bluuebunny/crossref_metadata_2025 huggingface dataset:
Abundance Ratios in Metal-Poor Globular Clusters: Deep Mixing and its Effect on Stellar Populations of the Galactic Halo
Authors: Kraft Robert P.
Published: June 2021

Only a bit more than 25 years ago, it seemed possible to assume that all Galactic globular clusters were chemically homogeneous. There were indications that star-to-star Fe abundance variations existed in ω Cen, but this massive cluster appeared to be unique. Following Osborn’s (1971) initial discovery, Zinn’s (1973) observation that M92 asymptotic giant branch (AGB) stars had weaker G-bands than subgiants with equivalent temperatures provided the first extensive evidence that there might be variations in the abundances of the light elements in an otherwise “normal” cluster. Since then star-to-star variations in the abundances of C, N, O, Na, Mg and Al have been observed in all cases in which sample sizes have exceeded 5-10 stars, e.g., in clusters such as M92, M15, M13, M3, ω Cen, MIO and M5. Among giants in these clusters one finds large surface O abundance differences, and these are intimately related to differences of other light element abundances, not only of C and N, but also of Na, Mg and Al (cf. reviews by Suntzeff 1993, Briley et al 1994, and Kraft 1994). The abundances of Na and O, as well as Al and Mg, are anticorrelated. Prime examples are found among giants in M15 (Sneden et al 1997), M13 (Pilachowski et al 1996; Shetrone 1996a,b; and Kraft et al 1997) and ω Cen (Norris & Da Costa 1995a,b).

These observed anticorrelations almost certainly result from proton- capture chains that convert C to N, 0 to N, Ne to Na and Mg to Al in or near the hydrogen fusion layers of evolved cluster stars. But which stars? An appealing idea is that during the giant branch lifetimes of the low-mass stars that we now observe, substantial portions of the stellar envelopes have been cycled through regions near the H-burning shell where proton-capture nucleosynthesis can occur. This so-called “evolutionary” scenario involving deep envelope mixing in first ascent red giant branch (RGB) stars has been studied by Denissenkov & Denissenkova (1990), Langer & Hoffman (1995), Cavallo et al (1996, 1997) and Langer et al (1997). The mixing mechanism that brings proton-capture products to the surface is poorly understood (Denissenkov & Weiss 1996, Denissenkov et al 1997, Langer et al 1997), but deep mixing driven by angular momentum has been suggested (Sweigart & Mengel 1979, Kraft 1994, Langer & Hoffman 1995, Sweigart 1997).
Abundances of Metal-Poor Stars and the Formation of the Halo
Authors: Cayrel R.
Published: June 2021

The origin of the elements in the early Galaxy has been thought to be fairly well understood as primordial matter polluted by ejectae of type II supernovae. Some recent observational results have led to reconsider in more detail this statement. As a result, it is confirmed in some respects, but curiously, when the same metallicity can be found both in the halo and in the thick disk, the stars contaminated by SN la ejectae are more the halo stars than the thick disk stars.
Element Abundance Ratios in Galactic Bulge Stars
Authors: Rich R. Michael
Published: June 2021

I review the current status of measurements of element ratios in metal rich stars. These include giants in the Galactic bulge, metal rich Galactic globular clusters, and high velocity dwarfs in the Solar vicinity. There is evidence for enhancement of Mg and Ti in the bulge. While s-process elements have Solar abundance in bulge giants, they are deficient in the metal rich, high velocity dwarfs. There are no secure measurements of oxygen abundance in the bulge, but present data indicate no evidence either for extremely low or high [O/Fe] in bulge giants. The current data are limited by resolution and S/N, and I outline goals for observations with the next generation of ground-based telescopes.

If the central bulge of the Milky Way formed rapidly, one would expect that enrichment could occur only through massive star SNe, with little or no contribution from core deflagration SNe. In this scenario, one expects alpha-capture elements to be enhanced at a given [Fe/H] compared to the Solar vicinity: element abundance ratios may record something of the history of star formation. The idea is developed in Wheeler, Sneden & Truran (1989) and its application to bulges and elliptical galaxies is developed in Matteucci & Brocato (1990). As Kraft reviews in this volume, the stellar evolution effects that modify surface abundances in globular cluster stars do not appear to be a problem for field giants.
Mid-Ir Emission of Low-Metallicity Galaxies
Authors: Plante S. , Sauvage M. , Kunth D.
Published: June 2021

NGC 595 is a giant Hɪɪ region located in the western part of the spiral galaxy M 33. It is the second in importance in this galaxy, after NGC 604. At 0.84 Mpc, HST is able to resolve its stellar content. Malumuth et al. (1996) obtained HST UV, U, B and V images of this region and derived an ionizing luminosity of 5 × 1050 phots-1 and an average reddening EB-V = 0.36±0.28 mag. The stars are mostly concentrated in the central part of the region, where little emission of gas is seen (the ionized gas lies more in a shell around the stars, figure 1a). Wilson & Scoville (1993) showed the molecular gas to be situated in the south-east part of the region, just outside of the bright knot of stars. Viallefond et al. (1986) found a reddening gradient in the north-east/south-west direction by observing the Hi gas, which was confirmed by Malumuth et al. (1996) with stellar photometry.

