bluuebunny/crossref_metadata_2025 huggingface dataset:
Globular Cluster Distances from the RR Lyrae Log (Period) – Infrared Magnitude Relation
Authors: Longmore A.J. , Dixon R. , Skillen I. , Jameson R.F. , Fernley J.A.
Published: July 2016

The log (Period) – infrared (2.2 micron) magnitude relationship has been measured for 7 clusters (M3, M4, M5, M15, M107, ω Cen and NGC 5466). For the clusters where there are several observations for each of the variables, enabling a good mean magnitude to be derived, there is no evidence for scatter in the relation outside observational error. This conclusion applies also to ω Cen, even though the variables observed covered a range of metallicity. It is argued that very accurate relative distances can be obtained which are insensitive to reddening errors and the effects of metallicity. Any mass difference between variables in different clusters may still introduce uncertainties in the relative distances. Recent Baade-Wesselink results by Fernley et al. have been used as an absolute calibration, including a small residual correction for metallicity effects. On this scale, the mean distance modulus for 6 of the clusters (excluding NGC5466) is essentially the same as that derived by Buonanno, Corsi and Fusi-Pecci (preprint) using a combination of horizontal branch magnitudes and main sequence fitting. However, individual distance moduli differ by typically 0.09 magnitudes. There is no clear correlation of this residual with metallicity.
Integrated X-ray Surface Brightnesses of Supemova Remnants and Comparison with Radio and Infrared Values
Authors: Dickel John , Norton Lisa , Gensheimer Paul
Published: July 2016

A weak linear correlation is found between the x-ray and radio surface brightnesses of galactic supernova remnants. A flatter slope is found for the infrared-radio correlation.
An EXOSAT Observation of Spectral Variability From the RS CVn Binary AR LAC
Authors: White N.E. , Shaffer R.A. , Parmar A.N. , Horne K. , Culhane J.L.
Published: July 2016

The eclipsing RS CVn system AR Lac (G2IV+K0IV) has been observed continuously for one 2 day binary cycle with the EXOSAT observatory. Below 1 keV a factor of two intensity modulation is seen with a flat bottomed minimum around the time of primary eclipse and a shallow dip preceeding primary eclipse. Above 1 keV, where only emission with temperatures > 107 K would be detected, no orbital modulation or eclipse is seen. This suggests that the > 20 million degree emission comes from a large region, comparable in size to the binary seperation. The modulation in the < 1 keV lightcurve has been modelled by x2 fitting to X-ray bright spots and by using maximum entropy deconvolution. The lower temperature emission is found to orginate in compact regions with a pressure and temperature similar to that of the flaring sun.
X-ray Spectroscopy of the Ultra-soft Transient 4U1543-47
Authors: Woerd H. van der , White N.E. , Kahn S.M.
Published: July 2016

The X-ray transient 4U1543-47 was observed in 1983 by the EXOSAT observatory near the maximum of an outburst. The X-ray spectrum was measured using a gas scintillation proportional counter (GSPC) and a transmission grating spectrometer (TGS). Two emission line features are resolved. A broad (FWHM ~2.7 keV) line at 5.9 keV is detected in the GSPC, which we interprete as a redshifted and broadened iron Kα line. The Une broadening and redshift may arise from either Compton scattering in a cool plasma with small optical depth (τ ≈ 5), or from Doppler and relativistic effects in the vicinity of a compact object. The spectrum below 2 keV, obtained with the TGS, shows evidence for a broad emission line feature at 0.74 keV, which may be an iron L-transition complex. However, we find that such an emission feature could be an artifact caused by an anomalously low interstellar absorption by neutral Oxygen. The continuum emission is extremely soft and is well described by an unsaturated Comptonized spectrum from a very cool plasma (kT = 0.84 keV) with large scattering depth (τ ≈ 27). The continuum spectrum is strikingly similar to that of black hole candidate LMC X-3.
Clusters of Galaxies and the Hot Intracluster Medium
Authors: Jones C. , Forman W. , David L.
Published: July 2016

The luminous material in clusters of galaxies falls primarily into two forms — the visible galaxies and the X-ray emitting intracluster medium. The hot intracluster medium is the major observed baryonic component of clusters with a mass equal to or greater than that of the stellar matter. In this paper we discuss changes in the efficiency of galaxy formation for different clusters and the origin of the intracluster medium.
The Thermal History and Structure of Cometary Nuclei
Authors: Rickman Hans
Published: July 2016

Cometary nuclei are often considered to be the most primitive bodies of the solar system. Thus it is particularly important to find out what structural changes may have been brought about as a result of their thermal evolution. Is there reason to believe that the bulk composition of the nucleus of a present-day short-period comet may differ from that of the original planetesimal in the solar nebula? Apart from the development of a non-volatile surface layer (‘dust mantle’), what further depth-dependent differentiation can we expect in such a nucleus? These are the ultimate questions addressed in this paper, and attention is focused on the two most active stages of thermal evolution: the early planetesimal stage with internal heating basically due to radioactive decay, and the recent or present cometary phase with strong external heating due to insolation of the surface.
Physical Properties of Cometary Dust
Authors: McDonnell J.A.M. , Lamy P.L. , Pankiewicz G.S.
Published: July 2016

