

    OpenAIRE

    Meunier, N.; Lagrange, A. -M.; Kabuiku, L. Mbemba; Alex, M; Mignon, L.; Borgniet, S.

    2016-01-01

    In solar-type stars, the attenuation of convective blueshift by stellar magnetic activity dominates the RV variations over the low amplitude signal induced by low mass planets. Models of stars that differ from the Sun will require a good knowledge of the attenuation of the convective blueshift to estimate its impact on the variations. It is therefore crucial to precisely determine not only the amplitude of the convective blueshift for different types of stars, but also the dependence of this ...

  2. HAT-P-55b: A Hot Jupiter Transiting a Sun-like Star

    CERN Document Server

    Juncher, D; Hartman, J D; Bakos, G Á; Bieryla, A; Kovács, T; Boisse, I; Latham, D W; Kovács, G; Bhatti, W; Csubry, Z; Penev, K; de Val-Borro, M; Falco, E; Torres, G; Noyes, R W; Lázár, J; Papp, I; Sári, P

    2015-01-01

    We report the discovery of a new transiting extrasolar planet, HAT-P-55b. The planet orbits a V = 13.207 +/- 0.039 sun-like star with a mass of 1.013 +/- 0.037 solar masses, a radius of 1.011 +/- 0.036 solar radii and a metallicity of -0.03 +/- 0.08. The planet itself is a typical hot Jupiter with a period of 3.5852467 +/- 0.0000064 days, a mass of 0.582 +/- 0.056 Jupiter masses and a radius of 1.182 +/- 0.055 Jupiter radii. This discovery adds to the increasing sample of transiting planets with measured bulk densities, which is needed to put constraints on models of planetary structure and formation theories.

  3. Rotation and surface abundance peculiarities in A-type stars

    CERN Document Server

    Takeda, Yoichi; Kang, Dong-Il; Lee, Byeong-Cheol; Kim, Kang-Min

    2008-01-01

    In an attempt of clarifying the connection between the photospheric abundance anomalies and the stellar rotation as well as of exploring the nature of "normal A" stars, the abundances of seven elements (C, O, Si, Ca, Ti, Fe, and Ba) and the projected rotational velocity for 46 A-type field stars were determined by applying the spectrum-fitting method to the high-dispersion spectral data obtained with BOES at BOAO. We found that the peculiarities (underabundances of C, O, and Ca; an overabundance of Ba) seen in slow rotators efficiently decrease with an increase of rotation, which almost disappear at v_e sin i > 100 km s^-1. This further suggests that stars with sufficiently large rotational velocity may retain the original composition at the surface without being altered. Considering the subsolar tendency (by several tenths dex below) exhibited by the elemental abundances of such rapidly-rotating (supposedly normal) A stars, we suspect that the gas metallicity may have decreased since our Sun was born, contra...

  4. On the rotation period distribution of CoRoT and Kepler Sun-like stars

    CERN Document Server

    Leao, I C; Lopes, C E Ferreira; Neves, V; Valcarce, A A R; de Oliveira, L L A; da Silva, D Freire; de Freitas, D B; Martins, B L Canto; Janot-Pacheco, E; Baglin, A; De Medeiros, J R

    2015-01-01

    We study the distribution of the photometric rotation period (Prot), which is a direct measurement of the surface rotation at active latitudes, for three subsamples of Sun-like stars: one from CoRoT data and two from Kepler data. We identify the main populations of these samples and interpret their main biases particularly for a comparison with the solar Prot. Prot and variability amplitude (A) measurements were obtained from public CoRoT and Kepler catalogs, which were combined with public data of physical parameters. Because these samples are subject to selection effects, we computed synthetic samples with simulated biases to compare with observations, particularly around the Sun's HR-diagram location. Theoretical grids and empirical relations were used to combine physical parameters with Prot and A. Biases were simulated by performing cutoffs on the physical and rotational parameters in the same way as in each observed sample. A crucial cutoff is related with the detectability of the rotational modulation,...

  5. Supernova enrichment and dynamical histories of solar-type stars in clusters

    CERN Document Server

    Parker, Richard J; Davies, Melvyn B; Meyer, Michael R

    2013-01-01

    We use N-body simulations of star cluster evolution to explore the hypothesis that short-lived radioactive isotopes found in meteorites, such as 26-Al, were delivered to the Sun's protoplanetary disc from a supernova at the epoch of Solar System formation. We cover a range of star cluster formation parameter space and model both clusters with primordial substructure, and those with smooth profiles. We also adopt different initial virial ratios - from cool, collapsing clusters to warm, expanding associations. In each cluster we place the same stellar population; the clusters each have 2100 stars, and contain one massive 25M_Sun star which is expected to explode as a supernova at about 6.6Myr. We determine the number of Solar (G)-type stars that are within 0.1 - 0.3pc of the 25M_Sun star at the time of the supernova, which is the distance required to enrich the protoplanetary disc with the 26-Al abundances found in meteorites. We then determine how many of these G-dwarfs are unperturbed `singletons'; stars whic...

  6. Research on Non-radial Oscillations of the Sun and Stars in the Early 1970s

    Science.gov (United States)

    Osaki, Y.

    2013-12-01

    I describe some historical background of helio- and astero-seismology research in the early 1970s from my personal recollection, particularly on how our Tokyo research group on non-radial oscillations of stars got started. I also describe my recent research on the super-outburst mechanism of SU UMa-type dwarf novae.

  7. CALCULATING THE HABITABLE ZONE OF BINARY STAR SYSTEMS. II. P-TYPE BINARIES

    Energy Technology Data Exchange (ETDEWEB)

    Haghighipour, Nader [Institute for Astronomy and NASA Astrobiology Institute, University of Hawaii-Manoa, Honolulu, HI 96822 (United States); Kaltenegger, Lisa [MPIA, Koenigstuhl 17, Heidelberg, D-69117 (Germany)

    2013-11-10

    We have developed a comprehensive methodology for calculating the circumbinary habitable zone (HZ) in planet-hosting P-type binary star systems. We present a general formalism for determining the contribution of each star of the binary to the total flux received at the top of the atmosphere of an Earth-like planet and use the Sun's HZ to calculate the inner and outer boundaries of the HZ around a binary star system. We apply our calculations to the Kepler's currently known circumbinary planetary systems and show the combined stellar flux that determines the boundaries of their HZs. We also show that the HZ in P-type systems is dynamic and, depending on the luminosity of the binary stars, their spectral types, and the binary eccentricity, its boundaries vary as the stars of the binary undergo their orbital motion. We present the details of our calculations and discuss the implications of the results.

  8. Richest Planetary System Discovered - Up to seven planets orbiting a Sun-like star

    Science.gov (United States)

    2010-08-01

    Astronomers using ESO's world-leading HARPS instrument have discovered a planetary system containing at least five planets, orbiting the Sun-like star HD 10180. The researchers also have tantalising evidence that two other planets may be present, one of which would have the lowest mass ever found. This would make the system similar to our Solar System in terms of the number of planets (seven as compared to the Solar System's eight planets). Furthermore, the team also found evidence that the distances of the planets from their star follow a regular pattern, as also seen in our Solar System. "We have found what is most likely the system with the most planets yet discovered," says Christophe Lovis, lead author of the paper reporting the result. "This remarkable discovery also highlights the fact that we are now entering a new era in exoplanet research: the study of complex planetary systems and not just of individual planets. Studies of planetary motions in the new system reveal complex gravitational interactions between the planets and give us insights into the long-term evolution of the system." The team of astronomers used the HARPS spectrograph, attached to ESO's 3.6-metre telescope at La Silla, Chile, for a six-year-long study of the Sun-like star HD 10180, located 127 light-years away in the southern constellation of Hydrus (the Male Water Snake). HARPS is an instrument with unrivalled measurement stability and great precision and is the world's most successful exoplanet hunter. Thanks to the 190 individual HARPS measurements, the astronomers detected the tiny back and forth motions of the star caused by the complex gravitational attractions from five or more planets. The five strongest signals correspond to planets with Neptune-like masses - between 13 and 25 Earth masses [1] - which orbit the star with periods ranging from about 6 to 600 days. These planets are located between 0.06 and 1.4 times the Earth-Sun distance from their central star. "We also have

  9. The Sun-as-a-star As Seen By Hinode XRT

    Science.gov (United States)

    Saar, Steven H.; DeLuca, E. E.

    2007-05-01

    We study full disk images of the Sun taken in multiple filters with the Hinode XRT during the current low state of the solar cycle (late 2006). Taking advantage of the wide temperature sensitivity of the XRT, we construct spatially averaged emission measure (EM) curves for each of several solar region types, including coronal holes, quiet Sun, bright points, and active regions of various description. These are used to determine the relative contribution of the various features to the total solar EM, as a starting point for a program to investigate their time variation. We also explore use of the average EM curves for understanding spatially unresolved stellar spectra and their correlation with underlying magnetic fields. The US XRT team is supported by a contract from NASA to SAO. Hinode is an international project supported by JAXA, NASA, PPARC and ESA. We are grateful to the Hinode team for all their efforts in the design, development and operation of the mission.

  10. On laminar convection in solar type stars

    CERN Document Server

    Bruevich, E A

    2010-01-01

    We present a new model of large-scale multilayer convection in solar type stars. This model allows us to understand such self-similar structures observed at solar surface as granulation, supergranulation and giant cells. We study the slow-rotated hydrogen star without magnetic field with the spherically-symmetric convective zone. The photon's flux comes to the convective zone from the central thermonuclear zone of the star. The interaction of these photons with the fully ionized hydrogen plasma with $T>10^5K$ is carried out by the Tomson scattering of photon flux on protons and electrons. Under these conditions plasma is optically thick relative to the Tomson scattering. This fact is the fundamental one for the multilayer convection formation. We find the stationary solution of the convective zone structure. This solution describes the convective layers responsible to the formation of the structures on the star's surface.

  11. The influence of the magnetic topology on the wind braking of sun-like stars.

    Science.gov (United States)

    Réville, V.; Brun, A. S.; Matt, S. P.; Strugarek, A.; Pinto, R.

    2014-12-01

    Stellar winds are thought to be the main process responsible for the spin down of main-sequence stars. The extraction of angular momentum by a magnetized wind has been studied for decades, leading to several formulations for the resulting torque. However, previous studies generally consider simple dipole or split monopole stellar magnetic topologies. Here we consider in addition to a dipolar stellar magnetic field, both quadrupolar and octupolar configurations, while also varying the rotation rate and the magnetic field strength. 60 simulations made with a 2.5D, cylindrical and axisymmetric set-up and computed with the PLUTO code were used to find torque formulations for each topology. We further succeed to give a unique law that fits the data for every topology by formulating the torque in terms of the amount of open magnetic flux in the wind. We also show that our formulation can be applied to even more realistic magnetic topologies, with examples of the Sun in its minimum and maximum phase as observed at the Wilcox Solar Observatory, and of a young K-star (TYC-0486-4943-1) whose topology has been obtained by Zeeman-Doppler Imaging (ZDI).

  12. Activity and Magnetic Field Structure of the Sun-Like Planet Hosting Star HD 1237

    CERN Document Server

    Alvarado-Gómez, J D; Grunhut, J; Fares, R; Donati, J -F; Alecian, E; Kochukhov, O; Oksala, M; Morin, J; Redfield, S; Cohen, O; Drake, J J; Jardine, M; Matt, S; Petit, P; Walter, F M

    2015-01-01

    We analyse the magnetic activity characteristics of the planet hosting Sun-like star, HD 1237, using HARPS spectro-polarimetric time-series data. We find evidence of rotational modulation of the magnetic longitudinal field measurements consistent with our ZDI analysis, with a period of 7 days. We investigate the effect of customising the LSD mask to the line depths of the observed spectrum and find that it has a minimal effect on shape of the extracted Stokes V profile but does result in a small increase in the S/N ($\\sim$ 7%). We find that using a Milne-Eddington solution to describe the local line profile provides a better fit to the LSD profiles in this slowly rotating star, which also impacts the recovered ZDI field distribution. We also introduce a fit-stopping criterion based on the information content (entropy) of the ZDI maps solution set. The recovered magnetic field maps show a strong (+90 G) ring-like azimuthal field distribution and a complex radial field dominating at mid latitudes ($\\sim$45 degr...

  13. B-type stars in eclipsing binaries

    Science.gov (United States)

    Ratajczak, Milena; Pigulski, Andrzej

    2016-07-01

    B-type stars in eclipsing binary systems are unique astrophysical tools to test several aspects of stellar evolution. Such objects can be used e.g. to determine the masses of Beta Cephei variable stars, as well as help to place tighter constraints on the value of the convective core overshooting parameter α. Both precise photometry and high-resolution spectroscopy with high SNR are required to achieve these goals, but since many of the targets are bright enough, the challenge is fair. Following this assumption, we shall explain how we plan to examine both the aforementioned aspects of stellar evolution using observations of B-type stars obtained with a wide range of spectrographs, as well as BRITE-Constellation satellites.

  14. Infrared Observations of Late Type Stars

    Science.gov (United States)

    Merrill, K. M.

    1977-01-01

    Substantive mass loss resulting in appreciable circumstellar dust envelopes is common in late-type stars. The evolutionary history and physical state of a cool star determine the chemistry within the outer stellar atmosphere mirrored by the molecular and particulate material present in the envelope. The observational consequences of this debris determined by moderate spectral resolution infrared spectrophotometry are reviewed. Significant information is provided by observations of the emergent energy flux of both the cool stellar photosphere and of the circumstellar dust envelope. The observation suggests that mass-loss occurs to some degree throughout late stellar evolutionary phases and that occasional periods of high mass loss are not uncommon.

  15. The influence of the magnetic topology on the braking of sun-like stars

    CERN Document Server

    Réville, Victor; Matt, Sean; Strugarek, Antoine; Pinto, Rui

    2014-01-01

    Stellar winds are thought to be the main process responsible for the spin down of main-sequence stars. The extraction of angular momentum by a magnetized wind has been studied for decades, leading to several formulations for the resulting torque. However, previous studies generally consider simple dipole or split monopole stellar magnetic topologies. Here we consider in addition to a dipolar stellar magnetic field, both quadrupolar and octupolar configurations, while also varying the rotation rate and the magnetic field strength. 60 simulations made with a 2.5D, cylindrical and axisymmetric set-up and computed with the PLUTO code were used to find torque formulations for each topology. We further succeed to give a unique law that fits the data for every topology by formulating the torque in terms of the amount of open magnetic flux in the wind. We also show that our formulation can be applied to even more realistic magnetic topologies, with examples of the Sun in its minimum and maximum phase as observed at t...

  16. Wide companions to Hipparcos stars within 67 pc of the Sun

    CERN Document Server

    Tokovinin, Andrei

    2012-01-01

    A catalog of common-proper-motion (CPM) companions to stars within 67 pc of the Sun is constructed based on the SUPERBLINK proper-motion survey. It contains 1392 CPM pairs with angular separations 30" < \\rho < 1800", relative proper motion between the two components less than 25 mas/yr, magnitudes and colors of the secondaries consistent with those of dwarfs in the (M_V,V-J) diagram. In addition, we list 21 candidate white-dwarf CPM companions with separations under 300", about half of which should be physical. We estimate a 0.31 fraction of pairs with red-dwarf companions to be physical systems (about 425 objects), while the rest (mostly wide pairs) are chance alignments. For each candidate companion, the probability of a physical association is evaluated. The distribution of projected separations s of the physical pairs between 2 kAU and 64 kAU follows f(s) ~ s^{-1.5}, which decreases faster than \\"Opik's law. We find that Solar-mass dwarfs have no less than 4.4% +/- 0.3% companions with separations l...

  17. Kepler-9: A System of Multiple Planets Transiting a Sun-Like Star, Confirmed by Timing Variations

    Science.gov (United States)

    Holman, Matthew J.; Fabrycky, Daniel C.; Ragozzine, Darin; Ford, Eric B.; Steffen, Jason H.; Welsh, William F.; Lissauer, Jack J.; Latham, David W.; Marcy, Geoffrey W.; Walkowicz, Lucianne M.; Batalha, Natalie M.; Jenkins, Jon M.; Rowe, Jason F.; Cochran, William D.; Fressin, Francois; Torres, Guillermo; Buchhave, Lars A.; Sasselov, Dimitar D.; Borucki, William J.; Koch, David G.; Basri, Gibor; Brown, Timothy M.; Caldwell, Douglas A.; Charbonneau, David; Dunham, Edward W.; Gautier, Thomas N.; Geary, John C.; Gilliland, Ronald L.; Haas, Michael R.; Howell, Steve B.; Ciardi, David R.; Endl, Michael; Fischer, Debra; Fürész, Gábor; Hartman, Joel D.; Isaacson, Howard; Johnson, John A.; MacQueen, Phillip J.; Moorhead, Althea V.; Morehead, Robert C.; Orosz, Jerome A.

    2010-10-01

    The Kepler spacecraft is monitoring more than 150,000 stars for evidence of planets transiting those stars. We report the detection of two Saturn-size planets that transit the same Sun-like star, based on 7 months of Kepler observations. Their 19.2- and 38.9-day periods are presently increasing and decreasing at respective average rates of 4 and 39 minutes per orbit; in addition, the transit times of the inner body display an alternating variation of smaller amplitude. These signatures are characteristic of gravitational interaction of two planets near a 2:1 orbital resonance. Six radial-velocity observations show that these two planets are the most massive objects orbiting close to the star and substantially improve the estimates of their masses. After removing the signal of the two confirmed giant planets, we identified an additional transiting super-Earth-size planet candidate with a period of 1.6 days.

  18. Kepler-9: a system of multiple planets transiting a Sun-like star, confirmed by timing variations.

    Science.gov (United States)

    Holman, Matthew J; Fabrycky, Daniel C; Ragozzine, Darin; Ford, Eric B; Steffen, Jason H; Welsh, William F; Lissauer, Jack J; Latham, David W; Marcy, Geoffrey W; Walkowicz, Lucianne M; Batalha, Natalie M; Jenkins, Jon M; Rowe, Jason F; Cochran, William D; Fressin, Francois; Torres, Guillermo; Buchhave, Lars A; Sasselov, Dimitar D; Borucki, William J; Koch, David G; Basri, Gibor; Brown, Timothy M; Caldwell, Douglas A; Charbonneau, David; Dunham, Edward W; Gautier, Thomas N; Geary, John C; Gilliland, Ronald L; Haas, Michael R; Howell, Steve B; Ciardi, David R; Endl, Michael; Fischer, Debra; Fürész, Gábor; Hartman, Joel D; Isaacson, Howard; Johnson, John A; MacQueen, Phillip J; Moorhead, Althea V; Morehead, Robert C; Orosz, Jerome A

    2010-10-01

    The Kepler spacecraft is monitoring more than 150,000 stars for evidence of planets transiting those stars. We report the detection of two Saturn-size planets that transit the same Sun-like star, based on 7 months of Kepler observations. Their 19.2- and 38.9-day periods are presently increasing and decreasing at respective average rates of 4 and 39 minutes per orbit; in addition, the transit times of the inner body display an alternating variation of smaller amplitude. These signatures are characteristic of gravitational interaction of two planets near a 2:1 orbital resonance. Six radial-velocity observations show that these two planets are the most massive objects orbiting close to the star and substantially improve the estimates of their masses. After removing the signal of the two confirmed giant planets, we identified an additional transiting super-Earth-size planet candidate with a period of 1.6 days.

  19. Zeeman-Doppler imaging of active young solar type stars

    CERN Document Server

    Hackman, Thomas; Rosén, Lisa; Kochukhov, Oleg; Käpylä, Maarit J

    2015-01-01

    By studying young magnetically active late-type stars, i.e. analogues to the young Sun, one can draw conclusions on the evolution of the solar dynamo. We determine the topology of the surface magnetic field and study the relation between the magnetic field and cool photospheric spots in three young late-type stars. High-resolution spectropolarimetry of the targets were obtained with the HARPSpol instrument mounted at the ESO 3.6 m telescope. The signal-to-noise ratio of the Stokes IV measurements were boosted by combining the signal from a large number of spectroscopic absorption lines through the least squares deconvolution technique. Surface brightness and magnetic field maps were calculated using the Zeeman-Doppler imaging technique. All the three targets show clear signs of both magnetic fields and cool spots. Only one of the targets, namely V1358 Ori, shows evidence of the dominance of non-axisymmetric modes. In two of the targets, the poloidal field is significantly stronger than the toroidal one, indic...

  20. Family of the Sun-and-Stars Time-Determining Instruments (Ilseong-jeongsi-ui) Invented During the Joseon Dynasty

    Science.gov (United States)

    Lee, Yong Sam; Kim, Sang Hyuk; Mihn, Byeong-Hee

    2016-09-01

    We analyze the design and specifications of the Sun-and-Stars Time-Determining group of instruments (Ilseong-jeongsi-ui, 日星定時儀) made during the Joseon dynasty. According to the records of the Sejong Sillok (Veritable Records of King Sejong), Sun-and-Stars Time-Determining Instruments measure the solar time of day and the sidereal time of night through three rings and an alidade. One such instrument, the Simplified Time-Determining Instrument (So-jeongsi-ui, 小定時儀), is made without the essential component for alignment with the celestial north pole. Among this group of instruments, only two bronze Hundred-Interval-Ring Sundials (Baekgak-hwan-Ilgu, 百刻環日晷) currently exist. A comparison of the functions of these two relics with two Time-Determining Instruments suggests that the Hundred-Interval-Ring Sundial is a Simplified Sundial (So-ilyeong, 小日影), as recorded in the Sejong Sillok and the Seongjong Sillok (Veritable Records of King Seongjong). Furthermore, the Simplified Sundial is a model derived from the Simplified Time-Determining Instrument. During the King Sejong reign, the Sun-and-Stars Time-Determining Instruments were used in military camps of the kingdom’s frontiers, in royal ancestral rituals, and in royal astronomical observatories.

  1. Star Clusters as Type Ia Supernova Factories

    CERN Document Server

    Shara, M M; Shara, Michael M.; Hurley, Jarrod R.

    2002-01-01

    We find a remarkably enhanced production rate in star clusters (relative to the field) of very short period, massive double-white-dwarf stars and of giant-white dwarf binaries. These results are based on N-body simulations performed with the new GRAPE-6 special purpose hardware and are important in identifying and characterizing the progenitors of type Ia supernovae. The high incidence of very close double-white-dwarf systems is the result of dynamical encounters between (mostly) primordial binaries and other cluster stars. Orbital hardening rapidly drives these degenerate binaries to periods under ~10 hours. Gravitational radiation emission and mergers producing supra-Chandrasekhar objects follow in less than a Hubble time. If most stars are born in clusters then estimates of the double white dwarf merger rates in galaxies (due to cluster dynamical interaction) must be increased more than tenfold. A majority of the Roche lobe overflow giant-white dwarf binaries are not primordial; they are produced in exchan...

  2. Kepler observations of the variability in B-type stars

    DEFF Research Database (Denmark)

    Balona, Luis A.; Pigulski, A.; De Cat, P.

    2011-01-01

    The analysis of the light curves of 48 B-type stars observed by Kepler is presented. Among these are 15 pulsating stars, all of which show low frequencies, characteristic of slowly pulsating B (SPB) stars. Seven of these stars also show a few weak, isolated high frequencies and they could be cons...

  3. Are sun- and shade-type anatomy required for the acclimation of Neoregelia cruenta?

    Science.gov (United States)

    Reinert, Fernanda; Leal-Costa, Marcos V; Junqueira, Nícia E; Tavares, Eliana S

    2013-01-01

    Sun and shade plants are often discriminated by a number of sun- and shade-type anatomies. Nonetheless, we propose that among tank-bromeliads, changes in rosette architecture satisfy the requirements for coping with contrasting light levels. The tank-bromeliad Neoregelia cruenta naturally colonises sub-habitats ranging from full exposure to direct sunlight, to shaded environments in sand ridge plains. We quantified anatomical and morphological traits of leaves and rosettes of N. cruenta grown under sun and shade conditions. Cells with undulated lateral walls within the water parenchyma are for the first time described for the family. Under high light, leaf blades were wider, shorter, and yellowish. The rosette diameter of sun plants was less than half that of shade plants. Sun leaves overlapped with neighbouring leaves for most of their length, forming a cylindrical rosette where water accumulates. Shade leaves only overlapped in the centre of the rosette. Most anatomical traits were similar under both growth conditions. Stomata were absent from the base of sun leaves, which is probably explained by limited gas exchange at the base of the tight sun-type rosette. Data suggest that the ability of N. cruenta to acclimate to sun and shade is better explained by changes in rosette architecture than by leaf anatomy.

  4. Are sun- and shade-type anatomy required for the acclimation of Neoregelia cruenta?

    Directory of Open Access Journals (Sweden)

    FERNANDA REINERT

    2013-06-01

    Full Text Available Sun and shade plants are often discriminated by a number of sun- and shade-type anatomies. Nonetheless, we propose that among tank-bromeliads, changes in rosette architecture satisfy the requirements for coping with contrasting light levels. The tank-bromeliad Neoregelia cruenta naturally colonises sub-habitats ranging from full exposure to direct sunlight, to shaded environments in sand ridge plains. We quantified anatomical and morphological traits of leaves and rosettes of N. cruenta grown under sun and shade conditions. Cells with undulated lateral walls within the water parenchyma are for the first time described for the family. Under high light, leaf blades were wider, shorter, and yellowish. The rosette diameter of sun plants was less than half that of shade plants. Sun leaves overlapped with neighbouring leaves for most of their length, forming a cylindrical rosette where water accumulates. Shade leaves only overlapped in the centre of the rosette. Most anatomical traits were similar under both growth conditions. Stomata were absent from the base of sun leaves, which is probably explained by limited gas exchange at the base of the tight sun-type rosette. Data suggest that the ability of N. cruenta to acclimate to sun and shade is better explained by changes in rosette architecture than by leaf anatomy.

  5. Origin of the Galactic Center S-Stars: Gravitational Torques from Lin-Shu-Type Spiral Density Waves

    Science.gov (United States)

    Griv, Evgeny

    2010-02-01

    The supermassive ~4 × 106 M sun black hole at the Galactic center is surrounded by a parsec-scale star disk, with several thousands of dynamically relaxed, evolved, late-type CO absorption line stars and a small ~100 population of luminous O and Wolf-Rayet stars which move in approximately circular Keplerian orbits. These bluish in color massive O and Wolf-Rayet stars are very young with an estimated age of 6 ± 2 Myr. Another small group of roughly 20 young (blue B stars with the orbital periods as short as 15 years ("S-stars") follow eccentric, randomly oriented orbits well inside the disk stars. A model is proposed to explain the S-stars. Accordingly, the stars formed originally in the parsec-scale disk through Jeans' gravitational fragmentation of gas. The newly formed S-stars then migrated inward to the Galactic center via the torques exerted by Lin-Shu-type spiral density waves on the stars at an inner Lindblad resonance. The model explains both the number of observed S-stars orbiting the Galactic black hole within the nuclear (<0.05 pc) star cluster and the key property of the S-star orbits, namely, their high eccentricities.

  6. SUPERFLARES ON SOLAR-TYPE STARS OBSERVED WITH KEPLER. I. STATISTICAL PROPERTIES OF SUPERFLARES

    Energy Technology Data Exchange (ETDEWEB)

    Shibayama, Takuya; Notsu, Shota; Notsu, Yuta; Nagao, Takashi [Department of Astronomy, Kyoto University, Sakyo, Kyoto 606-8502 (Japan); Maehara, Hiroyuki; Honda, Satoshi; Ishii, Takako T.; Nogami, Daisaku; Shibata, Kazunari, E-mail: shibayama@kwasan.kyoto-u.ac.jp [Kwasan and Hida Observatory, Kyoto University, Yamashina, Kyoto 607-8471 (Japan)

    2013-11-01

    By extending our previous study by Maehara et al., we searched for superflares on G-type dwarfs (solar-type stars) using Kepler data for a longer period (500 days) than that (120 days) in our previous study. As a result, we found 1547 superflares on 279 G-type dwarfs, which is much more than the previous 365 superflares on 148 stars. Using these new data, we studied the statistical properties of the occurrence rate of superflares, and confirmed the previous results, i.e., the occurrence rate (dN/dE) of superflares versus flare energy (E) shows a power-law distribution with dN/dE∝E {sup –α}, where α ∼ 2. It is interesting that this distribution is roughly similar to that for solar flares. In the case of the Sun-like stars (with surface temperature 5600-6000 K and slowly rotating with a period longer than 10 days), the occurrence rate of superflares with an energy of 10{sup 34}-10{sup 35} erg is once in 800-5000 yr. We also studied long-term (500 days) stellar brightness variation of these superflare stars and found that in some G-type dwarfs the occurrence rate of superflares was extremely high, ∼57 superflares in 500 days (i.e., once in 10 days). In the case of Sun-like stars, the most active stars show a frequency of one superflare (with 10{sup 34} erg) in 100 days. There is evidence that these superflare stars have extremely large starspots with a size about 10 times larger than that of the largest sunspot. We argue that the physical origin of the extremely high occurrence rate of superflares in these stars may be attributed to the existence of extremely large starspots.

  7. A unified normal mode approach to dynamic tides and its application to rotating Sun-like stars

    CERN Document Server

    Ivanov, P B; Chernov, S V

    2013-01-01

    We determine the response of a uniformly rotating star to tidal perturbations due to a companion. General periodic orbits and parabolic flybys are considered. We evaluate energy and angular momentum exchange rates as a sum of contributions from normal modes allowing for dissipative processes. We consider the case when the response is dominated by the contribution of an identifiable regular spectrum of low frequency modes, such as gravity modes and evaluate it in the limit of very weak dissipation. Our formalism may be applied both to Sun-like stars with radiative cores and convective envelopes and to more massive stars with convective cores and radiative envelopes. We provide general expressions for transfer of energy and angular momentum valid for an orbit with any eccentricity. Detailed calculations are made for Sun-like stars in the slow rotation regime where centrifugal distortion is neglected in the equilibrium and the traditional approximation is made for the normal modes. We use both a WKBJ procedure a...

  8. Convection in Oblate Solar-Type Stars

    CERN Document Server

    Wang, Junfeng; Liang, Chunlei

    2016-01-01

    We present the first global 3D simulations of thermal convection in the oblate envelopes of rapidly-rotating solar-type stars. This has been achieved by exploiting the capabilities of the new Compressible High-ORder Unstructured Spectral difference (CHORUS) code. We consider rotation rates up to 85\\% of the critical (breakup) rotation rate, which yields an equatorial radius that is up to 17\\% larger than the polar radius. This substantial oblateness enhances the disparity between polar and equatorial modes of convection. We find that the convection redistributes the heat flux emitted from the outer surface, leading to an enhancement of the heat flux in the polar and equatorial regions. This finding implies that lower-mass stars with convective envelopes may not have darker equators as predicted by classical gravity darkening arguments. The vigorous high-latitude convection also establishes elongated axisymmetric circulation cells and zonal jets in the polar regions. Though the overall amplitude of the surface...

  9. Fundamental properties of nearby single early B-type stars

    Science.gov (United States)

    Nieva, María-Fernanda; Przybilla, Norbert

    2014-06-01

    Aims: Fundamental parameters of a sample of 26 apparently slowly-rotating single early B-type stars in OB associations and in the field within a distance of ≲400 pc from the Sun are presented and compared to high-precision data from detached eclipsing binaries (DEBs). Together with surface abundances for light elements the data are used to discuss the evolutionary status of the stars in context of the most recent Geneva grid of models for core hydrogen-burning stars in the mass-range ~6 to 18 M⊙ at metallicity Z = 0.014. Methods: The fundamental parameters are derived on the basis of accurate and precise atmospheric parameters determined earlier by us from non-LTE analyses of high-quality spectra of the sample stars, utilising the new Geneva stellar evolution models. Results: Evolutionary masses plus radii and luminosities are determined to better than typically 5%, 10%, and 20% uncertainty, respectively, facilitating the mass-radius and mass-luminosity relationships to be recovered for single core hydrogen-burning objects with a similar precision as derived from DEBs. Good agreement between evolutionary and spectroscopic masses is found. Absolute visual and bolometric magnitudes are derived to typically ~0.15-0.20 mag uncertainty. Metallicities are constrained to better than 15-20% uncertainty and tight constraints on evolutionary ages of the stars are provided. Overall, the spectroscopic distances and ages of individual sample stars agree with independently derived values for the host OB associations. Signatures of mixing with CN-cycled material are found in 1/3 of the sample stars. Typically, these are consistent with the amount predicted by the new Geneva models with rotation. The presence of magnetic fields appears to augment the mixing efficiency. In addition, a few objects are possibly the product of binary evolution. In particular, the unusual characteristics of τ Sco point to a blue straggler nature, due to a binary merger. Conclusions: The accuracy

  10. Cool stars, stellar systems, and the sun; Proceedings of the 6th Cambridge Workshop, Seattle, WA, Sept. 18-21, 1989

    Science.gov (United States)

    Wallerstein, George (Editor)

    1990-01-01

    The present conference on cool stars, stellar systems, and the sun encompasses stellar chromospheres and coronae, binary stars, the stellar evolution of contracting stars and red giants, stellar evolution abundances of the elements, mass loss and envelopes, and stellar pulsation. Specific issues addressed include theories regarding the acoustic and magnetic heating of stellar chromospheres and coronae, stellar granulation, wave heating in magnetic flux tubes, observations of the solar Ca-II lines, longitudinal-transverse magnetic tube waves in the solar atmosphere, radio emission from rapidly rotating cool giant stars, and spot temperatures and area coverages on active dwarf stars. Also addressed are the optical and UV spectra of RS-CVn stars, emission lines from T-Tauri stars, the spectroscopy of HR1614 group stars, red giants in external galaxies, the rotation of evolved stars, the transition from red giant to planetary nebula, and radiative transfer in the dynamic atmospheres of variable stars.

  11. Occurrence and core-envelope structure of 1–4× Earth-size planets around Sun-like stars

    Science.gov (United States)

    Marcy, Geoffrey W.; Weiss, Lauren M.; Petigura, Erik A.; Isaacson, Howard; Howard, Andrew W.; Buchhave, Lars A.

    2014-01-01

    Small planets, 1–4× the size of Earth, are extremely common around Sun-like stars, and surprisingly so, as they are missing in our solar system. Recent detections have yielded enough information about this class of exoplanets to begin characterizing their occurrence rates, orbits, masses, densities, and internal structures. The Kepler mission finds the smallest planets to be most common, as 26% of Sun-like stars have small, 1–2 R⊕ planets with orbital periods under 100 d, and 11% have 1–2 R⊕ planets that receive 1–4× the incident stellar flux that warms our Earth. These Earth-size planets are sprinkled uniformly with orbital distance (logarithmically) out to 0.4 the Earth–Sun distance, and probably beyond. Mass measurements for 33 transiting planets of 1–4 R⊕ show that the smallest of them, R rocky planets. Their densities increase with increasing radius, likely caused by gravitational compression. Including solar system planets yields a relation: ρ=2.32+3.19R/R⊕ [g cm−3]. Larger planets, in the radius range 1.5–4.0 R⊕, have densities that decline with increasing radius, revealing increasing amounts of low-density material (H and He or ices) in an envelope surrounding a rocky core, befitting the appellation ‘‘mini-Neptunes.’’ The gas giant planets occur preferentially around stars that are rich in heavy elements, while rocky planets occur around stars having a range of heavy element abundances. Defining habitable zones remains difficult, without benefit of either detections of life elsewhere or an understanding of life’s biochemical origins. PMID:24912169

  12. Occurrence and core-envelope structure of 1-4× Earth-size planets around Sun-like stars.

    Science.gov (United States)

    Marcy, Geoffrey W; Weiss, Lauren M; Petigura, Erik A; Isaacson, Howard; Howard, Andrew W; Buchhave, Lars A

    2014-09-02

    Small planets, 1-4× the size of Earth, are extremely common around Sun-like stars, and surprisingly so, as they are missing in our solar system. Recent detections have yielded enough information about this class of exoplanets to begin characterizing their occurrence rates, orbits, masses, densities, and internal structures. The Kepler mission finds the smallest planets to be most common, as 26% of Sun-like stars have small, 1-2 R⊕ planets with orbital periods under 100 d, and 11% have 1-2 R⊕ planets that receive 1-4× the incident stellar flux that warms our Earth. These Earth-size planets are sprinkled uniformly with orbital distance (logarithmically) out to 0.4 the Earth-Sun distance, and probably beyond. Mass measurements for 33 transiting planets of 1-4 R⊕ show that the smallest of them, R planets. Their densities increase with increasing radius, likely caused by gravitational compression. Including solar system planets yields a relation: ρ = 2:32 + 3:19 R=R ⊕ [g cm(-3)]. Larger planets, in the radius range 1.5-4.0 R⊕, have densities that decline with increasing radius, revealing increasing amounts of low-density material (H and He or ices) in an envelope surrounding a rocky core, befitting the appellation ''mini-Neptunes.'' The gas giant planets occur preferentially around stars that are rich in heavy elements, while rocky planets occur around stars having a range of heavy element abundances. Defining habitable zones remains difficult, without benefit of either detections of life elsewhere or an understanding of life's biochemical origins.

  13. Forward modeling of the corona of the sun and solarlike stars

    DEFF Research Database (Denmark)

    Hardi, Peter; Gudiksen, Boris V.; Nordlund, Å.

    2006-01-01

    Transition Region Lines, AB-Initio Approach; Nonequilibrium Inozation; Doppler Shifts; Emission-Lines; Quiet-Sun; Sumer Telescope; Atomic Database; Magnetic-Field; Thin Plasmas......Transition Region Lines, AB-Initio Approach; Nonequilibrium Inozation; Doppler Shifts; Emission-Lines; Quiet-Sun; Sumer Telescope; Atomic Database; Magnetic-Field; Thin Plasmas...

  14. Superflares on the slowly rotating solar-type stars KIC10524994 and KIC07133671?

    CERN Document Server

    Kitze, M; Hambaryan, V; Ginski, C

    2014-01-01

    An investigation of the G-type stellar population with Kepler (as done by Maehara et al.) shows that less than 1 per cent of those stars show superflares. Due to the large pixel scale of Kepler ($\\sim4 arcsec \\: px^{-1}$), it is still not clear whether the detected superflares really occur on the G-type stars. Knowing the origin of such large brightenings is important to study their frequency statistics, which are uncertain due to the low number of sun-like stars ($T_{eff} = 5600-6000 \\:K$ and $P_{rot} > 10 \\:d$) which are currently considered to exhibit superflares. We present a complete Kepler data analysis of the sun-like stars KIC10524994 and KIC07133671 (the only two stars within this subsample of solar twins with flare energies larger than $10^{35}$ erg; Maehara et al.), regarding superflare properties and a study about their origin. We could detect four new superflares within the epoch Maehara et al. investigated and found 14 superflares in the remaining light curve for KIC10524994. Astrometric Kepler ...

  15. Solar-type dynamo behaviour in fully convective stars without a tachocline.

    Science.gov (United States)

    Wright, Nicholas J; Drake, Jeremy J

    2016-07-28

    In solar-type stars (with radiative cores and convective envelopes like our Sun), the magnetic field powers star spots, flares and other solar phenomena, as well as chromospheric and coronal emission at ultraviolet to X-ray wavelengths. The dynamo responsible for generating the field depends on the shearing of internal magnetic fields by differential rotation. The shearing has long been thought to take place in a boundary layer known as the tachocline between the radiative core and the convective envelope. Fully convective stars do not have a tachocline and their dynamo mechanism is expected to be very different, although its exact form and physical dependencies are not known. Here we report observations of four fully convective stars whose X-ray emission correlates with their rotation periods in the same way as in solar-type stars. As the X-ray activity-rotation relationship is a well-established proxy for the behaviour of the magnetic dynamo, these results imply that fully convective stars also operate a solar-type dynamo. The lack of a tachocline in fully convective stars therefore suggests that this is not a critical ingredient in the solar dynamo and supports models in which the dynamo originates throughout the convection zone.

  16. Solar-type dynamo behaviour in fully convective stars without a tachocline

    Science.gov (United States)

    Wright, Nicholas J.; Drake, Jeremy J.

    2016-07-01

    In solar-type stars (with radiative cores and convective envelopes like our Sun), the magnetic field powers star spots, flares and other solar phenomena, as well as chromospheric and coronal emission at ultraviolet to X-ray wavelengths. The dynamo responsible for generating the field depends on the shearing of internal magnetic fields by differential rotation. The shearing has long been thought to take place in a boundary layer known as the tachocline between the radiative core and the convective envelope. Fully convective stars do not have a tachocline and their dynamo mechanism is expected to be very different, although its exact form and physical dependencies are not known. Here we report observations of four fully convective stars whose X-ray emission correlates with their rotation periods in the same way as in solar-type stars. As the X-ray activity-rotation relationship is a well-established proxy for the behaviour of the magnetic dynamo, these results imply that fully convective stars also operate a solar-type dynamo. The lack of a tachocline in fully convective stars therefore suggests that this is not a critical ingredient in the solar dynamo and supports models in which the dynamo originates throughout the convection zone.

  17. Long-term magnetic field monitoring of the Sun-like star Ksi Boo A

    CERN Document Server

    Morgenthaler, A; Saar, S; Solanki, S K; Auriere, M; Dintrans, B; Fares, R; Gastine, T; Lanoux, J; Lignieres, F; Marsden, S C; Morin, J; Paletou, F; Velez, J C Ramirez; Theado, S; Van Grootel, V

    2011-01-01

    Aims. We aim at investigating the long-term temporal evolution of the magnetic field of the solar-type star Ksi Boo A, both from direct magnetic field measurements and from the simultaneous estimate of indirect activity indicators. Methods. We use 7 time-series of high-resolution, circularly-polarized spectra obtained with the NARVAL spectropolarimeter between 2007 and 2011, for a total of 76 spectra. Using about 6,100 photospheric spectral lines covering the visible domain, we employ a cross-correlation procedure to compute, from each spectrum, a mean polarized line profile. We model the large-scale photospheric magnetic field of the star by means of Zeeman-Doppler Imaging and follow the year-to-year evolution of the reconstructed magnetic topology. Simultaneously, we monitor the width of several magnetically-sensitive spectral lines, the radial velocity and line asymmetry of intensity line profiles and the chromospheric emission in the cores of the Ca II H and Halpha lines. Results. During the highest obser...

  18. TENTATIVE EVIDENCE FOR RELATIVISTIC ELECTRONS GENERATED BY THE JET OF THE YOUNG SUN-LIKE STAR DG Tau

    Energy Technology Data Exchange (ETDEWEB)

    Ainsworth, Rachael E.; Ray, Tom P.; Taylor, Andrew M. [Dublin Institute for Advanced Studies, 31 Fitzwilliam Place, Dublin 2 (Ireland); Scaife, Anna M. M. [School of Physics and Astronomy, University of Southampton, Highfield, Southampton, SO17 1BJ (United Kingdom); Green, David A.; Buckle, Jane V., E-mail: rainsworth@cp.dias.ie [Cavendish Laboratory, J J Thomson Avenue, Cambridge, CB3 0HE (United Kingdom)

    2014-09-01

    Synchrotron emission has recently been detected in the jet of a massive protostar, providing further evidence that certain jet formation characteristics for young stars are similar to those found for highly relativistic jets from active galactic nuclei. We present data at 325 and 610 MHz taken with the Giant Metrewave Radio Telescope of the young, low-mass star DG Tau, an analog of the Sun soon after its birth. This is the first investigation of a low-mass young stellar object at such low frequencies. We detect emission with a synchrotron spectral index in the proximity of the DG Tau jet and interpret this emission as a prominent bow shock associated with this outflow. This result provides tentative evidence for the acceleration of particles to relativistic energies due to the shock impact of this otherwise very low-power jet against the ambient medium. We calculate the equipartition magnetic field strength B {sub min} ≈ 0.11 mG and particle energy E {sub min} ≈ 4 × 10{sup 40} erg, which are the minimum requirements to account for the synchrotron emission of the DG Tau bow shock. These results suggest the possibility of low energy cosmic rays being generated by young Sun-like stars.

  19. The Sun among stars. IV - Albedos of Uranus and Neptune and the solar color

    Science.gov (United States)

    Hardorp, J.

    1981-01-01

    Geometric albedos in 48 adjacent 50 A bands from 3250 to 5600 A have been derived from observations of Uranus and Neptune. The solar analog found in earlier papers (Hardorp 1978, 1980) was chosen for these reductions, so these albedos are more reliable systematically than earlier ones and allow a choice among the scattering models of Savage et al. (1980). Green methane bands are stronger on Neptune. Strong solar absorption lines are found to be partially filled in by Raman-scattering. Neglect of this effect caused Croft et al. (1972) to find a solar color that is too blue. It probably also affected the classification of G-type stars in the Michigan Spectral Catalogue as well as Garrison's (1979) interpretation of IUE observations.

  20. Pulsation models for the 0.26M_sun star mimicking RR Lyrae pulsator. Model survey for the new class of variable stars

    CERN Document Server

    Smolec, R; Graczyk, D; Pilecki, B; Gieren, W; Thompson, I; Stepien, K; Karczmarek, P; Konorski, P; Gorski, M; Suchomska, K; Bono, G; Moroni, P G Prada; Nardetto, N

    2012-01-01

    We present non-linear hydrodynamic pulsation models for OGLE-BLG-RRLYR-02792 - a 0.26M_sun pulsator, component of the eclipsing binary system, analysed recently by Pietrzynski et al. The star's light and radial velocity curves mimic that of classical RR Lyrae stars, except for the bump in the middle of the ascending branch of the radial velocity curve. We show that the bump is caused by the 2:1 resonance between the fundamental mode and the second overtone - the same mechanism that causes the Hertzsprung bump progression in classical Cepheids. The models allow to constrain the parameters of the star, in particular to estimate its absolute luminosity (approx 33L_sun) and effective temperature (approx 6970K, close to the blue edge of the instability strip). We conduct a model survey for the new class of low mass pulsators similar to OGLE-BLG-RRLYR-02792 - products of evolution in the binary systems. We compute a grid of models with masses corresponding to half (and less) of the typical mass of RR Lyrae variable...

  1. Radio emission and mass loss rate limits of four young solar-type stars

    Science.gov (United States)

    Fichtinger, Bibiana; Güdel, Manuel; Mutel, Robert L.; Hallinan, Gregg; Gaidos, Eric; Skinner, Stephen L.; Lynch, Christene; Gayley, Kenneth G.

    2017-03-01

    Aims: Observations of free-free continuum radio emission of four young main-sequence solar-type stars (EK Dra, π1 UMa, χ1 Ori, and κ1 Cet) are studied to detect stellar winds or at least to place upper limits on their thermal radio emission, which is dominated by the ionized wind. The stars in our sample are members of The Sun in Time programme and cover ages of 0.1-0.65 Gyr on the main-sequence. They are similar in magnetic activity to the Sun and thus are excellent proxies for representing the young Sun. Upper limits on mass loss rates for this sample of stars are calculated using their observational radio emission. Our aim is to re-examine the faint young Sun paradox by assuming that the young Sun was more massive in its past, and hence to find a possible solution for this famous problem. Methods: The observations of our sample are performed with the Karl G. Jansky Very Large Array (VLA) with excellent sensitivity, using the C-band receiver from 4-8 GHz and the Ku-band from 12-18 GHz. Atacama Large Millimeter/Submillitmeter Array (ALMA) observations are performed at 100 GHz. The Common Astronomy Software Application (CASA) package is used for the data preparation, reduction, calibration, and imaging. For the estimation of the mass loss limits, spherically symmetric winds and stationary, anisotropic, ionized winds are assumed. We compare our results to 1) mass loss rate estimates of theoretical rotational evolution models; and 2) to results of the indirect technique of determining mass loss rates: Lyman-α absorption. Results: We are able to derive the most stringent direct upper limits on mass loss so far from radio observations. Two objects, EK Dra and χ1 Ori, are detected at 6 and 14 GHz down to an excellent noise level. These stars are very active and additional radio emission identified as non-thermal emission was detected, but limits for the mass loss rates of these objects are still derived. The emission of χ1 Ori does not come from the main target

  2. High Dispersion Spectroscopy of Solar-type Superflare Stars. III. Lithium Abundances

    CERN Document Server

    Honda, Satoshi; Maehara, Hiroyuki; Notsu, Shota; Shibayama, Takuya; Nogami, Daisaku; Shibata, Kazunari

    2015-01-01

    We report on the abundance analysis of Li in solar-type (G-type main sequence) superflare stars which were found by the analysis of Kepler photometric data. Li is a key element to understand the evolution of the stellar convection zone which reflects the age of solar-type stars. We performed the high dispersion spectroscopy of solar-type superflare stars with Subaru/HDS, and confirmed that 34 stars show no evidence of binarity in our previous study. In this study, we derived the Li abundances of these 34 objects. We investigate correlations of Li abundance with stellar atmospheric parameters, rotational velocity, and superflare activities to understand the nature of superflare stars and the possibility of the nucleosynthesis of Li by superflares. We confirm the large dispersion in the Li abundance, and the correlation with stellar parameters is not seen. As compared with the Li abundance in Hyades cluster which is younger than the Sun, it is suggested that half of the observed stars are younger than Hyades cl...

  3. High Dispersion Spectroscopy of Solar-Type Superflare Stars With Subaru/HDS

    Science.gov (United States)

    Notsu, Yuta; Honda, Satoshi; Maehara, Hiroyuki; Notsu, Shota; Shibayama, Takuya; Namekata, Kosuke; Nogami, Daisaku; Shibata, Kazunari

    2016-07-01

    Superflares are flares that release total energy 10-104times greater than that of the biggest solar flares ( 1032 erg). Recent Kepler-space-telescope observations found more than 1000superflares on a few hundred solar-type stars (Maehara et al. 2012, Nature; Shibayama et al. 2013, ApJS, Maehara et al. 2015 EPS).Suchsuperflare stars show quasi-periodicbrightnessvariations with the typical period of from one to a few tens of days. Such variations are thought to be caused by the rotation of the star with large starspots (Notsu et al. 2013, ApJ). However, spectroscopic observations are needed in order to confirm whether the variation is really due to the rotation and whether superflares can occur on ordinary single stars similar to our Sun.Then we have carried out spectroscopic observations for 50 solar-type superflare stars with Subaru/HDS (Notsu et al. 2015a&b, PASJ). As a result, more than half (34 stars) of the targetstars show no evidence of binarity, and the atmospheric parameters of these stars are in the range of solar-type stars.The detailed analyses for these 34 stars show that (1) the projected rotational velocities (v sin i) are consistent with the rotational velocities estimated from the brightness variations, (2)there is a correlation between the brightness variation amplitude and the intensity of Ca II IR triplet line. These results support that the brightness variation discussed above is explained bythe rotation of a star with large starspots. (The contents of this poster were already summarized in the proceeding of IAU Symposium S320 (Notsu et al. 2016 IAUS in press, arXiv:1510.08143))

  4. B- and A-Type Stars in the Taurus-Auriga Star-Forming Region

    Science.gov (United States)

    Mooley, Kunal; Hillenbrand, Lynne; Rebull, Luisa; Padgett, Deborah; Knapp, Gillian

    2013-01-01

    We describe the results of a search for early-type stars associated with the Taurus-Auriga molecular cloud complex, a diffuse nearby star-forming region noted as lacking young stars of intermediate and high mass. We investigate several sets of possible O, B, and early A spectral class members. The first is a group of stars for which mid-infrared images show bright nebulae, all of which can be associated with stars of spectral-type B. The second group consists of early-type stars compiled from (1) literature listings in SIMBAD, (2) B stars with infrared excesses selected from the Spitzer Space Telescope survey of the Taurus cloud, (3) magnitude- and color-selected point sources from the Two Micron All Sky Survey, and (4) spectroscopically identified early-type stars from the Sloan Digital Sky Survey coverage of the Taurus region. We evaluated stars for membership in the Taurus-Auriga star formation region based on criteria involving: spectroscopic and parallactic distances, proper motions and radial velocities, and infrared excesses or line emission indicative of stellar youth. For selected objects, we also model the scattered and emitted radiation from reflection nebulosity and compare the results with the observed spectral energy distributions to further test the plausibility of physical association of the B stars with the Taurus cloud. This investigation newly identifies as probable Taurus members three B-type stars: HR 1445 (HD 28929), t Tau (HD 29763), 72 Tau (HD 28149), and two A-type stars: HD 31305 and HD 26212, thus doubling the number of stars A5 or earlier associated with the Taurus clouds. Several additional early-type sources including HD 29659 and HD 283815 meet some, but not all, of the membership criteria and therefore are plausible, though not secure, members.

  5. Kepler-63b: A Giant Planet in a Polar Orbit around a Young Sun-like Star

    CERN Document Server

    Sanchis-Ojeda, Roberto; Marcy, Geoffrey W; Howard, Andrew W; Isaacson, Howard; Johnson, John Asher; Torres, Guillermo; Albrecht, Simon; Campante, Tiago L; Chaplin, William J; Davies, Guy R; Lund, Mikkel L; Carter, Joshua A; Dawson, Rebekah I; Buchhave, Lars A; Everett, Mark E; Fischer, Debra A; Geary, John C; Gilliland, Ronald L; Horch, Elliott P; Howell, Steve B; Latham, David W

    2013-01-01

    We present the discovery and characterization of a giant planet orbiting the young Sun-like star Kepler-63 (KOI-63, $m_{\\rm Kp} = 11.6$, $T_{\\rm eff} = 5576$ K, $M_\\star = 0.98\\, M_\\odot$). The planet transits every 9.43 days, with apparent depth variations and brightening anomalies caused by large starspots. The planet's radius is $6.1 \\pm 0.2 R_{\\earth}$, based on the transit light curve and the estimated stellar parameters. The planet's mass could not be measured with the existing radial-velocity data, due to the high level of stellar activity, but if we assume a circular orbit we can place a rough upper bound of $120 M_{\\earth}$ (3$\\sigma$). The host star has a high obliquity ($\\psi$ = $104^{\\circ}$), based on the Rossiter-McLaughlin effect and an analysis of starspot-crossing events. This result is valuable because almost all previous obliquity measurements are for stars with more massive planets and shorter-period orbits. In addition, the polar orbit of the planet combined with an analysis of spot-cross...

  6. Carbon-rich RR Lyr type stars

    CERN Document Server

    Wallerstein, George; Andrievsky, S M

    2009-01-01

    We have derived CNO abundances in 12 RR Lyrae stars. Four stars show [C/Fe] near 0.0 and two stars show [C/Fe] = 0.52 and 0.65. Red giant branch stars, which are known to be the predecessors of RR Lyrae stars, generally show a deficiency of carbon due to proton captures during their evolution from the main sequence up the giant branch. We suggest that the enhancement of carbon is due to production during the helium flash combined with mixing to the surface by vigorous convection induced by the flash itself.

  7. Modeling the exchange of comets between the Sun and passing stars in a low stellar density environment

    Science.gov (United States)

    Levine, Stephen; Gosmeyer, Catherine

    2016-10-01

    We investigated the importance of close encounters between our Sun and its Oort cloud and passing stars with similar Oort clouds in the low stellar density environment of the outer portion of our Galaxy. By constructing a set of interaction cross-sections that describe the interchange of material between the two passing Oort clouds, and then randomly computing sets of encounters that a star would have during its orbit in the Galaxy over a period of time equivalent to the life of the Sun after the dissolution of its birth cluster, we have examined how the ensemble of passing encounters could impact the evolution of our Oort cloud. From the set of 1,000 possible realizations of the interactions over a solar lifetime, we find that the resulting solar Oort cloud is likely to be significantly eroded as a result of the set of encounters, and is also likely today to contain a significant amount of material that was formed in passing extra-solar systems.

  8. Occurrence and core-envelope structure of 1--4x Earth-size planets around Sun-like stars

    CERN Document Server

    Marcy, Geoffrey W; Petigura, Erik A; Isaacson, Howard; Howard, Andrew W; Buchhave, Lars A

    2014-01-01

    Small planets, 1-4x the size of Earth, are extremely common around Sun-like stars, and surprisingly so, as they are missing in our solar system. Recent detections have yielded enough information about this class of exoplanets to begin characterizing their occurrence rates, orbits, masses, densities, and internal structures. The Kepler mission finds the smallest planets to be most common, as 26% of Sun-like stars have small, 1-2 R_e planets with orbital periods under 100 days, and 11% have 1-2 R_e planets that receive 1-4x the incident stellar flux that warms our Earth. These Earth-size planets are sprinkled uniformly with orbital distance (logarithmically) out to 0.4 AU, and probably beyond. Mass measurements for 33 transiting planets of 1-4 R_e show that the smallest of them, R < 1.5 R_e, have the density expected for rocky planets. Their densities increase with increasing radius, likely caused by gravitational compression. Including solar system planets yields a relation: rho = 2.32 + 3.19 R/R_e [g/cc]. ...

  9. solarFLAG hare and hounds: estimation of p-mode frequencies from Sun-as-star helioseismology data

    CERN Document Server

    Jiménez-Reyes, S J; García, R A; Appourchaux, T; Baudin, F; Boumier, P; Elsworth, Y; Fletcher, S T; Lazrek, M; Leibacher, J W; Lochard, J; New, R; Regulo, C; Salabert, D; Toutain, T; Verner, G A; Wachter, R

    2008-01-01

    We report on the results of the latest solarFLAG hare-and-hounds exercise, which was concerned with testing methods for extraction of frequencies of low-degree solar p modes from data collected by Sun-as-a-star observations. We have used the new solarFLAG simulator, which includes the effects of correlated mode excitation and correlations with background noise, to make artificial timeseries data that mimic Doppler velocity observations of the Sun as a star. The correlations give rise to asymmetry of mode peaks in the frequency power spectrum. Ten members of the group (the hounds) applied their ``peak bagging'' codes to a 3456-day dataset, and the estimated mode frequencies were returned to the hare (who was WJC) for comparison. Analysis of the results reveals a systematic bias in the estimated frequencies of modes above approximately 1.8 mHz. The bias is negative, meaning the estimated frequencies systematically underestimate the input frequencies. We identify two sources that are the dominant contributions t...

  10. High-mass star formation at high luminosities: W31 at >10^6 L_sun

    CERN Document Server

    Beuther, H; Henning, Th; Bik, A; Wyrowski, F; Schuller, F; Schilke, P; Thorwirth, S; Kim, K -T

    2011-01-01

    Context: High-mass star formation has been a very active field over the last decade, however, most studies targeted regions of luminosities between 10^4 and 10^5 L_sun. Methods: We selected the W31 star-forming complex with a total luminosity of ~6x10^6 L_sun for a multi-wavelength spectral line and continuum study covering wavelengths from the near- and mid-infrared via (sub)mm wavelength observations to radio data in the cm regime. Results: While the overall structure of the multi-wavelength continuum data resembles each other well, there are several intriguing differences. The 24mum emission stemming largely from small dust grains follows tightly the spatial structure of the cm emission tracing the ionized free-free emission. Hence warm dust resides in regions that are spatially associated with the ionized hot gas (~10^4 K) of the HII regions. Furthermore, we find several evolutionary stages within the same complexes, ranging from infrared-observable clusters, via deeply embedded regions associated with ac...

