bluuebunny/crossref_metadata_2025_split huggingface dataset:
Distances and Radii of Classical Cepheids
Authors: Barnes Thomas G. 
Published: March 2016

Suppose one of the current high angular resolution instruments were capable of measuring the instantaneous angular diameter of a Cepheid throughout its pulsation cycle. By comparing the angular diameter variation to the linear displacement variation, obtained from the integrated radial velocity curve, one could determine both the linear radius and the distance of the variable. This distance would be independent of all other astrophysical distance scales and would be geometric, i.e. independent of the effects of interstellar obscuration.Although none of the current instruments has this capability, the same result can be accomplished indirectly through use of the stellar surface brightness. Recall that the visual surface brightness can be expressed in terms of the apparent visual magnitude and the stellar angular diameter. At any phase in the Cepheid pulsation, knowledge of the visual surface brightness and the apparent magnitude permits inference of the angular diameter.From stars with measured angular diameters it is known that the visual surface brightness parameter Fv correlates remarkably well with the Johnson V-R color index (Barnes and Evans 1976; Barnes, Evans and Parsons 1976; Barnes, Evans and Moffett 1978). Johnson VR photometry may thus be used to determine the visual surface brightness and hence the stellar angular diameter. As shown in the referenced works, such angular diameters are essentially independent of the choice of interstellar obscuration corrections. This approach to stellar angular diameters and then to variable star distances is therefore nearly equivalent to direct measurements.
The Pulsation Properties of Red Variables
Authors: Feast M. W. 
Published: March 2016

AbstractRecently derived bolometric absolute magnitudes are used to investigate the pulsational properties of some classes of red variables. The Mira variables with periods over 200 days have pulsation constants appropriate to overtone pulsatore but the shorter period 135 day Miras seem to be hotter and less luminous and may be fundamental pulsators. The large amplitude Shapley-Nail variables in the SMC are probably fundamental pulsators with masses in the 5-10 solar range. Bright supergiant red variables in the LMC show evidence of the period-luminosity relation expected if they are in the early stages of core helium burning.
High Resolution X-Ray Spectroscopy of The Gas Surrounding M87 and NGC1275: Emission Line Detection and Evidence for Radiatively Regulated Accretion
Authors: Canizares C. R. , Berg C. , Clark G. , Jernigan J. G. , Kriss G. , Markert T. H. , Schattenburg M. , Winkler P. F. 
Published: March 2016

The topic of this paper really falls somewhere between this session on active galaxies and the session on clusters. What I will report is really a cluster phenomenon but one which depends on the presence of a dominant, massive galaxy in the cluster. Specifically, we have detected several X-ray emission lines from the vicinity of M87 in the Virgo Cluster and NGC 1275 in Perseus. The lines are indicative of material which is cooler than the bulk of the intracluster gas. This material is most likely accreting onto the central galaxy with the accretion rate controlled by the rate of radiative cooling.The observations I am reporting were made with the Focal Plane Crystal Spectrometer (FPCS)on the Einstein Observatory. The instrument is a Bragg crystal spectrometer which has a resolving power (E/ΔE) of 50 to 500 over the energy range of 0.2 to 3 keV. It operates much like an optical scanner in that it has a narrow passband which is swept over some restricted spectral range containing an emission line. Detailed descriptions are given elsewhere (Canizares et al. 1977, 1979, Giacconi et al. 1979).
X-Ray Observations of M87’s Halo
Authors: Fabricant D. , Lecar M. , Gorenstein P. 
Published: March 2016

We briefly describe the soft X-ray image of M87 obtained using the imaging proportional counter aboard the Einstein Observatory. These data provide further strong evidence for the existence of a massive halo of dark matter surrounding M87 and allow a much more precise determination of its mass. Two pointing positions of the satellite were analyzed; one centered on M87, the other 63’ south and 25’ east of M87. The field of view of the imaging proportional counter is 60’ × 60’, and it attains a two dimensional spatial resolution of ˜ 1.5’ in a spectral range spanning 0.1 to 4.5 keV.As previous reports had suggested (Gorenstein et al. 1977; Fabricant et al. 1978), the present observations show M87 to be a strong, very extended, thermal X-ray source with a temperature near 2 keV, surrounded by weaker and still more extended emission from hotter gas associated with the Virgo cluster as a whole (Davison, 1978; Lawrence, 1978). We find M87 to have a total 0.5-4.5 keV X-ray luminosity of about 2 × 1043 ergs/sec, and an extrapolated 2-6 keV luminosity of approximately 1 × 1043 ergs/sec. The total mass of gas inferred from the X-ray measurement exceeds 1012 solar masses.
Clusters of Galaxies
Authors: Bahcall Neta A. 
Published: March 2016

