bluuebunny/crossref_metadata_2025 huggingface dataset:
General Principles for Space Astrometry
Authors: Lacroute P.
Published: March 2016

In order to obtain very precise positions of the stars on a sphere, it seems absolutely necessary to go out the atmosphere.

1

– We avoid atmosphere refraction with always uncertain corrections.

2

– We avoid atmospheric turbulence. So the quality of the images is limited by diffraction and not by the seeing.

3

– We avoid atmospheric absorption and diffusion limiting the possibilities on the faint stars. Moreover if we observe from an artificial satellite we have no bending of the instruments.

In view of very high precision (0″.001) on the directions from an artificial satellite, the difficulty is to obtain sufficient stabilisation in attitude. Also, it is necessary to measure the angles between the stars, instead of the directions relative to the satellite.

The mapping of a sphere by angular measurement requires precise measures of large angles; Indeed BACCHUS has shown how that is possible to obtain a precise sphere with relative positions and proper motions, but absolute parallaxes only by precise measures of angles near one value, 90°. Those measures are possible by superposition of two fields in one telescope. A special complex mirror (Fig. I) images the two fields at basic constant angle. We have only to make differential measures to add a small value to the constant.
M Dwarfs at Lower z Distances
Authors: Gliese W.
Published: March 2016

Twelve years ago, during the International Summer Course at Lagonissi, Bart Bok (1966) presented a paper “Desiderata for Future Galactic Research”. He pointed to the importance of studies in the galactic polar caps which would allow us, as he hoped, to determine some basic data for galactic structure.

The significance of his statements was demonstrated already in the following years when the gradual increase of our knowledge of the objects in the solar neighbourhood was suddenly interrupted by new observational data from which diverging conclusions have been drawn. Never before have such controversial opinions on problems in the vicinity of the sun been so eagerly discussed: A formerly unknown numerous population of low-velocity red dwarfs, the mass density resulting from stars three times that formerly thought, a remarkably increased luminosity function - yes or no? Obviously, the controversies have smoothed down again during the last months. But what is the situation after this troubled period? Which problems are still unsolved? Which promising programmes will be proposed? I think this Joint Discussion is justified in 1976!
Available Stellar Data in Galactic Polar Areas
Authors: Jaschek C. , Hauck B.
Published: March 2016

One of the aims of the Strasbourg Stellar Data Centre is to collect and distribute the different stellar data available, so that they can be used for statistical work. As an example of the statistics which can be made, we present in the table some results for the galactic pole areas. The photometric data were obtained from a general file (Magnenat 1976) which lists the stars observed photoelectrically and the system in which observations were made. The results show clearly how fragmentary our knowledge still is; completeness exists at most up to m = 9.
The Luminosity Function of Late-Type Main-Sequence Stars in the Direction of the North Galactic Cap
Authors: Weistrop Donna
Published: March 2016

As a result of the recent discussion concerning the luminosity function of late-type main-sequence stars (Weistrop 1976 and references therein), a program of photoelectric photometry of all red stars in a field near the North Galactic Pole was undertaken. The sample is complete for stars redder than (B - V) = 1.40 magnitude for the following apparent magnitude and area limits: V = 12.0-14.0 magnitudes, 13.5 square degrees; V = 14.0-15.0 magnitudes, 3.0 square degrees; V = 15.0-17.5 magnitudes, 1.0 square degree. Observations in BVRI have been obtained for the 44 stars in the sample. Giants and dwarfs are distinguished by their location in the (B - V)-(V - I) diagram or from published proper motion data, where available. The absolute magnitudes of the dwarfs are determined from the MR - (R - I) relation.

The density distribution perpendicular to the galactic plane of the dwarfs is consistent with the distribution for K giants found by Oort (1960). The derived luminosity function does not differ significantly from that determined by Wielen (1974) for stars close to the Sun. The local space density for stars in the interval MV = 8.5-14.0 magnitudes is 0.099 stars pc−3. The corresponding stellar density derived from Wielen’s luminosity function is >0.066 stars pc−3. Sixty-six percent of the density derived here is contributed by two stars with absolute magnitude in the range MV = 13.0−14.0 magnitudes.
Some Results of Classification of Stars in Kapteyn Areas Applied to Galactic Structure in NGP
Authors: Kharadze E. K. , Bartaya R. A.
Published: March 2016

The observational base of our investigation consists of a two-dimensional MK classification of about 11.000 stars in the 42 Kapteyn Areas situated along the gal.lat-s from −17° up to +72° and 200 Ap, Am stars discovered in the same KA. The dispersion of the applied objective-prism spectra is 160 Â per mm. The data are of high accuracy, close to the Michigan level, and uniformity, which make them reliable. The limit is close to the 12-th ph.mg.

