bluuebunny/crossref_metadata_2025 huggingface dataset:
Evolutionary Models of the Dissociation Zones Surrounding HII Regions
Authors: Roger R. S. , Dewdney P. E.
Published: June 2019

Atomic hydrogen regions have been observed in λ21-cm emission around a number of galactic HII regions in various stages of evolution (Roger & Pedlar, 1981; Dewdney & Roger, 1982; Roger & Irwin, 1982). These HI zones are almost certainly formed by the dissociation of H2 with Lyman-Werner band photons in the UV from the exciting stars. We describe some results of the computer modelling of the advancement of dissociation fronts with time as functions of various parameters, principally stellar type and ambient gas density. The modelling has shown that for most conditions a substantial HI zone is formed fairly rapidly around a new star. When the dissociation front moves out to a distance where absorbing molecules are predominantly in the ground vibrational state, further advancement of the front is much slower.
CO and CS Observations in the Eastern Part of W5
Authors: Wramdemark S. , Lyngå G. , Johansson L.E.B.
Published: June 2019

At galactic longitudes between 132 and 139 degrees and distances of 2 to 2.5 kpc, the galactic disk contains an unusual concentration of gas clouds, young clusters and OB associations (W3, W4 and W5). The small nebula S 201 is situated to the east of W5, which contains the young open cluster IC 1848. Probably associated with S 201 is one of the originally proposed Bok globules; the region also contains three infrared sources.
An extremely Luminous H2 Flow in the Dr21 Star Forming Region
Authors: Garden Rognvald P.
Published: June 2019

Previously, mapping of the spatial distribution and velocity structure of vibrational molecular hydrogen (H2) line emission has necessarily been restricted to the central outflow region of the Orion Molecular Cloud (e.g. Beckwidth et al. 1983) where the line intensities are an order of magnitude larger than any other presently known H2 emission source. However, an improved understanding of the role played by highly energetic gas flows in sustaining the observed H2 line emission relies heavily on the collection of comparable data on other active star-forming regions. With this view in mind, we have undertaken a detailed H2 line emission survey of the DR21/W75S molecular cloud complex. We considered this region to be one of the best candidates because it was already known to possess a luminosity (Harvey et al. 1977), CO wind velocities (Dickel et al. 1978, Fischer et al. 1985) and extended H2 emission (Fischer et al. 1981) similar to those seen in Orion.
CO Observations of High-Velocity Flows in the Core of the NGC 7538 Molecular Cloud
Authors: Kameya Osamu , Hasegawa Tatsuhiko , Hirano Naomi , Takakubo Keiya , Seki Munezo
Published: June 2019

Observation of the high-velocity flows in the core region of the NGC7538 molecular cloud are carried out with CO (J=1-0) molecular line using NRO 45-m radio telescope. The beam size is 14″ and the mapping area covers about 4'x3′. Four high-velocity flows are found in the core region. The high-velocity flows are prominent at and around IRS1, 9, and 11.
CO Molecular Clouds in the Region of GL490
Authors: Moriguchi H. , Fukui Y.
Published: June 2019

GL490 is a solitary infrared source toward a heavily obscured region. The source exhibits indications of energetic mass outflows of the ionized and molecular gas (e.g. Simon et al. 1981, Lada and Harvey 1981). Generally, GL490 is considered as a young stellar object as suggested by the association with dense molecular gas (Morris et al. 1974, Kawabe et al 1984). In order to understand the distribution of the molecular gas around GL490, we have undertaken an extensive mapping in the J = 1-0 CO and 13CO lines with a 3′ beam (the Nagoya 4-m telescope) and a 15″ beam (the 45-m telescope).
Interaction of Protostellar Winds with the Orion Molecular Cloud
Authors: Okuda Toru
Published: June 2019

The effect of a strong protostellar wind on a dense molecular cloud with a magnetic field is investigated by time-dependent magnetohydrodynamic calculations which take into account the cooling due to H2 molecules as the dominant one. The shocked region obtained here seems to be responsible for the formation of the bright H2 emission with a high-velocity width observed in the Orion-KL Nebula.
The Energy Source of HH34 and its Highly Collimated Jet
Authors: Reipurth Bo , Bally John , Graham J. A. , Lane A. P. , Zealey W. J.
Published: June 2019

We have discovered a highly collimated optical jet emanating from a faint star and pointing towards the Herbig-Haro object HH34 (Reipurth 1985, Reipurth et al. 1986).
Wind Properties of Young Stars
Authors: Panagia Nino
Published: June 2019

The statistical properties of winds form young stars are summarized and discussed. One and the same mechanism, possibly related to the process of star formation, appears to be responsible for mass loss in all pre-main-sequence stars. Moreover, evidence is found that the ionization and the acceleration of the winds of very young stars are produced by processes different from those operating in main sequence and more evolved stars.
A Mechanism for Variability of Cometary Nebulae
Authors: Rudnitskij G. M.
Published: June 2019

