bluuebunny/crossref_metadata_2025_split huggingface dataset:
Can Spores Survive a Million Years in the Radiation in Outer Space? Part I: Protection against Photons above 0.5 KEV
Authors: Mileikowsky Curt 
Published: July 2016

AbstractIt is conceivable that microorganisms could be transported over long distances in space inside natural «vehicles» such as molecular clouds, comets or meteors. To traverse a distance of 30 ly at speeds of 10 km/s (to another planetary system) would then take a million years. Due to the intense radiation in space by both photons and cosmic ray charged particles, microorganisms, including the most radiation-resistant spores known, need radiation protection in order to survive the millionyear dormancy. From the absolute energy distribution in the interstellar medium of the photon radiation of energies from 0.5 keV and up – known by measurement – the dose rates, in Megarads per million years (Mrad/My), have been calculated for spores of volume (1μm3which are assumed to have escaped out into interstellar space. Taking into consideration the energy dependence of photon attenuation in organic material, of absorption restriction in small bodies and of attenuation in the shielding material, these calculations have been done for unprotected spores, for spores in the central regions of seven different molecular clouds characterized by radial column densities from 0.01 to 1.3 g/cm2, and for spores inside porous meteors and in comets. Unprotected spores get almost 1000 Mrad/My from photons over 0.5 keV. Dose reduction by a factor of 1000, necessary for survival against photon radiation can be achieved by: 1) clouds with radial column densities ≥ 0.5 g/cm2; 2) meteors of radius ≥ 2-3 mm; 3) comet ice of radius &gt; 5 mm. Cosmic ray charged particles are not treated in this Part I paper but will be the subject of a forthcomimg Part II paper.
A Galactic Center Search for Extraterrestrial Intelligent Signals
Authors: Sullivan Woodruff T. , Wellington Kelvin J. , Shostak G. Seth , Backus Peter R. , Cordes James M. 
Published: July 2016

AbstractIn June 1995 we used the Parkes 64-m radio telescope to search for narrowband or pulsing signals of extraterrestrial intelligent (ETI) origin from the direction of the galactic center. This strategy was chosen so as to maximize the number of possibly detectable ETI signals within the beam, assuming that they are associated with stars and that their luminosity function is such that they can be detected at a distance of at least a few kiloparsecs. A total of 190 1.2–minute integrations were taken in a region of size 5.0° × 0.6° centered on the galactic center. Many positions in this region were observed 2 or 3 times in order to allow for the possibility of strong interstellar scintillations arising in any ETI signal. The spectrum analyzer was that of Project Phoenix, configured such that it covered both circular polarizations over a 20-MHz bandwidth centered on 1425.0 MHz. This bandwidth was divided into 28.7 million channels with separations of 0.64 Hz. The signal analysis system searched both for slow pulses (periods of at least 2 sec) and narrowband signals with drifts from 0 to 1 Hz/sec. A second antenna located 200 km away was used for immediate follow-up on all candidate signals. No signals of ETI origin were found. A later search of smoothed spectra with 640 Hz resolution also revealed no new features not attributable to manmade interference.
Studies of Radio Frequency Interference at Parkes Observatory
Authors: Backus Peter R. , LaRoque Sam , Tarter Jill C. , Dreher John , Cullers Kent , Patrick Alan , Heiligman Gary 
Published: July 2016

AbstractFrom February through early June, 1995, Project Phoenix conducted SETI observations of 209 stars over the frequency range from 1195 to 3005 MHz. A byproduct of this search is a unique data set suitable for studying the Radio Frequency Interference (RFI) environment at the Parkes 64-m telescope in New South Wales, Australia. RFI is an increasing problem for SETI and other radio astronomy observations conducted outside of the «protected» frequency bands. The data analyzed for this paper were «mean baseline» spectra in Left and Right Circular Polarization (LCP, RCP), integrated for either 138 or 276 s, covering a 10 MHz bandwidth with 15,552 channels at a resolution of 643 Hz. Channels were identified as contaminated by RFI when the power in the channel exceeded the mean noise by 3%. The «spectral occupancy», the fraction of time RFI was seen, was determined for each channel. The RFI occupancy for LCP and RCP are distinctly different. Approximately 100 MHz of the spectrum was too heavily contaminated for SETI observations.
Preliminary Results of a Search for Variable Stars in the Globular Cluster M 13
Authors: Kopacki Grzegorz , Kołaczkowski Zbigniew , Pigulski Andrzej 
Published: July 2016

