Publications (41)50.64 Total impact
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Chapter: Interior and Exterior Clues of Solar Activity
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ABSTRACT: Two research paths are described to obtain better understanding of the origin of global solar activity. First, observations with a multichannel resonant spectrometer may reveal the dynamics of the solar core, the tachocline, and the temporal evolution of activity between the photosphere and chromosphere. Such new observations will deliver constraints for 3D simulations of solar activity. Second, we examine the ab-initio introduction of a non-force-free field expressed in spherical harmonics into the solar structure equations and estimate its impact on the inner and subsurface layers, its time evolution, and its role in angular momentum transport.12/2009: pages 368-373; -
Article: Radius determination of solar-type stars using asteroseismology: What to expect from the Kepler mission
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ABSTRACT: For distant stars, as observed by the NASA Kepler satellite, parallax information is currently of fairly low quality and is not complete. This limits the precision with which the absolute sizes of the stars and their potential transiting planets can be determined by traditional methods. Asteroseismology will be used to aid the radius determination of stars observed during NASA's Kepler mission. We report on the recent asteroFLAG hare-and-hounds Exercise#2, where a group of `hares' simulated data of F-K main-sequence stars that a group of `hounds' sought to analyze, aimed at determining the stellar radii. Based on the asteroseismic large frequency spacing, obtained from simulations of 4-year time series data from the Kepler mission, we demonstrate that the stellar radii can be correctly and precisely determined, when combined with traditional stellar parameters from the Kepler Input Catalogue. The radii found by the various methods used by each independent hound generally agree with the true values of the artificial stars to within 3%, when the large frequency spacing is used. This is 5--10 times better than the results where seismology is not applied. These results give strong confidence that radius estimation can be performed to better than 3% for solar-like stars using automatic pipeline reduction. Even when the stellar distance and luminosity are unknown we can obtain the same level of agreement. Comment: 14 pages, 10 figures, accepted by ApJThe Astrophysical Journal 08/2009; 700:1589. · 6.02 Impact Factor -
Article: The onset of solar cycle 24: What global acoustic modes are telling us
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ABSTRACT: We study the response of the low-degree, solar p-mode frequencies to the unusually extended minimum of solar surface activity since 2007. A total of 4768 days of observations collected by the space-based, Sun-as-a-star helioseismic GOLF instrument are analyzed. A multi-step iterative maximum-likelihood fitting method is applied to subseries of 365 days and 91.25 days to extract the p-mode parameters. Temporal variations of the l=0, 1, and 2 p-mode frequencies are then obtained from April 1996 to May 2009. While the p-mode frequency shifts are closely correlated with solar surface activity proxies during the past solar cycles, the frequency shifts of the l=0 and l=2 modes show an increase from the second half of 2007, when no significant surface activity is observable. On the other hand, the l=1 modes follow the general decreasing trend of the solar surface activity. The different behaviours between the l=0 and l=2 modes and the l=1 modes can be interpreted as different geometrical responses to the spatial distribution of the solar magnetic field beneath the surface of the Sun. The analysis of the low-degree, solar p-mode frequency shifts indicates that the solar activity cycle 24 started late 2007, despite the absence of activity on the solar surface. Comment: To be accepted by A&A (with minor revisions), 4 pages, 3 figures, 1 table07/2009; -
Article: Disk-integrated Intensity Pseudomodes Measured by SOHO/VIRGO
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ABSTRACT: The high-frequency spectrum above the acoustic cutoff frequency (νac) of the solar atmosphere has been observed in velocity measurements at low and high angular degrees and reveals significant evidence for the presence of pseudomodes characterized by their equally spaced signal. In this paper we study this region of the spectra using for the first time disk-integrated intensity measurements from the VIRGO/SPM photometers on board the SOHO probe. These pseudomodes have high visibility, and whereas the frequency separation between the pseudomodes is the same, some differences are found among the three wavelengths. We have studied the evolution of the pseudomodes with the solar cycle; nevertheless, no significant variations are found. Finally, the intensity pseudomodes of VIRGO/SPM are compared with those of velocity as seen by the GOLF instrument during the same periods and with the same analytical techniques.The Astrophysical Journal 12/2008; 623(2):1215. · 6.02 Impact Factor -
Article: A New Detached M Dwarf Eclipsing Binary
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ABSTRACT: We describe a newly discovered detached M dwarf eclipsing binary system. This system was first observed by the TrES network during a long-term photometry campaign of 54 nights. Analysis of the folded light curve indicates two very similar components orbiting each other with a period of 1.12079 ± 0.00001 days. Spectroscopic observations with the Hobby-Eberly Telescope show the system to consist of two M3e dwarfs in a near-circular orbit. Double-line radial velocity amplitudes, combined with the orbital inclination derived from light-curve fitting, yield Mtotal = 0.983 ± 0.007 M☉, with component masses of M1 = 0.493 ± 0.003 M☉ and M2 = 0.489 ± 0.003 M☉. The light-curve fit yields component radii of R1 = 0.453 ± 0.060 R☉ and R2 = 0.452 ± 0.050 R☉. Although a precise parallax is lacking, broadband VJHK colors and spectral typing suggest component absolute magnitudes of MV(1) = 11.18 ± 0.30 and MV(2) = 11.28 ± 0.30.The Astrophysical Journal 12/2008; 625(2):L127. · 6.02 Impact Factor -
