Browsing by Subject "stars: fundamental parameters"
Now showing 1 - 20 of 42
- Results Per Page
- Sort Options
Item The Apokasc Catalog: An Asteroseismic and Spectroscopic Joint Survey of Targets in the Kepler Fields(2014-12) Nidever, David L.; Zasowski, Gail; Majewski, Steven R.; Bird, Jonathan; Robin, Annie C.; Martinez-Valpuesta, Inma; Beaton, Rachael L.; Schoenrich, Ralph; Schultheis, Mathias; Wilson, John C.; Skrutskie, Michael F.; O'Connell, Robert W.; Shetrone, Matthew; Schiavon, Ricardo P.; Johnson, Jennifer A.; Weiner, Benjamin; Gerhard, Ortwin; Schneider, Donald P.; Prieto, Carlos Allende; Sellgren, Kris; Bizyaev, Dmitry; Brewington, Howard; Brinkmann, Jon; Eisenstein, Daniel J.; Frinchaboy, Peter M.; Perez, Ana Elia Garcia; Holtzman, Jon; Hearty, Fred R.; Malanushenko, Elena; Malanushenko, Viktor; Muna, Demitri; Oravetz, Daniel; Pan, Kaike; Simmons, Audrey; Snedden, Stephanie; Weaver, Benjamin A.; Shetrone, MatthewWe present the first APOKASC catalog of spectroscopic and asteroseismic properties of 1916 red giants observed in the Kepler fields. The spectroscopic parameters provided from the Apache Point Observatory Galactic Evolution Experiment project are complemented with asteroseismic surface gravities, masses, radii, and mean densities determined by members of the Kepler Asteroseismology Science Consortium. We assess both random and systematic sources of error and include a discussion of sample selection for giants in the Kepler fields. Total uncertainties in the main catalog properties are of the order of 80 K in Teff, 0.06 dex in [M/ H], 0.014 dex in log g, and 12% and 5% in mass and radius, respectively; these reflect a combination of systematic and random errors. Asteroseismic surface gravities are substantially more precise and accurate than spectroscopic ones, and we find good agreement between their mean values and the calibrated spectroscopic surface gravities. There are, however, systematic underlying trends with Teff and log g. Our effective temperature scale is between 0 and 200 K cooler than that expected from the infrared flux method, depending on the adopted extinction map, which provides evidence for a lower value on average than that inferred for the Kepler Input Catalog (KIC). We find a reasonable correspondence between the photometric KIC and spectroscopic APOKASC metallicity scales, with increased dispersion in KIC metallicities as the absolute metal abundance decreases, and offsets in T-eff and log g consistent with those derived in the literature. We present mean fitting relations between APOKASC and KIC observables and discuss future prospects, strengths, and limitations of the catalog data.Item Calibrating The Cepheid Period-Luminosity Relation From The Infrared Surface Brightness Technique I. The P-Factor, The Milky Way Relations, And A Universal K-Band Relation(2011-10) Storm, Jesper; Gieren, Wolfgang; Fouque, Pascal; Barnes, Thomas G.; Pietrzynski, G.; Nardetto, Nicolas; Weber, M.; Granzer, T.; Strassmeier, K. G.; Barnes, Thomas G.; Nicolas NardettoAims. We determine period-luminosity relations for Milky Way Cepheids in the optical and near-IR bands. These relations can be used directly as reference for extra-galactic distance determination to Cepheid populations with solar metallicity, and they form the basis for a direct comparison with relations obtained in exactly the same manner for stars in the Magellanic Clouds, presented in an accompanying paper. In that paper we show that the metallicity effect is very small and consistent with a null effect, particularly in the near-IR bands, and we combine here all 111 Cepheids from the Milky Way, the LMC and SMC to form a best relation. Methods. We employ the near-IR surface brightness (IRSB) method to determine direct distances to the individual Cepheids after we have recalibrated the projection factor using the recent parallax measurements to ten Galactic Cepheids and the constraint that Cepheid distances to the LMC should be independent of pulsation period. Results. We confirm our earlier finding that the projection factor for converting radial velocity to pulsational velocity depends quite steeply on pulsation period, p = 1.550-0.186 log(P) in disagrement with recent theoretical predictions. We find PL relations based on 70 MilkyWay fundamental mode Cepheids of M(K) = -3.33(+/- 0.09)(log(P)-1.0)-5.66(+/- 0.03), W(VI) = -3.26(+/- 0.11)(log(P)-1.0)-5.96(+/- 0.04). Combining the 70 Cepheids presented here with the results for 41 Magellanic Cloud Cepheids which are presented in an accompanying paper, we find M(K) = -3.30(+/- 0.06)(log(P) - 1.0) - 5.65(+/- 0.02), W(VI) = -3.32(+/- 0.08)(log(P) - 1.0) - 5.92(+/- 0.03). Conclusions. We delineate the Cepheid PL relation using 111 Cepheids with direct distances