Prior to the 1986 apparition of comet Halley, all attempts to determine the physical properties of cometary dust were limited to remote observations and the analysis of various particles captured by the Earth’s atmosphere. The in situ measurements made by the three spacecraft that passed within 10,000 km of the nucleus provided the first opportunity to investigate both the full size-range of particles and the complete process of dust production. Information on composition is derived through mass spectra and the scattering and emission of light from the grains, whilst the dynamics of the dust coma can be modeled from the three separate sets of measurements made over a period of eight days.
Chemical Properties of Cometary Dust and A Note on Carbon Isotopes
Authors: Jessberger Elmar K. , Kissel Jochen
Published: July 2016

On board the space probes Giotto and VEGAs and 2, which were sent through the coma of comet Halley, were the mass spectrometers PIA and PUMAs 1 and 2 for the in situ analysis of cometary dust. This paper summarizes the results obtained up to now, about four years after the flybys. It is sought to make the reader aware of the significance, but also of the limitations, of these unprecedented data gathered within a few hundred seconds with an innovative instrument about 1.5 x 108 km away from Earth. The first part of this paper shows how the bulk properties of the dust are derived—the main constituents CHON and silicates, the core-mantle structure, the molecular composition of the organic component, the average composition of the dust and of the whole comet, and the gas/dust ratio. The second part reviews what can safely be said about the properties of the individual grains—their similarity to a certain class of interplanetary dust particles and their distinction from others, and their density and masses. The final part of this paper shows that some cometary grains contain isotopically ultra-light carbon (12C/13C up to 5000), a finding that is significantly substantiated by reports of similar carbon isotopic composition in meteoritic graphite.
Hardware considerations for high-dynamic-range imaging
Authors: Bagri D.S. , Thompson A.R.
Published: July 2016

The dynamic range of an image obtained using an interferometer array depends on the (interferometer) gain closure errors. This paper discusses hardware imperfections which cause closure errors and how these errors can be minimised.
Multi-Frequency Synthesis
Authors: Conway J. E.
Published: July 2016

A method of improving image fidelity by using observations at multiple frequencies is described. We discuss the power and possible limitations of the technique. Results of narrow frequency range observations with MERLIN and global VLBI are presented. We conclude with a consideration of the possible future impact of this technique.
Linear polarization Sensitive VLBI
Authors: Roberts David H. , Brown Leslie F. , Wardle John F. C.
Published: July 2016

We describe the techniques currently used to produce linear polarization sensitive radio images at milliarcsecond resolution, and briefly discuss what will be possible in the next few years.
Global Fringe Fitting applied to Mk3 VLBI data
Authors: Bååth Lars B.
Published: July 2016

A system has been developed where data from a Mk3 VLBI processor can be read into the AlPS-package. Multiband and singleband delays can then be fitted globally by station. The technique has been used to phaserefence a background quasar to two radiogalaxies in the Abell cluster A2634.
Giant Metrewave Radio Telescope (GMRT)
Authors: Swarup Govind
Published: July 2016

The Giant Metrewave Radio Telescope (GMRT) is being set up near Pune in India consisting of 30 numbers of 45-m diameter parabolic dishes. Twelve of these are being placed in a central array, about 1 × 1 km2 in size, and the remaining eighteen along three 14-km long arms forming a Y-shaped array. GMRT will operate at six frequency bands near 38, 153, 233, 327, 611 and 1420 MHz. It is expected to be completed progressively by 1993, and will be the world’s largest radio telescope operating at metre and decimetre wavelengths.
The Very Long Baseline Array
Authors: Napier Peter J.
Published: July 2016

The Very Long Baseline Array, currently under construction, is a dedicated VLBI array consisting of ten 25m diameter antennas and a 20 station correlator. The key design features that make it a flexible, general purpose instrument are reviewed and some details are provided of the array layout, frequency coverage and sensitivity.
Supergiant Variables: Recent Observational Results
Authors: Percy J. R.
Published: July 2016

Recent observations of several types of supergiant variable stars are reviewed: massive blue, yellow and red supergiants; classical and population II Cepheids; RV Tauri stars; yellow semi-regular (SRd) variables, including UU Herculis stars; and R Coronae Borealis stars. The emphasis is on non-linear aspects such as: amplitude and shape of the light and velocity curves; multiperiodicity, irregularity and chaos; long-term changes in period and amplitude; episodic and continuous mass loss.
Variability in Active Galactic Nuclei
Authors: Matsuoka M.
Published: July 2016

AGN (Active Galactic Nuclei) have their profound time variability over a wide range of time scales. Although many results of AGN variability have been provided from wide band wavelength observations, I would like to concentrate the recent problems concerning a nearby region of their central engine based on the X-ray observations which are most efficient to investigate this region. In this paper we will investigate mainly the result of Seyfert galaxies which would be generalized to other AGN.
The Coupling Coefficients of Pulsation for Radiative Stellar Models
Authors: Yamakawa F. , Ishida T. , Takeuti M.
Published: July 2016

The second order theory of coupling is discussed regarding the radial pulsation of stellar models which are constructed ignoring convection. The formula including the nonadiabatic effect is presented. Numerical values given for model classical cepheids are considerably greater than the adiabatic values.
The Role of Convection in Reducing Nonadiabaticity and Mode Coupling in Cepheids
Authors: Zalewski J.
Published: July 2016

