bluuebunny/crossref_metadata_2025 huggingface dataset:
β Cephei and SPB stars in the Large Magellanic Cloud
Authors: Kołaczkowski Z. , Pigulski A. , Soszyński I. , Udalski A. , Szymański M. , Kubiak M. , Żebruń K. , Pietrzyński G. , Woźniak P.R. , Szewczyk O. , Wyrzykowski L. ,   the OGLE team
Published: July 2016

This is a progress report of the study of pulsating main-sequence stars in the LMC. Using the OGLE-II photometry supplemented by the MACHO photometry, we find 64 β Cephei stars in the LMC. Their periods are generally much longer than observed in stars of this type in the Galaxy (the median value is 0.27 d compared with 0.17 d in the Galaxy). In 20 stars with short periods attributable to the β Cephei-type instability, we also find modes with periods longer than ~0.4d. They are likely low-order g modes, which means that in these stars both kinds of variability, β Cephei and SPB, are observed. We also show examples of the multiperiodic SPB stars in the LMC, the first beyond our Galaxy.
Multisite spectroscopic and photometric observations of the pulsating sdB star PG 1605+072
Authors: O’Toole S.J. , Falter S. , Heber U. , Jeffery C.S. , Dreizier S. , Schuh S.L. ,   the MSST,   WET teams
Published: July 2016

We present the first results from the MultiSite Spectroscopic Telescope (MSST) observations of the sdBV star PG 1605+072. Pulsating sdB stars (V361 Hya stars) offer the chance to gain new insights into the formation and evolution of extreme Horizontal Branch stars using the tools of asteroseismology. PG 1605+072 is an outstanding object in its class, with the richest frequency spectrum, the longest periods, and the largest variations. The MSST campaign took place in 2002 May/June and we present here the massive data set, made up of 399 hr of photometry and 151 hr of spectroscopy. The overall aims of the project are to examine light/velocity amplitude ratios and phase differences, changes in equivalent width/line index, and λ-dependence of photometric amplitudes, and to use these properties for mode identification.
Direct detection of multiple periods in variable stars
Authors: Schoenaers C. , Cuypers J.
Published: July 2016

In some observational data sets of variable stars, multiperiodicity was not always recognized as such, and only became apparent when other observational material became available. In other cases, consecutive prewhitening starting with the obviously most significant frequency could lead to a wrong multifrequency solution. A few examples illustrating this are given. Searching directly for a multifrequency solution can often remedy this. Examples are given and the results of applying this technique to a large set of Hipparcos photometric data are communicated. An overview of the multiple periodicities found in β Cephei stars and SPB stars is reported in detail.
Interferometry of pulsating red giants from 0.65 to 3.5 microns
Authors: Ireland Michael , Tuthill Peter , Robertson Gordon , Bedding Timothy , Jacob Andrew , Monnier John , Danchi William
Published: July 2016

We present the results of two multi-wavelength studies of the angular diameters of the Mira-like stars ο Cet, W Hya and R Leo. The MAPPIT experiment was able to deliver diameters of these stars over a continuous wavelength region from 0.65 – 1 micron, while the Keck aperture-masking experiment was able to deliver diameters between 1.2 and 3.5 microns. Strong size variations with wavelength were recorded for all stars, and we discuss the implications for model atmospheres of these stars, and speculate on the necessity of including dust scattering in radiative transfer calculations.
Spectroscopic and photometric monitoring of southern post-AGB stars
Authors: Pooley D.J. , Cottrell P.L. , Pollard K.R. , Albrow M.D.
Published: July 2016

We present the results of contemporaneous photometric and spectroscopic monitoring of 20 post-AGB stars from Mt John University Observatory. Photometric measures were carried out using Johnson BV and Cousins RI filters, and the radial velocity measurements were acquired using spectra from an echelle spectrograph. Our programme spanned five years and the stars covered a range of spectral types from B to K in order to investigate the behaviour of post-AGB stars as they evolve away from the AGB. A number of stars proved to be variable in ways incompatible with post-AGB models and are reclassified. Periodicities are presented for a number of stars. Photometrically, HD 70379 was found to be pulsating in two modes with periods of 85 and 97 d. The radial velocities also varied, with the peak amplitude occurring when the photometry was also changing most. AI CMi presented three different types of spectra associated with photometric brightness, with varying strengths of narrow emission lines and molecular bandheads. The Hα profiles in almost all of the stars show evidence of emission which varies on time scales of days to months. The Na D line profiles are generally complex showing between 4 and 7 components due to both circumstellar and interstellar material.
Preliminary photometric study of a pulsating component in the eclipsing binary AB Per
Authors: Kim S.-L. , Kwon S.-G. , Lee D.J. , Lee C.-U. , Jin H. , Lee J.W.
Published: July 2016

We present new photometric results of the Algol-type semidetached eclipsing binary AB Per which was recently discovered to have a Delta Scuti pulsating component.
Nonlinear Radial Pulsations for Hot 20-M⊙ Models
Authors: Austin Benjamin A. , Guzik Joyce A. , Despain Kate M. , Templeton Matthew R.
Published: July 2016