from the IRSB analysis. The relations are by construction in agreement with the recent HST parallax distances to Cepheids and slopes are in excellent agreement with the slopes of apparent magnitudes versus period observed in the LMC.Item Calibrating The Cepheid Period-Luminosity Relation From The Infrared Surface Brightness Technique II. The Effect Of Metallicity And The Distance To The LMC(2011-10) Storm, Jesper; Gieren, Wolfgang; Fouque, Pascal; Barnes, Thomas G.; Soszynski, I.; Pietrzynski, G.; Nardetto, Nicolas; Queloz, D.; Barnes, Thomas G.; Nicolas NardettoContext. The extragalactic distance scale builds directly on the Cepheid period-luminosity (PL) relation as delineated by the sample of Cepheids in the Large Magellanic Cloud (LMC). However, the LMC is a dwarf irregular galaxy, quite different from the massive spiral galaxies used for calibrating the extragalactic distance scale. Recent investigations suggest that not only the zero-point but also the slope of the Milky Way PL relation differ significantly from that of the LMC, casting doubts on the universality of the Cepheid PL relation. Aims. We want to make a differential comparison of the PL relations in the two galaxies by delineating the PL relations using the same method, the infrared surface brightness method (IRSB), and the same precepts. We furthermore extend the metallicity baseline for investigating the zero-point dependence, by applying the method to five SMC Cepheids as well. Methods. The IRSB method is a Baade-Wesselink type method to determine individual distances to Cepheids. We apply a newly revised calibration of the method as described in an accompanying paper (Paper I) to 36 LMC and five SMC Cepheids and delineate new PL relations in the V, I, J, & K bands as well as in the Wesenheit indices in the optical and near-IR. Results. We present 509 new and accurate radial velocity measurements for a sample of 22 LMC Cepheids, enlarging our earlier sample of 14 stars to include 36 LMC Cepheids. The new calibration of the IRSB method is directly tied to the recent HST parallax measurements to ten MilkyWay Cepheids, and we find a LMC barycenter distance modulus of 18.45 +/- 0.04 (random error only) from the 36 individual LMC Cepheid distances. In the J, K bands we find identical slopes for the LMC and Milky Way PL relations and only a weak letallicity effect on the zero points (consistent with a zero effect), metal poor stars being fainter. In the optical we find the Milky Way slopes are slightly shallower than the LMC slopes (but again consistent with no difference in the slopes) and small effects on the zero points. However, the important Wesenheit index in V, (V - I) shows a metallicity effect on the slope and on the zero point which is likely to be significant. Conclusions. We find a significant metallicity effect on the W-VI index gamma(W-VI) = -0.23 +/- 0.10 mag dex(-1) as well as an effect on the slope. The K-band PL relation on the other hand is found to be an excellent extragalactic standard candle being metallicity insensitive in both slope and zero-point and at the same time being reddening insensitive and showing the least internal dispersion.Item Calibrations Of Atmospheric Parameters Obtained From The First Year Of Sdss-III APOGEE Observations(2013-11) Meszaros, S.; Holtzman, J.; Perez, A. E. Garcia; Prieto, C. Allende; Schiavon, R. P.; Basu, S.; Bizyaev, D.; Chaplin, W. J.; Chojnowski, S. D.; Cunha, K.; Elsworth, Y.; Epstein, C.; Frinchaboy, P. M.; Garcia, R. A.; Hearty, F. R.; Hekker, S.; Johnson, J. A.; Kallinger, T.; Koesterke, L.; Majewski, S. R.; Martell, S. L.; Nidever, D.; Pinsonneault, M. H.; O'Connell, J.; Shetrone, M.; Smith, V. V.; Wilson, J. C.; Zasowski, G.; Koesterke, L.The Sloan Digital Sky Survey III (SDSS-III) Apache Point Observatory Galactic Evolution Experiment (APOGEE) is a three-year survey that is collecting 105 high-resolution spectra in the near-IR across multiple Galactic populations. To derive stellar parameters and chemical compositions from this massive data set, the APOGEE Stellar Parameters and Chemical Abundances Pipeline (ASPCAP) has been developed. Here, we describe empirical calibrations of stellar parameters presented in the first SDSS-III APOGEE data release (DR10). These calibrations were enabled by observations of 559 stars in 20 globular and open clusters. The cluster observations were supplemented by observations of stars in NASA's Kepler field that have well determined surface gravities from asteroseismic analysis. We discuss the accuracy and precision of the derived stellar parameters, considering especially effective temperature, surface gravity, and metallicity; we also briefly discuss the derived results for the abundances of the a-elements, carbon, and