AbstractClusters and groups of galaxies contain the majority of galaxies in the universe. The rich clusters, while less numerous than the many poor groups, are the densest and largest systems known, and can be easily recognized and studied even at relatively large distances. Their study is important for understanding the formation and evolution of clusters and galaxies, and for a determination of the large-scale structure in the universe.
The Needs in the Radial Velocity Area in View of Impending Space Astrometry Projects
Authors: Andersen J. 
Published: March 2016

I have understood the title of this talk given to me by Dr. Westerhout to imply a review of our present ability to provide new radial velocity measurements for the many stars to be observed by the Space Astrometry projects, as well as an indication of the technical developments still required. And indeed, the quantity and quality of the existing radial velocity determinations are such that only a small fraction of the data needed can be considered available.The challenges presented by the two projects, the Astrometry Satellite and the Space Telescope, are somewhat different, corresponding to the complementary nature of the two programmes: The dedicated Astrometry Satellite will observe a very large number of relatively bright stars, while the Space Telescope is expected to give astrometric results for much fainter, but also far fewer objects (estimated currently at perhaps 20 per year). The two programmes will therefore be considered separately.
Rotational Studies of Lower Main Sequence Stars
Authors: Smith Myron A. 
Published: March 2016

This review summarizes the techniques and limitations involved in determining small rotational velocities in late-type stars. Recent results from photoelectric line profiles of field main sequence G stars will also be presented.Historically three techniques have been used to measure stellar rotational velocities: (1.) calibration of a “clean” line width in terms of computed profile models, (2.) use of the Fourier transform frequency domain (dissection of rotation and turbulent velocity fields from the thermal profile), and (3.) monitoring of the rotational modulation of a chromospherically active or spotted star. The results discussed below concern technique (2.). Technique (3.) has not been exploited much yet but holds considerable promise for the future, in particular for the measurement of ultra-slow rotation.
A Baker’s Dozen: Unsolved Problems with The RS Canum Venaticorum and by Draconis Stars
Authors: Hall Douglas S. 
Published: March 2016

The theme of this Joint Meeting of Commissions 10, 27, 40, 42, 44, and 48 is “Close Binaries and Stellar Activity”. At the time this meeting was initially conceived, we took stellar activity to mean activity such as we observe on the Sun: spots, flares, chromospheric emission, variable radio and X-ray emission, coronas, winds, and so forth. That is why the series of seven reviews presented at this meeting will deal for the most part with convective stars, in particular with the RS CVn-type and BY Dra-type stars, which we know are active in so many of these ways.It had been planned that Steven N. Shore would review briefly the situation from a theoretical viewpoint (briefly, I say, because theoretical treatment of the problem is still in the infant stages). Reference can be made, however to the contribution he presented at I.A.U. Symposium No. 88 in Toronto.One way to open this meeting, I hope a useful way, is simply to list some unsolved problems. Those on my list may not be equal in importance or difficulty. Different problems would no doubt appear on someone else’s list. It may even turn out that, after we have heard these reviews, a number of my unsolved problems have already been solved or soon will be, but that would be a pleasant surprise rather than a disappointment.
The Problem of Abundances for “Metal-Rich” Globular Clusters
Authors: Gustafsson Bengt 
Published: March 2016

AbstractThe discrepancy between the results of recent high-dispersion analyses and of studies at lower resolution for the classical metal-rich globular clusters is discussed and different explanations for this discrepancy are considered. It is concluded that further systematic investigations are motivated in order to establish the more or less interesting astrophysical explanations for it.
Stellar Populations in the Nuclei of Spiral Galaxies
Authors: O’Connell R. W. 
Published: March 2016

