Study of a sample of faint Be stars in the exofield of CoRoT. II. Pulsation and outburst events: Time series analysis of photometric variations

NASA Astrophysics Data System (ADS)

Semaan, T.; Hubert, A. M.; Zorec, J.; Gutiérrez-Soto, J.; Frémat, Y.; Martayan, C.; Fabregat, J.; Eggenberger, P.

2018-06-01

Context. The class of Be stars are the epitome of rapid rotators in the main sequence. These stars are privileged candidates for studying the incidence of rotation on the stellar internal structure and on non-radial pulsations. Pulsations are considered possible mechanisms to trigger mass-ejection phenomena required to build up the circumstellar disks of Be stars. Aims: Time series analyses of the light curves of 15 faint Be stars observed with the CoRoT satellite were performed to obtain the distribution of non-radial pulsation (NRP) frequencies in their power spectra at epochs with and without light outbursts and to discriminate pulsations from rotation-related photometric variations. Methods: Standard Fourier techniques were employed to analyze the CoRoT light curves. Fundamental parameters corrected for rapid-rotation effects were used to study the power spectrum as a function of the stellar location in the instability domains of the Hertzsprung-Russell (H-R) diagram. Results: Frequencies are concentrated in separate groups as predicted for g-modes in rapid B-type rotators, except for the two stars that are outside the H-R instability domain. In five objects the variations in the power spectrum are correlated with the time-dependent outbursts characteristics. Time-frequency analysis showed that during the outbursts the amplitudes of stable main frequencies within 0.03 c d-1 intervals strongly change, while transients and/or frequencies of low amplitude appear separated or not separated from the stellar frequencies. The frequency patterns and activities depend on evolution phases: (i) the average separations between groups of frequencies are larger in the zero-age main sequence (ZAMS) than in the terminal age main sequence (TAMS) and are the largest in the middle of the MS phase; (ii) a poor frequency spectrum with f ≲ 1 cd-1 of low amplitude characterizes the stars beyond the TAMS; and (iii) outbursts are seen in stars hotter than B4 spectral type and in the second half of the MS. Conclusions: The two main frequency groups are separated by δf = (1.24 ± 0.28) × frot in agreement with models of prograde sectoral g-modes (m = -1, -2) of intermediate-mass rapid rotators. The changes of amplitudes of individual frequencies and the presence of transients correlated with the outburst events deserve further studies of physical conditions in the subatmospheric layers to establish the relationship between pulsations and sporadic mass-ejection events. Tables 7 to 22 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/613/A70

A Baroclinic Eddy Mixer: Supercritical Transformation of Compensated Eddies

NASA Astrophysics Data System (ADS)

Sutyrin, G.

2016-02-01

In contrast to many real-ocean rings and eddies, circular vortices with initial lower layer at rest tend to be highly unstable in idealized two-layer models, unless their radius is made small or the lower layer depth is made artificially large. Numerical simulations of unstable vortices with parameters typical for ocean eddies revealed strong deformations and pulsations of the vortex core in the two-layer setup due to development of corotating tripolar structures in the lower layer during their supercritical transformation. The addition of a middle layer with the uniform potential vorticity weakens vertical coupling between the upper and lower layer that enhances vortex stability and makes the vortex lifespan more realistic. Such a three-layer vortex model possesses smaller lower interface slope than the two-layer model that reduces the potential vorticity gradient in the lower layer and provides with less unstable configurations. While cyclonic eddies become only slightly deformed and look nearly circular when the middle layer with uniform potential vorticity is added, anticyclonic eddies tend to corotating and pulsating elongated states through potential vorticity stripping and stirring. Enhanced vortex stability in such three-layer setup has important implications for adequate representation of the energy transfer across scales.

Impact of gaps in the asteroseismic characterization of pulsating stars. I. The efficiency of pre-whitening

NASA Astrophysics Data System (ADS)

Pascual-Granado, J.; Suárez, J. C.; Garrido, R.; Moya, A.; Hernández, A. García; Rodón, J. R.; Lares-Martiz, M.

2018-06-01

Context. It is known that the observed distribution of frequencies in CoRoT and Kepler δ Scuti stars has no parallelism with any theoretical model. Pre-whitening is a widespread technique in the analysis of time series with gaps from pulsating stars located in the classical instability strip, such as δ Scuti stars. However, some studies have pointed out that this technique might introduce biases in the results of the frequency analysis. Aims: This work aims at studying the biases that can result from pre-whitening in asteroseismology. The results will depend on the intrinsic range and distribution of frequencies of the stars. The periodic nature of the gaps in CoRoT observations, only in the range of the pulsational frequency content of the δ Scuti stars, is shown to be crucial to determining their oscillation frequencies, the first step in performing asteroseismology of these objects. Hence, here we focus on the impact of pre-whitening on the asteroseismic characterization of δ Scuti stars. Methods: We select a sample of 15 δ Scuti stars observed by the CoRoT satellite, for which ultra-high-quality photometric data have been obtained by its seismic channel. In order to study the impact on the asteroseismic characterization of δ Scuti stars we perform the pre-whitening procedure on three datasets: gapped data, linearly interpolated data, and data with gaps interpolated using Autoregressive and Moving Average models (ARMA). Results: The different results obtained show that at least in some cases pre-whitening is not an efficient procedure for the deconvolution of the spectral window. Therefore, in order to reduce the effect of the spectral window to a minimum, in addition to performing a pre-whitening of the data, it is necessary to interpolate with an algorithm that is aimed to preserve the original frequency content. Tables 5-49 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/614/A40

Probing Stellar Dynamics With Space Photometry

NASA Astrophysics Data System (ADS)

García, Rafael A.; Salabert, D.; Ballot, J.; Beck, P. G.; Bigot, L.; Corsaro, E.; Creevey, O.; Egeland, R.; Jiménez, A.; Mathur, S.; Metcalfe, T.; do Nascimento, J.; Pallé, P. L.; Pérez Hernández, F.; Regulo, C.

2016-08-01

The surface magnetic field has substantial influence on various stellar properties that can be probed through various techniques. With the advent of new space-borne facilities such as CoRoT and Kepler, uninterrupted long high-precision photometry is available for hundred of thousand of stars. This number will substantially grow through the forthcoming TESS and PLATO missions. The unique Kepler observations -covering up to 4 years with a 30-min cadence- allows studying stellar variability with different origins such as pulsations, convection, surface rotation, or magnetism at several time scales from hours to years. We study the photospheric magnetic activity of solar-like stars by means of the variability induced in the observed signal by starspots crossing the visible disk. We constructed a solar photometric magnetic activity proxy, Sph from SPM/VIRGO/SoHO, as if the Sun was a distant star and we compare it with several solar well-known magnetic proxies. The results validate this approach. Thus, we compute the Sph proxy for a set of CoRoT and Kepler solar-like stars for which pulsations were already detected. After characterizing the rotation and the magnetic properties of 300 solar-like stars, we use their seismic properties to characterize 18 solar analogs for which we study their magnetism. This allows us to put the Sun into context of its siblings.

A Review of the Low-Frequency Waves in the Giant Magnetospheres

NASA Astrophysics Data System (ADS)

Delamere, P. A.

2016-02-01

The giant magnetospheres harbor a plethora of low-frequency waves with both internal (i.e., moons) and external (i.e., solar wind) source mechanisms. This chapter summarizes the observation of low-frequency waves at Jupiter and Saturn and postulates the underlying physics based on our understanding of magnetodisc generation mechanisms. The source mechanisms of ULF pulsations at the giant magnetospheres are numerous. The satellite-magnetosphere interactions and mass loading of corotational flows generate many low-frequency waves. Observations of low-frequency bursts of radio emissions serve as an excellent diagnostic for understanding satellite-magnetosphere interactions. The outward radial transport of plasma through the magnetodisc and related magnetic flux circulation is a significant source of ULF pulsations; however, it is uncertain how the radial transport mechanism compares with solar wind induced perturbations.

Time-resolved FUSE photometric and spectroscopic observations: PG 1219+534, PG 1605+072, and PG 1613+426

NASA Astrophysics Data System (ADS)

Kuassivi; Bonanno, A.; Ferlet, R.

2005-11-01

We report the detection of pulsations in the far ultraviolet (FUV) light curves of PG 1219+534, PG 1605+072 and PG 1613+426 obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE) in time tagged mode (TTAG). Exposures of the order of a few ksec were sufficient to observe the main frequencies of PG 1219+534 and PG 1605+072 and confirm the detection of a pulsation mode at the surface of PG 1613+426 as reported from ground. For the first time we derive time resolved spectroscopic FUSE data of a sdB pulsator (PG 1605+072) and comment on its line profile variation diagram (lpv diagram). We observe the phase shift between the maximum luminosity and the maximum radius to be consistent with the model of an adiabatic pulsator. We also present evidence that the line broadening previously reported is not caused by rotation but is rather an observational bias due to the rapid Doppler shift of the lines with 17 km s-1 amplitude. Thus our observations do not support the previous claim that PG 1605+072 is (or will evolve into) an unusually fast rotating degenerate dwarf. These results demonstrate the asteroseismological potential of the FUSE satellite which should be viewed as another powerful means of investigating stellar pulsations, along with the MOST and COROT missions.

Existence of a component corotating with the earth in high-latitude disturbance magnetic fields

NASA Technical Reports Server (NTRS)

Suzuki, A.; Kim, J. S.; Sugiura, M.

1982-01-01

A study of the data from the high-latitude North American IMS network of magnetic stations suggests that there is a component in substorm perturbations that corotates with the earth. It is as yet not certain whether the existence of this component stems from the corotation of a part of the magnetospheric plasma involved in the substorm mechanism or if it is a 'phase change' resulting from the control of the substorm manifestations by the earth's main magnetic field which is not axially symmetric. There are other geophysical phenomena showing a persistence of longitudinal variations corotating with the earth. These phenomena are of significance for a better understanding of ionosphere-magnetosphere coupling.

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

Photometric variability of the Be star CoRoT-ID 102761769

NASA Astrophysics Data System (ADS)

Emilio, M.; Andrade, L.; Janot-Pacheco, E.; Baglin, A.; Gutiérrez-Soto, J.; Suárez, J. C.; de Batz, B.; Diago, P.; Fabregat, J.; Floquet, M.; Frémat, Y.; Huat, A. L.; Hubert, A. M.; Espinosa Lara, F.; Leroy, B.; Martayan, C.; Neiner, C.; Semaan, T.; Suso, J.

2010-11-01

Context. Classical Be stars are rapid rotators of spectral type late O to early A and luminosity class V-III, which exhibit Balmer emission lines and often a near infrared excess originating in an equatorially concentrated circumstellar envelope, both produced by sporadic mass ejection episodes. The causes of the abnormal mass loss (the so-called Be phenomenon) are as yet unknown. Aims: For the first time, we can now study in detail Be stars outside the Earth's atmosphere with sufficient temporal resolution. We investigate the variability of the Be Star CoRoT-ID 102761769 observed with the CoRoT satellite in the exoplanet field during the initial run. Methods: One low-resolution spectrum of the star was obtained with the INT telescope at the Observatorio del Roque de los Muchachos. A time series analysis was performed using both cleanest and singular spectrum analysis algorithms to the CoRoT light curve. To identify the pulsation modes of the observed frequencies, we computed a set of models representative of CoRoT-ID 102761769 by varying its main physical parameters inside the uncertainties discussed. Results: We found two close frequencies related to the star. They are 2.465 c d-1 (28.5 μHz) and 2.441 c d-1 (28.2 μHz). The precision to which those frequencies were found is 0.018 c d-1 (0.2 μHz). The projected stellar rotation was estimated to be 120 km s-1 from the Fourier transform of spectral lines. If CoRoT-ID 102761769 is a typical Galactic Be star it rotates near the critical velocity. The critical rotation frequency of a typical B5-6 star is about 3.5 c d-1 (40.5 μHz), which implies that the above frequencies are really caused by stellar pulsations rather than star's rotation. 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, Belgium, Brazil, Germany, and Spain.

Investigating the origin of cyclical wind variability in hot massive stars - II. Hydrodynamical simulations of corotating interaction regions using realistic spot parameters for the O giant ξ Persei

NASA Astrophysics Data System (ADS)

David-Uraz, A.; Owocki, S. P.; Wade, G. A.; Sundqvist, J. O.; Kee, N. D.

2017-09-01

OB stars exhibit various types of spectral variability historically associated with wind structures, including the apparently ubiquitous discrete absorption components (DACs). These features have been proposed to be caused either by magnetic fields or non-radial pulsations. In this second paper of this series, we revisit the canonical phenomenological hydrodynamical modelling used to explain the formation of DACs by taking into account modern observations and more realistic theoretical predictions. Using constraints on putative bright spots located on the surface of the O giant ξ Persei derived from high precision space-based broad-band optical photometry obtained with the Microvariability and Oscillations of Stars (MOST) space telescope, we generate 2D hydrodynamical simulations of corotating interaction regions in its wind. We then compute synthetic ultraviolet (UV) resonance line profiles using Sobolev Exact Integration and compare them with historical timeseries obtained by the International Ultraviolet Explorer (IUE) to evaluate if the observed behaviour of ξ Persei's DACs is reproduced. Testing three different models of spot size and strength, we find that the classical pattern of variability can be successfully reproduced for two of them: the model with the smallest spots yields absorption features that are incompatible with observations. Furthermore, we test the effect of the radial dependence of ionization levels on line driving, but cannot conclusively assess the importance of this factor. In conclusion, this study self-consistently links optical photometry and UV spectroscopy, paving the way to a better understanding of cyclical wind variability in massive stars in the context of the bright spot paradigm.

δ Scuti-type pulsation in the hot component of the Algol-type binary system BG Peg

NASA Astrophysics Data System (ADS)

Şenyüz, T.; Soydugan, E.

2014-02-01

In this study, 23 Algol-type binary systems, which were selected as candidate binaries with pulsating components, were observed at the Çanakkale Onsekiz Mart University Observatory. One of these systems was BG Peg. Its hotter component shows δ Scuti-type light variations. Physical parameters of BG Peg were derived from modelling the V light curve using the Wilson-Devinney code. The frequency analysis shows that the pulsational component of the BG Peg system pulsates in two modes with periods of 0.039 and 0.047 d. Mode identification indicates that both modes are most likely non-radial l = 2 modes.

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, Belgium, Brazil, Germany, and Spain. This work is based on ground-based observations made with ESO telescopes at the La Silla Observatory under the ESO Large Programme LP178.D-0361 and on data collected at the Observatorio de Sierra Nevada (Spain), at the Observatorio Astronómico Nacional San Pedro Mártir (Mexico), and at the Piszkéstetö Mountain Station of Konkoly Observatory (Hungary). Table 2 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/506/85 Current address: Laboratoire AIM, CEA/DSM CNRS Université Paris Diderot, CEA, IRFU, SAp, centre de Saclay, 91191 Gif-sur-Yvette, France.

On Long Baroclinic Rossby Waves in the Tropical North Atlantic Observed From Profiling Floats

DTIC Science & Technology

2007-05-16

15b and 15c). Reclosing of vortex isolines while forming a new corotating eddy pair typically indicates excitation of periodical auto-oscillations in...important dynamical effect as reclosing of vortex isolines between corotating eddies, which are components of the semiannual standing Rossby wave

Asm-Triggered too Observations of Z Sources at Low Accretion Rate

NASA Astrophysics Data System (ADS)

van der Klis, Michiel

We propose to perform a pointed observation if the ASM shows that a Z source has entered a state of low accretion rate. This would provide a unique opportunity to detect millisecond pulsations. In Sco X-1 we would expect to discover beat-frequency QPO, and could perform a unique high count rate study of them. At sufficiently low accretion rate it would be possible to study the accretion flow when the magnetospheric radius approaches the corotation radius. The frequency of the horizontal branch QPO should go to zero here, and centrifugal inhibition of the accretion should set in, providing direct tests of the magnetospheric model of Z sources.

Regular frequency patterns in the young δ Scuti star HD 261711 observed by the CoRoT and MOST satellites

NASA Astrophysics Data System (ADS)

Zwintz, K.; Fossati, L.; Guenther, D. B.; Ryabchikova, T.; Baglin, A.; Themessl, N.; Barnes, T. G.; Matthews, J. M.; Auvergne, M.; Bohlender, D.; Chaintreuil, S.; Kuschnig, R.; Moffat, A. F. J.; Rowe, J. F.; Rucinski, S. M.; Sasselov, D.; Weiss, W. W.

2013-04-01

Context. The internal structure of pre-main-sequence (PMS) stars is poorly constrained at present. This could change significantly through high-quality asteroseismological observations of a sample of such stars. Aims: We concentrate on an asteroseismological study of HD 261711, a rather hot δ Scuti-type pulsating member of the young open cluster NGC 2264 located at the blue border of the instability region. HD 261711 was discovered to be a PMS δ Scuti star using the time series photometry obtained by the MOST satellite in 2006. Methods: High-precision, time-series photometry of HD 261711 was obtained by the MOST and CoRoT satellites in four separate new observing runs that are put into context with the star's fundamental atmospheric parameters obtained from spectroscopy. Frequency Analysis was performed using Period04. The spectral analysis was performed using equivalent widths and spectral synthesis. Results: With the new MOST data set from 2011/12 and the two CoRoT light curves from 2008 and 2011/12, the δ Scuti variability was confirmed and regular groups of frequencies were discovered. The two pulsation frequencies identified in the data from the first MOST observing run in 2006 are confirmed and 23 new δ Scuti-type frequencies were discovered using the CoRoT data. Weighted average frequencies for each group were determined and are related to l = 0 and l = 1 p-modes. Evidence for amplitude modulation of the frequencies in two groups is seen. The effective temperature (Teff) was derived to be 8600 ± 200 K, log g is 4.1 ± 0.2, and the projected rotational velocity (υsini) is 53 ± 1 km s-1. Using our Teff value and the radius of 1.8 ± 0.5 R⊙ derived from spectral energy distribution (SED) fitting, we get a luminosity log L/L⊙ of 1.20 ± 0.14 which agrees well to the seismologically determined values of 1.65 R⊙ and, hence, a log L/L⊙ of 1.13. The radial velocity of 14 ± 2 km s-1 we derived for HD 261711, confirms the star's membership to NGC 2264. Conclusions: Our asteroseismic models suggest that HD 261711 is a δ Scuti-type star close to the zero-age main sequence (ZAMS) with a mass of 1.8 to 1.9 M⊙. With an age of about 10 million years derived from asteroseismology, the star is either a young ZAMS star or a late PMS star just before the onset of hydrogen-core burning. The observed splittings about the l = 0 and 1 parent modes may be an artifact of the Fourier derived spectrum of frequencies with varying amplitudes. 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, Belgium, Brazil, Germany, and Spain.Based on data from the MOST satellite, a Canadian Space Agency mission, jointly operated by Microsatellite Systems Canada Inc. (MSCI), formerly part of Dynacon, Inc., the University of Toronto Institute for Aerospace Studies and the University of British Columbia with the assistance of the University of Vienna.Reduced spectra are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/552/A68

Survey for δ Sct components in eclipsing binaries and new correlations between pulsation frequency and fundamental stellar characteristics

NASA Astrophysics Data System (ADS)

Liakos, A.; Niarchos, P.; Soydugan, E.; Zasche, P.

2012-05-01

CCD observations of 68 eclipsing binary systems, candidates for containing δ Scuti components, were obtained. Their light curves are analysed using the PERIOD04 software for possible pulsational behaviour. For the systems QY Aql, CZ Aqr, TY Cap, WY Cet, UW Cyg, HL Dra, HZ Dra, AU Lac, CL Lyn and IO UMa, complete light curves were observed due to the detection of a pulsating component. All of them, except QY Aql and IO UMa, are analysed with modern astronomical softwares in order to determine their geometrical and pulsational characteristics. Spectroscopic observations of WY Cet and UW Cyg were used to estimate the spectral class of their primary components, while for HZ Dra radial velocities of its primary were measured. O - C diagram analysis was performed for the cases showing peculiar orbital period variations, namely CZ Aqr, TY Cap, WY Cet and UW Cyg, with the aim of obtaining a comprehensive picture of these systems. An updated catalogue of 74 close binaries including a δ Scuti companion is presented. Moreover, a connection between orbital and pulsation periods, as well as a correlation between evolutionary status and dominant pulsation frequency for these systems, is discussed.

EVIDENCE FOR GRANULATION IN EARLY A-TYPE STARS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kallinger, Thomas; Matthews, Jaymie M.

2010-03-01

Stars with spectral types earlier than about F0 on (or close) to the main sequence have long been believed to lack observable surface convection, although evolutionary models of A-type stars do predict very thin surface convective zones. We present evidence for granulation in two {delta} Scuti stars of spectral type A2: HD 174936 and HD 50844. Recent analyses of space-based CoRoT data revealed up to some 1000 frequencies in the photometry of these stars. The frequencies were interpreted as individual pulsation modes. If true, there must be large numbers of nonradial modes of very high degree l which should suffermore » cancellation effects in disk-integrated photometry (even of high space-based precision). The p-mode interpretation of all the frequencies in HD 174936 and HD 50844 depends on the assumption of white (frequency-independent) noise. Our independent analyses of the data provide an alternative explanation: most of the peaks in the Fourier spectra are the signature of non-white granulation background noise, and less than about 100 of the frequencies are actual stellar p-modes in each star. We find granulation timescales which are consistent with scaling relations that describe cooler stars with known surface convection. If the granulation interpretation is correct, the hundreds of low-amplitude Fourier peaks reported in recent studies are falsely interpreted as independent pulsation modes and a significantly lower number of frequencies are associated with pulsation, consistent with only modes of low degree.« less

Photometric Study of the Pulsating, Eclipsing Binary OO Dra

NASA Astrophysics Data System (ADS)

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

Photometric study of the pulsating, eclipsing binary OO DRA

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, X. B.; Deng, L. C.; Tian, J. F.

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.more » 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.« less

OBSERVATIONS OF THE HIGH-MASS X-RAY BINARY A 0535+26 IN QUIESCENCE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rothschild, Richard; Markowitz, Alex; Hemphill, Paul

2013-06-10

We have analyzed three observations of the high-mass X-ray binary A 0535+26 performed by the Rossi X-Ray Timing Explorer (RXTE) three, five, and six months after the last outburst in 2011 February. We detect pulsations only in the second observation. The 3-20 keV spectra can be fit equally well with either an absorbed power law or absorbed thermal bremsstrahlung model. Reanalysis of two earlier RXTE observations made 4 yr after the 1994 outburst, original BeppoSAX observations 2 yr later, reanalysis of four EXOSAT observations made 2 yr after the last 1984 outburst, and a recent XMM-Newton observation in 2012 revealmore » a stacked, quiescent flux level decreasing from {approx}2 to <1 Multiplication-Sign 10{sup -11} erg cm{sup -2} s{sup -1} over 6.5 yr after outburst. The detection of pulsations during half of the quiescent observations would imply that accretion onto the magnetic poles of the neutron star continues despite the fact that the circumstellar disk may no longer be present. The accretion could come from material built up at the corotation radius or from an isotropic stellar wind.« less

Global MHD simulations driven by idealized Alfvenic fluctuations in the solar wind

NASA Astrophysics Data System (ADS)

Claudepierre, S. G.

2017-12-01

High speed solar wind streams (HSSs) and corotating interaction regions (CIRs) often lead to MeV electron flux enhancements the Earth's outer radiation belt. The relevant physical processes responsible for these enhancements are not entirely understood. We investigate the potential role that solar wind Alfvenic fluctuations, intrinsic structures embedded in the HSS/CIRs, play in radiation belt dynamics. In particular, we explore the hypothesis that magnetospheric ultra-low frequency (ULF) pulsations driven by interplanetary magnetic field fluctuations are the intermediary mechanism responsible for the pronounced effect that HSS/CIRs have on the outer electron radiation belt. We examine these effects using global, three-dimensional magnetohydrodynamic (MHD) simulations driven by idealized interplanetary Alfvenic fluctuations, both monochromatic and broadband noise (Kolmogorov turbulence).

Doubled-lined eclipsing binary system KIC~2306740 with pulsating component discovered from Kepler space photometry

NASA Astrophysics Data System (ADS)

Yakut, Kadri

2015-08-01

We present a detailed study of KIC 2306740, an eccentric double-lined eclipsing binary system with a pulsating component.Archive Kepler satellite data were combined with newly obtained spectroscopic data with 4.2\\,m William Herschel Telescope(WHT). This allowed us to determine rather precise orbital and physical parameters of this long period, slightly eccentric, pulsating binary system. Duplicity effects are extracted from the light curve in order to estimate pulsation frequencies from the residuals.We modelled the detached binary system assuming non-conservative evolution models with the Cambridge STARS(TWIN) code.

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.

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.

Spiral stellar density waves and the flattening of abundance gradients in the warm gas component of spiral galaxies

NASA Astrophysics Data System (ADS)

Vorobyov, E. I.

2006-08-01

Motivated by recent observations of plateaus and minima in the radial abundance distributions of heavy elements in the Milky Way and some other spiral galaxies, we propose a dynamical mechanism for the formation of such features around corotation. Our numerical simulations show that the non-axisymmetric gravitational field of spiral density waves generates cyclone and anticylone gas flows in the vicinity of corotation. The anticyclones flatten the pre-existing negative abundance gradients by exporting many more atoms of heavy elements outside corotation than importing inside it. This process is very efficient and forms plateaus of several kiloparsec in size around corotation after two revolution periods of a galaxy. The strength of anticyclones and, consequently, the sizes of plateaus depend on the pitch angle of spiral arms and are expected to increase along the Hubble sequence.

The flow in the spiral arms of slowly rotating bar-spiral models

NASA Astrophysics Data System (ADS)

Patsis, P. A.; Tsigaridi, L.

2017-07-01

We use response models to study the stellar and gaseous flows in the spiral arm regions of slow rotating barred-spiral potentials. We vary the pattern speed so that the corotation-to bar radius ratios (Rc/Rb) are in the range 2 < Rc/Rb < 3. We find in general two sets of spirals, one inside and one outside corotation, which are reinforced by two different dynamical mechanisms. The bar and the spirals inside corotation are supported by regular orbits, while the spirals beyond corotation are associated with the "chaotic spirals", both in the stellar as well as in the gaseous case. The main difference in the two flows is the larger dispersion of velocities we encounter in the stellar (test-particles) models. The inner and the outer spirals are in general not connected. In most cases we find an oval component inside corotation, that surrounds the inner barred-spiral structure and separates it from the outer spirals. In the gaseous models, clumps of local overdensities are formed along the inner arms as the gas shocks in the spirals region, while clumps in the spirals beyond corotation are formed as the flows along the two outer arms meet and join each other close to the unstable Lagrangian points of the system.

Second harmonic Pi2 pulsation observed near the plasmapause by the Asian-Oceanian SuperDARN radars and THEMIS satellites

NASA Astrophysics Data System (ADS)

Teramoto, M.; Nishitani, N.; Hori, T.; Devlin, J. C.; Angelopoulos, V.; Glassmeier, K.; Clausen, L.; Baumjohann, W.; Bonnell, J. W.; Mozer, F.

2012-12-01

Pi2 pulsations appear on the nightside at substorm onsets. Several studies suggested that transient Alfven waves might contribute to the excitation of Pi2 pulsations at nightside mid and high latitudes. On the other hand, fast mode waves trapped between the ionosphere and plasmapause are responsible for Pi2 pulsations at mid and low latitudes on the nightside. Using the Sweden And Britain auroral Radar Experiment (SABRE) coherent radar at auroral and sub-auroral latitudes, Yeoman et al. [1991] found that the radar could distinguish between these two types of Pi2 pulsations and suggested that the mid latitude region is the transition region of these two types of Pi2 pulsations. We report on one event of Pi2 pulsation starting at 09:12 UT on 19 August 2010 observed simultaneously by the Hokkaido (HOK), Tiger (TIG), and Unwin (UNW) SuperDARN radars and THEMIS-A, -D, -E satellites when they were located in the premidnight sector. The THEMIS satellites observed Pi2 pulsations at 13 mHz predominantly in the compressional and radial components of the magnetic field and the azimuthal component of the electric field when satellites were located at L < 5 inside the plasmasphere. These pulsations had high coherence (~1) with the H-component Pi2 pulsations at a low-latitude ground station, Kakioka (KAK: magnetic latitude 27.47; magnetic longitude 209.2 degrees). The Poynting flux indicates earthward and duskward flux of Pi2 energy. The radars observed oscillations of Doppler velocities at mid latitude while operating in themisscan mode, during which beam 4 of HOK, beam 4 of TIG, and beam 14 of UNW provide 8-s sampling data. These oscillations corresponded to approximately the east-west component of electric field in the ionosphere. Oscillations backscattered form the lower-latitude ionosphere had a predominant frequency at 13 mHz while Pi2 pulsations observed at higher latitude by the radars had predominant frequencies at both 13 and 25 mHz. The power of Doppler velocity oscillations at 25 mHz was greater than that at 13 mHz at 60-65° geomagnetic latitude. These results indicate that a fast mode wave propagating earthward and duskward causes fundamental and second harmonic structures in the plasmasphere. We will present the details of the observation.

Photometric and Spectroscopic Study of the Delta Scuti Stars FH Cam, CU CVn and CC Lyn

NASA Astrophysics Data System (ADS)

Conidis, G. J.; Gazeas, K. D.; Capobianco, C. C.; Ogloza, W.

2010-06-01

Three short period (P ˜ 1 day) variable stars from the Hipparcos catalogue targets were observed after suspected misclassification as Beta Lyr eclipsing systems (Perryman et al. 1997), as no secondary component had been noticed in the inspection of their Broadening Functions (BFs) (Rucinski 2002). FH Cam is found to be a multiple star system with a member exhibiting Delta Scuti behaviour. The dominant pulsation frequency is found to be 7.3411 ± 0.0002 c/d, which corresponds to a pulsation mode of l ≤ 1. We confirmed the pulsations of CU CVn using photometric observations and found a pulsation frequency of 14.7626 ± 0.0250 c/d, which is in agreement with the period given in literature. CC Lyn is a non-eclipsing visual binary (CCDM J07359+4302AB), the brighter component (A) is found to be a multi-mode Delta Scuti pulsator, with pulsation frequencies of 5.6402 ± 0.0004 c/d and 7.3368 ± 0.0005 c/d.

ON THE PULSATIONAL-ORBITAL-PERIOD RELATION OF ECLIPSING BINARIES WITH δ-SCT COMPONENTS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, X. B.; Luo, C. Q.; Fu, J. N.

2013-11-01

We have deduced a theoretical relation between the pulsation and orbital-periods of pulsating stars in close binaries based on their Roche lobe filling. It appears to be of a simple linear form, with the slope as a function of the pulsation constant, the mass ratio, and the filling factor for an individual system. Testing the data of 69 known eclipsing binaries containing δ-Sct-type components yields an empirical slope of 0.020 ± 0.006 for the P{sub pul}-P{sub orb} relation. We have further derived the upper limit of the P{sub pul}/P{sub orb} ratio for the δ-Sct stars in eclipsing binaries with amore » value of 0.09 ± 0.02. This value could serve as a criterion to distinguish whether or not a pulsator in an eclipsing binary pulsates in the p-mode. Applying the deduced P{sub pul}-P{sub orb} relation, we have computed the dominant pulsation constants for 37 δ-Sct stars in eclipsing systems with definite photometric solutions. These ranged between 0.008 and 0.033 days with a mean value of about 0.014 days, indicating that δ-Sct stars in eclipsing binaries mostly pulsate in the fourth or fifth overtones.« less

The γ Dor stars as revealed by Kepler: A key to reveal deep-layer rotation in A and F stars

NASA Astrophysics Data System (ADS)

Salmon, S. J. A. J.; Ouazzani, R.-M.; Antoci, V.; Bedding, T. R.; Murphy, S. J.

2017-09-01

The γ Dor pulsating stars present high-order gravity modes, which make them important targets in the intermediate-and low-mass main-sequence region of the Hertzsprung-Russell diagram. Whilst we have only access to rotation in the envelope of the Sun, the g modes of γ Dor stars can in principle deliver us constraints on the inner layers. With the puzzling discovery of unexpectedly low rotation rates in the core of red giants, the γ Dor stars appear now as unique targets to explore internal angular momentum transport in the progenitors of red giants. Yet, the γ Dor pulsations remain hard to detect from the ground for their periods are close to 1 day. While the CoRoT space mission first revealed intriguing frequency spectra, the almost uninterrupted 4-year photometry from the Kepler mission eventually shed a new light on them. It revealed regularities in the spectra, expected to bear signature of physical processes, including rotation, in the shear layers close to the convective core. We present here the first results of our effort to derive exploitable seismic diagnosis for mid- to fast rotators among γ Dor stars. We confirm their potential to explore the rotation history of this early phase of stellar evolution.

The MACHO Project Large Magellanic Cloud Variable-Star Inventory. IX. Frequency Analysis of the First-Overtone RR Lyrae Stars and the Indication for Nonradial Pulsations

NASA Astrophysics Data System (ADS)

Alcock, C.; Allsman, R.; Alves, D. R.; Axelrod, T.; Becker, A.; Bennett, D.; Clement, C.; Cook, K. H.; Drake, A.; Freeman, K.; Geha, M.; Griest, K.; Kovács, G.; Kurtz, D. W.; Lehner, M.; Marshall, S.; Minniti, D.; Nelson, C.; Peterson, B.; Popowski, P.; Pratt, M.; Quinn, P.; Rodgers, A.; Rowe, J.; Stubbs, C.; Sutherland, W.; Tomaney, A.; Vandehei, T.; Welch, D. L.

2000-10-01

More than 1300 variables classified provisionally as first-overtone RR Lyrae pulsators in the MACHO variable-star database of the Large Magellanic Cloud (LMC) have been subjected to standard frequency analysis. Based on the remnant power in the prewhitened spectra, we found 70% of the total population to be monoperiodic. The remaining 30% (411 stars) are classified as one of nine types according to their frequency spectra. Several types of RR Lyrae pulsational behavior are clearly identified here for the first time. Together with the earlier discovered double-mode (fundamental and first-overtone) variables, this study increased the number of known double-mode stars in the LMC to 181. During the total 6.5 yr time span of the data, 10% of the stars showed strong period changes. The size, and in general also the patterns of the period changes, exclude a simple evolutionary explanation. We also discovered two additional types of multifrequency pulsators with low occurrence rates of 2% for each. In the first type, there remains one closely spaced component after prewhitening by the main pulsation frequency. In the second type, the number of remnant components is two; they are also closely spaced, and are symmetric in their frequency spacing relative to the central component. This latter type of variables are associated with their relatives among the fundamental pulsators, known as Blazhko variables. Their high frequency (~20%) among the fundamental-mode variables versus the low occurrence rate of their first-overtone counterparts makes it more difficult to explain the Blazhko phenomenon by any theory depending mainly on the role of aspect angle or magnetic field. None of the current theoretical models are able to explain the observed close frequency components without invoking nonradial pulsation components in these stars.

Nuclear physics of reverse electron flow at pulsar polar caps

NASA Astrophysics Data System (ADS)

Jones, P. B.

2010-01-01

Protons produced in electromagnetic showers formed by the reverse electron flux are usually the largest component of the time-averaged polar cap open magnetic flux line current in neutron stars with positive corotational charge density. Although the electric field boundary conditions in the corotating frame are time independent, instabilities on both medium and short time-scales cause the current to alternate between states in which either protons or positrons and ions form the major component. These properties are briefly discussed in relation to nulling and microstructure in radio pulsars, pair production in an outer gap and neutron stars with high surface temperatures.

Suppressed phase variations in a high amplitude rapidly oscillating Ap star pulsating in a distorted quadrupole mode

NASA Astrophysics Data System (ADS)

Holdsworth, Daniel L.; Saio, H.; Bowman, D. M.; Kurtz, D. W.; Sefako, R. R.; Joyce, M.; Lambert, T.; Smalley, B.

2018-05-01

We present the results of a multisite photometric observing campaign on the rapidly oscillating Ap (roAp) star 2MASS 16400299-0737293 (J1640; V = 12.7). We analyse photometric B data to show the star pulsates at a frequency of 151.93 d-1 (1758.45 μHz; P = 9.5 min) with a peak-to-peak amplitude of 20.68 mmag, making it one of the highest amplitude roAp stars. No further pulsation modes are detected. The stellar rotation period is measured at 3.674 7 ± 0.000 5 d, and we show that rotational modulation due to spots is in antiphase between broad-band and B observations. Analysis and modelling of the pulsation reveals this star to be pulsating in a distorted quadrupole mode, but with a strong spherically symmetric component. The pulsational phase variation in this star is suppressed, leading to the conclusion that the contribution of ℓ > 2 components dictate the shape of phase variations in roAp stars that pulsate in quadrupole modes. This is only the fourth time such a strong pulsation phase suppression has been observed, leading us to question the mechanisms at work in these stars. We classify J1640 as an A7 Vp SrEu(Cr) star through analysis of classification resolution spectra.

Deep asteroseismic sounding of the compact hot B subdwarf pulsator KIC02697388 from Kepler time series photometry

NASA Astrophysics Data System (ADS)

Charpinet, S.; Van Grootel, V.; Fontaine, G.; Green, E. M.; Brassard, P.; Randall, S. K.; Silvotti, R.; Østensen, R. H.; Kjeldsen, H.; Christensen-Dalsgaard, J.; Kawaler, S. D.; Clarke, B. D.; Li, J.; Wohler, B.

2011-06-01

Context. Contemporary high precision photometry from space provided by the Kepler and CoRoT satellites generates significant breakthroughs in terms of exploiting the long-period, g-mode pulsating hot B subdwarf (sdBVs) stars with asteroseismology. Aims: We present a detailed asteroseismic study of the sdBVs star KIC02697388 monitored with Kepler, using the rich pulsation spectrum uncovered during the ~27-day-long exploratory run Q2.3. Methods: We analyse new high-S/N spectroscopy of KIC02697388 using appropriate NLTE model atmospheres to provide accurate atmospheric parameters for this star. We also reanalyse the Kepler light curve using standard prewhitening techniques. On this basis, we apply a forward modelling technique using our latest generation of sdB models. The simultaneous match of the independent periods observed in KIC02697388 with those of models leads objectively to the identification of the pulsation modes and, more importantly, to the determination of some of the parameters of the star. Results: The light curve analysis reveals 43 independent frequencies that can be associated with oscillation modes. All the modulations observed in this star correspond to g-mode pulsations except one high-frequency signal, which is typical of a p-mode oscillation. Although the presence of this p-mode is surprising considering the atmospheric parameters that we derive for this cool sdB star (Teff = 25 395 ± 227 K, log g = 5.500 ± 0.031 (cgs), and log N(He) /N(H) = -2.767 ± 0.122), we show that this mode can be accounted for particularly well by our optimal seismic models, both in terms of frequency match and nonadiabatic properties. The seismic analysis leads us to identify two model solutions that can both account for the observed pulsation properties of KIC02697388. Despite this remaining ambiguity, several key parameters of the star can be derived with stringent constraints, such as its mass, its H-rich envelope mass, its radius, and its luminosity. We derive the properties of the core proposing that it is a relatively young sdB star that has burnt less than ~34% (in mass) of its central helium and has a relatively large mixed He/C/O core. This latter measurement is in line with the trend already uncovered for two other g-mode sdB pulsators analysed with asteroseismology and suggests that extra mixing is occurring quite early in the evolution of He cores on the horizontal branch. Conclusions: Additional monitoring with Kepler of this particularly interesting sdB star should reveal the inner properties of KIC02697388 and provide important information about the mode driving mechanism and the helium core properties. Tables 3 and 4 are available in electronic form at http://www.aanda.org

Polarized curvature radiation in pulsar magnetosphere

NASA Astrophysics Data System (ADS)

Wang, P. F.; Wang, C.; Han, J. L.

2014-07-01

The propagation of polarized emission in pulsar magnetosphere is investigated in this paper. The polarized waves are generated through curvature radiation from the relativistic particles streaming along curved magnetic field lines and corotating with the pulsar magnetosphere. Within the 1/γ emission cone, the waves can be divided into two natural wave-mode components, the ordinary (O) mode and the extraordinary (X) mode, with comparable intensities. Both components propagate separately in magnetosphere, and are aligned within the cone by adiabatic walking. The refraction of O mode makes the two components separated and incoherent. The detectable emission at a given height and a given rotation phase consists of incoherent X-mode and O-mode components coming from discrete emission regions. For four particle-density models in the form of uniformity, cone, core and patches, we calculate the intensities for each mode numerically within the entire pulsar beam. If the corotation of relativistic particles with magnetosphere is not considered, the intensity distributions for the X-mode and O-mode components are quite similar within the pulsar beam, which causes serious depolarization. However, if the corotation of relativistic particles is considered, the intensity distributions of the two modes are very different, and the net polarization of outcoming emission should be significant. Our numerical results are compared with observations, and can naturally explain the orthogonal polarization modes of some pulsars. Strong linear polarizations of some parts of pulsar profile can be reproduced by curvature radiation and subsequent propagation effect.

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.

Latitudinal dependence on the frequency of Pi2 pulsations near the plasmapause using THEMIS satellites and Asian-Oceanian SuperDARN radars

NASA Astrophysics Data System (ADS)

Teramoto, Mariko; Nishitani, Nozomu; Nishimura, Yukitoshi; Nagatsuma, Tsutomu

2016-02-01

We herein describe a harmonic Pi2 wave that started at 09:12 UT on August 19, 2010, with data that were obtained simultaneously at 19:00-20:00 MLT by three mid-latitude Asian-Oceanian Super Dual Auroral Radar Network (SuperDARN) radars (Unwin, Tiger, and Hokkaido radars), three Time History of Events and Macroscale Interactions during Substorms (THEMIS) satellites (THEMIS A, THEMIS D, and THEMIS E), and ground-based magnetometers at low and high latitudes. All THEMIS satellites, which were located in the plasmasphere, observed Pi2 pulsations dominantly in the magnetic compressional ( B //) and electric azimuthal ( E A) components, i.e., the fast-mode component. The spectrum of Pi2 pulsations in the B // and E A components contained two spectral peaks at approximately 12 to 14 mHz ( f 1, fundamental) and 23 to 25 mHz ( f 2, second harmonic). The Poynting flux derived from the electric and magnetic fields indicated that these pulsations were waves propagating earthward and duskward. Doppler variations ( V) from the 6-s or 8-s resolution camping beams of the Tiger and Unwin SuperDARN radars, which are associated with Pi2 pulsations in the eastward electric field component in the ionosphere, observed Pi2 pulsations within and near the footprint of the plasmapause, whose location was estimated by the THEMIS satellites. The latitudinal profile of f 2 power normalized by f 1 power for Doppler velocities indicated that the enhancement of the normalized f 2 power was the largest near the plasmapause at an altitude-adjusted corrected geomagnetic (AACGM) latitude of 60° to 65°. Based on these features, we suggest that compressional waves propagate duskward away from the midnight sector, where the harmonic cavity mode is generated.

Massive pulsating stars observed by BRITE-Constellation. I. The triple system β Centauri (Agena)

NASA Astrophysics Data System (ADS)

Pigulski, A.; Cugier, H.; Popowicz, A.; Kuschnig, R.; Moffat, A. F. J.; Rucinski, S. M.; Schwarzenberg-Czerny, A.; Weiss, W. W.; Handler, G.; Wade, G. A.; Koudelka, O.; Matthews, J. M.; Mochnacki, St.; Orleański, P.; Pablo, H.; Ramiaramanantsoa, T.; Whittaker, G.; Zocłońska, E.; Zwintz, K.

2016-04-01

Context. Asteroseismology of massive pulsating stars of β Cep and SPB types can help us to uncover the internal structure of massive stars and understand certain physical phenomena that are taking place in their interiors. We study β Centauri (Agena), a triple system with two massive fast-rotating early B-type components which show p- and g-mode pulsations; the system's secondary is also known to have a measurable magnetic field. Aims: This paper aims to precisely determine the masses and detect pulsation modes in the two massive components of β Cen with BRITE-Constellation photometry. In addition, seismic models for the components are considered and the effects of fast rotation are discussed. This is done to test the limitations of seismic modeling for this very difficult case. Methods: A simultaneous fit of visual and spectroscopic orbits is used to self-consistently derive the orbital parameters, and subsequently the masses, of the components. Time-series analysis of BRITE-Constellation data is used to detect pulsation modes and derive their frequencies, amplitudes, phases, and rates of frequency change. Theoretically-predicted frequencies are calculated for the appropriate evolutionary models and their stability is checked. The effects of rotational splitting and coupling are also presented. Results: The derived masses of the two massive components are equal to 12.02 ± 0.13 and 10.58 ± 0.18 M⊙. The parameters of the wider, A-B system, presently approaching periastron passage, are constrained. Analysis of the combined blue- and red-filter BRITE-Constellation photometric data of the system revealed the presence of 19 periodic terms, of which eight are likely g modes, nine are p modes, and the remaining two are combination terms. It cannot be excluded that one or two low-frequency terms are rotational frequencies. It is possible that both components of β Cen are β Cep/SPB hybrids. An attempt to use the apparent changes of frequency to distinguish which modes originate in which component did not succeed, but there is potential for using this method when more BRITE data become available. Conclusions: Agena seems to be one of very few rapidly rotating massive objects with rich p- and g-mode spectra, and precisely known masses. It can therefore be used to gain a better understanding of the excitation of pulsations in relatively rapidly rotating stars and their seismic modeling. Lacking proper mode identification, the pulsation frequencies found in β Cen cannot yet be used to constrain the internal structure of the components, but it may be possible to achieve this in the future with the use of spectroscopy and spectropolarimetry. In particular, these kinds of data can be used for mode identification since they provide new radial velocities. In consequence, they may help to improve the orbital solution, derive more precise masses, magnetic field strength and geometry, inclination angles, and reveal rotation periods. They may also help to assign pulsation frequencies to components. Finally, the case studied here illustrates the potential of BRITE-Constellation data for the detection of rich-frequency spectra of small-amplitude modes in massive pulsating stars. Based on data collected by the BRITE-Constellation satellite mission, built, launched and operated thanks to support from the Austrian Aeronautics and Space Agency and the University of Vienna, the Canadian Space Agency (CSA) and the Foundation for Polish Science & Technology (FNiTP MNiSW) and National Centre for Science (NCN).

RED GIANTS IN ECLIPSING BINARY AND MULTIPLE-STAR SYSTEMS: MODELING AND ASTEROSEISMIC ANALYSIS OF 70 CANDIDATES FROM KEPLER DATA

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gaulme, P.; McKeever, J.; Rawls, M. L.

2013-04-10

Red giant stars are proving to be an incredible source of information for testing models of stellar evolution, as asteroseismology has opened up a window into their interiors. Such insights are a direct result of the unprecedented data from space missions CoRoT and Kepler as well as recent theoretical advances. Eclipsing binaries are also fundamental astrophysical objects, and when coupled with asteroseismology, binaries provide two independent methods to obtain masses and radii and exciting opportunities to develop highly constrained stellar models. The possibility of discovering pulsating red giants in eclipsing binary systems is therefore an important goal that could potentiallymore » offer very robust characterization of these systems. Until recently, only one case has been discovered with Kepler. We cross-correlate the detected red giant and eclipsing-binary catalogs from Kepler data to find possible candidate systems. Light-curve modeling and mean properties measured from asteroseismology are combined to yield specific measurements of periods, masses, radii, temperatures, eclipse timing variations, core rotation rates, and red giant evolutionary state. After using three different techniques to eliminate false positives, out of the 70 systems common to the red giant and eclipsing-binary catalogs we find 13 strong candidates (12 previously unknown) to be eclipsing binaries, one to be a non-eclipsing binary with tidally induced oscillations, and 10 more to be hierarchical triple systems, all of which include a pulsating red giant. The systems span a range of orbital eccentricities, periods, and spectral types F, G, K, and M for the companion of the red giant. One case even suggests an eclipsing binary composed of two red giant stars and another of a red giant with a {delta}-Scuti star. The discovery of multiple pulsating red giants in eclipsing binaries provides an exciting test bed for precise astrophysical modeling, and follow-up spectroscopic observations of many of the candidate systems are encouraged. The resulting highly constrained stellar parameters will allow, for example, the exploration of how binary tidal interactions affect pulsations when compared to the single-star case.« less

Anisotropy and corotation of galactic cosmic rays.

PubMed

Amenomori, M; Ayabe, S; Bi, X J; Chen, D; Cui, S W; Danzengluobu; Ding, L K; Ding, X H; Feng, C F; Feng, Zhaoyang; Feng, Z Y; Gao, X Y; Geng, Q X; Guo, H W; He, H H; He, M; Hibino, K; Hotta, N; Hu, Haibing; Hu, H B; Huang, J; Huang, Q; Jia, H Y; Kajino, F; Kasahara, K; Katayose, Y; Kato, C; Kawata, K; Labaciren; Le, G M; Li, A F; Li, J Y; Lou, Y-Q; Lu, H; Lu, S L; Meng, X R; Mizutani, K; Mu, J; Munakata, K; Nagai, A; Nanjo, H; Nishizawa, M; Ohnishi, M; Ohta, I; Onuma, H; Ouchi, T; Ozawa, S; Ren, J R; Saito, T; Saito, T Y; Sakata, M; Sako, T K; Sasaki, T; Shibata, M; Shiomi, A; Shirai, T; Sugimoto, H; Takita, M; Tan, Y H; Tateyama, N; Torii, S; Tsuchiya, H; Udo, S; Wang, B; Wang, H; Wang, X; Wang, Y G; Wu, H R; Xue, L; Yamamoto, Y; Yan, C T; Yang, X C; Yasue, S; Ye, Z H; Yu, G C; Yuan, A F; Yuda, T; Zhang, H M; Zhang, J L; Zhang, N J; Zhang, X Y; Zhang, Y; Zhang, Yi; Zhaxisangzhu; Zhou, X X

2006-10-20

The intensity of Galactic cosmic rays is nearly isotropic because of the influence of magnetic fields in the Milky Way. Here, we present two-dimensional high-precision anisotropy measurement for energies from a few to several hundred teraelectronvolts (TeV), using the large data sample of the Tibet Air Shower Arrays. Besides revealing finer details of the known anisotropies, a new component of Galactic cosmic ray anisotropy in sidereal time is uncovered around the Cygnus region direction. For cosmic-ray energies up to a few hundred TeV, all components of anisotropies fade away, showing a corotation of Galactic cosmic rays with the local Galactic magnetic environment. These results have broad implications for a comprehensive understanding of cosmic rays, supernovae, magnetic fields, and heliospheric and Galactic dynamic environments.

VizieR Online Data Catalog: CoRoT observation log (N2-4.4) (CoRoT, 2009-2016)

NASA Astrophysics Data System (ADS)

COROT Team

2014-03-01

CoRoT is a space astronomy mission devoted to the study of the variability with time of stars brightness, with an extremely high accuracy (100 times better than from the ground), on very long durations (up to 150 days) and a very high duty cycle (more than 90%). The mission was led by CNES in association with four french laboratories, and 7 participating countries and agencies (Austria, Belgium, Brazil, Germany, Spain, and the ESA Science Programme). The satellite is composed of a PROTEUS platform (the 3rd in the serie), and a unique instrument: a stellar photometer. It has been launched on December 27th 2006 by a Soyuz Rocket, from Baikonour. The mission has lasted almost 6 years (the nominal 3 years duration and a 3 years extension) and has observed more than 160 000 stars. It stopped to send data suddenly on November 2nd 2012. CoRoT is performing Ultra High Precision Photomery of Stars to detect and characterise the variability of their luminosity with two main directions: - variability of the object itself: oscillations, rotation, magnetic activity - variability due to external causes as bodies in orbit around the star: planets and stars The original scientific objectives were focussed on the study of stellar pulsations (asteroseismology) to probe the internal structure of stars, and the detection of small exoplanets through their "transit in front of their host star, and the measurement of their size. This lead to introduce two modes of observations, working simultaneously: - The bright star mode dedicated to very precise seismology of a small sample of bright and closeby stars (data presented in file momentarily named "astero.dat", but should change in the near future to to "bright star.dat") - The faint star mode, observing a very large number of stars at the same time, to detect transits, which are rare events, as they imply the alignment of the star, the planet and the observer (data presented in momentarily named "exo.dat" but should change in the near future to "faint star.dat"). The large amount of data gathered in this mode mode turned out to be extremely fruitful for many topics of stellar physics. Due to project constraints, two regions of the sky were accessible (circles of 10 degrees centered on the equator around alpha=06:50 and alpha=18:50). They are called the CoRoT eyes: the fisrt one is called the "anticenter" eye, whereas the second one is called the "center eye". Each pointing covers 1.4x2.8 square degrees The CoRoT project is still processing the data, aiming at at removing instrumental artifacts and defects. Therefore the format and content of the catalog is still somehow evolving. More details on the data can be found in the "CoRoTN2versions_30sept2014.pdf" document available on the vizier ftp as well as project websites listed in the "See also" field below. (3 data files).

Constraints on the core μ-gradient of the solar-like star HD 49385 via low-degree mixed modes

NASA Astrophysics Data System (ADS)

Deheuvels, S.; Michel, E.

2010-12-01

The existence of an ℓ=1 avoided crossing in the spectrum of the solar-like pulsator-target \\cible was established by Deheuvels & Michel (2009). It is the first confirmed detection of such a phenomenon. The authors showed in a preliminary modeling of the star that it was in a post main sequence status. Being a 1.3 M⊙-star, \\cible has had a convective core during its main sequence phase. The μ-gradient left by the withdrawal of this core bears information about the processes of transport at the boundary of the core. We here investigate the constraints that the observed avoided crossing brings on the μ-gradient in the core of the star. The CoRoT space mission, launched on 2006 December 27, was developed and is operated by the CNES with participation of the Science Programs of ESA; ESA's RSSD, Austria, Belgium, Brazil, Germany, and Spain.

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.

ON THE POLARIZATION PROPERTIES OF MAGNETAR GIANT FLARE PULSATING TAILS

DOE Office of Scientific and Technical Information (OSTI.GOV)

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

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 ofmore » 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.« less

Photometric and spectroscopic investigation of the oscillating Algol type binary: EW Boo

NASA Astrophysics Data System (ADS)

Doğruel, Mustafa Burak; Gürol, Birol

2015-10-01

We obtained the physical and geometrical parameters of the EW Boo system, which exhibits short period and small amplitude pulsations as well as brightness variations due to orbital motion of components. Towards this end we carried out photometric observations at Ankara University Kreiken Observatory (AUKO) as well as spectroscopic observations at TUBITAK National Observatory (TNO). The light and radial velocity curves obtained from these observations have been simultaneously analyzed with PHOEBE and the absolute parameters of the system along with the geometric parameters of the components have been determined. Using model light curves of EW Boo, light curve regions in which the pulsations are active have been determined and as a result of analyses performed in the frequency region, characteristic parameters of pulsations have been obtained. We find that the results are compatible with current parameters of similar systems in the literature. The evolutionary status of the components is propounded and discussed.

Discrete-vortex simulation of pulsating flow on a turbulent leading-edge separation bubble

NASA Technical Reports Server (NTRS)

Sung, Hyung Jin; Rhim, Jae Wook; Kiya, Masaru

1992-01-01

Studies are made of the turbulent separation bubble in a two-dimensional semi-infinite blunt plate aligned to a uniform free stream with a pulsating component. The discrete-vortex method is applied to simulate this flow situation because this approach is effective for representing the unsteady motions of the turbulent shear layer and the effect of viscosity near the solid surface. The numerical simulation provides reasonable predictions when compared with the experimental results. A particular frequency with a minimum reattachment is related to the drag reduction. The most effective frequency is dependent on the amplified shedding frequency. The turbulent flow structure is scrutinized. This includes the time-mean and fluctuations of the velocity and the surface pressure, together with correlations between the fluctuating components. A comparison between the pulsating flow and the non-pulsating flow at the particular frequency of the minimum reattachment length of the separation bubble suggests that the large-scale vortical structure is associated with the shedding frequency and the flow instabilities.

AMPTE CCE observations of Pi 2 pulsations in the inner magnetosphere

NASA Technical Reports Server (NTRS)

Takahashi, Kazue; Ohtani, Shin-Ichi; Yumoto, Kiyohumi

1992-01-01

Magnetic field data acquired with the AMPTE Charge Composition Explorer satellite in the inner magnetosphere (L = 2-5) often show Pi 2 pulsations whose waveforms match Pi 2 pulsations simultaneously observed on the ground at Kakioka (L = 1.2). From a study such events, it is found that the magnetic pulsations in the equatorial magnetosphere are dominated by poloidal-mode oscillations. The relative phase between the compressional component at CCE and the horizontal component at Kakioka is either near zero or near 180 deg, with the 180 lag observed only when the satellite is at L greater than 3. This observation implies that there is a node of a radial standing wave at L greater than 3. It is argued that the nodal structure arises from reflection of MHD fast-mode waves at some inner boundary of the magnetosphere and discuss the relevance of the nodal structure to cavity-mode resonances and oscillations in the inner magnetosphere forced by a source wave external to the inner magnetosphere.

Mass and p-factor of the Type II Cepheid OGLE-LMC-T2CEP-098 in a Binary System

NASA Astrophysics Data System (ADS)

Pilecki, Bogumił; Gieren, Wolfgang; Smolec, Radosław; Pietrzyński, Grzegorz; Thompson, Ian B.; Anderson, Richard I.; Bono, Giuseppe; Soszyński, Igor; Kervella, Pierre; Nardetto, Nicolas; Taormina, Mónica; Stȩpień, Kazimierz; Wielgórski, Piotr

2017-06-01

We present the results of a study of the type II Cepheid (P puls = 4.974 days) in the eclipsing binary system OGLE-LMC-T2CEP-098 (P orb = 397.2 days). The Cepheid belongs to the peculiar W Vir group, for which the evolutionary status is virtually unknown. It is the first single-lined system with a pulsating component analyzed using the method developed by Pilecki et al. We show that the presence of a pulsator makes it possible to derive accurate physical parameters of the stars even if radial velocities can be measured for only one of the components. We have used four different methods to limit and estimate the physical parameters, eventually obtaining precise results by combining pulsation theory with the spectroscopic and photometric solutions. The Cepheid radius, mass, and temperature are 25.3+/- 0.2 {R}⊙ , 1.51+/- 0.09 {M}⊙ , and 5300+/- 100 {{K}}, respectively, while its companion has a similar size (26.3 {R}⊙ ), but is more massive (6.8 {M}⊙ ) and hotter (9500 K). Our best estimate for the p-factor of the Cepheid is 1.30+/- 0.03. The mass, position on the period-luminosity diagram, and pulsation amplitude indicate that the pulsating component is very similar to the Anomalous Cepheids, although it has a much longer period and is redder in color. The very unusual combination of the components suggest that the system has passed through a mass-transfer phase in its evolution. More complicated internal structure would then explain its peculiarity. This paper includes data gathered with the 6.5 m Magellan Clay Telescope at Las Campanas Observatory, Chile.

A reexamination of ATS 6 magnetometer data for radially polarized Pc 3 magnetic pulsations

NASA Technical Reports Server (NTRS)

Takahashi, K.; Mcpherron, R. L.

1983-01-01

The polarization of Pc 3 (22-100 MHz) magnetic pulsations measured by the ATS 6 fluxgate magnetometer at synchronous orbit has been examined by using dynamic autospectral analysis. In contrast to the result obtained by Arthur et al. (1977) using the same data set, very few cases of radially polarized Pc 3 pulsations are found. It is suggested that satellite noise in the radial component, which depends on frequency f as 0.015/f (nT-squared/Hz), is responsible for this disagreement. In the presence of this type of noise, diagonalization of the spectral matrix can produce an erroneous major axis of polarization. Most Pc 3 pulsations classified as radially polarized by Arthur et al. appear to be a consequence of small amplitude azimuthal pulsations contaminated by satellite noise.

An in-depth study of HD 174966 with CoRoT photometry and HARPS spectroscopy. Large separation as a new observable for δ Scuti stars

NASA Astrophysics Data System (ADS)

García Hernández, A.; Moya, A.; Michel, E.; Suárez, J. C.; Poretti, E.; Martín-Ruíz, S.; Amado, P. J.; Garrido, R.; Rodríguez, E.; Rainer, M.; Uytterhoeven, K.; Rodrigo, C.; Solano, E.; Rodón, J. R.; Mathias, P.; Rolland, A.; Auvergne, M.; Baglin, A.; Baudin, F.; Catala, C.; Samadi, R.

2013-11-01

Aims: The aim of this work was to use a multi-approach technique to derive the most accurate values possible of the physical parameters of the δ Sct star HD 174966, which was observed with the CoRoT satellite. In addition, we searched for a periodic pattern in the frequency spectra with the goal of using it to determine the mean density of the star. Methods: First, we extracted the frequency content from the CoRoT light curve. Then, we derived the physical parameters of HD 174966 and carried a mode identification out from the spectroscopic and photometric observations. We used this information to look for the models fulfilling all the conditions and discussed the inaccuracies of the method because of the rotation effects. In a final step, we searched for patterns in the frequency set using a Fourier transform, discussed its origin, and studied the possibility of using the periodicity to obtain information about the physical parameters of the star. Results: A total of 185 peaks were obtained from the Fourier analysis of the CoRoT light curve, all of which were reliable pulsating frequencies. From the spectroscopic observations, 18 oscillation modes were detected and identified, and the inclination angle (62.5°-17.5+7.5) and the rotational velocity of the star (142 km s-1) were estimated. From the multi-colour photometric observations, only three frequencies were detected that correspond to the main ones in the CoRoT light curve. We looked for periodicities within the 185 frequencies and found a quasiperiodic pattern Δν ~ 64 μHz. Using the inclination angle, the rotational velocity, and an Echelle diagram (showing a double comb outside the asymptotic regime), we concluded that the periodicity corresponds to a large separation structure. The quasiperiodic pattern allowed us to discriminate models from a grid. As a result, the value of the mean density is achieved with a 6% uncertainty. So, the Δν pattern could be used as a new observable for A-F type stars. 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, Belgium, Brazil, Germany, and Spain.This work is based on ground-based observations made with the ESO 3.6 m telescope at La Silla Observatory under the ESO Large Programme LP182.D-0356, and on observations collected at the Centro Astronómico Hispano Alemán (CAHA) at Calar Alto, operated jointly by the Max-Planck-Institut für Astronomie and the Instituto de Astrofísica de Andalucía (CSIC), and on observations made at Observatoire de Haute Provence (CNRS), France, and at Observatorio de Sierra Nevada (OSN), Spain, operated by the Instituto de Astrofísica de Andalucía (CSIC). This research has made use of both the Simbad database, operated at CDS, Strasbourg, France, and the Astrophysics Data System, provided by NASA, USA.Table 6 is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/559/A63

Binarity and Variable Stars in the Open Cluster NGC 2126

NASA Astrophysics Data System (ADS)

Chehlaeh, Nareemas; Mkrtichian, David; Kim, Seung-Lee; Lampens, Patricia; Komonjinda, Siramas; Kusakin, Anatoly; Glazunova, Ljudmila

2018-04-01

We present the results of an analysis of photometric time-series observations for NGC 2126 acquired at the Thai National Observatory (TNO) in Thailand and the Mount Lemmon Optical Astronomy Observatory (LOAO) in USA during the years 2004, 2013 and 2015. The main purpose is to search for new variable stars and to study the light curves of binary systems as well as the oscillation spectra of pulsating stars. NGC 2126 is an intermediate-age open cluster which has a population of stars inside the δ Scuti instability strip. Several variable stars are reported including three eclipsing binary stars, one of which is an eclipsing binary star with a pulsating component (V551 Aur). The Wilson-Devinney technique was used to analyze its light curves and to determine a new set of the system’s parameters. A frequency analysis of the eclipse-subtracted light curve was also performed. Eclipsing binaries which are members of open clusters are capable of delivering strong constraints on the cluster’s properties which are in turn useful for a pulsational analysis of their pulsating components. Therefore, high-resolution, high-quality spectra will be needed to derive accurate component radial velocities of the faint eclipsing binaries which are located in the field of NGC 2126. The new Devasthal Optical Telescope, suitably equipped, could in principle do this.

The nature of EU Pegasi: An Algol-type binary with a δ Scuti-type component

NASA Astrophysics Data System (ADS)

Yang, Yuangui; Yuan, Huiyu; Dai, Haifeng; Zhang, Xiliang

2018-03-01

The comprehensive photometry and spectroscopy for the neglected eclipsing binary EU Pegasi are presented. We determine its spectral type to be A3V. With the W-D program, the photometric solution was deduced from the four-color light curves. The results imply that EU Peg is a detached binary with a mass ratio of q = 0.3105(± 0.0011), whose components nearly fill their Roche lobes. The low-amplitude pulsation occurs around the secondary eclipse, which may be attributed to the more massive component. Three frequencies are preliminarily explored by the Fourier analysis. The pulsating frequency at f1 = 34.1 c d-1 is a p-mode pulsation. The orbital period may be undergoing a secular decrease, superimposed by a cyclic variation. The period decreases at a rate of dP/dt = -7.34 ± 1.06 d yr-1, which may be attributed to mass loss from the system due to stellar wind. The cyclic oscillation, with Pmod = 31.0 ± 1.4 yr and A = 0.0054 ± 0.0010 d, may be caused by the light-time effect due to the assumed third body. With its evolution, the pulsating binary EU Peg will evolve from the detached configuration to the semi-detached case.

Comparison of stellar and gasdynamics of a barred galaxy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Contopoulos, G.; Gottesman, S.T.; Hunter, J.H. Jr.

1989-08-01

The stellar and gas dynamics of several models of barred galaxies were studied, and results for some representative cases are reported for galaxies in which the stars and gas respond to the same potentials. Inside corotation there are two main families of periodic orbits, designated x1 and 4/1. Close to the center, the x1 orbits are like elongated ellipses. As the 4/1 resonance is approached, these orbits become like lozenges, with apices along the bar and perpendicular to it. The family 4/1 consists of orbits like parallelograms which produce the boxy component of the bar. The orbits in spirals outsidemore » corotation enhance the spiral between the outer -4/1 resonance and the outer Lindblad resonance. Between corotation and the -4/1 resonance in strong spirals, the orbits are mostly stochastic and fill almost circular rings. A spiral field must be added to gasdynamical models to obtain gaseous arms extending from the end of a bar. 38 refs.« less

On the change in the spectral composition of solar ultraviolet emission preceding proton flares, and its connection with the preflare fluctuations in the horizontal component of the geomagnetic field

NASA Astrophysics Data System (ADS)

Sheiner, Olga; Snegirev, Sergei; Smirnova, Anna

The importance problem of Solar-terrestrial physics is regular forecasting of solar activity phenomena, which negatively influence the human’s health, operating safety, communication, radar sets and others. We previously reported the existence of long-period pulsations of H component of the geomagnetic field recorded at stations tested 2-3 days before the proton solar flares. There are the increasing of pulsation amplitude of the horizontal component of the magnetic field with periods of 30-60 minutes. The spectrum of the flux of ultraviolet solar radiation on the eve of proton flares was conducted to determine the presence of oscillations - precursors of flares, as one of the possible agents causing amplification of large periods pulsations of H component of the geomagnetic field. Used data on ultraviolet radiation of the sun with a wavelength of 115-127 nm are obtained from a geostationary satellite GOES 15, the method of wavelet analysis is used. It is found the congruence in the behavior of spectral components with periods of 30-60 minutes in the ground-based measurements and in UV emission for 3-1 days before the proton flare.

Relationship of oscillating and average components of laser Doppler flowmetry signal

NASA Astrophysics Data System (ADS)

Mizeva, Irina; Frick, Peter; Podtaev, Sergey

2016-08-01

Signals from laser Doppler flowmeters widely used in intravital studies of skin blood flow include, along with a slowly varying average component, an oscillating part. However, in most clinical studies, pulsations are usually smoothed by data preprocessing and only the mean blood flow is analyzed. To reveal the relationship between average and oscillating perfusion components measured by a laser Doppler flowmeter, we examined the microvascular response to the contralateral cold pressor test recorded at two different sites of the hand: dorsal part of the arm and finger pad. Such a protocol makes it possible to provide a wide range of perfusion. The average perfusion always decreases during cooling, while the oscillating component demonstrates a differently directed response. The wavelet analysis of laser Doppler flowmetry (LDF) signals shows that the pulsatile component is nonlinearly related to the average perfusion. Under low perfusion, the amplitude of pulsations is proportional to its mean value, but, as perfusion increases, the amplitude of pulsations becomes lower. The type of response is defined by the basal perfusion and the degree of vasoconstriction caused by cooling. Interpretation of the results is complicated by the nonlinear transfer function of the LDF device, the contribution of which is studied using artificial examples.

Multipoint Spacecraft Observations of Long-Lasting Poloidal Pc4 Pulsations in the Dayside Magnetosphere on 1-2 May 2014

NASA Technical Reports Server (NTRS)

Korotova, Galina; Sibeck, David; Engebretson, Mark; Wygant, John; Thaller, Scott; Spence, Harlan; Kletzing, Craig; Angelopoulos, Vassilis; Redmon, Robert

2016-01-01

We use magnetic field and plasma observations from the Van Allen Probes, Time History of Events and Macroscale Interactions during Substorms (THEMIS) and Geostationary Operational Environmental Satellite system (GOES) spacecraft to study the spatial and temporal characteristics of long-lasting poloidal Pc4 pulsations in the dayside magnetosphere. The pulsations were observed after the main phase of a moderate storm during low geomagnetic activity. The pulsations occurred during various interplanetary conditions and the solar wind parameters do not seem to control the occurrence of the pulsations. The most striking feature of the Pc4 magnetic field pulsations was their occurrence at similar locations during three of four successive orbits. We used this information to study the latitudinal nodal structure of the pulsations and demonstrated that the latitudinal extent of the magnetic field pulsations did not exceed 2 Earth radii (R(sub E)). A phase shift between the azimuthal and radial components of the electric and magnetic fields was observed from Z(sub SM) = 0.30 R(sub E) to Z(sub SM) = -0.16 R(sub E). We used magnetic and electric field data from Van Allen Probes to determine the structure of ULF waves. We showed that the Pc4 magnetic field pulsations were radially polarized and are the second-mode harmonic waves. We suggest that the spacecraft were near a magnetic field null during the second orbit when they failed to observe the magnetic field pulsations at the local times where pulsations were observed on previous and successive orbits. We investigated the spectral structure of the Pc4 pulsations. Each spacecraft observed a decrease of the dominant period as it moved to a smaller L shell (stronger magnetic field strength). We demonstrated that higher frequencies occurred at times and locations where Alfven velocities were greater, i.e., on Orbit 1. There is some evidence that the periods of the pulsations increased during the plasmasphere refilling following the storm.

Monitoring of the turbulent solar wind with the upgraded Large Phased Array of the Lebedev Institute of Physics: First results

NASA Astrophysics Data System (ADS)

Shishov, V. I.; Chashei, I. V.; Oreshko, V. V.; Logvinenko, S. V.; Tyul'bashev, S. A.; Subaev, I. A.; Svidskii, P. M.; Lapshin, V. B.; Dagkesamanskii, R. D.

2016-12-01

The design properties and technical characteristics of the upgraded Large Phased Array (LPA) are briefly described. The results of an annual cycle of observations of interplanetary scintillations of radio sources on the LPA with the new 96-beam BEAM 3 system are presented. Within a day, about 5000 radio sources displaying second-timescale fluctuations in their flux densities due to interplanetary scintillations were observed. At present, the parameters of many of these radio sources are unknown. Therefore, the number of sources with root-mean-square flux-density fluctuations greater than 0.2 Jy in a 3° × 3° area of sky was used to characterize the scintillation level. The observational data obtained during the period of the maximum of solar cycle 24 can be interpreted using a three-component model for the spatial structure of the solar wind, consisting of a stable global component, propagating disturbances, and corotating structures. The global component corresponds to the spherically symmetric structure of the distribution of the turbulent interplanetary plasma. Disturbances propagating from the Sun are observed against the background of the global structure. Propagating disturbances recorded at heliocentric distances of 0.4-1 AU and at all heliolatitudes reach the Earth's orbit one to two days after the scintillation enhancement. Enhancements of ionospheric scintillations are observed during night-time. Corotating disturbances have a recurrence period of 27 d . Disturbances of the ionosphere are observed as the coronal base of a corotating structure approaches the western edge of the solar limb.