  11. The Sun as a planet-host star: Proxies from SDO images for HARPS radial-velocity variations

    CERN Document Server

    Haywood, R D; Unruh, Y C; Lovis, C; Lanza, A F; Llama, J; Deleuil, M; Fares, R; Gillon, M; Moutou, C; Pepe, F; Pollacco, D; Queloz, D; Segransan, D

    2016-01-01

    The Sun is the only star whose surface can be directly resolved at high resolution, and therefore constitutes an excellent test case to explore the physical origin of stellar radial-velocity (RV) variability. We present HARPS observations of sunlight scattered off the bright asteroid 4/Vesta, from which we deduced the Sun's activity-driven RV variations. In parallel, the HMI instrument onboard the Solar Dynamics Observatory provided us with simultaneous high spatial resolution magnetograms, Dopplergrams, and continuum images of the Sun in the Fe I 6173A line. We determine the RV modulation arising from the suppression of granular blueshift in magnetised regions and the flux imbalance induced by dark spots and bright faculae. The rms velocity amplitudes of these contributions are 2.40 m/s and 0.41 m/s, respectively, which confirms that the inhibition of convection is the dominant source of activity-induced RV variations at play, in accordance with previous studies. We find the Doppler imbalances of spot and pl...

  12. Detection of dark-matter-radiation of stars during visible sun eclipses

    Energy Technology Data Exchange (ETDEWEB)

    Volkamer, Klaus E-mail: dr.volkamer@t-online.de

    2003-07-01

    Recently a so-far unknown form of quantized, cold dark matter was detected on a laboratory scale which shows a complementary structure as compared to known forms of matter. From the experiments results that the observed quanta of the new type of matter as integer multiples of the Planck mass (mp = n {center_dot} {radical}((h{center_dot}c)/((2 {center_dot} {pi} {center_dot} G))) = n 0 21.77 {mu}g, with n = 1, 2, 3 etc.) exhibit a spatially extended 'field-like' structure ranging over distances of centimetres or more, opposite to the 'point-like' structure of the known elementary particles of the standard model. Association of quanta of the new form of 'soft' (or subtle) matter to clusters was observed, as well as re-clustering after absorption. Thus, between such quanta a physical interaction must exist. In addition, the new form of matter shows at least two interactions with normal matter, a gravitational one due to its real mass content and a so-far unknown 'topological', i.e. form-specific, interaction at phase borders. Additional indications for a weak electromagnetic interaction exist. Furthermore, the experimental results reveal that some types of quanta of the new form of 'field-like' matter exhibit positive mass, as normal matter, but others exhibit a negative mass content, both in the order of magnitude of the Planck mass. Memory effects in normal matter were detected after absorption of quanta of the new form of soft matter. In general, the findings characterize the quanta of 'fieldlike' matter as WIMP candidates of a cosmic background radiation of cold dark matter (quanta with positive mass) as well as of a cosmic background radiation of dark energy (quanta with negative mass). During visible sun eclipses in 1989, 1996 and. 1999, as well as during full moon of 6 January 2001, a so-far unknown form of dark-matter-radiation ('dark radiation') was detected. The quanta of this &apos

  13. Solar-type dynamo behaviour in fully convective stars without a tachocline

    CERN Document Server

    Wright, Nicholas J

    2016-01-01

    In solar-type stars (with radiative cores and convective envelopes), the magnetic field powers star spots, flares and other solar phenomena, as well as chromospheric and coronal emission at ultraviolet to X-ray wavelengths. The dynamo responsible for generating the field depends on the shearing of internal magnetic fields by differential rotation. The shearing has long been thought to take place in a boundary layer known as the tachocline between the radiative core and the convective envelope. Fully convective stars do not have a tachocline and their dynamo mechanism is expected to be very different, although its exact form and physical dependencies are not known. Here we report observations of four fully convective stars whose X-ray emission correlates with their rotation periods in the same way as in Sun-like stars. As the X-ray activity - rotation relationship is a well-established proxy for the behaviour of the magnetic dynamo, these results imply that fully convective stars also operate a solar-type dyna...

  14. Two types of glitches in a solid quark star model

    CERN Document Server

    Lu, Jiguang

    2015-01-01

    The glitch of anomalous X-ray pulsars \\& soft gamma repeaters (AXP/SGRs) usually accompanied with detectable energy releases manifesting as X-ray bursts or outbursts, while the glitch of some pulsars like Vela release negligible energy. We find that these two types of glitch can naturally correspond to two types of starquake of solid stars. So far only quark star and quark cluster star model develop a solid star model. Then the two types of glitch may be an implication that the pulsar is composed by quark matter or quark cluster matter.

  15. B- and A-Type Stars in the Taurus-Auriga Star Forming Region

    CERN Document Server

    Mooley, Kunal P; Rebull, Luisa M; Padgett, Deborah L; Knapp, Gillian R

    2013-01-01

    We describe the results of a search for early-type stars associated with the Taurus-Auriga molecular cloud complex, a diffuse nearby star-forming region noted as lacking young stars of intermediate and high mass. We investigate several sets of possible O, B and early A spectral class members. The first is a group of stars for which mid-infrared images show bright nebulae, all of which can be associated with stars of spectral type B. The second group consists of early-type stars compiled from (i) literature listings in SIMBAD; (ii) B stars with infrared excesses selected from the Spitzer Space Telescope survey of the Taurus cloud; (iii) magnitude- and color-selected point sources from the 2MASS; and (iv) spectroscopically identified early-type stars from the SDSS coverage of the Taurus region. We evaluated stars for membership in the Taurus-Auriga star formation region based on criteria involving: spectroscopic and parallactic distances, proper motions and radial velocities, and infrared excesses or line emiss...

  16. Multiplicity of A-type and related stars

    CERN Document Server

    North, Pierre L

    2013-01-01

    The origin of chemically peculiar stars remains enigmatic, especially regarding their frequency among their "normal" peers. In addition to magnetic fields and rotation, multiplicity may shed light on the question. We mention the main surveys of the three kinds performed so far of intermediate mass stars, either normal or chemically peculiar, magnetic or not: imaging, spectroscopic, and photometric. We also consider the mulitiplicity of red giant stars, since many of them are descendants of A-type stars, through Mermilliod's radial velocity monitoring of open cluster members. We briefly review the orbital properties of binary systems hosting chemically peculiar stars. Some specific objects of special interest are mentioned as deserving further study. Finally, we recall that some binary systems composed of A-type stars are progenitors of Type Ia supernovae, and evoke the potentialities of future surveys like Gaia.

  17. Rotation Periods of Nine ROSAT Selected Solar-Type Stars

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    We monitored 16 X-ray selected young solar-type stars for light variation and found appreciable periodic light variability with amplitudes of a few hundredths of a magnitude in nine of the objects. Using the method of Phase Dispersion Minimization (PDM) and Fourier analysis (software PERIOD04), the rotation periods of these stars were determined from the photometric data. The rotation periods of all nine stars are shorter than about 3 days.It is suggested that, as with the Pleiades cluster, small amplitude light variations are quite common among young solar-type stars with rotation periods around 3 days or less. This gives further evidence for the spin up of solar-type stars predicted by models of angular momentum evolution of pre-main sequence stars.

  18. Sun's rap song

    Science.gov (United States)

    Hogan, M.; Lee, W.

    1995-07-01

    We present a rap song composed for the Sun, our star. This Sun's Rap Song can be utilized in classroom teaching to spark the students' interest and facilitate the students' learning of the relevant subjects.

  19. Continued Kinematic and Photometric Investigations of Hierarchical Solar-type Multiple Star Systems

    Science.gov (United States)

    Roberts, Lewis C., Jr.; Tokovinin, Andrei; Mason, Brian D.; Marinan, Anne D.

    2017-03-01

    We observed 15 of the solar-type binaries within 67 pc of the Sun previously observed by the Robo-AO system in the visible, with the PHARO near-infrared camera and the PALM-3000 adaptive optics system on the 5 m Hale telescope. The physical status of the binaries is confirmed through common proper motion and detection of orbital motion. In the process, we detected a new candidate companion to HIP 95309. We also resolved the primary of HIP 110626 into a close binary, making that system a triple. These detections increase the completeness of the multiplicity survey of the solar-type stars within 67 pc of the Sun. Combining our observations of HIP 103455 with archival astrometric measurements and RV measurements, we are able to compute the first orbit of HIP 103455, showing that the binary has a 68 year period. We place the components on a color–magnitude diagram and discuss each multiple system individually.

  20. Living with a Star: New Opportunities in Sun-Climate Research

    Science.gov (United States)

    Eddy, John Allen

    2003-01-01

    Enormous advances have been made in the last quarter century in all of these needed areas, covering the two essential halves of the Sun-Climate question: in what we know of solar variations and, equally important, in what we know of the climate system and of climatic changes. These research achievements allow us to examine all aspects of the question more directly and quantitatively than was ever possible before, and in the brighter light and more objective context of other known or suspected climate change mechanisms, including human-induced global greenhouse warming. Brief summaries of present status and current understanding are given below for nine facets of Sun-Climate science in which major progress has been made in recent years. At the same time it will be seen that in every instance, significant elements of uncertainty still remain, Some of the most important of these unanswered questions are considered later, in Section IV.

  1. A STAR-FORMING RING AROUND κ Ori 250 pc FROM THE SUN

    Energy Technology Data Exchange (ETDEWEB)

    Pillitteri, I.; Wolk, S. J. [Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138 (United States); Megeath, S. T., E-mail: ipillitt@cfa.harvard.edu [Ritter Astrophysical Research Center, Department of Physics and Astronomy, University of Toledo, Toledo, OH (United States)

    2016-04-01

    X-rays are a powerful probe of activity in early stages of star formation. They allow us to identify young stars even after they have lost the IR signatures of circumstellar disks and provide constraints on their distance. Here, we report on XMM-Newton observations that detect 121 young stellar objects (YSOs) in two fields between L1641 S and κ Ori. These observations extend the Survey of Orion A with XMM and Spitzer (SOXS). The YSOs are contained in a ring of gas and dust apparent at millimeter wavelengths, and in far-IR and near-IR surveys. The X-ray luminosity function of the YSOs detected in the two fields indicates a distance of 250–280 pc, much closer than the Orion A cloud and similar to distance estimates of κ Ori. We propose that the ring is a 5–8 pc diameter shell that has been swept up by κ Ori. This ring contains several groups of stars detected by Spitzer and WISE including one surrounding the Herbig Ae/Be stars V1818 Ori. In this interpretation, the κ Ori ring is one of several shells swept up by massive stars within the Orion Eridanus Superbubble and is unrelated to the southern portion of Orion A/L1641 S.

  2. Asteroseismic determination of fundamental parameters of Sun-like stars using multilayered neural networks

    Science.gov (United States)

    Verma, Kuldeep; Hanasoge, Shravan; Bhattacharya, Jishnu; Antia, H. M.; Krishnamurthi, Ganapathy

    2016-10-01

    The advent of space-based observatories such as Convection, Rotation and planetary Transits (CoRoT) and Kepler has enabled the testing of our understanding of stellar evolution on thousands of stars. Evolutionary models typically require five input parameters, the mass, initial helium abundance, initial metallicity, mixing length (assumed to be constant over time), and the age to which the star must be evolved. Some of these parameters are also very useful in characterizing the associated planets and in studying Galactic archaeology. How to obtain these parameters from observations rapidly and accurately, specifically in the context of surveys of thousands of stars, is an outstanding question, one that has eluded straightforward resolution. For a given star, we typically measure the effective temperature and surface metallicity spectroscopically and low-degree oscillation frequencies through space observatories. Here we demonstrate that statistical learning, using artificial neural networks, is successful in determining the evolutionary parameters based on spectroscopic and seismic measurements. Our trained networks show robustness over a broad range of parameter space, and critically, are entirely computationally inexpensive and fully automated. We analyse the observations of a few stars using this method and the results compare well to inferences obtained using other techniques. This method is both computationally cheap and inferentially accurate, paving the way for analysing the vast quantities of stellar observations from past, current, and future missions.

  3. Modelling of W UMa-type variable stars

    Directory of Open Access Journals (Sweden)

    P. L. Skelton

    2010-01-01

    Full Text Available W Ursae Majoris (W UMa-type variable stars are over-contact eclipsing binary stars. To understand how these systems form and evolve requires observations spanning many years, followed by detailed models of as many of them as possible. The All Sky Automated Survey (ASAS has an extensive database of these stars. Using the ASAS V band photometric data, models of W UMatype stars are being created to determine the parameters of these stars. This paper discusses the classification of eclipsing binary stars, the methods used to model them as well as the results of the modelling of ASAS 120036–3915.6, an over-contact eclipsing binary star that appears to be changing its period.

  4. The velocity fields of gas and stars within five KPC of the sun

    Science.gov (United States)

    Ovenden, M. W.; Pryce, M. H. L.; Shuter, W. L. H.

    A mathematical expression is considered for the most probable value of the line of sight velocity, Vr, of an element at a certain galactic longitude and a certain distance projected onto the plane of the galactic disk. Attention is given to the velocity field of O and B stars, the velocity field for idealized circular motion, the velocity field of 112 kinematically distinct H II regions, and the velocity field of nearby 21 cm emission. It is found that the velocity field describing the O and B stars is very close to pure circular motion. On the basis of plots presented in the investigation and an extensive statistical error analysis conducted by Pryce (1983), it is seen that the velocity fields for the nearby gas and H II regions and that of the stars are different.

  5. Kepler observations of variability in B-type stars

    CERN Document Server

    Balona, L A; De Cat, P; Handler, G; Gutierrez-Soto, J; Engelbrecht, C A; Frescura, F; Briquet, M; Cuypers, J; Daszynska-Daszkiewicz, J; Degroote, P; Dukes, R J; Garcia, R A; Green, E M; Heber, U; Kawaler, S D; Ostensen, R; Pricopi, D; Roxburgh, I; Salmon, S; Smith, M A; Suarez, J C; Suran, M; Szabo, R; Uytterhoeven, K; Christensen-Dalsgaard,; Kjeldsen, H; Caldwell, D A; Girouard, F R; Sanderfer, D T

    2011-01-01

    The analysis of the light curves of 48 B-type stars observed by Kepler is presented. Among these are 15 pulsating stars, all of which show low frequencies characteristic of SPB stars. Seven of these stars also show a few weak, isolated high frequencies and they could be considered as SPB/beta Cep hybrids. In all cases the frequency spectra are quite different from what is seen from ground-based observations. We suggest that this is because most of the low frequencies are modes of high degree which are predicted to be unstable in models of mid-B stars. We find that there are non-pulsating stars within the beta Cep and SPB instability strips. Apart from the pulsating stars, we can identify stars with frequency groupings similar to what is seen in Be stars but which are not Be stars. The origin of the groupings is not clear, but may be related to rotation. We find periodic variations in other stars which we attribute to proximity effects in binary systems or possibly rotational modulation. We find no evidence fo...

  6. A star forming ring around Kappa Ori 250 pc from the Sun

    CERN Document Server

    Pillitteri, I; Megeath, S T

    2016-01-01

    X-rays are a powerful probe of activity in early stages of star formation. They allow us to identify young stars even after they have lost the IR signatures of circumstellar disks and provide constraints on their distance. Here we report on XMM-Newton observations which detect 121 young stellar objects (YSOs) in two fields between L1641S and $\\kappa$ Ori. These observations extend the Survey of Orion A with XMM and Spitzer (SOXS). The YSOs are contained in a ring of gas and dust apparent at millimeter wavelengths, and in far-IR and near-IR surveys. The X-ray luminosity function of the young stellar objects detected in the two fields indicates a distance of 250-280 pc, much closer than the Orion A cloud and similar to distance estimates of $\\kappa$ Ori. We propose that the ring is a 5-8 pc diameter shell that has been swept up by $\\kappa$ Ori. This ring contains several groups of stars detected by Spitzer and WISE including one surrounding the Herbig Ae/Be stars V1818 Ori. In this interpretation, the $\\kappa$ ...

  7. THE DIFFERENT EVOLUTION OF GAS AND DUST IN DISKS AROUND SUN-LIKE AND COOL STARS

    NARCIS (Netherlands)

    Pascucci, I.; Apai, D.; Luhman, K.; Henning, Th.; Bouwman, J.; Meyer, M. R.; Lahuis, F.; Natta, A.

    2009-01-01

    Planet formation is profoundly impacted by the properties of protoplanetary disks and their central star. However, how disk properties vary with stellar parameters remains poorly known. Here, we present the first comprehensive, comparative Spitzer/IRS study of the dust and gas properties of disks ar

  8. A Precise Asteroseismic Age and Radius for the Evolved Sun-like Star KIC 11026764

    DEFF Research Database (Denmark)

    Metcalfe, Travis S.; Monteiro, Mario J.P.F.G.; Thompson, Michael J.

    2010-01-01

    that attempt to match the asteroseismic and spectroscopic constraints simultaneously. We determine both the radius and the age of KIC 11026764 with a precision near 1%, and an accuracy near 2% for the radius and 15% for the age. Continued observations of this star promise to reveal additional oscillation...

  9. Multi-types of Skyrmions in SU(N) Quantum Hall System

    Institute of Scientific and Technical Information of China (English)

    LIU Xin; DUAN Yi-Shi; ZHANG Peng-Ming

    2005-01-01

    The skyrmions in SU(N) quantum Hall (QH) system are discussed. By analyzing the gauge field structure and the topological properties of this QH system it is pointed out that in the SU( N) QH system there can exist ( N - 1)types of skyrmion structures, instead of only one type of skyrmions. In this paper, by means of the Abelian projections according to the (N - 1) Cartan subalgebra local bases, we obtain the (N - 1) U(1) electromagnetic field tensors in the SU(N) gauge field of the QH system, and then derive (N - 1) types of skyrmion structures from these U(1) sub-field tensors. Furthermore, in light of the φ-mapping topological current method, the topological charges and the motion of these skyrmions are also discussed.

  10. Stellar Activity on the Young Suns of Orion: COUP Observations of K5-7 Pre-Main Sequence Stars

    CERN Document Server

    Wolk, S J; Micela, G; Favata, F; Glassgold, A E; Shang, H; Feigelson, E D

    2005-01-01

    In January 2003, the Chandra Orion Ultradeep Project (COUP) detected about 1400 young stars during a 13.2 day observation of the Orion Nebula Cluster (ONC). This paper studies a well-defined sample of 28 solar-mass COUP sources to characterize the magnetic activity of analogs of the young Sun and thereby to improve understanding of the effects of solar X-rays on the solar nebula during the era of planet formation. We find that active young Suns spend 70% of their time in a characteristic state with relatively constant flux and magnetically confined plasma with temperatures kT_2 = 2.1 * kT_1. During characteristic periods, the 0.5-8 keV X-ray luminosity is about 0.03% of the bolometric luminosity. One or two powerful flares per week with peak luminosities logL_x ~ 30-32 erg/s are typically superposed on this characteristic emission accompanied by heating of the hot plasma component from ~2.4 keV to ~7 keV at the flare peak. The energy distribution of flares superposed on the characteristic emission level follo...

  11. The Origin of Superflares on G-Type Dwarf Stars of Various Ages

    CERN Document Server

    Katsova, M M

    2015-01-01

    We analyze new observations of superflares on G-stars discovered in the optical and near IR ranges with the Kepler mission. An evolution of solar-type activity is discussed. We give an estimate of the maximal total energy, $E_{tot} = 10^{34}\\;\\mbox{erg}$ of a flare that can occur on the young Sun at its age of 1 Gyr when the cycle was formed. We believe that the main source of the flare optical continuum is a low-temperature condensation forming in the course of the response of the chromosphere to an impulsive heating. For a superflare on the young Sun, we adopt the accelerated electron flux, $F_e (E>\\mbox{20 keV}) = 3 \\times 10^{11} \\: \\mbox{erg} \\; \\mbox{cm}^{-2} \\; \\mbox{s}^{-1}$, that is limited by the return current, and obtain the area of the optical continuum source on a G star, $S \\approx 10^{19} \\:\\mbox{cm}^2$. This value is close to the area of the $H_\\alpha$-ribbons in the largest solar flares, while the area of bright patches of a white-light flare on the contemporary Sun is smaller by about two o...

  12. DETECTABILITY OF EARTH-LIKE PLANETS IN CIRCUMSTELLAR HABITABLE ZONES OF BINARY STAR SYSTEMS WITH SUN-LIKE COMPONENTS

    Energy Technology Data Exchange (ETDEWEB)

    Eggl, Siegfried; Pilat-Lohinger, Elke [University of Vienna, Institute for Astrophysics, Tuerkenschanzstr. 17, A-1180 Vienna (Austria); Haghighipour, Nader, E-mail: siegfried.eggl@univie.ac.at [Institute for Astronomy and NASA Astrobiology Institute, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States)

    2013-02-20

    Given the considerable percentage of stars that are members of binaries or stellar multiples in the solar neighborhood, it is expected that many of these binaries host planets, possibly even habitable ones. The discovery of a terrestrial planet in the {alpha} Centauri system supports this notion. Due to the potentially strong gravitational interaction that an Earth-like planet may experience in such systems, classical approaches to determining habitable zones (HZ), especially in close S-type binary systems, can be rather inaccurate. Recent progress in this field, however, allows us to identify regions around the star permitting permanent habitability. While the discovery of {alpha} Cen Bb has shown that terrestrial planets can be detected in solar-type binary stars using current observational facilities, it remains to be shown whether this is also the case for Earth analogs in HZs. We provide analytical expressions for the maximum and rms values of radial velocity and astrometric signals, as well as transit probabilities of terrestrial planets in such systems, showing that the dynamical interaction of the second star with the planet may indeed facilitate the planets' detection. As an example, we discuss the detectability of additional Earth-like planets in the averaged, extended, and permanent HZs around both stars of the {alpha} Centauri system.

  13. Spectroscopic Binaries Among λ Bootis-type Stars

    NARCIS (Netherlands)

    Paunzen, Ernst; Fraga, Luciano; Heiter, Ulrike; Iliev, Ilian Kh.; Kamp, Inga; Pintado, Olga

    2012-01-01

    The small group of λ Bootis stars comprises late B to early F-type stars, with moderate to extreme (up to a factor 100) surface under-abundances of most Fe-peak elements and solar abundances of lighter elements (C, N, O, and S). The main mechanisms responsible for this phenomenon are atmospheric dif

  14. Completing the census of young stars near the Sun with the FunnelWeb spectroscopic survey

    Science.gov (United States)

    Lawson, Warrick; Murphy, Simon; Tinney, Christopher G.; Ireland, Michael; Bessell, Michael S.

    2016-06-01

    From late 2016, the Australian FunnelWeb survey will obtain medium-resolution (R~2000) spectra covering the full optical range for 2 million of the brightest stars (ITESS) and radial velocity exoplanet studies. In this poster contribution we introduce the FunnelWeb survey, its science goals and input catalogue, as well as provide an update on the status of the fibre positioner and spectrograph commissioning at Siding Spring.

  15. Formation and Evolution of Planetary Systems: Cold Outer Disks Associated with Sun-like stars

    CERN Document Server

    Kim, J S; Backman, D E; Hillenbrand, L A; Meyer, M R; Rodmann, J; Moro-Martin, A; Carpenter, J M; Silverstone, M D; Bouwman, J; Mamajek, E E; Wolf, S; Malhotra, R; Pascucci, I; Najita, J; Padgett, D L; Henning, T; Brooke, T Y; Cohen, M; Strom, S E; Stobie, E B; Engelbracht, C W; Gordon, K D; Misselt, K; Morrison, J E; Muzerolle, J; Su, K Y L; Kim, Jinyoung Serena; Hines, Dean C.; Backman, Dana E.; Hillenbrand, Lynne A.; Meyer, Michael R.; Rodmann, Jens; Moro-Martin, Amaya; Carpenter, John M.; Silverstone, Murray D.; Bouwman, Jeroen; Mamajek, Eric E.; Wolf, Sebastian; Malhotra, Renu; Pascucci, Ilaria; Najita, Joan; Padgett, Deborah L.; Henning, Thomas; Brooke, Timothy Y.; Cohen, Martin; Strom, Stephen E.; Stobie, Elizabeth B.; Engelbracht, Charles W.; Gordon, Karl D.; Misselt, Karl; Morrison, Jane E.; Muzerolle, James; Su, Kate Y. L.

    2005-01-01

    We present the discovery of debris systems around three solar mass stars based upon observations performed with the Spitzer Space Telescope as part of a Legacy Science Program, ``the Formation and Evolution of Planetary Systems'' (FEPS). We also confirm the presence of debris around two other stars. All the stars exhibit infrared emission in excess of the expected photospheres in the 70 micron band, but are consistent with photospheric emission at <= 33 micron. This restricts the maximum temperature of debris in equilibrium with the stellar radiation to T < 70 K. We find that these sources are relatively old in the FEPS sample, in the age range 0.7 - 3 Gyr. Based on models of the spectral energy distributions, we suggest that these debris systems represent materials generated by collisions of planetesimal belts. We speculate on the nature of these systems through comparisons to our own Kuiper Belt, and on the likely planet(s) responsible for stirring the system and ultimately releasing dust through coll...

  16. Direct Imaging of a Cold Jovian Exoplanet in Orbit around the Sun-Like Star GJ 504

    Science.gov (United States)

    Kuzuhara, M.; Tamura, M.; Kudo, T.; Janson, M; Kandori, R.; Brandt, T. D.; Thalmann, C.; Spiegel, D.; Biller, B.; Carson, J.; Hori, Y.; Suzuki, R.; Burrows, A.; Henning, T.; Turner, E. L.; McElwain, M. W.; Moro-Martin, A.; Suenaga, T.; Takahashi, Y. H.; Kwon, J.; Lucas, P.; Abe, L.; Brandner, W.; Grady, C. A.; Serabyn, E.

    2013-01-01

    Several exoplanets have recently been imaged at wide separations of >10 AU from their parent stars. These span a limited range of ages ( 0.5 mag), implying thick cloud covers. Furthermore, substantial model uncertainties exist at these young ages due to the unknown initial conditions at formation, which can lead to an order of magnitude of uncertainty in the modeled planet mass. Here, we report the direct imaging discovery of a Jovian exoplanet around the Sun-like star GJ 504, detected as part of the SEEDS survey. The system is older than all other known directly-imaged planets; as a result, its estimated mass remains in the planetary regime independent of uncertainties related to choices of initial conditions in the exoplanet modeling. Using the most common exoplanet cooling model, and given the system age of 160(+350/-60) Myr, GJ 504 b has an estimated mass of 4(+4.5/-1.0) Jupiter masses, among the lowest of directly imaged planets. Its projected separation of 43.5 AU exceeds the typical outer boundary of approx.. 30 AU predicted for the core accretion mechanism. GJ 504 b is also significantly cooler (510(+30/-20) K)) and has a bluer color (J - H = -0.23 mag) than previously imaged exoplanets, suggesting a largely cloud-free atmosphere accessible to spectroscopic characterization. Thus, it has the potential of providing novel insights into the origins of giant planets, as well as their atmospheric properties.

  17. Direct Imaging of a Cold Jovian Exoplanet in Orbit around the Sun-like Star GJ 504

    CERN Document Server

    Kuzuhara, M; Kudo, T; Janson, M; Kandori, R; Brandt, T D; Thalmann, C; Spiegel, D; Biller, B; Carson, J; Hori, Y; Suzuki, R; Burrows, A; Henning, T; Turner, E L; McElwain, M W; Moro-Martin, A; Suenaga, T; Takahashi, Y H; Kwon, J; Lucas, P; Abe, L; Brandner, W; Egner, S; Feldt, M; Fujiwara, H; Goto, M; Grady, C A; Guyon, O; Hashimoto, J; Hayano, Y; Hayashi, M; Hayashi, S S; Hodapp, K W; Ishii, M; Iye, M; Knapp, G R; Matsuo, T; Mayama, S; Miyama, S; Morino, J -I; Nishikawa, J; Nishimura, T; Kotani, T; Kusakabe, N; Pyo, T -S; Serabyn, E; Suto, H; Takami, M; Takato, N; Terada, H; Tomono, D; Watanabe, M; Wisniewski, J P; Yamada, T; Takami, H; Usuda, T

    2013-01-01

    Several exoplanets have recently been imaged at wide separations of >10 AU from their parent stars. These span a limited range of ages ( 0.5 mag), implying thick cloud covers. Furthermore, substantial model uncertainties exist at these young ages due to the unknown initial conditions at formation, which can lead to an order of magnitude of uncertainty in the modeled planet mass. Here, we report the direct imaging discovery of a Jovian exoplanet around the Sun-like star GJ 504, detected as part of the SEEDS survey. The system is older than all other known directly-imaged planets; as a result, its estimated mass remains in the planetary regime independent of uncertainties related to choices of initial conditions in the exoplanet modeling. Using the most common exoplanet cooling model, and given the system age of 160 [+350, -60] Myr, GJ 504 b has an estimated mass of 4 [+4.5, -1.0] Jupiter masses, among the lowest of directly imaged planets. Its projected separation of 43.5 AU exceeds the typical outer boundary ...

  18. Patrol of the short wavelength activity and flares of Sun as star

    Science.gov (United States)

    Afanasiev, I.; Avakyan, S.; Leonov, N.; Serova, A.; Voronin, N.

    Monitoring of the spectral range which most affects solar-terrestrial relationship - soft X-ray and extreme UV-radiations allows to solve ? problem of solar activity influence on all aspects of the Sun - Earth ties and to select the most important precursors of solar flares and the solar events related with a flare (such as proton events, high-velocity plasma streams in the solar wind, shock waves, coronal mass ejection and, the most important, the beginning of principal magnetic storms). Solar activity is constantly monitored at present (in the USA) only in two sections of the spectrum of ionizing radiation: 115 (119) nm. However, so far there has been no monitoring of the flux in the most geoeffective region of the spectrum (0.8-115 nm) from the entire disk of the sun; this region completely monitors the main part of the ionosphere of the earth and the ionosphere of the other planets of the solar system, including the formation and status of the main ionospheric maxima. This occurs solely because of technical and methodological difficulties in performing the measurements and calibration in this spectral range on spacecraft, because it is necessity to use only windowless optics. At the present the solar the optical - electronic equipment (OEE) is testing and there are plans to launch OEE of Space Solar Patrol (SSP) consisting of solar radiometers and spectrometers at the Russian Module of the International Space Station. So the solving the problem of the permanent monitoring-patrol of ionizing radiation from the full disk of the Sun appears in the main tasks of fundamental scientific studies in space. The results of this monitoring can be contribution in development of simultaneous studies in several sciences, such as: - solar astrophysics (state of all solar atmospheric regions), - meteorology, physics of atmosphere (the influence of solar activity on global changes, climate and weather including the effects of atmo s pheric electricity), - aeronomy, astronautics

  19. Einstein Observatory coronal temperatures of late-type stars

    Science.gov (United States)

    Schmitt, J. H. M. M.; Collura, A.; Sciortino, S.; Vaiana, G. S.; Harnden, F. R., Jr.

    1990-01-01

    The results are presented of a survey of the coronal temperatures of late-type stars using the Einstein Observatory IPC. The spectral analysis shows that the frequently found one- and two-temperature descriptions are mainly influenced by the SNR of the data and that models using continuous emission measure distributions can provide equally adequate and physically more meaningful and more plausible descriptions. Intrinsic differences in differential emission measure distributions are found for four groups of stars. M dwarfs generally show evidence for high-temperature gas in conjunction with lower-temperature material, while main-sequence stars of types F and G have the high-temperature component either absent or very weak. Very hot coronae without the lower-temperature component appearing in dwarf stars are evident in most of the giant stars studied. RS CVn systems show evidence for extremely hot coronae, sometimes with no accompanying lower-temperature material.

  20. How Dry is the Brown Dwarf Desert?: Quantifying the Relative Number of Planets, Brown Dwarfs and Stellar Companions around Nearby Sun-like Stars

    CERN Document Server

    Grether, D; Grether, Daniel; Lineweaver, Charles H.

    2004-01-01

    Sun-like stars have stellar, brown dwarf and planetary companions. To help constrain their formation and migration scenarios, we analyse the close companions (orbital period 2 M_Solar respectively. However, we find no evidence that companion mass scales with host mass in general. Approximately 16% of Sun-like stars have close (P < 5 years) companions more massive than Jupiter: 11% are stellar, 1% are brown dwarf and 4% are giant planets. The companion mass function in the brown dwarf and stellar mass range, has a different shape than the initial mass function of individual stars and free-floating brown dwarfs. This suggests either a different spectrum of gravitational fragmentation in the formation environment or post-formation migratory processes disinclined to leave brown dwarfs in close orbits.

  1. Anomalous Spectral Types and Intrinsic Colors of Young Stars

    CERN Document Server

    Pecaut, Mark J

    2016-01-01

    We highlight differences in spectral types and intrinsic colors observed in pre-main sequence (pre-MS) stars. Spectral types of pre-MS stars are wavelength-dependent, with near-infrared spectra being 3-5 spectral sub-classes later than the spectral types determined from optical spectra. In addition, the intrinsic colors of young stars differ from that of main-sequence stars at a given spectral type. We caution observers to adopt optical spectral types over near-infrared types, since Hertzsprung-Russell (H-R) diagram positions derived from optical spectral types provide consistency between dynamical masses and theoretical evolutionary tracks. We also urge observers to deredden pre-MS stars with tabulations of intrinsic colors specifically constructed for young stars, since their unreddened colors differ from that of main sequence dwarfs. Otherwise, V-band extinctions as much as ~0.6 mag erroneously higher than the true extinction may result, which would introduce systematic errors in the H-R diagram positions ...

  2. Anomalous Spectral Types and Intrinsic Colors of Young Stars

    Science.gov (United States)

    Pecaut, Mark J.

    2016-01-01

    We highlight differences in spectral types and intrinsic colors observed in pre-main sequence (pre-MS) stars. Spectral types of pre-MS stars are wavelength-dependent, with near-infrared spectra being 3-5 spectral sub-classes later than the spectral types determined from optical spectra. In addition, the intrinsic colors of young stars differ from that of main-sequence stars at a given spectral type. We caution observers to adopt optical spectral types over near-infrared types, since Hertzsprung-Russell (H-R) diagram positions derived from optical spectral types provide consistency between dynamical masses and theoretical evolutionary tracks. We also urge observers to deredden pre-MS stars with tabulations of intrinsic colors specifically constructed for young stars, since their unreddened colors differ from that of main sequence dwarfs. Otherwise, V-band extinctions as much as ~0.6 mag erroneously higher than the true extinction may result, which would introduce systematic errors in the H-R diagram positions and thus bias the inferred ages.

  3. Two types of glitches in a solid quark star model

    OpenAIRE

    Lu, Jiguang; Zhou, Enping

    2015-01-01

    TThe glitch of anomalous X-ray pulsars \\& soft gamma repeaters (AXP/SGRs) usually accompanied with detectable energy releases manifesting as X-ray bursts or outbursts, while the glitch of some pulsars like Vela release negligible energy. We find that these two types of glitches can naturally correspond to two types of starquake of solid strange stars. By applying the EoS of quark cluster star and some realistic pulsar parameters, we can reproduce consistent results compared with previous cons...

  4. Searching for IR excesses in Sun-like stars observed by WISE

    CERN Document Server

    de Miera, Fernando Cruz-Saenz; Bertone, Emanuele; Vega, Olga

    2013-01-01

    We present the results of a search of infrared excess candidates in a comprehensive (29\\,000 stars) magnitude limited sample of dwarf stars, spanning the spectral range F2-K0, and brighter than V$=$15 mag. We searched the sample within the {\\em WISE} all sky survey database for objects within 1 arcsecond of the coordinates provided by SIMBAD database and found over 9\\,000 sources detected in all {\\em WISE} bands. This latter sample excludes objects that are flagged as extended sources and those images which are affected by various optical artifacts. For each detected object, we compared the observed W4/W2 (22$\\mu$m/4.6$\\mu$m) flux ratio with the expected photospheric value and identified 197 excess candidates at 3$\\sigma$. For the vast majority of candidates, the results of this analysis represent the first reported evidence of an IR excess. Through the comparison with a simple black-body emission model, we derive estimates of the dust temperature, as well as of the dust fractional luminosities. For more than...

  5. A SPITZER MIPS STUDY OF 2.5-2.0 M{sub Sun} STARS IN SCORPIUS-CENTAURUS

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Christine H.; Bitner, Martin [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Pecaut, Mark; Mamajek, Eric E. [Department of Physics and Astronomy, University of Rochester, Rochester, NY 14627 (United States); Su, Kate Y. L., E-mail: cchen@stsci.edu [Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States)

    2012-09-10

    We have obtained Spitzer Space Telescope Multiband Imaging Photometer for Spitzer (MIPS) 24 {mu}m and 70 {mu}m observations of 215 nearby, Hipparcos B- and A-type common proper-motion single and binary systems in the nearest OB association, Scorpius-Centaurus. Combining our MIPS observations with those of other ScoCen stars in the literature, we estimate 24 {mu}m B+A-type disk fractions of 17/67 (25{sup +6}{sub -5}%), 36/131 (27{sup +4}{sub -4}%), and 23/95 (24{sup +5}{sub -4}%) for Upper Scorpius ({approx}11 Myr), Upper Centaurus Lupus ({approx}15 Myr), and Lower Centaurus Crux ({approx}17 Myr), respectively, somewhat smaller disk fractions than previously obtained for F- and G-type members. We confirm previous IRAS excess detections and present new discoveries of 51 protoplanetary and debris disk systems, with fractional infrared luminosities ranging from L{sub IR}/L{sub *} = 10{sup -6} to 10{sup -2} and grain temperatures ranging from T{sub gr} = 40 to 300 K. In addition, we confirm that the 24 {mu}m and 70 {mu}m excesses (or fractional infrared luminosities) around B+A-type stars are smaller than those measured toward F+G-type stars and hypothesize that the observed disk property dependence on stellar mass may be the result of a higher stellar companion fraction around B- and A-type stars at 10-200 AU. Finally, we note that the majority of the ScoCen 24 {mu}m excess sources also possess 12 {mu}m excess, indicating that Earth-like planets may be forming via collisions in the terrestrial planet zone at {approx}10-100 Myr.

  6. Rieger-type periodicities on the Sun and the Earth during solar cycles 21 and 22

    Science.gov (United States)

    Silva, H. G.; Lopes, I.

    2017-03-01

    Rieger-type periods of the magnetic sunspot area time series have been found in two atmospheric time-series variables: neutron monitor count rate and atmospheric electric potential gradient. The data considered comprises two solar cycles (21, 22) and spans from 1978 to 1990. The study reveals the existence of similar and correlated features in sunspot area as well as neutron counts and atmospheric electric potential gradient, favoring the possibility that the Sun's activity affects the Earth's atmosphere and weather at a time scale between 150-300 days. Moreover, five different Rieger-type periods in the sunspot area time series are found, four of which are detected in the neutron monitor count rate, and three in the atmospheric electric potential gradient. These values are consistent with the periods predicted for stationary solar Rossby waves existing inside the Sun. The possibility is discussed that instabilities on the solar magnetic field caused by solar Rossby waves in the Sun's interior might indirectly be affecting the activity of the heliosphere and the Earth's atmosphere.

  7. Verification of the Kepler Input Catalog from Asteroseismology of Solar-type Stars

    DEFF Research Database (Denmark)

    Verner, G.A.; Chaplin, W.J.; Basu, S.;

    2011-01-01

    -based multi-color photometry. For the stars in our sample, we find general agreement but we detect an average overestimation bias of 0.23 dex in the KIC determination of log (g) for stars with log (g)KIC > 4.0 dex, and a resultant underestimation bias of up to 50% in the KIC radii estimates for stars with R...... KIC sun. Part of the difference may arise from selection bias in the asteroseismic sample; nevertheless, this result implies there may be fewer stars characterized in the KIC with R ~ 1 R sun than is suggested by the physical properties in the KIC. Furthermore, if the radius estimates are taken...

  8. ENSEMBLE EMPIRICAL MODE DECOMPOSITION OF THE MAGNETIC FIELD OF THE SUN AS A STAR

    Energy Technology Data Exchange (ETDEWEB)

    Xiang, N. B. [Yunnan Observatories, Chinese Academy of Sciences, Kunming 650011 (China); Qu, Z. N., E-mail: znqu@ynao.ac.cn [Department of Physics, School of Science, Sichuan University of Science and Engineering, Zigong 643000 (China)

    2016-03-15

    The ensemble empirical mode decomposition (EEMD) analysis is utilized to extract the intrinsic mode functions (IMFs) of the solar mean magnetic field (SMMF) observed at the Wilcox Solar Observatory of Stanford University from 1975 to 2014, and then we analyze the periods of these IMFs as well as the relation of IMFs (SMMF) with some solar activity indices. The two special rotation cycles of 26.6 and 28.5 days should be derived from different magnetic flux elements in the SMMF. The rotation cycle of the weak magnetic flux element in the SMMF is 26.6 days, while the rotation cycle of the strong magnetic flux element in the SMMF is 28.5 days. The two rotation periods of the structure of the interplanetary magnetic field near the ecliptic plane are essentially related to weak and strong magnetic flux elements in the SMMF, respectively. The rotation cycle of weak magnetic flux in the SMMF did not vary over the last 40 years because the weak magnetic flux element derived from the weak magnetic activity on the full disk is not influenced by latitudinal migration. Neither the internal rotation of the Sun nor the solar magnetic activity on the disk (including the solar polar fields) causes the annual variation of SMMF. The variation of SMMF at timescales of a solar cycle is more related to weak magnetic activity on the full solar disk.

  9. The magnetic field vector of the Sun-as-a-star

    CERN Document Server

    Vidotto, A A

    2016-01-01

    Direct comparison between stellar and solar magnetic maps are hampered by their dramatic differences in resolution. Here, we present a method to filter out the small-scale component of vector fields, in such a way that comparison between solar and stellar (large-scale) magnetic field vector maps can be directly made. Our approach extends the technique widely used to decompose the radial component of the solar magnetic field to the azimuthal and meridional components as well. For that, we self-consistently decompose the three-components of the vector field using spherical harmonics of different $l$ degrees. By retaining the low $l$ degrees in the decomposition, we are able to calculate the large-scale magnetic field vector. Using a synoptic map of the solar vector field at Carrington Rotation CR2109, we derive the solar magnetic field vector at a similar resolution level as that from stellar magnetic images. We demonstrate that the large-scale field of the Sun is not purely radial, as often assumed -- at CR210...

  10. A Bcool magnetic snapshot survey of solar-type stars

    CERN Document Server

    Marsden, S C; Jeffers, S V; Morin, J; Fares, R; Reiners, A; Nascimento, J D do; Auriere, M; Bouvier, J; Carter, B D; Catala, C; Dintrans, B; Donati, J -F; Gastine, T; Jardine, M; Konstantinova-Antova, R; Lanoux, J; Lignieres, F; Morgenthaler, A; Ramirez-Velez, J C; Theado, S; Van Grootel, V

    2013-01-01

    Stellar magnetic field measurements obtained from spectropolarimetry offer key data for activity and dynamo studies, and we present the results of a major high-resolution spectropolarimetric Bcool project magnetic snapshot survey of 170 solar-type stars from observations with the Telescope Bernard Lyot and the Canada-France-Hawaii Telescope. For each target star a high signal-to-noise circularly polarised Stokes V profile has been obtained using Least-Squares Deconvolution, and used to detect surface magnetic fields and measure the corresponding mean surface longitudinal magnetic field ($B_{l}$). Chromospheric activity indicators were also measured. Surface magnetic fields were detected for 67 stars, with 21 of these stars classified as mature solar-type stars, a result that increases by a factor of four the number of mature solar-type stars on which magnetic fields have been observed. In addition, a magnetic field was detected for 3 out of 18 of the subgiant stars surveyed. For the population of K-dwarfs the...

  11. The Decay of Debris Disks around Solar-Type Stars

    CERN Document Server

    Sierchio, J M; Su, K Y L; Gaspar, Andras

    2014-01-01

    We present a Spitzer MIPS study of the decay of debris disk excesses at 24 and 70 $\\mu$m for 255 stars of types F4 - K2. We have used multiple tests, including consistency between chromospheric and X-ray activity and placement on the HR diagram, to assign accurate stellar ages. Within this spectral type range, at 24 $\\mu$m, $13.6 \\pm 2.8 \\%$ of the stars younger than 5 Gyr have excesses at the 3$\\sigma$ level or more, while none of the older stars do, confirming previous work. At 70 $\\mu$m, $22.5 \\pm 3.6\\%$ of the younger stars have excesses at $ \\ge$ 3 $\\sigma$ significance, while only $4.7^{+3.7}_{-2.2}$% of the older stars do. To characterize the far infrared behavior of debris disks more robustly, we double the sample by including stars from the DEBRIS and DUNES surveys. For the F4 - K4 stars in this combined sample, there is only a weak (statistically not significant) trend in the incidence of far infrared excess with spectral type (detected fractions of 21.9$^{+4.8}_{-4.3}\\%$, late F; 16.5$^{+3.9}_{-3.3...

  12. The decay of debris disks around solar-type stars

    Energy Technology Data Exchange (ETDEWEB)

    Sierchio, J. M.; Rieke, G. H.; Su, K. Y. L.; Gáspár, Andras, E-mail: sierchio@mit.edu [Steward Observatory, University of Arizona, Tucson, AZ 85721 (United States)

    2014-04-10

    We present a Spitzer MIPS study of the decay of debris disk excesses at 24 and 70 μm for 255 stars of types F4-K2. We have used multiple tests, including consistency between chromospheric and X-ray activity and placement on the H-R diagram, to assign accurate stellar ages. Within this spectral type range, at 24 μm, 13.6% ± 2.8% of the stars younger than 1 Gyr have excesses at the 3σ level or more, whereas none of the older stars do, confirming previous work. At 70 μm, 22.5% ± 3.6% of the younger stars have excesses at ≥3σ significance, whereas only 4.7{sub −2.2}{sup +3.7}% of the older stars do. To characterize the far-infrared behavior of debris disks more robustly, we doubled the sample by including stars from the DEBRIS and DUNES surveys. For the F4-K4 stars in this combined sample, there is only a weak (statistically not significant) trend in the incidence of far-infrared excess with spectral type (detected fractions of 21.9{sub −4.3}{sup +4.8}%, late F; 16.5{sub −3.3}{sup +3.9}%, G; and 16.9{sub −5.0}{sup +6.3}%, early K). Taking this spectral type range together, there is a significant decline between 3 and 4.5 Gyr in the incidence of excesses, with fractional luminosities just under 10{sup –5}. There is an indication that the timescale for decay of infrared excesses varies roughly inversely with the fractional luminosity. This behavior is consistent with theoretical expectations for passive evolution. However, more excesses are detected around the oldest stars than are expected from passive evolution, suggesting that there is late-phase dynamical activity around these stars.

  13. The Decay of Debris Disks around Solar-type Stars

    Science.gov (United States)

    Sierchio, J. M.; Rieke, G. H.; Su, K. Y. L.; Gáspár, Andras

    2014-04-01

    We present a Spitzer MIPS study of the decay of debris disk excesses at 24 and 70 μm for 255 stars of types F4-K2. We have used multiple tests, including consistency between chromospheric and X-ray activity and placement on the H-R diagram, to assign accurate stellar ages. Within this spectral type range, at 24 μm, 13.6% ± 2.8% of the stars younger than 1 Gyr have excesses at the 3σ level or more, whereas none of the older stars do, confirming previous work. At 70 μm, 22.5% ± 3.6% of the younger stars have excesses at >=3σ significance, whereas only 4.7^{+3.7}_{-2.2}% of the older stars do. To characterize the far-infrared behavior of debris disks more robustly, we doubled the sample by including stars from the DEBRIS and DUNES surveys. For the F4-K4 stars in this combined sample, there is only a weak (statistically not significant) trend in the incidence of far-infrared excess with spectral type (detected fractions of 21.9^{+4.8}_{-4.3}%, late F; 16.5^{+3.9}_{-3.3}%, G; and 16.9^{+6.3}_{-5.0}%, early K). Taking this spectral type range together, there is a significant decline between 3 and 4.5 Gyr in the incidence of excesses, with fractional luminosities just under 10-5. There is an indication that the timescale for decay of infrared excesses varies roughly inversely with the fractional luminosity. This behavior is consistent with theoretical expectations for passive evolution. However, more excesses are detected around the oldest stars than are expected from passive evolution, suggesting that there is late-phase dynamical activity around these stars.

  14. Large HI structures linked to southern O-type stars

    CERN Document Server

    Martín, M C; Romero, G A

    2008-01-01

    In our search for interstellar bubbles around massive stars we analyze the environs of the O-type stars HD 38666, HD 124979, HD 163758, and HD 171589. The location of the stars, which are placed far from the galactic plane, favors the formation of large wind bubbles. We investigate the distribution of the neutral and ionized gas based on HI, CO, and radio continuum data, and that of the interstellar dust based on far infrared IRIS images. Here we report the discovery of neutral gas cavities and slowly expanding shells associated with the four massive stars. IR and optical counterparts were also detected for some of the stars. We discuss the probability that the features have originated in the action of the stellar winds on the surrounding gas.

  15. New Suns in the Cosmos. IV. The Multifractal Nature of Stellar Magnetic Activity in Kepler Cool Stars

    Science.gov (United States)

    de Freitas, D. B.; Nepomuceno, M. M. F.; Gomes de Souza, M.; Leão, I. C.; Das Chagas, M. L.; Costa, A. D.; Canto Martins, B. L.; De Medeiros, J. R.

    2017-07-01

    In the present study, we investigate the multifractal nature of a long-cadence time series observed by the Kepler mission for a sample of 34 M dwarf stars and the Sun in its active phase. Using the Multifractal Detrending Moving Average algorithm, which enables the detection of multifractality in nonstationary time series, we define a set of multifractal indices based on the multifractal spectrum profile as a measure of the level of stellar magnetic activity. This set of indices is given by the (A, {{Δ }}α , C, H)-quartet, where A, {{Δ }}α , and C are related to geometric features from the multifractal spectrum and the global Hurst exponent H describes the global structure and memorability of time series dynamics. As a test, we measure these indices and compare them with a magnetic index defined as S ph and verify the degree of correlation among them. First, we apply the Poincaré plot method and find a strong correlation between the index and one of the descriptors that emerges from this method. As a result, we find that this index is strongly correlated with long-term features of the signal. From the multifractal perspective, the index is also strongly linked to the geometric properties of the multifractal spectrum except for the H index. Furthermore, our results emphasize that the rotation period of stars is scaled by the H index, which is consistent with Skumanich’s relationship. Finally, our approach suggests that the H index may be related to the evolution of stellar angular momentum and a star’s magnetic properties.

  16. Are sun- and shade-type anatomy required for the acclimation of Neoregelia cruenta?

    Directory of Open Access Journals (Sweden)

    FERNANDA REINERT

    2013-06-01

    Full Text Available Sun and shade plants are often discriminated by a number of sun- and shade-type anatomies. Nonetheless, we propose that among tank-bromeliads, changes in rosette architecture satisfy the requirements for coping with contrasting light levels. The tank-bromeliad Neoregelia cruenta naturally colonises sub-habitats ranging from full exposure to direct sunlight, to shaded environments in sand ridge plains. We quantified anatomical and morphological traits of leaves and rosettes of N. cruenta grown under sun and shade conditions. Cells with undulated lateral walls within the water parenchyma are for the first time described for the family. Under high light, leaf blades were wider, shorter, and yellowish. The rosette diameter of sun plants was less than half that of shade plants. Sun leaves overlapped with neighbouring leaves for most of their length, forming a cylindrical rosette where water accumulates. Shade leaves only overlapped in the centre of the rosette. Most anatomical traits were similar under both growth conditions. Stomata were absent from the base of sun leaves, which is probably explained by limited gas exchange at the base of the tight sun-type rosette. Data suggest that the ability of N. cruenta to acclimate to sun and shade is better explained by changes in rosette architecture than by leaf anatomy.Plantas de sol e sombra são frequentemente distinguíveis por diversos aspectos anatômicos. Não obstante, propomos que entre bromélias-tanque, mudanças na arquitetura da roseta satisfazem os requerimentos que permitem habitar extremos de luminosidade. A bromélia-tanque, Neoregelia cruenta naturalmente coloniza microhabitats que variam da exposição direta ao sol, a ambientes sombreados sob o dossel da vegetação de restinga. Quantifi camos aspectos anatômicos e morfológicos das folhas e rosetas de N. cruenta crescida sob sol e sombra. Células com paredes onduladas no parênquima aquífero são pela primeira vez descritas na fam

  17. Observations of Type I Bursts from Neutron Stars

    CERN Document Server

    Swank, J H

    2000-01-01

    Observations of Type I X-ray bursts have long been taken as evidence that the sources are neutron stars. Black body models approximate the spectral data and imply a suddenly heated neutron star cooling over characteristic times of seconds to minutes. The phenomena are convincingly explained in terms of nuclear burning of accreted gas on neutron stars with low mass companion stars. Prospects are promising that detailed theory and data from RXTE and future missions will lead to better determinations of important physical parameters (neutron star mass and radius, composition of the accreting gas, distance of the source). Among the variety of bursts observed, there are probably representatives of different kinds of explosive burning. RXTE's discovery of a 2.5 ms persistent coherent period from one Type I burster has now linked bursters indisputably to the epitome of a neutron star, a fast spinning magnetic compact object. Oscillations in some bursts had already been thought to arise from the neutron stars' rotati...

  18. A Be-type star with a black hole companion

    CERN Document Server

    Casares, J; Ribo, M; Ribas, I; Paredes, J M; Herrero, A; Simon-Diaz, S

    2014-01-01

    Stellar-mass black holes have all been discovered through X-ray emission, which arises from the accretion of gas from their binary companions (this gas is either stripped from low-mass stars or supplied as winds from massive ones). Binary evolution models also predict the existence of black holes accreting from the equatorial envelope of rapidly spinning Be-type stars (stars of the Be type are hot blue irregular variables showing characteristic spectral emission lines of hydrogen). Of the ~80 Be X-ray binaries known in the Galaxy, however, only pulsating neutron stars have been found as companions. A black hole was formally allowed as a solution for the companion to the Be star MWC 656 (also known as HD 215227), although that was based on a single radial velocity curve of the Be star, a mistaken spectral classification and rough estimates of the inclination angle. Here we report observations of an accretion disk line mirroring the orbit of the Be star. This, together with an improved radial velocity curve of ...

  19. The Sun

    CERN Document Server

    Golub, Leon

    2017-01-01

    Essential for life on earth and a major influence on our environment, the Sun is also the most fascinating object in the daytime sky. Every day we feel the effect of its coming and going – literally the difference between day and night. But figuring out what the Sun is, what it’s made of, why it glows so brightly, how old it is, how long it will last – all of these take thought and observation. Leon Golub and Jay M. Pasachoff offer an engaging and informative account of what scientists know about the Sun, and the history of these discoveries. Solar astronomers have studied the Sun over the centuries both for its intrinsic interest and in order to use it as a laboratory to reveal the secrets of other stars. The authors discuss the surface of the Sun, including sunspots and their eleven-year cycle, as well as the magnetism that causes them; the Sun’s insides, as studied mainly from seismic waves that astronomers record on its surface; the outer layers of the Sun that we see from Earth only at eclipses ...

  20. Automated Asteroseismic Analysis of Solar-type Stars

    DEFF Research Database (Denmark)

    Karoff, Christoffer; Campante, T.L.; Chaplin, W.J.

    2010-01-01

    The rapidly increasing volume of asteroseismic observations on solar-type stars has revealed a need for automated analysis tools. The reason for this is not only that individual analyses of single stars are rather time consuming, but more importantly that these large volumes of observations open...... the possibility to do population studies on large samples of stars and such population studies demand a consistent analysis. By consistent analysis we understand an analysis that can be performed without the need to make any subjective choices on e.g. mode identification and an analysis where the uncertainties...

  1. The Lick-Carnegie Exoplanet Survey: HD32963 -- A New Jupiter Analog Orbiting a Sun-like Star

    CERN Document Server

    Rowan, Dominick; Laughlin, Gregory; Vogt, Steven S; Butler, R Paul; Burt, Jennifer; Wang, Songhu; Holden, Brad; Hanson, Russell; Arriagada, Pamela; Keiser, Sandy; Teske, Johanna; Diaz, Matias

    2015-01-01

    We present a set of 109 new, high-precision Keck/HIRES radial velocity (RV) observations for the solar-type star HD 32963. Our dataset reveals a candidate planetary signal with a period of 6.49 $\\pm$ 0.07 years and a corresponding minimum mass of 0.7 $\\pm$ 0.03 Jupiter masses. Given Jupiter's crucial role in shaping the evolution of the early Solar System, we emphasize the importance of long-term radial velocity surveys. Finally, using our complete set of Keck radial velocities and correcting for the relative detectability of synthetic planetary candidates orbiting each of the 1,122 stars in our sample, we estimate the frequency of Jupiter analogs across our survey at approximately 3%.

  2. Statistical Properties of Blue Horizontal Branch Stars in the Spheroid: Detection of a Moving Group approximately 50 kpc from the Sun

    Energy Technology Data Exchange (ETDEWEB)

    Harrigan, Matthew J.; Newberg, Heidi Jo; Newberg, Lee A.; /Rensselaer Poly.; Yanny, Brian; /Fermilab; Beers, Timothy C.; Lee, Young Sun; /Michigan State U.; Fiorentin, Paola Re; /Ljubljana U. /Heidelberg, Max Planck Inst. Astron.

    2010-02-01

    A new moving group comprising at least four Blue Horizontal Branch (BHB) stars is identified at (l; b) = (65{sup o}; 48{sup o}). The horizontal branch at g{sub 0} = 18.9 magnitude implies a distance of 50 kpc from the Sun. The heliocentric radial velocity is = -157 {+-} 4 km s{sup -1}, corresponding to V{sub gsr} = -10 km s{sup -1}; the dispersion in line-of-sight velocity is consistent with the instrumental errors for these stars. The mean metallicity of the moving group is [Fe/H] {approx} -2.4, which is significantly more metal poor than the stellar spheroid. We estimate that the BHB stars in the outer halo have a mean metallicity of [Fe/H]=-2.0, with a wide scatter and a distribution that does not change much as a function of distance from the Sun. We explore the systematics of SDSS DR7 surface gravity metallicity determinations for faint BHB stars, and present a technique for estimating the significance of clumps discovered in multidimensional data. This moving group cannot be distinguished in density, and highlights the need to collect many more spectra of Galactic stars to unravel the merger history of the Galaxy.