We obtained ISO images for NGC 595 in the 5.0 to 8.5 μm range. The emission in this spectral range is dominated by the so-called PAH bands. Current interpretation of these has them originating from stochastically heated molecules. Two of these bands are located in the range observed, at 6.2 μm and 7.7 μm. Stochastic heating implies that the in-band flux is directly proportional to the number of photons absorbed by the molecules. For typical HII regions, Cohen et al. (1989) found 0.58 for the I6.2/I7.7 in-band ratio. However many processes, ionization, dehydrogenation, can modify this ratio. Furthermore, an underlying continuum is present though its exact origin is unknown.
The Nearby Young Dwarf Galaxy SBS 0335-052: Primordial Gas and Lyman-Alpha Emission
Authors: Thuan Trinh Xuan , Izotov Yuri I.
Published: June 2021

Ever since their discovery, blue compact dwarf (BCD) galaxies have been thought of as excellent candidates for being young galaxies, i.e. systems presently undergoing one of their very first bursts of star formation. This is mainly because BCDs are very metal-deficient, the metallicities of their ionized gas ranging between Zʘ/50 and Zʘ/3, which makes them the least chemically evolved galaxies in the Universe. Other evidence, such as the very high fractional neutral hydrogen gas content and the lack of an evident underlying old stellar population on optical images, also point to the relative youth of some BCDs.

Thuan, Izotov h Lipovetsky (1997) have argued SBS 0335-052 to be a young galaxy on the basis of the following evidence: 1) HST imaging of the BCD shows its underlying extended low surface brightness component to have an irregular and filamentary structure, suggesting that a significant part of the emission (~1/3) comes not from an underlying stellar population, but from ionized gas. Any underlying stellar population must be younger than ~108yr. Propagating star formation occurs in a chain of 6 super-star clusters with ages ranging between 4 and 30 Myr. 2) The underlying component shows unusually blue colors consistent with gaseous emission, in contrast to most BCDs which possess an underlying red component. 3) VLA 21 cm observations show the BCD to be embedded in an extraordinarily large HI cloud with dimensions some 64 × 24 kpc (the typical size of HI envelopes around BCDs is more like a few kpc in each dimension).
Extended HI Structures in the Irregular Galaxy NGC 4449
Authors: van Woerden Hugo , Hunter Deidre A. , Wilcots Eric M. , Gallagher Jay S.
Published: June 2021

NGC 4449 is a bright (B = 9.5), nearby (4 Mpc) irregular galaxy with a high surface brightness and strong star-formation activity; for photos see Hunter and Gallagher (1989). Using the Effelsberg 100-meter dish, van Woerden et al. (1975) - and later also Bajają et al. (1994) - found its HI distribution to extend, at the level 2 × 1019 atoms cm-2 over a full degree, or ten times the D25 diameter. Van Woerden et al. also mentioned that the HI velocity gradient in this outer disk was opposite to that measured at Westerbork over the innermost 4 arcminutes.

With the VLA D-array, we have used a mosaic of 3 × 3 pointings to map the HI at resolutions of 1.0’ and 10 kms-1 over a field (FWHM) of 1° diameter (Hunter et al. 1998). The HI distribution (Fig. 1) shows the following features: 1) a bright inner body, centred on the optical galaxy and dominated by an annulus of 5 kpc diameter; 2) a symmetric elliptical - probably highly inclined - disk of 35 × 15 kpc diameter, with strong condensations at its NE and SW ends; 3) a set of narrow streamers, consisting of straight segments making abrupt angles, and containing several bright clouds. The HI mass in the inner body and elliptical disk together is 12 × 10s Mʘ the streamers (about 7 × 108 Mʘ of HI) are surrounded by a diffuse HI distribution, missed by the VLA interferometers but detected by the Effelsberg single-dish.
Far-Infrared [C II] Properties of Low-Metallicity Galaxies
Authors: Mochizuki K. , Onaka T. , Nakagawa T.
Published: June 2021

The line flux ratio of the [C II] 158 μm fine-structure (2P3/2 → 2P3/2) emission to CO rotational emission is a probe of the intensity of the interstellar UV radiation in galaxies. The largest values for the [C II]/CO (J = 1-0) line ratios are found in starburst galaxies, none of which, however, show values larger than 6 ×103 (Stacey et al. 1991). The exception ([CII]/CO ≃ 2 × 104) are galaxies of Magellanic type which have low metallicity, an intense interstellar UV field, and irregular morphology (Table 1).

Mochizuki et al. (1994) showed that the two conditions, a low metallicity and an intense UV field are expected to result in the large [C II]/CO ratios in the Magellanic types. These conditions are likely to be common in more massive galaxies as well, but at an early epoch in their evolution. This suggests that bright [C II] emission can be a good indicator of young galaxies. However, the metal-poor galaxies previously observed in the [C II] line were exclusively Magellanic types. Observations of different types of dwarf galaxies are necessary to help us understand the physical conditions in the interstellar medium of low-metallicity systems.
Cosmology with Nearby Dwarf Galaxies: The View from HST
Authors: Tolstoy Eline
Published: June 2021

