bluuebunny/crossref_metadata_2025_split huggingface dataset:
Polarimetry of Emission Lines as a Probe of Stellar Winds
Authors: McLean Ian S. 
Published: March 2016

The motivation for obtaining optical polarization data of close binary systems and/or stars exhibiting stellar activity (i.e., flares, winds, chromospheres, spots, etc.) is that polarization is not only dependent on the physical condition of the stellar environment but is actually rather sensitive to geometric factors and can act as an excellent diagnostic of the latter.High resolution, multichannel spectropolarimetry of certain emission-line stars was demonstrated to be a powerful new technique in studying the physics and kinematics of stellar envelopes. Two sources of polarization were discussed viz., (l) fluorescent (resonant scattered) emission lines similar to those found in the solar chromosphere and corona, which can be highly polarized and sensitive to magnetic fields, and (2) Doppler broadened emission lines formed in a rotating/expanding stellar wind. The Doppler broadening effectively provides spatial resolution, so that as one scans a line polarimetrically, scattering from different regions of the stellar wind is observed according to its kinematical motion.
The Tully-Fisher Relation and its Application to the Distance Scale
Authors: Aaronson M. 
Published: March 2016

AbstractThe Tully-Fisher relation applied in the infrared appears to be the best global distance indicator presently available for determining the expansion rate and deviations from uniform Hubble flow. In this article recent results obtained using the IR/H I method are reviewed. A Virgo-directed Local Group velocity of about 300 km s–1 is indicated (implying a local value for the deceleration parameter qo ~ 0.05 – 0.1) along with a “best guess” value for the Hubble Constant of 85 km s-1 Mpc-1.
Uv Galaxies
Authors: Ye Khachikian E. 
Published: March 2016

The systematical statement of the concept of the activity of the nuclei of galaxies was first made public by Ambartsumian about 25 years ago (Ambartsumian 1958, 1962, 1965). Since 1965 he has been advancing and developing the idea of the basic role of the nuclei of galaxies in their life and evolution.According to Ambartsumian the “activity” of the nuclei of galaxies manifests itself mainly in the following forms:
1.Outflow of ordinary gas matter (in form of jets or clouds) from the nuclear region at the velocity of up to hundreds of kilometres per second.2.Continuous emission of the flux of relativistic particles or other agents, producing high energy particles, as a result of which a radio halo may form around the nucleus.3.Eruptive ejections of gas matter (M82 type).4.Eruptive ejections of concentrations of relativistic plasma (NGC 4486, 5128, etc.)I should like to emphasize on the form of activity which says:
5.Ejection of compact blue condensations with an absolute magnitude of the order of luminosity of dward galaxies (NGC 3561, IC 1182). Here the division of the nucleus into two or more comparable componentsis also presumed; initiating the formation of multiple galaxies.
Large-Scale Radio Jets
Authors: Laing R.A. 
Published: March 2016

The purpose of this review is to outline the systematic properties of radio jets on kpc scales, as derived from the basic observations of surface brightness and linear polarization and to emphasize the uncertainties in the determination of their physical parameters. These results come primarily from observations of about 100 jets with the VLA: a fuller account is given by Bridle (1982) and the proceedings of IAU Symposium 97 contain many illustrations and references, which must be omitted here.I take a “jet” to be a feature in the radio brightness distribution which is at least four times as long as it is wide, which can be clearly separated (spatially or by brightness contrast) from the rest of the source and points away from a radio core. Wilson (1982) has considered jets in spiral galaxies and I shall discuss only the more luminous jets found in elliptical radio galaxies and quasars.
Women in Astronomy - Italy
Authors: Padrielli L. 
Published: March 2016