  3. HATS-2b: A transiting extrasolar planet orbiting a K-type star showing starspot activity

    CERN Document Server

    Mohler-Fischer, M; Hartman, J D; Bakos, G B; Penev, K; Bayliss, D; Jordan, A; Csubry, Z; Zhou, G; Rabus, M; Nikolov, N; Brahm, R; Espinoza, N; Buchhave, L A; Beky, B; Suc, V; Csak, B; Henning, T; Wright, D J; Tinney, C G; Addison, B C; Schmidt, B; Noyes, R W; Papp, I; Lazar, J; Sari, P; Conroy, P

    2013-01-01

    We report the discovery of HATS-2b, the second transiting extrasolar planet detected by the HATSouth survey. HATS-2b is moving on a circular orbit around a V=13.6 mag, K-type dwarf star (GSC 6665-00236), at a separation of 0.0230 \\pm 0.0003 AU and with a period of 1.3541 days. The planetary parameters have been robustly determined using a simultaneous fit of the HATSouth, MPG/ESO~2.2\\,m/GROND, Faulkes Telescope South/Spectral transit photometry and MPG/ESO~2.2\\,m/FEROS, Euler~1.2\\,m/CORALIE, AAT~3.9\\,m/CYCLOPS radial-velocity measurements. HATS-2b has a mass of 1.37 \\pm 0.16 M_J, a radius of 1.14 \\pm 0.03 R_J and an equilibrium temperature of 1567 \\pm 30 K. The host star has a mass of 0.88 \\pm 0.04 M_Sun, radius of 0.89 \\pm 0.02 R_Sun and shows starspot activity. We characterized the stellar activity by analysing two photometric follow-up transit light curves taken with the GROND instrument, both obtained simultaneously in four optical bands (covering the wavelength range of 3860-9520 \\AA). The two light curv...

  4. Studying the evolution of a type III radio from the Sun up to 1 AU

    Science.gov (United States)

    Mann, Gottfried; Breitling, Frank; Vocks, Christian; Fallows, Richard; Melnik, Valentin; Konovalenko, Alexander

    2017-04-01

    On March 16, 2016, a type III burst was observed with the ground-based radio telescopes LOFAR and URAN-2 as well as with the radiospectrometer aboard the spacecraft WIND.It started at 80 MHz at 06:37 UT and reached 50 kHz after 23 minutes. A type III burst are considered as the radio signature of an electron beam travelling from the corona into the interplanetary space. The energetic electrons carrying the beam excites Langmuir waves, which convert into radio waves by wave-particle interaction. The relationship between the drift rate and the frequency as derived from the dynamic radio spectra reveals that the velocity of the electrons generating the radio waves of the type III burst is increasing with increasing distance from the center of the Sun.

  5. Metallicity calibration for solar type stars based on red spectra

    Institute of Scientific and Technical Information of China (English)

    Jing-Kun Zhao; Gang Zhao; Yu-Qin Chen; A-Li Luo

    2011-01-01

    Based on a high resolution and high signal-to-noise ratio (S/N) spectral analysis of 90 solar-type stars, we have established several new metallicity calibrations in the Teff range [5600, 6500] K based on red spectra with the wavelength range of 560-880 nm. The new metallicity calibrations are applied to determine the metallicity of solar analogs selected from Sloan Digital Sky Survey (SDSS) spectra. There is a good consistent result with the adopted value presented in SDSS-DR7 and a small scatter of 0.26 dex for stars with S/N > 50 being obtained. This study provides a new reliable way to derive the metallicity for solar-like stars with low resolution spectra.In particular, our calibrations are useful for finding metal-rich stars, which are missing in the SEGUE Stellar Parameter Pipeline.

  6. On the Structure and Properties of Differentially Rotating Main-Sequence Stars in the 1-2 M_sun Range

    CERN Document Server

    MacGregor, K B; Skumanich, Andrew; Metcalfe, T S

    2007-01-01

    We conduct a systematic examination of the properties of models for chemically homogeneous, differentially rotating, main-sequence stars of mass 1-2 M_sun. The models were constructed using a code based on a reformulation of the self-consistent field method of computing the equilibrium stellar structure for a specified conservative internal rotation law. [abridged] Relative to nonrotating stars of the same mass, these models all have reduced luminosities and effective temperatures, and flattened photospheric shapes (i.e., decreased polar radii) with equatorial radii that can be larger or smaller, depending on the degree of differential rotation. For a fixed ratio of the axial rotation rate to the surface equatorial rotation rate, increasingly rapid rotation generally deepens convective envelopes, shrinks convective cores, and can lead to the presence of a convective core (envelope) in a 1 M_sun (2 M_sun) model, a feature that is absent in a nonrotating star of the same mass. The positions of differentially ro...

  7. Early type stars at high galactic latitudes II. Four evolved B-type stars of unusual chemical composition

    CERN Document Server

    Ramspeck, M; Edelmann, H

    2001-01-01

    We present the result of differential spectral analyses of a further four apparently normal B-type stars. Abundance anomalies (e.g. He, C, N enrichment), slow rotation and/or high gravities suggest that the programme stars are evolved low-mass B-type stars. In order to trace their evolutionary status several scenarios are discussed. Post-AGB evolution can be ruled out. PG 0229+064 and PG 1400+389 could be horizontal branch (HB) stars, while HD 76431 and SB 939 have already evolved away from the extreme HB (EHB). The low helium abundance of HD 76431 is consistent with post-EHB evolution. The enrichment in helium, carbon and nitrogen of the remaining stars can be explained either by deep mixing of nuclearly processed material to the surface or by diffusion processes modified by magnetic fields and/or stellar winds. A kinematic study of their galactic orbits indicates that the stars belong to an old disk population.

  8. WASP-32b: A transiting hot Jupiter planet orbiting a lithium-poor, solar-type star

    CERN Document Server

    Maxted, P F L; Cameron, A Collier; Gillon, M; Hellier, C; Queloz, D; Smalley, B; Triaud, A H M J; West, R G; Enoch, R; Lister, T A; Pepe, F; Pollacco, D L; Ségransan, D; Skillen, I; Udry, S

    2010-01-01

    We report the discovery of a transiting planet orbiting the star TYC 2-1155-1. The star, WASP-32, is a moderately bright (V=11.3) solar-type star (Teff=6100 +- 100K, [Fe/H] = -0.13 +- 0.10). The lightcurve of the star obtained with the WASP-South and WASP-North instruments shows periodic transit-like features with a depth of about 1% and a duration of 0.10d every 2.72d. The presence of a transit-like feature in the lightcurve is confirmed using z-band photometry obtained with Faulkes Telescope North. High resolution spectroscopy obtained with the CORALIE spectrograph confirms the presence of a planetary mass companion. From a combined analysis of the spectroscopic and photometric data, assuming that the star is a typical main-sequence star, we estimate that the planet has a mass M_p = 3.60 +- 0.07 M_Jup and a radius R_p = 1.19 +- 0.06R_Jup. WASP-32 is one of a small group of hot Jupiters with masses M_p > 3M_Jup. We find that some stars with hot Jupiter companions and with masses M_* =~ 1.2M_sun, including WA...

  9. Are sun- and shade-type anatomy required for the acclimation of Neoregelia cruenta?

    OpenAIRE

    2013-01-01

    Sun and shade plants are often discriminated by a number of sun- and shade-type anatomies. Nonetheless, we propose that among tank-bromeliads, changes in rosette architecture satisfy the requirements for coping with contrasting light levels. The tank-bromeliad Neoregelia cruenta naturally colonises sub-habitats ranging from full exposure to direct sunlight, to shaded environments in sand ridge plains. We quantified anatomical and morphological traits of leaves and rosettes of N. cruenta grown...

  10. The Star Formation History of Late Type Galaxies

    CERN Document Server

    Fernandes, R C

    2007-01-01

    The combination of huge databases of galaxy spectra and advances in evolutionary synthesis models in the past few years has renewed interest in an old question: How to estimate the star formation history of a galaxy out of its integrated spectrum? Fresh approaches to this classical problem are making it possible to extract the best of both worlds, producing exquisite pixel-by-pixel fits to galaxy spectra with state-of-the-art stellar population models while at the same time exploring the fabulous statistics of mega-surveys to derive the star-formation and chemical enrichment histories of different types of galaxies with an unprecedented level of detail. This review covers some of these recent advances, focusing on results for late-type, star-forming galaxies, and outlines some of the issues which will keep us busy in the coming years.

  11. Formation and Evolution of Planetary Systems (FEPS): Primordial Warm Dust Evolution From 3-30 Myr around Sun-like Stars

    CERN Document Server

    Silverstone, M D; Mamajek, E E; Hines, D C; Hillenbrand, L A; Najita, J; Pascucci, I; Bouwman, J; Kim, J S; Carpenter, J M; Stauffer, J R; Backman, D E; Moro-Martin, A; Henning, T; Wolf, S; Brooke, T Y; Padgett, D L

    2006-01-01

    We present data obtained with the Infrared Array Camera (IRAC) aboard the Spitzer Space Telescope (Spitzer) for a sample of 74 young (t < 30 Myr old) Sun-like (0.7 < M(star)/M(Sun) < 1.5) stars. These are a sub-set of the observations that comprise the Spitzer Legacy science program entitled the Formation and Evolution of Planetary Systems (FEPS). Using IRAC we study the fraction of young stars that exhibit 3.6-8.0 micron infrared emission in excess of that expected from the stellar photosphere, as a function of age from 3-30 Myr. The most straightforward interpretation of such excess emission is the presence of hot (300-1000K) dust in the inner regions (< 3 AU) of a circumstellar disk. Five out of the 74 young stars show a strong infrared excess, four of which have estimated ages of 3-10 Myr. While we detect excesses from 5 optically thick disks, and photospheric emission from the remainder of our sample, we do not detect any excess emission from optically thin disks at these wavelengths. We comp...

  12. Statistical Properties of Blue Horizontal Branch Stars in the Spheroid: Detection of a Moving Group approximately 50 kpc from the Sun

    CERN Document Server

    Harrigan, Matthew J; Newberg, Lee A; Yanny, Brian; Beers, Timothy C; Lee, Young Sun; Fiorentin, Paola Re

    2010-01-01

    A new moving group comprising at least four Blue Horizontal Branch (BHB) stars is identified at (l,b) = (65 deg, 48 deg). The horizontal branch at g0=18.9 magnitude implies a distance of 50 kpc from the Sun. The heliocentric radial velocity is RV = -157 +/- 4 km/s, corresponding to V(gsr) = -10 km/s; the dispersion in line-of-sight velocity is consistent with the instrumental errors for these stars. The mean metallicity of the moving group is [Fe/H] approximately -2.4, which is significantly more metal poor than the stellar spheroid. We estimate that the BHB stars in the outer halo have a mean metallicity of [Fe/H] = -2.0, with a wide scatter and a distribution that does not change much as a function of distance from the Sun. We explore the systematics of SDSS DR7 surface gravity metallicity determinations for faint BHB stars, and present a technique for estimating the significance of clumps discovered in multidimensional data. This moving group cannot be distinguished in density, and highlights the need to c...

  13. Peculiar early-type galaxies with central star formation

    Institute of Scientific and Technical Information of China (English)

    Chong Ge; Qiu-Sheng Gu

    2012-01-01

    Early-type galaxies (ETGs) are very important for understanding the formation and evolution of galaxies.Recent observations suggest that ETGs are not simply old stellar spheroids as we previously thought.Widespread recent star formation,cool gas and dust have been detected in a substantial fraction of ETGs.We make use of the radial profiles of g - r color and the concentration index from the Sloan Digital Sky Survey database to pick out 31 peculiar ETGs with central blue cores.By analyzing the photometric and spectroscopic data,we suggest that the blue cores are caused by star formation activities rather than the central weak active galactic nucleus.From the results of stellar population synthesis,we find that the stellar population of the blue cores is relatively young,spreading from several Myr to less than one Gyr.In 14 galaxies with H I observations,we find that the average gas fraction of these galaxies is about 0.55.The bluer galaxies show a higher gas fraction,and the total star formation rate (SFR) correlates very well with the H l gas mass.The star formation history of these ETGs is affected by the environment,e.g.in the denser environment the H 1 gas is less and the total SFR is lower.We also discuss the origin of the central star formation of these early-type galaxies.

  14. AN ANALYTIC METHOD TO DETERMINE HABITABLE ZONES FOR S-TYPE PLANETARY ORBITS IN BINARY STAR SYSTEMS

    Energy Technology Data Exchange (ETDEWEB)

    Eggl, Siegfried; Pilat-Lohinger, Elke; Gyergyovits, Markus; Funk, Barbara [Institute for Astronomy, University of Vienna, Tuerkenschanzstr. 17, A-1180 Vienna (Austria); Georgakarakos, Nikolaos, E-mail: siegfried.eggl@univie.ac.at, E-mail: elke.pilat-lohinger@univie.ac.at [128 V. Olgas str., Thessaloniki 546 45 (Greece)

    2012-06-10

    With more and more extrasolar planets discovered in and around binary star systems, questions concerning the determination of the classical habitable zone have arisen. Do the radiative and gravitational perturbations of the second star influence the extent of the habitable zone significantly, or is it sufficient to consider the host star only? In this article, we investigate the implications of stellar companions with different spectral types on the insolation a terrestrial planet receives orbiting a Sun-like primary. We present time-independent analytical estimates and compare them to insolation statistics gained via high precision numerical orbit calculations. Results suggest a strong dependence of permanent habitability on the binary's eccentricity, as well as a possible extension of habitable zones toward the secondary in close binary systems.

  15. An Analytic Method to determine Habitable Zones for S-Type Planetary Orbits in Binary Star Systems

    CERN Document Server

    Eggl, Siegfried; Georgakarakos, Nikolaos; Gyergyovits, Markus; Funk, Barbara

    2012-01-01

    With more and more extrasolar planets discovered in and around binary star systems, questions concerning the determination of the classical Habitable Zone arise. Do the radiative and gravitational perturbations of the second star influence the extent of the Habitable Zone significantly, or is it sufficient to consider the host-star only? In this article we investigate the implications of stellar companions with different spectral types on the insolation a terrestrial planet receives orbiting a Sun-like primary. We present time independent analytical estimates and compare these to insolation statistics gained via high precision numerical orbit calculations. Results suggest a strong dependence of permanent habitability on the binary's eccentricity, as well as a possible extension of Habitable Zones towards the secondary in close binary systems.

  16. Acoustic glitches in solar-type stars from Kepler

    DEFF Research Database (Denmark)

    Mazumdar, A.; Monteiro, M. J. P. F. G.; Ballot, J

    2012-01-01

    We report the measurement of the acoustic locations of layers of sharp variation in sound speed in the interiors of 19 solar-type stars observed by the Kepler mission. The oscillatory signal in the frequencies arising due to the acoustic glitches at the base of the convection zone and the second...

  17. The Spitzer Spectroscopic Survey of S-type Stars

    CERN Document Server

    Smolders, K; Blommaert, J A D L; Hony, S; Van Winckel, H; Decin, L; Van Eck, S; Sloan, G C; Cami, J; Uttenthaler, S; Degroote, P; Barry, D; Feast, M; Groenewegen, M A T; Matsuura, M; Menzies, J; Sahai, R; van Loon, J Th; Zijlstra, A A; Acke, B; Bloemen, S; Cox, N; de Cat, P; Desmet, M; Exter, K; Ladjal, D; Ostensen, R; Saesen, S; van Wyk, F; Verhoest, T; Zima, W

    2012-01-01

    S-type AGB stars are thought to be in the transitional phase between M-type and C-type AGB stars. Because of their peculiar chemical composition, one may expect a strong influence of the stellar C/O ratio on the molecular chemistry and the mineralogy of the circumstellar dust. In this paper, we present a large sample of 87 intrinsic galactic S-type AGB stars, observed at infrared wavelengths with the Spitzer Space Telescope, and supplemented with ground-based optical data. On the one hand, we derive the stellar parameters from the optical spectroscopy and photometry, using a grid of model atmospheres. On the other, we decompose the infrared spectra to quantify the flux-contributions from the different dust species. Finally, we compare the independently determined stellar parameters and dust properties. For the stars without significant dust emission, we detect a strict relation between the presence of SiS absorption in the Spitzer spectra and the C/O ratio of the stellar atmosphere. These absorption bands can...

  18. Initial Assessment of the Spectrometer for Sky-Scanning, Sun-Tracking Atmospheric Research (4STAR-Based Aerosol Retrieval: Sensitivity Study

    Directory of Open Access Journals (Sweden)

    Alexander Sinyuk

    2012-10-01

    Full Text Available The Spectrometer for Sky-Scanning, Sun-Tracking Atmospheric Research (4STAR being developed for airborne measurements will offer retrievals of aerosol microphysical and optical properties from multi-angular and multi-spectral measurements of sky radiance and direct-beam sun transmittance. In this study, we assess the expected accuracy of the 4STAR-based aerosol retrieval and its sensitivity to major sources of anticipated perturbations in the 4STAR measurements. The major anticipated perturbations are (1 an apparent enhancement of sky radiance at small scattering angles associated with the necessarily compact design of the 4STAR and (2 an offset (i.e., uncertainty of sky radiance calibration independent of scattering angle. The assessment is performed through application of the operational AERONET aerosol retrieval and constructed synthetic 4STAR-like data. Particular attention is given to the impact of these perturbations on the broadband fluxes and the direct aerosol radiative forcing. The results from this study suggest that limitations in the accuracy of 4STAR-retrieved particle size distributions and scattering phase functions have diminished impact on the accuracy of retrieved bulk microphysical parameters, permitting quite accurate retrievals of properties including the effective radius (up to 10%, or 0.03, and the radiatively important optical properties, such as the asymmetry factor (up to 4%, or ±0.02 and single-scattering albedo (up to 6%, or ±0.04. Also, the obtained results indicate that the uncertainties in the retrieved aerosol optical properties are quite small in the context of the calculated fluxes and direct aerosol radiative forcing (up to 15%, or 3 W∙m−2.

  19. Sun protection attitudes and behaviours among first generation Australians with darker skin types: results from focus groups.

    Science.gov (United States)

    Bryant, Jamie; Zucca, Alison; Brozek, Irena; Rock, Vanessa; Bonevski, Billie

    2015-02-01

    Despite residing in a country that has the highest rates of skin cancer in the world, little is known about the knowledge, attitudes and sun protection practices of first generation Australian-born individuals with olive and darker skin types. Six focus groups with first generation Australian-born individuals of Asian, Mediterranean, Middle Eastern and Indian background were conducted. Participants had good knowledge of the dangers of skin cancer. Most correctly perceived darker skin types as protective and believed they were at low risk of skin cancer. Most participants could recall high profile mass media sun protection campaigns. Several participants suggested that greater representation of ethnic minorities and/or individuals with darker skin types would increase the personal relevance of campaigns. Beliefs that sun protection is not necessary on the basis of skin type highlights the need for further studies to explore fundamental differences in attitudes and practices between those with olive and darker skin and the general Australian population.

  20. Automated Asteroseismic Analysis of Solar-type Stars

    DEFF Research Database (Denmark)

    Karoff, Christoffer; Campante, T.L.; Chaplin, W.J.

    2010-01-01

    The rapidly increasing volume of asteroseismic observations on solar-type stars has revealed a need for automated analysis tools. The reason for this is not only that individual analyses of single stars are rather time consuming, but more importantly that these large volumes of observations open...... are calculated in a consistent way. Here we present a set of automated asterosesimic analysis tools. The main engine of these set of tools is an algorithm for modelling the autocovariance spectra of the stellar acoustic spectra allowing us to measure not only the frequency of maximum power and the large...

  1. A Survey of Stellar Families: Multiplicity of Solar-Type Stars

    CERN Document Server

    Raghavan, Deepak; Henry, Todd J; Latham, David W; Marcy, Geoffrey W; Mason, Brian D; Gies, Douglas R; White, Russel J; Brummelaar, Theo A ten

    2010-01-01

    We present the results of a comprehensive assessment of companions to solar-type stars. A sample of 454 stars, including the Sun, was selected from the Hipparcos catalog with {\\pi} > 40 mas, {\\sigma}_{\\pi}/{\\pi} < 0.05, 0.5 < B - V < 1.0 (~ F6-K3), and constrained by absolute magnitude and color to exclude evolved stars. New observational aspects of this work include surveys for (1) very close companions with long-baseline interferometry at the CHARA Array, (2) close companions with speckle interferometry, and (3) wide proper motion companions identified by blinking multi-epoch archival images. In addition, we include the results from extensive radial-velocity monitoring programs and evaluate companion information from various catalogs. The overall observed fractions of single, double, triple, and higher order systems are 56% \\pm 2%, 33% \\pm 2%, 8% \\pm 1%, and 3% \\pm 1%, respectively, counting all confirmed stellar and brown dwarf companions. Our completeness analysis indicates that only a few undisc...

  2. ON THE TEMPORAL EVOLUTION OF THE DISK COUNTERPART OF TYPE II SPICULES IN THE QUIET SUN

    Energy Technology Data Exchange (ETDEWEB)

    Sekse, D. H.; Rouppe van der Voort, L. [Institute of Theoretical Astrophysics, University of Oslo, P.O. Box 1029, Blindern, N-0315 Oslo (Norway); De Pontieu, B. [Lockheed Martin Solar and Astrophysics Lab, Org. A021S, Bldg. 252, 3251 Hanover Street, Palo Alto, CA 94304 (United States)

    2013-02-20

    The newly established type II spicule has been speculated to provide enough hot plasma to play an important role in the mass loading and heating of the solar corona. With the identification of rapid blueshifted excursions (RBEs) as the on-disk counterpart of type II spicules we have analyzed three different high-quality timeseries with the CRisp Imaging SpectroPolarimeter (CRISP) at the Swedish Solar Telescope on La Palma and subjected to an automated detection routine to detect a large number of RBEs for statistical purposes. Our observations are of a quiet-Sun region at disk center and we find lower Doppler velocities, 15-40 km s{sup -1}, and Doppler widths, 2-15 km s{sup -1}, of RBEs than in earlier coronal hole studies, 30-50 km s{sup -1} and 7-23 km s{sup -1}, respectively. In addition, we examine the spatial dependence of Doppler velocities and widths along the RBE axis and conclude that there is no clear trend to this over the field of view or in individual RBEs in the quiet Sun at disk center. These differences with previous coronal hole studies are attributed to the more varying magnetic field configuration in quiet-Sun conditions. Using an extremely high-cadence data set has allowed us to improve greatly on the determination of lifetimes of RBEs, which we find to range from 5 to 60 s with an average lifetime of 30 s, as well as the transverse motions in RBEs, with transverse velocities up to 55 km s{sup -1} and averaging 12 km s{sup -1}. Furthermore, our measurements of the recurrence rates of RBEs provide important new constraints on coronal heating by spicules. We also see many examples of a sinusoidal wave pattern in the transverse motion of RBEs with periods averaging 54 s and amplitudes from 21.5 to 129 km which agrees well with previous studies of wave motion in spicules at the limb. We interpret the appearance of RBEs over their full length within a few seconds as the result of a combination of three kinds of motions as is earlier reported for

  3. Kepler-22b: A 2.4 Earth-radius Planet in the Habitable Zone of a Sun-like Star

    DEFF Research Database (Denmark)

    Borucki, W.J.; Koch, D.G.; Batalha, N.

    2012-01-01

    A search of the time-series photometry from NASA's Kepler spacecraft reveals a transiting planet candidate orbiting the 11th magnitude G5 dwarf KIC 10593626 with a period of 290 days. The characteristics of the host star are well constrained by high-resolution spectroscopy combined with an astero......A search of the time-series photometry from NASA's Kepler spacecraft reveals a transiting planet candidate orbiting the 11th magnitude G5 dwarf KIC 10593626 with a period of 290 days. The characteristics of the host star are well constrained by high-resolution spectroscopy combined...... with an asteroseismic analysis of the Kepler photometry, leading to an estimated mass and radius of 0.970 ± 0.060 M sun and 0.979 ± 0.020 R sun. The depth of 492 ± 10 ppm for the three observed transits yields a radius of 2.38 ± 0.13 Re for the planet. The system passes a battery of tests for false positives, including...... masses, thus earning the designation Kepler-22b. The radiative equilibrium temperature is 262 K for a planet in Kepler-22b's orbit. Although there is no evidence that Kepler-22b is a rocky planet, it is the first confirmed planet with a measured radius to orbit in the habitable zone of any star other...

  4. The sky-disk of Nebra - sun, moon and stars (German Title: Die Himmelsscheibe von Nebra - Sonne, Mond und Sterne)

    Science.gov (United States)

    Schlosser, Wolfhard

    No prehistorical find anywhere shows such a clear proof for the interest of prehistoric mankind in cosmic events as does the Nebra sky-disk. With an almost 100 percent probability, the (originally) 32 centimeter-size gold plates represent stars. According to astronomical analysis, the group of seven closely arranged plates represent the Pleiades (The Seven Sisters). Statistical research strengthens the view that the remaining 25 gold plates cannot be assigned to individual constellations, but represent the general starry night sky. Without much restriction, the two lateral arcs (added at a later time) can be assigned to those horizon regions which are accessible to the sun over the year for the geographic latitude of Saxe-Anhalt. A slight asymmetry of these arcs with respect to the center of the disk makes it possible that the upper solar limb was observed. The lower pinnate arc with an interior drawing - also a later addition - can be interpreted as the solar barque, which, because of the above-mentioned asymmetry, indicates the southern direction of the sky-disk. An investigation of the visibilities of the Pleiades for the finding spot of the Mittelberg indicates that only their last evening visibility (March 10 of our calendar) and their first morning setting (October 17) were of calendary use in the early Bronze Age. At these times, the Pleiades were found in those parts of the sky which are the domain of the young crescent shortly after new moon (March) and of the full moon (October). This would make possible a suitable assignment of the sky-disk's crescent- and round object to both these phases of the moon. The said dates describe quite well the beginning and the end of the agricultural year for the region where the sky-disk was found. Such a working hypothesis (‘rural year’) is not at all unique, but is supported by numerous peasant-rules referring to the Pleiades from antiquity up to the present time. In particular, Lithuanian peasants observed until

  5. Central stars of planetary nebulae. II. New OB-type and emission-line stars

    Science.gov (United States)

    Weidmann, W. A.; Gamen, R.

    2011-07-01

    Context. There are more than 3000 confirmed and probably known Galactic planetary nebulae (PNe), but central star spectroscopic information is available for only 13% of them. Aims: We have undertaken a spectroscopic survey of the central stars in PNe to identify their spectral types. Methods: We performed spectroscopic observations at low resolution with the 2-m telescope at CASLEO, Argentina. Results: We present the spectra of 46 central stars of PNe, most of them are OB-type and emission-line stars. Based on data collected at the Complejo Astronómico El Leoncito (CASLEO), which is operated under agreement between the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina y Universidades Nacionales de La Plata, Córdoba y San Juan, Argentina.The reduced spectra (FITS files) are available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/531/A172

  6. First-Ever Census of Variable Mira-Type Stars in Galaxy Outside the Local Group

    Science.gov (United States)

    2003-05-01

    "variable star". The percentage is much higher among large, cool stars ("red giants") - in fact, almost all luminous stars of that type are variable. Such stars are known as Mira-variables ; the name comes from the most prominent member of this class, Omicron Ceti in the constellation Cetus (The Whale), also known as "Stella Mira" (The Wonderful Star). Its brightness changes with a period of 332 days and it is about 1500 times brighter at maximum (visible magnitude 2 and one of the fifty brightest stars in the sky) than at minimum (magnitude 10 and only visible in small telescopes) [2]. Stars like Omicron Ceti are nearing the end of their life. They are very large and have sizes from a few hundred to about a thousand times that of the Sun. The brightness variation is due to pulsations during which the star's temperature and size change dramatically. In the following evolutionary phase, Mira-variables will shed their outer layers into surrounding space and become visible as planetary nebulae with a hot and compact star (a "white dwarf") at the middle of a nebula of gas and dust (cf. the "Dumbbell Nebula" - ESO PR Photo 38a-b/98 ). Several thousand Mira-type stars are currently known in the Milky Way galaxy and a few hundred have been found in other nearby galaxies, including the Magellanic Clouds. The peculiar galaxy Centaurus A ESO PR Photo 14a/03 ESO PR Photo 14a/03 [Preview - JPEG: 400 x 451 pix - 53k [Normal - JPEG: 800 x 903 pix - 528k] [Hi-Res - JPEG: 3612 x 4075 pix - 8.4M] ESO PR Photo 14b/03 ESO PR Photo 14b/03 [Preview - JPEG: 570 x 400 pix - 52k [Normal - JPEG: 1140 x 800 pix - 392k] ESO PR Photo 14c/03 ESO PR Photo 14c/03 [Preview - JPEG: 400 x 451 pix - 61k [Normal - JPEG: 800 x 903 pix - 768k] ESO PR Photo 14d/03 ESO PR Photo 14d/03 [Preview - JPEG: 400 x 451 pix - 56k [Normal - JPEG: 800 x 903 pix - 760k] Captions : PR Photo 14a/03 is a colour composite photo of the peculiar galaxy Centaurus A (NGC 5128) , obtained with the Wide-Field Imager (WFI) camera at

  7. 3D climate modeling of Earth-like extrasolar planets orbiting different types of host stars

    Science.gov (United States)

    Godolt, M.; Grenfell, J. L.; Hamann-Reinus, A.; Kitzmann, D.; Kunze, M.; Langematz, U.; von Paris, P.; Patzer, A. B. C.; Rauer, H.; Stracke, B.

    2015-06-01

    The potential habitability of a terrestrial planet is usually defined by the possible existence of liquid water on its surface, since life as we know it needs liquid water at least during a part of its life cycle. The potential presence of liquid water on a planetary surface depends on many factors such as, most importantly, surface temperatures. The properties of the planetary atmosphere and its interaction with the radiative energy provided by the planet's host star are thereby of decisive importance. In this study we investigate the influence of different main-sequence stars (F, G, and K-type stars) upon the climate of Earth-like extrasolar planets and their potential habitability by applying a state-of-the-art three-dimensional (3D) Earth climate model accounting for local and dynamical processes. The calculations have been performed for planets with Earth-like atmospheres at orbital distances (and corresponding orbital periods) where the total amount of energy received from the various host stars equals the solar constant. In contrast to previous 3D modeling studies, we include the effect of ozone radiative heating upon the vertical temperature structure of the atmospheres. The global orbital mean results obtained have been compared to those of a one-dimensional (1D) radiative convective climate model to investigate the approximation of global mean 3D results by those of 1D models. The different stellar spectral energy distributions lead to different surface temperatures and due to ozone heating to very different vertical temperature structures. As previous 1D studies we find higher surface temperatures for the Earth-like planet around the K-type star, and lower temperatures for the planet around the F-type star compared to an Earth-like planet around the Sun. However, this effect is more pronounced in the 3D model results than in the 1D model because the 3D model accounts for feedback processes such as the ice-albedo and the water vapor feedback. Whether the

  8. Variability of stellar granulation and convective blueshift with spectral type and magnetic activity. I. K and G main sequence stars

    Science.gov (United States)

    Meunier, N.; Lagrange, A.-M.; Mbemba Kabuiku, L.; Alex, M.; Mignon, L.; Borgniet, S.

    2017-01-01

    Context. In solar-type stars, the attenuation of convective blueshift by stellar magnetic activity dominates the RV (radial velocity) variations over the low amplitude signal induced by low mass planets. Models of stars that differ from the Sun will require a good knowledge of the attenuation of the convective blueshift to estimate its impact on the variations. Aims: It is therefore crucial to precisely determine not only the amplitude of the convective blueshift for different types of stars, but also the dependence of this convective blueshift on magnetic activity, as these are key factors in our model producing the RV. Methods: We studied a sample of main sequence stars with spectral types from G0 to K2 and focused on their temporally averaged properties: the activity level and a criterion allowing to characterise the amplitude of the convective blueshift. This criterion is derived from the dependence of the convective blueshift with the intensity at the bottom of a large set of selected spectral lines. Results: We find the differential velocity shifts of spectral lines due to convection to depend on the spectral type, the wavelength (this dependence is correlated with the Teff and activity level), and on the activity level. This allows us to quantify the dependence of granulation properties on magnetic activity for stars other than the Sun. We are indeed able to derive a significant dependence of the convective blueshift on activity level for all types of stars. The attenuation factor of the convective blueshift appears to be constant over the considered range of spectral types. We derive a convective blueshift which decreases towards lower temperatures, with a trend in close agreement with models for Teff lower than 5800 K, but with a significantly larger global amplitude. Differences also remain to be examined in detail for larger Teff. We finally compare the observed RV variation amplitudes with those that could be derived from our convective blueshift using

  9. Variability of stellar granulation and convective blueshift with spectral type and magnetic activity. I. K and G main sequence stars

    CERN Document Server

    Meunier, N; Kabuiku, L Mbemba; Alex, M; Mignon, L; Borgniet, S

    2016-01-01

    In solar-type stars, the attenuation of convective blueshift by stellar magnetic activity dominates the RV variations over the low amplitude signal induced by low mass planets. Models of stars that differ from the Sun will require a good knowledge of the attenuation of the convective blueshift to estimate its impact on the variations. It is therefore crucial to precisely determine not only the amplitude of the convective blueshift for different types of stars, but also the dependence of this convective blueshift on magnetic activity, as these are key factors in our model producing the RV. We studied a sample of main sequence stars with spectral types from G0 to K2 and focused on their temporally averaged properties: the activity level and a criterion allowing to characterise the amplitude of the convective blueshift. We find the differential velocity shifts of spectral lines due to convection to depend on the spectral type, the wavelength (this dependence is correlated with the Teff and activity level), and o...

  10. EUV Flare Activity in Late-Type Stars

    CERN Document Server

    Audard, M; Drake, J J; Kashyap, V L; Audard, Marc; Guedel, Manuel; Drake, Jeremy J.

    2000-01-01

    \\textit{Extreme Ultraviolet Explorer} Deep Survey observations of cool stars (spectral type F to M) have been used to investigate the distribution of coronal flare rates in energy and its relation to activity indicators and rotation parameters. Cumulative and differential flare rate distributions were constructed and fitted with different methods. Power laws are found to approximately describe the distributions. A trend toward flatter distributions for later-type stars is suggested in our sample. Assuming that the power laws continue below the detection limit, we have estimated that the superposition of flares with radiated energies of about $10^{29}-10^{31}$ergs could explain the observed radiative power loss of these coronae, while the detected flares are contributing only $\\approx 10$%. While the power-law index is not correlated with rotation parameters (rotation period, projected rotational velocity, Rossby number) and only marginally with the X-ray luminosity, the flare occurrence rate is correlated wit...

  11. Transiting planets from WASP-South, Euler and TRAPPIST: WASP-68 b, WASP-73 b and WASP-88 b, three hot Jupiters transiting evolved solar-type stars

    CERN Document Server

    Delrez, L; Anderson, D R; Collier-Cameron, A; Doyle, A P; Fumel, A; Gillon, M; Hellier, C; Jehin, E; Lendl, M; Neveu-VanMalle, M; Maxted, P F L; Pepe, F; Pollacco, D; Queloz, D; Ségransan, D; Smalley, B; Smith, A M S; Southworth, J; Triaud, A H M J; Udry, S; West, R G

    2013-01-01

    We report the discovery by the WASP transit survey of three new hot Jupiters, WASP-68 b, WASP-73 b and WASP-88 b. WASP-68 b has a mass of 0.95+-0.03 M_Jup, a radius of 1.24-0.06+0.10 R_Jup, and orbits a V=10.7 G0-type star (1.24+-0.03 M_sun, 1.69-0.06+0.11 R_sun, T_eff=5911+-60 K) with a period of 5.084298+-0.000015 days. Its size is typical of hot Jupiters with similar masses. WASP-73 b is significantly more massive (1.88-0.06+0.07 M_Jup) and slightly larger (1.16-0.08+0.12 R_Jup) than Jupiter. It orbits a V=10.5 F9-type star (1.34-0.04+0.05 M_sun, 2.07-0.08+0.19 R_sun, T_eff=6036+-120 K) every 4.08722+-0.00022 days. Despite its high irradiation (2.3 10^9 erg s^-1 cm^-2), WASP-73 b has a high mean density (1.20-0.30+0.26 \\rho_Jup) that suggests an enrichment of the planet in heavy elements. WASP-88 b is a 0.56+-0.08 M_Jup planet orbiting a V=11.4 F6-type star (1.45+-0.05 M_sun, 2.08-0.06+0.12 R_sun, T_eff=6431+-130 K) with a period of 4.954000+-0.000019 days. With a radius of 1.70-0.07+0.13 R_Jup, it joins t...

  12. Beryllium, Lithium and Oxygen Abundances in F-type Stars

    CERN Document Server

    García-López, R J; Pérez de Taoro, M R; Casares, C; Rasilla, J L; Rebolo, R; Allende-Prieto, C

    1997-01-01

    Beryllium and oxygen abundances have been derived in a sample of F-type field stars for which lithium abundances had been measured previously, with the aim of obtaining observational constraints to discriminate between the different mixing mechanisms proposed. Mixing associated with the transport of angular momentum in the stellar interior and internal gravity waves within the framework of rotating evolutionary models, appear to be promising ways to explain the observations.

  13. Discovery of Peculiar Periodic Spectral Modulations in a Small Fraction of Solar-type Stars

    Science.gov (United States)

    Borra, Ermanno F.; Trottier, Eric

    2016-11-01

    A Fourier transform analysis of 2.5 million spectra in the Sloan Digital Sky Survey was carried out to detect periodic spectral modulations. Signals having the same period were found in only 234 stars overwhelmingly in the F2 to K1 spectral range. The signals cannot be caused by instrumental or data analysis effects because they are present in only a very small fraction of stars within a narrow spectral range and because signal-to-noise ratio considerations predict that the signal should mostly be detected in the brightest objects, while this is not the case. We consider several possibilities, such as rotational transitions in molecules, rapid pulsations, Fourier transform of spectral lines, and signals generated by extraterrestrial intelligence (ETI). They cannot be generated by molecules or rapid pulsations. It is highly unlikely that they come from the Fourier transform of spectral lines because too many strong lines located at nearly periodic frequencies are needed. Finally, we consider the possibility, predicted in a previous published paper, that the signals are caused by light pulses generated by ETI to makes us aware of their existence. We find that the detected signals have exactly the shape of an ETI signal predicted in the previous publication and are therefore in agreement with this hypothesis. The fact that they are only found in a very small fraction of stars within a narrow spectral range centered near the spectral type of the Sun is also in agreement with the ETI hypothesis. However, at this stage, this hypothesis needs to be confirmed with further work. Although unlikely, there is also a possibility that the signals are due to highly peculiar chemical compositions in a small fraction of galactic halo stars.

  14. Zeeman-Doppler imaging of active young solar-type stars

    Science.gov (United States)

    Hackman, T.; Lehtinen, J.; Rosén, L.; Kochukhov, O.; Käpylä, M. J.

    2016-03-01

    Context. By studying young magnetically active late-type stars, i.e. analogues to the young Sun, we can draw conclusions on the evolution of the solar dynamo. Aims: We determine the topology of the surface magnetic field and study the relation between the magnetic field and cool photospheric spots in three young late-type stars. Methods: High-resolution spectropolarimetry of the targets was obtained with the HARPSpol instrument mounted at the ESO 3.6 m telescope. The signal-to-noise ratios of the Stokes IV measurements were boosted by combining the signal from a large number of spectroscopic absorption lines through the least squares deconvolution technique. Surface brightness and magnetic field maps were calculated using the Zeeman-Doppler imaging technique. Results: All three targets show clear signs of magnetic fields and cool spots. Only one of the targets, V1358 Ori, shows evidence of the dominance of non-axisymmetric modes. In two of the targets, the poloidal field is significantly stronger than the toroidal one, indicative of an α2-type dynamo, in which convective turbulence effects dominate over the weak differential rotation. In two of the cases there is a slight anti-correlation between the cool spots and the strength of the radial magnetic field. However, even in these cases the correlation is much weaker than in the case of sunspots. Conclusions: The weak correlation between the measured radial magnetic field and cool spots may indicate a more complex magnetic field structure in the spots or spot groups involving mixed magnetic polarities. Comparison with a previously published magnetic field map shows that on one of the stars, HD 29615, the underlying magnetic field changed its polarity between 2009 and 2013. Based on observations made with the HARPSpol instrument on the ESO 3.6 m telescope at La Silla (Chile), under the program ID 091.D-0836.

  15. Evolution of Cold Circumstellar Dust Around Solar-Type Stars

    CERN Document Server

    Carpenter, J M; Schreyer, K; Launhardt, R; Henning, T; Carpenter, John M.; Wolf, Sebastian; Schreyer, Katharina; Launhardt, Ralf; Henning, Th.

    2004-01-01

    We present submillimeter (CSO 350um) and millimeter (SEST 1.2 mm, OVRO 3 mm) photometry for 125 solar-type stars from the FEPS Spitzer Legacy program that have masses between ~0.5 and 2.0 Msun and ages from 3 Myr to 3 Gyr. Continuum emission was detected toward four stars with a signal to noise ratio >= 3$: the classical T Tauri stars RX J1842.9-3532, RX J1852.3-3700, and PDS 66 with SEST, and the debris disk system HD 107146 with OVRO. RXJ1842.9-3532 and RXJ1852.3-3700 are located in projection nearby the R CrA molecular cloud with estimated ages of ~10 Myr, while PDS66 is a probable member of the 20 Myr old Lower Centaurus-Crux subgroup of the Sco-Cen OB association. The continuum emission toward these three sources is unresolved at the 24'' SEST resolution and likely originates from circumstellar accretion disks, each with estimated dust masses of ~5x10**-5 Msun. Analysis of the visibility data toward HD107146 (age 80-200 Myr) indicates that the 3 mm continuum emission is centered on the star within the as...

  16. Pre-explosion companion stars in Type Iax supernovae

    CERN Document Server

    Liu, Zheng-Wei; Abate, Carlo; Wang, Bo

    2015-01-01

    Type Iax supernovae (SNe Iax) are proposed as one new sub-class of SNe Ia since they present sufficiently distinct observational properties from the bulk of SNe Ia. SNe Iax are the most common of all types of peculiar SNe by both number and rate, with an estimated rate of occurrence of about 5-30% of the total SN Ia rate. However, the progenitor systems of SNe Iax are still uncertain. Analyzing pre-explosion images at SN Iax positions provides a direct way to place strong constraints on the nature of progenitor systems of SNe Iax. In this work, we predict pre-explosion properties of binary companion stars in a variety of potential progenitor systems by performing detailed binary evolution calculations with the one-dimensional stellar evolution code STARS. This will be helpful for constraining progenitor systems of SNe Iax from their pre-explosion observations. With our binary evolution calculations, it is found that the non-degenerate helium (He) companion star to both a massive C/O WD (> 1.1 solar mass) and ...

  17. The Kepler characterization of the variability amongst A- and F-type stars. I. General overview

    CERN Document Server

    Uytterhoeven, K; Grigahcene, A; Guzik, J A; Gutierrez-Soto, J; Smalley, B; Handler, G; Balona, L A; Niemczura, E; Machado, L Fox; Benatti, S; Chapellier, E; Tkachenko, A; Szabo, R; Suarez, J C; Ripepi, V; Pascual, J; Mathias, P; Martin-Ruiz, S; Lehmann, H; Jackiewicz, J; Hekker, S; Gruberbauer, M; Garcia, R A; Dumusque, X; Diaz-Fraile, D; Bradley, P; Antoci, V; Roth, M; Leroy, B; Murphy, S J; De Cat, P; Cuypers, J; Kjeldsen, H; Christensen-Dalsgaard, J; Breger, M; Pigulski, A; Kiss, L L; Still, M; Thompson, S E; Van Cleve, J

    2011-01-01

    The Kepler spacecraft is providing time series of photometric data with micromagnitude precision for hundreds of A-F type stars. We present a first general characterization of the pulsational behaviour of A-F type stars as observed in the Kepler light curves of a sample of 750 candidate A-F type stars. We propose three main groups to describe the observed variety in pulsating A-F type stars: gamma Dor, delta Sct, and hybrid stars. We assign 63% of our sample to one of the three groups, and identify the remaining part as rotationally modulated/active stars, binaries, stars of different spectral type, or stars that show no clear periodic variability. 23% of the stars (171 stars) are hybrid stars, which is a much larger fraction than what has been observed before. We characterize for the first time a large number of A-F type stars (475 stars) in terms of number of detected frequencies, frequency range, and typical pulsation amplitudes. The majority of hybrid stars show frequencies with all kinds of periodicities...

  18. CO fundamental bands in late-type stars. II - Spectrum simulations for F-K stars

    Science.gov (United States)

    Wiedemann, Guenter; Ayres, Thomas R.

    1991-01-01

    The procedure of Ayres and Wiedemann (1989) was applied to a range of stellar-atmosphere models to study the CO Delta-v = 1 spectrum and to establish its use as a remote sensor of thermal conditions in late-type stars. Spectra were computed to examine the sensitivity of the CO Delta-v = 1 to fundamental stellar parameters and to assess the errors introduced into the spectrum intepretation by uncertain input parameters and non-LTE effects. Results of the sensitivity study demonstrate that CO fundamental spectra are useful probes for the temperature structure of the outer layers of cool stellar atmospheres, but that their value is limited by the uncertainties introduced by non-LTE effects. However, in stars with surface gravities of log g of about 1.5 and greater, the values of these uncertainties are reasonably small.

  19. Signatures of A Companion Star in Type Ia Supernovae

    CERN Document Server

    Maeda, Keiichi; Shigeyama, Toshikazu

    2014-01-01

    While type Ia Supernovae (SNe Ia) have been used as precise cosmological distance indicators, their progenitor systems remain unresolved. One of the key questions is if there is a non-degenerate companion star at the time of a thermonuclear explosion of a white dwarf (WD). In this paper, we investigate if an interaction between the SN ejecta and the companion star may result in observable footprints around the maximum brightness and thereafter, by performing multi-dimensional radiation transfer simulations based on hydrodynamic simulations of the interaction. We find that such systems result in variations in various observational characteristics due to different viewing directions, while the predicted behaviors (redder and fainter for the companion direction) are opposite to what were suggested by the previous study. The variations are generally modest and within observed scatters. However, the model predicts trends between some observables different from observationally derived, thus a large sample of SNe Ia...

  20. Asteroseismology of solar-type stars with K2

    CERN Document Server

    Chaplin, W J; Handberg, R; Basu, S; Buchhave, L A; Campante, T L; Davies, G R; Huber, D; Latham, D W; Latham, C A; Serenelli, A; Antia, H M; Appourchaux, T; Ball, W H; Benomar, O; Casagrande, L; Christensen-Dalsgaard, J; Coelho, H R; Creevey, O L; Elsworth, Y; Garc, R A; Gaulme, P; Hekker, S; Kallinger, T; Karoff, C; Kawaler, S D; Kjeldsen, H; Lundkvist, M S; Marcadon, F; Mathur, S; Miglio, A; Mosser, B; R, C; Roxburgh, I W; Aguirre, V Silva; Stello, D; Verma, K; White, T R; Bedding, T R; Barclay, T; Buzasi, D L; Deheuvels, S; Gizon, L; Houdek, G; Howell, S B; Salabert, D; Soderblom, D R

    2015-01-01

    We present the first detections by the NASA K2 Mission of oscillations in solar-type stars, using short-cadence data collected during K2 Campaign\\,1 (C1). We understand the asteroseismic detection thresholds for C1-like levels of photometric performance, and we can detect oscillations in subgiants having dominant oscillation frequencies around $1000\\,\\rm \\mu Hz$. Changes to the operation of the fine-guidance sensors are expected to give significant improvements in the high-frequency performance from C3 onwards. A reduction in the excess high-frequency noise by a factor of two-and-a-half in amplitude would bring main-sequence stars with dominant oscillation frequencies as high as ${\\simeq 2500}\\,\\rm \\mu Hz$ into play as potential asteroseismic targets for K2.

  1. Activity trends in young solar-type stars

    CERN Document Server

    Lehtinen, Jyri; Hackman, Thomas; Kajatkari, Perttu; Henry, Gregory W

    2015-01-01

    We apply the Continuous Period Search (CPS) time series analysis method on Johnson B and V band photometry of 21 young and active solar-type, collected over 16 to 27 years and characterize the behaviour of their activity. Using the CPS method, differential rotation could be estimated from the observed variations of the photometric rotation period. Active longitudes were retrieved by applying a non-parametric period search on the light curve minimum epochs, and activity cycles by applying a secondary period search on the modelled light curve mean and amplitude values. We supplemented the time series results by calculating new $\\log{R'_{\\rm HK}}$ emission indices for the stars from high resolution spectroscopy. The measurements of the photometric rotation period variations point to a trend of increasing differential rotation coefficients towards longer rotation periods but do not reveal any dependence from the effective temperature of the stars. The secondary period searches revealed activity cycles in 18 of th...

  2. DIRECT IMAGING DISCOVERY OF A 'SUPER-JUPITER' AROUND THE LATE B-TYPE STAR {kappa} And

    Energy Technology Data Exchange (ETDEWEB)

    Carson, J.; Kozakis, T.; Stevens, L.; Wong, P.; Gainey, K. [Department of Physics and Astronomy, College of Charleston, 58 Coming Street, Charleston, SC 29424 (United States); Thalmann, C.; Bonnefoy, M.; Biller, B.; Schlieder, J.; Henning, T.; Brandner, W.; Feldt, M. [Max-Planck-Institut fuer Astronomie, Koenigstuhl 17, D-69117 Heidelberg (Germany); Janson, M. [Department of Astrophysical Sciences, Princeton University, NJ 08544 (United States); Currie, T.; McElwain, M. [ExoPlanets and Stellar Astrophysics Laboratory, Code 667, Goddard Space Flight Center, Greenbelt, MD 20771 (United States); Goto, M. [Young Stars and Star Formation Universitaets-Sternwarte Muenchen, Ludwig-Maximilians-Universitaet, D-81679 Muenchen (Germany); Kandori, R.; Kuzuhara, M. [National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 (Japan); Fukagawa, M.; Kuwada, Y. [Department of Earth and Space Science, Graduate School of Science, Osaka University, 1-1 Machikaneyama, Toyonaka, Osaka 560-0043 (Japan); and others

    2013-02-01

    We present the direct imaging discovery of an extrasolar planet, or possible low-mass brown dwarf, at a projected separation of 55 {+-} 2 AU (1.''058 {+-} 0.''007) from the B9-type star {kappa} And. The planet was detected with Subaru/HiCIAO during the SEEDS survey and confirmed as a bound companion via common proper motion measurements. Observed near-infrared magnitudes of J = 16.3 {+-} 0.3, H = 15.2 {+-} 0.2, K{sub s} = 14.6 {+-} 0.4, and L' = 13.12 {+-} 0.09 indicate a temperature of {approx}1700 K. The galactic kinematics of the host star are consistent with membership in the Columba Association, implying a corresponding age of 30{sup +20}{sub -10} Myr. The system's age, combined with the companion photometry, points to a model-dependent companion mass {approx}12.8 M{sub Jup}. The host star's estimated mass of 2.4-2.5 M{sub Sun} places it among the most massive stars ever known to harbor an extrasolar planet or low-mass brown dwarf. While the mass of the companion is close to the deuterium burning limit, its mass ratio, orbital separation, and likely planet-like formation scenario imply that it may be best defined as a 'super-Jupiter' with properties similar to other recently discovered companions to massive stars.

  3. The sun, moon and stars of the southern Levant at Gezer and Megiddo: Cultural astronomy in Chalcolithic/Early and Middle Bronze Ages

    Science.gov (United States)

    Gardner, Sara Lee

    Astronomical images are found on monumental structures and decorative art, and metaphorically in seasonal myths, and are documented by calendars. In Israel and the southern Levant, images of the sun, the moon, and the stars were common decorating motifs. They were found on walls, pottery, and seals and date to as early as the Chalcolithic period; for example, the wall painting of a star at Teleilat Ghassul (North 1961). This dissertation establishes that the people of the Levant were aware of the apparent movement of the sun, and this will be discussed in Chapter 4. They began recording through representation drawings, astronomical phenomena no later than the Chalcolithic/Early Bronze Age and continued to do so late into the Middle Bronze Age. The argument moves beyond the simple use of symbols to the use of images to represent constellations, with the focus on the constellation Leo in Chapter 5. Furthermore, the use of astronomy as a power and political tool is also suggested in Chapter 6. Nonetheless, the primary purpose that is addressed here is the tendency in Syro-Palestinian archaeology has been to attribute technological evidence found in the northern and southern Levant as diffused from Egypt or Assyria, particularly astronomy. This dissertation firmly establishes that astronomy was used in the southern Levant before any significant contact with the civilizations of Egypt or Assyria.

  4. Conditions for water ice lines and Mars-mass exomoons around accreting super-Jovian planets at 1 - 20 AU from Sun-like stars

    CERN Document Server

    Heller, René

    2015-01-01

    Exomoon detections might be feasible with NASA's Kepler or ESA's upcoming PLATO mission or the ground-based E-ELT. To use observational resources most efficiently we need to know where the largest, most easily detected moons can form. We explore the possibility of large exomoons by following the movement of water (H2O) ice lines in the accretion disks around young super-Jovian planets. We want to know how different heating sources in those disks affect the H2O ice lines. We simulate 2D rotationally symmetric accretion disks in hydrostatic equilibrium around super-Jovian exoplanets. The energy terms in our semi-analytical model -- (1) viscous heating, (2) planetary illumination, (3) accretional heating, and (4) stellar illumination -- are fed by precomputed planet evolution tracks. We consider planets accreting 1 to 12 Jupiter masses at distances between 1 and 20 AU to a Sun-like star. Accretion disks around Jupiter-mass planets closer than ~4.5 AU to Sun-like stars do not feature H2O ice lines, but the most m...

  5. Dynamo Action and Magnetic Cycles in F-type Stars

    Science.gov (United States)

    Augustson, Kyle C.; Brun, Allan Sacha; Toomre, Juri

    2013-11-01

    Magnetic activity and differential rotation are commonly observed features on main-sequence F-type stars. We seek to make contact with such observations and to provide a self-consistent picture of how differential rotation and magnetic fields arise in the interiors of these stars. The three-dimensional magnetohydrodynamic anelastic spherical harmonic code is employed to simulate global-scale convection and dynamo processes in a 1.2 M ⊙ F-type star at two rotation rates. The simulations are carried out in spherical shells that encompass most of the convection zone and a portion of the stably stratified radiative zone below it, allowing us to explore the effects a stable zone has upon the morphology of the global-scale magnetic fields. We find that dynamo action with a high degree of time variation occurs in the star rotating more rapidly at 20 Ω⊙, with the polarity of the mean field reversing on a timescale of about 1600 days. Between reversals, the magnetic energy rises and falls with a fairly regular period, with three magnetic energy cycles required to complete a reversal. The magnetic energy cycles and polarity reversals arise due to a linking of the polar-slip instability in the stable region and dynamo action present in the convection zone. For the more slowly rotating case (10 Ω⊙), persistent wreaths of magnetism are established and maintained by dynamo action. Compared to their hydrodynamic progenitors, the dynamo states here involve a marked reduction in the exhibited latitudinal differential rotation, which also vary during the course of a cycle.

  6. AXISYMMETRIC AB INITIO CORE-COLLAPSE SUPERNOVA SIMULATIONS OF 12-25 M{sub Sun} STARS

    Energy Technology Data Exchange (ETDEWEB)

    Bruenn, Stephen W.; Yakunin, Konstantin N. [Department of Physics, Florida Atlantic University, 777 Glades Road, Boca Raton, FL 33431-0991 (United States); Mezzacappa, Anthony; Hix, W. Raphael; Lingerfelt, Eric J. [Physics Division, Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN 37831-6354 (United States); Lentz, Eric J. [Department of Physics and Astronomy, University of Tennessee, Knoxville, TN 37996-1200 (United States); Messer, O. E. Bronson [National Center for Computational Sciences, Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN 37831-6164 (United States); Blondin, John M. [Department of Physics, North Carolina State University, Raleigh, NC 27695-8202 (United States); Endeve, Eirik [Computer Science and Mathematics Division, Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN 37831-6164 (United States); Marronetti, Pedro, E-mail: bruenn@fau.edu [Physics Division, National Science Foundation, Arlington, VA 22207 (United States)

    2013-04-10

    We present an overview of four ab initio axisymmetric core-collapse supernova simulations employing detailed spectral neutrino transport computed with our CHIMERA code and initiated from Woosley and Heger progenitors of mass 12, 15, 20, and 25 M{sub Sun }. All four models exhibit shock revival over {approx}200 ms (leading to the possibility of explosion), driven by neutrino energy deposition. Hydrodynamic instabilities that impart substantial asymmetries to the shock aid these revivals, with convection appearing first in the 12 M{sub Sun} model and the standing accretion shock instability appearing first in the 25 M{sub Sun} model. Three of the models have developed pronounced prolate morphologies (the 20 M{sub Sun} model has remained approximately spherical). By 500 ms after bounce the mean shock radii in all four models exceed 3000 km and the diagnostic explosion energies are 0.33, 0.66, 0.65, and 0.70 Bethe (B = 10{sup 51} erg) for the 12, 15, 20, and 25 M{sub Sun} models, respectively, and are increasing. The three least massive of our models are already sufficiently energetic to completely unbind the envelopes of their progenitors (i.e., to explode), as evidenced by our best estimate of their explosion energies, which first become positive at 320, 380, and 440 ms after bounce. By 850 ms the 12 M{sub Sun} diagnostic explosion energy has saturated at 0.38 B, and our estimate for the final kinetic energy of the ejecta is {approx}0.3 B, which is comparable to observations for lower mass progenitors.

  7. AGN-driven quenching of star formation: morphological and dynamical implications for early-type galaxies

    CERN Document Server

    Dubois, Yohan; Peirani, Sébastien; Silk, Joseph

    2013-01-01

    In order to understand the physical mechanisms at work during the formation of massive early-type galaxies, we performed six zoomed hydrodynamical cosmological simulations of halos in the mass range 4.3 10^12 < M_vir < 8.0 10^13 M_sun at z=0, using the Adaptive Mesh Refinement code RAMSES. These simulations explore the role of Active Galactic Nuclei (AGN), through jets powered by the accretion onto supermassive black holes on the formation of massive elliptical galaxies. In the absence of AGN feedback, large amounts of stars accumulate in the central galaxies to form overly massive, blue, compact and rotation-dominated galaxies. Powerful AGN jets transform the central galaxies into red extended and dispersion-dominated galaxies. This morphological transformation of disc galaxies into elliptical galaxies is driven by the efficient quenching of the in situ star formation due to AGN feedback, which transform these galaxies into systems built up by accretion. For galaxies mainly formed by accretion, the pro...

