WorldWideScience

Sample records for solar-like main-sequence stars

  1. Solar-Type Activity in Main-Sequence Stars

    CERN Document Server

    Gershberg, Roald E

    2005-01-01

    Solar-type activity over the whole range of the electromagnetic spectrum is a phenomenon inherent in the majority of low- and moderate-mass main sequence stars. In this monograph observational results are summarized in a systematic and comprehensive fashion. The analysis of the various manifestations of such stellar activity leads to the identification of these phenomena with macroscopic non-linear processes in a magnetized plasma. Comparative study of flare stars and the Sun has become increasingly fruitful and is presently an active field of research involving stellar and solar physicists, experts in plasma physics and high-energy astrophysicists. This book will provide them with both an introduction and overview of observational results from the first optical photometry and spectroscopy, from the satellite telescopes International Ultraviolet Explorer to Hubble Space Telescope, XMM-Newton and Chandra, as well as with the present physical interpretation of solar-type activity in main sequence stars. Gershbe...

  2. Main sequences defined by Hyades and field stars

    International Nuclear Information System (INIS)

    Upgren, A.R.

    1978-01-01

    The author reviews the main sequences defined by members of the Hyades cluster and by the field stars in the solar neighborhood. For this purpose, the discussion is limited primarily to the stars of the lower portions of the main sequence, especially those of spectral classes K and early M. There are two reasons for emphasis on the faint red dwarf stars. First, the value of a parallax depends on its size or, more accurately, on the error in parallax divided by the parallax itself. Large parallaxes of high precision occur in large numbers only for stars inhabiting the lower main sequence. Furthermore, brighter stars of earlier spectral classes are more likely to be influenced by evolutionary effects which may differ between the Hyades and field stars, and which are difficult to calibrate. (Auth.)

  3. Oscillation mode linewidths of main-sequence and subgiant stars observed by Kepler

    DEFF Research Database (Denmark)

    Appourchaux, T.; Benomar, O.; Gruberbauer, M.

    2012-01-01

    Solar-like oscillations have been observed by {{\\it Kepler}} and CoRoT in several solar-type stars. We study the variations of stellar p-mode linewidth as a function of effective temperature. Time series of 9 months of Kepler data have been used. The power spectra of 42 cool main-sequence stars a...

  4. The Lower Main Sequence of Stars in the Solar Neighborhood: Model Predictions Versus Observation

    Directory of Open Access Journals (Sweden)

    Bartašiūtė S.

    2012-09-01

    Full Text Available We have used the Simbad database and VizieR catalogue access tools to construct the observational color-absolute magnitude diagrams of nearby K-M dwarfs with precise Hipparcos parallaxes (σπ/π ≤ 0:05. Particular attention has been paid to removing unresolved double/multiple stars and variables. In addition to archival data, we have made use of nearly 2000 new radial-velocity measurements of K-M dwarfs to identify spectroscopic binary candidates. The main sequences, cleaned from unresolved binaries, variable stars, and old population stars which can also widen the sequence due to their presumably lower metallicity, were compared to available solar-metallicity models. Significant offsets of most of the model main-sequence lines are seen with respect to observational data, especially for the lower-mass stars. Only the location and slope of the Victoria-Regina and, partly, BaSTI isochrones match the data quite well.

  5. TESTING SCALING RELATIONS FOR SOLAR-LIKE OSCILLATIONS FROM THE MAIN SEQUENCE TO RED GIANTS USING KEPLER DATA

    Energy Technology Data Exchange (ETDEWEB)

    Huber, D.; Bedding, T. R.; Stello, D. [Sydney Institute for Astronomy (SIfA), School of Physics, University of Sydney, NSW 2006 (Australia); Hekker, S. [Astronomical Institute ' Anton Pannekoek' , University of Amsterdam, Science Park 904, 1098 XH Amsterdam (Netherlands); Mathur, S. [High Altitude Observatory, NCAR, P.O. Box 3000, Boulder, CO 80307 (United States); Mosser, B. [LESIA, CNRS, Universite Pierre et Marie Curie, Universite Denis, Diderot, Observatoire de Paris, 92195 Meudon cedex (France); Verner, G. A.; Elsworth, Y. P.; Hale, S. J.; Chaplin, W. J. [School of Physics and Astronomy, University of Birmingham, Birmingham B15 2TT (United Kingdom); Bonanno, A. [INAF Osservatorio Astrofisico di Catania (Italy); Buzasi, D. L. [Eureka Scientific, 2452 Delmer Street Suite 100, Oakland, CA 94602-3017 (United States); Campante, T. L. [Centro de Astrofisica da Universidade do Porto, Rua das Estrelas, 4150-762 Porto (Portugal); Kallinger, T. [Department of Physics and Astronomy, University of British Columbia, Vancouver (Canada); Silva Aguirre, V. [Max-Planck-Institut fuer Astrophysik, Karl-Schwarzschild-Str. 1, 85748 Garching (Germany); De Ridder, J. [Instituut voor Sterrenkunde, K.U.Leuven (Belgium); Garcia, R. A. [Laboratoire AIM, CEA/DSM-CNRS, Universite Paris 7 Diderot, IRFU/SAp, Centre de Saclay, 91191, Gif-sur-Yvette (France); Appourchaux, T. [Institut d' Astrophysique Spatiale, UMR 8617, Universite Paris Sud, 91405 Orsay Cedex (France); Frandsen, S. [Danish AsteroSeismology Centre (DASC), Department of Physics and Astronomy, Aarhus University, DK-8000 Aarhus C (Denmark); Houdek, G., E-mail: dhuber@physics.usyd.edu.au [Institute of Astronomy, University of Vienna, 1180 Vienna (Austria); and others

    2011-12-20

    We have analyzed solar-like oscillations in {approx}1700 stars observed by the Kepler Mission, spanning from the main sequence to the red clump. Using evolutionary models, we test asteroseismic scaling relations for the frequency of maximum power ({nu}{sub max}), the large frequency separation ({Delta}{nu}), and oscillation amplitudes. We show that the difference of the {Delta}{nu}-{nu}{sub max} relation for unevolved and evolved stars can be explained by different distributions in effective temperature and stellar mass, in agreement with what is expected from scaling relations. For oscillation amplitudes, we show that neither (L/M){sup s} scaling nor the revised scaling relation by Kjeldsen and Bedding is accurate for red-giant stars, and demonstrate that a revised scaling relation with a separate luminosity-mass dependence can be used to calculate amplitudes from the main sequence to red giants to a precision of {approx}25%. The residuals show an offset particularly for unevolved stars, suggesting that an additional physical dependency is necessary to fully reproduce the observed amplitudes. We investigate correlations between amplitudes and stellar activity, and find evidence that the effect of amplitude suppression is most pronounced for subgiant stars. Finally, we test the location of the cool edge of the instability strip in the Hertzsprung-Russell diagram using solar-like oscillations and find the detections in the hottest stars compatible with a domain of hybrid stochastically excited and opacity driven pulsation.

  6. The evolution of coronal activity in main sequence cool stars

    International Nuclear Information System (INIS)

    Stern, R.A.

    1984-01-01

    Stars spend most of their lifetime and show the least amount of nuclear evolution on the main sequence. However, the x-ray luminosities of cool star coronas change by orders of magnitude as a function of main sequence age. Such coronal evolution is discussed in relation to our knowledge of the solar corona, solar and stellar flares, stellar rotation and binarity. The relevance of X-ray observations to current speculations on stellar dynamos is also considered

  7. Testing Scaling Relations for Solar-like Oscillations from the Main Sequence to Red Giants Using Kepler Data

    DEFF Research Database (Denmark)

    Huber, D.; Bedding, T.R.; Stello, D.

    2011-01-01

    ), and oscillation amplitudes. We show that the difference of the Δν-νmax relation for unevolved and evolved stars can be explained by different distributions in effective temperature and stellar mass, in agreement with what is expected from scaling relations. For oscillation amplitudes, we show that neither (L/M) s......We have analyzed solar-like oscillations in ~1700 stars observed by the Kepler Mission, spanning from the main sequence to the red clump. Using evolutionary models, we test asteroseismic scaling relations for the frequency of maximum power (νmax), the large frequency separation (Δν...... scaling nor the revised scaling relation by Kjeldsen & Bedding is accurate for red-giant stars, and demonstrate that a revised scaling relation with a separate luminosity-mass dependence can be used to calculate amplitudes from the main sequence to red giants to a precision of ~25%. The residuals show...

  8. X-ray sources in regions of star formation. II. The pre-main-sequence G star HDE 283572

    International Nuclear Information System (INIS)

    Walter, F.M.; Brown, A.; Linsky, J.L.; Rydgren, A.E.; Vrba, F.; Joint Institute for Laboratory Astrophysics, Boulder, CO; Computer Sciences Corp., El Segundo, CA; Naval Observatory, Flagstaff, AZ)

    1987-01-01

    This paper reports the detection of HDE 283572, a ninth-magnitude G star 8 arcmin south of RY Tau, as a bright X-ray source. The observations reveal this object to be a fairly massive (about 2 solar masses) pre-main-sequence star associated with the Taurus-Auriga star formation complex. It exhibits few of the characteristics of the classical T Tauri stars and is a good example of a naked T Tauri star. The star is a mid-G subgiant, of about three solar radii and rotates with a period of 1.5 d. The coronal and chromospheric surface fluxes are similar to those of the most active late type stars (excluding T Tauri stars). The X-ray and UV lines most likely arise in different atmospheric structures. Radiative losses are some 1000 times the quiet solar value and compare favorably with those of T Tauri stars. 49 references

  9. Lithium depletion and rotation in main-sequence stars

    International Nuclear Information System (INIS)

    Balachandran, S.

    1990-01-01

    Lithium abundances were measured in nearly 200 old disk-population F stars to examine the effects of rotational braking on the depletion of Li. The sample was selected to be slightly evolved off the main sequence so that the stars have completed all the Li depletion they will undergo on the main sequence. A large scatter in Li abundances in the late F stars is found, indicating that the Li depletion is not related to age and spectral type alone. Conventional depletion mechanisms like convective overshoot and microscopic diffusion are unable to explain Li depletion in F stars with thin convective envelopes and are doubly taxed to explain such a scatter. No correlation is found between Li abundance and the present projected rotational velocity and some of the most rapid rotators are undepleted, ruling out meridional circulation as the cause of Li depletion. There is a somewhat larger spread in Li abundances in the spun-down late F stars compared to the early F stars which should remain rotationally unaltered on the main sequence. 85 refs

  10. ABSOLUTE PROPERTIES OF THE PRE-MAIN-SEQUENCE ECLIPSING BINARY STAR NP PERSEI

    Energy Technology Data Exchange (ETDEWEB)

    Lacy, Claud H. Sandberg [Physics Department, University of Arkansas, Fayetteville, AR 72701 (United States); Fekel, Francis C.; Muterspaugh, Matthew W. [Center of Excellence in Information Systems, Tennessee State University, Nashville, TN 37209 (United States); Pavlovski, Krešimir [Department of Physics, Faculty of Science, University of Zagreb, Bijenička cesta 32, 10000 Zagreb (Croatia); Torres, Guillermo, E-mail: clacy@uark.edu, E-mail: fekel@evans.tsuniv.edu, E-mail: pavlovski@phy.hr, E-mail: gtorres@cfa.harvard.edu, E-mail: matthew1@coe.tsuniv.edu [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)

    2016-07-01

    NP Per is a well-detached, 2.2 day eclipsing binary whose components are both pre-main-sequence stars that are still contracting toward the main-sequence phase of evolution. We report extensive photometric and spectroscopic observations with which we have determined their properties accurately. Their surface temperatures are quite different: 6420 ± 90 K for the larger F5 primary star and 4540 ± 160 K for the smaller K5e star. Their masses and radii are 1.3207 ± 0.0087 solar masses and 1.372 ± 0.013 solar radii for the primary, and 1.0456 ± 0.0046 solar masses and 1.229 ± 0.013 solar radii for the secondary. The orbital period is variable over long periods of time. A comparison of the observations with current stellar evolution models from MESA indicates that the stars cannot be fit at a single age: the secondary appears significantly younger than the primary. If the stars are assumed to be coeval and to have the age of the primary (17 Myr), then the secondary is larger and cooler than predicted by current models. The H α spectral line of the secondary component is completely filled by, presumably, chromospheric emission due to a magnetic activity cycle.

  11. Excitation of Solar-like Oscillations: From PMS to MS Stellar Models ...

    Indian Academy of Sciences (India)

    excited modes in pre-main sequence stars are also discussed. Key words. Turbulence—convection—oscillations—excitation—sun, stars: α Cen A—stars: main and pre-main sequence stars. 1. Introduction. In the past approximately five years, solar-like oscillations have been detected in several intermediate massive stars ...

  12. Stochastically excited oscillations on the upper main sequence

    DEFF Research Database (Denmark)

    Antoci, Victoria

    2013-01-01

    Convective envelopes in stars on the main sequence are usually connected only with stars of spectral types F5 or later. However, observations as well as theory indicate that the convective outer layers in earlier stars, despite being shallow, are still effective and turbulent enough to stochastic......Convective envelopes in stars on the main sequence are usually connected only with stars of spectral types F5 or later. However, observations as well as theory indicate that the convective outer layers in earlier stars, despite being shallow, are still effective and turbulent enough...... Pulsating B and Be stars, all in the context of solar-like oscillations....

  13. Nitrogen chronology of massive main sequence stars

    NARCIS (Netherlands)

    Köhler, K.; Borzyszkowski, M.; Brott, I.; Langer, N.; de Koter, A.

    2012-01-01

    Context. Rotational mixing in massive main sequence stars is predicted to monotonically increase their surface nitrogen abundance with time. Aims. We use this effect to design a method for constraining the age and the inclination angle of massive main sequence stars, given their observed luminosity,

  14. Impacts of WIMP dark matter upon stellar evolution: main-sequence stars

    CERN Document Server

    Scott, Pat; Edsjo, Joakim

    2008-01-01

    The presence of large amounts of WIMP dark matter in stellar cores has been shown to have significant effects upon models of stellar evolution. We present a series of detailed grids of WIMP-influenced stellar models for main sequence stars, computed using the DarkStars code. We describe the changes in stellar structure and main sequence evolution which occur for masses ranging from 0.3 to 2.0 solar masses and metallicities from Z = 0.0003-0.02, as a function of the rate of energy injection by WIMPs. We then go on to show what rates of energy injection can be obtained using realistic orbital parameters for stars near supermassive black holes, including detailed considerations of dark matter halo velocity and density profiles. Capture and annihilation rates are strongly boosted when stars follow elliptical rather than circular orbits, causing WIMP annihilation to provide up to 100 times the energy of hydrogen fusion in stars at the Galactic centre.

  15. Binary pulsar PSR 1718-19 contains a stripped main-sequence turn-off star

    International Nuclear Information System (INIS)

    Zwitter, T.

    1993-05-01

    Lyne et al. (1993) have recently announced the discovery of a 1-second globular cluster pulsar, 1718-19, in a 6.2-hour binary system which is embedded in a cloud of material originating from the companion star. However the incident flux of the pulsar's radiation on the companion is too low to ablate it and a main sequence companion is too small to fill its Roche lobe. Here I argue that the companion is a stripped turn-off star of 0.2-0.4 solar masses (M sun ) and with approx. 0.1M sun helium core. It has approx. 1.8-times larger radius than a main sequence star of equal mass. Its position in the Hertzsprung-Russell diagram overlaps that of a ∼ 0.65M sun main-sequence star. The evolutionary state of the companion and the highly magnetized slowly rotating neutron star place the system on the verge of the low mass X-ray binary phase. (author). 19 refs, 2 figs

  16. Common Warm Dust Temperatures Around Main Sequence Stars

    Science.gov (United States)

    Morales, Farisa; Rieke, George; Werner, Michael; Stapelfeldt, Karl; Bryden, Geoffrey; Su, Kate

    2011-01-01

    We compare the properties of warm dust emission from a sample of main-sequence A-type stars (B8-A7) to those of dust around solar-type stars (F5-KO) with similar Spitzer Space Telescope Infrared Spectrograph/MIPS data and similar ages. Both samples include stars with sources with infrared spectral energy distributions that show evidence of multiple components. Over the range of stellar types considered, we obtain nearly the same characteristic dust temperatures (∼ 190 K and ∼60 K for the inner and outer dust components, respectively)-slightly above the ice evaporation temperature for the inner belts. The warm inner dust temperature is readily explained if populations of small grains are being released by sublimation of ice from icy planetesimals. Evaporation of low-eccentricity icy bodies at ∼ 150 K can deposit particles into an inner/warm belt, where the small grains are heated to dust Temperatures of -190 K. Alternatively, enhanced collisional processing of an asteroid belt-like system of parent planetesimals just interior to the snow line may account for the observed uniformity in dust temperature. The similarity in temperature of the warmer dust across our B8-KO stellar sample strongly suggests that dust-producing planetesimals are not found at similar radial locations around all stars, but that dust production is favored at a characteristic temperature horizon.

  17. Frequency dependence of p-mode frequency shifts induced by magnetic activity in Kepler solar-like stars

    Science.gov (United States)

    Salabert, D.; Régulo, C.; Pérez Hernández, F.; García, R. A.

    2018-04-01

    The variations of the frequencies of the low-degree acoustic oscillations in the Sun induced by magnetic activity show a dependence on radial order. The frequency shifts are observed to increase towards higher-order modes to reach a maximum of about 0.8 μHz over the 11-yr solar cycle. A comparable frequency dependence is also measured in two other main sequence solar-like stars, the F-star HD 49933, and the young 1 Gyr-old solar analog KIC 10644253, although with different amplitudes of the shifts of about 2 μHz and 0.5 μHz, respectively. Our objective here is to extend this analysis to stars with different masses, metallicities, and evolutionary stages. From an initial set of 87 Kepler solar-like oscillating stars with known individual p-mode frequencies, we identify five stars showing frequency shifts that can be considered reliable using selection criteria based on Monte Carlo simulations and on the photospheric magnetic activity proxy Sph. The frequency dependence of the frequency shifts of four of these stars could be measured for the l = 0 and l = 1 modes individually. Given the quality of the data, the results could indicate that a physical source of perturbation different from that in the Sun is dominating in this sample of solar-like stars.

  18. Solar Luminosity on the Main Sequence, Standard Model and Variations

    Science.gov (United States)

    Ayukov, S. V.; Baturin, V. A.; Gorshkov, A. B.; Oreshina, A. V.

    2017-05-01

    Our Sun became Main Sequence star 4.6 Gyr ago according Standard Solar Model. At that time solar luminosity was 30% lower than current value. This conclusion is based on assumption that Sun is fueled by thermonuclear reactions. If Earth's albedo and emissivity in infrared are unchanged during Earth history, 2.3 Gyr ago oceans had to be frozen. This contradicts to geological data: there was liquid water 3.6-3.8 Gyr ago on Earth. This problem is known as Faint Young Sun Paradox. We analyze luminosity change in standard solar evolution theory. Increase of mean molecular weight in the central part of the Sun due to conversion of hydrogen to helium leads to gradual increase of luminosity with time on the Main Sequence. We also consider several exotic models: fully mixed Sun; drastic change of pp reaction rate; Sun consisting of hydrogen and helium only. Solar neutrino observations however exclude most non-standard solar models.

  19. HABITABLE ZONES OF POST-MAIN SEQUENCE STARS

    International Nuclear Information System (INIS)

    Ramirez, Ramses M.; Kaltenegger, Lisa

    2016-01-01

    Once a star leaves the main sequence and becomes a red giant, its Habitable Zone (HZ) moves outward, promoting detectable habitable conditions at larger orbital distances. We use a one-dimensional radiative-convective climate and stellar evolutionary models to calculate post-MS HZ distances for a grid of stars from 3700 to 10,000 K (∼M1 to A5 stellar types) for different stellar metallicities. The post-MS HZ limits are comparable to the distances of known directly imaged planets. We model the stellar as well as planetary atmospheric mass loss during the Red Giant Branch (RGB) and Asymptotic Giant Branch (AGB) phases for super-Moons to super-Earths. A planet can stay between 200 million years up to 9 Gyr in the post-MS HZ for our hottest and coldest grid stars, respectively, assuming solar metallicity. These numbers increase for increased stellar metallicity. Total atmospheric erosion only occurs for planets in close-in orbits. The post-MS HZ orbital distances are within detection capabilities of direct imaging techniques.

  20. HABITABLE ZONES OF POST-MAIN SEQUENCE STARS

    Energy Technology Data Exchange (ETDEWEB)

    Ramirez, Ramses M.; Kaltenegger, Lisa [Carl Sagan Institute, Cornell University, Ithaca, NY (United States)

    2016-05-20

    Once a star leaves the main sequence and becomes a red giant, its Habitable Zone (HZ) moves outward, promoting detectable habitable conditions at larger orbital distances. We use a one-dimensional radiative-convective climate and stellar evolutionary models to calculate post-MS HZ distances for a grid of stars from 3700 to 10,000 K (∼M1 to A5 stellar types) for different stellar metallicities. The post-MS HZ limits are comparable to the distances of known directly imaged planets. We model the stellar as well as planetary atmospheric mass loss during the Red Giant Branch (RGB) and Asymptotic Giant Branch (AGB) phases for super-Moons to super-Earths. A planet can stay between 200 million years up to 9 Gyr in the post-MS HZ for our hottest and coldest grid stars, respectively, assuming solar metallicity. These numbers increase for increased stellar metallicity. Total atmospheric erosion only occurs for planets in close-in orbits. The post-MS HZ orbital distances are within detection capabilities of direct imaging techniques.

  1. The SAMI Galaxy Survey: spatially resolving the main sequence of star formation

    Science.gov (United States)

    Medling, Anne M.; Cortese, Luca; Croom, Scott M.; Green, Andrew W.; Groves, Brent; Hampton, Elise; Ho, I.-Ting; Davies, Luke J. M.; Kewley, Lisa J.; Moffett, Amanda J.; Schaefer, Adam L.; Taylor, Edward; Zafar, Tayyaba; Bekki, Kenji; Bland-Hawthorn, Joss; Bloom, Jessica V.; Brough, Sarah; Bryant, Julia J.; Catinella, Barbara; Cecil, Gerald; Colless, Matthew; Couch, Warrick J.; Drinkwater, Michael J.; Driver, Simon P.; Federrath, Christoph; Foster, Caroline; Goldstein, Gregory; Goodwin, Michael; Hopkins, Andrew; Lawrence, J. S.; Leslie, Sarah K.; Lewis, Geraint F.; Lorente, Nuria P. F.; Owers, Matt S.; McDermid, Richard; Richards, Samuel N.; Sharp, Robert; Scott, Nicholas; Sweet, Sarah M.; Taranu, Dan S.; Tescari, Edoardo; Tonini, Chiara; van de Sande, Jesse; Walcher, C. Jakob; Wright, Angus

    2018-04-01

    We present the ˜800 star formation rate maps for the Sydney-AAO Multi-object Integral field spectrograph (SAMI) Galaxy Survey based on H α emission maps, corrected for dust attenuation via the Balmer decrement, that are included in the SAMI Public Data Release 1. We mask out spaxels contaminated by non-stellar emission using the [O III]/H β, [N II]/H α, [S II]/H α, and [O I]/H α line ratios. Using these maps, we examine the global and resolved star-forming main sequences of SAMI galaxies as a function of morphology, environmental density, and stellar mass. Galaxies further below the star-forming main sequence are more likely to have flatter star formation profiles. Early-type galaxies split into two populations with similar stellar masses and central stellar mass surface densities. The main-sequence population has centrally concentrated star formation similar to late-type galaxies, while galaxies >3σ below the main sequence show significantly reduced star formation most strikingly in the nuclear regions. The split populations support a two-step quenching mechanism, wherein halo mass first cuts off the gas supply and remaining gas continues to form stars until the local stellar mass surface density can stabilize the reduced remaining fuel against further star formation. Across all morphologies, galaxies in denser environments show a decreased specific star formation rate from the outside in, supporting an environmental cause for quenching, such as ram-pressure stripping or galaxy interactions.

  2. Photometric monitoring of pre-main sequence stars - 2

    International Nuclear Information System (INIS)

    Evans, A.; Davies, J.K.; Kilkenny, D.; Bode, M.F.

    1989-01-01

    A discussion is presented of the infrared and optical photometric variability of the pre-main sequence stars BF Ori and UX Ori. In the former case, the reddening that occurs during decline, at both optical and infrared wavelengths, is consistent with variable extinction by circumstellar grains having an interstellar-like reddening law. While in the case of UX Ori, the data suggest variability due to starspots. In both cases, a study of the polarimetric variability would be valuable to confirm these conclusions. (author)

  3. Discovery of three x-ray luminous pre-main-sequence stars

    International Nuclear Information System (INIS)

    Feigelson, E.D.; Kriss, G.A.

    1981-01-01

    Three X-ray sources found serendipitously in Einstein images of the Taurus-Auriga cloud complex were observed at the McGraw-Hill Observatory and are found to be associated with approx.12 mag stars with weak Hα emission. The stars lie on the edges of dark clouds and are spectroscopically similar to the least active emission-line pre-main-sequence stars. Although they lie well above the ZAMS in the H-R diagram, they do not exhibit ultraviolet excess, strong optical variability, or evidence for mass outflow/inflow characteristics of the more active T Tauri stars. Their only unusual property is high X-ray luminosity (approx.10 30 ergs s1). It is suggested that the X-ray emission from pre-main-sequence stars is not closely linked to the conditions giving rise to their unusual spectroscopic properties. The emission may instead represent an enhanced form of the coronal activity producing X-rays observed in late-type main-sequence stars

  4. The evolution of surface magnetic fields in young solar-type stars II: the early main sequence (250-650 Myr)

    Science.gov (United States)

    Folsom, C. P.; Bouvier, J.; Petit, P.; Lèbre, A.; Amard, L.; Palacios, A.; Morin, J.; Donati, J.-F.; Vidotto, A. A.

    2018-03-01

    There is a large change in surface rotation rates of sun-like stars on the pre-main sequence and early main sequence. Since these stars have dynamo-driven magnetic fields, this implies a strong evolution of their magnetic properties over this time period. The spin-down of these stars is controlled by interactions between stellar and magnetic fields, thus magnetic evolution in turn plays an important role in rotational evolution. We present here the second part of a study investigating the evolution of large-scale surface magnetic fields in this critical time period. We observed stars in open clusters and stellar associations with known ages between 120 and 650 Myr, and used spectropolarimetry and Zeeman Doppler Imaging to characterize their large-scale magnetic field strength and geometry. We report 15 stars with magnetic detections here. These stars have masses from 0.8 to 0.95 M⊙, rotation periods from 0.326 to 10.6 d, and we find large-scale magnetic field strengths from 8.5 to 195 G with a wide range of geometries. We find a clear trend towards decreasing magnetic field strength with age, and a power law decrease in magnetic field strength with Rossby number. There is some tentative evidence for saturation of the large-scale magnetic field strength at Rossby numbers below 0.1, although the saturation point is not yet well defined. Comparing to younger classical T Tauri stars, we support the hypothesis that differences in internal structure produce large differences in observed magnetic fields, however for weak-lined T Tauri stars this is less clear.

  5. A near-infrared survey for pre-main sequence stars in Taurus

    Science.gov (United States)

    Gomez, Mercedes; Kenyon, Scott J.; Hartmann, Lee

    1994-01-01

    We present a near-infrared survey of approximately 2 sq deg covering parts of L1537, L1538, and Heiles cloud 2 in the Taurus-Auriga molecular cloud. Although this study is more sensitive than previous attempts to identify pre-main sequence stars in Taurus-Auriga, our survey regions contain only one new optically visible, young star. We did find several candidate embedded protostars; additional 10 micrometer photometry is necessary to verify the pre-main sequence nature of these sources. Our results--combined with those of previous surveys--show that the L1537/L1538 clouds contain no pre-main sequence stars. These two clouds are less dense than the active star formation sites in Taurus-Auriga, which suggests a cloud must achieve a threshold density to form stars.

  6. The Star-forming Main Sequence of Dwarf Low Surface Brightness Galaxies

    Science.gov (United States)

    McGaugh, Stacy S.; Schombert, James M.; Lelli, Federico

    2017-12-01

    We explore the star-forming properties of late-type, low surface brightness (LSB) galaxies. The star-forming main sequence ({SFR}-{M}* ) of LSB dwarfs has a steep slope, indistinguishable from unity (1.04 ± 0.06). They form a distinct sequence from more massive spirals, which exhibit a shallower slope. The break occurs around {M}* ≈ {10}10 {M}⊙ , and can also be seen in the gas mass—stellar mass plane. The global Kennicutt-Schmidt law ({SFR}-{M}g) has a slope of 1.47 ± 0.11 without the break seen in the main sequence. There is an ample supply of gas in LSB galaxies, which have gas depletion times well in excess of a Hubble time, and often tens of Hubble times. Only ˜ 3 % of this cold gas needs be in the form of molecular gas to sustain the observed star formation. In analogy with the faint, long-lived stars of the lower stellar main sequence, it may be appropriate to consider the main sequence of star-forming galaxies to be defined by thriving dwarfs (with {M}* {10}10 {M}⊙ ) are weary giants that constitute more of a turn-off population.

  7. Calculating Asteroseismic Diagrams for Solar-Like Oscillations

    DEFF Research Database (Denmark)

    White, T.R.; Bedding, T.R.; Stello, D.

    2011-01-01

    With the success of the Kepler and CoRoT missions, the number of stars with detected solar-like oscillations has increased by several orders of magnitude; for the first time we are able to perform large-scale ensemble asteroseismology of these stars. In preparation for this golden age of asterose......With the success of the Kepler and CoRoT missions, the number of stars with detected solar-like oscillations has increased by several orders of magnitude; for the first time we are able to perform large-scale ensemble asteroseismology of these stars. In preparation for this golden age...... of these stars. We investigate the scaling relation between the large frequency separation, Δν, and mean stellar density. Furthermore we present model evolutionary tracks for several asteroseismic diagrams. We have extended the so-called C-D diagram beyond the main sequence to the subgiants and the red giant...

  8. Oscillation mode frequencies of 61 main-sequence and subgiant stars observed by Kepler

    DEFF Research Database (Denmark)

    Appourchaux, T.; Chaplin, W. J.; García, R. A.

    2012-01-01

    Solar-like oscillations have been observed by Kepler and CoRoT in several solar-type stars, thereby providing a way to probe the stars using asteroseismology Aims. We provide the mode frequencies of the oscillations of various stars required to perform a comparison with those obtained from stella...

  9. MASS LOSS IN PRE-MAIN-SEQUENCE STARS VIA CORONAL MASS EJECTIONS AND IMPLICATIONS FOR ANGULAR MOMENTUM LOSS

    Energy Technology Data Exchange (ETDEWEB)

    Aarnio, Alicia N. [Astronomy Department, University of Michigan, 830 Dennison Building, 500 Church Street, Ann Arbor, MI 48109 (United States); Matt, Sean P. [Laboratoire AIM Paris-Saclay, CEA/Irfu Universite Paris-Diderot CNRS/INSU, F-91191 Gif-sur-Yvette (France); Stassun, Keivan G., E-mail: aarnio@umich.edu [Department of Physics and Astronomy, Vanderbilt University, Nashville, TN 37235 (United States)

    2012-11-20

    We develop an empirical model to estimate mass-loss rates via coronal mass ejections (CMEs) for solar-type pre-main-sequence (PMS) stars. Our method estimates the CME mass-loss rate from the observed energies of PMS X-ray flares, using our empirically determined relationship between solar X-ray flare energy and CME mass: log (M {sub CME}[g]) = 0.63 Multiplication-Sign log (E {sub flare}[erg]) - 2.57. Using masses determined for the largest flaring magnetic structures observed on PMS stars, we suggest that this solar-calibrated relationship may hold over 10 orders of magnitude in flare energy and 7 orders of magnitude in CME mass. The total CME mass-loss rate we calculate for typical solar-type PMS stars is in the range 10{sup -12}-10{sup -9} M {sub Sun} yr{sup -1}. We then use these CME mass-loss rate estimates to infer the attendant angular momentum loss leading up to the main sequence. Assuming that the CME outflow rate for a typical {approx}1 M {sub Sun} T Tauri star is <10{sup -10} M {sub Sun} yr{sup -1}, the resulting spin-down torque is too small during the first {approx}1 Myr to counteract the stellar spin-up due to contraction and accretion. However, if the CME mass-loss rate is {approx}> 10{sup -10} M {sub Sun} yr{sup -1}, as permitted by our calculations, then the CME spin-down torque may influence the stellar spin evolution after an age of a few Myr.

  10. Metallicity and ultraviolet excesses of late main sequence stars

    International Nuclear Information System (INIS)

    Suchkov, A.A.; Marsakov, V.A.; Shevelev, Yu.G.

    1987-01-01

    The comparison of the characteristics of ultraviolet (UV) excesses δ(U-B) and metallicity [Fe/H] distributions of F, G, and K dwarfs reveals a number of discrepancies. It is shown that they can be eliminated if we assume that UV excesses of K and late G dwarfs, and [Fe/H] values from detailed analysis for F dwarfs are underestimated. Such an assumption enables to account for low values of for F, K and late G dwarfs, and for the difference of the free terms in the metallicity - UV-excess relation for these stars as compared to early G dwarfs. In this case the F5-F9 dwarfs turn out to be more metal-rich (by 0.1 in [Fe/H]) than G and K dwarfs, and the metallicity of the Hyades cluster turns out to be larger than the solar one, [Fe/H] Hyades =+0.1. The ''conditional'' metallicity - UV-excess calibrations are obtained for four groups of main-sequence stars: F5-F9, G0-G4, G5-G9, K0-K5

  11. Reconciling mass functions with the star-forming main sequence via mergers

    Science.gov (United States)

    Steinhardt, Charles L.; Yurk, Dominic; Capak, Peter

    2017-06-01

    We combine star formation along the 'main sequence', quiescence and clustering and merging to produce an empirical model for the evolution of individual galaxies. Main-sequence star formation alone would significantly steepen the stellar mass function towards low redshift, in sharp conflict with observation. However, a combination of star formation and merging produces a consistent result for correct choice of the merger rate function. As a result, we are motivated to propose a model in which hierarchical merging is disconnected from environmentally independent star formation. This model can be tested via correlation functions and would produce new constraints on clustering and merging.

  12. THE ORIGIN OF HVS17, AN UNBOUND MAIN SEQUENCE B STAR AT 50 kpc

    Energy Technology Data Exchange (ETDEWEB)

    Brown, Warren R.; Geller, Margaret J.; Kenyon, Scott J. [Smithsonian Astrophysical Observatory, 60 Garden Street, Cambridge, MA 02138 (United States); Cohen, Judith G., E-mail: wbrown@cfa.harvard.edu, E-mail: mgeller@cfa.harvard.edu, E-mail: skenyon@cfa.harvard.edu, E-mail: jlc@astro.caltech.edu [Palomar Observatory, Mail Stop 249-17, California Institute of Technology, Pasadena, CA 91125 (United States)

    2013-09-20

    We analyze Keck Echellette Spectrograph and Imager spectroscopy of HVS17, a B-type star traveling with a Galactic rest frame radial velocity of +445 km s{sup –1} in the outer halo of the Milky Way. HVS17 has the projected rotation of a main sequence B star and is chemically peculiar, with solar iron abundance and sub-solar alpha abundance. Comparing measured T{sub eff} and log g with stellar evolution tracks implies that HVS17 is a 3.91 ± 0.09 M{sub ☉}, 153 ± 9 Myr old star at a Galactocentric distance of r = 48.5 ± 4.6 kpc. The time between its formation and ejection significantly exceeds 10 Myr and thus is difficult to reconcile with any Galactic disk runaway scenario involving massive stars. The observations are consistent, on the other hand, with a hypervelocity star ejection from the Galactic center. We show that Gaia proper motion measurements will easily discriminate between a disk and Galactic center origin, thus allowing us to use HVS17 as a test particle to probe the shape of the Milky Way's dark matter halo.

  13. THE ORIGIN OF HVS17, AN UNBOUND MAIN SEQUENCE B STAR AT 50 kpc

    International Nuclear Information System (INIS)

    Brown, Warren R.; Geller, Margaret J.; Kenyon, Scott J.; Cohen, Judith G.

    2013-01-01

    We analyze Keck Echellette Spectrograph and Imager spectroscopy of HVS17, a B-type star traveling with a Galactic rest frame radial velocity of +445 km s –1 in the outer halo of the Milky Way. HVS17 has the projected rotation of a main sequence B star and is chemically peculiar, with solar iron abundance and sub-solar alpha abundance. Comparing measured T eff and log g with stellar evolution tracks implies that HVS17 is a 3.91 ± 0.09 M ☉ , 153 ± 9 Myr old star at a Galactocentric distance of r = 48.5 ± 4.6 kpc. The time between its formation and ejection significantly exceeds 10 Myr and thus is difficult to reconcile with any Galactic disk runaway scenario involving massive stars. The observations are consistent, on the other hand, with a hypervelocity star ejection from the Galactic center. We show that Gaia proper motion measurements will easily discriminate between a disk and Galactic center origin, thus allowing us to use HVS17 as a test particle to probe the shape of the Milky Way's dark matter halo

  14. The sun as a star: Solar phenomena and stellar applications

    International Nuclear Information System (INIS)

    Noyes, R.W.

    1981-01-01

    Our Sun is a run-of-the-mill star, having no obvious extremes of stellar properties. For this reason it is perhaps more, rather than less, interesting as an astrophysical object, for its sameness to other stars suggests that in studying the Sun, we are studying at close hand common, rather than unusual stellar phenomena. Conversely, comparative study of the Sun and other solar-type stars is an invaluable tool for solar physics, for two reasons: First, it allows us to explore how solar properties and phenomena depend on parameters we cannot vary on the Sun - most fundamentally, rotation rate and mass. Second, study of solar-like stars of different ages allows us to see how stellar and solar phenomena depend on age; study of other stars may be one of the best ways to infer the earlier history of the Sun, as well as its future history. In this review we shall concentrate on phenomena common to the Sun and solar-type (main sequence) stars with different fundamental properties such as mass, age, and rotation. (orig.)

  15. Hubble Tarantula Treasury Project - VI. Identification of Pre-Main-Sequence Stars using Machine Learning techniques

    Science.gov (United States)

    Ksoll, Victor F.; Gouliermis, Dimitrios A.; Klessen, Ralf S.; Grebel, Eva K.; Sabbi, Elena; Anderson, Jay; Lennon, Daniel J.; Cignoni, Michele; de Marchi, Guido; Smith, Linda J.; Tosi, Monica; van der Marel, Roeland P.

    2018-05-01

    The Hubble Tarantula Treasury Project (HTTP) has provided an unprecedented photometric coverage of the entire star-burst region of 30 Doradus down to the half Solar mass limit. We use the deep stellar catalogue of HTTP to identify all the pre-main-sequence (PMS) stars of the region, i.e., stars that have not started their lives on the main-sequence yet. The photometric distinction of these stars from the more evolved populations is not a trivial task due to several factors that alter their colour-magnitude diagram positions. The identification of PMS stars requires, thus, sophisticated statistical methods. We employ Machine Learning Classification techniques on the HTTP survey of more than 800,000 sources to identify the PMS stellar content of the observed field. Our methodology consists of 1) carefully selecting the most probable low-mass PMS stellar population of the star-forming cluster NGC2070, 2) using this sample to train classification algorithms to build a predictive model for PMS stars, and 3) applying this model in order to identify the most probable PMS content across the entire Tarantula Nebula. We employ Decision Tree, Random Forest and Support Vector Machine classifiers to categorise the stars as PMS and Non-PMS. The Random Forest and Support Vector Machine provided the most accurate models, predicting about 20,000 sources with a candidateship probability higher than 50 percent, and almost 10,000 PMS candidates with a probability higher than 95 percent. This is the richest and most accurate photometric catalogue of extragalactic PMS candidates across the extent of a whole star-forming complex.

  16. Rotation in moderate-mass pre-main-sequence radiative track G stars

    International Nuclear Information System (INIS)

    Mcnamara, B.

    1990-01-01

    Recent studies suggest that the observed high-mass radiative track velocity histograms for pre-main-sequence stars differ significantly. In the Vogel and Kuhi (1981) study, these stars were found to possess a rather broad distribution of rotational velocities with a moderate peak at low velocities. In contrast, Smith et al. (1983), found a very sharply peaked distribution located at low values of v sin i. The difference in these velocity distributions is shown to be due to inadequate allowance for field stars in the Smith, et al., work. Once these stars are removed, the high-mass velocity distributions of the two regions are remarkably similar. This result suggests that a unique velocity distribution might be used in modeling very young stars. Assuming that the Orion Ic proto-F stars continue to contract in a homologous fashion, their average current rotational velocity is in agreement with that expected for zero-age main sequence F stars. 27 refs

  17. Tracing early stellar evolution with asteroseismology: pre-main sequence stars in NGC 2264

    Directory of Open Access Journals (Sweden)

    Zwintz Konstanze

    2015-01-01

    Full Text Available Asteroseismology has been proven to be a successful tool to unravel details of the internal structure for different types of stars in various stages of their main sequence and post-main sequence evolution. Recently, we found a relation between the detected pulsation properties in a sample of 34 pre-main sequence (pre-MS δ Scuti stars and the relative phase in their pre-MS evolution. With this we are able to demonstrate that asteroseismology is similarly powerful if applied to stars in the earliest stages of evolution before the onset of hydrogen core burning.

  18. Effects of mass loss on the evolution of massive stars. I. Main-sequence evolution

    International Nuclear Information System (INIS)

    Dearborn, D.S.P.; Blake, J.B.; Hainebach, K.L.; Schramm, D.N.

    1978-01-01

    The effect of mass loss on the evolution and surface composition of massive stars during main-sequence evolution are examined. While some details of the evolutionary track depend on the formula used for the mass loss, the results appear most sensitive to the total mass removed during the main-sequence lifetime. It was found that low mass-loss rates have very little effect on the evolution of a star; the track is slightly subluminous, but the lifetime is almost unaffected. High rates of mass loss lead to a hot, high-luminosity stellar model with a helium core surrounded by a hydrogen-deficient (Xapprox.0.1) envelope. The main-sequence lifetime is extended by a factor of 2--3. These models may be identified with Wolf-Rayet stars. Between these mass-loss extremes are intermediate models which appear as OBN stars on the main sequence. The mass-loss rates required for significant observable effects range from 8 x 10 -7 to 10 -5 M/sub sun/ yr -1 , depending on the initial stellar mass. It is found that observationally consistent mass-loss rates for stars with M> or =30 M/sub sun/ may be sufficiently high that these stars lose mass on a time scale more rapidly than their main-sequence core evolution time. This result implies that the helium cores resulting from the main-sequence evolution of these massive stars may all be very similar to that of a star of Mapprox.30 M/sub sun/ regardless of the zero-age mass

  19. AN M DWARF COMPANION TO AN F-TYPE STAR IN A YOUNG MAIN-SEQUENCE BINARY

    Energy Technology Data Exchange (ETDEWEB)

    Eigmüller, Ph.; Csizmadia, Sz.; Erikson, A.; Fridlund, M.; Pasternacki, Th.; Rauer, H. [Institute of Planetary Research, German Aerospace Center Rutherfordstr. 2, D-12489 Berlin (Germany); Eislöffel, J.; Lehmann, H.; Hartmann, M.; Hatzes, A. [Thüringer Landessternwarte Tautenburg Sternwarte 5, D-07778 Tautenburg (Germany); Tkachenko, A. [Instituut voor Sterrenkunde, KU Leuven Celestijnenlaan 200D, 3001 Leuven (Belgium); Voss, H., E-mail: philipp.eigmueller@dlr.de [Universitat de Barcelona, Department of Astronomy and Meteorology Martí i Franquès, 1, E-08028 Barcelona (Spain)

    2016-03-15

    Only a few well characterized very low-mass M dwarfs are known today. Our understanding of M dwarfs is vital as these are the most common stars in our solar neighborhood. We aim to characterize the properties of a rare F+dM stellar system for a better understanding of the low-mass end of the Hertzsprung–Russel diagram. We used photometric light curves and radial velocity follow-up measurements to study the binary. Spectroscopic analysis was used in combination with isochrone fitting to characterize the primary star. The primary star is an early F-type main-sequence star with a mass of (1.493 ± 0.073) M{sub ⊙} and a radius of (1.474 ± 0.040) R{sub ⊙}. The companion is an M dwarf with a mass of (0.188 ± 0.014) M{sub ⊙} and a radius of (0.234 ± 0.009) R{sub ⊙}. The orbital period is (1.35121 ± 0.00001) days. The secondary star is among the lowest-mass M dwarfs known to date. The binary has not reached a 1:1 spin–orbit synchronization. This indicates a young main-sequence binary with an age below ∼250 Myr. The mass–radius relation of both components are in agreement with this finding.

  20. Radio emission from pre-main-sequence stars in Corona Australis

    International Nuclear Information System (INIS)

    Brown, A.

    1987-01-01

    The central region of the Corona Australis molecular cloud surrounding the stars R and TY CrA has been studied using the VLA at 6 cm. Eleven radio sources are detected including five associated with pre-main-sequence objects. The most striking is associated with the near-IR source IRS 7 and shows a complex structure comprising two strong pointlike sources positioned either side of the deeply embedded IR source and two extended lobes of radio emission. The IRS 7 radio source appears to be similar to that associated with Lynds 1551 IRS 5 but has a considerably larger angular size. The other detected sources include the massive pre-main-sequence star TY CrA, the near-IR sources IRS 1 and IRS 5, and the Herbig-Haro object HH 101. The stars R and T CrA were not detected. 35 references

  1. 13-colour photometry of pre-main sequence stars: preliminary report and results

    Energy Technology Data Exchange (ETDEWEB)

    Chavarria-K, C; de Lara, E [Universidad Nacional Autonoma de Mexico, Mexico City. Inst. de Astronomia

    1981-01-01

    Broad (UBVRI) and intermediate (13-colour) band photometry of 160 stars selected mainly from the Herbig Rao catalogue are being carried on currently, mainly to complement the published data of these stars in the optical window (for example shortward of the Balmer and longward of the Paschen discontinuities). The 13-colour photometric system and its applications to pre-main sequences stars are briefly discussed. First results are presented.

  2. Lithium Depletion in Solar-like Stars: Effect of Overshooting Based on Realistic Multi-dimensional Simulations

    Science.gov (United States)

    Baraffe, I.; Pratt, J.; Goffrey, T.; Constantino, T.; Folini, D.; Popov, M. V.; Walder, R.; Viallet, M.

    2017-08-01

    We study lithium depletion in low-mass and solar-like stars as a function of time, using a new diffusion coefficient describing extra-mixing taking place at the bottom of a convective envelope. This new form is motivated by multi-dimensional fully compressible, time-implicit hydrodynamic simulations performed with the MUSIC code. Intermittent convective mixing at the convective boundary in a star can be modeled using extreme value theory, a statistical analysis frequently used for finance, meteorology, and environmental science. In this Letter, we implement this statistical diffusion coefficient in a one-dimensional stellar evolution code, using parameters calibrated from multi-dimensional hydrodynamic simulations of a young low-mass star. We propose a new scenario that can explain observations of the surface abundance of lithium in the Sun and in clusters covering a wide range of ages, from ˜50 Myr to ˜4 Gyr. Because it relies on our physical model of convective penetration, this scenario has a limited number of assumptions. It can explain the observed trend between rotation and depletion, based on a single additional assumption, namely, that rotation affects the mixing efficiency at the convective boundary. We suggest the existence of a threshold in stellar rotation rate above which rotation strongly prevents the vertical penetration of plumes and below which rotation has small effects. In addition to providing a possible explanation for the long-standing problem of lithium depletion in pre-main-sequence and main-sequence stars, the strength of our scenario is that its basic assumptions can be tested by future hydrodynamic simulations.

  3. Lithium Depletion in Solar-like Stars: Effect of Overshooting Based on Realistic Multi-dimensional Simulations

    International Nuclear Information System (INIS)

    Baraffe, I.; Pratt, J.; Goffrey, T.; Constantino, T.; Viallet, M.; Folini, D.; Popov, M. V.; Walder, R.

    2017-01-01

    We study lithium depletion in low-mass and solar-like stars as a function of time, using a new diffusion coefficient describing extra-mixing taking place at the bottom of a convective envelope. This new form is motivated by multi-dimensional fully compressible, time-implicit hydrodynamic simulations performed with the MUSIC code. Intermittent convective mixing at the convective boundary in a star can be modeled using extreme value theory, a statistical analysis frequently used for finance, meteorology, and environmental science. In this Letter, we implement this statistical diffusion coefficient in a one-dimensional stellar evolution code, using parameters calibrated from multi-dimensional hydrodynamic simulations of a young low-mass star. We propose a new scenario that can explain observations of the surface abundance of lithium in the Sun and in clusters covering a wide range of ages, from ∼50 Myr to ∼4 Gyr. Because it relies on our physical model of convective penetration, this scenario has a limited number of assumptions. It can explain the observed trend between rotation and depletion, based on a single additional assumption, namely, that rotation affects the mixing efficiency at the convective boundary. We suggest the existence of a threshold in stellar rotation rate above which rotation strongly prevents the vertical penetration of plumes and below which rotation has small effects. In addition to providing a possible explanation for the long-standing problem of lithium depletion in pre-main-sequence and main-sequence stars, the strength of our scenario is that its basic assumptions can be tested by future hydrodynamic simulations.

  4. Lithium Depletion in Solar-like Stars: Effect of Overshooting Based on Realistic Multi-dimensional Simulations

    Energy Technology Data Exchange (ETDEWEB)

    Baraffe, I.; Pratt, J.; Goffrey, T.; Constantino, T.; Viallet, M. [Astrophysics Group, University of Exeter, Exeter EX4 4QL (United Kingdom); Folini, D.; Popov, M. V.; Walder, R., E-mail: i.baraffe@ex.ac.uk [Ecole Normale Supérieure de Lyon, CRAL, UMR CNRS 5574, F-69364 Lyon Cedex 07 (France)

    2017-08-10

    We study lithium depletion in low-mass and solar-like stars as a function of time, using a new diffusion coefficient describing extra-mixing taking place at the bottom of a convective envelope. This new form is motivated by multi-dimensional fully compressible, time-implicit hydrodynamic simulations performed with the MUSIC code. Intermittent convective mixing at the convective boundary in a star can be modeled using extreme value theory, a statistical analysis frequently used for finance, meteorology, and environmental science. In this Letter, we implement this statistical diffusion coefficient in a one-dimensional stellar evolution code, using parameters calibrated from multi-dimensional hydrodynamic simulations of a young low-mass star. We propose a new scenario that can explain observations of the surface abundance of lithium in the Sun and in clusters covering a wide range of ages, from ∼50 Myr to ∼4 Gyr. Because it relies on our physical model of convective penetration, this scenario has a limited number of assumptions. It can explain the observed trend between rotation and depletion, based on a single additional assumption, namely, that rotation affects the mixing efficiency at the convective boundary. We suggest the existence of a threshold in stellar rotation rate above which rotation strongly prevents the vertical penetration of plumes and below which rotation has small effects. In addition to providing a possible explanation for the long-standing problem of lithium depletion in pre-main-sequence and main-sequence stars, the strength of our scenario is that its basic assumptions can be tested by future hydrodynamic simulations.

  5. Lithium abundances and metallicities in stars near the main-sequence turnoff and a giant in M67

    International Nuclear Information System (INIS)

    Garcia Lopez, R.J.; Rebolo, R.; Beckman, J.E.

    1988-01-01

    The iron abundance of seven stars near the main-sequence (MS) turnoff and a giant in M67 are spectroscopically derived, and the results are discussed. The resulting mean iron abundance of the turnoff stars is (Fe/H) = 0.04 + or - 0.04. Taken together with previous determinations for younger clusters, this shows that there has been relatively little change of the iron abundance in the solar neighborhood during the last 5 Gyr. Lithium was detected in one unevolved star and marginally in the giant, while in the other MS stars only upper limits were found. The considerable differences in Li abundances for stars with similar surface temperature imply that there is at least one parameter affecting Li depletion apart from stellar mass and metallicity. Nonsimultaneous star formation in the cluster cloud explain the scatter in lithium abundances. 50 references

  6. SDSS-IV MaNGA: Spatially Resolved Star Formation Main Sequence and LI(N)ER Sequence

    Science.gov (United States)

    Hsieh, B. C.; Lin, Lihwai; Lin, J. H.; Pan, H. A.; Hsu, C. H.; Sánchez, S. F.; Cano-Díaz, M.; Zhang, K.; Yan, R.; Barrera-Ballesteros, J. K.; Boquien, M.; Riffel, R.; Brownstein, J.; Cruz-González, I.; Hagen, A.; Ibarra, H.; Pan, K.; Bizyaev, D.; Oravetz, D.; Simmons, A.

    2017-12-01

    We present our study on the spatially resolved Hα and M * relation for 536 star-forming and 424 quiescent galaxies taken from the MaNGA survey. We show that the star formation rate surface density ({{{Σ }}}{SFR}), derived based on the Hα emissions, is strongly correlated with the M * surface density ({{{Σ }}}* ) on kiloparsec scales for star-forming galaxies and can be directly connected to the global star-forming sequence. This suggests that the global main sequence may be a consequence of a more fundamental relation on small scales. On the other hand, our result suggests that ∼20% of quiescent galaxies in our sample still have star formation activities in the outer region with lower specific star formation rate (SSFR) than typical star-forming galaxies. Meanwhile, we also find a tight correlation between {{{Σ }}}{{H}α } and {{{Σ }}}* for LI(N)ER regions, named the resolved “LI(N)ER” sequence, in quiescent galaxies, which is consistent with the scenario that LI(N)ER emissions are primarily powered by the hot, evolved stars as suggested in the literature.

  7. How Dusty Is Alpha Centauri? Excess or Non-excess over the Infrared Photospheres of Main-sequence Stars

    Science.gov (United States)

    Wiegert, J.; Liseau, R.; Thebault, P.; Olofsson, G.; Mora, A.; Bryden, G.; Marshall, J. P.; Eiroa, C.; Montesinos, B.; Ardila, D.; hide

    2014-01-01

    Context. Debris discs around main-sequence stars indicate the presence of larger rocky bodies. The components of the nearby, solar-type binary Centauri have metallicities that are higher than solar, which is thought to promote giant planet formation. Aims. We aim to determine the level of emission from debris around the stars in the Cen system. This requires knowledge of their photospheres.Having already detected the temperature minimum, Tmin, of CenA at far-infrared wavelengths, we here attempt to do the same for the moreactive companion Cen B. Using the Cen stars as templates, we study the possible eects that Tmin may have on the detectability of unresolveddust discs around other stars. Methods.We used Herschel-PACS, Herschel-SPIRE, and APEX-LABOCA photometry to determine the stellar spectral energy distributions in thefar infrared and submillimetre. In addition, we used APEX-SHeFI observations for spectral line mapping to study the complex background around Cen seen in the photometric images. Models of stellar atmospheres and of particulate discs, based on particle simulations and in conjunctionwith radiative transfer calculations, were used to estimate the amount of debris around these stars. Results. For solar-type stars more distant than Cen, a fractional dust luminosity fd LdustLstar 2 107 could account for SEDs that do not exhibit the Tmin eect. This is comparable to estimates of fd for the Edgeworth-Kuiper belt of the solar system. In contrast to the far infrared,slight excesses at the 2:5 level are observed at 24 m for both CenA and B, which, if interpreted as due to zodiacal-type dust emission, wouldcorrespond to fd (13) 105, i.e. some 102 times that of the local zodiacal cloud. Assuming simple power-law size distributions of the dustgrains, dynamical disc modelling leads to rough mass estimates of the putative Zodi belts around the Cen stars, viz.4106 M$ of 4 to 1000 msize grains, distributed according to n(a) a3:5. Similarly, for filled-in Tmin

  8. Seismology of rapidly rotating and solar-like stars

    Science.gov (United States)

    Reese, Daniel Roy

    2018-05-01

    A great deal of progress has been made in stellar physics thanks to asteroseismology, the study of pulsating stars. Indeed, asteroseismology is currently the only way to probe the internal structure of stars. The work presented here focuses on some of the theoretical aspects of this domain and addresses two broad categories of stars, namely solar-like pulsators (including red giants), and rapidly rotating pulsating stars. The work on solar-like pulsators focuses on setting up methods for efficiently characterising a large number of stars, in preparation for space missions like TESS and PLATO 2.0. In particular, the AIMS code applies an MCMC algorithm to find stellar properties and a sample of stellar models which fit a set of seismic and classic observational constraints. In order to reduce computation time, this code interpolates within a precalculated grid of models, using a Delaunay tessellation which allows a greater flexibility on the construction of the grid. Using interpolated models based on the outputs from this code or models from other forward modelling codes, it is possible to obtain refined estimates of various stellar properties such as the mean density thanks to inversion methods put together by me and G. Buldgen, my former PhD student. Finally, I show how inversion-type methods can also be used to test more qualitative information such as whether a decreasing rotation profile is compatible with a set of observed rotational splittings and a given reference model. In contrast to solar-like pulsators, the pulsation modes of rapidly rotating stars remain much more difficult to interpret due to the complexity of the numerical calculations needed to calculate such modes, the lack of simple frequency patterns, and the fact that it is difficult to predict mode amplitudes. The work described here therefore focuses on addressing the above difficulties one at a time in the hopes that it will one day be possible to carry out detailed asteroseismology in these

  9. Lithium abundances for 185 main-sequence stars: Galactic evolution and stellar depletion of lithium

    Science.gov (United States)

    Chen, Y. Q.; Nissen, P. E.; Benoni, T.; Zhao, G.

    2001-06-01

    We present a survey of lithium abundances in 185 main-sequence field stars with 5600 interesting result from this study is the presence of a large gap in the log varepsilon (Li) - Teff plane, which distinguishes ``Li-dip'' stars like those first identified in the Hyades cluster by Boesgaard & Tripicco (\\cite{Boesgaard86}) from other stars with a much higher Li abundance. The Li-dip stars concentrate on a certain mass, which decreases with metallicity from about 1.4 Msun at solar metallicity to 1.1 Msun at [Fe/H] =~ -1.0. Excluding the Li-dip stars and a small group of lower mass stars with Teff rate of angular momentum loss. It cannot be excluded, however, that a cosmic scatter of the Li abundance in the Galaxy at a given metallicity contributes to the dispersion in Li abundance. These problems make it difficult to determine the Galactic evolution of Li from the data, but a comparison of the upper envelope of the distribution of stars in the log varepsilon (Li) - [Fe/H] plane with recent Galactic evolutionary models by Romano et al. (\\cite{Romano99}) suggests that novae are a major source for the Li production in the Galactic disk; their occurrence seems to be the explanation for the steep increase of Li abundance at [Fe/H] =~ -0.4. Based on observations carried out at Beijing Astronomical Observatory (Xinglong, PR China) and European Southern Observatory, La Silla, Chile. Table 1 is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/371/943 and at http://www.edpsciences.org

  10. Fast Rotating solar-like stars using asteroseismic datasets

    DEFF Research Database (Denmark)

    A. García, R.; Ceillier, T.; Campante, T.

    2011-01-01

    The NASA Kepler mission is providing an unprecedented set of asteroseismic data. In particular, short-cadence lightcurves (~60s samplings), allow us to study solar-like stars covering a wide range of masses, spectral types and evolutionary stages. Oscillations have been observed in around 600 out...

  11. Magnetic inhibition of convection and the fundamental properties of low-mass stars. II. Fully convective main-sequence stars

    Energy Technology Data Exchange (ETDEWEB)

    Feiden, Gregory A. [Department of Physics and Astronomy, Uppsala University, Box 516, SE-751 20 Uppsala (Sweden); Chaboyer, Brian, E-mail: gregory.a.feiden@gmail.com, E-mail: brian.chaboyer@dartmouth.edu [Department of Physics and Astronomy, Dartmouth College, 6127 Wilder Laboratory, Hanover, NH 03755 (United States)

    2014-07-01

    We examine the hypothesis that magnetic fields are inflating the radii of fully convective main-sequence stars in detached eclipsing binaries (DEBs). The magnetic Dartmouth stellar evolution code is used to analyze two systems in particular: Kepler-16 and CM Draconis. Magneto-convection is treated assuming stabilization of convection and also by assuming reductions in convective efficiency due to a turbulent dynamo. We find that magnetic stellar models are unable to reproduce the properties of inflated fully convective main-sequence stars, unless strong interior magnetic fields in excess of 10 MG are present. Validation of the magnetic field hypothesis given the current generation of magnetic stellar evolution models therefore depends critically on whether the generation and maintenance of strong interior magnetic fields is physically possible. An examination of this requirement is provided. Additionally, an analysis of previous studies invoking the influence of star spots is presented to assess the suggestion that star spots are inflating stars and biasing light curve analyses toward larger radii. From our analysis, we find that there is not yet sufficient evidence to definitively support the hypothesis that magnetic fields are responsible for the observed inflation among fully convective main-sequence stars in DEBs.

  12. Characterizing Intermediate-Mass, Pre-Main-Sequence Stars via X-Ray Emision

    Science.gov (United States)

    Haze Nunez, Evan; Povich, Matthew Samuel; Binder, Breanna Arlene; Broos, Patrick; Townsley, Leisa K.

    2018-01-01

    The X-ray emission from intermediate-mass, pre-main-sequence stars (IMPS) can provide useful constraints on the ages of very young (${getting power from the gravitational contraction of the star. Main-sequence late-B and A-type stars are not expected to be strong X-ray emitters, because they lack the both strong winds of more massive stars and the magneto-coronal activity of lower-mass stars. There is, however, mounting evidence that IMPS are powerful intrinsic x-ray emitters during their convection-dominated early evolution, before the development and rapid growth of a radiation zone. We present our prime candidates for intrinsic, coronal X-ray emission from IMPS identified in the Chandra Carina Complex Project. The Carina massive star-forming complex is of special interest due to the wide variation of star formation stages within the region. Candidate IMPS were identified using infrared spectral energy distribution (SED) models. X-ray properties, including thermal plasma temperatures and absorption-corrected fluxes, were derived from XSPEC fits performed using absorption ($N_{H}$) constrained by the extinction values returned by the infrared SED fits. We find that IMPS have systematically higher X-ray luminosities compared to their lower-mass cousins, the TTauri stars.This work is supported by the National Science Foundation under grant CAREER-1454334 and by NASA through Chandra Award 18200040.

  13. On the mass-spectrum relation for the main sequence stars

    International Nuclear Information System (INIS)

    Svechnikov, M.A.; Tajdakova, T.A.

    1984-01-01

    From 240 main-sequence stars with well-determined masses, a new mass-spectrum relation is obtained, which differs appreciably in certain intervals of spectral types from the mass-spectrum relations of Allen and Trimble. The accuracy of mass determination for the components of eclipsing binary systems of different types from their spectra given in the General Catalogue of Variable Stars (3rd edition) and in its supplements is evaluated

  14. Possible evidence for metal accretion onto the surfaces of metal-poor main-sequence stars

    Energy Technology Data Exchange (ETDEWEB)

    Hattori, Kohei; Yoshii, Yuzuru [Institute of Astronomy, School of Science, University of Tokyo, 2-21-1 Osawa, Mitaka, Tokyo 181-0015 (Japan); Beers, Timothy C. [National Optical Astronomy Observatories, Tucson, AZ 85719 (United States); Carollo, Daniela [Department of Physics and Astronomy, Macquarie University, Sydney, 2109 NSW (Australia); Lee, Young Sun, E-mail: khattori@ioa.s.u-tokyo.ac.jp [Department of Astronomy, New Mexico State University, Las Cruces, NM 88003 (United States)

    2014-04-01

    The entire evolution of the Milky Way, including its mass-assembly and star-formation history, is imprinted onto the chemo-dynamical distribution function of its member stars, f(x, v, [X/H]), in the multi-dimensional phase space spanned by position, velocity, and elemental abundance ratios. In particular, the chemo-dynamical distribution functions for low-mass stars (e.g., G- or K-type dwarfs) are precious tracers of the earliest stages of the Milky Way's formation, since their main-sequence lifetimes approach or exceed the age of the universe. A basic tenet of essentially all previous analyses is that the stellar metallicity, usually parameterized as [Fe/H], is conserved over time for main-sequence stars (at least those that have not been polluted due to mass transfer from binary companions). If this holds true, any correlations between metallicity and kinematics for long-lived main-sequence stars of different masses, effective temperatures, or spectral types must strictly be the same, since they reflect the same mass-assembly and star-formation histories. By analyzing a sample of nearby metal-poor halo and thick-disk stars on the main sequence, taken from Data Release 8 of the Sloan Digital Sky Survey, we find that the median metallicity of G-type dwarfs is systematically higher (by about 0.2 dex) than that of K-type dwarfs having the same median rotational velocity about the Galactic center. If it can be confirmed, this finding may invalidate the long-accepted assumption that the atmospheric metallicities of long-lived stars are conserved over time.

  15. Effects of main-sequence mass loss on stellar and galactic chemical evolution

    International Nuclear Information System (INIS)

    Guzik, J.A.

    1988-01-01

    L.A. Willson, G.H. Bowen and C. Struck-Marcell have proposed that 1 to 3 solar mass stars may experience evolutionarily significant mass loss during the early part of their main-sequence phase. The suggested mass-loss mechanism is pulsation, facilitated by rapid rotation. Initial mass-loss rates may be as large as several times 10 -9 M mass of sun/yr, diminishing over several times 10 8 years. The author attempts to test this hypothesis by comparing some theoretical implications with observations. Three areas are addressed: Solar models, cluster HR diagrams, and galactic chemical evolution. Mass-losing solar models were evolved that match the Sun's luminosity and radius at its present age. The most extreme viable models have initial mass 2.0 M 0 , and mass-loss rates decreasing exponentially over 2-3 x 10 8 years. Evolution calculations incorporating main-sequence mass loss were completed for a grid of models with initial masses 1.25 to 2.0 M mass of sun and mass loss timescales 0.2 to 2.0 Gry. Cluster HR diagrams synthesized with these models confirm the potential for the hypothesis to explain observed spreads or bifurcations in the upper main sequence, blue stragglers, anomalous giants, and poor fits of main-sequence turnoffs by standard isochrones. Simple closed galactic chemical evolution models were used to test the effects of main-sequence mass loss on the F and G dwarf distribution. Stars between 3.0 M mass of sun and a metallicity-dependent lower mass are assumed to lose mass. The models produce a 30 to 60% increase in the stars to stars-plus-remnants ratio, with fewer early-F dwarfs and many more late-F dwarfs remaining on the main sequence to the present

  16. A Population Study of Wide-Separation Brown Dwarf Companions to Main Sequence Stars

    Science.gov (United States)

    Smith, Jeffrey J.

    2005-01-01

    Increased interest in infrared astronomy has opened the frontier to study cooler objects that shed significant light on the formation of planetary systems. Brown dwarf research provides a wealth of information useful for sorting through a myriad of proposed formation theories. Our study combines observational data from 2MASS with rigorous computer simulations to estimate the true population of long-range (greater than 1000 AU) brown dwarf companions in the solar neighborhood (less than 25 pc from Earth). Expanding on Gizis et al. (2001), we have found the margin of error in previous estimates to be significantly underestimated after we included orbit eccentricity, longitude of pericenter, angle of inclination, field star density, and primary and secondary luminosities as parameters influencing the companion systems in observational studies. We apply our simulation results to current L- and T-dwarf catalogs to provide updated estimates on the frequency of wide-separation brown dwarf companions to main sequence stars.

  17. Rotational studies of late-type stars. II. Ages of solar-type stars and the rotational history of the sun

    International Nuclear Information System (INIS)

    Soderblom, D.R.

    1983-01-01

    In the first part of this investigation, age indicators for solar-type stars are discussed. A Li abundance-age calibration is derived; it indicates that 1 M/sub sun/ stars have lost as much as 80% of their initial Li before reaching the main sequence. The e-folding time for Li depletion on the main sequence is 1 1/4 Gyr. The distribution of Li abundances for 1 M/sub sun/ stars is consistent with a uniform initial Li abundance for all stars

  18. Asteroseismic measurement of surface-to-core rotation in a main-sequence star*

    Directory of Open Access Journals (Sweden)

    Kurtz Donald W.

    2015-01-01

    Full Text Available We have discovered rotationally split core g-mode triplets and surface p-mode triplets and quintuplets in a terminal age main-sequence A star, KIC 11145123, that shows both δ Sct p-mode pulsations and γ Dor g-mode pulsations. This gives the first robust determination of the rotation of the deep core and surface of a main-sequence star, essentially model-independently. We find its rotation to be nearly uniform with a period near 100 d, but we show with high confidence that the surface rotates slightly faster than the core. A strong angular momentum transfer mechanism must be operating to produce the nearly rigid rotation, and a mechanism other than viscosity must be operating to produce a more rapidly rotating surface than core. Our asteroseismic result, along with previous asteroseismic constraints on internal rotation in some B stars, and measurements of internal rotation in some subgiant, giant and white dwarf stars, has made angular momentum transport in stars throughout their lifetimes an observational science.

  19. HABITABLE ZONES AROUND MAIN-SEQUENCE STARS: NEW ESTIMATES

    International Nuclear Information System (INIS)

    Kopparapu, Ravi Kumar; Ramirez, Ramses; Kasting, James F.; Eymet, Vincent; Robinson, Tyler D.; Domagal-Goldman, Shawn; Meadows, Victoria; Mahadevan, Suvrath; Terrien, Ryan C.; Deshpande, Rohit

    2013-01-01

    Identifying terrestrial planets in the habitable zones (HZs) of other stars is one of the primary goals of ongoing radial velocity (RV) and transit exoplanet surveys and proposed future space missions. Most current estimates of the boundaries of the HZ are based on one-dimensional (1D), cloud-free, climate model calculations by Kasting et al. However, this model used band models that were based on older HITRAN and HITEMP line-by-line databases. The inner edge of the HZ in the Kasting et al. model was determined by loss of water, and the outer edge was determined by the maximum greenhouse provided by a CO 2 atmosphere. A conservative estimate for the width of the HZ from this model in our solar system is 0.95-1.67 AU. Here an updated 1D radiative-convective, cloud-free climate model is used to obtain new estimates for HZ widths around F, G, K, and M stars. New H 2 O and CO 2 absorption coefficients, derived from the HITRAN 2008 and HITEMP 2010 line-by-line databases, are important improvements to the climate model. According to the new model, the water-loss (inner HZ) and maximum greenhouse (outer HZ) limits for our solar system are at 0.99 and 1.70 AU, respectively, suggesting that the present Earth lies near the inner edge. Additional calculations are performed for stars with effective temperatures between 2600 and 7200 K, and the results are presented in parametric form, making them easy to apply to actual stars. The new model indicates that, near the inner edge of the HZ, there is no clear distinction between runaway greenhouse and water-loss limits for stars with T eff ∼ ⊕ , so that future flagship missions like TPF-C and Darwin are not undersized. Our model does not include the radiative effects of clouds; thus, the actual HZ boundaries may extend further in both directions than the estimates just given.