The effect of convection on the strength of coupling is examined. It is found that in Cepheid models the inclusion of convection smooths the sharp peak of entropy perturbation in the ionization region and reduces significantly the coupling.
Radiation Chemistry Approach to Cometary Chemistry
Authors: Ramos-Bernal Sergio , Negrón-Mendoza Alicia
Published: July 2016

The chemistry of comets is analyzed in the light of radiolytic processes occurring in the life-time of the comet due to its interaction with radiation. A simple model of a cometary nucleus is carried out at the laboratory which simulates as a first approximation the behavior of the organics in the comet. Most of the results obtained confirm that the parent molecules of the observed ones can be deduced from these simple simulated experiments. A variety of molecules were obtained (amino acids, carboxylic acids, gaseous products, etc.), even in frozen solutions the formation of oligomers was observed. The simplified mixture consisted of five compounds in a proportion in which they appear in a dense interstellar cloud (HCN/CH3OH/CH3CN/C2H5CN/HCOOH = 1:0.6:0.2:0.1:0.05). The total amount was adjusted to correspond to a C/N ratio 1.8. At this end, radiation chemistry can be a very precise and useful tool to simulate the evolution of organic molecules exposed to high energy radiation, as cosmic rays, during the life time of a comet.
The Impacts of D/Shoemaker-Levy 9 and Bioastronomy
Authors: A’Hearn Michael F.
Published: July 2016

The impacts of comet D/Shoemaker-Levy 9 into Jupiter provided the first chance to actually observe the effects which may be important in causing mass extinctions. The widely predicted global deposition of dust, leading to the phenomena associated with «nuclear winter», was readily observed, although Jupiter’s internal heat source causes a different response deep in the atmosphere than occurs on Earth. Less widely anticipated, despite recognition that global wildfires occurred during the K-T event on Earth, was the fact that material ejected above the stratosphere fell back onto the stratosphere producing a major heat pulse over a scale of 104km, by far the most easily and widely observed phenomenon during the impacts.
Accretion of the outer Planets and its Influence on the Surface Impact Process of the Terrestrial Planets
Authors: Fernández Julio A. , Ip Wing-H.
Published: July 2016

We study numerically the scattering of residual icy planetesimals towards the terrestrial planets zone during the accumulation of proto-Uranus and proto-Neptune. Our results show that an amount of icy material of severalM⊕(Earth mass) could have reached the terrestrial planets zone in a time scale of a few 108years. An already-formed Earth would have received an amount of about 3 × 1022kg of volatiles (this is about 20 times the amount of water contained in the oceans). Mars would have experienced a similar large volatile injection of about 5 × 1021kg. Yet, it is possible that part of the material injected by the accreting outer planets arrived to the inner planetary region before the terrestrial planets finished to sweep all the massive planetoids of their influence zones. If this was the case, the accreted volatile material would have subsequently been lost in megaimpacts. Moreover, massive icy planetesimals impacting at velocities much greater than the escape velocity might have led to a net erosion of volatile material, rather than accretion. Our numerical results show that the outer planets could have grown to sizes comparable to their current ones in time scales of a few 108years. The tail of residual material injected in the terrestrial planets zone lasted for several 108years, so it might have greatly contributed to the heavy bombardment of the Earth during the period 4.4-3.8 Gyr (before present). The material coming from the outer planetary region might have played a pivotal role in the development of the early atmosphere and life on Earth, though how much volatile material was retained is still an open question whose answer depends on several uncertain parameters.
The Infancy of Solar-Type Stars and its Relevance for the Origin of Life
Authors: Montmerle Thierry
Published: July 2016

For life to develop, planets are a necessary condition. Likewise, for planets to form, stars must be surrounded by circumstellar disks, at least some time during their pre-main sequence evolution. Much progress has been made recently in the study of young solar-like stars. In the optical domain, these stars are known as «T Tauri stars». A significant number show IR excess, and other phenomena indirectly suggesting the presence of circumstellar disks. The current wisdom is that there is an evolutionary sequence from protostars to T Tauri stars. This sequence is characterized by the initial presence of disks, with lifetimes ~ 1-10 Myr after the intial collapse of a dense envelope having given birth to a star. While they are present, about 30% of the disks have masses larger than the minimum solar nebula. Their disappearance may correspond to the growth of dust grains, followed by planetesimal and planet formation, but this is not yet demonstrated.
Detection and Characterization of earth-like Planets
Authors: Mariotti Jean Marie , Léger Alain , Mennesson Bertrand , Ollivier Marc
Published: July 2016