nitrogen. Overall, we find that ASPCAP achieves reasonably accurate results for temperature and metallicity, but suffers from systematic errors in surface gravity. We derive calibration relations that bring the raw ASPCAP results into better agreement with independently determined stellar parameters. The internal scatter of ASPCAP parameters within clusters suggests that metallicities are measured with a precision better than 0.1 dex, effective temperatures better than 150 K, and surface gravities better than 0.2 dex. The understanding provided by the clusters and Kepler giants on the current accuracy and precision will be invaluable for future improvements of the pipeline.Item Characterizing The Cool KOIs. VII. Refined Physical Properties Of The Transiting Brown Dwarf LHS 6343 C(2015-02) Montet, Benjamin T.; Johnson, John A.; Muirhead, Phillip S.; Villar, Ashley; Vassallo, Corinne; Baranec, Christoph; Law, Nicholas M.; Riddle, Reed; Marcy, Geoffrey W.; Howard, Andrew W.; Isaacson, Howard; Vassallo, CorinneWe present an updated analysis of LHS 6343, a triple system in the Kepler field which consists of a brown dwarf transiting one member of a widely separated M+M binary system. By analyzing the full Kepler data set and 34 Keck/HIgh Resolution Echelle Spectrometer radial velocity observations, we measure both the observed transit depth and Doppler semiamplitude to 0.5% precision. With Robo-AO and Palomar/PHARO adaptive optics imaging as well as TripleSpec spectroscopy, we measure a model-dependent mass for LHS 6343 C of 62.1 +/- 1.2 M-Jup and a radius of 0.783 +/- 0.011 R-Jup. We detect the secondary eclipse in the Kepler data at 3.5 sigma, measuring e cos omega = 0.0228 +/- 0.0008. We also derive a method to measure the mass and radius of a star and transiting companion directly, without any direct reliance on stellar models. The mass and radius of both objects depend only on the orbital period, stellar density, reduced semimajor axis, Doppler semiamplitude, eccentricity, and inclination, as well as the knowledge that the primary star falls on the main sequence. With this method, we calculate a mass and radius for LHS 6343 C to a precision of 3% and 2%, respectively.Item Chemical Signatures Of Planets: Beyond Solar-Twins(2014-01) Ramirez, I.; Melendez, J.; Asplund, M.; Ramirez, I.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 similar to 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 more likely explanation of our observations. More rocky material is necessary to explain the data of solar twins than metal-rich stars, and less for warm stars. However, the sizes of the stars' convective envelopes at the time of planet formation could be regulating these amplitudes. Our results could be explained if disk lifetimes were shorter in more massive stars, as independent observations indeed seem to suggest. Nevertheless, to reach stronger conclusions we will need a detailed knowledge of extrasolar planetary systems down to at least one Earth mass around a significant number of stars.Item Discovery And Rossiter-Mclaughlin Effect Of Exoplanet Kepler-8B(2010-12) Jenkins, Jon M.; Borucki, William J.; Koch, David G.; Marcy, Geoffrey W.; Cochran, William D.; Welsh, William F.; Basri, Gibor; Batalha, Natalie M.; Buchhave, Lars A.; Brown, Timothy M.; Caldwell, Douglas A.; Dunham, Edward W.; Endl, Michael; Fischer, Debra A.; Gautier, Thomas N., III; Geary, John C.; Gilliland, Ronald L.; Howell, Steve B.; Isaacson, Howard; Johnson, John Asher; Latham, David W.; Lissauer, Jack J.; Monet, David G.; Rowe, Jason F.; Sasselov, Dimitar D.; Howard, Andrew W.; MacQueen, Phillip; Orosz, Jerome A.; Chandrasekaran, Hema; Twicken, Joseph D.; Bryson, Stephen T.; Quintana, Elisa V.; Clarke, Bruce D.; Li, Jie; Allen, Christopher; Tenenbaum, Peter; Wu, Hayley; Meibom, Soren; Klaus, Todd C.; Middour, Christopher K.; Cote, Miles T.; McCauliff, Sean; Girouard, Forrest R.; Gunter, Jay P.; Wohler, Bill; Hall, Jennifer R.; Ibrahim, Khadeejah; Uddin, A. K. M. Kamal; Wu, Michael S.; Bhavsar, Paresh A.; Van Cleve, Jeffrey; Pletcher, David L.; Dotson, Jessie L.; Haas, Michael R.; Cochran, William; Endl, Michael; MacQueen, PhillipWe report on the discovery and the Rossiter-McLaughlin (R-M) effect of Kepler-8b, a transiting planet identified by the NASA Kepler Mission. Kepler photometry and Keck-HIRES radial velocities yield the radius and mass of the planet around this F8IV subgiant host star. The planet has a radius R(P) = 1.419 R(J) and a mass M(P) = 0.60 M(J), yielding a density of 0.26 g cm(-3), one of the lowest planetary densities known. The orbital period is P = 3.523 days and the orbital semimajor axis is 0.0483(-0.0012)(+0.0006) AU. The star has a large rotational v sin i of 10.5 +/- 0.7 kms(-1) and is relatively