bluuebunny/crossref_metadata_2025 huggingface dataset:
Abundances of Organic Molecules in Molecular Cloud Cores
Authors: Sutton Edmund C. , Sobolev Andrej M.
Published: June 2019

Molecular cloud cores are often found to contain regions with high abundances of organic molecules such as formaldehyde, methanol, ethanol, dimethyl ether, and methyl formate. First we will review the status of observations of these molecules in a number of sources and discuss some of the limitations of present techniques. Then we will discuss systematic factors involved in the conversion of column densities into fractional abundances and introduce an independent method of calibrating that conversion. Finally we will present recent results from high spatial resolution observations of W3(OH).
Circumstellar Carbonaceous Material Associated with Late-Type Dusty WC Wolf-Rayet Stars
Authors: Chiar Jean E. , Tielens A.G.G.M. , Peeters E.
Published: June 2019

Our own solar system and other planetary systems are composed of organic dust created in the outflows in dying stars. Here, we examine an unlikely source of carbonaceous material in interstellar space, the harsh environment of Wolf-Rayet (WR) stars. We have used spectroscopic data from the Short Wavelength Spectrometer on the Infrared Space Observatory to examine infrared emission and absorption features in the 6 to 9 μm spectral region of hot massive WC-type WR stars. We conclude that these features are due to amorphous carbon dust in their circumstellar environment.
TNO Recovery, Unlocking the Early Solar System
Authors: Kadooka M. A. , Meech K. J. , Chun T.
Published: June 2019

The recent discoveries of small bodies in the outer solar system in the vicinity of the Kuiper belt are revolutionizing solar system formation concepts by providing critical dynamical and compositional clues to its earliest epochs. However, the rapidly accelerating discovery rate means that follow-up observations for orbit determination cannot keep up. We report here on an innovative test program to assess the potential of a small (2-m class) educational outreach telescope to engage in an efficient recovery program. Recovery observations have been obtained over the course of 22 nights using the University of Hawaii 2.2m telescope during 9 observing runs. We targeted over 200 objects and have achieved a 75% success rate. We obtained time resolved resolved light curve photometry on 2000 OK67, and the partial light curve suggests a period T > 12 hr.
From Near-Synchronously Rotating Planets to Tidal Lock: A New Class of Habitable Planets Examined for Forest Habitability
Authors: Heath Martin J. , Doyle Laurance R.
Published: June 2019

Haberle et al. (1996) and Joshi, Haberle & Reynolds (1997) demonstrated that for a planet receiving Earth-level insolation, a 100 mb pure CO2 atmosphere would carry enough heat flux to the dark side of a synchronously rotating planet (SRP) to prevent the atmosphere freezing out there. For a 1,500 mb pure CO2 atmosphere and 0.8 Earth insolation, liquid water could survive over much of the planet. Such high partial pressures of CO2 may seem like special pleading, but in fact, they are not essential for habitable conditions. The effective grey optical depth of the present terrestrial atmosphere (with just 350 ppm CO2, and H2O as the principal greenhouse gas) is approximately 0.9, as against 1.0 for a 1,000 mb pure CO2 atmosphere, so the latter serves merely as a useful approximation (for a truly Earth-type atmosphere, temperatures would be a few degrees lower over the lit hemisphere). Heath et al. (1999) concluded that even forest-habitable conditions, suitable for Earth-like trees (Heath 1996) were not to be ruled out on the basis of present knowledge. Recent work by Joshi (2004) has modelled the range of climatic options for certain land-sea distributions, and these leave the door open for further investigations of combinations of geography and insolation compatible with forest-habitability.
Super-Eruptions and the Search for Extraterrestrial Intelligence (SETI)
Authors: Rampino Michael R.
Published: June 2019

Volcanic super-eruptions that produce >1000 km3 of ejected material and ≥ 1000 Mt (1015g) of stratospheric aerosols and sub-micron dust may be capable of creating global climatic disturbances sufficient to cause a severe setback or crash of modern civilization. Eruptions of similar magnitude are estimated to occur on average about every 50000 to 100000 years, which may be considerably more frequent than impacts by asteroids and comets that could cause similar climatic disasters. Prediction, prevention, and mitigation of global volcanic climatic disasters are potentially more difficult than planetary protection from large impactors, so that volcanism might provide an ultimate limit on the longevity of technological civilizations. If the lifetime of technological civilizations were limited to less than 50 000 years by volcanism, then the number of communicative civilizations in the Galaxy might be less than 1 per 10 million stars. Thus, super-eruptions on geologically active, habitable planets may strongly affect the prospects in radio telescopic SETI.
Captain Cook, the Terrestrial Planet Finder and the Search for Extraterrestrial Intelligence
Authors: Beichman Charles A.
Published: June 2019

