bluuebunny/crossref_metadata_2025 huggingface dataset:
Oscillation of the Magnetic Field in an Active Region
Authors: Horn T. , Staude J.
Published: June 2019

The Vacuum Tower Telescope (VTT) at Tenerife has been used together with a polarimeter in front of a two-dimensional imaging spectrometer with a Fabry-Perot interferometer. The spectrometer has been described by Bendlin et al. (1992) and Bendlin et al. (1995), the remaining instrumentation, calibration, and data reduction by Horn et al. (1996). Some parameters of the setup were: 384×286 pixel CCD-camera (0.2” per pixel); resolution for the images better than 0.8”; filtergrams in the photospheric spectral line Fe I 6173.4 Å with Δλ = 10.9 mÅ; 45 filtergrams for each scan; 127 scans within 114 min. Δt = 54 s. White-light images from the same field of view were taken strictly simultaneously to all narrow-band pictures to correct for image blurring and motion.

The present observations were obtained on July 20, 1994, and were focused on the main spot of the active region NOAA 7757, 30° NE from the disk center.
Dynamics of the Deep Solar Photosphere at Subgranular Scales
Authors: Nesis A. , Hammer R. , Kiefer M. , Schleicher H.
Published: June 2019

Extending our previous studies of the dynamics of solar granulation (Nesis et al., 1997) we investigated the relationship between granular flow and the emergence of turbulence in the deep photosphere. Our main goal is to explore if such a relationship exists, and if so, to define it quantitatively. To this end we take advantage of the excellent signal approximation property of wavelets. The material for the present work is a series of spectrograms of high spatial resolution covering a time span of 12 min. They were taken at the center of the solar disk with the German Vacuum Tower Telescope in Izaña (Tenerife, Spain) in 1994, and include several absorption lines of different strengths; for more details see Nesis et al. (1997). The spectrograms were digitized and processed with wavelet techniques and regression analysis, in order to investigate the granular convective flow, the associated turbulence, and their mutual connection.
MHD Oscillations Observed in the Solar Photosphere with the Michelson Doppler Imager
Authors: Norton A.A. , Ulrich R. K. , Bogart R.S. , Bush R.I. , Hoeksema J.T.
Published: June 2019

Magnetohydrodynamic (MHD) oscillations are observed in the solar photosphere with the Michelson Doppler Imager (MDI). The absorption of acoustic waves by sunspots (Braun et al., 1988) and the possible conversion of acoustic waves into MHD waves (Spruit et al., 1992) provide a plausible basis for the existence of MHD waves in the solar atmosphere and motivate this attempt at observation.
Observational Relationship Between Meso-Sized Convection and 5-Min Oscillation in the Solar Atmosphere
Authors: Ueno S. , Kitai R.
Published: June 2019

Solar convection has been studied theoretically and observationally for very long time. At present, three kinds of solar surface structures are supposed as manifestations of solar convection; granulation, mesogranulation, supergranulation, in increasing order of spatial size. Among them, observations of mesogranulation, however, do not have long history, yet, since November's discovery (1981). Their basic characteristics such as lifetime, velocity field, radial size, and relation to other kinds of convection, have not been precisely determined, yet.
Distributions of the Sources of the Magnetic Field During the Double Magnetic Cycle
Authors: Benevolenskaya Elena E.
Published: June 2019

The longitudinal and latitudinal distributions of the solar magnetic field have been investigated by many authors see e.g. (Bumba and Howard 1969; Gaizauskas et. al. 1983). The main longitudinal structures such as active longitudes, sector boundaries in the solar wind, and coronal holes appear to be the consequence of non-symmetric magnetic modes (Stix 1971; Ivanova and Ruzmaikin 1977) and can be explained within the framework of dynamo models. According to these models, solar magnetic fields are generated by helicity and differential rotation in the solar convection zone (Parker 1979) and the linear dynamo process may generate a carrier frequency ωc (ωc = 2π/T, T = 22 yr
Time Variation of the Global Solar Magnetic Field Inferred from the Sun's Shadow as Seen in 10 TeV Cosmic Rays
Authors: Ding L.K. , Nishizawa M. , Sasaki T. , Tan Y.H. , Yamamoto Y. , Yuda T. ,   The Other Members of the Tibet Asγ Collaboration
Published: June 2019

Air shower arrays with high counting rates at high altitude provide a unique means for the study of the time dependence of the Sun's shadow as seen in cosmic rays (Amenomori et al. 1992). With the Tibet-I array, operated from 1990 to 1993 at Yangbajing (4300m), we detected for the first time the influence of the solar and interplanetary magnetic fields (IMF) on the Sun's shadow. In this experiment the Sun's shadow seen by 10 TeV cosmic rays was found at a position 0.°7 away from the position of the Sun. This large displacement is considered to be caused by IMF which changed considerably in 1990-1993, near maximum, and during the declining phase of solar activity (cycle 22). A new Tibet-II array, enlarged in 1994, with a seven times larger effective area than the Tibet-I, has been operating since 1995 and allows us to observe the Sun's shadow every 3-4 months. The solar activity, being in the most quiet phase now in 1995-1997, will return to more active phase in 1998. Here, we present some results obtained in 1996 with Tibet-II array.
Observations of Star Formation
Authors: Lada Elizabeth A. , Alves João F.
Published: June 2019