A model is suggested to explain the variability of the optical structure and the integral brightness of cometary nebulae (CN) occurring at timescales of several years and tens of years (Gyulbudaghian et al. 1977, Cohen et al. 1977, 1981, Magakyan 1981, Gyulbudaghian 1982). A CN is assumed to be a reflection nebula; it is a wall of a conical cavity in the circumstellar gas-and-dust torus illuminated by the central star (Cohen 1974). I explain the CN's variability by the presence of small tilted circumstellar disc of gas-and-dust, located inside the internal channel of the large circumstellar torus (see Figure 1). A similar model was put forward by Ward-Thompson et al. (1985) to account for a tilt angle of about 30° between the direction of short optical jets (stellar wind, channelled by the small disc) and the large-scale bipolar outflow (focused by the large torus) in the CN NGC 6729 associated with the star R CrA. Tilt angles of about 30° between optical and radio structures exist in CN NGC 2261 (Cantó et al. 1981) and GM 1-29 (Levreault 1984).
A New Theory of Star Formation: Analytical Mass Function and Star Formation Rate
Authors: Di Fazio A.
Published: June 2019

An analytical, theoretical, time-dependent initial mass function is derived for the objects created in the fragmentation of a gravitationally unstable gas protocloud. The mass spectrum depends on the chemical-dynamical-radiative evolution of the protocloud and it peaks at a mass slightly greater than the minimum Jeans mass attained throughout the evolution. A fragmentation rate mass spectrum is also analytically derived.
Structure and Fragmentation of Molecular Complexes
Authors: Falgarone E. , Puget J. L. , Pérault M. , Bonazzola S. , Heywaerts J.
Published: June 2019

We propose a hierarchical model of large molecular complexes (mean density ∼ 10 cm−3, masses larger than 105 M⊙ relevant to their “cold phase”) which preceeds the formation of massive stars and H II regions, and investigate the gravitational stability of the different scales.
Dissipation of Magnetic Fields in Very Dense Interstellar Clouds and the Magnetic Flux of a Newborn Star
Authors: Umebayashi Toyoharu , Nakano Takenori
Published: June 2019

The magnetic flux to mass ratio of an interstellar cloud is 104 to 105 times the ratio in a typical magnetic star with a surface field of 1kG, and is at least several hundred times the ratio in most strongly magnetic stars. This excess magnetic flux must be lost in some stage of star formation. The dominant process of magnetic flux loss in ordinary clouds is the drift of charged particles and magnetic fields in the sea of neutral particles (plasma drift, also called ambipolar diffusion). However, even this process is inefficient in a cloud of hydrogen number density nH ≲ 1010 cm−3.
Large Scale Star Formation: Density Waves, Superassociations and Propagation
Authors: Elmegreen Bruce G.
Published: June 2019

The hypothesis that density waves trigger star formation is critically examined. Much of the former evidence in favor of the hypothesis is shown to be inconsistent with modern observations. A comparison between galaxies with and without density waves reveals no significant difference in their star formation rates. A new role for density waves in the context of star formation might be based on four principles: 1. density waves are intrinsically strong, 2. the gas is compressed more than the stars in the wave, 3. star formation follows the gas, with no preferential trigger related to the wave itself, and 4. regions of star formation are larger in the spiral arms than they are between the arms. This new role for density waves is primarily one of organization: the waves place most of the gas in the arms, so most of the star formation is in the arms too. The waves also promote the coagulation of small clouds into large cloud complexes, or superclouds, by what appears to be a combination of collisional agglomeration and large-scale gravitational instabilities. Special regions where density waves do trigger a true excess of star formation are discussed, and possible reasons for the difference between these triggering waves and the more common, organizing, waves are mentioned. Other aspects of large-scale star formation, such as the occurrence of kiloparsec-size regions of activity and kiloparsec-range propagation, are illustrated with numerous examples. The importance of these largest scales to the overall mechanism of star formation in galaxies is emphasized.
Star Formation in Outer Galaxy Molecular Clouds
Authors: Kutner Marc L.
Published: June 2019

A variety of observations of molecular clouds outside the solar circle (mostly around R = 14 kpc) are reported. Maps of CO, 13CO (J = 1 → 0) and CO (J = 2 → 1) emission are discussed. Cloud sizes and masses range up to the GMC class. However, envelope kinetic temperatures are lower than those in GMCs in the molecular ring. Continuum observations, using the VLA at 6 cm and 20 cm, and far infrared observations, taken on the Kuiper Airborne Observatory, suggest the presence of newly formed late O and early B stars.
How Many Star-Forming Regions are there in the Milky Way?
Authors: Lodén L.O.
Published: June 2019

There are very good reasons to believe that every stellar clustering in the Milky Way is a star-forming region or at least that every association is such a region and the minor clusterings adjacent sub-regions.

Some star-forming clusterings are still active but it seems as if a majority should be burned-out. The problem is to estimate the total number of clusterings in the present Milky Way, de-activated and disintegrated as well as active.
The Distance to the Center of the Galaxy
Authors: Reid M. J. , Schneps M. H. , Moran J. M. , Gwinn C. R. , Genzel R. , Downes D. , Ronnang B.
Published: June 2019

The distance to a star forming region can be determined by measuring the proper motions within H2O maser clusters. If the motions of the maser spots are random, the distance can be determined by applying the technique known as statistical parallax. Alternatively, if organized motions are evident in the proper motions, one can model the source to estimate its the distance. Both methods rely on a comparison of the radial component of the motion (in km/s) and the proper motion on the plane of the sky (in milli-arcseconds/year).
Molecular Gas in the Nucleus of M82
Authors: Lo K. Y. , Cheung K. W. , Masson C. R. , Phillips T. G. , Scoville N. Z. , Woody D. P.
Published: June 2019