We present the results of calculations that predict a radial pulsation instability region for hot 20-M⊙ stars within a narrow band around Teff = 22,000 K. These models have exhausted core hydrogen and are undergoing shell hydrogen burning, and have luminosities similar to the most massive β Cephei stars, but are slightly cooler and more evolved. The pulsations grow to a radial velocity amplitude of ~20 km s-1with a period of ~0.75 d. The amplitude increases for higher Z and lower Y models.
Mode Identification Using Photometry and Spectroscopy
Authors: De Ridder Joris , Aerts Conny , Dupret Marc-Antoine
Published: July 2016

We tested a stepwise approach to combine photometry and spectroscopy for mode identification where we first used the photometric amplitude ratios to restrict the degree l, then did a spectroscopic mode identification, and finally fitted the photometric amplitudes to restrict the list of candidate modes. For the spectroscopic mode identification, we implemented an efficient multi-mode moment method variant. We conclude that this new variant works well, but that the photometric amplitudes are too model sensitive to do any additional mode discrimination.
A Multi-Site Study of The Extreme Helium Star V2076 Oph
Authors: Wright D.J. , Cottrell P.L. , Lynas-Gray A.E. , Kilkenny D. , Shobbrook R.
Published: July 2016

Results from a three-site photometric and spectroscopic campaign of the hottest known extreme helium star V2076 Oph are presented. V2076 Oph shows complex multiple periods ranging from 0.3 to 3 d. However for the two campaigns in 1982 and 2000, no definitive single period can be identified in both datasets. Some of the extracted periods appear to be one-day aliases of others. The two most convincing periods are 0.52 d (22.28 mHz) and 2.75 d (4.21 mHz). The spectral lines identified in V2076 Oph were He I, He II, C II (emission), C III (both emission and absorption), C IV and N III. These lines showed profile variations that could not be linked to the photometric variations. Individual line velocities vary by species and ionisation level. The spectral lines vary in phase with an amplitude of ~25 kms−1 – the exception is the strong C III emission line at 5696 Å which shows different behaviour and has the lowest observed average velocity. This indicates that this emission line originates in the stellar wind rather than the photosphere.
A Possible Pulsation Mechanism for B Stars
Authors: Cox Arthur N.
Published: July 2016

Numerous possible mechanisms for the cause of B star radial and nonradial pulsations have been investigated in the last 30 years, but none have been clearly shown that they actually work. I briefly review these ideas, and then focus on a new idea about the driving due to time-dependent convection. I suggest that the outward going photons are absorbed by CNONe ions so that they capture the photon momentum. Previous investigations by many have shown that the acceleration of these ions can be two orders of magnitude larger than the local gravity. Levitation and concentration of these elements can occur between temperatures of 100,000K and 600,000K, the former temperature set by the complete ionization of the competing photon capturing helium, and the latter by the existence of simpler and less absorbing excited electron structures of the CNONe elements. Then I suggest that the concentration of these elements gives such a large local photon opacity that a thin convection zone exists down to maybe 10−5 of the mass of a typical B star. However, there would be no overlap with the outer surface convection zone that exists down to 50,000K in the outer 10−9 of the mass. The long time scale of the convection, or even its periodic turning on and off, gives a source of time-lagged luminosity which can be shown in some cases to drive mechanical pulsations in one or more modes. This envelope pulsation mechanism could apply equally to radial and low degree nonradial B star pulsations. It could also explain why not all B stars pulsate unless this unconventional composition structure occurs, disappears, and maybe reoccurs at some evolution stage.
Solar-Like Oscillations in Late Spectral Class Stars
Authors: Cox Arthur N. , Cahn Julius H.
Published: July 2016

There is interest in the minimum mass that can exhibit solar-like nonradial p-mode oscillations. Inspection of models for the solar case shows that there is approximately equal pulsational driving and damping due to the standard radiative effects. It is widely believed that coupling with surface convective elements occasionally tips the balance by strongly driving modes for a few days with the timescale of the convection at the top of the convection zone. Then both the convection and the radiative damping decrease the mode amplitude at the observed decay rate, (which is close to that calculated by Kidman and Cox (1984)) until the next convective reexcitation. Population I composition stellar models at 0.30, 0.45, and 0.75 solar mass have been constructed to see if the near equality of radiative driving and damping exists in them also. If so, then stars down to late spectral class could possibly display solar-like oscillations. We find that the convection timescale decreases to less than 100 seconds at 0.30 solar mass, but the near equality of radiative driving and damping occurs only down to about 0.5 solar mass. Thus there is the possibility that 100 to 300 second oscillations can be observed through most of the K spectral class, if the magnetic activity often seen in these stars does not overwhelm these small amplitude nonradial pulsations.
The Effects of Time-Dependent Convection on White Dwarf Radial Pulsations
Authors: Cox Arthur N. , Starrfield Sumner G.
Published: July 2016

After the discovery of pulsations in white dwarfs, predictions were made that these DA and the hotter DB stars should be pulsating in radial modes with periods of a few seconds or less. The mechanisms are the normal kappa and gamma effects that periodically block the flow of radiative luminosity and the blocking effect of the frozen-in convection at the bottom of the convection zone. Blue edges of the instability strips are between 12,000K and 13,000K for the DA and between 32,000K and 33,000K for the DB variables. Extensive observations, however, have shown that these stars pulsate only in the few-hundred-second nonradial modes and not in any few-second radial modes. We have added the time dependent convection model of Cox, Brownlee, and Eilers (1966) to our pulsation analyses to further investigate the white dwarf radial modes. Since the time scale of the convection is usually short compared to the radial pulsation periods, convection is able to carry luminosity rapidly enough to nullify the kappa and gamma effects periodic radiation blocking. We find that most, and maybe all, radial pulsations for 0.6 solar mass carbon-oxygen white dwarfs with thin hydrogen or helium surface layers are stabilized for both these DA and DB classes, now finally in agreement with observations.
Star Formation History of the Large Magellanic Cloud and Asymptotic Giant Branch Evolution Obtained from A Study of Long-Period Variables.
Authors: Hughes Shaun M.G. , Wood P.R.
Published: July 2016