Let me start with a short historical excursion, taking the Bologna University as an example. The Bologna University was founded in 1088, but only at the beginning of 1700, when a deep transformation in the tradition and female behaviour model occurred, women started to approach the academic life mostly in humanities. There were also examples of scientist women, often
without a real academic title working side by side with men (generally fathers or husbands).During the 19th century the female presence in the italian universities slowly increased, becoming a reality at the beginning of the 20th century. In the time interval from 1884 to 1900, 224 degrees were assigned to women in Italy (less than 10% of the total): 68.9% in Literature and Philosophy,7.8% in Mathematics, 11.7% in Natural Science, 9.3% in Medicine, and 2.3% in Law. Women were mostly involved in fields related to educational activities, however six out of 224 got a chair at the Universities, five of which in scientific fields.
Status of Women Astronomers in China
Authors: Shuhua Ye 
Published: March 2016

The percentages of women working in Astronomy including research and technical positions are as follows:If we look at the percentages of female students:It is easy to see, that since fewer women have the chance of higher education, it is not a surprise that fewer women can reach to the higher level in astronomy.Social discrimination and prejudice have been the obstacles for women to get higher education and choose a career in astronomy. For example:
—1. Home influence. A girl from her early childhood is educated to play with dolls and help in the kitchen.—2. Marriage. In the view of public, a man should not choose a wife with higher education nor in a higher position as compared to him. And thus, well educated women have less chance to get married.
Are the Opportunities in Astronomy and the Working Conditions Different for Women and Men?
Authors: Burbidge E. Margaret 
Published: March 2016

As the oldest speaker at this Joint Discussion, my lifetime in astronomy spans a larger number of decades than the lives of most of us here, and consequently I have seen great changes in the opportunities, working conditions, status, and rewards for their work that are now available to women, in comparison with the situation as it was 50 years ago. Nevertheless, one has to admit that the answers to two of the questions we have been asked to address have to be a qualified yes: there is still a problem, and there is need for improvement.The advances that we have seen, especially in the last 20 years, have been recognized throughout the worldwide community as being of immense benefit to astronomy. It is also recognized by the general public that the situation for women in astronomy is much different now from what it was in my early years.
Opportunities and Working Conditions
Authors: Griffin Elizabeth 
Published: March 2016

It is impossible to pose, explain and solve in a mere 15 minutes a complex puzzle like this that has been with us for centuries. There are so many different facets; it is hard to focus on a problem that has no nucleus and to summarize a situation that has neither beginning nor end, and some of you are therefore bound to disagree with at least some of what I say.I singled out the three questions, “Is there a problem?”, “Is there need for improvement?” and “What are the possible ways to improve the situation?”, because each seems to beg the next and all three can therefore be tackled together. The official answer to the first question is “No, there is no discrimination, and no Problem”, because the large majority of institutions declare themselves Equal Opportunity Employers, and statistics show that women are usually appointed to positions in at least the same proportion, relative to their malepeers, as they apply. The nagging worry is why they do not feel able to apply in the sort of numbers that reflect their population. This is more than a social problem; anyone who counts the cost of educating his or her daughter to the age of 25 will know that it has an economic side too. And the reality of the Problem? I attended the 1992 Baltimore meeting on “Women in Astronomy”, and for the first of the two days the 175 or so women in the 200-strong audience simply let off steam, flung mud, aired grievances, and demonstrated that a Problem was very much in evidence; everyone had one, in some disguise - except, possibly, those who occupied the seats on the Panel the next day and answered the political questions. But put 175 men together in a free-for-all, and they would probably discuss .... maybe how best to spend the next $M100 on space astronomy.
Two-tier system of astronomical constants
Authors: Lieske J.H. 
Published: March 2016