Stellar Evolution theory is based upon well understood physics and provides clear predictions as to how a Colour-Magnitude Diagram (CMD) will change due to effects of age and metallicity. The theory has been tested by looking at nearby coeval star clusters. The power of applying CMD analysis to galaxies has been demonstrated in studies of the Carina dSph (Smecker-Hane et al. 1996). In Carina the observation of separate, distinct Main Sequence (MS) Turnoffs has forced us to believe that this small, nearby companion of our Galaxy has had a very complex star formation history. No similar direct evidence for “bursting” behaviour on a global scale has been seen indisputably in larger systems. Partly this is due to the greater distances of larger systems, but also to the complications in distinguishing old star formation events (> 1 Gyr old) in systems which are currently forming stars. Where we lack MS turnoffs we have to resort to statistical modeling of the CMD. This has been applied using a a number of different approaches, but all generally based on Monte-Carlo techniques (e.g. Tosi et al. 1992; Bertelli et al. 1992; Tolstoy &; Saha 1996). However, even using these more sophisticated analysis techniques, it is difficult to find unique solutions. This is mostly due to the age-metallicity degeneracy on the Red Giant Branch (RGB). The RGB is usually the most populated, easiest to observe phase of stellar evolution. The Carina CMD reveals the dangers of blindly interpreting the RGB, because from the RGB alone it is impossible to extract the information revealed by the MS Turnoffs.
Blue Compact Galaxies and the Primordial Helium Abundance Determination
Authors: Izotov Y.I. , Thuan T.X.
Published: June 2021

We use a sample of 45 low-metallicity H II regions to determine the primordial helium abundance Yp. We have carefully investigated the physical effects which may make the He I line intensities deviate from their recombination values such as collisional and fluorescent enhancements, underlying He I stellar absorption and absorption by Galactic interstellar Na, I. By extrapolating the Y vs. O/H linear regression to O/H = 0, we obtain Yp = 0.245±0.002. Our Yp gives 0.06±0.01.
Observations of the Celestial Motion of the Earth’s Pole
Authors: Feissel M. , Gontier A.-M.
Published: June 2021

The accurate observation of the celestial motion of the Earth’s pole requires careful connection of the VLBI observables with quantities and reference frames related to the theoretical description of precession-nutation models. The analysis of the derived celestial pole offsets beyond the semi-empirical IERS(1996) precession-nutation model shows variability of some components, such as the seasonal term and a ~ 430 day term.
Latest Best Estimates of Astronomical Constants
Authors: McCarthy D.D.
Published: June 2021

Systematic errors caused by the use of inconsistent models and constants currently limit the accuracy of the most precise astro-geodetic observations. It is important, therefore, to provide conventional estimates of astronomical constants for general use in astronomy and geodesy. Establishment of such a set raises issues involving the accuracy of the constants, their internal consistency, and the reference system in which they are expressed. Future sets of constants will be updated at regular intervals to provide the most accurate values at that instant. Careful consideration must be given to their internal consistency. It is likely that they will be provided only in electronic format with references to their determination and to procedures for their use.
General Relativity And The IAU ResolutionsReport of the IAU WGAS Sub-Working Group on Relativity in Celestial Mechanics and Astrometry (RCMA SWG)
Authors: Brumberg V.A. , Bretagnon P. , Capitaine N. , Damour T. , Eubanks T.M. , Fukushima T. , Guinot B. , Klioner S.A. , Kopeikin S.M. , Krivov A.V. , Seidelmann P.K. , Soffel M.H.
Published: June 2021

RCMA SWG was appointed by the IAU WGAS (Working Group on Astronomical Standards) in accordance with IAU Resolution C6 (1994) with the aim ‘to provide definitions of the astronomical units, of the quantities linking these astronomical units to the units of the International System (SI), and of other astronomical quantities, compatible with the theory of General Relativity’. It is evident that the relativistic aspects of units of measurement cannot be isolated from the more general problem of astronomical constants and fundamental astronomy concepts in the relativistic framework. Therefore, along with the problem of units the main topics of discussion of RCMA SWG concerned also the IAU (1991) Resolutions on References Systems (RSs) and Time Scales (TSs) and their interpretation in IERS Standards (1992) and IERS Conventions (1996). In what follows we tried to summarize the results of these discussions.
A Mechanism for Asteroids to Avoid Close Approach and Collision to Planets
Authors: Kozai Yoshihide
Published: June 2021

In this paper it is explained how asteroids with large aphelion distances avoid very close approach to Jupiter. Namely, since for asteroids with resonant mean motions the critical arguments librate as it has been known for many years, and for those with non-resonant mean motions the eccentricities change with the argument of perihelion so the distance to Jupiter cannot be very small.

Also some behaviours of Kuiper-belt asteroids are studied by a similar way and it is found that the libration region for the argument of perihelion appears only when the eccentricity is very large. Therefore, even though the eccentricity is very large it is possible for any Kuiper-belt asteroid to avoid very close approach to any of the planets.
Searching for Neas from Earth or Space
Authors: Harris A.W.
Published: June 2021

Different options for searching for near-Earth asteroids that may pose an impact hazard to the Earth in the future are discussed. The space option has not been studied in as much detail as the ground-based survey option, so a more detailed study of the space option might be appropriate. It is not evident, however, that a space-based system can be competitive or superior to the ground-based option, because past experience argues very strongly to the contrary.
Extension of The Optical Reference Frame: Ground Based
Authors: Zacharias N.
Published: June 2021

The International Celestial Reference Frame (ICRF) is realized by the positions of 608 compact extragalactic radio sources (Ma & Feissel 1997) with milliarcsecond (mas) and sub-mas accuracy, all being on the same system, the International Celestial Reference System (ICRS). The Hipparcos Catalogue (ESA 1997) is the practical realization of the ICRF at optical wavelengths, giving accurate positions (≈ 1 mas) at the mean epoch of 1991.25 and proper motions (≈ 1 mas/yr) for 117995 stars. This is about 2.5 stars per square degree, most being in the 7 to 9 magnitude range and a few as faint as 12. However, for many astronomical applications the Hipparcos Catalogue is not dense enough and does not reach faint enough magnitudes.