The sdB pulsating star V391 Peg and its putative giant planet revisited after 13 years of time-series photometric data

NASA Astrophysics Data System (ADS)

Silvotti, R.; Schuh, S.; Kim, S.-L.; Lutz, R.; Reed, M.; Benatti, S.; Janulis, R.; Lanteri, L.; Østensen, R.; Marsh, T. R.; Dhillon, V. S.; Paparo, M.; Molnar, L.

2018-04-01

V391 Peg (alias HS 2201+2610) is a subdwarf B (sdB) pulsating star that shows both p- and g-modes. By studying the arrival times of the p-mode maxima and minima through the O-C method, in a previous article the presence of a planet was inferred with an orbital period of 3.2 years and a minimum mass of 3.2 MJup. Here we present an updated O-C analysis using a larger data set of 1066 h of photometric time series ( 2.5× larger in terms of the number of data points), which covers the period between 1999 and 2012 (compared with 1999-2006 of the previous analysis). Up to the end of 2008, the new O-C diagram of the main pulsation frequency (f1) is compatible with (and improves) the previous two-component solution representing the long-term variation of the pulsation period (parabolic component) and the giant planet (sine wave component). Since 2009, the O-C trend of f1 changes, and the time derivative of the pulsation period (p.) passes from positive to negative; the reason of this change of regime is not clear and could be related to nonlinear interactions between different pulsation modes. With the new data, the O-C diagram of the secondary pulsation frequency (f2) continues to show two components (parabola and sine wave), like in the previous analysis. Various solutions are proposed to fit the O-C diagrams of f1 and f2, but in all of them, the sinusoidal components of f1 and f2 differ or at least agree less well than before. The nice agreement found previously was a coincidence due to various small effects that are carefully analyzed. Now, with a larger dataset, the presence of a planet is more uncertain and would require confirmation with an independent method. The new data allow us to improve the measurement of p. for f1 and f2: using only the data up to the end of 2008, we obtain p.1 = (1.34 ± 0.04) × 10-12 and p.2 = (1.62 ± 0.22) × 10-12. The long-term variation of the two main pulsation periods (and the change of sign of p.1) is visible also in direct measurements made over several years. The absence of peaks near f1 in the Fourier transform and the secondary peak close to f2 confirm a previous identification as l = 0 and l = 1, respectively, and suggest a stellar rotation period of about 40 days. The new data allow constraining the main g-mode pulsation periods of the star. The complete set of data shown in Fig. 1 is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/611/A85Based on observations obtained at the following observatories: WHT 4.2m, TNG 3.6m, Calar Alto 2.2m, NOT 2.5m, Loiano 1.5m, LOAO 1.0m, MDM 1.3m, Moletai 1.6m, MONET-North 1.2m, Piszkéstető 1.0m, Mercator 1.2m, Wise 1.0m, Lulin 1.0m, Baker 0.6m.

Numerical evaluation of longitudinal motions of Wigley hulls advancing in waves by using Bessho form translating-pulsating source Green'S function

NASA Astrophysics Data System (ADS)

Xiao, Wenbin; Dong, Wencai

2016-06-01

In the framework of 3D potential flow theory, Bessho form translating-pulsating source Green's function in frequency domain is chosen as the integral kernel in this study and hybrid source-and-dipole distribution model of the boundary element method is applied to directly solve the velocity potential for advancing ship in regular waves. Numerical characteristics of the Green function show that the contribution of local-flow components to velocity potential is concentrated at the nearby source point area and the wave component dominates the magnitude of velocity potential in the far field. Two kinds of mathematical models, with or without local-flow components taken into account, are adopted to numerically calculate the longitudinal motions of Wigley hulls, which demonstrates the applicability of translating-pulsating source Green's function method for various ship forms. In addition, the mesh analysis of discrete surface is carried out from the perspective of ship-form characteristics. The study shows that the longitudinal motion results by the simplified model are somewhat greater than the experimental data in the resonant zone, and the model can be used as an effective tool to predict ship seakeeping properties. However, translating-pulsating source Green function method is only appropriate for the qualitative analysis of motion response in waves if the ship geometrical shape fails to satisfy the slender-body assumption.

Detection of large scale geomagnetic pulsations by MAGDAS-egypt stations during the solar minimum of the solar cycle 24

NASA Astrophysics Data System (ADS)

Fathy, Ibrahim

2016-07-01

This paper presents a statistical study of different types of large-scale geomagnetic pulsation (Pc3, Pc4, Pc5 and Pi2) detected simultaneously by two MAGDAS stations located at Fayum (Geo. Coordinates 29.18 N and 30.50 E) and Aswan (Geo. Coordinates 23.59 N and 32.51 E) in Egypt. The second order butter-worth band-pass filter has been used to filter and analyze the horizontal H-component of the geomagnetic field in one-second data. The data was collected during the solar minimum of the current solar cycle 24. We list the most energetic pulsations detected by the two stations instantaneously, in addition; the average amplitude of the pulsation signals was calculated.

Centrifugal compressor modifications and their effect on high-frequency pipe wall vibration

DOE Office of Scientific and Technical Information (OSTI.GOV)

Motriuk, R.W.; Harvey, D.P.

1998-08-01

High-frequency pulsation generated by centrifugal compressors, with pressure wave-lengths much smaller than the attached pipe diameter, can cause fatigue failures of the compressor internals, impair compressor performance, and damage the attached compressor piping. There are numerous sources producing pulsation in centrifugal compressors. Some of them are discussed in literature at large (Japikse, 1995; Niese, 1976). NGTL has experienced extreme high-frequency discharge pulsation and pipe wall vibration on many of its radial inlet high-flow centrifugal gas compressor facilities. These pulsations led to several piping attachment failures and compressor internal component failures while the compressor operated within the design envelope. This papermore » considers several pulsation conditions at an NGTL compression facility which resulted in unacceptable piping vibration. Significant vibration attenuation was achieved by modifying the compressor (pulsation source) through removal of the diffuser vanes and partial removal of the inlet guide vanes (IGV). Direct comparison of the changes in vibration, pulsation, and performance are made for each of the modifications. The vibration problem, probable causes, options available to address the problem, and the results of implementation are reviewed. The effects of diffuser vane removal on discharge pipe wall vibration as well as changes in compressor performance are described.« less

Pulsation damping of the reciprocating compressor with Helmholtz resonator

NASA Astrophysics Data System (ADS)

Wang, W.; Zhang, Y.; Zhou, Q.; Peng, X.; Feng, J.; Jia, X.

2017-08-01

Research presented in this paper investigated the mounting of a Helmholtz resonator near the valve chamber of a reciprocating compressor to attenuate the gas pulsation in the valve chamber as well as the pipeline downstream. Its attenuation characteristics were simulated with the plane wave theory together with the transfer matrix method, and the damping effect was checked by comparing the pressure pulsation levels before and after mounting the resonator. The results show that the Helmholtz resonator was effective in attenuating the gas pulsation in the valve chamber and piping downstream, and the pulsation level was decreased by 40% in the valve chamber and 30% at maximum in the piping downstream. The damping effect of the resonator was sensitive to its resonant frequency, and various resonators working simultaneously didn’t interfere with each other. When two resonators were mounted in parallel, with resonant frequencies equal to the second and fourth harmonic frequencies, the pressure pulsation components corresponding to the resonant frequencies were remarkably decreased at the same time, while the pulsation levels at other harmonic frequencies kept almost unchanged. After a series of simulations and experiments a design criterion of chock tube and volume parameter has been proposed for the targeted frequencies to be damped. Furthermore, the frequency-adjustable Helmholtz resonator which was applied to the variable speed compressor was investigated.

A corotation electric field model of the Earth derived from Swarm satellite magnetic field measurements

NASA Astrophysics Data System (ADS)

Maus, Stefan

2017-08-01

Rotation of the Earth in its own geomagnetic field sets up a primary corotation electric field, compensated by a secondary electric field of induced electrical charges. For the geomagnetic field measured by the Swarm constellation of satellites, a derivation of the global corotation electric field inside and outside of the corotation region is provided here, in both inertial and corotating reference frames. The Earth is assumed an electrical conductor, the lower atmosphere an insulator, followed by the corotating ionospheric E region again as a conductor. Outside of the Earth's core, the induced charge is immediately accessible from the spherical harmonic Gauss coefficients of the geomagnetic field. The charge density is positive at high northern and southern latitudes, negative at midlatitudes, and increases strongly toward the Earth's center. Small vertical electric fields of about 0.3 mV/m in the insulating atmospheric gap are caused by the corotation charges located in the ionosphere above and the Earth below. The corotation charges also flow outward into the region of closed magnetic field lines, forcing the plasmasphere to corotate. The electric field of the corotation charges further extends outside of the corotating regions, contributing radial outward electric fields of about 10 mV/m in the northern and southern polar caps. Depending on how the magnetosphere responds to these fields, the Earth may carry a net electric charge.

Loss of ring current O+ ions due to interaction with Pc 5 waves

NASA Astrophysics Data System (ADS)

Hudson, Mary; Chan, Anthony; Roth, Ilan

1993-01-01

The behavior of ring current ions in low-frequency geomagnetic pulsations is investigated analytically and numerically. We focus primarily on ring current O+ ions, whose flux increases dramatically during geomagnetic storms and decays at a rate which is not fully explained by collisional processes. This paper presents a new loss mechanism for the O+ ions due to the combined effects of convection and corotation electric fields and interaction with Pc 5 waves (wave period: 150-600 s) via a magnetic drift-bounce resonance. A test particle code has been developed to calculate the motion of the ring current O+ ions in a time-independent dipole magnetic field, and convection and corotation electric fields, plus Pc 5 wave fields, for which a simple analytical model has been formulated based on spacecraft observations. For given fields, whether a particle gains or loses energy depends on its initial kinetic energy, pitch angle at the equatorial plane, and the position of its guiding center with respect to the azimuthal phase of the wave. The ring current O+ ions show a dispersion in energies and L values with decreasing local time across the dayside, and a bulk shift to lower energies and higher L values. The former is due to the wave-particle interaction causing the ion to gain or lose energy, while the latter is due to the convection electric field. Our simulations show that, due to the interaction with the Pc 5 waves, the particle's kinetic energy can drop below that required to overcome the convection potential and the particle will be lost to the dayside magnetopause by a sunward E×B drift. This may contribute to the loss of O+ ions at intermediate energies (tens of keV) observed during the recovery phase of geomagnetic storms.

Resonances as the general cause of the outbursts in the symbiotic system AG Draconis

NASA Astrophysics Data System (ADS)

Gális, R.; Hric, L.; Friedjung, M.; Petrík, K.

1999-08-01

The general behaviour of the symbiotic system AG Dra is studied in the context of the long-term photometry monitoring and radial velocity analysis. Period analysis of the data gave two values of periods, 549fd73 +/- 1fd59 and 355fd27 +/- 1fd82 days for orbital motion and pulsations of cool giant respectively. The new orbital elements have been determined as well as the new orbital and pulsation ephemerides respectively. The ratio of the orbital to the pulsation period is actually very close to 14/9, so resonance might occur. We suggested, that this is the general cause of the recurrence time of the active stages. The pulsations of the cool component are very probably non-radial, so accretion by the white dwarf is particularly high when the material ejected due to the pulsations, is ejected in certain directions with respect to the line joining the two stars. The manifestations of this phenomena are the observed outbursts themselves.

Detection of a large sample of γ Doradus stars from Kepler space photometry and high-resolution ground-based spectroscopy

NASA Astrophysics Data System (ADS)

Tkachenko, A.; Aerts, C.; Yakushechkin, A.; Debosscher, J.; Degroote, P.; Bloemen, S.; Pápics, P. I.; de Vries, B. L.; Lombaert, R.; Hrudkova, M.; Frémat, Y.; Raskin, G.; Van Winckel, H.

2013-08-01

Context. The launches of the MOST, CoRoT, and Kepler missions opened up a new era in asteroseismology, the study of stellar interiors via interpretation of pulsation patterns observed at the surfaces of large groups of stars. These space missions deliver a huge amount of high-quality photometric data suitable to study numerous pulsating stars. Aims: Our ultimate goal is a detection and analysis of an extended sample of γ Dor-type pulsating stars with the aim to search for observational evidence of non-uniform period spacings and rotational splittings of gravity modes in main-sequence stars typically twice as massive as the Sun. This kind of diagnostic can be used to deduce the internal rotation law and to estimate the amount of rotational mixing in the near core regions. Methods: We applied an automated supervised photometric classification method to select a sample of 69 Gamma Doradus (γ Dor) candidate stars. We used an advanced method to extract the Kepler light curves from the pixel data information using custom masks. For 36 of the stars, we obtained high-resolution spectroscopy with the HERMES spectrograph installed at the Mercator telescope. The spectroscopic data are analysed to determine the fundamental parameters like Teff, log g, vsini, and [M/H]. Results: We find that all stars for which spectroscopic estimates of Teff and log g are available fall into the region of the HR diagram, where the γ Dor and δ Sct instability strips overlap. The stars cluster in a 700 K window in effective temperature; log g measurements suggest luminosity class IV-V, i.e. sub-giant or main-sequence stars. From the Kepler photometry, we identify 45 γ Dor-type pulsators, 14 γ Dor/δ Sct hybrids, and 10 stars, which are classified as "possibly γ Dor/δ Sct hybrid pulsators". We find a clear correlation between the spectroscopically derived vsini and the frequencies of independent pulsation modes. Conclusions: We have shown that our photometric classification based on the light curve morphology and colour information is very robust. The results of spectroscopic classification perfectly agree with the photometric classification. We show that the detected correlation between vsini and frequencies has nothing to do with rotational modulation of the stars but is related to their stellar pulsations. Our sample and frequency determinations offer a good starting point for seismic modelling of slow to moderately rotating γ Dor stars. Based on data gathered with NASA Discovery mission Kepler and spectra obtained with the HERMES spectrograph, which is 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 Fonds National de la Recherche Scientifique (F.R.S.-FNRS), Belgium, the Royal Observatory of Belgium, the Observatoire de Genève, Switzerland, and the Thüringer Landessternwarte Tautenburg, Germany.Tables A.1 and B.1 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/556/A52

Is the SDSS ZZ Ceti instability strip really pure?

NASA Astrophysics Data System (ADS)

de Souza Oliveira, Kepler

2006-08-01

We propose to obtain SNR > 60 optical spectra of the DA white dwarf stars for which the Sloan Digital Sky Survey spectra indicated temperatures inside de ZZ Ceti instability strip, but time series photometry show they are not variables. The Sloan spectra have insufficient SNR, specially below 4000A, where there are hydrogen lines whose strength can be used to measure surface gravity accurately. Theoretically and observationally, the location of the instability strip depends both on temperature and mass. To use the properties derived from the pulsating stars as applying to all white dwarf stars, and their progenitors, we must demonstrate pulsation is a normal evolutionary state. As the instability strip is only 1200K wide, accurate temperatures and log g must be obtained and therefore the spectra must include the log g sensitive lines Hgamma to H9. White dwarf stars, the objects of this proposal, are the end point of evolution of around 97% of all stars born. As they cool, they pass through instability strips, where they are seen as multi-periodic pulsators. Each pulsation is an independent measurement, placing another constraint on the stellar properties. Pulsations allow the determination of the stellar compositional layers, including the core, crucial to understand the progenitor's evolution, from AGB to planetary nebulae nuclei, "born again" phase, and their possible evolution to SNIa through accretion. As white dwarf progenitors lose at least half of their masses before turning into white dwarfs, they contribute to the interstellar medium enrichment, and measuring their structure in detail will allow us to decode nuclear reaction rates and convection, which determine their evolution. Pulsating white dwarf stars are also laboratories for physics at high densities as crystallization, neutrino cooling, and axion emission. White dwarf cooling, also measured through pulsations, allows an independent measurement of the age of the galactic components and was the first to indicate an age of 13 Gyr to the Universe, back in 1987. Now that we have observed white dwarf stars in all the components of our galaxy, possible differences in component ages are detectable. Our goal is to determine if the instalibity strip is pure, implying the information we obtain on the variables applies to white dwarf stars in general. As these stars are on average fainter than g=18.2, we require blue sensitive 8m class telescope.

The eclipsing system V404 Lyr: Light-travel times and γ Doradus pulsations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, Jae Woo; Kim, Seung-Lee; Hong, Kyeongsoo

We present the physical properties of V404 Lyr exhibiting eclipse timing variations and multiperiodic pulsations from all historical data including the Kepler and SuperWASP observations. Detailed analyses of 2922 minimum epochs showed that the orbital period has varied through a combination of an upward-opening parabola and two sinusoidal variations, with periods of P {sub 3} = 649 days and P {sub 4} = 2154 days and semi-amplitudes of K {sub 3} = 193 s and K {sub 4} = 49 s, respectively. The secular period increase at a rate of +1.41 × 10{sup –7} days yr{sup –1} could be interpretedmore » as a combination of the secondary to primary mass transfer and angular momentum loss. The most reasonable explanation for both sinusoids is a pair of light-travel-time effects due to two circumbinary objects with projected masses of M {sub 3} = 0.47 M {sub ☉} and M {sub 4} = 0.047 M {sub ☉}. The third-body parameters are consistent with those calculated using the Wilson-Devinney binary code. For the orbital inclinations i {sub 4} ≳ 43°, the fourth component has a mass within the hydrogen-burning limit of ∼0.07 M {sub ☉}, which implies that it is a brown dwarf. A satisfactory model for the Kepler light curves was obtained by applying a cool spot to the secondary component. The results demonstrate that the close eclipsing pair is in a semi-detached, but near-contact, configuration; the primary fills approximately 93% of its limiting lobe and is larger than the lobe-filling secondary. Multiple frequency analyses were applied to the light residuals after subtracting the synthetic eclipsing curve from the Kepler data. This revealed that the primary component of V404 Lyr is a γ Dor type pulsating star, exhibiting seven pulsation frequencies in the range of 1.85-2.11 day{sup –1} with amplitudes of 1.38-5.72 mmag and pulsation constants of 0.24-0.27 days. The seven frequencies were clearly identified as high-order low-degree gravity-mode oscillations which might be excited through tidal interaction. Only eight eclipsing binaries have been known to contain γ Dor pulsating components and, therefore, V404 Lyr will be an important test bed for investigating these rare and interesting objects.« less

Seismic evidence for non-synchronization in two close sdb+dM binaries from Kepler photometry

NASA Astrophysics Data System (ADS)

Pablo, Herbert; Kawaler, Steven D.; Reed, M. D.; Bloemen, S.; Charpinet, S.; Hu, H.; Telting, J.; Østensen, R. H.; Baran, A. S.; Green, E. M.; Hermes, J. J.; Barclay, T.; O'Toole, S. J.; Mullally, Fergal; Kurtz, D. W.; Christensen-Dalsgaard, J.; Caldwell, Douglas A.; Christiansen, Jessie L.; Kinemuchi, K.

2012-05-01

We report on extended photometry of two pulsating subdwarf B (sdB) stars in close binaries. For both cases, we use rotational splitting of the pulsation frequencies to show that the sdB component rotates much too slowly to be in synchronous rotation. We use a theory of tidal interaction in binary stars to place limits on the mass ratios that are independent of estimates based on the radial velocity curves. The companions have masses below 0.26 M⊙. The pulsation spectra show the signature of high-overtone g-mode pulsation. One star, KIC 11179657, has a clear sequence of g modes with equal period spacings as well as several periodicities that depart from that trend. KIC 02991403 shows a similar sequence, but has many more modes that do not fit the simple pattern.

Corot's 'gout' and a 'gipsy' girl.

PubMed

Panush, R B; Caldwell, J R; Panush, R S

1990-09-05

Representations of rheumatic disease in art provide insight into artistic expression, help us understand the evolution and perhaps the etiology of rheumatic diseases, and remind us of great contributions by artists in adverse circumstances. We noted hand deformities characteristic of inflammatory arthritis in Jean-Baptiste-Camille Corot's Gipsy Girl With Mandolin (1870 to 1875), National Gallery of Art, Washington, DC. Corot suffered with what probably was gout beginning in 1866. We are unaware that arthritis has been observed in Corot's subjects or that Corot's depiction of arthritis has been appreciated from the perspective of his own rheumatic disease. Examination of other Corot portraits identifies some with blurred hand details consistent with the artist's style and the remainder with normal hands. These observations suggest that the artist portrayed specific anatomic abnormalities in the "Gipsy Girl's" hand, indicating familiarity with inflammatory arthritis. It is speculative whether this was Corot's own or the model's arthritis; we favor the interpretation that Corot's gout was reflected in this particular work. We thus add a new perspective to Corot's Gipsy Girl With Mandolin-a subject with arthritis, a painter knowledgeable about arthritis, and a painting that therefore might be understood at least in part from an appreciation of the artist's specific illness.

Discovery of decaHz flaring in SAX J1808.4-3658

NASA Astrophysics Data System (ADS)

Bult, P.

2014-01-01

We report on the discovery of strong decaHz flaring in the early decay of two out of five outbursts of the accreting millisecond X-ray pulsar SAX J1808.4-3658. The decaHz flaring switches on and, after ~3 days, off again, on a time scale of 1-2 hours. When the flaring is present, the total 0.05-10 Hz variability has a fractional rms amplitude of 20 to 30 percent, well in excess of the 8 to 12 percent rms broad-band noise usually seen in power spectra of SAX J1808 in this frequency range. Coherent 401 Hz pulsations are seen throughout the observations in which the decaHz flaring is detected. We find that the absolute amplitude of the pulsations varies with the flux modulation of the decaHz flaring, indicating that the flaring is caused by an accretion rate modulation already present in the accretion flow prior to matter entering the accretion funnel. We suggest that the decaHz flaring is the result of the Spruit-Taam instability [1]. This instability arises when the inner accretion disk approaches co-rotation. The rotation of the stellar magnetosphere then acts as a propeller, suppressing accretion onto the neutron star. A matter reservoir forms in the inner accretion disk, which episodically empties onto the neutron star, causing flares at a decaHz timescale. A similar explanation was proposed earlier for 1 Hz flaring occurring late in three of five outbursts, mutually exclusive with the decaHz flaring. The 1 Hz flaring was observed at luminosities a factor 5 to 10 below where we see the decaHz flaring. That a different branch of the Spruit-Taam instability could also act at the much higher luminosity levels of the decaHz flaring had recently been predicted by D'Angelo & Spruit [2, 3]. We discuss these findings in the context of the parameters of the Spruit-Taam-d'Angelo model of the instability. If confirmed, after millisecond pulsations, 1 Hz and decaHz flaring would be another diagnostic of the presence of a magnetosphere in accreting low-magnetic field neutron stars.

Correlated Pc4-5 ULF waves, whistler-mode chorus, and pulsating aurora observed by the Van Allen Probes and ground-based systems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jaynes, A. N.; Lessard, M. R.; Takahashi, K.

Theory and observations have linked equatorial VLF waves with pulsating aurora for decades, invoking the process of pitch angle scattering of tens of keV electrons in the equatorial magnetosphere. Recently published satellite studies have strengthened this argument, by showing strong correlation between pulsating auroral patches and both lower-band chorus and tens of keV electron modulation in the vicinity of geosynchronous orbit. Additionally, a previous link has been made between Pc4–5 compressional pulsations and modulation of whistler-mode chorus using Time History of Events and Macroscale Interactions during Substorms. In the current study, we present simultaneous in situ observations of structured chorusmore » waves and an apparent field line resonance (in the Pc4–5 range) as a result of a substorm injection, observed by Van Allen Probes, along with ground-based observations of pulsating aurora. We demonstrate the likely scenario being one of substorm-driven Pc4–5 ULF pulsations modulating chorus waves, and thus providing the driver for pulsating particle precipitation into the Earth's atmosphere. Interestingly, the modulated chorus wave and ULF wave periods are well correlated, with chorus occurring at half the periodicity of the ULF waves. We also show, for the first time, a particular few-Hz modulation of individual chorus elements that coincides with the same modulation in a nearby pulsating aurora patch. As a result, such modulation has been noticed as a high-frequency component in ground-based camera data of pulsating aurora for decades and may be a result of nonlinear chorus wave interactions in the equatorial region.« less

Correlated Pc4-5 ULF waves, whistler-mode chorus, and pulsating aurora observed by the Van Allen Probes and ground-based systems

DOE PAGES

Jaynes, A. N.; Lessard, M. R.; Takahashi, K.; ...

2015-10-28

Theory and observations have linked equatorial VLF waves with pulsating aurora for decades, invoking the process of pitch angle scattering of tens of keV electrons in the equatorial magnetosphere. Recently published satellite studies have strengthened this argument, by showing strong correlation between pulsating auroral patches and both lower-band chorus and tens of keV electron modulation in the vicinity of geosynchronous orbit. Additionally, a previous link has been made between Pc4–5 compressional pulsations and modulation of whistler-mode chorus using Time History of Events and Macroscale Interactions during Substorms. In the current study, we present simultaneous in situ observations of structured chorusmore » waves and an apparent field line resonance (in the Pc4–5 range) as a result of a substorm injection, observed by Van Allen Probes, along with ground-based observations of pulsating aurora. We demonstrate the likely scenario being one of substorm-driven Pc4–5 ULF pulsations modulating chorus waves, and thus providing the driver for pulsating particle precipitation into the Earth's atmosphere. Interestingly, the modulated chorus wave and ULF wave periods are well correlated, with chorus occurring at half the periodicity of the ULF waves. We also show, for the first time, a particular few-Hz modulation of individual chorus elements that coincides with the same modulation in a nearby pulsating aurora patch. As a result, such modulation has been noticed as a high-frequency component in ground-based camera data of pulsating aurora for decades and may be a result of nonlinear chorus wave interactions in the equatorial region.« less

V850 Cyg: An eclipsing binary with a giant γ Dor pulsator

NASA Astrophysics Data System (ADS)

Çakırlı, Ö.; Ibanoglu, C.; Sipahi, E.; Akan, M. C.

2017-04-01

We present new spectroscopic observations of the double-lined eclipsing binary V850 Cyg. The long-cadence photometric observations obtained by Kepler were analysed and combined with the analysis of radial velocities for deriving the absolute parameters of the components. Masses and radii were determined as Mp=1.601 ± 0.076 M⊙ and Rp=4.239 ± 0.076 R⊙, Ms=0.851 ± 0.053 M⊙ and Rs=5.054 ± 0.087 R⊙ for the components of V850 Cyg. We estimate an interstellar reddening of 0.28 ± 0.12 mag and a distance of 1040 ± 160 pc for the system. The measured rotational velocity of the secondary appears to lower than that of synchronize rotation. However its spectral lines are too weak to be measured the rotational velocity with reasonable accuracy. We have extracted the synthetic light curve from the observations and excluded the data within the eclipses for the frequency analysis. We obtained at least nine frequencies in the γ Dor regime. It seems that the primary component oscillates with a dominant period of about 1.152549 ± 0.000009 days. We also compare pulsational properties of the primary star of V850 Cyg with the γ Dor type pulsating components in other binaries.

Waste heat recovery on multiple low-speed reciprocating engines

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mayhew, R.E.

1984-09-01

With rising fuel costs, energy conservation has taken on added significance. Installation of waste heat recovery units (WHRU's) on gas turbines is one method used in the past to reduce gas plant fuel consumption. More recently, waste heat recovery on multiple reciprocating compressor engines also has been identified as having energy conservation potential. This paper reviews the development and implementation of a WHRU for multiple low-speed engines at the Katy (TX) gas plant. WHRU's for these engines should be differentiated from high-speed engines and gas turbines in that low-speed engines produce low-frequency, high-amplitude pulsating exhaust. The design of a WHRUmore » system must take this potentially destructive pulsation into account. At Katy, the pulsation forces were measured at high-amplitude frequencies and then used to design a pulsation filter and structural stiffness into the various components of the WHRU to minimize vibration and improve system reliability.« less

A new method of measuring centre-of-mass velocities of radially pulsating stars from high-resolution spectroscopy

NASA Astrophysics Data System (ADS)

Britavskiy, N.; Pancino, E.; Tsymbal, V.; Romano, D.; Fossati, L.

2018-03-01

We present a radial velocity analysis of 20 solar neighbourhood RR Lyrae and three Population II Cepheid variables. We obtained high-resolution, moderate-to-high signal-to-noise ratio spectra for most stars; these spectra covered different pulsation phases for each star. To estimate the gamma (centre-of-mass) velocities of the programme stars, we use two independent methods. The first, `classic' method is based on RR Lyrae radial velocity curve templates. The second method is based on the analysis of absorption-line profile asymmetry to determine both pulsational and gamma velocities. This second method is based on the least-squares deconvolution (LSD) technique applied to analyse the line asymmetry that occurs in the spectra. We obtain measurements of the pulsation component of the radial velocity with an accuracy of ±3.5 km s-1. The gamma velocity was determined with an accuracy of ±10 km s-1, even for those stars having a small number of spectra. The main advantage of this method is the possibility of obtaining an estimation of gamma velocity even from one spectroscopic observation with uncertain pulsation phase. A detailed investigation of LSD profile asymmetry shows that the projection factor p varies as a function of the pulsation phase - this is a key parameter, which converts observed spectral line radial velocity variations into photospheric pulsation velocities. As a by-product of our study, we present 41 densely spaced synthetic grids of LSD profile bisectors based on atmospheric models of RR Lyr covering all pulsation phases.

Distinguishing Among Mechanisms That Determine Pi 2 Pulsation Period

NASA Astrophysics Data System (ADS)

Takahashi, K.; Lysak, R. L.; Hartinger, M.; Kletzing, C.; Smith, C. W.; Singer, H. J.

2017-12-01

Pi2 pulsations are an integral component of substorms, with their association with magnetic field dipolarization, particle injection, auroral brightening, and intensification of field-aligned currents. An important question about Pi2 pulsations is how their periodicity is established. Two possible mechanisms are forcing of the inner magnetosphere by periodic variations of the near-Earth plasma bulk flows, and the cavity mode response of the plasmasphere to impulsive or irregular disturbances propagating from the tail. We address this question using observations of four Pi2 pulsations that occurred in a 2-hour time span on 29 July 2013. These events were observed by THEMIS, Van Allen Probes (RBSP), and geostationary GOES and ETS-VIII, while some of these spacecraft were nearly radially aligned in the evening sector at radial distances between 2 and 10 Earth radii. Electron density data are available from THEMIS and RBSP to determine the spacecraft location relative to the plasmapause. We examine the time delay of oscillations among the spacecraft and the local wave properties such as polarization and phase delay between the electric and magnetic field components. We compare the observations with ULF wave simulations in a dipole magnetosphere to evaluate which of the two possible Pi2 generation mechanisms was more effective.

System for Measuring Conditional Amplitude, Phase, or Time Distributions of Pulsating Phenomena

PubMed Central

Van Brunt, Richard J.; Cernyar, Eric W.

1992-01-01

A detailed description is given of an electronic stochastic analyzer for use with direct “real-time” measurements of the conditional distributions needed for a complete stochastic characterization of pulsating phenomena that can be represented as random point processes. The measurement system described here is designed to reveal and quantify effects of pulse-to-pulse or phase-to-phase memory propagation. The unraveling of memory effects is required so that the physical basis for observed statistical properties of pulsating phenomena can be understood. The individual unique circuit components that comprise the system and the combinations of these components for various measurements, are thoroughly documented. The system has been applied to the measurement of pulsating partial discharges generated by applying alternating or constant voltage to a discharge gap. Examples are shown of data obtained for conditional and unconditional amplitude, time interval, and phase-of-occurrence distributions of partial-discharge pulses. The results unequivocally show the existence of significant memory effects as indicated, for example, by the observations that the most probable amplitudes and phases-of-occurrence of discharge pulses depend on the amplitudes and/or phases of the preceding pulses. Sources of error and fundamental limitations of the present measurement approach are analyzed. Possible extensions of the method are also discussed. PMID:28053450

Spatial features of mid-latitude field-line resonances from simultaneous ground-satellite measurements

NASA Astrophysics Data System (ADS)

Prikner, K.

1996-07-01

Three series of simultaneous pulsation measurements ( f<0.06 Hz) on the Freja satellite and at the Budkov Observatory have been spectrally processed (FFT) in 6-min intervals of Freja's transits near the local Budkov field line. Doppler-shifted, weighted spectral-peak frequencies, determined in both transverse magnetic components in the mean field-aligned coordinate system on Freja, allowed the estimation, by comparison with the stable frequency at Budkov, of fundamental frequencies of the local magnetic-field-line resonance ranged from 13 to 17 mHz in two pulsation events analyzed, with Kp=2+ to 0+. The ratio of total amplitudes of the spectral-pulsation components on the ground and on Freja at an altitude of ~1700 km (values <0.7) characterizes the transmissivity of the ionosphere. In the Pc3 frequency range this correlates well with simulation computations using models of the ionosphere under low solar activity. Acknowledgements. The Editor in Chief thanks two referees for their help in evaluating this paper.--> Correspondence to: L. Alperovich-->

Method of LSD profile asymmetry for estimating the center of mass velocities of pulsating stars

NASA Astrophysics Data System (ADS)

Britavskiy, Nikolay; Pancino, Elena; Romano, Donatella; Tsymbal, Vadim

2015-08-01

We present radial velocity analysis for 20 solar neighborhood RR Lyrae and 3 Population II Cepheids. High-resolution spectra were observed with either TNG/SARG or VLT/UVES over varying phases. To estimate the center of mass (barycentric) velocities of the program stars, we utilized two independent methods. First, the 'classic' method was employed, which is based on RR Lyrae radial velocity curve templates. Second, we provide the new method that used absorption line profile asymmetry to determine both the pulsation and the barycentric velocities even with a low number of high-resolution spectra and in cases where the phase of the observations is uncertain. This new method is based on a Least Squares Deconvolution (LSD) of the line profiles in order to analyze line asymmetry that occurs in the spectra of pulsating stars. By applying this method to our sample stars we attain accurate measurements (± 1 km/s) of the pulsation component of the radial velocity. This results in determination of the barycentric velocity to within 5 km/s even with a low number of high-resolution spectra. A detailed investigation of LSD profile asymmetry shows the variable nature of the project factor at different pulsation phases, which should be taken into account in the detailed spectroscopic analysis of pulsating stars.

Method of LSD profile asymmetry for estimating the center of mass velocities of pulsating stars

NASA Astrophysics Data System (ADS)

Britavskiy, N.; Pancino, E.; Tsymbal, V.; Romano, D.; Cacciari, C.; Clementini, C.

2016-05-01

We present radial velocity analysis for 20 solar neighborhood RR Lyrae and 3 Population II Cepheids. High-resolution spectra were observed with either TNG/SARG or VLT/UVES over varying phases. To estimate the center of mass (barycentric) velocities of the program stars, we utilized two independent methods. First, the 'classic' method was employed, which is based on RR Lyrae radial velocity curve templates. Second, we provide the new method that used absorption line profile asymmetry to determine both the pulsation and the barycentric velocities even with a low number of high-resolution spectra and in cases where the phase of the observations is uncertain. This new method is based on a least squares deconvolution (LSD) of the line profiles in order to an- alyze line asymmetry that occurs in the spectra of pulsating stars. By applying this method to our sample stars we attain accurate measurements (+- 2 kms^-1) of the pulsation component of the radial velocity. This results in determination of the barycentric velocity to within 5 kms^-1 even with a low number of high- resolution spectra. A detailed investigation of LSD profile asymmetry shows the variable nature of the project factor at different pulsation phases, which should be taken into account in the detailed spectroscopic analysis of pulsating stars.

KEPLER ECLIPSING BINARIES WITH DELTA SCUTI/GAMMA DORADUS PULSATING COMPONENTS. I. KIC 9851944

DOE Office of Scientific and Technical Information (OSTI.GOV)

Guo, Zhao; Gies, Douglas R.; Matson, Rachel A.

2016-07-20

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 {sub ⊙}, 3.19 R {sub ⊙}) but close masses (1.76 M {sub ⊙}, 1.79 M {sub ⊙}) 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 hasmore » 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.« less

Quantifying the influence of respiration and cardiac pulsations on cerebrospinal fluid dynamics using real-time phase-contrast MRI.

PubMed

Yildiz, Selda; Thyagaraj, Suraj; Jin, Ning; Zhong, Xiaodong; Heidari Pahlavian, Soroush; Martin, Bryn A; Loth, Francis; Oshinski, John; Sabra, Karim G

2017-08-01

To validate a real-time phase contrast magnetic resonance imaging (RT-PCMRI) sequence in a controlled phantom model, and to quantify the relative contributions of respiration and cardiac pulsations on cerebrospinal fluid (CSF) velocity at the level of the foramen magnum (FM). To validate the 3T MRI techniques, in vitro studies used a realistic model of the spinal subarachnoid space driven by pulsatile flow waveforms mimicking the respiratory and cardiac components of CSF flow. Subsequently, CSF flow was measured continuously during 1-minute RT-PCMRI acquisitions at the FM while healthy subjects (N = 20) performed natural breathing, deep breathing, breath-holding, and coughing. Conventional cardiac-gated PCMRI was obtained for comparison. A frequency domain power ratio analysis determined the relative contribution of respiration versus cardiac ([r/c]) components of CSF velocity. In vitro studies demonstrating the accuracy of RT-PCMRI within 5% of input values showed that conventional PCMRI measures only the cardiac component of CSF velocity (0.42 ± 0.02 cm/s), averages out respiratory effects, and underestimates the magnitude of CSF velocity (0.96 ± 0.07 cm/s). In vivo RT-PCMRI measurements indicated the ratio of respiratory to cardiac velocity pulsations averaged over all subjects as [r/c = 0.14 ± 0.27] and [r/c = 0.40 ± 0.47] for natural and deep breathing, respectively. During coughing, the peak CSF velocity increased by a factor of 2.27 ± 1.40. RT-PCMRI can noninvasively measure instantaneous CSF velocity driven by cardiac pulsations, respiration, and coughing in real time. A comparable contribution of respiration and cardiac pulsations on CSF velocity was found during deep breathing but not during natural breathing. 1 Technical Efficacy: Stage 1 J. MAGN. RESON. IMAGING 2017;46:431-439. © 2017 International Society for Magnetic Resonance in Medicine.

Counter-rotating accretion discs

NASA Astrophysics Data System (ADS)

Dyda, S.; Lovelace, R. V. E.; Ustyugova, G. V.; Romanova, M. M.; Koldoba, A. V.

2015-01-01

Counter-rotating discs can arise from the accretion of a counter-rotating gas cloud on to the surface of an existing corotating disc or from the counter-rotating gas moving radially inwards to the outer edge of an existing disc. At the interface, the two components mix to produce gas or plasma with zero net angular momentum which tends to free-fall towards the disc centre. We discuss high-resolution axisymmetric hydrodynamic simulations of viscous counter-rotating discs for the cases where the two components are vertically separated and radially separated. The viscosity is described by an isotropic α-viscosity including all terms in the viscous stress tensor. For the vertically separated components, a shear layer forms between them and the middle part of this layer free-falls to the disc centre. The accretion rates are increased by factors of ˜102-104 over that for a conventional disc rotating in one direction with the same viscosity. The vertical width of the shear layer and the accretion rate are strongly dependent on the viscosity and the mass fraction of the counter-rotating gas. In the case of radially separated components where the inner disc corotates and the outer disc rotates in the opposite direction, a gap between the two components opens and closes quasi-periodically. The accretion rates are ≳25 times larger than those for a disc rotating in one direction with the same viscosity.

Relationship between Relativistic Electron Flux in the Inner Magnetosphere and ULF Pulsation on the Ground Associated with Long-term Variations of Solar Wind

NASA Astrophysics Data System (ADS)

Kitamura, K.; Nagatsuma, T.; Troshichev, O. A.; Obara, T.; Koshiishi, H.; Saita, S.; Yoshikawa, A.; Yumoto, K.

2014-12-01

In the present study the relativistic electron flux (0.59-1.18MeV) measured by Standard Dose Monitor (SDOM) onboard DRTS (KODAMA) satellite at the Geostationary Earth Orbit (GEO) is analyzed to investigate the long term (from 2002 to 2014) variations of the electron flux enhancement (REF) during the passage of Corotating Interaction Regions (CIRs) and/or Coronal Mass Ejection (CMEs). The long term variations of the REF clearly shows the 27-days period associated with the high speed solar wind velocity caused by the CIRs, whereas it is very few that the enhancement of REF lasts for several days after passage of CMEs. The 27-days period enhancement of REF represents the quite strong peak in 2003 when the high speed stream of the solar wind were quit active. We also conducted the same analysis for the Pc5 pulsations observed on the ground. The ground magnetic variations data globally observed by National Institute of Information and Communications Technology (NICT) and International Center for Space Weather Science and Education (ICSWSE) Kyushu University are used to investigate the long term variations of Pc5 power. The same signature in the REF variations is shown in the time variability of the Pc5 power on the ground. These results indicate that the solar wind condition strongly affects the acceleration process of the relativistic electron flux by the ULF wave. In particular the dependence of the REF and Pc5 variations on the sector structures and their seasonal variations strongly suggest that the relationship between Pc5 and REF variations could be controlled by the Russell-McPherron effect.

Kepler's first view of O-star variability: K2 data of five O stars in Campaign 0 as a proof of concept for O-star asteroseismology

NASA Astrophysics Data System (ADS)

Buysschaert, B.; Aerts, C.; Bloemen, S.; Debosscher, J.; Neiner, C.; Briquet, M.; Vos, J.; Pápics, P. I.; Manick, R.; Schmid, V. S.; Van Winckel, H.; Tkachenko, A.

2015-10-01

We present high-precision photometric light curves of five O-type stars observed with the refurbished Kepler satellite during its Campaign 0. For one of the stars, we also assembled high-resolution ground-based spectroscopy with the HERMES spectrograph attached to the 1.2 m Mercator telescope. The stars EPIC 202060097 (O9.5V) and EPIC 202060098 (O7V) exhibit monoperiodic variability due to rotational modulation with an amplitude of 5.6 and 9.3 mmag and a rotation period of 2.63 and 5.03 d, respectively. EPIC 202060091 (O9V) and EPIC 202060093 (O9V:pe) reveal variability at low frequency but the cause is unclear. EPIC 202060092 (O9V:p) is discovered to be a spectroscopic binary with at least one multiperiodic β Cep-type pulsator whose detected mode frequencies occur in the range [0.11, 6.99] d-1 and have amplitudes between 0.8 and 2.0 mmag. Its pulsation spectrum is shown to be fully compatible with the ones predicted by core-hydrogen burning O-star models. Despite the short duration of some 33 d and the limited data quality with a precision near 100 μmag of these first K2 data, the diversity of possible causes for O-star variability already revealed from campaigns of similar duration by the MOST and CoRoT satellites is confirmed with Kepler. We provide an overview of O-star space photometry and give arguments why future K2 monitoring during Campaigns 11 and 13 at short cadence, accompanied by time-resolved high-precision high-resolution spectroscopy, opens up the possibility of in-depth O-star seismology.

The occurrence of binary evolution pulsators in classical instability strip of RR Lyrae and Cepheid variables

NASA Astrophysics Data System (ADS)

Karczmarek, P.; Wiktorowicz, G.; Iłkiewicz, K.; Smolec, R.; Stępień, K.; Pietrzyński, G.; Gieren, W.; Belczynski, K.

2017-04-01

Single star evolution does not allow extremely low-mass stars to cross the classical instability strip (IS) during the Hubble time. However, within binary evolution framework low-mass stars can appear inside the IS once the mass transfer (MT) is taken into account. Triggered by a discovery of low-mass (0.26 M⊙) RR Lyrae-like variable in a binary system, OGLE-BLG-RRLYR-02792, we investigate the occurrence of similar binary components in the IS, which set up a new class of low-mass pulsators. They are referred to as binary evolution pulsators (BEPs) to underline the interaction between components, which is crucial for substantial mass-loss prior to the IS entrance. We simulate a population of 500 000 metal-rich binaries and report that 28 143 components of binary systems experience severe MT (losing up to 90 per cent of mass), followed by at least one IS crossing in luminosity range of RR Lyrae (RRL) or Cepheid variables. A half of these systems enter the IS before the age of 4 Gyr. BEPs display a variety of physical and orbital parameters, with the most important being the BEP mass in range 0.2-0.8 M⊙, and the orbital period in range 10-2 500 d. Based on the light curve only, BEPs can be misclassified as genuine classical pulsators, and as such they would contaminate genuine RRL and classical Cepheid variables at levels of 0.8 and 5 per cent, respectively. We state that the majority of BEPs will remain undetected and we discuss relevant detection limitations.

Pulsation in the presence of a strong magnetic field: the roAp star HD166473

NASA Astrophysics Data System (ADS)

Mathys, G.; Kurtz, D. W.; Elkin, V. G.

2007-09-01

Phase-resolved high-resolution, high signal-to-noise ratio (S/N) observations of the strongly magnetic roAp star HD166473 are analysed. HD166473 was selected as the target of this study because it has one of the strongest magnetic fields of all the roAp stars known with resolved magnetically split lines. Indeed, we show that enhanced pulsation diagnosis can be achieved from consideration of the different pulsation behaviour of the π and σ Zeeman components of the resolved spectral lines. This study is based on a time-series of high spectral resolution observations obtained with the Ultraviolet and Visual Echelle Spectrograph of the Very Large Telescope of the European Southern Observatory. Radial velocity variations due to pulsation are observed in rare earth lines, with amplitudes up to 110ms-1. The variations occur with three frequencies, already detected in photometry, but which can in this work be determined with better precision: 1.833, 1.886 and 1.928mHz. The pulsation amplitudes and phases observed in the rare earth element lines vary with atmospheric height, as is the case in other roAp stars studied in detail. Lines of Fe and of other (mostly non-rare earth) elements do not show any variation to very high precision (1.5ms-1 in the case of Fe). The low amplitudes of the observed variations do not allow the original goal of studying differences between the behaviour of the resolved Zeeman line components to be reached; the S/N achieved in the radial velocity determinations is insufficient to establish definitely the possible existence of such differences. Yet the analysis provides a tantalizing hint at the occurrence of variations of the mean magnetic field modulus with the pulsation frequency, with an amplitude of 21 +/- 5G. Based on observations collected at the European Southern Observatory, Paranal, Chile, as part of programme 067.D-0272. E-mail: gmathys@eso.org

KIC 6048106: an Algol-type eclipsing system with long-term magnetic activity and hybrid pulsations - I. Binary modelling

NASA Astrophysics Data System (ADS)

Samadi Ghadim, A.; Lampens, P.; Jassur, M.

2018-03-01

The A-F-type stars and pulsators (δ Scuti-γ Dor) are in a critical regime where they experience a transition from radiative to convective transport of energy in their envelopes. Such stars can pulsate in both gravity and acoustic modes. Hence, the knowledge of their fundamental parameters along with their observed pulsation characteristics can help in improving the stellar models. When residing in a binary system, these pulsators provide more accurate and less model-dependent stellar parameters than in the case of their single counterparts. We present a light-curve model for the eclipsing system KIC 6048106 based on the Kepler photometry and the code PHOEBE. We aim to obtain accurate physical parameters and tough constraints for the stellar modelling of this intermediate-mass hybrid pulsator. We performed a separate modelling of three light-curve segments which show a distinct behaviour due to a difference in activity. We also analysed the Kepler Eclipse Time Variations (ETVs). KIC 6048106 is an Algol-type binary with F5-K5 components, a near-circular orbit and a 1.56-d period undergoing variations of the order of Δ P/P˜eq 3.60× 10^{-7} in 287 ± 7 d. The primary component is a main-sequence star with M1 = 1.55 ± 0.11 M⊙, R1 = 1.57 ± 0.12 R⊙. The secondary is a much cooler subgiant with M2 = 0.33 ± 0.07 M⊙, R2 = 1.77 ± 0.16 R⊙. Many small near-polar spots are active on its surface. The second quadrature phase shows a brightness modulation on a time-scale 290 ± 7 d, in good agreement with the ETV modulation. This study reveals a stable binary configuration along with clear evidence of a long-term activity of the secondary star.

Planetary transit candidates in Corot-IRa01 field

NASA Astrophysics Data System (ADS)

Carpano, S.; Cabrera, J.; Alonso, R.; Barge, P.; Aigrain, S.; Almenara, J.-M.; Bordé, P.; Bouchy, F.; Carone, L.; Deeg, H. J.; de La Reza, R.; Deleuil, M.; Dvorak, R.; Erikson, A.; Fressin, F.; Fridlund, M.; Gondoin, P.; Guillot, T.; Hatzes, A.; Jorda, L.; Lammer, H.; Léger, A.; Llebaria, A.; Magain, P.; Moutou, C.; Ofir, A.; Ollivier, M.; Janot-Pacheco, E.; Pätzold, M.; Pont, F.; Queloz, D.; Rauer, H.; Régulo, C.; Renner, S.; Rouan, D.; Samuel, B.; Schneider, J.; Wuchterl, G.

2009-10-01

Context: CoRoT is a pioneering space mission devoted to the analysis of stellar variability and the photometric detection of extrasolar planets. Aims: We present the list of planetary transit candidates detected in the first field observed by CoRoT, IRa01, the initial run toward the Galactic anticenter, which lasted for 60 days. Methods: We analysed 3898 sources in the coloured bands and 5974 in the monochromatic band. Instrumental noise and stellar variability were taken into account using detrending tools before applying various transit search algorithms. Results: Fifty sources were classified as planetary transit candidates and the most reliable 40 detections were declared targets for follow-up ground-based observations. Two of these targets have so far been confirmed as planets, CoRoT-1b and CoRoT-4b, for which a complete characterization and specific studies were performed. The CoRoT space mission, launched on December 27th 2006, has been developed and is operated by CNES, with contributions from Austria, Belgium, Brazil, ESA, Germany, and Spain. Four French laboratories associated with the CNRS (LESIA, LAM, IAS ,OMP) collaborate with CNES on the satellite development. First CoRoT data are available to the public from the CoRoT archive: http://idoc-corot.ias.u-psud.fr.

Observation and modeling of compressional Pi 3 magnetic pulsations

NASA Technical Reports Server (NTRS)

Matsuoka, Hitoshi; Takahashi, K.; Yumoto, K.; Anderson, B. J.; Sibeck, D. G.

1995-01-01

Compressional magnetic pulsations with irregular waveforms and periods longer than 150 s (here termed Pi 3) have been studied by using data from Active Magnetospheric Particle Tracer Explorers Charge Composition Explorer (AMPTE/CCE) and GOES 5 and 6 in the dayside magnetosphere and compared with signatures on the ground at low latitudes by using data from Kakioka station (L = 1.25). On the ground, the pulsations appear in the horizontal component. A study of 17 such concurrent events during a 2-month period in 1986 reveals the following pulsation characteristics. (1) The peak-to-peak amplitudes in space (delta B(sub T)) and on the ground (delta H) are comparable and are in the range of 0.5-7 nT. (2) On the ground the pulsations can be seen at all local times, even at midnight, while at geostationary orbit they are observed only on the dayside with a clear amplitude maximum at noon. (3) The pulsations on the ground lag those observed by CCE near local noon, and the lag increases as the local time separation between CCE and the ground station increases. The time lag is 1-2 min longer when the ground station is on the nightside than when it is on the dayside. (4) The time lag between pulsations observed at geostationary orbit and near noon by CCE varies systematically with local time and is about 2 min per 6 hours of local time separation. These observations indicate that some nightside pulsations in the Pi 3 band have dayside origins. The position dependence of the pulsation amplitude can be explained well by changes in the magnetopause current, which are in turn presumably caused by changes in the solar wind dynamic pressure. The time lags observed in space are consistent with signal propagation in the MHD fast mode, but the variation in space-ground time lags with ground station local time must be attributed to another mechanism.

Modulation of auroras by Pc5 pulsations in the dawn sector in association with reappearance of energetic particles at geosynchronous orbit

NASA Astrophysics Data System (ADS)

Saka, O.; Hayashi, K.; Klimushkin, D. Yu.; Mager, P. N.

2014-04-01

Geomagnetic Pc5 pulsations were observed in the dawn sector of the auroral zone on 17 January 1994 in association with increased energetic ion fluxes at geosynchronous orbit 10 min after the Pi2 onset. The characteristic properties of auroras associated with these pulsations were studied using movies taken by an all-sky imager. It was found that a pulsating aurora (PA) can be an optical manifestation of the Pc5 waves by a strong poloidal component observed with ground-based magnetometers. Goes7 observations showed compressional pulsations with the same period which can be attributed to the influence of the finite pressure of plasma and field line curvature on the poloidally polarized Alfvén waves. These poloidal pulsations may be generated by the ion injection observed with the LANL 1989-046 satellite. Two auroral arcs were observed north of the PA with optical features characteristic for the toroidal field line resonances: strong localization across L-shells, 180° phase change across the resonance, poleward phase propagation. Thus the Pc5 oscillations split into the toroidal and poloidal mode and oscillated coherently at latitudes from 62°N to 70°N. This study provides observational evidence of polarization splitting of the Alfven oscillation spectrum. Such a polarization splitting would occur in association with the reappearance of the energetic particles at geosynchronous orbit.

Outburst Activity Driven by Evolved Pulsating Star in the Symbiotic Binary AG Dra

NASA Astrophysics Data System (ADS)

Gális, R.; Hric, L.; Leedjärv, L.

2015-12-01

The symbiotic system AG Dra regularly undergoes quiescent and active stages which consist of the series of individual outbursts. The period analysis of new and historical photometric data, as well as radial velocities, confirmed the presence of the two periods. The longer one around ≈ 550 d is related to the orbital motion and the shorter one ≈355 d could be due to pulsation of the cool component of AG Dra.

Compositions of energetic particle populations in interplanetary space

NASA Technical Reports Server (NTRS)

Gloeckler, G.

1979-01-01

Observations of helium and heavier particles with energies below about 10 to 20 MeV/nucleon are discussed with emphasis on the composition of solar flare particles, corotating energetic particle streams, and the anomalous cosmic ray component. Future advances expected from results obtained from ISEE -3, Voyager, and the international solar polar spacecraft are reviewed.

CHARACTERIZATION OF CoRoT TARGET FIELDS WITH BERLIN EXOPLANET SEARCH TELESCOPE. II. IDENTIFICATION OF PERIODIC VARIABLE STARS IN THE LRc2 FIELD

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kabath, P.; Fruth, T.; Rauer, H.

2009-04-15

We report on photometric observations of the CoRoT LRc2 field with the new robotic Berlin Exoplanet Search Telescope II (BEST II). The telescope system was installed and commissioned at the Observatorio Cerro Armazones, Chile, in 2007. BEST II is a small aperture telescope with a wide field of view dedicated to the characterization of the stellar variability primarily in CoRoT target fields with high stellar densities. The CoRoT stellar field LRc2 was observed with BEST II up to 20 nights in 2007 July and August. From the acquired data containing about 100,000 stars, 426 new periodic variable stars were identifiedmore » and 90% of them are located within the CoRoT exoplanetary CCD segments and may be of further interest for CoRoT additional science programs.« less

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.

Intrinsic Variability in Multiple Systems and Clusters: Open Questions

NASA Astrophysics Data System (ADS)

Lampens, P.

2006-04-01

It is most interesting and rewarding to probe the stellar structure of stars which belong to a system originating from the same parent cloud as this provides additional and more accurate constraints for the models. New results on pulsating components in multiple systems and clusters are beginning to emerge regularly. Based on concrete studies, I will present still unsolved problems and discuss some of the issues which may affect our understanding of the pulsation physics in such systems but also in general.

The nature of arms in spiral galaxies. IV. Symmetries and asymmetries

NASA Astrophysics Data System (ADS)

del Río, M. S.; Cepa, J.

1999-01-01

A Fourier analysis of the intensity distribution in the planes of nine spiral galaxies is performed. In terms of the arm classification scheme of \\cite[Elmegreen & Elmegreen (1987)]{ee87} seven of the galaxies have well-defined arms (classes 12 and 9) and two have intermediate-type arms (class 5). The galaxies studied are NGC 157, 753, 895, 4321, 6764, 6814, 6951, 7479 and 7723. For each object Johnson B-band images are available which are decomposed into angular components, for different angular periodicities. No a priori assumption is made concerning the form of the arms. The base function used in the analysis is a logarithmic spiral. The main result obtained with this method is that the dominant component (or mode) usually changes at corotation. In some cases, this change to a different mode persists only for a short range about corotation, but in other cases the change is permanent. The agreement between pitch angles found with this method and by fitting logarithmic spirals to mean arm positions (del Río & Cepa 1998b, hereafter \\cite[Paper III]{p3}) is good, except for those cases where bars are strong and dominant. Finally, a comparison is made with the ``symmetrization'' method introduced by Elmegreen, Elmegreen & Montenegro (1992, hereafter EEM), which also shows the different symmetric components.

The Roles of Tidal Evolution and Evaporative Mass Loss in the Origin of CoRoT-7 b

NASA Technical Reports Server (NTRS)

Jackson, Brian; Miller, Neil; Barnes, Rory; Raymond, Sean N.; Fortney, Jonathan J.; Greenberg, Richard

2010-01-01

CoRoT-7 b is the first confirmed rocky exoplanet, but, with an orbital semimajor axis of 0.0172 au, its origins may be unlike any rocky planet in our Solar System. In this study, we consider the roles of tidal evolution and evaporative mass loss in CoRoT-7 b's history, which together have modified the planet's mass and orbit. If CoRoT-7 b has always been a rocky body, evaporation may have driven off almost half its original mass, but the mass loss may depend sensitively on the extent of tidal decay of its orbit. As tides caused CoRoT-7 b's orbit to decay, they brought the planet closer to its host star, thereby enhancing the mass loss rate. Such a large mass loss also suggests the possibility that CoRoT-7 b began as a gas giant planet and had its original atmosphere completely evaporated. In this case, we find that CoRoT-7 b's original mass probably did not exceed 200 Earth masses (about two-third of a Jupiter mass). Tides raised on the host star by the planet may have significantly reduced the orbital semimajor axis, perhaps causing the planet to migrate through mean-motion resonances with the other planet in the system, CoRoT-7 c. The coupling between tidal evolution and mass loss may be important not only for CoRoT-7 b but also for other close-in exoplanets, and future studies of mass loss and orbital evolution may provide insight into the origin and fate of close-in planets, both rocky and gaseous.

Sub-corotating region of Saturn's magnetosphere: Cassini observations of the azimuthal field and implications for the ionospheric Pederesen Current (Invited)

NASA Astrophysics Data System (ADS)

Smith, E. J.; Dougherty, M. K.; Zhou, X.

2010-12-01

A consensus model of Saturn’s magnetosphere that has broad acceptance consists of four regions in which the plasma and field are corotating, sub-corotating or undergoing Vasyliunas or Dungey convection. In this model, the sub-corotating magnetosphere contains a large scale circuital current system comprised of radial, field-aligned and ionospheric currents. A quantitative rendering of this system developed by S. Cowley and E. Bunch relates the azimuthal field component, B phi, that causes the field to spiral to the ionospheric Pedersen current , Ip. Cassini measurements of B phi over the four year interval between 2005 and 2008 that are widely distributed in radial distance, latitude and local time have been used to compute Ip from a Bunce-Cowley formula. A striking north-south asymmetry of the global magnetosphere has been found. In the southern hemisphere, the magnitude and variation of Ip with invariant colatitude, θ, agree qualitatively with the model but Ip (θ) is shifted poleward by about 10°. In the northern hemisphere, however, the data fail to reproduce the profile of Ip (θ) predicted by the model but are dominated by two high latitude currents having the wrong polarities. Possible causes of this asymmetry are seasonal variations (summer in the southern hemisphere) and/or asymmetric plasma outflow from the inner magnetosphere such as the plumes extending southward from Enceladus. Another finding is a significant local time dependence of Ip(θ) rather than the axisymmetry assumed in the model. There is a close correspondence with the model in the noon sector. The currents in the midnight and dawn sectors are significantly larger than in the noon sector and the current in the dusk sector is dramatically weaker.

Corotating Magnetic Reconnection Site in Saturn’s Magnetosphere

NASA Astrophysics Data System (ADS)

Yao, Z. H.; Coates, A. J.; Ray, L. C.; Rae, I. J.; Grodent, D.; Jones, G. H.; Dougherty, M. K.; Owen, C. J.; Guo, R. L.; Dunn, W. R.; Radioti, A.; Pu, Z. Y.; Lewis, G. R.; Waite, J. H.; Gérard, J.-C.

2017-09-01

Using measurements from the Cassini spacecraft in Saturn’s magnetosphere, we propose a 3D physical picture of a corotating reconnection site, which can only be driven by an internally generated source. Our results demonstrate that the corotating magnetic reconnection can drive an expansion of the current sheet in Saturn’s magnetosphere and, consequently, can produce Fermi acceleration of electrons. This reconnection site lasted for longer than one of Saturn’s rotation period. The long-lasting and corotating natures of the magnetic reconnection site at Saturn suggest fundamentally different roles of magnetic reconnection in driving magnetospheric dynamics (e.g., the auroral precipitation) from the Earth. Our corotating reconnection picture could also potentially shed light on the fast rotating magnetized plasma environments in the solar system and beyond.

KIC 4150611: a rare multi-eclipsing quintuple with a hybrid pulsator

NASA Astrophysics Data System (ADS)

Hełminiak, K. G.; Ukita, N.; Kambe, E.; Kozłowski, S. K.; Pawłaszek, R.; Maehara, H.; Baranec, C.; Konacki, M.

2017-06-01

Aims: We aim to analyse KIC 4150611 (HD 181469) - an interesting, bright quintuple system that includes a hybrid δ Sct/γ Dor pulsator. Four periods of eclipses - 94.2, 8.65, 1.52 and 1.43 d - have been observed by the Kepler satellite, and three point sources (A, B, and C) are seen in high angular resolution images. Methods: From spectroscopic observations made with the HIDES spectrograph attached to the 1.88-m telescope of the Okayama Astrophysical Observatory (OAO), we have calculated for the first time radial velocities (RVs) of the component B - a pair of G-type stars - and combined them with Kepler photometry in order to obtain absolute physical parameters of this pair. We also managed to directly measure RVs of the pulsator, for the first time. Additionally, we modelled the light curves of the 1.52 and 1.43-day pairs, and measured their eclipse timing variations (ETVs). We also performed relative astrometry and photometry of three sources seen on the images taken with the NIRC2 camera of the Keck II telescope. Finally, we compared our results with theoretical isochrones. Results: The brightest component Aa is the hybrid pulsator, transited every 94.2 days by a pair of K/M-type stars (Ab1+Ab2), which themselves form a 1.52-day eclipsing binary. The components Ba and Bb are late G-type stars, forming another eclipsing pair with a 8.65 day period. Their masses and radii are MBa = 0.894 ± 0.010 M⊙, RBa = 0.802 ± 0.044 R⊙ for the primary, and MBb = 0.888 ± 0.010 M⊙, RBb = 0.856 ± 0.038 R⊙ for the secondary. The remaining period of 1.43 days is possibly related to a faint third star C, which itself is most likely a background object. The system's properties are well-represented by a 35 Myr isochrone, basing on which the masses of the pulsator and the 1.52-day pair are MAa = 1.64(6) M⊙, and MAb,tot = 0.90(13) M⊙, respectively. There are also suggestions of additional bodies in the system.

Departure from corotation of the Io plasma torus - Local plasma production

NASA Technical Reports Server (NTRS)

Pontius, D. H., Jr.; Hill, T. W.

1982-01-01

The departure of the Jovian magnetosphere from rigid corotation is adequately explained by outward plasma transport at distances where L is greater than approximately 10. The departure of 5% observed in the Io plasma torus, however, is too large to be accounted for simply by plasma transport. Local plasma production is proposed as the main factor determining the corotation lag in the torus. The outward pick-up current provided by ionization of neutral atoms is calculated and related to the current produced in the ionosphere by the corotation lag. This leads to an expression giving the corotation lag of the torus as a function of radial distance. Charge transfer is found to be an important process, allowing the majority of the torus mass to be ejected from the magnetosphere in a neutral state. Thus, the mass loading rate is found to be several times that inferred from examination of the corotation lag associated with outward plasma transport.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pablo, Herbert; Kawaler, Steven D.; Green, Elizabeth M.

We report on Kepler photometry of the hot subdwarf B (sdB) star B4 in the open cluster NGC 6791. We confirm that B4 is a reflection effect binary with an sdB component and a low-mass main-sequence companion with a circular 0.3985 day orbit. The sdB star is a g-mode pulsator (a V1093 Her star) with periods ranging from 2384 s to 7643 s. Several of the pulsation modes show symmetric splitting by 0.62 {mu}Hz. Attributing this to rotational splitting, we conclude that the sdB component has a rotation period of approximately 9.63 days, indicating that tidal synchronization has not beenmore » achieved in this system. Comparison with theoretical synchronization time provides a discriminant between various theoretical models.« less

The Baade-Wesselink projection factor of the δ-Scuti stars AI Vel and β Cas

NASA Astrophysics Data System (ADS)

Guiglion, G.; Nardetto, N.; Domiciano de Souza, A.; Mathias, P.; Mourard, D.; Poretti, E.

2012-12-01

The Baade-Wesselink method of distance determination is based on the oscillations of pulsating stars. After determining the angular diameter and the linear radius variations, the distance is derived by a simple ratio. The linear radius variation is measured by integrating the pulsation velocity (hereafter V_{puls}) over one pulsating cycle. However, from observations we have only access to the radial velocity (V_{rad}) because of the projection along the line-of-sight. The projection factor, used to convert the radial velocity into the pulsation velocity, is defined by: p = V_{puls} / V_{rad}. We aim to derive the projection factor for two δ-Scuti stars, the high amplitude pulsator AI Vel and the fast rotator β Cas. The geometric component of the projection factor is derived using a limb-darkening model of the intensity distribution of AI Vel, and a fast rotator model for β Cas. Then, by comparing the radial velocity curves of several spectral lines forming at different levels in the atmosphere, we derive directly the velocity gradient (in a part of the atmosphere of the star) using SOPHIE/OHP data for β Cas and HARPS/ESO data for AI Vel, which is used to derive a dynamical projection factor for both stars. We find p = 1.44 ± 0.05 for AI Vel and p = 1.41 ± 0.25 for β Cas. By comparing Cepheids and δ-Scuti stars, these results bring valuable insights into the dynamical structure of pulsating star atmospheres.

Pi2 Pulsations During Extremely Quiet Geomagnetic Condition: Van Allen Probe Observations

NASA Astrophysics Data System (ADS)

Ghamry, Essam

2017-06-01

A ultra low frequency (ULF) wave, Pi2, has been reported to occur during periods of extremely quiet magnetospheric and solar wind conditions. And no statistical study on the Pi2 has been performed during extremely quiet conditions, using satellite observations to the author’s knowledge. Also Pi2 pulsations in the space fluxgate magnetometers near perigee failed to attract scientist’s attention previously. In this paper, Pi2 pulsations detected by the Van Allen probe satellites (VAP-A & VAP-B) were investigated statistically. During the period from October 2012 to December 2014, ninety six Pi2 events were identified using VAP when Kp = 0 while using Kakioka (KAK, L = 1.23) as a reference ground station. Seventy five events had high coherence between VAP-Bz and H components at KAK station. As a result, it was found that 77 % of the events had power spectra between 5 and 12 mHz, which differs from the regular Pi2 band range of from 6.7 to 25 mHz. In addition, it was shown that it is possible to observe Pi2 pulsations from space fluxgate magnetometers near perigee. Twenty two clean Pi2 pulsations were found where L < 4 and four examples of Pi2 oscillations at different L shells are presented in this paper.

A Model of the Pulsating Extremely Low-mass White Dwarf Precursor WASP 0247-25B

NASA Astrophysics Data System (ADS)

Istrate, A. G.; Fontaine, G.; Heuser, C.

2017-10-01

We present an analysis of the evolutionary and pulsation properties of the extremely low-mass white dwarf precursor (B) component of the double-lined eclipsing system WASP 0247-25. Given that the fundamental parameters of that star have been obtained previously at a unique level of precision, WASP 0247-25B represents the ideal case for testing evolutionary models of this newly found category of pulsators. Taking into account the known constraints on the mass, orbital period, effective temperature, surface gravity, and atmospheric composition, we present a model that is compatible with these constraints and show pulsation modes that have periods very close to the observed values. Importantly, these modes are predicted to be excited. Although the overall consistency remains perfectible, the observable properties of WASP 0247-25B are closely reproduced. A key ingredient of our binary evolutionary models is represented by rotational mixing as the main competitor against gravitational settling. Depending on assumptions made about the values of the degree index ℓ for the observed pulsation modes, we found three possible seismic solutions. We discuss two tests, rotational splitting and multicolor photometry, that should readily identify the modes and discriminate between these solutions. However, this will require improved temporal resolution and higher S/N observations, which are currently unavailable.

Oscillation Mode Variability in Evolved Compact Pulsators from Kepler Photometry. I. The Hot B Subdwarf Star KIC 3527751

NASA Astrophysics Data System (ADS)

Zong, Weikai; Charpinet, Stéphane; Fu, Jian-Ning; Vauclair, Gérard; Niu, Jia-Shu; Su, Jie

2018-02-01

We present the first results of an ensemble and systematic survey of oscillation mode variability in pulsating hot B subdwarf (sdB) and white dwarf stars observed with the original Kepler mission. The satellite provides uninterrupted high-quality photometric data with a time baseline that can reach up to 4 yr collected on pulsating stars. This is a unique opportunity to characterize long-term behaviors of oscillation modes. A mode modulation in amplitude and frequency can be independently inferred by its fine structure in the Fourier spectrum, from the sLSP, or with prewhitening methods applied to various parts of the light curve. We apply all these techniques to the sdB star KIC 3527751, a long-period-dominated hybrid pulsator. We find that all the detected modes with sufficiently large amplitudes to be thoroughly studied show amplitude and/or frequency variations. Components of three identified quintuplets around 92, 114, and 253 μHz show signatures that can be linked to nonlinear interactions according to the resonant mode coupling theory. This interpretation is further supported by the fact that many oscillation modes are found to have amplitudes and frequencies showing correlated or anticorrelated variations, a behavior that can be linked to the amplitude equation formalism, where nonlinear frequency corrections are determined by their amplitude variations. Our results suggest that oscillation modes varying with diverse patterns are a very common phenomenon in pulsating sdB stars. Close structures around main frequencies therefore need to be carefully interpreted in light of this finding to secure a robust identification of real eigenfrequencies, which is crucial for seismic modeling. The various modulation patterns uncovered should encourage further developments in the field of nonlinear stellar oscillation theory. It also raises a warning to any long-term project aiming at measuring the rate of period change of pulsations caused by stellar evolution, or at discovering stellar (planetary) companions around pulsating stars using timing methods, as both require very stable pulsation modes.

Ground-based Observations of Large Solar Flares Precursors

NASA Astrophysics Data System (ADS)

Sheyner, Olga; Smirnova, Anna; Snegirev, Sergey

2010-05-01

The importance problem of Solar-terrestrial physics is regular forecasting of solar activity phenomena, which negatively influence the human's health, operating safety, communication, radar sets and others. The opportunity of development of short-term forecasting technique of geoeffective solar flares is presented in this study. This technique is based on the effect of growth of pulsations of horizontal component of geomagnetic field before the solar proton flares. The long-period (30-60 minutes) pulsations of H-component of geomagnetic field are detected for the events of different intensity on March 22, 1991, November 4, 2001, and November 17, 2001 using the method of wavelet-analysis. Amplitudes of fluctuations of horizontal component of geomagnetic field with the 30-60 minute's periods grow at the most of tested stations during 0.5-3.5 days before the solar flares. The particularities of spectral component are studied for the stations situated on different latitudes. The assumptions about the reason of such precursors-fluctuations appearance are made.