  8. Kepler-22b: A 2.4 EARTH-RADIUS PLANET IN THE HABITABLE ZONE OF A SUN-LIKE STAR

    Energy Technology Data Exchange (ETDEWEB)

    Borucki, William J.; Koch, David G.; Bryson, Stephen T.; Howell, Steve B.; Lissauer, Jack J. [NASA-Ames Research Center, Moffett Field, CA 94035-0001 (United States); Batalha, Natalie [Department of Physics and Astronomy, San Jose State University, San Jose, CA, 95192 (United States); Rowe, Jason; Caldwell, Douglas A.; DeVore, Edna; Jenkins, Jon M. [SETI Institute, Mountain View, CA 94043 (United States); Fressin, Francois; Torres, Guillermo; Geary, John C.; Latham, David W. [Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138 (United States); Christensen-Dalsgaard, Jorgen [Department of Physics and Astronomy, Aarhus University, DK-8000 Aarhus C (Denmark); Cochran, William D. [McDonald Observatory, University of Texas at Austin, Austin, TX 78712 (United States); Gautier, Thomas N. [Jet Propulsion Laboratory, California Institute of Technology, Pasadena CA, 91109 (United States); Gilliland, Ronald [Space Telescope Science Institute, Baltimore, MD 21218 (United States); Gould, Alan [Lawrence Hall of Science, University of California, Berkeley, CA 94720 (United States); Marcy, Geoffrey W., E-mail: William.J.Borucki@nasa.gov [Department of Astronomy, University of California, Berkeley, CA 94720 (United States); and others

    2012-02-01

    A search of the time-series photometry from NASA's Kepler spacecraft reveals a transiting planet candidate orbiting the 11th magnitude G5 dwarf KIC 10593626 with a period of 290 days. The characteristics of the host star are well constrained by high-resolution spectroscopy combined with an asteroseismic analysis of the Kepler photometry, leading to an estimated mass and radius of 0.970 {+-} 0.060 M{sub Sun} and 0.979 {+-} 0.020 R{sub Sun }. The depth of 492 {+-} 10 ppm for the three observed transits yields a radius of 2.38 {+-} 0.13 Re for the planet. The system passes a battery of tests for false positives, including reconnaissance spectroscopy, high-resolution imaging, and centroid motion. A full BLENDER analysis provides further validation of the planet interpretation by showing that contamination of the target by an eclipsing system would rarely mimic the observed shape of the transits. The final validation of the planet is provided by 16 radial velocities (RVs) obtained with the High Resolution Echelle Spectrometer on Keck I over a one-year span. Although the velocities do not lead to a reliable orbit and mass determination, they are able to constrain the mass to a 3{sigma} upper limit of 124 M{sub Circled-Plus }, safely in the regime of planetary masses, thus earning the designation Kepler-22b. The radiative equilibrium temperature is 262 K for a planet in Kepler-22b's orbit. Although there is no evidence that Kepler-22b is a rocky planet, it is the first confirmed planet with a measured radius to orbit in the habitable zone of any star other than the Sun.

  9. Investigating the possible connection between lambda Bootis stars and intermediate Population II type stars

    CERN Document Server

    Paunzen, E; Fossati, L; Heiter, U; Weiss, W W

    2014-01-01

    The lambda Bootis (LB) stars are located at the upper main sequence of the H-R diagram and exhibit a peculiar abundance pattern. The light elements (C, N, O, and S) present solar abundances whereas all other elements are moderately to strongly underabundant. It has not yet been determined whether that abundance pattern is intrinsic, or is restricted to the stellar surface. If we follow the hypothesis that the LB stars are intrinsically metal-weak, then there should be a connection with the intermediate Population II and F-weak objects. Such a possible affinity has not been previously investigated. We present detailed elemental abundances, including those of the light elements carbon and oxygen, for 38 bright intermediate Population II and F-weak objects. In addition, we investigate the kinematic characteristics of the groups. From photometric, spectroscopic, and kinematic data, there is no distinction between the intermediate Population II and F-weak type stars. We therefore conclude that the two groups are i...

  10. Kinematics of gas and stars in circumnuclear star-forming regions of early type spirals

    CERN Document Server

    Hagele, Guillermo F; Cardaci, Monica V; Terlevich, Elena; Terlevich, Roberto

    2008-01-01

    (Abbr.) We present high resolution (R~20000) spectra in the blue and the far red of cicumnuclear star-forming regions (CNSFRs) in three early type spirals (NGC3351, NGC2903 and NGC3310) which have allowed the study of the kinematics of stars and ionized gas in these structures and, for the first time, the derivation of their dynamical masses for the first two. In some cases these regions, about 100 to 150 pc in size, are seen to be composed of several individual star clusters with sizes between 1.5 and 4.9 pc estimated from Hubble Space Telescope (HST) images. The stellar dispersions have been obtained from the Calcium triplet (CaT) lines at $\\lambda\\lambda$ 8494,8542,8662 \\AA, while the gas velocity dispersions have been measured by Gaussian fits to the H$\\beta$ and [OIII] $\\lambda\\lambda$ 5007 \\AA lines on the high dispersion spectra. Values of the stellar velocity dispersions are between 30 and 68 km/s. We apply the virial theorem to estimate dynamical masses of the clusters, assuming that systems are grav...

  11. Magnetic field measurements and wind-line variability of OB-type stars

    NARCIS (Netherlands)

    Schnerr, R.S.; Henrichs, H.F.; Neiner, C.; Verdugo, E.; de Jong, J.; Geers, V.C.; Wiersema, K.; van Dalen, B.; Tijani, A.; Plaggenborg, B.; Rygl, K.L.J.

    2008-01-01

    Context. The first magnetic fields in O- and B-type stars that do not belong to the Bp-star class, have been discovered. The cyclic UV wind-line variability, which has been observed in a significant fraction of early-type stars, is likely to be related to such magnetic fields. Aims. We attempt to

  12. The Near-Ultraviolet Continuum of Late-Type Stars

    CERN Document Server

    Allende-Prieto, C; Allende-Prieto, Carlos; Lambert, David L

    2000-01-01

    Analyses of the near-ultraviolet continuum of late-type stars have led to controversial results regarding the performance of state-of-the-art model atmospheres. The release of the homogeneous IUE final archive and the availability of the high-accuracy Hipparcos parallaxes provide an opportunity to revisit this issue, as accurate stellar distances make it possible to compare observed absolute fluxes with the predictions of model atmospheres. The near-UV continuum is highly sensitive to Teff and [Fe/H], and once the gravity is constrained from the parallax, these parameters may be derived from the analysis of low-dispersion "long-wavelength" (2000-3000 A) IUE spectra for stars previously studied by Alonso et al. (1996; A&AS 117, 227) using the Infrared Flux Method (IRFM). A second comparison is carried out against the stars spectroscopically investigated by Gratton et al. (1996; A&A 314, 191). It is shown that there is a good agreement between Teffs obtained from the IRFM and from the near-UV continuum,...

  13. Forming an Early O-type Star Through Gas Accretion?

    CERN Document Server

    Zapata, Luis A; HO, Paul; Schilke, Peter; Garrod, Robin T; Rodriguez, Luis F; Menten, Karl

    2007-01-01

    We present high angular resolution ($\\sim$ 3$''$) and sensitive 1.3 mm continuum, cyanogen (CN) and vinyl cyanide (C$_2$H$_3$CN) line observations made with the Submillimeter Array (SMA) toward one of most highly obscured objects of the W51 IRS2 region, W51 North. We find that the CN line exhibits a pronounced inverse P-Cygni profile indicating that the molecular gas is infalling inwards this object with a mass accretion rate between 4 and 7 $\\times$ 10$^{-2}$ M$_\\odot$ yr$^{-1}$. The C$_2$H$_3$CN traces an east-west rotating molecular envelope that surrounds either a single obscured (proto)star with a kinematic mass of 40 M$_{\\odot}$ or a small central cluster of B-type stars and that is associated with a compact high velocity bipolar outflow traced by H$_2$O masers and SiO molecular emission. We thus confirm that the W51 North region is part of the growing list of young massive star forming regions that have been associated with infalling motions and with large mass accretion rates ($\\sim$ 10$^{-2}$ -- 10$^...

  14. Starspot Activity and Superflares on Solar-type Stars

    Science.gov (United States)

    Maehara, Hiroyuki

    2017-10-01

    Recent high-precision photometry from space (e.g., Kepler) enables us to investigate the nature of ``superflares'' on solar-type stars. The bolometric energy of superflares detected by Kepler ranges from 1033 erg to 1036 erg which is 10-10,000 times larger than that released by a typical X10 class solar flare. The occurrence frequency (dN/dE) of superflares as a function of flare energy (E) shows the power-law distribution with the power-law index of ~-1.8 for 1034 < E < 1036 erg. Most of superflare stars show quasi-periodic light variations which suggest the presence of large starspots. The bolometric energy released by flares is consistent with the magnetic energy stored near the starspots. The occurrence frequency of superflares increases as the rotation period decreases. However, the energy of the largest flares observed in a given period bin does not show any clear correlation with the rotation period. These results suggest that superflares would occur on the slowly-rotating stars.

  15. ULTRA-DEEP HUBBLE SPACE TELESCOPE IMAGING OF THE SMALL MAGELLANIC CLOUD: THE INITIAL MASS FUNCTION OF STARS WITH M {approx}< 1 M {sub Sun}

    Energy Technology Data Exchange (ETDEWEB)

    Kalirai, Jason S.; Anderson, Jay; Dotter, Aaron; Reid, I. Neill [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Richer, Harvey B. [Department of Physics and Astronomy, University of British Columbia, Vancouver, BC (Canada); Fahlman, Gregory G. [National Research Council, Herzberg Institute of Astrophysics, Victoria, BC (Canada); Hansen, Brad M. S.; Rich, R. Michael [Division of Astronomy and Astrophysics, University of California at Los Angeles, Los Angeles, CA 90095 (United States); Hurley, Jarrod [Center for Astrophysics and Supercomputing, Swinburne University of Technology, Hawthorn VIC 3122 (Australia); Shara, Michael M., E-mail: jkalirai@stsci.edu, E-mail: jayander@stsci.edu, E-mail: dotter@stsci.edu, E-mail: richer@astro.ubc.ca, E-mail: greg.fahlman@nrc-cnrc.gc.ca, E-mail: hansen@astro.ucla.edu, E-mail: rmr@astro.ucla.edu, E-mail: jhurley@swin.edu.au, E-mail: mshara@amnh.org [Department of Astrophysics, American Museum of Natural History, Central Park West and 79th Street, New York, NY 10024 (United States)

    2013-02-15

    We present a new measurement of the stellar initial mass function (IMF) based on ultra-deep, high-resolution photometry of >5000 stars in the outskirts of the Small Magellanic Cloud (SMC) galaxy. The Hubble Space Telescope (HST) Advanced Camera for Surveys observations reveal this rich, cospatial population behind the foreground globular cluster 47 Tuc, which we targeted for 121 HST orbits. The stellar main sequence of the SMC is measured in the F606W, F814W color-magnitude diagram down to {approx}30th magnitude, and is cleanly separated from the foreground star cluster population using proper motions. We simulate the SMC population by extracting stellar masses (single and unresolved binaries) from specific IMFs and converting those masses to luminosities in our bandpasses. The corresponding photometry for these simulated stars is drawn directly from a rich cloud of 4 million artificial stars, thereby accounting for the real photometric scatter and completeness of the data. Over a continuous and well-populated mass range of M = 0.37-0.93 M {sub Sun} (e.g., down to a {approx}75% completeness limit at F606W = 28.7), we demonstrate that the IMF is well represented by a single power-law form with slope {alpha} = -1.90 ({sup +0.15} {sub -0.10}) (3{sigma} error) (e.g., dN/dM{proportional_to} M {sup {alpha}}). This is shallower than the Salpeter slope of {alpha} = -2.35, which agrees with the observed stellar luminosity function at higher masses. Our results indicate that the IMF does not turn over to a more shallow power-law form within this mass range. We discuss implications of this result for the theory of star formation, the inferred masses of galaxies, and the (lack of a) variation of the IMF with metallicity.

  16. Are peculiar Wolf-Rayet Stars of type WN8 Thorne-Zytkow Objects?

    CERN Document Server

    Foellmi, C

    2006-01-01

    Most population I Wolf-Rayet (WR) stars are the He-rich descendants of the most massive stars (M_i = 25 - 100 M_sun). Evidence has been accumulating over the years that among all pop I WR stars, those of the relatively cool, N-rich subtype "WN8" are among the most peculiar: 1. They tend to be runaways, with large space velocity and/or avoid clusters. 2. Unlike their equally luminous WN6,7 cousins, only a very small number of WN8 stars are known to belong to a close binary with an OB companion. 3. They are the systematically most highly stochastically variable among all (single) WR stars. Taken together, these suggest that many WN8 stars may originally have been in close binaries (like half of all stars), in which the original primary exploded as a supernova, leaving behind a very close binary containing a massive star with a neutron star/black hole companion (like Cyg X-3). When the massive remaining star evolved in turn, it engulfed and eventually swallowed the compact companion, leading to the presently puf...

  17. Star Product and Invariant Integration for Lie type Noncommutative Spacetimes

    CERN Document Server

    Chryssomalakos, Chryssomalis

    2007-01-01

    We present a star product for noncommutative spaces of Lie type, including the so called ``canonical'' case by introducing a central generator, which is compatible with translations and admits a simple, manageable definition of an invariant integral. A quasi-cyclicity property for the latter is shown to hold, which reduces to exact cyclicity when the adjoint representation of the underlying Lie algebra is traceless. Several explicit examples illuminate the formalism, dealing with kappa-Minkowski spacetime and the Heisenberg algebra (``canonical'' noncommutative 2-plane).

  18. Non-thermal emission from early-type stars

    CERN Document Server

    Benaglia, P

    2006-01-01

    Massive, early-type stars deposit energy and momentum in the interstellar medium through dense, supersonic winds. These objects are one of the most important sources of ionising radiation and chemical enrichment in the Galaxy. The physical conditions in the winds give rise to thermal and non-thermal emission, detectable from radio to gamma rays. In this report the relevant radiation processes will be described and studies on particular systems will be presented, discussing the information provided by multifrequency observations. Future steps aiming at understanding the stellar wind phenomenon as a whole will be outlined.

  19. Galactic membership of BL Her type variable stars

    Science.gov (United States)

    Jurkovic, M. I.; Stojanovic, M.; Ninkovic, S.

    2016-05-01

    As the RR Lyrae stars evolve on the Hertzsprung-Russell diagram they are believed to become short period Type II Cepheids, known as BL Her type (with a pulsation period from 1 to 3-8 days). Assuming that their mass is around 0.5-0.6M_Sol, and that they are low metallicity objects, they were thought to belong to the halo of the Milky Way. We investigated seven Galactic short period Type II Cepheids (BL Her, SW Tau, V553 Cen, DQ And, BD Cas, V383 Cyg, and KT Com) in order to establish their membership within the Galactic structure using the kinematic approach. Gaia should provide us with more data needed to conduct the study of the whole sample.

  20. Galactic membership of BL Her type variable stars

    CERN Document Server

    Jurkovic, Monika I; Ninković, Slobodan

    2016-01-01

    As the RR Lyrae stars evolve on the Hertzsprung-Russell diagram they are believed to become short period Type II Cepheids, known as BL Her type (with a pulsation period from $1$ to $3-8$ days). Assuming that their mass is around $0.5 - 0.6 {\\rm M}_{\\odot}$, and that they are low metallicity objects, they were thought to belong to the halo of the Milky Way. We investigated seven Galactic short period Type II Cepheids (BL Her, SW Tau, V553 Cen, DQ And, BD Cas, V383 Cyg, and KT Com) in order to establish their membership within the Galactic structure using the kinematic approach. $Gaia$ should provide us with more data needed to conduct the study of the whole sample.

  1. Spectroscopic survey of Kepler stars - II. FIES/NOT observations of A- and F-type stars

    Science.gov (United States)

    Niemczura, E.; Polińska, M.; Murphy, S. J.; Smalley, B.; Kołaczkowski, Z.; Jessen-Hansen, J.; Uytterhoeven, K.; Lykke, J. M.; Triviño Hage, A.; Michalska, G.

    2017-09-01

    We have analysed high-resolution spectra of 28 A and 22 F stars in the Kepler field, observed using the Fibre-Fed Échelle Spectrograph at the Nordic Optical Telescope. We provide spectral types, atmospheric parameters and chemical abundances for 50 stars. Balmer, Fe i and Fe ii lines were used to derive effective temperatures, surface gravities and microturbulent velocities. We determined chemical abundances and projected rotational velocities using a spectrum synthesis technique. Effective temperatures calculated by spectral energy distribution fitting are in good agreement with those determined from the spectral line analysis. The stars analysed include chemically peculiar stars of the Am and λ Boo types, as well as stars with approximately solar chemical abundances. The wide distribution of projected rotational velocity, vsin i, is typical for A and F stars. The microturbulence velocities obtained are typical for stars in the observed temperature and surface gravity ranges. Moreover, we affirm the results of Niemczura et al. that Am stars do not have systematically higher microturbulent velocities than normal stars of the same temperature.

  2. Surveying the Bright Stars by Optical Interferometry I: A Search for Multiplicity Among Stars of Spectral Types F - K

    CERN Document Server

    Hutter, Donald; Tycner, Christopher; Benson, James; Hummel, Christian; Sanborn, Jason; Franz, Otto G; Johnston, Kenneth

    2016-01-01

    We present the first results from an ongoing survey for multiplicity among the bright stars using the Navy Precision Optical Interferometer (NPOI). We first present a summary of NPOI observations of known multiple systems, including the first detection of the companion of $\\beta$ Scuti with precise relative astrometry, to illustrate the instrument's detection sensitivity for binaries at magnitude differences $\\Delta$$m$ $\\lessapprox$ 3 over the range of angular separation 3 - 860 milliarcseconds (mas). A limiting $\\Delta$$m_{700}$ $\\sim$ 3.5 is likely for binaries where the component spectral types differ by less than two. Model fits to these data show good agreement with published orbits, and we additionally present a new orbit solution for one of these stars, $\\sigma$ Her. We then discuss early results of the survey of bright stars at $\\delta$ $\\geq$ -20$\\deg$. This survey, which complements previous surveys of the bright stars by speckle interferometry, initially emphasizes bright stars of spectral types F...

  3. Dynamical Model for Spindown of Solar-type Stars

    Science.gov (United States)

    Sood, Aditi; Kim, Eun-jin; Hollerbach, Rainer

    2016-12-01

    After their formation, stars slow down their rotation rates by the removal of angular momentum from their surfaces, e.g., via stellar winds. Explaining how this rotation of solar-type stars evolves in time is currently an interesting but difficult problem in astrophysics. Despite the complexity of the processes involved, a traditional model, where the removal of angular momentum by magnetic fields is prescribed, has provided a useful framework to understand observational relations between stellar rotation, age, and magnetic field strength. Here, for the first time, a spindown model is proposed where loss of angular momentum by magnetic fields evolves dynamically, instead of being prescibed kinematically. To this end, we evolve the stellar rotation and magnetic field simultaneously over stellar evolution time by extending our previous work on a dynamo model which incorporates nonlinear feedback mechanisms on rotation and magnetic fields. We show that our extended model reproduces key observations and is capable of explaining the presence of the two branches of (fast and slow rotating) stars which have different relations between rotation rate Ω versus time (age), magnetic field strength | B| versus rotation rate, and frequency of magnetic field {ω }{cyc} versus rotation rate. For fast rotating stars we find that: (i) there is an exponential spindown {{Ω }}\\propto {e}-1.35t, with t measured in Gyr; (ii) magnetic activity saturates for higher rotation rate; (iii) {ω }{cyc}\\propto {{{Ω }}}0.83. For slow rotating stars we find: (i) a power-law spindown {{Ω }}\\propto {t}-0.52; (ii) that magnetic activity scales roughly linearly with rotation rate; (iii) {ω }{cyc}\\propto {{{Ω }}}1.16. The results obtained from our investigations are in good agreement with observations. The Vaughan-Preston gap is consistently explained in our model by the shortest spindown timescale in this transition from fast to slow rotators. Our results highlight the importance of self

  4. Mediterranean aerosol typing by integrating three-wavelength lidar and sun photometer measurements.

    Science.gov (United States)

    Perrone, M R; Burlizzi, P

    2016-07-01

    Backscatter lidar measurements at 355, 532, and 1064 nm combined with aerosol optical thicknesses (AOTs) from sun photometer measurements collocated in space and time were used to retrieve the vertical profiles of intensive and extensive aerosol parameters. Then, the vertical profiles of the Ångström coefficients for different wavelength pairs (Å(λ1, λ2, z)), the color ratio (CR(z)), the fine mode fraction (η(z)) at 532 nm, and the fine modal radius (R f (z)), which represent aerosol characteristic properties independent from the aerosol load, were used for typing the aerosol over the Central Mediterranean. The ability of the Ångström coefficients to identify the main aerosol types affecting the Central Mediterranean with the support of the backward trajectory analysis was first demonstrated. Three main aerosol types, which were designed as continental-polluted (CP), marine-polluted (MP), and desert-polluted (DP), were identified. We found that both the variability range and the vertical profile structure of the tested aerosol intensive parameters varied with the aerosol type. The variability range and the altitude dependence of the aerosol extinction coefficients at 355, 532, and 1064 nm, respectively, also varied with the identified aerosol types even if they are extensive aerosol parameters. DP, MP, and CP aerosols were characterized by the Å(532, 1064 nm) mean values ± 1 standard deviation equal to 0.5 ± 0.2, 1.1 ± 0.2, 1.6 ± 0.2, respectively. η(%) mean values ± 1SD were equal to 50 ± 10, 73 ± 7, and 86 ± 6 for DP, MP, and CP aerosols, respectively. The R f and CR mean values ± 1SD were equal to 0.16 ± 0.05 μm and 1.3 ± 0.3, respectively, for DP aerosols; to 0.12 ± 0.03 μm and 1.8 ± 0.4, respectively, for MP aerosols; and to 0.11 ± 0.02 μm and 1.7 ± 0.4, respectively, for CP aerosols. CP and DP aerosols were on average responsible for greater AOT and LR values, but

  5. New Rare Earth Element Abundance Distributions for the Sun and Five r-Process-Rich Very Metal-Poor Stars

    CERN Document Server

    Sneden, Christopher; Cowan, John J; Ivans, Inese I; Hartog, Elizabeth A Den

    2009-01-01

    We have derived new abundances of the rare-earth elements Pr, Dy, Tm, Yb, and Lu for the solar photosphere and for five very metal-poor, neutron-capture r-process-rich giant stars. The photospheric values for all five elements are in good agreement with meteoritic abundances. For the low metallicity sample, these abundances have been combined with new Ce abundances from a companion paper, and reconsideration of a few other elements in individual stars, to produce internally-consistent Ba, rare-earth, and Hf (56<= Z <= 72) element distributions. These have been used in a critical comparison between stellar and solar r-process abundance mixes.

  6. The Type IIn Supernova 2002kg: The Outburst of a Luminous Blue Variable Star in NGC 2403

    CERN Document Server

    Van Dyk, S D; Chornock, R; Filippenko, A V; Foley, R; Humphreys, R M; Li, W; Challis, Peter M.; Chornock, Ryan; Dyk, Schuyler D. Van; Filippenko, Alexei V.; Foley, Ryan; Humphreys, Roberta M.; Li, Weidong

    2006-01-01

    We show that Supernova (SN) 2002kg in NGC 2403, initially classified as Type II-narrow (IIn), has photometric and spectroscopic properties unlike those of normal SNe. Its behavior, instead, is more typical of highly massive stars which experience the short-lived luminous blue variable (LBV) phase toward the end of their lives. The star, in fact, most resembles the LBV S Doradus in outburst. The precursor of SN 2002kg is the irregular, bright blue variable star 37 (V37), catalogued by Tammann & Sandage in 1968. Using high-quality ground-based, multi-band images we can constrain the initial mass of V37 to be M_ini >~ 40 M_sun. We find that, although the spectra indicate a nitrogen enhancement, possibly revealing the products of CNO processing by V37 in the ejecta, the star lacks a substantial LBV nebula. The outburst from SN 2002kg/V37 is not nearly as energetic as the giant eruptions of the eta Carinae-like variables, such as SN 1954J/V12, also in NGC 2403. SN 2002kg/V37, however, is among a growing number...

  7. Improved Ni I log(gf) Values and Abundance Determinations in the Photospheres of the Sun and Metal-poor Star HD 84937

    CERN Document Server

    Wood, M P; Sneden, C; Cowan, J J

    2014-01-01

    Atomic transition probability measurements for 371 Ni I lines in the UV through near IR are reported. Branching fractions from data recorded using a Fourier transform spectrometer and a new echelle spectrograph are combined with published radiative lifetimes to determine these transition probabilities. Generally good agreement is found in comparisons to previously reported Ni I transition probability measurements. Use of the new echelle spectrograph, independent radiometric calibration methods, and independent data analysis routines enable a reduction of systematic errors and overall improvement in transition probability uncertainty over previous measurements. The new Ni I data are applied to high resolution visible and UV spectra of the Sun and metal-poor star HD 84937 to derive new, more accurate Ni abundances. Lines covering a wide range of wavelength and excitation potential are used to search for non-LTE effects.

  8. Two-dimensional hydrodynamic core-collapse supernova simulations with spectral neutrino transport. I. Numerical method and results for a 15 M_sun star

    CERN Document Server

    Buras, R; Janka, H T; Kifonidis, K

    2005-01-01

    Supernova models with a full spectral treatment of the neutrino transport are presented, employing the Prometheus/Vertex neutrino-hydrodynamics code with a ``ray-by-ray plus'' approximation for treating two- (or three-) dimensional problems. The method is described in detail and critically assessed with respect to its capabilities, limitations, and inaccuracies in the context of supernova simulations. In this first paper of a series, 1D and 2D core-collapse calculations for a (nonrotating) 15 M_sun star are discussed, uncertainties in the treatment of the equation of state -- numerical and physical -- are tested, Newtonian results are compared with simulations using a general relativistic potential, bremsstrahlung and interactions of neutrinos of different flavors are investigated, and the standard approximation in neutrino-nucleon interactions with zero energy transfer is replaced by rates that include corrections due to nucleon recoil, thermal motions, weak magnetism, and nucleon correlations. Models with t...

  9. Improved V II log($gf$) Values, Hyperfine Structure Constants, and Abundance Determinations in the Photospheres of the Sun and Metal-poor Star HD 84937

    CERN Document Server

    Wood, M P; Hartog, E A Den; Sneden, C; Cowan, J J

    2014-01-01

    New experimental absolute atomic transition probabilities are reported for 203 lines of V II. Branching fractions are measured from spectra recorded using a Fourier transform spectrometer and an echelle spectrometer. The branching fractions are normalized with radiative lifetime measurements to determine the new transition probabilities. Generally good agreement is found between this work and previously reported V II transition probabilities. Use of two spectrometers, independent radiometric calibration methods, and independent data analysis routines enables a reduction in systematic uncertainties, in particular those due to optical depth errors. In addition, new hyperfine structure constants are measured for selected levels by least squares fitting line profiles in the FTS spectra. The new V II data are applied to high resolution visible and UV spectra of the Sun and metal-poor star HD 84937 to determine new, more accurate V abundances. Lines covering a range of wavelength and excitation potential are used t...

  10. Direct Imaging of a Cold Jovian Exoplanet in Orbit around the Sun-like Star GJ 504

    NARCIS (Netherlands)

    Kuzuhara, M.; et al., [Unknown; Thalmann, C.

    2013-01-01

    Several exoplanets have recently been imaged at wide separations of >10 AU from their parent stars. These span a limited range of ages (<50 Myr) and atmospheric properties, with temperatures of 800-1800 K and very red colors (J - H > 0.5 mag), implying thick cloud covers. Furthermore, substantial mo

  11. Improved Cr II log(gf) Values and Abundance Determinations in the Photospheres of the Sun and Metal-poor Star HD 84937

    Science.gov (United States)

    Lawler, J. E.; Sneden, C.; Nave, G.; Den Hartog, E. A.; Emrahoğlu, N.; Cowan, J. J.

    2017-01-01

    New emission branching fraction (BF) measurements for 183 lines of the second spectrum of chromium (Cr ii) and new radiative lifetime measurements from laser-induced fluorescence for 8 levels of Cr+ are reported. The goals of this study are to improve transition probability measurements in Cr ii and reconcile solar and stellar Cr abundance values based on Cr i and Cr ii lines. Eighteen spectra from three Fourier Transform Spectrometers supplemented with ultraviolet spectra from a high-resolution echelle spectrometer are used in the BF measurements. Radiative lifetimes from this study and earlier publications are used to convert the BFs into absolute transition probabilities. These new laboratory data are applied to determine the Cr abundance log ε in the Sun and metal-poor star HD 84937. The mean result in the Sun is = 5.624 ± 0.009 compared to = 5.644 ± 0.006 on a scale with the hydrogen abundance log ε(H) = 12 and with the uncertainty representing only line-to-line scatter. A Saha (ionization balance) test on the photosphere of HD 84937 is also performed, yielding = 3.417 ± 0.006 and 0 eV)> = 3.374 ± 0.011 for this dwarf star. We find a correlation of Cr with the iron-peak element Ti, suggesting an associated nucleosynthetic production. Four iron-peak elements (Cr along with Ti, V, and Sc) appear to have a similar (or correlated) production history—other iron-peak elements appear not to be associated with Cr.

  12. Improved Cr II log(gf)s and Cr Abundances in the Photospheres of the Sun and Metal-Poor Star HD 84937

    Science.gov (United States)

    Lawler, James E.; Sneden, Chris; Nave, Gillian; Den Hartog, Elizabeth; Emrahoglu, Nuri; Cowan, John J.

    2017-01-01

    New laser induced fluorescence (LIF) data for eight levels of singly ionized chromium (Cr) and emission branching fraction (BF) measurements for 183 lines of the second spectrum of chromium (Cr II) are reported. A goal of this study is to reconcile Solar and stellar Cr abundance values based on Cr I and Cr II lines. Analyses of eighteen spectra from three Fourier Transform Spectrometers supplemented with ultraviolet spectra from a high resolution echelle spectrometer yield the BF measurements. Radiative lifetimes from LIF measurements are used to convert the BFs to absolute transition probabilities. These new laboratory data are applied to determine the Cr abundance log eps in the Sun and metal-poor star HD 84937. The mean result in the Sun is = 5.624 ± 0.009 compared to = 5.644 ± 0.006 on a scale with the H abundance log eps(H) = 12. Similarily the photosphere of HD 84937 is found to be in Saha balance with = 3.417 ± 0.006 and 0 eV) > = 3.374 ± 0.011 for this dwarf star. The resonance (E.P. = 0 eV) lines of Cr I reveal overionization of the ground level of neutral Cr. We find a correlation of Cr with the iron-peak element Ti, suggesting an associated or related nucleosynthetic production. Four iron-peak elements (Cr along with Ti, V and Sc) appear to have a similar (or correlated) production history - other iron-peak elements appear not to be associated with Cr.This work is supported in part by NASA grant NNX16AE96G (J.E.L.), by NSF grant AST-1516182 (J.E.L. & E.D.H.), by NASA interagency agreement NNH10AN381 (G.N.), and NSF grant AST-1211585 (C.S.). Postdoctoral research support for N. E. is from the Technological and Scientific Research Council of Turkey (TUBITAK).

  13. Circumstellar carbonaceous material associated with late-type dusty WC Wolf-Rayet stars

    NARCIS (Netherlands)

    Chiar, JE; Tielens, AGGM

    2001-01-01

    We have studied the 5-8.5 mum infrared spectra of the late-type Wolf-Rayet stars WR 118, WR 112, and WR 104, the WN star WR 147, the B5 hypergiant Cygnus OB2 No. 12, and the Galactic center luminous blue variable Pistol Star using the Short Wavelength Spectrometer on the Infrared Space Observatory.

  14. IMPROVED V I log(gf) VALUES AND ABUNDANCE DETERMINATIONS IN THE PHOTOSPHERES OF THE SUN AND METAL-POOR STAR HD 84937

    Energy Technology Data Exchange (ETDEWEB)

    Lawler, J. E.; Wood, M. P.; Den Hartog, E. A.; Feigenson, T. [Department of Physics, University of Wisconsin, Madison, WI 53706 (United States); Sneden, C. [Department of Astronomy and McDonald Observatory, University of Texas, Austin, TX 78712 (United States); Cowan, J. J., E-mail: jelawler@wisc.edu, E-mail: mpwood@wisc.edu, E-mail: eadenhar@wisc.edu, E-mail: tfeigenson@wisc.edu, E-mail: chris@verdi.as.utexas.edu, E-mail: cowan@nhn.ou.edu [Homer L. Dodge Department of Physics and Astronomy, University of Oklahoma, Norman, OK 73019 (United States)

    2015-01-01

    New emission branching fraction measurements for 836 lines of the first spectrum of vanadium (V I) are determined from hollow cathode lamp spectra recorded with the National Solar Observatory 1 m Fourier transform spectrometer (FTS) and a high-resolution echelle spectrometer. The branching fractions are combined with recently published radiative lifetimes from laser-induced fluorescence measurements to determine accurate absolute atomic transition probabilities for the 836 lines. The FTS data are also used to extract new hyperfine structure A coefficients for 26 levels of neutral vanadium. These new laboratory data are applied to determine the V abundance in the Sun and metal-poor star HD 84937, yielding log ε(V) = 3.956 ± 0.004 (σ = 0.037) based on 93 V I lines and log ε(V) = 1.89 ± 0.03 (σ = 0.07) based on nine V I lines, respectively, using the Holweger-Müller 1D model. These new V I abundance values for the Sun and HD 84937 agree well with our earlier determinations based upon V II.

  15. solarFLAG hare and hounds: on the extraction of rotational p-mode splittings from seismic, Sun-as-a-star data

    CERN Document Server

    Chaplin, W J; Baudin, F; Boumier, P; Elsworth, Y; Fletcher, S T; Fossat, E; García, R A; Isaak, G R; Jiménez, A; Jiménez-Reyes, S J; Lazrek, M; Leibacher, J W; Lochard, J; New, R; Pallé, P L; Regulo, C; Salabert, D; Seghouani, N; Toutain, T; Wachter, R

    2006-01-01

    We report on results from the first solar Fitting at Low-Angular degree Group (solar FLAG) hare-and-hounds exercise. The group is concerned with the development of methods for extracting the parameters of low-l solar p mode data (`peak bagging'), collected by Sun-as-a-star observations. Accurate and precise estimation of the fundamental parameters of the p modes is a vital pre-requisite of all subsequent studies. Nine members of the FLAG (the `hounds') fitted an artificial 3456-d dataset. The dataset was made by the `hare' (WJC) to simulate full-disc Doppler velocity observations of the Sun. The rotational frequency splittings of the l=1, 2 and 3 modes were the first parameter estimates chosen for scrutiny. Significant differences were uncovered at l=2 and 3 between the fitted splittings of the hounds. Evidence is presented that suggests this unwanted bias had its origins in several effects. The most important came from the different way in which the hounds modeled the visibility ratio of the different rotati...

  16. uvbybeta photometry of early type open cluster and field stars

    CERN Document Server

    Handler, G

    2011-01-01

    The beta Cephei stars and slowly pulsating B (SPB) stars are massive main sequence variables. The strength of their pulsational driving strongly depends on the opacity of iron-group elements. As many of those stars naturally occur in young open clusters, whose metallicities can be determined in several fundamental ways, it is logical to study the incidence of pulsation in several young open clusters. To provide the foundation for such an investigation, Str\\"omgren-Crawford uvbybeta photometry of open cluster target stars was carried out to determine effective temperatures, luminosities, and therefore cluster memberships. In the course of three observing runs, uvbybeta photometry for 168 target stars was acquired and transformed into the standard system by measurements of 117 standard stars. The list of target stars also included some known cluster and field beta Cephei stars, as well as beta Cephei and SPB candidates that are targets of the asteroseismic part of the Kepler satellite mission. The uvbybeta phot...

  17. Analysis of flares in the chromosphere and corona of main- and pre-main-sequence M-type stars

    Science.gov (United States)

    Crespo-Chacón, I.

    2015-11-01

    This Ph.D. Thesis revolves around flares on main- and pre-main-sequence M-type stars. We use observations in different wavelength ranges with the aim of analysing the effects of flares at different layers of stellar atmospheres. In particular, optical and X-ray observations are used so that we can study how flares affect, respectively, the chromosphere and the corona of stars. In the optical range we carry out a high temporal resolution spectroscopic monitoring of UV Ceti-type stars aimed at detecting non-white-light flares (the most typical kind of solar flares) in stars other than the Sun. With these data we confirm that non-white-light flares are a frequent phenomenon in UV Ceti-type stars, as observed in the Sun. We study and interpret the behaviour of different chromospheric lines during the flares detected on AD Leo. By using a simplified slab model of flares (Jevremović et al. 1998), we are able to determine the physical parameters of the chromospheric flaring plasma (electron density and electron temperature), the temperature of the underlying source, and the surface area covered by the flaring plasma. We also search for possible relationships between the physical parameters of the flaring plasma and other properties such as the flare duration, area, maximum flux and released energy. This work considerably extends the existing sample of stellar flares analysed with good quality spectroscopy in the optical range. In X-rays we take advantage of the great sensitivity, wide energy range, high energy resolution, and continuous time coverage of the EPIC detectors - on-board the XMMNewton satellite - in order to perform time-resolved spectral analysis of coronal flares. In particular, in the UV Ceti-type star CC Eri we study two flares that are weaker than those typically reported in the literature (allowing us to speculate about the role of flares as heating agents of stellar atmospheres); while in the pre-main-sequence M-type star TWA 11B (with no signatures of

  18. Could Ultracool Dwarfs Have Sun-Like Activity?

    Science.gov (United States)

    Kohler, Susanna

    2016-11-01

    Solar-like stars exhibit magnetic cycles; our Sun, for instance, displays an 11-year period in its activity, manifesting as cyclic changes in radiation levels, the number of sunspots and flares, and ejection of solar material. Over the span of two activity cycles, the Suns magnetic field flips polarity and then returns to its original state.An artists illustration comparing the Sun to TRAPPIST-1, an ultracool dwarf star known to host several planets. [ESO]But what about the magnetic behavior of objects near the cooler end of the stellar main sequence do they exhibit similar activity cycles?Effects of a Convecting InteriorDwarf stars have made headlines in recent years due to their potential to harbor exoplanets. Because these cooler stars have lower flux levels compared to the Sun, their habitable zones lie much closer to the stars. The magnetic behavior of these stars is therefore important to understand: could ultracool dwarfs exhibit solar-like activity cycles that would affect planets with close orbits?The differences in internal structure between different mass stars. Ultracool dwarfs have fully convective interiors. [www.sun.org]Theres a major difference between ultracool dwarfs (stars of spectral type higher than M7 and brown dwarfs) and Sun-like stars: their internal structures. Sun-like stars have a convective envelope that surrounds a radiative core. The interiors of cool, low-mass objects, on the other hand, are fully convective.Based on theoretical studies of how magnetism is generated in stars, its thought that the fully convective interiors of ultracool dwarfs cant support large-scale magnetic field formation. This should prevent these stars from exhibiting activity cycles like the Sun. But recent radio observations of dwarf stars have led scientist Matthew Route (ITaP Research Computing, Purdue University) to question these models.A Reversing Field?During observations of the brown dwarf star J1047+21 in 20102011, radio flares were detected with

  19. MagAO Imaging of Long-period Objects (MILO). II. A Puzzling White Dwarf around the Sun-like Star HD 11112

    CERN Document Server

    Rodigas, Timothy J; Simon, Amelie; Arriagada, Pamela; Faherty, Jackie; Anglada-Escude, Guillem; Mamajek, Eric E; Weinberger, Alycia; Butler, R Paul; Males, Jared R; Morzinski, Katie; Close, Laird M; Hinz, Philip M; Bailey, Jeremy; Carter, Brad; Jenkins, James S; Jones, Hugh; O'Toole, Simon; Tinney, C G; Wittenmyer, Rob; Debes, John

    2016-01-01

    HD 11112 is an old, Sun-like star that has a long-term radial velocity (RV) trend indicative of a massive companion on a wide orbit. Here we present direct images of the source responsible for the trend using the Magellan Adaptive Optics system. We detect the object (HD 11112B) at a separation of 2\\fasec 2 (100 AU) at multiple wavelengths spanning 0.6-4 \\microns ~and show that it is most likely a gravitationally-bound cool white dwarf. Modeling its spectral energy distribution (SED) suggests that its mass is 0.9-1.1 \\msun, which corresponds to very high-eccentricity, near edge-on orbits from Markov chain Monte Carlo analysis of the RV and imaging data together. The total age of the white dwarf is $>2\\sigma$ discrepant with that of the primary star under most assumptions. The problem can be resolved if the white dwarf progenitor was initially a double white dwarf binary that then merged into the observed high-mass white dwarf. HD 11112B is a unique and intriguing benchmark object that can be used to calibrate ...

  20. IMPROVED Co i log(gf) VALUES AND ABUNDANCE DETERMINATIONS IN THE PHOTOSPHERES OF THE SUN AND METAL-POOR STAR HD 84937

    Energy Technology Data Exchange (ETDEWEB)

    Lawler, J. E. [Department of Physics, University of Wisconsin-Madison, 1150 University Ave., Madison, WI 53706 (United States); Sneden, C. [Department of Astronomy and McDonald Observatory, University of Texas, Austin, TX 78712 (United States); Cowan, J. J., E-mail: jelawler@wisc.edu, E-mail: chris@verdi.as.utexas.edu, E-mail: jjcowan1@ou.edu [Homer L. Dodge Department of Physics and Astronomy, University of Oklahoma, Norman, OK 73019 (United States)

    2015-09-15

    New emission branching fraction measurements for 898 lines of the first spectrum of cobalt (Co i) are determined from hollow cathode lamp spectra recorded with the National Solar Observatory 1 m Fourier transform spectrometer on Kitt Peak, AZ and a high-resolution echelle spectrometer. Published radiative lifetimes from laser induced fluorescence measurements are combined with the branching fractions to determine accurate absolute atomic transition probabilities for the 898 lines. Hyperfine structure (hfs) constants for levels of neutral Co in the literature are surveyed and selected values are used to generate complete hfs component patterns for 195 transitions of Co i. These new laboratory data are applied to determine the Co abundance in the Sun and metal-poor star HD 84937, yielding log ϵ(Co) = 4.955 ± 0.007 (σ = 0.059) based on 82 Co i lines and log ϵ(Co) = 2.785 ± 0.008 (σ = 0.065) based on 66 Co i lines, respectively. A Saha or ionization balance test on the photosphere of HD 84937 is performed using 16 UV lines of Co ii, and good agreement is found with the Co i result in this metal-poor ([Fe i/H] = −2.32, [Fe ii/H] = −2.32) dwarf star. The resulting value of [Co/Fe] = +0.14 supports a rise of Co/Fe at low metallicity that has been suggested in other studies.

  1. The stability of tightly-packed, evenly-spaced systems of Earth-mass planets orbiting a Sun-like star

    Science.gov (United States)

    Obertas, Alysa; Van Laerhoven, Christa; Tamayo, Daniel

    2017-09-01

    Many of the multi-planet systems discovered to date have been notable for their compactness, with neighbouring planets closer together than any in the Solar System. Interestingly, planet-hosting stars have a wide range of ages, suggesting that such compact systems can survive for extended periods of time. We have used numerical simulations to investigate how quickly systems go unstable in relation to the spacing between planets, focusing on hypothetical systems of Earth-mass planets on evenly-spaced orbits (in mutual Hill radii). In general, the further apart the planets are initially, the longer it takes for a pair of planets to undergo a close encounter. We recover the results of previous studies, showing a linear trend in the initial planet spacing between 3 and 8 mutual Hill radii and the logarithm of the stability time. Investigating thousands of simulations with spacings up to 13 mutual Hill radii reveals distinct modulations superimposed on this relationship in the vicinity of first and second-order mean motion resonances of adjacent and next-adjacent planets. We discuss the impact of this structure and the implications on the stability of compact multi-planet systems. Applying the outcomes of our simulations, we show that isolated systems of up to five Earth-mass planets can fit in the habitable zone of a Sun-like star without close encounters for at least 109 orbits.

  2. Flares on A-type Stars: Evidence for Heating of Solar Corona by Nanoflares?

    Science.gov (United States)

    Švanda, Michal; Karlický, Marian

    2016-11-01

    We analyzed the occurrence rates of flares on stars of spectral types K, G, F, and A, observed by Kepler. We found that the histogram of occurrence frequencies of stellar flares is systematically shifted toward a high-energy tail for A-type stars compared to stars of cooler spectral types. We extrapolated the fitted power laws toward flares with smaller energies (nanoflares) and made estimates for total energy flux to stellar atmospheres by flares. We found that, for A-type stars, the total energy flux density was at least four-times smaller than for G stars. We speculate that this deficit in energy supply may explain the lack of hot coronae on A-type stars. Our results indicate the importance of nanoflares for heating and formation of the solar corona.

  3. Flares on A-type stars: Evidence for heating of solar corona by nanoflares?

    CERN Document Server

    Svanda, M

    2016-01-01

    We analyzed the occurrence rates of flares on stars of spectral types K, G, F, and A, observed by Kepler. We found that the histogram of occurrence frequencies of stellar flares is systematically shifted towards a high-energy tail for A-type stars compared to stars of cooler spectral types. We extrapolated the fitted power laws towards flares with smaller energies (nanoflares) and made estimates for total energy flux to stellar atmospheres by flares. We found that for A-type stars the total energy flux density was at least 4-times smaller than for G-stars. We speculate that this deficit in energy supply may explain the lack of hot coronae on A-type stars. Our results indicate an importance of nanoflares for heating and formation of the solar corona.

  4. Abundances of the elements in sharp-lined early-type stars from IUE high-dispersion spectrograms; 2, the nitrogen deficiency in mercury- manganese stars

    CERN Document Server

    Roby, S W; Adelman, S J

    1999-01-01

    For pt.I see ibid., vol.419, no.1, p.276-85 (1993). The authors determine nitrogen abundances from co-added IUE high-dispersion SWP spectrograms of four HgMn stars and five normal or superficially normal main-sequence B and A stars. They find N deficiencies in the HgMn stars greater than previously reported (depletion factors of 135-400 relative to the Sun). N abundance discrepancies from UV and IR studies of normal stars are discussed in light of possible non-LTE effects. Their data set for their sample of HgMn stars (observed with a consistent strategy to maximize the benefits of co-additions) is an improvement over the single or few images previously used to derive N abundances for most of these stars. (37 refs).

  5. Mass loss from late-type WN stars and its Z-dependence: very massive stars approaching the Eddington limit

    CERN Document Server

    Graefener, G

    2008-01-01

    The mass loss from Wolf-Rayet (WR) stars is of fundamental importance for the final fate of massive stars and their chemical yields. Its Z-dependence is discussed in relation to the formation of long-duration Gamma Ray Bursts (GRBs) and the yields from early stellar generations. However, the mechanism of formation of WR-type stellar winds is still under debate. We present the first fully self-consistent atmosphere/wind models for late-type WN stars. We investigate the mechanisms leading to their strong mass loss, and examine the dependence on stellar parameters, in particular on the metallicity Z. We identify WNL stars as very massive stars close to the Eddington limit, potentially still in the phase of central H-burning. Due to their high L/M ratios, these stars develop optically thick, radiatively driven winds. These winds show qualitatively different properties than the thin winds of OB stars. The resultant mass loss depends strongly on Z, but also on the Eddington factor, and the stellar temperature. We c...

  6. THE RUNAWAYS AND ISOLATED O-TYPE STAR SPECTROSCOPIC SURVEY OF THE SMC (RIOTS4)

    Energy Technology Data Exchange (ETDEWEB)

    Lamb, J. B.; Oey, M. S.; Segura-Cox, D. M.; Graus, A. S.; Golden-Marx, J. B. [Astronomy Department, University of Michigan, 1085 S. University Ave., Ann Arbor, MI 48109-1107 (United States); Kiminki, D. C. [Department of Astronomy, University of Arizona, Tucson, AZ 85721 (United States); Parker, J. Wm., E-mail: joellamb@umich.edu [Southwest Research Institute, Department of Space Studies, Suite 300, 1050 Walnut Street, Boulder, CO 80302-5150 (United States)

    2016-02-01

    We present the Runaways and Isolated O-Type Star Spectroscopic Survey of the SMC (RIOTS4), a spatially complete survey of uniformly selected field OB stars that covers the entire star-forming body of the Small Magellanic Cloud (SMC). Using the IMACS (Inamori-Magellan Areal Camera and Spectrograph) multislit spectrograph and MIKE (Magellan Inamori Kyocera Echelle) echelle spectrograph on the Magellan telescopes, we obtained spectra of 374 early-type field stars that are at least 28 pc from any other OB candidates. We also obtained spectra of an additional 23 field stars in the SMC bar identified from slightly different photometric criteria. Here, we present the observational catalog of stars in the RIOTS4 survey, including spectral classifications and radial velocities. For three multi-slit fields covering 8% of our sample, we carried out monitoring observations over 9–16 epochs to study binarity, finding a spectroscopic, massive binary frequency of at least ∼60% in this subsample. Classical Oe/Be stars represent a large fraction of RIOTS4 (42%), occurring at much higher frequency than in the Galaxy, consistent with expectation at low metallicity. RIOTS4 confirmed a steep upper initial mass function in the field, apparently caused by the inability of the most massive stars to form in the smallest clusters. Our survey also yields evidence for in situ field OB star formation, and properties of field emission-line star populations, including sgB[e] stars and classical Oe/Be stars. We also discuss the radial velocity distribution and its relation to SMC kinematics and runaway stars. RIOTS4 presents a first quantitative characterization of field OB stars in an external galaxy, including the contributions of sparse, but normal, star formation; runaway stars; and candidate isolated star formation.

  7. A survey for pulsations in A-type stars using SuperWASP

    Science.gov (United States)

    Holdsworth, Daniel L.

    2015-12-01

    "It is sound judgement to hope that in the not too distant future we shall be competent to understand so simple a thing as a star." - Sir Arthur Stanley Eddington, The Internal Constitution of Stars, 1926 A survey of A-type stars is conducted with the SuperWASP archive in the search for pulsationally variable stars. Over 1.5 million stars are selected based on their (J-H) colour. Periodograms are calculated for light curves which have been extracted from the archive and cleaned of spurious points. Peaks which have amplitudes greater than 0.5 millimagnitude are identified in the periodograms. In total, 202 656 stars are identified to show variability in the range 5-300 c/d. Spectroscopic follow-up was obtained for 38 stars which showed high-frequency pulsations between 60 and 235 c/d, and a further object with variability at 636 c/d. In this sample, 13 were identified to be normal A-type δ Sct stars, 14 to be pulsating metallic-lined Am stars, 11 to be rapidly oscillating Ap (roAp) stars, and one to be a subdwarf B variable star. The spectra were used not only to classify the stars, but to determine an effective temperature through Balmer line fitting. Hybrid stars have been identified in this study, which show pulsations in both the high- and low-overtone domains; an observation not predicted by theory. These stars are prime targets to perform follow-up observations, as a confirmed detection of this phenomenon will have significant impact on the theory of pulsations in A-type stars. The detected number of roAp stars has expanded the known number of this pulsator class by 22 per cent. Within these results both the hottest and coolest roAp star have been identified. Further to this, one object, KIC 7582608, was observed by the Kepler telescope for 4 yr, enabling a detailed frequency analysis. This analysis has identified significant frequency variations in this star, leading to the hypothesis that this is the first close binary star of its type. The observational

  8. Global Seismology of the Sun

    CERN Document Server

    Basu, Sarbani

    2016-01-01

    The seismic study of the Sun and other stars offers a unique window into the interior of these stars. Thanks to helioseismology, we know the structure of the Sun to admirable precision. In fact, our knowledge is good enough to use the Sun as a laboratory. We have also been able to study the dynamics of the Sun in great detail. Helioseismic data also allow us to probe the changes that take place in the Sun as solar activity waxes and wanes. The seismic study of stars other than the Sun is a fairly new endeavour, but we are making great strides in this field. In this review I discuss some of the techniques used in helioseismic analyses and the results obtained using those techniques. In this review I focus on results obtained with global helioseismology, i.e., the study of the Sun using its normal modes of oscillation. I also briefly touch upon asteroseismology, the seismic study of stars other than the Sun, and discuss how seismic data of others stars are interpreted.

  9. Exploring Photometric Methods for Identifying Emission-Line B-Type Stars

    Science.gov (United States)

    Glazier, Amy; Whelan, David

    2017-06-01

    Emission-line B-type stars, or Be stars, are a mysterious class of stars defined by their unique behavior: These stars eject material from their surfaces, forming a disc of gas that surrounds them. Furthermore, the gaseous disc is not necessarily a permanent feature of its host star. Some Be stars’ discs vary in structure over time, and may even disappear only to be regenerated later. Other Be stars may never show appreciable changes in the natures of their discs once they have been formed. The disc’s existence causes the appearance of characteristic emission lines in Be stars’ spectra, making spectroscopy the traditional method for identifying Be stars. However, spectroscopy is an inefficient and time-consuming method of finding Be stars, because it allows for only a single star to be observed in each exposure, and each star may require multiple exposures for durations of many minutes. Photometry, on the other hand, can be used to observe many stars simultaneously, but at the cost of the greater detail afforded by spectroscopy. While photometry has been used to identify Be stars, its success has been limited. In this work, we present a novel photometric technique that enables efficient identification of Be stars.

  10. Distribution of Late-type Stars around IC 4665

    Science.gov (United States)

    Fronto, A.; Balazs, L. G.; Paparo, M.

    1990-01-01

    We have investigated 424 stars of F8 spectral types and later in a 19.5 sq. degree field around IC 4665. The main purpose of our study in this low latitude field (b = +16.5 in our case) was the testing of the plane-parallel hypothesis of the density distribution, i.e. the hypothesis that the spatial density of the Population I stars observed at great angular distance from the galactic caps is well approximated by the z = r sin (b) scaling of the distributions obtained in the polar regions. We used the factor analysis of multivariate mathematical statistics in order to extract the effect of absorption from the photometric data. To identify the factor component describing the interstellar reddening we invoked the corresponding IRAS Sky Flux Data. We computed the spatial densities for the F8 - G5 dwarfs and the K giants separately. We used a maximum likelihood algorithm for oblating the space densities. We arrived at the following main conclusions in our paper: The absorbing material concentrates closer than 150 pc in our area. There is a weak but still significant correlation between the optical measures of absorption and the IRAS 100 micron Sky Flux Maps data. The spatial densities of F8 - G5 dwarfs essentially reflect the densities obtained in the galactic plane. The distribution of distance moduli of K giants in our sample can be well modelled by the z = sin (b) scaling of Upgren's data from the North Polar region. The actual form of the space density curve of the K giants can be satisfactorily fitted both by an isothermal model and an exponential model.

  11. The Wolf-Rayet stars in M31: I. Analysis of the late-type WN stars

    CERN Document Server

    Sander, Andreas; Hainich, Rainer; Hamann, Wolf-Rainer

    2014-01-01

    Context: Comprehensive studies of Wolf-Rayet stars were performed in the past for the Galactic and the LMC population. The results revealed significant differences, but also unexpected similarities between the WR populations of these different galaxies. Analyzing the WR stars in M31 will extend our understanding of these objects in different galactic environments. Aims: The present study aims at the late-type WN stars in M31. The stellar and wind parameters will tell about the formation of WR stars in other galaxies with different metallicity and star formation histories. The obtained parameters will provide constraints to the evolution of massive stars in the environment of M31. Methods: We used the latest version of the Potsdam Wolf-Rayet model atmosphere code to analyze the stars via fitting optical spectra and photometric data. To account for the relatively low temperatures of the late WN10 and WN11 subtypes, our WN models have been extended into this temperature regime. Results: Stellar and atmospheric p...

  12. The MiMeS survey of Magnetism in Massive Stars: magnetic analysis of the O-type stars

    Science.gov (United States)

    Grunhut, J. H.; Wade, G. A.; Neiner, C.; Oksala, M. E.; Petit, V.; Alecian, E.; Bohlender, D. A.; Bouret, J.-C.; Henrichs, H. F.; Hussain, G. A. J.; Kochukhov, O.; MiMeS Collaboration

    2017-02-01

    We present the analysis performed on spectropolarimetric data of 97 O-type targets included in the framework of the Magnetism in Massive Stars (MiMeS) Survey. Mean least-squares deconvolved Stokes I and V line profiles were extracted for each observation, from which we measured the radial velocity, rotational and non-rotational broadening velocities, and longitudinal magnetic field Bℓ. The investigation of the Stokes I profiles led to the discovery of two new multiline spectroscopic systems (HD 46106, HD 204827) and confirmed the presence of a suspected companion in HD 37041. We present a modified strategy of the least-squares deconvolution technique aimed at optimizing the detection of magnetic signatures while minimizing the detection of spurious signatures in Stokes V. Using this analysis, we confirm the detection of a magnetic field in six targets previously reported as magnetic by the MiMeS collaboration (HD 108, HD 47129A2, HD 57682, HD 148937, CPD-28 2561, and NGC 1624-2), as well as report the presence of signal in Stokes V in three new magnetic candidates (HD 36486, HD 162978, and HD 199579). Overall, we find a magnetic incidence rate of 7 ± 3 per cent, for 108 individual O stars (including all O-type components part of multiline systems), with a median uncertainty of the Bℓ measurements of about 50 G. An inspection of the data reveals no obvious biases affecting the incidence rate or the preference for detecting magnetic signatures in the magnetic stars. Similar to A- and B-type stars, we find no link between the stars' physical properties (e.g. Teff, mass, and age) and the presence of a magnetic field. However, the Of?p stars represent a distinct class of magnetic O-type stars.

  13. First Detection of Thermal Radio Emission from Solar-Type Stars with the Karl G. Jansky Very Large Array

    CERN Document Server

    Villadsen, Jackie; Bourke, Stephen; Güdel, Manuel; Rupen, Michael

    2014-01-01

    We present the first detections of thermal radio emission from the atmospheres of solar-type stars {\\tau} Cet, {\\eta} Cas A, and 40 Eri A. These stars all resemble the Sun in age and level of magnetic activity, as indicated by X-ray luminosity and chromospheric emission in calcium-II H and K lines. We observed these stars with the Karl G. Jansky Very Large Array with sensitivities of a few {\\mu}Jy at combinations of 10.0, 15.0, and 34.5 GHz. {\\tau} Cet, {\\eta} Cas A, and 40 Eri A are all detected at 34.5 GHz with signal-to-noise ratios of 6.5, 5.2, and 4.5, respectively. 15.0-GHz upper limits imply a rising spectral index greater than 1.0 for {\\tau} Cet and 1.6 for {\\eta} Cas A, at the 95% confidence level. The measured 34.5-GHz flux densities correspond to stellar disk-averaged brightness temperatures of roughly 10,000 K, similar to the solar brightness temperature at the same frequency. We explain this emission as optically- thick thermal free-free emission from the chromosphere, with possible contributions...