AbstractResults of a search for variable stars in the globular cluster M 13 are presented. Comments on the variability of all observed variable or suspected variable stars are given. Five new RR Lyrae stars and one SX Phoenicis star are identified.
AGAPEROS Variables in the LMC
Authors: Schultheis M. , Lebzelter T. , Melchior A.L. 
Published: July 2016

AbstractIn this work, we present preliminary results based on an LMC Bar sample (AGAPEROS) of ⷍ 400 variable stars combined with near-Infared photometry (DENIS). About 50% of our objects are semiregular Variables (SRVs) while 20% are regular Variables with a period range from 30d up to 600d. A second period is present in ∼ 40% of the SRVs. We find a large fraction of regular variables with P < 100d which could be SRVs undergoing a phase of periodic variability. The Period-Colour relation (log P versus I – J), unstudied so far on the LMC, differs from the one found in the Galactic bulge: an effect of metallicity?
A Comparison of the Anelastic and Subseismic Approximations for Low-Frequency Stellar Oscillations: an Application to Rapidly Rotating Stars
Authors: Dintrans B. , Rieutord M. 
Published: July 2016

AbstractAfter showing that the anelastic approximation is better than the subseismic one to filter out acoustic waves when studying low-frequency stellar oscillations, we compute gravito-inertial modes of a typical γ Doradus star using this approximation. We show that eigenmodes can be regular or singular, according to the possible focusing towards attractors of the underlying characteristics. Consequences on the oscillations spectrum are then discussed.
An Observational Overview of Pulsations in β Cep Stars and Slowly Pulsating B Stars
Authors: De Cat P. 
Published: July 2016

AbstractThe observational characteristics of the p-modes of β Cep stars are compared to those of the g-modes of slowly pulsating B stars (SPBs). For the β Cep stars, previous reviews based on photometric surveys are updated with recent results from our high-resolution spectroscopic surveys. For the slowly pulsating B stars, it is the first time a broad observational overview can be given.
Do Temperature Variations at the Surface of a Hot Non-Radial Pulsator Change Significantly the Line-Profile Variations?
Authors: De Ridder J. , Aerts C. , Dupret M.-A. , Neuforge C. 
Published: July 2016

AbstractWe present simulations of line-profile variations of Silicon lines in slowly-rotating non-radially pulsating β Cephei stars and SPB stars. Our goal is to examine how sensitive Si lines are to the non-adiabatic temperature variations at the surface of the star. We find that for realistic amplitudes of the velocity field, and for realistic amplitudes and phase differences for the non-adiabatic temperature and gravity variations, the Silicon lines variations are very little affected.
Spectroscopic Monitoring of 10 Northern SPB Candidates
Authors: Mathias P. , Le Contel J.-M. , Aerts C. , De Cat P. , Van Winckel H. , Robbrecht E. , Briquet M. , Cuypers J. 
Published: July 2016

AbstractWe present the results of 1.5 years of Spectroscopic monitoring of 10 bright northern SPB candidates discovered from the Hipparcos mission. All stars have line-profile variations and are periodic, with periods corresponding to high-order g-modes. We therefore confirm them to be new SPBs.
Line Profile and Photometric Variations of the Be Star η Cen
Authors: Levenhagen R. , Leister N. , Janot-Pacheco E. , Zorec J. , Hubert A. , Floquet M. 
Published: July 2016

AbstractWe review the current status of our monitoring project on Be stars. Line profile variations in Helλ667.8 nm were detected in the Be star η Cen, by means of high resolution and S/N Spectroscopic observations. They were interpreted in terms of nonradial pulsations (NRP). The fundamental parameters of η Cen obtained from BCD spectrophotometric data and interpreted using models of rapidly rotating stars, have been used to estimate the stellar rotational frequency.
Chemical Inhomogeneities and Pulsation
Authors: Turcotte S. 
Published: July 2016

AbstractMajor improvements in models of chemically peculiar stars have been achieved in the past few years. With these new models it has been possible to test quantitatively some of the processes involved in the formation of abundance anomalies and their effect on stellar structure. The models of metallic A (Am) stars have shown that a much deeper mixing has to be present to account for observed abundance anomalies. This has implications on their variability, which these models also reproduce qualitatively. These models also have implications for other chemically inhomogeneous stars such as HgMn B stars which are not known to be variable and λ Boötis stars which can be. The study of the variability of chemically inhomogeneous stars can provide unique information on the dynamic processes occurring in many types of stars in addition to modeling of the evolution of their surface composition.
Seismology of δ Scuti Stars: Problems and Prospects
Authors: Goupil M.J. , Talon S. 
Published: July 2016

