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Sample records for delta scuti pulsators

  1. Non-linear hydrodynamical simulations of delta Scuti star pulsations

    NASA Astrophysics Data System (ADS)

    Templeton, M. R.; Guzik, J. A.; McNamara, B. J.

    1998-12-01

    We present the initial results of non-linear hydrodynamic simulations of the pulsation modes of delta Scuti stars. These models use the Ostlie and Cox (1993) Lagrangian hydrodynamic code, adapted to use the most recent OPAL (1996) opacities, the Stellingwerf (1974) periodic relaxation method of obtaining stable limit cycle pulsations, and time-dependent convection. Initial tests of first- and second-overtone pulsation models are consistent with the models of Bono, et al (1997) showing asymmetric lightcurves for first overtone rather than fundamental pulsations. Future modeling work will test several stellar models with varying masses, ages, metal and helium abundances and envelope abundance gradients. Ultimately, we hope to determine the role that abundances and, more specifically, helium abundance gradients in delta Scuti envelopes play in light curve shape. This work will be applied to a test sample of known radially-pulsating delta Scuti field stars and the newly-discovered delta Scuti/SX Phoenicis variables in the Galactic Bulge.

  2. Numerical Simulations of High-Amplitude Delta Scuti Star Pulsations

    NASA Astrophysics Data System (ADS)

    Templeton, M. R.

    1999-12-01

    We present the results of a theoretical program to model high-amplitude delta Scuti (HADS) stars. We base this study on field HADS, and on the MACHO Project delta Scuti stars. We have generated a grid of evolution models with (X,Y,Z) = (0.76,0.24,0.0001) to (0.58,0.36,0.06) covering the delta Scuti/SX Phoenicis region of the instability strip. Linear pulsation tests were done to make theoretical Petersen diagrams for the double-mode pulsators, and to make period-luminosity relations. Petersen diagrams are consistent with previous observational and theoretical work, with all fundamental-first overtone pulsators having period ratios around 0.77. For a single metallicity, stars with masses separated by 0.1 Msun have distinct tracks in the Petersen diagram, which permits mass and age estimates for stars of known abundance. We also find that period ratios drop rapidly as these stars evolve toward the red giant branch. The two MACHO delta Scuti stars with period ratios around 0.75 may be highly evolved, cool (T = 6700 K) delta Scuti stars. Period-luminosity relations for stars of different masses but the same abundances have a large intrinsic scatter, indicating that a color term must be included in the P-L relation for delta Scuti stars. Hydrodynamic models of HADS have also been tested, using a variant of the Los Alamos DYNSTAR code (Ostlie and Cox, 1993, Astrophys. Space Sci 210, 311), modified to include the OPAL96 tabular opacities. We have obtained light curves that are similar to those of observed HADS, over a range of temperatures and masses. Our results are consistent with those of Bono et al. (1997; ApJ 477, 346) in that the light curves of fundamental mode pulsators are more sinusoidal than those of overtone pulsators. Work on the hydrodynamic models is being expanded to test the effects of helium enrichment on light curve shape, and to include convection in cooler HADS to better model the red edge of the instability strip.

  3. An AD HOC hypothesis on the pulsation of Delta Scuti stars

    NASA Astrophysics Data System (ADS)

    Antonello, E.

    It is proposed that the stars in the lower part of the instability strip are pulsating if they have sufficiently high rotational velocity and/or if they are in an appropriate binary system that provides some sort of nonradial hard excitation to pulsate. This should be valid at least for the low amplitude variables. The results of various studies on the Delta Scuti stars do not show a clear confirmation or rejection of this hypothesis, but for the stars in the well-studied Hyades cluster, the rotational velocity has some importance for the discrimination between variable and nonvariable stars in the sense of the hypothesis. The different incidence of spectroscopid binaries among variable and nonvariable stars also supports the hypothesis, at least for dwarfs.

  4. Delta Scuti variables. Lecture 6

    SciTech Connect

    Cox, A.N.

    1983-01-01

    The class of variables near or on the upper main sequence, the delta Scuti variables, are not only the usual ones about the masses, radii, and luminosities, but also the age, rotation, element diffusion to change the surface layer composition, the occurance of convection and the presence of radial and nonradial pulsation modes. (GHT)

  5. Delta Scuti stars: Theory

    NASA Technical Reports Server (NTRS)

    Guzik, J. A.

    1998-01-01

    The purpose of asteroseismology is not only to derive the internal structure of individual stars from their observed oscillation frequencies, but also to test and extend one's understanding of the physics of matter under the extremes of temperature, density, and pressure found in stellar interiors. In this review, the author hopes to point out what one can learn about the Sun by studying (delta) Scuti stars, as well as what one can learn about stars more massive or evolved than the Sun. He discusses some of the difficulties in theoretical approaches to asteroseismology for (delta) Scuti stars, using FG Vir, (delta) Scuti, and CD-24(degree) 7599 as examples.

  6. Delta Scuti stars: Theory

    SciTech Connect

    Guzik, J.A.

    1998-03-01

    The purpose of asteroseismology is not only to derive the internal structure of individual stars from their observed oscillation frequencies, but also to test and extend one`s understanding of the physics of matter under the extremes of temperature, density, and pressure found in stellar interiors. In this review, the author hopes to point out what one can learn about the Sun by studying {delta} Scuti stars, as well as what one can learn about stars more massive or evolved than the Sun. He discusses some of the difficulties in theoretical approaches to asteroseismology for {delta} Scuti stars, using FG Vir, {delta} Scuti, and CD-24{degree} 7599 as examples.

  7. Delta Scuti stars: Theory

    NASA Technical Reports Server (NTRS)

    Guzik, J. A.

    1998-01-01

    The purpose of asteroseismology is not only to derive the internal structure of individual stars from their observed oscillation frequencies, but also to test and extend one's understanding of the physics of matter under the extremes of temperature, density, and pressure found in stellar interiors. In this review, the author hopes to point out what one can learn about the Sun by studying (delta) Scuti stars, as well as what one can learn about stars more massive or evolved than the Sun. He discusses some of the difficulties in theoretical approaches to asteroseismology for (delta) Scuti stars, using FG Vir, (delta) Scuti, and CD-24(degree) 7599 as examples.

  8. HYBRID {gamma} DORADUS-{delta} SCUTI PULSATORS: NEW INSIGHTS INTO THE PHYSICS OF THE OSCILLATIONS FROM KEPLER OBSERVATIONS

    SciTech Connect

    Grigahcene, A.; Monteiro, M. J. P. F. G.; Antoci, V.; Handler, G.; Houdek, G.; Balona, L.; Catanzaro, G.; Daszynska-Daszkiewicz, J.; Guzik, J. A.; Kurtz, D. W.; Marconi, M.; Ripepi, V.; Moya, A.; Suarez, J.-C.; Uytterhoeven, K.; Brown, T. M.; Christensen-Dalsgaard, J.; Gilliland, R. L.; Jenkins, J. M.

    2010-04-20

    Observations of the pulsations of stars can be used to infer their interior structure and test theoretical models. The main-sequence {gamma} Doradus (Dor) and {delta} Scuti (Sct) stars with masses 1.2-2.5 M {sub sun} are particularly useful for these studies. The {gamma} Dor stars pulsate in high-order g-modes with periods of order 1 day, driven by convective blocking at the base of their envelope convection zone. The {delta} Sct stars pulsate in low-order g- and p-modes with periods of order 2 hr, driven by the {kappa} mechanism operating in the He II ionization zone. Theory predicts an overlap region in the Hertzsprung-Russell diagram between instability regions, where 'hybrid' stars pulsating in both types of modes should exist. The two types of modes with properties governed by different portions of the stellar interior provide complementary model constraints. Among the known {gamma} Dor and {delta} Sct stars, only four have been confirmed as hybrids. Now, analysis of combined Quarter 0 and Quarter 1 Kepler data for hundreds of variable stars shows that the frequency spectra are so rich that there are practically no pure {delta} Sct or {gamma} Dor pulsators, i.e., essentially all of the stars show frequencies in both the {delta} Sct and the {gamma} Dor frequency range. A new observational classification scheme is proposed that takes into account the amplitude as well as the frequency and is applied to categorize 234 stars as {delta} Sct, {gamma} Dor, {delta} Sct/{gamma} Dor or {gamma} Dor/{delta} Sct hybrids.

  9. Kepler Eclipsing Binaries with Delta Scuti/Gamma Doradus Pulsating Components I: KIC 9851944

    NASA Astrophysics Data System (ADS)

    Guo, Zhao; Gies, Douglas R.; Matson, Rachel A.; García Hernández, Antonio

    2016-07-01

    KIC 9851944 is a short-period (P = 2.16 days) eclipsing binary in the Kepler field of view. By combining the analysis of Kepler photometry and phase-resolved spectra from Kitt Peak National Observatory and Lowell Observatory, we determine the atmospheric and physical parameters of both stars. The two components have very different radii (2.27 R ⊙, 3.19 R ⊙) but close masses (1.76 M ⊙, 1.79 M ⊙) and effective temperatures (7026, 6902 K), indicating different evolutionary stages. The hotter primary is still on the main sequence (MS), while the cooler and larger secondary star has evolved to the post-MS, burning hydrogen in a shell. A comparison with coeval evolutionary models shows that it requires solar metallicity and a higher mass ratio to fit the radii and temperatures of both stars simultaneously. Both components show δ Scuti-type pulsations, which we interpret as p-modes and p and g mixed modes. After a close examination of the evolution of δ Scuti pulsational frequencies, we make a comparison of the observed frequencies with those calculated from MESA/GYRE.

  10. The Pulsational Behaviour of the High Amplitude Delta Scuti Star RS Gruis

    NASA Astrophysics Data System (ADS)

    Garcia, Jaime

    2011-05-01

    RS Gruis is a high amplitude delta Scuti type variable star with a mean amplitude of almost a half of a magnitude in V, and a period of almost 3.5 hours. The most recent study of this star due to Derekas et al. (2009) suggests the presence of a low-mass dwarf star companion close to the variable star with a period of 11.5 days. Rodriguez et al (1995) had also shown a decreasing rate of the period of dP/Pdt= -10.6 E-8/y. Using a extended dataset comprising BVIc CCD observations aquired at the Astronomical Observatory of the Instituto Copernico (1000 datapoints), a data set from ASAS (500) and the existing data in the AAVSO International Database (3900), we have performed an extensive periodogram analyses looking for long term variations. As a preliminary result, we have confirmed the period variation rate but we also found an harmonic in good shape with the period suggested for the binary companion.

  11. Bulge Delta Scuti Stars in the MACHO database

    SciTech Connect

    Minnniti, D; Alcock, C; Alves,D R; Axelrod, T S; Becker, A; Bennett, D P; Cook, K H; Freeman, K C; Rodgers, A W; Stubbs, C W; Sutherland, W; Tomanet, A; Vandehei, T; Welch, D L

    1997-07-29

    The authors describe the search for {delta} Scuti stars in the MACHO database of bulge fields. Concentrating on a sample of high amplitude {delta} Scutis, they examine the light curves and pulsation modes. They also discuss their spatial distribution and evolutionary status using mean colors and absolute magnitudes.

  12. The Delta Scuti star HD 127759

    NASA Astrophysics Data System (ADS)

    Li, Zhiping; Jiang, Shiyiang

    1992-06-01

    The results are reported of six nights of V-band observations of the newly discovered Delta Scuti variable HD 127759 during April 3-21, 1991 and its Stromgren uvby(beta) photometry. The period analysis indicates that HD 127759 is a single-sine frequency-dominant pulsation variable with a frequency of 14.78626 cycle/d and an amplitude of 0.0199 m. The times of maximum are given. The star is located at the blue edge of the Delta Scuti variable instability strip, with T(eff) about 8400 K and M(V) about 0.93 m.

  13. Spectroscopic Survey Of Delta Scuti Stars

    NASA Astrophysics Data System (ADS)

    Kahraman Alicavus, Filiz; Niemczura, Ewa; Polinska, Magdalena; Helminiak, Krzysztof G.; Lampens, Patricia; Molenda-Zakowicz, Joanna; Ukita, Nobuharu; Kambe, Eiji

    2016-07-01

    We present the results of a spectroscopic study of pulsating stars of Delta Scuti type. The spectral types and luminosity classes, fundamental atmospheric parameters (the effective temperature, surface gravity, microturbulent velocity), detailed chemical composition and projected rotational velocities of a significant number of Delta Scuti-type stars were derived. The spectral classification was performed by comparing the spectra of our targets with the spectra of standard stars. The atmospheric parameters were determined by using different methods. The initial atmospheric parameters were derived from the analysis of photometric indices, the spectral energy distribution and the hydrogen lines, while the final atmospheric parameters were obtained from the analysis of iron lines. The spectrum synthesis method was used to determine chemical compositions of the investigated stars. As a result, we derived accurate atmospheric parameters, the projected rotational velocities and the abundance patterns of analysed sample. These results allow us to examine the position of Delta Scuti-type stars in the H-R diagram, and to investigate the effect of the rotational velocity on pulsation properties and a chemical difference between the Delta Scuti-type stars and the Gamma Doradus and A-F type hybrid stars.

  14. A nonradial pulsation model for the rapidly rotating Delta Scuti star Kappa(2) Bootis

    NASA Technical Reports Server (NTRS)

    Kennelly, E. J.; Walker, G. A. H.; Hubeny, I.

    1991-01-01

    A sectorial nonradial pulsation model is used to construct theoretical line profiles which mimic the variations for Kappa(2) Boo. Synthetic spectra generated with the appropriate Teff and log g are used as input. It is found that the data can be reproduced by the combination of a high-degree l is approximately equal to 12 mode with P(osc) aproximately equal to 0.071 d, and a low-degree mode, l is approximately equal to 0-2 with P(osc) approximately equal to 0.071-0.079 d. The projected rotational velocity (v sin i - 115 +/-5 km/s) was determined by fitting synthetic line profiles to the observed spectra. The velocity amplitude of the high-degree oscillations is estimated to be about 3.5 km/s. It is found that the ratio of the horizontal and radial pulsation amplitudes is small (about 0.02) and consistent with p-mode oscillations. Comparisons are made with models invoking starspots, and it is impossible to fit the observations of Kappa(2) Boo by a starspot model without assuming unrealistic values of radius or equatorial velocity.

  15. Four new Delta Scuti stars

    NASA Technical Reports Server (NTRS)

    Schutt, R. L.

    1991-01-01

    Four new Delta Scuti stars are reported. Power, modified into amplitude, spectra, and light curves are used to determine periodicities. A complete frequency analysis is not performed due to the lack of a sufficient time base in the data. These new variables help verify the many predictions that Delta Scuti stars probably exist in prolific numbers as small amplitude variables. Two of these stars, HR 4344 and HD 107513, are possibly Am stars. If so, they are among the minority of variable stars which are also Am stars.

  16. Light curves and Fourier coefficients for a subsample of the MACHO Delta Scuti stars

    NASA Astrophysics Data System (ADS)

    Templeton, M.; McNamara, B.

    1998-07-01

    We have compiled a sample of Delta Scuti candidates from the MACHO catalog of variable stars in the direction of the Galactic Bulge, and a detailed spectral analysis of this time series data is in progress. The MACHO project (see Alcock et al. 1997) has collected a massive amount of photometry on millions of stars in the directions of the Galactic Bulge and the Large and Small Magellanic Clouds. Many thousands of variable stars have been detected, among them Delta Scuti stars (towards the Galactic Bulge only; Delta Scuti stars in the LMC and SMC are below the detection limits of MACHO). See the discovery paper of Minniti et al. (1997) for more background and sample light curves. Of our initial sample of 136 stars showing variability on timescales less than 0.3d and with (V-R) colors similar to those of Delta Scuti stars, we find that sim 90 are likely Delta Scuti stars, with the remainder being either eclipsing binaries of W Ursa Majoris type ``A'' or which require more detailed observations for classification. The ultimate goal of our study is to determine as accurately as possible the pulsation spectra and pulsation mode types of the candidate Delta Scuti stars. In the present paper, we discuss the general light curve shapes of these objects by analyzing the Fourier harmonics of observed pulsation modes. This technique has been explored in some detail for Cepheids (Simon & Lee 1981) and for Delta Scuti stars (Antonello et al. 1987; Poretti et al. 1990). Recent non-linear modeling work by Bono et al. (1997) suggests that the light curve shape is a strong indicator of the radial overtone number for radially pulsating Delta Scuti stars. Therefore, Fourier analysis of pulsation frequencies and their Fourier harmonics may indicate which overtone a given star is pulsating in. Here, we present the initial results for a subsample of the MACHO Delta Scuti stars.

  17. STATISTICAL PROPERTIES OF GALACTIC {delta} SCUTI STARS: REVISITED

    SciTech Connect

    Chang, S.-W.; Kim, D.-W.; Byun, Y.-I.; Protopapas, P. E-mail: kim@mpia-hd.mpg.de

    2013-05-15

    We present statistical characteristics of 1578 {delta} Scuti stars including nearby field stars and cluster member stars within the Milky Way. We obtained 46% of these stars (718 stars) from work by Rodriguez and collected the remaining 54% of stars (860 stars) from other literature. We updated the entries with the latest information of sky coordinates, color, rotational velocity, spectral type, period, amplitude, and binarity. The majority of our sample is well characterized in terms of typical period range (0.02-0.25 days), pulsation amplitudes (<0.5 mag), and spectral types (A-F type). Given this list of {delta} Scuti stars, we examined relations between their physical properties (i.e., periods, amplitudes, spectral types, and rotational velocities) for field stars and cluster members, and confirmed that the correlations of properties are not significantly different from those reported in Rodriguez's work. All the {delta} Scuti stars are cross-matched with several X-ray and UV catalogs, resulting in 27 X-ray and 41 UV-only counterparts. These counterparts are interesting targets for further study because of their uniqueness in showing {delta} Scuti-type variability and X-ray/UV emission at the same time. The compiled catalog can be accessed through the Web interface http://stardb.yonsei.ac.kr/DeltaScuti.

  18. High Amplitude (delta)-Scutis in the Large Magellanic Cloud

    SciTech Connect

    Garg, A; Cook, K H; Nikolaev, S; Huber, M E; Rest, A; Becker, A C; Challis, P; Clocchiatti, A; Miknaitis, G; Minniti, D; Morelli, L; Olsen, K; Prieto, J L; Suntzeff, N B; Welch, D L; Wood-Vasey, W M

    2010-01-25

    The authors present 2323 High-Amplitude {delta}-Scutis (HADS) candidates discovered in the Large Magellanic Cloud (LMC) by the SuperMACHO survey (Rest et al. 2005). Frequency analyses of these candidates reveal that several are multimode pulsators, including 119 whose largest amplitude of pulsation is in the fundamental (F) mode and 19 whose largest amplitude of pulsation is in the first overtone (FO) mode. Using Fourier decomposition of the HADS light curves, they find that the period-luminosity (PL) relation defined by the FO pulsators does not show a clear separation from the PL-relation defined by the F pulsators. This differs from other instability strip pulsators such as type c RR Lyrae. They also present evidence for a larger amplitude, subluminous population of HADS similar to that observed in Fornax (Poretti et al. 2008).

  19. KIC 8262223: A Post-mass Transfer Eclipsing Binary Consisting of a Delta Scuti Pulsator and a Helium White Dwarf Precursor

    NASA Astrophysics Data System (ADS)

    Guo, Zhao; Gies, Douglas R.; Matson, Rachel A.; García Hernández, Antonio; Han, Zhanwen; Chen, Xuefei

    2017-03-01

    KIC 8262223 is an eclipsing binary with a short orbital period (P = 1.61 day). The Kepler light curves are of Algol-type and display deep and partial eclipses, ellipsoidal variations, and pulsations of δ Scuti type. We analyzed the Kepler photometric data, complemented by phase-resolved spectra from the R-C Spectrograph on the 4 meter Mayall telescope at the Kitt Peak National Observatory and determined the fundamental parameters of this system. The low-mass and oversized secondary ({M}2=0.20{M}ȯ , {R}2=1.31{R}ȯ ) is the remnant of the donor star that transferred most of its mass to the gainer, and now the primary star. The current primary star is thus not a normal δ Scuti star but the result of mass accretion from a lower mass progenitor. We discuss the possible evolutionary history and demonstrate with the MESA evolution code that this system and several other systems discussed in prior literature can be understood as the result of non-conservative binary evolution for the formation of EL CVn-type binaries. The pulsations of the primary star can be explained as radial and non-radial pressure modes. The equilibrium models from single star evolutionary tracks can match the observed mass and radius ({M}1=1.94{M}ȯ , {R}1=1.67{R}ȯ ) but the predicted unstable modes associated with these models differ somewhat from those observed. We discuss the need for better theoretical understanding of such post-mass transfer δ Scuti pulsators.

  20. Pulsational frequencies in the delta Scuti stars V624 Tauri and HD 23194. Results of the STEPHI X campaign on the Pleiades cluster

    NASA Astrophysics Data System (ADS)

    Fox-Machado, L.; Álvarez, M.; Michel, E.; Li, Z. P.; Pérez Hernández, F.; Chevreton, M.; Barban, C.; Belmonte, J. A.; Dolez, N.; Fernandez, A.; Guo, J. P.; Haywood, M.; Liu, Y. Y.; Pau, S.; Planas, H.; Servan, B.

    2002-02-01

    The results of the tenth multi-site campaign of the STEPHI network are reported. The delta Scuti stars V624 Tau (HD 23156) and HD 23194, belonging to the Pleiades cluster, were observed photometrically for 34 days on three continents during 1999 November-December. An overall run of 343 hours of data was collected. Seven frequencies for V624 Tau and two frequencies for HD 23194 have been found above a 99% confidence level. These results greatly improve those found in previous studies with much less data. A preliminary comparison of observed and theoretical frequencies suggests that both stars may oscillate with radial and non-radial p modes of radial orders typical among delta Scuti stars.

  1. The MACHO Project Sample of Galactic Bulge High-Amplitude Scuti Stars: Pulsation Behavior and Stellar Properties

    SciTech Connect

    Bennett, D.P.; Cook, K.H.; Freeman, K.C.; Geha, M.; Griest, K.; Lehner, M.J.; Marshall, S.L.; McNamara, B.J.; Minniti, D.; Nelson, C.; Peterson, B.A.; Popowski, P.; Pratt, M.R.; Quinn, P.J.; Rodgers, A.W.; Sutherland, W.; Templeton, M.R.; Vandehei, T.; Welch, D.L.

    1999-11-16

    We have detected 90 objects with periods and lightcurve structure similar to those of field {delta} Scuti stars, using the Massive Compact Halo Object (MACHO) Project database of Galactic bulge photometry. If we assume similar extinction values for all candidates and absolute magnitudes similar to those of other field high-amplitude {delta} Scuti stars (HADS), the majority of these objects lie in or near the Galactic bulge. At least two of these objects are likely foreground {delta} Scuti stars, one of which may be an evolved nonradial pulsator, similar to other evolved, disk-population {delta} Scuti stars. We have analyzed the light curves of these objects and find that they are similar to the light curves of field {delta} Scuti stars and the {delta} Scuti stars found by the Optical Gravitational Lens Experiment (OGLE). However, the amplitude distribution of these sources lies between those of low- and high-amplitude {delta} Scuti stars, which suggests that they may be an intermediate population. We have found nine double-mode HADS with frequency ratios ranging from 0.75 to 0.79, four probable double- and multiple-mode objects, and another four objects with marginal detections of secondary modes. The low frequencies (5-14 cycles d{sup -1}) and the observed period ratios of {approx}0.77 suggest that the majority of these objects are evolved stars pulsating in fundamental or first overtone radial modes.

  2. Analysis of pre-main-sequence delta-Scuti stars

    NASA Astrophysics Data System (ADS)

    Casey, Michael Patrick

    Information on 72 confirmed or candidate pre-main-sequence delta-Scuti stars is collected and analysed to varying degree of sophistication and completeness. A systematic asteroseismic analysis of around 40 of these stars is performed, putting significant luminosity constraints on many of them simply by comparing the pulsation spectra of the stars to the fundamental and acoustic cut-off frequencies of a dense grid of stellar models. One star in particular, V1366 Ori, appears to be pulsating at or near the acoustic cut-off frequency. Many stars are found to otherwise defy proper asteroseismic analysis, in that matches between observed pulsation spectra and computed values are not able to be found. A simple test reveals that the most likely cause for these problems are the high stellar-rotation rates typically found in this class of star, with v sin i most typically between 60 and 200 km/s. The high rotation rates are found to significantly modify the pulsation spectrum of a star compared to a non-rotating star. These collective results reveal the richness and variety of phenomena within this group of stars, with stars pulsating anywhere from the lowest to the highest possible radial orders, including radial orders just below the acoustic cut-off frequency of some stars. Pulsation in non-radial orders is the normal case, not the exception to the rule, with all stars displaying low-amplitude delta-Scuti variability only.

  3. The Brightest Delta Scuti Star

    NASA Astrophysics Data System (ADS)

    Buzasi, D.; Bruntt, H.; Preston, H.; Mandeville, J.; Bedding, T.; Retter, A.; Kjeldsen, H.

    2003-12-01

    We present an analysis of observations of the bright star Altair (α Aql) obtained using the star camera on the Wide Field Infrared Explorer (WIRE) satellite. Although Altair lies within the δ Scuti instability strip, previous observations have not revealed the presence of oscillations. However, the WIRE observations show Altair to be a low amplitude (Δ m < 500 μ mag) δ Scuti star with at least 5 modes present. We further show that the detected frequencies are compatible with models for Altair.

  4. Asteroseismology of hybrid δ Scuti-γ Doradus pulsating stars

    NASA Astrophysics Data System (ADS)

    Sánchez Arias, J. P.; Córsico, A. H.; Althaus, L. G.

    2017-01-01

    Context. Hybrid δ Scuti-γ Doradus pulsating stars show acoustic (p) oscillation modes typical of δ Scuti variable stars, and gravity (g) pulsation modes characteristic of γ Doradus variable stars simultaneously excited. Observations from space missions such as MOST, CoRoT, and Kepler have revealed a large number of hybrid δ Scuti-γ Doradus pulsators, thus paving the way for an exciting new channel of asteroseismic studies. Aims: We perform detailed asteroseismological modelling of five hybrid δ Scuti-γ Doradus stars. Methods: A grid-based modeling approach was employed to sound the internal structure of the target stars using stellar models ranging from the zero-age main sequence to the terminal-age main sequence, varying parameters such as stellar mass, effective temperature, metallicity and core overshooting. Their adiabatic radial (ℓ = 0) and non-radial (ℓ = 1,2,3) p and g mode periods were computed. Two model-fitting procedures were used to search for asteroseismological models that best reproduce the observed pulsation spectra of each target star. Results: We derive the fundamental parameters and the evolutionary status of five hybrid δ Scuti-γ Doradus variable stars recently observed by the CoRoT and Kepler space missions: CoRoT 105733033, CoRoT 100866999, KIC 11145123, KIC 9244992, and HD 49434. The asteroseismological model for each star results from different criteria of model selection, in which we take full advantage of the richness of periods that characterises the pulsation spectra for this kind of star.

  5. Multiband photometric re-classification of ROTSE-I delta Scuti type stars

    NASA Astrophysics Data System (ADS)

    Jin, H.; Kim, S.-L.; Kwon, S.-G.; Youn, J.-H.; Lee, C.-U.; Lee, D.-J.; Kim, K.-S.

    2003-06-01

    We present multi-passband CCD photometry of 20 ROTSE-I delta Scuti type pulsating stars and 1 RR Lyrae star to re-classify their variable types using the comparison of amplitudes between V and I passbands. For the re-classification, we used a criterion that pulsating stars have larger amplitude differences between passbands than eclipsing binaries because brightness changes of pulsating stars are mainly due to the temperature variations. As a result, only six stars were re-confirmed as delta Scuti variables and thirteen stars turned out to be W UMa type eclipsing binaries. The other two stars were identified as one cataclysmic variable and one non-variable, respectively. Our results suggest that a number of ROTSE-I delta Scuti type stars, which do not show typical pulsating light curves of high amplitude delta Scuti stars, are W UMa type eclipsing binaries. Table 3 is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/404/621

  6. An asteroseismological analysis of Delta Scuti

    NASA Astrophysics Data System (ADS)

    Templeton, M. R.; McNamara, B. J.

    1996-10-01

    One of us (BJM) observed Delta Scuti during the period of June 1983 to September 1988; observations in 1983-85 were conducted at the Tortugas Moutain observatory, New Mexico; in 1987 were conducted in a multisite campaign from New Mexico (by S. Barch), CTIO (by BJM), and SAAO (by K. Sekiguchi); and in 1988 were conducted at CTIO. We have 6515 Stromgren y differential magnitudes spanning a total of 1928.6 days with a sigma per point of approx. 7 mmag.

  7. The Theta 2 Tau campaign by the Delta Scuti Network

    NASA Astrophysics Data System (ADS)

    Breger, M.

    1995-01-01

    The star Theta 2 Tau had already been studied by the Delta Scuti Network during two previous multisite campaigns (see Breger, M., Garrido, R., Huang Lin, Jiang Shi-Yang, Guo Zi-He, Frueh, M., Paparo M. Astron. Astrophys. 214, 209, 1989). The star offers a chance to study nonradial modes of different degrees and similar radial orders. The previous multisite campaigns have detected five frequencies from the photometric data. However, these data also show that there exist a number of additional, presently unidentified pulsation modes in the 10 to 15 c/d and the 25 to 30 c/d range. These new frequencies could be detected and confirmed in an additional campaign. Dziembowski and Goode (Astrophys. J.394, 670,1992) have successfully modelled the five previously identified modes, but the theoretical challenge will be provided by the frequencies of the additional modes. The star seems to differ from 4 CVn in that no variability of amplitudes could be detected so far, but the data are limited. Furthermore, during 1994 a spectroscopic MUSICOS campaign was undertaken. A new multisite photometric campaign was carried out with the Delta Scuti Network during 1994 November and December. Data has already been obtained from the McDonald, Lowell, Sierra Nevada, Xing-Long and Tien-Shan Observatories. Approximately 40 nights of photometric observations are presently being reduced.

  8. On the period variations of several low declination high amplitude delta Scuti variables

    NASA Astrophysics Data System (ADS)

    Boonyarak, Chayan; Fu, Jian-Ning; Khokhuntod, Pongsak; Jiang, Shi-Yang

    2011-05-01

    A 16-inch Schmidt-Cassegrain telescope on the campus of Naresuan University of Thailand and several similar-size telescopes in China equipped with CCD cameras were used to observe 14 high amplitude delta Scuti stars: GP And, CY Aqr, BS Aqr, YZ Boo, AD CMi, VZ Cnc, EH Lib, DY Her, V927 Her, KZ Hya, BE Lyn, V1162 Ori, DY Peg, and CW Ser, between the years 1999 and 2010. Data were also collected from scientific journals and sources on the Internet for these variable stars. Times of light maximum of these delta Scuti stars were then either determined from the observations or obtained from the literature to analyze the pulsation period variations. For the 14 delta Scuti stars we concluded that 7 stars (BS Aqr, CY Aqr, AD CMi, EH Lib, KZ Hya, BE Lyn and DY Peg) are binary or multiple systems. 10 delta Scuti stars are found with periods increasing with rates between 5.86×10-9 and 2.34×10-6 per year and the other 4 stars (BS Aqr, DY Her, BE Lyn and DY Peg) show periods decreasing with rates of about 10-9 to 10-8 per year.

  9. The High Amplitude delta Scuti Star AD Canis Minoris

    NASA Astrophysics Data System (ADS)

    Axelsen, R. A.; Napier-Munn, T.

    2016-12-01

    The high amplitude delta Scuti star AD Canis Minoris was studied by photoelectric photometry (PEP) during one night in in February 2011 and by digital single lens reflex (DSLR) photometry during seven nights in January and February 2016. Nine light curve peaks were captured, eight of them by DSLR photometry. A review of the literature enabled us to tabulate 109 times of maximum since 1959, to which we added 9 times of maximum from our data, thus creating the largest dataset to date for this star. Assuming a linear ephemeris, the period of AD CMi was calculated to be 0.122974511 (+/- 0.000000004) d, almost identical to that quoted in earlier literature. We constructed an observed minus computed (O-C) diagram which exhibited a quasi-sinusoidal shape, and fitted a weighted model characterised by combined quadratic and trigonometric functions. The fit indicates that the shape of the O-C diagram is attributable to the effects of a slow increase in the pulsation period of AD CMi at a constant rate, and the light time effect of a binary pair, confirming the results from previous authors, and updating most of the coefficients of the equation for the fitted model. The values of all of the coefficients in the function are statistically significant. The rate of increase in the pulsation period of AD CMi was calculated from the entire dataset to be dP/dt = 6.17 (+/- 0.75) x 10-9 d yr-1 or dP/Pdt = 5.01 (+/- 0.61) x 10-8 yr-1.

  10. PERIOD AND AMPLITUDE VARIABILITY OF THE HIGH-AMPLITUDE {delta} SCUTI STAR GP ANDROMEDAE

    SciTech Connect

    Zhou, A.-Y.; Jiang, S.-Y.

    2011-10-15

    Extensive differential time-series CCD photometry has been carried out between 2003 and 2009 for the high-amplitude {delta} Scuti (HADS) star GP And. We acquired 12,583 new measurements consisting of 41 nights (153.3 hr) spanning over 2221 days. This is the largest time-series data set to date for the star. Based upon these data and others available in the literature, a comprehensive analysis has been conducted to investigate the pulsational properties of the star. Except for the known fundamental period and its harmonics we failed to detect any additional pulsation periods either radial or nonradial. We show clear amplitude variability, but we failed to verify the previously claimed periodic amplitude modulation. Classic O-C analysis indicates that the fundamental pulsation period of GP And is slowly increasing at a rate of P-dot /P = (5.49 {+-} 0.1)x10{sup -8} yr{sup -1} in accordance with the predictions of stellar evolutionary models. Findings of nonradial oscillations in previously known radial high-amplitude pulsators are being increasingly reported. We have briefly reviewed the current status of multiperiodicity and nonradial pulsation features among the high-amplitude pulsators in the classic instability strip.

  11. The search for delta Scuti stars in open clusters

    NASA Astrophysics Data System (ADS)

    Frandsen, S.; Arentoft, T.

    1998-05-01

    In order to improve the tests of models of stellar evolution, observations giving tighter constraints on the models were initiated by the formation of an informal group STACC (Frandsen, 1992). The purpose of the group is to search for and make observations of delta Scuti stars in open clusters. This paper presents some of the results of the search, mainly for distant open clusters with a rich population of variables. Included is an announcement of a target list (Frandsen & Arentoft 1998, The Book) and four examples of new Colour-Magnitude (CM) diagrams of open clusters considered to be interesting targets. Finally, we present the fruits of extensive searching: an open cluster that contains many delta Scuti stars. Based on observations made at the European Southern Observatory, La Silla, the Nordic Optical Telescope, ORM, La Palma and the IAC80, OT, Tenerife

  12. Observations and a new interpretation for the delta Scuti variable star VZ Cancri

    SciTech Connect

    Cox, A.N.; McNamara, B.J.; Ryan, W.

    1984-09-01

    Extensive numbers of new photoelectric data have been collected and analyzed to investigate the modal behavior of VZ Cnc. Its previously observed periods yield a period ratio of 0.80 implying pulsation in the first and second radial overtones. Of the seventeen delta Scuti stars listed by Fitch and Sziedl which have well-determined periods, it is the only star which apparently does not pulsate in the fundamental mode. This peculiarity is investigated from the standpoint of a change with time of the dominant pulsation mode and atmospheric helium settling. The former suggestion is found to be untenable. The latter is found to increase the theoretical ratio of the first overtone/fundamental periods to that observed. It is thus suggested that VZ Cnc pulsates in these lowest order modes and that its atmosphere has been largely depleted of helium. However, if VZ Cnc has a temperatur as large as 7500 K, its position in the instability strip places this star near the transition line between the first and second overtone pulsation modes, beyond the fundamental mode blue edge. In this case the fundamental mode cannot exist, and the 1H and 2H modes are properly identified.

  13. Period variations and evolution of Delta Scuti variables

    NASA Astrophysics Data System (ADS)

    Jiang, Shi-Yang

    1993-12-01

    The Short periods of Delta Scuti Stars allow observational detection of the period changes expected from the stellar evolution within several tens years. For about 30 years we have kept this topic as a small systematic observational program with our 60 cm telescope. Here we publish the period variation of 18 stars . The data of 28 And are taken from R. Garrido et al. (1983), 211; the period variation rate of 4 CVn is given by M. Breger. Both of them are low amplitude variables.

  14. Masses and ages of Delta Scuti stars in eclipsing binary systems

    NASA Astrophysics Data System (ADS)

    Tsvetkov, Ts. G.; Petrova, Ts. C.

    1993-05-01

    By using data mainly from Frolov et al. (1982) for four Delta Scuti stars in eclipsing binary systems, AB Cas, Y Cam, RS Cha, and AI Hya, their physical parameters, distances, and radial pulsation modes are determined. The evolutionary track systems of Iben (1967), Paczynski (1970), and Maeder and Meynet (1988) are interpolated in order to estimate evolutionary masses Me and ages t of these variables. Their pulsation masses MQ are estimated from the fitting formulae of Faulkner (1977) and Fitch (1981). Our estimates of evolutionary masses M(e) and pulsation masses M(Q) are close to the masses M determined by Frolov et al. from the star binarity. The only exception is AB Cas, for which there is no agreement between certain star parameters. Another, independent approach is also applied to the stars RS Cha and AI Hya: by using their photometric indices b - y and c(1) from the catalog of Lopez de Coca et al. (1990) and appropriate photometric calibrations, other sets of physical parameters, distances, modes, ages, and evolutionary and pulsation masses of both variables are obtained.

  15. Chromospheric activity in Delta Scuti stars - The suspected variable Tau Cygni

    NASA Technical Reports Server (NTRS)

    Fracassini, M.; Pasinetti Fracassini, L. E.; Mariani, A.; Pastori, L.; Teays, T. J.

    1991-01-01

    High-resolution IUE spectra of the suspected variable Tau Cyg were obtained to search for a possible variability of the Mg II h, k double-peaked emission. The observations, spanning an interval of about 6.3 h, have shown flux excursions within or just near 15 percent, a value suggested as the detection limit of actual variations with IUE spectra. A variability, difficult to explain, could be present in the ratios Fk2v/Fk2r. The emission fluxes seem to be higher than those of the Delta Scuti variables Rho Pup and Beta Cas. This comparison could give some insights on the possible role of the convection on the pulsational and chromospheric activities of Tau Cyg. A positive correlation between the total emission fluxes and the rotational velocities of these stars was found.

  16. CzeV293 and CzeV581-Two new high-amplitude double-mode delta Scuti stars

    NASA Astrophysics Data System (ADS)

    Skarka, M.; Cagaš, P.

    2016-07-01

    We report on the discovery of two high-amplitude double-mode delta Scuti stars in constellations of Hercules and Auriga. The stars were observed photometrically in five and two seasons, respectively. Frequency analysis revealed that both stars show complex pulsation behaviour with two independent modes and several combination peaks. Placing the stars into the Petersen diagram allowed us to identify the pulsation modes as the fundamental and the first overtone. Both stars follow the general trend for F/1O pulsators in the short-period part of the Petersen diagram and turned out to be classical members of HADS group of variables. Using empirical formulae we roughly estimate visual absolute magnitude, intrinsic (B - V) 0 colour index and temperature of the target stars.

  17. K2 observations of 95 Vir: δ Scuti pulsations in a chromospherically active star

    NASA Astrophysics Data System (ADS)

    Paunzen, Ernst; Hümmerich, Stefan; Bernhard, Klaus; Walczak, Przemek

    2017-06-01

    We have searched for photometric variability in 95 Vir, a fast rotating, chromospherically active early F-type star, which was observed in the framework of Campaign 6 of the Kepler K2 mission. Available literature information on 95 Vir was procured, and well-established calibrations were employed to verify the derived astrophysical parameters. We have investigated the location of our target star in the MBol versus log Teff diagram, which provides information on the evolutionary status. We have discussed our results in detail, drawing on literature information and the theoretical predictions of state-of-the-art pulsation models, with the aim of unravelling the underlying variability mechanisms. From an analysis of 3400 long-cadence measurements, we have identified two main frequencies and several harmonics in our target star. We attribute the main frequency, f 1 = 9.537 28 d-1, to δ Scuti pulsations. The origin of the secondary signal, f 2 = 1.071 29 d-1, is less clear. We have investigated three possible interpretations of the low-frequency variation: binarity, pulsation and rotational modulation. Current evidence favours an interpretation of f 2 as a signature of the rotational period caused by the presence of cool star-spots, which goes along well with the observed chromospheric activity. However, phase-resolved spectroscopy is needed to verify this assumption. We briefly consider other chromospherically active δ Scuti stars that have been presented in the literature. A search for star-spot-induced photometric variability in these objects might be of great interest, as well as an investigation of the interplay between chromospheric and pulsational activity.

  18. Comparing the asteroseismic properties of pulsating extremely low-mass pre-white dwarf stars and δ Scuti stars

    NASA Astrophysics Data System (ADS)

    Arias, J. P. Sánchez; Córsico, A. H.; Romero, A. D.; Althaus, L. G.

    2017-09-01

    We present the first results of a detailed comparison between the pulsation properties of pulsating Extremely Low-Mass pre-white dwarf stars (the pre-ELMV variable stars) and δ Scuti stars. The instability domains of these very different kinds of stars nearly overlap in the log Teff vs. log g diagram, leading to a degeneracy in the classification of the stars. Our aim is to provide asteroseismic tools for their correct classification.

  19. HD 114839 - An Am star showing both δ Scuti and γ Dor pulsations discovered through MOST photometry

    NASA Astrophysics Data System (ADS)

    King, H.; Matthews, J. M.; Row, J. F.; Cameron, C.; Kuschnig, R.; Guenther, D. B.; Moffat, A. F. J.; Rucinski, S. M.; Sasselov, D.; Walker, G. A. H.; Weiss, W. W.

    2006-12-01

    Using MOST1 (Microvariability and Oscillations of STars) satellite guide star photometry, we have discovered a metallic A star showing hybrid p- and gmode pulsations. HD 114839 was observed nearly continuously for 10 days in March, 2005. We identify frequencies in three groups: the first centered near 2 cycles/day, in the γ Dor pulsation range, and two others near 8 and 20, both in the δ Scuti range. This is only the fourth known such hybrid pulsator, including another MOST discovery (Rowe et al. 2006).

  20. HR 7920: a very bright new Delta Scuti star with possible Gamma Doradus variations

    NASA Astrophysics Data System (ADS)

    Koen, C.; van Wyk, F.; Laney, C. D.; Kilkenny, D.

    2017-04-01

    We present photometric and high-dispersion spectroscopic measurements that show HR 7920 is a periodic variable. The photometry reveals at least four frequencies higher that 10 d-1, two of which are also probably present in the radial velocity variations. The frequencies are in a range typical of δ Scuti star pulsations. A further low frequency of about 2.8 d-1 may be present in both radial velocities and photometry; if real, this points to γ Doradus variability, which would make HR 7920 a hybrid pulsator. An attempt is made to identify the modes of the δ Scuti pulsations, which include both radial and non-radial modes. A new rotational velocity of 75 km s-1 is derived from co-added spectra, contrasting with published values in the range 128-150 km s-1.

  1. Pulsation analysis of the high amplitude δ Scuti star CW Serpentis

    NASA Astrophysics Data System (ADS)

    Niu, Jia-Shu; Fu, Jian-Ning; Zong, Wei-Kai

    2013-10-01

    Time-series photometric observations were made for the high amplitude δ Scuti star CW Ser between 2011 and 2012 at the Xinglong Station of National Astronomical Observatories, Chinese Academy of Sciences. After performing the frequency analysis of the light curves, we confirmed the fundamental frequency of f = 5.28677 c d-1, together with seven harmonics of the fundamental frequency, which are newly detected. No additional frequencies were detected. The O — C diagram, produced with the 21 newly determined times of maximum light combined with those provided in the literature, helps to obtain a new ephemeris formula of the times of maximum light with the pulsation period of 0.189150355 ± 0.000000003 d.

  2. Deep Infrared ZAMS Fits to Benchmark Open Clusters Hosting Delta Scuti Stars

    NASA Astrophysics Data System (ADS)

    Majaess, D. J.; Turner, D. G.; Lane, D. J.; Krajci, T.

    2011-09-01

    This research aims to secure precise distances for cluster δ Scuti stars in order to investigate their properties via a VI Wesenheit framework. Deep JHKs color-color and zero-age main sequence (ZAMS) relations derived from ~700 unreddened stars featuring 2MASS photometry and precise Hipparcos parallaxes (d≤25 pc) are applied to establish distances to several benchmark open clusters that host δ Scuti stars: Hyades, Pleiades, Praesepe, α Persei, and M67 (d = 47 ± 2, 138 ± 6, 183 ± 8, 171 ± 8, 815 ± 40 pc). That analysis provided constraints on the Δ Sct sample's absolute Wesenheit magnitudes (W_VI,0), evolutionary status, and pulsation modes (order, n). The reliability of JHKs established cluster parameters is demonstrated via a comparison with van Leeuwen (2009a) revised Hipparcos results. Distances for seven of nine nearby (d≤250 pc) clusters agree, and the discrepant cases (Pleiades and Blanco 1) are unrelated to (insignificant) Te-(J-Ks) variations with cluster age or iron abundance. JHKs photometry is tabulated for ~3x10^3 probable cluster members on the basis of proper motions (NOMAD). The deep JHKs photometry extends into the low mass regime (~0.4 M_sun) and ensures precise (≤5%) ZAMS fits. Pulsation modes inferred for the cluster δ Scuti stars from VI Wesenheit and independent analyses are comparable (±n), and the methods are consistent in identifying higher order pulsators. Most small-amplitude cluster δ Scuti stars lie on VI Wesenheit loci characterizing n≥1 pulsators. A distance established to NGC 1817 from δ Scuti stars (d~1.7 kpc) via a universal VI Wesenheit template agrees with estimates in the literature, assuming the variables delineate the n≥1 boundary. Small statistics in tandem with other factors presently encumber the use of mmag Δ Scuti stars as viable distance indicators to intermediate-age open clusters, yet a VI Wesenheit approach is a pertinent means for studying δ Scuti stars in harmony with other methods.

  3. The role of turbulent pressure as a coherent pulsational driving mechanism: the case of the δ Scuti star HD 187547

    SciTech Connect

    Antoci, V.; Houdek, G.; Kjeldsen, H.; Trampedach, R.; Arentoft, T.; Cunha, M.; Handler, G.; Lüftinger, T.; Murphy, S.

    2014-12-01

    HD 187547 was the first candidate that led to the suggestion that solar-like oscillations are present in δ Scuti stars. Longer observations, however, show that the modes interpreted as solar-like oscillations have either very long mode lifetimes, longer than 960 days, or are coherent. These results are incompatible with the nature of 'pure' stochastic excitation as observed in solar-like stars. Nonetheless, one point is certain: the opacity mechanism alone cannot explain the oscillation spectrum of HD 187547. Here we present new theoretical investigations showing that convection dynamics can intrinsically excite coherent pulsations in the chemically peculiar δ Scuti star HD 187547. More precisely, it is the perturbations of the mean Reynold stresses (turbulent pressure) that drives the pulsations and the excitation takes place predominantly in the hydrogen ionization zone.

  4. Pulsational frequencies of the eclipsing δ Scuti star HD 172189. Results of the STEPHI XIII campaign

    NASA Astrophysics Data System (ADS)

    Costa, J. E. S.; Michel, E.; Peña, J.; Creevey, O.; Li, Z. P.; Chevreton, M.; Belmonte, J. A.; Alvarez, M.; Fox Machado, L.; Parrao, L.; Pérez Hernández, F.; Fernández, A.; Fremy, J. R.; Pau, S.; Alonso, R.

    2007-06-01

    Context: The eclipsing δ Scuti star HD 172189 is a probable member of the open cluster IC 4756 and a promising candidate target for the CoRoT mission. Aims: The detection of pulsation modes is the first step in the asteroseismological study of the star. Further, the calculation of the orbital parameters of the binary system allows us to make a dynamical determination of the mass of the star, which works as an important constraint to test and calibrate the asteroseismological models. Methods: We performed a detailed frequency analysis of 210 hours of photometric data of HD 172189 obtained from the STEPHI XIII campaign. Results: We have identified six pulsation frequencies with a confidence level of 99% and a seventh with a 65% confidence level of 65%, in the range between 100-300 μHz. In addiction, three eclipses were observed during the campaign, allowing us to improve the determination of the orbital period of the system. Table 1 is only available in electronic form at http://www.aanda.org

  5. Turbulent convection and pulsation stability of stars - II. Theoretical instability strip for δ Scuti and γ Doradus stars

    NASA Astrophysics Data System (ADS)

    Xiong, D. R.; Deng, L.; Zhang, C.; Wang, K.

    2016-04-01

    By using a non-local and time-dependent convection theory, we have calculated radial and low-degree non-radial oscillations for stellar evolutionary models with M = 1.4-3.0 M⊙. The results of our study predict theoretical instability strips for δ Scuti and γ Doradus stars, which overlap with each other. The strip of γ Doradus is slightly redder in colour than that of δ Scuti. We have paid great attention to the excitation and stabilization mechanisms for these two types of oscillations, and we conclude that radiative κ mechanism plays a major role in the excitation of warm δ Scuti and γ Doradus stars, while the coupling between convection and oscillations is responsible for excitation and stabilization in cool stars. Generally speaking, turbulent pressure is an excitation of oscillations, especially in cool δ Scuti and γ Doradus stars and all cool Cepheid- and Mira-like stars. Turbulent thermal convection, on the other hand, is a damping mechanism against oscillations that actually plays the major role in giving rise to the red edge of the instability strip. Our study shows that oscillations of δ Scuti and γ Doradus stars are both due to the combination of κ mechanism and the coupling between convection and oscillations, and they belong to the same class of variables at the low-luminosity part of the Cepheid instability strip. Within the δ Scuti-γ Doradus instability strip, most of the pulsating variables are very likely hybrids that are excited in both p and g modes.

  6. First light curve analysis of the high-amplitude Delta Scuti star GSC 4552-1498

    NASA Astrophysics Data System (ADS)

    Jafarzadeh, S. J.; Poro, A.

    2017-07-01

    We carried out observation of the HADS (High-Amplitude Delta Scuti) variable GSC 4552-1498 through three filters. Our goal was to consider its periodic behavior using our photometry data in addition to previous observations. A new ephemeris and determination of oscillation modes of the star based on Fourier analysis are presented. The Two color diagram of the star as a function of its phase is shown. Finally, some of the star's physical parameters including mass, radius and luminosity are calculated.

  7. The Pulsational Behavior of the High Amplitude d Scuti Star RS Gruis

    NASA Astrophysics Data System (ADS)

    García, J.

    2012-06-01

    RS Gruis is a high-amplitude delta Scuti-type variable star with a mean amplitude of almost half a magnitude in V and a period of almost 3.5 hours. The most recent study of this star by Derekas et al. (2009) suggests the presence of a low-mass dwarf star companion close to the variable star with a period of 11.5 days. Rodriguez et al. (1995) have also shown a decreasing rate of the period of dP/Pdt = -10.6 • 10-8 / y. Using an extended dataset comprising BVIc CCD observations acquired at the Astronomical Observatory of the Instituto Copérnico, data from ASAS and HIPPARCOS, and the existing CCD observations in the AAVSO International Database, we have performed an extensive periodgram and times of maximum analysis looking for long term variations. As a preliminary result, we confirmed that the period varies, but, since 1995, instead of decreasing, it has increased. We also found a small peak in the power spectrum in good agreement with the period suggested for the binary companion.

  8. How to separate the low amplitude delta Scuti variation in CoRoT data unambigousely?

    NASA Astrophysics Data System (ADS)

    Benko, Jozsef M.; Paparo, Margit

    2015-08-01

    Rich regular frequency patterns were found in the Fourier spectra of low-amplitude Delta Scuti stars observed by CoRoT satellite. The CoRoT observations are, however, influenced by the disturbing effect of the SAA. The effect is marginal for high amplitude variable stars but it could be dangerous in the case of low amplitude variables, especially if the frequency range of the intrinsic variation overlaps the instrumental frequencies. Systematic tests were carried out both on synthetic and real data. Our aim was to determine a limit amplitude above which we were sure that the frequency pattern belonged to the stars.

  9. The effect of diffusion on pulsations of stars on the upper main sequence --- δ Scuti and metallic A stars

    NASA Astrophysics Data System (ADS)

    Turcotte, S.; Richer, J.; Michaud, G.; Christensen-Dalsgaard, J.

    2000-08-01

    Recent dramatic improvements in the modeling of abundance evolution due to diffusion in A stars have been achieved with the help of monochromatic opacity tables from the OPAL group. An important result in the context of stellar pulsations is the substantial helium abundance shown to be left over in the driving region of δ Scuti-type pulsations in chemically peculiar Am stars. An accurate opacity profile in the entire stellar envelope including the full effect of heavy elements is also now available for the first time. Pulsations are shown to be excluded for young Am stars but occur naturally when these stars evolve off the ZAMS. The predicted variable metallic A stars all lie towards the red edge of the instability strip, in qualitative agreement with the observed variable δ Delphini and mild Am stars. Results show little direct excitation from iron-peak elements in A-type stars. The main abundance effect is due to the settling of helium, along with a marginal effect due to the enhancement of hydrogen.

  10. High azimuthal number pulsation modes in fast rotating δ Scuti stars: the case of HD 101158 = V837 Cen.

    NASA Astrophysics Data System (ADS)

    Mantegazza, L.

    1997-07-01

    The frequency analysis of the line profile variations of the fast rotating (vsini=132km/s) δ Scuti star HD 101158, observed for three consecutive nights, shows the presence of two high azimuthal number non radial pulsation modes. The star is probably seen almost equator-on and both modes (ν_i_=12.9c/d and ν_2_=18.5 c/d) are prograde with m=-10 and m=-14 or -15 respectively; their frequencies are different with respect to the three frequencies identified in photometric data (Poretti 1991), which probably owe due to low l modes. Indications of the presence of these photometric modes have been found from the frequency analysis of the first two line moments. The line profile variations also show the possible presence of further modes with frequencies of 16.2, 20.3 and 21.1c/d and small amplitudes.

  11. Discovery of multiple pulsations in the new δ Scuti star HD 92277: Asteroseismology from Dome A, Antarctica

    SciTech Connect

    Zong, Weikai; Fu, Jian-Ning; Niu, Jia-Shu; Zhu, Zonghong; Charpinet, S.; Vauclair, G.; Ashley, Michael C. B.; Lawrence, Jon S.; Luong-Van, Daniel; Cui, Xiangqun; Gong, Xuefei; Feng, Longlong; Wang, Lifan; Yuan, Xiangyan; Zhu, Zhenxi; Liu, Qiang; Wang, Lingzhi; Zhou, Xu; Pennypacker, Carl R.; York, Donald G.

    2015-02-01

    We report the discovery of low-amplitude oscillations in the star HD 92277 from long, continuous observations in the r and g bands using the CSTAR telescopes in Antarctica. A total of more than 1950 hours of high-quality light curves were used to categorize HD 92277 as a new member of the δ Scuti class. We have detected 21 (20 frequencies are independent and one is the linear combination) and 14 (13 frequencies are independent and one is the linear combination) pulsation frequencies in the r and g bands, respectively, indicating a multi-periodic pulsation behavior. The primary frequency f{sub 1} = 10.810 days{sup −1} corresponds to a period of 0.0925 days and is an l = 1 mode. We estimate a B − V index of 0.39 and derive an effective temperature of 6800 K for HD 92277. We conclude that long, continuous and uninterrupted time-series photometry can be performed from Dome A, Antarctica, and that this is especially valuable for asteroseismology where multi-color observations (often not available from space-based telescopes) assist with mode identification.

  12. Intensive Observations of Cataclysmic, RR Lyr, and High Amplitude delta Scuti (HADS) Variable Stars

    NASA Astrophysics Data System (ADS)

    Hambsch, F.-J.

    2012-06-01

    An intensive observing campaign is ongoing to study cataclysmic, RR Lyr (with and without Blazhko effect), and High Amplitude delta Scuti (HADS) variable stars. These observations are based on requests and in collaboration with different organisations (CBA, VSNET, GEOS) and individuals. Observations are taken from my private observatories in Belgium, Chile, and through shared use of an observatory belonging to the AAVSOnet in New Mexico. Examples of individual stars intensively followed-up on are: CD Ind and BW Scl, two cataclysmic variables; NU Aur, an RR Lyr star with strong Blazhko effect; and GSC0762-0110, a HADS star. Many publications in different journals including Astronomy and Astrophysics have already emerged from this research.

  13. THE TAIWAN-AMERICAN OCCULTATION SURVEY PROJECT STELLAR VARIABILITY. I. DETECTION OF LOW-AMPLITUDE {delta} SCUTI STARS

    SciTech Connect

    Kim, D.-W.; Protopapas, P.; Alcock, C.; Wright, N. J.; Bianco, F. B.; Lehner, M. J.; Byun, Y.-I.; Kyeong, J.; Lee, B.-C.; Axelrod, T.; Chen, W.-P.; Lin, H.-C.; Coehlo, N. K.; Rice, J. A.; Cook, K. H.; Marshall, S. L.; Dave, R.; King, S.-K.; Lee, T.; Porrata, R.

    2010-02-15

    We analyzed data accumulated during 2005 and 2006 by the Taiwan-American Occultation Survey (TAOS) in order to detect short-period variable stars (periods of {approx}<1 hr) such as {delta} Scuti. TAOS is designed for the detection of stellar occultation by small-size Kuiper Belt Objects and is operating four 50 cm telescopes at an effective cadence of 5 Hz. The four telescopes simultaneously monitor the same patch of the sky in order to reduce false positives. To detect short-period variables, we used the fast Fourier transform algorithm (FFT) in as much as the data points in TAOS light curves are evenly spaced. Using FFT, we found 41 short-period variables with amplitudes smaller than a few hundredths of a magnitude and periods of about an hour, which suggest that they are low-amplitude {delta} Scuti stars. The light curves of TAOS {delta} Scuti stars are accessible online at the Time Series Center Web site (http://timemachine.iic.harvard.edu)

  14. VizieR Online Data Catalog: Delta Scuti variables. II. DY Her (Milone+, 1994)

    NASA Astrophysics Data System (ADS)

    Milone, E. F.; Wilson, W. J. F.; Fry, D. J. I.; Schiller, S. J.

    1995-02-01

    This is the second paper in a series on large-amplitude delta Scuti stars intended to determine Baade-Wesselink radii and luminosities with precision. The first paper (Wilson et al., 1993PASP..105..809W) discussed our method of analysis and its application to EH Librae; in this we discuss the observations and analysis of DY Herculis. Optical and infrared photometry and cross-correlated radial-velocity data have been obtained and analyzed. Fourier representations for the UBVRIJHK light curves and for the radial-velocity curves were used to derive a value for the minimum radius for each of 60 combinations of flux and color index. From these we adopt a mean value for the minimum radius of Rmin=2.77+/-0.20R⊙. When combined with effective temperatures from Breger et al. (1978PASP...90..754B), we find a mean bolometric luminosity of =21.70L⊙ and a mean absolute magnitude of =1.41. The radial excursion is 0.149R⊙. We use the same procedure to improve our results for EH Librae, deriving Rmin for each of 42 combinations of flux and color index, and obtain mean values of Rmin=2.62+/-0.19R⊙, =24.56L⊙ and =1.27. (3 data files).

  15. GSC 7672 2238: a new eclipsing binary system near the delta scuti star AI Vel

    NASA Astrophysics Data System (ADS)

    Santos-Júnior, J. M.; Pereira, P. C. R.; Cruz, W. S.; Andrade-Pilling, D. P.

    2003-08-01

    We report the discovery of a new eclipsing binary star in the field of the Delta Scuti variable star AI Vel. Initially used as a check star during a monitoring of AI Vel, GSC 7672: 2238 turned out to be variable as soon as we started the project. Time series CCD photometry were performed during 2002 and 2003 using the Meade LX200 (25cm) telescope of Fundação Planetário da Cidade do Rio de Janeiro. The observed times of primary minima provided an orbital period of 0.97188 day. The depth of the primary and secondary minima is about 0m.5 and 0m.2 respectively. The amount of data and the behavior of the light curve led us to interpret this modulation as related to the orbital motion of a short-period Algol. The light curves show discrepances around phases 0.1-0.2, just after the primary minimum. This behavior may be well explained in terms of mass transfer from the lobe-filling secundary star. In addition, we made spectroscopic observation at Perkin-Elmer 1.6m telescope on the Laboratório Nacional de Astrofí sica. The optical spectrum shows clearly the absorption Ha line, typical of short-period Algols with transient or absent disks.

  16. Understanding the dynamical structure of pulsating stars. HARPS spectroscopy of the δ Scuti stars ρ Puppis and DX Ceti

    NASA Astrophysics Data System (ADS)

    Nardetto, N.; Poretti, E.; Rainer, M.; Guiglion, G.; Scardia, M.; Schmid, V. S.; Mathias, P.

    2014-01-01

    Context. High-resolution spectroscopy is a powerful tool to study the dynamical structure of a pulsating star's atmosphere. Aims: We aim at comparing the line asymmetry and velocity of the two δ Sct stars ρ Pup and DX Cet with previous spectroscopic data obtained on classical Cepheids and β Cep stars. Methods: We obtained, analysed and discuss HARPS high-resolution spectra of ρ Pup and DX Cet. We derived the same physical quantities as used in previous studies, which are the first-moment radial velocities and the bi-Gaussian spectral line asymmetries. Results: The identification of f = 7.098 d-1 as a fundamental radial mode and the very accurate Hipparcos parallax promote ρ Pup as the best standard candle to test the period-luminosity relations of δ Sct stars. The action of small-amplitude nonradial modes can be seen as well-defined cycle-to-cycle variations in the radial velocity measurements of ρ Pup. Using the spectral-line asymmetry method, we also found the centre-of-mass velocities of ρ Pup and DX Cet, Vγ = 47.49 ± 0.07 km s-1 and Vγ = 25.75 ± 0.06 km s-1, respectively. By comparing our results with previous HARPS observations of classical Cepheids and β Cep stars, we confirm the linear relation between the atmospheric velocity gradient and the amplitude of the radial velocity curve, but only for amplitudes larger than 22.5 km s-1. For lower values of the velocity amplitude (i.e., <22.5 km s-1), our data on ρ Pup seem to indicate that the velocity gradient is null, but this result needs to be confirmed with additional data. We derived the Baade-Wesselink projection factor p = 1.36 ± 0.02 for ρ Pup and p = 1.39 ± 0.02 for DX Cet. We successfully extended the period-projection factor relation from classical Cepheids to δ Scuti stars. This work is based on observations made with the 3.6 m telescope at La Silla Observatory under the ESO Large Programme LP185.D-0056.

  17. DRIVING G-MODE PULSATIONS IN GAMMA DORADUS VARIABLES

    SciTech Connect

    J. GUZIK; A. KAYE; ET AL

    2000-10-10

    The {gamma} Doradus stars are a newly-discovered class of gravity-mode pulsators which lie just at or beyond the red edge of the {delta} Scuti instability strip. We present the results of calculations which predict pulsation instability of high-order g-modes with periods between 0.4 and 3 days, as observed in these stars. The pulsations are driven by the modulation of radiative flux by convection at the base of a deep envelope convection zone. Pulsation instability is predicted only for models with temperatures at the convection zone base between {approximately}200,000 and {approximately}480,000 K. The estimated shear dissipation due to turbulent viscosity within the convection zone, or in an overshoot region below the convection zone, can be comparable to or even exceed the predicted driving, and is likely to reduce the number of unstable modes, or possibly to quench the instability. Additional refinements in the pulsation modeling are required to determine the outcome. A few Doradus stars have been observed that also pulsate in {delta} Scuti-type p-modes, and at least two others have been identified as chemically peculiar. Since our calculated driving region is relatively deep, Doradus pulsations are not necessarily incompatible with surface abundance peculiarities or with {delta} Scuti p-mode pulsations driven by the H and He-ionization {kappa} effect. Such stars will provide useful observational constraints on the proposed Doradus pulsation mechanism.

  18. Recently Refined Periods for the High Amplitude delta Scuti Stars V1338 Centauri, V1430 Scorpii, and V1307 Scorpii

    NASA Astrophysics Data System (ADS)

    Axelsen, R. A.

    2015-12-01

    Digital Single Lens Reflex (DSLR) photometry of the high amplitude d Scuti stars V1338 Centauri, V1430 Scorpii, and V1307 Scorpii was taken during the southern autumn and winter of 2015. Fourier analysis revealed pulsation frequencies corresponding to periods very close to those previously reported with significant contributions from harmonics. Only in the case of V1430 Scorpii was another independent frequency detected. The oscillation periods were refined by calculating linear ephemerides based on previously published epochs for each star, and the epochs determined by the author. These periods are: V1338 Centauri, 0.13093808 d; V1430 Scorpii, 0.08377709 d; and V1307 Scorpii, 0.11703066 d.

  19. Statistical Properties of Galactic δ Scuti Stars: Revisited

    NASA Astrophysics Data System (ADS)

    Chang, S.-W.; Protopapas, P.; Kim, D.-W.; Byun, Y.-I.

    2013-05-01

    We present statistical characteristics of 1578 δ Scuti stars including nearby field stars and cluster member stars within the Milky Way. We obtained 46% of these stars (718 stars) from work by Rodríguez and collected the remaining 54% of stars (860 stars) from other literature. We updated the entries with the latest information of sky coordinates, color, rotational velocity, spectral type, period, amplitude, and binarity. The majority of our sample is well characterized in terms of typical period range (0.02-0.25 days), pulsation amplitudes (<0.5 mag), and spectral types (A-F type). Given this list of δ Scuti stars, we examined relations between their physical properties (i.e., periods, amplitudes, spectral types, and rotational velocities) for field stars and cluster members, and confirmed that the correlations of properties are not significantly different from those reported in Rodríguez's work. All the δ Scuti stars are cross-matched with several X-ray and UV catalogs, resulting in 27 X-ray and 41 UV-only counterparts. These counterparts are interesting targets for further study because of their uniqueness in showing δ Scuti-type variability and X-ray/UV emission at the same time. The compiled catalog can be accessed through the Web interface http://stardb.yonsei.ac.kr/DeltaScuti.

  20. Analysis of the Petersen Diagram of Double Mode High Amplitude delta Scuti Stars

    NASA Astrophysics Data System (ADS)

    Furgoni, R.

    2016-06-01

    I created the Petersen diagram relative to all the Double Mode High Amplitude ? Scuti stars listed in the AAVSO's International Variable Star Index (Watson et al. 2007-2015) up to date December 29, 2015. For the first time I noticed that the ratio between the two periods P1/P0 seems in evident linear relation with the duration of the period P0, a finding never explicitly described in literature regarding this topic.

  1. Observations and a new interpretation for the Delta Scuti variable star VZ CANCRI

    NASA Astrophysics Data System (ADS)

    Cox, A. N.; McNamara, B. J.; Ryan, W.

    1984-09-01

    The pulsation characteristics of VZ Cnc were examined, together with the possibility of He settling in the stellar envelope. Data were gathered with the 40 cm Tortugas telescope and photometry system and included comparison figures in UBV for HD 73938 and HD 74308. The observations were made in February-April 1983 and were subjected to Fourier transforms and least squares analysis. Light variations in VZ Cnc were attributed to coupling between two frequencies, a condition which produced higher amplitudes than either component alone. A stable period ratio of 0.80 was calculated, with the main pulsational energy concentrated in the first frequency, 5.6 cycles/day. The second frequency exhibited 7.0 cycles/day. The period ratio supports a He depletion process. A stellar temperature of 7500 K would eliminate the necessity of He settling as part of the model and confirm the presence of 1H and 2H, rather than fundamental, pulsation modes.

  2. Analysis of Pulsating Components in the Eclipsing Binary Systems LT Herculis, RZ Microscopii, LY Puppis, V632 Scorpii, and V638 Scorpii

    NASA Astrophysics Data System (ADS)

    Streamer, M.; Bohlsen, T.; Ogmen, Y.

    2016-06-01

    Eclipsing binary stars are especially valuable for studies of stellar evolution. If pulsating components are also present then the stellar interior can be studied using asteroseismology techniques. We present photometric data and the analysis of the delta Scuti pulsations that we have discovered in five eclipsing binary systems. The systems are: LT Herculis, RZ Microscopii, LY Puppis, V632 Scorpii and V638 Scorpii. The dominant pulsation frequencies range between 13 - 29 cycles per day with semi-amplitudes of 4 - 20 millimagnitudes.

  3. Linear nonradial pulsation theory. Lecture 7

    SciTech Connect

    Cox, A.N.

    1983-03-14

    Many of the upper main-sequence stars pulsate in spheroidal nonradial modes. We know this to be true in numerous cases, as we have tabulated for the ..beta.. Cephei and delta Scuti variables in previous lectures. However, we cannot identify the actual mode for any star except for the low-order pressure p and f modes of our sun. It remains a great challenge to clearly state what really is occurring, in the process we learn more about how stars evolve and pulsate.

  4. Relationship between low and high frequencies in the \\delta Scuti star KIC 9764965

    NASA Astrophysics Data System (ADS)

    Rostopchina, A.; Breger, M.

    2014-10-01

    Two years of Kepler spacecraft data of the \\delta Sct/\\gamma Dor star KIC 9764965 revealed 67 statistically significant frequencies from 0.45 to 59.17 c d-1 (0.005 to 0.685 mHz). The 19 low frequencies do not show equidistant period spacing predicted for gravity modes of successive radial order. We note a favored frequency spacing of 2.053 c d-1 that appears in both the low-frequency (gravity mode) region and high-frequency (pressure mode) regions. The value of this frequency spacing also occurs as a dominant low frequency and in a high-frequency triplet. A peak at exactly twice the value of the 2.053 c d-1 mode is shown not to be a Fourier harmonic of the low-frequency peak due to a different amplitude variability. This behavior is also seen in other \\delta Sct stars. The test for resonant mode coupling between low and high frequencies could not be carried out due to the small amplitudes of the peaks, making it difficult to separate the parent and child modes.

  5. Pulsation spectrum of δ Scuti stars: the binary HD 50870 as seen with CoRoT and HARPS

    NASA Astrophysics Data System (ADS)

    Mantegazza, L.; Poretti, E.; Michel, E.; Rainer, M.; Baudin, F.; García Hernández, A.; Semaan, T.; Alvarez, M.; Amado, P. J.; Garrido, R.; Mathias, P.; Moya, A.; Suárez, J. C.; Auvergne, M.; Baglin, A.; Catala, C.; Samadi, R.

