bluuebunny/crossref_metadata_2025_split huggingface dataset:
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.
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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.
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.
The Ultraviolet Spectrum of Beta Lyrae
Authors: Hack M. , Hutchings J. B. , Kondo Y. , McCluskey G. E. 
Published: March 2016

AbstractSelected 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.
Infrared Observations of the Galactic Nucleus
Authors: Lacy J. H. 
Published: March 2016

AbstractInfrared 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.
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.
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.
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⊙.