bluuebunny/crossref_metadata_2025 huggingface dataset:
Galaxy Mass Distribution from Galaxy-Galaxy Gravitational Lensing
Authors: Anthony Tyson J.
Published: June 2019

The average gravitational lens distortion of background galaxy images by foreground galaxies is an independent, non-kinematical measurement of galaxy mass distribution M(r)/r (Tyson, et al. 1984). The upper limit we obtained for the equivalent circular velocity, while small compared with some heavy halo models, is consistent with dynamical estimates for samples of galaxies of all types (e.g. Turner's binary data and the Rubin, et al. rotation curves). For example, for a mean cutoff radius of 65 kpc/h, our 3σ upper limit for the equivalent circular velocity (GM/r)1/2 = 190 km/sec. For a mass cutoff at 190 kpc/h our 2σ upper limit is 175 km/sec. If I weight a sample of asymptotical rotation curve velocities by recent field luminosity functions, I get mean circular velocities less than 170 km/sec.
The 0.3 to 100 Micron Continua of Type 1 Seyferts
Authors: Ward Martin J. , Carleton N.P. , Elvis M. , Fabbiano G. , Willner S.P. , Lawrence A.
Published: June 2019

The continua of type 1 Seyferts from 0.3 to 100 microns have been examined. We focus on the modifying effects of dust, both in terms of absorption and re-radiation. After allowance is made for dust and the presence of extranuclear contributions to the IRAS fluxes, there remains a ubiquitous underlying distribution which we believe to be non-thermal. There is evidence that the thermal infrared components corresponding to hot and warm dust may be associated with the broad and narrow emission line regions.
3C454.3: A New Kind of Superluminal Source?
Authors: Pauliny-Toth I.I.K.
Published: June 2019

The quasar 3C454.3 has a “core-jet” structure, on scales ranging from 50 kpc to 100 pc. VLBI observations made during the last 5 years show that the structural variations within the core region are very different from those seen in the “classical” superluminal sources. After a period of very rapid expansion (apparent velocity va ≥ 30c), the brightest features in the core region showed little relative motion (va < 3c), although at least one weak, more distant component appears to have separated from the others with va ~ 19c. The most likely interpretation of the stationary features involves stationary shocks excited by a relativistic flow.
Connection Between Optical Outbursts and Superluminal Motion in the Milliarcsecond Radio Structure of the Extragalactic Objects
Authors: Babadzhanyants M.K. , Belokon E.T.
Published: June 2019

The analysis of the optical variability of 3C 345 along with the apparent superluminal motions in the milliarcsecond jet suggests a connection between these forms of activity.

The optical variability of the quasar 3C 345 is presented including our 18-year photographic observations and all published data by 1984. The extrapolated moments of ejection of milliarcsecond jet components from nucleus coincide with the initial phases of the “slow” optical flares. The prediction about the arising of a new radiocomponent based on such treatment was confirmed later on. Some evidence of similar connection for the N-galaxy 3C 120 is given.

It has been discovered in recent years that some extragalactic objects have apparent superluminal motions in their milliarcsecond jets. It is obvious that independently of the concrete physical interpretation of this phenomenon it represents an evidence of nuclear activity. Consequently this phenomenon may be connected with the variability of the optical continuum source. The object most suitable for studying such a relationship is the quasar 3C 345. This superluminal object is the best-observed both by VLBI technique and by several optical monitoring programs which revealed very high degree of its optical variability ( in the B-band).
Multi - Frequency Observations of Multiple Nucleus Markarian Galaxies
Authors: Kollatschny W. , Fricke K.J.
Published: June 2019

Multiple nucleus Markarian Galaxies may owe their origin to merging processes among galaxies. They may therefore be key objects for our understanding of galaxy evolution and the origin of nuclear activity. From morphological and multi-spectral data we show that these objects are in an unusually high state of dynamical and nuclear activity (starbursts, Seyfert activity) as would be expected from advanced stages of galaxy mergers.
Radio Continuum Emission and Optical Emission-Line Activity in the Nuclei of Spirals
Authors: Giuricin G. , Mardirossian F. , Mezzetti M.
Published: June 2019

As a step towards the understanding of the phenomena occurring in galactic nuclei, we find that the ratio between the radio continuum emission of the nuclei of spiral galaxies and their optical luminosity is related to optical signs of nuclear activity, such as the emission line strengths of the H∝ and [NII] λ6584 lines.
Nests of Interacting Galaxies: What is It?
Authors: Arkhipova V.P. , Zasov A.V. , Noskova R.I. , Silchenko O.K.
Published: June 2019

Kinematical and photometric studies of nests of interacting galaxies are described. Velocity fields of 22 nests were obtained using the 6-meter telescope of the Special Astronomical Observatory of Sciences Academy of USSR. UBV-photometry carried out with 125-cm telescope of Sternberg Institute has shown that the majority of nests is blue and undergoes intense star formation. Nests are found to be of different types:among them there are single SB and dwarf Irr galaxies with super-giant HII -regions as well as tight pairs and multiple systems of galaxies. Multiple systems classified as nests are shown to be dynamically stable.
Concluding Remarks
Authors: Woltjer L.
Published: June 2019