Over two hundred years ago Capt. James Cook sailed up Whitsunday Passage, just a few miles from where we now sit, on a voyage of astronomical observation and discovery that remains an inspiration to us all. Since the prospects of our visiting planets beyond our solar system are slim, we will have to content ourselves with searching for life using remote sensing, not sailing ships. Fortunately, a recently completed NASA study has concluded that a Terrestrial Planet Finder could be launched within a decade to detect terrestrial planets around nearby stars. A visible light coronagraph using an 8–10 m telescope, or an infrared nulling interferometer, operated on either a ∼ 40 m structure or separated spacecraft, could survey over 150 stars, looking for habitable planets and signs of primitive life. Such a mission, complemented by projects (Kepler and Eddington) that will provide statistical information on the frequency of Earth-sized planets in the habitable zone, will determine key terms in the “Drake equation” that describes the number of intelligent civilizations in the Galaxy.
Using an Australian Mars Analogue Research Facility for Astrobiology, Education and Outreach
Authors: Laing Jennifer H. , Clarke J. , Deckert J. , Gostin V. , Hoogland J. , Lemke L. , Leyden J. , Mann G. , Murphy G. , Stoker C. , Thomas M. , Waldie J. , Walter M. , West M.
Published: June 2019

The Mars Society is an international private organisation advocating the exploration and settlement of Mars. Part of its mission involves selecting areas for Martian analogue research, to test hardware, technology, strategies and human factors relevant to sending people to Mars. Mars Society Australia has selected an area in the Arkaroola region in the Flinders Ranges as the site for the first Australian analogue facility. The facility will be an invaluable public education and outreach tool for Australian science, focusing on astrobiology, and its role in future human Mars missions; demonstrating Australian contributions to astrobiology related science and work on terrestrial analogues to Martian environments.
Polarized CMB: Reionization and Primordial Tensor Modes
Authors: Cooray Asantha
Published: June 2019

We discuss upcoming opportunities with cosmic microwave background (CMB) observations during the post-WMAP era. The curl-modes of CMB polarization probe inflationary gravitational waves (IGWs). While a significant source of confusion is expected from cosmic shear conversion of polarization related to density perturbations, higher resolution observations of CMB anisotropies can be used for a lensing reconstruction and to separate gravitational-wave polarization signature from that of lensing. Separations based on current lensing reconstruction techniques allow the possibility to probe inflationary energy scales below 1015GeV in a range that includes grand unified theories. The observational detection of primordial curl-modes is aided by rescattering at late times during the reionized epoch with optical depth to electron scattering at the level of 0.1 and above. An improved measurement of this optical depth is useful to optimize experimental parameters of a post-WMAP mission attempting to target the IGW background.
Large-Scale Structure from 2dFGRS
Authors: Peacock J. A.
Published: June 2019

The 2dF Galaxy Redshift Survey is now complete, and the full data are public. 2dFGRS was the first survey to observe more than 100,000 redshifts, making possible precise measurements of many aspects of galaxy clustering, which can be studied as a function of galaxy spectral type, and also of broad-band colour. Early-type galaxies are more strongly clustered than late types, with a relative bias of b = 1.25 ± 0.09 on large scales. For both types, luminosity dependence of clustering is detected at high significance, and is well described by a relative bias of b/b* = 0.85 + 0.15(L/L*). This is consistent with the observation that L* in rich clusters is brighter than the global value by 0.28 ± 0.08 mag. Redshift-space distortions from large-scale infall velocities measure the distortion parameter β = Ω0.6m/b = 0.49 ± 0.09. The power spectrum is measured to ≲ 10% accuracy for k > 0.02 h Mpc--1, and is well fitted by a CDM model with Ωmh = 0.18 ± 0.02 and a baryon fraction of 0.17 ± 0.06. The 2dFGRS plays an essential role in breaking model degeneracies inherent in CMB data; a joint analysis with WMAP results requires Ωm = 0.25 ± 15% and h = 0.73 ± 5%, assuming scalar fluctuations.
Simulations of Large-Scale Structure in the New Millennium
Authors: Suto Yasushi
Published: June 2019

Simulations of large-scale structure in the universe have played a vital role in observational cosmology since the 1980's in particular. Their important role will definitely continue to be true in the 21st century; indeed the requirements for simulations in the precision cosmology era will become more progressively demanding as they are supposed to fill the missing link in an accurate and reliable manner between the “initial” condition at z=1000 revealed by WMAP and the galaxy/quasar distribution at z=0 − 6 surveyed by 2dF and SDSS. In this review, I will summarize what we have learned so far from the previous cosmological simulations, and discuss several remaining problems for the new millennium.
Emergent Structure: the First Two Centuries of the First Two Eons
Authors: Trimble Virginia
Published: June 2019

“Early” maps of the cosmos included the 26th dynasty air god Shu supporting the sky goddess Nut above the earth god Geb, Descartes' Voronoi tesselation, William Herschel's star gauging, and Carl Charlier's 1922 plot of the nebulae in NGC, which he intended as observational support for the fractal nature of large scale cosmic structure (about which he was probably wrong, though right about there being more than one level of clustering). Because Shapley, van Maanen, and others were still denying the very existence of external galaxies at the same time that Lundmark and Opik were measuring their distances and masses and Charlier plotting hierarchies, the story of the discovery of very large scale structure (and streaming) in the universe cannot be told in perfectly linear fashion. There are, however, half a dozen or so discrete phases that can be recognized and three underlying themes, (1) expanding horizons, (2) additional levels of structure, and (3) increasing mediocrity of our vantage point.
2MASS and the Nearby Universe
Authors: Huchra John , Martimbeau Nathalie , Jarrett Thomas , Cutri Roc , Skrutskie Michael , Schneider Stephen , Steining Rae , Macri Lucas , Mader Jeff , George Teddy
Published: June 2019