  14. Physical characterization of Galactic O-type stars targeted by the IACOB and OWN surveys

    Science.gov (United States)

    Holgado, G.; Simón-Díaz, S.; Barbá, R.

    2017-03-01

    We present first results from the quantitative spectroscopic analysis of ˜ 270 Galactic O-type stars targeted by the IACOB and OWN surveys (implying the largest sample of stars of this type analyzed homogeneously). We also evaluate what is the present situation regarding available information about distances, as provided by the Hipparcos and Gaia missions

  15. Stellar populations and star formation histories in late-type dwarfs

    CERN Document Server

    Tosi, M P

    2003-01-01

    Studies of the resolved stellar populations in nearby systems are crucial to understand galaxy evolution. Here, we summarize how the interpretation of the colour-magnitude diagrams of field stars in late-type dwarfs inside and outside the Local Group has allowed us to infer their star formation histories and put useful constraints on the evolution of this type of galaxies.

  16. Physical characterization of Galactic O-type stars targeted by the IACOB and OWN surveys

    CERN Document Server

    Holgado, G; Barbá, R H

    2016-01-01

    We present first results from the quantitative spectroscopic analysis of 266 Galactic O-type stars targeted by the IACOB and OWN surveys (implying the largest sample of stars of this type analyzed homogeneously). We also evaluate what is the present situation regarding available information about distances, as provided by the Hipparcos and Gaia missions.

  17. Revealing the nature of star forming blue early-type galaxies at low redshift

    CERN Document Server

    George, Koshy

    2015-01-01

    Context: Star forming early-type galaxies with blue optical colours at low redshift can be used to test our current understanding of galaxy formation and evolution. Aims: We want to reveal the fuel and triggering mechanism for star formation in these otherwise passively evolving red and dead stellar systems. Methods: We undertook an optical and ultraviolet study of 55 star forming blue early-type galaxies, searching for signatures of recent interactions that could be driving the molecular gas into the galaxy and potentially triggering the star formation. Results: We report here our results on star forming blue early-type galaxies with tidal trails and in close proximity to neighbouring galaxies that are evidence of ongoing or recent interactions between galaxies. There are 12 galaxies with close companions with similar redshifts, among which two galaxies are having ongoing interactions that potentially trigger the star formation. Two galaxies show a jet feature that could be due to the complete tidal disrupti...

  18. A Helicity-Based Method to Infer the CME Magnetic Field Magnitude in Sun and Geospace: Generalization and Extension to Sun-Like and M-Dwarf Stars and Implications for Exoplanet Habitability

    Science.gov (United States)

    Patsourakos, S.; Georgoulis, M. K.

    2017-07-01

    Patsourakos et al. ( Astrophys. J. 817, 14, 2016) and Patsourakos and Georgoulis ( Astron. Astrophys. 595, A121, 2016) introduced a method to infer the axial magnetic field in flux-rope coronal mass ejections (CMEs) in the solar corona and farther away in the interplanetary medium. The method, based on the conservation principle of magnetic helicity, uses the relative magnetic helicity of the solar source region as input estimates, along with the radius and length of the corresponding CME flux rope. The method was initially applied to cylindrical force-free flux ropes, with encouraging results. We hereby extend our framework along two distinct lines. First, we generalize our formalism to several possible flux-rope configurations (linear and nonlinear force-free, non-force-free, spheromak, and torus) to investigate the dependence of the resulting CME axial magnetic field on input parameters and the employed flux-rope configuration. Second, we generalize our framework to both Sun-like and active M-dwarf stars hosting superflares. In a qualitative sense, we find that Earth may not experience severe atmosphere-eroding magnetospheric compression even for eruptive solar superflares with energies {≈} 104 times higher than those of the largest Geostationary Operational Environmental Satellite (GOES) X-class flares currently observed. In addition, the two recently discovered exoplanets with the highest Earth-similarity index, Kepler 438b and Proxima b, seem to lie in the prohibitive zone of atmospheric erosion due to interplanetary CMEs (ICMEs), except when they possess planetary magnetic fields that are much higher than that of Earth.

  19. Lessons from the Sun

    Directory of Open Access Journals (Sweden)

    Robitaille P.-M.

    2011-07-01

    Full Text Available In this brief note, the implications of a condensed Sun will be examined. A celestial body composed of liquid metallic hydrogen brings great promise to astronomy, relative to understanding thermal emission and solar structure. At the same time, as an incom- pressible liquid, a condensed Sun calls into question virtually everything which is cur- rently believed with respect to the evolution and nature of the stars. Should the Sun be condensed, then neutron stars and white dwarfs will fail to reach the enormous densities they are currently believed to possess. Much of cosmology also falls into question, as the incompressibility of matter curtails any thought that a primordial atom once existed. Aging stars can no longer collapse and black holes will know no formative mechanism. A condensed Sun also hints that great strides must still be made in understanding the nature of liquids. The Sun has revealed that liquids possess a much greater potential for lattice order than previously believed. In addition, lessons may be gained with regards to the synthesis of liquid metallic hydrogen and the use of condensed matter as the basis for initiating fusion on Earth.

  20. Multi-Mode Oscillations in Classical Cepheids and RR Lyrae-Type Stars

    CERN Document Server

    Moskalik, Paweł

    2014-01-01

    I review different types of multi-mode pulsations observed in classical Cepheids and in RR Lyrae-type star. The presentation concentrates on the newest results, with special emphasis on recently detected nonradial oscillations.

  1. Origin of the Lyman excess in early-type stars

    CERN Document Server

    Cesaroni, R; Beltrán, M T; Molinari, S; Olmi, L; Treviño-Morales, S P

    2016-01-01

    Ionized regions around early-type stars are believed to be well-known objects, but until recently, our knowledge of the relation between the free-free radio emission and the IR emission has been observationally hindered by the limited angular resolution in the far-IR. The advent of Herschel has now made it possible to obtain a more precise comparison between the two regimes, and it has been found that about a third of the young HII regions emit more Lyman continuum photons than expected, thus presenting a Lyman excess. With the present study we wish to distinguish between two scenarios that have been proposed to explain the existence of the Lyman excess: (i) underestimation of the bolometric luminosity, or (ii) additional emission of Lyman-continuum photons from an accretion shock. We observed an outflow (SiO) and an infall (HCO+) tracer toward a complete sample of 200 HII regions, 67 of which present the Lyman excess. Our goal was to search for any systematic difference between sources with Lyman excess and ...

  2. Spectroscopic survey of Kepler stars. I. HERMES/Mercator observations of A- and F-type stars

    CERN Document Server

    Niemczura, E; Smalley, B; Uytterhoeven, K; Pigulski, A; Lehmann, H; Bowman, D M; Catanzaro, G; van Aarle, E; Bloemen, S; Briquet, M; De Cat, P; Drobek, D; Eyer, L; Gameiro, J F S; Gorlova, N; Kaminski, K; Lampens, P; Marcos-Arenal, P; Papics, P I; Vandenbussche, B; Van Winckel, H; Steslicki, M; Fagas, M

    2015-01-01

    The Kepler space mission provided near-continuous and high-precision photometry of about 207,000 stars, which can be used for asteroseismology. However, for successful seismic modelling it is equally important to have accurate stellar physical parameters. Therefore, supplementary ground-based data are needed. We report the results of the analysis of high-resolution spectroscopic data of A- and F-type stars from the Kepler field, which were obtained with the HERMES spectrograph on the Mercator telescope. We determined spectral types, atmospheric parameters and chemical abundances for a sample of 117 stars. Hydrogen Balmer, Fe I, and Fe II lines were used to derive effective temperatures, surface gravities, and microturbulent velocities. We determined chemical abundances and projected rotational velocities using a spectrum synthesis technique. The atmospheric parameters obtained were compared with those from the Kepler Input Catalogue (KIC), confirming that the KIC effective temperatures are underestimated for ...

  3. Kepler-20: A Sun-like Star with Three Sub-Neptune Exoplanets and Two Earth-size Candidates

    CERN Document Server

    Gautier, Thomas N; Rowe, Jason F; Marcy, Geoffrey W; Isaacson, Howard; Torres, Guillermo; Fressin, Francois; Rogers, Leslie A; Désert, Jean-Michel; Buchhave, Lars A; Latham, David W; Quinn, Samuel N; Ciardi, David R; Fabrycky, Daniel C; Ford, Eric B; Gilliland, Ronald L; Walkowicz, Lucianne M; Bryson, Stephen T; Cochran, William D; Endl, Michael; Fischer, Debra A; Howel, Steve B; Horch, Elliott P; Barclay, Thomas; Batalha, Natalie; Borucki, William J; Christiansen, Jessie L; Geary, John C; Henze, Christopher E; Holman, Matthew J; Ibrahim, Khadeejah; Jenkins, Jon M; Kinemuchi, Karen; Koch, David G; Lissauer, Jack J; Sanderfer, Dwight T; Sasselov, Dimitar D; Seager, Sara; Silverio, Kathryn; Smith, Jeffrey C; Still, Martin; Stumpe, Martin C; Tenenbaum, Peter; Van Cleve, Jeffrey

    2011-01-01

    We present the discovery of the Kepler-20 planetary system, which we initially identified through the detection of five distinct periodic transit signals in the Kepler light curve of the host star 2MASSJ19104752+4220194. We find a stellar effective temperature Teff=5455+-100K, a metallicity of [Fe/H]=0.01+-0.04, and a surface gravity of log(g)=4.4+-0.1. Combined with an estimate of the stellar density from the transit light curves we deduce a stellar mass of Mstar=0.912+-0.034 Msun and a stellar radius of Rstar=0.944^{+0.060}_{-0.095} Rsun. For three of the transit signals, our results strongly disfavor the possibility that these result from astrophysical false positives. We conclude that the planetary scenario is more likely than that of an astrophysical false positive by a factor of 2e5 (Kepler-20b), 1e5 (Kepler-20c), and 1.1e3 (Kepler-20d), sufficient to validate these objects as planetary companions. For Kepler-20c and Kepler-20d, the blend scenario is independently disfavored by the achromaticity of the ...

  4. Circumnuclear Regions of Star Formation in Early Type Galaxies

    CERN Document Server

    Diaz, Angeles I; Hagele, Guillermo F; Castellanos, Marcelo

    2008-01-01

    Circumnuclear star forming regions, also called hotspots, are often found in the inner regions of some spiral galaxies where intense processes of star formation are taking place. In the UV, massive stars dominate the observed circumnuclear emission even in the presence of an active nucleus, contributing between 30 and 50% to the H$\\beta$ total emission of the nuclear zone. Spectrophotometric data of moderate resolution (3000 < R < 11000) are presented from which the physical properties of the ionized gas: electron density, oxygen abundances, ionization structure etc. have been derived.

  5. Properties of an Earth-like planet orbiting a Sun-like star: Earth observed by the EPOXI mission.

    Science.gov (United States)

    Livengood, Timothy A; Deming, L Drake; A'hearn, Michael F; Charbonneau, David; Hewagama, Tilak; Lisse, Carey M; McFadden, Lucy A; Meadows, Victoria S; Robinson, Tyler D; Seager, Sara; Wellnitz, Dennis D

    2011-11-01

    NASA's EPOXI mission observed the disc-integrated Earth and Moon to test techniques for reconnoitering extrasolar terrestrial planets, using the Deep Impact flyby spacecraft to observe Earth at the beginning and end of Northern Hemisphere spring, 2008, from a range of ∼1/6 to 1/3 AU. These observations furnish high-precision and high-cadence empirical photometry and spectroscopy of Earth, suitable as "ground truth" for numerically simulating realistic observational scenarios for an Earth-like exoplanet with finite signal-to-noise ratio. Earth was observed at near-equatorial sub-spacecraft latitude on 18-19 March, 28-29 May, and 4-5 June (UT), in the range of 372-4540 nm wavelength with low visible resolving power (λ/Δλ=5-13) and moderate IR resolving power (λ/Δλ=215-730). Spectrophotometry in seven filters yields light curves at ∼372-948 nm filter-averaged wavelength, modulated by Earth's rotation with peak-to-peak amplitude of ≤20%. The spatially resolved Sun glint is a minor contributor to disc-integrated reflectance. Spectroscopy at 1100-4540 nm reveals gaseous water and carbon dioxide, with minor features of molecular oxygen, methane, and nitrous oxide. One-day changes in global cloud cover resulted in differences between the light curve beginning and end of ≤5%. The light curve of a lunar transit of Earth on 29 May is color-dependent due to the Moon's red spectrum partially occulting Earth's relatively blue spectrum. The "vegetation red edge" spectral contrast observed between two long-wavelength visible/near-IR bands is ambiguous, not clearly distinguishing between the verdant Earth diluted by cloud cover versus the desolate mineral regolith of the Moon. Spectrophotometry in at least one other comparison band at short wavelength is required to distinguish between Earth-like and Moon-like surfaces in reconnaissance observations. However, measurements at 850 nm alone, the high-reflectance side of the red edge, could be sufficient to

  6. Sun Allergy

    Science.gov (United States)

    ... if you have unusual, bothersome skin reactions after exposure to sunlight. For severe or persistent symptoms, you may need ... m. when the sun is brightest. Avoid sudden exposure to lots of sunlight. Many people have sun allergy symptoms when they ...

  7. A nova re-accretion model for J-type carbon stars

    CERN Document Server

    Sengupta, S; Lau, H H B

    2013-01-01

    The J-type carbon (J)-stars constitute 10-15% of the observed carbon stars in both our Galaxy and the Large Magellanic Cloud (LMC). They are characterized by strong 13C absorption bands with low 12C/13C ratios along with other chemical signatures peculiar for typical carbon stars, e.g. a lack of s-process enhancement. Most of the J-stars are dimmer than the N-type carbon stars some of which, by hot-bottom burning, make 13C only in a narrow range of masses. We investigate a binary-star formation channel for J-stars involving re-accretion of carbon-rich nova ejecta on main-sequence companions to low-mass carbon-oxygen white-dwarfs. The subsequent evolution of the companion stars in such systems is studied with a rapid binary evolutionary code to predict chemical signatures of nova pollution in systems which merge into giant single stars. A detailed population synthesis study is performed to estimate the number of these mergers and compare their properties with observed J-stars. Our results predict that such nov...

  8. IMPROVED V II log(gf) VALUES, HYPERFINE STRUCTURE CONSTANTS, AND ABUNDANCE DETERMINATIONS IN THE PHOTOSPHERES OF THE SUN AND METAL-POOR STAR HD 84937

    Energy Technology Data Exchange (ETDEWEB)

    Wood, M. P.; Lawler, J. E.; Den Hartog, E. A. [Department of Physics, University of Wisconsin, Madison, WI 53706 (United States); Sneden, C. [Department of Astronomy and McDonald Observatory, University of Texas, Austin, TX 78712 (United States); Cowan, J. J., E-mail: mpwood@wisc.edu, E-mail: jelawler@wisc.edu, E-mail: eadenhar@wisc.edu, E-mail: chris@verdi.as.utexas.edu, E-mail: cowan@nhn.ou.edu [Homer L. Dodge Department of Physics and Astronomy, University of Oklahoma, Norman, OK 73019 (United States)

    2014-10-01

    New experimental absolute atomic transition probabilities are reported for 203 lines of V II. Branching fractions are measured from spectra recorded using a Fourier transform spectrometer and an echelle spectrometer. The branching fractions are normalized with radiative lifetime measurements to determine the new transition probabilities. Generally good agreement is found between this work and previously reported V II transition probabilities. Two spectrometers, independent radiometric calibration methods, and independent data analysis routines enable a reduction in systematic uncertainties, in particular those due to optical depth errors. In addition, new hyperfine structure constants are measured for selected levels by least squares fitting line profiles in the FTS spectra. The new V II data are applied to high resolution visible and UV spectra of the Sun and metal-poor star HD 84937 to determine new, more accurate V abundances. Lines covering a range of wavelength and excitation potential are used to search for non-LTE effects. Very good agreement is found between our new solar photospheric V abundance, log ε(V) = 3.95 from 15 V II lines, and the solar-system meteoritic value. In HD 84937, we derive [V/H] = –2.08 from 68 lines, leading to a value of [V/Fe] = 0.24.

  9. Improved log(gf) Values for Lines of V I and V II, New Vanadium Abundances in the Sun and the Metal-Poor Star HD 84937

    Science.gov (United States)

    Lawler, James E.; Wood, Michael P.; Den Hartog, Elizabeth; Feigenson, Thomas; Sneden, Chris; Cowan, John J.

    2015-01-01

    New emission branching fraction measurements for 836 lines of the first spectrum of vanadium (V I) and 203 lines of V II are determined from hollow cathode lamp spectra recorded with the National Solar Observatory 1m Fourier transform spectrometer (FTS) and a high resolution echelle spectrometer. The branching fractions are combined with new radiative lifetimes from laser induced fluorescence measurements to determine accurate absolute atomic transition probabilities for 1039 lines of V I and V II. The FTS data are also used to extract new hyperfine structure A coefficients for both spectra. These new laboratory data are applied to determine the V abundance in the Sun and metal-poor star HD 84937, yielding log ɛ(V) = 3.96 (σ = 0.04) based on 93 V I lines and log ɛ(V) = 1.89 (σ = 0.07) based on nine V I lines respectively, and yielding log ɛ(V) = 3.95 (σ = 0.05) based on 15 V II lines and log ɛ(V) = 1.87 (σ = 0.07) based on 68 V II lines respectively1-3.1. Wood et al., ApJS 214:18 (2014), 2. Den Hartog et al. ApJS in press (2014), 3. Lawler et al. ApJS submitted (2014). This work is supported by NASA grant NNX10AN93G (JEL), NSF AST-1211055 (EDH & JEL), and NSF AST-1211585 (CS).

  10. MagAO Imaging of Long-period Objects (MILO). I. A Benchmark M Dwarf Companion Exciting a Massive Planet around the Sun-like Star HD 7449

    CERN Document Server

    Rodigas, Timothy J; Faherty, Jackie; Anglada-Escude, Guillem; Kaib, Nathan; Butler, R Paul; Shectman, Stephen; Weinberger, Alycia; Males, Jared R; Morzinski, Katie M; Close, Laird M; Hinz, Philip M; Crane, Jeffrey D; Thompson, Ian; Teske, Johanna; Diaz, Matias; Minniti, Dante; Lopez-Morales, Mercedes; Adams, Fred C; Boss, Alan P

    2015-01-01

    We present high-contrast Magellan adaptive optics (MagAO) images of HD 7449, a Sun-like star with one planet and a long-term radial velocity (RV) trend. We unambiguously detect the source of the long-term trend from 0.6-2.15 \\microns ~at a separation of \\about 0\\fasec 54. We use the object's colors and spectral energy distribution to show that it is most likely an M4-M5 dwarf (mass \\about 0.1-0.2 \\msun) at the same distance as the primary and is therefore likely bound. We also present new RVs measured with the Magellan/MIKE and PFS spectrometers and compile these with archival data from CORALIE and HARPS. We use a new Markov chain Monte Carlo procedure to constrain both the mass ($> 0.17$ \\msun ~at 99$\\%$ confidence) and semimajor axis (\\about 18 AU) of the M dwarf companion (HD 7449B). We also refine the parameters of the known massive planet (HD 7449Ab), finding that its minimum mass is $7.8^{+3.7}_{-1.35}$ \\mj, its semimajor axis is $2.33^{+0.01}_{-0.02}$ AU, and its eccentricity is $0.8^{+0.08}_{-0.06}$. ...

  11. Synthetic spectra for O and B type subdwarf stars

    CERN Document Server

    Nemeth, Peter; Tremblay, Pier-Emmanuel; Hubeny, Ivan

    2013-01-01

    We present a grid of optical (3200--7200 \\AA) synthetic spectra calculated with Tlusty/Synspec. The new NLTE model atmospheres include the most recent hydrogen Stark broadening profiles; were calculated in opacity sampling and limited to pure H/He composition. The grid covers the observed parameter space of (He-)sdB and (He-)sdO stars, therefore it is suitable for the homogeneous spectral analyses of such evolved stars.

  12. Copernicus observations of the N v resonance doublet in 53 early-type stars

    Science.gov (United States)

    Abbott, D. C.; Bohlin, R. C.; Savage, B. D.

    1982-01-01

    UV spectra in the wavelength interval 1170-1270 A are presented for 53 early-type stars ranging in spectral type from O6.5 V to B2.5 IV. The sample includes four Wolf-Rayet stars, seven known Oe-Be stars, and six galactic halo OB stars. A qualitative analysis of the stellar N v doublet reveals that: (1) N v is present in all stars hotter and more luminous than type B0 for the main sequence, B1 for giants, and B2 for supergiants; (2) shell components of N v and an unidentified absorption feature at 1230 A are present in about half of the stars; (3) the column density of N v is well correlated with bolometric luminosity over the spectral range O6 to B2; and (4) the ratio of emission to absorption equivalent width is a factor of 2 smaller in the main sequence stars than in supergiants, which suggests that the wind structure changes as a star evolves. For several stars, this ratio is too small to be explained by traditional wind models.

  13. WASP-50b: a hot Jupiter transiting a moderately active solar-type star

    CERN Document Server

    Gillon, M; Lendl, M; Maxted, P F L; Triaud, A H M J; Anderson, D R; Barros, S C C; Bento, J; Collier-Cameron, A; Enoch, B; Faedi, F; Hellier, C; Jehin, E; Magain, P; Montalban, J; Pepe, F; Pollacco, D; Queloz, D; Smalley, B; Segransan, D; Smith, A M S; Southworth, J; Udry, S; West, R G; Wheatley, P J

    2011-01-01

    We report the discovery by the WASP transit survey of a giant planet in a close orbit (0.0295+-0.0009 AU) around a moderately bright (V=11.6, K=10) G9 dwarf (0.89+-0.08 M_sun, 0.84+-0.03 R_sun) in the Southern constellation Eridanus. Thanks to high-precision follow-up photometry and spectroscopy obtained by the telescopes TRAPPIST and Euler, the mass and size of this planet, WASP-50b, are well constrained to 1.47+-0.09 M_jup and 1.15+-0.05 R_jup, respectively. The transit ephemeris is 2455558.6120 (+-0.0002) + N x 1.955096 (+-0.000005) HJD_UTC. The size of the planet is consistent with basic models of irradiated giant planets. The chromospheric activity (log R'_HK = -4.67) and rotational period (P_rot = 16.3+-0.5 days) of the host star suggest an age of 0.8+-0.4 Gy that is discrepant with a stellar-evolution estimate based on the measured stellar parameters (rho_star = 1.48+-0.10 rho_sun, Teff = 5400+-100 K, [Fe/H]= -0.12+-0.08) which favours an age of 7+-3.5 Gy. This discrepancy could be explained by the tid...

  14. Spectroscopic observations of active solar-analog stars with high X-ray luminosity, as a proxy of superflare stars

    Science.gov (United States)

    Notsu, Yuta; Honda, Satoshi; Maehara, Hiroyuki; Notsu, Shota; Namekata, Kosuke; Nogami, Daisaku; Shibata, Kazunari

    2017-02-01

    Recent studies of solar-type superflare stars have suggested that even old slowly rotating stars similar to the Sun can have large starspots and superflares. We conducted high-dispersion spectroscopy of 49 nearby solar-analog stars (G-type main-sequence stars with Teff ≈ 5600-6000 K) identified as ROSAT soft X-ray sources, which are not binary stars from previous studies. We expected that these stars could be used as a proxy of bright solar-analog superflare stars, since superflare stars are expected to show strong X-ray luminosity. More than half (37) of the 49 target stars show no evidence of binarity, and their atmospheric parameters (temperature, surface gravity, and metallicity) are within the range of ordinary solar-analog stars. We measured the intensity of Ca II 8542 and Hα lines, which are good indicators of the stellar chromospheric activity. The intensity of these lines indicates that all the target stars have large starspots. We also measured v sin i (projected rotational velocity) and lithium abundance for the target stars. Li abundance is a key to understanding the evolution of the stellar convection zone, which reflects the stellar age, mass and rotational history. We confirmed that many of the target stars rapidly rotate and have high Li abundance, compared with the Sun, as suggested by many previous studies. There are, however, also some target stars that rotate slowly (v sin i = 2-3 km s-1) and have low Li abundance like the Sun. These results support that old and slowly rotating stars similar to the Sun could have high activity levels and large starspots. This is consistent with the results of our previous studies of solar-type superflare stars. In the future, it is important to conduct long-term monitoring observations of these active solar-analog stars in order to investigate detailed properties of large starspots from the viewpoint of stellar dynamo theory.

  15. A 40 Myr OLD GASEOUS CIRCUMSTELLAR DISK AT 49 CETI: MASSIVE CO-RICH COMET CLOUDS AT YOUNG A-TYPE STARS

    Energy Technology Data Exchange (ETDEWEB)

    Zuckerman, B. [Department of Physics and Astronomy, University of California, Los Angeles, CA 90095 (United States); Song, Inseok, E-mail: ben@astro.ucla.edu, E-mail: song@physast.uga.edu [Department of Physics and Astronomy, University of Georgia, Athens, GA 30602-2451 (United States)

    2012-10-20

    The gaseous molecular disk that orbits the main-sequence A-type star 49 Ceti has been known since 1995, but the stellar age and the origin of the observed carbon monoxide molecules have been unknown. We now identify 49 Ceti as a member of the 40 Myr old Argus Association and present a colliding comet model to explain the high CO concentrations seen at 49 Ceti and the 30 Myr old A-type star HD 21997. The model suggests that massive-400 Earth mass-analogs of the Sun's Kuiper Belt are in orbit around some A-type stars, that these large masses are composed primarily of comet-like objects, and that these objects are rich in CO and perhaps also CO{sub 2}. We identify additional early-type members of the Argus Association and the Tucana/Horologium and Columba Associations; some of these stars display excess mid-infrared emission as measured with the Widefield Infrared Survey Explorer.

  16. Steady-state evolution of debris disks around solar-type stars

    CERN Document Server

    Kains, N; Greaves, J S

    2011-01-01

    We present an analysis of debris disk data around Solar-type stars (spectral types F0-K5) using the steady-state analytical model of Wyatt et al. (2007). Models are fitted to published data from the FEPS (Meyer et al. 2006) project and various GTO programs obtained with MIPS on the Spitzer Space Telescope at 24 micron and 70 micron, and compared to a previously published analysis of debris disks around A stars using the same evolutionary model. We find that the model reproduces most features found in the data sets, noting that the model disk parameters for solar-type stars are different to those of A stars. Although this could mean that disks around Solar-type stars have different properties from their counterparts around earlier-type stars, it is also possible that the properties of disks around stars of different spectral types appear more different than they are because the blackbody disk radius underestimates the true disk radius by a factor $X_r$ which varies with spectral type. We use results from reali...

  17. Discovery of a magnetic field in the early B-type star σ Lupi

    NARCIS (Netherlands)

    Henrichs, H.F.; Kolenberg, K.; Plaggenborg, B.; Marsden, S.C.; Waite, I.A.; Landstreet, J.D.; Wade, G.A.; Grunhut, J.H.; Oksala, M.E.

    2012-01-01

    Context. Magnetic early B-type stars are rare. Indirect indicators are needed to identify them before investing in time-intensive spectropolarimetric observations. Aims. We use the strongest indirect indicator of a magnetic field in B stars, which is periodic variability of ultraviolet (UV) stellar

  18. Deep infrared imaging of close companions to austral A- and F-type stars

    CERN Document Server

    Ehrenreich, David; Montagnier, Guillaume; Chauvin, Gaël; Galland, Franck; Beuzit, Jean-Luc; Rameau, Julien

    2010-01-01

    The search for substellar companions around stars with different masses along the main sequence is critical to understand the different processes leading to the formation of low-mass stars, brown dwarfs, and planets. In particular, the existence of a large population of low-mass stars and brown dwarfs physically bound to early-type main-sequence stars could imply that the massive planets recently imaged at wide separations (10-100 AU) around A-type stars are disc-born objects in the low-mass tail of the binary distribution. Our aim is to characterize the environment of early-type main-sequence stars by detecting brown dwarf or low-mass star companions between 10 and 500 AU. High contrast and high angular resolution near-infrared images of a sample of 38 southern A- and F-type stars have been obtained between 2005 and 2009 with the instruments VLT/NaCo and CFHT/PUEO. Multi-epoch observations were performed to discriminate comoving companions from background contaminants. About 41 companion candidates were imag...

  19. Change in activity character of coronae of low-mass stars of various spectral types

    CERN Document Server

    Nizamov, B A; Livshits, M A

    2016-01-01

    We study the dependence of the coronal activity index on the star's rotation rate. This question was considered earlier for 824 late-type stars on the basis of a consolidated catalogue of the soft X-ray fluxes. We carry out a more refined analysis separately for G, K and M dwarfs. They distinctively exhibit two modes of activity. The first one is the saturation mode, it is characteristic of young stars and is practically not related to their rotation. The second one refers to the solar-type activity the level of which strongly depends on the rotation period. We show that the transition from one mode to another takes place at the rotation periods of 1.1, 3.3 and 7.2 days for the stars of spectral types G2, K4 and M3 respectively. In the light of the discovery of superflares on G and K stars on the Kepler spacecraft there arises a question of how these objects differ from other active late-type stars. We analyse the location of superflare stars relative to the stars observed by Kepler on the "amplitude of rotat...

  20. Asteroseismology of solar-type stars with Kepler: II. Stellar modeling

    DEFF Research Database (Denmark)

    Metcalfe , T.S.; Karoff, Christoffer

    2010-01-01

    Observations from the Kepler satellite were recently published for three bright G-type stars, which were monitored during the first 33.5 days of science operations. One of these stars, KIC 11026764, exhibits a characteristic pattern of oscillation frequencies suggesting that the star has evolved...... significantly. We have derived initial estimates of the properties of KIC 11026764 from the oscillation frequencies observed by Kepler, combined with ground-based spectroscopic data. We present preliminary results from detailed modeling of this star, employing a variety of independent codes and analyses...

  1. Weak magnetic fields in early-type stars: failed fossils

    CERN Document Server

    Braithwaite, Jonathan

    2012-01-01

    Weak magnetic fields have recently been detected in Vega and Sirius. Here, we explore the possibility that these fields are the remnants of some field inherited or created during or shortly after star formation and, unlike true fossil fields, are still evolving as we observe them. The timescale of this evolution is given in terms of the Alfven timescale and the rotation frequency by tau_evol ~ tau_A^2 Omega, which would be comparable to the age of the star. It is shown that it is likely that all intermediate- and high-mass stars contain fields of at least the order of the strength found so far in Vega and Sirius. Faster rotators are expected to have stronger magnetic fields. Stars may experience an increase in field strength during their early main-sequence, but for most of their lives field strength will decrease slowly. The length scale of the magnetic structure on the surface may be small in very young stars but should quickly increase to at least very approximately a fifth of the stellar radius.

  2. Tracking Planets around the Sun

    Science.gov (United States)

    Riddle, Bob

    2008-01-01

    In earlier columns, the celestial coordinate system of hour circles of right ascension and degrees of declination was introduced along with the use of an equatorial star chart (see SFA Star Charts in Resources). This system shows the planets' motion relative to the ecliptic, the apparent path the Sun follows during the year. An alternate system,…

  3. Tracking Planets around the Sun

    Science.gov (United States)

    Riddle, Bob

    2008-01-01

    In earlier columns, the celestial coordinate system of hour circles of right ascension and degrees of declination was introduced along with the use of an equatorial star chart (see SFA Star Charts in Resources). This system shows the planets' motion relative to the ecliptic, the apparent path the Sun follows during the year. An alternate system,…

  4. A grid of MARCS model atmospheres for late-type stars. II. S stars and their properties

    Science.gov (United States)

    Van Eck, Sophie; Neyskens, Pieter; Jorissen, Alain; Plez, Bertrand; Edvardsson, Bengt; Eriksson, Kjell; Gustafsson, Bengt; Jørgensen, Uffe Gråe; Nordlund, Åke

    2017-05-01

    S-type stars are late-type giants whose atmospheres are enriched in carbon and s-process elements because of either extrinsic pollution by a binary companion or intrinsic nucleosynthesis and dredge-up on the thermally-pulsing asymptotic giant branch. A grid of MARCS model atmospheres has been computed for S stars, covering the range 2700 ≤ Teff(K) ≤ 4000, 0.50 ≤ C/O ≤ 0.99, 0 ≤ log g ≤ 5, [Fe/H] = 0., -0.5 dex, and [s/Fe] = 0, 1, and 2 dex (where the latter quantity refers to the global overabundance of s-process elements). The MARCS models make use of a new ZrO line list. Synthetic spectra computed from these models are used to derive photometric indices in the Johnson and Geneva systems, as well as TiO and ZrO band strengths. A method is proposed to select the model best matching any given S star, a non-trivial operation since the grid contains more than 3500 models covering a five-dimensional parameter space. The method is based on the comparison between observed and synthetic photometric indices and spectral band strengths, and has been applied on a vast subsample of the Henize sample of S stars. Our results confirm the old claim by Piccirillo (1980, MNRAS, 190, 441) that ZrO bands in warm S stars (Teff>3200 K) are not caused by the C/O ratio being close to unity, as traditionally believed, but rather by some Zr overabundance. The TiO and ZrO band strengths, combined with V-K and J-K photometric indices, are used to select Teff, C/O, [Fe/H] and [s/Fe]. The Geneva U-B1 and B2-V1 indices (or any equivalent) are good at selecting the gravity. The defining spectral features of dwarf S stars are outlined, but none is found among the Henize S stars. More generally, it is found that, at Teff = 3200 K, a change of C/O from 0.5 to 0.99 has a strong impact on V-K (2 mag). Conversely, a range of 2 mag in V-K corresponds to a 200 K shift along the (Teff, V-K) relationship (for a fixed C/O value). Hence, the use of a (Teff, V-K) calibration established for M

  5. Extracting Radial Velocities of A- and B-type Stars from Echelle Spectrograph Calibration Spectra

    Science.gov (United States)

    Becker, Juliette C.; Johnson, John Asher; Vanderburg, Andrew; Morton, Timothy D.

    2015-04-01

    We present a technique to extract radial velocity (RV) measurements from echelle spectrograph observations of rapidly rotating stars (V sin i≳ 50 km s-1). This type of measurement is difficult because the line widths of such stars are often comparable to the width of a single echelle order. To compensate for the scarcity of lines and Doppler information content, we have developed a process that forward-models the observations, fitting the RV shift of the star for all echelle orders simultaneously with the echelle blaze function. We use our technique to extract RV measurements from a sample of rapidly rotating A- and B-type stars used as calibrator stars observed by the California Planet Survey observations. We measure absolute RVs with a precision ranging from 0.5-2.0 km s-1 per epoch for more than 100 A- and B-type stars. In our sample of 10 well-sampled stars with RV scatter in excess of their measurement uncertainties, three of these are single-lined binaries with long observational baselines. From this subsample, we present detections of two previously unknown spectroscopic binaries and one known astrometric system. Our technique will be useful in measuring or placing upper limits on the masses of sub-stellar companions discovered by wide-field transit surveys, and conducting future spectroscopic binarity surveys and Galactic space-motion studies of massive and/or young, rapidly rotating stars.

  6. Spectroscopic properties of nearby late-type stars, members of stellar kinematic groups

    CERN Document Server

    Maldonado, J; Eiroa, C; Montes, D; Montesinos, B

    2010-01-01

    Nearby late-type stars are excellent targets to look for young objects in stellar associations and moving groups. The study of these groups goes back more than one century ago however, their origin is still misunderstood. Although their existence have been confirmed by statistical studies of large sample of stars, the identification of a group of stars as member of moving groups, is not an easy task, list of members often change with time and most members have been identified by means of kinematics criteria which is not sufficient since many old stars can share the same spatial motion of those stars in moving groups. In this contribution we attempt to identify unambiguous moving groups members, among a sample of nearby-late type stars. High resolution echelle spectra is used to i) derive accurate radial velocities which allow us to study the stars' kinematics and make a first selection of moving groups members; and ii) analyze several age-related properties for young late-type stars (i.e., lithium LiI 6707.8 ...

  7. A BCool survey of the magnetic fields of planet-hosting solar-type stars

    Science.gov (United States)

    Mengel, M. W.; Marsden, S. C.; Carter, B. D.; Horner, J.; King, R.; Fares, R.; Jeffers, S. V.; Petit, P.; Vidotto, A. A.; Morin, J.; BCool Collaboration

    2017-03-01

    We present a spectropolarimetric snapshot survey of solar-type planet-hosting stars. In addition to 14 planet-hosting stars observed as part of the BCool magnetic snapshot survey, we obtained magnetic observations of a further 19 planet-hosting solar-type stars in order to see if the presence of close-in planets had an effect on the measured surface magnetic field (|Bℓ|). Our results indicate that the magnetic activity of this sample is congruent with that of the overall BCool sample. The effects of the planetary systems on the magnetic activity of the parent star, if any, are too subtle to detect compared to the intrinsic dispersion and correlations with rotation, age and stellar activity proxies in our sample. Four of the 19 newly observed stars, two of which are subgiants, have unambiguously detected magnetic fields and are future targets for Zeeman-Doppler mapping.

  8. A BCool survey of the magnetic fields of planet-hosting solar-type stars

    CERN Document Server

    Mengel, M W; Carter, B D; Horner, J; King, R; Fares, R; Jeffers, S V; Petit, P; Vidotto, A A; Morin, J

    2016-01-01

    We present a spectropolarimetric snapshot survey of solar-type planet hosting stars. In addition to 14 planet-hosting stars observed as part of the BCool magnetic snapshot survey, we obtained magnetic observations of a further 19 planet-hosting solar-type stars in order to see if the presence of close-in planets had an effect on the measured surface magnetic field (|B$_{\\ell}$|). Our results indicate that the magnetic activity of this sample is congruent with that of the overall BCool sample. The effects of the planetary systems on the magnetic activity of the parent star, if any, are too subtle to detect compared to the intrinsic dispersion and correlations with rotation, age and stellar activity proxies in our sample. Four of the 19 newly observed stars, two of which are subgiants, have unambiguously detected magnetic fields and are future targets for Zeeman Doppler Mapping.

  9. PROJECTED ROTATIONAL VELOCITIES OF 136 EARLY B-TYPE STARS IN THE OUTER GALACTIC DISK

    Energy Technology Data Exchange (ETDEWEB)

    Garmany, C. D.; Glaspey, J. W. [National Optical Astronomy Observatory, 950 N. Cherry Ave., Tucson, AZ 85719 (United States); Bragança, G. A.; Daflon, S.; Fernandes, M. Borges; Cunha, K. [Observatório Nacional-MCTI, Rua José Cristino, 77. CEP: 20921-400, Rio de Janeiro, RJ (Brazil); Oey, M. S. [University of Michigan, Department of Astronomy, 311 West Hall, 1085 S. University Ave., Ann Arbor, MI: 48109-1107 (United States); Bensby, T., E-mail: garmany@noao.edu [Lund Observatory, Department of Astronomy and Theoretical Physics, Box 43, SE-22100, Lund (Sweden)

    2015-08-15

    We have determined projected rotational velocities, v sin i, from Magellan/MIKE echelle spectra for a sample of 136 early B-type stars having large Galactocentric distances. The target selection was done independently of their possible membership in clusters, associations or field stars. We subsequently examined the literature and assigned each star as Field, Association, or Cluster. Our v sin i results are consistent with a difference in aggregate v sin i with stellar density. We fit bimodal Maxwellian distributions to the Field, Association, and Cluster subsamples representing sharp-lined and broad-lined components. The first two distributions, in particular, for the Field and Association are consistent with strong bimodality in v sin i. Radial velocities are also presented, which are useful for further studies of binarity in B-type stars, and we also identify a sample of possible new double-lined spectroscopic binaries. In addition, we find 18 candidate Be stars showing emission at Hα.

  10. Exploring the origin of magnetic fields in massive stars: A survey of O-type stars in clusters and in the field

    CERN Document Server

    Hubrig, S; Kharchenko, N V; Langer, N; de Wit, W J; Ilyin, I; Kholtygin, A F; Piskunov, A E; Przybilla, N

    2011-01-01

    To investigate statistically whether magnetic fields in massive stars are ubiquitous or appear in stars with specific spectral classification, certain ages, or in a special environment, we acquired 41 new spectropolarimetric observations for 36 stars. Among the observed sample roughly half of the stars are probable members of clusters at different ages, whereas the remaining stars are field stars not known to belong to any cluster or association. Spectropolarimetric observations were obtained during three different nights using the low-resolution spectropolarimetric mode of FORS2 (FOcal Reducer low dispersion Spectrograph) mounted on the 8-m Antu telescope of the VLT. To assess the membership in open clusters and associations, we used astrometric catalogues with the best currently available kinematic and photometric data. A field at a significance level of 3sigma was detected in ten O-type stars. Importantly, the largest longitudinal magnetic fields were measured in two Of?p stars: =-381+-122G for CPD-282561 ...

  11. NEW SUNS IN THE COSMOS?

    Energy Technology Data Exchange (ETDEWEB)

    De Freitas, D. B.; Leao, I. C.; Lopes, C. E. Ferreira; Paz-Chinchon, F.; Canto Martins, B. L.; Alves, S.; De Medeiros, J. R. [Departamento de Fisica, Universidade Federal do Rio Grande do Norte, 59072-970 Natal, RN (Brazil); Catelan, M. [Departamento de Astronomia y Astrofisica, Pontificia Universidad Catolica de Chile, Av. Vicuna Mackenna 4860, 782-0436 Macul, Santiago (Chile)

    2013-08-20

    The present work reports on the discovery of three stars that we have identified to be rotating Sun-like stars, based on rotational modulation signatures inferred from light curves from the CoRoT mission's Public Archives. In our analysis, we performed an initial selection based on the rotation period and position in the period-T{sub eff} diagram. This revealed that the stars CoRoT IDs 100746852, 102709980, and 105693572 provide potentially good matches to the Sun with a similar rotation period. To refine our analysis, we applied a novel procedure, taking into account the fluctuations of the features associated with photometric modulation at different time intervals and the fractality traces that are present in the light curves of the Sun and of these ''New Sun'' candidates alike. In this sense, we computed the so-called Hurst exponent for the referred stars, for a sample of 14 CoRoT stars with sub- and super-solar rotational periods, and for the Sun itself in its active and quiet phases. We found that the Hurst exponent can provide a strong discriminant of Sun-like behavior, going beyond what can be achieved with solely the rotation period itself. In particular, we find that CoRoT ID 105693572 is the star that most closely matches the solar rotation properties as far as the latter's imprints on light curve behavior are concerned. The stars CoRoT IDs 100746852 and 102709980 have significant smaller Hurst exponents than the Sun, notwithstanding their similarity in rotation periods.

  12. The multiplicity of O-type stars in NGC 2244

    NARCIS (Netherlands)

    Mahy, L.; Rauw, G.; Martins, F.; Gosset, E.; Nazé, Y.; Godart, M.; Sana, H.A.A.; De Becker, M.; Eenens, P.

    2011-01-01

    The investigation of the multiplicity of massive stars is crucial to determine a robust binary fraction but also for understanding the physical properties of these objects. In this contribution, we will present the main results from our long-term spectroscopic survey devoted to the young open cluste

  13. A new type of compact stellar population: dark star clusters

    CERN Document Server

    Banerjee, Sambaran; 10.1088/2041-8205/741/1/L12

    2011-01-01

    Among the most explored directions in the study of dense stellar systems is the investigation of the effects of the retention of supernova remnants, especially that of the massive stellar remnant black holes (BHs), in star clusters. By virtue of their eventual high central concentration, these stellar mass BHs potentially invoke a wide variety of physical phenomena, the most important ones being emission of gravitational waves (GWs), formation of X-ray binaries, and modification of the dynamical evolution of the cluster. Here we propose, for the first time, that rapid removal of stars from the outer parts of a cluster by the strong tidal field in the inner region of our Galaxy can unveil its BH sub-cluster, which appears as a star cluster that is gravitationally bound by an invisible mass. We study the formation and properties of such systems through direct N-body computations and estimate that they can be present in significant numbers in the inner region of the Milky Way. We call such objects "dark star clu...

  14. A rare early-type star revealed in the Wing of the Small Magellanic Cloud

    CERN Document Server

    Evans, C J; Oskinova, L M; Gallagher, J S; Chu, Y -H; Gruendl, R A; Hamann, W -R; Hénault-Brunet, V; Todt, H

    2012-01-01

    Sk 183 is the visually-brightest star in the N90 nebula, a young star-forming region in the Wing of the Small Magellanic Cloud (SMC). We present new optical spectroscopy from the Very Large Telescope which reveals Sk 183 to be one of the most massive O-type stars in the SMC. Classified as an O3-type dwarf on the basis of its nitrogen spectrum, the star also displays broadened He I absorption which suggests a later type. We propose that Sk 183 has a composite spectrum and that it is similar to another star in the SMC, MPG 324. This brings the number of rare O2- and O3-type stars known in the whole of the SMC to a mere three. We estimate physical parameters for Sk 183 from analysis of its spectrum. For a single-star model, we estimate an effective temperature of 46+/-2 kK, a low mass-loss rate of ~10^-7 Msun yr^-1, and a spectroscopic mass of 46^+9_-8 Msun (for an adopted distance modulus of 18.7 mag to the young population in the SMC Wing). An illustrative binary model requires a slightly hotter temperature (~...

  15. Magnetic field measurements and wind-line variability of OB-type stars

    CERN Document Server

    Schnerr, R S; Neiner, C; Verdugo, E; de Jong, J; Geers, V C; Wiersema, K; van Dalen, B; Tijani, A; Plaggenborg, B; Rygl, K L J

    2010-01-01

    Context. The first magnetic fields in O- and B-type stars that do not belong to the Bp-star class, have been discovered. The cyclic UV wind-line variability, which has been observed in a significant fraction of early-type stars, is likely to be related to such magnetic fields. Aims. We attempt to improve our understanding of massive-star magnetic fields, and observe twenty-five carefully-selected, OB-type stars. Methods. Of these stars we obtain 136 magnetic field strength measurements. We present the UV wind-line variability of all selected targets and summarise spectropolarimetric observations acquired using the MUSICOS spectropolarimeter, mounted at the TBL, Pic du Midi, between December 1998 and November 2004. From the average Stokes I and V line profiles, derived using the LSD method, we measure the magnetic field strengths, radial velocities, and first moment of the line profiles. Results. No significant magnetic field is detected in any OB-type star that we observed. Typical 1{\\sigma} errors are betwee...

  16. High Dispersion Spectroscopy of Solar-type Superflare Stars. II. Stellar Rotation, Starspots, and Chromospheric Activities

    CERN Document Server

    Notsu, Yuta; Maehara, Hiroyuki; Notsu, Shota; Shibayama, Takuya; Nogami, Daisaku; Shibata, Kazunari

    2014-01-01

    We conducted high dispersion spectroscopic observations of 50 superflare stars with Subaru/HDS. These 50 stars were selected from the solar-type superflare stars that we had discovered from the Kepler data. More than half (34 stars) of these 50 target superflare stars show no evidence of binarity, and we estimated stellar parameters of these 34 stars in our previous study (Notsu et al. 2015, hereafter called Paper I). According to our previous studies using Kepler data, superflare stars show quasi-periodic brightness variations whose amplitude (0.1-10\\%) is much larger than that of the solar brightness variations (0.01-0.1\\%) caused by the existence of sunspots on the rotating solar surface. In this study, we investigated whether these quasi-periodic brightness variations of superflare stars are explained by the rotation of a star with fairly large starspots, by using stellar parameters derived in Paper I. First, we confirmed that the value of the projected rotational velocity $v \\sin i$ is consistent with th...

  17. Why Study the Sun?

    Indian Academy of Sciences (India)

    Arvind Bhatnagar

    2006-06-01

    In this presentation we briefly describe the Sun through large number of illustrations and pictures of the Sun taken from early times to the present day space missions. The importance of the study of the Sun is emphasized as it is the nearest star which presents unparallelled views of surface details and numerous phenomena. Our Sun offers a unique celestial laboratory where a large variety of phenomena take place, ranging in temporal domain from a few milliseconds to several decades, in spatial domain from a few hundred kilometers to thousands of kilometers, and in the temperature domain from a few thousand degrees to several million degrees. Its mass motion ranges from thousandths to thousands of kilometers per second. Such an object provides us with a unique laboratory to study the state of matter in the Universe. The existing solar ground-based and space missions have already revealed several mysteries of the outer environment of our Sun and much more is going to come in the near future from planned new sophisticated ground-based solar telescopes and Space missions. The new technique of helioseismology has unravelled many secrets of the solar interior and has put the Standard Solar Model (SSM) on firm footing. The long-standing problem of solar neutrinos has been recently sorted out, and even the ‘back side’ view of the Sun can be seen using the technique of holographic helioseismology.

  18. The Galactic O-Star Spectroscopic Survey (GOSSS). III. 142 Additional O-type Systems.

    Science.gov (United States)

    Maíz Apellániz, J.; Sota, A.; Arias, J. I.; Barbá, R. H.; Walborn, N. R.; Simón-Díaz, S.; Negueruela, I.; Marco, A.; Leão, J. R. S.; Herrero, A.; Gamen, R. C.; Alfaro, E. J.

    2016-05-01

    This is the third installment of the Galactic O-Star Spectroscopic Survey (GOSSS), a massive spectroscopic survey of Galactic O stars, based on new homogeneous, high signal-to-noise ratio, R ˜ 2500 digital observations selected from the Galactic O-Star Catalog. In this paper, we present 142 additional stellar systems with O stars from both hemispheres, bringing the total of O-type systems published within the project to 590. Among the new objects, there are 20 new O stars. We also identify 11 new double-lined spectroscopic binaries, 6 of which are of O+O type and 5 of O+B type, and an additional new tripled-lined spectroscopic binary of O+O+B type. We also revise some of the previous GOSSS classifications, present some egregious examples of stars erroneously classified as O-type in the past, introduce the use of luminosity class IV at spectral types O4-O5.5, and adapt the classification scheme to the work of Arias et al. The GOSSS spectroscopic data in this article were gathered with five facilities: the 1.5 m Telescope at the Observatorio de Sierra Nevada (OSN), the 2.5 m du Pont Telescope at Las Campanas Observatory (LCO), the 3.5 m Telescope at Calar Alto Observatory (CAHA), and the 4.2 m William Herschel Telescope (WHT) and 10.4 m Gran Telescopio Canarias (GTC) at Observatorio del Roque de los Muchachos (ORM).

  19. Statistical studies of superflares on G-, K-, M- type stars from Kepler data

    Science.gov (United States)

    Notsu, Yuta; Maehara, Hiroyuki; Honda, Satoshi; Notsu, Shota; Namekata, Kosuke; Ikuta, Kai; Nogami, Daisaku; Shibata, Kazunari

    2017-05-01

    Flares are thought to be sudden releases of magnetic energy stored around starspots. Recent space high-precision photometry shows “superflares”, 10-104 times more energetic than the largest solar flares, occur on many G, K, M-type stars (e.g., Maehara+2012 Nature). Harmful UV/X-ray radiation and high-energy particles such as protons are caused by such superflares. This may suggest that exoplanet host stars have severe effects on the physical and chemical evolution of exoplanetary atmospheres (cf. Segura+2010 Astrobiology, Takahashi+2016 ApJL).We here present statistical properties of superflares on G, K, M-type stars on the basis of our analyses of Kepler photometric data (Maehara+2012 Nature, Shibayama+2013 ApJS, Notsu+2013 ApJ, Canderaresi+2014 ApJ, Maehara+2015 EPS, Maehara+2017 PASJ). We found more than 5000 superflares on 800 G, K, M-type main-sequence stars, and the occurrence frequency (dN/dE) of superflares as a function of flare energy (E) shows the power-law distribution with the index of -1.8 -1.9. This power-law distribution is consistent with that of solar flares.Flare frequency increases as stellar temperature decreases. As for M-type stars, energy of the largest flares is smaller compared with G,K-type stars, but more frequent “hazardous” flares for the habitable planets since the habitable zone around M-type stars is much smaller compared with G, K-type stars.Rotation period and starspot coverage can be estimated from the quasi-periodic brightness variation of the superflare stars. The intensity of Ca II 8542 line of superflare stars, which is measured from spectroscopic observations with Subaru Telescope, has a well correlation with the brightness variation amplitude (Notsu+2015a&b PASJ).Flare frequency has a correlation with rotation period, and this suggests young rapidly-rotating stars (like “young Sun”) have more severe impacts of flares on the planetary atmosphere (cf. Airapetian+2016 ApJL). Flare energy and frequency also depends

  20. Egg consumption and risk of type 2 diabetes in a Mediterranean cohort: the SUN project

    OpenAIRE

    Itziar Zazpe; Juan José Beunza; Maira Bes-Rastrollo; Francisco Javier Basterra-Gortari; Amelia Mari-Sanchis; Miguel Ángel Martínez-González

    2013-01-01

    Introduction & Aim: The prevalence of diabetes is increasing at an alarming rate in nearly all countries. Some studies from non-Mediterranean populations suggest that higher egg consumption is associated with an increased risk of diabetes. The aim of our study was to prospectively assess the association between egg consumption and the incidence of type 2 diabetes in a large cohort of Spanish university graduates. Methods: In this prospective cohort including 15,956 ...

  1. High--cadence observations of spicular-type events on the Sun

    CERN Document Server

    Shetye, J; Scullion, E; Nelson, C J; Kuridze, D; Henriques, V; Woeger, F; Ray, T

    2016-01-01

    Chromospheric observations taken at high cadence and high spatial resolution show a range of spicule like features, including Type I, Type II (as well as RBEs and RREs) and those which seem to appear within a few seconds, which if interpreted as flows would imply mass flow velocities in excess of 1000 km/s. This article seeks to quantify and study rapidly appearing spicular type events. We also compare the MOMFBD and speckle reconstruction techniques in order to understand if such spicules are more favourably observed using a particular technique. We use spectral imaging observations taken with the CRISP on the Swedish 1 m Solar Telescope. Data was sampled at multiple positions within the Halpha line profile for both an ondisk and limb location. The data is host to numerous rapidly appearing features which are observed at different locations within the Halpha line profile. The feature's durations vary between 10 and 20 s and lengths around 3500 km. Sometimes, a time delay in their appearance between the blue ...

  2. DUst around NEarby Stars (DUNES): searching for Kuiper-belt analogues around solar-type stars

    Science.gov (United States)

    Montesinos, B.; Dunes Consortium

    2011-11-01

    In this paper we summarize some of the results of the Herschel Open Time Key Programme DUNES (DUst around NEarby Stars). This project aims at detecting and studying cold dust discs, i.e. Edgeworth-Kuiper-belt analogues, around FGK stars of the solar neighbourhood, in a volume-limited sample. The sensitivity and wavelengths of the two instruments used, namely PACS (70, 100 and 160 micron) and SPIRE (250, 350 and 500 micron) are the appropriate ones for these tasks. Despite of the fact that, at the time of writing these proceedings, only about half of the sample has been observed, new results and increased statistics with respect to previous surveys and observations have emerged. Some new, unexpected results, in the form of very cold discs, pose some challenges to the current modelling paradigms. Note that at the time this paper is published, the results given and some of the conclusions will be obviously out of date.

  3. Dynamical model for spindown of solar-type stars

    CERN Document Server

    Sood, Aditi; Hollerbach, Rainer

    2016-01-01

    Since their formation, stars slow down their rotation rates by the removal of angular momentum from their surfaces, e.g. via stellar winds. Despite the complexity of the processes involved, a traditional model, where the removal of angular momentum loss by magnetic fields is prescribed, has provided a useful framework to understand observational relations between stellar rotation and age and magnetic field strength. Here, a spindown model is proposed where loss of angular momentum by magnetic fields is evolved dynamically, instead of being kinematically prescribed. To this end, we evolve the stellar rotation and magnetic field simultaneously over stellar evolution time by extending our previous work on a dynamo model which incorporates the nonlinear feedback mechanisms on rotation and magnetic fields. Our extended model reproduces key observations and explains the presence of the two branches of (fast and slow rotating) stars which have different relations between rotation rate $\\Omega$ vs. time (age), magnet...

  4. Magnetic Cycles and Rotation Periods of Late Type Stars from photometric time series

    CERN Document Server

    Mascareño, A Suárez; Hernández, J I González

    2016-01-01

    We investigate the photometric modulation induced by magnetic activity cycles and study the relationship between rotation period and activity cycle(s) in late-type (FGKM) stars. We analyse light-curves spanning up to 9 years of 125 nearby stars provided by the ASAS survey. The sample is mainly conformed by low-activity main sequence late A to mid M-type stars. A search is performed for short (days) and long-term (years) periodic variations in the photometry. We modelled with combinations of sinusoids the light-curves to measure the properties of these periodic signals. To provide a better statistical interpretation of our results we complement them with the results from previous similar works. We have been able to measure long-term photometric cycles of 47 stars. Rotational modulation was also detected and rotational periods measured in 36 stars. For 28 stars we have simultaneous measurements of both, activity cycles and rotational periods, being 17 of them M-type stars. From sinusoidal fits we measured both ...

  5. High-cadence observations of spicular-type events on the Sun

    Science.gov (United States)

    Shetye, J.; Doyle, J. G.; Scullion, E.; Nelson, C. J.; Kuridze, D.; Henriques, V.; Woeger, F.; Ray, T.