  20. Exploration of the brown dwarf regime around solar-like stars by CoRoT

    OpenAIRE

    Csizmadia, Szilárd

    2016-01-01

    Aims. A summary of the CoRoT brown dwarf investigations are presented. Methods. Transiting brown dwarfs around solar like stars were studied by using the photometric time-series of CoRoT, and ground based radial velocity measurements. Results. CoRoT detected three transiting brown dwarfs around F and G dwarf stars. The occurence rate of brown dwarfs was found to be 0.20 +/- 0.15% around solar-like stars which is compatible with the value obtained by Kepler-data.

  1. HABITABLE ZONES AROUND MAIN-SEQUENCE STARS: DEPENDENCE ON PLANETARY MASS

    International Nuclear Information System (INIS)

    Kopparapu, Ravi Kumar; Ramirez, Ramses M.; Kasting, James F.; SchottelKotte, James; Domagal-Goldman, Shawn; Eymet, Vincent

    2014-01-01

    The ongoing discoveries of extra-solar planets are unveiling a wide range of terrestrial mass (size) planets around their host stars. In this Letter, we present estimates of habitable zones (HZs) around stars with stellar effective temperatures in the range 2600 K-7200 K, for planetary masses between 0.1 M ⊕ and 5 M ⊕ . Assuming H 2 O-(inner HZ) and CO 2 -(outer HZ) dominated atmospheres, and scaling the background N 2 atmospheric pressure with the radius of the planet, our results indicate that larger planets have wider HZs than do smaller ones. Specifically, with the assumption that smaller planets will have less dense atmospheres, the inner edge of the HZ (runaway greenhouse limit) moves outward (∼10% lower than Earth flux) for low mass planets due to larger greenhouse effect arising from the increased H 2 O column depth. For larger planets, the H 2 O column depth is smaller, and higher temperatures are needed before water vapor completely dominates the outgoing longwave radiation. Hence the inner edge moves inward (∼7% higher than Earth's flux). The outer HZ changes little due to the competing effects of the greenhouse effect and an increase in albedo. New, three-dimensional climate model results from other groups are also summarized, and we argue that further, independent studies are needed to verify their predictions. Combined with our previous work, the results presented here provide refined estimates of HZs around main-sequence stars and provide a step toward a more comprehensive analysis of HZs

  2. Habitable Zones Around Main-Sequence Stars: Dependence on Planetary Mass

    Science.gov (United States)

    Kopparapu, Ravi Kumar; Ramirez, Ramses M.; Kotte, James Schottel; Kasting, James F.; Domagal-Goldman, Shawn; Eymet, Vincent

    2014-01-01

    The ongoing discoveries of extra-solar planets are unveiling a wide range of terrestrial mass (size) planets around their host stars. In this Letter, we present estimates of habitable zones (HZs) around stars with stellar effective temperatures in the range 2600 K-7200 K, for planetary masses between 0.1M and 5M. Assuming H2O-(inner HZ) and CO2-(outer HZ) dominated atmospheres, and scaling the background N2 atmospheric pressure with the radius of the planet, our results indicate that larger planets have wider HZs than do smaller ones. Specifically, with the assumption that smaller planets will have less dense atmospheres, the inner edge of the HZ (runaway greenhouse limit) moves outward (approx.10% lower than Earth flux) for low mass planets due to larger greenhouse effect arising from the increased H2O column depth. For larger planets, the H2O column depth is smaller, and higher temperatures are needed before water vapor completely dominates the outgoing long-wave radiation. Hence the inner edge moves inward (approx.7% higher than Earth's flux). The outer HZ changes little due to the competing effects of the greenhouse effect and an increase in albedo. New, three-dimensional climate model results from other groups are also summarized, and we argue that further, independent studies are needed to verify their predictions. Combined with our previous work, the results presented here provide refined estimates of HZs around main-sequence stars and provide a step toward a more comprehensive analysis of HZs.

  3. HABITABLE ZONES AROUND MAIN-SEQUENCE STARS: DEPENDENCE ON PLANETARY MASS

    Energy Technology Data Exchange (ETDEWEB)

    Kopparapu, Ravi Kumar; Ramirez, Ramses M.; Kasting, James F. [Department of Geosciences, Penn State University, 443 Deike Building, University Park, PA 16802 (United States); SchottelKotte, James [Department of Astronomy and Astrophysics, The Pennsylvania State University, 525 Davey Laboratory, University Park, PA 16802 (United States); Domagal-Goldman, Shawn [NASA Astrobiology Institute' s Virtual Planetary Laboratory, P.O. Box 351580, Seattle, WA 98195 (United States); Eymet, Vincent, E-mail: ruk15@psu.edu [Laboratoire d' Astrophysique de Bordeaux, Universite de Bordeaux 1, UMR 5804, F-33270 Floirac (France)

    2014-06-01

    The ongoing discoveries of extra-solar planets are unveiling a wide range of terrestrial mass (size) planets around their host stars. In this Letter, we present estimates of habitable zones (HZs) around stars with stellar effective temperatures in the range 2600 K-7200 K, for planetary masses between 0.1 M {sub ⊕} and 5 M {sub ⊕}. Assuming H{sub 2}O-(inner HZ) and CO{sub 2}-(outer HZ) dominated atmospheres, and scaling the background N{sub 2} atmospheric pressure with the radius of the planet, our results indicate that larger planets have wider HZs than do smaller ones. Specifically, with the assumption that smaller planets will have less dense atmospheres, the inner edge of the HZ (runaway greenhouse limit) moves outward (∼10% lower than Earth flux) for low mass planets due to larger greenhouse effect arising from the increased H{sub 2}O column depth. For larger planets, the H{sub 2}O column depth is smaller, and higher temperatures are needed before water vapor completely dominates the outgoing longwave radiation. Hence the inner edge moves inward (∼7% higher than Earth's flux). The outer HZ changes little due to the competing effects of the greenhouse effect and an increase in albedo. New, three-dimensional climate model results from other groups are also summarized, and we argue that further, independent studies are needed to verify their predictions. Combined with our previous work, the results presented here provide refined estimates of HZs around main-sequence stars and provide a step toward a more comprehensive analysis of HZs.

  4. Three aspects of stellar evolution near the main sequence

    International Nuclear Information System (INIS)

    Morgan, J.C.

    1979-05-01

    Three problems of stellar evolution are considered: the gap in the HR diagram of M67, the evolutionary status of RS CVn binaries and the solar neutrino problem. The physical basis of the Eggleton stellar evolution computer program is described. The program was used to calculate a grid of evolutionary tracks for models with masses between 0.7 and 1.29 solar masses. The more massive stars considered here have expanding convective cores during their main sequence evolution. The isochrone of the old galactic cluster M67 has a gap at the top of its main sequence because of the rapid evolution of stars at hydrogen exhaustion. RS CVn binaries present a complex collection of observational phenomena although they appear to be detached binaries. Their evolutionary status has remained controversial because of their high space density. Here it is shown that a post main sequence interpretation is satisfactory. Models of the Sun with metal poor interiors have been proposed in an attempt to resolve the solar neutrino problem. Here the evolution of two such models is calculated in detail, including a gradual contamination of the surface convection zone to produce the observed metal abundance, giving fully consistent models of the Sun as it is observed. (author)

  5. Infrared photometry of upper main sequence stars in M39

    International Nuclear Information System (INIS)

    Manteiga, M.; Martinez-Roger, C.; Morales, C.; Sabau, L.

    1991-01-01

    Infrared photometry of 19 Main sequence stars in the open cluster M39 is presented. Infrared-infrared and optical-infrared colour-colour and colour-magnitude diagrams are presented and compared with mean intrinsic colours for Population I stars. An interstellar reddening of E(B - V) = 0.01 is obtained by analysis of the colour-colour diagrams. Comparison with a set of theoretical isochrones leads to an age estimate for the cluster between 2.4 and 4.8 x 10 8 years

  6. Infrared photometry of upper main sequence stars in M39

    Energy Technology Data Exchange (ETDEWEB)

    Manteiga, M.; Martinez-Roger, C. (Instituto de Astrofisica de Canarias, Tenerife, (ES)); Morales, C.; Sabau, L. (Instituto de Tecnica Aeroespacial, Madrid, (ES))

    1991-03-01

    Infrared photometry of 19 Main sequence stars in the open cluster M39 is presented. Infrared-infrared and optical-infrared colour-colour and colour-magnitude diagrams are presented and compared with mean intrinsic colours for Population I stars. An interstellar reddening of E(B - V) = 0.01 is obtained by analysis of the colour-colour diagrams. Comparison with a set of theoretical isochrones leads to an age estimate for the cluster between 2.4 and 4.8 x 10{sup 8} years.

  7. Modelling solar-like oscillators

    Energy Technology Data Exchange (ETDEWEB)

    Eggenberger, P; Miglio, A [Institut d' Astrophysique et de Geophysique de l' Universite de Liege, 17 Allee du 6 Aout, B-4000 Liege (Belgium); Carrier, F [Institute of Astronomy, University of Leuven, Celestijnenlaan 200 D, B-3001 Leuven (Belgium); Mathis, S [CEA/DSM/DAPNIA/Service d' Astrophysique, CEA/Saclay, AIM-Unite Mixte de Recherche CEA-CNRS-Universite Paris VII, UMR 7158, 91191 Gif-sur-Yvette Cedex (France)], E-mail: eggenberger@Qastro.ulg.ac.be

    2008-10-15

    The computation of models of stars for which solar-like oscillations have been observed is discussed. After a brief intoduction on the observations of solar-like oscillations, the modelling of isolated stars and of stars belonging to a binary system is presented with specific examples of recent theoretical calibrations. Finally the input physics introduced in stellar evolution codes for the computation of solar-type stars is discussed with a peculiar emphasis on the modelling of rotation for these stars.

  8. STELLAR DIAMETERS AND TEMPERATURES. III. MAIN-SEQUENCE A, F, G, AND K STARS: ADDITIONAL HIGH-PRECISION MEASUREMENTS AND EMPIRICAL RELATIONS

    International Nuclear Information System (INIS)

    Boyajian, Tabetha S.; Jones, Jeremy; White, Russel; McAlister, Harold A.; Gies, Douglas; Von Braun, Kaspar; Van Belle, Gerard; Farrington, Chris; Schaefer, Gail; Ten Brummelaar, Theo A.; Sturmann, Laszlo; Sturmann, Judit; Turner, Nils H.; Goldfinger, P. J.; Vargas, Norm; Ridgway, Stephen

    2013-01-01

    Based on CHARA Array measurements, we present the angular diameters of 23 nearby, main-sequence stars, ranging from spectral types A7 to K0, 5 of which are exoplanet host stars. We derive linear radii, effective temperatures, and absolute luminosities of the stars using Hipparcos parallaxes and measured bolometric fluxes. The new data are combined with previously published values to create an Angular Diameter Anthology of measured angular diameters to main-sequence stars (luminosity classes V and IV). This compilation consists of 125 stars with diameter uncertainties of less than 5%, ranging in spectral types from A to M. The large quantity of empirical data is used to derive color-temperature relations to an assortment of color indices in the Johnson (BVR J I J JHK), Cousins (R C I C ), Kron (R K I K ), Sloan (griz), and WISE (W 3 W 4 ) photometric systems. These relations have an average standard deviation of ∼3% and are valid for stars with spectral types A0-M4. To derive even more accurate relations for Sun-like stars, we also determined these temperature relations omitting early-type stars (T eff > 6750 K) that may have biased luminosity estimates because of rapid rotation; for this subset the dispersion is only ∼2.5%. We find effective temperatures in agreement within a couple of percent for the interferometrically characterized sample of main-sequence stars compared to those derived via the infrared flux method and spectroscopic analysis.

  9. ASTEROSEISMIC DIAGRAMS FROM A SURVEY OF SOLAR-LIKE OSCILLATIONS WITH KEPLER

    Energy Technology Data Exchange (ETDEWEB)

    White, Timothy R.; Bedding, Timothy R.; Stello, Dennis; Benomar, Othman; Huber, Daniel [Sydney Institute for Astronomy (SIfA), School of Physics, University of Sydney, NSW 2006 (Australia); Appourchaux, Thierry; Gaulme, Patrick [Institut d' Astrophysique Spatiale, UMR8617, Universite Paris XI, Batiment 121, 91405 Orsay Cedex (France); Ballot, Jerome [Institut de Recherche en Astrophysique et Planetologie, CNRS, 14 avenue E. Belin, 31400 Toulouse (France); Bonanno, Alfio; Corsaro, Enrico [INAF Observatorio Astrofisico di Catania, Via S. Sofia 78, 95123 Catania (Italy); Broomhall, Anne-Marie; Chaplin, William J.; Elsworth, Yvonne P.; Hekker, Saskia [School of Physics and Astronomy, University of Birmingham, Birmingham B15 2TT (United Kingdom); Campante, Tiago L. [Centro de Astrofisica and Faculdade de Ciencias, Universidade do Porto, Rua das Estrelas, 4150-762 Porto (Portugal); Christensen-Dalsgaard, Jorgen; Dogan, Guelnur; Handberg, Rasmus [Danish AsteroSeismology Centre (DASC), Department of Physics and Astronomy, Aarhus University, DK-8000 Aarhus C (Denmark); Fletcher, Stephen T. [Materials Engineering Research Institute, Faculty of Arts, Computing, Engineering and Sciences, Sheffield Hallam University, Sheffield, S1 1WB (United Kingdom); Garcia, Rafael A., E-mail: t.white@physics.usyd.edu.au [Laboratoire AIM, CEA/DSM-CNRS, Universite Paris 7 Diderot, IRFU/SAp, Centre de Saclay, 91191 Gif-sur-Yvette (France); and others

    2011-11-20

    Photometric observations made by the NASA Kepler Mission have led to a dramatic increase in the number of main-sequence and subgiant stars with detected solar-like oscillations. We present an ensemble asteroseismic analysis of 76 solar-type stars. Using frequencies determined from the Kepler time-series photometry, we have measured three asteroseismic parameters that characterize the oscillations: the large frequency separation ({Delta}{nu}), the small frequency separation between modes of l = 0 and l = 2 ({delta}{nu}{sub 02}), and the dimensionless offset ({epsilon}). These measurements allow us to construct asteroseismic diagrams, namely the so-called Christensen-Dalsgaard diagram of {delta}{nu}{sub 02} versus {Delta}{nu}, and the recently re-introduced {epsilon} diagram. We compare the Kepler results with previously observed solar-type stars and with theoretical models. The positions of stars in these diagrams places constraints on their masses and ages. Additionally, we confirm the observational relationship between {epsilon} and T{sub eff} that allows for the unambiguous determination of radial order and should help resolve the problem of mode identification in F stars.

  10. Effects of Main-Sequence Mass Loss on Stellar and Galactic Chemical Evolution.

    Science.gov (United States)

    Guzik, Joyce Ann

    1988-06-01

    L. A. Willson, G. H. Bowen and C. Struck -Marcell have proposed that 1 to 3 solar mass stars may experience evolutionarily significant mass loss during the early part of their main-sequence phase. The suggested mass-loss mechanism is pulsation, facilitated by rapid rotation. Initial mass-loss rates may be as large as several times 10^{-9}M o/yr, diminishing over several times 10^8 years. We attempted to test this hypothesis by comparing some theoretical implications with observations. Three areas are addressed: Solar models, cluster HR diagrams, and galactic chemical evolution. Mass-losing solar models were evolved that match the Sun's luminosity and radius at its present age. The most extreme viable models have initial mass 2.0 M o, and mass-loss rates decreasing exponentially over 2-3 times 10^8 years. Compared to a constant -mass model, these models require a reduced initial ^4He abundance, have deeper envelope convection zones and higher ^8B neutrino fluxes. Early processing of present surface layers at higher interior temperatures increases the surface ^3He abundance, destroys Li, Be and B, and decreases the surface C/N ratio following first dredge-up. Evolution calculations incorporating main-sequence mass loss were completed for a grid of models with initial masses 1.25 to 2.0 Mo and mass loss timescales 0.2 to 2.0 Gyr. Cluster HR diagrams synthesized with these models confirm the potential for the hypothesis to explain observed spreads or bifurcations in the upper main sequence, blue stragglers, anomalous giants, and poor fits of main-sequence turnoffs by standard isochrones. Simple closed galactic chemical evolution models were used to test the effects of main-sequence mass loss on the F and G dwarf distribution. Stars between 3.0 M o and a metallicity -dependent lower mass are assumed to lose mass. The models produce a 30 to 60% increase in the stars to stars-plus -remnants ratio, with fewer early-F dwarfs and many more late-F dwarfs remaining on the main

  11. Main sequence mass loss

    International Nuclear Information System (INIS)

    Brunish, W.M.; Guzik, J.A.; Willson, L.A.; Bowen, G.

    1987-01-01

    It has been hypothesized that variable stars may experience mass loss, driven, at least in part, by oscillations. The class of stars we are discussing here are the δ Scuti variables. These are variable stars with masses between about 1.2 and 2.25 M/sub θ/, lying on or very near the main sequence. According to this theory, high rotation rates enhance the rate of mass loss, so main sequence stars born in this mass range would have a range of mass loss rates, depending on their initial rotation velocity and the amplitude of the oscillations. The stars would evolve rapidly down the main sequence until (at about 1.25 M/sub θ/) a surface convection zone began to form. The presence of this convective region would slow the rotation, perhaps allowing magnetic braking to occur, and thus sharply reduce the mass loss rate. 7 refs

  12. Pre-main-sequence evolution of the sun

    International Nuclear Information System (INIS)

    Gough, D.

    1980-01-01

    The phase of solar evolution after the dynamical collapse is considered. The physics of the Kelvin-Helmholtz phase of gravitational collapse is described, attention being given to the early stages of the star when it was completely convective. It is noted that subsequently, a radiative core developed and evolution was controlled by the rate at which heat can diffuse through it by radiative transfer. Since the study of the Kelvin-Helmholtz contraction alone does not give enough information regarding the state of the sun when it first settled down to approximate hydrostatic equilibrium, other stars are studied, and information on the sun is obtained by analogy. Many young solar-type stars, such as the T Tauri stars, are not in the completely convective Hayashi (1961) phase hence it is proposed that the sun was completely mixed soon after its formation, which has some bearing on the sun's chemical structure. It is suggested that the surface of the sun was very nonuniform compared with the photosphere of today. The simple solar evolution model presented gives a good guide to the general way in which the sun contracted to the main sequence

  13. On precise ZAMSs, the solar color, and pre-main-sequence lithium depletion

    International Nuclear Information System (INIS)

    Vandenberg, D.A.; Poll, H.E.

    1989-01-01

    This paper describes a semiempirical main-sequence-fitting method for the determination of distances to stellar systems, which uses a ZAMS locus carefully normalized to the sun, and whose shape is defined by a quartic over the color range for (B-V)0 values between 0.2 and 1.0 such that the morphology of the Pleiades C-M diagram is accurately reproduced. Using this technique, distances were derived for a number of star clusters. It was found that the observed depletion of lithium among cool main-sequence stars in the Hyades and Pleiades can be matched quite well by the present models. Calculations also show that the depletion of Li at a fixed T(eff) along the main sequence is a sensitive function of Fe/H. 98 refs

  14. Asteroseismology of solar-type stars: particular physical effects

    Energy Technology Data Exchange (ETDEWEB)

    Carrier, F [Instituut voor Sterrenkunde, Katholieke Universiteit Leuven, Celestijnenlaan 200D, 3001 Leuven (Belgium); Eggenberger, P; Leyder, J-C [Institut d' Astrophysique et de Geophysique de l' Universite de Liege, 17 Allee du 6 aout, 4000 Liege (Belgium)], E-mail: fabien@ster.kuleuven.be

    2008-10-15

    Since the success of helioseismology, numerous efforts have been made to detect solar-like oscillations on other stars. The measurement of the frequencies of p-mode oscillations provides an insight into the internal structure and is nowadays the most powerful constraint on the theory of stellar evolution. The existing asteroseismic observations were mainly motivated by the need to explore the seismological properties of stars with various global parameters, i.e. various locations in the HR diagram. With the aim of testing different physical effects on solar-like oscillations, we report here detection of acoustic modes on solar-like targets achieved with the spectrograph HARPS installed on the 3.6-m telescope at ESO La Silla Observatory.

  15. The excitation of solar-like oscillations in a δ Sct star by efficient envelope convection

    DEFF Research Database (Denmark)

    Antoci, V.; Handler, G.; Kallinger, T.

    2011-01-01

    Delta Scuti (δSct) stars are opacity-driven pulsators with masses of 1.5-2.5Msolar, their pulsations resulting from the varying ionization of helium. In less massive stars such as the Sun, convection transports mass and energy through the outer 30per cent of the star and excites a rich spectrum...... of resonant acoustic modes. Based on the solar example, with no firm theoretical basis, models predict that the convective envelope in δSct stars extends only about 1per cent of the radius, but with sufficient energy to excite solar-like oscillations. This was not observed before the Kepler mission, so...... the presence of a convective envelope in the models has been questioned. Here we report the detection of solar-like oscillations in the δSct star HD187547, implying that surface convection operates efficiently in stars about twice as massive as the Sun, as the ad hoc models predicted....

  16. HABITABLE ZONES AROUND MAIN-SEQUENCE STARS: NEW ESTIMATES

    Energy Technology Data Exchange (ETDEWEB)

    Kopparapu, Ravi Kumar; Ramirez, Ramses; Kasting, James F. [Department of Geosciences, Penn State University, 443 Deike Building, University Park, PA 16802 (United States); Eymet, Vincent [Laboratoire d' Astrophysique de Bordeaux, Universite de Bordeaux 1, UMR 5804, F-33270 Floirac (France); Robinson, Tyler D.; Domagal-Goldman, Shawn; Meadows, Victoria [NASA Astrobiology Institute' s Virtual Planetary Laboratory (United States); Mahadevan, Suvrath; Terrien, Ryan C.; Deshpande, Rohit [Center for Exoplanets and Habitable Worlds, The Pennsylvania State University, University Park, PA 16802 (United States)

    2013-03-10

    Identifying terrestrial planets in the habitable zones (HZs) of other stars is one of the primary goals of ongoing radial velocity (RV) and transit exoplanet surveys and proposed future space missions. Most current estimates of the boundaries of the HZ are based on one-dimensional (1D), cloud-free, climate model calculations by Kasting et al. However, this model used band models that were based on older HITRAN and HITEMP line-by-line databases. The inner edge of the HZ in the Kasting et al. model was determined by loss of water, and the outer edge was determined by the maximum greenhouse provided by a CO{sub 2} atmosphere. A conservative estimate for the width of the HZ from this model in our solar system is 0.95-1.67 AU. Here an updated 1D radiative-convective, cloud-free climate model is used to obtain new estimates for HZ widths around F, G, K, and M stars. New H{sub 2}O and CO{sub 2} absorption coefficients, derived from the HITRAN 2008 and HITEMP 2010 line-by-line databases, are important improvements to the climate model. According to the new model, the water-loss (inner HZ) and maximum greenhouse (outer HZ) limits for our solar system are at 0.99 and 1.70 AU, respectively, suggesting that the present Earth lies near the inner edge. Additional calculations are performed for stars with effective temperatures between 2600 and 7200 K, and the results are presented in parametric form, making them easy to apply to actual stars. The new model indicates that, near the inner edge of the HZ, there is no clear distinction between runaway greenhouse and water-loss limits for stars with T{sub eff} {approx}< 5000 K, which has implications for ongoing planet searches around K and M stars. To assess the potential habitability of extrasolar terrestrial planets, we propose using stellar flux incident on a planet rather than equilibrium temperature. This removes the dependence on planetary (Bond) albedo, which varies depending on the host star's spectral type. We suggest

  17. STELLAR DIAMETERS AND TEMPERATURES. III. MAIN-SEQUENCE A, F, G, AND K STARS: ADDITIONAL HIGH-PRECISION MEASUREMENTS AND EMPIRICAL RELATIONS

    Energy Technology Data Exchange (ETDEWEB)

    Boyajian, Tabetha S.; Jones, Jeremy; White, Russel; McAlister, Harold A.; Gies, Douglas [Center for High Angular Resolution Astronomy and Department of Physics and Astronomy, Georgia State University, P.O. Box 4106, Atlanta, GA 30302-4106 (United States); Von Braun, Kaspar [NASA Exoplanet Science Institute, California Institute of Technology, MC 100-22, Pasadena, CA 91125 (United States); Van Belle, Gerard [Lowell Observatory, Flagstaff, AZ 86001 (United States); Farrington, Chris; Schaefer, Gail; Ten Brummelaar, Theo A.; Sturmann, Laszlo; Sturmann, Judit; Turner, Nils H.; Goldfinger, P. J.; Vargas, Norm [CHARA Array, Mount Wilson Observatory, Mount Wilson, CA 91023 (United States); Ridgway, Stephen [National Optical Astronomy Observatory, P.O. Box 26732, Tucson, AZ 85726-6732 (United States)

    2013-07-01

    Based on CHARA Array measurements, we present the angular diameters of 23 nearby, main-sequence stars, ranging from spectral types A7 to K0, 5 of which are exoplanet host stars. We derive linear radii, effective temperatures, and absolute luminosities of the stars using Hipparcos parallaxes and measured bolometric fluxes. The new data are combined with previously published values to create an Angular Diameter Anthology of measured angular diameters to main-sequence stars (luminosity classes V and IV). This compilation consists of 125 stars with diameter uncertainties of less than 5%, ranging in spectral types from A to M. The large quantity of empirical data is used to derive color-temperature relations to an assortment of color indices in the Johnson (BVR{sub J} I{sub J} JHK), Cousins (R{sub C} I{sub C}), Kron (R{sub K} I{sub K}), Sloan (griz), and WISE (W{sub 3} W{sub 4}) photometric systems. These relations have an average standard deviation of {approx}3% and are valid for stars with spectral types A0-M4. To derive even more accurate relations for Sun-like stars, we also determined these temperature relations omitting early-type stars (T{sub eff} > 6750 K) that may have biased luminosity estimates because of rapid rotation; for this subset the dispersion is only {approx}2.5%. We find effective temperatures in agreement within a couple of percent for the interferometrically characterized sample of main-sequence stars compared to those derived via the infrared flux method and spectroscopic analysis.

  18. An extensive VLT/X-shooter library of photospheric templates of pre-main sequence stars

    Science.gov (United States)

    Manara, C. F.; Frasca, A.; Alcalá, J. M.; Natta, A.; Stelzer, B.; Testi, L.

    2017-09-01

    Context. Studies of the formation and evolution of young stars and their disks rely on knowledge of the stellar parameters of the young stars. The derivation of these parameters is commonly based on comparison with photospheric template spectra. Furthermore, chromospheric emission in young active stars impacts the measurement of mass accretion rates, a key quantity for studying disk evolution. Aims: Here we derive stellar properties of low-mass (M⋆≲ 2 M⊙) pre-main sequence stars without disks, which represent ideal photospheric templates for studies of young stars. We also use these spectra to constrain the impact of chromospheric emission on the measurements of mass accretion rates. The spectra are reduced, flux-calibrated, and corrected for telluric absorption, and are made available to the community. Methods: We derive the spectral type for our targets by analyzing the photospheric molecular features present in their VLT/X-shooter spectra by means of spectral indices and comparison of the relative strength of photospheric absorption features. We also measure effective temperature, gravity, projected rotational velocity, and radial velocity from our spectra by fitting them with synthetic spectra with the ROTFIT tool. The targets have negligible extinction (AVpresented in our previous publication. We perform synthetic photometry on the spectra to derive the typical colors of young stars in different filters. We measure the luminosity of the emission lines present in the spectra and estimate the noise due to chromospheric emission in the measurements of accretion luminosity in accreting stars. Results: We provide a calibration of the photospheric colors of young pre-main sequence stars as a function of their spectral type in a set of standard broad-band optical and near-infrared filters. The logarithm of the noise on the accretion luminosity normalized to the stellar luminosity is roughly constant and equal to -2.3 for targets with masses larger than 1 solar

  19. The V Band Empirical Mass-Luminosity Relation for Main Sequence Stars

    Science.gov (United States)

    Xia, F.; Fu, Y. N.

    2010-01-01

    Stellar mass is an indispensable parameter in the studies of stellar physics and stellar dynamics. On the one hand, the most reliable way to determine the stellar dynamical mass is via orbital determination of binaries. On the other hand, however, most stellar masses have to be estimated by using the mass-luminosity relation (MLR). Therefore, it is important to obtain the empirical MLR through fitting the data of stellar dynamical mass and luminosity. The effect of metallicity can make this relation disperse in the V-band, but studies show that this is mainly limited to the case when the stellar mass is less than 0.6M⊙. Recently, many relevant data have been accumulated for main sequence stars with larger mass, which make it possible to significantly improve the corresponding MLR. Using a fitting method which can reasonably assign weight to the observational data including two quantities with different dimensions, we obtain a V-band MLR based on the dynamical masses and luminosities of 203 main sequence stars. Compared with the previous work, the improved MLR is statistically significant, and the relative error of mass estimation reaches about 5%. Therefore, our MLR is useful not only in studies of statistical nature, but also in studies of concrete stellar systems, such as the long-term dynamical study and the short-term positioning study of a specific multiple star system.

  20. The V-band Empirical Mass-luminosity Relation for Main Sequence Stars

    Science.gov (United States)

    Xia, Fang; Fu, Yan-Ning

    2010-07-01

    Stellar mass is an indispensable parameter in the studies of stellar physics and stellar dynamics. On the one hand, the most reliable way to determine the stellar dynamical mass is via orbital determinations of binaries. On the other hand, however, most stellar masses have to be estimated by using the mass luminosity relation (MLR). Therefore, it is important to obtain the empirical MLR through fitting the data of stellar dynamical mass and luminosity. The effect of metallicity can make this relation disperse in the V-band, but studies show that this is mainly limited to the case when the stellar mass is less than 0.6M⊙ Recently, many relevant data have been accumulated for main sequence stars with larger masses, which make it possible to significantly improve the corresponding MLR. Using a fitting method which can reasonably assign weights to the observational data including two quantities with different dimensions, we obtain a V-band MLR based on the dynamical masses and luminosities of 203 main sequence stars. In comparison with the previous work, the improved MLR is statistically significant, and the relative error of mass estimation reaches about 5%. Therefore, our MLR is useful not only in the studies of statistical nature, but also in the studies of concrete stellar systems, such as the long-term dynamical study and the short-term positioning study of a specific multiple star system.

  1. INTRINSIC COLORS, TEMPERATURES, AND BOLOMETRIC CORRECTIONS OF PRE-MAIN-SEQUENCE STARS

    Energy Technology Data Exchange (ETDEWEB)

    Pecaut, Mark J.; Mamajek, Eric E. [University of Rochester, Department of Physics and Astronomy, Rochester, NY 14627-0171 (United States)

    2013-09-01

    We present an analysis of the intrinsic colors and temperatures of 5-30 Myr old pre-main-sequence (pre-MS) stars using the F0- through M9-type members of nearby, negligibly reddened groups: the η Cha cluster, the TW Hydra Association, the β Pic Moving Group, and the Tucana-Horologium Association. To check the consistency of spectral types from the literature, we estimate new spectral types for 52 nearby pre-MS stars with spectral types F3 through M4 using optical spectra taken with the SMARTS 1.5 m telescope. Combining these new types with published spectral types and photometry from the literature (Johnson-Cousins BVI{sub C} , 2MASS JHK{sub S} and WISE W1, W2, W3, and W4), we derive a new empirical spectral type-color sequence for 5-30 Myr old pre-MS stars. Colors for pre-MS stars match dwarf colors for some spectral types and colors, but for other spectral types and colors, deviations can exceed 0.3 mag. We estimate effective temperatures (T {sub eff}) and bolometric corrections (BCs) for our pre-MS star sample through comparing their photometry to synthetic photometry generated using the BT-Settl grid of model atmosphere spectra. We derive a new T {sub eff} and BC scale for pre-MS stars, which should be a more appropriate match for T Tauri stars than often-adopted dwarf star scales. While our new T {sub eff} scale for pre-MS stars is within ≅100 K of dwarfs at a given spectral type for stars stars are ∼250 K cooler than their MS counterparts. Lastly, we present (1) a modern T {sub eff}, optical/IR color, and BC sequence for O9V-M9V MS stars based on an extensive literature survey, (2) a revised Q-method relation for dereddening UBV photometry of OB-type stars, and (3) introduce two candidate spectral standard stars as representatives of spectral types K8V and K9V.

  2. The age-metallicity relation in the solar neighbourhood from a pilot sample of white dwarf-main sequence binaries

    OpenAIRE

    Rebassa-Mansergas, A.; Anguiano, B.; García-Berro, E.; Freeman, K. C.; Cojocaru, R.; Manser, C. J.; Pala, A. F.; Gänsicke, B. T.; Liu, X. -W.

    2016-01-01

    The age–metallicity relation (AMR) is a fundamental observational constraint for understanding how the Galactic disc formed and evolved chemically in time. However, there is not yet an agreement on the observational properties of the AMR for the solar neighbourhood, primarily due to the difficulty in obtaining accurate stellar ages for individual field stars. We have started an observational campaign for providing the much needed observational input by using wide white-dwarf–main-sequence (WD...

  3. Limits on surface gravities of Kepler planet-candidate host stars from non-detection of solar-like oscillations

    Energy Technology Data Exchange (ETDEWEB)

    Campante, T. L.; Chaplin, W. J.; Handberg, R.; Miglio, A.; Davies, G. R.; Elsworth, Y. P. [School of Physics and Astronomy, University of Birmingham, Edgbaston, Birmingham B15 2TT (United Kingdom); Lund, M. N.; Arentoft, T.; Christensen-Dalsgaard, J.; Karoff, C.; Kjeldsen, H.; Lundkvist, M. [Stellar Astrophysics Centre (SAC), Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, DK-8000 Aarhus C (Denmark); Huber, D. [NASA Ames Research Center, MS 244-30, Moffett Field, CA 94035 (United States); Hekker, S. [Astronomical Institute, " Anton Pannekoek," University of Amsterdam, Amsterdam (Netherlands); García, R. A. [Laboratoire AIM, CEA/DSM-CNRS-Université Paris Diderot (France); IRFU/SAp, Centre de Saclay, F-91191 Gif-sur-Yvette Cedex (France); Corsaro, E. [Instituut voor Sterrenkunde, KU Leuven, Celestijnenlaan 200D, B-3001 Leuven (Belgium); Basu, S. [Department of Astronomy, Yale University, New Haven, CT 06520 (United States); Bedding, T. R. [Sydney Institute for Astronomy, School of Physics, University of Sydney, Sydney (Australia); Gilliland, R. L. [Center for Exoplanets and Habitable Worlds, The Pennsylvania State University, University Park, PA 16802 (United States); Kawaler, S. D., E-mail: campante@bison.ph.bham.ac.uk [Department of Physics and Astronomy, Iowa State University, Ames, IA 50011 (United States); and others

    2014-03-10

    We present a novel method for estimating lower-limit surface gravities (log g) of Kepler targets whose data do not allow the detection of solar-like oscillations. The method is tested using an ensemble of solar-type stars observed in the context of the Kepler Asteroseismic Science Consortium. We then proceed to estimate lower-limit log g for a cohort of Kepler solar-type planet-candidate host stars with no detected oscillations. Limits on fundamental stellar properties, as provided by this work, are likely to be useful in the characterization of the corresponding candidate planetary systems. Furthermore, an important byproduct of the current work is the confirmation that amplitudes of solar-like oscillations are suppressed in stars with increased levels of surface magnetic activity.

  4. Lithium evolution in metal-poor stars: from Pre-Main Sequence to the Spite plateau

    OpenAIRE

    Fu, Xiaoting; Bressan, Alessandro; Molaro, Paolo; Marigo, Paola

    2015-01-01

    Lithium abundance derived in metal-poor main sequence stars is about three times lower than the value of primordial Li predicted by the standard Big Bang nucleosynthesis when the baryon density is taken from the CMB or the deuterium measurements. This disagreement is generally referred as the lithium problem. We here reconsider the stellar Li evolution from the pre-main sequence to the end of the main sequence phase by introducing the effects of convective overshooting and residual mass accre...

  5. Magnetic fields in O-, B- and A-type stars on the main sequence

    Directory of Open Access Journals (Sweden)

    Briquet Maryline

    2015-01-01

    Full Text Available In this review, the latest observational results on magnetic fields in main-sequence stars with radiative envelopes are summarised together with the theoretical works aimed at explaining them.

  6. Evolution Models of Helium White Dwarf–Main-sequence Star Merger Remnants

    International Nuclear Information System (INIS)

    Zhang, Xianfei; Bi, Shaolan; Hall, Philip D.; Jeffery, C. Simon

    2017-01-01

    It is predicted that orbital decay by gravitational-wave radiation and tidal interaction will cause some close binary stars to merge within a Hubble time. The merger of a helium-core white dwarf with a main-sequence (MS) star can produce a red giant branch star that has a low-mass hydrogen envelope when helium is ignited and thus become a hot subdwarf. Because detailed calculations have not been made, we compute post-merger models with a stellar evolution code. We find the evolutionary paths available to merger remnants and find the pre-merger conditions that lead to the formation of hot subdwarfs. We find that some such mergers result in the formation of stars with intermediate helium-rich surfaces. These stars later develop helium-poor surfaces owing to diffusion. Combining our results with a model population and comparing to observed stars, we find that some observed intermediate helium-rich hot subdwarfs can be explained as the remnants of the mergers of helium-core white dwarfs with low-mass MS stars.

  7. Evolution Models of Helium White Dwarf–Main-sequence Star Merger Remnants

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Xianfei; Bi, Shaolan [Department of Astronomy, Beijing Normal University, Beijing, 100875 (China); Hall, Philip D.; Jeffery, C. Simon, E-mail: zxf@bnu.edu.cn [Armagh Observatory, College Hill, Armagh BT61 9DG (United Kingdom)

    2017-02-01

    It is predicted that orbital decay by gravitational-wave radiation and tidal interaction will cause some close binary stars to merge within a Hubble time. The merger of a helium-core white dwarf with a main-sequence (MS) star can produce a red giant branch star that has a low-mass hydrogen envelope when helium is ignited and thus become a hot subdwarf. Because detailed calculations have not been made, we compute post-merger models with a stellar evolution code. We find the evolutionary paths available to merger remnants and find the pre-merger conditions that lead to the formation of hot subdwarfs. We find that some such mergers result in the formation of stars with intermediate helium-rich surfaces. These stars later develop helium-poor surfaces owing to diffusion. Combining our results with a model population and comparing to observed stars, we find that some observed intermediate helium-rich hot subdwarfs can be explained as the remnants of the mergers of helium-core white dwarfs with low-mass MS stars.

  8. On the detectability of solar-like oscillations with the NASA TESS mission

    Science.gov (United States)

    Campante, Tiago L.

    2017-10-01

    The upcoming NASA TESS mission will perform an all-sky survey for planets transiting bright nearby stars. In addition, its excellent photometric precision will enable asteroseismology of solar-type and red-giant stars. We apply a newly developed detection test along a sequence of stellar evolutionary tracks in order to predict the detectability of solar-like oscillations with TESS.

  9. THE DISCOVERY OF SOLAR-LIKE ACTIVITY CYCLES BEYOND THE END OF THE MAIN SEQUENCE?

    Energy Technology Data Exchange (ETDEWEB)

    Route, Matthew, E-mail: mroute@purdue.edu [Research Computing, Information Technology at Purdue, Purdue University, 155 S. Grant Street, West Lafayette, IN 47907 (United States)

    2016-10-20

    The long-term magnetic behavior of objects near the cooler end of the stellar main sequence is poorly understood. Most theoretical work on the generation of magnetism in these ultracool dwarfs (spectral type ≥M7 stars and brown dwarfs) suggests that their magnetic fields should not change in strength and direction. Using polarized radio emission measurements of their magnetic field orientations, I demonstrate that these cool, low-mass, fully convective objects appear to undergo magnetic polarity reversals analogous to those that occur on the Sun. This powerful new technique potentially indicates that the patterns of magnetic activity displayed by the Sun continue to exist, despite the fully convective interiors of these objects, in contravention of several leading theories of the generation of magnetic fields by internal dynamos.

  10. Globules, dark clouds, and low mass pre-main sequence stars

    International Nuclear Information System (INIS)

    Hyland, A.R.

    1981-01-01

    The current observational and theoretical literature on Bok globules and their relationship to star formation is reviewed. Recent observations of globules at optical, infrared, and far infrared wavelengths are shown to provide important constraints on their structure and evolutionary status, and the suggestion that many globules are gravitationally unstable is seriously questioned. Dark clouds associated with T associations are well-known sites of recent and continuing star formation. In recent years molecular observations and far infrared surveys have provided maps of such regions from which possible sites of star formation may be identified. Optical (Hα) and near infrared surveys have enabled a clear identification of pre-main sequence (PMS) objects within the clouds. Methods of distinguishing these from background objects and the nature of their infrared excesses are examined in the light of recent observations in the near and far infrared. The perennial question as to the existence of anomalous reddening within dark clouds is also investigated. (Auth.)

  11. Stellar dynamism. Activity and rotation of solar stars observed from the Kepler satellite

    International Nuclear Information System (INIS)

    Ceillier, Tugdual

    2015-01-01

    This thesis concerns the study of seismic solar-like stars' rotation and magnetic activity. We use data from the Kepler satellite to study the rotational history of these stars throughout their evolution. This allows to have a more complete picture of stellar rotation and magnetism. In the first part, we present the context of this PhD: astro-seismology, the seismic study of stars. We continue by describing the tool we developed to measure surface rotation of stars using photometric data from Kepler. We compare it to other methodologies used by the community and show that its efficiency is very high. In the second part, we apply this tool to around 500 main-sequence and sub-giant solar-like stars. We measure surface rotation periods and activity levels for 300 of them. We show that the measured periods and the ages from astro-seismology do not agree well with the standard period-age relationships and propose to modify these relationships for stars older than the Sun. We also use the surface rotation as a constraint to estimate the internal rotation of a small number of seismic targets. We demonstrate that these stars have, like the Sun, a very low differential rotation ratio. In the third part, we apply our surface rotation-measuring tool to the most extensive sample of red giants observed by Kepler, comprising more than 17,000 stars. We identify more than 360 fast rotating red giants and compare our detection rates with the ones predicted by theory to better understand the reasons for this rapid rotation. We also use stellar modelling to reproduce the internal rotation profile of a particular red giant. This allows us to emphasize how important implementing new angular momentum transport mechanisms in stellar evolution codes is. This work offers new results that are useful to a very wide community of stellar physicists. It also puts strong constraints on the evolution of solar-like stars' rotation and magnetic activity. (author) [fr

  12. New radio detections of early-type pre-main-sequence stars

    Science.gov (United States)

    Skinner, Stephen L.; Brown, Alexander; Linsky, Jeffrey L.

    1990-01-01

    Results of VLA radio continuum observations of 13 early-type pre-main-sequence stars selected from the 1984 catalog of Finkenzeller and Mundt are presented. The stars HD 259431 and MWC 1080 were detected at 3.6 cm, while HD 200775 and TY CrA were detected at both 3.6 and 6 cm. The flux density of HD 200775 has a frequency dependence consistent with the behavior expected for free-free emission originating in a fully ionized wind. However, an observation in A configuration suggests that the source geometry may not be spherically symmetric. In contrast, the spectral index of TY CrA is negative with a flux behavior implying nonthermal emission. The physical mechanism responsible for the nonthermal emission has not yet been identified, although gyrosynchrotron and synchrotron processes cannot be ruled out.

  13. THE CONTRIBUTIONS OF INTERACTIVE BINARY STARS TO DOUBLE MAIN-SEQUENCE TURNOFFS AND DUAL RED CLUMP OF INTERMEDIATE-AGE STAR CLUSTERS

    International Nuclear Information System (INIS)

    Yang Wuming; Bi Shaolan; Tian Zhijia; Li Tanda; Liu Kang; Meng Xiangcun

    2011-01-01

    Double or extended main-sequence turnoffs (DMSTOs) and dual red clump (RC) were observed in intermediate-age clusters, such as in NGC 1846 and 419. The DMSTOs are interpreted as that the cluster has two distinct stellar populations with differences in age of about 200-300 Myr but with the same metallicity. The dual RC is interpreted as a result of a prolonged star formation. Using a stellar population-synthesis method, we calculated the evolution of a binary-star stellar population. We found that binary interactions and merging can reproduce the dual RC in the color-magnitude diagrams of an intermediate-age cluster, whereas in actuality only a single population exists. Moreover, the binary interactions can lead to an extended main-sequence turnoff (MSTO) rather than DMSTOs. However, the rest of the main sequence, subgiant branch, and first giant branch are hardly spread by the binary interactions. Part of the observed dual RC and extended MSTO may be the results of binary interactions and mergers.

  14. STELLAR DIAMETERS AND TEMPERATURES. II. MAIN-SEQUENCE K- AND M-STARS

    Energy Technology Data Exchange (ETDEWEB)

    Boyajian, Tabetha S.; McAlister, Harold A.; Jones, Jeremy; White, Russel; Henry, Todd; Gies, Douglas; Jao, Wei-Chun; Parks, J. Robert [Center for High Angular Resolution Astronomy and Department of Physics and Astronomy, Georgia State University, P.O. Box 4106, Atlanta, GA 30302-4106 (United States); Von Braun, Kaspar; Kane, Stephen R.; Ciardi, David [NASA Exoplanet Science Institute, California Institute of Technology, MC 100-22, Pasadena, CA 91125 (United States); Van Belle, Gerard [Lowell Observatory, Flagstaff, AZ 86001 (United States); Ten Brummelaar, Theo A.; Schaefer, Gail; Sturmann, Laszlo; Sturmann, Judit [The CHARA Array, Mount Wilson Observatory, Mount Wilson, CA 91023 (United States); Muirhead, Philip S. [Department of Astronomy, California Institute of Technology, 1200 East California Boulevard, MC 249-17, Pasadena, CA 91125 (United States); Lopez-Morales, Mercedes [Institut de Ciencies de L' Espai (CSIC-IEEC), E-08193 Bellaterra (Spain); Ridgway, Stephen [National Optical Astronomy Observatory, P.O. Box 26732, Tucson, AZ 85726-6732 (United States); Rojas-Ayala, Barbara [Department of Astrophysics, Division of Physical Sciences, American Museum of Natural History, Central Park West at 79th Street, New York, NY 10024 (United States); and others

    2012-10-01

    We present interferometric angular diameter measurements of 21 low-mass, K- and M-dwarfs made with the CHARA Array. This sample is enhanced by adding a collection of radius measurements published in the literature to form a total data set of 33 K-M-dwarfs with diameters measured to better than 5%. We use these data in combination with the Hipparcos parallax and new measurements of the star's bolometric flux to compute absolute luminosities, linear radii, and effective temperatures for the stars. We develop empirical relations for {approx}K0 to M4 main-sequence stars that link the stellar temperature, radius, and luminosity to the observed (B - V), (V - R), (V - I), (V - J), (V - H), and (V - K) broadband color index and stellar metallicity [Fe/H]. These relations are valid for metallicities ranging from [Fe/H] = -0.5 to +0.1 dex and are accurate to {approx}2%, {approx}5%, and {approx}4% for temperature, radius, and luminosity, respectively. Our results show that it is necessary to use metallicity-dependent transformations in order to properly convert colors into stellar temperatures, radii, and luminosities. Alternatively, we find no sensitivity to metallicity on relations we construct to the global properties of a star omitting color information, e.g., temperature-radius and temperature-luminosity. Thus, we are able to empirically quantify to what order the star's observed color index is impacted by the stellar iron abundance. In addition to the empirical relations, we also provide a representative look-up table via stellar spectral classifications using this collection of data. Robust examinations of single star temperatures and radii compared to evolutionary model predictions on the luminosity-temperature and luminosity-radius planes reveal that models overestimate the temperatures of stars with surface temperatures <5000 K by {approx}3%, and underestimate the radii of stars with radii <0.7 R{sub Sun} by {approx}5%. These conclusions additionally

  15. Turbulence and the Li abundance in main sequence and giant stars

    International Nuclear Information System (INIS)

    Charbonneau, P.; Michaud, G.

    1990-01-01

    Calculations of Li burning via turbulent transport are conducted to determine the extent to which observed Li abundances in first ascent giants constrain the various turbulence parameterizations used to model the main-sequence surface Li abundance evolution. A full time-dependent solution to the transport equation is performed, including nuclear reaction terms and evolutionary effects. It is found that turbulence can lead to the extreme Li underabundances observed in giants of M67 and NGC 752. Consideration is given to the possibility of using observations of Li abundances to discriminate between turbulent particle transport and meridional circulation transport. Numerical solutions of the turbulent diffusion coefficient of Vauclair (1988) is used to model the Hyades Li abundance gap. The astrophysical implications of the results for main-sequence and giant stars are discussed. 36 refs

  16. New radio detections of early-type pre-main-sequence stars

    International Nuclear Information System (INIS)

    Skinner, S.L.; Brown, A.; Linsky, J.L.

    1990-01-01

    Results of VLA radio continuum observations of 13 early-type pre-main-sequence stars selected from the 1984 catalog of Finkenzeller and Mundt are presented. The stars HD 259431 and MWC 1080 were detected at 3.6 cm, while HD 200775 and TY CrA were detected at both 3.6 and 6 cm. The flux density of HD 200775 has a frequency dependence consistent with the behavior expected for free-free emission originating in a fully ionized wind. However, an observation in A configuration suggests that the source geometry may not be spherically symmetric. In contrast, the spectral index of TY CrA is negative with a flux behavior implying nonthermal emission. The physical mechanism responsible for the nonthermal emission has not yet been identified, although gyrosynchrotron and synchrotron processes cannot be ruled out. 32 refs

  17. Carbon, nitrogen, and oxygen abundances in main-sequence stars. II. 20 F and G stars

    International Nuclear Information System (INIS)

    Clegg, R.E.S.; Lambert, D.L.; Tomkin, J.

    1981-01-01

    High-resolution Reticon spectra of red and near-infrared C I, N I, and O I lines have been analyzed to determine C, N, and O abundances in a sample of 20 F and G main-sequence stars. Their iron abundances, which have been determined from analysis of additional Reticon spectra of red Fe I lines, cover the range -0.9< or =[Fe/H]< or =+0.4. Sulfur abundances have also been obtained

  18. Be ABUNDANCES IN COOL MAIN-SEQUENCE STARS WITH EXOPLANETS

    International Nuclear Information System (INIS)

    Delgado Mena, E.; Israelian, G.; González Hernández, J. I.; Rebolo, R.; Santos, N. C.

    2012-01-01

    We present new Ultraviolet and Visual Echelle Spectrograph (UVES) spectra of a sample of 15 cool unevolved stars with and without detected planetary companions. Together with previous determinations, we study Be depletion and possible differences in Be abundances between the two groups of stars. We obtain a final sample of 89 and 40 stars with and without planets, respectively, which covers a wide range of effective temperatures, from 4700 K to 6400 K, and includes several cool dwarf stars for the first time. We determine Be abundances for these stars and find that for most of them (the coolest ones) the Be II resonance lines are often undetectable, implying significant Be depletion. While for hot stars Be abundances are approximately constant, with a slight fall as T eff decreases and the Li-Be gap around 6300 K, we find a steep drop of Be content as T eff decreases for T eff < 5500 K, confirming the results of previous papers. Therefore, for these stars there is an unknown mechanism destroying Be that is not reflected in current models of Be depletion. Moreover, this strong Be depletion in cool objects takes place for all the stars regardless of the presence of planets; thus, the effect of extra Li depletion in solar-type stars with planets when compared with stars without detected planets does not seem to be present for Be, although the number of stars at those temperatures is still small to reach a final conclusion.

  19. Be ABUNDANCES IN COOL MAIN-SEQUENCE STARS WITH EXOPLANETS

    Energy Technology Data Exchange (ETDEWEB)

    Delgado Mena, E.; Israelian, G.; Gonzalez Hernandez, J. I.; Rebolo, R. [Instituto de Astrofisica de Canarias, 38200 La Laguna, Tenerife (Spain); Santos, N. C., E-mail: edm@iac.es [Centro de Astrofisica, Universidade do Porto, Rua das Estrelas, 4150-762 Porto (Portugal)

    2012-02-10

    We present new Ultraviolet and Visual Echelle Spectrograph (UVES) spectra of a sample of 15 cool unevolved stars with and without detected planetary companions. Together with previous determinations, we study Be depletion and possible differences in Be abundances between the two groups of stars. We obtain a final sample of 89 and 40 stars with and without planets, respectively, which covers a wide range of effective temperatures, from 4700 K to 6400 K, and includes several cool dwarf stars for the first time. We determine Be abundances for these stars and find that for most of them (the coolest ones) the Be II resonance lines are often undetectable, implying significant Be depletion. While for hot stars Be abundances are approximately constant, with a slight fall as T{sub eff} decreases and the Li-Be gap around 6300 K, we find a steep drop of Be content as T{sub eff} decreases for T{sub eff} < 5500 K, confirming the results of previous papers. Therefore, for these stars there is an unknown mechanism destroying Be that is not reflected in current models of Be depletion. Moreover, this strong Be depletion in cool objects takes place for all the stars regardless of the presence of planets; thus, the effect of extra Li depletion in solar-type stars with planets when compared with stars without detected planets does not seem to be present for Be, although the number of stars at those temperatures is still small to reach a final conclusion.

  20. Elevation or Suppression? The Resolved Star Formation Main Sequence of Galaxies with Two Different Assembly Modes

    Science.gov (United States)

    Liu, Qing; Wang, Enci; Lin, Zesen; Gao, Yulong; Liu, Haiyang; Berhane Teklu, Berzaf; Kong, Xu

    2018-04-01

    We investigate the spatially resolved star formation main sequence in star-forming galaxies using Integral Field Spectroscopic observations from the Mapping Nearby Galaxies at the Apache Point Observatory survey. We demonstrate that the correlation between the stellar mass surface density (Σ*) and star formation rate surface density (ΣSFR) holds down to the sub-galactic scale, leading to the sub-galactic main sequence (SGMS). By dividing galaxies into two populations based on their recent mass assembly modes, we find the resolved main sequence in galaxies with the “outside-in” mode is steeper than that in galaxies with the “inside-out” mode. This is also confirmed on a galaxy-by-galaxy level, where we find the distributions of SGMS slopes for individual galaxies are clearly separated for the two populations. When normalizing and stacking the SGMS of individual galaxies on one panel for the two populations, we find that the inner regions of galaxies with the “inside-out” mode statistically exhibit a suppression in star formation, with a less significant trend in the outer regions of galaxies with the “outside-in” mode. In contrast, the inner regions of galaxies with “outside-in” mode and the outer regions of galaxies with “inside-out” mode follow a slightly sublinear scaling relation with a slope ∼0.9, which is in good agreement with previous findings, suggesting that they are experiencing a universal regulation without influences of additional physical processes.

  1. A search for pre-main-sequence stars in high-latitude molecular clouds. 3: A survey of the Einstein database

    Science.gov (United States)

    Caillault, Jean-Pierre; Magnani, Loris; Fryer, Chris

    1995-01-01

    In order to discern whether the high-latitude molecular clouds are regions of ongoing star formation, we have used X-ray emission as a tracer of youthful stars. The entire Einstein database yields 18 images which overlap 10 of the clouds mapped partially or completely in the CO (1-0) transition, providing a total of approximately 6 deg squared of overlap. Five previously unidentified X-ray sources were detected: one has an optical counterpart which is a pre-main-sequence (PMS) star, and two have normal main-sequence stellar counterparts, while the other two are probably extragalactic sources. The PMS star is located in a high Galactic latitude Lynds dark cloud, so this result is not too suprising. The translucent clouds, though, have yet to reveal any evidence of star formation.

  2. Seismic analysis of four solar-like stars observed during more than eight months by Kepler

    DEFF Research Database (Denmark)

    Mathur, S.; L. Campante, T.; Handberg, R.

    2011-01-01

    Having started science operations in May 2009, the Kepler photometer has been able to provide exquisite data of solar-like stars. Five out of the 42 stars observed continuously during the survey phase show evidence of oscillations, even though they are rather faint (magnitudes from 10.5 to 12). I......). In this paper, we present an overview of the results of the seismic analysis of 4 of these stars observed during more than eight months....

  3. Seismic Analysis of Four Solar-like Stars Observed during More Than Eight Months by Kepler

    Science.gov (United States)

    Mathur, S.; Campante, T. L.; Handberg, R.; García, R. A.; Appourchaux, T.; Bedding, T. R.; Mosser, B.; Chaplin, W. J.; Ballot, J.; Benomar, O.; Bonanno, A.; Corsaro, E.; Gaulme, P.; Hekker, S.; Régulo, C.; Salabert, D.; Verner, G.; White, T. R.; Brandão, I. M.; Creevey, O. L.; Dogan, G.; Bazot, M.; Cunha, M. S.; Elsworth, Y.; Huber, D.; Hale, S. J.; Houdek, G.; Karoff, C.; Lundkvist, M.; Metcalfe, T. S.; Molenda-Zakowicz, J.; Monteiro, M. J. P. F. G.; Thompson, M. J.; Stello, D.; Christensen-Dalsgaard, J.; Gilliland, R. L.; Kawaler, S. D.; Kjeldsen, H.; Clarke, B. D.; Girouard, F. R.; Hall, J. R.; Quintana, E. V.; Sanderfer, D. T.; Seader, S. E.

    2012-09-01

    Having started science operations in May 2009, the Kepler photometer has been able to provide exquisite data for solar-like stars. Five out of the 42 stars observed continuously during the survey phase show evidence of oscillations, even though they are rather faint (magnitudes from 10.5 to 12). In this paper, we present an overview of the results of the seismic analysis of 4 of these stars observed during more than eight months.

  4. Verifying reddening and extinction for Gaia DR1 TGAS main sequence stars

    Science.gov (United States)

    Gontcharov, George A.; Mosenkov, Aleksandr V.

    2017-12-01

    We compare eight sources of reddening and extinction estimates for approximately 60 000 Gaia DR1 Tycho-Gaia Astrometric Solution (TGAS) main sequence stars younger than 3 Gyr with a relative error of the Gaia parallax less than 0.1. For the majority of the stars, the best 2D dust emission-based reddening maps show considerable differences between the reddening to infinity and the one calculated to the stellar distance using the barometric law of the dust distribution. This proves that the majority of the TGAS stars are embedded in the Galactic dust layer and a proper 3D treatment of the reddening/extinction is required to calculate their dereddened colours and absolute magnitudes reliably. Sources with 3D estimates of reddening are tested in their ability to put the stars among the PARSEC and MIST theoretical isochrones in the Hertzsprung-Russell diagram based on the precise Gaia, Tycho-2, 2MASS and WISE photometry. Only the reddening/extinction estimates by Arenou et al. and Gontcharov, being appropriate for nearby stars within 280 pc, provide both the minimal number of outliers bluer than any reasonable isochrone and the correct number of stars younger than 3 Gyr in agreement with the Besançon Galaxy model.

  5. Star Masses and Star-Planet Distances for Earth-like Habitability.

    Science.gov (United States)

    Waltham, David

    2017-01-01

    This paper presents statistical estimates for the location and duration of habitable zones (HZs) around stars of different mass. The approach is based upon the assumption that Earth's location, and the Sun's mass, should not be highly atypical of inhabited planets. The results support climate-model-based estimates for the location of the Sun's HZ except models giving a present-day outer-edge beyond 1.64 AU. The statistical approach also demonstrates that there is a habitability issue for stars smaller than 0.65 solar masses since, otherwise, Earth would be an extremely atypical inhabited world. It is difficult to remove this anomaly using the assumption that poor habitability of planets orbiting low-mass stars results from unfavorable radiation regimes either before, or after, their stars enter the main sequence. However, the anomaly is well explained if poor habitability results from tidal locking of planets in the HZs of small stars. The expected host-star mass for planets with intelligent life then has a 95% confidence range of 0.78 M ⊙ planets with at least simple life is 0.57 M ⊙  < M < 1.64 M ⊙ . Key Words: Habitability-Habitable zone-Anthropic-Red dwarfs-Initial mass function. Astrobiology 17, 61-77.

  6. Post-main-sequence Evolution of Icy Minor Planets. II. Water Retention and White Dwarf Pollution around Massive Progenitor Stars

    Energy Technology Data Exchange (ETDEWEB)

    Malamud, Uri; Perets, Hagai B., E-mail: uri.mal@tx.technion.ac.il, E-mail: hperets@physics.technion.ac.il [Department of Physics, Technion (Israel)

    2017-06-10

    Most studies suggest that the pollution of white dwarf (WD) atmospheres arises from the accretion of minor planets, but the exact properties of polluting material, and in particular the evidence for water in some cases, are not yet understood. Here we study the water retention of small icy bodies in exo-solar planetary systems, as their respective host stars evolve through and off the main sequence and eventually become WDs. We explore, for the first time, a wide range of star masses and metallicities. We find that the mass of the WD progenitor star is of crucial importance for the retention of water, while its metallicity is relatively unimportant. We predict that minor planets around lower-mass WD progenitors would generally retain more water and would do so at closer distances from the WD than compared with high-mass progenitors. The dependence of water retention on progenitor mass and other parameters has direct implications for the origin of observed WD pollution, and we discuss how our results and predictions might be tested in the future as more observations of WDs with long cooling ages become available.

  7. X-ray sources in regions of star formation. I. The naked T Tauri stars

    International Nuclear Information System (INIS)

    Walter, F.M.

    1986-01-01

    Einstein X-ray observations of regions of active star formation in Taurus, Ophiuchus, and Corona Australis show a greatly enhanced surface density of stellar X-ray sources over that seen in other parts of the sky. Many of the X-ray sources are identified with low-mass, pre-main-sequence stars which are not classical T Tauri stars. The X-ray, photometric, and spectroscopic data for these stars are discussed. Seven early K stars in Oph and CrA are likely to be 1-solar-mass post-T Tauri stars with ages of 10-million yr. The late K stars in Taurus are not post-T Tauri, but naked T Tauri stars, which are coeval with the T Tauri stars, differing mainly in the lack of a circumstellar envelope. 72 references

  8. THE MASS-DEPENDENCE OF ANGULAR MOMENTUM EVOLUTION IN SUN-LIKE STARS

    International Nuclear Information System (INIS)

    Matt, Sean P.; Baraffe, Isabelle; Chabrier, Gilles; Brun, A. Sacha; Bouvier, Jérôme

    2015-01-01

    To better understand the observed distributions of the rotation rate and magnetic activity of Sun-like and low-mass stars, we derive a physically motivated scaling for the dependence of the stellar wind torque on the Rossby number. The torque also contains an empirically derived scaling with stellar mass (and radius), which provides new insight into the mass-dependence of stellar magnetic and wind properties. We demonstrate that this new formulation explains why the lowest mass stars are observed to maintain rapid rotation for much longer than solar-mass stars, and simultaneously why older populations exhibit a sequence of slowly rotating stars, in which the low-mass stars rotate more slowly than solar-mass stars. The model also reproduces some previously unexplained features in the period-mass diagram for the Kepler field, notably: the particular shape of the ''upper envelope'' of the distribution, suggesting that ∼95% of Kepler field stars with measured rotation periods are younger than ∼4 Gyr; and the shape of the ''lower envelope'', corresponding to the location where stars transition between magnetically saturated and unsaturated regimes

  9. AN OBJECTIVE DEFINITION FOR THE MAIN SEQUENCE OF STAR-FORMING GALAXIES

    Energy Technology Data Exchange (ETDEWEB)

    Renzini, Alvio [INAF—Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, I-35122 Padova (Italy); Peng, Ying-jie, E-mail: alvio.renzini@oapd.inaf.it, E-mail: y.peng@mrao.cam.ac.uk [Cavendish Laboratory, University of Cambridge, 19 J. J. Thomson Avenue, Cambridge CB3 0HE (United Kingdom)

    2015-03-10

    The main sequence (MS) of star-forming (SF) galaxies plays a fundamental role in driving galaxy evolution and our efforts to understand it. However, different studies find significant differences in the normalization, slope, and shape of the MS. These discrepancies arise mainly from the different selection criteria adopted to isolate SF galaxies, which may include or exclude galaxies with a specific star formation rate (SFR) substantially below the MS value. To obviate this limitation of all current criteria, we propose an objective definition of the MS that does not rely at all on a pre-selection of SF galaxies. Constructing the 3D SFR–mass–number plot, the MS is then defined as the ridge line of the SF peak, as illustrated with various figures. The advantages of such a definition are manifold. If generally adopted, it will facilitate the inter-comparison of results from different groups using the same SFR and stellar mass diagnostics, or it will highlight the relative systematics of different diagnostics. All of this could help to understand MS galaxies as systems in a quasi-steady state equilibrium and would also provide a more objective criterion for identifying quenching galaxies.

  10. AN OBJECTIVE DEFINITION FOR THE MAIN SEQUENCE OF STAR-FORMING GALAXIES

    International Nuclear Information System (INIS)

    Renzini, Alvio; Peng, Ying-jie

    2015-01-01

    The main sequence (MS) of star-forming (SF) galaxies plays a fundamental role in driving galaxy evolution and our efforts to understand it. However, different studies find significant differences in the normalization, slope, and shape of the MS. These discrepancies arise mainly from the different selection criteria adopted to isolate SF galaxies, which may include or exclude galaxies with a specific star formation rate (SFR) substantially below the MS value. To obviate this limitation of all current criteria, we propose an objective definition of the MS that does not rely at all on a pre-selection of SF galaxies. Constructing the 3D SFR–mass–number plot, the MS is then defined as the ridge line of the SF peak, as illustrated with various figures. The advantages of such a definition are manifold. If generally adopted, it will facilitate the inter-comparison of results from different groups using the same SFR and stellar mass diagnostics, or it will highlight the relative systematics of different diagnostics. All of this could help to understand MS galaxies as systems in a quasi-steady state equilibrium and would also provide a more objective criterion for identifying quenching galaxies

  11. CALIBRATING CONVECTIVE PROPERTIES OF SOLAR-LIKE STARS IN THE KEPLER FIELD OF VIEW

    Energy Technology Data Exchange (ETDEWEB)

    Bonaca, Ana; Tanner, Joel D.; Basu, Sarbani [Department of Astronomy, Yale University, P.O. Box 208101, New Haven, CT 06520-8101 (United States); Chaplin, William J.; Metcalfe, Travis S.; Christensen-Dalsgaard, Jorgen; Garcia, Rafael A.; Mathur, Savita [Kavli Institute for Theoretical Physics, Kohn Hall, University of California, Santa Barbara, CA 93106 (United States); Monteiro, Mario J. P. F. G.; Campante, Tiago L. [Centro de Astrofisica and Faculdade de Ciencias, Universidade do Porto, Rua das Estrelas, 4150-762 Porto (Portugal); Ballot, Jerome [CNRS, Institut de Recherche en Astrophysique et Planetologie, 14 avenue Edouard Belin, F-31400 Toulouse (France); Bedding, Timothy R.; Corsaro, Enrico [Sydney Institute for Astronomy (SIfA), School of Physics, University of Sydney, NSW 2006 (Australia); Bonanno, Alfio [INAF-Osservatorio Astrofisico di Catania, Via S.Sofia 78, I-95123 Catania (Italy); Broomhall, Anne-Marie; Elsworth, Yvonne [School of Physics and Astronomy, University of Birmingham, Edgbaston, Birmingham, B15 2TT (United Kingdom); Bruntt, Hans; Karoff, Christoffer; Kjeldsen, Hans [Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, DK-8000 Aarhus C (Denmark); Hekker, Saskia, E-mail: ana.bonaca@yale.edu, E-mail: sarbani.basu@yale.edu, E-mail: joel.tanner@yale.edu [Astronomical Institute Anton Pannekoek, University of Amsterdam, Science Park 904, 1098-XH Amsterdam (Netherlands); and others

    2012-08-10

    Stellar models generally use simple parameterizations to treat convection. The most widely used parameterization is the so-called mixing-length theory where the convective eddy sizes are described using a single number, {alpha}, the mixing-length parameter. This is a free parameter, and the general practice is to calibrate {alpha} using the known properties of the Sun and apply that to all stars. Using data from NASA's Kepler mission we show that using the solar-calibrated {alpha} is not always appropriate, and that in many cases it would lead to estimates of initial helium abundances that are lower than the primordial helium abundance. Kepler data allow us to calibrate {alpha} for many other stars and we show that for the sample of stars we have studied, the mixing-length parameter is generally lower than the solar value. We studied the correlation between {alpha} and stellar properties, and we find that {alpha} increases with metallicity. We therefore conclude that results obtained by fitting stellar models or by using population-synthesis models constructed with solar values of {alpha} are likely to have large systematic errors. Our results also confirm theoretical expectations that the mixing-length parameter should vary with stellar properties.

  12. On the Statistical Properties of the Lower Main Sequence

    International Nuclear Information System (INIS)

    Angelou, George C.; Bellinger, Earl P.; Hekker, Saskia; Basu, Sarbani

    2017-01-01

    Astronomy is in an era where all-sky surveys are mapping the Galaxy. The plethora of photometric, spectroscopic, asteroseismic, and astrometric data allows us to characterize the comprising stars in detail. Here we quantify to what extent precise stellar observations reveal information about the properties of a star, including properties that are unobserved, or even unobservable. We analyze the diagnostic potential of classical and asteroseismic observations for inferring stellar parameters such as age, mass, and radius from evolutionary tracks of solar-like oscillators on the lower main sequence. We perform rank correlation tests in order to determine the capacity of each observable quantity to probe structural components of stars and infer their evolutionary histories. We also analyze the principal components of classic and asteroseismic observables to highlight the degree of redundancy present in the measured quantities and demonstrate the extent to which information of the model parameters can be extracted. We perform multiple regression using combinations of observable quantities in a grid of evolutionary simulations and appraise the predictive utility of each combination in determining the properties of stars. We identify the combinations that are useful and provide limits to where each type of observable quantity can reveal information about a star. We investigate the accuracy with which targets in the upcoming TESS and PLATO missions can be characterized. We demonstrate that the combination of observations from GAIA and PLATO will allow us to tightly constrain stellar masses, ages, and radii with machine learning for the purposes of Galactic and planetary studies.