The general conclusion of the undoubted importance is stated: the galactic concentration of dwarfs is closer than it had been assumed until now; on the other hand - the giants are not so closely concentrated to the galactic plane as it has been accepted.
Mean Chemical Abundance of the F Stars as a Function of Distance from the Galactic Plane
Authors: Blaauw A.
Published: March 2016

At the Tbilisi European Regional Meeting 1975, I reported on results of uvby, Hß photometry of F-type stars in the north and south galactic polar caps (Blaauw and Garmany, 1976), based on stars in the McCormick proper motion fields between latitudes 60° and the poles. A relation was shown to exist between the quantity Am. as determined in this photometric system, and the distance, z, from the galactic plane; Δm1. being a measure of the metal abundance in these stars. The spectral range we deal with is defined by b-y = 0.25 to 0.40, corresponding with F0 to G2. It was found that, from the solar neighbourhood near z = 0, to z = 700 pc, the mean relative metal abundance M/H decreases by a factor of about one third.
RGU Three-Colour-Photometry Towards the North Galactic Pole: Halo-To-Disk Mass Ratio
Authors: Fenkart R. P. , Steinlin U. W.
Published: March 2016

The halo program of the Basel observatory, initiated by Becker in 1965, is based on a three colour photometry in test fields along the circle through the galactic centre and the galactic poles. The more favourable direction of the blanketing vector relative to the main sequence in the two colour diagram for RGU makes it possible to separate at least statistically the disk population and the halo populatior within the interval of absolute magnitudes + 3 ≦ MG ≦ + 8. It is therefore possible to derive density functions for both populations and for different intervals in absolute magnitude for each test direction within the test plane defined above. This allows one to draw isodensity curves in the test plane and, assuming rotational symmetry of the halo, also isodensity surfaces. The last assumption is tested at least locally by test fields with different inclinations towards the test plane (Fenkart, R.P. and Wagner, R., 1975).
Polarization Measurements and Extinction Near the NGP
Authors: Markkanen T.
Published: March 2016

In order to study interstellar extinction near the NGP a polarization observation programme has been undertaken at the Metsähovi Observatory of the University of Helsinki. 32 stars (b>80°) have been measured with an accuracy of a few hundredths of a percent. To this list observations of 42 stars made by Appenzeller (1968) were added. The stars measured have distances up to 400 pc (Figure 1).
Progress Report on a Search for Parallax Stars in the Region of the South Galactic Cap
Authors: Murray C. A.
Published: March 2016

A series of plates is being taken with the U.K. 48-inch Schmidt Telescope at Siding Spring on a field centred on the star GC 1110 near the South Galactic Pole, in order to detect any stars brighter than about mpg = 18, which may have significant trigonometric parallaxes.

A search list of more than 16, 300 objects in an area 4¼° × 4¼° has been formed from a preliminary scan on the Galaxy machine at R.G.O. Prom 1974 January to 1976 January some 30 plates have been obtained, nearly half of which have been measured in each of two orientations on Galaxy; each measuring run takes about 16 hours.
Berkeley Studies of Faint Stars at High Latitudes
Authors: Kron Richard G. , Chiu Liang-Tai George , Brooks Kate O.
Published: March 2016

Several Lick 3-m prime-focus plates of Selected Areas 57, 68, and 51 (taken by I. King) in B, V, and R have been measured for stellar magnitudes down to the plate limit by L. Hinrichs and King, and are currently being measured by Chiu for proper motions (several hundred stars per plate) with the Berkeley PDS microdensitometer. Prime-focus plates are also available from the Hale 5-m and Mayall 4-m telescopes, giving an overall baseline of 20 years. Work so far indicates that on the Lick plates stars brighter then V = 19 can be measured to within one micron standard error; the error becomes unacceptably large for stars fainter than V = 20. A large number of stars bluer than B-V =0.4 show proper motion and are therefore excellent candidates for white dwarfs. For 0.4 ≤ B-V ≤ 0.8, the proper motion stars are expected to be predominantly subdwarfs.

The frequency distributions of the stars in V and B-V for the three fields are being analysed by Brooks; the fields are advantageously placed for study of the density distributions in both the disk and the halo. These data should allow the halo stars to be studied out to a distance of 10 to 15 kpc, as well as a determination of the degree of flattening of the halo. Also, a study will be made of the z and ῶ density gradients in the disk, and the luminosity function of disk stars.
Motions of Near-Polar K-Giants Along the Z-Coordinate
Authors: Balakirev A. N.
Published: March 2016

The motion of G8-K5 III, IV stars near galactic poles (|b|>60°) was investigated. The main attention was paid to motion in the z-direction. The spectral types, visual magnitudes, colors and radial velocities (vr) were taken mainly from Schild (1973), Heard (1956), Blanco et al (1968) and Wilson (1953). To reduce the values vr by Heard to those by Wilson, the correction of -1 km/sec was made. The stars with variable vr and spectroscopic binaries were excluded from the investigation.
The Role of Proper Motions in Determining the Luminosity and Density Functions
Authors: Luyten Willem J.
Published: March 2016

The papers presented this morning form a good illustration of the old adage that you should never publish a paper that is completely correct, for then you can write only one paper. But if you publish a paper with a lot of errors, you are sure to be criticized, and you can write a second paper to answer your critics, and if the heat proves to be too much you can write a third paper withdrawing everything.