    2012-06-01

    Aims: We present the results obtained with the CoRoT satellite for HD 50870, a δ Sct star which was observed for 114.4 d. The aim of these observations was to evaluate the results obtained for HD 50844, the first δ Sct star monitored with CoRoT, on a longer time baseline. Methods: The 307,570 CoRoT datapoints were analysed with different techniques. The photometric observations were complemented over 15 nights of high-resolution spectroscopy with HARPS on a baseline of 25 d. These spectra were analysed to study the line profile variations and to derive the stellar physical parameters. Some uvby photometric observations were also obtained to better characterize the pulsation modes. Results: HD 50870 proved to be a low-amplitude, long-period spectroscopic binary system seen almost pole-on (i ≃ 21°). The brighter component, which also has the higher rotational velocity (vsini = 37.5 km s-1), is a δ Sct-type variable with a full light amplitude variation of about 0.04 mag. There is a dominant axisymmetric mode (17.16 d-1). Moreover, there are two groups of frequencies (about 19) in the intervals 6 - 9 and 13 - 18 d-1, with amplitudes ranging from a few mmag to 0.3 mmag. After the detection of about 250 terms (corresponding to an amplitude of about 0.045 mmag) a flat plateau appears in the power spectrum in the low-frequency region up to about 35 d-1. We were able to detect this plateau only thanks to the short cadence sampling of the CoRoT measurements (32 s). The density distribution vs. frequency of the detected frequencies seems to rule out the possibility that this plateau is the result of a process with a continuum power spectrum. The spacings of the strongest modes suggest a quasi-periodic pattern. We failed to find a satisfactory seismic model that simultaneously matches the frequency range, the position in the HR diagram, and the quasi-periodic pattern interpreted as a large separation. Nineteen modes were detected spectroscopically from the line profile

  6. New Perspectives on Stellar Pulsation and Pulsating Variable Stars

    NASA Astrophysics Data System (ADS)

    Nemec, James M.; Matthews, Jaymie M.

    The study of pulsating variable stars has undergone dramatic changes in the past decade. The use of Cepheids and RR Lyrae stars as distance indicators has been extended by the increased sensitivity afforded by CCD detectors and by infrared observations. Meanwhile, other classes of pulsators, such as Mira and SX Phe variables are providing independent checks of the distance scale. Long-standing discrepancies between "pulsational" and "evolutionary" masses are finally being resolved by the new OP and OPAL opacity calculations, as is the mystery of the β Cephei excitation mechanism. Seismology of the oscillations of the Sun, white dwarfs, Ap stars and delta Scuti stars has opened windows on internal stellar structure, while Doppler Imaging reveals an entire range of high-degree pulsations hitherto undetectable by conventional photometry or radial velocity measurements. Observations of Long Period Variables have cast a new light on the implications of mass loss for stellar evolution and the history of the interstellar medium. On other fronts, more rigorous treatments of convection and radiative diffusion are starting to bring theory and observation into closer agreement.This book, the proceedings of the International Astronomical Union's Colloquium 139 held in Victoria, British Columbia, Canada in July 1992, contains over thirty comprehensive reviews as well as summaries of over 100 contributed papers, reflecting the current scope of stellar pulsation research. It is an overview of the most recent developments in the field, and a preview of some of the advances expected in the decade to come.

  7. H-alpha/H-beta Light Curves for Pulsating Variable Stars

    NASA Astrophysics Data System (ADS)

    Hintz, Eric G.; Joner, Michael D.; Barnes, Jonathan

    2017-06-01

    In Joner & Hintz (2015) they discuss the development of a new calibrated H-alpha index similar in nature to the traditional H-beta index. It is demonstrated that the new H-alpha index tracks very well with the equivalent width of the line and the surface temperature. Therefore, we selected a sample of pulsating variable stars to test the possible use of the new index to track temperature changes in those stars over a pulsation cycle. We will present data on a sample of Cepheid, RR Lyrae, and delta Scuti variables. We will also examine changes in the H-alpha index potentially related to period changes in these objects.

  8. Observations and Orbital Analysis of the High-Amplitude Delta Scuti Star SZLyncis: The Unusual Orbital Precession

    NASA Astrophysics Data System (ADS)

    Li, Lin-Jia; Qian, Sheng-Bang

    2013-12-01

    We determined forty-two new times of light maximum from our photometry observations and WASP project, and collected all times of light maximum observed between 1961 and 2013 in order to calculate the orbital elements of the SZ Lyncis system and the secular change of the pulsation period with the classical O - C method. We confirmed the decrease of the longitude of the periastron passage with a rate of (-1.˚15 ±0.˚25) yr-1 , and discussed the causative mechanism. The results show that the precession of the star's orbit might be due to a close binary system, which means that the companion of SZ Lyncis is actually a binary system. We used the Hipparcos Intermediate Astrometric Data to obtain the complete orbital elements of the SZ Lyncis system, and found that the inclination, i, and parallax, πt , are 39.˚5 ± 17.˚7 and 2.61 ± 0.98 mas (corresponds to 380 ± 140 pc), respectively. We reanalyzed the mean radial velocities of SZ Lyncis given by Bardin and Imbert (1984), and noticed a weak variation existing in the residuals from a single-Keplerian fit. We suggest that more detailed high-precision spectroscopic observations are definitely needed in the future to check this short periodic change.

  9. Pulsation behavior of classical Am star 60 Tauri

    NASA Astrophysics Data System (ADS)

    Zhiping, Li

    2000-08-01

    Five nights photoelectric photometric observations through v and y bands confirm the pulsation of classical Am δ Scuti variable 60 Tau. Power spectrum of light curves shows multi-period pulsation behavior of 60 Tau and two pulsation modes f1=13.0364 and f2=11.8521 cycles per day are definitely identified. Classical Am star 60 Tau is a complicated pulsation δ Scuti variable. Considering the pulsation constant Q, 60 Tau is identified to be low overtone f or p1 modes tendentiously.

  10. RELATIONSHIP BETWEEN LOW AND HIGH FREQUENCIES IN {delta} SCUTI STARS: PHOTOMETRIC KEPLER AND SPECTROSCOPIC ANALYSES OF THE RAPID ROTATOR KIC 8054146

    SciTech Connect

    Breger, M.; Robertson, P.; Fossati, L.; Balona, L.; Kurtz, D. W.; Bohlender, D.; Lenz, P.; Mueller, I.; Lueftinger, Th.; Clarke, Bruce D.

    2012-11-01

    Two years of Kepler data of KIC 8054146 ({delta} Sct/{gamma} Dor hybrid) revealed 349 statistically significant frequencies between 0.54 and 191.36 cycles day{sup -1} (6.3 {mu}Hz to 2.21 mHz). The 117 low frequencies cluster in specific frequency bands, but do not show the equidistant period spacings predicted for gravity modes of successive radial order, n, and reported for at least one other hybrid pulsator. The four dominant low frequencies in the 2.8-3.0 cycles day{sup -1} (32-35 {mu}Hz) range show strong amplitude variability with timescales of months and years. These four low frequencies also determine the spacing of the higher frequencies in and beyond the {delta} Sct pressure-mode frequency domain. In fact, most of the higher frequencies belong to one of three families with spacings linked to a specific dominant low frequency. In the Fourier spectrum, these family regularities show up as triplets, high-frequency sequences with absolutely equidistant frequency spacings, side lobes (amplitude modulations), and other regularities in frequency spacings. Furthermore, within two families the amplitude variations between the low and high frequencies are related. We conclude that the low frequencies (gravity modes, rotation) and observed high frequencies (mostly pressure modes) are physically connected. This unusual behavior may be related to the very rapid rotation of the star: from a combination of high- and low-resolution spectroscopy we determined that KIC 8054146 is a very fast rotator ({upsilon} sin i = 300 {+-} 20 km s{sup -1}) with an effective temperature of 7600 {+-} 200 K and a surface gravity log g of 3.9 {+-} 0.3. Several astrophysical ideas explaining the origin of the relationship between the low and high frequencies are explored.

  11. Discovery of a magnetic field in the δ Scuti F2m star ρ Pup

    NASA Astrophysics Data System (ADS)

    Neiner, C.; Wade, G. A.; Sikora, J.

    2017-06-01

    ρ Pup is a δ Scuti F2 pulsator, known to host a main radial mode as well as non-radial pulsations, with chemical peculiarities typical of evolved Am stars. We present a high-precision spectropolarimetric observations of this star, obtained with ESPaDOnS at the Canada-France-Hawaii Telescope in the frame of the BRITE spectropolarimetric survey. A magnetic field is clearly detected in ρ Pup, with a longitudinal field strength below 1 G. This makes ρ Pup the second known magnetic δ Scuti discovered, after HD 188774, and a possible cool evolved counterpart of the recently discovered ultraweakly magnetic Am family.

  12. Photometry of ET Andromedae and pulsation of HD 219891

    NASA Astrophysics Data System (ADS)

    Weiss, W. W.; Kuschnig, R.; Mkrtichian, D. E.; Kusakin, A. V.; Kreidl, T. J.; Bus, S. J.; Osip, D. J.; Guo, Z.; Hao, J.; Huang, L.; Sareyan, J.-P.; Alvarez, M.; Bedolla, S. G.; Zverko, J.; Ziznovsky, J. \\V.; Mittermayer, P.; Zwintz, K.; Polosukhina, N.; Mironov, A. V.; Dorokhov, N. I.; Goranskij, V. P.; Dorokhova, T. N.; Schneider, H.; Hiesberger, F.

    1998-10-01

    ET And is a binary system with a B9p(Si) star as the main component. We report on the photometric observing campaigns in 1988, 1989 and 1994 which confirmed the rotation period of 1.618875 deg for ET And while refuting other published values. Furthermore, the controversial issue of pulsational stability of ET And is resolved since we have discovered pulsation for HD 219891, which was the main comparison star and sometimes exclusively used. The frequency of 10.0816 d(-1) , a semi-amplitude of 2.5 mmag, T_eff\\ and M_v suggest this comparison star to be a delta Scuti variable close to the blue border of the instability strip. The pulsational stability of ET And could be clearly established and hence no need exists to derive new driving mechanisms for stars between the classical instability strip and the region of slowly pulsating B-type (SPB) stars. Based on observations obtained at the Bulgarian National Observatory, Crimean Astrophysical Observatory (Ukraine), Lowell Observatory (USA), Mauna Kea (USA), Mt. Dushak-Erekdak (Turkmenistan), San Pedro (Mexico), Skalnate Pleso (Slovakia), Tien Shan (Kazakhstan) and Wise Observatory (Israel)

  13. VizieR Online Data Catalog: Pulsation model data for delta Cep and eta Aql (Merand+, 2015)

    NASA Astrophysics Data System (ADS)

    Merand, A.; Kervella, P.; Breitfelder, J.; Gallenne, A.; Coude du Foresto, V.; ten Brummelaar, T. A.; McAlister, H. A.; Ridgway, S.; Sturmann, L.; Sturmann, J.; Turner, N. H.

    2015-09-01

    FITS files containing the stars' (delta Cep and eta Aql) data and model presented in the paper. Each fits file has 3 HDU: 1- primary HDU: contains no data apart from the header. The header has the parameters of the model (keywords 'HIERARCH PARAM') as well as some other quantities derived from the modeling (keywords 'HIERARCH MODEL'). These quantities are aimed at people who would like to reproduce or compare their results with us. 2- 'DATA' HDU: this contains the data used for the fit. Each line is a scalar measurement described as follow: col1='MJD' (E) modified Julian date of the observations col2='OBS' (A50) description of the data point: the string before ";" defines the type, after ";" is the source. after | are anciliary data: for diam, UDdiam: [wavelengthum, interfbaseline_m] for mag: photometric band for color: photometric band1 - photometric band2 col3='MEAS' (E) the actual measurements. units are km/s for Vpuls or Vrad (which includes the p-factor correction), and mas (milli-arcseconds) for diameters (diam of UDdiam). col4='ERR' (E) the uncertainty on the measurement. col5='MODEL' (E) corresponding value predicted by the model col6='PHASE' (E) pulsation phase computed from the model ranges from 0 to 1. col7='PERIOD' (E) pulsation period computed from the model in days 3- 'MODEL' HDU: a tabulation of the pulsation model, as a function of pulsation phase. col1='PHASE' (E) phase from 0 to 1. col2='Vpuls' (E) pulsation velocity, in km/s. col3='Vrad' (E) radial velocity, in km/s. It is Vpuls/p-factor + Vgamma. col4='diam' (E) Rosseland angular diameter, in milliarcseconds (mas). col5='Teff' (E) effective temperature, in Kelvin. col6='Lum' (E) Luminosity in solar luminosities. col7='logg' (E) surface gravity, in log_10(cm/s2). col8,9,10='diamK xxxm' (E) biased angular diameters measured by an interferometer at baselines xxx (in m), for xxx=[100, 200, 300]. In milliarcseconds col>=11= 'MAG ...' or 'COLOR ...' (E) reddenned magnitudes or colors in various bands

  14. Detection of high-degree nonradial pulsations in Gamma Bootis

    NASA Technical Reports Server (NTRS)

    Kennelly, E. J.; Yang, S.; Walker, G. A. H.; Hubeny, I.

    1992-01-01

    The line-profile variations of the rapidly rotating Delta-Scuti star Gamma Bootis can be explained by high-degree nonradial pulsations (NRPs) with an apparent period approximately equal to 0.047 days. This same period was derived from two data sets taken three months apart wherein the amplitude increased by 30 percent. Such high-degree NRP cannot explain the apparent reversals previously observed by Auvergne at al. (1979) for this star in the cores of the hydrogen Balmer lines and Ca-II K line. The present radial-velocity variations can be reconciled with their 0.25-day spectroscopic period if an amplitude of about 1 km/s is adopted, an order of magnitude less than previous measurements. The presence of line-profile variations from high-degree modes probably limits the accuracy of radial-velocity measurents and can appear as bumps in the radial-velocity curve.

  15. On the Role of Resonances in Nonradial Pulsators

    NASA Technical Reports Server (NTRS)

    Buchler, J. R.; Goupil, M. J.; Hansen, C. J.

    1997-01-01

    dwarfs and delta Scuti stars.

  16. Pulsations of B star models by an opacity mechanism

    SciTech Connect

    Cox, A.N. ); Morgan, S.M. . Dept. of Astronomy)

    1990-01-01

    The pulsation mechanism for B stars has been sought for 30 years. No proposed radial or nonradial mechanism, either deeply seated or in the surface layers, has been successful in explaining all the observational details. Perhaps the missing piece in the puzzle is the opacity of the stellar material. Many times the first author has tried to make unconventional surface compositions give instability, but none were ever found. We now propose that the sudden appearance of a tremendous number of iron lines, as the temperature rises above about 150,000 K, gives a high sensitivity of the opacity to temperature at the very low densities found in these blue giants. Opacities need to increase quickly to a factor of three or more above the Cox-Tabor (1976) values in the range around 200,000 K. These increases are the same needed to decrease theoretical period ratios of double-mode Cepheids and {delta} Scuti variables to agree better with observations for conventional yellow giant masses. The reason why not all B stars pulsate is that a slight primordial deficit in the iron abundance in the surface layer (1 {times} 10{sup {minus}6} of the mass) can reduce the opacity and its sensitivity to temperature. A slight amount of iron concentration by radiative levitation could make a star pulsate even if it did not originally have enough primordial iron to cause this opacity mechanism to operate. Then any slow slight mixing caused by the unstable nonradial pulsations could restabilize the pulsations as actually observed in {alpha} Vir and {beta} CMa. Rapid levitation and mixing for the very luminous B stars with their very low density envelopes could even explain the puzzling luminous blue variables with this standard {kappa} mechanism. Large amplitude pulsations like those seen in BW Vul would indicate a somewhat larger iron abundance compared to all other B stars.

  17. The Music of the Stars : Spectroscopy of Pulsations in gamma Doradus Stars

    NASA Astrophysics Data System (ADS)

    Brunsden, Emily

    2013-05-01

    p>The mysteries of the interior structures of stars are being tackled with asteroseismology. The observable parameters of the surface pulsations of stars inform us of the interior characteristics of numerous classes of stars. The main-sequence gamma Doradus stars, just a little hotter than the Sun, offer the potential of determining stellar structure right down to the core. To determine the structural profile of a star, the observed frequencies and a full geometric description must be determined. This is only possible with long-term spectroscopic monitoring and careful analysis of the pulsation signature in spectral lines. This work seeks to identify the pulsational geometry of several gamma Doradus stars and to identify areas of improvement for current observation, analysis and modelling techniques. More than 4500 spectra were gathered on five stars for this purpose. For three stars a successful multi-frequency and mode identification solution was determined and significant progress has been made towards the understanding of a binary system involving a gamma Doradus star. A hybrid gamma Doradus/nbsp;delta Scuti pulsator was also intensely monitored and results from this work raise important questions about the classification of this type of star. Current analysis techniques were found to be fit-for-purpose for pure gamma Doradus stars, but stars with complexities such as hybrid pulsations and/or fast rotation require future development of the current models./p>

  18. Pulsation of λ Bootis stars: who wants to be a (non-)millionnaire interested in diffusion theories?

    NASA Astrophysics Data System (ADS)

    Matthews, Jaymie M.

    2002-02-01

    The lambda Bootis stars are globally 'normal' A-F stars which show abundance peculiarities for which two mechanisms have been mainly considered: diffusion combined with mass loss, and diffusion confined with accretion from the interstellar medium. The first theory implies ages for lambda Boo stars of at least 10^9 years, while the second cannot be effective if these objects are older than a few times 10^6 years. Preliminary photometric and spectroscopic variability surveys indicate that delta-Scuti-like pulsation occurs among about half of the lambda Boo class. The multiperiodic pulsators offer the prospect of applying asteroseismology to settle the age/origin debate. However, progress has been slow for the same reasons that confront attempts to model delta Scuti stars based on their eigenspectra. This frustration parallels that felt by many of us in our careers as poor astrophysicists, so I have incorporated into this paper a popular TV game show format to allow the reader to actively explore the problems while reading the Proceedings.

  19. Ultra-precise analysis of the light curves of CoRoT and Kepler δ Scuti stars

    NASA Astrophysics Data System (ADS)

    Pascual-Granado, Javier; Suárez, Juan Carlos; Garrido, Rafael

    2017-09-01

    It is well known that the residuals of the multifrequency analysis of δ Scuti stars are correlated, giving rise to challenging features such as a plateau (HD 50844, HD 50870, HD 49434, …) of non-resolved frequencies with amplitude higher than the expected noise level. Several hypotheses have been advanced to explain these features: effective convection, rotation, non-linear interactions, etc. We have recently demonstrated that in some cases the underlying function describing the light variations of δ Scuti stars has not the property of being analytic. The strong consequence of this result is that the Fourier expansion on which the harmonic analysis is based could be not justified. In order to know the extension of this phenomenon among δ Scuti stars, we have used photometric data from CoRoT seismofield and a set of Kepler stars. The results show that this inconsistency in the application of harmonic analysis is almost ubiquitous to the δ Scuti pulsating stars.

  20. Amplitude Variability in gamma Dor and delta Sct Stars Observed by Kepler

    SciTech Connect

    Guzik, Joyce Ann; Kosak, Mary Katherine; Bradley, Paul Andrew; Jackiewicz, Jason

    2015-08-17

    The NASA Kepler spacecraft data revealed a large number of new multimode nonradially pulsating gamma Dor and delta Sct variable stars. The Kepler high-precision long time-series photometry makes it possible to study amplitude variations of the frequencies, and recent literature on amplitude and frequency variations in nonradially pulsating variables is summarized. Several methods are applied to study amplitude variability in about a dozen gamma Doradus or delta Scuti candidate variable stars observed for several quarters as part of the Kepler Guest Observer program. The magnitude and timescale of the amplitude variations are discussed, along with the presence or absence of correlations between amplitude variations for different frequencies of a given star. Proposed causes of amplitude spectrum variability that will require further investigation are also discussed.

  1. High-resolution spectroscopy and abundance analysis of δ Scuti stars near the γ Doradus instability strip

    NASA Astrophysics Data System (ADS)

    Kahraman Aliçavuş, F.; Niemczura, E.; Polińska, M.; Hełminiak, K. G.; Lampens, P.; Molenda-Żakowicz, J.; Ukita, N.; Kambe, E.

    2017-10-01

    δ Scuti stars are remarkable objects for asteroseismology. In spite of decades of investigations, there are still important questions about these pulsating stars to be answered, such as their positions in log Teff-log g diagram, or the dependence of the pulsation modes on atmospheric parameters and rotation. Therefore, we performed a detailed spectroscopic study of 41 δ Scuti stars. The selected objects are located near the γ Doradus instability strip to make a reliable comparison between both types of variables. Spectral classification, stellar atmospheric parameters (Teff, log g, ξ) and v sin i values were determined. The spectral types and luminosity classes of stars were found to be A1-F5 and III-V, respectively. The Teff ranges from 6600 to 9400 K, whereas the obtained log g values are from 3.4 to 4.3. The v sin i values were found between 10 and 222 km s-1. The derived chemical abundances of δ Scuti stars were compared to those of the non-pulsating stars and γ Doradus variables. It turned out that both δ Scuti and γ Doradus variables have similar abundance patterns, which are slightly different from the non-pulsating stars. These chemical differences can help us to understand why there are non-pulsating stars in classical instability strip. Effects of the obtained parameters on pulsation period and amplitude were examined. It appears that the pulsation period decreases with increasing Teff. No significant correlations were found between pulsation period, amplitude and v sin i.

  2. Discovery and Photometric Analysis of the ? Scuti Variable TYC 2168-132-1

    NASA Astrophysics Data System (ADS)

    Joner, M. D.; Hintz, E. G.; Corfini, G.

    2016-12-01

    Abstract We detail the discovery of the short-period variable star presently known as TYC 2168-132-1. We have examined four nights of photometric observations of this star secured in 2015 and find it to be a delta Scuti variable with a primary period of 0.0737523 days. The star is multiperiodic with three dominant frequencies at 13.556, 7.047, and 11.757 cycles/day. Evidence from light curve morphology supports the delta Scuti classification. We estimate intrinsic values for color and luminosity that place TYC 2168-132-1 within the lower part of the instability strip.

  3. DISCOVERY OF 14 NEW SLOWLY PULSATING B STARS IN THE OPEN CLUSTER NGC 7654

    SciTech Connect

    Luo, Y. P.; Han, Z. W.

    2012-02-10

    We carried out time-series BV CCD photometric observations of the open cluster NGC 7654 (Messier 52) to search for variable stars. Eighteen slowly pulsating B (SPB) stars have been detected, among which 14 candidates are newly discovered, three known ones are confirmed, and a previously found {delta} Scuti star is also identified as an SPB candidate. Twelve SPBs are probable cluster members based on membership analysis. This makes NGC 7654 the richest galactic open cluster in terms of SPB star content. It is also a new discovery that NGC 7654 hosts three {gamma} Dor star candidates. We found that all these stars (18 SPB and 3 {gamma} Dor stars) have periods longer than their corresponding fundamental radial mode. With such a big sample of g-mode pulsators in a single cluster, it is clear that multi-mode pulsation is more common in the upper part of the main sequence than in the lower part. All the stars span a narrow strip on the period-luminosity plane, which also includes the {gamma} Dor stars at the low-luminosity extension. This result implies that there may be a single period-luminosity relation applicable to all g-mode main-sequence pulsators. As a by-product, three EA-type eclipsing binaries and an EW-type eclipsing binary are also discovered.

  4. An astrometric and spectroscopic study of the δ Scuti variable HD 21190 and its wide companion CPD -83° 64B

    NASA Astrophysics Data System (ADS)

    Niemczura, E.; Scholz, R.-D.; Hubrig, S.; Järvinen, S. P.; Schöller, M.; Ilyin, I.; Kahraman Aliçavuş, F.

    2017-10-01

    Although pulsations of δ Scuti type are not expected among Ap stars from a theoretical point of view, previous observations of the known δ Scuti star HD 21190 indicated a spectral classification F2 III SrEuSi:, making it the most evolved Ap star known. Our atmospheric chemical analysis based on recent High Accuracy Radial velocity Planet Searcher observations confirms the presence of chemical peculiarities in HD 21190. This star is also the only target known to host a magnetic field along with its δ Scuti pulsation properties. Using an astrometric analysis, we show that HD 21190 forms a physical binary system with the companion CPD -83° 64B. The presented astrometric and spectroscopic study of the binary components is important to understand the complex interplay between stellar pulsations, magnetic fields and chemical composition.

  5. Asteroseismology of the Multiply Periodic δ Scuti Star θ Tucanae

    NASA Astrophysics Data System (ADS)

    Templeton, Matthew R.; Bradley, Paul A.; Guzik, Joyce A.

    2000-01-01

    We present an asteroseismological analysis of the δ Scuti component of the binary star system θ Tucanae, using the 10 pulsational frequencies obtained photometrically by Paparó et al. and the mode identifications of Sterken. We have tested theoretical models with masses between 1.8 and 2.8 Msolar that have solar metal abundances, and we find that based upon mode stability arguments, the photometrically derived mass estimate of 2.1+/-0.1 Msolar is probably accurate. The models with the best frequency match to θ Tucanae have masses of 1.9-2.1 Msolar, luminosities between 20 and 25 Lsolar, effective temperatures between 7500 and 7685 K, logg values between 3.82 and 3.92, and rotational velocities between 70 and 90 km s-1. The luminosities of our models are more than a factor of 2 less than the Hipparcos-derived luminosity of 54 Lsolar, which suggests that the secondary star must be of comparable luminosity. We cannot determine whether tidal distortion is causing nonspherical perturbations in the pulsating component of this system with our current models, but the frequency spacing of observed pulsation modes suggests that rotation has a strong effect on the observed spectrum. Our models are consistent with the observed pulsation spectrum if rotational splitting is taken into account. Recently, De Mey, Daems, & Sterken determined spectroscopically that the θ Tucanae system is a spectroscopic binary with an anomalous mass ratio of 0.0896. In their model of this system, the δ Scuti component of the system is probably the beneficiary of mass transfer from the secondary, and the system was likely once an Algol-type system. The secondary is probably a 0.2 Msolar post-red giant branch object at ~7000 K (logg~3.0), which has lost most of its mass via mass transfer and winds. This scenario raises the possibility that the interior of the δ Scuti star may be radically different from what single-star evolution models predict, although our results do not show any obvious

  6. IRAS Observations of Delta Scuti Stars

    NASA Astrophysics Data System (ADS)

    Templeton, M. R.; Harrison, T. E.

    1998-07-01

    Mid-far infrared and radio observations of A-F stars are important for constraining the level of mass loss from these stars. It was theorized by Willson et al. (1987) that mass loss could play a significant role in the evolution of these stars, and could be responsible for shifting a star in the HR diagram by as much as one spectral class. Observations of normal A-F stars at 6 cm by Brown et al. (1990) and at the IRAS 12, 25, and 60 5m bands by Patten and Willson (1991) have shown that extreme mass loss rates (on the order of 10^-8 to 10^-9 solar masses per year) are not seen in these stars, but lower mass loss rates could still have significant impact on the evolution of these stars [see Guzik and Cox (1995) for example].

  7. Asteroseismology of the δ Scuti star HD 50844

    NASA Astrophysics Data System (ADS)

    Chen, X. H.; Li, Y.; Lai, X. J.; Wu, T.

    2016-09-01

    Aims: We aim to probe the internal structure and investigate with asteroseismology for more detailed information on the δ Scuti star HD 50844. Methods: We analyse the observed frequencies of the δ Scuti star HD 50844 and search for possible multiplets, which are based on the rotational splitting law of g-mode. We tried to disentangle the frequency spectra of HD 50844 only by means of rotational splitting. We then compare these with theoretical pulsation modes, which correspond to stellar evolutionary models with various sets of initial metallicity and stellar mass, to find the best-fitting model. Results: There are three multiplets, including two complete triplets and one incomplete quintuplet, in which mode identifications for spherical harmonic degree l and azimuthal number m are unique. The corresponding rotational period of HD 50844 is found to be 2.44 days. The physical parameters of HD 50844 are well limited in a small region by three modes that have been identified as nonradial ones (f11, f22, and f29) and by the fundamental radial mode (f4). Our results show that the three nonradial modes (f11, f22, and f29) are all mixed modes, which mainly represent the property of the helium core. The fundamental radial mode (f4) mainly represents the property of the stellar envelope. To fit these four pulsation modes, both the helium core and the stellar envelope need to be matched to the actual structure of HD 50844. Finally, the mass of the helium core of HD 50844 is estimated to be 0.173 ± 0.004 M⊙ for the first time. The physical parameters of HD 50844 are determined to be M = 1.81 ± 0.01 M⊙, Z = 0.008 ± 0.001. Teff = 7508 ± 125 K, log g = 3.658 ± 0.004, R = 3.300 ± 0.023 R⊙, L = 30.98 ± 2.39 L⊙.

  8. Pulsating Stars

    NASA Astrophysics Data System (ADS)

    Catelan, M.; Smith, H. A.

    2015-03-01

    This book surveys our understanding of stars which change in brightness because they pulsate. Pulsating variable stars are keys to distance scales inside and beyond the Milky Way galaxy. They test our understanding not only of stellar pulsation theory but also of stellar structure and evolution theory. Moreover, pulsating stars are important probes of the formation and evolution of our own and neighboring galaxies. Our understanding of pulsating stars has greatly increased in recent years as large-scale surveys of pulsating stars in the Milky Way and other Local Group galaxies have provided a wealth of new observations and as space-based instruments have studied particular pulsating stars in unprecedented detail.

  9. Current Light Elements of the δ Scuti Star V393 Carinae

    NASA Astrophysics Data System (ADS)

    Axelsen, R. A.

    2014-12-01

    V393 Carinae is a 7th magnitude delta Scuti star which has a principal period of 0.1413 d and an amplitude of 0.2 magnitude in V. Previous publications have suggested the existence of a second period, but its duration has so far evaded discovery. In view of the uncertainty, and since the only two papers on this star were published in 1984 and 2001, DSLR photometry was performed to obtain time series data. Images were taken during 6 nights from December 2013 to March 2014. The data were analyzed using a discrete Fourier transform, which yielded a principal frequency of 7.07727 (± 0.00005) cycles/day, corresponding to a period of 0.141297 (± 0.000001) day. Prewhitening for this frequency revealed a harmonic frequency precisely twice that of the principal, but no further dominant frequencies could be found. O-C diagrams suggested that it would appropriate to derive a new linear ephemeris from three times of maximum obtained by another author from 1977 to 1979, combined with the 6 new times of maximum reported in this paper. The light elements are: Tmax = HJD 2456732.0484 (6) + 0.14129328 (1). It is concluded that the current principal period of this star is almost identical to the period determined approximately 37 years ago. The issue of a second period is unresolved. None was detected, but it cannot be excluded that a second pulsation frequency of low amplitude could be hidden due to a low signal to noise ratio.

  10. Altair: The Brightest δ Scuti Star

    NASA Astrophysics Data System (ADS)

    Buzasi, D. L.; Bruntt, H.; Bedding, T. R.; Retter, A.; Kjeldsen, H.; Preston, H. L.; Mandeville, W. J.; Suarez, J. C.; Catanzarite, J.; Conrow, T.; Laher, R.

    2005-02-01

    We present an analysis of observations of the bright star Altair (α Aql) obtained using the star camera on the Wide Field Infrared Explorer (WIRE) satellite. Although Altair lies within the δ Scuti instability strip, previous observations have not revealed the presence of oscillations. However, the WIRE observations show Altair to be a low-amplitude (Δm<1 parts per thousand [ppt]) δ Scuti star with at least seven modes present.

  11. Moment Method and Pixel-by-Pixel Method: Complementary Mode Identification I. Testing FG Vir-like pulsation modes

    NASA Astrophysics Data System (ADS)

    Zima, W.; Kolenberg, K.; Briquet, M.; Breger, M.

    2004-06-01

    We have carried out a Hare-and-Hound test to determine the reliability of the Moment Method (Briquet & Aerts 2003) and the Pixel-by-Pixel Method (Mantegazza 2000) for the identification of pulsation modes in Delta Scuti stars. For this purpose we calculated synthetic line profiles, exhibiting six pulsation modes of low degree and with input parameters initially unknown to us. The aim was to test and increase the quality of the mode identification by applying both methods independently and by using a combined technique. Our results show that, whereas the azimuthal order m and its sign can be fixed by both methods, the degree l is not determined unambiguously. Both identification methods show a better reliability if multiple modes are fitted simultaneously. In particular, the inclination angle is better determined. We have to emphasize that the outcome of this test is only meaningful for stars having pulsational velocities below 0.2 vsini. This is the first part of a series of articles, in which we will test these spectroscopic identification methods.

  12. Multi-site, multi-colour and space photometry of a southern δ Scuti star, 38 Eri

    NASA Astrophysics Data System (ADS)

    Paparó, Margit; Benkö, József

    2017-09-01

    38 Eri is a δ Scuti star in the shell hydrogen burning stage of evolution, with a 0.04 mag peak-to-peak amplitude and a very complex light variation. It was discovered in 1971. In the subsequent investigation the star always showed a different frequency content. A ground-based multi-site campaign and a MOST observation were devoted to resolve the contradicting pulsational behaviour. We present the preliminary result of our investigation obtained on Stromgren b and MOST data. The complexity of the pulsation is confirmed, but the comprehensive analysis helps to resolve the frequencies of the fast rotating star.

  13. Core overshoot and convection in δ Scuti and γ Doradus stars

    NASA Astrophysics Data System (ADS)

    Lovekin, Catherine; Guzik, Joyce A.

    2017-09-01

    The effects of rotation on pulsation in δ Scuti and γ Doradus stars are poorly understood. Stars in this mass range span the transition from convective envelopes to convective cores, and realistic models of convection are thus a key part of understanding these stars. In this work, we use 2D asteroseismic modelling of 5 stars observed with the Kepler spacecraft to provide constraints on the age, mass, rotation rate, and convective core overshoot. We use Period04 to calculate the frequencies based on short cadence Kepler observations of five γ Doradus and δ Scuti stars. We fit these stars with rotating models calculated using MESA and adiabatic pulsation frequencies calculated with GYRE. Comparison of these models with the pulsation frequencies of three stars observed with Kepler allowed us to place constraints on the age, mass, and rotation rate of these stars. All frequencies not identified as possible combinations were compared to theoretical frequencies calculated using models including the effects of rotation and overshoot. The best fitting models for all five stars are slowly rotating at the best fitting age and have moderate convective core overshoot. In this work, we will discuss the results of the frequency extraction and fitting process.

  14. Linear radial pulsation theory. Lecture 5

    SciTech Connect

    Cox, A.N.

    1983-01-01

    We describe a method for getting an equilibrium stellar envelope model using as input the total mass, the envelope mass, the surface effective temperature, the total surface luminosity, and the composition of the envelope. Then wih the structure of the envelope model known, we present a method for obtaining the raidal pulsation periods and growth rates for low order modes. The large amplitude pulsations observed for the yellow and red giants and supergiants are always these radial models, but for the stars nearer the main sequence, as for all of our stars and for the white dwarfs, there frequently are nonradial modes occuring also. Application of linear theory radial pulsation theory is made to the giant star sigma Scuti variables, while the linear nonradial theory will be used for the B stars in later lectures.

  15. Why the peculiar δ Scuti star HD 187547 is a superstar

    NASA Astrophysics Data System (ADS)

    Antoci, V.; Cunha, M.; Houdek, G.

    2013-12-01

    The δ Scuti pulsators occupy a region in the Hertzsprung-Russell diagram where several physical processes occur: the subsurface convection layers change from being deep and vigorous to being shallow and ineffective to transport energy. This transition has a large impact not only on pulsational stability but also on stellar evolution, activity, transport of angular momentum, mixing processes, etc.. It is therefore of great interest to understand how exactly the stellar structure changes with increasing temperature and mass. Theoretical models (Houdek et al. 1999; Samadi et al. 2002) predicted that the convection in the outer layers of δ Scuti stars is still efficient enough to excite solar-like oscillations. The Kepler target, HD 187547 (a.k.a. Superstar), was the first δ Scuti star to suggest that solar-like oscillations are indeed present in this type of stars (Antoci et al. 2011). There were several reasons to conclude that HD 187547 is a δ Scuti/solar-like hybrid pulsator. (1) The peaks at high frequencies are modes of pulsations approximately equidistantly spaced, as expected for high radial order pressure modes; these peaks are not combination frequencies as it is sometimes observed in δ Scuti stars. (2) The opacity mechanism cannot excite a continuous frequency range as observed in HD 187547 (Pamyatnykh 2000). (3) The identification as an Am star consistent with the low v sini, makes it very unlikely to be a δ Scuti/roAp hybrid, because strong large-scale magnetic fields, a necessity for roAp pulsators, have never been detected in Am stars (Auriere et al. 2010). (4) Although a large number of Am stars are found in binary systems, we find no evidence in the observed spectra for a companion, i.e. no significant RV shift over 170 days can be detected and the absorption lines can perfectly be reproduced by assuming a slowly-rotating chemically peculiar Am star. This means that the peaks at high frequencies are unlikely to be from a companion, because such a

  16. Measuring mean densities of δ Scuti stars with asteroseismology. Theoretical properties of large separations using TOUCAN

    NASA Astrophysics Data System (ADS)

    Suárez, J. C.; García Hernández, A.; Moya, A.; Rodrigo, C.; Solano, E.; Garrido, R.; Rodón, J. R.

    2014-03-01

    Aims: We study the theoretical properties of the regular spacings found in the oscillation spectra of δ Scuti stars. Methods: We performed a multivariable analysis that covered a wide range of stellar structure, seismic properties and model parameters that are representative of intermediate-mass, main-sequence stars. The workflow was entirely performed using a new Virtual Observatory tool: TOUCAN (the VO gateway for asteroseismic models), which is presented in this paper. Results: A linear relation between the large separation and the mean density is predicted to be found in the low-frequency domain (i.e. radial orders spanning from 1 to 8, approximately) of the main-sequence, δ Scuti stars' oscillation spectrum. We found that this linear behavior remains the same whatever the mass, metallicity, mixing length, and overshooting parameters considered. The intrinsic error of the method is discussed. This includes the uncertainty in the large separation determination and the role of rotation. The validity of the relation found is only guaranteed for stars rotating up to 40% of their break-up velocity. Finally, we applied the diagnostic method presented in this work to five stars for which regular patterns have been found. Our estimates for the mean density and the frequency of the fundamental radial mode match with those given in the literature within a 20% of deviation. Conclusions: Asteroseismology has thus revealed an independent direct measure of the average density of δ Scuti stars, which is analogous to that of the Sun. This places tight constraints on the mode identification and hence on the stellar internal structure and dynamics, and allows determining the radius of planets orbiting δ Scuti stars with unprecedented precision. This opens the way for studying the evolution of regular patterns in pulsating stars, and its relation with stellar structure and evolution. Appendices A and B are available in electronic form at http://www.aanda.org

  17. Detection of a Weak Magnetic Field in the High-Amplitude δ Scuti-Type Star 1 Monocerotis

    NASA Astrophysics Data System (ADS)

    Baklanova, D.; Mkrtichian, D.; Plachinda, S.; Baklanov, A.

    2017-06-01

    We present preliminary results of magnetic field measurements in the 1 Monocerotis. 1 Mon is a multiperiodic, high amplitude δ Scuti type star, showing a total pulsation amplitude of ˜ 0.4 mag and three pulsation periods of P1 = 0.136 d, P2 = 0.134 d, P3 = 0.139 d. The spectropolarimetric observations of 1 Mon were obtained during three nights in 2007 using the fiber-fed BOES échelle spectrometer of the 1.8-m telescope of the Bohyunsan Optical Astronomy Observatory. We report about detection of weak magnetic field, variable from -58±8 Gs to +48±8 Gs during the pulsation period.

  18. AE Ursae Majoris - a δ Scuti Star in the Hertzsprung Gap

    NASA Astrophysics Data System (ADS)

    Niu, Jia-Shu; Fu, Jian-Ning; Li, Yan; Yang, Xiao-Hu; Zong, Weikai; Xue, Hui-Fang; Zhang, Yan-Ping; Liu, Nian; Du, Bing; Zuo, Fang

    2017-01-01

    We analyze the photometric data and spectroscopic data that collect on the δ Scuti star AE UMa. The fundamental and the first overtone frequencies are confirmed as f0 = 11.62560 c d-1 and f1 = 15.03124 c d-1, respectively, from the frequency content by analyzing of the 40 nights light curve spanning from 2009 to 2012. Additionally, another 37 frequencies are identified as either the harmonics or the linear combinations of the fundamental and the first overtone frequencies, among which 25 are newly detected. The rate of period change of the fundamental mode is determined as (1/P0)(dP0/dt) = 5.4( ± 1.9) × 10-9 yr-1 as revealed from the O - C diagram based on the 84 newly determined times of maximum light combined with those derived from the literature. The spectroscopic data suggests that AE UMa is a population I δ Scuti star. With these physical properties, we perform theoretical explorations based on the stellar evolution code MESA on this target, considering that the variation of pulsation period is caused by secular evolutionary effects. We finally constraint the AE UMa with the physical parameters as: the mass of 1.805 ± 0.055 M⊙, the radius of 1.647 ± 0.032 × 1011 cm, the luminosity of 1.381 ± 0.048 (log L/L⊙) and the age of 1.055 ± 0.095 × 109 yr. AE UMa can be the (Pop. I) δ Scuti star that locates just after the second turn-off of its evolutional track leaving the main sequence, a star in the phase of the Hertzsprung Gap with a helium core and a hydrogen-burning shell.

  19. AE Ursae Majoris - a δ Scuti star in the Hertzsprung Gap

    NASA Astrophysics Data System (ADS)

    Niu, Jia-Shu; Fu, Jian-Ning; Li, Yan; Yang, Xiao-Hu; Zong, Weikai; Xue, Hui-Fang; Zhang, Yan-Ping; Liu, Nian; Du, Bing; Zuo, Fang

    2017-05-01

    We analyse the photometric data and spectroscopic data collected on the δ Scuti star AE Ursae Majoris (AE UMa). The fundamental and the first overtone frequencies are confirmed as f0 = 11.625 60 c d-1 and f1 = 15.031 24 c d-1, respectively, from the frequency content by analysing light curves over 40 nights, spanning from 2009 to 2012. Additionally, another 37 frequencies are identified as either the harmonics or the linear combinations of the fundamental and the first overtone frequencies, among which 25 are newly detected. The rate of period change of the fundamental mode is determined as (1/P0)(dP0/dt) = 5.4(±1.9) × 10-9 yr-1 as revealed from the O - C diagram based on the 84 newly determined times of maximum light combined with those derived from the literature. The spectroscopic data suggest that AE UMa is a Population I δ Scuti star. With these physical properties, we perform theoretical explorations based on the stellar evolution codemesa on this target, considering that the variation of pulsation period is caused by secular evolutionary effects. We finally constrain AE UMa with physical parameters as follows: mass of 1.805 ± 0.055 M⊙, radius of 1.647 ± 0.032 × 1011 cm, luminosity of 1.381 ± 0.048(log L/L⊙) and age of 1.055 ± 0.095 × 109 yr. AE UMa can be the (Population I) δ Scuti star that locates just after the second turn-off of its evolutional track leaving the main sequence, a star in the phase of the Hertzsprung Gap with a helium core and a hydrogen-burning shell.

  20. LOOKING FOR A CONNECTION BETWEEN THE Am PHENOMENON AND HYBRID {delta} Sct -{gamma} Dor PULSATION: DETERMINATION OF THE FUNDAMENTAL PARAMETERS AND ABUNDANCES OF HD 114839 AND BD +18 4914

    SciTech Connect

    Hareter, M.; Weiss, W.; Fossati, L.; Suarez, J. C.; Rainer, M.; Poretti, E.

    2011-12-20

    {delta} Sct-{gamma} Dor hybrids pulsate simultaneously in p- and g-modes, which carry information on the structure of the envelope as well as to the core. Hence, they are key objects for investigating A and F type stars with asteroseismic techniques. An important requirement for seismic modeling is small errors in temperature, gravity, and chemical composition. Furthermore, we want to investigate the existence of an abundance indicator typical for hybrids, something that is well established for the roAp stars. Previous to the present investigation, the abundance pattern of only one hybrid and another hybrid candidate has been published. We obtained high-resolution spectra of HD 114839 and BD +18 4914 using the SOPHIE spectrograph of the Observatoire de Haute-Provence and the HARPS spectrograph at ESO La Silla. For each star we determined fundamental parameters and photospheric abundances of 16 chemical elements by comparing synthetic spectra with the observations. We compare our results to that of seven {delta} Sct and nine {gamma} Dor stars. For the evolved BD +18 4914 we found an abundance pattern typical for an Am star, but could not confirm this peculiarity for the less evolved star HD 114839, which is classified in the literature as uncertain Am star. Our result supports the concept of evolved Am stars being unstable. With our investigation we nearly doubled the number of spectroscopically analyzed {delta} Sct-{gamma} Dor hybrid stars, but did not yet succeed in identifying a spectroscopic signature for this group of pulsating stars. A statistically significant spectroscopic investigation of {delta} Sct- {gamma} Dor hybrid stars is still missing, but would be rewarding considering the asteroseismological potential of this group.

  1. Pulsations and metallicity of the pre-main sequence eclipsing spectroscopic binary RS Cha

    NASA Astrophysics Data System (ADS)

    Alecian, E.; Catala, C.; van't Veer-Menneret, C.; Goupil, M.-J.; Balona, L.

    2005-11-01

    We present new spectroscopic observations of the pre-main sequence eclipsing spectroscopic binary RS Cha. A sample of 174 spectra were obtained with the GIRAFFE spectrograph at the SAAO at 32 000 resolution. The radial velocity curves derived from these spectra were combined with previous observations spanning a period of about 30 years to correct the ephemeris of the system, and the result indicates that the orbital period is not constant. Residuals of the binary radial velocity curve for both components with amplitudes up to a few km s-1 and periods on the order of 1 h are clearly seen in our data, which we interpret as the signatures of delta-Scuti type pulsations. We revisited the masses of both components and determined the surface metallicity Z of both components of the RS Cha system by fitting synthetic spectra to observed spectra in a set of selected spectral regions. The synthetic spectra are calculated with the SYNTH code using stellar atmosphere models computed with the Kurucz ATLAS 9 code, along with a list of lines obtained from the VALD database. A selection of the best spectra and the most relevant spectral regions allowed us to determine Z = 0.028 ± 0.005. We also derived new values of v sin i: 64 ± 6 km s-1 and 70 ± 6 km s-1 for the primary and the secondary star, respectively. Finally, we observationally confirm that the RS Cha system is a synchronized and circularized system.

  2. DELTAE

    SciTech Connect

    Ward, W.C.; Swift, G.W. )

    1993-11-01

    In thermoacoustic engines and refrigerators, and in many simple acoustic systems, a one dimensional wave equation determines the spatial dependence of the acoustic pressure and velocity. DELTAE numerically integrates such wave equations in the acoustic approximation, in gases or liquids, in user-defined geometries. Boundary conditions can include conventional acoustic boundary conditions of geometry and impedance, as well as temperature and thermal power in thermoacoustic systems. DELTAE can be used easily for apparatus ranging from simple duct networks and resonators to thermoacoustic engines refrigerators and combinations thereof. It can predict how a given apparatus will perform, or can allow the user to design an apparatus to achieve desired performance. DELTAE views systems as a series of segments; twenty segment types are supported. The purely acoustic segments include ducts and cones, and lumped impedances including compliances, series impedances, and endcaps. Electroacoustics tranducer segments can be defined using either frequency-independent coefficients or the conventional parameters of loudspeaker-style drivers: mass, spring constant, magnetic field strength, etc. Tranducers can be current driven, voltage driven, or connected to an electrical load impedance. Thermoacoustic segment geometries include parallel plates, circular and rectangular pores, and pin arrays. Side branches can be defined with fixed impedances, frequency-dependent radiation impedances, or as an auxiliary series of segments of any types. The user can select working fluids from among air, helium, neon, argon, hydrogen, deuterium, carbon dioxide, nitrogen, helium-argon mixtures, helium-xenon mixtures, liquid sodium, and eutectic sodium-potassium. Additional fluids and solids can be defined by the user.

  3. DELTAE

    SciTech Connect

    Ward, W.C. ); Swift, G.W. )

    1993-11-01

    In thermoacoustic engines and refrigerators, and in many simple acoustic systems, a one dimensional wave equation determines the spatial dependence of the acoustic pressure and velocity. DELTAE numerically integrates such wave equations in the acoustic approximation, in gases or liquids, in user-defined geometries. Boundary conditions can include conventional acoustic boundary conditions of geometry and impedance, as well as temperature and thermal power in thermoacoustic systems. DELTAE can be used easily for apparatus ranging from simple duct networks and resonators to thermoacoustic engines refrigerators and combinations thereof. It can predict how a given apparatus will perform, or can allow the user to design an apparatus to achieve desired performance. DELTAE views systems as a series of segments; twenty segment types are supported. The purely acoustic segments include ducts and cones, and lumped impedances including compliances, series impedances, and endcaps. Electroacoustics tranducer segments can be defined using either frequency-independent coefficients or the conventional parameters of loudspeaker-style drivers: mass, spring constant, magnetic field strength, etc. Tranducers can be current driven, voltage driven, or connected to an electrical load impedance. Thermoacoustic segment geometries include parallel plates, circular and rectangular pores, and pin arrays. Side branches can be defined with fixed impedances, frequency-dependent radiation impedances, or as an auxiliary series of segments of any types. The user can select working fluids from among air, helium, neon, argon, hydrogen, deuterium, carbon dioxide, nitrogen, helium-argon mixtures, helium-xenon mixtures, liquid sodium, and eutectic sodium-potassium. Additional fluids and solids can be defined by the user.

  4. STEREO observations of HD90386 (RX Sex): a δ-Scuti or a hybrid star?

    NASA Astrophysics Data System (ADS)

    Ozuyar, D.; Stevens, I. R.; Whittaker, G.; Sangaralingam, V.

    2016-04-01

    HD90386 is a rarely studied bright A2V type δ Scuti star (V = 6.66 mag). It displays short-term light curve variations which are originated due to either a beating phenomenon or a non-periodic variation. In this paper, we presented high-precision photometric data of HD90386 taken by the STEREO satellite between 2007 and 2011 to shed light on its internal structure and evolution stage. From the frequency analysis of the four-year data, we detected that HD90386 had at least six different frequencies between 1 and 15 c d-1. The most dominant frequencies were found at around 10.25258 c d-1 (A ∼ 1.92 mmag) and 12.40076 c d-1 (A ∼ 0.61 mmag). Based on the ratio between these frequencies, the star was considered as an overtone pulsator. The variation in pulsation period over 35 years was calculated to be dP/Pdt = 5.39(2) x 10-3 yr-1. Other variabilities at around 1.0 c d-1 in the amplitude spectrum of HD90386 were also discussed. In order to explain these variabilities, possible rotational effects and γ Dor type variations were focused. Consequently, depending on the rotation velocity of HD90386, we speculated that these changes might be related to γ Dor type high-order g-modes shifted to the higher frequencies and that HD90386 might be a hybrid star.

  5. Learning from Pulsating Stars: Progress over the Last Century (Abstract)

    NASA Astrophysics Data System (ADS)

    Smith, H.

    2016-12-01

    (Abstract only) Scarcely more than a century has elapsed since it began to be widely accepted that pulsation plays an important role in the variability of stars. During that century pulsating stars have been used as tools to explore a variety of astrophysical questions, including the determination of distances to other galaxies, the testing of timescales of evolution through the HR diagram, and the identification of the ages and star formation histories of stellar populations. Among the significant early milestones along this investigative path are Henrietta Leavitt's discovery of a relation between the periods and luminosities of Cepheids, Harlow Shapley's proposal that all Cepheids are pulsating stars, and Arthur Stanley Eddington's use of the observed period change of d Cephei to constrain its power source. Today our explorations of pulsating stars are bolstered by long observational histories of brighter variables, surveys involving unprecedentedly large numbers of stars, and improved theoretical analyses. This talk will review aspects of the history and our current understanding of pulsating stars, paying particular attention to RR Lyrae, d Scuti, and Cepheid variables. Observations by AAVSO members have provided insight into several questions regarding the behavior of these stars.

  6. The Pulsation Spectrum of VX Hydrae

    NASA Astrophysics Data System (ADS)

    Templeton, M. R.; Samolyk, G.; Dvorak, S.; Poklar, R.; Butterworth, N.; Gerner, H.

    2009-10-01

    We present the results of a two-year, multisite observing campaign investigating the high-amplitude δ Scuti star VX Hydrae during the 2006 and 2007 observing seasons. The final data set consists of nearly 8500 V-band observations spanning HJD 2453763.6 to 2454212.7 (2006 January 28 to 2007 April 22). Separate analyses of the two individual seasons of data yield 25 confidently detected frequencies common to both data sets, of which two are pulsation modes, and the remaining 23 are Fourier harmonics or beat frequencies of these two modes. The 2006 data set had five additional frequencies with amplitudes less than 1.5 mmag, and the 2007 data had one additional frequency. Analysis of the full 2006–2007 data set yields 22 of the 25 frequencies found in the individual seasons of data. There are no significant peaks in the spectrum other than these between 0 and 60 cycles day-1. The frequencies of the two main pulsation modes derived from the 2006 and 2007 observing seasons individually do not differ at the level of 3σ, and thus we find no conclusive evidence for period change over the span of these observations. However, the amplitude of changed significantly between the two seasons, while the amplitude of remained constant; amplitudes of the Fourier harmonics and beat frequencies of f1 also changed. Similar behavior was seen in the 1950s, and it is clear that VX Hydrae undergoes significant amplitude changes over time.

  7. Unexpected series of regular frequency spacing of δ Scuti stars in the non-asymptotic regime. II. Sample-Echelle diagrams and rotation

    SciTech Connect

    Paparo, M.; Benko, J. M.; Hareter, M.; Guzik, J. A.

    2016-06-17

    A sequence search method was developed for searching for regular frequency spacing in δ Scuti stars by visual inspection (VI) and algorithmic search. The sample contains 90 δ Scuti stars observed by CoRoT. An example is given to represent the VI. The algorithm (SSA) is described in detail. The data treatment of the CoRoT light curves, the criteria for frequency filtering, and the spacings derived by two methods (i.e., three approaches: VI, SSA, and FT) are given for each target. Echelle diagrams are presented for 77 targets for which at least one sequence of regular spacing was identified. Comparing the spacing and the shifts between pairs of echelle ridges revealed that at least one pair of echelle ridges is shifted to midway between the spacing for 22 stars. The estimated rotational frequencies compared to the shifts revealed rotationally split doublets, triplets, and multiplets not only for single frequencies, but for the complete echelle ridges in 31 δ Scuti stars. Furthermore, using several possible assumptions for the origin of the spacings, we derived the large separation (${\\rm{\\Delta }}\

  8. Unexpected series of regular frequency spacing of δ Scuti stars in the non-asymptotic regime. II. Sample-Echelle diagrams and rotation

    DOE PAGES

    Paparo, M.; Benko, J. M.; Hareter, M.; ...

    2016-06-17

    A sequence search method was developed for searching for regular frequency spacing in δ Scuti stars by visual inspection (VI) and algorithmic search. The sample contains 90 δ Scuti stars observed by CoRoT. An example is given to represent the VI. The algorithm (SSA) is described in detail. The data treatment of the CoRoT light curves, the criteria for frequency filtering, and the spacings derived by two methods (i.e., three approaches: VI, SSA, and FT) are given for each target. Echelle diagrams are presented for 77 targets for which at least one sequence of regular spacing was identified. Comparing the spacing and the shifts between pairs of echelle ridges revealed that at least one pair of echelle ridges is shifted to midway between the spacing for 22 stars. The estimated rotational frequencies compared to the shifts revealed rotationally split doublets, triplets, and multiplets not only for single frequencies, but for the complete echelle ridges in 31 δ Scuti stars. Furthermore, using several possible assumptions for the origin of the spacings, we derived the large separation (more » $${\\rm{\\Delta }}\

  9. Unexpected series of regular frequency spacing of δ Scuti stars in the non-asymptotic regime. II. Sample-Echelle diagrams and rotation

    SciTech Connect

    Paparo, M.; Benko, J. M.; Hareter, M.; Guzik, J. A.

    2016-06-17

    A sequence search method was developed for searching for regular frequency spacing in δ Scuti stars by visual inspection (VI) and algorithmic search. The sample contains 90 δ Scuti stars observed by CoRoT. An example is given to represent the VI. The algorithm (SSA) is described in detail. The data treatment of the CoRoT light curves, the criteria for frequency filtering, and the spacings derived by two methods (i.e., three approaches: VI, SSA, and FT) are given for each target. Echelle diagrams are presented for 77 targets for which at least one sequence of regular spacing was identified. Comparing the spacing and the shifts between pairs of echelle ridges revealed that at least one pair of echelle ridges is shifted to midway between the spacing for 22 stars. The estimated rotational frequencies compared to the shifts revealed rotationally split doublets, triplets, and multiplets not only for single frequencies, but for the complete echelle ridges in 31 δ Scuti stars. Furthermore, using several possible assumptions for the origin of the spacings, we derived the large separation (${\\rm{\\Delta }}\

  10. The impact of prewhitening in the characterization of pulsating stars observed by space missions

    NASA Astrophysics Data System (ADS)

    Pascual-Granado, J.; Garrido, R.; Suárez, J. C.; Verdes-Montenegro, L.; Rodón, J. R.

    2017-03-01

    Even when ultraprecise observations are performed by space missions for determining the frequency content of multiperiodic pulsating stars, gaps associated to wrong data acquisition are unavoidable. In these cases, the most extended method in asteroseismology for determining the frequency content consists of an iterative process called prewhitening. The usual assumption is that this method does not alter the original frequency content of the time series. Here we test this assumption by performing frequency analyses of a set of δ-Scuti stars from the seismofield of CoRoT satellite. The frequency analyses performed on gapped data show that only the very first frequencies are preserved. It follows from these results that the standard techniques applied in asteroseismology to infer the internal structure of pulsating stars cannot be applied if a reliable filling of the gaps is not performed previously.

  11. Pulsating white dwarfs

    NASA Astrophysics Data System (ADS)

    Kepler, S. O.; Romero, Alejandra D.

    2017-09-01

    The Sloan Digital Sky Survey has allowed us to increase the number of known white dwarfs by a factor of five and consequently the number of known pulsating white dwarfs also by a factor of five. It has also led to the discovery of new types of variable white dwarfs, as the variable hot DQs, and the pulsating Extremely Low Mass white dwarfs. With the Kepler Mission, it has been possible to discover new phenomena, the outbursts present in a few pulsating white dwarfs.

  12. Pulsation analysis and its impact on primary transit modeling in WASP-33

    NASA Astrophysics Data System (ADS)

    von Essen, C.; Czesla, S.; Wolter, U.; Breger, M.; Herrero, E.; Mallonn, M.; Ribas, I.; Strassmeier, K. G.; Morales, J. C.

    2014-01-01

    Aims: To date, WASP-33 is the only δ Scuti star known to be orbited by a hot Jupiter. The pronounced stellar pulsations, showing periods comparable to the primary transit duration, interfere with the transit modeling. Therefore our main goal is to study the pulsation spectrum of the host star to redetermine the orbital parameters of the system by means of pulsation-cleaned primary transit light curves. Methods: Between August 2010 and October 2012 we obtained 457 h of photometry of WASP-33 using small and middle-class telescopes located mostly in Spain and in Germany. Our observations comprise the wavelength range between the blue and the red, and provide full phase coverage of the planetary orbit. After a careful detrend, we focus our pulsation studies in the high frequency regime, where the pulsations that mostly deform the primary transit exist. Results: The data allow us to identify, for the first time in the system, eight significant pulsation frequencies. The pulsations are likely associated with low-order p-modes. Furthermore, we find that pulsation phases evolve in time. We use our knowledge of the pulsations to clean the primary transit light curves and carry out an improved transit modeling. Surprisingly, taking into account the pulsations in the modeling has little influence on the derived orbital parameters. However, the uncertainties in the best-fit parameters decrease. Additionally, we find indications for a possible dependence between wavelength and transit depth, but only with marginal significance. A clear pulsation solution, in combination with an accurate orbital period, allows us to extend our studies and search for star-planet interactions (SPI). Although we find no conclusive evidence of SPI, we believe that the pulsation nature of the host star and the proximity between members make WASP-33 a promising system for further SPI studies. Tables 1 and 10 and Fig. 8 are available in electronic form at http://www.aanda.orgPhotometry is only

  13. Pulsating stars in NGC 6231. Frequency analysis and photometric mode identification near the main-sequence

    NASA Astrophysics Data System (ADS)

    Meingast, Stefan; Handler, Gerald; Shobbrook, Robert R.

    2013-11-01

    Aims: We used Johnson UBV photometric CCD observations to identify pulsating and other variable stars in the young open cluster NGC 6231. The multi-colour information was used to classify pulsating variables, perform frequency analysis, and, where possible, to compare observed to theoretical amplitude ratios for mode identification. Methods: The CCD data were used to investigate a total of 473 stars in the field. The data reduction was performed with standard IRAF tools, while the extraction of light curves was done with combined aperture and point-spread-function photometry routines delivered with the DAOPHOT package. Differential light curves were obtained by identifying a set of suitable comparison stars and the frequency analysis was then conducted on the basis of Fourier methods. Our classification of pulsating stars was based on the time scales and amplitudes of the variability with respect to the different filters and stellar parameters as calculated from published Strömgren and Geneva photometry. Attempts to set constraints on the pulsation mode were performed for stars with sufficiently high amplitude based on the significant dependence of amplitudes on wavelength. Results: We identified 32 variable stars in the field of the cluster, of which 21 are confirmed members of NGC 6231 and 12 are newly detected variable stars. Ten stars were classified as slowly pulsating B (SPB) stars in NGC 6231, of which seven are new discoveries. We also analysed six previously reported β Cephei variables in more detail. One of them may be a hybrid β Cephei/SPB pulsator. In addition, we also investigated five previously suspected pulsators of this group that we cannot convincingly confirm owing to their small pulsation amplitudes. The remaining 11 variable stars are either not members of NGC 6231 or the membership status is questionable. Among them are three previously known δ Scuti stars, two newly detected pulsators of this class, one new and two already known eclipsing

  14. GSC 02505-00411: A new delta Sct star in the field of RZ LMi

    NASA Astrophysics Data System (ADS)

    Ishioka, R.; Kokumbaeva, R.

    2017-04-01

    We present the time series analysis of CCD photometry from ``EAST'' Zeiss-1000 telescope at Tien-Shan Astronomical Observatory (Almaty, Kazakhstan) for GSC 02505-00411. GSC 02505-00411 is a new multi-frequency delta Scuti variable with a primary frequency of 43.84 c/d.

  15. V2551 Cyg: a pulsating star with enigmatic peculiarities

    NASA Astrophysics Data System (ADS)

    Kjurkchieva, Diana P.; Popov, Velimir A.; Marchev, Dragomir V.; Menzies, Kenneth T.; Petrov, Nikola I.

    2017-07-01

    Intensive photometric and spectral observations of the variable star V2551 Cyg are presented. The light curve shape reveals that the target is a pulsating star, contrary to its previous classification as an eclipsing binary. The period and amplitude of the light curve, the amplitudes of color changes and the radial velocity curve of V2551 Cyg are similar to those of a high-amplitude δ Scuti variable. The target seems to pulsate with the fundamental mode. However, V2551 Cyg exhibits several important peculiarities: (i) the decreasing branch of its light curve is steeper than the increasing one; (ii) the radial velocity curve has a flat section in the phase range 0.7-1.2 and short increase of the negative radial velocity at phase 0.7; (iii) the rotational velocity is quite big for a HADS star; (iv) the Fourier coefficients of V2551 Cyg are quite different from those of HADS stars. The target classification is difficult due to these peculiarities.

  16. Characteristics of Pulsating Aurora

    NASA Astrophysics Data System (ADS)

    Humberset, B. K.; Gjerloev, J. W.; Mann, I. R.; Samara, M.; Michell, R.

    2013-12-01

    We have investigated the spatiotemporal characteristics of pulsating auroral patches observed with an all-sky imager located at Poker Flat, Alaska. Pulsating aurora often covers the entire sky with intermixed large and small-scale patches that vary in intensity or disappear and reappear on different time scales and timings. The broad definition of pulsating aurora covers patches and bands from tens to several tens of km which have a quasi-periodic temporal variation from 1 s to tens of seconds. In this paper we examine >15 patches from different events. We analyze all-sky movies (557.7 nm, 3.31 Hz) with a simple, yet robust, technique that allows us to determine the scale size dependent variability of the >15 individual patches. A spatial 2D Fourier Transform is used to separate the aurora into different horizontal scale sizes, and by correlating each patch for all image separations and available scale sizes smaller than the patch itself, we reveal what scale sizes are pulsating and their variability. The patches are found to be persistent, meaning that we can follow them for typically 5 minutes. The period of the pulsations is often remarkably variable and it seems that only certain scale sizes pulsate (typically the size of the patch). The patches drift with the background ExB plasma drift indicating that the magnetospheric source mechanism drifts with the field lines.

  17. Simultaneous intensive photometry and high resolution spectroscopy of δ Scuti stars. II. X Caeli: a star with unusual spectral features.

    NASA Astrophysics Data System (ADS)

    Mantegazza, L.; Poretti, E.

    1996-08-01

    Simultaneous photometric B, V (14 consecutive nights; 100 hours of observations) and high resolution spectroscopic observations (4 consecutive nights; 27 hours) were performed on the δ Scuti star X Caeli at La Silla Observatory in 1992. The photometric data allow the detection of 14 pulsation terms, some of which coincide in frequency with the second harmonics or the non-linear coupling terms of the lower frequency components. Possible excitation by resonance is suggested. The comparison with our previous observations of 1989 shows that while the amplitude of the strongest term (ν=7.39c/d) is very stable, a few other terms have changed their amplitudes. From the study of line profiles and their variations we derive vsin i=70km/s, 65deg<=i<=90deg, and that the dominant photometric term is a prograde mode with m=-1 and l=1 or 2. The other terms are probably non radial p modes with l=2+/-1. There is no evidence of the presence of high-degree sectorial modes with l=|m|. The stellar spectral lines have a narrow absorption core which could be due to the presence of a circumstellar shell.

  18. Pulsating Star Mystery Solved

    NASA Astrophysics Data System (ADS)

    2010-11-01

    outcome of this work, and the team hopes to find other examples of these remarkably useful pairs of stars to exploit the method further. They also believe that from such binary systems they will eventually be able to pin down the distance to the Large Magellanic Cloud to 1%, which would mean an extremely important improvement of the cosmic distance scale. Notes [1] The first Cepheid variables were spotted in the 18th century and the brightest ones can easily be seen to vary from night to night with the unaided eye. They take their name from the star Delta Cephei in the constellation of Cepheus (the King), which was first seen to vary by John Goodricke in England in 1784. Remarkably, Goodricke was also the first to explain the light variations of another kind of variable star, eclipsing binaries. In this case two stars are in orbit around each other and pass in front of each other for part of their orbits and so the total brightness of the pair drops. The very rare object studied by the current team is both a Cepheid and an eclipsing binary. Classical Cepheids are massive stars, distinct from similar pulsating stars of lower mass that do not share the same evolutionary history. [2] The period luminosity relation for Cepheids, discovered by Henrietta Leavitt in 1908, was used by Edwin Hubble to make the first estimates of the distance to what we now know to be galaxies. More recently Cepheids have been observed with the Hubble Space Telescope and with the ESO VLT on Paranal to make highly accurate distance estimates to many nearby galaxies. [3] In particular, astronomers can determine the masses of the stars to high accuracy if both stars happen to have a similar brightness and therefore the spectral lines belonging to each of the two stars can be seen in the observed spectrum of the two stars together, as is the case for this object. This allows the accurate measurement of the motions of both stars towards and away from Earth as they orbit, using the Doppler effect. [4

  19. Catalogue and properties of δ Scuti stars in binaries

    NASA Astrophysics Data System (ADS)

    Liakos, Alexios; Niarchos, Panagiotis

    2017-02-01

    The catalogue contains 199 confirmed cases of binary systems containing at least one pulsating component of δ Sct type. The sample is divided into subgroups in order to describe the properties and characteristics of the δ Sct-type stars in binaries according to their Roche geometry. Demographics describing quantitatively our knowledge for these systems as well as the distributions of their pulsating components in the mass-radius, colour-magnitude, and evolutionary status-temperature diagrams are presented and discussed. It is shown that a threshold of ∼13 d of the orbital period regarding the influence of binarity on the pulsations is established. Finally, the correlations between the pulsation periods and the orbital periods, evolutionary status, and companion's gravity influence are updated based on the largest sample to date.

  20. Pulsating Soft Corals

    NASA Astrophysics Data System (ADS)

    Khatri, Shilpa; Holzman, Roi; Miller, Laura; Samson, Julia; Shavit, Uri

    2016-11-01

    Soft corals of the family Xeniidae have a pulsating motion, a behavior not observed in many other sessile organisms. We are studying how this behavior may give these corals a competitive advantage. We will present experimental data and computational simulations of the pulsations of the coral. Video data and kinematic analysis will be shown from the lab and the field. We will present direct numerical simulations of the pulsations of the coral and the resulting fluid flow by solving the Navier-Stokes equations coupled with the immersed boundary method. Furthermore, parameter sweeps studying the resulting fluid flow will be discussed. This work is supported by NSF PoLS #1505061 (to S. Khatri) and #1504777 (to L. Miller).

  1. Hydroacoustic pulsating jet generator

    NASA Astrophysics Data System (ADS)

    Unrau, A.; Meier, G. E. A.

    1987-04-01

    A high pressure turbulent jet generator connected to a low pressure hydraulic tube is studied to investigate water hammer in tubes with fast flow variations, generating high pressure pulsating water jets. The pulsating jet generator consists of a tube, a hydraulic valve, a spring, and a water container. The jet is the effect of the combination of turbulent pipe flow with a valve for flow nozzle. The jet pressure depends on specific oscillation impedance and flow velocity variations. For inlet pressure of 0.5 to 2 bar the pressure rises to 40 bar. The described pulsating jet generator is more effective than the earlier model. A piezoelectric pressure controller is used to register pressure signals and high speed photos are made of the jet. Test results are consistent with theoretical calculation.

  2. The 1995 FG VIR campaign: will 550 hours of new data and 19 frequencies be enough to do asteroseismology?

    NASA Astrophysics Data System (ADS)

    Breger, M.