faint (V approximate to 13.89 mag); both properties are deleterious to precise Doppler measurements. The velocities are indeed noisy, with scatter of 30 ms(-1), but exhibit a period and phase that are consistent with those implied by transit photometry. We securely detect the R-M effect, confirming the planet's existence and establishing its orbit as prograde. We measure an inclination between the projected planetary orbital axis and the projected stellar rotation axis of lambda = -26 degrees.4 +/- 10 degrees.1, indicating a significant inclination of the planetary orbit. R-M measurements of a large sample of transiting planets from Kepler will provide a statistically robust measure of the true distribution of spin-orbit orientations for hot Jupiters around F and early G stars.Item Discovery Of Binarity, Spectroscopic Frequency Analysis, And Mode Identification Of The Delta Scuti Star 4 CVn(2014-10) Schmid, V. S.; Themessl, N.; Breger, M.; Degroote, P.; Aerts, C.; Beck, P. G.; Tkachenko, A.; Van Reeth, T.; Bloemen, S.; Debosscher, J.; Castanheira, B. G.; McArthur, B. E.; Papics, P. I.; Fritz, V.; Falcon, R. E.; Castanheira, B. G.; McArthur, B. E.; Falcon, R. E.More than 40 years of ground-based photometric observations of the delta Sct star 4 CVn has revealed 18 independent oscillation frequencies, including radial as well as non-radial p-modes of low spherical degree l <= 2. From 2008 to 2011, more than 2000 spectra were obtained at the 2.1m Otto-Struve telescope at the McDonald Observatory. We present the analysis of the line-profile variations, based on the Fourier-parameter fit method, detected in the absorption lines of 4 CVn, which carry clear signatures of the pulsations. From a non-sinusoidal, periodic variation of the radial velocities, we discover that 4 CVn is an eccentric binary system with an orbital period P-orb = 124.44 +/- 0.03 d and an eccentricity e = 0.311 +/- 0.003. We detect 20 oscillation frequencies, 9 of which previously unseen in photometric data; attempt mode identification for the two dominant modes, f(1) = 7.3764 d(-1) and f(2) = 5.8496 d(-1); and determine the prograde or retrograde nature of 7 of the modes. The projected rotational velocity of the star, v(eq) sin i similar or equal to 106.7 km s(-1), translates to a rotation rate of v(eq)/v(crit) >= 33%. This relatively high rotation rate hampers unique mode identification, since higher order effects of rotation are not included in the current methodology. We conclude that, in order to achieve unambiguous mode identification for 4CVn, a complete description of rotation and the use of blended lines have to be included in mode-identification techniques.Item Dynamical Masses of Young M Dwarfs: Masses and Orbital Parameters of GJ 3305 AB, the Wide Binary Companion To the Imaged Exoplanet Host 51 Eri(2015-11) Montet, Benjamin T.; Bowler, Brendan P.; Shkolnik, Evgenya L.; Deck, Katherine M.; Wang, Ji; Horch, Elliott P.; Liu, Michael C.; Hillenbrand, Lynne A.; Kraus, Adam L.; Charbonneau, David; Kraus, Adam L.We combine new high resolution imaging and spectroscopy from Keck/NIRC2, Discovery Channel Telescope/DSSI, and Keck/HIRES with published astrometry and radial velocities to measure individual masses and orbital elements of the GJ 3305 AB system, a young (similar to 20 Myr) M+M binary (unresolved spectral type M0) member of the beta Pictoris moving group comoving with the imaged exoplanet host 51 Eri. We measure a total system mass of 1.11 +/- 0.04 M-circle dot, a period of 29.03 +/- 0.50 year, a semimajor axis of 9.78 +/- 0.14 AU, and an eccentricity of 0.19 +/- 0.02. The primary component has a dynamical mass of 0.67 +/- 0.05 M-circle dot and the secondary has a mass of 0.44 +/- 0.05 M-circle dot. The recently updated BHAC15 models are consistent with the masses of both stars to within 1.5 sigma. Given the observed masses the models predict an age of the GJ 3305 AB system of 37 +/- 9 Myr. Based on the observed system architecture and our dynamical mass measurement, it is unlikely that the orbit of 51 Eri b has been significantly altered by the Kozai-Lidov mechanism.Item Elemental Abundances Of Solar Sibling Candidates(2014-06) Ramirez, Ivan; Bajkova, A. T.; Bobylev, V. V.; Roederer, Ian U.; Lambert, David L.; Endl, Michael; Cochran, William D.; MacQueen, Phillip J.; Wittenmyer, Robert A.; Bajkova, A. T.; Lambert, David L.; Endl, Michael; Cochran, William D.; MacQueen, Phillip J.Dynamical information along with survey data on metallicity and in some cases age have been used recently by some authors to search for candidates of stars that were born in the cluster where the Sun formed. We have acquired high-resolution, high signal-to-noise ratio spectra for 30 of these objects to determine, using detailed elemental