It was during the fifties that Academician Ambartsumian first raised the issue of the activity of nuclei of galaxies, long before the subject became fashionable. An elaboration on these ideas may be found for example in Ambartsumian's report to the 1970 Vatican meeting. The issues which he raised pertain to the physics of the nuclei and their interaction with the surrounding galaxy, and perhaps even beyond. In the meantime, a large body of data has become available and has been reported at this meeting, and it is clear that the activity of nuclei is of paramount importance, even though a common view on all aspects has not yet been achieved.
Comparison of solar oscillation data obtained from a study of the Na and K Fraunhoffer absorption lines
Authors: Isaak G.R. , McLeod C.P. , van der Raay H.B. , Palle P.L. , Cortes T. Roca
Published: June 2019

Two independent resonant scattering spectrometers one using a sodium and the other a potassium vapour cell, were operated simultaneously at the same site. Due to the differing abundances of ground state atoms of these two elements different depths of the photosphere are sampled. An inter-comparison of solar p modes obtained with these spectrometers is given.
On the 160 minute oscillation
Authors: P.L. Pallé , Cortés T. Roca
Published: June 2019

Solar velocity data collected at Izaña (Tenerife) over the years 1980–1985 have been used to search for the 160 minute oscillation. The peculiar behaviour of the ninth harmonic of a day, in amplitude and phase, suggests the existence of a solar signal with a 160.02 ± .01 minute period, which can be interpreted as a g-mode.
Asymptotic properties of low degree gravity modes
Authors: Berthomieu Gabrielle , Provost Janine
Published: June 2019

Asymptotic properties of low degree gravity modes and their relation to the stratification of the model through the Brunt-Väissälä frequency are discussed for a solar type model and for a 10 M⊙ model. For the solar model, taking into account the quasiadiabaticity of the solar convection zone, it is shown that two global constraints on the deep interior of the solar model can be derived from a set of g-modes periods in the observed range. However modes with large periods, i.e. larger than those up to now observed, are required to obtain informations on the stratification just below the convection zone. For the 10 M⊙ model, the preliminary results show that the existence of a layer with a large mean molecular weight gradient destroys the equidistance of the periods of gravity modes of a given degree and that some informations on the properties of this layer can be obtained from the analysis of the g-modes periods.
Magnetic perturbations to stellar oscillation eigenfrequencies
Authors: Gough D.O. , Thompson M.J.
Published: June 2019

Magnetic fields contribute to the splitting of the degeneracy of modes of like order and degree. The splitting is estimated for some simple hypothetical toroidal magnetic field configurations in the sun, and the results are compared with previous asymptotic estimates. Splitting by a field confined to a thin layer at the base of the convection zone is found not to agree with recent measurements.
Magnetic effects on solar p-modes
Authors: Campbell W R , Roberts B
Published: June 2019

Both analytical and numerical studies of the effect of a magnetic field at the base of the convection zone on p-modes are presented. It is argued that the recently reported changes in the low degree p-mode frequencies, from 1980 to 1984, may result from corresponding changes in the magnetic field strength. A lower limit of some 5 × 105–106 gauss is implied for the field strength at the base of the convection zone.
The radius and the pulsation constant of the primary of Spica
Authors: Jerzykiewicz M. , Sterken C.
Published: June 2019

In the late sixties, Spica (α Virginia, a 4.01454-day SB2 and interferometric binary, with a B1 IV primary component) was showing a light variation that consisted of two periodic terms. One term had the form of a double wave with the above-mentioned orbital period, the other was sinusoidal in shape and had a period equal to 0.1738 days. The double-wave term was clearly an ellipsoidal variation, caused by aspect changes of the tidally distorted primary, whereas the short-period term could only be explained as due to the primary's β Cephei-type pulsations. However, in 1972 these pulsations became undetectable.
Internal constitution and oscillation spectrum of Procyon
Authors: Demarque P. , Guenther D. B.
Published: June 2019

In a previous paper on Procyon A, we analyzed the best available observational data (summarized here in Table 1), discussed its evolutionary status in terms of theoretical evolutionary tracks, and evaluated on the basis of these models its expected characteristic p-mode frequency spacing (Demarque and Guenther 1986). We reached the following conclusions:

(1)

that the published astrometric mass of Procyon A is inconsistent with stellar models and seems too large by about 15 per cent.

(2)

that evolutionary models have too high effective temperatures unless convective overshoot at the edge of the convective core, of the order of a tenth of a pressure scale height, is taken into account.

(3)

that the p-mode characteristic frequency spacing for Procyon A should be in the range 25–30 μHz.

The aim of this paper is to explore theoretically the potential ability of the p-mode and g-mode non-radial oscillation spectrum to throw light on two fundamental problems raised by our first study: Procyon A's evolutionary status, and its mass-luminosity relation.
The non linear dynamic of the ZZ Ceti variable GD 66
Authors: Auvergne Michel , Baglin Annie , Vauclair Gérard
Published: June 2019

We present here a new method for analysing stellar variability: a geometrical study of the attractor associated with a variable star. In contrary to Fourier analysis, which focuses on times scales, this approach attemps to define the shape of the attractor in its phase space. It presents the advantage of being almost unsensitive to gaps in the data as long as uninterrupted sequences contain several tens of characteristic times. But, its noise sensitivity calls for very accurate photometry (10−4), still extremely difficult to perform up to now.