A survey for Long-Period Variables has been made of the Bar and southern regions of the Large Magellanic Cloud. This has been combined with the results of Reid, Glass and Catchpole (1988) to present a global survey of the LMC. Periods are used as age indicators, giving the star formation history of the LMC from 1 to 10 Gyr, which indicates a major burst of star formation occurred approximately 4 Gyr ago.
Preliminary Results of A World Wide Photoelectric Campaign on δ Scuti
Authors: McNamara B. , Baggett S. , Pena J. , Thompson K. , Moore G. , Mantegazza L. , Sekiguchi K. , Candy M.
Published: July 2016

During June 17-27, 1987 observers in Mexico, Chile, Italy, South Africa, Australia and the United States monitored the light output of the prototype variable star, δ Scuti. The goal of the network was to obtain this star’s frequency spectrum. During the campaign, over 17,000 observations were obtained in the Stromgren b and y filters. A preliminary analysis has been performed and the frequencies listed in Table 1 have been tentatively identified.
The Importance of 3:1 Resonances in Stellar Pulsations
Authors: Moskalik Pawel , Buchler J. Robert
Published: July 2016

The 2:1 resonance between the fundamental and the second overtone modes has received a great deal of attention in the context of Cepheids. It was clearly shown that it causes the Hertzsprung bump progression and brings about the very characteristic observed variation of the Fourier phases with period (Buchler & Goupil, 1984, Ap.J.,279, 394; Klapp, Goupil & Buchler, 1985, Ap.J.,296, 514; Buchler & Kovacs, 1986, Ap.J.,303, 749).
Nonlinear RR Lyrae Models and Double Mode Pulsation
Authors: Ostlie Dale A.
Published: July 2016

Nonlinear models of RR Lyrae variables were calculated in the region of the HR diagram containing double mode pulsation. In all models Teff = 7000 K, the luminosity was 60 times solar, X = 0.70, Y = 0.299, and P1/P0 = 0.746, characteristic of double mode RR Lyrae variables in M15 (Cox, Hodson, and Clancy, 1983). Models of 0.65 solar masses were calculated using standard opacities and models of 0.75 solar masses were calculated with opacities artificially enhanced by a factor of 1.2 between log(T) = 5.2 and log(T) = 5.9 (Andreasen and Petersen, 1988).
Pulsations of Eötvös Spheres
Authors: Pesnell W. Dean
Published: July 2016

A derivation of Eötvös spheres and their pulsations is presented. These spheres incorporate a short range force in their gravitational potential. We used a Yukawa formulation to agree with other workers in this field, although a slightly different form would guarantee a gravitational force that is always attractive. Various relationships are obeyed by these obejcts, much like the polytropes to which they are similar. An attempt is made to test whether a short range force can resolve two outstanding problems in astrophysics. These are the Cepheid mass discrepancy and the frequencies of high-order solar p-modes. The disagreement in predicted and observed Cepheid masses cannot be explained by a repulsive force, but the solar p-modes have their asympotoic frequency decreased. Linear fits to sequences of models are presented for the radial eigenfrequencies and asymptotic frequencies for nonradial pulsations.
Tokamak Plasmas: A Paradigm for Coronal Equilibrium and Disequilibrium
Authors: Petrasso Richard D.
Published: July 2016

Tokamaks operate over a wide parameter space, allowing access to plasma conditions relevant to astrophysical plasmas. For high electron density discharges, for example, the central electron density and temperature are ~ 3 × 1014cm-3 and ~ 1.5 keV, and the central plasma region is in coronal equilibrium. Towards the edge of the plasma, however, many ion species will be far out of coronal equilibrium. A novel feature of the edge region is the seemingly contradictory property that it is, simultaneously, both a strongly recombining and a strongly ionizing plasma. Recent tokamak observations of strongly recombining plasmas also show that the G parameter (the ratio of forbidden plus intercombination to resonance lines) is larger by a factor of 3 than the ratio of statistical weights of the triplet-singlet series. Such observations can be of direct consequence to the interpretation of non-equilibrium astrophysical plasmas.
Merging of Iron Lines in Spectra of X-ray Burst Sources
Authors: Madej J.
Published: July 2016

Model atmospheres and synthetic spectra of neutron star of the effective temperature 107 K are presented. All the iron spectral features in the energy range 6-10 keV (uncorrected for redshift) are washed out by instrumental or intrinsic broadening, which leaves only a single line of the equivalent width comparable with the observations.
X-ray Spectral Synthesis in Hydrodynamic Flare Models
Authors: Serio S. , Antonucci E. , Dodero M.A. , Peres G. , Reale F.
Published: July 2016