First a bit of history. It is difficult to pin-point when exactly this question of the star density in high latitudes first came up, but I feel sure that it is Implied, to say the least, in the early work on faint blue stars by Malmquist (1927, 1938) and by Humason and Zwicky (1947). This morning Ivan King showed us a table of the changes in the frequency of occurrence among the stars in high galactic latitude as one goes to fainter and fainter magnitudes. This is exactly what I did in 1960 when I published a color-magnitude diagram for 4000 stars down to 19th photographic magnitude near the South Galactic Pole (Luyten 1960). These data had been obtained with the Palomar 48-inch telescope using Haro’s three-image method. I also made up a similar diagram calculated from what I thought were then the best available data on the luminosity and density functions. The conclusion of my analysis was that there seemed to be rather fewer M stars than had been expected, and a great many more stars with the color of F and G stars than expected. This idea was not popular at the time; hence this paper has been carefully ignored until these ideas were used by others twelve years later without reference to the 1960 paper.
[no title]
Authors: Pagel B. E. J.
Published: March 2016

Welcome to this Joint Discussion on stellar atmospheres and interiors. For stellar structure, the atmospheres are of importance for two reasons, first as a source of information on effective temperature, gravity (or mass: luminosity ratio), chemical composition and dynamical effects, and secondly as an outer boundary condition for stellar models.

In the last few years there have been substantial advances in stellar atmospheres as a result of both improved theories and new measurements. In the particular field of abundance determination, non-LTE theory has at last come of age and provided a certain number of corrections that are both realistic and significant, for example in reconciling the neon abundance in B stars with that in nebulae and solar flare particles. Solar abundances have been improved by the provision of better oscillator strengths and better treatment of line broadening, generally with the effect of leading to still closer agreement with carbonaceous meteorites. Nevertheless, he would be a bold man who claimed to know the initial solar abundance parameters Y and Z to better than, say 25 per cent, even if we grant that the photosphere is a true sample of the initial interior abundances - an assumption that is now being questioned (again) in view of the solar neutrino problem.
Behaviour of Microturbulence with Evolution
Authors: Foy Renaud
Published: March 2016

It is reasonable to suppose that the state of the convective zone underlying the atmosphere of cool stars correlates with the atmospheric kinematics. Following Iben (1967), as a star evolves from the red giant tip to the helium burning core phase, the convection rapidly decreases. Then the microturbulence can be expected to decrease too.
Sensitivity of Internal Structure to the Surface Boundary Condition
Authors: Demarque Pierre
Published: March 2016

It is now nearly fifty years since Eddington and Milne had a lively controversy on the importance of the surface boundary condition on the internal structure of stars [see Eddington (1930) and Milne (1930)]. We remember that Eddington believed that the internal structure of stars is basically determined by the physical processes occurring in the deep interior and that what happens in the surface layers has little effect on the total stellar luminosity. On the other hand, Milne emphasized the importance of the properties of the outer layers and the effect these could have on the run of pressure and temperature in the deep interior of the stars. We know now that both Eddington and Milne were correct. Eddington’s considerations apply to the hot stars, the early-type stars which have surface layers in radiative equilibrium. Milne’s arguments are relevant to the cool stars, the late-type stars which have deep convective envelopes. In the former case, one can safely assume in calculations of stellar structure that the density and the temperature both approach zero simultaneously at the surface (the so-called “zero” surface boundary conditions).
Decay of Light Elements in Stellar Envelopes
Authors: Boesgaard Ann Merchant
Published: March 2016

I should like to confine this discussion of the decay of the light elements to Li, Be, and B since the observations of D and He in stars are not relevant to the decay in stellar envelopes. The light elements are trace constituents best observed in the resonance lines. Only Li I and Be II have resonance lines which can be studied from ground-based observations. Therefore we know the most about abundances in stars where these ions can be observed and how those abundances are affected by stellar evolution. I will first discuss the cosmic or initial abundances of Li, Be, and B to establish the “zero-point” from which the decay occurs. Then observations and interpretations relevant to the decay and to stellar evolution will be considered.
Conclusion
Authors: Cayrel R.
Published: March 2016

This joint discussion has amply demonstrated that stellar atmospheres are not passive and dumb bodies just sitting there at the surface of a star.

First of all the surface “feel” fundamental parameters of the star as a whole, specifically the ratio L/R2 and m/R2. As these fundamental parameters are affected by stellar evolution, the surface layers reflect to a large extent the degree of evolution of the star. This is the main basis for photometric and spectral classification systems. One could even claim that the observation of the stellar atmosphere would univocally determine the state of evolution of the star if i) it was always possible to determine the atmospheric abundances of the key elements to internal structure and ii) if the chemical composition of the atmosphere was always representative of the chemical composition of the whole star. Unfortunately a serious problem occurs for i) with the abundance of helium which element has no photospheric absorption line for all spectral types later than B and also with ii) in a more limited portion of the HR diagram, mainly in late B and A slow rotators. But whereas point i) is a mere problem of contingency, point ii) is a basic problem, greatly overlooked in the past, and to which one fourth of the joint discussion was devoted.
Some Comments on the Measurement of Small Scale Strong Magnetic Fields on the Sun
Authors: Wiehr E.
Published: March 2016

Since Dr. Harvey has already mentioned the main results of my observations, I want to restrict myself to two topics:

i)

a brief description of the improvements of my method as compared to that used by Stenflo (1973),

ii)

some puzzeling aspects of my results which might be discussed in this meeting.