A preliminary test has been done on the variable white dwarf GD 66 on data obtained by classical photometry from the ground.
Full-Disk solar Dopplergrams observed with a 1024 × 1024-Pixel CCD Camera
Authors: Rhodes Edward J. , Cacciani Alessandro , Tomczyk Steven
Published: June 2019

We present here the first full-disk solar Dopplergram obtained with the new 1024 × 1024-pixel CCD camera which has recently been installed at the 60-Foot Tower Telescope of the Mt. Wilson Observatory. This Dopplergram has a spatial resolution of 2.2 arcseconds and was obtained in less than one minute of time. The Dopplergram was obtained with a magneto-optical filter which was designed to obtain images in the two Na D lines. The filter and the camera were operated together as part of the development of a Solar Oscillations Imager (SOI) esperiment which is currently being designed at JPL for the joint NASA/ESA Solar and Heliospheric Observatory (SOHO) mission.
Sodium cell spectrophotometer for detection of stellar oscillations
Authors: Schmider F.X. , Fossat E. , Grec G. , Gelly B.
Published: June 2019

This paper describes the new version of our instrument used for detection of stellar oscillations. It is planned to use it next year for observations of Procyon and α Can in order to confirm the results already obtained. Because the prototype used in these first attempts did not succeed to be photon noise limited, it has been significantly redesigned in order to improve the situation regarding every source of noise.
Multiplexed interferometric stellar oscillation spectrometry - MISOS
Authors: Pietraszewski K.A.R.B. , Bell C.R. , Ring J. , Reay N.K. , Leeper M.
Published: June 2019

Interferometric spectrometry techniques for measuring stellar oscillations have been developed at Imperial College, resulting in two separate interferometers, the Michelson and the Fabry-Perot based instruments. They have both been used on large telescopes; the Michelson instrument to search for oscillations in solar-type stars and the Fabry-Perot instrument to measure oscillations in δScuti-type stars. So far there has been only marginal evidence for solar-type oscillations, including our observations of εCyg with ~1ms−1 precision. In order to increase the significance of future observations we are currently improving both instruments and aim to achieve a ten-fold increase in precision, i.e. ~10cms−1, by using up to 100 separate spectral lines simultaneously. Such an improvement will allow us to continue the search for solar-type oscillations.
Helioseismology from space, the SOHO project
Authors: Domingo V.
Published: June 2019

As a cornerstone of its long term plan for space science research, the European Space Agency (ESA) is developing the Solar Terrestrial Physics Programme that consists of two parts: one, the Solar and Heliospheric Observatory (SOHO) for the study of the solar internal structure and the physics of the solar corona and the solar wind, and another, CLUSTER, a series of four spacecraft flying in formation to study small scale plasma phenomena in several regions of the magnetosphere and in the near Earth solar wind. The feasibility of the missions was demonstrated in Phase A studies carried out by industrial consortia under the supervision of ESA (1,2). According to the current plans an announcement of opportunity calling for instrument proposals will be issued by ESA during the first quarter of 1987. It is foreseen that the spacecraft will be launched by the end of 1994.
Observations of stellar oscillations with the Hubble Space Telescope
Authors: Soderblom David R.
Published: June 2019

A rationale and plan for using the Hubble Space Telescope to observe solar-like oscillations in stars is presented.
New Planetary Nebulae
Authors: Marcout J.
Published: June 2019

As a complement to the “Strasbourg–ESO Catalogue of Galactic Planetary Nebulae” (Acker et al. 1992), we give the list of newly discovered planetary nebulae.
The Properties of Planetary Nebulae Nuclei: Stellar Winds
Authors: Bianchi L. , De Francesco G.
Published: June 2019

We present IUE observations of some nuclei of Planetary Nebulae. From these data we derive the stellar photospheric parameters (Teff Lbol, log g), and the wind characteristics (velocity, mass loss rate). Teff, R∗, Lbol are derived from UV low resolution spectra, combining optical and radio data, from Bianchi (1988) or from new IUE data, with the same method (fit of the UV continuum with model atmospheres for high gravity stars, after correcting for reddening and for the contribution of continuum emission by the nebular gas). P Cygni profiles from IUE high resolution spectra are fitted with the SEI method and V∞ is derived. The non-LTE ionisation in the wind and the mass loss rate are computed as in Bianchi et al. (1986). Details are given in a forthcoming paper. The results for a first group of objects are given in the Table below.
E2 and M1 Transition Probabilities in Ions of the Nitrogen Isoelectronic Sequence Calculated using MBPT
Authors: Gaigalas G. , Kisielius R. , Merkelis G. , Vilkas M.
Published: June 2019

Forbidden electric quadrupole (E2) and magnetic dipole (M1) transitions are of extreme importance in astrophysics. Up to now the most extensive calculations for the nitrogen isoelectronic sequence have been done using the method proposed by C.J. Zeippen [1] or in MCHF approximation [2]. To account for electron correlations both these methods use a large list of configurations. We have chosen the stationary many-body perturbation theory (MBPT) [3] for the inclusion of the electron correlations. The calculations have been perfomed in the second order in the complete model space 1s22s2p3+ 1s22p5. Relativistic corrections have been accounted for in the Breit-Pauli approximation. In the Table we present probabilities for electric quadrupole W(E2) and magnetic dipole W(M1) transitions (in s−1), wavelengths λ (in A). The comparision of the results shows that our second order calculation data in the most cases are closer to term-energy corrected ones from [1].
Distances of Planetary Nebulae
Authors: Terzian Yervant
Published: June 2019

