Journal articles: 'Solar-type star'

1

Smith, Keith T. "Is the Sun a solar-type star?" Science 357, no. 6347 (July 13, 2017): 159.1–159. http://dx.doi.org/10.1126/science.357.6347.159-a.

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Mirzoyan, L. V. "Flare stars in star clusters, associations and solar vicinity." Symposium - International Astronomical Union 137 (1990): 1–13. http://dx.doi.org/10.1017/s0074180900187303.

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The observational data on flare stars observed in star clusters and associations as well as in the solar vicinity (the UV Ceti type stars) are discussed. The analysis of these data show that they constitute one common class of objects possessing flare activity and the differences between them are conditioned by the age differences. The stage of flare activity is an evolutionary stage, one of the earliest stages of evolution passed by all red dwarf stars. It comes before the end of their T Tau stage of evolution. The UV Ceti type flare stars in the solar vicinity seem to be the population of the general galactic field, which were formed in the systems, already desintegrated. Most probably the stellar flares are the result of the release of the the surplus energy having intra-stellar origin.

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He, Han, Huaning Wang, Yan Yan, and Duo Yun. "Magnetic Activity Discrepancies of Solar-Type Stars Revealed by Kepler Light Curves." Proceedings of the International Astronomical Union 13, S335 (July 2017): 7–10. http://dx.doi.org/10.1017/s1743921317007670.

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AbstractMagnetic activity information is concealed in the shape of stellar light curves owing to the process of rotational modulation. We developed approaches to extract magnetic activity characteristics from stellar light curves, and applied the method to a solar-type star observed with Kepler space telescope and also to the Sun for comparison. The result reveals distinct magnetic activity discrepancies between the solar-type star and the Sun. (1) The light-curve periodicity of the solar-type star is generally stronger than that of the Sun. (2) For the solar-type star, when the range of light-curve fluctuation is larger, the periodicity is also higher; while for the Sun, only during the solar minima with minimal range of fluctuation, the light curves show some periodicity. We propose that on the solar-type star, it is the large-scale magnetic field that leads to the light curves with both high periodicity and large range of fluctuation.

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Roberts, Lewis C., Andrei Tokovinin, Brian D. Mason, William I. Hartkopf, and Reed L. Riddle. "OBSERVATIONS OF HIERARCHICAL SOLAR-TYPE MULTIPLE STAR SYSTEMS." Astronomical Journal 150, no. 4 (September 30, 2015): 130. http://dx.doi.org/10.1088/0004-6256/150/4/130.

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Porto de Mello, G. F., and L. da Silva. "HR 6094: A Young Solar-Type, Solar-Metallicity Barium Dwarf Star." Astrophysical Journal 476, no. 2 (February 20, 1997): L89—L92. http://dx.doi.org/10.1086/310504.

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da Silva, L., and G. F. Porto de Mello. "Lithium Abundances in Solar-Type Stars." Symposium - International Astronomical Union 198 (2000): 495–97. http://dx.doi.org/10.1017/s0074180900167142.

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We report Li abundances from the λ6707 line for 19 nearby dwarf and subgiant solar-type stars. The unevolved stars in this sample present high (> 2.00) Li abundances. We found a few cases of subgiant stars which present high Li content. The Sun seems to be part of a population of nearly unevolved stars which have depleted their Li to a high degree: all other metal-normal, near ZAMS stars in our sample show higher than solar Li content. There seems to be no correlation of the degree of Li depletion with mass, atmospheric parameters or state of evolution: as an example we found a star (HR1532) almost identical to the Sun in its state of evolution and atmospheric parameters, but with over ten times the solar Li abundance. We propose that different histories of angular momentum distribution at star birth, and/or post-birth angular momentum evolution, may account for these differences.

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Mayor, Michel, and Didier Queloz. "A Jupiter-mass companion to a solar-type star." Nature 378, no. 6555 (November 1995): 355–59. http://dx.doi.org/10.1038/378355a0.

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Soderblom, David R. "Determining the temperatures of solar-type stars - Do star spots produce color anomalies?" Astrophysical Journal 342 (July 1989): 823. http://dx.doi.org/10.1086/167639.

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Brown, Carolyn, Brad Carter, Stephen Marsden, and Ian Waite. "Starspots on Young Solar-Type Stars." Proceedings of the International Astronomical Union 9, S302 (August 2013): 148–49. http://dx.doi.org/10.1017/s1743921314001938.

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AbstractDoppler Imaging of starspots on young solar analogues is a way to investigate the early history of solar magnetic activity by proxy. Doppler images of young G-dwarfs have yielded the presence of large polar spots, extending to moderate latitudes, along with measurements of the surface differential rotation. The differential rotation measurement for one star (RX J0850.1-7554) suggests it is possibly the first example of a young G-type dwarf whose surface rotates as almost a solid body, in marked contrast to the differential rotation of other rapidly rotating young G-dwarfs and the present-day Sun. Overall, our Doppler imaging results show that the young Sun possessed a fundamentally different dynamo to today.

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Barker, Adrian J., and Gordon I. Ogilvie. "Internal wave breaking and the fate of planets around solar-type stars." Proceedings of the International Astronomical Union 6, S271 (June 2010): 363–64. http://dx.doi.org/10.1017/s1743921311017807.