Star formation is a continuous ongoing process occurring over the lifetime of our Galaxy and the universe. However understanding how stars form from their pre-natal clouds of gas and dust remains a mystery. During the last two decades we have made remarkable progress toward unraveling this mystery mainly due to advances in observational technology especially at infrared and millimeter wavelengths which allow direct observation of the sites of star birth. Such observations suggest that embedded clusters may be the fundamental units of star formation in molecular clouds. Low star formation efficiency and rapid gas dispersal make these clusters disperse to provide the field star population. Consequently embedded clusters provide important laboratories for investigating fundamental issues of star formation within our Galaxy.
Hot Molecular Cores and High Mass Star Formation
Authors: Van Der Tak F.F.S.
Published: June 2019

This review covers hot cores in the context of high-mass star formation. After giving an overview of chemical processes and diversity during high-mass star formation, it reviews the ‘warm envelope’ phase which probably precedes the formation of hot cores. Some recent determinations of the cosmic-ray ionization rate are discussed, as well as recent evidence for hot cores around low-mass stars. Routes for future hot core research are outlined.
Is the Magnetic Field Preserved During Core Formation?
Authors: Matthews Brenda C. , Lai Shih-Ping , Crutcher Richard M. , Wilson Christine D.
Published: June 2019

We present recent JCMT and BIMA array polarimetry data of nearby star-forming regions in order to compare the core and cloud-scale magnetic field geometries in two regions of Orion. The similarity of the magnetic field geometry in these cores to that of their ambient clouds is contrasted with JCMT data toward the Barnard 1 dark cloud in Perseus, which reveal a different magnetic field orientation between the majority of the cores and the surrounding cloud; each of the cores exhibits a different mean polarization position angle. We conclude that the preservation of the magnetic field geometry is better in cores formed within clouds with ordered large scale structures. In Barnard 1, the cores may quickly exhibit a different polarization pattern if they have, for example, rotation which differs from the large scale cloud motions, or a weaker component of ordered fields. This could also explain why the cores exhibit such different geometries from each other in Barnard 1.
Extra-Galactic Star Formation Revealed
Authors: Schinnerer Eva
Published: June 2019

High angular resolution observations of nearby galaxies in the optical using ground-based and space-based telescopes have not only revealed the presence of young stellar clusters, but also allowed to study their properties in various dynamical environments. These studies have shown that young massive clusters (YMCs) have typical masses of a few 1000 M⊙ and sizes of a few parsec irrespective of their site of formation (such as bulges, spiral arms, starburst rings, or mergers). This points toward a universal formation mechanism for these stellar clusters.

Observations of the dust and gas content in high redshift galaxies allows one to study the reservoir for star formation in the early universe. These studies reveal extremely high star formation rates of a few 1000 M⊙ yr−1, while the distribution of the molecular gas still seems to be comparable to what is observed in the local universe. The detection of considerable amounts of molecular gas via its CO lines in the highest redshifted QSOs known today (up to z=6.4) indicates that star formation in the early universe has already produced considerable amounts of metals.
Molecular Gas & Star Formation in Nearby Galaxies
Authors: Wong Tony , Thornley Michele D.
Published: June 2019

We review recent observations of molecular gas in nearby galaxies and their implications for the star formation law on large (> 1 kpc) scales. High-resolution data provided by millimetre interferometers are now adding to the basic understanding that has been provided by single-dish telescopes. In particular, they confirm the good correlation between star formation rate (SFR) and molecular gas surface densities, while at the same time revealing a greater degree of heterogeneity in the CO distribution. Galaxies classified as SAB or SB tend to show radial CO profiles that peak sharply in the inner ∼20″, indicative of bar-driven inflow. The observed Schmidt law index of ≍1.5 may result from a nearly linear relation between SFR and H2 mass coupled with a modest dependence of the molecular gas fraction on the total gas density. The normalisation of the Schmidt law, giving the characteristic timescale for star formation, may stem from the generic nature of interstellar turbulence.
Watching the Birth of Super Star Clusters
Authors: Turner Jean L. , Beck Sara C.
Published: June 2019

Subarcsecond infrared and radio observations yield important information about the formation of super star clusters from their surrounding gas. We discuss the general properties of ionized and molecular gas near young, forming SSCs, as illustrated by the prototypical young, forming super star cluster nebula in the dwarf galaxy NGC 5253. This super star cluster appears to have a gravitationally bound nebula, and the lack of molecular gas suggests a very high star formation efficiency, consistent with the formation of a large, bound cluster.
Masers: High Resolution Probes of Massive Star Formation
Authors: Ellingsen S P
Published: June 2019

Astrophysical masers are one of the most readily detected signposts of high-mass star formation. Their presence indicates special conditions, probably indicative of a specific evolutionary phase. Masers also represent the ultimate high-resolution probe of star formation with the potential to reveal information on the kinematics and physical conditions within the region at milli-arcsecond resolution. To date this potential has largely remained unfulfilled, however, recent advances suggest that this will soon change.