The main differences between the two methods of simultaneous Zeeman polarization measurements used by Stenflo (1973) and by myself are based on suggestions by Schröter (1973):

a)

use of three instead of only two differently split lines;

b)

use of less temperature sensitive lines;

c)

use of model atmospheres instead of a Milne-Eddington model for the calculation of the ‘calibration curves’;

d)

observation of selected Ca+K features in order to avoid the statistical method with the scatter-plot diagram.
Facular Models, the K-Line, and Magnetic Fields
Authors: Chapman G. A.
Published: March 2016

Photospheric faculae are now believed to be closely associated with the small-scale solar magnetic field. In order to obtain reliable observations of solar magnetic fields, one needs to have a good description of faculae, which is presently lacking. The problem in obtaining good observational data is severe because faculae are usually not spatially resolved, particularly so in the case of spectroscopic observations. Proper use of spectroscopic observations also requires some knowledge of solar velocity fields and atomic physics in the case of a non LTE analysis. Many of these problems can be avoided by making use of the wings of the Ca II K-line. The wing of this line is unaffected by magnetic and velocity effects. The formation of the line has become increasingly well understood and most of the wing (with the exception of the inner 1 - 2 Å) is formed in LTE. The line is so strong that its formation spans the whole depth of the photosphere.
Behaviors of B Star Continua and Absorption Features Determined from the TD1 S2/68 “Ultraviolet Bright Star Spectrophotometric Catalogue” and from Copernicus Spectra
Authors: Vreux J. M. , Swings J. P.
Published: March 2016

Ultraviolet low resolution spectra of most of the B stars observed with the S2/68 experiment onboard the TD1 satellite in the spectral range 1350 A - 2500 A are computer-investigated in order to define a grid of standard behaviors (J.M. Vreux and J.P. Swings, 1976 Astron. Astrophys., in press). The behavior of the relative intensities of the Balmer and Paschen continua is studied as a function of the spectral type and the visible photometric index Q: both relations are shown to be luminosity dependent. A comparison to theoretical predictions and to previous studies is also presented. A measure of the slope of the pseudo-continuum drawn between ~ λ 1660 A and ~ λ 2550 A is studied in the same way: the effect of luminosity is discussed in connection with recently proposed temperature scales for super-giants. The behavior of the depths of the absorption features at λλ 1550 A, 1940 A, 2000 A, 2055 A, 2105 A, 2340 A and 2395 A with respect to the spectral type, the Q index and the luminosity class is also briefly presented. Special emphasis is given to the absorption features at λ 1550 A in connection to the discussion of the Felll lines in the ultraviolet spectra of early B stars by J.P. Swings, M. Klutz, J.M. Vreux and E. Peytremann (1976, Astron. Astrophys. Suppl. 25, 193). Preliminary results of a study of high resolution Copernicus spectra in the A 1550 A region are also presented: it is shown that the role of Felll remains predominant for stars of spectral type as early as about BIII - BIIII (J.P. Swings and J.M. Vreux, to be published).
Spectral Classification Using ANS Photometric Data
Authors: van Duinen R. J. , Wesselius P. R.
Published: March 2016

In this contribution we will discuss the extension of visual photoelectrical photometry into the ultraviolet and its potential impact on stellar classification. As is the case in the visual, classification by photoelectrical photometry in the ultraviolet has some important advantages over classification by inspection of individual spectra. Studies that require global characteristics of stellar properties -such as studies of stellar distribution, extinction properties of interstellar dust, galactic structure - often require large numbers of observations to derive statistical properties. In photoelectric photometry such a large number of observations can usually be obtained in a reasonable amount of time and relatively conveniently processed without subjective criteria being applied to the data. Comparatively, the classical way to obtain stellar classification is a complex process that requires many steps.
The Ultraviolet Spectrum of Beta Lyrae
Authors: Hack M. , Hutchings J. B. , Kondo Y. , McCluskey G. E.
Published: March 2016

Selected regions of the ultraviolet spectrum of Beta Lyrae were observed in 1973 and 1974 at the epochs of the two eclipses and of the two quadratures with the Copernicus Princeton University spectrometer. The results were published in the Astrophysical Journal (Hack et al. 1975, 1976). Here we summarize the results of a third series of observations with the same instrument covering the whole period of 12.93 days. The following spectral regions were observed in June 1975 during 13 consecutive days: λ 1036–1060; 1300–1326; 1398–1416; 2050–2098; 2580–2632; 2777–2812 in the low resolution mode; λ 1172–1177 and 2795–2799 in the high resolution mode. The main results are the following: 1) The radial velocity curve for λ 1175 C III is almost 180° out of phase with the orbital velocity curve of the primary star and the mean velocity is - 240 km s−1; K = 70 km s−1. This suggests that λ 1175 C III is formed in an expanding envelope associated with the secondary. The mass ratio can be determined: m2 /m1 = 2.7 −1.1/+0.2 .2) The continuum variation confirms the results obtained with 0A0-2. At λ 2100 we observe the light of a continuum indicating that the temperature of the body eclipsing the primary star is lower than that of the primary and of about 9000 K. The light curves at λ 1900, 2100 can be explained with the contribution of Fe III emission in the circumbinary plasma. On the contrary, the depth of the secondary minimum at λ 1311–1326 and at λ 1410 cannot be explained with the Si III and Si IV emissions. A possible explanation is the presence of a hot spot in the region of the eclipsing body (probably a disk surrounding the companion) where the stream from the primary impinges on the disk. The hot spot can also explain the behavior of the infrared light curves observed by Jameson and Longmore (1976).
The Mg II Features Near 2800Å and Spectral Classification
Authors: Kondo Yoji
Published: March 2016