abundance analysis, if they could be true solar siblings. Only two of the candidates are found to have solar chemical composition. Updated modeling of the stars' past orbits in a realistic Galactic potential reveals that one of them, HD 162826, satisfies both chemical and dynamical conditions for being a sibling of the Sun. Measurements of rare-element abundances for this star further confirm its solar composition, with the only possible exception of Sm. Analysis of long-term high-precision radial velocity data rules out the presence of hot Jupiters and confirms that this star is not in a binary system. We find that chemical tagging does not necessarily benefit from studying as many elements as possible but instead from identifying and carefully measuring the abundances of those elements that show large star-to-star scatter at a given metallicity. Future searches employing data products from ongoing massive astrometric and spectroscopic surveys can be optimized by acknowledging this fact.Item An Empirical Calibration To Estimate Cool Dwarf Fundamental Parameters From H-Band Spectra(2015-02) Newton, Elisabeth R.; Charbonneau, David; Irwin, Jonathan; Mann, Andrew W.; Mann, Andrew W.Interferometric radius measurements provide a direct probe of the fundamental parameters of M dwarfs. However, interferometry is within reach for only a limited sample of nearby, bright stars. We use interferometrically measured radii, bolometric luminosities, and effective temperatures to develop new empirical calibrations based on low-resolution, near-infrared spectra. We find that H-band Mg and Al spectral features are good tracers of stellar properties, and derive functions that relate effective temperature, radius, and log luminosity to these features. The standard deviations in the residuals of our best fits are, respectively, 73 K, 0.027R(circle dot), and 0.049 dex (an 11% error on luminosity). Our calibrations are valid from mid K to midMdwarf stars, roughly corresponding to temperatures between 3100 and 4800 K. We apply our H-band relationships to M dwarfs targeted by the MEarth transiting planet survey and to the cool Kepler Objects of Interest (KOIs). We present spectral measurements and estimated stellar parameters for these stars. Parallaxes are also available for many of the MEarth targets, allowing us to independently validate our calibrations by demonstrating a clear relationship between our inferred parameters and the stars' absolute K magnitudes. We identify objects with magnitudes that are too bright for their inferred luminosities as candidate multiple systems. We also use our estimated luminosities to address the applicability of near-infrared metallicity calibrations to mid and late M dwarfs. The temperatures we infer for the KOIs agree remarkably well with those from the literature; however, our stellar radii are systematically larger than those presented in previous works that derive radii from model isochrones. This results in a mean planet radius that is 15% larger than one would infer using the stellar properties from recent catalogs. Our results confirm the derived parameters from previous in-depth studies of KOIs 961 (Kepler-42), 254 (Kepler-45), and 571 (Kepler-186), the latter of which hosts a rocky planet orbiting in its star's habitable zone.Item How To Constrain Your M Dwarf: Measuring Effective Temperature, Bolometric Luminosity, Mass, And Radius(2015-05) Mann, Andrew W.; Feiden, Gregory A.; Gaidos, Eric; Boyajian, Tabetha; von Braun, Kaspar; Mann, Andrew W.Precise and accurate parameters for late-type (late K and M) dwarf stars are important for characterization of any orbiting planets, but such determinations have been hampered by these stars' complex spectra and dissimilarity to the Sun. We exploit an empirically calibrated method to estimate spectroscopic effective temperature (T-eff) and the Stefan-Boltzmann law to determine radii of 183 nearby K7-M7 single stars with a precision of 2%-5%. Our improved stellar parameters enable us to develop model-independent relations between Teff or absolute magnitude and radius, as well as between color and T-eff. The derived T-eff-radius relation depends strongly on [Fe/H], as predicted by theory. The relation between absolute K-S magnitude and radius can predict radii accurate to similar or equal to 3%. We derive bolometric corrections to the VR(C)I(C)grizJHK(S) and Gaia passbands as a function of color, accurate to 1%-3%. We confront the reliability of predictions from Dartmouth stellar evolution models using a Markov chain Monte Carlo to find the values of unobservable model parameters (mass, age) that best reproduce the observed effective temperature and bolometric flux while satisfying constraints on distance and metallicity as