Compact solar flares are triggered by sudden energy release in magnetically confined plasma. This class of flares is well suited to be studied with numerical hydrodynamic models. In particular, one can compare the evolution of observed and synthetic X-ray spectra, computed under various assumptions for the mechanism of impulsive energy deposition, to constrain theoretical models and their parameter space. We discuss recent results on solar flares along this line, non thermal to models of energy depositions by relativistic electron beams. We shall also discuss possible applications of X-ray spectral synthesis to stellar flares.
Evolution of the Coronae in Early-Type Galaxies
Authors: David L.P. , Forman W. , Jones C.
Published: July 2016

We present numerical simulations of the gaseous coronae in elliptical galaxies. These models consist of a modified King profile for the luminous portion of the galaxy and an isothermal dark halo. We include evolving stellar mass loss from planetary nebulae, and type I and II supernovae. Our models show that elliptical galaxies are likely to produce strong galactic winds at early times with x-ray luminosities of 1042 — 1044 ergs s-1 and temperatures of 10 keV. Galaxies can lose approximately 10-30% of their initial luminous mass in the wind which has an oxygen-to-iron ratio twice the solar value. Since elliptical galaxies are a principle component of rich clusters and compact groups this early wind phase affects the metallicity and temperature of the intracluster medium.
Innovative Techniques for X-ray Calorimetry
Authors: Labov S. , Silver E. , Landis D. , Madden N. , Goulding F. , Beeman J. , Haller E. , Rutledge J. , Bernstein G. , Timbie P.
Published: July 2016

In our x-ray calorimetry effort, we have developed several techniques which may be helpful to other groups working in this field. We are studying several different monolithic and composite calorimeter designs. In our readout configuration, the preamplifier circuit employs negative voltage feedback which allows us to accurately measure the temporal profile of the thermal pulse produced by an x-ray absorbed in a micro-calorimeter. Rise times of less than two microseconds have been observed in monolithic devices operating at .3 K. Furthermore, the feedback preamplifier can be configured for either positive or negative electro-thermal feedback. This preamplifier system is followed by an analog pulse shaping amplifier with a frequency response that can be adjusted to yield the maximum signal to noise ratio for a given thermal response of the calorimeter. In addition, we have developed several diagnostic procedures which have been useful in determining the operating and noise characteristics of our devices. These include an infrared light-emitting diode which flashes a discrete amount of energy on to the calorimeter, and a capacitively coupled test input to the preamplifier which allows us to directly determine the total noise in the thermal detection system. Finally, we are developing an adiabatic demagnetization refrigerator with a temperature control system that is designed to stabilize the 0.1 K cold stage to better than 8 μK. This is required for a resistive thermal detector with resolving power of 1000.
Stigmatic Spectroscopic Instruments for the Wavelength Range 30-300 Å With High Angular and Spectral Resolution Using Multi-layer Mirrors
Authors: Ragozin E.N.
Published: July 2016

A concept of stigmatic spectroscopic instruments for the range λ ~30-300 Å is presented, A parallel beam is dispersed by means of a plane diffraction grating at grazing incidence, whereas focusing of the XUV radiation is performed by a concave multilayer mirror at normal incidence. A spectroheliograph of the new type may have dispersion an order of magnitude higher than traditional Wadsworth-type instruments. The theoretical resolving power of a spectrograph of the new type is limited by apertures of the multilayer mirrors or by the total number of grooves of the grating and many reach (λ/δλ)theor ~ mN ~ 3.105 using presently available optical elements.
P/Halley, the Model Comet, in View of the Imaging Experiment Aboard the Vega Spacecraft
Authors: Szegő K.
Published: July 2016

In this paper, those results of the VEGA imaging experiments are summarized that probably have general validity for any comet. Shape, size, surface structure, jet activity, and rotation pattern are considered in this respect. It is pointed out that imaging data provide indispensable information for an understanding of cometary activity.
Plasma Processes in the Outer Coma
Authors: Galeev A. A.
Published: July 2016

Spacecraft encounters with comets Giacobini-Zinner and Halley revealed a great variety of collective plasma phenomena accompanying the interaction of the solar wind with comets. In this review, we discuss the theory and in situ measurements of the Alfvén wave turbulence and the solar wind loading by cometary ions, and the structure of the cometary bow shock.
Cryogenically-cooled, HEMT amplifiers and receivers in 1-50 GHz range: state-of-the-art
Authors: Pospieszalski Marian W.
Published: July 2016

A review of the recent developments in the design, construction and performance of cryogenicallycoolable, high-electron-mobility transistor (HEMT, MODFET) amplifiers and their application in compact cryogenic receivers for radio astronomy applications is presented.
IVS - a second generation space VLBI mission
Authors: Pilbratt Göran
Published: July 2016

The International VLBI Satellite is under assessment study by the European Space Agency and the USSR Academy of Sciences. The IVS mission is conceived as a second generation space VLBI mission with the goal of providing higher sensitivity, greater maximum resolution and a wider spectral coverage compared to the precursor missions and, in addition, some single-dish capability.
Some Highlights of Interferometry in early Radio Astronomy
Authors: Sullivan Woodruff T.
Published: July 2016

Two important episodes in the early development of interferometry in radio astronomy are traced in detail. The first is the use of the sea-cliff interferometer at the Radiophysics Laboratory in Sydney, first by Pawsey for solar observations and later by Bolton for radio star surveys. The second is the development of the Michelson interferometer and the phase switch by Ryle in Cambridge. This also was employed for important observations of the sun and radio stars.
The early technical development of the VLA
Authors: Swenson George W.
Published: July 2016