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AbstractInternal gravity waves are excited at the interface of convection and radiation zones of a solar-type star, by the tidal forcing of a short-period planet. The fate of these waves as they approach the centre of the star depends on their amplitude. We discuss the results of numerical simulations of these waves approaching the centre of a star, and the resulting evolution of the spin of the central regions of the star and the orbit of the planet. If the waves break, we find efficient tidal dissipation, which is not present if the waves perfectly reflect from the centre. This highlights an important amplitude dependence of the (stellar) tidal quality factor Q′, which has implications for the survival of planets on short-period orbits around solar-type stars, with radiative cores.

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Soderblom, David R. "Using lithium to estimate ages for solar-type stars." Proceedings of the International Astronomical Union 5, S268 (November 2009): 359–60. http://dx.doi.org/10.1017/s1743921310004461.

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12

Gough, D. O., and E. Novotny. "The Asteroseismic Calibration of Solar-Type Stars." International Astronomical Union Colloquium 137 (1993): 550–53. http://dx.doi.org/10.1017/s0252921100018418.

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AbstractThe addition of seismic parameters to stellar-model calibrations substantially increases the constraints one can place on the properties of stars. We present some preliminary calculations to assess the accuracy with which certain stellar parameters can be inferred. For simplicity we use just two of the three most basic seismic parameters characterizing the low-degree p modes that might be measured from intensity variations by instruments such as photometers planned for the ESA spacecraft PRISMA. We ascertain the accuracy of a calibration of an isolated star and of a cluster of N solar-type stars.

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Kamp, Inga, and Fatima Sammar. "Circumstellar Disks around Young Solar-type Stars." Symposium - International Astronomical Union 219 (2004): 385–89. http://dx.doi.org/10.1017/s0074180900182361.

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The chemistry of circumstellar disks around young (a few 10 Myr) solar-type stars is mainly driven by the strong UV radiation field of the central star. As a starting point for a detailed UV radiation field, the rocket and satellite observations of the solar chromosphere are used and scaled according to the time-dependent behaviour of stellar activity. The disk chemistry as well as dust and gas temperatures are then derived self-consistently from the model. The results of these calculations can be used for the identification of the most promising gas tracers as well as for the interpretation of present and future observations.

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Käpylä, P. J. "Star-in-a-box simulations of fully convective stars." Astronomy & Astrophysics 651 (July 2021): A66. http://dx.doi.org/10.1051/0004-6361/202040049.

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Context. Main-sequence late-type stars with masses of less than 0.35 M⊙ are fully convective. Aims. The goal is to study convection, differential rotation, and dynamos as functions of rotation in fully convective stars. Methods. Three-dimensional hydrodynamic and magnetohydrodynamic numerical simulations with a star-in-a-box model, in which a spherical star is immersed inside of a Cartesian cube, are used. The model corresponds to a 0.2 M⊙ main-sequence M5 dwarf. A range of rotation periods (Prot) between 4.3 and 430 d is explored. Results. The slowly rotating model with Prot = 430 days produces anti-solar differential rotation with a slow equator and fast poles, along with predominantly axisymmetric quasi-steady large-scale magnetic fields. For intermediate rotation (Prot = 144 and 43 days) the differential rotation is solar-like (fast equator, slow poles), and the large-scale magnetic fields are mostly axisymmetric and either quasi-stationary or cyclic. The latter occurs in a similar parameter regime as in other numerical studies in spherical shells, and the cycle period is similar to observed cycles in fully convective stars with rotation periods of roughly 100 days. In the rapid rotation regime the differential rotation is weak and the large-scale magnetic fields are increasingly non-axisymmetric with a dominating m = 1 mode. This large-scale non-axisymmetric field also exhibits azimuthal dynamo waves. Conclusions. The results of the star-in-a-box models agree with simulations of partially convective late-type stars in spherical shells in that the transitions in differential rotation and dynamo regimes occur at similar rotational regimes in terms of the Coriolis (inverse Rossby) number. This similarity between partially and fully convective stars suggests that the processes generating differential rotation and large-scale magnetism are insensitive to the geometry of the star.

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Jardine, M., J. Barnes, Y. Unruh, and A. Collier Cameron. "Prominences on Rapidly-Rotating Solar-Type Stars." International Astronomical Union Colloquium 167 (1998): 235–38. http://dx.doi.org/10.1017/s0252921100047655.

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AbstractWe present Hα observations of two rapidly-rotating G2 dwarfs in the Alpha Persei cluster and of AB Dor, a young K0 dwarf. All three stars have projected rotational velocities of about 90 km s−1 and axial rotation periods ranging from 11 to 15 hours. He 520 and AB Dor show very clear transient features that move through the profile. The most likely explanation for these features is that they are huge prominences in co-rotation with the star. We also use the recently developed technique of least squares deconvolution to present simultaneous dynamic profiles of the stars’ photospheric lines which show the locations of the surface spots. This technique has allowed us to extend our studies to a greater range of stars.

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Giampapa, Mark S. "The Photometric Variability of Solar-Type Stars." Proceedings of the International Astronomical Union 11, A29A (August 2015): 365–71. http://dx.doi.org/10.1017/s174392131600329x.

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AbstractThe joint variability of chromospheric emission with the integrated flux in the Kepler visible band for the Sun as a star is examined. No correlation between our Ca II K line parameter and the Kepler passband is seen, suggesting that visible-band variability in solar-like stars is mostly independent of solar-like chromospheric activity. However, the K-line parameter time series and the total solar flux in the infrared K band appear weakly correlated, reflecting the wavelength dependence of the relationship between magnetic activity and broadband variability. We then apply a schematic, three-component model as a framework for the discussion of stellar photometric variability as observed by Kepler. The model confirms that spots tend to dominate stellar photometric variability in the visible though interesting cases do emerge where the facular disk coverage may become important in determining the amplitude of broadband variability.