The key to unlocking the potential of masers lies in identifying where they fit within the star formation jigsaw puzzle. I will review recent high resolution observations of OH, water and methanol maser transitions and what they reveal. I also briefly discuss how multi-transition observations of OH and methanol masers are being used to constrain maser pumping models and through this estimate the physical conditions in the masing region.
(Sub-)mm Interferometry in Massive Star Forming Regions
Authors: Beuther Henrik
Published: June 2019

(Sub-)mm interferometry is the most favorable technique to investigate the earliest stages of massive star formation. I will outline general applications in that field and discuss results of different sub-topics (hot core chemistry and massive molecular outflows). Furthermore, recent data obtained with the Submillimeter Array will be shown to present the unique capabilities of this new instrument. Finally, I will give a short outlook on the main physical topics of massive star formation to be tackled with (sub-)mm interferometry within the next decade.
Observations of Binary Protostellar Systems
Authors: Launhardt Ralf
Published: June 2019

A major gap in our understanding of star formation concerns the origins of binary stars although there is growing evidence that most stars form in binary and multiple systems. While some theoretical predictions of fragmentation models are indirectly supported by statistical studies of evolved binary stars at shorter wavelengths, direct observations of the formation phase became only possible with the advance of large millimeter interferometers. Molecular line spectroscopy and dust continuum observations at high angular resolution can address some of the key questions in binary star formation theories. Observing methods and results of recent studies of binary protostellar systems are reviewed in this paper.
T Tauri Multiple Systems
Authors: Brandeker Alexis
Published: June 2019

New high-resolution adaptive optics systems provide an unprecedentedly detailed view of nearby star forming regions. In particular, young nearby T Tauri stars can be probed at much smaller physical scales (a few AU) than possible just a decade ago (several tens of AU). Of major importance is closing the sensitivity gap between imaging and spectral surveys for stellar companions. This allows for 1) calibration of pre-main-sequence evolutionary tracks by obtaining accurate dynamical masses, 2) resolving confusion problems arising by placing unresolved systems in colour-magnitude diagrams, and 3) well defined and determined multiplicity fractions of young stellar systems, important for discriminating star formation scenarios. This article briefly reviews the current status of high resolution imaging of T Tauri multiple systems, and what we can expect to learn from them in the near future.
The Variation of the Initial Mass Function in Clusters
Authors: Luhman K. L.
Published: June 2019

I review recent measurements of the initial mass function of stars and brown dwarfs in star-forming regions and open clusters and summarize the implications of these data for theories of star formation.
Theory of Young Clusters
Authors: Bate Matthew R. , Bonnell Ian A.
Published: June 2019

We review recent results from hydrodynamical calculations of the formation of young stellar clusters. The calculations present a highly dynamical picture of star formation where the mass function of stars originates from competitive accretion between protostars and dynamical ejections which halt accretion. Large star clusters form hierarchically; a molecular cloud forms many small clusters that later merge into one large cluster, erasing the initial substructure. Using calculations that resolve fragmentation down to the opacity limit, we examine the implications of dynamical star formation for the IMF, the formation of brown dwarfs and close binaries, and the sizes of protoplanetary discs. Finally, we discuss the dependence of the results on the initial conditions.
Adaptive Optics Imaging of Circumstellar Environments
Authors: Apai Dániel , Pascucci Ilaria , Wang Hongchi , Brandner Wolfgang , Henning Thomas , Grady Carol , Potter Dan
Published: June 2019

We present results from our high-resolution, high-contrast imaging campaign targeting the circumstellar environments of young, nearby stars of different masses. The observations have been conducted using the ALFA/CA 3.5m and NACO UT4/VLT adaptive optics systems. In order to enhance the contrast we applied the methods PSF-subtraction and polarimetric differential imaging (PDI). The observations of young stars yielded the identification of numerous new companion candidates, the most interesting one being ∼ 0.5″ from FU Ori. We also obtained high-resolution near-infrared imaging of the circumstellar envelope of SU Aur and AB Aur. Our PDI of the TW Hya circumstellar disk traced back the disk emission as close as 0.1″ ≃ 6 AU from the star, the closest yet. Our results demonstrate the potential of the adaptive optics systems in achieving high-resolution and high-contrast imaging and thus in the study of circumstellar disks, envelopes and companions.
Adaptive Optics in Star Formation
Authors: Brandner Wolfgang
Published: June 2019

Over the past ten years, the concept of adaptive optics has evolved from early experimental stages to a standard observing tool now available at almost all major optical and near-infrared telescope facilities. Adaptive optics will also be essential in exploiting the full potential of the large optical/infrared interferometers currently under construction. Both observations with high-angular resolution and at high contrast, and with a high point source sensitivity are facilitated by adaptive optics. Among the areas which benefit most from the use of adaptive optics are studies of the circumstellar environment (envelopes, disks, outflows), substellar companions and multiple systems, and dense young stellar populations. This contribution highlights some of the recent advances in star formation studies facilitated by adaptive optics, and gives a brief tutorial on optimized observing and data reduction strategies.
Outflow-Circumstellar Envelope Interactions in Protostars
Authors: Arce Héctor G.
Published: June 2019

We present the results of a high angular resolution (< 5″) survey of protostars with outflows, at different evolutionary stages, using the Owens Valley Radio Observatory Millimeter Array. This survey aims to understand the evolution of the interaction between protostellar outflows and the infalling circumstellar envelopes. Our data enable us to probe the structure and kinematics of the molecular outflow and the circumstellar envelope, as well as the outflow-envelope interaction at scales of less than 0.02 pc, for every source in our sample. Our results indicate that outflows have a considerable impact on the dense circumstellar envelope. Also, we show that the nature of the outflow-envelope interaction depends on the protostar's evolutionary stage.
High Angular Resolution Studies of Disks-the Millimetre
Authors: Wilner David J.
Published: June 2019