The Two Micron All-Sky Survey was conceived over a decade ago for the express purpose of mapping the Milky Way and the Universe nearby. 2MASS is now complete and the final data products, including the extended source catalog (XSC), have been released. The XSC contains nearly a million galaxies to the stated completeness goal of K=13.5. While the catalog becomes incomplete at the faintest magnitudes and lowest galactic latitudes due to confusion, at the bright end the catalog is essentially complete down to very low latitudes (b less than 5 degrees), which makes it an excellent survey for the distribution of matter in the nearby Universe. Redshift information is now nearly complete for the 24,000 galaxies brighter than K=11.25 and above |b|=5°. We now have an amazing census of galaxy (baryonic mass) concentrations over the whole sky and inside z=0.04. Several new structures are elucidated and the characteristics of the structures are described. We also examine the match between the predicted gravitational velocity vector of the Local Group and the motions determined by other experiments including the CMB dipole.
The Local Large-Scale Structure from HIPASS
Authors: Zwaan Martin , Meyer Martin , Webster Rachel , Staveley-Smith Lister
Published: June 2019

The HI Parkes All Sky Survey (HIPASS) offers a unique perspective on the galaxy population in the local universe. A catalogue of 4315 HI-selected galaxies has been extracted from the southern region of the survey (δ < +2°). This catalogue gives a clear view of the local large-scale structure and is used to study the two-point correlation function, the Tully-Fisher relation, and galaxy luminosity and mass functions. Some initial results are discussed here.
Verifying the Use of Supernovae as Probes of the Cosmic Expansion
Authors: Ellis Richard , Sullivan Mark
Published: June 2019

We present preliminary results of a follow-up survey which aims to characterise in detail those galaxies which hosted Type Ia supernovae found by the Supernova Cosmology Project. Our survey has two components: Hubble Space Telescope imaging with STIS and Keck spectroscopy with ESI, the goal being to classify each host galaxy into one of three broad morphological/spectral classes and hence to investigate the dependence of supernovae properties on host galaxy type over a large range in redshift. Of particular interest is the supernova Hubble diagram characterised by host galaxy class which suggests that most of the scatter arises from those occurring in late-type irregulars. Supernovae hosted by (presumed dust-free) E/SO galaxies closely follow the adopted SCP cosmological model. Although larger datasets are required, we cannot yet find any significant difference in the light curves of distant supernovae hosted in different galaxy types.
Scalar Field Models for an Accelerating Universe
Authors: Sahni Varun.
Published: June 2019

I describe a new class of quintessence+CDM models in which late time scalar field oscillations can give rise to both quintessence and cold dark matter. Additionally, a versatile ansatz for the luminosity distance is used to reconstruct the quintessence equation of state in amodel independentmanner from observations of high redshift supernovae.
AMiBA: Array for Microwave Background Anisotropy
Authors: Lo K. Y. , Chiueh T. H. , Martin R. N. , Ng Kin-Wang , Liang H. , Pen Ue-Li , Ma Chung-Pei
Published: June 2019

As part of a 4-year Cosmology and Particle Astrophysics (CosPA) Research Excellence Initiative in Taiwan, AMiBA - a 19-element dual-channel 85-105 GHz interferometer array is being specifically built to search for high redshift clusters of galaxies via the Sunyaev-Zeldovich Effect (SZE). In addition, AMiBA will have full polarization capabilities, in order to probe the polarization properties of the Cosmic Microwave Background. AMiBA, to be sited on Mauna Kea in Hawaii or in Chile, will reach a sensitivity of ˜ 1 mJy or 7μK in 1 hour. The project involves extensive international scientific and technical collaborations. The construction of AMiBA is scheduled to starting operating in early 2004.
Globular Clusters as Probes of the Virgo gE NGC 4472
Authors: Bridges Terry , Ashman Keith , Beasley Mike , Geisler Doug , Hanes Dave , Sharpies Ray , Zepf Steve
Published: June 2019

We present radial velocities for 144 globular clusters (GCs) around the Virgo gE NGC 4472 (M49), and ages and metallicities for 131 GCs. We confirm our earlier finding that the metal-poor GCs have a significantly higher velocity dispersion than the metal-rich GCs, and we find little or no rotation in the metal-rich GCs. The velocity dispersion profile is consistent with isotropic GC orbits and the mass distribution inferred from X-ray data. Our sample of GCs spans a metallicity range of −1.6 ≤ [Fe/H] ≤ 0 dex. The metal-poor and metal-rich GCs are coeval within the errors, and all GCs older than 6 Gyr at 95% confidence.
Angular Distribution of Gamma-Ray Bursts: An Observational Probe of Cosmological Principle
Authors: Mészáros Attila , Balázs Lajos G. , Vavrek Roland. , Horváth István , Bagoly Zsolt.
Published: June 2019