In the spring of 1964, having qualified for a sabbattical leave from the University of Illinois and having recently completed two years as Chairman of the Visiting Committee of the National Radio Astronomy Observatory, I inquired of the NRAO staff as to whether a desk and possibly some augmentation of my University half-salary might be available at Green Bank for the following academic year. Instead I was invited to join the staff as a fulltime employee and to take a coordinating role in the development of the “very large array” as Chairman of the Design Committee. The University granted me a year’s leave of absence which eventually stretched to four years.
Numerical Experiments with Low SNR data in Radio Interferometry
Authors: Wilkinson P.N. , Woodall P.
Published: July 2016

We outline the results of numerical experiments on low SNR interferometer data. We confirm several theoretical analyses of the effect of averaging on visibility amplitude and closure phase data. However the triple product method for estimating the closure phase, which is useful in optical interferometry, does not provide a significant improvement over existing practice in radio interferometry. We introduce a way of using the triple product to estimate visibility amplitudes from arrays dominated by a single large telescope.
VLBI phase-referencing for observations of weak radio sources
Authors: Lestrade J.-F
Published: July 2016

Phase-referencing is a technique used in VLBI to extend the signal coherence time from a few minutes to a few hours in order to enhance significantly its sensitivity. With this technique, VLBI observations of milliJansky radio sources can be conducted for high-accuracy differential astrometry as well as imaging. We describe the technique in some details and present, as an example, a submilliarcsecond differential astrometric experiment design to identify the star responsible for the weak radio emission in the binary system Algol.
Progress on Chinese VLBI network project
Authors: Shuhua Ye , Tongshan Wan , Zhihan Qian
Published: July 2016

The Chinese VLBI Network (CVN) project is supported by the Astronomy Committee, Chinese Academy of Sciences. At present, the CVN project consists of three dedicated VLBI stations, two part-time VLBI stations, and a data analysis center. The sites and equipment of the CVN stations are listed in Tables I and II, respectively. The current status of the CVN data analysis center will be described in the last section of this paper.
The AAVSO Database of Variable Star Observations
Authors: Percy J. R. , Mattei J. A.
Published: July 2016

The American Association of Variable Star Observers (AAVSO) is the largest organization of variable star observers in the world, with members in 42 countries. The purpose of the AAVSO is to coordinate variable star observing, done primarily by amateur astronomers, evaluate the accuracy of these observations, compile, process and publish them, and make them available to researchers and educators around the world. Over 6.5 million observations of variable stars have been complied since the AAVSO was founded in 1911. Those since about 1960 are in computerized form, and it is intended to have all observations in this form within the next year. About 250,000 observations are submitted to and archived by the AAVSO each year, over half of them from outside the USA. Most of the observations are visual, but there is also an active photoelectric program which concentrates on semi-regular and irregular stars such as small-amplitude red variables. In 1990, over 200 requests for AAVSO data and services were received from researchers and educators; this number has increased by a factor of 10 in the last two decades.
On the Observed Complexity of Chaotic Stellar Pulsation
Authors: Kolláth Z.
Published: July 2016

The existence of some variable stars producing very complicated light curves is well known. Theoretical calculations suggest that the irregular behaviour of the pulsation models in the RV Tauri and W Virginis regime is low dimensional is the result of period-doubling or tangent bifurcations (see e.g. Buchler and Kovács 1987, Kovács and Buchler 1988, Tanaka and Takeuti 1988).

The light variation of the RV Tauri star R Scuti covering 150 years was analyzed by Kolláth (1990). A striking similarity was found between the reconstructed attractor of the Rössler model and that of the light variation of R Scuti. This result confirms the theoretical prediction of the existence of chaos, but a discrepancy still exists between the theory and observation. We could not find evidence for low dimension (D = 2– 3). The analyses of other stars also show rather erratic behaviour (e.g. Cannizzo and Goodings 1988, Cannizzo et al. 1990). A possible answer for this discrepancy is the treatment of stochastic perturbations by convection (Perdang 1991).
The Effect of Convection in Nonlinear One-Zone Stellar Models
Authors: Saitou M.
Published: July 2016

We study the convective nonlinear one-zone models of the pulsating variable stars. In the small convective case, the solution shows chaotic behavior through the period doubling bifurcation as the temperature is lower although the temperature at which the chaos appears is lower than in the case of no convection. On the other hand, in the strong convective case, the solution only shows period-one limit cycle.
A Search for Extraterrestrial Eukaryotes: Biological and Planetary Science Aspects
Authors: Chela-Flores Julian
Published: July 2016