    2016-05-01

    Context. Chromospheric observations taken at high-cadence and high-spatial resolution show a range of spicule-like features, including Type-I, Type-II (as well as rapid blue-shifted excursions (RBEs) and rapid red-shifted excursions (RREs) which are thought to be on-disk counterparts of Type-II spicules) and those which seem to appear within a few seconds, which if interpreted as flows would imply mass flow velocities in excess of 1000 km s-1. Aims: This article seeks to quantify and study rapidly appearing spicular-type events. We also compare the multi-object multi-frame blind deconvolution (MOMFBD) and speckle reconstruction techniques to understand if these spicules are more favourably observed using a particular technique. Methods: We use spectral imaging observations taken with the CRisp Imaging SpectroPolarimeter (CRISP) on the Swedish 1-m Solar Telescope. Data was sampled at multiple positions within the Hα line profile for both an on-disk and limb location. Results: The data is host to numerous rapidly appearing features which are observed at different locations within the Hα line profile. The feature's durations vary between 10-20 s and lengths around 3500 km. Sometimes, a time delay in their appearance between the blue and red wings of 3-5 s is evident, whereas, sometimes they are near simultaneous. In some instances, features are observed to fade and then re-emerge at the same location several tens of seconds later. Conclusions: We provide the first statistical analysis of these spicules and suggest that these observations can be interpreted as the line-of-sight (LOS) movement of highly dynamic spicules moving in and out of the narrow 60 mÅ transmission filter that is used to observe in different parts of the Hα line profile. The LOS velocity component of the observed fast chromospheric features, manifested as Doppler shifts, are responsible for their appearance in the red and blue wings of Hα line. Additional work involving data at other

  6. A New Type of Extremely Metal Poor Star

    CERN Document Server

    Cohen, J G; Christlieb, N; Shectman, S; Thompson, I; Melendez, J; Reimers, L W D; Cohen, Judith G.; William, Andrew Mc; Christlieb, Norbert; Shectman, Stephen; Thompson, Ian; Melendez, Jorge; Reimers, Lutz Wisotzki & Dieter

    2007-01-01

    We present an abundance analysis for the extremely metal poor star HE1424-0241 based on high dispersion spectra from HIRES at Keck. This star is a giant on the lower red giant branch with [Fe/H] ~ -4.0 dex. Relative to Fe, HE1424-0241 has normal Mg, but it shows a very large deficiency of Si, with epsilon(Si)/epsilon(Fe) ~ 1/10 and epsilon(Si)/epsilon(Mg) ~ 1/25 that of all previously known extremely metal poor giants or dwarfs. It also has a moderately large deficiency of Ca and a smaller deficit of Ti, combined with enhanced Mn and Co and normal or low C. We suggest that in HE1424-0241 we see the effect of a very small number of contributing supernovae, and that the SNII contributing to the chemical inventory of HE1424-0241 were biased in progenitor mass or in explosion characteristics so as to reproduce its abnormal extremely low Si/Mg ratio. HE1424-0241 shows a deficiency of the explosive alpha-burning elements Si, Ca and Ti coupled with a ratio [Mg/Fe] normal for EMP stars; Mg is produced via hydrostatic...

  7. Binary star detectability in $Kepler$ data from phase modulation of different types of oscillations

    CERN Document Server

    Compton, Douglas L; Murphy, Simon J; Stello, Dennis

    2016-01-01

    Detecting binary stars in photometric time series is traditionally done by measuring eclipses. This requires the orbital plane to be aligned with the observer. A new method without that requirement uses stellar oscillations to measure delays in the light arrival time and has been successfully applied to $\\delta$ Scuti stars. However, application to other types of stars has not been explored. To investigate this we simulated light curves with a range of input parameters. We find a correlation between the signal-to-noise of the pulsation modes and the time delay required to detect binary motion. The detectability of the binarity in the simulations and in real $Kepler$ data shows strong agreement, hence, we describe the factors that have prevented this method from discovering binary companions to stars belonging to various classes of pulsating stars.

  8. Aztec Suns

    Science.gov (United States)

    Petersen, Hugh

    2010-01-01

    The Aztec Sun Stone is a revered Mexican artifact. It is said to be perhaps the most famous symbol of Mexico, besides its flag. It primarily depicts the four great disasters that led to the migration of the Mexica people to modern-day Mexico City. The Aztec Sun Stone also contains pictographs depicting the way the Mexica measured time, and was…

  9. Aztec Suns

    Science.gov (United States)

    Petersen, Hugh

    2010-01-01

    The Aztec Sun Stone is a revered Mexican artifact. It is said to be perhaps the most famous symbol of Mexico, besides its flag. It primarily depicts the four great disasters that led to the migration of the Mexica people to modern-day Mexico City. The Aztec Sun Stone also contains pictographs depicting the way the Mexica measured time, and was…

  10. Pulsating B-type stars in the open cluster NGC 884: frequencies, mode identification and asteroseismology

    CERN Document Server

    Saesen, S; Aerts, C; Miglio, A; Carrier, F

    2013-01-01

    Recent progress in the seismic interpretation of field beta Cep stars has resulted in improvements of the physics in the stellar structure and evolution models of massive stars. Further asteroseismic constraints can be obtained from studying ensembles of stars in a young open cluster, which all have similar age, distance and chemical composition. We present an observational asteroseismology study based on the discovery of numerous multi-periodic and mono-periodic B-stars in the open cluster NGC 884. We describe a thorough investigation of the pulsational properties of all B-type stars in the cluster. Overall, our detailed frequency analysis resulted in 115 detected frequencies in 65 stars. We found 36 mono-periodic, 16 bi-periodic, 10 tri-periodic, and 2 quadru-periodic stars and one star with 9 independent frequencies. We also derived the amplitudes and phases of all detected frequencies in the U, B, V and I filter, if available. We achieved unambiguous identifications of the mode degree for twelve of the de...

  11. On Helium-Dominated Stellar Evolution: The Mysterious Role of the O(He)-Type Stars

    Science.gov (United States)

    Reindl, N.; Rauch, T.; Werner, K.; Kruk, J. W.; Todt, H.

    2014-01-01

    Context. About a quarter of all post-asymptotic giant branch (AGB) stars are hydrogen-deficient. Stellar evolutionary models explain the carbon-dominated H-deficient stars by a (very) late thermal pulse scenario where the hydrogen-rich envelope is mixed with the helium-rich intershell layer. Depending on the particular time at which the final flash occurs, the entire hydrogen envelope may be burned. In contrast, helium-dominated post-AGB stars and their evolution are not yet understood. Aims. A small group of very hot, helium-dominated stars is formed by O(He)-type stars. A precise analysis of their photospheric abundances will establish constraints to their evolution. Methods. We performed a detailed spectral analysis of ultraviolet and optical spectra of four O(He) stars by means of state-of-the-art non-LTE model-atmosphere techniques. Results. We determined effective temperatures, surface gravities, and the abundances of H, He, C, N, O, F, Ne, Si, P, S, Ar, and Fe. By deriving upper limits for the mass-loss rates of the O(He) stars, we found that they do not exhibit enhanced mass-loss. The comparison with evolutionary models shows that the status of the O(He) stars remains uncertain. Their abundances match predictions of a double helium white dwarf (WD) merger scenario, suggesting that they might be the progeny of the compact and of the luminous helium-rich sdO-type stars. The existence of planetary nebulae that do not show helium enrichment around every other O(He) star precludes a merger origin for these stars. These stars must have formed in a different way, for instance via enhanced mass-loss during their post-AGB evolution or a merger within a common-envelope (CE) of a CO-WD and a red giant or AGB star. Conclusions. A helium-dominated stellar evolutionary sequence exists that may be fed by different types of mergers or CE scenarios. It appears likely that all these pass through the O(He) phase just before they become WDs.

  12. Abundance analysis of 5 early-type stars in the young open cluster IC2391

    CERN Document Server

    Stuetz, C; Jehin, E; Ledoux, C; Cabanac, R A; Melo, C; Smoker, J V; Stuetz, Ch.

    2006-01-01

    It is unclear whether chemically peculiar stars of the upper main sequence represent a class completely distinct from normal A-type stars, or whether there exists a continuous transition from the normal to the most peculiar late F- to early B-type stars. A systematic abundance analysis of open cluster early-type stars would help to relate the observed differences of the chemical abundances of the photospheres to other stellar characteristics, without being concerned by possible different original chemical composition. Furthermore, if a continuous transition region from the very peculiar to the so called normal A-F stars exists, it should be possible to detect objects with mild peculiarities. As a first step of a larger project, an abundance analysis of 5 F-A type stars in the young cluster IC2391 was performed using high resolution spectra obtained with the UVES instrument of the ESO VLT. Our targets seem to follow a general abundance pattern: close to solar abundance of the light elements and iron peak eleme...

  13. Age dependence of wind properties for solar type stars: a 3d study

    CERN Document Server

    Réville, Victor; Strugarek, Antoine; Brun, Allan Sacha

    2016-01-01

    Young and rapidly rotating stars are known for intense, dynamo generated magnetic fields. Spectropolarimetric observations of those stars in precisely aged clusters are key input for gyrochronology and magnetochronology. We use ZDI maps of several young K-type stars of similar mass and radius but with various ages and rotational periods, to perform 3D numerical MHD simulations of their coronae and follow the evolution of their magnetic properties with age. Those simulations yield the coronal structure as well as the instant torque exerted by the magnetized, rotating wind on the star. As stars get older, we find that the angular momentum loss decreases with $\\Omega^3$, which is the reason for the convergence on the Skumanich law. For the youngest stars of our sample, the angular momentum loss show signs of saturation around $8\\Omega_{\\odot}$, which is a common value used in spin evolution models for K-type stars. We compare these results to semi-analytical models and existing braking laws. We observe a complex...

  14. The Runaways and Isolated O-Type Star Spectroscopic Survey of the SMC (RIOTS4)

    CERN Document Server

    Lamb, J B; Segura-Cox, D M; Graus, A S; Kiminki, D C; Golden-Marx, J B; Parker, J Wm

    2015-01-01

    We present the Runaways and Isolated O-Type Star Spectroscopic Survey of the SMC (RIOTS4), a spatially complete survey of uniformly selected field OB stars that covers the entire star-forming body of the SMC. Using the IMACS multislit spectrograph and MIKE echelle spectrograph on the Magellan telescopes, we obtained spectra of 374 early-type field stars that are at least 28 pc from any other OB candidates. We also obtained spectra of an additional 23 field stars in the SMC bar identified from slightly different photometric criteria. Here, we present the observational catalog of stars in the RIOTS4 survey, including spectral classifications and radial velocities. For three multi-slit fields covering 8% of our sample, we carried out monitoring observations over 9-16 epochs to study binarity, finding a spectroscopic, massive binary frequency of at least $\\sim$60% in this subsample. Classical Oe/Be stars represent a large fraction of RIOTS4 (42%), occurring at much higher frequency than in the Galaxy, consistent ...

  15. Rotational velocities of single and binary O-type stars in the Tarantula Nebula

    CERN Document Server

    Ramírez-Agudelo, O H; de Koter, A; Simón-Díaz, S; de Mink, S E; Tramper, F; Dufton, P L; Evans, C J; Gräfener, G; Herrero, A; Langer, N; Lennon, D J; Apellániz, J Maíz; Markova, N; Najarro, F; Puls, J; Taylor, W D; Vink, J S

    2014-01-01

    Rotation is a key parameter in the evolution of massive stars, affecting their evolution, chemical yields, ionizing photon budget, and final fate. We determined the projected rotational velocity, $v_e\\sin i$, of $\\sim$330 O-type objects, i.e. $\\sim$210 spectroscopic single stars and $\\sim$110 primaries in binary systems, in the Tarantula nebula or 30 Doradus (30\\,Dor) region. The observations were taken using VLT/FLAMES and constitute the largest homogeneous dataset of multi-epoch spectroscopy of O-type stars currently available. The most distinctive feature of the $v_e\\sin i$ distributions of the presumed-single stars and primaries in 30 Dor is a low-velocity peak at around 100\\,$\\rm{km s^{-1}}$. Stellar winds are not expected to have spun-down the bulk of the stars significantly since their arrival on the main sequence and therefore the peak in the single star sample is likely to represent the outcome of the formation process. Whereas the spin distribution of presumed-single stars shows a well developed tai...

  16. The domain of attraction of the α-sun operator for type II and type III distributions

    NARCIS (Netherlands)

    Hooghiemstra, G.; Greenwood, P.E.

    1996-01-01

    Let be a sequence of independent random variables with common distribution and define the iteration , , . We denote by the domain of maximal attraction of , the extreme value distribution of the first type. Greenwood and Hooghiemstra showed in 1991 that for there exist norming constants and such tha

  17. Emission from the Centrifugal Magnetospheres of Magnetic B-type Stars

    Science.gov (United States)

    Shultz, M.; Wade, G.; Rivinius, T.; Townsend, R.; MiMeS Collaboration

    2016-11-01

    Approximately 10% of B-type stars possess strong magnetic fields, and of these, 25% host centrifugal magnetospheres in which the radiative wind, magnetic field, and rotational support interact to form a dense circumstellar plasma visible in a variety of diagnostic lines. In this article we review the basic theory behind CMs, outline current theoretical and observational problems, compare the observational properties of CM host stars to those of classical Be stars, and finally present preliminary results of a population study aimed at clarifying the characteristics of this growing sub-class.

  18. Detection of Neutral Phosphorus in the Near Ultraviolet Spectra of Late-Type Stars

    CERN Document Server

    Roederer, Ian U; Thanathibodee, Thanawuth; Frebel, Anna; Toller, Elizabeth

    2014-01-01

    We report the detection of several absorption lines of neutral phosphorus (P, Z=15) in archival near ultraviolet spectra obtained with the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope. We derive phosphorus abundances or interesting upper limits in 14 late-type stars with metallicities spanning -3.8-1.0, the [P/Fe] ratio decreases toward the solar value with increasing metallicity, in agreement with previous observational studies. In stars with [Fe/H]=+0.04+/-0.10, which overlaps with the [P/Fe] ratios found in several high-redshift damped Lyman-alpha systems. This behavior hints at a primary origin in massive stars.

  19. Emission from the Centrifugal Magnetospheres of Magnetic B-type Stars

    CERN Document Server

    Shultz, Matt; Rivinius, Thomas; Townsend, Richard

    2014-01-01

    Approximately 10% of B-type stars possess strong magnetic fields, and of these, 25% host centrifugal magnetospheres (CMs) in which the radiative wind, magnetic field, and rotational support interact to form a dense circumstellar plasma visible in a variety of diagnostic lines. In this article we review the basic theory behind CMs, outline current theoretical and observational problems, compare the observational properties of CM host stars to those of classical Be stars, and finally present preliminary results of a population study aimed at clarifying the characteristics of this growing sub-class.

  20. The Galactic O-Star Spectroscopic Survey (GOSSS). III. 142 additional O-type systems

    CERN Document Server

    Apellániz, J Maíz; Arias, J I; Barbá, R H; Walborn, N R; Simón-Díaz, S; Negueruela, I; Marco, A; Leão, J R S; Herrero, A; Gamen, R C; Alfaro, E J

    2016-01-01

    This is the third installment of GOSSS, a massive spectroscopic survey of Galactic O stars, based on new homogeneous, high signal-to-noise ratio, R~2500 digital observations selected from the Galactic O-Star Catalog (GOSC). In this paper we present 142 additional stellar systems with O stars from both hemispheres, bringing the total of O-type systems published within the project to 590. Among the new objects there are 20 new O stars. We also identify 11 new double-lined spectroscopic binaries (SB2s), of which 6 are of O+O type and 5 of O+B type, and an additional new tripled-lined spectroscopic binary (SB3) of O+O+B type. We also revise some of the previous GOSSS classifications, present some egregious examples of stars erroneously classified as O-type in the past, introduce the use of luminosity class IV at spectral types O4-O5.5, and adapt the classification scheme to the work of Arias et al. (2016).

  1. Principal component analysis-based inversion of effective temperatures for late-type stars

    CERN Document Server

    Paletou, F; Houdebine, E R; Watson, V

    2015-01-01

    We show how the range of application of the principal component analysis-based inversion method of Paletou et al. (2015) can be extended to late-type stars data. Besides being an extension of its original application domain, for FGK stars, we also used synthetic spectra for our learning database. We discuss our results on effective temperatures against previous evaluations made available from Vizier and Simbad services at CDS.

  2. Granulation in K-type Dwarf Stars. I. Spectroscopic observations

    CERN Document Server

    Ramírez, I; Lambert, D L

    2008-01-01

    Very high resolution (R~160,000-210,000), high signal-to-noise ratio (S/N>300) spectra of nine bright K-dwarfs were obtained with the 2dcoude spectrograph on the 2.7m Telescope at McDonald Observatory to determine wavelength shifts and asymmetries of Fe I lines. The observed shapes and positions of Fe I lines reveal asymmetries and wavelength shifts that indicate the presence of granulation. In particular, line bisectors show characteristic C-shapes while line core wavelengths are blueshifted by an amount that increases with decreasing equivalent width (EW). On average, Fe I line bisectors have a span that ranges from nearly 0 for the weakest lines (residual core flux > 0.7) to about 75 m/s for the strongest lines (residual core flux ~ 0.3) while wavelength shifts range from about -150 m/s in the weakest (EW ~ 10 mA) lines to 0 in the strongest (EW > 100 mA) features. A more detailed inspection of the bisectors and wavelength shifts reveals star-to-star differences that are likely associated with differences ...

  3. Meat Consumption and Risk of Developing Type 2 Diabetes in the SUN Project: A Highly Educated Middle-Class Population.

    Science.gov (United States)

    Mari-Sanchis, A; Gea, A; Basterra-Gortari, F J; Martinez-Gonzalez, M A; Beunza, J J; Bes-Rastrollo, M

    2016-01-01

    Meat consumption has been consistently associated with the risk of diabetes in different populations. The aim of our study was to investigate the incidence of type 2 diabetes according to baseline total meat consumption in a longitudinal assessment of a middle-aged Mediterranean population. We followed 18,527 participants (mean age: 38 years, 61% women) in the SUN Project, an open-enrolment cohort of a highly educated population of middle-class Spanish graduate students. All participants were initially free of diabetes. Diet was assessed at baseline using a semi-quantitative food frequency questionnaire of 136-items previously validated. Incident diabetes was defined according to the American Diabetes Association's criteria. We identified 146 incident cases of diabetes after a maximum of 14 years of follow-up period (mean: 8.7 years). In the fully adjusted model, the consumption of ≥3 servings/day of all types of meat was significantly associated with a higher risk of diabetes (HR: 1.85; 95% CI: 1.03-3.31; p for trend = 0.031) in comparison with the reference category (<2 servings/day). When we separated processed from non-processed meat, we observed a non-significant higher risk associated with greater consumption of processed meat and a non-significant lower risk associated with non-processed meat consumption (p for trend = 0.123 and 0.487, respectively). No significant difference was found between the two types of meat (p = 0.594). Our results suggest that meat consumption, especially processed meat, was associated with a higher risk of developing diabetes in our young Mediterranean cohort.

  4. Meat Consumption and Risk of Developing Type 2 Diabetes in the SUN Project: A Highly Educated Middle-Class Population.

    Directory of Open Access Journals (Sweden)

    A Mari-Sanchis

    Full Text Available Meat consumption has been consistently associated with the risk of diabetes in different populations. The aim of our study was to investigate the incidence of type 2 diabetes according to baseline total meat consumption in a longitudinal assessment of a middle-aged Mediterranean population.We followed 18,527 participants (mean age: 38 years, 61% women in the SUN Project, an open-enrolment cohort of a highly educated population of middle-class Spanish graduate students. All participants were initially free of diabetes. Diet was assessed at baseline using a semi-quantitative food frequency questionnaire of 136-items previously validated. Incident diabetes was defined according to the American Diabetes Association's criteria.We identified 146 incident cases of diabetes after a maximum of 14 years of follow-up period (mean: 8.7 years. In the fully adjusted model, the consumption of ≥3 servings/day of all types of meat was significantly associated with a higher risk of diabetes (HR: 1.85; 95% CI: 1.03-3.31; p for trend = 0.031 in comparison with the reference category (<2 servings/day. When we separated processed from non-processed meat, we observed a non-significant higher risk associated with greater consumption of processed meat and a non-significant lower risk associated with non-processed meat consumption (p for trend = 0.123 and 0.487, respectively. No significant difference was found between the two types of meat (p = 0.594.Our results suggest that meat consumption, especially processed meat, was associated with a higher risk of developing diabetes in our young Mediterranean cohort.

  5. Improving the surface-brightness color relation for early-type stars using optical interferometry

    CERN Document Server

    Challouf, M; Mourard, D; Graczyk, D; Aroui, H; Chesneau, O; Delaa, O; Pietrzyński, G; Gieren, W; Ligi, R; Meilland, A; Perraut, K; Tallon-Bosc, I; McAlister, H; Brummelaar, T ten; Sturmann, J; Sturmann, L; Turner, N; Farrington, C; Vargas, N; Scott, N

    2014-01-01

    The aim of this work is to improve the SBC relation for early-type stars in the $-1 \\leq V-K \\leq 0$ color domain, using optical interferometry. Observations of eight B- and A-type stars were secured with the VEGA/CHARA instrument in the visible. The derived uniform disc angular diameters were converted into limb darkened angular diameters and included in a larger sample of twenty four stars, already observed by interferometry, in order to derive a revised empirical relation for O, B, A spectral type stars with a V-K color index ranging from -1 to 0. We also take the opportunity to check the consistency of the SBC relation up to $V-K \\simeq 4$ using 100 additional measurements. We determined the uniform disc angular diameter for the eight following stars: $\\gamma$ Ori, $\\zeta$ Per, $8$ Cyg, $\\iota$ Her, $\\lambda$ Aql, $\\zeta$ Peg, $\\gamma$ Lyr and $\\delta$ Cyg with V-K color ranging from -0.70 to 0.02 and typical precision of about $1.5\\%$. Using our total sample of 132 stars with $V-K$ colors index ranging f...

  6. A catalog of M-type star candidates in the LAMOST data release 1

    Science.gov (United States)

    Zhong, Jing; Lépine, Sébastien; Li, Jing; Chen, Li; Hou, Jinliang

    2016-08-01

    In this work, we present a set of M-type star candidates selected from the LAMOST DR1. A discrimination method with the spectral index diagram is used to separate M giants and M dwarfs. Then, we have successfully assembled a set of M giants templates from M0 to M6, using the spectra identified from the LAMOST spectral database. After combining the M dwarf templates in Zhong et al. (2015a) and the new created M giant templates, we use the M-type spectral library to perform the template-fit method to classify and identify M-type stars in the LAMOST DR1. A catalog of M-type star candidates including 8639 M giants and 101690 M dwarfs/subdwarfs is provided. As an additional results, we also present other fundamental parameters like proper motion, photometry, radial velocity and spectroscopic distance.

  7. Precise mass and radius measurements for the components of the bright solar-type eclipsing binary star V1094 Tau

    CERN Document Server

    Maxted, P F L; Torres, G; Lacy, C H S; Southworth, J; Smalley, B; Pavlovski, K; Marschall, L A; Clausen, J V

    2015-01-01

    V1094 Tau is bright eclipsing binary star with an orbital period close to 9 days containing two stars similar to the Sun. Our aim is to test models of Sun-like stars using precise and accurate mass and radius measurements for both stars in V1094 Tau. We present new spectroscopy of V1094 Tau which we use to estimate the effective temperatures of both stars and to refine their spectroscopic orbits. We also present new, high-quality photometry covering both eclipses of V1094 Tau in the Stroemgren uvby system and in the Johnson V-band. The masses, radii and effective temperatures of the stars in V1094 Tau are found to be M$_A$ = 1.0964 $\\pm$ 0.0040 M$_{\\odot}$, R$_A$ = 1.4129 $\\pm$ 0.0058 R$_{\\odot}$, T$_{\\rm eff,A}$ = 5850 $\\pm$ 100 K, and M$_B$ = 1.0120 $\\pm$ 0.0028 M$_{\\odot}$, R$_B$ = 1.0913 $\\pm$ 0.0066 R$_{\\odot}$, T$_{\\rm eff,B}$ = 5700 $\\pm$ 100 K. An analysis of the times of mid-eclipse and the radial velocity data reveals apsidal motion with a period of 14500 $\\pm$ 3700 years. The observed masses, radii...

  8. Sun meter

    Science.gov (United States)

    Younskevicius, Robert E.

    1978-01-01

    A simple, inexpensive device for measuring the radiation energy of the sun impinging on the device. The measurement of the energy over an extended period of time is accomplished without moving parts or tracking mechanisms.

  9. Synthetic activity indicators for M-type dwarf stars

    CERN Document Server

    Wedemeyer, Sven

    2015-01-01

    Here, we present a set of time-dependent 3D RMHD simulations of a M-dwarf star representative of AD Leo, which extend from the upper convection zone into the chromosphere. The 3D model atmospheres are characterized by a very dynamic and intermittent structure on small spatial and temporal scales and a wealth of physical processes, which by nature cannot be described by means of 1D static model atmospheres. Artificial observations of these models imply that a combination of complementary diagnostics such as Ca II lines and the continuum intensity from UV to millimeter wavelengths, probe various properties of the dynamics, thermal and magnetic structure of the photosphere and the chromosphere and thus provide measures of stellar activity, which can be compared to observations. The complicated magnetic field structure and its imprint in synthetic diagnostics may have important implications for the understanding and characterization of stellar activity and with it possibly for the evaluation of planetary habitabi...

  10. KMOS view of the Galactic Centre - II. Metallicity distribution of late-type stars

    Science.gov (United States)

    Feldmeier-Krause, A.; Kerzendorf, W.; Neumayer, N.; Schödel, R.; Nogueras-Lara, F.; Do, T.; de Zeeuw, P. T.; Kuntschner, H.

    2017-01-01

    Knowing the metallicity distribution of stars in the Galactic Centre has important implications for the formation history of the Milky Way nuclear star cluster. However, this distribution is not well known, and is currently based on a small sample of fewer than 100 stars. We obtained near-infrared K-band spectra of more than 700 late-type stars in the central 4 pc2 of the Milky Way nuclear star cluster with the integral-field spectrograph KMOS (VLT). We analyse the medium-resolution spectra using a full-spectral fitting method employing the Göttingen spectral library of synthetic PHOENIX spectra. The derived stellar metallicities range from metal-rich [M/H] > +0.3 dex to metal-poor [M/H] 0 dex), a globular cluster origin can be ruled out. As there is only a very low fraction of metal-poor stars in the central 4 pc2 of the Galactic Centre, we believe that our data can discard a scenario in which the Milky Way nuclear star cluster is purely formed from infalling globular clusters.

  11. KMOS view of the Galactic Centre - II. Metallicity distribution of late-type stars

    CERN Document Server

    Feldmeier-Krause, A; Neumayer, N; Schödel, R; Nogueras-Lara, F; Do, T; de Zeeuw, P T; Kuntschner, H

    2016-01-01

    Knowing the metallicity distribution of stars in the Galactic Centre has important implications for the formation history of the Milky Way nuclear star cluster. However, this distribution is not well known, and is currently based on a small sample of fewer than 100 stars. We obtained near-infrared K-band spectra of more than 700 late-type stars in the central 4 pc^2 of the Milky Way nuclear star cluster with the integral-field spectrograph KMOS (VLT). We analyse the medium-resolution spectra using a full-spectral fitting method employing the G\\"ottingen Spectral library of synthetic PHOENIX spectra. The derived stellar metallicities range from metal-rich [M/H]>+0.3 dex to metal-poor [M/H]0 dex) a globular cluster origin can be ruled out. As there is only a very low fraction of metal-poor stars in the central 4 pc^2 of the Galactic Centre, we believe that our data can discard a scenario in which the Milky Way nuclear star cluster is purely formed from infalling globular clusters.

  12. The age-mass-metallicity-activity relation for solar-type stars: comparisons with asteroseismology and the NGC 188 open cluster

    Science.gov (United States)

    Lorenzo-Oliveira, D.; Porto de Mello, G. F.; Schiavon, R. P.

    2016-10-01

    Context. The Mount Wilson Ca ii index log(R'_HK) is the accepted standard metric of calibration for the chromospheric activity versus age relation for FGK stars. Recent results claim its inability to discern activity levels, and thus ages, for stars older than ~2 Gyr, which would severely hamper its application to date disk stars older than the Sun. Aims: We present a new activity-age calibration of the Mt. Wilson index that explicitly takes mass and [Fe/H] biases into account; these biases are implicit in samples of stars selected to have precise ages, which have so far not been appreciated. Methods: We show that these selection biases tend to blur the activity-age relation for large age ranges. We calibrate the Mt. Wilson index for a sample of field FGK stars with precise ages, covering a wide range of mass and [Fe/H] , augmented with data from the Pleiades, Hyades, M 67 clusters, and the Ursa Major moving group. Results: We further test the calibration with extensive new Gemini/GMOS log ()R'HK) data of the old, solar [Fe/H] clusters, M 67 and NGC 188. The observed NGC 188 activity level is clearly lower than M 67. We correctly recover the isochronal age of both clusters and establish the viability of deriving usable chromospheric ages for solar-type stars up to at least ~6 Gyr, where average errors are ~0.14 dex provided that we explicitly account for the mass and [Fe/H] dimensions. We test our calibration against asteroseismological ages, finding excellent correlation (ρ = + 0.89). We show that our calibration improves the chromospheric age determination for a wide range of ages, masses, and metallicities in comparison to previous age-activity relations.

  13. Exploring the origin of magnetic fields in massive stars: a survey of O-type stars in clusters and in the field

    NARCIS (Netherlands)

    Hubrig, S.; Schöller, M.; Kharchenko, N.V.; Langer, N.; de Wit, W.J.M.; Ilyin, I.; Kholtygin, A.F.; Piskunov, A.E.; Przybilla, N.

    2011-01-01

    Context. Although the effects of magnetic fields in massive stars have been found to be substantial by recent models and observations, the magnetic fields of only a small number of massive O-type stars have so far been investigated. Additional observations are of the utmost importance to constrainin

  14. Investigation of the binary fraction among candidate A-F type hybrid stars detected by Kepler

    Directory of Open Access Journals (Sweden)

    Lampens P.

    2015-01-01

    Full Text Available We are currently monitoring up to 40 Kepler candidate δ Scuti-γ Doradus (resp. γ Doradus-δ Scuti hybrid stars in radial velocity in order to identify the physical cause behind the low frequencies observed in the periodograms based on the ultra-high accuracy Kepler space photometry. The presence of low frequency variability in unevolved or slightly evolved oscillating A/F-type stars can generally be explained in three ways: either 1 the star is an (undetected binary or multiple system, or 2 the star is a g-mode pulsator (i.e. a genuine hybrid, or 3 the star’s atmosphere displays an asymmetric intensity distribution (caused by spots, i.e. chemical anomalies, or by (very high rotation, which is detected through rotational modulation. Our targets were selected from the globally characterized variable A/F-type stars of the Kepler mission [7]. We observe each star at least 4 times unevenly spread over a time lapse up to 2 months with the HERMES spectrograph [6]. In the case of composite, multiple-lined spectra, these observations also provide the atmospheric properties of each component. Our principal goal is to estimate the fraction of short-period, spectroscopic systems in the sample.

  15. Extrasolar planets and brown dwarfs around AF-type stars. IX. The HARPS southern sample

    CERN Document Server

    Borgniet, Simon; Meunier, Nadège; Galland, Franck

    2016-01-01

    Massive, Main-Sequence AF-type stars have so far remained unexplored in past radial velocity surveys, due to their small number of spectral lines and their high rotational velocities that prevent the classic RV computation method. Our aim was to search for giant planets around AF MS stars, to get first statistical information on their occurrence rate and to compare the results with evolved stars and lower-mass MS stars. We used the HARPS spectrograph located on the 3.6m telescope at ESO La Silla Observatory to observe 108 AF MS stars with B-V in the -0.04 to 0.58 range and masses in the range 1.1-3.6 Msun. We used our SAFIR software specifically developed to compute the radial velocities of these early-type stars. We report the new detection of a mpsini = 4.51 Mjup companion with a ~826-day period to the F6V dwarf HD111998. We present new data on the 2-planet system around the F6IV-V dwarf HD60532. We also report the detection of 14 binaries with long-term RV trends. 70% of our targets show detection limits b...

  16. Statistical properties of superflares on solar-type stars with Kepler data

    CERN Document Server

    Notsu, Yuta; Shibayama, Takuya; Honda, Satoshi; Notsu, Shota; Namekata, Kosuke; Nogami, Daisaku; Shibata, Kazunari

    2016-01-01

    Superflares are flares that release total energy 10$\\sim$10$^{4}$ times greater than that of the biggest solar flares with energy of $\\sim$10$^{32}$ erg. We searched superflares on solar-type stars (G-type main sequence stars) using the Kepler 30-min (long) and 1-min (short) cadence data. We found more than 1500 superflares on 279 stars from 30-min cadence data (Q0-6) and 187 superflares on 23 stars from 1-min cadence data (Q0-17). The bolometric energy of detected superflares ranges from the order of 10$^{32}$ erg to 10$^{36}$ erg. Using these data, we found that the occurrence frequency ($dN/dE$) of superflares is expressed as a power-law function of flare energy ($E$) with the index of -1.5 for $10^{33}$ Most of the superflare stars show quasi-periodic light variations with the amplitude of a few percent, which can be explained by the rotation of the star with large starspots. The bolometric energy released by flares is consistent with the magnetic energy stored around such large starspots. Furthermore, ou...

  17. The chemical abundance analysis of normal early A- and late B-type stars

    CERN Document Server

    Fossati, L; Bagnulo, S; Alecian, E; Grunhut, J; Kochukhov, O; Wade, G

    2009-01-01

    Modern spectroscopy of early-type stars often aims at studying complex physical phenomena. Comparatively less attention is paid to identifying and studying the "normal" A- and B-type stars and testing how the basic atomic parameters and standard spectral analysis allow one to fit the observations. We wish to stablish whether the chemical composition of the solar photosphere can be regarded as a reference for early A- and late B-type stars. We have obtained optical high-resolution, high signal-to-noise ratio spectra of three slowly rotating early-type stars (HD 145788, 21 Peg and pi Cet) that show no obvious sign of chemical peculiarity, and performed a very accurate LTE abundance analysis of up to 38 ions of 26 elements (for 21 Peg), using a vast amount of spectral lines visible in the spectral region covered by our spectra. We provide an exhaustive description of the abundance characteristics of the three analysed stars with a critical review of the line parameters used to derive the abundances. We compiled ...

  18. An Einstein Observatory SAO-based catalog of B-type stars

    Science.gov (United States)

    Grillo, F.; Sciortino, S.; Micela, G.; Vaiana, G. S.; Harnden, F. R., Jr.

    1992-01-01

    About 4000 X-ray images obtained with the Einstein Observatory are used to measure the 0.16-4.0 keV emission from 1545 B-type SAO stars falling in the about 10 percent of the sky surveyed with the IPC. Seventy-four detected X-ray sources with B-type stars are identified, and it is estimated that no more than 15 can be misidentified. Upper limits to the X-ray emission of the remaining stars are presented. In addition to summarizing the X-ray measurements and giving other relevant optical data, the present extensive catalog discusses the reduction process and analyzes selection effects associated with both SAO catalog completeness and IPC target selection procedures. It is concluded that X-ray emission, at the level of Lx not less than 10 exp 30 ergs/s, is quite common in B stars of early spectral types (B0-B3), regardless of luminosity class, but that emission, at the same level, becomes less common, or nonexistent, in later B-type stars.

  19. Models of rotating boson stars and geodesics around them: New type of orbits

    Science.gov (United States)

    Grandclément, Philippe; Somé, Claire; Gourgoulhon, Eric

    2014-07-01

    We have developed a highly accurate numerical code capable of solving the coupled Einstein-Klein-Gordon system, in order to construct rotating boson stars in general relativity. Free fields and self-interacting fields, with quartic and sextic potentials, are considered. In particular, we present the first numerical solutions of rotating boson stars with rotational quantum number k=3 and k=4, as well as the first determination of the maximum mass of free-field boson stars with k=2. We have also investigated timelike geodesics in the spacetime generated by a rotating boson star for k=1, 2 and 3. A numerical integration of the geodesic equation has enabled us to identify a peculiar type of orbit: the zero-angular-momentum ones. These orbits pass very close to the center and are qualitatively different from orbits around a Kerr black hole. Should such orbits be observed, they would put stringent constraints on astrophysical compact objects like the Galactic center.

  20. A Bcool spectropolarimetric survey of over 150 solar-type stars

    CERN Document Server

    Marsden, Stephen; Jeffers, Sandra; Nascimento, Jose-Dias do; Carter, Bradley; Brown, Carolyn

    2013-01-01

    As part of the Bcool project, over 150 solar-type stars chosen mainly from planet search databases have been observed between 2006 and 2013 using the NARVAL and ESPaDOnS spectropolarimeters on the Telescope Bernard Lyot (Pic du Midi, France) and the Canada France Hawaii Telescope (Mauna Kea, USA), respectively. These single 'snapshot' observations have been used to detect the presence of magnetic fields on 40% of our sample, with the highest detection rates occurring for the youngest stars. From our observations we have determined the mean surface longitudinal field (or an upper limit for stars without detections) and the chromospheric surface fluxes, and find that the upper envelope of the absolute value of the mean surface longitudinal field is directly correlated to the chromospheric emission from the star and increases with rotation rate and decreases with age.

  1. Models of rotating boson stars and geodesics around them: new type of orbits

    CERN Document Server

    Grandclement, Philippe; Gourgoulhon, Eric

    2014-01-01

    We have developed a highly accurate numerical code capable of solving the coupled Einstein-Klein-Gordon system, in order to construct rotating boson stars in general relativity. Free fields and self-interacting fields, with quartic and sextic potentials, are considered. In particular, we present the first numerical solutions of rotating boson stars with rotational quantum number $k=3$ and $k=4$, as well as the first determination of the maximum mass of free-field boson stars with $k=2$. We have also investigated timelike geodesics in the spacetime generated by a rotating boson star for $k=1$, $2$ and $3$. A numerical integration of the geodesic equation has enabled us to identify a peculiar type of orbits: the zero-angular-momentum ones. These orbits pass very close to the center and are qualitatively different from orbits around a Kerr black hole. Should such orbits be observed, they would put stringent constraints on astrophysical compact objects like the Galactic center.

  2. Probing Spin-Orbit Misalignment Processes Around Early-Type Stars

    Science.gov (United States)

    Ahlers, Johnathon; Barnes, Jason W.

    2016-10-01

    Planets in early-type systems seem to frequently misalign from their host star's spin axis. These spin-orbit misaligned systems challenge conventional planet-formation theories because planets probably do not form with initially misaligned orbits -- their angular momenta must be conserved with the stellar nursery in which they formed. In such a case, planets must migrate to their misaligned positions. However, very few transiting exoplanets have had their spin-orbit alignment angles measured. Our model constrains spin-orbit alignment angles via photometry and asteroseismology while accounting for the brightness effects of stellar variability and rapid rotation that commonly occur in early-type stars, making the analysis of hundreds of Kepler transit light curves possible for the first time. We will employ these techniques to probe spin-orbit misalignment theories by empirically testing the spin-orbit state of exoplanets orbiting early-type stars.

  3. NuSTAR Reveals Extreme Absorption in z <0.5 Type 2 Quasars

    DEFF Research Database (Denmark)

    Lansbury, G. B.; Gandhi, P.; Alexander, D. M.

    2015-01-01

    The intrinsic column density (N-H) distribution of quasars is poorly known. At the high obscuration end of the quasar population and for redshifts z ...-ray observatory NuSTAR, along with archival Chandra and XMM-Newton data, we study the broad-band X-ray spectra of nine optically selected (from the SDSS), candidate Compton-thick (N-H > 1.5 x 10(24) cm(-2)) type 2 quasars (CTQSO2s); five new NuSTAR observations are reported herein, and four have been previously......STAR-detected type 2 quasars are representative of other Compton-thick candidates, we make a correction to the N-H distribution for optically selected type 2 quasars as measured by Chandra and XMM-Newton for 39 objects. With this approach, we predict a Compton-thick fraction of f(CT) = 36(-12)(+14)%, although higher...

  4. BUILDING LATE-TYPE SPIRAL GALAXIES BY IN-SITU AND EX-SITU STAR FORMATION

    Energy Technology Data Exchange (ETDEWEB)

    Pillepich, Annalisa [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Madau, Piero [Department of Astronomy and Astrophysics, University of California Santa Cruz, 1156 High St., Santa Cruz, CA 95064 (United States); Mayer, Lucio [Center for Theoretical Astrophysics and Cosmology, Institute for Computational Science, University of Zurich, Winterthurerstrasse 190, CH-9057 Zurich (Switzerland)

    2015-02-01

    We analyze the formation and evolution of the stellar components in ''Eris'', a 120 pc resolution cosmological hydrodynamic simulation of a late-type spiral galaxy. The simulation includes the effects of a uniform UV background, a delayed-radiative-cooling scheme for supernova feedback, and a star formation recipe based on a high gas density threshold. It allows a detailed study of the relative contributions of ''in-situ'' (within the main host) and ''ex-situ'' (within satellite galaxies) star formation to each major Galactic component in a close Milky Way analog. We investigate these two star-formation channels as a function of galactocentric distance, along different lines of sight above and along the disk plane, and as a function of cosmic time. We find that: (1) approximately 70% of today's stars formed in-situ; (2) more than two thirds of the ex-situ stars formed within satellites after infall; (3) the majority of ex-situ stars are found today in the disk and in the bulge; (4) the stellar halo is dominated by ex-situ stars, whereas in-situ stars dominate the mass profile at distances ≲ 5 kpc from the center at high latitudes; and (5) approximately 25% of the inner, r ≲ 20 kpc, halo is composed of in-situ stars that have been displaced from their original birth sites during Eris' early assembly history.

  5. A Be-type star with a black-hole companion.

    Science.gov (United States)

    Casares, J; Negueruela, I; Ribó, M; Ribas, I; Paredes, J M; Herrero, A; Simón-Díaz, S

    2014-01-16

    Stellar-mass black holes have all been discovered through X-ray emission, which arises from the accretion of gas from their binary companions (this gas is either stripped from low-mass stars or supplied as winds from massive ones). Binary evolution models also predict the existence of black holes accreting from the equatorial envelope of rapidly spinning Be-type stars (stars of the Be type are hot blue irregular variables showing characteristic spectral emission lines of hydrogen). Of the approximately 80 Be X-ray binaries known in the Galaxy, however, only pulsating neutron stars have been found as companions. A black hole was formally allowed as a solution for the companion to the Be star MWC 656 (ref. 5; also known as HD 215227), although that conclusion was based on a single radial velocity curve of the Be star, a mistaken spectral classification and rough estimates of the inclination angle. Here we report observations of an accretion disk line mirroring the orbit of MWC 656. This, together with an improved radial velocity curve of the Be star through fitting sharp Fe II profiles from the equatorial disk, and a refined Be classification (to that of a B1.5-B2 III star), indicates that a black hole of 3.8 to 6.9 solar masses orbits MWC 656, the candidate counterpart of the γ-ray source AGL J2241+4454 (refs 5, 6). The black hole is X-ray quiescent and fed by a radiatively inefficient accretion flow giving a luminosity less than 1.6 × 10(-7) times the Eddington luminosity. This implies that Be binaries with black-hole companions are difficult to detect in conventional X-ray surveys.

  6. A JVLA survey of the high-frequency radio emission of the massive magnetic B- and O-type stars

    Science.gov (United States)

    Kurapati, Sushma; Chandra, Poonam; Wade, Gregg; Cohen, David H.; David-Uraz, Alexandre; Gagne, Marc; Grunhut, Jason; Oksala, Mary E.; Petit, Veronique; Shultz, Matt; Sundqvist, Jon; Townsend, Richard H. D.; ud-Doula, Asif

    2017-02-01

    We conducted a survey of seven magnetic O-type stars and eleven B-type stars with masses above 8 M⊙ using the Very Large Array in the 1, 3 and 13 cm bands. The survey resulted in a detection of two O- and two B-type stars. While the detected O-type stars - HD 37742 and HD 47129 - are in binary systems, the detected B-type stars, HD 156424 and ALS 9522, are not known to be in binaries. All four stars were detected at 3 cm, whereas three were detected at 1 cm and only one star was detected at 13 cm. The detected B-type stars are significantly more radio luminous than the non-detected ones, which is not the case for O-type stars. The non-detections at 13 cm are interpreted as due to thermal free-free absorption. Mass-loss rates were estimated using 3 cm flux densities and were compared with theoretical mass-loss rates, which assume free-free emission. For HD 37742, the two values of the mass-loss rates were in good agreement, possibly suggesting that the radio emission for this star is mainly thermal. For the other three stars, the estimated mass-loss rates from radio observations were much higher than those expected from theory, suggesting either a possible contribution from non-thermal emission from the magnetic star or thermal or non-thermal emission due to interacting winds of the binary system, especially for HD 47129. All the detected stars are predicted to host centrifugal magnetospheres except HD 37742, which is likely to host a dynamical magnetosphere. This suggests that non-thermal radio emission is favoured in stars with centrifugal magnetospheres.

  7. Midnight sun

    Energy Technology Data Exchange (ETDEWEB)

    Brunger, A.P.; Lambert, S.B.; Gagnon, M.P.

    1990-09-01

    Midnight Sun, the University of Waterloo's solar-electric car, was designed and built by about 30 engineering, kinesiology and physics students for the GM Sunrayce USA held in July 1990. The car measures 2 m by 4.2 m, weighs 224 kg, can collect about 1000 W of solar electricity in full sun, and had a top speed of 79 km/h. The race took 11 days to cover the 1644 miles from the Epcot Center in Lake Buena Vista, Florida to the GM Technical Center in Warren, Michigan. Thirty-two cars, powered only by solar energy, competed in this race. Midnight Sun showed its potential during the race qualifying runs by completing the required qualifying course with the 12th fastest time of 52.83 seconds, and the 6th fastest trap speed of 63 km/h. During the Sunrayce, Midnight Sun came in second on day 1 of the race, tenth on day 6, and eighth on day 7, and was one of only 17 solar cars that were able to make it up the toughest hill in the race on day 8. The most serious problems encountered by the car were a weak rear suspension, power losses, and failure of bypass diodes in the photovoltaic array. Midnight Sun was in 17th place overall at the end of day 9. At about 11:00 am on day 10 in Ohio, the Waterloo car was moving at 60 km/h when it was bumped off the road by an out of control pickup truck. The solar car driver was not hurt. Despite the difficulties, the next day Midnight Sun was repaired and driven across the finish line at the ceremonial finish. After receiving time penalties for not completing the last day and a half of the race, Midnight Sun was awarded 24th place with an official cumulative time of 114 h 37 min 15 s. 4 figs., 4 tabs.

  8. New planet hints at life in the stars

    CERN Multimedia

    Dalton, A W

    2002-01-01

    Astronomers have detected a distant planet 100 light years from Earth, circling Tau1 Gruis, its star, in the constellation of Grus (the crane). The planet, similar in appearance to Jupiter, is three times as far away from its star as the Earth is from the Sun and takes four years to revolve around the star, in a roughly circular orbit. Scientists believe this type of planetary orbit is the most promising for finding worlds that contain life (1 page).

  9. Asteroseismic modelling of the solar-type subgiant star β Hydri

    DEFF Research Database (Denmark)

    Brandão, I.M.; Dogan, Gülnur; Christensen-Dalsgaard, Jørgen;

    2011-01-01

    the surface layers of stars. Because β Hydri is an evolved solar-type pulsator with mixed modes in its frequency spectrum, it is very interesting for asteroseismic studies. Aims: The goal of the present work is to search for a representative model of the solar-type star β Hydri, based on up-to-date non...... and different physics, using the stellar evolutionary code ASTEC. For the models that are inside the observed error box of β Hydri, we computed their frequencies with the pulsation code ADIPLS. We used two approaches to find the model that oscillates with the frequencies that are closest to the observed...

  10. Determining element abundances of [WC]-type Central Stars for probing stellar evolution and nucleosynthesis

    CERN Document Server

    Todt, H; Hamann, W -R; Gräfener, G

    2007-01-01

    [WC]-type CSPNs are hydrogen-deficient Central Stars of Planetary Nebulae showing strong stellar winds and a carbon-rich chemistry. We have analyzed new high-resolution spectra of [WC]-type CSPNs with the Potsdam Wolf-Rayet (PoWR) non-LTE expanding atmosphere models, using upgraded model atoms and atomic data. Previous analyses are repeated on the basis of the current models which account for iron-line blanketing. We especially focus on determining the chemical composition, including some trace elements like nitrogen which are of key importance for understanding the evolutionary origin of the hydrogen-deficient Central Stars.

  11. Atmospheric Parameters of 169 F, G, K and M-type Stars in the Kepler Field

    CERN Document Server

    Molenda-Zakowicz, J; Frasca, A; Uytterhoeven, K; Briquet, M; Van Winckel, H; Drobek, D; Niemczura, E; Lampens, P; Lykke, J; Bloemen, S; Gameiro, J F; Jean, C; Volpi, D; Gorlova, N; Mortier, A; Tsantaki, M; Raskin, G

    2013-01-01

    The asteroseismic and planetary studies, like all research related to stars, need precise and accurate stellar atmospheric parameters as input. We aim at deriving the effective temperature (Teff), the surface gravity (log g), the metallicity ([Fe/H]), the projected rotational velocity (v sin i) and the MK type for 169 F, G, K, and M-type Kepler targets which were observed spectroscopically from the ground with five different instruments. We use two different spectroscopic methods to analyse 189 high-resolution, high-signal-to-noise spectra acquired for the 169 stars. For 67 stars, the spectroscopic atmospheric parameters are derived for the ?first time. KIC 9693187 and 11179629 are discovered to be double-lined spectroscopic binary systems. The results obtained for those stars for which independent determinations of the atmospheric parameters are available in the literature are used for a comparative analysis. As a result, we show that for solar-type stars the accuracy of present determinations of atmospheric...

  12. Two Wide Planetary-Mass Companions to Solar-Type Stars in Upper Scorpius

    CERN Document Server

    Ireland, Michael J; Martinache, Frantz; Law, Nicholas M; Hillenbrand, Lynne A

    2010-01-01

    At wide separations, planetary-mass and brown dwarf companions to solar type stars occupy a curious region of parameters space not obviously linked to binary star formation or solar-system scale planet formation. These companions provide insight into the extreme case of companion formation (either binary or planetary), and due to their relative ease of observation when compared to close companions, they offer a useful template for our expectations of more typical planets. We present the results from an adaptive optics imaging survey for wide (50-500 AU) companions to solar type stars in Upper Scorpius. We report one new discovery of a ~14 M_J companion around GSC 06214-00210, and confirm that the candidate planetary mass companion 1RXS J160929.1-210524 detected by Lafreniere et al (2008) is in fact co-moving with its primary star. In our survey, these two detections correspond to ~4% of solar type stars having companions in the 6-20 M_J mass and 200-500 AU separation range. This figure is higher than would be...

  13. A spectroscopy study of nearby late-type stars, possible members of stellar kinematic groups

    CERN Document Server

    Maldonado, J; Eiroa, C; Montes, D; Montesinos, B; 10.1051/0004-6361/201014948

    2010-01-01

    Nearby late-type stars are excellent targets for seeking young objects in stellar associations and moving groups. The origin of these structures is still misunderstood, and lists of moving group members often change with time and also from author to author. Most members of these groups have been identified by means of kinematic criteria, leading to an important contamination of previous lists by old field stars. We attempt to identify unambiguous moving group members among a sample of nearby-late type stars by studying their kinematics, lithium abundance, chromospheric activity, and other age-related properties. High-resolution echelle spectra ($R \\sim 57000$) of a sample of nearby late-type stars are used to derive accurate radial velocities that are combined with the precise Hipparcos parallaxes and proper motions to compute galactic-spatial velocity components. Stars are classified as possible members of the classical moving groups according to their kinematics. The spectra are also used to study several a...

  14. Activity Of T Tauri Type Stars And Objects Similar To Them

    Science.gov (United States)

    Ibryamov, Sunay

    2016-06-01

    The main purpose of the dissertation is on the basis of long-term light curves, to be classified the variability of 28 PMS stars and to be draw conclusions about the physical mechanisms initiating observed changes in their brightness. 22 of the investigated stars are located in the dense molecular cloud L935, known as 'Gulf of Mexico' (NGC 7000/IC 5070), and 6 stars are located in the vicinity of the reflection nebula NGC 7129. The multicolour photometric observations that we present were performed from 1993 to 2015 with the 2-m RCC, the 50/70-cm Schmidt and the 60-cm Cassegrain telescopes of the Rozhen NAO (Bulgaria) and the 1.3-m RC telescope of the Skinakas Observatory (Greece). All frames were taken through a standard Johnson-Cousins set of filters. The studied stars were classified as follows: V752 Cyg, V1539 Cyg, V1716 Cyg, FHO 26, FHO 29, LkHα 186, LkHα 187, LkHα 191, [KW97] 53-17, [KW97] 53-22, [KW97] 53-23, V391 Cep, NGC 7129 S V2 and 2MASS J21403576+6635000 show characteristics for classical T Tauri stars; V1538 Cyg, V1929 Cyg, [KW97] 53-20 and NGC 7129 S V1 are probably weak-line T Tauri stars; LkHα 189 and [KW97] 53-11 show characteristics for both type T Tauri stars and spectral observations are needed for their exact classification; V350 Cep shows indications for EXor and/or FUor-type variability; V521 Cyg, FHO 27, FHO 28 and NGC 7129 S V3 show characteristics for UXor-type variability; V1957 Cyg, V2051 Cyg and [KW97] 53-36 likely are evolved PMS stars or post-T Tauri stars. Periodicity was discovered for 3 of the investigated stars. V1716 Cyg indicates 4.15-day period, V1929 Cyg indicates 0.43-day period and LkHα 189 indicates 2.45-day period.

  15. Sun, Earth and Sky

    Science.gov (United States)

    Lang, Kenneth R.

    1995-01-01

    The Sun is enveloped by a hot, tenuous million-degree corona that expands to create a continuous solar wind that sweeps past all the planets and fills the heliosphere. The solar wind is modulated by strong gusts that are initiated by powerful explosions on the Sun, including solar flares and coronal mass ejections. This dynamic, invisible outer atmosphere of the Sun is currently under observation with the soft X-ray telescope aboard the Yohkoh spacecraft, whose results are presented. We also show observations from the Ulysses spacecraft that is now passing over the solar pole, sampling the solar wind in this region for the first time. Two other spacecraft, Voyager 1 and 2, have recently detected the outer edge of the invisible heliosphere, roughly halfway to the nearest star. Magnetic solar activity, the total radiative output from the Sun, and the Earth's mean global surface temperature all vary with the 11-year sunspot cycle in which the total number of sunspots varies from a maximum to a minimum and back to a maximum again in about 11 years. The terrestrial magnetic field hollows out a protective magnetic cavity, called the magnetosphere, within the solar wind. This protection is incomplete, however, so the Sun feeds an unseen world of high-speed particles and magnetic fields that encircle the Earth in space. These particles endanger spacecraft and astronauts, and also produce terrestrial aurorae. An international flotilla of spacecraft is now sampling the weak points in this magnetic defense. Similar spacecraft have also discovered a new radiation belt, in addition to the familiar Van Allen belts, except fed by interstellar ions instead of electrons and protons from the Sun.

  16. Building Late-Type Spiral Galaxies by In-Situ and Ex-Situ Star Formation

    CERN Document Server

    Pillepich, Annalisa; Mayer, Lucio

    2014-01-01

    We analyze the formation and evolution of the stellar components in "Eris", a 120 pc-resolution cosmological hydrodynamic simulation of a late-type spiral galaxy. The simulation includes the effects of a uniform UV background, a delayed-radiative-cooling scheme for supernova feedback, and a star formation recipe based on a high gas density threshold. It allows a detailed study of the relative contributions of "in-situ" (within the main host) and "ex-situ" (within satellite galaxies) star formation to each major Galactic component in a close Milky Way analog. We investigate these two star-formation channels as a function of galactocentric distance, along different lines of sight above and along the disk plane, and as a function of cosmic time. We find that: 1) approximately 70 percent of today's stars formed in-situ; 2) more than two thirds of the ex-situ stars formed within satellites after infall; 3) the majority of ex-situ stars are found today in the disk and in the bulge; 4) the stellar halo is dominated ...

  17. The Peculiar Type Ib Supernova 2006jc: A WC Star Explosion

    CERN Document Server

    Tominaga, N; Suzuki, T; Tanaka, M; Nomoto, K; Maeda, K; Chieffi, A; Tornambé, A; Minezaki, T; Yoshii, Y; Sakon, I; Wada, T; Ohyama, Y; Tanabé, T; Kaneda, H; Onaka, T; Nozawa, T; Kozasa, T; Kawabata, K S; Anupama, G C; Sahu, D K; Gurugubelli, U K; Prabhu, T P; Deng, J

    2007-01-01

    We present a theoretical model for Type Ib supernova (SN) 2006jc associated with a luminous blue variable (LBV)-like event. We calculate the presupernova evolution of the progenitor star, hydrodynamics and nucleosynthesis of the SN explosion, and the SN bolometric light curve (LC). The observed bolometic LC is constructed by integrating the UV, optical, near-infrared (NIR), and mid-infrared (MIR) fluxes. The progenitor is assumed to be as massive as $40\\Msun$ on the zero-age. The star undergoes extensive mass loss to reduce its mass down to as small as $6.9\\Msun$, thus becoming a WC Wolf-Rayet star at the presupernova stage. The WC star model has a thick carbon-rich layer, in which amorphous carbon grains can be formed during the explosion. This could explain the brightening in the NIR flux and the observed dust feature in MIR. The typical main-sequence mass of a WC Wolf-Rayet star and thus the progenitor of SN 2006jc is more massive than $40\\Msun$. We suggest that the explosions of stars more massive than $4...

  18. Discovery of a magnetic field in the early B-type star sigma Lupi

    CERN Document Server

    Henrichs, H F; Plaggenborg, B; Marsden, S C; Waite, I A; Landstreet, J D; Wade, G A; Grunhut, J H; Oksala, M E

    2012-01-01

    Magnetic early B-type stars are rare. To identify them, we use the strongest indirect indicator of a magnetic field in B stars, which is periodic variability of UV stellar wind lines occurring symmetric about the approximate rest wavelength. Probable magnetic candidates are targets for follow-up spectropolarimetry to search for a magnetic field. From the UV wind line variability the B1/B2V star sigma Lupi emerged as a new magnetic candidate star. AAT spectropolarimetric measurements with SEMPOL were obtained. The longitudinal component of the magnetic field integrated over the visible surface of the star was determined with the Least-Squares Deconvolution method. The UV line variations of sigma Lupi are similar to what is known in magnetic B stars, but no periodicity could be determined. We detected a varying longitudinal magnetic field with amplitude of about 100 G with error bars of typically 20 G, which supports an oblique magnetic-rotator configuration. The EW variations of the UV lines, the magnetic and ...

  19. X-ray Emission from Nitrogen-Type Wolf-Rayet Stars

    CERN Document Server

    Skinner, S L; Guedel, M; Schmutz, W; Sokal, K R

    2009-01-01

    We summarize new X-ray detections of four nitrogen-type Wolf-Rayet (WR) stars obtained in a limited survey aimed at establishing the X-ray properties of WN stars across their full range of spectral subtypes. None of the detected stars is so far known to be a close binary. We report Chandra detections of WR 2 (WN2), WR 18 (WN4), and WR 134 (WN6), and an XMM-Newton detection of WR79a (WN9ha). These observations clearly demonstrate that both WNE and WNL stars are X-ray sources. We also discuss Chandra archive detections of the WN6h stars WR 20b, WR 24, and WR 136 and ROSAT non-detections of WR 16 (WN8h) and WR 78 (WN7h). The X-ray spectra of all WN detections show prominent emission lines and an admixture of cool (kT 2 keV) plasma. The hotter plasma is not predicted by radiative wind shock models and other as yet unidentified mechanisms are at work. Most stars show X-ray absorption in excess of that expected from visual extinction (Av), likely due to their strong winds or cold circumstellar gas. Existing data s...