Bayesian priors. With the inferred masses we derive a semi-empirical mass-absolute magnitude relation with a scatter of 2% in mass. The best-agreement models overpredict stellar T-eff values by an average of 2.2% and underpredict stellar radii by 4.6%, similar to differences with values from low-mass eclipsing binaries. These differences are not correlated with metallicity, mass, or indicators of activity, suggesting issues with the underlying model assumptions, e.g., opacities or convective mixing length.Item HR 8257: A Three-Dimensional Orbit And Basic Properties(2009-04) Fekel, Francis C.; Boden, Andrew F.; Tomkin, Jocelyn; Torres, Guillermo; Tomkin, JocelynWe have used interferometric and spectroscopic observations of HR 8257 to determine a three-dimensional orbit of the system. The orbit has a period of 12.21345 days and an eccentricity of 0.2895. The masses of the F0 and F2 dwarf components are 1.56 and 1.38M(circle dot), respectively, with fractional errors of 1.4%. Our orbital parallax of 13.632 +/- 0.095 mas, corresponding to a distance of 73.4 +/- 0.6 pc, differs from the Hipparcos result by just 2% and has a significantly smaller uncertainty. From our spectroscopic observations and spectral energy distribution modeling we determine the component effective temperatures and luminosities to be T(eff)(A) = 7030 +/- 200K and T(eff)(B) = 6560 +/- 200K and L(A) = 9.4 +/- 0.3 L(circle dot) and L(B) = 4.7 +/- 0.2 L(circle dot). The primary rotates pseudosynchronously, while the secondary is not far from its pseudosynchronous rotational velocity. Although both early-F stars are slowly rotating, neither component of this close binary is an Am star. A comparison with evolutionary tracks indicates that the stars are slightly metal poor, and although the components have evolved away from the zero-age main sequence, they are both still dwarfs.Item An In-Depth Spectroscopic Analysis Of The Blazhko Star Rr Lyrae I. Characterisation Of The Star: Abundance Analysis And Fundamental Parameters(2010-09) Kolenberg, K.; Fossati, L.; Shulyak, D.; Pikall, H.; Barnes, T. G.; Kochukhov, O.; Tsymbal, V.; Barnes, T. G.Context. The knowledge of accurate stellar parameters is a keystone in several fields of stellar astrophysics, such as asteroseismology and stellar evolution. Although the fundamental parameters can be derived from both spectroscopy and multicolour photometry, the results obtained are sometimes affected by systematic uncertainties. Stellar pulsation reaches high amplitudes in RR Lyrae stars, and as a consequence the stellar parameters vary significantly over the pulsation cycle. The abundances of the star, however, are not expected to change. Aims. We present a self-consistent spectral analysis of the pulsating star RR Lyr, which is the primary target of our study of the Blazhko effect. Methods. We used high-resolution and high signal-to-noise ratio spectra to carry out a consistent parameter determination and abundance analysis for RR Lyr. The LLmodels code was employed for model atmosphere calculations, while the SYNTH3 and WIDTH9 codes were used for line profile calculations and LTE abundance analysis. We describe in detail the methodology adopted to derive the fundamental parameters and the abundances. From a set of available high-resolution spectra of RR Lyr, we selected the phase of maximum radius at which the spectra are least disturbed by the pulsation. Using the abundances determined at this phase as a starting point, we expect to be able to determine the fundamental parameters determined at other phases more accurately. Results. The set of fundamental parameters obtained in this work fits the observed spectrum accurately. From the abundance analysis, we find clear indications of a depth-dependent microturbulent velocity, that we quantify. Conclusions. We confirm the importance of a consistent analysis of relevant spectroscopic features, the application of advanced model atmospheres, and the use of up-to-date atomic line data for determining stellar parameters. These results are crucial for further studies, e. g., detailed theoretical modelling of the observed pulsations.Item The Infrared Colors Of The Sun(2012-12) Casagrande, L.; Ramirez, Ivan; Melendez, Jorge; Asplund, Martin; Ramirez, IvanSolar infrared colors provide powerful constraints on the stellar effective temperature scale, but they must be measured with both accuracy and precision in order to do so. We fulfill this requirement by using line-depth ratios to derive in a model-independent way the infrared colors of the Sun, and we use the latter to test the zero point of the Casagrande et al. effective temperature scale, confirming its accuracy. Solar colors in the widely used Two Micron All Sky Survey (2MASS) JHK(s) and WISE W1-4 