Browsing by Subject "spectral classification"
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Item The Kepler Characterization Of The Variability Among A- And F-Type Stars I. General Overview(2011-10) Uytterhoeven, K.; Moya, A.; Grigahcene, A.; Guzik, J. A.; Gutierrez-Soto, J.; Smalley, B.; Handler, G.; Balona, L. A.; Niemczura, E.; Machado, L. F.; Benatti, S.; Chapellier, E.; Tkachenko, A.; Szabo, R.; Suarez, J. C.; Ripepi, V.; Pascual, J.; Mathias, P.; Martin-Ruiz, S.; Lehmann, H.; Jackiewicz, J.; Hekker, S.; Gruberbauer, M.; Garcia, R. A.; Dumusque, X.; Diaz-Fraile, D.; Bradley, P.; Antoci, V.; Roth, M.; Leroy, B.; Murphy, S. J.; De Cat, P.; Cuypers, J.; Kjeldsen, H.; Christensen-Dalsgaard, J.; Breger, M.; Pigulski, A.; Kiss, L. L.; Still, M.; Thompson, S. E.; Van Cleve, J.; Breger, MContext. The Kepler spacecraft is providing time series of photometric data with micromagnitude precision for hundreds of A-F type stars. Aims. We present a first general characterization of the pulsational behaviour of A-F type stars as observed in the Kepler light curves of a sample of 750 candidate A-F type stars, and observationally investigate the relation between gamma Doradus (gamma Dor), delta Scuti (delta Sct), and hybrid stars. Methods. We compile a database of physical parameters for the sample stars from the literature and new ground-based observations. We analyse the Kepler light curve of each star and extract the pulsational frequencies using different frequency analysis methods. We construct two new observables, >energy> and >efficiency>, related to the driving energy of the pulsation mode and the convective efficiency of the outer convective zone, respectively. Results. We propose three main groups to describe the observed variety in pulsating A-F type stars: gamma Dor, delta Sct, and hybrid stars. We assign 63% of our sample to one of the three groups, and identify the remaining part as rotationally modulated/active stars, binaries, stars of different spectral type, or stars that show no clear periodic variability. 23% of the stars (171 stars) are hybrid stars, which is a much higher fraction than what has been observed before. We characterize for the first time a large number of A-F type stars (475 stars) in terms of number of detected frequencies, frequency range, and typical pulsation amplitudes. The majority of hybrid stars show frequencies with all kinds of periodicities within the gamma Dor and delta Sct range, also between 5 and 10 d(-1), which is a challenge for the current models. We find indications for the existence of delta Sct and gamma Dor stars beyond the edges of the current observational instability strips. The hybrid stars occupy the entire region within the delta Sct and gamma Dor instability strips and beyond. Non-variable stars seem to exist within the instability strips. The location of gamma Dor and delta Sct classes in the (T-eff, log g)-diagram has been extended. We investigate two newly constructed variables, >efficiency> and >energy>, as a means to explore the relation between gamma Dor and delta Sct stars. Conclusions. Our results suggest a revision of the current observational instability strips of delta Sct and gamma Dor stars and imply an investigation of pulsation mechanisms to supplement the kappa mechanism and convective blocking effect to drive hybrid pulsations. Accurate physical parameters for all stars are needed to confirm these findings.Item The Mass-Luminosity Relation In The L/T Transition: Individual Dynamical Masses For The New J-Band Flux Reversal Binary SDSS J105213.51+442255.7Ab(2015-05) Dupuy, Trent J.; Liu, Michael C.; Leggett, S. K.; Ireland, Michael J.; Chiu, Kuenley; Golimowski, David A.; Dupuy, Trent J.We have discovered that SDSS J105213.51+442255.7 (T0.5 +/- 1.0) is a binary in Keck laser guide star adaptive optics imaging, displaying a large J- to K-band flux reversal (Delta J = -0.45 +/- 0.09 mag, Delta