Spiral galaxies are a composite of two dynamical population types: the spheroidal and disk populations. These can be studied in isolation in E and Irr galaxies, respectively. It is natural to expect that the combination in a spiral of a dense spheroidal population, having a deep central potential well, with a repository of interstellar gas and dust in the disk gives rise to special conditions not usually found in E or Irr galaxies. And in fact, we find spectacular concentrations of star forming regions in some spiral nuclei.In this review, I will limit most of the discussion to later spiral types which are classified as “intermediate” in the Yerkes system (Morgan and Osterbrock 1969). Types earlier than Sbc usually have “k-nuclei,” where the spheroidal population dominates; excellent reviews are available for these types (van den Bergh 1975, Faber 1977).
Stellar Populations and Hubble Type
Authors: van den Bergh Sidney 
Published: March 2016

Men are more apt to be mistaken in their generalization than in their particular observations. MachiavelliIt was already realized by Hubble (1936) that galaxy morphology and stellar content were correlated. He pointed out that resolution into stars increases along the classification sequence Sa-Sb-Sc. Simultaneously the colours of spirals become bluer and their integrated spectral types become earlier as one proceeds from Sa to Sc. Baade (1944) speculated that the red stars in ellipticals and in the nuclear bulges of spirals were identical to those in globular clusters. He suggested that stars in galaxies belong to two distinct populations: young metal-rich stars of Population I which inhabit the disc and spiral arm regions of spirals, and old metal-poor stars of Population II which dominate the light of elliptical galaxies and the nuclear bulges of spirals. Subsequently Baade (1950) emphasized the strong correlation between the occurrence of gas and dust and the presence of young stars. As Baade put it so succinctly “No dust, no Population I”. Belief in a clear cut dichotomy between Population I and Population II was strengthened by the differences in their radial luminosity distributions. The surface brightness of Population I in spirals is well represented by an exponential disc, whereas the surface brightness of Population II stars in ellipticals and the bulges of spirals may be described by an r1/4 law (de Vaucouleurs 1959).
Introductory Remarks
Authors: Hodge P. W. 
Published: March 2016

It is not easy to measure distances to galaxies. That we even try is as much a measure of our audacity as it is an indication of our ingenuity. But we do try, and we feel that we must try, because so many of our grandest questions and most basic problems about the universe depend on our knowledge of its size and scale.This Joint Discussion brings together some of the astronomers who have concerned themselves with this difficult task. They do not all agree among themselves. This is not a topic that has reached a state of selfcomplacent fixity, but rather is still a subject of controversy and doubt. The Joint Discussion was designed by its organizers to expose the problems rather than to solve them, to discover the questions rather than to agree on an answer to them.
Hubble Type Dependence in the Tolly-Fisher Relationship
Authors: Thonnard Norbert , Rubin Vera C. 
Published: March 2016

Data from 60 field spiral galaxies shows that the Tully-Fisher (TF) relationships, MB vs. log(Vmax) and log(Dkpc) vs. log(Vmax), are both Hubble type dependent and that the slope in the MB–log(Vmax) correlation is steep, ~10.Our study, conducted in collaboration with W.K. Ford, Jr. and D. Burstein, is principally aimed at elucidating the intrinsic range of properties of spiral galaxies. Hence, we picked a sample of 21 Sc’s, 23 Sb’s and 16 Sa’s with the widest range in luminosity and radius we could find at each Hubble type. Type classifications come principally from Sandage and Tammann (RSA); a few from de Vaucouleurs et al. (RC2) and Nilson (UGC). We stress that this is not a volume limited sample; the end members in the luminosity or radius range of the galaxies at each Hubble type are quite rare. Vmax comes from the maximum observed optical rotation velocity. We also have 21-cm profiles for all Sc’s, 2/3 of the Sb’s and 1/2 of the Sa’s; the result remains the same whether Vmax comes from 21-cm profiles or optical rotation curves. But note, ~1/3 of the Sa galaxies observed were undetectable at 21-cm. This must introduce a bias in the infrared 21-cm TF results. Magnitude corrections come from Heiles and Burstein (1978), but corrections from the RC2 give the same result. We currently have data for 8 galaxies in the Pegasus I and Cancer clusters, which are also consistent with the results shown below.
Cometary Spectroscopy and Implications to the Chemical Composition, Physical Properties and Origin of Comets
Authors: Rahe Jürgen 
Published: March 2016