  13. On the Statistical Properties of the Lower Main Sequence

    Energy Technology Data Exchange (ETDEWEB)

    Angelou, George C.; Bellinger, Earl P.; Hekker, Saskia [Max-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-Weg 3, D-37077 Göttingen (Germany); Basu, Sarbani [Department of Astronomy, Yale University, New Haven, CT 06520 (United States)

    2017-04-20

    Astronomy is in an era where all-sky surveys are mapping the Galaxy. The plethora of photometric, spectroscopic, asteroseismic, and astrometric data allows us to characterize the comprising stars in detail. Here we quantify to what extent precise stellar observations reveal information about the properties of a star, including properties that are unobserved, or even unobservable. We analyze the diagnostic potential of classical and asteroseismic observations for inferring stellar parameters such as age, mass, and radius from evolutionary tracks of solar-like oscillators on the lower main sequence. We perform rank correlation tests in order to determine the capacity of each observable quantity to probe structural components of stars and infer their evolutionary histories. We also analyze the principal components of classic and asteroseismic observables to highlight the degree of redundancy present in the measured quantities and demonstrate the extent to which information of the model parameters can be extracted. We perform multiple regression using combinations of observable quantities in a grid of evolutionary simulations and appraise the predictive utility of each combination in determining the properties of stars. We identify the combinations that are useful and provide limits to where each type of observable quantity can reveal information about a star. We investigate the accuracy with which targets in the upcoming TESS and PLATO missions can be characterized. We demonstrate that the combination of observations from GAIA and PLATO will allow us to tightly constrain stellar masses, ages, and radii with machine learning for the purposes of Galactic and planetary studies.

  14. Observations spotted solar type stars in Pleiades

    International Nuclear Information System (INIS)

    Magnitskij, A.K.

    1987-01-01

    The september - october 1986 observations discovered periodic light variations in three solar type stars in the Pleiades cluster: Hz 296 (0.8 M Sun ), Hz152(0.91 M Sun ) and Hz739(1.15 M Sun ). Periods and amplitudes are accordingly 2 d and 0 m .11, 4 d .12 and 0 m .07, 2 d .70 and 0 m .05. Considerable light variations of these stars in Pleiades are due to the rotation of spotted stars. Contrast spots of solar type stars likely exist when stars are young and rapidly rotate

  15. Radio-emission of pre-main sequence stars of the Rho Ophiuchi cloud: observations and interpretation

    International Nuclear Information System (INIS)

    Andre, P.

    1987-11-01

    Observations of the radio continuum emission of a young star population have been made at VLA on the whole molecular cloud Rho Ophiuchi, one of the closest site of star formation. A dozen of stellar sources have been detected. Radio emission of some identified objects seems to have a magnetic nature and be produced by gyrosynchrotron mechanism. In particular, one of the sources shows a radio radiation circularly polarized; two other stars have a radiation strongly variable probably due to magnetic eruptions more important than those detected in X radiation. More generally, radio observations select probably a specific population of young stars characterized by magnetic field presence extended on several stellar radii and by absence of dense circumstellar environment. Spatial distribution of these objects suggest, they are younger than most of the pre-main sequence stars [fr

  16. Did A Planet Survive A Post-Main Sequence Evolutionary Event?

    Science.gov (United States)

    Sorber, Rebecca; Jang-Condell, Hannah; Zimmerman, Mara

    2018-06-01

    The GL86 is star system approximately 10 pc away with a main sequence K- type ~ 0.77 M⊙ star (GL 86A) with a white dwarf ~0.49 M⊙ companion (GL86 B). The system has a ~ 18.4 AU semi-major axis, an orbital period of ~353 yrs, and an eccentricity of ~ 0.39. A 4.5 MJ planet orbits the main sequence star with a semi-major axis of 0.113 AU, an orbital period of 15.76 days, in a near circular orbit with an eccentricity of 0.046. If we assume that this planet was formed during the time when the white dwarf was a main sequence star, it would be difficult for the planet to have remained in a stable orbit during the post-main sequence evolution of GL86 B. The post-main sequence evolution with planet survival will be examined by modeling using the program Mercury (Chambers 1999). Using the model, we examine the origins of the planet: whether it formed before or after the post-main sequence evolution of GL86B. The modeling will give us insight into the dynamical evolution of, not only, the binary star system, but also the planet’s life cycle.

  17. Spectroscopic and asteroseismic analysis of the remarkable main-sequence A star KIC 11145123

    Science.gov (United States)

    Takada-Hidai, Masahide; Kurtz, Donald W.; Shibahashi, Hiromoto; Murphy, Simon J.; Takata, Masao; Saio, Hideyuki; Sekii, Takashi

    2017-10-01

    A spectroscopic analysis was carried out to clarify the properties of KIC 11145123 - the first main-sequence star with a directly measured core-to-surface rotation profile - based on spectra observed with the High Dispersion Spectrograph (HDS) of the Subaru telescope. The atmospheric parameters (Teff = 7600 K, log g = 4.2, ξ = 3.1 km s-1 and [Fe/H] = -0.71 dex), the radial and rotation velocities, and elemental abundances were obtained by analysing line strengths and fitting line profiles, which were calculated with a 1D LTE model atmosphere. The main properties of KIC 11145123 are: (1) a low [Fe/H] = -0.71 ± 0.11 dex and a high radial velocity of -135.4 ± 0.2 km s-1. These are remarkable among late-A stars. Our best asteroseismic models with this low [Fe/H] have slightly high helium abundance and low masses of 1.4 M⊙. All of these results strongly suggest that KIC 11145123 is a Population II blue straggler; (2) the projected rotation velocity confirms the asteroseismically predicted slow rotation of the star; (3) comparisons of abundance patterns between KIC 11145123 and Am, Ap, and blue stragglers show that KIC 11145123 is neither an Am star nor an Ap star, but has abundances consistent with a blue straggler. We conclude that the remarkably long 100-d rotation period of this star is a consequence of it being a blue straggler, but both pathways for the formation of blue stragglers - merger and mass loss in a binary system - pose difficulties for our understanding of the exceedingly slow rotation. In particular, we show that there is no evidence of any secondary companion star, and we put stringent limits on the possible mass of any such purported companion through the phase modulation technique.

  18. Spectroscopic and asteroseismic analysis of the remarkable main-sequence A star KIC 11145123

    DEFF Research Database (Denmark)

    Takada-Hidai, Masahide; Kurtz, Donald W.; Shibahashi, Hiromoto

    2017-01-01

    A spectroscopic analysis was carried out to clarify the properties of KIC 11145123 - the first main-sequence star with a directly measured core-to-surface rotation profile - based on spectra observed with the High Dispersion Spectrograph (HDS) of the Subaru telescope. The atmospheric parameters (T......-eff = 7600 K, log g = 4.2, xi = 3.1 kms(-1) and [Fe/H] = -0.71 dex), the radial and rotation velocities, and elemental abundances were obtained by analysing line strengths and fitting line profiles, which were calculated with a 1D LTE model atmosphere. The main properties of KIC 11145123 are: (1) a low [Fe...

  19. Systematic main sequence photometry of globular cluster stars for age determination

    International Nuclear Information System (INIS)

    Alcaino, G.; Liller, W.

    1984-01-01

    The individual photometric study of the coeval stars in globular clusters presents one of the best observational tests of the stellar evolution theory. Our own globular cluster system provides fundamental clues to the dynamical and chemical evolutionary history of the galaxy, and the study of their ages give a lower limit to the age of the galaxy as well as to that of the universe. The authors have undertaken a systematic research program, and discuss the ages deduced by fitting main sequence photometry to theoretical isochrones of six galactic globular clusters: M4, M22, M30, NGC 288, NGC 3201 and NGC 6397. (Auth.)

  20. Additional measurements of pre-main-sequence stellar rotation

    International Nuclear Information System (INIS)

    Hartmann, L.; Stauffer, J.R.

    1989-01-01

    New rotational-velocity measurements for pre-main-sequence stars in the Taurus-Auriga molecular cloud are reported. Rotational velocities or upper limits of 10 km/s are now available for 90 percent of the T Tauri stars with V less than 14.7 in the catalog of Cohen and Kuhi. Measurements of 'continuum emission' stars, thought to be accreting high-angular-momentum material from a circumstellar disk, show that these objects are not especially rapid rotators. The results confirm earlier findings that angular-momentum loss proceeds very efficiently in the earliest stages of star formation, and suggest that stars older than about one million yr contract to the main sequence at nearly constant angular momentum. The slow rotation of T Tauri stars probably requires substantial angular-momentum loss via a magnetically coupled wind. 35 references

  1. STELLAR AGES AND CONVECTIVE CORES IN FIELD MAIN-SEQUENCE STARS: FIRST ASTEROSEISMIC APPLICATION TO TWO KEPLER TARGETS

    Energy Technology Data Exchange (ETDEWEB)

    Silva Aguirre, V.; Christensen-Dalsgaard, J.; Chaplin, W. J. [Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, DK-8000 Aarhus C (Denmark); Basu, S.; Deheuvels, S. [Department of Astronomy, Yale University, P.O. Box 208101, New Haven, CT 06520-8101 (United States); Brandao, I. M.; Cunha, M. S.; Sousa, S. G. [Centro de Astrofisica and Faculdade de Ciencias, Universidade do Porto, Rua das Estrelas, 4150-762 Porto (Portugal); Dogan, G. [High Altitude Observatory, NCAR, P.O. Box 3000, Boulder, CO 80307 (United States); Metcalfe, T. S. [Space Science Institute, Boulder, CO 80301 (United States); Serenelli, A. M.; Garcia, R. A. [Kavli Institute for Theoretical Physics, Santa Barbara, CA 93106 (United States); Ballot, J. [Institut de Recherche en Astrophysique et Planetologie, CNRS, 14 avenue Edouard Belin, F-31400 Toulouse (France); Weiss, A. [Max Planck Institute for Astrophysics, Karl-Schwarzschild-Str. 1, D-85748 Garching bei Muenchen (Germany); Appourchaux, T. [Institut d' Astrophysique Spatiale, Universite Paris Sud-CNRS (UMR8617) Batiment 121, F-91405 Orsay Cedex (France); Casagrande, L. [Research School of Astronomy and Astrophysics, Mount Stromlo Observatory, The Australian National University, ACT 2611 (Australia); Cassisi, S. [INAF-Astronomical Observatory of Teramo, Via M. Maggini sn, I-64100 Teramo (Italy); Creevey, O. L. [Laboratoire Lagrange, Universite de Nice Sophia-Antipolis, CNRS, I-06300 Nice, France. (France); Lebreton, Y. [Observatoire de Paris, GEPI, CNRS UMR 8111, F-92195 Meudon (France); Noels, A. [Institute of Astrophysics and Geophysics, University of Liege, B-4000 Liege (Belgium); and others

    2013-06-01

    Using asteroseismic data and stellar evolution models we obtain the first detection of a convective core in a Kepler field main-sequence star, putting a stringent constraint on the total size of the mixed zone and showing that extra mixing beyond the formal convective boundary exists. In a slightly less massive target the presence of a convective core cannot be conclusively discarded, and thus its remaining main-sequence lifetime is uncertain. Our results reveal that best-fit models found solely by matching individual frequencies of oscillations corrected for surface effects do not always properly reproduce frequency combinations. Moreover, slightly different criteria to define what the best-fit model is can lead to solutions with similar global properties but very different interior structures. We argue that the use of frequency ratios is a more reliable way to obtain accurate stellar parameters, and show that our analysis in field main-sequence stars can yield an overall precision of 1.5%, 4%, and 10% in radius, mass, and age, respectively. We compare our results with those obtained from global oscillation properties, and discuss the possible sources of uncertainties in asteroseismic stellar modeling where further studies are still needed.

  2. Formation of a contact binary star system

    International Nuclear Information System (INIS)

    Mullen, E.F.F.

    1974-01-01

    The process of forming a contact binary star system is investigated in the light of current knowledge of the W Ursae Majoris type eclipsing binaries and the current rotational braking theories for contracting stars. A preliminary stage of mass transfer is proposed and studied through the use of a computer program which calculates evolutionary model sequences. The detailed development of both stars is followed in these calculations, and findings regarding the internal structure of the star which is receiving the mass are presented. Relaxation of the mass-gaining star is also studied; for these stars of low mass and essentially zero age, the star eventually settles to a state very similar to a zero-age main sequence star of the new mass. A contact system was formed through these calculations; it exhibits the general properties of a W Ursae Majoris system. The initial masses selected for the calculation were 1.29 M/sub solar mass/ and 0.56 M/sub solar mass/. An initial mass transfer rate of about 10 -10 solar masses per year gradually increased to about 10 -8 solar masses per year. After about 2.5 x 10 7 years, the less massive star filled its Roche lobe and an initial contact system was obtained. The final masses were 1.01359 M/sub solar mass/ and 0.83641 M/sub solar mass/. The internal structure of the secondary component is considerably different from that of a main sequence star of the same mass

  3. Young solar-type stars evolution: the lithium and seismology contributions

    International Nuclear Information System (INIS)

    Piau, Laurent Eric

    2001-01-01

    This PhD thesis is devoted to young low-mass stars. We modeled many of them since their formation until the solar age covering the range between 0.65 and 1.4 solar masses and metallicity values ranging from -0.1 to 0.1 dex. The theoretical computations are related to observations in nearby open-clusters: Hyades, Pleiades... This comparison demonstrates that the lithium evolution is still poorly understood in such stars. In stellar interiors, this nuclide is destroyed by nuclear processes at low temperatures. Its surface abundance evolution traduces mixing phenomena between surface and deeper layers and therefore allows a direct insight into stellar structure and evolution. Both of which depend on microscopic and macroscopic physical phenomena whose effects we systematically examine. As regards microphysics we mainly concentrate upon changes in metallicity, in distribution among metals and their consequences on stellar opacity. We also address atmospheric models while the star still lies close to its Hayashi track. Accretion and convective parameters are the macroscopic phenomena we address during pre-main sequence. The rotational effects are considered along the entire evolution including the much realistic rotation laws. The last part of this PhD thesis makes use of seismology. Today this Discipline allows direct probing of the solar internal structure and motions. Its future application in the realm of stars will substantially improve their understanding. We derive here some relevant seismic variables for the understanding of stellar evolution. Then we show how this powerful tool permits to determine fundamental stellar parameters such as the mass or the helium fraction. (author) [fr

  4. Circumstellar Material on and off the Main Sequence

    Science.gov (United States)

    Steele, Amy; Debes, John H.; Deming, Drake

    2017-06-01

    There is evidence of circumstellar material around main sequence, giant, and white dwarf stars that originates from the small-body population of planetary systems. These bodies tell us something about the chemistry and evolution of protoplanetary disks and the planetary systems they form. What happens to this material as its host star evolves off the main sequence, and how does that inform our understanding of the typical chemistry of rocky bodies in planetary systems? In this talk, I will discuss the composition(s) of circumstellar material on and off the main sequence to begin to answer the question, “Is Earth normal?” In particular, I look at three types of debris disks to understand the typical chemistry of planetary systems—young debris disks, debris disks around giant stars, and dust around white dwarfs. I will review the current understanding on how to infer dust composition for each class of disk, and present new work on constraining dust composition from infrared excesses around main sequence and giant stars. Finally, dusty and polluted white dwarfs hold a unique key to our understanding of the composition of rocky bodies around other stars. In particular, I will discuss WD1145+017, which has a transiting, disintegrating planetesimal. I will review what we know about this system through high speed photometry and spectroscopy and present new work on understanding the complex interplay of physics that creates white dwarf pollution from the disintegration of rocky bodies.

  5. The Solar Neighborhood. XLI. A Study of the Wide Main Sequence for M Dwarfs—Long-term Photometric Variability

    Energy Technology Data Exchange (ETDEWEB)

    Clements, Tiffany D.; Jao, Wei-Chun; Silverstein, Michele L. [Department of Physics and Astronomy, Georgia State University, Atlanta, GA 30303 (United States); Henry, Todd J.; Hosey, Altonio D. [RECONS Institute, Chambersburg, PA 17201 (United States); Winters, Jennifer G. [Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138 (United States); Dieterich, Sergio B. [Carnegie Institution for Science, Washington, DC 20015 (United States); Riedel, Adric R., E-mail: pewett@astro.gsu.edu, E-mail: jao@astro.gsu.edu, E-mail: silverstein@astro.gsu.edu, E-mail: toddhenry28@gmail.com, E-mail: altoniohosey@gmail.com, E-mail: jennifer.winters@cfa.harvard.edu, E-mail: sdieterich@carnegiescience.edu, E-mail: adric.riedel@gmail.com [Space Telescope Science Institute, Baltimore, MD 21218 (United States)

    2017-09-01

    We report findings from a long-term photometric variability study of M dwarfs carried out at the SMARTS 0.9 m telescope at the Cerro Tololo Inter-American Observatory. As part of a multi-faceted effort to investigate the range of luminosities of M dwarfs of a given color on the Hertzsprung–Russell Diagram, 76 M dwarfs have been observed for 3–17 years in the Johnson–Kron–Cousins V band. We find that stars elevated above the center of the main sequence distribution tend to have higher levels of variability, likely caused by magnetic activity, than their fainter counterparts below the center. This study provides insight into how the long-term magnetic activity of these stars may be affecting their sizes, luminosities, and thus positions on the H-R Diagram.

  6. THE 'MAIN SEQUENCE' OF EXPLOSIVE SOLAR ACTIVE REGIONS: DISCOVERY AND INTERPRETATION

    Energy Technology Data Exchange (ETDEWEB)

    Falconer, David A; Moore, Ronald L; Adams, Mitzi [Space Science Office, VP62, Marshall Space Flight Center, Huntsville, AL 35812 (United States); Gary, G. Allen [Center for Space Plasma and Aeronomic Research, University of Alabama in Huntsville, Huntsville, AL 35899 (United States)], E-mail: David.falconer@msfc.nasa.gov

    2009-08-01

    We examine the location and distribution of the production of coronal mass ejections (CMEs) and major flares by sunspot active regions in the phase space of two whole-active-region magnetic quantities measured from 1897 SOHO/MDI magnetograms. These magnetograms track the evolution of 44 active regions across the central disk of radius 0.5 R {sub Sun}. The two quantities are {sup L}WL{sub SG}, a gauge of the total free energy in an active region's magnetic field, and {sup L}{phi}, a measure of the active region's total magnetic flux. From these data and each active region's history of production of CMEs, X flares, and M flares, we find (1) that CME/flare-productive active regions are concentrated in a straight-line 'main sequence' in (log {sup L}WL{sub SG}, log {sup L}{phi}) space, (2) that main-sequence active regions have nearly their maximum attainable free magnetic energy, and (3) evidence that this arrangement plausibly results from equilibrium between input of free energy to an explosive active region's magnetic field in the chromosphere and corona by contortion of the field via convection in and below the photosphere and loss of free energy via CMEs, flares, and coronal heating, an equilibrium between energy gain and loss that is analogous to that of the main sequence of hydrogen-burning stars in (mass, luminosity) space.

  7. THE 'MAIN SEQUENCE' OF EXPLOSIVE SOLAR ACTIVE REGIONS: DISCOVERY AND INTERPRETATION

    International Nuclear Information System (INIS)

    Falconer, David A.; Moore, Ronald L.; Adams, Mitzi; Gary, G. Allen

    2009-01-01

    We examine the location and distribution of the production of coronal mass ejections (CMEs) and major flares by sunspot active regions in the phase space of two whole-active-region magnetic quantities measured from 1897 SOHO/MDI magnetograms. These magnetograms track the evolution of 44 active regions across the central disk of radius 0.5 R Sun . The two quantities are L WL SG , a gauge of the total free energy in an active region's magnetic field, and L Φ, a measure of the active region's total magnetic flux. From these data and each active region's history of production of CMEs, X flares, and M flares, we find (1) that CME/flare-productive active regions are concentrated in a straight-line 'main sequence' in (log L WL SG , log L Φ) space, (2) that main-sequence active regions have nearly their maximum attainable free magnetic energy, and (3) evidence that this arrangement plausibly results from equilibrium between input of free energy to an explosive active region's magnetic field in the chromosphere and corona by contortion of the field via convection in and below the photosphere and loss of free energy via CMEs, flares, and coronal heating, an equilibrium between energy gain and loss that is analogous to that of the main sequence of hydrogen-burning stars in (mass, luminosity) space.

  8. Evolution models of helium white dwarf-main-sequence star merger remnants: the mass distribution of single low-mass white dwarfs

    Science.gov (United States)

    Zhang, Xianfei; Hall, Philip D.; Jeffery, C. Simon; Bi, Shaolan

    2018-02-01

    It is not known how single white dwarfs with masses less than 0.5Msolar -- low-mass white dwarfs -- are formed. One way in which such a white dwarf might be formed is after the merger of a helium-core white dwarf with a main-sequence star that produces a red giant branch star and fails to ignite helium. We use a stellar-evolution code to compute models of the remnants of these mergers and find a relation between the pre-merger masses and the final white dwarf mass. Combining our results with a model population, we predict that the mass distribution of single low-mass white dwarfs formed through this channel spans the range 0.37 to 0.5Msolar and peaks between 0.45 and 0.46Msolar. Helium white dwarf--main-sequence star mergers can also lead to the formation of single helium white dwarfs with masses up to 0.51Msolar. In our model the Galactic formation rate of single low-mass white dwarfs through this channel is about 8.7X10^-3yr^-1. Comparing our models with observations, we find that the majority of single low-mass white dwarfs (<0.5Msolar) are formed from helium white dwarf--main-sequence star mergers, at a rate which is about $2$ per cent of the total white dwarf formation rate.

  9. Lithium abundances, K line emission and ages of nearby solar type stars

    International Nuclear Information System (INIS)

    Duncan, D.K.

    1981-01-01

    Li abundances and chromospheric emission fluxes measured in the core of the Ca II K line have been determined in over 100 field F5--G5 dwarfs and subgiants. Although both quantities are known statistically to decrease in older stars, the correlation between them is not good. In particular, there are a number of anomalous solar type stars which show high Li abundances and very little chromospheric flux; the converse is rare. This might be understood if the intensity of chromospheric emission undergoes a sudden decrease when stars reach an age of 1 to 2 x 10 9 years, before much Li depletion occurs. Some of the anomalous stars appear to be older than this, however. Such stars must have preserved their Li from main sequence destruction

  10. Advanced evolution of a 15 solar mass star

    International Nuclear Information System (INIS)

    Endal, A.S.

    1974-01-01

    The evolution of a 15 solar mass star has been followed from the zero-age main sequence to the neon-ignition phase by use of the Henyey method for solving the equations of quasi-hydrostatic evolution. The detailed results of nucleosynthesis during carbon burning were calculated by a second-order, backwards-differencing scheme, with the effects of convection included in an approximate manner. The results of the evolution calculations and of the nucleosynthesis calculations are described and a detailed analysis of the effects of convection on nucleosynthesis is presented. The quiescent nature of evolution through the hydrogen, helium, and carbon burning stages is confirmed. Comparison with previous studies of the post-carbon burning evolution of massive stars shows that calculations in which degeneracy is neglected will not yield realistic results

  11. PROBABILITY OF CME IMPACT ON EXOPLANETS ORBITING M DWARFS AND SOLAR-LIKE STARS

    Energy Technology Data Exchange (ETDEWEB)

    Kay, C. [Solar Physics Laboratory, NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States); Opher, M.; Kornbleuth, M., E-mail: ckay@bu.edu [Astronomy Department, Boston University, Boston, MA 02215 (United States)

    2016-08-01

    Solar coronal mass ejections (CMEs) produce adverse space weather effects at Earth. Planets in the close habitable zone of magnetically active M dwarfs may experience more extreme space weather than at Earth, including frequent CME impacts leading to atmospheric erosion and leaving the surface exposed to extreme flare activity. Similar erosion may occur for hot Jupiters with close orbits around solar-like stars. We have developed a model, Forecasting a CME's Altered Trajectory (ForeCAT), which predicts a CME's deflection. We adapt ForeCAT to simulate CME deflections for the mid-type M dwarf V374 Peg and hot Jupiters with solar-type hosts. V374 Peg's strong magnetic fields can trap CMEs at the M dwarfs's Astrospheric Current Sheet, that is, the location of the minimum in the background magnetic field. Solar-type CMEs behave similarly, but have much smaller deflections and do not become trapped at the Astrospheric Current Sheet. The probability of planetary impact decreases with increasing inclination of the planetary orbit with respect to the Astrospheric Current Sheet: 0.5–5 CME impacts per day for M dwarf exoplanets, 0.05–0.5 CME impacts per day for solar-type hot Jupiters. We determine the minimum planetary magnetic field necessary to shield a planet's atmosphere from CME impacts. M dwarf exoplanets require values between tens and hundreds of Gauss. Hot Jupiters around a solar-type star, however, require a more reasonable <30 G. These values exceed the magnitude required to shield a planet from the stellar wind, suggesting that CMEs may be the key driver of atmospheric losses.

  12. PROBABILITY OF CME IMPACT ON EXOPLANETS ORBITING M DWARFS AND SOLAR-LIKE STARS

    International Nuclear Information System (INIS)

    Kay, C.; Opher, M.; Kornbleuth, M.

    2016-01-01

    Solar coronal mass ejections (CMEs) produce adverse space weather effects at Earth. Planets in the close habitable zone of magnetically active M dwarfs may experience more extreme space weather than at Earth, including frequent CME impacts leading to atmospheric erosion and leaving the surface exposed to extreme flare activity. Similar erosion may occur for hot Jupiters with close orbits around solar-like stars. We have developed a model, Forecasting a CME's Altered Trajectory (ForeCAT), which predicts a CME's deflection. We adapt ForeCAT to simulate CME deflections for the mid-type M dwarf V374 Peg and hot Jupiters with solar-type hosts. V374 Peg's strong magnetic fields can trap CMEs at the M dwarfs's Astrospheric Current Sheet, that is, the location of the minimum in the background magnetic field. Solar-type CMEs behave similarly, but have much smaller deflections and do not become trapped at the Astrospheric Current Sheet. The probability of planetary impact decreases with increasing inclination of the planetary orbit with respect to the Astrospheric Current Sheet: 0.5–5 CME impacts per day for M dwarf exoplanets, 0.05–0.5 CME impacts per day for solar-type hot Jupiters. We determine the minimum planetary magnetic field necessary to shield a planet's atmosphere from CME impacts. M dwarf exoplanets require values between tens and hundreds of Gauss. Hot Jupiters around a solar-type star, however, require a more reasonable <30 G. These values exceed the magnitude required to shield a planet from the stellar wind, suggesting that CMEs may be the key driver of atmospheric losses.

  13. DISCOVERY OF A RED GIANT WITH SOLAR-LIKE OSCILLATIONS IN AN ECLIPSING BINARY SYSTEM FROM KEPLER SPACE-BASED PHOTOMETRY

    International Nuclear Information System (INIS)

    Hekker, S.; Debosscher, J.; De Ridder, J.; Aerts, C.; Van Winckel, H.; Beck, P. G.; Blomme, J.; Huber, D.; Hidas, M. G.; Stello, D.; Bedding, T. R.; Gilliland, R. L.; Christensen-Dalsgaard, J.; Kjeldsen, H.; Brown, T. M.; Borucki, W. J.; Koch, D.; Jenkins, J. M.; Southworth, J.; Pigulski, A.

    2010-01-01

    Oscillating stars in binary systems are among the most interesting stellar laboratories, as these can provide information on the stellar parameters and stellar internal structures. Here we present a red giant with solar-like oscillations in an eclipsing binary observed with the NASA Kepler satellite. We compute stellar parameters of the red giant from spectra and the asteroseismic mass and radius from the oscillations. Although only one eclipse has been observed so far, we can already determine that the secondary is a main-sequence F star in an eccentric orbit with a semi-major axis larger than 0.5 AU and orbital period longer than 75 days.

  14. LINEAR RELATION FOR WIND-BLOWN BUBBLE SIZES OF MAIN-SEQUENCE OB STARS IN A MOLECULAR ENVIRONMENT AND IMPLICATION FOR SUPERNOVA PROGENITORS

    Energy Technology Data Exchange (ETDEWEB)

    Chen Yang; Zhou Ping [Department of Astronomy, Nanjing University, Nanjing 210093 (China); Chu Youhua [Department of Astronomy, University of Illinois at Urbana-Champaign, 1002 West Green Street, Urbana, IL 61801 (United States)

    2013-05-20

    We find a linear relationship between the size of a massive star's main-sequence bubble in a molecular environment and the star's initial mass: R{sub b} Almost-Equal-To 1.22 M/M{sub Sun} - 9.16 pc, assuming a constant interclump pressure. Since stars in the mass range of 8 to 25-30 M{sub Sun} will end their evolution in the red supergiant phase without launching a Wolf-Rayet wind, the main-sequence wind-blown bubbles are mainly responsible for the extent of molecular gas cavities, while the effect of the photoionization is comparatively small. This linear relation can thus be used to infer the masses of the massive star progenitors of supernova remnants (SNRs) that are discovered to evolve in molecular cavities, while few other means are available for inferring the properties of SNR progenitors. We have used this method to estimate the initial masses of the progenitors of eight SNRs: Kes 69, Kes 75, Kes 78, 3C 396, 3C 397, HC 40, Vela, and RX J1713-3946.

  15. UCLA, British astronomers discover wake of planet around nearby star. Strong evidence for solar system like ours

    CERN Multimedia

    2002-01-01

    "An international team of astronomers reports the first strong evidence for the existence of massive planets on wide orbits - like those of Saturn, Uranus and Neptune - around many stars. The new research provides some of the strongest evidence so far that solar systems similar to our own, or even larger, are likely to exist: (1 page).

  16. ON THE MULTIPLICITY OF THE ZERO-AGE MAIN-SEQUENCE O STAR HERSCHEL 36

    International Nuclear Information System (INIS)

    Arias, Julia I.; Barba, Rodolfo H.; Gamen, Roberto C.; Morrell, Nidia I.; Apellaniz, Jesus MaIz; Alfaro, Emilio J.; Sota, Alfredo; Walborn, Nolan R.; Bidin, Christian Moni

    2010-01-01

    We present the analysis of high-resolution optical spectroscopic observations of the zero-age main-sequence O star Herschel 36 spanning six years. This star is definitely a multiple system, with at least three components detected in its spectrum. Based on our radial-velocity (RV) study, we propose a picture of a close massive binary and a more distant companion, most probably in wide orbit about each other. The orbital solution for the binary, whose components we identify as O9 V and B0.5 V, is characterized by a period of 1.5415 ± 0.0006 days. With a spectral type O7.5 V, the third body is the most luminous component of the system and also presents RV variations with a period close to 498 days. Some possible hypotheses to explain the variability are briefly addressed and further observations are suggested.

  17. THE DUSTIEST POST-MAIN SEQUENCE STARS IN THE MAGELLANIC CLOUDS

    Energy Technology Data Exchange (ETDEWEB)

    Jones, Olivia C.; Meixner, Margaret; Roman-Duval, Julia [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Sargent, Benjamin A. [Center for Imaging Science and Laboratory for Multiwavelength Astrophysics, Rochester Institute of Technology, 54 Lomb Memorial Drive, Rochester, NY 14623 (United States); Boyer, Martha L. [Observational Cosmology Lab, Code 665, NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States); Sewiło, Marta [The Johns Hopkins University, Department of Physics and Astronomy, 366 Bloomberg Center, 3400 N. Charles Street, Baltimore, MD 21218 (United States); Hony, Sacha [Institut für Theoretische Astrophysik, Zentrum für Astronomie, Universitt Heidelberg, Albert-Ueberle-Str. 2, D-69120 Heidelberg (Germany)

    2015-10-01

    Using observations from the Herschel Inventory of The Agents of Galaxy Evolution (HERITAGE) survey of the Magellanic Clouds (MC), we have found 35 evolved stars and stellar end products that are bright in the far-infrared. These 28 (LMC) and 7 (SMC) sources were selected from the 529 evolved star candidates in the HERITAGE far-infrared point source catalogs. Our source identification method is based on spectral confirmation, spectral energy distribution characteristics, careful examination of the multiwavelength images and includes constraints on the luminosity, resulting in a thoroughly vetted list of evolved stars. These sources span a wide range in luminosity and hence initial mass. We found 13 low- to intermediate-mass evolved stars, including asymptotic giant branch (AGB) stars, post-AGB stars, planetary nebulae, and a symbiotic star. We also identify 10 high mass stars, including 4 of the 15 known B[e] stars in the MC, 3 extreme red supergiants that are highly enshrouded by dust, a Luminous Blue Variable, a Wolf–Rayet star, and two supernova remnants. Further, we report the detection of 9 probable evolved objects which were previously undescribed in the literature. These sources are likely to be among the dustiest evolved objects in the MC. The Herschel emission may either be due to dust produced by the evolved star or it may arise from swept-up interstellar medium material.

  18. IRAS 18153-1651: an H II region with a possible wind bubble blown by a young main-sequence B star

    Science.gov (United States)

    Gvaramadze, V. V.; Mackey, J.; Kniazev, A. Y.; Langer, N.; Chené, A.-N.; Castro, N.; Haworth, T. J.; Grebel, E. K.

    2017-04-01

    We report the results of spectroscopic observations and numerical modelling of the H II region IRAS 18153-1651. Our study was motivated by the discovery of an optical arc and two main-sequence stars of spectral type B1 and B3 near the centre of IRAS 18153-1651. We interpret the arc as the edge of the wind bubble (blown by the B1 star), whose brightness is enhanced by the interaction with a photoevaporation flow from a nearby molecular cloud. This interpretation implies that we deal with a unique case of a young massive star (the most massive member of a recently formed low-mass star cluster) caught just tens of thousands of years after its stellar wind has begun to blow a bubble into the surrounding dense medium. Our 2D, radiation-hydrodynamics simulations of the wind bubble and the H II region around the B1 star provide a reasonable match to observations, both in terms of morphology and absolute brightness of the optical and mid-infrared emission, and verify the young age of IRAS 18153-1651. Taken together our results strongly suggest that we have revealed the first example of a wind bubble blown by a main-sequence B star.

  19. AMPLITUDES OF SOLAR-LIKE OSCILLATIONS: CONSTRAINTS FROM RED GIANTS IN OPEN CLUSTERS OBSERVED BY KEPLER

    International Nuclear Information System (INIS)

    Stello, Dennis; Huber, Daniel; Bedding, Timothy R.; Benomar, Othman; Kallinger, Thomas; Basu, Sarbani; Mosser, BenoIt; Hekker, Saskia; Mathur, Savita; GarcIa, Rafael A.; Kjeldsen, Hans; Grundahl, Frank; Christensen-Dalsgaard, Joergen; Gilliland, Ronald L.; Verner, Graham A.; Chaplin, William J.; Elsworth, Yvonne P.; Meibom, Soeren; Molenda-Zakowicz, Joanna; Szabo, Robert

    2011-01-01

    Scaling relations that link asteroseismic quantities to global stellar properties are important for gaining understanding of the intricate physics that underpins stellar pulsations. The common notion that all stars in an open cluster have essentially the same distance, age, and initial composition implies that the stellar parameters can be measured to much higher precision than what is usually achievable for single stars. This makes clusters ideal for exploring the relation between the mode amplitude of solar-like oscillations and the global stellar properties. We have analyzed data obtained with NASA's Kepler space telescope to study solar-like oscillations in 100 red giant stars located in either of the three open clusters, NGC 6791, NGC 6819, and NGC 6811. By fitting the measured amplitudes to predictions from simple scaling relations that depend on luminosity, mass, and effective temperature, we find that the data cannot be described by any power of the luminosity-to-mass ratio as previously assumed. As a result we provide a new improved empirical relation which treats luminosity and mass separately. This relation turns out to also work remarkably well for main-sequence and subgiant stars. In addition, the measured amplitudes reveal the potential presence of a number of previously unknown unresolved binaries in the red clump in NGC 6791 and NGC 6819, pointing to an interesting new application for asteroseismology as a probe into the formation history of open clusters.

  20. Variations of the ISM conditions accross the Main Sequence of star forming galaxies: observations and simulations.

    Science.gov (United States)

    Martinez Galarza, Juan R.; Smith, Howard Alan; Lanz, Lauranne; Hayward, Christopher C.; Zezas, Andreas; Hung, Chao-Ling; Rosenthal, Lee; Weiner, Aaron

    2015-01-01

    A significant amount of evidence has been gathered that leads to the existence of a main sequence (MS) of star formation in galaxies. This MS is expressed in terms of a correlation between the SFR and the stellar mass of the form SFR ∝ M* and spans a few orders of magnitude in both quantities. Several ideas have been suggested to explain fundamental properties of the MS, such as its slope, its dispersion, and its evolution with redshift, but no consensus has been reached regarding its true nature, and whether the membership or not of particular galaxies to this MS underlies the existence of two different modes of star formation. In order to advance in the understanding of the MS, here we use a statistically robust Bayesian SED analysis method (CHIBURST) to consistently analyze the star-forming properties of a set of hydro-dynamical simulations of mergers, as well as observations of real mergers, both local and at intermediate redshift. We find a remarkable, very tight correlation between the specific star formation rate (sSFR) of galaxies, and the typical ISM conditions near their inernal star-forming regions, parametrized via a novel quantity: the compactness parameter (C). The evolution of mergers along this correlation explains the spread of the MS, and implies that the physical conditions of the ISM smoothly evolve between on-MS (secular) conditions and off-MS (coalescence/starburst) conditions. Furthermore, we show that the slope of the correlation can be interpreted in terms of the efficiency in the conversion of gas into stars, and that this efficiency remains unchanged along and across the MS. Finally, we discuss differences in the normalization of the correlation as a function of merger mass and redshift, and conclude that these differences imply the existence of two different modes of star formation, unrelated to the smooth evolution across the MS: a disk-like, low pressure mode and a compact nuclear-starburst mode.

  1. Effect of Generalized Uncertainty Principle on Main-Sequence Stars and White Dwarfs

    Directory of Open Access Journals (Sweden)

    Mohamed Moussa

    2015-01-01

    Full Text Available This paper addresses the effect of generalized uncertainty principle, emerged from different approaches of quantum gravity within Planck scale, on thermodynamic properties of photon, nonrelativistic ideal gases, and degenerate fermions. A modification in pressure, particle number, and energy density are calculated. Astrophysical objects such as main-sequence stars and white dwarfs are examined and discussed as an application. A modification in Lane-Emden equation due to a change in a polytropic relation caused by the presence of quantum gravity is investigated. The applicable range of quantum gravity parameters is estimated. The bounds in the perturbed parameters are relatively large but they may be considered reasonable values in the astrophysical regime.

  2. Entropy Production of Stars

    Directory of Open Access Journals (Sweden)

    Leonid M. Martyushev

    2015-06-01

    Full Text Available The entropy production (inside the volume bounded by a photosphere of main-sequence stars, subgiants, giants, and supergiants is calculated based on B–V photometry data. A non-linear inverse relationship of thermodynamic fluxes and forces as well as an almost constant specific (per volume entropy production of main-sequence stars (for 95% of stars, this quantity lies within 0.5 to 2.2 of the corresponding solar magnitude is found. The obtained results are discussed from the perspective of known extreme principles related to entropy production.

  3. From clouds to stars

    International Nuclear Information System (INIS)

    Elmegreen, B.G.

    1982-01-01

    At the present time, the theory of star formation must be limited to what we know about the lowest density gas, or about the pre-main sequence stars themselves. We would like to understand two basic processes: 1) how star-forming clouds are created from the ambient interstellar gas in the first place, and 2) how small parts of these clouds condense to form individual stars. We are interested also in knowing what pre-main sequence stars are like, and how they can interact with their environment. These topics are reviewed in what follows. In this series of lectures, what we know about the formation of stars is tentatively described. The lectures begin with a description of the interstellar medium, and then they proceed along the same direction that a young star would follow during its creation, namely from clouds through the collapse phase and onto the proto-stellar phase. The evolution of viscous disks and two models for the formation of the solar system are described in the last lectures. The longest lectures, and the topics that are covered in most detail, are not necessarily the ones for which we have the most information. Physically intuitive explanations for the various processes are emphasized, rather then mathematical explanations. In some cases, the mathematical aspects are developed as well, but only when the equations can be used to give important numerical values for comparison with the observations

  4. A search for pre-main sequence stars in the high-latitude molecular clouds. II - A survey of the Einstein database

    Science.gov (United States)

    Caillault, Jean-Pierre; Magnani, Loris

    1990-01-01

    The preliminary results are reported of a survey of every EINSTEIN image which overlaps any high-latitude molecular cloud in a search for X-ray emitting pre-main sequence stars. This survey, together with complementary KPNO and IRAS data, will allow the determination of how prevalent low mass star formation is in these clouds in general and, particularly, in the translucent molecular clouds.

  5. Fundamental properties of stars using asteroseismology from Kepler and CoRoT and interferometry from the CHARA Array

    DEFF Research Database (Denmark)

    Huber, D.; Ireland, M.J.; Bedding, T.R.

    2012-01-01

    We present results of a long-baseline interferometry campaign using the PAVO beam combiner at the CHARA Array to measure the angular sizes of five main-sequence stars, one subgiant and four red giant stars for which solar-like oscillations have been detected by either Kepler or CoRoT. By combinin...

  6. Pre-main sequence masses and the age spread in the Orion cluster

    International Nuclear Information System (INIS)

    McNamara, B.J.

    1975-01-01

    The spread in formation times for stars earlier than GO in the Orion cluster is investigated. The range of stellar ages in this cluster is found to extend from at least 10 6 years to about 10 7 years. On the basis of this evidence and the similarity of the color--magnitude diagrams of other young clusters to the Orion cluster, it is suggested that the current method of dating these clusters (from the point at which the most massive stars just reach the zero-age main sequence) might not be valid. The masses of forty-one pre-main sequence stars within the ranges 4.05 less than or equal to log(Te) less than or equal to 3.77 and 0.6 less than or equal to log (L/L/sub sun/) less than or equal to 2.1 are determined from observed effective temperatures, luminosities, and gravities. These masses were then compared with those expected from Iben's (1965) pre-main sequence evolutionary calculations. In most cases, the agreement between these values was found to be within the observational errors. Finally, the pre-main sequence stars possessing infrared excesses are found to be apparently among the most massive and youngest stars still contracting toward the zero-age main sequence

  7. POPULATION PARAMETERS OF INTERMEDIATE-AGE STAR CLUSTERS IN THE LARGE MAGELLANIC CLOUD. II. NEW INSIGHTS FROM EXTENDED MAIN-SEQUENCE TURNOFFS IN SEVEN STAR CLUSTERS

    International Nuclear Information System (INIS)

    Goudfrooij, Paul; Kozhurina-Platais, Vera; Puzia, Thomas H.; Chandar, Rupali

    2011-01-01

    We discuss new photometry from high-resolution images of seven intermediate-age (1-2 Gyr) star clusters in the Large Magellanic Cloud taken with the Advanced Camera for Surveys on board the Hubble Space Telescope. We fit color-magnitude diagrams (CMDs) with several different sets of theoretical isochrones and determine systematic uncertainties for population parameters when derived using any one set of isochrones. The cluster CMDs show several interesting features, including extended main-sequence turnoff (MSTO) regions, narrow red giant branches, and clear sequences of unresolved binary stars. We show that the extended MSTOs are not caused by photometric uncertainties, contamination by field stars, or the presence of binary stars. Enhanced helium abundances in a fraction of cluster stars are also ruled out as the reason for the extended MSTOs. Quantitative comparisons with simulations indicate that the MSTO regions are better described by a spread in ages than by a bimodal age distribution, although we cannot formally rule out the latter for the three lowest-mass clusters in our sample (which have masses lower than ∼3 x 10 4 M sun ). This conclusion differs from that of some previous works which suggested that the age distribution in massive clusters in our sample is bimodal. This suggests that any secondary star formation occurred in an extended fashion rather than through short bursts. We discuss these results in the context of the nature of multiple stellar populations in star clusters.

  8. RADIO PROPERTIES OF THE BAT AGNs: THE FIR–RADIO RELATION, THE FUNDAMENTAL PLANE, AND THE MAIN SEQUENCE OF STAR FORMATION

    Energy Technology Data Exchange (ETDEWEB)

    Smith, Krista Lynne; Mushotzky, Richard F.; Vogel, Stuart; Shimizu, Thomas T. [Department of Astronomy, University of Maryland, College Park, MD 20742 (United States); Miller, Neal, E-mail: klsmith@astro.umd.edu [Department of Mathematics and Physics, Stevenson University, Stevenson, MD 21117 (United States)

    2016-12-01

    We conducted 22 GHz 1″ JVLA imaging of 70 radio-quiet active galactic nuclei (AGNs) from the Swift -BAT survey. We find radio cores in all but three objects. The radio morphologies of the sample fall into three groups: compact and core-dominated, extended, and jet-like. We spatially decompose each image into core flux and extended flux, and compare the extended radio emission with that predicted from previous Herschel observations using the canonical FIR–radio relation. After removing the AGN contribution to the FIR and radio flux densities, we find that the relation holds remarkably well despite the potentially different star formation physics in the circumnuclear environment. We also compare our core radio flux densities with predictions of coronal models and scale-invariant jet models for the origin of radio emission in radio-quiet AGNs, and find general consistency with both models. However, we find that the L {sub R}/ L {sub X} relation does not distinguish between star formation and non-relativistic AGN-driven outflows as the origin of radio emission in radio-quiet AGNs. Finally, we examine where objects with different radio morphologies fall in relation to the main sequence (MS) of star formation, and conclude that those AGNs that fall below the MS, as X-ray selected AGNs have been found to do, have core-dominated or jet-like 22 GHz morphologies.

  9. First ultraviolet observations of the transition regions of X-ray bright solar-type stars in the Pleiades

    Science.gov (United States)

    Caillault, J.-P.; Vilhu, O.; Linsky, J. L.

    1990-01-01

    Results are reported from A UV study of the transition regions of two X-ray-bright solar-type stars from the Pleiades, in an attempt to extend the main sequence age baseline for the transition-region activity-age relation over more than two orders of magnitude. However, no emission lines were detected from either star; the upper limits to the fluxes are consistent with previously determined saturation levels, but do not help to further constrain evolutionary models.

  10. A catalog of pre-main-sequence emission-line stars with IRAS source associations

    International Nuclear Information System (INIS)

    Weintraub, D.A.

    1990-01-01

    To aid in finding premain-sequence (PMS) emission-line stars that might have dusty circumstellar environments, 361 PMS stars that are associated with 304 separate IRAS sources were identified. These stars include 200 classical T Tauri stars, 25 weak-lined (naked) T Tauri stars, 56 Herbig Ae/Be stars, six FU Orionis stars, and two SU Aurigae stars. All six of the FU Orionis stars surveyed by IRAS were detected. Of the PMS-IRAS Point Source Catalog (PSC) associations, 90 are new and are not noted in the PSC. The other 271 entries include 104 that are correctly identified in the PSC but have not yet appeared in the literature, 56 more that can be found in both the PSC and in the published and unpublished iterature, and 111 that are in the literature but not in the PSC. Spectral slope diagrams constructed from the 12-, 25-, and 60-micron flux densities reveal unique distributions for the different PMS subclasses; these diagrams may help identify the best candidate PMS stars for observations of circumstellar dust. 30 refs

  11. Relation of chromospheric activity to convection, rotation, and pre-main-sequence evolution

    International Nuclear Information System (INIS)

    Gilliland, R.L.

    1986-01-01

    Pre-main-sequence, or T Tauri, stars are characterized by much larger fluxes of nonradiative origin than their main-sequence counterparts. As a class, the T Tauri stars have only moderate rotation rates, making an explanation of their chromospheric properties based on rapid rotation problematic. The recent success of correlating nonradiative fluxes to the Rossby number, Ro = P/sub rot//tau/sub conv/, a central parameter of simple dynamo theories of magnetic field generation, has led to the suggestion that the same relation might be of use in explaining the pre-main-sequence (PMS) stars if tau/sub conv/ is very large. We show that tau/sub conv/ does depend strongly on evolutionary effects above the main sequence (MS), but that this dependence alone cannot account for the high observed nonradiative fluxes. The acoustic flux is also strongly dependent on PMS evolutionary state, and when coupled to the parameterization of magnetic activity based on Ro, these two mechanisms seem capable of explaining the high observed level of chromospheric activity in T Tauri stars. The moment of inertia decreases by two to three order of magnitude during PMS evolution. Since young MS stars do not rotate two to three orders of magnitude faster than PMS stars, rapid loss or redistribution of angular momentum must occur

  12. THE CLUSTERED NATURE OF STAR FORMATION. PRE-MAIN-SEQUENCE CLUSTERS IN THE STAR-FORMING REGION NGC 602/N90 IN THE SMALL MAGELLANIC CLOUD

    International Nuclear Information System (INIS)

    Gouliermis, Dimitrios A.; Gennaro, Mario; Schmeja, Stefan; Dolphin, Andrew E.; Tognelli, Emanuele; Prada Moroni, Pier Giorgio

    2012-01-01

    Located at the tip of the wing of the Small Magellanic Cloud (SMC), the star-forming region NGC 602/N90 is characterized by the H II nebular ring N90 and the young cluster of pre-main-sequence (PMS) and early-type main-sequence stars NGC 602, located in the central area of the ring. We present a thorough cluster analysis of the stellar sample identified with Hubble Space Telescope/Advanced Camera for Surveys in the region. We show that apart from the central cluster low-mass PMS stars are congregated in 13 additional small, compact sub-clusters at the periphery of NGC 602, identified in terms of their higher stellar density with respect to the average background density derived from star counts. We find that the spatial distribution of the PMS stars is bimodal, with an unusually large fraction (∼60%) of the total population being clustered, while the remaining is diffusely distributed in the intercluster area, covering the whole central part of the region. From the corresponding color-magnitude diagrams we disentangle an age difference of ∼2.5 Myr between NGC 602 and the compact sub-clusters, which appear younger, on the basis of comparison of the brighter PMS stars with evolutionary models, which we accurately calculated for the metal abundance of the SMC. The diffuse PMS population appears to host stars as old as those in NGC 602. Almost all detected PMS sub-clusters appear to be centrally concentrated. When the complete PMS stellar sample, including both clustered and diffused stars, is considered in our cluster analysis, it appears as a single centrally concentrated stellar agglomeration, covering the whole central area of the region. Considering also the hot massive stars of the system, we find evidence that this agglomeration is hierarchically structured. Based on our findings, we propose a scenario according to which the region NGC 602/N90 experiences an active clustered star formation for the last ∼5 Myr. The central cluster NGC 602 was formed first

  13. PHIBSS: MOLECULAR GAS CONTENT AND SCALING RELATIONS IN z ∼ 1-3 MASSIVE, MAIN-SEQUENCE STAR-FORMING GALAXIES

    International Nuclear Information System (INIS)

    Tacconi, L. J.; Genzel, R.; Wuyts, S.; Förster Schreiber, N. M.; Gracia-Carpio, J.; Lutz, D.; Saintonge, A.; Neri, R.; Cox, P.; Combes, F.; Bolatto, A.; Cooper, M. C.; Bournaud, F.; Burkert, A.; Comerford, J.; Davis, M.; Newman, S.; García-Burillo, S.; Naab, T.; Omont, A.

    2013-01-01

    We present PHIBSS, the IRAM Plateau de Bure high-z blue sequence CO 3-2 survey of the molecular gas properties in massive, main-sequence star-forming galaxies (SFGs) near the cosmic star formation peak. PHIBSS provides 52 CO detections in two redshift slices at z ∼ 1.2 and 2.2, with log(M * (M ☉ )) ≥ 10.4 and log(SFR(M ☉ /yr)) ≥ 1.5. Including a correction for the incomplete coverage of the M * -SFR plane, and adopting a ''Galactic'' value for the CO-H 2 conversion factor, we infer average gas fractions of ∼0.33 at z ∼ 1.2 and ∼0.47 at z ∼ 2.2. Gas fractions drop with stellar mass, in agreement with cosmological simulations including strong star formation feedback. Most of the z ∼ 1-3 SFGs are rotationally supported turbulent disks. The sizes of CO and UV/optical emission are comparable. The molecular-gas-star-formation relation for the z = 1-3 SFGs is near-linear, with a ∼0.7 Gyr gas depletion timescale; changes in depletion time are only a secondary effect. Since this timescale is much less than the Hubble time in all SFGs between z ∼ 0 and 2, fresh gas must be supplied with a fairly high duty cycle over several billion years. At given z and M * , gas fractions correlate strongly with the specific star formation rate (sSFR). The variation of sSFR between z ∼ 0 and 3 is mainly controlled by the fraction of baryonic mass that resides in cold gas.

  14. Post-main-sequence planetary system evolution

    Science.gov (United States)

    Veras, Dimitri

    2016-01-01

    The fates of planetary systems provide unassailable insights into their formation and represent rich cross-disciplinary dynamical laboratories. Mounting observations of post-main-sequence planetary systems necessitate a complementary level of theoretical scrutiny. Here, I review the diverse dynamical processes which affect planets, asteroids, comets and pebbles as their parent stars evolve into giant branch, white dwarf and neutron stars. This reference provides a foundation for the interpretation and modelling of currently known systems and upcoming discoveries. PMID:26998326

  15. ULTRAVIOLET-SELECTED FIELD AND PRE-MAIN-SEQUENCE STARS TOWARD TAURUS AND UPPER SCORPIUS

    International Nuclear Information System (INIS)

    Findeisen, K.; Hillenbrand, L.

    2010-01-01

    We have carried out a Galaxy Evolution Explorer (GALEX) Cycle 1 guest investigator program covering 56 deg 2 near the Taurus T association and 12 deg 2 along the northern edge of the Upper Scorpius OB association. We combined photometry in the GALEX far-ultraviolet and near-ultraviolet bands with data from the Two Micron All Sky Survey to identify candidate young (∼<100 Myr old) stars as those with an ultraviolet excess relative to older main-sequence stars. Follow-up spectroscopy of a partial sample of these candidates suggests five new members of Taurus, with 8-20 expected from additional observations, and five new members of Upper Scorpius, with three to six expected from additional observations. These candidate new members appear to represent a distributed, non-clustered population in either region, although our sample statistics are as of yet too poor to constrain the nature or extent of this population. Rather, our study demonstrates the ability of GALEX observations to identify young stellar populations distributed over a wide area of the sky. We also highlight the necessity of a better understanding of the Galactic ultraviolet source population to support similar investigations. In particular, we report a large population of stars with an ultraviolet excess but no optical indicators of stellar activity or accretion, and briefly argue against several interpretations of these sources.

  16. Turbulent transport coefficients in spherical wedge dynamo simulations of solar-like stars

    Science.gov (United States)

    Warnecke, J.; Rheinhardt, M.; Tuomisto, S.; Käpylä, P. J.; Käpylä, M. J.; Brandenburg, A.

    2018-01-01

    Aims: We investigate dynamo action in global compressible solar-like convective dynamos in the framework of mean-field theory. Methods: We simulate a solar-type star in a wedge-shaped spherical shell, where the interplay between convection and rotation self-consistently drives a large-scale dynamo. To analyze the dynamo mechanism we apply the test-field method for azimuthally (φ) averaged fields to determine the 27 turbulent transport coefficients of the electromotive force, of which six are related to the α tensor. This method has previously been used either in simulations in Cartesian coordinates or in the geodynamo context and is applied here for the first time to fully compressible simulations of solar-like dynamos. Results: We find that the φφ-component of the α tensor does not follow the profile expected from that of kinetic helicity. The turbulent pumping velocities significantly alter the effective mean flows acting on the magnetic field and therefore challenge the flux transport dynamo concept. All coefficients are significantly affected by dynamically important magnetic fields. Quenching as well as enhancement are being observed. This leads to a modulation of the coefficients with the activity cycle. The temporal variations are found to be comparable to the time-averaged values and seem to be responsible for a nonlinear feedback on the magnetic field generation. Furthermore, we quantify the validity of the Parker-Yoshimura rule for the equatorward propagation of the mean magnetic field in the present case.

  17. End of the Line for a Star like Ours

    Science.gov (United States)

    Riddle, Bob

    2010-01-01

    Stars of different masses have varying life spans, with the more massive stars "burning out" more quickly than stars of lower masses. How or what they do when they burn out also varies, depending on the mass of the star. All stars are called "main sequence stars" as they continue fusing hydrogen and staying in a state of equilibrium--a balance…

  18. Investigation of superflares frequency variability of solar-type stars

    International Nuclear Information System (INIS)

    Akopian, A.A.

    2015-01-01

    Statistical study of the variability of the superflares frequency of 46 solar-type stars detected by orbital observatory 'Kepler' is presented. Two possible scenarios for changes in frequency are considered. In the first, the temporal sequence of superflares is regarded as a piecewise stationary Poissonian process. Statistically significant change in the frequency of superflares by several times is revealed at five stars. Moments of change of frequency are accompanied by sudden changes in the behavior of the star's brightness. Brightness of a star for a short time becomes irregular, with a significant decrease in the amplitude

  19. The Solar system.Stars and constellations

    Science.gov (United States)

    Horia Minda, Octavian

    2017-04-01

    It is important for students to understand what is in our Solar System. The Students need to know that there are other things besides the Earth, Sun and Moon in the solar sky. The students will learn about the other eight planets and a few other celestial objects like stars and constellations. Constellations are useful because they can help people to recognize stars in the sky. By looking for patterns, the stars and locations can be much easier to spot. The constellations had uses in ancient times. They were used to help keep track of the calendar. This was very important so that people knew when to plant and harvest crops. Another important use for constellations was navigation. By finding Ursa Minor it is fairly easy to spot the North Star (Polaris). Using the height of the North Star in the sky, navigators could figure out their latitude helping ships to travel across the oceans. Objective: 1. The students will be introduced to the origin of the stars they see at night. 2. They will learn that there are groups of stars called constellations. The students will individually create their own constellations. They will be given the chance to tell the class a small story explaining their constellation. Evaluation of Children: The children will be evaluated through the creation of their constellations and ability to work in groups on the computers.

  20. Extended Main-sequence Turn-offs in Intermediate-age Star Clusters: Stellar Rotation Diminishes, but Does Not Eliminate, Age Spreads

    Energy Technology Data Exchange (ETDEWEB)

    Goudfrooij, Paul; Correnti, Matteo [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Girardi, Léo, E-mail: goudfroo@stsci.edu [Osservatorio Astronomico di Padova—INAF, Vicolo dell’Osservatorio 5, I-35122 Padova (Italy)

    2017-09-01

    Extended main-sequence turn-off (eMSTO) regions are a common feature in color–magnitude diagrams of young- and intermediate-age star clusters in the Magellanic Clouds. The nature of eMSTOs remains debated in the literature. The currently most popular scenarios are extended star formation activity and ranges of stellar rotation rates. Here we study details of differences in main-sequence turn-off (MSTO) morphology expected from spreads in age versus spreads in rotation rates, using Monte Carlo simulations with the Geneva syclist isochrone models that include the effects of stellar rotation. We confirm a recent finding of Niederhofer et al. that a distribution of stellar rotation velocities yields an MSTO extent that is proportional to the cluster age, as observed. However, we find that stellar rotation yields MSTO crosscut widths that are generally smaller than observed ones at a given age. We compare the simulations with high-quality Hubble Space Telescope data of NGC 1987 and NGC 2249, which are the two only relatively massive star clusters with an age of ∼1 Gyr for which such data is available. We find that the distribution of stars across the eMSTOs of these clusters cannot be explained solely by a distribution of stellar rotation velocities, unless the orientations of rapidly rotating stars are heavily biased toward an equator-on configuration. Under the assumption of random viewing angles, stellar rotation can account for ∼60% and ∼40% of the observed FWHM widths of the eMSTOs of NGC 1987 and NGC 2249, respectively. In contrast, a combination of distributions of stellar rotation velocities and stellar ages fits the observed eMSTO morphologies very well.

  1. The Star Formation Main Sequence in the Hubble Space Telescope Frontier Fields

    Science.gov (United States)

    Santini, Paola; Fontana, Adriano; Castellano, Marco; Di Criscienzo, Marcella; Merlin, Emiliano; Amorin, Ricardo; Cullen, Fergus; Daddi, Emanuele; Dickinson, Mark; Dunlop, James S.; Grazian, Andrea; Lamastra, Alessandra; McLure, Ross J.; Michałowski, Michał. J.; Pentericci, Laura; Shu, Xinwen

    2017-09-01

    We investigate the relation between star formation rate (SFR) and stellar mass (M), I.e., the main sequence (MS) relation of star-forming galaxies, at 1.3≤slant zFrontier Fields, on the basis of rest-frame UV observations. Gravitational lensing combined with deep HST observations allows us to extend the analysis of the MS down to {log} M/{M}⊙ ˜ 7.5 at z≲ 4 and {log} M/{M}⊙ ˜ 8 at higher redshifts, a factor of ˜10 below most previous results. We perform an accurate simulation to take into account the effect of observational uncertainties and correct for the Eddington bias. This step allows us to reliably measure the MS and in particular its slope. While the normalization increases with redshift, we fit an unevolving and approximately linear slope. We nicely extend to lower masses the results of brighter surveys. Thanks to the large dynamic range in mass and by making use of the simulation, we analyzed any possible mass dependence of the dispersion around the MS. We find tentative evidence that the scatter decreases with increasing mass, suggesting a larger variety of star formation histories in low-mass galaxies. This trend agrees with theoretical predictions and is explained as either a consequence of the smaller number of progenitors of low-mass galaxies in a hierarchical scenario and/or of the efficient but intermittent stellar feedback processes in low-mass halos. Finally, we observe an increase in the SFR per unit stellar mass with redshift milder than predicted by theoretical models, implying a still incomplete understanding of the processes responsible for galaxy growth.

  2. Radius Determination of Solar-type Stars Using Asteroseismology: What to Expect from the Kepler Mission

    Science.gov (United States)

    Stello, Dennis; Chaplin, William J.; Bruntt, Hans; Creevey, Orlagh L.; García-Hernández, Antonio; Monteiro, Mario J. P. F. G.; Moya, Andrés; Quirion, Pierre-Olivier; Sousa, Sergio G.; Suárez, Juan-Carlos; Appourchaux, Thierry; Arentoft, Torben; Ballot, Jerome; Bedding, Timothy R.; Christensen-Dalsgaard, Jørgen; Elsworth, Yvonne; Fletcher, Stephen T.; García, Rafael A.; Houdek, Günter; Jiménez-Reyes, Sebastian J.; Kjeldsen, Hans; New, Roger; Régulo, Clara; Salabert, David; Toutain, Thierry

    2009-08-01

    For distant stars, as observed by the NASA Kepler satellite, parallax information is currently of fairly low quality and is not complete. This limits the precision with which the absolute sizes of the stars and their potential transiting planets can be determined by traditional methods. Asteroseismology will be used to aid the radius determination of stars observed during NASA's Kepler mission. We report on the recent asteroFLAG hare-and-hounds Exercise#2, where a group of "hares" simulated data of F-K main-sequence stars that a group of "hounds" sought to analyze, aimed at determining the stellar radii. We investigated stars in the range 9 values of the artificial stars to within 3%, when the large frequency spacing is used. This is 5-10 times better than the results where seismology is not applied. These results give strong confidence that radius estimation can be performed to better than 3% for solar-like stars using automatic pipeline reduction. Even when the stellar distance and luminosity are unknown we can obtain the same level of agreement. Given the uncertainties used for this exercise we find that the input log g and parallax do not help to constrain the radius, and that T eff and metallicity are the only parameters we need in addition to the large frequency spacing. It is the uncertainty in the metallicity that dominates the uncertainty in the radius.

  3. Pre-main-sequence depletion of Li-6 and Li-7

    International Nuclear Information System (INIS)

    Proffitt, C.R.; Michaud, G.

    1989-01-01

    Depletion of Li-6 and Li-7 during premain-sequence contraction has been calculated for several evolutionary sequences. Slightly greater Li-7 depletion was found than by other recent workers. On the premain sequence, Li-6 is depleted by a factor of at least 10 in the present models for stars with T(eff) lower than 6800 K on the main sequence. Because of the shorter destruction time scale for Li-6 as compared to Li-7, the determination of the abundances of these two isotopes would place strict constraints on the structure of premain-sequence stars. 39 refs

  4. The evolution of the lithium abundances of solar-type stars. I. The Hyades and Coma Berenices clusters

    International Nuclear Information System (INIS)

    Sonderblom, D.R.; Oey, M.S.; Johnson, D.R.H.; Stone, R.P.S.

    1990-01-01

    High-resolution, high signal-to-noise spectra of the lithium region at 6708 A in 28 solar-type stars of the Hyades and Coma Berenices clusters are reported. Given an observational uncertainty of less than about 5 mA in W-lambda (Li), no significant scatter about the mean relation was seen for most stars. However, there are several stars that have anomalous abundances. Two of them fall well below the mean relation, and appear to have no distinctive qualities that might account for their low Li. Two others are close binaries and have significantly greater than average Li. A means by which close binaries might preserve Li is suggested, and Li depletion timescales for stars near the zero-age main sequence (ZAMS) are estimated by comparing the Hyades to the Pleiades. This comparison indicates that Li depletion for stars near 1 solar mass starts on the ZAMS, not before, and that depletion occurs at a much slower rate after the age of the Hyades than before. 87 refs

  5. Main-sequence photometry in NGC 2808

    International Nuclear Information System (INIS)

    Buonanno, R.; Corsi, C.E.; Fusi Pecci, F.; Harris, W.E.

    1984-01-01

    We have obtained a color-magnitude diagram for the southern globular cluster NGC 2808, to V/sub lim/approx. =21 (about 2 mag below the main-sequence turnoff). The internal photographic errors are sigma/sub V/approx. =0.02, sigma/sub B/-Vapprox. =0.03, small enough to permit a precise definition of the turnoff region and an estimate of the ''cosmic scatter'' along the main sequence. Fitting of the CMD to VandenBerg's [Astrophys. J. Suppl. 51, 29 (1983)] isochrones shows that an excellent match to the observations is achieved for model parameters of Yapprox. =0.2, Zapprox. =0.003 ([Fe/H]approx. =-0.8), and an age of (16 +- 2) billion years. All these characteristics are within the expected range from other observational constraints; no new clues from the main-sequence data alone have arisen to help explain the presence of the anomalous blue horizontal-branch stars

  6. The environmental impacts on the star formation main sequence: An Hα study of the newly discovered rich cluster at z = 1.52

    Energy Technology Data Exchange (ETDEWEB)

    Koyama, Yusei; Kodama, Tadayuki; Tadaki, Ken-ichi; Hayashi, Masao [National Astronomical Observatory of Japan, Mitaka, Tokyo 181-8588 (Japan); Tanaka, Ichi [Subaru Telescope, National Astronomical Observatory of Japan, 650 North A' ohoku Place, Hilo, HI 96720 (United States); Shimakawa, Rhythm, E-mail: koyama.yusei@nao.ac.jp [Department of Astronomical Science, The Graduate University for Advanced Studies, Mitaka, Tokyo 181-8588 (Japan)

    2014-07-01

    We report the discovery of a strong over-density of galaxies in the field of a radio galaxy at z = 1.52 (4C 65.22) based on our broadband and narrow-band (Hα) photometry with the Subaru Telescope. We find that Hα emitters are located in the outskirts of the density peak (cluster core) dominated by passive red-sequence galaxies. This resembles the situation in lower-redshift clusters, suggesting that the newly discovered structure is a well-evolved rich galaxy cluster at z = 1.5. Our data suggest that the color-density and stellar mass-density relations are already in place at z ∼ 1.5, mostly driven by the passive red massive galaxies residing within r{sub c} ≲ 200 kpc from the cluster core. These environmental trends almost disappear when we consider only star-forming (SF) galaxies. We do not find SFR-density or SSFR-density relations amongst SF galaxies, and the location of the SF main sequence does not significantly change with environment. Nevertheless, we find a tentative hint that star-bursting galaxies (up-scattered objects from the main sequence) are preferentially located in a small group at ∼1 Mpc away from the main body of the cluster. We also argue that the scatter of the SF main sequence could be dependent on the distance to the nearest neighboring galaxy.

  7. Are coronae of late type stars made of solar-like structures? The Fx-HR diagram and the pressure-temperature correlation

    OpenAIRE

    Peres, G.; Orlando, S.; Reale, F.

    2004-01-01

    We show that stellar coronae can be composed of X-ray emitting structures like those in the solar corona, using a large set of ROSAT/PSPC observations of late-type-stars, and a large set of solar X-ray data collected with Yohkoh/SXT. We have considered data on the solar corona at various phases of the cycle and various kinds of X-ray coronal structures, from flares to the background corona. The surface flux (F_x) vs. spectral hardness ratio (HR) diagram is a fundamental tool for our study. We...

  8. A HIGHER EFFICIENCY OF CONVERTING GAS TO STARS PUSHES GALAXIES AT z ∼ 1.6 WELL ABOVE THE STAR-FORMING MAIN SEQUENCE

    Energy Technology Data Exchange (ETDEWEB)

    Silverman, J. D.; Rujopakarn, W. [Kavli Institute for the Physics and Mathematics of the Universe (WPI), The University of Tokyo Institutes for Advanced Study, The University of Tokyo, Kashiwa, Chiba 277-8583 (Japan); Daddi, E.; Liu, D. [Laboratoire AIM, CEA/DSM-CNRS-Universite Paris Diderot, Irfu/Service d’Astrophysique, CEA Saclay (France); Rodighiero, G. [Dipartimento di Fisica e Astronomia, Universita di Padova, vicolo Osservatorio, 3, I-35122 Padova (Italy); Sargent, M. [Astronomy Centre, Department of Physics and Astronomy, University of Sussex, Brighton BN1 9QH (United Kingdom); Renzini, A. [Instituto Nazionale de Astrofisica, Osservatorio Astronomico di Padova, v.co dell’Osservatorio 5, I-35122 Padova (Italy); Feruglio, C. [IRAM—Institut de RadioAstronomie Millimétrique, 300 rue de la Piscine, F-38406 Saint Martin d’Hères (France); Kashino, D. [Division of Particle and Astrophysical Science, Graduate School of Science, Nagoya University, Nagoya 464-8602 (Japan); Sanders, D. [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); Kartaltepe, J. [National Optical Astronomy Observatory, 950 N. Cherry Avenue, Tucson, AZ 85719 (United States); Nagao, T. [Graduate School of Science and Engineering, Ehime University, 2-5 Bunkyo-cho, Matsuyama 790-8577 (Japan); Arimoto, N. [Subaru Telescope, 650 North A’ohoku Place, Hilo, HI-96720 (United States); Berta, S.; Lutz, D. [Max-Planck-Institut für extraterrestrische Physik, D-84571 Garching (Germany); Béthermin, M. [European Southern Observatory, Karl-Schwarzschild-Strasse 2, D-85748 Garching (Germany); Koekemoer, A., E-mail: john.silverman@ipmu.jp [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD, 21218 (United States); and others

    2015-10-20

    Local starbursts have a higher efficiency of converting gas into stars, as compared to typical star-forming galaxies at a given stellar mass, possibly indicative of different modes of star formation. With the peak epoch of galaxy formation occurring at z > 1, it remains to be established whether such an efficient mode of star formation is occurring at high redshift. To address this issue, we measure the molecular gas content of seven high-redshift (z ∼ 1.6) starburst galaxies with the Atacama Large Millimeter/submillimeter Array and IRAM/Plateau de Bure Interferometer. Our targets are selected from the sample of Herschel far-infrared-detected galaxies having star formation rates (∼300–800 M{sub ⊙} yr{sup −1}) elevated (≳4×) above the star-forming main sequence (MS) and included in the FMOS-COSMOS near-infrared spectroscopic survey of star-forming galaxies at z ∼ 1.6 with Subaru. We detect CO emission in all cases at high levels of significance, indicative of high gas fractions (∼30%–50%). Even more compelling, we firmly establish with a clean and systematic selection that starbursts, identified as MS outliers, at high redshift generally have a lower ratio of CO to total infrared luminosity as compared to typical MS star-forming galaxies, although with a smaller offset than expected based on past studies of local starbursts. We put forward a hypothesis that there exists a continuous increase in star formation efficiency with elevation from the MS with galaxy mergers as a possible physical driver. Along with a heightened star formation efficiency, our high-redshift sample is similar in other respects to local starbursts, such as being metal rich and having a higher ionization state of the interstellar medium.