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Zubrin, Robert. "Exchange of material between solar systems by random stellar encounters." International Journal of Astrobiology 19, no. 1 (June 18, 2019): 43–48. http://dx.doi.org/10.1017/s1473550419000144.

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AbstractIt is shown that a mechanism involving only random motion of the sun with respect to the surrounding star field can account for the ~1 per 25 Myr characteristic frequency of large cometary impacts on Earth. In the proposed mechanism, the sun travels through the Oort Cloud of an encounter star, most typically a Type M dwarf, while the dwarf flies through the Oort cloud of our Sun. As a result, Oort Cloud objects from our Solar System are precipitated in large numbers to impact planets in the dwarf star system, while the dwarf's Oort Cloud objects are destabilized to impact planets in our Solar System. It is shown that it is this exchange of Oort cloud object between stellar systems, rather than the precipitation of Oort Cloud objects within a stellar system, that can account for the apparent periodicity of mass extinctions. Because the sun is more massive than ~90% of stars, its Oort cloud extends further, resulting in it delivering about a factor of three more bombardments on other solar systems than our Solar System receives. About 60% of the bombardments on our Solar System are found to be delivered by Type M dwarfs, about 20% by type K dwarfs, with the remaining 20% being delivered by stars of type G or larger. Foreign star Oort cloud objects can be captured by our Sun at typical ranges of 10 AU, resulting in a cometary approach to perihelion within a few years. It is found that assuming an effective Oort Cloud radius of 40 000 AU for a star of solar mass, increasing in size with the square root of the mass, accounts for the observed characteristic frequency of mass extinction events on Earth, given the local stellar number density of 0.003 stars per cubic light year. The frequency of mass extinction events in other solar systems would increase or decrease in linear proportion to the local stellar number density. It is shown that this exchange of materials between solar systems during close stellar encounters could be an important mechanism for spreading life throughout the galaxy. Implications for the evolution of life on Earth and in other solar systems are discussed.

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Queloz, Didier, and Mejd Alsari. "The Discovery of the First Exoplanet Orbiting a Solar-Type Star." Scientific Video Protocols 1, no. 1 (March 20, 2020): 1–3. http://dx.doi.org/10.32386/scivpro.000017.

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Didier Queloz is Professor of Physics at the Cavendish Laboratory (University of Cambridge) and Geneva University. He was jointly awarded the 2019 Nobel Prize in Physics for “the discovery of an exoplanet orbiting a solar-type star”. In the first part of his conversation with Mejd Alsari he discusses the impact of his 1995 discovery on the theory of planetary systems formation.

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19

Short, C. I., and P. H. Hauschildt. "A Non‐LTE Line‐Blanketed Model of a Solar‐Type Star." Astrophysical Journal 618, no. 2 (January 10, 2005): 926–38. http://dx.doi.org/10.1086/426128.

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20

Favata, F., G. Micela, S. Orlando, J. H. M. M. Schmitt, S. Sciortino, and J. Hall. "The X-ray cycle in the solar-type star HD 81809." Astronomy & Astrophysics 490, no. 3 (June 24, 2008): 1121–26. http://dx.doi.org/10.1051/0004-6361:200809694.

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21

Théado, Sylvie, Elise Bohuon, and Sylvie Vauclair. "Lithium destruction induced by planetary accretion in solar-type stars." Proceedings of the International Astronomical Union 5, S268 (November 2009): 427–28. http://dx.doi.org/10.1017/s1743921310004588.

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AbstractAccretion of planetary (metal-rich) material onto a star in its early phases can produce episodes of thermohaline convection below the outer convective zone. These extra-mixing phases lead to rapid lithium destruction. The observed dispersion of lithium abundances in solar-type stars can be related to such events.

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22

Sheminova, V. A. "The line asymmetry in the spectra of the Sun and solar-type stars." Kinematika i fizika nebesnyh tel (Online) 36, no. 6 (November 1, 2020): 65–87. http://dx.doi.org/10.15407/kfnt2020.06.065.

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We have analysed the asymmetry of lines Fe I and Fe II in spectra of a solar flux using three FTS atlases and the HARPS atlas and also in spectra of 13 stars using observation data on the HARPS spectrograph. To reduce observation noise individual line bisectors of each star have been averaged. The obtained average bisectors in the stellar spectra are more or less similar to the shape C well known to the Sun. In stars with rotation velocities greater than 5 km/s the shape of the bisectors is more like /. The curvature and span of the bisectors increase with the temperature of the star. Our results confirm the known facts about strong influence of rotation velocity on the span and shape of bisectors. The average convective velocity was determined based on the span of the average bisector, which shows the largest difference between the velocity of cold falling and hot rising convective flows of the matter. It’s equal to -420 m/s for the Sun as a star. In stars, it grows from -150 to -700 m/s with an effective temperature of 4800 to 6200 K, respectively. For stars with greater surface gravity and greater metallicity, the average convective velocity decreases. It also decreases with star age and correlates with the velocity of micro and macroturbulent movements. The results of solar flux analysis showed that absolute wavelength scales in the atlases used coincide with an accuracy of about -10 m/s, except for the FTS-atlas of Hinkle et al., whose scale is shifted and depends on the wavelength. In the range from 450 to 650 nm, the scale shift of this atlas varies from -100 to -330 m/s, respectively, and it equals on average of 240 m/s. The resulting average star bisectors contain information about the fields of convective velocities and may be useful for hydrodynamic modeling of stellar atmospheres in order to study the characteristic features of surface convection.