The Tycho Catalogue (ESA 1997) provides accurate positions (≈ 25 mas) for about one million stars to magnitude 11, but lacks precise proper motions. Ground-based observations are an efficient way to complement the Hipparcos mission and to extend the optical reference frame to fainter magnitudes and yield a denser grid of astrometric standard stars. New reductions of early epoch photographic data will be used to provide highly accurate proper motions for stars to about magnitude 12. Current and new observational projects will extend the optical reference frame to even fainter magnitudes.
Maintenance of the ICRF: Optical
Authors: Zacharias N.
Published: June 2021

The International Celestial Reference Frame (ICRF) is presently realized by the positions of 608 compact, extragalactic radio sources (Ma & Feissel 1997) with milliarcsecond (mas) and sub-mas accuracy, all being on the same system, the International Celestial Reference System (ICRS). The Hipparcos Catalogue (ESA 1997) is the practical realization of the ICRF at optical wavelengths, giving high accuracy positions (≈1 mas) and proper motions (≈1 mas/yr) for 117955 stars (ESA 1997). The link between the radio and optical frames has been achieved by various methods (Kovalevsky et al. 1997). The accuracy of this link is estimated to be 0.6 mas at the mean epoch of Hipparcos (1991.25) for the orientation, and 0.25 mas/year for the system rotation.
Maintenance of ICRP: Complex Optical Objects
Authors: Worley Charles E.
Published: June 2021

Heretofore, double and multiple stars have presented a tolerable but manageable problem in most astrometric programs. However, the drive to ever greater precision, with detections in the milli-to-micro arcsecond range of these complex objects, over a wide range of wavelengths, presents new and as yet unsolved problems in both the astrometry and photometry of such systems.

This discussion is aimed at a better delineation of the implications of the problem.
An Analysis of Almagest Magnitudes for the Study of Stellar Evolution
Authors: Hearnshaw J.B.
Published: June 2021

Visual magnitude data in Ptolemy’s Almagest are analysed by comparing them with modern photoelectric magnitudes on the Pogson scale, after taking extinction into account. This result is used to transform Almagest magnitudes to the Pogson scale.

A study is made of changes in the vusual magnitudes of supergiant stars in the Almagest between classical and modern times (an interval of nearly 19 centuries). No evidence is found for any secular changes in the mean brightness of these stars, contrary to the conclusion of Mayer (Observatory 104, 77, 1984). However, it is shown that the Almagest magnitudes for stars in the Milky Way are on average 0.34 Pogson magnitudes too faint and about the Almagest supergiants are affected by this. Finally, some evidence is cited for the visual atmospheric extinction in classical times being significantly less than today. If this is the case, and is not taken into account, it would mimic an apparent supergiant brightening of about 0.1 magnitudes over this time interval.
Long-Term Variations in the β CEPHEI Stars 16 (EN) LAC and ν ERI
Authors: Jerzykiewicz M. , Pigulski A.
Published: June 2021

Using all available data, we investigate long-term variations of the amplitudes of the three strongest pulsation modes of 16 (EN) Lac and the period of the strongest mode of ν Eri. We show that in case of 16 (EN) Lac there are feasible explanations of the observed variations. The explanations involve non-linear interaction between pulsation modes (the first two observed modes) and beating between two non-interacting modes (the third observed mode). In case of ν Eri, however, we can only indicate the difficulty of accounting for the long-term period variation.

MJ gratefully acknowledges an IAU travel grant. This work was supported by KBN grant 2P03D01611.
Light Curve Variations of the Old Disk Eclipsing Binary R Canis Majoris
Authors: Kang Y.W. , Guinan E.R.
Published: June 2021

R CMa is one of the best observed low mass Algol-type systems, believed to be a semidetached system composed of a nearly spherical FOV primary and a less massive highly distorted K3 IV-V star. Most of the published light curves have asymmetries of one kind or another. Analysis of the individual light curves, dating back to over 75 years, yielded somewhat different orbital solutions depending on the epoch. These inconsistencies are caused by obvious differences in the shape of the light curves obtained at different epochs and by the different models used to find solutions.

A series of light curves of R CMa (obtained at different epochs) have been analyzed by a new version of the Wilson-Devinney computing program to find a homogeneous solution. All parameters were adjusted to fit a light curve of each epoch. Then we found the weighted mean value of each parameter. These mean values were used as initial parameters and the potential and radius of each component were re-adjusted for each epoch to see the variation of radii for over 30 years. Several radial velocity curves were used to find spectroscopic parameters. The photometric parameters were combined with the corresponding spectroscopic parameters to calculate an absolute dimension of R CMa.