Conventional astronomical standards are applied to a wide range of applications, many of which do not require state-of-the-art precision. Stability of the standards is of great importance, although there is a trend by some in the astronomical community to promote frequent revision of the values of astronomical constants. It is possible to employ stable standards and to differentially correct them by use of the IERS formulation when very precise observations require such action.The IERS formulation for the transformation from a fixed frame to an of-date frame involves precession and nutation along with two parameters δψ and δ which can represent modifications to the standard precession and nutation formulation. The transformation from the mean-of-date frame to the true-of-date frame in the IERS formulation using rotation matrices is rtrue = NrMean whereN = R1(−εm − Δε − δε) R3 (−ΔΨ − δΨ) R1(ε)mwhere εm is the mean obliquity, ΔΨ and Δε are the nutations in longitude and obliquity, and where δψ and δε are IERS parameters which allow for changes to the IAU system. They are tabulated in the IERS reports and are generally thought of as observationally-determined values, but the IERS formulation can be used to introduce corrections of an arbitrary nature.
Astronomical Units and Constants in a Relativistic Framework
Authors: Capitaine N. , Guinot B. 
Published: March 2016

In 1991, IAU Resolution A4 introduced General Relativity as the theoretical background for defining celestial space-time reference sytems. It is now essential that units and constants used in dynamical astronomy be defined in the same framework, at least in a manner which is compatible with the minimum degree of approximation of the metrics given in Resolution A4.This resolution states that astronomical constants and quantities should be expressed in SI units, but does not consider the use of astronomical units. We should first evaluate the usefulness of maintaining the system of astronomical units. If this system is kept, it must be defined in the spirit of Resolution A4. According to Huang T.-Y., Han C.-H., Yi Z.-H., Xu B.-X. (What is the astronomical unit of length?, to be published in Asttron. Astrophys.), the astronomical units for time and length are units for proper quantities and are therefore proper quantities. We fully concur with this point of view. Astronomical units are used to establish the system of graduation of coordinates which appear in ephemerides: the graduation units are not, properly speaking astronomical units. Astronomical constants, expressed in SI or astronomical units, are also proper quantities.
Modulation of the Cosmic Radiation and its Manifestation in Cosmogenic Isotopes
Authors: Beer J. 
Published: March 2016

An issue of increasing importance in solar physics and climatology is solar variability (Sofia and Fox, 1994). It seems that most solar type stars show some magnetic variability at the surface (Baliunas and Jastrow, 1990). To understand the underlying processes and to model them is a big challengein solar physics.When satellites began to observe the sun outside the disturbing atmosphere it soon became clear that the solar irradiance is also variable and seems to be related to the 11- year Schwabe cycle (Willson, et al., 1986), (Foukal, this volume). This result is of great importance because the sun is the engine which drives the climate system on earth. Although the variations are small (0.1-0.2%) there is clear evidence from observational data of solar type stars (Baliunas and Jastrow, 1990) and from theoretical considerations as well that much larger fluctuations over longer time scales potentially could occur.This raises the question what role the sun plays in today’s climate change and possibly in the near future. There are basically two approaches to address this question. 1. The solar irradiance and the climate have to be monitored continuously with high precision in order to detect changes and to understand how they are caused. 2. Since there are reasons to believe that the sun also exhibits long-term changes which cannot be detected during short periods of direct observations, one has to investigate the past by looking for connections between climate and solar variability.To reconstruct past climate changes is comparatively simple. There is a large amount of climatic observations available for the last 2-3 centuries. The climatic conditions of earlier times can be reconstructed quite reliably based on isotopic ratios, pollen assemblages, and many other parameters measured in natural archives.
Asteroseismology of white dwarf stars
Authors: Nather R.E. 
Published: March 2016

Perhaps the hardest scientific problems to solve are those most scientists believe have already been solved, but which have not. Any model we make of an astronomical process is doomed to be incomplete at some level; the “broad-brush” picture of stellar structure and evolution is often accepted as a solved problem, but in fact many discrepancies exist between our models and the observations.For example, the “standard solar model” fails to predict the observed neutrino flux from the Sun, and its insistence that the Sun’s luminosity increased by 30% over geological time is not in accord with the evidence. White dwarf stars were thought to be stable against pulsation because the models did not pulsate, and it took a long time to improve them to the point where they did, and could then begin to match our observations of pulsating white dwarfs. For several years their outer hydrogen layers were thought to be extremely thin because models with thicker layers did not pulsate; once the zoning problem was found and solved in the models they could begin to match observations better. These past difficulties illustrate a common danger: it is very easy to confuse our models with the observed reality they try to mimic, and to assume they match better than they do. In what follows I will try to keep the observations and our models of them separate.
Recent Advances in Convection Theory and Modelling
Authors: Sofia S. 
Published: March 2016