The Mg II resonance lines at 2795.523 and 2802.698Å and their respective subordinate lines at 2797.989 and 2790.768Å are probably among the most prominent and interesting spectral features in the ultraviolet; they are perhaps the most significant in the mid-ultraviolet. They are also observable in one form or the other in stars of practically all spectral types. We shall discuss relatively high (about 0.4Å) resolution observations of these features.

In the early spectral types both the resonance and subordinate lines are seen primarily as absorption lines. An interstellar absorption of varying strengths is superimposed on the photospheric absorption of the resonance lines. The strengths of the photospheric resonance and subordinate lines increase from 0 to B, e.g., Lamers et al. (1973) and Kondo et al. (1975). The subordinate lines begin to merge with the resonance lines in late-B stars. In mid-A type stars, the resonance and subordinate absorption strengths become maximum. In F-type stars, the photospheric absorption strenghts continue to decrease. Chromospheric emissions become definitely detectable in F-type stars (Kondo et al. 1972). In a G2 V star, the sun, the chromospheric emission is fairly prominent at the core of relatively weak photospheric absorption. In K and M-type stars, this region is presumably dominated by the chromospheric emissions of Mg II resonance lines with the photospheric absorption becoming negligible in late-K stars; the only extant observation in this region is that of e Eri (K2 V) (McClintock et al. 1975).
Concluding Remarks
Authors: Houziaux L.
Published: March 2016

We have had today for the first time a confrontation of the views of many astronomers about the use of ultraviolet spectroscopic and photometric data in the field of spectral classification.

Dr. Jaschek recalled us that much work has still to be done from the ground since only 14% of the stars up to the tenth visual magnitude have M.K. spectral types. The current accuracy is around one tenth of a spectral type and 0.6 of a luminosity class. Jaschek notes that the luminosity classification from spectral inspection is superior to what is obtained from photometric data, a fact which is not surprising if we recall that lines are much more sensitive to pressure effects than the continuum. However, the introduction of a third parameter seems necessary, although it is not clear what this parameter should be.
[no title]
Authors: Mullan D. J.
Published: March 2016

Heterogeneities in the solar atmosphere exist on many different length scales ranging from values as large as the solar radius (~106km) down to features which are identifiable only by interferometry (~102km). Rather than simply cataloguing the observed parameters of each and every known type of heterogeneity, I would like to concentrate on a few types of heterogeneities, with a view to identifying the information which is currently available concerning the physical mechanisms responsible for creating the in homogeneities. It is only if we can first identify the physics of each type of heterogeneity that we can hope to take even the first step towards predicting how each particular heterogeneity should scale to other stars. Since the present session is a joint discussion among mainly stellar astronomers, I feel that this approach is probably the most favorable method to present some of the large amount of information now available on solar features. Of course we expect that our solar information will be of most use to stellar astronomers in interpreting observations of stars which have similar spectral types to the sun. Nevertheless, we hope that nature will be kind enough to allow us to scale at least some of our information over a non-negligible area in the H.R. diagram.
The Interplay of Molecular Spectroscopy and Astronomy
Authors: Herzberg G.
Published: March 2016

Carlyle S. Beals, former Dominion Astronomer of Canada and one of the most distinguished astronomers Canada has produced, died on 2 July, 1979. Carl Beals was not only a great astronomer, known throughout the astronomical world for his studies of Wolf-Rayet stars and many other contributions to astronomy, but he was also a great human person who exercised considerable influence on the development of astronomy in Canada and elsewhere. I should like to dedicate this lecture to the memory of Carl Beals.
The Structure of Galactic Nuclei: Recent Observations
Authors: Faber S. M.
Published: March 2016

Nuclei are often envisioned as sites for energetic and explosive phenomena in galaxies and may even be the birthplaces of quasars. Regardless of what models are chosen to represent such sources, a knowledge of the surrounding mass density and gravitational potential field is bound to be important for the creation and maintenance of the central engine. Moreover, galactic nuclei are worthy of close scrutiny even for their own sake. They constitute the brightest, most easily observed portions of galaxies and, in ellipticals, yield the central mass-to-light ratio, a quantity which cannot be determined for ellipticals using the ordinary rotation-curve method.
Infrared Observations of the Galactic Nucleus
Authors: Lacy J. H.
Published: March 2016