  20. Abundances of Refractory Elements for G-type Stars with Extrasolar Planets

    CERN Document Server

    Kang, Wonseok; Kim, Kang-Min

    2011-01-01

    We confirm the difference of chemical abundance between stars with and without exoplanet, as well as present the relation between chemical abundances and the physical properties of exoplanets such as planetary mass and semi-major axis of planetary orbit. We have obtained the spectra of 52 G-type stars with BOES (BOAO Echelle Spectrograph) and carried out the abundance analysis for 12 elements of Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Co, and Ni. We first have found that the [Mn/Fe] ratios of planet-host stars are higher than those of comparisons in the whole metallicity range, and in metal-poor stars of [Fe/H] $<$ -0.4, the abundance difference have been larger than in metal-rich samples, especially for the elements of Mg, Al, Sc, Ti, V, and Co. When examined the relation between planet properties and metallicities of planet-host stars, we have observed that planet-host stars with low-metallicity tend to bear several low-mass planets ($< M_J$) instead of a massive gas-giant planet.

  1. Early-type massive stars in Carina Nebula within the Gaia-ESO Survey.

    Science.gov (United States)

    Berlanas, S. R.; Herrero, A.; Martins, F.; Simón-Díaz, S.; Mahy, L.; Blomme, R.; GES WG-13

    2017-03-01

    The Gaia-ESO Survey (GES) is obtaining high quality spectra of ˜ 10^5 stars in our Galaxy, providing an homogeneous and unique overview of all the main components of the Milky Way, its formation history and the evolution of young, mature and ancient Galactic populations. Our group is in charge of the early-type massive stars that define the youngest population in the survey. In this contribution, we present the results of the quantitative spectroscopic analysis of O-type stars in the Carina Nebula within the Gaia-ESO Survey. For this aim, we have used FASTWIND and CMFGEN stellar atmosphere codes, providing stellar parameters for the current sample (GES data release iDR4).

  2. Quantifying Star Formation in Early-Type Galaxies using Spatially-Resolved UV-Optical Photometry

    Science.gov (United States)

    Kaviraj, Sugata

    2013-01-01

    Our understanding of star formation in nearby early-type galaxies (ETGs) has evolved rapidly in recent years, due to new UV data from GALEX and HST. Contrary to the classical notion of them being old, passively-evolving systems, recent work has demonstrated widespread late-epoch star formation in ETGs, which builds ~20% of their stellar mass after 1, via minor mergers between ETGs and gas-rich dwarfs. While survey data from GALEX has indicated the average properties of star formation in the ETG population as a whole, I demonstrate how spatially-resolved UV studies can offer detailed insights into the star formation histories of individual galaxies, using an HST-WFC3 case study of NGC 4150. Using a pixel-by-pixel analysis in 5 WFC3 filters, spanning UV to i-band, reveals a central 0.9 Gyr old young stellar population, with a median metallicity of 0.5 solar, that contributes around 3% of the stellar mass and coincides spatially with a small, kinematically-decoupled core (indicating a recent minor merger). Assuming that the metallicity of the young stars traces the gas-phase metallicity of the satellite that fuels the star formation, we use the mass-metallicity relation to estimate the mass ratio of the merger to be ~1:20. An WFC3 study of globular clusters reveals a substantial population of young star clusters coincident with the central region of star formation and indicates that the bulk of the stellar mass in this galaxy probably formed 6-8 Gyrs in the past. This study demonstrates the utility of high-resolution imaging from future instruments such as the extremely large telescopes. (Based on Early Release Science observations by the WFC3 Scientific Oversight Committee. We are grateful to the Director of the Space Telescope Science Institute for awarding Director's Discretionary time for this program.)

  3. On Iron Enrichment, Star Formation, and Type Ia Supernovae in Galaxy Clusters

    Science.gov (United States)

    Loewenstein, Michael

    2006-01-01

    The nature of star formation and Type Ia supernovae (SNIa) in galaxies in the field and in rich galaxy clusters are contrasted by juxtaposing the buildup of heavy metals in the universe inferred from observed star formation and supernovae rate histories with data on the evolution of Fe abundances in the intracluster medium (ICM). Models for the chemical evolution of Fe in these environments are constructed, subject to observational constraints, for this purpose. While models with a mean delay for SNIa of 3 Gyr and standard initial mass function (IMF) are fully consistent with observations in the field, cluster Fe enrichment immediately tracked a rapid, top-heavy phase of star formation - although transport of Fe into the ICM may have been more prolonged and star formation likely continued beyond redshift 1. The means of this prompt enrichment consisted of SNII yielding greater than or equal to 0.1 solar mass per explosion (if the SNIa rate normalization is scaled down from its value in the field according to the relative number of candidate progenitor stars in the 3 - 8 solar mass range) and/or SNIa with short delay times originating during the rapid star formation epoch. Star formation is greater than 3 times more efficient in rich clusters than in the field, mitigating the overcooling problem in numerical cluster simulations. Both the fraction of baryons cycled through stars, and the fraction of the total present-day stellar mass in the form of stellar remnants, are substantially greater in clusters than in the field.

  4. Little Sun

    DEFF Research Database (Denmark)

    Ebbesen, Toke Riis

    2017-01-01

    the ideas of Alfred Gell’s anthropology of art and the indicative framework derived from Argentinian semiotician Juan Pablo Bonta and Jørn Guldberg. The toy-like solar lamp Little Sun by Olafur Eliasson and Frederik Ottesen is used as case that blends the registers of social design and art......, and as an example of how designers attempt to determine meaning potentials through design in a complex interplay of different strategies. In the final analysis, what characterise objects like Little Sun is seldom that they communicate their meanings in themselves, but instead rely on forceful mediations to gain...

  5. Little sun

    DEFF Research Database (Denmark)

    Ebbesen, Toke Riis

    2017-01-01

    the ideas of Alfred Gell’s anthropology of art and the indicative framework derived from Argentinian semiotician Juan Pablo Bonta and Jørn Guldberg. The toy-like solar lamp Little Sun by Olafur Eliasson and Frederik Ottesen is used as case that blends the registers of social design and art......, and as an example of how designers attempt to determine meaning potentials through design in a complex interplay of different strategies. In the final analysis, what characterise objects like Little Sun is seldom that they communicate their meanings in themselves, but instead rely on forceful mediations to gain...

  6. BESO échelle spectroscopy of solar-type stars at Cerro Armazones

    Science.gov (United States)

    Fuhrmann, K.; Chini, R.; Hoffmeister, V. H.; Lemke, R.; Murphy, M.; Seifert, W.; Stahl, O.

    2011-03-01

    The Bochum Échelle Spectroscopic Observer BESO is a fibre-fed high-resolution spectrograph for the 1.5-m Hexapod Telescope at the Cerro Armazones Observatory in the Atacama desert in Chile. Here we report on the first BESO observations and model atmosphere analyses of solar-type stars secured in 2010 April. The quality of the data is first tested with a reflected sunlight spectrum as well as the standard G-type subgiant 70 Vir. We then investigate the bright and supposedly single F-type star ξ Gem and present the spectroscopic evidence that instead favours an equal-mass binary. We present also the first composite synthetic modelling of the G-type visual binary HR 3430 and discuss the spectroscopic observations that identify this as a triple system. We conclude with another triple, the famous and very nearby α Cen, and the basic stellar parameters of its inner, solar-type visual binary.

  7. Do AGN suppress star formation in early-type galaxies?

    OpenAIRE

    Schawinski, Kevin

    2010-01-01

    The observation that AGN host galaxies preferentially inhabit the "green valley" between the blue cloud and the red sequence has significant consequences for our understanding of the co-evolution of galaxies and black holes via accretion events. I discuss the interpretation of green valley AGN host galaxy colours with particular focus on early-type galaxies.

  8. The NaI D resonance lines in main-sequence late-type stars

    Science.gov (United States)

    Díaz, Rodrigo F.; Cincunegui, Carolina; Mauas, Pablo J. D.

    2007-07-01

    We study the sodium D lines (D1: 5895.92Å D2: 5889.95Å) in late-type dwarf stars. The stars have spectral types between F6 and M5.5 (B - V between 0.457 and 1.807) and metallicity between [Fe/H] = -0.82 and 0.6. We obtained medium-resolution echelle spectra using the 2.15-m telescope at the Argentinian observatory Complejo Astronómico El Leoncito (CASLEO). The observations have been performed periodically since 1999. The spectra were calibrated in wavelength and in flux. A definition of the pseudo-continuum level is found for all our observations. We also define a continuum level for calibration purposes. The equivalent width of the D lines is computed in detail for all our spectra and related to the colour index (B - V) of the stars. When possible, we perform a careful comparison with previous studies. Finally, we construct a spectral index (R'D) as the ratio between the flux in the D lines and the bolometric flux. We find that, once corrected for the photospheric contribution, this index can be used as a chromospheric activity indicator in stars with a high level of activity. Additionally, we find that combining some of our results, we obtain a method to calibrate in flux stars of unknown colour.

  9. Strömgren and Hß photometry of O and B type stars in star-forming regions. II. Moneceros OB2, Canis Major OB1 and Collinder 121

    DEFF Research Database (Denmark)

    Kaltcheva, N.T.; Olsen, Erik Heyn; Clausen, J.V.

    1999-01-01

    Stars: Early-type - Galaxy: Open clusters and associations: Individual: Mon OB2, CMa OB1, Col 121......Stars: Early-type - Galaxy: Open clusters and associations: Individual: Mon OB2, CMa OB1, Col 121...

  10. NLTE analysis of spectra I : Departures from LTE for A-type stars

    NARCIS (Netherlands)

    Kamp, I.; Monier, R.; Smalley, B.; Wahlgren, G.; Stee, Ph.

    2010-01-01

    A-type stars with their shallow convection zones serve as ideal physics laboratories for stellar atmosphere research. In the absence of large scale mixing, processes such as diffusion, mass loss and accretion leave their characteristic imprint on the chemical composition of the photosphere. This cha

  11. NLTE analysis of spectra i: Departures from LTE for A-type stars

    NARCIS (Netherlands)

    Kamp, I.

    2010-01-01

    A-type stars with their shallow convection zones serve as ideal physics laboratories for stellar atmosphere research. In the absence of large scale mixing, processes such as diffusion, mass loss and accretion leave their characteristic imprint on the chemical composition of the photosphere. This cha

  12. Ensemble asteroseismology of solar-type stars with the NASA Kepler mission

    NARCIS (Netherlands)

    Chaplin, W.J.; Kjeldsen, H.; Christensen-Dalsgaard, J.; Basu, S.; Miglio, A.; Appourchaux, T.; Bedding, T.R.; Elsworth, Y.; Garcia, R.A.; Gilliland, R.L.; Girardi, L.; Houdek, G.; Karoff, C.; Kawaler, S.D.; Metcalfe, T.S.; Molenda-Zakowicz, J.; Monteiro, M.J.P.F.G.; Thompson, M.J.; Verner, G.A.; Ballot, J.; Bonanno, A.; Brandao, I.M.; Broomhall, A.M.; Bruntt, H.; Campante, T.L.; Corsaro, E.; Creevey, O.L.; Esch, L.; Gai, N.; Gaulme, P.; Hale, S.J.; Handberg, R.; Hekker, S.; Huber, D.; Jimenez, A.; Mathur, S.; Mazumdar, A.; Mosser, B.; New, R.; Pinsonneault, M.H.; Pricopi, D.; Quirion, P.O.; Regulo, C.; Salabert, D.; Serenelli, A.M.; Silva Aguirre, V.; Sousa, S.G.; Stello, D.; Stevens, I.R.; Suran, M.D.; Uytterhoeven, K.; White, T.R.; Borucki, W.J.; Brown, T.M.; Jenkins, J.M.; Kinemuchi, K.; Van Cleve, J.; Klaus, T.C.

    2011-01-01

    In addition to its search for extrasolar planets, the NASA Kepler mission provides exquisite data on stellar oscillations. We report the detections of oscillations in 500 solar-type stars in the Kepler field of view, an ensemble that is large enough to allow statistical studies of intrinsic stellar

  13. The VLT-FLAMES Tarantula Survey. XXII. Multiplicity properties of the B-type stars

    NARCIS (Netherlands)

    Dunstall, P.R.; Dufton, P.L.; Sana, H.; Evans, C.J.; Howarth, I.D.; Simón-Díaz, S.; de Mink, S.E.; Langer, N.; Maíz Apellániz, J.; Taylor, W.D.

    2015-01-01

    We investigate the multiplicity properties of 408 B-type stars observed in the 30 Doradus region of the Large Magellanic Cloud with multi-epoch spectroscopy from the VLT-FLAMES Tarantula Survey (VFTS). We use a cross-correlation method to estimate relative radial velocities from the helium and metal

  14. Ensemble Asteroseismology of Solar-Type Stars with the NASA Kepler Mission

    DEFF Research Database (Denmark)

    Chaplin, William J.; Kjeldsen, Hans; Christensen-Dalsgaard, Jørgen

    2011-01-01

    In addition to its search for extrasolar planets, the NASA Kepler mission provides exquisite data on stellar oscillations. We report the detections of oscillations in 500 solar-type stars in the Kepler field of view, an ensemble that is large enough to allow statistical studies of intrinsic stellar...

  15. Verification of the Kepler Input Catalog from asteroseismology of solar-type stars

    NARCIS (Netherlands)

    G.A. Verner; W.J. Chaplin; S. Basu; T.M. Brown; S. Hekker; D. Huber; C. Karoff; S. Mathur; T.S. Metcalfe; B. Mosser; P.O. Quirion; T. Appourchaux; T.R. Bedding; H. Bruntt; T.L. Campante; Y. Elsworth; R.A. Garcia; R. Handberg; C. Regulo; I.W. Roxburgh; D. Stello; J. Christensen-Dalsgaard; R.L. Gilliland; S.D. Kawaler; H. Kjeldsen; C. Allen; B.D. Clarke; F.R. Girouard

    2011-01-01

    We calculate precise stellar radii and surface gravities from the asteroseismic analysis of over 500 solar-type pulsating stars observed by the Kepler space telescope. These physical stellar properties are compared with those given in the Kepler Input Catalog (KIC), determined from ground-based mult

  16. Planet Occurrence within 0.25 AU of Solar-type Stars from Kepler

    DEFF Research Database (Denmark)

    Howard, Andrew W.; Marcy, Geoffrey W.; Bryson, Stephen T.

    2012-01-01

    We report the distribution of planets as a function of planet radius, orbital period, and stellar effective temperature for orbital periods less than 50 days around solar-type (GK) stars. These results are based on the 1235 planets (formally "planet candidates") from the Kepler mission that inclu...

  17. Finding the lost siblings of the Sun

    Science.gov (United States)

    Liu, Cheng; Feltzing, Sofia; Ruchti, Gregory

    2014-01-01

    We have performed a spectral analysis on 18 stars solar sibling candidate. We found that only one one of the candidateshas solar metallicity and at the same time might have an age comparable to that of the Sun.

  18. Sun Proof

    Centers for Disease Control (CDC) Podcasts

    2012-10-23

    In this podcast for kids, the Kidtastics talk about the harmful effects of the sun and how to protect yourself from it.  Created: 10/23/2012 by Centers for Disease Control and Prevention (CDC).   Date Released: 10/23/2012.

  19. A JVLA survey of the high frequency radio emission of the massive magnetic B- and O-type stars

    CERN Document Server

    Kurapati, Sushma; Wade, Gregg; Cohen, David H; David-Uraz, Alexandre; Gagne, Marc; Grunhut, Jason; Oksala, Mary E; Petit, Veronique; Shultz, Matt; Sundqvist, Jon; Townsend, Richard H D; ud-Doula, Asif

    2016-01-01

    We conducted a survey of seven magnetic O and eleven B-type stars with masses above $8M_{\\odot}$ using the Very Large Array in the 1cm, 3cm and 13cm bands. The survey resulted in a detection of two O and two B-type stars. While the detected O-type stars - HD 37742 and HD 47129 - are in binary systems, the detected B-type stars, HD 156424 and ALS 9522, are not known to be in binaries. All four stars were detected at 3cm, whereas three were detected at 1cm and only one star was detected at 13cm. The detected B-type stars are significantly more radio luminous than the non-detected ones, which is not the case for O-type stars. The non-detections at 13cm are interpreted as due to thermal free-free absorption. Mass-loss rates were estimated using 3cm flux densities and were compared with theoretical mass-loss rates, which assume free-free emission. For HD 37742, the two values of the mass-loss rates were in good agreement, possibly suggesting that the radio emission for this star is mainly thermal. For the other th...

  20. A Statistical Reconstruction of the Planet Population Around Kepler Solar-Type Stars

    CERN Document Server

    Silburt, Ari; Wu, Yanqin

    2014-01-01

    Using the most recent Kepler catalog, we reconstruct the occurrence rate of small (Neptune-sized or below) planets as a function of orbital period and planet radius, taking careful account of various detection biases. We analyze a sample of $76,000$ Sun-like stars and their associated planet candidates with periods between $20$ and $200$ days, and sizes between $1$ and $4 R_\\oplus$. Such planets have likely experienced little photoevaporation, and may reflect the "primordial" planet population. Assuming that the size distribution of planets are independent of their orbital periods (and vice versa), we conclude that Kepler planets are preferentially peaked at $2-2.8 R_\\oplus$, with their numbers decreasing gradually toward smaller sizes. These planets are found roughly uniformly in logarithmic period. The average number of planets per star, in the stated period and size ranges, is $0.46 \\pm 0.03$. This number rises by $\\sim 0.2$ if one includes planets inward of $20$ days. Upon extrapolation we obtain an occur...

  1. Non-LTE modeling of the near UV band of late-type stars

    CERN Document Server

    Short, C Ian

    2008-01-01

    We investigate the ability of both LTE and Non-LTE models to fit the near UV band absolute flux distribution and individual spectral line profiles of three standard stars for which high quality spectrophotometry and high resolution spectroscopy are available: The Sun (G2 V), Arcturus (K2 III), and Procyon (F5 IV-V). We investigate 1) the effect of the choice of atomic line list on the ability of NLTE models to fit the near UV band flux level, 2) the amount of a hypothesized continuous thermal absorption extinction source required to allow NLTE models to fit the observations, and 3) the semi-empirical temperature structure required to fit the observations with NLTE models and standard continuous near UV extinction. We find that all models that are computed with high quality atomic line lists predict too much flux in the near UV band for Arcturus, but fit the warmer stars well. The variance among independent measurements of the solar irradiance in the near UV is sufficiently large that we cannot definitely conc...

  2. Early-type stars in the young open cluster NGC 2244 and in the Mon OB2 association I. The multiplicity of O-type stars

    CERN Document Server

    Mahy, L; Rauw, G; Gosset, E; De Becker, M; Sana, H; Eenens, P

    2009-01-01

    Aims. We present the results obtained from a long-term spectroscopic campaign devoted to the multiplicity of O-type stars in the young open cluster NGC2244 and in the Mon OB2 association. Methods. Our spectroscopic monitoring was performed over several years, allowing us to probe different time-scales. For each star, several spectral diagnostic tools are applied, in order to search for line shifts and profile variations. We also measure the projected rotational velocity and revisit the spectral classification. Results. In our sample, several stars were previously considered as spectroscopic binaries, though only a few scattered observations were available. Our results now reveal a more complex situation. Our study identifies two new spectroscopic binaries (HD46149 in NGC2244 and HD46573 in MonOB2). The first object is a long-period double-lined spectroscopic binary, though the exact value of its period remains uncertain and the second object is classified as an SB1 system with a period of about 10.67 days but...

  3. Gamma-ray emission from early-type stars interacting with AGN jets

    Directory of Open Access Journals (Sweden)

    Araudo Anabella T.

    2013-12-01

    Full Text Available We study the interaction of early-type stars with the jets of active galactic nuclei. A bow-shock will form as a consequence of the interaction of the jet with the winds of stars and particles can be accelerated up to relativistic energies in these shocks. We compute the non-thermal radiation produced by relativistic electrons from radio to gamma-rays. This radiation may be significant, and its detection might yield information on the properties of the stellar population in the galaxy nucleus, as well as on the relativistic jet. This emission is expected to be relevant for nearby non-blazar sources.

  4. Nine New Variable Stars in Cygnus and Variability Type Determination of [Wm2007] 1176

    CERN Document Server

    Furgoni, Riccardo

    2014-01-01

    I report the discovery of nine new variable stars in Cygnus: five pulsating (VSX J192319.8+280832, VSX J192405.8+280352, VSX J192220.7+275518, VSX J192304.4+280231, VSX J192255.1+274744) and four eclipsing (VSX J192252.4+280217, VSX J192251.4+280456, VSX J192226.0+281019, VSX J192524.9+275342). The variability type of the variable star [WM2007] 1176, that was considered in literature a possible RRC, was found to be a W UMa variable with an obvious O'Connell effect.

  5. Coronal thermal structure and abundances of supermetal-rich solar-type stars

    Science.gov (United States)

    Brickhouse, Nancy S. (Principal Investigator); Mushotzky, Richard F. (Technical Monitor)

    2005-01-01

    This observation is for grating spectroscopy of Tau Boo, a late-type star with very high metallicity (about twice solar). Despite the extreme condition of high metallicity in the photosphere, the abundance ratios of the corona appear consistent with the general picture of a coronal abundance/activity relation. The target was obtained by XMM-Newton on 24 June 2003 for 71900 sec. The European PI Antonio Maggio is responsible for data reduction. Members of our team presented at the Cool Stars Workshop 13 held in Hamburg, Germany in July 2004 and conferred at that time on the publication of results. This project is complete except for the final publication.

  6. A spectroscopic orbit for the late-type Be star β CMi

    Science.gov (United States)

    Dulaney, Nick; Richardson, Noel; Gerhartz, Cody; Bjorkman, Jon Eric; Bjorkman, Karen S.; Carciofi, Alex C.; Wang, Luqian; Morrison, Nancy D.; Klement, Robert; Ritter Observing Team

    2017-01-01

    The late-type Be star beta CMi is remarkably stable compared to other Be stars that have been studied. This has led to a realistic model of the outflowing Be disk by Klement et al. (2015) These results showed that the disk is likely truncated at a finite radius from the star, which is easily accomplished by a binary companion in orbit. We report on an analysis of the Ritter Observatory spectroscopic archive of beta CMi in hopes of discovering evidence of the elusive companion. We detect orbital motion caused by a companion from small shifts in the H-alpha emission line. We then compared the small changes in the violet-to-red peak height changes (V/R) with the orbital motion. While some V/R variability seems to be present in the H-alpha profile, there is only weak evidence that it follows the orbital motion, as suggested by recent Be binary models by Panoglou et al. (2016). We also analyze several epochs of near-infrared moderate resolution spectra from the InfraRed Telescope Facility with the SpeX spectrograph. Near-infrared spectra show variations of the Pa-beta and Br-gamma lines, suggesting structure could be present in the inner parts of the Be disk. These results suggest that beta CMi is similar to several other Be stars, and is a product of binary evolution where Roche lobe overflow has spun up the current Be star, likely leaving a hot subdwarf or white dwarf in orbit around the star. Unfortunately, no sign of this star is found in the very limited archive of International Ultraviolet Explorer spectra, so future UV studies of the system are necessary.We are grateful for support of the NSF REU program at the University of Toledo through NSF grant 1262810 and addtional support from the NSF under grant AST-1412135.

  7. NuSTAR Reveals Extreme Absorption in z < 0.5 Type 2 Quasars

    CERN Document Server

    Lansbury, G B; Alexander, D M; Assef, R J; Aird, J; Annuar, A; Ballantyne, D R; Balokovic, M; Bauer, F E; Boggs, S E; Brandt, W N; Brightman, M; Christensen, F E; Civano, F; Comastri, A; Craig, W W; Del Moro, A; Grefenstette, B W; Hailey, C J; Harrison, F A; Hickox, R C; Koss, M; LaMassa, S M; Luo, B; Puccetti, S; Stern, D; Treister, E; Vignali, C; Zappacosta, L; Zhang, W W

    2015-01-01

    The intrinsic column density (NH) distribution of quasars is poorly known. At the high obscuration end of the quasar population and for redshifts z 1.5e24 cm^-2) type 2 quasars (CTQSO2s); five new NuSTAR observations are reported herein, and four have been previously published. The candidate CTQSO2s lie at z~ 90 net source counts at 8-24 keV). For these NuSTAR-detected sources direct (i.e., X-ray spectral) constraints on the intrinsic AGN properties are feasible, and we measure column densities ~2.5-1600 times higher and intrinsic (unabsorbed) X-ray luminosities ~10-70 times higher than pre-NuSTAR constraints from Chandra and XMM-Newton. Assuming the NuSTAR-detected type 2 quasars are representative of other Compton-thick candidates, we make a correction to the NH distribution for optically selected type 2 quasars as measured by Chandra and XMM-Newton for 39 objects. With this approach, we predict a Compton-thick fraction of f_CT = 36^{+14}_{-12} %, although higher fractions (up to 76%) are possible if indire...

  8. Molecular Gas and Star Formation in Local Early-Type Galaxies

    CERN Document Server

    Bureau, M; Alatalo, K; Crocker, A F; Blitz, L; Young, L M; Combes, F; Bois, M; Bournaud, F; Cappellari, M; Davies, R L; de Zeeuw, P T; Duc, P -A; Emsellem, E; Khochfar, S; Krajnovic, D; Kuntschner, H; Lablanche, P -Y; McDermid, R M; Morganti, R; Naab, T; Oosterloo, T; Sarzi, M; Scott, N; Serra, P; Weijmans, A

    2011-01-01

    The molecular gas content of local early-type galaxies is constrained and discussed in relation to their evolution. First, as part of the Atlas3D survey, we present the first complete, large (260 objects), volume-limited single-dish survey of CO in normal local early-type galaxies. We find a surprisingly high detection rate of 22%, independent of luminosity and at best weakly dependent on environment. Second, the extent of the molecular gas is constrained with CO synthesis imaging, and a variety of morphologies is revealed. The kinematics of the molecular gas and stars are often misaligned, implying an external gas origin in over a third of the systems, although this behaviour is drastically diffferent between field and cluster environments. Third, many objects appear to be in the process of forming regular kpc-size decoupled disks, and a star formation sequence can be sketched by piecing together multi-wavelength information on the molecular gas, current star formation, and young stars. Last, early-type gala...

  9. A Consistency Test of Spectroscopic Gravities for Late-Type Stars

    CERN Document Server

    Allende-Prieto, C; Lambert, D L; Gustafsson, B; Prieto, Carlos Allende; Lopez, Ramon J. Garcia; Lambert, David L.; Gustafsson, Bengt

    1999-01-01

    Chemical analyses of late-type stars are usually carried out following the classical recipe: LTE line formation and homogeneous, plane-parallel, flux-constant, and LTE model atmospheres. We review different results in the literature that have suggested significant inconsistencies in the spectroscopic analyses, pointing out the difficulties in deriving independent estimates of the stellar fundamental parameters and hence,detecting systematic errors. The trigonometric parallaxes measured by the HIPPARCOS mission provide accurate appraisals of the stellar surface gravity for nearby stars, which are used here to check the gravities obtained from the photospheric iron ionization balance. We find an approximate agreement for stars in the metallicity range -1 <= [Fe/H] <= 0, but the comparison shows that the differences between the spectroscopic and trigonometric gravities decrease towards lower metallicities for more metal-deficient dwarfs (-2.5 <= [Fe/H] <= -1.0), which casts a shadow upon the abundanc...

  10. On the metallicity dependance of the [Y/Mg] - age relation for solar type stars

    CERN Document Server

    Feltzing, S; McMillan, P J; Stonkute, E

    2016-01-01

    Several recent studies of Solar twins in the Solar neighbourhood have shown a tight correlation between various elemental abundances and age, in particular [Y/Mg]. If this relation is real and valid for other types of stars as well as elsewhere in the Galaxy it would provide a very powerful tool to derive ages of stars without the need to resort to determining their masses (evolutionary stage) very precisely. The method would also likely work if the stellar parameters have relatively large errors. The studies presented in the recent literature span a narrow range of [Fe/H]. By studying a larger sample of Solar neighbourhood dwarfs with a much larger range in [Fe/H], we find that the relation between [Y/Mg] and age depends on the [Fe/H] of the stars. Hence, it appears that the [Y/Mg] - age relation is unique to Solar analogues.

  11. On the metallicity dependence of the [Y/Mg]-age relation for solar-type stars

    Science.gov (United States)

    Feltzing, Sofia; Howes, Louise M.; McMillan, Paul J.; Stonkutė, Edita

    2017-02-01

    Several recent studies of solar twins in the solar neighbourhood have shown a tight correlation between various elemental abundances and age, in particular [Y/Mg]. If this relation is real and valid for other types of stars as well as elsewhere in the Galaxy, it would provide a very powerful tool to derive ages of stars without the need to resort to determining their masses (evolutionary stage) very precisely. The method would also likely work if the stellar parameters have relatively large errors. The studies presented in the recent literature span a narrow range of [Fe/H]. By studying a larger sample of solar neighbourhood dwarfs with a much larger range of [Fe/H], we find that the relation between [Y/Mg] and age depends on the [Fe/H] of the stars. Hence, it appears that the [Y/Mg]-age relation is unique to solar analogues.

  12. Magnetic fields around late-type stars using water maser observations

    CERN Document Server

    Vlemmings, W H T; Diamond, P J

    2005-01-01

    We present the analysis of the circular polarization, due to Zeeman splitting, of the water masers around a sample of late-type stars to determine the magnetic fields in their circumstellar envelopes. The magnetic field strengths in the water maser regions around the Mira variable stars U Ori and U Her are shown to be several Gauss while those of the supergiants S Per, NML Cyg and VY CMa are several hundred mG. We also show that large scale magnetic fields permeate the CSE of an evolved star; the polarization of the water masers around VX Sgr reveals a dipole field structure. We shortly discuss the coupling of the magnetic field with the stellar outflow, as such fields could possibly be the cause of distinctly aspherical mass-loss and the resulting aspherical planetary nebulae.

  13. OBSERVATIONS OF HIERARCHICAL SOLAR-TYPE MULTIPLE STAR SYSTEMS

    Energy Technology Data Exchange (ETDEWEB)

    Roberts, Lewis C. Jr. [Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena CA 91109 (United States); Tokovinin, Andrei [Cerro Tololo Inter-American Observatory, Casilla 603, La Serena (Chile); Mason, Brian D.; Hartkopf, William I. [U.S. Naval Observatory, 3450 Massachusetts Avenue, NW, Washington, DC 20392-5420 (United States); Riddle, Reed L., E-mail: lewis.c.roberts@jpl.nasa.gov [Division of Physics, Mathematics, and Astronomy, California Institute of Technology, Pasadena, CA 91125 (United States)

    2015-10-15

    Twenty multiple stellar systems with solar-type primaries were observed at high angular resolution using the PALM-3000 adaptive optics system at the 5 m Hale telescope. The goal was to complement the knowledge of hierarchical multiplicity in the solar neighborhood by confirming recent discoveries by the visible Robo-AO system with new near-infrared observations with PALM-3000. The physical status of most, but not all, of the new pairs is confirmed by photometry in the Ks band and new positional measurements. In addition, we resolved for the first time five close sub-systems: the known astrometric binary in HIP 17129AB, companions to the primaries of HIP 33555, and HIP 118213, and the companions to the secondaries in HIP 25300 and HIP 101430. We place the components on a color–magnitude diagram and discuss each multiple system individually.

  14. Observations of Hierarchical Solar-Type Multiple Star Systems

    CERN Document Server

    Roberts,, Lewis C; Mason, Brian D; Hartkopf, William I; Riddle, Reed L

    2015-01-01

    Twenty multiple stellar systems with solar-type primaries were observed at high angular resolution using the PALM-3000 adaptive optics system at the 5 m Hale telescope. The goal was to complement the knowledge of hierarchical multiplicity in the solar neighborhood by confirming recent discoveries by the visible Robo-AO system with new near-infrared observations with PALM-3000. The physical status of most, but not all, of the new pairs is confirmed by photometry in the Ks band and new positional measurements. In addition, we resolved for the first time five close sub-systems: the known astrometric binary in HIP 17129AB, companions to the primaries of HIP 33555, and HIP 118213, and the companions to the secondaries in HIP 25300 and HIP 101430. We place the components on a color-magnitude diagram and discuss each multiple system individually.

  15. PyHammer: An Automatic and Visual Suite for Spectral Typing Stars

    Science.gov (United States)

    Kesseli, Aurora; West, Andrew A.; Harrison, Brandon; Veyette, Mark; Feldman, Daniel

    2017-01-01

    We present a computing product (dubbed "PyHammer"), which can automatically assign estimates of spectral type, metallicity and radial velocity, and/or be used to visually classify stellar spectra. PyHammer uses empirical templates with known spectral types and metallicities as comparisons to automatically determine the spectral type and an estimate of the metallicity of a star by measuring prominent line indices and performing a weighted least squares minimization. The PyHammer GUI allows the user to visually compare their spectra to the templates and determine the spectral type and metallicity. We have created the templates used by PyHammer by co-adding individual spectra from the Sloan Digital Sky Survey's Baryon Oscillation Spectroscopic Survey (BOSS). The templates cover spectral types O5 through L3, are binned by metallicity from -2.0 dex through +1.0 dex, and are separated into main sequence (dwarf) stars and giant stars. This code is based on the “Hammer” spectral typing facility (Covey et al. 2007) and has been updated to include metallicity information, radial velocity calculations, improved automatic estimates, and now is in python (instead of IDL). PyHammer is publicly available to the community on GitHub (github.com/BU-hammerTeam/PyHammer).

  16. Photometry and Polarization of the UXor Type Young Star GM Cep

    Science.gov (United States)

    Huang, Po-Chieh; Chen, Chang-Yao; Hu, Chia-Ling; Chen, Wen-Ping

    2015-08-01

    UX Orionis stars, or UXORs, are a sub-type of Herbig Ae/be or T Tauri stars exhibiting sporadic extinction of stellar light due to circumstellar dust obscuration. GM Cep is such a UXOR in the young (~4 Myr) open cluster Trumper 37 at ~900 pc, showing prominent infrared access, H-alpha emission, and abrupt brightness variation. Here we present intense multi-color photometric monitoring from 2009 to 2015, together with the century-long photometric behavior reported in the literature, to add to the study by Chen et al. (2012) that GM Cep showed (i) sporadic brightening on a time scale of days due to young stellar accretion, (ii) occultation events, each lasting for a couple months, with a probable recurrence time of about two years, (iii) normal dust reddening as the star became redder when dimmer, (iv) the unusual “blueing” phenomena near the brightness minima when the star appeared bluer when dimmer. The occultation events may be caused by a dust clump, signifying the density inhomogeneity in a young stellar disk from grain coagulation to planetesimal formation. We present evidence of possible radial drift of the clump toward the star, stretching longer along the orbit and thinner in the line of sight. GM Cep is moderately polarized, from 4% to 9% in g, r, and i bands, with the level of polarization anticorrelated with the brightness in the bright state, during which the dust clump is back-scattering stellar light.

  17. On Iron Enrichment, Star Formation, and Type Ia Supernovae in Galaxy Clusters

    CERN Document Server

    Loewenstein, M

    2006-01-01

    The nature of star formation and Type Ia supernovae (SNIa) in galaxies in the field and in rich galaxy clusters are contrasted by juxtaposing the build-up of heavy metals in the universe inferred from observed star formation and supernovae rate histories with data on the evolution of Fe abundances in the intracluster medium (ICM). Models for the chemical evolution of Fe in these environments are constructed, subject to observational constraints, for this purpose. While models with a mean delay for SNIa of 3 Gyr and standard initial mass function (IMF) are consistent with observations in the field, cluster Fe enrichment immediately tracks a rapid, top-heavy phase of star formation -- although transport of Fe into the ICM may be more prolonged and star formation likely continues to redshifts 3 times more efficient in rich clusters than in the field, mitigating the overcooling problem in numerical cluster simulations. Both the fraction of baryons cycled through stars, and the fraction of the total present-day st...

  18. Oxygen abundances in G- and F-type stars from HARPS

    CERN Document Server

    de Lis, S Bertran; Adibekyan, V Zh; Santos, N C; Sousa, S G

    2015-01-01

    We present a detailed and uniform study of oxygen abundance from two different oxygen lines at 6158$\\AA$ and 6300$\\AA$ in a large sample of solar-type stars. The results are used to check the behaviour of these spectral lines as oxygen abundance indicators and to study the evolution of oxygen in thick and thin disk populations of the Galaxy. Equivalent width measurements were carried out for the [OI]~6158$\\AA$ and OI~6300$\\AA$ lines. LTE abundances were obtained from these two lines in 610 and 535 stars, respectively. We were able to measure oxygen abundance from both indicators in 447 stars, enabling us, for the first time, to compare them in a uniform way. Careful error analysis has been performed. We found that oxygen abundances derived from the 6158$\\AA$ and 6300$\\AA$ lines agree to within 0.1dex in 58\\% of the stars in our sample, and this result improves for higher signal-to-noise values. We confirm an oxygen enhancement in stars of the thick disk, as has also been seen for other $\\alpha$-elements. The ...

  19. Superflare occurrence and energies on G, K and M type stars

    CERN Document Server

    Candelaresi, Simon; Maehara, Hiroyuki; Brandenburg, Alex; Shibata, Kazunari

    2014-01-01

    Kepler data from G, K and M type stars are used to study conditions that lead to superflares of energies above $10^{34} {\\rm erg}$. From the 117661 included stars, 795 show superflares with a total of 6830 such events. We study if parameters, like the surface temperature or the rotation rate, have any effect on the superflare occurrence rate or energy. For slowly rotating stars we find a quadratic increase of the mean occurrence rate with the rotation rate up to a critical point, after which the rate decreases linearly. Motivated by standard dynamo theory, we study the behavior of the relative starspot coverage, approximated as the relative brightness variation. For faster rotating stars, an increased fraction of stars shows higher spot coverage, which leads to higher superflare rates. A turbulent dynamo is used to study the dependence of the Ohmic dissipation as a proxy of the flare energy on the differential rotation or shear rate. The resulting statistics of the dissipation energy as a function of dynamo n...

  20. Mid- to Far-IR Emission and Star Formation in Early-Type Galaxies

    CERN Document Server

    Young, L M; Lucero, Danielle

    2008-01-01

    Many early-type galaxies have been detected at wavelengths of 24 to 160 micron, but the emission is usually dominated by heating from an AGN or from the evolved stellar population. Here we present Spitzer MIPS observations of a sample of elliptical and lenticular galaxies that are rich in cold molecular gas, and we investigate whether the MIR to FIR emission could be associated with star formation activity. The 24 micron images show a rich variety of structures, including nuclear point sources, rings, disks, and smooth extended emission. Comparisons to matched-resolution CO and radio continuum images suggest that the bulk of the 24 micron emission can be traced to star formation with some notable exceptions. The 24 micron luminosities of the CO-rich galaxies are typically a factor of 15 larger than what would be expected from the dust associated with their evolved stars. In addition, FIR/radio flux density ratios are consistent with star formation. We conclude that the star formation rates in z=0 elliptical a...

  1. Magnetic fields in non-convective regions of stars

    CERN Document Server

    Braithwaite, J

    2015-01-01

    We review the current state of knowledge of magnetic fields inside stars, concentrating on recent developments concerning magnetic fields in stably stratified (zones of) stars, leaving out convective dynamo theories and observations of convective envelopes. We include the observational properties of A, B and O-type main-sequence stars, which have radiative envelopes, and the fossil field model which is normally invoked to explain the strong fields sometimes seen in these stars. Observations seem to show that Ap-type stable fields are excluded in stars with convective envelopes. Most stars contain both radiative and convective zones, and there are potentially important effects arising from the interaction of magnetic fields at the boundaries between them, the solar cycle being one of the better known examples. Related to this, we discuss whether the Sun could harbour a magnetic field in its core. Recent developments regarding the various convective and radiative layers near the surfaces of early-type stars and...

  2. Improved Laboratory Transition Probabilities for Ce II, Application to the Cerium Abundances of the Sun and Five r-process Rich, Metal-Poor Stars, and Rare Earth Lab Data

    CERN Document Server

    Lawler, J E; Cowan, J J; Ivans, I I; Hartog, E A Den

    2009-01-01

    Recent radiative lifetime measurements accurate to +/- 5% using laser-induced fluorescence (LIF) on 43 even-parity and 15 odd-parity levels of Ce II have been combined with new branching fractions measured using a Fourier transform spectrometer (FTS) to determine transition probabilities for 921 lines of Ce II. This improved laboratory data set has been used to determine a new solar photospheric Ce abundance, log epsilon = 1.61 +/- 0.01 (sigma = 0.06 from 45 lines), a value in excellent agreement with the recommended meteoritic abundance, log epsilon = 1.61 +/- 0.02. Revised Ce abundances have also been derived for the r-process-rich metal-poor giant stars BD+17 3248, CS 22892-052, CS 31082-001, HD 115444 and HD 221170. Between 26 and 40 lines were used for determining the Ce abundance in these five stars, yielding a small statistical uncertainty of 0.01 dex similar to the Solar result. The relative abundances in the metal-poor stars of Ce and Eu, a nearly pure r-process element in the Sun, matches r-process ...

  3. A Copernicus survey of Mg II emission in late-type stars

    Science.gov (United States)

    Weiler, E. J.; Oegerle, W. R.

    1979-01-01

    The behavior of Mg II emission in late-type stars is examined using scan data obtained with the Copernicus satellite. The luminosity in the Mg II k emission line was found to be closely related to stellar absolute magnitude, leading to the suggestion that such correlation may be very useful for future UV observations. The stellar surface flux in the k line was observed to be roughly constant or to decrease slowly with later spectral type, a finding which is then used to show that the pressure at the top of the chromosphere decreases with later spectral type, in agreement with the conclusions by McClintock et al. (1975). An asymmetry in the Mg II k line was noticed to be present in the available data for the stars later than K2-K5.

  4. The VLT-FLAMES Tarantula Survey. XII. Rotational velocities of the single O-type stars

    Science.gov (United States)

    Ramírez-Agudelo, O. H.; Simón-Díaz, S.; Sana, H.; de Koter, A.; Sabín-Sanjulían, C.; de Mink, S. E.; Dufton, P. L.; Gräfener, G.; Evans, C. J.; Herrero, A.; Langer, N.; Lennon, D. J.; Maíz Apellániz, J.; Markova, N.; Najarro, F.; Puls, J.; Taylor, W. D.; Vink, J. S.

    2013-12-01

    Context. The 30 Doradus (30 Dor) region of the Large Magellanic Cloud, also known as the Tarantula nebula, is the nearest starburst region. It contains the richest population of massive stars in the Local Group, and it is thus the best possible laboratory to investigate open questions on the formation and evolution of massive stars. Aims: Using ground-based multi-object optical spectroscopy obtained in the framework of the VLT-FLAMES Tarantula Survey (VFTS), we aim to establish the (projected) rotational velocity distribution for a sample of 216 presumably single O-type stars in 30 Dor. The sample is large enough to obtain statistically significant information and to search for variations among subpopulations - in terms of spectral type, luminosity class, and spatial location - in the field of view. Methods: We measured projected rotational velocities, νesini, by means of a Fourier transform method and a profile fitting method applied to a set of isolated spectral lines. We also used an iterative deconvolution procedure to infer the probability density, P(νe), of the equatorial rotational velocity, νe. Results: The distribution of νesini shows a two-component structure: a peak around 80 kms-1 and a high-velocity tail extending up to ~600 kms-1. This structure is also present in the inferred distribution P(νe) with around 80% of the sample having 0 low-velocity peak is consistent with what has been found in other studies for late O- and early B-type stars. Conclusions: Most of the stars in our sample rotate with a rate less than 20% of their break-up velocity. For the bulk of the sample, mass loss in a stellar wind and/or envelope expansion is not efficient enough to significantly spin down these stars within the first few Myr of evolution. If massive-star formation results in stars rotating at birth with a large portion of their break-up velocities, an alternative braking mechanism, possibly magnetic fields, is thus required to explain the present

  5. Deriving precise parameters for cool solar-type stars. Optimizing the iron line list

    Science.gov (United States)

    Tsantaki, M.; Sousa, S. G.; Adibekyan, V. Zh.; Santos, N. C.; Mortier, A.; Israelian, G.

    2013-07-01

    Context. Temperature, surface gravity, and metallicitity are basic stellar atmospheric parameters necessary to characterize a star. There are several methods to derive these parameters and a comparison of their results often shows considerable discrepancies, even in the restricted group of solar-type FGK dwarfs. Aims: We want to check the differences in temperature between the standard spectroscopic technique based on iron lines and the infrared flux method (IRFM). We aim to improve the description of the spectroscopic temperatures especially for the cooler stars where the differences between the two methods are higher, as presented in a previous work. Methods: Our spectroscopic analysis was based on the iron excitation and ionization balance, assuming Kurucz model atmospheres in LTE. The abundance analysis was determined using the code MOOG. We optimized the line list using a cool star (HD 21749) with high resolution and high signal-to-noise spectrum, as a reference in order to check for weak, isolated lines. Results: We test the quality of the new line list by re-deriving stellar parameters for 451 stars with high resolution and signal-to-noise HARPS spectra, that were analyzed in a previous work with a larger line list. The comparison in temperatures between this work and the latest IRFM for the stars in common shows that the differences for the cooler stars are significantly smaller and more homogeneously distributed than in previous studies for stars with temperatures below 5000 K. Moreover, a comparison is presented between interferometric temperatures with our results that shows good agreement, even though the sample is small and the errors of the mean differences are large. We use the new line list to re-derive parameters for some of the cooler stars that host planets. Finally, we present the impact of the new temperatures on the [Cr i/Cr ii] and [Ti i/Ti ii] abundance ratios that previously showed systematic trends with temperature. We show that the slopes

  6. Sulphur molecules in the circumstellar envelopes of M-type AGB stars

    CERN Document Server

    Danilovich, Taissa; Black, J H; Olofsson, H; Justtanont, K

    2016-01-01

    The sulphur compounds SO and SO$_2$ have not been widely studied in the circumstellar envelopes of asymptotic giant branch (AGB) stars. By presenting and modelling a large number of SO and SO$_2$ lines in the low mass-loss rate M-type AGB star R Dor, and modelling the available lines of those molecules in a further four M-type AGB stars, we aim to determine their circumstellar abundances and distributions. We use a detailed radiative transfer analysis based on the accelerated lambda iteration method to model circumstellar SO and SO$_2$ line emission and molecular data files for both SO and SO$_2$ that are more extensive than those previously available. Using 17 SO lines and 98 SO2 lines to constrain our models for R Dor, we find an SO abundance of 6.7x10$^{-6}$ and an SO$_2$ abundance of 5x10$^{-6}$ with both species having high abundances close to the star. We also modelled $^{34}$SO and found an abundance of 3.1x10$^{-7}$, giving an $^{32}$SO/$^{34}$SO ratio of 21.6. We derive similar results for the circum...

  7. A barium central star binary in the Type-I diamond ring planetary nebula Abell 70

    CERN Document Server

    Miszalski, B; Frew, D J; Acker, A; Köppen, J; Moffat, A F J; Parker, Q A

    2011-01-01

    Abell 70 (PN G038.1-25.4, hereafter A 70) is a planetary nebula (PN) known for its diamond ring appearance due a superposition with a background galaxy. The previously unstudied central star is found to be a binary consisting of a G8IV-V secondary at optical wavelengths and a hot white dwarf (WD) at UV wavelengths. The secondary shows Ba II and Sr II features enhanced for its spectral type that, combined with the chromospheric Halpha emission and possible 20-30 km/s radial velocity amplitude, firmly classifies the binary as a Barium star. The proposed origin of Barium stars is intimately linked to PNe whereby wind accretion pollutes the companion with dredged-up material rich in carbon and s-process elements when the primary is experiencing thermal pulses on the Asymptotic Giant Branch (AGB). A 70 provides further evidence for this scenario together with the other very few examples of Barium central stars. The nebula is found to have Type-I chemical abundances with helium and nitrogen enrichment, which when c...

  8. The Unseen Population of F to K-type Companions to Hot Subdwarf Stars

    CERN Document Server

    Girven, J; Heber, U; Gänsicke, B T; Marsh, T R; Breedt, E; Copperwheat, C M; Pyrzas, S; Peña, P Longa

    2012-01-01

    We present a method to select hot subdwarf stars with A to M-type companions using photometric selection criteria. We cover a wide range in wavelength by combining GALEX ultraviolet data, optical photometry from the SDSS and the Carlsberg Meridian telescope, near-infrared data from 2MASS and UKIDSS. We construct two complimentary samples, one by matching GALEX, CMC and 2MASS, as well as a smaller, but deeper, sample using GALEX, SDSS and UKIDSS. In both cases, a large number of composite subdwarf plus main-sequence star candidates were found. We fit their spectral energy distributions with a composite model in order to estimate the subdwarf and companion star effective temperatures along with the distance to each system. The distribution of subdwarf effective temperature was found to primarily lie in the 20,000 - 30,000 K regime, but we also find cooler subdwarf candidates, making up ~5-10 per cent. The most prevalent companion spectral types were seen to be main-sequence stars between F0 and K0, while subdwa...

  9. Measurement of acoustic glitches in solar-type stars from oscillation frequencies observed by Kepler

    Energy Technology Data Exchange (ETDEWEB)

    Mazumdar, A. [Homi Bhabha Centre for Science Education, TIFR, V. N. Purav Marg, Mankhurd, Mumbai 400088 (India); Monteiro, M. J. P. F. G.; Cunha, M. S. [Centro de Astrofísica da Universidade do Porto, Rua das Estrelas, 4150-762 Porto (Portugal); Ballot, J. [CNRS, Institut de Recherche en Astrophysique et Planétologie, 14 avenue Edouard Belin, F-31400 Toulouse (France); Antia, H. M. [Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400005 (India); Basu, S. [Astronomy Department, Yale University, P.O. Box 208101, New Haven, CT 065208101 (United States); Houdek, G.; Silva Aguirre, V.; Christensen-Dalsgaard, J.; Metcalfe, T. S. [Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, DK-8000 Aarhus C (Denmark); Mathur, S. [High Altitude Observatory, NCAR, P.O. Box 3000, Boulder, CO 80307 (United States); García, R. A. [Laboratoire AIM, CEA/DSM, CNRS, Université Paris Diderot, IRFU/SAp, Centre de Saclay, F-91191 Gif-sur-Yvette Cedex (France); Salabert, D. [Laboratoire Lagrange, UMR7293, Université de Nice Sophia-Antipolis, CNRS, Observatoire de la Côte d' Azur, F-06304 Nice (France); Verner, G. A.; Chaplin, W. J. [School of Physics and Astronomy, University of Birmingham, Edgbaston, Birmingham B15 2TT (United Kingdom); Sanderfer, D. T. [NASA Ames Research Center, Moffett Field, CA 94035 (United States); Seader, S. E.; Smith, J. C. [SETI Institute/NASA Ames Research Center, Moffett Field, CA 94035 (United States)

    2014-02-10

    For the very best and brightest asteroseismic solar-type targets observed by Kepler, the frequency precision is sufficient to determine the acoustic depths of the surface convective layer and the helium ionization zone. Such sharp features inside the acoustic cavity of the star, which we call acoustic glitches, create small oscillatory deviations from the uniform spacing of frequencies in a sequence of oscillation modes with the same spherical harmonic degree. We use these oscillatory signals to determine the acoustic locations of such features in 19 solar-type stars observed by the Kepler mission. Four independent groups of researchers utilized the oscillation frequencies themselves, the second differences of the frequencies and the ratio of the small and large separation to locate the base of the convection zone and the second helium ionization zone. Despite the significantly different methods of analysis, good agreement was found between the results of these four groups, barring a few cases. These results also agree reasonably well with the locations of these layers in representative models of the stars. These results firmly establish the presence of the oscillatory signals in the asteroseismic data and the viability of several techniques to determine the location of acoustic glitches inside stars.

  10. WASP-26b: a 1-Jupiter-mass planet around an early-G-type star

    Science.gov (United States)

    Smalley, B.; Anderson, D. R.; Collier Cameron, A.; Gillon, M.; Hellier, C.; Lister, T. A.; Maxted, P. F. L.; Queloz, D.; Triaud, A. H. M. J.; West, R. G.; Bentley, S. J.; Enoch, B.; Pepe, F.; Pollacco, D. L.; Segransan, D.; Smith, A. M. S.; Southworth, J.; Udry, S.; Wheatley, P. J.; Wood, P. L.; Bento, J.

    2010-09-01

    We report the discovery of WASP-26b, a moderately over-sized Jupiter-mass exoplanet transiting its 11.3-mag early-G-type host star (1SWASP J001824.70-151602.3; TYC 5839-876-1) every 2.7566 days. A simultaneous fit to transit photometry and radial-velocity measurements yields a planetary mass of 1.02 ± 0.03 MJup and radius of 1.32 ± 0.08 RJup. The host star, WASP-26, has a mass of 1.12 ± 0.03 M⊙ and a radius of 1.34 ± 0.06 R⊙ and is in a visual double with a fainter K-type star. The two stars are at least a common-proper motion pair with a common distance of around 250 ± 15 pc and an age of 6 ± 2 Gy. RV and photometric data are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/520/A56

  11. The VLT-FLAMES Tarantula Survey VIII. Multiplicity properties of the O-type star population

    CERN Document Server

    Sana, H; de Mink, S E; Dunstall, P R; Evans, C J; Henault-Brunet, V; Apellaniz, J Maiz; Ramirez-Agudelo, O H; Taylor, W D; Walborn, N R; Clark, J S; Crowther, P A; Herrero, A; Gieles, M; Langer, N; Lennon, D J; Vink, J S

    2012-01-01

    Aims. We analyze the multiplicity properties of the massive O-type star population. With 360 O-type stars, this is the largest homogeneous sample of massive stars analyzed to date. Methods. We use multi-epoch spectroscopy and variability analysis to identify spectroscopic binaries. We also use a Monte-Carlo method to correct for observational biases. Results. We observe a spectroscopic binary fraction of 0.35\\pm0.03, which corresponds to the fraction of objects displaying statistically significant radial velocity variations with an amplitude of at least 20km/s. We compute the intrinsic binary fraction to be 0.51\\pm0.04. We adopt power-laws to describe the intrinsic period and mass-ratio distributions: f_P ~ (log P)^\\pi\\ (with 0.15 7.8', i.e. approx117 pc) and among the O9.7 I/II objects are however significantly lower than expected from statistical fluctuations. Conclusions. Using simple evolutionary considerations, we estimate that over 50% of the current O star population in 30 Dor will exchange mass with ...

  12. CALCULATING THE HABITABLE ZONE OF BINARY STAR SYSTEMS. I. S-TYPE BINARIES

    Energy Technology Data Exchange (ETDEWEB)

    Kaltenegger, Lisa [MPIA, Koenigstuhl 17, D-69117 Heidelberg (Germany); Haghighipour, Nader, E-mail: kaltenegger@mpia.de [Institute for Astronomy and NASA Astrobiology Institute, University of Hawaii-Manoa, Honolulu, HI 96822 (United States)

    2013-11-10

    We have developed a comprehensive methodology for calculating the boundaries of the habitable zone (HZ) of planet-hosting S-type binary star systems. Our approach is general and takes into account the contribution of both stars to the location and extent of the binary HZ with different stellar spectral types. We have studied how the binary eccentricity and stellar energy distribution affect the extent of the HZ. Results indicate that in binaries where the combination of mass-ratio and orbital eccentricity allows planet formation around a star of the system to proceed successfully, the effect of a less luminous secondary on the location of the primary's HZ is generally negligible. However, when the secondary is more luminous, it can influence the extent of the HZ. We present the details of the derivations of our methodology and discuss its application to the binary HZ around the primary and secondary main-sequence stars of an FF, MM, and FM binary, as well as two known planet-hosting binaries α Cen AB and HD 196886.

  13. Mid-infrared observations of O-type stars: spectral morphology

    Science.gov (United States)

    Marcolino, W. L. F.; Bouret, J.-C.; Lanz, T.; Maia, D. S.; Audard, M.

    2017-09-01

    We present mid-infrared (mid-IR) observations for a sample of 16 O-type stars. The data were acquired with the NASA Spitzer Space Telescope, using the IRS instrument at moderate resolution (R ∼ 600), covering the range of ∼10-37 μm. Our sample includes early, mid and late O supergiants and dwarfs. We explore for the first time their mid-IR spectral morphology in a quantitative way. We use NLTE expanding atmosphere models to help with line identifications, analyse profile contributions and line-formation regions. The O supergiants present a rich emission line spectra. The most intense features are from hydrogen - 6 α, 7 α and 8 α - that have non-negligible contributions of He i or He ii lines, depending on the spectral type. The spectrum of early O supergiants is a composite of H i and He ii lines, He i lines being absent. On the other hand, late O supergiants present features composed mainly by H i and He i lines. All emission lines are formed throughout the stellar wind. We found that O dwarfs exhibit a featureless mid-IR spectrum. Two stars of our sample exhibit very similar mid-IR features, despite having a very different optical spectral classification. The analysis of O-type stars based on mid-IR spectra alone to infer spectral classes or to estimate physical parameters may thus be prone to substantial errors. Our results may therefore inform spectroscopic observations of massive stars located in heavily obscured regions and help establish an initial framework for observations of massive stars using the Mid-Infrared Instrument on the James Webb Space Telescope.

  14. Magnetic activity and hot Jupiters of young Suns: the weak-line T Tauri stars V819 Tau and V830 Tau

    CERN Document Server

    Donati, JF; Hussain, G; Moutou, C; Malo, L; Grankin, K; Vidotto, AA; Alencar, SHP; Gregory, SG; Jardine, MM; Herczeg, G; Morin, J; Fares, R; Ménard, F; Bouvier, J; Delfosse, X; Doyon, R; Takami, M; Figueira, P; Petit, P; Boisse, I

    2015-01-01

    We report results of a spectropolarimetric and photometric monitoring of the weak-line T Tauri stars (wTTSs) V819 Tau and V830 Tau within the MaTYSSE programme, involving the ESPaDOnS spectropolarimeter at the Canada-France-Hawaii Telescope. At ~3 Myr, both stars dissipated their discs recently and are interesting objects for probing star and planet formation. Profile distortions and Zeeman signatures are detected in the unpolarized and circularly-polarized lines, whose rotational modulation we modelled using tomographic imaging, yielding brightness and magnetic maps for both stars. We find that the large-scale magnetic fields of V819 Tau and V830 Tau are mostly poloidal and can be approximated at large radii by 350-400 G dipoles tilted at ~30 degrees to the rotation axis. They are significantly weaker than the field of GQ Lup, an accreting classical T Tauri star (cTTS) with similar mass and age which can be used to compare the magnetic properties of wTTSs and cTTSs. The reconstructed brightness maps of both ...