This Joint Discussion (Number 13), took place on August 22, 1994 at The Hague, in connection with the XXII General Assembly of the IAU. At the one-day long meeting, there were presentations by 15 invited speakers and 15 posters.The Joint Discussions had been organized in response to the considerable progress made in this field of research during the previous decade. Although it had long been known that the prevailing mixing length theory (MLT), used extensively and very successfully in Astrophysics for several decades had become needlessly limited, until recently it was impractical to contemplate more realistic approaches. The situation has changed recently as a consequence of advances in numerical techniques and computational capabilities, and thus JD 13 was organized to discuss the advances, and perhaps to understand the strengths and weaknesses of each approach.There were two presentations which addressed the main issues in convection theory (E. Schatzman), and the astrophysical implications (P. Demarque). Several talks covered current numerical codes, which included deep convection in a rotating reference frame (K. Chan), convection in the presence of magnetic fields (P. Fox), and shallower solar convection simulations on a wide range of spatial scales (A. Nordlund). Although these approaches have enriched (and are continuing to enrich) our understanding of the physics of convective fluids, they are much too detailed (both in space and in time) to be integrated in the study of stellar evolution. To overcome this shortcoming, S. Sofia described a technique developed together with Lydon and Fox to use relationships between dynamical and thermodynamic properties of convective flows derived in numerical models to be applied in stellar structure and evolution codes by performing small modifications of the standard MLT formalism. The advantage of this technique is that it does not contain a mixing length or any other arbitrary parameter, and it was used successfully in modeling the evolution of the Sun and other solar analogues. V. Canuto also presented a formulation of convection both amenable to be used in stellar evolution studies, and not requiring an arbitrary mixing length-like parameter. His formulation uses the Reynolds stress method, which has the advantage of modeling the full eddy spectrum of the turbulence, rather than the narrow wave number range for energy containing eddies assumed in the MLT. Additionally, this technique can address the problems of non-locality and overshoot. M. Stix also addressed non-locality and overshoot by presenting results of a non-local mixing length model of the Sun derived from the Shaviv and Salpeter model.
Lithium Abundances of Solar-Type Stars in Open Clusters
Authors: Soderblom D.R. 
Published: March 2016

This paper discusses the lithium abundances of late-F through mid-F dwarfs in the nearby open clusters. That means that I am considering young disk stars, of course, with metallicities similar to the Sun’s. I will not discuss the chasm seen among mid-F dwarfs. Li is not easily studied because only one spectroscopic feature is available and that feature is often weak. Thus high spectroscopic resolution and good signal to noise are needed. But Li is still the most easily studied of the light-element pentateuch (D, He, Li, Be, B).The few clusters now accessible to large telescopes at high spectroscopic resolution include the Hyades, Pleiades, a Persei, as well as smaller samples in a few others (such as Coma, M67, NGC 752, the Ursa Major Group). The samples within clusters are often substantial, and allow one to examine differences in Li between stars of the same mass, age, and composition. However the total number of clusters observed is still small, so one must assume that each cluster is fully representative for its age and composition.Much recent work on Li in stars has been for Population II objects because of the importance of Li for cosmology. We study Li in Pop I stars for three reasons: First, to understand how the Galaxy has come to be enriched in Li since the Pop II stars formed. Second, to understand the stellar physics behind Li depletion in Pop I stars as a means to understanding what happens in the outer layers of such a star over time. Third, to apply that understanding of the stellar physics to Pop II stars so we can correctly infer the Big Bang Li abundance.
Lithium in Giants
Authors: Balachandran Suchitra 
Published: March 2016