Infrared observations of the galactic nucleus and conclusions regarding the nature of the objects present there are reviewed. Observations of three sources of infrared radiation are discussed: near-infrared emission from cool stars, mid- and far-infrared emission from dust, and line emission from ionized gas. These observations provide information about the mass distribution, the stellar population, and the origin and ionization of the compact mid-infrared sources. The possibility of the existence of a massive central black hole is discussed.
Activity in the Nuclei of Normal Galaxies
Authors: Heckman T. M.
Published: March 2016

The principal motivation behind the work summarized below was to define the nature of a “typical” galactic nucleus and thereby determine whether such nuclei differ from active nuclei in a qualitative or only quantitative sense. I hoped that such a study would then yield clues as to the origin and duration of nuclear activity and the effects such activity might have on the structure and evolution of the surrounding galaxy. For a more complete discussion of the results below, see my Ph. D. dissertation (Heckman, 1978) or the series of three papers (Heckman, 1979) to be published elsewhere.
The Stellar Content of The Nuclei of Spiral Galaxies
Authors: Crampton David
Published: March 2016

Widened, image-tube spectra at a dispersion of 120 Å mm-1 were obtained of the nuclei of 36 spiral (Shapley-Ames) galaxies. Spectral features in the region λλ 3800 - 4300 Å were used to assign a spectral index to each galaxy and to estimate the luminosity classes of the stars contributing the majority of the light at these wavelengths. Bulge magnitudes were either estimated or determined from published aperture photometry, and converted to absolute magnitudes, MN, assuming H = 100 km s-1 kpc-1. A correlation was found between the spectral index and MN such that the luminosities of galaxies can be estimated to an accuracy of ˜1 mag.

The nuclei of late type spirals have spectra which resemble those of A and F stars, and it has been assumed that this indicated that these nuclei contain younger stars than those of early type spirals and elliptical galaxies. However, inspection of the luminosity sensitive features in the spectra indicate a preponderance of giant stars, and since A giants are relatively rare, it is probable that these blue stars are metal poor horizontal branch stars which are spectroscopically similar in appearance. The spectral index variation is thus due to metal abundance rather than age.

Complete details are to be published in the Astrophysical Journal by McClure, Cowley, and Crampton (1979).
Centers of Star Formation in the Nuclei of Galaxies
Authors: Pronik V. I.
Published: March 2016

Nuclei of galaxies are the phenomena intimately connected with the structure of galaxies, their origin and evolution. Spectral and photometrical characteristics and therefore the stellar population of the most nuclei of normal galaxies are like that of central regions or bulges (Walker, 1962, 1964; Vorontsov-Velyaminov, 1965, 1968). Processes of star formation in the nuclei must be considered together with the problem of formation of the central regions (bulges) or even of all galaxies as a whole.

The term “galactic nucleus” is usually applied to the central region (or center of symmetry) having the maximum stellar density (maximum surface brightness) and dimensions less than 100 pc (dimension of a globular cluster). The observational evidence of star formation at the present epoch is related to the nuclear regions within radii of 100-1000 pc or more. Information about the physical condition of the gas and about star formation just in the center of galaxies (≤ 1 pc) can be obtained only by theory. The red colour of the central star cluster of normal galaxies is evidence that star formation in this region is practically finished.
Ultraviolet Spectroscopic Measurements of Cool Stars
Authors: Dupree A. K.
Published: March 2016

A vast increase in the amount of information on cool stars has occurred during the past 3 years starting with the spectroscopy of the brightest objects from the Princeton experiment on Copernicus, the near ultraviolet balloon measurements from BUSS, low dispersion observations in the far ultraviolet from rocket instruments, and most recently, spectra from the International Ultraviolet Explorer satellite (IUE). IUE now gives access to a wide variety of cool stars and stellar systems enabling systematic studies to be made.

Drawing on the most recent material from IUE, we discuss the presence and structure of chromospheres and coronae in single stars of varying gravities, surface temperatures, and activity. Evidence of mass loss and the concurrent presence of a corona are also noted. Binary systems of late-type stars (the RS CVn and W UMa type) are briefly discussed since they display extremes of surface activity. A binary system such as VV Cep containing a late-type star and an early-type companion provides a unique probe of cool extended stellar atmospheres.
Extragalactic Astronomy and IUE
Authors: Longair M. S.
Published: March 2016

The first thing to say is that IUE has been a great success and we should all congratulate the agencies in the U.S.A., Europe and the U.K. and the many scientists and engineers involved in the project on making it possible. In surveying what has been achieved so far, it is important to remember that we may well have IUE with us for a further 3 or even 5 years, meaning that it may be operating right up to the time of launch of Space Telescope. Undoubtedly, observations with IUE will pioneer many fields which will be explored in much more depth by the Space Telescope - there is no reason why IUE should not scoop some of the topics originally thought to be only the province of the Space Telescope.