    1995-09-01

    Investigators researching Delta Scuti stars have to live with a smaller number of detected pulsation frequencies than the astronomers studying white dwarfs and PG 1159-035 stars. For example, for the star PG 1159-035 over 200 pulsation frequencies are known, while below we are pleased to report a new record for Delta Scuti stars: 19 frequencies for FG Vir. The situation, however, is not as bleak for Delta Scuti stars as it may appear. In white dwarfs, due to the high order of the excited pulsation modes in this star, the values of the frequencies obey the asymptotic limits of frequency spacing. Consequently, a certain amount of redundancy is present. This is not the case for the Delta Scuti stars, where every single newly discovered frequency provides additional, almost independent information on low-order p and g mode pulsation, allowing refinements of the models.

  3. Alleviating pulsations in turbines

    SciTech Connect

    Wedmark, A.B.

    1994-10-01

    Pressure pulsations resulting from vortices in the draft tube are a persistent problem with Francis turbines. Air injection through the turbine shaft often can solve the problem, but this approach may not be possible after the turbine unit has been manufactured. In such cases, new and innovative solutions may be required.

  4. Eclipsing binary stars with a δ Scuti component

    NASA Astrophysics Data System (ADS)

    Kahraman Aliçavuş, F.; Soydugan, E.; Smalley, B.; Kubát, J.

    2017-09-01

    Eclipsing binaries with a δ Sct component are powerful tools to derive the fundamental parameters and probe the internal structure of stars. In this study, spectral analysis of six primary δ Sct components in eclipsing binaries has been performed. Values of Teff, v sin i, and metallicity for the stars have been derived from medium-resolution spectroscopy. Additionally, a revised list of δ Sct stars in eclipsing binaries is presented. In this list, we have only given the δ Sct stars in eclipsing binaries to show the effects of the secondary components and tidal-locking on the pulsations of primary δ Sct components. The stellar pulsation, atmospheric and fundamental parameters (e.g. mass, radius) of 92 δ Sct stars in eclipsing binaries have been gathered. Comparison of the properties of single and eclipsing binary member δ Sct stars has been made. We find that single δ Sct stars pulsate in longer periods and with higher amplitudes than the primary δ Sct components in eclipsing binaries. The v sin i of δ Sct components is found to be significantly lower than that of single δ Sct stars. Relationships between the pulsation periods, amplitudes and stellar parameters in our list have been examined. Significant correlations between the pulsation periods and the orbital periods, Teff, log g, radius, mass ratio, v sin i and the filling factor have been found.

  5. Stellar variability in open clusters . II. Discovery of a new period-luminosity relation in a class of fast-rotating pulsating stars in NGC 3766

    NASA Astrophysics Data System (ADS)

    Mowlavi, N.; Saesen, S.; Semaan, T.; Eggenberger, P.; Barblan, F.; Eyer, L.; Ekström, S.; Georgy, C.

    2016-10-01

    Context. Pulsating stars are windows to the physics of stars enabling us to see glimpses of their interior. Not all stars pulsate, however. On the main sequence, pulsating stars form an almost continuous sequence in brightness, except for a magnitude range between δ Scuti and slowly pulsating B stars. Against all expectations, 36 periodic variables were discovered in 2013 in this luminosity range in the open cluster NGC 3766, the origins of which was a mystery. Aims: We investigate the properties of those new variability class candidates in relation to their stellar rotation rates and stellar multiplicity. Methods: We took multi-epoch spectra over three consecutive nights using ESO's Very Large Telescope. Results: We find that the majority of the new variability class candidates are fast-rotating pulsators that obey a new period-luminosity relation. We argue that the new relation discovered here has a different physical origin to the period-luminosity relations observed for Cepheids. Conclusions: We anticipate that our discovery will boost the relatively new field of stellar pulsation in fast-rotating stars, will open new doors for asteroseismology, and will potentially offer a new tool to estimate stellar ages or cosmic distances. Based on observations made with the FLAMES instruments on the VLT/UT2 telescope at the Paranal Observatory, Chile, under the program ID 69.A-0123(A).

  6. The CoRoT star ID 100866999: a hybrid γ Doradus-δ Scuti star in an eclipsing binary system

    NASA Astrophysics Data System (ADS)

    Chapellier, E.; Mathias, P.

    2013-08-01

    Context. The presence of g- and p-modes allows testing stellar models from the core to the envelope. Moreover, binarity in an eclipsing system constrains the physical parameters of the pulsating star. Aims: CoRot ID 100866999 is a relatively large-amplitude hybrid γ Doradus-δ Scuti star with two clearly distinct frequency domains. The large number of detected frequencies allows a detailed study of the interaction between them. In addition, we can derive the fundamental parameters of both components from the study of the eclipsing light curve. Methods: After removing the eclipsing phases, we analyzed the data with the Period04 package up to a signal-to-noise ratio S/N = 4. The light curve was then prewhitened with these oscillation frequencies to derive the fundamental parameters of the two components. Results: The eclipsing light curve analysis results in a (1.8+1.1) M⊙ system, both components being main sequence stars. We detect 124 frequencies related to luminosity variations of the primary. They are present in two well-separated domains: 89 frequencies in the interval [0.30;3.64] d-1 and 35 in the interval [14.57; 33.96] d-1. There are 22 γ Doradus frequencies separated by a constant period interval ΔP = 0.03493 d. These frequencies correspond to a series of g-modes of degree ℓ = 1 with successive radial orders k. We identify 21 linear combinations between the first nine γ Doradus frequencies. The δ Scuti domain is dominated by a large-amplitude frequency F = 16.9803 d-1. The eight first γ Doradus frequencies fi are present with much lower amplitude in the δ Scuti domain as F ± fi. These interactions between g- and p-modes confirm the phenomenon we detected in another CoRoT star. The amplitude and the phase of the main frequency F shows a double-wave modulation along the orbital phase, giving rise to series of combination frequencies. Such combination frequencies are also detected, with lower amplitude, for the first γ Doradus modes. The Co

  7. Pulsations of rapidly rotating stars. II. Realistic modelling for intermediate-mass stars

    NASA Astrophysics Data System (ADS)

    Ouazzani, R.-M.; Roxburgh, I. W.; Dupret, M.-A.

    2015-07-01

    Context. Very high precision seismic space missions such as CoRoT and Kepler provide the means for testing the modelling of transport processes in stellar interiors. For some stars, such as δ Scuti, γ Doradus, and Be stars, the observed pulsation spectra are modified by rotation to such an extent that it prevents any fruitful interpretation. Aims: Our aim is to characterise acoustic pulsation spectra of realistic stellar models in order to be able to interpret asteroseismic data from such stars. Methods: The 2D oscillation code ACOR, which treats rotation in a non-perturbative manner, is used to study pulsation spectra of highly distorted evolved models of stars. Two-dimensional models of stars are obtained by a self-consistent method that distorts spherically averaged stellar models a posteriori, at any stage of evolution, and for any type of rotation law. Results: Four types of modes are calculated in a very dense frequency spectrum, among which are island modes. The regularity of the island modes spectrum is confirmed and yields a new set of quantum numbers, with which an échelle diagram can be built. Mixed gravito-acoustic modes are calculated in rapidly rotating models for the first time.

  8. Precise surface gravities of δ Scuti stars from asteroseismology

    NASA Astrophysics Data System (ADS)

    García Hernández, A.; Suárez, J. C.; Moya, A.; Monteiro, M. J. P. F. G.; Guo, Z.; Reese, D. R.; Pascual-Granado, J.; Barceló Forteza, S.; Martín-Ruiz, S.; Garrido, R.; Nieto, J.

    2017-10-01

    The work reported here demonstrates that it is possible to accurately determine surface gravities of $\\delta$ Sct stars using the frequency content from high precision photometry and a measurement of the parallax. Using a sample of 10 eclipsing binary systems with a $\\delta$ Sct component and the unique $\\delta$ Sct star discovered with a transiting planet, WASP-33, we were able to refine the $\\Delta\

  9. Classical Cepheid pulsations

    SciTech Connect

    Moskalik, P.; Buchler, J.R.; Kovacs, G. )

    1990-12-01

    Theoretical models of classical Cepheid variable stars are examined by means of test computations focusing on (1) the systematic period change known as the Hertzsprung or bump progression and (2) the hypothesis (Simon and Schmidt, 1976) that (1) is due to a 2:1 resonance between the fundamental mode and the second overtone. One-parameter families or sequences of models are calculated which represent 'snapshots' of pulsational behavior at different points on the Cepheid evolutionary tracks, and a remarkable uniformity is found when the Fourier coefficients for sequences with moderate luminosity/mass ratios are plottted against the linear period ratio. The complete disappearance of this uniformity when the coefficients are plotted against the pulsation period itself is shown to be consistent with (2). The description of these phenomena with amplitude equations is explained, and expressions for estimating the width of the instability strip are derived. 32 refs.

  10. Photometric studies of δ Scuti stars. I. IP Virginis

    USGS Publications Warehouse

    Joner, Michael D.; Hintz, Eric G.; Collier, Matthew W.

    1998-01-01

    We report 15 new times of maximum light for the δ Scuti star IP Virginis (formerly known as SA 106‐1024). An analysis of all times of maximum light indicates that IP Vir has been decreasing in period at a constant rate of − days day−1. Evidence is also presented that IP Vir is a double‐mode variable with a period ratio of . This period ratio predicts a [Fe/H] value of −0.3. From photometric (uvbyβ) observations, we find a foreground reddening of .008 mag and a metallicity of [Fe/H] = +0.05. It is shown that [Fe/H] = −0.3 is most likely the correct value. Intrinsic ‐ and c1‐values, plotted in a model atmosphere grid, indicate a mean effective temperature, K, and a mean surface gravity, . All of these physical parameters support Landolt's initial conclusion that IP Vir is an ordinary δ Sct star.

  11. Nonperiodic eddy pulsations

    USGS Publications Warehouse

    Rubin, David M.; McDonald, Richard R.

    1995-01-01

    Recirculating flow in lateral separation eddies is typically weaker than main stem flow and provides an effective environment for trapping sediment. Observations of recirculating flow and sedimentary structures demonstrate that eddies pulsate in size and in flow velocity even when main stem flow is steady. Time series measurements of flow velocity and location of the reattachment point indicate that these pulsations are nonperiodic. Nonperiodic flow in the lee of a channel margin constriction is grossly different from the periodic flow in the lee of a cylinder that is isolated in a flow. Our experiments demonstrate that placing a flow-parallel plate adjacent to a cylinder is sufficient to cause the leeside flow to change from a periodic sequence of vortices to a nonperiodically pulsating lateral separation eddy, even if flow conditions are otherwise unchanged. Two processes cause the leeside flow to become nonperiodic when the plate is added. First, vortices that are shed from the cylinder deform and become irregular as they impact the plate or interfere with remnants of other vortices near the reattachment point. Second, these deformed vortices and other flow structures are recirculated in the lateral separation eddy, thereby influencing the future state (pressure and momentum distribution) of the recirculating flow. The vortex deformation process was confirmed experimentally by documenting spatial differences in leeside flow; vortex shedding that is evident near the separation point is undetectable near the reattachment point. Nonlinear forecasting techniques were used in an attempt to distinguish among several possible kinds of nonperiodic flows. The computational techniques were unable to demonstrate that any of the nonperiodic flows result from low-dimensional nonlinear processes.

  12. Computational astrophysics: Pulsating stars

    NASA Astrophysics Data System (ADS)

    Davis, C. G.

    The field of computational astrophysics in pulsating star studies has grown considerably since the advent of the computer. Initially calculations were done on the IBM 704 with 32K of memory and now we use the CRAY YMP computers with considerably more memory. Our early studies were for models of pulsating stars using a 1D Lagrangian hydrodynamic code (SPEC) with radiation diffusion. The radiative transfer was treated in the equilibrium diffusion approximation and the hydrodynamics was done utilizing the approximation of artificial viscosity. The early calculations took many hours of 704 CPU time. Early in 1965 we decided to improve on the usual treatment of the radiative transfer used in our codes by utilizing the method of moments, the so-called variable Eddington approximation. In this approximation the material energy field is uncoupled from the radiation energy field and the angular dependence is introduced through the Eddington factor. A multigroup frequency dependent method may also be applied. The Eddington factor is determined by snapshots of the stars structure utilizing a y-line approximation. The full radiative transfer approximation appears necessary in order to understand the light curves for W Virginia stars and may be important for the light curves of RR Lyrae stars. A detailed radiative transfer method does not appear to be necessary for the understanding of Cepheid light curves. A recent improvement to our models for pulsating stars is in the use of an adaptive mesh scheme to resolve the sharp features in the nonlinear hydrodynamic structure. From these improved structures, better analysis of the radius, velocity, and light curves could be obtained.

  13. Experimental study of large-scale pulsations of a fluidized bed

    SciTech Connect

    Glinskii, V.A.; Protod'yakonov, I.O.; Chesnokov, Yu.G.

    1980-01-01

    In experimental investigations of the hydrodynamics of fluidized beds, study of large- and small-scale pulsations of the most important characteristics of the fluidized bed: voidage, hydraulic resistance, velocities of the gaseous and solid phases, etc., is of considerable interest. The character of these pulsations is determined by the heterogeneity of the structure of the fluidized bed, due to the presence of channels, bubbles, stagnant zones, and circulation currents. The object of the present work was experimental study of fluctuations of the height h of the surface of a fluidized bed, with simultaneous recording of the corresponding fluctuations of the hydraulic resistance ..delta..P of the bed. The existence of a direct connection between large-scale pulsations of the hydraulic resistance ..delta..P of the fluidized bed and large-scale pulsations of the bed height h is demonstrated in the paper. It is proved on this basis that large-scale pulsations of h and ..delta..P can be described by equations of the same type. The coefficients of the equation are determined from experimental data on pulsations, and its solutions for different fluidization regimes are analyzed.

  14. Pulsating slurry flow in pipelines

    NASA Astrophysics Data System (ADS)

    El Masry, O. A.; El Shobaky, K.

    1989-07-01

    An experimental study on pulsating turbulent flow of sand-water suspension was carried out. The objective was to investigate the effect of pulsating flow parameters, such as, frequency and amplitude on the critical velocity, the pressure drop per unit length of pipeline and hence the energy requirements for hydraulic transportation of a unit mass of solids. The apparatus was constructed as a closed loop of 11.4 m length and 3.3 cm inner diameter of steel tubing. Solid volumetric concentrations of up to 20% were used in turbulent flow at a mean Reynolds number of 33,000 82,000. Pulsation was generated using compressed air in a controlled pulsation unit. Frequencies of 0.1 1.0 Hz and amplitude ratios of up to 30% were used. Instantaneous pressure drop and flow rate curves were digitized to calculate the energy dissipation associated with pulsation. The critical velocity in pulsating flow was found to be less than that for the corresponding steady flow at the same volumetric concentration. Energy dissipation for pulsating flow was found to be a function of both frequency and amplitude of pulsation. A possible energy saving was indicated at frequencies of 0.4 0.8 Hz and moderate amplitudes ratios of less than 25%.

  15. Two new pulsating low-mass pre-white dwarfs or SX Phoenicis stars?

    NASA Astrophysics Data System (ADS)

    Corti, M. A.; Kanaan, A.; Córsico, A. H.; Kepler, S. O.; Althaus, L. G.; Koester, D.; Sánchez Arias, J. P.

    2016-03-01

    Context. The discovery of pulsations in low-mass stars opens an opportunity to probe their interiors and determine their evolution by employing the tools of asteroseismology. Aims: We aim to analyse high-speed photometry of SDSS J145847.02+070754.46 and SDSS J173001.94+070600.25 and discover brightness variabilities. In order to locate these stars in the Teff - log g diagram, we fit optical spectra (SDSS) with synthetic non-magnetic spectra derived from model atmospheres. Methods: To carry out this study, we used the photometric data we obtained for these stars with the 2.15 m telescope at CASLEO, Argentina. We analysed their light curves and applied the discrete Fourier transform (FT) to determine the pulsation frequencies. Finally, we compare both stars in the Teff - log g diagram, with two known pre-white dwarfs and seven pulsating pre-ELM white dwarf stars, δ Scuti, and SX Phe stars Results: We report the discovery of pulsations in SDSS J145847.02+070754.46 and SDSS J173001.94+070600.25. We determine their effective temperature and surface gravity to be Teff = 7972 ± 200 K, log g = 4.25 ± 0.5 and Teff = 7925 ± 200 K, log g = 4.25 ± 0.5, respectively. With these parameters, these new pulsating low-mass stars can be identified with either ELM white dwarfs (with ~0.17 M⊙) or more massive SX Phe stars. We identified pulsation periods of 3278.7 and 1633.9 s for SDSS J145847.02+070754.46 and a pulsation period of 3367.1 s for SDSS J173001.94+070600.25. These two new objects, together with those of Maxted et al. (2013, 2014), indicate the possible existence of a new instability domain towards the late stages of evolution of low-mass white dwarf stars, although their identification with SX Phe stars cannot be discarded. Visiting Astronomer, Complejo Astronómico El Leoncito operated under agreement between the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina and the National Universities of La Plata, Córdoba, and San Juan.

  16. Characterizing Accreting White Dwarf Pulsators

    NASA Astrophysics Data System (ADS)

    Szkody, Paula; Mukadam, Anjum

    2014-02-01

    Understanding the population, mass distribution, and evolution of accreting white dwarfs impacts the entire realm of binary interaction, including the creation of Type Ia supernovae. We are concentrating on accreting white dwarf pulsators, as the pulsation properties allow us a view of how the accretion affects the interior of the star. Our ground- based photometry on 11 accreting pulsators with corresponding temperatures from HST UV spectra suggest a broad instability strip in the range of 10500 to 16000K. Additionally, tracking a post-outburst heated white dwarf as it cools and crosses the blue edge and resumes pulsation provides an independent method to locate the empirical instability strip. Determining a post-outburst cooling curve yields an estimate of the amount of heating and the accreted mass during the outburst. We request additional photometry of 2 objects that present unique properties: GW Lib which has not yet returned to its pre-outburst pulsation spectrum after 6 yrs, and EQ Lyn which returned to its pre- outburst pulsation after 3 yrs but is now turning on and off without ongoing outbursts. Following the pulsation spectrum changes over stretches of several nights in a row will provide specific knowledge of the stability of the observed modes.

  17. CoD - 24 7599, a new Delta Scuti star discovered with the Whole Earth Telescope

    NASA Astrophysics Data System (ADS)

    Handler, G.

    1993-05-01

    During observing run XCOV7 of the WET (Whole Earth Telescope, R. E. Nather et al. 1990, ApJ 361, 309) network devoted to the recently discovered dwarf nova 1H0857-242 one of the recommended comparison stars, CoD -24o 7599, turned out to be variable. As a result CoD -24o 7599 was chosen as a second target object. After 11 days of high-speed photometry observations, 110.8 hours of Johnson B measurements had been obtained. Including some overlaps, a duty cycle of 40 % was achieved, resulting in the excellent spectral window shown in the upper panel of the figure.

  18. Pulsation of Ap-Stars

    NASA Astrophysics Data System (ADS)

    Weiss, W. W.; Schneider, H.

    1983-09-01

    It has been known for many centuries that one can determine by simple means if a barrel of wine is full, half empty, or- horribile dictu - empty. One knocks against the wall and listens to the echo. Another example of the same technique, but less interesting for the connaisseur en vin is given by seismology. Seismographs distributed all over the globe register earthquakes and since they are differently located with respect to an earthquake centre the registrations look different. From a comparison of such registrations geologists have extracted most of our knowledge about the structure and composition of the terrestrial interior. Corresponding experiments were also planned and successfully executed on the Moon and on Mars. Stellar astronomers, however, are not in the lucky position of their colleagues who work in our solar system with the help of satellites. They are limited to stars which pulsate voluntarily. We will not discuss here the question why some groups of stars pulsate and others do not. We shall only mention that pulsating stars have at least one layer in their interior which does not absorb pulsational energy, as is the case for the rest of the star, but produces energy of variable amount and in phase with PUlsation. This mechanism keeps the star pulsating as long as this (these) layer(s) exists. Oue to stellar evolution, diffusion, magnetic fields, to name only some possible mechanisms, these layers can disappear or undergo substantial changes so that the energy losses due to pulsation cannot be compensated anymore. Oamping will result and finally the star will become stable against pulsation.

  19. Viscoelastic pulsational mode

    NASA Astrophysics Data System (ADS)

    Dutta, Pranamika; Karmakar, Pralay Kumar

    2017-08-01

    We present a theoretical model analysis to study the linear pulsational mode dynamics in viscoelastic complex self-gravitating infinitely extended clouds in the presence of active frictional coupling and dust-charge fluctuations. The complex cloud consists of uniformly distributed lighter hot mutually thermalized electrons and ions, and heavier cold dust grains amid partial ionization in a homogeneous, quasi-neutral, hydrostatic equilibrium configuration. A normal mode analysis over the closed set of slightly perturbed cloud governing equations is employed to obtain a generalized dispersion relation (septic) of unique analytic construct on the plasma parameters. Two extreme cases of physical interest depending on the perturbation scaling, hydrodynamic limits and kinetic limits are considered. It is shown that the grain mass and viscoelastic relaxation time associated with the charged dust fluid play stabilizing roles to the fluctuations in the hydrodynamic regime. In contrast, however in the kinetic regime, the stabilizing effects are introduced by the dust mass, dust equilibrium density and equilibrium ionic population distribution. Besides, the oscillatory and propagatory features are illustrated numerically and interpreted in detail. The results are in good agreement with the previously reported findings as special corollaries in like situations. Finally, a focalized indication to new implications and applications of the outcomes in the astronomical context is foregrounded.

  20. The Pulsating Pulsar Magnetosphere

    NASA Astrophysics Data System (ADS)

    Tsui, K. H.

    2015-06-01

    Following the basic principles of a charge-separated pulsar magnetosphere, we consider the magnetosphere to be stationary in space, instead of corotating, and the electric field to be uploaded from the potential distribution on the pulsar surface, set up by the unipolar induction. Consequently, the plasma of the magnetosphere undergoes guiding center drifts of the gyromotion due to the forces transverse to the magnetic field. These forces are the electric force, magnetic gradient force, and field line curvature force. Since these plasma velocities are of drift nature, there is no need to introduce an emf along the field lines, which would contradict the {{E}\\parallel }={\\boldsymbol{E}} \\cdot {\\boldsymbol{B}} =0 plasma condition. Furthermore, there is also no need to introduce the critical field line separating the electron and ion open field lines. We present a self-consistent description where the magnetosphere is described in terms of electric and magnetic fields and also in terms of plasma velocities. The fields and velocities are then connected through the space-charge densities self-consistently. We solve the pulsar equation analytically for the fields and construct the standard steady-state pulsar magnetosphere. By considering the unipolar induction inside the pulsar and the magnetosphere outside the pulsar as one coupled system, and under the condition that the unipolar pumping rate exceeds the Poynting flux in the open field lines, plasma pressure can build up in the magnetosphere, in particular, in the closed region. This could cause a periodic opening up of the closed region, leading to a pulsating magnetosphere, which could be an alternative to pulsar beacons. The closed region can also be opened periodically by the build up of toroidal magnetic field through a positive feedback cycle.

  1. Pulsating aurora: The importance of the ionosphere

    SciTech Connect

    Stenbaek-Nielsen, H.C.

    1980-05-01

    A number of different, but mainly optical, observations made in pulsating auroras are presented. These observations indicate that active ionospheric processes are likely to play an important role in causing and/or modifying pulsating aurora.

  2. Ground-satellite observation of Pc 4 pulsations by MAGDAS/CPMN and ETS-VIII geosynchronous orbit satellite

    NASA Astrophysics Data System (ADS)

    Ikeda, A.; Yumoto, K.; Koga, K.; Obara, T.; Baishev, D. G.; Shevtsov, B. M.; Uozumi, T.; Abe, S.; Shishime, A.

    2011-12-01

    Electromagnetic pulsations in ULF range have been studied extensively using ground and satellite observations. However, how Pc 4 pulsations (6.7-22.2 mHz) propagate from the magnetosphere to the ground is not fully understand. Especially the propagation to low latitudes is unclear. We examined data obtained by the ETS-VIII satellite at the geosynchronous orbit (G.M.Lat. -12 degree, G.G.Lon. 146.0 degree) (Koga et al., 2010). We also analyzed ground data of MAGDAS/CPMN (Yumoto and the MAGDAS Group, 2006). The ground data were obtained at high-latitude CHD station (G.M.Lat. 64.9 degree, G.M.Lon. 212.7 degree) and at low-latitude KUJ station (G.M.Lat. 26.1 degree, G.M.Lon. 203.0 degree). The magnetic longitudes of these ground stations are almost same as that of the ETS-VIII. Pc 4 events at ETS-VIII were selected by an automated routine using FFT method which was developed by Takahashi and Ukhorskiy (2007). These Pc 4 events were classified into 2 types. One type is a poloidal Pc 4, in which Hp (northward) component is dominant. Another type is a toroidal mode, in which Hn (eastward) component is dominant. About 10 % of the poloidal/toroidal Pc 4 pulsations, the peak frequency is identical with that of ground Pc 4 pulsations, and the coherence between pulsations observed aboard ETS-VII and on the ground stations is high at the peak frequencies. Thus, about 10 % of the poloidal/toroidal Pc 4 in the magnetosphere can be concluded to transmit to high-latitude ground stations as well as low-latitude stations. For such Pc 4 events, H (horizontal northward) and D (horizontal eastward) components at CHD showed higher amplitude (delta(H)/delta(Hn) = 6.8, delta(H)/delta(Hp) = 10.8, delta(D)/delta(Hn) = 6.8, delta(D)/delta(Hp) = 7.4) than that at the geosynchronous orbit. On the other hand, H and D components at KUJ was attenuated considerably (delta(H)/delta(Hn) = 0.66, delta(H)/delta(Hp) = 0.89, delta(D)/delta(Hn) = 0.35, delta(D)/delta(Hp) = 0.37).

  3. Pulsational mode-typing in line profile variables. I - Four Beta Cephei stars

    NASA Technical Reports Server (NTRS)

    Campos, A. J.; Smith, M. A.

    1980-01-01

    The detailed variations of line profiles in the Beta Cephei-type variable stars Gamma Pegasi, Beta Cephei, Delta Ceti and Sigma Scorpii are modeled throughout their pulsation cycles in order to classify the dominant pulsation mode as radial or nonradial. High-dispersion Reticon observations of the variables were obtained for the Si III line at 4567 A, and line profiles broadened by radial or nonradial pulsations, rotation and radial-tangential macroturbulence were calculated based on a model atmosphere. It is found that only a radial pulsation mode can reproduce the radial velocity amplitude, changes in line asymmetry and uniform line width observed in all four stars. Results are in agreement with the color-to-light arguments of Stamford and Watson (1978), and suggest that radial pulsation plays the dominant role in the observed variations in most Beta Cephei stars. Evidence for shocks or moving shells is also found in visual line data for Sigma Scorpii and an ultraviolet line of Beta Cephei, together with evidence of smooth, secular period changes in Beta Cephei and Delta Ceti.

  4. VizieR Online Data Catalog: Frequency spacing of δ Scuti stars. II. (Paparo+, 2016)

    NASA Astrophysics Data System (ADS)

    Paparo, M.; Benko, J. M.; Hareter, M.; Guzik, J. A.

    2016-07-01

    The CoRoT satellite was launched in 2006. LRa01, the first long run in the direction of anti-center, started on 2007 October 15 and finished on 2008 March 3, resulting in a ΔT=131d time span. Both chromatic and monochromatic data were obtained on the EXO field with a regular sampling of 8 minutes, although for some stars an oversampling mode (32s) was applied. We systematically searched in the CoRoT data archive all light curves in the EXO field for δ Scuti and γ Doradus light curves (Hareter M., 2013, PhD thesis Univ. Vienna). (2 data files).

  5. Chaotic pulsations in stellar models

    SciTech Connect

    Buchler, J.R. )

    1990-12-01

    The irregular behavior of large-amplitude pulsating stars undergoing radial oscillations is examined theoretically, with a focus on hydrodynamic simulations of the W Virginis population II Cepheids (stars which show both regular and RV Tau characteristics). Sequences of models are constructed as one-parameter families (with luminosity, mass, and composition fixed and Teff as the control parameter) and analyzed to derive a systematic map of the bifurcation set; i.e., of the possible types of pulsations. The results are presented graphically, and it is shown that both cascades of period doubling (via destabilization of an overtone through a half-integer-type resonance) and tangent bifurcation are possible routes to chaos in these systems, depending on the stellar parameters. The general robustness of the chaotic behavior and the existence of a 'chaotic blue edge' in stellar-parameter space are demonstrated. 55 refs.

  6. Pressure pulsations above turbomolecular pumps

    NASA Technical Reports Server (NTRS)

    Danziger, S.; Kendall, B. R. F.; Dormer, J.

    1982-01-01

    Lange and Singleton (1978) have observed pressure pulses above a turbomolecular pump. They reported that the mean pulse frequency increased with the temperature of the pump cooling water and that the evolved gas was mainly hydrogen. The present investigation takes into account tests conducted with a similar pumping system. The pumping system was equipped with additional pressure-monitoring equipment in order to study these pulsations in more detail. It was found that at least two distinct types of pressure pulsations may be present in a turbomolecular-pumped ultrahigh vacuum system. The random hydrogen pulses are easily eliminated for period of days by changing the cooling water temperature. The cyclic pulses consisting mainly of water vapor are not likely to be a problem in normal experiments.

  7. Search for exoplanets around pulsating stars of A-F type in Kepler short-cadence data and the case of KIC 8197761

    NASA Astrophysics Data System (ADS)

    Sowicka, Paulina; Handler, Gerald; Dębski, Bartłomiej; Jones, David; Van de Sande, Marie; Pápics, Péter I.

    2017-06-01

    We searched for extrasolar planets around pulsating stars by examining Kepler data for transit-like events hidden in the intrinsic variability. All short-cadence observations for targets with 6000 < Teff < 8500 K were visually inspected for transit-like events following the removal of pulsational signals by sinusoidal fits. Clear transit-like events were detected in KIC 5613330 and KIC 8197761. KIC 5613330 is a confirmed exoplanet host (Kepler-635b), where the transit period determined here is consistent with the literature value. KIC 8197761 is a γ Doradus-δ Scuti star exhibiting eclipses/transits occurring every 9.868 6667(27) d, having durations of 8.37 h and causing brightness drops Δ F/F = 0.006 29(29). The star's pulsation spectrum contains several mode doublets and triplets, identified as l = 1, with a mean spacing of 0.001 659(15) d-1 , implying an internal rotation period of 301 ± 3 d. Trials to calculate the size of the light travel time effect (LTTE) from the pulsations to constrain the companion's mass ended inconclusive. Finding planets around γ Doradus stars from the pulsational LTTE, therefore, is concluded to be unrealistic. Spectroscopic monitoring of KIC 8197761 revealed sinusoidal radial velocity variations with a semi-amplitude of 19.75 ± 0.32 km s-1, while individual spectra present rotational broadening consistent with vsin i = 9 ± 1 km s-1. This suggests that the stellar surface rotation is synchronized with the orbit, whereas the stellar core rotates ˜30 times slower. Combining the observed radial velocity variability with the transit photometry, constrains the companion's mass to be ≈0.28 M⊙, ruling out an exoplanet hypothesis.

  8. Four new subdwarf B pulsators

    NASA Astrophysics Data System (ADS)

    Østensen, R.; Heber, U.; Silvotti, R.; Solheim, J.-E.; Dreizler, S.; Edelmann, H.

    2001-11-01

    We report the detection of short period oscillations in the sdB stars HS 0039+4302, HS 0444+0408, HS 1824+5745 and HS 2151+0857 from time-series photometry made at the Nordic Optical Telescope (NOT) of a sample of 55 candidates. Hence these four hot subdwarfs are new members of the EC 14026 class of pulsating sdB stars. HS 0039+4302 is a multi-mode pulsator with at least four distinct periods in the range between 182 and 234 s, and amplitudes up to 8 mma. HS 0444+0408 shows one dominant pulsation at 137 s (A ~ 12 mma) and a second weaker pulsation at 170 s (A ~ 3 mma). For HS 1824+5745 we find a single period of 139 s with an amplitude of about 5 mma. HS 2151+0857 shows four periods in the range 129-151 s with amplitudes between 2 and 5 mma. Our NLTE model atmosphere analysis of the time-averaged optical spectra place all stars well within the theoretical sdBV instability strip. Based on observations obtained at the Nordic Optical Telescope, operated on the island of La Palma jointly by Denmark, Finland, Iceland, Norway, and Sweden, in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias. }\\fnmsep\\thanks{ Based on observations collected at the German-Spanish Astronomical Center, Calar Alto, operated by the Max-Plank-Institute für Astronomie Heidelberg jointly with the Spanish National Commission for Astronomy. Based on observations collected at the European Southern Observatory, Chile (ESO No. 66.D-0031).

  9. KIC 10080943: An eccentric binary system containing two pressure- and gravity-mode hybrid pulsators

    NASA Astrophysics Data System (ADS)

    Schmid, V. S.; Tkachenko, A.; Aerts, C.; Degroote, P.; Bloemen, S.; Murphy, S. J.; Van Reeth, T.; Pápics, P. I.; Bedding, T. R.; Keen, M. A.; Prša, A.; Menu, J.; Debosscher, J.; Hrudková, M.; De Smedt, K.; Lombaert, R.; Németh, P.

    2015-12-01

    Context. γ Doradus and δ Scuti pulsators cover the transition region between low mass and massive main-sequence stars, and as such, are critical for testing stellar models. When they reside in binary systems, we can combine two independent methods to derive critical information, such as precise fundamental parameters to aid asteroseismic modelling. In the Kepler light curve of KIC 10080943, clear signatures of gravity- and pressure-mode pulsations have been found. Ground-based spectroscopy revealed this target to be a double-lined binary system. Aims: We present the analysis of four years of Kepler photometry and high-resolution spectroscopy to derive observational constraints with which to evaluate theoretical predictions of the stellar structure and evolution for intermediate-mass stars. Methods: We used the method of spectral disentangling to determine atmospheric parameters for both components and derive the orbital elements. With phoebe, we modelled the ellipsoidal variation and reflection signal of the binary in the light curve and used classical Fourier techniques to analyse the pulsation modes. Results: We show that the eccentric binary system KIC 10080943 contains two hybrid pulsators with masses M1 = 2.0 ± 0.1 M⊙ and M2 = 1.9 ± 0.1 M⊙, with radii R1 = 2.9 ± 0.1 R⊙ and R2 = 2.1 ± 0.2 R⊙. We detect rotational splitting in the g and p modes for both stars and use them to determine a first rough estimate of the core-to-surface rotation rates for the two components, which will be improved by future detailed seismic modelling. Based on the data gathered with NASA's Discovery mission, Kepler, and with the HERMES spectrograph, installed at the Mercator Telescope, operated on the island of La Palma by the Flemish Community, at the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias and supported by the Fund for Scientific Research of Flanders (FWO), Belgium, the Research Council of KU Leuven, Belgium, the

  10. Head pulsations in a centrifugal pump

    NASA Astrophysics Data System (ADS)

    Boiko, V. S.; Sotnyk, M. I.; Moskalenko, V. V.

    2017-08-01

    This article investigated the factors, which affect to the character of the head pulsations of a centrifugal pump. We investigated the dependence of the shape and depth of these pulsations from the operation mode of the pump. Was determined, that the head pulsations at the outlet of the impeller (pulsations on the blade passing frequency) cause head pulsations at the outlet of the pump, that have the same frequency, but differ in shape and depth. These pulsations depend on the design features of the flow-through part of the pump (from the ratio of hydraulic losses on the friction and losses on the vortex formation). A feature of the researches that were conducted is also the using of not only hydraulic but also electric modeling methods. It allows determining the values of the components of hydraulic losses.

  11. The morphology of displays of pulsating auroras.

    NASA Technical Reports Server (NTRS)

    Cresswell, G. R.

    1972-01-01

    An auroral substorm generates displays of pulsating auroras in ways which show a dependence upon both local time and latitude relative to the auroral oval. For several hours after midnight pulsating auroras can be observed in the wake of poleward expansions or within equatorward spreading diffuse envelopes of meridional extent of several hundred kilometers. As the dawn meridian is approached the displays of pulsating auroras tend increasingly to be comprised of distinct eastward drifting patches easily recorded by all-sky cameras.

  12. First Kepler results on compact pulsators - I. Survey target selection and the first pulsators

    NASA Astrophysics Data System (ADS)

    Østensen, R. H.; Silvotti, R.; Charpinet, S.; Oreiro, R.; Handler, G.; Green, E. M.; Bloemen, S.; Heber, U.; Gänsicke, B. T.; Marsh, T. R.; Kurtz, D. W.; Telting, J. H.; Reed, M. D.; Kawaler, S. D.; Aerts, C.; Rodríguez-López, C.; Vučković, M.; Ottosen, T. A.; Liimets, T.; Quint, A. C.; Van Grootel, V.; Randall, S. K.; Gilliland, R. L.; Kjeldsen, H.; Christensen-Dalsgaard, J.; Borucki, W. J.; Koch, D.; Quintana, E. V.

    2010-12-01

    We present results from the first two quarters of a survey to search for pulsations in compact stellar objects with the Kepler spacecraft. The survey sample and the various methods applied in its compilation are described, and spectroscopic observations are presented to separate the objects into accurate classes. From the Kepler photometry we clearly identify nine compact pulsators and a number of interesting binary stars. Of the pulsators, one shows the strong, rapid pulsations typical of a V361 Hya-type sdB variable (sdBV); seven show long-period pulsation characteristics of V1093 Her-type sdBVs; and one shows low-amplitude pulsations with both short and long periods. We derive effective temperatures and surface gravities for all the subdwarf B stars in the sample and demonstrate that below the boundary region where hybrid sdB pulsators are found, all our targets are pulsating. For the stars hotter than this boundary temperature a low fraction of strong pulsators (<10 per cent) is confirmed. Interestingly, the short-period pulsator also shows a low-amplitude mode in the long-period region, and several of the V1093 Her pulsators show low-amplitude modes in the short-period region, indicating that hybrid behaviour may be common in these stars, also outside the boundary temperature region where hybrid pulsators have hitherto been found.

  13. Evidence of chaotic modes in the analysis of four δ Scuti stars

    NASA Astrophysics Data System (ADS)

    Barceló Forteza, S.; Roca Cortés, T.; García Hernández, A.; García, R. A.

    2017-05-01

    Context. Since CoRoT observations unveiled the very low amplitude modes that form a flat plateau in the power spectrum structure of δ Scuti stars, the nature of this phenomenon, including the possibility of spurious signals due to the light curve analysis, has been a matter of long-standing scientific debate. Aims: We contribute to this debate by finding the structural parameters of a sample of four δ Scuti stars, CID 546, CID 3619, CID 8669, and KIC 5892969, and looking for a possible relation between these stars' structural parameters and their power spectrum structure. Methods: For the purposes of characterization, we developed a method of studying and analysing the power spectrum with high precision and have applied it to both CoRoT and Kepler light curves. Results: We obtain the best estimates to date of these stars' structural parameters. Moreover, we observe that the power spectrum structure depends on the inclination, oblateness, and convective efficiency of each star. Conclusions: Our results suggest that the power spectrum structure is real and is possibly formed by 2-period island modes and chaotic modes.

  14. Nile Delta

    Atmospheric Science Data Center

    2013-04-15

    article title:  The Nile River Delta     View Larger Image ... of eastern Africa. At the apex of the fertile Nile River Delta is the Egyptian capital city of Cairo. To the west are the Great Pyramids ...

  15. Period-luminosity-metallicity relations, pulsation modes, absolute magnitudes, and distances for population 2 variable stars

    NASA Astrophysics Data System (ADS)

    Nemec, James M.; Nemec, Amanda F. Linnell; Lutz, Thomas E.

    1994-07-01

    Period-luminosity-metallicity (P-L-(Fe/H) relations are presented for RR Lyrae stars, Pop. II Cepheids, anomalous Cepheids and SX Phe stars pulsating in the fundamental (F) and first-overtone (H) modes. The relations were derived by fitting regression lines to the observed pulsation periods and mean B, V, and K magnitudes of over 1200 stars in approximately 40 stellar systems. Analysis of covariance methods, which allow the simultaneous computation of more than one P-L-(Fe/H) relation, were used to estimate the slopes and intercepts. Of the 24 possible P-L-(Fe/H) relations for the four kinds of stars, two pulsation modes, and three passbands considered here, 18 relations have been derived-the others could not be derived because of a lack of photometry in one or more of the three passbands. The slopes for the F and H pulsators were tested for departures from equality for all types of stars and passbands; the results suggest that the observations are consistent with the assumption that, for each kind of star (except possibly the Pop. II Cepheids), the P-L-(Fe/h) relations for the F and H pulsation modes are parallel but vertically offset, with a family of lines corresponding to a range of metallicities. Pulsation modes and absolute magnitudes are presented for the non-RR Lyrae variable stars considered in the analysis, and distances are estimated for the program clusters. It is well established from previous studies that the P-L relations for RR Lyrae stars are approximately flat for the B passband, and have a slope delta mk/ delta log P approximately 2.4 for the K passband. We recover these slopes and find that the P-L-(Fe/H) relation in V has an intermediate slope, delta mv/delta log P = -0.52 plus or minus 0.11. A similar dependence of slope on passband is seen for classical Cepheids (see Madore & Freedman, PASP, 103, 933 (1991). The available B, V photometry for approximately 40 of the known globular cluster Cepheids are found to be consistent with Arp's AJ, 60

  16. Volga Delta

    Atmospheric Science Data Center

    2013-04-17

    article title:  Volga Delta and the Caspian Sea     View ... appear reddish. A small cloud near the center of the delta separates into red, green, and blue components due to geometric parallax ... include several linear features located near the Volga Delta shoreline. These long, thin lines are artificially maintained shipping ...

  17. The mitigation of pulsation in ventilated supercavities

    NASA Astrophysics Data System (ADS)

    Skidmore, Grant

    It is desirable to use ventilated supercavities to reduce the drag created by underwater bodies and obtain velocities much higher than those that are possible with fully wetted bodies. Ventilated supercavities, however, are prone to an autoresonant phenomenon known as pulsation where the supercavity radius and length oscillate with time. These oscillations in radius and length are oftentimes severe enough to cause issues with body stability and control. In this dissertation, a method to mitigate pulsation in ventilated supercavities is presented. The method, which modulates or adds a sinusoidal component to the ventilation rate, is shown to suppress pulsation numerically, experimentally, and computationally. Additionally in this dissertation, the near-field acoustic characteristics of twin vortex, re-entrant jet, and pulsating ventilated supercavities are studied experimentally. This study is then repeated computationally, with a focus on the generation and mitigation of pulsation in ventilated supercavities. The study of the near-field radiated noise from supercavities shows that pulsating supercavities generate noise that is two orders of magnitude (i.e., 40 dB) greater in level than that from comparable twin vortex and re-entrant jet supercavities. For pulsating supercavities, it is found that the interior cavity pressure and near-field radiated noise are both monotonic in frequency, with said frequency being related to the freestream velocity and the length of the dominant waves on the supercavity air/water interface. For pulsating supercavities, it is also found that, at the pulsation frequency, the cavity interior pressure spectrum level is related to the near-field and far-field noise spectrum level through spherical spreading of the sound waves from the supercavity interface. As a result, the cavity interior pressure can be used as a measure of the radiated noise. The developed method for mitigating pulsation in ventilated supercavities is shown to

  18. Transition to turbulence in pulsating pipe flow

    NASA Astrophysics Data System (ADS)

    Xu, Duo; Warnecke, Sascha; Hof, Bjoern; Avila, Marc

    2014-11-01

    We report an experimental investigation of the transition to turbulence in a pulsating pipe flow. This flow is a prototype of various pulsating flows in both nature and engineering, such as in the cardiovascular system where the onset of turbulence is often possibly related to various diseases (e.g., the formation of aneurysms). The experiments are carried out in a straight rigid pipe using water with a sinusoidal modulation of the flow rate. The governing parameters, Reynolds number, Womersley number α (dimensionless pulsating frequency) and the pulsating amplitude A, cover a wide range 3 < α < 23 and 0 < A < 1 . To characterize the transition to turbulence, we determine how the characteristic lifetime of turbulent spots (/puffs) are affected by the pulsation. While at high pulsation frequencies (α > 12) lifetimes of turbulent spots are entirely unaffected by the pulsation, at lower frequencies they are substantially affected. With decreasing frequency much larger Reynolds numbers are needed to obtain spots of the same characteristic lifetime. Hence at low frequency transition is delayed significantly. In addition the effect of the pulsation amplitude on the transition delay is quantified. Duo Xu would like to acknowledge the support from Humboldt Foundation.

  19. Nonradial Pulsations in ɛ Persei

    NASA Astrophysics Data System (ADS)

    Saio, Hideyuki; Kambe, Eiji; Lee, Umin

    2000-11-01

    We consider the question of whether all the modes detected in the line profile variations of ɛ Persei are consistent with nonradial pulsations excited by the kappa mechanism at the opacity Z-bump. We have computed massive (12.5-14 Msolar) main-sequence models, adjusting the parameters such that the evolutionary tracks pass around the approximate position of ɛ Per on the H-R diagram. A linear nonadiabatic, nonradial pulsation analysis is applied to these models. The periods in the frame corotating with the stellar surface for the observed 2.3-4.5 hr modes are found to be consistent with the Z-bump kappa mechanism. We have found, however, that the longest-period mode (8.48 hr in the observer's frame) cannot be explained by the kappa mechanism. We have examined the effect of rotation on the stability of oscillations and found that the stabilizing effect is weak, so that only a few of the shortest-period modes are stabilized for the rotation speed of ɛ Per. No significant difference is found between prograde and retrograde modes in the stability. It is a puzzle why no retrograde mode has been detected in ɛ Per, which should equally be excited by the kappa mechanism. We also discuss the observed and theoretical line profile variations of ɛ Per in the Appendix.

  20. Models of cylindrical bubble pulsation

    PubMed Central

    Ilinskii, Yurii A.; Zabolotskaya, Evgenia A.; Hay, Todd A.; Hamilton, Mark F.

    2012-01-01

    Three models are considered for describing the dynamics of a pulsating cylindrical bubble. A linear solution is derived for a cylindrical bubble in an infinite compressible liquid. The solution accounts for losses due to viscosity, heat conduction, and acoustic radiation. It reveals that radiation is the dominant loss mechanism, and that it is 22 times greater than for a spherical bubble of the same radius. The predicted resonance frequency provides a basis of comparison for limiting forms of other models. The second model considered is a commonly used equation in Rayleigh-Plesset form that requires an incompressible liquid to be finite in extent in order for bubble pulsation to occur. The radial extent of the liquid becomes a fitting parameter, and it is found that considerably different values of the parameter are required for modeling inertial motion versus acoustical oscillations. The third model was developed by V. K. Kedrinskii [Hydrodynamics of Explosion (Springer, New York, 2005), pp. 23–26] in the form of the Gilmore equation for compressible liquids of infinite extent. While the correct resonance frequency and loss factor are not recovered from this model in the linear approximation, it provides reasonable agreement with observations of inertial motion. PMID:22978863

  1. Pulsating star research from Antarctica

    NASA Astrophysics Data System (ADS)

    Chadid, Merieme

    2017-09-01

    This invited talk discusses the pulsating star research from the heart of Antarctica and the scientific polar challenges in the extreme environment of Antarctica, and how the new polar technology could cope with unresolved stellar pulsation enigmas and evolutionary properties challenges towards an understanding of the mysteries of the Universe. PAIX, the first robotic photometer Antarctica program, has been successfully launched during the polar night 2007. This ongoing program gives a new insight to cope with unresolved stellar enigmas and stellar oscillation challenges with a great opportunity to benefit from an access to the best astronomical site on Earth, Dome C. PAIX achieves astrophysical measurement time-series of stellar fields, challenging photometry from space. A continuous and an uninterrupted series of multi-color photometric observations has been collected each polar night - 150 days - without regular interruption, Earth's rotation effect. PAIX shows the first light curve from Antarctica and first step for the astronomy in Antarctica giving new insights in remote polar observing runs and robotic instruments towards a new technology.

  2. Occurrence and average behavior of pulsating aurora

    NASA Astrophysics Data System (ADS)

    Partamies, N.; Whiter, D.; Kadokura, A.; Kauristie, K.; Nesse Tyssøy, H.; Massetti, S.; Stauning, P.; Raita, T.

    2017-05-01

    Motivated by recent event studies and modeling efforts on pulsating aurora, which conclude that the precipitation energy during these events is high enough to cause significant chemical changes in the mesosphere, this study looks for the bulk behavior of auroral pulsations. Based on about 400 pulsating aurora events, we outline the typical duration, geomagnetic conditions, and change in the peak emission height for the events. We show that the auroral peak emission height for both green and blue emission decreases by about 8 km at the start of the pulsating aurora interval. This brings the hardest 10% of the electrons down to about 90 km altitude. The median duration of pulsating aurora is about 1.4 h. This value is a conservative estimate since in many cases the end of event is limited by the end of auroral imaging for the night or the aurora drifting out of the camera field of view. The longest durations of auroral pulsations are observed during events which start within the substorm recovery phases. As a result, the geomagnetic indices are not able to describe pulsating aurora. Simultaneous Antarctic auroral images were found for 10 pulsating aurora events. In eight cases auroral pulsations were seen in the southern hemispheric data as well, suggesting an equatorial precipitation source and a frequent interhemispheric occurrence. The long lifetimes of pulsating aurora, their interhemispheric occurrence, and the relatively high-precipitation energies make this type of aurora an effective energy deposition process which is easy to identify from the ground-based image data.

  3. A Planet Found by Pulsations

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2016-10-01

    Searching for planets around very hot stars is much more challenging than looking around cool stars. For this reason, the recent discovery of a planet around a main-sequence A star is an important find both because of its unique position near the stars habitable zone, and because of the way in which the planet was discovered.Challenges in VariabilityIn the past three decades, weve discovered thousands of exoplanets yet most of them have been found around cool stars (like M dwarfs) or moderate stars (like G stars like our Sun). Very few of the planets that weve found orbit hot stars; in fact, weve only discovered ~20 planets orbiting the very hot, main-sequence A stars.The instability strip, indicated on an H-R diagram. Stellar classification types are listed across the bottom of the diagram. Many main-sequence A stars reside in the instability strip. [Rursus]Why is this? We dont expect that main-sequence A stars host fewer planets than cooler stars. Instead, its primarily because the two main techniques that we use to find planets namely, transits and radial velocity cant be used as effectively on the main-sequence A stars that are most likely to host planets, because the luminosities of these stars are often variable.These stars can lie on whats known as the classical instability strip in the Herzsprung-Russell diagram. Such variable stars pulsate due to changes in the ionization state of atoms deep in their interiors, which causes the stars to puff up and then collapse back inward. For variable main-sequence A stars, the periods for these pulsations can be several to several tens of times per day.These very pulsations that make transits and radial-velocity measurements so difficult, however, can potentially be used to detect planets in a different way. Led by Simon Murphy (University of Sydney, Australia and Aarhus University, Denmark), a team of scientists has recently detected the first planet ever to be discovered around a main-sequence A star from the timing

  4. The extended atmosphere and evolution of the RV Tauri star, R Scuti

    NASA Astrophysics Data System (ADS)

    Yamamura, Issei; Matsuura, Mikako; Zijlstra, Albert A.; Bedding, Timothy R.

    2003-02-01

    We analyze ISO/SWS spectra of the RV Tau star, R Scuti. The data were obtained from the ISO data archive, and processed with OLP ver.10.1 and OSIA ver.2.0. We found that the infrared spectra of this star are dominated by emission bands of H2O vapour. We also identify CO, SiO and CO2 bands. Unlike the other RV Tau stars, the infrared spectra of R Sct are very similar to those of the oxygen-rich Mira variable, o Cet (Mira). However, 10 μm silicate band is very weak in R Sct. With these newly found properties of the star, we discuss structure and evolutionary stage of the star. This study is an example that the uniform and high-quality data in the ISO Archive have a lot of potential to give an impact on stellar evolution.

  5. HUBBLE SPACE TELESCOPE Images of the Compact Nebula around RY Scuti

    NASA Astrophysics Data System (ADS)

    Smith, Nathan; Gehrz, Robert D.; Humphreys, Roberta M.; Davidson, Kris; Jones, Terry J.; Krautter, Joachim

    1999-08-01

    We present HST Wide Field Planetary Camera 2 images of the very massive eclipsing binary RY Scuti. The HST Hα image shows a very complex ionized nebula roughly 1" in size. Several interesting structures are revealed, including what appears to be a pair of concentric ionized rings above and below the equatorial plane of the system, located at the inner edge of a more extended dust torus. We reexamine some essential physical characteristics of the nebula, such as a possible magnetic field and the complicated mass-loss geometry of this near-Eddington limit contact binary. The effects of a rotating illumination source are considered to explain the brightness distribution in the rings. We suggest a model for the origin of the mass and detailed structure in the nebula. This model invokes a previous mass ejection that is shaped by nonspherical interacting winds and possibly magnetic fields.

  6. Pulsations and outbursts of luminous blue variables

    SciTech Connect

    Cox, A.N.; Guzik, J.A.; Soukup, M.S.; Despain, K.M.

    1997-06-01

    We propose an outburst mechanism for the most luminous stars in our and other galaxies. These million solar luminosity stars, with masses (after earlier mass loss) of between 20 and maybe 70 solar masses, are pulsationally unstable for both radial and low-degree nonradial modes. Some of these modes are ``strange,`` meaning mostly that the pulsations are concentrated near the stellar surface and have very rapid growth rates in linear theory. The pulsation driving is by both the high iron line opacity (near 150,000 K) and the helium opacity (near 30,000 K) kappa effects. Periods range from 5 to 40 days. Depending on the composition, pulsations periodically produce luminosities above the Eddington limit for deep layers. The radiative luminosity creates an outward push that readily eases the very low gamma envelope to very large outburst radii. A key point is that a super-Eddington luminosity cannot be taken up by the sluggish convection rapidly enough to prevent an outward acceleration of much of the envelope. As the helium abundance in the envelope stellar material increases by ordinary wind mass loss and the luminous blue variable outbursts, the opacity in the deep pulsation driving layers decreases. This makes the current Eddington luminosity even higher so that pulsations can then no longer give radiative luminosities exceeding the limit. For the lower mass and luminosity luminous blue variables there is considerably less iron line opacity driving, and pulsations are almost all caused by the helium ionization kappa effect.

  7. CHARACTERIZING PULSATING MIXING OF SLURRIES

    SciTech Connect

    Bamberger, Judith A.; Meyer, Perry A.

    2007-12-01

    This paper describes the physical properties for defining the operation of a pulse jet mixing system. Pulse jet mixing operates with no moving parts located in the vessel to be mixed. Pulse tubes submerged in the vessel provide a pulsating flow due to a controlled combination of applied pressure to expel the fluid from the pulse tube nozzle followed by suction to refill the pulse tube through the same nozzle. For mixing slurries nondimensional parameters to define mixing operation include slurry properties, geometric properties and operational parameters. Primary parameters include jet Reynolds number and Froude number; alternate parameters may include particle Galileo number, particle Reynolds number, settling velocity ratio, and hindered settling velocity ratio. Rating metrics for system performance include just suspended velocity, concentration distribution as a function of elevation, and blend time.

  8. Survey of Candidate Pulsating Eclipsing Binaries - I

    NASA Astrophysics Data System (ADS)

    Dvorak, S.

    2009-08-01

    Initial results from a photometric survey of stars selected from the list of eclipsing binaries that may contain a pulsating component by Soydugan et al. (2006) are reported. A minimum of two nights of CCD observations with V and/or B filters of each of the 35 stars from this list was collected. Of the 35 stars stud- ied, a pulsating component was detected in three of the systems. Pulsations were also serendiptiously detected in the eclipsing binary RR Leporis, which is not on the candidate list.

  9. Theoretical interpretations of anomalous Cepheid pulsations

    SciTech Connect

    Cox, A.N.; Proffitt, C.R.

    1988-01-01

    Detailed pulsation studies have been made of five anomalous Cepheids in the Draco galaxy, one in the galactic globular cluster NGC 5466 and a possible anomalous Cepheid in M15. Observed quantities are periods, luminosities, and effective temperatures. Pulsation masses range from 1.0 to 1.8 solar masses, as found by others before. The variables with effective temperatures above 7000 K seem to be in the first overtone radial mode, while the others are fundamental pulsators. Investigations show that the masses and pulsation modes are independent of the assumed composition and details of the convection such as inclusion of the considerable turbulent pressure as part of the total pressure in the convection zone. 19 references.

  10. Small-scale Features in Pulsating Aurora

    NASA Astrophysics Data System (ADS)

    Jones, S.; Jaynes, A. N.; Knudsen, D. J.; Trondsen, T.; Lessard, M.

    2011-12-01

    A field study was conducted from March 12-16, 2002 using a narrow-field intensified CCD camera installed at Churchill, Manitoba. The camera was oriented along the local magnetic zenith where small-scale black auroral forms are often visible. This analysis focuses on such forms occurring within a region of pulsating aurora. The observations show black forms with irregular shape and nonuniform drift with respect to the relatively stationary pulsating patches. The pulsating patches occur within a diffuse auroral background as a modulation of the auroral brightness in a localized region. The images analyzed show a decrease in the brightness of the diffuse background in the region of the pulsating patch at the beginning of the 'off' phase of the modulation. Throughout the off phase the brightness of the diffuse aurora gradually increases back to the average intensity. The time constant for this increase is measured as the first step toward determining the physical process.

  11. Small-Scale Features in Pulsating Aurora

    NASA Technical Reports Server (NTRS)

    Jones, Sarah; Jaynes, Allison N.; Knudsen, David J.; Trondsen, Trond; Lessard, Marc

    2011-01-01

    A field study was conducted from March 12-16, 2002 using a narrow-field intensified CCD camera installed at Churchill, Manitoba. The camera was oriented along the local magnetic zenith where small-scale black auroral forms are often visible. This analysis focuses on such forms occurring within a region of pulsating aurora. The observations show black forms with irregular shape and nonuniform drift with respect to the relatively stationary pulsating patches. The pulsating patches occur within a diffuse auroral background as a modulation of the auroral brightness in a localized region. The images analyzed show a decrease in the brightness of the diffuse background in the region of the pulsating patch at the beginning of the offphase of the modulation. Throughout the off phase the brightness of the diffuse aurora gradually increases back to the average intensity. The time constant for this increase is measured as the first step toward determining the physical process.

  12. A motion picture presentation of magnetic pulsations

    NASA Technical Reports Server (NTRS)

    Suzuki, A.; Kim, J. S.; Sugura, M.; Nagano, H.

    1981-01-01

    Using the data obtained from the IMS North American magnetometer network stations at high latitudes, a motion picture was made by a computer technique, describing time changes of Pc5 and Pi3 magnetic pulsation vectors. Examples of pulsation characteristics derived from this presentation are regional polarization changes including shifts of polarization demarcation lines, changes in the extent of an active region and its movement with time.

  13. Statistical study of dayside pulsating aurora

    NASA Astrophysics Data System (ADS)

    Kanmae, T.; Kadokura, A.; Ogawa, Y.; Ebihara, Y.; Motoba, T.; Gerrard, A. J.; Weatherwax, A. T.

    2015-12-01

    Pulsating aurora normally occurs after a substorm breakup in the midnight sector, often observed to persist through the morning sector and beyond. Indeed, it has also been observed on the dayside; however, the characteristics of the dayside pulsating aurora are poorly known. A handful of observational studies have been reported, but the results are somewhat disputable because most of the studies had non-uniform sampling of the dark dayside region. Furthermore, the previous studies used photometer data, with which the spatial characteristics of the pulsating aurora cannot be examined. To determine both temporal and spatial characteristics of the pulsating aurora, we have studied three years of all-sky image data obtained at the South Pole station. Because of its unique geographical location, the station has 24 hours of darkness during the austral winter from April to August, providing an ideal platform for studying dayside aurora. In a preliminary survey of the data, we have identified the pulsating auroras in 198 days out of 365 days of observations. The magnetic local time (MLT) distribution of the occurrence peaks between 9:00 and 11:00, but shows no or little dependence on the geomagnetic activity. In many events, pulsating patches initially appear as east-west aligned arc segments and later in the afternoon sector develop into large, diffuse patches, which occasionally fill a large part of the field of view. Using the long-term data, we will statistically examine both temporal (occurrence rate, duration and pulsation period) and spatial (sizes and shapes) characteristics of the dayside pulsating aurora.

  14. Stellar pulsation and rotation in NGC 6811

    NASA Astrophysics Data System (ADS)

    Rodríguez, E.; Ocando, S.; López-González, M. J.; Martín-Ruiz, S.

    2017-03-01

    We present the results of the frequency analysis for a selected sample of pulsating δ Sct- and γ Dor-type stars in the field of the open cluster NGC 6811, which have been observed in short-cadence (SC) mode by the Kepler satellite. In all cases, the resulting frequency spectra are very complex, especially when the dominant pulsation is that of the δ Sct type, that is, short-period pulsations corresponding to excited pressure (p) modes. In all cases, the δ Sct stars are shown to be essentially δ Sct/ γ Dor hybrid pulsators. However, the opposite seems not to be true. We also find that the δ Sct-type peaks commonly are not stable in amplitude. Many of the main peaks significantly change their amplitudes over relatively short time scales. For a large percentage of pulsators in our sample we also find that the variability shown in the light curves is not produced by a single cause, but a combination of various sources: δ Sct- and γ Dor-type pulsations together with rotational modulation produced by starspots in the surfaces of these stars. This is an indication of stellar activity in the surfaces of these relatively hot stars of spectral type A(-F). Sometimes, activity dominates the luminosity variations in various pulsating stars in our sample. Eclipsing binarity is also detected in a few cases. Flares are also detected in one of the δ Sct-type pulsators. This is an indication of unusual strong activity for this kind of hot stars.

  15. Radial pulsations in DB white dwarfs?

    NASA Technical Reports Server (NTRS)

    Kawaler, Steven D.

    1993-01-01

    Theoretical models of DB white dwarfs are unstable against radial pulsation at effective temperatures near 20,000-30,000 K. Many high-overtone modes are unstable, with periods ranging from 12 s down to the acoustic cutoff period of approximately 0.1 s. The blue edge for radial instability lies at slightly higher effective temperatures than for nonradial pulsations, with the temperature of the blue edge dependent on the assumed efficiency of convection. Models with increased convective efficiency have radial blue edges that are increasingly closer to the nonradial blue edge; in all models the instability persists into the nonradial instability strip. Radial pulsations therefore may exist in the hottest DB stars that lie below the DB gap; the greatest chance for detection would be observations in the ultraviolet. These models also explain why searches for radial pulsations in DA white dwarfs have failed: the efficient convection needed to explain the blue edge for nonradial DA pulsation means that the radial instability strip is 1000 K cooler than found in previous investigations. The multiperiodic nature of the expected pulsations can be used to advantage to identify very low amplitude modes using the uniform spacing of the modes in frequency. This frequency spacing is a direct indicator of the mass of the star.

  16. Temperature effects in pulsating superfluid neutron stars

    SciTech Connect

    Kantor, Elena M.; Gusakov, Mikhail E.

    2011-05-15

    We study the effects of finite stellar temperatures on the oscillations of superfluid neutron stars. The importance of these effects is illustrated with a simple example of a radially pulsating general relativistic star. Two main effects are taken into account: (i) temperature dependence of the entrainment matrix and (ii) the variation of the size of superfluid region with temperature. Four models are considered, which include either one or both of these two effects. Pulsation spectra are calculated for these models, and asymptotes for eigenfrequencies at temperatures close to critical temperature of neutron superfluidity are derived. It is demonstrated that models that allow for the temperature effect (ii) but disregard the effect (i), yield unrealistic results. Eigenfunctions for the normal- and superfluid-type pulsations are analyzed. It is shown that superfluid pulsation modes practically do not appear at the neutron-star surface and, therefore, can hardly be observed by measuring the modulation of the electromagnetic radiation from the star. The e-folding times for damping of pulsations due to the shear viscosity and nonequilibrium modified Urca processes are calculated and their asymptotes at temperatures close to the neutron critical temperature, are obtained. It is demonstrated that superfluid pulsation modes are damped by 1-3 orders of magnitude faster than normal modes.

  17. Two new extremely hot pulsating white dwarfs

    NASA Technical Reports Server (NTRS)

    Bond, H. E.; Grauer, A. D.; Green, R. F.; Liebert, J. W.

    1984-01-01

    High speed photometry of the extremely hot, nearly degenerate stars PG 1707 + 427 and PG 2131 + 066 reveals that they are low-amplitude pulsating variables. Power spectral analysis shows both to be multiperiodic, with dominant periods of 7.5 and 6.4-6.9 minutes, respectively. Together with the known pulsators PG 1159 - 035 and the central star of the planetary nebula Kohoutek 1-16, these objects define a new pulsational instability strip at the hot edge of the H-R diagram. The variations of these objects closely resemble those of the much cooler pulsating ZZ Ceti DA white dwarfs; both groups are probably nonradial g-mode pulsators. Evolutionary contraction of the PG 1159 - 035 variables may lead to period changes that would be detectable in as little as 1 year. The optical and IUE spectra of the PG 1159 - 035 variables are characterized by absorption lines of C IV and other CNO ions, indicating radiative levitation of species heavier than helium. He II is also present in the spectra, but the hydrogen Balmer lines are absent. Effective temperatures near 100,000 K are required, and the He II 4686 A profiles indicate log g greater than 6. These helium-rich pulsators form the hottest known subgroup of the DO white dwarfs.

  18. Asteroseismology from Space: The Delta Scuti Star Theta(sup 2) Tauri Monitored by the WIRE Satellite

    NASA Technical Reports Server (NTRS)

    Poretti, E.; Buzasi, Derek; Laher, R.; Catanzarite, J.; Conrow, T.

    2002-01-01

    The bright variable star theta(sup 2) Tau was monitored with the star camera on the Wide-Field Infrared Explorer satellite. Twelve independent frequencies were detected down to the 0.5 mmag amplitude level. Their reality was investigated by searching for them using two different algorithms and by some internal checks: both procedures strengthened our confidence in the results. All the frequencies are in the range 10.8-14.6 cd(exp -1). The histogram of the frequency spacings shows that 81% are below 1.8 d; rotation may thus play a role in the mode excitation. The fundamental radial mode is not observed, although it is expected to occur in a region where the noise level is very low (55 mu mag). The rms residual is about two times lower than that usually obtained from successful groundbased multisite campaigns. The comparison of the results of previous campaigns with the new ones establishes the amplitude variability of some modes.

  19. Asteroseismology from Space: The Delta Scuti Star Theta(sup 2) Tauri Monitored by the WIRE Satellite

    NASA Technical Reports Server (NTRS)

    Poretti, E.; Buzasi, D.; Laher, R.; Catanzarite, J.; Conrow, T.

    2002-01-01

    The bright variable star (theta)(sup 2) Tau was monitored with the star camera on the Wide-Field Infrared Explorer satellite. Twelve independent frequencies were detected down to the 0.5 mmag amplitude level. Their reality was investigated by searching for them using two different algorithms and by some internal checks: both procedures strengthened our confidence in the results. All the frequencies are in the range 10.8 - 14.6 cd(exp -1). The histogram of the frequency spacings shows that 81% are below 1.8 d; rotation may thus play a role in the mode excitation. The fundamental radial mode is not observed, although it is expected to occur in a region where the noise level is very low (55 (micro)mag). The rms (root mean square) residual is about two times lower than that usually obtained from successful groundbased multisite campaigns. The comparison of the results of previous campaigns with the new ones establishes the amplitude variability of some modes.

  20. Delta II

    NASA Technical Reports Server (NTRS)

    1990-01-01

    The Delta II expendable launch vehicle with the ROSAT (Roentgen Satellite), cooperative space X-ray astronomy mission between NASA, Germany and United Kingdom, was launched from the Cape Canaveral Air Force Station on June 1, 1990.

  1. Finding binaries from phase modulation of pulsating stars with Kepler - IV. Detection limits and radial velocity verification

    NASA Astrophysics Data System (ADS)

    Murphy, Simon J.; Shibahashi, Hiromoto; Bedding, Timothy R.

    2016-10-01

    We explore the detection limits of the phase modulation (PM) method of finding binary systems among multiperiodic pulsating stars. The method is an attractive way of finding non-transiting planets in the habitable zones of intermediate-mass stars, whose rapid rotation inhibits detections via the radial velocity (RV) method. While oscillation amplitudes of a few mmag are required to find planets, many δ Scuti stars have these amplitudes. In suboptimal cases where the signal to noise of the oscillations is lower, low-mass brown dwarfs (˜13MJup) are detectable at orbital periods longer than about 1 yr, and the lowest mass main-sequence stars (0.1-0.2 M⊙) are detectable at all orbital periods where the PM method can be applied. We use purpose-written Markov chain Monte Carlo (MCMC) software for the calculation of the PM orbits, which offers robust uncertainties for comparison with RV solutions. Using Kepler data and ground-based RVs, we verify that these two methods are in agreement, even at short orbital periods where the PM method undersamples the orbit. We develop new theory to account for the undersampling of the time delays, which is also necessary for the inclusion of RVs as observational data in the MCMC software. We show that combining RVs with time delays substantially refines the orbits because of the complementarity of working in both the spatial (PM) and velocity (RV) domains simultaneously. Software outputs were tested through an extensive hare-and-hounds exercise, covering a wide range of orbital configurations including binaries containing two pulsators.

  2. Application of the Baade-Wesselink method to a pulsating cluster Herbig Ae star: H254 in IC348

    NASA Astrophysics Data System (ADS)

    Ripepi, V.; Molinaro, R.; Marconi, M.; Catanzaro, G.; Claudi, R.; Daszyńska-Daszkiewicz, J.; Palla, F.; Leccia, S.; Bernabei, S.

    2014-01-01

    In this paper we present new photometric and radial velocity data for the PMS δ Sct star H254, member of the young cluster IC 348. Photometric V, RC, IC light curves were obtained at the Loiano and Asiago telescopes. The radial velocity data were acquired by means of the SARG@Telescopio Nazionale Galileo spectrograph. High-resolution spectroscopy allowed us to derive precise stellar parameters and the chemical composition of the star, obtaining Teff = 6750 ± 150 K; log g = 14.1 ± 0.4 dex and [Fe/H] = -0.07 ± 0.12 dex. Photometric and spectroscopic data were used to estimate the total absorption in the V band AV = 2.06 ± 0.05 mag, in agreement with previous estimates. We adopted the technique of the difference in phase and amplitude between different photometric bands and radial velocities to verify that H254 is (definitely) pulsating in a radial mode. This occurrence allowed us to apply the CORS realization of the Baade-Wesselink method to obtain a value for the linear radius of H254 equal to 3.3 ± 0.7 R⊙. This result was used in conjunction with photometry and effective temperature to derive a distance estimate of 273 ± 23 pc for H254, and, in turn for IC 348, the host cluster. This value is in agreement within the errors with the results derived from several past determinations and the evaluation obtained through the Hipparcos parallaxes. Finally, we derived the luminosity of H254 and studied its position in the Hertzsprung-Russell diagram. From this analysis it results that this δ Scuti occupies a position close to the red edge of the instability strip, pulsates in the fundamental mode, has a mass of about 2.2 M⊙ and an age of 5 ± 1 Myr, older than previous estimates.