In the standard stellar model, lithium burning does not occur during the first-ascent giant branch phase. The surface lithium abundance in a first-ascent or clump giant is thus the product of the lithium abundance of its main sequence progenitor and subsequent dilution by the deepening convective envelope. Iben’s (1967a, b) early calculations predicted that the dilution factor would vary between a factor of about 28 in a 1 M⊙ star to a factor of 60 in a 5 M⊙ star. More recent calculations with improved physics show remarkably little change in these predicted dilution factors (Pinson-neault, pvt. comm.). Since Li only survives in the outer 2-3 % by mass of a main sequence star, the maximum redgiant ∼ abundance is predicted to be ∼ log e(Li)=1.5 to within a factor of two. Even lower abundances will result if surface Li is destroyed during the main sequence phase. Lithium depletion on the main sequence has been well documented in stars of spectral type mid-F and later and have been explained by a variety of non-standard mechanisms (e.g., rotation, diffusion and turbulence). Mixing induced by such mechanisms is not expected in high-mass stars (M⊙ > 1.5) which have insignificant surface convection. Yet recent observations reveal that non-standard processes may be at work in these stars as well.Lithium abundances far below the predicted maximum value are seen in high-mass cluster giants, and in some clusters large spreads in Li are observed in giants of roughly the same mass (Gilroy 1989). If, in concordance with the standard-model prediction, one assumes that Li burning on the giant branch is unlikely, then both the destruction and the scatter of Li must be accounted for on the main sequence. Since the surface convection zones are insignificant, other forms of Li-loss (e.g. mass loss, meridional circulation) may have to be resorted to. Unfortunately the main sequence progenitors of most of these giants are too hot to have a measurable Li I feature, but observations of field late-A stars by Burkhart and Coupry (1991) reveal some evidence for surface Li-loss. Follow-up observations of Li inclusters, and Be and B abundance determinations would be useful. Lithium burning on the giant branch should be investigated theoretically.
Chemical Abundances from Planetary Nebulae in the Magellanic Clouds
Authors: Barlow M.J. 
Published: March 2016

AbstractHeavy element abundances, in particular those of oxygen, obtained from recent spectroscopic surveys of Magellanic Cloud planetary nebulae (PN), are reviewed and compared with those derived for H regions and objects in our own galaxy. These abundances have been based on collisionally excited lines and are very sensitive to the adopted electron temperature. There is increasing evidence that temperature or density fluctuations within nebulae lead to the electron temperatures being overestimated, with the corollary that the heavy element abundances have been underestimated.
Challenges of Using Planetary Nebulae for Extragalactic Distances
Authors: Bottinelli L. , Gouguenheim L. , Paturel G. , Teerikorpi P. 
Published: March 2016

The planetary nebulae (hereafter PN) distance criterion (Ciardullo et al. 1989a) relies on the shape adopted for the luminosity function (hereafter LF) and its adequate fit to the observed data. Crucial hypothesis concerning the LF are its universal shape with an universal value of the absolute magnitude cut-off and concerning the sample, its completeness and the selection of the rejected data.Because the completeness is achieved only in the bright part of the LF, the brighest PN play a crucial role in the distance determination and it is well known that the brightest objects (with intrinsic scatter) in a giant galaxy are brighter than in a dwarf galaxy. Thus more luminous galaxies are given smaller distances. Because giant galaxies are rare they are not seen at small distances; on the contrary, they are typically observed at large distances. This effect induces a progressive compression of the distance scale.
The Circumnuclear Region in NGC 4321
Authors: Knapen J.H. , Beckman J.E. , Shlosman I. , Heller C.H. , Peletier R.F. , De Jong R.S. 
Published: March 2016

AbstractWe present results from a recent study of the inner 1 kpc zone of the weakly barred spiral galaxy NGC 4321 (M100), which reveals a circumnuclear starburst, organized in a pair of tightly-wound spiral arms. Combining high-resolution imaging in the optical and near-IR with a detailed dynamical model, we show that the morphology of this region can be explained by a resonance interaction between the disk and the stellar bar and its effects on the gas.