I briefly review progress in high angular resolution observations of disks at millimetre wavelengths, with a focus on dust continuum observations of the disks surrounding low mass pre-main-sequence stars. I summarize the utility of observations at millimetre wavelengths, where dust emission is largely optically thin, and I touch on several recent directions, including imaging surveys using interferometers, testing physical models of disks with resolved observations, and the complexities introduced by stellar multiplicity.
Observation of Chemistry in Protoplanetary Disks
Authors: Dutrey Anne
Published: June 2019

Protoplanetary disks are now intensively observed by mm arrays. While resolved images of CO rotation lines permit a better understanding of their physical structure, molecular surveys provided by current mm telescopes are currently sensitivity limited and do not allow a quantitative analysis of the chemical properties of disks. In this paper, I review the actual observational knowledge of the chemistry in the outer disks surrounding low and intermediate PMS stars and traced by mm data.
Optical/IR Interferometry: Star Formation at sub-AU Scales
Authors: Tuthill Peter
Published: June 2019

Intermediate to late stages of star formation are characterized by rising infrared and visible luminosities, with much of the most interesting physics concentrated in the inner regions within the immediate vicinity of the central protostar(s). Long-baseline optical and infrared interferometry is ideally suited to study of such bright, compact structures. Contributions from presently operational arrays, which are capable of resolving the brightest few dozen, will be reviewed. These results presage the potential for further dramatic advances in our understanding of star formation with observations from more advanced instruments now being built.
ACS Coronagraphic Observations of Optically Thin Debris Disks
Authors: Clampin Mark , Krist John , Ardila David R. , Golimowski David A. , Ford Holland C. , Illingworth Garth
Published: June 2019

The Advanced Camera for Surveys (ACS) offers a coronagraphic imaging mode with angular resolution of 0.026″pixel−1. In combination with with the appropriate subtraction of reference star point spread functions (PSF) the coronagraph is capable of achieving contrast ratios of ∼1000. We present some of the first ACS observations of the optically thin debris disk HD141569A and discuss new results from these observations.
Star Formation at High Angular Resolution: Summary and Outlook
Authors: Zinnecker Hans
Published: June 2019

I give a personal summary of IAU-Symposium 221 “Star Formation at High Angular Resolution”, including general impressions and scientific highlights (both observations and theory). Some future directions, like infrared interferometry and advanced SPH numerical simulations, are described. In passing, I also make some critical comments about information overload and the dangers of decreasing information transfer efficiency in the age of power-point.
The discovery of the spiral arms of the Milky Way
Authors: Gingerich Owen
Published: June 2019

Attempts in the 1930s and 1940s to determine the spiral structure of the Milky Way by star counting methods, essentially the continuation of the work of the Kapteyn Astronomical Laboratory, failed to reach this goal. A new foundation for the search was laid by Walter Baade in his studies of stellar populations. With the recognition that highly luminous objects, especially H II regions, would outline the spiral structure, W.W. Morgan and his young associates Sharpless and Osterbrock carried out the observational program that first delineated, in 1951, the nearby arms of the Milky Way. The full paper was never published, so the historical details have remained somewhat vague, primarily because the 21-cm discoveries so quickly overtook the optical researches.
Models of the mass distribution of the Galaxy
Authors: Schmidt Maarten
Published: June 2019

Mass models of the Galaxy play an important role in studies of the structure of the Galaxy. The various populations or components combine to yield a gravitational field that produces the observed rotation curve. For the spheroid and disk this requirement can be used to set limits on some of their properties. The properties of the dark corona are entirely defined this way.
A model of our Galaxy
Authors: Haud U. , Jôeveer M. , Einasto J.
Published: June 2019

The construction of models is the most effective tool for a synthesis of various observational data and for a quantitative study of physical and dynamical structure and evolution of stellar systems. Classical models of spiral galaxies were based on rotational velocities, which were identified with circular velocities. They were designed to represent the galactic attraction force in the radial direction.
Mass models of three southern late-type dwarf spirals
Authors: Carignan C.
Published: June 2019

Although rotation-curve studies of spiral galaxies have unambiguously established the presence of dark matter, and theoretical studies have shown that its location is likely to be in a separate spheroidal halo component (Binney, 1978; Tubbs and Sanders, 1979; Monet, Richstone and Schechter, 1981), very little is known about its spatial distribution and its nature. Recently, Faber and Lin (Faber and Lin, 1983; Lin and Faber, 1983) have shown that, if one can get a rough idea of fundamental parameters like the halo scale length and the halo-to-disk ratio, it is also possible to put strong constraints on the nature of non-luminous matter.
Galactic rotation outside the solar circle
Authors: Chini R.
Published: June 2019

New radial velocities and optical distances for partly very distant HII regions give evidence for a rising rotation curve in the outer parts of the Galaxy.
Infrared studies of the stellar population in Baade'S Window
Authors: Ruelas-Mayorga R.A. , Hyland A. R. , Jones T. J.
Published: June 2019

An IR-scan of the Baade's Window () area (BW) has been obtained (Ruelas-Mayorga etal., 1983). The Cumulative Counts Function (CCF) at 2.2 μm (No. of sources per sq. degree down to a given K magnitude) down to K ≃ +13.5 was formed by combining 1.9-m telescope scans with Anglo Australian Telescope (AAT) scans.
Galaxy population structure from proper motions
Authors: Reid N. , Murray C. A.
Published: June 2019