Preface

NASA Astrophysics Data System (ADS)

Schuh, S.; Handler, G.

2009-03-01

The Joint European and National Astronomy Meeting 2008 (JENAM 2008) was held from September 8-12, 2008 in Vienna, Austria, as the joint meeting of the Austrian Society of Astronomy and Astrophysics (ÖGAA), the Astronomische Gesellschaft (AG), and the European Astronomical Society (EAS). It hosted nine symposia under the overall topic ''New Challenges To European Astronomy''. This special volume of Communications in Asteroseismology holds the proceedings of the JENAM 2008 Symposium No 4: ''Asteroseismology and Stellar Evolution''. The Asteroseismology and Stellar Evolution Symposium has been generously sponsored by the ÖGAA, by the HELAS Forum (an activity of the European Helio- and Asteroseismology Network, initiative funded by the European Commission since April 1st, 2006, as a Co-ordination Action under its Sixth Framework Programme, FP6), and by the Kulturabteilung der Stadt Wien (Magistratsabteilung 7). The Symposium program was put together by the Scientific Organizing Committee consisting of Conny Aerts (University of Leuven, Belgium), Annie Baglin (Observatoire de Paris, France), Wolfgang Glatzel (University of Göttingen, Germany), Gerald Handler (University of Vienna, Austria, Co-convener), Uli Heber (University of Erlangen-Nürnberg, Germany), Katrien Kolenberg (University of Vienna, Austria), Suzanna Randall (European Southern Observatory) and Sonja Schuh (University of Göttingen, Germany, Convener). Out of a total of 60 oral and poster contributions, 15 contributed talks were selected for presentation during the three half-day session program, with ample time for questions and discussion. There also was an opportunity to introduce the poster contributions during 2-min oral presentations. The scientific topics covered diverse object classes divided into Stochastically excited pulsators (main sequence, red giants, AGB supergiants), Heat-driven pulsators along the main sequence, and Compact pulsators, as well as additional topics that we have summarized as contributions on Eruptive variable and binary stars, and contributions presenting Methods and tools. The three session topics were introduced by two invited review speakers per field. In the first session, Jadwiga Daszynska-Daszkiewicz summarized current ''Challenges for stellar pulsation and evolution theory'', and Konstanze Zwintz reported ''A preliminary glimpse on CoRoT results and expectations'' (for Eric Michel), together giving an overview of the observational and theoretical status of the field. Anne Thoul and Oleg Kochukhov presented the state of the art in ''Asteroseismology of B stars'' and ''Asteroseismology of chemically peculiar stars'', respectively, in the second session, highlighting the hot issues in understanding and interpreting the pulsational behaviour of these groups. The stellar evolution aspect was given special consideration in ''Asteroseismology and Evolution of EHB stars'' by Roy Østensen and ''Asteroseismology and evolution of GW Vir stars'' by Pierre-Oliver Quirion in the concluding third session. A dedicated audience (on average 45 participants in each session), the excellent speakers, and our colleague Patrick Lenz who acted as the friendly and competent technician made this Symposium a highly interesting, enjoyable and successful event. We would like to thank all speakers, poster authors, and participants for coming to Vienna, the SOC and the referees for their work, the local organizers at Vienna for providing all the necessary infrastructure, and all sponsors for having made possible this event and the proceedings at hand.

Stellar Rotation: New Insight from CoRoT

NASA Astrophysics Data System (ADS)

Catala, C.; Goupil, M. J.; Michel, E.; Baglin, A.; de Medeiros, J. Renan; Gondoin, Ph.

2009-02-01

We present an overview of the new insight provided by the CoRoT satellite on stellar rotation. Thanks to its ultra-high precision, high duty cycle, long photometric monitoring of thousands of stars, CoRoT gives us a powerful tool to study stellar rotational modulation, and therefore to measure stellar rotational periods and to study active structures at the surface of stars. This paper presents preliminary results concerning this type of study. CoRoT will also provide us with an insight of internal stellar rotation via the measurement and exploitation of rotational splittings of oscillation modes. This approach to stellar rotation with CoRoT will require a careful analysis of the oscillation power spectra, which is in progress, but prospects for such measurements are presented.

TIME-DEPENDENT COROTATION RESONANCE IN BARRED GALAXIES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Yu-Ting; Taam, Ronald E.; Pfenniger, Daniel, E-mail: ytwu@asiaa.sinica.edu.tw, E-mail: daniel.pfenniger@unige.ch, E-mail: taam@asiaa.sinica.edu.tw

2016-10-20

The effective potential neighboring the corotation resonance region in barred galaxies is shown to be strongly time-dependent in any rotating frame, due to the competition of nearby perturbations of similar strengths with differing rotation speeds. Contrary to the generally adopted assumption that in the bar rotating frame the corotation region should possess four stationary equilibrium points (Lagrange points), with high quality N -body simulations, we localize the instantaneous equilibrium points (EPs) and find that they circulate or oscillate broadly in azimuth with respect to the pattern speeds of the inner or outer perturbations. This implies that at the particle levelmore » the Jacobi integral is not well conserved around the corotation radius. That is, angular momentum exchanges decouple from energy exchanges, enhancing the chaotic diffusion of stars through the corotation region.« less

Discovery of 105 Hz coherent pulsations in the ultracompact binary IGR J16597-3704

NASA Astrophysics Data System (ADS)

Sanna, A.; Bahramian, A.; Bozzo, E.; Heinke, C.; Altamirano, D.; Wijnands, R.; Degenaar, N.; Maccarone, T.; Riggio, A.; Di Salvo, T.; Iaria, R.; Burgay, M.; Possenti, A.; Ferrigno, C.; Papitto, A.; Sivakoff, G. R.; D'Amico, N.; Burderi, L.

2018-02-01

We report the discovery of X-ray pulsations at 105.2 Hz (9.5 ms) from the transient X-ray binary IGR J16597-3704 using NuSTAR and Swift. The source was discovered by INTEGRAL in the globular cluster NGC 6256 at a distance of 9.1 kpc. The X-ray pulsations show a clear Doppler modulation that implies an orbital period of 46 min and a projected semi-major axis of 5 lt-ms, which makes IGR J16597-3704 an ultracompact X-ray binary system. We estimated a minimum companion mass of 6.5 × 10-10 M⊙, assuming a neutron star mass of 1.4 M⊙, and an inclination angle of <75° (suggested by the absence of eclipses or dips in its light curve). The broad-band energy spectrum of the source is well described by a disk blackbody component (kT 1.4 keV) plus a comptonised power-law with photon index 2.3 and an electron temperature of 30 keV. Radio pulsations from the source were unsuccessfully searched for with the Parkes Observatory.

Geomagnetic Pulsations as Observed from Ground-Based Searchcoil Magnetometers (P52)

NASA Astrophysics Data System (ADS)

Sinha, A. K.; Pathan, B. M.; Vohat, P.

2006-11-01

ak50266@yahoo.com Magnetometer data from Searchcoil magnetometers in the Indian sectors have been analyzed to study geomagnetic pulsations in the low latitude region. On April 01 2005, we observe Pc 4 events at ~ 19 UT in the frequency range 10-15 mHz. The oscillations are seen in all the components (H, D, Z) indicating thereby that oscillations are compressional in nature. These pulsations are very much on the line of expectations at these latitudes. Apart from these normal pulsations, we observe the presence of pearl-type oscillations (~ 4 Hz) which is very unlikely at these latitude. These waves are common features of high latitude regions. The interesting aspect of these observed pearl-type features is that they follow a spike of broad-band source as revealed by the dynamic spectra. We are examining the role of thunderstorm lightening in generating these pearl-type pulses. Schumann resonances serve as indicators of lightning phenomena and we use their occurrences as parameter for lightening for correlating observed pulses to spiky broadband features preceding these pulses.

Fluctuating pressures in pump diffuser and collector scrolls, part 1

NASA Technical Reports Server (NTRS)

Sloteman, Donald P.

1989-01-01

The cracking of scroll liners on the SSME High Pressure Fuel Turbo Pump (HPFTP) on hot gas engine test firings has prompted a study into the nature of pressure fluctuations in centrifugal pump states. The amplitudes of these fluctuations and where they originate in the pump stage are quantified. To accomplish this, a test program was conducted to map the pressure pulsation activity in a centrifugal pump stage. This stage is based on typical commercial (or generic) pump design practice and not the specialized design of the HPFTP. Measurements made in the various elements comprising the stage indicate that pulsation activity is dominated by synchronous related phenomena. Pulsation amplitudes measured in the scroll are low, on the order of 2 to 7 percent of the impeller exit tip speed velocity head. Significant non-sychronous pressure fluctuations occur at low flow, and while of interest to commercial pump designers, have little meaning to the HPFTP experience. Results obtained with the generic components do provide insights into possible pulsation related scroll failures on the HPFTP, and provide a basis for further study.

Transiting exoplanets from the CoRoT space mission. XI. CoRoT-8b: a hot and dense sub-Saturn around a K1 dwarf

NASA Astrophysics Data System (ADS)

Bordé, P.; Bouchy, F.; Deleuil, M.; Cabrera, J.; Jorda, L.; Lovis, C.; Csizmadia, S.; Aigrain, S.; Almenara, J. M.; Alonso, R.; Auvergne, M.; Baglin, A.; Barge, P.; Benz, W.; Bonomo, A. S.; Bruntt, H.; Carone, L.; Carpano, S.; Deeg, H.; Dvorak, R.; Erikson, A.; Ferraz-Mello, S.; Fridlund, M.; Gandolfi, D.; Gazzano, J.-C.; Gillon, M.; Guenther, E.; Guillot, T.; Guterman, P.; Hatzes, A.; Havel, M.; Hébrard, G.; Lammer, H.; Léger, A.; Mayor, M.; Mazeh, T.; Moutou, C.; Pätzold, M.; Pepe, F.; Ollivier, M.; Queloz, D.; Rauer, H.; Rouan, D.; Samuel, B.; Santerne, A.; Schneider, J.; Tingley, B.; Udry, S.; Weingrill, J.; Wuchterl, G.

2010-09-01

Aims: We report the discovery of CoRoT-8b, a dense small Saturn-class exoplanet that orbits a K1 dwarf in 6.2 days, and we derive its orbital parameters, mass, and radius. Methods: We analyzed two complementary data sets: the photometric transit curve of CoRoT-8b as measured by CoRoT and the radial velocity curve of CoRoT-8 as measured by the HARPS spectrometer. Results: We find that CoRoT-8b is on a circular orbit with a semi-major axis of 0.063 ± 0.001 AU. It has a radius of 0.57 ± 0.02 RJ, a mass of 0.22 ± 0.03 MJ, and therefore a mean density of 1.6 ± 0.1 g cm-3. Conclusions: With 67% of the size of Saturn and 72% of its mass, CoRoT-8b has a density comparable to that of Neptune (1.76 g cm-3). We estimate its content in heavy elements to be 47-63 {M}_⊕, and the mass of its hydrogen-helium envelope to be 7-23 {M}_⊕. At 0.063 AU, the thermal loss of hydrogen of CoRoT-8b should be no more than 0.1% over an assumed integrated lifetime of 3 Ga. Observations made with SOPHIE spectrograph at Observatoire de Haute Provence, France (PNP.07B.MOUT), and the HARPS spectrograph at ESO La Silla Observatory (081.C-0388 and 083.C-0186). The CoRoT space mission, launched on December 27, 2006, has been developed and is operated by the CNES with the contribution of Austria, Belgium, Brasil, ESA, Germany, and Spain.Both data sets are available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/520/A66

Observational Δν-ρ¯ Relation for δ Sct Stars using Eclipsing Binaries and Space Photometry

NASA Astrophysics Data System (ADS)

García Hernández, A.; Martín-Ruiz, S.; Monteiro, Mário J. P. F. G.; Suárez, J. C.; Reese, D. R.; Pascual-Granado, J.; Garrido, R.

2015-10-01

Delta Scuti (δ Sct) stars are intermediate-mass pulsators, whose intrinsic oscillations have been studied for decades. However, modeling their pulsations remains a real theoretical challenge, thereby even hampering the precise determination of global stellar parameters. In this work, we used space photometry observations of eclipsing binaries with a δ Sct component to obtain reliable physical parameters and oscillation frequencies. Using that information, we derived an observational scaling relation between the stellar mean density and a frequency pattern in the oscillation spectrum. This pattern is analogous to the solar-like large separation but in the low order regime. We also show that this relation is independent of the rotation rate. These findings open the possibility of accurately characterizing this type of pulsator and validate the frequency pattern as a new observable for δ Sct stars.

Mathematical Modelling of the Infusion Test

NASA Astrophysics Data System (ADS)

Cieslicki, Krzysztof

2007-01-01

The objective of this paper was to improve the well established in clinical practice Marmarou model for intracranial volume-pressure compensation by adding the pulsatile components. It was demonstrated that complicated pulsation and growth in intracranial pressure during infusion test could be successfully modeled by the relatively simple analytical expression derived in this paper. The CSF dynamics were tested in 25 patients with clinical symptoms of hydrocephalus. Basing on the frequency spectrum of the patient's baseline pressure and identified parameters of CSF dynamic, for each patient an "ideal" infusion test curve free from artefacts and slow waves was simulated. The degree of correlation between simulated and real curves obtained from clinical observations gave insight into the adequacy of assumptions of Marmarou model. The proposed method of infusion tests analysis designates more exactly the value of the reference pressure, which is usually treated as a secondary and of uncertain significance. The properly identified value of the reference pressure decides on the degree of pulsation amplitude growth during IT, as well as on the value of elastance coefficient. The artificially generated tests with various pulsation components were also applied to examine the correctness of the used algorithm of identification of the original Marmarou model parameters.

CoRoT-7b: SUPER-EARTH OR SUPER-Io?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Barnes, Rory; Kaib, Nathan A.; Raymond, Sean N.

2010-02-01

CoRoT-7b, a planet about 70% larger than the Earth orbiting a Sun-like star, is the first-discovered rocky exoplanet, and hence has been dubbed a 'super-Earth'. Some initial studies suggested that since the planet is so close to its host star, it receives enough insolation to partially melt its surface. However, these past studies failed to take into consideration the role that tides may play in this system. Even if the planet's eccentricity has always been zero, we show that tidal decay of the semimajor axis could have been large enough that the planet formed on a wider orbit which receivedmore » less insolation. Moreover, CoRoT-7b could be tidally heated at a rate that dominates its geophysics and drives extreme volcanism. In this case, CoRoT-7b is a 'super-Io' that, like Jupiter's volcanic moon, is dominated by volcanism and rapid resurfacing. Such heating could occur with an eccentricity of just 10{sup -5}. This small value could be driven by CoRoT-7c if its own eccentricity is larger than {approx}10{sup -4}. CoRoT-7b may be the first of a class of planetary super-Ios likely to be revealed by the CoRoT and Kepler spacecraft.« less

Excitation of Non-Axisymmetric g-MOde Oscillations by Corotation Resonance in Thin Relativistic Disks

NASA Astrophysics Data System (ADS)

Kato, Shoji

2002-02-01

Various modes of oscillations are trapped in the inner region of geometrically thin relativistic disks. Among these oscillations, non-axisymmetric g-mode oscillations have been less studied compared with other modes of oscillations. The modes are, however, interesting since a corotation resonance appears in the trapped region. We mathematically examine whether the modes can be excited by the effects of the corotation resonance. This examination is made under an assumption that the inner and outer Lindblad radii are sufficiently separated in the opposite directions from the corotation radius. The results of analyses suggest that the waves are excited by the corotation resonance. The presence of the excitation suggests that the non-axisymmetric trapped g-mode oscillations are one of possible candidates for the quasi-periodic oscillations of a few hundred to kHz observed in some X-ray sources.

A Model of the Pulsating Extremely Low-mass White Dwarf Precursor WASP 0247–25B

DOE Office of Scientific and Technical Information (OSTI.GOV)

Istrate, A. G.; Fontaine, G.; Heuser, C., E-mail: istrate@uwm.edu

We present an analysis of the evolutionary and pulsation properties of the extremely low-mass white dwarf precursor (B) component of the double-lined eclipsing system WASP 0247−25. Given that the fundamental parameters of that star have been obtained previously at a unique level of precision, WASP 0247−25B represents the ideal case for testing evolutionary models of this newly found category of pulsators. Taking into account the known constraints on the mass, orbital period, effective temperature, surface gravity, and atmospheric composition, we present a model that is compatible with these constraints and show pulsation modes that have periods very close to themore » observed values. Importantly, these modes are predicted to be excited. Although the overall consistency remains perfectible, the observable properties of WASP 0247−25B are closely reproduced. A key ingredient of our binary evolutionary models is represented by rotational mixing as the main competitor against gravitational settling. Depending on assumptions made about the values of the degree index ℓ for the observed pulsation modes, we found three possible seismic solutions. We discuss two tests, rotational splitting and multicolor photometry, that should readily identify the modes and discriminate between these solutions. However, this will require improved temporal resolution and higher S/N observations, which are currently unavailable.« less

The COROT Archive at LAEFF

NASA Astrophysics Data System (ADS)

Velasco, Almudena; Gutiérrez, Raúl; Solano, Enrique; García-Torres, Miguel; López, Mauro; Sarro, Luis Manuel

We describe here the main capabilities of the COROT archive. The archive (http://sdc.laeff.inta.es/corotfa/jsp/searchform.jsp), managed at LAEFF in the framework of the Spanish Virtual Observatory (http://svo.laeff.inta.es), has been developed following the standards and requirements defined by IVOA (http://www.ivoa.net). The COROT archive at LAEFF will be publicly available by the end of 2008.

Flow visualization in radial flow through stationary and corotating parallel disks

NASA Astrophysics Data System (ADS)

Mochizuki, S.; Tanaka, M.; Yang, Wen-Jei

Paraffin mist is used here as a tracer to observe the patterns in the radial flow through both stationary and corotating parallel disks. The periodic and alternative generation of separation bubbles on both disks and the resulting flow fluctuation and turbulent flow in the radial channel are studied. Stall cells are visualized around the outer rim of the corotating disks.

Waste heat recovery on multiple low-speed reciprocating engines

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mayhew, R.E.

1982-09-01

With rising fuel costs, energy conservation has taken on added significance. Installation of Waste Heat Recovery Units (WHRU) on gas turbines is one method used in the past to reduce gas plant fuel consumption. More recently, waste heat recovery on multiple reciprocating compressor engines has also been identified as having energy conservation potential. This paper reviews the development and implementation of a Waste Heat Recovery Unit (WHRU) for multiple low speed engines at the Katy Gas Plant. WHRU's for these engines should be differentiated from high speed engines and gas turbines in that low speed engines produce low frequency, highmore » amplitude pulsating exhaust. The design of a waste heat system must take this potentially destructive pulsation into account. At Katy, the pulsation forces were measured at high amplitude frequencies and then used to design structural stiffness into the various components of the WHRU to minimize vibration and improve system reliability.« less

Low mass planet migration in magnetically torqued dead zones - I. Static migration torque

NASA Astrophysics Data System (ADS)

McNally, Colin P.; Nelson, Richard P.; Paardekooper, Sijme-Jan; Gressel, Oliver; Lyra, Wladimir

2017-12-01

Motivated by models suggesting that the inner planet forming regions of protoplanetary discs are predominantly lacking in viscosity-inducing turbulence, and are possibly threaded by Hall-effect generated large-scale horizontal magnetic fields, we examine the dynamics of the corotation region of a low-mass planet in such an environment. The corotation torque in an inviscid, isothermal, dead zone ought to saturate, with the libration region becoming both symmetrical and of a uniform vortensity, leading to fast inward migration driven by the Lindblad torques alone. However, in such a low viscosity situation, the material on librating streamlines essentially preserves its vortensity. If there is relative radial motion between the disc gas and the planet, the librating streamlines will no longer be symmetrical. Hence, if the gas is torqued by a large-scale magnetic field so that it undergoes a net inflow or outflow past the planet, driving evolution of the vortensity and inducing asymmetry of the corotation region, the corotation torque can grow, leading to a positive torque. In this paper, we treat this effect by applying a symmetry argument to the previously studied case of a migrating planet in an inviscid disc. Our results show that the corotation torque due to a laminar Hall-induced magnetic field in a dead zone behaves quite differently from that studied previously for a viscous disc. Furthermore, the magnetic field induced corotation torque and the dynamical corotation torque in a low viscosity disc can be regarded as one unified effect.

Investigating light curve modulation via kernel smoothing. I. Application to 53 fundamental mode and first-overtone Cepheids in the LMC

NASA Astrophysics Data System (ADS)

Süveges, Maria; Anderson, Richard I.

2018-03-01

Context. Recent studies have revealed a hitherto unknown complexity of Cepheid pulsations by discovering irregular modulated variability using photometry, radial velocities, and interferometry. Aim. We aim to perform a statistically rigorous search and characterization of such phenomena in continuous time, applying it to 53 classical Cepheids from the OGLE-III catalog. Methods: We have used local kernel regression to search for both period and amplitude modulations simultaneously in continuous time and to investigate their detectability. We determined confidence intervals using parametric and non-parametric bootstrap sampling to estimate significance, and investigated multi-periodicity using a modified pre-whitening approach that relies on time-dependent light curve parameters. Results: We find a wide variety of period and amplitude modulations and confirm that first overtone pulsators are less stable than fundamental mode Cepheids. Significant temporal variations in period are more frequently detected than those in amplitude. We find a range of modulation intensities, suggesting that both amplitude and period modulations are ubiquitous among Cepheids. Over the 12-year baseline offered by OGLE-III, we find that period changes are often nonlinear, sometimes cyclic, suggesting physical origins beyond secular evolution. Our method detects modulations (period and amplitude) more efficiently than conventional methods that are reliant on certain features in the Fourier spectrum, and pre-whitens time series more accurately than using constant light curve parameters, removing spurious secondary peaks effectively. Conclusions: Period and amplitude modulations appear to be ubiquitous among Cepheids. Current detectability is limited by observational cadence and photometric precision: detection of amplitude modulation below 3 mmag requires space-based facilities. Recent and ongoing space missions (K2, BRITE, MOST, CoRoT) as well as upcoming ones (TESS, PLATO) will significantly improve detectability of fast modulations, such as cycle-to-cycle variations, by providing high-cadence high-precision photometry. High-quality long-term ground-based photometric time series will remain crucial to study longer-term modulations and to disentangle random fluctuations from secular evolution.

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.

Search for Pulsating Stars in the Open Cluster NGC 1502

NASA Astrophysics Data System (ADS)

Stęślicki, M.

2006-04-01

We present results of a variability search in the field of the young open cluster NGC 1502. We confirm that a beta Cephei suspect WEBDA 26 is indeed pulsating with a period of 0.09612 d and semi-amplitude of about 3 mmag in V. A new VI light curve of the bright eclipsing binary and cluster member SZ Cam was obtained. In addition, we found two new variable stars. One is an interesting eclipsing binary showing total eclipses, which can be used to derive the distance to the cluster once radial velocities of the components will be obtained.

Understanding the dynamical structure of pulsating stars: The Baade-Wesselink projection factor of the δ Scuti stars AI Velorum and β Cassiopeiae

NASA Astrophysics Data System (ADS)

Guiglion, G.; Nardetto, N.; Mathias, P.; Domiciano de Souza, A.; Poretti, E.; Rainer, M.; Fokin, A.; Mourard, D.; Gieren, W.

2013-02-01

Aims: The Baade-Wesselink method of distance determination is based on the oscillations of pulsating stars. The key parameter of this method is the projection factor used to convert the radial velocity into the pulsation velocity. Our analysis was aimed at deriving for the first time the projection factor of δ Scuti stars, using high-resolution spectra of the high-amplitude pulsator AI Vel and of the fast rotator β Cas. Methods: The geometric component of the projection factor (i.e. p0) was calculated using a limb-darkening model of the intensity distribution for AI Vel, and a fast-rotator model for β Cas. Then, using SOPHIE/OHP data for β Cas and HARPS/ESO data for AI Vel, we compared the radial velocity curves of several spectral lines forming at different levels in the atmosphere and derived the velocity gradient associated to the spectral-line-forming regions in the atmosphere of the star. This velocity gradient was used to derive a dynamical projection factor p. Results: We find a flat velocity gradient for both stars and finally p = p0 = 1.44 for AI Vel and p = p0 = 1.41 for β Cas. By comparing Cepheids and δ Scuti stars, these results bring valuable insights into the dynamical structure of pulsating star atmospheres. They suggest that the period-projection factor relation derived for Cepheids is also applicable to δ Scuti stars pulsating in a dominant radial mode. This work uses observations made with the HARPS instrument at the 3.6 m telescope (La Silla, Chile) in the framework of the LP185.D-0056 and with the SOPHIE instrument at OHP (France).

TIME-SERIES SPECTROSCOPY OF THE ECLIPSING BINARY Y CAM WITH A PULSATING COMPONENT

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hong, Kyeongsoo; Lee, Jae Woo; Kim, Seung-Lee

We present the physical properties of the semi-detached Algol-type eclipsing binary Y Cam based on high resolution spectra obtained using the Bohyunsan Optical Echelle Spectrograph. This is the first spectroscopic monitoring data obtained for this interesting binary system, which has a δ Sct-type pulsating component. We obtained a total of 59 spectra over 14 nights from 2009 December to 2011 March. Double-lined spectral features from the hot primary and cool secondary components were well identified. We determined the effective temperatures of the two stars to be T{sub eff,1} = 8000 ± 250 K and T{sub eff,2} = 4629 ± 150more » K. The projected rotational velocities are v{sub 1}sin i{sub 1} = 51 ± 4 km s{sup −1} and v{sub 2}sin i{sub 2} = 50 ± 10 km s{sup −1}, which are very similar to a synchronous rotation with the orbital motion. Physical parameters of each component were derived by analyzing our radial velocity data together with previous photometric light curves from the literature. The masses and radii are M{sub 1} = 2.08 ± 0.09 M{sub ⊙}, M{sub 2} = 0.48 ± 0.03 M{sub ⊙}, R{sub 1} = 3.14 ± 0.05 R{sub ⊙}, and R{sub 2} = 3.33 ± 0.05 R{sub ⊙}, respectively. A comparison of these parameters with the theoretical evolution tracks showed that the primary component is located between the zero-age main sequence and the terminal-age main sequence, while the low-mass secondary is noticeably evolved. This indicates that the two components have experienced mass exchange with each other and the primary has undergone an evolution process different from that of single δ Sct-type pulsators.« less

Absolute Properties of the Pulsating Post-mass Transfer Eclipsing Binary OO Draconis

NASA Astrophysics Data System (ADS)

Lee, Jae Woo; Hong, Kyeongsoo; Koo, Jae-Rim; Park, Jang-Ho

2018-01-01

OO Dra is a short-period Algol system with a δ Sct-like pulsator. We obtained time-series spectra between 2016 February and May to derive the fundamental parameters of the binary star and to study its evolutionary scenario. The radial velocity (RV) curves for both components were presented, and the effective temperature of the hotter and more massive primary was determined to be {T}{eff,1}=8260+/- 210 K by comparing the disentangling spectrum and the Kurucz models. Our RV measurements were solved with the BV light curves of Zhang et al. using the Wilson-Devinney binary code. The absolute dimensions of each component are determined as follows: M 1 = 2.03 ± 0.06 {M}⊙ , M 2 = 0.19 ± 0.01 {M}⊙ , R 1 = 2.08 ± 0.03 {R}⊙ , R 2 = 1.20 ± 0.02 {R}⊙ , L 1 = 18 ± 2 {L}⊙ , and L 2 = 2.0 ± 0.2 {L}⊙ . Comparison with stellar evolution models indicated that the primary star resides inside the δ Sct instability strip on the main sequence, while the cool secondary component is noticeably overluminous and oversized. We demonstrated that OO Dra is an oscillating post-mass transfer R CMa-type binary; the originally more massive star became the low-mass secondary component through mass loss caused by stellar wind and mass transfer, and the gainer became the pulsating primary as the result of mass accretion. The R CMa stars, such as OO Dra, are thought to have formed by non-conservative binary evolution and ultimately to evolve into EL CVn stars.

Follow-Up Observations of the Second and Third Known Pulsating Hot DQ White Dwarfs

NASA Astrophysics Data System (ADS)

Dufour, P.; Green, E. M.; Fontaine, G.; Brassard, P.; Francoeur, M.; Latour, M.

2009-09-01

We present follow-up time-series photometric observations that confirm and extend the results of the significant discovery made by Barlow et al. that the Hot DQ white dwarfs SDSS J220029.08 - 074121.5 and SDSS J234843.30 - 094245.3 are luminosity variable. These are the second and third known members of a new class of pulsating white dwarfs, after the prototype SDSS J142625.71+575218.3. We find that the light curve of SDSS J220029.08 - 074121.5 is dominated by an oscillation at 654.397 ± 0.056 s, and that the light pulse folded on that period is highly nonlinear due to the presence of the first and second harmonic of the main pulsation. We also present evidence for the possible detection of two additional pulsation modes with low amplitudes and periods of 577.576 ± 0.226 s and 254.732 ± 0.048 s in that star. Likewise, we find that the light curve of SDSS J234843.30 - 094245.3 is dominated by a pulsation with a period of 1044.168 ± 0.012 s, but with no sign of harmonic components. A new oscillation, with a low amplitude and a period of 416.919 ± 0.004 s, is also probably detected in that second star. We argue, on the basis of the very different folded pulse shapes, that SDSS J220029.08 - 074121.5 is likely magnetic, while SDSS J234843.30 - 094245.3 is probably not.

Long periods (1 -10 mHz) geomagnetic pulsations variation with solar cycle in South Atlantic Magnetic Anomaly

NASA Astrophysics Data System (ADS)

Rigon Silva, Willian; Schuch, Nelson Jorge; Guimarães Dutra, Severino Luiz; Babulal Trivedi, Nalin; Claudir da Silva, Andirlei; Souza Savian, Fernando; Ronan Coelho Stekel, Tardelli; de Siqueira, Josemar; Espindola Antunes, Cassio

The occurrence and intensity of the geomagnetic pulsations Pc-5 (2-7 mHz) and its relationship with the solar cycle in the South Atlantic Magnetic Anomaly -SAMA is presented. The study of geomagnetic pulsations is important to help the understanding of the physical processes that occurs in the magnetosphere region and help to predict geomagnetic storms. The fluxgate mag-netometers H, D and Z, three axis geomagnetic field data from the Southern Space Observatory -SSO/CRS/INPE -MCT, São Martinho da Serra (29.42° S, 53.87° W, 480m a.s.l.), RS, Brasil, a were analyzed and correlated with the solar wind parameters (speed, density and temperature) from the ACE and SOHO satellites. A digital filtering to enhance the 2-7 mHz geomagnetic pulsations was used. Five quiet days and five perturbed days in the solar minimum and in the solar maximum were selected for this analysis. The days were chosen based on the IAGA definition and on the Bartels Musical Diagrams (Kp index) for 2001 (solar maximum) and 2008 (solar minimum). The biggest Pc-5 amplitude averages differences between the H-component is 78,35 nT for the perturbed days and 1,60nT for the quiet days during the solar maximum. For perturbed days the average amplitude during the solar minimum is 8,32 nT, confirming a direct solar cycle influence in the geomagnetic pulsations intensity for long periods.

KIC 11401845: An Eclipsing Binary with Multiperiodic Pulsations and Light-travel Time

NASA Astrophysics Data System (ADS)

Lee, Jae Woo; Hong, Kyeongsoo; Kim, Seung-Lee; Koo, Jae-Rim

2017-02-01

We report the {\\text{}}{Kepler} photometry of KIC 11401845 displaying multiperiodic pulsations, superimposed on binary effects. Light-curve synthesis shows that the binary star is a short-period detached system with a very low mass ratio of q = 0.070 and filling factors of F1 = 45% and F2 = 99%. Multiple-frequency analyses were applied to the light residuals after subtracting the synthetic eclipsing curve from the observed data. We detected 23 frequencies with signal-to-noise ratios larger than 4.0, of which the orbital harmonics (f4, f6, f9, f15) in the low-frequency domain may originate from tidally excited modes. For the high frequencies of 13.7-23.8 day-1, the period ratios and pulsation constants are in the ranges of {P}{pul}/{P}{orb}=0.020{--}0.034 and Q = 0.018-0.031 days, respectively. These values and the position on the Hertzsprung-Russell diagram demonstrate that the primary component is a δ Sct pulsating star. We examined the eclipse timing variation of KIC 11401845 from the pulsation-subtracted data and found a delay of 56 ± 17 s in the arrival times of the secondary eclipses relative to the primary eclipses. A possible explanation of the time shift may be some combination of a light-travel-time delay of about 34 s and a very small eccentricity of e\\cos ω < 0.0002. This result represents the first measurement of the Rømer delay in noncompact binaries.

Europe looks forward to COROT launch

NASA Astrophysics Data System (ADS)

2006-12-01

While CNES is completing preparations for the launch from Baikonur/Kazakhstan, ESA and a large number of European scientists involved in the mission are eagerly awaiting this event and the first scientific results to come through. What is COROT? COROT stands for ‘Convection Rotation and planetary Transits’. The name describes the mission’s scientific goals. ‘Convection and rotation’ refer to the satellite’s capability to probe stellar interiors, studying the acoustic waves that ripple across the surface of stars, a technique called asteroseismology. ‘Transit’ refers to the technique whereby the presence of a planet orbiting a star can be inferred from the dimming starlight caused when the planet passes in front of it. To achieve its twin scientific objectives, COROT will monitor some 120,000 stars with its 30-centimetre telescope. COROT will lead a bold new search for planets around other stars. In the decade since the first discovery in 1995 of an exoplanet (51 Pegasi b), more than 200 other such planets outside our solar system have been detected using ground-based observatories. The COROT space telescope promises to find many more during its two-and-a-half-year mission, expanding the frontiers of our knowledge towards ever-smaller planets. Many of the planets COROT will detect are expected to be 'hot Jupiters', gaseous worlds. An unknown percentage of those detected are expected to be rocky planets, maybe just a few times larger than the Earth (or smaller, even). If COROT finds such planets, they will constitute a new class of planet altogether. While it is looking at a star, COROT will also be able to detect 'starquakes', acoustic waves generated deep inside a star that send ripples across its surface, altering its brightness. The exact nature of the ripples allows astronomers to calculate the star's precise mass, age and chemical composition. COROT’s European dimension The COROT mission was first proposed by CNES back in 1996. A call for potential European partners was issued in 1999. CNES gave the green light to build the spacecraft in 2000 and is now leading the mission. Its international partners are ESA, Austria, Belgium, Germany, Spain and Brazil. CNES is responsible for the overall system and for the launch contract with Franco-Russian company Starsem, which is providing the Soyuz launch service. The contributions of the other international partners range from the provision of hardware items to ground stations, complementary ground-based observation of targets to be studied by COROT and analysis of the scientific data to come. ESA is playing a crucial role in the mission. It has contributed the optics for the telescope positioned at the heart of the spacecraft and has carried out payload testing. The telescope’s baffle was developed by a team at ESA’s technical centre ESTEC. ESA has also provided the onboard data processing units. And under this truly collaborative effort, a number of scientists from various European countries - Denmark, Switzerland, the United Kingdom and Portugal - have been selected as Co-Investigators following open competition. As a result of ESA’s participation, scientists from its Member States will also be given access to COROT data.

Identification and classification of transient pulses observed in magnetometer array data by time-domain principal component analysis filtering

NASA Astrophysics Data System (ADS)

Kappler, Karl N.; Schneider, Daniel D.; MacLean, Laura S.; Bleier, Thomas E.

2017-08-01

A method for identification of pulsations in time series of magnetic field data which are simultaneously present in multiple channels of data at one or more sensor locations is described. Candidate pulsations of interest are first identified in geomagnetic time series by inspection. Time series of these "training events" are represented in matrix form and transpose-multiplied to generate time-domain covariance matrices. The ranked eigenvectors of this matrix are stored as a feature of the pulsation. In the second stage of the algorithm, a sliding window (approximately the width of the training event) is moved across the vector-valued time-series comprising the channels on which the training event was observed. At each window position, the data covariance matrix and associated eigenvectors are calculated. We compare the orientation of the dominant eigenvectors of the training data to those from the windowed data and flag windows where the dominant eigenvectors directions are similar. This was successful in automatically identifying pulses which share polarization and appear to be from the same source process. We apply the method to a case study of continuously sampled (50 Hz) data from six observatories, each equipped with three-component induction coil magnetometers. We examine a 90-day interval of data associated with a cluster of four observatories located within 50 km of Napa, California, together with two remote reference stations-one 100 km to the north of the cluster and the other 350 km south. When the training data contains signals present in the remote reference observatories, we are reliably able to identify and extract global geomagnetic signals such as solar-generated noise. When training data contains pulsations only observed in the cluster of local observatories, we identify several types of non-plane wave signals having similar polarization.

A Generalized Equatorial Model for the Accelerating Solar Wind

NASA Astrophysics Data System (ADS)

Tasnim, S.; Cairns, Iver H.; Wheatland, M. S.

2018-02-01

A new theoretical model for the solar wind is developed that includes the wind's acceleration, conservation of angular momentum, deviations from corotation, and nonradial velocity and magnetic field components from an inner boundary (corresponding to the onset of the solar wind) to beyond 1 AU. The model uses a solution of the time-steady isothermal equation of motion to describe the acceleration and analytically predicts the Alfvénic critical radius. We fit the model to near-Earth observations of the Wind spacecraft during the solar rotation period of 1-27 August 2010. The resulting data-driven model demonstrates the existence of noncorotating, nonradial flows and fields from the inner boundary (r = rs) outward and predicts the magnetic field B = (Br,Bϕ), velocity v = (vr,vϕ), and density n(r,ϕ,t), which vary with heliocentric distance r, heliolatitude ϕ, and time t in a Sun-centered standard inertial plane. The description applies formally only in the equatorial plane. In a frame corotating with the Sun, the transformed velocity v' and a field B' are not parallel, resulting in an electric field with a component Ez' along the z axis. The resulting E'×B'=E'×B drift lies in the equatorial plane, while the ∇B and curvature drifts are out of the plane. Together these may lead to enhanced scattering/heating of sufficiently energetic particles. The model predicts that deviations δvϕ from corotation at the inner boundary are common, with δvϕ(rs,ϕs,ts) comparable to the transverse velocities due to granulation and supergranulation motions. Abrupt changes in δvϕ(rs,ϕs,ts) are interpreted in terms of converging and diverging flows at the cell boundaries and centers, respectively. Large-scale variations in the predicted angular momentum demonstrate that the solar wind can drive vorticity and turbulence from near the Sun to 1 AU and beyond.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yao, Z. H.; Coates, A. J.; Ray, L. C.

Using measurements from the Cassini spacecraft in Saturn’s magnetosphere, we propose a 3D physical picture of a corotating reconnection site, which can only be driven by an internally generated source. Our results demonstrate that the corotating magnetic reconnection can drive an expansion of the current sheet in Saturn’s magnetosphere and, consequently, can produce Fermi acceleration of electrons. This reconnection site lasted for longer than one of Saturn’s rotation period. The long-lasting and corotating natures of the magnetic reconnection site at Saturn suggest fundamentally different roles of magnetic reconnection in driving magnetospheric dynamics (e.g., the auroral precipitation) from the Earth. Ourmore » corotating reconnection picture could also potentially shed light on the fast rotating magnetized plasma environments in the solar system and beyond.« less

A search for tight hierarchical triple systems amongst the eclipsing binaries in the CoRoT fields

NASA Astrophysics Data System (ADS)

Hajdu, T.; Borkovits, T.; Forgács-Dajka, E.; Sztakovics, J.; Marschalkó, G.; Benkő, J. M.; Klagyivik, P.; Sallai, M. J.

2017-10-01

We report a comprehensive search for hierarchical triple stellar system candidates amongst eclipsing binaries (EBs) observed by the CoRoT spacecraft. We calculate and check eclipse timing variation (ETV) diagrams for almost 1500 EBs in an automated manner. We identify five relatively short period Algol systems for which our combined light-curve and complex ETV analyses (including both the light-travel time effect and short-term dynamical third-body perturbations) resulted in consistent third-body solutions. The computed periods of the outer bodies are between 82 and 272 d (with an alternative solution of 831 d for one of the targets). We find that the inner and outer orbits are near coplanar in all but one case. The dynamical masses of the outer subsystems determined from the ETV analyses are consistent with both the results of our light-curve analyses and the spectroscopic information available in the literature. One of our candidate systems exhibits outer eclipsing events as well, the locations of which are in good agreement with the ETV solution. We also report another certain triply eclipsing triple system that, however, is lacking a reliable ETV solution due to the very short time range of the data, and four new blended systems (composite light curves of two EBs each), where we cannot decide whether the components are gravitationally bounded or not. Amongst these blended systems, we identify the longest period and highest eccentricity EB in the entire CoRoT sample.

Investigation of Co-rotation Lag in Saturn's Dayside Magnetosphere and Comparison with the Nightside

NASA Astrophysics Data System (ADS)

Smith, E. J.; Dougherty, M. K.

2016-12-01

Two previous studies of co-rotation lag concentrated on 13 identical high-inclination Cassini orbits. In the first, measurements of the magnetospheric field azimuthal component, Bϕ, were restricted to the southern hemisphere, near midnight, from the equator and perikron to maximum latitude 70°. Comparison with the prevailing model of the magnetosphere-ionosphere interaction yielded conclusions that the ionospheric conductivity, Σp, was independent of ionospheric co-latitude, θi, and the ratio of magnetospheric to planetary field angular velocities, ω/Ωs, equaled, 1- exp(-Bθi), an unexpected exponential dependence on a single parameter. Both model parameters exhibited significant temporal variations from orbit to orbit leading to variations in the ionospheric profiles of Pedersen current, Ip. The second 13 orbit study of Bϕ extended to the north hemisphere where lagging fields alternated with leading and co-rotating fields. It was concluded that the difference was actually a local- time dependence with lagging -fields- only occurring after midnight and the mixed rotations before midnight. Again, Σp was independent of θi and ω/Ωs = 1- exp(-Bθi). Both studies raised the questions: How general is the exponential dependence of 1-ω/Ωs? Is it restricted to midnight or hold as well in the dayside magnetosphere? What is the cause of this dependence that differs from the model? The analysis of Bϕ has been extended to four nearly-identical north-south orbits near noon. The results and conclusions of this third study will be reported.

Requirements for Radial Migration: How Does the Migrating Fraction Depend on Stellar Velocity Dispersion?

NASA Astrophysics Data System (ADS)

Tolfree, K. J. D.; Wyse, R. F. G.

2014-03-01

Radial migration is a mechanism that can rearrange the orbital angular momentum of stars in a spiral disk without inducing kinematic heating. When radial migration is very efficient, a large fraction of disk stars experience significant changes in their orbital angular momenta over a short period of time. Such scenarios have strong implications for the chemical and kinematic evolution of disk galaxies. We have undertaken an investigation of the physical dependencies of the efficiency of radial migration on stellar kinematics and spiral structure by deriving the fraction of stars that can migrate radially. In order for a star in a spiral disk to migrate radially, it must first be “captured” in a family of resonant orbits near the radius of corotation with a transient spiral pattern. To date, the only analytic criterion for capture has been for stars in circular orbits. We present the capture criterion for disk stars on non-circular orbits. We then use our analytically derived capture criterion to model the radial distribution of the captured fraction in an exponential disk with a flat rotation curve. Further, we derive the dependence of the total captured fraction in the disk on the radial component of the stellar velocity dispersion (σR) and the amplitude of the spiral perturbation to the underlying potential evaluated at corotation (|Φs|CR). We find that within an annulus centered around corotation where σR is constant, the captured fraction goes as e-σR2/|Φs|CR.

Phase Variations, Transits and Eclipses of the Misfit CoRoT-2b

NASA Astrophysics Data System (ADS)

Cowan, Nicolas; Deming, Drake; Gillon, Michael; Knutson, Heather; Madhusudhan, Nikku; Rauscher, Emily

2011-05-01

We propose to observe the nearby transiting hot Jupiter CoRoT-2b for a little over one planetary orbit on two occasions, yielding two secondary eclipses, a transit, and a full phase curve in each of the 3.6 and 4.5 micron channels. These data will help resolve the unique nature of this bloated planet: CoRoT-2b is the only hot Jupiter that is poorly fit by either inverted or non-inverted spectral models (Deming et al. 2011). Two hypotheses have been proposed to explain the peculiar mid-IR colors of CoRoT-2b, and thermal phase measurements with Spitzer's continuous, high-precision photometry will be able to distinguish between them: the planet has a non-inverted atmosphere but is losing mass to its host star, or the planet has a peculiar kind of temperature inversion due to mysterious atmospheric scatterers. CoRoT-2b is also among the most inflated hot Jupiters and, because of its relatively large mass, cannot be reconciled with interior evolution models, despite a small but non-zero eccentricity. A recent planetary collision may be necessary to explain the planet's youthful radius (Guillot & Havel 2011). Finally, the planet's extremely young host star, CoRoT-2, is the most chromospherically active of all transit hosts. This appears to be a common thread connecting all of its planet's peculiarities: the high UV flux of the star will drive mass loss, as well as photochemistry. Most importantly, the radius measurement of the planet at optical wavelengths may be contaminated by star spots. Mid-IR transit measurements from Spitzer will help resolve the mystery of CoRoT-2b's inflated radius.

Alterations of pulsation absorber characteristics in experimental hydrocephalus.

PubMed

Park, Eun-Hyoung; Dombrowski, Stephen; Luciano, Mark; Zurakowski, David; Madsen, Joseph R

2010-08-01

Analysis of waveform data in previous studies suggests that the pulsatile movement of CSF may play a role in attenuating strong arterial pulsations entering the cranium, and its effectiveness in attenuating these pulsations may be altered by changes in intracranial pressure (ICP). These findings were obtained in studies performed in canines with normal anatomy of the CSF spaces. How then would pulsation absorbance respond to changes in CSF movement under obstructive conditions such as the development of hydrocephalus? In the present study, chronic obstructive hydrocephalus was induced by the injection of cyanoacrylate gel into the fourth ventricle of canines, and pulsation absorbance was compared before and after hydrocephalus induction. Five animals were evaluated with simultaneous recordings of ICP and arterial blood pressure (ABP) before and at 4 and 12 weeks after fourth ventricle obstruction by cyanoacrylate. To assess how the intracranial system responds to the arterial pulsatile component, ABP and ICP waveforms recorded in a time domain had to be analyzed in a frequency domain. In an earlier study the authors introduced a particular technique that allows characterization of the intracranial system in the frequency domain with sufficient accuracy and efficiency. This same method was used to analyze the relationship between ABP and ICP waveforms recorded during several acute states including hyperventilation as well as CSF withdrawal and infusion under conditions before and after inducing chronic obstructive hydrocephalus. Such a relationship is reflected in terms of a gain, which is a function of frequency. The cardiac pulsation absorbance (CPA) index, which is simply derived from a gain evaluated at the cardiac frequency, was used to quantitatively evaluate the changes in pulsation absorber function associated with the development of hydrocephalus within each of the animals, which did become hydrocephalic. To account for normal and hydrocephalic conditions within the same animal and at multiple time points, statistical analysis was performed by repeated-measures ANOVA. The performance of the pulsation absorber as assessed by CPA significantly deteriorated after the development of chronic hydrocephalus. In these animals the decrement in CPA was far more significant than other anticipated changes including those in ICP, compliance, or ICP pulse amplitude. To the extent that the free CSF movement acts as a buffer of arterial pulsation input to flow in microvessels, alterations in the pulsation absorber may play a pathophysiological role. One measure of alterations in the way the brain deals with pulsatile input-the CPA measurement-changes dramatically with the imposition of hydrocephalus. Results in the present study suggest that CPA may serve as a complementary metric to the conventional static measure of intracranial compliance in other experimental and clinical studies.

Elemental abundances in corotating events

NASA Technical Reports Server (NTRS)

Vonrosenvinge, T. T.; Mcguire, R. E.

1986-01-01

Large, persistent solar-wind streams in 1973 and 1974 produced corotating interaction regions which accelerated particles to energies of a few MeV/nucleon. The proton to helium ratio (H/He) reported was remarkably constant at a value (22 + or - 5) equal to that in the solar wind (32 + or - 3), suggesting that particles were being accelerated directly out of the solar wind. Preliminary results from a similar study approximately 11 years (i.e., one solar cycle) later are reported. Corotating events were identified by surveying the solar wind data, energetic particle time-histories and anisotropies. This data was all obtained from the ISEE-3/ICE spacecraft. These events also show H/He ratios similar to that in the solar wind. In addition, other corotating events were examined at times when solar flare events could have injected particles into the corresponding corotating interaction regions. It was found that in these cases there is evidence for H/He ratios which are significantly different from that of the solar wind but which are consistent with the range of values found in solar flare events.

Numerical assessment of pulsating water jet in the conical diffusers

NASA Astrophysics Data System (ADS)

Tanasa, Constantin; Ciocan, Tiberiu; Muntean, Sebastian

2017-11-01

The hydraulic fluctuations associated with partial load operating conditions of Francis turbines are often periodic and characterized by the presence of a vortex rope. Two types of pressure fluctuations associated with the draft tube surge are identified in the literature. The first is an asynchronous (rotating) pressure fluctuation due to the precession of the helical vortex around the axis of the draft tube. The second type of fluctuation is a synchronous (plunging) fluctuation. The plunging fluctuations correspond to the flow field oscillations in the whole hydraulic passage, and are generally propagated overall in the hydraulic system. The paper introduced a new control method, which consists in injecting a pulsating axial water jet along to the draft tube axis. Nevertheless, the great calling of this control method is to mitigate the vortex rope effects targeting the vortex sheet and corresponding plunging component. In this paper, is presented our 3D numerical investigations with and without pulsating axial water jet control method in order to evaluate the concept.

An asteroseismic constraint on the mass of the axion from the period drift of the pulsating DA white dwarf star L19-2

DOE Office of Scientific and Technical Information (OSTI.GOV)

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

We employ an asteroseismic model of L19-2, a relatively massive ( M {sub *} ∼ 0.75 M {sub ⊙}) and hot ( T {sub eff} ∼ 12 100 K) pulsating DA (H-rich atmosphere) white dwarf star (DAV or ZZ Ceti variable), and use the observed values of the temporal rates of period change of its dominant pulsation modes (Π ∼ 113 s and Π ∼ 192 s), to derive a new constraint on the mass of the axion, the hypothetical non-barionic particle considered as a possible component of the dark matter of the Universe. If the asteroseismic model employed ismore » an accurate representation of L19-2, then our results indicate hints of extra cooling in this star, compatible with emission of axions of mass m {sub a} cos{sup 2}β ∼< 25 meV or an axion-electron coupling constant of g {sub ae} ∼< 7 × 10{sup −13}.« less

Kepler eclipsing binaries with δ Scuti components and tidally induced heartbeat stars

NASA Astrophysics Data System (ADS)

Guo, Zhao; Gies, Douglas R.; Matson, Rachel A.

δ Scuti stars are generally fast rotators and their pulsations are not in the asymptotic regime, so the interpretation of their pulsation spectra is a very difficult task. Binary stars, especially eclipsing systems, offer us the opportunity to constrain the space of fundamental stellar parameters. Firstly, we show the results of KIC9851944 and KIC4851217 as two case studies. We found the signature of the large frequency separation in the pulsational spectrum of both stars. The observed mean stellar density and the large frequency separation obey the linear relation in the log-log space as found by Suarez et al. (2014) and García Hernández et al. (2015). Second, we apply the simple `one-layer model' of Moreno & Koenigsberger (1999) to the prototype heartbeat star KOI-54. The model naturally reproduces the tidally induced high frequency oscillations and their frequencies are very close to the observed frequency at 90 and 91 times the orbital frequency.

VizieR Online Data Catalog: Algorithm for correcting CoRoT raw light curves (Mislis+, 2010)

NASA Astrophysics Data System (ADS)

Mislis, D.; Schmitt, J. H. M. M.; Carone, L.; Guenther, E. W.; Patzold, M.

2010-10-01

Requirements : gfortran (or g77, ifort) compiler Input Files : The input files sould be raw CoRoT txt files (http://idoc-corot.ias.u-psud.fr/index.jsp) with names CoRoT*.txt Run the cda by typing C>: ./cda.csh (code and data sould be in the same directory) Output files : CDA creates one ascii output file with name - CoRoT*.R.cor for R filter (2 data files).

Convective heat transfer from a pulsating radial jet reattachment (PRJR) nozzle

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pak, J.Y.; James, D.L.; Parameswaran, S.

1999-07-01

Impinging jets of fluid have been used to cool, heat or dry surfaces in many industries including high temperature gas turbines, paper and glass manufacturing, textile drying, and electronic components. Jets may be broadly classified as either inline or radial. Inline jets typically have some type of circular or planer opening through which the fluid exits. The circular opening may be converging, well rounded, or of the same diameter as the nozzle or tube through which the fluid is delivered. Here, a numerical investigation for air exiting a Pulsating Radial Jet Reattachment (PRJR) nozzle was performed with various flow andmore » geometric conditions. The transient ensemble averaged Navier-Stokes equation with the standard {kappa}-{epsilon} turbulence model and the standard transient turbulent energy equation were solved to predict the velocity, pressure, and temperature distributions as a function of the pulsation rate, nondimensionalized nozzle-to-plate spacing, amplitude ratio, exit angle and gap Reynolds number. Sinusoidal profile, square and triangular pulsation profiles were simulated to determine the effect on the convective heat transfer during pulsation of nozzle. Grid movement is coupled to the flow field in a manner by a grid convection. Calculated reattachment radii for various conditions correlated well with previously obtained experimental results. Calculated convective heat transfer coefficients and surface pressure profiles for various geometric and flow conditions were compared with experimental results. Convective heat transfer coefficient calculations matched the experimental values very well outside the reattachment regions and underpredicted the convective heat transfer data underneath the nozzle in the dead water region and on the reattachment radius.« less

Noise properties of the CoRoT data. A planet-finding perspective

NASA Astrophysics Data System (ADS)

Aigrain, S.; Pont, F.; Fressin, F.; Alapini, A.; Alonso, R.; Auvergne, M.; Barbieri, M.; Barge, P.; Bordé, P.; Bouchy, F.; Deeg, H.; de La Reza, R.; Deleuil, M.; Dvorak, R.; Erikson, A.; Fridlund, M.; Gondoin, P.; Guterman, P.; Jorda, L.; Lammer, H.; Léger, A.; Llebaria, A.; Magain, P.; Mazeh, T.; Moutou, C.; Ollivier, M.; Pätzold, M.; Queloz, D.; Rauer, H.; Rouan, D.; Schneider, J.; Wuchter, G.; Zucker, S.

2009-10-01

In this short paper, we study the photometric precision of stellar light curves obtained by the CoRoT satellite in its planet-finding channel, with a particular emphasis on the time scales characteristic of planetary transits. Together with other articles in the same issue of this journal, it forms an attempt to provide the building blocks for a statistical interpretation of the CoRoT planet and eclipsing binary catch to date. After pre-processing the light curves so as to minimise long-term variations and outliers, we measure the scatter of the light curves in the first three CoRoT runs lasting more than 1 month, using an iterative non-linear filter to isolate signal on the time scales of interest. The behaviour of the noise on 2 h time scales is described well by a power-law with index 0.25 in R-magnitude, ranging from 0.1 mmag at R=11.5 to 1 mmag at R=16, which is close to the pre-launch specification, though still a factor 2-3 above the photon noise due to residual jitter noise and hot pixel events. There is evidence of slight degradation in the performance over time. We find clear evidence of enhanced variability on hour time scales (at the level of 0.5 mmag) in stars identified as likely giants from their R magnitude and B-V colour, which represent approximately 60 and 20% of the observed population in the directions of Aquila and Monoceros, respectively. On the other hand, median correlated noise levels over 2 h for dwarf stars are extremely low, reaching 0.05 mmag at the bright end. The CoRoT space mission, launched on December 27, 2006, has been developed and is operated by the CNES, with the contribution of Austria, Belgium, Brazil, ESA, Germany, and Spain. CoRoT data become publicly available one year after release to the Co-Is of the mission from the CoRoT archive: http://idoc-corot.ias.u-psud.fr/.

Transiting exoplanets from the CoRoT space mission. IV. CoRoT-Exo-4b: a transiting planet in a 9.2 day synchronous orbit

NASA Astrophysics Data System (ADS)

Aigrain, S.; Collier Cameron, A.; Ollivier, M.; Pont, F.; Jorda, L.; Almenara, J. M.; Alonso, R.; Barge, P.; Bordé, P.; Bouchy, F.; Deeg, H.; de La Reza, R.; Deleuil, M.; Dvorak, R.; Erikson, A.; Fridlund, M.; Gondoin, P.; Gillon, M.; Guillot, T.; Hatzes, A.; Lammer, H.; Lanza, A. F.; Léger, A.; Llebaria, A.; Magain, P.; Mazeh, T.; Moutou, C.; Paetzold, M.; Pinte, C.; Queloz, D.; Rauer, H.; Rouan, D.; Schneider, J.; Wuchter, G.; Zucker, S.

2008-09-01

CoRoT, the first space-based transit search, provides ultra-high-precision light curves with continuous time-sampling over periods of up to 5 months. This allows the detection of transiting planets with relatively long periods, and the simultaneous study of the host star's photometric variability. In this Letter, we report the discovery of the transiting giant planet CoRoT-Exo-4b and use the CoRoT light curve to perform a detailed analysis of the transit and determine the stellar rotation period. The CoRoT light curve was pre-processed to remove outliers and correct for orbital residuals and artefacts due to hot pixels on the detector. After removing stellar variability about each transit, the transit light curve was analysed to determine the transit parameters. A discrete autocorrelation function method was used to derive the rotation period of the star from the out-of-transit light curve. We determine the periods of the planetary orbit and star's rotation of 9.20205 ± 0.00037 and 8.87 ± 1.12 days respectively, which is consistent with this being a synchronised system. We also derive the inclination, i = 90.00_-0.085+0.000 in degrees, the ratio of the orbital distance to the stellar radius, a/Rs = 17.36-0.25+0.05, and the planet-to-star radius ratio R_p/R_s=0.1047-0.0022+0.0041. We discuss briefly the coincidence between the orbital period of the planet and the stellar rotation period and its possible implications for the system's migration and star-planet interaction history. The CoRoT space mission, launched on December 27th 2006, has been developed and is operated by CNES, with the contribution of Austria, Belgium, Brazil, ESA, Germany, and Spain. The first CoRoT data will be available to the public in February 2009 from the CoRoT archive: http://idoc-corot.ias.u-psud.fr/ Figures 1, 4 and 5 are only available in electronic form at http://www.aanda.org

Geomagnetic disturbances and pulsations as a high-latitude response to considerable alternating IMF Variations during the magnetic storm recovery phase (Case study: May 30, 2003)

NASA Astrophysics Data System (ADS)

Levitin, A. E.; Kleimenova, N. G.; Gromova, L. I.; Antonova, E. E.; Dremukhina, L. A.; Zelinsky, N. R.; Gromov, S. V.; Malysheva, L. M.

2015-11-01

Features of high-latitude geomagnetic disturbances during the magnetic storm ( Dst min =-144 nT) recovery phase were studied based on the observations on the Scandinavian profile of magnetometers (IMAGE). Certain non-typical effects that occur under the conditions of large positive IMF Bz values (about +20-25 nT) and large negative IMF By values (to-20 nT) were revealed. Thus, an intense (about 400 nT) negative bay in the X component of the magnetic field (the polar electrojet, PE) was observed in the dayside sector at geomagnetic latitudes higher than 70°. As the IMF B y reverses its sign from negative to positive, the bay in the X component was replaced by the bay in the Y component. The possible distribution of the fieldaligned currents of the NBZ system was analyzed based on the CHAMP satellite data. The results were compared with the position of the auroral oval (the OVATION model) and the ion and electron flux observations on the DMSP satellite. Analysis of the particle spectra indicated that these spectra correspond to the auroral oval dayside sector crossings by the satellite, i.e., to the dayside projection of the plasma ring surrounding the Earth. Arguments are presented for the assumption that the discussed dayside electrojet ( PE) is localized near the polar edge of the dayside auroral oval in a the closed magnetosphere. The features of the spectral and spatial dynamics of intense Pc5 geomagnetic pulsations were studied in this time interval. It was established that the spectrum of high-latitude (higher than ~70°) pulsations does not coincide with the spectrum of fluctuations in the solar wind and IMF. It was shown that Pc5 geomagnetic pulsations can be considered as resonance oscillations at latitudes lower than 70° and apparently reflect fluctuations in turbulent sheets adjacent to the magnetopause (the low-latitude boundary layer, a cusp throat) or in a turbulent magnetosheath at higher latitudes.

Modules for Experiments in Stellar Astrophysics (MESA): Planets, Oscillations, Rotation, and Massive Stars

NASA Astrophysics Data System (ADS)

Paxton, Bill; Cantiello, Matteo; Arras, Phil; Bildsten, Lars; Brown, Edward F.; Dotter, Aaron; Mankovich, Christopher; Montgomery, M. H.; Stello, Dennis; Timmes, F. X.; Townsend, Richard

2013-09-01

We substantially update the capabilities of the open source software package Modules for Experiments in Stellar Astrophysics (MESA), and its one-dimensional stellar evolution module, MESA star. Improvements in MESA star's ability to model the evolution of giant planets now extends its applicability down to masses as low as one-tenth that of Jupiter. The dramatic improvement in asteroseismology enabled by the space-based Kepler and CoRoT missions motivates our full coupling of the ADIPLS adiabatic pulsation code with MESA star. This also motivates a numerical recasting of the Ledoux criterion that is more easily implemented when many nuclei are present at non-negligible abundances. This impacts the way in which MESA star calculates semi-convective and thermohaline mixing. We exhibit the evolution of 3-8 M ⊙ stars through the end of core He burning, the onset of He thermal pulses, and arrival on the white dwarf cooling sequence. We implement diffusion of angular momentum and chemical abundances that enable calculations of rotating-star models, which we compare thoroughly with earlier work. We introduce a new treatment of radiation-dominated envelopes that allows the uninterrupted evolution of massive stars to core collapse. This enables the generation of new sets of supernovae, long gamma-ray burst, and pair-instability progenitor models. We substantially modify the way in which MESA star solves the fully coupled stellar structure and composition equations, and we show how this has improved the scaling of MESA's calculational speed on multi-core processors. Updates to the modules for equation of state, opacity, nuclear reaction rates, and atmospheric boundary conditions are also provided. We describe the MESA Software Development Kit that packages all the required components needed to form a unified, maintained, and well-validated build environment for MESA. We also highlight a few tools developed by the community for rapid visualization of MESA star results.

76 FR 51876 - Medical Devices; Ophthalmic Devices; Classification of the Eyelid Thermal Pulsation System

Federal Register 2010, 2011, 2012, 2013, 2014

2011-08-19

... meibomian gland dysfunction (MGD), also known as evaporative dry eye or lipid deficiency dry eye. The system... evaporative dry eye or lipid deficiency dry eye. The system consists of a component that is inserted around...

Large Amplitude IMF Fluctuations in Corotating Interaction Regions: Ulysses at Midlatitudes

NASA Technical Reports Server (NTRS)

Tsurutani, Bruce T.; Ho, Christian M.; Arballo, John K.; Goldstein, Bruce E.; Balogh, Andre

1995-01-01

Corotating Interaction Regions (CIRs), formed by high-speed corotating streams interacting with slow speed streams, have been examined from -20 deg to -36 deg heliolatitudes. The high-speed streams emanate from a polar coronal hole that Ulysses eventually becomes fully embedded in as it travels towards the south pole. We find that the trailing portion of the CIR, from the interface surface (IF) to the reverse shock (RS), contains both large amplitude transverse fluctuations and magnitude fluctuations. Similar fluctuations have been previously noted to exist within CIRs detected in the ecliptic plane, but their existence has not been explained. The normalized magnetic field component variances within this portion of the CIR and in the trailing high-speed stream are approximately the same, indicating that the fluctuations in the CIR are compressed Alfven waves. Mirror mode structures with lower intensities are also observed in the trailing portion of the CIR, presumably generated from a local instability driven by free energy associated with compression of the high-speed solar wind plasma. The mixture of these two modes (compressed Alfven waves and mirror modes) plus other modes generated by three wave processes (wave-shock interactions) lead to a lower Alfvenicity within the trailing portion of the CfR than in the high-speed stream proper. The results presented in this paper suggest a mechanism for generation of large amplitude B(sub z) fluctuations within CIRS. Such phenomena have been noted to be responsible for the generation of moderate geomagnetic storms during the declining phase of the solar cycle.

The SpaceInn SISMA archive

NASA Astrophysics Data System (ADS)

Rainer, Monica; Poretti, Ennio; Mistò, Angelo; Rosa Panzera, Maria

2017-10-01

The Spectroscopic Indicators in a SeisMic Archive (SISMA) has been built in the framework of the FP7 SpaceInn project to contain the 7013 HARPS spectra observed during the CoRoT asteroseismic groundbased program, along with their variability and asteroseismic indicators. The spectra pertain to 261 stars spread around the whole Herztsprung-Russell diagram: 72 of them were CoRoT targets while the others were observed in order to better characterize their variability classes. The Legacy Data lightcurves of the CoRoT targets are also stored in the archive.

Models of red giants in the CoRoT asteroseismology fields combining asteroseismic and spectroscopic constraints

NASA Astrophysics Data System (ADS)

Nadège, Lagarde

The availability of asteroseismic constraints for a large sample of red-giant stars from the CoRoT and Kepler missions paves the way for various statistical studies of the seismic properties of stellar populations. We use a detailed spectroscopic study of 19 CoRoT red-giant stars (Morel et al. 2014) to compare theoretical stellar evolution models to observations of the open cluster NGC 6633 and field stars. This study is already published in Lagarde et al. (2015)

ExoDat Information System at CeSAM

NASA Astrophysics Data System (ADS)

Agneray, F.; Moreau, C.; Chabaud, P.; Damiani, C.; Deleuil, M.

2014-05-01

CoRoT (Convection Rotation and planetary transits) is a space based mission led by French space agency (CNES) in association with French and international laboratories. One of CoRoT's goal is to detect exoplanets by the transit method. The Exoplanet Database (Exodat) is a VO compliant information system for the CoRoT exoplanet program. The main functions of ExoDat are to provide a source catalog for the observation fields and targets selection; to characterize the CoRoT targets (spectral type, variability , contamination...);and to support follow up programs. ExoDat is built using the AstroNomical Information System (ANIS) developed by the CeSAM (Centre de donneeS Astrophysique de Marseille). It offers download of observation catalogs and additional services like: search, extract and display data by using a combination of criteria, object list, and cone-search interfaces. Web services have been developed to provide easy access for user's softwares and pipelines.

Observations of Cepheids with the MOST satellite: contrast between pulsation modes

NASA Astrophysics Data System (ADS)

Evans, N. R.; Szabó, R.; Derekas, A.; Szabados, L.; Cameron, C.; Matthews, J. M.; Sasselov, D.; Kuschnig, R.; Rowe, J. F.; Guenther, D. B.; Moffat, A. F. J.; Rucinski, S. M.; Weiss, W. W.

2015-02-01

The quantity and quality of satellite photometric data strings is revealing details in Cepheid variation at very low levels. Specifically, we observed a Cepheid pulsating in the fundamental mode and one pulsating in the first overtone with the Canadian MOST (Microvariability and Oscillations of Stars) satellite. The 3.7-d period fundamental mode pulsator (RT Aur) has a light curve that repeats precisely, and can be modelled by a Fourier series very accurately. The overtone pulsator (SZ Tau, 3.1 d period) on the other hand shows light-curve variation from cycle to cycle which we characterize by the variations in the Fourier parameters. We present arguments that we are seeing instability in the pulsation cycle of the overtone pulsator, and that this is also a characteristic of the O - C curves of overtone pulsators. On the other hand, deviations from cycle to cycle as a function of pulsation phase follow a similar pattern in both stars, increasing after minimum radius. In summary, pulsation in the overtone pulsator is less stable than that of the fundamental mode pulsator at both long and short time-scales.

EXO-DAT: AN INFORMATION SYSTEM IN SUPPORT OF THE CoRoT/EXOPLANET SCIENCE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Deleuil, M.; Meunier, J. C.; Moutou, C.

2009-08-15

Exo-Dat is a database and an information system created primarily in support of the exoplanet program of the COnvection ROtation and planetary Transits (CoRoT) mission. In the directions of CoRoT pointings, it provides a united interface to several sets of data: stellar published catalogs, photometric and spectroscopic data obtained during the mission preparation, results from the mission and from follow-up observations, and several mission-specific technical parameters. The new photometric data constitute the subcatalog Exo-Cat, and give consistent 4-color photometry of 14.0 million stars with a completeness to 19th magnitude in the r-filter. It covers several zones in the galactic planemore » around CoRoT pointings, with a total area of 209 deg{sup 2}. This Exo-Dat information system provides essential technical support to the ongoing CoRoT light-curve analyses and ground-based follow-up by supplying additional complementary information such as the prior knowledge of the star's fundamental parameters or its contamination level inside the large CoRoT photometric mask. The database is fully interfaced with VO tools and thus benefits from existing visualization and analysis tools like TOPCAT or ALADIN. It is accessible to the CoRoT community through the Web, and will be gradually opened to the public. It is the ideal tool to prepare the foreseen statistical studies of the properties of the exoplanetary systems. As a VO-compliant system, such analyses could thus benefit from the most up-to-date classifier tools.« less

Observations and analysis of Alfvén wave phase mixing in the Earth's magnetosphere

NASA Astrophysics Data System (ADS)

Sarris, T. E.; Wright, A. N.; Li, X.

2009-03-01

Signatures of Alfvén wave phase mixing in the Earth's magnetosphere, observed as polarization rotation of a transverse, Pc5 magnetospheric pulsation, are presented and compared to theory. The polarization rotation occurred during a rare event of a dayside narrowband ULF magnetospheric pulsation that lasted for 5 consecutive days, from 24 to 30 November 1997; details of this event were reported by Sarris et al. (2009) through observations at geosynchronous orbit and on the ground. In this paper we investigate the polarization signatures of the pulsation by performing a detailed analysis of its transverse components as observed through hodogram plots. Density measurements from one of the Los Alamos National Laboratory (LANL) spacecraft which had its L shells closest to GOES-8 are used to calculate field line resonance frequencies at geosynchronous orbit; these frequency calculations show good agreement with the observed pulsations but also have a local time offset. For an instance of an observed polarization rotation we estimate the observed poloidal lifetime of the pulsation by the time taken for the poloidal and toroidal amplitudes to become equal, which we compare with the theoretical approximation to the poloidal lifetime, as calculated in a box model magnetosphere by Mann and Wright (1995). Density measurements from different LANL spacecraft at geosynchronous orbit and their varying L shells as derived from their varying local times are used to estimate a local gradient in the local Alfvén speed, which is then used in the calculation of the predicted poloidal lifetime. This is the first time that such polarization rotations are directly observed and compared with theoretical predictions.

Maser mechanism of optical pulsations from anomalous X-ray pulsar 4U 0142+61

NASA Astrophysics Data System (ADS)

Lu, Y.; Zhang, S. N.