One pressing question in bioastronomy is to attempt to devise assays in the search for extraterrestrial eukaryotes (SETE). In the positive case of encountering a fossil of a certain microorganism, it is not yet clear how to identify it in an unequivocal manner, even if found arrested and preserved in the midst of biological activity, as in some known Archean sediments on Earth. On the other hand, for living microorganisms the present approach may have some advantages over the straightforward probe of the morphological features of the putative eukaryote, as we argue that we are not constrained to base identification on morphological properties, such as the presence of organelles, which are known to be missing in some higher taxa. We sketch a possible experimental set-up required for a robot to investigate whether eukaryogenesis has already taken place in Mars or Europa. Besides, we also discuss the biological and astronomical implications of a SETE program. Previous observation and theoretical work have suggested that underneath the ice crust of the Jovian satellite Europa there may be an ocean of liquid water. We therefore argue that as hot springs may be present at the bottom of that ocean, eukaryotes should be searched for, not only deep in the Martian permafrost, as discussed by others, but a SETE program should be extended to the aquatic environment of the Jovian satellite as well. Our current work emphasising gene silencing, may suggest how to decide on the degree evolution which microbiota may have reached in the Europa ocean, a topic which deserves our attention, as eukaryogenesis is the process which introduced the basic cellular plan of those Earth-bound organisms that have been raised to the level of intelligent beings. We make a specific suggestion for a robotic investigation of eukaryogenesis in solar system exploration.
The Ohio Seti Program and the Argus Telescope
Authors: Dixon Robert S.
Published: July 2016

The Ohio State SETI program has been in operation since 1974, making it the longest-running search. The Ohio State radio telescope is equivalent in size to a 175-foot circular dish. The latest and best all-sky meridian-transit survey is about 60% complete, searching in the Water Hole (1.4 to 1.7 GHz). Signals detected are automatically examined at greater resolution and then tracked for up to 1 hour. A dual-beam pattern-matching system is used for real-time signal detection and RFI rejection. A new 4 million channel receiver built at UC Berkeley is now being installed. A simultaneous broadband continuum survey at 1415 MHz is in progress, searching for natural radio sources that have changed since the previous OSU continuum survey was made 20 years ago. A new radio telescope called Argus is being designed that will look in all directions simultaneously, allow usage by everyone simultaneously, and have no moving or machined parts. It is a large timed array which is based on computers rather than steel. All possible beams are formed all the time, so there is no scanning or need to «point» the telescope. This approach has many advantages over dish-type telescopes, such as RFI rejection and retroactive observations. Ohio State University has decided to abandon its radio telescope at the end of 1997 and allow it to be torn down by land developers.
Twenty Years of Serendip, The Berkeley Seti Effort: Past Results and Future Plans
Authors: Bowyer Stuart , Werthimer Dan , Donnelly Charles , Cobb Jeff , Ng David , Lampton Michael
Published: July 2016

The Berkeley SETI effort has been ongoing for more than twenty years. During this period we have carried out extensive SETI searches, but of at least equal importance, we have been on the forefront of instrumentation development, the development of interference rejection and detection algorithms, and educational efforts. Our instrumentation has evolved from a 100 channel spectrometer (SERENDIP I) to our latest machine (SERENDIP IV) with 168 million channels. In addition to supporting our SETI work, our hardware has been used by NASA for RFI surveys and to check the Mars Survey relay transmitter. Our designs have influenced several of the major SETI hardware systems, and a SERENDIP III system is currently being used in the Ohio State SETI group. Our hardware has also been incorporated in pulsar instrumentation at NAIC (Arecibo), NRAO (Greenbank) and Bonn, Germany. We have just completed a 4 year search at the world’s largest radio telescope at Arecibo. We covered 93% of the observable sky at least once, and 44% of the sky at least 5 times, with a sensitivity of ~ 3 × l0−25Wm−2. We collected and analyzed information from over 1014spectral bins and logged and analyzed over 2 × 108signals of potential special interest. We have developed extensive analysis programs to identify and remove interference and to search for signal characteristics which are expected from an extraterrestrial signal. Our algorithms were successful in removing all but 0.01% of spurious RFI in the Arecibo data set. We have involved over 30 undergraduate and graduate students in our effort, and 5 Master's theses have been awarded for work on the SERENDIP project. Our next effort will use our SERENDIP IV hardware at Arecibo Observatory to carry out a 21 cm survey of the Arecibo sky.
The Berkeley Seti Program: Serendip IV Instrumentation
Authors: Werthimer Dan , Bowyer Stuart , Ng David , Donnelly Charles , Cobb Jeff , Lampton Michael , Airieau Sabine
Published: July 2016

The SERENDIP program is an ongoing search for narrow band radio signals from extraterrestrial civilizations. Each generation SERENDIP instrument has on average been about 35 times more powerful than its predecessor. In this paper we discuss the hardware design of the latest generation instrument, SERENDIP IV, which will be deployed in early 1997 for a 21 cm sky survey at the National Astronomy and Ionospheric Center’s 305 meter radio telescope in Arecibo, Puerto Rico. SERENDIP IV is a 167 million channel spectrum analyzer, covering a 100 Mhz bandwidth, with 0.6 Hz resolution and a 1.7 second integration time. SERENDIP IV’s modular design incorporates a bank of digital mixers and filters to separate the 100 MHz band into forty 2.5 MHz sub-bands. Each 2.5 MHz sub-band is further broken down into 0.6 Hz bins by means of a four million point fast Fourier transform. The resulting power spectra are analyzed by 40 high speed processors. Narrow band signals having power significantly above background noise levels are recorded along with telescope coordinates, time, and frequency. The data are sent in real time to Berkeley for analysis. SERENDIP IV hardware is also utilized by the Ohio State University SETI program and pulsar programs at Nancay Observatory (France), the US Naval Research Lab, the Effelsberg telescope (Germany), NRAO’s Greenbank Observatory and NAIC’s Arecibo Observatory.
A New Class of Seti Targets
Authors: Shostak G. Seth
Published: July 2016