Finally, we examined the IUE spectra of R CMa for existence of circumstellar gas in the system and evidence of magnetic activity on the cooler component. We also discuss the evolution of the system and possible observable real time evolutionary processes.
Synchronization Anomalies in Close Binaries as a Test of Rapid Evolutionary Processes
Authors: Giménez A. , Claret A.
Published: June 2021

Close binaries with late-type components generally present rotational velocities synchronized with their orbital period. This is a well known effect of tidal evolution in binary systems which is particularly efficient in stars with convective envelopes. Nevertheless, some cases are known where the angular velocities of the componenent stars are clearly different from each other or even from that of the orbit. Good examples are the evolved systems TZ For and a Aur.

We have made a detailed study of the tidal evolution history of these binaries through integration of the relevant differential equations using the formalisms by Zahn as well as Tassoul. Our results show that a satisfactory explanation of the synchronization status of the component stars can be achieved when the influence of the rapid expansion phases, suffered by the stars after leaving the main sequence and starting core He combustion, in the actual rotational velocities is taken into account.
The Remarkable Evolution of the Post-Agb Star FG SGE
Authors: Jurcsik Johanna , Montesinos Benjamin
Published: June 2021

FG Sagittae is one of the most important key objects of post-AGB stellar evolutionary studies. As a consequence of a final helium shell flash, this unique variable has shown real evolutionary changes on human time scales during this century. The observational history was reviewed in comparison with predictions from evolutionary models.

The central star of the old planetary nebula (Hel-5) evolved from left to right in the HR diagram, going in just hundred years from the hot region of exciting sources of planetary nebulae to the cool red supergiant domain just before our eyes becoming a newly-born post-AGB star. The effective temperature of the star was around 50,000 K at the beginning of this century, and the last estimates in the late 1980s give 5,000-6,500 K. Recent spectroscopic observations obtained by Ingemar Lundström show definite changes in the nebular line intensities. This fact undoubtedly rules out the possibility that, instead of FG Sge, a hidden hot object would be the true central star of the nebula. Consequently, the observed evolutionary changes are connected with the evolution of a single star.
Evolution of Nova 1934 DQ Herculis over 40 years
Authors: Dmitrienko E.S.
Published: June 2021

We present the results of the analysis of the photometrical behaviour of Nova 1934 DQ Her for a time interval about 40 years based on our data and those published by different authors. Our observation were done in UBVRI in 1982-1997 during apptoximatly 170 nights. They give the possibility of investigating different types of the activity of the old nova with amplitudes of brightness variability from several tenths of magnitudes to 1m. The light oscillations on a time-scale of either several days or several dozens of days would be conditioned by the change of the velocity of the accretion from the disc on the white dwarf caused by the intrinsic disc instability or by the irregular receiving of matter from the secondary component of the system - a red dwarf. The cyclic change of the light of DQ Her on a time-scale of about several years could be the reaction of the accretion disc in response to the activity of the secondary star.
The Crab Nebula and other Anomalous Astrophysical Arthropods
Authors: Trimble Virginia
Published: June 2021

1. Supernovae and Their Remnants

The Crab Nebula is expanding and its pulsar is slowing down, both on time scales that indicate some very interesting real-time stellar evolution must have occurred about 1000 years ago, as indeed we know from Chinese and other ancient records. The Crab was, in fact, the first SNR to be confidently identified as such and to have its expansion rate measured and the first pulsar to have its first and second time derivatives measured. Among the interesting related details are (a) the current expansion is a bit faster than the average since the 1054 explosion, indicating outward pressure from the relativistic electrons and magnetic field responsible for the synchrotron emission, (b) some of the central synchrotron emission features wiggle and oscillate around at much larger speeds than the expansion but in a non-secular way, (c) the braking index of the pulsar is about 2.5 rather than 3.0 (as predicted for a pure magnetic dipole emitter), (d) energy is conserved (it wasn’t obviously so before 1968), in that the pulsar is losing rotational kinetic energy fast enough to keep up the supply of optical and X-ray emitting electrons, and (e) glitches in the slowing of the pulsar (for which data go back to a 1964 balloon flight) indicate complex coupling of crust to interior, presumably a magnetic one.
Multiple Time Scales in Cataclysmic Variables: Observations Vs. Mathematical Models
Authors: Andronov I.L.
Published: June 2021

Theoretical models and observational evidence for various processes in magnetic cataclysmic variables are briefly reviewed. Among them: modulation of the accretion rate by the magnetic field of the white dwarf; excitation of the orientation change of the magnetic axis of the white dwarf with respect to the secondary; structure of the accretion column and its instability; mass and angular momentum transfer; magnetic activity of the secondary; high/low luminosity state transitions; QPO’s, ”shot noise” and ”red noise” in polars, intermediate polars and nova-like objects.
Observation of the Crab Pulsar With Bepposax: Phase Resolved Spectroscopy and Study of the Pulsar Profile.
Authors: Cusumano G. , Maccarone C. , Mineo T. , Segreto A. , Sacco B. , Massaro E. , Nicastro L.
Published: June 2021

The Crab Pulsar(PSR 0531+21) was observed by the four Narrow Field Instruments on board the Italian-Dutch satellite BeppoSAX on August and September 1996, during the Science Verificado Phase. The fine time resolution (15 μs) and the high statistic of the data provided phase histogram of very good quality, well suited for phase resolved spettroscopy over the entire energy band (0.1-300 keV) covered by BeppoSAX payload. In this contribution we present preliminary results of the spectra distribution of the peaks and the inter peak region. Moreover, we also carried out a detailed analysis of the P1 shape and the behaviour of the P2/P1 ratio with the energy.
On The Profiles and The Polarization of Raman Scattered Emission Linesin the Symbiotic Stars: II
Authors: Lee K.W. , Lee H.-W.
Published: June 2021

A Monte Carlo code is used to calculate the profiles and the polarization of Raman scattered O VI lines(λλ6827, 7088) in symbiotic stars. Various wind models around the cool giant are investigated including disk type and bipolar wind models. We obtain a large degree of polarization in the blue part and the red-asymmetric profile, which is generic to the Raman scattered feature in symbiotic stars.