systems are provided: (V - J)(circle dot) = 1.198, (V - H)(circle dot) = 1.484, (V - K-s)(circle dot) = 1.560, (J - H)(circle dot) = 0.286, (J - K-s)(circle dot) = 0.362, (H - K-s)(circle dot) = 0.076, (V - W1)(circle dot) = 1.608, (V - W2)(circle dot) = 1.563, (V - W3)(circle dot) = 1.552, and (V - W4)(circle dot) = 1.604. A cross-check of the effective temperatures derived implementing 2MASS or WISE magnitudes in the infrared flux method confirms that the absolute calibration of the two systems agrees within the errors, possibly suggesting a 1% offset between the two, thus validating extant near-and mid-infrared absolute calibrations. While 2MASS magnitudes are usually well suited to derive T-eff, we find that a number of bright, solar-like stars exhibit anomalous WISE colors. In most cases, this effect is spurious and can be attributed to lower-quality measurements, although for a couple of objects (3%+/- 2% of the total sample) it might be real, and may hint at the presence of warm/hot debris disks.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 Kepler-22B: A 2.4 Earth-Radius Planet In The Habitable Zone Of A Sun-Like Star(2012-02) Borucki, William J.; Koch, David G.; Batalha, Natalie; Bryson, Stephen T.; Rowe, Jason; Fressin, Francois; Torres, Guillermo; Caldwell, Douglas A.; Christensen-Dalsgaard, Jorgen; Cochran, William D.; DeVore, Edna; Gautier, Thomas N., III; Geary, John C.; Gilliland, Ronald; Gould, Alan; Howell, Steve B.; Jenkins, Jon M.; Latham, David W.; Lissauer, Jack J.; Marcy, Geoffrey W.; Sasselov, Dimitar; Boss, Alan; Charbonneau, David; Ciardi, David; Kaltenegger, Lisa; Doyle, Laurance; Dupree, Andrea K.; Ford, Eric B.; Fortney, Jonathan; Holman, Matthew J.; Steffen, Jason H.; Mullally, Fergal; Still, Martin; Tarter, Jill; Ballard, Sarah; Buchhave, Lars A.; Carter, Josh; Christiansen, Jessie L.; Demory, Brice-Olivier; Desert, Jean-Michel; Dressing, Courtney; Endl, Michael; Fabrycky, Daniel; Fischer, Debra; Haas, Michael R.; Henze, Christopher; Horch, Elliott; Howard, Andrew W.; Isaacson, Howard; Kjeldsen, Hans; Johnson, John Asher; Klaus, Todd; Kolodziejczak, Jeffery; Barclay, Thomas; Li, Jie; Meibom, Soren; Prsa, Andrej; Quinn, Samuel N.; Quintana, Elisa V.; Robertson, Paul; Sherry, William; Shporer, Avi; Tenenbaum, Peter; Thompson, Susan E.; Twicken, Joseph D.; Van Cleve, Jeffrey; Welsh, William F.; Basu, Sarbani; Chaplin, William; Miglio, Andrea; Kawaler, Steven D.; Arentoft, Torben; Stello, Dennis; Metcalfe, Travis S.; Verner, Graham A.; Karoff, Christoffer; Lundkvist, Mia; Lund, Mikkel N.; Handberg, Rasmus; Elsworth, Yvonne; Hekker, Saskia; Huber, Daniel; Bedding, Timothy R.; Rapin, William; Cochran, William D.; Endl, MichaelA search of the time-series photometry from NASA's Kepler spacecraft reveals a transiting planet candidate orbiting the 11th magnitude G5 dwarf KIC 10593626 with a period of 290 days. The characteristics of the host star are well constrained by high-resolution spectroscopy combined with an asteroseismic analysis of the Kepler photometry, leading to an estimated mass and radius of 0.970 +/- 0.060 M-circle dot and 0.979 +/- 0.020 R-circle dot. The depth of 492 +/- 10 ppm for the three observed transits yields a radius of 2.38 +/- 0.13 Re for the planet. The system passes a battery of tests for false positives, including reconnaissance spectroscopy, high-resolution imaging, and centroid motion. A full BLENDER analysis provides further validation of the planet interpretation by showing that contamination of the target by an eclipsing system would rarely mimic the observed shape of the transits. The final validation of the planet is provided by 16 radial velocities (RVs) obtained with the High Resolution Echelle Spectrometer on Keck I over a one-year span. Although the velocities do not lead to a reliable orbit and mass determination, they are able to constrain the mass to a 3 sigma upper limit of 124 M-circle plus, safely in the regime of planetary masses, thus earning the designation Kepler-22b. The radiative equilibrium temperature is 262 K for a planet in Kepler-22b's orbit. Although there is no evidence that Kepler-22b is a rocky planet, it is the first confirmed planet with a measured radius to orbit in the habitable zone of any star other than the Sun.Item Kepler-445, Kepler-446 And The Occurrence Of Compact Multiples Orbiting Mid-M Dwarf Stars(2015-03) Muirhead, Phillip S.; Mann, Andrew W.; Vanderburg, Andrew; Morton, Timothy D.; Kraus, Adam; Ireland, Michael; Swift, Jonathan J.; Feiden, Gregory A.; Gaidos, Eric; Gazak, J. Zachary; Mann, Andrew W.; Kraus, AdamWe confirm and characterize the exoplanetary systems Kepler-445 and Kepler-446: two mid-M dwarf stars, each with multiple, small, short-period transiting planets. Kepler-445 is