A new class of SETI targets is proposed, consisting of stellar systems whose ecliptic planes coincide with our line-of-sight. The most favorable of these systems are moderately separated, edge-on binary stars with at least one solar-type component. Such targets maximize the likelihood that a transmitting civilization’s antennas are beamed in our direction, and therefore represent an improvement over current experiments by approximately 106per target. While few favorable systems are known, this is a consequence of historical selection effects in the observation of binaries. An estimate of their frequency shows that a thousand such systems exist within 1,200 ly of the Sun.
A New Major Seti Project Based on Project Serendip Data and 100,000 Personal Computers
Authors: Sullivan Woodruff T. , Werthimer Dan , Bowyer Stuart , Cobb Jeff , Gedye David , Anderson David
Published: July 2016

We are now developing an innovative SETI project, tentatively named seti@home, involving massively parallel computation on desktop computers scattered around the world. The public will be uniquely involved in a real scientific project. Individuals will download a Screensaver program that will not only provide the usual attractive graphics when their computer is idle, but will also perform sophisticated analysis of SETI data using the host computer. The data are tapped off Project Serendip IV’s receiver and SETI survey operating on the 305-meter diameter Arecibo radio telescope. We make a continuous tape-recording of a 2 MHz bandwidth signal centered on the 21 cm H I line. The data on these tapes are then preliminarily screened and parceled out by a server that supplies small chunks of data (50 sec of 20 kHz bandwidth, a total of 0.25 MB) over the Internet to clients possessing the screen-saver software. After the client computer has automatically analyzed a complete chunk of data (in a much more detailed manner than Serendip normally does) a report on the best candidate signals is sent back to the server, whereupon a new chunk of data is sent out. If 50,000-100,000 customers can be achieved, the computing power will be equivalent to a substantial fraction of a typical supercomputer, and seti@home will cover a comparable volume of parameter space to that of Serendip IV.
Internal Dynamics of Slowly Rotating Stars: the Effect of μ-Gradients on the Meridional Circulation
Authors: Théado S. , Vauclair S.
Published: July 2016

In slowly rotating stars, the coupling of helium settling and meridional circulation leads to a particular hydrodynamical process which was not introduced in previous computations of abundance variations. The μ-gradients induced by element settling can lead to a quasi-paralysis stage in which the efficiencies of both the meridional circulation and the microscopic diffusion are strongly reduced. Such an effect was studied in the eighties for nuclear-induced μ-gradients by Mestel et al., who called it “creeping paralysis”. Below convective zones, this process has important consequences. Here we discuss the case of the halo stars and the sun.
RR Lyrae Variables in Local Group Galaxies: M31
Authors: Clementini G. , Federici L. , Cacciari C. , Bellazzini M. , Corsi C. , Smith H.A.
Published: July 2016

Candidate RR Lyrae variables have been identified for the first time in four globular clusters of the Andromeda galaxy (M31). Using HST-WFPC2 archive observations we have found 2, 4, 11 and 8 RR Lyrae variables of both ab and c Bailey types in G11, G33, G64 and G322 (Sargent et al., 1977), respectively. These numbers are quite consistent with the horizontal branch morphology exhibited by the four clusters.
The Contribution of GEOS to the Study of Stellar Pulsations
Authors: Boninsegna R. , Vandenbroere J. ,   the GEOS team, Le Borgne J.F.
Published: July 2016

The GEOS, Groupe Européen d’Observation Stellaires, is composed of observers living in France, Italy, Spain, Belgium and Switzerland. The main purpose is to give amateur astronomers the opportunity of carrying out scientific analyses in specific fields. Further details can be found at the web site http://www.upv.es/geos/

In the past years, GEOS has approached the analysis of visual estimates of variable stars (Ralincourt et al., 1987) in an original manner, obtaining accurate light curves on red semiregulars. Moreover, the collaboration with teams of professional researchers allowed the group to obtain interesting results on the double-mode Cepheid EW Set (Figer et al., 1991), on the Be star OT Gem (Arellano Ferro et al., 1998) and on the eclipsing binary V753 Cyg (Beltraminelli et al., 2000). More recently, several GEOS members have started collecting a large sample of times of maximum brightness of RR Lyr stars in order to build-up a database as extensive as possible. Such a database is decribed below together with the results of a campaign on RR Lyr itself.
A Spectroscopic Search for Non-Radial Pulsations in Early B-Type Stars
Authors: Schrijvers C. , Telting J.H. , De Ridder J.
Published: July 2016

It is known that early-B type main-sequence stars can be unstable against pulsations induced by the κ mechanism. Traditionally, radial and low-degree non-radial β Cephei-like pulsations have been detected photometrically; nowadays radial, low-degree and intermediate-degree pulsations can be detected spectroscopically through line-profile variations (LPVs). Whereas most of the brightest early-B type stars have been photometrically monitored for variability (72 of the 541 O9.5-B3 III-V stars in the BSC are classified as β Cephei stars), a systematic LPV survey to look for pulsational behaviour was lacking. Here we present some preliminary results of the southern part of our Spectroscopic survey of early-B type stars. We have made a high spectral resolution survey of the Si III λ 4552, 4567, 4574 Å triplet in early-B type stars in order to look for LPVs due to non-radial pulsation (NRP). Our sample consists of 82 southern O9.5-B3 stars with spectral classes III-V, taken from the BSC; 27% of all O9.5-B2.5 III-V stars in the BSC were sampled. This sample is not fully representative for all nearby early-B stars, because we concentrated on stars with high rotational velocities, because many of the stars are members of the Sco-Cen associations, and because we focused on the β Cephei stars in the BSC. As much as 40% of the β Cephei stars in the BSC with v sin г ≥ 25 km s-1 were sampled. The observations were carried out with the ESO CAT telescope at resolution R∼65000. Our targets were observed during 6 runs in September 1995 – June 1998. Some stars were observed many times, but most targets were observed only once or twice.
Search for Nonradial Pulsations in the Be Star ω Ori during the MuSiCoS Campaign 1998
Authors: Neiner C. , Hubert A.-M. , Floquet M. , Henrichs H.F. ,   the MuSiCoS team
Published: July 2016