We also investigate the effect of the orbital motion of the hot component around the cool giant, where the orbital velocity is comparable to the wind terminal velocity. In the case of small inclination angle of the orbitalplane, we obtain the polarization flip around the red wing of the scatteredfeature and the triple peak structure in the polarized flux, which is characteristic of many symbiotic systems including RR Tel.

Brief observational consequences are discussed and it is concluded that spectropolarimetry may provide a powerful diagnostic about the physical conditions of symbiotic stars.
Discovery of Infrared Stars in Globular Clusters in the Magellanic Clouds and Their Light Variations
Authors: Nishida S. , Tanabé T. , Matsumoto S. , Onaka T. , Nakada Y. , Sekiguchi K. , Glass I.S.
Published: June 2021

A systematic near-infrared survey was made for globular clusters in the Magellanic Clouds. Two infrared stars were discovered in NGC419 (SMC) and NGC1783 (LMC). NGC419 and NGC1783 are well-studied rich globular clusters whose turn-off masses and ages are estimated MTO ~ 2.0 Mʘ and т ~1.2 Gyr for NGC419, and MT0 ~ 2.0 Mʘ and т ʘ 0.9 Gyr for NGC1783, respectively.

The periods of the infrared light variations were determined to be 540 dfor NGC419IR1 and to be 480 d for NGC1783IR1, respectively. Comparison of the measurements with the period—if magnitude relation for carbon Miras in the LMC by Groenewegen and Whitelock(1996) revealed that the Kmagnitudes of the infrared stars were fainter by about 0.3 — 0.8 magnitude than those predicted by the P — K relation. This deviation can be explained if the infrared stars are surrounded by thick dust shells and are obscured even in the K band. The positions of NGC419IR1and NGC1783IR1 on the P — K diagram suggest that AGB stars with the main sequence masses of about 2 Mʘ start their heavy mass-loss when P ʘ 500 d.
A Peculiar Variable Star HD229221 - From 1994 to 1997
Authors: Wang Jun-Jie , Hu Jing-Yao
Published: June 2021

From 1994 to 1997, we observed the star HD229221 several times spectroscopically by using the Beijing Astronomical Observatory 2.16 m telescope and the spectrograph Universal.

From the spectra we clearly see that the H-α spectral feature of this star underwent a peculiar variation, from a single emission line to one composed of three components, i.e. emission+absorption+filled emission. In our paper, based on an analysis of its spectral line variation and some physical parameters (e.g. luminosity, age, etc.), we discuss the possible reasons that might cause this peculiar variation.
Stellar Evolution in Real Time: Current and Future Expectations
Authors: Kondo Yoji
Published: June 2021

Directly measuring stellar evolution may be accomplished in at least two distinctly different ways. The first approach will be observing it in real time as the phenomenon is taking place; the examples will include explosive events in recurrent novae, stellar oscillations in Cepheid and RR Lyrae variables, and mass flow in and out of interacting binaries. The second approach will be to observe a number of stars that are believed to belong to the same class at different stages of their evolutionary paths.

In this talk, I will focus on the first method of direct observations. The most direct method will probably be to observe images of the events thatwe wish to investigate. The same astronomical phenomena can and should alsobe studied using high-time and spectroscopic resolution data; however, thisis already being done with increasingly better spectral-and-temporal resolutions and will probably be reported elsewhere in this Joint Discussion. It is also noted that over the past two decades multiwavelength observations, using various telescopes on the ground and in space, have come to play a crucial role in astronomy, although I am not addressing this subject in this paper. I will talk primarily about imaging using interferometry that will soon become possible due to the advances in technology.
Disk Mass From Large-Scale Dynamics
Authors: Sellwood J.A.
Published: June 2021

The radial distribution of mass in a disk galaxy is strongly constrained by its rotation curve. The separate contributions from the individual stellar populations and dark matter (DM) are not easily disentangled, however, especially since there is generally no feature to indicate where the component dominating the central attraction switches from luminous to dark matter. Here I summarize three recent thesis projects at Rutgers University which all suggest that DM has a low density in the inner parts of bright galaxies, and that most of the mass therefore resides in the disk. In addition, I present some preliminary work on the Milky Way. If we are able to determine the M/L of a typical disk stellar population, it should provide a useful constraint on the numbers of low mass stars.
Dynamical Constraints on The Mass Function
Authors: Evans N.W.
Published: June 2021

The aim of this paper is to summarise the dynamical constraints on the contribution of low luminosity stars. Important restrictions come from disk stability and the Oort Limit. These are reviewed elsewhere in these Proceedings in the contributions from Sellwood and Binney. Here, our attention is concentrated on two further pieces of evidence - constraints from (1) the stochastic heating of wide binaries and from (2) microlensing.
Very Low-Luminosity Objects in Star-Forming Regions
Authors: Tamura Motohide , Itoh Yoichi , Oasa Yumiko , Tokunaga Alan , Sugitani Koji
Published: June 2021