2004-11-01

Based on the work of Luo & Melrose from the early 1990s, a maser curvature emission mechanism in the presence of curvature drift is used to explain the optical pulsations from anomalous X-ray pulsars (AXPs). The model comprises a rotating neutron star with a strong surface magnetic field, i.e. a magnetar. Assuming the space-charge-limited flow acceleration mechanism, in which the strongly magnetized neutron star induces strong electric fields that pull the charges from its surface and flow along the open field lines, the neutron star generates a dense flow of electrons and positrons (relativistic pair plasma) by either two-photon pair production or one-photon pair creation resulting from inverse Compton scattering of the thermal photons above the pulsar polar cap (PC). The motion of the pair plasma is essentially one-dimensional along the field lines. We propose that optical pulsations from AXPs are generated by a curvature-drift-induced maser developing in the PC of magnetars. Pair plasma is considered as an active medium that can amplify its normal modes. The curvature drift, which is energy-dependent, is another essential ingredient in allowing negative absorption (maser action) to occur. For the source AXP 4U 0142+61, we find that the optical pulsation triggered by curvature-drift maser radiation occurs at the radial distance R(νM) ~ 4.75 × 109 cm to the neutron star. The corresponding curvature maser frequency is about νM~ 1.39 × 1014 Hz, and the pulse component from the maser amplification is about 27 per cent. The result is consistent with the observation of the optical pulsations from AXP 4U 0142+61.

An XMM-Newton and NuSTAR Study of IGR J18214-1318: A Non-pulsating High-mass X-Ray Binary with a Neutron Star

NASA Astrophysics Data System (ADS)

Fornasini, Francesca M.; Tomsick, John A.; Bachetti, Matteo; Krivonos, Roman A.; Fürst, Felix; Natalucci, Lorenzo; Pottschmidt, Katja; Wilms, Jörn

2017-05-01

IGR J18214-1318, a Galactic source discovered by the International Gamma-Ray Astrophysics Laboratory, is a high-mass X-ray binary (HMXB) with a supergiant O-type stellar donor. We report on the XMM-Newton and NuSTAR observations that were undertaken to determine the nature of the compact object in this system. This source exhibits high levels of aperiodic variability, but no periodic pulsations are detected with a 90% confidence upper limit of 2% fractional rms between 0.00003-88 Hz, a frequency range that includes the typical pulse periods of neutron stars (NSs) in HMXBs (0.1-103 s). Although the lack of pulsations prevents us from definitively identifying the compact object in IGR J18214-1318, the presence of an exponential cutoff with e-folding energy ≲ 30 {keV} in its 0.3-79 keV spectrum strongly suggests that the compact object is an NS. The X-ray spectrum also shows a Fe Kα emission line and a soft excess, which can be accounted for by either a partial-covering absorber with {N}{{H}}≈ {10}23 cm-2, which could be due to the inhomogeneous supergiant wind, or a blackbody component with {kT}={1.74}-0.05+0.04 keV and {R}{BB}≈ 0.3 km, which may originate from NS hot spots. Although neither explanation for the soft excess can be excluded, the former is more consistent with the properties observed in other supergiant HMXBs. We compare IGR J18214-1318 to other HMXBs that lack pulsations or have long pulsation periods beyond the range covered by our observations.

Transiting exoplanets from the CoRoT space mission . VI. CoRoT-Exo-3b: the first secure inhabitant of the brown-dwarf desert

NASA Astrophysics Data System (ADS)

Deleuil, M.; Deeg, H. J.; Alonso, R.; Bouchy, F.; Rouan, D.; Auvergne, M.; Baglin, A.; Aigrain, S.; Almenara, J. M.; Barbieri, M.; Barge, P.; Bruntt, H.; Bordé, P.; Collier Cameron, A.; Csizmadia, Sz.; de La Reza, R.; Dvorak, R.; Erikson, A.; Fridlund, M.; Gandolfi, D.; Gillon, M.; Guenther, E.; Guillot, T.; Hatzes, A.; Hébrard, G.; Jorda, L.; Lammer, H.; Léger, A.; Llebaria, A.; Loeillet, B.; Mayor, M.; Mazeh, T.; Moutou, C.; Ollivier, M.; Pätzold, M.; Pont, F.; Queloz, D.; Rauer, H.; Schneider, J.; Shporer, A.; Wuchterl, G.; Zucker, S.

2008-12-01

Context: The CoRoT space mission routinely provides high-precision photometric measurements of thousands of stars that have been continuously observed for months. Aims: The discovery and characterization of the first very massive transiting planetary companion with a short orbital period is reported. Methods: A series of 34 transits was detected in the CoRoT light curve of an F3V star, observed from May to October 2007 for 152 days. The radius was accurately determined and the mass derived for this new transiting, thanks to the combined analysis of the light curve and complementary ground-based observations: high-precision radial-velocity measurements, on-off photometry, and high signal-to-noise spectroscopic observations. Results: CoRoT-Exo-3b has a radius of 1.01 ± 0.07 R_Jup and transits around its F3-type primary every 4.26 days in a synchronous orbit. Its mass of 21.66 ± 1.0 M_Jup, density of 26.4 ± 5.6 g cm-3, and surface gravity of logg = 4.72 clearly distinguish it from the regular close-in planet population, making it the most intriguing transiting substellar object discovered so far. Conclusions: With the current data, the nature of CoRoT-Exo-3b is ambiguous, as it could either be a low-mass brown-dwarf or a member of a new class of “superplanets”. Its discovery may help constrain the evolution of close-in planets and brown-dwarfs better. Finally, CoRoT-Exo-3b confirms the trend that massive transiting giant planets (M ≥ 4 M_Jup) are found preferentially around more massive stars than the Sun. The CoRoT space mission, launched on December 27th 2006, has been developed and is operating by CNES, with the contribution of Austria, Belgium, Brasil, ESA, Germany and Spain. The first CoRoT data will be available to the public in February 2009 from the CoRoT archive: http://idoc-corot.ias.u-psud.fr/ Table of the COROT photometry 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/491/889

Plasma observations near Saturn - Initial results from Voyager 1

NASA Technical Reports Server (NTRS)

Bridge, H. S.; Belcher, J. W.; Lazarus, A. J.; Olbert, S.; Sullivan, J. D.; Bagenal, F.; Gazis, P. R.; Hartle, R. E.; Ogilvie, K. W.; Scudder, J. D.

1981-01-01

The Voyager 1 encounter with Saturn and its satellites yielded extensive measurements of magnetospheric low-energy plasma electrons and positive ions, both heavy and light, probably of hydrogen and nitrogen or oxygen. At radial distances between 15 and 7 Saturn radii on the inbound trajectory, the plasma appears to corotate with a velocity within 20% of that theoretically expected for rigid corotation. The Titan data, taken while the moon was inside the Saturn magnetosphere, shows a clear signature characteristic of the interaction between a subsonic corotating magnetospheric plasma and the atmospheric or ionospheric exosphere of Titan.

A Study of Small Satellites Captured in Corotation Resonance

NASA Astrophysics Data System (ADS)

Santos Araújo, Nilton Carlos; Vieira Neto, E.

2013-05-01

Abstract (2,250 Maximum Characters): Currently we find in the solar system several types of celestial objects such as planets, satellites, rings, etc.. The dynamics of these objects have always been interesting for studies, mainly the satellites and rings of Saturn. We have the knowledge that these satellites and rings undergo various types of orbital resonances. These resonances are responsible for the formation of numerous structures in the rings such as, for example, almost the entire structure of A ring. Thus we see how important it is to examine the nature of these resonant interactions in order to understand the characteristics observed in the satellites and rings of Saturn. In this work we highlight the corotation resonance, which occurs when the velocity pattern of the potential disturbing frequency is equal to the orbital frequency of a satellite. In the Saturnian system there are three satellites, Aegaeon, Anthe and Methone that are in corotation resonance with Mimas. In this paper we study, through numerical simulations, corotation resonance of the G ring arc of Saturn with Tethys and Mimas, while Mimas is migrating. Ours initial results show that no particles escape from the corotational resonance while Mimas migrate, that is, it is very robust. We also show the effects and consequences of Tethys migration on Mimas and de G arc.

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.

MOST discovers a multimode δ Scuti star in a triple system: HD 61199

NASA Astrophysics Data System (ADS)

Hareter, M.; Kochukhov, O.; Lehmann, H.; Tsymbal, V.; Huber, D.; Lenz, P.; Weiss, W. W.; Matthews, J. M.; Rucinski, S.; Rowe, J. F.; Kuschnig, R.; Guenther, D. B.; Moffat, A. F. J.; Sasselov, D.; Walker, G. A. H.; Scholtz, A.

2008-12-01

Context: A field star, HD 61199 (V ≈ 8), simultaneously observed with Procyon by the MOST (Microvariability & Oscillations of STars) satellite in continuous runs of 34, 17, and 34 days in 2004, 2005, and 2007, was found to pulsate in 11 frequencies in the δ Scuti range with amplitudes from 1.7 down to 0.09 mmag. The photometry also showed variations with a period of about four days. To investigate the nature of the longer period, 45 days of time-resolved spectroscopy was obtained at the Thüringer Landessternwarte Tautenburg in 2004. The radial velocity measurements indicate that HD 61199 is a triple system. Aims: A δ Scuti pulsator with a rich eigenspectrum in a multiple system is promising for asteroseismology. Our objectives were to identify which of the stars in the system is the δ Scuti variable and to obtain the orbital elements of the system and the fundamental parameters of the individual components, which are constrained by the pulsation frequencies of the δ Scuti star. Methods: Classical Fourier techniques and least-squares multi-sinusoidal fits were applied to the MOST photometry to identify the pulsation frequencies. The groundbased spectroscopy was analysed with least-squares-deconvolution (LSD) techniques, and the orbital elements derived with the KOREL and ORBITX routines. Asteroseismic models were also generated. Results: The photometric and spectroscopic data are compatible with a triple system consisting of a close binary with an orbital period of 3.57 days and a δ Scuti companion (HD 61199 A) as the most luminous component. The δ Scuti star is a rapid rotator with about v\\cdot sin{i} = 130 {km s-1} and an upper mass limit of about 2.1 M⊙. For the close binary components, we find they are of nearly equal mass, with lower mass limits of about 0.7 M⊙. Comparisons to synthetic spectra indicate these stars have a late-F spectral type. The observed oscillation frequencies are compared to pulsation models to further constrain the evolutionary state and mass of HD 61199 A. The orbit frequency of the close binary corresponds to the difference of the two δ Scuti frequencies with the highest amplitudes - a coincidence that is remarkable, but not explained. Based on data from the MOST satellite, a Canadian Space Agency mission, jointly operated by Dynacon Inc., the University of Toronto Institute for Aerospace Studies and the University of British Columbia, with the assistance of the University of Vienna and on spectra taken with the Coudé-echelle spectrograph attached to the 2-m telescope of the Thueringer Landessternwarte Tautenburg.

Francis-99 turbine numerical flow simulation of steady state operation using RANS and RANS/LES turbulence model

NASA Astrophysics Data System (ADS)

Minakov, A.; Platonov, D.; Sentyabov, A.; Gavrilov, A.

2017-01-01

We performed numerical simulation of flow in a laboratory model of a Francis hydroturbine at three regimes, using two eddy-viscosity- (EVM) and a Reynolds stress (RSM) RANS models (realizable k-ɛ, k-ω SST, LRR) and detached-eddy-simulations (DES), as well as large-eddy simulations (LES). Comparison of calculation results with the experimental data was carried out. Unlike the linear EVMs, the RSM, DES, and LES reproduced well the mean velocity components, and pressure pulsations in the diffusor draft tube. Despite relatively coarse meshes and insufficient resolution of the near-wall region, LES, DES also reproduced well the intrinsic flow unsteadiness and the dominant flow structures and the associated pressure pulsations in the draft tube.

COROT mission: accurate stellar photometry

NASA Astrophysics Data System (ADS)

Costes, Vincent; Bodin, Pierre; Levacher, Patrick; Auvergne, Michel

2004-06-01

The COROT mission is dedicated to stellar seismology and search for telluric extra-solar planets. The development is led by CNES in association with French laboratories (LESIA, LAM and IAS) and several European partners (Germany, Belgium, Austria, Spain, ESA and Brasilia). The COROT seismology program will measure periodic variations with amplitude of 2.10 -6 of the photon flux emitted by bright stars. The COROT exoplanet program will detect the presence of exoplanets using the radiometric occultation method. The need is to detect photons flux variations about 7×10-4 for one hour integration time. Such performance will permit to detect occultations on a very large number of stars: magnitude between 12 and 15.5. The satellite Preliminary Design Review has been held on January 2004 while the instrument is already in development phase with a Critical Design Review in April 2004 and a delivery of the flight model in March 2005. The launch is scheduled in June 2006. This paper recalls the mission, describes the payload and its main noise performances.

A search for the cause of cyclical wind variability in O stars. Simultaneous UV and optical observations including magnetic field measurements of the O7.5III star xi Persei

NASA Astrophysics Data System (ADS)

de Jong, J. A.; Henrichs, H. F.; Kaper, L.; Nichols, J. S.; Bjorkman, K.; Bohlender, D. A.; Cao, H.; Gordon, K.; Hill, G.; Jiang, Y.; Kolka, I.; Morrison, N.; Neff, J.; O'Neal, D.; Scheers, B.; Telting, J. H.

2001-03-01

We present the results of an extensive observing campaign on the O7.5 III star xi Persei. The UV observations were obtained with the International Ultraviolet Explorer. xi Per was monitored continuously in October 1994 during 10 days at ultraviolet and visual wavelengths. The ground-based optical observations include magnetic field measurements, Hα and He I lambda 6678 spectra, and were partially covered by photometry and polarimetry. We describe a method to automatically remove the variable contamination of telluric lines in the groundbased spectra. The aim of this campaign was to search for the origin of the cyclical wind variability in this star. We determined a very accurate period of 2.086(2) d in the resonance lines of Si Iv and in the subordinate N Iv and Hα line profiles. The epochs of maximum absorption in the UV resonance lines due to discrete absorption components (DACs) coincide in phase with the maxima in blue-shifted Hα absorption. This implies that the periodic variability originates close to the stellar surface. The phase-velocity relation shows a maximum at -1400 km s-1. The general trend of these observations can be well explained by the corotating interaction region (CIR) model. In this model the wind is perturbed by one or more fixed patches on the stellar surface, which are most probably due to small magnetic field structures. Our magnetic field measurements gave, however, only a null-detection with a 1sigma errorbar of 70 G in the longitudinal component. Some observations are more difficult to fit into this picture. The 2-day period is not detected in the photospheric/transition region line He I lambda 6678. The dynamic spectrum of this line shows a pattern indicating the presence of non-radial pulsation, consistent with the previously reported period of 3.5 h. The edge variability around -2300 km s-1 in the saturated wind lines of C Iv and N V is nearly identical to the edge variability in the unsaturated Si Iv line, supporting the view that this type of variability is also due to the moving DACs. A detailed analysis using Fourier reconstructions reveals that each DAC actually consists of 2 different components: a ``fast'' and a ``slow'' one which merge at higher velocities. Based on observations obtained using the International Ultraviolet Explorer, collected at NASA Goddard Space Flight Center and Villafranca Satellite Tracking Station of the European Space Agency.

Servo Driven Corotation: Development of AN Inertial Clock.

NASA Astrophysics Data System (ADS)

Cheung, Wah-Kwan Stephen

An inertial clock to test non-metricity of gravity is proposed here. A first, room-temperature, servo corotation -protected, double magnetically suspended precision rotor system is developed for this purpose. The specific goal was to exhibit the properties of such a clock in its entirety at whatever level of precision was achievable. A monolithic system has been completed for these preliminary studies. It includes particular development of individual experimental sub-systems (a hybrid double magnetic suspension; a diffusion pumping system; a microcomputer -controlled eddy-current drive system; and the angular period measuring schemes for the doubly suspended rotors). Double magnetic suspension had been investigated by Beams for other purposes. The upper transducer is optical but parametrized and the lower transducer employs the frequency modulation characteristic of a LC tank circuit. The doubly suspended rotors corotate so that the upper rotor is servoed to rotate at the same angular velocity as that of the lower rotor. This creates a "drag free" environment for the lower rotor and effectively eliminates the gas drag on the lower rotor. Consequently, the decay time constant of the lower rotor increases. With other means of protection, the lower rotor will then, with perfect system operation, suffer no drag and therefore become the inertial time keeper. A commercial microcomputer is introduced to execute the servo-corotation. The tests thus far are, with one exception, run at atmospheric pressure. An idealized analysis for open and closed loop corotation is shown. Such analysis includes only the viscous drag acting on the corotating rotors. The analysis suggests that angular position control be added to the present feedback drive which is of derivative nature only. Open and closed corotation runs show that a strong torsional coupling besides that of the gas drag exists between the rotors. When misalignment of the support pole pieces is deliberately made significant, a stronger coupling between the rotors results. The coupling is suspected to be magnetic in nature. The complicated geometry of the double magnetic suspension scheme makes it difficult to evaluate the known mechanical cranking effect applied to this situation.

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

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

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

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

Long-Term Photometric and Spectroscopic Behavior of a Symbiotic System AG DRA

NASA Astrophysics Data System (ADS)

Gális, R.; Hric, L.; Petrík, K.

A symbiotic binary, AG Dra, is studied using long-term photometry and radial velocity measurements. New radial velocities confirm the presence of a second period, found in our previous analysis, which could be due to pulsation of the cool component of the AG Dra system.

The use of twin screw extruders for feeding coal against pressures of up to 1500 PSI

NASA Technical Reports Server (NTRS)

Wiedmann, W.; Mack, W. A.

1977-01-01

Recent tests with a twin-screw, co-rotating extruder which was successfully used to convey and feed coal against pressures of up to 1500 psi are described. Intermeshing and self-wiping, co-rotating twin-screws give greatly improved conveying and pressure built-up capabilities and avoid hangup and eventual decomposition of coal particles in the screw flights. The conveying action of intermeshing, self-wiping, co-rotating extruder systems approaches that of a positive displacement pump. With this feature, it is possible to maintain very accurate control over all aspects of product conveyance in the extruder, i.e., intake, conveyance and pressure buildup.

VizieR Online Data Catalog: Corot photometry of TYC 455-791-1 (Strassmeier+, 2017)

NASA Astrophysics Data System (ADS)

Strassmeier, K. G.; Granzer, T.; Mallonn, M.; Weber, M.; Weingrill, J.

2016-11-01

From the original CoRoT white-light flux obtained on two consecutive runs, we filter out obvious outliers from the SAA (south Atlantic Anomaly). The third column are the remaining CoRoT data points. The two data set were merged using individual zero-points of 716386.54e- for the first data set and 721882.56e- for the second data set, respectively. The magnitudes thus calculates are in column four. The last column is the combined model of the transit plus a 12th order Fourier-series fit to the out-of-transit data. (1 data file).

Consistent linearization of the element-independent corotational formulation for the structural analysis of general shells

NASA Technical Reports Server (NTRS)

Rankin, C. C.

1988-01-01

A consistent linearization is provided for the element-dependent corotational formulation, providing the proper first and second variation of the strain energy. As a result, the warping problem that has plagued flat elements has been overcome, with beneficial effects carried over to linear solutions. True Newton quadratic convergence has been restored to the Structural Analysis of General Shells (STAGS) code for conservative loading using the full corotational implementation. Some implications for general finite element analysis are discussed, including what effect the automatic frame invariance provided by this work might have on the development of new, improved elements.

Inference of the angular velocity of plasma in the Jovian magnetosphere from the sweepback of magnetic field

NASA Technical Reports Server (NTRS)

Khurana, Krishan K.; Kivelson, Margaret G.

1993-01-01

The averaged angular velocity of plasma from magnetic observations is evaluated using plasma outflow rate as a parameter. New techniques are developed to calculate the normal and azimuthal components of the magnetic field in and near to the plasma sheet in a plasma sheet coordinate system. The revised field components differ substantially from the quantities used in previous analyses. With the revised field values, it appears that during the Voyager 2 flyby for an outflow rate of 2.5 x 10 exp 29 amu/s, the observed magnetic torque may be sufficient to keep the plasma in corotation to radial distances of 50 Rj in the postmidnight quadrant.

The COROT ground-based archive and access system

NASA Astrophysics Data System (ADS)

Solano, E.; González-Riestra, R.; Catala, C.; Baglin, A.

2002-01-01

A prototype of the COROT ground-based archive and access system is presented here. The system has been developed at LAEFF and it is based on the experience gained at Laboratorio de Astrofisica Espacial y Fisica Fundamental (LAEFF) with the INES (IUE Newly Extracted System) Archive.

Long-Period Variability in o Ceti

NASA Astrophysics Data System (ADS)

Templeton, Matthew R.; Karovska, Margarita

2009-02-01

We carried out a new and sensitive search for long-period variability in the prototype of the Mira class of long-period pulsating variables, o Ceti (Mira A), the closest and brightest Mira variable. We conducted this search using an unbroken light curve from 1902 to the present, assembled from the visual data archives of five major variable star observing organizations from around the world. We applied several time-series analysis techniques to search for two specific kinds of variability: long secondary periods (LSPs) longer than the dominant pulsation period of ~333 days, and long-term period variation in the dominant pulsation period itself. The data quality is sufficient to detect coherent periodic variations with photometric amplitudes of 0.05 mag or less. We do not find evidence for coherent LSPs in o Ceti to a limit of 0.1 mag, where the amplitude limit is set by intrinsic, stochastic, low-frequency variability of approximately 0.1 mag. We marginally detect a slight modulation of the pulsation period similar in timescale to that observed in the Miras with meandering periods, but with a much lower period amplitude of ±2 days. However, we do find clear evidence of a low-frequency power-law component in the Fourier spectrum of o Ceti's long-term light curve. The amplitude of this stochastic variability is approximately 0.1 mag at a period of 1000 days, and it exhibits a turnover for periods longer than this. This spectrum is similar to the red noise spectra observed in red supergiants.

Transiting exoplanets from the CoRoT space mission. VIII. CoRoT-7b: the first super-Earth with measured radius

NASA Astrophysics Data System (ADS)

Léger, A.; Rouan, D.; Schneider, J.; Barge, P.; Fridlund, M.; Samuel, B.; Ollivier, M.; Guenther, E.; Deleuil, M.; Deeg, H. J.; Auvergne, M.; Alonso, R.; Aigrain, S.; Alapini, A.; Almenara, J. M.; Baglin, A.; Barbieri, M.; Bruntt, H.; Bordé, P.; Bouchy, F.; Cabrera, J.; Catala, C.; Carone, L.; Carpano, S.; Csizmadia, Sz.; Dvorak, R.; Erikson, A.; Ferraz-Mello, S.; Foing, B.; Fressin, F.; Gandolfi, D.; Gillon, M.; Gondoin, Ph.; Grasset, O.; Guillot, T.; Hatzes, A.; Hébrard, G.; Jorda, L.; Lammer, H.; Llebaria, A.; Loeillet, B.; Mayor, M.; Mazeh, T.; Moutou, C.; Pätzold, M.; Pont, F.; Queloz, D.; Rauer, H.; Renner, S.; Samadi, R.; Shporer, A.; Sotin, Ch.; Tingley, B.; Wuchterl, G.; Adda, M.; Agogu, P.; Appourchaux, T.; Ballans, H.; Baron, P.; Beaufort, T.; Bellenger, R.; Berlin, R.; Bernardi, P.; Blouin, D.; Baudin, F.; Bodin, P.; Boisnard, L.; Boit, L.; Bonneau, F.; Borzeix, S.; Briet, R.; Buey, J.-T.; Butler, B.; Cailleau, D.; Cautain, R.; Chabaud, P.-Y.; Chaintreuil, S.; Chiavassa, F.; Costes, V.; Cuna Parrho, V.; de Oliveira Fialho, F.; Decaudin, M.; Defise, J.-M.; Djalal, S.; Epstein, G.; Exil, G.-E.; Fauré, C.; Fenouillet, T.; Gaboriaud, A.; Gallic, A.; Gamet, P.; Gavalda, P.; Grolleau, E.; Gruneisen, R.; Gueguen, L.; Guis, V.; Guivarc'h, V.; Guterman, P.; Hallouard, D.; Hasiba, J.; Heuripeau, F.; Huntzinger, G.; Hustaix, H.; Imad, C.; Imbert, C.; Johlander, B.; Jouret, M.; Journoud, P.; Karioty, F.; Kerjean, L.; Lafaille, V.; Lafond, L.; Lam-Trong, T.; Landiech, P.; Lapeyrere, V.; Larqué, T.; Laudet, P.; Lautier, N.; Lecann, H.; Lefevre, L.; Leruyet, B.; Levacher, P.; Magnan, A.; Mazy, E.; Mertens, F.; Mesnager, J.-M.; Meunier, J.-C.; Michel, J.-P.; Monjoin, W.; Naudet, D.; Nguyen-Kim, K.; Orcesi, J.-L.; Ottacher, H.; Perez, R.; Peter, G.; Plasson, P.; Plesseria, J.-Y.; Pontet, B.; Pradines, A.; Quentin, C.; Reynaud, J.-L.; Rolland, G.; Rollenhagen, F.; Romagnan, R.; Russ, N.; Schmidt, R.; Schwartz, N.; Sebbag, I.; Sedes, G.; Smit, H.; Steller, M. B.; Sunter, W.; Surace, C.; Tello, M.; Tiphène, D.; Toulouse, P.; Ulmer, B.; Vandermarcq, O.; Vergnault, E.; Vuillemin, A.; Zanatta, P.

2009-10-01

Aims: We report the discovery of very shallow (Δ F/F ≈ 3.4× 10-4), periodic dips in the light curve of an active V = 11.7 G9V star observed by the CoRoT satellite, which we interpret as caused by a transiting companion. We describe the 3-colour CoRoT data and complementary ground-based observations that support the planetary nature of the companion. Methods: We used CoRoT colours information, good angular resolution ground-based photometric observations in- and out- of transit, adaptive optics imaging, near-infrared spectroscopy, and preliminary results from radial velocity measurements, to test the diluted eclipsing binary scenarios. The parameters of the host star were derived from optical spectra, which were then combined with the CoRoT light curve to derive parameters of the companion. Results: We examined all conceivable cases of false positives carefully, and all the tests support the planetary hypothesis. Blends with separation >0.40´´or triple systems are almost excluded with a 8 × 10-4 risk left. We conclude that, inasmuch we have been exhaustive, we have discovered a planetary companion, named CoRoT-7b, for which we derive a period of 0.853 59 ± 3 × 10-5 day and a radius of Rp = 1.68 ± 0.09 R_Earth. Analysis of preliminary radial velocity data yields an upper limit of 21 M_Earth for the companion mass, supporting the finding. Conclusions: CoRoT-7b is very likely the first Super-Earth with a measured radius. This object illustrates what will probably become a common situation with missions such as Kepler, namely the need to establish the planetary origin of transits in the absence of a firm radial velocity detection and mass measurement. The composition of CoRoT-7b remains loosely constrained without a precise mass. A very high surface temperature on its irradiated face, ≈1800-2600 K at the substellar point, and a very low one, ≈50 K, on its dark face assuming no atmosphere, have been derived. The CoRoT space mission, launched on 27 December 2006, has been developed and is operated by CNES, with the contribution of Austria, Belgium, Brazil, ESA, Germany, and Spain. First CoRoT data are available to the public from the CoRoT archive: http://idoc-corot.ias.u-psud.fr. The complementary observations were obtained with MegaPrime/MegaCam, a joint project of CFHT and CEA/DAPNIA, at the Canada-France-Hawaii Telescope (CFHT) which is operated by NRC in Canada, INSU-CNRS in France, and the University of Hawaii; ESO Telescopes at the La Silla and Paranal Observatories under programme ID 081.C-0413(C), DDT 282.C-5015; the IAC80 telescope operated by the Instituto de Astrofísica de Tenerife at the Observatorio del Teide; the Isaac Newton Telescope (INT), operated on the island of La Palma by the Isaac Newton group in the Spanish Observatorio del Roque de Los Muchachos of the Instituto de Astrofisica de Canarias; and at the Anglo-Australian Telescope that have been funded by the Optical Infrared Coordination network (OPTICON), a major international collaboration supported by the Research Infrastructures Programme of the European Commissions Sixth Framework Programme; Radial-velocity observations were obtained with the SOPHIE spectrograph at the 1.93m telescope of Observatoire de Haute Provence, France.

Second harmonic poloidal waves observed by Van Allen Probes in the dusk-midnight sector

DOE PAGES

Min, Kyungguk; Takahashi, Kazue; Ukhorskiy, Aleksandr Y.; ...

2017-02-24

This paper presents observations of ultralow-frequency (ULF) waves from Van Allen Probes. The event that generated the ULF waves occurred 2 days after a minor geomagnetic storm during a geomagnetically quiet time. Narrowband pulsations with a frequency of about 7 mHz with moderate amplitudes were registered in the premidnight sector when Probe A was passing through an enhanced density region near geosynchronous orbit. Probe B, which passed through the region earlier, did not detect the narrowband pulsations but only broadband noise. Despite the single-spacecraft measurements, we were able to determine various wave properties. We find that the observed waves aremore » a second harmonic poloidal mode propagating westward with an azimuthal wave number estimated to be ~100; the magnetic field fluctuations have a finite compressional component due to small but finite plasma beta (~0.1); the energetic proton fluxes in the energy ranging from above 10 keV to about 100 keV exhibit pulsations with the same frequency as the poloidal mode and energy-dependent phase delays relative to the azimuthal component of the electric field, providing evidence for drift-bounce resonance; and the second harmonic poloidal mode may have been excited via the drift-bounce resonance mechanism with free energy fed by the inward radial gradient of ~80 keV protons. Here, we show that the wave active region is where the plume overlaps the outer edge of ring current and suggest that this region can have a wide longitudinal extent near geosynchronous orbit.« less

Second harmonic poloidal waves observed by Van Allen Probes in the dusk-midnight sector

DOE Office of Scientific and Technical Information (OSTI.GOV)

Min, Kyungguk; Takahashi, Kazue; Ukhorskiy, Aleksandr Y.

This paper presents observations of ultralow-frequency (ULF) waves from Van Allen Probes. The event that generated the ULF waves occurred 2 days after a minor geomagnetic storm during a geomagnetically quiet time. Narrowband pulsations with a frequency of about 7 mHz with moderate amplitudes were registered in the premidnight sector when Probe A was passing through an enhanced density region near geosynchronous orbit. Probe B, which passed through the region earlier, did not detect the narrowband pulsations but only broadband noise. Despite the single-spacecraft measurements, we were able to determine various wave properties. We find that the observed waves aremore » a second harmonic poloidal mode propagating westward with an azimuthal wave number estimated to be ~100; the magnetic field fluctuations have a finite compressional component due to small but finite plasma beta (~0.1); the energetic proton fluxes in the energy ranging from above 10 keV to about 100 keV exhibit pulsations with the same frequency as the poloidal mode and energy-dependent phase delays relative to the azimuthal component of the electric field, providing evidence for drift-bounce resonance; and the second harmonic poloidal mode may have been excited via the drift-bounce resonance mechanism with free energy fed by the inward radial gradient of ~80 keV protons. Here, we show that the wave active region is where the plume overlaps the outer edge of ring current and suggest that this region can have a wide longitudinal extent near geosynchronous orbit.« less

Identification and period investigation of pulsation variable star UY Camelopardalis, an RR Lyrae star in binary system

NASA Astrophysics Data System (ADS)

Li, Lin-Jia; Qian, Sheng-Bang; Voloshina, Irina; Metlov, Vladimir G.; Zhu, Li-Ying; Liao, Wen-Ping

2018-06-01

We present photometric measurements of the short period variable star UY Cam, which has been classified as a δ Scuti or c-type RR Lyrae (RRc) variable in different catalogs. Based on the analyses on Fourier coefficients and (NUV - V)0, we find that UY Cam is probably an RRc star. We obtain 58 new times of light maximum for UY Cam based on several sky surveys and our observations. Combining these with the times of light maximum in literature, a total of 154 times of light maximum are used to analyze the O - C diagram of UY Cam. The results show that the O - C pattern can be described by a downward parabolic component with a rate of -6.86 ± 0.47 × 10-11 d d-1, and a cyclic variation with a period of 65.7 ± 2.4 yr. We suppose these components are caused by the stellar evolution and the light travel time effect (LiTE) of a companion in elliptical orbit, respectively. By calculation, the minimum mass of the potential companion is about 0.17 M⊙, and its mass should be less than or equal to the pulsation primary star when the inclination i > 22.5°D. Therefore, the companion should be a low-mass star, like a late-type main-sequence star or a white dwarf. Due to the unique property of UY Cam, we suggest that more observations and studies on UY Cam and other RRc stars are needed to check the nature of these stars, including the pulsations and binarities.

[Assessment of blood flow in the middle cerebral artery and the umbilical artery in fetuses with umbilical venous pulsations].

PubMed

Borowski, Dariusz; Czuba, Bartosz; Kaczmarek, Piotr; Włoch, Agata; Pawłowicz, Paweł; Wyrwas, Dorota; Wielgos, Mirosław; Sodowski, Krzysztof; Szaflik, Krzysztof

2006-03-01

Umbilical venous pulsation is an important sign of hemodynamic compromise, especially during fetal heart failure and asphyxia. The aim of this study was to determine of the blow flow in the middle cerebral artery and the umbilical artery in fetuses with umbilical venous pulsations. The investigation included 18 fetuses with signs of the intrauterine growth restriction and umbilical venous pulsations after 28th weeks of gestation. We evaluated cerebral-placental ratio (CPR) and pulsation index (PI) in the middle cerebral artery (MCA) and the umbilical artery (UA). We observed brain sparring effect in all cases of analyzing fetuses. There were 77,8% of abnormal flow pattern in umbilical artery. 13 fetuses had a single pulsation pattern in umbilical vein and another 5 had double pulsation pattern. The coexistence of umbilical vein pulsation and abnormal flow pattern in umbilical artery is closely related to increased perinatal mortality.

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.

Dynamics of multiple bodies in a corotation resonance

NASA Astrophysics Data System (ADS)

A'Hearn, Joseph; Hedman, Matthew

2018-04-01

The orbital evolution of multiple massive bodies trapped in the same corotation resonance site has not yet been studied in depth, but could be relevant to the origins and history of small moons like Saturn's moon Aegaeon. We conduct numerical simulations of multiple bodies trapped within a corotation resonance and examine what happens to these bodies when they have close encounters. Compared to simulations with equal mass bodies, simulations with one body more massive than the others may be more likely to feature an asymmetry in the phase space of semi-major axis and mean longitude. That is, bodies on one side of phase space have a slightly greater tendency to lose angular momentum, while bodies on the other side gain angular momentum. With this asymmetry, the transfer of angular momentum during gravitational encounters makes it more likely for the most massive body rather than other bodies to approach the center of the corotation site. More work is needed to determine if this sort of process can significantly affect the orbital evolution of small moons like Aegaeon.

Strong Ionospheric Electron Heating Associated With Pulsating Auroras - A Swarm Survey

NASA Astrophysics Data System (ADS)

Liang, J.; Yang, B.; Burchill, J. K.; Donovan, E.; Knudsen, D. J.

2016-12-01

A pulsating aurora is a repetitive modulation of auroral luminosity with periods typically of the order of 1-30 sec. It is often observed in the equatorward portion of the auroral oval. While it is generally recognized that the ultimate source of the pulsating auroral precipitation comes from energetic electrons of magnetospheric origin, investigating the ionospheric signature of the pulsating aurora may offer clues to the magnetosphere-ionosphere coupling aspect of the pulsating aurora and, under certain circumstance, to the generation mechanism of the pulsating aurora. In this study, we perform an extensive survey on the ionospheric signatures (electron temperature, plasma density and field-aligned current etc.) of pulsating auroras using Swarm satellite data. Via the survey we repeatedly identify a strong electron temperature enhancement associated with the pulsating aurora. On average, the electron temperature at Swarm satellite altitude ( 500 km) increases from 2100 K at subauroral altitudes to a peak of 2900 K upon entering the pulsating aurora patch. This indicates that the pulsating auroras may act as an important heating source of the nightside ionosphere/thermosphere. On the other hand, no well-defined trend of plasma density variation associated with pulsating auroras is identified in the survey. There often exist moderate upward field-aligned currents (up to a few mA/m2) within the pulsating auroral patch when the patch is "on" during the traversal of satellites [Gillies et al., 2015], and the electron temperature enhancement is found to be positively correlated with the magnitude of the field-aligned current. In a few events with high-resolution Swarm electric field instrument (EFI) data, we find that the on-time pulsating auroral patch is associated with structured electric field disturbances with peaks exceeding 10 mV/m. Based upon observations and ionospheric models, we consider and evaluate several possible mechanisms that may account for the strong electron heating associated with the pulsating aurora, including the Joule heating related to the field-aligned current and to the structured electric field, the backscattered secondary electrons led by the impact of pulsating auroral precipitation, and the vertical conductive heat transport.

Studies of the Long Secondary Periods in Pulsating Red Giants. II. Lower-Luminosity Stars

NASA Astrophysics Data System (ADS)

Percy, J. R.; Leung, H. W.

2017-06-01

We have used AAVSO visual and photoelectric V data, and the AAVSO time-series package VSTAR and the Lomb-Scargle time-series algorithm to determine improved pulsation periods, "long secondary periods" (LSPs), and their amplitudes in 51 shorter-period pulsating red giants in the AAVSO photoelectric photometry program, and in the AAVSO long-period variable (LPV) binocular program. As is well known, radial pulsation becomes detectable in red giants at about spectral type M0, with periods of about 20 days. We find that the LSP phenomenon is also first detectable at about M0. Pulsation and LSP amplitudes increase from near zero to about 0.1 at pulsation periods of 100 days. At longer periods, the pulsation amplitudes continue to increase, but the LSP amplitudes are generally between 0.1 and 0.2 on average. The ratios of LSP to pulsation period cluster around 5 and 10, presumably depending on whether the pulsation period is the fundamental or first overtone. The pulsation and LSP phase curves are generally close to sinusoidal, except when the amplitude is small, in which case they may be distorted by observational scatter or, in the case of the LSP amplitude, by the pulsational variability. As with longer-period stars, the LSP amplitude i ncreases and decreases by a factor of two or more, for unknown reasons, on a time scale of about 20 LSPs. The LSP phenomenon is thus present and similar in radially pulsating red giants of all periods. Its cause remains unknown.

Mode extraction from time series: from the challenges of COROT to those of Eddington

NASA Astrophysics Data System (ADS)

Appourchaux, T.; Moreira, O.; Berthomieu, G.; Toutain, T.

2004-01-01

With more than 30 years of experience in extraction of eigenmodes from power spectra of solar signals, we are now almost ready to apply this knowledge onto the forecoming missions: COROT and Eddington. However the fitting task differs by 3 orders of magnitude; COROT will be able to get time series of stellar light for some 30 stars, while Eddington will be able to gather such data for about 50000 stars. While for COROT, our current tools can be applied by hand, the case of Eddington is significantly more complex. We are looking forward having automatic fitting procedures that will allow to recover mode parameters for about 90% of the solar-like stars. Unfortunately, about 10% of these stars will require some more delicate attention that will cost time to take care of. We will use the example of the infamous HD 57006, known to be quite evolved with a difficult eigenmode spectrum, to explain how a star can evolve from an easy-to-fit target (90% of the solar-like stars) to a difficult-to-fit (10% of the remaining stars). In the latter case, new techniques for detecting narrow peaks (g-mode like) out of broad peaks (p-mode like) has been devised in the context of the hare-and-hound exercise of COROT. This and other techniques will be used to implement the automatic fitting procedure for the remaining 10% of Eddington solar-like stars.

Radiation effects on space-based stellar photometry: theoretical models and empirical results for CoRoT Space Telescope

NASA Astrophysics Data System (ADS)

Pinheiro da Silva, L.; Rolland, G.; Lapeyrere, V.; Auvergne, M.

2008-03-01

Convection, Rotation and planetary Transits (CoRoT) is a space mission dedicated to stellar seismology and the search for extrasolar planets. Both scientific programs are based on very high precision photometry and require long, uninterrupted observations. The instrument is based on an afocal telescope and a wide-field camera, consisting of four E2V-4280 CCD devices. This set is mounted on a recurrent platform for insertion in low Earth orbit. The CoRoT satellite has been recently launched for a nominal mission duration of three years. In this work, we discuss the impact of space radiation on CoRoT CCDs, in sight of the in-flight characterization results obtained during the satellite's commissioning phase, as well as the very first observational data. We start by describing the population of trapped particles at the satellite altitude, and by presenting a theoretical prediction for the incoming radiation fluxes seen by the CCDs behind shielding. Empirical results regarding particle impact rates and their geographical distribution are then presented and discussed. The effect of particle impacts is also statistically characterized, with respect to the ionizing energy imparted to the CCDs and the size of impact trails. Based on these results, we discuss the effects of space radiation on precise and time-resolved stellar photometry from space. Finally, we present preliminary results concerning permanent radiation damage on CoRoT CCDs, as extrapolated from the data available at the beginning of the satellite's lifetime.

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.

A 0.8-2.4 μm Transmission spectrum of the hot Jupiter CoRoT-1b

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schlawin, E.; Herter, T.; Zhao, M.

Hot Jupiters with brightness temperatures ≳2000 K can have TiO and VO molecules as gaseous species in their atmospheres. The TiO and VO molecules can potentially induce temperature inversions in hot Jupiter atmospheres and also have an observable signature of large optical to infrared transit depth ratios. Previous transmission spectra of very hot Jupiters have shown a lack of TiO and VO, but only in planets that also appear to lack temperature inversions. We measure the transmission spectrum of CoRoT-1b, a hot Jupiter that was predicted to have a temperature inversion potentially due to significant TiO and VO in itsmore » atmosphere. We employ the multi-object spectroscopy method using the SpeX and MORIS instruments on the Infrared Telescope Facility (IRTF) and the Gaussian process method to model red noise. By using a simultaneous reference star on the slit for calibration and a wide slit to minimize slit losses, we achieve transit depth precision of 0.03%-0.09%, comparable to the atmospheric scale height but detect no statistically significant molecular features. We combine our IRTF data with optical CoRoT transmission measurements to search for differences in the optical and near-infrared absorption that would arise from TiO/VO. Our IRTF spectrum and the CoRoT photometry disfavor a TiO/VO-rich spectrum for CoRoT-1b, suggesting that the atmosphere has another absorber that could create a temperature inversion or that the blackbody-like emission from the planet is due to a spectroscopically flat cloud, dust, or haze layer that smoothes out molecular features in both CoRoT-1b's emission and transmission spectra. This system represents the faintest planet hosting star (K = 12.2) with a measured planetary transmission spectrum.« less

Effect of isoproterenol, phenylephrine, and sodium nitroprusside on fundus pulsations in healthy volunteers.

PubMed

Schmetterer, L; Wolzt, M; Salomon, A; Rheinberger, A; Unfried, C; Zanaschka, G; Fercher, A F

1996-03-01

Recently a laser interferometric method for topical measurement of fundus pulsations has been developed. Fundus pulsations in the macular region are caused by the inflow and outflow of blood into the choroid. The purpose of this work was to study the influence of a peripheral vasoconstricting (the alpha 1 adrenoceptor agonist phenylephrine), a predominantly positive inotropic (the non-specific beta adrenoceptor agonist isoproterenol), and a non-specific vasodilating (sodium nitroprusside) model drug on ocular fundus pulsations to determine reproducibility and sensitivity of the method. In a double masked randomised crossover study the drugs were administered in stepwise increasing doses to 10 male and nine female healthy volunteers. Systemic haemodynamic variables and fundus pulsations were measured at all infusion steps. Fundus pulsation increased during infusion of isoproterenol with statistical significance versus baseline at the lowest dose of 0.1 microgram/min. Neither peripheral vasoconstriction nor peripheral vasodilatation affected the ocular fundus pulsations. Measurements of fundus pulsations is a highly reproducible method in healthy subjects with low ametropy. Changes of local pulsatile ocular blood flow were detectable with our method following the infusion of isoproterenol. As systemic pharmacological vasodilatation or vasoconstriction did not change fundus pulsations, further experimental work has to be done to evaluate the sensitivity of the laser interferometric fundus pulsation measurement in various eye diseases.

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 flow in that channel. Because the Santa Anita Wash tests afforded excellent data for analysis, further development of the photographic ,technique at Haines Creek was discontinued. Three methods for obtaining the data needed to compute discharge during pulsating flow are proposed. In two of the methods--the photographic method and the depth-recorder method--the dimensions and velocities of translatory waves are recorded, and discharge is then computed by the procedure developed in this report. The third method?the constant-rate-dye-dilution method--yields the discharge more directly. The discharge is computed from the dye-injection rate and the ratio of the concentration of dye in the injected solution to the concentration of dye in the water sampled at a site downstream. The three methods should be developed and tested in ,the Santa Anita Wash flood control channel under controlled conditions similar to those in the test of April 1965.

Transiting exoplanets from the CoRoT space mission. XXVII. CoRoT-28b, a planet orbiting an evolved star, and CoRoT-29b, a planet showing an asymmetric transit

NASA Astrophysics Data System (ADS)

Cabrera, J.; Csizmadia, Sz.; Montagnier, G.; Fridlund, M.; Ammler-von Eiff, M.; Chaintreuil, S.; Damiani, C.; Deleuil, M.; Ferraz-Mello, S.; Ferrigno, A.; Gandolfi, D.; Guillot, T.; Guenther, E. W.; Hatzes, A.; Hébrard, G.; Klagyivik, P.; Parviainen, H.; Pasternacki, Th.; Pätzold, M.; Sebastian, D.; Tadeu dos Santos, M.; Wuchterl, G.; Aigrain, S.; Alonso, R.; Almenara, J.-M.; Armstrong, J. D.; Auvergne, M.; Baglin, A.; Barge, P.; Barros, S. C. C.; Bonomo, A. S.; Bordé, P.; Bouchy, F.; Carpano, S.; Chaffey, C.; Deeg, H. J.; Díaz, R. F.; Dvorak, R.; Erikson, A.; Grziwa, S.; Korth, J.; Lammer, H.; Lindsay, C.; Mazeh, T.; Moutou, C.; Ofir, A.; Ollivier, M.; Pallé, E.; Rauer, H.; Rouan, D.; Samuel, B.; Santerne, A.; Schneider, J.

2015-07-01

Context. We present the discovery of two transiting extrasolar planets by the satellite CoRoT. Aims: We aim at a characterization of the planetary bulk parameters, which allow us to further investigate the formation and evolution of the planetary systems and the main properties of the host stars. Methods: We used the transit light curve to characterize the planetary parameters relative to the stellar parameters. The analysis of HARPS spectra established the planetary nature of the detections, providing their masses. Further photometric and spectroscopic ground-based observations provided stellar parameters (log g, Teff, v sin i) to characterize the host stars. Our model takes the geometry of the transit to constrain the stellar density into account, which when linked to stellar evolutionary models, determines the bulk parameters of the star. Because of the asymmetric shape of the light curve of one of the planets, we had to include the possibility in our model that the stellar surface was not strictly spherical. Results: We present the planetary parameters of CoRoT-28b, a Jupiter-sized planet (mass 0.484 ± 0.087 MJup; radius 0.955 ± 0.066 RJup) orbiting an evolved star with an orbital period of 5.208 51 ± 0.000 38 days, and CoRoT-29b, another Jupiter-sized planet (mass 0.85 ± 0.20 MJup; radius 0.90 ± 0.16 RJup) orbiting an oblate star with an orbital period of 2.850 570 ± 0.000 006 days. The reason behind the asymmetry of the transit shape is not understood at this point. Conclusions: These two new planetary systems have very interesting properties and deserve further study, particularly in the case of the star CoRoT-29. The CoRoT space mission, launched on December 27th 2006, was developed and is operated by CNES, with the contribution of Austria, Belgium, Brazil, ESA (RSSD and Science Programme), Germany, and Spain. Based on observations obtained with 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, in time allocated by OPTICON and the Spanish Time Allocation Committee (CAT). The research leading to these results has received funding from the European Community's Seventh Framework Programme (FP7/2007-2013) under grant agreement number RG226604 (OPTICON). This work makes use of observations from the LCOGT network.Appendices are available in electronic form at http://www.aanda.org

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.

Comment on "Pulsating Auroras Produced by Interactions of Electrons and Time Domain Structures" by Mozer Et Al.

NASA Astrophysics Data System (ADS)

Nishimura, Y.; Bortnik, J.; Li, W.; Angelopoulos, V.; Donovan, E. F.; Spanswick, E. L.

2018-03-01

Mozer et al. (2017, https://doi.org/10.1002/2017JA024223) suggested that time domain structures (TDSs) drive pulsating aurora (with additional contributions by kinetic Alfvén waves (KAWs)) and that chorus waves have negligible effects. In this comment, we point out that electrons scattered by TDS or KAW (dominantly at 0.1-3 keV, <1 s modulation) cannot explain key features of pulsating aurora, which require precipitation above a few keV with a couple of tens of second modulation. Their study did not conduct quantitative evaluations of wave-aurora correlation. The use of short burst mode data ( <10 s) may only cover a single pulse of pulsating aurora and is not suitable for examining connections to pulsating aurora. "Field-aligned" electrons do not necessarily represent loss cone population, and their characteristic energy (hundreds of eV) is much lower than typical precipitation over pulsating aurora. By reexamining the events studied by Mozer et al., we quantitatively demonstrate that TDS and KAW are uncorrelated with pulsating aurora and that only chorus waves showed high correlations with pulsating aurora. Occasional simultaneous occurrence of TDS/KAW and pulsating aurora is found to be coincidental, because the correlation over a time scale of minutes is poor. Several auroral features analyzed in that paper are not pulsating aurora but other types of aurora. We also show that the chorus-pulsating aurora correlation can last for 2 h or longer and can be used to highlight dynamic changes in magnetic field mapping. Chorus waves can resonate with electrons above a few keV and are in agreement with pulsating auroral properties.

Coevality in Young Eclipsing Binaries

NASA Astrophysics Data System (ADS)

Simon, M.; Toraskar, Jayashree

2017-06-01

The ages of the components in very short period pre-main-sequence (PMS) binaries are essential to an understanding of their formation. We considered a sample of seven PMS eclipsing binaries (EBs) with ages 1-6.3 MY and component masses 0.2-1.4 {M}⊙ . The very high precision with which their masses and radii have been measured and the capability provided by the Modules for Experiments in Stellar Astrophysics to calculate their evolutionary tracks at exactly the measured masses allows the determination of age differences of the components independent of their luminosities and effective temperatures. We found that the components of five EBs, ASAS J052821+0338.5, Parenago 1802, JW 380, CoRoT 223992193, and UScoCTIO 5, formed within 0.3 MY of each other. The parameters for the components of V1174 Ori imply an implausible large age difference of 2.7 MY and should be reconsidered. The seventh EB in our sample, RX J0529.4+0041 fell outside the applicability of our analysis.

Ionospheric electron heating associated with pulsating auroras: joint optical and PFISR observations

NASA Astrophysics Data System (ADS)

Liang, J.; Donovan, E.; Spanswick, E.; Reimer, A.; Hampton, D. L.; Varney, R. H.

2017-12-01

In a recent survey based upon Swarm satellite data, Liang et al. [2017] repeatedly identified a strong electron temperature (Te) enhancement associated with the pulsating aurora at Swarm altitudes ( 460 km). The observation of Te enhancement is not contingent upon whether the pulsating patch is "on" or "off" at the satellite traversal epoch. In this study, we use joint optical and Poker Flat Incoherent Scatter Radar (PFISR) observations to further investigate the 4D (space-time) variations of the Te enhancement in association with the pulsating aurora. In a long-lasting pulsating auroral event on 19 March 2015, we identify strong Te enhancements ( 600-1200 K) in the upper F-region ionosphere ( 300-600 km altitude) in conjunction to the passage of pulsating auroras over PFISR beams. The spatial-temporal variations of PFISR Te enhancement are found to generally conform to the variations of pulsating auroras. However, collocated meridian spectrograph observations suggest that the pulsating auroras of interest are composed of energetic electron precipitation with characteristic energy ≥10 keV, which is not supposed to be efficient in heating electrons in the upper F-region. On the other hand, only moderate (<27%) Ne enhancements are found in the upper F-region during the pulsating aurora and Te enhancement interval. There are also moderate Te enhancements ( 100 K) in the E-region accompanying the pulsating auroras, but no clue of Te enhancement is found in the lower F-region. Based upon the above observations and simulations using the model developed in Liang et al. [2017], we propose that thermal conduction from the topside ionosphere, led by magnetospheric heat fluxes, constitutes the most likely underlying mechanism for the upper F-region electron heating associated with pulsating auroras. Such magnetospheric heat fluxes may be pertinent to one long-hypothesized feature of pulsating auroras, namely the existence of an enhanced low-energy plasma population in magnetospheric magnetic flux tubes threading the pulsating auroral patch. Liang, J. B. Yang, E. Donovan, J. Burchill, and D. Knudsen (2017), Ionospheric electron heating associated with pulsating auroras: A Swarm survey and model simulation, JGRA53073, in press

Multiyear and multisite photometric campaigns on the bright high-amplitude pulsating subdwarf B star EC 01541-1409

NASA Astrophysics Data System (ADS)

Reed, M. D.; Kilkenny, D.; O'Toole, S.; Østensen, R. H.; Honer, C.; Gilker, J. T.; Quint, A. C.; Doennig, A. M.; Hicks, L. H.; Thompson, M. A.; McCart, P. A.; Zietsman, E.; Chen, W.-P.; Chen, C.-W.; Lin, C.-C.; Beck, P.; Degroote, P.; Barlow, B. N.; Reichart, D. E.; Nysewander, M. C.; Lacluyze, A. P.; Ivarsen, K. M.; Haislip, J. B.; Baran, A.; Winiarski, M.; Drozdz, M.

2012-03-01

We present follow-up observations of the pulsating subdwarf B (sdB) star EC 01541-1409 as part of our efforts to resolve pulsation spectra for use in asteroseismological analyses. This paper reports on data obtained from a single-site campaign, during 2008, and a multisite campaign, during 2009. From limited 2008 data, we were able to clearly resolve and pre-whiten 24 periods. A subsequent multisite campaign spanning nearly 2 months found over 30 individual periodicities most of which were unstable in amplitude and/or phase. Pulsation amplitudes were found to the detection limit, meaning that further observations would likely reveal more periodicities. EC 01541-1409 reveals itself to be one of two sdB pulsators with many pulsation frequencies covering a large frequency range. Unlike the other star of this type (PG 0048+091), it has one high-amplitude periodicity which appears phase stable, making EC 01541-1409 an excellent candidate for exoplanet studies via pulsation phases. No multiplets were detected leaving EC 01541-1409 as yet another rich p-mode sdB pulsator without these features, limiting observational constraints on pulsation modes.

Effect of isoproterenol, phenylephrine, and sodium nitroprusside on fundus pulsations in healthy volunteers.

PubMed Central

Schmetterer, L; Wolzt, M; Salomon, A; Rheinberger, A; Unfried, C; Zanaschka, G; Fercher, A F

1996-01-01

AIMS/BACKGROUND: Recently a laser interferometric method for topical measurement of fundus pulsations has been developed. Fundus pulsations in the macular region are caused by the inflow and outflow of blood into the choroid. The purpose of this work was to study the influence of a peripheral vasoconstricting (the alpha 1 adrenoceptor agonist phenylephrine), a predominantly positive inotropic (the non-specific beta adrenoceptor agonist isoproterenol), and a non-specific vasodilating (sodium nitroprusside) model drug on ocular fundus pulsations to determine reproducibility and sensitivity of the method. METHODS: In a double masked randomised crossover study the drugs were administered in stepwise increasing doses to 10 male and nine female healthy volunteers. Systemic haemodynamic variables and fundus pulsations were measured at all infusion steps. RESULTS: Fundus pulsation increased during infusion of isoproterenol with statistical significance versus baseline at the lowest dose of 0.1 microgram/min. Neither peripheral vasoconstriction nor peripheral vasodilatation affected the ocular fundus pulsations. CONCLUSIONS: Measurements of fundus pulsations is a highly reproducible method in healthy subjects with low ametropy. Changes of local pulsatile ocular blood flow were detectable with our method following the infusion of isoproterenol. As systemic pharmacological vasodilatation or vasoconstriction did not change fundus pulsations, further experimental work has to be done to evaluate the sensitivity of the laser interferometric fundus pulsation measurement in various eye diseases. PMID:8703859

Effect of counter-pulsation control of a pulsatile left ventricular assist device on working load variations of the native heart.

PubMed

Choi, Seong Wook; Nam, Kyoung Won; Lim, Ki Moo; Shim, Eun Bo; Won, Yong Soon; Woo, Heung Myong; Kwak, Ho Hyun; Noh, Mi Ryoung; Kim, In Young; Park, Sung Min

2014-04-03

When using a pulsatile left ventricular assist device (LVAD), it is important to reduce the cardiac load variations of the native heart because severe cardiac load variations can induce ventricular arrhythmia. In this study, we investigated the effect of counter-pulsation control of the LVAD on the reduction of cardiac load variation. A ventricular electrocardiogram-based counter-pulsation control algorithm for a LVAD was implemented, and the effects of counter-pulsation control of the LVAD on the reduction of the working load variations of the left ventricle were determined in three animal experiments. Deviations of the working load of the left ventricle were reduced by 51.3%, 67.9%, and 71.5% in each case, and the beat-to-beat variation rates in the working load were reduced by 84.8%, 82.7%, and 88.2% in each ease after counter-pulsation control. There were 3 to 12 premature ventricle contractions (PVCs) before counter-pulsation control, but no PVCs were observed during counter-pulsation control. Counter-pulsation control of the pulsatile LVAD can reduce severe cardiac load variations, but the average working load is not markedly affected by application of counter-pulsation control because it is also influenced by temporary cardiac outflow variations. We believe that counter-pulsation control of the LVAD can improve the long-term safety of heart failure patients equipped with LVADs.

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.

First Solid Evidence for a Rocky Exoplanet - Mass and density of smallest exoplanet finally measured

NASA Astrophysics Data System (ADS)

2009-09-01

The longest set of HARPS measurements ever made has firmly established the nature of the smallest and fastest-orbiting exoplanet known, CoRoT-7b, revealing its mass as five times that of Earth's. Combined with CoRoT-7b's known radius, which is less than twice that of our terrestrial home, this tells us that the exoplanet's density is quite similar to the Earth's, suggesting a solid, rocky world. The extensive dataset also reveals the presence of another so-called super-Earth in this alien solar system. "This is science at its thrilling and amazing best," says Didier Queloz, leader of the team that made the observations. "We did everything we could to learn what the object discovered by the CoRoT satellite looks like and we found a unique system." In February 2009, the discovery by the CoRoT satellite [1] of a small exoplanet around a rather unremarkable star named TYC 4799-1733-1 was announced one year after its detection and after several months of painstaking measurements with many telescopes on the ground, including several from ESO. The star, now known as CoRoT-7, is located towards the constellation of Monoceros (the Unicorn) at a distance of about 500 light-years. Slightly smaller and cooler than our Sun, CoRoT-7 is also thought to be younger, with an age of about 1.5 billion years. Every 20.4 hours, the planet eclipses a small fraction of the light of the star for a little over one hour by one part in 3000 [2]. This planet, designated CoRoT-7b, is only 2.5 million kilometres away from its host star, or 23 times closer than Mercury is to the Sun. It has a radius that is about 80% greater than the Earth's. The initial set of measurements, however, could not provide the mass of the exoplanet. Such a result requires extremely precise measurements of the velocity of the star, which is pulled a tiny amount by the gravitational tug of the orbiting exoplanet. The problem with CoRoT-7b is that these tiny signals are blurred by stellar activity in the form of "starspots" (just like sunspots on our Sun), which are cooler regions on the surface of the star. Therefore, the main signal is linked to the rotation of the star, with makes one complete revolution in about 23 days. To get an answer, astronomers had to call upon the best exoplanet-hunting device in the world, the High Accuracy Radial velocity Planet Searcher (HARPS) spectrograph attached to the ESO 3.6-metre telescope at the La Silla Observatory in Chile. "Even though HARPS is certainly unbeaten when it comes to detecting small exoplanets, the measurements of CoRoT-7b proved to be so demanding that we had to gather 70 hours of observations on the star," says co-author François Bouchy. HARPS delivered, allowing the astronomers to tease out the 20.4-hour signal in the data. This figure led them to infer that CoRoT-7b has a mass of about five Earth masses, placing it in rare company as one of the lightest exoplanets yet found. "Since the planet's orbit is aligned so that we see it crossing the face of its parent star - it is said to be transiting - we can actually measure, and not simply infer, the mass of the exoplanet, which is the smallest that has been precisely measured for an exoplanet [3]," says team member Claire Moutou. "Moreover, as we have both the radius and the mass, we can determine the density and get a better idea of the internal structure of this planet." With a mass much closer to that of Earth than, for example, ice giant Neptune's 17 Earth masses, CoRoT-7b belongs to the category of "super-Earth" exoplanets. About a dozen of these bodies have been detected, though in the case of CoRoT-7b, this is the first time that the density has been measured for such a small exoplanet. The calculated density is close to Earth's, suggesting that the planet's composition is similarly rocky. "CoRoT-7b resulted in a 'tour de force' of astronomical measurements. The superb light curves of the space telescope CoRoT gave us the best radius measurement, and HARPS the best mass measurement for an exoplanet. Both were needed to discover a rocky planet with the same density as the Earth," says co-author Artie Hatzes. CoRoT-7b earns another distinction as the closest known exoplanet to its host star, which also makes it the fastest - it orbits its star at a speed of more than 750 000 kilometres per hour, more than seven times faster than the Earth's motion around the Sun. "In fact, CoRoT-7b is so close that the place may well look like Dante's Inferno, with a probable temperature on its 'day-face' above 2000 degrees and minus 200 degrees on its night face. Theoretical models suggest that the planet may have lava or boiling oceans on its surface. With such extreme conditions this planet is definitively not a place for life to develop," says Queloz. As a further testament to HARPS' sublime precision, the astronomers found from their dataset that CoRoT-7 hosts another exoplanet slightly further away than CoRoT-7b. Designated CoRoT-7c, it circles its host star in 3 days and 17 hours and has a mass about eight times that of Earth, so it too is classified as a super-Earth. Unlike CoRoT-7b, this sister world does not pass in front of its star as seen from Earth, so astronomers cannot measure its radius and thus its density. Given these findings, CoRoT-7 stands as the first star known to have a planetary system made of two short period super-Earths with one that transits its host. Notes [1] The CoRoT mission is a cooperation between France and its international partners: ESA, Austria, Belgium, Brazil, Germany and Spain. [2] We see exactly the same effect in our Solar System when Mercury or Venus transits the solar disc, as Venus did on 8 June 2004. In the past centuries such events were used to estimate the Sun-Earth distance, with extremely useful implications for astrophysics and celestial mechanics. [3] Gliese 581e, also discovered with HARPS, has a minimum mass about twice the Earth's mass (see ESO 15/09), but the exact geometry of the orbit is undefined, making its real mass unknown. In the case of CoRoT-7b, as the planet is transiting, the geometry is well defined, allowing the astronomers to measure the mass of the planet precisely. More information This research was presented in a paper to appear in a special issue of the Astronomy and Astrophysics journal on CoRoT, volume 506-1, 22 October 2009: "The CoRoT-7 planetary system: two orbiting Super-Earths", by D. Queloz et al. The team is composed of D. Queloz, R. Alonso, C. Lovis, M. Mayor, F. Pepe, D. Segransan, and S. Udry (Observatoire de Genève, Switzerland), F. Bouchy, F. and G. Hébrard, G. (IAP, Paris, France), C. Moutou, M. Barbieri, P. Barge, M. Deleuil, L. Jorda, and A. Llebaria (Laboratoire d'Astrophysique de Marseille, France), A. Hatzes, D. Gandolfi, E. Guenther, M. Hartmann, and G. Wuchterl (Thüringer Landessternwarte Tautenburg, Germany), M. Auvergne, A. Baglin, D. Rouan, and J. Schneider (LESIA, CNRS, Observatoire de Paris, France), W. Benz (University of Bern, Switzerland), P. Bordé, A. Léger, and M. Ollivier (IAS, UMR 8617 CNRS, Université Paris-Sud, France), H. Deeg (Instituto de Astrofísica de Canarias, Spain), R. Dvorak (University of Vienna, Austria), A. Erikson and H. Rauer (DLR, Berlin, Germany), S. Ferraz Mello (IAG-Universidade de Sao Paulo, Brazil), M. Fridlund (European Space Agency, ESTEC, The Netherlands), M. Gillon and P. Magain (Université de Liège, Belgium), T. Guillot (Observatoire de la Côte d'Azur, CNRS UMR 6202, Nice France), H. Lammer (Austrian Academy of Sciences), T. Mazeh (Tel Aviv University, Israel), and M. Pätzold (Köln University, Germany). ESO, the European Southern Observatory, is the foremost intergovernmental astronomy organisation in Europe and the world's most productive astronomical observatory. It is supported by 14 countries: Austria, Belgium, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Portugal, Spain, Sweden, Switzerland and the United Kingdom. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world's most advanced visible-light astronomical observatory. ESO is the European partner of a revolutionary astronomical telescope ALMA, the largest astronomical project in existence. ESO is currently planning a 42-metre European Extremely Large optical/near-infrared Telescope, the E-ELT, which will become "the world's biggest eye on the sky".

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.

Superposed Epoch Studies of the Response of the High-Latitude Magnetosphere-Ionosphere-Thermosphere System to Solar Wind High-Speed Stream Driving

NASA Astrophysics Data System (ADS)

Grandin, M.; Aikio, A. T.; Kozlovsky, A.; Ulich, T.; Raita, T.

2016-12-01

During the declining phase of the solar cycle, the Earth's magnetosphere-ionosphere-thermosphere system is mainly disturbed by solar wind high-speed streams (HSSs). Their ionospheric response, especially at high latitudes, is not fully understood yet. The perturbations in the ionosphere last for several days. We have examined the effect of HSS in two studies, which apply the superposed epoch method to data to reveal the statistical response in the ionospheric F, E and D regions to such perturbations. We use ionosonde, geomagnetic and cosmic noise absorption data obtained from Finnish stations during 95 high-speed stream events detected between 2006 and 2008. Results show a long-lasting decrease in the F layer critical frequency foF2 between 12 and 23 MLT in summer and equinox. This depletion of the F layer is interpreted as a result of enhanced electric fields inducing ion-neutral frictional heating in the auroral and subauroral regions. The response near noon is different, since foF2 is increased shortly upon arrival of the co-rotating stream interaction region (CIR), possibly because of precipitation of particles from the dayside plasma sheet provoked by the associated solar wind pressure pulse. In the morning sector, both foF2 and foEs show increases for several days, indicating particle precipitation having a soft component. In the study of cosmic noise absorption (CNA), we observe a different response depending on the L-value of the station. Within the auroral oval (L=5-6), CNA gets maximum values in the morning sector 0-12 MLT during the first and second day following the zero epoch. Values are greater during events with longer-lasting high solar wind speed. The CNA maximum shifts to later MLT at lower L values, and in JYV (L=3.8), the maximum takes place at 14 MLT during day 4. Substorm energization events dominate during the first days at 00-01 MLT. We also address the role of Pc5 geomagnetic pulsations observed in association with CNA events. These results may contribute to improve nowcasting and forecasting of space weather activity during high-speed stream events.

The COROT telescope

NASA Astrophysics Data System (ADS)

Viard, Thierry

2017-11-01

The COROT telescope, of which the customer is the French "INSU" / "CNES" (Institut National des Sciences de l'Univers / Centre National des Etudes Spatiales) is in fact a very precise and stable imaging instrument, which will be pointed towards fixed areas in the sky (each containing more than 3000 target stars) for periods of at least 5 months, in order to carry out its two missions.

The SpaceInn-SISMA Database: Characterization of a Large Sample of Variable and Active Stars by Means of Harps Spectra

NASA Astrophysics Data System (ADS)

Rainer, M.; Poretti, E.; Mistò, A.; Panzera, M. R.; Molinaro, M.; Cepparo, F.; Roth, M.; Michel, E.; Monteiro, M. J. P. F. G.

2016-12-01

We created a large database of physical parameters and variability indicators by fully reducing and analyzing the large number of spectra taken to complement the asteroseismic observations of the COnvection, ROtation and planetary Transits (CoRoT) satellite. 7103 spectra of 261 stars obtained with the ESO echelle spectrograph HARPS have been stored in the VO-compliant database Spectroscopic Indicators in a SeisMic Archive (SISMA), along with the CoRoT photometric data of the 72 CoRoT asteroseismic targets. The remaining stars belong to the same variable classes of the CoRoT targets and were observed to better characterize the properties of such classes. Several useful variability indicators (mean line profiles, indices of differential rotation, activity and emission lines) together with v\\sin I and radial-velocity measurements have been extracted from the spectra. The atmospheric parameters {T}{eff},{log}g, and [Fe/H] have been computed following a homogeneous procedure. As a result, we fully characterize a sample of new and known variable stars by computing several spectroscopic indicators, also providing some cases of simultaneous photometry and spectroscopy.

Corotating pressure waves without streams in the solar wind

NASA Technical Reports Server (NTRS)

Burlaga, L. F.

1983-01-01

Voyager 1 and 2 magnetic field and plasma data are presented which demonstrate the existence of large scale, corotating, non-linear pressure waves between 2 AU and 4 AU that are not accompanied by fast streams. The pressure waves are presumed to be generated by corotating streams near the Sun. For two of the three pressure waves that are discussed, the absence of a stream is probably a real, physical effect, viz., a consequence of deceleration of the stream by the associated compression wave. For the third pressure wave, the apparent absence of a stream may be a geometrical effect; it is likely that the stream was at latitudes just above those of the spacecraft, while the associated shocks and compression wave extended over a broader range of latitudes so that they could be observed by the spacecraft. It is suggested that the development of large-scale non-linear pressure waves at the expense of the kinetic energy of streams produces a qualitative change in the solar wind in the outer heliosphere. Within a few AU the quasi-stationary solar wind structure is determined by corotating streams whose structure is determined by the boundary conditions near the Sun.

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.

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

The occurrence of non-pulsating stars in the γ Dor and δ Sct pulsation instability regions: Results from Kepler quarter 14–17 data

DOE Office of Scientific and Technical Information (OSTI.GOV)

Guzik, J. A.; Bradley, P. A.; Jackiewicz, J.

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

Seismic Analysis of Pulsating Subdwarf B Star EPIC 212508753 Using the K2 Mission

NASA Astrophysics Data System (ADS)

Crooke, John; Reed, Michael D.; Baran, Andrzej; Telting, John H.; Østensen, Roy H.

2018-01-01

EPIC 212508753 is a subdwarf B (hot horizontal branch, sdB) star which has been observed by the Kepler Space Telescope during its extended mission, K2, in short cadence mode where a new image is obtained roughly every minute for about 75 days. Using time series analysis of the data we have found the star to be a rare hybrid pulsator with both g- and p-mode pulsations where most of the pulsations are p modes. These pulsators are extremely important as p modes sample near the surface and g modes can sample deeper, near to the core. This means that hybrid pulsators allow us to characterize the entire star. The hotter, predominantly p-mode pulsators are rarer so that makes EPIC 212508753 particularly interesting for seismic study. In this poster we will present preliminary results of our analysis of K2 data. We have discovered frequency multiplets in both the p- and g-mode regions which we use to identify pulsation modes and determine that EPIC 212508753 rotates like a solid body, in contrast to some other sdB stars.

On the evolutionary status and pulsations of the recently discovered blue large-amplitude pulsators (BLAPs)

NASA Astrophysics Data System (ADS)

Romero, Alejandra D.; Córsico, A. H.; Althaus, L. G.; Pelisoli, I.; Kepler, S. O.