The test of the isotropy in the angular distribution of the gamma-ray bursts collected in BATSE Catalog (Meegan C. A. et al. 2000) is a test of cosmological principle itself, because the gamma-ray bursts are at cosmological distances. Several articles of the authors study this question (Balázs L. G., Mészáros A., & Horváth I., Astron. Astrophys., 339, 1, 1998; Balázs L. G., Mészáros A., Horváth I., & Vavrek R., Astron. Astrophys. Suppl., 138, 417, 1999; Mészáros A., Bagoly Z., & Vavrek R. Astron. Astrophys., 354, 1, 2000; Mészáros A., Bagoly Z., Horváth I., Balázs L.G. & Vavrek R. Astrophys. J., 539, 98, 2000). The final conclusion concerning the validity of isotropy is complicated both by instrumental effects and by the fact that there are three subgroups of gamma-ray bursts (“short”, “intermediate”, “long”; separation is done with respect to the duration of bursts). The long bursts are surely up to z ⋍ 4 (z is the redshift); for the remaining two subclasses the redshifts are unknown. The done tests of isotropy suggest (after the elimination of instrumental effects) the existence of anisotropy for the intermediate subclass on the confidence level > 95%. On the other hand, for the remaining two subclasses the situation is unclear; there is no unambiguous rejection of isotropy for them yet on the higher than 95% confidence level. If the bursts of intermediate subclass are at high z-s (say, at z > 0.1), then the validity of cosmological principle would be in serious doubt.
Bulk Motion of Galaxies and Hubble Flow Anisotropy on a Scale of 100 Mpc
Authors: Parnovsky S. L. , Karachentseva V. E. , Kudrya Yu. N. , Karachentsev I. D.
Published: June 2019

We study a large-scale bulk motion of thin edge-on spiral galaxies from the RFGC catalogue using a multipole decomposition of velocity field. The quadrupole and octupole components are statistically significant. The first one corresponds to the Hubble flow anisotropy, the second one leads to decrease of modulus of dipole component due to the strong dipole-octupole interaction.
Star Formation History from Radio Observations: A New Look at an Important Cosmological Parameter
Authors: Partridge R. B.
Published: June 2019

The radio wavelength luminosity of starburst galaxies correlates well with their star formation rates (Condon, 1992). Using this connection and three deep radio surveys, Haarsma and I constructed the global star formation history. Our results (see Haarsma et al., Ap. J., 2000 for details) show a steep increase from z = 0 to z = 1, matching calculations of the global SFR based on optical observations, when those observations have been corrected for the obscuration caused by dust. We note that our method requires no corrections for dust obscuration. We do, however, need to correct our results for radio emission from AGN. We do so using the extensive optical identifications available in these three fields.
Star formation: relationship between the maser species
Authors: Caswell Jim L.
Published: June 2019

Masers in Star Formation Regions arise chiefly from the molecules of methanol, hydroxyl, and water; in the case of methanol and hydroxyl, masing transitions are numerous. Exploring the relationship between the maser species (and their relationship to any associated ultracompact HII region detectable at radio wavelengths) can be made at two levels: first, at the general level, assessing whether the occurrence together of some species, and the absence of others, reveals significant properties of the site as a whole; second, at a deeper level, to assess whether the masing spots are coincident in both velocity and space.

The first may be used as a diagnostic of the evolutionary state of the embedded young massive star. The second reveals physical conditions.

New studies relevant to these issues are discussed here. Substantial unbiased surveys of the major masing transitions are especially valuable in allowing a more effective interpretation of existing targeted observations.
Unusual properties of the methanol maser emission in W48
Authors: Val'tts Irina E. , Lyubchenko Stella Yu.
Published: June 2019

In the star forming region W48 the spectrum of methanol lines is studied. It is found that the intensity of the 20 − 3−1E (12.2 GHz) line anti-correlates with the intensity of the 51-60A+ (6.7 GHz). All other class II methanol lines in the spectrum of W48 (21 − 30A+ (157 GHz), 31 − 40A+ (107 GHz) (possibly) and J0 - J−1E (157 GHz)) demonstrate the same behaviour as 20 − 3−1E (12.2 GHz) line. This fact contradicts to the current models of the class II methanol maser emission. The effect is confirmed in the sample of 67 sources. For the explanation of this fact some possibilities are considered.
Testing extragalactic H2O masers against the thin disk model: the present and the future
Authors: Braatz James
Published: June 2019

Water maser emission is detected towards the nuclei of 22 galaxies, all of them showing some sign of nuclear activity. Except for a couple of cases, maser features have been found only within 150 km s−1 of the systemic galaxy recession velocity but are often offset from systemic within that window. Spectral features in maser-detected galaxies are monitored regularly and these observations show that velocity drifts like those seen in the systemic masers of NGC 4258 are rare. Hence the conclusion that either masers in other galaxies are generally located farther from the central black hole than in NGC 4258, that the black holes in those galaxies are less massive than the one in NGC 4258, or that the masers' acceleration is in the plane of the sky (as in the case of maser gas at the projected extremities of an edge-on disk). Assuming the disk model holds, the last of these options leads to the possibility that, despite the relative faintness of high velocity maser features in the case of NGC 4258, the brightest maser emission originates from the projected edges of the disk, in general. A selection effect would have caused a bias, then, in previous surveys whereby masers in larger, more slowly rotating disks are favorably detected. New wide-bandwidth capabilities at the 100-m Effelsberg telescope and the emergence of the GBT will help to overcome any such bias and provide new examples of maser sources.
OH megamasers
Authors: Lonsdale Colin J.
Published: June 2019