It was always recognized that the study of extragalactic objects would be difficult with IUE. As Michael Penston expresses it, most astronomers don’t try to do extragalactic astronomy with an 18-inch telescope. Nonetheless, many observers have used their observing time to make long exposures on faint objects and there is no question about the significance of the science which has been accomplished. My own experience has been entirely with quasars and radio galaxies and, now that many of the obvious bright objects have been observed, we have settled into a pattern of only attempting one object per 8 hour shift, switching between the long and short wavelength spectrographs in mid-shift. We then repeat the observations in the following shift. Our experience is that this procedure is valuable in distinguishing whether faint features are real or not. Because of the long projected life of IUE, we do not regard this as an extravagant use of time and it is to be hoped that many more observers will adopt this point of view.
Hot Gas in Clusters of Galaxies
Authors: Culhane J. L.
Published: March 2016

The discovery of extended X-ray sources associated with clusters of galaxies which resulted from the Uhuru X-ray sky survey was one of the most important observations to come from that programme. Following Uhuru, the Ariel V and HEAO-1 sky surveys have found many more cluster X-ray sources and the recently launched Einstein observatory has begun to increase further the number of identifications. However there is in any case evidence from the X-ray cluster luminosity function that all rich clusters of galaxies will emit X-rays at some level.

Preliminary results from the Einstein observatory (Murray, 1979) suggest that the extended X-ray emission from centrally condensed (cD) clusters is itself centrally condensed and spherically symmetrical in appearance. However irregular clusters have non-uniform X-ray surface brightness distributions. In addition there are some galaxies in clusters of irregular morphology that have associated X-ray halos.
Acceleration Mechanisms, Flares, Magnetic Reconnection And Shock Waves
Authors: Colgate Stirling A.
Published: March 2016

Acceleration in astrophysics usually means converting a significant fraction of the energy of some source into particles whose individual kinetic energy greatly exceeds the average temperature of the medium. There are three general classifications of acceleration processes. The first is hydrodynamic, second coherent electromagnetic, and third stochastic electromagnetic processes. We shall discuss each of these briefly in terms of the spectrum of accelerated particles. This can be related to an efficiency by the relationships N(>E) α E┌ or an energy efficiency N(>E) α EI-г In astrophysics we frequently emphasize Г without realizing the constraints this imposes upon the efficiency of the acceleration mechanism. So often the relatively flat spectra result in efficiency requirements that challenge the ingenuity of those who wish to invent acceleration mechanisms.
Hot Gas in Galactic Haloes and Winds
Authors: Cowie Lennox L.
Published: March 2016

At this time we have no direct evidence for the presence of hot gaseous haloes or winds associated with galaxies. We do know that hot gas exists in conjunction with cold gas in the disks of the spirals and that this gas is hot enough to form a substantial corona. There are also a number of indirect observations which would suggest that hot gas flows and possibly bound hot gas occur in both elliptical and spiral galaxies.

In the case of elliptical galaxies the expected accumulated mass loss from the stars is not observed. Typical upper limits to the mass of cold gas at less than 1040K are around 108 M based on 21cm emission studies of the galaxies (reviewed by Van Woerden 1977). We would expect almost two orders of magnitude more material than this to have been ejected from the stars. Burke (1968), Johnson and Axford (1971) and Mathews and Baker (1971) postulated the existance of a hot galactic wind with temperatures of a few times 1060K powered by supernovae, in order to clear material from these galaxies. The evidence for hot galactic haloes around spiral galaxies is even more indirect and is based on the existance of high latitude cold clouds in our own galaxy. The velocities and number of these clouds imply that they almost certainly lie high above the galactic cold gas which extends only to a height of 130 Fc in the solar neighborhood. Spitzer therefore suggested in 1956 that an intercloud gas would have to exist to keep these clouds confined, and that to have such a large scaleheight it would have to be hot with temperatures of around 1060K. (An alternative suggestion by Pickelner (1955) was that the halo was cold but supported by turbulent velocities of around 70 km s-1.) The Spitzer Halo was assumed to be maintained by energetic particles from SN in the plane.
Observations of Solar Pulsations
Authors: Hill Henry A.
Published: March 2016

There have been several interesting developments during the last year with regard to global oscillations of the sun. However, because of the very full program of this Joint Discussion and the resulting tight schedule, only one point will be addressed here: the observational evidence for global oscillations of the sun with periods ≤ 1 hr and > 5 min.

The most decisive test currently available for identifying global oscillations is their examination for coherence of phase over an extended period of time. This test discriminates against both nonsolar phenomena, such as effects caused by observing through the earth’s atmosphere, and solar phenomena which occur in the frequency range of interest but which are not global oscillations of the sun. The search for this coherence has been conducted using 2 sets of observations from SCLERA, the 1973 observations of Hill and Stebbins (1975) and the 1978 observations described by Caudell et al. (1979). The results of these examinations strongly support the interpretation of the reported oscillations as solar in origin and as global in character.

The above observations consist of time chains of diameter measurements made at SCLERA. A list of references may be found in Hill and Stebbins (1975) and Hill (1978) which describe the telescope, the method for defining the solar diameter, the means of measuring the solar diameter, and the data reduction techniques used to produce the final Fourier transforms and associated power spectra of the diameter measurements.
Amplitudes and Frequencies of δ Scuti Stars: Systematics
Authors: Breger Michel
Published: March 2016

Delta Scuti stars are short-period pulsating A/F stars situated on or above the main sequence. They often pulsate with two more excited modes. The knowledge of the period lengths and period ratios is very important to deduce the nature of the pulsation modes, e.g. is the pulsation radial or nonradial? Furthermore, these values provide valuable information on the interior structure of these stars.