2018-06-01

The blue large-amplitude pulsators (BLAPs) constitute a new class of pulsating stars. They are hot stars with effective temperatures of ˜30 000 K and surface gravities of log g ˜ 4.9, that pulsate with periods in the range 20-40 min. Until now, their origin and evolutionary state, as well as the nature of their pulsations, were not been unveiled. In this paper, we propose that the BLAPs are the hot counterpart of the already known pulsating pre-extremely low mass (pre-ELM) white dwarf (WD) stars, that are He-core low-mass stars resulting from interacting binary evolution. Using fully evolutionary sequences, we show that the BLAPs are well represented by pre-ELM WD models with high effective temperature and stellar masses ˜0.34 M⊙. From the analysis of their pulsational properties, we find that the observed variabilities can be explained by high-order non-radial g-mode pulsations or, in the case of the shortest periods, also by low-order radial modes, including the fundamental radial mode. The theoretical modes with periods in the observed range are unstable due to the κ mechanism associated with the Z-bump in the opacity at log T ˜ 5.25.

Thermal-diffusional Instability in White Dwarf Flames: Regimes of Flame Pulsation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xing, Guangzheng; Zhao, Yibo; Zhou, Cheng

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 × 10{sup 7} g cm{sup −3}) and of spherical flames (with curvature c = −0.01, 0, 0.01, and 0.05) at a particular density ( ρ = 2 × 10{sup 7} g cm{supmore » −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 × 10{sup 7} g cm{sup −3} and temperature of 0.6 × 10{sup 9} 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.« less

ɛ-mechanism driven pulsations in hot subdwarf stars with mixed H-He atmospheres

NASA Astrophysics Data System (ADS)

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

2017-12-01

The ɛ mechanism is a self-excitation mechanism of stellar pulsations which acts in regions where nuclear burning takes place. It has been shown that the ɛ mechanism can excite pulsations in hot pre-horizontal branch stars before they settle into the stable helium core-burning phase and that the shortest periods of LS IV-14º116 could be explained that way.We aim to study the ɛ mechanism in stellar models appropriate for hot pre-horizontal branch stars to predict their pulsational properties.We perform detailed computations of non-adiabatic non-radial pulsations on such stellar models.We predict a new instability domain of long-period gravity modes in the log g - log Teff plane at roughly 22000 K ≲ Teff ≲ 50000 K and 4.67 ≲ log g ≲ 6.15, with a period range from 200 to 2000 s. Comparison with the three known pulsating He-rich subdwarfs shows that the ɛ mechanism can excite pulsations in models with similar surface properties except for modes with the shortest observed periods. Based on simple estimates we expect at least 3 stars in the current samples of hot-subdwarf stars to be pulsating by the ɛ mechanism. Our results could constitute a theoretical basis for future searches of pulsators in the Galactic field.

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.

The origin of the eccentricities of the rings of Uranus

NASA Technical Reports Server (NTRS)

Goldreich, P.; Tremaine, S.

1981-01-01

The effect of gravitational perturbations from a nearby satellite on the eccentricity e of a narrow particulate ring is considered. The perturbations near a resonance in an eccentric ring may be divided into corotation and Lindblad terms. For small e, the corotation terms damp e, whereas the Lindblad terms excite e. In the absence of saturation the corotation terms win by a small margin, and e damps. However, if the perturbations open gaps at the strongest resonances, then the Lindblad terms win, and e grows. This result offers an explanation for the existence of both circular and eccentric rings around Uranus. It is also shown that eccentricity changes induced by circular rings on eccentric satellite orbits are similar to those induced by satellites with circular orbits on eccentric rings.

NuSTAR Discovery of a Cyclotron Line in the Accreting X-Ray Pulsar IGR J16393-4643

NASA Technical Reports Server (NTRS)

Bodaghee, Arash; Tomsick, John A.; Fornasini, Francesca M.; Krivonos, Roman; Stern, Daniel; Mori, Kaya; Rahoui, Farid; Boggs, Steven E.; Christensen, Finn E.; Craig, William W.;

Petersen diagram revolution

NASA Astrophysics Data System (ADS)

Smolec, Radoslaw; Dziembowski, Wojciech; Moskalik, Pawel; Netzel, Henryka; Prudil, Zdenek; Skarka, Marek; Soszynski, Igor

2017-09-01

Over the recent years, the Petersen diagram for classical pulsators, Cepheids and RR Lyr stars, populated with a few hundreds of new multiperiodic variables. We review our analyses of the OGLE data, which resulted in a significant extension of the known, and in the discovery of a few new and distinct forms of multiperiodic pulsation. The showcase includes not only radial mode pulsators, but also radial-non-radial pulsators and stars with significant modulation observed on top of the beat pulsation. First theoretical models explaining the new forms of stellar variability are briefly discussed.

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.

Simultaneous observation of Pc 3-4 pulsations in the solar wind and in the earth's magnetosphere

NASA Technical Reports Server (NTRS)

Engebretson, M. J.; Zanetti, L. J.; Potemra, T. A.; Baumjohann, W.; Luehr, H.; Acuna, M. H.

1987-01-01

The equatorially orbiting Active Magnetospheric Particle Tracer Explorers CCE and IRM satellites have made numerous observations of Pc 3-4 magnetic field pulsations (10-s to 100-s period) simultaneously at locations upstream of the earth's bow shock and inside the magnetosphere. These observations show solar wind/IMF control of two categories of dayside magnetospheric pulsations. Harmonically structured, azimuthally polarized pulsations are commonly observed from L = 4 to 9 in association with upstream waves. More monochromatic compressional pulsations are clearly evident on occasion, with periods identical to those observed simultaneously in the solar wind. The observations reported here are consistent with a high-latitude (cusp) entry mechanism for wave energy related to harmonically structured pulsations.

Pulsation Detection from Noisy Ultrasound-Echo Moving Images of Newborn Baby Head Using Fourier Transform

NASA Astrophysics Data System (ADS)

Yamada, Masayoshi; Fukuzawa, Masayuki; Kitsunezuka, Yoshiki; Kishida, Jun; Nakamori, Nobuyuki; Kanamori, Hitoshi; Sakurai, Takashi; Kodama, Souichi

1995-05-01

In order to detect pulsation from a series of noisy ultrasound-echo moving images of a newborn baby's head for pediatric diagnosis, a digital image processing system capable of recording at the video rate and processing the recorded series of images was constructed. The time-sequence variations of each pixel value in a series of moving images were analyzed and then an algorithm based on Fourier transform was developed for the pulsation detection, noting that the pulsation associated with blood flow was periodically changed by heartbeat. Pulsation detection for pediatric diagnosis was successfully made from a series of noisy ultrasound-echo moving images of newborn baby's head by using the image processing system and the pulsation detection algorithm developed here.

Transiting exoplanets from the CoRoT space mission. XVII. The hot Jupiter CoRoT-17b: a very old planet

NASA Astrophysics Data System (ADS)

Csizmadia, Sz.; Moutou, C.; Deleuil, M.; Cabrera, J.; Fridlund, M.; Gandolfi, D.; Aigrain, S.; Alonso, R.; Almenara, J.-M.; Auvergne, M.; Baglin, A.; Barge, P.; Bonomo, A. S.; Bordé, P.; Bouchy, F.; Bruntt, H.; Carone, L.; Carpano, S.; Cavarroc, C.; Cochran, W.; Deeg, H. J.; Díaz, R. F.; Dvorak, R.; Endl, M.; Erikson, A.; Ferraz-Mello, S.; Fruth, Th.; Gazzano, J.-C.; Gillon, M.; Guenther, E. W.; Guillot, T.; Hatzes, A.; Havel, M.; Hébrard, G.; Jehin, E.; Jorda, L.; Léger, A.; Llebaria, A.; Lammer, H.; Lovis, C.; MacQueen, P. J.; Mazeh, T.; Ollivier, M.; Pätzold, M.; Queloz, D.; Rauer, H.; Rouan, D.; Santerne, A.; Schneider, J.; Tingley, B.; Titz-Weider, R.; Wuchterl, G.

2011-07-01

We report on the discovery of a hot Jupiter-type exoplanet, CoRoT-17b, detected by the CoRoT satellite. It has a mass of 2.43 ± 0.30 MJup and a radius of 1.02 ± 0.07 RJup, while its mean density is 2.82 ± 0.38 g/cm3. CoRoT-17b is in a circular orbit with a period of 3.7681 ± 0.0003 days. The host star is an old (10.7 ± 1.0 Gyr) main-sequence star, which makes it an intriguing object for planetary evolution studies. The planet's internal composition is not well constrained and can range from pure H/He to one that can contain ~380 earth masses of heavier elements. The CoRoT space mission, launched on December 27th 2006, has been developed and is operated by CNES, with the contribution of Austria, Belgium, Brazil, ESA (RSSD and Science Programme), Germany and Spain. Part of the observations were obtained at the Canada-France-Hawaii Telescope (CFHT) which is operated by the National Research Council of Canada, the Institut National des Sciences de l'Univers of the Centre National de la Recherche Scientifique of France, and the University of Hawaii. Based on observations made with HARPS spectrograph on the 3.6-m European Organisation for Astronomical Research in the Southern Hemisphere telescope at La Silla Observatory, Chile (ESO program 184.C-0639). Based on observations made with the IAC80 telescope operated on the island of Tenerife by the Instituto de Astrofísica de Canarias in the Spanish Observatorio del Teide. Part of the data presented herein were obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W.M. Keck Foundation.

UNEXPECTED SERIES OF REGULAR FREQUENCY SPACING OF δ SCUTI STARS IN THE NON-ASYMPTOTIC REGIME. I. THE METHODOLOGY

DOE Office of Scientific and Technical Information (OSTI.GOV)

Paparó, M.; Benkő, J. M.; Hareter, M.

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)more » were found in the 5–21 d{sup −1} region where the pairs of the sequences are shifted (between 0.5 and 0.59 d{sup −1}) by twice the value of the estimated rotational splitting frequency (0.269 d{sup −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{sup −1}) are in better agreement with the sum of a possible 1.710 d{sup −1} large separation and two or one times, respectively, the value of the rotational frequency.« less

Unusual Emissions at Various Energies and Coronal Mass Ejection Prior to the November 4, 2003 Large Solar Flare

NASA Astrophysics Data System (ADS)

Kaufmann, Pierre; Holman, G. D.; Su, Y.; Gimenez de Castro, C.; Correia, E.; de Souza, R. V.; Marun, A.; Pereyra, P.

2010-05-01

The November 4, 2003 GOES X28 flare was the largest ever recorded in its class. It produced the first evidence of the two spectrally separated radio/far-infrared emission components, one at microwaves and another in the THz range of frequencies (Kaufmann et al. 2004). We analyzed the 20 minutes before the impulsive onset of this event and found unusual activity at X-rays (RHESSI), at sub-THz frequencies (SST), at H-alpha (BBSO) and at microwaves (Itapetinga 7 GHz polarimeter, RSTN and OVSA). SOHO LASCO images have shown a large CME launched well before the large burst onset. The unusual activity began at about 19 27 UT with a slow rise at 6-10 keV and the start of a precursor at 7 GHz. Pulsations at sub-THz became pronounced, exhibiting correlations with RHESSI 25-50 keV pulsations and similar pulsations at 7 GHz. Impulsive bursts were detected with peaks at 19 34 UT at 100-300 keV and 7 GHz. LASCO movie show a large CME which linear extrapolation to the solar surface correspond to the first H-alpha BBSO brightening, suggesting an approximate launch time at about 1934 UT, close to the hard X-ray and microwave impulsive bursts and nearly 8 minutes before the onset of the large flare. These events had different locations within the AR that included the major flare location at the solar west limb, as indicated by SST pulses positions and images obtained by RHESSI and BBSO. The pulsations phenomena and superimposed impulsive events might represent the complex energy buildup mechanisms leading to the CME launch, quite distinct in time and space from the major flare that exploded afterwards.

High-Speed Real-Time Resting-State fMRI Using Multi-Slab Echo-Volumar Imaging

PubMed Central

Posse, Stefan; Ackley, Elena; Mutihac, Radu; Zhang, Tongsheng; Hummatov, Ruslan; Akhtari, Massoud; Chohan, Muhammad; Fisch, Bruce; Yonas, Howard

2013-01-01

We recently demonstrated that ultra-high-speed real-time fMRI using multi-slab echo-volumar imaging (MEVI) significantly increases sensitivity for mapping task-related activation and resting-state networks (RSNs) compared to echo-planar imaging (Posse et al., 2012). In the present study we characterize the sensitivity of MEVI for mapping RSN connectivity dynamics, comparing independent component analysis (ICA) and a novel seed-based connectivity analysis (SBCA) that combines sliding-window correlation analysis with meta-statistics. This SBCA approach is shown to minimize the effects of confounds, such as movement, and CSF and white matter signal changes, and enables real-time monitoring of RSN dynamics at time scales of tens of seconds. We demonstrate highly sensitive mapping of eloquent cortex in the vicinity of brain tumors and arterio-venous malformations, and detection of abnormal resting-state connectivity in epilepsy. In patients with motor impairment, resting-state fMRI provided focal localization of sensorimotor cortex compared with more diffuse activation in task-based fMRI. The fast acquisition speed of MEVI enabled segregation of cardiac-related signal pulsation using ICA, which revealed distinct regional differences in pulsation amplitude and waveform, elevated signal pulsation in patients with arterio-venous malformations and a trend toward reduced pulsatility in gray matter of patients compared with healthy controls. Mapping cardiac pulsation in cortical gray matter may carry important functional information that distinguishes healthy from diseased tissue vasculature. This novel fMRI methodology is particularly promising for mapping eloquent cortex in patients with neurological disease, having variable degree of cooperation in task-based fMRI. In conclusion, ultra-high-real-time speed fMRI enhances the sensitivity of mapping the dynamics of resting-state connectivity and cerebro-vascular pulsatility for clinical and neuroscience research applications. PMID:23986677

Ionospheric Electron Heating Associated With Pulsating Auroras: Joint Optical and PFISR Observations

NASA Astrophysics Data System (ADS)

Liang, Jun; Donovan, E.; Reimer, A.; Hampton, D.; Zou, S.; Varney, R.

2018-05-01

In a recent study, Liang et al. (2017, https://doi.org/10.1002/2017JA024127) repeatedly identified strong electron temperature (Te) enhancements when Swarm satellites traversed pulsating auroral patches. In this study, we use joint optical and Poker Flat Incoherent Scatter Radar (PFISR) observations to further investigate the F region plasma signatures related to pulsating auroras. On 19 March 2015 night, which contained multiple intervals of pulsating auroral activities, we identify a statistical trend, albeit not a one-to-one correspondence, of strong Te enhancements ( 500-1000 K) in the upper F region ionosphere during the passages of pulsating auroras over PFISR. On the other hand, there is no discernible and repeatable density enhancement in the upper F region during pulsating auroral intervals. Collocated optical and NOAA satellite observations suggest that the pulsating auroras are composed of energetic electron precipitation with characteristic energy >10 keV, which is inefficient in electron heating in the upper F region. Based upon PFISR observations and simulations from Liang et al. (2017) model, we propose that thermal conduction from the topside ionosphere, which is heated by precipitating low-energy electrons, offers the most likely explanation for the observed electron heating in the upper F region associated with pulsating auroras. Such a heating mechanism is similar to that underlying the "stable auroral red arcs" in the subauroral ionosphere. Our proposal conforms to the notion on the coexistence of an enhanced cold plasma population and the energetic electron precipitation, in magnetospheric flux tubes threading the pulsating auroral patch. In addition, we find a trend of enhanced ion upflows during pulsating auroral intervals.

Gaseous isotope separation using solar wind phenomena.

PubMed

Wang, C G

1980-12-01

A large evacuated drum-like chamber fitted with supersonic nozzles in the center, with the chamber and the nozzles corotating, can separate gaseous fluids according to their molecular weights. The principle of separation is essentially the same as that of the solar wind propagation, in which components of the plasma fluid are separated due to their difference in the time-of-flight. The process can inherently be very efficient, serving as a pump as well as a separator, and producing well over 10(5) separative work units (kg/year) for the hydrogen/deuterium mixture at high-velocity flows.

An additional pulsating mode (7.35 mHz) and pulsations timing variations of PG 1613+426

NASA Astrophysics Data System (ADS)

Otani, Tomomi; Oswalt, Terry D.; Majewski, Patrice; Jordan, Riley; Amaral, Marc; Moss, Adam

2017-12-01

We present the detection of an additional pulsation mode (7.35 mHz) of a subdwarf B star, PG 1613+426, and periodic Observed minus Calculated (O-C) variations for two existing pulsations. PG 1613+426 is near the hot end of the sdB instability strip. One pulsation mode (6.94 mHz) was detected so far by Bonanno et al. (2002) and another pulsation mode candidate (7.05 mHz) was proposed with a confidence level above 90% by Kuassivi and Ferlet (2005). To constrain sdB star evolutional scenarios, this star was monitored in 2010, 2011, 2015, and 2017 as a part of a project for finding companions to sdB stars using the pulsation timing method. The photometric analysis of those data shows an additional 7.35 mHz pulsation mode as well as the previously detected 6.93 mHz mode. However the 7.05 mHz mode was not detected. Nightly amplitude changes of 7.35 mHz mode were observed in the 2011 data, however the 2017 data did not show nightly amplitude shifts. O-C variations were detected in both 6.93 mHz and 7.35 mHz pulsations, indicating that PG 1613+426 may have a low mass companion star. However, more observations are needed to confirm it.

Vorticity and helicity decompositions and dynamics with real Schur form of the velocity gradient

NASA Astrophysics Data System (ADS)

Zhu, Jian-Zhou

2018-03-01

The real Schur form (RSF) of a generic velocity gradient field ∇u is exploited to expose the structures of flows, in particular, our field decomposition resulting in two vorticities with only mutual linkage as the topological content of the global helicity (accordingly decomposed into two equal parts). The local transformation to the RSF may indicate alternative (co)rotating frame(s) for specifying the objective argument(s) of the constitutive equation. When ∇u is uniformly of RSF in a fixed Cartesian coordinate frame, i.e., ux = ux(x, y) and uy = uy(x, y), but uz = uz(x, y, z), the model, with the decomposed vorticities both frozen-in to u, is for two-component-two-dimensional-coupled-with-one-component-three-dimensional flows in between two-dimensional-three-component (2D3C) and fully three-dimensional-three-component ones and may help curing the pathology in the helical 2D3C absolute equilibrium, making the latter effectively work in more realistic situations.

Modeling of High Capacity Passive Cooling System

DTIC Science & Technology

2009-03-01

Pulsating Heat Pipes : Closed Loop Pulsating Heat Pipes , which is also known as Meandering Capillary Tube Heat Pipe or Closed Loop Oscillating Heat ... Pipe , has emerged in the recent years as a new electronics cooling technology. The Pulsating Heat Pipe is an innovating technology that has gained...horizontal orientation, the operating temperatures are lower. Pulsating heat pipes are capable of higher heat

Coupled pulsating and cellular structure in the propagation of globally planar detonations in free space

DOE Office of Scientific and Technical Information (OSTI.GOV)

Han, Wenhu; Key Laboratory for Thermal Science and Power Engineering of Ministry of Education, Department of Thermal Engineering, Tsinghua University, Beijing 100084; Gao, Yang, E-mail: gaoyang-00@mails.tsinghua.edu.cn

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.more » 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.« less

The Structure of a Quasi-Keplerian Accretion Disk around Magnetized Stars

NASA Astrophysics Data System (ADS)

Habumugisha, Isaac; Jurua, Edward; Tessema, Solomon B.; Simon, Anguma K.

2018-06-01

In this paper, we present the complete structure of a quasi-Keplerian thin accretion disk with an internal dynamo around a magnetized neutron star. We assume a full quasi-Keplerian disk with the azimuthal velocity deviating from the Keplerian fashion by a factor of ξ (0 < ξ < 2). In our approach, we vertically integrate the radial component of the momentum equation to obtain the radial pressure gradient equation for a thin quasi-Keplerian accretion disk. Our results show that, at large radial distance, the accretion disk behaves in a Keplerian fashion. However, close to the neutron star, pressure gradient force (PGF) largely modifies the disk structure, resulting into sudden dynamical changes in the accretion disk. The corotation radius is shifted inward (outward) for ξ > 1 (for ξ < 1), and the position of the inner edge with respect to the new corotation radius is also relocated accordingly, as compared to the Keplerian model. The resulting PGF torque couples with viscous torque (when ξ < 1) to provide a spin-down torque and a spin-up torque (when ξ > 1) while in the advective state. Therefore, neglecting the PGF, as has been the case in previous models, is a glaring omission. Our result has the potential to explain the observable dynamic consequences of accretion disks around magnetized neutron stars.

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.

Pressure pulsations and hydraulic efficiency at Smeland power plant

NASA Astrophysics Data System (ADS)

Ulvan, V. S.; Kverno, J. O.; Dahlhaug, O. G.

2018-06-01

Smeland power plant in Norway is experiencing pressure pulsations in their Francis turbine when running above best efficiency point. By measuring both the pressure pulsations and runner efficiency, the cause and effect of the pulsations are to be investigated thoroughly, which is this works main purpose. To find the Francis runners efficiency the thermodynamic method has been used, which builds on the principle that all of the hydraulic losses turns into heat in the flow itself. By measuring the change of temperature before and after the turbine one can, with little other data, calculate the hydraulic efficiency. To identify the pressure pulsations, pressure transducers were placed on the inlet to the spiral casing, draft tube, and upper labyrinth. While doing measurements, air-injection through the runner was tested on full load, which nearly eradicated the pressure pulsations. This might be due to an increase of volume in a pulsating full load vortex that changed its eigenfrequency, and therefore stopped resonating.

Population Pulsation Resonances of Excitons in Monolayer MoSe 2 with Sub-1 μeV Linewidths

DOE PAGES

Schaibley, John R.; Karin, Todd; Yu, Hongyi; ...

2015-04-01

Monolayer transition metal dichalcogenides, a new class of atomically thin semiconductors, possess optically coupled 2D valley excitons. The nature of exciton relaxation in these systems is currently poorly understood. In this paper, we investigate exciton relaxation in monolayer MoSe 2 using polarization-resolved coherent nonlinear optical spectroscopy with high spectral resolution. We report strikingly narrow population pulsation resonances with two different characteristic linewidths of 1 and <0.2 μeV at low temperature. These linewidths are more than 3 orders of magnitude narrower than the photoluminescence and absorption linewidth, and indicate that a component of the exciton relaxation dynamics occurs on time scalesmore » longer than 1 ns. Finally, the ultranarrow resonance (<0.2 μeV) emerges with increasing excitation intensity, and implies the existence of a long-lived state whose lifetime exceeds 6 ns.« less

A whirling plane of satellite galaxies around Centaurus A challenges cold dark matter cosmology

NASA Astrophysics Data System (ADS)

Müller, Oliver; Pawlowski, Marcel S.; Jerjen, Helmut; Lelli, Federico

2018-02-01

The Milky Way and Andromeda galaxies are each surrounded by a thin plane of satellite dwarf galaxies that may be corotating. Cosmological simulations predict that most satellite galaxy systems are close to isotropic with random motions, so those two well-studied systems are often interpreted as rare statistical outliers. We test this assumption using the kinematics of satellite galaxies around the Centaurus A galaxy. Our statistical analysis reveals evidence for corotation in a narrow plane: Of the 16 Centaurus A satellites with kinematic data, 14 follow a coherent velocity pattern aligned with the long axis of their spatial distribution. In standard cosmological simulations, <0.5% of Centaurus A–like systems show such behavior. Corotating satellite systems may be common in the universe, challenging small-scale structure formation in the prevailing cosmological paradigm.

The SARS algorithm: detrending CoRoT light curves with Sysrem using simultaneous external parameters

NASA Astrophysics Data System (ADS)

Ofir, Aviv; Alonso, Roi; Bonomo, Aldo Stefano; Carone, Ludmila; Carpano, Stefania; Samuel, Benjamin; Weingrill, Jörg; Aigrain, Suzanne; Auvergne, Michel; Baglin, Annie; Barge, Pierre; Borde, Pascal; Bouchy, Francois; Deeg, Hans J.; Deleuil, Magali; Dvorak, Rudolf; Erikson, Anders; Mello, Sylvio Ferraz; Fridlund, Malcolm; Gillon, Michel; Guillot, Tristan; Hatzes, Artie; Jorda, Laurent; Lammer, Helmut; Leger, Alain; Llebaria, Antoine; Moutou, Claire; Ollivier, Marc; Päetzold, Martin; Queloz, Didier; Rauer, Heike; Rouan, Daniel; Schneider, Jean; Wuchterl, Guenther

2010-05-01

Surveys for exoplanetary transits are usually limited not by photon noise but rather by the amount of red noise in their data. In particular, although the CoRoT space-based survey data are being carefully scrutinized, significant new sources of systematic noises are still being discovered. Recently, a magnitude-dependant systematic effect was discovered in the CoRoT data by Mazeh et al. and a phenomenological correction was proposed. Here we tie the observed effect to a particular type of effect, and in the process generalize the popular Sysrem algorithm to include external parameters in a simultaneous solution with the unknown effects. We show that a post-processing scheme based on this algorithm performs well and indeed allows for the detection of new transit-like signals that were not previously detected.

Relations between morning sector Pi 1 pulsation activity and particle and field characteristics observed by the DE 2 satellite

NASA Technical Reports Server (NTRS)

Engebretson, M. J.; Cahill, L. J., Jr.; Winningham, J. D.; Rosenberg, T. J.; Arnoldy, R. L.; Maynard, N. C.; Sugiura, M.

1986-01-01

Ground-based magnetometer, photometer, and riometer data are combined with low-altitude particle and electric and magnetic field data from the DE-2 spacecraft to provide a more complete characterization of the magnetospheric and tropospheric environment in which morning sector asymmetric Pi 1 pulsations are observed. The results of the study are in agreement with recent conclusions that morning sector asymmetric Pi 1 pulsations are physically related to pulsating aurorae. Precipitation of energetic electrons (E greater than 35 keV) coincides in every instance with the occurrence of these pulsations.

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.

Inertia-gravity wave radiation from the merging of two co-rotating vortices in the f-plane shallow water system

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sugimoto, Norihiko, E-mail: nori@phys-h.keio.ac.jp

Inertia-gravity wave radiation from the merging of two co-rotating vortices is investigated numerically in a rotating shallow water system in order to focus on cyclone–anticyclone asymmetry at different values of the Rossby number (Ro). A numerical study is conducted on a model using a spectral method in an unbounded domain to estimate the gravity wave flux with high accuracy. Continuous gravity wave radiation is observed in three stages of vortical flows: co-rotating of the vortices, merging of the vortices, and unsteady motion of the merged vortex. A cyclone–anticyclone asymmetry appears at all stages at smaller Ro (≤20). Gravity waves frommore » anticyclones are always larger than those from cyclones and have a local maximum at smaller Ro (∼2) compared with that for an idealized case of a co-rotating vortex pair with a constant rotation rate. The source originating in the Coriolis acceleration has a key role in cyclone–anticyclone asymmetry in gravity waves. An additional important factor is that at later stages, the merged axisymmetric anticyclone rotates faster than the elliptical cyclone due to the effect of the Rossby deformation radius, since a rotation rate higher than the inertial cutoff frequency is required to radiate gravity waves.« less

A modified CoRoT detrend algorithm and the discovery of a new planetary companion

NASA Astrophysics Data System (ADS)

Boufleur, Rodrigo C.; Emilio, Marcelo; Janot-Pacheco, Eduardo; Andrade, Laerte; Ferraz-Mello, Sylvio; do Nascimento, José-Dias, Jr.; de La Reza, Ramiro

2018-01-01

We present MCDA, a modification of the COnvection ROtation and planetary Transits (CoRoT) detrend algorithm (CDA) suitable to detrend chromatic light curves. By means of robust statistics and better handling of short-term variability, the implementation decreases the systematic light-curve variations and improves the detection of exoplanets when compared with the original algorithm. All CoRoT chromatic light curves (a total of 65 655) were analysed with our algorithm. Dozens of new transit candidates and all previously known CoRoT exoplanets were rediscovered in those light curves using a box-fitting algorithm. For three of the new cases, spectroscopic measurements of the candidates' host stars were retrieved from the ESO Science Archive Facility and used to calculate stellar parameters and, in the best cases, radial velocities. In addition to our improved detrend technique, we announce the discovery of a planet that orbits a 0.79_{-0.09}^{+0.08} R⊙ star with a period of 6.718 37 ± 0.000 01 d and has 0.57_{-0.05}^{+0.06} RJ and 0.15 ± 0.10 MJ. We also present the analysis of two cases in which parameters found suggest the existence of possible planetary companions.

Whole Earth Telescope discovery of a strongly distorted quadrupole pulsation in the largest amplitude rapidly oscillating Ap star

NASA Astrophysics Data System (ADS)

Holdsworth, Daniel L.; Kurtz, D. W.; Saio, H.; Provencal, J. L.; Letarte, B.; Sefako, R. R.; Petit, V.; Smalley, B.; Thomsen, H.; Fletcher, C. L.

2018-01-01

We present a new analysis of the rapidly oscillating Ap (roAp) star, 2MASS J19400781 - 4420093 (J1940; V = 13.1). The star was discovered using SuperWASP broad-band photometry to have a frequency of 176.39 d-1 (2041.55 μHz; P = 8.2 min; Holdsworth et al. 2014a) and is shown here to have a peak-to-peak amplitude of 34 mmag. J1940 has been observed during three seasons at the South African Astronomical Observatory, and has been the target of a Whole Earth Telescope campaign. The observations reveal that J1940 pulsates in a distorted quadrupole mode with unusual pulsational phase variations. A higher signal-to-noise ratio spectrum has been obtained since J1940's first announcement, which allows us to classify the star as A7 Vp Eu(Cr). The observing campaigns presented here reveal no pulsations other than the initially detected frequency. We model the pulsation in J1940 and conclude that the pulsation is distorted by a magnetic field of strength 1.5 kG. A difference in the times of rotational maximum light and pulsation maximum suggests a significant offset between the spots and pulsation axis, as can be seen in roAp stars.

Plasma convection in Saturn's magnetosphere: A diagnosis using Cassini observations of the magnetic field spiral

NASA Astrophysics Data System (ADS)

Smith, Edward; Dougherty, Michele K.

The global distribution of plasma and its flows inside Saturn's magnetosphere is complex. The large satellites in the inner magnetosphere are a persistent source of plasma that must make its way into the outer magnetosphere and exit through the magnetotail. The mass loaded into the magnetic field stretches the field lines outward resulting in the formation of the equatorial current sheet. The outward radial flow causes the closed stretched fields to spiral out of magnetic meridian planes. The angle associated with the spiralling is given by the ratio of the azimuthal field component, B , to the radial component Br : tan = B / Br . The magnetic spiral is directly related to the corresponding components of plasma velocity, v and v r, provided the conductivity of the ionosphere, , is high enough to enforce co-rotation of the field lines. If, as has been inferred, the conductivity is low, the field and plasma do not co-rotate and the conductivity also enters the expression for . Conditions are more uncertain further out in the magnetosphere where convective motions associated with magnetic reconnection between planetary and interplanetary fields and the motion of the shocked solar wind become dominant. The prevailing model is a superposition of two modes of plasma circulation inside the magnetosphere and magnetotail, the Dungey and Vasyliunas cycles, that depend on radial distance and local time with an x-line in the midnight sector that separates the two cycles. The measured spiral angle will be affected by this complexity and holds the promise of distinguishing the relative influences of v ,v r and . The two field components that define the spiral angle are also involved in the transfer of angular momentum from the ionosphere to the magnetospheric plasma and the outward mass flux. The spiral should also contain evidence, especially at high latitudes, of the return of the current to the ionosphere from the current sheet. Our major objective, therefore, is to characterize as a function of radius, latitude and local time using the global coverage provided by Cassini and apply the findings to the topics listed above.

Testing theoretical models of subdwarf B stars using multicolor photometry

NASA Astrophysics Data System (ADS)

Reed, Mike; Baran, Andrzej; Ostensen, Roy; O'Toole, Simon

2012-08-01

Pulsating stars allow a direct investigation of their structure and evolutionary history from the evaluation of pulsation modes. However, the observed pulsation frequencies must first be identified with spherical harmonics (modes). For subdwarfs B (sdB) stars, such identifications using white light photometry currently have significant limitations. We intend to use multicolor photometry to identify pulsation modes and constrain structure models. We propose to observe the pulsating sdB star PG0154+182 (BI Ari) with our multicolor instrument GT Cam. Our observations will be compared with perturbative atmospheric models (BRUCE/KYLIE) to identify the pulsation modes. This is part of our NSF grant to obtain seismic tools to test structure and evolution models; constraining stellar parameters including total mass, envelope mass, internal composition discontinuities and internal rotation. During winter/spring 2012, we were allocated three runs on the 2.1 m to collect multicolor data on other promising pulsating subdwarf B stars as part of this work. Those runs were very successful, prompting our continued proposals. In addition, we will obtain 3-color data using MAIA on the Mercator Telescope (using guaranteed institutional time).

Crystallization of the Pulsating White Dwarf Star, BPM 37093

NASA Astrophysics Data System (ADS)

Salois, Amee; Winget, D.

2010-01-01

BPM 37093 is unique among pulsating white dwarf stars because it is expected to have a highly crystallized interior. By understanding how this star is crystallizing, we gain a better understanding of extreme physics. Theoretical models of the evolution of white dwarf stars suggest that they crystallize from the inside out. The pulsations of the star, which we see as intensity variations, cannot penetrate this crystallized interior. Therefore, as the star crystallizes there is a smaller volume for the propagation of the pulsations and the pulsation periods are changed accordingly. We studied these changes in the periods of the pulsations of the star over ten weeks during the McDonald Observatory Research Experience for Undergraduates Program. By studying the changes in the pulsations periods of the star we can determine the mass fraction of the star that is crystallized. Comparing Fourier transforms of our observed light curves taken in 2004 and 2005 at CTIO with data taken in 1998 and 1999 by Kanaan et al. we hope to see the changes that have occurred in the star as well as determining a better approximation of the star's crystallized mass fraction.

Stream interfaces and energetic ions II: Ulysses test of Pioneer results

NASA Technical Reports Server (NTRS)

Intriligator, Devrie S.; Siscoe, George L.; Wibberenz, Gerd; Kunow, Horst; Gosling, John T.

1995-01-01

Ulysses measurements of energetic and solar wind particles taken near 5 AU between 20 and 30 degrees south latitude during a well-developed recurring corotating interaction region (CIR) show that the CIR's corotating energetic ion population (CEIP) associated with the trailing reverse shock starts within the CIR at the stream interface. This is consistent with an earlier result obtained by Pioneers 10 and 11 in the ecliptic plane between 4 and 6 AU. The Ulysses/Pioneer finding is noteworthy since the stream interface is not magnetically connected to the reverse shock, but lies 12-17 corotation hours from it. Thus, the finding seems to be inconsistent with the basic model that generates CEIP particles at the reverse shock and propagates them along field lines. Eliminating the inconsistency probably entails an extension of the standard model such as cross-field diffusion or a non-shock energization process operating near the stream interface closer to the sun.

Elemental abundances in corotating events

NASA Technical Reports Server (NTRS)

Vonrosenvinge, T. T.; Mcguire, R. E.

1985-01-01

Large, persistent solar-wind streams in 1973 and 1974 produced corotating interaction regions which accelerated particles to energies of a few MeV/nucleon. The proton to helium ratio (H/He) was remarkably constant at a value (22 + or 5) equal to that in the solar wind (21 + or - 3), suggesting that particles were being accelerated directly out of the solar wind. Preliminary results were presented from a similar study approximately 11 years (i.e., one solar cycle) later. Corotating events have been identified by surveying the solar wind data, energetic particle time-histories and anisotropies. This data was all obtained from the ISEE-3/ICE spacecraft. These events also show H/He ratios similar to that in the solar wind. It is flund that in these cases there is evidence for H/He ratios which are significantly different from that of the solar wind but which are consistent with the range of values found in solar flare events.

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.

Time-resolved Spectroscopy and Multi-color Photometry Of The Pulsating and Short-period Binary Subdwarf B Star Feige 48

NASA Astrophysics Data System (ADS)

Reed, Mike; Baran, A.; O'Toole, S.

2012-05-01

Pulsating subdwarf B (sdB) stars can be used as probes of the helium fusing cores of horizontal branch stars. To probe these stars, asteroseismology must be able to observationally associate pulsation frequencies with modes. Time-resolved spectroscopy and multicolor photometry have been employed with mixed results for short-period pulsating sdB stars. Time-resolved spectroscopy has successfully measured radial velocity, temperature, and gravity variations in six pulsators, yet interpreting results is far from straightforward. Multicolor photometry requires extremely high precision to discern between low-degree modes, yet has been used effectively to eliminate high-degree modes. Combining RV and multicolor measurements has also been shows as an effective means of constraining mode identifications. I will present results for Feige 48 using both time-resolved spectroscopy and multicolor photometry and attempts to constrain their pulsation modes using the atmospheric codes BRUCE and KYLIE.

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.

Searching for X-ray Pulsations from Neutron Stars Using NICER

NASA Astrophysics Data System (ADS)

Ray, Paul S.; Arzoumanian, Zaven; Gendreau, Keith C.; Bogdanov, Slavko; Bult, Peter; Chakrabarty, Deepto; Chakrabarty, Deepto; Guillot, Sebastien; Harding, Alice; Ho, Wynn C. G.; Lamb, Frederick; Mahmoodifar, Simin; Miller, Cole; Strohmayer, Tod; Wilson-Hodge, Colleen; Wolff, Michael T.; NICER Science Team Working Group on Pulsation Searches and Multiwavelength Coordination

2018-01-01

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 present our science plan and initial results from the first months of the NICER mission.

Test Characteristics of Neck Fullness and Witnessed Neck Pulsations in the Diagnosis of Typical AV Nodal Reentrant Tachycardia

PubMed Central

Sakhuja, Rahul; Smith, Lisa M; Tseng, Zian H; Badhwar, Nitish; Lee, Byron K; Lee, Randall J; Scheinman, Melvin M; Olgin, Jeffrey E; Marcus, Gregory M

2011-01-01

Summary Background Claims in the medical literature suggest that neck fullness and witnessed neck pulsations are useful in the diagnosis of typical AV nodal reentrant tachycardia (AVNRT). Hypothesis Neck fullness and witnessed neck pulsations have a high positive predictive value in the diagnosis of typical AVNRT. Methods We performed a cross sectional study of consecutive patients with palpitations presenting to a single electrophysiology (EP) laboratory over a 1 year period. Each patient underwent a standard questionnaire regarding neck fullness and/or witnessed neck pulsations during their palpitations. The reference standard for diagnosis was determined by electrocardiogram and invasive EP studies. Results Comparing typical AVNRT to atrial fibrillation (AF) or atrial flutter (AFL) patients, the proportions with neck fullness and witnessed neck pulsations did not significantly differ: in the best case scenario (using the upper end of the 95% confidence interval [CI]), none of the positive or negative predictive values exceeded 79%. After restricting the population to those with supraventricular tachycardia other than AF or AFL (SVT), neck fullness again exhibited poor test characteristics; however, witnessed neck pulsations exhibited a specificity of 97% (95% CI 90–100%) and a positive predictive value of 83% (95% CI 52–98%). After adjustment for potential confounders, SVT patients with witnessed neck pulsations had a 7 fold greater odds of having typical AVNRT, p=0.029. Conclusions Although neither neck fullness nor witnessed neck pulsations are useful in distinguishing typical AVNRT from AF or AFL, witnessed neck pulsations are specific for the presence of typical AVNRT among those with SVT. PMID:19479968

Blue large-amplitude pulsators as a new class of variable stars

NASA Astrophysics Data System (ADS)

Pietrukowicz, Paweł; Dziembowski, Wojciech A.; Latour, Marilyn; Angeloni, Rodolfo; Poleski, Radosław; di Mille, Francesco; Soszyński, Igor; Udalski, Andrzej; Szymański, Michał K.; Wyrzykowski, Łukasz; Kozłowski, Szymon; Skowron, Jan; Skowron, Dorota; Mróz, Przemek; Pawlak, Michał; Ulaczyk, Krzysztof

2017-08-01

Regular intrinsic brightness variations observed in many stars are caused by pulsations. These pulsations provide information on the global and structural parameters of the star. The pulsation periods range from seconds to years, depending on the compactness of the star and properties of the matter that forms its outer layers. Here, we report the discovery of more than a dozen previously unknown short-period variable stars: blue large-amplitude pulsators. These objects show very regular brightness variations with periods in the range of 20-40 min and amplitudes of 0.2-0.4 mag in the optical passbands. The phased light curves have a characteristic sawtooth shape, similar to the shape of classical Cepheids and RR Lyrae-type stars pulsating in the fundamental mode. The objects are significantly bluer than main-sequence stars observed in the same fields, which indicates that all of them are hot stars. Follow-up spectroscopy confirms a high surface temperature of about 30,000 K. Temperature and colour changes over the cycle prove the pulsational nature of the variables. However, large-amplitude pulsations at such short periods are not observed in any known type of stars, including hot objects. Long-term photometric observations show that the variable stars are very stable over time. Derived rates of period change are of the order of 10-7 per year and, in most cases, they are positive. According to pulsation theory, such large-amplitude oscillations may occur in evolved low-mass stars that have inflated helium-enriched envelopes. The evolutionary path that could lead to such stellar configurations remains unknown.

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.

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.

Ultra-fast magnetic resonance encephalography of physiological brain activity – Glymphatic pulsation mechanisms?

PubMed Central

Wang, Xindi; Korhonen, Vesa; Keinänen, Tuija; Tuovinen, Timo; Autio, Joonas; LeVan, Pierre; Keilholz, Shella; Zang, Yu-Feng; Hennig, Jürgen; Nedergaard, Maiken

2015-01-01

The theory on the glymphatic convection mechanism of cerebrospinal fluid holds that cardiac pulsations in part pump cerebrospinal fluid from the peri-arterial spaces through the extracellular tissue into the peri-venous spaces facilitated by aquaporin water channels. Since cardiac pulses cannot be the sole mechanism of glymphatic propulsion, we searched for additional cerebrospinal fluid pulsations in the human brain with ultra-fast magnetic resonance encephalography. We detected three types of physiological mechanisms affecting cerebral cerebrospinal fluid pulsations: cardiac, respiratory, and very low frequency pulsations. The cardiac pulsations induce a negative magnetic resonance encephalography signal change in peri-arterial regions that extends centrifugally and covers the brain in ≈1 Hz cycles. The respiratory ≈0.3 Hz pulsations are centripetal periodical pulses that occur dominantly in peri-venous areas. The third type of pulsation was very low frequency (VLF 0.001–0.023 Hz) and low frequency (LF 0.023–0.73 Hz) waves that both propagate with unique spatiotemporal patterns. Our findings using critically sampled magnetic resonance encephalography open a new view into cerebral fluid dynamics. Since glymphatic system failure may precede protein accumulations in diseases such as Alzheimer's dementia, this methodological advance offers a novel approach to image brain fluid dynamics that potentially can enable early detection and intervention in neurodegenerative diseases. PMID:26690495

Ultra-fast magnetic resonance encephalography of physiological brain activity - Glymphatic pulsation mechanisms?

PubMed

Kiviniemi, Vesa; Wang, Xindi; Korhonen, Vesa; Keinänen, Tuija; Tuovinen, Timo; Autio, Joonas; LeVan, Pierre; Keilholz, Shella; Zang, Yu-Feng; Hennig, Jürgen; Nedergaard, Maiken

2016-06-01

The theory on the glymphatic convection mechanism of cerebrospinal fluid holds that cardiac pulsations in part pump cerebrospinal fluid from the peri-arterial spaces through the extracellular tissue into the peri-venous spaces facilitated by aquaporin water channels. Since cardiac pulses cannot be the sole mechanism of glymphatic propulsion, we searched for additional cerebrospinal fluid pulsations in the human brain with ultra-fast magnetic resonance encephalography. We detected three types of physiological mechanisms affecting cerebral cerebrospinal fluid pulsations: cardiac, respiratory, and very low frequency pulsations. The cardiac pulsations induce a negative magnetic resonance encephalography signal change in peri-arterial regions that extends centrifugally and covers the brain in ≈1 Hz cycles. The respiratory ≈0.3 Hz pulsations are centripetal periodical pulses that occur dominantly in peri-venous areas. The third type of pulsation was very low frequency (VLF 0.001-0.023 Hz) and low frequency (LF 0.023-0.73 Hz) waves that both propagate with unique spatiotemporal patterns. Our findings using critically sampled magnetic resonance encephalography open a new view into cerebral fluid dynamics. Since glymphatic system failure may precede protein accumulations in diseases such as Alzheimer's dementia, this methodological advance offers a novel approach to image brain fluid dynamics that potentially can enable early detection and intervention in neurodegenerative diseases. © The Author(s) 2015.

An accurate nonlinear finite element analysis and test correlation of a stiffened composite wing panel

NASA Astrophysics Data System (ADS)

Davis, D. D., Jr.; Krishnamurthy, T.; Stroud, W. J.; McCleary, S. L.

1991-05-01

State-of-the-art nonlinear finite element analysis techniques are evaluated by applying them to a realistic aircraft structural component. A wing panel from the V-22 tiltrotor aircraft is chosen because it is a typical modern aircraft structural component for which there is experimental data for comparison of results. From blueprints and drawings, a very detailed finite element model containing 2284 9-node Assumed Natural-Coordinate Strain elements was generated. A novel solution strategy which accounts for geometric nonlinearity through the use of corotating element reference frames and nonlinear strain-displacement relations is used to analyze this detailed model. Results from linear analyses using the same finite element model are presented in order to illustrate the advantages and costs of the nonlinear analysis as compared with the more traditional linear analysis.

An accurate nonlinear finite element analysis and test correlation of a stiffened composite wing panel

NASA Technical Reports Server (NTRS)

Davis, D. D., Jr.; Krishnamurthy, T.; Stroud, W. J.; Mccleary, S. L.

1991-01-01

State-of-the-art nonlinear finite element analysis techniques are evaluated by applying them to a realistic aircraft structural component. A wing panel from the V-22 tiltrotor aircraft is chosen because it is a typical modern aircraft structural component for which there is experimental data for comparison of results. From blueprints and drawings, a very detailed finite element model containing 2284 9-node Assumed Natural-Coordinate Strain elements was generated. A novel solution strategy which accounts for geometric nonlinearity through the use of corotating element reference frames and nonlinear strain-displacement relations is used to analyze this detailed model. Results from linear analyses using the same finite element model are presented in order to illustrate the advantages and costs of the nonlinear analysis as compared with the more traditional linear analysis.

Global 3D radiation-hydrodynamics models of AGB stars. Effects of convection and radial pulsations on atmospheric structures

NASA Astrophysics Data System (ADS)

Freytag, B.; Liljegren, S.; Höfner, S.

2017-04-01

Context. Observations of asymptotic giant branch (AGB) stars with increasing spatial resolution reveal new layers of complexity of atmospheric processes on a variety of scales. Aims: To analyze the physical mechanisms that cause asymmetries and surface structures in observed images, we use detailed 3D dynamical simulations of AGB stars; these simulations self-consistently describe convection and pulsations. Methods: We used the CO5BOLD radiation-hydrodynamics code to produce an exploratory grid of global "star-in-a-box" models of the outer convective envelope and the inner atmosphere of AGB stars to study convection, pulsations, and shock waves and their dependence on stellar and numerical parameters. Results: The model dynamics are governed by the interaction of long-lasting giant convection cells, short-lived surface granules, and strong, radial, fundamental-mode pulsations. Radial pulsations and shorter wavelength, traveling, acoustic waves induce shocks on various scales in the atmosphere. Convection, waves, and shocks all contribute to the dynamical pressure and, thus, to an increase of the stellar radius and to a levitation of material into layers where dust can form. Consequently, the resulting relation of pulsation period and stellar radius is shifted toward larger radii compared to that of non-linear 1D models. The dependence of pulsation period on luminosity agrees well with observed relations. The interaction of the pulsation mode with the non-stationary convective flow causes occasional amplitude changes and phase shifts. The regularity of the pulsations decreases with decreasing gravity as the relative size of convection cells increases. The model stars do not have a well-defined surface. Instead, the light is emitted from a very extended inhomogeneous atmosphere with a complex dynamic pattern of high-contrast features. Conclusions: Our models self-consistently describe convection, convectively generated acoustic noise, fundamental-mode radial pulsations, and atmospheric shocks of various scales, which give rise to complex changing structures in the atmospheres of AGB stars.

The tip of the iceberg: the frequency content of the δ Sct star HD 50844 from CoRoT space photometry

NASA Astrophysics Data System (ADS)

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

2009-09-01

It has been suggested that the detection of a wealth of very low amplitude modes in δ Sct stars was only a matter of signal-to-noise ratio. Access to this treasure, impossible from the ground, is one of the scientific aims of the space mission CoRoT, developed and operated by CNES. This work presents the results obtained on HD 50844: the 140,016 datapoints allowed us to reach the level of 10-5 mag in the amplitude spectra. The frequency analysis of the CoRoT timeseries revealed hundreds of terms in the frequency range 0-30 d-1. 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 = 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. The predominant term (f1 = 6.92 d-1) has been identified as the fundamental radial mode combining ground-based photometric and spectroscopic data.

Corotation of an intermittent solar wind source

NASA Technical Reports Server (NTRS)

Croft, T. A.

1972-01-01

The measured electron content of the solar wind in mid-1970 exhibited a region of relatively high electron density that reappeared at intervals of about 27.8 days. It is shown that the repeating event cannot be reconciled with the concept of a long-enduring steady flow, even though the recurrence period is close to the rotation period of the sun. This evidence of transients is inferred from the short duration of each appearance of the interval of higher density; each should last for roughly one corotation interval if it is caused by a steady stream. The radio path was approximately 0.8 AU long, and the corotation interval exceeded 3 days. Other aspects of the content data patterns support the view that such transient events are common in the solar wind. The mid-1970 repeating event is an unusually good example of the intermittent character of flow regions in the solar wind that fluctuate on a time scale of days but endure as identifiable regions for many months. A sputtering corotating source of thin solar plasma streams could explain this series of events; it could also be explained in terms of a stream that is steady in density and speed but undulating north-south so that it passes into and out of the 0.8 AU radio path in a matter of a day or less.

CoRoT 101186644: A transiting low-mass dense M-dwarf on an eccentric 20.7-day period orbit around a late F-star. Discovered in the CoRoT lightcurves

NASA Astrophysics Data System (ADS)

Tal-Or, L.; Mazeh, T.; Alonso, R.; Bouchy, F.; Cabrera, J.; Deeg, H. J.; Deleuil, M.; Faigler, S.; Fridlund, M.; Hébrard, G.; Moutou, C.; Santerne, A.; Tingley, B.

2013-05-01

We present the study of the CoRoT transiting planet candidate 101186644, also named LRc01_E1_4780. Analysis of the CoRoT lightcurve and the HARPS spectroscopic follow-up observations of this faint (mV = 16) candidate revealed an eclipsing binary composed of a late F-type primary (Teff = 6090 ± 200 K) and a low-mass, dense late M-dwarf secondary on an eccentric (e = 0.4) orbit with a period of ~20.7 days. The M-dwarf has a mass of 0.096 ± 0.011 M⊙, and a radius of 0.104-0.006+0.026 R⊙, which possibly makes it the smallest and densest late M-dwarf reported so far. Unlike the claim that theoretical models predict radii that are 5-15% smaller than measured for low-mass stars, this one seems to have a radius that is consistent and might even be below the radius predicted by theoretical models. Based on observations made with the 1-m telescope at the Wise Observatory, Israel, the Swiss 1.2-m Leonhard Euler telescope at La Silla Observatory, Chile, the IAC-80 telescope at the Observatory del Teide, Canarias, Spain, and the 3.6-m telescope at La Silla Observatory (ESO), Chile (program 184.C-0639).

An experimental study of large-scale vortices over a blunt-faced flat plate in pulsating flow

NASA Astrophysics Data System (ADS)

Hwang, K. S.; Sung, H. J.; Hyun, J. M.

Laboratory measurements are made of flow over a blunt flat plate of finite thickness, which is placed in a pulsating free stream, U=Uo(1+Aocos 2πfpt). Low turbulence-intensity wind tunnel experiments are conducted in the ranges of Stp<=1.23 and Ao<=0.118 at ReH=560. Pulsation is generated by means of a woofer speaker. Variations of the time-mean reattachment length xR as functions of Stp and Ao are scrutinized by using the forward-time fraction and surface pressure distributions (Cp). The shedding frequency of large-scale vortices due to pulsation is measured. Flow visualizations depict the behavior of large-scale vortices. The results for non-pulsating flows (Ao=0) are consistent with the published data. In the lower range of Ao, as Stp increases, xR attains a minimum value at a particular pulsation frequency. For large Ao, the results show complicated behaviors of xR. For Stp>=0.80, changes in xR are insignificant as Ao increases. The shedding frequency of large-scale vortices is locked-in to the pulsation frequency. A vortex-pairing process takes place between two neighboring large-scale vortices in the separated shear layer.

Statistics of bow shock nonuniformity.

NASA Technical Reports Server (NTRS)

Greenstadt, E. W.

1973-01-01

The statistical occurrence of pulsation or oblique structure about the earth's generally nonuniform bow shock is estimated at selected points by combining a three-dimensional distribution of interplanetary field directions obtained for a six-day solar wind sector with an index of local pulsation geometry. The result, obtained with a pulsation index of 1.6, is a set of distribution patterns showing the dependence of the pulsation index on the field orientation at the selected shock loci for this value of the index.

Physics and Chemistry of MW Laser-induced Discharge in Gas Flows and Plasma Jets

DTIC Science & Technology

2007-12-01

with the large scaled flow pulsations . In 3.3 the results of numerical modeling of a thin low-density heated channel of limited length – shock layer...in Fig. 3.2.13. The red points correspond to the values of time moments for Fig. 3.2.11, 12. Mechanism of heated area boundary pulsations ...Mechanism of heated area boundary pulsations is analogical to described above mechanism of the bow shock position pulsations and is connected with

Terahertz spectroscopic polarimetry of generalized anisotropic media composed of Archimedean spiral arrays: Experiments and simulations.

PubMed

Aschaffenburg, Daniel J; Williams, Michael R C; Schmuttenmaer, Charles A

2016-05-07

Terahertz time-domain spectroscopic polarimetry has been used to measure the polarization state of all spectral components in a broadband THz pulse upon transmission through generalized anisotropic media consisting of two-dimensional arrays of lithographically defined Archimedean spirals. The technique allows a full determination of the frequency-dependent, complex-valued transmission matrix and eigenpolarizations of the spiral arrays. Measurements were made on a series of spiral array orientations. The frequency-dependent transmission matrix elements as well as the eigenpolarizations were determined, and the eigenpolarizations were found be to elliptically corotating, as expected from their symmetry. Numerical simulations are in quantitative agreement with measured spectra.

Measurement of direct current electric fields and plasma flow speeds in Jupiter's magnetosphere

NASA Technical Reports Server (NTRS)

Kellogg, Paul J.; Goetz, K.; Howard, R. L.; Monson, S. J.; Balogh, A.; Forsyth, R. J.

1993-01-01

During the encounter of Ulysses with Jupiter, we have measured two components of the dc electric field and deduced from them the flow speed in the Io toms, as well as the presence of a polar cap region end what we interpret as a cleft region. Within the toms the flow speed is approximately equal to the speed of a plasma corotating with Jupiter but has significant deviations. The dominant deviations have an apparent period of the order of Jupiter's rotation period, but this might be a latitudinal effect. Other important periods are about 40 min and less than 25 min.

UltraPulse--simulating a human arterial pulse with focussed airborne ultrasound.

PubMed

Hung, G M Y; John, N W; Hancock, C; Gould, D A; Hoshi, T

2013-01-01

Medical simulators provide a risk-free environment for trainee doctors to practice and improve their skills. UltraPulse is a new tactile system designed to utilise focussed airborne ultrasound to mimic a pulsation effect such as that of a human arterial pulse. In this paper, we focus on the construction of the haptics component, which can later be integrated into a variety of medical procedure training simulators.

Asiago eclipsing binaries program IV. SZ Camelopardalis, a β Cephei pulsator in a quadruple, eclipsing system

NASA Astrophysics Data System (ADS)

Tamajo, E.; Munari, U.; Siviero, A.; Tomasella, L.; Dallaporta, S.

2012-03-01

We present a spectroscopic and photometric analysis of the multiple system and early-type eclipsing binary SZ Cam (O9 IV + B0.5 V), which consists of an eclipsing SB2 pair of orbital period P = 2.7 days in a long orbit (~55 yrs) around a non-eclipsing SB1 pair of orbital period P = 2.8 days. We have reconstructed the spectra of the individual components of SZ Cam from the observed composite spectra using the technique of spectral disentangling. We used them together with extensive and accurate BVIC CCD photometry to obtain an orbital solution. Our photometry revealed the presence of a β Cep variable in the SZ Cam hierarchical system, probably located within the non-eclipsing SB1 pair. The pulsation period is (0.33265 ± 0.00005) days and the observed total amplitude in the B band is (0.0105 ± 0.0005) mag. NLTE analysis of the disentangled spectra provided atmospheric parameters for all three components, consistent with those derived from orbital solution. Full Table 3 is only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/539/A139

Solid-state transformer-based new traction drive system and control

NASA Astrophysics Data System (ADS)

Feng, Jianghua; Shang, Jing; Zhang, Zhixue; Liu, Huadong; Huang, Zihao

2017-11-01

A new type of traction drive system consisting of solid-state traction transformer (SSTT), inverter unit, auxiliary inverter, traction motor and other key components is built in order to suit the demand of developing the next-generation electric traction system which will be efficient and lightweight, with high power density. For the purpose of reducing system volume and weight and improving efficiency and grid-side power quality, an efficient SSTT optimized topology combining high-voltage cascaded rectifiers with high-power high-frequency LLC resonant converter is proposed. On this basis, an integrated control strategy built upon synchronous rotating reference frame is presented to achieve unified control over fundamental active, reactive and harmonic components. The carrier-interleaving phase shift modulation strategy is proposed to improve the harmonic performance of cascaded rectifiers. In view of the secondary pulsating existing in a single-phase system, the mathematical model of secondary power transfer is built, and the mechanism of pulsating voltage resulting in beat frequency of LLC resonant converter is revealed, so as to design optimum matching of system parameters. Simulation and experimental results have verified that the traction system and control scheme mentioned in this paper are reasonable and superior and that they meet the future application requirements for rail transit.

Pulsating flow past a tube bundle

NASA Astrophysics Data System (ADS)

Molochnikov, V. M.; Mikheev, N. I.; Vazeev, T. A.; Paereliy, A. A.

2017-11-01

Visualization of the pulsating cross-flow past the in-line and staggered tube bundles has been performed. The frequency and amplitude of forced flow pulsations and the tube pitch in the bundle varied in the experiments. The main attention was focused on the flow pattern in the near wake of the third-row tube. The most indicative regimes of flow past a tube in a bundle have been revealed depending on forced flow unsteadiness parameters. The obtained data have been generalized in the flow maps in the space of dimensionless frequency (Strouhal number, St) and relative pulsation amplitude, β, individually for the in-line and staggered tube arrangement. Three most indicative regimes of pulsating flow past the tubes in a bundle have been singled out in each flow map.

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 N 2>+ 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 auroralmore » 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.« less

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.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

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

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 N 2>+ 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 auroralmore » 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.« less

Nonlinear convective pulsation models of type II Cepheids

NASA Astrophysics Data System (ADS)

Smolec, Radoslaw

2015-08-01

We present a grid of nonlinear convective pulsation models of type-II Cepheids: BL Her stars, W Vir stars and RV Tau stars. The models cover a wide range of masses, luminosities, effective temperatures and chemical compositions. The most interesting result is detection of deterministic chaos in the models. Different routes to chaos are detected (period doubling, intermittent route) as well as variety of phenomena intrinsic to chaotic dynamics (periodic islands within chaotic bands, crisis bifurcation, type-I and type-III intermittency). Some of the phenomena (period doubling in BL Her and in RV Tau stars, irregular pulsation of RV Tau stars) are well known in the pulsation of type-II Cepheids. Prospects of discovering the other are briefly discussed. Transition from BL Her type pulsation through W Vir type till RV Tau type is analysed. In the most luminous models a dynamical instability is detected, which indicates that pulsation driven mass loss is important process occurring in type-II Cepheids.

Statistical studies of Pc 3-5 pulsations and their relevance for possible source mechanisms of ULF waves

NASA Technical Reports Server (NTRS)

Anderson, Brian J.

1993-01-01

A number of statistical studies using spacecraft data have been made of ULF waves in the magnetosphere. These studies provide an overview of ULF pulsation activity for r = 5-15 R(E) and allow an assessment of likely source mechanisms. In this review pulsations are categorized into five general types: compressional Pc 5, poloidal Pc 4, toroidal harmonics, toroidal Pc 5 (fundamental mode), and incoherent noise. The occurrence distributions and/or distributions of wave power of the different types suggest that compressional Pc 5 and poloidal Pc 4 derive their energy locally, most likely from energetic protons. The toroidal pulsations, both harmonic and fundamental mode, appear to be driven by an energy source outside the magnetopause - directly upstream in the sheath and solar wind for harmonics and the flanks for fundamentals. Incoherent pulsations are a prominent pulsation type but from their occurrence distribution alone it is unclear what their dominant energy source may be.

YSOVAR II: Mapping YSO Inner Disk Structure in NGC 2264 with Simultaneous Spitzer and CoRoT Time Series Photometry

NASA Astrophysics Data System (ADS)

Stauffer, John; Morales-Calderon, Maria; Rebull, Luisa; Affer, Laura; Alencar, Sylvia; Allen, Lori; Barrado, David; Bouvier, Jerome; Calvet, Nuria; Carey, Sean; Carpenter, John; Ciardi, David; Covey, Kevin; D'Alessio, Paola; Espaillat, Catherine; Favata, Fabio; Flaccomio, Ettore; Forbrich, Jan; Furesz, Gabor; Hartman, Lee; Herbst, William; Hillenbrand, Lynne; Holtzman, Jon; Hora, Joe; Marchis, Franck; McCaughrean, Mark; Micela, Giusi; Mundt, Reinhard; Plavchan, Peter; Turner, Neal; Skrutzkie, Mike; Smith, Howard; Song, Inseok; Szentgyorgi, Andy; Terebey, Susan; Vrba, Fred; Wasserman, Lawrence; Watson, Alan; Whitney, Barbara; Winston, Elaine; Wood, Kenny

2011-05-01

We propose a simultaneous, continuous 30 day observation of the star forming region NGC2264 with Spitzer and CoRoT. NGC2264 is the only nearby, rich star-forming region which can be observed with CoRoT; it is by definition then the only nearby, rich star-forming region where a simultaneous Spitzer/CoRoT campaign is possible. Fortunately, the visibility windows for the two spacecraft overlap, allowing this program to be done in the Nov. 25, 2011 to Jan. 4, 2012 time period. For 10 days, we propose to map the majority of the cluster (a 35'x35' region) to a depth of 48 seconds per point, with each epoch taking 1.7 hours, allowing of order 12 epochs per day. For the other 20 days, we propose to obtaining staring-mode data for two positions in the cluster having a high density of cluster members. We also plan to propose for a variety of other ground and space-based data, most of which would also be simultaneous with the Spitzer and CoRoT observing. These data will allow us to address many astrophysical questions related to the structure and evolution of the disks of young stars and the interaction of those disks with the forming star. The data may also help inform models of planet formation since planets form and migrate through the pre-main sequence disks during the 0.5-5 Myr age range of stars in NGC2264. The data we collect will also provide an archive of the variability properties of young stars that is unmatched in its accuracy, sensitivity, cadence and duration and which therefore could inspire investigation of phenomena which we cannot now imagine. The CoRoT observations have been approved, contingent on approval of a simultaneous Spitzer observing program (this proposal).

Nonlinear Modeling of Radial Stellar Pulsations

NASA Astrophysics Data System (ADS)

Smolec, R.

2009-09-01

In this thesis, I present the results of my work concerning the nonlinear modeling of radial stellar pulsations. I will focus on classical Cepheids, particularly on the double-mode phenomenon. History of nonlinear modeling of radial stellar pulsations begins in the sixties of the previous century. At the beginning convection was disregarded in model equations. Qualitatively, almost all features of the radial pulsators were successfully modeled with purely radiative hydrocodes. Among problems that remained, the most disturbing was modeling of the double-mode phenomenon. This long-standing problem seemed to be finally solved with the inclusion of turbulent convection into the model equations (Kollath et al. 1998, Feuchtinger 1998). Although dynamical aspects of the double-mode behaviour were extensively studied, its origin, particularly the specific role played by convection, remained obscure. To study this and other problems of radial stellar pulsations, I implemented the convection into pulsation hydrocodes. The codes adopt the Kuhfuss (1986) convection model. In other codes, particularly in the Florida-Budapest hydrocode (e.g. Kollath et al. 2002), used in comput! ation of most of the published double-mode models, different approximations concerning e.g. eddy-viscous terms or treatment of convectively stable regions are adopted. Particularly the neglect of negative buoyancy effects in the Florida-Budapest code and its consequences, were never discussed in the literature. These consequences are severe. Concerning the single-mode pulsators, neglect of negative buoyancy leads to smaller pulsation amplitudes, in comparison to amplitudes computed with code including these effects. Particularly, neglect of negative buoyancy reduces the amplitude of the fundamental mode very strong. This property of the Florida-Budapest models is crucial in bringing up the stable non-resonant double-mode Cepheid pulsation involving fundamental and first overtone modes (F/1O). Such pulsation is not observed in models computed including negative buoyancy. As the neglect of negative buoyancy is physically not correct, so are the double-mode Cepheid models computed with the Florida-Budapest hydrocode. Extensive search for F/1O double-mode Cepheid pulsation with the codes including negative buoyancy effects yielded null result. Some resonant double-mode F/1O Cepheid models were found, but their occurrence was restricted to a very narrow domain in the Hertzsprung-Russel diagram. Model computations intended to model the double-overtone (1O/2O) Cepheids in the Large Magellanic Cloud, also revealed some stable double-mode pulsations, however, restricted to a narrow period range. Resonances are most likely conductive in bringing up the double-mode behaviour observed in these models. However, majority of the double-overtone LMC Cepheids cannot be reproduced with our codes. Hence, the modeling of double-overtone Cepheids with convective hydrocodes is not satisfactory, either. Double-mode pulsation still lacks satisfactory explanation, and problem of its modeling remains open.

Cranial diameter pulsations measured by non-invasive ultrasound decrease with tilt

NASA Technical Reports Server (NTRS)

Ueno, Toshiaki; Ballard, Richard E.; Macias, Brandon R.; Yost, William T.; Hargens, Alan R.

2003-01-01

INTRODUCTION: Intracranial pressure (ICP) may play a significant role in physiological responses to microgravity by contributing to the nausea associated with microgravity exposure. However, effects of altered gravity on ICP in astronauts have not been investigated, primarily due to the invasiveness of currently available techniques. We have developed an ultrasonic device that monitors changes in cranial diameter pulsation non-invasively so that we can evaluate ICP dynamics in astronauts during spaceflight. This study was designed to demonstrate the feasibility of our ultrasound technique under the physiological condition in which ICP dynamics are changed due to altered gravitational force. METHODS: Six healthy volunteers were placed at 60 degrees head-up, 30 degrees headup, supine, and 15 degrees head-down positions for 3 min at each angle. We measured arterial blood pressure (ABP) with a finger pressure cuff, and cranial diameter pulsation with a pulsed phase lock loop device (PPLL). RESULTS: Analysis of covariance demonstrated that amplitudes of cranial diameter pulsations were significantly altered with the angle of tilt (p < 0.001). The 95% confidence interval for linear regression coefficients of the cranial diameter pulsation amplitudes with tilt angle was 0.862 to 0.968. However, ABP amplitudes did not show this relationship. DISCUSSION: Our noninvasive ultrasonic technique reveals that the amplitude of cranial diameter pulsation decreases as a function of tilt angle, suggesting that ICP pulsation follows the same relationship. It is demonstrated that the PPLL device has a sufficient sensitivity to detect changes non-invasively in ICP pulsation caused by altered gravity.

[Intranuclear distribution of rat liver ribosomal RNA].

PubMed

Dabeva, M D; Todorov, B N; Khadzhiolova, A A

1976-03-01

A method is described for the isolation of pure liver nuclei with minimal cytoplasmic contaminants, loss of nuclear RNA and degradation of nuclear RNA. The RNA components are extracted in three distinct fractions by subsequent treatment with phenol at 4 degrees, 50 degrees and 85 degrees C. The total and 14C-orotate labelled RNA components in the three nuclear RNA fractions are characterized by nucleotide composition, poly(A)-RNA content and agar-gel electrophoresis. The results show that the RNA in three fractions correspond to the nucleosol, nucleolus and chromatin compartments of the nucleus. The nuclear HnRNA components are exclusively in the 85 degrees C RNA. Nuclear ribosomal RNA is extracted in the 4 degrees C and 50 degrees C RNA fractions. These two nuclear RNA fractions are distinct in constituent pre-rRNA species and the rate of labelling of their rRNA components. The amount of the pre-rRNA and rRNA species is determined. The results show that the nucleolus-nucleosol and nucleosol-cytoplasm transitions of ribosomal subparticles are markedly slower processes than the preceeding steps of ribosome biogenesis.

Monitoring a high-amplitude δ Scuti star for 152 days: discovery of 12 additional modes and modulation effects in the light curve of CoRoT 101155310

NASA Astrophysics Data System (ADS)

Poretti, E.; Rainer, M.; Weiss, W. W.; Bognár, Zs.; Moya, A.; Niemczura, E.; Suárez, J. C.; Auvergne, M.; Baglin, A.; Baudin, F.; Benkő, J. M.; Debosscher, J.; Garrido, R.; Mantegazza, L.; Paparó, M.

2011-04-01

Aims: The detection of small-amplitude nonradial modes in high-amplitude δ Sct (HADS) variables has been very elusive until at least five of them were detected in the light curve of V974 Oph obtained from ground-based observations. The combination of radial and nonradial modes has a high asteroseismic potential, thanks to the strong constraints we can put in the modelling. The continuous monitoring of ASAS 192647-0030.0 ≡ CoRoT 101155310 (P = 0.1258 d, V = 13.4) ensured from space by the CoRoT (COnvection, ROtation and planetary Transits) mission constitutes a unique opportunity to exploit such potential. Methods: The 22270 CoRoT measurements were performed in the chromatic mode. They span 152 d and cover 1208 consecutive cycles. After the correction for one jump and the long-term drift, the level of the noise turned out to be 29 μmag. The phase shifts and amplitude ratios of the coloured CoRoT data, the HARPS spectra, and the period-luminosity relation were used to determine a self-consistent physical model. In turn, it allowed us to model the oscillation spectrum, also giving feedback on the internal structure of the star. Results: In addition to the fundamental radial mode f1 = 7.949 d-1 with harmonics up to 10f1, we detected 12 independent terms. Linear combinations were also found and the light curve was solved by means of 61 frequencies (smallest amplitude 0.10 mmag). The newest result is the detection of a periodic modulation of the f1 mode (triplets at ± 0.193 d-1 centred on f1 and 2f1), discussed as a rotational effect or as an extension of the Blazhko effect to HADS stars. The physical model suggests that CoRoT 101155310 is an evolved star, with a slight subsolar metallic abundance, close to the terminal age main sequence. All the 12 additional terms are identified with mixed modes in the predicted overstable region. The CoRoT space mission was developed and is operated by the French space agency CNES, with the participation of ESA's RSSD and Science Programmes, Austria, Belgium, Brazil, Germany, and Spain. This work uses ground-based spectroscopic observations made with the HARPS instrument at the 3.6 m-ESO telescope (La Silla, Chile) under the ESO Large Programme LP182.D-0356 and complementary photometric measurements made at the Piszkéstető Mountain Station of Konkoly Observatory (Hungary).Table 1 is also, and Table 2 only, available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/528/A147

21 CFR 886.5200 - Eyelid thermal pulsation system.

Code of Federal Regulations, 2014 CFR

2014-04-01

... 21 Food and Drugs 8 2014-04-01 2014-04-01 false Eyelid thermal pulsation system. 886.5200 Section 886.5200 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) MEDICAL DEVICES OPHTHALMIC DEVICES Therapeutic Devices § 886.5200 Eyelid thermal pulsation system...