Indirect methods of detection of exo-planets (by radial velocity, astrometry, occultations,...) have revealed recently the first cases of exo-planets, and will in the near future expand our knowledge of these systems. They will provide statistical informations on the dynamical parameters: semi-major axis, eccentricities, inclinations,... But the physical nature of these planets will remain mostly unknown. Only for the larger ones (exo-Jupiters), an estimate of the mass will be accessible. To characterize in more details Earth-like exo-planets, direct detection (i.e., direct observation of photons from the planet) is required. This is a much more challenging observational program. The exo-planets are extremely faint with respect to their star: the contrast ratio is about 10−10at visible wavelengths. Also the angular size of the apparent orbit is small, typically 0.1 second of arc. While the first point calls for observations in the infrared (where the contrast goes up to 10−7) and with a coronograph, the latter implies using an interferometer. Several space projects combining these techniques have been recently proposed. They aim at surveying a few hundreds of nearby single solar-like stars in search for Earth-like planets, and at performing a low resolution spectroscopic analysis of their infrared emission in order to reveal the presence in the atmosphere of the planet of CO H2O and O3. The latter is a good tracer of the presence of oxygen which could be, like on our Earth, released by biological activity. Although extremely ambitious, these projects could be realized using space technology either already available or in development for others missions. They could be built and launched during the first decades on the next century.
The Origin of Biological Structures: Information Theory and the Creation of Order. Some New Insights
Authors: Bauer Carlo , Morelli Roberto , Spanedda Andrea , Paolini Moreno
Published: July 2016

Some concepts in thermodynamics and information theory are selected for their importance in the study of the spontaneous formation of structures in closed systems at constant temperature and pressure, and are reexamined in order to clarify the origin of the information needed and its dynamics. If there is a spontaneous creation of order in the system (ΔSsys< 0), a generously compensating increase of entropy in the environment (−ΔHsys/T) must be produced. The net decrease of total (or statistical) information (I = −S) in the universe is thus ΔGsys/T, otherwise stated as ΔGsys= −TΔSuniv. Remembering the existence of two types of entropy: geometric and energetic entropy, we explain the spontaneous formation of order with a draft of geometric information by the destruction of a suitable amount of energetic information. Thus the original chaos was a geometric chaos, but rich in energetic information. We propose finally that if there is a variation in the degrees of freedom in the system, due to some quantum restrictions, the ensuing variation of microscopic kinetic energy at constant T must be subtracted from both the enthalpic and entropic terms of ΔG, resulting in a restatement of the conditions of spontaneity which may even be very great. This (ΔEk)Tcorrective term is linked to the difference of heat capacities ΔCp in the process. Biochemical examples are given in the main text.
Homochirality as the Signature of Extra-Terrestrial Life
Authors: MacDermott Alexandra J. , Barron Laurence D. , Brack Andrè , Buhse Thomas , Cronin John R. , Drake Alex F. , Emery Roger J. , Gottarelli Giovanni , Greenberg J Mayo , Haberle Robert , Hegstrom Roger A. , Hobbs Kevin , Jones Brad T. , Kondepudi Dilip K. , Matthews Clifford N. , McKay Christopher P. , Moorbath Stephen , Raulin François , Sandford Michael C.W. , Schwartzman David W. , Thiemann Wolfram , Tranter George E. , Zarnecki John C.
Published: July 2016

The most characteristic hallmark of life is its homochirality: all biomolecules are usually of one hand, e.g. on Earth life uses only L-amino acids for protein synthesis and not their D mirror images. We therefore suggest that a search for extra-terrestrial life can be approached as a Search for Extra- Terrestrial Homochirality (SETH). The natural choice for a SETH instrument is optical rotation, and we describe a novel miniaturized space polarimeter, called the SETH Cigar, which could be used to detect optical rotation as the homochiral signature of life on other planets. Moving parts are avoided by replacing the normal rotating polarizer by multiple fixed polarizers at different angles as in the eye of the bee. We believe that homochirality may be found in the subsurface layers on Mars as a relic of extinct life, and on other solar system bodies as a sign of advanced pre-biotic chemistry. We discuss the chiral GC-MS planned for the Roland lander of the Rosetta mission to a comet and conclude with theories of the physical origin of homochirality.
Search for Life in the Universe with terrestrial microbes which Thrive under Extreme Conditions
Authors: Seckbach Joseph
Published: July 2016

It is reasonable to believe that life exists in many places throughout the Universe. Among the many billions of heavenly bodies, there are galaxies with millions of stars that may harbor lower or even higher forms of living organisms («life» in the meaning as we know it, e.g., carbon chemistry, liquid water etc.). This article lists Extremophiles and their various terrestrial enigmatic environments. We discuss the possibilities of Martian life and the origin and evolution of the eukaryotic cell and present some early protists and the Acidothermophilic algae. Among several microbes which can «fit» for extraterrestrial life, one eukaryotic algal group (Cyanidiophyceae) is treated here. The hot springCyanidium caldariummembers (there are three genera and several species in this family) thrive in excessive growth conditions like in acidic medium (close to IN H2SO4), under pure CO2atmosphere, in elevated temperature and auto or heterotrophic conditions. These hot spring unicellular algae do not require oxygen for such conditions of growth. Studies have shown that they present one of the earliest and simplest eukaryotic algae. Also, these microbes may be candidates for existing on planets with similar ecological conditions which might support life forms.
On the Existence of Stable Isolated Ecosystems outside the Earth
Authors: Benci Vieri , Galleni Lodovico , Santini Francesco
Published: July 2016

The planetary biosphere can easily be recognised because, according to the British scientist James Lovelock, living beings maintain the atmosphere of a planet far from chemical equilibrium. According to this idea it is thought that within the solar system there is no life outside the planet Earth. But this is true if we suppose that all the ecosystems are interconnected and easily detectable, because their presence would have effects at a planetary level. After the discovery since the end of the seventies of a series of ecosystems that do not have their source of energy in solar light and which are more or less isolated from other ecosystems is it possible to hypothesize the existence of biospheres being smaller than the planetary biosphere?
Non-Repeatable Seti Signals due to Gravity-Plasma Lenses of Stars
Authors: Eshleman Von R.
Published: July 2016