  3. Pulsational Pair-instability Supernovae

    NASA Astrophysics Data System (ADS)

    Woosley, S. E.

    2017-02-01

    The final evolution of stars in the mass range 70-140 {\\text{}}{M}⊙ is explored. Depending upon their mass loss history and rotation rates, these stars will end their lives as pulsational pair-instability supernovae (PPISN) producing a great variety of observational transients with total durations ranging from weeks to millennia and luminosities from 1041 to over 1044 erg s-1. No nonrotating model radiates more than 5× {10}50 erg of light or has a kinetic energy exceeding 5× {10}51 erg, but greater energies are possible, in principle, in magnetar-powered explosions, which are explored. Many events resemble SNe Ibn, SNe Icn, and SNe IIn, and some potential observational counterparts are mentioned. Some PPISN can exist in a dormant state for extended periods, producing explosions millennia after their first violent pulse. These dormant supernovae contain bright Wolf-Rayet stars, possibly embedded in bright X-ray and radio sources. The relevance of PPISN to supernova impostors like Eta Carinae, to superluminous supernovae, and to sources of gravitational radiation is discussed. No black holes between 52 and 133 {\\text{}}{M}⊙ are expected from stellar evolution in close binaries.

  4. Objective detection of retinal vessel pulsation.

    PubMed

    Morgan, William H; Abdul-Rahman, Anmar; Yu, Dao-Yi; Hazelton, Martin L; Betz-Stablein, Brigid; Lind, Christopher R P

    2015-01-01

    Retinal venous pulsation detection is a subjective sign, which varies in elevated intracranial pressure, venous obstruction and glaucoma. To date no method can objectively measure and identify pulsating regions. Using high resolution video-recordings of the optic disk and retina we measured fluctuating light absorption by haemoglobin during pulsation. Pulsation amplitude was calculated from all regions of the retinal image video-frames in a raster pattern. Segmented retinal images were formed by objectively selecting regions with amplitudes above a range of threshold values. These were compared to two observers manually drawing an outline of the pulsating areas while viewing video-clips in order to generate receiver operator characteristics. 216,515 image segments were analysed from 26 eyes in 18 research participants. Using data from each eye, the median area under the receiver operator curve (AU-ROC) was 0.95. With all data analysed together the AU-ROC was 0.89. We defined the ideal threshold amplitude for detection of any pulsating segment being that with maximal sensitivity and specificity. This was 5 units (95% confidence interval 4.3 to 6.0) compared to 12 units before any regions were missed. A multivariate model demonstrated that ideal threshold amplitude increased with increased variation in video-sequence illumination (p = 0.0119), but between the two observers (p = 0.0919) or other variables. This technique demonstrates accurate identification of retinal vessel pulsating regions with no areas identified manually being missed with the objective technique. The amplitude values are derived objectively and may be a significant advance upon subjective ophthalmodynamometric threshold techniques.

  5. High-resolution spectroscopy and mode identification in non-radially pulsating stars

    NASA Astrophysics Data System (ADS)

    Pollard, K. R.; Wright, D. J.; Zima, W.; Cottrell, P. L.; De Cat, P.

    2008-12-01

    We have obtained high-resolution spectroscopic data of a sample of non-radially pulsating stars with the HERCULES spectrograph on the 1.0-m telescope at the Mt John University Observatory in New Zealand. We have developed and used a new technique which cross- correlates stellar spectra with scaled delta function templates to obtain high signal-to-noise representative spectral line profiles for further analysis. Using these profiles, and employing the Fourier Parameter Fit method, we have been able to place constraints on the degree, ℓ, and azimuthal order, m, of the non-radial pulsation modes in one β Cephei star, V2052 Oph and two γ Doradus stars, QW Pup and HD 139095.

  6. White Dwarf Pulsational Constraints on Stellar Evolution

    NASA Astrophysics Data System (ADS)

    Dunlap, Bart H.; Clemens, J. Christopher; O'Brien, Patrick C.; Hermes, J. J.; Fuchs, Joshua T.

    2017-01-01

    The complex processes that convert a protostellar cloud into a carbon/oxygen-core white dwarf star are distilled and modeled in state of the art stellar evolution codes. Many of these processes are well-constrained, but several are uncertain or must be parameterized in the models because a complete treatment would be computationally prohibitive—turbulent motions such as convective overshoot cannot, for example, be modeled in 1D. Various free parameters in the models must therefore be calibrated. We will discuss how white dwarf pulsations can inform such calibrations. The results of all prior evolution are cemented into the interiors of white dwarf stars and, so, hidden from view. However, during certain phases of their cooling, pulsations translate the star's evolutionary history into observable surface phenomena. Because the periods of a pulsating white dwarf star depend on an internal structure assembled as it evolved to its final state, white dwarf pulsation periods can be viewed as observable endpoints of stellar evolution. For example, the thickness of the helium layer in a white dwarf directly affects its pulsations; the observed periods are, therefore, a function of the number of thermal pulses during which the star converts helium into core material on the asymptotic giant branch. Because they are also a function of several other significant evolutionary processes, several pulsation modes are necessary to tease all of these apart. Unfortunately, white dwarf pulsators typically do not display enough oscillation modes to constrain stellar evolution. To avoid this limitation, we consider the pulsations of the entire collection of hot pulsating hydrogen-atmosphere white dwarf stars (DAVs). Though any one star may not have sufficient information to place interesting constraints on its evolutionary history, taken together, the stars show a pattern of modes that allows us to test evolutionary models. For an example set of published evolutionary models, we show a

  7. Thermal Management Using Pulsating Jet Cooling Technology

    NASA Astrophysics Data System (ADS)

    Alimohammadi, S.; Dinneen, P.; Persoons, T.; Murray, D. B.

    2014-07-01

    The existing methods of heat removal from compact electronic devises are known to be deficient as the evolving technology demands more power density and accordingly better cooling techniques. Impinging jets can be used as a satisfactory method for thermal management of electronic devices with limited space and volume. Pulsating flows can produce an additional enhancement in heat transfer rate compared to steady flows. This article is part of a comprehensive experimental and numerical study performed on pulsating jet cooling technology. The experimental approach explores heat transfer performance of a pulsating air jet impinging onto a flat surface for nozzle-to-surface distances 1 <= H/D <= 6, Reynolds numbers 1,300 <= Re <= 2,800 pulsation frequency 2Hz <= f <= 65Hz, and Strouhal number 0.0012 <= Sr = fD/Um <= 0.084. The time-resolved velocity at the nozzle exit is measured to quantify the turbulence intensity profile. The numerical methodology is firstly validated using the experimental local Nusselt number distribution for the steady jet with the same geometry and boundary conditions. For a time-averaged Reynolds number of 6,000, the heat transfer enhancement using the pulsating jet for 9Hz <= f <= 55Hz and 0.017 <= Sr <= 0.102 and 1 <= H/D <= 6 are calculated. For the same range of Sr number, the numerical and experimental methods show consistent results.

  8. Modeling of pulsating heat pipes.

    SciTech Connect

    Givler, Richard C.; Martinez, Mario J.

    2009-08-01

    This report summarizes the results of a computer model that describes the behavior of pulsating heat pipes (PHP). The purpose of the project was to develop a highly efficient (as compared to the heat transfer capability of solid copper) thermal groundplane (TGP) using silicon carbide (SiC) as the substrate material and water as the working fluid. The objective of this project is to develop a multi-physics model for this complex phenomenon to assist with an understanding of how PHPs operate and to be able to understand how various parameters (geometry, fill ratio, materials, working fluid, etc.) affect its performance. The physical processes describing a PHP are highly coupled. Understanding its operation is further complicated by the non-equilibrium nature of the interplay between evaporation/condensation, bubble growth and collapse or coalescence, and the coupled response of the multiphase fluid dynamics among the different channels. A comprehensive theory of operation and design tools for PHPs is still an unrealized task. In the following we first analyze, in some detail, a simple model that has been proposed to describe PHP behavior. Although it includes fundamental features of a PHP, it also makes some assumptions to keep the model tractable. In an effort to improve on current modeling practice, we constructed a model for a PHP using some unique features available in FLOW-3D, version 9.2-3 (Flow Science, 2007). We believe that this flow modeling software retains more of the salient features of a PHP and thus, provides a closer representation of its behavior.

  9. A cool stellar companion to the δ Scuti variable star GW UMa

    NASA Astrophysics Data System (ADS)

    Wang, S.-M.; Qian, S.-B.; Li, L.-J.; Zhu, L.-Y.; Zhao, E.-G.; Zhou, X.

    2015-01-01

    GW UMa is a new high-amplitude δ Scuti variable star with a period of 0d.20319367. By using a few new determined times of light maximum together with those collected from the literature, the changes in Observed-Calculated (O-C) diagram were analyzed. It is discovered that the O-C curve of GW UMa shows a cyclic variation with a period of 13.2 years and a semi-amplitude of 0.0023 days. The periodic variation was analyzed for the light-travel time effect that may be due to the presence of a stellar companion. The mass of the stellar companion is determined to be M2 sin i=0.11(±0.01)M⊙ when a mass of 1.76 M⊙ for GW UMa is adopted. The two component stars in the binary system are orbiting each other at an orbital separation about 6.5(±0.8) AU. For orbital inclinations i⩾22.6°, the mass of the companion star would be M2<0.3M⊙ and it is a fully convective star. The detection suggests that hidden stellar companions to bright stars may be not unusual.

  10. Space- and ground-based observations of pulsating aurora

    NASA Astrophysics Data System (ADS)

    Jones, Sarah

    Pulsating aurora is a frequently occurring phenomenon generally believed to occur mainly in the aftermath of a substorm, resulting in widespread auroral luminosity corresponding to a significant transfer of power from the magnetosphere to the ionosphere. A handful of theories have been proposed to explain the associated precipitation mechanism, which have been shown to ineffectively explain certain aspects of pulsating aurora. Previous research into pulsating aurora has provided a wealth of observations, yet much remains unknown about this phenomenon and some previous observations are contradictory. The focus of this presentation is the analysis of ground- and space-based measurements of pulsating aurora (primarily THEMIS ASI array, Poker Flat ISR, and Rocket Observations of Pulsating Aurora) to provide information regarding the large-scale spatial and temporal evolution of pulsating aurora events and the relationship to substorms, to determine the altitude extent and precipitating electron distribution corresponding to pulsating aurora, and to understand commonly occurring features within pulsating aurora.

  11. Pulsating star research and the Gaia revolution

    NASA Astrophysics Data System (ADS)

    Eyer, Laurent; Clementini, Gisella; Guy, Leanne P.; Rimoldini, Lorenzo; Glass, Florian; Audard, Marc; Holl, Berry; Charnas, Jonathan; Cuypers, Jan; Ridder, Joris De; Evans, Dafydd W.; de Fombelle, Gregory Jevardat; Lanzafame, Alessandro; Lecoeur-Taibi, Isabelle; Mowlavi, Nami; Nienartowicz, Krzysztof; Riello, Marco; Ripepi, Vincenzo; Sarro, Luis; Süveges, Maria

    2017-09-01

    In this article we present an overview of the ESA Gaia mission and of the unprecedented impact that Gaia will have on the field of variable star research. We summarise the contents and impact of the first Gaia data release on the description of variability phenomena, with particular emphasis on pulsating star research. The Tycho-Gaia astrometric solution, although limited to 2.1 million stars, has been used in many studies related to pulsating stars. Furthermore a set of 3,194 Cepheids and RR Lyrae stars with their times series have been released. Finally we present the plans for the ongoing study of variable phenomena with Gaia and highlight some of the possible impacts of the second data release on variable, and specifically, pulsating stars.

  12. Transition to turbulence in pulsating pipe flow

    NASA Astrophysics Data System (ADS)

    Hof, Bjorn; Warnecke, Sascha; Xu, Duo

    2013-11-01

    We report an experimental study of the transition to turbulence in a pulsating pipe flow the most important example of pulsating flows is the cardiovascular system where the onset of fluctuations and turbulence can be a possible cause for various diseases such as the formation of aneurysms. The present study is limited to a straight rigid pipe, sinusoidal modulation of the flow rate and a Newtonian fluid. The dimensionless parameters (Womersley and Reynolds numbers) were chosen to include the parameter range encountered in larger arteries. We observe that at large frequencies the critical point for the onset of turbulence remains completely unaffected by pulsation for all amplitudes investigated (up to 40%). However for smaller frequencies (Womersley numbers below 10) the critical point considerably increases. Furthermore we investigate how the transition scenario is affected for a fixed frequency and increasing amplitudes (approaching oscillatory flow).

  13. The research on flow pulsation characteristics of axial piston pump

    NASA Astrophysics Data System (ADS)

    Wang, Bingchao; Wang, Yulin

    2017-01-01

    The flow pulsation is an important factor influencing the axial piston pump performance. In this paper we implement modeling and simulation of the axial piston pump with AMESim software to explore the flow pulsation characteristics under various factors . Theory analysis shows the loading pressure, angular speed, piston numbers and the accumulator impose evident influence on the flow pulsation characteristics. This simulation and analysis can be used for reducing the flow pulsation rate via properly setting the related factors.

  14. Benefit of pulsation in soft corals

    PubMed Central

    Kremien, Maya; Shavit, Uri; Mass, Tali; Genin, Amatzia

    2013-01-01

    Soft corals of the family Xeniidae exhibit a unique, rhythmic pulsation of their tentacles (Movie S1), first noted by Lamarck nearly 200 y ago. However, the adaptive benefit of this perpetual, energetically costly motion is poorly understood. Using in situ underwater particle image velocimetry, we found that the pulsation motions thrust water upward and enhance mixing across the coral–water boundary layer. The induced upward motion effectively prevents refiltration of water by neighboring polyps, while the intensification of mixing, together with the upward flow, greatly enhances the coral’s photosynthesis. A series of controlled laboratory experiments with the common xeniid coral Heteroxenia fuscescens showed that the net photosynthesis rate during pulsation was up to an order of magnitude higher than during the coral’s resting, nonpulsating state. This enhancement diminished when the concentration of oxygen in the ambient water was artificially raised, indicating that the enhancement of photosynthesis was due to a greater efflux of oxygen from the coral tissues. By lowering the internal oxygen concentration, pulsation alleviates the problem of reduced affinity of ribulose-1,5-bisphosphate carboxylase oxygenase (RuBisCO) to CO2 under conditions of high oxygen concentrations. The photosynthesis–respiration ratio of the pulsating H. fuscescens was markedly higher than the ratios reported for nonpulsating soft and stony corals. Although pulsation is commonly used for locomotion and filtration in marine mobile animals, its occurrence in sessile (bottom-attached) species is limited to members of the ancient phylum Cnidaria, where it is used to accelerate water and enhance physiological processes. PMID:23610420

  15. Benefit of pulsation in soft corals.

    PubMed

    Kremien, Maya; Shavit, Uri; Mass, Tali; Genin, Amatzia

    2013-05-28

    Soft corals of the family Xeniidae exhibit a unique, rhythmic pulsation of their tentacles (Movie S1), first noted by Lamarck nearly 200 y ago. However, the adaptive benefit of this perpetual, energetically costly motion is poorly understood. Using in situ underwater particle image velocimetry, we found that the pulsation motions thrust water upward and enhance mixing across the coral-water boundary layer. The induced upward motion effectively prevents refiltration of water by neighboring polyps, while the intensification of mixing, together with the upward flow, greatly enhances the coral's photosynthesis. A series of controlled laboratory experiments with the common xeniid coral Heteroxenia fuscescens showed that the net photosynthesis rate during pulsation was up to an order of magnitude higher than during the coral's resting, nonpulsating state. This enhancement diminished when the concentration of oxygen in the ambient water was artificially raised, indicating that the enhancement of photosynthesis was due to a greater efflux of oxygen from the coral tissues. By lowering the internal oxygen concentration, pulsation alleviates the problem of reduced affinity of ribulose-1,5-bisphosphate carboxylase oxygenase (RuBisCO) to CO2 under conditions of high oxygen concentrations. The photosynthesis-respiration ratio of the pulsating H. fuscescens was markedly higher than the ratios reported for nonpulsating soft and stony corals. Although pulsation is commonly used for locomotion and filtration in marine mobile animals, its occurrence in sessile (bottom-attached) species is limited to members of the ancient phylum Cnidaria, where it is used to accelerate water and enhance physiological processes.

  16. Pulsating White Dwarfs in Globular Clusters

    NASA Astrophysics Data System (ADS)

    Kanaan, A.; Zabot, A.; Fraga, L.

    2012-09-01

    We present our current efforts to detect pulsating white dwarfs in globular clusters and analyze the future of this area when the Extremely Large Telescope (ELT), the Giant Magellan Telescope (GMT) and the Thirty-Meter Telescope (TMT) all become operational. Today we are able to detect pulsating white dwarfs in M 4, NGC 6397 and NGC 6752. When ELT comes on line we should be able to improve the quality of data for the nearby clusters and push the limit to at least 3 magnitudes further, up to NGC 6626, increasing the number of observable clusters from 3 to 20.

  17. Polaris: history of pulsation activity since discovery.

    NASA Astrophysics Data System (ADS)

    Usenko, I. O.; Kovtyukh, V. V.; Miroshnichenko, A. S.; Danford, S.

    2017-02-01

    The pulsation activity of small-amplitude Cepheid Alpha UMi (Polaris) during the period of its radial velocity observations has been analyzed. In the 20th century, Polaris was known to demonstrate a decrease in radial velocity amplitude to the minimum, in the 1980s. Thereafter, the amplitude has increased. The observations of September-December 2015 (21 spectra) obtained by 81cm telescope TCO with spectrograph have showed that radial velocity amplitude comes to 4.16 km/s and is approximately twice higher than the estimates made in 2007, with pulsation period adding 8.6 min.

  18. Gas compressor with side branch absorber for pulsation control

    DOEpatents

    Harris, Ralph E [San Antonio, TX; Scrivner, Christine M [San Antonio, TX; Broerman, III, Eugene L.

    2011-05-24

    A method and system for reducing pulsation in lateral piping associated with a gas compressor system. A tunable side branch absorber (TSBA) is installed on the lateral piping. A pulsation sensor is placed in the lateral piping, to measure pulsation within the piping. The sensor output signals are delivered to a controller, which controls actuators that change the acoustic dimensions of the SBA.

  19. Unexpected series of regular frequency spacing of δ Scuti stars in the non-asymptotic regime - I. The methodology

    DOE PAGES

    Paparo, M.; Benko, J. M.; Hareter, M.; ...

    2016-05-11

    In this study, a sequence search method was developed to search the regular frequency spacing in δ Scuti stars through visual inspection and an algorithmic search. We searched for sequences of quasi-equally spaced frequencies, containing at least four members per sequence, in 90 δ Scuti stars observed by CoRoT. We found an unexpectedly large number of independent series of regular frequency spacing in 77 δ Scuti stars (from one to eight sequences) in the non-asymptotic regime. We introduce the sequence search method presenting the sequences and echelle diagram of CoRoT 102675756 and the structure of the algorithmic search. Four sequencesmore » (echelle ridges) were found in the 5–21 d–1 region where the pairs of the sequences are shifted (between 0.5 and 0.59 d–1) by twice the value of the estimated rotational splitting frequency (0.269 d–1). The general conclusions for the whole sample are also presented in this paper. The statistics of the spacings derived by the sequence search method, by FT (Fourier transform of the frequencies), and the statistics of the shifts are also compared. In many stars more than one almost equally valid spacing appeared. The model frequencies of FG Vir and their rotationally split components were used to formulate the possible explanation that one spacing is the large separation while the other is the sum of the large separation and the rotational frequency. In CoRoT 102675756, the two spacings (2.249 and 1.977 d–1) are in better agreement with the sum of a possible 1.710 d–1 large separation and two or one times, respectively, the value of the rotational frequency.« less

  20. Unexpected Series of Regular Frequency Spacing of δ Scuti Stars in the Non-asymptotic Regime. I. The Methodology

    NASA Astrophysics Data System (ADS)

    Paparó, M.; Benkő, J. M.; Hareter, M.; Guzik, J. A.

    2016-05-01

    A sequence search method was developed to search the regular frequency spacing in δ Scuti stars through visual inspection and an algorithmic search. We searched for sequences of quasi-equally spaced frequencies, containing at least four members per sequence, in 90 δ Scuti stars observed by CoRoT. We found an unexpectedly large number of independent series of regular frequency spacing in 77 δ Scuti stars (from one to eight sequences) in the non-asymptotic regime. We introduce the sequence search method presenting the sequences and echelle diagram of CoRoT 102675756 and the structure of the algorithmic search. Four sequences (echelle ridges) were found in the 5-21 d-1 region where the pairs of the sequences are shifted (between 0.5 and 0.59 d-1) by twice the value of the estimated rotational splitting frequency (0.269 d-1). The general conclusions for the whole sample are also presented in this paper. The statistics of the spacings derived by the sequence search method, by FT (Fourier transform of the frequencies), and the statistics of the shifts are also compared. In many stars more than one almost equally valid spacing appeared. The model frequencies of FG Vir and their rotationally split components were used to formulate the possible explanation that one spacing is the large separation while the other is the sum of the large separation and the rotational frequency. In CoRoT 102675756, the two spacings (2.249 and 1.977 d-1) are in better agreement with the sum of a possible 1.710 d-1 large separation and two or one times, respectively, the value of the rotational frequency.

  1. Evaluation of pump pulsation in respirable size-selective sampling: part I. Pulsation measurements.

    PubMed

    Lee, Eun Gyung; Lee, Larry; Möhlmann, Carsten; Flemmer, Michael M; Kashon, Michael; Harper, Martin

    2014-01-01

    Pulsations generated by personal sampling pumps modulate the airflow through the sampling trains, thereby varying sampling efficiencies, and possibly invalidating collection or monitoring. The purpose of this study was to characterize pulsations generated by personal sampling pumps relative to a nominal flow rate at the inlet of different respirable cyclones. Experiments were conducted using a factorial combination of 13 widely used sampling pumps (11 medium and 2 high volumetric flow rate pumps having a diaphragm mechanism) and 7 cyclones [10-mm nylon also known as Dorr-Oliver (DO), Higgins-Dewell (HD), GS-1, GS-3, Aluminum, GK2.69, and FSP-10]. A hot-wire anemometer probe cemented to the inlet of each cyclone type was used to obtain pulsation readings. The three medium flow rate pump models showing the highest, a midrange, and the lowest pulsations and two high flow rate pump models for each cyclone type were tested with dust-loaded filters (0.05, 0.21, and 1.25mg) to determine the effects of filter loading on pulsations. The effects of different tubing materials and lengths on pulsations were also investigated. The fundamental frequency range was 22-110 Hz and the magnitude of pulsation as a proportion of the mean flow rate ranged from 4.4 to 73.1%. Most pump/cyclone combinations generated pulse magnitudes ≥10% (48 out of 59 combinations), while pulse shapes varied considerably. Pulsation magnitudes were not considerably different for the clean and dust-loaded filters for the DO, HD, and Aluminum cyclones, but no consistent pattern was observed for the other cyclone types. Tubing material had less effect on pulsations than tubing length; when the tubing length was 183cm, pronounced damping was observed for a pump with high pulsation (>60%) for all tested tubing materials except for the Tygon Inert tubing. The findings in this study prompted a further study to determine the possibility of shifts in cyclone sampling efficiency due to sampling pump pulsations

  2. VOLUME COMPENSATING MEANS FOR PULSATING PUMPS

    DOEpatents

    Weaver, D.L.W.; MacCormack, R.S. Jr.

    1959-12-01

    A double diaphragm, two-liquid pulsating pump for remote control use, having as an improvement an apparatus for maintaining constant the volume of the liquid such as kerosene between the two diaphragms is described. Phase difficulties encountered in the operation of such pumps when the volume of the liquid is altered by changes in temperature are avoided.

  3. Blackworms, Blood Vessel Pulsations and Drug Effects.

    ERIC Educational Resources Information Center

    Lesiuk, Nalena M.; Drewes, Charles D.

    1999-01-01

    Introduces the freshwater oligochaete worm, lumbriculus variegatus (common name: blackworms), an organism that is well suited for classroom study because of its closed circulatory system. Describes a set of simple, fast, noninvasive, and inexpensive methods for observing pulsations of the worm's dorsal blood vessels under baseline conditions, and…

  4. Blackworms, Blood Vessel Pulsations and Drug Effects.

    ERIC Educational Resources Information Center

    Lesiuk, Nalena M.; Drewes, Charles D.

    1999-01-01

    Introduces the freshwater oligochaete worm, lumbriculus variegatus (common name: blackworms), an organism that is well suited for classroom study because of its closed circulatory system. Describes a set of simple, fast, noninvasive, and inexpensive methods for observing pulsations of the worm's dorsal blood vessels under baseline conditions, and…

  5. Pulsations in total columnar electron content

    NASA Technical Reports Server (NTRS)

    Okuzawa, T.; Davies, K.

    1981-01-01

    Radio signals from the ATS 6 beacon received at Boulder reveal small-amplitude, quasi-sinusoidal fluctuations with periods in the range of 10 to 50 s. Visual comparisons of these data (116 events for October 1974 to April 1975) shows a good correspondence with simultaneous geomagnetic pulsations at Boulder in two thirds of the cases for which Boulder magnetograms were available, but they do not necessarily correspond with magnetic pulsations on ATS 6. Spectral analyses, by the method of maximum entropy, were made on sample records. The principal results are the following: (1) The occurrence of the pulsations is higher on magnetically disturbed days. (2) The maximum likelihood of occurrence is around 2100 UT (1400 LT). (3) The dominant spectrum peaks of the radio fluctuations and geomagnetic field on the ground generally coincide. Cases are found also in which temporal characteristics of the spectra are similar. These results indicate a close association of the radio fluctuations with the Pc 3-4 type pulsations of the geomagnetic field on the ground. It is suggested that the radio fluctuations originate mainly in the F region of the ionosphere, while some of them could be due to plasmapause effects.

  6. HD 51844: An Am δ Scuti in a binary showing periastron brightening

    NASA Astrophysics Data System (ADS)

    Hareter, M.; Paparó, M.; Weiss, W.; García Hernández, A.; Borkovits, T.; Lampens, P.; Rainer, M.; De Cat, P.; Marcos-Arenal, P.; Vos, J.; Poretti, E.; Baglin, A.; Michel, E.; Baudin, F.; Catala, C.

    2014-07-01

    Context. Pulsating stars in binary systems are ideal laboratories to test stellar evolution and pulsation theory, since a direct, model-independent determination of component masses is possible. The high-precision CoRoT photometry allows a detailed view of the frequency content of pulsating stars, enabling detection of patterns in their distribution. The object HD 51844 is such a case showing periastron brightening instead of eclipses. Aims: We present a comprehensive study of the HD 51844 system, where we derive physical parameters of both components, the pulsation content and frequency patterns. Additionally, we obtain the orbital elements, including masses, and the chemical composition of the stars. Methods: Time series analysis using standard tools was employed to extract the pulsation frequencies. Photospheric abundances of 21 chemical elements were derived by means of spectrum synthesis. We derived orbital elements both by fitting the observed radial velocities and the light curves, and we did asteroseismic modelling as well. Results: We found that HD 51844 is a double lined spectroscopic binary. The determined abundances are consistent with δ Delphini classification. We determined the orbital period (33.498 ± 0.002 d), the eccentricity (0.484 ± 0.020), the mass ratio (0.988 ± 0.02), and the masses to 2.0 ± 0.2 M⊙ for both components. Only one component showed pulsation. Two p modes (f22 and f36) and one g mode (forb) may be tidally excited. Among the 115 frequencies, we detected triplets due to the frequency modulation, frequency differences connected to the orbital period, and unexpected resonances (3:2, 3:5, and 3:4), which is a new discovery for a δ Sct star. The observed frequency differences among the dominant modes suggest a large separation of 2.0-2.2 d-1, which are consistent with models of mean density of 0.063 g cm-3, and with the binary solution and TAMS evolutionary phase for the pulsating component. The binary evolution is in an

  7. A Pulsation Mechanism for GW Virginis Variables

    NASA Astrophysics Data System (ADS)

    Cox, Arthur N.

    2003-03-01

    The mechanism that produces pulsations in the hottest pre-white dwarfs has been uncertain since the early work indicated that helium is a poison that smooths opacity bumps in the opacity-temperature plane caused by the ionizations of the large observed amounts of carbon and oxygen. Very little helium seemed to be needed to prevent the kappa effect pulsation driving, but helium amounts of almost half of the mass in the surface composition are observed in the pulsating PG 1159-035 stars called the GW Virginis variables. Rather little change in the C and O surface abundances is observed from the hottest (RX J2117.1+3412 at 170,000 K) to the coolest (PG 0122+200 at 80,000 K) GW Vir variables. Actually the shortest observed periods (300-400 s) of these variables are generally predicted to be unstable in all models, but the longest observed periods (up to 1000 s) are difficult to excite. Three recent investigations differ in their conclusions, with two finding that helium and even a slight amount of hydrogen does not prevent the kappa effect of C and O ionizations. A more detailed study reported here confirms the poisoning effect of helium. However, the ionization K- and L-edge opacity of the original iron, whose global abundance is unaffected by all previous evolution, especially if enhanced by radiation absorption levitation, can give different, previously unexplored, opacity driving that can explain the observed pulsations. But even this iron ionization driving can be somewhat poisoned by bump smoothing if the C and O abundances are large. Nonvariable GW Vir stars in the observed instability strip could be the result of small composition variations in the pulsation driving layers.

  8. Orbital period analysis of some classical Algols with pulsating components

    NASA Astrophysics Data System (ADS)

    Soydugan, F.; Kacar, Y.; Soydugan, E.; Bakıs, V.; Tuysuz, M.; Senyuz, T.; Donmez, A.; Bilir, S.; Erdem, A.; Cicek, C.; Demircan, C.

    2008-12-01

    The long-term orbital period variations of the Algol-type binaries with δ Scuti compo- nent(oEA) AB Cas, CT Her, and TW Dra are investigated. An upward parabola is seen in all of these systems O-C diagrams, as is expected from the evolutionary scenario of clas- sical Algols. In addition to parabolic variations, the periodic variations on the parabola were explained with light-time effect due to probable unseen components around the eclipsing pairs.

  9. Pulsation tomography of rapidly oscillating Ap stars. Resolving the third dimension in peculiar pulsating stellar atmospheres

    NASA Astrophysics Data System (ADS)

    Ryabchikova, T.; Sachkov, M.; Kochukhov, O.; Lyashko, D.

    2007-10-01

    Aims:We present detailed analysis of the vertical pulsation mode cross-section in ten rapidly oscillating Ap (roAp) stars based on spectroscopic time-series observations. The aim of this analysis is to derive from observations a complete picture of how the amplitude and phase of magnetoacoustic waves depend on depth. Methods: We use the unique properties of roAp stars, in particular chemical stratification, to resolve the vertical structure of p-modes. Our approach consists of characterising pulsational behaviour of a carefully chosen, but extensive sample of spectral lines. We analyse the resulting amplitude-phase diagrams and interpret observations in terms of pulsation wave propagation. Results: We find common features in the pulsational behaviour of roAp stars. Within a sample of representative elements the lowest amplitudes are detected for Eu ii (and Fe in 33 Lib and in HD 19918), then pulsations go through the layers where Hα core, Nd, and Pr lines are formed. There RV amplitude reaches its maximum, and after that decreases in most stars. The maximum RV of the second REE ions is always delayed relative to the first ions. The largest phase shifts are detected in Tb iii and Th iii lines. Pulsational variability of the Th iii lines is detected here for the first time. The Y ii lines deviate from this picture, showing even lower amplitudes than Eu ii lines but half a period phase shift relative to other weakly pulsating lines. We measured an extra broadening, equivalent to a macroturbulent velocity from 4 to 11-12 km s-1 (where maximum values are observed for Tb iii and Th iii lines), for pulsating REE lines. The surface magnetic field strength is derived for the first time for three roAp stars: HD 9289 (2 kG), HD 12932 (1.7 kG), and HD 19918 (1.6 kG). Conclusions: The roAp stars exhibit similarity in the depth-dependence of pulsation phase and amplitude, indicating similar chemical stratification and comparable vertical mode cross-sections. In general

  10. Evaluation of hydro-mechanical pulsation for rocket injector research

    NASA Astrophysics Data System (ADS)

    Wilson, Matthew B.

    The Propulsion Research Center at the University of Alabama in Huntsville has designed and built a hydro-mechanical pulsator to simulate the pressure fluctuations created by high frequency combustion instability. The pressure response characteristics were evaluated in an atmospheric test rig using filtered de-ionized water as the working fluid. The outlet of the pulsator was connected to a swirl injector post to provide downstream flow resistance. Previous low pressure and mass flow experimental data revealed a complex relationship between the control parameters and the pulsation response. For each test, the average mass flow rates of the waste water, water lost through the seals, and injector mass flow rates are measured. A dynamic pressure transducer at the pulsator exit measures and records the pressure waveform. Pulsation magnitude, reliability, repeatability, pulsation effects, and detailed variable control are examined. The data shows the pulsator is capable of generating 30% pulsation at 1575 Hz input. The repeatability of the pulsator is questionable because the standard deviations exceeded 40% of the average. The detailed data obtained during this research provides is sufficient to develop a pulsator tuning procedure for future applications.

  11. Mississippi Delta

    NASA Technical Reports Server (NTRS)

    2002-01-01

    The streamers of clouds draped over the Gulf of Mexico in this true-color MODIS image from February 27, 2002, suggest that a cold, dry wind was blowing southward over the United States and began to pick up moisture over the Gulf, causing these strips of clouds. That the clouds didn't pick up until some distance from the coastline allowed MODIS to get a perfect view of the dynamic Gulf Coast environment spanning (left to right) Texas, Louisiana, Mississippi, Alabama, and Florida's Western Panhandle. The Mississippi River runs roughly down the center of the image, and is joined in Louisiana by the Red River coming in from the northwest. Over the past 7000 years, the actual delta, where the main river channel empties into the Gulf, has wandered around what we now think of as the Louisiana coast. Considering all the sediment visible in this image, it's not hard to imagine that the river carries about 2.4 billion kilograms of sediment into the Gulf each year. Deposition of some of this sediment has been building up the current delta, called the Birdfoot Delta, for obvious reasons, for about 700 years. The coastal waters are alive with microscopic organisms called phytoplankton, which contain colorful pigments, including chlorophyll, for harvesting sunlight. Beyond the sediment plume off Louisiana, the waters are very dark, which could indicate that a large amount of chlorophyll is present, absorbing lots of sunlight and causing the water to appear dark. Farther south, the waters appear bright blue, which could be a signature of coccolithophores, which use highly reflective calcium carbonate to build scaly coverings for themselves. The brighter offshore waters could also be caused by a blue-green algae called Trichodesmium, an organism that can not only harness carbon dioxide for photosynthesis, but can also take nitrogen from the air and turn it into a form that can be used by living organisms. Credit: Jacques Descloitres, MODIS Land Rapid Response Team, NASA/GSFC

  12. Mississippi Delta

    NASA Technical Reports Server (NTRS)

    2002-01-01

    The streamers of clouds draped over the Gulf of Mexico in this true-color MODIS image from February 27, 2002, suggest that a cold, dry wind was blowing southward over the United States and began to pick up moisture over the Gulf, causing these strips of clouds. That the clouds didn't pick up until some distance from the coastline allowed MODIS to get a perfect view of the dynamic Gulf Coast environment spanning (left to right) Texas, Louisiana, Mississippi, Alabama, and Florida's Western Panhandle. The Mississippi River runs roughly down the center of the image, and is joined in Louisiana by the Red River coming in from the northwest. Over the past 7000 years, the actual delta, where the main river channel empties into the Gulf, has wandered around what we now think of as the Louisiana coast. Considering all the sediment visible in this image, it's not hard to imagine that the river carries about 2.4 billion kilograms of sediment into the Gulf each year. Deposition of some of this sediment has been building up the current delta, called the Birdfoot Delta, for obvious reasons, for about 700 years. The coastal waters are alive with microscopic organisms called phytoplankton, which contain colorful pigments, including chlorophyll, for harvesting sunlight. Beyond the sediment plume off Louisiana, the waters are very dark, which could indicate that a large amount of chlorophyll is present, absorbing lots of sunlight and causing the water to appear dark. Farther south, the waters appear bright blue, which could be a signature of coccolithophores, which use highly reflective calcium carbonate to build scaly coverings for themselves. The brighter offshore waters could also be caused by a blue-green algae called Trichodesmium, an organism that can not only harness carbon dioxide for photosynthesis, but can also take nitrogen from the air and turn it into a form that can be used by living organisms. Credit: Jacques Descloitres, MODIS Land Rapid Response Team, NASA/GSFC

  13. Pulsation and mass loss in Mira variables

    NASA Technical Reports Server (NTRS)

    Wood, P. R.

    1980-01-01

    The behavior of pulsation in the outer layers of a typical Mira variable was studied in the adiabatic and isothermal limits. A shock wave propagates outward once per period and the radial velocity obtained from observations of hydrogen emission lines is identified with the velocity of gas in the post shock region. In the adiabatic case, mass loss in the form of a steady stellar wind was produced. In the isothermal case, no continuous mass loss was produced but occasional ejection of shells occur. Pulsation introduced into a star undergoing steady mass loss as a result of radiation pressure acting on grains caused the mass loss rate to increase by a factor of approximately 40, while the terminal velocity of the flow was almost unaltered.

  14. Stellar pulsations in beyond Horndeski gravity theories

    NASA Astrophysics Data System (ADS)

    Sakstein, Jeremy; Kenna-Allison, Michael; Koyama, Kazuya

    2017-03-01

    Theories of gravity in the beyond Horndeski class recover the predictions of general relativity in the solar system whilst admitting novel cosmologies, including late-time de Sitter solutions in the absence of a cosmological constant. Deviations from Newton's law are predicted inside astrophysical bodies, which allow for falsifiable, smoking-gun tests of the theory. In this work we study the pulsations of stars by deriving and solving the wave equation governing linear adiabatic oscillations to find the modified period of pulsation. Using both semi-analytic and numerical models, we perform a preliminary survey of the stellar zoo in an attempt to identify the best candidate objects for testing the theory. Brown dwarfs and Cepheid stars are found to be particularly sensitive objects and we discuss the possibility of using both to test the theory.

  15. Reverse Fluid Transport Due to Boundary Pulsations

    NASA Astrophysics Data System (ADS)

    Coloma, Mikhail; Schaffer, David; Chiarot, Paul; Huang, Peter

    2016-11-01

    We investigate a reverse fluid transport mechanism consisting of peristaltic flow and boundary wave reflections. The reverse flow occurs in a rectangular conduit aligned in parallel between two cylindrical channels embedded in an elastic PDMS medium. The pulsating flow in the cylindrical channels, driven by a peristaltic pump, deform the PDMS medium and induce a pulsating flow in the rectangular conduit. Waveforms along the conduit boundaries, and their transmission and reflections, can be controlled by changing the PDMS rigidity. Our results show that while the overall wave propagation direction is in the forward direction, a reverse flow in the rectangular conduit can be preferentially induced by varying the elastic rigidity in one of the cylindrical channels. We study the overall flow velocity and direction under various PDMS rigidities. The identified set of experimental parameters that leads to a reverse flow will provide insights in understanding metabolic waste transport within the arterial walls in the brain.

  16. BRUCE/KYLIE: Pulsating star spectra synthesizer

    NASA Astrophysics Data System (ADS)

    Townsend, Rich

    2014-12-01

    BRUCE and KYLIE, written in Fortran 77, synthesize the spectra of pulsating stars. BRUCE constructs a point-sampled model for the surface of a rotating, gravity-darkened star, and then subjects this model to perturbations arising from one or more non-radial pulsation modes. Departures from adiabaticity can be taken into account, as can the Coriolis force through adoption of the so-called traditional approximation. BRUCE writes out a time-sequence of perturbed surface models. This sequence is read in by KYLIE, which synthesizes disk-integrated spectra for the models by co-adding the specific intensity emanating from each visible point toward the observer. The specific intensity is calculated by interpolation in a large temperature-gravity-wavelength-angle grid of pre-calculated intensity spectra.

  17. Pulsating White Dwarf Star GD99

    NASA Astrophysics Data System (ADS)

    Chynoweth, K. M.; Thompson, S.; Mullally, F.; Yeates, C.

    2004-12-01

    We present 15 hours of time-series photometry of the variable white dwarf star GD99. These data were obtained at the McDonald Observatory 2.1m Otto Struve Telescope in January 2003, using the Argos CCD photometer. We achieved a noise level as low as 0.07 %, as measured from the power spectrum of our first night. Our observations confirm that GD99 is a unique pulsating white dwarf whose modes show characteristics of both the hot and cold type of DA variable stars. Additionally, GD99 has a large number of modes, making it a good candidate for asteroseismological study. Our preliminary results indicate that this star merits further study to decipher its abundant set of unusual modes. With such a rich period structure, longer continuous data sets will be required to fully resolve the pulsation spectrum.

  18. Pulsating White Dwarf Stars and Precision Asteroseismology

    NASA Astrophysics Data System (ADS)

    Winget, D. E.; Kepler, S. O.

    2008-09-01

    Galactic history is written in the white dwarf stars. Their surface properties hint at interiors composed of matter under extreme conditions. In the forty years since their discovery, pulsating white dwarf stars have moved from side-show curiosities to center stage as important tools for unraveling the deep mysteries of the Universe. Innovative observational techniques and theoretical modeling tools have breathed life into precision asteroseismology. We are just learning to use this powerful tool, confronting theoretical models with observed frequencies and their time rate-of-change. With this tool, we calibrate white dwarf cosmochronology; we explore equations of state; we measure stellar masses, rotation rates, and nuclear reaction rates; we explore the physics of interior crystallization; we study the structure of the progenitors of Type Ia supernovae, and we test models of dark matter. The white dwarf pulsations are at once the heartbeat of galactic history and a window into unexplored and exotic physics.

  19. Pulsating Radio Sources near the Crab Nebula.

    PubMed

    Staelin, D H; Reifenstein, E C

    1968-12-27

    Two new pulsating radio sources, designated NP 0527 and NP 0532, were found near the Crab Nebula and could be coincident with it. Both sources are sporadic, and no periodicities are evident. The pulse dispersions indicate that 1.58 +/- 0.03 and 1.74 +/- 0.02 x 10(20) electrons per square centimeter lie in the direction of NP 0527 and NP 0532, respectively.

  20. DISCOVERY OF AN ULTRAMASSIVE PULSATING WHITE DWARF

    SciTech Connect

    Hermes, J. J.; Castanheira, Barbara G.; Winget, D. E.; Montgomery, M. H.; Harrold, Samuel T.; Kepler, S. O.; Gianninas, A.; Brown, Warren R.

    2013-07-01

    We announce the discovery of the most massive pulsating hydrogen-atmosphere white dwarf (WD) ever discovered, GD 518. Model atmosphere fits to the optical spectrum of this star show it is a 12, 030 {+-} 210 K WD with a log g =9.08 {+-} 0.06, which corresponds to a mass of 1.20 {+-} 0.03 M{sub Sun }. Stellar evolution models indicate that the progenitor of such a high-mass WD endured a stable carbon-burning phase, producing an oxygen-neon-core WD. The discovery of pulsations in GD 518 thus offers the first opportunity to probe the interior of a WD with a possible oxygen-neon core. Such a massive WD should also be significantly crystallized at this temperature. The star exhibits multi-periodic luminosity variations at timescales ranging from roughly 425 to 595 s and amplitudes up to 0.7%, consistent in period and amplitude with the observed variability of typical ZZ Ceti stars, which exhibit non-radial g-mode pulsations driven by a hydrogen partial ionization zone. Successfully unraveling both the total mass and core composition of GD 518 provides a unique opportunity to investigate intermediate-mass stellar evolution, and can possibly place an upper limit to the mass of a carbon-oxygen-core WD, which in turn constrains Type Ia supernovae progenitor systems.

  1. Beyond Binarity: Spots, Pulsations, and Triple Systems

    NASA Astrophysics Data System (ADS)

    Johnston, Cole; Prsa, A.

    2014-01-01

    We use the Kepler Eclipsing Binary Catalog (Prsa et al. 2011) to find and explore previously unstudied intrinsic stellar variability and stellar multiplicity. All but the highest-amplitude intrinsic variation in these systems is dominated by the eclipsing binary signature, however by fitting a physical model to the eclipsing binary signal and then subtracting this model from the lightcurve, we effectively remove binary effects and can search the residuals for other sources of variability. Using 120 stars for our sample, observed at a 1-min cadence by NASA's Kepler satellite (Borucki et al. 2009), we find low amplitude spot variation, pulsations, and background eclipsing binary stars. Frequencies derived from the spot variations and pulsations provide us with information on the rotation rates, internal structure and physical parameters of the stars that comprise each system. Using frequency and period relations derived by Tassoul (1980), we identify g-mode and p-mode pulsations from the derived signals. We apply asteroseismic methods to interpret these signals and determine the radii and masses of the system components, differential surface and interior rotation, and evolutionary state of these stars. Binary star modeling of these systems yields independent values of the masses, radii, and temperatures of both components, as well as any tidal deformation that may occur. By coupling these approaches, we aim able to construct a fully consistent model of the systems that undergo these variations. We highlight systems of particular interest and discuss frequently observed features in the power spectra.

  2. Amplitude of Supersonic Diffuser Flow Pulsations

    NASA Technical Reports Server (NTRS)

    Sterbentz, William H.; Davids, Joseph

    1952-01-01

    A theoretical method for evaluating the stability characteristics and the amplitude and the frequency of pulsation of ram-jet engines without heat addition is presented herein. Experimental verification of the theoretical results are included where data were available. Theory and experiment show that the pulsation amplitude of a high mass-flow-ratio diffuser having no cone surface flow separation increases with decreasing mass flow. The theoretical trends for changes in amplitude, frequency, and mean-pressure recovery with changes in plenum-chamber volume were experimentally confirmed. For perforated convergent-divergent-type diffusers, a stability hysteresis loop was predicted on the pressure-recovery mass-flow-ratio curve. At a given mean mass-flow ratio, the higher.value of mean pressure recovery corresponded to oscillatory flow in the diffuser while the lower branch was stable. This hysteresis has been observed experimentally. The theory indicates that for a ram-jet engine of given diameter, the amplitude of pulsation of a supersonic diffuser is increased by decreasing the relative size of the plenum chamber with respect to the diffuser volume down to a critical value at which oscillations cease. In the region of these critical values, the stable mass-flow range of the diffuser may be increased either by decreasing the combustion chamber volume or by increasing the length of the diffuser.

  3. SuperWASP discovery and SALT confirmation of a semi-detached eclipsing binary that contains a δ Scuti star

    NASA Astrophysics Data System (ADS)

    Norton, A. J.; Lohr, M. E.; Smalley, B.; Wheatley, P. J.; West, R. G.

    2016-03-01

    Aims: We searched the SuperWASP archive for objects that display multiply periodic photometric variations. Methods: Specifically we sought evidence for eclipsing binary stars that display a further non-harmonically related signal in their power spectra. Results: The object 1SWASP J050634.16-353648.4 has been identified as a relatively bright (V ~ 11.5) semi-detached eclipsing binary with a 5.104 d orbital period that displays coherent pulsations with a semi-amplitude of 65 mmag at a frequency of 13.45 d-1. Follow-up radial velocity spectroscopy with the Southern African Large Telescope confirmed the binary nature of the system. Using the phoebe code to model the radial velocity curve with the SuperWASP photometry enabled parameters of both stellar components to be determined. This yielded a primary (pulsating) star with a mass of 1.73 ± 0.11 M⊙ and a radius of 2.41 ± 0.06 R⊙, as well as a Roche-lobe filling secondary star with a mass of 0.41 ± 0.03 M⊙ and a radius of 4.21 ± 0.11 R⊙. Conclusions: 1SWASP J050634.16-353648.4 is therefore a bright δ Sct pulsator in a semi-detached eclipsing binary with one of the largest pulsation amplitudes of any such system known. The pulsation constant indicates that the mode is likely a first overtone radial pulsation.

  4. Discovery of five new massive pulsating white dwarf stars

    NASA Astrophysics Data System (ADS)

    Castanheira, B. G.; Kepler, S. O.; Kleinman, S. J.; Nitta, A.; Fraga, L.

    2013-03-01

    Using the SOuthern Astrophysical Research telescope (SOAR) Optical Imager at the SOAR 4.1 m telescope, we report on the discovery of five new massive pulsating white dwarf stars. Our results represent an increase of about 20 per cent in the number of massive pulsators. We have detected both short and long periods, low and high amplitude pulsation modes, covering the whole range of the ZZ Ceti instability strip. In this paper, we present a first seismological study of the new massive pulsators based on the few frequencies detected. Our analysis indicates that these stars have masses higher than average, in agreement with the spectroscopic determinations. In addition, we study for the first time the ensemble properties of the pulsating white dwarf stars with masses above 0.8 M⊙. We found a bimodal distribution of the main pulsation period with the effective temperature for the massive DAVs, which indicates mode selection mechanisms.

  5. Radial pulsation stability as a function of hydrogen abundance

    NASA Astrophysics Data System (ADS)

    Jeffery, Simon; Saio, Hideyuki

    2015-08-01

    Following the discovery of pulsation in an extremely low-mass pre-white dwarf by Maxted et al. (2011, 2013), Jeffery & Saio (2013) showed that pulsations in such stars would be excited in high radial overtones provided that the driving zone was sufficiently depleted in hydrogen. Following previous work which shows that pulsations are more easily excited in stars where the damping effects of hydrogen are somehow reduced (Jeffery & Saio 2006), we have completed a survey of radial pulsation stability across a substantially larger parameter space. The object is to identify new regions of the HR diagram where stars should be unstable to radial pulsations, or where closely related p-modes might be excited. These would enable targeted surveys for new classes of pulsating variable. This poster reports the survey results and the identification of new instability regions.

  6. Pc5 geomagnetic pulsations, pulsating particle precipitation, and VLF chorus: Case study on 24 November 2006

    NASA Astrophysics Data System (ADS)

    Manninen, J.; Kleimenova, N. G.; Kozyreva, O. V.; Turunen, T.

    2010-08-01

    The event (24 November 2006, ˜0400-0500 UT) of the simultaneous observations of Pc5 ULF geomagnetic pulsations, electron precipitation (CNA riometer absorption), and whistler-mode chorus, as well as solar wind (SW) and IMF parameters have been analyzed based on the data from IMAGE magnetometers, Finnish riometer array, and temporal VLF station. The visible correlation between the simultaneous occurrence of several minutes scale patches of chorus and pulsating CNA enhancements was found. The dynamic spectra of the riometer data showed a maximum at ˜3.5 mHz in the first half-hour interval and at ˜2.0 mHz in the second one, while the ULF pulsation spectra exhibit these two maxima in both intervals simultaneously. In the first time interval, the Pc5 pulsations at ˜3.5 mHz demonstrated the typical FLR feature. The SW dynamic pressure fluctuations showed a broad (1.5-3.5 mHz) spectral maximum in the first interval; however, in the second one, the simultaneous oscillations at ˜2.0 mHz were observed in SW pressure and in IMF Bz. The similar ˜2.0 mHz peak has been found in the spectra of Pc5 pulsations from auroral zone to the equator, in riometer absorption, and in VLF chorus power. We suggest that the modulation of particle precipitation and whistler-mode chorus patches was caused by the 2.0 mHz compressional component of Pc5 poloidal geomagnetic pulsations driven in the magnetosphere by SW dynamic pressure and IMF Bz disturbances.

  7. Contamination of RR Lyrae stars from Binary Evolution Pulsators

    NASA Astrophysics Data System (ADS)

    Karczmarek, Paulina; Pietrzyński, Grzegorz; Belczyński, Krzysztof; Stępień, Kazimierz; Wiktorowicz, Grzegorz; Iłkiewicz, Krystian

    2016-06-01

    Binary Evolution Pulsator (BEP) is an extremely low-mass member of a binary system, which pulsates as a result of a former mass transfer to its companion. BEP mimics RR Lyrae-type pulsations but has different internal structure and evolution history. We present possible evolution channels to produce BEPs, and evaluate the contamination value, i.e. how many objects classified as RR Lyrae stars can be undetected BEPs. In this analysis we use population synthesis code StarTrack.

  8. Bone pulsating metastasis due to renal cell carcinoma.

    PubMed

    Cınar, Murat; Derincek, Alihan; Karan, Belgin; Akpınar, Sercan; Tuncay, Cengiz

    2010-11-01

    Pulsation on the bone cortex surface is a rare condition. Pulsative palpation of the superficial-located bone tumors can be misperceived as an aneurysm. Fifty-eight-year-old man is presented with pulsating bone mass in his proximal tibia. During angiographic examination, hypervascular masses were diagnosed both at right kidney and at right proximal tibia. Renal cell carcinoma was diagnosed after abdominal CT scan. Proximal tibia biopsy was complicated with projectile bleeding.

  9. A search for low-metallicity pulsating B stars

    NASA Astrophysics Data System (ADS)

    Engelbrecht, Chris; Kgoadi, Refilwe; Frescura, Fabio

    2017-09-01

    We report on some recent results from a long-term UBVI survey of various fields in the Large Magellanic Cloud (LMC), which is aimed at identifying and classifying pulsating B stars in the selected LMC fields. Difference Imaging Analysis shows a clear advantage over conventional PSF fitting. Tentative indications have been found of a varying incidence of pulsation amplitudes (and, by inference, of metal content of the pulsators) across the LMC bar.

  10. Decoupling of superfluid and normal modes in pulsating neutron stars

    SciTech Connect

    Gusakov, Mikhail E.; Kantor, Elena M.

    2011-04-15

    We show that equations governing pulsations of superfluid neutron stars can be split into two sets of weakly coupled equations, one describing the superfluid modes and another one, the normal modes. The coupling parameter s is small, |s|{approx}0.01-0.05, for realistic equations of state. Already an approximation s=0 is sufficient to calculate the pulsation spectrum within the accuracy of a few percent. Our results indicate, in particular, that emission of gravitational waves from superfluid pulsation modes is suppressed in comparison to that from normal modes. The proposed approach allows to drastically simplify modeling of pulsations of superfluid neutron stars.

  11. Large-Scale Aspects and Temporal Evolution of Pulsating Aurora

    NASA Technical Reports Server (NTRS)

    Jones, S. L.; Lessard, M. R.; Rychert, K.; Spanswick, E.; Donovan, E.

    2010-01-01

    Pulsating aurora is a common phenomenon generally believed to occur mainly in the aftermath of a, substorm, where dim long-period pulsating patches appear. The study determines the temporal and spatial evolution of pulsating events using two THEN IIIS ASI stations, at Gillam (66.18 mlat, 332.78 mlon, magnetic midnight at 0634 UT) and Fort Smith, (67.38 mlat, 306.64 mlon, magnetic midnight at, 0806 UT) along roughly the same invariant latitude. Parameters have been calculated from a database of 74 pulsating aurora events from 119 days of good optical data within the period from September 2007 through March 2008 as identified with the Gillam camera. It is shown that the source region of pulsating aurora drifts or expands eastward, away from magnetic midnight, for pre-midnight onsets and that the spatial evolution is more complicated for post midnight onsets, which has implications for the source mechanism. The most probable duration of a pulsating aurora event is roughly 1.5 hours while the distribution of possible event durations includes many long (several hours) events. This may suggest that pulsating aurora is not strictly a substorm recovery phase phenomenon but rather a persistent, long-lived phenomenon that may be temporarily disrupted by auroral substorms. Observations from the Gillam station show that in fact, pulsating aurora is quite common with the occurrence rate increasing to around 60% for morning hours, with 6910 of pulsating aurora onsets occurring after substorm breakup.

  12. Mississippi Delta

    NASA Technical Reports Server (NTRS)

    2002-01-01

    The Mississippi River delta teems with sediment deposited by the river as it flows into the Gulf of Mexico in this true-color image captured by MODIS on October 15, 2001. The sediment, which is marked by brown swirls in the Gulf, provides nutrients for the bloom of phytoplankton visible as blue-green swirls off the coastline. In the high-resolution image the city of Memphis can be seen in the southwest corner of Tennessee, which is just to left of center at the top of the image. The brown coloration that encompasses Memphis and either side of the river, as flows north to south along the left side of the image, is the river's flood plain. Also visible, in the upper-right hand corner of the image is the southern end of the Appalachian Mountains.

  13. Contrasting Accreting White Dwarf Pulsators with the ZZ Ceti Stars

    NASA Astrophysics Data System (ADS)

    Mukadam, A. S.; Szkody, P.; Gänsicke, B. T.; Pala, A.

    2017-03-01

    Understanding the similarities and differences between the accreting white dwarf pulsators and their non-interacting counterparts, the ZZ Ceti stars, will eventually help us deduce how accretion affects pulsations. ZZ Ceti stars pulsate in a narrow instability strip in the range 10800-12300 K due to H ionization in their pure H envelopes; their pulsation characteristics depend on their temperature and stellar mass. Models of accreting white dwarfs are found to be pulsationally unstable due to the H/HeI ionization zone, and even show a second instability strip around 15000 K due to HeII ionization. Both these strips are expected to merge for a He abundance higher than 0.48 to form a broad instability strip, which is consistent with the empirical determination of 10500-16000 K. Accreting pulsators undergo outbursts, during which the white dwarf is heated to temperatures well beyond the instability strip and is observed to cease pulsations. The white dwarf then cools to quiescence in a few years as its outer layers cool more than a million times faster than the evolutionary rate. This provides us with an exceptional opportunity to track the evolution of pulsations from the blue edge to quiescence in a few years, while ZZ Ceti stars evolve on Myr timescales. Some accreting pulsators have also been observed to cease pulsations without any apparent evidence of an outburst. This is a distinct difference between this class of pulsators and the non-interacting ZZ Ceti stars. While the ZZ Ceti instability strip is well sampled, the strip for the accreting white dwarfs is sparsely sampled and we hereby add two new potential discoveries to improve the statistics.

  14. A Study of Chemical Composition of δ Scuti-Type Stars Based on the Observations with the BTA and RTT-150

    NASA Astrophysics Data System (ADS)

    Galeev, A. I.; Berdnikova, V. M.; Ivanova, D. V.; Kudryavtsev, D. O.; Shimanskaya, N. N.; Shimansky, V. V.; Balashova, M. O.

    2017-06-01

    The results of a study of a sample of δ Scuti-type stars obtained from the observations with the BTA and RTT-150 are presented. Based on photometric data, we measured and analyzed the fundamental parameters of all the studied stars. For eight stars (for two of them for the first time), the fundamental parameters of the atmospheres (Teff, log g, [Fe/H]) and the chemical composition for 29 elements in the LTE-approximation are received using spectroscopic observations. The chemical composition analysis demonstrates both the solar abundances of chemical elements and the anomalies of chemical composition typical of Am stars in the studied sample of δ Scuti-type stars.

  15. Pulsating stars in SuperWASP

    NASA Astrophysics Data System (ADS)

    Holdsworth, Daniel L.

    2017-09-01

    SuperWASP is one of the largest ground-based surveys for transiting exoplanets. To date, it has observed over 31 million stars. Such an extensive database of time resolved photometry holds the potential for extensive searches of stellar variability, and provide solid candidates for the upcoming TESS mission. Previous work by e.g. [15], [5], [12] has shown that the WASP archive provides a wealth of pulsationally variable stars. In this talk I will provide an overview of the SuperWASP project, present some of the published results from the survey, and some of the on-going work to identify key targets for the TESS mission.

  16. Pulsating stars in the VMC survey

    NASA Astrophysics Data System (ADS)

    Cioni, Maria-Rosa L.; Ripepi, Vincenzo; Clementini, Gisella; Groenewegen, Martin A. T.; Moretti, Maria I.; Muraveva, Tatiana; Subramanian, Smitha

    2017-09-01

    The VISTA survey of the Magellanic Clouds system (VMC) began observations in 2009 and since then, it has collected multi-epoch data at Ks and in addition multi-band data in Y and J for a wide range of stellar populations across the Magellanic system. Among them are pulsating variable stars: Cepheids, RR Lyrae, and asymptotic giant branch stars that represent useful tracers of the host system geometry. Based on observations made with VISTA at ESO under programme ID 179.B-2003.

  17. Pulsations, interpulsations, and sea-floor spreading.

    NASA Technical Reports Server (NTRS)

    Pessagno, E. A., Jr.

    1973-01-01

    It is postulated that worldwide transgressions (pulsations) and regressions (interpulsations) through the course of geologic time are related to the elevation and subsidence of oceanic ridge systems and to sea-floor spreading. Two multiple working hypotheses are advanced to explain major transgressions and regressions and the elevation and subsidence of oceanic ridge systems. One hypothesis interrelates the sea-floor spreading hypothesis to the hypothesis of sub-Mohorovicic serpentinization. The second hypothesis relates the sea-floor spreading hypothesis to a hypothesis involving thermal expansion and contraction.

  18. Optical multichannel sensing of skin blood pulsations

    NASA Astrophysics Data System (ADS)

    Spigulis, Janis; Erts, Renars; Kukulis, Indulis; Ozols, Maris; Prieditis, Karlis

    2004-09-01

    Time resolved detection and analysis of the skin back-scattered optical signals (reflection photoplethysmography or PPG) provide information on skin blood volume pulsations and can serve for cardiovascular assessment. The multi-channel PPG concept has been developed and clinically verified in this study. Portable two- and four-channel PPG monitoring devices have been designed for real-time data acquisition and processing. The multi-channel devices were successfully applied for cardiovascular fitness tests and for early detection of arterial occlusions in extremities. The optically measured heartbeat pulse wave propagation made possible to estimate relative arterial resistances for numerous patients and healthy volunteers.

  19. Pulsations, interpulsations, and sea-floor spreading.

    NASA Technical Reports Server (NTRS)

    Pessagno, E. A., Jr.

    1973-01-01

    It is postulated that worldwide transgressions (pulsations) and regressions (interpulsations) through the course of geologic time are related to the elevation and subsidence of oceanic ridge systems and to sea-floor spreading. Two multiple working hypotheses are advanced to explain major transgressions and regressions and the elevation and subsidence of oceanic ridge systems. One hypothesis interrelates the sea-floor spreading hypothesis to the hypothesis of sub-Mohorovicic serpentinization. The second hypothesis relates the sea-floor spreading hypothesis to a hypothesis involving thermal expansion and contraction.

  20. Acoustic radiation force control: Pulsating spherical carriers.

    PubMed

    Rajabi, Majid; Mojahed, Alireza

    2017-06-13

    The interaction between harmonic plane progressive acoustic beams and a pulsating spherical radiator is studied. The acoustic radiation force function exerted on the spherical body is derived as a function of the incident wave pressure and the monopole vibration characteristics (i.e., amplitude and phase) of the body. Two distinct strategies are presented in order to alter the radiation force effects (i.e., pushing and pulling states) by changing its magnitude and direction. In the first strategy, an incident wave field with known amplitude and phase is considered. It is analytically shown that the zero- radiation force state (i.e., radiation force function cancellation) is achievable for specific pulsation characteristics belong to a frequency-dependent straight line equation in the plane of real-imaginary components (i.e., Nyquist Plane) of prescribed surface displacement. It is illustrated that these characteristic lines divide the mentioned displacement plane into two regions of positive (i.e., pushing) and negative (i.e., pulling) radiation forces. In the second strategy, the zero, negative and positive states of radiation force are obtained through adjusting the incident wave field characteristics (i.e., amplitude and phase) which insonifies the radiator with prescribed pulsation characteristics. It is proved that zero radiation force state occurs for incident wave pressure characteristics belong to specific frequency-dependent circles in Nyquist plane of incident wave pressure. These characteristic circles divide the Nyquist plane into two distinct regions corresponding to positive (out of circles) and negative (in the circles) values of radiation force function. It is analytically shown that the maximum amplitude of negative radiation force is exactly equal to the amplitude of the (positive) radiation force exerted upon the sphere in the passive state, by the same incident field. The developed concepts are much more deepened by considering the required

  1. Design of a Hydrogen Pulsating Heat Pipe

    NASA Astrophysics Data System (ADS)

    Liu, Yumeng; Deng, Haoren; Pfotenhauer, John; Gan, Zhihua

    In order to enhance the application of a cryocooler that provides cooling capacity at the cold head location, and effectively spread that cooling over an extended region, one requires an efficient heat transfer method. The pulsating heat pipe affords a highly effective heat transfer component that has been extensively researched at room temperature, but is recently being investigated for cryogenic applications. This paper describes the design. The experimental setup is designed to characterize the thermal performance of the PHP as a function of the applied heat, number of turns, filling ratio, inclination angle, and length of adiabatic section.

  2. First Kepler results on compact pulsators - VII. Pulsating subdwarf B stars detected in the second half of the survey phase

    NASA Astrophysics Data System (ADS)

    Baran, A. S.; Kawaler, S. D.; Reed, M. D.; Quint, A. C.; O'Toole, S. J.; Østensen, R. H.; Telting, J. H.; Silvotti, R.; Charpinet, S.; Christensen-Dalsgaard, J.; Still, M.; Hall, J. R.; Uddin, K.

    2011-07-01

    We present five new pulsating subdwarf B (sdB) stars discovered by the Kepler spacecraft during the asteroseismology survey phase. We perform time series analysis on the nearly continuous month-long Kepler data sets of these five objects; these data sets provide nearly alias-free time series photometry at unprecedented precision. Following an iterative pre-whitening process, we derive the pulsational frequency spectra of these stars, separating out artefacts of known instrumental origin. We find that these new pulsating sdB stars are multiperiodic long-period pulsators of the V1093 Her type, with the number of periodicities ranging from eight (KIC 8302197) to 53 (KIC 11558725). The frequencies and amplitudes are typical of g-mode pulsators of this type. We do not find any evidence for binarity in the five stars from their observed pulsation frequencies. As these are g-mode pulsators, we briefly looked for period spacings for mode identification and found average spacings of about 260 and 145 s. This may indicate l= 1 and 2 patterns. Some modes may show evidence of rotational splitting. These discoveries complete the list of compact pulsators found in the survey phase. Of the 13 compact pulsators, only one star was identified as a short-period (p-mode) V361 Hya pulsator, while all other new pulsators turned out to be V1093 Her class objects. Among the latter objects, two of them seemed to be pure V1093 Her while the others show additional low-amplitude peaks in the p-mode frequency range, suggesting their hybrid nature. Authenticity of these peaks will be tested with longer runs currently under analysis.

  3. Review and prospect of research on hydraulic pulsation attenuator

    NASA Astrophysics Data System (ADS)

    Shan, Chang-ji; Zhao, Qi-jun; Dai, Ting-ting; Bian, Yi-duo; Cai, Yan

    2017-09-01

    The pressure pulsation attenuator is able to decrease the fluid fluctuation of the hydraulic pump effectively, so it is widely used in construction machinery. This paper reviews the history and progresses of the research on the pressure pulsation attenuator in China and overseas, summarizes its two types: H-type rigid structure and built-in flexible material, meanwhile, discusses its future research area.

  4. Hydrodynamics and heat transfer for pulsating laminar flow in channels

    NASA Astrophysics Data System (ADS)

    Valueva, E. P.; Purdin, M. S.

    2015-09-01

    The problem about laminar pulsating flow and heat transfer with high pulsation amplitudes of average cross-section velocity in a round tube and in a flat channel is solved using the finite element method. The difference scheme's optimal parameters are determined. Data on the pulsation amplitude and phase are obtained for the hydraulic friction coefficient, tangential stress on the wall, liquid temperature, heat flux on the wall q w (at ϑw = const), and wall temperature ϑw (at q w = const) are obtained. Two characteristic modes, namely, quasi steady-state and high-frequency ones are separated based on the value of dimensionless pulsation frequency. During operation in the quasi steady-state mode, the values of all hydrodynamic and thermal quantities correspond to the values of time-average velocity at the given time instant. For operation in the high-frequency mode, it is shown that the dependences of the pulsating components of hydrodynamic and thermal quantities on the dimensionless pulsation frequency have the same pattern for rectilinear channels having different shapes of their cross section. It is found that certain nodal points exist on the distribution of thermal characteristics along the tube (liquid temperature, heat flux density on the wall at ϑw = const, and wall temperature at q w = const) in which the values of these quantities remain unchanged. The distances between the nodal points decrease with increasing the pulsation frequency. The pulsations of thermal quantities decay over the tube length.

  5. Delta III—an evolutionary delta growth

    NASA Astrophysics Data System (ADS)

    Arvesen, R. J.; Simpson, J. S.

    1996-03-01

    In order to remain competitive in the future and expand the McDonnell Douglas Aerospace market share, MDA has developed an expendable launch system strategy that devices cost-effective launch systems from the Delta II with a growth vehicle configuration called Delta III. The Delta III evolves from the Delta II launch system through development of a larger payload fairing (4-meter diameter), new cryogenically propelled upper stage, new first stage fuel tank, and larger strap-on solid rocket motors. We are developing the Delta III using Integrated Product Development Teams that capitalize on the experience base that has led us to a world record breaking mission success of 49 consecutive Delta II missions. The Delta III first-launch capability is currently planned for the spring of 1998 in support of our first spacecraft customer, Hughes Space and Communications International.

  6. Unexpected Series of Regular Frequency Spacing of δ Scuti Stars in the Non-asymptotic Regime. II. Sample-Echelle Diagrams and Rotation

    NASA Astrophysics Data System (ADS)

    Paparó, M.; Benkő, J. M.; Hareter, M.; Guzik, J. A.

    2016-06-01

    A sequence search method was developed for searching for regular frequency spacing in δ Scuti stars by visual inspection (VI) and algorithmic search. The sample contains 90 δ Scuti stars observed by CoRoT. An example is given to represent the VI. The algorithm (SSA) is described in detail. The data treatment of the CoRoT light curves, the criteria for frequency filtering, and the spacings derived by two methods (i.e., three approaches: VI, SSA, and FT) are given for each target. Echelle diagrams are presented for 77 targets for which at least one sequence of regular spacing was identified. Comparing the spacing and the shifts between pairs of echelle ridges revealed that at least one pair of echelle ridges is shifted to midway between the spacing for 22 stars. The estimated rotational frequencies compared to the shifts revealed rotationally split doublets, triplets, and multiplets not only for single frequencies, but for the complete echelle ridges in 31 δ Scuti stars. Using several possible assumptions for the origin of the spacings, we derived the large separation ({{Δ }}ν ) that are distributed along the mean density versus large separations relation derived from stellar models.