ω Ori is a rapidly rotating B2IIIe star with known spectral variability. We applied a frequency analysis to the MuSiCoS (MUlti Site Continuous Spectroscopy) campaign 1998-dataset to search for line-profile variations (Ipv). Variability was found in all studied spectral lines and interpreted as due to non-radial pulsations (NRP).
HR 4074: an Emission-Free NRP Twin of the Be Star 28 CMa
Authors: Štefl S. , Rivinius Th. , Baade D.
Published: July 2016

In spite of considerable progress in the investigation of rapid line-profile variations (lpv) of Be stars, at least two models still compete in the literature: the rotational modulation, assuming mostly corotating circumstellar structures (Balona, 2000), and nonradial pulsations (Maintz et al. and Rivinius et al., these proceedings). Attempts to explain the lpv of Be stars were often connected with the proto-typical star 28 (ω) CMa (HR 2749 = HD 56139, B2IV-Ve, v sin i = 80 km/s). Štefl et al. (1998) described variability in three line-profile components: in the narrow component of the line core, in the line core itself and in the wings. The Balmer emission of 28 CMa is variable and has always been observed to be at least moderate, mostly strong.

HR 4074 (HD 89890, B3 III, v sin i = 70 km/s) has a different history of its emission activity. From a single spectrogram taken in 1893, Pickering (1898) reported an emission in Hβ. Subsequent observations never confirmed this. If it was not mis-identified by Pickering, HR 4074 would be in the probably longest B-star phase known of any Be star. HR 4074 is very probably not an SPB star - the spectral type is too early, the rotational velocity too high and light variations too low for this classification. Baade (1984) detected rapid lpv with a period P ≈ 2.25 d. Our time series analysis of radial velocity (RV) variations, measured as line modes, and that of full profiles give P = (2.3179 ± 0.0008) d.
Spectroscopy of Rapidly Oscillating Ap Stars
Authors: Weiss W.W. , Ryabchikova T.A. , Savanov I. , Piskunov N. , Tsymbal V. , Mittermayer P. , Martinez P. , Kochukhov O. , Nesvacil N.
Published: July 2016

We identify Spectroscopic differences between roAp stars and Ap stars with no observational evidence for pulsation, but with otherwise similar Teff and log g values. These differences concern the abundance pattern, Hydrogen line profile anomalies, evidence for stratification, and effects of pulsation on spectral lines.
Seismic Tests of Theoretical Models of HR 1217
Authors: Cunha M.S. , Fernandes J.M.M.B. , Monteiro M.J.P.F.G.
Published: July 2016

A way in which we might learn about the physics of the interior of roAp stars is by studying their oscillations. To that aim we have initiated a study in order to investigate what additional constraints might be imposed to the physics of the interior of roAp stars from the study of their oscillation spectra. We have chosen to start this work by studying the well known multi-periodic roAp star HR 1217. The observed data used for HR1217 were L/L⊙=7.8±0.7 and Teff=7400±100 K, from Matthews et al. (1999), Zs=0.009 estimated from Ryabchikova et al. (1997), and Δv=67.91±0.12μHz from Kurtz et al. (1989).
Problems with the Pulsation Mode Selection Mechanism in the Lower Instability Strip (Observations and Theory)
Authors: Breger M. , Pamyatnykh A.A.
Published: July 2016

We examine the severe disagreement between the number of predicted and observed pulsation modes for δ Scuti stars. The selection of nonradial modes trapped in the outer envelope is considered on the basis of kinetic energy arguments. The trapped l = 1 modes for the star 4 CVn are in good, but not perfect agreement with the observations. The trapping of the l = 2 modes is weaker, so that this simple rule of mode selection may apply to l = 1, and possibly not to l = 2 modes.
P-Mode Observations on α Cen A with CORALIE
Authors: Carrier F. , Bouchy F. , Meynet G. , Maeder A. , Provost J. , Berthomieu G. , Morel P. , Thévenin F.
Published: July 2016

We have made a clear detection of p-mode oscillations in the G2V star α Cen A with the CORALIE spectrograph. The power spectrum clearly shows several identifiable peaks between 1.8 and 2.9 mHz. A preliminary astrophysical interpretation of these p-modes is presented.
Periodic and Nonperiodic Phenomena in AGB Stars
Authors: Lebzelter T. , Hinkle K.H.
Published: July 2016

We discuss velocity variations in different layers of an AGB star’s atmosphere. Periodic and nonperiodic changes are observed. From a large sample of data we derive mean velocity curves for miras and semiregular variables.