  15. Numerical models of protoneutron stars and type-II supernovae - recent developments

    Energy Technology Data Exchange (ETDEWEB)

    Janka, H.T. [Max-Planck-Institut fuer Astrophysik, Garching (Germany)

    1996-11-01

    The results of recent multi-dimensional simulations of type-II supernovae are reviewed. They show that convective instabilities in the collapsed stellar core might play an important role already during the first second after the formation of the supernovae shock. Convectively unstable situations occur below and near the neutrinosphere as well as in the neutrino-heated region between the nascent neutron star and the supernova shock after the latter has stalled at a radiums of typically 100-200 km. While convective overturn in the layer of neutrino energy deposition clearly helps the explosion to develop and potentially provides an explanation of strong mantle and envelope mixing, asphericities, and non-uniform {sup 56}Ni distribution observed in supernova SN 1987A, its presence and importance depends on the strength of the neutrino heating and thus on the size of the neutrino fluxes from the neutrino star. Convection in the hot-bubble region can only be developed if the growth timescale of the instabilities and the heating timescale are both shorter than the accretion timescale of the matter advected through the stagnant shock. For too small neutrino luminosities this requirement is not fulfilled and convective activity cannot develop, leading to very weak explosions or even fizzling models, just as in the one-dimensional situations. Convectively enhanced neutrino luminosities from the protoneutron star can therefore provide an essential condition for the explosion of the star. Very recent two-dimensional, self-consistent, general relativistic simulations of the cooling of a newly-formed neutron star demonstrate and confirm the possibility that Ledoux convection, driven by negative lepton number and entropy gradients, may encompass the whole protoneutron star within less than one second and can lead to an increase of the neutrino fluxes by up to a factor of two. (author) 9 figs., refs.

  16. StarBench: The D-type expansion of an HII region

    CERN Document Server

    Bisbas, T G; Williams, R J R; Mackey, J; Tremblin, P; Raga, A C; Arthur, S J; Baczynski, C; Dale, J E; Frostholm, T; Geen, S; Haugboelle, T; Hubber, D; Iliev, I T; Kuiper, R; Rosdahl, J; Sullivan, D; Walch, S; Wuensch, R

    2015-01-01

    StarBench is a project focused on benchmarking and validating different star-formation and stellar feedback codes. In this first StarBench paper we perform a comparison study of the D-type expansion of an HII region. The aim of this work is to understand the differences observed between the twelve participating numerical codes against the various analytical expressions examining the D-type phase of HII region expansion. To do this, we propose two well-defined tests which are tackled by 1D and 3D grid- and SPH- based codes. The first test examines the `early phase' D-type scenario during which the mechanical pressure driving the expansion is significantly larger than the thermal pressure of the neutral medium. The second test examines the `late phase' D-type scenario during which the system relaxes to pressure equilibrium with the external medium. Although they are mutually in excellent agreement, all twelve participating codes follow a modified expansion law that deviates significantly from the classical Spit...

  17. EXPORT optical photometry and polarimetry of Vega-type and pre-main sequence stars

    CERN Document Server

    Oudmaijer, R D; Eiroa, C

    2001-01-01

    This paper presents optical UBVRI broadband photo-polarimetry of the EXPORT sample obtained at the 2.5m Nordic Optical Telescope. The database consists of multi-epoch photo-polarimetry of 68 pre-main-sequence and main-sequence stars. An investigation of the polarization variability indicates that 22 objects are variable at the 3sigma level in our data. All these objects are pre-main sequence stars, consisting of both T Tauri and Herbig Ae/Be objects while the main sequence, Vega type and post-T Tauri type objects are not variable. The polarization properties of the variable sources are mostly indicative of the UXOR-type behaviour; the objects show highest polarization when the brightness is at minimum. We add seven new objects to the class of UXOR variables (BH Cep, VX Cas, DK Tau, HK Ori, LkHa 234, KK Oph and RY Ori). The main reason for their discovery is the fact that our data-set is the largest in its kind, indicating that many more young UXOR-type pre-main sequence stars remain to be discovered. The set ...

  18. Chromospheric changes in K stars with activity

    CERN Document Server

    Vieytes, Mariela; Diaz, Rodrigo

    2009-01-01

    We study the differences in chromospheric structure induced in K stars by stellar activity, to expand our previous work for G stars, including the Sun as a star. We selected six stars of spectral type K with 0.82$stars in the sample, in most cases in two different moments of activity. The models were constructed to obtain the best possible match with the Ca II K and the H$\\beta$ observed profiles. We also computed in detail the net radiative losses for each model to constrain the heating mechanism that can maintain the structure in the atmosphere. We find a strong correlation between these losses and \\Sc, the index generally used as a proxy for activity, as we found for G stars.

  19. A non-LTE study of neutral and singly-ionized calcium in late-type stars

    Science.gov (United States)

    Mashonkina, L.; Korn, A. J.; Przybilla, N.

    2007-01-01

    Aims:Non-local thermodynamical equilibrium (NLTE) line formation for neutral and singly-ionized calcium is considered through a range of spectral types when the Ca abundance varies from the solar value down to [Ca/H] = -5. We evaluate the influence of departures from LTE on Ca abundance determinations and inspect the possibility of using Ca I / Ca II line-strength ratios as indicators of surface gravity for extremely metal-poor stars. Methods: A comprehensive model atom for Ca I and Ca II is presented. Accurate radiative and electron collisional atomic data are incorporated. The role of inelastic collisions with hydrogen atoms in the statistical equilibrium of Ca I/II is estimated empirically from inspection of their different influences on the Ca I and Ca II lines in selected stars with well determined stellar parameters and high-quality observed spectra. Results: The dependence of NLTE effects on the atmospheric parameters is discussed. Departures from LTE significantly affect the profiles of Ca I lines over the whole range of stellar parameters being considered. However, at [Ca/H] ≥ -2, NLTE abundance correction of individual lines have a low absolute value due to the different influence of NLTE effects on line wings and the line core. At lower Ca abundances, NLTE leads to systematically depleted total absorption in the line and positive abundance corrections, exceeding +0.5 dex for Ca I λ 4226 at [Ca/H] = -4.9. In contrast, the NLTE effects strengthen the Ca II lines and lead to negative abundance corrections. NLTE corrections are small, ≤0.02 dex, for the Ca II resonance lines, and they grow in absolute value with decreasing Ca abundance for the IR lines of multiplet 3d-4p, exceeding 0.4 dex in the metal-poor models with [Fe/H] ≤ -3. As a test and first application of the Ca I/II model atom, Ca abundances are determined on the basis of plane-parallel LTE model atmospheres for the Sun, Procyon (F IV-V), and seven metal-poor stars, using high S/N and high

  20. Measurement of acoustic glitches in solar-type stars from oscillation frequencies observed by Kepler

    CERN Document Server

    Mazumdar, A; Ballot, J; Antia, H M; Basu, S; Houdek, G; Mathur, S; Cunha, M S; Aguirre, V Silva; Garcia, R A; Salabert, D; Verner, G A; Christensen-Dalsgaard, J; Metcalfe, T S; Sanderfer, D T; Seader, S E; Smith, J C; Chaplin, W J

    2013-01-01

    For the very best and brightest asteroseismic solar-type targets observed by Kepler, the frequency precision is sufficient to determine the acoustic depths of the surface convective layer and the helium ionization zone. Such sharp features inside the acoustic cavity of the star, which we call acoustic glitches, create small oscillatory deviations from the uniform spacing of frequencies in a sequence of oscillation modes with the same spherical harmonic degree. We use these oscillatory signals to determine the acoustic locations of such features in 19 solar-type stars observed by the Kepler mission. Four independent groups of researchers utilized the oscillation frequencies themselves, the second differences of the frequencies and the ratio of the small and large separation to locate the base of the convection zone and the second helium ionization zone. Despite the significantly different methods of analysis, good agreement was found between the results of these four groups, barring a few cases. These results ...

  1. Is there a compact companion orbiting the late O-type binary star HD 164816?

    Science.gov (United States)

    Trepl, L.; Hambaryan, V. V.; Pribulla, T.; Tetzlaff, N.; Chini, R.; Neuhäuser, R.; Popov, S. B.; Stahl, O.; Walter, F. M.; Hohle, M. M.

    2012-12-01

    We present a multi-wavelength (X-ray, γ-ray, optical and radio) study of HD 164816, a late O-type X-ray detected spectroscopic binary. X-ray spectra are analysed and the X-ray photon arrival times are checked for pulsation. In addition, newly obtained optical spectroscopic monitoring data on HD 164816 are presented. They are complemented by available radio data from several large-scale surveys as well as the Fermi γ-ray data from its Large Area Telescope. We report the detection of a low energy excess in the X-ray spectrum that can be described by a simple absorbed blackbody model with a temperature of ˜50 eV as well as a 9.78 s pulsation of the X-ray source. The soft X-ray excess, the X-ray pulsation and the kinematical age would all be consistent with a compact object like a neutron star as companion to HD 164816. The size of the soft X-ray excess emitting area is consistent with a circular region with a radius of about 7 km, typical for neutron stars, while the emission measure (EM) of the remaining harder emission is typical for late O-type single or binary stars. If HD 164816 includes a neutron star born in a supernova, this supernova should have been very recent and should have given the system a kick, which is consistent with the observation that the star HD 164816 has a significantly different radial velocity than the cluster mean. In addition we confirm the binarity of HD 164816 itself by obtaining an orbital period of 3.82 d, projected masses m1sin3i = 2.355(69) M⊙, m2sin3i = 2.103(62) M⊙ apparently seen at low inclination angle, determined from high-resolution optical spectra.

  2. The Extreme Ultraviolet and X-Ray Sun in Time: High-Energy Evolutionary Tracks of a Solar-Like Star

    CERN Document Server

    Tu, Lin; Güdel, Manuel; Lammer, Helmut

    2015-01-01

    Aims. We aim to describe the pre-main sequence and main-sequence evolution of X-ray and extreme-ultaviolet radiation of a solar mass star based on its rotational evolution starting with a realistic range of initial rotation rates. Methods. We derive evolutionary tracks of X-ray radiation based on a rotational evolution model for solar mass stars and the rotation-activity relation. We compare these tracks to X-ray luminosity distributions of stars in clusters with different ages. Results. We find agreement between the evolutionary tracks derived from rotation and the X-ray luminosity distributions from observations. Depending on the initial rotation rate, a star might remain at the X-ray saturation level for very different time periods, approximately from 10 Myr to 300 Myr for slow and fast rotators, respectively. Conclusions. Rotational evolution with a spread of initial conditions leads to a particularly wide distribution of possible X-ray luminosities in the age range of 20 to 500 Myrs, before rotational co...

  3. The extreme ultraviolet and X-ray Sun in Time: High-energy evolutionary tracks of a solar-like star

    Science.gov (United States)

    Tu, Lin; Johnstone, Colin P.; Güdel, Manuel; Lammer, Helmut

    2015-05-01

    Aims: We aim to describe the pre-main-sequence and main-sequence evolution of X-ray and extreme-ultaviolet radiation of a solar-mass star based on its rotational evolution starting with a realistic range of initial rotation rates. Methods: We derive evolutionary tracks of X-ray radiation based on a rotational evolution model for solar-mass stars and the rotation-activity relation. We compare these tracks to X-ray luminosity distributions of stars in clusters with different ages. Results: We find agreement between the evolutionary tracks derived from rotation and the X-ray luminosity distributions from observations. Depending on the initial rotation rate, a star might remain at the X-ray saturation level for very different time periods, from ≈10 Myr to ≈300 Myr for slow and fast rotators, respectively. Conclusions: Rotational evolution with a spread of initial conditions leads to a particularly wide distribution of possible X-ray luminosities in the age range of 20-500 Myr, before rotational convergence and therefore X-ray luminosity convergence sets in. This age range is crucial for the evolution of young planetary atmospheres and may thus lead to very different planetary evolution histories.

  4. Kepler-22b: a 2.4 Earth-radius Planet in the Habitable Zone of a Sun-like Star

    NARCIS (Netherlands)

    Borucki, W.J.; Koch, D.G.; Batalha, N.; Bryson, S.T.; Rowe, J.; Fressin, F.; Torres, G.; Caldwell, D.A.; Christensen-Dalsgaard, J.; Cochran, W.D.; DeVore, E.; Gautier, T.N.; Geary, J.C.; Gilliland, R.; Gould, A.; Howell, S.B.; Jenkins, J.M.; Latham, D.W.; Lissauer, J.J.; Marcy, G.W.; Sasselov, D.; Boss, A.; Charbonneau, D.; Ciardi, D.; Kaltenegger, L.; Doyle, L.; Dupree, A.K.; Ford, E.B.; Fortney, J.; Holman, M.J.; Steffen, J.H.; Mullally, F.; Still, M.; Tarter, J.; Ballard, S.; Buchhave, L.A.; Carter, J.; Christiansen, J.L.; Demory, B.O.; Désert, J.M.; Dressing, C.; Endl, M.; Fabrycky, D.; Fischer, D.; Haas, M.R.; Henze, C.; Horch, E.; Howard, A.W.; Isaacson, H.; Kjeldsen, H.; Johnson, J.A.; Klaus, T.; Kolodziejczak, J.; Barclay, T.; Li, J.; Meibom, S.; Prsa, A.; Quinn, S.N.; Quintana, E.V.; Robertson, P.; Sherry, W.; Shporer, A.; Tenenbaum, P.; Thompson, S.E.; Twicken, J.D.; Van Cleve, J.; Welsh, W.F.; Basu, S.; Chaplin, W.; Miglio, A.; Kawaler, S.D.; Arentoft, T.; Stello, D.; Metcalfe, T.S.; Verner, G.A.; Karoff, C.; Lundkvist, M.; Lund, M.N.; Handberg, R.; Elsworth, Y.; Hekker, S.; Huber, D.; Bedding, T.R.; Rapin, W.

    2012-01-01

    A search of the time-series photometry from NASA's Kepler spacecraft reveals a transiting planet candidate orbiting the 11th magnitude G5 dwarf KIC 10593626 with a period of 290 days. The characteristics of the host star are well constrained by high-resolution spectroscopy combined with an

  5. Modelling the magnetic activity & filtering radial velocity curves of young Suns: the weak-line T Tauri star LkCa 4

    CERN Document Server

    Donati, J -F; Hussain, G; Moutou, C; Grankin, K; Boisse, I; Morin, J; Gregory, S G; Vidotto, A A; Bouvier, J; Alencar, S H P; Delfosse, X; Doyon, R; Takami, M; Jardine, M M; Fares, R; Cameron, A C; Menard, F; Dougados, C; Herczeg, G

    2014-01-01

    We report results of a spectropolarimetric and photometric monitoring of the weak-line T Tauri star LkCa4 within the MaTYSSE programme, involving ESPaDOnS at the Canada-France-Hawaii Telescope. Despite an age of only 2Myr and a similarity with prototypical classical T Tauri stars, LkCa4 shows no evidence for accretion and probes an interesting transition stage for star and planet formation. Large profile distortions and Zeeman signatures are detected in the unpolarized and circularly-polarized lines of LkCa4 using Least-Squares Deconvolution (LSD), indicating the presence of brightness inhomogeneities and magnetic fields at the surface of LkCa4. Using tomographic imaging, we reconstruct brightness and magnetic maps of LkCa4 from sets of unpolarized and circularly-polarized LSD profiles. The large-scale field is strong and mainly axisymmetric, featuring a ~2kG poloidal component and a ~1kG toroidal component encircling the star at equatorial latitudes - the latter making LkCa4 markedly different from classical...

  6. Predicting the Detectability of Oscillations in Solar-type Stars Observed by Kepler

    DEFF Research Database (Denmark)

    Chaplin, William J.; Kjeldsen, Hans; Bedding, Timothy R.

    2011-01-01

    Asteroseismology of solar-type stars has an important part to play in the exoplanet program of the NASA Kepler Mission. Precise and accurate inferences on the stellar properties that are made possible by the seismic data allow very tight constraints to be placed on the exoplanetary systems. Here,......, we outline how to make an estimate of the detectability of solar-like oscillations in any given Kepler target, using rough estimates of the temperature and radius, and the Kepler apparent magnitude....

  7. Young Stars with SALT

    Science.gov (United States)

    Riedel, Adric R.; Alam, Munazza K.; Rice, Emily L.; Cruz, Kelle L.; Henry, Todd J.

    2017-05-01

    We present a spectroscopic and kinematic analysis of 79 nearby M dwarfs in 77 systems. All of these dwarfs are low-proper-motion southern hemisphere objects and were identified in a nearby star survey with a demonstrated sensitivity to young stars. Using low-resolution optical spectroscopy from the Red Side Spectrograph on the South African Large Telescope, we have determined radial velocities, H-alpha, lithium 6708 Å, and potassium 7699 Å equivalent widths linked to age and activity, and spectral types for all of our targets. Combined with astrometric information from literature sources, we identify 44 young stars. Eighteen are previously known members of moving groups within 100 pc of the Sun. Twelve are new members, including one member of the TW Hydra moving group, one member of the 32 Orionis moving group, 9 members of Tucana-Horologium, one member of Argus, and two new members of AB Doradus. We also find 14 young star systems that are not members of any known groups. The remaining 33 star systems do not appear to be young. This appears to be evidence of a new population of nearby young stars not related to the known nearby young moving groups. Based on observations made with the Southern African Large Telescope (SALT).

  8. Oxygen abundance determination of B-type stars with the OI 7771-5A lines

    CERN Document Server

    Takeda, Yoichi

    2016-01-01

    Oxygen abundances of 34 B-type stars in the effective temperature range of Teff~10000-28000K with diversified rotational velocities (vesini~ 0-250km/s) were determined from the OI triplet lines at 7771-5A, with an aim to examine whether this OI feature can be a reliable abundance indicator for such high-temperature stars including rapid rotators. It revealed that the required non-LTE abundance correction is distinctly large (ranging from ~-0.6dex to ~-1.7dex) and its consideration is indispensable. On the condition that the non-LTE effect is taken into account, this triplet is a useful O abundance indicator (with a precision of ~200mA). In contrast, it is not adequate for abundance derivation for stars at Teff >~25000K, where its strength rapidly drops down toward a hardly detectable level (except for sharp-lined stars) and its sensitivity to Teff or log g becomes considerably large. The resulting non-LTE oxygen abundances turned out to be almost normal (i.e., near-solar around ~8.7-8.8 within +/-~0.2dex) for...

  9. The magnetic field around late-type stars revealed by the circumstellar H2O masers

    CERN Document Server

    Vlemmings, W H T; Diamond, P J

    2005-01-01

    Through polarization observations, circumstellar masers are excellent probes of the magnetic field in the envelopes of late-type stars. Whereas observations of the polarization of the SiO masers close to the star and on the OH masers much further out were fairly commonplace, observations of the magnetic field strength in the intermediate density and temperature region where the 22 GHz water masers occur have only recently become possible. Here we present the analysis of the circular polarization, due to Zeeman splitting, of the water masers around the Mira variable stars U Her and U Ori and the supergiant VX Sgr. We present an upper limit of the field around U Her that is lower but consistent with previous measurements, reflecting possible changes in the circumstellar envelope. The field strengths around U Ori and VX Sgr are shown to be of the order of several Gauss. Moreover, we show for the first time that large scale magnetic fields permeate the circumstellar envelopes of an evolved star; the polarization ...

  10. Time-resolved multicolour photometry of bright B-type variable stars in Scorpius

    CERN Document Server

    Handler, G

    2013-01-01

    The first two of a total of six nano-satellites that will constitute the BRITE-Constellation space photometry mission have recently been launched successfully. In preparation for this project, we carried out time-resolved colour photometry in a field that is an excellent candidate for BRITE measurements from space. We acquired 117 h of Stromgren uvy data during 19 nights. Our targets comprised the Beta Cephei stars Kappa and Lambda Sco, the eclipsing binary Mu 1 Sco, and the variable super/hypergiant Zeta 1 Sco. For Kappa Sco, a photometric mode identification in combination with results from the spectroscopic literature suggests a dominant (l, m) = (1, -1) Beta Cephei-type pulsation mode of the primary star. The longer period of the star may be a rotational variation or a g-mode pulsation. For Lambda Sco, we recover the known dominant Beta Cephei pulsation, a longer-period variation, and observed part of an eclipse. Lack of ultraviolet data precludes mode identification for this star. We noticed that the spe...

  11. HE 0437-5439 -- an unbound hyper-velocity main-sequence B-type star

    CERN Document Server

    Edelmann, H; Heber, U; Christlieb, N; Reimers, D; Edelmann, Heinz; Napiwotzki, Ralf; Heber, Uli; Christlieb, Norbert; Reimers, Dieter

    2005-01-01

    We report the discovery of a 16th magnitude star, HE0437-5439, with a heliocentric radial velocity of +723+-3km/s. A quantitative spectral analysis of high-resolution optical spectra obtained with the VLT and the UVES spectrograph shows that HE0437-5439 is a main sequence B-type star with Teff=20350K, log g=3.77, solar within a factor of a few helium abundance and metal content, rotating at v sin i=54km/s. Using appropriate evolutionary tracks we derive a mass of 8 Msun and a corresponding distance of 61 kpc. Its galactic rest frame velocity is at least 563km/s, almost twice the local Galactic escape velocity, indicating that the star is unbound to the Galaxy. Numerical kinematical experiments are carried out to constrain its place of birth. It has been suggested that such hyper-velocity stars can be formed by the tidal disruption of a binary through interaction with the super-massive black hole at the Galactic center (GC). HE0437-5439 needs about 100Myrs to travel from the GC to its presentposition, much lon...

  12. Evolutionary tracks and isochrones for low- and intermediate-mass stars from 0.15 to 7 M$_sun$, and from Z=0.0004 to 0.03

    CERN Document Server

    Girardi, L; Bertelli, G; Chiosi, C; Girardi, Leo; Bressan, Alessandro; Bertelli, Gianpaolo; Chiosi, Cesare

    2000-01-01

    We present a large grid of stellar evolutionary tracks, which are suitable to modelling star clusters and galaxies by means of population synthesis. The tracks are presented for the initial chemical compositions [Z=0.0004, Y=0.23], [Z=0.001, Y=0.23], [Z=0.004, Y=0.24], [Z=0.008, Y=0.25], [Z=0.019, Y=0.273] (solar composition), and [Z=0.03, Y=0.30]. They are computed with updated opacities and equation of state, and a moderate amount of convective overshoot. The range of initial masses goes from 0.15 M_sun to 7 M_sun, and the evolutionary phases extend from the zero age main sequence (ZAMS) till either the thermally pulsing AGB regime or carbon ignition. We also present an additional set of models with solar composition, computed using the classical Schwarzschild's criterion for convective boundaries. From all these tracks, we derive the theoretical isochrones in the Johnson-Cousins UBVRIJHK broad-band photometric system.

  13. The VLT-FLAMES Tarantula Survey XXII. Multiplicity properties of the B-type stars

    CERN Document Server

    Dunstall, P R; Sana, H; Evans, C J; Howarth, I D; Simón-Díaz, S; de Mink, S E; Langer, N; Apellániz, J Maíz; Taylor, W D

    2015-01-01

    We investigate the multiplicity properties of 408 B-type stars observed in the 30 Doradus region of the Large Magellanic Cloud with multi-epoch spectroscopy from the VLT-FLAMES Tarantula Survey (VFTS). We use a cross-correlation method to estimate relative radial velocities from the helium and metal absorption lines for each of our targets. Objects with significant radial-velocity variations (and with an amplitude larger than 16 km/s) are classified as spectroscopic binaries. We find an observed spectroscopic binary fraction (defined by periods of 0.1) for the B-type stars, f_B(obs) = 0.25 +/- 0.02, which appears constant across the field of view, except for the two older clusters (Hodge 301 and SL 639). These two clusters have significantly lower fractions of 0.08 +/- 0.08 and 0.10 +/- 0.09, respectively. Using synthetic populations and a model of our observed epochs and their potential biases, we constrain the intrinsic multiplicity properties of the dwarf and giant (i.e. relatively unevolved) B-type stars ...

  14. Age-rotation relationship for late-type main-sequence stars

    Science.gov (United States)

    Rengarajan, T. N.

    1984-01-01

    With advancing spectral type and increasing age, late main-sequence stars exhibit monotonic decrease in rotational velocity. It is of great interest to extend the rotation-age relationship to stars of later spectral type. In recent times it has become possible to measure directly the rotational periods from the photometric modulation by Ca II H and K line emission. There have also been successful attempts to relate the chromospheric activity as manifested through Ca II H and K lines to the rotation period, and it was shown that the fraction of total stellar luminosity in Ca II H and K lines, corrected for photospheric contribution, is a function of a single parameter related to P and B-V. In the present investigation, this rotation-activity relation is utilized to infer the rotation periods as a function of spectral type. The period versus B-V plot is employed as a basis to infer that the rotational period of main-sequence stars is a single-valued function of mass (B-V color) and age.

  15. The SAURON project - XV. Modes of star formation in early-type galaxies and the evolution of the red sequence

    NARCIS (Netherlands)

    Shapiro, Kristen L.; Falcón-Barroso, Jesús; van de Ven, Glenn; de Zeeuw, P. Tim; Sarzi, Marc; Bacon, Roland; Bolatto, Alberto; Cappellari, Michele; Croton, Darren; Davies, Roger L.; Emsellem, Eric; Fakhouri, Onsi; Krajnović, Davor; Kuntschner, Harald; McDermid, Richard M.; Peletier, Reynier F.; van den Bosch, Remco C. E.; van der Wolk, Guido

    2010-01-01

    We combine SAURON integral field data of a representative sample of local early-type, red sequence galaxies with Spitzer/Infrared Array Camera imaging in order to investigate the presence of trace star formation in these systems. With the Spitzer data, we identify galaxies hosting low-level star for

  16. The SAURON project : XV. Modes of star formation in early-type galaxies and the evolution of the red sequence

    NARCIS (Netherlands)

    Shapiro, Kristen L.; Falcon-Barroso, Jesus; van de Ven, Glenn; de Zeeuw, P. Tim; Sarzi, Marc; Bacon, Roland; Bolatto, Alberto; Cappellari, Michele; Croton, Darren; Davies, Roger L.; Emsellem, Eric; Fakhouri, Onsi; Krajnovic, Davor; Kuntschner, Harald; McDermid, Richard M.; Peletier, Reynier F.; van den Bosch, Remco C. E.; van der Wolk, Guido

    2010-01-01

    We combine SAURON integral field data of a representative sample of local early-type, red sequence galaxies with Spitzer/Infrared Array Camera imaging in order to investigate the presence of trace star formation in these systems. With the Spitzer data, we identify galaxies hosting low-level star for

  17. Rotation-Activity-Age Relations For Solar-Type And Cooler Stars

    Science.gov (United States)

    Basri, Gibor

    2016-08-01

    The fact that stellar rotation and chromospheric emission are correlated with age was explicitly noted by Wilson (1963) and reinforced by Kraft (1967). Wilson knew that Ca II emission was correlated with surface magnetic field in the Sun. Skumanich (1972) suggested a simple functional for the age-activity relation, and suggested that magnetic braking was the likely reason for the decline in activity. A theory for the rotation-activity connection was elucidated by Noyes et al. (1984), who invoked the Rossby number as important to the stellar dynamo. This calibrated the relation by convection zone depth and turnover time, although it was noted early and recently confirmed that it is not clear whether Rossby number is empirically superior to the rotation period itself in producing a clear rotation-activity relation. In fact, turnover times are hard to properly define, and the Rossby number is itself calibrated to tighten the relations. The number of stars in samples used to study this has increased dramatically, as have the diagnostics available to assess magnetic activity. It remains clear is that there is a strong relationship between magnetic activity and stellar rotation, and that magnetic braking forces both activity and rotation to decrease with age. These relations are also subject to modification as a function of stellar mass. There has recently been a great increase in the number of measured stellar rotation periods, and in the calibration of these relations using star clusters (whose ages can be independently assessed). I will summarize some of the ongoing progress on this topic.

  18. On the interpretation of new late B- and early A-type periodic variable stars in NGC 3766

    CERN Document Server

    Mowlavi, N; Barblan, F; Eyer, L

    2013-01-01

    We investigate possible interpretations of the new periodic B- and A-type variable stars discovered in NGC 3766. They lie in the region of the Hertzsprung-Russell diagram between slowly pulsating B and delta Sct stars, a region where no pulsation is predicted by standard models of pulsating stars. We show that the two other possible causes of periodic light curve variations, rotational modulation and binarity, cannot provide a satisfactory explanation for all the properties observed in those stars either. The question of their origin is thus currently an open issue.

  19. The use of webcam images to determine tourist-climate aptitude: favourable weather types for sun and beach tourism on the Alicante coast (Spain)

    Science.gov (United States)

    Ibarra, Emilio Martínez

    2011-05-01

    Climate has an obvious influence on tourism as a resource and as a location factor for tourist activities. Consequently, the tourist phenomenon in general is heavily controlled by meteorological conditions—in short, by the climate. In this article, the author proposes a set of weather types with which to establish the climate aptitude for sun and beach tourism. To determine these types, the density of use of one of the beaches with the lowest seasonality in continental Europe, the Levante Beach in Benidorm (Alicante, Spain), was analysed. Beach attendance was monitored using a webcam installed by the "Agencia Valenciana de Turismo". The relationship between the density of use of the lower and upper beach areas on the one hand, and meteorological variables on the other, allowed comfort (physiological equivalent temperature) and enjoyment (fractions of solar radiation) thresholds to be established. The appropriate hydric comfort values were obtained by comparing the ranges proposed by Besancenot in 1989 [Besancenot (1989) Clima et turismes. Massom, París] with numbers of visitors to the beach. The wind velocity and precipitation thresholds were selected following consultation with the literature and considering the climatic characteristics of the environment under analysis. Based on a combination of these thresholds, weather types suitable for this specific tourist activity are defined. Thus, this article presents a method for assessing the extent to which a day on the beach can be enjoyed. This has a number of applications, for planners, the tourism business and consumers alike. The use of this (filter) method in climate databases and meteorological forecasts could help determine the tourist season, the suitability of setting up a business associated with sun and beach tourism, as well as help plan holidays and program a day's leisure activities. Thus, the article seeks to improve our understanding of the climate preferences of that tourist activity par

  20. The use of webcam images to determine tourist-climate aptitude: favourable weather types for sun and beach tourism on the Alicante coast (Spain).

    Science.gov (United States)

    Ibarra, Emilio Martínez

    2011-05-01

    Climate has an obvious influence on tourism as a resource and as a location factor for tourist activities. Consequently, the tourist phenomenon in general is heavily controlled by meteorological conditions-in short, by the climate. In this article, the author proposes a set of weather types with which to establish the climate aptitude for sun and beach tourism. To determine these types, the density of use of one of the beaches with the lowest seasonality in continental Europe, the Levante Beach in Benidorm (Alicante, Spain), was analysed. Beach attendance was monitored using a webcam installed by the "Agencia Valenciana de Turismo". The relationship between the density of use of the lower and upper beach areas on the one hand, and meteorological variables on the other, allowed comfort (physiological equivalent temperature) and enjoyment (fractions of solar radiation) thresholds to be established. The appropriate hydric comfort values were obtained by comparing the ranges proposed by Besancenot in 1989 [Besancenot (1989) Clima et turismes. Massom, París] with numbers of visitors to the beach. The wind velocity and precipitation thresholds were selected following consultation with the literature and considering the climatic characteristics of the environment under analysis. Based on a combination of these thresholds, weather types suitable for this specific tourist activity are defined. Thus, this article presents a method for assessing the extent to which a day on the beach can be enjoyed. This has a number of applications, for planners, the tourism business and consumers alike. The use of this (filter) method in climate databases and meteorological forecasts could help determine the tourist season, the suitability of setting up a business associated with sun and beach tourism, as well as help plan holidays and program a day's leisure activities. Thus, the article seeks to improve our understanding of the climate preferences of that tourist activity par excellence

  1. The VLT-FLAMES Tarantula Survey. VIII. Multiplicity properties of the O-type star population

    Science.gov (United States)

    Sana, H.; de Koter, A.; de Mink, S. E.; Dunstall, P. R.; Evans, C. J.; Hénault-Brunet, V.; Maíz Apellániz, J.; Ramírez-Agudelo, O. H.; Taylor, W. D.; Walborn, N. R.; Clark, J. S.; Crowther, P. A.; Herrero, A.; Gieles, M.; Langer, N.; Lennon, D. J.; Vink, J. S.

    2013-02-01

    Context. The Tarantula Nebula in the Large Magellanic Cloud is our closest view of a starburst region and is the ideal environment to investigate important questions regarding the formation, evolution and final fate of the most massive stars. Aims: We analyze the multiplicity properties of the massive O-type star population observed through multi-epoch spectroscopy in the framework of the VLT-FLAMES Tarantula Survey. With 360 O-type stars, this is the largest homogeneous sample of massive stars analyzed to date. Methods: We use multi-epoch spectroscopy and variability analysis to identify spectroscopic binaries. We also use a Monte-Carlo method to correct for observational biases. By modeling simultaneously the observed binary fraction, the distributions of the amplitudes of the radial velocity variations and the distribution of the time scales of these variations, we constrain the intrinsic current binary fraction and period and mass-ratio distributions. Results: We observe a spectroscopic binary fraction of 0.35 ± 0.03, which corresponds to the fraction of objects displaying statistically significant radial velocity variations with an amplitude of at least 20 km s-1. We compute the intrinsic binary fraction to be 0.51 ± 0.04. We adopt power-laws to describe the intrinsic period and mass-ratio distributions: f(log 10P/d) ~ (log 10P/d)π (with log 10P/d in the range 0.15-3.5) and f(q) ~ qκ with 0.1 ≤ q = M2/M1 ≤ 1.0. The power-law indexes that best reproduce the observed quantities are π = -0.45 ± 0.30 and κ = -1.0 ± 0.4. The period distribution that we obtain thus favours shorter period systems compared to an Öpik law (π = 0). The mass ratio distribution is slightly skewed towards low mass ratio systems but remains incompatible with a random sampling of a classical mass function (κ = -2.35). The binary fraction seems mostly uniform across the field of view and independent of the spectral types and luminosity classes. The binary fraction in the outer

  2. PLANET OCCURRENCE WITHIN 0.25 AU OF SOLAR-TYPE STARS FROM KEPLER

    Energy Technology Data Exchange (ETDEWEB)

    Howard, Andrew W.; Marcy, Geoffrey W. [Department of Astronomy, University of California, Berkeley, CA 94720 (United States); Bryson, Stephen T.; Rowe, Jason F.; Borucki, William J.; Koch, David G.; Lissauer, Jack J. [NASA Ames Research Center, Moffett Field, CA 94035 (United States); Jenkins, Jon M.; Van Cleve, Jeffrey; Caldwell, Douglas A. [SETI Institute/NASA Ames Research Center, Moffett Field, CA 94035 (United States); Batalha, Natalie M. [Department of Physics and Astronomy, San Jose State University, San Jose, CA 95192 (United States); Dunham, Edward W. [Lowell Observatory, Flagstaff, AZ 86001 (United States); Gautier, Thomas N. [Jet Propulsion Laboratory/Caltech, Pasadena, CA 91109 (United States); Cochran, William D. [Department of Astronomy, University of Texas, Austin, TX 78712 (United States); Latham, David W.; Torres, Guillermo [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Brown, Timothy M. [Las Cumbres Observatory Global Telescope, Goleta, CA 93117 (United States); Gilliland, Ronald L. [Space Telescope Science Institute, Baltimore, MD 21218 (United States); Buchhave, Lars A. [Niels Bohr Institute, Copenhagen University (Denmark); Christensen-Dalsgaard, Jorgen, E-mail: howard@astro.berkeley.edu [Department of Physics and Astronomy, Aarhus University, DK-8000 Aarhus C (Denmark); and others

    2012-08-01

    We report the distribution of planets as a function of planet radius, orbital period, and stellar effective temperature for orbital periods less than 50 days around solar-type (GK) stars. These results are based on the 1235 planets (formally 'planet candidates') from the Kepler mission that include a nearly complete set of detected planets as small as 2 R{sub Circled-Plus }. For each of the 156,000 target stars, we assess the detectability of planets as a function of planet radius, R{sub p}, and orbital period, P, using a measure of the detection efficiency for each star. We also correct for the geometric probability of transit, R{sub *}/a. We consider first Kepler target stars within the 'solar subset' having T{sub eff} = 4100-6100 K, log g 4.0-4.9, and Kepler magnitude Kp < 15 mag, i.e., bright, main-sequence GK stars. We include only those stars having photometric noise low enough to permit detection of planets down to 2 R{sub Circled-Plus }. We count planets in small domains of R{sub p} and P and divide by the included target stars to calculate planet occurrence in each domain. The resulting occurrence of planets varies by more than three orders of magnitude in the radius-orbital period plane and increases substantially down to the smallest radius (2 R{sub Circled-Plus }) and out to the longest orbital period (50 days, {approx}0.25 AU) in our study. For P < 50 days, the distribution of planet radii is given by a power law, df/dlog R = k{sub R}R{sup {alpha}} with k{sub R} = 2.9{sup +0.5}{sub -0.4}, {alpha} = -1.92 {+-} 0.11, and R {identical_to} R{sub p}/R{sub Circled-Plus }. This rapid increase in planet occurrence with decreasing planet size agrees with the prediction of core-accretion formation but disagrees with population synthesis models that predict a desert at super-Earth and Neptune sizes for close-in orbits. Planets with orbital periods shorter than 2 days are extremely rare; for R{sub p} > 2 R{sub Circled-Plus} we measure an

  3. V4046 Sgr: Touchstone to Investigate Spectral Type Discrepancies for Pre-main Sequence Stars

    CERN Document Server

    Kastner, Joel H; Sargent, Benjamin; Smith, C T; Rayner, John

    2014-01-01

    Determinations of the fundamental properties (e.g., masses and ages) of late-type, pre-main sequence (pre-MS) stars are complicated by the potential for significant discrepancies between the spectral types of such stars as ascertained via optical vs. near-infrared observations. To address this problem, we have obtained near-IR spectroscopy of the nearby, close binary T Tauri system V4046 Sgr AB with the NASA Infrared Telescope Facility (IRTF) SPEX spectrometer. The V4046 Sgr close binary (and circumbinary disk) system provides an important test case for spectral type determination thanks to the stringent observational constraints on its component stellar masses (i.e., ~0.9 Msun each) as well as on its age (12-21 Myr) and distance (73 pc). Analysis of the IRTF data indicates that the composite near-IR spectral type for V4046 Sgr AB lies in the range M0-M1, i.e., significantly later than the K5+K7 composite type previously determined from optical spectroscopy. However, the K5+K7 composite type is in better agre...

  4. Neptune as a Mirror for the Sun

    Science.gov (United States)

    Kohler, Susanna

    2017-01-01

    How would the Kepler mission see a star like the Sun? We now know the answer to this question due to a creative approach: a new study has used the Kepler K2 mission to detect signals from the Sun reflected off of the surface of Neptune.Asteroseismology uses different oscillation modes of a star to probe its internal structure and properties. [Tosaka]Information in OscillationsKeplers most glamorous work is in discovering new planets around other stars. To successfully do this, however, the spacecraft is also quietly doing a lot of very useful work in the background, characterizing the many stars in our vicinity that planets might be found around.One of the ways Kepler gets information about these stars is from oscillations of the stars intensities. In asteroseismology, we look at oscillatory modes that are caused by convection-driven pressure changes on the inside of the star. All stars with near-surface convection oscillate like this including the Sun and by measuring the oscillations in intensity of these stars, we can make inferences about the stars properties.A Planetary MirrorWe do this by first understanding our Suns oscillations especially well (made easier by the fact that its nearby!). Then we use asteroseimic scaling relations determined empirically that relate characteristics like mass and radius of other stars to those of the Sun, based on the relation between the stars oscillation properties to the Suns.The trouble is, those oscillation properties are difficult to measure, and different instruments often measure different values. For this reason, wed like to measure the Suns oscillations with the same instrument we use to measure other stars oscillations: Kepler.Top panel: Kepler K2 49-day light curve of Neptune. Bottom panel: power density spectrum as a function of frequency (grey). Neptunes rotation frequencies and harmonics appear toward the left side (blue); the excess power due to the solar modes is visible toward the bottom right. The green curve

  5. Reconnection on the Sun

    Science.gov (United States)

    Kohler, Susanna

    2016-05-01

    Because the Sun is so close, it makes an excellent laboratory to study processes we cant examinein distant stars. One openquestion is that of how solar magnetic fields rearrange themselves, producing the tremendous releases of energy we observe as solar flares and coronal mass ejections (CMEs).What is Magnetic Reconnection?Magnetic reconnection occurs when a magnetic field rearranges itself to move to a lower-energy state. As field lines of opposite polarity reconnect, magnetic energy is suddenly converted into thermal and kinetic energy.This processis believed to be behind the sudden releases of energy from the solar surface in the form of solar flares and CMEs. But there are many different models for how magnetic reconnection could occur in the magnetic field at the Suns surface, and we arent sure which one of these reconnection types is responsible for the events we see.Recently, however, several studies have been published presenting some of the first observational support of specific reconnection models. Taken together, these observations suggest that there are likely several different types of reconnection happening on the solar surface. Heres a closer look at two of these recent publications:A pre-eruption SDO image of a flaring region (b) looks remarkably similar to a 3D cartoon for typical breakout configuration (a). Click for a closer look! [Adapted from Chen et al. 2016]Study 1:Magnetic BreakoutLed by Yao Chen (Shandong University in China), a team of scientists has presented observations made by the Solar Dynamics Observatory (SDO) of a flare and CME event that appears to have been caused by magnetic breakout.In the magnetic breakout model, a series of loops in the Suns lower corona are confined by a surrounding larger loop structure called an arcade higher in the corona. As the lower loops push upward, reconnection occurs in the upper corona, removing the overlying, confining arcade. Without that extra confinement, the lower coronal loops expand upward

  6. Star formation associated with neutral hydrogen in the outskirts of early-type galaxies

    Science.gov (United States)

    Yldz, Mustafa K.; Serra, Paolo; Peletier, Reynier F.; Oosterloo, Tom A.; Duc, Pierre-Alain

    2016-09-01

    About 20 percent of all nearby early-type galaxies (M⋆ ≳ ~6~ × 109~M⊙) outside the Virgo cluster are surrounded by a disc or ring of low-column-density neutral hydrogen (H I) gas with typical radii of tens of kpc, much larger than the stellar body. In order to understand the impact of these gas reservoirs on the host galaxies, we analyse the distribution of star formation out to large radii as a function of H I properties using GALEX UV and SDSS optical images. Our sample consists of 18 H I-rich galaxies as well as 55 control galaxies where no H I has been detected. In half of the H I-rich galaxies the radial UV profile changes slope at the position of the H I radial profile peak. To study the stellar populations, we calculate the FUV-NUV and UV-optical colours in two apertures, 1-3 and 3-10 Reff. We find that H I-rich galaxies are on average 0.5 and 0.8 mag bluer than the H I-poor ones, respectively. This indicates that a significant fraction of the UV emission traces recent star formation and is associated with the H I gas. Using FUV emission as a proxy for star formation, we estimate the integrated star formation rate in the outer regions (R > 1Reff) to be on average ˜ 6× 10-3 M⊙~yr-1 for the H I-rich galaxies. This rate is too low to build a substantial stellar disc and, therefore, change the morphology of the host. We find that the star formation efficiency and the gas depletion time are similar to those at the outskirts of spirals.

  7. Star formation associated with neutral hydrogen in the outskirts of early-type galaxies

    Science.gov (United States)

    Yıldız, Mustafa K.; Serra, Paolo; Peletier, Reynier F.; Oosterloo, Tom A.; Duc, Pierre-Alain

    2017-01-01

    About 20 per cent of all nearby early-type galaxies (M⋆ ≳ 6 × 109 M⊙) outside the Virgo cluster are surrounded by a disc or ring of low-column-density neutral hydrogen (H I) gas with typical radii of tens of kpc, much larger than the stellar body. In order to understand the impact of these gas reservoirs on the host galaxies, we analyse the distribution of star formation out to large radii as a function of H I properties using GALEX UV and SDSS optical images. Our sample consists of 18 H I-rich galaxies as well as 55 control galaxies where no H I has been detected. In half of the H I-rich galaxies, the radial UV profile changes slope at the position of the H I radial profile peak. To study the stellar populations, we calculate the FUV-NUV and UV-optical colours in two apertures, 1-3 and 3-10 Reff. We find that H I-rich galaxies are on average 0.5 and 0.8 mag bluer than the H I-poor ones, respectively. This indicates that a significant fraction of the UV emission traces recent star formation and is associated with the H I gas. Using FUV emission as a proxy for star formation, we estimate the integrated star formation rate in the outer regions (R > 1Reff) to be on average ˜6 × 10-3 M⊙ yr-1 for the H I-rich galaxies. This rate is too low to build a substantial stellar disc and, therefore, change the morphology of the host. We find that the star formation efficiency and the gas depletion time are similar to those at the outskirts of spirals.

  8. A STATISTICAL RECONSTRUCTION OF THE PLANET POPULATION AROUND KEPLER SOLAR-TYPE STARS

    Energy Technology Data Exchange (ETDEWEB)

    Silburt, Ari; Wu, Yanqin [Department of Astronomy and Astrophysics, University of Toronto, Toronto, ON M5S 3H4 (Canada); Gaidos, Eric [Department of Geology and Geophysics, University of Hawai' i at Mānoa, Honolulu, HI 96822 (United States)

    2015-02-01

    Using the cumulative catalog of planets detected by the NASA Kepler mission, we reconstruct the intrinsic occurrence of Earth- to Neptune-size (1-4 R {sub ⊕}) planets and their distributions with radius and orbital period. We analyze 76,711 solar-type (0.8 < R {sub *}/R {sub ☉} < 1.2) stars with 430 planets on 20-200 day orbits, excluding close-in planets that may have been affected by the proximity to the host star. Our analysis considers errors in planet radii and includes an ''iterative simulation'' technique that does not bin the data. We find a radius distribution that peaks at 2-2.8 Earth radii, with lower numbers of smaller and larger planets. These planets are uniformly distributed with logarithmic period, and the mean number of such planets per star is 0.46 ± 0.03. The occurrence is ∼0.66 if planets interior to 20 days are included. We estimate the occurrence of Earth-size planets in the ''habitable zone'' (defined as 1-2 R {sub ⊕}, 0.99-1.7 AU for solar-twin stars) as 6.4{sub −1.1}{sup +3.4}%. Our results largely agree with those of Petigura et al., although we find a higher occurrence of 2.8-4 Earth-radii planets. The reasons for this excess are the inclusion of errors in planet radius, updated Huber et al. stellar parameters, and also the exclusion of planets that may have been affected by proximity to the host star.

  9. The MiMeS survey of magnetism in massive stars: Magnetic analysis of the O-type stars

    CERN Document Server

    Grunhut, J H; Neiner, C; Oksala, M E; Petit, V; Alecian, E; Bohlender, D A; Bouret, J -C; Henrichs, H F; Hussain, G A J; Kochukhov, O

    2016-01-01

    We present the analysis performed on spectropolarimetric data of 97 O-type targets included in the framework of the MiMeS (Magnetism in Massive Stars) Survey. Mean Least-Squares Deconvolved Stokes I and V line profiles were extracted for each observation, from which we measured the radial velocity, rotational and non-rotational broadening velocities, and longitudinal magnetic field. The investigation of the Stokes I profiles led to the discovery of 2 new multi-line spectroscopic systems (HD46106, HD204827) and confirmed the presence of a suspected companion in HD37041. We present a modified strategy of the Least-Squares Deconvolution technique aimed at optimising the detection of magnetic signatures while minimising the detection of spurious signatures in Stokes V. Using this analysis, we confirm the detection of a magnetic field in 6 targets previously reported as magnetic by the MiMeS collaboration (HD108, HD47129A2, HD57682, HD148937, CPD-28 2561, and NGC 1624-2), as well as report the presence of signal i...

  10. Star formation in early-type galaxies: the role of stellar winds and kinematics

    CERN Document Server

    Pellegrini, S; Ciotti, L

    2015-01-01

    Early-type galaxies (ETGs) host a hot ISM produced mainly by stellar winds, and heated by Type Ia supernovae and the thermalization of stellar motions. High resolution 2D hydrodynamical simulations showed that ordered rotation in the stellar component results in the formation of a centrifugally supported cold equatorial disc. In a recent numerical investigation we found that subsequent generations of stars are formed in this cold disc; this process consumes most of the cold gas, leaving at the present epoch cold masses comparable to those observed. Most of the new stellar mass formed a few Gyrs ago, and resides in a disc.

  11. The Effective Temperatures of O-type Stars from UV spectroscopy

    CERN Document Server

    Bianchi, Luciana

    2013-01-01

    We present an analysis of high resolution spectra in the far-UV -- UV range (~905-2000\\AA) with non-LTE, spherical, hydrodynamical, line-blanketed models, of three O-type Galactic stars, and derive their photospheric and wind parameters. These data extend previously analyzed samples and fill a gap in spectral type coverage. The combined sample confirms a revised (downward) effective temperature scale with respect to canonical calibrations, as found in our previous works from UV and optical spectra, and in recent works by other authors.

  12. ALFALFA HI Content and Star Formation in Virgo Cluster Early-Type Dwarfs

    CERN Document Server

    Koopmann, R A; Haynes, M P; Brosch, N

    2009-01-01

    The ALFALFA (Arecibo Legacy Fast ALFA) blind survey is providing a census of HI in galaxies of all types in a range of environments. Here we report on ALFALFA results for Virgo Cluster early-type dwarfs between declinations of 4 and 16 degrees. Less than 2% of the Virgo early-type dwarf population is detected, compared to 70-80% of the Im/BCD dwarf population. Most of the dwarfs detected in HI show evidence for ongoing or recent star formation. Early-type galaxies with HI tend to be located in the outer regions of the cluster and to be brighter. Early-type dwarfs with HI may be undergoing morphological transition due to cluster environmental effects.

  13. Present-day cosmic abundances. A comprehensive study of nearby early B-type stars and implications for stellar and Galactic evolution and interstellar dust models

    Science.gov (United States)

    Nieva, M.-F.; Przybilla, N.

    2012-03-01

    Context. Early B-type stars are ideal indicators for present-day cosmic abundances since they preserve their pristine abundances and typically do not migrate far beyond their birth environments over their short lifetimes, in contrast to older stars like the Sun. They are also unaffected by depletion onto dust grains, unlike the cold/warm interstellar medium (ISM) or H ii regions. Aims: A carefully selected sample of early B-type stars in OB associations and the field within the solar neighbourhood is studied comprehensively. Quantitative spectroscopy is used to characterise their atmospheric properties in a self-consistent way. Present-day abundances for the astrophysically most interesting chemical elements are derived in order to investigate whether a present-day cosmic abundance standard can be established. Methods: High-resolution and high-S/N FOCES, FEROS and ELODIE spectra of well-studied sharp-lined early B-type stars are analysed in non-LTE. Line-profile fits based on extensive model grids and an iterative analysis methodology are used to constrain stellar parameters and elemental abundances at high accuracy and precision. Atmospheric parameters are derived from the simultaneous establishment of independent indicators, from multiple ionization equilibria and the Stark-broadened hydrogen Balmer lines, and they are confirmed by reproduction of the stars' global spectral energy distributions. Results: Effective temperatures are constrained to 1-2% and surface gravities to less than 15% uncertainty, along with accurate rotational, micro- and macroturbulence velocities. Good agreement of the resulting spectroscopic parallaxes with those from the new reduction of the Hipparcos catalogue is obtained. Absolute values for abundances of He, C, N, O, Ne, Mg, Si and Fe are determined to better than 25% uncertainty. The synthetic spectra match the observations reliably over almost the entire visual spectral range. Three sample stars, γ Ori, o Per and θ1 Ori D, are

  14. H-alpha as a Luminosity Class Diagnostic for K- and M-type Stars

    CERN Document Server

    Jennings, Jeff

    2016-01-01

    We have identified the H-alpha absorption feature as a new spectroscopic diagnostic of luminosity class in K- and M-type stars. From high-resolution spectra of 19 stars with well-determined physical properties (including effective temperatures and stellar radii), we measured equivalent widths for H-alpha and the Ca II triplet and examined their dependence on both luminosity class and stellar radius. H-alpha shows a strong relation with both luminosity class and radius that extends down to late M spectral types. This behavior in H-alpha has been predicted as a result of the density-dependent overpopulation of the metastable 2S level in hydrogen, an effect that should become dominant for Balmer line formation in non-LTE conditions. We conclude that this new metallicity-insensitive diagnostic of luminosity class in cool stars could serve as an effective means of discerning between populations such as Milky Way giants and supergiant members of background galaxies.

  15. Link between Mass-loss and Variability Type for AGB Stars?

    CERN Document Server

    Ivezic, Z; Ivezic, Zeljko; Knapp, Gillian R.

    1998-01-01

    We find that AGB stars separate in the 25-12 vs. 12-K color-color diagram according to their chemistry (O, S vs. C) and variability type (Miras vs. SRb/Lb). While discrimination according to the chemical composition is not surprising, the separation of Miras from SRb/Lb variables is unexpected. We show that ``standard'' steady-state radiatively driven models provide excellent fits to the color distribution of Miras of all chemical types. However, these models are incapable of explaining the dust emission from O-rich SRb/Lb stars. The models can be altered to fit the data by postulating different optical properties for silicate grains, or by assuming that the dust temperature at the inner envelope radius is significantly lower (300-400 K) than typical condensation temperatures (800-1000 K), a possibility which is also supported by the detailed characteristics of LRS data. The absence of hot dust for SRb/Lb stars can be interpreted as a recent (order of 100 yr) decrease in the mass-loss rate. The distribution o...

  16. New bright optical spectrophotometric standards: A-type stars from the STIS Next Generation Spectral Library

    CERN Document Server

    Prieto, Carlos Allende

    2015-01-01

    Exoplanets have sparked interest in extremely high signal-to-noise ratio spectroscopic observations of very bright stars, in a regime where flux calibrators, in particular DA white dwarfs, are not available. We argue that A-type stars offer a useful alternative and reliable space-based spectrophotometry is now available for a number of bright ones in the range 3type flux standards for the optical range (400-800 nm), and provide scaled model fluxes for them. Our tests suggest that the absolute fluxes for these stars in the optical are reliable to within 3%. We limit the spectral range to 400-800 nm, since our models have difficulties to reproduce the observed fluxes in the near-infrared and, especially, in the near-UV, where the discrepancies rise up to ~ 10%. Based on our model fits, we derive angular diameters with an estimated accuracy of about 1%.

  17. Membership, metallicity and lithium abundances for solar-type stars in NGC 6633

    CERN Document Server

    Jeffries, R D; Harmer, S; Deliyannis, C P

    2002-01-01

    We present spectroscopic observations of candidate F, G and K type stars in NGC 6633, an open cluster with a similar age to the Hyades. We identify 10 new cluster members including one short period binary system. Combining this survey with that of Jeffries (1997), we identify a total of 30 solar-type members. We have used the F and early G stars to spectroscopically estimate [Fe/H]=-0.096+/-0.081 for NGC 6633 and with more precision that NGC 6633 has (0.074+/-0.041) dex less iron than the Pleiades and (0.206+/-0.040) dex less iron than the Hyades. Lithium abundances have been estimated for the NGC 6633 members and compared with consistently determined Li abundances in other clusters. Several mid F stars in NGC 6633 show strong Li depletion at approximately the same effective temperature that this phenomenon is seen in the Hyades. At cooler temperatures the Li abundance patterns in several open clusters with similar ages (NGC 6633, Hyades, Praesepe and Coma Berenices) are remarkably similar, despite their diff...

  18. The Na I D resonance lines in main sequence late-type stars

    CERN Document Server

    Díaz, Rodrigo F; Mauas, Pablo J D

    2007-01-01

    We study the sodium D lines (D1: 5895.92 \\AA; D2: 5889.95 \\AA) in late-type dwarf stars. The stars have spectral types between F6 and M5.5 (B-V between 0.457 and 1.807) and metallicity between [Fe/H] = -0.82 and 0.6. We obtained medium resolution echelle spectra using the 2.15-m telescope at the argentinian observatory CASLEO. The observations have been performed periodically since 1999. The spectra were calibrated in wavelength and in flux. A definition of the pseudo-continuum level is found for all our observations. We also define a continuum level for calibration purposes. The equivalent width of the D lines is computed in detail for all our spectra and related to the colour index (B-V) of the stars. When possible, we perform a careful comparison with previous studies. Finally, we construct a spectral index (R_D') as the ratio between the flux in the D lines, and the bolometric flux. We find that, once corrected for the photospheric contribution, this index can be used as a chromospheric activity indicator...

  19. Young stars of low mass in the Gum nebula

    Science.gov (United States)

    Graham, J. A.; Heyer, Mark H.

    1989-01-01

    Observations are presented for four recently formed stars in the vicinity of the Gum nebula which are heavily obscured by surrounding dust and are associated with small reflection nebulae. HH46 is the only currently active star of the sample, and it is found to have a spectral type in the range of late G-early K, with superimposed emission lines of H-alpha, Ca II, Fe I, Fe II, and weak He I at near zero velocities. It is suggested that the observed scenario of low-mass stars in an older massive star environment may be analogous to the circumstances surrounding the birth of the sun.

  20. Oscillation frequencies for 35 \\Kepler solar-type planet-hosting stars using Bayesian techniques and machine learning

    CERN Document Server

    Davies, G R; Bedding, T R; Handberg, R; Lund, M N; Chaplin, W J; Huber, D; White, T R; Benomar, O; Hekker, S; Basu, S; Campante, T L; Christensen-Dalsgaard, J; Elsworth, Y; Karoff, C; Kjeldsen, H; Lundkvist, M S; Metcalfe, T S; Stello, D

    2015-01-01

    \\Kepler has revolutionised our understanding of both exoplanets and their host stars. Asteroseismology is a valuable tool in the characterisation of stars and \\Kepler is an excellent observing facility to perform asteroseismology. Here we select a sample of 35 \\Kepler solar-type stars which host transiting exoplanets (or planet candidates) with detected solar-like oscillations. Using available \\Kepler short cadence data up to Quarter 16 we create power spectra optimised for asteroseismology of solar-type stars. We identify modes of oscillation and estimate mode frequencies by ``peak bagging'' using a Bayesian MCMC framework. In addition, we expand the methodology of quality assurance using a Bayesian unsupervised machine learning approach. We report the measured frequencies of the modes of oscillation for all 35 stars and frequency ratios commonly used in detailed asteroseismic modelling. Due to the high correlations associated with frequency ratios we report the covariance matrix of all frequencies measured ...