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Gallet, F., C. Zanni, and L. Amard. "Rotational evolution of solar-type protostars during the star-disk interaction phase." Astronomy & Astrophysics 632 (November 21, 2019): A6. http://dx.doi.org/10.1051/0004-6361/201935432.

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Context. The early pre-main sequence phase during which solar-mass stars are still likely surrounded by an accretion disk represents a puzzling stage of their rotational evolution. While solar-mass stars are accreting and contracting, they do not seem to spin up substantially. Aims. It is usually assumed that the magnetospheric star-disk interaction tends to maintain the stellar rotation period constant (“disk-locking”), but this hypothesis has never been thoroughly verified. Our aim is to investigate the impact of the star-disk interaction mechanism on the stellar spin evolution during the accreting pre-main sequence phases. Methods. We devised a model for the torques acting on the stellar envelope based on studies of stellar winds, and we developed a new prescription for the star-disk coupling founded on numerical simulations of star-disk interaction and magnetospheric ejections. We then used this torque model to follow the long-term evolution of the stellar rotation. Results. Strong dipolar magnetic field components up to a few kG are required to extract enough angular momentum so as to keep the surface rotation rate of solar-type stars approximately constant for a few Myr. Furthermore an efficient enough spin-down torque can be provided by either one of the following: a stellar wind with a mass outflow rate corresponding to ≈10% of the accretion rate, or a lighter stellar wind combined with a disk that is truncated around the corotation radius entering a propeller regime. Conclusions. Magnetospheric ejections and accretion powered stellar winds play an important role in the spin evolution of solar-type stars. However, kG dipolar magnetic fields are neither uncommon or ubiquitous. Besides, it is unclear how massive stellar winds can be powered while numerical models of the propeller regime display a strong variability that has no observational confirmation. Better observational statistics and more realistic models could contribute to help lessen our calculations’ requirements.

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He, Han, Huaning Wang, Mei Zhang, Ahmad Mehrabi, Yan Yan, and Duo Yun. "Phase difference between long-term magnetic feature activity and flare activity of solar-type stars." Proceedings of the International Astronomical Union 13, S340 (February 2018): 217–20. http://dx.doi.org/10.1017/s1743921318000960.

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AbstractIn the light curves of some solar-type stars, both rotational modulation (caused by corotating bright or dark magnetic features) and flare phenomena can be seen simultaneously. Based on these light curve observations, the relation between stellar magnetic feature activity (reflected by the rotational modulation component of the light curves) and flare activity can be investigated. Here, we analyze the light curve data of a flare-abundant solar-type star, KIC 6034120, observed with Kepler space telescope, and describe magnetic feature activity property by fluctuation range of light curves and flare activity property by time occupation ratio of flares. Distinct phase difference between long-term magnetic feature activity and flare activity is found for this star, which indicates that the source regions of stellar flares (e.g., starspots) on this star do not dominate the rotational modulation of light curves, yet they might be related to a same stellar dynamo process.

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Barnes, Sydney, Sabatino Sofia, and Marc Pinsonneault. "Disk Locking and the Presence of Slow Rotators among Solar‐Type Stars in Young Star Clusters." Astrophysical Journal 548, no. 2 (February 20, 2001): 1071–80. http://dx.doi.org/10.1086/318988.

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Namekata, Kosuke, James R. A. Davenport, Brett M. Morris, Suzanne L. Hawley, Hiroyuki Maehara, Yuta Notsu, Shin Toriumi, et al. "Temporal Evolution of Spatially Resolved Individual Star Spots on a Planet-hosting Solar-type Star: Kepler-17." Astrophysical Journal 891, no. 2 (March 11, 2020): 103. http://dx.doi.org/10.3847/1538-4357/ab7384.

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27

Matloff, Gregory L., and John Pazmino. "Detecting Interstellar Migrations." International Astronomical Union Colloquium 161 (January 1997): 757–59. http://dx.doi.org/10.1017/s0252921100015360.

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AbstractInterstellar Migrations may occur when a civilization’s star enters the Red Giant phase, thereby dooming the life-bearing planet(s). Ecologically self-contained «world ships», massing billions of kilograms and propelled by hyperthin, space-manufactured solar sails thousands of kilometers in diameter unfurled near the home star are possible vehicles to transfer a threatened civilization to a neighboring star. Consideration of the nearest Red Giants reveals that Pollux is the nearest formerly solar-type Red Giant. Known stellar neighbors of Pollux are surveyed to determine likely directions for an interstellar migration departing Pollux. Such migrations might consist of many world ships launched over millenia on voyages of about 1000 terrestrial-year duration; discovery of such events will be serendipitous. The difficulties of observing solar-sail star ships near Pollux are considered. A facility dedicated to imaging extrasolar planets within 10 parsecs might be capable of detecting these large spacecraft.

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Roberts, Lewis C., Andrei Tokovinin, Brian D. Mason, and Anne D. Marinan. "Continued Kinematic and Photometric Investigations of Hierarchical Solar-type Multiple Star Systems." Astronomical Journal 153, no. 3 (February 7, 2017): 100. http://dx.doi.org/10.3847/1538-3881/153/3/100.