The current state of seismology of δ Scuti stars is reviewed with particular emphasis on seismic signatures of the extension of their mixed central region and of rotation. We refer also to Goupil et al. (2000) and more generally to Breger & Montgomery (2000) for more details.δ Scuti stars are population I pulsating stars with spectral type A-early F, located on or near the main sequence. They are found in the lower part of the classical instability strip in a HR diagram (Fig. 1). Masses range from ∼ 1.5M⊙ to ∼ 2.5M⊙ and δ Scuti stars are either in a stage of H-core or H-shell burning. On the main sequence, the high temperature sensitivity of the dominant CNO cycle causes a large convective core to develop, which later shrinks leaving behind a gradient ∇μ in the mean molecular weight.
δ Scuti Variables with Periods Longer than 0.25 Days
Authors: Rodríguez E. , Breger M. 
Published: July 2016

AbstractVariables listed as δ Scuti-type pulsators in the R00 catalogue (Rodriguez et al., 2000) with periods longer than 0.d25 are examined on a star-by-star basis, in order to discriminate their true nature (δ Scuti, RR Lyr or γ Dor-type). From this study, it seems that three stars (DH Peg, UY Cam and YZ Cap) are RR Lyr pulsators rather than δ Scuti variables. Moreover, two variables (AD Ari and DE Oct) seem to be γ Dor variables with the shortest periods known to date (0.d2699 and 0.d2778, respectively).
Amplitude and Period Changes in the δ Sct Star AN Lyncis
Authors: Zhou A.-Y. 
Published: July 2016

AbstractWe report a study of time-dependent behaviour of the light variations in the δ Set star AN Lyn, based on an analysis of new time-series CCD observations and existing data. The amplitude of the main frequency increased from 1994 to 2000 at a rate of 0.006 mmag/yr. The light variation of AN Lyn can be explained currently by amplitude variability mixed with multiperiodic pulsation. With the extended data base, results on XX Cyg are also reported.
Radial Velocities for the Pulsating Subdwarf B Star PG 1605+072
Authors: Woolf V.M. , Jeffery C.S. , Pollacco D.L. 
Published: July 2016

AbstractWe have performed high-speed spectroscopy of the pulsating subdwarf B star PG 1605+072. Its radial velocity variations have frequencies similar to those reported from photometric observations. Peak amplitude ratios are different, probably as a result of power shifting between modes over time. Line-shape variations have also been detected.
Nonradial Pulsations in Classical Pulsators
Authors: Kovács G. 
Published: July 2016

AbstractRecent analyses of photometric data on globular clusters and galaxies enabled us to study more closely the long-periodic amplitude/phase modulation (Blazhko effect) in classical variables. In the frequency spectra of these stars we see either a doublet or an equally-spaced triplet with a very small frequency separation close to the main component. None of the available theoretical models are able to explain this behavior without invoking some form of nonradial pulsation. In this review we describe the observational status of the Blazhko variables, and discuss the limits of the applicability of the current models to these stars.
Synthetic Nonlinear RR Lyrae Instability Strips
Authors: Szabó R. , Csubry Z. , Kolláth Z. , Buchler J.R. 
Published: July 2016

AbstractA recently recognized problem is revisited, namely the discrepancy between the structure of the theoretical and the empirical, observationally derived RR Lyrae instability strips. The essence of the discrepancy is that the slope of the empirical fundamental-mode blue edge is much less steep than its theoretical counterpart. The issue was investigated by means of stellar evolution and mode selection captured by nonlinear models.
The Blazhko Effect Unravelled?
Authors: Kolenberg K. , Aerts C. , Chadid M. , Gillet D. 
Published: July 2016

AbstractA detailed frequency analysis on ELODIE observations of the Blazhko star RR Lyrae (Chadid et al., 1999) clearly revealed the importance of non-linear effects upon the radial fundamental mode (with frequency fP), and a multiplet structure with a separation equal to the Blazhko frequency (f/B) around the main frequency and its harmonics. These results provided strong evidence for the presence of non-radial modes in the star. The identification of these non-radial modes is the following step in our work.
Time-Resolved Spectral Analysis of the Pulsating Helium Star V 652 Her
Authors: Jeffery C.S. , Woolf V.M. , Pollacco D.L. 
Published: July 2016