7″-resolution CO (1-0) observations of M82 with the Owens Valley millimeter-wave interferometer have resolved 2 components of molecular gas in the central 1.5 arcmin of the galaxy: (1) a high plane of M82, and (2) shell-like or filamentary structures of molecular gas, with size-scale as large as 400 pc, extending most likely out of the plane of the galaxy.
Disk Galaxies: The Global Properties of Star Formation and the Chemical Abundance Gradients
Authors: Dopita Michael A. , Evans Ian R.
Published: June 2019

In the relatively gas-rich, pure exponential disk galaxies, available data is accumulating which suggests that the distribution of starformation in the disk either shows no radial variation, or else has a scale-length which is much longer than that of the stars.
Molecular Clouds in Barred Galaxies
Authors: Combes F. , Gérin M.
Published: June 2019

A stellar bar is an essential dynamical component for the behaviour of gas and molecular clouds in a spiral galaxy. It can trigger the formation of the arms and provokes radial transfer of gas. N-body simulations have shown that the bar forms easily and is very stable; according to classification, the majority of spiral galaxies are barred.
A Survey and Follow-up Observations of Starburst Galaxies
Authors: Maehara H. , Takase B. , Heidmann J.
Published: June 2019

A survey of UV-excess galaxies (KUGs) has been made on UGR three image plates taken with the 105-cm Kiso Schmidt telescope (105/150/330) by Takase and Miyauchi-Isobe (1984, 1985a,b). Up to now, about 1 800 objects down to 17-17.5 mag have been catalogued in the surveyed areas of about 900 square degrees.
CO in NGC 5055
Authors: Johansson L.E.B. , Booth R. S.
Published: June 2019

The flocculent spiral galaxy NGC 5055 has been mapped along the major axis in the 12CO (J = 1-0) line using the Onsala 20-m telescope (HPBW = 33″). Figure 1, which gives the spatial velocity diagram of CO emission on the major axis with observed Hα velocities (Kruit and Bosma, 1978) superimposed, seems to imply higher velocities of the regions responsible for the optical emission. Taking into account the cruder spatial resolution of the CO observations, this effect is expected in a region where the rotation curve rises rapidly provided that the CO emission increases toward the centre. Figure 2 shows the rotation velocities for the eastern and western parts of the galaxy separately, as observed in Hα and CO. For CO we only give the portion of the rotation curve which is accurately determined, i.e. where it is relatively flat. The CO velocities in this region agree closely with those observed in HI (Bosma, 1978). These data suggest a difference of 10-20 km s−1 between the Hα and CO velocities at a distance of ∼ 60″ from the centre. The radial distribution of the CO emission, also indicated in Fig. 2, is defined by an iterative fitting procedure to the observed line profiles (see Scoville et al. 1983). This procedure requests an a priori knowledge of the velocity field, here assumed to be defined by the Hα data inside a radius of 60″. However, the shapes of the observed spectra and “best fit” model profiles differ significantly in some cases, again indicating that the Hα velocities do not apply to the molecular gas. The derived radial distribution of the CO emission is dependent on the assumed velocity field; however, the gross characteristics are retained for more feasible rotation curves (i.e. rotation curves giving better fits to the observed profiles).
High Velocity Clouds in the Galaxy
Authors: Lockman Felix J.
Published: June 2019

Early observers measuring 21 cm HI profiles away from the Galactic plane found not only the emission near zero velocity expected from gas in the immediate vicinity of the Sun, but also occasional emission at velocities reaching several hundred km s−1. It seemed unlikely that these spectral lines could come from gas in normal galactic rotation (they are sometimes found at |b| > 45°), and so began the puzzle of “high-velocity clouds” (HVCs). The early result that all HVCs had negative velocity implying that they were infalling was soon shown to be incorrect with the discovery of many positive velocity clouds in the southern hemisphere. Attempts to determine the distance to HVCs by searching for them in absorption against stars yielded only lower limits, typically > 1 kpc. By 1984 several large-scale surveys had established that a significant fraction of the sky was covered with high velocity HI (e.g., Oort, 1966; Giovanelli, 1980). A recent major review is by Wakker (1991a; see also van Woerden, 1993). For this brief presentation to a specialized audience, I will concentrate on issues that may be relevant to the topic of stellar populations.
Chemical Evolution of the Galactic Disk and Bulge
Authors: Wyse Rosemary F.G.
Published: June 2019

The Milky Way Galaxy offers a unique opportunity for testing theories of galaxy formation and evolution. The study of the spatial distribution, kinematics and chemical abundances of stars in the Milky Way Galaxy allows one to address specific questions pertinent to this meeting such as

(i)

When was the Galaxy assembled? Is this an ongoing process? What was the merging history of the Milky Way?

(ii)

When did star formation occur in what is now “The Milky Way Galaxy”? Where did the star formation occur then? What was the stellar Initial Mass Function?

(iii)

How much dissipation of energy was there before and during the formation of the different stellar components of the Galaxy?

(iv)

What are the relationships among the different stellar components of the Galaxy?

(v)

Was angular momentum conserved during formation of the disk(s) of the Galaxy?