The history of OH megamaser (OHM) research is reviewed, and recent developments in the field are summarized. Particular attention is paid to results from VLBI, and the recognition of a wide range of maser properties within a single galaxy. A peculiar characteristic of compact parsec-scale OHM features is a very broad velocity width, which poses a challenge for radiative pumping models, and suggests filamentary geometries for the emitting clouds. The compact masers may be associated with shocks in a violent nuclear environment, and collisional pumping may play a role. A link between the compact masers and newly formed active galactic nuclei (AGNs) cannot be ruled out. The low-gain amplification model of the diffuse maser component is strongly supported by recent data, and detailed information about the parameters of the amplifying screen is starting to emerge. OHM can be used as powerful probes of dusty, obscured IR galaxy nuclei, and the prospects for these objects being detectable, and therefore useful as probes, at cosmological distances is discussed.
The Star Cluster Systems of the Magellanic Clouds
Authors: Da Costa G.S.
Published: June 2019

The characteristics of the cluster systems of the Magellanic Clouds, as inferred from integrated properties, are compared with those from individual cluster studies and from the field population. The agreement is generally satisfactory though in the case of the LMC, the lack of clusters older than ∼3 Gyr is not reflected in the field population. The possible origin(s) for this cluster “age-gap” are discussed. The SMC cluster age-metallicity relation is also presented and discussed.
OGLE II Observations of Star Clusters in the Magellanic Clouds
Authors: Pietrzyński G.
Published: June 2019

In the course of the OGLE II experiment we have collected up to now about one billion BVI observations of ten million stars in the Magellanic Clouds. Based on that data about 1000 star clusters were detected with an automatic algorithm. In a series of papers we published catalogs of clusters, multiple cluster candidates and variable stars located in the fields of detected clusters. We also presented analysis of the properties of detected clusters. This year the new phase of the OGLE project — OGLE III — has started. With the new mosaic detector we will increase the data flow by about an order of magnitude.
Two New Massive Binary Stars in the Magellanic Clouds
Authors: Niemela Virpi S.
Published: June 2019

The discovery and preliminary spectroscopic orbits of two early O type binaries in very young open clusters in the Magellanic Clouds is reported. The binaries are NGC 346–1 in the Small Magellanic Cloud, and HDE 270145 in NGC 2122 in the Large Magellanic Cloud.
Spectroscopy of Globular Clusters in NGC 1399 - A Progress Report
Authors: Richtler T. , Dirsch B. , Geisler D. , Gebhardt K. , Hilker M. , Infante L. , Minniti D. , Rejkuba M. , Forte J. C. , Larsen S. , Grebel E. K. , Alonso V.
Published: June 2019

We performed spectroscopy of globular clusters associated with NGC 1399 and measured radial velocities of about 450 clusters, the largest sample ever obtained for dynamical studies. In this progress report, we present the sample and the first preliminary results. Red and blue clusters have slightly different velocity dispersions in accordance with their different density profiles in the case of a spherical and isotropic model. We then measure a constant circular velocity of 422 ± 20 km/s, which agrees well with that of the inner luminous component.
The Globular Cluster Systems of the Sculptor Group
Authors: Olsen Knut , Miller Bryan , Schommer Robert , Suntzeff Nick , Bright John
Published: June 2019

We present results from a study to identify the globular cluster systems of six of the brightest galaxies of the Sculptor Group. From Mosaic IICMRimages of the area surrounding the galaxies NGC 45, NGC 55, NGC 247, NGC 253, NGC 300, and NGC 7793, we identify cluster candidates through their morphology, luminosity, and color. We show that many of the Milky Way's globular clusters would appear extended in our images if placed in the Sculptor Group; only in the two most distant galaxies, NGC 45 and NGC 7793, is the discrimination difficult. We find 50–100 candidates per galaxy with integrated properties similar to Milky Way clusters. Published spectroscopic identifications of candidates in NGC 253 lead us to expect that ∼50% of the candidates are true clusters, while the remainder are background galaxies. Study of the Sculptor Group galaxies increases the sample of late-type spiral and Magellanic-type galaxies with known globular cluster systems from 2 to ∼10.
Globular Clusters as Probes of the Formation History of Elliptical Galaxies: Results for NGC 4472
Authors: Rhode K.L. , Zepf S.E.
Published: June 2019

We have undertaken a survey of the globular cluster systems of a large sample of elliptical and spiral galaxies in order to test predictions of elliptical galaxy formation models. Here we outline the survey and present a summary of our results for the Virgo elliptical NGC 4472.
IC 1613 OB Associations and Star Cluster Candidates
Authors: Borissova J. , Kurtev R. , Georgiev L. , Rosado M. , Ivanov G.
Published: June 2019

Moderately deep ground based UBV images are used to investigate the OB associations and star clusters in IC 1613. Fifty eight OB associations with sizes between 30 and 130 pc are outlined. The iteration between associations and superbubbles in IC 1613 was analyzed. The lack of star clusters was confirmed.
A Revised CO View of the Large Magellanic Cloud with NANTEN: New Deep Observations
Authors: Fukui Yasuo
Published: June 2019

I will present a revised CO view of the Large Magellanic Cloud based on the new NANTEN survey, which is ∼ 2–3 times more sensitive than the first one.
Sydney Work on 21-cm Observations of the HI Galactic Disk
Authors: Kerr F. J.
Published: June 2019

This paper reports briefly on the provisional results of the 21-cm galactic work at the Radiophysics Laboratory, Sydney. Observations were made with a 36-ft, transit-type radio-telescope whose beam width at half-power is 1°.5 and a 4-channel receiver whose band width, 40 kcps, is equivalent to 8 km/sec.