AbstractWe present a summary of a new time-dependent Spectroscopic analysis of the pulsating helium star V652 Her. The instantaneous properties of the star (effective temperature, surface gravity, radial displacement, etc.) are evaluated throughout the pulsation cycle. The data are used to establish measurements of the mean stellar radius and mass more accurately than hitherto. The first direct evidence of a supersonic shock at minimum radius is also obtained.
Solar-Like Oscillations in β Hydri: Evidence for Short-Lived High-Amplitude Oscillations
Authors: Bedding T.R. , Kjeldsen H. , Baldry I.K. , Bouchy F. , Butler R.P. , Carrier F. , Kienzle F. , Marcy G.W. , O’Toole S.J. , Tinney C.G. 
Published: July 2016

AbstractVelocity measurements of the G2 subgiant β Hyi with both UCLES and CORALIE show a clear excess of power centred at 1.0 mHz. In the UCLES data we find evidence for a short-lived, high-amplitude oscillation event. If confirmed as a feature of subgiants, such ‘starquakes’ would make it harder to measure accurate mode frequencies and perform asteroseismology.
Asteroseismology with CORALIE: Results on Procyon and β Hydri
Authors: Carrier F. , Bouchy F. , Kienzle F. , Blecha A. 
Published: July 2016

AbstractThe spectrograph CORALIE reaches the radial velocity precision needed for an asteroseismological program on bright solar-like stars. We present here two results obtained with this instrument on the stars Procyon and β Hydri. A third campaign, on α Cen A, is presented independently in these proceedings by Carrier et al.
Confirmation of Solar-Like Oscillations in η Bootis
Authors: Kjeldsen H. , Bedding T.R. , Baldry I.K. , Frandsen S. , Bruntt H. , Grundahl F. , Lang K. , Butler R.P. , Fischer D.A. , Marcy G.W. , Misch A. , Vogt S.S. 
Published: July 2016

Kjeldsen et al. (1995) detected excess power in the GO subgiant η Boo from measurements of Balmer-line equivalent widths. The excess was at the expected level, and these authors were able to extract frequency separations and individual frequencies which agreed well with theoretical models (Christensen-Dalsgaard et al., 1995; Guenther & Demarque, 1996). A more detailed discussion of theoretical models for η Bootis was given by Di Mauro & Christensen-Dalsgaard (2001).Kjeldsen et al. (1995) estimated the average amplitude of the strongest modes to be 7 times solar, corresponding to 1.6 m/s in velocity. 13 individual oscillation modes were identified consistent with a large frequency separation of 40.3 μHz. We note, however, that a search for velocity oscillations in this star by Brown et al. (1997) failed to detect a signal, setting limits at a level below that expected on the basis of the Kjeldsen et al. result.In this paper we report further observations made in 1998. We observed this star in Balmer-line equivalent width with the 2.5-m Nordic Optical Telescope and in velocity with the 24-inch Lick CAT.
Playing Music with Magnetic Fields
Authors: Foullon C. 
Published: July 2016

AbstractThrough an increase in magnetic field strength, solar magnetic fields in the atmosphere or subsurface of the Sun can explain the frequency shifts observed on the time scale of the solar activity cycle. A separate study of the contribution of internal magnetic layers clarifies the relative importance of these effects. However, at the base of the convection zone, the cyclical change of orientation of magnetic field lines has a larger effect on global mode frequencies than an increase in field strength alone.
Driving g-Mode Pulsation in γ Doradus Variables
Authors: Wu Yanqin 
Published: July 2016

AbstractSurface convection zones in γ Doradus variables (early F-type g-mode pulsators) can drive pulsation via the ‘convective driving’ mechanism. This mechanism is first proposed and studied in the context of ZZ Cetis (hydrogen-envelope white dwarfs with g-mode pulsations) by Brickhill (1991) and Goldreich & Wu (1999). We implement and develop the convective driving theory to suit the environments on γ Dors, in particular, stronger super-adiabatic gradient and weaker convective flux than those in white dwarfs. This results in a spectrum of gravity-modes being excited in the observed temperature range. However, there are more remaining problems than those that are solved.
On the Equatorial Mass-Loss Rate of Be Stars
Authors: Okazaki A.T. 
Published: July 2016

AbstractWe numerically study the formation process of equatorial disks around isolated Be stars, using an SPH code. We find that the viscous decretion disk model naturally explains the observed disk formation episode of X Per, giving the equatorial mass-loss rate of several ×10−9 (ρ0/10−10 g cm−3) M⊙ yr−1, where ρ0 is the base density of the disk.
Insights from Pulsating Nova Envelopes
Authors: Schenker K. 
Published: July 2016