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Ayal, Shai, Mario Livio, and Tsvi Piran. "Tidal Disruption of a Solar‐Type Star by a Supermassive Black Hole." Astrophysical Journal 545, no. 2 (December 20, 2000): 772–80. http://dx.doi.org/10.1086/317835.

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Donahue, Robert A., and Sallie L. Baliunas. "Evidence of differential surface rotation in the solar-type star HD 114710." Astrophysical Journal 393 (July 1992): L63. http://dx.doi.org/10.1086/186452.

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Lefloch, Bertrand, C. Vastel, S. Viti, I. Jimenez-Serra, C. Codella, L. Podio, C. Ceccarelli, E. Mendoza, J. R. D. Lepine, and R. Bachiller. "Phosphorus-bearing molecules in solar-type star-forming regions: first PO detection." Monthly Notices of the Royal Astronomical Society 462, no. 4 (August 2, 2016): 3937–44. http://dx.doi.org/10.1093/mnras/stw1918.

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Lebreton, J., J. C. Augereau, W. F. Thi, A. Roberge, J. Donaldson, G. Schneider, S. T. Maddison, et al. "An icy Kuiper belt around the young solar-type star HD 181327." Astronomy & Astrophysics 539 (February 20, 2012): A17. http://dx.doi.org/10.1051/0004-6361/201117714.

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von Rekowski, B., and N. Piskunov. "Global 3-D solar-type star-disc dynamo systems: I. MHD modeling." Astronomische Nachrichten 327, no. 4 (May 2006): 340–54. http://dx.doi.org/10.1002/asna.200510526.

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Buccino, Andrea P., Mariela C. Vieytes, and Pablo J. D. Mauas. "A statistical analysis of Hα-Ca II relation for solar-type stars of different activity levels." Proceedings of the International Astronomical Union 7, S286 (October 2011): 324–27. http://dx.doi.org/10.1017/s1743921312005030.

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AbstractBased on our large spectral database obtained at CASLEO Argentinian Observatory, we analyzed the relation between simultaneous measurements of Hα and Ca ii H+K fluxes. Although the correlation between both proxies is positive for the solar case, in 2007 our group found that while some stars exhibit correlations between Hα and the Ca ii lines, the slopes change from star to star, including cases where no correlation was found. To discern if this flux-flux relation depends on the level of activity of the star and if it is associated with the distribution of active regions in the stellar atmosphere, in this work we analyze the relation between Hα-Ca ii fluxes for the whole set of 44 G dwarf stars and individually for a subset of several solar-type stars of different level of activity.

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Charbonneau, Paul, and Keith B. Macgregor. "Spin-Down of Solar-Type Stars with Internal Magnetic Fields." International Astronomical Union Colloquium 137 (1993): 464–68. http://dx.doi.org/10.1017/s0252921100018261.

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AbstractWe present a selection of results from a large set of numerical simulations of the spin-down of a solar-type star containing a large scale magnetic field in its radiative interior. Our computations are dynamical, in that they take into account both the generation of the toroidal component by the wind-induced shear endits back-reaction on the azimuthal flow. Our results demonstrate the existence of classes of internal magnetic fields that can accomodate rapid spin-down near the ZAMS, and yield weak internal differential rotation by the solar age.

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Nissen, P. E., J. Christensen-Dalsgaard, J. R. Mosumgaard, V. Silva Aguirre, E. Spitoni, and K. Verma. "High-precision abundances of elements in solar-type stars." Astronomy & Astrophysics 640 (August 2020): A81. http://dx.doi.org/10.1051/0004-6361/202038300.

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Aims. Previous high-precision studies of abundances of elements in solar twin stars are extended to a wider metallicity range to see how the trends of element ratios with stellar age depend on [Fe/H]. Methods. HARPS spectra with signal-to-noise ratios S/N ≳ 600 at λ ∼ 6000 Å were analysed with MARCS model atmospheres to obtain 1D LTE abundances of C, O, Na, Mg, Al, Si, Ca, Ti, Cr, Fe, Ni, Sr, and Y for 72 nearby solar-type stars with metallicities in the range of −0.3 ≲ [Fe/H] ≲ +0.3 and ASTEC stellar models were used to determine stellar ages from effective temperatures, luminosities obtained via Gaia DR2 parallaxes, and heavy element abundances. Results. The age-metallicity distribution appears to consist of the following two distinct populations: a sequence of old stars with a steep rise of [Fe/H] to ∼ + 0.3 dex at an age of ∼7 Gyr and a younger sequence with [Fe/H] increasing from about −0.3 dex to ∼ + 0.2 dex over the last 6 Gyr. Furthermore, the trends of several abundance ratios, [O/Fe], [Na/Fe], [Ca/Fe], and [Ni/Fe], as a function of stellar age, split into two corresponding sequences. The [Y/Mg]-age relation, on the other hand, shows no offset between the two age sequences and has no significant dependence on [Fe/H], but the components of a visual binary star, ζ Reticuli, have a large and puzzling deviation. Conclusions. The split of the age-metallicity distribution into two sequences may be interpreted as evidence of two episodes of accretion of gas onto the Galactic disk with a quenching of star formation in between. Some of the [X/Fe]-age relations support this scenario but other relations are not so easy to explain, which calls for a deeper study of systematic errors in the derived abundances as a function of [Fe/H], in particular 3D non-LTE effects.