One of the most fundamental physical parameter in astronomy is the distance to the objects we detect in the universe. For many classes of astronomical objects, accurate and proven methods have been developed to determine their distances. Such classes of objects include stars within ∼100 pc from the sun, binary stellar systems, variable stars, stellar clusters, main sequence stars, and other galaxies. It has been, however, more difficult to develop satisfactory methods to determine accurate distances to the more than 1000 planetary nebulae that have been discovered in our galaxy.
Dust in Planetary Nebulae and in Post-AGB Objects
Authors: Barlow M. J.
Published: June 2019

Developments in the field since the review of Roche (1989) are discussed. Section 1 describes the results from detailed models of the dust emission from planetary nebulae and summarises the derived dust-to-gas mass ratios. The properties of the remarkable gas-poor planetary nebula IRAS 18333–2357, located in the globular cluster M22, are discussed in Section 2. The use of thermal infrared imaging to map the distribution of different dust components is reviewed in Section 3, and two recently applied optical probes of nebular dust properties are described: emission line spectropolarimetry, and spectroscopy of the Extended Red Emission (ERE). The final section describes recent results from infrared spectroscopy. The spectra of carbon-rich post-AGB objects have provided valuable new insights into the nature and evolution of the materials responsible for the UIR bands, while unusual oxide grains and crystalline ice emission have been detected around oxygen-rich post-AGB objects. The spectra of a small number of objects show evidence for the simultaneous presence of both oxygen-rich and carbon-rich material.
Imaging Spectrophotometry of the Ring Nebula
Authors: Lame Nancy Jo , Pogge Richard W.
Published: June 2019

We present new results from a program of emission-line imaging spectrophotometry of planetary nebulae using the Ohio State University Imaging Fabry-Perot Spectrograph (IFPS). High-quality emission-line maps of the important diagnostic lines [NII]λλ5755,6583, [SII]λλ6717,6731, [OI]λ6300, [OIII]λ5007, Hα, and Hβ have been obtained. Maps of the ionization structure ([S II]/Hα, [N II]/Hα, [O III]/Hβ, and [O I]/[O III]), temperature in the N+ region, density in the S+ region, and Balmer decrement across the nebula are presented. These show considerable variation in ionization state, temperature and density. This detailed information will provide powerful constraints on photoionization models for the Ring Nebula.
Millimetre and Submillimetre Continuum Observations of Planetary Nebulae
Authors: Hoare M.G. , Roche P.F. , Clegg R.E.S.
Published: June 2019

Continuum emission has been detected at millimetre and submillimetre wavelengths from a total of thirteen planetary nebulae, all but one for the first time. The observations were obtained with the liquid 3He–cooled UKT14 bolometer on the JCMT and UKIRT telescopes on Mauna Kea, Hawaii.
Comparative Analysis Miras/PPN
Authors: Barthes D. , Mennessier M.O. , Gleizes F. , Lèbre A.
Published: June 2019

The spectrum of R Sct, a star firstly classified as an RV Tau one and located in the highest part of the instability strip, indicates a Na ejected shell at about 1000 R∗ with an expansion velocity close to 50 km/s (Lèbre and Gillet, 1991). This confirms the post AGB character of this star as already mentionned by Jura (1986). So it is interesting to compare the R Sct with some “classical” RV Tauri (AC Her and U Mon) and some “exceptional” miras (R Cen, U CMi and R Nor) with light curves exhibiting a double maximum and with spectral types earlier than those of the other miras with similar periods.
The Morphology of MID-Infrared UIR Feature Emission in the PPN M 2–9 and IRAS 21282+5050
Authors: Deutsch L. K. , Hora J. L. , Hoffmann W. F. , Fazio G. G. , Shivanandan K.
Published: June 2019

The carbon-rich PPN M 2–9 and IRAS 21282+5050 are known to exhibit UIR feature emission at 7.7, 8.6, and 11.22 μm. The two nebulae have been imaged in the mid-IR with the UA/SAO/NRL Mid-Infrared Array Camera (MIRAC) in bandpasses which include UIR feature emission (8.8 and 11.22 μm). Near-infrared images of the nebulae have also been taken with the NICMOS 3 Hg:Cd:Te array camera at J, H, and K for M 2–9 and at K for IRAS 21282+5050.
The Nature of the High Velocity Flow in CRL 618
Authors: Neri R. , Guélin M. , Guilloteau S. , Lucas R. , Garcia-Burillo S. , Cernicharo J.
Published: June 2019

Using the IRAM interferometer, we have mapped with a 2″.4 = 3″.4 resolution the J = 1 → 0 HCN line emission in the proto–planetary nebula CRL 618. Our maps resolve the 200 kms−1 molecular outflow (Cernicharo et al. 1989), as well as the slowly expanding circumstellar envelope (Bujarrabal et al. 1988), allowing a very precise positioning (≤ 0″.1) of these components with respect to the central HII region. 70% of the HCN envelope emission comes from a very compact, spherically symmetric core of size ≃ 3″.2. The core surrounds the high velocity gas which appears localized in a number of small ‘clumps’ (≤ 0″.5) – see figure. The large range of velocities observed in the ‘clumps’ suggests that we are not observing a decelerating molecular flow, but the impacts of a bipolar outflow on the slowly moving core, close to the HII region. The collision of a neutral gas outflow with high density regions (the ‘clumps’) results in the generation of dissociative shock-waves pushing and tearing the inner surface of the envelope. CRL 618 appears to have reached the stage where the stellar winds begin to disrupt and to scrape through the massive envelope, shortly before it evolves towards a Planetary Nebula.
Evolutionary Properties of Post-AGB and Post-EAGB Stars
Authors: Limongi Marco , Tornambe Amedeo , Castellani Marco
Published: June 2019