AbstractBased on a linear and non-linear study of radial pulsations in the envelopes of classical novae (Schenker, 1999), I discuss the results both from the point of view of pulsation theory as well as their consequences for current nova models. Starting from initially static envelope structures at various stages during the decline of a nova outburst, strong ‘running-wave’ instabilities have been found that rapidly grow into shocks. Improved analytical concepts give a new direction to the interpretation of such highly non-adiabatic radial pulsations. For direct observational confirmation, a search for short period variability in the UV and soft X-ray is suggested during the very late decline phase. Speculative consequences for mass-loss scenarios in novae due to these instabilities will need some more work in the future.
Quasi-Periodic Oscillations in Accretion Discs
Authors: Warner Brian , Woudt Patrick A. 
Published: July 2016

Quasi-Periodic Oscillations (QPOs) in Cataclysmic Variable stars (CVs) with periods in the range 100 – 2000 s have been known for 25 years (see Chapter 8 of Warner, 1995a). We distinguish here between QPOs and Dwarf Nova Oscillations (DNOs) – the latter being of shorter period (5 – 50 s) and greater coherence. QPOs appear as brightness modulations and typically have quite short coherence lengths (a few cycles).QPOs are largely associated with discs transferring mass at a high rate – i.e., dwarf novae during outburst or nova-like variables; but the QPOs are not always present and many systems have not shown QPOs at all.Generally it is thought that QPOs result from non-radial oscillations of the accretion discs surrounding the white dwarf component in CVs (Carroll et al., 1985; Collins et al., 2000). They could, e.g., be quite coherent oscillations of individual annuli in a disc, each with a different period. Alternatively, a particular oscillation mode may be excited for only a few cycles and then be re-excited at an arbitrary phase. Most theoretical proposals have sought to make the QPOs self-luminous pulsations of the disc, in analogy with the kappa or epsilon processes of stellar pulsation.
Seismic Inversions for White Dwarf Stars
Authors: Takata M. , Montgomery M.H. 
Published: July 2016

AbstractInversion methods have been used successfully for the Sun. The stars with the next richest set of observed frequencies are the white dwarfs. We consider here the viability of numerical inversions for these stars. We find that, while the number of presently observed modes in the white dwarf GD 358 is too small for structural inversions, such inversions would be possible if the frequencies of all modes with 1 ≤ l ≤ 3 were observed. This is possible for space observations by e.g. Eddington.
Asteroseismology: The Impact of Solar Space Observations
Authors: Hudson H.S. 
Published: July 2016

AbstractObservations from space relevant to solar global properties (oscillations, magnetic activity, etc.) are helpful both scientifically and technically in preparing for stellar observations. This paper summarizes the results from the main previous experiments (ACRIM, SOUP, and IPHIR), and also give an initial technical report from the SXT instrument on board Yohkoh, launched in August 1991. The solar observations to date demonstrate the existence of several mechanisms for low–level variability: spots, faculae, the photospheric network, granulation, and p–mode oscillations. The observations of oscillations have been particularly helpful in setting limits on solar interior rotation. In addition to the solar processes, stars of other types may have different mechanisms of variability. These may include the analogues of coronal holes or solar flares, modes of oscillation not detected in the Sun, collisions with small bodies, duplicity, and probably mechanisms not invented yet but related in interesting ways to stellar convection and magnetism.
Two-Dimensional Helioseismic Inversions
Authors: Schou J. , Christensen-Dalsgaard J. , Thompson M.J. 
Published: July 2016

We present results of investigations of different inversion methods for inferring from helioseismic observations the rotation rate in the solar interior as a function of radius and latitude, using a mode set similar to that which is expected from the GONG network.The rotation of a star perturbs the frequency wnlm of a normal mode bywhere n, l and m are the mode ‘quantum’ numbers, θ the colatitude, Ω the rotation rate and Knlm a known function. Until now the observations have not been in terms of individual Δwnlm ’s; rather, coefficients ai(n,l) of a parametrization of the m-dependence of Δwnlm have been given. By representing the latitudinal dependence of the rotation rate in terms of an expansion in cos θ, an inversion of the ai, can be carried out as a series of 1-dimensional inversions. Such inversions have been dubbed “1.5-dimensional”. Our present implementation of a 1.5D procedure follows Schou et al. (1992), and uses a1, a3 and a5.