AbstractRecent spectroscopic observations of comets, obtained especially in the vacuum ultraviolet spectral region from sounding rockets and satellites, have considerably increased our knowledge of the chemical composition of comets, and the physical and chemical processes occurring in their head and tail. From the UV spectra of comets observed so far, one can perhaps conclude that they have a very similar, homogeneous chemical composition, and possibly also a common origin.
Properties of Ices and Grains: An experimental study
Authors: Dorm Bertram 
Published: March 2016

AbstractProton irradiation of a variety of ice mixtures were carried out to study the effect of galactic cosmic ray irradiation of comets in the Oort Cloud. Three significant effects were noted (1) production of new molecules; (2) production of a more energetic ice at low temperatures; (3) production of a non-volatile, complex organic residue. These phenomena suggest various effects on new comets approaching the sun including enhanced activity. Experiments on the condensation of silicate grains provide information on the condensation mechanism and properties of grains. Controlled annealing of the amorphous condensates shows how crystallization occurs. Infrared spectra of different stages of crystallization contain features that may identify composition, structure and history of refractory material.
Physical Conditions in the Central Region, and the Nature of the Engine
Authors: Cavaliere A. 
Published: March 2016

AbstractThe phenomena associated with Active Galactic Nuclei raise three main astrophysical problems: (1) the nature of the primary source of energy; (2) the physical conditions within the radiation source; (3) the nature of the population evolution over cosmological time-scales.I shall outline the links between (1) and (2), (1) and (3), that briefly go as follows. The Prime Mover is very likely to be a converter of gravitational energy in a very compact mass configuration. The associated radiation source, if it is also very compact, is so efficient and loss-dominated as to require specific conditions for the power transport and supply to the radiating particles: collisionless, effected by electromagnetic fields coherent on scales collective or macroscopic, to the point of producing at times anisotropic bulk motions. Very compact Prime Movers working at high regimes need also a compact mass supply; the output from these compound engines undergoes a characteristic change that accounts for the type of population evolutions of the associated sources.
Positron-Electron Annihilation Radiation from the Galactic Center
Authors: Ramaty R. , Lingenfelter R. E. 
Published: March 2016

AbstractWe discuss observations of the intense, time variable and very narrow 0.511 MeV positron-electron annihilation line from the Galactic Center, and the implications of these and other observations on the source of the positrons and their annihilation site.
Mass Loss from Novae and Supernovae
Authors: Friedjung Michael 
Published: March 2016

AbstractThe physics of mass loss from these objects is reviewed. Both winds of different types and nearly instantaneous ejection are involved. Supercritical winds driven by the pressure of radiation from an object above the Eddington limit, probably exist for novae after their outbursts. Observations outside the optical region and in particular in the satellite UV have been very important.
Infrared Properties of Extragalactic HII Complexes
Authors: Telesco C. M. 
Published: March 2016

Many galaxies emit significantly more infrared radiation than expected as directly observable photospheric emission. This emission is not restricted solely, or even predominantly, to the galactic nuclei. Rather, where detailed observations exist, they indicate that pronounced emission often originates throughout the disks and especially in the more extended central regions which are distinct from the nuclei. The process which invariably dominates the emission at wavelengths longer than a few microns is radiation from heated dust. At shorter infrared wavelengths, nebular continuum and line radiation, as well as the stellar photospheres, has been observed. In many cases, this emission has been unambiguously associated with HII complexes.In this review, we focus first on infrared observations of relatively isolated giant HII complexes in the LMC and the spiral arms of M33 and Ml01. We then examine complexes which extend over several kiloparsecs near the galaxian centers. We will not consider the large body of data on extragalactic infrared emission which, although surely relevant to our discussion, is not straightforwardly attributable to HII complexes rather than unusual phenomena in the nuclei (see Rieke and Lebofsky 1979).
Structure of Atomic Spectra: Some Recent Laboratory Research of Interest for Stellar Spectroscopy
Authors: Martin William C. 
Published: March 2016