We discuss the evolutionary properties of shell burning star models which, due to the erosion of the external hydrogen envelope, leave the Hayashi track and evolve to the blue of the HR diagram. We analyze the properties of star models which evolve off the Asymptotic Giant Branch (AGB), the Early-AGB or the Red Giant Branch (RGB).
Numerical Study of the Shaping of Planetary Nebulae
Authors: Igumenshchev I. V.
Published: June 2019

An axisymmetric density distribution likely to be representative for many Planetary Nebulae (PN). We suggest that the axial symmetry of PN results from a predominant ejection of matter in the equatorial direction due to the duplicity of the central star (Livio et al.,1979, Ap. J.,188,1). We present an illustrative example of the formation of the bipolar PN Soutern Crab (He 2–104). In this model high velocity matter ejected by hot central star interacts with an outer oblate envelope located around a symbiotic binary star. The binary consists of a Mira variable, ejected matter forming a thick disk, and a hot component (Lutz et al.,1989, PASP 101,966). Accretion of some disk matter onto the hot component (dwarf) may lead to recurrent thermal shell flashes (Igumenshchev et al., 1990, Astrofizika,30,282). which result in the double shell nebula, observed in the Southern Crab (Burgarella et al., 1991, A&A,249,199). The phase of forming a single shell stucture of the Southern Crab was simulated numerically. The results of a 2D hydrodynamical nonadiabatic calculation are illustrated in the Figure. The density contours with logarithmic spacing of 0.25 and the velocity field (arrows) of the model are shown at time t ≃ 360 yrs after the central star outburst with energy 1044erg. The dense shell may be observed as a Crab-like nebula (“hour-glass” type). In this model the mass of the envelope is 7 · 10−4M⊙ and the maximal velocity is over of 200 km/s.
Is there Any Connection Between Planetary Nebulae and Symbiotic Stars ?
Authors: Friedjung Michael
Published: June 2019

Symbiotic stars have sometimes been misidentified as planetary nebulae, because their line spectra are similar to those of planetary nebulae particularly in the ultraviolet L.(Houziaux 1982 in “The Nature of Symbiotic Stars”, M. Friedjung & R. Viotti eds., Reidel. p 229), while the infrared shows the presence of the spectrum of a cool star. The similarity is not complete; when H. E. Schwarz (1988 in “The Symbiotic Phenomenon”, J. Mikolajewska et al eds., Kluwer, p 123) plotted a graph of two ratios derived from emission line fluxes, symbiotic stars did not occupy the regions of the diagram occupied by planetary nebulae and H II regions.
Elemental Abundances in Symbiotic Stars
Authors: Schmid H.M. , Nussbaumer H.
Published: June 2019

Symbiotic objects are related to planetary nebulae in that they represent late stages of stellar evolution. They are interacting binary systems where a hot companion star ionizes the stellar wind of a red giant. This configuration offers the unique possibility for deriving elemental abundances for cool giants from a nebular spectrum with the diagnostic tools employed for HII regions. The analysis can be applied to different types of symbiotic systems having a G, K or M giant, a Mira variable or a carbon star as cool component. The great advantage of this technique is, that it does not depend on stellar parameters or molecular data, and that it can therefore be used as a test or an alternative for the traditional photospheric abundance determinations.
The Evolution of the Planetary Nebulae in the Magellanic Clouds and the Galactic Bulge
Authors: Dopita M.A.
Published: June 2019

From self-consistent photoionisation modelling of 147 Magellanic Cloud PN, we have constructed the H-R Diagram for the central stars, and have derived both the chemical abundances and the nebular parameters. We find that the central stars have core masses generally between 0.55 and 0.7 M⊙, and find strong evidence to support the model that they leave the AGB as helium-burning stars following the final shell flash. Type I PN have more massive cores, up to near the Schwartzschild limit, and show clear evidence for the Third dredge-up episode. From HST images, younger PN are very compact. The expansion velocity of the nebula is closely correlated with the position of the central star on the H-R Diagram.
Detection of Evolution of the Nucleus of NGC 2392
Authors: Heap Sara R.
Published: June 2019

Ultraviolet spectra taken with the IUE satellite indicate that the central star of the planetary nebula, NGC 2392, has declined in brightness by 7% per decade. We interpret this fading as a consequence of evolution toward higher temperature. With this interpretation, the rate of optical fading suggests that the stellar mass is 0.73 M⊙.
Global Photometric Campaigns on Pulsating Planetary Nuclei
Authors: Ciardullo Robin , Bond Howard E.
Published: June 2019

As reported in a contributed paper at this symposium, six “O VI”-type planetary nuclei are known to be pulsating variables. Through the techniques of asteroseismology, it should be possible to explore the interior structures of these stars, determine their masses and rotation rates, and measure the stellar evolutionary timescales through observations of changes in the pulsation periods.
Photoelectric Photometry of Five PNNi
Authors: Silvotti R. , Bartolini C. , Boffi F.R. , Cosentino G. , Guarnieri A. , Piccioni A. , Stanghellini L.
Published: June 2019