We are currently engaged in astrometry of Kapteyn Selected Area photographic plates covering the period 1908 to the present day using the GALAXY measuring engine at RGO. Our intention is to use the apparent motions to investigate the stellar velocity structure within a kiloparsec of the Sun. We have completed a preliminary analysis of SA 68 (ℓ = 1110, b = 460), deriving positions and proper motions using the central overlap method on measures of plates spanning the period 1909 to 1980. These include the original (1909) and second epoch (1925) plates taken with the Radcliffe refractor at Oxford, and used in the compilation of the Radcliffe Catalogue (Knox-Shaw and Scott-Barrett, 1934), as well as more recent plates taken using the 26-inch refractor at Herstmonceux. For stars present on all thirteen exposures (including double exposures on the same plate) the internal residuals in positions in each co-ordinate are per plate, giving annual motions accurate to ~1 milli-arcsecond over the 71 year baseline. Since our plates have a limiting magnitude of only B ~15, we have used 17 stars in common with Chiu (1980) to transform our relative motions to the absolute frame. Our motions are in very good agreement with those by Chiu, with a scatter of less than 3 milliarcseconds in each co-ordinate and linearity of scale between the two datasets.
Distribution and motions of CO in M51
Authors: Rydbeck G. , Hjalmarson å. , Rydbeck O.
Published: June 2019

We present results (partly preliminary) of an extensive map (73 positions) of CO (J=1–0) emission in M51 (Fig. 1). The spectra were obtained with the Onsala 20-m antenna (beam size 33″), equipped with a cooled mixer and a 512×1 MHz multichannel receiver. The data are not yet fully analyzed but our preliminary results are as follows:

1. A small central minimum in the CO emission is apparent (Fig. 2). The average radial CO distribution shows a maximum at ~ 15″ (corresponding to 0.7 kpc, for an assumed distance of 9.6 Mpc).

2. The above minimum results from what seems to be an oval ridge structure in the emission intensity around the center, with an extent of about 30″ by 40″ (Fig. 3). This could be the markings of an elongated hole or the beginning of the spiral arms. (The ridges are fairly well correlated with the innermost parts of the spiral arms as delineated by continuum observations by Segalowitz, 1976.)

3. It seems that a central oval velocity pattern is needed to explain a dip at 450 km s-1 in the central spectrum. (The dip is present in all and independent parts of our data.)

4. The outer parts of the galaxy have only been covered in strips (Fig. 1). Clearly there is structure in these strips, i.e. not only a radial decrease. The “on-arm” spectrum (88″, 0″) has for example a greater integrated and peak intensity than the “interarm” spectrum (77″, 0″). Such arm-interarm contrast is not always clear, though. Observations covering a larger section of an arm-interarm region, where contrast has been seen, are being planned for the next observing season.

5. We also note that the observed apparent velocity differences between CO and ionized gas, reported by Rydbeck et al. (1983), persist. A fully convincing argument on this point (taking into account the finite beam etc.) requires some further model work, however.
CO (2–1) observations of Maffei 2
Authors: Sargent Anneila I. , Sutton E. C. , Masson C. R. , Phillips T. G. , Lo K.-Y.
Published: June 2019

Maffei 2 is a highly obscured galaxy, probably of type Sbc, at a distance of 5 Mpc (Allen and Raimond 1972; Spinrad et al. 1973). Since it lies close to the Galactic plane, there is considerable confusion in infrared and 21-cm HI observations due to Galactic emission, but investigations of its structure can be carried out at millimeter wavelengths where the Galaxy contribution is confined to a limited velocity range. The high resolution (30″) of our CO J=2–1 observations permits both a detailed examination of Maffei 2 and a study of the nature of the gas in its nucleus, through comparison with the CO J=1–0 observations.
Outer-Galaxy molecular clouds
Authors: Kutner Marc L. , Mead Kathryn N.
Published: June 2019

Since our original report of CO emission from outside the solar circle in the first quadrant (Kutner and Mead, 1981) we have extended the observations in two ways: (1) We have improved latitude and longitude coverage. Preliminary results on the latitude distribution were reported by Kutner (1983). (2) We have extended our cloud mapping, giving us at least partial CO maps of 55 clouds, along with 13CO, C18O, CO (2–1), and 2-mm H2CO observations of some clouds.
The high-latitude distribution of Galactic gamma rays and possible evidence for a gamma-ray halo
Authors: Strong A. W.
Published: June 2019

During its 6.7-year lifetime the COS-B experiment included about 15 months of observations towards latitudes |b|> 20° and covered almost all latitudes from the South to North galactic poles. Studies comparing the local gamma-ray emission with the distribution of gas (Lebrun et al. 1982, Strong et al. 1982) have so far been limited to 10°<|b|< 20°, where the correlation is found to be fairly good and the structured emission can therefore be attributed mainly to cosmic-ray interactions with gas. The extension of this type of analysis to higher latitudes is now possible using the COS-B database.
On the ultraviolet background radiation of the Galaxy
Authors: Zvereva A. , Severny A. , Granitsky L. , Courtès G. , Cruvellier P. , Hua C. T.
Published: June 2019