It is possible that signals from other technological societies have been received at radio listening sites on Earth, but their artifactual nature was not recognized. Such unrecognized SETI detections could come about if the amplitudes of the signals were above receiver thresholds only because of strong focusing by the compound gravity-plasma lens of a star. Variations in time and space of the plasma envelope of the star, and the temporary geometry of a star being situated directly on the line between Earth and the source, results in lensed signals that may never be repeated. Perhaps the only hope of recognizing a SETI source by means of transitory lensing rests with the attainment of a detailed understanding of the characteristics of the gravity-plasma lenses of stars. These lenses produce extended focal surfaces, a semi-infinite focal line, and a single point double-caustic focus, all of which vary in position and strength with the wavelength of the radiation. If the direction to a SETI source were to be determined, it might be possible to maintain the connection by use of spacecraft sent far from the sun so as to employ its gravity-plasma lens.
On a Broader Concept of Circumstellar Habitable Zones
Authors: Illés-Almár Erzsebet , Almár Ivan , Bérczi Szaniszlo , Lukács Bela
Published: July 2016

We suggest the possibility of a broader circumstellar habitable zone than considered so far. The factors taken into account – in addition to greenhouse effect – are tidal heating, and the role of ammonia (A) as a possible solvent instead of water (W) for biogenic materials. These factors can push the outer limit of the circumstellar habitable zones even further from their central stars.
δ Sct-Type Pulsators in Eclipsing Binary Systems: the Case of RZ Cas
Authors: Rodríguez E. , Costa V. , López-González M.J. , García J.M. , Kim S.L. , Lee J.W. , Yoon J.H. , Hintz E. , Mkrtichian D.E. , Gamarova A.Y. , Kusakin A.V.
Published: July 2016

RZ Cas is an Algol-type eclipsing binary system where the primary component was recently discovered as a δ Set pulsator. A three-continent multisite photometric campaign was carried out during 1999. Preliminary results are reported here indicating a semi-detached system where the secondary fills its Roche lobe. The light curves also suggest a hot spot on the surface of the primary component as a consequence of the impact of the mass stream from the secondary. The pulsational behaviour can be well described with only one frequency.
The Carina Dwarf Galaxy Variable Star Population
Authors: Ripepi V. , Dall’Ora M. , Pulone L. , Castellani M. , Corsi C. , Monelli M. , Bono G. , Brocato E. , Caputo F. , Castellani V. , Marconi M. , Nonino M. , Smith H. , Walker A.R.
Published: July 2016

We present some preliminary results based on new observations of the variable stars belonging to the Carina Dwarf Galaxy (DG). Photometric data were collected with the two wide field imagers available at ESO (WFI@2.2.) and CTIO (4m prime focus).
Search for New γ Doradus Variable Stars in Open Clusters: Praesepe and α Persei
Authors: Martín S. , Rodríguez E.
Published: July 2016

Photometric observations of A-F stars in the uvbyβ system have been performed in order to detect γ Doradus variables in open clusters of different ages. In the clusters Praesepe and α Per, several stars show some type of variability but only three of them, KW370 (Praesepe) and HE104 and HE876 (α Per), can be classified as γ Doradus-type pulsators.
WWW Archive of Fourier Coefficients
Authors: Morgan S.
Published: July 2016

Fourier coefficients are a valuable tool in the study of a wide variety of pulsating stars. They can be used to derive various physical parameters, including mass, luminosity, metallicity and effective temperature and are frequently used to discriminate between different pulsation modes. With the increase in large-scale surveys and the availability of data on the Internet, the number of Fourier coefficients available for study has expanded greatly and it is difficult to find all current data for individual stars or a subset of stars. To assist others in obtaining and making use of Fourier coefficients, an archive of published values of Fourier coefficients has been set up. Users can search for data on individual stars or for a range of parameters. Several Java programs are used to display the data in a variety of ways. The archive is located at the Web site http://www.earth.uni.edu/fourier/.
Primary Observational Distributions of δ Scuti Variables
Authors: Rodríguez E. , Breger M.
Published: July 2016

The distribution of the known δ Scuti-type variables (R00 catalogue, Rodríguez et al., 2000) is analysed on the basis of some primary observational properties such as visual amplitude, period, visual magnitude and rotational velocities. The present distributions are also compared with those resulting from the earlier catalogue by Rodríguez et al. (1994, R94). The contributions from the Hipparcos, OGLE and MACHO long-term monitoring projects are also discussed. These contributions are quite different in the N-ΔV and N-V diagrams, in the sense that the variables discovered by the Hipparcos satellite are much brighter and with shorter periods than those discovered by the OGLE and MACHO projects.