In September 1991 we started a photoelectric monitoring of O VI PNNi that are candidate to be non radial pulsators. The observations were obtained using the two head photometer described by Piccioni et al. (1979, Acta Astron. 29,463), mounted on the 1.5 m telescope of the Bologna Observatory. We generally used the B and sometimes the U filter; only BA 1 was always observed without filters because of its faintness. The reductions have been pursued by means of a program that yields the moving averages of the counts of the variable and comparison star. For the search of periodicities the methods of Deeming (Kurtz 1985, MNRAS 213,773) and Scargle (1982, Ap J 263,835) were principally used. The list of observations is reported in the following Table, where σ is the mean value of the standard deviations obtained by computing the moving averages.
Precision Asteroseismology of Pre-White Dwarfs and PN Central Stars
Authors: Kawaler Steven D. , Bradley Paul A.
Published: June 2019

The nonradially pulsating GW Vir (a.k.a. DOV, or pulsating PG1159) stars and the K1–16 type variable stars provide an unparalleled opportunity to probe the internal structure of planetary nebula central stars and their immediate descendants, hot pre-white dwarfs. Recent global photometry campaigns have provided data of sufficient quality to severely constrain evolutionary models of these stars.
UV and Optical Abundances for a Sample of Southern Galactic Planetary Nebulae
Authors: Kingsburgh Robin L. , Barlow M.J.
Published: June 2019

We present abundances for a sample of 57 southern hemisphere galactic planetary nebulae (PN). Optical spectra covering the 3100–7400 Å range were obtained at the AAT. Low resolution UV spectra obtained with the IUE satellite were available for half of these objects and were accessed via the IUE Uniform Low–Dispersion Archive. Additionally, new low resolution IUE SWP observations of Fg 1, M 3-1 and M 3-3 were obtained.
Chemical Enrichment and Central Star Properties
Authors: Zhang C.Y.
Published: June 2019

We have selected a sample of planetary nebulae, for which the core masses are determined using distance-independent parameters (Zhang and Kwok 1992). The chemical abundances of He, N, O, and C are taken from the literature for them. Relationships of the ratios of He/H, N/O, and C/O with various stellar parameters of planetary nebulae (PN), such as the core mass, the mass of the core plus the ionized nebular gas, the stellar age and temperature, are examined. It is found that the N/O increases with increasing mass, while the C/O first increases and then decreases with the core mass. No strong correlation seems to exist between the He/H and the core mass. A correlation of the N/O and He/H with the stellar temperature exists. The current dredge-up theory for the progenitor AGB stars cannot satisfactorily account for these patterns of chemical enrichment in PN. Furthermore, the correlations of the N/O and He/H with the stellar age and temperature indicate that besides the dredge-ups in the RG and AGB stages, physical processes that happen in the planetary nebula stage may also play a role in forming the observed patterns of chemical enrichment in the planetary nebulae.
Chemical Composition of Planetary Nebulae: A New Determination
Authors: Golovaty V.V. , Malkov Yu. F.
Published: June 2019

A new method of the determination of planetary nebulae abundances is proposed. Unobserved ionization stages are taken into account with aid of the correlations between relative abundances of various ions which had been obtained from the grid of the photoionization models of planetary nebulae luminescence calculated by us. Simple approximative expressions for the determination of He/H, C/H, N/H, O/H, Ne/H, Mg/H, Si/H, S/H, and Ar/H are found. The chemical composition of 130 galactic planetary nebulae is revised. The observational data were compiled from 73 papers of many authors published in 1972–1991. Our mean abundances of C, N, O, Ne, S, Ar are 0.1–0.3 dex lower than the mean abundances of these elements found previously by other authors. Such a discrepancy may be due to an overestimation of “empirical” ionization correction factors in previous works. It is shown that the abundance of oxygen in massive stars-precursors may be reduced by 0.2 dex on average due to the ON-cycle, but the abundance of neon remains practically unchanged. A comparative analysis of the abundances in the galactic disk, bulge and halo nebulae is carried out. We found that helium is enhanced in the galactic bulge nebulae relative to the disk ones, but the mean nitrogen abundance and mean ratio N/O are lower in the bulge. Our data suggest that the second dredge-up did not take place in the stars-precursors of the bulge planetaries, and the helium and nitrogen enhancement in these nebulae is due to other mixing processes. The mean abundances of O, Ne, S, Ar in the galactic disk and galactic bulge nebulae are quite similar, and we must conclude that the stars-precursors of the bulge planetaries had been formed during the same burst of star formation as the stars-precursors of the disk nebulae, while the halo nebulae correspond to the previous burst.
The Virtual Planetary Laboratory: Towards Characterization of Extrasolar Terrestrial Planets
Authors: Meadows Victoria , Crisp David
Published: June 2019