Experimental study of pressure pulsations in the flow duct of a medium-size model hydroelectric generator with Francis turbine

NASA Astrophysics Data System (ADS)

Platonov, D. V.; Maslennikova, A. V.; Dekterev, D. A.; Minakov, A. V.; Abramov, A. V.

2018-01-01

In the present study, we report on the results of an experimental study of pressure pulsations in the flow duct of a medium-scale hydrodynamic bench with Francis turbine. In various regimes, integral and pulsation characteristics of the turbine were measured. With the help of high-speed filming, the structure of the flow behind the turbine runner was analyzed, and the influence of this structure on the intensity and frequency of pressure pulsations in the flow duct was demonstrated.

SPIPS: Spectro-Photo-Interferometry of Pulsating Stars

NASA Astrophysics Data System (ADS)

Mérand, Antoine

2017-10-01

SPIPS (Spectro-Photo-Interferometry of Pulsating Stars) combines radial velocimetry, interferometry, and photometry to estimate physical parameters of pulsating stars, including presence of infrared excess, color excess, Teff, and ratio distance/p-factor. The global model-based parallax-of-pulsation method is implemented in Python. Derived parameters have a high level of confidence; statistical precision is improved (compared to other methods) due to the large number of data taken into account, accuracy is improved by using consistent physical modeling and reliability of the derived parameters is strengthened by redundancy in the data.

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.

The Development of Early Pulsation Theory, or, How Cepheids Are Like Steam Engines

NASA Astrophysics Data System (ADS)

Stanley, M.

2012-06-01

The pulsation theory of Cepheid variable stars was a major breakthrough of early twentieth-century astrophysics. At the beginning of that century, the basic physics of normal stars was very poorly understood, and variable stars were even more mysterious. Breaking with accepted explanations in terms of eclipsing binaries, Harlow Shapley and A. S. Eddington pioneered novel theories that considered Cepheids as pulsating spheres of gas. Surprisingly, the pulsation theory not only depended on novel developments in stellar physics, but the theory also drove many of those developments. In particular, models of stars in radiative balance and theories of stellar energy were heavily inspired and shaped by ideas about variable stars. Further, the success of the pulsation theory helped justify the new approaches to astrophysics being developed before World War II.

Exploring the relative boundaries of the patchy pulsating aurora

NASA Astrophysics Data System (ADS)

Carlisle, E.; Donovan, E.; Jackel, B. J.

2017-12-01

Pulsating aurora is a common auroral feature that occurs most frequently on the nightside, in the equatorward part of the auroral oval. It is caused by pitch angle scattering of electrons due to wave-particle interactions near the equatorial plane. As such, observations of pulsating aurora provide information about the distribution of the plasma waves in the magnetosphere. Anecdotal evidence suggests that pulsating aurora occur equatorward of the proton aurora, and hence in the largely dipolar region at or inside the inner edge of the plasma sheet. Here we present results of a statistical survey of photometer observations of proton aurora and simultaneous all-sky imager observations of electron aurora. Our objective is to provide a definitive statement regarding the location of pulsating aurora relative to the proton aurora.

A Method to Estimate the Masses of Asymptotic Giant Branch Variable Stars

NASA Astrophysics Data System (ADS)

Takeuti, Mine; Nakagawa, Akiharu; Kurayama, Tomoharu; Honma, Mareki

2013-06-01

AGB variable stars are at the transient phase between low and high mass-loss rates; estimating the masses of these stars is necessary to study the evolutionary processes and mass-loss processes during the AGB stage. We applied the pulsation constant theoretically derived by Xiong and Deng (2007 MNRAS, 378, 1270) to 15 galactic AGB stars in order to estimate their masses. We found that using the pulsation constant is effective to estimate the mass of a star pulsating with two different pulsation modes, such as S Crt and RX Boo, which provides mass estimates comparable to theoretical results of AGB star evolution. We also extended the use of the pulsation constant to single-mode variables, and analyzed the properties of AGB stars related to their masses.

Time course and topographic distribution of ocular fundus pulsation measured by low-coherence tissue interferometry

NASA Astrophysics Data System (ADS)

Dragostinoff, Nikolaus; Werkmeister, René M.; Klaizer, József; Gröschl, Martin; Schmetterer, Leopold

2013-12-01

Low-coherence tissue interferometry is a technique for the depth-resolved measurement of ocular fundus pulsations. Whereas fundus pulsation amplitudes at preselected axial positions can readily be assessed by this method, coupling of the interferometer with a pulse oximeter additionally allows for the reconstruction of the time course of ocular fundus pulsation with respect to the cardiac cycle of the subject. For this purpose, the interferogram resulting from the superposition of waves reflected at the cornea and the ocular fundus is recorded synchronously with the plethysmogram. A new method for evaluating the time course of synthetic interferograms in combination with plethysmograms based on averaging several pulse periods has been developed. This technique allows for the analysis of amplitudes, time courses, and phase differences of fundus pulsations at preselected axial and transversal positions and for creating fundus pulsation movies. Measurements are performed in three healthy emmetropic subjects at angles from 0 deg to 18 deg to the axis of vision. Considerably different time courses, amplitudes, and phases with respect to the cardiac cycle are found at different angles. Data on ocular fundus pulsation obtained with this technique can-among other applications-be used to verify and to improve biomechanical models of the eye.

Studies on the latitudinal distribution of ground-based geomagnetic pulsations and fluctuations in the interplanetary medium using discrete mathematical analysis methods

NASA Astrophysics Data System (ADS)

Zelinsky, N. R.; Kleimenova, N. G.; Malysheva, L. M.

2014-07-01

Ground-based geomagnetic Pc5 (2-7 mHz) pulsations, caused by the passage of dense transients (density disturbances) in the solar wind, were analyzed. It was shown that intensive bursts can appear in the density of the solar wind and its fluctuations, up to Np ˜ 30-50 cm3, even during the most magnetically calm year in the past decades (2009). The analysis, performed using one of the latest methods of discrete mathematical analysis (DMA), is presented. The energy functional of a time-series fragment (called "anomaly rectification" in DMA terms) of two such events was calculated. It was established that fluctuations in the dynamic pressure (density) of the solar wind (SW) cause the global excitation of Pc5 geomagnetic pulsations in the daytime sector of the Earth's magnetosphere, i.e., from polar to equatorial latitudes. Such pulsations started and ended suddenly and simultaneously at all latitudes. Fluctuations in the interplanetary magnetic field (IMF) have turned up to be less geoeffective in exciting geomagnetic pulsations than fluctuations in the SW density. The pulsation generation mechanisms in various structural regions of the magnetosphere were probably different. It was therefore concluded that the most probable source of ground-based pulsations are fluctuations of the corresponding periods in the SW density.

Binary Model for the Heartbeat Star System KIC 4142768

NASA Astrophysics Data System (ADS)

Manuel, Joseph; Hambleton, Kelly

2018-01-01

Heartbeat stars are a class of eccentric (e > 0.2) binary systems that undergo strong tidal forces. These tidal forces cause the shape of each star and the temperature across the stellar surfaces to change. This effect also generates variations in the light curve in the form of tidally-induced pulsations, which are theorized to have a significant effect on the circularization of eccentric orbits (Zahn, 1975). Using the binary modeling software PHOEBE (Prša & Zwitter 2005) on the Kepler photometric data and Keck radial velocity data for the eclipsing, heartbeat star KIC 4142768, we have determined the fundamental parameters including masses and radii. The frequency analysis of the residual data has surprisingly revealed approximately 29 pulsations with 8 being Delta Scuti pulsations, 10 being Gamma Doradus pulsations, and 11 being tidally-induced pulsations. After subtracting an initial binary model from the original, detrended photometric data, we analyzed the pulsation frequencies in the residual data. We then were able to disentangle the identified pulsations from the original data in order to conduct subsequent binary modeling. We plan to continue this study by applying asteroseismology to KIC 4142768. Through our continued investigation, we hope to extract information about the star’s internal structure and expect this will yield additional, interesting results.

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.

In-water gas combustion for thrust production

NASA Astrophysics Data System (ADS)

Teslenko, V. S.; Drozhzhin, A. P.; Medvedev, R. N.

2017-07-01

The paper presents the results of experimental study for hydrodynamic processes occurring during combustion of a stoichiometric mixture propane-oxygen in combustion chambers with different configurations and submerged into water. The pulses of force acting upon a thrust wall were measured for different geometries: cylindrical, conic, hemispherical, including the case of gas combustion near a flat thrust wall. After a single charge of stoichiometric mixture propane-oxygen is burnt near the thrust wall, the process of cyclic generation of force pulses develops. The first pulse is generated due to pressure growth during gas combustion, and the following pulses are the result of hydrodynamic pulsations of the gaseous cavity. Experiments demonstrated that efficient generation of thrust occurs if all bubble pulsations are used during combustion of a single gas combustion. In the series of experiments, the specific impulse on the thrust wall was in the range 104-105 s (105-106 m/s) with account for positive and negative components of impulse.

Toroidal standing waves excited by a storm sudden commencement - DE 1 observations

NASA Technical Reports Server (NTRS)

Cahill, L. J., Jr.; Lin, N. G.; Engebretson, M. J.; Waite, J. H.; Sugiura, M.

1990-01-01

A 74-nT sudden commencement on July 13, 1982, was observed in the magnetosphere, with instruments on the Dynamics Explorer 1 satellite. Inbound, near L = 4.5, the satellite was located at 1524 magnetic local time and 20 deg magnetic latitude. The sudden commmencement established a strong, east-west oscillation, with 100-s period, which was observed in the magnetic field, the electric field, and the plasma flow velocity records. There was also a compressional component of this 100-s oscillation and a rapidly damped 300-s compressional pulsation. The compressional oscillations may be an evidence of cavity resonances, excited by the sudden commencement. The cavity waves may, in turn, couple to toroidal waves in field line resonance at the satellite location. In addition, the sudden commencement caused the onset of waves with frequencies from 0.1 up to at least 0.5 Hz. The observations are compared with similar reports from earlier pulsations related to sudden commencements.

Evidence for a Millisecond Pulsar in 4U 1636-53 During a Superburst

NASA Technical Reports Server (NTRS)

Strohmayer, Tod E.; Markwardt, Craig B.; White, Nicholas E. (Technical Monitor)

2002-01-01

We report the discovery with the Proportional Counter Array on board the Rossi X-ray Timing Explorer of highly coherent 582 Hz pulsations during the February 22, 2001 (UT) 'superburst' from 4U 1636-53. The pulsations are detected during an 800 s interval spanning the flux maximum of the burst. Within this interval the barycentric oscillation frequency increases in a monotonic fashion from 581.89 to 581.93 Hz. The predicted orbital motion of the neutron star during this interval is consistent with such an increase as long as optical maximum corresponds roughly with superior conjunction of V801 Arae, the optical companion to the neutron star in 4U 1636-53. We show that a range of circular orbits with 90 < v(sub ns) sin i < 175 km/s and 0.336 > phi(sub 0) > 0.277 for the neutron star can provide an excellent description of the frequency and phase evolution. The brevity of the observed pulse train with respect to the 3.8 hour orbital period unfortunately does not allow more precise constraints. The average pulse profile is sinusoidal and the time averaged pulsation amplitude, as inferred from the half amplitude of the sinusoid is 1%, smaller than typical for burst oscillations observed in normal thermonuclear bursts. We do not detect any higher harmonics nor the putative subharmonic near 290 Hz. The 90% upper limits on signal amplitude at the subharmonic and first harmonic are 0.1 and 0.06%, respectively. The highly coherent pulsation, with a Q = v(sub 0)/delta-v > 4.5 x 10(exp 5) provides compelling evidence for a rapidly rotating neutron star in 4U 1636-53, and further supports the connection of burst oscillation frequencies with the spin frequencies of neutron stars. Our results provide further evidence that some millisecond pulsars are spun up via accretion in LMXBs. We also discuss the implications of our orbital velocity constraint for the masses of the components of 4U 1636-53.

Stream interfaces and energetic ions 2: Ulysses test of Pioneer results

NASA Technical Reports Server (NTRS)

Intriligator, Devrie S.; Siscoe, George L.; Wibberez, Gerd; Kunow, Horst; Gosling, John T.

1995-01-01

Ulysses measurements of energetic and solar wind particles taken near 5 AU between 20 and 30 degrees south latitude during a well-developed recurring corotating interaction region (CIR) show that the CIR's corotating energetic ion population (CEIP) associated with the trailing reverse shock starts within the CIR at the stream interface. This is consistent with an earlier result obtained by Pioneers 10 and 11 in the ecliptic plane between 4 and 6 AU. The Ulysses/Pioneer finding noteworthy since the stream interface is not magnetically connected to the reverse shock but lies 12-17 corotation hours from it. Thus, the finding to be inconsistent with the basic model that generates CEIP particles at the reverse shock and propagates them along field lines Eliminating the inconsistency probably entails an extension of the standard model. We consider two possible extensions cross-field diffusion and energetic particles generation closer to the sun in the gap between the stream interface and the reverse shock.

Stream dynamics between 1 AU and 2 AU: A detailed comparison of observations and theory

NASA Technical Reports Server (NTRS)

Burlaga, L. F.; Pizzo, V.; Lazarus, A.; Gazis, P. R.

1984-01-01

A radial alignment of three solar wind stream structures observed by IMP-7 and -8 (at 1.0 AU) and Voyager 1 and 2 (in the range 1.4 to 1.8 AU) in late 1977 is presented. It is demonstrated that several important aspects of the observed dynamical evolution can be both qualitatively and quantitatively described with a single-fluid 2-D MHD numerical model of quasi-steady corotating flow, including accurate prediction of: (1) the formation of a corotating shock pair at 1.75 AU in the case of a simple, quasi-steady stream; (2) the coalescence of the thermodynamic and magnetic structures associated with the compression regions of two neighboring, interacting, corotating streams; and (3) the dynamical destruction of a small (i.e., low velocity-amplitude, short spatial-scale) stream by its overtaking of a slower moving, high-density region associated with a preceding transient flow. The evolution of these flow systems is discussed in terms of the concepts of filtering and entrainment.

Comparisons between stellar models and reliability of the theoretical models

NASA Astrophysics Data System (ADS)

Lebreton, Yveline; Montalbán, Josefina

2010-07-01

The high quality of the asteroseismic data provided by space missions such as CoRoT (Michel et al. in The CoRoT Mission, ESA Spec. Publ. vol. 1306, p. 39, 2006) or expected from new operating missions such as Kepler (Christensen-Dalsgaard et al. in Commun. Asteroseismol. 150:350, 2007) requires the capacity of stellar evolution codes to provide accurate models whose numerical precision is better than the expected observational errors (i.e. below 0.1 μHz on the frequencies in the case of CoRoT). We present a review of some thorough comparisons of stellar models produced by different evolution codes, involved in the CoRoT/ESTA activities (Monteiro in Evolution and Seismic Tools for Stellar Astrophysics, 2009). We examine the numerical aspects of the computations as well as the effects of different implementations of the same physics on the global quantities, physical structure and oscillations properties of the stellar models. We also discuss a few aspects of the input physics.

A whirling plane of satellite galaxies around Centaurus A challenges cold dark matter cosmology.

PubMed

Müller, Oliver; Pawlowski, Marcel S; Jerjen, Helmut; Lelli, Federico

2018-02-02

The Milky Way and Andromeda galaxies are each surrounded by a thin plane of satellite dwarf galaxies that may be corotating. Cosmological simulations predict that most satellite galaxy systems are close to isotropic with random motions, so those two well-studied systems are often interpreted as rare statistical outliers. We test this assumption using the kinematics of satellite galaxies around the Centaurus A galaxy. Our statistical analysis reveals evidence for corotation in a narrow plane: Of the 16 Centaurus A satellites with kinematic data, 14 follow a coherent velocity pattern aligned with the long axis of their spatial distribution. In standard cosmological simulations, <0.5% of Centaurus A-like systems show such behavior. Corotating satellite systems may be common in the universe, challenging small-scale structure formation in the prevailing cosmological paradigm. Copyright © 2018 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.

A pulsation zoo in the hot subdwarf B star KIC 10139564 observed by Kepler

NASA Astrophysics Data System (ADS)

Baran, A. S.; Reed, M. D.; Stello, D.; Østensen, R. H.; Telting, J. H.; Pakštienë, E.; O'Toole, S. J.; Silvotti, R.; Degroote, P.; Bloemen, S.; Hu, H.; Van Grootel, V.; Clarke, B. D.; Van Cleve, J.; Thompson, S. E.; Kawaler, S. D.

2012-08-01

We present our analyses of 15 months of Kepler data on KIC 10139564. We detected 57 periodicities with a variety of properties not previously observed all together in one pulsating subdwarf B (sdB) star. Ten of the periodicities were found in the low-frequency region, and we associate them with nonradial g modes. The other periodicities were found in the high-frequency region, which are likely p modes. We discovered that most of the periodicities are components of multiplets with a common spacing. Assuming that multiplets are caused by rotation, we derive a rotation period of 25.6 ± 1.8 d. The multiplets also allow us to identify the pulsations to an unprecedented extent for this class of pulsator. We also detect l ≥ 2 multiplets, which are sensitive to the pulsation inclination and can constrain limb darkening via geometric cancellation factors. While most periodicities are stable, we detected several regions that show complex patterns. Detailed analyses showed that these regions are complicated by several factors. Two are combination frequencies that originate in the super-Nyquist region and were found to be reflected below the Nyquist frequency. The Fourier peaks are clear in the super-Nyquist region, but the orbital motion of Kepler smears the Nyquist frequency in the barycentric reference frame and this effect is passed on to the sub-Nyquist reflections. Others are likely multiplets but unstable in amplitudes and/or frequencies. The density of periodicities also makes KIC 10139564 challenging to explain using published models. This menagerie of properties should provide tight constraints on structural models, making this sdB star the most promising for applying asteroseismology. To support our photometric analysis, we have obtained spectroscopic radial-velocity measurements of KIC 10139564 using low-resolution spectra in the Balmer-line region. We did not find any radial-velocity variation. We used our high signal-to-noise average spectrum to improve the atmospheric parameters of the sdB star, deriving Teff = 31 859 K and log g = 5.673 dex. Based also on observations made with 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.

Optical observations of Magnetosphere-Ionosphere coupling: Inter-hemispheric electron reflections within pulsating aurora

NASA Astrophysics Data System (ADS)

Samara, M.; Michell, R.; Khazanov, G. V.; Grubbs, G. A., II

2017-12-01

Magnetosphere-Ionosphere coupling is exhibited in reflected primary and secondary electrons which constitute the second step in the formation of the total precipitating electron distribution. While they have largely been missing from the current theoretical studies of particle precipitation, ground based observations point to the existence of a reflected electron population. We present evidence that pulsating aurora is caused by electrons bouncing back and forth between the two hemispheres. This means that these electrons are responsible for some of the total light in the aurora, a possibility that has largely been ignored in theoretical models. Pulsating auroral events imaged optically at high time resolution present direct observational evidence in agreement with the inter-hemispheric electron bouncing predicted by the SuperThermal Electron Trans-port (STET) model. Immediately following each of the `pulsation-on' times are equally spaced, and subsequently fainter pulsations, which can be explained by the primary precipitating electrons reflecting upwards from the ionosphere, traveling to the opposite hemisphere, and reflecting upwards again. The high time-resolution of these data, combined with the short duration of the `pulsation-on' time ( 1 s) and the relatively long spacing between pulsations ( 6 to 9 s) made it possible to observe the faint optical pulses caused by the reflected electrons coming from the opposite hemisphere. These results are significant and have broad implications because they highlight that the formation of the auroral electron distributions within regions of diffuse and pulsating aurora contain contributions from reflected primary and secondary electrons. These processes can ultimately lead to larger fluxes than expected when considering only the primary injection of magnetospheric electrons.

Survey of non-linear hydrodynamic models of type-II Cepheids

NASA Astrophysics Data System (ADS)

Smolec, R.

2016-03-01

We present a grid of non-linear convective type-II Cepheid models. The dense model grids are computed for 0.6 M⊙ and a range of metallicities ([Fe/H] = -2.0, -1.5, -1.0), and for 0.8 M⊙ ([Fe/H] = -1.5). Two sets of convective parameters are considered. The models cover the full temperature extent of the classical instability strip, but are limited in luminosity; for the most luminous models, violent pulsation leads to the decoupling of the outermost model shell. Hence, our survey reaches only the shortest period RV Tau domain. In the Hertzsprung-Russell diagram, we detect two domains in which period-doubled pulsation is possible. The first extends through the BL Her domain and low-luminosity W Vir domain (pulsation periods ˜2-6.5 d). The second domain extends at higher luminosities (W Vir domain; periods >9.5 d). Some models within these domains display period-4 pulsation. We also detect very narrow domains (˜10 K wide) in which modulation of pulsation is possible. Another interesting phenomenon we detect is double-mode pulsation in the fundamental mode and in the fourth radial overtone. Fourth overtone is a surface mode, trapped in the outer model layers. Single-mode pulsation in the fourth overtone is also possible on the hot side of the classical instability strip. The origin of the above phenomena is discussed. In particular, the role of resonances in driving different pulsation dynamics as well as in shaping the morphology of the radius variation curves is analysed.

PULSATION-TRIGGERED MASS LOSS FROM AGB STARS: THE 60 DAY CRITICAL PERIOD

DOE Office of Scientific and Technical Information (OSTI.GOV)

McDonald, I.; Zijlstra, A. A., E-mail: iain.mcdonald-2@jb.man.ac.uk, E-mail: albert.zijlstra@manchester.ac.uk

2016-06-01

Low- and intermediate-mass stars eject much of their mass during the late, red giant branch (RGB) phase of evolution. The physics of their strong stellar winds is still poorly understood. In the standard model, stellar pulsations extend the atmosphere, allowing a wind to be driven through radiation pressure on condensing dust particles. Here, we investigate the onset of the wind, using nearby RGB stars drawn from the Hipparcos catalog. We find a sharp onset of dust production when the star first reaches a pulsation period of 60 days. This approximately coincides with the point where the star transitions to themore » first overtone pulsation mode. Models of the spectral energy distributions show stellar mass-loss rate suddenly increasing at this point, by a factor of ∼10 over the existing (chromospherically driven) wind. The dust emission is strongly correlated with both pulsation period and amplitude, indicating stellar pulsation is the main trigger for the strong mass loss, and determines the mass-loss rate. Dust emission does not strongly correlate with stellar luminosity, indicating radiation pressure on dust has little effect on the mass-loss rate. RGB stars do not normally appear to produce dust, whereas dust production by asymptotic giant branch stars appears commonplace, and is probably ubiquitous above the RGB-tip luminosity. We conclude that the strong wind begins with a step change in mass-loss rate and is triggered by stellar pulsations. A second rapid mass-loss-rate enhancement is suggested when the star transitions to the fundamental pulsation mode at a period of ∼300 days.« less

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.

New pulsating white dwarfs in cataclysmic variables

NASA Astrophysics Data System (ADS)

Nilsson, R.; Uthas, H.; Ytre-Eide, M.; Solheim, J.-E.; Warner, B.

2006-07-01

The number of discovered non-radially pulsating white dwarfs (WDs) in cataclysmic variables (CVs) is increasing rapidly by the aid of the Sloan Digital Sky Survey (SDSS). We performed photometric observations of two additional objects, SDSS J133941.11+484727.5 (SDSS 1339), independently discovered as a pulsator by Gänsicke et al., and SDSS J151413.72+454911.9, which we identified as a CV/ZZ Ceti hybrid. In this Letter we present the results of the remote observations of these targets performed with the Nordic Optical Telescope (NOT) during the Nordic-Baltic Research School at Molėtai Observatory, and follow-up observations executed by NOT in service mode. We also present three candidates we found to be non-pulsating. The results of our observations show that the main pulsation frequencies agree with those found in previous CV/ZZ Ceti hybrids, but specifically for SDSS 1339 the principal period differs slightly between individual observations and also from the recent independent observation by Gänsicke et al. Analysis of SDSS colour data for the small sample of pulsating and non-pulsating CV/ZZ Ceti hybrids found so far seems to indicate that the r - i colour could be a good marker for the instability strip of this class of pulsating WDs. Based on observations made with 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. E-mail: ricky@astro.lu.se

Design Strategies to Mitigate Unsteady Forcing (Preprint)

DTIC Science & Technology

2008-04-01

Verification and Validation of CFD Simulation of Pulsating Laminar Flow in a Straight Pipe ,” AIAA Paper No. 2005-4863. [48] Guide for the...reduce the heat load to downstream components [41-44]. Although there is no effect on the potential field inside the vane row [45], there is...effect of design changes on the time-mean characteristics of the machine (e.g. aero- performance or heat load) or to estimate resonant stresses on

Observações no âmbito dos "additional programs" do satélite COROT

NASA Astrophysics Data System (ADS)

Janot Pacheco, E.

2003-08-01

O satélite Fraco-europeu COROT fará fotometria de altissima precisão (pretende-se atingir uma parte em um milhão), grande campo (3x3 graus) e por longos períodos, de duas regiões pré-determinadas do céu, com 10 graus de raio. Suas finalidades básicas serão estudos em sismologia estelar e a procura de exoplanetas. A comunidade astronômica brasileira participará dessa missão espacial, com direitos iguais aos dos parceiros europeus. Isso se deve a que o satélite utilizará a estação de recepção de dados de Natal (INPE), 5 a 6 brasileiros participarão das equipes de software e cientistas do país atuarão na fase de pré-lançamento. Apresentamos nesta comunicação sugestões para a preparação de propostas de observações com COROT, no âmbito dos Programas Adicionais, que contemplam outros projetos que não de sismologia ou exoplanetas. As últimas definições técnicas e decisões tomadas na 4th Corot Week de junho último serão igualmente apresentadas, em particular quanto às regiões de observação escolhidas e quanto aos procedimentos a seguir para se propor observações.

A Model for Plasma Transport in a Corotation-Dominated Magnetosphere.

NASA Astrophysics Data System (ADS)

Pontius, Duane Henry, Jr.

1988-06-01

The gross structures of the magnetospheres of the outer planets are decided by processes quite different from those predominant in that of the earth. The terrestrial plasmapause, the boundary beyond which plasma motion is principally determined by magnetospheric interaction with the solar wind, is typically inside geosynchronous orbit. Within the plasmasphere, rotational effects are present, but gravity exceeds the centrifugal force of corotation. In contrast, the Jovian plasmasphere extends to a distance at least twenty times farther than synchronous orbit, affording a large region where rotational effects are expected to he clearly manifest (Brice and Ioannidis, 1970). The goal of this thesis is to develop an appropriate theoretical model for treating the problem of plasma transport in a corotation dominated plasmasphere. The model presented here is intended to describe the radial transport of relatively cold plasma having an azimuthally uniform distribution in a dipolar magnetic field. The approach is conceptually similar to that of the radial diffusion model in that small scale motions are examined to infer global consequences, but the physical understanding of those small scale motions is quite different. In particular, discrete flux tubes of small cross section are assumed to move over distances large compared to their widths. The present model also differs from the corotating convection model by introducing a mechanism whereby the conservation of flux tube content along flowlines is violated. However, it is quite possible that a global convection pattern co -exists with the motions described here, leading to longitudinal asymmetries in the plasma distribution.

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.

Effects of rotation and tidal distortions on the shapes of radial velocity curves of polytropic models of pulsating variable stars

NASA Astrophysics Data System (ADS)

Kumar, Tarun; Lal, Arvind Kumar; Pathania, Ankush

2018-06-01

Anharmonic oscillations of rotating stars have been studied by various authors in literature to explain the observed features of certain variable stars. However, there is no study available in literature that has discussed the combined effect of rotation and tidal distortions on the anharmonic oscillations of stars. In this paper, we have created a model to determine the effect of rotation and tidal distortions on the anharmonic radial oscillations associated with various polytropic models of pulsating variable stars. For this study we have used the theory of Rosseland to obtain the anharmonic pulsation equation for rotationally and tidally distorted polytropicmodels of pulsating variable stars. The main objective of this study is to investigate the effect of rotation and tidal distortions on the shapes of the radial velocity curves for rotationally and tidally distorted polytropic models of pulsating variable stars. The results of the present study show that the rotational effects cause more deviations in the shapes of radial velocity curves of pulsating variable stars as compared to tidal effects.

White dwarf variability with gPhoton: pulsators

NASA Astrophysics Data System (ADS)

Tucker, Michael A.; Fleming, Scott W.; Pelisoli, Ingrid; Romero, Alejandra; Bell, Keaton J.; Kepler, S. O.; Caton, Daniel B.; Debes, John; Montgomery, Michael H.; Thompson, Susan E.; Koester, Detlev; Million, Chase; Shiao, Bernie

2018-04-01

We present results from a search for short time-scale white dwarf variability using gPhoton, a time-tagged data base of GALEX photon events and associated software package. We conducted a survey of 320 white dwarf stars in the McCook-Sion catalogue, inspecting each for photometric variability with particular emphasis on variability over time-scales less than ˜30 min. From that survey, we present the discovery of a new pulsating white dwarf: WD 2246-069. A Ca II K line is found in archival ESO spectra and an IR excess is seen in WISE W1 and W2 bands. Its independent modes are identified in follow-up optical photometry and used to model its interior structure. Additionally, we detect UV pulsations in four previously known pulsating ZZ Ceti-type (DAVs). Included in this group is the simultaneous fitting of the pulsations of WD 1401-147 in optical, near-ultraviolet and far-ultraviolet bands using nearly concurrent Whole Earth Telescope and GALEX data, providing observational insight into the wavelength dependence of white dwarf pulsation amplitudes.

Kelvin-Helmholtz instability of counter-rotating discs

NASA Astrophysics Data System (ADS)

Quach, Dan; Dyda, Sergei; Lovelace, Richard V. E.

2015-01-01

Observations of galaxies and models of accreting systems point to the occurrence of counter-rotating discs where the inner part of the disc (r < r0) is corotating and the outer part is counter-rotating. This work analyses the linear stability of radially separated co- and counter-rotating thin discs. The strong instability found is the supersonic Kelvin-Helmholtz instability. The growth rates are of the order of or larger than the angular rotation rate at the interface. The instability is absent if there is no vertical dependence of the perturbation. That is, the instability is essentially three dimensional. The non-linear evolution of the instability is predicted to lead to a mixing of the two components, strong heating of the mixed gas, and vertical expansion of the gas, and annihilation of the angular momenta of the two components. As a result, the heated gas will free-fall towards the disc's centre over the surface of the inner disc.

Local time asymmetry of Saturn's magnetosheath flows

NASA Astrophysics Data System (ADS)

Burkholder, B.; Delamere, P. A.; Ma, X.; Thomsen, M. F.; Wilson, R. J.; Bagenal, F.

2017-06-01

Using gross averages of the azimuthal component of flow in Saturn's magnetosheath, we find that flows in the prenoon sector reach a maximum value of roughly half that of the postnoon side. Corotational magnetodisc plasma creates a much larger flow shear with solar wind plasma prenoon than postnoon. Maxwell stress tensor analysis shows that momentum can be transferred out of the magnetosphere along tangential field lines if a normal component to the boundary is present, i.e., field lines which pierce the magnetopause. A Kelvin-Helmholtz unstable flow gives rise to precisely this situation, as intermittent reconnection allows the magnetic field to thread the boundary. We interpret the Kelvin-Helmholtz instability acting along the magnetopause as a tangetial drag, facilitating two-way transport of momentum through the boundary. We use reduced magnetosheath flows in the dawn sector as evidence of the importance of this interaction in Saturn's magnetosphere.

CFD simulation of pulsation noise in a small centrifugal compressor with volute and resonance tube

NASA Astrophysics Data System (ADS)

Wakaki, Daich; Sakuka, Yuta; Inokuchi, Yuzo; Ueda, Kosuke; Yamasaki, Nobuhiko; Yamagata, Akihiro

2015-02-01

The rotational frequency tone noise emitted from the automobile turbocharger is called the pulsation noise. The cause of the pulsation noise is not fully understood, but is considered to be due to some manufacturing errors, which is called the mistuning. The effects of the mistuning of the impeller blade on the noise field inside the flow passage of the compressor are numerically investigated. Here, the flow passage includes the volute and duct located downstream of the compressor impeller. Our numerical approach is found to successfully capture the wavelength of the pulsation noise at given rotational speeds by the comparison with the experiments. One of the significant findings is that the noise field of the pulsation noise in the duct is highly one-dimensional although the flow fields are highly three-dimensional.

Precision asteroseismology of the pulsating white dwarf GD 1212 using a two-wheel-controlled Kepler spacecraft

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hermes, J. J.; Charpinet, S.; Barclay, Thomas

We present a preliminary analysis of the cool pulsating white dwarf (WD) GD 1212, enabled by more than 11.5 days of space-based photometry obtained during an engineering test of the two-reaction-wheel-controlled Kepler spacecraft. We detect at least 19 independent pulsation modes, ranging from 828.2-1220.8 s, and at least 17 nonlinear combination frequencies of those independent pulsations. Our longest uninterrupted light curve, 9.0 days in length, evidences coherent difference frequencies at periods inaccessible from the ground, up to 14.5 hr, the longest-period signals ever detected in a pulsating WD. These results mark some of the first science to come from amore » two-wheel-controlled Kepler spacecraft, proving the capability for unprecedented discoveries afforded by extending Kepler observations to the ecliptic.« less

Spectro-Interferometry Studies of Velocity-Related Phenomena at the Surface of Stars: Pulsation and Rotation

NASA Astrophysics Data System (ADS)

Mérand, Antoine; Patru, Fabien; Aufdenberg, Jason

We illustrate here two applications of spectro-interferometry to the study of velocity fields at the surface of stars: pulsation and rotation. Stellar pulsation has been resolved spectroscopically for a long time, and interferometry has resolved stellar diameters variations due to pulsation. Combining the two provides unique insights to the study of Cepheids, in particular regarding the structure of the photosphere or investigating the infamous projection factor which biases distances measured by the Baade-Wesselink method. On the other hand, resolving the surface velocity field of rotating stars offers a unique opportunity to potentially study differential rotation in other cases than for the Sun. We also present the model we have implemented recently, as well as two applications to VLTI/AMBER Data: the pulsation of Cepheids and the rotation of intermediate mass main sequence stars.

Low-Resolution Radial-Velocity Monitoring of Pulsating sdBs in the Kepler Field

NASA Astrophysics Data System (ADS)

Telting, J.; Östensen, R.; Reed, M.; Kiæerad, F.; Farris, L.; Baran, A.; Oreiro, R.; O'Toole, S.

2014-04-01

We present preliminary results from an ongoing spectroscopic campaign to uncover the binary status of the 18 known pulsating subdwarf B stars and the one pulsating BHB star observed with the Kepler spacecraft. During the 2010-2012 observing seasons, we have used the KP4m Mayall, NOT, and WHT telescopes to obtain low-resolution (R˜2000-2500) Balmer-line spectroscopy of our sample stars. We applied a standard cross-correlation technique to derive radial velocities, and find clear evidence for binarity in several of the pulsators, some of which were not previously known to be binaries.

[Pulsative hematoma--a penile fracture complication].

PubMed

Dorde, Nale; Mićić, Sava

2007-01-01

Fracture of the penis is a direct blunt trauma of the erect or semi-erect penis. It can be treated by conservative or surgical means. Retrospective analyses of conservative penile fracture treatment reveal frequent immediate and later complications. We presented a 41-year-old patient with pulsative hematoma caused by an unusual fracture of the penis. Fracture had appeared 40 days before the admittance during a sexual intercourse. The patient was treated surgically. Pulsative hematoma (pulsative diverticulum) is a very rare, early complication of a conservatively treated penile fracture. Surgical treatment has an advantage over surgical one, which was confirmed by our case report.

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.

An improved arterial pulsation measurement system based on optical triangulation and its application in the traditional Chinese medicine

NASA Astrophysics Data System (ADS)

Wu, Jih-Huah; Lee, Wen-Li; Lee, Yun-Parn; Lin, Ching-Huang; Chiou, Ji-Yi; Tai, Chuan-Fu; Jiang, Joe-Air

2011-08-01

An improved arterial pulsation measurement (APM) system that uses three LED light sources and a CCD image sensor to measure pulse waveforms of artery is presented. The relative variations of the pulses at three measurement points near wrist joints can be determined by the APM system simultaneously. The height of the arterial pulsations measured by the APM system achieves a resolution of better than 2 μm. These pulsations contain useful information that can be used as diagnostic references in the traditional Chinese medicine (TCM) in the future.

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.

Evaluation of runner cone extension to dampen pressure pulsations in a Francis model turbine

NASA Astrophysics Data System (ADS)

Gogstad, Peter Joachim; Dahlhaug, Ole Gunnar

2016-11-01

Today's energy market has a high demand of flexibility due to introduction of other intermittent renewables as wind and solar. To ensure a steady power supply, hydro turbines are often forced to operate more at part load conditions. Originally, turbines were built for steady operation around the best efficiency point. The demand of flexibility, combined with old designs has showed an increase in turbines having problems with hydrodynamic instabilities such as pressure pulsations. Different methods have been investigated to mitigate pressure pulsations. Air injection shows a significant reduction of pressure pulsation amplitudes. However, installation of air injection requires extra piping and a compressor. Investigation of other methods such as shaft extension shows promising results for some operational points, but may significantly reduce the efficiency of the turbine at other operational points. The installation of an extension of the runner cone has been investigated at NTNU by Vekve in 2004. This has resulted in a cylindrical extension at Litjfossen Power Plant in Norway, where the bolt suffered mechanical failure. This indicates high amplitude pressure pulsations in the draft tube centre. The high pressure pulsation amplitudes are believed to be related to high tangential velocity in the draft tube. The mentioned runner cone extension has further been developed to a freely rotating extension. The objective is to reduce the tangential velocity in the draft tube and thereby the pressure pulsation amplitudes.

A New Approach in Examining the Influence of Drugs on Pulsation Rates in Blackworms ("Lumbriculus Variegatus")

ERIC Educational Resources Information Center

Ryan, Amy B.; Elwess, Nancy L.

2017-01-01

This investigative laboratory activity engages students in observing, recording, graphing and analyzing pulsation rates in a commonly used laboratory organism, blackworms. This activity stresses how various drugs can impact the pulsation rate in blackworms at varying concentrations. In addition, we have incorporated two new ways to view the…

International Field Reversible Thermal Connector (RevCon) Challenge

DTIC Science & Technology

2016-07-01

Design ....................................................................... 80 Figure 74: Pulsating - heat - pipe Embedded Design Delivered by MissStateU...University MissStateU finally delivered a pulsating - heat - pipe thermal connector. However, the performance did not amaze the audiences. The size and...We also cannot observe any oscillating dynamics during heating . Figure 74: Pulsating - heat - pipe Embedded Design Delivered by MissStateU

An Overview of Energetic Particle Measurements in the Jovian Magnetosphere with the EPAC Sensor on Ulysses.

PubMed

Keppler, E; Blake, J B; Fränz, M; Korth, A; Krupp, N; Quenby, J J; Witte, M; Woch, J

1992-09-11

Observations of ions and electrons of probable Jovian origin upstream of Jupiter were observed after a corotating interplanetary particle event. During the passage of Ulysses through the Jovian bow shock, magnetopause, and outer magnetosphere, the fluxes of energetic particles were surprisingly low. During the passage through the "middle magnetosphere," corotating fluxes were observed within the current sheet near the jovimagnetic equato. During the outbound pass, fluxes were variably directed; in the later part of the flyby, they were probably related to high-latitude phenomena.

Comparisons for ESTA-Task3: ASTEC, CESAM and CLÉS

NASA Astrophysics Data System (ADS)

Christensen-Dalsgaard, J.

The ESTA activity under the CoRoT project aims at testing the tools for computing stellar models and oscillation frequencies that will be used in the analysis of asteroseismic data from CoRoT and other large-scale upcoming asteroseismic projects. Here I report results of comparisons between calculations using the Aarhus code (ASTEC) and two other codes, for models that include diffusion and settling. It is found that there are likely deficiencies, requiring further study, in the ASTEC computation of models including convective cores.

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 (Imperial College, London), J. C. Samson (University of Alberta, Edmonton), L. J. Lanzerotti (AT&T Bell Laboratories), A. Wolfe (New York City Technical College) and to Dr. M. Vellante (University of LÁquila) for helpful discussions. They also thank Dr. A. Meloni (Istituto Nazionale di Geofisica, Roma) who made available geomagnetic field observations from LÁquila Geomagnetic Observatory. This research activity at LÁquila is supported by MURST (40% and 60% contracts) and by GIFCO/CNR. Topical Editor K.-H. Glaßmeier thanks C. Waters and S. Fujita for their help in evaluating this paper.-> Correspondence to :P. Francia->

The discovery of two pulsating subdwarf B stars in NGC 6791 using Kepler data

NASA Astrophysics Data System (ADS)

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

2012-12-01

We report the discovery of two new pulsating subdwarf B (sdB) stars in the open cluster NGC 6791 using data from the Kepler spacecraft. Three sdB stars were observed for one month in short-cadence (1 min) mode and three months in long-cadence (30 min) mode during Quarter 11 (fall 2011). The stars have Kepler Input Catalogue numbers of 2437937, 2569576 and 2569583 with previous designations of B5, B3 and B6, respectively. Another sdB star exists in the cluster and it is also known to be a pulsator. We also obtained Nordic Optical Telescope spectra to update effective temperatures, surface gravities and helium abundances and compare the spectroscopic properties of all four stars on a uniform model grid. We detect four periodicities between 0.9 and 2.4 h in B3 above a detection limit of 0.53 parts per thousand (ppt) and nine periodicities between 1.1 and 2.2 h in B5 above a detection limit of 0.37 ppt. No pulsations were detected in B6 to the detection threshold of 0.29 ppt. The long-cadence data were less useful as few observations are obtained per pulsation period, yet they do indicate that the pulsations are variable from month to month. The spacings between the pulsation periods are similar to other g-mode pulsating sdB stars observed by Kepler, indicating that the periodicities can be associated witquals; 1 modes. A fit to the periods give spacings of 234.6 ± 0.6 and 242.6 ± 1.5 s for B3 and B5, respectively.

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.

Computational predictions of flame spread over alcohol pools

NASA Technical Reports Server (NTRS)

Schiller, D. N.; Ross, H. D.; Sirignano, W. A.

1993-01-01

The effects of buoyancy and thermocapillarity on pulsating and uniform flame spread above n-propanol fuel pools have been studied using a numerical model. Data obtained indicate that the existence of pulsating flame spread is dependent upon the formation of a gas-phase recirculation cell which entrains evaporating fuel vapor in front of the leading edge of the flame. The size of the recirculation cell which is affected by the extent of liquid motion ahead of the flame, is shown to dictate whether flame spread is uniform or pulsating. The amplitude and period of the flame pulsations are found to be proportional to the maximum extent of the flow head. Under conditions considered, liquid motion was not affected appreciably by buoyancy. Horizontal convection in the liquid is the dominant mechanism for transporting heat ahead of the flame for both the pulsating and uniform regimes.

Researching of the reduction of shock waves intensivity in the “pseudo boiling” layer

NASA Astrophysics Data System (ADS)

Pavlov, G. I.; Telyashov, D. A.; Kochergin, A. V.; Nakoryakov, P. V.; Sukhovaya, E. A.

2017-09-01

This article applies to the field of acoustics and deals with noise reduction of pulsating combustion chambers, in particular the reduction of the shock waves’ intensity with the help of pseudo boiling layer. In the course of work on a test stand that included a pulsator, a compressor with the receiver and a high pressure fan was simulated gas jet flowing from the chamber pulsating combustion and studied the effect of different types of fluidization on effect of reducing the sound pressure levels. Were obtained the experimental dependence of the sound pressure levels from parameters such as: height of the layer of granules; diameter of the used granules; amplitude of the pressure pulsations in the gas stream at the entrance to the camera; frequency of pressure pulsations. Based on the results of the study, it was concluded that the using of a pseudo boiling layer is promising for reducing shock wave noise.

Dynamical behavior of the random field on the pulsating and snaking solitons in cubic-quintic complex Ginzburg-Landau equation

NASA Astrophysics Data System (ADS)

Bakhtiar, Nurizatul Syarfinas Ahmad; Abdullah, Farah Aini; Hasan, Yahya Abu

2017-08-01

In this paper, we consider the dynamical behaviour of the random field on the pulsating and snaking solitons in a dissipative systems described by the one-dimensional cubic-quintic complex Ginzburg-Landau equation (cqCGLE). The dynamical behaviour of the random filed was simulated by adding a random field to the initial pulse. Then, we solve it numerically by fixing the initial amplitude profile for the pulsating and snaking solitons without losing any generality. In order to create the random field, we choose 0 ≤ ɛ ≤ 1.0. As a result, multiple soliton trains are formed when the random field is applied to a pulse like initial profile for the parameters of the pulsating and snaking solitons. The results also show the effects of varying the random field of the transient energy peaks in pulsating and snaking solitons.

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.

The development of early pulsation theory, or, how Cepheids are like steam engines"

NASA Astrophysics Data System (ADS)

Stanley, Matthew

2011-05-01

The pulsation theory of Cepheid variable stars was a major breakthrough of early twentieth-century astrophysics. At the beginning of that century, the basic physics of normal stars was very poorly understood, and variable stars were even more mysterious. Breaking with accepted explanations in terms of eclipsing binaries, Harlow Shapley and A.S. Eddington pioneered novel theories that considered Cepheids as pulsating spheres of gas. These theoretical models relied on highly speculative physics, but nonetheless returned very impressive results despite attacks from figures such as James Jeans. Surprisingly, the pulsation theory not only depended on developments in stellar physics, but also drove many of those developments. In particular, models of stars in radiative balance and theories of stellar energy were heavily inspired and shaped by ideas about variable stars. Further, the success of the pulsation theory helped justify the new approaches to astrophysics being developed before World War II.

An ultraviolet and visible spectroscopic study of a pulsational cycle of RY Sagittarii

NASA Technical Reports Server (NTRS)

Clayton, Geoffrey C.; Lawson, W. A.; Cottrell, P. L.; Whitney, Barbara A.; Stanford, S. Adam; De Ruyter, Frank

1994-01-01

High-dispersion visible and ultraviolet spectra and UBVRI photometry, covering a complete pulsation of the R Coronae Borealis star RY Sgr, have been obtained. The UV spectra were the first high-dispersion data ever obtained for the star. Together these observations comprise the most complete data set covering an RCB star pulsation cycle. The cycle observed was somewhat anomalous as it was affected by a second 55 day pulsation period as well as the primary 38 day period. However, the visible spectra showed the typical line splitting and radial velocity variations which have been observed previously. The simultaneous UV spectra showed much smaller, and phase-shifted, velocity variations than those seen in the visible. No evidence was seen of shock-induced emission at Mg II. These observations provide some support for the models of pulsating hydrogen deficient stars developed by Saio & Wheeler.

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.

Laser-velocimeter surveys of merging vortices in a wind tunnel: Complete data and analysis

NASA Technical Reports Server (NTRS)

Corsiglia, V. R.; Iversen, J. D.; Orloff, K. L.

1978-01-01

The merger of two corotating vortices was studied with a laser velocimeter designed to measure the two cross-stream components of velocity. Measurements were made at several downstream distances in the vortex wake shed by two semispan wings mounted on the wind-tunnel walls. The velocity data provided wall-defined contours of crossflow velocity, stream function, and vorticity for a variety of test conditions. Downstream of the merger point, the vorticity was found to be independent of the downstream distance for radii smaller than r/b = 0.05. For larger radii, the vorticity depended on the distance from the wing. Upstream of the merger, a multicell vorticity pattern was found.

The pulsation-rotation interaction: Greatest hits and the B-side

NASA Astrophysics Data System (ADS)

Townsend, Rich

2014-02-01

It has long been known that rotation can have an appreciable impact on stellar pulsation - by modifying the usual p and g modes found in the non-rotating case, and by introducing new classes of modes. However, it's only relatively recently that advances in numerical simulations and complementary theoretical treatments have enabled us to model these phenomena in any great detail. In this talk I'll review highlights in this area (the `Greatest Hits'), before considering the flip side (or the `B-side', for those of us old enough to remember vinyl records) of the pulsation-rotation interaction: how pulsation can itself influence internal rotation profiles.

Observed Oceanic Response over the Upper Continental Slope and Outer Shelf during Hurricane Ivan

DTIC Science & Technology

2007-09-01

the slope and rise. In addition, they were presumed to be along-shelf and cross-shelf components of group veloci- generated by pulsations of the Loop ...hits. Fortunately, all of exchange of mass, momentum, heat , and water proper- the SEED moorings survived this powerful storm and ties across the shelf...15. SUBJECT TERMS SEED, continental shelf, Doppler, waves 16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF 18. NUMBER 19a. NAME OF RESPONSIBLE

Experimental estimation of convective heat transfer coefficient from pulsating semi-confined impingement air slot jet by using inverse method

NASA Astrophysics Data System (ADS)

Farahani, Somayeh Davoodabadi; Kowsary, Farshad

2017-09-01

An experimental study on pulsating impingement semi-confined slot jet has been performed. The effect of pulsations frequency was examined for various Reynolds numbers and Nozzle to plate distances. Convective heat transfer coefficient is estimated using the measured temperatures in the target plate and conjugate gradient method with adjoint equation. Heat transfer coefficient in Re < 3000 tended to increase with increasing frequency. The pulsations enhance mixing, which results in an enhancement of mean flow velocity. In case of turbulent jet (Re > 3000), heat transfer coefficient is affected by the pulsation from particular frequency. In this study, the threshold Strouhal number (St) is 0.11. No significant heat transfer enhancement was obtained for St < 0.11. The thermal resistance is smaller each time due to the newly forming thermal boundary layers. Heat transfer coefficient increases due to decrease thermal resistance. This study shows that maximum enhancement in heat transfer due to pulsations occurs in St = 0.169. Results show the configuration geometry has an important effect on the heat transfer performances in pulsed impinging jet. Heat transfer enhancement can be described to reflect flow by the confinement plate.

A Search for Rapidly Pulsating Hot Subdwarf Stars in the GALEX Survey

NASA Astrophysics Data System (ADS)

Boudreaux, Thomas M.; Barlow, Brad N.; Fleming, Scott W.; Vasquez Soto, Alan; Million, Chase; Reichart, Dan E.; Haislip, Josh B.; Linder, Tyler R.; Moore, Justin P.

2017-08-01

NASA’s Galaxy Evolution Explorer (GALEX) provided near- and far-UV observations for approximately 77% of the sky over a 10-year period; however, the data reduction pipeline initially only released single NUV and FUV images to the community. The recently released Python module gPhoton changes this, allowing calibrated time-series aperture photometry to be extracted easily from the raw GALEX data set. Here we use gPhoton to generate light curves for all hot subdwarf B (sdB) stars that were observed by GALEX, with the intention of identifying short-period, p-mode pulsations. We find that the spacecraft’s short visit durations, uneven gaps between visits, and dither pattern make the detection of hot subdwarf pulsations difficult. Nonetheless, we detect UV variations in four previously known pulsating targets and report their UV pulsation amplitudes and frequencies. Additionally, we find that several other sdB targets not previously known to vary show promising signals in their periodograms. Using optical follow-up photometry with the Skynet Robotic Telescope Network, we confirm p-mode pulsations in one of these targets, LAMOST J082517.99+113106.3, and report it as the most recent addition to the sdBV r class of variable stars.

An Analysis of Pulsating Subdwarf B Star EPIC 203948264 Observed During Campaign 2 of K2

NASA Astrophysics Data System (ADS)

Ketzer, Laura; Reed, Mike

2017-10-01

We present a preliminary analysis of the newly-discovered pulsating subdwarf B (sdB) star EPIC 203948264. The target was observed for 83 days in short cadence mode during Campaign 2 of K2, the two-gyro mission of the Kepler space telescope. A time-series analysis of the data revealed 22 independent pulsation frequencies in the g-mode region ranging from 100 to 600 μHz (0:5 to 2:8 hours). The main method we use to identify pulsation modes is asymptotic period spacing, and we were able to assign all but one of the pulsations to either l = 1 or l = 2. The average period spacings of both sequences are 261:34 ± 0.78 s and 151:18 ± 0.34 s, respectively. The pulsation amplitudes range from 0.77 ppt down to the detection limit at 0.212 ppt, and are not stable over the duration of the campaign. We detected one possible low-amplitude, l = 2, rotationally split multiplet, which allowed us to constrain the rotation period to 46 days or longer. This makes EPIC 203948264 another slowly rotating sdB star.

Pulsation phenomena observed in long-duration vlf whistler-mode signals.

NASA Technical Reports Server (NTRS)

Bell, T. F.; Helliwell, R. A.

1971-01-01

Whistler-mode signals from station NAA (14.7 and 17.8 kHz), Cutler, Maine, show periodic fluctuations (?pulsations') in amplitude and bandwidth. The data were recorded at Eights station, Antarctica, during unmodulated (?key-down') transmissions from NAA lasting up to 2 min. In three of four instances, the pulsations consist of a series of moderate enhancements of the amplitude and bandwidth of the signal, each pulsation lasting about 50 msec. The fourth instance, however, was unusual in that the key-down signal exhibited remarkably regular and intense amplitude variations. In all four occurrences, the period of the pulsation was in the range from 0.3 to 0.6 sec. In three occurrences, this period was roughly the same as the one-hop whistler-mode delay along the field-line path; however, no demonstrable mechanism to explain this association could be found. An explanation of pulsations in terms of multipath fading effects could not be supported by the data. More likely explanations include intrinsic oscillation in the emission generation mechanism, natural oscillation in the energetic-particle population, or modulation of the VLF growth rate by Pc 1 micropulsations in the region of wave growth.

Development of pulsating twin jets mechanism for mixing flow heat transfer analysis.

PubMed

Gitan, Ali Ahmed; Zulkifli, Rozli; Abdullah, Shahrir; Sopian, Kamaruzzaman

2014-01-01

Pulsating twin jets mechanism (PTJM) was developed in the present work to study the effect of pulsating twin jets mixing region on the enhancement of heat transfer. Controllable characteristics twin pulsed jets were the main objective of our design. The variable nozzle-nozzle distance was considered to study the effect of two jets interaction at the mixing region. Also, the phase change between the frequencies of twin jets was taken into account to develop PTJM. All of these factors in addition to the ability of producing high velocity pulsed jet led to more appropriate design for a comprehensive study of multijet impingement heat transfer problems. The performance of PTJM was verified by measuring the pulse profile at frequency of 20 Hz, where equal velocity peak of around 64 m/s for both jets was obtained. Moreover, the jet velocity profile at different pulsation frequencies was tested to verify system performance, so the results revealed reasonable velocity profile configuration. Furthermore, the effect of pulsation frequency on surface temperature of flat hot plate in the midpoint between twin jets was studied experimentally. Noticeable enhancement in heat transfer was obtained with the increasing of pulsation frequency.

Study on the Pressure Pulsation inside Runner with Splitter Blades in Ultra-High Head Turbine

NASA Astrophysics Data System (ADS)

Meng, L.; Zhang, S. P.; Zhou, L. J.; Wang, Z. W.

2014-03-01

Runners with splitter blades were used widely for the high efficiency and stability. In this paper, the unsteady simulation of an ultra-high head turbine at the best efficiency point, 50% and 75% discharge points were established, to analyze the pressure pulsation in the vaneless space, rotating domain and the draft tube. First of all, runners with different length splitter blades and without splitter blades were compared to learn the efficiency and the pressure distribution on the blade surface. And then the amplitude of the pressure pulsation was analysed. The peak efficiency of the runner with splitter blades is remarkably higher than that of the corresponding impeller without splitter blades. And the efficiency of the turbine is the highest when the length ratio of the splitter blades is 0.75 times the main blades. The pressure pulsation characteristics were also influenced, because the amplitudes of the pulsation induced by the RSI phenomenon were changed as a result of more blades. At last, the best design plan of the length of the splitter blades (length ratio=0.825) was obtained, which improved the pressure pulsation characteristics without significant prejudice to the efficiency.

Development of Pulsating Twin Jets Mechanism for Mixing Flow Heat Transfer Analysis

PubMed Central

Abdullah, Shahrir

2014-01-01

Pulsating twin jets mechanism (PTJM) was developed in the present work to study the effect of pulsating twin jets mixing region on the enhancement of heat transfer. Controllable characteristics twin pulsed jets were the main objective of our design. The variable nozzle-nozzle distance was considered to study the effect of two jets interaction at the mixing region. Also, the phase change between the frequencies of twin jets was taken into account to develop PTJM. All of these factors in addition to the ability of producing high velocity pulsed jet led to more appropriate design for a comprehensive study of multijet impingement heat transfer problems. The performance of PTJM was verified by measuring the pulse profile at frequency of 20 Hz, where equal velocity peak of around 64 m/s for both jets was obtained. Moreover, the jet velocity profile at different pulsation frequencies was tested to verify system performance, so the results revealed reasonable velocity profile configuration. Furthermore, the effect of pulsation frequency on surface temperature of flat hot plate in the midpoint between twin jets was studied experimentally. Noticeable enhancement in heat transfer was obtained with the increasing of pulsation frequency. PMID:24672370

Fluidization and drying of biomass particles in a vibrating fluidized bed with pulsed gas flow

DOE PAGES

Jia, Dening; Cathary, Océane; Peng, Jianghong; ...

2015-10-01

Fluidization of biomass particles in the absence of inert bed materials has been tested in a pulsed fluidized bed with vibration, with the pulsation frequency ranging from 033 to 6.67 Hz. Intermittent fluidization at 033 Hz and apparently 'normal' fluidization at 6.67 Hz with regular bubble patterns were observed. Pulsation has proven to be effective in overcoming the bridging of irregular biomass particles induced by strong inter-particle forces. The vibration is only effective when the pulsation is inadequate, either at too low a frequency or too low in amplitude. We dried biomass in order to quantify the effectiveness of gasmore » pulsation for fluidized bed dryers and torrefiers in terms of gas-solid contact efficiency and heat and mass transfer rates. Furthermore, the effects of gas flow rate, bed temperature, pulsation frequency and vibration intensity on drying performance have been systematically investigated. While higher temperature and gas flow rate are favored in drying, there exists an optimal range of pulsation frequency between 0.75 Hz and 1.5 Hz where gas-solid contact is enhanced in both the constant rate drying and falling rate drying periods.« less

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.

Plasmapause Dynamics Observed During the 17 March and 28 June 2013 Storms

NASA Astrophysics Data System (ADS)

Bishop, R. L.; Coster, A. J.; Turner, D. L.; Nikoukar, R.; Lemon, C.; Roeder, J. L.; Shumko, M.; Bhatt, R.; Payne, C.; Bust, G. S.

2017-12-01

Earth's plasmasphere is a region of cold (T ≤ 1 eV), dense (n 101 to 104 cm-3) plasma located in the inner magnetosphere and coincident with a portion of the ionosphere that co-rotates with the planet in the geomagnetic field. Plasmaspheric plasma originates in the ionosphere and fills the magnetic flux tubes on which the corotation electric field dominates over the convection electric field. The corotation electric field results from Earth's spinning magnetic field while the convection electric field results from the solar wind driving of global plasma convection within the magnetosphere. The outer boundary of the plasmasphere is the plasmapause, and it corresponds to the transition region between corotation-driven vs. convection-driven plasmas. When the convection electric field is enhanced during active solar wind periods, such as magnetic storms, the plasmasphere can rapidly erode to L 2.5 or less. During subsequent quiet periods of low solar wind speed and weak interplanetary magnetic field (IMF), ionospheric outflow from lower altitudes refills the plasmasphere over the course of several days or more, with the plasmapause expanding to higher L-shells. The combination of convection, corotation, and ionospheric plasma outflow during and after a storm leads to characteristic features such as plasmaspheric shoulders, notches, and plumes. In this presentation, we focus on the dynamics of the plasmapause during two storms in 2013: March 17 and June 28. The minimum Dst for the two storms were -139 and -98 nT, respectively. We examine plasmapause dynamics utilizing data from an extensive global network of ground-based scientific GPS receivers ( 4000) and line-of-sight observations from the GPS receivers on the COSMIC and C/NOFS satellites, along with data from THEMIS and van Allen Probes, and Millstone Hill Incoherent Scatter Radar. Using the various datasets, we will compare the pre-storm and storm-time plasmasphere. We will also examine the location, evolution, and erosion time scales of the plasmapause during the active portion of the storm using a combination of the observational data, the assimilative PDA model, and the RCM-E model.

Sweet taste enhancement through pulsatile stimulation depends on pulsation period not on conscious pulse perception.

PubMed

Burseg, Kerstin Martha Mensien; Brattinga, Celine; de Kok, Petrus Maria Theresia; Bult, Johannes Hendrikus Franciscus

2010-06-16

When aqueous NaCl solutions are tasted at continuously alternating concentrations, overall saltiness ratings exceed those observed for solutions with the same averaged, but non-alternating concentrations. In the present study, this effect is replicated for alternating aqueous sucrose solutions. We tested the hypothesis that enhancement depends on the conscious perception of intensity contrasts. High sucrose pulses were continuously alternated with low sucrose intervals at pulsation periods between 1.5s and 20s. Tastant pulsation enhanced sweetness intensity and this enhancement varied between 8 and 14%, peaking for periods from 4.5s to 6s (Study 1). This range coincided with the average pulsation period at which perceived taste pulses blended into a continuous stimulus, i.e. the taste fusion period (TFP). When comparing intensity ratings of sucrose solutions at individualized pulse periods of 0.5, 1.0 and 2.0 times TFP to ratings for continuous sucrose solutions of the same net concentration, pulsatile stimuli were perceived as significantly sweeter (p<0.01; Study 2). However, sweetness intensity enhancement was the same for all pulsation periods. It was shown that sweet taste enhancement peaks at pulsation periods ranging from 0.5 to 2.0 TFP and that the level of conscious pulsation perception does not affect taste enhancement. The results suggest the introduction of enhancement effects at pre-conscious stages of gustatory processing. Further mechanisms that may account for such pre-conscious effects are discussed. (c) 2010 Elsevier Inc. All rights reserved.

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

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.

Monitoring Period and Amplitude Changes in Classical Cepheids

NASA Astrophysics Data System (ADS)

Erickson, Mary; Engle, Scott; Guinan, Edward; Wells, Mark

2018-01-01

Classical Cepheids are a specific class of radially pulsating variable stars and are fundamentally important to Astronomy and Cosmology. Their pulsations can be used to determine accurate distances, both inside the Milky Way and to other galaxies throughout the Universe, via the well-studied Period-Luminosity Relationship (the Leavitt Law). This makes Cepheids “standard candles,” and they are helping Astronomers refine the expansion rate and age of the Universe.Though Cepheid pulsations were long-theorized to be completely stable, we now know that they undergo small but observable changes in their pulsation periods. The rates of the period change give us invaluable information on the Cepheids themselves, and the advent of reliable all-sky photometry surveys has allowed Cepheid pulsations to be monitored more easily than ever before.Five Cepheids were analyzed for this study – AA Gem, BB Gem, RZ Gem, AD Gem, and DX Gem. Photometric data were obtained from two sources: ASAS (the All-Sky Automated Survey) and the RCT (Robotically Controlled Telescope) at Kitt Peak National Observatory in Arizona, whose consortium Villanova is a member of. This photometry is combined with available data from the literature. The two instruments combined give a longer time span, and increased precision, from which period variations can be monitored. This gives us an excellent look at how the pulsations of these 5 Cepheids are evolving over time. The pulsation behavior of the 5 Cepheids studies will be presented, along with their calculated stellar parameters.

Periodic Variations in the O - C Diagrams of Five Pulsation Frequencies of the DB White Dwarf EC 20058-5234

NASA Astrophysics Data System (ADS)

Dalessio, J.; Sullivan, D. J.; Provencal, J. L.; Shipman, H. L.; Sullivan, T.; Kilkenny, D.; Fraga, L.; Sefako, R.

2013-03-01

Variations in the pulsation arrival time of five independent pulsation frequencies of the DB white dwarf EC 20058-5234 individually imitate the effects of reflex motion induced by a planet or companion but are inconsistent when considered in unison. The pulsation frequencies vary periodically in a 12.9 year cycle and undergo secular changes that are inconsistent with simple neutrino plus photon-cooling models. The magnitude of the periodic and secular variations increases with the period of the pulsations, possibly hinting that the corresponding physical mechanism is located near the surface of the star. The phase of the periodic variations appears coupled to the sign of the secular variations. The standards for pulsation-timing-based detection of planetary companions around pulsating white dwarfs, and possibly other variables such as subdwarf B stars, should be re-evaluated. The physical mechanism responsible for this surprising result may involve a redistribution of angular momentum or a magnetic cycle. Additionally, variations in a supposed combination frequency are shown to match the sum of the variations of the parent frequencies to remarkable precision, an expected but unprecedented confirmation of theoretical predictions. Based on observations obtained at the Southern Astrophysical Research (SOAR) telescope, which is a joint project of the Ministério da Ciência, Tecnologia, e Inovação (MCTI) da República Federativa do Brasil, the US National Optical Astronomy Observatory (NOAO), the University of North Carolina at Chapel Hill (UNC), and Michigan State University (MSU).

Dynamic Young Stars and their Disks: A Temporal View of NGC 2264 with Spitzer and CoRoT

NASA Astrophysics Data System (ADS)

Cody, Ann Marie; Stauffer, John; Bouvier, Jèrôme

2014-01-01

Variability is a signature feature of young stars. Among the well known light curve phenomena are periodic variations attributed to surface spots and irregular changes associated with accretion or circumstellar disk material. While decades of photometric monitoring have provided a framework for classifying young star variability, we still know surprisingly little about its underlying mechanisms and connections to the surrounding disks. In the past few years, dedicated photometric monitoring campaigns from the ground and space have revolutionized our view of young stars in the time domain. We present a selection of optical and infrared time series from several recent campaigns, highlighting the Coordinated Synoptic Investigation of NGC 2264 ("CSI 2264")- a joint30-day effort with the Spitzer, CoRoT, and MOST telescopes. The extraordinary photometric precision, high cadence, and long time baseline of these observations is now enabling correlation of variability properties at very different wavelengths, corresponding to locations from the stellar surface to the inner 0.1 AU of the disk. We present some results of the CSI 2264 program, including new classes of optical/infrared behavior. Further efforts to tie observed variability features to physical models will provide insights into the inner disk environment at a time when planet formation may be underway. Based on data from the Spitzer and CoRoT missions. 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, Belgium, Brazil, Germany, and Spain.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Do Nascimento, J.-D. Jr.; Da Costa, J. S.; Castro, M.

The question of whether the Sun is peculiar within the class of solar-type stars has been the subject of active investigation over the past three decades. Although several solar twins have been found with stellar parameters similar to those of the Sun (albeit in a range of Li abundances and with somewhat different compositions), their rotation periods are unknown, except for 18 Sco, which is younger than the Sun and with a rotation period shorter than solar. It is difficult to obtain rotation periods for stars of solar age from ground-based observations, as a low-activity level implies a shallow rotationalmore » modulation of their light curves. CoRoT has provided space-based long time series from which the rotation periods of solar twins as old as the Sun could be estimated. Based on high-signal-to-noise, high-resolution spectroscopic observations gathered at the Subaru Telescope, we show that the star CoRoT ID 102684698 is a somewhat evolved solar twin with a low Li abundance. Its rotation period is 29 {+-} 5 days, compatible with its age (6.7 Gyr) and low lithium content, A{sub Li} {approx}< 0.85 dex. Interestingly, our CoRoT solar twin seems to have enhanced abundances of the refractory elements with respect to the Sun, a typical characteristic of most nearby twins. With a magnitude V {approx_equal} 14.1, ID 102684698 is the first solar twin revealed by CoRoT, the farthest field solar twin so far known, and the only solar twin older than the Sun for which a rotation period has been determined.« less

Detection of a westward hotspot offset in the atmosphere of hot gas giant CoRoT-2b

NASA Astrophysics Data System (ADS)

Dang, Lisa; Cowan, Nicolas B.; Schwartz, Joel C.; Rauscher, Emily; Zhang, Michael; Knutson, Heather A.; Line, Michael; Dobbs-Dixon, Ian; Deming, Drake; Sundararajan, Sudarsan; Fortney, Jonathan J.; Zhao, Ming

2018-03-01

Short-period planets exhibit day-night temperature contrasts of hundreds to thousands of kelvin. They also exhibit eastward hotspot offsets whereby the hottest region on the planet is east of the substellar point1; this has been widely interpreted as advection of heat due to eastward winds2. We present thermal phase observations of the hot Jupiter CoRoT-2b obtained with the Infrared Array Camera (IRAC) on the Spitzer Space Telescope. These measurements show the most robust detection to date of a westward hotspot offset of 23 ± 4°, in contrast with the nine other planets with equivalent measurements3-10. The peculiar infrared flux map of CoRoT-2b may result from westward winds due to non-synchronous rotation11 or magnetic effects12,13, or partial cloud coverage, that obscure the emergent flux from the planet's eastern hemisphere14-17. Non-synchronous rotation and magnetic effects may also explain the planet's anomalously large radius12,18. On the other hand, partial cloud coverage could explain the featureless dayside emission spectrum of the planet19,20. If CoRoT-2b is not tidally locked, then it means that our understanding of star-planet tidal interaction is incomplete. If the westward offset is due to magnetic effects, our result represents an opportunity to study an exoplanet's magnetic field. If it has eastern clouds, then it means that a greater understanding of large-scale circulation on tidally locked planets is required.

Pickup ion acceleration in the successive appearance of corotating interaction regions

NASA Astrophysics Data System (ADS)

Tsubouchi, K.

2017-04-01

Acceleration of pickup ions (PUIs) in an environment surrounded by a pair of corotating interaction regions (CIRs) was investigated by numerical simulations using a hybrid code. Energetic particles associated with CIRs have been considered to be a result of the acceleration at their shock boundaries, but recent observations identified the ion flux peaks in the sub-MeV to MeV energy range in the rarefaction region, where two separate CIRs were likely connected by the magnetic field. Our simulation results confirmed these observational features. As the accelerated PUIs repeatedly bounce back and forth along the field lines between the reverse shock of the first CIR and the forward shock of the second one, the energetic population is accumulated in the rarefaction region. It was also verified that PUI acceleration in the dual CIR system had two different stages. First, because PUIs have large gyroradii, multiple shock crossing is possible for several tens of gyroperiods, and there is an energy gain in the component parallel to the magnetic field via shock drift acceleration. Second, as the field rarefaction evolves and the radial magnetic field becomes dominant, Fermi-type reflection takes place at the shock. The converging nature of two shocks results in a net energy gain. The PUI energy acquired through these processes is close to 0.5 MeV, which may be large enough for further acceleration, possibly resulting in the source of anomalous cosmic rays.

Requirements for Radial Migration: How does the migrating fraction depend on stellar velocity dispersion?

NASA Astrophysics Data System (ADS)

Tolfree, Kathryne; Wyse, R. F.

2014-01-01

Radial migration is a way to rearrange the orbital angular momentum of stars in an spiral disk without inducing kinematic heating. When radial migration is very efficient, a large fraction of disk stars experience significant changes in their orbital angular momenta in a short period of time. Such scenarios have strong implications for the chemical and kinematic evolution of disk galaxies. We have undertaken an investigation of the physical dependencies of the efficiency of radial migration on stellar kinematics and spiral structure by deriving the fraction of stars that can migrate radially given certain conditions. In order for a star in a spiral disk to migrate radially, it must first be “captured" in a family of resonant orbits near the radius of corotation with a spiral pattern. Thus far, the only analytic criterion for capture has been for stars in circular orbits. We present the capture criterion for stars on non-circular orbits in a disk galaxy. We then use our analytically derived capture criteria to model the radial distribution of the captured fraction in an exponential disk with a flat rotation curve as well as the dependence of the total captured fraction in the disk on the radial component of the stellar velocity dispersion (σR) and the amplitude of the spiral perturbation to the underlying potential at corotation (|Φs|CR). We find that the captured fraction goes as Exp[-σR2/|Φs|CR].