Concerning the N-ΔV diagram, we find that the gap, which was evident in the R94 catalogue for variables with visual amplitudes between 0.m1 to 0.m3, has disappeared. Thus, it seems that there is not a strict separation in two groups relative to the amplitude (low amplitude for variables with ΔV<0.m1 and high amplitude for variables with ΔV>0.m3) for the δ Scuti-type pulsatore.
Multiperiodicity in the Delta Scuti Star HR 4047
Authors: Rolland A. , Rodríguez E. , Costa V. , Olivares I. , García-Pelayo J.M. , de Coca P. López , Hobart M.A.
Published: July 2016

HR 4047 (HD 89343, EN UMa, V = 592, A7Vn) was found to be variable (Plume & Percy, 1988) with an amplitude of hundredths of a magnitude. Since then, this star has been observed by HIPPARCOS. Koen (2001), analysing those data, obtained two frequencies 6.43185 c d-1 and 4.31308 c d-1.

Our observations were made at the Observatorio de Sierra Nevada in Spain in 1997 and 1998 with the telescope of 0.9m. The comparisons stars for 1997 were C1 = HD 88983 (V = 577, A8III) and C2 = HD 88815 (V = 642, F2V), while for 1998 we add the check star C3 = HD 90838 (V = 7.30, F2). The photometric data obtained were analyzed using the Fourier Transform method in the Strömgren v filter. The periodogram of the v band data is shown in Fig. 1. The periodogram presents six clear frequencies and after prewhitening these there is still more power, but the frequencies found are not consistent between the different bands. Applying these frequencies to the data of the 1997 and 1998 separately, we obtain the results shown in Table 1. Note that the amplitudes have changed from one year to another. The results of 1998 agree with the two frequencies found by Koen (2001). Fig. 1 shows the light curves of the observed data for both campaigns in the v filter. The points represent the observations while the solid lines represent the fit for the frequencies listed in Table 1. Further observations are needed to obtain a more detailed pulsational behaviour of this star.
Identifying Modes in a Pulsating sdB (EC 14026) Star
Authors: Reed M.D. ,   the Whole Earth Telescope Xcov 17 and 21 teams
Published: July 2016

We present a preliminary analysis of time series photometry on the pulsating subdwarf B star PG 1336-018 acquired as part of two Whole Earth Telescope runs. PG 1336-018 is a multi-mode pulsator with at least 15 periods centered around 175 seconds. It is also an HW Vir-type eclipsing binary with a period of 2.4 hours. Although over 20 pulsating subdwarf B stars have been discovered, only a few have resolved temporal spectra and still fewer have identified pulsation modes. We analyze features unique to the eclipsing binary system of PG 1336-018 as a means of identifying pulsation modes.
Seismic Constraint on the Plausible Explanations of the Metal Rich Feature of Planetary System Stars
Authors: Shibahashi H. , Watanabe S.
Published: July 2016

From Spectroscopic observations showing that the parent stars of planetary systems are metal rich, it is suspected that this feature results from the accompanying planetary system. With the rich helioseismic data so far obtained, we determine the metal abundance distribution in the solar interior with respect to the distance from the center. This result gives constraints on the possible explanations about the metal rich feature of the stars accompanied by a planetary system.
Criteria of Classification of Long Period Variables Based on their Light Curve Changes
Authors: Marsakova V.I.
Published: July 2016

Some numerical parameters of long-term changes of light curves in Long Period Variables (LPVs) are obtained. Results of analysis of the sample of 53 LPVs and classification of these stars are discussed.
Wavelet Analysis of the RV Tauri Star U Mon
Authors: McSaveney J.A. , Cottrell P.L. , Pollard K.R. , Mattei J.A.
Published: July 2016

Wavelet analysis has been performed on the American Association of Variable Star Observers (AAVSO) visual estimates of the RV Tauri star U Mon from 1961-2000 using the AAVSO WWZ wavelet analysis program. Periods of 46.07, 92.40 and 2498 days are present but the 92 day period is not always detectable. A constant ratio between the amplitudes of the 46 and 92 day periods is found during one single long-term deep minimum but not another.
Constraints on 12C(α,γ)16O from White Dwarf Seismology
Authors: Metcalfe T.S. , Salaris M. , Winget D.E.
Published: July 2016

For many years, astronomers have promised that the study of pulsating white dwarfs would ultimately lead to useful information about the physics of matter under extreme conditions of temperature and pressure. We can now make good on that promise. Using observational data from the Whole Earth Telescope and a new analysis method employing a genetic algorithm, we empirically determine the central oxygen abundance of the helium-atmosphere variable white dwarf GD 358. We use this value, combined with detailed evolutionary calculations of the internal chemical profiles, to place constraints on the 12C(α, γ)16O nuclear reaction cross-section.
Energy Distributions and Fundamental Parameters of 6 A Stars
Authors: Monier R.
Published: July 2016

The energy distributions (EDs) of 6 peculiar (3 Aps and 3 λ Bootis) stars are presented from 1200Ȧ up to about 12000Ȧ. For those stars having infrared photometry, the integrated flux from 1200& to 22000Å has been calculated and the Infrared Flux Method (IRFM, Blackwell and Shallis, 1977) applied to derive effective temperatures and angular diameters. For all stars, the effective temperature Teff, the surface gravity logg and metallicity [M/H] were also derived by matching the EDs to a grid of model atmospheres. A chisquare techniques is used to sort out the best fit to the observed EDs.
Beryllium in Lithium–Deficient F Stars: Constraints on Stellar Evolution
Authors: Deliyannis Constantine P. , Pinsonneault M.H.
Published: July 2016