NASA and ESA are currently undertaking mission studies for space-based observatories designed to search for life on other worlds. To optimize the designs of these missions, and to ultimately interpret the data sent back by them, we need to recognize habitable worlds and to discriminate between planets with and without life based only on remotely-sensed information. This paper provides an overview of the characteristics we would look for on an extrasolar terrestrial planet that might indicate habitability or the presence of life. It also describes a new NASA Astrobiology Institute research project to develop an innovative suite of modeling tools to simulate the environments and spectra of extrasolar planets. These modeling tools will constitute a Virtual Planetary Laboratory, which will be used to explore the plausible range of atmospheric compositions and globally-averaged spectra for early Earth and for plausible terrestrial planets both with and without life. Products of this research will provide an improved basis for recommending spacecraft and instrument characteristics, as well as search strategies required to remotely sense the signs of life in the atmosphere or on the surface of another world.
Objectivity in the Study of Intelligence: The Cornerstone of New Methods and Discoveries
Authors: Marino Lori
Published: June 2019

Science requires objectivity - the ability to see the relationships among things in the natural world free of assumptions and biases. To achieve this goal one has to use objective methods of observation and testing but also maintain a philosophy of objectivity when deciding upon which research questions to pursue and which conclusions to draw from one's findings. The field of bioastronomy relies upon objectivity on both a methodological level and, perhaps to the greatest extent among all sciences, on a conceptual level. Bioastronomy is the multidisciplinary and interdisciplinary science of investigating, understanding, and explaining the origin, nature, prevalence, and distribution of life in the universe. As a scientific field of inquiry bioastronomy relies upon methodological objectivity. Furthermore, bioastronomy demands conceptual objectivity because its content domain is, by nature, largely unknown and subject to more degrees of freedom than perhaps any other discipline. Therefore, objectivity, through and through, is the cornerstone of bioastronomy.
Life in Solid Ice on Earth and Other Planetary Bodies
Authors: Price P. Buford
Published: June 2019

Theory and direct observation indicate that micro-organisms exist in liquid veins in ice and permafrost, provided the temperature is above the eutectic for H2O and soluble impurities present. Microbes can exist and metabolize in glacial ice and permafrost on Earth, Mars, and Europa. One can search directly (with fluorescence microscopy at liquid veins in Vostok ice core samples) or with a biologging instrument (for microbial fluorescence in a borehole in terrestrial or martian permafrost or ice). The viability lifetime against DNA destruction of bacterial spores can be measured with analytical techniques that identify calcium dipicolinate, which is unique to spores.
Information Theory Applied to Animal Communication Systems and Its Possible Application to SETI
Authors: Hanser Sean F. , Doyle Laurance R. , McCowan Brenda , Jenkins Jon M.
Published: June 2019

Information theory, as first introduced by Claude Shannon (Shannon & Weaver 1949) quantitatively evaluates the organizational complexity of communication systems. At the same time George Zipf was examining linguistic structure in a way that was mathematically similar to the components of the Shannon first-order entropy (Zipf 1949). Both Shannon's and Zipf's mathematical procedures have been applied to animal communication and recently have been providing insightful results. The Zipf plot is a useful tool for a first estimate of the characterization of a communication system's complexity (which can later be examined for complex structure at deeper levels using Shannon entropic analysis). In this paper we shall discuss some of the applications and pitfalls of using the Zipf distribution as a preliminary evaluator of the communication complexity of a signaling system.
The Very Small Array: Observations and Latest Results
Authors: Slosar Anže , Dickinson Clive
Published: June 2019

The Very Small Array (VSA) is a unique interferometric telescope operating at 33 GHz at Tenerife. It has the ability to measure fluctuations in the CMB over a large range of angular scales by means of three main array configurations: compact, extended and super-extended. These angular scales correspond to the multipole range ℓ = 150 —2500. Here we present new results from further observations of the extended array (February 2002 - June 2003). We cover ℓ-values up to ℓ ∼ 1600, thus doubling the ℓ-range of WMAP. The resulting power spectrum in the ℓ-range 800 – 1600 has very low noise coupled with good ℓ-resolution (Δℓ ∼ 80). Furthermore, the use of independently tracking aerials along with the dedicated source subtraction baseline allows unprecedented control of systematics. The latter is essential, since discrete sources are the dominant foreground at these angular scales. These measurements over larger ℓ-ranges are important in confirming the present cosmological paradigm and breaking degeneracies in the extraction of cosmological parameters.
The Universe Behind the Southern Milky Way
Authors: C. Kraan-Korteweg Renée , Staveley-Smith Lister , Donley Jennifer , Koribalski Bärbel , Henning Patricia A.
Published: June 2019

A first analysis of a deep blind HI survey covering the southern Zone of Avoidance plus an extension towards the north (196† ≤ ℓ ≤ 52†) obtained with the Multibeam receiver at the 64-m Parkes telescope reveals slightly over a thousand galaxies within the latitude completeness limit of |b| ≤ 5†. The characteristics and the uncovered large-scale structures of this survey are described, in particular the prominence of the Norma Supercluster, the possible cluster around PKS 1343–601 (both in the Great Attractor region), as well as the Local Void and the clustering in the Puppis region. In this blind HI survey HIZOA J0836–43 was discovered, one of the most massive spiral galaxies known to date (MHI = 7.3 × 1010 M⊙, MT = 1.1 × 1012 M⊙; H0 = 75 km/s/Mpc). Although of similar mass to Malin 1-like objects, this galaxy does not share their typical low-surface brightness properties, but seems an exceptionally massive but normal, high surface brightness, star-forming galaxy.
A CS survey of massive stars embedded in molecular clouds
Authors: Bronfman L. , May J. , Nyman L. A. , Thaddeus P.
Published: June 2019

the CS J=2 →1 molecular line at 98 GHz, a normally optically thin line requiring high densities to be excited, has been detected with SEST (Swedish ESO Submillimeter Telescope) toward 294 IRAS pointlike sources having the characteristic FIR colors of embedded stellar objects and apparently associated with the largest molecular cloud complexes in the southern Milky Way. We present here their Galactocentric radial distribution and a correlation between their FIR and CS luminosities.
Structure in the gas and magnetic field in S106
Authors: Crutcher Richard M.
Published: June 2019