  9. Asteroseismology of solar-type stars with Kepler: III. Ground-based data

    DEFF Research Database (Denmark)

    Karoff, Christoffer; Molenda-Żakowicz , J.

    2010-01-01

    We report on the ground-based follow-up program of spectroscopic and photometric observations of solar-like asteroseismic targets for the Kepler space mission. These stars constitute a large group of more than a thousand objects which are the subject of an intensive study by the Kepler Asteroseis......We report on the ground-based follow-up program of spectroscopic and photometric observations of solar-like asteroseismic targets for the Kepler space mission. These stars constitute a large group of more than a thousand objects which are the subject of an intensive study by the Kepler...

  10. Photometric Determination of the Mass Accretion Rates of Pre-main-sequence Stars. V. Recent Star Formation in the 30 Dor Nebula

    Science.gov (United States)

    De Marchi, Guido; Panagia, Nino; Beccari, Giacomo

    2017-09-01

    We report on the properties of the low-mass stars that recently formed in the central ˜ 2\\buildrel{ \\prime}\\over{.} 7× 2\\buildrel{ \\prime}\\over{.} 7 of 30 Dor, including the R136 cluster. Using the photometric catalog of De Marchi et al., based on observations with the Hubble Space Telescope, and the most recent extinction law for this field, we identify 1035 bona fide pre-main-sequence (PMS) stars showing {{H}}α excess emission at the 4σ level with an {{H}}α equivalent width of 20 Å or more. We find a wide spread in age spanning the range ˜ 0.1{--}50 {Myr}. We also find that the older PMS objects are placed in front of the R136 cluster and are separated from it by a conspicuous amount of absorbing material, indicating that star formation has proceeded from the periphery into the interior of the region. We derive physical parameters for all PMS stars, including masses m, ages t, and mass accretion rates {\\dot{M}}{acc}. To identify reliable correlations between these parameters, which are intertwined, we use a multivariate linear regression fit of the type {log}{\\dot{M}}{acc}=a× {log}t+b× {log}m+c. The values of a and b for 30 Dor are compatible with those found in NGC 346 and NGC 602. We extend the fit to a uniform sample of 1307 PMS stars with 0.5contract NAS5-26555.

  11. Some aspects of cool main sequence star ages derived from stellar rotation (gyrochronology)

    Science.gov (United States)

    Barnes, S. A.; Spada, F.; Weingrill, J.

    2016-09-01

    Rotation periods for cool stars can be measured with good precision by monitoring starspot light modulation. Observations have shown that the rotation periods of dwarf stars of roughly solar metallicity have such systematic dependencies on stellar age and mass that they can be used to derive reliable ages, a procedure called gyrochronology. We review the method and show illustrative cases, including recent ground- and space-based data. The age uncertainties approach 10 % in the best cases, making them a valuable complement to, and constraint on, asteroseismic or other ages. Edited, updated, and refereed version of a presentation at the WE-Heraeus-Seminar in Bad Honnef, Germany: Reconstructing the Milky Way's History: Spectroscopic Surveys, Asteroseismology and Chemodynamical Models

  12. Evolution models of helium white dwarf--main-sequence star merger remnants: the mass distribution of single low-mass white dwarfs

    OpenAIRE

    Zhang, Xianfei; Hall, Philip D.; Jeffery, C. Simon; Bi, Shaolan

    2017-01-01

    It is not known how single white dwarfs with masses less than 0.5Msolar -- low-mass white dwarfs -- are formed. One way in which such a white dwarf might be formed is after the merger of a helium-core white dwarf with a main-sequence star that produces a red giant branch star and fails to ignite helium. We use a stellar-evolution code to compute models of the remnants of these mergers and find a relation between the pre-merger masses and the final white dwarf mass. Combining our results with ...

  13. T Tauri stars - Wild as dust

    International Nuclear Information System (INIS)

    Bertout, C.

    1989-01-01

    T Tauri stars (TTSs), their surroundings, and their common evolution toward the main sequence are discussed. The photospheric properties of TTSs and their solar-type outer atmospheres, recent evidence for circumstellar disks around classical TTSs (CTTSs), and CTTS mass outflows are examined. TTSs are depicted as complex systems whose properties depend mostly on the initial conditions of star formation and on their rotation rates, which appear to control the magnetodynamic activity in the stars. The most exotic traits of CTTSs are primarily due to the disk and its interaction with the star, and the properties of weak-line TTSs (WTTSs) are mainly manifestations of the enhanced solar-type magnetic activity expected from their rotation rates. CTTSs are expected to become WTTSs when their disks dissipate. 217 refs

  14. EFFECT OF METALLICITY ON THE EVOLUTION OF THE HABITABLE ZONE FROM THE PRE-MAIN SEQUENCE TO THE ASYMPTOTIC GIANT BRANCH AND THE SEARCH FOR LIFE

    Energy Technology Data Exchange (ETDEWEB)

    Danchi, William C. [Exoplanets and Stellar Astrophysics Laboratory, NASA Goddard Space Flight Center, Code 667, Greenbelt, MD 20771 (United States); Lopez, Bruno, E-mail: william.c.danchi@nasa.gov, E-mail: bruno.lopez@oca.eu [Observatoire de la Cote d' Azur, Laboratoire Lagrange UMR 7293, BP 4229, F-06034 Nice Cedex 4 (France)

    2013-05-20

    During the course of stellar evolution, the location and width of the habitable zone changes as the luminosity and radius of the star evolves. The duration of habitability for a planet located at a given distance from a star is greatly affected by the characteristics of the host star. A quantification of these effects can be used observationally in the search for life around nearby stars. The longer the duration of habitability, the more likely it is that life has evolved. The preparation of observational techniques aimed at detecting life would benefit from the scientific requirements deduced from the evolution of the habitable zone. We present a study of the evolution of the habitable zone around stars of 1.0, 1.5, and 2.0 M{sub Sun} for metallicities ranging from Z = 0.0001 to Z = 0.070. We also consider the evolution of the habitable zone from the pre-main sequence until the asymptotic giant branch is reached. We find that metallicity strongly affects the duration of the habitable zone for a planet as well as the distance from the host star where the duration is maximized. For a 1.0 M{sub Sun} star with near solar metallicity, Z = 0.017, the duration of the habitable zone is >10 Gyr at distances 1.2-2.0 AU from the star, whereas the duration is >20 Gyr for high-metallicity stars (Z = 0.070) at distances of 0.7-1.8 AU, and {approx}4 Gyr at distances of 1.8-3.3 AU for low-metallicity stars (Z = 0.0001). Corresponding results have been obtained for stars of 1.5 and 2.0 solar masses.

  15. EFFECT OF METALLICITY ON THE EVOLUTION OF THE HABITABLE ZONE FROM THE PRE-MAIN SEQUENCE TO THE ASYMPTOTIC GIANT BRANCH AND THE SEARCH FOR LIFE

    International Nuclear Information System (INIS)

    Danchi, William C.; Lopez, Bruno

    2013-01-01

    During the course of stellar evolution, the location and width of the habitable zone changes as the luminosity and radius of the star evolves. The duration of habitability for a planet located at a given distance from a star is greatly affected by the characteristics of the host star. A quantification of these effects can be used observationally in the search for life around nearby stars. The longer the duration of habitability, the more likely it is that life has evolved. The preparation of observational techniques aimed at detecting life would benefit from the scientific requirements deduced from the evolution of the habitable zone. We present a study of the evolution of the habitable zone around stars of 1.0, 1.5, and 2.0 M ☉ for metallicities ranging from Z = 0.0001 to Z = 0.070. We also consider the evolution of the habitable zone from the pre-main sequence until the asymptotic giant branch is reached. We find that metallicity strongly affects the duration of the habitable zone for a planet as well as the distance from the host star where the duration is maximized. For a 1.0 M ☉ star with near solar metallicity, Z = 0.017, the duration of the habitable zone is >10 Gyr at distances 1.2-2.0 AU from the star, whereas the duration is >20 Gyr for high-metallicity stars (Z = 0.070) at distances of 0.7-1.8 AU, and ∼4 Gyr at distances of 1.8-3.3 AU for low-metallicity stars (Z = 0.0001). Corresponding results have been obtained for stars of 1.5 and 2.0 solar masses.

  16. Retired A Stars and Their Companions. III. Comparing the Mass-Period Distributions of Planets Around A-Type Stars and Sun-Like Stars

    Science.gov (United States)

    Bowler, Brendan P.; Johnson, John Asher; Marcy, Geoffrey W.; Henry, Gregory W.; Peek, Kathryn M. G.; Fischer, Debra A.; Clubb, Kelsey I.; Liu, Michael C.; Reffert, Sabine; Schwab, Christian; Lowe, Thomas B.

    2010-01-01

    We present an analysis of ~5 years of Lick Observatory radial velocity measurements targeting a uniform sample of 31 intermediate-mass (IM) subgiants (1.5 lsim M */M sunlsim 2.0) with the goal of measuring the occurrence rate of Jovian planets around (evolved) A-type stars and comparing the distributions of their orbital and physical characteristics to those of planets around Sun-like stars. We provide updated orbital solutions incorporating new radial velocity measurements for five known planet-hosting stars in our sample; uncertainties in the fitted parameters are assessed using a Markov-Chain Monte Carlo method. The frequency of Jovian planets interior to 3 AU is 26+9 -8%, which is significantly higher than the 5%-10% frequency observed around solar-mass stars. The median detection threshold for our sample includes minimum masses down to {0.2, 0.3, 0.5, 0.6, 1.3} M Jup within {0.1, 0.3, 0.6, 1.0, 3.0} AU. To compare the properties of planets around IM stars to those around solar-mass stars we synthesize a population of planets based on the parametric relationship dN vprop M α P β dlnMdlnP, the observed planet frequency, and the detection limits we derived. We find that the values of α and β for planets around solar-type stars from Cumming et al. fail to reproduce the observed properties of planets in our sample at the 4σ level, even when accounting for the different planet occurrence rates. Thus, the properties of planets around A stars are markedly different than those around Sun-like stars, suggesting that only a small (~50%) increase in stellar mass has a large influence on the formation and orbital evolution of planets. Based on observations obtained at the Lick Observatory, which is operated by the University of California.

  17. Origin of faint blue stars

    International Nuclear Information System (INIS)

    Tutukov, A.; Iungelson, L.

    1987-01-01

    The origin of field faint blue stars that are placed in the HR diagram to the left of the main sequence is discussed. These include degenerate dwarfs and O and B subdwarfs. Degenerate dwarfs belong to two main populations with helium and carbon-oxygen cores. The majority of the hot subdwarfs most possibly are helium nondegenerate stars that are produced by mass exchange close binaries of moderate mass cores (3-15 solar masses). The theoretical estimates of the numbers of faint blue stars of different types brighter than certain stellar magnitudes agree with star counts based on the Palomar Green Survey. 28 references

  18. EXTENDED MAGNETOSPHERES IN PRE-MAIN-SEQUENCE EVOLUTION: FROM T TAURI STARS TO THE BROWN DWARF LIMIT

    Energy Technology Data Exchange (ETDEWEB)

    Gomez de Castro, Ana I.; Marcos-Arenal, Pablo [Grupo de Investigacion Complutense AEGORA, Universidad Complutense de Madrid, 28040 Madrid (Spain)

    2012-04-20

    Low-mass pre-main-sequence stars, i.e., T Tauri stars (TTSs), strongly radiate at high energies, from X-rays to the ultraviolet (UV). This excess radiation with respect to main-sequence cool stars (MSCSs) is associated with the accretion process, i.e., it is produced in the extended magnetospheres, in the accretion shocks on the stellar surface, and in the outflows. Although evidence of accretion shocks and outflow contribution to the high-energy excess have been recently addressed, there is not an updated revision of the magnetospheric contribution. This article addresses this issue. The UV observations of the TTSs in the well-known Taurus region have been analyzed together with the XMM-Newton observations compiled in the XEST survey. For the first time the high sensitivity of the Hubble Space Telescope UV instrumentation has allowed measurement of the UV line fluxes of TTSs to M8 type. UV- and X-ray-normalized fluxes have been determined to study the extent and properties of the TTS magnetospheres as a class. They have been compared with the atmospheres of the MSCSs. The main results from this analysis are (1) the normalized fluxes of all the tracers are correlated; this correlation is independent of the broad mass range and the hardness of the X-ray radiation field; (2) the TTS correlations are different than the MSCS correlations; (3) there is a very significant excess emission in O I in the TTSs compared with MSCSs that seems to be caused by recombination radiation from the disk atmosphere after photoionization by extreme UV radiation; the Fe II/Mg II recombination continuum has also been detected in several TTSs and most prominently in AA Tau; and (4) the normalized flux of the UV tracers anticorrelates with the strength of the X-ray flux, i.e., the stronger the X-ray surface flux is, the weaker the observed UV flux. This last behavior is counterintuitive within the framework of stellar dynamo theory and suggests that UV emission can be produced in the

  19. A Search for Coronal Emission at the Bottom of the Main-Sequence: Stars and Brown Dwarf Candidates with Spectral Types Later than M7 and the Rotation-Activity Relation

    Science.gov (United States)

    Stringfellow, Guy

    2004-01-01

    This program intended to test whether the lowest mass stars at the bottom end of the main sequence and the lower mass brown dwarfs have coronae. If they have coronae, what are the coronal characteristics and what drives them? In the classical dynamo picture, the closed magnetic loop structure is generated near the boundary of the convective envelope and the radiative core. Stars with mass below 0.30 Msun however are fully convective, and the nature of the dynamo responsible for the generation of the coronae in this regime is poorly understood. Previous results from the ROSAT mission (e.g., Fleming et al. 1993, 1995; Schmitt et al. 1995) had confirmed three very important characteristics of M-star coronae: (1) a very high percentage of all M dwarfs have coronae (of order 85% in the local 7 pc sample), (2) those M dwarfs showing high chromospheric activity, such as having the Balmer series in emission or large/numerous optical flaring, indeed exhibit the highest coronal activity, and (3) that the maximum saturation boundary in X-ray luminosity, which amounts to 0.0001-0.001 for Lx/Lbol for the dMe stars, extends down to the current detection limit, through spectral types M7. It was likely that the incompleteness noted for result (1) above was simply a detection limit problem; for more distant sources, the X-ray fainter dM stars will drop below detection thresholds before the more X-ray luminous dMe stars. The latest stars for which direct detection of the corona had been successful were of spectral type dM7 (e.g., VB8, LHS 3003). This program proposed to obtain ROSAT HRI observations for a large number of the coolest known (at that time) stars at the bottom of the main-sequence, which had spectral types of M9 or later. Three stars were approved for observations with ROSAT-HRI totaling 180 ksec. The goal was to obtain X-ray detections or low upper limits for the three approved stars.

  20. Luminous carbon star in Canis Major OB1

    International Nuclear Information System (INIS)

    Herbst, W.; Racine, R.; Richer, H.B.

    1977-01-01

    The fact that W CMa illuminates a reflection nebula is used to argue that it is spatially associated with the CMa OBl/CMa Rl complex. An apparent cluster around the carbon star is found to consist primarly of field stars, although a few probable late B-type members of CMa OBl are identified. On the basis of its likely association with CMa OBl, a luminosity for W CMa is derived. The values M/sub v/ = -4.7 and M/sub bol/ = - 7.2 are found. It seems likely that the progenitor of W CMa was an O-type member of CMa OBl with a mass greater than 20 M/sub solar/ and a main-sequence lifetime less than 3 x 10 6 years

  1. Effects of magnetic fields on main sequence stars

    International Nuclear Information System (INIS)

    Hubbard, E.N.

    1981-01-01

    A number of effects of low to medium strength ( 2 /8π) magnetic field pressure term so that the only effect of such a field may come from its inhibiting convection in the core. Isochrones of both convective and radiative core models of 2-5 M are presented. In the deep envelope, mixing of partially nuclear processed material driven by rising and falling magnetic flux tubes may be seen. The effects of this mixing will be brought to the surface during the deep convection phase of the star's tenure as a red giant. This model is used to predict a signature for magnetic mixing based on the CNO isotope and abundance ratios. In the outer envelope the gas pressure is low enough that one might expect to see a perturbation of the stellar structure due to the magnetic field pressure itself. This perturbation is calculated under several physical models for intermediate and high mass stars and it is determined that sufficient magnetic field energy may be available in the outer envelope to expand a star by about 20% over its unperturbed radius. Finally the evidence for the existence of non-magnetic neutron stars is considered, concluding that while no non-magnetic neutron stars have ever been positively identified, there is no evidence that prevents the existence of at least as many non-magnetic as magnetic neutron stars

  2. GOODS-HERSCHEL: STAR FORMATION, DUST ATTENUATION, AND THE FIR–RADIO CORRELATION ON THE MAIN SEQUENCE OF STAR-FORMING GALAXIES UP TO z ≃ 4

    Energy Technology Data Exchange (ETDEWEB)

    Pannella, M.; Elbaz, D.; Daddi, E.; Hwang, H. S.; Schreiber, C.; Strazzullo, V.; Aussel, H.; Bethermin, M.; Cibinel, A.; Juneau, S.; Floc’h, E. Le; Leiton, R. [Laboratoire AIM-Paris-Saclay, CEA/DSM/Irfu—CNRS—Université Paris Diderot, CEA-Saclay, F-91191 Gif-sur-Yvette (France); Dickinson, M. [National Optical Astronomy Observatory, 950 North Cherry Avenue, Tucson, AZ 85719 (United States); Buat, V. [Aix-Marseille Université, CNRS, LAM (Laboratoire d’Astrophysique de Marseille) UMR7326, F-13388, Marseille (France); Charmandaris, V.; Magdis, G. [Institute for Astronomy, Astrophysics, Space Applications and Remote Sensing, National Observatory of Athens, 15236, Penteli (Greece); Ivison, R. J. [European Southern Observatory, Karl-Schwarzschild-Strasse 2, D-85748 Garching (Germany); Borgne, D. Le [Institut d’Astrophysique de Paris, UMR 7095, CNRS, 98bis boulevard Arago, F-75005 Paris (France); Lin, L. [Institute of Astronomy and Astrophysics, Academia Sinica, Taipei 106, Taiwan (China); Morrison, G. E. [Institute for Astronomy, University of Hawaii, Honolulu, Hawaii, HI-96822 (United States); and others

    2015-07-10

    We use deep panchromatic data sets in the GOODS-N field, from GALEX to the deepest Herschel far-infrared (FIR) and VLA radio continuum imaging, to explore the evolution of star-formation activity and dust attenuation properties of star-forming galaxies to z ≃ 4, using mass-complete samples. Our main results can be summarized as follows: (i) the slope of the star-formation rate–M{sub *} correlation is consistent with being constant ≃0.8 up to z ≃ 1.5, while its normalization keeps increasing with redshift; (ii) for the first time we are able to explore the FIR–radio correlation for a mass-selected sample of star-forming galaxies: the correlation does not evolve up to z ≃ 4; (iii) we confirm that galaxy stellar mass is a robust proxy for UV dust attenuation in star-forming galaxies, with more massive galaxies being more dust attenuated. Strikingly, we find that this attenuation relation evolves very weakly with redshift, with the amount of dust attenuation increasing by less than 0.3 mag over the redshift range [0.5–4] for a fixed stellar mass; (iv) the correlation between dust attenuation and the UV spectral slope evolves with redshift, with the median UV slope becoming bluer with redshift. By z ≃ 3, typical UV slopes are inconsistent, given the measured dust attenuations, with the predictions of commonly used empirical laws. (v) Finally, building on existing results, we show that gas reddening is marginally larger (by a factor of around 1.3) than the stellar reddening at all redshifts probed. Our results support a scenario where the ISM conditions of typical star-forming galaxies evolve with redshift, such that at z ≥ 1.5 Main Sequence galaxies have ISM conditions moving closer to those of local starbursts.

  3. RETIRED A STARS AND THEIR COMPANIONS. III. COMPARING THE MASS-PERIOD DISTRIBUTIONS OF PLANETS AROUND A-TYPE STARS AND SUN-LIKE STARS

    International Nuclear Information System (INIS)

    Bowler, Brendan P.; Johnson, John Asher; Liu, Michael C.; Marcy, Geoffrey W.; Peek, Kathryn M. G.; Henry, Gregory W.; Fischer, Debra A.; Clubb, Kelsey I.; Reffert, Sabine; Schwab, Christian; Lowe, Thomas B.

    2010-01-01

    We present an analysis of ∼5 years of Lick Observatory radial velocity measurements targeting a uniform sample of 31 intermediate-mass (IM) subgiants (1.5 ∼ * /M sun ∼ +9 -8 %, which is significantly higher than the 5%-10% frequency observed around solar-mass stars. The median detection threshold for our sample includes minimum masses down to {0.2, 0.3, 0.5, 0.6, 1.3} M Jup within {0.1, 0.3, 0.6, 1.0, 3.0} AU. To compare the properties of planets around IM stars to those around solar-mass stars we synthesize a population of planets based on the parametric relationship dN ∝ M α P β dlnMdlnP, the observed planet frequency, and the detection limits we derived. We find that the values of α and β for planets around solar-type stars from Cumming et al. fail to reproduce the observed properties of planets in our sample at the 4σ level, even when accounting for the different planet occurrence rates. Thus, the properties of planets around A stars are markedly different than those around Sun-like stars, suggesting that only a small (∼50%) increase in stellar mass has a large influence on the formation and orbital evolution of planets.

  4. Differential Rotation in Sun-like Stars from Surface Variability and Asteroseismology

    Science.gov (United States)

    Nielsen, Martin Bo

    2017-03-01

    The Sun and other stars are known to oscillate. Through the study of small perturbations to the frequencies of these oscillations the rotation of the deep interior can be inferred. However, thus far the internal rotation of other Sun-like stars is unknown. The NASA Kepler mission has observed a multitude of Sun-like stars over a period of four years. This has provided high-quality photometric data that can be used to study the rotation of stars with two different techniques: asteroseismology and surface activity. Asteroseismology provides a means of measuring rotation in the stellar interior, while photometric variability from magnetically active regions are sensitive to rotation at the stellar surface. The combination of these two methods can be used to constrain the radial differential rotation in Sun-like stars. First, we developed an automated method for measuring the rotation of stars using surface variability. This method was initially applied to the entire Kepler catalog, out of which we detected signatures of rotation in 12,000 stars across the main sequence, providing robust estimates of the surface rotation rates and the associated errors. Second, we performed an asteroseismic analysis of six Sun-like stars, where we were able to measure the rotational splitting as a function of frequency in the p-mode envelope. This was done by dividing the oscillation spectrum into individual segments, and fitting a model independently to each segment. We found that the measured splittings were all consistent with a constant value, indicating little differential rotation. Third, we compared the asteroseismic rotation rates of five Sun-like stars to their surface rotation rates. We found that the values were in good agreement, again indicating little differential rotation between the regions where the two methods are most sensitive. Finally, we discuss how the surface rotation rates may be used as a prior on the seismic envelope rotation rate in a double-zone model

  5. Stars of type MS with evidence of white dwarf companions. [IUE, Main Sequence (MS)

    Science.gov (United States)

    Peery, Benjamin F., Jr.

    1986-01-01

    A search for white dwarf companions of MS-type stars was conducted, using IUE. The overendowments of these stars in typical S-process nuclides suggest that they, like the Ba II stars, may owe their peculiar compositions to earlier mass transfer. Short-wavelength IUE spectra show striking emission line variability in HD35155, HD61913, and 4 Ori; HD35155 and 4 Ori show evidence of white dwarf companions.

  6. Halo Star Lithium Depletion

    International Nuclear Information System (INIS)

    Pinsonneault, M. H.; Walker, T. P.; Steigman, G.; Narayanan, Vijay K.

    1999-01-01

    The depletion of lithium during the pre-main-sequence and main-sequence phases of stellar evolution plays a crucial role in the comparison of the predictions of big bang nucleosynthesis with the abundances observed in halo stars. Previous work has indicated a wide range of possible depletion factors, ranging from minimal in standard (nonrotating) stellar models to as much as an order of magnitude in models that include rotational mixing. Recent progress in the study of the angular momentum evolution of low-mass stars permits the construction of theoretical models capable of reproducing the angular momentum evolution of low-mass open cluster stars. The distribution of initial angular momenta can be inferred from stellar rotation data in young open clusters. In this paper we report on the application of these models to the study of lithium depletion in main-sequence halo stars. A range of initial angular momenta produces a range of lithium depletion factors on the main sequence. Using the distribution of initial conditions inferred from young open clusters leads to a well-defined halo lithium plateau with modest scatter and a small population of outliers. The mass-dependent angular momentum loss law inferred from open cluster studies produces a nearly flat plateau, unlike previous models that exhibited a downward curvature for hotter temperatures in the 7Li-Teff plane. The overall depletion factor for the plateau stars is sensitive primarily to the solar initial angular momentum used in the calibration for the mixing diffusion coefficients. Uncertainties remain in the treatment of the internal angular momentum transport in the models, and the potential impact of these uncertainties on our results is discussed. The 6Li/7Li depletion ratio is also examined. We find that the dispersion in the plateau and the 6Li/7Li depletion ratio scale with the absolute 7Li depletion in the plateau, and we use observational data to set bounds on the 7Li depletion in main-sequence halo

  7. DISCOVERY OF A LOW-MASS COMPANION TO THE SOLAR-TYPE STAR TYC 2534-698-1

    International Nuclear Information System (INIS)

    Kane, Stephen R.; Mahadevan, Suvrath; Sivarani, Thirupathi; Cochran, William D.; Street, Rachel A.; Henry, Gregory W.; Williamson, Michael H.

    2009-01-01

    Brown dwarfs and low-mass stellar companions are interesting objects to study since they occupy the mass region between deuterium and hydrogen burning. We report here the serendipitous discovery of a low-mass companion in an eccentric orbit around a solar-type main-sequence star. The stellar primary, TYC 2534-698-1, is a G2V star that was monitored both spectroscopically and photometrically over the course of several months. Radial velocity observations indicate a minimum mass of 0.037 M sun and an orbital period of ∼103 days for the companion. Photometry outside of the transit window shows the star to be stable to within ∼6 millimags. The semimajor axis of the orbit places the companion in the 'brown dwarf desert' and we discuss potential follow-up observations that could constrain the mass of the companion.

  8. Accretion Disks around Young Stars: An Observational Perspective

    Science.gov (United States)

    Ménard, F.; Bertout, C.

    Accretion disks are pivotal elements in the formation and early evolution of solar-like stars. On top of supplying the raw material, their internal conditions also regulate the formation of planets. Their study therefore holds the key to solve this long standing mystery: how did our Solar System form? This chapter focuses on observational studies of the circumstellar environment, and in particular of circumstellar disks, associated with pre-main sequence solar-like stars. The direct measurement of disk parameters poses an obvious challenge: at the distance of the typical star forming regions ( e.g. 140 pc for Taurus), a planetary system like ours (with diameter simeq50 AU out to Pluto, but excluding the Kuiper belt which could extend much farther out) subtends only 0.35''. Yet its surface brightness is low in comparison to the bright central star and high angular and high contrast imaging techniques are required if one hopes to resolve and measure these protoplanetary disks. Fortunately, capable instruments providing 0.1'' resolution or better and high contrast have been available for just about 10 years now. They are covering a large part of the electromagnetic spectrum, from the UV/Optical with HST and the near-infrared from ground-based adaptive optics systems, to the millimetric range with long-baseline radio interferometers. It is therefore not surprising that our knowledge of the structure of the disks surrounding low-mass stars has made a gigantic leap forward in the last decade. In the following pages we will attempt to describe, in a historical perpective, the road that led to the idea that most solar-like stars are surrounded by an accretion disk at one point in their early life and how, nowadays, their structural and physical parameters can be estimated from direct observations. We will follow by a short discussion of a few of the constraints available regarding the evolution and dissipation of these disks. This last topic is particularly relevant today

  9. Stars Just Got Bigger - A 300 Solar Mass Star Uncovered

    Science.gov (United States)

    2010-07-01

    Using a combination of instruments on ESO's Very Large Telescope, astronomers have discovered the most massive stars to date, one weighing at birth more than 300 times the mass of the Sun, or twice as much as the currently accepted limit of 150 solar masses. The existence of these monsters - millions of times more luminous than the Sun, losing weight through very powerful winds - may provide an answer to the question "how massive can stars be?" A team of astronomers led by Paul Crowther, Professor of Astrophysics at the University of Sheffield, has used ESO's Very Large Telescope (VLT), as well as archival data from the NASA/ESA Hubble Space Telescope, to study two young clusters of stars, NGC 3603 and RMC 136a in detail. NGC 3603 is a cosmic factory where stars form frantically from the nebula's extended clouds of gas and dust, located 22 000 light-years away from the Sun (eso1005). RMC 136a (more often known as R136) is another cluster of young, massive and hot stars, which is located inside the Tarantula Nebula, in one of our neighbouring galaxies, the Large Magellanic Cloud, 165 000 light-years away (eso0613). The team found several stars with surface temperatures over 40 000 degrees, more than seven times hotter than our Sun, and a few tens of times larger and several million times brighter. Comparisons with models imply that several of these stars were born with masses in excess of 150 solar masses. The star R136a1, found in the R136 cluster, is the most massive star ever found, with a current mass of about 265 solar masses and with a birthweight of as much as 320 times that of the Sun. In NGC 3603, the astronomers could also directly measure the masses of two stars that belong to a double star system [1], as a validation of the models used. The stars A1, B and C in this cluster have estimated masses at birth above or close to 150 solar masses. Very massive stars produce very powerful outflows. "Unlike humans, these stars are born heavy and lose weight as

  10. SOLAR-LIKE OSCILLATIONS IN A METAL-POOR GLOBULAR CLUSTER WITH THE HUBBLE SPACE TELESCOPE

    International Nuclear Information System (INIS)

    Stello, Dennis; Gilliland, Ronald L.

    2009-01-01

    We present analyses of variability in the red giant stars in the metal-poor globular cluster NGC 6397, based on data obtained with the Hubble Space Telescope. We use a nonstandard data reduction approach to turn a 23 day observing run originally aimed at imaging the white dwarf population, into time-series photometry of the cluster's highly saturated red giant stars. With this technique we obtain noise levels in the final power spectra down to 50 parts per million, which allows us to search for low-amplitude solar-like oscillations. We compare the observed excess power seen in the power spectra with estimates of the typical frequency range, frequency spacing, and amplitude from scaling the solar oscillations. We see evidence that the detected variability is consistent with solar-like oscillations in at least one and perhaps up to four stars. With metallicities 2 orders of magnitude lower than those of the Sun, these stars present so far the best evidence of solar-like oscillations in such a low-metallicity environment.

  11. Spectral fingerprints of Earth-like planets around FGK stars.

    Science.gov (United States)

    Rugheimer, Sarah; Kaltenegger, Lisa; Zsom, Andras; Segura, Antígona; Sasselov, Dimitar

    2013-03-01

    We present model atmospheres for an Earth-like planet orbiting the entire grid of main sequence FGK stars with effective temperatures ranging from Teff=4250 K to Teff=7000 K in 250 K intervals. We have modeled the remotely detectable spectra of Earth-like planets for clear and cloudy atmospheres at the 1 AU equivalent distance from the VIS to IR (0.4 to 20 μm) to compare detectability of features in different wavelength ranges in accordance with the James Webb Space Telescope and future design concepts to characterize exo-Earths. We have also explored the effect of the stellar UV levels as well as spectral energy distribution on a terrestrial atmosphere, concentrating on detectable atmospheric features that indicate habitability on Earth, namely, H2O, O3, CH4, N2O, and CH3Cl. The increase in UV dominates changes of O3, OH, CH4, N2O, and CH3Cl, whereas the increase in stellar temperature dominates changes in H2O. The overall effect as stellar effective temperatures and corresponding UV increase is a lower surface temperature of the planet due to a bigger part of the stellar flux being reflected at short wavelengths, as well as increased photolysis. Earth-like atmosphere models show more O3 and OH but less stratospheric CH4, N2O, CH3Cl, and tropospheric H2O (but more stratospheric H2O) with increasing effective temperature of main sequence stars. The corresponding detectable spectral features, on the other hand, show different detectability depending on the wavelength observed. We concentrate on directly imaged planets here as a framework to interpret future light curves, direct imaging, and secondary eclipse measurements of atmospheres of terrestrial planets in the habitable zone at varying orbital positions.

  12. Grain temperature, radiation pressure and electric potential in the vicinity of main sequence and white dwarf stars

    Energy Technology Data Exchange (ETDEWEB)

    Leiknes, J.; Havnes, O. (University of Tromso, Auroral Observatory (Norway))

    1984-08-01

    We present results of calculations of the grain physical parameters temperature, lifetime against evaporation, radiation pressure and electric potential for spherical grains near main sequence stars, hydrogen type (DA) white dwarfs and helium type (DB) white dwarfs. These parameters are essential in determining the behaviour of grains near such stars. The grain temperature as a function of stellar distance is calculated for grains of sizes 0.1 and 1 ..mu.. (micron) for grain materials of silicate (obsidian), iron and graphite. The lifetime due to thermal evaporation as a function of grain temperature of these materials is also given. The radiation pressure is given for grain sizes from 0.01 to 10 ..mu.. for the same three grain materials. Grain potentials have been calculated as functions of stellar distance for one photoelectron high yield material (silicate) and one low yield material (graphite) for grains of radius 0.1 ..mu.. embedded in a thermal plasma of temperature T = 10/sup 4/ K.

  13. DETECTION OF SOLAR-LIKE OSCILLATIONS, OBSERVATIONAL CONSTRAINTS, AND STELLAR MODELS FOR θ CYG, THE BRIGHTEST STAR OBSERVED BY THE KEPLER MISSION

    Energy Technology Data Exchange (ETDEWEB)

    Guzik, J. A. [Los Alamos National Laboratory, XTD-NTA, MS T-082, Los Alamos, NM 87545 (United States); Houdek, G.; Chaplin, W. J.; Antoci, V.; Bedding, T. R.; Huber, D.; Kjeldsen, H. [Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, DK-8000 Aarhus C (Denmark); Smalley, B. [Astrophysics Group, School of Physical and Geographical Sciences, Lennard-Jones Laboratories, Keele University, Staffordshire, ST5 5BG (United Kingdom); Kurtz, D. W. [Jeremiah Horrocks Institute, University of Central Lancashire, Preston PR1 2HE (United Kingdom); Gilliland, R. L. [Center for Exoplanets and Habitable Worlds, The Pennsylvania State University, University Park, PA 16802 (United States); Mullally, F.; Rowe, J. F. [SETI Institute/NASA Ames Research Center, Moffett Field, CA 94035 (United States); Bryson, S. T.; Still, M. D. [NASA Ames Research Center, Bldg. 244, MS-244-30, Moffett Field, CA 94035 (United States); Appourchaux, T. [Institut d’Astrophysique Spatiale, Universitè de Paris Sud–CNRS, Batiment 121, F-91405 ORSAY Cedex (France); Basu, S. [Department of Astronomy, Yale University, P.O. Box 208101, New Haven, CT 06520-8101 (United States); Benomar, O. [Sydney Institute for Astronomy (SIfA), School of Physics, University of Sydney, NSW 2006 (Australia); Garcia, R. A. [Laboratoire AIM, CEA/DRF—CNRS—Univ. Paris Diderot—IRFU/SAp, Centre de Saclay, F-91191 Gif-sur-Yvette Cedex (France); Latham, D. W. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Metcalfe, T. S. [Space Science Institute, 4750 Walnut Street, Suite 205, Boulder, CO 80301 (United States); and others

    2016-11-01

    θ Cygni is an F3 spectral type magnitude V = 4.48 main-sequence star that was the brightest star observed by the original Kepler spacecraft mission. Short-cadence (58.8 s) photometric data using a custom aperture were first obtained during Quarter 6 (2010 June–September) and subsequently in Quarters 8 and 12–17. We present analyses of solar-like oscillations based on Q6 and Q8 data, identifying angular degree l = 0, 1, and 2 modes with frequencies of 1000–2700 μ Hz, a large frequency separation of 83.9 ± 0.4 μ Hz, and maximum oscillation amplitude at frequency ν {sub max} = 1829 ± 54 μ Hz. We also present analyses of new ground-based spectroscopic observations, which, combined with interferometric angular diameter measurements, give T {sub eff} = 6697 ± 78 K, radius 1.49 ± 0.03 R {sub ⊙}, [Fe/H] = -0.02 ± 0.06 dex, and log g = 4.23 ± 0.03. We calculate stellar models matching these constraints using the Yale Rotating Evolution Code and the Asteroseismic Modeling Portal. The best-fit models have masses of 1.35–1.39 M {sub ⊙} and ages of 1.0–1.6 Gyr. θ Cyg’s T {sub eff} and log g place it cooler than the red edge of the γ Doradus instability region established from pre- Kepler ground-based observations, but just at the red edge derived from pulsation modeling. The pulsation models show γ Dor gravity modes driven by the convective blocking mechanism, with frequencies of 1–3 cycles per day (11 to 33 μ Hz). However, gravity modes were not seen in Kepler data; one signal at 1.776 cycles per day (20.56 μ Hz) may be attributable to a faint, possibly background, binary.

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

    International Nuclear Information System (INIS)

    Eggl, Siegfried; Pilat-Lohinger, Elke; Haghighipour, Nader

    2013-01-01

    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 α 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 α 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 α Centauri system.

  15. 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.

  16. Modelling the evolution of solar-mass stars with a range of metallicities using MESA

    Directory of Open Access Journals (Sweden)

    Jones E.F.

    2015-01-01

    Full Text Available The nuclides 1,2H, 3,4He, 7Li, 7Be, 8B, 12,13C, 13-15N, 14-18O, 17-19F, 18-22Ne, 22Mg, and 24Mg were used in the code package MESA (Modules for Experiments in Stellar Astrophysics[Paxton] to model a one-solar-mass star with a range of metallicities, z, from 0 to 0.1. On HR diagrams of each star model’s luminosity and effective temperature from before zero-age main sequence (pre-ZAMS to white dwarf, oscillations were noted in the horizontal branch at intervals from z = 0 to 0.0070. At z, = 0, the calculated stellar lifetime is 6.09x109 years. The calculated lifetime of the model stars increases to a maximum of 1.25x1010 years at z = 0.022 and then decreases to 2.59x109 years at z = 0.1. A piecewise fit of the model lifetimes vs. metallicity was obtained.

  17. A fitting LEGACY – modelling Kepler's best stars

    Directory of Open Access Journals (Sweden)

    Aarslev Magnus J.

    2017-01-01

    Full Text Available The LEGACY sample represents the best solar-like stars observed in the Kepler mission[5, 8]. The 66 stars in the sample are all on the main sequence or only slightly more evolved. They each have more than one year's observation data in short cadence, allowing for precise extraction of individual frequencies. Here we present model fits using a modified ASTFIT procedure employing two different near-surface-effect corrections, one by Christensen-Dalsgaard[4] and a newer correction proposed by Ball & Gizon[1]. We then compare the results obtained using the different corrections. We find that using the latter correction yields lower masses and significantly lower χ2 values for a large part of the sample.

  18. Cyanogen strengths of globular cluster post-main-sequence stars

    International Nuclear Information System (INIS)

    Hesser, J.E.; Hartwick, F.D.A.; McClure, R.D.

    1976-01-01

    CN strengths in the peculiar clusters ω Cen and M22 and the metal-rich clusters 47 Tuc, M71, and NGC 6352 are found to vary markedly from star to star. The strong variations in CN strength found earlier for ω Cen by Norris and Bessell and by Dickens and Bell are shown to extend to fainter stars, although expected correlations of CN strength with position in the color-magnitude (C-M) diagram are less evident in our sample. Several CN and metal-strong stars were also observed in M22. We conclude that CN, once it appears in globular clusters, can vary much more than it does in equivalent Population I samples, a result we briefly examine in light of current understanding regarding physical processes in the stars themselves and of models of galactic chemical evolution

  19. Lithium abundances in high- and low-alpha halo stars

    DEFF Research Database (Denmark)

    Nissen, P. E.; Schuster, W. J.

    2012-01-01

    A previous study of F and G main-sequence stars in the solar neighborhood has revealed the existence of two distinct halo populations with a clear separation in [alpha /Fe] for the metallicity range -1.4 < [Fe/H] < -0.7. The kinematics of the stars and models of galaxy formation suggest that the ......A previous study of F and G main-sequence stars in the solar neighborhood has revealed the existence of two distinct halo populations with a clear separation in [alpha /Fe] for the metallicity range -1.4 ... that the ``high-alpha '' stars were formed in situ in the inner parts of the Galaxy, whereas the ``low-alpha '' ones have been accreted from satellite galaxies. In order to see if there is any systematic difference in the lithium abundances of high- and low-alpha stars, equivalent widths of the iLi 6707.8 Å line...... have been measured from VLT/UVES and NOT/FIES spectra and used to derive Li abundances. Furthermore, stellar masses are determined from evolutionary tracks in the log T_eff - log g diagram. For stars with masses 0.7 lithium abundance...

  20. Analysing Solar-like Oscillations with an Automatic Pipeline

    International Nuclear Information System (INIS)

    Mathur, S.; Garcia, R. A.; Regulo, C.; Ballot, J.; Salabert, D.; Chaplin, W. J.

    2009-01-01

    The Kepler mission will provide a huge amount of asteroseismic data during the next few years, among which hundreds of solar-like stars will be targeted. The amount of stars and their observation length represent a step forward in the comprehension of the stellar evolution that has already been initiated by CoRoT and MOST missions. Up to now, the slow cadence of observed targets allowed an individual and personalized analysis of each star. During the survey phase of Kepler, this will be impossible. This is the reason why, within the AsteroFLAG team, we have been developing automatic pipelines for the Kepler solar-like oscillation stars. Our code starts by finding the frequency-range where p-mode power is present and, after fitting the background, it looks for the mode amplitudes as well as the central frequency of the p-mode hump. A good estimation of the large separation can thus be inferred in this region. If the signal to noise is high enough, the code obtains the characteristics of the p modes by doing a global fitting on the power spectrum. Here, we will first describe a few features of this pipeline and its application to AsteroFLAG synthetic data to check the validity of the code.

  1. OLD MAIN-SEQUENCE TURNOFF PHOTOMETRY IN THE SMALL MAGELLANIC CLOUD. II. STAR FORMATION HISTORY AND ITS SPATIAL GRADIENTS

    International Nuclear Information System (INIS)

    Noel, Noelia E. D.; Gallart, Carme; Hidalgo, Sebastian L.; Aparicio, Antonio; Costa, Edgardo; Mendez, Rene A.

    2009-01-01

    We present a quantitative analysis of the star formation history (SFH) of 12 fields in the Small Magellanic Cloud (SMC) based on unprecedented deep [(B - R), R] color-magnitude diagrams (CMDs). Our fields reach down to the oldest main-sequence turnoff with a high photometric accuracy, which is vital for obtaining accurate SFHs, particularly at intermediate and old ages. We use the IAC-pop code to obtain the SFH, using synthetic CMDs generated with IAC-star. We obtain the SFH as a function ψ(t, z) of age and metallicity. We also consider several auxiliary functions: the initial mass function (IMF), φ(m), and a function accounting for the frequency and relative mass distribution of binary stars, β(f, q). We find that there are several main periods of enhancement of star formation: a young one peaked at ∼0.2-0.5 Gyr old, only present in the eastern and in the central-most fields; two at intermediate ages present in all fields: a conspicuous one peaked at ∼4-5 Gyr, and a less significant one peaked at ∼1.5-2.5; and an old one, peaked at ∼10 Gyr in all fields but the western ones. In the western fields, this old enhancement splits into two, one peaked at ∼8 Gyr old and another at ∼12 Gyr old. This 'two-enhancement' zone is unaffected by our choice of stellar evolutionary library but more data covering other fields of the SMC are necessary in order to ascertain its significancy. Correlation between star formation rate enhancements and SMC-Milky Way encounters is not clear. Some correlation could exist with encounters taken from the orbit determination of Kallivayalil et al. But our results would also fit in a first pericenter passage scenario like the one claimed by Besla et al. For SMC-Large Magellanic Cloud encounters, we find a correlation only for the most recent encounter ∼0.2 Gyr ago. This coincides with the youngest ψ(t) enhancement peaked at these ages in our eastern fields. The population younger than 1 Gyr represents ∼7%-12% of the total

  2. Discovery and characterization of 3000+ main-sequence binaries from APOGEE spectra

    Science.gov (United States)

    El-Badry, Kareem; Ting, Yuan-Sen; Rix, Hans-Walter; Quataert, Eliot; Weisz, Daniel R.; Cargile, Phillip; Conroy, Charlie; Hogg, David W.; Bergemann, Maria; Liu, Chao

    2018-05-01

    We develop a data-driven spectral model for identifying and characterizing spatially unresolved multiple-star systems and apply it to APOGEE DR13 spectra of main-sequence stars. Binaries and triples are identified as targets whose spectra can be significantly better fit by a superposition of two or three model spectra, drawn from the same isochrone, than any single-star model. From an initial sample of ˜20 000 main-sequence targets, we identify ˜2500 binaries in which both the primary and secondary stars contribute detectably to the spectrum, simultaneously fitting for the velocities and stellar parameters of both components. We additionally identify and fit ˜200 triple systems, as well as ˜700 velocity-variable systems in which the secondary does not contribute detectably to the spectrum. Our model simplifies the process of simultaneously fitting single- or multi-epoch spectra with composite models and does not depend on a velocity offset between the two components of a binary, making it sensitive to traditionally undetectable systems with periods of hundreds or thousands of years. In agreement with conventional expectations, almost all the spectrally identified binaries with measured parallaxes fall above the main sequence in the colour-magnitude diagram. We find excellent agreement between spectrally and dynamically inferred mass ratios for the ˜600 binaries in which a dynamical mass ratio can be measured from multi-epoch radial velocities. We obtain full orbital solutions for 64 systems, including 14 close binaries within hierarchical triples. We make available catalogues of stellar parameters, abundances, mass ratios, and orbital parameters.

  3. RESOLVED MILLIMETER-WAVELENGTH OBSERVATIONS OF DEBRIS DISKS AROUND SOLAR-TYPE STARS

    Energy Technology Data Exchange (ETDEWEB)

    Steele, Amy; Hughes, A. Meredith [Department of Astronomy, Van Vleck Observatory, Wesleyan University, 96 Foss Hill Drive, Middletown, CT, 06459 (United States); Carpenter, John [Division of Physics, Mathematics, and Astronomy, MC249-17, California Institute of Technology, Pasadena, CA 91125 (United States); Ricarte, Angelo [J. W. Gibbs Laboratory, Department of Astronomy, Yale University, 260 Whitney Avenue, New Haven, CT 06511 (United States); Andrews, Sean M.; Wilner, David J. [Harvard-Smithsonian Center for Astrophysics, MS-42, 60 Garden Street, Cambridge, MA 02138 (United States); Chiang, Eugene, E-mail: asteele@wesleyan.edu [Department of Astronomy, 501 Campbell Hall, University of California, Berkeley, CA 94720-3411 (United States)

    2016-01-01

    The presence of debris disks around young main-sequence stars hints at the existence and structure of planetary systems. Millimeter-wavelength observations probe large grains that trace the location of planetesimal belts. The Formation and Evolution of Planetary Systems Spitzer Legacy survey of nearby young solar analogues yielded a sample of five debris disk-hosting stars with millimeter flux suitable for interferometric follow-up. We present observations with the Submillimeter Array (SMA) and the Combined Array for Research in Millimeter-wave Astronomy at ∼2″ resolution that spatially resolve the debris disks around these nearby (d ∼ 50 pc) stars. Two of the five disks (HD 377, HD 8907) are spatially resolved for the first time and one (HD 104860) is resolved at millimeter wavelengths for the first time. We combine our new observations with archival SMA and Atacama Large Millimeter/Submillimeter Array data to enable a uniform analysis of the full five-object sample. We simultaneously model the broadband photometric data and resolved millimeter visibilities to constrain the dust temperatures and disk morphologies, and perform a Markov Chain Monte Carlo analysis to fit for basic structural parameters. We find that the radii and widths of the cold outer belts exhibit properties consistent with scaled-up versions of the Solar System's Kuiper Belt. All the disks exhibit characteristic grain sizes comparable to the blowout size, and all the resolved observations of emission from large dust grains are consistent with an axisymmetric dust distribution to within the uncertainties. These results are consistent with comparable studies carried out at infrared wavelengths.

  4. On the Roche constants for main-sequence binaries

    International Nuclear Information System (INIS)

    Giannuzzi, M.A.

    1979-01-01

    The ratios C 1 /C 2 of the constants defining the equipotential surfaces which describe the external forms of the components of a close binary system have been calculated on the basis of evolutionary models. Theoretical systems have been considered allowing for a wide range of input parameters (masses and separation) and taking into account the evolutionary effects on the radii of the stars during their Main-Sequence lifetime. The systems have not undergone any transfer of matter and are representative of detached binaries with Main-sequence components. The ratios of the constants are confined in limited intervals and, for the highest values of the mass-ratios, they are clustered around the unit. (Auth.)

  5. SUN-LIKE MAGNETIC CYCLES IN THE RAPIDLY ROTATING YOUNG SOLAR ANALOG HD 30495

    International Nuclear Information System (INIS)

    Egeland, Ricky; Metcalfe, Travis S.; Hall, Jeffrey C.; Henry, Gregory W.

    2015-01-01

    A growing body of evidence suggests that multiple dynamo mechanisms can drive magnetic variability on different timescales, not only in the Sun but also in other stars. Many solar activity proxies exhibit a quasi-biennial (∼2 year) variation, which is superimposed upon the dominant 11 year cycle. A well-characterized stellar sample suggests at least two different relationships between rotation period and cycle period, with some stars exhibiting long and short cycles simultaneously. Within this sample, the solar cycle periods are typical of a more rapidly rotating star, implying that the Sun might be in a transitional state or that it has an unusual evolutionary history. In this work, we present new and archival observations of dual magnetic cycles in the young solar analog HD 30495, a ∼1 Gyr old G1.5 V star with a rotation period near 11 days. This star falls squarely on the relationships established by the broader stellar sample, with short-period variations at ∼1.7 years and a long cycle of ∼12 years. We measure three individual long-period cycles and find durations ranging from 9.6 to 15.5 years. We find the short-term variability to be intermittent, but present throughout the majority of the time series, though its occurrence and amplitude are uncorrelated with the longer cycle. These essentially solar-like variations occur in a Sun-like star with more rapid rotation, though surface differential rotation measurements leave open the possibility of a solar equivalence

  6. A Survey of Ca II H and K Chromospheric Emission in Southern Solar-Type Stars

    Science.gov (United States)

    Henry, Todd J.; Soderblom, David R.; Donahue, Robert A.; Baliunas, Sallie L.

    1996-01-01

    More than 800 southern stars within 50 pc have been observed for chromospheric emission in the cores of the Ca II H and K lines. Most of the sample targets were chosen to be G dwarfs on the basis of colors and spectral types. The bimodal distribution in stellar activity first noted in a sample of northern stars by Vaughan and Preston in 1980 is confirmed, and the percentage of active stars, about 30%, is remarkably consistent between the northern and southern surveys. This is especially compelling given that we have used an entirely different instrumental setup and stellar sample than used in the previous study. Comparisons to the Sun, a relatively inactive star, show that most nearby solar-type stars have a similar activity level, and presumably a similar age. We identify two additional subsamples of stars -- a very active group, and a very inactive group. The very active group may be made up of young stars near the Sun, accounting for only a few percent of the sample, and appears to be less than ~0.1 Gyr old. Included in this high-activity tail of the distribution, however, is a subset of very close binaries of the RS CVn or W UMa types. The remaining members of this population may be undetected close binaries or very young single stars. The very inactive group of stars, contributting ~5%--10% to the total sample, may be those caught in a Maunder Minimum type phase. If the observations of the survey stars are considered to be a sequence of snapshots of the Sun during its life, we might expect that the Sun will spend about 10% of the remainder of its main sequence life in a Maunder Minimum phase.

  7. Determining global parameters of the oscillations of solar-like stars

    DEFF Research Database (Denmark)

    Mathur, S.; García, R. A.; Régulo, C.

    2010-01-01

    Context. Helioseismology has enabled us to better understand the solar interior, while also allowing us to better constrain solar models. But now is a tremendous epoch for asteroseismology as space missions dedicated to studying stellar oscillations have been launched within the last years (MOST....... Aims. The goal of this research work is to estimate the global parameters of any solar-like oscillating target in an automatic manner. We want to determine the global parameters of the acoustic modes (large separation, range of excited pressure modes, maximum amplitude, and its corresponding frequency...

  8. Solar neighbourhood flare stars - a review

    International Nuclear Information System (INIS)

    Kunkel, W.E.

    1975-01-01

    The review concentrates on 'astronomical' aspects of flare activity, such as where, and under what circumstances flare activity is found in the solar vicinity. Non-classical activity is briefly described (without regard for completeness) and the influence of detection effects on flare observations is treated. Flare stars discovered during the last four years are described and flare activity of local dMe stars is compared. The BY Draconis syndrome is discussed followed by some remarks about rotation. Pleiades flare activity is compared to that of the solar neighbourhood and evidence for the evolution of flare activity in stars is examined. (Auth.)

  9. A Constraint on the Formation Timescale of the Young Open Cluster NGC 2264: Lithium Abundance of Pre-main Sequence Stars

    Science.gov (United States)

    Lim, Beomdu; Sung, Hwankyung; Kim, Jinyoung S.; Bessell, Michael S.; Hwang, Narae; Park, Byeong-Gon

    2016-11-01

    The timescale of cluster formation is an essential parameter in order to understand the formation process of star clusters. Pre-main sequence (PMS) stars in nearby young open clusters reveal a large spread in brightness. If the spread were considered to be a result of a real spread in age, the corresponding cluster formation timescale would be about 5-20 Myr. Hence it could be interpreted that star formation in an open cluster is prolonged for up to a few tens of Myr. However, difficulties in reddening correction, observational errors, and systematic uncertainties introduced by imperfect evolutionary models for PMS stars can result in an artificial age spread. Alternatively, we can utilize Li abundance as a relative age indicator of PMS star to determine the cluster formation timescale. The optical spectra of 134 PMS stars in NGC 2264 have been obtained with MMT/Hectochelle. The equivalent widths have been measured for 86 PMS stars with a detectable Li line (3500\\lt {T}{eff}[{{K}}]≤slant 6500). Li abundance under the condition of local thermodynamic equilibrium (LTE) was derived using the conventional curve of growth method. After correction for non-LTE effects, we find that the initial Li abundance of NGC 2264 is A({Li})=3.2+/- 0.2. From the distribution of the Li abundances, the underlying age spread of the visible PMS stars is estimated to be about 3-4 Myr and this, together with the presence of embedded populations in NGC 2264, suggests that the cluster formed on a timescale shorter than 5 Myr.

  10. What stars become peculiar type I supernovae?

    International Nuclear Information System (INIS)

    Uomoto, A.

    1986-01-01

    Hot hydrogen-deficient binaries such as Upsilon Sgr and KS Per are suggested as the stars most likely to become Type Ib supernovae. These systems satisfy the preexplosion constraints imposed by Type Ib observations by not having any hydrogen in their atmospheres (explaining their spectra), being truncated at the Roche lobe (explaining their light curves), and having large main-sequence masses (explaining their presence in extreme Population I locations). Although none of those known seems to be in danger of exploding, a system with a current primary mass of about solar masses may do so by core collapse. 36 references

  11. Evolution of the solar system in the presence of a solar companion star

    International Nuclear Information System (INIS)

    Hut, P.

    1986-01-01

    A review is presented of the dynamical implications of a companion star in a wide orbit around the sun, with a semimajor axis of about half a parsec. The motivation behind the hypothesis of a solar companion star is reviewed briefly along with alternative hypotheses, and the general problem of solar system dynamics with a solar companion star is discussed. Four principal questions are posed and answered concerning the consistency of the solar companion theory in providing the required modulation in comet arrival times: (1) What is the expected lifetime of a solar companion? (2) How stable is the orbital period? (3) Does a single perihelion passage of a solar companion perturb enough comets? (4) Do repeated perihelion passages of a solar companion perturb too many comets? Some applications outside the solar system involving wide binaries, interstellar clouds, and dark matter in the Galactic disk are discussed, and the viability of the solar companion theory is critically assessed

  12. THE MULTIPLE PRE-MAIN-SEQUENCE SYSTEM HBC 515 IN L1622

    International Nuclear Information System (INIS)

    Reipurth, Bo; Aspin, Colin; Herbig, George

    2010-01-01

    The bright pre-main-sequence star HBC 515 (HD 288313) located in the L1622 cometary cloud in Orion has been studied extensively with optical/infrared imaging and ultraviolet/optical/infrared spectroscopy. The spectra indicate that HBC 515 is a weakline T Tauri star (TTS) of spectral type K2V. Adaptive optics imaging in the K band reveals that HBC 515 is a binary with two equally bright components separated by 0.''5. A very faint third component is found 5'' to the northwest. Spitzer IRAC and MIPS observations show that at mid-infrared wavelengths this third source dominates the system, suggesting that it is a protostar still embedded in the nascent cloud of HBC 515. The close association of a weakline TTS with a newborn protostar in a multiple system is noteworthy. Two nearby TTSs are likely associated with the HBC 515 multiple system, and the dynamical evolution of the complex that would lead to such a configuration is considered.

  13. Tables and intercomparisons of evolutionary sequences of models for massive stars

    International Nuclear Information System (INIS)

    Chin, Chaowen; Stothers, R.B.

    1990-01-01

    Tables of evolutionary sequences of models for massive stars have been prepared for a variety of physical input parameters that are normally treated as free. These parameters include the interior convective mixing scheme, the mixing length in the outer convective envelope, the rate of stellar-wind mass loss, the initial stellar mass, and the initial chemical composition. Ranges of specified initial mass and initial chemical composition are M = 10-120 solar masses, Xe = 0.602-0.739, and Ze = 0.021-0.044. The tables cover evolution of the star from the ZAMS to either the end of core H burning or the end of core He burning. Differences among the evolutionary tracks are illustrated primarily in terms of the interior mixing scheme, since the amount and timing of stellar wind mass loss are still very uncertain for initial masses above about 30 solar masses. 52 refs

  14. Transit detections of extrasolar planets around main-sequence stars. I. Sky maps for hot Jupiters

    Science.gov (United States)

    Heller, R.; Mislis, D.; Antoniadis, J.

    2009-12-01

    Context: The findings of more than 350 extrasolar planets, most of them nontransiting Hot Jupiters, have revealed correlations between the metallicity of the main-sequence (MS) host stars and planetary incidence. This connection can be used to calculate the planet formation probability around other stars, not yet known to have planetary companions. Numerous wide-field surveys have recently been initiated, aiming at the transit detection of extrasolar planets in front of their host stars. Depending on instrumental properties and the planetary distribution probability, the promising transit locations on the celestial plane will differ among these surveys. Aims: We want to locate the promising spots for transit surveys on the celestial plane and strive for absolute values of the expected number of transits in general. Our study will also clarify the impact of instrumental properties such as pixel size, field of view (FOV), and magnitude range on the detection probability. Methods: We used data of the Tycho catalog for ≈1 million objects to locate all the stars with 0^m~≲~m_V~≲~11.5m on the celestial plane. We took several empirical relations between the parameters listed in the Tycho catalog, such as distance to Earth, m_V, and (B-V), and those parameters needed to account for the probability of a star to host an observable, transiting exoplanet. The empirical relations between stellar metallicity and planet occurrence combined with geometrical considerations were used to yield transit probabilities for the MS stars in the Tycho catalog. Magnitude variations in the FOV were simulated to test whether this fluctuations would be detected by BEST, XO, SuperWASP and HATNet. Results: We present a sky map of the expected number of Hot Jupiter transit events on the basis of the Tycho catalog. Conditioned by the accumulation of stars towards the galactic plane, the zone of the highest number of transits follows the same trace, interrupted by spots of very low and high

  15. RADIO AND MID-INFRARED PROPERTIES OF COMPACT STARBURSTS: DISTANCING THEMSELVES FROM THE MAIN SEQUENCE

    Energy Technology Data Exchange (ETDEWEB)

    Murphy, E. J. [Observatories of the Carnegie Institution for Science, 813 Santa Barbara Street, Pasadena, CA 91101 (United States); Stierwalt, S.; Armus, L. [Spitzer Science Center, California Institute of Technology, MC 314-6, Pasadena, CA 91125 (United States); Condon, J. J. [National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903 (United States); Evans, A. S., E-mail: emurphy@obs.carnegiescience.edu [Department of Astronomy, University of Virginia, 530 McCormick Road, Charlottesville, VA 22904 (United States)

    2013-05-01

    We investigate the relationship between 8.44 GHz brightness temperatures and 1.4 to 8.44 GHz radio spectral indices with 6.2 {mu}m polycyclic aromatic hydrocarbon (PAH) emission and 9.7 {mu}m silicate absorption features for a sample of 36 local luminous and ultraluminous infrared galaxies. We find that galaxies having small 6.2 {mu}m PAH equivalent widths (EQWs), which signal the presence of weak PAH emission and/or an excess of very hot dust, also have flat spectral indices. The three active galactic nuclei (AGN) identified through their excessively large 8.44 GHz brightness temperatures are also identified as AGN via their small 6.2 {mu}m PAH EQWs. We also find that the flattening of the radio spectrum increases with increasing silicate optical depth, 8.44 GHz brightness temperature, and decreasing size of the radio source even after removing potential AGN, supporting the idea that compact starbursts show spectral flattening as the result of increased free-free absorption. These correlations additionally suggest that the dust obscuration in these galaxies must largely be coming from the vicinity of the compact starburst itself, and is not distributed throughout the (foreground) disk of the galaxy. Finally, we investigate the location of these infrared-bright systems relative to the main sequence (star formation rate versus stellar mass) of star-forming galaxies in the local universe. We find that the radio spectral indices of galaxies flatten with increasing distance above the main sequence, or in other words, with increasing specific star formation rate. This indicates that galaxies located above the main sequence, having high specific star formation rates, are typically compact starbursts hosting deeply embedded star formation that becomes more optically thick in the radio and infrared with increased distance above the main sequence.

  16. The Problem of Hipparcos Distances to Open Clusters. II. Constraints from Nearby Field Theory. Report 2; ClustersConstraints from nearly Field Stars

    Science.gov (United States)

    Soderblom, David R.; King, Jeremy R.; Hanson, Robert B.; Jones, Burton F.; Fischer, Debra; Stauffer, John R.; Pinsonneault, Marc H.

    1998-01-01

    This paper examines the discrepancy between distances to nearby open clusters as determined by parallaxes from Hipparcos compared to traditional main-sequence fitting. The biggest difference is seen for the Pleiades, and our hypothesis is that if the Hipparcos distance to the Pleiades is correct, then similar subluminous zero-age main-sequence (ZAMS) stars should exist elsewhere, including in the immediate solar neighborhood. We examine a color-magnitude diagram of very young and nearby solar-type stars and show that none of them lie below the traditional ZAMS, despite the fact that the Hipparcos Pleiades parallax would place its members 0.3 mag below that ZAMS. We also present analyses and observations of solar-type stars that do lie below the ZAMS, and we show that they are subluminous because of low metallicity and that they have the kinematics of old stars.

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

    Science.gov (United States)

    García, Rafael A.

    2017-10-01

    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.

  18. RECONCILING THE OBSERVED STAR-FORMING SEQUENCE WITH THE OBSERVED STELLAR MASS FUNCTION

    International Nuclear Information System (INIS)

    Leja, Joel; Van Dokkum, Pieter G.; Franx, Marijn; Whitaker, Katherine E.

    2015-01-01

    We examine the connection between the observed star-forming sequence (SFR ∝ M α ) and the observed evolution of the stellar mass function in the range 0.2 < z < 2.5. We find that the star-forming sequence cannot have a slope α ≲ 0.9 at all masses and redshifts because this would result in a much higher number density at 10 < log (M/M ☉ ) < 11 by z = 1 than is observed. We show that a transition in the slope of the star-forming sequence, such that α = 1 at log (M/M ☉ ) < 10.5 and α = 0.7-0.13z (Whitaker et al.) at log (M/M ☉ ) > 10.5, greatly improves agreement with the evolution of the stellar mass function. We then derive a star-forming sequence that reproduces the evolution of the mass function by design. This star-forming sequence is also well described by a broken power law, with a shallow slope at high masses and a steep slope at low masses. At z = 2, it is offset by ∼0.3 dex from the observed star-forming sequence, consistent with the mild disagreement between the cosmic star formation rate (SFR) and recent observations of the growth of the stellar mass density. It is unclear whether this problem stems from errors in stellar mass estimates, errors in SFRs, or other effects. We show that a mass-dependent slope is also seen in other self-consistent models of galaxy evolution, including semianalytical, hydrodynamical, and abundance-matching models. As part of the analysis, we demonstrate that neither mergers nor hidden low-mass quiescent galaxies are likely to reconcile the evolution of the mass function and the star-forming sequence. These results are supported by observations from Whitaker et al

  19. Kinematic and spatial distributions of barium stars - are the barium stars and Am stars related?

    International Nuclear Information System (INIS)

    Hakkila, J.

    1989-01-01

    The possibility of an evolutionary link between Am stars and barium stars is considered, and an examination of previous data suggests that barium star precursors are main-sequence stars of intermediate mass, are most likely A and/or F dwarfs, and are intermediate-mass binaries with close to intermediate orbital separations. The possible role of mass transfer in the later development of Am systems is explored. Mass transfer and loss from systems with a range of masses and orbital separations may explain such statistical peculiarities of barium stars as the large dispersion in absolute magnitude, the large range of elemental abundances from star to star, and the small number of stars with large peculiar velocities. 93 refs

  20. Main-sequence turnoff of the Draco dwarf galaxy

    International Nuclear Information System (INIS)

    Stetson, P.B.; Mcclure, R.D.; Vandenberg, D.A.; Victoria Univ., Canada)

    1985-01-01

    Deep photometry on the B,V system for 182 stars in the dwarf spheroidal galaxy in Draco was obtained with a CCD camera at the Cassegrain focus of the Canada-France-Hawaii 3.6-m telescope. Draco's main-sequence turnoff if found near V(to) = 23.5, which is about 3.4 magnitudes below the galaxy's horizontal branch. This leads to the interpretation that Draco is not measurably younger than the clusters or Ursa Minor: the age of Draco is about 18 Gyr according to current star-revolution chronologies. No blue stragglers are definitely detected in Draco, and it is concluded that any young population in Draco probably represents less than 10 percent of the total. 30 references

  1. Evidence for the impact of stellar activity on the detectability of solar-like oscillations observed by Kepler

    NARCIS (Netherlands)

    Chaplin, W.J.; Bedding, T.R.; Bonanno, A.; Broomhall, A.M.; Garcia, R.A.; Hekker, S.; Huber, D.; Verner, G.A.; Basu, S.; Elsworth, Y.; Houdek, G.; Mathur, S.; Mosser, B.; New, R.; Stevens, I.R.; Appourchaux, T.; Karoff, C.; Metcalfe, T.S.; Molenda-Zakowicz, J.; Monteiro, M.J.P.F.G.; Thompson, M.J.; Christensen-Dalsgaard, J.; Gilliland, R.L.; Kawaler, S.D.; Kjeldsen, H.; Ballot, J.; Benomar, O.; Corsaro, E.; Campante, T.L.; Gaulme, P.; Hale, S.J.; Handberg, R.; Jarvis, E.; Regulo, C.; Roxburgh, I.W.; Salabert, D.; Stello, D.; Mullally, F.; Li, J.; Wohler, W.

    2011-01-01

    We use photometric observations of solar-type stars, made by the NASA Kepler Mission, to conduct a statistical study of the impact of stellar surface activity on the detectability of solar-like oscillations. We find that the number of stars with detected oscillations falls significantly with

  2. Evolution of solar ultraviolet luminosity

    International Nuclear Information System (INIS)

    Zahnle, K.J.; Walker, J.C.G.

    1982-01-01

    In view of the major role of the sun in defining the properties of planetary atmospheres, their evolution cannot be fully understood outside the context of an evolving sun. The ultraviolet radiation is especially interesting because of its strong interaction with planetary atmospheres. We use astronomical observation of stars that are analogous to the sun in order to reconstruct a tentative account of the evolution of solar UV luminosity. A wealth of evidence indicates that the young sun was a much more powerful source of energetic particles and radiation than it is today. While on the main sequence, solar activity has declined as an inverse power law of age (between t -5 and t/sup -1.2/) as a consequence of angular momentum loss to the solar wind. Recent IUE satellite observations of premain sequence stars suggest that before the sun reached the main sequence (at an age of about 50 m.y.), it may have emitted as much as 10 4 times as much ultraviolet radiation (γ<2000 A) than it does today. These results could impact our understanding of the photochemistry and escape of constituents of primordial planetary atmospheres

  3. Halo star streams in the solar neighborhood

    NARCIS (Netherlands)

    Kepley, Amanda A.; Morrison, Heather L.; Helmi, Amina; Kinman, T. D.; Van Duyne, Jeffrey; Martin, John C.; Harding, Paul; Norris, John E.; Freeman, Kenneth C.

    2007-01-01

    We have assembled a sample of halo stars in the solar neighborhood to look for halo substructure in velocity and angular momentum space. Our sample ( 231 stars) includes red giants, RR Lyrae variable stars, and red horizontal branch stars within 2.5 kpc of the Sun with [Fe/H] less than -1.0. It was

  4. 2D dynamics of the radiative core of low mass stars

    Directory of Open Access Journals (Sweden)

    Hypolite Delphine

    2017-01-01

    Full Text Available Understanding the internal rotation of low mass stars all along their evolution is of primary interest when studying their rotational dynamics, internal mixing and magnetic field generation. In this context, helio- and asteroseismology probe angular velocity gradients deep within solar type stars at different evolutionary stages. Still the rotation close to the center of such stars on the main sequence is hardly detectable and the dynamical interaction of the radiative core with the surface convective envelope is not well understood. For instance, the influence of the differential rotation profile sustained by convection and applied as a boundary condition to the radiation zone is very important in the formation of tachoclines. In this work, we study a 2D hydrodynamical model of a radiative core when an imposed, solar or anti-solar, differential rotation is applied at the upper boundary. This model uses the Boussinesq approximation and we find that the shear induces a cylindrical differential rotation associated with a unique cell of meridional circulation in each hemisphere (counterclockwise when the shear is solar-like and clockwise when it is anti-solar. The results are discussed in the framework of seismic observables (internal rotation rate, core-to-surface rotation ratio while perspectives to improve our modeling by including magnetic field or transport by internal gravity waves will be discussed.