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Flores, M., J. F. González, M. Jaque Arancibia, C. Saffe, A. Buccino, F. M. López, R. V. Ibañez Bustos, and P. Miquelarena. "HD 38858: a solar-type star with an activity cycle of ∼10.8 yr." Astronomy & Astrophysics 620 (November 27, 2018): A34. http://dx.doi.org/10.1051/0004-6361/201833330.

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Context. The detection of chromospheric activity cycles in solar-analogue and twin stars can be used to place the solar cycle in a wider context. However, relatively few of these stars with activity cycles have been detected. It is well known that the cores of the Ca II H&K lines are modulated by stellar activity. The behaviour of the Balmer and other optical lines with stellar activity is not yet completely understood. Aims. We search for variations in the Ca II H&K, Balmer, and Fe II lines modulated by stellar activity. In particular, we apply a novel strategy to detect possible shape variations in the Hα line. Methods. We analysed activity signatures in HD 38858 using HARPS and CASLEO spectra obtained between 2003 and 2017. We calculated the Mount Wilson index (SMW), log(R′HK), and the statistical moments of the Ca II H&K, Balmer, and other optical lines. We searched for periodicities using the generalized Lomb-Scargle periodogram. Results. We detect a long-term activity cycle of 10.8 yr in Ca II H&K and Hα in the solar-analogue star HD 38858. In contrast, this cycle is marginally detected in the Fe II lines. We also detect a noticeable variation in radial velocity that seems to be produced by stellar activity. Conclusions. HD 38858 is the second solar-analogue star where we find a clear activity cycle that is replicated in the Balmer lines. Spectral indexes based on the shape of Hα line seem to be more reliable than the fluxes in the same line for detecting activity variations. The cyclic modulation we detected gives place to a variation in radial velocity that previously has been associated with a super-Earth planet. Finally, due to the similarity of HD 38858 with the Sun, we recommend to continue monitoring this star.

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Bladh, S., K. Eriksson, P. Marigo, S. Liljegren, and B. Aringer. "Carbon star wind models at solar and sub-solar metallicities: a comparative study." Astronomy & Astrophysics 623 (March 2019): A119. http://dx.doi.org/10.1051/0004-6361/201834778.

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Context. The heavy mass loss observed in evolved stars on the asymptotic giant branch (AGB) is usually attributed to dust-driven winds, but it is still an open question how much AGB stars contribute to the dust production in the interstellar medium, especially at lower metallicities. In the case of C-type AGB stars, where the wind is thought to be driven by radiation pressure on amorphous carbon grains, there should be significant dust production even in metal-poor environments. Carbon stars can manufacture the building blocks needed to form the wind-driving dust species themselves, irrespective of the chemical composition they have, by dredging up carbon from the stellar interior during thermal pulses. Aims. We investigate how the mass loss in carbon stars is affected by a low-metallicity environment, similar to the Large and Small Magellanic Clouds (LMC and SMC). Methods. The atmospheres and winds of C-type AGB stars are modeled with the 1D spherically symmetric radiation-hydrodynamical code Dynamic Atmosphere and Radiation-driven Wind models based on Implicit Numerics (DARWIN). The models include a time-dependent description for nucleation, growth, and evaporation of amorphous carbon grains directly out of the gas phase. To explore the metallicity-dependence of mass loss we calculate model grids at three different chemical abundances (solar, LMC, and SMC). Since carbon may be dredged up during the thermal pulses as AGB stars evolve, we keep the carbon abundance as a free parameter. The models in these three different grids all have a current mass of one solar mass; effective temperatures of 2600, 2800, 3000, or 3200 K; and stellar luminosities equal to logL*∕L⊙ = 3.70, 3.85, or 4.00. Results. The DARWIN models show that mass loss in carbon stars is facilitated by high luminosities, low effective temperatures, and a high carbon excess (C–O) at both solar and subsolar metallicities. Similar combinations of effective temperature, luminosity, and carbon excess produce outflows at both solar and subsolar metallicities. There are no large systematic differences in the mass-loss rates and wind velocities produced by these wind models with respect to metallicity, nor any systematic difference concerning the distribution of grain sizes or how much carbon is condensed into dust. DARWIN models at subsolar metallicity have approximately 15% lower mass-loss rates compared to DARWIN models at solar metallicity with the same stellar parameters and carbon excess. For both solar and subsolar environments typical grain sizes range between 0.1 and 0.5 μm, the degree of condensed carbon varies between 5 and 40%, and the gas-to-dust ratios between 500 and 10 000. Conclusions. C-type AGB stars can contribute to the dust production at subsolar metallicities (down to at least [Fe∕H] = −1) as long as they dredge up sufficient amounts of carbon from the stellar interior. Furthermore, stellar evolution models can use the mass-loss rates calculated from DARWIN models at solar metallicity when modeling the AGB phase at subsolar metallicities if carbon excess is used as the critical abundance parameter instead of the C/O ratio.

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Mittag, M., J. H. M. M. Schmitt, T. S. Metcalfe, A. Hempelmann, and K. P. Schröder. "Magnetic activity of the solar-like star HD 140538." Astronomy & Astrophysics 628 (August 2019): A107. http://dx.doi.org/10.1051/0004-6361/201935654.