a metal-rich ([ Fe/H] = + 0.25 0.10) M4 dwarf with three transiting planets, and Kepler-446 is a metal-poor ([ Fe/H] = -0.30 0.10) M4 dwarf also with three transiting planets. Kepler-445c is similar toGJ 1214b: both in planetary radius and the properties of the host star. The Kepler-446 system is similar to the Kepler-42 system: both are metal-poor with large galactic space velocities and three short-period, likely rocky transiting planets that were initially assigned erroneously large planet-to-star radius ratios. We independently determined stellar parameters from spectroscopy and searched for and fitted the transit light curves for the planets, imposing a strict prior on stellar density in order to remove correlations between the fitted impact parameter and planet-to-star radius ratio for short-duration transits. Combining Kepler-445, Kepler-446, and Kepler-42, and isolating all mid-M dwarf stars observed by Kepler with the precision necessary to detect similar systems, we calculate that 21+ 7 -5 % of mid-M dwarf stars host compact multiples ( multiple planets with periods of less than 10 days) for a wide range of metallicities. We suggest that the inferred planet masses for these systems support highly efficient accretion of protoplanetary disk metals by mid-M dwarf protoplanets.Item Kepler-4B: A Hot Neptune-Like Planet of A G0 Star Near Main-Sequence Turnoff(2010-04) Borucki, William J.; Koch, David G.; Brown, Timothy M.; Basri, Gibor; Batalha, Natalie M.; Caldwell, Douglas A.; Cochran, William D.; Dunham, Edward W.; Gautier, Thomas N., III; Geary, John C.; Gilliland, Ronald L.; Howell, Steve B.; Jenkins, Jon M.; Latham, David W.; Lissauer, Jack J.; Marcy, Geoffrey W.; Monet, David; Rowe, Jason F.; Sasselov, Dimitar; Cochran, William D.Early time-series photometry from NASA's Kepler spacecraft has revealed a planet transiting the star we term Kepler-4, at R.A. = 19(h)02(m)27.(s)68, delta = +50 degrees 08'08 '' 7. The planet has an orbital period of 3.213 days and shows transits with a relative depth of 0.87 x 10(-3) and a duration of about 3.95 hr. Radial velocity (RV) measurements from the Keck High Resolution Echelle Spectrometer show a reflex Doppler signal of 9.3(-1.9)(+1.1) m s(-1), consistent with a low-eccentricity orbit with the phase expected from the transits. Various tests show no evidence for any companion star near enough to affect the light curve or the RVs for this system. From a transit-based estimate of the host star's mean density, combined with analysis of high-resolution spectra, we infer that the host star is near turnoff from the main sequence, with estimated mass and radius of 1.223(-0.091)(+0.053) M(circle dot) and 1.487(-0.084)(+0.071) R(circle dot).We estimate the planet mass and radius to be {M(P), R(P)} = {24.5 +/- 3.8 M(circle plus), 3.99 +/- 0.21 R(circle plus)}. The planet's density is near 1.9 g cm(-3); it is thus slightly denser and more massive than Neptune, but about the same size.Item M Dwarf Metallicities And Giant Planet Occurrence: Ironing Out Uncertainties And Systematics(2014-08) Gaidos, Eric; Mann, Andrew W.; Mann, Andrew W.Comparisons between the planet populations around solar-type stars and those orbiting M dwarfs shed light on the possible dependence of planet formation and evolution on stellar mass. However, such analyses must control for other factors, i.e., metallicity, a stellar parameter that strongly influences the occurrence of gas giant planets. We obtained infrared spectra of 121 M dwarfs stars monitored by the California Planet Search and determined metallicities with an accuracy of 0.08 dex. The mean and standard deviation of the sample are -0.05 and 0.20 dex, respectively. We parameterized the metallicity dependence of the occurrence of giant planets on orbits with a period less than two years around solar-type stars and applied this to our M dwarf sample to estimate the expected number of giant planets. The number of detected planets (3) is lower than the predicted number (6.4), but the difference is not very significant (12% probability of finding as many or fewer planets). The three M dwarf planet hosts are not especially metal rich and the most likely value of the power-law index relating planet occurrence to metallicity is 1.06 dex per dex for M dwarfs compared to 1.80 for solar-type stars; this difference, however, is comparable to uncertainties. Giant planet occurrence around both types of stars allows, but does not necessarily require, a mass dependence of similar to 1 dex per dex. The actual planet-mass-metallicity relation may be complex, and elucidating it will require larger surveys like those to be conducted by ground-based infrared spectrographs and the Gaia space astrometry mission.
- «
- 1 (current)
- 2
- 3
- »