(vi)

What is the shape of the dark halo?

(vii)

Is there dissipative (disk) dark matter?
M31 and Companions: A Key to Baade's Stellar Populations Then and Now
Authors: Freedman W. L.
Published: June 2019

The stellar populations in M31 and its companions are reviewed from both historical and more modern contexts. Recent data for nearby resolved galaxies suggest that a revision of Baade's original population concept, particularly as applied to elliptical galaxies, is required. In addition, these new data highlight the difficulties in interpreting the data for, and the lack of direct information on, the more distant giant elliptical galaxies being used for cosmological studies.
The Stellar Populations in Local Group Dwarf Galaxies
Authors: Saha Abhijit
Published: June 2019

The aim of the study of the populations in a stellar system is to understand and be able to describe the stellar content of a system in terms of physical parameters such as the age, star formation history, chemical enrichment history, initial mass function (IMF), environment, and dynamical history of the system. This is done given an understanding of stellar evolution and the ability to express the outcome in “observer parameters”, particularly a color-magnitude diagram (CMD), kinematics, and metallicity. From this perspective, the simplest systems are the galactic clusters and the globular clusters, where all the component stars are coeval and of the same metallicity. The current state of knowledge for these are discussed by others in this conference. We proceed to the next level of complexity (where metallicities are not necessarily all the same, and nor are the stars all coeval), and try to decompose their stellar content, particularly in terms of star formation rate and metallicity. In this regard the two classes of objects that come to mind are the dwarf spheroidals, and the dwarf irregulars. Both these classes of objects are more massive than the open clusters and globular clusters, and show evidence of complexities in their star formation histories, without being so convolved as to make such a study intractable. As we shall see, recent studies along these lines have presented some puzzling problems. Moreover, these are the smallest independent galaxies, and the study of star formation in these is likely to shed light on the history and formation of larger and more complex galaxies.
Dark Matter in Clusters of Galaxies
Authors: Canizares Claude R.
Published: June 2019

An appropriate subtitle for this talk might be “Newton meets Einstein.” For many decades, the prime tool for studying the amount and distribution of matter in galaxy clusters was decidedly Newtonian, involving at first the measurements of the dynamics of the galaxies themselves and, for the past 15 years or so, the imputed dynamics of the hot, X-ray emitting intra-cluster gas. Einstein enters more recently with the introduction of gravitational lensing as a tool for studying cluster mass distributions. Rapid progress is being made in each of these areas, and there are now attempts to bring them together to give a consistent and more accurate picture of clusters.
The UV Upturn in Elliptical Galaxies
Authors: Ferguson H.C.
Published: June 2019

The hot stellar component in elliptical galaxies offers clues to both stellar evolution and galaxy evolution. Current observations suggest that extreme horizontal branch (EHB) stars dominate the far-UV emission from galaxies with the strongest “UV upturns,” while post asymptotic giant branch (PAGB) stars are probably significant contributors for weaker galaxies. Spectra near the Lyman limit indicate that a rather narrow range of temperature (and hence EHB star mass) is required. However, other arguments suggest that most of the helium-burning stars in elliptical galaxies are in the red clump. The HB star mass distribution therefore appears to be strongly bimodal. Such bimodality is qualitatively reproduced by two radically different stellar population models, (those of Lee and Bressan et al.), both of which require that the galaxies be very old. However, the Galactic open cluster NGC 6791 also contains EHB stars and exhibits strong bimodality, indicating that old age may not necessarily be a requirement for the UV upturn phenomenon.
Formation Models of Galaxies
Authors: White S.D.M.
Published: June 2019

Unfortunately Dr. White was not able to finish a written version of his presentation at the Symposium in time for inclusion in these proceedings. He refers the interested readers to his lecture notes at the August 1993 Les Houches summer school (White, 1995).
Panel Discussion on the Classification and Terminology of Stellar Populations
Authors: King Ivan R.
Published: June 2019

It was the feeling of the Scientific Organizing Committee that 50 years after the introduction of the concept of stellar populations it might be desirable to attempt to rationalize their classification and terminology. Toward this end a panel discussion was organized, which was followed by a period of audience participation. Although not all those who contributed to the latter section turned in a written version of their remarks, that section is reported as well as possible here.
Conference Summary
Authors: Mould Jeremy
Published: June 2019

Of all the subfields which make up the discipline of astronomy today stellar populations must surely be one of the most difficult to explain to the lay person. From the first day of this meeting I took the notion that this was the invention of a charismatic individual with a particular genius for bridging the gap between stellar and extragalactic research, a bridge which is probably still very relevant to maintain today.
Elemental Abundances of Sharp-Lined Pop I Main Sequence B, A, and F Stars and Pop II A Stars
Authors: Adelman Saul J. , Philip A.G. Davis
Published: June 2019

The elemental abundances of late B and early A stars should be among the most reliably derived as these stars have well known atmospheric physics, and non-crowded optical spectra with lines of many species with good oscillator strengths. We obtained elemental abundances of sharp-lined stars from high dispersion, S/N > 50, spectra taken at DAO and KPNO. We performed fine analyses using ATLAS6 and more recently ATLAS9 model atmospheres. Our papers (mostly in MNRAS) contain consistent studies of about 35 B3 to F7 superficially normal, Mercury-Manganese (HgMn), Am, and Field Horizontal Branch (FHB) A stars. The abundances of the normal main sequence B, A, and F stars are indicators of Galactic metallicity during the most recent epoch of Galactic history.
Automated Spectral Classification of Stars by Means of Objective Prism Spectra
Authors: Shvelidze T. , Malyuto V.
Published: June 2019