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

    Directory of Open Access Journals (Sweden)

    García Rafael A.

    2017-01-01

    Full Text Available 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.

  6. Solar neutrinos: a scientific puzzle

    International Nuclear Information System (INIS)

    Bahcall, J.N.; Davis, R.

    1975-01-01

    An experiment designed to capture neutrinos produced by solar thermonuclear reactions is a crucial one for the theory of stellar evolution. The conventional wisdom regarding nuclear fusion as the energy source for main sequence stars like the sun is briefly outlined. It is assumed that the sun shines because of fusion reactions similar to those envisioned for terrestrial fusion reactors. The basic solar process is the fusion of four protons to form an alpha particle, two positrons (e + ), and two neutrinos (νsub(e)), i.e., 4p → α + 2e + + 2νsub(e). The principal reactions are shown and the percentage of each reaction is given. Several experiments carried out toward this aim are discussed. (B.G.)

  7. A planet in a polar orbit of 1.4 solar-mass star

    Directory of Open Access Journals (Sweden)

    Guenther E.W.

    2015-01-01

    Full Text Available Although more than a thousand transiting extrasolar planets have been discovered, only very few of them orbit stars that are more massive than the Sun. The discovery of such planets is interesting, because they have formed in disks that are more massive but had a shorter life time than those of solar-like stars. Studies of planets more massive than the Sun thus tell us how the properties of the proto-planetary disks effect the formation of planets. Another aspect that makes these planets interesting is that they have kept their original orbital inclinations. By studying them we can thus find out whether the orbital axes planets are initially aligned to the stars rotational axes, or not. Here we report on the discovery of a planet of a 1.4 solar-mass star with a period of 5.6 days in a polar orbit made by CoRoT. This new planet thus is one of the few known close-in planets orbiting a star that is substantially more massive than the Sun.

  8. Stellar model chromospheres. IX - Chromospheric activity in dwarf stars

    Science.gov (United States)

    Kelch, W. L.; Worden, S. P.; Linsky, J. L.

    1979-01-01

    High-resolution Ca II K line profiles are used to model the upper photospheres and lower chromospheres of eight main-sequence stars ranging in spectral type from F0 to M0 and exhibiting different degrees of chromospheric activity. The model chromospheres are studied as a function of spectral type and activity for stars of similar spectral type in order to obtain evidence of enhanced nonradiative heating in the upper-photospheric models and in the ratio of minimum temperature at the base of the chromosphere to effective temperature, a correlation between activity and temperature in the lower chromospheres, and a correlation of the width at the base of the K-line emission core and at the K2 features with activity. Chromospheric radiative losses are estimated for the modelled stars and other previously analyzed main-sequence stars. The results obtained strengthen the argument that dMe flare stars exhibit fundamentally solar-type activity but on an increased scale.

  9. Stellar Variability at the Main-sequence Turnoff of the Intermediate-age LMC Cluster NGC 1846

    Science.gov (United States)

    Salinas, R.; Pajkos, M. A.; Vivas, A. K.; Strader, J.; Contreras Ramos, R.

    2018-04-01

    Intermediate-age (IA) star clusters in the Large Magellanic Cloud (LMC) present extended main-sequence turn-offs (MSTO) that have been attributed to either multiple stellar populations or an effect of stellar rotation. Recently it has been proposed that these extended main sequences can also be produced by ill-characterized stellar variability. Here we present Gemini-S/Gemini Multi-Object Spectrometer (GMOS) time series observations of the IA cluster NGC 1846. Using differential image analysis, we identified 73 new variable stars, with 55 of those being of the Delta Scuti type, that is, pulsating variables close the MSTO for the cluster age. Considering completeness and background contamination effects, we estimate the number of δ Sct belonging to the cluster between 40 and 60 members, although this number is based on the detection of a single δ Sct within the cluster half-light radius. This amount of variable stars at the MSTO level will not produce significant broadening of the MSTO, albeit higher-resolution imaging will be needed to rule out variable stars as a major contributor to the extended MSTO phenomenon. Though modest, this amount of δ Sct makes NGC 1846 the star cluster with the highest number of these variables ever discovered. Lastly, our results present a cautionary tale about the adequacy of shallow variability surveys in the LMC (like OGLE) to derive properties of its δ Sct population. Based on observations obtained at the Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (United States), the National Research Council (Canada), CONICYT (Chile), Ministerio de Ciencia, Tecnología e Innovación Productiva (Argentina), and Ministério da Ciência, Tecnologia e Inovação (Brazil).

  10. Gas and dust from solar metallicity AGB stars

    Science.gov (United States)

    Ventura, P.; Karakas, A.; Dell'Agli, F.; García-Hernández, D. A.; Guzman-Ramirez, L.

    2018-04-01

    We study the asymptotic giant branch (AGB) evolution of stars with masses between 1 M⊙and8.5 M⊙. We focus on stars with a solar chemical composition, which allows us to interpret evolved stars in the Galaxy. We present a detailed comparison with models of the same chemistry, calculated with a different evolution code and based on a different set of physical assumptions. We find that stars of mass ≥3.5 M⊙ experience hot bottom burning at the base of the envelope. They have AGB lifetimes shorter than ˜3 × 105 yr and eject into their surroundings gas contaminated by proton-capture nucleosynthesis, at an extent sensitive to the treatment of convection. Low-mass stars with 1.5 M⊙ ≤ M ≤ 3 M⊙ become carbon stars. During the final phases, the C/O ratio grows to ˜3. We find a remarkable agreement between the two codes for the low-mass models and conclude that predictions for the physical and chemical properties of these stars, and the AGB lifetime, are not that sensitive to the modelling of the AGB phase. The dust produced is also dependent on the mass: low-mass stars produce mainly solid carbon and silicon carbide dust, whereas higher mass stars produce silicates and alumina dust. Possible future observations potentially able to add more robustness to the present results are also discussed.

  11. Astrospheres and Solar-like Stellar Winds

    Directory of Open Access Journals (Sweden)

    Wood Brian E.

    2004-07-01

    Full Text Available Stellar analogs for the solar wind have proven to be frustratingly difficult to detect directly. However, these stellar winds can be studied indirectly by observing the interaction regions carved out by the collisions between these winds and the interstellar medium (ISM. These interaction regions are called "astrospheres", analogous to the "heliosphere" surrounding the Sun. The heliosphere and astrospheres contain a population of hydrogen heated by charge exchange processes that can produce enough H I Ly alpha absorption to be detectable in UV spectra of nearby stars from the Hubble Space Telescope (HST. The amount of astrospheric absorption is a diagnostic for the strength of the stellar wind, so these observations have provided the first measurements of solar-like stellar winds. Results from these stellar wind studies and their implications for our understanding of the solar wind are reviewed here. Of particular interest are results concerning the past history of the solar wind and its impact on planetary atmospheres.

  12. Neutrino-heated stars and broad-line emission from active galactic nuclei

    Science.gov (United States)

    Macdonald, James; Stanev, Todor; Biermann, Peter L.

    1991-01-01

    Nonthermal radiation from active galactic nuclei indicates the presence of highly relativistic particles. The interaction of these high-energy particles with matter and photons gives rise to a flux of high-energy neutrinos. In this paper, the influence of the expected high neutrino fluxes on the structure and evolution of single, main-sequence stars is investigated. Sequences of models of neutrino-heated stars in thermal equilibrium are presented for masses 0.25, 0.5, 0.8, and 1.0 solar mass. In addition, a set of evolutionary sequences for mass 0.5 solar mass have been computed for different assumed values for the incident neutrino energy flux. It is found that winds driven by the heating due to high-energy particles and hard electromagnetic radiation of the outer layers of neutrino-bloated stars may satisfy the requirements of the model of Kazanas (1989) for the broad-line emission clouds in active galactic nuclei.

  13. A HIGHLY CONSISTENT FRAMEWORK FOR THE EVOLUTION OF THE STAR-FORMING ''MAIN SEQUENCE'' FROM z ∼ 0-6

    Energy Technology Data Exchange (ETDEWEB)

    Speagle, J. S. [Harvard University Department of Astronomy, 60 Garden Street, MS 46, Cambridge, MA 02138 (United States); Steinhardt, C. L.; Silverman, J. D. [Kavli IPMU, University of Tokyo, Kashiwanoha 5-1-5, Kashiwa-shi, Chiba 277-8583 (Japan); Capak, P. L., E-mail: jspeagle@cfa.harvard.edu [California Institute of Technology, MC 105-24, 1200 East California Boulevard, Pasadena, CA 91125 (United States)

    2014-10-01

    Using a compilation of 25 studies from the literature, we investigate the evolution of the star-forming galaxy (SFG) main sequence (MS) in stellar mass and star formation rate (SFR) out to z ∼ 6. After converting all observations to a common set of calibrations, we find a remarkable consensus among MS observations (∼0.1 dex 1σ interpublication scatter). By fitting for time evolution of the MS in bins of constant mass, we deconvolve the observed scatter about the MS within each observed redshift bin. After accounting for observed scatter between different SFR indicators, we find the width of the MS distribution is ∼0.2 dex and remains constant over cosmic time. Our best fits indicate the slope of the MS is likely time-dependent, with our best-fit log SFR(M {sub *}, t) = (0.84 ± 0.02 – 0.026 ± 0.003 × t)log M {sub *} – (6.51 ± 0.24 – 0.11 ± 0.03 × t), where t is the age of the universe in Gyr. We use our fits to create empirical evolutionary tracks in order to constrain MS galaxy star formation histories (SFHs), finding that (1) the most accurate representations of MS SFHs are given by delayed-τ models, (2) the decline in fractional stellar mass growth for a ''typical'' MS galaxy today is approximately linear for most of its lifetime, and (3) scatter about the MS can be generated by galaxies evolving along identical evolutionary tracks assuming an initial 1σ spread in formation times of ∼1.4 Gyr.

  14. The evolution of stellar metallicity gradients of the Milky Way disk from LSS-GAC main sequence turn-off stars: a two-phase disk formation history?

    International Nuclear Information System (INIS)

    Xiang, Mao-Sheng; Liu, Xiao-Wei; Huang, Yang; Wang, Chun; Ren, Juan-Juan; Chen, Bing-Qiu; Sun, Ning-Chen; Zhang, Hua-Wei; Yuan, Hai-Bo; Rebassa-Mansergas, Alberto; Huo, Zhi-Ying

    2015-01-01

    Accurate measurements of stellar metallicity gradients in the radial and vertical directions of the disk and their temporal variations provide important constraints on the formation and evolution of the Milky Way disk. We use 297 042 main sequence turn-off stars selected from the LAMOST Spectroscopic Survey of the Galactic Anti-center (LSS-GAC) to determine the radial and vertical gradients of stellar metallicity, Δ[Fe/H]/ΔR and Δ[Fe/H]/Δ|Z| of the Milky Way disk in the direction of the anticenter. We determine ages of those turn-off stars by isochrone fitting and measure the temporal variations of metallicity gradients. We have carried out a detailed analysis of the selection effects resulting from the selection, observation and data reduction of LSS-GAC targets and the potential biases of a magnitude limited sample on the determinations of metallicity gradients. Our results show that the gradients, both in the radial and vertical directions, exhibit significant spatial and temporal variations. The radial gradients yielded by stars with the oldest ages (≳ 11 Gyr) are essentially zero at all heights from the disk midplane, while those given by younger stars are always negative. The vertical gradients deduced from stars with the oldest ages (≳ 11 Gyr) are negative and only show very weak variations with Galactocentric distance in the disk plane, R, while those yielded by younger stars show strong variations with R. After being essentially flat at the earliest epochs of disk formation, the radial gradients steepen as age decreases, reaching a maximum (steepest) at age 7–8 Gyr, and then they flatten again. Similar temporal trends are also found for the vertical gradients. We infer that the assembly of the Milky Way disk may have experienced at least two distinct phases. The earlier phase is probably related to a slow, pressure-supported collapse of gas, when the gas settles down to the disk mainly in the vertical direction. In the later phase, there are

  15. The SFR-M∗ main sequence archetypal star-formation history and analytical models

    Science.gov (United States)

    Ciesla, L.; Elbaz, D.; Fensch, J.

    2017-12-01

    The star-formation history (SFH) of galaxies is a key assumption to derive their physical properties and can lead to strong biases. In this work, we derive the SFH of main sequence (MS) galaxies and show how the peak SFH of a galaxy depends on its seed mass at, for example, z = 5. This seed mass reflects the galaxy's underlying dark matter (DM) halo environment. We show that, following the MS, galaxies undergo a drastic slow down of their stellar mass growth after reaching the peak of their SFH. According to abundance matching, these masses correspond to hot and massive DM halos which state could result in less efficient gas inflows on the galaxies and thus could be the origin of limited stellar mass growth. As a result, we show that galaxies, still on the MS, can enter the passive region of the UVJ diagram while still forming stars. The best fit to the MS SFH is provided by a right skew peak function for which we provide parameters depending on the seed mass of the galaxy. The ability of the classical analytical SFHs to retrieve the star-formation rate (SFR) of galaxies from spectral energy distribution (SED) fitting is studied. Due to mathematical limitations, the exponentially declining and delayed SFH struggle to model high SFR, which starts to be problematic at z > 2. The exponentially rising and log-normal SFHs exhibit the opposite behavior with the ability to reach very high SFR, and thus model starburst galaxies, but they are not able to model low values such as those expected at low redshift for massive galaxies. By simulating galaxies SED from the MS SFH, we show that these four analytical forms recover the SFR of MS galaxies with an error dependent on the model and the redshift. They are, however, sensitive enough to probe small variations of SFR within the MS, with an error ranging from 5 to 40% depending on the SFH assumption and redshift; but all the four fail to recover the SFR of rapidly quenched galaxies. However, these SFHs lead to an artificial

  16. Stellar oscillations in planet-hosting giant stars

    Energy Technology Data Exchange (ETDEWEB)

    Hatzes, Artie P; Zechmeister, Mathias [Thueringer Landessternwarte, Sternwarte 5, D-07778 (Germany)], E-mail: artie@tls-tautenburg.de

    2008-10-15

    Recently a number of giant extrasolar planets have been discovered around giant stars. These discoveries are important because many of these giant stars have intermediate masses in the range 1.2-3 Msun. Early-type main sequence stars of this mass range have been avoided by radial velocity planet search surveys due the difficulty of getting the requisite radial velocity precision needed for planet discoveries. Thus, giant stars can tell us about planet formation for stars more massive than the sun. However, the determination of stellar masses for giant stars is difficult due to the fact that evolutionary tracks for stars covering a wide range of masses converge to the same region of the H-R diagram. We report here on stellar oscillations in three planet-hosting giant stars: HD 13189, {beta} Gem, and {iota} Dra. Precise stellar radial velocity measurements for these stars show variations whose periods and amplitudes are consistent with solar-like p-mode oscillations. The implied stellar masses for these objects based on the characteristics of the stellar oscillations are consistent with the predictions of stellar isochrones. An investigation of stellar oscillations in planet hosting giant stars offers us the possibility of getting an independent determination of the stellar mass for these objects which is of crucial importance for extrasolar planet studies.

  17. Orbital motion in pre-main sequence binaries

    Energy Technology Data Exchange (ETDEWEB)

    Schaefer, G. H. [The CHARA Array of Georgia State University, Mount Wilson Observatory, Mount Wilson, CA 91023 (United States); Prato, L. [Lowell Observatory, 1400 West Mars Hill Road, Flagstaff, AZ 86001 (United States); Simon, M. [Department of Physics and Astronomy, Stony Brook University, Stony Brook, NY 11794 (United States); Patience, J., E-mail: schaefer@chara-array.org [Astrophysics Group, School of Physics, University of Exeter, Exeter, EX4 4QL (United Kingdom)

    2014-06-01

    We present results from our ongoing program to map the visual orbits of pre-main sequence (PMS) binaries in the Taurus star forming region using adaptive optics imaging at the Keck Observatory. We combine our results with measurements reported in the literature to analyze the orbital motion for each binary. We present preliminary orbits for DF Tau, T Tau S, ZZ Tau, and the Pleiades binary HBC 351. Seven additional binaries show curvature in their relative motion. Currently, we can place lower limits on the orbital periods for these systems; full solutions will be possible with more orbital coverage. Five other binaries show motion that is indistinguishable from linear motion. We suspect that these systems are bound and might show curvature with additional measurements in the future. The observations reported herein lay critical groundwork toward the goal of measuring precise masses for low-mass PMS stars.

  18. XMM-Newton detects X-ray 'solar cycle' in distant star

    Science.gov (United States)

    2004-05-01

    The Sun as observed by SOHO hi-res Size hi-res: 708 Kb The Sun as observed by SOHO The Sun as observed by the ESA/NASA SOHO observatory near the minimum of the solar cycle (left) and near its maximum (right). The signs of solar activity near the maximum are clearly seen. New XMM-Newton observations suggest that this behaviour may be typical of stars like the Sun, such as HD 81809 in the constellation Hydra. Solar flare - 4 November 2003 The huge flare produced on 4 November 2003 This image of the Sun, obtained by the ESA/NASA SOHO observatory, shows the powerful X-ray flare that took place on 4 November 2003. The associated coronal mass ejection, coming out of the Sun at a speed of 8.2 million kilometres per hour, hit the Earth several hours later and caused disruptions to telecommunication and power distribution lines. New XMM-Newton observations suggest that this behaviour may be typical of stars like the Sun, such as HD 81809 in the constellation Hydra. Since the time Galileo discovered sunspots, in 1610, astronomers have measured their number, size and location on the disc of the Sun. Sunspots are relatively cooler areas on the Sun that are observed as dark patches. Their number rises and falls with the level of activity of the Sun in a cycle of about 11 years. When the Sun is very active, large-scale phenomena take place, such as the flares and coronal mass ejections observed by the ESA/NASA solar observatory SOHO. These events release a large amount of energy and charged particles that hit the Earth and can cause powerful magnetic storms, affecting radio communications, power distribution lines and even our weather and climate. During the solar cycle, the X-ray emission from the Sun varies by a large amount (about a factor of 100) and is strongest when the cycle is at its peak and the surface of the Sun is covered by the largest number of spots. ESA's X-ray observatory, XMM-Newton, has now shown for the first time that this cyclic X-ray behaviour is common to

  19. FUNDAMENTAL PROPERTIES OF STARS USING ASTEROSEISMOLOGY FROM KEPLER AND CoRoT AND INTERFEROMETRY FROM THE CHARA ARRAY

    Energy Technology Data Exchange (ETDEWEB)

    Huber, D.; Ireland, M. J.; Bedding, T. R.; Maestro, V.; White, T. R. [Sydney Institute for Astronomy (SIfA), School of Physics, University of Sydney, NSW 2006 (Australia); Brandao, I. M.; Sousa, S. G.; Cunha, M. S. [Centro de Astrofo Latin-Small-Letter-Dotless-I sica and Faculdade de Ciencias, Universidade do Porto, Rua das Estrelas, P-4150-762 Porto (Portugal); Piau, L. [Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48823-2320 (United States); Bruntt, H.; Aguirre, V. Silva; Christensen-Dalsgaard, J. [Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, DK-8000 Aarhus C (Denmark); Casagrande, L. [Research School of Astronomy and Astrophysics, Mount Stromlo Observatory, The Australian National University, ACT 2611 (Australia); Molenda-Zakowicz, J. [Astronomical Institute of the University of Wroclaw, ul. Kopernika 11, 51-622 Wroclaw (Poland); Barclay, T. [Bay Area Environmental Research Institute/NASA Ames Research Center, Moffett Field, CA 94035 (United States); Burke, C. J. [SETI Institute/NASA Ames Research Center, Moffett Field, CA 94035 (United States); Chaplin, W. J. [School of Physics and Astronomy, University of Birmingham, Birmingham B15 2TT (United Kingdom); De Ridder, J. [Instituut voor Sterrenkunde, K. U. Leuven, B-3001 Leuven (Belgium); Farrington, C. D. [Center for High Angular Resolution Astronomy, Georgia State University, P.O. Box 3969, Atlanta, GA 30302 (United States); Frasca, A., E-mail: daniel.huber@nasa.gov [INAF Osservatorio Astrofisico di Catania, I-95123 Catania (Italy); and others

    2012-11-20

    We present results of a long-baseline interferometry campaign using the PAVO beam combiner at the CHARA Array to measure the angular sizes of five main-sequence stars, one subgiant and four red giant stars for which solar-like oscillations have been detected by either Kepler or CoRoT. By combining interferometric angular diameters, Hipparcos parallaxes, asteroseismic densities, bolometric fluxes, and high-resolution spectroscopy, we derive a full set of near-model-independent fundamental properties for the sample. We first use these properties to test asteroseismic scaling relations for the frequency of maximum power ({nu}{sub max}) and the large frequency separation ({Delta}{nu}). We find excellent agreement within the observational uncertainties, and empirically show that simple estimates of asteroseismic radii for main-sequence stars are accurate to {approx}< 4%. We furthermore find good agreement of our measured effective temperatures with spectroscopic and photometric estimates with mean deviations for stars between T {sub eff} = 4600-6200 K of -22 {+-} 32 K (with a scatter of 97 K) and -58 {+-} 31 K (with a scatter of 93 K), respectively. Finally, we present a first comparison with evolutionary models, and find differences between observed and theoretical properties for the metal-rich main-sequence star HD 173701. We conclude that the constraints presented in this study will have strong potential for testing stellar model physics, in particular when combined with detailed modeling of individual oscillation frequencies.

  20. Asteroseismic modelling of the solar-type subgiant star β Hydri

    Science.gov (United States)

    Brandão, I. M.; Doğan, G.; Christensen-Dalsgaard, J.; Cunha, M. S.; Bedding, T. R.; Metcalfe, T. S.; Kjeldsen, H.; Bruntt, H.; Arentoft, T.

    2011-03-01

    Context. Comparing models and data of pulsating stars is a powerful way to understand the stellar structure better. Moreover, such comparisons are necessary to make improvements to the physics of the stellar models, since they do not yet perfectly represent either the interior or especially 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-seismic and seismic data. Methods: We present a revised list of frequencies for 33 modes, which we produced by analysing the power spectrum of the published observations again using a new weighting scheme that minimises the daily sidelobes. We ran several grids of evolutionary models with different input parameters 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 frequencies of β Hydri: (i) we assume that the best model is the one that reproduces the star's interior based on the radial oscillation frequencies alone, to which we have applied the correction for the near-surface effects; (ii) we assume that the best model is the one that produces the lowest value of the chi-square (χ2), i.e. that minimises the difference between the observed frequencies of all available modes and the model predictions, after all model frequencies are corrected for near-surface effects. Results: We show that after applying a correction for near-surface effects to the frequencies of the best models, we can reproduce the observed modes well, including those that have mixed mode character. The model that gives the lowest value of the χ2 is a post-main-sequence

  1. Kinematics and age of 15 stars-photometric solar analogs

    Science.gov (United States)

    Galeev, A. I.; Shimansky, V. V.

    2008-03-01

    The radial and space velocities are inferred for 15 stars that are photometric analogs of the Sun. The space velocity components (U, V, W) of most of these stars lie within the 10-60 km/s interval. The star HD 225239, which in our previous papers we classified as a subgiant, has a space velocity exceeding 100 km/s, and belongs to the thick disk. The inferred fundamental parameters of the atmospheres of solar analogs are combined with published evolutionary tracks to estimate the masses and ages of the stars studied. The kinematics of photometric analogs is compared to the data for a large group of solar-type stars.

  2. Analysis of the Herschel DEBRIS Sun-like star sample

    Science.gov (United States)

    Sibthorpe, B.; Kennedy, G. M.; Wyatt, M. C.; Lestrade, J.-F.; Greaves, J. S.; Matthews, B. C.; Duchêne, G.

    2018-04-01

    This paper presents a study of circumstellar debris around Sun-like stars using data from the Herschel DEBRIS Key Programme. DEBRIS is an unbiased survey comprising the nearest ˜90 stars of each spectral type A-M. Analysis of the 275 F-K stars shows that excess emission from a debris disc was detected around 47 stars, giving a detection rate of 17.1^{+2.6}_{-2.3} per cent, with lower rates for later spectral types. For each target a blackbody spectrum was fitted to the dust emission to determine its fractional luminosity and temperature. The derived underlying distribution of fractional luminosity versus blackbody radius in the population showed that most detected discs are concentrated at f ˜ 10-5 and at temperatures corresponding to blackbody radii 7-40 au, which scales to ˜40 au for realistic dust properties (similar to the current Kuiper belt). Two outlying populations are also evident; five stars have exceptionally bright emission ( f > 5 × 10-5), and one has unusually hot dust <4 au. The excess emission distributions at all wavelengths were fitted with a steady-state evolution model, showing that these are compatible with all stars being born with a narrow belt that then undergoes collisional grinding. However, the model cannot explain the hot dust systems - likely originating in transient events - and bright emission systems - arising potentially from atypically massive discs or recent stirring. The emission from the present-day Kuiper belt is predicted to be close to the median of the population, suggesting that half of stars have either depleted their Kuiper belts (similar to the Solar system) or had a lower planetesimal formation efficiency.

  3. Convection and magnetism of solar-type stars (G and K)

    International Nuclear Information System (INIS)

    Do-Cao, Olivier Long

    2013-01-01

    This thesis aims at understanding the internal dynamics of solar-type stars and the origin of their magnetism. We will explore the complex nonlinear interactions between convection, rotation and magnetism conducting both 2D (STELEM code) and 3D (ASH code) numerical simulations. This dual approach will unveil the mechanisms and key parameters behind those physical processes. While the Sun has played a central role in previous studies, this work extends our knowledge to G and K stars. This manuscript is divided into 4 parts. The first one introduces the concepts behind internal stellar dynamics, and emphasizes the dynamo effect. Accurate observations of the Sun will be compared to stellar data, allowing us to determine what is specific to the Sun and what is generic for all stars. The second part reports the results obtained with the 2D STELEM code. This code allows us to study the generation and evolution of the large scale magnetic fields on a timescale comparable to the solar cycle period (11 years), giving us insight into the underlying dynamo processes at work. We show that the current solar models cannot reproduce the observations, when applied to rapidly rotating stars, unless we consider a turbulent pumping mechanism under specific conditions. Then, we have improved these kinematic models by taking into account the large scale magnetic field feedback on the longitudinal velocity component, called the Malkus Proctor effect. The models are now able to reproduce the solar torsional oscillations and can predict how their properties evolve with rotation rate. The third part focuses on 3D numerical simulations running on massively parallel supercomputers, using the ASH code. In contrast with the previously described code, ASH explicitly resolves the full MHD equations. We have studied (hydrodynamically) how the convective properties of G and K stars change as function of mass and rotation rate, first by considering the convective envelope alone, then by taking into

  4. Cold DUst around NEarby Stars (DUNES). First results. A resolved exo-Kuiper belt around the solar-like star ζ2 Ret

    NARCIS (Netherlands)

    Eiroa, C.; Fedele, D.; Maldonado, J.; Gonzalez-Garcia, B. M.; Rodmann, J.; Heras, A. M.; Pilbratt, G. L.; Augereau, J. -Ch.; Mora, A.; Montesinos, B.; Ardila, D.; Bryden, G.; Liseau, R.; Stapelfeldt, K.; Launhardt, R.; Solano, E.; Bayo, A.; Absil, O.; Arevalo, M.; Barrado, D.; Beichmann, C.; Danchi, W.; del Burgo, C.; Ertel, S.; Fridlund, M.; Fukagawa, M.; Gutierrez, R.; Gruen, E.; Kamp, I.; Krivov, A.; Lebreton, J.; Loehne, T.; Lorente, R.; Marshall, J.; Martinez-Arnaiz, R.; Meeus, G.; Montes, D.; Morbidelli, A.; Mueller, S.; Mutschke, H.; Nakagawa, T.; Olofsson, G.; Ribas, I.; Roberge, A.; Sanz-Forcada, J.; Thebault, P.; White, G. J.; Wolf, S.; Walker, H.

    We present the first far-IR observations of the solar-type stars δ Pav, HR 8501, 51 Peg and ζ2 Ret, taken within the context of the DUNES Herschel open time key programme (OTKP). This project uses the PACS and SPIRE instruments with the objective of studying infrared excesses due to exo-Kuiper belts

  5. Interesting features in the combined Galex and Sloan color diagrams of solar-like galactic populations

    Energy Technology Data Exchange (ETDEWEB)

    Smith, Myron A.; Shiao, Bernard [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Bianchi, Luciana, E-mail: myronmeister@gmail.com, E-mail: shiao@stsci.edu, E-mail: bianchi@pha.jhu.edu [Johns Hopkins University, 3700 San Martin Drive, Baltimore, MD 21218 (United States)

    2014-06-01

    We report on intriguing photometric properties of Galactic stars observed in the Galaxy Evolution Explorer (GALEX) satellite's far-UV (FUV) and near-UV (NUV) bandpasses, as well as from the ground-based Sloan Digital Sky Survey (SDSS) and the Kepler Input Catalog. The first property is that the (FUV – NUV) color distribution of stars in the Kepler field consists of two well-separated peaks. A second and more perplexing property is that for stars with spectral types G or later the mean (FUV – NUV) color becomes much bluer, contrary to expectation. Investigating this tendency further, we found in two samples of mid-F through K type stars that 17%-22% of them exhibit FUV excesses relative to their NUV fluxes and spectral types. A correction for FUV incompleteness of the FUV magnitude-limited star sample brings this ratio to 14%-18%. Nearly the same fractions are also discovered among members of the Kepler Eclipsing Binary Catalog and in the published list of Kepler Objects of Interest. These UV-excess ('UVe') colors are confirmed by the negative UV continuum slopes in GALEX spectra of members of the population. The SDSS spectra of some UVe stars exhibit metallic line weakening, especially in the blue. This suggests an enhanced contribution of UV flux relative to photospheric flux of a solar-type single star. We consider the possibility that the UV excesses originate from various types of hot stars, including white dwarf DA and sdB stars, binaries, and strong chromosphere stars that are young or in active binaries. The space density of compact stars is too low to explain the observed frequency of the UVe stars. Our model atmosphere-derived simulations of colors for binaries with main-sequence pairs with a hot secondary demonstrate that the color loci conflict with the observed sequence. As a preferred alternative we are left with the active chromospheres explanation, whether in active close binaries or young single stars, despite the expected paucity

  6. On p-mode oscillations in stars from 1 solar mass to 2 solar masses

    Science.gov (United States)

    Audard, N.; Provost, J.

    1994-06-01

    The structure of stars more massive than about 1.2 solar masses is characterized by a convective core. We have studied the evolution with age and mass of acoustic frequencies of high radical order n and low degree l for models of stars of 1, 1.5 and 2 solar masses. Using a polynomial approximation for the frequency, the p-mode spectrum can be characterized by derived global asteroseismic coefficients, i.e. the mean separation nu0 is approximately equal to nun, l - nun - 1, l and the small frequency separation Delta nu0, 2 is approximately equal to nun, l = 0 - nun - 1, l = 2. The diagram (nu0, delta nu0, 2/nu0) plotted along the evolutionary tracks would help to separate the effects of age and mass. We study the sensitivity of these coefficients and other observable quantities, like the radius and luminosity, to stellar parameters in the vicinity of 1 solar mass and 2 solar masses; this sensitivity substantially depends on the stellar mass and must be taken into account for asteroseismic calibration of stellar clusters. Considering finally some rapid variations of the internal structure, we show that the second frequency difference delta2 nu = nu(subn, l) - 2 nun - 1, l + nun - 2, l exponent gamma in the He II ionization zone.

  7. Young Stars in Orion May Solve Mystery of Our Solar System

    Science.gov (United States)

    2001-09-01

    Scientists may have to give the Sun a little more credit. Exotic isotopes present in the early Solar System--which scientists have long-assumed were sprinkled there by a powerful, nearby star explosion--may have instead been forged locally by our Sun during the colossal solar-flare tantrums of its baby years. The isotopes--special forms of atomic nuclei, such as aluminum-26, calcium-41, and beryllium-10--can form in the X-ray solar flares of young stars in the Orion Nebula, which behave just like our Sun would have at such an early age. The finding, based on observations by the Chandra X-ray Observatory, has broad implications for the formation of our own Solar System. Eric Feigelson, professor of astronomy and astrophysics at Penn State, led a team of scientists on this Chandra observation and presents these results in Washington, D.C., today at a conference entitled "Two Years of Science with Chandra". "The Chandra study of Orion gives us the first chance to study the flaring properties of stars resembling the Sun when our solar system was forming," said Feigelson. "We found a much higher rate of flares than expected, sufficient to explain the production of many unusual isotopes locked away in ancient meteorites. If the young stars in Orion can do it, then our Sun should have been able to do it too." Scientists who study how our Solar System formed from a collapsed cloud of dust and gas have been hard pressed to explain the presence of these extremely unusual chemical isotopes. The isotopes are short-lived and had to have been formed no earlier than the creation of the Solar System, some five billion years ago. Yet these elements cannot be produced by a star as massive as our Sun under normal circumstances. (Other elements, such as silver and gold, were created long before the creation of the solar system.) The perplexing presence of these isotopic anomalies, found in ancient meteoroids orbiting the Earth, led to the theory that a supernova explosion occurred

  8. New Insights into the Formation of the Blue Main Sequence in NGC 1850

    Science.gov (United States)

    Yang, Yujiao; Li, Chengyuan; Deng, Licai; de Grijs, Richard; Milone, Antonino P.

    2018-06-01

    Recent discoveries of bimodal main sequences (MSs) associated with young clusters (with ages ≲1 Gyr) in the Magellanic Clouds have drawn a lot of attention. One of the prevailing formation scenarios attributes these split MSs to a bimodal distribution in stellar rotation rates, with most stars belonging to a rapidly rotating population. In this scenario, only a small fraction of stars populating a secondary blue sequence are slowly or non-rotating stars. Here, we focus on the blue MS in the young cluster NGC 1850. We compare the cumulative number fraction of the observed blue-MS stars to that of the high-mass-ratio binary systems at different radii. The cumulative distributions of both populations exhibit a clear anti-correlation, characterized by a highly significant Pearson coefficient of ‑0.97. Our observations are consistent with the possibility that blue-MS stars are low-mass-ratio binaries, and therefore their dynamical disruption is still ongoing. High-mass-ratio binaries, on the other hand, are more centrally concentrated.

  9. Solar rotation and activity in the past and their possible influence upon the evolution of life

    Energy Technology Data Exchange (ETDEWEB)

    Geyer, E H

    1980-01-01

    Observations of enhanced spot active main sequence stars of solar type led to the formulation of the hypothesis which states that the rotational angular momentum, J/sub r/, of stars with spectral types later than F5 determines the intensity of their magnetic activity, bar A. Such very spot active stars are exclusively found as the components of fairly close binary stars, and show rotation periods smaller or more or less synchronous to the orbital period. Single stars of the lower main sequence are generally slow rotators, and do not show detectable activity in optical spectral regions, similar to the Sun if observed from stellar distances.

  10. Understanding the star formation modes in the distant universe

    International Nuclear Information System (INIS)

    Salmi, Fadia

    2012-01-01

    The goal of my PhD study consists at attempt to understand what are the main processes at the origin of the star formation in the galaxies over the last 10 billion years. While it was proposed in the past that merging of galaxies has a dominant role to explain the triggering of the star formation in the distant galaxies having high star formation rates, in the opposite, more recent studies revealed scaling laws linking the star formation rate in the galaxies to their stellar mass or their gas mass. The small dispersion of these laws seems to be in contradiction with the idea of powerful stochastic events due to interactions, but rather in agreement with the new vision of galaxy history where the latter are continuously fed by intergalactic gas. We were especially interested in one of this scaling law, the relation between the star formation (SFR) and the stellar mass (M*) of galaxies, commonly called the main sequence of star forming galaxies. We studied this main sequence, SFR-M"*, in function of the morphology and other physical parameters like the radius, the colour, the clumpiness. The goal was to understand the origin of the sequence's dispersion related to the physical processes underlying this sequence in order to identify the main mode of star formation controlling this sequence. This work needed a multi-wavelength approach as well as the use of galaxies profile simulation to distinguish between the different galaxy morphological types implied in the main sequence. (author) [fr

  11. Asteroseismology of Exoplanet-Host Stars in the TESS Era

    DEFF Research Database (Denmark)

    Campante, Tiago L.; Schofield, Mathew; Chaplin, William J.

    2015-01-01

    -mass main-sequence hosts, as well as for the cohort of “full-frame image” stars (observed at a 30-min cadence). The latter cohort offers the exciting prospect of conducting asteroseismology on a significant number of evolved hosts. Also, the brightest solar-type hosts with asteroseismology will become some...

  12. Long-Term Variability of the Sun in the Context of Solar-Analog Stars

    Science.gov (United States)

    Egeland, Ricky

    2018-06-01

    The Sun is the best observed object in astrophysics, but despite this distinction the nature of its well-ordered generation of magnetic field in 11-year activity cycles remains a mystery. In this work, we place the solar cycle in a broader context by examining the long-term variability of solar analog stars within 5% of the solar effective temperature, but varied in rotation rate and metallicity. Emission in the Fraunhofer H & K line cores from singly-ionized calcium in the lower chromosphere is due to magnetic heating, and is a proven proxy for magnetic flux on the Sun. We use Ca H & K observations from the Mount Wilson Observatory HK project, the Lowell Observatory Solar Stellar Spectrograph, and other sources to construct composite activity time series of over 100 years in length for the Sun and up to 50 years for 26 nearby solar analogs. Archival Ca H & K observations of reflected sunlight from the Moon using the Mount Wilson instrument allow us to properly calibrate the solar time series to the S-index scale used in stellar studies. We find the mean solar S-index to be 5–9% lower than previously estimated, and the amplitude of activity to be small compared to active stars in our sample. A detailed look at the young solar analog HD 30495, which rotates 2.3 times faster than the Sun, reveals a large amplitude ~12-year activity cycle and an intermittent short-period variation of 1.7 years, comparable to the solar variability time scales despite its faster rotation. Finally, time series analyses of the solar analog ensemble and a quantitative analysis of results from the literature indicate that truly Sun-like cyclic variability is rare, and that the amplitude of activity over both long and short timescales is linearly proportional to the mean activity. We conclude that the physical conditions conducive to a quasi-periodic magnetic activity cycle like the Sun’s are rare in stars of approximately the solar mass, and that the proper conditions may be restricted

  13. 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......, radius, luminosity, effective temperature, surface gravity and age based on grid modeling. All the tools take into account the window function of the observations which means that they work equally well for space-based photometry observations from e.g. the NASA Kepler satellite and ground-based velocity...

  14. Spectrophotometry of peculiar B and A stars. II. Eleven mercury-manganese stars

    International Nuclear Information System (INIS)

    Adelman, S.J.; Pyper, D.M.

    1979-01-01

    Spectrophotometry of eleven HgMn stars is presented for the optical region. As found in Paper I, the HgMn stars have systematically larger Δiota* and Δa values than the normal main sequence stars due to differences with respect to the mean continuum particularly of the lambda4464 values and the lambda5200 region, respectively. The HgMn stars exhibit a continuous range in the behavior of both the lambda4200 and lambda5200 regions between those stars that have index values larger than the appropriate criterion of presence and present definite evidence for the features to those stars with only a slight possibility of such features. The strengths of the lambda4200 and lambda5200 features appear not to be correlated. In the HgMn stars, both features may be due to differential line blocking. In the energy distribution of all eleven stars, the Balmer jump regions best fit the predictions of slightly hotter solar composition, log g=4.0, fully line blanketed model atmospheres than do the corresponding Paschen continua

  15. The character and behaviour of circumstellar shells at T Tauri stars

    International Nuclear Information System (INIS)

    Goetz, W.

    1988-01-01

    T Tauri stars are extremely young low-mass stars in the pre-main sequence stage. A brief review of investigations made at the Sonneberg observatory concerning the character and the behaviour of circumstellar shells at T Tauri stars is given. They lead to the construction of a shell model on the basis of observational facts. The idea rests upon the causal connection between the gas and dust shell phenomenon and the cosmogonic mass loss of the stars, which is the connecting link between the stars and their shells and which appears in the early phase of the pre-main sequence stage and decreases, like the accompanying shell phenomena, during the evolution of the stars. (author)

  16. Magnetic massive stars as progenitors of `heavy' stellar-mass black holes

    Science.gov (United States)

    Petit, V.; Keszthelyi, Z.; MacInnis, R.; Cohen, D. H.; Townsend, R. H. D.; Wade, G. A.; Thomas, S. L.; Owocki, S. P.; Puls, J.; ud-Doula, A.

    2017-04-01

    The groundbreaking detection of gravitational waves produced by the inspiralling and coalescence of the black hole (BH) binary GW150914 confirms the existence of 'heavy' stellar-mass BHs with masses >25 M⊙. Initial characterization of the system by Abbott et al. supposes that the formation of BHs with such large masses from the evolution of single massive stars is only feasible if the wind mass-loss rates of the progenitors were greatly reduced relative to the mass-loss rates of massive stars in the Galaxy, concluding that heavy BHs must form in low-metallicity (Z ≲ 0.25-0.5 Z⊙) environments. However, strong surface magnetic fields also provide a powerful mechanism for modifying mass-loss and rotation of massive stars, independent of environmental metallicity. In this paper, we explore the hypothesis that some heavy BHs, with masses >25 M⊙ such as those inferred to compose GW150914, could be the natural end-point of evolution of magnetic massive stars in a solar-metallicity environment. Using the MESA code, we developed a new grid of single, non-rotating, solar-metallicity evolutionary models for initial zero-age main sequence masses from 40 to 80 M⊙ that include, for the first time, the quenching of the mass-loss due to a realistic dipolar surface magnetic field. The new models predict terminal-age main-sequence (TAMS) masses that are significantly greater than those from equivalent non-magnetic models, reducing the total mass lost by a strongly magnetized 80 M⊙ star during its main-sequence evolution by 20 M⊙. This corresponds approximately to the mass-loss reduction expected from an environment with metallicity Z = 1/30 Z⊙.

  17. AK Sco: a tidally induced atmospheric dynamo in a pre-main sequence binary?

    Science.gov (United States)

    Gómez de Castro, A. I.

    2009-02-01

    AK Sco is a unique source: a 10-30 Myrs old pre-main sequence spectroscopic binary composed by two nearly equal F5 stars that at periastron are separated by barely eleven stellar radii so, the stellar magnetospheres fill the Roche lobe at periastron. The orbit is not yet circularized (e = 0.47) and very strong tides are expected. This makes of AK Sco, the ideal laboratory to study the effect of gravitational tides in the stellar magnetic field building up during pre-main sequence evolution. Evidence of this effect is reported in this contribution.

  18. Stellar Rotation with Kepler and Gaia: Evidence for a Bimodal Star Formation History

    Science.gov (United States)

    Davenport, James

    2018-01-01

    Kepler stars with rotation periods measured via starspot modulations in their light curves have been matched against the astrometric data from Gaia Data Release 1. A total of 1,299 bright rotating stars were recovered, most with temperatures hotter than 5000 K. From these, 894 were selected as being near the main sequence. These main sequence stars show a bimodality in their rotation period distribution, centered around a ~600 Myr rotation-isochrone. This feature matches the bimodal period distribution found in cooler stars with Kepler, but was previously undetected for solar-type stars due to sample contamination by subgiant and binary stars. A tenuous connection between the rotation period and total proper motion is found, suggesting the period bimodality is due to the age distribution of stars within 300pc of the Sun, rather than a phase of rapid angular momentum loss. I will discuss how the combination of Kepler/K2/TESS with Gaia will enable us to map the star formation history of our galactic neighborhood.

  19. Amplitudes of solar-like oscillations: Constraints from red giants in open clusters observed by Kepler

    DEFF Research Database (Denmark)

    Stello, Dennis; Huber, Daniel; Kallinger, Thomas

    2011-01-01

    implies that the stellar parameters can be measured to much higher precision than what is usually achievable for single stars. This makes clusters ideal for exploring the relation between the mode amplitude of solar-like oscillations and the global stellar properties. We have analyzed data obtained......Scaling relations that link asteroseismic quantities to global stellar properties are important for gaining understanding of the intricate physics that underpins stellar pulsations. The common notion that all stars in an open cluster have essentially the same distance, age, and initial composition...... with NASA's Kepler space telescope to study solar-like oscillations in 100 red giant stars located in either of the three open clusters, NGC 6791, NGC 6819, and NGC 6811. By fitting the measured amplitudes to predictions from simple scaling relations that depend on luminosity, mass, and effective...

  20. IUE observations of solar-type stars in the Pleiades and the Hyades

    Science.gov (United States)

    Caillault, Jean-Pierre; Vilhu, Osmi; Linsky, Jeffrey L.

    1991-01-01

    An extensive set of IUE observations of solar-type stars (spectral types F5-G5) in the Pleiades is presented. Spectra were obtained in January and August 1988 for both the transition region and chromospheric emission wavelength regions, respectively. Mg II fluxes were detected for two out of three Pleiades stars and C IV upper limits for two of these stars. Long-wavelength high-resolution spectra were also obtained for previously unobserved solar-type stars in the Hyades. With the inclusion of spectra of additional Hyades stars obtained from the IUE archives, surface fluxes and fractional luminosities for both clusters' solar-type stars are calculated; these values provide a better estimate for the Mg II saturation line for single stars.

  1. New light on faint stars

    International Nuclear Information System (INIS)

    Reid, N.; Gilmore, G.

    1982-01-01

    This paper presents the first purely photometric derivation of the stellar main-sequence luminosity function to absolute magnitude Msub(V) = + 19, which is comparable to the minimum mass for thermonuclear burning. The observations consist of COSMOS measures of UK Schmidt telescope plates in the V, R and I bands. They provide a complete sample of every star in 18.24 square degrees towards the South Galactic Pole, brighter than I = 17.0. Absolute magnitudes and distances are derived by photometric parallax from the Msub(V)/V-I and Msub(V)/I-K relations, which have been carefully calibrated on our photometric system. For +9<=Msub(V)<=+19, the photometrically defined luminosity function is in agreement with that derived from samples of nearby stars, and by proper motion techniques. There is no evidence for any excess of intrinsically faint stars, even though this survey reaches some 5 mag deeper into the luminosity function than previous photometric surveys. Re-analysis of subsamples of other photometric studies of the local stellar density removes any evidence for a significant excess of M dwarfs relative to the kinematically derived luminosity function. The missing mass in the solar neighbourhood, if any, does not reside in main-sequence stars brighter than Msub(V) approx. = + 17 mag. (author)

  2. The onset of chromospheric activity among the A and F stars

    Science.gov (United States)

    Simon, Theodore; Landsman, Wayne

    1991-01-01

    Results are reported from a search for an upper boundary for the onset of main-sequence star activity based on a quest for high-temperature UV line emission in a large collection of IUE spectra. It is shown that strong chromospheric emission is common among early F dwarf and subgiant stars. At its brightest, the emission is equal to that of the most active solar-type stars and is exceeded only by that of the spotted RS CVn and BY Dra variables. It is suggested that the emission from the main-sequence stars reaches a peak near B-V = 0.28, in the vicinity of spectral type F0 V, before it declines to lower flux levels among the late A stars. Emission is seen in some dwarf stars as early as B-V = 0.25. It is demonstrated that the C II emission of stars earlier than the spectral type F5 is uncorrelated with rotation. Previous findings that the coronal X-ray:chromospheric UV flux ratio is lower for stars earlier than spectral type F5 than for those later than F5 are confirmed.

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

    Energy Technology Data Exchange (ETDEWEB)

    Lopes, Ilídio [Centro Multidisciplinar de Astrofísica, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1049-001 Lisboa (Portugal); Silk, Joseph, E-mail: ilidio.lopes@tecnico.ulisboa.pt, E-mail: silk@astro.ox.ac.uk [Institut d’Astrophysique de Paris, UMR 7095 CNRS, Université Pierre et Marie Curie, 98 bis Boulevard Arago, Paris F-75014 (France)

    2017-07-20

    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 1–10{sup 3} 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.

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

    OpenAIRE

    Marcy, Geoffrey W.; Weiss, Lauren M.; 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...

  5. PRE-MAIN-SEQUENCE TURN-ON AS A CHRONOMETER FOR YOUNG CLUSTERS: NGC 346 AS A BENCHMARK

    International Nuclear Information System (INIS)

    Cignoni, M.; Tosi, M.; Sabbi, E.; Nota, A.; Degl'Innocenti, S.; Moroni, P. G. Prada; Gallagher, J. S.

    2010-01-01

    We present a novel approach to deriving the age of very young star clusters, by using the Turn-On (TOn). The TOn is the point in the color-magnitude diagram (CMD) where the pre-main sequence (PMS) joins the main sequence (MS). In the MS luminosity function (LF) of the cluster, the TOn is identified as a peak followed by a dip. We propose that by combining the CMD analysis with the monitoring of the spatial distribution of MS stars it is possible to reliably identify the TOn in extragalactic star-forming regions. Compared to alternative methods, this technique is complementary to the turnoff dating and avoids the systematic biases affecting the PMS phase. We describe the method and its uncertainties and apply it to the star-forming region NGC 346, which has been extensively imaged with the Hubble Space Telescope (HST). This study extends the LF approach in crowded extragalactic regions and opens the way for future studies with HST/WFC3, the James Webb Space Telescope and from the ground with adaptive optics.

  6. Kepler Mission: A Wide-FOV Photometer Designed to Determine the Frequency of Earth-Size and Larger Planets Around Solar-like stars

    Science.gov (United States)

    Borucki, William; Koch, David; Lissauer, Jack; Basri, Gibor; Caldwell, John; Cochran, William; Dunham, Edward W.; Gilliland, Ronald; Jenkins, Jon M.; Caldwell, Douglas; hide

    2002-01-01

    The first step in discovering the extent of life in our galaxy is to determine the number of terrestrial planets in the habitable zone (HZ). The Kepler Mission is designed around a 0.95 m aperture Schmidt-type telescope with an array of 42 CCDs designed to continuously monitor the brightness of 100,000 solar-like stars to detect the transits of Earth-size and larger planets. The photometer is scheduled to be launched into heliocentric orbit in 2007. Measurements of the depth and repetition time of transits provide the size of the planet relative to the star and its orbital period. When combined with ground-based spectroscopy of these stars to fix the stellar parameters, the true planet radius and orbit scale, hence the position relative to the HZ are determined. These spectra are also used to discover the relationships between the characteristics of planets and the stars they orbit. In particular, the association of planet size and occurrence frequency with stellar mass and metallicity will be investigated. At the end of the four year mission, hundreds of terrestrial planets should be discovered in and near the HZ of their stars if such planets are common. A null result would imply that terrestrial planets in the HZ occur in less than 1% of the stars and that life might be quite rare. Based on the results of the current doppler-velocity discoveries, detection of a thousand giant planets is expected. Information on their albedos and densities of those giants showing transits will be obtained.

  7. Dust discs around low-mass main-sequence stars

    International Nuclear Information System (INIS)

    Wolstencroft, R.D.; Walker, H.J.

    1988-01-01

    Current understanding of the formation of circumstellar discs as a natural accompaniment to the process of low-mass star formation is briefly reviewed. Models of the thermal emission from the dust discs around the prototype stars α Lyr, α PsA, β Pic and ε Eri are discussed, which indicate that the central regions of three of these discs are almost devoid of dust within radii ranging between 17 and 26 AU, with the temperature of the hottest dust lying between about 115 and 210 K. One possible explanation of the dust-free zones is the presence of a planet at the inner boundary of each cloud that sweeps up grains crossing its orbit. The colour, diameter and thickness of the optical image of β Pic, obtained by coronagraphic techniques, have provided further information on the size, radial distribution of number density and orbital inclination of the grains. The difference in surface brightness on the two sides of the disc is puzzling, but might be explained if the grains are elongated and aligned by the combined effects of a stellar wind and a magnetic field of spiral configuration. Finally, we discuss the orbital evolution and lifetimes of particles in these discs, which are governed primarily by radiation pressure, Poynting-Robertson drag and grain-grain collisions. (author)

  8. Hydrodynamic ejection of bipolar flows from objects undergoing disk accretion: T Tauri stars, massive pre-main-sequence objects, and cataclysmic variables

    International Nuclear Information System (INIS)

    Torbett, M.V.

    1984-01-01

    A general mechanism is presented for generating pressure-driven winds that are intrinsically bipolar from objects undergoing disk accretion. The energy librated in a boundary layer shock as the disk matter impacts the central object is shown to be sufficient to eject a fraction βapprox.10 -2 to 10 -3 of the accreted mass. These winds are driven by a mechanism that accelerates the flow perpendicular to the plane of the disk and can therefore account for the bipolar geometry of the mass loss observed near young stars. The mass loss contained in these winds is comparable to that inferred for young stars. Thus, disk accretion-driven winds may constitute the T Tauri phase of stellar evolution. This mechanism is generally applicable, and thus massive pre-main-sequence objects as well as cataclysmic variables at times of enhanced accretion are predicted to eject bipolar outflows as well. Unmagnetized accreting neutron stas are also expected to eject bipolar flows. Since this mechanism requires stellar surfaces, however, it will not operate in disk accretion onto black holes

  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. Chemical abundances of primary stars in the Sirius-like binary systems

    Science.gov (United States)

    Kong, X. M.; Zhao, G.; Zhao, J. K.; Shi, J. R.; Kumar, Y. Bharat; Wang, L.; Zhang, J. B.; Wang, Y.; Zhou, Y. T.

    2018-05-01

    Study of primary stars lying in Sirius-like systems with various masses of white dwarf (WD) companions and orbital separations is one of the key aspects to understand the origin and nature of barium (Ba) stars. In this paper, based on high-resolution and high-S/N spectra, we present systematic analysis of photospheric abundances for 18 FGK primary stars of Sirius-like systems including six giants and 12 dwarfs. Atmospheric parameters, stellar masses, and abundances of 24 elements (C, Na, Mg, Al, Si, S, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Sr, Y, Zr, Ba, La, Ce, and Nd) are determined homogeneously. The abundance patterns in these sample stars show that most of the elements in our sample follow the behaviour of field stars with similar metallicity. As expected, s-process elements in four known Ba giants show overabundance. A weak correlation was found between anomalies of s-process elemental abundance and orbital separation, suggesting that the orbital separation of the binaries could not be the main constraint to differentiate strong Ba stars from mild Ba stars. Our study shows that the large mass (>0.51 M⊙) of a WD companion in a binary system is not a sufficient condition to form a Ba star, even if the separation between the two components is small. Although not sufficient, it seems to be a necessary condition since Ba stars with lower mass WDs in the observed sample were not found. Our results support that [s/Fe] and [hs/ls] ratios of Ba stars are anti-correlated with the metallicity. However, the different levels of s-process overabundance among Ba stars may not be dominated mainly by the metallicity.

  11. ROTATION PERIODS AND AGES OF SOLAR ANALOGS AND SOLAR TWINS REVEALED BY THE KEPLER MISSION

    International Nuclear Information System (INIS)

    Do Nascimento Jr, J.-D.; Meibom, S.; García, R. A.; Salabert, D.; Ceillier, T.; Mathur, S.; Anthony, F.; Da Costa, J. S.; Castro, M.; Barnes, S. A.

    2014-01-01

    A new sample of solar analogs and twin candidates has been constructed and studied, paying particular attention to their light curves from NASA's Kepler mission. This Letter aims to assess their evolutionary status, derive their rotation and ages, and identify those which are solar analogs or solar twin candidates. We separate out the subgiants that compose a large fraction of the asteroseismic sample, and which show an increase in the average rotation period as the stars ascend the subgiant branch. The rotation periods of the dwarfs, ranging from 6 to 30 days and averaging 19 days, allow us to assess their individual evolutionary states on the main sequence and to derive their ages using gyrochronology. These ages are found to be in agreement with a correlation coefficient of r = 0.79 with independent asteroseismic ages, where available. As a result of this investigation, we are able to identify 34 stars as solar analogs and 22 of them as solar twin candidates

  12. ROTATION PERIODS AND AGES OF SOLAR ANALOGS AND SOLAR TWINS REVEALED BY THE KEPLER MISSION

    Energy Technology Data Exchange (ETDEWEB)

    Do Nascimento Jr, J.-D.; Meibom, S. [Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138 (United States); García, R. A.; Salabert, D.; Ceillier, T. [Laboratoire AIM, CEA/DSM,CNRS, Univ. Paris Diderot-IRFU/SAp, Centre de Saclay, F-91191 Gif-sur-Yvette Cedex (France); Mathur, S. [Space Science Institute, 4750 Walnut Street Suite 205, Boulder CO 80301 (United States); Anthony, F.; Da Costa, J. S.; Castro, M. [Universidade Federal do Rio Grande do Norte, UFRN, Dep. de Física Teórica e Experimental, DFTE, CP 1641, 59072-970 Natal, RN (Brazil); Barnes, S. A., E-mail: jdonascimento@cfa.harvard.edu [Leibniz-Institute for Astrophysics, Potsdam D-14467 (Germany)

    2014-08-01

    A new sample of solar analogs and twin candidates has been constructed and studied, paying particular attention to their light curves from NASA's Kepler mission. This Letter aims to assess their evolutionary status, derive their rotation and ages, and identify those which are solar analogs or solar twin candidates. We separate out the subgiants that compose a large fraction of the asteroseismic sample, and which show an increase in the average rotation period as the stars ascend the subgiant branch. The rotation periods of the dwarfs, ranging from 6 to 30 days and averaging 19 days, allow us to assess their individual evolutionary states on the main sequence and to derive their ages using gyrochronology. These ages are found to be in agreement with a correlation coefficient of r = 0.79 with independent asteroseismic ages, where available. As a result of this investigation, we are able to identify 34 stars as solar analogs and 22 of them as solar twin candidates.

  13. Amplitudes of solar-like oscillations in red giants: Departures from the quasi-adiabatic approximation

    Directory of Open Access Journals (Sweden)

    Barban C.

    2013-03-01

    Full Text Available CoRoT and Kepler measurements reveal us that the amplitudes of solar-like oscillations detected in red giant stars scale from stars to stars in a characteristic way. This observed scaling relation is not yet fully understood but constitutes potentially a powerful diagnostic about mode physics. Quasi-adiabatic theoretical scaling relations in terms of mode amplitudes result in systematic and large differences with the measurements performed for red giant stars. The use of a non-adiabatic intensity-velocity relation derived from a non-adiabatic pulsation code significantly reduces the discrepancy with the CoRoT measurements. The origin of the remaining difference is still unknown. Departure from adiabatic eigenfunction is a very likely explanation that is investigated in the present work using a 3D hydrodynamical model of the surface layers of a representative red giant star.

  14. IRAS IDENTIFICATION OF PRE-MAIN-SEQUENCE STARS IN THE CHAMELEON-II ASSOCIATION

    NARCIS (Netherlands)

    PRUSTI, T; WHITTET, DCB; ASSENDORP, R; WESSELIUS, PR

    We report the results of a search for new pre-main sequence candidates in the Chamaeleon II dark cloud based on three IRAS catalogues (the Point Source Catalog, the Serendipitous Survey Catalog and the Faint Source Survey). A total of 30 sources were selected. Twelve of these display IRAS colours

  15. BVRI main-sequence photometry of the globular cluster M4

    International Nuclear Information System (INIS)

    Alcaino, G.; Liller, W.

    1984-01-01

    We present BV and RI photographic photometry of 1421 and 189 stars, respectively, in the intermediate metallicity globular cluster M4 (NGC 6121). This investigation includes the first results of RI main-sequence photometry of a globular cluster. The use of longer wavelengths and longer color baselines provides the potential of improved isochrone fittings and underscores the urgent need for calculations of RI synthetic isochrones to be compared with observations. The Pickering-Racine wedge was used with the ESO 3.6 m telescope, the Las Campanas 2.5 m du Pont telescope, and the CTIO 1 m Yale telescope to extend the photoelectric limit from Vroughly-equal16.1 to Vroughly-equal19.1. We have determined the position of the main-sequence turnoff to lie at V = 16.6 +- 0.2 (m.e.) and B-V = 0.80 +- 0.03 (m.e.). A comparison of our BV observations with the CCD data of Richer and Fahlman shows excellent agreement: the two fifucial main sequences agree at all points to within 0.025 mag and, on average, to 0.013 mag. For the cluster we derive a distance modulus (m-M)/sub V/ = 12.52 +- 0.2 and reddening E(B-V) = 0.44 +- 0.03, results which confirm that at a distance of 2 kpc, M4 is the closest globular clusters to the Sun. Using the isochrones of VandenBerg, we deduce an age 13 +- 2 Gyr. As noted in several other investigations, there is a striking deficiency of stars in certain parts of the color-magnitude diagram; in M4 we find a pronounced gap over approx.0.6 mag at the base of the subgiant branch

  16. Chemical evolution with rotating massive star yields - I. The solar neighbourhood and the s-process elements

    Science.gov (United States)

    Prantzos, N.; Abia, C.; Limongi, M.; Chieffi, A.; Cristallo, S.

    2018-05-01

    We present a comprehensive study of the abundance evolution of the elements from H to U in the Milky Way halo and local disc. We use a consistent chemical evolution model, metallicity-dependent isotopic yields from low and intermediate mass stars and yields from massive stars which include, for the first time, the combined effect of metallicity, mass loss, and rotation for a large grid of stellar masses and for all stages of stellar evolution. The yields of massive stars are weighted by a metallicity-dependent function of the rotational velocities, constrained by observations as to obtain a primary-like 14N behaviour at low metallicity and to avoid overproduction of s-elements at intermediate metallicities. We show that the Solar system isotopic composition can be reproduced to better than a factor of 2 for isotopes up to the Fe-peak, and at the 10 per cent level for most pure s-isotopes, both light ones (resulting from the weak s-process in rotating massive stars) and the heavy ones (resulting from the main s-process in low and intermediate mass stars). We conclude that the light element primary process (LEPP), invoked to explain the apparent abundance deficiency of the s-elements with A values of ^{12}C/^{13}C in halo red giants, which is rather due to internal processes in those stars.

  17. Kepler Mission: a Discovery-Class Mission Designed to Determine the Frequency of Earth-Size and Larger Planets Around Solar-Like Stars

    Science.gov (United States)

    Borucki, William; Koch, David; Lissauer, Jack; Basri, Gibor; Caldwell, John; Cochran, William; Dunham, Edward W.; Gilliland, Ronald; Caldwell, Douglas; Kondo, Yoji; hide

    2002-01-01

    The first step in discovering the extent of life in our galaxy is to determine the number of terrestrial planets in the habitable zone (HZ). The Kepler Mission is designed around a 0.95 in aperture Schmidt-type telescope with an array of 42 CCDs designed to continuously monitor the brightness of 100,000 solar-like stars to detect the transits of Earth-size and larger planets. The photometer is scheduled to be launched into heliocentric orbit in 2007. Measurements of the depth and repetition time of transits provide the size of the planet relative to the star and its orbital period. When combined with ground-based spectroscopy of these stars to fix the stellar parameters, the true planet radius and orbit scale, hence the position relative to the HZ are determined. These spectra are also used to discover the relationships between the characteristics of planets and the stars they orbit. In particular, the association of planet size and occurrence frequency with stellar mass and metallicity will be investigated. At the end of the four year mission, hundreds of terrestrial planets should be discovered in and near the HZ of their stars if such planets are common. Extending the mission to six years doubles the expected number of Earth-size planets in the HZ. A null result would imply that terrestrial planets in the HZ occur in less than 1% of the stars and that life might be quite rare. Based on the results of the current Doppler-velocity discoveries, detection of a thousand giant planets is expected. Information on their albedos and densities of those giants showing transits will be obtained.

  18. Pre-main-sequence disk accretion in Z Canis Majoris

    International Nuclear Information System (INIS)

    Hartmann, L.; Kenyon, S.J.; Hewett, R.; Edwards, S.; Strom, K.M.; Strom, S.E.; Stauffer, J.R.

    1989-01-01

    It is suggested that the pre-main-sequence object Z CMa is a luminous accretion disk, similar in many respects to the FU Orionis variables. Z CMa shows the broad, doubled optical absorption lines expected from a rapidly rotating accretion disk. The first overtone CO absorption detected in Z CMa is blue-shifted, suggesting line formation in a disk wind. Accretion at rates about 0.001 solar mass/yr over 100 yr is required to explain the luminosity of Z CMa. The large amount of material accreted (0.1 solar mass/yr) indicates that Z CMa is in a very early stage of stellar evolution, possibly in an initial phase of massive disk accretion. 41 references

  19. Pre-main-sequence disk accretion in Z Canis Majoris

    Science.gov (United States)

    Hartmann, L.; Kenyon, S. J.; Hewett, R.; Edwards, S.; Strom, K. M.; Strom, S. E.; Stauffer, J. R.

    1989-01-01

    It is suggested that the pre-main-sequence object Z CMa is a luminous accretion disk, similar in many respects to the FU Orionis variables. Z CMa shows the broad, doubled optical absorption lines expected from a rapidly rotating accretion disk. The first overtone CO absorption detected in Z CMa is blue-shifted, suggesting line formation in a disk wind. Accretion at rates about 0.001 solar mass/yr over 100 yr is required to explain the luminosity of Z CMa. The large amount of material accreted (0.1 solar mass/yr) indicates that Z CMa is in a very early stage of stellar evolution, possibly in an initial phase of massive disk accretion.

  20. Giant CP stars

    International Nuclear Information System (INIS)

    Loden, L.O.; Sundman, A.

    1989-01-01

    This study is part of an investigation of the possibility of using chemically peculiar (CP) stars to map local galactic structure. Correct luminosities of these stars are therefore crucial. CP stars are generally regarded as main-sequence or near-main-sequence objects. However, some CP stars have been classified as giants. A selection of stars, classified in literature as CP giants, are compared to normal stars in the same effective temperature interval and to ordinary 'non giant' CP stars. There is no clear confirmation of a higher luminosity for 'CP giants', than for CP stars in general. In addition, CP characteristics seem to be individual properties not repeated in a component star or other cluster members. (author). 50 refs., 5 tabs., 3 figs

  1. Relation between initial and minimum final white dwarf mass for Population I stars

    Energy Technology Data Exchange (ETDEWEB)

    Mazzitelli, I.; Dantona, F.

    1986-12-01

    The evolutionary paths for Population I stars having initial masses 1, 2.5, 3, 4, and 5 solar masses were computed from the homogeneous main sequence to the onset of the first major thermal pulse to evaluate the minimum mass and the chemical stratification of the remnant white dwarf (WD) associated with each parent mass. The helium flash phase was followed in detail for a 2.5 solar masses star, whereas for the 1 solar mass star the flash was bypassed, and the models at the beginning of the steady central helium burning phase were obtained by means of a scaling procedure upon the properly computed total and core masses. The results show that for a parent ranging between 1-3 solar masses the core mass at the first thermal pulse ranges only from 0.64-0.69 solar mass. If some very fast mass-loss mechanism is triggered in connection with the early stages of the thermal pulse phase, as suggested by the observed deficiency of asymptotic giant branch stars, the relation between final and initial mass is almost flat at least up to an initial mass of 3 solar masses, and the mass spectrum of the WDs is narrow and heavily peaked around 0.65 solar mass. 53 references.

  2. Relation between initial and minimum final white dwarf mass for Population I stars

    International Nuclear Information System (INIS)

    Mazzitelli, I.; Dantona, F.; CNR, Istituto di Astrofisica Spaziale, Frascati; Roma, Osservatorio Astronomico, Rome, Italy)

    1986-01-01

    The evolutionary paths for Population I stars having initial masses 1, 2.5, 3, 4, and 5 solar masses were computed from the homogeneous main sequence to the onset of the first major thermal pulse to evaluate the minimum mass and the chemical stratification of the remnant white dwarf (WD) associated with each parent mass. The helium flash phase was followed in detail for a 2.5 solar masses star, whereas for the 1 solar mass star the flash was bypassed, and the models at the beginning of the steady central helium burning phase were obtained by means of a scaling procedure upon the properly computed total and core masses. The results show that for a parent ranging between 1-3 solar masses the core mass at the first thermal pulse ranges only from 0.64-0.69 solar mass. If some very fast mass-loss mechanism is triggered in connection with the early stages of the thermal pulse phase, as suggested by the observed deficiency of asymptotic giant branch stars, the relation between final and initial mass is almost flat at least up to an initial mass of 3 solar masses, and the mass spectrum of the WDs is narrow and heavily peaked around 0.65 solar mass. 53 references

  3. A tale of two anomalies: Depletion, dispersion, and the connection between the stellar lithium spread and inflated radii on the pre-main sequence

    Energy Technology Data Exchange (ETDEWEB)

    Somers, Garrett; Pinsonneault, Marc H., E-mail: somers@astronomy.ohio-state.edu, E-mail: pinsono@astronomy.ohio-state.edu [Department of Astronomy, The Ohio State University, 140 West 18th Avenue, Columbus, OH 43201 (United States)

    2014-07-20

    We investigate lithium depletion in standard stellar models (SSMs) and main sequence (MS) open clusters, and explore the origin of the Li dispersion in young, cool stars of equal mass, age, and composition. We first demonstrate that SSMs accurately predict the Li abundances of solar analogs at the zero-age main sequence (ZAMS) within theoretical uncertainties. We then measure the rate of MS Li depletion by removing the [Fe/H]-dependent ZAMS Li pattern from three well-studied clusters, and comparing the detrended data. MS depletion is found to be mass-dependent, in the sense of more depletion at low mass. A dispersion in Li abundance at fixed T{sub eff} is nearly universal, and sets in by ∼200 Myr. We discuss mass and age dispersion trends, and the pattern is mixed. We argue that metallicity impacts the ZAMS Li pattern, in agreement with theoretical expectations but contrary to the findings of some previous studies, and suggest Li as a test of cluster metallicity. Finally, we argue that a radius dispersion in stars of fixed mass and age, during the epoch of pre-MS Li destruction, is responsible for the spread in Li abundances and the correlation between rotation and Li in young cool stars, most well known in the Pleiades. We calculate stellar models, inflated to match observed radius anomalies in magnetically active systems, and the resulting range of Li abundances reproduces the observed patterns of young clusters. We discuss ramifications for pre-MS evolutionary tracks and age measurements of young clusters, and suggest an observational test.

  4. A tale of two anomalies: Depletion, dispersion, and the connection between the stellar lithium spread and inflated radii on the pre-main sequence

    International Nuclear Information System (INIS)

    Somers, Garrett; Pinsonneault, Marc H.