Article: On the Spatial Dependence of Low-Degree Solar p-Mode Frequency Shifts from Full-Disk and Resolved-Sun Observations
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ABSTRACT: We have analyzed low angular degree (low-ℓ) solar p-mode frequency shifts extracted from two types of observations, both made by instruments on board the ESA/NASA Solar and Heliospheric Observatory satellite during a period that covers the rising phase of activity, cycle 23 (1995-2002). The first are full-disk (Sun-as-a-star) averages made in Doppler velocity by the Global Oscillations at Low Frequency spectrophotometer; the second are Doppler velocity observations made with high spatial resolution by the Michelson Doppler Imager. We compare the eigenfrequency shifts from both sets of data and find that they are consistent at the level of precision of the observations. Furthermore, the sizes of the shifts uncovered for different mode components are found to scale in proportion to the corresponding spherical harmonic components of the observed line-of-sight surface magnetic field, with the sectoral mode components showing (as expected) the largest shifts.The Astrophysical Journal 12/2008; 610(1):L65. · 6.02 Impact Factor -
Article: On the Variation of the Peak Asymmetry of Low-ℓ Solar p Modes
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ABSTRACT: The resonant peaks of solar p modes show small amounts of asymmetry in frequency. Here, we use five independent sets of contemporaneous data, collected over a 8 yr period, to investigate whether peak asymmetry in low angular degree p modes changes over the solar activity cycle. Three of the data sets are from instruments on board the ESA/NASA SOHO spacecraft (GOLF, MDI, and VIRGO/SPM); and two are from ground-based networks (BiSON and GONG). Evidence for variation in asymmetry, well correlated with the activity cycle, is uncovered in the GOLF and BiSON Doppler velocity data. Suggestions of a similar trend are present in the GONG Doppler velocity data. Apparent changes in the MDI Doppler velocity data are somewhat less significant. Meanwhile, analysis of the SPM intensity data failed to uncover any evidence for significant change of the asymmetry parameter.The Astrophysical Journal 12/2008; 654(2):1135. · 6.02 Impact Factor -
Article: Preliminary results on the contribution of the convection motions to the Doppler velocity signal
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ABSTRACT: This investigation aims to study the correlation of the solar background with atmosphere. We used high resolution observations of the NaDl spectral line. In fact the large span in formation heights of this spectral line allowed us to infer the signal from photosphere to chromosphere. We analyzed the data by applying the SIR code (Stokes Inversion based on response functions). It is an inversion method of the RTE (Radiative transfer equation) that provides physical information on the region where the spectral lines are sensitive to changes in thermal and dynamical parameters of the atmosphere. The survey has been divided in two different steps: 1) identification of a model of the atmosphere that reproduce our observations; 2) determination of the degree of correlation of convective motions with the solar atmosphere. Here we present the results of the first step: we identified in the model presented by Vernazza the best model that matches our observations.Journal of Physics Conference Series 10/2008; 118(1):012089. -
Article: Update on g‐mode research
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ABSTRACT: Since the beginning of this century we have attended a blooming of the gravity-mode research thanks to the unprecedented quality of the data available, either from space with SoHO, or from the ground-based networks as BiSON or GONG. From the first upper limit of the gravity-mode amplitudes fixed at 10 mm/s at 200 μ Hz given by Appourchaux et al. (2000), on one hand, a peak was supposed to be a component of the = 1, n = 1 mixed mode (García et al. 2001a, 2001b; Gabriel et al. 2002) and, on the other hand, a couple of patterns – multiplets – were attributed to gravity modes (Turck-Chièze et al. 2004; Mathur et al. 2007). One of these patterns, found around 220 μ Hz, could be labeled as the = 2, n = –3 g mode, which is expected to be the one with the highest surface amplitude (Cox & Guzik 2004). Finally, in 2007, García et al. were able to measure the fingertips of the dipole gravity modes looking for their asymptotic properties. In the present paper we present an update of the recent developments on this subject with special attention to the 220 μ Hz region, the dipole asymptotic properties and the impact of the incoming g-mode observations on the knowledge of the solar structure and rotation profile. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)Astronomische Nachrichten 05/2008; 329(5):476 - 484. · 1.01 Impact Factor -
Article: AsteroFLAG: First results from hare‐and‐hounds Exercise #1
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ABSTRACT: We report on initial results from the first phase of Exercise #1 of the asteroFLAG hare and hounds. The asteroFLAG group is helping to prepare for the asteroseismology component of NASA's Kepler mission, and the first phase of Exercise #1 is concerned with testing extraction of estimates of the large and small frequency spacings of the low-degree p modes from Kepler-like artificial data. These seismic frequency spacings will provide key input for complementing the exoplanet search data. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)Astronomische Nachrichten 05/2008; 329(5):549 - 557. · 1.01 Impact Factor -
Article: Helioseismology program for the PICARD satellite