  7. First Optical Observations of Interhemispheric Electron Reflections Within Pulsating Aurora

    NASA Technical Reports Server (NTRS)

    Samara, M.; Michell, R. G.; Khazanov, G. V.

    2017-01-01

    A case study of a pulsating auroral event imaged optically at high time resolution presents direct observational evidence in agreement with the interhemispheric electron bouncing predicted by the Super Thermal Electron Transport model. Pulsation-on times are identified and subsequent equally spaced fainter pulsations are also noted and can be explained by a portion/percentage of the primary precipitating electrons reflecting upward from the ionosphere, traveling to the opposite hemisphere and reflecting upward again. The high time resolution of these data, combined with the short duration of the pulsation-on time (approx. 1 s) and the relatively long spacing between pulsations (approx. 6 to 9 s) made it possible to observe the faint optical pulses caused by the reflected electrons coming from the opposite hemisphere.

  8. Nighttime Pc3 pulsations: MM100 and MAGDAS observations

    NASA Astrophysics Data System (ADS)

    Yagova, Nadezda V.; Heilig, Balazs; Pilipenko, Vyacheslav A.; Yoshikawa, Akimasa; Nosikova, Nataliya S.; Yumoto, Kiyohumi; Reda, Jan

    2017-05-01

    In this paper, we present a statistical and case analysis of nighttime Pc3 pulsations observed from middle to equatorial latitudes during the year 2003. We found two groups of nighttime Pc3 pulsations. Pc3s of the first group are in fact the nightside counterpart of morning Pc3 pulsations with large azimuthal scales slowly attenuating toward midnight. Such night signatures of morning Pc3 waves are observed during the periods of fast solar wind (V>500 km/s). The second type is the locally generated night Pc3 pulsations. They can be observed under moderate solar wind velocities. Maximal occurrence rates and amplitudes for these pulsations are recorded at middle geomagnetic latitudes near the local magnetic midnight. Probably, they are associated with auroral activations or local non-substorm bursty processes.[Figure not available: see fulltext.][Figure not available: see fulltext.

  9. Recurrent pulsations in Saturn's high latitude magnetosphere

    NASA Astrophysics Data System (ADS)

    Mitchell, D. G.; Carbary, J. F.; Bunce, E. J.; Radioti, A.; Badman, S. V.; Pryor, W. R.; Hospodarsky, G. B.; Kurth, W. S.

    2016-01-01

    Over the course of about 6 h on Day 129, 2008, the UV imaging spectrograph (UVIS) on the Cassini spacecraft observed a repeated intensification and broadening of the high latitude auroral oval into the polar cap. This feature repeated at least 5 times with about a 1 h period, as it rotated in the direction of corotation, somewhat below the planetary rotation rate, such that it moved from noon to post-dusk, and from roughly 77° to 82° northern latitudes during the observing interval. The recurring UV observation was accompanied by pronounced ∼1 h pulsations in auroral hiss power, magnetic perturbations consistent with small-scale field aligned currents, and energetic ion conics and electrons beaming upward parallel to the local magnetic field at the spacecraft location. The magnetic field and particle events are in phase with the auroral hiss pulsation. This event, taken in the context of the more thoroughly documented auroral hiss and particle signatures (seen on many high latitude Cassini orbits), sheds light on the possible driving mechanisms, the most likely of which are magnetopause reconnection and/or Kelvin Helmholtz waves.

  10. Impulsively started, steady and pulsated annular inflows

    NASA Astrophysics Data System (ADS)

    Abdel-Raouf, Emad; Sharif, Muhammad A. R.; Baker, John

    2017-04-01

    A computational investigation was carried out on low Reynolds number laminar inflow starting annular jets using multiple blocking ratios and atmospheric ambient conditions. The jet exit velocity conditions are imposed as steady, unit pulsed, and sinusoidal pulsed while the jet surroundings and the far-field jet inlet upstream conditions are left atmospheric. The reason is to examine the flow behavior in and around the jet inlet under these conditions. The pulsation mode behavior is analyzed based on the resultant of the momentum and pressure forces at the entry of the annulus, the circulation and vortex formation, and the propulsion efficiency of the inflow jets. The results show that under certain conditions, the net force of inflow jets (sinusoidal pulsed jets in particular) could point opposite to the flow direction due to the adverse pressure drops in the flow. The propulsion efficiency is also found to increase with pulsation frequency and the sinusoidal pulsed inflow jets are more efficient than the unit pulsed inflow jets. In addition, steady inflow jets did not trigger the formation of vortices, while unit and sinusoidal pulsed inflow jets triggered the formation of vortices under a certain range of frequencies.

  11. Nonlinear pulsations of the RV Tauri stars

    NASA Astrophysics Data System (ADS)

    Fokin, A. B.

    1994-12-01

    The nonlinear pulsations of luminous 0.6 solar mass models for RV Tauri stars are studied by numerical simulation. We find typical RV Tauri behavior in a number of models within 3123 less than or equal to L/Solar Luminosity less than or equal to 7000 and a wide range of Teff below 5400 K, whereas hotter models exhibit pulsations in the first or second overtone. Fourier analysis of the alternating RV Tauri models reveals two strong peaks with 2:1 frequency ratio, but the origin of the low-frequency peak can hardly be explained by the period doubling hypothesis. As comparison with the linear results shows, those peaks are more likely due to the fundamental mode and the first overtone. This result supports the long-standing hypothesis of the 2:1 resonance between these modes in RV Tauri stars. The phase space reconstructions of RV Tauri models reveal chaotic behavior similar to that found in the semiregular W Virginis models. The principal physical processes in the envelopes of alternating models are discussed, and a possible explanation for the secondary variability of RVb stars is presented.

  12. Optical pulsations from a transitional millisecond pulsar

    NASA Astrophysics Data System (ADS)

    Ambrosino, F.; Papitto, A.; Stella, L.; Meddi, F.; Cretaro, P.; Burderi, L.; Di Salvo, T.; Israel, G. L.; Ghedina, A.; Di Fabrizio, L.; Riverol, L.

    2017-10-01

    Millisecond pulsars are neutron stars that attain their very fast rotation during a 108-109-yr-long phase of disk accretion of matter from a low-mass companion star1,2. They can be detected as accretion-powered millisecond X-ray pulsars if towards the end of this phase their magnetic field is strong enough to channel the in-flowing matter towards their magnetic poles3. When mass transfer is reduced or ceases altogether, pulsed emission generated by magnetospheric particle acceleration and powered by the star rotation is observed, preferentially in the radio4 and gamma-ray5 bands. A few transitional millisecond pulsars that swing between an accretion-powered X-ray pulsar regime and a rotationally powered radio pulsar regime in response to variations of the mass in-flow rate have been recently identified6,7. Here, we report the detection of optical pulsations from a transitional millisecond pulsar. The pulsations were observed when the pulsar was surrounded by an accretion disk, and originated inside the magnetosphere or within a few hundreds of kilometres from it. Energy arguments rule out reprocessing of accretion-powered X-ray emission and argue against a process related to accretion onto the pulsar polar caps; synchrotron emission of electrons in a rotation-powered pulsar magnetosphere8 seems more likely.

  13. Pulsating variable stars and large spectroscopic surveys

    NASA Astrophysics Data System (ADS)

    De Cat, Peter

    2017-09-01

    In the past decade, the research of pulsating variable stars has taken a giant leap forward thanks to the photometric measurements provided by space missions like Most, CoRoT, Kepler/K2, and Brite. These missions have provided quasi uninterrupted photometric time-series with an ultra-high quality and a total length that is not achievable from Earth. However, many of the success stories could not have been told without ground-based spectroscopic follow-up observations. Indeed, spectroscopy has some important assets as it can provide (more) accurate information about stellar parameters (like the effective temperature, surface gravity, metallicity, and abundances that are mandatory parameters for an in-depth asteroseismic study), the radial velocity (that is important for the detection of binaries and for the confirmation of cluster membership, if applicable), and the projected rotational velocity (that allows the study of the effects of rotation on pulsations). Fortunately, several large spectroscopic surveys are (becoming) available that can be used for these purposes. For some of these surveys, sub-projects have been initiated with the specific goal to complement space-based photometry. In this review, several spectroscopic surveys are introduced and compared with each other. We show that a large amount of spectroscopic data is (becoming) available for a large variety of objects.

  14. Computational model of miniature pulsating heat pipes

    SciTech Connect

    Martinez, Mario J.; Givler, Richard C.

    2013-01-01

    The modeling work described herein represents Sandia National Laboratories (SNL) portion of a collaborative three-year project with Northrop Grumman Electronic Systems (NGES) and the University of Missouri to develop an advanced, thermal ground-plane (TGP), which is a device, of planar configuration, that delivers heat from a source to an ambient environment with high efficiency. Work at all three institutions was funded by DARPA/MTO; Sandia was funded under DARPA/MTO project number 015070924. This is the final report on this project for SNL. This report presents a numerical model of a pulsating heat pipe, a device employing a two phase (liquid and its vapor) working fluid confined in a closed loop channel etched/milled into a serpentine configuration in a solid metal plate. The device delivers heat from an evaporator (hot zone) to a condenser (cold zone). This new model includes key physical processes important to the operation of flat plate pulsating heat pipes (e.g. dynamic bubble nucleation, evaporation and condensation), together with conjugate heat transfer with the solid portion of the device. The model qualitatively and quantitatively predicts performance characteristics and metrics, which was demonstrated by favorable comparisons with experimental results on similar configurations. Application of the model also corroborated many previous performance observations with respect to key parameters such as heat load, fill ratio and orientation.

  15. Non-radially pulsating Be stars

    NASA Astrophysics Data System (ADS)

    Rivinius, Th.; Baade, D.; Štefl, S.

    2003-11-01

    Based on more than 3000 high-resolution echelle spectra of 27 early-type Be stars, taken over six years, it is shown that the short-term periodic line profile variability of these objects is due to non-radial pulsation. The appearance of the line profile variability depends mostly on the projected rotational velocity v sin i and thus, since all Be stars rotate rapidly, on the inclination i. The observed variability of the investigated stars is described, and for some of them line profile variability periods are given for the first time. For two of the investigated stars the line profile variability was successfully modeled as non-radial pulsation with l=m=+2 already in previous works. Since Be stars with similarly low v sin i share the same variability properties, these are in general explainable under the same model assumptions. The line profile variability of stars with higher v sin i is different from the one observed in low v sin i stars, but can be reproduced by the same model, if only the model inclination is modified to more equatorial values. Only for a few stars with periodic line profile variability the l=m=2 non-radial pulsation mode is not able to provide a satisfying explanation. These objects might pulsate in different modes (e.g. tesseral ones, l != |m|). Almost all stars in the sample show traces of outburst-like variability, pointing to an ephemeral nature of the mass-loss phenomenon responsible for the formation of the circumstellar disk of early-type Be stars, rather than a steady star-to-disk mass transfer. In addition to the variability due to non-radial pulsation present in most stars, several objects were found to show other periods residing in the immediate circumstellar environment. The presence of these secondary periods is enhanced in the outburst phases. Short-lived aperiodic phenomena were clearly seen in two stars. But, given the unfavourable sampling of our database to follow rapid variability of transient nature, they might be more

  16. Determination of discharge during pulsating flow

    USGS Publications Warehouse

    Thompson, T.H.

    1968-01-01

    Pulsating flow in an open channel is a manifestation of unstable-flow conditions in which a series of translatory waves of perceptible magnitude develops and moves rapidly downstream. Pulsating flow is a matter of concern in the design and operation of steep-gradient channels. If it should occur at high stages in a channel designed for stable flow, the capacity of the channel may be inadequate at a discharge that is much smaller than that for which the channel was designed. If the overriding translatory wave carries an appreciable part of the total flow, conventional stream-gaging procedures cannot be used to determine the discharge; neither the conventional instrumentation nor conventional methodology is adequate. A method of determining the discharge during pulsating flow was tested in the Santa Anita Wash flood control channel in Arcadia, Calif., April 16, 1965. Observations of the dimensions and velocities of translatory waves were made during a period of controlled reservoir releases of about 100, 200, and 300 cfs (cubic feet per second). The method of computing discharge was based on (1) computation of the discharge in the overriding waves and (2) computation of the discharge in the shallow-depth, or overrun, part of the flow. Satisfactory results were obtained by this method. However, the procedure used-separating the flow into two components and then treating the shallow-depth component as though it were steady--has no theoretical basis. It is simply an expedient for use until laboratory investigation can provide a satisfactory analytical solution to the problem of computing discharge during pulsating flow. Sixteen months prior to the test in Santa Anita Wash, a robot camera had been designed .and programmed to obtain the data needed to compute discharge by the method described above. The photographic equipment had been installed in Haines Creek flood control channel in Los Angeles, Calif., but it had not been completely tested because of the infrequency of

  17. Binaries with a δ Scuti Component: Results from a Long-Term Observational Survey, Updated Catalog, and Future Prospects

    NASA Astrophysics Data System (ADS)

    Liakos, A.; Niarchos, P.

    2015-07-01

    Results are presented from a six-year systematic observational survey of candidate eclipsing binaries with a δ Sct component. More than one hundred systems with component(s) of spectral type A-F were observed in order to check for possible pulsational behavior. Some ˜14% (13 cases) among the currently known systems of this class were confirmed. We present an updated list of all currently known δ Sct systems in eclipsing binaries based on all available information from the literature. Possible correlations between their pulsational and binary properties are discussed.

  18. The Delta 2 launcher

    NASA Astrophysics Data System (ADS)

    Ousley, Gilbert W., Sr.

    1991-12-01

    The utilization of the Delta 2 as the vehicle for launching Aristoteles into its near Sun synchronous orbit is addressed. Delta is NASA's most reliable launch vehicle and is well suited for placing the present Aristoteles spacecraft into a 400 m circular orbit. A summary of some of the Delta 2 flight parameters is presented. Diagrams of a typical Delta 2 two stage separation are included along with statistics on delta reliability and launch plans.

  19. Effects of pulsation rate and viscosity on pulsation-induced taste enhancement: new insights into texture-taste interactions.

    PubMed

    Burseg, Kerstin Martha Mensien; Camacho, Sara; Bult, Johannes Hendrikus Franciscus

    2011-05-25

    Oral stimulation with high-tastant concentrations that are alternared with low-tastant concentrations or water rinses (pulsatile stimulation) results in taste intensity ratings that are higher than continuous stimulation with the same average tastant concentration. This study tested the combined effects of taste pulsation rate and viscosity on pulsation-induced taste enhancement in apple juice. According to a tastant-kinetics hypothesis, less pulsation-induced taste enhancement is expected at enhanced pulsation rates in the high-viscous proximal stimulus compared to lower viscous stimuli. High-concentration sucrose apple juice pulses and low-concentration sucrose apple juice intervals were alternated at different pulsation periods (pulse + interval in seconds) every 2.5 s (period length = 5 s) or every 1.25 s (period length = 2.5 s). Pulsed stimuli were presented at two viscosity levels by the addition of pectin (0 and 10 g/L). Sweetness intensities of pulsed stimuli were compared to a continuous reference of the same net but nonalternating sucrose concentration. Sweetness ratings were higher for pulsatile stimuli than for continuous stimuli. In low-viscous stimuli, enhancement depended on the pulsation period and peaked at 5 s periods. In high-viscous stimuli, the same enhancement was observed for both pulsation periods. These results contradict a tastant-kinetics hypothesis of viscosity-induced taste suppression because impaired tastant kinetics by viscosity would predict the opposite: lower pulsation-induced taste enhancement for viscous stimuli, especially at higher pulsation rates. Instead, these observations favor an explanation based on perceptual texture-taste interactions, which predict the observed independence between viscosity and pulsation rate.

  20. Accreting Pulsating White Dwarfs: Hotter than Single DAVs

    NASA Astrophysics Data System (ADS)

    Szkody, Paula; Mukadam, A.; Gaensicke, B. T.; Woudt, P. A.; Solheim, J.; Sion, E. M.; Nitta, A.; Warner, B.; Sahu, D. K.; Prabhu, T.; Henden, A.

    2006-12-01

    Single DAV pulsating white dwarfs are known to show non-radial g-mode pulsations with periods around 50-1400s and have temperatures in the specific range of 11,000-12,500K. With the discovery of several pulsating white dwarfs in the accreting close binary systems of cataclysmic variables, it is possible to probe the effects of mass transfer and accretion, external heat input, He enriched envelopes and fast rotation on the location of the instability strip. Our UV observations of three pulsating accreting white dwarfs in the cataclysmic variables SDSSJ013132-0901, SDSSJ161033-0102 and SDSSJ220553+1155 with the Solar Blind Channel on HST show enhanced pulsation amplitudes over the optical and white dwarf temperatures near 15,000K. Combined with temperatures of two other known accreting pulsators (GW Lib and HS2331+3905), it appears that there is a wide range in the instability strip for accreting pulsators. This range may be due to different white dwarf masses or compositions compared to single DAVs. This research was supported by NASA grant GO-10233.01A from STScI.

  1. Laser dynamics in self-pulsating quantum dot systems

    NASA Astrophysics Data System (ADS)

    Summers, Huw D.; Matthews, Daniel R.; Smowton, Peter M.; Rees, Paul; Hopkinson, Mark

    2004-02-01

    We have studied self-pulsation in InGaAs quantum dot lasers with an emission wavelength in the 1 μm band. The use of saturable absorption to produce internal optical feedback in semiconductor lasers is well established and leads to the phenomenon of self-pulsation. The characteristics of this self-sustaining oscillation in the optical intensity are determined by the optical characteristics of the amplifying and absorbing media. These experiments therefore provide a direct measure of the intrinsic dynamics of the dot laser system free of any external parasitics. At room temperature, pulsation is observed up to a drive current of 1.5Ith with a maximum pulsation frequency of 700 MHz. The self-pulsation is strongly temperature dependent, and cannot be maintained below a temperature of 150 K. Studies of the optical gain and carrier lifetime within the lasers indicate that the dynamic characteristics are controlled by the interaction of the quantum dots with the two-dimensional wetting layer surrounding them. The relatively low pulsation frequency results from the strong saturation of the gain with increasing injection at room temperature, while the thermal switch-off of pulsation is due to changes in the absorber recovery time.

  2. A pulsational approach to the luminosity of RR Lyrae variables

    NASA Astrophysics Data System (ADS)

    Castellani, V.; de Santis, R.

    1994-08-01

    We show that the temperature scale of Butler, Dickens, & Epps (1978) for RR Lyrae pulsators appears tightly correlated with the two pulsational parameters, amplitude and period of the pulsation. Application of these 'pulsational' temperatures to the well-studied Galactic globular clusters M3 and M15 gives for these clusters a reddening E(B - V) = 0.01 and 0.08, respectively. Moreover, we show that pulsational parameters should give rather severe constraints on the visual magnitude of the pulsators. Calibration of a similar relation to pulsator magnitudes as given by Baade-Wesselink (BW) analyses supports this suggestion, though producing Mnu values in systematic disagreement with current evolutionary computations. We discuss the problem, showing that BW results can be reconciled with the current evolutionary scenario only assuming a value of the original He as low as Y = 0.19 plus a systematic error in the temperature scale. Conversely, one may save the evolutionary scenario with Y = 0.23 by assuming a systematic error in BW magnitudes.

  3. Pulsations in the free oscillations of the Earth

    NASA Astrophysics Data System (ADS)

    Sobolev, G. A.

    2015-05-01

    The records from wideband IRIS stations after a strong earthquake are analyzed. A few days after the earthquake, pulsations with a period of 128 min arise and last for about a week. They appear as a periodical variation in the amplitude of the free radial oscillation of the Earth 0S0 having a period of 20.46 min. The period of the pulsations is more than double the period of the lowest-frequency free spheroidal oscillations of the Earth (53.9 min). The pulsations are most pronounced at the mid-latitudinal and equatorial stations and less distinct near the poles. The pulsations are phase synchronous at the nearby stations and antiphase at the stations located in the western and eastern hemispheres. The pulsation amplitude does not depend on the phase of the Earth's tide. The shape and period of the pulsations are fitted by the model of beatings appearing in the Van der Pol oscillator with periodic forcing. The pulsations are hypothesized to result from asynchronous interaction between the free oscillations of the Earth.

  4. Observations and Theory of Pulsating Helium White Dwarfs

    NASA Astrophysics Data System (ADS)

    Steinfadt, Justin D.

    Average C/O-core white dwarf stars pulsate in observable normal modes of oscillation with amplitudes of a few percent and periods of 100-1,000 seconds. As of this dissertation, no WD of less than 0.5 M sun has been observed to pulsate. White dwarfs of this low mass likely possess a He core and are products of very different stellar evolution. In this dissertation, we have constructed very low mass He-core WD models and predict the parameter space in which they may be observed to pulsate. We have also observed 13 stars, most of which are He-core WDs, in a search for the first He-core WD pulsator. While we were unsuccessful in discovering a pulsator, our detection limits offer unique constraints on He-core WD pulsation parameter space. As a fortuitous result of our pulsation search, we have discovered two unique eclipsing binary systems. One of these is the first eclipsing detached double white dwarf binary system offering the first opportunity to make model independent constraints on He-core WD models and evolution.

  5. Pulsational Modes of Mira Variables Examined through IR Interferometry

    NASA Astrophysics Data System (ADS)

    Creech-Eakman, M. J.; Thompson, R. R.; van Belle, G. T.

    1999-12-01

    We have undertaken a program with the Palomar Testbed Interferometer (PTI) to measure the angular size variations, with respect to pulsational phase, of a group of about 20 mainly O-rich Mira variables. While previous groups have attempted to measure angular size with phase (van Belle et al. 1996, 1997; Tej et al. 1999) these are the first dedicated, spatially-resolved K band observations designed to detect size variations in a large sample of Miras at regular intervals over their pulsation periods. Our first goal has been the unambiguous detection of the mira pulsational cycle with phase, already shown in previous work to be as much as 35% of the radial size over the course of a pulsational period (van Belle et al. 1996; Burns et al. 1997; Tuthill et al. 1995; Perrin et al. 1999 ). We will ultimately use these data, along with the best estimates of stellar distance and effective temperatures for these sources, to determine the mode of pulsation. There has long been a debate as to whether Mira variables pulsate in their fundamental or first-overtone mode (Barthes 1999; Feast 1998; Wood and Sebo 1996). Determination of the pulsation behavior of Mira variables may eventually render them suitable as standard candles for distance determination.

  6. There and Back Again?: The Disappearing Pulsations of CS 1246

    NASA Astrophysics Data System (ADS)

    Vasquez Soto, Alan; Barlow, Brad

    2016-01-01

    Hot subdwarf stars were once main sequence stars, like the sun, that deviated from normal stellar evolution due to binary interactions and evolved into extreme horizontal branch stars. Several of these stars exhibit rapid pulsations driven by iron opacity instabilities. CS 1246 is a rapidly pulsating hot subdwarf discovered in 2009 that is dominated by a single 371 second pulsation. At the time of its discovery, the pulsational amplitude was one of the largest known, making CS 1246 an ideal candidate for follow up studies. Observations in 2013 implied that the pulsational amplitude had decreased significantly. Since then we have continued monitoring the star using the robotic SKYNET telescopes in Chile, in order to further characterize any changes. Our recent observations show that the pulsational amplitude has gone down by a factor of six: CS 1246 is barely a pulsator anymore. The decay in amplitude over time is reminiscent of a damped harmonic oscillator. Here we present six years of photometry for CS 1246 and discuss possible scenarios that might explain its interesting behavior.

  7. Multiscale temporal variations of pulsating auroras: On-off pulsation and a few Hz modulation

    NASA Astrophysics Data System (ADS)

    Nishiyama, Takanori; Sakanoi, Takeshi; Miyoshi, Yoshizumi; Hampton, Donald L.; Katoh, Yuto; Kataoka, Ryuho; Okano, Shoichi

    2014-05-01

    A statistical study on the cross-scale property on the temporal variations of pulsating aurora intensity was conducted on 53 events observed at the Poker Flat Research Range during the period from 1 December 2011 to 1 March 2012. The observed modulation frequency ranged from 1.5 to 3.3 Hz, and strong modulations were not seen in the frequency range higher than about 3 Hz. This suggests that the time of flight of electrons has a time-smoothing effect on the more rapid variations above 3 Hz. Furthermore, the frequency of modulation showed relatively strong correlation to auroral intensity (correlation coefficient of 0.58), and it can be explained with nonlinear wave growth theory, in which the modulation frequency increases with the wave amplitude of the whistler mode chorus. In contrast, the on-off pulsations showed no significant correlations with auroral intensity. This result probably implies that several different plasma processes with different time scales from nonlinear wave growth should be taken into account when determining the on-off periods. In particular, we suggest that long-term variations in the cold plasma density play a dominant role in controlling the conditions of wave-particle interactions that have temporal scale of the on-off pulsation periods.

  8. Supergiant radial and nonradial pulsations. Lecture 10

    SciTech Connect

    Cox, A.N.

    1983-03-14

    The stars that we consider here have luminosities above 10,000 solar luminosities and masses above 15 solar masses. We contact the 53 Per stars such as ..nu.. Ori, 10 Lac, and iota CMa at our lower luminosity limit, and at the most luminous limit, we have the famous stars eta Car, Cyg OB12, and P Cyg. Evolution tracks including a reasonable mass loss rate are given for 15, 30, 60, and 120 solar masses. It appears that our pulsators have masses less than 60 solar masses, but how do the most luminous stars observed survive mass loss. Do they have masses above 100 solar masses as indicated, or are these stars somehow superluminous due to their erratic mass loss behavior. Popper (1980) studying the masses in binary systems has never found one with a value greater than 27 solar masses.

  9. Total pressure averaging in pulsating flows

    NASA Technical Reports Server (NTRS)

    Krause, L. N.; Dudzinski, T. J.; Johnson, R. C.

    1972-01-01

    A number of total-pressure tubes were tested in a non-steady flow generator in which the fraction of period that pressure is a maximum is approximately 0.8, thereby simulating turbomachine-type flow conditions. Most of the tubes indicated a pressure which was higher than the true average. Organ-pipe resonance which further increased the indicated pressure was encountered within the tubes at discrete frequencies. There was no obvious combination of tube diameter, length, and/or geometry variation used in the tests which resulted in negligible averaging error. A pneumatic-type probe was found to measure true average pressure, and is suggested as a comparison instrument to determine whether nonlinear averaging effects are serious in unknown pulsation profiles. The experiments were performed at a pressure level of 1 bar, for Mach number up to near 1, and frequencies up to 3 kHz.

  10. Optical noninvasive monitoring of skin blood pulsations.

    PubMed

    Spigulis, Janis

    2005-04-01

    Time-resolved detection and analysis of skin backscattered optical signals (remission photoplethysmography or PPG) provide rich information on skin blood volume pulsations and can serve for reliable cardiovascular assessment. Single- and multiple-channel PPG concepts are discussed. Simultaneous data flow from several locations on the human body allows us to study heartbeat pulse-wave propagation in real time and to evaluate vascular resistance. Portable single-, dual-, and four-channel PPG monitoring devices with special software have been designed for real-time data acquisition and processing. The prototype devices have been clinically studied, and their potential for monitoring heart arrhythmias, drug-efficiency tests, steady-state cardiovascular assessment, body fitness control, and express diagnostics of the arterial occlusions has been confirmed.

  11. THE PULSATION MODE OF THE CEPHEID POLARIS

    SciTech Connect

    Turner, D. G.; Kovtyukh, V. V.; Usenko, I. A.; Gorlova, N. I.

    2013-01-01

    A previously derived photometric parallax of 10.10 {+-} 0.20 mas, d = 99 {+-} 2 pc, is confirmed for Polaris by a spectroscopic parallax derived using line ratios in high dispersion spectra for the Cepheid. The resulting estimates for the mean luminosity of (M{sub V} ) = -3.07 {+-} 0.01 s.e., average effective temperature of (T{sub eff}) = 6025 {+-} 1 K s.e., and intrinsic color of ((B) - (V)){sub 0} = +0.56 {+-} 0.01 s.e., which match values obtained previously from the photometric parallax for a space reddening of E{sub B-V} = 0.02 {+-} 0.01, are consistent with fundamental mode pulsation for Polaris and a first crossing of the instability strip, as also argued by its rapid rate of period increase. The systematically smaller Hipparcos parallax for Polaris appears discrepant by comparison.

  12. RY Scuti: Infrared and radio observations of the mass-loss wind of a massive binary star system

    NASA Technical Reports Server (NTRS)

    Gehrz, R. D.; Hayward, T. L.; Houck, J. R.; Miles, J. W.; Hjellming, R. M.; Jones, T. J.; Woodward, Charles E.; Prentice, Ricarda; Forrest, W. J.; Libonate, S.

    1995-01-01

    We report infrared (IR) imaging, IR photometry, IR spectroscopy, optical/IR photopolarimetry, and Very Large Array (VLA) radio observations of the peculiar binary star RY Scuti. These observations provide an unprecedented view of the detailed spatial structure of the equatorial mass-loss wind of a massive, luminous, 'overcontact' binary system. The binary star (0.43 AU separation) is surrounded by a flattened equatorial disk with an outer radius of approximately = 3 x 10(exp 16) cm (2000 AU) that emits strongly in the IR and radio. The inside of the disk is ionized and emits free-free radiation from hydrogen and 12.8 micrometers forbidden-line emission from (Ne II); the outside of the disk emits thermal radiation from silicate dust. Radio continuum emission is also produced in a compact H II region surrounding the binary. The dust may have a polycyclic aromatic hydrocarbon (PAH) component. We use a rudimentary geometric model in which the thermal IR and radio emission from the disk are assumed to arise in a pair of concentric toroidal rings to estimate the physical properties of the disk. The mean radius of the ionized gas toroid is approximately = 1.3 x 10(exp 16) cm (870 AU), and the mean radius of the dust toroid is approximately = 2.2 x 10(exp 16) cm (1470 AU). RY Scuti has a small intrinsic polarization, with the electric vector perpendicular to the equatorial disk, that is probably caused by electron scattering from hot gas close to the central binary. We conclude that neon in the nebula is overabundant with respect to hydrogen and helium by a factor of between 1.6 and 10. Our IR/radio image data suggest that the circumstellar disk is part of an extensive radiation driven mass-loss outflow that is strongly confined to the equatorial plane of the binary system. The sharp spatial separation of the outer dust torous from the inner ionized gas torus confirms earlier suggestions that dust formation in the circumstellar ejecta of very hot stars must occur in

  13. RY Scuti: Infrared and radio observations of the mass-loss wind of a massive binary star system

    NASA Technical Reports Server (NTRS)

    Gehrz, R. D.; Hayward, T. L.; Houck, J. R.; Miles, J. W.; Hjellming, R. M.; Jones, T. J.; Woodward, Charles E.; Prentice, Ricarda; Forrest, W. J.; Libonate, S.

    1995-01-01

    We report infrared (IR) imaging, IR photometry, IR spectroscopy, optical/IR photopolarimetry, and Very Large Array (VLA) radio observations of the peculiar binary star RY Scuti. These observations provide an unprecedented view of the detailed spatial structure of the equatorial mass-loss wind of a massive, luminous, 'overcontact' binary system. The binary star (0.43 AU separation) is surrounded by a flattened equatorial disk with an outer radius of approximately = 3 x 10(exp 16) cm (2000 AU) that emits strongly in the IR and radio. The inside of the disk is ionized and emits free-free radiation from hydrogen and 12.8 micrometers forbidden-line emission from (Ne II); the outside of the disk emits thermal radiation from silicate dust. Radio continuum emission is also produced in a compact H II region surrounding the binary. The dust may have a polycyclic aromatic hydrocarbon (PAH) component. We use a rudimentary geometric model in which the thermal IR and radio emission from the disk are assumed to arise in a pair of concentric toroidal rings to estimate the physical properties of the disk. The mean radius of the ionized gas toroid is approximately = 1.3 x 10(exp 16) cm (870 AU), and the mean radius of the dust toroid is approximately = 2.2 x 10(exp 16) cm (1470 AU). RY Scuti has a small intrinsic polarization, with the electric vector perpendicular to the equatorial disk, that is probably caused by electron scattering from hot gas close to the central binary. We conclude that neon in the nebula is overabundant with respect to hydrogen and helium by a factor of between 1.6 and 10. Our IR/radio image data suggest that the circumstellar disk is part of an extensive radiation driven mass-loss outflow that is strongly confined to the equatorial plane of the binary system. The sharp spatial separation of the outer dust torous from the inner ionized gas torus confirms earlier suggestions that dust formation in the circumstellar ejecta of very hot stars must occur in

  14. White dwarf evolution - Cradle-to-grave constraints via pulsation

    NASA Technical Reports Server (NTRS)

    Kawaler, Steven D.

    1990-01-01

    White dwarf evolution, particularly in the early phases, is not very strongly constrained by observation. Fortunately, white dwarfs undergo nonradial pulsation in three distinct regions of the H-R diagram. These pulsations provide accurate masses, surface compositional structure and rotation velocities, and help constrain other important physical properties. We demonstrate the application of the tools of stellar seismology to white dwarf evolution using the hot white dwarf star PG 1159-035 and the cool DAV (or ZZ Ceti) stars as examples. From pulsation studies, significant challenges to the theory of white dwarf evolution emerge.

  15. White dwarf evolution - Cradle-to-grave constraints via pulsation

    NASA Technical Reports Server (NTRS)

    Kawaler, Steven D.

    1990-01-01

    White dwarf evolution, particularly in the early phases, is not very strongly constrained by observation. Fortunately, white dwarfs undergo nonradial pulsation in three distinct regions of the H-R diagram. These pulsations provide accurate masses, surface compositional structure and rotation velocities, and help constrain other important physical properties. We demonstrate the application of the tools of stellar seismology to white dwarf evolution using the hot white dwarf star PG 1159-035 and the cool DAV (or ZZ Ceti) stars as examples. From pulsation studies, significant challenges to the theory of white dwarf evolution emerge.

  16. Finding binaries from phase modulation of pulsating stars with Kepler

    NASA Astrophysics Data System (ADS)

    Shibahashi, Hiromoto; Murphy, Simon; Bedding, Tim

    2017-09-01

    Binary orbital motion causes a periodic variation in the path length travelled by light emitted from a star towards us. Hence, if the star is pulsating, the observed phase of the pulsation varies over the orbit. Conversely, once we have observed such phase variation, we can extract information about the binary orbit from photometry alone. Continuous and precise space-based photometry has made it possible to measure these light travel time effects on the pulsating stars in binary systems. This opens up a new way of finding unseen brown dwarfs, planets, or massive compact stellar remnants: neutron stars and black holes.

  17. The attractor dimension of solar decimetric radio pulsations

    NASA Technical Reports Server (NTRS)

    Kurths, J.; Benz, A. O.; Aschwanden, M. J.

    1991-01-01

    The temporal characteristics of decimetric pulsations and related radio emissions during solar flares are analyzed using statistical methods recently developed for nonlinear dynamic systems. The results of the analysis is consistent with earlier reports on low-dimensional attractors of such events and yield a quantitative description of their temporal characteristics and hidden order. The estimated dimensions of typical decimetric pulsations are generally in the range of 3.0 + or - 0.5. Quasi-periodic oscillations and sudden reductions may have dimensions as low as 2. Pulsations of decimetric type IV continua have typically a dimension of about 4.

  18. Ambiguity of mapping the relative phase of blood pulsations

    PubMed Central

    Teplov, Victor; Nippolainen, Ervin; Makarenko, Alexander A.; Giniatullin, Rashid; Kamshilin, Alexei A.

    2014-01-01

    Blood pulsation imaging (BPI) is a non-invasive optical method based on photoplethysmography (PPG). It is used for the visualization of changes in the spatial distribution of blood in the microvascular bed. BPI specifically allows measurements of the relative phase of blood pulsations and using it we detected a novel type of PPG fast waveforms, which were observable in limited areas with asynchronous regional blood supply. In all subjects studied, these fast waveforms coexisted with traditional slow waveforms of PPG. We are therefore presenting a novel lock-in image processing technique of blood pulsation imaging, which can be used for detailed temporal characterization of peripheral microcirculation. PMID:25401026

  19. Theoretical Period Changes in Yellow Giant Pulsators

    NASA Astrophysics Data System (ADS)

    Cox, Arthur N.

    1998-03-01

    Period changes in RR Lyrae variables and Cepheids, known for more than 60 years, can possibly be explained by small changes in a helium composition gradient below the hydrogen and helium convection zones. The particular cases for the globular cluster M15 double-mode RR Lyrae variable V53 and the Cepheid Polaris are studied. For the last 80 years, the fundamental mode period of V53 has been decreasing while the overtone mode period in this same star has been increasing. The rather steady overtone mode period increase for Polaris stopped very recently, and the period now seems constant. Diffusive settling of helium in these kinds of stars has been known to be slight because of the two convection zones and the long diffusion timescale below them. But a small amount of helium settling, even before the star begins to pulsate, and then a dredge-up of just a little helium by an occasional overshooting can change surface layer structures and periods. This dredge-up can have a timescale as short as the convection turnover time, i.e., a few days. A slight helium dredge-up episode may now have temporarily stopped the decaying pulsations and period increase of Polaris. Such an episode cannot explain the double-mode V53 case, but possibly the helium composition gradient is deepened enough by matter accretion in only 80 years to explain its observed opposite period changes. Another mechanism that might be important for period changes is tidal mixing of the small composition gradients caused by occasional close encounters of stars in clusters. Significant stellar rotation would keep the surface layer composition homogeneous and not allow the anomalous period changes discussed here.

  20. Multisatellite observations of a giant pulsation event

    NASA Astrophysics Data System (ADS)

    Takahashi, Kazue; Glassmeier, Karl-Heinz; Angelopoulos, Vassilis; Bonnell, John; Nishimura, Yukitoshi; Singer, Howard J.; Russell, Christopher T.

    2011-11-01

    Giant pulsations (Pgs; frequency ˜10 mHz) were detected with ground magnetometers on the North American continent on 19 October 2008, when the GOES-10, -11, -12, and -13 geostationary satellites and the THEMIS-A probe were magnetically connected to the region of the ground pulsation activity. This unique configuration allowed us to determine the properties of magnetospheric ultra-low-frequency (ULF) waves that caused the Pgs on the ground. All spacecraft detected monochromatic ULF waves at ˜10 mHz, and the coherence between the Pg at the Gillam ground station and the ULF wave at THEMIS-A was high when the magnetic field foot point of the spacecraft came close to the ground station. The ULF waves observed by the five spacecraft had perturbations in the radial and compressional components of the magnetic field and in the azimuthal component of the electric field, which are attributed to poloidal mode standing Alfvén waves. The poloidal waves were accompanied by multiharmonic toroidal waves, and from the frequency relationship among these, it is concluded that the ˜10 mHz oscillations correspond to the fundamental (odd, or symmetric) mode. The standing wave mode also explains the amplitude variation with latitude and the phase delay between the magnetic and electric fields. Numerical models of poloidal waves incorporating finite height integrated ionospheric conductivity indicate that the fundamental mode interpretation is valid even when the damping of the standing waves is strong. Our observations are the most comprehensive to date in terms of spacecraft data, and we believe that theoretical work on the Pg generation mechanism should focus on mechanisms specific to odd mode standing waves, such as drift resonance of ring current ions.

  1. Multisatellite Observations of a Giant Pulsation Event

    NASA Astrophysics Data System (ADS)

    Takahashi, K.; Glassmeier, K.; Angelopoulos, V.; Bonnell, J. W.; Nishimura, T.; Singer, H. J.; Russell, C. T.

    2011-12-01

    Giant pulsations (Pgs; frequency ~10 mHz) were detected with ground magnetometers in the North American continent on October 2008, when the GOES-10, -11, -12, and -13 geostationary satellites and the THEMIS-A probe were magnetically connected to the region of the ground pulsation activity. This unique observational configuration allowed us to determine the properties of magnetospheric ultra-low-frequency (ULF) waves that caused the Pgs on the ground. All spacecraft detected monochromatic ULF waves at ~10 mHz, and the coherence between the Pg at the Gillam ground station and the ULF wave at THEMIS-A was high when the magnetic field foot point of the spacecraft came close to the ground station, indicating a causal relationship between the two oscillation phenomena. The ULF waves observed by the five spacecraft had perturbations in the radial and compressional components of the magnetic field and in the azimuthal component of the electric field, which are attributed to poloidal mode standing Alfvén waves. The poloidal waves were accompanied by multiharmonic toroidal waves, and from the frequency relationship among these, it is concluded that the ~10 mHz oscillations correspond to the fundamental (odd, or symmetric) mode. The standing wave mode also explains the amplitude variation with latitude and the phase delay between the magnetic and electric fields. Numerical models of poloidal waves incorporating finite ionospheric conductivity indicate that the fundamental mode interpretation is valid even when the damping of the standing waves is strong. Our observations are the most comprehensive to date in terms of spacecraft data, and we believe that theoretical work on the Pg generation mechanism should focus on mechanisms specific to odd mode standing waves, such as drift resonance of ring current ions.

  2. Nonradial and radial period changes of the δ Scuti star 4 CVn. II. Systematic behavior over 40 years

    NASA Astrophysics Data System (ADS)

    Breger, M.; Montgomery, M. H.; Lenz, P.; Pamyatnykh, A. A.

    2017-03-01

    Aims: Radial and nonradial pulsators on and near the main sequence show period and amplitude changes that are too large to be the product of stellar evolution. The multiperiodic δ Sct stars are well suited to study this, as the period changes of different modes excited in the same star can be compared. This requires a very large amount of photometric data covering years and decades as well as mode identifications. Methods: We have examined over 800 nights of high-precision photometry of the multiperiodic pulsator 4 CVn obtained from 1966 through 2012. Because most of the data were obtained in adjacent observing seasons, it is possible to derive very accurate period values for a number of the excited pulsation modes and to study their systematic changes from 1974 to 2012. Results: Most pulsation modes show systematic significant period and amplitude changes on a timescale of decades. For the well-studied modes, around 1986 a general reversal of the directions of both the positive and negative period changes occurred. Furthermore, the period changes between the different modes are strongly correlated, although they differ in size and sign. For the modes with known values of the spherical degree and azimuthal order, we find a correlation between the direction of the period changes and the identified azimuthal order, m. The associated amplitude changes generally have similar timescales of years or decades, but show little systematic or correlated behavior from mode to mode. Conclusions: A natural explanation for the opposite behavior of the prograde and retrograde modes is that their period changes are driven by a changing rotation profile. The changes in the rotation profile could in turn be driven by processes, perhaps the pulsations themselves, that redistribute angular momentum within the star. In general, different modes have different rotation kernels, so this will produce period shifts of varying magnitude for different modes.

  3. Discovery of binarity, spectroscopic frequency analysis, and mode identification of the δ Scuti star 4 CVn

    NASA Astrophysics Data System (ADS)

    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.; Pápics, P. I.; Fritz, V.; Falcon, R. E.

    2014-10-01

    More than 40 years of ground-based photometric observations of the δ 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 2.1 m 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 Porb = 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, f1 = 7.3764 d-1 and f2 = 5.8496 d-1; and determine the prograde or retrograde nature of 7 of the modes. The projected rotational velocity of the star, veqsini ≃ 106.7 km s-1, translates to a rotation rate of veq/vcrit ≥ 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 4 CVn, a complete description of rotation and the use of blended lines have to be included in mode-identification techniques. This paper includes data taken at The McDonald Observatory of The University of Texas at Austin.The software package FAMIAS, developed in the framework of the FP6 European Coordination Action HELAS (http://www.helas-eu.org/), has been used in this research.Appendices are available in electronic form at http://www.aanda.org

  4. delta-Hexachlorocyclohexane (delta-HCH)

    Integrated Risk Information System (IRIS)

    delta - Hexachlorocyclohexane ( delta - HCH ) ; CASRN 319 - 86 - 8 Human health assessment information on a chemical substance is included in the IRIS database only after a comprehensive review of toxicity data , as outlined in the IRIS assessment development process . Sections I ( Health Hazard Ass

  5. Report of geomagnetic pulsation indices for space weather applications

    USGS Publications Warehouse

    Xu, Z.; Gannon, Jennifer L.; Rigler, Erin J.

    2013-01-01

    The phenomenon of ultra-low frequency geomagnetic pulsations was first observed in the ground-based measurements of the 1859 Carrington Event and has been studied for over 100 years. Pulsation frequency is considered to be “ultra” low when it is lower than the natural frequencies of the plasma, such as the ion gyrofrequency. Ultra-low frequency pulsations are considered a source of noise in some geophysical analysis techniques, such as aeromagnetic surveys and transient electromagnetics, so it is critical to develop near real-time space weather products to monitor these geomagnetic pulsations. The proper spectral analysis of magnetometer data, such as using wavelet analysis techniques, can also be important to Geomagnetically Induced Current risk assessment.

  6. Unilateral Loss of Spontaneous Venous Pulsations in an Astronaut

    NASA Technical Reports Server (NTRS)

    Mader, Thomas H.; Gibson, C. Robert; Lee, Andrew G.; Patel, Nimesh; Hart, Steven; Pettit, Donald R.

    2014-01-01

    Spontaneous venous pulsations seen on the optic nerve head (optic disc) are presumed to be caused by fluctuations in the pressure gradient between the intraocular and retrolaminar venous systems. The disappearance of previously documented spontaneous venous pulsations is a well-recognized clinical sign usually associated with a rise in intracranial pressure and a concomitant bilateral elevation of pressure in the subarachnoid space surrounding the optic nerves. In this correspondence we report the unilateral loss of spontaneous venous pulsations in an astronaut 5 months into a long duration space flight. We documented a normal lumbar puncture opening pressure 8 days post mission. The spontaneous venous pulsations were also documented to be absent 21 months following return to Earth.. We hypothesize that these changes may have resulted from a chronic unilateral rise in optic nerve sheath pressure caused by a microgravity-induced optic nerve sheath compartment syndrome.

  7. Pulsations of B stars: A review of observations and theories

    SciTech Connect

    Cox, A.N.

    1986-01-01

    The observational and theoretical status are discussed for several classes of variable B stars. The older classes now seem to be better understood in terms of those stars that probably have at least one radial mode and those that have only nonradial modes. The former are the ..beta.. Cephei variables, and the latter are the slowly rotating 53 Persei and the rapidly rotating zeta Ophiuchi variables. It seems that in this last class there are also some Be stars that show nonradial pulsations from the variations of the line shapes and their light. Among the nonradial pulsators, we must also include the supergiants which show pulsations with very short lifetimes. A review of the present observational and theoretical problems is given. The most persistent problem of the cause for the pulsations is briefly discussed, and many proposed mechanisms plus some new thoughts are presented. 57 refs., 4 figs.

  8. Contamination of RR Lyrae stars from Binary Evolution Pulsators

    NASA Astrophysics Data System (ADS)

    Karczmarek, P.

    2015-09-01

    A Binary Evolution Pulsator (BEP) is a low-mass (0.26 M_⊙) member of a binary system, which pulsates as a result of a former mass transfer to its companion. The BEP mimics RR~Lyrae-type pulsations, but has completely different internal structure and evolution history. Although there is only one known BEP (OGLE-BLG-RRLYR-02792), it has been estimated that approximately 0.2% of objects classified as RR Lyrae stars can be undetected Binary Evolution Pulsators. In the present work, this contamination value is re-evaluated using the population synthesis method. The output falls inside a range of values dependent on tuning the parameters in the StarTrack code, and varies from 0.06% to 0.43%.

  9. Photometric study of the pulsating, eclipsing binary OO DRA

    SciTech Connect

    Zhang, X. B.; Deng, L. C.; Tian, J. F.; Wang, K.; Yan, Z. Z.; Luo, C. Q.; Sun, J. J.; Liu, Q. L.; Xin, H. Q.; Zhou, Q.; Luo, Z. Q.

    2014-12-01

    We present a comprehensive photometric study of the pulsating, eclipsing binary OO Dra. Simultaneous B- and V-band photometry of the star was carried out on 14 nights. A revised orbital period and a new ephemeris were derived from the data. The first photometric solution of the binary system and the physical parameters of the component stars are determined. They reveal that OO Dra could be a detached system with a less-massive secondary component nearly filling its Roche lobe. By subtracting the eclipsing light changes from the data, we obtained the intrinsic pulsating light curves of the hotter, massive primary component. A frequency analysis of the residual light yields two confident pulsation modes in both B- and V-band data with the dominant frequency detected at 41.865 c/d. A brief discussion concerning the evolutionary status and the pulsation nature of the binary system is finally given.

  10. Rhythmic pulsations in inferior vena cava in pericardial constriction.

    PubMed

    Mittal, S R

    2016-09-01

    A case of pericardial constriction with rhythmic, nonrespiratory pulsations in inferior vena cava is presented. Hepatic vein flow showed wave form classical of pericardial constriction. Backward transmission of changes in right atrial pressure resulted in rhythmic, nonrespiratory pulsations in inferior vena cava. This echocardiographic finding could help in diagnosis of pericardial constriction. Copyright © 2015 Cardiological Society of India. Published by Elsevier B.V. All rights reserved.

  11. Unsolved Problems for Main-Sequence Variable Stars Revealed by the NASA Kepler Data (Abstract)

    NASA Astrophysics Data System (ADS)

    Guzik, J. A.

    2016-12-01

    (Abstract only) The NASA Kepler spacecraft's long time-series photometric data have enabled interesting studies of g Doradus, delta Scuti, slowly-pulsating B, and beta Cephei variable stars by revealing many new variables and characterizing frequencies and amplitudes to high precision. These stars pulsate in multiple nonradial modes, with periods of hours to days.We will discuss some questions that the Kepler data have raised and are helping to solve, including: Why have so many "hybrid" g Dor/delta Sct variables been discovered? Why are there apparently "constant" non-pulsating stars within the pulsation instability regions? What are the causes of amplitude variations that occur over relatively short timescales? Can we find patterns in the frequencies and amplitude spectra that will help with mode identification and facilitate asteroseismology? Are large increases in the opacities used for stellar models needed to explain the B-type pulsators and to solve the "solar abundance problem"?

  12. Stochastic pulsations in the subdwarf-B star KIC 2991276

    NASA Astrophysics Data System (ADS)

    Østensen, R. H.; Reed, M. D.; Baran, A. S.; Telting, J. H.

    2014-04-01

    The subdwarf-B star KIC 2991276 was monitored with the Kepler spacecraft for nearly three years. Two pulsation modes with periods of 122 and 132 s are clearly detected in the Fourier spectrum, as well as a few weaker modes with periods ranging from 118 to 216 s. Unlike the other subdwarf-B pulsators with similar high-quality Kepler lightcurves, the modes in KIC 2991276 do not display long-term coherency. Rather, their pulsation amplitudes vary substantially in amplitude and phase on timescales of about a month, sometimes disappearing completely. Thus, while the pulsations are seen to have amplitudes of up to 1.4% in individual months, the amplitude spectrum of the full lightcurve shows a broad, messy peak with an amplitude of only 0.23%. Such stochastic oscillations are normal in the Sun and other cool stars with solar-like pulsations and have been suspected for V361-Hya pulsators, but thanks to the exceptional coverage of Kepler data, this is the first unambiguous case established for a hot subdwarf.

  13. Frequency-domain analysis for pulsating combustion of gaseous fuel

    NASA Astrophysics Data System (ADS)

    Berg, I. A.; Porshnev, S. V.; Oshchepkova, V. Y.; Medvedev, A. N.

    2017-06-01

    Pulsating combustion is among combustion control methods used to suppress formation of NOx. Past experiments showed that the dependency of NOx content from pulsation rate has a minimum. A measuring unit was set up to study torch behavior in infrared band. To study pulsating combustion of gaseous fuel a thermographic camera was used. Thermographic sequences were recorded using the instrument FLIR 7700M with the resolution of 320×240 pixels at the frame rate of 412 Hz. The experiments resulted in obtaining thermographic sequences radiation intensity fields in the longitudinal section of the torch at different pulsation rates. The obtained raw data was preprocessed to obtain distributions of quantities of pixels corresponding to temperatures in each frame, as well as time-domain series for changes of the torch core longitudinal section area. Frequency-domain analysis was run for each time-domain series using Fast Fourier transform (FFT). The results demonstrate that the first maximum of spectral density coincides with the control action rate. The spectrum also contains pronounced second and third harmonics. For each spectrum of the time-domain series signal-to-noise ratio (SNR) was calculated. Comparison of different SNR shows that maximum impact of pulsation control on torch radiation intensity takes place at the on/off valve opening rate of 4 Hz. This method of torch diagnostics can be helpful for future studies and development of pulsating combustion control systems.

  14. An Update on the Quirks of Pulsating, Accreting White Dwarfs

    NASA Astrophysics Data System (ADS)

    Szkody, Paula; Mukadam, Anjum S.; Gänsicke, Boris T.; Hermes, J. J.; Toloza, Odette

    2015-06-01

    At the 18th European White Dwarf Workshop, we reported results for several dwarf novae containing pulsating white dwarfs that had undergone an outburst in 2006-2007. HST and optical data on the white dwarfs in GW Lib, EQ Lyn and V455 And all showed different behaviors in the years following their outbursts. We continued to follow these objects for the last 2 years, providing timescales of 6-7 years past outburst. All three reached their optical quiescent values within 4 years but pulsational stability has not returned. EQ Lyn showed its pre-outburst pulsation period after 3 years, but it continues to show photometric variability that alternates between pulsation and disk superhump periods while remaining at quiescence. V455 And has almost reached its pre-outburst pulsation period, while GW Lib still remains heated and with a different pulsation spectrum than at quiescence. These results indicate that asteroseismology provides a unique picture of the effects of outburst heating on the white dwarf.

  15. Pulsations and Hydrodynamics of Luminous Blue Variable Stars

    NASA Astrophysics Data System (ADS)

    Guzik, Joyce Ann; Lovekin, Catherine C.

    2012-07-01

    The Luminous Blue Variable stars exhibit behavior ranging from light curve 'microvariations' on timescales of tens of days, to 'outbursts' accompanied by mass loss of ~10-3 Msun occurring decades apart, to 'giant eruptions' such as seen in Eta Carinae, ejecting one or more solar masses and recurring on timescales of centuries. Here we review the work of the Los Alamos group since 1993, to investigate pulsations and instabilities in massive stars using linear pulsation models and non-linear hydrodynamic models. The models predict pulsational variability that may be associated with the microvariations. We show using a nonlinear pulsation hydrodynamics code with a time-dependent convection treatment, that in some circumstances the Eddington limit is exceeded periodically in the pulsation driving region of the stellar envelope, accelerating the outer layers, and perhaps initiating mass loss or the LBV outbursts. We discuss how pulsations and mass loss may be responsible for the location of the Humphreys- Davidson Limit in the H-R diagram. The 'giant eruptions', however, must involve much deeper regions in the stellar core to cause such large amounts of mass to be ejected. We review and suggest some possible explanations, including mixing from gravity modes, secular instabilities, the epsilon mechanism, or the SASI instability as proposed for Type II supernovae. We outline future work and required stellar modeling capabilities to investigate these possibilities.

  16. Structure of black aurora associated with pulsating aurora

    NASA Astrophysics Data System (ADS)

    Fritz, Bruce A.; Lessard, Marc L.; Blandin, Matthew J.; Fernandes, Philip A.

    2015-11-01

    Morphological behavior of black aurora as it relates to pulsating aurora is investigated by examining a collection of ground-based observations from January 2007 in support of the Rocket Observations of Pulsating Aurora rocket campaign. Images were sampled from video recorded by a Xybion intensified camera (30 fps) at Poker Flat Research Range, AK. The primary observations of black aurora recorded during the substorm recovery phase were between separate patches of pulsating aurora as well as pulsating aurora separated from diffuse aurora. In these observations the black aurora forms an apparent firm boundary between the auroral forms in a new behavior that is in contrast with previously reported observations. Also presented for the first time are black curls in conjunction with pulsating aurora. Curl structures that indicate shear plasma flows in the ionosphere may be used as a proxy for converging/diverging electric fields in and above the ionosphere. This new subset of black auroral behavior may provide visual evidence of black aurora as an ionospheric feedback mechanism as related to pulsating aurora.

  17. Non-Invasive Measurement of Intracranial Pressure Pulsation using Ultrasound

    NASA Technical Reports Server (NTRS)

    Ueno, Toshiaki; Ballard, R. E.; Yost, W. T.; Hargens, A. R.

    1997-01-01

    Exposure to microgravity causes a cephalad fluid shift which may elevate intracranial pressure (ICP). Elevation in ICP may affect cerebral hemodynamics in astronauts during space flight. ICP is, however, a difficult parameter to measure due to the invasiveness of currently available techniques. We already reported our development of a non-invasive ultrasound device for measurement of ICP. We recently modified the device so that we might reproducibly estimate ICP changes in association with cardiac cycles. In the first experiment, we measured changes in cranial distance with the ultrasound device in cadavera while changing ICP by infusing saline into the lateral ventricle. In the second experiment, we measured changes in cranial distance in five healthy volunteers while placing them in 60 deg, 30 deg head-up tilt, supine, and 10 deg head-down tilt position. In the cadaver study, fast Fourier transformation revealed that cranial pulsation is clearly associated with ICP pulsation. The ratio of cranial distance and ICP pulsation is 1.3microns/mmHg. In the tilting study, the magnitudes of cranial pulsation are linearly correlated to tilt angles (r=0.87). The ultrasound device has sufficient sensitivity to detect cranial pulsation in association with cardiac cycles. By analyzing the magnitude of cranial pulsation, estimates of ICP during space flight are possible.

  18. Detailed Analysis of the Pulsations During and After Bursts from the Bursting Pulsar (GROJ1744-28)

    NASA Technical Reports Server (NTRS)

    Woods, Peter M.; Kouveliotou, Chryssa; vanParadijs, Jan; Koshut, Thomas M.; Finger, Mark H.; Briggs, Michael S.; Fishman, G. J.; Lewin, W. H. G.

    2000-01-01

    The hard X-ray bursts observed during both major outbursts of the Bursting Pulsar (GRO J1744-28) show pulsations near the neutron star spin frequency with an enhanced amplitude relative to that of the persistent emission. Consistent with previous work, we find that the pulsations within bursts lag behind their expected arrival times based upon the persistent pulsar ephemeris. For an ensemble of 1293 bursts recorded with the Burst and Transient Source Experiment, the average burst pulse time delay (DELTA t (sub FWHM)) is 61.0 plus or minus 0.8 ms in the 25 - 50 keV energy range and 72 plus or minus 5 ms in the 50 - 100 keV band. The residual time delay (DELTA t (sub resid)) from 10 to 240 s following the start of the burst is 18.1 plus or minus 0.7 ms (25 - 50 keV). A significant correlation of the average burst time delay with burst peak flux is found. Our results are consistent with the model of the pulse time lags presented by Miller (1996).

  19. PULSATION FREQUENCIES AND MODES OF GIANT EXOPLANETS

    SciTech Connect

    Le Bihan, Bastien; Burrows, Adam E-mail: burrows@astro.princeton.edu

    2013-02-10

    We calculate the eigenfrequencies and eigenfunctions of the acoustic oscillations of giant exoplanets and explore the dependence of the characteristic frequency {nu}{sub 0} and the eigenfrequencies on several parameters: the planet mass, the planet radius, the core mass, and the heavy element mass fraction in the envelope. We provide the eigenvalues for degree l up to 8 and radial order n up to 12. For the selected values of l and n, we find that the pulsation eigenfrequencies depend strongly on the planet mass and radius, especially at high frequency. We quantify this dependence through the calculation of the characteristic frequency {nu}{sub 0} which gives us an estimate of the scale of the eigenvalue spectrum at high frequency. For the mass range 0.5 M{sub J} {<=} M{sub P} {<=} 15 M{sub J} , and fixing the planet radius to the Jovian value, we find that {nu}{sub 0} {approx} 164.0 Multiplication-Sign (M{sub P} /M{sub J} ){sup 0.48}{mu}Hz, where M{sub P} is the planet mass and M{sub J} is Jupiter's mass. For the radius range from 0.9 to 2.0 R{sub J} , and fixing the planet's mass to the Jovian value, we find that {nu}{sub 0} {approx} 164.0 Multiplication-Sign (R{sub P} /R{sub J} ){sup -2.09}{mu}Hz, where R{sub P} is the planet radius and R{sub J} is Jupiter's radius. We explore the influence of the presence of a dense core on the pulsation frequencies and on the characteristic frequency of giant exoplanets. We find that the presence of heavy elements in the envelope affects the eigenvalue distribution in ways similar to the presence of a dense core. Additionally, we apply our formalism to Jupiter and Saturn and find results consistent with both the observational data of Gaulme et al. and previous theoretical work.

  20. Unexpected series of regular frequency spacing of δ Scuti stars in the non-asymptotic regime - I. The methodology

    SciTech Connect

    Paparo, M.; Benko, J. M.; Hareter, M.; Guzik, J. A.

    2016-05-11

    In this study, a sequence search method was developed to search the regular frequency spacing in δ Scuti stars through visual inspection and an algorithmic search. We searched for sequences of quasi-equally spaced frequencies, containing at least four members per sequence, in 90 δ Scuti stars observed by CoRoT. We found an unexpectedly large number of independent series of regular frequency spacing in 77 δ Scuti stars (from one to eight sequences) in the non-asymptotic regime. We introduce the sequence search method presenting the sequences and echelle diagram of CoRoT 102675756 and the structure of the algorithmic search. Four sequences (echelle ridges) were found in the 5–21 d–1 region where the pairs of the sequences are shifted (between 0.5 and 0.59 d–1) by twice the value of the estimated rotational splitting frequency (0.269 d–1). The general conclusions for the whole sample are also presented in this paper. The statistics of the spacings derived by the sequence search method, by FT (Fourier transform of the frequencies), and the statistics of the shifts are also compared. In many stars more than one almost equally valid spacing appeared. The model frequencies of FG Vir and their rotationally split components were used to formulate the possible explanation that one spacing is the large separation while the other is the sum of the large separation and the rotational frequency. In CoRoT 102675756, the two spacings (2.249 and 1.977 d–1) are in better agreement with the sum of a possible 1.710 d–1 large separation and two or one times, respectively, the value of the rotational frequency.

  1. Unexpected series of regular frequency spacing of δ Scuti stars in the non-asymptotic regime - I. The methodology

    SciTech Connect

    Paparo, M.; Benko, J. M.; Hareter, M.; Guzik, J. A.

    2016-05-11

    In this study, a sequence search method was developed to search the regular frequency spacing in δ Scuti stars through visual inspection and an algorithmic search. We searched for sequences of quasi-equally spaced frequencies, containing at least four members per sequence, in 90 δ Scuti stars observed by CoRoT. We found an unexpectedly large number of independent series of regular frequency spacing in 77 δ Scuti stars (from one to eight sequences) in the non-asymptotic regime. We introduce the sequence search method presenting the sequences and echelle diagram of CoRoT 102675756 and the structure of the algorithmic search. Four sequences (echelle ridges) were found in the 5–21 d–1 region where the pairs of the sequences are shifted (between 0.5 and 0.59 d–1) by twice the value of the estimated rotational splitting frequency (0.269 d–1). The general conclusions for the whole sample are also presented in this paper. The statistics of the spacings derived by the sequence search method, by FT (Fourier transform of the frequencies), and the statistics of the shifts are also compared. In many stars more than one almost equally valid spacing appeared. The model frequencies of FG Vir and their rotationally split components were used to formulate the possible explanation that one spacing is the large separation while the other is the sum of the large separation and the rotational frequency. In CoRoT 102675756, the two spacings (2.249 and 1.977 d–1) are in better agreement with the sum of a possible 1.710 d–1 large separation and two or one times, respectively, the value of the rotational frequency.

  2. Post-main-sequence and POST red giant branch variables with pulsation periods less than one day

    NASA Astrophysics Data System (ADS)

    Eggen, Olin J.

    1994-06-01

    Post-main-sequence (mass 1 to 3 solar masses) and post-giant branch (0.5 to 1 solar mass) pulsators are discussed on the basis of four color and H beta light curves published elsewhere. The post-main-sequence variables, called ultrashort period cepheid (USPC) (delta Sct), pulsate in the fundamental and first harmonic modes of radial pulsation and, in many cases, in nonradial modes. The variables for which photometry allows accurate, luminosity estimates and are known to pulsate simultaneously in the fundamental and first harmonic or in the fundamental mode alone, define a PL relation (MV = -2.80 log P - 0.60, fundamental). It is notable that the slope of this relation is in the range of slopes found for classical cepheids. Accurate V photometry is lacking for many of the variables known as 'anomalous cepheids', but the available data divide them into low mass, pseudocepheids (BL Her and W Vir stars) and post-main-sequence USPC (delta Sct) variables. Four USPC in NGC 5053 and six in NGC 6466, for which accurate photometry is available, give remarkably consistent moduli of 16.06 +/- 0.05 and 15.98 +/- 0.08 mag, respectively, for the clusters, in which they are blue stragglers similar to SX Phe in Kapteyn's star group. The assumption that the four post-giant branch variables, called VSPC (RR Lyr), S Ari, SU Dra, and ST Leo in Kapteyn's star group and RR Lyr in the Groombridge 1830 group, are physical members of these groups and share their V-velocities, leads to a calibration of the photometry for the derivation of reddening, luminosity, and heavy element abundance of 45 field variables. The resulting reddenings are consistent with values obtained by other methods and the metallicities are consistent with the most accurately available spectroscopic determinations of delta S and of Ca II K. The luminosities of the bulk of the variables confirm Sandage's (1993) relation between MV and (Fe/H). Four or five of the field variables are probably binary, including BB Vir

  3. Dependence of Pulsation Stability on the Helium Abundance of Stellar Convective Envelope

    NASA Astrophysics Data System (ADS)

    Xiong, Da-Run; Deng, Li-Cai; Wang, Kun

    2015-01-01

    By using a non-local and time-dependent theory of convection, the linear non-adiabatic oscillations of radial and low-degree non-radial F-p8 modes are calculated for the stellar evolutionary models in the mass range of 1.4∼3.0 Mʘ, with three helium abundances of convective envelope (Y =0.28, 0.13, 0.00), and the solar metal abundance (Z =0.02). The numerical results show that the red edge of theoretical δ Scuti instability strip almost does not change with the helium abundance. With the decrease of the helium abundance, the blue edge of the δ Scuti instability strip moves toward the direction of low temperatures, the high-temperature stars on the hot side of instability strip become more stable, while the low-temperature stars on the cold side of instability strip become more instable. It seems to be impossible to explain the non-variable stars in the δ Scuti instability strip by using the diffusion of helium. However, the ratios of non-variable stars to variable stars in the hot and cold sides of the δ Scuti strip may be taken as the observational evidence of helium diffusion.

  4. SABRE observations of Pi2 pulsations: case studies

    NASA Astrophysics Data System (ADS)

    Bradshaw, E. G.; Lester, M.

    1997-01-01

    The characteristics of substorm-associated Pi2 pulsations observed by the SABRE coherent radar system during three separate case studies are presented. The SABRE field of view is well positioned to observe the differences between the auroral zone pulsation signature and that observed at mid-latitudes. During the first case study the SABRE field of view is initially in the eastward electrojet, equatorward and to the west of the substorm-enhanced electrojet current. As the interval progresses, the western, upward field-aligned current of the substorm current wedge moves westward across the longitudes of the radar field of view. The westward motion of the wedge is apparent in the spatial and temporal signatures of the associated Pi2 pulsation spectra and polarisation sense. During the second case study, the complex field-aligned and ionospheric currents associated with the pulsation generation region move equatorward into the SABRE field of view and then poleward out of it again after the third pulsation in the series. The spectral content of the four pulsations during the interval indicate different auroral zone and mid-latitude signatures. The final case study is from a period of low magnetic activity when SABRE observes a Pi2 pulsation signature from regions equatorward of the enhanced substorm currents. There is an apparent mode change between the signature observed by SABRE in the ionosphere and that on the ground by magnetometers at latitudes slightly equatorward of the radar field of view. The observations are discussed in terms of published theories of the generation mechanisms for this type of pulsation. Different signatures are observed by SABRE depending on the level of magnetic activity and the position of the SABRE field of view relative to the pulsation generation region. A twin source model for Pi2 pulsation generation provides the clearest explanation of the signatures observed Acknowledgements. The authors are grateful to Prof. D. J. Southwood

  5. Nonradial and radial period changes in the δ Scuti star 4 CVn. I. 700+ nights of photometry

    NASA Astrophysics Data System (ADS)

    Breger, M.

    2016-08-01

    Context. The nature of period and amplitude changes in nonradial pulsators is presently unknown. Aims: It is therefore important to examine the correlations between these changes in stars with a large number of simultaneously excited pulsation modes. However, the small amplitudes require extensive high-precision photometry covering many years. Methods: We present 702 nights of high-precision photometry of the evolved δ Sct variable 4 CVn obtained from 2005-2012 with a dedicated telescope. Results: We detected 64 frequencies, of which 38 can be identified as combinations and harmonics. The relative amplitudes of the combination frequencies are similar to those found in 44 Tau and show no evidence for resonant mode coupling. Significant period and amplitude changes are detected for the dominant modes. The known prograde and retrograde modes show period changes with opposite signs, while the radial mode exhibits only small, cyclical period changes. For each mode, the period changes are constant over the eight years and range from (1 /P)dP/ dt = -16 × 10-6 to 13 × 10-6. On the other hand, the amplitude variations show no systematic behavior between different pulsation modes. Conclusions: The behavior of the prograde, axisymmetric, and retrograde modes indicate a constant decrease in the rotational splitting over the eight years.

  6. Numerical simulation of pulsating turbulent channel flow

    NASA Astrophysics Data System (ADS)

    Scotti, Alberto; Piomelli, Ugo

    2001-05-01

    Direct and large-eddy simulations of the Navier-Stokes equations are used to study the pulsating flow in a channel. The cases examined span a wide range of frequencies of the driving pressure gradient, and encompass different physical behaviors, from the quasi-Stokes flow observed at high frequencies, to a quasisteady behavior at the lowest ones. The validity of the dynamic Smagorinsky model to study this kind of unsteady flow is established by a posteriori comparison with direct simulations and experimental data. It is shown that the fluctuations generated in the near-wall region by the unsteady pressure gradient do not propagate beyond a certain distance lt from the wall, which can be estimated quite accurately by a simple eddy viscosity argument. No substantial departure from the Stokes regime at very high frequency (ω+ as high as 0.1) is observed. The time-dependent characteristics of the flow are examined in detail, as well as the topology of the coherent structures.

  7. Sher 25: pulsating but apparently alone

    NASA Astrophysics Data System (ADS)

    Taylor, William D.; Evans, Christopher J.; Simón-Díaz, Sergio; Sana, Hugues; Langer, Norbert; Smith, Nathan; Smartt, Stephen J.