K= 0.52 +/- 0.05 mag). We determine a total dynamical mass from Keck orbital monitoring (88 +/- 5 M-Jup) and a mass ratio by measuring the photocenter orbit from CFHT/WIRCam absolute astrometry (M-B/M-A= 0.78 +/- 0.07). Combining these provides the first individual dynamical masses for any field L or T dwarfs, 49 +/- 3 M-Jup for the L6.5 +/- 1.5 primary and 39 +/- 3 M-Jup for the T1.5 +/- 1.0 secondary. Such a low mass ratio for a nearly equal luminosity binary implies a shallow mass-luminosity relation over the L/T transition (Delta log L-bol/Delta log M = 0.6(-0.8)(+0.6)). This provides the first observational support that cloud dispersal plays a significant role in the luminosity evolution of substellar objects. Fully cloudy models fail our coevality test for this binary, giving ages for the two components that disagree by 0.2 dex (2.0 sigma). In contrast, our observed masses and luminosities can be reproduced at a single age by "hybrid" evolutionary tracks where a smooth change from a cloudy to cloudless photosphere around 1300 K causes slowing of luminosity evolution. Remarkably, such models also match our observed JHK flux ratios and colors well. Overall, it seems that the distinguishing features SDSS J1052+ 4422AB, like a J-band flux reversal and high-amplitude variability, are normal for a field L/T binary caught during the process of cloud dispersal, given that the age (1.11(-0.20)(+0.17) Gyr) and surface gravity (log g = 5.0-5.2) of SDSS J1052+ 4422AB are typical for field ultracool dwarfs.Item New Precision Orbits Of Bright Double-Lined Spectroscopic Binaries. III. HD 82191, Omega Draconis, And 108 Herculis(2009-04) Fekel, Francis C.; Tomkin, Jocelyn; Williamson, Michael H.; Fekel, Francis C.; Tomkin, Jocelyn; Williamson, Michael H.We have determined improved spectroscopic orbits for three double-lined binaries, HD 82191 (Am), omega Dra (F5 V), and 108 Her (Am), using radial velocities from the 2.1 m telescope at McDonald Observatory, the coude feed telescope at Kitt Peak National Observatory, and 2 m telescope at Fairborn Observatory. The orbital periods range from 5.28 to 9.01 days, and all three systems have circular orbits. The new orbital dimensions (a(1) sin i and a(2) sin i) and minimum masses (m(1) sin(3) i and m(2) sin(3) i) have accuracies of 0.2% or better. Our improved results confirm the large minimum masses of HD 82191 and also agree with the values previously found for. Dra. However, for the components of 108 Her our minimum masses are about 20% larger than the previous best values. We conclude that both components of HD 82191 as well as the primary of 108 Her are Am stars. However, the A9 secondary of 108 Her has normal abundances. We estimate spectral types of F4 dwarf and G0 dwarf for the components of. Dra. The primaries of the three binaries are synchronously rotating as is the secondary of 108 Her. The secondaries of HD 82191 and omega Dra are possibly synchronously rotating.Item New Precision Orbits Of Bright Double-Lined Spectroscopic Binaries. IX. HD 54371, HR 2692, And 16 Ursa Majoris(2015-02) Fekel, Francis C.; Williamson, Michael H.; Muterspaugh, Matthew W.; Pourbaix, Dimitri; Willmarth, Daryl; Tomkin, Jocelyn; Tomkin, JocelynWith extensive sets of new radial velocities we have determined orbital elements for three previously known spectroscopic binaries, HD 54371, HR 2692, and 16 UMa. All three systems have had the lines of their secondaries detected for the first time. The orbital periods range from 16.24 to 113.23 days, and the three binaries have modestly or moderately eccentric orbits. The secondary to primary mass ratios range from 0.50 to 0.64. The orbital dimensions (a(1) sin i and a(2) sin i) and minimum masses (m(1) sin(3) i and m(2) sin(3) i) of the binary components all have accuracies of <= 1%. With our spectroscopic results and the Hipparcos data, we also have determined astrometric orbits for two of the