BIMA molecular-line observations show evidence for an expanding molecular ring around IRS 4, a newly formed massive star at the center of the bipolar nebula S106. VLA observations of the Zeeman effect in the OH 1665 MHz line show that the magnetic field strength is about 1 mG and that it reverses direction from one lobe of the bipolar nebula to the other.
Chemistry and small-scale structure of diffuse and translucent clouds
Authors: Black John H. , van Dishoeck Ewine F.
Published: June 2019

The small, thin diffuse and translucent molecular clouds are excellent laboratories for studying the ways in which small—scale structure and interstellar chemistry affect each other. Variations of density or column density and chemical stratification can be found on scales as small as 0.01 pc. The origin of such structures and the evolutionary states of small clouds remain elusive.
Physical and chemical parameters in dense cores
Authors: Walmsley C. M.
Published: June 2019

The current state of our knowledge of the physical parameters and the chemical composition of dense cores in molecular clouds is discussed. In particular, I summarize what is known about the rate at which molecules condense out on grain surfaces. I discuss in turn: a) dense cores in nearby dust complexes such as Taurus, b) clumps in regions of massive star formation such as Orion and M17, c) hot dense cores near to newly formed O stars such as the Orion-KL hot core and d) the high density condensations which give rise to interstellar masers. Recent work on each of these categories is reviewed with emphasis on the chemical abundance determinations and estimates of the local density and temperature. Particular attention is given to recent work on OH, methanol, and ammonia masers.
Abundance variations of tracers and their effects on our determination of molecular cloud structure
Authors: Goldsmith Paul F.
Published: June 2019

Our understanding of the molecular phase of the interstellar medium is critically dependent on use of various lines from different molecular species to trace this dense material. As our knowledge of molecular clouds becomes more refined, and we pursue in detail issues of molecular cloud structure, stability, and how star formation depends on and affects the molecular gas, it is appropriate to examine the basis by which we determine the morphology of clouds, their density, and other key parameters. This is obviously a major undertaking, well beyond the scope of the short presentation at this conference, so I will concentrate on one very basic, but critical issue, which is that of abundance variations of tracers of density and molecular column density which are widely used to delineate the denser portions of all types of molecular clouds. In this summary, I will first highlight some of the apparent indications of significant variations of abundance within individual clouds, as a way of indicating some potential dangers and the importance of the molecular tracer selected. I will also briefly suggest how such variations may be themselves important diagnostics of cloud structure and evolution.
MagnetoHydrodynamic shock waves in molecular clouds
Authors: Draine B. T.
Published: June 2019

The fluid dynamics of MHD shock waves in magnetized molecular gas is reviewed. The different types of shock solutions, and the circumstances under which the different types occur, are delineated. Current theoretical work on C∗- and J-type shocks, and on the stability of C-type shocks, is briefly described. Observations of the line emission from MHD shocks in different regions appear to be in conflict with theoretical expectations for single, plane-parallel shocks. Replacement of plane-parallel shocks by bow shocks may help reconcile theory and observation, but it is also possible that the observed shocks may not be “steady”, or that theoretical models have omitted some important physics.
Thermal processes in molecular gas
Authors: Chièze J.P. , de Boisanger C.
Published: June 2019

The dynamics of the cold atomic and molecular gas, on which we focus here, is strongly affected by non equilibrium heating and cooling processes. We give two different examples, in which the breaking of the thermal balance is due respectively to variations of the incident ultraviolet radiation flux, and non equilibrium abundances of H2 molecules in molecular clouds envelopes. Fluctuations of the ultraviolet radiation flux in clumpy molecular cloud envelopes result in the formation or the destruction of dense regions. Large density contrasts, greater than one order of magnitude, are easily achieved in cloud regions of moderate visual extinction. Condensation or expansion develop on quite short time scales, of the order of a few tenth of million year, and induce collective motions which can feed turbulence.

Another example of the importance of out of equilibrium thermochemical processes is furnished by the study of the H — H2 transition layers in molecular clouds envelopes. They turn out to be unstable against convection-like motions, driven by the energy released by H2 photodestruction. The gas velocities involved in these motions are, again, typical of the observed turbulent velocity in clouds envelopes.
Large-scale fragmentation of gas cloud rotating at the Galactic center
Authors: Fujimoto M. , Tatematsu Y.
Published: June 2019

A rotating and slowly-contracting gas cloud is followed in the deep gravitational potential of the galactic center. When the gas density increases as high as (102 — 103)H2 cm—3, which is more than twenty times as large as the background matter density, the self-gravity of the cloud becomes dominant to govern its dynamical structure. The cloud elongates and then splits into two separated objects, as observed at the centers of IC342, NGC6946, and Maffei 2 where we have two symmetric peaks on the major axis of the 12CO (J=1-0) cloud.