Some years ago a complex program of studying the main meridional section of the Galaxy was initiated with the aim of improving our knowledge of spatial and kinematic characteristics of stellar populations. To classify stars, objective prism stellar spectra (D = 166 A/mm at Hγ), are used. The field diameter is 4° 50′, the limiting photographic stellar magnitude is about 12m. Our automated quantitative spectral classification of F-K stars applies criteria evaluation and is based mainly on the SDR package for spectrophotometric data reduction (Malyuto, Pelt, Shvelidze, 1993) and the CTATEC-2 package for the definition of a multiple linear regression model “criteria values versus main physical parameters” (Malyuto, Shvelidze, 1989). Our regression model was based on the final sample of calibration stars containing 95 standard (bright) stars and 96 program faint (8m < B < 11m.6) stars from our areas near the North Galactic Pole. The standard deviations of our calibration with the use of all data taken together are ±0.015 for log Teff, ±0m.96 for Mv and ±0.25 for [Fe/H]. These results are encouraging for application of our method to a large set of Abastumani objective prism spectra.
Stability and Instability of Hierarchical Triple Systems
Authors: Kiseleva L. , Anosova J. , Eggleton P. , Colin J. , Orlov V.
Published: June 2019

We computed the dynamical evolution of hierarchical triple stars in which both orbits are initially circular, and determine the lower limit to the ratio of periods (outer/inner) for which there is dynamical stability. We found for some mass ratios resonance-like behaviour that occurs in a limited range of initial period ratio. Some resonances are ‘disruptive’; that is, for a small range of initial period ratio we find that the system is not able to settle down to a quasi-steady hierarchical state, but instead disrupts. However, below as well as above this disruptive range there are considerable ranges of initial period ratio where the hierarchical state appears to be stable, at least for the length of integration time we took which was sometimes as much as 10,000 outer orbits. The mass ratios are identified for which different types of unstable behaviour, such as an escape of the distant body without exchange, many exchanges in the limited space without escape, formation of new long-live hierarchy, or an escape of one body after a few exchanges, occur for ratios of periods slightly below the limit of stability. We discuss the relevance of the above behaviour to observed close triples, the closest of which is λ Tau (period ratio 8.3).
Kinematics of Orion Association Members
Authors: Smart R.L.
Published: June 2019

We discuss the determination of the expansion of the Orion association. Previous estimates of expansion in associations have employed simplified linear approximations which only required the observation of proper motions (cf. Lesh, J.R., ApJ, 152, 905, 1968). We have used proper motions obtained by Smart (PhD Thesis, Univ. of Florida, 1993) with previously obtained membership criteria to investigate this hypothesised expansion without conclusive results.
Some Physical Parameters and uv by β Photometry of Trapezium Type Multiple Systems
Authors: Salukvadze G.N. , Javakhishvili G.Sh.
Published: June 2019

The present paper deals with the results of electrophotometric observations of 59 components of 19 trapezia in the Stroemgren and Crawford six-colour photometric system.
α-Elements in Bulge Stars: Arp 1145, Terzan 1-2
Authors: Barbuy B. , Ortolani S. , Renzini A. , Bica E. , Castro S.
Published: June 2019

The Caspec échelle spectrograph at the ESO 3.6m telescope was used to obtain high resolution spectra for Arp 1145, and the star 2 of the metal-rich cluster Terzan 1. Arp 1145 was selected from Pickles & van der Kruit (1990). The star Tz1-2 was selected from Terzan 1 BVRI photometry carried out by Ortolani, Bica & Barbuy (1993) New HST CMDs show that Terzan 1 appears to be located nearby the Galactic center.
Kinematics of RR Lyraes in the Inner (Old?) Halo
Authors: Layden Andrew C. , Zinn Robert J.
Published: June 2019

Zinn & Lee (1994, in prep.) have shown that the halo globular clusters with Rgc < 6 kpc are dominated by clusters with relatively blue horizontal branches for their metal abundance, which they interpret as a sign of their old relative ages. Of these “Old Halo” clusters having −1.7 < [Fe/H] < −0.8 dex, they find a net rotation about the galactic center of Vrot = 59 ± 22 km s−1, and a line-of-sight velocity dispersion of σlos = 62 ± 10 km s−1.
The Velocity Dispersions of the Draco and Ursa Minor Dwarf Spheroidal Galaxies
Authors: Pryor C. , Olszewski E. W. , Armandroff T. E.
Published: June 2019

We have used the Hydra fiber positioner and the bench spectrograph on the KPNO 4 m telescope to measure radial velocities for giants in the Draco (Dra) and Ursa Minor (UMi) dwarf spheroidal galaxies. The measurement uncertainties are 1–10 km s−1 per observation, with the median uncertainty being 3.6 km s−1. To date, we have reduced the data from two of our three runs. In UMi these have yielded 150 velocities for 85 member giants; 52 stars have two or more measurements. In Dra we have 108 velocities for 84 member giants and 20 stars have two or more measurements. There is good agreement between the repeat observations and with the Olszewski, Aaronson, & Hill (1995) MMT echelle velocities.
Size and Kinematic Aspects of the SMC According to the Catalogue of Bischoff-Florsch-Marcout
Authors: Florsch A. , Marcout J. , Florsch J.
Published: June 2019