    2014-08-01

    The blue supergiant Sher 25 is surrounded by an asymmetric, hourglass-shaped circumstellar nebula, which shows similarities to the triple-ring structure seen around SN 1987A. From optical spectroscopy over six consecutive nights, we detect periodic radial velocity variations in the stellar spectrum of Sher 25 with a peak-to-peak amplitude of ˜12 km s-1 on a time-scale of about 6 d, confirming the tentative detection of similar variations by Hendry et al. From consideration of the amplitude and time-scale of the signal, coupled with observed line profile variations, we propose that the physical origin of these variations is related to pulsations in the stellar atmosphere, rejecting the previous hypothesis of a massive, short-period binary companion. The radial velocities of two other blue supergiants with similar bipolar nebulae, SBW1 and HD 168625, were also monitored over the course of six nights, but these did not display any significant radial velocity variations.

  8. New Links Between Pulsation and Stellar History

    NASA Astrophysics Data System (ADS)

    Evans, Nancy Remage

    New instrumentation is providing new insights into intermediate mass pulsating Cepheids, particularly about their formation and history. Three approaches are discussed, using space (Hubble and Chandra) and ground-based studies (radial velocities). First, we are conducting a survey of Cepheids with the Hubble Space Telescope Wide Field Camera 3 (WFC3) to identify possible resolved companions (for example Eta Aql) and thus provide constraints on star formation. Followup X-ray observations (Chandra and XMM-Newton) can confirm whether possible low mass companions are young enough to be physical companions of Cepheids. In a related study of intermediate mass stars, Chandra X-ray observations of late B stars in Tr 16 have been used to determine the fraction which have X-ray active low mass companions. Finally, the Tennessee State Automatic Spectroscopic Telescope AST and the Moscow University group have obtained velocities of a number of Cepheids. As an example, the orbit of V350 Sgr has been redetermined, providing a new level of accuracy to the orbital velocity amplitude, which is needed for mass determination.

  9. Some simple properties of stellar pulsation modes

    NASA Technical Reports Server (NTRS)

    Wolff, C. L.

    1979-01-01

    Except for the lowest harmonics, small-amplitude stellar pulsation modes possess many simple properties whose evaluation does not require numerical integration of the fourth-order equations of motion. All antinodes tend to have the same total kinetic energy except for those lying near physical or geometric boundaries. However, when kinetic energy per unit volume is considered, order-of-magnitude enhancements are seen in antinodes lying near the center of the star, and factor-of-2 enhancements occur near the polar axis. The nodes are distributed very regularly along the radius. They follow an exponential law in g-regions, and their separation is proportional to the sound travel time in p-regions. A simple graphical procedure is described for surveying the oscillation frequencies of a new stellar model. A precise condition is derived giving the division of energy between radial and angular motion. Another condition gives the fractional contribution to the velocity field of its two sources, the divergence and the curl. Certain simplifying results of weak coupling among the linear modes are briefly described.

  10. Constraining the neutrino magnetic dipole moment from white dwarf pulsations

    SciTech Connect

    Córsico, A.H.; Althaus, L.G.; García-Berro, E. E-mail: althaus@fcaglp.unlp.edu.ar E-mail: kepler@if.ufrgs.br

    2014-08-01

    Pulsating white dwarf stars can be used as astrophysical laboratories to constrain the properties of weakly interacting particles. Comparing the cooling rates of these stars with the expected values from theoretical models allows us to search for additional sources of cooling due to the emission of axions, neutralinos, or neutrinos with magnetic dipole moment. In this work, we derive an upper bound to the neutrino magnetic dipole moment (μ{sub ν}) using an estimate of the rate of period change of the pulsating DB white dwarf star PG 1351+489. We employ state-of-the-art evolutionary and pulsational codes which allow us to perform a detailed asteroseismological period fit based on fully DB white dwarf evolutionary sequences. Plasmon neutrino emission is the dominant cooling mechanism for this class of hot pulsating white dwarfs, and so it is the main contributor to the rate of change of period with time (Pidot) for the DBV class. Thus, the inclusion of an anomalous neutrino emission through a non-vanishing magnetic dipole moment in these sequences notably influences the evolutionary timescales, and also the expected pulsational properties of the DBV stars. By comparing the theoretical Pidot value with the rate of change of period with time of PG 1351+489, we assess the possible existence of additional cooling by neutrinos with magnetic dipole moment. Our models suggest the existence of some additional cooling in this pulsating DB white dwarf, consistent with a non-zero magnetic dipole moment with an upper limit of μ{sub ν} ∼< 10{sup -11} μ{sub B}. This bound is somewhat less restrictive than, but still compatible with, other limits inferred from the white dwarf luminosity function or from the color-magnitude diagram of the Globular cluster M5. Further improvements of the measurement of the rate of period change of the dominant pulsation mode of PG 1351+489 will be necessary to confirm our bound.

  11. Ionospheric signatures of cusp latitude Pc 3 pulsations

    SciTech Connect

    Engebretson, M.J.; Anderson, B.J. ); Cahill, L.J. Jr. ); Arnoldy, R.L. ); Rosenberg, T.J. ); Carpenter, D.L. ); Gail, W.B. ); Eather, R.H. )

    1990-03-01

    The authors have compared search coil magnetometer, riometer, photometer, and ELF-VLF receiver data obtained at South Pole Station and McMurdo, Antarctica, during selected days in March and April 1986. Narrow-band magnetic pulsations in the Pc 3 period range are observed simultaneously at both stations in the dayside sector during times of low interplanetary magnetic field (IMF) cone angle, but are considerably stronger at South Pole, which is located at a latitude near the nominal foot point of the daysie cusp/cleft region. Pulsations in auroral light a 427.8 nm wavelength are often observed with magnetic pulsations at South Pole, but such optical pulsations are not observed at McMurdo. When Pc 3 pulsations are present, they exhibit nearly identical frequencies, proportional to the magnitude of the IMF, in magnetometer, photometer, and ELF-VLF receiver signals at South Pole Station and in magnetometer signals at McMurdo. Singals from the 30-MHz riometer at South Pole are modulated in concert with the magnetic and optical variations during periods of broadband pulsation activity, but no riometer variations are noted during periods of narrow-band activity. Because riometers are sensitive to electrons of auroral energies (several keV and above), while the 427.8-nm photometer is sensitive to precipitation with much lower energies, they interpret these observatons as showing that precipitating magnetosheathlike electrons (with energies {le} 1 keV) at nominal dayside cleft latitudes are at times modulated with frequencies similar to those of upstream waves. They suggest that these particles may play an important role, via modification of ionospheric currents and conductivities, in the transmission of upstream wave signals into the magnetosphere and in the generation of dayside high-latitude Pc 3 pulsations.

  12. Constraining the neutrino magnetic dipole moment from white dwarf pulsations

    NASA Astrophysics Data System (ADS)

    Córsico, A. H.; Althaus, L. G.; Miller Bertolami, M. M.; Kepler, S. O.; García-Berro, E.

    2014-08-01

    Pulsating white dwarf stars can be used as astrophysical laboratories to constrain the properties of weakly interacting particles. Comparing the cooling rates of these stars with the expected values from theoretical models allows us to search for additional sources of cooling due to the emission of axions, neutralinos, or neutrinos with magnetic dipole moment. In this work, we derive an upper bound to the neutrino magnetic dipole moment (μν) using an estimate of the rate of period change of the pulsating DB white dwarf star PG 1351+489. We employ state-of-the-art evolutionary and pulsational codes which allow us to perform a detailed asteroseismological period fit based on fully DB white dwarf evolutionary sequences. Plasmon neutrino emission is the dominant cooling mechanism for this class of hot pulsating white dwarfs, and so it is the main contributor to the rate of change of period with time (Pi dot) for the DBV class. Thus, the inclusion of an anomalous neutrino emission through a non-vanishing magnetic dipole moment in these sequences notably influences the evolutionary timescales, and also the expected pulsational properties of the DBV stars. By comparing the theoretical Pi dot value with the rate of change of period with time of PG 1351+489, we assess the possible existence of additional cooling by neutrinos with magnetic dipole moment. Our models suggest the existence of some additional cooling in this pulsating DB white dwarf, consistent with a non-zero magnetic dipole moment with an upper limit of μν lesssim 10-11 μB. This bound is somewhat less restrictive than, but still compatible with, other limits inferred from the white dwarf luminosity function or from the color-magnitude diagram of the Globular cluster M5. Further improvements of the measurement of the rate of period change of the dominant pulsation mode of PG 1351+489 will be necessary to confirm our bound.

  13. HD 50844: a new look at δ Scuti stars from CoRoT space photometry

    NASA Astrophysics Data System (ADS)

    Poretti, E.; Michel, E.; Garrido, R.; Lefèvre, L.; Mantegazza, L.; Rainer, M.; Rodríguez, E.; Uytterhoeven, K.; Amado, P. J.; Martín-Ruiz, S.; Moya, A.; Niemczura, E.; Suárez, J. C.; Zima, W.; Baglin, A.; Auvergne, M.; Baudin, F.; Catala, C.; Samadi, R.; Alvarez, M.; Mathias, P.; Paparò, M.; Pápics, P.; Plachy, E.

    2009-10-01

    Context: Aims: This work presents the results obtained by CoRoT on HD 50844, the only δ Sct star observed in the CoRoT initial run (57.6 d). The aim of these CoRoT observations was to investigate and characterize for the first time the pulsational behaviour of a δ Sct star, when observed at a level of precision and with a much better duty cycle than from the ground. Methods: The 140 016 datapoints were analysed using independent approaches (SigSpec software and different iterative sine-wave fittings) and several checks performed (splitting of the timeseries in different subsets, investigation of the residual light curves and spectra). A level of 10-5 mag was reached in the amplitude spectra of the CoRoT timeseries. The space monitoring was complemented by ground-based high-resolution spectroscopy, which allowed the mode identification of 30 terms. Results: The frequency analysis of the CoRoT timeseries revealed hundreds of terms in the frequency range 0-30 d-1. All the cross-checks confirmed this new result. The initial guess that δ Sct stars have a very rich frequency content is confirmed. The spectroscopic mode identification gives theoretical support since very high-degree modes (up to ℓ=14) are identified. We also prove that cancellation effects are not sufficient in removing the flux variations associated to these modes at the noise level of the CoRoT measurements. The ground-based observations indicate that HD 50844 is an evolved star that is slightly underabundant in heavy elements, located on the Terminal Age Main Sequence. Probably due to this unfavourable evolutionary status, no clear regular distribution is observed in the frequency set. The predominant term (f_1=6.92 d-1) has been identified as the fundamental radial mode combining ground-based photometric and spectroscopic data. Conclusions: The CoRoT space mission was developed and is operated by the French space agency CNES, with participation of ESA's RSSD and Science Programmes, Austria

  14. Quasi-periodic rapid motion of pulsating auroras

    NASA Astrophysics Data System (ADS)

    Fukuda, Yoko; Kataoka, Ryuho; Miyoshi, Yoshizumi; Katoh, Yuto; Nishiyama, Takanori; Shiokawa, Kazuo; Ebihara, Yusuke; Hampton, Donald; Iwagami, Naomoto

    2016-09-01

    We report rapid motion of pulsating auroras associated with so called ​3 ± 1 Hz modulations embedded in the main pulsations. During the pulsation ON phase, repetitive expansions are often observed around the edges of pulsating patches. Some events show a few detached expansions traveling away from the main deformed pulsating patch. Approximately 80% of all expansion speeds were found to be less than 70 km s-1 at ionospheric altitudes, which is less than the projected Alfvén speed from the magnetospheric equator to the ionosphere. The rapid motions with speeds of tens of km s-1 are unlikely to be explained by obliquely propagating chorus elements, which are known to cause the 3 ± 1 Hz modulation, because the perpendicular speed of the oblique chorus waves is higher than the Alfvén speed. We discuss the slow-mode Alfvén wave as a candidate modulation source to generate the rapid motions. A few non-repetitive expansion events with a speed of more than 150 km s-1 also appear at the onset of the ON phase. These non-repetitive expanding motions are characterized by a long displacement compared to the repetitive expanding motions. The differences in the expansion speeds indicate different formation mechanisms of the patch motions.

  15. Variability of Microcirculation Detected by Blood Pulsation Imaging

    PubMed Central

    Kamshilin, Alexei A.; Teplov, Victor; Nippolainen, Ervin; Miridonov, Serguei; Giniatullin, Rashid

    2013-01-01

    The non-invasive assessment of blood flow is invaluable for the diagnostic and monitoring treatment of numerous vascular and neurological diseases. We developed a non-invasive and non-contact method of blood pulsation imaging capable of visualizing and monitoring of the two-dimensional distribution of two key parameters of peripheral blood flow: the blood pulsation amplitude and blood pulsation phase. The method is based on the photoplethysmographic imaging in the reflection mode. In contrast with previous imaging systems we use new algorithm for data processing which allows two dimensional mapping of blood pulsations in large object's areas after every cardiac cycle. In our study we carried out the occlusion test of the arm and found (i) the extensive variability of 2D-distribution of blood pulsation amplitude from one cardiac cycle to another, and (ii) existence of the adjacent spots to which the blood is asynchronously supplied. These observations show that the method can be used for studying of the multicomponent regulation of peripheral blood circulation. The proposed technique is technologically simple and cost-effective, which makes it applicable for monitoring the peripheral microcirculation in clinical settings for example, in diagnostics or testing the efficiency of new medicines. PMID:23431399

  16. The Effects of Pulsating Flow on Eruption Column Dynamics

    NASA Astrophysics Data System (ADS)

    Black, T.; Dufek, J.; Benage, M. C.

    2015-12-01

    Pulsating flow, at frequencies ranging from 10-2 to 101 Hz, has been recorded in explosive eruptions through video, thermal imagery, and infrasonic and seismic data. Such pulsating flow can be generated from instabilities in bubbly magma, and from granular instabilities in post-fragmentation conduit flow. Variable fluxes of gas and particles at the vent can alter entrainment conditions, and consequently affect eruption column stability. However, volcanic eruption models typically assume steady flow from the vent, and regime diagrams of eruption column stability are based on such steady flow assumptions. Using Eulerian-Eulerian multiphase numerical simulations of eruption columns with both steady and pulsating sources, we compared the relative behavior of steady and pulsed columns across a range of pulse frequencies and mass fluxes at the vent (mass flux is time-averaged for pulsating cases). Preliminary results suggest that pulsating flow increases air entrainment into the column relative to steady flow for otherwise constant eruption conditions, and that entrainment increases with decreasing pulse frequency. Increased entrainment at low frequency implies that low-frequency pulsed columns are more buoyant and potentially more stable than their steady counterparts, for a given mass flux. This effect disrupts the steady flow-based understanding of eruption column stability regimes and may be a factor to consider for future assessment of volcanic hazards and interpreting mass flux conditions from deposits.

  17. THE DISCOVERY OF PULSATING HOT SUBDWARFS IN NGC 2808

    SciTech Connect

    Brown, Thomas M.; Landsman, Wayne B.; Randall, Suzanna K.; Sweigart, Allen V.; Lanz, Thierry E-mail: Wayne.Landsman@nasa.gov E-mail: allen.sweigart@gmail.com

    2013-11-10

    We present the results of a Hubble Space Telescope program to search for pulsating hot subdwarfs in the core of NGC 2808. These observations were motivated by the recent discovery of such stars in the outskirts of ω Cen. Both NGC 2808 and ω Cen are massive globular clusters exhibiting complex stellar populations and large numbers of extreme horizontal branch stars. Our far-UV photometric monitoring of over 100 hot evolved stars has revealed six pulsating subdwarfs with periods ranging from 85 to 149 s and UV amplitudes of 2.0%-6.8%. In the UV color-magnitude diagram of NGC 2808, all six of these stars lie immediately below the canonical horizontal branch, a region populated by the subluminous 'blue-hook' stars. For three of these six pulsators, we also have low-resolution far-UV spectroscopy that is sufficient to broadly constrain their atmospheric abundances and effective temperatures. Curiously, and in contrast to the ω Cen pulsators, the NGC 2808 pulsators do not exhibit the spectroscopic or photometric uniformity one might expect from a well-defined instability strip, although they all fall within a narrow band (0.2 mag) of far-UV luminosity.

  18. Structure of Black Aurora Associated With Pulsating Aurora

    NASA Astrophysics Data System (ADS)

    Kenward, D. R.; Fritz, B.; Lessard, M.; Fernandes, P. A.; Blandin, M.

    2015-12-01

    Morphological behavior of black aurora as it relates to pulsating aurora is investigated by examining a collection of ground-based observations from January 2007 in support of the ROPA rocket campaign. Images were sampled from video recorded by a Xybion intensified camera (30 fps) at Poker Flat Research Range, AK. The primary observations of black aurora were observed during the substorm recovery phase and separate patches of pulsating aurora as well as pulsating aurora from diffuse aurora. In these observations the black aurora forms an apparent firm boundary between the auroral forms in a new behavior that is in contrast with previously reported observations. Also presented for the first time are black curls in conjunction with pulsating aurora. Curl structures that indicate shear plasma flows in the ionosphere may be used as a proxy for converging/diverging electric fields in and above the ionosphere. This new subset of black auroral behavior may provide visual evidence of black aurora as an ionospheric feedback mechanism as related to pulsating aurora.

  19. The Discovery of Pulsating Hot Subdwarfs in NGC 2808

    NASA Technical Reports Server (NTRS)

    Brown, Thomas M.; Landsman, Wayne B.; Randall, Suzanna K.; Sweigert, Allen V.; Lanz, Thierry

    2013-01-01

    We present the results of a Hubble Space Telescope program to search for pulsating hot subdwarfs in the core of NGC 2808. These observations were motivated by the recent discovery of such stars in the outskirts of Omega Cen. Both NGC 2808 and ? Cen are massive globular clusters exhibiting complex stellar populations and large numbers of extreme horizontal branch stars. Our far-UV photometric monitoring of over 100 hot evolved stars has revealed six pulsating subdwarfs with periods ranging from 85 to 149 s and UV amplitudes of 2.0%-6.8%. In the UV color-magnitude diagram of NGC 2808, all six of these stars lie immediately below the canonical horizontal branch, a region populated by the subluminous "blue-hook" stars. For three of these six pulsators, we also have low-resolution far-UV spectroscopy that is sufficient to broadly constrain their atmospheric abundances and effective temperatures. Curiously, and in contrast to the ? Cen pulsators, the NGC 2808 pulsators do not exhibit the spectroscopic or photometric uniformity one might expect from a well-defined instability strip, although they all fall within a narrow band (0.2 mag) of far-UV luminosity.

  20. Ionospheric signatures of cusp latitude Pc 3 pulsations

    NASA Technical Reports Server (NTRS)

    Engebretson, M. J.; Anderson, B. J.; Cahill, L. J., Jr.; Arnoldy, R. L.; Rosenberg, T. J.

    1990-01-01

    Search coil magnetometer, riometer, photometer, and ELF-VLF receiver data obtained at South Pole Station and McMurdo, Antarctica during selected days in March and April 1986 are compared. Narrow-band magnetic pulsations in the Pc 3 period range are observed simultaneously at both stations in the dayside sector during times of low IMF cone angle, but are considerably stronger at South Pole, which is located at a latitude near the nominal foot point of the dayside cusp/cleft region. Pulsations in auroral light at 427.8 nm wavelength are often observed with magnetic pulsations at South Pole, but such optical pulsations are not observed at McMurdo. The observations suggest that precipitating magnetosheathlike electrons at nominal dayside cleft latitudes are at times modulated with frequencies similar to those of upstream waves. These particles may play an important role, via modification of ionospheric currents and conductivities, in the transmission of upstream wave signals into the magnetosphere and in the generation of dayside high-latitude Pc 3 pulsations.

  1. Heartbeat Stars and the Ringing of Tidal Pulsations

    NASA Astrophysics Data System (ADS)

    Hambleton, Kelly; Kurtz, Don; Prša, Andrej; Fuller, Jim; Thompson, Susan

    2015-09-01

    With the advent of high precision photometry from satellites such as Kepler and CoRoT, a whole new layer of interesting and astounding astronomical objects has been revealed: heartbeat stars are an example of such objects. Heartbeat stars are eccentric ellipsoidal variables that undergo strong tidal interactions when the stars are almost in contact at the time of closest approach. These interactions deform of the stars and cause a notable light curve variation in the form of a tidal pulse. A subset of these objects (~20%) show prominent tidally induced pulsations: pulsations forced by the binary orbit. We now have a fully functional code that models binary star features (using PHOEBE) and stellar pulsations simultaneously, enabling a complete and accurate heartbeat star model to be determined. In this paper we show the results of our new code, which uses emcee, a variant of mcmc, to generate a full set of stellar parameters. We further highlight the interesting features of KIC 8164262, including its tidally induced pulsations and resonantly locked pulsations.

  2. Lattice melting and rotation in perpetually pulsating equilibria

    SciTech Connect

    Pichon, C.; Lynden-Bell, D.; Pichon, J.; Lynden-Bell, R.

    2007-01-15

    Systems whose potential energies consists of pieces that scale as r{sup -2} together with pieces that scale as r{sup 2}, show no violent relaxation to Virial equilibrium but may pulsate at considerable amplitude forever. Despite this pulsation these systems form lattices when the nonpulsational ''energy'' is low, and these disintegrate as that energy is increased. The ''specific heats'' show the expected halving as the ''solid'' is gradually replaced by the ''fluid'' of independent particles. The forms of the lattices are described here for N{<=}18 and they become hexagonal close packed for large N. In the larger N limit, a shell structure is formed. Their large N behavior is analogous to a {gamma}=5/3 polytropic fluid with a quasigravity such that every element of fluid attracts every other in proportion to their separation. For such a fluid, we study the ''rotating pulsating equilibria'' and their relaxation back to uniform but pulsating rotation. We also compare the rotating pulsating fluid to its discrete counterpart, and study the rate at which the rotating crystal redistributes angular momentum and mixes as a function of extra heat content.

  3. Epsilon Aur monitoring during predicted pulsation phase

    NASA Astrophysics Data System (ADS)

    Waagen, Elizabeth O.; Templeton, Matthew R.

    2014-09-01

    Dr. Robert Stencel (University of Denver Astronomy Program) has requested that AAVSO observers monitor epsilon Aurigae from now through the end of the observing season. "Studies of the long-term, out-of-eclipse photometry of this enigmatic binary suggest that intervals of coherent pulsation occur at roughly 1/3 of the 27.1-year orbital period. Kloppenborg, et al. noted that stable variation patterns develop at 3,200-day intervals' implying that 'the next span of dates when such events might happen are circa JD ~2457000 (2014 December)'. "These out-of-eclipse light variations often have amplitudes of ~0.1 magnitude in U, and ~0.05 in V, with characteristic timescales of 60-100 days. The AAVSO light curve data to the present may indicate that this coherent phenomenon has begun, but we encourage renewed efforts by observers...to help deduce whether these events are internal to the F star, or externally-driven by tidal interaction with the companion star." Nightly observations or one observation every few days (CCD/PEP/DSLR, VUBR (amplitude too small for visual)) are requested. Finder charts with sequence may be created using the AAVSO Variable Star Plotter (http://www.aavso.org/vsp). Observations should be submitted to the AAVSO International Database. Epsilon Aur was the subject of major international campaigns and the AAVSO's Citizen Sky project as it went through its 27.1-year eclipse in 2009-2011. Over 700 observers worldwide submitted over 20,000 multicolor observations to the AAVSO International Database for this project. Much information on eps Aur is available from the AAVSO, including material on the Citizen Sky website (http://www.aavso.org/epsilon-aurigae and http://www.citizensky.org/content/star-our-project). The Journal of the AAVSO, Volume 40, No. 2 (2012) was devoted to discussion of and research results from this event. See full Alert Notice for more details and observations.

  4. Commentary on fast atmospheric pulsations. Technical report

    SciTech Connect

    Vampola, A.L.

    1988-11-22

    A recent paper proposed that Fast Atmospheric Light Pulsations (FAPs), which have been observed at L=1.5-2.2 in the northern hemisphere, are optical signatures of >2-MeV electrons associated with Lightning-induced Electron Precipitation (LEP) events produced by lightning strokes in the southern hemisphere. FAPs cannot be produced by >2-MeV electrons in the inner radiation belt because the upper limit for fluxes of such particles is only about 0.2% of the value that was used in the analysis and would lead to an unrealistically short electron lifetime. The discrepancy comes from using an electron model, AE-2, which included the Starfish fission electrons. Later inner-zone electron environment models show the inner-zone to have negligible fluxes of electrons in excess of 2 MeV. The use of a model in which southern hemisphere lightning strokes result in northern hemisphere FAPs via a cyclotron mode interaction between magnetospheric electrons and lightning generated waves is also untenable because it would result in FAP intensities two orders of magnitude greater in the southern hemisphere than in the northern hemisphere, leading to a further two orders of magnitude reduction in estimated inner-zone electron lifetimes. The estimated light intensity of FAPs is within acceptable bounds compared to the lifetime of inner zone electrons if all electrons above 100 keV contribute to the light production, if southern hemisphere FAP intensity is no greater than the FAP intensity observed in the northern hemisphere, and if the light-production efficiency is of the order of .001.

  5. FINDING THE INSTABILITY STRIP FOR ACCRETING PULSATING WHITE DWARFS FROM HUBBLE SPACE TELESCOPE AND OPTICAL OBSERVATIONS

    SciTech Connect

    Szkody, Paula; Mukadam, Anjum; Gaensicke, Boris T.; Henden, Arne; Templeton, Matthew; Dillon, William; Holtzman, Jon; Montgomery, Michael H.; Howell, Steve B.; Nitta, Atsuko; Sion, Edward M.; Schwartz, Richard D.

    2010-02-10

    Time-resolved low resolution Hubble Space Telescope ultraviolet spectra together with ground-based optical photometry and spectra are used to constrain the temperatures and pulsation properties of six cataclysmic variables containing pulsating white dwarfs (WDs). Combining our temperature determinations for the five pulsating WDs that are several years past outburst with past results on six other systems shows that the instability strip for accreting pulsating WDs ranges from 10,500 to 15,000 K, a wider range than evident for ZZ Ceti pulsators. Analysis of the UV/optical pulsation properties reveals some puzzling aspects. While half the systems show high pulsation amplitudes in the UV compared to their optical counterparts, others show UV/optical amplitude ratios that are less than one or no pulsations at either wavelength region.

  6. EVIDENCE FOR TEMPERATURE CHANGE AND OBLIQUE PULSATION FROM LIGHT CURVE FITS OF THE PULSATING WHITE DWARF GD 358

    SciTech Connect

    Montgomery, M. H.; Winget, D. E.; Provencal, J. L.; Thompson, S. E.; Kanaan, A.; Mukadam, Anjum S.; Dalessio, J.; Shipman, H. L.; Kepler, S. O.; Koester, D.

    2010-06-10

    Convective driving, the mechanism originally proposed by Brickhill for pulsating white dwarf stars, has gained general acceptance as the generic linear instability mechanism in DAV and DBV white dwarfs. This physical mechanism naturally leads to a nonlinear formulation, reproducing the observed light curves of many pulsating white dwarfs. This numerical model can also provide information on the average depth of a star's convection zone and the inclination angle of its pulsation axis. In this paper, we give two sets of results of nonlinear light curve fits to data on the DBV GD 358. Our first fit is based on data gathered in 2006 by the Whole Earth Telescope; this data set was multiperiodic containing at least 12 individual modes. Our second fit utilizes data obtained in 1996, when GD 358 underwent a dramatic change in excited frequencies accompanied by a rapid increase in fractional amplitude; during this event it was essentially monoperiodic. We argue that GD 358's convection zone was much thinner in 1996 than in 2006, and we interpret this as a result of a short-lived increase in its surface temperature. In addition, we find strong evidence of oblique pulsation using two sets of evenly split triplets in the 2006 data. This marks the first time that oblique pulsation has been identified in a variable white dwarf star.

  7. EPIC 211779126: a rare hybrid pulsating subdwarf B star richly pulsating in both pressure and gravity modes

    NASA Astrophysics Data System (ADS)

    Baran, A. S.; Reed, M. D.; Østensen, R. H.; Telting, J. H.; Jeffery, C. S.

    2017-01-01

    We present our analysis of EPIC 211779126, a pulsating subdwarf B star discovered with the Kepler spacecraft during K2 Campaign 5. We found 154 frequencies in the g-mode region as well as 29 frequencies in the p-mode region. This makes EPIC 211779126 a rare hybrid pulsator with a rich pulsation spectrum in both regions. We successfully identified modal degrees and relative radial orders of most of the g-modes using asymptotic period spacing, and modal degrees of some of the p-modes using rotational splitting. We detected trapped modes, which are a very important feature for constraining theoretical models. Our ground-based spectroscopic observations revealed no companion, therefore EPIC 211779126 is likely a single sdB star. Using p-mode multiplets, we derived a rotation period of approximately 16 days, making EPIC 211779126 the fastest rotating non-binary subdwarf B pulsator observed with Kepler. However, we do not find any resolved multiplets among the high-amplitude g-mode pulsations that correspond to the rotation rate inferred from the p-mode splittings. This may indicate that the star's core is rotating more slowly than its envelope.

  8. Modelling of Pc5 pulsation structure in the magnetosphere

    NASA Astrophysics Data System (ADS)

    Walker, A. D. M.

    1980-03-01

    Magnetohydrodynamic resonance theory is used to model the structure of the magnetospheric and ionospheric electric and magnetic fields associated with Pc5 geomagnetic pulsations. In this paper the variation of the fields across the invariant latitude of the resonance are computed. The results are combined with calculations of the variation along a field line to map the fields down to the ionosphere. In one case the results are compared with measurements obtained by the STARE auroral radar and show good agreement. The relationship between the width of the resonance region and ionospheric height-integrated Pedersen conductivity is computed and it is shown how auroral radar measurements of Pc5 oscillations could be used to determine ionospheric height-integrated Pedersen conductivity. It is pointed out that from these calculations it would be possible to identify the field line on which a satellite was located by comparing a Pc5 pulsation observed by the satellite, and the same pulsation observed by STARE.

  9. On permanent and sporadic pulsations of the magnetosphere

    NASA Astrophysics Data System (ADS)

    Guglielmi, A. V.

    2015-05-01

    A question concerning the influence of permanent Pc3-band pulsations (periods from 10 to 45 s) on the excitation of sporadic Pi2-band pulsations (40 to 150 s) is raised. It is hypothesized that, being generated ahead of the front of the Earth's magnetosphere, the Pc3 penetrate into the geomagnetic tail where they cause local depression in the electric current in the neutral sheet and, under favorable conditions, initiate tearing instability. This leads to the reconnection of the magnetic field lines and explosion-like release of the magnetic energy stored in the tail. As a result, a substorm arises with the sporadic Pi2 pulsations being its important element. Ways are suggested to theoretically substantiate and experimentally validate this hypothesis.

  10. Geomagnetic pulsations observed simultaneously on three geostationary satellites

    NASA Technical Reports Server (NTRS)

    Hughes, W. J.; Mcpherron, R. L.; Barfield, J. N.

    1978-01-01

    Simultaneous observations of magnetic pulsations have been made by three geostationary satellites carrying similar magnetometers and acting as an azimuthal array. Autospectral and cross-spectral analysis yields coherence and phase differences between the pulsations at the satellite positions. The majority of the data fit the Kelvin-Helmholtz generation mechanism. The azimuthal wave number changes sign near noon and corresponds to propagation away from noon. Usually, the wave number is less than 10 deg per degree of longitude. Later in the afternoon, however, strong pulsations are observed with low coherence, implying large wave numbers. This suggests an instability driven by a gradient in the intensity of energetic protons, which may be expected at this local time. The data also suggest that some of the observed phase difference between the azimuthal components is due to small separations in magnetic shell, whereas this is not the case for the radial components. This implies a localized field-line resonance.

  11. Theory of auroral zone PiB pulsation spectra

    SciTech Connect

    Lysak, R.L. )

    1988-06-01

    Changes in the auroral zone current system are often accompanied by magnetic pulsations with periods of about 1 s. These so-called bursts of irregular pulsations (PiB) have been observed both on ground magnetograms and with in situ satellite observations. These pulsations can be understood as excitations of a resonant cavity in the topside ionosphere, where the Alfven speed has a strong gradient due to the exponential decrease of density above the ionosphere. These waves have a frequency which scales as the ratio of the Alfven speed at the ionosphere divided by the ionospheric scale height. For a pure exponential Alfven speed profile, the mode frequencies are related to zeros of the zeroth-order Bessel function. For other profiles of the density, and therefore Alfven speed, the frequencies are not exactly given by the simple theory, but the frequency and mode structure are similar provided the Alfven speed sharply increases above the ionosphere.

  12. Outbursts in Two New Cool Pulsating DA White Dwarfs

    NASA Astrophysics Data System (ADS)

    Bell, Keaton J.; Hermes, J. J.; Montgomery, M. H.; Gentile Fusillo, N. P.; Raddi, R.; Gänsicke, B. T.; Winget, D. E.; Dennihy, E.; Gianninas, A.; Tremblay, P.-E.; Chote, P.; Winget, K. I.

    2016-10-01

    The unprecedented extent of coverage provided by Kepler observations recently revealed outbursts in two hydrogen-atmosphere pulsating white dwarfs (DAVs) that cause hours-long increases in the overall mean flux of up to 14%. We have identified two new outbursting pulsating white dwarfs in K2, bringing the total number of known outbursting white dwarfs to four. EPIC 211629697, with {T}{eff} = 10,780 ± 140 K and {log} g = 7.94 ± 0.08, shows outbursts recurring on average every 5.0 days, increasing the overall flux by up to 15%. EPIC 229227292, with {T}{eff} = 11,190 ± 170 K and {log} g = 8.02 ± 0.05, has outbursts that recur roughly every 2.4 days with amplitudes up to 9%. We establish that only the coolest pulsating white dwarfs within a small temperature range near the cool, red edge of the DAV instability strip exhibit these outbursts.

  13. Ground magnetic field fluctuations associated with pulsating aurora

    NASA Astrophysics Data System (ADS)

    Michell, R. G.; Samara, M.

    2015-10-01

    A case study of an intense pulsating auroral event is presented where the large-scale (100-200 km) optical intensity variations are anticorrelated with fluctuations in the ground magnetometer data at a frequency of 0.1 Hz. The auroral event occurred over Poker Flat, Alaska, on 1 March 2012 and was imaged optically with several different fields of view and filters. The fluctuations in the magnetometer data were most prominent in the D component and had magnitudes of 1 to 5 nT. The auroral intensity variations had amplitudes of 200 to 400 R, comprising 25% to 50% of the total auroral luminosity at 427.8 nm. The direction of the magnetometer deflections is consistent with a south-to-north ionospheric current present when each pulsation is on, thus providing closure for the field-aligned currents associated with each of the pulsating patches.

  14. On the Stenbaek-Nielsen and Hallinan pulsating auroras

    SciTech Connect

    D'Angelo, N. )

    1991-02-01

    Stenbaek-Nielsen and Hallinan (1979) argued that if the pulsating auroras are caused by precipitating electrons, the data suggest that noncollisional interactions, localized in the lower E region (90-107 km), where most of the pulsations are observed, may play a dominant role in thermalizing the particles. They also stated that one type of process that comes to mind is a wave-particle interaction in the ionosphere. If, through one or more instabilities, waves grow at the expense of beam energy and, in turn, energize ambient electrons, the energized ambient electrons could ionize the background gas and, in process, produce luminosity. The exceptionally thin pulsating auroral patches observed by Stenbaek-Nielsen and Hallinan (1979) may be caused by an ionization instability occurring at the end of the range of precipitating electrons. A comparison is made to laboratory results reported by Johnson et al. (1990).

  15. Fibre-grating sensors for the measurement of physiological pulsations

    NASA Astrophysics Data System (ADS)

    Petrović, M. D.; Daničić, A.; Atanasoski, V.; Radosavljević, S.; Prodanović, V.; Miljković, N.; Petrović, J.; Petrović, D.; Bojović, B.; Hadžievski, Lj; Allsop, T.; Lloyd, G.; Webb, D. J.

    2013-11-01

    Mechanical physiological pulsations are movements of a body surface incited by the movements of muscles in organs inside the body. Here we demonstrate the use of long-period grating sensors in the detection of cardio-vascular pulsations (CVP), in particular apex and carotid pulsations. To calibrate the sensors, we use a mechanical tool designed specifically to measure the sensor response to a localized perturbation at different grating curvatures as working points. From the data we infer the amplitude of the CVP. Together with the electrophysiological signals, the CVP signals obtained from the sensors can provide significant information on heart function which is inaccessible to the electrocardiogram. The low cost and easy handling of the fibre sensors increase their prospects to become the sensors of choice for novel diagnostic devices.

  16. γ Doradus Pulsations in the Eclipsing Binary Star KIC 6048106

    NASA Astrophysics Data System (ADS)

    Lee, Jae Woo

    2016-12-01

    We present the Kepler photometry of KIC 6048106, which is exhibiting the O’Connell effect and multiperiodic pulsations. Including a starspot on either of the components, light-curve synthesis indicates that this system is a semi-detached Algol with a mass ratio of 0.211, an orbital inclination of 73.°9, and a large temperature difference of 2534 K. To examine in detail both the spot variations and pulsations, we separately analyzed the Kepler time-series data at the interval of an orbital period in an iterative way. The results reveal that the variable asymmetries of the light maxima can be interpreted as the changes with time of a magnetic cool spot on the secondary component. Multiple frequency analyses were performed in the outside-eclipse light residuals after removal of the binarity effects from the observed Kepler data. We detected 30 frequencies with signal to noise amplitude ratios larger than 4.0, of which six (f 2-f 6 and f 10) can be identified as high-order (17 ≤ n ≤ 25) low-degree (ℓ = 2) gravity-mode pulsations that were stable during the observing run of 200 days. In contrast, the other frequencies may be harmonic and combination terms. For the six frequencies, the pulsation periods and pulsation constants are in the ranges of 0.352-0.506 days and 0.232-0.333 days, respectively. These values and the position on the Hertzsprung-Russell diagram demonstrate that the primary star is a γ Dor variable. The evolutionary status and the pulsation nature of KIC 6048106 are discussed.

  17. Search for optical pulsations in PSR J0337+1715

    NASA Astrophysics Data System (ADS)

    Strader, M. J.; Archibald, A. M.; Meeker, S. R.; Szypryt, P.; Walter, A. B.; van Eyken, J. C.; Ulbricht, G.; Stoughton, C.; Bumble, B.; Kaplan, D. L.; Mazin, B. A.

    2016-06-01

    We report on a search for optical pulsations from PSR J0337+1715 at its observed radio pulse period. PSR J0337+1715 is a millisecond pulsar (2.7 ms spin period) in a triple hierarchical system with two white dwarfs, and has a known optical counterpart with g-band magnitude 18. The observations were done with the ARray Camera for Optical to Near-IR Spectrophotometry at the 200 arcsec Hale telescope at Palomar Observatory. No significant pulsations were found in the range 4000-11 000 Å, and we can limit pulsed emission in g band to be fainter than 25 mag.

  18. Cycles of self-pulsations in a photonic integrated circuit.

    PubMed

    Karsaklian Dal Bosco, Andreas; Kanno, Kazutaka; Uchida, Atsushi; Sciamanna, Marc; Harayama, Takahisa; Yoshimura, Kazuyuki

    2015-12-01

    We report experimentally on the bifurcation cascade leading to the appearance of self-pulsation in a photonic integrated circuit in which a laser diode is subjected to delayed optical feedback. We study the evolution of the self-pulsing frequency with the increase of both the feedback strength and the injection current. Experimental observations show good qualitative accordance with numerical results carried out with the Lang-Kobayashi rate equation model. We explain the mechanism underlying the self-pulsations by a phenomenon of beating between successive pairs of external cavity modes and antimodes.

  19. Search for optical pulsations in PSR J0337+1715

    DOE PAGES

    Strader, M. J.; Archibald, A. M.; Meeker, S. R.; ...

    2016-03-20

    In this study, we report on a search for optical pulsations from PSR J0337+1715 at its observed radio pulse period. PSR J0337+1715 is a millisecond pulsar (2.7 ms spin period) in a triple hierarchical system with two white dwarfs, and has a known optical counterpart with g-band magnitude 18. The observations were done with the Array Camera for Optical to Near-IR Spectrophotometry (ARCONS) at the 200" Hale telescope at Palomar Observatory. No significant pulsations were found in the range 4000-11000 angstroms, and we can limit pulsed emission in g-band to be fainter than 25 mag.

  20. Mode identification from spectroscopy of gravity-mode pulsators

    NASA Astrophysics Data System (ADS)

    Pollard, K. R.; Brunsden, E.; Cottrell, P. L.; Davie, M.; Greenwood, A.; Wright, D. J.; De Cat, P.

    2014-02-01

    The gravity modes present in γ Doradus stars probe the deep stellar interiors and are thus of particular interest in asteroseismology. For the MUSICIAN programme at the University of Canterbury, we obtain extensive high-resolution echelle spectra of γ Dor stars from the Mt John University Observatory in New Zealand. We analyze these to obtain the pulsational frequencies and identify these with the multiple pulsational modes excited in the star. A summary of recent results from our spectroscopic mode-identification programme is given.

  1. The Post-outburst Pulsations of GW Librae

    NASA Astrophysics Data System (ADS)

    Chote, P.; Mukadam, A. S.; Aungwerojwit, A.; Szkody, P.; Gänsicke, B. T.; Sullivan, D. J.; Poshyachinda, S.; Reichart, D. E.; Haislip, J. B.; Moore, J. P.

    2017-03-01

    We present new observations of GW Librae obtained between 2012 and 2016. GW Librae was the first accreting white dwarf to be discovered with non-radial pulsations, which were wiped out in 2007 when a dwarf nova outburst heated the surface of the WD outside the instability strip. In the years that followed, we have seen pulsations return with periods near 280 and 1200 seconds, but find that their periods and amplitudes vary on timescales longer than a few hours. Some of these changes are found to correlate with changes in the mysterious 2/3/4 hour modulation that has been seen both before and after the outburst.

  2. Effects of pulsating flow on current meter performance

    USGS Publications Warehouse

    Fulford, Janice M.; ,

    1995-01-01

    Summarized are laboratory tests for current meter response to pulsating flows. Included are results for mechanical and electromagnetic water-current meters that are commonly used for stream gaging. Most of the vertical-axis and horizontal-axis types of mechanical meters that were tested significantly underregistered the mean flow velocity when the magnitude of the pulsating portion of the flow velocity was greater than half the mean velocity but less than the mean velocity. Errors for all meters tested were largest at the lowest mean flow velocity, 0.076 m/s.

  3. Resonant self-pulsations in coupled nonlinear microcavities

    SciTech Connect

    Grigoriev, Victor; Biancalana, Fabio

    2011-04-15

    A different point of view on the phenomenon of self-pulsations is presented, which shows that they are a balanced state formed by two counteracting processes: beating of modes and bistable switching. A structure based on two coupled nonlinear microcavities provides a generic example of a system with enhanced ability to support this phenomenon. The specific design of such a structure in the form of multilayered media is proposed, and the coupled-mode theory is applied to describe its dynamical properties. It is emphasized that the frequency of self-pulsations is related to the frequency splitting between resonant modes and can be adjusted over a broad range.

  4. A New Subdwarf-OB Pulsator J23341+4622

    NASA Astrophysics Data System (ADS)

    Pakštiene, E.; Qvam, J. K. T.; Østensen, R. H.; Telting, J. H.

    2014-12-01

    A new sdOB variable star, J23341+4622 (SDSS J233406.10+462249.3), was discovered during photometric observations with the Nordic Optical Telescope (La Palma). We found its main pulsation frequency at 7422(±9) μHz with an amplitude of 4.5(±0.5) mma. The star is possibly a complex pulsator, as we found another significant peak at 7759(±11) μHz with an amplitude of 2.0(±0.3) mma and a possible subharmonic of the main frequency at 3508 μHz with an amplitude of 2.3 mma.

  5. Spectral peculiarities of turbulent pulsations of submerged water jets

    NASA Astrophysics Data System (ADS)

    Znamenskaya, I. A.; Koroteeva, E. Yu.; Novinskaya, A. M.; Sysoev, N. N.

    2016-07-01

    The spectra of turbulent jet temperature pulsations at 1-40 Hz frequencies have been experimentally studied based on high-speed thermography of the water boundary layer: the region where an impact jet interacts with a surface transparent to IR radiation, as well as the near-wall region where two submerged jets interact in a disc-shaped tee-joint. It has been indicated that the slopes of the spectra of impact submerged jet turbulent pulsations are close to-5/3 and a double inertial interval exists in a quasi-2D turbulent flow that is formed when two jets mix.

  6. Inconsistencies in the harmonic analysis applied to pulsating stars

    NASA Astrophysics Data System (ADS)

    Pascual-Granado, J.; Garrido, R.; Suárez, J. C.

    2015-05-01

    Harmonic analysis is the fundamental mathematical method used for the identification of pulsation frequencies in asteroseismology and other fields of physics. Here we introduce a test to evaluate the validity of the hypothesis in which Fourier theorem is based: the convergence of the expansion series. The huge number of difficulties found in the interpretation of the periodograms of pulsating stars observed by CoRoT and Kepler satellites lead us to test whether the function underlying these time series is analytic or not. Surprisingly, the main result is that these are originated from non-analytic functions, therefore, the condition for Parseval's theorem is not guaranteed.

  7. Model for bubble pulsation in liquid between parallel viscoelastic layers

    PubMed Central

    Hay, Todd A.; Ilinskii, Yurii A.; Zabolotskaya, Evgenia A.; Hamilton, Mark F.

    2012-01-01

    A model is presented for a pulsating spherical bubble positioned at a fixed location in a viscous, compressible liquid between parallel viscoelastic layers of finite thickness. The Green’s function for particle displacement is found and utilized to derive an expression for the radiation load imposed on the bubble by the layers. Although the radiation load is derived for linear harmonic motion it may be incorporated into an equation for the nonlinear radial dynamics of the bubble. This expression is valid if the strain magnitudes in the viscoelastic layer remain small. Dependence of bubble pulsation on the viscoelastic and geometric parameters of the layers is demonstrated through numerical simulations. PMID:22779461

  8. Connectivity in river deltas

    NASA Astrophysics Data System (ADS)

    Passalacqua, P.; Hiatt, M. R.; Sendrowski, A.

    2016-12-01

    Deltas host approximately half a billion people and are rich in ecosystem diversity and economic resources. However, human-induced activities and climatic shifts are significantly impacting deltas around the world; anthropogenic disturbance, natural subsidence, and eustatic sea-level rise are major causes of threat to deltas and in many cases have compromised their safety and sustainability, putting at risk the people that live on them. In this presentation, I will introduce a framework called Delta Connectome for studying connectivity in river deltas based on different representations of a delta as a network. Here connectivity indicates both physical connectivity (how different portions of the system interact with each other) as well as conceptual (pathways of process coupling). I will explore several network representations and show how quantifying connectivity can advance our understanding of system functioning and can be used to inform coastal management and restoration. From connectivity considerations, the delta emerges as a leaky network that evolves over time and is characterized by continuous exchanges of fluxes of matter, energy, and information. I will discuss the implications of connectivity on delta functioning, land growth, and potential for nutrient removal.

  9. Pen Branch delta expansion

    SciTech Connect

    Nelson, E.A.; Christensen, E.J.; Mackey, H.E.; Sharitz, R.R.; Jensen, J.R.; Hodgson, M.E.

    1984-02-01

    Since 1954, cooling water discharges from K Reactor ({anti X} = 370 cfs {at} 59 C) to Pen Branch have altered vegetation and deposited sediment in the Savannah River Swamp forming the Pen Branch delta. Currently, the delta covers over 300 acres and continues to expand at a rate of about 16 acres/yr. Examination of delta expansion can provide important information on environmental impacts to wetlands exposed to elevated temperature and flow conditions. To assess the current status and predict future expansion of the Pen Branch delta, historic aerial photographs were analyzed using both basic photo interpretation and computer techniques to provide the following information: (1) past and current expansion rates; (2) location and changes of impacted areas; (3) total acreage presently affected. Delta acreage changes were then compared to historic reactor discharge temperature and flow data to see if expansion rate variations could be related to reactor operations.

  10. V496 Scuti: Detection of CO Emission and Dust Shell in a Moderately Fast Fe II Nova

    NASA Astrophysics Data System (ADS)

    Raj, A.; Ashok, N. M.; Banerjee, D. P. K.; Munari, U.; Valisa, P.; Dallaporta, S.

    2014-12-01

    We present near-infrared and optical observations of moderately fast FeII-class Nova Scuti 2009 (V496 Sct) covering various phases; pre-maximum, early decline and nebular, during the first 10 months after its discovery followed by limited observations up to 2011 April. In the initial phase the nova spectra show prominent P Cygni profiles and later all the lines are seen in emission. The notable feature of the near-IR spectra in the early decline phase is the rare presence of the first overtone bands of carbon monoxide (CO) in emission. The IR spectra show clear dust formation in the expanding ejecta at later phase about 150 days after the peak brightness. The presence of lines of elements with low ionization potentials like Na and Mg in the early IR spectra and the detection of CO bands in emission and the dust formation in V496 Sct represents a complete expected sequence in the dust formation in nova ejecta. The light curve shows a slow rise to the maximum and a slow decline indicating a prolonged mass loss. This is corroborated by the strengthening of P Cygni profiles during the first 30 days. The broad and single absorption components seen in many lines in the optical spectra at the time of discovery are replaced by two sharper components in the spectra taken close to the optical maximum brightness. These sharp dips seen in the P Cygni absorption components of Fe II and H I lines during the early decline phase show increasing outflow velocities. The onset of the nebular phase is evident from the optical spectra in 2010 March. During the nebular phase, several emission lines display saddle-like profiles. In the nebular stage, the observed fluxes of [O III] and Hβ lines are used to estimate the electron number densities and the mass of the ejecta. The optical spectra show that the nova is evolved in the PfeAo spectral sequence. The absolute magnitude and the distance to the nova are estimated to be MV = 7.0 ± 0.2 and d = 2.9 ± 0.3 kpc, respectively.

  11. Low-Altitude Satellite Measurements of Pulsating Auroral Electrons

    NASA Technical Reports Server (NTRS)

    Samara, M.; Michell, R. G.; Redmon, R. J.

    2015-01-01

    We present observations from the Defense Meteorological Satellite Program and Reimei satellites, where common-volume high-resolution ground-based auroral imaging data are available. These satellite overpasses of ground-based all-sky imagers reveal the specific features of the electron populations responsible for different types of pulsating aurora modulations. The energies causing the pulsating aurora mostly range from 3 keV to 20 keV but can at times extend up to 30 keV. The secondary, low-energy electrons (<1 keV) are diminished from the precipitating distribution when there are strong temporal variations in auroral intensity. There are often persistent spatial structures present inside regions of pulsating aurora, and in these regions there are secondary electrons in the precipitating populations. The reduction of secondary electrons is consistent with the strongly temporally varying pulsating aurora being associated with field-aligned currents and hence parallel potential drops of up to 1 kV.

  12. Solar Microwave and Geomagnetic Field Pulsations as Space Weather Factors

    NASA Astrophysics Data System (ADS)

    Snegirev, S. D.; Fridman, V. M.; Sheiner, O. A.

    The procedure of short-term prediction of main solar flares was created on the basis of temporal behavior of long-period microwave pulsations [Kobrin et al., 1997]. At the same time it was shown that before these flares one could observe long-period (T > 20 min) pulsations of geomagnetic field [Kobrin et al, 1985]. The resemblance between microwave and geomagnetic pulsations (duration and temporal behaviour) allows us to propose the common nature of these variations: the reflection of solar energy accumulation and instabilities in solar centers of activity. To be an important factor of Space Weather above mentioned pulsations can be useful for constructing the procedures to predict the near Earth's conditions. This work was supported by the Russian Foundation for Fundamental Research and Russian Federal Programm "Astronomy" (grant N 1.5.5.5). Kobrin M.M, Malygin V.I., Snegirev S.D. Plan. Space Sci., 33, N11, p. 1251 (1985). Kobrin M.M., Pakhomov V.V., Snegirev S.D., Fridman V.M., Sheiner O.A. Proc. Workshop `STPW-96', Tokyo: RCW, p. 200 (1997).

  13. Severe Vertebral Erosion by Huge Symptomatic Pulsating Aortic Aneurysm

    PubMed Central

    Jang, Jung Hwan; Kim, Hyeun Sung

    2008-01-01

    Aortic abdominal aneurysm rarely has been reported as causing osteolytic lesions of the spine. It may produce back and radiating pain patterns similar to those of several commonly encountered neurosurgical processes. We report a uncommon complication of huge pulsating aortic aneurysm causing severe vertebral erosion with incapacitating back and radiating pain. PMID:19096617

  14. Low-Altitude Satellite Measurements of Pulsating Auroral Electrons

    NASA Technical Reports Server (NTRS)

    Samara, M.; Michell, R. G.; Redmon, R. J.

    2015-01-01

    We present observations from the Defense Meteorological Satellite Program and Reimei satellites, where common-volume high-resolution ground-based auroral imaging data are available. These satellite overpasses of ground-based all-sky imagers reveal the specific features of the electron populations responsible for different types of pulsating aurora modulations. The energies causing the pulsating aurora mostly range from 3 keV to 20 keV but can at times extend up to 30 keV. The secondary, low-energy electrons (<1 keV) are diminished from the precipitating distribution when there are strong temporal variations in auroral intensity. There are often persistent spatial structures present inside regions of pulsating aurora, and in these regions there are secondary electrons in the precipitating populations. The reduction of secondary electrons is consistent with the strongly temporally varying pulsating aurora being associated with field-aligned currents and hence parallel potential drops of up to 1 kV.

  15. Tracking patchy pulsating aurora through all-sky images

    NASA Astrophysics Data System (ADS)

    Grono, Eric; Donovan, Eric; Murphy, Kyle R.

    2017-07-01

    Pulsating aurora is frequently observed in the evening and morning sector auroral oval. While the precipitating electrons span a wide range of energies, there is increasing evidence that the shape of pulsating auroral patches is controlled by structures in near-equatorial cold plasma; these patches appear to move with convection, for example. Given the tremendous and rapidly increasing amount of auroral image data from which the velocity of these patches can be inferred, it is timely to develop and implement techniques for the automatic identification of pulsating auroral patch events in these data and for the automatic determination of the velocity of individual patches from that data. As a first step towards this, we have implemented an automatic technique for determining patch velocities from sequences of images from the Time History of Events and Macroscale Interactions during Substorms (THEMIS) all-sky imager (ASI) and applied it to many pulsating aurora events. Here we demonstrate the use of this technique and present the initial results, including a comparison between ewograms (east-west keograms) and time series of patch position as determined by the algorithm. We discuss the implications of this technique for remote sensing convection in the inner magnetosphere.

  16. Large-scale coordinated observations of Pc5 pulsation events

    NASA Astrophysics Data System (ADS)

    Mtumela, Zolile; Walker, Anthony D. M.; Stephenson, Judy A. E.; Kosch, Michael J.

    2016-09-01

    HF (high-frequency) radars belonging to SuperDARN (Super Dual Auroral Radar Network) receive backscatter over substantial fields of view which, when combined, allow for simultaneous returns over extensive regions of the polar caps and midlatitudes. This makes them ideal instruments for the observation of pulsations in the Pc5 (1-5 mHz) frequency band. Relatively few pulsation events observed by multiple radars have been reported in the literature. Here we describe observations of three such events which extend over more than 120° of magnetic longitude in the Northern Hemisphere and one of which is also detected in the Southern Hemisphere. All three events show characteristics of field line resonances. In one case the pulsation has also been observed by magnetometers under or near the radar fields of view. The extensive longitudinal coverage allows accurate determination of azimuthal wave numbers. These are at the upper end of the lower values associated with external sources such as those in the solar wind. Such sources imply antisunward flow. However, the azimuthal wave number is negative, implying westward propagation at magnetic local times on both sides of noon, as would be expected from drift-bounce resonance with positive particles. Quiet conditions and a very low ring current during the events argue against this. The identification of the source of pulsations from a number of different mechanisms remains a problem of interest.

  17. Low-altitude satellite measurements of pulsating auroral electrons

    NASA Astrophysics Data System (ADS)

    Samara, M.; Michell, R. G.; Redmon, R. J.

    2015-09-01

    We present observations from the Defense Meteorological Satellite Program and Reimei satellites, where common-volume high-resolution ground-based auroral imaging data are available. These satellite overpasses of ground-based all-sky imagers reveal the specific features of the electron populations responsible for different types of pulsating aurora modulations. The energies causing the pulsating aurora mostly range from 3 keV to 20 keV but can at times extend up to 30 keV. The secondary, low-energy electrons (<1 keV) are diminished from the precipitating distribution when there are strong temporal variations in auroral intensity. There are often persistent spatial structures present inside regions of pulsating aurora, and in these regions there are secondary electrons in the precipitating populations. The reduction of secondary electrons is consistent with the strongly temporally varying pulsating aurora being associated with field-aligned currents and hence parallel potential drops of up to 1 kV.

  18. Radar auroral observations during a burst of irregular magnetic pulsations

    SciTech Connect

    Haldoupis, C.I.; Nielsen, E.; Holtet, J.A.; Egeland, A.; Chivers, H.A.

    1982-03-01

    Micropulsation data from an auroral state are compared with concurrent STARE radar observations from the E region above the station during a substorm event. The substorm onset is marked by a strong burst of irregular pulsations, (Pi B) accompanied by abrupt intensifications in the equivalent current, the backscatter intensity, and the riometer absorption. The magnetic Px and Py pulsation components have a reasonable degree of correlation and the polarization properties of the horizontal disturbance vetor exhibit well-defined changes during the first few minutes after onset. The radio signal undergoes deep quasiperiodic fading that is closely related to simultaneous PiB amplitude variations. The radar Dopplar data, which show normal fluctuations in the electron drift velocity, exclude modulation of radio backscatter by directional variations of the electric field. It is argued that the PiB pulsations and the variations seen in the backscatter are reflecting changes of the ionospheric currents due to conductivity modifications dictated by variations in the field-aligned currents flowing in the region. The possibility exists that the Pi B is closely related to precipitation pulsations as reported by Heacock and Hunsucker (1977).

  19. Observation of pulsating aurora signatures in cosmic noise absorption data

    NASA Astrophysics Data System (ADS)

    Grandin, M.; Kero, A.; Partamies, N.; McKay, D.; Whiter, D.; Kozlovsky, A.; Miyoshi, Y.

    2017-06-01

    This study investigates the contribution of energetic (E > 30 keV) particle precipitation during a pulsating aurora event over Kilpisjärvi (L = 6.2) on 26 February 2014. It is based on the comparison of auroral blue-line emission (427.8 nm) data from an all-sky camera and cosmic noise absorption (CNA) data obtained from a multibeam experiment of the Kilpisjärvi Atmospheric Imaging Receiver Array (KAIRA) riometer. The data sets are compared for three KAIRA beams close to magnetic zenith. Results show a clear correlation between the measured CNA and the auroral blue-line emission during the event, for each beam. In addition, individual pulsations are observed for the first time in the cosmic noise absorption data measured by KAIRA and are found to be close-to-identical to the optical pulsations. This suggests that the modulation of electron precipitation during pulsating aurora takes place in a consistent way over a broad range of energies.

  20. Photometric study of two β Cephei pulsators in eclipsing systems

    NASA Astrophysics Data System (ADS)

    Drobek, D.; Pigulski, A.; Shobbrook, R. R.; Narwid, A.

    2010-12-01

    We present results of a photometric study of the young southern open cluster Stock 14. This cluster is known to contain two eclipsing systems with presumed β Cephei components, HD 101794 and HD 101838. We confirm variability due to pulsations and eclipses in both targets and announce the discovery of other variable stars in the observed field.

  1. Pulsational instabilities in hot pre-horizontal branch stars

    NASA Astrophysics Data System (ADS)

    Battich, Tiara; Miller Bertolami, Marcelo M.; Córsico, Alejandro H.; Althaus, Leandro G.

    2017-09-01

    The ɛ mechanism is a self-excitation mechanism of pulsations which acts on the regions where nuclear burning takes place. It has been shown that the ɛ mechanism can excite pulsations in models of hot helium-core flash, and that the pulsations of LS IV-14· 116, a He-enriched hot subdwarf star, could be explained that way. We aim to study the ɛmechanism effects on models of hot pre-horizontal branch stars and determine, if possible, a domain of instability in the log g — log Teff plane. We compute non-adiabatic non-radial pulsations on such stellar models, adopting different values of initial chemical abundances and mass of the hydrogen envelope at the time of the main helium flash. We find an instability domain of long-period (400 s ≲ P ≲ 2500 s) g-modes for models with 22000K ≲ Teff ≲ 50000K and 4.67 ≲ log g ≲ 6.15.

  2. Discovery of X-ray pulsations from a massive star.

    PubMed

    Oskinova, Lidia M; Nazé, Yael; Todt, Helge; Huenemoerder, David P; Ignace, Richard; Hubrig, Swetlana; Hamann, Wolf-Rainer

    2014-06-03

    X-ray emission from stars much more massive than the Sun was discovered only 35 years ago. Such stars drive fast stellar winds where shocks can develop, and it is commonly assumed that the X-rays emerge from the shock-heated plasma. Many massive stars additionally pulsate. However, hitherto it was neither theoretically predicted nor observed that these pulsations would affect their X-ray emission. All X-ray pulsars known so far are associated with degenerate objects, either neutron stars or white dwarfs. Here we report the discovery of pulsating X-rays from a non-degenerate object, the massive B-type star ξ(1) CMa. This star is a variable of β Cep-type and has a strong magnetic field. Our observations with the X-ray Multi-Mirror (XMM-Newton) telescope reveal X-ray pulsations with the same period as the fundamental stellar oscillations. This discovery challenges our understanding of stellar winds from massive stars, their X-ray emission and their magnetism.

  3. Experimental and numerical study of pulsating transversal jets

    NASA Astrophysics Data System (ADS)

    Goldfeld, M. A.; Fedorova, N. N.; Fedorchenko, I. A.; Pozdnyakov, G. A.; Timofeev, K. Yu.; Zhakharova, Yu. V.

    2015-06-01

    Paper presents results of joint experimental and numerical investigation of pulsating jet penetration into still air and supersonic flow. Goal of the study is to investigate two-dimensional (2D) Hartmann generator (HG) properties and clear up its possibilities in providing better mixing between air and secondary (injected) gases.

  4. The triple-mode pulsating variable V823 Cassiopeiae

    NASA Astrophysics Data System (ADS)

    Jurcsik, J.; Szeidl, B.; Váradi, M.; Henden, A.; Hurta, Zs.; Lakatos, B.; Posztobányi, K.; Klagyivik, P.; Sódor, Á.

    2006-01-01

    Using extended multicolour CCD photometry of the triple-mode radial pulsator V823 Cas we studied the properties of the coupling frequencies invoked by nonlinear processes. Our results support that a resonance connection affects the mode coupling behaviour. The P1/P0 period ratio of V823 Cas has an “out of range” value if compared with the period ratios of the known double mode pulsators, while the P2/P1 period ratio is normal. The periods and period ratios cannot be consistently interpreted without conflict with pulsation and/or evolution models. We describe this failure with the suggestion that at present, the periods of V823 Cas are in a transient, resonance affected state, thus do not reflect the true parameters of the object. The anomalous period change behaviour of the fundamental and second overtone modes supports this idea. We have also raised the possibility that a f0 +f2 = 2f1 resonance may act in triple mode pulsators.

  5. New pulsational properties of eight `anomalous' RR Lyrae variables

    NASA Astrophysics Data System (ADS)

    Clementini, G.; Tosi, M.; Bragaglia, A.; Merighi, R.; Maceroni, C.

    1995-08-01

    CCD photometry in the V band is presented for seven field RR Lyrae stars selected from a sample of eight variables; these, according to data collected in the literature, are expected to be ab-type pulsators, to have short periods (and hence high metallicity), and to be located at a high z from the Galactic plane. New periods and epochs are derived for them. The new periods are only slightly shorter than the values published in the fourth edition of the General Catalogue of Variable Stars (GCVS4). In six cases our amplitude of the light variation is significantly smaller than that published in the GCVS4, and in at least three cases the actual pulsation appears to be in the first harmonic rather than in the fundamental mode. All the suggested c-type pulsators show variations in the amplitude and/or quite scattered light curves. Some possible explanations are given. From a spectrophotometric analysis of the sample, only DL Com is confirmed to pulsate in the fundamental mode, to have a short period, and to be located at a relatively high z. However, a single object cannot be taken as evidence for a significant metal-rich population at a large distance from the Galactic plane.

  6. The detection of photospheric X-ray pulsations from PG 1159-035 with EXOSAT

    NASA Technical Reports Server (NTRS)

    Barstow, M. A.; Holberg, J. B.; Grauer, A. D.; Winget, D. E.

    1986-01-01

    The detection of soft X-ray pulsations from the hot, helium-rich, degenerate object, PG 1159-035 is reported. These observations, obtained with the Low Energy experiment on EXOSAT, show the presence of large-amplitude soft X-ray (44-150 A) pulsations analogous to several of the low-amplitude, nonradial, g-mode pulsations which are observed in the optical. These soft X-ray pulsations, with periods of 516 s, 524 s, and 539 s, arise from the photosphere of PG 1159-035 and constitute the first observations of stellar atmospheric pulsational phenomena in the X-ray band.

  7. Delta hepatitis in Malaysia.

    PubMed

    Sinniah, M; Dimitrakakis, M; Tan, D S

    1986-06-01

    Sera from one hundred and fifty nine Malaysian individuals were screened for the prevalence of delta markers. These included 15 HBsAg positive homosexuals, 16 acute hepatitis B cases, 9 chronic hepatitis B patients, 13 healthy HBsAg carriers and 106 intravenous (i.v.) drug abusers, of whom 27 were positive for HBsAg only and the rest were anti-HBc IgG positive but HBsAg negative. The prevalence of delta markers in the homosexuals was found to be 6.7%, in the HBsAg positive drug abusers 17.8%, in acute hepatitis B cases 12.5%. No evidence of delta infection was detected in healthy HBsAg carriers, chronic hepatitis B cases and HBsAg negative i.v. drug abusers. With reference to i.v. drug abusers, the prevalence of delta markers was higher in Malays (23%) than in Chinese (7%) although the latter had a higher HBsAg carrier rate. Although the HBsAg carrier rate in the homosexuals was high, their delta prevalence rate was low as compared to drug abusers. In Malaysia, as in other non-endemic regions, hepatitis delta virus transmission appeared to occur mainly via the parenteral and sexual routes. This is the first time in Malaysia that a reservoir of delta infection has been demonstrated in certain groups of the population at high risk for hepatitis B.

  8. Nile River Delta, Egypt

    NASA Technical Reports Server (NTRS)

    1984-01-01

    The Nile River Delta of Egypt (30.0N, 31.0E) irrigated by the Nile River and its many distributaries, is some of the richest farm land in the world and home to some 45 million people, over half of Egypt's population. The capital city of Cairo is at the apex of the delta. Just across the river from Cairo can be seen the ancient three big pyramids and sphinx at Giza and the Suez Canal is just to the right of the delta.

  9. Nile Delta, Egypt

    NASA Technical Reports Server (NTRS)

    1982-01-01

    The Nile Delta of Egypt (30.0N, 31.0E) irrigated by the Nile River and its many distributaries, is some of the richest farm land in the world and home to some 45 million people, over half of Egypt's population of 57 million. The capital city of Cairo is at the apex of the delta in the middle of the scene. Across the river from Cairo can be seen the three big pyramids and sphinx at Giza and the Suez Canal is just to the right of the delta.

  10. Nile River Delta, Egypt

    NASA Technical Reports Server (NTRS)

    1984-01-01

    The Nile River Delta of Egypt (30.0N, 31.0E) irrigated by the Nile River and its many distributaries, is some of the richest farm land in the world and home to some 45 million people, over half of Egypt's population. The capital city of Cairo is at the apex of the delta. Just across the river from Cairo can be seen the ancient three big pyramids and sphinx at Giza and the Suez Canal is just to the right of the delta.

  11. Modeling river delta formation

    PubMed Central

    Seybold, Hansjörg; Andrade, José S.; Herrmann, Hans J.

    2007-01-01

    A model to simulate the time evolution of river delta formation process is presented. It is based on the continuity equation for water and sediment flow and a phenomenological sedimentation/erosion law. Different delta types are reproduced by using different parameters and erosion rules. The structures of the calculated patterns are analyzed in space and time and compared with real data patterns. Furthermore, our model is capable of simulating the rich dynamics related to the switching of the mouth of the river delta. The simulation results are then compared with geological records for the Mississippi River. PMID:17940031

  12. Nile River Delta, Egypt

    NASA Image and Video Library

    1984-10-13

    The Nile River Delta of Egypt (30.0N, 31.0E) irrigated by the Nile River and its many distributaries, is some of the richest farm land in the world and home to some 45 million people, over half of Egypt's population. The capital city of Cairo is at the apex of the delta. Just across the river from Cairo can be seen the ancient three big pyramids and sphinx at Giza and the Suez Canal is just to the right of the delta.

  13. ON THE POLARIZATION PROPERTIES OF MAGNETAR GIANT FLARE PULSATING TAILS

    SciTech Connect

    Yang, Yuan-Pei; Zhang, Bing E-mail: zhang@physics.unlv.edu

    2015-12-10

    Three giant flares have been detected so far from soft gamma-ray repeaters, each characterized by an initial short hard spike and a pulsating tail. The observed pulsating tails are characterized by a duration of ∼100 s, an isotropic energy of ∼10{sup 44} erg, and a pulse period of a few seconds. The pulsating tail emission likely originates from the residual energy after the intense energy release during the initial spike, which forms a trapped fireball composed of a photon-pair plasma in a closed-field-line region of the magnetars. Observationally the spectra of pulsating tails can be fitted by the superposition of a thermal component and a power-law component, with the thermal component dominating the emission in the early and late stages of the pulsating-tail observations. In this paper, assuming that the trapped fireball is from a closed-field-line region in the magnetosphere, we calculate the atmospheric structure of the optically thick trapped fireball and the polarization properties of the trapped fireball. By properly treating the photon propagation in a hot, highly magnetized, electron–positron pair plasma, we tally photons in two modes (O mode and E mode) at a certain observational angle through Monte Carlo simulations. Our results suggest that the polarization degree depends on the viewing angle with respect to the magnetic axis of the magnetar, and can be as high as Π ≃ 30% in the 1–30 keV band, and Π ≃ 10% in the 30–100 keV band, if the line of sight is perpendicular to the magnetic axis.

  14. Kappa effect pulsational instability for hot extreme helium stars

    SciTech Connect

    Cox, A.N.