    2014-01-01

    We investigate lithium depletion in standard stellar models (SSMs) and main sequence (MS) open clusters, and explore the origin of the Li dispersion in young, cool stars of equal mass, age, and composition. We first demonstrate that SSMs accurately predict the Li abundances of solar analogs at the zero-age main sequence (ZAMS) within theoretical uncertainties. We then measure the rate of MS Li depletion by removing the [Fe/H]-dependent ZAMS Li pattern from three well-studied clusters, and comparing the detrended data. MS depletion is found to be mass-dependent, in the sense of more depletion at low mass. A dispersion in Li abundance at fixed T eff is nearly universal, and sets in by ∼200 Myr. We discuss mass and age dispersion trends, and the pattern is mixed. We argue that metallicity impacts the ZAMS Li pattern, in agreement with theoretical expectations but contrary to the findings of some previous studies, and suggest Li as a test of cluster metallicity. Finally, we argue that a radius dispersion in stars of fixed mass and age, during the epoch of pre-MS Li destruction, is responsible for the spread in Li abundances and the correlation between rotation and Li in young cool stars, most well known in the Pleiades. We calculate stellar models, inflated to match observed radius anomalies in magnetically active systems, and the resulting range of Li abundances reproduces the observed patterns of young clusters. We discuss ramifications for pre-MS evolutionary tracks and age measurements of young clusters, and suggest an observational test.

  5. Effects of main-sequence mass loss on the turnoff ages of globular clusters

    International Nuclear Information System (INIS)

    Guzik, J.A.

    1989-01-01

    Willson, Bowen, and Struck-Marcell have proposed that globular cluster main-sequence turnoff ages can be reconciled with the lower ages of the Galaxy and universe deduced from other methods by incorporating an epoch of early main-sequence mass-loss by stars of spectral types A through early-F. The proposed mass loss is pulsation-driven, and facilitated by rapid rotation. This paper presents stellar evolution calculations of Pop. II (Z = 0.001) mass-losing stars of initial mass 0.8 to 1.6 M circle dot , with exponentially-decreasing mass loss rates of e-folding times 0.5 to 2.0 Gyr, evolving to a final mass of 0.7 M circle dot . The calculations indicate that a globular cluster with apparent turnoff age 18 Gyr could have an actual age as low as ∼12 Gyr. Observational implications that may help to verify the hypothesis, e.g. low C/N abundance ratios among red giants following first dredge-up, blue stragglers, red giant deficiencies, and signatures in cluster mass/luminosity functions, are also discussed.25 refs., 4 figs., 3 tabs

  6. The star book an introduction to stargazing and the solar system

    CERN Document Server

    Grego, Peter

    2012-01-01

    An Introduction to Stargazing and the Solar System is an introductory section taken from The Star Book that guides you through the night skies, from the history and lives of the stars, to deep-sky objects beyond the Milky Way, and the Celestial Sphere. Followed by an introductory guide to the solar system with high quality images and observational drawings of the planets, covering the Sun, Moon, Inferior and Superior planets. Everyone is interested in the stars and on a clear night astonished by them. The Star Book will answer any questions you may have whe

  7. Astrophysics of “Extreme” Solar-Like Stars

    Czech Academy of Sciences Publication Activity Database

    Caballero-García, María Dolores; Castro-Tirado, A.J.; Claret, A.; Gazeas, K.; Šimon, Vojtěch; Jelínek, Martin; Cwiek, A.; Zarnecki, A.F.; Oates, S.; Jeong, S.; Hudec, René

    2016-01-01

    Roč. 48, č. 2 (2016), s. 59-63 ISSN 1405-2059. [Workshop on Robotic Autonomous Observatories /4./. Malaga, 28.09.2015-02.10.2015] Grant - others:GA ČR(CZ) GA13-33324S Institutional support: RVO:67985815 Keywords : gamma-rays * observations * stars Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics

  8. The [Y/Mg] clock works for evolved solar metallicity stars

    Science.gov (United States)

    Slumstrup, D.; Grundahl, F.; Brogaard, K.; Thygesen, A. O.; Nissen, P. E.; Jessen-Hansen, J.; Van Eylen, V.; Pedersen, M. G.

    2017-08-01

    Aims: Previously [Y/Mg] has been proven to be an age indicator for solar twins. Here, we investigate if this relation also holds for helium-core-burning stars of solar metallicity. Methods: High resolution and high signal-to-noise ratio (S/N) spectroscopic data of stars in the helium-core-burning phase have been obtained with the FIES spectrograph on the NOT 2.56 m telescope and the HIRES spectrograph on the Keck I 10 m telescope. They have been analyzed to determine the chemical abundances of four open clusters with close to solar metallicity; NGC 6811, NGC 6819, M 67 and NGC 188. The abundances are derived from equivalent widths of spectral lines using ATLAS9 model atmospheres with parameters determined from the excitation and ionization balance of Fe lines. Results from asteroseismology and binary studies were used as priors on the atmospheric parameters, where especially the log g is determined to much higher precision than what is possible with spectroscopy. Results: It is confirmed that the four open clusters are close to solar metallicity and they follow the [Y/Mg] vs. age trend previously found for solar twins. Conclusions: The [Y/Mg] vs. age clock also works for giant stars in the helium-core burning phase, which vastly increases the possibilities to estimate the age of stars not only in the solar neighborhood, but in large parts of the Galaxy, due to the brighter nature of evolved stars compared to dwarfs. Based on spectroscopic observations made with two telescopes: the Nordic Optical Telescope operated by NOTSA at the Observatorio del Roque de los Muchachos (La Palma, Spain) of the Instituto de Astrofísica de Canarias and the Keck I Telescope at the W.M. Keck Observatory (Mauna Kea, Hawaii, USA) operated by the California Institute of Technology, the University of California and the National Aeronautics and Space Administration.

  9. The Main Asteroid Belt: The Crossroads of the Solar System

    Science.gov (United States)

    Michel, Patrick

    2015-08-01

    Orbiting the Sun between Mars and Jupiter, main belt asteroids are leftover planetary building blocks that never accreted enough material to become planets. They are therefore keys to understanding how the Solar System formed and evolved. They may also provide clues to the origin of life, as similar bodies may have delivered organics and water to the early Earth.Strong associations between asteroids and meteorites emerged thanks to multi-technique observations, modeling, in situ and sample return analyses. Spacecraft images revolutionized our knowledge of these small worlds. Asteroids are stunning in their diversity in terms of physical properties. Their gravity varies by more orders of magnitude than its variation among the terrestrial planets, including the Moon. Each rendezvous with an asteroid thus turned our geological understanding on its head as each asteroid is affected in different ways by a variety of processes such as landslides, faulting, and impact cratering. Composition also varies, from ice-rich to lunar-like to chondritic.Nearly every asteroid we see today, whether of primitive or evolved compositions, is the product of a complex history involving accretion and one or more episodes of catastrophic disruption that sometimes resulted in families of smaller asteroids that have distinct and indicative petrogenic relationships. These families provide the best data to study the impact disruption process at scales far larger than those accessible in laboratory. Tens, perhaps hundreds, of early asteroids grew large enough to thermally differentiate. Their traces are scattered pieces of their metal-rich cores and, more rarely, their mantles and crusts.Asteroids represent stages on the rocky road to planet formation. They have great stories to tell about the formation and evolution of our Solar System as well as other planetary systems: asteroid belts seem common around Sun-like stars. We will review our current knowledge on their properties, their link to

  10. SPB stars in the open SMC cluster NGC 371

    Science.gov (United States)

    Karoff, C.; Arentoft, T.; Glowienka, L.; Coutures, C.; Nielsen, T. B.; Dogan, G.; Grundahl, F.; Kjeldsen, H.

    2008-05-01

    Pulsation in β Cep and slowly pulsating B (SPB) stars are driven by the κ mechanism which depends critically on the metallicity. It has therefore been suggested that β Cep and SPB stars should be rare in the Magellanic Clouds which have lower metallicities than the solar neighbourhood. To test this prediction we have observed the open Small Magellanic Cloud (SMC) cluster NGC 371 for 12 nights in order to search for β Cep and SPB stars. Surprisingly, we find 29 short-period B-type variables in the upper part of the main sequence, many of which are probably SPB stars. This result indicates that pulsation is still driven by the κ mechanism even in low-metallicity environments. All the identified variables have periods longer than the fundamental radial period which means that they cannot be β Cep stars. Within an amplitude detection limit of 5 mmag no stars in the top of the Hertzsprung-Russell diagram show variability with periods shorter than the fundamental radial period. So if β Cep stars are present in the cluster they oscillate with amplitudes below 5 mmag, which is significantly lower than the mean amplitude of β Cep stars in the Galaxy. We see evidence that multimode pulsation is more common in the upper part of the main sequence than in the lower. We have also identified five eclipsing binaries and three periodic pulsating Be stars in the cluster field.

  11. Properties of evolved mass-losing stars in the Milky Way and variations in the interstellar dust composition

    International Nuclear Information System (INIS)

    Thronson, H.A. Jr.; Latter, W.B.; Black, J.H.; Bally, J.; Hacking, P.; Steward Observatory, Tucson, AZ; AT and T Bell Laboratories, Holmdel, NJ; Cornell Univ., Ithaca, NY; California Institute of Technology, Pasadena)

    1987-01-01

    A large sample of evolved carbon-rich and oxygen-rich objects has been studied using data from the IRAS Point Source Catalog. The number density of infrared-emitting carbon stars shows no variation with Galactocentric radius, while the evolved oxygen star volume density can be well fitted by a given law. A law is given for the number of carbon stars; a total is found in the Galaxy of 48,000 highly evolved oxygen stars. The mass-return rate for all evolved stars is found to be 0.35 solar mass/yr, with a small percentage contribution from carbon stars. The mass-loss rates for both types of stars are dominated by the small number of objects with the smallest rates. A mean lifetime of about 200,000 yr is obtained for both carbon and oxygen stars. Main-sequence stars in the mass range of three to five solar masses are the probable precursors of the carbon stars. 53 references

  12. Incidence of Debris Discs Around FGK Stars in the Solar Neighbourhood

    Science.gov (United States)

    Montesinos, B.; Eiroa, C.; Krivov, A. V.; Marshall, J. P.; Pilbratt, G. L.; Liseau, R.; Mora, A.; Maldonado, J.; Wolf, S.; Ertel, S.; hide

    2016-01-01

    Context. Debris discs are a consequence of the planet formation process and constitute the fingerprints of planetesimal systems. Their counterparts in the solar system are the asteroid and Edgeworth-Kuiper belts. Aims. The aim of this paper is to provide robust numbers for the incidence of debris discs around FGK stars in the solar neighborhood. Methods. The full sample of 177 FGK stars with d approx. less than 20 pc proposed for the DUst around NEarby Stars (DUNES) survey is presented. Herschel/PACS observations at 100 and 160 micrometers were obtained, and were complemented in some cases with data at 70 micrometers and at 250, 350, and 500 micrometer SPIRE photometry. The 123 objects observed by the DUNES collaboration were presented in a previous paper. The remaining 54 stars, shared with the Disc Emission via a Bias-free Reconnaissance in IR and Sub-mm (DEBRIS) consortium and observed by them, and the combined full sample are studied in this paper. The incidence of debris discs per spectral type is analyzed and put into context together with other parameters of the sample, like metallicity, rotation and activity, and age. Results. The subsample of 105 stars with d approx. less than 15 pc containing 23 F, 33 G, and 49 K stars is complete for F stars, almost complete for G stars, and contains a substantial number of K stars from which we draw solid conclusions on objects of this spectral type. The incidence rates of debris discs per spectral type are 0.26(+0.21/-0.14) (6 objects with excesses out of 23 F stars), 0.21(+0.17/-0.11) (7 out of 33 G stars), and 0.20(+0.14/-0.09) (10 out of 49 K stars); the fraction for all three spectral types together is 0.22(+0.08/-0.07) (23 out of 105 stars).The uncertainties correspond to a 95 confidence level. The medians of the upper limits of L(sub dust)/L(sub *) for each spectral type are 7.8 x 10(exp -7) (F), 1.4 x 10(exp -6) (G), and 2.2 x 10(exp -6) (K); the lowest values are around 4.0 x 10(exp -7). The incidence of debris

  13. Coronal Diagnostics of Intermediate Activity Star XI Boo A

    Science.gov (United States)

    Drake, Jeremy

    2005-01-01

    The analysis of Xi Boo A proved difficult to adapt to our line-by-line approach because of the strong wings of the RGS instrumental profile, as has been detailed in earlier reports. While progress was also delayed because of problems in using SAS v4, we succeeded in the past year or so to bring the analysis to conclusion. Abundances have been derived using both EPIC and RGS data, confirming earlier EUVE findings of a mild solar-like FIP effect, though with some evidence of a turn-up in abundances of elements with higher FIP. Plasma densities appear normal for a moderately active stellar corona. Xi Boo A nicely bridges the gap between the very active stars and stars like the Sun, and it indeed does appear that these are the stars in which the solar-like FIP effects begins to change to the "inverse FIP" type of effect seen in the very active stars. Probing this divide was the main goal of the proposal. These results are in the process of being prepared for publication, though we have not decided the target journal as yet.

  14. Star formation is boosted (and quenched) from the inside-out: radial star formation profiles from MaNGA

    Science.gov (United States)

    Ellison, Sara L.; Sánchez, Sebastian F.; Ibarra-Medel, Hector; Antonio, Braulio; Mendel, J. Trevor; Barrera-Ballesteros, Jorge

    2018-02-01

    The tight correlation between total galaxy stellar mass and star formation rate (SFR) has become known as the star-forming main sequence. Using ˜487 000 spaxels from galaxies observed as part of the Sloan Digital Sky Survey Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey, we confirm previous results that a correlation also exists between the surface densities of star formation (ΣSFR) and stellar mass (Σ⋆) on kpc scales, representing a `resolved' main sequence. Using a new metric (ΔΣSFR), which measures the relative enhancement or deficit of star formation on a spaxel-by-spaxel basis relative to the resolved main sequence, we investigate the SFR profiles of 864 galaxies as a function of their position relative to the global star-forming main sequence (ΔSFR). For galaxies above the global main sequence (positive ΔSFR) ΔΣSFR is elevated throughout the galaxy, but the greatest enhancement in star formation occurs at small radii (<3 kpc, or 0.5Re). Moreover, galaxies that are at least a factor of 3 above the main sequence show diluted gas phase metallicities out to 2Re, indicative of metal-poor gas inflows accompanying the starbursts. For quiescent/passive galaxies that lie at least a factor of 10 below the star-forming main sequence, there is an analogous deficit of star formation throughout the galaxy with the lowest values of ΔΣSFR in the central 3 kpc. Our results are in qualitative agreement with the `compaction' scenario in which a central starburst leads to mass growth in the bulge and may ultimately precede galactic quenching from the inside-out.

  15. 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

  16. Investigations on physics of planetary atmospheres and small bodies of the Solar system, extrasolar planets and disk structures around the stars

    Science.gov (United States)

    Vidmachenko, A. P.; Delets, O. S.; Dlugach, J. M.; Zakhozhay, O. V.; Kostogryz, N. M.; Krushevska, V. M.; Kuznyetsova, Y. G.; Morozhenko, O. V.; Nevodovskyi, P. V.; Ovsak, O. S.; Rozenbush, O. E.; Romanyuk, Ya. O.; Shavlovskiy, V. I.; Yanovitskij, E. G.

    2015-12-01

    The history and main becoming stages of Planetary system physics Department of the Main astronomical observatory of National academy of Sciences of Ukraine are considered. Fundamental subjects of department researches and science achievements of employees are presented. Fields of theoretical and experimental researches are Solar system planets and their satellites; vertical structures of planet atmospheres; radiative transfer in planet atmospheres; exoplanet systems of Milky Way; stars having disc structures; astronomical engineering. Employees of the department carry out spectral, photometrical and polarimetrical observations of Solar system planets, exoplanet systems and stars with disc structures. 1. From the history of department 2. The main directions of department research 3. Scientific instrumentation 4. Telescopes and observation stations 5. Theoretical studies 6. The results of observations of planets and small Solar system bodies and their interpretation 7. The study of exoplanets around the stars of our galaxy 8. Spectral energy distribution of fragmenting protostellar disks 9. Cooperation with the National Technical University of Ukraine (KPI) and National University of Ukraine "Lviv Polytechnic" to study the impact of stratospheric aerosol changes on weather and climate of the Earth 10. International relations. Scientific and organizational work. Scientific conferences, congresses, symposia 11. The main achievements of the department 12. Current researches 13. Anniversaries and awards

  17. 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.

  18. PHOTOMETRIC VARIABILITY IN KEPLER TARGET STARS: THE SUN AMONG STARS-A FIRST LOOK

    International Nuclear Information System (INIS)

    Basri, Gibor; Walkowicz, Lucianne M.; Batalha, Natalie; Jenkins, Jon; Borucki, William J.; Koch, David; Caldwell, Doug; Gilliland, Ronald L.; 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 light curves 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 very similar to rather different stellar properties, at a wide variety of ages. Although Kepler data are 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 than mid-K spectral types.

  19. Characteristics of solar-like oscillations in red giants observed in the CoRoT exoplanet field

    Science.gov (United States)

    Hekker, S.; Kallinger, T.; Baudin, F.; De Ridder, J.; Barban, C.; Carrier, F.; Hatzes, A. P.; Weiss, W. W.; Baglin, A.

    2009-10-01

    Context: Observations during the first long run (~150 days) in the exo-planet field of CoRoT increase the number of G-K giant stars for which solar-like oscillations are observed by a factor of 100. This opens the possibility to study the characteristics of their oscillations in a statistical sense. Aims: We aim to understand the statistical distribution of the frequencies of maximum oscillation power (ν_max) in red giants and to search for a possible correlation between ν_max and the large separation (Δ ν). Methods: Red giants with detectable solar-like oscillations are identified using both semi-automatic and manual procedures. For these stars, we determine ν_max as the centre of a Gaussian fit to the oscillation power excess. For the determination of Δ ν, we use the autocorrelation of the Fourier spectra, the comb response function and the power spectrum of the power spectrum. Results: The resulting ν_max distribution shows a pronounced peak between 20-40 μHz. For about half of the stars we obtain Δ ν with at least two methods. The correlation between ν_max and Δ ν follows the same scaling relation as inferred for solar-like stars. Conclusions: The shape of the ν_max distribution can partly be explained by granulation at low frequencies and by white noise at high frequencies, but the population density of the observed stars turns out to be also an important factor. From the fact that the correlation between Δ ν and ν_max for red giants follows the same scaling relation as obtained for sun-like stars, we conclude that the sound travel time over the pressure scale height of the atmosphere scales with the sound travel time through the whole star irrespective of evolution. The fraction of stars for which we determine Δ ν does not correlate with ν_max in the investigated frequency range, which confirms theoretical predictions. The CoRoT space mission which was developed and is operated by the French space agency CNES, with participation of ESA

  20. Massive stars on the verge of exploding: the properties of oxygen sequence Wolf-Rayet stars

    NARCIS (Netherlands)

    Tramper, F.; Straal, S.M.; Sanyal, D.; Sana, H.; de Koter, A.; Gräfener, G.; Langer, N.; Vink, J.S.; de Mink, S.E.; Kaper, L.

    2015-01-01

    Context. Oxygen sequence Wolf-Rayet (WO) stars are a very rare stage in the evolution of massive stars. Their spectra show strong emission lines of helium-burning products, in particular highly ionized carbon and oxygen. The properties of WO stars can be used to provide unique constraints on the

  1. Convective shells and the core He-burning phase of massive stars

    Energy Technology Data Exchange (ETDEWEB)

    Chiosi, C [Padua Univ. (Italy). Ist. di Astronomia; Nasi, E [Osservatorio Astronomico, Padova, Italy

    1978-07-01

    In this paper the effect of complete homogenization in the intermediate unstable layers of massive stars is briefly discussed on the effective temperature of the core He-burning models. To this end, a 20 solar masses star of Population I chemical composition (X=0.700, Z=0.020) has been allowed to evolve from the Main Sequence into the core He-exhaustion stage without taking into account semiconvective mixing. The results show that the models are systematically bluer than those computed with the same physical parameters but with the inclusion of semiconvection.

  2. Which of Kepler's Stars Flare?

    Science.gov (United States)

    Kohler, Susanna

    2017-12-01

    The habitability of distant exoplanets is dependent upon many factors one of which is the activity of their host stars. To learn about which stars are most likely to flare, a recent study examines tens of thousands of stellar flares observed by Kepler.Need for a Broader SampleArtists rendering of a flaring dwarf star. [NASAs Goddard Space Flight Center/S. Wiessinger]Most of our understanding of what causes a star to flare is based on observations of the only star near enough to examine in detail the Sun. But in learning from a sample size of one, a challenge arises: we must determine which conclusions are unique to the Sun (or Sun-like stars), and which apply to other stellar types as well.Based on observations and modeling, astronomers think that stellar flares result from the reconnection of magnetic field lines in a stars outer atmosphere, the corona. The magnetic activity is thought to be driven by a dynamo caused by motions in the stars convective zone.HR diagram of the Kepler stars, with flaring main-sequence (yellow), giant (red) and A-star (green) stars in the authors sample indicated. [Van Doorsselaere et al. 2017]To test whether these ideas are true generally, we need to understand what types of stars exhibit flares, and what stellar properties correlate with flaring activity. A team of scientists led by Tom Van Doorsselaere (KU Leuven, Belgium) has now used an enormous sample of flares observed by Kepler to explore these statistics.Intriguing TrendsVan Doorsselaere and collaborators used a new automated flare detection and characterization algorithm to search through the raw light curves from Quarter 15 of the Kepler mission, building a sample of 16,850 flares on 6,662 stars. They then used these to study the dependence of the flare occurrence rate, duration, energy, and amplitude on the stellar spectral type and rotation period.This large statistical study led the authors to several interesting conclusions, including:Flare star incidence rate as a a

  3. CARBON-TO-OXYGEN RATIOS IN M DWARFS AND SOLAR-TYPE STARS

    International Nuclear Information System (INIS)

    Nakajima, Tadashi; Sorahana, Satoko

    2016-01-01

    It has been suggested that high C/O ratios (>0.8) in circumstellar disks lead to the formation of carbon-dominated planets. Based on the expectation that elemental abundances in the stellar photospheres give the initial abundances in the circumstellar disks, the frequency distributions of C/O ratios of solar-type stars have been obtained by several groups. The results of these investigations are mixed. Some find C/O > 0.8 in more than 20% of stars, and C/O > 1.0 in more than 6%. Others find C/O > 0.8 in none of the sample stars. These works on solar-type stars are all differential abundance analyses with respect to the Sun and depend on the adopted C/O ratio in the Sun. Recently, a method of molecular line spectroscopy of M dwarfs, in which carbon and oxygen abundances are derived respectively from CO and H 2 O lines in the K band, has been developed. The resolution of the K- band spectrum is 20,000. Carbon and oxygen abundances of 46 M dwarfs have been obtained by this nondifferential abundance analysis. Carbon-to-oxygen ratios in M dwarfs derived by this method are more robust than those in solar-type stars derived from neutral carbon and oxygen lines in the visible spectra because of the difficulty in the treatment of oxygen lines. We have compared the frequency distribution of C/O distributions in M dwarfs with those of solar-type stars and have found that the low frequency of high-C/O ratios is preferred.

  4. CARBON-TO-OXYGEN RATIOS IN M DWARFS AND SOLAR-TYPE STARS

    Energy Technology Data Exchange (ETDEWEB)

    Nakajima, Tadashi [Astrobiology Center, 2-21-1, Osawa, Mitaka, Tokyo, 181-8588 (Japan); Sorahana, Satoko, E-mail: tadashi.nakajima@nao.ac.jp, E-mail: sorahana@astron.s.u-tokyo.ac.jp [Department of Astronomy, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033 (Japan)

    2016-10-20

    It has been suggested that high C/O ratios (>0.8) in circumstellar disks lead to the formation of carbon-dominated planets. Based on the expectation that elemental abundances in the stellar photospheres give the initial abundances in the circumstellar disks, the frequency distributions of C/O ratios of solar-type stars have been obtained by several groups. The results of these investigations are mixed. Some find C/O > 0.8 in more than 20% of stars, and C/O > 1.0 in more than 6%. Others find C/O > 0.8 in none of the sample stars. These works on solar-type stars are all differential abundance analyses with respect to the Sun and depend on the adopted C/O ratio in the Sun. Recently, a method of molecular line spectroscopy of M dwarfs, in which carbon and oxygen abundances are derived respectively from CO and H{sub 2}O lines in the K band, has been developed. The resolution of the K- band spectrum is 20,000. Carbon and oxygen abundances of 46 M dwarfs have been obtained by this nondifferential abundance analysis. Carbon-to-oxygen ratios in M dwarfs derived by this method are more robust than those in solar-type stars derived from neutral carbon and oxygen lines in the visible spectra because of the difficulty in the treatment of oxygen lines. We have compared the frequency distribution of C/O distributions in M dwarfs with those of solar-type stars and have found that the low frequency of high-C/O ratios is preferred.

  5. High-precision atmospheric parameter and abundance determination of massive stars, and consequences for stellar and Galactic evolution

    International Nuclear Information System (INIS)

    Nieva, Maria-Fernanda; Przybilla, Norbert; Irrgang, Andreas

    2011-01-01

    The derivation of high precision/accuracy parameters and chemical abundances of massive stars is of utmost importance to the fields of stellar evolution and Galactic chemical evolution. We concentrate on the study of OB-type stars near the main sequence and their evolved progeny, the BA-type supergiants, covering masses of ∼6 to 25 solar masses and a range in effective temperature from ∼8000 to 35 000 K. The minimization of the main sources of systematic errors in the atmospheric model computation, the observed spectra and the quantitative spectral analysis play a critical role in the final results. Our self-consistent spectrum analysis technique employing a robust non-LTE line formation allows precise atmospheric parameters of massive stars to be derived, achieving 1σ-uncertainties as low as 1% in effective temperature and ∼0.05–0.10 dex in surface gravity. Consequences on the behaviour of the chemical elements carbon, nitrogen and oxygen are discussed here in the context of massive star evolution and Galactic chemical evolution, showing tight relations covered in previous work by too large statistical and systematic uncertainties. The spectral analysis of larger star samples, like from the upcoming Gaia-ESO survey, may benefit from these findings.

  6. Chemical Abundances of Main-sequence, Turnoff, Subgiant, and Red Giant Stars from APOGEE Spectra. I. Signatures of Diffusion in the Open Cluster M67

    Science.gov (United States)

    Souto, Diogo; Cunha, Katia; Smith, Verne V.; Allende Prieto, C.; García-Hernández, D. A.; Pinsonneault, Marc; Holzer, Parker; Frinchaboy, Peter; Holtzman, Jon; Johnson, J. A.; Jönsson, Henrik; Majewski, Steven R.; Shetrone, Matthew; Sobeck, Jennifer; Stringfellow, Guy; Teske, Johanna; Zamora, Olga; Zasowski, Gail; Carrera, Ricardo; Stassun, Keivan; Fernandez-Trincado, J. G.; Villanova, Sandro; Minniti, Dante; Santana, Felipe

    2018-04-01

    Detailed chemical abundance distributions for 14 elements are derived for eight high-probability stellar members of the solar metallicity old open cluster M67 with an age of ∼4 Gyr. The eight stars consist of four pairs, with each pair occupying a distinct phase of stellar evolution: two G dwarfs, two turnoff stars, two G subgiants, and two red clump (RC) K giants. The abundance analysis uses near-IR high-resolution spectra (λ1.5–1.7 μm) from the Apache Point Observatory Galactic Evolution Experiment survey and derives abundances for C, N, O, Na, Mg, Al, Si, K, Ca, Ti, V, Cr, Mn, and Fe. Our derived stellar parameters and metallicity for 2M08510076+1153115 suggest that this star is a solar twin, exhibiting abundance differences relative to the Sun of ≤0.04 dex for all elements. Chemical homogeneity is found within each class of stars (∼0.02 dex), while significant abundance variations (∼0.05–0.20 dex) are found across the different evolutionary phases; the turnoff stars typically have the lowest abundances, while the RCs tend to have the largest. Non-LTE corrections to the LTE-derived abundances are unlikely to explain the differences. A detailed comparison of the derived Fe, Mg, Si, and Ca abundances with recently published surface abundances from stellar models that include chemical diffusion provides a good match between the observed and predicted abundances as a function of stellar mass. Such agreement would indicate the detection of chemical diffusion processes in the stellar members of M67.

  7. Revisiting the Microlensing Event OGLE 2012-BLG-0026: A Solar Mass Star with Two Cold Giant Planets

    Science.gov (United States)

    Beaulieu, J.-P.; Bennett, D. P.; Batista, V.; Fukui, A.; Marquette, J.-B.; Brillant, S.; Cole, A. A.; Rogers, L. A.; Sumi, T.; Abe, F.

    2016-01-01

    Two cold gas giant planets orbiting a G-type main-sequence star in the galactic disk were previously discovered in the high-magnification microlensing event OGLE-2012-BLG-0026. Here, we present revised host star flux measurements and a refined model for the two-planet system using additional light curve data. We performed high angular resolution adaptive optics imaging with the Keck and Subaru telescopes at two epochs while the source star was still amplified. We detected the lens flux, H = 16.39 +/- 0.08. The lens, a disk star, is brighter than predicted from the modeling in the original study. We revisited the light curve modeling using additional photometric data from the B and C telescope in New Zealand and CTIO 1.3 m H-band light curve. We then include the Keck and Subaru adaptive optic observation constraints. The system is composed of an approximately 4-9 Gyr lens star of M(sub lens) = 1.06 +/- 0.05 solar mass at a distance of D(sub lens) = 4.0 +/- 0.3 kpc, orbited by two giant planets of 0.145 +/- 0.008 M(sub Jup) and 0.86 +/- 0.06 M(sub Jup), with projected separations of 4.0 +/- 0.5 au and 4.8 +/- 0.7 au, respectively. Because the lens is brighter than the source star by 16 +/- 8% in H, with no other blend within one arcsec, it will be possible to estimate its metallicity using subsequent IR spectroscopy with 8-10 m class telescopes. By adding a constraint on the metallicity it will be possible to refine the age of the system.

  8. 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

  9. Detection of [O III] at z ∼ 3: A Galaxy Above the Main Sequence, Rapidly Assembling Its Stellar Mass

    Science.gov (United States)

    Vishwas, Amit; Ferkinhoff, Carl; Nikola, Thomas; Parshley, Stephen C.; Schoenwald, Justin P.; Stacey, Gordon J.; Higdon, Sarah J. U.; Higdon, James L.; Weiss, Axel; Güsten, Rolf; Menten, Karl M.

    2018-04-01

    We detect bright emission in the far-infrared (far-IR) fine structure [O III] 88 μm line from a strong lensing candidate galaxy, H-ATLAS J113526.3-014605, hereafter G12v2.43, at z = 3.127, using the second-generation Redshift (z) and Early Universe Spectrometer (ZEUS-2) at the Atacama Pathfinder Experiment Telescope (APEX). This is only the fifth detection of this far-IR line from a submillimeter galaxy at the epoch of galaxy assembly. The observed [O III] luminosity of 7.1 × 109 ≤ft(\\tfrac{10}{μ }\\right) L ⊙ likely arises from H II regions around massive stars, and the amount of Lyman continuum photons required to support the ionization indicate the presence of (1.2–5.2) × 106 ≤ft(\\tfrac{10}{μ }\\right) equivalent O5.5 or higher stars, where μ would be the lensing magnification factor. The observed line luminosity also requires a minimum mass of ∼2 × 108 ≤ft(\\tfrac{10}{μ }\\right) M ⊙ in ionized gas, that is 0.33% of the estimated total molecular gas mass of 6 × 1010 ≤ft(\\tfrac{10}{μ }\\right) M ⊙. We compile multi-band photometry tracing rest-frame ultraviolet to millimeter continuum emission to further constrain the properties of this dusty high-redshift, star-forming galaxy. Via SED modeling we find G12v2.43 is forming stars at a rate of 916 ≤ft(\\tfrac{10}{μ }\\right) M ⊙ yr‑1 and already has a stellar mass of 8 × 1010 ≤ft(\\tfrac{10}{μ }\\right) M ⊙. We also constrain the age of the current starburst to be ≤slant 5 Myr, making G12v2.43 a gas-rich galaxy lying above the star-forming main sequence at z ∼ 3, undergoing a growth spurt, and it could be on the main sequence within the derived gas depletion timescale of ∼66 Myr.

  10. From strange stars to strange dwarfs

    International Nuclear Information System (INIS)

    Glendenning, N.K.; Kettner, C.; Weber, F.

    1995-01-01

    We determine all possible equilibrium sequences of compact strange-matter stars with nuclear crusts, which range from massive strange stars to strange white dwarf endash like objects (strange dwarfs). The properties of such stars are compared with those of their nonstrange counterparts emdash neutron stars and ordinary white dwarfs. The main emphasis of this paper is on strange dwarfs, which we divide into two distinct categories. The first one consists of a core of strange matter enveloped within ordinary white dwarf matter. Such stars are hydrostatically stable with or without the strange core and are therefore referred to as open-quote open-quote trivial close-quote close-quote strange dwarfs. This is different for the second category which forms an entirely new class of dwarf stars that contain nuclear material up to 4x10 4 times denser than in ordinary white dwarfs of average mass, M∼0.6 M circle-dot , and still about 400 times denser than in the densest white dwarfs. The entire family of such dwarfs, denoted dense strange dwarfs, owes its hydrostatic stability to the strange core. A striking features of strange dwarfs is that the entire sequence from the maximum-mass strange star to the maximum-mass strange dwarf is stable to radial oscillations. The minimum-mass star is only conditionally stable, and the sequences on both sides are stable. Such a stable, continuous connection does not exist between ordinary white dwarfs and neutron stars, which are known to be separated by a broad range of unstable stars. We find an expansive range of very low mass (planetary-like) strange-matter stars (masses even below 10 -4 M circle-dot are possible) that arise as natural dark-matter candidates, which if abundant enough in our Galaxy, should be seen in the gravitational microlensing searches that are presently being performed. copyright 1995 The American Astronomical Society

  11. MAGNETIC ACTIVITY ANALYSIS FOR A SAMPLE OF G-TYPE MAIN SEQUENCE KEPLER TARGETS

    Energy Technology Data Exchange (ETDEWEB)

    Mehrabi, Ahmad [Department of Physics, Bu Ali Sina University, 65178, 016016, Hamedan (Iran, Islamic Republic of); He, Han [National Astronomical Observatories, Chinese Academy of Sciences, Beijing (China); Khosroshahi, Habib, E-mail: mehrabi@basu.ac.ir [School of Astronomy, Institute for Research in Fundamental Sciences (IPM), 19395-5531, Tehran (Iran, Islamic Republic of)

    2017-01-10

    The variation of a stellar light curve owing to rotational modulation by magnetic features (starspots and faculae) on the star’s surface can be used to investigate the magnetic properties of the host star. In this paper, we use the periodicity and magnitude of the light-curve variation as two proxies to study the stellar magnetic properties for a large sample of G-type main sequence Kepler targets, for which the rotation periods were recently determined. By analyzing the correlation between the two magnetic proxies, it is found that: (1) the two proxies are positively correlated for most of the stars in our sample, and the percentages of negative, zero, and positive correlations are 4.27%, 6.81%, and 88.91%, respectively; (2) negative correlation stars cannot have a large magnitude of light-curve variation; and (3) with the increase of rotation period, the relative number of positive correlation stars decreases and the negative correlation one increases. These results indicate that stars with shorter rotation period tend to have positive correlation between the two proxies, and a good portion of the positive correlation stars have a larger magnitude of light-curve variation (and hence more intense magnetic activities) than negative correlation stars.

  12. VERY LOW MASS STELLAR AND SUBSTELLAR COMPANIONS TO SOLAR-LIKE STARS FROM MARVELS. I. A LOW-MASS RATIO STELLAR COMPANION TO TYC 4110-01037-1 IN A 79 DAY ORBIT

    International Nuclear Information System (INIS)

    Wisniewski, John P.; Agol, Eric; Barnes, Rory; Ge, Jian; De Lee, Nathan; Fleming, Scott W.; Lee, Brian L.; Chang, Liang; Crepp, Justin R.; Eastman, Jason; Gaudi, B. Scott; Esposito, Massimiliano; Gonzalez Hernandez, Jonay I.; Prieto, Carlos Allende; Ghezzi, Luan; Da Costa, Luiz N.; Porto De Mello, G. F.; Stassun, Keivan G.; Cargile, Phillip; Bizyaev, Dmitry

    2012-01-01

    TYC 4110-01037-1 has a low-mass stellar companion, whose small mass ratio and short orbital period are atypical among binary systems with solar-like (T eff ∼ ☉ and radius of 0.99 ± 0.18 R ☉ . We analyze 32 radial velocity (RV) measurements from the SDSS-III MARVELS survey as well as 6 supporting RV measurements from the SARG spectrograph on the 3.6 m Telescopio Nazionale Galileo telescope obtained over a period of ∼2 years. The best Keplerian orbital fit parameters were found to have a period of 78.994 ± 0.012 days, an eccentricity of 0.1095 ± 0.0023, and a semi-amplitude of 4199 ± 11 m s –1 . We determine the minimum companion mass (if sin i = 1) to be 97.7 ± 5.8 M Jup . The system's companion to host star mass ratio, ≥0.087 ± 0.003, places it at the lowest end of observed values for short period stellar companions to solar-like (T eff ∼< 6000 K) stars. One possible way to create such a system would be if a triple-component stellar multiple broke up into a short period, low q binary during the cluster dispersal phase of its lifetime. A candidate tertiary body has been identified in the system via single-epoch, high contrast imagery. If this object is confirmed to be comoving, we estimate it would be a dM4 star. We present these results in the context of our larger-scale effort to constrain the statistics of low-mass stellar and brown dwarf companions to FGK-type stars via the MARVELS survey.

  13. Are sdAs helium core stars?

    Directory of Open Access Journals (Sweden)

    Pelisoli Ingrid

    2017-12-01

    Full Text Available Evolved stars with a helium core can be formed by non-conservative mass exchange interaction with a companion or by strong mass loss. Their masses are smaller than 0.5 M⊙. In the database of the Sloan Digital Sky Survey (SDSS, there are several thousand stars which were classified by the pipeline as dwarf O, B and A stars. Considering the lifetimes of these classes on the main sequence, and their distance modulus at the SDSS bright saturation, if these were common main sequence stars, there would be a considerable population of young stars very far from the galactic disk. Their spectra are dominated by Balmer lines which suggest effective temperatures around 8 000-10 000 K. Several thousand have significant proper motions, indicative of distances smaller than 1 kpc. Many show surface gravity in intermediate values between main sequence and white dwarf, 4.75 < log g < 6.5, hence they have been called sdA stars. Their physical nature and evolutionary history remains a puzzle. We propose they are not H-core main sequence stars, but helium core stars and the outcomes of binary evolution. We report the discovery of two new extremely-low mass white dwarfs among the sdAs to support this statement.

  14. Star's death and rebirth. White dwarfs, supernovae, pulsars, black holes

    Energy Technology Data Exchange (ETDEWEB)

    Otzen Petersen, J [Copenhagen Univ. (Denmark)

    1975-01-01

    The evolution of a star from a main sequence star of approximately solar mass, first to a red giant, thereafter to a white dwarf is described in detail. The evolution of more massive stars to supernovae, neutron stars and pulsars is then discussed with special reference to the Crab Nebula. Black holes and X-ray sources are also discussed, in this case with reference to the Cygnus X-1 system. In conclusion, it is pointed out that after their active phase white dwarfs, neutron stars and black holes may exist as dead bodies in space, and only be observeable through their gravitational fields. It is possible that a great number of such bodies may exist, and contribute to the stability of galaxies, also possibly facilitating the explanation of the galaxies' red shifts by means of simple universe models.

  15. 2D and 3D Models of Convective Turbulence and Oscillations in Intermediate-Mass Main-Sequence Stars

    Science.gov (United States)

    Guzik, Joyce Ann; Morgan, Taylor H.; Nelson, Nicholas J.; Lovekin, Catherine; Kitiashvili, Irina N.; Mansour, Nagi N.; Kosovichev, Alexander

    2015-08-01

    We present multidimensional modeling of convection and oscillations in main-sequence stars somewhat more massive than the sun, using three separate approaches: 1) Applying the spherical 3D MHD ASH (Anelastic Spherical Harmonics) code to simulate the core convection and radiative zone. Our goal is to determine whether core convection can excite low-frequency gravity modes, and thereby explain the presence of low frequencies for some hybrid gamma Dor/delta Sct variables for which the envelope convection zone is too shallow for the convective blocking mechanism to drive g modes; 2) Using the 3D planar ‘StellarBox’ radiation hydrodynamics code to model the envelope convection zone and part of the radiative zone. Our goals are to examine the interaction of stellar pulsations with turbulent convection in the envelope, excitation of acoustic modes, and the role of convective overshooting; 3) Applying the ROTORC 2D stellar evolution and dynamics code to calculate evolution with a variety of initial rotation rates and extents of core convective overshooting. The nonradial adiabatic pulsation frequencies of these nonspherical models will be calculated using the 2D pulsation code NRO of Clement. We will present new insights into gamma Dor and delta Sct pulsations gained by multidimensional modeling compared to 1D model expectations.

  16. Symbiotic star UV emission and theoretical models

    International Nuclear Information System (INIS)

    Kafatos, M.

    1982-01-01

    Observations of symbiotic stars in the far UV have provided important information on the nature of these objects. The canonical spectrum of a symbiotic star, e.g. RW Hya, Z And, AG Peg, is dominated by strong allowed and semiforbidden lines of a variety of at least twice ionized elements. Weaker emission from neutral and singly ionized species is also present. A continuum may or may not be present in the 1200 - 2000 A range but is generally present in the range 2000 - 3200 A range. The suspected hot subdwarf continuum is seen in some cases in the range 1200 - 2000 A (RW Hya, AG Peg, SY Mus). The presence of an accretion disk is difficult to demonstrate and to this date the best candidate for accretion to a main sequence star remains CI Cyg. A number of equations have been derived by the author that can yield the accretion parameters from the observable quantities. Boundary layer temperatures approximately 10 5 K and accretion rates approximately > 10 -5 solar masses/yr are required for accreting main sequence companions. To this date, though, most of the symbiotics may only require the presence of a approximately 10 5 K hot subdwarf. (Auth.)

  17. On the Incidence of Wise Infrared Excess Among Solar Analog, Twin, and Sibling Stars

    Energy Technology Data Exchange (ETDEWEB)

    Da Costa, A. D.; Martins, B. L. Canto; Lima Jr, J. E.; Silva, D. Freire da; Medeiros, J. R. De [Departamento de Física Teórica e Experimental, Universidade Federal do Rio Grande do Norte, Campus Universitário, Natal, RN, 59072-970 (Brazil); Leão, I. C. [European Southern Observatory, Karl-Schwarzschild-Str. 2, D-85748 Garching (Germany); Freitas, D. B. de, E-mail: dgerson@fisica.ufrn.br [Departamento de Física, Universidade Federal do Ceará, Caixa Postal 6030, Campus do Pici, 60455-900, Fortaleza, Ceará (Brazil)

    2017-03-01

    This study presents a search for infrared (IR) excess in the 3.4, 4.6, 12, and 22 μ m bands in a sample of 216 targets, composed of solar sibling, twin, and analog stars observed by the Wide-field Infrared Survey Explorer ( WISE ) mission. In general, an IR excess suggests the existence of warm dust around a star. We detected 12 μ m and/or 22 μ m excesses at the 3 σ level of confidence in five solar analog stars, corresponding to a frequency of 4.1% of the entire sample of solar analogs analyzed, and in one out of 29 solar sibling candidates, confirming previous studies. The estimation of the dust properties shows that the sources with IR excesses possess circumstellar material with temperatures that, within the uncertainties, are similar to that of the material found in the asteroid belt in our solar system. No photospheric flux excess was identified at the W1 (3.4 μ m) and W2 (4.6 μ m) WISE bands, indicating that, in the majority of stars of the present sample, no detectable dust is generated. Interestingly, among the 60 solar twin stars analyzed in this work, no WISE photospheric flux excess was detected. However, a null-detection excess does not necessarily indicate the absence of dust around a star because different causes, including dynamic processes and instrument limitations, can mask its presence.

  18. 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

    Context. Comparing models and data of pulsating stars is a powerful way to understand the stellar structure better. Moreover, such comparisons are necessary to make improvements to the physics of the stellar models, since they do not yet perfectly represent either the interior or especially...... 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...... frequencies of β Hydri: (i) we assume that the best model is the one that reproduces the star's interior based on the radial oscillation frequencies alone, to which we have applied the correction for the near-surface effects; (ii) we assume that the best model is the one that produces the lowest value...

  19. X-Ray Flare Oscillations Track Plasma Sloshing along Star-disk Magnetic Tubes in the Orion Star-forming Region

    Science.gov (United States)

    Reale, Fabio; Lopez-Santiago, Javier; Flaccomio, Ettore; Petralia, Antonino; Sciortino, Salvatore

    2018-03-01

    Pulsing X-ray emission tracks the plasma “echo” traveling in an extremely long magnetic tube that flares in an Orion pre-main sequence (PMS) star. On the Sun, flares last from minutes to a few hours and the longest-lasting ones typically involve arcades of closed magnetic tubes. Long-lasting X-ray flares are observed in PMS stars. Large-amplitude (∼20%), long-period (∼3 hr) pulsations are detected in the light curve of day-long flares observed by the Advanced CCD Imaging Spectrometer on-board Chandra from PMS stars in the Orion cluster. Detailed hydrodynamic modeling of two flares observed on V772 Ori and OW Ori shows that these pulsations may track the sloshing of plasma along a single long magnetic tube, triggered by a sufficiently short (∼1 hr) heat pulse. These magnetic tubes are ≥20 solar radii long, enough to connect the star with the surrounding disk.

  20. Baby Solar System

    Science.gov (United States)

    Currie, Thayne; Grady, Carol

    2012-01-01

    What did our solar system look like in its infancy,...... when the planets were forming? We cannot travel back in time to take an image of the early solar system, but in principle we can have the next best thing: images of infant planetary systems around Sun-like stars with ages of 1 to 5 million years, the time we think it took for the giant planets to form. Infant exoplanetary systems are critically important because they can help us understand how our solar system fits within the context of planet formation in general. More than 80% of stars are born with gas- and dust-rich disks, and thus have the potential to form planets. Through many methods we have identified more than 760 planetary systems around middle-aged stars like the Sun, but many of these have architectures that look nothing like our solar system. Young planetary systems are important missing links between various endpoints and may help us understand how and when these differences emerge. Well-known star-forming regions in Taurus, Scorpius. and Orion contain stars that could have infant planetary systems. But these stars are much more distant than our nearest neighbors such as Alpha Centauri or Sirius, making it extremely challenging to produce clear images of systems that can reveal signs of recent planet formation, let alone reveal the planets themselves. Recently, a star with the unassuming name LkCa 15 may have given us our first detailed "baby picture" of a young planetary system similar to our solar system. Located about 450 light-years away in the Taurus starforming region. LkCa 15 has a mass comparable to the Sun (0.97 solar mass) and an age of l to 5 million years, comparable to the time at which Saturn and perhaps Jupiter formed. The star is surrounded by a gas-rich disk similar in structure to the one in our solar system from which the planets formed. With new technologies and observing strategies, we have confirmed suspicions that LkCa 15's disk harbors a young planetary system.

  1. Carbon Monoxide and the Potential for Prebiotic Chemistry on Habitable Planets Around Main Sequence M Stars

    Science.gov (United States)

    Nava-Sedeno, J. Manik; Ortiz-Cervantes, Adrian; Segura, Antigona; Domagal-Goldman, Shawn D.

    2016-01-01

    Lifeless planets with CO2 atmospheres produce CO by CO2 photolysis. On planets around M dwarfs, CO is a long-lived atmospheric compound, as long as UV emission due to the stars chromospheric activity lasts, and the sink of CO and O2 in seawater is small compared to its atmospheric production. Atmospheres containing reduced compounds, like CO, may undergo further energetic and chemical processing to give rise to organic compounds of potential importance for the origin of life. We calculated the yield of organic compounds from CO2-rich atmospheres of planets orbiting M dwarf stars, which were previously simulated by Domagal- Goldman et al. (2014) and Harman et al. (2015), by cosmic rays and lightning using results of experiments by Miyakawaet al. (2002) and Schlesinger and Miller (1983a, 1983b). Stellar protons from active stars may be important energy sources for abiotic synthesis and increase production rates of biological compounds by at least 2 orders of magnitude compared to cosmic rays. Simple compounds such as HCN and H2CO are more readily synthesized than more complex ones, such as amino acids and uracil (considered here as an example), resulting in higher yields for the former and lower yields for the latter. Electric discharges are most efficient when a reducing atmosphere is present. Nonetheless, atmospheres with high quantities of CO2 are capable of producing higher amounts of prebiotic compounds, given that CO is constantly produced in the atmosphere. Our results further support planetary systems around M dwarf stars as candidates for supporting life or its origin.

  2. Using solar oscillations to probe the effects of element diffusion in the solar interior

    International Nuclear Information System (INIS)

    Guzik, J.A.; Cox, A.N.

    1993-01-01

    There is growing evidence from solar oscillation and evolution studies that the Sun's convection zone helium mass fraction has decreased by about 0.03 due to element diffusion. Evolution calculations show that diffusion also produces a steep Y and Z composition gradient below the convection zone. Comparisons between calculated and observed solar p-mode frequencies of angular degrees 5 thru 60 that are sensitive to solar structure near the convection zone bottom support this steep composition gradient, rather than one smoothed significantly by turbulent mixing. Turbulent mixing induced by convective overshoot or rotation has been the favored explanation for much of the solar surface lithium depletion by a factor of 200 from its presumed primordial value. These limits on the extent of turbulent mixing imply that either most of the solar lithium destruction occurred pre-main sequence, which is not supported by observation of young star, or that some other mechanism, for example a small amount of early main-sequence mass loss, is responsible for the low observed lithium abundance. Solar models including such mass loss as well as diffusion have a slightly steeper central density gradient. Comparisons between observed and calculated low-degree p-mode frequencies that are sensitive to the Sun's central structure can be used to probe this density gradient and constrain the possible amount of mass loss

  3. Constructing a One-solar-mass Evolutionary Sequence Using Asteroseismic Data from Kepler

    DEFF Research Database (Denmark)

    Silva Aguirre, V.; Chaplin, W.J.; Ballot, J.

    2011-01-01

    Asteroseismology of solar-type stars has entered a new era of large surveys with the success of the NASA Kepler mission, which is providing exquisite data on oscillations of stars across the Hertzsprung-Russell diagram. From the time-series photometry, the two seismic parameters that can be most...... readily extracted are the large frequency separation (Δν) and the frequency of maximum oscillation power (νmax). After the survey phase, these quantities are available for hundreds of solar-type stars. By scaling from solar values, we use these two asteroseismic observables to identify for the first time...

  4. A new interpretation of luminous blue stars

    International Nuclear Information System (INIS)

    Stothers, R.

    1976-01-01

    A major revision of current theoretical ideas about the brightest blue stars must be made if Carson's new radiative opacities are adopted in stellar models. Unlike earlier opacities, the new opacities exhibit a large ''bump'' due to CNO ionization, which leads to very strong central condensation, convective instability, and pulsational instability in hot, diffuse stellar envelopes (typically those in which L/M>10 3 solar units). Despite a number of theoretical uncertainties, the new picture of the structure of very luminous stars is reasonably successful in accounting for a variety of previously unexplained observations. Thus, the new stellar models for the phase of core hydrogen burning predict large radii and rather cool effective temperatures (which are yet to be observationally confirmed) for O stars, and a spreading out of the main-sequence band in the H-R diagram toward luminous cool supergiants for masses higher than approx.20 M/sub sun/, beginning at M/sub v/=-4.5 and Sp=B1. They also predict slower surface rotations for O stars compared with B stars; and, in binary systems, slower apsidal motions, closer rotational-revolutional synchronism, and smaller orbital eccentricities. In massive X-ray binary systems, circular orbits and supergiant-like visual companions are expected to be quite common. Radial pulsations of the models have been calculated by employing linearized nonadiabatic pulsation theory. Long-period variability is predicted to exist for massive blue supergiants of luminosity class Ia. The new models for helium stars predict large radii and rather cool effective temperatures for Wolf-Rayet stars, as well as multimodal pulsational instability and, possibly, surface turbulence for these stars. Ultrashort-period variability, observed in many classes of hot luminous stars, may be due, in part, to high radial overtone pulsations (or, possibly, to nonradial pulsation or convective modes)

  5. Polycyclic aromatic hydrocarbons in disks around young solar-type stars

    NARCIS (Netherlands)

    Geers, Vincent Carlo

    2007-01-01

    In this thesis we study the dust around solar-type young stars. In particular, we focus on one specific species of dust, namely the Polycyclic Aromatic Hydrocarbons (PAHs), a family of large molecules, or small grains, that are widely observed in nearby star-forming regions. We address the following

  6. 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 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

  7. Black Hole Universe Model for Explaining GRBs, X-Ray Flares, and Quasars as Emissions of Dynamic Star-like, Massive, and Supermassive Black Holes

    Science.gov (United States)

    Zhang, Tianxi

    2014-01-01

    Slightly modifying the standard big bang theory, the author has recently developed a new cosmological model called black hole universe, which is consistent with Mach’s principle, governed by Einstein’s general theory of relativity, and able to explain all observations of the universe. Previous studies accounted for the origin, structure, evolution, expansion, cosmic microwave background radiation, and acceleration of the black hole universe, which grew from a star-like black hole with several solar masses through a supermassive black hole with billions of solar masses to the present state with hundred billion-trillions of solar masses by accreting ambient matter and merging with other black holes. This study investigates the emissions of dynamic black holes according to the black hole universe model and provides a self-consistent explanation for the observations of gamma ray bursts (GRBs), X-ray flares, and quasars as emissions of dynamic star-like, massive, and supermassive black holes. It is shown that a black hole, when it accretes its ambient matter or merges with other black holes, becomes dynamic. Since the event horizon of a dynamic black hole is broken, the inside hot (or high-frequency) blackbody radiation leaks out. The leakage of the inside hot blackbody radiation leads to a GRB if it is a star-like black hole, an X-ray flare if it is a massive black hole like the one at the center of the Milky Way, or a quasar if it is a supermassive black hole like an active galactic nucleus (AGN). The energy spectra and amount of emissions produced by the dynamic star-like, massive, and supermassive black holes can be consistent with the measurements of GRBs, X-ray flares, and quasars.

  8. Super-solar Metallicity Stars in the Galactic Center Nuclear Star Cluster: Unusual Sc, V, and Y Abundances

    Science.gov (United States)

    Do, Tuan; Kerzendorf, Wolfgang; Konopacky, Quinn; Marcinik, Joseph M.; Ghez, Andrea; Lu, Jessica R.; Morris, Mark R.

    2018-03-01

    We present adaptive-optics assisted near-infrared high-spectral-resolution observations of late-type giants in the nuclear star cluster of the Milky Way. The metallicity and elemental abundance measurements of these stars offer us an opportunity to understand the formation and evolution of the nuclear star cluster. In addition, their proximity to the supermassive black hole (∼0.5 pc) offers a unique probe of the star formation and chemical enrichment in this extreme environment. We observed two stars identified by medium spectral-resolution observations as potentially having very high metallicities. We use spectral-template fitting with the PHOENIX grid and Bayesian inference to simultaneously constrain the overall metallicity, [M/H], alpha-element abundance [α/Fe], effective temperature, and surface gravity of these stars. We find that one of the stars has very high metallicity ([M/H] > 0.6) and the other is slightly above solar metallicity. Both Galactic center stars have lines from scandium (Sc), vanadium (V), and yttrium (Y) that are much stronger than allowed by the PHOENIX grid. We find, using the spectral synthesis code Spectroscopy Made Easy, that [Sc/Fe] may be an order of magnitude above solar. For comparison, we also observed an empirical calibrator in NGC 6791, the highest metallicity cluster known ([M/H] ∼ 0.4). Most lines are well matched between the calibrator and the Galactic center stars, except for Sc, V, and Y, which confirms that their abundances must be anomalously high in these stars. These unusual abundances, which may be a unique signature of nuclear star clusters, offer an opportunity to test models of chemical enrichment in this region.

  9. Röntgen spheres around active stars

    Science.gov (United States)

    Locci, Daniele; Cecchi-Pestellini, Cesare; Micela, Giuseppina; Ciaravella, Angela; Aresu, Giambattista

    2018-01-01

    X-rays are an important ingredient of the radiation environment of a variety of stars of different spectral types and age. We have modelled the X-ray transfer and energy deposition into a gas with solar composition, through an accurate description of the electron cascade following the history of the primary photoelectron energy deposition. We test and validate this description studying the possible formation of regions in which X-rays are the major ionization channel. Such regions, called Röntgen spheres may have considerable importance in the chemical and physical evolution of the gas embedding the emitting star. Around massive stars the concept of Röntgen sphere appears to be of limited use, as the formation of extended volumes with relevant levels of ionization is efficient just in a narrow range of gas volume densities. In clouds embedding low-mass pre-main-sequence stars significant volumes of gas are affected by ionization levels exceeding largely the cosmic-ray background ionization. In clusters arising in regions of vigorous star formation X-rays create an ionization network pervading densely the interstellar medium, and providing a natural feedback mechanism, which may affect planet and star formation processes.

  10. Making Sense of Atmospheric Models and Fundamental Stellar Properties at the Bottom of the Main Sequence

    Science.gov (United States)

    Dieterich, Sergio; Henry, Todd; Jao, W.-C.; Washington, Robert; Silverstein, Michele; Winters, J.; RECONS

    2018-01-01

    We present a detailed comparison of atmospheric model predictions and photometric observations for late M and L dwarfs. We discuss which wavelength regions are best for determining the fundamental properties of these cool stellar and substellar atmospheres and use this analysis to refine the HR diagram for the hydrogen burning limit first presented in 2014. We also add several new objects to the HR diagram and find little qualitative difference in the HR diagram's overall morphology when compared to our 2014 results. The L2 dwarf 2MASS 0523-1403 remains the smallest hydrogen burning star for which we calculated a radius, thus likely indicating the end of the stellar main sequence. This work is supported by the NSF Astronomy and Astrophysics Postdoctoral Fellowship program through grant AST-1400680.

  11. Realistic limitations of detecting planets around young active stars

    Directory of Open Access Journals (Sweden)

    Pinfield D.

    2013-04-01

    Full Text Available Current planet hunting methods using the radial velocity method are limited to observing middle-aged main-sequence stars where the signatures of stellar activity are much less than on young stars that have just arrived on the main-sequence. In this work we apply our knowledge from the surface imaging of these young stars to place realistic limitations on the possibility of detecting orbiting planets. In general we find that the magnitude of the stellar jitter is directly proportional to the stellar vsini. For G and K dwarfs, we find that it is possible, for models with high stellar activity and low stellar vsini, to be able to detect a 1 MJupiter mass planet within 50 epochs of observations and for the M dwarfs it is possible to detect a habitable zone Earth-like planet in 10s of observational epochs.

  12. Constraining the Final Fates of Massive Stars by Oxygen and Iron Enrichment History in the Galaxy

    Science.gov (United States)

    Suzuki, Akihiro; Maeda, Keiichi

    2018-01-01

    Recent observational studies of core-collapse supernovae suggest that only stars with zero-age main-sequence masses smaller than 16–18 {M}ȯ explode when they are red supergiants, producing Type IIP supernovae. This may imply that more massive stars produce other types of supernovae or they simply collapse to black holes without giving rise to bright supernovae. This failed supernova hypothesis can lead to significantly inefficient oxygen production because oxygen abundantly produced in inner layers of massive stars with zero-age main-sequence masses around 20–30 {M}ȯ might not be ejected into the surrounding interstellar space. We first assume an unspecified population of oxygen injection events related to massive stars and obtain a model-independent constraint on how much oxygen should be released in a single event and how frequently such events should happen. We further carry out one-box galactic chemical enrichment calculations with different mass ranges of massive stars exploding as core-collapse supernovae. Our results suggest that the model assuming that all massive stars with 9–100 {M}ȯ explode as core-collapse supernovae is still most appropriate in explaining the solar abundances of oxygen and iron and their enrichment history in the Galaxy. The oxygen mass in the Galaxy is not explained when assuming that only massive stars with zero-age main-sequence masses in the range of 9–17 {M}ȯ contribute to the galactic oxygen enrichment. This finding implies that a good fraction of stars more massive than 17 {M}ȯ should eject their oxygen layers in either supernova explosions or some other mass-loss processes.

  13. Solar maximum mission

    International Nuclear Information System (INIS)

    Ryan, J.

    1981-01-01

    By understanding the sun, astrophysicists hope to expand this knowledge to understanding other stars. To study the sun, NASA launched a satellite on February 14, 1980. The project is named the Solar Maximum Mission (SMM). The satellite conducted detailed observations of the sun in collaboration with other satellites and ground-based optical and radio observations until its failure 10 months into the mission. The main objective of the SMM was to investigate one aspect of solar activity: solar flares. A brief description of the flare mechanism is given. The SMM satellite was valuable in providing information on where and how a solar flare occurs. A sequence of photographs of a solar flare taken from SMM satellite shows how a solar flare develops in a particular layer of the solar atmosphere. Two flares especially suitable for detailed observations by a joint effort occurred on April 30 and May 21 of 1980. These flares and observations of the flares are discussed. Also discussed are significant discoveries made by individual experiments

  14. EXTENDED STAR FORMATION IN THE INTERMEDIATE-AGE LARGE MAGELLANIC CLOUD STAR CLUSTER NGC 2209

    International Nuclear Information System (INIS)

    Keller, Stefan C.; Mackey, A. Dougal; Da Costa, Gary S.

    2012-01-01

    We present observations of the 1 Gyr old star cluster NGC 2209 in the Large Magellanic Cloud made with the GMOS imager on the Gemini South Telescope. These observations show that the cluster exhibits a main-sequence turnoff that spans a broader range in luminosity than can be explained by a single-aged stellar population. This places NGC 2209 amongst a growing list of intermediate-age (1-3 Gyr) clusters that show evidence for extended or multiple epochs of star formation of between 50 and 460 Myr in extent. The extended main-sequence turnoff observed in NGC 2209 is a confirmation of the prediction in Keller et al. made on the basis of the cluster's large core radius. We propose that secondary star formation is a defining feature of the evolution of massive star clusters. Dissolution of lower mass clusters through evaporation results in only clusters that have experienced secondary star formation surviving for a Hubble time, thus providing a natural connection between the extended main-sequence turnoff phenomenon and the ubiquitous light-element abundance ranges seen in the ancient Galactic globular clusters.

  15. He stars and He-accreting CO white dwarfs

    International Nuclear Information System (INIS)

    Limongi, M.; Tornambe, A.

    1991-01-01

    He star models in the mass range 0.4-1.0 solar mass have been evolved until the red giant phase or, depending on their mass, until crystallization on the white-dwarf cooling sequence. Some of the degenerate structures obtained in these computations have been successively accreted at various He accretion rates in order to better define the fate of the accreting dwarf versus its mass and accretion rate for a fixed degeneracy level of the accreting dwarf. He stars have been further induced to transfer mass to a degenerate companion through Roche lobe overflow, in conditions of large gravitational wave radiation by the system. CO dwarfs in binary systems with He stars are found to experience a thermal behavior whose effects are such to locate the structure on the verge of obtaining a strong SN-like explosive event. 22 refs

  16. Einstein Observatory magnitude-limited X-ray survey of late-type giant and supergiant stars

    Science.gov (United States)

    Maggio, A.; Vaiana, G. S.; Haisch, B. M.; Stern, R. A.; Bookbinder, J.

    1990-01-01

    Results are presented of an extensive X-ray survey of 380 giant and supergiant stars of spectral types from F to M, carried out with the Einstein Observatory. It was found that the observed F giants or subgiants (slightly evolved stars with a mass M less than about 2 solar masses) are X-ray emitters at the same level of main-sequence stars of similar spectral type. The G giants show a range of emissions more than 3 orders of magnitude wide; some single G giants exist with X-ray luminosities comparable to RS CVn systems, while some nearby large G giants have upper limits on the X-ray emission below typical solar values. The K giants have an observed X-ray emission level significantly lower than F and F giants. None of the 29 M giants were detected, except for one spectroscopic binary.

  17. Is life most likely around Sun-like stars?

    Science.gov (United States)

    Lingam, Manasvi; Loeb, Abraham

    2018-05-01

    We consider the habitability of Earth-analogs around stars of different masses, which is regulated by the stellar lifetime, stellar wind-induced atmospheric erosion, and biologically active ultraviolet (UV) irradiance. By estimating the timescales associated with each of these processes, we show that they collectively impose limits on the habitability of Earth-analogs. We conclude that planets orbiting most M-dwarfs are not likely to host life, and that the highest probability of complex biospheres is for planets around K- and G-type stars. Our analysis suggests that the current existence of life near the Sun is slightly unusual, but not significantly anomalous.

  18. AK SCO, FIRST DETECTION OF A HIGHLY DISTURBED ATMOSPHERE IN A PRE-MAIN-SEQUENCE CLOSE BINARY

    International Nuclear Information System (INIS)

    Gomez de Castro, Ana I.

    2009-01-01

    AK Sco is a unique source: a ∼10 Myr old pre-main-sequence (PMS) spectroscopic binary composed of two nearly equal F5 stars that at periastron are separated by barely 11 stellar radii, so the stellar magnetospheres fill the Roche lobe at periastron. The orbit is not yet circularized (e = 0.47) and very strong tides are expected. This makes AK Sco the ideal laboratory to study the effect of gravitational tides in the stellar magnetic field building up during PMS evolution. In this Letter, the detection of a highly disturbed (σ ≅ 100 km s -1 ) and very dense atmosphere (n e = 1.6 x 10 10 cm -3 ) is reported. Significant line broadening blurs any signs of ion belts or bow shocks in the spectrum of the atmospheric plasma. The radiative losses cannot be accounted for solely by the dissipation of energy from the tidal wave propagating in the stellar atmosphere or by the accreting material. The release of internal energy from the star seems to be the most likely source of the plasma heating. This is the first clear indication of a highly disturbed atmosphere surrounding a PMS close binary.

  19. AK Sco, First Detection of a Highly Disturbed Atmosphere in a Pre-Main-Sequence Close Binary

    Science.gov (United States)

    Gómez de Castro, Ana I.

    2009-06-01

    AK Sco is a unique source: a ~10 Myr old pre-main-sequence (PMS) spectroscopic binary composed of two nearly equal F5 stars that at periastron are separated by barely 11 stellar radii, so the stellar magnetospheres fill the Roche lobe at periastron. The orbit is not yet circularized (e = 0.47) and very strong tides are expected. This makes AK Sco the ideal laboratory to study the effect of gravitational tides in the stellar magnetic field building up during PMS evolution. In this Letter, the detection of a highly disturbed (σ sime 100 km s-1) and very dense atmosphere (n e = 1.6 × 1010 cm-3) is reported. Significant line broadening blurs any signs of ion belts or bow shocks in the spectrum of the atmospheric plasma. The radiative losses cannot be accounted for solely by the dissipation of energy from the tidal wave propagating in the stellar atmosphere or by the accreting material. The release of internal energy from the star seems to be the most likely source of the plasma heating. This is the first clear indication of a highly disturbed atmosphere surrounding a PMS close binary.

  20. FLUORINE IN THE SOLAR NEIGHBORHOOD: IS IT ALL PRODUCED IN ASYMPTOTIC GIANT BRANCH STARS?

    Energy Technology Data Exchange (ETDEWEB)

    Jönsson, H.; Ryde, N. [Lund Observatory, Department of Astronomy and Theoretical Physics, Lund University, Box 43, SE-221 00 Lund (Sweden); Harper, G. M. [School of Physics, Trinity College, Dublin 2 (Ireland); Richter, M. J. [Physics Department, University of California, Davis, CA 95616 (United States); Hinkle, K. H., E-mail: henrikj@astro.lu.se [National Optical Astronomy Observatory, P.O. Box 26732, Tucson, AZ 85726 (United States)

    2014-07-10

    The origin of ''cosmic'' fluorine is uncertain, but there are three proposed production sites/mechanisms for the origin: asymptotic giant branch (AGB) stars, ν nucleosynthesis in Type II supernovae, and/or the winds of Wolf-Rayet stars. The relative importance of these production sites has not been established even for the solar neighborhood, leading to uncertainties in stellar evolution models of these stars as well as uncertainties in the chemical evolution models of stellar populations. We determine the fluorine and oxygen abundances in seven bright, nearby giants with well determined stellar parameters. We use the 2.3 μm vibrational-rotational HF line and explore a pure rotational HF line at 12.2 μm. The latter has never been used before for an abundance analysis. To be able to do this, we have calculated a line list for pure rotational HF lines. We find that the abundances derived from the two diagnostics agree. Our derived abundances are well reproduced by chemical evolution models including only fluorine production in AGB stars and, therefore, we draw the conclusion that this might be the main production site of fluorine in the solar neighborhood. Furthermore, we highlight the advantages of using the 12 μm HF lines to determine the possible contribution of the ν process to the fluorine budget at low metallicities where the difference between models including and excluding this process is dramatic.

  1. FLUORINE IN THE SOLAR NEIGHBORHOOD: IS IT ALL PRODUCED IN ASYMPTOTIC GIANT BRANCH STARS?

    International Nuclear Information System (INIS)

    Jönsson, H.; Ryde, N.; Harper, G. M.; Richter, M. J.; Hinkle, K. H.

    2014-01-01

    The origin of ''cosmic'' fluorine is uncertain, but there are three proposed production sites/mechanisms for the origin: asymptotic giant branch (AGB) stars, ν nucleosynthesis in Type II supernovae, and/or the winds of Wolf-Rayet stars. The relative importance of these production sites has not been established even for the solar neighborhood, leading to uncertainties in stellar evolution models of these stars as well as uncertainties in the chemical evolution models of stellar populations. We determine the fluorine and oxygen abundances in seven bright, nearby giants with well determined stellar parameters. We use the 2.3 μm vibrational-rotational HF line and explore a pure rotational HF line at 12.2 μm. The latter has never been used before for an abundance analysis. To be able to do this, we have calculated a line list for pure rotational HF lines. We find that the abundances derived from the two diagnostics agree. Our derived abundances are well reproduced by chemical evolution models including only fluorine production in AGB stars and, therefore, we draw the conclusion that this might be the main production site of fluorine in the solar neighborhood. Furthermore, we highlight the advantages of using the 12 μm HF lines to determine the possible contribution of the ν process to the fluorine budget at low metallicities where the difference between models including and excluding this process is dramatic

  2. IN-SYNC. II. VIRIAL STARS FROM SUBVIRIAL CORES—THE VELOCITY DISPERSION OF EMBEDDED PRE-MAIN-SEQUENCE STARS IN NGC 1333

    International Nuclear Information System (INIS)

    Foster, Jonathan B.; Cottaar, Michiel; Meyer, Michael R.; Covey, Kevin R.; Arce, Héctor G.; Nidever, David L.; Stassun, Keivan G.; Tan, Jonathan C.; Da Rio, Nicola; Chojnowski, S. Drew; Majewski, Steven R.; Skrutskie, Michael; Wilson, John C.; Flaherty, Kevin M.; Rebull, Luisa; Frinchaboy, Peter M.; Zasowski, Gail

    2015-01-01

    The initial velocity dispersion of newborn stars is a major unconstrained aspect of star formation theory. Using near-infrared spectra obtained with the APOGEE spectrograph, we show that the velocity dispersion of young (1-2 Myr) stars in NGC 1333 is 0.92 ± 0.12 km s –1 after correcting for measurement uncertainties and the effect of binaries. This velocity dispersion is consistent with the virial velocity of the region and the diffuse gas velocity dispersion, but significantly larger than the velocity dispersion of the dense, star-forming cores, which have a subvirial velocity dispersion of 0.5 km s –1 . Since the NGC 1333 cluster is dynamically young and deeply embedded, this measurement provides a strong constraint on the initial velocity dispersion of newly formed stars. We propose that the difference in velocity dispersion between stars and dense cores may be due to the influence of a 70 μG magnetic field acting on the dense cores or be the signature of a cluster with initial substructure undergoing global collapse

  3. Planet Occurrence within 0.25 AU of Solar-type Stars from Kepler

    DEFF Research Database (Denmark)

    Howard, A.W.; Geoffrey, G.W.; Bryson, S.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 include...... a nearly complete set of detected planets as small as 2 R ⊕. For each of the 156,000 target stars, we assess the detectability of planets as a function of planet radius, R 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 /a. We consider first Kepler target stars within the "solar subset" having T eff = 4100-6100 K, log g = 4.0-4.9, and Kepler magnitude Kp planets down to 2 R...