In order to tackle the problems of low-mass end of the initial mass function (IMF) in star-forming regions and the formation mechanisms of brown dwarfs, we have conducted deep infrared surveys of nearby molecular clouds. We have found a significant population of very low-luminosity sources with IR excesses in the Taurus cloud and the Chamaeleon cloud core regions whose extinction corrected J magnitudes are 3 to 8 mag fainter than those of typical T Tauri stars in the same cloud. Some of them are associated with even fainter companions. Follow-up IR spectroscopy has confirmed for the selected sources that their photospheric temperature is around 2000 to 3000 K. Thus, these very low-luminosity young stellar sources are most likely very low-mass T Tauri stars, and some of them might even be young brown dwarfs.
Contribution of White Dwarfs to Cluster Masses
Authors: Von Hippel Ted
Published: June 2021

The study of cluster white dwarfs (WDs) has been invigorated recently bythe Hubble Space Telescope (HST). Recent WD studies have been motivated by the new and independent cluster distance (Renzini et al. 1996), age (von Hippel et al. 1995; Richer et al. 1997), and stellar evolution (Koester & Reimers 1996) information that cluster WDs can provide. An important byproduct of these studies has been an estimate of the WD mass contribution in open and globular clusters. The cluster WD mass fraction is of importance for understanding the dynamical state and history of star clusters. It also bears an important connection to the WD mass fractions of the Galactic disk and halo. Current evidence indicates that the open clusters (e.g. von Hippel et al. 1996; Reid this volume) have essentially the same luminosity function (LF) as the solar neighborhood population. The case for the halo is less clear, despite the number of very good globular cluster LFs down to nearly 0.1 solar masses (e.g. Cool et al. 1996; Piotto, this volume), as the field halo LF is poorly known. For most clusters dynamical evolution should cause evaporation of the lowest mass members, biasing clusters to have flatter present-day mass functions (PDMFs) than the disk and halo field populations. Dynamical evolution should also allow cluster WDs to escape, though not in the same numbers as the much lower mass main sequence stars. The detailed connection between cluster PDMFs and the field IMF awaits elucidation from observations and the new combined N-body and stellar evolution models (Tout, this volume). Nevertheless, the WD mass fraction of clusters already provides an estimate for the WD mass fraction of the disk and halo field populations. A literature search to collect cluster WDs and a simple interpretive model follow. This is a work in progress and the full details of the literature search and the model will be published elsewhere.
Optical and Infrared Spectroscopy of CM Draconis
Authors: Viti S. , Jones H.R.A. , Allard F. , Schweitzer A. , Hauschildt P.
Published: June 2021

We compare observations of the binary system CM Draconis with synthetic spectra. Spectroscopic observations from 0.40 to 2.41μm, combined with photometry and the accurately known surface gravity enable us to estimate the temperature and metallicity using detailed spectra synthesis. We find discrepancies between the analysis of the infrared and optical spectrum: while the optical spectral energy distribution (SED) yields a metal-rich solution with Teff = 3000K, the infrared SED yields around 3200K and —0.8 ≤ [M/H] ≤ —0.6 compatible with the high space motion of the system. The low-metallicity characteristics of the infrared SED could be real and is partly supported by the detailed analysis of the atomic lines in the optical region. Although, the known incompleteness of the TiO and H2O line lists in the models may cause substantial systematic errors.
New Membership Criteria For 437 Flare Stars in the Pleiades
Authors: Szécsényi-Nagy G. , Schilbach E. , Hirte S. , Scholz R.-D.
Published: June 2021

Most of the flare stars (FSs) discovered in that field are very faint and are missing from all previously published lists of Pleiades cluster members. Reliable membership probabilities (MPs) were only determined for one third of these objects while the rest were supposed to be more or less probable members with a few exceptions. A recent proper motion survey of that field (Schilbach et al. 1995) based on plates taken with the Tautenburg Schmidt telescope and extended to an area of 16.5 square degrees provided new cluster MPs and also photometric data even for a number of the lowest luminosity stars (in fact the faintest object measured has V = 18.26). Of the 520 known FSs in the field 437 (85%) were successfully identified, their J2000.0 coordinates, high precision proper motion components and apparent photographic R magnitudes (and for the majority of them their V and B magnitudes too) determined. Based on these data new cluster MPs have been deduced which show that a considerable number (40%) of the so called Pleiades FSs are not members of that cluster at all. This conclusion follows the tendency already found: when we involve more and more faint FSs into the investigations the percentage of non-members monotonically increases (cf. Haro et al. 1982 and references therein).
Liquid-Mirror Telescope Surveys
Authors: Hickson P.
Published: June 2021

Recent advances in the technology of rotating liquid-mirrors now make feasible the construction of large optical telescopes for dedicated survey programs. Two three-metre-class astronomical telescopes have been built and asix-metre telescope is under construction. These instruments observe in zenith-pointing mode, using drift-scanning CCD cameras to record continuous imaging of a strip of sky typically 20 arcmin wide. This enables them to observe of order 100 square degrees of sky with an integration time of a few minutes per night. Data can be co-added from night to night in order to increase the depth of the survey. Liquid-mirror telescopes are particularly wellsuited to surveys using broad or intermediate bandwidth filters to obtain photometric redshifts and spectral energy distributions for faint galaxies and quasars.
The Deep Project
Authors: Koo David C.
Published: June 2021