three systems, HR 2692 and 16 UMa. The primaries of HD 54371 and 16 UMa are solar-type stars, and their secondaries are likely K or M dwarfs. The primary of HR 2692 is a late-type subgiant and its secondary is a G or K dwarf. The primaries of both HR 2692 and 16 UMa may be pseudosynchronously rotating, while that of HD 54371 is rotating faster than its pseudosynchronous velocity.Item New Precision Orbits Of Bright Double-Lined Spectroscopic Binaries. VIII. HR 1528, HR 6993, 2 Sagittae, And 18 Vulpeculae(2013-11) Fekel, Francis C.; Tomkin, Jocelyn; Williamson, Michael H.; Tomkin, JocelynImproved orbital elements for four A-star double-lined spectroscopic binaries have been determined with numerous new radial velocities. Three of the four systems, HR 1528, 2 Sge, and 18 Vul, have moderately short orbital periods of 7.05, 7.39, and 9.31 days, respectively, and also have circular or nearly circular orbits. Only HR 6993 with a period of 14.68 days has a significantly eccentric orbit. The close visual companion of 2 Sge has been detected spectroscopically, and its velocity measured. The orbital dimensions (a(1) sin i and a(2) sin i) and minimum masses (m(1) sin(3) i and m(2) sin(3) i) of the short-period binary components all have accuracies of 0.5% or better. We determine basic properties of the individual stars and compare them with solar-abundance evolutionary tracks to estimate their masses. Half of the eight components may be synchronously or pseudosynchronously rotating.Item New Precision Orbits Of Bright Double-Lined Spectroscopic Binaries. VIII. HR 1528, HR 6993, 2 Sagittae, And 18 Vulpeculae(2013-11) Fekel, Francis C.; Tomkin, Jocelyn; Williamson, Michael H.; Tomkin, JocelynImproved orbital elements for four A-star double-lined spectroscopic binaries have been determined with numerous new radial velocities. Three of the four systems, HR 1528, 2 Sge, and 18 Vul, have moderately short orbital periods of 7.05, 7.39, and 9.31 days, respectively, and also have circular or nearly circular orbits. Only HR 6993 with a period of 14.68 days has a significantly eccentric orbit. The close visual companion of 2 Sge has been detected spectroscopically, and its velocity measured. The orbital dimensions (a(1) sin i and a(2) sin i) and minimum masses (m(1) sin(3) i and m(2) sin(3) i) of the short-period binary components all have accuracies of 0.5% or better. We determine basic properties of the individual stars and compare them with solar-abundance evolutionary tracks to estimate their masses. Half of the eight components may be synchronously or pseudosynchronously rotating.Item Overview Of The SDSS-IV Manga Survey: Mapping Nearby Galaxies At Apache Point Observatory(2015-01) Bundy, Kevin; Bershady, Matthew A.; Law, David R.; Yan, Renbin; Drory, Niv; MacDonald, Nicholas; Wake, David A.; Cherinka, Brian; Sanchez-Gallego, Jose R.; Weijmans, Anne-Marie; Thomas, Daniel; Tremonti, Christy; Masters, Karen; Coccato, Lodovico; Diamond-Stanic, Aleksandar M.; Aragon-Salamanca, Alfonso; Avila-Reese, Vladimir; Badenes, Carles; Falcon-Barroso, Jesus; Belfiore, Francesco; Bizyaev, Dmitry; Blanc, Guillermo A.; Bland-Hawthorn, Joss; Blanton, Michael R.; Brownstein, Joel R.; Byler, Nell; Cappellari, Michele; Conroy, Charlie; Dutton, Aaron A.; Emsellem, Eric; Etherington, James; Frinchaboy, Peter M.; Fu, Hai; Gunn, James E.; Harding, Paul; Johnston, Evelyn J.; Kauffmann, Guinevere; Kinemuchi, Karen; Klaene, Mark A.; Knapen, Johan H.; Leauthaud, Alexie; Li, Cheng; Lin, Lihwai; Maiolino, Roberto; Malanushenko, Viktor; Malanushenko, Elena; Mao, Shude; Maraston, Claudia; McDermid, Richard M.; Merrifield, Michael R.; Nichol, Robert C.; Oravetz, Daniel; Pan, Kaike; Parejko, John K.; Sanchez, Sebastian F.; Schlegel, David; Simmons, Audrey; Steele, Oliver; Steinmetz, Matthias; Thanjavur, Karun; Thompson, Benjamin A.; Tinker, Jeremy L.; van den Bosch, Remco C. E.; Westfall, Kyle