  4. Presupernova evolution of massive stars

    International Nuclear Information System (INIS)

    Weaver, T.A.; Zimmerman, G.B.; Woosley, S.E.

    1977-01-01

    Population I stars of 15 M/sub mass/ and 25 M/sub mass/ have been evolved from the zero-age main sequence through iron core collapse utilizing a numerical model that incorporates both implicit hydrodynamics and a detailed treatment of nuclear reactions. The stars end their presupernova evolution as red supergiants with photospheric radii of 3.9 x 10 13 cm and 6.7 x 10 13 cm, respectively, and density structures similar to those invoked to explain Type II supernova light curves on a strictly hydrodynamic basis. Both stars are found to form substantially neutronized ''iron'' cores of 1.56 M/sub mass/ and 1.61 M/sub mass/, and central electron abundances of 0.427 and 0.439 moles/g, respectively, during hydrostatic silicon burning. Just prior to collapse, the abundances of the elements in the 25 M/sub mass/ star (excluding the neutronized iron core) have ratios strikingly close to their solar system values over the mass range from oxygen to calcium, while the 15 M/sub mass/ star is characterized by large enhancements of Ne, Mg, and Si. It is pointed out on nucleosynthetic grounds that the mass of the neutronized core must represent a lower limit to the mass of the neutron star or black hole remnant that stars in this mass range can normally produce

  5. White dwarfs: connection with masses of the parent stars

    International Nuclear Information System (INIS)

    Amnuel', P.R.; Guseinov, O.Kh.; Novruzova, Kh.I.; Rustamov, Yu.S.

    1988-01-01

    A relationship between the mass of a white dwarf and the mass of the parent star on the main sequence is established. The white dwarf birth-rate matches the birth-rate (death-rate) of main sequence stars

  6. Solar Probe: Humanity's First Visit to a Star

    Science.gov (United States)

    Hassler, D. M.; Solar Probe Science; Technology Definition Team

    Solar Probe will experience first hand the processes and conditions in the solar atmosphere that ultimately impact our planet and shape the harsh solar system environment It will be humanity s first visit to a star and will explore a previously inaccessible region of the inner heliosphere The 2003 Space Science Enterprise Strategy called for study of a Solar Probe to fly through the solar atmosphere to answer fundamental questions that can be answered in no other way The mission received highest priority in the National Academy of Sciences decadal research strategy in solar and space physics in 2002 Significant advances have been made in the areas of solar and solar wind science instrument technology mission resources and the mission environment since the previous Solar Probe Science Definition Team reports of 1989 1995 and 1999 The 2004-05 Solar Probe Science and Technology Definition Team STDT recently completed a detailed study of the Solar Probe Mission based on an earliest launch date of October 2014 The report and its Executive Summary were published by NASA in September 2005 and can be found at the website http solarprobe gsfc nasa gov This talk provides an overview of the Solar Probe mission and a summary of the efforts of the STDT

  7. A spectroscopic survey of the youngest field stars in the solar neighborhood . II. The optically faint sample

    Science.gov (United States)

    Frasca, A.; Guillout, P.; Klutsch, A.; Ferrero, R. Freire; Marilli, E.; Biazzo, K.; Gandolfi, D.; Montes, D.

    2018-05-01

    Context. Star formation in the solar neighborhood is mainly traced by young stars in open clusters, associations, and in the field, which can be identified, for example, by their X-ray emission. The determination of stellar parameters for the optical counterparts of X-ray sources is crucial for a full characterization of these stars. Aims: This work extends the spectroscopic study of the RasTyc sample, obtained by the cross-correlation of the Tycho and ROSAT All-Sky Survey catalogs, to stars fainter than V = 9.5 mag and aims to identify sparse populations of young stars in the solar neighborhood. Methods: We acquired 625 high-resolution spectra for 443 presumably young stars with four different instruments in the northern hemisphere. The radial and rotational velocity (vsini) of our targets were measured by means of the cross-correlation technique, which is also helpful to discover single-lined (SB1), double-lined spectroscopic binaries (SB2), and multiple systems. We used the code ROTFIT to perform an MK spectral classification and to determine the atmospheric parameters (Teff, logg, [Fe/H]) and vsini of the single stars and SB1 systems. For these objects, we used the spectral subtraction of slowly rotating templates to measure the equivalent widths of the Hα and Li I 6708 Å lines, which enabled us to derive their chromospheric activity level and lithium abundance. We made use of Gaia DR1 parallaxes and proper motions to locate the targets in the Hertzsprung-Russell (HR) diagram and to compute the space velocity components of the youngest objects. Results: We find a remarkable percentage (at least 35%) of binaries and multiple systems. On the basis of the lithium abundance, the sample of single stars and SB1 systems appears to be mostly ( 60%) composed of stars younger than the members of the UMa cluster. The remaining sources are in the age range between the UMa and Hyades clusters ( 20%) or older ( 20%). In total, we identify 42 very young (PMS-like) stars

  8. Rotational velocities of low-mass stars

    International Nuclear Information System (INIS)

    Stauffer, J.B.; Hartmann, L.W.; Harvard-Smithsonian Center for Astrophysics, Cambridge, MA)

    1986-01-01

    The rotational velocities of stars provide important clues to how stars form and evolve. Yet until recently, studies of stellar rotation were limited to stars more massive than the sun. This is beginning to change, and an observational outline of the rotational velocity evolution of stars less massive than the sun can now be provided. Low-mass stars rotate slowly during the early stages of premain-sequence evolution, and spin up as they contract to the main sequence. This spin-up culminates in a brief period of very rapid rotation at an age of order 50 million years. Physical interpretation of this increase in rotation and the subsequent main-sequence spin-down are complicated by the possibility of differential internal rotation. The observed rapidity of spin-down among G dwarfs suggests that initially only the outer convective envelopes of these stars are slowed. The data suggest an intrinsic spread in angular momentum among young stars of the same mass and age, a spread which is apparently minimized by the angular-momentum loss mechanism in old low-mass stars. 83 references

  9. Infrared Observations of FS CMa Stars

    Science.gov (United States)

    Sitko, Michael L.; Russell, R. W.; Lynch, D. K.; Grady, C. A.; Hammel, H. B.; Beerman, L. C.; Day, A. N.; Huelsman, D.; Rudy, R. J.; Brafford, S. M.; Halbedel, E. M.

    2009-01-01

    A subset of non-supergiant B[e] stars has recently been recognized as forming a fairly unique class of objects with very strong emission lines, infrared excesses, and locations not associated with star formation. The exact evolutionary state of these stars, named for the prototype FS CMa, is uncertain, and they have often been classified as isolated Herbig AeBe stars. We present infrared observations of two of these stars, HD 45677 (FS CMa), HD 50138 (MWC 158), and the candidate FS CMa star HD 190073 (V1295 Aql) that span over a decade in time. All three exhibit an emission band at 10 microns due to amorphous silicates, confirming that much (if not all) of the infrared excess is due to dust. HD 50138 is found to exhibit 20% variability between 3-13 microns that resembles that found in pre-main sequence systems (HD 163296 and HD 31648). HD 45677, despite large changes at visual wavelengths, has remained relatively stable in the infrared. To date, no significant changes have been observed in HD 190073. This work is supported in part by NASA Origins of Solar Systems grant NAG5-9475, NASA Astrophysics Data Program contract NNH05CD30C, and the Independent Research and Development program at The Aerospace Corporation.

  10. MAGNETIC FIELDS OF STARS

    OpenAIRE

    Bychkov, V. D.; Bychkova, L. V.; Madej, J.

    2008-01-01

    Now it is known about 1212 stars of the main sequence and giants (from them 610 stars - it is chemically peculiarity (CP) stars) for which direct measurements of magnetic fields were spent (Bychkov et al.,2008). Let's consider, what representations were generated about magnetic fields (MT) of stars on the basis of available observations data.

  11. The origin of the Crab Nebula and the electron capture supernova in 8-10 M solar mass stars

    Science.gov (United States)

    Nomoto, K.

    1981-01-01

    The chemical composition of the Crab Nebula is compared with several presupernova models. The small carbon and oxygen abundances in the helium-rich nebula are consistent with only the presupernova model of the star whose main sequence mass was MMS approximately 8-9.5 M. More massive stars contain too much carbon in the helium layer and smaller mass stars do not leave neutron stars. The progenitor star of the Crab Nebula lost appreciable part of the hydrogen-rich envelope before the hydrogen-rich and helium layers were mixed by convection. Finally it exploded as the electron capture supernova; the O+Ne+Mg core collapsed to form a neutron star and only the extended helium-rich envelope was ejected by the weak shock wave.

  12. Apparent Solar Tornado-Like Prominences

    Science.gov (United States)

    Panasenco, Olga; Martin, Sara F.; Velli, Marco

    2014-02-01

    Recent high-resolution observations from the Solar Dynamics Observatory (SDO) have reawakened interest in the old and fascinating phenomenon of solar tornado-like prominences. This class of prominences was first introduced by Pettit ( Astrophys. J. 76, 9, 1932), who studied them over many years. Observations of tornado prominences similar to the ones seen by SDO had already been documented by Secchi ( Le Soleil, 1877). High-resolution and high-cadence multiwavelength data obtained by SDO reveal that the tornado-like appearance of these prominences is mainly an illusion due to projection effects. We discuss two different cases where prominences on the limb might appear to have a tornado-like behavior. One case of apparent vortical motions in prominence spines and barbs arises from the (mostly) 2D counterstreaming plasma motion along the prominence spine and barbs together with oscillations along individual threads. The other case of apparent rotational motion is observed in a prominence cavity and results from the 3D plasma motion along the writhed magnetic fields inside and along the prominence cavity as seen projected on the limb. Thus, the "tornado" impression results either from counterstreaming and oscillations or from the projection on the plane of the sky of plasma motion along magnetic-field lines, rather than from a true vortical motion around an (apparent) vertical or horizontal axis. We discuss the link between tornado-like prominences, filament barbs, and photospheric vortices at their base.

  13. 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...

  14. Nucleosynthesis and remnants in massive stars of solar metallicity

    International Nuclear Information System (INIS)

    Woosley, S.E.; Heger, A.

    2007-01-01

    Hans Bethe contributed in many ways to our understanding of the supernovae that happen in massive stars, but, to this day, a first principles model of how the explosion is energized is lacking. Nevertheless, a quantitative theory of nucleosynthesis is possible. We present a survey of the nucleosynthesis that occurs in 32 stars of solar metallicity in the mass range 12-120M sun . The most recent set of solar abundances, opacities, mass loss rates, and current estimates of nuclear reaction rates are employed. Restrictions on the mass cut and explosion energy of the supernovae based upon nucleosynthesis, measured neutron star masses, and light curves are discussed and applied. The nucleosynthetic results, when integrated over a Salpeter initial mass function (IMF), agree quite well with what is seen in the sun. We discuss in some detail the production of the long lived radioactivities, 26 Al and 60 Fe, and why recent model-based estimates of the ratio 60 Fe/ 26 Al are overly large compared with what satellites have observed. A major source of the discrepancy is the uncertain nuclear cross sections for the creation and destruction of these unstable isotopes

  15. Discovery of Extended Main-sequence Turnoffs in Four Young Massive Clusters in the Magellanic Clouds

    Energy Technology Data Exchange (ETDEWEB)

    Li, Chengyuan [Department of Physics and Astronomy, Macquarie University, Sydney, NSW 2109 (Australia); De Grijs, Richard [Kavli Institute for Astronomy and Astrophysics and Department of Astronomy, Peking University, Yi He Yuan Lu 5, Hai Dian District, Beijing 100871 (China); Deng, Licai [Key Laboratory for Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences, 20A Datun Road, Chaoyang District, Beijing 100012 (China); Milone, Antonino P. [Research School of Astronomy and Astrophysics, Australian National University, Mt. Stromlo Observatory, Cotter Road, Weston, ACT 2611 (Australia)

    2017-08-01

    An increasing number of young massive clusters (YMCs) in the Magellanic Clouds have been found to exhibit bimodal or extended main sequences (MSs) in their color–magnitude diagrams (CMDs). These features are usually interpreted in terms of a coeval stellar population with different stellar rotational rates, where the blue and red MS stars are populated by non- (or slowly) and rapidly rotating stellar populations, respectively. However, some studies have shown that an age spread of several million years is required to reproduce the observed wide turnoff regions in some YMCs. Here we present the ultraviolet–visual CMDs of four Large and Small Magellanic Cloud YMCs, NGC 330, NGC 1805, NGC 1818, and NGC 2164, based on high-precision Hubble Space Telescope photometry. We show that they all exhibit extended main-sequence turnoffs (MSTOs). The importance of age spreads and stellar rotation in reproducing the observations is investigated. The observed extended MSTOs cannot be explained by stellar rotation alone. Adopting an age spread of 35–50 Myr can alleviate this difficulty. We conclude that stars in these clusters are characterized by ranges in both their ages and rotation properties, but the origin of the age spread in these clusters remains unknown.

  16. Constraints on Climate and Habitability for Earth-like Exoplanets Determined from a General Circulation Model

    International Nuclear Information System (INIS)

    Wolf, Eric T.; Toon, Owen B.; Shields, Aomawa L.; Kopparapu, Ravi K.; Haqq-Misra, Jacob

    2017-01-01

    Conventional definitions of habitability require abundant liquid surface water to exist continuously over geologic timescales. Water in each of its thermodynamic phases interacts with solar and thermal radiation and is the cause for strong climatic feedbacks. Thus, assessments of the habitable zone require models to include a complete treatment of the hydrological cycle over geologic time. Here, we use the Community Atmosphere Model from the National Center for Atmospheric Research to study the evolution of climate for an Earth-like planet at constant CO 2 , under a wide range of stellar fluxes from F-, G-, and K-dwarf main sequence stars. Around each star we find four stable climate states defined by mutually exclusive global mean surface temperatures ( T s ); snowball ( T s ≤ 235 K), waterbelt (235 K ≤ T s ≤ 250 K), temperate (275 K ≤ T s ≤ 315 K), and moist greenhouse ( T s ≥ 330 K). Each is separated by abrupt climatic transitions. Waterbelt, temperate, and cooler moist greenhouse climates can maintain open-ocean against both sea ice albedo and hydrogen escape processes respectively, and thus constitute habitable worlds. We consider the warmest possible habitable planet as having T s ∼ 355 K, at which point diffusion limited water-loss could remove an Earth ocean in ∼1 Gyr. Without long timescale regulation of non-condensable greenhouse species at Earth-like temperatures and pressures, such as CO 2 , habitability can be maintained for an upper limit of ∼2.2, ∼2.4, and ∼4.7 Gyr around F-, G-, and K-dwarf stars respectively, due to main sequence brightening.

  17. Constraints on Climate and Habitability for Earth-like Exoplanets Determined from a General Circulation Model

    Energy Technology Data Exchange (ETDEWEB)

    Wolf, Eric T.; Toon, Owen B. [Laboratory for Atmospheric and Space Physics, Department of Atmospheric and Oceanic Sciences, University of Colorado, Boulder, CO (United States); Shields, Aomawa L. [University of California, Irvine, Department of Physics and Astronomy, 4129 Frederick Reines Hall, Irvine, CA 92697 (United States); Kopparapu, Ravi K.; Haqq-Misra, Jacob, E-mail: eric.wolf@colorado.edu [NASA Astrobiology Institute' s Virtual Planetary Laboratory, P.O. Box 351580, Seattle, WA 98195 (United States)

    2017-03-10

    Conventional definitions of habitability require abundant liquid surface water to exist continuously over geologic timescales. Water in each of its thermodynamic phases interacts with solar and thermal radiation and is the cause for strong climatic feedbacks. Thus, assessments of the habitable zone require models to include a complete treatment of the hydrological cycle over geologic time. Here, we use the Community Atmosphere Model from the National Center for Atmospheric Research to study the evolution of climate for an Earth-like planet at constant CO{sub 2}, under a wide range of stellar fluxes from F-, G-, and K-dwarf main sequence stars. Around each star we find four stable climate states defined by mutually exclusive global mean surface temperatures ( T {sub s}); snowball ( T {sub s} ≤ 235 K), waterbelt (235 K ≤ T {sub s} ≤ 250 K), temperate (275 K ≤ T {sub s} ≤ 315 K), and moist greenhouse ( T {sub s} ≥ 330 K). Each is separated by abrupt climatic transitions. Waterbelt, temperate, and cooler moist greenhouse climates can maintain open-ocean against both sea ice albedo and hydrogen escape processes respectively, and thus constitute habitable worlds. We consider the warmest possible habitable planet as having T {sub s} ∼ 355 K, at which point diffusion limited water-loss could remove an Earth ocean in ∼1 Gyr. Without long timescale regulation of non-condensable greenhouse species at Earth-like temperatures and pressures, such as CO{sub 2}, habitability can be maintained for an upper limit of ∼2.2, ∼2.4, and ∼4.7 Gyr around F-, G-, and K-dwarf stars respectively, due to main sequence brightening.

  18. Life of a star

    International Nuclear Information System (INIS)

    Henbest, Nigel.

    1988-01-01

    The paper concerns the theory of stellar evolution. A description is given of:- how a star is born, main sequence stars, red giants, white dwarfs, supernovae, neutron stars and black holes. A brief explanation is given of how the death of a star as a supernova can trigger off the birth of a new generation of stars. Classification of stars and the fate of our sun, are also described. (U.K.)

  19. Behavior of Abundances in Chemically Peculiar Dwarf and Subgiant A-Type Stars: HD 23193 and HD 170920

    Science.gov (United States)

    Kılıçoğlu, Tolgahan; Çalışkan, Şeyma; Ünal, Kübraözge

    2018-01-01

    To understand the origin of the abundance peculiarities of non-magnetic A-type stars, we present the first detailed chemical abundance analysis of a metallic line star HD 23193 (A2m) and an A-type subgiant HD 170920 (A5), which could have been a HgMn star on the main sequence. Our analysis is based on medium (R ∼ 14,000) and high (R ∼ 40,000) resolution spectroscopic data of the stars. The abundances of 18 elements are derived: C, O, Na, Mg, Al, Si, S, Ca, Sc, Ti, Cr, Mn, Fe, Ni, Zn, Sr, Y, and Ba. The masses of HD 23193 and HD 170920 are estimated from evolutionary tracks as 2.3 ± 0.1 M ⊙ and 2.9 ± 0.1 M ⊙. The ages are found to be 635 ± 33 Myr for HD 23193 and 480 ± 50 Myr for HD 170920 using isochrones. The abundance pattern of HD 23193 shows deviations from solar values in the iron-peak elements and indicates remarkable overabundances of Sr (1.16), Y (1.03), and Ba (1.24) with respect to the solar abundances. We compare the derived abundances of this moderately rotating (v\\sin i =37.5 km s‑1) Am star to the theoretical chemical evolution models including rotational mixing. The theoretically predicted abundances resemble our derived abundance pattern, except for a few elements (Si and Cr). For HD 170920, we find nearly solar abundances, except for C (‑0.43), S (0.16), Ti (0.15), Ni (0.16), Zn (0.41), Y (0.57), and Ba (0.97). Its low rotational velocity (v\\sin i=14.5 km s‑1), reduced carbon abundance, and enhanced heavy element abundances suggest that the star is most likely an evolved HgMn star. Based on observations made at the TÜBITAK National Observatory (Program ID 14BRTT150–671), and the Ankara University Observatory, Turkey.

  20. The Solar Probe Plus Mission: Humanity's First Visit to Our Star

    Science.gov (United States)

    Fox, N. J.; Velli, M. C.; Bale, S. D.; Decker, R.; Driesman, A.; Howard, R. A.; Kasper, J. C.; Kinnison, J.; Kusterer, M.; Lario, D.; hide

    2015-01-01

    Solar Probe Plus (SPP) will be the first spacecraft to fly into the low solar corona. SPPs main science goal is to determine the structure and dynamics of the Suns coronal magnetic field, understand how the solar corona and wind are heated and accelerated, and determine what processes accelerate energetic particles. Understanding these fundamental phenomena has been a top-priority science goal for over five decades, dating back to the 1958 Simpson Committee Report. The scale and concept of such a mission has been revised at intervals since that time, yet the core has always been a close encounter with the Sun. The mission design and the technology and engineering developments enable SPP to meet its science objectives to: (1) Trace the flow of energy that heats and accelerates the solar corona and solar wind; (2) Determine the structure and dynamics of the plasma and magnetic fields at the sources of the solar wind; and (3) Explore mechanisms that accelerate and transport energetic particles. The SPP mission was confirmed in March 2014 and is under development as a part of NASAs Living with a Star (LWS) Program. SPP is scheduled for launch in mid-2018, and will perform 24 orbits over a 7-year nominal mission duration. Seven Venus gravity assists gradually reduce SPPs perihelion from 35 solar radii (RS) for the first orbit to less than 10 RS for the final three orbits. In this paper we present the science, mission concept and the baseline vehicle for SPP, and examine how the mission will address the key science questions.

  1. The structural evolution of Milky-Way-like star-forming galaxies since z ∼ 1.3

    International Nuclear Information System (INIS)

    Patel, Shannon G.; Fumagalli, Mattia; Franx, Marijn; Labbé, Ivo; Muzzin, Adam; Van Dokkum, Pieter G.; Leja, Joel; Skelton, Rosalind E.; Momcheva, Ivelina; Nelson, Erica June; Van der Wel, Arjen; Rix, Hans-Walter; Brammer, Gabriel; Whitaker, Katherine E.; Lundgren, Britt; Wake, David A.; Quadri, Ryan F.

    2013-01-01

    We follow the structural evolution of star-forming galaxies (SFGs) like the Milky Way by selecting progenitors to z ∼ 1.3 based on the stellar mass growth inferred from the evolution of the star-forming sequence. We select our sample from the 3D-HST survey, which utilizes spectroscopy from the HST/WFC3 G141 near-IR grism and enables precise redshift measurements for our sample of SFGs. Structural properties are obtained from Sérsic profile fits to CANDELS WFC3 imaging. The progenitors of z = 0 SFGs with stellar mass M = 10 10.5 M ☉ are typically half as massive at z ∼ 1. This late-time stellar mass growth is consistent with recent studies that employ abundance matching techniques. The descendant SFGs at z ∼ 0 have grown in half-light radius by a factor of ∼1.4 since z ∼ 1. The half-light radius grows with stellar mass as r e ∝M 0.29 . While most of the stellar mass is clearly assembling at large radii, the mass surface density profiles reveal ongoing mass growth also in the central regions where bulges and pseudobulges are common features in present day late-type galaxies. Some portion of this growth in the central regions is due to star formation as recent observations of Hα maps for SFGs at z ∼ 1 are found to be extended but centrally peaked. Connecting our lookback study with galactic archeology, we find the stellar mass surface density at R = 8 kpc to have increased by a factor of ∼2 since z ∼ 1, in good agreement with measurements derived for the solar neighborhood of the Milky Way.

  2. Solar History An Introduction

    CERN Document Server

    Vita-Finzi, Claudio

    2013-01-01

    Beyond the four centuries of sunspot observation and the five decades during which artificial satellites have monitored the Sun – that is to say for 99.99999% of the Sun’s existence – our knowledge of solar history depends largely on analogy with kindred main sequence stars, on the outcome of various kinds of modelling, and on indirect measures of solar activity. They include the analysis of lunar rocks and meteorites for evidence of solar flares and other components of the solar cosmic-ray (SCR) flux, and the measurement of cosmogenic isotopes in wood, stratified ice and marine sediments to evaluate changes in the galactic cosmic-ray (GCR) flux and thus infer changes in the sheltering magnetic fields of the solar wind. In addition, shifts in the global atmospheric circulation which appear to result from cyclic fluctuations in solar irradiance have left their mark in river sediments and in the isotopic composition of cave deposits. In this volume the results these sources have already produced have bee...

  3. A Novel Method for Age Estimation in Solar-Type Stars Through GALEX FUV Magnitudes

    Science.gov (United States)

    Ho, Kelly; Subramonian, Arjun; Smith, Graeme; Shouru Shieh

    2018-01-01

    Utilizing an inverse association known to exist between Galaxy Evolution Explorer (GALEX) far ultraviolet (FUV) magnitudes and the chromospheric activity of F, G, and K dwarfs, we explored a method of age estimation in solar-type stars through GALEX FUV magnitudes. Sample solar-type star data were collected from refereed publications and filtered by B-V and absolute visual magnitude to ensure similarities in temperature and luminosity to the Sun. We determined FUV-B and calculated a residual index Q for all the stars, using the temperature-induced upper bound on FUV-B as the fiducial. Plotting current age estimates for the stars against Q, we discovered a strong and significant association between the variables. By applying a log-linear transformation to the data to produce a strong correlation between Q and loge Age, we confirmed the association between Q and age to be exponential. Thus, least-squares regression was used to generate an exponential model relating Q to age in solar-type stars, which can be used by astronomers. The Q-method of stellar age estimation is simple and more efficient than existing spectroscopic methods and has applications to galactic archaeology and stellar chemical composition analysis.

  4. 78 FR 29130 - Solar Star California XIX, LLC; Supplemental Notice that Initial Market-Based Rate Filing...

    Science.gov (United States)

    2013-05-17

    ... DEPARTMENT OF ENERGY Federal Energy Regulatory Commission [Docket No. ER13-1441-000] Solar Star California XIX, LLC; Supplemental Notice that Initial Market-Based Rate Filing Includes Request for Blanket Section 204 Authorization This is a supplemental notice in the above-referenced proceeding, of Solar Star...

  5. Rotation-induced YORP break-up of small bodies to produce post-main-sequence debris

    Science.gov (United States)

    Veras, D.; Jacobson, S. A.; Gänsicke, B. T.

    2017-09-01

    We hypothesize that the in situ break-up of small bodies such as asteroids spun to fission during the giant branch phases of stellar evolution provides an important contribution to the debris orbiting and ultimately polluting white dwarfs. The YORP (Yarkovsky-O'Keefe-Radviesvki-Paddock) effect, which arises from radiation pressure, accelerates the spin rate of asymmetric asteroids, which can eventually shear themselves apart. This pressure is maintained and enhanced around dying stars because the outward push of an asteroid due to stellar mass loss is insignificant compared to the resulting stellar luminosity increase. Consequently, giant star radiation will destroy nearly all bodies with radii in the range 100 m-10 km that survive their parent star's main-sequence lifetime within a distance of about 7 au; smaller bodies are spun apart to their strongest, competent components. This estimate is conservative and would increase for highly asymmetric shapes or incorporation of the inward drag due to giant star stellar wind. The resulting debris field, which could extend to thousands of au, may be perturbed by remnant planetary systems to reproduce the observed dusty and gaseous discs which accompany polluted white dwarfs.

  6. Kepler Asteroseismology of Red-giant Stars

    DEFF Research Database (Denmark)

    Christensen-Dalsgaard, J.

    2012-01-01

    The Kepler mission, launched in March 2009, has revolutionized asteroseismology, providing detailed observations of thousands of stars. This has allowed in-depth analyses of stars ranging from compact hot subdwarfs to red giants, and including the detection of solar-like oscillations in hundreds ...

  7. The sun in time

    International Nuclear Information System (INIS)

    Sonett, C.P.; Giampapa, M.S.; Matthews, M.S.

    1991-01-01

    Various papers on solar science are presented. The topics considered include: variability of solar irradiance, sunspot number, solar diameter, and solar wind properties; theory of luminosity and radius variations; standard solar models; the sun and the IMF; variations of cosmic-ray flux with time; accelerated particles in solar flares; solar cosmic ray fluxes during the last 10 million yrs; solar neutrinos and solar history; time variations of Be-10 and solar activity; solar and terrestrial components of the atmospheric C-14 variation spectrum; solar flare heavy-ion tracks in extraterrestrial objects. Also addressed are: the faint young sun problem; atmospheric responses to solar irradiation; quaternary glaciations; solar-terrestrial relationships in recent sea sediments; magnetic history of the sun; pre- and main-sequence evolution of solar activity; magnetic activity in pre-main-sequence stars; classical T Tauri stars; relict magnetism of meteorites; luminosity variability of solar-type stars; evolution of angular momentum in solar-mass stars; time evolution of magnetic fields on solarlike stars

  8. He-like spectra from laboratory plasmas and solar flares

    International Nuclear Information System (INIS)

    Kato, Takako

    1990-01-01

    The X-ray spectra of He-like ions from tokamaks and solar flares have been measured. Several physical parameters of plasma can be derived from the X-ray spectra of He-like ions. The ion temperature can be derived from the doppler width of a resonance line. The electron temperature is obtained from the intensity ratio of dielectronic satellite lines to a resonance line. The energy level for the prominent lines is shown. The line q is produced mainly by the inner-shell excitation of Li-like ions, and line beta is produced by the inner-shell excitation of Be-like ions. The intensity ratios give the ion density ratios. The intensities of the intercombination and the forbidden lines are affected by the recombination from H-like ions. The synthetic spectra including excitation, ionization and recombination processes are fitted to the measurement. In this paper, the He-like X-ray spectra of the titanium ions from TFTR tokamak plasma and of the iron ions from solar flares are discussed, paying attention to the presence of high energy electrons which affect the spectra and ionization balance. Atomic data, the spectra from the TFTR tokamak, the spectra from solar flares and so on are described. (K.I.)

  9. Discovery of a Red Giant with Solar-like Oscillations in an Eclipsing Binary System from Kepler Space-based Photometry

    DEFF Research Database (Denmark)

    Hekker, S.; Debosscher, J.; Huber, D.

    2010-01-01

    Oscillating stars in binary systems are among the most interesting stellar laboratories, as these can provide information on the stellar parameters and stellar internal structures. Here we present a red giant with solar-like oscillations in an eclipsing binary observed with the NASA Kepler...

  10. Revolution evolution: tracing angular momentum during star and planetary system formation

    Science.gov (United States)

    Davies, Claire Louise

    2015-04-01

    Stars form via the gravitational collapse of molecular clouds during which time the protostellar object contracts by over seven orders of magnitude. If all the angular momentum present in the natal cloud was conserved during collapse, stars would approach rotational velocities rapid enough to tear themselves apart within just a few Myr. In contrast to this, observations of pre-main sequence rotation rates are relatively slow (∼ 1 - 15 days) indicating that significant quantities of angular momentum must be removed from the star. I use observations of fully convective pre-main sequence stars in two well-studied, nearby regions of star formation (namely the Orion Nebula Cluster and Taurus-Auriga) to determine the removal rate of stellar angular momentum. I find the accretion disc-hosting stars to be rotating at a slower rate and contain less specific angular momentum than the disc-less stars. I interpret this as indicating a period of accretion disc-regulated angular momentum evolution followed by near-constant rotational evolution following disc dispersal. Furthermore, assuming that the age spread inferred from the Hertzsprung-Russell diagram constructed for the star forming region is real, I find that the removal rate of angular momentum during the accretion-disc hosting phase to be more rapid than that expected from simple disc-locking theory whereby contraction occurs at a fixed rotation period. This indicates a more efficient process of angular momentum removal must operate, most likely in the form of an accretion-driven stellar wind or outflow emanating from the star-disc interaction. The initial circumstellar envelope that surrounds a protostellar object during the earliest stages of star formation is rotationally flattened into a disc as the star contracts. An effective viscosity, present within the disc, enables the disc to evolve: mass accretes inwards through the disc and onto the star while momentum migrates outwards, forcing the outer regions of the

  11. The Sun among the stars. Pt. 3

    International Nuclear Information System (INIS)

    Hardorp, J.

    1980-01-01

    Energy distributions from 3308 to 8390 Angstroem of two candidates for a solar spectral analog and of 14 other northern G-type dwarfs are compared to the solar energy distribution via stellar spectrophotometric standards. The reliability of the stellar and solar flux-calibrations is evaluated. While the stellar calibration seems to be in good shape, solar calibrations differ widely. Labs.and Neckel's calibration is the best match to the energy distributions from 4500 to 8390 Angstroem of those four stars that share the Sun's ultraviolet line spectrum (16 Cyg B, G5V, and the three Hyades stars VB 64, 106, and 142). Below 4500 Angstroem, discrepancies of up to 6% remain which do not seem to be genuine Sun-star differences. An error in the Labs and Neckel tables between 5700 and 6000 Angstroem is corrected. The NASA Standard Tables of Solar Spectral Irradiance cannot be trusted, since there seems to be no star in the sky that look like the NASA-sun. The four stars mentioned are taken to be perfect solar spectral analogs. An improved table of solar spectral irradiance is then given by the magnitudes of 16 Cyg B minus 32.945, based on Tueg's atellar and Labs and Neckel's solar calibrations. The Sun's place in the UBV system is V = -26.71 +- 0.03, B-V = 0.665 +- 0.005, and U-B = 0.20 +- 0.01. Most previous photometric investigations found a bluer Sun because they used the wrong solar calibration. For deriving accurate albedos of planets, any one of the calibrated G-type stars can be used as a standard star, when corrections are applied, although the solar analogs themselves are to be preferred. The MK system of spectral classification should be revised. (orig.)

  12. Asteroseismic modelling of the solar-like star β Hydri

    Science.gov (United States)

    Doğan, G.; Brandão, I. M.; Bedding, T. R.; Christensen-Dalsgaard, J.; Cunha, M. S.; Kjeldsen, H.

    2010-07-01

    We present the results of modelling the subgiant star β Hydri using seismic observational constraints. We have computed several grids of stellar evolutionary tracks using the Aarhus STellar Evolution Code (ASTEC, Christensen-Dalsgaard in Astrophys. Space Sci. 316:13, 2008a), with and without helium diffusion and settling. For those models on each track that are located at the observationally determined position of β Hydri in the Hertzsprung-Russell (HR) diagram, we have calculated the oscillation frequencies using the Aarhus adiabatic pulsation package (ADIPLS, Christensen-Dalsgaard in Astrophys. Space Sci. 316:113, 2008b). Applying the near-surface corrections to the calculated frequencies using the empirical law presented by Kjeldsen et al. (Astrophys. J. 683:L175, 2008), we have compared the corrected model frequencies with the observed frequencies of the star. We show that after correcting the frequencies for the near-surface effects, we have a fairly good fit for both l=0 and l=2 frequencies. We also have good agreement between the observed and calculated l=1 mode frequencies, although there is room for improvement in order to fit all the observed mixed modes simultaneously.

  13. A STAR IN THE M31 GIANT STREAM: THE HIGHEST NEGATIVE STELLAR VELOCITY KNOWN

    International Nuclear Information System (INIS)

    Caldwell, Nelson; Kenyon, Scott J.; Morrison, Heather; Harding, Paul; Schiavon, Ricardo; Rose, James A.

    2010-01-01

    We report on a single star, B030D, observed as part of a large survey of objects in M31, which has the unusual radial velocity of -780 km s -1 . Based on details of its spectrum, we find that the star is an F supergiant, with a circumstellar shell. The evolutionary status of the star could be one of a post-main-sequence close binary, a symbiotic nova, or less likely, a post-asymptotic giant branch star, which additional observations could help sort out. Membership of the star in the Andromeda Giant Stream can explain its highly negative velocity.

  14. Low coverage sequencing of three echinoderm genomes: the brittle star Ophionereis fasciata, the sea star Patiriella regularis, and the sea cucumber Australostichopus mollis.

    Science.gov (United States)

    Long, Kyle A; Nossa, Carlos W; Sewell, Mary A; Putnam, Nicholas H; Ryan, Joseph F

    2016-01-01

    There are five major extant groups of Echinodermata: Crinoidea (feather stars and sea lillies), Ophiuroidea (brittle stars and basket stars), Asteroidea (sea stars), Echinoidea (sea urchins, sea biscuits, and sand dollars), and Holothuroidea (sea cucumbers). These animals are known for their pentaradial symmetry as adults, unique water vascular system, mutable collagenous tissues, and endoskeletons of high magnesium calcite. To our knowledge, the only echinoderm species with a genome sequence available to date is Strongylocentrotus pupuratus (Echinoidea). The availability of additional echinoderm genome sequences is crucial for understanding the biology of these animals. Here we present assembled draft genomes of the brittle star Ophionereis fasciata, the sea star Patiriella regularis, and the sea cucumber Australostichopus mollis from Illumina sequence data with coverages of 12.5x, 22.5x, and 21.4x, respectively. These data provide a resource for mining gene superfamilies, identifying non-coding RNAs, confirming gene losses, and designing experimental constructs. They will be important comparative resources for future genomic studies in echinoderms.

  15. Neutron star/red giant encounters in globular clusters

    International Nuclear Information System (INIS)

    Bailyn, C.D.

    1988-01-01

    The author presents a simple expression for the amount by which xsub(crit) is diminished as a star evolves xsub(crit) Rsub(crit)/R*, where Rsub(crit) is the maximum distance of closest approach between two stars for which the tidal energy is sufficient to bind the system, and R* is the radius of the star on which tides are being raised. Also it is concluded that tidal capture of giants by neutron stars resulting in binary systems is unlikely in globular clusters. However, collisions between neutron stars and red giants, or an alternative process involving tidal capture of a main-sequence star into an initially detached binary system, may result either in rapidly rotating neutron stars or in white dwarf/neutron star binaries. (author)

  16. Classification of O Stars in the Yellow-Green: The Exciting Star VES 735

    Science.gov (United States)

    Kerton, C. R.; Ballantyne, D. R.; Martin, P. G.

    1999-05-01

    Acquiring data for spectral classification of heavily reddened stars using traditional criteria in the blue-violet region of the spectrum can be prohibitively time consuming using small to medium sized telescopes. One such star is the Vatican Observatory emission-line star VES 735, which we have found excites the H II region KR 140. In order to classify VES 735, we have constructed an atlas of stellar spectra of O stars in the yellow-green (4800-5420 Å). We calibrate spectral type versus the line ratio He I lambda4922:He II lambda5411, showing that this ratio should be useful for the classification of heavily reddened O stars associated with H II regions. Application to VES 735 shows that the spectral type is O8.5. The absolute magnitude suggests luminosity class V. Comparison of the rate of emission of ionizing photons and the bolometric luminosity of VES 735, inferred from radio and infrared measurements of the KR 140 region, to recent stellar models gives consistent evidence for a main-sequence star of mass 25 M_solar and age less than a few million years with a covering factor 0.4-0.5 by the nebular material. Spectra taken in the red (6500-6700 Å) show that the stellar Hα emission is double-peaked about the systemic velocity and slightly variable. Hβ is in absorption, so that the emission-line classification is ``(e)''. However, unlike the case of the more well-known O(e) star zeta Oph, the emission from VES 735 appears to be long-lived rather than episodic.

  17. The impact of Einstein observations on our understanding of low mass star formation

    International Nuclear Information System (INIS)

    Walter, F.M.

    1990-01-01

    Prior to 1980, the world of pre-main sequence stars, if not well understood, was at least well defined. The Herbig and Rao (1972) catalog listed 69 pre-main sequence stars in Tau-Aur, with the vast majority clearly being T Tauri stars. The characteristics of the classical T Tauri stars include strong Hα emission, with W λ (Hα)>5-10A; forbidden line emission; continuum ultraviolet and IR excesses; veiling of the absorption line spectrum; significant stellar variability; Li I λ6707A absorption; and association with dark clouds and/or emission nebulosities. Star forming regions were observed extensively with the Einstein Observatory, and showed the abundance of stellar X-ray sources in the Orion Nebula. About 1/3 of the known T Tauri stars were detected as X-ray sources, yet the vast majority of the X-ray sources detected were coincident with anonymous stars not suspected to be pre-main sequence stars. In the grand tradition of X-ray astronomy, X-ray astronomers trooped to telescopes to identify the optical counterparts. It was shown that 5 of the counterparts were K7-M0 stars, above the main sequence, with strong Li I absorption and that these stars were kinematic members of the Tau-Aur star formation complex. Since then, additional members of this class of naked T Tauri Stars (NTTS) have been studied, and charts provided for X-ray selected pre-main sequence star candidates in the general vicinity of Tau-Aur. Thirty five X-ray sources have been selected and optically confirmed as NTTS in Tau-Aur

  18. PROPERTIES OF 42 SOLAR-TYPE KEPLER TARGETS FROM THE ASTEROSEISMIC MODELING PORTAL

    Energy Technology Data Exchange (ETDEWEB)

    Metcalfe, T. S.; Mathur, S. [Space Science Institute, 4750 Walnut Street Suite 205, Boulder, CO 80301 (United States); Creevey, O. L. [Institut d' Astrophysique Spatiale, Université Paris XI, UMR 8617, CNRS, Batiment 121, F-91405 Orsay Cedex (France); Doğan, G.; Christensen-Dalsgaard, J.; Karoff, C.; Trampedach, R. [Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, DK-8000 Aarhus C (Denmark); Xu, H. [Computational and Information Systems Laboratory, NCAR, P.O. Box 3000, Boulder, CO 80307 (United States); Bedding, T. R.; Benomar, O. [Sydney Institute for Astronomy (SIfA), School of Physics, University of Sydney, NSW 2006 (Australia); Chaplin, W. J.; Campante, T. L.; Davies, G. R. [School of Physics and Astronomy, University of Birmingham, Birmingham B15 2TT (United Kingdom); Brown, B. P. [Department of Astronomy and Center for Magnetic Self Organization in Laboratory and Astrophysical Plasmas, University of Wisconsin, Madison, WI 53706 (United States); Buzasi, D. L. [Department of Chemistry and Physics, Florida Gulf Coast University, Fort Myers, FL 33965 (United States); Çelik, Z. [Ege University, Department of Astronomy and Space Sciences, Bornova, 35100, Izmir (Turkey); Cunha, M. S. [Centro de Astrofísica e Faculdade de Ciências, Universidade do Porto, Rua das Estrelas, 4150-762, Porto (Portugal); Deheuvels, S. [Université de Toulouse, UPS-OMP, IRAP, Toulouse (France); Derekas, A. [Konkoly Observatory, MTA CSFK, H-1121 Budapest, Konkoly Thege M. út 15-17 (Hungary); Mauro, M. P. Di [INAF-IAPS Istituto di Astrofisica e Planetologia Spaziali, Via del Fosso del Cavaliere 100, I-00133 Roma (Italy); and others

    2014-10-01

    Recently the number of main-sequence and subgiant stars exhibiting solar-like oscillations that are resolved into individual mode frequencies has increased dramatically. While only a few such data sets were available for detailed modeling just a decade ago, the Kepler mission has produced suitable observations for hundreds of new targets. This rapid expansion in observational capacity has been accompanied by a shift in analysis and modeling strategies to yield uniform sets of derived stellar properties more quickly and easily. We use previously published asteroseismic and spectroscopic data sets to provide a uniform analysis of 42 solar-type Kepler targets from the Asteroseismic Modeling Portal. We find that fitting the individual frequencies typically doubles the precision of the asteroseismic radius, mass, and age compared to grid-based modeling of the global oscillation properties, and improves the precision of the radius and mass by about a factor of three over empirical scaling relations. We demonstrate the utility of the derived properties with several applications.

  19. MAGNETIC ACTIVITY CYCLES IN THE EXOPLANET HOST STAR ε ERIDANI

    International Nuclear Information System (INIS)

    Metcalfe, T. S.; Mathur, S.; Buccino, A. P.; Mauas, P. J. D.; Petrucci, R.; Brown, B. P.; Soderblom, D. R.; Henry, T. J.; Hall, J. C.; Basu, S.

    2013-01-01

    The active K2 dwarf ε Eri has been extensively characterized both as a young solar analog and more recently as an exoplanet host star. As one of the nearest and brightest stars in the sky, it provides an unparalleled opportunity to constrain stellar dynamo theory beyond the Sun. We confirm and document the 3-year magnetic activity cycle in ε Eri originally reported by Hatzes and coworkers, and we examine the archival data from previous observations spanning 45 years. The data show coexisting 3-year and 13-year periods leading into a broad activity minimum that resembles a Maunder minimum-like state, followed by the resurgence of a coherent 3-year cycle. The nearly continuous activity record suggests the simultaneous operation of two stellar dynamos with cycle periods of 2.95 ± 0.03 years and 12.7 ± 0.3 years, which, by analogy with the solar case, suggests a revised identification of the dynamo mechanisms that are responsible for the so-called 'active' and 'inactive' sequences as proposed by Böhm-Vitense. Finally, based on the observed properties of ε Eri, we argue that the rotational history of the Sun is what makes it an outlier in the context of magnetic cycles observed in other stars (as also suggested by its Li depletion), and that a Jovian-mass companion cannot be the universal explanation for the solar peculiarities.

  20. Effective temperatures, angular diameters, distances and linear radii for 160 O and B stars

    International Nuclear Information System (INIS)

    Underhill, A.B.; Divan, L.; Prevot-Burnichon, M.L.; Doazan, V.

    1979-01-01

    The significance is explained of the effective temperatures, angular diameters, distances and linear diameters which have been found from published ultraviolet spectrophotometry, visible and near infrared intermediate-band photometry and model-atmosphere fluxes for 160 O and B stars using a method which is fully explained and evaluated in the full paper which is reproduced on Microfiche MN 189/1. An appendix to the full paper presents BCD spectrophotometry for 77 of the program stars. The angular diameters are systematically the same as those measured previously, and the flux effective temperatures of the main-sequence and giant stars reproduce well the relationship established by other authors, for main-sequence and giant O and B stars. The O8 - B9 supergiants have systematically lower temperatures than do main-sequence stars of the same subtype. The Beta Cephei stars and most Be stars have the same effective temperature as normal stars of the same spectral type. The radii of O and B stars increase from main-sequence to supergiant. The late B supergiants are about twice as large as the O9 supergiants. (author)

  1. Thai student existing understanding about the solar system model and the motion of the stars

    Science.gov (United States)

    Anantasook, Sakanan; Yuenyong, Chokchai

    2018-01-01

    The paper examined Thai student existing understanding about the solar system model and the motion of the stars. The participants included 141 Grade 9 students in four different schools of the Surin province, Thailand. Methodology regarded interpretive paradigm. The tool of interpretation included the Student Celestial Motion Conception Questionnaire (SCMCQ) and informal interview. Given understandings in the SCMCQ were read through and categorized according to students' understandings. Then, students were further probed as informal interview. Students' understandings in each category were counted and percentages computed. Finally, students' understandings across four different schools were compared and contrasted using the percentage of student responses in each category. The findings revealed that most students understand about Sun-Moon-Earth (SME) system and solar system model as well, they can use scientific explanations to explain the celestial objects in solar system and how they orbiting. Unfortunately, most of students (more than 70%) never know about the Polaris, the North Star, and 90.1% of them never know about the ecliptic, and probably also the 12 zodiac constellations. These existing understanding suggested some ideas of teaching and learning about solar system model and the motion of the stars. The paper, then, discussed some learning activities to enhance students to further construct meaning about solar system model and the motion of the stars.

  2. 78 FR 29131 - Solar Star California XX, LLC; Supplemental Notice that Initial Market-Based Rate Filing Includes...

    Science.gov (United States)

    2013-05-17

    ... DEPARTMENT OF ENERGY Federal Energy Regulatory Commission [Docket No. ER13-1442-000] Solar Star California XX, LLC; Supplemental Notice that Initial Market-Based Rate Filing Includes Request for Blanket Section 204 Authorization This is a supplemental notice in the above-referenced proceeding, of Solar Star...

  3. Sounds of a Star

    Science.gov (United States)

    2001-06-01

    Acoustic Oscillations in Solar-Twin "Alpha Cen A" Observed from La Silla by Swiss Team Summary Sound waves running through a star can help astronomers reveal its inner properties. This particular branch of modern astrophysics is known as "asteroseismology" . In the case of our Sun, the brightest star in the sky, such waves have been observed since some time, and have greatly improved our knowledge about what is going on inside. However, because they are much fainter, it has turned out to be very difficult to detect similar waves in other stars. Nevertheless, tiny oscillations in a solar-twin star have now been unambiguously detected by Swiss astronomers François Bouchy and Fabien Carrier from the Geneva Observatory, using the CORALIE spectrometer on the Swiss 1.2-m Leonard Euler telescope at the ESO La Silla Observatory. This telescope is mostly used for discovering exoplanets (see ESO PR 07/01 ). The star Alpha Centauri A is the nearest star visible to the naked eye, at a distance of a little more than 4 light-years. The new measurements show that it pulsates with a 7-minute cycle, very similar to what is observed in the Sun . Asteroseismology for Sun-like stars is likely to become an important probe of stellar theory in the near future. The state-of-the-art HARPS spectrograph , to be mounted on the ESO 3.6-m telescope at La Silla, will be able to search for oscillations in stars that are 100 times fainter than those for which such demanding observations are possible with CORALIE. PR Photo 23a/01 : Oscillations in a solar-like star (schematic picture). PR Photo 23b/01 : Acoustic spectrum of Alpha Centauri A , as observed with CORALIE. Asteroseismology: listening to the stars ESO PR Photo 23a/01 ESO PR Photo 23a/01 [Preview - JPEG: 357 x 400 pix - 96k] [Normal - JPEG: 713 x 800 pix - 256k] [HiRes - JPEG: 2673 x 3000 pix - 2.1Mb Caption : PR Photo 23a/01 is a graphical representation of resonating acoustic waves in the interior of a solar-like star. Red and blue

  4. 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.

  5. X-ray emission from open star clusters with Spectrum-Rontgen-Gamma

    DEFF Research Database (Denmark)

    Singh, K.P.; Ojha, D.K.; Schnopper, H.W.

    1998-01-01

    The study of X-ray emission from co-evolving populations of stars in open dusters is extremely important for understanding the dynamo activity among the stars. With this objective, we propose to observe a number of open clusters in the X-ray and UV bands using SPECTRUM-Rontgen-Gamma. The high...... throughput of SPECTRUM-Rontgen-Gamma will help detect main sequence stars like Sun in middle-aged and old clusters. We will study the relationships between various parameters - age, rotation, abundance, UBV colors, X-ray luminosity, coronal temperature etc. X-ray spectra of younger and brighter populations...

  6. Multiple star formation : chemistry, physics and coevality

    NARCIS (Netherlands)

    Murillo, Mejias N.M.

    2017-01-01

    Multiple stars, that is two or more stars composing a gravitationally bound system, are common in the universe.They are the cause of many interesting phenomena, from supernovae and planetary nebulae, to binary black hole mergers. Observations of main sequence stars, young stars and forming

  7. DEBRIS DISKS AROUND SOLAR-TYPE STARS: OBSERVATIONS OF THE PLEIADES WITH THE SPITZER SPACE TELESCOPE

    International Nuclear Information System (INIS)

    Sierchio, J. M.; Rieke, G. H.; Su, K. Y. L.; Plavchan, P.; Stauffer, J. R.; Gorlova, N. I.

    2010-01-01

    We present Spitzer MIPS observations at 24 μm of 37 solar-type stars in the Pleiades and combine them with previous observations to obtain a sample of 71 stars. We report that 23 stars, or 32% ± 6.8%, have excesses at 24 μm at least 10% above their photospheric emission. We compare our results with studies of debris disks in other open clusters and with a study of A stars to show that debris disks around solar-type stars at 115 Myr occur at nearly the same rate as around A-type stars. We analyze the effects of binarity and X-ray activity on the excess flux. Stars with warm excesses tend not to be in equal-mass binary systems, possibly due to clearing of planetesimals by binary companions in similar orbits. We find that the apparent anti-correlations in the incidence of excess and both the rate of stellar rotation and also the level of activity as judged by X-ray emission are statistically weak.

  8. Stellar evolution IV: evolution of a star of 1.5 M(S) from the main-sequence to the red-giant branch with and without overshooting from convective core

    International Nuclear Information System (INIS)

    Maeder, A.

    1975-01-01

    For a star of 1.5 M(S) with an initial composition given by X=0.70 and Z=0.03, three sets of evolutionary models are computed with different assumptions on the non-local effects characterizing the turbulent motions in the convective core. Some overshooting from the convective core may occur during Main-sequence evolution. The changes in the stellar structure, lifetimes and evolutionary tracks brought about by this process are studied. Some characteristics of the evolutionary tracks in the theoretical HR diagram have a very high sensitivity to the exact extent of the convective core, and this may provide powerful tests of events occurring in the deep stellar interior. (orig./BJ) [de

  9. A new interferometric study of four exoplanet host stars: θ Cygni, 14 Andromedae, υ Andromedae and 42 Draconis

    Science.gov (United States)

    Ligi, R.; Mourard, D.; Lagrange, A. M.; Perraut, K.; Boyajian, T.; Bério, Ph.; Nardetto, N.; Tallon-Bosc, I.; McAlister, H.; ten Brummelaar, T.; Ridgway, S.; Sturmann, J.; Sturmann, L.; Turner, N.; Farrington, C.; Goldfinger, P. J.

    2012-09-01

    Context. Since the discovery of the first exoplanet in 1995 around a solar-type star, the interest in exoplanetary systems has kept increasing. Studying exoplanet host stars is of the utmost importance to establish the link between the presence of exoplanets around various types of stars and to understand the respective evolution of stars and exoplanets. Aims: Using the limb-darkened diameter (LDD) obtained from interferometric data, we determine the fundamental parameters of four exoplanet host stars. We are particularly interested in the F4 main-sequence star, θ Cyg, for which Kepler has recently revealed solar-like oscillations that are unexpected for this type of star. Furthermore, recent photometric and spectroscopic measurements with SOPHIE and ELODIE (OHP) show evidence of a quasi-periodic radial velocity of ~150 days. Models of this periodic change in radial velocity predict either a complex planetary system orbiting the star, or a new and unidentified stellar pulsation mode. Methods: We performed interferometric observations of θ Cyg, 14 Andromedae, υ Andromedae and 42 Draconis for two years with VEGA/CHARA (Mount Wilson, California) in several three-telescope configurations. We measured accurate limb darkened diameters and derived their radius, mass and temperature using empirical laws. Results: We obtain new accurate fundamental parameters for stars 14 And, υ And and 42 Dra. We also obtained limb darkened diameters with a minimum precision of ~1.3%, leading to minimum planet masses of Msini = 5.33 ± 0.57, 0.62 ± 0.09 and 3.79 ± 0.29 MJup for 14 And b, υ And b and 42 Dra b, respectively. The interferometric measurements of θ Cyg show a significant diameter variability that remains unexplained up to now. We propose that the presence of these discrepancies in the interferometric data is caused either by an intrinsic variation of the star or an unknown close companion orbiting around it. Based on interferometric observations with the VEGA

  10. VERY LOW MASS STELLAR AND SUBSTELLAR COMPANIONS TO SOLAR-LIKE STARS FROM MARVELS. IV. A CANDIDATE BROWN DWARF OR LOW-MASS STELLAR COMPANION TO HIP 67526

    Energy Technology Data Exchange (ETDEWEB)

    Jiang Peng; Ge Jian; De Lee, Nathan; Fleming, Scott W.; Lee, Brian L.; Ma Bo; Wang, Ji [Astronomy Department, University of Florida, 211 Bryant Space Science Center, P.O. Box 112055, Gainesville, FL 32611 (United States); Cargile, Phillip; Hebb, Leslie; Stassun, Keivan G. [Department of Physics and Astronomy, Vanderbilt University, Nashville, TN 37235 (United States); Crepp, Justin R. [Department of Physics, University of Notre Dame, 225 Nieuwland Science Hall, Notre Dame, IN 46556 (United States); Porto de Mello, Gustavo F.; Ferreira, Leticia D. [Observatorio do Valongo, Universidade Federal do Rio de Janeiro, Ladeira do Pedro Antonio, 43, CEP: 20080-090, Rio de Janeiro, RJ (Brazil); Esposito, Massimiliano; Femenia, Bruno; Gonzalez Hernandez, Jonay I. [Instituto de Astrofisica de Canarias, C/Via Lactea S/N, E-38200 La Laguna (Spain); Gaudi, B. Scott [Department of Astronomy, The Ohio State University, 140 West 18th Avenue, Columbus, OH 43210 (United States); Ghezzi, Luan [Laboratorio Interinstitucional de e-Astronomia (LIneA), Rio de Janeiro, RJ 20921-400 (Brazil); Wisniewski, John P. [Homer L. Dodge Department of Physics and Astronomy, University of Oklahoma, 440 West Brooks Street, Norman, OK 73019 (United States); Agol, Eric, E-mail: jpaty@mail.ustc.edu.cn [Department of Astronomy, University of Washington, Box 351580, Seattle, WA 98195-1580 (United States); and others

    2013-09-15

    We report the discovery of a candidate brown dwarf (BD) or a very low mass stellar companion (MARVELS-5b) to the star HIP 67526 from the Multi-object Apache point observatory Radial Velocity Exoplanet Large-area Survey (MARVELS). The radial velocity curve for this object contains 31 epochs spread over 2.5 yr. Our Keplerian fit, using a Markov Chain Monte Carlo approach, reveals that the companion has an orbital period of 90.2695{sup +0.0188}{sub -0.0187} days, an eccentricity of 0.4375 {+-} 0.0040, and a semi-amplitude of 2948.14{sup +16.65}{sub -16.55} m s{sup -1}. Using additional high-resolution spectroscopy, we find the host star has an effective temperature T{sub eff} = 6004 {+-} 34 K, a surface gravity log g (cgs) =4.55 {+-} 0.17, and a metallicity [Fe/H] =+0.04 {+-} 0.06. The stellar mass and radius determined through the empirical relationship of Torres et al. yields 1.10 {+-} 0.09 M{sub Sun} and 0.92 {+-} 0.19 R{sub Sun }. The minimum mass of MARVELS-5b is 65.0 {+-} 2.9M{sub Jup}, indicating that it is likely to be either a BD or a very low mass star, thus occupying a relatively sparsely populated region of the mass function of companions to solar-type stars. The distance to this system is 101 {+-} 10 pc from the astrometric measurements of Hipparcos. No stellar tertiary is detected in the high-contrast images taken by either FastCam lucky imaging or Keck adaptive optics imaging, ruling out any star with mass greater than 0.2 M{sub Sun} at a separation larger than 40 AU.

  11. Photometric search for variable stars in the young open cluster Berkeley 59

    Science.gov (United States)

    Lata, Sneh; Pandey, A. K.; Maheswar, G.; Mondal, Soumen; Kumar, Brijesh

    2011-12-01

    We present the time series photometry of stars located in the extremely young open cluster Berkeley 59. Using the 1.04-m telescope at Aryabhatta Research Institute of Observational Sciences (ARIES), Nainital, we have identified 42 variables in a field of ˜13 × 13 arcmin2 around the cluster. The probable members of the cluster have been identified using a (V, V-I) colour-magnitude diagram and a (J-H, H-K) colour-colour diagram. 31 variables have been found to be pre-main-sequence stars associated with the cluster. The ages and masses of the pre-main-sequence stars have been derived from the colour-magnitude diagram by fitting theoretical models to the observed data points. The ages of the majority of the probable pre-main-sequence variable candidates range from 1 to 5 Myr. The masses of these pre-main-sequence variable stars have been found to be in the range of ˜0.3 to ˜3.5 M⊙, and these could be T Tauri stars. The present statistics reveal that about 90 per cent T Tauri stars have period dispersal of the discs of relatively massive stars.

  12. MMT hypervelocity star survey. III. The complete survey

    Energy Technology Data Exchange (ETDEWEB)

    Brown, Warren R.; Geller, Margaret J.; Kenyon, Scott J., E-mail: wbrown@cfa.harvard.edu, E-mail: mgeller@cfa.harvard.edu, E-mail: skenyon@cfa.harvard.edu [Smithsonian Astrophysical Observatory, 60 Garden Street, Cambridge, MA 02138 (United States)

    2014-05-20

    We describe our completed spectroscopic survey for unbound hypervelocity stars (HVSs) ejected from the Milky Way. Three new discoveries bring the total number of unbound late B-type stars to 21. We place new constraints on the nature of the stars and on their distances using moderate resolution MMT spectroscopy. Half of the stars are fast rotators; they are certain 2.5-4 M {sub ☉} main sequence stars at 50-120 kpc distances. Correcting for stellar lifetime, our survey implies that unbound 2.5-4 M {sub ☉} stars are ejected from the Milky Way at a rate of 1.5 × 10{sup –6} yr{sup –1}. These unbound HVSs are likely ejected continuously over the past 200 Myr and do not share a common flight time. The anisotropic spatial distribution of HVSs on the sky remains puzzling. Southern hemisphere surveys like SkyMapper will soon allow us to map the all-sky distribution of HVSs. Future proper motion measurements with Hubble Space Telescope and Gaia will provide strong constraints on origin. Existing observations are all consistent with HVS ejections from encounters with the massive black hole in the Galactic center.

  13. MMT hypervelocity star survey. III. The complete survey

    International Nuclear Information System (INIS)

    Brown, Warren R.; Geller, Margaret J.; Kenyon, Scott J.

    2014-01-01

    We describe our completed spectroscopic survey for unbound hypervelocity stars (HVSs) ejected from the Milky Way. Three new discoveries bring the total number of unbound late B-type stars to 21. We place new constraints on the nature of the stars and on their distances using moderate resolution MMT spectroscopy. Half of the stars are fast rotators; they are certain 2.5-4 M ☉ main sequence stars at 50-120 kpc distances. Correcting for stellar lifetime, our survey implies that unbound 2.5-4 M ☉ stars are ejected from the Milky Way at a rate of 1.5 × 10 –6 yr –1 . These unbound HVSs are likely ejected continuously over the past 200 Myr and do not share a common flight time. The anisotropic spatial distribution of HVSs on the sky remains puzzling. Southern hemisphere surveys like SkyMapper will soon allow us to map the all-sky distribution of HVSs. Future proper motion measurements with Hubble Space Telescope and Gaia will provide strong constraints on origin. Existing observations are all consistent with HVS ejections from encounters with the massive black hole in the Galactic center.

  14. Chemical signatures of planets: beyond solar-twins

    Science.gov (United States)

    Ramírez, I.; Meléndez, J.; Asplund, M.

    2014-01-01

    Context. Elemental abundance studies of solar twin stars suggest that the solar chemical composition contains signatures of the formation of terrestrial planets in the solar system, namely small but significant depletions of the refractory elements. Aims: To test whether these chemical signatures of planets are real, we study stars which, compared to solar twins, have less massive convective envelopes (therefore increasing the amplitude of the predicted effect) or are, arguably, more likely to host planets (thus increasing the frequency of signature detections). Methods: We measure relative atmospheric parameters and elemental abundances of two groups of stars: a "warm" late-F type dwarf sample (52 stars), and a sample of "metal-rich" solar analogs (59 stars). The strict differential approach that we adopt allows us to determine with high precision (errors ~0.01 dex) the degree of refractory element depletion in our stars independently of Galactic chemical evolution. By examining relative abundance ratio versus condensation temperature plots we are able to identify stars with "pristine" composition in each sample and to determine the degree of refractory-element depletion for the rest of our stars. We calculate what mixture of Earth-like and meteorite-like material corresponds to these depletions. Results: We detect refractory-element depletions with amplitudes up to about 0.15 dex. The distribution of depletion amplitudes for stars known to host gas giant planets is not different from that of the rest of stars. The maximum amplitude of depletion increases with effective temperature from 5650 K to 5950 K, while it appears to be constant for warmer stars (up to 6300 K). The depletions observed in solar twin stars have a maximum amplitude that is very similar to that seen here for both of our samples. Conclusions: Gas giant planet formation alone cannot explain the observed distributions of refractory-element depletions, leaving the formation of rocky material as a

  15. Black Hole Growth Is Mainly Linked to Host-galaxy Stellar Mass Rather Than Star Formation Rate

    Science.gov (United States)

    Yang, G.; Chen, C.-T. J.; Vito, F.; Brandt, W. N.; Alexander, D. M.; Luo, B.; Sun, M. Y.; Xue, Y. Q.; Bauer, F. E.; Koekemoer, A. M.; Lehmer, B. D.; Liu, T.; Schneider, D. P.; Shemmer, O.; Trump, J. R.; Vignali, C.; Wang, J.-X.

    2017-06-01

    We investigate the dependence of black hole accretion rate (BHAR) on host-galaxy star formation rate (SFR) and stellar mass (M *) in the CANDELS/GOODS-South field in the redshift range of 0.5≤slant zteam through spectral energy distribution fitting. The average BHAR is correlated positively with both SFR and M *, and the BHAR-SFR and BHAR-M * relations can both be described acceptably by linear models with a slope of unity. However, BHAR appears to be correlated more strongly with M * than SFR. This result indicates that M * is the primary host-galaxy property related to supermassive black hole (SMBH) growth, and the apparent BHAR-SFR relation is largely a secondary effect due to the star-forming main sequence. Among our sources, massive galaxies ({M}* ≳ {10}10{M}⊙ ) have significantly higher BHAR/SFR ratios than less massive galaxies, indicating that the former have higher SMBH fueling efficiency and/or higher SMBH occupation fraction than the latter. Our results can naturally explain the observed proportionality between {M}{BH} and M * for local giant ellipticals and suggest that their {M}{BH}/{M}* is higher than that of local star-forming galaxies. Among local star-forming galaxies, massive systems might have higher {M}{BH}/{M}* compared to dwarfs.

  16. The convective noise floor for the spectroscopic detection of low mass companions to solar type stars

    Science.gov (United States)

    Deming, D.; Espenak, F.; Jennings, D. E.; Brault, J. W.

    1986-01-01

    The threshold mass for the unambiguous spectroscopic detection of low mass companions to solar type stars is defined here as the time when the maximum acceleration in the stellar radial velocity due to the Doppler reflex of the companion exceeds the apparent acceleration produced by changes in convection. An apparent acceleration of 11 m/s/yr in integrated sunlight was measured using near infrared Fourier transform spectroscopy. This drift in the apparent solar velocity is attributed to a lessening in the magnetic inhibition of granular convection as solar minimum approaches. The threshold mass for spectroscopic detection of companions to a one solar mass star is estimated at below one Jupiter mass.

  17. Magnetic fields driven by tidal mixing in radiative stars

    Science.gov (United States)

    Vidal, Jérémie; Cébron, David; Schaeffer, Nathanaël; Hollerbach, Rainer

    2018-04-01

    Stellar magnetism plays an important role in stellar evolution theory. Approximatively 10 per cent of observed main sequence (MS) and pre-main-sequence (PMS) radiative stars exhibit surface magnetic fields above the detection limit, raising the question of their origin. These stars host outer radiative envelopes, which are stably stratified. Therefore, they are assumed to be motionless in standard models of stellar structure and evolution. We focus on rapidly rotating, radiative stars which may be prone to the tidal instability, due to an orbital companion. Using direct numerical simulations in a sphere, we study the interplay between a stable stratification and the tidal instability, and assess its dynamo capability. We show that the tidal instability is triggered regardless of the strength of the stratification (Brunt-Väisälä frequency). Furthermore, the tidal instability can lead to both mixing and self-induced magnetic fields in stably stratified layers (provided that the Brunt-Väisälä frequency does not exceed the stellar spin rate in the simulations too much). The application to stars suggests that the resulting magnetic fields could be observable at the stellar surfaces. Indeed, we expect magnetic field strengths up to several Gauss. Consequently, tidally driven dynamos should be considered as a (complementary) dynamo mechanism, possibly operating in radiative MS and PMS stars hosting orbital companions. In particular, tidally driven dynamos may explain the observed magnetism of tidally deformed and rapidly rotating Vega-like stars.

  18. ON THE CARBON-TO-OXYGEN RATIO MEASUREMENT IN NEARBY SUN-LIKE STARS: IMPLICATIONS FOR PLANET FORMATION AND THE DETERMINATION OF STELLAR ABUNDANCES

    International Nuclear Information System (INIS)

    Fortney, Jonathan J.

    2012-01-01

    Recent high-resolution spectroscopic analysis of nearby FGK stars suggests that a high C/O ratio of greater than 0.8, or even 1.0, is relatively common. Two published catalogs find C/O > 0.8 in 25%-30% of systems, and C/O > 1.0 in ∼6%-10%. It has been suggested that in protoplanetary disks with C/O > 0.8 that the condensation pathways to refractory solids will differ from what occurred in our solar system, where C/O = 0.55. The carbon-rich disks are calculated to make carbon-dominated rocky planets, rather than oxygen-dominated ones. Here we suggest that the derived stellar C/O ratios are overestimated. One constraint on the frequency of high C/O is the relative paucity of carbon dwarf stars (10 –3 -10 –5 ) found in large samples of low-mass stars. We suggest reasons for this overestimation, including a high C/O ratio for the solar atmosphere model used for differential abundance analysis, the treatment of a Ni blend that affects the O abundance, and limitations of one-dimensional LTE stellar atmosphere models. Furthermore, from the estimated errors on the measured stellar C/O ratios, we find that the significance of the high C/O tail is weakened, with a true measured fraction of C/O > 0.8 in 10%-15% of stars, and C/O > 1.0 in 1%-5%, although these are still likely overestimates. We suggest that infrared T-dwarf spectra could show how common high C/O is in the stellar neighborhood, as the chemistry and spectra of such objects would differ compared to those with solar-like abundances. While possible at C/O > 0.8, we expect that carbon-dominated rocky planets are rarer than others have suggested.