    1990-01-01

    A long standing problem for the hydrogen deficient stars has been the mechanism for the pulsation instability for the hottest members of this class. The usual {kappa} mechanism works well for stars that are in the hydrogen and helium ionization instability strip, and this strip extends to perhaps 20,000K at high luminosity. However, several stars are definitely hotter. Investigations for another ionization instability strip, such as for carbon, have always shown that there is not enough carbon to produce a rapid enough increase of opacity with temperature to give the well-known {kappa} effect. This is so even though these hydrogen deficient stars do show enhanced carbon in their spectra. A strong stellar wind can produce the observed hydrogen deficiency. Another popular mechanism is mass loss in a binary system through the Roche lobe. It now is possible that the missing pulsational instability mechanism is the rapid increase of iron lines absorption as the temperature increases above about 150,000K in the low density envelopes of these luminous stars. Recent calculations shows that the n = 3 to n = 3 transitions in iron that were assumed unimportant in the earlier Los Alamos calculations can double or triple the opacity suddenly as the iron lines appear in a very sensitive part of the spectrum of the diffusing photons. It has been proposed that these iron lines also cause the many varieties of normal B star pulsations, and the hydrogen deficient stars are merely another example of this new {kappa} effect for pulsating stars. The extreme helium star V2076 Oph at 31,900K, and 38,900 L{sub {circle dot}} for a mass of 1.4 M{sub {circle dot}} pulsates in the radial fundamental model at about 1 day period with a very large linear growth rate when the iron lines more than double the opacity, but is stable otherwise.

  15. On the Polarization Properties of Magnetar Giant Flare Pulsating Tails

    NASA Astrophysics Data System (ADS)

    Yang, Yuan-Pei; Zhang, Bing

    2015-12-01

    Three giant flares have been detected so far from soft gamma-ray repeaters, each characterized by an initial short hard spike and a pulsating tail. The observed pulsating tails are characterized by a duration of ˜100 s, an isotropic energy of ˜1044 erg, and a pulse period of a few seconds. The pulsating tail emission likely originates from the residual energy after the intense energy release during the initial spike, which forms a trapped fireball composed of a photon-pair plasma in a closed-field-line region of the magnetars. Observationally the spectra of pulsating tails can be fitted by the superposition of a thermal component and a power-law component, with the thermal component dominating the emission in the early and late stages of the pulsating-tail observations. In this paper, assuming that the trapped fireball is from a closed-field-line region in the magnetosphere, we calculate the atmospheric structure of the optically thick trapped fireball and the polarization properties of the trapped fireball. By properly treating the photon propagation in a hot, highly magnetized, electron-positron pair plasma, we tally photons in two modes (O mode and E mode) at a certain observational angle through Monte Carlo simulations. Our results suggest that the polarization degree depends on the viewing angle with respect to the magnetic axis of the magnetar, and can be as high as Π ≃ 30% in the 1-30 keV band, and Π ≃ 10% in the 30-100 keV band, if the line of sight is perpendicular to the magnetic axis.

  16. Conjugate Event Study of Geomagnetic ULF Pulsations with Wavelet-based Indices

    NASA Astrophysics Data System (ADS)

    Xu, Z.; Clauer, C. R.; Kim, H.; Weimer, D. R.; Cai, X.

    2013-12-01

    The interactions between the solar wind and geomagnetic field produce a variety of space weather phenomena, which can impact the advanced technology systems of modern society including, for example, power systems, communication systems, and navigation systems. One type of phenomena is the geomagnetic ULF pulsation observed by ground-based or in-situ satellite measurements. Here, we describe a wavelet-based index and apply it to study the geomagnetic ULF pulsations observed in Antarctica and Greenland magnetometer arrays. The wavelet indices computed from these data show spectrum, correlation, and magnitudes information regarding the geomagnetic pulsations. The results show that the geomagnetic field at conjugate locations responds differently according to the frequency of pulsations. The index is effective for identification of the pulsation events and measures important characteristics of the pulsations. It could be a useful tool for the purpose of monitoring geomagnetic pulsations.

  17. Fast modulations of pulsating proton aurora related to subpacket structures of Pc1 geomagnetic pulsations at subauroral latitudes

    SciTech Connect

    Ozaki, M.; Shiokawa, K.; Miyoshi, Y.; Kataoka, R.; Yagitani, S.; Inoue, T.; Ebihara, Y.; Jun, C. -W; Nomura, R.; Sakaguchi, K.; Otsuka, Y.; Shoji, M.; Schofield, I.; Connors, M.; Jordanova, V. K.

    2016-08-16

    To understand the role of electromagnetic ion cyclotron (EMIC) waves in determining the temporal features of pulsating proton aurora (PPA) via wave-particle interactions at subauroral latitudes, high-time-resolution (1/8 s) images of proton-induced N2>+ emissions were recorded using a new electron multiplying charge-coupled device camera, along with related Pc1 pulsations on the ground. The observed Pc1 pulsations consisted of successive rising-tone elements with a spacing for each element of 100 s and subpacket structures, which manifest as amplitude modulations with a period of a few tens of seconds. In accordance with the temporal features of the Pc1 pulsations, the auroral intensity showed a similar repetition period of 100 s and an unpredicted fast modulation of a few tens of seconds. Furthermore, these results indicate that PPA is generated by pitch angle scattering, nonlinearly interacting with Pc1/EMIC waves at the magnetic equator.

  18. Fast modulations of pulsating proton aurora related to subpacket structures of Pc1 geomagnetic pulsations at subauroral latitudes

    DOE PAGES

    Ozaki, M.; Shiokawa, K.; Miyoshi, Y.; ...

    2016-08-16

    To understand the role of electromagnetic ion cyclotron (EMIC) waves in determining the temporal features of pulsating proton aurora (PPA) via wave-particle interactions at subauroral latitudes, high-time-resolution (1/8 s) images of proton-induced N2>+ emissions were recorded using a new electron multiplying charge-coupled device camera, along with related Pc1 pulsations on the ground. The observed Pc1 pulsations consisted of successive rising-tone elements with a spacing for each element of 100 s and subpacket structures, which manifest as amplitude modulations with a period of a few tens of seconds. In accordance with the temporal features of the Pc1 pulsations, the auroral intensitymore » showed a similar repetition period of 100 s and an unpredicted fast modulation of a few tens of seconds. Furthermore, these results indicate that PPA is generated by pitch angle scattering, nonlinearly interacting with Pc1/EMIC waves at the magnetic equator.« less

  19. RADIAL STELLAR PULSATION AND THREE-DIMENSIONAL CONVECTION. II. TWO-DIMENSIONAL CONVECTION IN FULL AMPLITUDE RADIAL PULSATION

    SciTech Connect

    Geroux, Chris M.; Deupree, Robert G.

    2013-07-10

    We have developed a three-dimensional radiation hydrodynamics code to simulate the interaction of convection and radial pulsation in classical variable stars. One key goal is the ability to carry these simulations to full amplitude in order to compare them with observed light curves. Previous multi-dimensional calculations were prevented from reaching full amplitude because of drift in the radial coordinate system, due to the algorithm defining radial movement of the coordinate system during the pulsation cycle. We have removed this difficulty by defining our radial coordinate flow algorithm to require that the mass in a spherical shell remain constant for every time step throughout the pulsation cycle. We have used our new code to perform two-dimensional (2D) simulations of the interaction of radial pulsation and convection. We have made comparisons between light curves from our 2D convective simulations with observed light curves and find that our 2D simulated light curves are better able to match the observed light curve shape near the red edge of the RR Lyrae instability strip than light curves from previous one-dimensional time-dependent convective models.

  20. Fast modulations of pulsating proton aurora related to subpacket structures of Pc1 geomagnetic pulsations at subauroral latitudes

    SciTech Connect

    Ozaki, M.; Shiokawa, K.; Miyoshi, Y.; Kataoka, R.; Yagitani, S.; Inoue, T.; Ebihara, Y.; Jun, C. -W; Nomura, R.; Sakaguchi, K.; Otsuka, Y.; Shoji, M.; Schofield, I.; Connors, M.; Jordanova, V. K.

    2016-08-16

    To understand the role of electromagnetic ion cyclotron (EMIC) waves in determining the temporal features of pulsating proton aurora (PPA) via wave-particle interactions at subauroral latitudes, high-time-resolution (1/8 s) images of proton-induced N2>+ emissions were recorded using a new electron multiplying charge-coupled device camera, along with related Pc1 pulsations on the ground. The observed Pc1 pulsations consisted of successive rising-tone elements with a spacing for each element of 100 s and subpacket structures, which manifest as amplitude modulations with a period of a few tens of seconds. In accordance with the temporal features of the Pc1 pulsations, the auroral intensity showed a similar repetition period of 100 s and an unpredicted fast modulation of a few tens of seconds. Furthermore, these results indicate that PPA is generated by pitch angle scattering, nonlinearly interacting with Pc1/EMIC waves at the magnetic equator.

  1. Effects of self-pulsation on the spray characteristics of gas-liquid swirl coaxial injector

    NASA Astrophysics Data System (ADS)

    Kang, Zhongtao; Li, Qinglian; Cheng, Peng; Zhang, Xinqiao; Wang, Zhen-guo

    2016-10-01

    To understand the influence of self-pulsation on the spray characteristics of gas-liquid swirl coaxial injector, a back-lighting photography technique has been employed to capture the instantaneous self-pulsated spray and stable spray images with a high speed camera. The diameter and velocity of the droplets in the spray have been characterized with a Dantec Phase Doppler Anemometry (PDA) system. The effects of self-pulsation on the spray pattern, primary breakup, spray angle, diameter and velocity distribution and mass flow rate distribution are analyzed and discussed. The results show that the spray morphology is greatly influenced by self-pulsation. The stable spray has a cone shape, while the self-pulsated spray looks like a Christmas tree. The main difference of these two sprays is the primary breakup. The liquid film of stable spray keeps stable while that of self-pulsated spray oscillates periodically. The film width of self-pulsated spray varies in a large range with 'neck' and 'shoulder' features existing. The liquid film of self-pulsated spray breaks up at the second neck, and then the second shoulder begins to breakup into ligaments. The self-pulsated spray produces droplet clusters periodically, varies horizontal spray width and mass flux periodically. From the point of spatial distribution, self-pulsation is good for the spray, it uniformizes the mass flux along radius and increases the spray angle. However, when self-pulsation occurs, the SMD distribution varies from an inverted V shape to a hollow cone shape, and SMD increases at all the measuring points. Namely, from the point of atomization performance, self-pulsation has negative effects even when the breakup length is smaller. The effects of self-pulsation on the diameter and velocity distributions of the spray are mainly in the center part of the spray. The periphery of stable and self-pulsated spray has similar diameter and velocity distribution.

  2. Delta agent (Hepatitis D)

    MedlinePlus

    ... this page: //medlineplus.gov/ency/article/000216.htm Hepatitis D (Delta agent) To use the sharing features on this page, please enable JavaScript. Hepatitis D is a viral infection caused by the ...

  3. Delta in Terra Cimmeria

    NASA Image and Video Library

    2011-02-18

    This unnamed crater in northern Terra Cimmeria has a small channel that created a delta feature. Such features are important indicators of liquid water in Mars past as shown in this image from NASA Mars Odyssey.

  4. Federal Funding in the Delta.

    ERIC Educational Resources Information Center

    Reeder, Richard J.; Calhoun, Samuel D.

    2002-01-01

    The Lower Mississippi Delta region, especially the rural Delta, faces many economic challenges. The rural Delta has received much federal aid in basic income support and funding for human resource development, but less for community resource programs, which are important for economic development. Federal aid to the Delta is analyzed in terms of…

  5. Pioneer 10 observations of the Beta Cephei stars Gamma Pegasi and Delta Ceti

    NASA Technical Reports Server (NTRS)

    Peters, Geraldine J.; Ogawa, H. S.; Judge, K. S.; Judge, D. L.

    1987-01-01

    The results of analyzing broad-band Pioneer 10 photometric observations of the low-amplitude pulsating Beta Cephei stars Gamma Pegasi and Delta Ceti are reported. Periods and light curve amplitudes of 3.649 + or - 0.020 hr, 0.05 + or - 0.02 mag for Gamma Peg and 3.869 + or - 0.020 hr, 0.13 + or - 0.02 mag for Delta Ceti are obtained; a power spectrum analysis of the data reveals no other periods. No evidence is found for a phase shift between the light curve maxima in the UV and visible regions. The observed amplitudes combined with published visual and near-UV data suggest a flux and temperature variability of about 200 solar luminosities and 250 K for Gamma Peg and about 600 solar luminosities and 450 K for Delta Cet. These results are compared with others obtained with satellite and ground-based instrumentation.

  6. A Statistical Study of Pulsating Aurora using THEMIS All-sky Ground Imagers

    NASA Astrophysics Data System (ADS)

    Rychert, K. M.; Jones, S.; Lessard, M.; Donovan, E. F.; Spanswick, E. L.

    2009-12-01

    Pulsating aurora is a common phenomenon that occurs primarily in the aftermath of substorms where dim, long period pulsating patches appear. Previous studies on pulsating aurora have used minimal data sets to investigate pulsation periods and MLAT distribution. None of these studies were based on very large data sets, as we now have available. In this study, which includes over half a year of optical data, we determine occurrence rates of pulsating aurora in terms of magnetic latitude and local time, pulsating auroral onsets at different stations to show temporal evolution, relationship to substorms, etc. Preliminary results obtained from the Gillam All-Sky Camera (66°N, 327°E) over 119 days with good optical data beginning September 2007 through the end of March 2008, 74 of which contain pulsating aurora, include: 31.48% of all clear optical data exhibits pulsating aurora, 68.75% of all optically observed pulsating aurora onsets occur post substorm breakup, and a greater likelihood for observing pulsating aurora after midnight (54% probability versus a 14% probability before midnight)

  7. Features of Pc5 pulsations in the geomagnetic field, auroral luminosity, and Riometer absorption

    NASA Astrophysics Data System (ADS)

    Belakhovsky, V. B.; Pilipenko, V. A.; Samsonov, S. N.; Lorentsen, D.

    2016-01-01

    Simultaneous morning Pc5 pulsations ( f ~ 3-5 mHz) in the geomagnetic field, aurora intensities (in the 557.7 and 630.0 nm oxygen emissions and the 471.0 nm nitrogen emission), and riometer absorption, were studied based on the CARISMA, CANMOS, and NORSTAR network data for the event of January 1, 2000. According to the GOES-8 satellite observations, these Pc5 geomagnetic pulsations are observed as incompressible Alfvén waves with toroidal polarization in the magnetosphere. Although the Pc5 pulsation frequencies in auroras, the geomagnetic field, and riometer absorption are close to one another, stable phase relationships are not observed between them. Far from all trains of geomagnetic Pc5 pulsations are accompanied by corresponding auroral pulsations; consequently, geomagnetic pulsations are primary with respect to auroral pulsations. Both geomagnetic and auroral pulsations propagate poleward, and the frequency decreases with increasing geomagnetic latitude. When auroral Pc5 pulsations appear, the ratio of the 557.7/630.0 nm emission intensity sharply increases, which indicates that auroral pulsations result from not simply modulated particle precipitation but also an additional periodic acceleration of auroral electrons by the wave field. A high correlation is not observed between Pc5 pulsations in auroras and the riometer absorption, which indicates that these pulsations have a common source but different generation mechanisms. Auroral luminosity modulation is supposedly related to the interaction between Alfvén waves and the region with the field-aligned potential drop above the auroral ionosphere, and riometer absorption modulation is caused by the scattering of energetic electrons by VLF noise pulsations.

  8. The occurrence of non-pulsating stars in the γ Dor and δ Sct pulsation instability regions: Results from Kepler quarter 14–17 data

    DOE PAGES

    Guzik, J. A.; Bradley, P. A.; Jackiewicz, J.; ...

    2015-04-21

    In this study, the high precision long time-series photometry of the NASA Kepler spacecraft provides an excellent means to discover and characterize variability in main-sequence stars, and to make progress in interpreting the pulsations to derive stellar interior structure and test stellar models. For stars of spectral types A–F, the Kepler data revealed a number of surprises, such as more hybrid pulsating Sct and Dor pulsators than expected, pulsators lying outside of the instability regions predicted by theory, and stars that were expected to pulsate, but showed no variability. In our 2013 Astronomical Review article, we discussed the statistics ofmore » variability for 633 faint (Kepler magnitude 14–16) spectral type A–F stars observed by Kepler during Quarters 6–13 (June 2010–June 2012).« less

  9. The occurrence of non-pulsating stars in the γ Dor and δ Sct pulsation instability regions: Results from Kepler quarter 14–17 data

    SciTech Connect

    Guzik, J. A.; Bradley, P. A.; Jackiewicz, J.; Molenda-Zakowicz, J.; Uytterhoeven, K.; Kinemuchi, K.

    2015-04-21

    In this study, the high precision long time-series photometry of the NASA Kepler spacecraft provides an excellent means to discover and characterize variability in main-sequence stars, and to make progress in interpreting the pulsations to derive stellar interior structure and test stellar models. For stars of spectral types A–F, the Kepler data revealed a number of surprises, such as more hybrid pulsating Sct and Dor pulsators than expected, pulsators lying outside of the instability regions predicted by theory, and stars that were expected to pulsate, but showed no variability. In our 2013 Astronomical Review article, we discussed the statistics of variability for 633 faint (Kepler magnitude 14–16) spectral type A–F stars observed by Kepler during Quarters 6–13 (June 2010–June 2012).

  10. SEISMOLOGY OF A MASSIVE PULSATING HYDROGEN ATMOSPHERE WHITE DWARF

    SciTech Connect

    Kepler, S. O.; Pelisoli, Ingrid; Pecanha, Viviane; Costa, J. E. S.; Fraga, Luciano; Hermes, J. J.; Winget, D. E.; Castanheira, Barbara; Corsico, A. H.; Romero, A. D.; Althaus, Leandro; Kleinman, S. J.; Nitta, A.; Koester, D.; Kuelebi, Baybars; Kanaan, Antonio

    2012-10-01

    We report our observations of the new pulsating hydrogen atmosphere white dwarf SDSS J132350.28+010304.22. We discovered periodic photometric variations in frequency and amplitude that are commensurate with nonradial g-mode pulsations in ZZ Ceti stars. This, along with estimates for the star's temperature and gravity, establishes it as a massive ZZ Ceti star. We used time-series photometric observations with the 4.1 m SOAR Telescope, complemented by contemporary McDonald Observatory 2.1 m data, to discover the photometric variability. The light curve of SDSS J132350.28+010304.22 shows at least nine detectable frequencies. We used these frequencies to make an asteroseismic determination of the total mass and effective temperature of the star: M{sub *} = 0.88 {+-} 0.02 M{sub Sun} and T{sub eff} = 12, 100 {+-} 140 K. These values are consistent with those derived from the optical spectra and photometric colors.

  11. Seismology of a Massive Pulsating Hydrogen Atmosphere White Dwarf

    NASA Astrophysics Data System (ADS)

    Kepler, S. O.; Pelisoli, Ingrid; Peçanha, Viviane; Costa, J. E. S.; Fraga, Luciano; Hermes, J. J.; Winget, D. E.; Castanheira, Barbara; Córsico, A. H.; Romero, A. D.; Althaus, Leandro; Kleinman, S. J.; Nitta, A.; Koester, D.; Külebi, Baybars; Jordan, Stefan; Kanaan, Antonio

    2012-10-01

    We report our observations of the new pulsating hydrogen atmosphere white dwarf SDSS J132350.28+010304.22. We discovered periodic photometric variations in frequency and amplitude that are commensurate with nonradial g-mode pulsations in ZZ Ceti stars. This, along with estimates for the star's temperature and gravity, establishes it as a massive ZZ Ceti star. We used time-series photometric observations with the 4.1 m SOAR Telescope, complemented by contemporary McDonald Observatory 2.1 m data, to discover the photometric variability. The light curve of SDSS J132350.28+010304.22 shows at least nine detectable frequencies. We used these frequencies to make an asteroseismic determination of the total mass and effective temperature of the star: M sstarf = 0.88 ± 0.02 M ⊙ and T eff = 12, 100 ± 140 K. These values are consistent with those derived from the optical spectra and photometric colors.

  12. The Pulsating, Accreting White Dwarf in GW Lib after Outburst

    NASA Astrophysics Data System (ADS)

    Szkody, Paula

    The first known pulsating white dwarf in an accreting close binary system (GW Lib) underwent an outburst in April, 2007. We aim to follow the pulsation spectrum as the white dwarf cools back to to its quiescent temperature from its heating due to the outburst which should take about 3 years. As it cools, it should re-enter the instability strip and we can witness changes in the driving mechanism and detect modes that are excited by the temperature changes. The higher pulse amplitude in UV vs optical and the available time-tag mode makes GALEX the instrument of choice. The data in 2008 will be combined with our DOT time in May, June 2007 to provide coverage of the largest cooling that takes place in the year following outburst. Since the few known systems only outburst every 20-30 yrs, this is the first opportunity to accomplish a study of this type."

  13. Quantitative results of stellar evolution and pulsation theories.

    NASA Technical Reports Server (NTRS)

    Fricke, K.; Stobie, R. S.; Strittmatter, P. A.

    1971-01-01

    The discrepancy between the masses of Cepheid variables deduced from evolution theory and pulsation theory is examined. The effect of input physics on evolutionary tracks is first discussed; in particular, changes in the opacity are considered. The sensitivity of pulsation masses to opacity changes and to the ascribed values of luminosity and effective temperature are then analyzed. The Cepheid mass discrepancy is discussed in the light of the results already obtained. Other astronomical evidence, including the mass-luminosity relation for main sequence stars, the solar neutrino flux, and cluster ages are also considered in an attempt to determine the most likely source of error in the event that substantial mass loss has not occurred.

  14. Quasi-periodic pulsations in partially occulted flares

    NASA Astrophysics Data System (ADS)

    Szaforz, Zaneta; Tomczak, Michal

    The model of oscillating magnetic traps (OMT) suggests that the cusp-like magnetic structures located in an upper part of flare loops are responsible for quasi-periodic pulsations (QPP) observed sometimes in hard X-rays (HXR). Electrons within these oscillating traps are efficiently accelerated and confined, therefore the traps should be recognize as loop-top HXR sources. However, these sources are difficult for reconstruction in the presence of the stronger footpoint HXR sources. To overcome this problem, we analyzed partially occulted flares, observed by Yohkoh, from the survey of Tomczak (2009). We will present the correlation between the diameter of the loop-top HXR source and the period of pulsations. We will present also some interesting examples of observations, for which changes in QPPs coincide with the changes in appearance of loop-top sources.

  15. Pulsating aurora induced by upper atmospheric barium releases

    NASA Technical Reports Server (NTRS)

    Deehr, C.; Romick, G.

    1977-01-01

    The paper reports the apparent generation of pulsating aurora by explosive releases of barium vapor near 250 km altitude. This effect occurred only when the explosions were in the path of precipitating electrons associated with the visible aurora. Each explosive charge was a standard 1.5 kg thermite mixture of Ba and CuO with an excess of Ba metal which was vaporized and dispersed by the thermite explosion. Traces of Sr, Na, and Li were added to some of the charges, and monitoring was achieved by ground-based spectrophotometric observations. On March 28, 1976, an increase in emission at 5577 A and at 4278 A was observed in association with the first two bursts, these emissions pulsating with roughly a 10 sec period for approximately 60 to 100 sec after the burst.

  16. Comparative pulsation calculations with OP and OPAL opacities

    NASA Technical Reports Server (NTRS)

    Kanbur, Shashi M.; Simon, Norman R.

    1994-01-01

    Comparative linear nonadiabatic pulsation calculations are presented using the OPAL and Opacity Project opacities. The two sets of opacities include effects due to intermediate coupling and fine structure as well as new abundances. We used two mass luminosity (M-L) relations, one standard (BIT), and one employing substantial convective core overshoot (COV). The two sets of opacities cannot be differentiated on the basis of the stellar pulsation calculations presented here. The BIT relation can model the beat and bump Cepheids with masses between 4 and 7 solar mass, while if the overshoot relation is used, masses between 2 and 6 solar mass are required. In the RR Lyrae regime, we find the inferred masses of globular cluster RRd stars to be little influenced by the choice of OPAL or OP. Finally, the limited modeling we have done is not able to constrain the Cepheid M-L relation based upon period ratios observed in the beat and bump stars.

  17. New radial pulsation constants for the Beta Cephei variables

    NASA Astrophysics Data System (ADS)

    Shobbrook, R. R.

    1985-05-01

    Recent new calibrations of luminosities, temperatures and bolometric corrections for B stars in terms of the β index and the Strömgren parameter c0 have necessitated the recalculation of the radial pulsation constants, Q, for the β Cephei (of β Canis Majoris) variable stars. Corrections for the effect of binaries on the absolute magnitudes, derived both from the luminosity calibration and from the mean distance moduli of those variables in clusters, are calculated in an Appendix. The mean value of Q, although determined from absolute magnitudes which are about 0.4 mag fainter than those from previous calibrations of the β index, still suggests that the majority of the variables are pulsating in the first overtone radial mode, as have most investigations in recent years.

  18. The unique dynamical system underlying RR Lyrae pulsations

    NASA Astrophysics Data System (ADS)

    Kollath, Z.

    2016-05-01

    Hydrodynamic models of RR Lyrae pulsation display a very rich behaviour. Contrary to earlier expectations, high order resonances play a crucial role in the nonlinear dynamics representing the interacting modes. Chaotic attractors can be found at different time scales: both in the pulsation itself and in the amplitude equations shaping the possible modulation of the oscillations. Although there is no one-to-one connection between the nonlinear features found in the numerical models and the observed behaviour, the richness of the found phenomena suggests that the interaction of modes should be taken seriously in the study of the still unsolved puzzle of Blazhko effect. One of the main lessons of this complex system is that we should rethink the simple interpretation of the observed effect of resonances.

  19. HST observations of the pulsating white dwarf GD 358

    NASA Astrophysics Data System (ADS)

    Castanheira, B. G.; Nitta, A.; Kepler, S. O.; Winget, D. E.; Koester, D.

    2005-03-01

    We used time-resolved ultraviolet spectroscopy obtained with the FOS and STIS spectrographs of the Hubble Space Telescope (HST), together with archival IUE observations to measure the effective temperature (Teff), surface gravity (log g) and distance (d) of the pulsating DB white dwarf GD 358 with unprecedented accuracy, and to show that the temperature did not change during the 1996 sforzando, when the star changed basically to a single mode pulsator. We also measured for the first time for a DBV the spherical harmonic degree (ℓ) for two modes, with k=8 and k=9, which was only possible because the stellar light curve was dominated by a single mode in 1996. The independent spectra provide the following values: Teff=24 100± 400 K, log g=7.91±0.26 and d=42.7±2.5 pc. The ultraviolet spectroscopic distance is in better agreement with the seismological value, than the one derived by parallax.

  20. The First Six Outbursting Cool DA White Dwarf Pulsators

    NASA Astrophysics Data System (ADS)

    Bell, K. J.; Hermes, J. J.; Montgomery, M. H.; Winget, D. E.; Gentile Fusillo, N. P.; Raddi, R.; Gänsicke, B. T.

    2017-03-01

    Extensive observations from the Kepler spacecraft have recently revealed a new outburst phenomenon operating in cool pulsating DA (hydrogen atmosphere) white dwarfs (DAVs). With the introduction of two new outbursting DAVs from K2 Fields 7 (EPIC 229228364) and 8 (EPIC 220453225) in these proceedings, we presently know of six total members of this class of object. We present the observational commonalities of the outbursting DAVs: (1) outbursts that increase the mean stellar flux by up to ≍15%, last many hours, and recur irregularly on timescales of days; (2) effective temperatures that locate them near the cool edge of the DAV instability strip; and (3) rich pulsation spectra with modes that are observed to wander in amplitude/frequency.

  1. Some insights into stellar structure from nonlinear pulsations

    NASA Astrophysics Data System (ADS)

    Goupil, M. J.

    1993-12-01

    Efficient tools of investigation of stellar pulsation are the integral relations which link oscillation frequencies to the static structure of stellar models, as provided by the linear theory of pulsation. Similarly, oscillation amplitudes and phases, which arise from nonlinear processes, can be related to the stellar structure by means of amplitude equation formalisms. For the simple case of a monoperiodic oscillation, involving only one unstable marginal mode, such a formalism shows that the (limit cycle) radius variations, at time t and mass level m, can be approximated, up to second order of approximation. The nonlinear, nonadiabatic coefficients, are integrals over mass of kernels which depend on eigenfrequencies, eigenfunctions, on second and third order Taylor quantities from the equations modelling the star. They can either be computed from static models (Klapp et al., 1985) or obtained by numerical fits of hydrodynamical results (Kovacs and Buchler, 1989).

  2. Comparative pulsation calculations with OP and OPAL opacities

    NASA Technical Reports Server (NTRS)

    Kanbur, Shashi M.; Simon, Norman R.

    1994-01-01

    Comparative linear nonadiabatic pulsation calculations are presented using the OPAL and Opacity Project opacities. The two sets of opacities include effects due to intermediate coupling and fine structure as well as new abundances. We used two mass luminosity (M-L) relations, one standard (BIT), and one employing substantial convective core overshoot (COV). The two sets of opacities cannot be differentiated on the basis of the stellar pulsation calculations presented here. The BIT relation can model the beat and bump Cepheids with masses between 4 and 7 solar mass, while if the overshoot relation is used, masses between 2 and 6 solar mass are required. In the RR Lyrae regime, we find the inferred masses of globular cluster RRd stars to be little influenced by the choice of OPAL or OP. Finally, the limited modeling we have done is not able to constrain the Cepheid M-L relation based upon period ratios observed in the beat and bump stars.

  3. Quantitative results of stellar evolution and pulsation theories.

    NASA Technical Reports Server (NTRS)

    Fricke, K.; Stobie, R. S.; Strittmatter, P. A.

    1971-01-01

    The discrepancy between the masses of Cepheid variables deduced from evolution theory and pulsation theory is examined. The effect of input physics on evolutionary tracks is first discussed; in particular, changes in the opacity are considered. The sensitivity of pulsation masses to opacity changes and to the ascribed values of luminosity and effective temperature are then analyzed. The Cepheid mass discrepancy is discussed in the light of the results already obtained. Other astronomical evidence, including the mass-luminosity relation for main sequence stars, the solar neutrino flux, and cluster ages are also considered in an attempt to determine the most likely source of error in the event that substantial mass loss has not occurred.

  4. Experimental investigation on a pulsating heat pipe with hydrogen

    NASA Astrophysics Data System (ADS)

    Deng, H. R.; Liu, Y. M.; Ma, R. F.; Han, D. Y.; Gan, Z. H.; Pfotenhauer, J. M.

    2015-12-01

    The pulsating heat pipe (PHP) has been increasingly studied in cryogenic application, for its high transfer coefficient and quick response. Compared with Nb3Sn and NbTi, MgB2 whose critical transformation temperature is 39 K, is expected to replace some high-temperature superconducting materials at 25 K. In order to cool MgB2, this paper designs a Hydrogen Pulsating Heat Pipe, which allows a study of applied heat, filling ratio, turn number, inclination angle and length of adiabatic section on the thermal performance of the PHP. The thermal performance of the hydrogen PHP is investigated for filling ratios of 35%, 51%, 70% at different heat inputs, and provides information regarding the starting process is received at three filling ratios.

  5. Mississippi River Delta

    NASA Image and Video Library

    2002-06-11

    As the Mississippi River enters the Gulf of Mexico, it loses energy and dumps its load of sediment that it has carried on its journey through the mid continent. This pile of sediment, or mud, accumulates over the years building up the delta front. As one part of the delta becomes clogged with sediment, the delta front will migrate in search of new areas to grow. The area shown on this image is the currently active delta front of the Mississippi. The migratory nature of the delta forms natural traps for oil. Most of the land in the image consists of mud flats and marsh lands. There is little human settlement in this area due to the instability of the sediments. The main shipping channel of the Mississippi River is the broad stripe running northwest to southeast. This image was acquired on May 24, 2001 by the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) on NASA's Terra satellite. With its 14 spectral bands from the visible to the thermal infrared wavelength region, and its high spatial resolution of 15 to 90 meters (about 50 to 300 feet), ASTER will image Earth for the next 6 years to map and monitor the changing surface of our planet. http://photojournal.jpl.nasa.gov/catalog/PIA03497

  6. Turbulent heat exchanger {Delta}T and {Delta}P

    SciTech Connect

    Steinmeyer, D.

    1996-12-31

    Optimum pressure drop ({Delta}P) and temperature difference ({Delta}T) in turbulent flow heat exchangers are presented in three frameworks: as quantitatively defined by fluid properties, the value of energy and the cost of heat exchange surface (with a little help from a relationship between [power/mass] and heat transfer); as the energy cost for heat recovery (with the {Delta}T cost being about equal to the heat exchanger cost and the {Delta}P cost being about 1/3 as great); and as the second law lost work inherent in heat exchange (with the {Delta}T loss being {approximately}3 times the {Delta}T loss).

  7. Self-Sustained Ultrafast Pulsation in Coupled VCSELs

    NASA Technical Reports Server (NTRS)

    Ning, Cun-Zheng

    2001-01-01

    High frequency, narrow-band self-pulsating operation is demonstrated in two coupled vertical-cavity surface-emitting lasers (VCSELs). The coupled VCSELs provide an ideal source for high-repetition rate (over 40 GHz), sinusoidal-like modulated laser source with Gaussian-like near- and far-field profiles. We also show that the frequency of the modulation can be tuned by the inter-VCSEL separation or by DC-bias level.

  8. The effect of cushion-ram pulsation on hot stamping

    NASA Astrophysics Data System (ADS)

    Landgrebe, Dirk; Rautenstrauch, Anja; Kunke, Andreas; Polster, Stefan; Kriechenbauer, Sebastian; Mauermann, Reinhard

    2016-10-01

    Hot stamping is an important technology for manufacturing high-strength components. This technology offers the possibility to achieve significant weight reductions. In this study, cushion-ram pulsation (CRP), a new technology for hot stamping on servo-screw presses, was investigated and applied for hot stamping. Compared to a conventional process, the tests yielded a significantly higher drawing depth. In this paper, the CRP technology and the first test results with hot stamping were described in comparison to the conventional process.

  9. Self-pulsation threshold of Raman amplified Brillouin fiber cavities.

    PubMed

    Ott, J R; Pedersen, M E V; Rottwitt, K

    2009-08-31

    An implicit equation for the oscillation threshold of stimulated Brillouin scattering from Raman amplified signals in fibers with external feedback is derived under the assumption of no depletion. This is compared to numerical investigations of Raman amplification schemes showing good agreement for high reflectivities. For low reflectivities and high attenuation or long fibers, the assumption of no depletion is shown not to be valid. In these cases the effects of the depletion on the self-pulsation is examined.

  10. Mapping the Properties of Convection in Pulsating White Dwarfs

    NASA Astrophysics Data System (ADS)

    Dalessio, J.; Provencal, J. L.; Montgomery, M. H.; Shipman, H. L.

    2013-01-01

    Montgomery (2005) showed that the properties of a pulsating white dwarf's convection zone can be determined by fitting the observed lightcurves with model simulations. The Whole Earth Telescope (WET) and the Delaware Asteroseismic Research Center (DARC) are using this technique to map the properties of convection across the DA and DB instability strips. We present the current status of the project, including preliminary analysis of light curves and from recent WET campaigns.

  11. Pulsating stars as distance indicators and stellar population tracers

    NASA Astrophysics Data System (ADS)

    Musella, I.

    Pulsating stars can play a fundamental role as distance indicators to set the astronomical distance scale and to trace different stellar populations to infer information on the star formation history of the host galaxy. The most interesting variables are Classical Cepheids and RR Lyrae. A review of the properties of these variables and of the theoretical and observational approaches adopted in the literature are presented.

  12. Photometric Analysis of Two Candidate Pulsating Early Stars

    NASA Astrophysics Data System (ADS)

    Sonnett, S. M.; Dukes, R. J.

    2004-12-01

    Both HD199122 and HD213617 are found to be periodic with frequencies within the characteristic range of g-mode pulsation for either the Slowly Pulsating B Stars (SPBs) or the Gamma Doradus stars. We began observing HD199122 as a SPB based on its appearance in the list of such stars found through Hipparcos data examination by Koen (MNRAS, 321, 44, 2001). However, as noted by Koen, its reported spectral type A2 is late for an SPB. Based on published photometric indices, he suggests that its spectral type is closer to B7 and thus it is likely to be a SPB. Using Stromgren uvby photometry, we have examined over 600 differential measures of this star. We find two clear frequencies of f1 = 0.80209 c/d and f2 = 0.82444 c/d, which is within the characteristic range for g-mode pulsation of hotter main sequence stars. Our data suggests the possible presence of a third frequency, but confirmation is pending more data analysis. A preliminary analysis of Hipparcos satellite data for HD 213617 proposes a frequency of 0.55672 c/d (Handler, G.MNRAS 309, L19-L23,1999). However, Castellano (private communication) has found a period closer to 0.8 c/d from his analysis of the Hipparcos data. Since this star is an early F type, confirmation of this pulsational value could classify this star as a Gamma Doradus variable. We are presently obtaining observations for both subjects and will continue analysis as data arrives. Observations of HD213617 were begun as part of a summer project as part of the NASA Academy at Ames. This work has been supported by South Carolina Space Grant and NSF grant AST-0071260 to the College of Charleston,.

  13. Studies of the Long Secondary Periods in Pulsating Red Giants

    NASA Astrophysics Data System (ADS)

    Percy, J. R.; Deibert, E.

    2016-12-01

    We have used systematic, sustained visual observations from the AAVSO International Database and the AAVSO time-series analysis package VSTAR to study the unexplained "long secondary periods" (LSPs) in 27 pulsating red giants. In our sample, the LSPs range from 479 to 2967 days, and are on average 8.1 +/- 1.3 times the excited pulsation period. There is no evidence for more than one LSP in each star. In stars with both the fundamental and first overtone radial period present, the LSP is more often about 10 times the latter. The visual amplitudes of the LSPs are typically 0.1 magnitude and do not correlate with the LSP. The phase curves tend to be sinusoidal, but at least two are sawtooth. The LSPs are stable, within their errors, over the timespan of our data, which is typically 25,000 days. The amplitudes, however, vary by up to a factor of two or more on a time scale of roughly 20-30 LSPs. There is no obvious difference between the carbon (C) stars and the normal oxygen (M) stars. Previous multicolor observations showed that the LSP color variations are similar to those of the pulsation period, and of the LSPs in the Magellanic Clouds, and not like those of eclipsing stars. We note that the LSPs are similar to the estimated rotation periods of the stars, though the latter have large uncertainties. This suggests that the LSP phenomenon may be a form of modulated rotational variability.

  14. Interhemispheric asymmetry of the amplitudes of Pc3 geomagnetic pulsations

    NASA Astrophysics Data System (ADS)

    Heilig, B.; Pilipenko, V.; Sutcliffe, P.

    2012-04-01

    The interhemispheric asymmetry between the amplitude of geomagnetic pulsations was realised already in the 1960s'. Most of the observers (Yumoto et al., 1988; Saito et al., 1989; Takahashi et al., 1994; Obana et al., 2005) reported that the energy of Pc3 (Pc4) pulsations were found to be significantly larger on the winter hemisphere (i.e. in December on the Northern hemisphere and in June in the Southern hemisphere) when comparing conjugate observations. The authors linked this behaviour to the seasonal conductivity changes of the ionosphere, however, no modelling effort were made to explain the observed behaviour. In the presented paper we make an attempt to model the seasonal asymmetry based on the model of Pilipenko et al (2008). Using data recorded at geomagnetically conjugate stations, Tihany (THY, Hungary) and Hermanus (HER, South Africa) between 2002 and 2007 we present a case where an anomalous seasonal variation can be observed. The observed amplitudes were significantly larger in local summer than in local winter, but only in years near the sunspot maximum. This is exactly the opposite what was found for other station pairs. It was also observed that the range of the seasonal variation of the HER/THY ratio diminishes with the decrease of the solar index F10.7. The phenomenon was first realised by Vero (1965) who linked the anomalous winter attenuation of pulsations to the anomalously high F2 region electron density of the ionosphere. A clear physical interpretation of these results is still missing.

  15. Temporal Characteristics and Energy Deposition of Pulsating Auroral Patches

    NASA Technical Reports Server (NTRS)

    Humberset, B. K.; Gjerloev, J. W.; Samara, M.; Michell, R. G.; Mann, I. R.

    2016-01-01

    We present a careful statistical analysis of pulsating aurora (PA) using all-sky green line (557.7 nm) images obtained at 3.3 Hz. Six well-defined individual PA patches are identified and extracted using a contouring technique. Quantitative parameters such as the patch duration (on-time and off-time), peak intensity, and integrated intensity are determined for each patch and each pulsation. The resulting characteristics serve as strict observational constraints that any of the many competing theories attempting to explain PA must predict. The purpose of this paper is to determine the characteristics of PA patches in order to provide better observational constraints on the suggested mechanisms. All aspects of the temporal behavior of the individual patches appear to be erratic. Historically, PA has been defined very loosely and we argue that the use of the term pulsating is inappropriate since our findings and other published results are not regularly periodic and thus a more appropriate term may be fluctuating aurora. Further, we find that the observational constraints do not fit well with the flow cyclotron maser theory, which in particular is suggested to create PA patches. There is no clear candidate of the suggested mechanisms and drivers to explain the observational constraints set by the PA patches in a satisfactory manner.

  16. Accreting Pulsators Gw Lib and V455 and after Superoutburst

    NASA Astrophysics Data System (ADS)

    Szkody, Paula

    Two cataclysmic variables containing pulsating white dwarfs underwent rare outbursts in 2007 (GW Lib and V455 And). As we know outbursts heat the white dwarfs by more than 10,000K and they gradually cool to their quiescent temperatures over the course of about 3 years, these two objects present the first unique opportunity to follow the pulsation spectrum of a white dwarf as it cools on much more rapid timescales than evolutionary ones for single white dwarfs. As these 2 objects cool, they should re-enter their instability strips and we can witness changes in the driving mechanism and detect modes that are excited by the T changes. Our 2008 ground-based data on GW Lib showed an intermittent new pulsation at a longer period than at quiescence. The data in 2010 will be the critical 3rd year and will be combined with our DOT and Cycle 4,5 GI observations to determine the long term cooling of GW Lib. Similar information will be obtained for V455 And. The higher pulse amplitude in UV vs optical and the time-tag mode means that GALEX can provide optimum data over the optical. Data on both systems will provide an important contrast in how the white dwarfs react to an outburst, as GW Lib at quiescence has a hot white dwarf far outside the normal instability strip for non-accreting white dwarfs, while V455 And is cool and inside this strip.

  17. Mass-spring model of a self-pulsating drop.

    PubMed

    Antoine, Charles; Pimienta, Véronique

    2013-12-03

    Self-pulsating sessile drops are a striking example of the richness of far-from-equilibrium liquid/liquid systems. The complex dynamics of such systems is still not fully understood, and simple models are required to grasp the mechanisms at stake. In this article, we present a simple mass-spring mechanical model of the highly regular drop pulsations observed in Pimienta, V.; Brost, M.; Kovalchuk, N.; Bresch, S.; Steinbock, O. Complex shapes and dynamics of dissolving drops of dichloromethane. Angew. Chem., Int. Ed. 2011, 50, 10728-10731. We introduce an effective time-dependent spreading coefficient that sums up all of the forces (due to evaporation, solubilization, surfactant transfer, coffee ring effect, solutal and thermal Marangoni flows, drop elasticity, etc.) that pull or push the edge of a dichloromethane liquid lens, and we show how to account for the periodic rim breakup. The model is examined and compared against experimental observations. The spreading parts of the pulsations are very rapid and cannot be explained by a constant positive spreading coefficient or superspreading.

  18. Development of a balloon volume sensor for pulsating balloon catheters.

    PubMed

    Nolan, Timothy D C; Hattler, Brack G; Federspiel, William J

    2004-01-01

    Helium pulsed balloons are integral components of several cardiovascular devices, including intraaortic balloon pumps (IABP) and a novel intravenous respiratory support catheter. Effective use of these devices clinically requires full inflation and deflation of the balloon, and improper operating conditions that lead to balloon under-inflation can potentially reduce respiratory or cardiac support provided to the patient. The goal of the present study was to extend basic spirographic techniques to develop a system to dynamically measure balloon volumes suitable for use in rapidly pulsating balloon catheters. The dynamic balloon volume sensor system (DBVSS) developed here used hot wire anemometry to measure helium flow in the drive line from console to catheter and integrated the flow to determine the volume delivered in each balloon pulsation. An important component of the DBVSS was an algorithm to automatically detect and adjust flow signals and measured balloon volumes in the presence of gas composition changes that arise from helium leaks occurring in these systems. The DBVSS was capable of measuring balloon volumes within 5-10% of actual balloon volumes over a broad range of operating conditions relevant to IABP and the respiratory support catheter. This includes variations in helium concentration from 70-100%, pulsation frequencies from 120-480 beats per minute, and simulated clinical conditions of reduced balloon filling caused by constricted vessels, increased driveline, or catheter resistance.

  19. THE PULSATION MODE AND DISTANCE OF THE CEPHEID FF AQUILAE

    SciTech Connect

    Turner, D. G.; Kovtyukh, V. V.; Luck, R. E.; Berdnikov, L. N. E-mail: val@deneb1.odessa.ua E-mail: leonid.berdnikov@gmail.com

    2013-07-20

    The determination of pulsation mode and distance for field Cepheids is a complicated problem best resolved by a luminosity estimate. For illustration a technique based on spectroscopic luminosity discrimination is applied to the 4.47 day s-Cepheid FF Aql. Line ratios in high dispersion spectra of the variable yield values of (M{sub V} ) = -3.40 {+-} 0.02 s.e. ({+-}0.04 s.d.), average effective temperature T{sub eff} = 6195 {+-} 24 K, and intrinsic color ((B) - (V)){sub 0} = +0.506 {+-} 0.007, corresponding to a reddening of E{sub B-V} = 0.25 {+-} 0.01, or E{sub B-V}(B0) = 0.26 {+-} 0.01. The skewed light curve, intrinsic color, and luminosity of FF Aql are consistent with fundamental mode pulsation for a small-amplitude classical Cepheid on the blue side of the instability strip, not a sinusoidal pulsator. A distance of 413 {+-} 14 pc is estimated from the Cepheid's angular diameter in conjunction with a mean radius of (R) = 39.0 {+-} 0.7 R{sub Sun} inferred from its luminosity and effective temperature. The dust extinction toward FF Aql is described by a ratio of total-to-selective extinction of R{sub V} = A{sub V} /E(B - V) = 3.16 {+-} 0.34 according to the star's apparent distance modulus.

  20. Temporal characteristics and energy deposition of pulsating auroral patches

    NASA Astrophysics Data System (ADS)

    Humberset, B. K.; Gjerloev, J. W.; Samara, M.; Michell, R. G.; Mann, I. R.

    2016-07-01

    We present a careful statistical analysis of pulsating aurora (PA) using all-sky green line (557.7 nm) images obtained at 3.3 Hz. Six well-defined individual PA patches are identified and extracted using a contouring technique. Quantitative parameters such as the patch duration (on-time and off-time), peak intensity, and integrated intensity are determined for each patch and each pulsation. The resulting characteristics serve as strict observational constraints that any of the many competing theories attempting to explain PA must predict. The purpose of this paper is to determine the characteristics of PA patches in order to provide better observational constraints on the suggested mechanisms. All aspects of the temporal behavior of the individual patches appear to be erratic. Historically, PA has been defined very loosely and we argue that the use of the term "pulsating" is inappropriate since our findings and other published results are not regularly periodic and thus a more appropriate term may be fluctuating aurora. Further, we find that the observational constraints do not fit well with the flow cyclotron maser theory, which in particular is suggested to create PA patches. There is no clear candidate of the suggested mechanisms and drivers to explain the observational constraints set by the PA patches in a satisfactory manner.

  1. HST Observations of the Pulsating White Dwarf GD 358

    NASA Astrophysics Data System (ADS)

    Castanheira, B. G.; Kepler, S. O.; Nitta, A.; Winget, D. E.; Koester, D.

    2005-07-01

    We used time-resolved ultraviolet spectroscopy obtained with the FOS and STIS spectrographs of the Hubble Space Telescope (HST), together with archival IUE observations to measure the effective temperature (Teff}), surface gravity (log g) and distance (d) of the pulsating DB white dwarf GD 358 with unprecedented accuracy, and to show the temperature did not change during the 1996 sforzando, when the star changed basically to a single mode pulsator. We also measured, for the first time for a DBV, the spherical harmonic degree (ℓ) for two modes, with k=8 and k=9, which was only possible because the stellar light curve was dominated by a single mode in 1996. In addition, we constrain ℓ to be 1 or 2 for the main pulsations in the normal multiperiodic state. The spectra are best fit for Teff}=24 100± 400 K, log g=7.91±0.26 and d=42.7±2.5 pc. The ultraviolet spectroscopic distance is in better agreement with the seismological value, than the one derived by parallax.

  2. An Observational Study of Pulsations in Proto-Planetary Nebulae

    NASA Astrophysics Data System (ADS)

    Hrivnak, Bruce J.; Lu, Wenxian; Henson, Gary D.; Hillwig, Todd C.

    2016-01-01

    We have been carrying out a long-term monitoring program to study the light variability in proto-planetary nebulae (PPNe). PPNe are post-Asymptotic Giant Branch objects in transition between the AGB and PN phases in the evolution of low and intermediate-mass stars. As such, it is not surprising that they display pulsational variability. We have been carrying out photometric monitoring of 30 of these at the Valparaiso University campus observatory over the last 20 years, with the assistance of undergraduate students. The sample size has been enlarged over the past six years by observations made using telescopes in the SARA consortium at KPNO and CTIO. Periods have been determined for those of F-G spectral types. We have also enlarged the sample with PPNe from outside the Milky Way by determining periods of eight PPNe in the lower metalicity environment of the Magellanic Clouds. Periods for the entire sample range from 35 to 160 days. Some clear patterns have emerged, with those of higher temperature possessing shorter periods and smaller amplitudes, indicating a reduction in period and pulsation amplitude as the objects evolve. Radial velocity monitoring of several of the brightest of these has allowed us to document their changes in brightness, color, and size during a pulsation cycle. The results of this study will be presented. This research is supported by grants from the National Science Foundation (most recently AST 1413660), with additional student support from the Indiana Space Grant Consortium.

  3. RR Lyrae pulsators as helium indicators in globular clusters

    NASA Astrophysics Data System (ADS)

    Caputo, F.; Tornambe, A.; Castellani, V.

    1980-02-01

    Synthetic Horizontal Branches have been constructed adopting evolutionary horizontal branch models computed by Caputo, Castellani, and Wood for the case Z = 10-3 and assuming Y = 0.20, 0.25, and 0.30. On this basis the expected evolutionary properties of RR Lyrae pulsators in population II Clusters have been studied. It has been found that some pulsational quantities (Pminab, ¯P and ¯Pab) are strongly correlated with the original helium content Y and that, under fairly wide assumptions, they do not depend on evolutionary parameters such as mass loss and/or mass dispersion. From the above quoted RR Lyrae properties one obtains suggestions for an original He content Y ˜ 0.30 in Oosterhoff type I Globular Clusters. Some theoretical results have been found which disagree with observations. From the latter, it is inferred that in the adopted evolutionary computations lifetimes in the last phases of horizontal branch evolution are likely to be overestimated; this is tentatively confirmed by comparing with the computations of Sweigart and Gross. Pulsational properties are little affected by such an occurrence.

  4. Russian Pulsating Mixer Pump. Innovative Technology Summary Report

    SciTech Connect

    2002-03-01

    This sludge mixing/mobilization system was developed in Russia. A prototype system was evaluated by the Tanks Focus Area (TFA) and Industry and University Programs (INDP). The Russian Pulsating Mixer Pump showed promise for mixing highly viscous sludges. This project is to refine the system design (especially the control subsystem) and manufacture the system in Russia in accordance with quality standards required for deployment in radioactive waste storage tanks. Specifications and requirements are being developed by the TFA and INDP. The requirements may call for two or three of the sludge mixing systems to be delivered to Oak Ridge. DOE-Oak Ridge and the Oak Ridge National Laboratory will deploy the pulsating mixing pump system in their Gunite Tanks. These tanks are being emptied and cleaned prior to closure. Oak Ridge has deployed a number of innovative technologies in these efforts. If successful at Oak Ridge, the pulsating mixing pump system has potential application at several other DOE sites, including Savannah River, Hanford, and Idaho.

  5. Heavy Metal Stars: puzzling pulsations and chaotic kinematics.

    NASA Astrophysics Data System (ADS)

    Jeffery, Simon; Martin, Pamela; N, Naslim

    2015-08-01

    A new group of chemically-peculiar stars has been discovered in recent years. Being blue and less luminous than main-sequence stars of the same colour, they are members of the much larger class of hot subdwarfs. They form a tiny subgroup of a small subgroup which are moderately enriched in helium. Their spectra show lines of ions never before observed in stellar spectra, and represent an excess relative to solar of up to 4.5 dex in zirconium, strontium, yttrium, germanium and even lead. The most likely explanation is radiatively-driven diffusion concentrating these ions in a very thin layer of the photosphere. At least one of these peculiar stars pulsates, although the driving mechansim for the pulsations in LS IV-14 116 remains a mystery. All three heavy-metal subdwarfs have unmeasurably small rotation velocities, but halo-like space velocities. We will discuss how these characteristics, along with Hubble Space Telescope and ESO Very Large Telescope observations to be obtained just after the General Assembly, will attempt to solve the mystery of their unknown origin and unexplained pulsations.

  6. Are dayside long-period pulsations related to the cusp?

    NASA Astrophysics Data System (ADS)

    Pilipenko, V.; Belakhovsky, V.; Engebretson, M. J.; Kozlovsky, A.; Yeoman, T.

    2015-03-01

    We compare simultaneous observations of long-period ultra-low-frequency (ULF) wave activity from a Svalbard/IMAGE fluxgate magnetometer latitudinal profile covering the expected cusp geomagnetic latitudes. Irregular Pulsations at Cusp Latitudes (IPCL) and narrowband Pc5 waves are found to be a ubiquitous element of ULF activity in the dayside high-latitude region. To identify the ionospheric projections of the cusp, we use the width of return signal of the Super Dual Auroral Radar Network (SuperDARN) radar covering the Svalbard archipelago, predictions of empirical cusp models, augmented whenever possible by Defense Meteorological Satellite Program (DMSP) identification of magnetospheric boundary domains. The meridional spatial structure of broadband dayside Pc5-6 pulsation spectral power has been found to have a localized latitudinal peak, not under the cusp proper as was previously thought, but several degrees southward from the equatorward cusp boundary. The earlier claims of the dayside monochromatic Pc5 wave association with the open-closed boundary also seems doubtful. Transient currents producing broadband Pc5-6 probably originate at the low-latitude boundary layer/central plasma sheet (LLBL/CPS) interface, though such identification with available DMSP data is not very precise. The occurrence of broadband Pc5-6 pulsations in the dayside boundary layers is a challenge to modelers because so far their mechanism has not been firmly identified.

  7. The pulsating laminar flow in a rectangular channel

    NASA Astrophysics Data System (ADS)

    Valueva, E. P.; Purdin, M. S.

    2015-11-01

    The finite difference method is used to solve the task of the developed pulsating laminar flow in a rectangular channel. The optimum of the difference scheme parameters was determined. Data on the amplitude and phase of the longitudinal velocity oscillations, the hydraulic and friction drag coefficients, the shear stress on the wall have been obtained. Using the dimensionless value of the frequency pulsations two characteristic regimes — the quasisteady-state regime and the high-frequency regime have been identified. In the quasi-steady-state regime, the values of all hydrodynamic quantities at each instant of time correspond to the velocity value averaged over the cross section at a given moment of time. It is shown that in the high-frequency regime, the dependences on the dimensionless oscillation frequency of oscillating components of hydrodynamic quantities are identical for rectilinear channels with a different cross-sectional form (round pipe, flat and a rectangular channels). The effect of the aspect ratio of the rectangular channel sides channel on the pulsating flow dynamics has been analyzed.

  8. Temporal Characteristics and Energy Deposition of Pulsating Auroral Patches

    NASA Technical Reports Server (NTRS)

    Humberset, B. K.; Gjerloev, J. W.; Samara, M.; Michell, R. G.; Mann, I. R.

    2016-01-01

    We present a careful statistical analysis of pulsating aurora (PA) using all-sky green line (557.7 nm) images obtained at 3.3 Hz. Six well-defined individual PA patches are identified and extracted using a contouring technique. Quantitative parameters such as the patch duration (on-time and off-time), peak intensity, and integrated intensity are determined for each patch and each pulsation. The resulting characteristics serve as strict observational constraints that any of the many competing theories attempting to explain PA must predict. The purpose of this paper is to determine the characteristics of PA patches in order to provide better observational constraints on the suggested mechanisms. All aspects of the temporal behavior of the individual patches appear to be erratic. Historically, PA has been defined very loosely and we argue that the use of the term pulsating is inappropriate since our findings and other published results are not regularly periodic and thus a more appropriate term may be fluctuating aurora. Further, we find that the observational constraints do not fit well with the flow cyclotron maser theory, which in particular is suggested to create PA patches. There is no clear candidate of the suggested mechanisms and drivers to explain the observational constraints set by the PA patches in a satisfactory manner.

  9. Ganges River Delta

    NASA Technical Reports Server (NTRS)

    2002-01-01

    The Ganges River forms an extensive delta where it empties into the Bay of Bengal. The delta is largely covered with a swamp forest known as the Sunderbans, which is home to the Royal Bengal Tiger. It is also home to most of Bangladesh, one of the world's most densely populated countries. Roughly 120 million people live on the Ganges Delta under threat of repeated catastrophic floods due to heavy runoff of meltwater from the Himalayas, and due to the intense rainfall during the monsoon season. This image was acquired by Landsat 7's Enhanced Thematic Mapper plus (ETM+) sensor on February 28, 2000. This is a false-color composite image made using green, infrared, and blue wavelengths. Image provided by the USGS EROS Data Center Satellite Systems Branch

  10. Zambezi River Delta

    NASA Image and Video Library

    2013-08-29

    It drains a watershed that spans eight countries and nearly 1.6 million square kilometers 600,000 square miles. The Zambezi also Zambeze is the fourth largest river in Africa, and the largest east-flowing waterway. The Operational Land Imager on the Landsat 8 satellite acquired this natural-color image of the Zambezi Delta on August 29, 2013. Sandbars and barrier spits stretch across the mouths of the delta, and suspended sediment extends tens of kilometers out into the sea. The sandy outflow turns the coastal waters to a milky blue-green compared to the deep blue of open water in the Indian Ocean. The Zambezi Delta includes 230 kilometers of coastline fronting 18,000 square kilometers (7,00 square miles) of swamps, floodplains, and even savannahs (inland). The area has long been prized by subsistence fishermen and farmers, who find fertile ground for crops like sugar and fertile waters for prawns and fish. Two species of endangered cranes and one of the largest concentration of buffalo in Africa -- among many other species of wildlife -- have found a haven in this internationally recognized wetland. However, the past six decades have brought great changes to the Zambezi Delta, which used to pour more water and sediment off of the continent. Hydropower dams upstream-most prominently, the Kariba and the Cahora Bassa-greatly reduce river flows during the wet season; they also trap sediments that would otherwise flow downstream. The result has been less water reaching the delta and the floodplains, which rely on pulses of nutrients and sediments from annual (and mostly benign) natural flooding. The change in the flow of the river affects freshwater availability and quality in the delta. Strong flows push fresh water further out into the sea and naturally keep most of a delta full of fresh (or mostly fresh) water. When that fresh flow eases, the wetlands become drier and more prone to fire. Salt water from the Indian Ocean also can penetrate further into the marsh

  11. The Nile Delta, Egypt

    NASA Technical Reports Server (NTRS)

    2002-01-01

    This pair of true- and false-color images from the Moderate Resolution Imaging Spectroradiometer was acquired on June 3, 2002. The fertile land along the Nile River supports lush green vegetation, amid the desert landscape. At its delta at the Mediterranean Sea, the Nile broadens into a large fan-shaped delta. All of Egypt's large cities fall along the Nile, which sustains life in a region of scant rainfall. At the point where the river widens into the delta, a grayish cluster of pixels marks the location of Cairo. To the east is the Sinai Peninsula, whose impermanent water courses create silvery streaks on the pale brown, arid landscape. At lower right is the Red Sea. Credit: Jacques Descloitres, MODIS Land Rapid Response Team, NASA/GSFC

  12. Investigations on the Aerodynamic Characteristics and Blade Excitations of the Radial Turbine with Pulsating Inlet Flow

    NASA Astrophysics Data System (ADS)

    Liu, Yixiong; Yang, Ce; Yang, Dengfeng; Zhang, Rui

    2016-04-01

    The aerodynamic performance, detailed unsteady flow and time-based excitations acting on blade surfaces of a radial flow turbine have been investigated with pulsation flow condition. The results show that the turbine instantaneous performance under pulsation flow condition deviates from the quasi-steady value significantly and forms obvious hysteretic loops around the quasi-steady conditions. The detailed analysis of unsteady flow shows that the characteristic of pulsation flow field in radial turbine is highly influenced by the pulsation inlet condition. The blade torque, power and loading fluctuate with the inlet pulsation wave in a pulse period. For the blade excitations, the maximum and the minimum blade excitations conform to the wave crest and wave trough of the inlet pulsation, respectively, in time-based scale. And toward blade chord direction, the maximum loading distributes along the blade leading edge until 20% chord position and decreases from the leading to trailing edge.

  13. Double throat pressure pulsation dampener for oil-free screw compressors

    NASA Astrophysics Data System (ADS)

    Lucas, Michael J.

    2005-09-01

    This paper describes a recent invention at Ingersoll-Rand for reducing the pressure pulsations in an oil-free screw compressor. Pressure pulsation is a term used in the air compressor industry to describe the rapid change in pressure with time measured in the downstream piping of the air compressor. The pulsations are due to the rapid opening and closing of the screws as the compressed air is eject from the compressor into the piping system. The pulsations are known to produce excessive noise levels and high levels of vibration in the piping system. Reducing these pulsations is critical to achieving a quiet running compressor. This paper will describe the methodology used to analyze the data and show both computational and experimental results achieved using the pulsation dampener. A patent for this design has been filed with the US patent office.

  14. Reducing the effect of penstock pressure pulsations on hydro electric plant power system stabilizer signals

    SciTech Connect

    Nettleton, L.D.; Gurney, J.H.; Bollinger, K.E.

    1993-12-01

    A characteristic trait of Francis turbines operating at low-head is pressure pulsations that occur during certain load levels of the generator. These stem from pressure variations across the turbine due to pulsating flow in the draft-tube. This surging action of the water column is related to draft-tube geometry and flow-rate of water in the penstock. The pressure pulsations cause torque variations on the turbine and corresponding electric power pulsations. If electric power is used as a feedback signal to the Power System Stabilizer (PSS), then Mvar and terminal voltage pulsations will occur when the generator is operating in the ``rough zone``. This paper describes field test results for investigating feedforward control from the penstock, draft tube and spiral case pressure to reduce the effects of Mw pulsations on PSS output signals. This investigation involved a PSS with generator power as the feedback signal and the PSS tuned for local and inter-area damping.

  15. Delta II Mars Pathfinder

    NASA Technical Reports Server (NTRS)

    1998-01-01

    Final preparations for lift off of the DELTA II Mars Pathfinder Rocket are shown. Activities include loading the liquid oxygen, completing the construction of the Rover, and placing the Rover into the Lander. After the countdown, important visual events include the launch of the Delta Rocket, burnout and separation of the three Solid Rocket Boosters, and the main engine cutoff. The cutoff of the main engine marks the beginning of the second stage engine. After the completion of the second stage, the third stage engine ignites and then cuts off. Once the third stage engine cuts off spacecraft separation occurs.

  16. Investigation on the Possible Relationship between Magnetic Pulsations and Earthquakes

    NASA Astrophysics Data System (ADS)

    Jusoh, M.; Liu, H.; Yumoto, K.; Uozumi, T.; Takla, E. M.; Yousif Suliman, M. E.; Kawano, H.; Yoshikawa, A.; Asillam, M.; Hashim, M.

    2012-12-01

    The sun is the main source of energy to the solar system, and it plays a major role in affecting the ionosphere, atmosphere and the earth surface. The connection between solar wind and the ground magnetic pulsations has been proven empirically by several researchers previously (H. J. Singer et al., 1977, E. W. Greenstadt, 1979, I. A. Ansari 2006 to name a few). In our preliminary statistical analysis on relationship between solar and seismic activities (Jusoh and Yumoto, 2011, Jusoh et al., 2012), we observed a high possibility of solar-terrestrial coupling. We observed high tendency of earthquakes to occur during lower phase solar cycles which significantly related with solar wind parameters (i.e solar wind dynamic pressure, speed and input energy). However a clear coupling mechanism was not established yet. To connect the solar impact on seismicity, we investigate the possibility of ground magnetic pulsations as one of the connecting agent. In our analysis, the recorded ground magnetic pulsations are analyzed at different ranges of ultra low frequency; Pc3 (22-100 mHz), Pc4 (6.7-22 mHz) and Pc5 (1.7-6.7 mHz) with the occurrence of local earthquake events at certain time periods. This analysis focuses at 2 different major seismic regions; north Japan (mid latitude) and north Sumatera, Indonesia (low latitude). Solar wind parameters were obtained from the Goddard Space Flight Center, NASA via the OMNIWeb Data Explorer and the Space Physics Data Facility. Earthquake events were extracted from the Advanced National Seismic System (ANSS) database. The localized Pc3-Pc5 magnetic pulsations data were extracted from Magnetic Data Acquisition System (MAGDAS)/Circum Pan Magnetic Network (CPMN) located at Ashibetsu (Japan); for earthquakes monitored at north Japan and Langkawi (Malaysia); for earthquakes observed at north Sumatera. This magnetometer arrays has established by International Center for Space Weather Science and Education, Kyushu University, Japan. From the

  17. Detection of new pulsations in the roAp star HD 177765

    NASA Astrophysics Data System (ADS)

    Holdsworth, Daniel L.

    2016-10-01

    We report the discovery of 2 previously undetected pulsation frequencies in the known roAp star HD 177765. Photometric observations by the Kepler space telescope during K2 Campaign 7 show low-amplitude pulsations (4-11 micro mag) previously unseen in photometry. We show the pulsations to be stable over the observation period, and demonstrate that the separation of the frequencies is not representative of the large frequency separation quantity needed to perform asteroseismic analysis.

  18. Substructures with luminosity modulation and horizontal oscillation in pulsating patch: Principal component analysis application to pulsating aurora

    NASA Astrophysics Data System (ADS)

    Nishiyama, Takanori; Miyoshi, Yoshizumi; Katoh, Yuto; Sakanoi, Takeshi; Kataoka, Ryuho; Okano, Shoichi

    2016-03-01

    We observed a mesoscale aurora (100 km × 100 km) with patchy structure and equatorward propagation at Poker Flat Research Range on 1 December 2011. Fast Fourier transform (FFT) analysis revealed that this pulsating patch clearly exhibited temporal variations that can be categorized into two types: on-off pulsation (7.8-10 s) with large amplitudes and luminosity modulations excited during on phase with a frequency of about 3.0 Hz. In addition, we applied principal component analysis (PCA) to time series image data of the pulsating aurora for the first time. Time coefficients were estimated by PCA for the whole patch and the substructures were consistent with those obtained from the FFT analysis, and therefore, we concluded that PCA is capable of decomposing several structures that have different coherent spatiotemporal characteristics. Another new insight in this study is that the rapid variations were highly localized; they were excited in only the substructures embedded in the whole structure. Moreover, the whole patch propagated equatorward because of E × B drift of cold plasma, while the substructures did not show such systematic propagation but rather forward-backward oscillations. The horizontal scale of the substructures was estimated to be no smaller than 410 km at the magnetic equator, which is comparable to that of the wave packet structure of a whistler mode chorus perpendicular to the field line. We suggest that the apparent horizontal oscillation of the substructures is associated with field-aligned propagations of the whistler mode chorus in a duct.

  19. Pulsation tectonics as the control of continental breakup

    NASA Astrophysics Data System (ADS)

    Sheridan, Robert E.

    1987-11-01

    New data from the recent IPOD drilling of DSDP Site 534 in the Blake-Bahama Basin give a definitive age for the spreading-center shift involved in the breakup of the North American Atlantic margin. A basal Callovian age (~155 m.y.) is determined for the Blake Spur anomaly marking this spreading-center shift that signals the birth of the modern North Atlantic Ocean. This is some 20 m.y. younger than previously thought. One implication of this result is that this spreading-center shift starting North Atlantic breakup is now of an age which could be assigned to the spreading-center shift needed to end the rifting in the Gulf of Mexico. It is suggested that this might be one and the same event. Another implication of this younger age for the Blake Spur event is that relatively high spreading rates are now required for the Jurassic outer magnetic quiet zone along the North American margin. This association of a relatively high spreading rate with a magnetic quiet zone is similar to that for the mid-Cretaceous and implies a link between the processes controlling plate spreading, which are in the upper mantle, and the processes controlling the magnetic field, which are in the outer core. The cycles of fast and slow spreading and quiet and reversing magnetic field have a period of 60-100 m.y. A theory of pulsation tectonics involving the cyclic eruption of plumes of hot mantle material from the lowermost D″ layer of the mantle could explain the correlation. Plumes carry heat away from the core/mantle boundary and later reach the asthenosphere and lithosphere to induce faster spreading. The pulse of fast spreading in the Jurassic apparently caused the breakup of the North Atlantic. Other pulses of fast spreading appear to correlate with major ocean openings on various parts of the globe, implying that this might be a prevalent process. I suggest rifting of passive margins may be controlled by the more fundamental global processes described by the theory of pulsation

  20. Observations of candidate oscillating eclipsing binaries and two newly discovered pulsating variables

    NASA Astrophysics Data System (ADS)

    Liakos, A.; Niarchos, P.

    2009-03-01

    CCD observations of 24 eclipsing binary systems with spectral types ranging between A0-F0, candidate for containing pulsating components, were obtained. Appropriate exposure times in one or more photometric filters were used so that short-periodic pulsations could be detected. Their light curves were analyzed using the Period04 software in order to search for pulsational behaviour. Two new variable stars, namely GSC 2673-1583 and GSC 3641-0359, were discov- ered as by-product during the observations of eclipsing variables. The Fourier analysis of the observations of each star, the dominant pulsation frequencies and the derived frequency spectra are also presented.