Standard stellar evolution predicts that F stars should retain their initial surface lithium (Li) abundance because their convection zones are too shallow to destroy it at their base. Yet, observations reveal a severe Li depletion (the “Boesgaard Gap”), perhaps by as much as about two orders of magnitude, in a narrow Teff range. Several physical mechanisms, not usually included in stellar evolution calculations, have been proposed to account for this Li deficiency. These include diffusion, mass loss, meridional circulation, and rotationally-induced mixing driven by angular momentum loss. Identifying which of these (if any) might really be at work is not only of vital interest to stellar evolution, but may also have serious implications elsewhere (e.g. cosmology, Deliyannis et al. 1991). We bring attention to beryllium (Be) observations in F stars, which are crucial for discriminating between scenarios. Particularly important is the star 110 Her, which is depleted in Be by about a factor of 5 -10, but still has a detectable Li abundance (depleted by a factor of 100 - 200). Depleting surface Be without having depleted nearly all of the surface Li requires specific circumstances; we discuss how this depletion property severely constrains or eliminates most of the proposed mechanisms. One mechanism, rotationally-induced mixing, predicts relative depletions for these elements that agree well with what is observed.
Oxygen Abundances in LI-Depleted F-Type Stars
Authors: Lopez Ramon J. Garcia , Rebolo Rafael , Herrero Artemio , Beckman John E.
Published: July 2016

We have obtained the oxygen abundance in a sample of 44 F-type dwarfs in the Ursa Major group and the Hyades open cluster, using an NLTE analysis of the O I infrared triplet at λλ 7771-7775 Å. These clusters show the “lithium gap” in the F spectral range, and it has been suggested that if this phenomenon were due to microscopic diffusion, their Li-depleted stars could also show oxygen and/or nitrogen depletion. Our results here show a substantial measure of uniformity in the oxygen abundances. The data might indicate a very small dip (< 0.1 dex) in the O abundance for stars located in the Li gap. Microscopic diffusion seems to be the only known mechanism able to produce an oxygen dip. If this mechanism were responsible for the Li gap, it would have to account for a depletion of up to two orders of magnitude in Li and, at the same time, less than 0.1 dex in oxygen. We note that turbulent mixing could modify a microscopic diffusion pattern in order to yield the observed abundances of the two elements.
Evolution of massive stars: main sequence and close to it
Authors: Langer Norbert
Published: July 2016

We discuss the status of current models for the early evolutionary stages of stars in the initial mass range 10-40 M⊙. Effects of the pre-main sequence evolution, mass loss, internal mixing, and changes in atomic and nuclear data are outlined and confronted with several basic observational facts, which are unexplained by standard models. We conclude that especially internal mixing processes deserve much more attention in future investigations, and we show why convective mixing may be less efficient than generally assumed, but more mixing should be present in the radiative zones of at least a fraction of all massive stars.
About Seismological Properties of Intermediate Mass Stars
Authors: Audard N. , Provost J.
Published: July 2016

Stars more massive than about 1.2M⊙ are characterised by a convective core, which induces at its frontier a rapid variation of the sound speed and of the Brunt-Väissälä frequency, close to a discontinuity. We present preliminary results about the search of the signature this core could have on the p-mode spectra. For a set of frequencies of three stars of 1, 1.5 and 2 M⊙, we study in particular the small frequency separation Δν0,2, ~ νn,l, νn-1,l+2 for high order and low degree oscillation modes, which is particularly sensitive to the interior of stars. We underline characteristic behaviours of the 1.5 and 2 M⊙ stars, through the comparison between computed frequencies and their approximation obtained by asymptotic and polynomial fittings, and also through second order quantities relatively to the frequencies.
How May Seismological Measurements Constrain Parameters of Stellar Structure?
Authors: Brown Timothy M. , Christensen-Dalsgaard Jørgen , Mihalas Barbara W.
Published: July 2016

Pulsation frequency separations, combined with other observations, can constrain the structural parameters of Sun-like stars. As an example, we treat a hypothetical visual binary system resembling α Cen.
Dust Driven Winds from Pulsating Stars
Authors: Dorfi E.A. , Feuchtinger M.U. , Höfner S.
Published: July 2016

The cool extended atmospheres of late type giants are sites where dust formation takes place. Radiation pressure on the dust grains is an important force for driving the slow but massive winds observed in such objects. Existing calculations of dust driven stellar winds (e.g. Bowen 1988, Fleischer et al. 1991) suffer from the fact that they include approximations at various levels for different parts of the problem like the hydrodynamics or the dust formation. Furthermore they do not include time-dependent radiative transfer.

In order to overcome these insufficiencies we plan to calculate self-consistent models of dust driven winds with a full description of both the radiation hydrodynamics and the time-dependent dust formation. As a first step, however, we concentrate our investigations on the self-consistent description of the radiation hydrodynamics adopting only a simple description of the dust opacities.
Asteroseismology From The Ground
Authors: Frandsen S.
Published: July 2016

In stars which pulsate in more than one mode, be it acoustic or gravity modes, radial or non-radial, we have a chance to study the interior structure by use of seismic techniques. Generally the greater the number of modes observable the greater the chances will be to obtain valuable direct information about the stellar interior not accessible by any other technique.