The determination of the period ratios from the light curves is difficult, since only a few cycles can be covered during a night. The small amplitudes of about 0.01 mag in some variables also makes the multiperiod analysis difficult. While every star should be considered on its own merit, a rough estimate of about 5 nights per deduced period appears to be a minimum requirement. Even then different analyses can give different results. A recent example is the star 38 Cnc (=BT Cnc). An excellent set of observations by Guerrero, Mantegazza and Scardia (1979) gave three periods with nonradial period ratios and a good fit. Our subsequent analysis of the same data gave three radial periods with an even better fit!
White Dwarf Pulsations
Authors: Dziembowski W.
Published: March 2016

It has been known for a long time that white dwarfs are pulsationally unstable if nuclear burning takes place in their envelopes. Perturbation of energy generation rate promotes pulsational instability and this effect is frequently referred to as ε-mechanism. In recent years, with the advent of high-speed photometry, many rapidly varying white dwarfs have been discovered. However, periods of variability were found to be significantly longer than the periods of radial pulsations which were the only type of oscillations considered before the discovery. Furthermore, the case of ε-mechanism as being responsible for the observed variability has never been made strong for any of the observed objects.

Variable white dwarfs are found among: Iosingle DA-type objects in the effective temperature range 10000-15000K; 2omembers of close, usually but not always, cataclysmic binary systems. Although, following an early suggestion by Warner and Robinson (1972), the excitation of nonradial oscillation is postulated in both cases, the two types represent very different physical situations and they will be discussed here separately.
Supergiant Pulsations
Authors: Maeder A.
Published: March 2016

The main data concerning the amplitudes and periods of super-giant variations are reviewed. The period-luminosity-colour relation of intermediate-term variations is compatible with pulsation motions. The Q-values seem to be larger than those corresponding to the fundamental mode and there are arguments favouring non-radial oscillations.
Recent Theoretical Results for Cepheid Pulsation
Authors: Cox Arthur N.
Published: March 2016

Detailed theoretical investigations of stellar pulsation need a mass and a composition before models can be constructed for study. Unfortunately, for the last ten years the masses of the Cepheids, which can be determined with reasonable accuracy by six different methods, have been in dispute. One possible way to resolve these various mass anomalies is to postulate an inhomogeneous composition envelope structure. Thus the principal problem in current theoretical studies is: What are both the masses and envelope compositions of Cepheids?

Stellar evolution theory has indicated that main sequence B stars evolve to become red giants or supergiants and then loop blueward in the Hertzsprung-Russell diagram to cross again the pulsation instability strip the second and third (or even more) times. The second and third crossings are the slowest for models of evolutionary masses between 4 and 13 M⊙. Both below and above this mass the stars become Cepheids (or δ Scuti variables at the lowest masses) on their sole crossing to the red. Massive stars do not become cool enough to become Cepheids if the main sequence mass is above 18 M⊙.
Rr Lyrae Variable Stars
Authors: Romanov Yu. S. , Tsesevich V. P. , Zaikova L. P. , Firmanyuk B. N. , Udovichenko S. N. , Fenina Z. N. , Shakun L. I.
Published: March 2016

Some twenty years have passed since the decision was taken by the General Assembly of IAU in 1958 to resume a regular control of light variation stability in RR Lyrae stars. With this end in view the revision of elements is carried out at the Odessa Astronomical Observatory yearly, whereas ephemerides of RR Lyrae stars are published at the Krakov Observatory. Now 164 stars brighter than at maximum light visible in the northern hemisphere have entered the list.

Considerable photometric observational material analyzed has shown that some RR Lyrae stars have stable periods of light variation (e.g. TV Lib, UY Cyg, SU Dra), while other ones have periods which vary regularly or proportionally to time (e.g. SV Eri, AV Peg, RV CrB) (Tsesevich, 1966; Firmanyuk, 1976; Romanov et al., 1978). In case of DR And at comparatively small amplitude of O-C variation, about 0.15, a synchronous variation in mean light at maximum nearly by has been found (Romanov, 1978). Unfortunately, necessary observational material is frequently unavailable to obtain the unambiguous classification of period stability character. The property of RR Lyrae stars light variation stability is connected with the weakening of KCall absorption line (Tsesevich, 1966, 1971).
Non-Radial Oscillations in Red Giants
Authors: Keeley Douglas
Published: March 2016

The structure of red giant stars allows non-radial oscillation modes which propagate as p-modes near the surface, to propagate below the convection zone as g-modes with very high radial wave number [Dziembowski (1971, 1977), Shibahashi and Osaki (1976)]. Under some conditions the oscillations in these two propagation regions can be treated as virtually independent normal modes [Shibahashi and Osaki (1976)]. This paper examines the situation in which this approximation is not good, and discusses possible observational consequences of the interaction of the two propagation regions.

The linearized differential equations describing non-radial adiabatic oscillations in stars can be written in the form,
1a1b