DEEP is a multi-institutional program designed to undertake a major new spectroscopic survey of faint field galaxies with the Keck II 10-m telescope. The scientific goals are broad and include exploring galaxy formation and evolution, mapping the large scale structure at moderate to high redshifts, and constraining the nature and distribution of dark matter and cosmology. Besides the primary goal of securing large numbers of redshifts (10, 000+) to very faint limits of I ~ 23, DEEP intends to acquire spectra of high enough quality and spectral resolution to extract rotation curves, velocity dispersions, age estimates, and chemical abundances for a brighter subset of galaxies. A new imaging spectrograph for Keck called DEIMOS has been specifically designed to achieve these goals and is currently scheduled for completion by the end of 1998. DEIMOS will provide anoverall gain for multi-object spectroscopy of about 7x compared to the current low-resolution spectrograph (LRIS). While awaiting for DEIMOS to be operational, the interim DEEP science programs have been diverse, but largely concentrated on spectroscopy of faint galaxies observed with HST, especially in the “Groth Strip” and Hubble Deep Field (HDF) and its flanking fields. Recent highlights include redshift and kinematic studies of compact galaxies, high redshift (z ~ 3) galaxies, and distantspirals.
Redshift Surveys With 2DF
Authors: Colless Matthew , Boyle Brian
Published: June 2021

This IAU Joint Discussion proposes to address the subject of redshift surveys in the 21st century. This paper, however, deals with two major new redshift surveys that those involved sincerely hope will be completed in the 20th century. Nonetheless, these surveys are relevant to the topic of the meeting, as they clearly foreshadow the scope and style of redshift surveys, if not in the coming millennium, at least in the coming decade.

The surveys are being carried out with the new Two Degree Field (2dF) facility on the Anglo-Australian Telescope (AAT), a 400-fibre multi-object spectrograph with the capability, as described in Section 2, to increase the size of redshift surveys by an order of magnitude over current best efforts. The main scientific goals, survey strategy and some preliminary results from the 2dF Galaxy Redshift Survey are outlined in Section 3, while Section 4 similarly describes the 2dF QSO Redshift Survey. Further information can be found on the WWW at http://www.aao.gov.au/2df/ for the 2dF facility, at http://msowww.anu.edu.au/~colless/2dF/ for thegalaxy survey and at http://www.aao.gov.au/local/www/rs/qso_surv.html for the QSO survey.
Connectivity in the Astronomy Digital Library Through the Ads
Authors: Eichhorn Guenther , Kurtz Michael J. , Accomazzi Alberto , Grant Carolyn S. , Murray Stephen S.
Published: June 2021

The Astrophysics Data System (ADS) is an integral part of the Astronomy Digital Library and the collaboration Urania. It provides access to 1 million references and connects these references with many other information centers and their data, such as on-line journals, object databases, and scanned journal articles. This article describes some of the features and links between the ADS and other on-line services.
Electronic Publishing. Impact on Developing Countries
Authors: Onuora Lesley
Published: June 2021

The developing countries at the low end of the scale face almost insurmountable problems in accessing electronic information. In Nigeria, only two of 40 universities have e-mail. Although electronic access to current information could revoutionize the educational situation at these places, the communication infrastructure does not exist, nor does the necessary funding.
Hipparcos Astrometric Results
Authors: Kovalevsky J.
Published: June 2021

The astrometric results of Hipparcos include the positions at epoch (1991.25), the proper motion in the new IAU extragalactic reference system (ICRS), and parallaxes for about 118 000 stars. One dimensional positions are also given for 48 asteroids and 3 satellites. Due to the non-isotropy of the scanning law, the uncertainties are position dependent. Some indications of the remaining correlations are given. Various tests and comparisons show that systematic errors in parallax, if any, are not larger than 0.1 millisecond of arc.
Astrometry of Poss-II Plates Using Tycho
Authors: Bucciarelli B. , Morrison J.E. , McLean B.J. , Sturch C.R.
Published: June 2021

We present a first attempt to compute an astrometric solution of POSS-IIplates using TYCHO stars as the reference catalogue. Also, we have made use of a special catalogue of stars observed with the Carlsberg Meridian Circlein La Palma between 1994 and 1995, brought into the HIPPARCOS reference system. Such a catalogue consists of a double strip along the equator, fairly dense (approximately 10 stars per square degree), faint (average magnitude 12.5), with an average error at epoch of ~ 150 mas per coordinate. Since the limiting magnitude of TYCHO stars is about 11.5, almost exactly one magnitude less than the CAMC special catalogues’ average, the latter has served as a very useful external comparison, although a more interesting magnitude range would have been 14-15. In this respect, we note that the Schmidt plates under study cover a large area (6.4 x 6.4 degree) and have fairly long exposures (~ 60 min); therefore, a possible magnitude dependence of the model needs to be carefully investigated. The results shown in the table above, which were obtained using a 2nd order polynomial in conjunction with a mask method using 5 plates only are very promising. The average external error over the entire plate area is about 0.2 arsecper coordinate, after the CAMC error have been subtracted.