  1. Cepheids in Magellanic Cloud star clusters - Fundamental and overtone pulsators in NGC 2157

    SciTech Connect

    Mateo, M.; Olszewski, E.W.; Madore, B.F. Steward Observatory, Tucson, AZ JPL, Pasadena, CA )

    1990-04-01

    CCD survey data are employed to examine Cepheids in young Magellanic Cloud star clusters. The properties of three Cepheids observed in NGC 2157 are described. It is detected that the two short-period (3 days) Cepheids have photometric properties that correspond to overtone pulsators and the long-period (7.7 days) Cepheid pulses in the fundamental mode. The pulsational masses for the three Cepheids are calculated to be about 5 solar masses. This mass value does not correlate with the average pulsational mass for Cepheids of 3.0 + or - 0.4 solar masses. The potential cause of this deviation in evolutionary/pulsational mass is investigated. 23 refs.

  2. First Satellite Imaging of Auroral Pulsations by the Fast Auroral Imager on e-POP

    NASA Astrophysics Data System (ADS)

    Lui, A.; Cogger, L.; Howarth, A. D.; Yau, A. W.

    2015-12-01

    We report the first satellite imaging of auroral pulsations by the Fast Auroral Imager (FAI) onboard the Enhanced Polar Outflow Probe (e-POP) satellite. The near-infrared camera of FAI is capable of providing up to two auroral images per second, ideal for investigation of pulsating auroras. The auroral pulsations were observed within the auroral bulge formed during a substorm interval on 2014 February 19. This first satellite view of these pulsations from FAI reveals that (1) several pulsating auroral channels (PACs) occur within the auroral bulge, (2) periods of the intensity pulsations span over one decade within the auroral bulge, and (3) there is no apparent trend of longer pulsation periods associated with higher latitudes for these PACs. Although PACs resemble in some respect stable pulsating auroras reported previously but they have several important differences in characteristics.PACs are not embedded in or emerging from omega bands or torches and are located at significant distances from the equatorward boundary of the auroral oval, unlike the characteristics of stable pulsating auroras.

  3. White Dwarf Period Tables I. Pulsators with hydrogen-dominated atmospheres

    NASA Astrophysics Data System (ADS)

    Bognar, Zs.; Sodor, A.

    2016-09-01

    We aimed at collecting all known white dwarf pulsators with hydrogen-dominated atmospheres and list their main photometric and atmospheric parameters together with their pulsation periods and amplitudes observed at different epochs. For this purpose, we explored the pulsating white dwarf related literature with the systematic use of the SIMBAD and the NASA's Astrophysics Data System (ADS) databases. We summarized our results in four tables listing seven ZZ Ceti stars in detached white dwarf plus main-sequence binaries, seven extremely low-mass DA pulsators, three hot DAVs and 180 ZZ Ceti stars.

  4. Analysis of a subdwarf B pulsator observed during Campaign 2 of K2

    NASA Astrophysics Data System (ADS)

    Ketzer, Laura; Baran, Andrzej; Reed, Mike; Telting, John H.; Nemeth, Peter

    2016-06-01

    We present an analysis of the pulsating subdwarf B (sdB) star EPIC 203948264, observed during Campaign 2 of the extended Kepler mission. A time series analysis of the short cadence data set has revealed a rich g-mode pulsation spectrum with 17 independent pulsation periods between 0.5 and 2.8 hours. All of the pulsations fit the asymptotic period sequences for ell=1 or 2, with average period spacings of 259+/-1.4 and 149+/-0.3 s, respectively. The pulsation amplitudes range from 0.77 to the detection limit at 0.26 ppt, with amplitudes that vary over time. Radial velocity measurements give no indication for binarity in this star. We did not find rotationally induced pulsation multiplets, which indicates that the rotation period of the star is longer than about 45 days, which would make the data too short to resolve multiplets. By characterizing the various pulsation modes present in pulsating sdB stars, and by examining the time-dependence of pulsation amplitudes, we can constrain structural models of the interiors of sdB stars. This is a promising approach to enhancing our understanding of these stars.

  5. Lessons from KIPP Delta

    ERIC Educational Resources Information Center

    Maranto, Robert; Shuls, James V.

    2011-01-01

    KIPP Delta succeeds at its stated mission, probably because of its careful attention to culture building. What distinguishes this KIPP school is thoughtful work linking the daily processes of schooling to the goals of schooling, in this case success in college. Day to day tactics reflect broader themes: having a clear mission and hiring staff who…

  6. DELTA PHASE PLUTONIUM ALLOYS

    DOEpatents

    Cramer, E.M.; Ellinger, F.H.; Land. C.C.

    1960-03-22

    Delta-phase plutonium alloys were developed suitable for use as reactor fuels. The alloys consist of from 1 to 4 at.% zinc and the balance plutonium. The alloys have good neutronic, corrosion, and fabrication characteristics snd possess good dimensional characteristics throughout an operating temperature range from 300 to 490 deg C.

  7. Delta Airlines LOFT training

    NASA Technical Reports Server (NTRS)

    Whitehead, J.

    1981-01-01

    A LOFT program was developed as part of the DC-9 training program which serves as a prototype for much of Delta's other aircraft training programs. The LOFT used differs little from the ideology presented in the Advisory Circular. Difficulty and experienced concerns regarding the effectiveness of LOFT as a complete training vehicle are explored.

  8. Therapy of Delta Hepatitis

    PubMed Central

    Yurdaydin, Cihan; Idilman, Ramazan

    2015-01-01

    Delta hepatitis is the less frequently encountered but most severe form of viral hepatitis. Acute delta hepatitis, as a result of coinfection with hepatitis B and hepatitis delta, is rare, but may lead to fulminant hepatitis, and no therapy exists for this form. Chronic delta hepatitis (CDH) mostly develops as a result of superinfection of a hepatitis B surface antigen (HBsAg) carrier with hepatitis delta virus (HDV). In general, HDV is the dominant virus. However, a dynamic shift of the dominant virus may occur with time in rare instances, and hepatitis B virus (HBV) may become the dominant virus, at which time nucleos(t)ide analog therapy may be indicated. Otherwise, the only established management of CDH consists of conventional or pegylated interferon therapy, which has to be administered at doses used for hepatitis B for a duration of at least 1 year. Posttreatment week-24 virologic response is the most widely used surrogate marker of treatment efficacy, but it does not represent a sustained virologic response, and late relapse can occur. As an easy-to-use simple serological test, anti-HDV-immunoglobulin M (IgM) correlates with histological inflammatory activity and clinical long-term outcome; however, it is not as sensitive as HDV RNA in assessing treatment response. No evidence-based rules for treating CDH exist, and treatment duration needs to be individualized based on virologic response at end of treatment or end of follow-up. Effective treatment may decrease liver-related complications, such as decompensation or liver-related mortality. In patients with decompensated cirrhosis, interferons are contraindicated and liver transplantation has to be considered. Alternative treatment options are an urgent need in CDH. New treatment strategies targeting different steps of the HDV life cycle, such as hepatocyte entry inhibitors or prenylation inhibitors, are emerging and provide hope for the future. PMID:26253093

  9. The Devil's in the Delta

    ERIC Educational Resources Information Center

    Luyben, William L.

    2007-01-01

    Students frequently confuse and incorrectly apply the several "deltas" that are used in chemical engineering. The deltas come in three different flavors: "out minus in", "big minus little" and "now versus then." The first applies to a change in a stream property as the stream flows through a process. For example, the "[delta]H" in an energy…

  10. The Devil's in the Delta

    ERIC Educational Resources Information Center

    Luyben, William L.

    2007-01-01

    Students frequently confuse and incorrectly apply the several "deltas" that are used in chemical engineering. The deltas come in three different flavors: "out minus in", "big minus little" and "now versus then." The first applies to a change in a stream property as the stream flows through a process. For example, the "[delta]H" in an energy…

  11. DELTAS: A new Global Delta Sustainability Initiative (Invited)

    NASA Astrophysics Data System (ADS)

    Foufoula-Georgiou, E.

    2013-12-01

    Deltas are economic and environmental hotspots, food baskets for many nations, home to a large part of the world population, and hosts of exceptional biodiversity and rich ecosystems. Deltas, being at the land-water interface, are international, regional, and local transport hubs, thus providing the basis for intense economic activities. Yet, deltas are deteriorating at an alarming rate as 'victims' of human actions (e.g. water and sediment reduction due to upstream basin development), climatic impacts (e.g. sea level rise and flooding from rivers and intense tropical storms), and local exploration (e.g. sand or aggregates, groundwater and hydrocarbon extraction). Although many efforts exist on individual deltas around the world, a comprehensive global delta sustainability initiative that promotes awareness, science integration, data and knowledge sharing, and development of decision support tools for an effective dialogue between scientists, managers and policy makers is lacking. Recently, the international scientific community proposed to establish the International Year of Deltas (IYD) to serve as the beginning of such a Global Delta Sustainability Initiative. The IYD was proposed as a year to: (1) increase awareness and attention to the value and vulnerability of deltas worldwide; (2) promote and enhance international and regional cooperation at the scientific, policy, and stakeholder level; and (3) serve as a launching pad for a 10-year committed effort to understand deltas as complex socio-ecological systems and ensure preparedness in protecting and restoring them in a rapidly changing environment. In this talk, the vision for such an international coordinated effort on delta sustainability will be presented as developed by a large number of international experts and recently funded through the Belmont Forum International Opportunities Fund. Participating countries include: U.S., France, Germany, U.K., India, Japan, Netherlands, Norway, Brazil, Bangladesh

  12. Four new massive pulsating white dwarfs including an ultramassive DAV

    NASA Astrophysics Data System (ADS)

    Curd, Brandon; Gianninas, A.; Bell, Keaton J.; Kilic, Mukremin; Romero, A. D.; Allende Prieto, Carlos; Winget, D. E.; Winget, K. I.

    2017-06-01

    We report the discovery of four massive (M > 0.8 M⊙) ZZ Ceti white dwarfs, including an ultramassive 1.16 M⊙ star. We obtained ground-based, time series photometry for 13 white dwarfs from the Sloan Digital Sky Survey Data Release 7 and Data Release 10 whose atmospheric parameters place them within the ZZ Ceti instability strip. We detect monoperiodic pulsations in three of our targets (J1015, J1554 and J2038) and identify three periods of pulsation in J0840 (173, 327 and 797 s). Fourier analysis of the remaining nine objects does not indicate variability above the 4 detection threshold. Our preliminary asteroseismic analysis of J0840 yields a stellar mass M = 1.14 ± 0.01 M⊙, hydrogen and helium envelope masses of MH = 5.8 × 10-7 M⊙ and MHe = 4.5 × 10-4 M⊙ and an expected core crystallized mass ratio of 50-70 per cent. J1015, J1554 and J2038 have masses in the range 0.84-0.91 M⊙ and are expected to have a CO core; however, the core of J0840 could consist of highly crystallized CO or ONeMg given its high mass. These newly discovered massive pulsators represent a significant increase in the number of known ZZ Ceti white dwarfs with mass M > 0.85 M⊙, and detailed asteroseismic modelling of J0840 will allow for significant tests of crystallization theory in CO and ONeMg core white dwarfs.

  13. The domains of instability for the pulsating PG1159 stars.

    SciTech Connect

    Quirion, P.-O.; Fontaine, Gilles.; Brassard, Pierre; Herwig, F. H.

    2004-01-01

    The fact that we find pulsating and nonpulsating stars mixed together in the PG 1159 region of the log g - T{sub eff} diagram has been a long standing puzzle. The poor understanding of the driving mechanism in those stars has been the reason why it has taken so long to address properly this problem. Following the work of Saio (1996) and Gautschy (1997) based on the OPAL opacities, Quirion, Fontaine, & Brassard (2004) recently showed that we are now able to understand and reproduce the ranges of observed periods in the pulsating PG 1159 stars in terms of the original {kappa}-mechanism associated with the partial ionization of the K-shell electrons of C and O which, along with He, make up the composition of the envelope of those stars. Contrary to others, those three studies agree in that no composition gradients are needed between the atmospheric layers and the driving region. Furthermore, the cohabitation of pulsating and nonpulsating PG 1159 stars is naturally explained in terms of a dispersion in atmospheric parameters and in terms of a variation in surface composition from star to star. In particular, the most He-rich stars tend to be stable. We go beyond the findings discussed by Quirion et al. (2004) in this paper, and present the results of additional calculations aimed at describing better the role of the chemical composition (in particular the role of metallicity) as well as that of the stellar mass on the boundaries of the instability domain in the log g - T{sub eff} plane.

  14. DARK STARS: IMPROVED MODELS AND FIRST PULSATION RESULTS

    SciTech Connect

    Rindler-Daller, T.; Freese, K.; Montgomery, M. H.; Winget, D. E.; Paxton, B.

    2015-02-01

    We use the stellar evolution code MESA to study dark stars (DSs). DSs, which are powered by dark matter (DM) self-annihilation rather than by nuclear fusion, may be the first stars to form in the universe. We compute stellar models for accreting DSs with masses up to 10{sup 6} M {sub ☉}. The heating due to DM annihilation is self-consistently included, assuming extended adiabatic contraction of DM within the minihalos in which DSs form. We find remarkably good overall agreement with previous models, which assumed polytropic interiors. There are some differences in the details, with positive implications for observability. We found that, in the mass range of 10{sup 4}-10{sup 5} M {sub ☉}, our DSs are hotter by a factor of 1.5 than those in Freese et al., are smaller in radius by a factor of 0.6, denser by a factor of three to four, and more luminous by a factor of two. Our models also confirm previous results, according to which supermassive DSs are very well approximated by (n = 3)-polytropes. We also perform a first study of DS pulsations. Our DS models have pulsation modes with timescales ranging from less than a day to more than two years in their rest frames, at z ∼ 15, depending on DM particle mass and overtone number. Such pulsations may someday be used to identify bright, cool objects uniquely as DSs; if properly calibrated, they might, in principle, also supply novel standard candles for cosmological studies.

  15. Dissipative double-well potential: Nonlinear stationary and pulsating modes

    SciTech Connect

    Zezyulin, Dmitry A.; Konotop, Vladimir V.; Alfimov, Georgy L.

    2010-11-15

    The analysis of nonlinear modes in a complex absorbing double-well potential supported by linear gain is presented. Families of the nonlinear modes and their bifurcations are found numerically by means of the properly modified 'shooting' method. Linear stability and dynamics of the modes are studied. It is shown that no stable modes exist in the case of attractive nonlinearity, while stable modes, including nonsymmetric ones, are found when the nonlinearity is repulsive. Varying a control parameter (e.g., the height of barrier between the wells) results in switching from one mode to another. Apart from stationary modes we have found pulsating solutions emergent from unstable modes.

  16. Electrodynamic response of the middle atmosphere to auroral pulsations

    NASA Technical Reports Server (NTRS)

    Goldberg, R. A.; Croskey, C. L.; Hale, L. C.; Mitchell, J. D.; Barcus, J. R.

    1990-01-01

    The MAC/EPSILON observational campaign encompassed the use of two Nike Orion rocket payloads which studied the effects of auroral energetics on the middle atmosphere. While one payload was launched during the recovery phase of a moderate magnetic substorm, during fairly stable auroral conditions, the other was launched during highly active postbreakup conditions during which Pc5 pulsations were in progress. The energetic radiation of the first event was composed almost entirely of relativistic electrons below 200 keV, while that of the second was dominated by much softer electrons whose high X-ray fluxes exceeded the cosmic ray background as an ionizing source down to below 30 km.

  17. Discovery of a new PG 1159 (GW Vir) pulsator

    NASA Astrophysics Data System (ADS)

    Kepler, S. O.; Fraga, Luciano; Winget, Don Earl; Bell, Keaton; Córsico, Alejandro H.; Werner, Klaus

    2014-08-01

    We report the discovery of pulsations in the spectroscopic PG 1159 type pre-white dwarf SDSS J075415.12 + 085232.18. Analysis of the spectrum by Werner et al. indicated Teff = 120 000 ± 10 000 K, log g = 7.0 ± 0.3, mass {M}=0.52 ± 0.02 M_{⊙}, C/He = 0.33 by number. We obtained time series images with the SOAR 4.1 m telescope and 2.1 m Otto Struve telescope at McDonald Observatory and show the star is also a variable PG 1159 type star, with dominant period of 525 s.

  18. Pulsations powered by hydrogen shell burning in white dwarfs

    NASA Astrophysics Data System (ADS)

    Camisassa, M. E.; Córsico, A. H.; Althaus, L. G.; Shibahashi, H.

    2016-10-01

    Context. In the absence of a third dredge-up episode during the asymptotic giant-branch phase, white dwarf models evolved from low-metallicity progenitors have a thick hydrogen envelope, which makes hydrogen shell burning be the most important energy source. Aims: We investigate the pulsational stability of white dwarf models with thick envelopes to see whether nonradial g-mode pulsations are triggered by hydrogen burning, with the aim of placing constraints on hydrogen shell burning in cool white dwarfs and on a third dredge-up during the asymptotic giant-branch evolution of their progenitor stars. Methods: We construct white-dwarf sequences from low-metallicity progenitors by means of full evolutionary calculations that take into account the entire history of progenitor stars, including the thermally pulsing and the post-asymptotic giant-branch phases, and analyze their pulsation stability by solving the linear, nonadiabatic, nonradial pulsation equations for the models in the range of effective temperatures Teff 15 000-8000 K. Results: We demonstrate that, for white dwarf models with masses M⋆ ≲ 0.71 M⊙ and effective temperatures 8500 ≲ Teff ≲ 11 600 K that evolved from low-metallicity progenitors (Z = 0.0001, 0.0005, and 0.001), the dipole (ℓ = 1) and quadrupole (ℓ = 2) g1-modes are excited mostly as a result of the hydrogen-burning shell through the ɛ-mechanism, in addition to other g-modes driven by either the κ - γ or the convective driving mechanism. However, the ɛ mechanism is insufficient to drive these modes in white dwarfs evolved from solar-metallicity progenitors. Conclusions: We suggest that efforts should be made to observe the dipole g1-mode in white dwarfs associated with low-metallicity environments, such as globular clusters and/or the galactic halo, to place constraints on hydrogen shell burning in cool white dwarfs and the third dredge-up episode during the preceding asymptotic giant-branch phase.

  19. Limits in the application of harmonic analysis to pulsating stars

    NASA Astrophysics Data System (ADS)

    Pascual-Granado, J.; Garrido, R.; Suárez, J. C.

    2015-09-01

    Using ultra-precise data from space instrumentation, we found that the underlying functions of stellar light curves from some AF pulsating stars are non-analytic, and consequently their Fourier expansion is not guaranteed. This result demonstrates that periodograms do not provide a mathematically consistent estimator of the frequency content for this type of variable stars. More importantly, this constitutes the first counterexample against the current paradigm, which considers that any physical process is described by a continuous (band-limited) function that is infinitely differentiable.

  20. Entropic rectification and current inversion in a pulsating channel

    NASA Astrophysics Data System (ADS)

    Carusela, M. Florencia; Rubí, J. Miguel

    2017-05-01

    We show the existence of a resonant behavior of the current of Brownian particles confined in a pulsating channel. The interplay between the periodic oscillations of the shape of the channel and a force applied along its axis leads to an increase of the particle current as a function of the diffusion coefficient. A regime of current inversion is also observed for particular values of the oscillation frequency and the applied force. The model proposed is based on the Fick-Jacobs equation in which the entropic barrier and the effective diffusion coefficient depend on time. The phenomenon observed could be used to optimize transport in microfluidic devices or biological channels.

  1. Understanding pesticides in California's Delta

    USGS Publications Warehouse

    Kuivila, Kathryn; Orlando, James L.

    2012-01-01

    The Sacramento-San Joaquin River Delta (Delta) is the hub of California’s water system and also an important habitat for imperiled fish and wildlife. Aquatic organisms are exposed to mixtures of pesticides that flow through the maze of Delta water channels from sources including agricultural, landscape, and urban pest-control applications. While we do not know all of the effects pesticides have on the ecosystem, there is evidence that they cause some damage to organisms in the Delta. Decades of USGS research have provided a good understanding of when, where, and how pesticides enter the Delta. However, pesticide use is continually changing. New field studies and methods are needed so that scientists can analyze which pesticides are present in the Delta, and at what concentrations, enabling them to estimate exposure and ultimate effects on organisms. Continuing research will provide resource managers and stakeholders with crucial information to manage the Delta wisely.

  2. Martian deltas: Morphology and distribution

    NASA Technical Reports Server (NTRS)

    Rice, J. W., Jr.; Scott, D. H.

    1993-01-01

    Recent detailed mapping has revealed numerous examples of Martian deltas. The location and morphology of these deltas are described. Factors that contribute to delta morphology are river regime, coastal processes, structural stability, and climate. The largest delta systems on Mars are located near the mouths of Maja, Maumee, Vedra, Ma'adim, Kasei, and Brazos Valles. There are also several smaller-scale deltas emplaced near channel mouths situated in Ismenius Lacus, Memnonia, and Arabia. Delta morphology was used to reconstruct type, quantity, and sediment load size transported by the debouching channel systems. Methods initially developed for terrestrial systems were used to gain information on the relationships between Martian delta morphology, river regime, and coastal processes.

  3. Radial stellar pulsation and three-dimensional convection. III. Comparison of two-dimensional and three-dimensional convection effects on radial pulsation

    SciTech Connect

    Geroux, Christopher M.; Deupree, Robert G.

    2014-03-10

    We have developed a multi-dimensional radiation hydrodynamics code to simulate the interaction of radial stellar pulsation and convection for full-amplitude pulsating models. Convection is computed using large eddy simulations. Here, we perform three-dimensional (3D) simulations of RR Lyrae stars for comparison with previously reported 2D simulations. We find that the time-dependent behavior of the peak convective flux on pulsation phase is very similar in both the 2D and 3D calculations. The growth rates of the pulsation in the 2D calculations are about 0.1% higher than in the 3D calculations. The amplitude of the light curve for a 6500 K RR Lyrae model is essentially the same for our 2D and 3D calculations, as is the rising light curve. There are differences in the slope at various times during falling light.

  4. Search for A-F Spectral type pulsating components in Algol-type eclipsing binary systems

    NASA Astrophysics Data System (ADS)

    Kim, S.-L.; Lee, J. W.; Kwon, S.-G.; Youn, J.-H.; Mkrtichian, D. E.; Kim, C.

    2003-07-01

    We present the results of a systematic search for pulsating components in Algol-type eclipsing binary systems. A total number of 14 eclipsing binaries with A-F spectral type primary components were observed for 22 nights. We confirmed small-amplitude oscillating features of a recently detected pulsator TW Dra, which has a pulsating period of 0.053 day and a semi-amplitude of about 5 mmag in B-passband. We discovered new pulsating components in two eclipsing binaries of RX Hya and AB Per. The primary component of RX Hya is pulsating with a dominant period of 0.052 day and a semi-amplitude of about 7 mmag. AB Per has also a pulsating component with a period of 0.196 day and a semi-amplitude of about 10 mmag in B-passband. We suggest that these two new pulsators are members of the newly introduced group of mass-accreting pulsating stars in semi-detached Algol-type eclipsing binary systems. Table 4 is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/405/231

  5. Searching for frequency multiplets in the pulsating subdwarf B star PG 1219+534

    NASA Astrophysics Data System (ADS)

    Crooke, John; Roessler, Ryan; Reed, Michael

    2017-01-01

    Subdwarf B (sdB) stars represent the stripped cores of horizontal branch stars. Pulsating sdB stars allow us to probe this important stage in evolution. Thanks to Kepler data, we now know that sdB star rotation periods are long; on the order of tens of days. This explains why they were not measured using ground-based follow-up data, which typically only spanned a week or two. Azimuthal pulsation degeneracies are removed by rotation, and so by detected pulsation frequency multiplets, we can determine pulsation modes and apply constraints to models, which tell us stellar structure. We need the ground-based observations as Kepler did not detect many p-mode pulsators, but rather almost exclusively g-mode pulsators. The shorter-period p-modes occur in hotter sdB stars, and so we need these to measure the pulsation dependence across the horizontal branch. During 2015, we observed PG 1219+534 (hereafter PG1219) over several months using our local 16 inch robotic telescope. Here we report preliminary results of processing those data to search for pulsation multiplets.

  6. Thermal-diffusional Instability in White Dwarf Flames: Regimes of Flame Pulsation

    NASA Astrophysics Data System (ADS)

    Xing, Guangzheng; Zhao, Yibo; Modestov, Mikhail; Zhou, Cheng; Gao, Yang; Law, Chung K.

    2017-05-01

    Thermal-diffusional pulsation behaviors in planar as well as outwardly and inwardly propagating white dwarf (WD) carbon flames are systematically studied. In the 1D numerical simulation, the asymptotic degenerate equation of state and simplified one-step reaction rates for nuclear reactions are used to study the flame propagation and pulsation in WDs. The numerical critical Zel’dovich numbers of planar flames at different densities (ρ = 2, 3, and 4 × 107 g cm-3) and of spherical flames (with curvature c = -0.01, 0, 0.01, and 0.05) at a particular density (ρ = 2 × 107 g cm-3) are presented. Flame front pulsation in different environmental densities and temperatures are obtained to form the regime diagram of pulsation, showing that carbon flames pulsate in the typical density of 2 × 107 g cm-3 and temperature of 0.6 × 109 K. While being stable at higher temperatures, at relatively lower temperatures, the amplitude of the flame pulsation becomes larger. In outwardly propagating spherical flames the pulsation instability is enhanced and flames are also easier to quench due to pulsation at small radius, while the inwardly propagating flames are more stable.

  7. Nonisothermal flow of a polymeric liquid under a pulsating pressure gradient

    SciTech Connect

    Shul'man, Z.P.; Khusid, B.M.; Shabunina, Z.A.

    1987-03-01

    Increasing flow rates is a major problem in transporting petroleum as well as polymer solutions and melts. Industrial methods are often directed to reducing the effective viscosity: heating and pulsation. The latter is related to the nonlinearity in the properties. This paper studies the effects of pressure-gradient pulsations on the nonisothermal flow of a nonlinear liquid with memory in an annular channel.

  8. Delta-doping of Semiconductors

    NASA Astrophysics Data System (ADS)

    Schubert, E. F.

    2005-08-01

    Part I: 1. Introduction E. F. Schubert; Part II: 2. Electronic structure of delta-doped semiconductors C. R. Proetto; Part III: 3. Recent progress in delta-like confinement of impurities in GaAs K. H. Ploog; 4. Flow-rate modulation epitaxy (FME) of III-V semiconductors T. Makimoto and Y. Horikoshi; 5. Gas source molecular beam epitaxy (MBE) of delta-doped III-V semiconductors D. Ritter; 6. Solid phase epitaxy for delta-doping in silicon I. Eisele; 7. Low temperature MBE of silicon H.-J. Gossmann; Part IV: 8. Secondary ion mass spectrometry of delta-doped semiconductors H. S. Luftmann; 9. Capacitance-voltage profiling E. F. Schubert; 10. Redistribution of impurities in III-V semiconductors E. F. Schubert; 11. Dopant diffusion and segregation in delta-doped silicon films H.-J. Gossmann; 12. Characterisation of silicon and delta-doped structures in GaAs R. C. Newman; 13. The DX-center in silicon delta-doped GaAs and AlxGa1-xAs P. M. Koenraad; Part V: 14. Luminescence and ellipsometry spectroscopy H. Yao and E. F. Schubert; 15. Photoluminescence and Raman spectroscopy of single delta-doped III-V semiconductor heterostructures J. Wagner and D. Richards; 16. Electron transport in delta-doped quantum wells W. T. Masselink; 17. Electron mobility in delta-doped layers P. M. Koenraad; 18. Hot electrons in delta-doped GaAs M. Asche; 19. Ordered delta-doping R. L. Headrick, L. C. Feldman and B. E. Weir; Part IV: 20. Delta-doped channel III-V field effect transistors (FETs) W.-P. Hong; 21. Selectively doped heterostructure devices E. F. Schubert; 22. Silicon atomic layer doping FET K. Nakagawa and K. Yamaguchi; 23. Planar doped barrier devices R. J. Malik; 24. Silicon interband and intersubband photodetectors I. Eisele; 25. Doping superlattice devices E. F. Schubert.

  9. V2653 Ophiuchii with a pulsating component and Ppuls - Porb, Ppuls - g correlations for γ Dor type pulsators

    NASA Astrophysics Data System (ADS)

    Çakırlı, Ö.; Ibanoglu, C.

    2016-05-01

    We present new spectroscopic observations of the double-lined eclipsing binary V2653 Ophiuchii. The photometric observations obtained by ASAS were analyzed and combined with the analysis of radial velocities for deriving the absolute parameters of the components. Masses and radii were determined for the first time as Mp = 1.537 ± 0.021 M⊙ and Rp = 2.215 ± 0.055 R⊙, Ms = 1.273 ± 0.019 M⊙ and Rs = 2.000 ± 0.056 R⊙ for the components of V2653 Oph. We estimate an interstellar reddening of 0.15 ± 0.08 mag and a distance of 300 ± 50 pc for the system, both supporting the membership of the open cluster Collinder 359. Using the out-of-eclipse photometric data we have made frequency analysis and detected a periodic signal at 1.0029 ± 0.0019 c/d. This frequency and the location of the more massive star on the HR diagram lead to classification of a γ Dor type variable. Up to date only eleven γ Dor type pulsators in the eclipsing binaries have been discovered. For six out of 11 systems, the physical parameters were determined. Although a small sample, we find empirical relations that Ppuls ∝ Porb0.43 and Ppuls ∝ g-0.83. While the pulsation periods increase with longer orbital periods, they decrease with increasing surface gravities of pulsating components and gravitational pull exerted by the companions. We present, briefly, the underlying physics behind the correlations we derived.

  10. Pulsation versus metallicism in Am stars as revealed by LAMOST and WASP

    NASA Astrophysics Data System (ADS)

    Smalley, B.; Antoci, V.; Holdsworth, D. L.; Kurtz, D. W.; Murphy, S. J.; De Cat, P.; Anderson, D. R.; Catanzaro, G.; Cameron, A. Collier; Hellier, C.; Maxted, P. F. L.; Norton, A. J.; Pollacco, D.; Ripepi, V.; West, R. G.; Wheatley, P. J.

    2017-03-01

    We present the results of a study of a large sample of A and Am stars with spectral types from Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) and light curves from Wide Area Search for Planets (WASP). We find that, unlike normal A stars, δ Sct pulsations in Am stars are mostly confined to the effective temperature range 6900 < {{T_eff}} < 7600 K. We find evidence that the incidence of pulsations in Am stars decreases with increasing metallicism (degree of chemical peculiarity). The maximum amplitude of the pulsations in Am stars does not appear to vary significantly with metallicism. The amplitude distributions of the principal pulsation frequencies for both A and Am stars appear very similar and agree with results obtained from Kepler photometry. We present evidence that suggests turbulent pressure is the main driving mechanism in pulsating Am stars, rather than the κ-mechanism, which is expected to be suppressed by gravitational settling in these stars.

  11. K2 observations of pulsating subdwarf B stars: Analysis of EPIC 203948264 observed during Campaign 2

    NASA Astrophysics Data System (ADS)

    Ketzer, L.; Reed, M. D.; Baran, A. S.; Németh, P.; Telting, J. H.; Østensen, R. H.; Jeffery, C. S.

    2017-01-01

    We apply asteroseismic tools to the newly-discovered pulsator EPIC 203948264, observed with K2, the two-gyro mission of the Kepler space telescope. A time series analysis of the 83 day Campaign 2 (C2) short cadence data set has revealed a g -mode pulsation spectrum with 22 independent pulsation periods between 0.5 and 2.8 hours. Most of the pulsations fit the asymptotic period sequences for ℓ = 1 or 2, with average period spacings of 261.3 ± 1.1 s and 151.18 ± 0.37 s, respectively. The pulsation amplitudes are below 0.77 ppt and vary over time. We include updated spectroscopic parameters, including atmospheric abundances and radial velocities which give no indication for binarity in this star. We detect one possible low-amplitude multiplet which corresponds to a rotation period of 46 days or longer. EPIC 203948264 appears as another slowly rotating sdB star.

  12. Enhancing cell viability with pulsating flow in a hollow fiber bioartificial liver.

    PubMed

    Nguyen, Diem T; Brotherton, John D; Chau, Pao C

    2005-10-01

    A pulsating flow of medium was used to alleviate diffusion and transport limitations in a hollow fiber bioreactor containing a human hepatoblastoma cell line. The strategy is easy to implement but effective. The pulsating flow is introduced by a solenoid pinch valve at the outlet of the bioreactor and regulated by a timing circuit. In a permeability test, the system with pulsating flow had much less membrane fouling as compared to the control, a conventional hollow fiber unit. In hepatocyte culture test runs, the pulsating-flow bioreactor demonstrated the ability to maintain a higher cell viability. Histological sections indicated significantly smaller necrotic regions in the pulsating-flow bioreactor as compared to the conventional unit.

  13. Searching for X-ray Pulsations from Neutron Stars Using NICER

    NASA Astrophysics Data System (ADS)

    Ray, Paul S.; Arzoumanian, Zaven; Bogdanov, Slavko; Bult, Peter; Chakrabarty, Deepto; Guillot, Sebastien; Kust Harding, Alice; Ho, Wynn C. G.; Lamb, Frederick K.; Mahmoodifar, Simin; Miller, M. Coleman; Strohmayer, Tod E.; Wilson-Hodge, Colleen A.; Wolff, Michael Thomas

    2017-08-01

    The Neutron Star Interior Composition Explorer (NICER) presents an exciting new capability for discovering new modulation properties of X-ray emitting neutron stars, including large area, low background, extremely precise absolute time stamps, superb low-energy response and flexible scheduling. The Pulsation Searches and Multiwavelength Coordination working group has designed a 2.5 Ms observing program to search for pulsations and characterize the modulation properties of about 30 known or suspected neutron star sources across a number of source categories. A key early goal will be to search for pulsations from millisecond pulsars that might exhibit thermal pulsations from the surface suitable for pulse profile modeling to constrain the neutron star equation of state. In addition, we will search for pulsations from transitional millisecond pulsars, isolated neutron stars, LMXBs, accretion-powered millisecond pulsars, central compact objects and other sources. We will present our science plan and initial results from the first months of the NICER mission.

  14. Mississippi River Delta

    NASA Technical Reports Server (NTRS)

    2002-01-01

    As the Mississippi River enters the Gulf of Mexico, it loses energy and dumps its load of sediment that it has carried on its journey through the mid continent. This pile of sediment, or mud, accumulates over the years building up the delta front. As one part of the delta becomes clogged with sediment, the delta front will migrate in search of new areas to grow. The area shown on this image is the currently active delta front of the Mississippi. The migratory nature of the delta forms natural traps for oil. Most of the land in the image consists of mud flats and marsh lands. There is little human settlement in this area due to the instability of the sediments. The main shipping channel of the Mississippi River is the broad stripe running northwest to southeast.

    This image was acquired on May 24, 2001 by the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) on NASA's Terra satellite. With its 14 spectral bands from the visible to the thermal infrared wavelength region, and its high spatial resolution of 15 to 90 meters (about 50 to 300 feet), ASTER will image Earth for the next 6 years to map and monitor the changing surface of our planet.

    ASTER is one of five Earth-observing instruments launched December 18,1999, on NASA's Terra satellite. The instrument was built by Japan's Ministry of Economy, Trade and Industry. A joint U.S./Japan science team is responsible for validation and calibration of the instrument and the data products. Dr. Anne Kahle at NASA's Jet Propulsion Laboratory, Pasadena, California, is the U.S. Science team leader; Bjorn Eng of JPL is the project manager. The Terra mission is part of NASA's Earth Science Enterprise, a long-term research and technology program designed to examine Earth's land, oceans, atmosphere, ice and life as a total integrated system.

    The broad spectral coverage and high spectral resolution of ASTER will provide scientists in numerous disciplines with critical information for surface mapping

  15. HADS in the Large Magellanic Cloud: Initial findings from the SuperMACHO project

    SciTech Connect

    Garg, A

    2009-07-14

    The SuperMACHO Project is a five-year survey toward the Large Magellanic Cloud (LMC) aimed at understanding the nature of the populations of lenses responsible for the excess microlensing rates observed by the MACHO project. Survey observations were completed in 2006. A rich side-product of this survey is a catalog of variable sources down to a depth of VR 23, including many classes of pulsating variables such as {delta}-Scuti and RR Lyrae. Through their position in the Period-Luminosity diagram and their light curve characteristics we have identified 2323 high amplitude {delta}-Scuti (HADS) having high quality light curves. sing Fourier decomposition of the HADS light curves, we find that the period-luminosity (PL) relation defined by the firt-overtone (FO) pulsators does not show a clear separation from the PL-relation defined by the fundamental (F) pulsators. This differs from other instability strip pulsators such as type c RR Lyrae. We also present evidence for a larger amplitude, subluminous population of HADS similar to that observed in Fornax.

  16. PULSATING REVERSE DETONATION MODELS OF TYPE Ia SUPERNOVAE. II. EXPLOSION

    SciTech Connect

    Bravo, Eduardo; Garcia-Senz, Domingo; Cabezon, Ruben M.; DomInguez, Inmaculada E-mail: domingo.garcia@upc.edu E-mail: inma@ugr.es

    2009-04-20

    Observational evidences point to a common explosion mechanism of Type Ia supernovae based on a delayed detonation of a white dwarf (WD). However, all attempts to find a convincing ignition mechanism based on a delayed detonation in a destabilized, expanding, white dwarf have been elusive so far. One of the possibilities that has been invoked is that an inefficient deflagration leads to pulsation of a Chandrasekhar-mass WD, followed by formation of an accretion shock that confines a carbon-oxygen rich core, while transforming the kinetic energy of the collapsing halo into thermal energy of the core, until an inward moving detonation is formed. This chain of events has been termed Pulsating Reverse Detonation (PRD). In this work, we present three-dimensional numerical simulations of PRD models from the time of detonation initiation up to homologous expansion. Different models characterized by the amount of mass burned during the deflagration phase, M {sub defl}, give explosions spanning a range of kinetic energies, K {approx} (1.0-1.2) x 10{sup 51} erg, and {sup 56}Ni masses, M({sup 56}Ni) {approx} 0.6-0.8 M {sub sun}, which are compatible with what is expected for typical Type Ia supernovae. Spectra and light curves of angle-averaged spherically symmetric versions of the PRD models are discussed. Type Ia supernova spectra pose the most stringent requirements on PRD models.

  17. Empirical Determination of Convection in Pulsating White Dwarfs

    NASA Astrophysics Data System (ADS)

    Provencal, Judith L.; Hermes, J. J.; Montgomery, M.; Reed, Mike; Shipman, Harry; Fraga, Luciano

    2013-02-01

    We propose high speed photometric observations of WD J1518+0658 with SOAR and the KPNO 2m as important components of a coordinated international campaign designed to survey the properties of convection in white dwarf atmospheres. Convection remains the largest source of theoretical uncertainty in our understanding of stellar physics. Asteroseismology has proven a powerful tool to attack this problem. White dwarf pulsations appear as local surface temperature variations. The extreme temperature sensitivity of convection leads to local variations in the convection zone's depth. This in turn modulates the local energy flux, producing nonsinusoidal light curves. The observed nonlinearities provide a self-consistent observational test of convection in white dwarf atmospheres. WD J1518+0658 is a member of the newly discovered class of extremely low mass white dwarf pulsators (ELMVs). ELMVs offer the opportunity to extend our investigation to unexplored regions of lower effective temperatures and surface gravities, where conditions are closer to those found in main sequence stars. High precision light curves from SOAR, combined with frequency, amplitude, and phase information provided by the KPNO 2m and the entire WET run, will allow us to recover WD J1518+0658's convective thermal response timescale.

  18. Tidally Induced Pulsations in Kepler Eclipsing Binary KIC 3230227

    NASA Astrophysics Data System (ADS)

    Guo, Zhao; Gies, Douglas R.; Fuller, Jim

    2017-01-01

    KIC 3230227 is a short period (P ≈ 7.0 days) eclipsing binary with a very eccentric orbit (e = 0.6). From combined analysis of radial velocities and Kepler light curves, this system is found to be composed of two A-type stars, with masses of M1 = 1.84 ± 0.18 M⊙, M2 = 1.73 ± 0.17 M⊙ and radii of R1 = 2.01 ± 0.09 R⊙, R2 = 1.68 ± 0.08 R⊙ for the primary and secondary, respectively. In addition to an eclipse, the binary light curve shows a brightening and dimming near periastron, making this a somewhat rare eclipsing heartbeat star system. After removing the binary light curve model, more than 10 pulsational frequencies are present in the Fourier spectrum of the residuals, and most of them are integer multiples of the orbital frequency. These pulsations are tidally driven, and both the amplitudes and phases are in agreement with predictions from linear tidal theory for l = 2, m = ‑2 prograde modes.

  19. Pulsational instability of complex charge-fluctuating magnetized turbulent astroclouds

    NASA Astrophysics Data System (ADS)

    Karmakar, Pralay Kumar; Haloi, Archana

    2017-09-01

    We develop a theoretic model to study the linear stability behaviour of pulsational (gravito-electrostatic) mode in a self-gravitating, magnetized, collisional, turbulent and unbounded dust molecular cloud (DMC). The analytic model consists of lighter electrons and ions; and massive charged dust grains with partial ionization over the geometrically infinite extension. The semi-empirically obtained Larson logatropic equation of state, correlating all the thermo-turbo-magnetic pressures concurrently, is included afresh to model the constituent fluid turbulence pressures arising because of multiple randomized aperiodic flow scales of space and time. A linear normal mode analysis over the slightly perturbed composite cloud, relative to the defined homogeneous hydrostatic equilibrium, results in a unique mathematical construct of generalized polynomial (octic) dispersion relation with different coefficients sensitively dependent upon the diversified equilibrium cloud parameters. The main features of the modified pulsational mode dynamics are numerically explored over a commodious window of parametric values. It is shown and established that the grain mass introduces a dispersive stabilizing effect to the mode (with enhancement in phase speed), and vice-versa. A spatiotemporal illustrative tapestry is also portrayed for further confirmation of the dispersive mode with sporadic properties. The tentative application of our findings in different space and astrophysical circumstances is briefly outlined.

  20. Pulsating fronts in periodically modulated neural field models

    NASA Astrophysics Data System (ADS)

    Coombes, S.; Laing, C. R.

    2011-01-01

    We consider a coarse-grained neural field model for synaptic activity in spatially extended cortical tissue that possesses an underlying periodicity in its microstructure. The model is written as an integrodifferential equation with periodic modulation of a translationally invariant spatial kernel. This modulation can have a strong effect on wave propagation through the tissue, including the creation of pulsating fronts with widely varying speeds and wave-propagation failure. Here we develop a new analysis for the study of such phenomena, using two complementary techniques. The first uses linearized information from the leading edge of a traveling periodic wave to obtain wave speed estimates for pulsating fronts, and the second develops an interface description for waves in the full nonlinear model. For weak modulation and a Heaviside firing rate function the interface dynamics can be analyzed exactly and gives predictions that are in excellent agreement with direct numerical simulations. Importantly, the interface dynamics description improves on the standard homogenization calculation, which is restricted to modulation that is both fast and weak.

  1. Pulsation Properties of Carbon and Oxygen Red Giants

    NASA Astrophysics Data System (ADS)

    Percy, J. R.; Huang, D. J.

    2015-07-01

    We have used up to 12 decades of AAVSO visual observations, and the AAVSO VSTAR software package to determine new and/or improved periods of 5 pulsating biperiodic carbon (C-type) red giants, and 12 pulsating biperiodic oxygen (M-type) red giants. We have also determined improved periods for 43 additional C-type red giants, in part to search for more biperiodic C-type stars, and also for 46 M-type red giants. For a small sample of the biperiodic C-type and M-type stars, we have used wavelet analysis to determine the time scales of the cycles of amplitude increase and decrease. The C-type and M-type stars do not differ significantly in their period ratios (first overtone to fundamental). There is a marginal difference in the lengths of their amplitude cycles. The most important result of this study is that, because of the semiregularity of these stars, and the presence of alias, harmonic, and spurious periods, the periods which we and others derive for these stars—especially the smaller-amplitude ones—must be determined and interpreted with great care and caution. For instance: spurious periods of a year can produce an apparent excess of stars, at that period, in the period distribution.

  2. Fundamental parameters of pulsating stars from atmospheric models

    NASA Astrophysics Data System (ADS)

    Barcza, S.

    2006-12-01

    A purely photometric method is reviewed to determine distance, mass, equilibrium temperature, and luminosity of pulsating stars by using model atmospheres and hydrodynamics. T Sex is given as an example: on the basis of Kurucz atmospheric models and UBVRI (in both Johnson and Kron-Cousins systems) data, variation of angular diameter, effective temperature, and surface gravity is derived as a function of phase, mass M=(0.76± 0.09) M⊙, distance d=530± 67 pc, Rmax=2.99R⊙, Rmin=2.87R⊙, magnitude averaged visual absolute brightness < MVmag>=1.17± 0.26 mag are found. During a pulsation cycle four standstills of the atmosphere are pointed out indicating the occurrence of two shocks in the atmosphere. The derived equilibrium temperature Teq=7781 K and luminosity (28.3± 8.8)L⊙ locate T Sex on the blue edge of the instability strip in a theoretical Hertzsprung-Russell diagram. The differences of the physical parameters from this study and Liu & Janes (1990) are discussed.

  3. Pulsations of the polar cusp aurora at Saturn

    NASA Astrophysics Data System (ADS)

    Palmaerts, B.; Radioti, A.; Roussos, E.; Grodent, D.; Gérard, J.-C.; Krupp, N.; Mitchell, D. G.

    2016-12-01

    The magnetospheric cusp is a region connecting the interplanetary environment to the ionosphere and enabling solar wind particles to reach the ionosphere. We report the detection of several isolated high-latitude auroral emissions with the Ultraviolet Imaging Spectrograph of the Cassini spacecraft. We suggest that these auroral spots, located in the dawn-to-noon sector and poleward of the main emission, are the ionospheric signatures of the magnetospheric cusp, in agreement with some previous observations with the Hubble Space Telescope. The high-latitude cusp auroral signature has been associated with high-latitude lobe reconnection in the presence of a southward interplanetary magnetic field. The occurrence rate of the polar cusp aurora suggests that lobe reconnection is frequent at Saturn. Several auroral imaging sequences reveal a quasiperiodic brightening of the polar cusp aurora with a period in the range of 60 to 70 min. Similar pulsations in the energetic electron fluxes and in the azimuthal component of the magnetic field are simultaneously observed by Cassini instruments, suggesting the presence of field-aligned currents. Pulsed dayside magnetopause reconnection is a likely common triggering process for the cusp auroral brightenings at Saturn and the quasiperiodic pulsations in the high-latitude energetic electron fluxes.

  4. Numerical simulation of pressure pulsations in Francis turbines

    NASA Astrophysics Data System (ADS)

    Magnoli, M. V.; Schilling, R.

    2012-11-01

    In the last decades, hydraulic turbines have experienced the increase of their power density and the extension of their operating range, leading the fluid and mechanical dynamic effects to become significantly more pronounced. The understanding of the transient fluid flow and of the associated unsteady effects is essential for the reduction of the pressure pulsation level and improvement of the machine dynamic behaviour. In this study, the instationary fluid flow through the complete turbine was numerically calculated for an existing Francis machine with high specific speed. The hybrid turbulence models DES (detached eddy simulation) and SAS (scale adaptive simulation) allowed the accurate simulation of complex dynamic flow effects, such as the rotor-stator-interaction and the draft tube instabilities. Different operating conditions, as full load, part load, higher part load and deep part load, were successfully simulated and showed very tight agreement with the experimental results from the model tests. The transient pressure field history, obtained from the CFD (computational fluid dynamics) simulation and stored for each time step, was used as input for the full instationary FEA (finite element analysis) of turbine components. The assessment of the machine dynamic motion also offered the possibility to contribute to the understanding of the pressure pulsation effects and to further increase the turbine stability. This research project was developed at the Institute of Fluid Mechanics of the TU München.

  5. Pulsations of rapidly rotating stars with compositional discontinuities

    NASA Astrophysics Data System (ADS)

    Reese, Daniel R.; Lara, Francisco Espinosa; Rieutord, Michel

    2014-02-01

    Recent observations of rapidly rotating stars have revealed the presence of regular patterns in their pulsation spectra. This has raised the question as to their physical origin, and, in particular, whether they can be explained by an asymptotic frequency formula for low-degree acoustic modes, as recently discovered through numerical calculations and theoretical considerations. In this context, a key question is whether compositional/density gradients can adversely affect such patterns to the point of hindering their identification. To answer this question, we calculate frequency spectra using two-dimensional ESTER stellar models. These models use a multi-domain spectral approach, allowing us to easily insert a compositional discontinuity while retaining a high numerical accuracy. We analyse the effects of such discontinuities on both the frequencies and eigenfunctions of pulsation modes in the asymptotic regime. We find that although there is more scatter around the asymptotic frequency formula, the semi-large frequency separation can still be clearly identified in a spectrum of low-degree acoustic modes.

  6. Characterization of ultra low frequency (ULF) pulsations and the investigation of their possible source

    NASA Astrophysics Data System (ADS)

    Mthembu, S. H.; Malinga, S. B.; Walker, A. D. M.; Magnus, L.

    2009-08-01

    In this paper we present the results from the observation of ultra low frequency (ULF) pulsations in the Doppler velocity data from SuperDARN HF radar located at Goose Bay (61.94° N, 23.02° E, geomagnetic). Fourier spectral techniques were used to determine the spectral content of the data and the results show Pc 5 ULF pulsations (with a frequency range of 1 to 4 mHz) where the magnetic field lines were oscillating at discrete frequencies of about 1.3 and 1.9 mHz. These pulsations are classified as field lines resonance (FLR) since the 1.9 mHz component exhibited an enhancement in amplitude with an associated phase change of approximately 180° across a resonance latitude of 71.3°. The spatial and temporal structure of the ULF pulsations was examined by investigating their instantaneous amplitude which was calculated as the amplitude of the analytic signal. The results presented a full field of view which exhibit pulsations activity simultaneously from all beams. This representation shows that the peak amplitude of the 1.9 mHz component was observed over the longitudinal range of 13°. The temporal structure of the pulsations was investigated from the evolution of the 1.9 mHz component and the results showed that the ULF pulsations had a duration of about 1 h. Wavelet analysis was used to investigate solar wind as a probable source of the observed ULF pulsations. The time delay compared well with the solar wind travel time estimates and the results suggest a possible link between the solar wind and the observed pulsations. The sudden change in dynamic pressure also proved to be a possible source of the observed ULF pulsations.

  7. Ventricular dilation and elevated aqueductal pulsations in a new experimental model of communicating hydrocephalus.

    PubMed

    Wagshul, M E; McAllister, J P; Rashid, S; Li, J; Egnor, M R; Walker, M L; Yu, M; Smith, S D; Zhang, G; Chen, J J; Benveniste, H

    2009-07-01

    In communicating hydrocephalus (CH), explanations for the symptoms and clear-cut effective treatments remain elusive. Pulsatile flow through the cerebral aqueduct is often significantly elevated, but a clear link between abnormal pulsations and ventriculomegaly has yet to be identified. We sought to demonstrate measurement of pulsatile aqueductal flow of CSF in the rat, and to characterize the temporal changes in CSF pulsations in a new model of CH. Hydrocephalus was induced by injection of kaolin into the basal cisterns of adult rats (n = 18). Ventricular volume and aqueductal pulsations were measured on a 9.4 T MRI over a one month period. Half of the animals developed ventricular dilation, with increased ventricular volume and pulsations as early as one day post-induction, and marked chronic elevations compared to intact controls (volume: 130.15 +/- 83.21 microl vs. 15.52 +/- 2.00 microl; pulsations: 114.51 nl +/- 106.29 vs. 0.72 +/- 0.13 nl). Similar to the clinical presentation, the relationship between ventricular size and pulsations was quite variable. However, the pulsation time-course revealed two distinct sub-types of hydrocephalic animals: those with markedly elevated pulsations which persisted over time, and those with mildly elevated pulsations which returned to near normal levels after one week. These groups were associated with severe and mild ventriculomegaly respectively. Thus, aqueductal flow can be measured in the rat using high-field MRI and basal cistern-induced CH is associated with an immediate change in CSF pulsatility. At the same time, our results highlight the complex nature of aqueductal pulsation and its relationship to ventricular dilation.

  8. Ventricular dilation and elevated aqueductal pulsations in a new experimental model of communicating hydrocephalus

    SciTech Connect

    Wagshul, M.; Smith, S.; Wagshul, M.; McAllister, J.P.; Rashid, S.; Li, J.; Egnor, M.R.; Walker, M.L.; Yu, M.; Smith, S.D.; Zhang, G.; Chen, J.J.; Beneveniste, H.

    2009-03-01

    In communicating hydrocephalus (CH), explanations for the symptoms and clear-cut effective treatments remain elusive. Pulsatile flow through the cerebral aqueduct is often significantly elevated, but a clear link between abnormal pulsations and ventriculomegaly has yet to be identified. We sought to demonstrate measurement of pulsatile aqueductal flow of CSF in the rat, and to characterize the temporal changes in CSF pulsations in a new model of CH. Hydrocephalus was induced by injection of kaolin into the basal cisterns of adult rats (n = 18). Ventricular volume and aqueductal pulsations were measured on a 9.4 T MRI over a one month period. Half of the animals developed ventricular dilation, with increased ventricular volume and pulsations as early as one day post-induction, and marked chronic elevations compared to intact controls (volume: 130.15 {+-} 83.21 {mu}l vs. 15.52 {+-} 2.00 {mu}l; pulsations: 114.51 nl {+-} 106.29 vs. 0.72 {+-} 0.13 nl). Similar to the clinical presentation, the relationship between ventricular size and pulsations was quite variable. However, the pulsation time-course revealed two distinct sub-types of hydrocephalic animals: those with markedly elevated pulsations which persisted over time, and those with mildly elevated pulsations which returned to near normal levels after one week. These groups were associated with severe and mild ventriculomegaly respectively. Thus, aqueductal flow can be measured in the rat using high-field MRI and basal cistern-induced CH is associated with an immediate change in CSF pulsatility. At the same time, our results highlight the complex nature of aqueductal pulsation and its relationship to ventricular dilation.

  9. Experimental investigation of high-incidence delta-wing flow control

    NASA Astrophysics Data System (ADS)

    Buzica, Andrei; Bartasevicius, Julius; Breitsamter, Christian

    2017-09-01

    The possibility of extending the flight envelope for configurations with slender delta-shaped wings is investigated in this study by means of active flow control through pulsating jets from slot pairs distributed along the leading edge. The experiments comprise stereoscopic particle image velocimetry as well as force and moment measurements on a half-delta wing model. The analysis focuses on three high-incidence regimes: pre-stall, stall, and post-stall. This study also compares different perturbation methods: blowing with spatially constant and variable parameters, frequency and phase. At an incidence of 45°, the unison pulsed blowing facilitates the most significant flow transformation. Here, the separated shear layer reattaches on the wing's suction side, thus increasing the lift. Phase-averaged flow field measurements describe, in this particular case, the underlying physics of the flow-disturbance interaction.

  10. Natural processes in delta restoration: application to the Mississippi Delta.

    PubMed

    Paola, Chris; Twilley, Robert R; Edmonds, Douglas A; Kim, Wonsuck; Mohrig, David; Parker, Gary; Viparelli, Enrica; Voller, Vaughan R

    2011-01-01

    Restoration of river deltas involves diverting sediment and water from major channels into adjoining drowned areas, where the sediment can build new land and provide a platform for regenerating wetland ecosystems. Except for local engineered structures at the points of diversion, restoration mainly relies on natural delta-building processes. Present understanding of such processes is sufficient to provide a basis for determining the feasibility of restoration projects through quantitative estimates of land-building rates and sustainable wetland area under different scenarios of sediment supply, subsidence, and sea-level rise. We are not yet to the point of being able to predict the evolution of a restored delta in detail. Predictions of delta evolution are based on field studies of active deltas, deltas in mine-tailings ponds, experimental deltas, and countless natural experiments contained in the stratigraphic record. These studies provide input for a variety of mechanistic delta models, ranging from radially averaged formulations to more detailed models that can resolve channels, topography, and ecosystem processes. Especially exciting areas for future research include understanding the mechanisms by which deltaic channel networks self-organize, grow, and distribute sediment and nutrients over the delta surface and coupling these to ecosystem processes, especially the interplay of topography, network geometry, and ecosystem dynamics.

  11. Delta in Eberswalde

    NASA Technical Reports Server (NTRS)

    2006-01-01

    This HiRISE image covers a portion of a delta that partially fills Eberswalde crater in Margaritifer Sinus. The delta was first recognized and mapped using MOC images that revealed various features whose presence required sustained flow and deposition into a lake that once occupied the crater. The HiRISE image resolves meter-scale features that record the migration of channels and delta distributaries as the delta grew over time. Differences in grain-size of sediments within the environments on the delta enable differential erosion of the deposits. As a result, coarser channel deposits are slightly more resistant and stand in relief relative to finer-grained over-bank and more easily eroded distal delta deposits. Close examination of the relict channel deposits confirms the presence of some meter-size blocks that were likely too coarse to have been transported by water flowing within the channels. These blocks may be formed of the sand and gravel that more likely moved along the channels that was lithified and eroded. Numerous meter-scale polygonal structures are common on many surfaces, but mostly those associated with more quiescent depositional environments removed from the channels. The polygons could be the result of deposition of fine-grained sediments that were either exposed and desiccated (dried out), rich in clays that shrunk when the water was removed, turned into rock and then fractured and eroded, or some combination of these processes.

    Image PSP_001336_1560 was taken by the High Resolution Imaging Science Experiment (HiRISE) camera onboard the Mars Reconnaissance Orbiter spacecraft on November 8, 2006. The complete image is centered at -23.8 degrees latitude, 326.4 degrees East longitude. The range to the target site was 256.3 km (160.2 miles). At this distance the image scale is 25.6 cm/pixel (with 1 x 1 binning) so objects 77 cm across are resolved. The image shown here has been map-projected to 25 cm/pixel and north is up. The image was

  12. Delta in Eberswalde

    NASA Technical Reports Server (NTRS)

    2006-01-01

    This HiRISE image covers a portion of a delta that partially fills Eberswalde crater in Margaritifer Sinus. The delta was first recognized and mapped using MOC images that revealed various features whose presence required sustained flow and deposition into a lake that once occupied the crater. The HiRISE image resolves meter-scale features that record the migration of channels and delta distributaries as the delta grew over time. Differences in grain-size of sediments within the environments on the delta enable differential erosion of the deposits. As a result, coarser channel deposits are slightly more resistant and stand in relief relative to finer-grained over-bank and more easily eroded distal delta deposits. Close examination of the relict channel deposits confirms the presence of some meter-size blocks that were likely too coarse to have been transported by water flowing within the channels. These blocks may be formed of the sand and gravel that more likely moved along the channels that was lithified and eroded. Numerous meter-scale polygonal structures are common on many surfaces, but mostly those associated with more quiescent depositional environments removed from the channels. The polygons could be the result of deposition of fine-grained sediments that were either exposed and desiccated (dried out), rich in clays that shrunk when the water was removed, turned into rock and then fractured and eroded, or some combination of these processes.

    Image PSP_001336_1560 was taken by the High Resolution Imaging Science Experiment (HiRISE) camera onboard the Mars Reconnaissance Orbiter spacecraft on November 8, 2006. The complete image is centered at -23.8 degrees latitude, 326.4 degrees East longitude. The range to the target site was 256.3 km (160.2 miles). At this distance the image scale is 25.6 cm/pixel (with 1 x 1 binning) so objects 77 cm across are resolved. The image shown here has been map-projected to 25 cm/pixel and north is up. The image was

  13. Pioneer Launch on Delta Vehicle

    NASA Technical Reports Server (NTRS)

    1969-01-01

    NASA launches the last in the series of interplanetary Pioneer spacecraft, Pioneer 10 from Cape Kennedy, Florida. The long-tank Delta launch vehicle placed the spacecraft in a solar orbit along the path of Earth's orbit. The spacecraft then passed inside and outside Earth's orbit, alternately speeding up and slowing down relative to Earth. The Delta launch vehicle family started development in 1959. The Delta was composed of parts from the Thor, an intermediate-range ballistic missile, as its first stage, and the Vanguard as its second. The first Delta was launched from Cape Canaveral on May 13, 1960 and was powerful enough to deliver a 100-pound spacecraft into geostationary transfer orbit. Delta has been used to launch civil, commercial, and military satellites into orbit. For more information about Delta, please see Chapter 3 in Roger Launius and Dennis Jenkins' book To Reach the High Frontier published by The University Press of Kentucky in 2002.

  14. Hugli River Delta, India

    NASA Image and Video Library

    2001-10-22

    The western-most part of the Ganges Delta is seen in this 54.5 by 60 km ASTER sub-scene acquired on January 6, 2005. The Hugli River branches off from the Ganges River 300 km to the north, and flows by the city of Calcutta before emptying into the Bay of Bengal. High sediment load is evident by the light tan colors in the water, particularly downstream from off-shore islands. The deep green colors of some of these islands are mangrove swamps. The image is centered at 21.9 degrees north latitude, 88 degrees east longitude. http://photojournal.jpl.nasa.gov/catalog/PIA11158

  15. Classical Cepheid Pulsation Models. IX. New Input Physics

    NASA Astrophysics Data System (ADS)

    Petroni, Silvia; Bono, Giuseppe; Marconi, Marcella; Stellingwerf, Robert F.

    2003-12-01

    We constructed several sequences of classical Cepheid envelope models at solar chemical composition (Y=0.28,Z=0.02) to investigate the dependence of the pulsation properties predicted by linear and nonlinear hydrodynamic models on input physics. To study the dependence on the equation of state (EOS) we performed several numerical experiments by using the simplified analytical EOS originally developed by Stellingwerf and the recent analytical EOS developed by Irwin. Current findings suggest that the pulsation amplitudes, as well as the topology of the instability strip, marginally depend on the adopted EOS. To compromise between accuracy and numerical complexity we computed new EOS tables using the Irwin analytical EOS. We found that the difference between analytical and tabular thermodynamic quantities and their derivatives are smaller than 2% when adopting suitable steps in temperature and density. To improve the numerical accuracy of physical quantities, we are now adopting bicubic splines to interpolate both opacity and EOS tables. The new approach presents a substantial advantage to avoiding numerical derivatives in both linear and nonlinear models. The EOS first- and second-order derivatives are estimated by means of the analytical EOS or by means of analytical derivatives of the interpolating function. The opacity first-order derivatives are evaluated by means of analytical derivatives of the interpolating function. We also investigated the dependence of observables predicted by theoretical models on the mass-luminosity (ML) relation and on the spatial resolution across the hydrogen and the helium partial ionization regions. We found that nonlinear models are marginally affected by these physical and numerical assumptions. In particular, the difference between new and old models in the location as well as in the temperature width of the instability strip is, on average, less than 200 K. However, the spatial resolution somehow affects the pulsation properties

  16. The magnetic field of the pulsating subdwarf Balloon 090100001

    NASA Astrophysics Data System (ADS)

    Savanov, I. S.; Romanyuk, I. I.; Semenko, E. A.; Dmitrienko, E. S.

    2011-12-01

    We have analyzed polarization observations of the subdwarf Bal 09, which is one of a group of hybrid sdB stars that display simultaneously both short- and long-period pulsations. Certain properties previously unknown for subdwarfs have been established for Bal 09, such as variations of the pulsation amplitude of the main oscillation mode, rotational splitting of multiplets, and variations of this splitting. Information about the stellar magnetic field must be considered if we wish to explain these properties. New observational data enabling estimation of the longitudinal magnetic field of Bal 09 have been obtained on the main stellar spectrograph of the 6-m telescope of the Special Astrophysical Observatory. Studies of the longitudinal component of the magnetic field < B z > were carried out using a regression analysis. This method simultaneously yields estimates of the uncertainty in < B z >. Test measurements of < B z > were carried out using the same method. For the star HD 158974, which has zero total magnetic field, the estimated longitudinal magnetic field is < B z > = -4 ± 5 G. The standard magnetic field for the Ap star α 2CVn was measured to be -363 ± 17 G, in very good agreement with measurements in the literature. The estimated longitudinal magnetic field for Bal 09 is 34 ± 63G—appreciably lower than values established earlier for six subdwarfs, ≈1.5 kG. The results of the regression analysis for both individual spectral subranges and for intervals containing characteristic spectral features did not indicate reliable detections of a magnetic field exceeding the uncertainties in < B z >. The uncertainty in < B z >, which was 60-80 G for the entire spectral range and 140-200 G for selected spectral intervals, leads to an estimated upper limit on the longitudinal magnetic field < B z > for Bal 09. This estimate for < B z > can place observational constraints on theoretical explanations for the amplitude variations of the pulsations, rotational

  17. Soft X-Ray Pulsations in Solar Flares

    NASA Astrophysics Data System (ADS)

    Simões, P. J. A.; Hudson, H. S.; Fletcher, L.

    2015-12-01

    The soft X-ray emissions ( hν>1.5 keV) of solar flares mainly come from the bright coronal loops at the highest temperatures normally achieved in the flare process. Their ubiquity has led to their use as a standard measure of flare occurrence and energy, although the overwhelming bulk of the total flare energy goes elsewhere. Recently Dolla et al. ( Astrophys. J. Lett. 749, L16, 2012) noted quasi-periodic pulsations (QPP) in the soft X-ray signature of the X-class flare SOL2011-02-15, as observed by the standard photometric data from the GOES ( Geostationary Operational Environmental Satellite) spacecraft. In this article we analyse the suitability of the GOES data for this type of analysis and find them to be generally valuable after September, 2010 (GOES-15). We then extend the result of Dolla et al. to a complete list of X-class flares from Cycle 24 and show that most of them (80 %) display QPPs in the impulsive phase. The pulsations show up cleanly in both channels of the GOES data, making use of time-series of irradiance differences (the digital time derivative on the 2-s sampling). We deploy different techniques to characterise the periodicity of GOES pulsations, considering the red-noise properties of the flare signals, finding a range of characteristic time scales of the QPPs for each event, but usually with no strong signature of a single period dominating in the power spectrum. The QPP may also appear on somewhat longer time scales during the later gradual phase, possibly with a greater tendency towards coherence, but the sampling noise in GOES difference data for high irradiance values (X-class flares) makes these more uncertain. We show that there is minimal phase difference between the differenced GOES energy channels, or between them and the hard X-ray variations on short time scales. During the impulsive phase, the footpoints of the newly forming flare loops may also contribute to the observed soft X-ray variations.

  18. Peculiar variations of white dwarf pulsation frequencies and maestro

    NASA Astrophysics Data System (ADS)

    Dalessio, James Ruland

    In Part I we report on variations of the normal mode frequencies of the pulsating DB white dwarfs EC 20058-5234 and KIC 8626021 and the pulsating DA white dwarf GD 66. The observations of EC 20058-5234 and KIC 8626021 were motivated by the possibility of measuring the plasmon neutrino production rate of a white dwarf, while the observations of GD 66 were part of a white dwarf pulsation timing based planet search. We announce the discovery of periodic and quasi-periodic variations of multiple normal mode frequencies that cannot be due to the presence of planetary companions. We note the possible signature of a planetary companion to EC 20058-5234 and show that GD 66 cannot have a planet in a several AU orbit down to half a Jupiter mass. We also announce the discovery of secular variations of the normal mode frequencies of all three stars that are inconsistent with cooling alone. Importantly, the rates of period change of several modes of KIC 8626021 are consistent with evolutionary cooling, but are not yet statistically significant. These modes offer the best possibility of measuring the neutrino production rate in a white dwarf. We also observe periodic and secular variations in the frequency of a combination mode that exactly matches the variations predicted by the parent modes, strong observational evidence that combination modes are created by the convection zone and are not normal modes. Periodic variations in the amplitudes of many of these modes is also noted. We hypothesize that these frequency variations are caused by complex variations of the magnetic field strength and geometry, analogous to behavior observed in the Sun. In Part II we describe the MAESTRO software framework and the MAESTRO REDUCE algorithm. MAESTRO is a collection of astronomy specific MatLab software developed by the Whole Earth Telescope. REDUCE is an an algorithm that can extract the brightness of stars on a set of CCD images with minimal configuration and human interaction. The key to

  19. Retinal venous pulsation: Expanding our understanding and use of this enigmatic phenomenon.

    PubMed

    Morgan, William H; Hazelton, Martin L; Yu, Dao-Yi

    2016-11-01

    Retinal vein pulsation was first noted soon after the invention of the ophthalmoscope 170 years ago and was seen to change with cerebrospinal fluid pressure (CSFP) variation in the 1920s. The classical explanation for vein pulsation was that the cardiac cycle induced systolic peak in intraocular pressure (IOP) tended to intermittently collapse the retinal vein close to its exit in the central optic disk, causing pulsation to be counter-phase to IOP. Recently, improved ophthalmodynamometry and video recording techniques have allowed us to explore the fundamentals of retinal vein pulsation. This demonstrates that retinal venous collapse is in phase with both IOP and CSFP diastole, indicating the dependence upon CSFP pulse. We describe in some detail the mathematical and physical models of Starling resistors and how their results can be applied to understand the physiology of retinal vein pulsation. We discuss various techniques for measuring retinal venous pulsation, including a novel modified photo-plethysmographic technique developed in our laboratory. With these techniques, non-invasive measurement of CSFP is beginning to look feasible. Venous pulsation properties also have significant prognostic value in predicting long-term outcomes for both glaucoma and central retinal vein occlusion, as well as utility in other retinal vasculopathies and orbital disease. We demonstrate the potential use of modified photo-plethysmographic images in assessing these various disorders. A revised understanding of retinal vein pulse wave transmission along with improved measurement techniques may generate useful clinical tools for assessing these disorders. Copyright © 2016 Elsevier Ltd. All rights reserved.

  20. Coupled pulsating and cellular structure in the propagation of globally planar detonations in free space

    SciTech Connect

    Han, Wenhu; Gao, Yang; Wang, Cheng; Law, Chung K.

    2015-10-15

    The globally planar detonation in free space is numerically simulated, with particular interest to understand and quantify the emergence and evolution of the one-dimensional pulsating instability and the two-dimensional cellular structure which is inherently also affected by pulsating instability. It is found that the pulsation includes three stages: rapid decay of the overdrive, approach to the Chapman-Jouguet state and emergence of weak pulsations, and the formation of strong pulsations; while evolution of the cellular structure also exhibits distinct behavior at these three stages: no cell formation, formation of small-scale, irregular cells, and formation of regular cells of a larger scale. Furthermore, the average shock pressure in the detonation front consists of fine-scale oscillations reflecting the collision dynamics of the triple-shock structure and large-scale oscillations affected by the global pulsation. The common stages of evolution between the cellular structure and the pulsating behavior, as well as the existence of shock-front pressure oscillation, suggest highly correlated mechanisms between them. Detonations with period doubling, period quadrupling, and chaotic amplitudes were also observed and studied for progressively increasing activation energies.