Improving the API dissolution rate during pharmaceutical hot-melt extrusion I: Effect of the API particle size, and the co-rotating, twin-screw extruder screw configuration on the API dissolution rate.

PubMed

Li, Meng; Gogos, Costas G; Ioannidis, Nicolas

2015-01-15

The dissolution rate of the active pharmaceutical ingredients in pharmaceutical hot-melt extrusion is the most critical elementary step during the extrusion of amorphous solid solutions - total dissolution has to be achieved within the short residence time in the extruder. Dissolution and dissolution rates are affected by process, material and equipment variables. In this work, we examine the effect of one of the material variables and one of the equipment variables, namely, the API particle size and extruder screw configuration on the API dissolution rate, in a co-rotating, twin-screw extruder. By rapidly removing the extruder screws from the barrel after achieving a steady state, we collected samples along the length of the extruder screws that were characterized by polarized optical microscopy (POM) and differential scanning calorimetry (DSC) to determine the amount of undissolved API. Analyses of samples indicate that reduction of particle size of the API and appropriate selection of screw design can markedly improve the dissolution rate of the API during extrusion. In addition, angle of repose measurements and light microscopy images show that the reduction of particle size of the API can improve the flowability of the physical mixture feed and the adhesiveness between its components, respectively, through dry coating of the polymer particles by the API particles. Copyright © 2014. Published by Elsevier B.V.

3D MHD Simulations of Waves Excited in an Accretion Disk by a Rotating Magnetized Star

NASA Astrophysics Data System (ADS)

Lovelace, R. V. E.; Romanova, M. M.

2014-01-01

We present results of global 3D MHD simulations of warp and density waves in accretion disks excited by a rotating star with a misaligned dipole magnetic field. A wide range of cases are considered. We find for example that if the star's magnetosphere corotates approximately with the inner disk, then a strong one-arm bending wave or warp forms. The warp corotates with the star and has a maximum amplitude (|zω|/r ~ 0.3) between the corotation radius and the radius of the vertical resonance. If the magnetosphere rotates more slowly than the inner disk, then a bending wave is excited at the disk-magnetosphere boundary, but it does not form a large-scale warp. In this case the angular rotation of the disk [Ω(r,z = 0)] has a maximum as a function of r so that there is an inner region where dΩ/dr > 0. In this region we observe radially trapped density waves in approximate agreement with the theoretical prediction of a Rossby wave instability in this region.

Variations of the Electron Fluxes in the Terrestrial Radiation Belts Due To the Impact of Corotating Interaction Regions and Interplanetary Coronal Mass Ejections

NASA Astrophysics Data System (ADS)

Benacquista, R.; Boscher, D.; Rochel, S.; Maget, V.

2018-02-01

In this paper, we study the variations of the radiation belts electron fluxes induced by the interaction of two types of solar wind structures with the Earth magnetosphere: the corotating interaction regions and the interplanetary coronal mass ejections. We use a statistical method based on the comparison of the preevent and postevent fluxes. Applied to the National Oceanic and Atmospheric Administration-Polar Operational Environmental Satellites data, this gives us the opportunity to extend previous studies focused on relativistic electrons at geosynchronous orbit. We enlighten how corotating interaction regions and Interplanetary Coronal Mass Ejections can impact differently the electron belts depending on the energy and the L shell. In addition, we provide a new insight concerning these variations by considering their amplitude. Finally, we show strong relations between the intensity of the magnetic storms related to the events and the variation of the flux. These relations concern both the capacity of the events to increase the flux and the deepness of these increases.

Implications of the Corotation Theorem on the MRI in Axial Symmetry

NASA Astrophysics Data System (ADS)

Montani, G.; Cianfrani, F.; Pugliese, D.

2016-08-01

We analyze the linear stability of an axially symmetric ideal plasma disk, embedded in a magnetic field and endowed with a differential rotation. This study is performed by adopting the magnetic flux function as the fundamental dynamical variable, in order to outline the role played by the corotation theorem on the linear mode structure. Using some specific assumptions (e.g., plasma incompressibility and propagation of the perturbations along the background magnetic field), we select the Alfvénic nature of the magnetorotational instability, and, in the geometric optics limit, we determine the dispersion relation describing the linear spectrum. We show how the implementation of the corotation theorem (valid for the background configuration) on the linear dynamics produces the cancellation of the vertical derivative of the disk angular velocity (we check such a feature also in the standard vector formalism to facilitate comparison with previous literature, in both the axisymmetric and three-dimensional cases). As a result, we clarify that the unstable modes have, for a stratified disk, the same morphology, proper of a thin-disk profile, and the z-dependence has a simple parametric role.

Towards a theory for Neptune's arc rings

NASA Technical Reports Server (NTRS)

Goldreich, P.; Tremaine, S.; Borderies, N.

1986-01-01

It is proposed that the incomplete rings of Neptune consist of a number of short arcs centered on the corotation resonances of a single satellite. The satellite must have a radius of the order of 100 km or more and move on an inclined orbit. Corotation resonances are located at potential maxima. Thus, mechanical energy dissipated by interparticle collisions must be continually replenished to prevent the arcs from spreading. It is shown that each corotation resonance is associated with a nearby Lindblad resonance, which excites the ring particles' orbital eccentricity, thus supplying the energy required to maintain the arc. The ultimate energy reservoir is the satellite's orbital energy. Therefore, interaction with the arcs damps the satellite's orbital inclination. The self-gravity of the arcs limits their contraction and enforces a relation between arc length and mass. The estimated arc masses are so small, of the order of 10 to the 16th g, that the satellite's orbital inclination suffers negligible decay over the age of the solar system. The inferred surface mass densities are comparable to those found in the major rings of Saturn and Uranus.

Measurements of the rotation rate of the jovian mid-to-low latitude ionosphere

NASA Astrophysics Data System (ADS)

Johnson, Rosie E.; Stallard, Tom S.; Melin, Henrik; Miller, Steve; Nichols, Jonathan D.

2016-12-01

Previous studies of Jupiter's upper atmosphere often assume that the mid-to-low latitude ionosphere is corotating, but a model describing an observed asymmetry in hydrogen Lyman-α emission (∼1000 km above the 1 bar level) disagrees with this assumption. From measurements of the Doppler shifted H3+ν2 Q (1 ,0-) line at 3.953 μm using the IRTF, the line-of-sight velocities of the H3+ ions were derived in the planetary reference frame and found to be 0.091 ± 0.25 km s-1, 0.0082 ± 0.30 km s-1 and 0.31 ± 0.51 km s-1 in 1998, 2007 and 2013 respectively. These zero velocities represent corotation at the mid-to-low latitude region of Jupiter's ionosphere. There is no evidence of flows associated with the hydrogen Lyman-α emission asymmetries detected in the peak H3+ emission layer (∼550 km above the 1 bar level), and we assert that the H3+ ions in Jupiter's mid-to-low latitude are rigidly corotating.

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.

From CoRoT 102899501 to the Sun. A time evolution model of chromospheric activity on the main sequence

NASA Astrophysics Data System (ADS)

Gondoin, P.; Gandolfi, D.; Fridlund, M.; Frasca, A.; Guenther, E. W.; Hatzes, A.; Deeg, H. J.; Parviainen, H.; Eigmüller, P.; Deleuil, M.

2012-12-01

Aims: The present study reports measurements of the rotation period of a young solar analogue, estimates of its surface coverage by photospheric starspots and of its chromospheric activity level, and derivations of its evolutionary status. Detailed observations of many young solar-type stars, such as the one reported in the present paper, provide insight into rotation and magnetic properties that may have prevailed on the Sun in its early evolution. Methods: Using a model based on the rotational modulation of the visibility of active regions, we analysed the high-accuracy CoRoT lightcurve of the active star CoRoT 102899501. Spectroscopic follow-up observations were used to derive its fundamental parameters. We compared the chromospheric activity level of Corot 102899501 with the R'HK index distribution vs age established on a large sample of solar-type dwarfs in open clusters. We also compared the chromospheric activity level of this young star with a model of chromospheric activity evolution established by combining relationships between the R'HK index and the Rossby number with a recent model of stellar rotation evolution on the main sequence. Results: We measure the spot coverage of the stellar surface as a function of time and find evidence for a tentative increase from 5 - 14% at the beginning of the observing run to 13-29% 35 days later. A high level of magnetic activity on Corot 102899501 is corroborated by a strong emission in the Balmer and Ca ii H and K lines (R'HK ~ -4). The starspots used as tracers of the star rotation constrain the rotation period to 1.625 ± 0.002 days and do not show evidence for differential rotation. The effective temperature (Teff = 5180 ± 80 K), surface gravity (log g = 4.35 ± 0.1), and metallicity ([M/H] = 0.05 ± 0.07 dex) indicate that the object is located near the evolutionary track of a 1.09 ± 0.12 M⊙ pre-main sequence star at an age of 23 ± 10 Myr. This value is consistent with the "gyro-age" of about 8-25 Myr, inferred using a parameterization of the stellar rotation period as a function of colour index and time established for the I-sequence of stars in stellar clusters. Conclusions: We conclude that the high magnetic activity level and fast rotation of CoRoT 102899501 are manifestations of its stellar youth consistent with its estimated evolutionary status and with the detection of a strong Li i λ6707.8 Å absorption line in its spectrum. We argue that a magnetic activity level comparable to that observed on CoRot 102899501 could have been present on the Sun at the time of planet formation. Based on observations obtained with CoRoT, a space project operated by the French Space Agency, CNES, with participation of the Science Programme of ESA, ESTEC/RSSD, Austria, Belgium, Brazil, Germany and Spain.Based on observations made with the Anglo-Australian Telescope; the 2.1-m Otto Struve telescope at McDonald Observatory, Texas, USA; 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, in time allocated by the NOT "Fast-Track" Service Programme, OPTICON, and the Spanish Time Allocation Committee (CAT).The research leading to these results has received funding from the European Community's Seventh Framework Programme (FP7/2007-2013) under grant agreement number RG226604 (OPTICON).

Amplitude Modulation of Pulsation Modes in Delta Scuti Stars

NASA Astrophysics Data System (ADS)

Bowman, Dominic M.

2017-10-01

The pulsations in δ Sct stars are excited by a heat engine driving mechanism caused by increased opacity in their surface layers, and have pulsation periods of order a few hours. Space based observations in the last decade have revealed a diverse range of pulsational behaviour in these stars, which is investigated using an ensemble of 983 δ Sct stars observed continuously for 4 yr by the Kepler Space Telescope. A statistical search for amplitude modulation of pulsation modes is carried out and it is shown that 61.3 per cent of the 983 δ Sct stars exhibit significant amplitude modulation in at least a single pulsation mode, and that this is uncorrelated with effective temperature and surface gravity. Hence, the majority of δ Sct stars exhibit amplitude modulation, with time-scales of years and longer demonstrated to be significant in these stars both observationally and theoretically. An archetypal example of amplitude modulation in a δ Sct star is KIC 7106205, which contains only a single pulsation mode that varies significantly in amplitude whilst all other pulsation modes stay constant in amplitude and phase throughout the 4-yr Kepler data set. Therefore, the visible pulsational energy budget in this star, and many others, is not conserved over 4 yr. Models of beating of close-frequency pulsation modes are used to identify δ Sct stars with frequencies that lie closer than 0.001 d^{-1}, which are barely resolved using 4 yr of Kepler observations, and maintain their independent identities over 4 yr. Mode coupling models are used to quantify the strength of coupling and distinguish between non-linearity in the form of combination frequencies and non-linearity in the form of resonant mode coupling for families of pulsation modes in several stars. The changes in stellar structure caused by stellar evolution are investigated for two high amplitude δ Sct (HADS) stars in the Kepler data set, revealing a positive quadratic change in phase for the fundamental and first overtone radial modes in KIC 5950759. The observed phase modulation of the radial modes in this star is two orders of magnitude larger than predicted by stellar evolutionary models, yet is consistent with the prediction of increasing periods of radial modes for stars on the main sequence. The statistical analysis of 983 δ Sct stars, including the results from the search for amplitude modulation, is a valuable resource for ongoing and future space missions such as K2, TESS and PLATO, because the high quality 4-yr Kepler data set will not be surpassed for some time. The observational studies of individual stars in this thesis provide strong evidence that non-linear processes are clearly at work in the majority of δ Sct stars, and provide valuable constraints for future asteroseismic modelling.

[Sterilization effect analysis of B-class pulsation table top vacuum sterilizer to dental handpieces].

PubMed

Zeng, Shu-Rong; Jiang, Bo; Xiao, Xiao-Rong

2007-06-01

Discuss sterilization effect of B-class pulsation table top vacuum pressure steam sterilizer for dental handpiece. Analysis selection of sterilizer for dental handpiece and sterilization management processes and sterilization effect monitoring, evaluation of monitoring result and effective sterilization method. The B-class pulsation table top vacuum pressure steam sterilizer to dental handpiece in West China Stomatological Hospital of Sichuan University met the requirement of the chemical and biological monitoring. Its efficiency of sterilization was 100%. The results of aerobic culture, anaerobic culture, B-type hepatitis mark monitoring to sterilized dental handpiece were negative. It is effective method for dental handpiece sterilization to use B-class pulsation table top vacuum pressure steam sterilizer.

A Novel Approach to Solve Linearized Stellar Pulsation Equations

NASA Astrophysics Data System (ADS)

Bard, Christopher; Teitler, S.

2011-01-01

We present a new approach to modeling linearized, non-radial pulsations in differentially rotating, massive stars. As a first step in this direction, we consider adiabatic pulsations and adopt the Cowling approximation that perturbations of the gravitational potential and its radial derivative are negligible. The angular dependence of the pulsation modes is expressed as a series expansion of associated Legendre polynomials; the resulting coupled system of differential equations is then solved by finding the eigenfrequencies at which the determinant of a characteristic matrix vanishes. Our method improves on previous treatments by removing the requirement that an arbitrary normalization be applied to the eigenfunctions; this brings the benefit of improved numerical robustness.

Pulsatile and steady-state hemodynamics of the human patella bone by diffuse optical spectroscopy.

PubMed

Farzam, Parisa; Zirak, Peyman; Binzoni, Tiziano; Durduran, Turgut

2013-08-01

The cardiac cycle related pulsatile behavior of the absorption and scattering coefficients of diffuse light and the corresponding alterations in hemoglobin concentrations in the human patella was studied. The pulsations in scattering is considerably smaller than absorption. The difference in amplitude of absorption coefficient pulsations for different wavelengths was translated to pulsations in oxygenated and deoxygenated hemoglobin, which leads to strong pulsations in the total hemoglobin concentration and oxygen saturation. The physiological origin of the observed signals was confirmed by applying a thigh-cuff. Moreover, we have investigated the optical and physiological properties of the patella bone and their changes in response to arterial cuff occlusion.

Solar Wind Features Responsible for Magnetic Storms and Substorms During the Declining Phase of the Solar Cycle: 197

NASA Technical Reports Server (NTRS)

Tsurutani, B.; Arballo, J.

1994-01-01

We examine interplanetary data and geomagnetic activity indices during 1974 when two long-lasting solar wind corotating streams existed. We find that only 3 major storms occurred during 1974, and all were associated with coronal mass ejections. Each high speed stream was led by a shock, so the three storms had sudden commencements. Two of the 1974 major storms were associated with shock compression of preexisting southward fields and one was caused by southward fields within a magnetic cloud. Corotating streams were responsible for recurring moderate to weak magnetic storms.

Affirmation of triggered Jovian radio emissions and their attribution to corotating radio lasers

NASA Technical Reports Server (NTRS)

Calvert, W.

1985-01-01

It is argued that the original statistical evidence for the existence of triggered radio emissions and corotating radio lasers on Jupiter remains valid notwithstanding the critique of Desch and Kaiser (1985). The Voyager radio spectrograms used to identify the triggered emissions are analyzed and the results are discussed. It is shown that the critique by Desch and Kaiser is unjustified because it is not based on the original event criteria, i.e., the correlation between the occurrence of Jovian auroral kilometric radiation and fast-drift type III solar bursts in the same frequency.

Type Ia supernovae: Pulsating delayed detonation models, IR light curves, and the formation of molecules

NASA Technical Reports Server (NTRS)

Hoflich, Peter; Khokhlov, A.; Wheeler, C.

1995-01-01

We computed optical and infrared light curves of the pulsating class of delayed detonation models for Type Ia supernovae (SNe Ia). It is demonstrated that observations of the IR light curves can be used to identify subluminous SNe Ia by testing whether secondary maxima occur in the IR. Our pulsating delayed detonation models are in agreement with current observations both for subluminous and normal bright SN Ia, namely SN1991bg, SN1992bo, and SN1992bc. Observations of molecular bands provide a test to distinguish whether strongly subluminous supernovae are a consequence of the pulsating mechanism occurring in a high-mass white dwarf (WD) or, alternatively, are formed by the helium detonation in a low-mass WD as was suggested by Woosley. In the latter case, no carbon is left after the explosion of low-mass WDs whereas a log of C/O-rich material is present in pulsating delayed detonation models.

Pulsations in the Earth's Lower Ionosphere Synchronized With Solar Flare Emission

NASA Astrophysics Data System (ADS)

Hayes, Laura A.; Gallagher, Peter T.; McCauley, Joseph; Dennis, Brian R.; Ireland, Jack; Inglis, Andrew

2017-10-01

Solar flare emission at X-ray and extreme ultraviolet (EUV) energies can cause substantial enhancements in the electron density in the Earth's lower ionosphere. It has now become clear that flares exhibit quasi-periodic pulsations with timescales of minutes at X-ray energies, but to date, it has not been known if the ionosphere is sensitive to this variability. Here using a combination of very low frequency (24 kHz) measurement together with space-based X-ray and EUV observations, we report pulsations of the ionospheric D region, which are synchronized with a set of pulsating flare loops. Modeling of the ionosphere show that the D region electron density varies by up to an order of magnitude over the timescale of the pulsations (˜ 20 min). Our results reveal that the Earth's ionosphere is more sensitive to small-scale changes in solar soft X-ray flux than previously thought and implies that planetary ionospheres are closely coupled to small-scale changes in solar/stellar activity.

Characteristics of low-temperature short heat pipes with a nozzle-shaped vapor channel

NASA Astrophysics Data System (ADS)

Seryakov, A. V.

2016-01-01

This paper presents the results of experimental and numerical studies of heat transfer and swirling pulsating flows in short low-temperature heat pipes whose vapor channels have the form of a conical nozzle. It has been found that as the evaporator of the heat pipe is heated, pressure pulsations occur in the vapor channel starting at a certain threshold value of the heat power, which is due to the start of boiling in the evaporator. The frequency of the pulsations has been measured, and their dependence on the superheat of the evaporator has been determined. It has been found that in heat pipes with a conical vapor channel, pulsations occur at lower evaporator superheats and the pulsation frequency is greater than in heat pipes of the same size with a standard cylindrical vapor channel. It has been shown that the curve of the heat-transfer coefficient versus thermal load on the evaporator has an inflection corresponding to the start of boiling in the capillary porous evaporator of the heat pipe.

A1540-53, an eclipsing X-ray binary pulsator

NASA Technical Reports Server (NTRS)

Becker, R. H.; Swank, J. H.; Boldt, E. A.; Holt, S. S.; Serlemitsos, P. J.; Pravdo, S. H.; Saba, J. R.

1977-01-01

An eclipsing X-ray binary pulsator consistent with the location of A1540-53 has been observed. The source pulse period was 528.93 + or - 0.10 s. The binary nature is confirmed by a Doppler curve for the pulsation period. The eclipse angle of 30.5 + or - 3 deg and the 4-hour transition to and from eclipse suggest an early-type giant or supergiant primary star.

Study of the velocity distribution influence upon the pressure pulsations in draft tube model of hydro-turbine

NASA Astrophysics Data System (ADS)

Sonin, V.; Ustimenko, A.; Kuibin, P.; Litvinov, I.; Shtork, S.

2016-11-01

One of the mechanisms of generation of powerful pressure pulsations in the circuit of the turbine is a precessing vortex core, formed behind the runner at the operation points with partial or forced loads, when the flow has significant residual swirl. To study periodic pressure pulsations behind the runner the authors of this paper use approaches of experimental modeling and methods of computational fluid dynamics. The influence of velocity distributions at the output of the hydro turbine runner on pressure pulsations was studied based on analysis of the existing and possible velocity distributions in hydraulic turbines and selection of the distribution in the extended range. Preliminary numerical calculations have showed that the velocity distribution can be modeled without reproduction of the entire geometry of the circuit, using a combination of two blade cascades of the rotor and stator. Experimental verification of numerical results was carried out in an air bench, using the method of 3D-printing for fabrication of the blade cascades and the geometry of the draft tube of hydraulic turbine. Measurements of the velocity field at the input to a draft tube cone and registration of pressure pulsations due to precessing vortex core have allowed building correlations between the velocity distribution character and the amplitude-frequency characteristics of the pulsations.

The dynamical mass of a classical Cepheid variable star in an eclipsing binary system.

PubMed

Pietrzyński, G; Thompson, I B; Gieren, W; Graczyk, D; Bono, G; Udalski, A; Soszyński, I; Minniti, D; Pilecki, B

2010-11-25

Stellar pulsation theory provides a means of determining the masses of pulsating classical Cepheid supergiants-it is the pulsation that causes their luminosity to vary. Such pulsational masses are found to be smaller than the masses derived from stellar evolution theory: this is the Cepheid mass discrepancy problem, for which a solution is missing. An independent, accurate dynamical mass determination for a classical Cepheid variable star (as opposed to type-II Cepheids, low-mass stars with a very different evolutionary history) in a binary system is needed in order to determine which is correct. The accuracy of previous efforts to establish a dynamical Cepheid mass from Galactic single-lined non-eclipsing binaries was typically about 15-30% (refs 6, 7), which is not good enough to resolve the mass discrepancy problem. In spite of many observational efforts, no firm detection of a classical Cepheid in an eclipsing double-lined binary has hitherto been reported. Here we report the discovery of a classical Cepheid in a well detached, double-lined eclipsing binary in the Large Magellanic Cloud. We determine the mass to a precision of 1% and show that it agrees with its pulsation mass, providing strong evidence that pulsation theory correctly and precisely predicts the masses of classical Cepheids.

On the origin of the 1-hour pulsations in the Saturn's magnetosphere

NASA Astrophysics Data System (ADS)

Rusaitis, L.; Walker, R. J.; Khurana, K. K.; Kivelson, M.

2016-12-01

The quasi-periodic pulsations of approximately 1-hour periodicity in the magnetic field and particle fluxes have been regularly detected in the outer Saturnian magnetosphere by the Cassini spacecraft since the orbital insertion in 2004 [Palmaerts, 2016; Roussos, 2016]. In this study we focus on the Cassini's magnetometer (MAG) and the Cassini Plasma Spectrometer (CAPS) data from the July 1st, 2004 to June 4th, 2012 (when the CAPS instrument was turned off). Throughout this 8-year period we find over 130 pulsation events in the MAG data, ranging in periodicity from 40 to 90 minutes, and having a typical amplitude of 0.5-1nT in the transverse (φ ) direction. The pulsations typically last 4-6 hours before decaying, and occur both in the dawn and dusk sectors during the crossings of the outer magnetosphere. We study the pulsations in the azimuthal magnetic field as signatures for the periodic enhancements detected in the CAPS data in the plasma temperature and densities. Additionally, we investigate a high temporal resolution 3-D MHD simulation of Saturn's magnetosphere to look for the signatures of these pulsations at the equivalent positions, and use the simulation results to suggest their physical origin and the triggering mechanism by varying the solar wind parameters.

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.

A Search for Rapidly Pulsating Hot Subdwarf Stars in the GALEX Survey

DOE Office of Scientific and Technical Information (OSTI.GOV)

Boudreaux, Thomas M.; Barlow, Brad N.; Soto, Alan Vasquez

NASA’s Galaxy Evolution Explorer ( GALEX ) provided near- and far-UV observations for approximately 77% of the sky over a 10-year period; however, the data reduction pipeline initially only released single NUV and FUV images to the community. The recently released Python module gPhoton changes this, allowing calibrated time-series aperture photometry to be extracted easily from the raw GALEX data set. Here we use gPhoton to generate light curves for all hot subdwarf B (sdB) stars that were observed by GALEX , with the intention of identifying short-period, p-mode pulsations. We find that the spacecraft’s short visit durations, uneven gapsmore » between visits, and dither pattern make the detection of hot subdwarf pulsations difficult. Nonetheless, we detect UV variations in four previously known pulsating targets and report their UV pulsation amplitudes and frequencies. Additionally, we find that several other sdB targets not previously known to vary show promising signals in their periodograms. Using optical follow-up photometry with the Skynet Robotic Telescope Network, we confirm p-mode pulsations in one of these targets, LAMOST J082517.99+113106.3, and report it as the most recent addition to the sdBV{sub r} class of variable stars.« less

Mesospheric ozone destruction by high-energy electron precipitation associated with pulsating aurora

NASA Astrophysics Data System (ADS)

Turunen, Esa; Kero, Antti; Verronen, Pekka T.; Miyoshi, Yoshizumi; Oyama, Shin-Ichiro; Saito, Shinji

2016-10-01

Energetic particle precipitation into the upper atmosphere creates excess amounts of odd nitrogen and odd hydrogen. These destroy mesospheric and upper stratospheric ozone in catalytic reaction chains, either in situ at the altitude of the energy deposition or indirectly due to transport to other altitudes and latitudes. Recent statistical analysis of satellite data on mesospheric ozone reveals that the variations during energetic electron precipitation from Earth's radiation belts can be tens of percent. Here we report model calculations of ozone destruction due to a single event of pulsating aurora early in the morning on 17 November 2012. The presence of high-energy component in the precipitating electron flux (>200 keV) was detected as ionization down to 68 km altitude, by the VHF incoherent scatter radar of European Incoherent Scatter (EISCAT) Scientific Association (EISCAT VHF) in Tromsø, Norway. Observations by the Van Allen Probes satellite B showed the occurrence of rising tone lower band chorus waves, which cause the precipitation. We model the effect of high-energy electron precipitation on ozone concentration using a detailed coupled ion and neutral chemistry model. Due to a 30 min, recorded electron precipitation event we find 14% odd oxygen depletion at 75 km altitude. The uncertainty of the higher-energy electron fluxes leads to different possible energy deposition estimates during the pulsating aurora event. We find depletion of odd oxygen by several tens of percent, depending on the precipitation characteristics used in modeling. The effect is notably maximized at the sunset time following the occurrence of the precipitation.

Low and middle altitude cusp particle signatures for general magnetopause reconnection rate variations. 1: Theory

NASA Technical Reports Server (NTRS)

Lockwood, M.; Smith, M. F.

1994-01-01

We present predictions of the signatures of magnetosheath particle precipitation (in the regions classified as open low-latitude boundary layer, cusp, mantle and polar cap) for periods when the interplanetary magnetic field has a southward component. These are made using the 'pulsating cusp' model of the effects of time-varying magnetic reconnection at the dayside magnetopause. Predictions are made for both low-altitude satellites in the topside ionosphere and for midaltitude spacecraft in the magnetosphere. Low-altitude cusp signatures, which show a continuous ion dispersion signature, reveal 'quasi-steady reconnection' (one limit of the pulsating cusp model), which persists for a period of at least 10 min. We estimate that 'quasi-steady' in this context corresponds to fluctuations in the reconnection rate of a factor of 2 or less. The other limit of the pulsating cusp model explains the instantaneous jumps in the precipitating ion spectrum that have been observed at low altitudes. Such jumps are produced by isolated pulses of reconnection: that is, they are separated by intervals when the reconnection rate is zero. These also generate convecting patches on the magnetopause in which the field lines thread the boundary via a rotational discontinuity separated by more extensive regions of tangential discontinuity. Predictions of the corresponding ion precipitation signatures seen by midaltitude spacecraft are presented. We resolve the apparent contradiction between estimates of the width of the injection region from midaltitude data and the concept of continuous entry of solar wind plasma along open field lines. In addition, we reevaluate the use of pitch angle-energy dispersion to estimate the injection distance.

Method of calculating gas dynamics and heat transfer in single stage refrigeration units

NASA Technical Reports Server (NTRS)

Zhitomirskiy, I. S.; Popolskiy, A. B.

1974-01-01

A generalized mathematical model of gas-dynamic and heat transfer processes in single-stage regenerative installations operating in Stirling, MacMahon, Gifford-MacMahon, and pulsating tube cycles is proposed. A numerical method os solving initial equations on a digital computer is given. This makes it possible to calculate the change in the thermodynamic parameters in the working cycle in different machine components, as well as the dependence of cold productivity on the temperature level in the steady regime.

Embedded spacecraft thermal control using ultrasonic consolidation

NASA Astrophysics Data System (ADS)

Clements, Jared W.

Research has been completed in order to rapidly manufacture spacecraft thermal control technologies embedded in spacecraft structural panels using ultrasonic consolidation. This rapid manufacturing process enables custom thermal control designs in the time frame necessary for responsive space. Successfully embedded components include temperature sensors, heaters, wire harnessing, pre-manufactured heat pipes, and custom integral heat pipes. High conductivity inserts and custom integral pulsating heat pipes were unsuccessfully attempted. This research shows the viability of rapid manufacturing of spacecraft structures with embedded thermal control using ultrasonic consolidation.

Generation of traveling atmospheric disturbances during pulsating geomagnetic storms

NASA Astrophysics Data System (ADS)

Gardner, Larry; Schunk, Robert

Traveling Atmospheric Disturbances (TADs) are effective in transporting momentum and en-ergy deposited at high latitudes to the mid and low latitude regions of the thermosphere. They also act to transport momentum and energy from the lower thermosphere into the upper ther-mosphere. Previously, model studies have been conducted to determine the characteristics of isolated, single-pulse TADs, but the generation of multiple TADs excited during pulsating storms have not been considered before. Here, a high-resolution global thermosphere-ionosphere model was used to study the basic characteristic of multiple TADs excited during pulsating storms, including idealized weak and strong pulsating storms, and an approximation of the May 4, 1998 pulsating storm. For all three pulsating storm simulations, multiple TADs were excited that propagated away form the auroral oval both toward the poles and toward the equator at all longitudes, with the maximum amplitudes between midnight and dawn. The TAD amplitudes were a maximum near the poles, diminished towards the equator and were larger on the nightside than on the dayside. The TADs propagated at a slight upward angle to the horizontal, with the result that the lower boundary of the TADs increased with decreas-ing latitude. The TADs crossed the equator and propagated to mid-latitudes in the opposite hemisphere, where wave interference occurred for the strong pulsating storm cases. The TAD wavelengths vary from 2500-3000 km and the phase speeds from 800-1000 m/s. The maximum TAD perturbations are 20% for the mass density 14% for the neutral temperature and 100 m/s for the winds.

Generation of traveling atmospheric disturbances during pulsating geomagnetic storms

NASA Astrophysics Data System (ADS)

Gardner, L. C.; Schunk, R. W.

2010-08-01

Traveling atmospheric disturbances (TADs) are effective in transporting momentum and energy deposited at high latitudes to the midlatitude and low-latitude regions of the thermosphere. They also act to transport momentum and energy from the lower thermosphere into the upper thermosphere. Previously, model studies have been conducted to determine the characteristics of isolated, single-pulse TADs, but the generation of multiple TADs excited during pulsating storms have not been considered before. Here a high-resolution global thermosphere-ionosphere model was used to study the basic characteristics of multiple TADs excited during pulsating storms, including idealized weak and strong pulsating storms, and an approximation of the 4 May 1998 pulsating storm. For all three pulsating storm simulations, multiple TADs that propagated away from the auroral oval toward both the poles and the equator at all longitudes, with the maximum amplitudes between midnight and dawn, were excited. The TAD amplitudes were at maximum near the poles and diminished toward the equator and were larger on the nightside than on the dayside. The TADs propagated at a slightly upward angle to the horizontal, with the result that the lower boundary of the TADs increased with decreasing latitude. The TADs crossed the equator and propagated to midlatitudes in the opposite hemisphere, where wave interference occurred for the strong pulsating storm cases. The TAD wavelengths vary from 2500 to 3000 km and the phase speeds vary from 800 to 1000 m/s. The maximum TAD perturbations are 20% for the mass density, 14% for the neutral temperature, and 100 m/s for the winds.

FAMIAS User Manual

NASA Astrophysics Data System (ADS)

Zima, Wolfgang

2008-10-01

The excitation of pulsation modes in Beta Cephei and Slowly Pulsating B stars is known to be very sensitive to opacity changes in the stellar interior where T ~ 2 x 10E5 K. In this region differences in opacity up to ~ 50% can be induced by the choice between OPAL and OP opacity tables, and between two different metal mixtures (Grevesse & Noels 1993 and Asplund et al. 2005). We have extended the non-adiabatic computations presented in Miglio et al. (2007) towards models of higher mass and pulsation modes of degree l = 3, and we present here the instability domains in the HR- and log P-log Teff diagrams resulting from different choices of opacity tables, and for three different metallicities. FAMIAS (Frequency Analysis and Mode Identification for AsteroSeismology) is a collection of state-of-the-art software tools for the analysis of photometric and spectroscopic time series data. It is one of the deliverables of the Work Package NA5: Asteroseismology of the European Coordination Action in Helio-and Asteroseismology (HELAS). Two main sets of tools are incorporated in FAMIAS. The first set allows to search for periodicities in the data using Fourier and non-linear least-squares fitting algorithms. The other set allows to carry out a mode identification for the detected pulsation frequencies to determine their pulsational quantum numbers, the harmonic degree, m. The types of stars to which famias is applicable are main-sequence pulsators hotter than the Sun. This includes the Gamma Dor stars, Delta Sct stars, the slowly pulsating B stars and the Beta Cep stars - basically all pulsating main-sequence stars, for which empirical mode identification is required to successfully carry out asteroseismology. This user manual describes how to use the different features of FAMIAS and provides two tutorials that demonstrate the usage of FAMIAS for spectroscopic and photometric mode identification.

DISCOVERY OF PULSATIONS, INCLUDING POSSIBLE PRESSURE MODES, IN TWO NEW EXTREMELY LOW MASS, He-CORE WHITE DWARFS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hermes, J. J.; Montgomery, M. H.; Winget, D. E.

2013-03-10

We report the discovery of the second and third pulsating extremely low mass (ELM) white dwarfs (WDs), SDSS J111215.82+111745.0 (hereafter J1112) and SDSS J151826.68+065813.2 (hereafter J1518). Both have masses < 0.25 M{sub Sun} and effective temperatures below 10, 000 K, establishing these putatively He-core WDs as a cooler class of pulsating hydrogen-atmosphere WDs (DAVs, or ZZ Ceti stars). The short-period pulsations evidenced in the light curve of J1112 may also represent the first observation of acoustic (p-mode) pulsations in any WD, which provide an exciting opportunity to probe this WD in a complimentary way compared to the long-period g-modes thatmore » are also present. J1112 is a T{sub eff} =9590 {+-} 140 K and log g =6.36 {+-} 0.06 WD. The star displays sinusoidal variability at five distinct periodicities between 1792 and 2855 s. In this star, we also see short-period variability, strongest at 134.3 s, well short of the expected g-modes for such a low-mass WD. The other new pulsating WD, J1518, is a T{sub eff} =9900 {+-} 140 K and log g =6.80 {+-} 0.05 WD. The light curve of J1518 is highly non-sinusoidal, with at least seven significant periods between 1335 and 3848 s. Consistent with the expectation that ELM WDs must be formed in binaries, these two new pulsating He-core WDs, in addition to the prototype SDSS J184037.78+642312.3, have close companions. However, the observed variability is inconsistent with tidally induced pulsations and is so far best explained by the same hydrogen partial-ionization driving mechanism at work in classic C/O-core ZZ Ceti stars.« less

Pulsating B and Be stars in the Small Magellanic Cloud

NASA Astrophysics Data System (ADS)

Diago, P. D.; Gutiérrez-Soto, J.; Fabregat, J.; Martayan, C.

2008-03-01

Context: Stellar pulsations in main-sequence B-type stars are driven by the κ-mechanism due to the Fe-group opacity bump. The current models do not predict the presence of instability strips in the B spectral domain at very low metallicities. As the metallicity of the SMC is lower than Z = 0.005, it constitutes a very suitable object to test these predictions. Aims: The main objective is to investigate the existence of B-type pulsators at low metallicities, searching for short-term periodic variability in absorption-line B and Be stars in the SMC. The analysis has been performed in a sample of 313 B and Be stars with fundamental astrophysical parameters accurately determined from high-resolution spectroscopy. Methods: Photometric light curves of the MACHO project have been analyzed using standard Fourier techniques and linear and non-linear least squares fitting methods. The position of the pulsating stars in the HR diagram has been used to ascertain their nature and to map the instability regions in the SMC. Results: We have detected 9 absorption-line B stars showing short-period variability, two among them being multiperiodic. One star is most likely a β Cephei variable and the remaining 8 are SPB stars. The SPB instability strip in the SMC is shifted towards higher temperatures than the Galaxy. In the Be star sample, 32 stars are short-period variables, 20 among them multiperiodic. 4.9% of B stars and 25.3% of Be stars are pulsating stars. Conclusions: β Cephei and SPB stars do exist at the SMC metallicity. The fractions of SPB stars and pulsating Be stars in the SMC are lower than in the Galaxy. The fraction of pulsating Be stars in the SMC is much higher than the fraction of pulsating absorption-line B stars, as in the Galaxy.

Ultrasonic Apparatus and Method to Assess Compartment Syndrome

NASA Technical Reports Server (NTRS)

Yost, William T. (Inventor); Ueno, Toshiaki (Inventor); Hargens, Alan R. (Inventor)

2009-01-01

A process and apparatus for measuring pressure buildup in a body compartment that encases muscular tissue. The method includes assessing the body compartment configuration and identifying the effect of pulsatible components on compartment dimensions and muscle tissue characteristics. This process is used in preventing tissue necrosis, and in decisions of whether to perform surgery on the body compartment for prevention of Compartment Syndrome. An apparatus is used for measuring pressure build-up in the body compartment having components for imparting ultrasonic waves such as a transducer, placing the transducer to impart the ultrasonic waves, capturing the imparted ultrasonic waves, mathematically manipulating the captured ultrasonic waves and categorizing pressure build-up in the body compartment from the mathematical manipulations.

Acoustic radiation force control: Pulsating spherical carriers.

PubMed

Rajabi, Majid; Mojahed, Alireza

2018-02-01

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 power supply for distinct cases of zero, negative and positive radiation force states along with the frequency dependent asymmetry index. In addition, considering the effect of phase difference between the incident wave field and the pulsating object, and its possible variation with respect to spatial position of object, some practical points about the spatial average of generated radiation force, the optimal state of operation, the stability of zero radiation force states and the possibly of precise motion control are discussed. This work would extend the novel concept of smart carriers to and may be helpful for robust single-beam acoustic handling techniques. Furthermore, the shown capability of precise motion control may be considered as a new way toward smart acoustic driven micro-mechanisms and micro-machines. Copyright © 2017 Elsevier B.V. All rights reserved.

Evaluation of Pump Pulsation in Respirable Size-Selective Sampling: Part II. Changes in Sampling Efficiency

PubMed Central

Lee, Eun Gyung; Lee, Taekhee; Kim, Seung Won; Lee, Larry; Flemmer, Michael M.; Harper, Martin

2015-01-01

This second, and concluding, part of this study evaluated changes in sampling efficiency of respirable size-selective samplers due to air pulsations generated by the selected personal sampling pumps characterized in Part I (Lee E, Lee L, Möhlmann C et al. Evaluation of pump pulsation in respirable size-selective sampling: Part I. Pulsation measurements. Ann Occup Hyg 2013). Nine particle sizes of monodisperse ammonium fluorescein (from 1 to 9 μm mass median aerodynamic diameter) were generated individually by a vibrating orifice aerosol generator from dilute solutions of fluorescein in aqueous ammonia and then injected into an environmental chamber. To collect these particles, 10-mm nylon cyclones, also known as Dorr-Oliver (DO) cyclones, were used with five medium volumetric flow rate pumps. Those were the Apex IS, HFS513, GilAir5, Elite5, and Basic5 pumps, which were found in Part I to generate pulsations of 5% (the lowest), 25%, 30%, 56%, and 70% (the highest), respectively. GK2.69 cyclones were used with the Legacy [pump pulsation (PP) = 15%] and Elite12 (PP = 41%) pumps for collection at high flows. The DO cyclone was also used to evaluate changes in sampling efficiency due to pulse shape. The HFS513 pump, which generates a more complex pulse shape, was compared to a single sine wave fluctuation generated by a piston. The luminescent intensity of the fluorescein extracted from each sample was measured with a luminescence spectrometer. Sampling efficiencies were obtained by dividing the intensity of the fluorescein extracted from the filter placed in a cyclone with the intensity obtained from the filter used with a sharp-edged reference sampler. Then, sampling efficiency curves were generated using a sigmoid function with three parameters and each sampling efficiency curve was compared to that of the reference cyclone by constructing bias maps. In general, no change in sampling efficiency (bias under ±10%) was observed until pulsations exceeded 25% for the DO cyclone. However, for three models of pumps producing 30%, 56%, and 70% pulsations, substantial changes were confirmed. The GK2.69 cyclone showed a similar pattern to that of the DO cyclone, i.e. no change in sampling efficiency for the Legacy producing 15% pulsation and a substantial change for the Elite12 producing 41% pulsation. Pulse shape did not cause any change in sampling efficiency when compared to the single sine wave. The findings suggest that 25% pulsation at the inlet of the cyclone as measured by this test can be acceptable for the respirable particle collection. If this test is used in place of that currently in European standards (EN 1232–1997 and EN 12919-1999) or is used in any International Organization for Standardization standard, then a 25% pulsation criterion could be adopted. This work suggests that a 10% criterion as currently specified in the European standards for testing may be overly restrictive and not able to be met by many pumps on the market. Further work is recommended to determine which criterion would be applicable to this test if it is to be retained in its current form. PMID:24064963

Evaluation of pump pulsation in respirable size-selective sampling: part II. Changes in sampling efficiency.

PubMed

Lee, Eun Gyung; Lee, Taekhee; Kim, Seung Won; Lee, Larry; Flemmer, Michael M; Harper, Martin

2014-01-01

This second, and concluding, part of this study evaluated changes in sampling efficiency of respirable size-selective samplers due to air pulsations generated by the selected personal sampling pumps characterized in Part I (Lee E, Lee L, Möhlmann C et al. Evaluation of pump pulsation in respirable size-selective sampling: Part I. Pulsation measurements. Ann Occup Hyg 2013). Nine particle sizes of monodisperse ammonium fluorescein (from 1 to 9 μm mass median aerodynamic diameter) were generated individually by a vibrating orifice aerosol generator from dilute solutions of fluorescein in aqueous ammonia and then injected into an environmental chamber. To collect these particles, 10-mm nylon cyclones, also known as Dorr-Oliver (DO) cyclones, were used with five medium volumetric flow rate pumps. Those were the Apex IS, HFS513, GilAir5, Elite5, and Basic5 pumps, which were found in Part I to generate pulsations of 5% (the lowest), 25%, 30%, 56%, and 70% (the highest), respectively. GK2.69 cyclones were used with the Legacy [pump pulsation (PP) = 15%] and Elite12 (PP = 41%) pumps for collection at high flows. The DO cyclone was also used to evaluate changes in sampling efficiency due to pulse shape. The HFS513 pump, which generates a more complex pulse shape, was compared to a single sine wave fluctuation generated by a piston. The luminescent intensity of the fluorescein extracted from each sample was measured with a luminescence spectrometer. Sampling efficiencies were obtained by dividing the intensity of the fluorescein extracted from the filter placed in a cyclone with the intensity obtained from the filter used with a sharp-edged reference sampler. Then, sampling efficiency curves were generated using a sigmoid function with three parameters and each sampling efficiency curve was compared to that of the reference cyclone by constructing bias maps. In general, no change in sampling efficiency (bias under ±10%) was observed until pulsations exceeded 25% for the DO cyclone. However, for three models of pumps producing 30%, 56%, and 70% pulsations, substantial changes were confirmed. The GK2.69 cyclone showed a similar pattern to that of the DO cyclone, i.e. no change in sampling efficiency for the Legacy producing 15% pulsation and a substantial change for the Elite12 producing 41% pulsation. Pulse shape did not cause any change in sampling efficiency when compared to the single sine wave. The findings suggest that 25% pulsation at the inlet of the cyclone as measured by this test can be acceptable for the respirable particle collection. If this test is used in place of that currently in European standards (EN 1232-1997 and EN 12919-1999) or is used in any International Organization for Standardization standard, then a 25% pulsation criterion could be adopted. This work suggests that a 10% criterion as currently specified in the European standards for testing may be overly restrictive and not able to be met by many pumps on the market. Further work is recommended to determine which criterion would be applicable to this test if it is to be retained in its current form.

[Aspects of vascular physiology in clinical and vascular surgical practice: basic principles of vascular mechanics].

PubMed

Nocke, H; Meyer, F; Lessmann, V

2014-10-01

To be able to evaluate properly a vascular problem, basic concepts of vascular physiology need to be considered, as they have been taught in physiology for a long time. This article deals with selected definitions and laws of passive vascular mechanics, subdivided into parameters of vascular filling and parameters of vascular flow. PARAMETERS OF VASCULAR FILLING: During vascular filling the transmural pressure distends the vascular wall until it is balanced by the wall tension. The extent of this distension up to the point of balance depends on the elasticity of the wall. Transmural pressure, wall tension and elasticity are defined, and their respective importance is described by clinical examples, e.g. aneurysm and varix. PARAMETERS OF VASCULAR FLOW: The vascular flow can be divided into stationary and pulsating components. Both components are relevant for the bloodstream. Since the blood flow is directed in the circuit, it can be understood in first approximation as stationary ("direct current").The direct current model uses only the average values of the pulsating variables. The great advantage of the direct current model is that it can be described with simple laws, which are not valid without reservation, but often allow a first theoretical approach to a vascular problem: Ohm's law, driving pressure, flow resistance, Hagen-Poiseuille law, wall shear stress, law of continuity, Bernoulli's equation and Reynold's number are described and associated with clinical examples.The heart is a pressure-suction pump and produces a pulsating flow, the pulse. The pulse runs with pulse wave velocity, which is much larger than the blood flow velocity, through the arterial vascular system. During propagation, the pulse has to overcome the wave resistance (impedance). Wherever the wave resistance changes, e.g., at vascular bifurcations and in the periphery, it comes to reflections. The incident (forward) and reflected (backward) waves are superimposed to yield the resulting pulse wave. This pulse wave allows one to distinguish pressure and flow pulse by measurement. Both are described separately, and their respective clinical meaning is illustrated by appropriate examples, e.g., arterial stiffness and pre-/postocclusive high/low resistance flow, respectively. Georg Thieme Verlag KG Stuttgart · New York.

A1540-53, an eclipsing X-ray binary pulsator

NASA Technical Reports Server (NTRS)

Becker, R. H.; Swank, J. H.; Boldt, E. A.; Holt, S. S.; Pravdo, S. H.; Saba, J. R.; Serlemitsos, P. J.

1977-01-01

An eclipsing X-ray binary pulsator consistent with the location of A1540-53 was observed. The source pulse period was 528.93 plus or minus 0.10 seconds. The binary nature is confirmed by a Doppler curve for the pulsation period. The eclipse angle of 30.5 deg plus or minus 3 deg and the 4 h transition to and from eclipse suggest an early type, giant or supergiant, primary star.

Ocular pulsation correlates with ocular tension: the choroid as piston for an aqueous pump?

PubMed

Phillips, C I; Tsukahara, S; Hosaka, O; Adams, W

1992-01-01

In 26 random out-patients, including 13 treated glaucoma patients and ocular hypertensives, the higher the ocular tension, the greater the pulse amplitude, by Alcon pneumotonometry, at a statistically significant level. In a single untreated hypertensive, when 2-hourly pneumotonometry was done for 24 h, the correlation was similar and significant. The higher the diastolic blood pressure, the higher the ocular pulsation, also significantly. Pulsation is suggested to be a pump, the choroid being the piston, contributing (1) to an increase in the outflow of aqueous humour and (2) to a homeostatic mechanism contributing to normalization of the intra-ocular pressure, wherein pulsation increases or decreases, as the intraocular pressure increases or decreases, respectively.

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.

Sparsely-Observed Pulsating Red Giants in the AAVSO Observing Program

NASA Astrophysics Data System (ADS)

Percy, J. R.

2018-06-01

This paper reports on time-series analysis of 156 pulsating red giants (21 SRa, 52 SRb, 33 SR, 50 Lb) in the AAVSO observing program for which there are no more than 150-250 observations in total. Some results were obtained for 68 of these stars: 17 SRa, 14 SRb, 20 SR, and 17 Lb. These results generally include only an average period and amplitude. Many, if not most of the stars are undoubtedly more complex; pulsating red giants are known to have wandering periods, variable amplitudes, and often multiple periods including "long secondary periods" of unknown origin. These results (or lack thereof) raise the question of how the AAVSO should best manage the observation of these and other sparsely-observed pulsating red giants.

Exhaust pressure pulsation observation from turbocharger instantaneous speed measurement

NASA Astrophysics Data System (ADS)

Macián, V.; Luján, J. M.; Bermúdez, V.; Guardiola, C.

2004-06-01

In internal combustion engines, instantaneous exhaust pressure measurements are difficult to perform in a production environment. The high temperature of the exhaust manifold and its pulsating character make its application to exhaust gas recirculation control algorithms impossible. In this paper an alternative method for estimating the exhaust pressure pulsation is presented. A numerical model is built which enables the exhaust pressure pulses to be predicted from instantaneous turbocharger speed measurements. Although the model is data based, a theoretical description of the process is also provided. This combined approach makes it possible to export the model for different engine operating points. Also, compressor contribution in the turbocharger speed pulsation is discussed extensively. The compressor contribution is initially neglected, and effects of this simplified approach are analysed.

New observations, new theoretical results and controversies regarding PC 3-5 waves

NASA Astrophysics Data System (ADS)

Takahashi, K.

Observations and theories of medium- to long-period (Pc 3-5) magnetic pulsations excited by magnetospheric particles are described. Satellite observations indicate that most pulsations can be classified into two groups according to their magnetic field polarization. One group has a transverse magnetic perturbation and the other strongly compressional perturbation. Despite this difference in polarization they share common characteristics, including large azimuthal wave number, westward propagation, and antisymmetric field-aligned structure. Recent theories describe these observations in a unified framework. It has been pointed out that trapped energetic ions play an important role in determining the instability threshold and the mode structure of the pulsations. Observations and theories of energetic particle response to the excited pulsations are also described.

The challenge of measuring magnetic fields in strongly pulsating stars: the case of HD 96446

NASA Astrophysics Data System (ADS)

Järvinen, S. P.; Hubrig, S.; Ilyin, I.; Schöller, M.; Briquet, M.

2017-01-01

Among the early B-type stars, He-rich Bp stars exhibit the strongest large-scale organized magnetic fields with a predominant dipole contribution. The presence of β Cep-like pulsations in the typical magnetic early Bp-type star HD 96446 was announced a few years ago, but the analysis of the magnetic field geometry was hampered by the absence of a reliable rotation period and a sophisticated procedure for accounting for the impact of pulsations on the magnetic field measurements. Using new spectropolarimetric observations and a recently determined rotation period based on an extensive spectroscopic time series, we investigate the magnetic field model parameters of this star under more detailed considerations of the pulsation behaviour of line profiles.

Could CoRoT-7b and Kepler-10b be remnants of evaporated gas or ice giants?

PubMed Central

Leitzinger, M.; Odert, P.; Kulikov, Yu.N.; Lammer, H.; Wuchterl, G.; Penz, T.; Guarcello, M.G.; Micela, G.; Khodachenko, M.L.; Weingrill, J.; Hanslmeier, A.; Biernat, H.K.; Schneider, J.

2011-01-01

We present thermal mass loss calculations over evolutionary time scales for the investigation if the smallest transiting rocky exoplanets CoRoT-7b (∼1.68REarth) and Kepler-10b (∼1.416REarth) could be remnants of an initially more massive hydrogen-rich gas giant or a hot Neptune-class exoplanet. We apply a thermal mass loss formula which yields results that are comparable to hydrodynamic loss models. Our approach considers the effect of the Roche lobe, realistic heating efficiencies and a radius scaling law derived from observations of hot Jupiters. We study the influence of the mean planetary density on the thermal mass loss by placing hypothetical exoplanets with the characteristics of Jupiter, Saturn, Neptune, and Uranus to the orbital location of CoRoT-7b at 0.017 AU and Kepler-10b at 0.01684 AU and assuming that these planets orbit a K- or G-type host star. Our findings indicate that hydrogen-rich gas giants within the mass domain of Saturn or Jupiter cannot thermally lose such an amount of mass that CoRoT-7b and Kepler-10b would result in a rocky residue. Moreover, our calculations show that the present time mass of both rocky exoplanets can be neither a result of evaporation of a hydrogen envelope of a “Hot Neptune” nor a “Hot Uranus”-class object. Depending on the initial density and mass, these planets most likely were always rocky planets which could lose a thin hydrogen envelope, but not cores of thermally evaporated initially much more massive and larger objects. PMID:21969736

Vortex Generators in a Streamline-Traced, External-Compression Supersonic Inlet

NASA Technical Reports Server (NTRS)

Baydar, Ezgihan; Lu, Frank K.; Slater, John W.; Trefny, Charles J.

2017-01-01

Vortex generators within a streamline-traced, external-compression supersonic inlet for Mach 1.66 were investigated to determine their ability to increase total pressure recovery and reduce total pressure distortion. The vortex generators studied were rectangular vanes arranged in counter-rotating and co-rotating arrays. The vane geometric factors of interest included height, length, spacing, angle-of-incidence, and positions upstream and downstream of the inlet terminal shock. The flow through the inlet was simulated numerically through the solution of the steady-state, Reynolds-averaged Navier-Stokes equations on multi-block, structured grids using the Wind-US flow solver. The vanes were simulated using a vortex generator model. The inlet performance was characterized by the inlet total pressure recovery and the radial and circumferential total pressure distortion indices at the engine face. Design of experiments and statistical analysis methods were applied to quantify the effect of the geometric factors of the vanes and search for optimal vane arrays. Co-rotating vane arrays with negative angles-of-incidence positioned on the supersonic diffuser were effective in sweeping low-momentum flow from the top toward the sides of the subsonic diffuser. This distributed the low-momentum flow more evenly about the circumference of the subsonic diffuser and reduced distortion. Co-rotating vane arrays with negative angles-of-incidence or counter-rotating vane arrays positioned downstream of the terminal shock were effective in mixing higher-momentum flow with lower-momentum flow to increase recovery and decrease distortion. A strategy of combining a co-rotating vane array on the supersonic diffuser with a counter-rotating vane array on the subsonic diffuser was effective in increasing recovery and reducing distortion.

Collective dynamics of large aspect ratio dusty plasma in an inhomogeneous plasma background: Formation of the co-rotating vortex series

NASA Astrophysics Data System (ADS)

Choudhary, Mangilal; Mukherjee, S.; Bandyopadhyay, P.

2018-02-01

In this paper, the collective dynamics of large aspect ratio dusty plasma is studied over a wide range of discharge parameters. An inductively coupled diffused plasma, which creates an electrostatic trap to confine the negatively charged grains, is used to form a large volume (or large aspect ratio) dusty plasma at low pressure. For introducing the dust grains into the potential well, a unique technique using secondary DC glow discharge plasma is employed. The dust dynamics is recorded in a two-dimension (2D) plane at a given axial location. The dust fluid exhibits wave-like behavior at low pressure (p < 0.06 mbar) and high rf power (P > 3 W). The mixed motion, waves and vortices, is observed at an intermediate gas pressure (p ˜ 0.08 mbar) and low power (P < 3 W). Above the threshold value of gas pressure (p > 0.1 mbar), the clockwise and anti-clockwise co-rotating vortex series are observed on edges of the dust cloud, whereas the particles in the central region show random motion. These vortices are only observed above the threshold width of the dust cloud. The occurrence of the co-rotating vortices is understood on the basis of the charge gradient of dust particles, which is orthogonal to the gravity. The charge gradient is a consequence of the plasma inhomogeneity from the central region to the outer edge of the dust fluid. Since a vortex has the characteristic size in the dissipative medium; therefore, a series of the co-rotating vortex on both sides of dusty plasma is observed. The experimental results on the vortex formation and its multiplicity are compared to an available theoretical model and are found to be in close agreement.

Could CoRoT-7b and Kepler-10b be remnants of evaporated gas or ice giants?

PubMed

Leitzinger, M; Odert, P; Kulikov, Yu N; Lammer, H; Wuchterl, G; Penz, T; Guarcello, M G; Micela, G; Khodachenko, M L; Weingrill, J; Hanslmeier, A; Biernat, H K; Schneider, J

2011-10-01

We present thermal mass loss calculations over evolutionary time scales for the investigation if the smallest transiting rocky exoplanets CoRoT-7b (∼1.68REarth) and Kepler-10b (∼1.416REarth) could be remnants of an initially more massive hydrogen-rich gas giant or a hot Neptune-class exoplanet. We apply a thermal mass loss formula which yields results that are comparable to hydrodynamic loss models. Our approach considers the effect of the Roche lobe, realistic heating efficiencies and a radius scaling law derived from observations of hot Jupiters. We study the influence of the mean planetary density on the thermal mass loss by placing hypothetical exoplanets with the characteristics of Jupiter, Saturn, Neptune, and Uranus to the orbital location of CoRoT-7b at 0.017 AU and Kepler-10b at 0.01684 AU and assuming that these planets orbit a K- or G-type host star. Our findings indicate that hydrogen-rich gas giants within the mass domain of Saturn or Jupiter cannot thermally lose such an amount of mass that CoRoT-7b and Kepler-10b would result in a rocky residue. Moreover, our calculations show that the present time mass of both rocky exoplanets can be neither a result of evaporation of a hydrogen envelope of a "Hot Neptune" nor a "Hot Uranus"-class object. Depending on the initial density and mass, these planets most likely were always rocky planets which could lose a thin hydrogen envelope, but not cores of thermally evaporated initially much more massive and larger objects.

Presenting new exoplanet candidates for the CoRoT chromatic light curves

NASA Astrophysics Data System (ADS)

Boufleur, Rodrigo; Emilio, Marcelo; Andrade, Laerte; Janot-Pacheco, Eduardo; De La Reza, Ramiro

2015-08-01

One of the most promising topics of modern Astronomy is the discovery and characterization of extrasolar planets due to its importance for the comprehension of planetary formation and evolution. Missions like MOST (Microvariability and Oscillations of Stars Telescope) (Walker et al., 2003) and especially the satellites dedicated to the search for exoplanets CoRoT (Convection, Rotation and planetary Transits) (Baglin et al., 1998) and Kepler (Borucki et al., 2003) produced a great amount of data and together account for hundreds of new discoveries. An important source of error in the search for planets with light curves obtained from space observatories are the displacements occuring in the data due to external causes. This artificial charge generation phenomenon associated with the data is mainly caused by the impact of high energy particles onto the CCD (Pinheiro da Silva et al. 2008), although other sources of error, not as well known also need to be taken into account. So, an effective analysis of the light curves depends a lot on the mechanisms employed to deal with these phenomena. To perform our research, we developed and applied a different method to fix the light curves, the CDAM (Corot Detrend Algorithm Modified), inspired by the work of Mislis et al. (2012). The paradigms were obtained using the BLS method (Kovács et al., 2002). After a semiautomatic pre-analysis associated with a visual inspection of the planetary transits signatures, we obtained dozens of exoplanet candidates in very good agreement with the literature and also new unpublished cases. We present the study results and characterization of the new cases for the chromatic channel public light curves of the CoRoT satellite.

Interaction of the plasma tail of comet Bradfield 1979L on 1980 February 6 with a possibly flare-generated solar-wind disturbance

NASA Technical Reports Server (NTRS)

Niedner, M. B., Jr.; Brandt, J. C.; Zwickl, R. D.; Bame, S. J.

1983-01-01

Solar-wind plasma data from the ISEE-3 and Helios 2 spacecraft were examined in order to explain a uniquely rapid 10 deg turning of the plasma tail of comet Bradfield 1979l on 1980 February 6. An earlier study conducted before the availability of in situ solar-wind data (Brandt et al., 1980) suggested that the tail position angle change occurred in response to a solar-wind velocity shear across the polar component changed by approximately 50 km/s. The present contribution confirms this result and further suggests that the comet-tail activity was caused by non-corotating, disturbed plasma flows probably associated with an Importance 1B solar flare.

Reducing vibration transfer from power plants by active methods

NASA Astrophysics Data System (ADS)

Kiryukhin, A. V.; Milman, O. O.; Ptakhin, A. V.

2017-12-01

The possibility of applying the methods of active damping of vibration and pressure pulsations for reducing their transfer from power plants into the environment, the seating, and the industrial premises are considered. The results of experimental works implemented by the authors on the active broadband damping of vibration and dynamic forces after shock-absorption up to 15 dB in the frequency band up to 150 Hz, of water pressure pulsations in the pipeline up to 20 dB in the frequency band up to 600 Hz, and of spatial low-frequency air noise indoors of a diesel generator at discrete frequency up to 20 dB are presented. It is shown that a reduction of vibration transfer through a vibration-isolating junction (expansion joints) of pipelines with liquid is the most complicated and has hardly been developed so far. This problem is essential for vibration isolation of power equipment from the seating and the environment through pipelines with water and steam in the power and transport engineering, shipbuilding, and in oil and gas pipelines in pumping stations. For improving efficiency, reducing the energy consumption, and decreasing the overall dimensions of equipment, it is advisable to combine the work of an active system with passive damping means, the use of which is not always sufficient. The executive component of the systems of active damping should be placed behind the vibration isolators (expansion joints). It is shown that the existence of working medium and connection of vibration with pressure pulsations in existing designs of pipeline expansion joints lead to growth of vibration stiffness of the expansion joint with the environment by two and more orders as compared with the static stiffness and makes difficulties for using the active methods. For active damping of vibration transfer through expansion joints of pipelines with a liquid, it is necessary to develop expansion joint structures with minimal connection of vibrations and pulsations and minimal vibration stiffness in the specified frequency range. The example of structure of such expansion joint and its test results are presented.

Time-resolved multicolour photometry of bright B-type variable stars in Scorpius

NASA Astrophysics Data System (ADS)

Handler, G.; Schwarzenberg-Czerny, A.

2013-09-01

Context. The first two of a total of six nano-satellites that will constitute the BRITE-Constellation space photometry mission have recently been launched successfully. Aims: In preparation for this project, we carried out time-resolved colour photometry in a field that is an excellent candidate for BRITE measurements from space. Methods: We acquired 117 h of Strömgren uvy data during 19 nights. Our targets comprised the β Cephei stars κ and λ Sco, the eclipsing binary μ1 Sco, and the variable super/hypergiant ζ1 Sco. Results: For κ Sco, a photometric mode identification in combination with results from the spectroscopic literature suggests a dominant (l,m) = (1, -1) β Cephei-type pulsation mode of the primary star. The longer period of the star may be a rotational variation or a g-mode pulsation. For λ Sco, we recover the known dominant β Cephei pulsation, a longer-period variation, and observed part of an eclipse. Lack of ultraviolet data precludes mode identification for this star. We noticed that the spectroscopic orbital ephemeris of the closer pair in this triple system is inconsistent with eclipse timings and propose a refined value for the orbital period of the closer pair of 5.95189 ± 0.00003 d. We also argue that the components of the λ Sco system are some 30% more massive than previously thought. The binary light curve solution of μ1 Sco requires inclusion of the irradiation effect to explain the u light curve, and the system could show additional low amplitude variations on top of the orbital light changes. ζ1 Sco shows long-term variability on a time scale of at least two weeks that we prefer to interpret in terms of a variable wind or strange mode pulsations. Based on observations carried out at the South African Astronomical ObservatoryReduced time series for all stars are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/557/A1

Estimation of the radial diffusion coefficient using REE-associated ground Pc 5 pulsations

NASA Astrophysics Data System (ADS)

Fujimoto, A.; Yumoto, K.

2010-12-01

Pc 5 pulsations with frequencies between 1.67 and 6.67 mHz are believed to contribute to the REE in the outer radiation belt during magnetic storms, by means of the observations [Baker et al., 1998; Rostoker et al., 1998; Mathie and Mann, 2000; O'Brien et al., 2001, 2003] and several theoretical studies. The latter studies are roughly categorized into two themes: in-situ acceleration at L lower than 6.6 by wave-particle interactions [Liu et al., 199 9; Summers et al., 1999; Summers and Ma, 2000] and acceleration by radial diffusion from the outer to the inner magnetosphere [Elkington et al., 1999, 2003; Hudson et al., 2000; Kim et al., 2001]. One possible acceleration mechanism is the resonant interaction with Pc 5 toroidal and poloidal pulsations, referred as the radial diffusion mechanism. One of unsolved problems is where and which Pc 5 pulsation mode (toroidal and/or poloidal) play effective role in the radial diffusion process. In order to verify Pc 5 pulsation as the major roles for REEs, we have to examine the time variation of electron phase space density (cf. Green et al., 2004). Electron phase space density is not directly measured, but we can estimate radial diffusion coefficients which determine the electron transportation efficiency, using ground-based magnetic field data. We estimated the radial diffusion coefficient of ground Pc 5 pulsations associated with the Relativistic Electron Enhancement (REE) in the geosynchronous orbit. In order to estimate the radial diffusion coefficient D_LL, we need the value of in-situ Pc 5 electric field power spectral density. In this paper, however, we estimated the equatorial electric field mapped from Pc 5 pulsations power spectral density on the ground. Reciprocal of radial diffusion coefficient describes the timescale T_LL for an electron to diffuse 1 Re. Applying a superposed epoch analysis about timescales T_LL of the radial diffusion for 12 REE events in 2008, we found that when the relativistic electron enhancements occur, T_LL at higher latitude (L larger than 5) is predominantly diffusional, whereas T_LL at lower latitude (L less than 4) is mainly convectional. We concluded that higher-latitude Pc 5 pulsations play more effective roles than lower latitude Pc 5 pulsations in the radial diffusion process.

Time-resolved spectral analysis of the pulsating helium star V652 Her

NASA Astrophysics Data System (ADS)

Jeffery, C. S.; Woolf, V. M.; Pollacco, D. L.

2001-09-01

A series of 59 moderate-resolution high signal-to-noise spectra of the pulsating helium star V652 Her covering 1.06 pulsation cycles was obtained with the William Herschel Telescope. These have been supplemented by archival ultraviolet and visual spectrophotometry and used to make a time-dependent study of the properties of V652 Her throughout the pulsation cycle. This study includes the following features: the most precise radial velocity curve for V652 Her measured so far, new software for the automatic measurement of effective temperature, surface gravity and projected rotation velocities from moderate-resolution spectra, self-consistent high-precision measurements of effective temperature and surface gravity around the pulsation cycle, a demonstration of excessive line-broadening at minimum radius and evidence for a pulsation-driven shock front, a new method for the direct measurement of the radius of a pulsating star using radial velocity and surface gravity measurements alone, new software for the automatic measurement of chemical abundances and microturbulent velocity, updated chemical abundances for V652 Her compared with previous work (\\cite{Jef99}), a reanalysis of the total flux variations (cf. \\cite{Lyn84}) in good agreement with previous work, and revised measurements of the stellar mass and radius which are similar to recent results for another pulsating helium star, BX Cir. Masses measured without reference to the ultraviolet fluxes turn out to be unphysically low (~0.18 M{\\odot}). The best estimate for the dimensions of V652 Her averaged over the pulsation cycle is given by: lt; Teff >=22 930+/-10 K and < log g > =3.46+/-0.05 (ionization equilibrium), < Teff > =20 950+/-70 K (total flux method), < R>=2.31+/-0.02 R{\\odot}, < L>=919+/-14 L{\\odot}, M=0.59+/-0.18 M{\\odot} and d=1.70+/-0.02 kpc. Two significant problems were encountered. The line-blanketed hydrogen-deficient model atmospheres used yield effective temperatures from the optical spectrum (ionization equilibrium) and visual and UV photometry (bolometric flux) that are inconsistent. Secondly, the IUE spectra are poorly distributed in phase and have low signal-to-noise. These problems may introduce systematic errors of up to 0.1 M{\\odot}. Based on observations obtained with the William Herschel Telescope, the United Kingdom Infrared Telescope, and on INES data from the IUE satellite.

Swarm observations of field-aligned currents associated with pulsating auroral patches

NASA Astrophysics Data System (ADS)

Gillies, D. M.; Knudsen, D.; Spanswick, E.; Donovan, E.; Burchill, J.; Patrick, M.

2015-11-01

We have performed a superposed epoch study of in situ field-aligned currents located near the edges of regions of pulsating aurora observed simultaneously using ground-based optical data from the Time History of Events and Macroscale Interactions during Substorms (THEMIS) all-sky imager (ASI) network and magnetometers on board the Swarm satellites. A total of nine traversals of Swarm over regions of pulsating aurora identified using THEMIS ASI were studied. We determined that in the cases where a clear boundary can be identified, strong downward currents are seen just poleward and equatorward of the pulsating patches. A downward current in the range of ~1-6 μA/m2 can be seen just poleward of the boundary. A weaker upward current of ~1-3 μA/m2 is observed throughout the interior of the patch. These observations indicate that currents carried by precipitating electrons within patches could close through horizontal currents and be returned at the edges, in agreement with Oguti and Hayashi (1984) and Hosokawa et al. (2010b). In addition to confirming these earlier results and adding to their statistical significance, the contribution of this study is to quantify the upward and downward current magnitudes, in some cases using two satellites traversing the same pulsating regions. Finally, we compare Swarm's two-satellite field-aligned current product to the single-satellite results and determine that the data product can be compromised in regions of pulsating aurora, a phenomenon that occurs over widespread regions and tends to persist for long periods of time. These results underscore the importance of electrical coupling between the ionosphere and magnetosphere in regions of patchy pulsating aurora.

A Search for Extreme Horizontal Branch Stars in the General Field Population (Abstract)

NASA Astrophysics Data System (ADS)

Walker, D.; Albrow, M.

2014-12-01

(Abstract only) The study of pulsating Extreme Horizontal Branch (EHB) stars in globular clusters is a new field of stellar research. The initial discovery of three rapidly pulsating EHB stars in w Centauri was announced at the Fourth Meeting on Hot Subdwarfs and Related Objects held in Shanghai in July 2009. A fourth sdB pulsator was discovered in the remaining photometry data soon afterwards; all were discovered in data obtained by the New Techology Telescope. In March 2013, the Space Telescope Imaging Spectrograph (STIS) was utilized on five consecutive orbits to obtain far-UV imagery of NGC 2808’s core, revealing six sdB pulsators with periods 85 to 149 seconds and UV amplitudes from 2.0 to 6.8%. To date (April 2014), these ten EHB pulsators in w Centauri and NGC 2808 form a unique class of EHB variable closely clustered around Teff ~ 50,000 K. This talk describes an initial candidate search for EHB rapidly pulsating sdB stars in the general galactic field population. The search was conducted with the 1-m McLellan telescope at the Mt. John University Observatory (MJUO) at Lake Tekapo, New Zealand. Observations were conducted utilizing a special high speed f/8 frame-transfer camera called the Puoko-nui. The candidate set of stars was taken from the Edinburgh-Cape Blue Object Survey based on the selection criteria of a (B-V) value of -0.32 to -0.36, corresponding to the desired temperature range Teff ranging from 40,000 to 64,000 K. The objective of this search was to determine whether smaller size telescopes could identify promising sets of candidate sdB pulsators which could be followed up with larger professional systems.