The data covered are wavelength, line classifications, and energy levels, and the references (numbers in brackets) are mainly supplementary to those supplied by Working Group 4 for the 1982 Report of Commission 14.New compilations of the energy levels for all the spectra of Fe (Fe I - XXVI) [42] and Co (Co I - XXVII) [43] have been published. Although compilations of the levels for the 235 iron-group spectra (K through Ni) by the NBS AEL Data Center have been published by element during the past five years, the single-volume collection of these levels now under preparation will incorporate fairly extensive additions and revisions for many of the spectra. A compilation of the levels for Si (Si I – XIV) has been completed and should appear early in 1983.
Report of the IAU WGAS Sub-group on Electronic Distribution
Authors: Kaplan G.H. 
Published: March 2016

The task of the Sub-Group on Electronic Distribution (SGED) of the Working Group on Astronomical Standards (WGAS) is to make recommendations for direct worldwide computer access to astronomical standards of various kinds. Specifically, part of the charter of the WGAS was ”to prepare a draft report on possible electronic access to these units, constants, quantities, and procedures...”Like the other sub-groups, the SGED operated as a ”committee of the whole”, the whole being the entire Working Group on Astronomical Standards. The scope of interest includes numeric data and software that has some sanction by the IAU or has been validated (in some way) as implementing some IAU-adopted model, set of constants, catalog, ephemeris, or algorithm. Thus, the controversial matters of what defines an IAU standard, whether such standards are still useful, what subject areas are appropriate, what specific standards are to be adopted, how software is to be validated, etc., are addressed by the other sub-groups.
Determination of LC and LB
Authors: Fukushima T. 
Published: March 2016

The location-independent part of TCB-TCG, the difference between the two new time scales adopted by the IAU (1992), was integrated numerically for three JPL planetary/lunar ephemerides; DE102, DE200, and DE245. The differences among these three integrations were mostly explained by the difference in the adopted constants of the ephemerides. It was shown that the post-Newtonian correction and the perturbation by asteroids are negligible except for the mean rate, LC. The comparison of these numerical integrations with the analytical formulas of Hirayama et al. (1987) and Fairhead and Bretagnon (1990) as well as their extended versions lead to the best estimate of LC asCombining this with the recent value of the geoid potential in Bursa et al. (1992), we estimated the value of LB, the scale difference between TCB and TT, asTable I summarizes these conclusions. These estimates of LC and LB are more reliable than the former values we gave (Fukushima et al. 1986). The new estimate of LB will be useful in converting the numerical values of some precisely determined astronomical constants such as AU measured in meter from those in TDB to those in TCB. Also the numerically integrated TCB-TCG, which are to be called Time Ephemeris, will be useful when converting between TCB and TDB, i.e. the time scales themselves. The full paper will be appeared in A & A with the title of Time Ephemeris.
The IAU Nutation Theory and Perspectives of its Change
Authors: McCarthy D. , Dehant V. 
Published: March 2016

The IAU General Assembly has adopted in 1980 a nutation series, on the one hand, based on rigid Earth’s contributions theorically computed from celestial mechanics, and on the other hand, based on non-rigid Earth’s contributions theoretically computed from Earth deformation equations using geophysical parameters.1.From the previous papers (see Session 1) of this Joint Discussion, we know that there are differences of this adopted theory with respect to the observations of precession and nutations. These differences can reach several mas, which is well above the present accuracy of the observations.2.From previous papers (see Session 2) and from the posters, we also know that there exist new rigid-Earth nutations (Kinoshita-Souchay, Roosbeek, Hartmann) of which the accuracy has increased by one order of magnitude.3.From Session 3 papers, we know that there are some additional geophysical effects that are not yet taken into account in Wahr’s nutation theory adopted in 1980 by the IAU which have a contribution at a level above the present precision of the observations. These additional geophysical aspects can be accounted for either from a semi-analytical theory (like Mathews, Herring, Shapiro and Buffett are doing), or from an integration of deformation equations through the whole Earth (Dehant, Wahr).