Observations of the far-UV spectrum (1300–1800 å) of the sky background at different galactic latitudes are presented. The measurements were made in deep space, at distances up to 2 × 105 km from the Earth with the photoelectric spectrometer (“Galaktika”) on board the “Prognoz-6” satellite. The highly elongated orbit of the satellite permitted corrections for scattered Lα-light. The contribution of stars was eliminated using fluxes measured in the TD-I and OAO-2 experiments.
Loop I (the north Polar Spur) region - a quasi radio halo
Authors: Milogradov-Tuin Jelena
Published: June 2019

The distribution of total spectral indices between 38 and 408 MHz with a resolution of for δ>-25° has the following main properties:

1. Relatively small variations of spectral indices over the sky.

2. High indices in the central region at high galactic latitudes.

3. Moderately low spectral indices in the anticentre region.

4. Lower indices in the low-brightness regions (cold holes).

5. The lowest indices in regions containing large amounts of HII.
Giant clouds and star-forming regions as spiral-arm tracers
Authors: Elmegreen Bruce G.
Published: June 2019

A variety of observations suggest that clouds of 106-107 M⊙ and extended regions of star formation are the best tracers of spiral structure in the Milky Way.
Atomic hydrogen towards 3C10
Authors: Albinson James S.
Published: June 2019

New aperture-synthesis observations of HI in absorption towards 3C10 with high velocity resolution (0.6 km s-1) and moderate angular resolution (1 arcmin) have been made with the Westerbork Synthesis Radio Telescope. These are an extension of the survey by Schwarz, Arnal & Goss (1980). A selection of the data has been studied in a preliminary way, covering the Perseus-Arm absorption feature (~ −50 km s−1 with respect to the Local Standard of Rest).
Interferometric observations of the small-scale structure of Galactic neutral hydrogen
Authors: Crovisier J. , Dickey J. M.
Published: June 2019

The small-scale structure of galactic neutral hydrogen may be statistically described by the spatial power spectrum of the 21-cm line. This latter may be readily observed by interferometer arrays since it is the squared modulus of the visibility function. We have observed the , region with the Westerbork Synthesis Radio Telescope (Crovisier and Dickey, 1983). Brightness fluctuations of the 21-cm line were detected in this region on scales as small as 1.7 arcmin (corresponding to less than 5 pc). The Westerbork observations, combined with single-dish observations made at Nançay and Arecibo, allow determination of the spatial power spectrum over a dynamic range of about 106 in intensity. The spectrum follows roughly a power law with indices ~ −3 to −2. An interpretation in terms of the turbulence spectrum is proposed by Dickey (1985).
Phenomena at the Galactic Centre - a massive black hole?
Authors: Rees Martin J.
Published: June 2019

About 107 L⊙ of luminosity, mainly in ionizing flux and infrared radiation, emerges from the central pc3 of our Galaxy. This exceeds the luminosity from the corresponding region of most nearby galaxies, though it is surpassed by M82 and NGC 253 (Reike and Lebofsky 1982), but perhaps involves nothing more exotic than a starburst 106 − 107 years ago. But the manifestations of activity at the Galactic Centre that are unambiguously non-thermal in character are at a much lower level: the γ-ray annihilation line (~ 1038 erg s−1) and the compact radio source (~ 1034 erg s−1). I shall comment briefly on these two phenomena, and also suggest an interpretation of the remarkable pseudo-spiral structures revealed by the NeII infrared and the radio-continuum maps. These phenomena relate to the old question (cf. Lynden-Bell and Rees 1971) of whether our Galaxy has ever experienced a more violent phase, leaving a massive collapsed remnant.
Observations of high-velocity clouds colliding in the anticenter
Authors: Morras R. , Mirabel I. F.
Published: June 2019

High-velocity clouds that are colliding with Milky-Way material in the anticenter were observed in the 21-cm line of neutral hydrogen, using the Arecibo telescope with a system temperature of 40 K. We confirm the reported (Mirabel, 1982) positional and kinetic correlations between a high-velocity cloud that is infalling with a velocity of −200 km s−1 and a strong disturbance in the interstellar medium (see figure 1).
Radial distributions of constituents in M33, the Galaxy, and M51
Authors: Berkhuijsen Elly M. , Klein Ulrich
Published: June 2019

The radial distributions of the surface brightness or column density of thermal and nonthermal radio emission, far-infrared (FIR) emission, blue light, HI and CO in the Sc galaxies M33 and M51 are compared with the corresponding distributions in the Galaxy. Information on the variation of the absorption at Hα and on the variation of the abundance ratio O/H is also shown.
Slippery evidence on masses in the Local Group
Authors: Lynden-Bell D.
Published: June 2019

Once it is agreed that not all mass gives a significant contribution to light or any other emission, then one must rely on the dynamics of the visible objects to determine the total gravity field. It is clearly impossible to do this without subsidiary hypotheses. Here we shall assume that all members of the Local Group began together in the Big Bang, and that their dynamics have been governed by their mutual gravitational interactions since the system first achieved a size of some 200 kpc. This must have been some 109 years after the Big Bang.
Evolution of the vertical structure of galactic disks
Authors: Villumsen Jens Verner
Published: June 2019