The catalogue is a cross-identification catalogue containing 11800 galactic and SMC member stars. It gives individual results of various authors before 1988, but no mean values. The best is to make statistics inside individual systems, comparing them afterwards. Fig.1 concerns the radial velocities obtained for BAF stars in 1963 by FLORSCH using an objective-prism. Since the largest gradient lies in a dirction near the north (FLORSCH 1972), we reported velocities to the declinations of the stars. It appears that the velocities belong to three groups separated by two empty strips showing each a gradient of about 30 km/s/deg falling down from north to south. The same structure appears for other homogeneous populations, like K type stars (fig.2). This gradient agrees with HINDMAN's HI measurements and was recently confirmed by the results obtained by Le COAR etal for HII, as shown by the crosses on figure 1 which represent mean values of HII velocities calculated by using Le COAER's values. In order to find out the structure by using the Cepheids and eventually confirm the great depth we announced in 1972, 73 and 81, we corrected their mean magnitudes by the formula m1=m+2.03 logP to calculate the fictive magnitudes they would have if their common period was one day. Fig.3 gives the result for the Bar of the Cloud. Out of an important thickness, it appears that the northern end is nearer than the southern by a mean value of about 20 kpc. If one consider the whole Cloud, out of the Wing, fig.4, one can see that the extreme northern Arm is folded and slightly extended.
Where Does Star Formation End in NGC1058?
Authors: Ferguson Annette , Wyse Rosemary , Gallagher Jay , Hunter Deidre
Published: June 2019

As part of a large project to study the rate, distribution and history of star formation in the outer parts of galactic disks (Ferguson, PhD thesis), we have obtained very deep Hα and B-band images of the nearby face-on spiral NGC1058. Our images reveal extremely low surface brightness outer spiral arms in the B-band which extend well beyond the Holmberg radius and appear to be aligned with underlying HI spiral arms. These features contrast greatly to the flocculent appearance of the innermost regions of the disk and the complete absence of any well defined-arms in the Hα image. The surface brightness profile derived from the B-band image exhibits a sharp fall off in the inner regions of the disk followed by a much shallower decline beyond ~ R25 and consequently a single exponential disk cannot be fit to the entire profile.
Stellar Populations of Dwarf Galaxies
Authors: Almoznino Elchanan , Brosch Noah
Published: June 2019

We selected a sample of dwarf galaxies in the Virgo cluster from the original catalog of Bingelli, Sandage and Tamman (1985), which have been measured at 21 cm by Hoffman et al. (1987). The original sample was selected to have both high surface brightness objects (classified as BCD or anything/BCD), and low surface brightness galaxies (classified as ImIII, ImIV or ImV). An additional selection was done on the total amount of HI, as given in Hoffman et al. We selected from each surface brightness group objects with high HI content (flux integral larger than a set threshold), and others with low HI content. We thus defined four samples differing in surface brightness level and total HI content.
Stellar Populations in Mixed Pairs of Galaxies
Authors: De Mello D.F. , Keel W.C. , Sulentic J.W. , Rampazzo R.
Published: June 2019

The interpration of the interaction in galaxies is simplified in mixed pairs (E+S) because most or all of the cold gas can be traced to an origin in a single galaxy (S). We used spectroscopy, imaging, far–IR, and stellar population synthesis to study the stellar content and history of star formation in the nuclear region of the early–type galaxy in the mixed pair AM0327–285. We used the procedure for stellar population synthesis developed by Bica (1988) to estimate the star-formation history of the nucleus of the elliptical galaxy. The method uses a library of star clusters, and estimates the chemical evolution in a test population with two parameters: age and metallicity; no assumptions on gravity or details of stellar evolution are necessary, and the IMF is implicit in the cluster spectra. The procedure allows one to both determine the chemical enrichment and date successive generations of star formation. The result indicates that the dominant population is old and metal–rich ([Z/Z]⊙=0.3), while ~ 10% of the flux at 5870 Å arises from a young stellar population (age ≤ 5 × 108 yr), confirming that this early-type galaxy had recent star formation as suggested also by photometry and far–IR data (de Mello et al 1994). This age is close to several estimates of the characteristic timescale of the interaction, suggesting that the mass influx associated with this star formation occurred as a result of an earlier phase of the interaction and not as a result of the present geometry of the pair.
The Dark Massive Halo in the Elliptical Galaxy NGC 5266
Authors: Pizzella A. , Morganti R. , Sadler M.E. , Bertola F.
Published: June 2019