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The periods of rotation and activity cycles are among the most important properties of the magnetic dynamo thought to be operating in late-type, main-sequence stars. In this paper, we present a SMWO-index time series composed from different data sources for the solar-like star HD 140538 and derive a period of 3.88 ± 0.02 yr for its activity cycle. Furthermore, we analyse the high-cadence, seasonal SMWO data taken with the TIGRE telescope and find a rotational period of 20.71 ± 0.32 days. In addition, we estimate the stellar age of HD 140538 as 3.7 Gyrs via a matching evolutionary track. This is slightly older than the ages obtained from gyrochronology based on the above rotation period, as well as the activity-age relation. These results, together with its stellar parameters that are very similar to a younger Sun, make HD 140538 a relevant case study for our understanding of solar activity and its evolution with time.

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Raghavan, Deepak, H. A. McAlister, T. J. Henry, and B. D. Mason. "A Survey of Stellar Families: Multiplicity Among Solar-type Stars." Proceedings of the International Astronomical Union 2, S240 (August 2006): 254–57. http://dx.doi.org/10.1017/s1743921307004115.

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AbstractStellar multiplicity is a fundamental astrophysical property. In addition to being the only physical basis for accurate mass determination, this parameter is believed to influence important aspects such as planet formation and stability. Contrary to earlier expectations, recent studies have shown that even against selection biases, as many as 23% of the planetary systems reside in multiple star systems (Raghavan et al. 2006)). Leveraging recent efforts in identifying stellar and substellar companions to solar-type stars, and augmenting them with targeted observations, we are conducting a comprehensive survey, aimed at providing a modern update to the seminal work of Duquennoy & Mayor (1991). The details of our sample, survey methods, and some preliminary results are presented here.

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Kallinger, T. "MOST found evidence for solar-type oscillations in the K2 giant star HD20884." Communications in Asteroseismology 153 (2008): 84–102. http://dx.doi.org/10.1553/cia_153s84.

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Brown, Benjamin P., Mark S. Miesch, Matthew K. Browning, Allan Sacha Brun, and Juri Toomre. "MAGNETIC CYCLES IN A CONVECTIVE DYNAMO SIMULATION OF A YOUNG SOLAR-TYPE STAR." Astrophysical Journal 731, no. 1 (March 24, 2011): 69. http://dx.doi.org/10.1088/0004-637x/731/1/69.

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Kovács, G., G. Á. Bakos, J. D. Hartman, G. Torres, R. W. Noyes, D. W. Latham, A. W. Howard, et al. "HAT-P-15b: A 10.9 DAY EXTRASOLAR PLANET TRANSITING A SOLAR-TYPE STAR." Astrophysical Journal 724, no. 2 (November 9, 2010): 866–77. http://dx.doi.org/10.1088/0004-637x/724/2/866.

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Gillon, M., A. P. Doyle, M. Lendl, P. F. L. Maxted, A. H. M. J. Triaud, D. R. Anderson, S. C. C. Barros, et al. "WASP-50 b: a hot Jupiter transiting a moderately active solar-type star." Astronomy & Astrophysics 533 (September 2011): A88. http://dx.doi.org/10.1051/0004-6361/201117198.

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Buccino, A. P., L. Sraibman, P. M. Olivar, and F. O. Minotti. "An application of a solar-type dynamo model for ε Eridani." Monthly Notices of the Royal Astronomical Society 497, no. 3 (August 20, 2020): 3968–75. http://dx.doi.org/10.1093/mnras/staa1908.

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ABSTRACT During the last decade, the relation between activity cycle periods and stellar parameters has received special attention. The construction of reliable registries of activity reveals that solar-type stars exhibit activity cycles with periods from few years to decades and, in some cases, long and short activity cycles coexist suggesting that two dynamos could operate in these stars. In particular, ε Eridani is an active young K2V star (0.8 Gyr), which exhibits short and long-term chromospheric cycles of ∼3 and ∼13-yr periods. Additionally, between 1985 and 1992, the star went through a broad activity minimum, similar to the solar Maunder Minimum state. Motivated by these results, we found in ε Eridani a great opportunity to test the dynamo theory. Based on the model developed in Sraibman & Minotti, in this work we built a non-linear axisymmetric dynamo for ε Eridani. The time series of the simulated magnetic field components near the surface integrated in all the stellar disc exhibits both the long and short activity cycles with periods similar to the ones detected from observations and also time intervals of low activity that could be associated with the broad Minimum. The short activity cycle associated with the magnetic reversal could be explained by the differential rotation, while the long cycle is associated with the meridional mass flows induced by the Lorentz force. In this way, we show that a single non-linear dynamo model derived from first principles with accurate stellar parameters could reproduce coexisting activity cycles.

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Jiang, S. Y. "The history of KZ Hya and its unseen companions." Proceedings of the International Astronomical Union 4, S252 (April 2008): 421–22. http://dx.doi.org/10.1017/s1743921308023375.