Numerical simulations of the evolution of the vertical structure of galactic disks have been performed. The physical mechanism for the evolution is the scattering of stars off Giant Molecular Clouds (GMCs) as proposed by Spitzer and Schwarzschild (1951). A model galaxy consists of a fixed, nearly isothermal halo plus an axisymmetric, thin exponential disk consisting of 1000 stars. A population of GMCs is embedded in the disk. The stars interact with each other via a self-consistent axisymmetric field determined from an expansion in spherical harmonics to twelfth order. The stars scatter off the GMCs that are modelled as soft particles. The equations of motion of the stars and the GMCs are integrated directly to high accuracy. Adiabatic cooling is therefore included implicitly. In order to avoid axisymmetric instabilities, the stellar component is initially relatively hot in the plane of the disk. Nineteen simulations were performed with varying parameters to check the consistency of the results.
3-dimensional particle simulation of vertical oscillations in gas discs
Authors: Johns T. C. , Nelson A. H.
Published: June 2019

The problem of the persistence of warping in the outer regions of many galactic HI discs is now well known. Such a warp is observed in the Milky Way, where further deviations from a flat plane are seen in the form of a systematic tilt of the gas disc near the centre, with a short-wavelength (approximately 2 kpc) corrugation at intermediate radius.
Periodic orbits relevant for the formation of inner rings in barred galaxies
Authors: Michalodimitrakis M. , Terzides Ch.
Published: June 2019

The study of orbits of a test particle in the gravitational field of a model barred galaxy is a first step toward the understanding of the origin of the morphological characterstics observed in real barred galaxies. In this paper we confine our attention to the inner rings. Inner rings are a very common characteristic of barred galaxies. They are narrow, round or slightly elongated along the bar (with typical axial ratios from 0.7 to near 1.0), and of the same size as the bar. A first step to test the old hypothesis that inner rings consist of stars trapped near stable periodic orbits would be a study of particle trapping around periodic orbits encircling the bar. Such a study is contained in the work of several authors (Danby 1965, de Vaucouleurs and Freeman 1972, Michalodimitrakis 1975, Contopoulos and Papayannopoulos 1980, Athanassoula et al. 1983). In the above works the stability of periodic orbits was studied with respect to perturbations which lie on the plane of motion z = 0 (planar stability). To ensure the possibility of formation of rings, a study of stability with respect to perturbations perpendicular to the plane of motion (vertical stability) is necessary. In this paper we investigate the properties of periodic orbits which we believe to be relevant for the inner-ring problem using a sufficiently general model for the galaxy and sets of values for the parameters which cover a wide range of different possible cases. We also study the stability, planar and vertical, with respect to large perturbations in order to estimate the extent of particle trapping. A detailed numerical investigation of three-dimensional periodic orbits will be given in a future paper.
Chemical composition of interstellar material
Authors: Pottasch S. R.
Published: June 2019

Abundances in interstellar clouds, as determined from interstellar absorption lines, are discussed first, including abundances in ‘abnormal’ (high-velocity) clouds. HII-region abundances are then discussed and compared to results from the interstellar clouds. The present status of an abundance gradient as determined from HII regions is given. Abundances in planetary nebulae are then given for various categories of nebulae, and compared to HII regions. Finally a short status report on abundances near the galactic center is given.
II / Taxonomy of the Mogollon Culture
Authors: Wheat Joe Ben
Published: June 2019

Before 1933, a number of sites had been dug in the area including the drainage of the upper Gila, the San Francisco, and the Mimbres rivers. Most of these were late Pueblo sites. Customarily they were thought to represent a regional variant of the culture now called Anasazi. A few investigators, however, suspected that these remains might have had a separate origin. In 1933, Haury excavated Mogollon Village for Gila Pueblo, and the following summer, Harris Village. These were published in 1936 (Haury 1936a and 1936b). For the first time there appeared a clear statement of se'quent phases in the area. But equally important was the resultant hypothesis that these cultural remains were not a regional variation of Anasazi but, instead, represented a hitherto unrecognized group.
IX / Mogollon Social Organization
Authors: Wheat Joe Ben
Published: June 2019

Martin and his associates (1950b:556-569) have essayed a most Interesting reconstruction of the social organization of the Mogollon Indians of Pine Lawn Valley. It is not my purpose here to criticize this attempt in toto, for I consider it valuable and stimulating, if not proven or provable; nor to offer an alternative reconstruction. However, from the point of view of the total Mogollon cultural pattern, I should like to point out certain discrepancies in the Martin hypothesis and to indicate another approach to the matter that has recently received some attention.
X / The-Mogollon Culture Pattern
Authors: Wheat Joe Ben
Published: June 2019

Having surveyed the cultural content of the sites called Mogollon by their excavators, and those obviously belonging to the same cultural expression, we may now ask whether there is, or was at any period, a pattern which may be recognized as a functioning cultural entity. This, of course, leaves aside the question of relationships with other cultural patterns, which does not affect the problem at hand. Table 16 brings together the culture elements which characterize the Mogollon Culture Pattern.
XII / The Relation of Mogollon to Prepottery Horizons
Authors: Wheat Joe Ben
Published: June 2019