Recent observations with the Australia Telescope reveal that the elliptical galaxy NGC 5266 has a disk like structure of neutral hydrogen extending as far as almost 10 Re which approximatively lies along the galaxy's major axis, at 65° apart from the inner minor–axis dust lane (Varnas et al 1987). From the present data is not clear whether the HI structure and the dust lane are two distinct disks or a single warped structure. The regularity of the velocity field of the HI structure allow us to use it as a probe of the potential of NGC 5266. The velocity curve along the major axis is flat till the last measured point (rmax ~ 10′) at Vrot = 200km/s. Assuming that the gas in moving in circular orbits, we can derive the mass of the galaxy inside to this radius. The mass–to–light ratio M/LB rises from about 3 in the central regions to 12 at 9 Re (D = 57.6 Mpc), thus indicating that NGC 5266 is embedded in a dark massive halo. Moreover the representative point (cumulative M/LB within the last measured point) of NGC 5266 in the diagram log(M/LB) – log(Re) falls well within the region characteristic of spiral galaxies (Figure 2, Bertola et al. 1993), as do ellipticals previously studied in HI, thus reinforcing the suggestion (Bertola et al. 1993) of a parallel behaviour of the dark matter in elliptical and spiral galaxies.
Remarks concerning reference frames
Authors: Hughes James A.
Published: June 2019

Twenty years ago I published A Catalog of 939 PZT Stars on the System of the FK4. At the time it was well received and indeed it did tighten up various PZT results. As I recall, the catalog, among other things, confirmed an empirical relationship between the Richmond, Florida and Washington, DC instruments which had been derived by Prof. Markowitz. In any event, I planned to follow up on this work, but an assignment to El Leoncito, Argentina intervened. Perhaps it was just as well because other things were happening. Astronauts were soon tramping about the moon and littering up the place with a used car and something called a retro-reflector. Radio astronomers were constantly refining the astrometric potential of their interferometric techniques; strange, high-z, starlike objects had been detected a few years earlier; shiny, new satellites were launched; and shortly the science of determining Earth Rotation Parameters (ERP), or “Orientation Parameters” if you prefer, was to explode with vitality and to reach precisions and accuracies never before achieved. As a matter of fact, the new riches became so numerous that, like the proverbial kid in the candy store, the ERP community was, to some extent, forced to choose among some of them. Thus was born the MERIT campaign.
A non-rotating origin on the instantaneous equator
Authors: Capitaine N. , Guinot B.
Published: June 2019

In order to give an exact and clear description of the angle of rotation of the Earth, we propose to use, as the reference point in space, a “non-rotating origin” (Guinot 1979) such that its hour angle, reckoned from the origin of the longitudes (or “non-rotating origin” in the Earth), represents strictly the specific rotation of the Earth. The position of this origin on the instantaneous equator depends only on the trajectory of the pole of rotation. We show that the estimation of the deduced angle of rotation is not critically affected by the precision with which this trajectory is known. We give therefore the formulae to obtain the non-rotating origin, at any date t, from a chosen fixed reference, and we propose a definition of the Universal Time which will remain valid, even if the adopted model for the precession and the nutation is revised. We show that the use of the non-rotating origin also simplifies the transformation of coordinates between the terrestrial and celestial reference systems.
A re-interpretation of the definition of UT1
Authors: Sinclair A. T.
Published: June 2019

Universal time is a commonplace quantity, and yet it has no generally accepted definition. The expression for sidereal time is often quoted as a definition, but this does not convey much meaning to the average person. Also sidereal time is measured from the equinox of date, and so involves the precession formulae of the stellar reference frame, and hence may not be ideal for other modern techniques of observation. Guinot (1979) has proposed a broad definition of UT1:

“UT1 is an angle which is proportional to the sidereal rotation of the Earth, the coefficient of proportionality being chosen so that UT1, in the long term, remains in phase with the alternation of day and night. In some applications, UT1 can be considered as a non-uniform time scale”.
Relationship between the JPL radio celestial reference frame and a preliminary FK5 frame
Authors: Lestrade Jean-François , Requième Yves , Rapaport Michel , Preston Robert A.
Published: June 2019

Very Long Baseline Interferometry (VLBI) and optical positions of 8 radio stars are compared in the J2000.0 system. The mean differences in right ascension and declination found are +0.02″ ± 0.04″ and −0.02″ ± 0.07″, respectively. These differences show that the JPL radio celestial reference frame is aligned on a preliminary FK5 frame to at least this level.
Celestial reference coordinate system of VLBI with US-Japan joint VLBI experiments
Authors: Takahashi Yukio , Kawaguchi Noriyuki , Heki Kosuke , Kunimori Hiroo , Kondo Tetsuro
Published: June 2019

The right ascension of 3C273B has been a reference of the celestial VLBI coordinate system. However it seems that 3C273B is inadequate for the reference because 3C273B has the jet component which was detected on long baselines in our experiments. We present the best reference source for celestial coordinate system. Next we estimated the source positions, taking the new reference radio source. The nutation and plate motion were considered in our analysis. We show the change of 3C273B position. The estimated source positions are compared with those given in GSFC source catalog (1985).
Radio source structures in VLBI astrometry
Authors: Charlot Patrick , Lestrade Jean-François , Boucher Claude
Published: June 2019

In astrometry, celestial radio sources with extended structures are useful. An algorithm to correct for structure in VLBI delays and delay rates is developed. The radio source NRAO140 is mapped from data with limited u-v coverage by the hybrid method and the Maximum Entropy procedure. The magnitude of the structure corrections in astrometry is discussed in the case of NRAO140.
An analysis of MLRS Near-Real-Time Earth orientation results
Authors: Ricklefs Randall L. , Shelus Peter J.
Published: June 2019