  19. Flaring red dwarf stars: news from Crimea

    International Nuclear Information System (INIS)

    Gershberg, Roald E

    1998-01-01

    Important phenomena are briefly described which have recently been discovered in the Crimean studies of flaring red dwarf stars believed to be the most common type of variable stars in the Galaxy. These phenomena include (i) long-lived radiation from a blueshifted component in the ionized-helium λ 4686 A emission line in the active state of one such star, (ii) a long-lived absorption component in the stellar flare light curves with a lifetime exceeding that of the conventional flare emission, and (iii) solarcycle-like activity periodicity of the star EV Lac, whose mass is only 0.3 solar masses. In theoretical terms, a red dwarf star spot model is constructed which, in contrast to the commonly accepted model, agrees well with the solar spot picture. (physics of our days)

  20. Flaring red dwarf stars: news from Crimea

    Energy Technology Data Exchange (ETDEWEB)

    Gershberg, Roald E [Crimean Astrophysical Observatory, Nauchnyi, Crimea (Ukraine)

    1998-08-31

    Important phenomena are briefly described which have recently been discovered in the Crimean studies of flaring red dwarf stars believed to be the most common type of variable stars in the Galaxy. These phenomena include (i) long-lived radiation from a blueshifted component in the ionized-helium {lambda} 4686 A emission line in the active state of one such star, (ii) a long-lived absorption component in the stellar flare light curves with a lifetime exceeding that of the conventional flare emission, and (iii) solarcycle-like activity periodicity of the star EV Lac, whose mass is only 0.3 solar masses. In theoretical terms, a red dwarf star spot model is constructed which, in contrast to the commonly accepted model, agrees well with the solar spot picture. (physics of our days)

  1. The Physical Nature of Subdwarf A Stars: White Dwarf Impostors

    Science.gov (United States)

    Brown, Warren R.; Kilic, Mukremin; Gianninas, A.

    2017-04-01

    We address the physical nature of subdwarf A-type (sdA) stars and their possible link to extremely low mass (ELM) white dwarfs (WDs). The two classes of objects are confused in low-resolution spectroscopy. However, colors and proper motions indicate that sdA stars are cooler and more luminous, and thus larger in radius, than published ELM WDs. We demonstrate that surface gravities derived from pure hydrogen models suffer a systematic ˜1 dex error for sdA stars, likely explained by metal line blanketing below 9000 K. A detailed study of five eclipsing binaries with radial velocity orbital solutions and infrared excess establishes that these sdA stars are metal-poor ≃1.2 M ⊙ main sequence stars with ≃0.8 M ⊙ companions. While WDs must exist at sdA temperatures, only ˜1% of a magnitude-limited sdA sample should be ELM WDs. We conclude that the majority of sdA stars are metal-poor A-F type stars in the halo, and that recently discovered pulsating ELM WD-like stars with no obvious radial velocity variations may be SX Phe variables, not pulsating WDs.

  2. The Physical Nature of Subdwarf A Stars: White Dwarf Impostors

    International Nuclear Information System (INIS)

    Brown, Warren R.; Kilic, Mukremin; Gianninas, A.

    2017-01-01

    We address the physical nature of subdwarf A-type (sdA) stars and their possible link to extremely low mass (ELM) white dwarfs (WDs). The two classes of objects are confused in low-resolution spectroscopy. However, colors and proper motions indicate that sdA stars are cooler and more luminous, and thus larger in radius, than published ELM WDs. We demonstrate that surface gravities derived from pure hydrogen models suffer a systematic ∼1 dex error for sdA stars, likely explained by metal line blanketing below 9000 K. A detailed study of five eclipsing binaries with radial velocity orbital solutions and infrared excess establishes that these sdA stars are metal-poor ≃1.2 M ⊙ main sequence stars with ≃0.8 M ⊙ companions. While WDs must exist at sdA temperatures, only ∼1% of a magnitude-limited sdA sample should be ELM WDs. We conclude that the majority of sdA stars are metal-poor A–F type stars in the halo, and that recently discovered pulsating ELM WD-like stars with no obvious radial velocity variations may be SX Phe variables, not pulsating WDs.

  3. The Physical Nature of Subdwarf A Stars: White Dwarf Impostors

    Energy Technology Data Exchange (ETDEWEB)

    Brown, Warren R. [Smithsonian Astrophysical Observatory, 60 Garden Street, Cambridge, MA 02138 (United States); Kilic, Mukremin; Gianninas, A., E-mail: wbrown@cfa.harvard.edu, E-mail: kilic@ou.edu, E-mail: alexg@nhn.ou.edu [Homer L. Dodge Department of Physics and Astronomy, University of Oklahoma, 440 W. Brooks Street, Norman, OK, 73019 (United States)

    2017-04-10

    We address the physical nature of subdwarf A-type (sdA) stars and their possible link to extremely low mass (ELM) white dwarfs (WDs). The two classes of objects are confused in low-resolution spectroscopy. However, colors and proper motions indicate that sdA stars are cooler and more luminous, and thus larger in radius, than published ELM WDs. We demonstrate that surface gravities derived from pure hydrogen models suffer a systematic ∼1 dex error for sdA stars, likely explained by metal line blanketing below 9000 K. A detailed study of five eclipsing binaries with radial velocity orbital solutions and infrared excess establishes that these sdA stars are metal-poor ≃1.2 M {sub ⊙} main sequence stars with ≃0.8 M {sub ⊙} companions. While WDs must exist at sdA temperatures, only ∼1% of a magnitude-limited sdA sample should be ELM WDs. We conclude that the majority of sdA stars are metal-poor A–F type stars in the halo, and that recently discovered pulsating ELM WD-like stars with no obvious radial velocity variations may be SX Phe variables, not pulsating WDs.

  4. Physics of star formation in galaxies

    CERN Document Server

    Palla, F

    2002-01-01

    Begining with a historical introduction, ""Star Formation: The Early History"", this text then presents two long articles on ""Pre-Main-Sequence Evolution of Stars and Young Clusters"" and ""Observations of Young Stellar Objects"".

  5. Evidence for feedback and stellar-dynamically regulated bursty star cluster formation: the case of the Orion Nebula Cluster

    Science.gov (United States)

    Kroupa, Pavel; Jeřábková, Tereza; Dinnbier, František; Beccari, Giacomo; Yan, Zhiqiang

    2018-04-01

    A scenario for the formation of multiple co-eval populations separated in age by about 1 Myr in very young clusters (VYCs, ages less than 10 Myr) and with masses in the range 600-20 000 M⊙ is outlined. It rests upon a converging inflow of molecular gas building up a first population of pre-main sequence stars. The associated just-formed O stars ionise the inflow and suppress star formation in the embedded cluster. However, they typically eject each other out of the embedded cluster within 106 yr, that is before the molecular cloud filament can be ionised entirely. The inflow of molecular gas can then resume forming a second population. This sequence of events can be repeated maximally over the life-time of the molecular cloud (about 10 Myr), but is not likely to be possible in VYCs with mass <300 M⊙, because such populations are not likely to contain an O star. Stellar populations heavier than about 2000 M⊙ are likely to have too many O stars for all of these to eject each other from the embedded cluster before they disperse their natal cloud. VYCs with masses in the range 600-2000 M⊙ are likely to have such multi-age populations, while VYCs with masses in the range 2000-20 000 M⊙ can also be composed solely of co-eval, mono-age populations. More massive VYCs are not likely to host sub-populations with age differences of about 1 Myr. This model is applied to the Orion Nebula Cluster (ONC), in which three well-separated pre-main sequences in the colour-magnitude diagram of the cluster have recently been discovered. The mass-inflow history is constrained using this model and the number of OB stars ejected from each population are estimated for verification using Gaia data. As a further consequence of the proposed model, the three runaway O star systems, AE Aur, μ Col and ι Ori, are considered as significant observational evidence for stellar-dynamical ejections of massive stars from the oldest population in the ONC. Evidence for stellar

  6. Transiting exoplanets from the CoRoT space mission. XXIII. CoRoT-21b: a doomed large Jupiter around a faint subgiant star

    DEFF Research Database (Denmark)

    Pätzold, M.; Endl, M.; Csizmadia, Sz.

    2012-01-01

    -up observations, however, were performed mainly by the 10-m Keck telescope in January 2010. The companion CoRoT-21b is a Jupiter-like planet of 2.26 ± 0.33 Jupiter masses and 1.30 ± 0.14 Jupiter radii in an circular orbit of semi-major axis 0.0417 ± 0.0011 AU and an orbital period of 2.72474 ± 0.00014 days....... The planetary bulk density is (1.36   ±   0.48) × 103 kg m-3, very similar to the bulk density of Jupiter, and follows an M1/3 − R relation like Jupiter. The F8IV star is a sub-giant star of 1.29 ± 0.09 solar masses and 1.95 ± 0.2 solar radii. The star and the planet exchange extremetidal forces that will lead...

  7. Astrochemical evolution along star formation: Overview of the IRAM Large Program ASAI

    Science.gov (United States)

    Lefloch, Bertrand; Bachiller, R.; Ceccarelli, C.; Cernicharo, J.; Codella, C.; Fuente, A.; Kahane, C.; López-Sepulcre, A.; Tafalla, M.; Vastel, C.; Caux, E.; González-García, M.; Bianchi, E.; Gómez-Ruiz, A.; Holdship, J.; Mendoza, E.; Ospina-Zamudio, J.; Podio, L.; Quénard, D.; Roueff, E.; Sakai, N.; Viti, S.; Yamamoto, S.; Yoshida, K.; Favre, C.; Monfredini, T.; Quitián-Lara, H. M.; Marcelino, N.; Roberty, H. Boechat; Cabrit, S.

    2018-04-01

    Evidence is mounting that the small bodies of our Solar System, such as comets and asteroids, have at least partially inherited their chemical composition from the first phases of the Solar System formation. It then appears that the molecular complexity of these small bodies is most likely related to the earliest stages of star formation. It is therefore important to characterize and to understand how the chemical evolution changes with solar-type protostellar evolution. We present here the Large Program "Astrochemical Surveys At IRAM" (ASAI). Its goal is to carry out unbiased millimeter line surveys between 80 and 272 GHz of a sample of ten template sources, which fully cover the first stages of the formation process of solar-type stars, from prestellar cores to the late protostellar phase. In this article, we present an overview of the surveys and results obtained from the analysis of the 3 mm band observations. The number of detected main isotopic species barely varies with the evolutionary stage and is found to be very similar to that of massive star-forming regions. The molecular content in O- and C- bearing species allows us to define two chemical classes of envelopes, whose composition is dominated by either a) a rich content in O-rich complex organic molecules, associated with hot corino sources, or b) a rich content in hydrocarbons, typical of Warm Carbon Chain Chemistry sources. Overall, a high chemical richness is found to be present already in the initial phases of solar-type star formation.

  8. A mysterious dust clump in a disk around an evolved binary star system.

    Science.gov (United States)

    Jura, M; Turner, J

    1998-09-10

    The discovery of planets in orbit around the pulsar PSR1257+12 shows that planets may form around post-main-sequence stars. Other evolved stars, such as HD44179 (an evolved star which is part of the binary system that has expelled the gas and dust that make the Red Rectangle nebula), possess gravitationally bound orbiting dust disks. It is possible that planets might form from gravitational collapse in such disks. Here we report high-angular-resolution observations at millimetre and submillimetre wavelengths of the dusk disk associated with the Red Rectangle. We find a dust clump with an estimated mass near that of Jupiter in the outer region of the disk. The clump is larger than our Solar System, and far beyond where planet formation would normally be expected, so its nature is at present unclear.

  9. HD 89345: a bright oscillating star hosting a transiting warm Saturn-sized planet observed by K2

    Science.gov (United States)

    Van Eylen, V.; Dai, F.; Mathur, S.; Gandolfi, D.; Albrecht, S.; Fridlund, M.; García, R. A.; Guenther, E.; Hjorth, M.; Justesen, A. B.; Livingston, J.; Lund, M. N.; Pérez Hernández, F.; Prieto-Arranz, J.; Regulo, C.; Bugnet, L.; Everett, M. E.; Hirano, T.; Nespral, D.; Nowak, G.; Palle, E.; Silva Aguirre, V.; Trifonov, T.; Winn, J. N.; Barragán, O.; Beck, P. G.; Chaplin, W. J.; Cochran, W. D.; Csizmadia, S.; Deeg, H.; Endl, M.; Heeren, P.; Grziwa, S.; Hatzes, A. P.; Hidalgo, D.; Korth, J.; Mathis, S.; Montañes Rodriguez, P.; Narita, N.; Patzold, M.; Persson, C. M.; Rodler, F.; Smith, A. M. S.

    2018-05-01

    We report the discovery and characterization of HD 89345b (K2-234b; EPIC 248777106b), a Saturn-sized planet orbiting a slightly evolved star. HD 89345 is a bright star (V = 9.3 mag) observed by the K2 mission with one-minute time sampling. It exhibits solar-like oscillations. We conducted asteroseismology to determine the parameters of the star, finding the mass and radius to be 1.12^{+0.04}_{-0.01} M_⊙ and 1.657^{+0.020}_{-0.004} R_⊙, respectively. The star appears to have recently left the main sequence, based on the inferred age, 9.4^{+0.4}_{-1.3} Gyr, and the non-detection of mixed modes. The star hosts a "warm Saturn" (P = 11.8 days, Rp = 6.86 ± 0.14 R⊕). Radial-velocity follow-up observations performed with the FIES, HARPS, and HARPS-N spectrographs show that the planet has a mass of 35.7 ± 3.3 M⊕. The data also show that the planet's orbit is eccentric (e ≈ 0.2). An investigation of the rotational splitting of the oscillation frequencies of the star yields no conclusive evidence on the stellar inclination angle. We further obtained Rossiter-McLaughlin observations, which result in a broad posterior of the stellar obliquity. The planet seems to conform to the same patterns that have been observed for other sub-Saturns regarding planet mass and multiplicity, orbital eccentricity, and stellar metallicity.

  10. ON USING THE COLOR-MAGNITUDE DIAGRAM MORPHOLOGY OF M67 TO TEST SOLAR ABUNDANCES

    International Nuclear Information System (INIS)

    Magic, Z.; Serenelli, A.; Weiss, A.; Chaboyer, B.

    2010-01-01

    The open cluster M67 has solar metallicity and an age of about 4 Gyr. The turnoff (TO) mass is close to the minimum mass for which solar metallicity stars develop a convective core during main sequence evolution as a result of the development of hydrogen burning through the CNO cycle. The morphology of the color-magnitude diagram (CMD) of M67 around the TO shows a clear hook-like feature, a direct sign that stars close to the TO have convective cores. VandenBerg et al. investigated the possibility of using the morphology of the M67 TO to put constraints on the solar metallicity, particularly CNO elements, for which solar abundances have been revised downward by more than 30% over the last few years. Here, we extend their work, filling the gaps in their analysis. To this aim, we compute isochrones appropriate for M67 using new (low metallicity) and old (high metallicity) solar abundances and study whether the characteristic TO in the CMD of M67 can be reproduced or not. We also study the importance of other constitutive physics on determining the presence of such a hook, particularly element diffusion, overshooting and nuclear reaction rates. We find that using the new solar abundance determinations, with low CNO abundances, makes it more difficult to reproduce the characteristic CMD of M67. This result is in agreement with results by VandenBerg et al. However, changes in the constitutive physics of the models, particularly overshooting, can influence and alter this result to the extent that isochrones constructed with models using low CNO solar abundances can also reproduce the TO morphology in M67. We conclude that only if all factors affecting the TO morphology are completely under control (and this is not the case), M67 could be used to put constraints on solar abundances.

  11. MAGNETIC ACTIVITY CYCLES IN THE EXOPLANET HOST STAR {epsilon} ERIDANI

    Energy Technology Data Exchange (ETDEWEB)

    Metcalfe, T. S.; Mathur, S. [Space Science Institute, 4750 Walnut Street, Suite 205, Boulder, CO 80301 (United States); Buccino, A. P.; Mauas, P. J. D.; Petrucci, R. [Instituto de Astronomia y Fisica del Espacio (CONICET), C.C. 67 Sucursal 28, C1428EHA-Buenos Aires (Argentina); Brown, B. P. [Department of Astronomy and Center for Magnetic Self-Organization, University of Wisconsin, Madison, WI 53706-1582 (United States); Soderblom, D. R. [Space Telescope Science Institute, 3700 San Martin Dr., Baltimore, MD 21218 (United States); Henry, T. J. [Department of Physics and Astronomy, Georgia State University, Atlanta, GA 30302 (United States); Hall, J. C. [Lowell Observatory, 1400 West Mars Hill Road, Flagstaff, AZ 86001 (United States); Basu, S. [Department of Astronomy, Yale University, P.O. Box 208101, New Haven, CT 06520 (United States)

    2013-02-01

    The active K2 dwarf {epsilon} Eri has been extensively characterized both as a young solar analog and more recently as an exoplanet host star. As one of the nearest and brightest stars in the sky, it provides an unparalleled opportunity to constrain stellar dynamo theory beyond the Sun. We confirm and document the 3-year magnetic activity cycle in {epsilon} Eri originally reported by Hatzes and coworkers, and we examine the archival data from previous observations spanning 45 years. The data show coexisting 3-year and 13-year periods leading into a broad activity minimum that resembles a Maunder minimum-like state, followed by the resurgence of a coherent 3-year cycle. The nearly continuous activity record suggests the simultaneous operation of two stellar dynamos with cycle periods of 2.95 {+-} 0.03 years and 12.7 {+-} 0.3 years, which, by analogy with the solar case, suggests a revised identification of the dynamo mechanisms that are responsible for the so-called 'active' and 'inactive' sequences as proposed by Boehm-Vitense. Finally, based on the observed properties of {epsilon} Eri, we argue that the rotational history of the Sun is what makes it an outlier in the context of magnetic cycles observed in other stars (as also suggested by its Li depletion), and that a Jovian-mass companion cannot be the universal explanation for the solar peculiarities.

  12. Mass-loss Rates from Coronal Mass Ejections: A Predictive Theoretical Model for Solar-type Stars

    Energy Technology Data Exchange (ETDEWEB)

    Cranmer, Steven R. [Department of Astrophysical and Planetary Sciences, Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, CO 80309 (United States)

    2017-05-10

    Coronal mass ejections (CMEs) are eruptive events that cause a solar-type star to shed mass and magnetic flux. CMEs tend to occur together with flares, radio storms, and bursts of energetic particles. On the Sun, CME-related mass loss is roughly an order of magnitude less intense than that of the background solar wind. However, on other types of stars, CMEs have been proposed to carry away much more mass and energy than the time-steady wind. Earlier papers have used observed correlations between solar CMEs and flare energies, in combination with stellar flare observations, to estimate stellar CME rates. This paper sidesteps flares and attempts to calibrate a more fundamental correlation between surface-averaged magnetic fluxes and CME properties. For the Sun, there exists a power-law relationship between the magnetic filling factor and the CME kinetic energy flux, and it is generalized for use on other stars. An example prediction of the time evolution of wind/CME mass-loss rates for a solar-mass star is given. A key result is that for ages younger than about 1 Gyr (i.e., activity levels only slightly higher than the present-day Sun), the CME mass loss exceeds that of the time-steady wind. At younger ages, CMEs carry 10–100 times more mass than the wind, and such high rates may be powerful enough to dispel circumstellar disks and affect the habitability of nearby planets. The cumulative CME mass lost by the young Sun may have been as much as 1% of a solar mass.

  13. Luminosity and Intrinsic Color Calibration of Main-Sequence Stars With 2Mass Photometry: All Sky Local Extinction

    Directory of Open Access Journals (Sweden)

    Knude Jens

    2003-12-01

    Full Text Available We present a new color index vs. absolute magnitude calibration of 2MASS JHK photometry. For the A0 to ~G5 and M segments of the main sequence information on the amount of interstellar extinction and its location in space may be obtained.

  14. Kepler-423b: a half-Jupiter mass planet transiting a very old solar-like star

    Science.gov (United States)

    Gandolfi, D.; Parviainen, H.; Deeg, H. J.; Lanza, A. F.; Fridlund, M.; Prada Moroni, P. G.; Alonso, R.; Augusteijn, T.; Cabrera, J.; Evans, T.; Geier, S.; Hatzes, A. P.; Holczer, T.; Hoyer, S.; Kangas, T.; Mazeh, T.; Pagano, I.; Tal-Or, L.; Tingley, B.

    2015-04-01

    We report the spectroscopic confirmation of the Kepler object of interest KOI-183.01 (Kepler-423b), a half-Jupiter mass planet transiting an old solar-like star every 2.7 days. Our analysis is the first to combine the full Kepler photometry (quarters 1-17) with high-precision radial velocity measurements taken with the FIES spectrograph at the Nordic Optical Telescope. We simultaneously modelled the photometric and spectroscopic data-sets using Bayesian approach coupled with Markov chain Monte Carlo sampling. We found that the Kepler pre-search data conditioned light curve of Kepler-423 exhibits quarter-to-quarter systematic variations of the transit depth, with a peak-to-peak amplitude of ~4.3% and seasonal trends reoccurring every four quarters. We attributed these systematics to an incorrect assessment of the quarterly variation of the crowding metric. The host star Kepler-423 is a G4 dwarf with M⋆ = 0.85 ± 0.04 M⊙, R⋆ = 0.95 ± 0.04 R⊙, Teff= 5560 ± 80 K, [M/H] = - 0.10 ± 0.05 dex, and with an age of 11 ± 2 Gyr. The planet Kepler-423b has a mass of Mp= 0.595 ± 0.081MJup and a radius of Rp= 1.192 ± 0.052RJup, yielding a planetary bulk density of ρp = 0.459 ± 0.083 g cm-3. The radius of Kepler-423b is consistent with both theoretical models for irradiated coreless giant planets and expectations based on empirical laws. The inclination of the stellar spin axis suggests that the system is aligned along the line of sight. We detected a tentative secondary eclipse of the planet at a 2σ confidence level (ΔFec = 14.2 ± 6.6 ppm) and found that the orbit might have asmall non-zero eccentricity of 0.019+0.028-0.014. With a Bond albedo of AB = 0.037 ± 0.019, Kepler-423b is one of the gas-giant planets with the lowest albedo known so far. Based on observations obtained with the Nordic Optical Telescope, operated on the island of La Palma jointly by Denmark, Finland, Iceland, Norway, and Sweden, in the Spanish Observatorio del Roque de los Muchachos of

  15. Light-curve Modulation of Low-mass Stars in K2. I. Identification of 481 Fast Rotators in the Solar Neighborhood

    Science.gov (United States)

    Saylor, Dicy; Lepine, Sebastien; Crossfield, Ian; Petigura, Erik A.

    2018-01-01

    The K2 mission is targeting large numbers of nearby (d 40 mas yr‑1, V < 20). Additionally, the mission is targeting low-mass, high proper motion stars associated with the local (d < 500 pc) Galactic halo population also selected from SUPERBLINK. K2 campaigns 0 through 8 monitored a total of 26,518 of these cool main-sequence stars. We used the auto-correlation function to search for fast rotators by identifying short-period photometric modulations in the K2 light curves. We identified 481 candidate fast rotators with rotation periods <4 days that show light-curve modulations consistent with starspots. Their kinematics show low average transverse velocities, suggesting that they are part of the young disk population. A subset (13) of the fast rotators is found among those targets with colors and kinematics consistent with the local Galactic halo population and may represent stars spun up by tidal interactions in close binary systems. We further demonstrate that the M dwarf fast rotators selected from the K2 light curves are significantly more likely to have UV excess and discuss the potential of the K2 mission to identify new nearby young GKM dwarfs on the basis of their fast rotation rates. Finally, we discuss the possible use of local halo stars as fiducial, non-variable sources in the Kepler fields.

  16. A search for strong, ordered magnetic fields in Herbig Ae/Be stars

    Science.gov (United States)

    Wade, G. A.; Bagnulo, S.; Drouin, D.; Landstreet, J. D.; Monin, D.

    2007-04-01

    The origin of magnetic fields in intermediate- and high-mass stars is fundamentally a mystery. Clues towards solving this basic astrophysical problem can likely be found at the pre-main-sequence (PMS) evolutionary stage. With this work, we perform the largest and most sensitive search for magnetic fields in PMS Herbig Ae/Be (HAeBe) stars. We seek to determine whether strong, ordered magnetic fields, similar to those of main-sequence Ap/Bp stars, can be detected in these objects, and if so, to determine the intensities, geometrical characteristics, and statistical incidence of such fields. 68 observations of 50 HAeBe stars have been obtained in circularly polarized light using the FORS1 spectropolarimeter at the ESO VLT. An analysis of both Balmer and metallic lines reveals the possible presence of weak longitudinal magnetic fields in photospheric lines of two HAeBe stars, HD 101412 and BF Ori. Results for two additional stars, CPD-53 295 and HD 36112, are suggestive of the presence of magnetic fields, but no firm conclusions can be drawn based on the available data. The intensity of the longitudinal fields detected in HD 101412 and BF Ori suggest that they correspond to globally ordered magnetic fields with surface intensities of order 1 kG. On the other hand, no magnetic field is detected in 4 other HAeBe stars in our sample in which magnetic fields had previously been confirmed. Monte Carlo simulations of the longitudinal field measurements of the undetected stars allow us to place an upper limit of about 300 G on the general presence of aligned magnetic dipole magnetic fields, and of about 500 G on perpendicular dipole fields. Taking into account the results of our survey and other published results, we find that the observed bulk incidence of magnetic HAeBe stars in our sample is 8-12 per cent, in good agreement with that of magnetic main-sequence stars of similar masses. We also find that the rms longitudinal field intensity of magnetically detected HAe

  17. R CORONAE BOREALIS STARS ARE VIABLE FACTORIES OF PRE-SOLAR GRAINS

    International Nuclear Information System (INIS)

    Karakas, Amanda I.; Ruiter, Ashley J.; Hampel, Melanie

    2015-01-01

    We present a new theoretical estimate for the birthrate of R Coronae Borealis (RCB) stars that is in agreement with recent observational data. We find the current Galactic birthrate of RCB stars to be ≈25% of the Galactic rate of Type Ia supernovae, assuming that RCB stars are formed through the merger of carbon–oxygen and helium-rich white dwarfs. Our new RCB birthrate (1.8 × 10 −3 yr −1 ) is a factor of 10 lower than previous theoretical estimates. This results in roughly 180–540 RCB stars in the Galaxy, depending on the RCB lifetime. From the theoretical and observational estimates, we calculate the total dust production from RCB stars and compare this rate to dust production from novae and born-again asymptotic giant branch (AGB) stars. We find that the amount of dust produced by RCB stars is comparable to the amounts produced by novae or born-again post-AGB stars, indicating that these merger objects are a viable source of carbonaceous pre-solar grains in the Galaxy. There are graphite grains with carbon and oxygen isotopic ratios consistent with the observed composition of RCB stars, adding weight to the suggestion that these rare objects are a source of stardust grains

  18. On-Orbit Solar Dynamics Observatory (SDO) Star Tracker Warm Pixel Analysis

    Science.gov (United States)

    Felikson, Denis; Ekinci, Matthew; Hashmall, Joseph A.; Vess, Melissa

    2011-01-01

    This paper describes the process of identification and analysis of warm pixels in two autonomous star trackers on the Solar Dynamics Observatory (SDO) mission. A brief description of the mission orbit and attitude regimes is discussed and pertinent star tracker hardware specifications are given. Warm pixels are defined and the Quality Index parameter is introduced, which can be explained qualitatively as a manifestation of a possible warm pixel event. A description of the algorithm used to identify warm pixel candidates is given. Finally, analysis of dumps of on-orbit star tracker charge coupled devices (CCD) images is presented and an operational plan going forward is discussed. SDO, launched on February 11, 2010, is operated from the NASA Goddard Space Flight Center (GSFC). SDO is in a geosynchronous orbit with a 28.5 inclination. The nominal mission attitude points the spacecraft X-axis at the Sun, with the spacecraft Z-axis roughly aligned with the Solar North Pole. The spacecraft Y-axis completes the triad. In attitude, SDO moves approximately 0.04 per hour, mostly about the spacecraft Z-axis. The SDO star trackers, manufactured by Galileo Avionica, project the images of stars in their 16.4deg x 16.4deg fields-of-view onto CCD detectors consisting of 512 x 512 pixels. The trackers autonomously identify the star patterns and provide an attitude estimate. Each unit is able to track up to 9 stars. Additionally, each tracker calculates a parameter called the Quality Index, which is a measure of the quality of the attitude solution. Each pixel in the CCD measures the intensity of light and a warns pixel is defined as having a measurement consistently and significantly higher than the mean background intensity level. A warns pixel should also have lower intensity than a pixel containing a star image and will not move across the field of view as the attitude changes (as would a dim star image). It should be noted that the maximum error introduced in the star tracker

  19. The HOSTS Survey—Exozodiacal Dust Measurements for 30 Stars

    Science.gov (United States)

    Ertel, S.; Defrère, D.; Hinz, P.; Mennesson, B.; Kennedy, G. M.; Danchi, W. C.; Gelino, C.; Hill, J. M.; Hoffmann, W. F.; Rieke, G.; Shannon, A.; Spalding, E.; Stone, J. M.; Vaz, A.; Weinberger, A. J.; Willems, P.; Absil, O.; Arbo, P.; Bailey, V. P.; Beichman, C.; Bryden, G.; Downey, E. C.; Durney, O.; Esposito, S.; Gaspar, A.; Grenz, P.; Haniff, C. A.; Leisenring, J. M.; Marion, L.; McMahon, T. J.; Millan-Gabet, R.; Montoya, M.; Morzinski, K. M.; Pinna, E.; Power, J.; Puglisi, A.; Roberge, A.; Serabyn, E.; Skemer, A. J.; Stapelfeldt, K.; Su, K. Y. L.; Vaitheeswaran, V.; Wyatt, M. C.

    2018-05-01

    The Hunt for Observable Signatures of Terrestrial Systems survey searches for dust near the habitable zones (HZs) around nearby, bright main-sequence stars. We use nulling interferometry in the N band to suppress the bright stellar light and to probe for low levels of HZ dust around the 30 stars observed so far. Our overall detection rate is 18%, including four new detections, among which are the first three around Sun-like stars and the first two around stars without any previously known circumstellar dust. The inferred occurrence rates are comparable for early-type and Sun-like stars, but decrease from {60}-21+16% for stars with previously detected cold dust to {8}-3+10% for stars without such excess, confirming earlier results at higher sensitivity. For completed observations on individual stars, our sensitivity is five to ten times better than previous results. Assuming a lognormal excess luminosity function, we put upper limits on the median HZ dust level of 13 zodis (95% confidence) for a sample of stars without cold dust and of 26 zodis when focusing on Sun-like stars without cold dust. However, our data suggest that a more complex luminosity function may be more appropriate. For stars without detectable Large Binocular Telescope Interferometer (LBTI) excess, our upper limits are almost reduced by a factor of two, demonstrating the strength of LBTI target vetting for future exo-Earth imaging missions. Our statistics are limited so far, and extending the survey is critical to informing the design of future exo-Earth imaging surveys.

  20. Star-formation history of very young clusters

    International Nuclear Information System (INIS)

    Stahler, S.W.

    1985-01-01

    The popular idea that star formation has proceeded sequentially from lowest to highest mass members in open clusters is examined critically. For extremely young clusters, such as NGC 2264 and NGC 6530, this sequential hypothesis is a consequence of the assignment of pre-main-sequence contraction ages to all member stars. However, such ages yield a formation history which is implausible from a physical point of view, since the critical time for the onset of formation at any stellar mass is equal to the pre-main-sequence contraction time for that mass. Moreover, these ages are in conflict with the strong observational evidence that a substantial fraction of cluster members have already reached the main sequence. After reconsideration of the probable main-sequence members, the stellar ages in NGC 2264 and NGC 6530 are consistent with a variety of formation histories, and, in particular, with the view that all stellar masses form in approximately the same interval of time within a given cluster, i.e., that there is no mass-age correlation. A notion closely related to the sequential hypothesis, that the total star-formation rate increases exponentially with time, is subject to the same criticism

  1. A survey of TiOλ567 nm absorption in solar-type stars

    Science.gov (United States)

    Azizi, Fatemeh; Mirtorabi, Mohammad Taghi

    2018-04-01

    Molecular absorption bands are estimators of stellar activity and spot cycles on magnetically active stars. We have previously introduced a new colour index that compares absorption strength of the titanium oxide (TiO) at 567 nm with nearby continuum. In this paper, we implement this index to measure long-term activity variations and the statistical properties of the index in a sample of 302 solar-type stars from the High Accuracy Radial Velocity Planet search Spectrograph planet search programme. The results indicate a pattern of change in star's activity, covers a range of periods from 2 yr up to 17 yr.

  2. How Planet Nine could change the fate of the Solar system

    Science.gov (United States)

    Veras, D.

    2017-09-01

    The potential existence of a distant planet ('Planet Nine') in the Solar system has prompted a re-think about the evolution of planetary systems. As the Sun transitions from a main-sequence star into a white dwarf, Jupiter, Saturn, Uranus and Neptune are currently assumed to survive in expanded but otherwise unchanged orbits. However, a sufficiently distant and sufficiently massive extra planet would alter this quiescent end scenario through the combined effects of Solar giant branch mass-loss and Galactic tides. Here I estimate bounds for the mass and orbit of a distant extra planet that would incite future instability in systems with a Sun-like star and giant planets with masses and orbits equivalent to those of Jupiter, Saturn, Uranus and Neptune. I find that this boundary is diffuse and strongly dependent on each of the distant planet's orbital parameters. Nevertheless, I claim that instability occurs more often than not when the planet is as massive as Jupiter and harbours a semimajor axis exceeding about 300 au, or has a mass of a super-Earth and a semimajor axis exceeding about 3000 au. These results hold for orbital pericentres ranging from 100 to at least 400 au. This instability scenario might represent a common occurrence, as potentially evidenced by the ubiquity of metal pollution in white dwarf atmospheres throughout the Galaxy.

  3. Solar and Stellar Flares and Their Effects on Planets

    Science.gov (United States)

    Shibata, Kazunari

    2015-08-01

    Recent space observations of the Sun revealed that the solar atmosphere is full of explosions, such as flares and flare-like phenomena. These flares generate not only strong electromagnetic emissions but also nonthermal particles and bulk plasma ejections, which sometimes lead to geomagnetic storms and affect terrestrial environment and our civilization, damaging satellite, power-grids, radio communication etc. Solar flares are prototype of various explosions in our universe, and hence are important not only for geophysics and environmental science but also for astrophysics. The energy source of solar flares is now established to be magnetic energy stored near sunspots. There is now increasing observational evidence that solar flares are caused by magnetic reconnection, merging of anti-parallel magnetic field lines and associated magneto-plasma dynamics (Shibata and Magara 2011, Living Review). It has also been known that many stars show flares similar to solar flares, and often such stellar flares are much more energetic than solar flares. The total energy of a solar flare is typically 10^29 - 10^32 erg. On the other hand, there are much more energetic flares (10^33 - 10^38 erg) in stars, especially in young stars. These are called superflares. We argue that these superflares on stars can also be understood in a unified way based on the reconnection mechanism. Finally we show evidence of occurrence of superflares on Sun-like stars according to recent stellar observations (Maehara et al. 2012, Nature, Shibayama et al. 2013), which revealed that superflares with energy of 10^34 - 10^35 erg (100 - 1000 times of the largest solar flares) occur with frequency of once in 800 - 5000 years on Sun-like stars which are very similar to our Sun. Against the previous belief, these new observations as well as theory (Shibata et al. 2013) suggest that we cannot deny the possibility of superflares on the present Sun. Finally, we shall discuss possible impacts of these superflares

  4. LAMOST telescope reveals that Neptunian cousins of hot Jupiters are mostly single offspring of stars that are rich in heavy elements.

    Science.gov (United States)

    Dong, Subo; Xie, Ji-Wei; Zhou, Ji-Lin; Zheng, Zheng; Luo, Ali

    2018-01-09

    We discover a population of short-period, Neptune-size planets sharing key similarities with hot Jupiters: both populations are preferentially hosted by metal-rich stars, and both are preferentially found in Kepler systems with single-transiting planets. We use accurate Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) Data Release 4 (DR4) stellar parameters for main-sequence stars to study the distributions of short-period [Formula: see text] Kepler planets as a function of host star metallicity. The radius distribution of planets around metal-rich stars is more "puffed up" compared with that around metal-poor hosts. In two period-radius regimes, planets preferentially reside around metal-rich stars, while there are hardly any planets around metal-poor stars. One is the well-known hot Jupiters, and the other one is a population of Neptune-size planets ([Formula: see text]), dubbed "Hoptunes." Also like hot Jupiters, Hoptunes occur more frequently in systems with single-transiting planets although the fraction of Hoptunes occurring in multiples is larger than that of hot Jupiters. About [Formula: see text] of solar-type stars host Hoptunes, and the frequencies of Hoptunes and hot Jupiters increase with consistent trends as a function of [Fe/H]. In the planet radius distribution, hot Jupiters and Hoptunes are separated by a "valley" at approximately Saturn size (in the range of [Formula: see text]), and this "hot-Saturn valley" represents approximately an order-of-magnitude decrease in planet frequency compared with hot Jupiters and Hoptunes. The empirical "kinship" between Hoptunes and hot Jupiters suggests likely common processes (migration and/or formation) responsible for their existence.

  5. The Pisa pre-main sequence tracks and isochrones. A database covering a wide range of Z, Y, mass, and age values

    Science.gov (United States)

    Tognelli, E.; Prada Moroni, P. G.; Degl'Innocenti, S.

    2011-09-01

    Context. In recent years new observations of pre-main sequence stars (pre-MS) with Z ≤ Z⊙ have been made available. To take full advantage of the continuously growing amount of data of pre-MS stars in different environments, we need to develop updated pre-MS models for a wide range of metallicity to assign reliable ages and masses to the observed stars. Aims: We present updated evolutionary pre-MS models and isochrones for a fine grid of mass, age, metallicity, and helium values. Methods: We use a standard and well-tested stellar evolutionary code (i.e. FRANEC), that adopts outer boundary conditions from detailed and realistic atmosphere models. In this code, we incorporate additional improvements to the physical inputs related to the equation of state and the low temperature radiative opacities essential to computing low-mass stellar models. Results: We make available via internet a large database of pre-MS tracks and isochrones for a wide range of chemical compositions (Z = 0.0002-0.03), masses (M = 0.2-7.0 M⊙), and ages (1-100 Myr) for a solar-calibrated mixing length parameter α (i.e. 1.68). For each chemical composition, additional models were computed with two different mixing length values, namely α = 1.2 and 1.9. Moreover, for Z ≥ 0.008, we also provided models with two different initial deuterium abundances. The characteristics of the models have been discussed in detail and compared with other work in the literature. The main uncertainties affecting theoretical predictions have been critically discussed. Comparisons with selected data indicate that there is close agreement between theory and observation. Tracks and isochrones are available on the web at the http://astro.df.unipi.it/stellar-models/Tracks and isochrones are also 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/533/A109

  6. THE AGE OF THE YOUNG BULGE-LIKE POPULATION IN THE STELLAR SYSTEM TERZAN 5: LINKING THE GALACTIC BULGE TO THE HIGH- Z UNIVERSE

    Energy Technology Data Exchange (ETDEWEB)

    Ferraro, F. R.; Dalessandro, E.; Lanzoni, B.; Mucciarelli, A. [Dipartimento di Fisica e Astronomia, Università degli Studi di Bologna, Viale Berti Pichat 6/2, I–40127 Bologna (Italy); Massari, D. [INAF-Osservatorio Astronomico di Bologna, Via Ranzani, 1, I-40127 Bologna (Italy); Origlia, L. [Kapteyn Astronomical Institute, University of Gröningen, Kapteyn Astron Institute, NL-9747 AD Gröningen (Netherlands); Rich, R. M. [Department of Physics and Astronomy, 430 Portola Plaza, Box 951547, Los Angeles, CA 90095-1547 (United States)

    2016-09-10

    The Galactic bulge is dominated by an old, metal-rich stellar population. The possible presence and the amount of a young (a few gigayears old) minor component is one of the major issues debated in the literature. Recently, the bulge stellar system Terzan 5 was found to harbor three sub-populations with iron content varying by more than one order of magnitude (from 0.2 up to two times the solar value), with chemical abundance patterns strikingly similar to those observed in bulge field stars. Here we report on the detection of two distinct main-sequence turnoff points in Terzan 5, providing the age of the two main stellar populations: 12 Gyr for the (dominant) sub-solar component and 4.5 Gyr for the component at super-solar metallicity. This discovery classifies Terzan 5 as a site in the Galactic bulge where multiple bursts of star formation occurred, thus suggesting a quite massive progenitor possibly resembling the giant clumps observed in star-forming galaxies at high redshifts. This connection opens a new route of investigation into the formation process and evolution of spheroids and their stellar content.

  7. PRE-SUPERNOVA EVOLUTION OF ROTATING SOLAR METALLICITY STARS IN THE MASS RANGE 13-120 M {sub Sun} AND THEIR EXPLOSIVE YIELDS

    Energy Technology Data Exchange (ETDEWEB)

    Chieffi, Alessandro [Istituto Nazionale di Astrofisica-Istituto di Astrofisica e Planetologia Spaziali, Via Fosso del Cavaliere 100, I-00133 Roma (Italy); Limongi, Marco, E-mail: alessandro.chieffi@inaf.it, E-mail: marco.limongi@oa-roma.inaf.it [Centre for Stellar and Planetary Astrophysics, School of Mathematical Sciences, P.O. Box 28M, Monash University, Victoria 3800 (Australia)

    2013-02-10

    We present the first set of a new generation of models of massive stars with a solar composition extending between 13 and 120 M {sub Sun }, computed with and without the effects of rotation. We included two instabilities induced by rotation: the meridional circulation and the shear instability. We implemented two alternative schemes to treat the transport of the angular momentum: the advection-diffusion formalism and the simpler purely diffusive one. The full evolution from the pre-main sequence up to the pre-supernova stage is followed in detail with a very extended nuclear network. The explosive yields are provided for a variety of possible mass cuts and are available at the Web site http://www.iasf-roma.inaf.it/orfeo/public{sub h}tml. We find that both the He and the CO core masses are larger than those of their non-rotating counterparts. Also the C abundance left by the He burning is lower than in the non-rotating case, especially for stars with an initial mass of 13-25 M {sub Sun }, and this affects the final mass-radius relation, basically the final binding energy, at the pre-supernova stage. The elemental yields produced by a generation of stars rotating initially at 300 km s{sup -1} do not change substantially with respect to those produced by a generation of non-rotating massive stars, the main differences being a slight overproduction of the weak s-component and a larger production of F. Since rotation also affects the mass-loss rate, either directly or indirectly, we find substantial differences in the lifetimes as O-type and Wolf-Rayet subtypes between the rotating and non-rotating models. The maximum mass exploding as Type IIP supernova ranges between 15 and 20 M {sub Sun} in both sets of models (this value depends basically on the larger mass-loss rates in the red supergiant phase due to the inclusion of the dust-driven wind). This limiting value is in remarkably good agreement with current estimates.

  8. Solar and stellar flares and their impact on planets

    Science.gov (United States)

    Shibata, Kazunari

    Recent observations of the Sun revealed that the solar atmosphere is full of flares and flare-like phenomena, which affect terrestrial environment and our civilization. It has been established that flares are caused by the release of magnetic energy through magnetic reconnection. Many stars show flares similar to solar flares, and such stellar flares especially in stars with fast rotation are much more energetic than solar flares. These are called superflares. The total energy of a solar flare is 1029 - 1032 erg, while that of a superflare is 1033 - 1038 erg. Recently, it was found that superflares (with 1034 - 1035 erg) occur on Sun-like stars with slow rotation with frequency once in 800 - 5000 years. This suggests the possibility of superflares on the Sun. We review recent development of solar and stellar flare research, and briefly discuss possible impacts of superflares on the Earth and exoplanets.

  9. Ultrabass Sounds of the Giant Star xi Hya

    Science.gov (United States)

    2002-05-01

    of the star is necessary before the observed oscillation frequencies (periods) can be properly interpreted. Current models of the Sun are accurate and represent a typical main-sequence star at midlife, and the oscillations are well understood. The sound spectrum corresponding to the full disk - i.e., what we would observe if the Sun were as distant as other stars and we would therefore see it as a light point in the sky - shows a regular pattern in which the observed frequencies are separated by two different and constant intervals, the "large" and the "small" separations. It is much more difficult to "model" the interior of a giant star as the core has changed a lot during the evolution of the star. The nuclear fuel has been exhausted, the stellar core has contracted and the envelope has expanded substantially [3]. The resulting sound spectrum has therefore also changed considerably. Now there is only a small group of oscillating modes that display the same regular pattern as seen in the Sun. They are the radial modes , pressure modes that correspond to a radial expansion and contraction of the star (up and down motion of the surface). The modes in the Sun are sound waves for which most of the oscillation energy is concentrated in the outer parts of the Sun. In stars as highly evolved as xi Hya , they partly take on the character of gravity modes in the interior of the star. Gravity modes are oscillations that move matter up and down in the gravity field, under the influence of buoyancy, with only small changes of the pressure. This is the same effect that makes an air-filled ball pop to the surface when released under water. Gravity modes are normally trapped in the stable interior inside the upper (convective) envelope of a star. So far gravity modes have not been detected in the Sun. In a giant star, however, there is a chance to see some, because some of the oscillations have a mixed character : they behave like gravity modes in the interior and like sound waves

  10. Fixed-head star tracker magnitude calibration on the solar maximum mission

    Science.gov (United States)

    Pitone, Daniel S.; Twambly, B. J.; Eudell, A. H.; Roberts, D. A.

    1990-01-01

    The sensitivity of the fixed-head star trackers (FHSTs) on the Solar Maximum Mission (SMM) is defined as the accuracy of the electronic response to the magnitude of a star in the sensor field-of-view, which is measured as intensity in volts. To identify stars during attitude determination and control processes, a transformation equation is required to convert from star intensity in volts to units of magnitude and vice versa. To maintain high accuracy standards, this transformation is calibrated frequently. A sensitivity index is defined as the observed intensity in volts divided by the predicted intensity in volts; thus, the sensitivity index is a measure of the accuracy of the calibration. Using the sensitivity index, analysis is presented that compares the strengths and weaknesses of two possible transformation equations. The effect on the transformation equations of variables, such as position in the sensor field-of-view, star color, and star magnitude, is investigated. In addition, results are given that evaluate the aging process of each sensor. The results in this work can be used by future missions as an aid to employing data from star cameras as effectively as possible.

  11. CONNECTING FLARES AND TRANSIENT MASS-LOSS EVENTS IN MAGNETICALLY ACTIVE STARS

    Energy Technology Data Exchange (ETDEWEB)

    Osten, Rachel A. [Space Telescope Science Institute 3700 San Martin Drive, Baltimore, MD 21218 (United States); Wolk, Scott J., E-mail: osten@stsci.edu [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge MA 02138 (United States)

    2015-08-10

    We explore the ramification of associating the energetics of extreme magnetic reconnection events with transient mass-loss in a stellar analogy with solar eruptive events. We establish energy partitions relative to the total bolometric radiated flare energy for different observed components of stellar flares and show that there is rough agreement for these values with solar flares. We apply an equipartition between the bolometric radiated flare energy and kinetic energy in an accompanying mass ejection, seen in solar eruptive events and expected from reconnection. This allows an integrated flare rate in a particular waveband to be used to estimate the amount of associated transient mass-loss. This approach is supported by a good correspondence between observational flare signatures on high flaring rate stars and the Sun, which suggests a common physical origin. If the frequent and extreme flares that young solar-like stars and low-mass stars experience are accompanied by transient mass-loss in the form of coronal mass ejections, then the cumulative effect of this mass-loss could be large. We find that for young solar-like stars and active M dwarfs, the total mass lost due to transient magnetic eruptions could have significant impacts on disk evolution, and thus planet formation, and also exoplanet habitability.

  12. ROSAT observations of the x ray binary HD 154791

    Science.gov (United States)

    Kenyon, Scott J.

    1994-01-01

    We have been surveying the Taurus dark cloud for young stars using a variety of techniques. Two optical proper motion surveys identified 8 new pre-main sequence stars; an IRAS-based program discovered 6 new embedded sources and 4-6 new T Tauri stars. Finally, an optical objective prism survey found 12 new T Tauri stars. Our goal in this project is to examine and compare star formation in the dark clouds: Heiles cloud 2 (HCL2), L1537, L1538, and L1544. HCL2 is a very dense region actively forming young stars and contains 5-6 very young, deeply embedded sources; L1537 and L1538 have no known pre-main sequence stars; L1544 contains 7 optically visible T Tauri stars. These clouds appear roughly similar on optical sky survey plates. We would like to know why some of the clouds are active and why some are not. The first goal of the project is to survey the regions using IR photometry to identify very red pre-main sequence stars and X-ray imaging to identify solar-type young stars missed in the near-IR survey. We will follow up these observations with molecular line surveys to compare the conditions in various clouds with their star formation efficiencies.

  13. International Living With a Star (ILWS), a new collaborative space program in Solar, Heliospheric and Solar-Terrestrial Physics

    Science.gov (United States)

    Opgenoorth, H. J.; Guhathakurta, M.; Liu, W.; Kosugi, T.; Zelenyi, L.

    2003-04-01

    International cooperation has long been a vital element in the scientific investigation of solar variability and its impact on Earth and its space environment. Recently a new international cooeperative program in solar terrestrial physics has been established by the major space agencies of the world, called the International Living With a Star (ILWS) program. ILWS is a follow on to the highly successful International Solar Terrestrial Physics (ISTP) program which involved international parterners. ISTP, with its steady flow of discoveries and new knowledge in solar Terrestrial physics, has laid the foundation for the coordinated study of the Sun-Earth sytem as a connected stellar-planetary system, system which is humanity's home. The first step in establishing ILWS was taken in the fall of 2000 when funding was approved for the NASA's Living With a Star (LWS) program whose goal is to develop the scientific understanding necessary to effectively address those aspects of the connected Sun-Earth system that directly affect life and society. The scientific goals of ILWS are defined in a broader sense, aiming to include future solar, heliospheric and solar terrestrial missions of both applied and fundamental scientific focus. The ultimate goal of ILWS wil be to increase our understanding of how solar variability affects the terrestrial and other planetary environments both in the short and long term, and in particular how man and society may be affected by solar variability and its consequences. The mission charter of ILWS is 'to stimulate, strengthen and coordinate space research in order to understand the governing processes of the connected Sun-Earth System as an integrated entity'. More detailed ILWS Objectives are to stimulate and facilitate: - The study of the Sun Earth connected system and the effects which influence life and society - Collaboration among all potential partners in solar-terrestrial space missions - Synergistic coordination of international

  14. Some properties of spectral binary stars

    International Nuclear Information System (INIS)

    Krajcheva, Z.T.; Popova, E.I.; Tutukov, A.V.; Yungel'son, L.R.; AN SSSR, Moscow. Astronomicheskij Sovet)

    1978-01-01

    Statistical investigations of spectra binary stars are carried out. Binary systems consisting of main sequence stars are considered. For 826 binary stars masses of components, ratios of component masses, semiaxes of orbits and orbital angular momenta are calculated. The distributions of these parameters and their correlations are analyzed. The dependences of statistical properties of spectral binary stars on their origin and evolution are discussed

  15. Statistical Studies of Solar White-light Flares and Comparisons with Superflares on Solar-type Stars

    Science.gov (United States)

    Namekata, Kosuke; Sakaue, Takahito; Watanabe, Kyoko; Asai, Ayumi; Maehara, Hiroyuki; Notsu, Yuta; Notsu, Shota; Honda, Satoshi; Ishii, Takako T.; Ikuta, Kai; Nogami, Daisaku; Shibata, Kazunari

    2017-12-01

    Recently, many superflares on solar-type stars have been discovered as white-light flares (WLFs). The statistical study found a correlation between their energies (E) and durations (τ): τ \\propto {E}0.39, similar to those of solar hard/soft X-ray flares, τ \\propto {E}0.2{--0.33}. This indicates a universal mechanism of energy release on solar and stellar flares, i.e., magnetic reconnection. We here carried out statistical research on 50 solar WLFs observed with Solar Dynamics Observatory/HMI and examined the correlation between the energies and durations. As a result, the E–τ relation on solar WLFs (τ \\propto {E}0.38) is quite similar to that on stellar superflares (τ \\propto {E}0.39). However, the durations of stellar superflares are one order of magnitude shorter than those expected from solar WLFs. We present the following two interpretations for the discrepancy: (1) in solar flares, the cooling timescale of WLFs may be longer than the reconnection one, and the decay time of solar WLFs can be elongated by the cooling effect; (2) the distribution can be understood by applying a scaling law (τ \\propto {E}1/3{B}-5/3) derived from the magnetic reconnection theory. In the latter case, the observed superflares are expected to have 2–4 times stronger magnetic field strength than solar flares.

  16. THE OCCURRENCE RATE OF EARTH ANALOG PLANETS ORBITING SUN-LIKE STARS

    International Nuclear Information System (INIS)

    Catanzarite, Joseph; Shao, Michael

    2011-01-01

    Kepler is a space telescope that searches Sun-like stars for planets. Its major goal is to determine η Earth , the fraction of Sun-like stars that have planets like Earth. When a planet 'transits' or moves in front of a star, Kepler can measure the concomitant dimming of the starlight. From analysis of the first four months of those measurements for over 150,000 stars, Kepler's Science Team has determined sizes, surface temperatures, orbit sizes, and periods for over a thousand new planet candidates. In this paper, we characterize the period probability distribution function of the super-Earth and Neptune planet candidates with periods up to 132 days, and find three distinct period regimes. For candidates with periods below 3 days, the density increases sharply with increasing period; for periods between 3 and 30 days, the density rises more gradually with increasing period, and for periods longer than 30 days, the density drops gradually with increasing period. We estimate that 1%-3% of stars like the Sun are expected to have Earth analog planets, based on the Kepler data release of 2011 February. This estimate of η Earth is based on extrapolation from a fiducial subsample of the Kepler planet candidates that we chose to be nominally 'complete' (i.e., no missed detections) to the realm of the Earth-like planets, by means of simple power-law models. The accuracy of the extrapolation will improve as more data from the Kepler mission are folded in. Accurate knowledge of η Earth is essential for the planning of future missions that will image and take spectra of Earth-like planets. Our result that Earths are relatively scarce means that a substantial effort will be needed to identify suitable target stars prior to these future missions.

  17. DK UMa: A Star on the Ascent

    Science.gov (United States)

    Simon, Theodore

    1999-01-01

    DK UMa (= 24 UMa = HD 82210) is a G4 IV-III star. According to its M(sub v) and B - V color, it is located at the base of the red giant branch, having recently exited from the Hertzsprung Gap. Now poised to start its first ascent along the giant branch, DK UMa is at a significant juncture in its post-main-sequence evolution, offering an important evolutionary comparison for magnetic activity with stars like 31 Comae, which is just entering the Hertzsprung Gap, and older stars like the Hyades giants or P Ceti, which have passed the tip of the giant branch and lie in the so-called 'clump'. As part of a major survey of the ultraviolet and X ray properties of a well-defined sample of evolved giant stars, DK UMa was observed with the Extreme Ultraviolet Explorer (EUVE) spacecraft in March 1997, for a total exposure time of 230 kiloseconds. A plot of the extracted short-wavelength (SW) spectrum of this star is shown, where it is compared with similar EUVE exposures for other yellow and red giant stars in the activity survey. In terms of the spectral lines of different ionization stages present in these spectra, the transition region and coronal temperature of DK UMa appears to be intermediate between those of 31 Com and P Ceti. Combining the relative strengths of the EUVE lines with Hubble Space Telescope (HST) data at near UV wavelengths and with ROSAT X-ray fluxes, the differential emission measure (DEM) distributions of these stars form a sequence in coronal temperature, which peaks at 10(exp 7.2) K for 31 Com, at 10(exp 6.8) K for B Ceti, and at intermediate temperatures for DK UMa - consistent with the evolutionary stages represented by the three stars. The integrated fluxes of the strongest emission lines found in the EUVE spectrum of DK UMa are listed, again compared with similar measurements for other giant stars that were observed in the course of other EUVE Guest Observer programs.

  18. EVOLUTIONARY TRACKS OF THE CLIMATE OF EARTH-LIKE PLANETS AROUND DIFFERENT MASS STARS

    Energy Technology Data Exchange (ETDEWEB)

    Kadoya, S.; Tajika, E., E-mail: kadoya@astrobio.k.u-tokyo.ac.jp, E-mail: tajika@eps.s.u-tokyo.ac.jp [Department of Earth and Planetary Science, The University of Tokyo, Faculty of Science Bldg. 1 #711, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033 (Japan)

    2016-07-10

    The climatic evolution of the Earth depends strongly on the evolution of the insolation from the Sun and the amount of the greenhouse gasses, especially CO{sub 2} in the atmosphere. Here, we investigate the evolution of the climate of hypothetical Earths around stars whose masses are different from the solar mass with a luminosity evolution model of the stars, a mantle degassing model coupled with a parameterized convection model of the planetary interiors, and an energy balance climate model of the planetary surface. In the habitable zone (HZ), the climate of the planets is initially warm or hot, depending on the orbital semimajor axes. We found that, in the inner HZ, the climate of the planets becomes hotter with time owing to the increase in the luminosity of the central stars, while, in the outer HZ, it becomes colder and eventually globally ice-covered owing to the decrease in the CO{sub 2} degassing rate of the planets. The orbital condition for maintaining the warm climate similar to the present Earth becomes very limited, and more interestingly, the planet orbiting in the outer HZ becomes globally ice-covered after a certain critical age (∼3 Gyr for the hypothetical Earth with standard parameters), irrespective of the mass of the central star. This is because the critical age depends on the evolution of the planets and planetary factors, rather than on the stellar mass. The habitability of the Earth-like planet is shown to be limited with age even though it is orbiting within the HZ.

  19. EVOLUTIONARY TRACKS OF THE CLIMATE OF EARTH-LIKE PLANETS AROUND DIFFERENT MASS STARS

    International Nuclear Information System (INIS)

    Kadoya, S.; Tajika, E.

    2016-01-01

    The climatic evolution of the Earth depends strongly on the evolution of the insolation from the Sun and the amount of the greenhouse gasses, especially CO_2 in the atmosphere. Here, we investigate the evolution of the climate of hypothetical Earths around stars whose masses are different from the solar mass with a luminosity evolution model of the stars, a mantle degassing model coupled with a parameterized convection model of the planetary interiors, and an energy balance climate model of the planetary surface. In the habitable zone (HZ), the climate of the planets is initially warm or hot, depending on the orbital semimajor axes. We found that, in the inner HZ, the climate of the planets becomes hotter with time owing to the increase in the luminosity of the central stars, while, in the outer HZ, it becomes colder and eventually globally ice-covered owing to the decrease in the CO_2 degassing rate of the planets. The orbital condition for maintaining the warm climate similar to the present Earth becomes very limited, and more interestingly, the planet orbiting in the outer HZ becomes globally ice-covered after a certain critical age (∼3 Gyr for the hypothetical Earth with standard parameters), irrespective of the mass of the central star. This is because the critical age depends on the evolution of the planets and planetary factors, rather than on the stellar mass. The habitability of the Earth-like planet is shown to be limited with age even though it is orbiting within the HZ.

  20. THE GALACTIC POTENTIAL AND THE ASYMMETRIC DISTRIBUTION OF HYPERVELOCITY STARS

    International Nuclear Information System (INIS)

    Perets, Hagai B.; Alexander, Tal; Wu Xufen; Zhao Hongsheng; Famaey, Benoit; Gentile, Gianfranco

    2009-01-01

    In recent years several hypervelocity stars (HVSs) have been observed in the halo of our Galaxy. Such HVSs have possibly been ejected from the Galactic center and then propagated in the Galactic potential up to their current position. The recent survey for candidate HVSs show an asymmetry in the kinematics of candidate HVSs (position and velocity vectors), where more outgoing stars than ingoing stars (i.e., positive Galactocentric velocities versus negative ones) are observed. We show that such kinematic asymmetry, which is likely due to the finite lifetime of the stars and Galactic potential structure, could be used in a novel method to probe and constrain the Galactic potential, identify the stellar type of the stars in the survey and estimate the number of HVSs. Kinematics-independent identification of the stellar types of the stars in such surveys (e.g., spectroscopic identification) could further improve these results. We find that the observed asymmetry between ingoing and outgoing stars favors specific Galactic potential models. It also implies a lower limit of ∼54 ± 8 main-sequence HVSs in the survey sample (∼>648 ± 96 in the Galaxy), assuming that all of the MS stars in the survey originate from the GC. The other stars in the survey are likely to be hot blue horizontal branch stars born in the halo rather than stars ejected from the GC.

  1. Important consequences of atomic diffusion inside main-sequence stars: opacities, extra-mixing, oscillations

    Directory of Open Access Journals (Sweden)

    Deal M.

    2017-01-01

    Full Text Available Atomic diffusion, including the effects of radiative accelerations on individual elements, leads to important variations of the chemical composition inside stars. The accumulation of important elements in specific layers leads to a local increase of the average opacity and to hydrodynamic instabilities that modify the internal stellar structure. This can also have important consequences for asteroseismology.

  2. 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

  3. Linear series of stellar models. Pt. 4. Helium-carbon stars of 3.5Msub(o) and 1Msub(o)

    International Nuclear Information System (INIS)

    Kozlowski, M.; Paczynski, B.; Popova, K.

    1973-01-01

    One linear series of models for a star of 3.5Msub(o) and two linear series of models for a star of 1Msub(o) are constructed. Models consist of helium rich envelopes (Y = 0.97, Z = 0.03) and pure carbon cores, and they have a rectangular helium profile, Y(Msub(r)). The linear series for a star of 3.5Msub(o) begins on the normal branch of the helium main sequence and terminates on the normal branch of the carbon main sequence. This series has eight turning points at which the core mass attains a local extremum. One of the two linear series for a star of 1Msub(o) begins on the normal branch of the helium main sequence, terminates on the high density branch of the helium main sequence, and has one turning point. The second linear series for a star of 1Msub(o) begins on the normal branch of the carbon main sequence, terminates on the high density branch of the carbon main sequence, and has three turning points. Two such linear series may have a common bifurcation point for a star of about 1.26Msub(o). (author)

  4. Paradoxical gap in the relative ages of T Tauri stars

    International Nuclear Information System (INIS)

    Weaer, W.B.

    1984-01-01

    The frequency distribution of T Tauri stars of different Youth (relative age) shows a pronounced gap at 5% of their time to the zero-age main sequence. This gap, which occurs in all of the four major T Tauri associations, is too large to be filled by unclassifiable veiled stars. It is nearly vertical on the Hertzsprung-Russell diagram, is centered near spectral class K5, and lies close to the transition between the convective and radiative tracks of the pre-main-sequence stars

  5. UBV-photometry of flare stars in pleiades

    International Nuclear Information System (INIS)

    Chavushyan, O.S.; Garibdzhanyan, A.T.

    1975-01-01

    The results are presented of UBV-photometry of 283 flare stars at the minimum of brightness in the Pleiad region. A new method has been developed and used of taking into account the background in photographic UBV-photometry with an iris microphotometer. The data obtained indicate that the flare Pleiad stars are located on both sides of the main sequence in the light-luminosity (V,B-V) diagram, while in the (U-B,B-V) diagram they are largely located above the main sequence

  6. ON THE RELIABILITY OF STELLAR AGES AND AGE SPREADS INFERRED FROM PRE-MAIN-SEQUENCE EVOLUTIONARY MODELS

    International Nuclear Information System (INIS)

    Hosokawa, Takashi; Offner, Stella S. R.; Krumholz, Mark R.

    2011-01-01

    We revisit the problem of low-mass pre-main-sequence stellar evolution and its observational consequences for where stars fall on the Hertzsprung-Russell diagram (HRD). In contrast to most previous work, our models follow stars as they grow from small masses via accretion, and we perform a systematic study of how the stars' HRD evolution is influenced by their initial radius, by the radiative properties of the accretion flow, and by the accretion history, using both simple idealized accretion histories and histories taken from numerical simulations of star cluster formation. We compare our numerical results to both non-accreting isochrones and to the positions of observed stars in the HRD, with a goal of determining whether both the absolute ages and the age dispersions inferred from non-accreting isochrones are reliable. We show that non-accreting isochrones can sometimes overestimate stellar ages for more massive stars (those with effective temperatures above ∼3500 K), thereby explaining why non-accreting isochrones often suggest a systematic age difference between more and less massive stars in the same cluster. However, we also find the only way to produce a similar overestimate for the ages of cooler stars is if these stars grow from ∼0.01 M sun seed protostars that are an order of magnitude smaller than predicted by current theoretical models, and if the size of the seed protostar correlates systematically with the final stellar mass at the end of accretion. We therefore conclude that, unless both of these conditions are met, inferred ages and age spreads for cool stars are reliable, at least to the extent that the observed bolometric luminosities and temperatures are accurate. Finally, we note that the time dependence of the mass accretion rate has remarkably little effect on low-mass stars' evolution on the HRD, and that such time dependence may be neglected for all stars except those with effective temperatures above ∼4000 K.

  7. A Herschel view of IC 1396 A: Unveiling the different sequences of star formation

    NARCIS (Netherlands)

    Sicilia-Aguilar, Aurora; Roccatagliata, Veronica; Getman, Konstantin; Henning, Thomas; Merín, Bruno; Eiroa, Carlos; Rivière-Marichalar, Pablo; Currie, Thayne

    Context. The IC 1396 A globule, located to the west of the young cluster Tr 37, is known to host many very young stars and protostars, and is also assumed to be a site of triggered star formation. Aims: Our aim is to test the triggering mechanisms and sequences leading to star formation in Tr 37 and

  8. MASSIVE STARS IN THE Cl 1813-178 CLUSTER: AN EPISODE OF MASSIVE STAR FORMATION IN THE W33 COMPLEX

    International Nuclear Information System (INIS)

    Messineo, Maria; Davies, Ben; Figer, Donald F.; Trombley, Christine; Kudritzki, R. P.; Valenti, Elena; Najarro, F.; Michael Rich, R.

    2011-01-01

    Young massive (M > 10 4 M sun ) stellar clusters are a good laboratory to study the evolution of massive stars. Only a dozen of such clusters are known in the Galaxy. Here, we report about a new young massive stellar cluster in the Milky Way. Near-infrared medium-resolution spectroscopy with UIST on the UKIRT telescope and NIRSPEC on the Keck telescope, and X-ray observations with the Chandra and XMM satellites, of the Cl 1813-178 cluster confirm a large number of massive stars. We detected 1 red supergiant, 2 Wolf-Rayet stars, 1 candidate luminous blue variable, 2 OIf, and 19 OB stars. Among the latter, twelve are likely supergiants, four giants, and the faintest three dwarf stars. We detected post-main-sequence stars with masses between 25 and 100 M sun . A population with age of 4-4.5 Myr and a mass of ∼10, 000 M sun can reproduce such a mixture of massive evolved stars. This massive stellar cluster is the first detection of a cluster in the W33 complex. Six supernova remnants and several other candidate clusters are found in the direction of the same complex.

  9. Acne at The Bottom Of The Main Sequence

    Science.gov (United States)

    Barnes, John; Haswell, C.; Jenkins, J.; Jeffers, S.; Jones, H. R. A.; Lohr, M.; Pavlenko, Y.

    2016-08-01

    Starspots are an important manifestation of stellar activity and yet their distribution patterns on the lowest mass stars is not well known. Time series spectra of fully convective M dwarfs taken in the red-optical with UVES reveal numerous line profile distortions which are interpreted as starspots. We derive Doppler images for four M4.5V - M9V stars and find that contrast ratios corresponding to photosphere-spot temperature differences of only 200-300 K are sufficient to model the timeseries spectra. Although more starspot structure is found at high latitudes, spots are reconstructed at a range of phases and latitudes with mean spot filling factors of only a few per cent. The occurrence of low-contrast spots at predominantly high latitudes is in general likely to be responsible for the low amplitude photometric variability seen in late-M dwarfs. The recovered starspot patterns are used to assess their effect on precision radial velocity surveys aimed at detecting planets around this population of stars.

  10. Observations of Hα-emission stars in the young cluster NGC 2264

    International Nuclear Information System (INIS)

    Rydgren, A.E.

    1979-01-01

    UBVRI photometry is given for a sample of 25 late-type Hα-emission stars in the young cluster NGC 2264. The stars are in the magnitude range 12< or =V<16. Some but not all appear to be T Tauri stars. The color--color diagrams support the view that the deviations from normal photospheric colors (due to ''spectral veiling'' and line emission) decrease with increasing wavelength between the U and I filters. In the (V, V-R) diagram, the Hα-emission stars lie in a well-defined pre-main-sequence band. Within this sample, there is a trend toward stronger line emission and spectral veiling with later spectral type. All of the likely legitimate T Tauri stars have inferred spectral types later than about K3. The question of cluster membership for stars in the cluster field with very small proper motions is considered

  11. Formation of Neutral Disk-Like Zone Around the Active Hot Stars in Symbiotic Binaries

    Directory of Open Access Journals (Sweden)

    Cariková Z.

    2012-06-01

    Full Text Available In this contribution we present the ionization structure in the enhanced wind from the hot star in symbiotic binaries during active phases. Rotation of the hot star leads to the compression of the outflowing material towards its equatorial plane. As a result, a neutral disk-like zone around the active hot star near the orbital plane is created. We modeled the compression of the wind and calculated the neutral disk-like zone in the enhanced wind from the hot star using the equation of the photoionization equilibrium. the presence of such neutral disk-like zones was also suggested on the basis of the modeling the spectral energy distribution of symbiotic binaries. We confront the calculated ionization structures in the enhanced wind from the hot star with the observations. the calculated column density of the neutral hydrogen atoms in the neutral disk-like zone and the emission measure of the ionized part of the wind from the hot star are in a good agreement with the quantities derived from observations during active phases. the presence of such neutral disk-like zones is transient, being connected with the active phases of symbiotic binaries. During quiescent phases, such neutral disk-like zones cannot be created because of insufficient mass-loss rate from the hot star.

  12. On the evolution of stars

    International Nuclear Information System (INIS)

    Kippenhahn, R.

    1989-01-01

    A popular survey is given of the present knowledge on evolution and ageing of stars. Main sequence stars, white dwarf stars, and red giant stars are classified in the Hertzsprung-Russell (HR)-diagram by measurable quantities: surface temperature and luminosity. From the HR-diagram it can be concluded to star mass and age. Star-forming processes in interstellar clouds as well as stellar burning processes are illustrated. The changes occurring in a star due to the depletion of the nuclear energy reserve are described. In this frame the phenomena of planetary nebulae, supernovae, pulsars, neutron stars as well as of black holes are explained

  13. A STATISTICAL RECONSTRUCTION OF THE PLANET POPULATION AROUND KEPLER SOLAR-TYPE STARS

    International Nuclear Information System (INIS)

    Silburt, Ari; Wu, Yanqin; Gaidos, Eric

    2015-01-01

    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 ⊕ ) planets and their distributions with radius and orbital period. We analyze 76,711 solar-type (0.8 < R * /R ☉ < 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 ⊕ , 0.99-1.7 AU for solar-twin stars) as 6.4 −1.1 +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

  14. Star Formation in the Orion Nebula Cluster

    Science.gov (United States)

    Palla, Francesco; Stahler, Steven W.

    1999-11-01

    We study the record of star formation activity within the dense cluster associated with the Orion Nebula. The bolometric luminosity function of 900 visible members is well matched by a simplified theoretical model for cluster formation. This model assumes th