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AbstractKZ Hya is a short-period high amplitude metal pool population II pulsating variable. Its spectral type is B9-A7 III/IV. Its average effective temperature is 7640K. But its mass is only 0.97 solar mass. From normal stellar evolution and H-R diagram, we can not get such a solar mass star at post main sequence stage with so high effective temperature and so early type spectra. We observe this star since 1984 till now, 23years past. Finally we prove it is inside a binary with at least 2 unseen companions. The most massive companion has mass larger than 0.76 solar mass, mostly may be 0.99 to 3.99 solar mass. That means this companion must be a massive white dwarf. The distance between tow companions is about 10 AU. If the companion is white dwarf, this binary are fairly inside the nebula. This system is very old, older than 7.59 billion years. The nebula should be already diluted to very low density so that we can see the nebula directly. As its spectra type is B9III/VI at some time of maximum light and the visual absolute magnitude is 2.78, about 2 magnitudes higher than our sun. We can image that at the end of AGB stage of the companion, the strong fast winds from hot central core push away the outer atmosphere of KZ Hya. Later KZ Hya absorbed a part of Helium rich material from the companion. This will cause hydrogen content X decrease from 0.75 to about 0.62. Then KZ Hya looks like a hot post main sequence star

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Rao, Suvrat, Camilla Pezzotti, Georges Meynet, Patrick Eggenberger, Gaël Buldgen, Christoph Mordasini, Vincent Bourrier, Sylvia Ekström, and Cyril Georgy. "Star-planet interactions." Astronomy & Astrophysics 651 (July 2021): A50. http://dx.doi.org/10.1051/0004-6361/202039965.

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Context. Tidal interactions and planetary evaporation processes impact the evolution of close-in star–planet systems. Aims. We study the impact of stellar rotation on these processes. Methods. We compute the time evolution of star–planet systems consisting of a planet with an initial mass between 0.02 and 2.5 MJup (6 and 800 MEarth) in a quasi-circular orbit with an initial orbital distance between 0.01 and 0.10 au, around a solar-type star evolving from the pre-main-sequence (PMS) phase until the end of the main-sequence phase. We account for the evolution of: the stellar structure, the stellar angular momentum due to tides and magnetic braking, the tidal interactions (equilibrium and dynamical tides in stellar convective zones), the mass evaporation of the planet, and the secular evolution of the planetary orbit. We consider that at the beginning of the evolution, the proto-planetary disk has fully dissipated and planet formation is complete. Results. We find that both a rapid initial stellar rotation and a more efficient angular momentum transport inside the star, in general, contribute to the enlargement of the domain that is devoid of planets after the PMS phase, in the plane of planet mass versus orbital distance. Comparisons with the observed distribution of exoplanets orbiting solar mass stars, in the plane of planet mass versus orbital distance (addressing the “Neptunian desert” feature), show an encouraging agreement with the present simulations, especially since no attempts have been made to fine-tune the initial parameters of the models to fit the observations. We also obtain an upper limit for the orbital period of bare-core planets that agrees with observations of the “radius valley” feature in the plane of planetary radius versus the orbital period. Conclusions. The two effects, namely, tides and planetary evaporation, should be accounted for simultaneously and in a consistent way, with a detailed model for the evolution of the star.

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Bertulani, C. A., M. Naizer, and W. Newton. "Stellar oscillations induced by the passage of a fast stellar object." International Journal of Modern Physics D 23, no. 10 (September 2014): 1450084. http://dx.doi.org/10.1142/s0218271814500849.

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In this paper, we investigate induced oscillations by the gravitational field of a fast stellar object, such as a neutron star or a black-hole in a near miss collision with another star. Nonadiabatic collision conditions may lead to large amplitude oscillations in the star. We show that for a solar-type star a resonant condition can be achieved by a fast moving stellar object with velocity in the range of 100 to 1000 km/s, passing at a distance of a few multiples of the star radius. Although such collisions are rare, they are more frequent than head-on collisions, and their effects could be observed through a visible change of the star luminosity occurring within a few hours.

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Eberle, J., M. Cuntz, B. Quarles, and Z. E. Musielak. "Case studies of habitable Trojan planets in the system of HD 23079." International Journal of Astrobiology 10, no. 4 (May 18, 2011): 325–34. http://dx.doi.org/10.1017/s1473550411000176.

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AbstractWe investigate the possibility of habitable Trojan planets in the HD 23079 star–planet system. This system consists of a solar-type star and a Jupiter-type planet, which orbits the star near the outer edge of the stellar habitable zone in an orbit of low eccentricity. We find that in agreement with previous studies Earth-mass habitable Trojan planets are possible in this system, although the success of staying within the zone of habitability is significantly affected by the orbital parameters of the giant planet and by the initial condition of the theoretical Earth-mass planet. In one of our simulations, the Earth-mass planet is captured by the giant planet and thus becomes a habitable moon.

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Marsden, Stephen, Pascal Petit, Sandra Jeffers, Jose-Dias do Nascimento, Bradley Carter, and Carolyn Brown. "A Bcool spectropolarimetric survey of over 150 solar-type stars." Proceedings of the International Astronomical Union 9, S302 (August 2013): 138–41. http://dx.doi.org/10.1017/s1743921314001896.

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AbstractAs part of the Bcool project, over 150 solar-type stars chosen mainly from planet search databases have been observed between 2006 and 2013 using the NARVAL and ESPaDOnS spectropolarimeters on the Telescope Bernard Lyot (Pic du Midi, France) and the Canada France Hawaii Telescope (Mauna Kea, USA), respectively. These single “snapshot” observations have been used to detect the presence of magnetic fields on 40% of our sample, with the highest detection rates occurring for the youngest stars. From our observations we have determined the mean surface longitudinal field (or an upper limit for stars without detections) and the chromospheric surface fluxes, and find that the upper envelope of the absolute value of the mean surface longitudinal field is directly correlated to the chromospheric emission from the star and increases with rotation rate and decreases with age.

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Journal articles on the topic 'Solar-type star'

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