Possible link of sudden onset and short-time periodic pulsation of polar mesosphere summer echoes to ULF Pc5 geomagnetic pulsations and solar wind dynamic pressure enhancement

NASA Astrophysics Data System (ADS)

Lee, Y.; Kirkwood, S.; Kwak, Y. S.

2016-12-01

The EISCAT VHF incoherent scatter radar in Tromsö, Norway, makes occasional observations of electron densities and Polar Mesosphere Summer Echoes, in the summer polar D-region ionosphere. In one of those datasets, pulsating polar mesospheric summer echoes (PMSE) are observed, with periodicities in the ultra-low frequency (ULF) Pc5 band (1.6-6.7 mHz), following an abrupt increase of the radar reflectivity when a geomagnetic field excursion is started, in turn linked to dynamic pressure (Pdyn) enhancement in the solar wind. At the excursion of the magnetic field, at auroral altitudes of 90 km and above, electron density is abruptly enhanced, followed by a series of short-lived peaks, superimposed on an enhanced level. The short-lived peaks are likely a signature of transient Pc5 geomagnetic pulsations and associated energetic electron precipitation from pitch-angle scattering into the loss cone in the magnetosphere. At the same time, at altitudes around 80-90 km, a sharp increase of PMSE reflectivity occurs, 100 times greater than the increase of electron density, and is followed by pulsating PMSE reflectivity with periodicities in the Pc5 band, increasing and decreasing in magnitude during the course of the next hour. The increase of the pulsation magnitude may be attributed to an increase of high-energy electron precipitation flux ( >30 keV) penetrating to at least the height of maximum PMSE reflectivity. This study suggests that Pc5 pulsation bursts in both magnetic field and high energy electron precipitation could play a crucial role in producing PMSE fluctuations on minute-to-minute time scales.

Relationship between intracranial pressure and phase contrast cine MRI derived measures of intracranial pulsations in idiopathic normal pressure hydrocephalus.

PubMed

Jaeger, Matthias; Khoo, Angela K; Conforti, David A; Cuganesan, Ramesh

2016-11-01

Phase contrast cine MRI with determination of pulsatile aqueductal cerebrospinal fluid (CSF) stroke volume and flow velocity has been suggested to assess intracranial pulsations in idiopathic normal pressure hydrocephalus (iNPH). We aimed to compare this non-invasive measure of pulsations to intracranial pressure (ICP) pulse wave amplitude from continuous ICP monitoring. We hypothesised that a significant correlation between these two markers of intracranial pulsations exists. Fifteen patients with suspected iNPH had continuous computerised ICP monitoring with calculation of mean ICP pulse wave amplitude (MWA) from time-domain analysis. MRI measured CSF aqueductal stroke volume and peak flow velocity. Mean MWA was 5.4mmHg (range 2.3-12.4mmHg). Mean CSF stroke volume and peak flow velocity were 65μl (range 3-195μl) and 9.31cm/s (range 1.68-15.0cm/s), respectively. No significant correlation between the invasive and non-invasive measures of pulsations existed (Spearman r=-0.30 and r=-0.27, respectively; p>0.05). We observed marked intra-individual fluctuation of MWA during continuous ICP monitoring of an average of 6.0mmHg (range 2.8-12.2mmHg). The results suggest a complex interplay between measures of pulsations derived from snapshot MRI measurements and continuous computerised ICP measurements, as no significant relationship existed in our data. Further study is needed to better understand the temporal profile of CSF MRI flow studies, as substantial variation in MWA over the course of several hours of ICP monitoring is common, suggesting that these physiologic fluctuations might obscure MRI snapshot measures of intracranial pulsations. Copyright © 2016 Elsevier Ltd. All rights reserved.

First axion bounds from a pulsating helium-rich white dwarf star

DOE Office of Scientific and Technical Information (OSTI.GOV)

Battich, T.; Córsico, A.H.; Althaus, L.G.

The Peccei-Quinn mechanism proposed to solve the CP problem of Quantum Chromodynamics has as consequence the existence of axions, hypothetical weakly interacting particles whose mass is constrained to be on the sub-eV range. If these particles exist and interact with electrons, they would be emitted from the dense interior of white dwarfs, becoming an important energy sink for the star. Due to their well known physics, white dwarfs are good laboratories to study the properties of fundamental particles such as the axions. We study the general effect of axion emission on the evolution of helium-rich white dwarfs and on theirmore » pulsational properties. To this aim, we calculate evolutionary helium-rich white dwarf models with axion emission, and assess the pulsational properties of this models. Our results indicate that the rates of change of pulsation periods are significantly affected by the existence of axions. We are able for the first time to independently constrain the mass of the axion from the study of pulsating helium-rich white dwarfs. To do this, we use an estimation of the rate of change of period of the pulsating white dwarf PG 1351+489 corresponding to the dominant pulsation period. From an asteroseismological model of PG 1351+489 we obtain g {sub ae} < 3.3 × 10{sup -13} for the axion-electron coupling constant, or m {sub a} cos{sup 2}β ∼< 11.5 meV for the axion mass. This constraint is relaxed to g {sub ae} < 5.5 × 10{sup -13} ( m {sub a} cos{sup 2}β ∼< 19.5 meV), when no detailed asteroseismological model is adopted for the comparison with observations.« less

Just how hot are the ω Centauri extreme horizontal branch pulsators?

NASA Astrophysics Data System (ADS)

Latour, M.; Randall, S. K.; Chayer, P.; Fontaine, G.; Calamida, A.; Ely, J.; Brown, T. M.; Landsman, W.

2017-04-01

Context. Past studies based on optical spectroscopy suggest that the five ω Cen pulsators form a rather homogeneous group of hydrogen-rich subdwarf O stars with effective temperatures of around 50 000 K. This places the stars below the red edge of the theoretical instability strip in the log g-Teff diagram, where no pulsation modes are predicted to be excited. Aims: Our goal is to determine whether this temperature discrepancy is real, or whether the stars' effective temperatures were simply underestimated. Methods: We present a spectral analysis of two rapidly pulsating extreme horizontal branch (EHB) stars found in ω Cen. We obtained Hubble Space Telescope/COS UV spectra of two ω Cen pulsators, V1 and V5, and used the ionisation equilibrium of UV metallic lines to better constrain their effective temperatures. As a by-product we also obtained FUV lightcurves of the two pulsators. Results: Using the relative strength of the N iv and N v lines as a temperature indicator yields Teff values close to 60 000 K, significantly hotter than the temperatures previously derived. From the FUV light curves we were able to confirm the main pulsation periods known from optical data. Conclusions: With the UV spectra indicating higher effective temperatures than previously assumed, the sdO stars would now be found within the predicted instability strip. Such higher temperatures also provide consistent spectroscopic masses for both the cool and hot EHB stars of our previously studied sample. Based on observations (proposal GO-13707) with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26666.

Oscillations in stellar atmospheres

NASA Technical Reports Server (NTRS)

Costa, A.; Ringuelet, A. E.; Fontenla, J. M.

1989-01-01

Atmospheric excitation and propagation of oscillations are analyzed for typical pulsating stars. The linear, plane-parallel approach for the pulsating atmosphere gives a local description of the phenomenon. From the local analysis of oscillations, the minimum frequencies are obtained for radially propagating waves. The comparison of the minimum frequencies obtained for a variety of stellar types is in good agreement with the observed periods of the oscillations. The role of the atmosphere in the globar stellar pulsations is thus emphasized.

Parameters of the plasma of a dc pulsating discharge in a supersonic air flow

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shibkov, V. M., E-mail: shibkov@phys.msu.ru; Shibkova, L. V.; Logunov, A. A.

A dc discharge in a cold (T = 200 K) supersonic air flow at a static pressure of 200–400 Torr was studied experimentally. The excited unsteady pulsating discharge has the form of a thin plasma channel with a diameter of ≤1 mm, stretched downstream the flow. Depending on the discharge current, the pulsation frequency varies from 800 to 1600 Hz and the electron temperature varies from 8000 to 15000 K.

Discovery of Three Pulsating, Mixed-atmosphere, Extremely Low-mass White Dwarf Precursors

NASA Astrophysics Data System (ADS)

Gianninas, A.; Curd, Brandon; Fontaine, G.; Brown, Warren R.; Kilic, Mukremin

2016-05-01

We report the discovery of pulsations in three mixed-atmosphere, extremely low-mass white dwarf (ELM WD, M ≤slant 0.3 M ⊙) precursors. Following the recent discoveries of pulsations in both ELM and pre-ELM WDs, we targeted pre-ELM WDs with mixed H/He atmospheres with high-speed photometry. We find significant optical variability in all three observed targets with periods in the range 320-590 s, consistent in timescale with theoretical predictions of p-mode pulsations in mixed-atmosphere ≈0.18 M ⊙ He-core pre-ELM WDs. This represents the first empirical evidence that pulsations in pre-ELM WDs can only occur if a significant amount of He is present in the atmosphere. Future, more extensive, timeseries photometry of the brightest of the three new pulsators offers an excellent opportunity to constrain the thickness of the surface H layer, which regulates the cooling timescales for ELM WDs. Based on observations obtained at the Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (United States), the National Research Council (Canada), CONICYT (Chile), Ministerio de Ciencia, Tecnología e Innovación Productiva (Argentina), and Ministério da Ciência, Tecnologia e Inovação (Brazil).

Contribution of cardiac-induced brain pulsation to the noise of the diffusion tensor in Turboprop diffusion tensor imaging (DTI).

PubMed

Gui, Minzhi; Tamhane, Ashish A; Arfanakis, Konstantinos

2008-05-01

To assess the effects of cardiac-induced brain pulsation on the noise of the diffusion tensor in Turboprop (a form of periodically rotated overlapping parallel lines with enhanced reconstruction [PROPELLER] imaging) diffusion tensor imaging (DTI). A total of six healthy human subjects were imaged with cardiac-gated as well as nongated Turboprop DTI. Gated and nongated Turboprop DTI datasets were also simulated using actual data acquired exclusively during the diastolic or systolic period of the cardiac cycle. The total variance of the diffusion tensor (TVDT) was measured and compared between acquisitions. The TVDT near the ventricles was significantly reduced in cardiac-gated compared to nongated Turboprop DTI acquisitions. Furthermore, the effects of brain pulsation were reduced, but not eliminated, when increasing the amount of data collected. Finally, data corrupted by cardiac-induced pulsation were not consistently detected by the step of the conventional Turboprop reconstruction algorithm that evaluates the quality of data in different blades. Thus, the inherent quality weighting of the conventional Turboprop reconstruction algorithm was unable to compensate for the increased noise in the diffusion tensor due to brain pulsation. Cardiac-induced brain pulsation increases the TVDT in Turboprop DTI. Use of cardiac gating to limit data acquisition to the diastolic period of the cardiac cycle reduces the TVDT at the expense of imaging time. (c) 2008 Wiley-Liss, Inc.

Planet-induced Stellar Pulsations in HAT-P-2's Eccentric System

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wit, Julien de; Lewis, Nikole K.; Knutson, Heather A.

2017-02-20

Extrasolar planets on eccentric short-period orbits provide a laboratory in which to study radiative and tidal interactions between a planet and its host star under extreme forcing conditions. Studying such systems probes how the planet’s atmosphere redistributes the time-varying heat flux from its host and how the host star responds to transient tidal distortion. Here, we report the insights into the planet–star interactions in HAT-P-2's eccentric planetary system gained from the analysis of ∼350 hr of 4.5 μ m observations with the Spitzer Space Telescope . The observations show no sign of orbit-to-orbit variability nor of orbital evolution of themore » eccentric planetary companion, HAT-P-2 b. The extensive coverage allows us to better differentiate instrumental systematics from the transient heating of HAT-P-2 b’s 4.5 μ m photosphere and yields the detection of stellar pulsations with an amplitude of approximately 40 ppm. These pulsation modes correspond to exact harmonics of the planet’s orbital frequency, indicative of a tidal origin. Transient tidal effects can excite pulsation modes in the envelope of a star, but, to date, such pulsations had only been detected in highly eccentric stellar binaries. Current stellar models are unable to reproduce HAT-P-2's pulsations, suggesting that our understanding of the interactions at play in this system is incomplete.« less

Quasi-Periodic Pulsations in the Earth's Ionosphere Synchronized with Solar Flare Emission

NASA Astrophysics Data System (ADS)

Hayes, L.; Gallagher, P.; McCauley, J.; Dennis, B. R.; Ireland, J.; Inglis, A. R.

2017-12-01

Solar flare activity is a powerful factor affecting the geophysical processes in the Earth's ionosphere. In particular, X-ray photons with wavelength < 10 A can penetrate down to the D-region ( 60-90 km in altitude) resulting in a dramatic increase of ionization in this lowest lying region of the Earth's ionosphere. This manifests as a substantial enhancement of electron density height profile at these altitudes to extents large enough to change the propagation conditions for Very Low Frequency (VLF 3-30 kHz) radio waves that travel in the waveguide formed by the Earth and the lower ionosphere. Recently, it has become clear that flares exhibit quasi-periodic pulsations with periods of seconds to minutes at EUV, X-ray and gamma-ray wavelengths. To date, it has not been known if the Earth's ionosphere is sensitive to these dynamic solar pulsations. Here, we report ionospheric pulsations with periods of 20 minutes that are synchronized with a set of pulsating flare loops using VLF observations of the ionospheric D-layer together with X-ray and EUV observations of a solar flare from the NOAA/GOES and NASA/SDO satellites. Modeling of the ionosphere show that the D-region electron density varies by up to an order of magnitude over the timescale of the pulsations. Our results show that the Earth's ionosphere is more sensitive to small-scale changes in solar activity than previously thought.

Topical fundus pulsation measurement in patients with active central serous chorioretinopathy.

PubMed

Tittl, Michael; Polska, Elzbieta; Kircher, Karl; Kruger, Andreas; Maar, Noemi; Stur, Michael; Schmetterer, Leopold

2003-07-01

To determine regional pulsatile choroidal blood flow using laser interferometry in patients with active central serous chorioretinopathy (CSC). The study compared an equally sized age-, sex-, and refractive error-matched control group of healthy volunteers obtained from the Department of Clinical Pharmacology with 18 consecutive patients who had newly diagnosed active, unilateral CSC obtained from the University of Vienna Eye Clinic, Vienna, Austria. Regional fundus pulsation amplitude as assessed using laser interferometry. The median age of the patients was 40 years; the male-female ratio was 16:2. Foveal fundus pulsation amplitude was significantly higher in eyes with CSC (mean [SD], 5.5 [1.7] micro m) than in the eyes of the control subjects (4.1 [1.1] micro m; P =.005). In addition, eyes with CSC had a significantly higher variability in fundus pulsation amplitude (mean [SD], 48% [20%]) assessed at different fundus locations around the leak than the controls did (20% [9%]; P<.001). To our knowledge, this is the first study that measures topical fundus pulsations in patients who have active, unilateral CSC. These data indicate a generally increased foveal pulsatile choroidal blood flow and an abnormal distribution of fundus pulsation amplitude in the area close to the leak. Whether these findings reinforce the concept that choroidal perfusion abnormalities play a role in the pathogenesis of CSC remains to be established.

Planet-induced Stellar Pulsations in HAT-P-2's Eccentric System

NASA Astrophysics Data System (ADS)

de Wit, Julien; Lewis, Nikole K.; Knutson, Heather A.; Fuller, Jim; Antoci, Victoria; Fulton, Benjamin J.; Laughlin, Gregory; Deming, Drake; Shporer, Avi; Batygin, Konstantin; Cowan, Nicolas B.; Agol, Eric; Burrows, Adam S.; Fortney, Jonathan J.; Langton, Jonathan; Showman, Adam P.

2017-02-01

Extrasolar planets on eccentric short-period orbits provide a laboratory in which to study radiative and tidal interactions between a planet and its host star under extreme forcing conditions. Studying such systems probes how the planet’s atmosphere redistributes the time-varying heat flux from its host and how the host star responds to transient tidal distortion. Here, we report the insights into the planet-star interactions in HAT-P-2's eccentric planetary system gained from the analysis of ˜350 hr of 4.5 μm observations with the Spitzer Space Telescope. The observations show no sign of orbit-to-orbit variability nor of orbital evolution of the eccentric planetary companion, HAT-P-2 b. The extensive coverage allows us to better differentiate instrumental systematics from the transient heating of HAT-P-2 b’s 4.5 μm photosphere and yields the detection of stellar pulsations with an amplitude of approximately 40 ppm. These pulsation modes correspond to exact harmonics of the planet’s orbital frequency, indicative of a tidal origin. Transient tidal effects can excite pulsation modes in the envelope of a star, but, to date, such pulsations had only been detected in highly eccentric stellar binaries. Current stellar models are unable to reproduce HAT-P-2's pulsations, suggesting that our understanding of the interactions at play in this system is incomplete.

Pressure pulsations in piping system excited by a centrifugal turbomachinery taking the damping characteristics into consideration

NASA Astrophysics Data System (ADS)

Hayashi, I.; Kaneko, S.

2014-02-01

Pressure pulsations excited by a centrifugal turbomachinery such as compressor, fan or pump at the blade passing frequency may cause severe noise and vibrations in piping system. Therefore, the practical evaluation method of pressure pulsations is strongly recommended. In particular, the maximum pressure amplitude under the resonant conditions should be appropriately evaluated. In this study, a one-dimensional excitation source model for a compressor or pump is introduced based on the equation of motion, so as to incorporate the non-linear damping proportional to velocity squared in the total piping system including the compressor or pump. The damping characteristics of the compressor or pump are investigated by using the semi-empirical model. It is shown that the resistance coefficient of the compressor or pump depends on the Reynolds number that is defined using the equivalent velocity of the pulsating flow. The frequency response of the pressure amplitude and the pressure distribution in the piping system can be evaluated by introducing the equivalent resistance of the compressor or pump and that of piping system. In particular, the relation of the maximum pressure amplitude in piping system to the location of the excitation source under resonant conditions can be evaluated. Finally, the reduction of the pressure pulsations by use of an orifice plate is discussed in terms of the pulsation energy loss.

The origin and pulsations of extreme helium stars†

NASA Astrophysics Data System (ADS)

Jeffery, C. Simon

2014-02-01

Stars consume hydrogen in their interiors but, generally speaking, their surfaces continue to contain some 70% hydrogen (by mass) throughout their lives. Nevertheless, many types of star can be found with hydrogen-deficient surfaces, in some cases with as little as one hydrogen atom in 10 000. Amongst these, the luminous B- and A-type extreme helium stars are genuinely rare; only ~15 are known within a very substantial volume of the Galaxy. Evidence from surface composition suggests a connection to the cooler R CrB variables and some of the hotter helium-rich subdwarf O stars. Arguments currently favour an origin in the merger of two white dwarfs; thus there are also connections with AM CVn variables and Type Ia supernovae. Pulsations in many extreme helium stars provide an opportune window into their interiors. These pulsations have unusual properties, some being ``strange'' modes, and others being driven by Z-bump opacities. They have the potential to deliver distance-independent masses and to provide a unique view of pulsation physics. We review the evolutionary origin and pulsations of these stars, and introduce recent progress and continuing challenges.

Pulsation Modes of sdBV Stars Observed with Kepler

NASA Astrophysics Data System (ADS)

Reed, M. D.; Baran, A. S.; Quint, A. C.; Telting, J. H.; Østensen, R. H.; O'Toole, S. J.

2012-03-01

During the Kepler satellite's first year of operation, its short cadence observations were obtained in a survey mode where targets received one month of nearly continuous observations. 48 subdwarf B stars were observed of which 14 were found to be pulsators, with only one of these having predominantly short periods. The other 13 were mostly long-period (g-mode) pulsators. With Kepler's exquisite duty cycle and data quality, an average of 23 periods per star were detected with ranges from 6 to 44. As the g-mode pulsations are high-overtone (typically n > 10), asymptotic period relations could apply and so we searched for evenly spaced periods. We found these for l =1 and 2 modes in all but one of the Kepler stars and that one outlier has a very complex temporal spectrum caused by a close companion. We were able to associate 204 of 299 measured periods with l = 1 and 2 modes. Those results should provide tight constraints on pulsation models. However, they also offer a surprise as current structure models predict significant mode trapping, which is inconsistent with the period spacings we have found.

Viscous Analysis of Pulsating Hydrodynamic Instability and Thermal Coupling Liquid-Propellant Combustion

NASA Technical Reports Server (NTRS)

Margolis, Stephen B.; Sacksteder, Kurt (Technical Monitor)

2000-01-01

A pulsating form of hydrodynamic instability has recently been shown to arise during liquid-propellant deflagration in those parameter regimes where the pressure-dependent burning rate is characterized by a negative pressure sensitivity. This type of instability can coexist with the classical cellular, or Landau form of hydrodynamic instability, with the occurrence of either dependent on whether the pressure sensitivity is sufficiently large or small in magnitude. For the inviscid problem, it has been shown that, when the burning rate is realistically allowed to depend on temperature as well as pressure, sufficiently large values of the temperature sensitivity relative to the pressure sensitivity causes like pulsating form of hydrodynamic instability to become dominant. In that regime, steady, planar burning becomes intrinsically unstable to pulsating disturbances whose wave numbers are sufficiently small. This analysis is extended to the fully viscous case, where it is shown that although viscosity is stabilizing for intermediate and larger wave number perturbations, the intrinsic pulsating instability for small wave numbers remains. Under these conditions, liquid-propellant combustion is predicted to be characterized by large unsteady cells along the liquid/gas interface.

Electron precipitation response to geomagnetic pulsations: Riometer revelation

NASA Astrophysics Data System (ADS)

Honary, Farideh; Kavanagh, Andrew

Electron precipitation modulations by geomagnetic pulsation have been observed in cosmic noise absorption (CNA) as early as 1965 by widebeam riometers (Barcus and Rosenberg, 1965). The first observation of pulsation with high m-number was reported by Kikuchi et al.(1988) em-ploying a scanning narrow-beam riometer to investigate the spatial structure in one dimension with a high resolution. However, the advances in high spatial resolution imaging riometers has provided the ability to observe pulsating cosmic noise absorption with azimuthal wave numbers as high as 380 as well as providing the capability of mapping their structures. These waves are commonly observed during the morning and early afternoon and exhibit eastward propagation. In this presentation a complete generating mechanism for these high m-number waves is dis-cussed as a five step process, beginning with the solar wind as a source for the excitation of dayside magnetospheric cavity modes, mode conversion, energisation of drift-bounce protons by Landau damping, followed by inverse Landau damping as a driving mechanism for the high m number secondary waves that ultimately modulate the electron precipitation. This modulation is observed as pulsations in cosmic noise absorption.

Discovery of Coherent Pulsations from the Ultraluminous X-Ray Source NGC 7793 P13

NASA Technical Reports Server (NTRS)

Furst, F.; Walton, D. J.; Harrison, F. A.; Stern, D.; Barret, D.; Brightman, M.; Fabian, A. C.; Grefenstette, B.; Madsen, K. K.; Middleton, M. J.;

Radial variations of large-scale magnetohydrodynamic fluctuations in the solar wind

NASA Technical Reports Server (NTRS)

Burlaga, L. F.; Goldstein, M. L.

1983-01-01

Two time periods are studied for which comprehensive data coverage is available at both 1 AU using IMP-8 and ISEE-3 and beyond using Voyager 1. One of these periods is characterized by the predominance of corotating stream interactions. Relatively small scale transient flows characterize the second period. The evolution of these flows with heliocentric distance is studied using power spectral techniques. The evolution of the transient dominated period is consistent with the hypothesis of turbulent evolution including an inverse cascade of large scales. The evolution of the corotating period is consistent with the entrainment of slow streams by faster streams in a deterministic model.

Dispersion and characterization of Thermoplastic Polyurethane/Multiwalled Carbon Nanotubes in co-rotative twin screw extruder

NASA Astrophysics Data System (ADS)

Benedito, Adolfo; Buezas, Ignacio; Giménez, Enrique; Galindo, Begoña

2010-06-01

The dispersion of multi-walled carbon nanotubes in thermoplastic polyurethanes has been done in co-rotative twin screw extruder through a melt blending process. A specific experimental design was prepared taking into account different compounding parameters such as feeding, temperature profile, screw speed, screw design, and carbon nanotube loading. The obtained samples were characterized by thermogravimetric analysis (TGA), light transmission microscopy, dynamic rheometry, and dynamic mechanical analysis. The objective of this work has been to study the dispersion quality of the carbon nanotubes and the effect of different compounding parameters to optimize them for industrial scale-up to final applications.

The formation of fragments at corotation in isothermal protoplanetary disks

NASA Astrophysics Data System (ADS)

Durisen, Richard H.; Hartquist, Thomas W.; Pickett, Megan K.

2008-09-01

Numerical hydrodynamics simulations have established that disks which are evolved under the condition of local isothermality will fragment into small dense clumps due to gravitational instabilities when the Toomre stability parameter Q is sufficiently low. Because fragmentation through disk instability has been suggested as a gas giant planet formation mechanism, it is important to understand the physics underlying this process as thoroughly as possible. In this paper, we offer analytic arguments for why, at low Q, fragments are most likely to form first at the corotation radii of growing spiral modes, and we support these arguments with results from 3D hydrodynamics simulations.

Relatively stable, large-amplitude Alfvenic waves seen at 2.5 and 5.0 AU

NASA Technical Reports Server (NTRS)

Mavromichalaki, H.; Moussas, X.; Quenby, J. J.; Valdes-Galicia, J. F.; Smith, E. J.

1988-01-01

Pioneer 11 and 10 observations of the wave structure seen in a corotating interaction region at 2.5 AU on day 284 of 1973 and 8 days later at 5 AU reveal large-amplitude Alfvenic structures with many detailed correlations seen between their features at the two radial distances. Hodogram analysis suggests the dominance of near plane polarized, transverse Alfvenic mode fluctuations with periods between 2 min and one hour or more. Some wave evolution close to the Corotating Interaction Region (CIR) shock is noticed, but waves towards the center of the compression seem to propagate with little damping between the spacecraft observation positions.

The Formation of CIRs at Stream-Stream Interfaces and Resultant Geomagnetic Activity

NASA Technical Reports Server (NTRS)

Richardson, I. G.

2005-01-01

Corotating interaction regions (CIRs) are regions of compressed plasma formed at the leading edges of corotating high-speed solar wind streams originating in coronal holes as they interact with the preceding slow solar wind. Although particularly prominent features of the solar wind during the declining and minimum phases of the 11-year solar cycle, they may also be present at times of higher solar activity. We describe how CIRs are formed, and their geomagnetic effects, which principally result from brief southward interplanetary magnetic field excursions associated with Alfven waves. Seasonal and long-term variations in these effects are briefly discussed.

CSI 2264: Characterizing Young Stars in NGC 2264 With Short-Duration Periodic Flux Dips in Their Light Curves

NASA Astrophysics Data System (ADS)

Stauffer, John; Cody, Ann Marie; McGinnis, Pauline; Rebull, Luisa; Hillenbrand, Lynne A.; Turner, Neal J.; Carpenter, John; Plavchan, Peter; Carey, Sean; Terebey, Susan; Morales-Calderón, María; Alencar, Silvia H. P.; Bouvier, Jerome; Venuti, Laura; Hartmann, Lee; Calvet, Nuria; Micela, Giusi; Flaccomio, Ettore; Song, Inseok; Gutermuth, Rob; Barrado, David; Vrba, Frederick J.; Covey, Kevin; Padgett, Debbie; Herbst, William; Gillen, Edward; Lyra, Wladimir; Medeiros Guimaraes, Marcelo; Bouy, Herve; Favata, Fabio

2015-04-01

We identify nine young stellar objects (YSOs) in the NGC 2264 star-forming region with optical CoRoT light curves exhibiting short-duration, shallow periodic flux dips. All of these stars have infrared excesses that are consistent with their having inner disk walls near the Keplerian co-rotation radius. The repeating photometric dips have FWHMs generally less than 1 day, depths almost always less than 15%, and periods (3 < P < 11 days) consistent with dust near the Keplerian co-rotation period. The flux dips vary considerably in their depth from epoch to epoch, but usually persist for several weeks and, in two cases, were present in data collected in successive years. For several of these stars, we also measure the photospheric rotation period and find that the rotation and dip periods are the same, as predicted by standard “disk-locking” models. We attribute these flux dips to clumps of material in or near the inner disk wall, passing through our line of sight to the stellar photosphere. In some cases, these dips are also present in simultaneous Spitzer IRAC light curves at 3.6 and 4.5 microns. We characterize the properties of these dips, and compare the stars with light curves exhibiting this behavior to other classes of YSOs in NGC 2264. A number of physical mechanisms could locally increase the dust scale height near the inner disk wall, and we discuss several of those mechanisms; the most plausible mechanisms are either a disk warp due to interaction with the stellar magnetic field or dust entrained in funnel-flow accretion columns arising near the inner disk wall. Based on data from the Spitzer and CoRoT missions, as well as the Canada France Hawaii Telescope (CFHT) MegaCam CCD, and the European Southern Observatory Very Large Telescope, Paranal Chile, under program 088.C-0239. 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, Belgium, Brazil, Germany, and Spain. MegaCam is a joint project of CFHT and CEA/DAPNIA, which is operated by the National Research Council (NRC) of Canada, the Institute National des Sciences de l’Univers of the Centre National de la Recherche Scientifique of France, and the University of Hawaii.

Homogeneous studies of transiting extrasolar planets - IV. Thirty systems with space-based light curves

NASA Astrophysics Data System (ADS)

Southworth, John

2011-11-01

I calculate the physical properties of 32 transiting extrasolar planet and brown-dwarf systems from existing photometric observations and measured spectroscopic parameters. The systems studied include 15 observed by the CoRoT satellite, 10 by Kepler and five by the Deep Impact spacecraft. Inclusion of the objects studied in previous papers leads to a sample of 58 transiting systems with homogeneously measured properties. The Kepler data include observations from Quarter 2, and my analyses of several of the systems are the first to be based on short-cadence data from this satellite. The light curves are modelled using the JKTEBOP code, with attention paid to the treatment of limb darkening, contaminating light, orbital eccentricity, correlated noise and numerical integration over long exposure times. The physical properties are derived from the light-curve parameters, spectroscopic characteristics of the host star and constraints from five sets of theoretical stellar model predictions. An alternative approach using a calibration from eclipsing binary star systems is explored and found to give comparable results whilst imposing a much smaller computational burden. My results are in good agreement with published properties for most of the transiting systems, but discrepancies are identified for CoRoT-5, CoRoT-8, CoRoT-13, Kepler-5 and Kepler-7. Many of the error bars quoted in the literature are underestimated. Refined orbital ephemerides are given for CoRoT-8 and for the Kepler planets. Asteroseismic constraints on the density of the host stars are in good agreement with the photometric equivalents for HD 17156 and TrES-2, but not for HAT-P-7 and HAT-P-11. Complete error budgets are generated for each transiting system, allowing identification of the observations best-suited to improve measurements of their physical properties. Whilst most systems would benefit from further photometry and spectroscopy, HD 17156, HD 80606, HAT-P-7 and TrES-2 are now extremely well characterized. HAT-P-11 is an exceptional candidate for studying starspots. The orbital ephemerides of some transiting systems are becoming uncertain and they should be re-observed in the near future. The primary results from the current work and from previous papers in the series have been placed in an online catalogue, from where they can be obtained in a range of formats for reference and further study. TEPCat is available at

Transiting exoplanets from the CoRoT space mission . XIII. CoRoT-13b: a dense hot Jupiter in transit around a star with solar metallicity and super-solar lithium content

NASA Astrophysics Data System (ADS)

Cabrera, J.; Bruntt, H.; Ollivier, M.; Díaz, R. F.; Csizmadia, Sz.; Aigrain, S.; Alonso, R.; Almenara, J.-M.; Auvergne, M.; Baglin, A.; Barge, P.; Bonomo, A. S.; Bordé, P.; Bouchy, F.; Carone, L.; Carpano, S.; Deleuil, M.; Deeg, H. J.; Dvorak, R.; Erikson, A.; Ferraz-Mello, S.; Fridlund, M.; Gandolfi, D.; Gazzano, J.-C.; Gillon, M.; Guenther, E. W.; Guillot, T.; Hatzes, A.; Havel, M.; Hébrard, G.; Jorda, L.; Léger, A.; Llebaria, A.; Lammer, H.; Lovis, C.; Mazeh, T.; Moutou, C.; Ofir, A.; von Paris, P.; Pätzold, M.; Queloz, D.; Rauer, H.; Rouan, D.; Santerne, A.; Schneider, J.; Tingley, B.; Titz-Weider, R.; Wuchterl, G.

2010-11-01

We announce the discovery of the transiting planet CoRoT-13b. Ground-based follow-up in CFHT and IAC80 confirmed CoRoT's observations. The mass of the planet was measured with the HARPS spectrograph and the properties of the host star were obtained analyzing HIRES spectra from the Keck telescope. It is a hot Jupiter-like planet with an orbital period of 4.04 days, 1.3 Jupiter masses, 0.9 Jupiter radii, and a density of 2.34 g cm-3. It orbits a G0V star with T_eff = 5 945 K, M* = 1.09 M⊙, R_* = 1.01 R⊙, solar metallicity, a lithium content of + 1.45 dex, and an estimated age of between 0.12 and 3.15 Gyr. The lithium abundance of the star is consistent with its effective temperature, activity level, and age range derived from the stellar analysis. The density of the planet is extreme for its mass, implies that heavy elements are present with a mass of between about 140 and 300 {M}⊕. The CoRoT space mission, launched on December 27th 2006, has been developed and is operated by CNES, with the contribution of Austria, Belgium, Brazil, ESA (RSSD and Science Programme), Germany and Spain. Part of the observations were obtained at the Canada-France-Hawaii Telescope (CFHT) which is operated by the National Research Council of Canada, the Institut National des Sciences de l'Univers of the Centre National de la Recherche Scientifique of France, and the University of Hawaii. Based on observations made with HARPS spectrograph on the 3.6-m European Organisation for Astronomical Research in the Southern Hemisphere telescope at La Silla Observatory, Chile (ESO program 184.C-0639). Based on observations made with the IAC80 telescope operated on the island of Tenerife by the Instituto de Astrofísica de Canarias in the Spanish Observatorio del Teide. Part of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.

The rigid shell component for superrotation in planetary atmospheres: Angular momentum budget, mechanical analog and simulation of the spin up process

NASA Technical Reports Server (NTRS)

Mayr, H. G.; Harris, I.

1981-01-01

An analysis of superrotation in the atmosphere of planets, with rotation axis perpendicular to the orbital plane is presented. As the atmosphere expands, Hadley cells develop producing a redistribution of mass and angular momentum. A three dimensional thermally driven zonally symmetric spectral model and Laplace transformation simulate the time evolution of a fluid leading from corotation under globally uniform heating to superrotation under globally nonuniform heating. For high viscosities the rigid shell component of atmospheric superrotation can be understood in analogy with a pirouette. During spin up angular momentum is transferred to the planet. For low iscosities, the process is reversed. A tendency toward geostrophy, combined with increase of surface pressure toward the poles (due to meridional mass transport), induces the atmosphere to subrotate temporarily at lower altitudes. Resultant viscous shear near the surface permits angular momentum to flow from the planet into the atmosphere propagating upwards to produce high altitude superrotation rates.

On an apparent discrepancy between pulsation and evolution masses for Cepheids.

NASA Technical Reports Server (NTRS)

Iben, I., Jr.; Tuggle, R. S.

1972-01-01

Results of new theoretical pulsation calculations in the linear nonadiabatic approximation are presented. Emphasis is placed on the location of blue edges (the borderline between stability and instability against pulsation) for pulsation in the fundamental mode. The results of evolutionary calculations for the helium-burning phase are introduced, and a theoretical period-luminosity relationship is obtained for Cepheids that lie on the blue edge of the instability strip. The theoretical results are then compared with current estimates of the intrinsic bulk properties of 13 Cepheids, and it is shown how theoretical and observational properties may be reconciled without assuming significant mass loss or the necessity of major adjustments in the theory. Finally, it is argued that the required revision in Cepheid luminosities lies within the observational uncertainties.

The nature of the driving mechanism in the pulsating hybrid PG 1159 star Abell 43

NASA Astrophysics Data System (ADS)

Quirion, P.-O.; Fontaine, G.; Brassard, P.

2005-10-01

We extend our previous pulsational stability analyses of PG 1159 stars by modeling the hybrid PG 1159 type star Abell 43. We show that the standard κ-mechanism due to the ionization of C and O in the envelope of this H-rich PG 1159 star is perfectly able to drive g-mode pulsations. Thus, contrary to a recent suggestion, there is no need to invoke any new or exotic mechanism to explain the pulsational instabilities observed in this particular star. Our expected instability band for l=1 modes extends in period from ~2604 s to ~5529 s, which is consistent with the available photometric observations of Abell 43. We also suggest that efforts to detect luminosity variations in its sibling NGC 7094 be pursued.

Search for Optical Pulsation in M82 X-2

NASA Astrophysics Data System (ADS)

Collura, G.; Strader, P.; Meeker, S. R.; Szypryt, P.; Walter, A. B.; Bockstiegel, C.; Mazin, B. A.; Prince, T. A.

2017-11-01

We report on a search for optical pulsation from M82 X-2 over a range of periods. M82 X-2 is an X-ray pulsar with a 1.37s average spin period and a 2.5 day sinusoidal modulation. The observations were done with the ARray Camera for Optical to Near-IR Spectrophotometry at the 200 inch Hale telescope at the Palomar Observatory. We performed H test and χ 2 statistical analysis. No significant optical pulsations were found in the wavelength range of 3000-11000 Å with a pulsation period between 1.36262 and 1.37462 s. We found an upper limit on pulsed emission in the 4000-8000 Å wavelength range to be fainter than ˜20.5 mag AB , corresponding to ˜23 μJy.

A search for optical pulsations from GX 1+4 at H-alpha

NASA Technical Reports Server (NTRS)

Krzeminski, W.; Priedhorsky, W. C.

1978-01-01

H-alpha observations of the binary-star candidate for the slowly pulsating hard X-ray source GX 1+4 are reported which were undertaken to search for pulsations in the H-alpha flux that are synchronous with the X-ray period of about 2 min. No significant periodic variation of the candidate star was detected in the frequency band searched. Three-sigma upper limits of 1.7% (sinusoidal pulse shape) and 0.7% (X-ray pulse shape) are set for the pulsed fraction of the H-alpha flux. It is noted that because of possible diffusion from a cloud that is optically thick to Balmer radiation, the observed lack of pulsations in the H-alpha flux need not compromise the identification of GX 1+4 with the candidate star.

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.

Experimental study of air delivery into water-conveyance system of the radial-axial turbine

NASA Astrophysics Data System (ADS)

Maslennikova, Alexandra; Platonov, Dmitry; Minakov, Andrey; Dekterev, Dmitry

2017-10-01

The paper presents an experimental study of oscillatory response in the Francis turbine of hydraulic unit. The experiment was performed on large-scale hydrodynamic test-bench with impeller diameter of 0.3 m. The effect of air injection on the intensity of pressure pulsations was studied at the maximum pressure pulsations in the hydraulic unit. It was revealed that air delivery into the water-conveyance system of the turbine results in almost two-fold reduction of pressure pulsations.

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.

Exact solution for flow in a porous pipe with unsteady wall suction and/or injection

NASA Astrophysics Data System (ADS)

Tsangaris, S.; Kondaxakis, D.; Vlachakis, N. W.

2007-10-01

This paper presents an extension of the exact solution of the steady laminar axisymmetric flow in a straight pipe of circular cross section with porous wall, given by R.M. Terrill, to the case of unsteady wall injection and/or suction. The cases of the pulsating parabolic profile and of the developed pulsating flow are investigated as examples. The pulsating flow in porous ducts has many applications in biomedical engineering and in other engineering areas.

The Relationship Between Dipolarization Fronts and Pi2 Pulsations in the Near-Earth Magnetotail - A MHD Case Study

NASA Astrophysics Data System (ADS)

Ream, J. B.; Walker, R. J.; Ashour-Abdalla, M.; El-Alaoui, M.

2011-12-01

We performed a global MHD simulation of a substorm event on 14 September 2004 in order to investigate the link between Pi2 generation and dipolarization fronts. Pi2 pulsations (T = 40-150 s) measured by ground-based instruments are typically used as an indicator of substorm onset, therefore, understanding how and where they are generated is vital to understanding the series of events leading up to onset. Kepko et al. [1999] suggested that the compression regions and velocity variations associated with earthward propagating dipolarization fronts directly drive Pi2 pulsations. Similarly, Panov et al. [2011] suggested that Pi2 pulsations are generated by the overshoot and rebound of bursty bulk flows. Dipolarization fronts are step-wise enhancements in Bz which are associated with fast (>100km/s) earthward flows and are followed by tailward expansion due to pile-up at the high pressure region where the magnetic field lines transition from a stretched to a dipolar configuration. Cao et al. [2009] have presented observations from Double Star (TC1), Cluster 4 and Polar of a substorm with onset at 18:22 UT. During this event a dipolarization front was observed by Double Star at ~18:25, and dipolarization associated expansion was observed by Cluster 4 at ~18:50 and Polar at ~18:55 UT. The spacecraft were positioned at (-10.2, -1.6, 1.2), (-16.4, 1.6, 2.2) and (-7.5, -1.8, -4.9) RE in GSM coordinates respectively. The simulation was carried out with the UCLA global MHD code [El-Alaoui (2001), Raeder (1998)], using Geotail, located near the bow shock at ~24 RE, as the solar wind monitor. The solar wind magnetic field data were rotated into a minimum variance frame to be used as input for the simulation. The results from the simulation have been compared to observations and do a good job reproducing the structures observed by all three satellites. Around the time of onset, we have identified a dipolarization front near midnight which originates at ~12 RE. We show that as the dipolarization front begins to travel earthward, Pi2 fluctuations are generated in the pressure and velocity components which propagate along the plasma sheet into the inner magnetosphere. Inside ~-7 RE the frequency seen in the velocity perturbations is matched by perturbations in pressure and magnetic field components. References Ashour-Abdalla, M., et al (2011), Observations and simulations of non-local acceleration of electrons in magnetotail magnetic reconnection events, Nature Physics, vol.7. Cao, X., et al. (2008), Multispacecraft and ground-based observations of substorm timing and activations: Two case studies, J. Geophys. Res., 113, A07S25. El-Alaoui, M. (2001), Current disruption during November 24, 1996 substorm, J. Geophys. Res., 106, 6229- 6245. Kepko, L. and M. Kivelson (1999) Generation of Pi2 pulsations by bursty bulk flows, J. Geophys Res. 104(A11),25,021-25,034. Panov, E. V., et al (2010), Multiple overshoot and rebound of a bursty bulk flow, Geophys. Res. Lett., 37, L08103. Raeder, J., et al. (1998), The Geospace Environment Modeling Grand Challenge: Results from a global geospace circulation model, J. Geophys. Res., 103, 14,787.

MOST light-curve analysis of the γ Doradus pulsator HR 8799, showing resonances and amplitude variations

NASA Astrophysics Data System (ADS)

Sódor, Á.; Chené, A.-N.; De Cat, P.; Bognár, Zs.; Wright, D. J.; Marois, C.; Walker, G. A. H.; Matthews, J. M.; Kallinger, T.; Rowe, J. F.; Kuschnig, R.; Guenther, D. B.; Moffat, A. F. J.; Rucinski, S. M.; Sasselov, D.; Weiss, W. W.

2014-08-01

Context. The central star of the HR 8799 system is a γ Doradus-type pulsator. The system harbours four planetary-mass companions detected by direct imaging, and is a good solar system analogue. The masses of the companions are not accurately known because the estimation depends greatly on the age of the system, which is also not known with sufficient accuracy. Asteroseismic studies of the star might help to better constrain the age of HR 8799. We organized an extensive photometric and multi-site spectroscopic observing campaign to study the pulsations of the central star. Aims: The aim of the present study is to investigate the pulsation properties of HR 8799 in detail via the ultra-precise 47 d nearly continuous photometry obtained with the Microvariability and Oscillations in STars (MOST) space telescope, and to find as many independent pulsation modes as possible, which is the prerequisite for an asteroseismic age determination. Methods: We carried out Fourier analysis of the wide-band photometric time series. Results: We find that resonance and sudden amplitude changes characterize the pulsation of HR 8799. The dominant frequency is always at f1 = 1.978 d-1.Many multiples of one-ninth of the dominant frequency appear in the Fourier spectrum of the MOST data: n/9 f1, where n = {1,2,3,4,5,6,7,8,9,10,13,14,17,18}. Our analysis also reveals that many of these peaks show strong amplitude decrease and phase variations even on the 47 d time scale. The dependencies between the pulsation frequencies of HR 8799 make the planned subsequent asteroseismic analysis rather difficult. We point out some resemblance between the light curve of HR 8799 and the modulated pulsation light curves of Blazhko RR Lyrae stars. Based on data from the MOST satellite, a Canadian Space Agency mission, jointly operated by Dynacon Inc., the University of Toronto Institute for Aerospace Studies and the University of British Columbia, with the assistance of the University of Vienna.

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.

Regulation of Pyrimidine Biosynthesis in Intact Cells of Cucurbita pepo.

PubMed

Lovatt, C J; Albert, L S

1979-10-01

The occurrence of the complete orotic acid pathway for the biosynthesis de novo of pyrimidine nucleotides was demonstrated in the intact cells of roots excised from summer squash (Cucurbita pepo L. cv. Early Prolific Straightneck). Evidence that the biosynthesis of pyrimidine nucleotides proceeds via the orotate pathway in C. pepo included: (a) demonstration of the incorporation of [(14)C]NaHCO(3), [(14)C]carbamylaspartate, and [(14)C]orotic acid into uridine nucleotides; (b) the isolation of [(14)C]orotic acid when [(14)C]NaHCO(3) and [(14)C]carbamylaspartate were used as precursors; (c) the observation that 6-azauridine, a known inhibitor of the pathway, blocked the incorporation of early precursors into uridine nucleotides while causing a concomitant accumulation of orotic acid; and (d) demonstration of the activities of the component enzymes of the orotate pathway in assays employing cell-free extracts.Regulation of the activity of the orotate pathway by end product inhibition was demonstrated in the intact cells of excised roots by measuring the influence of added pyrimidine nucleosides on the incorporation of [(14)C]NaHCO(3) into uridine nucleotides. The addition of either uridine or cytidine inhibited the incorporation of [(14)C]NaHCO(3) into uridine nucleotides by about 80%. The observed inhibition was demonstrated to be readily reversible upon transfer of the roots to a nucleoside-free medium. Experiments employing various radiolabeled precursors indicated that one or both of the first two enzymes in the orotate pathway are the only site(s) of regulation of physiological importance.

Retinal vascular and structural changes are associated with amyloid burden in the elderly: ophthalmic biomarkers of preclinical Alzheimer's disease.

PubMed

Golzan, S Mojtaba; Goozee, Kathryn; Georgevsky, Dana; Avolio, Alberto; Chatterjee, Pratishtha; Shen, Kaikai; Gupta, Vivek; Chung, Roger; Savage, Greg; Orr, Carolyn F; Martins, Ralph N; Graham, Stuart L

2017-03-01

Retinal imaging may serve as an alternative approach to monitor brain pathology in Alzheimer's disease (AD). In this study, we investigated the association between retinal vascular and structural changes and cerebral amyloid-β (Aβ) plaque load in an elderly cohort. We studied a total of 101 participants, including 73 elderly subjects (79 ± 5 years, 22 male) with no clinical diagnosis of AD but reporting some subjective memory change and an additional 28 subjects (70 ± 9 years, 16 male) with clinically established AD. Following a complete dilated ocular examination, the amplitude of retinal vascular pulsations and dynamic response, retinal nerve fibre layer thickness and retinal ganglion cell layer (RGCL) thickness were determined in all patients. Systemic blood pressure and carotid-to-femoral pulse wave velocity were measured. The elderly cohort also underwent magnetic resonance imaging and 18 F-florbetaben (FBB)-positron emission tomographic amyloid imaging to measure neocortical Aβ standardised uptake value ratio (SUVR), and this was used to characterise a 'preclinical' group (SUVR >1.4). The mean FBB neocortical SUVR was 1.35 ± 0.3. The amplitude of retinal venous pulsations correlated negatively with the neocortical Aβ scores (p < 0.001), whereas the amplitude of retinal arterial pulsations correlated positively with neocortical Aβ scores (p < 0.01). RGCL thickness was significantly lower in the clinical AD group (p < 0.05). The correlation between retinal vascular changes and Aβ plaque load supports the possibility of a vascular component to AD. Dynamic retinal vascular parameters may provide an additional inexpensive tool to aid in the preclinical assessment of AD.

Low-mass Pre-He White Dwarf Stars in Kepler Eclipsing Binaries with Multi-periodic Pulsations

NASA Astrophysics Data System (ADS)

Zhang, X. B.; Fu, J. N.; Liu, N.; Luo, C. Q.; Ren, A. B.

2017-12-01

We report the discovery of two thermally bloated low-mass pre-He white dwarfs (WDs) in two eclipsing binaries, KIC 10989032 and KIC 8087799. Based on the Kepler long-cadence photometry, we determined comprehensive photometric solutions of the two binary systems. The light curve analysis reveals that KIC 10989032 is a partially eclipsed detached binary system containing a probable low-mass WD with the temperature of about 10,300 K. Having a WD with the temperature of about 13,300, KKIC 8087799 is typical of an EL CVn system. By utilizing radial velocity measurements available for the A-type primary star of KIC 10989032, the mass and radius of the WD component are determined to be 0.24+/- 0.02 {M}⊙ and 0.50+/- 0.01 {R}⊙ , respectively. The values of mass and radius of the WD in KIC 8087799 are estimated as 0.16 ± 0.02 M ⊙ and 0.21 ± 0.01 R ⊙, respectively, according to the effective temperature and mean density of the A-type star derived from the photometric solution. We therefore introduce KIC 10989032 and KIC 8087799 as the eleventh and twelfth dA+WD eclipsing binaries in the Kepler field. Moreover, both binaries display marked multi-periodic pulsations superimposed on binary effects. A preliminary frequency analysis is applied to the light residuals when subtracting the synthetic eclipsing light curves from the observations, revealing that the light pulsations of the two systems are both due to the δ Sct-type primaries. We hence classify KIC 10989032 and KIC 8087799 as two WD+δ Sct binaries.

Experimental study on heat transfer performance of pulsating heat pipe with refrigerants

NASA Astrophysics Data System (ADS)

Wang, Xingyu; Jia, Li

2016-10-01

The effects of different refrigerants on heat transfer performance of pulsating heat pipe (PHP) are investigated experimentally. The working temperature of pulsating heat pipe is kept in the range of 20°C-50°C. The startup time of the pulsating heat pipe with refrigerants can be shorter than 4 min, when heating power is in the range of 10W?100W. The startup time decreases with heating power. Thermal resistances of PHP with filling ratio 20.55% were obviously larger than those with other filling ratios. Thermal resistance of the PHP with R134a is much smaller than that with R404A and R600a. It indicates that the heat transfer ability of R134a is better. In addition, a correlation to predict thermal resistance of PHP with refrigerants was suggested.

Multicolor Photometry and Time-resolved Spectroscopy of Two sdBV Stars

NASA Astrophysics Data System (ADS)

Reed, M. D.; O'Toole, S. J.; Telting, J. H.; Østensen, R. H.; Heber, U.; Barlow, B. N.; Reichart, D. E.; Nysewander, M. C.; LaCluyze, A. P.; Ivarsen, K. M.; Haislip, J. B.; Bean, J.

2012-03-01

Observational mode constraints have mostly been lacking for short period pulsating sdB stars, yet such identifications are vital to constrain models. Time-resolved spectroscopy and multicolor photometry have been employed with mixed results for short-period pulsating sdB stars. Time-resolved spectroscopy has successfully measured radial velocity, temperature, and gravity variations in six pulsators, yet interpreting results is far from straightforward. Multicolor photometry requires extremely high precision to discern between low-degree modes, yet has been used effectively to eliminate high-degree modes. Combining radial velocity (RV) and multicolor measurements has also been shown as an effective means of constraining mode identifications. We present preliminary results for Feige 48 and EC 01541-1409 using both time-resolved spectroscopy and multicolor photometry and an initial examination of their pulsation modes using the atmospheric codes BRUCE and KYLIE.

Observations of a gradual transition between Ps 6 activity with auroral torches and surgelike pulsations during strong geomagnetic disturbances

NASA Technical Reports Server (NTRS)

Steen, A.; Collis, P. N.; Evans, D.; Kremser, G.; Capelle, S.; Rees, D.; Tsurutani, B. T.

1988-01-01

This paper describes a long-lasting large-amplitude pulsation event, which occurred on January 10, 1983 in the ionosphere and magnetosphere and was characterized by Steen and Rees (1983). Over the 4-h period (0200-0600 UT), the characteristics of the pulsations in the ionosphere changed from being Ps 6 auroral torches toward substorms and back to Ps 6. At GEO, the corresponding characteristics were a modulation of the high-energy particle intensity and plasma dropouts. Based on the ideas presented by Rostoker and Samson (1984), an interpretation of the event is offered, according to which the pulsations are caused by the Kelvin-Helmholtz instability during an interval of strong magnetospheric convection. On the basis of this explanation, a new interpretation of the substorm time sequence is proposed.

A Refined Search for Pulsations in White Dwarf Companions to Millisecond Pulsars

NASA Astrophysics Data System (ADS)

Kilic, Mukremin; Hermes, J. J.; Córsico, A. H.; Kosakowski, Alekzander; Brown, Warren R.; Antoniadis, John; Calcaferro, Leila M.; Gianninas, A.; Althaus, Leandro G.; Green, M. J.

2018-06-01

We present optical high-speed photometry of three millisecond pulsars with low-mass (<0.3 M⊙) white dwarf companions, bringing the total number of such systems with follow-up time-series photometry to five. We confirm the detection of pulsations in one system, the white dwarf companion to PSR J1738+0333, and show that the pulsation frequencies and amplitudes are variable over many months. A full asteroseismic analysis for this star is under-constrained, but the mode periods we observe are consistent with expectations for a M⋆ = 0.16 - 0.19M⊙ white dwarf, as suggested from spectroscopy. We also present the empirical boundaries of the instability strip for low-mass white dwarfs based on the full sample of white dwarfs, and discuss the distinction between pulsating low-mass white dwarfs and subdwarf A/F stars.

K2 Campaign 5 observations of pulsating subdwarf B stars: binaries and super-Nyquist frequencies

NASA Astrophysics Data System (ADS)

Reed, M. D.; Armbrecht, E. L.; Telting, J. H.; Baran, A. S.; Østensen, R. H.; Blay, Pere; Kvammen, A.; Kuutma, Teet; Pursimo, T.; Ketzer, L.; Jeffery, C. S.

2018-03-01

We report the discovery of three pulsating subdwarf B stars in binary systems observed with the Kepler space telescope during Campaign 5 of K2. EPIC 211696659 (SDSS J083603.98+155216.4) is a g-mode pulsator with a white dwarf companion and a binary period of 3.16 d. EPICs 211823779 (SDSS J082003.35+173914.2) and 211938328 (LB 378) are both p-mode pulsators with main-sequence F companions. The orbit of EPIC 211938328 is long (635 ± 146 d) while we cannot constrain that of EPIC 211823779. The p modes are near the Nyquist frequency and so we investigate ways to discriminate super- from sub-Nyquist frequencies. We search for rotationally induced frequency multiplets and all three stars appear to be slow rotators with EPIC 211696659 subsynchronous to its orbit.

The superslow pulsation X-ray pulsars in high mass X-ray binaries

NASA Astrophysics Data System (ADS)

Wang, Wei

2013-03-01

There exists a special class of X-ray pulsars that exhibit very slow pulsation of P spin > 1000 s in the high mass X-ray binaries (HMXBs). We have studied the temporal and spectral properties of these superslow pulsation neutron star binaries in hard X-ray bands with INTEGRAL observations. Long-term monitoring observations find spin period evolution of two sources: spin-down trend for 4U 2206+54 (P spin ~ 5560 s with Ṗ spin ~ 4.9 × 10-7 s s-1) and long-term spin-up trend for 2S 0114+65 (P spin ~ 9600 s with Ṗ spin ~ -1 × 10-6 s s-1) in the last 20 years. A Be X-ray transient, SXP 1062 (P spin ~ 1062 s), also showed a fast spin-down rate of Ṗ spin ~ 3 × 10-6 s s-1 during an outburst. These superslow pulsation neutron stars cannot be produced in the standard X-ray binary evolution model unless the neutron star has a much stronger surface magnetic field (B > 1014 G). The physical origin of the superslow spin period is still unclear. The possible origin and evolution channels of the superslow pulsation X-ray pulsars are discussed. Superslow pulsation X-ray pulsars could be younger X-ray binary systems, still in the fast evolution phase preceding the final equilibrium state. Alternatively, they could be a new class of neutron star system - accreting magnetars.

Functional Changes of Diaphragm Type Shunt Valves Induced by Pressure Pulsation

NASA Astrophysics Data System (ADS)

Lee, Chong-Sun; Suh, Chang-Min; Ra, Young-Shin

Shunt valves used to treat patients with hydrocephalus were tested to investigate influence of pressure pulsation on their flow control characteristics. Our focus was on flow dynamic and functional changes of the small and thin diaphragms in the valves that serve as the main flow control mechanism and are made from silicone elastomer. Firstly, pressure-flow control curves were compared under pulsed and steady flow (without pulsation) conditions. Secondly, functional changes of the valves were tested after a long-term continuous pulsation with a peristaltic pump. Thirdly, flushing procedures selectively conducted by neurosurgeons were simulated with a fingertip pressed on the dome of the valves. As 20cc/hr of flow rate was adjusted at a constant pressure, application of 40mmH2O of pressure pulse increased flow rate through shunt valves more than 60%. As a 90cm length silicone catheter was connected to the valve outlet, increase in the flow rate was substantially reduced to 17.5%. Pressure-flow control characteristics of some valves showed significant changes after twenty-eight days of pressure pulsation at 1.0 Hz under 50.0cc/hr of flow rate. Flushing simulation resulted in temporary decrease in the pressure level. It took three hours to fully recover the normal pressure-flow control characteristics after the flushing. Our results suggest that shunt valves with a thin elastic diaphragm as the main flow control mechanism are sensitive to intracranial pressure pulsation or pressure spikes enough to change their pressure-flow control characteristics.

Quasi-Periodic Pulsations During the Impulsive and Decay Phases of an X-Class Flare

NASA Technical Reports Server (NTRS)

Hays, L. A.; Gallagher, P. T.; Dennis, B. R.; Ireland, J.; Inglis, A. R.; Ryan, D. F.

2016-01-01

Quasi-periodic pulsations (QPPs) are often observed in X-ray emission from solar flares. To date, it is unclear what their physical origins are. Here, we present a multi-instrument investigation of the nature of QPP during the impulsive and decay phases of the X1.0 flare of 2013 October 28. We focus on the character of the fine structure pulsations evident in the soft X-ray (SXR) time derivatives and compare this variability with structure across multiple wavelengths including hard X-ray and microwave emission. We find that during the impulsive phase of the flare, high correlations between pulsations in the thermal and non-thermal emissions are seen. A characteristic timescale of 20 s is observed in all channels and a second timescale of 55 s is observed in the non-thermal emissions. SXR pulsations are seen to persist into the decay phase of this flare, up to 20 minutes after the non-thermal emission has ceased. We find that these decay phase thermal pulsations have very small amplitude and show an increase in characteristic timescale from 40 s up to 70 s. We interpret the bursty nature of the co-existing multi-wavelength QPPs during the impulsive phase in terms of episodic particle acceleration and plasma heating. The persistent thermal decay phase QPPs are most likely connected with compressive magnetohydrodynamic processes in the post-flare loops such as the fast sausage mode or the vertical kink mode.

Seismology of rapidly rotating and solar-like stars

NASA Astrophysics Data System (ADS)

Reese, Daniel Roy

2018-05-01

A great deal of progress has been made in stellar physics thanks to asteroseismology, the study of pulsating stars. Indeed, asteroseismology is currently the only way to probe the internal structure of stars. The work presented here focuses on some of the theoretical aspects of this domain and addresses two broad categories of stars, namely solar-like pulsators (including red giants), and rapidly rotating pulsating stars. The work on solar-like pulsators focuses on setting up methods for efficiently characterising a large number of stars, in preparation for space missions like TESS and PLATO 2.0. In particular, the AIMS code applies an MCMC algorithm to find stellar properties and a sample of stellar models which fit a set of seismic and classic observational constraints. In order to reduce computation time, this code interpolates within a precalculated grid of models, using a Delaunay tessellation which allows a greater flexibility on the construction of the grid. Using interpolated models based on the outputs from this code or models from other forward modelling codes, it is possible to obtain refined estimates of various stellar properties such as the mean density thanks to inversion methods put together by me and G. Buldgen, my former PhD student. Finally, I show how inversion-type methods can also be used to test more qualitative information such as whether a decreasing rotation profile is compatible with a set of observed rotational splittings and a given reference model. In contrast to solar-like pulsators, the pulsation modes of rapidly rotating stars remain much more difficult to interpret due to the complexity of the numerical calculations needed to calculate such modes, the lack of simple frequency patterns, and the fact that it is difficult to predict mode amplitudes. The work described here therefore focuses on addressing the above difficulties one at a time in the hopes that it will one day be possible to carry out detailed asteroseismology in these stars. First of all, the non-adiabatic pulsation equations and their numerical implementation are described. The variational principle and work integrals are addressed. This is followed by a brief classification of the pulsation modes one can expect in rapidly rotating stars. I then address the frequencies patterns resulting from acoustic island modes and the interpretations of observed pulsation spectra based on these. This is then followed by a description of mode identification techniques and the ongoing efforts to adapt them to rapid rotation. Finally, the last part briefly deals with mode excitation.

Flow control by combining radial pulsation and rotation of a cylinder in uniform flow

NASA Astrophysics Data System (ADS)

Oualli, H.; Hanchi, S.; Bouabdallah, A.; Gad-El-Hak, M.

2008-11-01

Flow visualizations and hot-wire measurements are carried out to study a circular cylinder undergoing simultaneous radial pulsation and rotation and placed in a uniform flow. The Reynolds number is in the range of 1,000--22,000, for which transition in the shear layers and near wake is expected. Our previous experimental and numerical investigations in this subcritical flow regime have established the existence of an important energy transfer mechanism from the mean flow to the fluctuations. Radial pulsations cause and enhance that energy transfer. Certain values of the amplitude and frequency of the pulsations lead to negative drag (i.e. thrust). The nonlinear interaction between the Magnus effect induced by the steady rotation of the cylinder and the near-wake modulated by the bluff body's pulsation leads to alteration of the omnipresent Kármán vortices and the possibility of optimizing the lift-to-drag ratio as well as the rates of heat and mass transfer. Other useful applications include the ability to enhance or suppress the turbulence intensity, and to avoid the potentially destructive lock-in phenomenon in the wake of bridges, electric cables and other structures.

Numerical Simulation of Pulsation Flow in the Vapour Channel of Short Low Temperature Heat Pipes at High Heat Loads

NASA Astrophysics Data System (ADS)

Seryakov, A. V.; Konkin, A. V.

2017-11-01

The results of the numerical simulation of pulsations in the Laval-liked vapour channel of short low-temperature range heat pipes (HPs) are presented. The numerical results confirmed the experimentally obtained increase of the frequency of pulsations in the vapour channel of short HPs with increasing overheat of the porous evaporator relative to the boiling point of the working fluid. The occurrence of pressure pulsations inside the vapour channel in a short HPs is a complex phenomenon associated with the boiling beginning in the capillary-porous evaporator at high heat loads, and appearance the excess amount of vapour above it, leading to the increase in pressure P to a value at which the boiling point TB of the working fluid becomes higher than the evaporator temperature Tev. Vapour clot spreads through the vapour channel and condense, and then a rarefaction wave return from condenser in the evaporator, the boiling in which is resumed and the next cycle of the pulsations is repeated. Numerical simulation was performed using finite element method implemented in the commercial program ANSYS Multiphisics 14.5 in the two-dimensional setting of axis symmetric moist vapour flow with third kind boundary conditions.

ON THE CHALLENGING VARIABILITY OF LS IV-14{sup 0}116: PULSATIONAL INSTABILITIES EXCITED BY THE {epsilon}-MECHANISM

DOE Office of Scientific and Technical Information (OSTI.GOV)

Miller Bertolami, M. M.; Corsico, A. H.; Althaus, L. G., E-mail: mmiller@fcaglp.unlp.edu.ar

2011-11-01

We investigate the pulsation driving mechanism responsible for the long-period photometric variations observed in LS IV-14{sup 0}116, a subdwarf B star showing a He-enriched atmospheric composition. To this end, we perform detailed nonadiabatic pulsation computations over fully evolutionary post-He-core-flash stellar structure models, appropriate for hot subdwarf stars at evolutionary phases previous to the He-core burning stage. We found that the variability of LS IV-14{sup 0}116 can be attributed to non-radial g-mode pulsations excited by the {epsilon}-mechanism acting in the He-burning shells that appear before the star settles in the He-core burning stage. Even more interestingly, our results show that LSmore » IV-14{sup 0}116 could be the first known pulsating star in which the {epsilon}-mechanism of mode excitation is operating. Last but not the least, we find that the period range of destabilized modes is sensitive to the exact location of the burning shell, something that might help in distinguishing between the different evolutionary scenarios proposed for the formation of this star.« less

Wave and plasma observations during a compressional Pc 5 wave event August 10, 1982

NASA Technical Reports Server (NTRS)

Engebretson, M. J.; Cahill, L. J., Jr.; Waite, J. H., Jr.; Gallagher, D. L.; Chandler, M. O.; Sugiura, M.

1986-01-01

Magnetometer and thermal plasma instruments on the polar-orbiting Dynamics Explorer 1 satellite observed a small-amplitude ultralow frequency pulsation event at the outer edge of the plasmapause near the geomagnetic equator in the midafternoon sector on August 10, 1982, during the recovery phase of a magnetic storm. Transverse pulsations of 30-50 s period were observed throughout the event, and a 270-s period, purely compressional Pc 5 pulsation with several shifts in phase occurred within + or - 5 deg of the geomagnetic equator. Electric fields and the motion of thermal ions appeared to be in quadrature with pulsations in magnetic field magnitude throughout the event. This suggests that the net Poynting flux for the compressional waves was zero, consistent with their being standing waves. Large fluxes of trapped 90 deg pitch angle 10-eV protons, also symmetric about the geomagnetic equator, were observed in conjunction with the waves. These may serve as a source of free energy for the pulsations. These observations lend support to recent studies suggesting that many dayside compressional wave events are related to localized field line resonance near plasmapauselike boundaries, but also include features that cannot be explained by existing theories.

Wave and plasma observations during a compressional Pc 5 wave event August 10, 1982

NASA Astrophysics Data System (ADS)

Engebretson, M. J.; Cahill, L. J., Jr.; Waite, J. H., Jr.; Gallagher, D. L.; Chandler, M. O.; Sugiura, M.; Weimer, D. R.

1986-06-01

Magnetometer and thermal plasma instruments on the polar-orbiting Dynamics Explorer 1 satellite observed a small-amplitude ultralow frequency pulsation event at the outer edge of the plasmapause near the geomagnetic equator in the midafternoon sector on August 10, 1982, during the recovery phase of a magnetic storm. Transverse pulsations of 30-50 s period were observed throughout the event, and a 270-s period, purely compressional Pc 5 pulsation with several shifts in phase occurred within + or - 5 deg of the geomagnetic equator. Electric fields and the motion of thermal ions appeared to be in quadrature with pulsations in magnetic field magnitude throughout the event. This suggests that the net Poynting flux for the compressional waves was zero, consistent with their being standing waves. Large fluxes of trapped 90 deg pitch angle 10-eV protons, also symmetric about the geomagnetic equator, were observed in conjunction with the waves. These may serve as a source of free energy for the pulsations. These observations lend support to recent studies suggesting that many dayside compressional wave events are related to localized field line resonance near plasmapauselike boundaries, but also include features that cannot be explained by existing theories.

Development and Characterization Testing of an Air Pulsation Valve for a Pulse Detonation Engine Supersonic Parametric Inlet Test Section

NASA Technical Reports Server (NTRS)

Tornabene, Robert

2005-01-01

In pulse detonation engines, the potential exists for gas pulses from the combustor to travel upstream and adversely affect the inlet performance of the engine. In order to determine the effect of these high frequency pulses on the inlet performance, an air pulsation valve was developed to provide air pulses downstream of a supersonic parametric inlet test section. The purpose of this report is to document the design and characterization tests that were performed on a pulsation valve that was tested at the NASA Glenn Research Center 1x1 Supersonic Wind Tunnel (SWT) test facility. The high air flow pulsation valve design philosophy and analyses performed are discussed and characterization test results are presented. The pulsation valve model was devised based on the concept of using a free spinning ball valve driven from a variable speed electric motor to generate air flow pulses at preset frequencies. In order to deliver the proper flow rate, the flow port was contoured to maximize flow rate and minimize pressure drop. To obtain sharp pressure spikes the valve flow port was designed to be as narrow as possible to minimize port dwell time.

KIC 8164262: a heartbeat star showing tidally induced pulsations with resonant locking

NASA Astrophysics Data System (ADS)

Hambleton, K.; Fuller, J.; Thompson, S.; Prša, A.; Kurtz, D. W.; Shporer, A.; Isaacson, H.; Howard, A. W.; Endl, M.; Cochran, W.; Murphy, S. J.

2018-02-01

We present the analysis of KIC 8164262, a heartbeat star with a high-amplitude (∼1 mmag), tidally resonant pulsation (a mode in resonance with the orbit) at 229 times the orbital frequency and a plethora of tidally induced g-mode pulsations (modes excited by the orbit). The analysis combines Kepler light curves with follow-up spectroscopic data from the Keck telescope, KPNO (Kitt Peak National Observatory) 4-m Mayall telescope and the 2.7-m telescope at the McDonald observatory. We apply the binary modelling software, PHOEBE, to the Kepler light curve and radial velocity data to determine a detailed binary star model that includes the prominent pulsation and Doppler boosting, alongside the usual attributes of a binary star model (including tidal distortion and reflection). The results show that the system contains a slightly evolved F star with an M secondary companion in a highly eccentric orbit (e = 0.886). We use the results of the binary star model in a companion paper (Fuller) where we show that the prominent pulsation can be explained by a tidally excited oscillation mode held near resonance by a resonance locking mechanism.

Impact of Pulsation Activity on the Light Curves of Symbiotic Variables

NASA Astrophysics Data System (ADS)

Marsakova, Vladyslava I.; Andronov, Ivan L.; Chinarova, Lidia L.; Chyzhyk, Maksym S.; Andrych, Kateryna D.

2015-12-01

We used long-term visual amateur observations of several symbiotic variables for detection of periods that may be caused by pulsation. The examples of multiple periodicities are discussed individually in each case.

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.

Pulsation research during the IMS. [International Magnetospheric Study

NASA Technical Reports Server (NTRS)

Hughes, W. J.

1982-01-01

After describing the development status of the field of magnetic pulsations in 1975, before the initiation of the International Magnetospheric Study (IMS), attention is given to the IMS's novel observational results and an attempt is made to identify the most effective research methods employed. It is found that the most fruitful work involved small-scale collaboration between a few individuals or a few groups possessing complementary data sets. Consideration is restricted to research on the long period pulsations which can be broadly classified as field line resonances. Recommendations are made for future research efforts.