The large scale structure of the galaxy has been studied by Kerr, Hindman, and Carpenter. They derive a general picture of the spiral structure in the southern hemisphere extending the Leiden results (see Fig. 1) and, in addition, a “relief map” of the galaxy showing the location of the densest parts of the hydrogen layer with respect to a central plane (see Fig. 2). Analysis of the spiral structure is for the present limited to regions beyond 3 kpc from the center. The Sydney and Leiden data agree well where they overlap, but location of spiral arms is sensitive to the choice of rotational model. Four or five spiral arms, or sections of arms, are indicated in the longitude interval l= 170° to l= 320°. The arms are clearly trailing in the rotation.
On the Nature of the Galactic Halo
Authors: Pickelner S. B. , Shklovsky I. S.
Published: June 2019

In 1952 it was shown by one of us that the sources of galactic nonthermal radio emission form a nearly spherical system concentrating toward the plane and the center of the galaxy. It was pointed out independently by the other author that the field between the clouds must be sufficiently strong to retain the cosmic rays in the galaxy. The density of the kinetic energy of the gas between the clouds could be taken as equal to that of the magnetic energy. Thus the velocity dispersion of the rarefied gas in the space between the clouds should be large and form a spherical, not a flat, subsystem. The spherical distribution of the radio emission supports this suggestion. The wide H and K absorption lines appearing in the spectra of early supergiants are also an argument in favor of the reality of fast movements of the rarefied gas. However, L. Spitzer points out that at least a part of these lines belong to the stars. Spectrograms taken by G. Münch show that some of the wide lines consist of a few faint narrow lines. These phenomena may be explained by the density fluctuations of rarefied gas (kv ∝ n2), but some other interpretations are also possible. This phenomenon supports the hypothesis that the more rarefied gas possesses a higher velocity dispersion. The existence of wide H and K lines is not the principal argument of this theory. It will be shown below that the gas of the halo is too rarefied to give observable lines.
Validity of the Cloud Model of the Interstellar Medium
Authors: Donn Bertram
Published: June 2019

Because of the extreme irregularity in distribution of interstellar matter, some idealized model must be adopted in discussing the interstellar medium. Three simple models have been considered. The original one, long-since discarded, was a uniform distribution. This has been largely replaced by the random cloud picture in which space is visualized as filled with isolated clouds, 5–10 per kpc, about 10 pc in diameter, the array having an exponential velocity distribution with a mean of about 8 km/sec. Lastly, there is a turbulent or a random density fluctuation model.

Although the random cloud hypothesis has received most attenuation from astronomers, it has been well recognized that it is an over simplified model and should be used with some caution. This point of view has been clearly stated by many workers in this field, as the following statements by Oort and by Minkowski, respectively, demonstrate.
Microstructure of the Galactic Magnetic Field
Authors: Serkowski K.
Published: June 2019

The polarization of the stars in open clusters, explained on the basis of the Davis-Greenstein theory, gives some information on the microstructure of the galactic magnetic field.

The polarization is most conveniently described by the parameters Q, U, proportional to the Stokes parameters and defined by

where p is the amount of polarization, θ is the position angle of the electric vector, and θ̄ is the mean value of θ for the region under consideration.
Local Density Variations in Planetary Nebulae
Authors: Seaton M. J.
Published: June 2019

Densities in ionized nebulae may be estimated from the surface brightness, which essentially gives an rms density,.
Internal Motions in the Orion Nebula
Authors: Münch G.
Published: June 2019

In the first and second Symposia of this series von Weizsäcker and von Hoerner discussed the problem of turbulence in the Orion Nebula, while in the second Symposium Courtès has further treated the problem. Von Hoerner has presented a detailed discussion of the methodologies of the treatment. It was suggested that the observed variations in radial velocity in the nebula are consistent with the predictions of the Kolmogoroff equilibrium theory of turbulence, which is valid at sufficiently high Reynolds numbers. However, their results to some extent were inconclusive, mainly because the observations which they analyzed were not sufficiently numerous and accurate. With the purpose of reanalyzing the whole problem, Dr. O. C. Wilson and I undertook the task of determining radial velocities and profiles of selected emission lines in the spectrum of the nebula, using the largest practical resolving power in angle and frequency available with the 200-in. telescope. In order to use advantageously the efficiency of the instrument, we have photographed the brighter parts of the nebula (roughly subtending a solid angle of about 6′ aperture) with the Coudé spectrograph fitted with 31 parallel entrance slits, which are separated from each other by a distance of 1 mm in the focal plane or 1″.3 in the sky. In this manner we obtain in one exposure the spectrum of an area about 40″X40″ with a dispersion such that 1 μ = 0.27 km/sec. In each of these plates about 600 Doppler shifts of the lines [OII] λ3726, Hγ, and [OII] λ5007 have been measured, each of which represents some average value (not necessarily the same for the three lines) of the velocities of nebular matter along the line of sight. Altogether we have about 50 000 radial velocities measured. The accuracy with which a radial velocity may be determined is set by the intrinsic shape of the lines, which reflects the distribution of velocities along the line of sight. To give an idea of the orders of magnitude of the quantities involved, I may mention here that typical values of the mean widths h at half-intensity of the hydrogen, [OIII], and Fe—comparison lines are h(H) = 28.6 km/sec, h(OIII) = 20.0 km/sec, h(Fe) = 8.3 km/sec. The bisection of a line with a cross wire to an accuracy around 0.5 km/sec is thus feasible; repeated measurements have, indeed, shown such precision. On the assumption that the profiles to which the above widths correspond are Gaussian, we may easily disentangle the thermal and turbulent components of the mean square radial velocities, through the dependence on atomic weight of the former. We find from the representative values given above