It has been stated that with the addition of pottery the Cochise Culture became the Mogollon. The idea is not new. Although the first reports on the Mogollon (Gladwin 1934, 1935. 1936; Haury 1936b) visualized them as intruders into the Southwest from an eastern source, by 194-1 tn e idea was being expressed that there was a genetic connection between the prepottery Cochise and the later Mogollon. Haury (1941: 130) suggested that pottery, house building, earth burial, agriculture, and a few minor traits added to San Pedro Stage was the beginning of the Mogollon. Sayles (Sayles and Antevs 194-1:61) suggested that the introduction of pottery terminated the last stage of Cochise. McGregor (1941:189) also proposed this sequence. The excavation of Ventana Cave led Haury (1943) to suggest that Hohokam, as well as Mogollon, had its source in Cochise. In Ventana Cave Haury (1950) detailed the transition for the Hohokam.
XIII / Mogollon - Hohokam Relationships
Authors: Wheat Joe Ben
Published: June 2019

Haury (1943, 1950) has demonstrated that Hohokam was an outgrowth of a western and slightly differentiated branch of San Pedro Stage, as Mogollon developed out of the eastern branch. Certain similarities in ceramic and lithic complexes of Mogollon and Hohokam in the earliest phases of each leave little doubt that there were close relationships at that time. Nevertheless, there existed technological differences in the pottery, and other differences, which require explanations before we can judge the nature of the relationships and whether or not more than a single source for pottery is indicated.
Warsaw Variability Surveys
Authors: Kaluzny Janusz
Published: June 2019

Four large-to-medium size photometric surveys are being conducted by Warsaw astronomers: the Warsaw-LCO survey of globular clusters, OGLE, DIRECT, and ASAS. In this contribution I provide short descriptions of these projects and discuss briefly some results obtained for pulsating variables.
Variability Survey with the HST
Authors: Weiss Werner W. , Kuschnig Rainer , Zwintz Konstanze
Published: June 2019

We report on the analysis of HST archival data obtained with the Fine Guidance Sensors concerning a magnitude limited survey of microvariability among guide stars.
Two Aspects of Using Hipparcos Data for Studying Multiperiodic Stellar Pulsations
Authors: Jerzykiewicz M.
Published: June 2019

Two aspects of using Hipparcos data for studying multiperiodic stellar pulsations involve (1) deriving frequencies of multiperiodic pulsators from Hipparcos Epoch Photometry, and (2) using Hipparcos parallaxes together with other data, such as the frequencies, frequency ratios and multicolor photometry, to identify pulsation modes. Details are examined by looking at the δ Scuti star DK Virginis. From Hipparcos Epoch Photometry, two frequencies are derived. These frequencies are then verified by showing that they also fit all available ground-based observations of the star. In addition, Hipparcos parallax and a photometric effective temperature are used to compare the position of DK Vir in the HR diagram with evolutionary tracks. The star turns out to be at the end of core-hydrogen-burning stage of its evolution or slightly beyond, with a mass of 2.2 M⊙, or somewhat smaller. The observed frequencies indicate that the two detected modes are p3 and p2, while the relatively large photometric amplitudes imply ℓ ≲ 2.
A Search of Variable Stars in the Tycho Observations
Authors: Piquard Sandrine , Halbwachs Jean-Louis , Fabricius Claus , Geckeler Ralf , Wicenec Andreas
Published: June 2019

The selection of variable stars in the Tycho catalogue was re-considered. A method based on a Kolmogorov–Smirnov test was elaborated, giving 729 candidate variable stars. This number could increase to about 1000 in the future.
Light Curve Analysis of Tycho Variable Stars
Authors: Andronov Ivan L. , Cuypers Jan , Piquard Sandrine
Published: June 2019

A variety of methods has been applied to the Tycho suspected variable stars to find reliable periods.
RV Tauri Stars and Type II Cepheids in the Magellanic Clouds - Results from the MACHO Database
Authors: Pollard Karen R. , Alcock C. , Allsman R. A. , Alves D. , Axelrod T. S. , Becker A. C. , Bennett D. P. , Cook K. H. , Freeman K. C. , Griest K. , Lehner M. J. , Marshall S. L. , Peterson B. A. , Pratt M. R. , Quinn P. J. , Sutherland W. , Tomaney A. , Welch D. L. ,   The MACHO Collaboration
Published: June 2019

A review of the properties of Type II Cepheids and RV Tauri stars in the Magellanic Clouds is presented. In the behaviour of their light and colour curves, the RV Tauri stars appear to be a direct extension of the Type II Cepheids to longer periods. A single P – L – C relationship describes both the Type II Cepheids and RV Tauri stars in the LMC. The derived high intrinsic magnitudes for the RV Tauri variables supports the proposition that these objects are luminous stars evolving off the AGB. Preliminary analysis of the long time-series MACHO photometry indicates one star (MACHO*05:37:45.0–69:54:16) has an obvious ‘period-quadrupled’ periodicity, which is supporting evidence for a period-doubling bifurcation transition to chaotic pulsations.
Polarization Observations of RV Tauri Stars at the Dodaira Station of the National Astronomical Observatory in Japan
Authors: Yoshioka K. , Saijo K. , Sato H.
Published: June 2019

We made multicolor linear polarimetric observations of RV Tauri stars using the 91-cm reflector at the Dodaira Station of the National Astronomical Observatory in Japan. We report the main results for 17 RV Tauri stars obtained until now.
UBVRIJHK Photometry of Short-Period Red Variables Identified by the Hipparcos Survey
Authors: Laney C. D. , Koen C.
Published: June 2019

The Hipparcos survey team discovered thousands of new variables, including M giants with periods as short as a day, which appear to have maintained rough phase coherence over a period of more than three years. New optical and infrared photometry has been obtained as part of an effort to understand the nature of these anomalous stars.