The observational problem of acquiring high quality data divides the stars where seismic techniques can be applied into two groups: A group of stars with intensity amplitudes in the range of millimagnitudes and the stars with very small amplitudes around 10 μmagnitudes or less. The first group contains the white dwarfs, the rapidly oscillating Ap stars, the δ-Scuti stars and the β-Cephei stars. The modes are excited directly or indirectly by some form of к-mechanism due to an opacity source which vary from class to class. The second group is made up of stars with outer convective envelopes which generate acoustic noise that may excite resonant modes, often a very large number.

This paper is a discussion of the possibilities for observing these stars with ground based techniques, and also a statement about what can not be done from the ground.
The Space Bonus
Authors: Weiss Werner W.
Published: July 2016

We will discuss the opportunities opened by space experiments to make measurements that cannot - or only marginally - be made from ground.
The AFOE—A New Instrument for Asteroseismology
Authors: Noyes R.W. , Brown T.M. , Horner S. , Korzennik S. , Nisenson P.
Published: July 2016

We describe technical aspects and performance characteristics of an Advanced Fiber Optic Spectrograph (AFOE), planned for the Mt. Hopkins 1.5 m telescope for asteroseismology of sun-like stars.
SOHO: A Prisma Precursor
Authors: Lemaire P.
Published: July 2016

Probing the interior of the Sun, a slow rotator G2 V main sequence star, and connecting the atmospheric structure to inside phenomena is one of the objectives of the SOHO mission. An overview of the helioseismology and of the coronal instruments is given. It furnishes a guide line for missions that are dedicated to the probing of stellar interiors in using microvariability and activity as tracers, such as the PRISMA study.
Millimeter and Submillimeterwave Receivers
Authors: Phillips T.G.
Published: July 2016

Various types of receivers can be used for millimeter and submillimeterwave astronomy. The choices are amplifiers or mixer detectors. For the millimeter band, in the past, maser and paramp devices have been successfully used, but in the last few years HEMT amplifiers have proved to be the best option up to about 40 GHz, because they are inexpensive, quite low noise (about 1-2 K/GHz), stable and wideband. However, currently, above ~40 GHz the best performance is obtained from mixer receivers and this review will address that topic only. When used in either interferometers or in single dish spectroscopy, the receivers measure simultaneously the amplitude and phase of the astronomical signal and are therefore fundamentally limited by the quantum noise inherent in the measurement process, which increases linearly with frequency. A receiver which achieves a noise temperature within a factor of 10 of this limit is considered to be well optimized, so that the usual criterion for the noise temperature characterizing a single side-band receiver is that it should be ≲ 10hv/k or equivalently ≲ 0.5 K/GHz.
Signal Processing Developments for the OVRO Array
Authors: Padin Stephen , Soares Schubert F.
Published: July 2016

An optical fiber IF transmission and tracking delay system and a wideband continuum correlator have been developed for the Owens Valley (OVRO) Millimeter Array. The IF system processes two 1-2 GHz bands which are frequency multiplexed through an optical fiber link. This allows simultaneous dual wavelength observations in the 2.7 and 1.3-mm bands or dual polarization observations in either band.
10GHz Sky Survey Project, Waseda FFT Interferometer
Authors: Nakajima J. , Otobe E. , Asuma K. , Daishido T.
Published: July 2016

Large-field radio interferometer at 10.65GHz have been developed to search for transient radio objects such as radio supernovae and radio bursts in stellar systems (Daishido et al. 1984). This is a spatial fast-fourier transform (FFT) type radio interferometer, being an equally-spaced, maximum redundant, two-dimensional (2D) array in an 8 × 8 configuration. Sixty-four identically-designed frontend elements are comprised of 2.4 m diameter cassegrain antennas and 200K HEMT receivers. These are steerable in elevetion and are fixed in azimuth. Although it is only partially operating, the completed system having 64 beams in the northern hemisphere is expected to provide maps having 0.1° angular resolution and a sensitivity of 50 mJy. The beams are formed by a newly-developed “Digital Lens” (complex amplitude equalizer + 2D FFT pipelined processor), with the array’s overall size being 20 × 20m.
Inclination of the HCO+ Torus in the NGC7027 Molecular Envelope
Authors: Yamamura Issei , Deguchi Shuji
Published: July 2016

We have determined the inclination of the axis of the HCO+torus in NGC 7027 to the line of sight, based on interferometrie observations and model calculations. We found that the deduced inclination of the HCO+ torus is misaligned with the inclination of the major axis of the ionized core. The result may imply the precession of the axis of the axisymmetric mass loss.
Disks Around T Tauri Stars
Authors: Sargent Anneila , Beckwith Steven
Published: July 2016

A variety of evidence suggests that at least 50% of T Tauri stars are surrounded by disks of gas and dust. Inferred disk properties are compatible with those generally attributed to the solar nebula, before the formation of planets. Millimeter-wave aperture synthesis mapping of molecular line and dust continuum emission from T Tauri stars provides a direct way to ascertain if disks are present. The technique enables detailed studies of disk temperature and density distributions, chemical properties and velocity fields. These results inform our understanding of both star formation and solar system evolution. We review the observations to date and discuss directions for future research.