B.; Wilkinson, David; Wright, Shelley; Xiao, Ting; Zhang, Kai; Drory, NivWe present an overview of a new integral field spectroscopic survey called MaNGA (Mapping Nearby Galaxies at Apache Point Observatory), one of three core programs in the fourth-generation Sloan Digital Sky Survey (SDSS-IV) that began on 2014 July 1. MaNGA will investigate the internal kinematic structure and composition of gas and stars in an unprecedented sample of 10,000 nearby galaxies. We summarize essential characteristics of the instrument and survey design in the context of MaNGA's key science goals and present prototype observations to demonstrate MaNGA's scientific potential. MaNGA employs dithered observations with 17 fiber-bundle integral field units that vary in diameter from 12 '' (19 fibers) to 32 '' (127 fibers). Two dual-channel spectrographs provide simultaneous wavelength coverage over 3600-10300 angstrom at R similar to 2000. With a typical integration time of 3 hr, MaNGA reaches a target r-band signal-to-noise ratio of 4-8 (angstrom(-1) per 2 '' fiber) at 23 AB mag arcsec(-2), which is typical for the outskirts of MaNGA galaxies. Targets are selected with M* greater than or similar to 10(9) M-circle dot using SDSS-I redshifts and i-band luminosity to achieve uniform radial coverage in terms of the effective radius, an approximately flat distribution in stellar mass, and a sample spanning a wide range of environments. Analysis of our prototype observations demonstrates MaNGA's ability to probe gas ionization, shed light on recent star formation and quenching, enable dynamical modeling, decompose constituent components, and map the composition of stellar populations. MaNGA's spatially resolved spectra will enable an unprecedented study of the astrophysics of nearby galaxies in the coming 6 yr.Item The Ultracool-Field Dwarf Luminosity-Function And Space Density From The Canada-France Brown Dwarf Survey(2010-11) Reyle, C.; Delorme, P.; Willott, C. J.; Albert, L.; Delfosse, X.; Forveille, T.; Artigau, E.; Malo, L.; Hill, G. J.; Doyon, R.; Hill, G. J.Context. Thanks to recent and ongoing large scale surveys, hundreds of brown dwarfs have been discovered in the last decade. The Canada-France Brown Dwarf Survey is a wide-field survey for cool brown dwarfs conducted with the MegaCam camera on the Canada-France-Hawaii Telescope. Aims. Our objectives are to find ultracool brown dwarfs and to constrain the field brown-dwarf luminosity function and the mass function from a large and homogeneous sample of L and T dwarfs. Methods. We identify candidates in CFHT/MegaCam i' and z' images and follow them up with pointed near infrared (NIR) imaging on several telescopes. Halfway through our survey we found similar to 50 T dwarfs and similar to 170 L or ultra cool M dwarfs drawn from a larger sample of 1400 candidates with typical ultracool dwarfs i' - z' colours, found in 780 square degrees. Results. We have currently completed the NIR follow-up on a large part of the survey for all candidates from mid-L dwarfs down to the latest T dwarfs known with utracool dwarfs' colours. This allows us to draw on a complete and well defined sample of 102 ultracool dwarfs to investigate the luminosity function and space density of field dwarfs. Conclusions. We found the density of late L5 to T0 dwarfs to be 2.0(0.7)(+0.8) x 10(-3) objects pc(-3), the density of T0.5 to T5.5 dwarfs to be 1.4(-0.2)(+0.3) x 10(-3) objects pc(-3), and the density of T6 to T8 dwarfs to be 5.3(-2.2)(+3.1) x 10(-3) objects pc(-3). We found that these results agree better with a flat substellar mass function. Three latest dwarfs at the boundary between T and Y dwarfs give the high density 8.3(5.1)(+9.0) x 10(-3) objects pc(-3). Although the uncertainties are very large this suggests that many brown dwarfs should be found in this late spectral type range, as expected from the cooling of brown dwarfs, whatever their mass, down to very low temperature.