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ABSTRACT: The PICARD mission is a CNES micro-satellite to be launched in 2009. Its goal is to better understand the Sun and the potential impact of its activity on earth climate by measuring simultaneously the solar total and spectral irradiance, diameter, shape and oscillations. We present the scientific objectives, instrumental requirements and data products of the helioseismology program of PICARD which aims to observe the low to medium l p-mode oscillations in intensity and search for g-mode oscillation signatures at the limb. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)Astronomische Nachrichten 05/2008; 329(5):508 - 516. · 1.01 Impact Factor -
Article: p‐mode power variation with solar atmosphere as observed in the Na D1 and K spectral lines
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ABSTRACT: In this work we investigate p-mode power variation with solar atmosphere. To this aim, we use THÉMIS observations of the Na D1 (λ 5896 Å) and K (λ 7699 Å) spectral lines. While the formation heights of the K spectral line are essentially located in the photospheric layer, the formation heights of the Na D1 line span a much wider region: from photosphere up to chromosphere. Hence, we had the opportunity to infer p-mode power variation up to the chromospheric layer. By analyzing power spectra obtained by temporal series at different points of the Na D1 and K spectral lines, we confirm and quantify the increase in p-mode power towards higher atmospheric layers. Furthermore, the large span in formation heights of the Na D1 line induces a larger enhancement of p-mode power with solar atmosphere compared to the K spectral line. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)Astronomische Nachrichten 05/2008; 329(5):494 - 497. · 1.01 Impact Factor -
Article: HELAS IT-platform: A new tool for the European Helio- and Asteroseismology community.
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ABSTRACT: HELAS is a Coordination Action funded under the European Commission's Sixth Framework Programme (FP6) since April 1st, 2006 till March 31st, 2010. The HELAS Consortium includes 10 partner institutions that host researchers active in helio- and asteroseismology. This initiative offers a unique chance to advance the field further by coordinating the activities of researchers, enhancing the quality and quantity of science performed in Europe. The HELAS Forum is one of its Networking Activities. Its main goal is to encourage, provide, and support the tools, activities, and initiatives emanating from the European helio- and asterosesimology scientific communities. Thus, the HELAS Forum should ensure European competence and competitiveness in these areas by better coordinating the groups. It also enhances the synergies between the helio- and astero communities and between those and other non-European related activities. Here, we present the Helas Forum IT-platform (www.helas-eu.org), developed to facilitate the coordinated activities such as data and software package exchange, information about workshops and meetings, knowledge of the community, etc., as well as to allow tracking the development of HELAS activities.Communications in Asteroseismology 03/2008; 153:108-115. -
Article: The complementary roles of interferometry and asteroseismology in determining the mass of solar-type stars
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ABSTRACT: How important is an independent diameter measurement for the determination of stellar parameters of solar-type stars? When coupled with seismic observables, how well can we determine the stellar mass? If we can determine the radius of the star to between 1% and 4%, how does this affect the theoretical uncertainties? Interferometry can provide an independent radius determination and it has been suggested that we should expect at least a 4% precision on such a measurement for nearby solar-type stars. This study aims to provide both qualitative and quantitive answers to these questions for a star such as our Sun, where seismic information will be available. We show that the importance of an independent radius measurement depends on the combination of observables available and the size of the measurement errors. It is important for determining all stellar parameters and in particular the mass, where a good radius measurement can even allow us to determine the mass with a precision better than 2%. Our results also show that measuring the small frequency separation significantly improves the determination of the evolutionary stage and the mixing-length parameter.The Astrophysical Journal 04/2007; 659:616-625. · 6.02 Impact Factor -
Article: A new method to estimate the acoustic cut-off frequency of the Sun using the different properties between p-modes and pseudomodes of low degree
09/2006; 624:86. -
Article: Comparison of the solar velocity spectrum from MDI and GOLF during cycle 23
09/2006; 624:94. -
Article: Analysis of velocity-noise variations arising from photon-noise in data from the GOLF instrument
09/2006; 624:100. -
Article: On the direct determination of sensitivity, resolution and information content of helioseismic data application to the inversion of the solar core rotation rate
09/2006; 624:84. -
Article: Solar-cycle variations in p-mode frequencies and even-order splitting coefficients from LOWL observations
09/2006; 624:90. -
Article: Dynamics study of solar oscillations and granulation with THÉMIS observations
09/2006; 624:50.
Top co-authors
Top Journals
Institutions
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2008–2009
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Universidad de La Laguna
- • Departamento de Astrofísica
- • Departamento de Edafología y Geología
La Laguna, Canary Islands, Spain
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2004–2009
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Instituto de Astrofísica de Canarias
La Laguna, Canary Islands, Spain
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