The corresponding kinetic temperature is 9700°K, in close agreement with the value of the electron temperature determined by other methods.
Evidence for Non-Velocity Redshifts
Authors: Arp Halton
Published: June 2019

Evidence for non-cosmological redshifts is reviewed. It is shown that all current statistical tests favor association of QSRs with galaxies close by, in distance, to our own. It is possible that all QSRs originate from galaxies of much lower redshift. It is shown that in the four cases where QSRs fall projected closest to bright galaxies, that in all four cases the galaxies show evidence of physical interaction. Evidence for high redshift, compact and peculiar companion galaxies is reviewed. From the individual associations of high redshift QSRs and companions, an empirical continuity of observed characteristics is shown between compactness (youth) and excess redshift. Some theoretical explanations for intrinsic redshifts are mentioned.
Quantum Descriptions of Singularities Leading to Pair Creation
Authors: Misner Charles W.
Published: June 2019

Inhomogeneous generalizations of the Kasner cosmological models have been found by Gowdy, and can be used to exhibit simplified models of quantized gravitational fields. One finds that a quantum description can be given arbitrarily near the singularity. Graviton pair creation occurs, and can be seen to convert anisotropic expansion rates into the energy of graviton pairs.
The Observational Evidence
Authors: Eggen O. J.
Published: June 2019

The domain in the (U, V) plane of old-disk-population stars is defined by a sample of F- and G-type stars brighter than visual magnitude 6.5 for which luminosities are available from intermediate-band photometry. The majority of these old-disk stars avoid the domain of the young-disk population in the (U, V) plane except for (1) several objects with V near − 17 km s–1 and (2) a half dozen possible members of a solar group. The sample of stars used to define the old-disk population is confined to distances less than 100 parsec from the Sun and those with V near − 17 km s–1 may represent several generations of the objects formed in what is now the solar neighbourhood and which keep returning to this neighbourhood because they are isoperiodic (V near − 17 km s–1) with the local standard of rest. The half dozen possible members of a solar group indicate an evolutionary age of some 5 × 109 yr. In addition to some of the previously recognized stellar groups in the old-disk population (e.g. Wolf 630 and ζ Her), a new group with U = +40 to 50 km s–1 and V = −36 km s–1 is also discussed. The sample of red giants: (VE≤5m.0 and (R–I)0 > + 0m.42) contains eight probable members of the halo population of which five are members of the Arcturus group. Possible structure in the old-disk-population giant sequence is discussed on the basis of published narrow-band indices, and the luminosity functions of the old- and the young-disk-population red giants are compared.

Most of the material presented can be found in Eggen, O. J.: 1973, Publ. Astron. Soc. Pacific85, 542.
Population I Cepheids – Theory and Observation
Authors: Stobie R. S.
Published: June 2019

The quantitative discrepancies between theory and observation with regard to population I Cepheids are discussed. The discrepancies cannot be reconciled by mass loss or by changes in the luminosity or effective temperature of the variables. It is concluded that the present pulsation models both linear and non-linear are in error.
Pulsation Modes and Period-Luminosity-Color Relations for the Short-Period δ Scuti Stars
Authors: Breger Michel
Published: June 2019

Due to recent contradictory results, the period-luminosity-color relation of δ Scuti stars has been examined by a maximum likelihood method. δ Scuti stars are found to definitely obey a period-luminosity-color relation. The derived coefficients are very similar to those derived for RR Lyrae variables. Care has to be taken to allow for the large mass differences between the population I variables, such as δ Scuti stars, and population II ultrashort period pulsators.
The Dwarf Cepheids
Authors: McNamara D. H. , Langford W. R.
Published: June 2019

Intermediate-band photometry has been used to derive effective temperatures, metal abundances, and surface gravities of nine stars of the dwarf Cepheid group of variable stars. A strong correlation exists between the metal-line strengths and the period of pulsation in the sense that the shorter-period stars have weaker metal lines. The dwarf Cepheids are evidentally found among both population I and population II stars.
Recent Studies of the Brightest Stars in the Magellanic Clouds
Authors: Osmer Patrick S.
Published: June 2019

The objective prism surveys carried out by Sanduleak (1968, 1969) make available for the first time a relatively complete and homogeneous list of the brightest stars in both Magellanic Clouds for the range of spectral types O–G5. Photometric observations in the four color, Hβ system of the 169 candidates in the SMC and the 45 brightest stars in the LMC as well as spectroscopic observations of the most luminous early-type stars, lead to the following picture of the stability and evolution of very massive stars:

(1)

The reddening is the same for the most luminous stars in both Clouds and there is a sharply defined upper limit to the stellar luminosity, which is also the same in both Clouds. This limit corresponds to Mbol = −11 ± 1 or 90 in good agreement with the classic study of Feast et al. (1960).

(2)

The stars of highest total luminosity are the blue supergiants, and in both Clouds the high temperature limit corresponds to type B1.5 or Te ~ 25000 K for Mv ~ −8. The SMC appears to be deficient in luminous F5–G5 supergiants.