In this paper a comparison is presented between near-real-time earth orientation parameters, produced on-site by the McDonald Laser Ranging System (MLRS) at McDonald Observatory, using observations to the Apollo 15 lunar retroreflector, and those results which are obtained after the fact at the University of Texas at Austin and elsewhere, as well as the results obtained from other techniques. The MLRS data set which is included in this study spans the interval from the commencement of on-site earth orientation solutions at MLRS in February 1985, through the present time, September 1986. This research is supported by the National Aeronautics and Space Administration under Grant NAG5-754 and Contract NAS5-29404 to McDonald Observatory and the University of Texas at Austin from the Goddard Space Flight Center in Greenbelt, Maryland.
Multi-windowed spectrum estimates of the ILS polar motion
Authors: Hinnov L. A. , Park J.
Published: June 2019

We present a set of spectrum analysis techniques described by Thomson (1982) in which the discrete Fourier transform (DFT) is windowed by an expanding set of prolate spheroidal wave functions. The homogeneous ILS polar motion series was chosen for the presentation because of its interesting spectrum. It contains lines at the annual and semi-annual frequencies, a band of uncertain width and structure around Chandler's frequency, and evidence for a 30-year periodicity. None has been measured with great certainty by traditional single-taper DFT spectrum analysis. Here, a multi-taper algorithm significantly improves the bias control and consistency of high-resolution DFT spectrum estimates. An analysis of variance is performed to locate significant harmonic lines, and jackknifed statistics are used as additional cross-checks on the stability of the results. In addition, multi-tapered coherence estimates confirm a previously noted correlation between a meteorological forcing function and a polar motion excitation derived from the ILS series.
Combination of data from different space geodetic systems for the determination of Earth rotation parameters
Authors: Archinal Brent A.
Published: June 2019

Simulation experiments have been performed in order to compare the Earth Rotation Parameter (ERP) results obtained from a) individual observational systems, b) the weighted mean of the results from a), and c) all of the observational data, via the combination of the normal equations obtained in a). These experiments included the use of 15 days of simulated Lunar Laser Ranging (LLR), Satellite Laser Ranging (SLR) to Lageos, and Very Long Baseline Interferometry (VLBI) data using realistic station positions and accuracies. Under the assumptions chosen, the normal equation combination solutions usually provide the best ERP over recovery periods of 6 and 12 hours, and 1, 2, and 5 days. However, solutions by the weighted mean (and even by VLBI alone) provide results that are nearly as good, i.e., within a factor of one to two in accuracy. Complete details are presented in [Archinal, 1987].
The role of Japan in the new international Earth rotation service (expected contribution of the planned Japanese VLBI system VERA)
Authors: Yokoyama K. , Manabe S.
Published: June 2019

The outline of the planned Japanese VLBI system for the Earth rotation study and astrometry (VERA) is described. As a result of simulation study, it is concluded that precision and accuracy of the VLBI estimates of astronomical and geophysical parameters are remarkably improved when VERA participates in the present IRIS network.
Cataclysmic Binaries: Optical and Geometrical Thickness of Disks and the Visibility of the Primary Components
Authors: Smak Józef. I.
Published: June 2019

Accretion disks in cataclysmic binaries are optically thick (in the vertical direction), except for the case of inner parts of cool disks in dwarf novae at quiescence, which are optically thin. In long period Algols disks are cool and optically thick; their atmospheres can be quite extensive.

Except for inclinations close to i = 0°, disks obscure either one or both hemispheres of the central star, the obscuration being either partial or total. In particular:

(a)

In stationary accretion cataclysmic binaries (old novae and nova-like systems), at inclinations close to 90° the white dwarf is fully obscured; at i < 85° only its top hemisphere becomes visible.

(b)

In dwarf novae at quiescence, at inclinations close to 90°, the obscuration of the white dwarf is either complete (for disk radii Rd ≥ 4 × 1010 cm), or limited to its equatorial parts (for Rd ≤ 2 × 1010 cm); at i ≈ 85 – 88° the top hemisphere becomes fully visible, while the bottom hemisphere is fully obscured; at i < 85°, due to the low optical thickness of the inner disk, parts of the bottom hemisphere near the equator also become visible.

(c)

In long period Algols the situations is similar as under (a); in addition, depending on inclination, part of the obscuration can be due to the atmosphere of the disk.
Binary and Other Recycled Pulsars
Authors: Trimble Virginia
Published: June 2019

Binary pulsars and others with weak fields and rapid rotation now number several dozen and appear to have been spun up by close binary mass transfer. Some are lineal descendents of X-ray binaries; others may result from accretion-induced collapse of binary white dwarfs or from captures, exchanges, and collisions in clusters. Seven accurate neutron star masses, 1.27-1.44 Mo, have been measured so far. Outstanding issues include the dominant formation process in various sites and the time history of the neutron stars' magnetic fields in and out of binaries.
Outburst Phenomena in X-Ray Binaries
Authors: Tanaka Y.
Published: June 2019

Three distinctly different types of outburst phenomenon in X-ray binaries are discussed: (1) the so-called type 1 burst which is a thermonuclear flash of matter accreted on the surface of neutron stars, (2) the so-called type 2 burst which is a burst-like X-ray emission caused by a spasmodic accretion, and (3) the nova-like outburst which is triggered by a sudden commencement of accretion.