(3)

With few exceptions the most luminous stars are not known to show more than low amplitude variations in light. They do show Hβ emission as expected, and four stars in the LMC have anomalously strong emission, indicative of unusual atmospheric activity. Bright Wolf-Rayet stars have long been known in the Clouds; in addition, several candidate Of stars are indicated by the photometry.

(4)

The brightest B-type supergiants in the SMC appear to be deficient in N, Si, O, and probably Mg and C, although helium is normal, a result worth pursuing in the less luminous stars.

(5)

Judging from the numbers of the brightest stars, the recent rate of star formation in both galaxies per unit mass is quite similar despite the fact that the SMC has a larger fraction of neutral hydrogen and the LMC a more conspicuous display of Hii regions.
Rotational Instabilities and Stellar Evolution
Authors: Zahn Jean-Paul
Published: June 2019

This review deals with the local instabilities arising when the effects of rotation are taken into account in the evolution of a non-magnetic star.

The Rayleigh and shear instabilities will be examined under the conditions prevailing in radiative zones where the effect of density stratification, thermal diffusion, viscosity and varying chemical composition must be taken into account. The possible consequences on the evolution of a star are finally outlined.
Helioseismic Data Reduction
Authors: Hill F.
Published: June 2019

Helioseismology seeks to infer the properties of the solar interior using measurements of the global normal mode oscillations as a function of spherical harmonic degreel, azimuthal orderm, and radial ordernas observed on the solar surface. The frequencies,v0(l, m, n), of the modes are influenced by the physical conditions of the solar plasma through which the p-mode (pressure) waves propagate, while the power,P(l, m, n), and line widths, Γ(l, m, n), provide clues about the excitation and damping of the oscillations. These mode parameters are extracted from observations of the solar surface using a long and complex data reduction procedure. It is thus important to precisely describe the steps in the reduction and to assess the influence of the choices on the resulting inferred physical conditions.
Searching for G-Modes at the Solar Limb
Authors: Toner C.G. , Jefferies S.M.
Published: June 2019

We have used a differential technique to look for the signature of g-modes at the limb of full-disk intensity images of the Sun. Our spectra show tentative evidence for a set of peaks that are equally spaced in period, as predicted by asymptotic theory. The period spacing that we find is ~ 27.5 minutes. If interpreted as ℓ = 1 g-modes, this implies To ~ 39.0 minutes.
A Seismic Model of the Solar Convective Envelope
Authors: Shibahashi H. , Hiremath K.M. , Takata M.
Published: June 2019

We determine the structure of the solar convective envelope by solving the basic equations for mass conservation and hydrostatic equilibrium with the imposition of the sound-speed profile determined from helioseismology and the equation of state. The solution is required to match with the structure of the radiative core, which is also determined with the imposition of the sound speed profile. The helium abundance is obtained as a part of the solutions.
Amplitude Modulation of Radial P-Modes from Virgo
Authors: Leifsen T. , Andersen B.N. ,   The Virgo Team
Published: June 2019

The radial order solar p-modes show an amplitude modulation at the equatorial siderial rotation frequency of the Sun. The peak is clearly separated from the peak at the synodic rotation visible in the irradiance data.
Nonlinear Inversion for the Hydrostatic Structure of the Solar Interior
Authors: Marchenkov K.I. , Roxburgh I.W. , Vorontsov S.V.
Published: June 2019

The technique which we use is based on the “quasi-asymptotic” description of solar p-modes developed by Roxburgh & Vorontsov (1996). As a significant improvement of the standard asymptotic analysis, this description incorporates a Born approximation to allow for a detailed treatment of the regions of rapid variation of seismic parameters with depth (base of the convection zone) and strong influence of gravity perturbations (low-degree modes which penetrate deep into the solar core).
Time Variation of Velocity Flows from Ring Diagrams: A First Approach
Authors: Patrón J. , Hernández I. González , Chou D.-Y. ,   The Ton Team
Published: June 2019

The Ring Diagram analysis is a technique designed to infer the presence of horizontal velocity flows under the solar surface by the analysis of the power spectra of solar oscillations in three dimensions: the two components of the horizontal wave number and temporal frequency (Hill, 1988 and Patrón et al., 1995). This procedure is applied as a local analysis technique, performed for a region of the Sun of several heliographic degrees (typically around 15×15 degrees square). As the Sun is rotating, we must track a chosen region as long as it is present at the visible part of the solar disk, and we can continue the tracking after several solar rotations. The comparison of the estimated flow fields obtained at different times can give some ideas about the temporal variations of the flows.
Pumping of Rossby Waves and Vortices at the Base of the Solar Convection Zone
Authors: Tikhomolov Evgeniy
Published: June 2019

Rossby vortices excited near the base of the solar convection zone are very appealing objects for interpretation of a number of solar phenomena such as long-lived large-scale magnetic structures, the poleward drift of the axisymmetric components after the polar field reversal, and a peculiar long-term behavior of the nonaxisymmetric components (Tikhomolov and Mordvinov 1996).
Local Properties of the Sun‘s Seismic Events
Authors: Goode Philip R. , Strous Louis H. , Rimmele Thomas R.
Published: June 2019

We made simultaneous high resolution observations of the solar granular field and the Sun‘s seismic events. We find that these events occur in the dark intergranular lanes. The events are preceded by the darkening of an already dark lane. On the leading edge of each event, there is a second more abrupt and precipitous darkening lasting a minute or two.